TREATISE 
 
 ELECTRICITY, 
 
 IN' 
 
 THEORY AND PRACTICE. 
 
 BY AUG. DE LA KIVE, 
 
 EX-PROFESSOR IN THE ACADEMY OF GENEVA; AND HONORARY DOCTOR 
 IN THE UNIVERSITY OF PRAGUE: 
 
 FOREIGN MEMBER OF THE ROYAL SOCIETY OF LONDON: 
 
 CORRESPONDING MEMBER OF THE ACADEMY OF SCIENCES OF PARIS; 
 
 OF THE ACADEMY OF MEDICINE OF PARIS; OF THE ACADEMIES 
 
 OF BERLIN, OF TURIN, OF BRUSSELS, AND OF NAPLES: 
 
 MEMBER OF THE SOCIETIES OF ARTS AND OF 
 
 NATURAL SCIENCES OF GENEVA, 
 
 ETC. ETC. 
 
 TRANSLATED FOR THE AUTHOR 
 BY CHARLES V. WALKER, F.R.S. 
 
 IN THREE VOLUMES. 
 VOL. IT. 
 
 LONDON: 
 
 LONGMAN, BROWN, GREEN, AND LONGMANS. 
 
 1856. 
 
 'J'/if A iittior I-CKI rr, .< to himself the ri'jht oftranflnttny tit!,* nv>/-/, , 
 

ADVERTISEMENT 
 
 TO 
 
 THE SECOND VOLUME. 
 
 IT is three years since the First Volume of the Treatise on 
 Electricity in Theory and Practice appeared. This long in- 
 terval, which has elapsed between the publication of these 
 two volumes, is due to the desire, that I have entertained, of 
 not allowing the Second to appear, until after my having 
 succeeded in giving a satisfactory theory of the voltaic pile. 
 I hope to have solved this difficult and contested question, 
 in a manner that will be accepted by all who have turned 
 their attention to it. 
 
 I have also to justify myself on another point ; it is the 
 necessity in which I am placed of publishing a Supplementary 
 Volume. The very great development, that I have felt it 
 necessary to give to the subjects discussed in this volume, on 
 account of their importance, and of the very great numbers ol 
 works of which they have been the object, have rendered 
 it impossible for me to include in it the Applications of Elec- 
 tricity. I have therefore determined to devote to them a 
 supplementary volume, which will enable me to give to them 
 the extension, which they merit. 
 
 This change in my original plan has led me to introduce 
 a second change, namely, the addition of a new Part to the 
 Six of which the Treatise should have consisted. This part, 
 which will be the Sivth, the applications becoming the 
 
VI ADVERTISEMENT TO THE SECOND VOLUME. 
 
 Seventh, will have for its object The Relations of Electric!/'/ 
 to Natural Phenomena, and will be at the head of the supple- 
 mentary volume. It may be considered as being as it were 
 a kind of application of the electric theories and pheno- 
 mena, explained in the first two volumes. It will contain 
 the study of the electricity produced by physiological actions 
 both in animals as well as in vegetables, that of atmospheric 
 electricity and of terrestrial magnetism, as well as the me- 
 teorological phenomena, that depend upon them. 
 
 Undoubtedly the points, that I have been advancing, 
 might have been treated upon in the Chapter, devoted to the 
 Sources of Electricity ; but, independently of the impossi- 
 bility there would have been, had I decided upon this plan, 
 of entering with sufficient development into the natural phe- 
 nomena, with which they are connected, it is at the same 
 time more rational and more advantageous to devote to 
 them a special part of this Treatise. Indeed the question is 
 not of sources of the same kind as calorific, mechanical, and 
 chemical actions ; they are electric manifestations, due to the 
 setting in action directly by nature herself of probably the 
 same forces, but under different forms, as those by means of 
 which the hand of man produces electricity. These are there- 
 fore complex phenomena, the study of which is rather an 
 application, as we have said, than a continuation of that 
 of electric sources. 
 
 The supplementary volume therefore will contain Two 
 Parts devoted, one to the Relations of Electricity with 
 Natural Phenomena, the other to the applications properly so 
 called, either to the art of healing, or to the chemical or the 
 mechanical arts. It will appear in the course of the year 
 1856. 
 
 Geneva, November, 1855. 
 
CONTENTS 
 
 OF 
 
 THE SECOND VOLUME. 
 
 APPENDIX 
 
 TO THE FIFTH AND SIXTH CHAPTERS OF THE THIRD PART. 
 
 Page 
 I. Addition to the Laws that regulate the Mutual Action 
 
 of Electric Currents - 1 
 
 II. Additions to the Phenomena of Induction - 10 
 
 III. Additions to the Chapter relating to the Action of 
 
 Magnetism upon all Bodies - 24 
 
 1st. New Researches relative to the Action of the 
 
 Magnet upon all Bodies - 25 
 
 2nd. General Theory of the Phenomena, that are due 
 to Magnetic Power - 36 
 
 PART IV. 
 
 TRANSMISSION OF ELECTRICITY. 
 CHAPTER I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 General Notions upon the. Propagation of Electricity - 59 
 
 Laws of the Propagation of Electricity in good Conductors 65 
 
\111 CONTENTS OF 
 
 Electric Conductibility of Solids and Liquids - 91 
 
 Propagation of Electricity in imperfect Solid and Liquid 
 
 Conductors - - 121 
 
 Propagation of Electricity in Elastic Fluids - 141 
 
 General Considerations on the Mode of the Transmission of 
 Electricity in Bodies and in Vacuo ; and on certain Mole- 
 cular Phenomena, that are its Result - - 1 67 
 Velocity of the Propagation of Electricity - - 182 
 
 CHAPTER II. 
 
 CALORIFIC AND LUMINOUS EFFECTS OF DYNAMIC ELECTRICITY. 
 
 Forms and Conditions under which Heat and Light are 
 produced by Dynamic Electricity - - 203 
 
 Calorific Effects, produced by the Passage of Dynamic Elec- 
 tricity through good Conductors - - 205 
 
 Laws which regulate the Calorific Effects of Discharges in 
 good Conductors - - - I. 14 
 
 Laws of the Calorific Effects, produced by the Passage of 
 continuous Currents through good Conductors - - 233 
 
 Incandescence and Fusion of Metals by Dynamic Electricity ; 
 and the Molecular Effects with which they are attended - 253 
 
 Calorific and Luminous Effects of Discharges through imper- 
 fect Conductors - - 262 
 
 Calorific and Luminous Effects of Electric Currents through 
 imperfect Conductors. Voltaic Arc - 280 
 
 General Considerations on Electric Heat and Light. Spe- 
 cial Properties of this Light - 303 
 
 CHAPTER III. 
 
 CHEMICAL EFFECTS OF DYNAMIC ELECTRICITY. 
 
 Decompositions brought about by the Voltaic Current - 336 
 
 Laws of Electro-chemical Decompositions. Definite Action 
 of the Current - - - 352 
 
 Apparent Exceptions to the Laws of Electrolysis, and Con- 
 firmation of these Laws - - - 375 
 
 Influence of the Electrodes upon Electro-chemical Decora- 
 position - - 391 
 
THE SECOND VOLUME. IX 
 
 Movements produced in Electrolytic Liquids by the Passage 
 
 of the Current - - 424 
 
 Chemical Effects of ordinary Electricity, and of the Electric 
 
 Spark - - 443 
 
 Production and Properties of Ozone - 469 
 
 CHAPTER IV. 
 
 PHYSIOLOGICAL EFFECTS OF DYNAMIC ELECTRICITY. 
 
 Nature of the Effects that are exercised upon Organised 
 Bodies by Dynamic Electricity - - 483 
 
 Fundamental Analysis of the Action of the Electric Cur- 
 rent upon Animals - - 495 
 
 PART V. 
 
 SOURCES OF ELECTRICITY. 
 CHAPTER I. 
 
 ELECTRICITY PRODUCED BY THE ACTION OF HEAT. 
 
 Development of Electricity by Calorific Action in bad Con- 
 ductors - - - - - -518 
 
 Liberation of Electricity by Calorific Action in good Con- 
 ducting Bodies. Thermo-electric Currents - 53 IT 
 
 Relation between Thermo-electricity and the Molecular 
 Structure of Bodies - 549 
 
 Thermo-electric Piles, and Application of Thermo-electri- 
 city to the Measurement of Temperatures - 563 
 
 Comparison between the Calorific Effects of the Current and 
 Thermo-Electric Phenomena. Attempt at a Theory - 581 
 
 CHAPTER II. 
 
 ELECTRICITY PRODUCED BY MECHANICAL ACTIONS. 
 
 Development of Electricity by the Friction of insulating 
 
 solid Bodies - . - 595 
 
 VOL. II. fl 
 
X CONTENTS OF 
 
 Liberation of Electricity in the Friction of Bodies in 
 Powder, of Liquids and of Gases Hydro-Electric Ma- 
 chine - - 618 
 
 Liberation of Electricity in the Friction of two good Con- 
 ducting Bodies - - 632 
 
 Liberation of Electricity in Mechanical Actions, other than 
 Friction - 635 
 
 General Considerations on the Liberation of Electricity by 
 Mechanical Actions ; and on its Relations with the Libe- 
 ration of Heat - - - - - - 644 
 
 CHAPTER III. 
 
 ELECTRICITY PRODUCED BY CHEMICAL ACTIONS. 
 
 Production of Electricity by the Chemical Action of Liquids 
 upon Solids ; Voltaic Pair and Pile - 65 1 
 
 Production of Electricity by the Chemical Action of Solu- 
 tions upon each other - 695 
 
 Production of Electricity in the Chemical Action of Liquids 
 upon the thin Films with which solid Surfaces are covered. 
 Secondary Polarities ; Gas-pile; Passive Iron - 716 
 
 Production of Electricity in Combustion ; and by the com- 
 bined Action of Heat and Chemical Affinity - 746 
 
 Applications of the preceding Principles to the Construction 
 and to the Theory of the different Voltaic Piles - 761 
 
 Measure of the relative Electro-motive Force of the different 
 Voltaic Combinations - - 783 
 
 Electricity of Contact. Dry Piles - - 828 
 
 Relations between Electricity and Chemical Actions. 
 Electro-chemical Theories 
 
 NOTEX. (p. 58.) 
 
 List of the principal Works relative to the Subjects treated 
 on in the Second and Third Parts of this Treatise, 
 which are contained in the First Volume ; and in the 
 Appendix at the Commencement of the present Volume - 
 
THE SECOND VOLUME. XI 
 
 NOTES 
 
 RELATIVE TO MATHEMATICAL DEVELOPMENTS OF 
 CERTAIN PARTICULAR POINTS. 
 
 NOTE A. (p. 69.) 
 Note relative to the Propagation of Electricity - - 893 
 
 NOTEB. (p. 86.) 
 Note relative to Derived Currents - - 895 
 
 NOTE C. (pp. 153. and 217.) 
 
 Note relative to the Laws of the Discharges of Electric 
 Batteries - - 899 
 
 NOTE D. (p. 230.) 
 
 Note relative to the Formula relating to the Electric 
 Thermometer, and to the Laws of Heating by Electric 
 Discharges - - 900 
 
 NOTE E. (p. 375.) 
 
 Note relative to the Eiectolytic Decomposition of Complex 
 Compounds - 904 
 
 NOTE F. (p. 787.) 
 
 Note relative to M. PoggendorfFs Method for the Deter- 
 mination of the Electro-motive Force of a non-constant 
 Current - - - 906 
 
 NOTEG. (p. 821.) 
 Note relative to the Mathematical Theory of the Pile - 909 
 
TREATISE ON ELECTRICITY 
 
 THEORY AND PRACTICE. 
 
 APPENDIX 
 
 TO 
 
 THE FIFTH AND SIXTH CHAPTERS OF THE 
 THIRD PART. 
 
 BEFORE entering upon the Fourth Part of this treatise, which 
 treats of the phenomena, that arise from the transmission 
 of electricity through different media, we have some important 
 additions to make to certain of the subjects, that have been 
 discussed in the Third Part. These additions, which have 
 been called for on account of the progress, that has been 
 made in the science during the interval that has elapsed 
 between the publication of the first and second volumes of 
 this treatise, are indispensable for the comprehension of the 
 remainder of the work. They relate, first, to the Laws that 
 regulate the Mutual Action of Electric Currents ; secondly, to 
 the Phenomena of Induction ; thirdly, to the Action of the 
 Magnet upon all Bodies. 
 
 I. Addition to the Laws that regulate the Mutual Action of 
 Electric Currents. 
 
 Ampere, setting out from the law that regulates the 
 
 VOL. II. B 
 
2 MAGNETISM AND ELECTRIC CURRENTS 
 
 mutual action of two electric currents, was led, by means of 
 calculation, to connect with the same principle the action of 
 magnets upon each other, and the mutual action of electric 
 currents and magnets. Having realised by experiment 
 certain cases of equilibrium, to which he had been led by ma- 
 thematical analysis, he succeeded in finding the elementary 
 law of the mutual action of two infinitely small portions of 
 electric currents, and in establishing, with M. Savary, the 
 identity between a magnet and a solenoid, that is to say, an 
 assemblage of closed electric currents, all moving in the same 
 direction, and perpendicular to a common rectilinear or cur- 
 vilinear axis. 
 
 Ampere's theory, however, failed in certain points of direct 
 experimental demonstration. M. Weber succeeded in filling 
 up this gap, demonstrating by certain experiments, which 
 were as accurate as they were delicate, the complete identity 
 between the laws that regulate the mutual action of two so- 
 lenoids, and those to which the mutual action of two magnets 
 is subject. This important result has been the means of re- 
 moving all doubts, that might still have remained, as to the 
 accuracy of Ampere's theory, and consequently has given to 
 it a degree of probability, which approaches almost to cer- 
 tainty. 
 
 Weber's apparatus is composed of two rings, formed 
 of copper-wires covered with silk, and arranged with perfect 
 regularity. The interior of one of the rings contains a space 
 sufficiently large for the other to move freely within it. 
 When an electric current is sent through the wire of each of 
 the two rings, the fixed one, which is the outer of the two, 
 tends to make the inner and movable one turn with a force 
 that is at its maximum when their two centres coincide and 
 the planes of their currents are perpendicular to each other. 
 The diameter of the two rings is the axis of rotation ; it has 
 a vertical direction. The movable ring is supported by two 
 very fine wires, each of which supports only one-half, so as 
 to be in an equal state of tension. These wires, which are con- 
 nected at their lower ends with the two ends of the wire of 
 the movable ring, serve to transmit the current to it, by means 
 
WEBER'S DYNAMOMETER. 3 
 
 of the two metal supports to which they are attached at their 
 upper extremities ; the arrangement of the conductors is such 
 as to allow also of the wire of the fixed ring being placed in 
 the circuit, without the slightest friction arising to disturb the 
 motion of the movable ring. 
 
 The two suspending wires serve also to measure the force 
 with which the t\vo rings act upon each other; seeing that 
 
 Fig. 170. 
 
 Fig. 171, 
 
 B 2 
 
MAGNETISM AND ELECTRIC CURRENTS. 
 
 every time the movable ring is displaced in a certain angle, a 
 movement of rotation is produced, proportional to the sine of 
 this angle. This is an application of the principle that 
 Gauss employed in the bifilar magnetometer, which we shall 
 describe in the chapters on Terrestrial Magnetism. The 
 movable ring carries a mirror, which serves to measure small 
 angles, by means of a fixed division that is reflected, and then 
 observed by means of a small telescope. Figs. 170. and 171. 
 represent two vertical sections of Weber's apparatus, at right 
 
 angles to each other; and fig. 
 172. a horizontal section of the 
 instrument, seen from above, 
 downwards. The two suspend- 
 ing wires originating at the 
 bobbin R, which they support, 
 rest against two small metal pul- 
 lies, a and a, and are secured 
 around two small stems, b and b, 
 fixed in an ivory pulley, B. 
 This pulley may be lowered or 
 raised, by means of the screw, 
 e e, which moves in the nut//, so that the movable ring may 
 be brought into the most convenient position, in respect to the 
 fixed one, in the middle of which it is suspended, and 
 of which m m f represents a transverse section. The pulley B, 
 which is movable around a central pivot, is held in equilibrio 
 by means of the mutual action that is exerted at b and b', by 
 the two wires that support the movable ring, the weight of 
 which is thus uniformly distributed between the two wires. 
 The mirror n n, and its counterpoise p p, are erected outside 
 the frame of the fixed ring, which requires, in order to avoid 
 the agitation of the air, that all the apparatus shall be 
 enclosed in a wooden case, provided with two large open- 
 ings, closed by a plate of glass, so that the movements of the 
 mirror may be followed ; its upper part is also of glass, and 
 allows of the passage of a tube, in which the suspending 
 wires are contained, and enables the circular division to be 
 
 Fig. 172. 
 
seen as well as the index i i, that is carried by the movable 
 ring. (Yide fig. 172.) Thr second vertical section (Jig. 
 171.), enables us readily to trace the course of the current; 
 the four metal knobs u u, z and z', fixed against the wooden 
 case, are used for closing the circuit ; u and u', are in com- 
 munication with the two extremities of the wire of the fixed 
 ring, in such a manner that the current setting out from u, 
 arrives at u' y and after having traversed this wire, it ascends 
 along the wire g g, arrives at the screw e e, then to the little 
 pulley a, whence it descends along the suspension wire into 
 the movable ring, passes thence to the second suspension wire, 
 from which it reaches the pulley a, and thence, by the second 
 screw c c, to the wire g g, and to the button z 9 which is in 
 communication with the negative pole of the battery. If 
 these conductors are suitably combined, by means of the 
 four knobs, we can easily change the direction of the 
 current in one of the rings alone, on in both. 
 
 We should add that the wire of the movable ring is 
 656 ft. in length, and makes 1200 convolutions ; and that 
 of the fixed ring 984 ft. making only 900 convolutions. 
 The two suspension wires, which are very fine, are of silver 
 and have been heated to redness ; they are a little over 
 19^ in. in length from the ring to the pullies a and a'. 
 
 The first law that Weber established by this apparatus, 
 which he calls a Dynamometer, is, that the electro-dynamic 
 force produced by the reciprocal action of two conducting wires, 
 which are transmitting currents of equal intensity, is proportional 
 to the square of their intensity. The following are the ex- 
 periments that lead to this law. Three currents of different 
 intensities, produced successively by 3, 2, and 1 pair of 
 Grove's, are passed through the two wires of the dynamometer 
 (Fig. 170.) ; and simultaneous observations are made of the 
 deviations of the dynamometer and those of a galvanometer 
 placed at the same time in the circuit. After having worked 
 out the necessary reductions, the following are the mean 
 values of the inductions of the two instruments : 
 
 B 3 
 
MAGNETISM AND ELECTRIC CURRENTS. 
 
 
 Indications 
 
 
 of the Dynamometer. 
 
 of the Galvanometer. 
 
 3 
 
 440-038 
 
 108-426 
 
 2 
 
 198-255 
 
 72-398 
 
 1 
 
 50-915 
 
 36-932 
 
 These observations have been reduced, so that the first 
 gives a measure of the electro-dynamic force, with which 
 the two conductors of the dynamometer act upon each other 
 when currents of the same intensity are made to pass 
 through them, whilst the second gives a measure of this 
 intensity itself. If P represents the dynamo- metric indi- 
 cations, and p, the galvano-metric indications, we have p = 
 5*19534 V/P; if we actually calculate from this formula 
 the value of p, by means of those obtained from P, we 
 
 obtain : 
 
 p= 108-144 
 
 72-589 
 36-786 ; 
 
 numbers which, in respect of the value of p, are as near 
 to those furnished by experiment as is possible within the 
 limits of the accuracy that can be given to experiment. So 
 that the law given above is properly the result of the inter- 
 pretation of experimental data. 
 
 The second law established in a direct manner by Weber, 
 and which had only been indirectly established by Ampere, 
 is that electro-dynamic actions are governed) in respect to dis- 
 tance, by the same laws as magnetic actions. In order to arrive 
 at this law, we must have the means of varying the distance 
 of the movable ring, in respect to the fixed ring ; the 
 movable ring is, in this case, exterior, and the respective 
 distances of the two rings is measured by the distance of 
 their two centres; and it is necessary also to measure the 
 angle formed by the right line passing through the two 
 centres with the axis of the movable ring ; these two lines 
 are always in the same horizontal plane. Four directions 
 have been chosen, corresponding with the four cardinal 
 
WEBER'S LAWS. 
 
 points ; which signifies that if the axis of the movable ring 
 is supposed to be adjusted according to the magnetic meri- 
 dian, as the axis of a magnetic needle would be, the centre 
 of the fixed ring is found to be deflected, in regard to that 
 of the movable ring, sometimes in the direction of the 
 magnetic meridian, either from south to north, or from 
 north to south ; sometimes in a direction perpendicular to this 
 meridian, from west to east, or from east to west. In each 
 of these four directions, the two rings, or rather their two 
 centres, are arranged at different distances from each other. 
 Care was taken that the same current that passed through 
 the dynamometer was also transmitted through the galva- 
 nometer, in order that the observations made with the 
 former instrument might be reduced to the same intensity 
 of current, by making use of the first law already demon- 
 strated. The following is a Table, presenting an abridged 
 summary of means, reduced to the same intensity, that 
 had been obtained in the different cases observed. The 
 first column contains, the numbers expressing the distances 
 between the centres of the two rings, and the others have at 
 their head the indication of the angle formed by the right 
 line which joins the two centres with the axis of the movable 
 ring set in the direction of the magnetic meridian. 
 
 Distances in 
 Inches. 
 
 North, 
 0. 
 
 East, 
 90. 
 
 South, 
 1800. 
 
 West, 
 
 270. 
 
 
 
 22960 
 
 22960 
 
 22960 
 
 22960 
 
 11-29 
 
 77-14 
 
 189-24 
 
 77-06 
 
 190-62 
 
 15-72 
 
 3478 
 
 77-61 
 
 34-77 
 
 77-28 
 
 19-65 
 
 18-17 
 
 39-37 
 
 18-30 
 
 39-16 
 
 23-58 
 
 - 
 
 22-53 
 
 - 
 
 22-38 
 
 It is evident that in the case where the distance is 0, 
 namely, when the centres of the two rings coincide, there 
 can be no difference arising from the angle made with the axis 
 of the movable ring by the line that joins the centres of the 
 two rings, since this line is reduced to a point situated on 
 the axis. 
 
 This table shows us also that the results obtained for the 
 
 B 4 
 
MAGNETISM AND ELECTRIC CURRENTS. 
 
 same distance, but in directions diametrically opposed, suffi- 
 ciently agree with each other to authorise our finding in 
 this agreement a guarantee of accuracy in the observations. 
 By supposing these values equal, two and two, and taking 
 their mean, we obtain the following table, in which the 
 divisions of the arbitrary scale are transformed into degrees, 
 minutes, and seconds, R being the distance, V" and V being 
 respectively the angles of deviation. 
 
 R 
 
 v 
 
 v 
 
 03 
 
 
 
 49' 
 
 22" 
 
 
 
 20' 
 
 3" 
 
 0-4 
 
 
 
 20' 
 
 8" 
 
 
 
 9' 
 
 2" 
 
 0-5 
 
 
 
 10' 
 
 12" 
 
 
 
 4' 
 
 44 '/ 
 
 06 
 
 
 
 5' 
 
 50" 
 
 
 
 
 According to the fundamental principle of electro-dyna- 
 mics, the tangents of the angles of deviation should be 
 developed, according to the inverse powers of the distance, 
 which gives : 
 
 tang, v = R - 3 + 6 R ~ 3 
 tang, v' = i R - 3 -f c R ~ 3 . 
 
 In these formula? a, b, and c, are the constants, that must 
 be supplied by observation ; if in the case before us, we 
 suppose : 
 
 tang, v = 0-0003572 R- 3 + 0-000002755 R~ 3 
 tang. v' = 0-0001786 R- 3 + 000001886 R~ 3 ; 
 
 we obtain the following table of calculated deviations, which 
 differs but very slightly from the observed deviations, as may 
 be seen by the third and fifth columns, which give these 
 differences. 
 
 R 
 
 V 
 
 Difference* 
 
 V' 
 
 Difference. 
 
 03 
 
 49' 22" 
 
 + 0" 
 
 20' 4'' 
 
 1" 
 
 0-4 
 
 20' 7" 
 
 + 1" 
 
 8' 58" 
 
 + 4" 
 
 0-5 
 
 10' 8" 
 
 + 4" 
 
 4' 42" 
 
 + 2" 
 
 0-6 
 
 5' 49" 
 
 + 1" 
 
 
 
WEBER'S LAWS. 
 
 9 
 
 The method employed, which is exactly the same as that 
 adopted by Gauss for measuring magnetic force (Institutions 
 Magneticce, Annalen 1833, t. xxviii. p. 604.), leading to the 
 same results, enables us to establish in a direct manner one 
 of the most general and most important consequences of 
 the principle of electro- dynamics ; namely, that the same 
 laws regulate electro-dynamic and magnetic actions, at a 
 distance. 
 
 In comparing electro-dynamic with magnetic actions, it has 
 been needful to exclude from the former the cases in which 
 the centres of the two rings of the dynamometer coincide 
 with each other, because this case cannot be realised in the 
 mutual action of two magnets. We may further add that 
 in this application of magnetic laws to electro-dynamics, 
 instead of deducing the values of the three constants a, b, 
 and c, from the observations themselves, we may obtain 
 them directly by calculation, by means of the fundamental 
 principle of electro-dynamics ; for, by means of this principle, 
 we may find, with a sufficient degree of approximation, the 
 momentum of electro-dynamic rotation, which the fixed ring 
 exerts upon the movable ring, suspended by the two wires, when 
 a current of an intensity i, is sent through the two rings. We 
 shall not produce here the series of calculations, by which Mr. 
 Weber succeeded in obtaining numerical results almost iden- 
 tical with those, that had been furnished to him by direct ob- 
 servation in the first Table that we have given above, in 
 establishing the second law. We shall content ourselves 
 with giving this Table calculated, and with the differences 
 that it presents, in relation to the corresponding results 
 obtained by experiment. 
 
 Distances in 
 Inches. 
 
 North or South, 
 or 180. 
 
 Differences. 
 
 East or West, 
 900 or 2700. 
 
 Difference. 
 
 
 
 + 22680-00 
 
 + 280-00 
 
 + 22680-00 
 
 + 280-00 
 
 11-29 
 
 189-03 
 
 + 0-90 
 
 77-17 
 
 0-06 
 
 1572 
 
 77-79 
 
 0-34 
 
 34-74 
 
 + 0-03 
 
 19-65 
 
 39-37 
 
 0-10 
 
 18-31 
 
 - 0-07 
 
 23-58 
 
 22-64 
 
 0-18 
 
 
 
10 PHENOMENA OF INDUCTION. 
 
 In this comparison between theory and experiment, one 
 factor alone was deduced from observations ; and this because, 
 on account of its nature, we could not obtain this factor in a 
 sufficiently exact manner by direct measures. 
 
 In conclusion, we believe, we have said enough to explain 
 the immense service M. Weber has done to science, by 
 establishing on such solid bases the laws of electro-dynamics, 
 and by thus giving to Ampere's theory an almost mathe- 
 matical certainty. 
 
 II. Additions to the Phenomena of Induction, 
 
 We have seen (Vol. I. p. 363.) that, after having discovered 
 inductive currents, Faraday was not long in showing that 
 the existence of these currents might give a very satisfactory 
 explanation of Arago's magnetism of rotation. He had even 
 made a very ingenious analysis of the manner in which the 
 indirect currents must be established and circulated in the 
 metal disc. MM. Nobili and Antinori had succeeded in 
 collecting those currents ; but their processes and results 
 were not entirely free from objection. M. Matteucci has 
 lately taken up this particular point, which is of very great 
 interest in respect to the theory of rotation ; and, while he 
 confirms the views that were entertained by Faraday, he has 
 succeeded in making a detailed and accurate experimental 
 analysis of the complicated phenomena in question. 
 
 Matteucci's method consists in causing a very smooth 
 copper disc to rotate in a vertical plane, under the influence 
 of the two poles of an electro-magnet, the horizontal branches 
 of which reach very near to the disc without touching it, 
 and at equal distances from its centre. N and s (Jig. 173.), 
 are these two poles. After having demonstrated that the 
 disc is maintained by induction, in the same electric state as 
 a metal plate would have if in communication with the two 
 poles of a battery, M. Matteucci found in it, as in the plate, 
 lines of no current, which are indicated on the figure by the 
 numbers 1, 2, 3, 4, and 6. These lines of no current bend 
 near the edges of the plate, so as always to cut them normally. 
 
LINES OF NO CURRENT. 
 
 11 
 
 It is always a very easy matter to find them, by keeping one 
 of the terminations of the galvanometer fixed, and moving 
 
 Fig. 173. 
 
 the other ever so little ; for on the right, or on the left of 
 the line, the currents obtained are in the contrary direction. 
 With regard to the electric currents, that is, the filaments of 
 maximum intensity, they always cut the lines of no current 
 normally ; they are represented on the figure by the closed 
 and dotted curves. The direction of these currents can only 
 be determined, when we have previously discovered the lines 
 of no current. 
 
 Besides the lines of no current already indicated, there is 
 one, marked in the figures with the number 6, which is 
 circular, and which separates the opposite electric states. 
 M. Matteucci calls it the neutral and the inversion line ; it is 
 analogous to the right line, which, in the case of a plate 
 traversed by an electric current, cuts through the middle of 
 the line that connects the poles of the battery. It is the 
 existence of this neutral or inversion line, which necessarily 
 compels us to admit the existence of four systems of currents, 
 
12 PHENOMENA OF INDUCTION. 
 
 that is, two and two symmetrically on the side of each pole. 
 It is through not having known this line, that the philo- 
 sophers, whom we have just mentioned, had not been able to 
 analyse the effect of the magnetism of rotation in Arago's 
 disc. The dotted line F, F, is also a neutral line ; but it is 
 displaced by rotation, and in proportion to the rotation. 
 Around this line all is symmetrical, and all consequently is 
 displaced with it. 
 
 Thus, induction determines in the disc, rotating in presence 
 of a magnet, a state of dynamic equilibrium, which may be 
 considered as fixed in space, and which is represented by 
 neutral lines, and by lines of no current, that are cut normally 
 by filaments or electric currents. In proportion as the 
 velocity of the rotation of the disc increases, it is found that 
 these lines and the system of induced currents, is displaced 
 in the direction of the motion, and proportionately to the 
 velocity of rotation. 
 
 M. Matteucci, in order to show the accuracy of his 
 analysis, succeeded in verifying, by means of electric 
 currents, distributed artificially, as he admits they are, by 
 the effect of induction in the copper disc, all the effects of 
 compound differences found by M. Arago. For this 
 purpose, he arranges a silk-covered copper wire upon a plane 
 of wax, so as to have circuits resembling those of the rotating 
 disc, and he sends an electric current through these circuits, 
 taking care to place the bar-magnet in the proper position. 
 In order to complete the resemblance, we have merely to 
 take into account the displacement of the circuits due to 
 rotation, in the case of the disc. 
 
 We can now easily comprehend the influence that is 
 exercised, in the phenomena of magnetism by rotation, 
 by solutions of continuity in the disc ; if they diminish the 
 action in proportion as they are more numerous, it is 
 because they oppose the circulation of the induction currents, 
 by thus modifying their numbers and direction ; in fact, we 
 have merely to fill up the slits of the disc with a conducting 
 metal, in order tore-establish the interrupted circuits, and thus 
 to restore to the action almost the entire of its primitive energy. 
 
LENZ'S LAW. 13 
 
 With induction, also, is connected Weber's phenomenon, 
 known by the name of unipolar induction, and of which we 
 have endeavoured to give an explanation, contrary to the 
 first ideas of Weber and of Faraday, on this particular point. 
 Our explanation is found to enter implicitly into the more 
 general laws due to Lenz, and which we think it useful to 
 repeat in this place, adding to them some researches of 
 Faraday's of the same nature, and a theory of these phe- 
 nomena, that has been suggested to us by the labours of 
 Lenz and Faraday. 
 
 A short time after Faraday's discovery of electro-dynamic 
 induction, Lenz succeeded in reducing the results into formulae, 
 in a very simple and very satisfactory manner. The fol- 
 lowing is the principle that he established : If a metal 
 conductor is in the vicinity of an electric current, or of a magnet, 
 an electric current is developed in it, the direction of ivhich is the 
 same as would have been produced in this wire by a motion directly 
 contrary to that which had been given to it in order to develope 
 the induction current, supposing that the wire could only be put 
 in motion in the same direction in which it had been moved, or in 
 a precisely opposite direction. It follows from this principle 
 that it is always an easy matter to know in what direction 
 the induction current ought to travel, bearing in mind that 
 the direction is the inverse of that in which a current 
 would travel that would produce by electro-dynamic action 
 the same motion that is imparted mechanically in order to 
 develope the induction. Lenz thus connects in an inti- 
 mate manner the phenomena of induction with Ampere's 
 electro-dynamic phenomena ; for to each phenomenon of 
 electro-dynamic motion corresponds a magneto-electric phe- 
 nomenon, or one of electro-dynamic induction. This may 
 be easily demonstrated by examining different cases succes- 
 sively. 
 
 1st. Case of two parallel conducting wires, each traversed 
 by currents, which attract or repel each other according as 
 they pass in the same or contrary directions. Corresponding 
 case of two parallel conducting wires, of which one alone 
 is traversed by a current, while the other is mechanically 
 
14 PHENOMENA OF INDUCTION. 
 
 made to approach or to recede, which determines in it a cur- 
 rent in the contrary direction or in the same direction. 
 
 2nd. Case of two conducting wires bent into rectilinear 
 forms, or into circles of the same size, and capable of moving 
 around the same axis in vertical planes, and arranged first so 
 that their two planes are perpendicular to each other ; they 
 move and place themselves one against the other, when they 
 form part of an electric circuit, in such a manner that the 
 currents have the same direction in both. Corresponding 
 case of two similar conductors, the one fixed and traversed 
 by a current, the other movable, in which a current is deve- 
 loped moving in a contrary direction to that of the fixed one 
 when it is applied mechanically against it. 
 
 3rd. The case of a movable and limited rectilinear con- 
 ductor, capable of being moved parallel to itself, along an in- 
 definite rectilinear conductor ; when both are traversed by a 
 current, the movable one moves along the fixed one in the 
 direction of the current of the latter, if its own current is 
 receding, and in the contrary direction if it is approaching. 
 Corresponding case of an indefinite and fixed conductor, tra- 
 versed by a current, along which a movable and limited 
 conductor is made mechanically to pass ; a current is deve- 
 loped in it directed towards the indefinite conductor, when it 
 travels in the direction of the current of this conductor, and 
 a current directed in the reverse way when it travels in a 
 direction opposite to that of the current of the indefinite con- 
 ductor. 
 
 4th. Case of a magnet directed from south to north, and a 
 conductor parallel to the axis of the magnet, to which an an- 
 gular motion is given, sometimes to the east, sometimes to the 
 west ; there is developed in it an inductive current, moving 
 in a contrary direction to that which should traverse the 
 conductor, in order that the latter might give to the magnet 
 a deviation in the same direction as that which is mechanicallv 
 given to it. 
 
 5th. Case of a ring or helix, formed of wire, which is 
 made to move to the middle of a magnet, that forms its 
 axis, there is developed in it a current, moving in the in- 
 
INDUCTION AND MOTION. 15 
 
 verse direction to that which should traverse the wire of 
 the ring in order that the latter might be attracted to the 
 middle of the magnet if the pole of this magnet should be 
 presented to the centre of the movable ring. 
 
 6th. Case of a metal disc, moving in a circular direction 
 in a horizontal plane between the poles of a horse-shoe 
 magnet, one of which is above and the other below it ; there 
 is developed in it a current, moving from the centre to the 
 circumference, when the disc travels in the direction of the 
 hands of a watch, and the north pole of the magnet is above 
 and the south below ; the current has the reverse direction 
 if the disc travels in the opposite direction, or the poles of 
 the magnet are reversed. This experiment corresponds in 
 electro- dynamics with Barlow's experiment, in which a 
 wheel traversed by an electric current, moving from its 
 centre to its circumference, turns between the poles of a 
 magnet (jig. 115. p. 264. Vol. I.). The induced current has 
 an opposite direction to that which the current should have, 
 that would give to a wheel a motion occurring in the same 
 direction as that which is impressed upon it mechanically. 
 
 7th. Case of a magnet, turning on its axis under the ac- 
 tion of a current moving from the middle to one of its 
 extremities, or from one of its extremities to the middle ; the 
 magnet moves by the effect of the currents in the mercury 
 into which it is plunged, or of the fixed conductors, by 
 which it is placed in the electric circuit (figs. 104. and 
 105. p. 250. Vol. I.). Corresponding case of a magnet, one 
 of the poles of which and the medium are put into commu- 
 nication with the ends of a galvanometer. On imparting 
 to the magnet a motion of rotation upon its axis, a current 
 is obtained in the galvanometer moving in a direction con- 
 trary to that which, if it traversed conductors arranged in 
 respect to the magnet as the ends of the wire of the galvano- 
 meter are, would impart to the magnet a motion on its axis, 
 having the same direction as that, which had been imparted 
 to it mechanically. 
 
 As may be seen, the phenomenon of unipolar induction 
 enters into the seventh case, and consequently into Lenz's law. 
 
16 PHENOMENA OF INDUCTION. 
 
 This law, moreover, has this remarkable feature, that it 
 establishes the link between the nature of electro-dynamic 
 motion and that of the corresponding induced current. 
 Indeed, whenever the mutual action of two currents, or of a 
 current and a magnet, gives rise to a limited motion, such as 
 an attraction or a repulsion, or a deviation in one direction 
 or another, the corresponding inducing action determines an 
 instantaneous current; whilst, when the electro-dynamic 
 action produces a continuous motion, such as a rotation, the 
 corresponding inducing action developes a continuous cur- 
 rent. Thus, the induced currents of the cases 1, 2, 4, and 5, 
 are instantaneous, either in one direction or the other ; whilst 
 the currents of the cases 3, 6, and 7, are continuous, and in 
 the direction conformable to the law. 
 
 Still more recently, Faraday, with a view of studying the 
 magnetic field, namely, the distribution of the forces that 
 emanate exteriorly from the poles of a magnet, by making 
 conductors rotate under the influence of a magnet or 
 of terrestrial magnetism, obtained induction effects, that are 
 a remarkable confirmation of Lenz's law. We shall return 
 to these experiments further on, when we are speaking 
 of Faraday's lines of magnetic force; for the present we 
 shall confine ourselves to the particular point of induction. 
 It is obtained in the following manner in this case. Two 
 magnets are arranged one beside the other with their homo- 
 logous poles situated towards the same extremity, so that they 
 may act like a single magnet, and turn around a common 
 axis. A wire, coming from one of the polar ends, follows 
 the direction of the axis, to the middle of the magnetic 
 system (that is the axial part), and thence taking a direction 
 perpendicular to the axis (this is the radial part), returns to 
 its starting point, by describing a curved line of greater or 
 less extent, which is completely exterior to the magnets. 
 These different parts of the wire may have independent 
 motions, but they communicate metallicly together by means 
 of copper rings, to which the ends of the axial part are at- 
 tached, and against which the extremities of the radial parts 
 press. Motion may be imparted to the magnets around their 
 
INDUCTION AND MOTION. 17 
 
 common axis ; and in this case, the inducing wire remains 
 fixed ; instead of imparting motion to this wire, it is the 
 magnets that are moveable. When the radial part and the 
 exterior part, namely, all the part of the conducting wire 
 comprised between the two points where it reaches the axis, 
 are set in motion in the same direction, there is not the least 
 trace of a current, which is due to there being two equal 
 and contrary currents developed, one in the radial part, the 
 other in the exterior part ; this is easily proved by moving 
 each of the parts separately. When the axial part of the 
 wire is alone set in motion, there is no effect ; this portion 
 then acts only as a conductor, a duty which might equally 
 be discharged by the substance of the magnet itself. The 
 nullity of effect, that we have been pointing out, is in 
 strict accordance with one of the consequences of the laws of 
 electro-dynamics, laid down by Ampere in one of his later 
 memoirs ; namely, that the action of a magnet on a closed 
 current which enters its axis by its two extremities, is per- 
 fectly null ; and this, whatever be the form or extent of the 
 curve that the current describes, and whatever be the points 
 of the axis at which the extremities of the wire that conducts 
 the current, enter. Now, this is exactly the case in Fara- 
 day's experiment. 
 
 This very remarkable correspondence between the pheno- 
 mena of electro-dynamics and those of magneto-electric in- 
 duction, and which presents itself in each individual fact, has 
 naturally led philosophers to endeavour to comprehend them 
 under one theory ; we have already succinctly described the 
 labours of Weber and those of Newmann on this subject ; but 
 it appeared to me that, without going into notions and calcu- 
 lations so deep as those of Weber and Newmann, we may 
 consider induction as the result of decomposition by influence 
 of the natural electricity of each particle of the induced con- 
 ductor, by the electricities, that are already separated, of each 
 corresponding particle of the inducing wire. For this pur- 
 pose we must admit, that the propagation of the current is 
 made by a series of decompositions and recompositions of the 
 electricities of the successive molecules, in the same manner 
 
 VOL II. C 
 
18 PHENOMENA OP INDUCTION. 
 
 as in the case of insulated bodies, as we have seen in the 
 Fifth Chapter of the Second Part.* We shall give in the 
 Fourth Part the numerous proofs that operate in favour of this 
 mode of the propagation of the electric current. 
 
 Let, therefore A B (Jig. 174.), be a conductor, traversed by 
 
 -1+1 r.-l +1 - +\ - * 
 
 Fig. 174. 
 
 a current in the direction from A to B ; the successive parti- 
 cles, of which it is constituted, have their natural electricity 
 decomposed, the turned to the side A, where the positive 
 pole of the apparatus is the + turned towards B, where 
 the negative pole is. The electricities, as soon as they are 
 separated, combine from particle to particle ; namely, the 
 negative of a with the positive of the pole A, the negative of 
 by with the positive of a, and so on to the positive of h, which 
 combines with the negative of the pole B. This recomposition 
 which is instantaneous, is immediately followed by a new de- 
 composition ; and this by a recomposition, and so on. This 
 succession of decompositions and recompositions is so rapid, 
 that there is always, as we discover by experiment, an electric 
 tension in each particle of the conductor ; so that we may 
 consider that the state in which it is represented in fig. 174., 
 which we call a state of polarisation, is very nearly per- 
 manent. 
 
 Let there now be a second conductor A! B' (fy. 174.), si- 
 
 * Vide Vol. I. p. 139. 
 
INDUCTION AND MOTION. 19 
 
 milar to the first, as near to it as possible, but insulated from 
 it by silk or wax ; at the moment when the current is sent 
 along A B, and when consequently its particles are polarised, 
 an opposite molecular polarisation is produced in A' B', the 4- 
 of each particle being opposite to the of each particle of A 
 B ; and the opposite to the + . It follows, that if, at the 
 moment when A B is traversed by a current, the extremities 
 of A' B', are connected by a conductor, as, for instance, the 
 wire of a galvanometer, the + of the molecule a', combines, 
 through this conductor with the of the molecule hf, and 
 thus produces an instantaneous current, directed from A' to B' 
 in the conductor, but from B' to A' in the wire A' B' itself; 
 namely, in a contrary direction to the inducing current. In 
 like manner if, instead of being connected by a conductor, the 
 extremities A 7 and B', are in communication with the two 
 plates of a condenser, A' gives to it a change of positive 
 electricity, and B' one of negative. As soon as a! has lost its 
 positive, and li' its negative electricity, the negative of h! , is 
 disguised by the positive of b', and so on, to the negative of 
 </, which is disguised by the positive of h' , these electricities 
 neutralise each other, because they are retained by the 
 opposite electricities of the particles of A B ; but, at the 
 moment when the current ceases to pass along A B, then if 
 the two extremities of A' B' are united by a conductor, the 
 negative electricity of. a, unites with the positive of h, and at 
 the same time, the contrary extremities of each of the parti- 
 cles a', b' ', c', d ', /, /', and ^, combine and produce a current 
 moving in the direction from B' to A', and from A' to B', in the 
 wire A' B' itself. Thus A' B' is in this case traversed by 
 a current, moving in the same direction as the inducing 
 current. The state of electric tension, in which the wire A' B' 
 is found, while the current is traversing the wire A B, is 
 what Faraday called the electro-tonic state ; and the cessation 
 of this state produces the second inductive current, whilst its 
 creation, produced the first. We may conceive from the pre- 
 ceding theory, that the electric tension of the extreme mole- 
 cules will be stronger, in proportion as the induced wire is 
 longer ; for if it is short, the two electricities accumulated at 
 
 c 2 
 
20 PHENOMENA OF INDUCTION. 
 
 its two extremities, will unite more easily through the wire 
 itself*; on the other hand, in order to produce a strong 
 current, it is necessary to have a good conductor, so that the 
 decomposition of the natural electricities of each of its parti- 
 cles and their recomposition may be brought about more easily. 
 Finally, in the theory that we have just given, the produc- 
 tion of the two instantaneous inductive currents, is similar to 
 what takes place in the charge and discharge by cascade of 
 consecutive Ley den jars, the interior coating of each of them 
 being in communication with the exterior of the preceding. 
 
 It is well known that, instead of developing the induced 
 current by sending a current along the inducing wire, we 
 may produce it by mechanically moving A B, which is 
 traversed by the current to or from A' B', which is not ; 
 we thus obtain an induced current, which is stronger in 
 proportion as the mechanical motion is brought about more 
 rapidly; but, however, never so strong as in the former 
 case, all other circumstances being the same. It is true 
 that the current has in this latter instance a little longer 
 duration. In this case, the molecules of A'B' do not, as in 
 the case of the invasion of A B by the current, suddenly 
 experience the influence of the molecules a, b, and c ; thus 
 instead of a single and instantaneous current, we obtain a 
 series of little instantaneous currents, the intensity of which 
 increases in proportion as the approximation goes on, and the 
 sum of which constitutes a temporary current. 
 
 When, instead of producing the induction by the electric 
 current, we obtain it by means of a magnet, the theory is 
 exactly the same providing we bear in mind that a magnet 
 may be compared to a series of currents all moving in the 
 same direction, and perpendicularly to the axis of the 
 magnet; only the action of the currents of the magnet 
 is much more energetic than that of true electric currents, 
 which is probably due to their greater number. 
 
 It remains for us to examine the case, in which the in- 
 
 * MM. Guillemin and Burnouf have even succeeded in obtaining electro- 
 dynamic induction in a long telegraphic wire, insulated at one of its extre- 
 mities. 
 
INDUCTION AND MOTION. 21 
 
 ducing and induced wires, having a continuous movement 
 in respect to each other, the inductive current is also found 
 to be continuous ; the same theory fully explains the effects. 
 Suppose the conductor AB (Jig. 175.), traversed by a current 
 
 Fig. 175. 
 
 from B to A, to be moving along the indefinite conductor 
 A'B' ; the -f of the molecule a of AB, travelling from A 7 to B' 
 decomposes the natural electricity of each of the particles 
 a'b'c'd' &c., before which it passes; it attracts the , and 
 repels the + , which immediately gives rise to a current 
 directed towards B', and going from & to A' in a conductor, 
 connecting the two extremities of A' B' ; this current is re- 
 produced every time that a passes before a molecule in A' B', 
 and consequently so long as the motion of AB continues 
 before A'B'. The direction of this current entirely corre- 
 sponds with what it should be according to Lenz's law ; 
 for it is the reverse of that which would give to AB a 
 motion having the same direction as that of the mechanical 
 motion that is imparted to it; but its intensity is very 
 feeble, which is due to there being only the extreme particles 
 
 c 3 
 
22 PHENOMENA OF INDUCTION. 
 
 of AB, namely, those which are nearest to A'B', that can 
 act upon it.* 
 
 With regard to the current induced in the inducing wire 
 itself, which occurs at the moment when the current ceases 
 to pass, it is simply the effect of the return of the molecules 
 to their ordinary state, when the molecular polarisation 
 has ceased. For instance, let us suppose that, in the wire 
 AB of fig. 175., we suspend the passage of the current, 
 and at the same time connect A and B by a conductor, the 
 positive electricity of h is united through this conductor, 
 with the negative electricity of a, the positive of a with the 
 negative of , and so on ; we shall then have a current 
 directed from B to A in the conductor, and from A to B in 
 the wire itself; and consequently, in the same direction as 
 that which had been traversing it, but it will be merely 
 instantaneous. It is easy to understand why, when we 
 collect the extra-current, the current induced in the wire 
 A'B' almost entirely ceases; this is because the direction 
 in which the electricities of the molecules of AB were tra- 
 velling draws those of A' B' in a contrary direction to that 
 which would have given rise to the induced current. 
 
 The numerous experiments of M. Masson, relative to the 
 induction of a current upon itself, are altogether favourable 
 to the explanation I have been giving of the extra-current.f 
 
 * M. Wartmann had even believed that there was no production of inductive 
 current, in the case in which the induced wire was perpendicular to the inducing 
 wire ; his error arises from the circumstance of the current being very feeble, 
 and, perhaps, also from M. Wartmann's having operated with conductors that 
 crossed each other, whilst it is necessary that one of the wires should be entirely 
 on the same side as the other, as in Jig. 175. 
 
 f The helical form given to the conductor favours, in a very decided manner, 
 as far as equal lengths are concerned, the production of the extra-current. 
 And for this reason ; that in addition to the cause that we have just assigned 
 to this production, and which acts alone in the case of a rectilinear conductor, 
 we have here added the inductive action of each spiral of the helix upon the 
 neighbouring spirals, the effect of which must be added to that of the general 
 cause, since it is exercised in the same direction, at the moment when the current 
 ceases to pass. It is for the same reason, that the introduction of a bar of soft iron 
 into the interior of the helix, favours the induction of the extra current. The ex- 
 cellent analysis that M. Masson has made, of his own researches, of those of 
 Jenkins, and of those of Faraday, upon the extra-current, establish a very 
 remarkable analogy between the force of the current, and the discharge of a 
 Leyden jar ; an analogy that Faraday had already proved for ordinary indue- 
 
INSTRUMENT BY M. RUHMKOEFF. 23 
 
 A very important point in our theory is the explanation 
 it gives of the influence exercised over the intensity of the 
 induced current, by the velocity with which the movable 
 conductor is brought near to the fixed one. If this approxi- 
 mation occurs too slowly, the molecular polarisation of the 
 induced conductor is destroyed as fast as it is brought about, 
 without being able to give rise to a sensible current; in 
 order to the production of a current, it is necessary that the 
 + of one of the two extreme molecules of the induced wire 
 should combine, by means of the conductors that connect 
 them with the of the other extreme molecule, which 
 requires a rapid movement, without which the + and the 
 of each particle combine together, as soon as they have been 
 separated. This influence of velocity has been appreciated 
 by M. Wartmann who, even when approximating to actual 
 contact, but very slowly, a soft iron armature of a mag- 
 net, succeeded in obtaining no inductive current in the 
 wire that surrounded the armature ; he was able to obtain 
 the same result by substituting electric currents for the 
 magnet. 
 
 We will terminate the additions that we had to make on 
 induction, by the description of a very powerful instrument, 
 contrived and constructed by M. Ruhmkorff, and of which 
 we shall frequently have occasion to make use, in the Fourth 
 Part of the Treatise. This instrument (Jig. 176.) consists 
 of a very long bobbin, of above 12 or 15 in., surrounded by 
 two wires wound in a helix ; the larger one is intended for 
 receiving the inducing current, and in the other which is 
 finer, the induction current is produced. The rheotome is 
 also founded upon the attraction of a small piece of soft iron, 
 by the electro-magnet of the bobbin an attraction, which by 
 breaking the inducing circuit causes the magnetisation to 
 cease, and, consequently, itself re-establishes the circuit. 
 
 live currents, and which agrees very well with the explanation we have endea- 
 voured to give, of the induction of these currents. We shall, however, return 
 to this subject, and especially to the researches of M. JViasson, when we are 
 studying the physiological effects of inductive currents, to which this philosopher 
 has devoted a great portion of the work, of which we have been speaking. 
 
 c 4 
 
24 ACTION OF THE MAGNET UPON ALL BODIES. 
 
 The wires are insulated by means of either silk or resin, and 
 a commutator enables us to change at pleasure the direction 
 of the inducing currents. The discharges given by this 
 apparatus are of alarming intensity ; and the light produced 
 by the passage, in vacuo, of the discharge from the induced 
 wire, is of remarkable magnificence. In order to increase 
 the power of the apparatus, M. Fizeau conceived the idea of 
 adding to it a condenser, the two plates of which being bent 
 around each other, and separated by an insulating stratum 
 of waxed silk, communicate respectively with either end of 
 the inducing wire, so as to become charged when the circuit 
 is interrupted, and to be discharged when it is re-established, 
 which greatly increases the power of the current, the dis- 
 charge having the same direction as the current. 
 
 Fig. 176. 
 
 III. Additions to the Chapter relating to the Action of Magnetism 
 upon all Bodies. 
 
 We have described in detail in this Chapter the works of 
 Faraday, of Plucker, and of several other philosophers, on 
 the magnetism and diamagnetism of bodies; but since our 
 publication, new works have appeared, to enrich this branch 
 of physics; and we have ourselves arrived at a theory, 
 which seems to us to possess the advantage of embracing, 
 under the same general principle, all the phenomena that are 
 due to the magnetic power. It is these new researches and 
 
RESEARCHES OF M. E. BECQUEREL. 
 
 25 
 
 this theory, that we desire to explain in this place, in order 
 to complete what we have already said on this subject, in the 
 Sixth Chapter of our Third Part. 
 
 1st. New Researches relative to the Action of the Magnet 
 upon all Bodies. 
 
 First we will give a Table, drawn out by M. Plucker, of 
 the numerical results that he obtained by magnetising 
 successively electro-magnets with currents of different inten- 
 sities ; this Table demonstrates the variations, that occur in 
 magnetic attractions and repulsions with the intensity of the 
 current : 
 
 
 Current of a single 
 
 Current of 
 
 
 Grove's Pair ; an 
 
 an Intensity 4 times 
 
 
 Intensity = 1. 
 
 greater. 
 
 Iron - 
 
 1,000,000 
 
 1,000,000 
 
 Cobalt - 
 
 1,008,900 
 
 912,200 
 
 Nickel - 
 
 465,700 
 
 350,900 
 
 Oxide of iron 
 
 758 
 
 954 
 
 Oxide of nickel - 
 
 286 
 
 405 
 
 Hydrated oxide of cobalt 
 
 2-178 
 
 5-015 
 
 Bismuth 
 
 236 
 
 39-03 
 
 Phosphorus 
 
 16-45 
 
 27-31 
 
 We will now pass on to the latest researches of M. E. Bec- 
 querel. Instead of employing the ordinary balance, and 
 estimating by weights, the specific magnetism and diamagne- 
 tism of bodies, M. E. Becquerel, as we have previously said, 
 made use of the torsion balance, placed over the poles of an 
 enormous electro-magnet, upon which it rests. To check the 
 continual oscillations of the extremity of the tension thread 
 that sustains the bar, the subject of experiment, he suspends 
 to the middle of this bar, by means of a double-woven thread, 
 a small leaden ball immersed in water at a distance of 
 a little more than half an inch ; it is easily proved that the 
 presence of this sphere introduces no disturbance to the ob- 
 servations, which are thus made with much more precision. 
 A microscope fixed to one of the sides of the torsion-balance, 
 carries a micrometer in the focus of the eye-piece, to which 
 
26 ACTION OF THE MAGNET UPON ALL BODIES. 
 
 are successively brought, by torsion, the bars that are the 
 subject of experiment, after having taken the precaution to 
 trace a cross at the end of each of them, to serve as the point 
 of reference. The number of degrees of torsion necessary 
 in order to bring back the point of crossing to the centre of 
 the micrometer, are measured ; and thus the exact measure 
 is obtained of the effect due to the action of the magnet ; to 
 be freed from causes of error the direction of magnetisation in 
 the electro -magnet is changed, by means of a commutator, 
 and the effect produced is again measured, which is almost 
 always identical with the first observation. Finally, the 
 constancy of the current employed, is insured by means of a 
 sine-galvanometer, placed in the circuit. 
 
 M. E. Becquerel moreover proposed to determine the 
 value of magnetic actions in different media, always setting 
 out from the principle that all bodies are magnetic, after the 
 manner of iron, and that the attractive or repulsive effect 
 observed is due to the difference existing between the specific 
 magnetism of a body and that of the medium in which it is 
 placed. But, whatever theory be adopted, the numbers 
 obtained by M. Becquerel remain not the less as important 
 data to be preserved. In order to have a fixed term of com- 
 parison, he has referred all the determinations to the specific 
 magnetism of water in air, which he has made equal to 10, 
 water being repelled by the magnet in air, and also in vacuo. 
 Finally, by measuring the action of the magnet upon two bars, 
 one of sulphur, the other of white wax,, placed, first in air, and 
 then in different media, he deduced the specific magnetism of 
 these different media, as well as that of the sulphur and the wax, 
 in respect to equal volumes ; by making use of the rod of 
 sulphur, the results to which he arrived are almost identical 
 for each medium, with those that were furnished to him with 
 the rod of wax. 
 
 The following are two Tables, which contain the numerical 
 determination of the action of the magnet upon different sub- 
 stances of the same size, placed in the air ; these numbers 
 express, therefore, according to M. E. Becquerel, the action 
 of the magnet upon the body placed in vacuo, minus the 
 
RESEARCHES OF M. E. BECQUEREL. 27 
 
 action of the magnet on an equal volume of air. The sign 
 indicates a repulsion ; the sign + , an attraction : 
 
 Water - - - - 10 
 
 Ordinary zinc - - - - 2*5 
 
 White wax - - 5-68 
 
 Sulphur, sublimed, then melted - 11 '37 
 
 Plumber's lead - 15-28 
 
 Phosphorus - - - - 16 '39 
 
 Selenium - - 16'52 
 
 Bismuth - - - 217'60 
 
 The relative values between zinc and white wax being 
 more feeble than those which refer to water, these two sub- 
 stances ought to be attracted by the magnet in water ; they 
 are actually so, as in almost all liquids. 
 
 The following Table, constructed on the same basis as the 
 preceding, contains the results relative to liquids and saline 
 solutions : 
 
 Water (density = 1) 10- 
 
 Concentrated alcohol (density = 0'8059) - - - 7'89 
 
 Sulphuret of carbon - - 13-30 
 
 Chloride of sodium (density =1-2084) - - 11-28 
 
 Chloride of magnesium (density =1-3 197) - 12'05 
 Crystallised sulphate of ^copper of commerce (density = 
 
 1-1265) - - + 8-14 
 Sulphate of nickel (density =1-0827) - -+21-60 
 Protosulphate of iron, prepared with the crystallised sulphate 
 
 of commerce (density =1-1 923) - -f- 211-16 
 Protosulphate of iron, prepared with sulphuric acid and 
 
 iron (density =1-1728) - - + 180-22 
 Protochloride of iron, No. 3. prepared with hydro-chloric 
 
 acid and iron (density = 1-0695) - + 91'93 
 
 Protochloride of iron, No. 1. (density = 1-276 7) - - + 36070 
 Protochloride of iron, No. 2. concentrated (density = 
 
 1-4334) - - - + 658-13 
 Protosulphate of iron, with slight excess of sulphuric acid 
 
 (density =1-1587) - + 137-70 
 
 In this last Table which contains only liquids, the effect has 
 been determined by the difference that these solutions expe- 
 rience on the part of magnetism, by means of a solid substance 
 always the same, subjected to the action of the magnet, while 
 
28 ACTION OF THE MAGNET UPON ALL BODIES. 
 
 plunged in the different liquids. We arrive at the same re- 
 sults, whatever solid body may be employed for these deter- 
 minations, providing it remains the same in all the comparative 
 experiments. 
 
 All the numbers in these two Tables are referred, as we 
 have said, to volumes ; by dividing them by the densities, we 
 should obtain the magnetic power for equal weights. This 
 operation was gone through in M. Plucker's table ; it seems 
 useless to repeat it here, seeing that the results obtained by 
 these two philosophers differ too much for any useful com- 
 parison to be made between them. We may add that, on 
 mixing very fine and very pure iron-filings, in various pro- 
 portions with white wax, and forming of it small cylinders 
 about two inches long, and half-an-inch or less in diameter, 
 M. Becquerel, by comparing the action exercised upon them 
 by the magnet with that which occurred on a tube of the 
 same size filled with protochloride of iron, succeeded in deter- 
 mining the magnetic powers of proto- chloride of iron and of 
 water in respect to iron of equal volume and weight. In 
 order to arrive at this determination, he sought by trials 
 for the proportion of iron that ought to be contained in the 
 cylinder of wax, so that it might experience the same 
 action as the equal volume of proto-chloride of iron ; he 
 found that it was about *003 gr. Troy, to "061 cubic in. 
 whence he deduced the following magnetic powers for equal 
 weights : 
 
 Iron - - + 1,000,000 
 
 Proto-chloride of iron - - - + 140 
 
 Water - - 3 
 
 We have also to report the important results, to which 
 M. E. Becquerel arrived, in respect to the magnetic pro- 
 perties of gases, results that he obtained by observing the 
 repulsion exercised by the poles of the electro-magnet upon 
 a very thin bar of glass, closed at its two extremities by the 
 blowpipe, plunged successively into different gaseous media ; 
 this bar was 1*37 in. long, *27 in. in diameter and weighed 
 11-45 gr. Troy; it was slightly magnetic. In the air, it 
 
RESEARCHES OF M. E. BECQUEREL. 29 
 
 was less attracted than in vacuo, which seemed to indicate 
 that air was a magnetic medium. The attraction of the 
 glass being diminished in the air, the repulsion of a dia- 
 magnetic body, such as sulphur, ought on the contrary 
 to be stronger in air than in vocuo ; and this is confirmed 
 by experiment. Hydrogen, nitrogen, carbonic acid give 
 no appreciable effect of this ; but oxygen manifested the 
 same property as air, and this with an intensity five times 
 greater; which proves that it is its presence which gives 
 to air its magnetic property, and the more so as nitrogen is 
 insensible to this action. Here, then, is a direct experimental 
 proof that oxygen is attractable by the magnet, in the same 
 manner as iron ; and that it is even very strongly magnetic. 
 In order to determine more accurately the magnetic 
 power of oxygen, M. Becquerel took a small glass tube, 
 which he filled with melted wax ; the glass being slightly 
 attracted and the wax repelled by the electro-magnet, he 
 thus obtained a body very nearly indifferent, being just 
 slightly diamagnetic. He determined the effect of the 
 magnet upon the glass tube in vacuo, in air, in oxygen 
 and in water, and he found : 
 
 In vacuo .... - 0'1145 
 
 In oxygen - - 0*2675 
 
 In air - ... 01453 
 
 In water - - + 07033 
 
 which gives for the magnetic force of oxygen in respect 
 to water in vacuo, + 1*871, and in respect to water in 
 air, + 1-80. Thus with equal volumes and at the pressure 
 of 30 in. the magnetic power of oxygen is half that of water ; 
 but taken with the contrary sign, oxygen being attracted 
 by the magnet, whilst water is repelled, a slightly different 
 method gave 1*73 instead of 1-80. 
 
 Finally, M. E. Becquerel studied the action of the magnet 
 upon gases, by condensing them into a porous substance, 
 such as charcoal. He prepared cylinders of oak charcoal, 
 an inch to an inch and a quarter in length, and a third 
 of an inch in diameter, which were calcined to redness in 
 
30 
 
 ACTION OF THE MAGNET UPON ALL BODIES. 
 
 sand, before each experiment. Repelled in vacua, these 
 cylinders were strongly attracted in air, and especially in 
 oxygen, of which they absorb about nine times their own 
 volume. It is probable that the very various results ob- 
 tained by different philosophers in respect to the action 
 of the magnet upon charcoal in air, are due to its absorbing 
 air and water, and on which account it must experience 
 different effects according to the proportion of these sub- 
 stances, the air giving to it an attracting and the water 
 a repelling power. The trials made with other gases furnished 
 results that were too undecided to furnish conclusions, with 
 any degree of accuracy, as to the magnetic or diamagnetic 
 power of these gases. It is otherwise with oxygen and with 
 air ; so that we may regard the following conclusions as 
 sufficiently near to truth, namely that the specific magnetism 
 is for 
 
 
 Equal 
 Volumes. 
 
 Equal 
 Weights. 
 
 Oxygen at the pressure of 30 in. - 
 Air ------- 
 
 Water ... - 
 
 + 1-80 
 + 0-38 
 10-00 
 
 + 1257 
 + 293 
 10 
 
 On comparing these values with iron, from the table given 
 above, where, for equal weights we had, for water 3, iron 
 being 1,000,000, we obtain for specific magnetism in respect 
 of equal weights : 
 
 Iron 
 Oxygen 
 Air - 
 
 - 1,000,000 
 
 377 
 
 88 
 
 We had obtained for the most magnetic liquid (proto- 
 chloride of iron) + 140, iron being 1,000,000; so that 
 oxygen is, weight for weight, three times more magnetic 
 than the most magnetic of liquids ; therefore, after the 
 magnetic metals (iron, cobalt, and nickel), this body is the 
 most magnetic, weight for weight. 
 
 The following is a Table containing the last results ob- 
 tained by Faraday on the magnetic and diamagnetic powers 
 
RESULTS OBTAINED BY FAKADAY. 31 
 
 of certain bodies by employing a large magnet, constructed 
 by M. Logeman, according to the principles of Dr. Elias, 
 which weighs a little more than 100 Ib. and which is 
 capable of supporting 430 Ib. In this Table, the angles 
 of torsion necessary to balance the attractive and repulsive 
 force of the magnet, express the magnetic and diamagnetic 
 powers of the various substances, volume for volume : 
 
 Proto-ammo. of copper - ... 134-23 
 
 Per-ammo. of - 119 '83 
 
 Oxygen - - - - 17 '5 
 
 Air - - .3-4 
 
 Olefiant gas - - - - - '6 
 
 Nitrogen - - - - - '3 
 
 Vacuum - - - - - *0 
 
 Carbonic acid gas - - - - '0 
 
 Hydrogen - - - - '1 
 
 Ammonia gas - - - - '5 
 
 Cyanogen - - - - -0-9 
 
 Glass - 18 -2 
 
 Pure zinc - - - - - 74 *6 
 
 Ether - 75 -3 
 
 Alcohol absolute - 78 -7 
 
 Oil of lemons - - - - 80 
 
 Camphor - - - - 82 59 
 
 Camphine - - 82 '96 
 
 Linseed oil - - - 85 '56 
 
 Olive oil - - 85 -80 
 
 Wax - - - - - -86-73 
 
 Nitric acid - - - - 87 '96 
 
 Water - - - - 96 '6 
 
 ' Solution of ammonia - - - - 98 *5 
 
 Bisulphate of carbon - 99 -64 
 
 Sat. sol. nitre - - - - 100 *08 
 
 Sulphuric acid - - 104 *47 
 
 Sulphur - - 118 
 
 Chloride of arsenic - 121 '73 
 
 Fused borate of lead - -136-6 
 
 Bismuth - 1967 '6 
 
 
 
 M. Plucker, who had at first thought that air and oxygen 
 were diamagnetic, recognised afterwards the magnetism 
 of oxygen ; he also proved that two of the nitrous compounds 
 were magnetic; namely, the deutoxlde of nitrogen and 
 
32 ACTION OF THE MAGNET UPON ALL BODIES. 
 
 nitrous acid in the state of gas, which is due probably 
 to their being less powerful combinations than the others ; he 
 also remarked that the presence of a small quantity of free 
 oxygen in a gas is sufficient to make it attractive to the 
 magnet. 
 
 We may also remark that M. Plucker came to the conclu- 
 sion, as did M. E. Becquerel and Mr. Faraday, that the mag- 
 netism of oxygen, and in general of magnetic mixtures and 
 combinations, is proportional to the density of the gas. He 
 operated in all his experiments with a bubble of glass, 
 the feeble magnetism of which was compensated by that of 
 the surrounding air, so that the action of the magnet upon 
 the bubble empty of air was perfectly null ; it was 1'77 in. in 
 diameter, and at the ordinary pressure contained a volume of 
 oxygen, weighing only 0*87 gr. The attraction exercised 
 upon this gas by the electro-magnet was equivalent to a weight 
 of O308 gr., which gave M. Plucker for the specific mag- 
 netism of oxygen, compared weight for weight with iron taken 
 as unity, -OOOSoOO instead of -0000377, found by M. E. 
 Becquerel. Mr. Faraday, in the Table we have just intro- 
 duced, gives 17 '5 for the magnetism of oxygen, the diamag- 
 netism of water being 96*6; which leads to + 1'81 for 
 oxygen, water being 10. But this result is perfectly in 
 accordance with that of M. E. Becquerel (p. 29.); a proof 
 that his number, and not M. Plucker's, should be accepted. 
 
 Thus, it follows equally from the experiments of MM. E. 
 Becquerel, Faraday, and Plucker, that oxygen is a body emi- 
 nently magnetic ; and that with respect to other gases, if we 
 except some that are magnetic on account of the oxygen they 
 contain, the greater numbers do not experience from the elec- 
 tro-magnet any kind of action, the diamagnetism, which we 
 suppose we have remarked in them, being apparent only, and 
 arising, as we have said, from the experiments being made in 
 air, which is a magnetic fluid. 
 
 We have described the works of MM. Tyndall and 
 Knoblauch on magneto -crystalline phenomena; since that 
 time Mr. Tyndall has added some new facts in confirmation 
 of the very simple and ingenious theory, which makes the 
 
MATTEUCCl'S EXPERIMENTS. 33 
 
 effects, produced by the action of the magnet upon crystals, 
 to depend solely upon the particular mode of the groupment 
 of their particles. This clever philosopher has in particu- 
 lar succeeded in imparting to solid substances by strong 
 pressure, and without the necessity of reducing them to 
 powder, a molecular state, which causes them to assume, 
 between the poles of an electro-magnet, a direction depend- 
 ing upon the direction of the pressure, that has been exercised 
 upon them. 
 
 M. Matteucci obtained the same effects from compression, 
 both upon sulphur and upon stearic acid, as well as upon 
 bismuth. The pieces submitted to compression were placed 
 between two glass cheeks in a vice, so that all the points of 
 their two surfaces were equally compressed ; they were then 
 washed in hydrochloric acid to free them of all infpurity ; the 
 form of cubes had been given to them ; and these cubes, being 
 suspended, so that the line of compression was horizontal, 
 constantly took a direction between the poles of the electro- 
 magnet, so that this line was perpendicular to the polar line. 
 On taking a cube of 0*39 in., and cutting from the side 
 that had been strongly compressed prismatic needles in dif- 
 ferent directions, they directed themselves equatorially or 
 axially, according as the line of compression, was parallel or 
 perpendicular to their axis, which depends on the manner in 
 which they have been cut. If the prismatic needles are cut 
 from masses of crystallised bismuth, very decided differences 
 are observed between them, according as their cleavage 
 faces, which are always parallel to their length, are horizontal 
 or vertical. Thus three needles of the same length (O72 
 in.), but of different weights, from 17 to 126 grains 
 Troy, suspended between polar surfaces 1-37 in. apart, 
 always made the same number of oscillations in a time sen- 
 sibly shorter, when the cleavage faces were vertical, than 
 when they were horizontal: the one that was 126 grs. in 
 weight, made 20 oscillations in 52 seconds in the former case, 
 and in 136 seconds in the latter. If the polar extremities are 
 elongated into a point, the differences are less. When the 
 
 VOL. ir. D 
 
34 ACTION OF THE MAGNET UPON ALL BODIES. 
 
 planes of cleavage are perpendicular to the axis, the needle 
 directs itself axially between the poles, providing the polar 
 extremities are not too near together, in which case it is re- 
 pelled toward the equatorial line. 
 
 M. Matteucci succeeded in imitating all the effects of 
 crystallised bismuth, by forming cubes and needles, by 
 means of small very thin plates of bismuth, obtained by 
 dropping liquid bismuth in small drops from a certain 
 height upon a marble plane : this is one more proof that the 
 cleavage planes act as separated plates. Moreover, M. Mat- 
 teucci felt a difficulty in explaining all magneto- crystalline 
 phenomena by the theory of MM. Tyndall and Knoblauch ; 
 he does not see to what, in this theory, he must trace the 
 very great difference of the repulsive force, that causes a 
 needle of frismuth to oscillate, whose planes of cleavage are 
 parallel to its axis, according as these planes are vertical or 
 horizontal. He also finds the following experiment far from 
 reconcilable with this theory; when, having suspended 
 between the poles of the electro-magnet a needle of sulphate 
 of lime, to the extremities of which are fixed two cubes of 
 bismuth, he saw the needle always repelled in the equatorial 
 line, when the cleavage faces were either horizontal or 
 parallel to its length ; and, on the contrary, travel to the line 
 of the poles, when the cleavage faces were perpendicular to 
 the length of the needle. The polar faces in this case were 
 square, and 2 in. apart. This experiment does not appear to 
 us, as it did to M. Matteucci, contrary to the theoretical ideas 
 of M. Tyndall ; in fact, the two cubes of bismuth, when the 
 needle of sulphate of lime is placed axially, have their planes 
 of cleavage perpendicular to this line, as ought to be the 
 case. It is true that they seem to be attracted by the 
 magnetic poles, whilst the bismuth, naturally diamagnetic, 
 ought to be repelled ; but if the needle, which carries the 
 two cubes, is placed equatorially, then the cleavage planes 
 would be parallel to the axial line, which would be contrary 
 to theory. There is in this case, therefore, an opposition 
 between two contrary tendencies ; and, if the influence of the 
 cleavage plane has the superiority, it is due to the size of the 
 
MATTEUCCl'S EXPERIMENTS. 35 
 
 magnetic field, which is itself due to the extent of the polar 
 surfaces, and to their distance. 
 
 With regard to the influence of the horizontal or vertical ar- 
 rangement of the plane of cleavage upon the diamagnetic 
 power of a crystal of bismuth, it is very probably due to an 
 effect of induction. M. Matteucci has appositely made the 
 very curious remark, that of two perfectly equal cubes of 
 crystallised bismuth, subjected to the action of a rotating 
 electro-magnet, the one whose cleavage planes are vertical 
 and perpendicular to the planes of the current of the electro- 
 magnet, is drawn in with much more force than is that, whose 
 cleavage planes are horizontal : in all cases, amorphous 
 masses of bismuth experience a more considerable action than 
 those, that are crystallised. The difference is still more sen- 
 sible when, instead of cubes of crystallised bismuth, we take 
 two cubes formed of very thin plates of copper, insulated 
 from each other by a coat of varnish. The cube whose plates 
 are vertical assumes a very rapid rotatory motion, under 
 the influence of a rotating electro -magnet over which it is 
 suspended ; whilst the one whose plates are horizontal does 
 not feel the action of the electro-magnet. It appears that, 
 in the former arrangement, the induced currents may be 
 freely developed, and can circulate in each plate, which is 
 not the case with the second arrangement, in which the 
 induced currents do not possess for the completion of their 
 circuit any conductor beyond the inducing influence. 
 
 Matteucci's experiments point out, as Faraday had pre- 
 viously remarked, the important part induction may play, 
 when the action of the magnet upon conducting bodies is being 
 studied. This part may even be manifested in cases where 
 beforehand we should not have thought it possible. The 
 following are some curious examples, which we also owe to 
 Matteucci. Having obtained copper, silver, and bismuth in 
 a state of extreme division, by decomposing very pure solu- 
 tions of these metals with a very powerful battery, he first 
 satisfied himself, by placing these metallic powders in tubes 
 of straw or quill, that they were very powerfully diamag- 
 netic ; he then made of them homogeneous mixtures by mixing 
 
 D 2 
 
36 PHENOMENA DUE TO MAGNETIC POWEK. 
 
 them rapidly with melted resin. These mixtures were dia- 
 magnetic and perfectly insulating, as might be proved by 
 placing them with a sensitive galvanometer in the circuit of a 
 powerful battery. However, spheres of 0'47 in. in diameter, 
 formed of these mixtures of resin and metallic powders sus- 
 pended by a cocoon thread at a very little height above the 
 poles of an electro-magnet that was set rotating, turned in 
 the same direction as this electro-magnet, accomplishing 
 in this way several revolutions. This effect could not be 
 due to the diamagnetism of the mixtures, for phosphorus and 
 stearic acid, which have a much higher degree of diamag- 
 netic power, do not acquire the magnetism of rotation under 
 the action of the same electro-magnet. On the other hand, 
 it was difficult to attribute this rotation to induced currents, 
 similar to those which are developed in continuous metallic 
 masses, for the particles of which these powders are composed 
 are less than 0*00039 in. in diameter. However, it is clearly 
 in induction that we must seek for the explanation of these 
 phenomena ; and the proof is, that the mixtures, formed with 
 the powders of silver and of copper, manifest them with more 
 intensity than those which contain divided bismuth, a metal 
 that is not so good a conductor : the powders made with the 
 oxides of the same metals, which are not conductors, do not 
 produce any effect. It is probable, therefore, that a molecular 
 induction is brought about in the particles, which gives rise 
 to a molecular current when the particle is insulated, and to 
 a finite induced current when several particles are agglo- 
 merated, so as to form a continuous mass. We should find 
 in this a remarkable confirmation of the theory of induction 
 that we have given above. 
 
 2nd. General Theory of the Phenomena that are due to 
 Magnetic Power. 
 
 For a long time, led to be regarded as only a special action, 
 being exercised upon a very small number of bodies, the action 
 of the magnet is now universal, namely, all bodies are sus- 
 ceptible of experiencing it. It is true that it is manifested 
 
FORMS OF MAGNETIC ACTION. 37 
 
 under divers forms, but these forms themselves are connected 
 together and are attached to one general principle ; this is the 
 point, that we shall now endeavour to establish. But, in the 
 outset, we must call to mind that the action of the magnet 
 is identical with the action exercised by closed electric 
 currents exteriorly to the circuit which they are traversing ; 
 this is now generally admitted by all philosophers, for this 
 identity rests at once upon mathematical and upon experi- 
 mental proofs, and particularly upon the fact that the two 
 species of action may in all cases be substituted for each other, 
 to produce the same effects under the same circumstances. 
 
 The various forms under which the action of the magnet, 
 or that of closed electric currents, is manifested, may be re- 
 duced to four principal heads. 
 
 1st. Action upon magnetic bodies, which consists of an 
 attraction, a directive force the consequence of this attrac- 
 tion, with a magnetic polarity. 
 
 2nd. Action upon diamagnetic bodies, which consists of a 
 repulsion, and a directive force the consequence of this 
 repulsion, but without sensible magnetic polarity. 
 
 3rd. Action upon transparent bodies, both solid and liquid, 
 which consists of the property they acquire under the influ- 
 ence of this action, of rotating the plane of polarisation of a 
 ray of polarised light that traverses them, through a greater 
 or less angle. 
 
 4th. Action upon all very good conducting bodies, which 
 consists in the development in these bodies of instantaneous 
 currents, called currents of induction. 
 
 If we endeavour to discover the common and character- 
 istic properties on the one hand of magnetic bodies, and on 
 the other hand of diamagnetic, we find that the former are 
 they which, volume for volume, contain the greatest number 
 of chemical atoms, and the latter they which contain the 
 least. This law which had been already noticed in reference 
 to magnetic bodies, when only iron, nickel, and cobalt were 
 reckoned among magnetic metals, is found to acquire a re- 
 markable confirmation and generalisation, since Faraday 
 has added to the list of these metals, manganese, chromium, 
 
 D 3 
 
38 PHENOMENA DUE TO MAGNETIC POWER. 
 
 titanium, cerium, palladium, platinum, and osmium. In fact, 
 whilst the three former metals contain under the same 
 volume 230 atoms, the seven following 170, the diamagnetic 
 metals, as gold and silver, contain only 150, antimony and lead 
 85, and bismuth only 74.* Two metals alone are an ex- 
 ception; copper, which contains 230 atoms, and zinc, 170; 
 but these two metals are excellent conductors of electricity, 
 whilst all the other metals of the two same categories, which 
 are magnetic, are very bad conductors. It would therefore 
 appear that the magnetic power would be a direct function 
 of the number of atoms contained in the same volume, and 
 inversely to the electric conductibility; on this account it 
 is that gold and silver should each of them be diamagnetic, 
 and not magnetic; they are so in fact, together with copper 
 and zinc, which are the best conductors of electricity, and 
 they moreover contain only 150 atoms, volume for volume, 
 instead of 230 and 170. 
 
 Diamagnetic bodies would therefore be those which, volume 
 for volume, contain the smallest number of atoms, or which, 
 if they contain more, are very good conductors of electricity. 
 It is remarkable that these latter are very slightly diamag- 
 netic, and consequently very near the limit ; and that even, 
 as we shall see hereafter, they may under certain circum- 
 stances become magnetic. But an important point to be 
 noticed is the relation existing between the diamagnetisrn 
 of bodies and their magnetic rotatory power. It is in error 
 that several philosophers, who have been engaged upon this 
 subject, have regarded these two properties as independent of 
 each other. From the very commencement of these researches, 
 Faraday had happily recognised this dependence; and it is 
 not without reason that, after having discovered that the in- 
 fluence of magnetism caused the plane of polarisation in a 
 prism of heavy glass to rotate, he found that this prism 
 directed itself equatorially between the poles of the electro- 
 magnet. 
 
 The following then are the relations, that connect these 
 
 * For the calculation of these numbers, the atomic weights deduced from the 
 specific heats have been taken. 
 
DIAMAGNETISM AND ROTATORY POWER. 39 
 
 t\vo properties with each other. The former, which is the 
 position that the diamagnetic hody assumes in order to escape 
 from the action of the magnet, namely, the equatorial position, 
 is that in which the body ceases to possess rotatory magnetic 
 power, supposing that the polarised ray always traverses it 
 in the direction of its length. The latter is that all the cir- 
 cumstances, which increase in the same body the rotatory 
 magnetic power, equally increase its diamagnetic power. 
 Thus M. Wiedemann demonstrates that the rotation of the 
 plane of polarisation is proportional to the intensity of the 
 current, or of the magnet that is acting upon the substance ; 
 and we have seen, on the other hand, that the diamagnetism 
 is in like manner proportional to this intensity. We know 
 that crystals have a very feeble rotatory magnetic power : 
 now their diamagnetism is also feeble on account of their 
 molecular constitution, which causes them to be directed 
 sometimes axially instead of equatorially. The third relation 
 is that substances, which by their nature have the greatest 
 amount of diamagnetism, are also they which exercise the 
 most powerful rotatory action upon the plane of polarisation; 
 and reciprocally, the more a substance is magnetic, the less 
 decided is this action. This fact is derived from the experi- 
 ments of M. E. Becquerel, and from those of M. Bertin. 
 Thus the rotatory power and the diamagnetism of water 
 being each of them 10, chloride of magnesium has 16 for its 
 rotatory power, and 12 for its diamagnetism; sulphuret of 
 carbon, 2 9 '3 and 13 -3; chloride of calcium 16 and 11*6. 
 With regard to magnetic bodies, sulphate of nickel has 13-55 
 for its rotatory power, and 21-60 for its magnetism; diluted 
 protochloride of iron 9-45 and 92; and concentrated proto- 
 chloride of iron 3 and 6 -58. The fact observed by M. Ma- 
 thiessen, that when a glass contains a magnetic metal, but 
 in such small quantity that its transparency is not too much 
 altered, the rotation increases with its thickness, is not op- 
 posed to the law that we have just laid down ; for in this case 
 the body that acts upon the light is not magnetic crystal, 
 but glass; and the metal only seems to transmit into the 
 interior of the glass the magnetic power, that emanates from 
 
 D 4 
 
40 PHENOMENA DUE TO MAGNETIC POWEE. 
 
 the poles by which it is itself magnetised. I have myself sub- 
 mitted a great number of liquid substances to the action of 
 the electro-magnet, in order to determine their relative dia- 
 magnetism by means of a torsion balance, to the wire of which 
 were suspended tubes of very thin and very white glass, 
 filled successively with the different liquids ; and I constantly 
 found that the order of their diamagnetic power was the 
 same as that of their rotatory magnetic power. The num- 
 bers, it is true, that express the two powers, are not pro- 
 portional ; but this is not to be wondered at ; for, seeing the 
 very different form of the two phenomena manifested upon 
 the substance by the action of the magnet, it is impossible to 
 admit that the two results are the same function of forces put 
 into play in this double action. 
 
 We have nothing to add to what we have already 
 said upon induction ; we have merely to repeat that its 
 intensity is a function of the conductibility of bodies for 
 electricity, and that it depends consequently both upon 
 their dimensions, and the greater or less conducting power 
 of their particles. 
 
 After having thus analysed the phenomena, that are due 
 to the action of the magnet, and having endeavoured to 
 establish the relations and differences, that exist between 
 them, it remains for us to seek for a theory, which may 
 collect them under one and the same general principle. 
 
 The first point that I wish to establish is that dia- 
 magnetism is not a magnetism relatively more feeble. I 
 have already combated this opinion, which assimilates 
 diamagnetism to magnetism, an opinion that had strongly 
 induced M. E. Becquerel to admit that vacuum is magnetic, 
 and is more so than a very great number of bodies : I shall 
 not, therefore, return to it; I shall merely add that there 
 have never been found in diamagnetic bodies, when they 
 are under the influence of powerful magnets, any traces 
 of poles, such as they ought to acquire, if these bodies are 
 really endowed with magnetism. It is true, on the other 
 hand, that some experimentalists think they have detected 
 contrary poles to those which they ought to have according 
 to M. E. Becquerel's theory, namely, poles of the same 
 
WEBER'S THEORY. 41 
 
 name as the magnetic poles nearest to them ; which would 
 make diamagnetism seem to be the antagonism of mag- 
 netism. We have already given the experiments by which 
 Poggendorff, Reich, and Weber thought they had de- 
 monstrated that magnets determine in diamagnetic bodies 
 polarity homogeneous to their own. We have seen that 
 these experiments might receive another interpretation; 
 and that, in particular, their effects were essentially due to 
 the production of induction currents over the surface of the 
 metals submitted to the influence of electro-magnets, or 
 merely to that of closed currents. But Weber took up the 
 subject anew and arrived at results, that really seem favour- 
 able to the idea of diamagnetic polarity. In this work, 
 in which he has discussed \vith remarkable care all magnetic 
 and diamagnetic phenomena, while attributing the former 
 to molecular currents pre-existing around the particles and 
 only movable with them, according to Ampere's theory, 
 he is led to consider the latter as depending upon the 
 existence, in the interior of the bodies, of electric fluids 
 put into the state of current by a powerful exterior cause, 
 such as the poles of an electro-magnet. In this case, the 
 currents would not pre-exist, and would not be connected 
 in an indissoluble manner with the particles, as in the case 
 of magnetic bodies. But he was still led by his theory to 
 admit a diamagnetic polarity, the inverse of magnetic polarity. 
 Two series of experiments seem to him to prove the ex- 
 istence of this polarity. In the first, a long helix is placed 
 vertically between the two poles of a very light horse-shoe 
 magnet, and delicately suspended by a vertical silk thread, 
 fixed by its lower extremity to the middle of a cross-piece 
 which unites, near the bend, the two parallel branches 
 of the magnet, which is situated in a horizontal plane. 
 When the helix is traversed by the current, all is symmetrical 
 in every respect ; the magnet does not move, the two poles 
 being equally either attracted or repelled by the helix, 
 according to the direction of the current that traverses it ; 
 but if a cylinder of bismuth is made to move in the interior 
 of the helix, we observe, setting out from the position in 
 which the middle of the cylinder is in the plane of the 
 
42 PHENOMENA DUE TO MAGNETIC POWER. 
 
 magnet, that if we raise it the magnet moves in one direc- 
 tion, and that if we lower it it moves in the other direction, 
 which seems to indicate two opposite poles at the extremities 
 of the cylinder. With an iron wire, substituted for the 
 bismuth, the same movement is observed, but in an opposite 
 direction. But what is singular is that a similar movement, 
 and almost equally powerful, occurs when the bismuth is 
 moved in the helix, without the latter being traversed by 
 an electric current ; only the movement occurs in an 
 opposite direction : it is more powerful when the bismuth 
 is raised than when it is lowered, which is the reverse of 
 what happens when the helix is traversed by the electric 
 current. It is evident that, in these experiments, the 
 bismuth experiences a modification in its magnetic or electro- 
 dynamic relations, from the mere circumstance of its being 
 surrounded by electric currents : this is not astonishing ; 
 since, if it were transparent, this modification would be de- 
 tected by the rotation of the plane of polarisation. The 
 whole of these experiments, in fact, seem to prove that this 
 modification consists in the production of a polarity such 
 as Weber conceived. However, how are we to explain 
 the action of the bismuth, when it is not surrounded by 
 electric currents? In this case, it ought to repel equally 
 both poles of the movable magnet ; and the latter, con- 
 sequently, ought to have no movement. Finally, in order, 
 to be quite assured that the induction currents played no 
 part in this new form, given to these experiments, Weber 
 ought to have employed other metals besides bismuth, and 
 to have shown that the effects obtained are less with metals 
 that are less diamagnetic. 
 
 The same observation applies, and with still greater 
 force, to the second series of Weber's experiments. In 
 this series there are two concentric helices, well insulated 
 from each other; the outer one is traversed by an electric 
 current, the inner one is placed in communication by its 
 two extremities with a galvanometer ; and a cylinder of 
 bismuth is moved within it. Care is taken to wind one half 
 of the spiral of this interior helix in a contrary direction 
 to that of the other half, so that the inductive effects, pro- 
 
WEBER'S EXPERIMENTS. 43 
 
 duced by the successive introduction of two different 
 magnetic poles, may be added together. The experiment 
 is conducted in such a manner that a commutator sets the 
 bismuth in motion at the same time that it changes the 
 communications of the helix with the galvanometer, so that 
 the induction currents always travel in the latter in the 
 same direction, and their effects are consequently added 
 together. A series of induced currents is thus obtained, 
 which are detected by their action upon the galvanometer ; 
 and, by substituting an iron wire for the rod of bismuth, 
 we also obtain currents, but, under the same conditions, 
 moving in opposite directions. We might, perhaps, propose 
 to M. Weber the objection that the presence of the cylinder 
 of bismuth ought to modify the action of the exterior helix 
 upon the interior, and consequently explain the development 
 of the currents, that are detected by the galvanometer. In 
 this series of experiments, as well as in the former, M. Weber 
 ought to have employed not only other metals besides 
 bismuth, but also metals drawn into thin wires and made 
 up into bundles, in order to compare their effects with those 
 of similar metals forming solid cylinders ; which is the only 
 mode of thoroughly distinguishing the effects due to polarity 
 from those which arise from induction currents, developed 
 upon the surface of masses introduced into the helix. 
 
 The fact of diamagnetic polarity appears to us however to 
 have been very well established by M. Weber's recent re- 
 searches, although there are still against him certain nega- 
 tive facts, such especially as those recently pointed out by 
 M. Matteucci. This philosopher constructed four helices 
 perfectly similar, which he arranged vertically at the four 
 corners of a square wooden slab ; an astatic needle was deli- 
 cately suspended in the middle of the four helices ; and the 
 apparatus was so constructed that no motion was produced 
 upon the needle, when a discharge or a series of discharges 
 passed in the helices. He had merely to fill the interior of the 
 two helices placed at the extremity of one of the diagonals 
 with a mixture of wax and small quantities of colcothar (oxide 
 of iron) in order to obtain very marked effects at the moment 
 when the discharge was passing. By substituting cylinders 
 
44 PHENOMENA DUE TO MAGNETIC POWER. 
 
 of bismuth for the magnetic cylinders, not the slightest motion 
 of the astatic needle was obtained. However, the diamag- 
 netic power of bismuth was far superior to the magnetic 
 powers of the mixture of wax and colcothar ; which seems to 
 prove that diamagnetism is not the result of a polarity of the 
 same kind as magnetic polarity. M. Matteucci also proved 
 that by employing non-conducting diamagnetic bodies, such 
 as phosphorus, sulphur, or stearic acid, instead of metals, no 
 inductive effect was produced either in one direction or in the 
 other. We shall see further on that the interesting facts 
 observed by Matteucci are not in opposition to the existence 
 within diamagnetic bodies of a particular species of polarity. 
 
 Mr. Faraday does not admit of diamagnetic polarity ; we 
 have already said that he regards the action exercised by 
 magnets upon magnetic and diamagnetic bodies as the results 
 of forces emanating from the poles of magnets, according to 
 certain directions, and which he calls lines of force, and the 
 whole of which constitute the magnetic field. The presence 
 of a body in this magnetic field modifies the directions of the 
 lines of force : if the body is magnetic, it concentrates the lines 
 of force ; if diamagnetic, it makes them diverge. This modifica- 
 tion, brought about in the distribution previously uniform of 
 these lines of force, gives rise to attractive movements for mag- 
 netic bodies, and repulsive for diamagnetic. Mr. Faraday en- 
 tered into a detailed study of the magnetic field, and the direction 
 of the lines of force, a very exact idea of which is given by 
 the distribution of iron filings around and between the poles 
 of magnets. We have already seen that he succeeded in em- 
 ploying induction to demonstrate the equality and the distribu- 
 tion of these lines of force in the magnetic field. It follows 
 indeed from the experiments to which we have referred in the 
 chapter on induction that, at whatever distance from the mag- 
 net these lines are cut, the induction current, collected by 
 the movable wire by which they are cut, possesses the same in- 
 tensity ; which proves that magnetic force has a definite value, 
 and that for the same lines of force, this value remains the 
 same at all distances from the magnet: neither the con- 
 vergence or divergence of the. lines, nor yet the greater or 
 less obliquity of the intersection introduces any difference 
 
FARADAY S THEORY. 45 
 
 into the sum of their power. The study of the internal part 
 of the magnet leads us to recognise that the lines of force 
 have there also a definite power, and perfectly equal to that 
 of the exterior lines, which are only the continuation of the 
 others; and this whatever the distance may be,, which may 
 be infinite, to which they are prolonged. 
 
 We must not forget that Mr. Faraday, by the term lines 
 of magnetic force, expresses the power of the force of mag- 
 netic polarity, and the direction according to which it is ex- 
 ercised. If the magnetic field is composed of equal forces 
 equally distributed, as may easily be obtained with a horse- 
 shoe electro-magnet, we have merely to place a sphere of iron 
 or nickel in this field, to cause an immediate disturbance in 
 the direction of the lines of force. The forces are not only 
 concentrated, but are bent or modified in their direction by 
 the metal spheres that are introduced ; they experience a con- 
 vergence upon the opposite faces of a magnetic sphere and a cor- 
 responding divergence upon the opposite sides of a diamagnetic 
 sphere. It is this property that Faraday expresses by the 
 words conduction polarity. Temperature diminishes the power 
 possessed by bodies of affecting the direction of the lines of 
 force, and even causes them to disappear at a certain point. 
 This may be proved by observing that a small magnetised 
 needle, about the tenth of an inch in length, which always 
 places itself parallel to the lines of force, in the different 
 points of the magnetic field, first changes its direction near 
 spheres of iron or nickel, then recovers its parallelism when 
 the two spheres are raised to a sufficient temperature. The 
 oxygen of the air, which, in virtue of its magnetic properties, 
 ought to modify the direction of the lines of force of terres- 
 trial magnetism, loses in great part also this property by the 
 elevation of temperature, which furnished Mr. Faraday, as 
 we shall see, with an ingenious explanation of the diurnal 
 variations of the magnetised needle. 
 
 The few words, that we have been devoting to Faraday's 
 theoretic ideas, are sufficient to make them understood : the 
 fundamental idea of the illustrious philosopher is in the main 
 the negation of all action at a distance, and the explanation 
 of the phenomena by continuous force, forming what he calls 
 
46 PHENOMENA DUE TO MAGNETIC POWER. 
 
 lines of force. Bodies, by their presence, modify these lines 
 of force; and there arise directive motions, which are 
 manifested by the disposition of these bodies to place them- 
 selves according to their nature, either axially or equa- 
 torially, namely, in the places where the force is A 
 its maximum, or in those where it is at its minimum. A 
 learned English philosopher, Mr. Thomson, on applying 
 calculation and notions of mechanics to Faraday's ideas, found 
 that they represented, in a remarkably exact manner, what 
 takes place in this order of phenomena, providing we take into 
 account the mutual action of the parts of which the bodies are 
 composed that are submitted to magnetic influence. Mr. 
 Thomson has also made a great many experiments upon 
 small wires, and upon cubes of iron, arranged in different 
 manners, by suspending them near to or within a ring tra- 
 versed by an electric current; and he always perceived that 
 these bodies placed themselves parallel to the lines of force. 
 
 We cannot altogether acquiesce in Faraday's ideas, how- 
 ever ingenious they may be. Does the magnetic field really 
 exist, as the learned philosopher conceives it to be, namely, 
 independently of the bodies by which its existence is made 
 manifest? This is the point upon which I have some 
 doubts. I am rather disposed to admit that magnetic forces 
 are exercised only so long as there is a body which determines 
 their manifestation. M. E. Becquerel has already demon- 
 strated that the action of the magnet upon magnetic and 
 diamagnetic bodies is proportional to the square of the inten- 
 sity of the magnet or of the current, and not to the simple 
 intensity, which shows that these bodies enter, on their own 
 part, into the production of the effect, and that they do not 
 play simply a passive part. Mr. Tyndall arrives at the 
 same conclusion, as the result of numerous experiments, 
 made equally upon diamagnetic and magnetic bodies. He 
 even believes he has found that bismuth acquires a magnetic 
 polarity, analogous to that acquired by iron, but merely trans- 
 verse instead of longitudinal. He deduces this last conclusion 
 from the results he obtained by surrounding a piece of either 
 ordinary or crystallised bismuth, when suspended in the mag- 
 netic field, with a helix traversed by an electric current. He 
 
DEDUCTIONS. 47 
 
 found, on placing the helix, sometimes parallel at other times 
 perpendicular to the axial line, considerable deviations from 
 the direction which the bismuth ought to take, when not sur- 
 rounded by an electric helix ; and he considers that these devi- 
 ations are explained by a transverse magnetism imparted to it 
 by the magnet. But, on the other hand, how is the repulsion to 
 be explained? What can be said with most truth is, as Mr. 
 Tyndall himself remarks, that the presence of the helix, tra- 
 versed by an electric current, brings into the magnetic field 
 modifications, that cause the greater and the less lines of 
 magnetic force to exchange places, which become inclined to 
 the axial or equatorial direction. Finally, we may remark 
 further, that if the lines of force are sufficient, as Faraday 
 admits they are, to explain all the phenomena, why have 
 these lines need of the intervention of a body in order to 
 act upon the polarised ray, and cannot they act directly 
 upon this ray in vacuo ? a result which we have not been 
 able to succeed in obtaining although employing even a very 
 considerable magnetic power. 
 
 From this long discussion, we deduce : 
 
 1st. That bodies, submitted to the action of magnetic 
 force, undergo modifications which determine the motions 
 they execute under the action of this force, as well as other 
 effects which they become capable of producing, such as the 
 rotation of the plane of polarisation : 
 
 2nd. That these modifications are not of the same order in 
 magnetic and in diamagnetic bodies ; in other words, that these 
 latter do not acquire a polarity similar to that acquired by 
 magnetic bodies : 
 
 3rd. That, consequently, neither M. E. Becquerel's theory, 
 which assimilates diamagnetic bodies to magnetic, nor 
 Faraday's, which attributes to the bodies only a passive part, 
 appears to us to explain in a satisfactory manner the different 
 forms under which magnetic power is manifested, whilst 
 Weber's theory would seem better to represent this order of 
 phenomena. 
 
 Let us inquire, then, whether or not there are any means 
 of attaching this latter theory to a general principle, allowing 
 ourselves to be simply guided by the results of experiment. 
 
48 PHENOMENA DUE TO MAGNETIC POWER. 
 
 When we study electro-chemical phenomena, we are for- 
 cibly led, as we shall see, to admit a simple relation between 
 the atom and electricity. Ampere had supposed that each 
 atom of matter possesses an electricity proper to itself either 
 positive or negative, and that, in the state of equilibrium, it is 
 surrounded by an atmosphere of electricity of a contrary nature 
 to its own, and which disguises the latter. This hypothesis, 
 which very elegantly explains a certain number of facts, is 
 open to grave objections; in particular, it does not at all explain 
 how the same atom can be sometimes positive, at other times 
 negative, according to the atom with which it is put in relation, 
 which we must admit, if we would explain a great number of 
 chemical facts. Berzelius had admitted that each atom has 
 two electric poles, one positive, the other negative. He had 
 founded his hypothesis on the existence of these two poles in 
 the molecules of tourmaline and of certain crystals. But to 
 this simple hypothesis, another was added, which was not at 
 all probable, founded upon the fact that there are some con- 
 ductors which conduct one of the electricities better than 
 the other, an assumption since demonstrated to be inaccurate. 
 This hypothesis was that atoms are unipolar, that is to say, 
 that they keep but one of their electricities in combining 
 together, and abandon the other. We shall see hereafter 
 that this hypothesis is not necessary to the explanation of 
 chemical and electro-chemical phenomena, which may be 
 very well reconciled with the idea of polarity, such as 
 Berzelius had supposed, without any need of adding thereto 
 unipolarity. I am therefore disposed to admit in the atom 
 a natural polarity ; all the facts relating to the development 
 of electricity, particularly by heat, seem to lead in this ; and 
 with respect to the objection raised, that the atom being 
 naturally spherical, there is no obvious reason that it should 
 have a polarity in one direction rather than in another, we 
 have only to suppose, which is far from being improbable, 
 that each atom of matter originally received a motion of 
 rotation upon itself; and we then obtain for the atom an axis 
 and a direction of rotation, and consequently a different pole 
 at each extremity of the axis. 
 
DEDUCTIONS. 49 
 
 Setting out from this primitive polarity of the atom, it is 
 easy for us to deduce from it, according to the known laws of 
 electricity, the properties that are manifested by bodies under 
 the action of the magnet or of closed electric currents. We 
 may first remark that, when an atom is isolated, that is to say, 
 at too great a distance to be influenced by the neighbouring 
 atoms, the two electricities, accumulated at the extremities of its 
 axis, ought constantly to unite by its very surface, and this 
 with the greater facility as it is in itself of a better conducting 
 nature. For instance, let a (Jig. 177.), be the atom, b and c, 
 the extremities of its axis or its two 
 poles ; the -f electricity, constantly 
 carried to b, tends to unite itself by 
 the surface of the atom with the ne- 
 gative electricity that is carried to c ; 
 there arises, therefore, from this a 
 current going from c to 6, through 
 Fig. 177. the axis, and from b to con the whole 
 
 surface of the atom. Thus, we may consider the atom as 
 traversed by a current, that returns to its point of departure, 
 by the surface of the atom itself. The latter is, therefore, in 
 a state of electric equilibrium, since the two currents, one of 
 which traverses, and the other surrounds it, are equal and in 
 contrary directions. But, if a certain number of atoms are 
 
 approximated to within 
 such a very small distance 
 of each other, that their 
 mutual influence may be 
 exercised, then they become 
 so arranged (fig. 178.), 
 that the pole -f of the atom 
 a is in contact with the 
 pole of the atom b ; the 
 + pole of b, with the 
 of c ; and so on, until they 
 form a chain, of which the 
 last atom, for example, has 
 its -t- pole in contact with 
 
 VOL. II. E 
 
50 PHENOMENA DUE TO MAGNETIC POWER. 
 
 the of a. We have thus an integrant molecule, sur- 
 rounded by one electric current, circulating about it. The 
 number of atoms that enters into its formation, depends upon 
 the molecular constitution of the body, which is not regu- 
 lated any more than cohesion is, by electric polarity, but 
 which descends probably on the mass of the atom.* In order 
 that this electric current, whose formation we have been de- 
 scribing, may be established around the integrant molecule, 
 the latter must be composed of atoms, that are very near to- 
 gether. Now, which are the bodies that are in this condition? 
 We have seen, at the commencement of this paragraph, that 
 they are the magnetic bodies. Thus, therefore, magnetic 
 bodies are, by the very fact of the approximation of their atoms, 
 bodies each of whose integrant particles, compounded of a 
 greater or less number of atoms, is surrounded by an electric 
 current. In the natural state, the particles, left to themselves, 
 so arrange themselves that all these electric currents mutually 
 neutralise each other ; but if we now exert on the magnetic 
 body an exterior action, by presenting to it a magnet or 
 an electric current, we compel the particles so to arrange 
 themselves, that their currents are parallel to those of the 
 magnet, or of the current presented to them. And thus mag- 
 netism is produced ; it is temporary if the particles do not pre- 
 serve the position, which the exterior force has impressed upon 
 them, after this force has ceased ; it is permanent, if they do pre- 
 serve it ; furthermore, it is the molecular constitution of bodies 
 that determines the more or less decided degree of this pro- 
 perty, which we have termed coercitive force. We are thus 
 led a priori to Ampere's theory of the constitution of magnets, 
 and to admit that electric currents pre-exist around par- 
 ticles, and that magnetisation simply consists in arranging 
 them in a common direction a consequence already deduced 
 from the molecular effects that accompany them. We may 
 remark that it is essentially the particles of the surface that 
 experience this effect of direction, which tends, on the con- 
 
 * We admit here, with all philosophers, that the difference existing between the 
 chemical atom, and the integrant or physical molecule, is, that the molecule is 
 only an agglomeration of a greater or less number of atoms. 
 
HEAT DIMINISHES MAGNETISM. 51 
 
 trary, to destroy the influence of the interior particles ; and 
 this explains the property of tempering, and why a hollow 
 magnet is more powerful than a solid one of the same 
 volume. 
 
 Two metals alone are exceptions to the law that we have 
 just laid down ; these are copper and zinc ; they ought to be 
 magnetic, according to their atomic volume, and they are not 
 so ; it is true that they are only very feebly diamagnetic, but 
 they are diamagnetic. We have already remarked that these 
 two same metals are much better conductors than all those 
 that have the same atomic volume : now this explains to us 
 why they are not magnetic, like the others. Indeed, in order 
 that the electric current may be established around the inte- 
 grant molecule (which is the characteristic of a magnetic body), 
 it is not only necessary that the atoms be very near together, 
 but also that they be not of a nature sufficiently conductible to 
 enable the electricities accumulated at their two poles easily to 
 unite by means of their surface, even when they are insulated, 
 rather than to unite with the contrary electricities of the two 
 atoms, between which each of them is interposed. Now this 
 actually occurs with the atoms of copper and zinc, on ac- 
 count of their great electric conductibility. And so copper 
 may be rendered magnetic, by combining it with oxygen or 
 chlorine, which diminish its conducting powers. 
 
 The very decided magnetism of oxygen is explained by 
 admitting that each molecule of oxygen is formed of a very 
 dense group of elementary atoms ; an hypothesis that confirms, 
 as we shall see, the ozonised condition of oxygen that is ob- 
 tained on disaggregating its particles. It is very remarkable 
 that oxygen, which is the only magnetic gas, is the only one 
 also whose particles can be disaggregated. 
 
 We may finally remark, that heat diminishes magnetism, 
 and even makes it disappear ; because, on separating the atoms 
 from each other, it breaks the electric chains which these 
 atoms formed, or at least diminishes the intensity of the current 
 that traverses them.* 
 
 * The recent experiments made on the dilatation of bodies, and particularly 
 those of Magnus and Kegnault, on the dilatation of gases, have effectually de- 
 
 E 2 
 
52 PHENOMENA DUE TO MAGNETIC POWER. 
 
 Let us now pass on to diamagnetism. That which dis- 
 tinguishes diamagnetic bodies from those that are not so, 
 is that their atoms being more distant, there cannot be es- 
 tablished among them any natural electro-atomic chain; 
 the atoms are, therefore, independent of each other, in an 
 electric point of view, and are consequently in that state 
 of equilibrium in which their exterior currents neutralise 
 the interior current that is directed along their axis. But, 
 if we present to the integrant molecules, composed of a 
 greater or less number of these atoms, a closed exterior 
 current *, this current is not able to impress upon them a 
 particular direction, since they are not surrounded by an 
 electro- atomic current, as the magnetic particles are ; but, 
 if it is sufficiently energetic, it determines among such of these 
 atoms as are the nearest to it a direction such that their axis is 
 parallel to its own direction, and that their poles are at the 
 same time turned in a contrary direction to that of the 
 polarised particles of the conductor of the current, in a 
 manner analogous to that which occurs in electro-dynamic 
 induction. These atoms, thus directed under this powerful 
 influence, will in their turn oblige the other atoms of the 
 molecule, of which they form a part, to direct themselves 
 so as to correspond by their opposite poles, and thus to 
 form an electric chain ; the current of which will necessarily 
 have a contrary direction to that of the exterior current, 
 since this direction is determined by the first atoms that 
 are directly subject to the action of this current. Things 
 will happen similarly for the other particles of the diamag- 
 netic body, providing they are surrounded at least all that 
 are under the exterior influence by electric currents having 
 a contrary direction to that of the currents that are acting 
 upon them, and which will necessarily produce a repulsion. 
 
 The difference between a magnetic and a diamagnetic 
 
 monstrated that dilatation by heat not only consists in the separation of the 
 integrant molecules from each one ; but also in a dilatation proper of these 
 particles themselves, and consequently, in a separation of the atoms themselves, 
 of which they are formed. 
 
 * I understand, by action of closed exterior current, the action either of a 
 closed voltaic current, or of an electro -magnet, or of an ordinary magnet. 
 
MAGNETIC AND DIAMAGNETIC DIFFERENCES. 53 
 
 body will, therefore, consist in this, that, in the former, 
 as the currents are pre-existing around the particles, the 
 exterior action of a closed current has no other effect than 
 to impress upon their particles a common direction, and 
 such that these currents are parallel to those acting upon 
 them, and moving in the same direction ; this constitutes 
 magnetisation ; whilst in the latter, as the particles are not 
 surrounded by a natural electro-atomic current, they do 
 not themselves change place, but they are forced, by the 
 arrangement which the exterior action impresses upon their 
 atoms, to be surrounded by an electric current moving in 
 a direction contrary to that of the currents that are acting 
 upon them. We see that we thus arrive at the same con- 
 clusions as Weber, with regard to the difference between 
 magnetism and diamagnetism. 
 
 In truth it is a real phenomenon of induction that occurs in 
 the action exercised over the diamagnetic molecule, with this 
 difference, that the induction occurs only in the molecule, and 
 not in the whole conductor, and that it lasts as long as the in- 
 ducing cause, instead of being instantaneous. Another differ- 
 ence is that the molecular induction occurs as well in non- 
 conducting as in conducting bodies, whilst that which gives 
 rise to currents of a finite size, can only be produced in con- 
 ducting bodies. 
 
 The causes of these differences can easily be apprehended, 
 when we compare the actual nature of the two phenomena. 
 Electro-dynamic induction is the result, as we have seen, of 
 the polarisation of the successive integrant molecules, and of 
 the discharges of the contrary electricities of these consecutive 
 molecules ; this is a purely physical phenomenon, in which 
 the mere nature of the particles plays no part, except in as 
 far as their greater or less degree of electric conductibility 
 is concerned ; it is altogether analogous to the effects of the 
 induction of static electricity, and to those of disguised 
 electricities. Thus induction is manifested in the same 
 manner in magnetic bodies, whose integrant molecules are 
 surrounded by a natural electric current, and in diamagnetic 
 bodies, in which this molecular current is induced; it is 
 
 E 3 
 
54 PHENOMENA DUE TO MAGNETIC POWER. 
 
 merely necessary that the body shall be a conductor; and 
 the intensity of the effect depends on the greater or less 
 degree of the conductibility of the body. It is not the same 
 with molecular induction, which is the cause of diamagnetism. 
 Being due to a particular arrangement of the atoms of the 
 molecules, itlastsonly so long as the action exists by which this 
 arrangement is produced. We can conceive that this action 
 should be very energetic, in order to be able to disturb the 
 natural arrangement of the atoms, and then to determine the 
 continuous neutralisation of the contrary electricities of the 
 consecutive atoms, even though they are not very near 
 together, and are often bad conductors of electricity. All 
 the facts agree with this mode of regarding this order of 
 phenomena. Thus not only is electro-dynamic induction 
 manifested in magnetic and even in magnetised bodies, as if 
 they were not such, but it is also simultaneous with dia- 
 magnetism, and disturbs its effects, when circumstances, 
 favourable to its production, are united. 
 
 We therefore see that, by causes of an entirely different 
 order, diamagnetic bodies, so long as they are under the 
 influence of closed currents, have their particles surrounded 
 by currents having a direction contrary to those of these closed 
 currents, whilst the particles of magnetic bodies, under this 
 influence, have their currents determined in the same direction. 
 This opposition very naturally explains all the differential 
 effects that are observed, on mixing together magnetic and 
 diamagnetic substances, and also the method of arriving at 
 a mixture, which is indifferent to the action of the magnet. 
 It equally explains the opposite effects observed by Weber, 
 when he introduced into the helix, while being traversed by 
 electric currents, sometimes a rod of iron, at other times a 
 cylinder of bismuth ; only, in all this class of phenomena, we 
 must guard against the influence of superficial inductive cur- 
 rents ; and for this purpose only operate with masses that are 
 very much divided and not continuous. The experiments in 
 which Matteueci had never succeeded in obtaining the least 
 effect upon the magnetised needle, when passing a powerful 
 discharge into the helix, in the centre of which was a piece of 
 
ROTATION OF PLANE OF POLARISATION. 55 
 
 bismuth, whilst it was merely necessary for the bismuth to 
 be replaced by a body containing an almost inappreciable 
 quantity of iron, in order to obtain an action, is due to dia- 
 magnetism, requiring for its development, first, a certain 
 arrangement of atoms, and then the production of the current, 
 which is the consequence of this arrangement, and its not 
 being able to be produced under the influence of an instan- 
 taneous charge * ; whilst magnetisation, being only the result 
 of a direction impressed upon particles already surrounded 
 by an electric current, may be determined instantaneously. 
 Finally, it is easy to see that all magnetic and diamagnetic 
 phenomena peculiar to crystals, being traceable according 
 to the works of MM. Tyndall and Knoblauch, to those pre- 
 sented by an agglomeration of independent magnetic and 
 diamagnetic plates, may be perfectly well reconciled with 
 the theory, which explains the effects that are produced 
 upon these plates. 
 
 With regard to the rotation of the plane of polarisation ex- 
 ercised by transparent diamagnetic substances, it is evidently 
 not due to molecular electric currents, resulting from the action 
 of exterior currents upon these substances, but to the arrange- 
 ment of atoms brought about by this action. Thus the two 
 phenomena, rotation of the plane of polarisation and diamag- 
 netism, have not between them the dependence of cause and 
 effect, but that of being due to the same cause, namely, a par- 
 ticular arrangement of the atoms in the integrant molecules, 
 which very well accords with the observation of M. Biot, 
 that is generally admitted, namely, that the rotation of the 
 plane of polarisation is a phenomenon altogether molecular. 
 We likewise perceive how the direction of the rotation must 
 depend upon the direction of the current by which it is pro- 
 duced, since this direction determines the arrangement of the 
 atoms of the particles in a certain direction, and in a direction 
 precisely opposite, when it is itself changed. The proof that 
 the rotation of the plane of polarisation is not due to molecular 
 
 * Mr. Faraday and M. E. Becquerel have both remarked, that a certain time 
 (some seconds) is required for a diamagnetic body to acquire all the rotatory 
 power of which it is susceptible. 
 
 E 4 
 
56 PHENOMENA DUE TO MAGNETIC POWER. 
 
 currents is found in the fact, that magnetic liquids, in which 
 these currents exist naturally, do not produce the phenome- 
 non when an exterior action gives a similar direction to all the 
 currents ; or produces it in so feeble a degree, that we may 
 conclude the effect only arises from the diamagnetic liquid 
 (commonly water) in which the magnetic body is dissolved. It 
 likewise appears that in magnetic substances, the atoms of 
 which the integrant molecule is constituted, are too near 
 together, even when their mutual polarisation imparts to them 
 a regular arrangement, for their being able to act upon the 
 polarised ray. It is otherwise for diamagnetic bodies, in 
 which the exterior action, although it gives to the atoms of 
 the molecule an arrangement analogous to that which the 
 atoms of the magnetic molecules naturally have, cannot de- 
 termine among them a similar approximation ; which causes 
 that the current resulting from the common direction im- 
 pressed upon them is always very feeble, but which at the 
 same time permits these atoms to act individually upon po- 
 larised light, and to produce the rotation of the plane of 
 polarisation with an intensity depending at once upon their 
 proper nature, and upon the energy of the action, by which 
 they are directed. 
 
 This is the theory which, in the present state of science, 
 seems to us to give the best representation of all the pheno- 
 mena relating to magnetism and to the exterior action of 
 electric currents. It seems to us to agree very well with 
 the various observations that we have described. It is true 
 that it does not explain the particular nature of the action of 
 the atom upon polarised light; but it merely shows that, 
 whatever this action may be, the magnetic influence must 
 give to the atoms a common direction, which causes all their 
 actions to concur, and the molecule, consequently, to act in 
 a certain manner on the interposed ether. 
 
 We shall not terminate this subject without relating also 
 some very recent experiments by which Mr. Tyndall has 
 succeeded in demonstrating the existence of diamagnetic 
 polarity. In this recent investigation, Mr. Tyndall, after 
 having established primary characteristics of the magnetic 
 
DIAMAGNETIC POLARITY. 57 
 
 force, institutes a searching comparison between the phe- 
 nomena of magnetic and diamagnetic bodies, in three distinct 
 cases ; first, when operated on by the magnet alone ; se- 
 condly, when operated on by the current alone ; and, thirdly, 
 when operated on by the magnet and the current combined. 
 It was found necessary, in order to avoid the gravest errors, 
 to take strict account of the molecular structure of the 
 bismuth used in these experiments. A bar of this substance 
 cut, in a certain manner, from the crystallised mass exhibits, 
 between the poles of a magnet, precisely the same visible de- 
 portment as a bar of iron ; while it is well known that the 
 normal deportment of bismuth is opposed to that of iron. 
 The author, in his examination of the points before us, 
 divides magnetic bodies into two distinct classes, and he 
 classified diamagnetic bodies in a similar manner ; one class he 
 calls ?iormal, and the other, a abnormal. A normal magnetic 
 bar is one which sets its length from pole to pole in the 
 magnetic field ; and a normal diamagnetic bar is one which 
 sets its length, at right angles to the line joining the poles. 
 An abnormal magnetic bar is one which sets equatorial in 
 the magnetic field ; while an abnormal diamagnetic bar sets 
 its length axial. In all the three cases mentioned, whether 
 operated on by the magnet alone, by the current alone, or by 
 the magnet and the current combined, the deportment 
 of the normal magnetic bar is precisely antithetical to that of 
 the normal diamagnetic bar ; while the deportment of the 
 abnormal paramagnetic bar is antithetical to that of the 
 abnormal diamagnetic one. But the normal magnetic bar 
 presents to the eye the same phenomena as the abnormal 
 diamagnetic one ; while the normal diamagnetic bar presents 
 the same deportment as the abnormal magnetic one. A 
 want of attention to the peculiarities of structure, which pro- 
 duce these remarkable effects, has introduced considerable 
 error into this portion of science. 
 
 A bar of iron, surrounded by an electric current, exhibits 
 that tivoness of action, those phenomena of attraction and 
 repulsion at its two ends, to which we give the name of 
 polarity. TyndalPs paper contains an account of experi- 
 
58 PHENOMENA DUE TO MAGNETIC POWER. 
 
 ments made with the view of ascertaining whether similar 
 phenomena are exhibited by a bar of bismuth ; such experi- 
 ments have been attempted by others without success ; but, 
 when sufficient power is combined with sufficient delicacy, 
 the most complete mastery is obtained over the motions of 
 the bar of bismuth. With one disposition of the forces the 
 ends of the bar of bismuth were promptly repelled by the 
 magnetic poles; with another arrangement they were just 
 as promptly attracted. In all cases, where an iron bar was sub- 
 stituted for a bismuth one, a deflection precisely opposite to 
 that of the latter was produced. The action was augmented 
 by bringing four magnetic poles to bear simultaneously upon 
 the suspected bismuth ; the two poles, to the right of the bis- 
 muth bar, were always of the same name ; while the two to 
 the left of the bar, were of the opposite quality : with this 
 arrangement the experiment has been repeated in the pre- 
 sence of many eminent men ; the approach and recession of 
 the bismuth bar, in obedience to the direction of the current 
 around it, or the polarity of the magnets acting upon it, 
 were rendered strikingly manifest to all. In a recent inves- 
 tigation, Tyndall has reversed the conditions of experiment, 
 by making the magnet the movable body, and permitting 
 an excited diamagnetic bar to act upon it ; he has succeeded 
 in completely establishing the result already announced by 
 Weber, but questioned by several physicists of eminence, 
 and has produced with insulators all the results hitherto 
 obtained with bismuth alone. The question of diamagnetic 
 polarity may therefore be regarded as settled in the affirm- 
 ative ; indeed, no proof can be brought forward in favour of 
 the polarity of a magnetic body of the same capacity for 
 magnetisation as bismuth, and equally devoid of coercive 
 force, which cannot be matched, by proofs of equal value of 
 the polarity of the diamagnetic body.* 
 
 * See, in the final note X, the title of the principal works relative to the sub- 
 jects treated on in the present Appendix, as well as in the Second and Third 
 Parts of this Treatise, which are contained in the First Volume. 
 
59 
 
 PART IV. 
 
 TRANSMISSION OF ELECTRICITY. 
 CHAPTER I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 General Notions upon the Propagation of Electricity. 
 
 AFTEK having studied the general laws of electricity, both 
 in the static and in the dynamic state, our attention is called 
 to the more special phenomena that result from the trans- 
 mission of this agent through different media. 
 
 The fundamental characteristic of these phenomena by 
 which they are distinguished from those that have formed the 
 subject of our study in the Second and Third Parts, is that they 
 depend essentially upon the particular nature of the medium 
 that is traversed by the electricity; while the former, which 
 are independent of this, and remain the same, whatever the 
 medium may be, constitute the general laws of electricity. 
 
 Before entering upon the examination of the varied and 
 numerous effects that are produced in bodies by the trans- 
 mission of electricity, we shall devote this First Chapter to the 
 consideration of the transmission itself, viewed both in respect 
 to the mariner in which it takes place, and to the influence 
 that is exercised upon it by the medium through which it is 
 operating. Certain general notions on the propagation of 
 electricity will serve as an introduction to this study. 
 
 The word propagation carries with it the idea of motion ; 
 and, in our opinion, electricity in motion is electricity in that 
 state which results from the reunion or neutralisation of the 
 two opposite electrical principles. We have seen that this 
 reunion may be either continuous or instantaneous ; that, in 
 
60 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the former case, it constitutes a current, in the latter, a simple 
 discharge. A very rapid succession of discharges, sometimes 
 called instantaneous currents, may form a continuous current 
 just as the latter may be decomposed into a series of discon- 
 tinuous currents by means of a rheotome. The characteristic 
 of the current which sometimes exists for an instant only, 
 and is then called temporary, is that it acts on the magnetic 
 galvanometer ; whilst the discharge, which is completely 
 instantaneous, exercises no action upon this instrument, 
 although it produces a great number of other effects. 
 When we purpose studying the laws of propagation, we must 
 for the most part make use of currents, except in certain ex- 
 ceptional cases, in which the employment of discharges may 
 be necessary, in order to discover certain special features of 
 the phenomenon. 
 
 The most simple manner of looking into the propagation 
 of electricity is to consider it in a conducting body by which 
 the two poles of a voltaic pile are united : the two electricities 
 which are being constantly liberated at each of the two poles, 
 neutralise each other continuously, in proportion as they are 
 produced, through the conductor, and constitute the current, 
 whose exterior properties or general laws we have already 
 studied in the Third Part. As this current is propagated in 
 the entire mass of the conductor, the direction of its propa- 
 gation is determined by the mere form of the conduction ; it 
 will be rectilinear if this conductor is in a straight line ; curvi- 
 linear, if in a curved line. 
 
 When the conductor has no very determinate dimensions, 
 or is almost undefined in all directions, as, for example, an 
 arm of the sea would be with the two poles of a pile plunged 
 into the water at a certain distance apart, the current deter- 
 minates itself in all directions, as we shall see further on; still, 
 however, being subject to this condition, that all the infinitely 
 minute filaments, into which it may be supposed to be sub- 
 divided, abut by their extremities upon the two poles. We 
 perceive from this that we cannot possibly compare the pro- 
 pagation of electricity in a conducting medium with that of 
 light or radiant heat; for in these two latter cases, the propa- 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 61 
 
 gation emanates from a single radiating centre, and occurs in 
 all directions in a straight line, at least so long as the medium 
 does not change ; whilst, in the case of dynamic electricity, 
 instead of a single one, there are two points, which may 
 equally be considered as centres of emanation ; that is to say, 
 the two poles towards which are constantly directed, or from 
 which as constantly emanate, the contrary electricities, whose 
 reunion forms the current that is propagating in the 
 surrounding medium. Moreover, M. Wartmann has demon- 
 strated by a great number of experiments, that in its propa- 
 gation dynamic electricity is susceptible of neither reflection 
 nor refraction ; and consequently that all the analogy \v hich 
 we might be disposed to establish between it and light or ra- 
 diant heat, is completely void of foundation. 
 
 We may, however, inquire whether electricity in the static 
 or tension state, as it is manifested on an insulated body, is 
 not susceptible of propagating itself in the surrounding 
 medium ; in this case, we are concerned with only one elec- 
 tricity, either the positive or negative. We well know that an 
 insulated and electrised body loses its electricity with greater 
 or less rapidity, according to the state of the surrounding air, 
 and the greater or less insulating powers of its support. Belli, 
 and other philosophers after him, have even proved that nega- 
 tive electricity, under like circumstances, is dissipated more 
 easily than positive. But the mere fact of the electric tension 
 of the electrised body diminishing, proves that electricity pro- 
 pagates itself out of this body. More than this, Faraday, in his 
 researches on static induction, has demonstrated, as we saw in 
 the Sixth Chapter of the Second Part, that this propagation 
 does not operate to a distance, but occurs by the intervention of 
 bodies, even of those that are apparently the best insulators. 
 These bodies become polarised under the influence of the elec- 
 trised body ; that is, that each of their particles present the two 
 electricities separated from each other, so that, if the elec- 
 trised body is positive, the negative electricities of each par- 
 ticle are all turned on the side of the body, and the positive 
 on the opposite side. This is what constitutes induction. It 
 even sometimes happens that the contrary electricities of 
 contiguous particles neutralise each other, constituting a veri- 
 
62 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 table transmission of electricity, what Faraday calls conduc- 
 tion, in opposition to simple induction, which in his opinion 
 always precedes conduction. It follows from this that the 
 distinction between insulating and conducting bodies is not 
 absolute; for even the best conductors, as we shall see here- 
 after, always oppose a certain resistance to the passage of elec- 
 tricity ; and thehinderance that it suffers, although much less in 
 degree, is of the same kind as that which is observed with even 
 the best insulating bodies, as spermaceti, lac, or sulphur. 
 
 M. Matteucci, as the result of a great number of experi- 
 ments made upon the propagation of electricity in solid in- 
 sulating bodies, has confirmed and extended the results that 
 had been obtained by Faraday. He established in all insu- 
 lating bodies, but in different degrees, according to their nature, 
 the development of the molecular electric state, of which we 
 have been speaking ; so that each molecule has the two con- 
 trary electric states developed upon its opposite faces. He 
 has also shown that these molecular electric states may destroy 
 each other; and consequently that the electricity may propa- 
 gate itself either upon the surface or within the interior of the 
 body. The property of insulation, therefore, consists only in 
 the greater or less resistance opposed by bodies that are en- 
 dowed with it, to the destruction of the molecular electric 
 states, by the entry or the escape of the electric fluids from 
 the molecules themselves; a resistance that depends upon 
 several circumstances, due either to the nature, the dimen- 
 sions, or the other physical conditions of the body, or to the 
 intensity of the electricity with which the insulating body is 
 charged. Hereafter, when we are engaged in a more special 
 manner on the propagation of electricity in insulating bodies, 
 we shall return to the facts from which M. Matteucci 
 draws the conclusions to which we have been referring. 
 
 We may therefore admit, as we have already incidentally 
 mentioned in the Fifth Chapter of the Third Part, p. 18, that 
 the propagation of electricity in all cases takes place by 
 means of the neutralisation of the opposite electricities of the 
 particles of the body, through which the transmission is taking 
 place, a neutralisation that is always preceded by a mole- 
 
CHAP. I. PROPAGATION OP ELECTRICITY. 63 
 
 cular induction, that is to say, by the separation of these 
 electricities in each molecule. In very good conducting bodies 
 these successive inductions and neutralisations take place 
 with very great rapidity ; in insulating bodies they take place 
 less rapidly, and the more slowly as the body is a better in- 
 sulator. It is manifest, therefore, that there is never any 
 propagation of a single electricity ; and that the only difference 
 existing between the case in which the medium is in com- 
 munication with a single electrised body, and that in which 
 it is placed between two bodies charged with contrary elec- 
 tricity, is that in the latter case there is an effect double of 
 what occurs in the former ; for it is easy to see that the two 
 effects, instead of destroying each other, must be added to- 
 gether. For if we suppose (Jig. 179.) two series of molecules 
 
 Fig. 179. 
 
 between the body A charged with positive electricity, and 
 the body B charged with negative, the series of molecules 
 a, b, c, d, e, upon which A is acting, will be polarised exactly 
 like the series of molecules a', b' 9 c', df, e upon which B is acting; 
 but in fact the two series, or rather all the series of molecules 
 comprised between A and B, are subjected at once to the action 
 of A and the action of B, which must produce upon them an 
 effect the double of what would have resulted from the sole 
 action of A or B. This principle is equally true, whether we 
 are concerned with a continuous current or a simple discharge. 
 The direction according to which the propagation occurs, 
 when two bodies charged with contrary electricities, as the two 
 poles of a pile, are presented to each other, is determined by the 
 direction according to which the consecutive molecules inter- 
 posed between these two bodies are placed, and through which 
 this propagation takes place. When there is only one electrised 
 
64 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 body, it is the ground, or rather the nearest conductor 
 communicating with the ground, which fulfils the office of the 
 second electrised body, as follows from the analysis that we 
 have been making of the phenomenon. We must not in either 
 case suppose that the particles composing the most conducting 
 portion of the interposed medium are the only ones through 
 which the propagation takes place ; under certain circum- 
 stances, this propagation occurs through the others also. Thus, 
 Sir. W. S. Harris has remarked that, if the discharge of a 
 highly charged battery of Leyden jars of twenty-five square 
 feet is passed through a fine iron wire enclosed in a receiver 
 in which the air has been highly rarefied, the wire appears 
 in no way affected, but the surrounding air becomes luminous, 
 whilst, on allowing the air to enter into the receiver, the wire 
 is immediately melted, even when a battery of only five 
 square feet is employed. The same occurs in rarefied air, if 
 a voltaic pile is employed instead of a battery of Leyden jars. 
 These differences are due to there being nothing absolute in 
 the conducting faculty of bodies, and to their depending upon 
 different conditions, relating either to the condition of the 
 medium or to the origin, that is to say, the intensity of 
 the electricity. 
 
 The decomposition and recomposition of the two electrici- 
 ties in each particle of the medium through which the pro- 
 pagation of the electricity takes place, may be accompanied by 
 effects, either chemical, calorific luminous, or physical, accord- 
 ing to the nature of this medium and the physiological condi- 
 tions under which it exists, and according to the mode of pro- 
 duction of the electric agent. It may also happen, in certain 
 cases, when the medium presents a great resistance to this neu- 
 tralisation of the contrary electricities of the consecutive par- 
 ticles, that these particles undergo a mechanical displacement, 
 whence arises a motion in the medium if it is liquid or gaseous, 
 and a rupture if it is solid. We shall carefully examine these 
 different phenomena, the study of which will furnish a con- 
 firmation of the manner in which we are explaining the 
 mode of the propagation of electricity. 
 
 After this first general glance that we have made at the 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 65 
 
 propagation of electricity, we shall in the present Chapter 
 first investigate the laws to which it is subject in good con^ 
 ductors, both solid and liquid ; we shall then determine the 
 influence that is exerted upon it by the particular nature of 
 these good conductors, and the physical conditions in which 
 they occur. We shall then study this same propagation in 
 solids and liquids that are insulators, or rather imperfect 
 conductors, as well as in elastic fluids and in vacuo. We 
 slmll terminate the examination by the exposition of the re- 
 searches that have been made on the actual velocity with 
 which the propagation takes place. This is the object of this 
 First Chapter. 
 
 The chemical, physical, and physiological effects, that ac- 
 company the transmission of electricity, will be the object 
 of the following chapters. 
 
 In the study that we are about to enter upon, we shall make 
 use of the voltameters that we have described in the First Part 
 of this work, as well as of the magnetic galvanometers, to the 
 description of which we have devoted the Fourth Chapter of 
 the Third Part. We shall employ, as sources of electricity, 
 either the electric machine, the voltaic pile, or the magneto, 
 electric machine, which produces induction currents. These 
 three apparatus, although each capable, as we shall presently 
 see, of producing electricity under all forms, are nevertheless 
 more particularly suited, the electric machine for producing 
 it under the form of the discharge, the pile under the form 
 of a continuous current, the magneto-electric machine under 
 the form of a discontinuous current. On this account we 
 shall in preference employ one or other of these three ap- 
 paratus, according as we shall require electricity under one 
 or other of these three forms. We shall be directed in our 
 choice by the nature also of the bodies through which we 
 shall have occasion to bring about the transmission of the 
 electricity, and by that of the effects that we are desirous of 
 producing. 
 
 Laws of the Propagation of Electricity in good Conductors. 
 We have just seen that no conductors, however good, are 
 
 VOL. II. P 
 
66 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 absolutely perfect conductors of electricity ; but that all 
 bodies, even those which appear to conduct it best, oppose a 
 certain resistance to its propagation. However, we shall con- 
 sider as good conductors all those which permit of a tolerably 
 rapid propagation of electricity, so that the current resulting 
 therefrom is able to act upon the magnetised needle, and 
 consequently to produce the general phenomena of electro- 
 dynamics. It is true that this definition has still the incon- 
 venience of not being absolute ; for the same body pure 
 water, for example may be classed or not classed among good 
 conductors, and according to the apparatus employed for pro- 
 ducing the electricity ; according to the mode of communication 
 that is established between it and this apparatus ; and, finally, 
 according to the physical conditions under which it is placed. 
 But this is of little importance so long as we are only con- 
 cerned in determining the laws of the propagation itself: it 
 is in the subsequent paragraph, which is devoted to the study 
 of the conducting powers of different bodies, that we must 
 have regard to these anomalies. It is also of little importance 
 whether the apparatus, of which we are about to avail 
 ourselves for the production of the electricity, be of one 
 kind or of another. The only conditions with which it must 
 comply, are to be sufficiently powerful to give us, with the 
 conductor that we are about to employ, a continuous 
 current, capable of acting directly and at will without the 
 employment of the galvanometer upon the magnetised needle, 
 and sufficiently constant that this current may preserve the 
 same intensity during the continuance of the experiments. A 
 Daniell's or a Grove's pile, of two or three pairs, as an 
 electro-motive apparatus, wires or metal plates, and saline 
 or acid solutions as conductors, will perfectly satisfy the re- 
 quired conditions. 
 
 The first law that we shall encounter, when we are stu- 
 dying the propagation of electricity in a conductor, is the 
 tendency that the electric current possesses of distributing 
 itself, or rather of being disseminated, throughout the whole 
 extent of this conductor. This law, which I established for 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 67 
 
 solid conductors in 1824*, and for liquids in 1825, may be 
 easily demonstrated in various ways. In order to demonstrate 
 it in solid conductors, we have merely to take a very wide 
 plate of copper, one of 5 or 6 inches for instance, and about a 
 foot in length, terminated at its extremities by two wires, also 
 of copper, placed on the prolongation of the line that divides 
 the plate into two equal parts, and intended for placing it in 
 the voltaic circuit. This plate is arranged vertically within 
 the cage of a torsion-balance, the wire of which carries an 
 astatic conductor ; and which is so placed that its different 
 longitudinal sections are successively opposite to the vertical 
 branch of this conductor. The current is then so directed 
 that it shall pass in opposite directions in the plate, and in 
 the movable conducting wire, which gives rise to a repulsion. 
 We find, on taking the mean of many experiments, that the 
 angles of torsion necessary to bring the movable conductor 
 back and into contact with the fixed conductor, are sensibly 
 the same, whatever be the portion of the latter that is 
 acting upon it. If the current is directed so that attraction 
 takes place, we find that the angles of torsion, necessary for 
 detaching the movable conductor from the fixed one, are the 
 same, whatever portion of the latter be made to act upon 
 the other. In order to measure their force of mutual at- 
 traction or repulsion, we place the two conductors at an 
 almost imperceptible distance from each other, so as to be 
 sure that the action is due only to the actual section of the fixed 
 conductor that is situated opposite to the movable conductor, 
 the action of the other sections being exerted too obliquely to 
 produce an appreciable effect. It follows from this experiment, 
 that dynamic electricity appears to be equally distributed 
 throughout the whole extent of a plate serving as its con- 
 ductor, and gives rise to as many parallel currents, of equal 
 intensity with each other, as we may suppose there are infi- 
 nitely thin sections in the rectangular plate. 
 
 * Mem. dela Soc. de Physique etde VHistoire Nat. de Geneve, torn. iii. p. 109. ; 
 and Ann. de Ch. et de Phys. torn, xxviii. p. 190. 
 
 F 2 
 
68 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 We arrive at the same result by placing horizontally, in 
 the direction of the magnetic meridian, the copper plate, or 
 a surface of mercury, to which we may give -a width of as 
 much as 8 or 10 inches; and by bringing as near to it as 
 possible a very small magnetised needle, perfectly horizontal, 
 and very delicately suspended. The deviation that occurs 
 to this needle, when the conducting surface above which it is 
 situate is placed on the circuit, is the same, whatever be the 
 portion of this surface that is acting directly upon it, provided 
 that the needle is never so near to the edge that, when it is 
 deflected, its extremity is situated beyond the surface. Thus 
 we are led to admit that the electric current, on entering into 
 a solid conductor, distributes itself through the whole extent 
 of this conductor, by small parallel filaments, all of equal 
 intensity ; whence it follows necessarily, that the less con- 
 siderable this extent is, the more will the electric current be 
 condensed, and the greater consequently will be its intensity 
 in each section of the conductor ; a result that is fully con- 
 firmed by experiment, when we employ a conducting plate of 
 uniform thickness, but wider in a certain part of its length 
 than in others ; the action of the plate upon the needle is 
 more intense in proportion as the portion over which the 
 needle is placed, is narrower. This same condensation of 
 the current is demonstrated by the power, which the narrow 
 part of the conducting plate possesses, of attracting iron 
 filings, whilst the wide part does not attract the slightest 
 quantity. To the same cause also, as we shall presently see, 
 is due the development of heat that accompanies the passage 
 of the electric current in the narrow parts of a conductor, 
 whose wide parts suffer no sensible change of temperature, 
 although they are traversed by the same current during 
 the same time. 
 
 The law, that we have just laid down, is only verified in an 
 accurate manner in conductors in which one of the dimensions, 
 the length, exceeds the others, which constitutes the case of 
 linear propagation. In other cases, the law is less simple. 
 M. Kirchoff, who made a particular study of this subject, has, 
 however, arrived at results which are altogether in con- 
 
ciiAi>. I. PROPAGATION OF ELECTRICITY. 69 
 
 formity with the theory whereby the propagation of elec- 
 tricity is explained.* 
 
 Dynamic electricity equally manifests this same tendency 
 of distributing itself in a liquid conductor that is susceptible of 
 being decomposed, as well as in a solid conductor, or a liquid 
 such as mercury. I proved this in the following manner in 1825. 
 Take a large trough, some 2 ft. or more in diameter, for in- 
 stance, and 3 or 4 inches deep, and fill it with salt water or 
 diluted acid, and then plunge into it the two poles of the pile, 
 each at a distance of 2 or 3 inches from the edge, and so that 
 they are situated on the same diameter. It is well to employ 
 as electrodes two platinum spheres, of about half an inch, for in- 
 stance, in diameter, each surmounted by a metal stem, covered 
 with an insulating coating, serving to sustain them, and to 
 make communication with the poles of the pile. Then attach 
 to each of the extremities of the wire of a magnetic galvano- 
 meter a small rod of platinum, and by means of a piece of 
 ivory or any other insulating body, maintain these two rods, 
 which are of the same diameter and the same length, always 
 at the same distance apart, 2 inches, for example. Then plunge 
 this species of fork into various parts of the liquid that is 
 traversed by the current, taking care that the extent of the 
 portion immersed is always the same. In this way we collect 
 the portion of the current that traversed the section of liquid 
 interposed between the two platinum points of the galvano- 
 meter. "VYe find that it is greatest in quantity on the right line 
 that joins the two poles of the pile and between these poles, 
 but that upon this line itself it increases in intensity, 
 setting out from the middle, where it is most feeble, to 
 near the poles, where it attains its maximum. However, 
 we find currents in all parts of the liquid, even behind 
 the poles, that is, in the parts comprised between each 
 pole and the edge of the trough. The diffusion of the cur- 
 rents is the more decided, in proportion as the liquid is a 
 worse conductor ; so that it seems as if the currents describe, 
 from one pole to the other, curves of greater or less curvature. 
 
 * See the final noto A., for the explanation of M. Kirchoff's researches. 
 
 F 3 
 
70 TRANSMISSION OF ELECTRICITY. PAKT iv. 
 
 It would be an interesting matter to determine exactly the 
 form of these curves, by searching, by means of platinum 
 gauges, for all the elements of the filament that have the same 
 intensity; which would enable us to trace out the polygon, and 
 consequently the isodynamic curve, which would probably 
 vary with the conductibility of the liquid. 
 
 M. Matteucci, who published in 1839 some researches on 
 the same subject, adopted also the same method, but employ- 
 ing as gauges plates instead of wires of platinum. The chief 
 object of his experiments was to determine the influence 
 which the extent and distance of the immersed plates exercise 
 over the intensity of the current that they are able to absorb ; 
 and he found, that in proportion as the liquid is a better -con- 
 ductor, so must their surface and their mutual distance be 
 increased in order to collect a current of the same force. 
 And if the immersed surfaces of the plates are equal, their 
 distance, in a saturated solution of sulphate of copper, 
 must be twenty times greater than in distilled water. When 
 the two poles are not in the line that divides the liquid mass 
 in the middle, it is found that the current absorbed by the 
 gauges, at an equal distance from the middle line, but on the 
 two different sides of this line, is always more powerful on the 
 side that is nearer the edge of the trough, namely, in the 
 stratum that contains the less liquid. I should add, that M. 
 Matteucci made his experiments, by employing a double 
 galvanometer, and two perfectly similar systems of gauges, 
 so arranged that the current collected by one was led in a 
 contrary direction to that collected by the other. Hence it 
 followed, that whenever the two collected currents were per- 
 fectly equal, the needle of the galvanometer remained at rest ; 
 and that the direction of its deviation, when it occurred, in- 
 dicated which of the two currents w T as the more intense. 
 
 The second law, to which the propagation of electricity in a 
 conductor is subject, is, that two or more electric currents may 
 be propagated in the same conductor without mutually 
 modifying each other, and consequently in a manner altogether 
 independent of each other. M. Marianini has proved this 
 property by passing through a liquid, placed in a cubical 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 71 
 
 vessel, two currents, so arranged that the filaments of which 
 they are composed cross each other at right angles, without 
 any variation occurring in the intensity of either of them ; 
 an intensity which remains the same whether they pass 
 separately or both together through the liquid conducting 
 mass. A third current may be also transmitted through the 
 same liquid that is already transmitting the other two, and in a 
 direction perpendicular to them ; and this transmission ope- 
 rates in the same manner as if this liquid were not traversed 
 by any current. This independence in the propagation of 
 currents has been also established by passing two or even three 
 currents through a column of liquid, in directions more or less 
 oblique to each other, and even by transmitting them through 
 the wire of the same galvanometer, upon which the effect 
 observed is always the sum or the difference of the individual 
 effects of the partial currents. 
 
 These facts, at first sight, seem to establish a great analogy 
 between dynamic electricity and light, the rays of which may 
 all cross each other in the same small hole without under- 
 going the least alteration, and each preserving its own 
 character and its special properties. However, the analogy 
 is more apparent than real ; for, as we have remarked in the 
 preceding section, the propagation of electricity cannot be as- 
 similated to a radiation, and in fact it possesses none of its 
 properties, not having of itself a rectilinear direction, nor 
 being capable of undergoing reflection, refraction, or polari- 
 sation. 
 
 A third law, which at the first glance seems also to be 
 favourable to the analogy that we have just rejected, is the 
 diminution of intensity that electricity undergoes in its pro- 
 pagation through a liquid mass, when it is intercepted on its 
 route by metal plates or diaphragms interposed in the liquid. 
 This phenomenon, which, I pointed out in 1825, is easily de- 
 monstrated by separating with metal plates, into two or more 
 distinct compartments, a conducting mass of liquid contained 
 in a rectangular vessel 10 or 12 inches long, into the two 
 extremities of which the poles of a pile are inserted. A gal- 
 vanometer, placed in the circuit of the transmitted current, 
 
72 TRANSMISSION OF ELECTRICITY. TAUT iv. 
 
 indicates, by the amplitude of its deviations, that this current 
 suffers a sensible diminution of intensity, by the interposition 
 of one or more metal diaphragms, even when the diaphragm is 
 a better conductor than the liquid section that it replaces. But 
 this diminution is proportionately less for the same diaphragm, 
 as the number of diaphragms already interposed is greater, 
 and as the number of pairs constituting the pile employed is 
 greater. Thus a current, which by the interposition of two 
 diaphragms is not more than 75 is reduced to 73 only, by the 
 interposition of a third; whereas a current of an initial inten- 
 sity of 75 is reduced to 67 by the interposition of a single 
 diaphragm. M. Marianini and other philosophers, who have 
 made a great number of experiments on this subject, have all 
 confirmed my conclusions. This influence of diaphragms is 
 also rendered evident by calorific and chemical voltameters, 
 as well as by the magnetic galvanometer. Thus, a current, 
 which when transmitted through nitric acid marks 38 on 
 the calorific galvanometer placed in its circuit, gives only 30 
 when a platinum diaphragm divides the column of nitric 
 acid into two compartments, and when there are two dia- 
 phragms instead of one. The first diaphragm, which reduces 
 the calorific effect to the yV* n ^ wna t it was originally, re- 
 duces the chemical effect only to Jth. In fact, with the chemi- 
 cal voltameter placed in the circuit of the current, instead of 
 the calorific we find that it requires 5' for the liberation of 
 a certain quantity of gas, when there is no diaphragm, whilst 
 it requires 25' if there is one diaphragm. 
 
 It is well known that light and radiant heat undergo a 
 diminution of intensity, which is subject to the same laws, 
 when we interpose in their course one or more diaphragms 
 that are more or less capable of transmitting them under their 
 radiant form ; this had given rise to the analogy to which we 
 referred just now. Here also the analogy is in fact more 
 apparent than real ; for it is easy to prove that the phenomenon 
 of diaphragms, in the case of electricity, is only a phenome- 
 non of conductibility. I had noticed, as far back as 1825, 
 that so long as the metal diaphragm does not entirely prevent 
 the two portions of liquid that it separates from communicating 
 
CHAP. r. PROPAGATION OF ELECTRICITY. 73 
 
 together, the current deviates in great part from its route, 
 rather than traverse the diaphragm. M. Matteucci obtained a 
 still more significant result, by placing within a large trough 
 filled with a conducting liquid a box about Jin. wide and 4in. 
 long, closed at its two ends by two platinum plates, whilst its 
 two longer sides were of wood. After having filled it with 
 the same conducting liquid, and to the same level, he places it 
 so that its two platinum faces were in front of the poles of the 
 pile, which were placed in the large trough. One of the two 
 systems of gauges is plunged inside the box, and the other 
 outside; but both are placed symmetrically in respect to the 
 line, that joins the two poles. When the deviation of the 
 galvanometer which is in favour of the system exterior to 
 the box, has become constant, the interior system is to be 
 taken away; and this makes no change whatever in the 
 deviation; a proof that no current was transmitted in the 
 liquid withinside the box, and that the current instead of 
 traversing the two plates, is inflected round the sides, so as 
 to pass only through the continuous portion of the liquid. 
 
 Independently, however, of the resistance proper, opposed 
 by a liquid and a solid to the transmission of an electric 
 current, there is a special resistance due to the mere fact of 
 the passage of the current from a solid into a liquid, or 
 from a liquid into a solid. We call this resistance, the resist- 
 ance to passage. It always takes place while a liquid is being 
 traversed by an electric current; for, in order to put this 
 liquid into the circuit, solid conductors, called electrodes, 
 must necessarily be employed. This resistance to passage 
 does not appear, as several philosophers have supposed, 
 to be the effect of a peculiar property appertaining to 
 the very nature of the electric current, as is the case in 
 respect of the action of screens upon light, and upon ra- 
 diant heat. It is rather the result of the electro-chemical 
 phenomena which, in virtue .of the decomposing action of 
 the current, necessarily occur on the surfaces of the solid 
 conductors that are in contact with the liquids in which 
 they are transmitting this current. These very complex 
 phenomena, which we shall study hereafter, must depend 
 
74 TKANSM1SSION OF ELECTKICITY. PART iv. 
 
 upon the chemical nature of the solid and liquid conductors 
 that are in contact, and upon the various circumstances by 
 which their mutual action may be modified. And in re- 
 ference to this, I had already remarked in 1825, that the re- 
 sistance to passage is less, in proportion as the liquid exercises a 
 more powerful chemical action upon the solid conductor; 
 and I observed subsequently, that the elevation of the tempe- 
 rature of the electrodes, more particularly of the negative elec- 
 trode, also diminishes it. I had also succeeded in completely 
 annihilating it, by employing currents passing alternately in a 
 contrary direction, as those which are obtained with a mag- 
 neto-electric machine, or by simply placing a commutator or 
 rheotrope in the circuit of an ordinary voltaic current. In 
 this case, for example, the currents that alternately succeed 
 each other, produce upon the solid surfaces chemical effects 
 that are alternately contrary, and consequently which 
 neutralise each other; and then, by taking certain pre- 
 cautions, such as employing tolerably energetic currents, 
 and causing them to succeed each other with great rapidity, 
 we succeed, as we have just mentioned, in annihilating 
 the resistance to passage. In the Chapter wherein we shall 
 be engaged with the electro-chemical decomposition of bodies, 
 we shall return to this class of phenomena, which immediately 
 depend upon it. 
 
 A fourth law, that regulates the propagation of electricity, 
 is, that all the successive parts of a closed circuit, including 
 also the apparatus itself which produces the electric current, 
 are traversed at the same time by the same quantity of 
 electricity, whatever be the diversity of their nature, their 
 form, and their extent ; circumstances, which influence only 
 the absolute quantity of electricity that is in circulation, and 
 not its relative intensity in different parts of the circuit. 
 Also, if we have in the same circuit, first the pile, then a 
 wire coming from one of its poles and entering into a liquid, 
 and two or more parallel wires extending from this liquid to 
 the other pole, the quantity of electricity that, under the 
 form of a current, traverses the pile itself, the first wire, the 
 liquid, and the two or more parallel wires, is exactly the 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 75 
 
 same. It is clear that, if this latter system of conductors is 
 composed of two wires, and these two wires are perfectly 
 similar in all respects, the quantity of electricity that 
 circulates in each of them is the half of what is circulating 
 in the first wire ; it would be the third if there were three 
 wires, and so on; but in the two or three united, it is 
 together the same a? in the first wire. Ampere had obtained 
 a glimpse of this important law, when he showed that the 
 effect produced upon the magnetised -needle is the same 
 whatever be the portion of a voltaic circuit, including the 
 pile, that acts upon it. M. Becquerel had proved it in a 
 more accurate manner, by soldering wires at different points, 
 taken at equal distances, on a metal conductor that connects 
 the two poles of a pile, which wires he connected with the 
 ends of a galvanometer, and finding that the currents 
 conducted by these wires two by two were equal in force, 
 when the portions of the principal conductor, intercepted by 
 the two systems of soldered wire were themselves equal. 
 
 I have myself on several occasions announced the same 
 principle, founding it upon facts that I shall set forth in 
 the Chapter of the Fifth Part in which I shall be treating 
 of the theory of the voltaic pile. Finally, Pouillet and 
 Fechner have demonstrated this law in a direct manner. M. 
 Pouillet placed all the successive elements of a thermo- 
 electric pile in the magnetic meridian, as he did also the 
 conductor employed for the completion of the circuit ; and 
 he found that a magnetised needle placed above any part of 
 the whole circuit always obtained the same deviation, what- 
 ever this part was. M. Fechner on his part obtained a si- 
 milar result by making a magnetised needle oscillate over the 
 different solid portions of a voltaic circuit, placed perpen- 
 dicularly to the direction of the needle, and discovering that 
 these oscillations are executed in the same time, which 
 proves the equality of the intensity of the current in these 
 different parts. However, he did not verify by direct 
 experiment, that this equality extends to the liquid con- 
 ductors of the pile, which is however generally admitted. 
 
 The law to which we are referring, admitted implicitly by 
 
76 TRANSMISSION OF ELECTEICITi". PART iv. 
 
 Ohm in his theory of the pile, has been proved less by direct 
 experiments, than by the consequences that have been 
 derived from it, and which have always been verified. It 
 appears to me, however, to be necessary to give it a positive 
 experimental demonstration. The following is the description 
 of the apparatus that I have constructed for this purpose. 
 (Fig. 180.) 
 
 The ends of glass tubes which are all of the same diameter, 
 
 Fig. 180. 
 
 and perfectly symmetrical throughout, are united to each 
 other by solid or hollow metal cylinders of the same exterior 
 diameter as the tubes, and presenting a face of zinc at one 
 of their extremities and a face of copper at the other. The 
 glass tubes are filled with different conducting liquids ; and 
 the circuit is completed by means of a glass tube, also of the 
 same diameter as the others, and filled with mercury. We 
 thus obtain a circuit composed of voltaic pairs, of liquids, of 
 hollow and of solid metal conductors, and of a column of 
 mercury ; in a word, of parts that are all conductors, although 
 some only of them are active ; and the transverse section is 
 the same to all. If the different parts of this circuit are 
 successively arranged so that they are parallel to the mag- 
 netic meridian, a magnetised needle, delicately suspended 
 over each of them, executes the same number of oscillations ; 
 the needle does not suffer any deviation, when it is placed 
 exactly between two opposite parts of this circuit, each parallel 
 to the meridian. These results prove that the sum of the 
 electric forces, that are traversing at the same time each of 
 the transverse sections of this circuit, is absolutely the same, 
 We have merely to substitute for the liquid in one of the 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 77 
 
 compartments, another liquid that is a worse or a better con- 
 ductor, and we diminish or increase the absolute intensity of 
 the current, not only in the part of the circuit that is modi- 
 fied, but equally in the whole of the circuit ; so that its force 
 remains always the same in all portions at the same instant. 
 
 In the preceding experiment, I have supposed that the 
 circuit, although heterogeneous, is however such that all its 
 transverse sections are equal. The law equally holds good, 
 when they are unequal. To prove this, we have merely to 
 supply the place of the mercury that is in the tube, by a 
 wire of any diameter, either homogeneous or composed of 
 pieces of different metals soldered end to end, taking care 
 to put the wire in the axis of the same tube which was pre- 
 viously occupied by the mercury, and in such a manner that it 
 also completes the circuit. If the magnetised needle is placed 
 above the different parts of this wire, it will be found to give 
 the same number of oscillations as when it is placed over the 
 different liquid or solid conductors that are in the rest of the 
 circuit. Only, in order to neutralise the differences that might 
 arise from the diversity of diameters of the different parts of 
 the circuit, we must take the precaution of so placing the 
 needle, that it may not be too near, but always in such a 
 position that it is everywhere at the same distance from the 
 axis of the conductors that are acting upon it. 
 
 It follows from this fourth law, that the absolute intensity 
 of the electricity, that travels in the form of a current through 
 a closed circuit, depends upon two circumstances alone, the 
 force or forces that produce the electricity, and which we 
 may call electro-motive forces, and the resistances to con- 
 ductibility presented by all the circuit taken together. This 
 latter element, which had never previously been taken into 
 account, was pointed out by myself, both in 1825, in the 
 memoir to which I have already alluded above and also in 
 the subsequent researches that I published in 1828 and after- 
 wards. In an important work which appeared in 1827, M. 
 Ohm, as a result of purely theoretical speculations, came to 
 the conclusion that the force of the current in a closed 
 circuit is directly proportional to the sum of the electro- 
 
78 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 motive forces that are in activity in the circuit, and which 
 we will call E, and inversely proportional to the total resist- 
 ance, or the sum of the resistances of all the parts of the 
 circuit, which we will designate by R ; in other words, that 
 the intensity of the current, I, is equal to the sum of the 
 electro-motive forces, divided by the sum of the resistances : 
 
 "P 
 
 I = . Experiment has proved the accuracy of this for- 
 mula, within limits sufficient for the purposes, to which we 
 are required to apply it in the present chapter. We shall 
 return to this in the sequel, when we are engaged upon the 
 theory of the pile. 
 
 A fifth law, which arises immediately out of the preceding, 
 is, that if we increase or diminish the resistance of any part 
 of a circuit, the total intensity of the current diminishes or 
 increases, all other circumstances remaining the same, in a 
 proportion, which is the same as that existing between the 
 resistance added or removed, and the total new resistance of 
 the entire circuit. 
 
 E 
 
 If in the formula, i = -, R becomes R + r, or R r, I 
 
 R 
 E E 
 
 becomes ; or . Calling i' the intensity in the 
 
 R + r R r 
 
 former case, and i" the intensity in the latter, we have 
 
 , .. E E Ell 1 
 
 i : i' : i" =- : - - : - _ = - : : - - ; whence 
 
 R R + 7- R r R R-fr R r 
 
 we deduce, I i' : I = r : R + r, and i" I : I =r r : R r ; 
 namely, that the diminution of intensity is to the primitive 
 intensity as the added resistance, r, is to the new total re- 
 sistance R + r ; and the increase i" I is to the primitive 
 intensity, as the suppressed resistance r is to the new total 
 resistance R r. 
 
 Fechner verified experimentally, by means of the oscil- 
 lations made by the needle under the action of the magnet, 
 the accuracy of the law that we have just stated. He hence 
 concluded that a pile whose electro-motive force is repre- 
 sented by 1, and whose poles are connected by a conductor 
 whose resistance is also equal to 1, and in which 9 represents 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 79 
 
 the resistance of the pile itself, would have a force represented 
 by <pjT = ^ft By doubling the resistance of the conductor, 
 it is evident that we do not render the force of the pile one- 
 half less ; for it becomes ^ = - = -, in place of , as it 
 
 y "|" -L i -* 1 J- ivJ 
 
 was at first. If it is the resistance of the conductor inter- 
 posed between the poles, that is 9 times that of the pile, then 
 by doubling this resistance, the force of the pile, which was 
 
 at first equal to g = -jg, becomes j^g = fjj- From 
 
 this we can readily perceive that, the greater the resistance 
 of the interposed conductor, the less is the influence of the 
 resistance of the other parts of the circuit. M. Pouillet ar- 
 rived at the same verification by employing the tangent gal- 
 vanometer, and by means of the following experiments. He 
 took a single pair of Darnell's constant pile, the current 
 from which he passed through this tangent galvanometer 
 (Jig. 182.), by means of two copper rods; then, with silk- 
 covered copper wire, he made series of different lengths, of 
 5, 10, 40, 70, and 100 metres, which he rolled up and co- 
 vered, wrapping them in a ribbon, so that the two ends, 
 being bent back into a hook, might easily be plunged into 
 cups of mercury, arranged for establishing communication. 
 The following is then the mode of proceeding: The current 
 is passed direct through the tangent galvanometer, and the 
 deviation is observed ; then all the wires of the series are 
 successively introduced into the circuit, the corresponding 
 deviations being carefully noted, bearing in mind that the 
 intensities of the successive currents are proportional to the 
 tangents of the angles of deviation obtained. The resistance 
 of the total circuit (which is composed of the resistances of 
 the pair before the wires were introduced, of the wire of the 
 galvanometer, and of the various conductors employed for 
 establishing the communication), being R, this resistance 
 becomes successively, in proportion as the wires of different 
 lengths are introduced, R + 5 m , R + 10 m , &c. 
 
80 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV, 
 
 The following table was obtained from these experi- 
 ments : 
 
 Resistances. 
 
 Deviations observed. 
 
 Tangents of the Deviations. 
 
 R 
 
 62 C -00 
 
 1-880 
 
 R+ 5 m 
 
 40.20 
 
 0-849 
 
 R + 10 m 
 
 28-30 
 
 0-543 
 
 R + 40 m 
 
 9'45 
 
 0-172 
 
 R + 70 m 
 
 6'00 
 
 0-105 
 
 R + 100 m 
 
 4-15 
 
 0-074 
 
 By comparing the first observation with each of the others, 
 we deduce for R the values 4 m 'll; 4 m -06 ; 4 m -01 ; 4 m -14; 
 and 4 m -09 ; the mean of which is 4 m -08. For this purpose 
 we make use of the formula i i' : i = r : R + r, putting in 
 place of I, the value 1-880; and in place of i' the successive 
 values 0-849, 0-543., &c., and in the place of r, the cor- 
 responding values 5 m , 10 m , 40 m , &c. 
 
 This result shows that, with some very trifling differences, 
 which can only be attributed to small errors of experiment, 
 we obtain the same value for R, whichever of the subsequent 
 observations is compared with the first; a proof that 
 we were right in our statement, that I i' : i = r : R + r; 
 for, by substituting for I the number 1*880, we obtain 
 for R the same value, when we put successively for r, 5 m , 
 10 m , 40 m , 70 m , and 100 m ; and for i', the corresponding 
 values 0-849, 0-543, 0-172, 0-105, and 0-074. Thus the 
 law, which gave us the formula, is quite true, since it leads, 
 on being applied in all possible cases, to a same value for a 
 quantity which is indeed necessarily the same. 
 
 The value of R = 4 m< 08, indicates that the resistance of all 
 the primitive circuit, not including consequently the copper 
 wires that are added to it, is equal to the resistance that 
 would be offered by a length of the same copper wire equal 
 to 4 m -08 ; this is called the reduced length. Thus the reduced 
 length of a circuit is the length of a wire, of a given nature and 
 thickness, whose resistance is equal to the sum of the resistances of 
 this circuit. It is a very convenient mode of expressing the 
 resistance to conductibility, presented by the whole or by a 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 81 
 
 part of a circuit, to reduce it to that which would be pre- 
 sented by a certain length of wire of a given nature and 
 diameter. We shall see presently the advantage that has 
 been taken of this principle, for the construction of a very 
 valuable apparatus, intended for measuring electric currents. 
 
 But before coming to this, we have yet to establish two 
 important laws, .which follow implicitly from the preceding, 
 but which may be demonstrated directly; these laws are, 
 that the resistance opposed to a current by any conductor is 
 proportional to its length and the inverse of its section. We 
 have implicitly admitted the first of these two laws in respect 
 to a wire, when we represented by their respective lengths 
 the resistances added by the interposition of each of the wires 
 of 5 m , 10 m , 40 m , 70 m , and 100 m , all having the same dia- 
 meter, and being of the same nature. Now the result to 
 which we have arrived by this hypothesis, when applied to 
 many different experiments, having, as we have seen, always 
 been in accordance with the facts, we may regard it as a 
 truth. However, our formula rested upon another hypothesis, 
 which it was intended also to verify, namely, the existence of 
 the fifth law, in respect to the relation between the variations 
 of intensity of the current and the variations of resistance. Is 
 the accordance of this single formula with facts sufficient to 
 demonstrate, at the same time, both the law which has served 
 for establishing it, and also that which has been admitted in 
 the interpretation of the experiments ? We might doubt this, 
 if there were but one single experiment ; but since there are 
 a great number, and all lead to the same result, we must 
 hence conclude that the supposition which has been made, 
 of the proportionality between the length of a conductor and 
 the resistance that it opposes to the current, is very exact. 
 
 The second law relative to section may be verified by a 
 series of experiments, similar to those which have served us 
 for obtaining the laws relating to lengths, by putting succes- 
 sively into the circuit wires of the same nature and the same 
 length, but of different diameters, and by determining in each 
 case the value of the total resistance, or rather that of the 
 diminution or the increase that this resistance experiences by 
 
 VOL. II. G 
 
82 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the substitution of wires of diameters differing from each 
 other. 
 
 Davy, Becquerel, Harris, Gumming, and generally all 
 philosophers who have directed their attention to the con- 
 ductibility of bodies for electricity, have commenced by 
 proving that the conducting power of a wire is in inverse ratio 
 of the length, and in direct ratio of the section of the wire, 
 a law which amounts to precisely the same as the one 
 we have just given. We shall make known the various 
 processes of these philosophers in the part of this Chapter 
 which is devoted to the determination of the conducting 
 power of different bodies, and to the study of the causes, 
 by which it may be modified. 
 
 Between the two laws, that we have just laid down, there 
 is an important difference. The first, namely, the one relating 
 to lengths, requires being proved directly by experiment ; the 
 second, that of sections, is a consequence of the uniform dis- 
 tribution of electricity in motion in all parts of a homogeneous 
 conductor. Indeed, this distribution, which shows us that 
 dynamic electricity does not tend, like static electricity, to 
 the surface of bodies, but diffuses itself throughout their 
 whole interiors, leads us to recognise, since it is uniform in a 
 homogeneous conducting mass, that electric conductibility 
 must increase, and consequently resistance must diminish, 
 with the number of points, or rather with the size or the 
 extent of the section made in the conductors. The only 
 condition is, that the conductor must necessarily be homo- 
 geneous in the transverse direction; for if it were not so, 
 the distribution of electricity would no longer be uniform, and 
 the law could evidently no longer be maintained. 
 
 The law of lengths and sections is not only applicable to 
 solid conductors, but is equally so to liquids. Only it is 
 more difficult of demonstration in the latter case than in the 
 former, because, in order to put the liquid into the circuit, 
 metal electrodes must be employed ; and, as we have seen, 
 by the mere fact of the passage of the current from the solid 
 into the liquid, and from the liquid into the solid, there is 
 a diminution of intensity, which is completely independent 
 
CHAP. T. PROPAGATION OF ELECTRICITY. 83 
 
 of the conductibility proper of the liquid itself. However, 
 we may eliminate the effect of this element by employing a 
 liquid column, that may be elongated or shortened without 
 making any change in the electrodes. A tube, closed at one 
 of its ends by a disc of platinum, serving as one of the 
 electrodes, and in which a piston moves, whose platinum, 
 base serves as the other electrode, answers the purpose well ; 
 for, when once the tube is full of liquid, we are able, by 
 moving the piston onward, either to elongate or to shorten 
 the portion of the liquid column that is included in the 
 circuit. We shall describe this apparatus more in detail, 
 when engaged on the conductibility of liquids. 
 
 Fechner, in his great work, of which we have already 
 spoken, had determined the law by which the resistance of 
 the conductor is connected with its length, as well in the case 
 of a liquid as of a solid conductor. He found, always by the 
 method of oscillations, that the addition of equal lengths of 
 wire increases the resistance by equal quantities ; and he 
 hence concluded, that the resistance of wires is proportional 
 to their lengths. He afterwards arrived at the same law for 
 the liquid conductor, by successively separating the plates of 
 the pairs of the pile by a quantity always the same ; and he 
 thus found that the resistance of liquids is proportional to 
 the thickness of the liquid stratum, that the current has to 
 traverse. This law is equally true, whether the section of 
 the liquid is equal to the surface of the plates of the electrodes, 
 or whether it is greater. With regard to the law that con- 
 nects the resistance of the liquid with the size of its section, 
 Fechner found that it is verified only so long as the surface 
 of the electrode is equal to that of the section. Thus, if we 
 place vertically in a trough two metal plates, serving as 
 electrodes, and pour into the trough an increasing proportion 
 of a conducting liquid, the total resistance diminishes by 
 quantities corresponding with the quantity of liquid that is 
 added. But when once the extension of the liquid has 
 passed, by a certain degree, the size of the surface of 
 metal that is immersed, an increase in the section of the 
 liquid no longer diminishes sensibly the resistance ; at least, 
 
 G 2 
 
84 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 this is what Fechner believes. We shall see further on, 
 when occupied with the conductibility of the terrestrial globe, 
 that this opinion is true, but that the limit at which an 
 increase of the section ceases to exercise any influence over 
 the resistance or the conductibility of a body, depends upon 
 a great many circumstances, and especially upon the intensity 
 itself of the electricity in motion. 
 
 Finally, a last important law, which is equally the result 
 of the preceding and also confirmed by experiment, is that 
 which regulates the distribution of the electric current 
 between two parallel conductors placed in the circuit. If 
 they are of the same nature, of the same diameter, and of 
 the same length, a condition which is realised for in- 
 stance by two similar wires, it is evident that the current 
 divides itself equally between them. But if they are 
 of different lengths, still being of the same nature and 
 the same diameter, let the length of one be ra, and that 
 of the other n, then the proportion of the current that 
 traverses each of them is inversely as its length, and the 
 total intensity of the current is the same as if, instead of the 
 two wires of the lengths m and n, a single wire were placed 
 
 in the circuit of a length ^L* Generally, if a and b re- 
 
 Tfl ~\~ Yl 
 
 present the respective resistances of any two conductors 
 interposed parallelly in the circuit, the complete resistance 
 of the two conductors is the same as that of a single con- 
 ductor the resistance of which might be expressed by a . 
 
 a + b' 
 
 The two conductors may differ in their nature, their length, 
 and their section, or in these three circumstances together. 
 
 _ * In fact, from the law of lengths, by letting V and i" represent the inten- 
 
 i 1 + i' n + m 
 We obtain also, i' + i" or i : i' = m : x;x being the length sought for ; whence 
 
 y n m n 
 
 x T, rr, x m = x m = 
 
 ' + ' n + m m + n 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 85 
 
 Only it is necessary that they be both metallic or both li- 
 quid ; for if one is metallic and the other liquid, the law is 
 not verified, on account of the new element arising out 
 of the resistance to passage. The following experiment of 
 Poggendorff's makes evident this important exception to 
 the law. In the axis of a vertical glass tube, he inserted a 
 platinum wire 80'5 in. in length, the resistance of which 
 was the same as that of 86 in. of German silver wire. He 
 filled this tube with diluted sulphuric acid, containing 10 per 
 cent, of concentrated acid ; and he found that the resistance 
 of this liquid column, when placed alone in the circuit, was 
 the same as that of 10 in. of German silver wire; and con- 
 sequently at least 8^ times less than that of the platinum 
 wire. By means of a very sensitive galvanometer, capable 
 of detecting a difference of ^th of a line in the length of the 
 platinum wire, or of the liquid column, he proved that the 
 resistance of the platinum wire, as determined when it was 
 alone in the tube, is not diminished when this tube is filled 
 with the conducting liquid ; a proof that no portion of the 
 current passes through the liquid, and that consequently, 
 although the latter is a much better conductor than the 
 wire, no division of the current takes place between it 
 and the wire, which would have occurred between two 
 metals and even between two liquid conductors. We may in 
 like manner prove that there is no diffusion of current from 
 the metal to the liquid, by arranging the platinum wire 
 through a horizontal vessel filled with an acid solution, and 
 by plunging into the solution, very near to the wire, two 
 platinum plates in communication with the extremities of a 
 very sensitive galvanometer. If the current is then passed 
 through the platinum wire, not the slightest effect is obtained 
 upon the galvanometer. 
 
 The law that we have last set forth, leads us to say a 
 few words upon derived currents, to which we shall fre- 
 quently have occasion to direct our attention, the theory of 
 which is a consequence of this law. When, in a closed 
 circuit, we connect two points of this circuit by an additional 
 conductor, we bring about what is called a derivation of the 
 
 o 3 
 
86 TRANSMISSION OF ELECTKICITY. PART iv. 
 
 current. The two points of the circuit, from one of which the 
 new conductor is led out, and to the other of which it returns, 
 are termed points of derivation ; and the interval by which 
 they are separated, the distance of derivation ; the conductor, 
 or added wire, is the derivation wire ; the portion of the 
 current that passes by this wire is termed the derived current ; 
 that which continues to pass by the part of the circuit, com- 
 prised between the two points of derivation, partial current ; 
 and, finally, we designate by the name of primitive current 
 the current as it existed before the derivation was made ; and 
 of principal current , the whole of the new current necessarily 
 more powerful, that traverses the entire circuit, when the de- 
 rivation wire has been added. 
 
 From the principles we have laid down, and the laws we 
 have traced out, it is easy to determine the intensities of the 
 principal current, of the derived current, and of the par- 
 tial current, if we know that of the primitive current, the 
 reduced length of the primitive circuit, the distance of the 
 points of derivation, and the conductibility or the resistance 
 of the derivation wire. We shall defer to the Note B. at 
 the end, the determination of these intensities, as well as the 
 description of the processes by means of which different 
 philosophers, and Wheatstone especially, have applied the 
 laws that regulate the properties of derived currents to the 
 construction of apparatus and instruments suitable for 
 determining with great precision, in a multitude of cases, 
 the intensity of electric forces.* We shall confine ourselves 
 in this place to describing the apparatus of Wheatstone's that 
 is most frequently employed. This is the Rheostat. It is 
 founded upon one of the laws, that we have already laid 
 down, namely, that the resistance to conductibility of an 
 homogeneous wire is proportional to its length. 
 
 The object to be accomplished by this apparatus of Wheat- 
 stone's is, to introduce into the circuit of the current, whose 
 intensity we are desirous of measuring, a wire the inter- 
 position of which produces a known resistance ; then to vary 
 the length of this wire, by a quantity that may be measured 
 
 * Vide Note B. at the end. 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 87 
 
 with great accuracy, and without making any change in the 
 rest of the circuit, so as to produce a resistance which shall 
 cause the current to come back to a given intensity that is 
 always the same. This operation being performed upon 
 different currents, gives immediately the relations existing 
 between their relative intensities. The great advantage it 
 presents is, that it enables us to bring back always to the 
 same degree the indications of the galvanometer that is 
 placed in the circuit, by making the resistance vary ; which 
 does away with the necessity of our knowing the relations 
 that exist between the deviation of the galvanometer needle 
 and the intensity of the corresponding current, which rela- 
 tions cannot easily be determined, and never exactly. We 
 have only to admit the self-evident principle, that every time 
 we obtain the same deviation with the same galvanometer, 
 it indicates that the intensity of the currents producing this 
 deviation is the same. 
 
 Jacobi and Poggendorff had also each of them contrived 
 an apparatus analogous to Wheatstone's, founded on the same 
 principle, and accomplishing the same object. In Poggen- 
 dorff's apparatus, the wire, whose length was made to vary, 
 is of German silver ; in Jacobi's, which is termed by its in- 
 ventor Volta-agometer, it is of platinum. In Wheatstone's, the 
 wire is of copper or of brass. These apparatus differ from 
 each other in respect to the details of their construction : we 
 shall confine ourselves to a description of Wheatstone's, the 
 employment of which appears to us more convenient and more 
 generally known. The author has constructed two upon the 
 same principle ; one for circuits in which the resistance is 
 considerable, the other for those in which it is feeble. 
 
 The former instrument (Jig. 181.) is at A; g is a cy- 
 linder of wood, h a cylinder of brass, both of the same dia- 
 meters, and having their axes parallel. On the wooden cy- 
 linder a spiral groove is cut ; and at one of its extremities a 
 brass ring is fixed, to which is attached one of the ends of a 
 long wire of very small diameter. When this wire is coiled 
 round the wooden cylinder, it fills the entire groove ; it is 
 fixed by its other end to the opposite extremity of the brass 
 
 G 4 
 
88 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 cylinder. Two springs^' and&, pressing, one against the brass 
 ring of the wooden cylinder, and the other against the extre- 
 mity of the brass cylinder h, may be connected by means of 
 two binding screws with the wires of the circuit. The mov- 
 able handle m is for turning the cylinders on their axes. When 
 
 Fig. 181. 
 
 it is fitted on the cylinder 7i, and turned from left to right, the 
 wire is uncoiled from the wooden cylinder, and coiled upon 
 the brass cylinder; but when it is fitted to the cylinder g, and is 
 turned from right to left, the reverse takes place. The con- 
 volutions upon the wooden cylinder being insulated and kept 
 separate from each other by the groove, the current passes 
 the entire length of wire coiled upon that cylinder ; but the 
 convolutions upon the brass cylinder not being insulated, the 
 current passes immediately from the point of wire in contact 
 with the cylinder to the spring L The effective part of the 
 length of wire is reduced, therefore, to the variable portion 
 coiled around the wooden cylinder. In the instrument 
 commonly employed by Mr. Wheatstone, the cylinders are 
 6 inches in length by 1J inch in diameter, the threads of 
 the screw are forty to an inch, and the wire, which is of brass, 
 is yiyth of an inch in diameter. The wire, as may be per- 
 ceived, is very fine and a very bad conductor, so that we are 
 thus enabled to introduce a greater resistance into the circuit. 
 A scale measures the number of convolutions wound off, and 
 
CHAP. I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 89 
 
 divides the fractions of convolutions by means of an index, 
 fixed to the axis of one of the cylinders, which traverse the 
 divisions of a graduated circle. It follows from this, that we 
 are able to determine the exact length of the portion of wire 
 that is introduced into the circuit, as well as the value of the 
 variations that are made in this length. Fig. 181. shows the 
 arrangement of the apparatus, when it is in use for an expe- 
 riment. B is a very sensitive galvanometer with an astatic 
 needle, carrying a microscope for reading off the divisions 
 of the circle, which greatly facilitates the observations, c is 
 a voltaic pair, whose electro-motive force is to be measured. 
 D are bobbins of wire covered with silk, of which one or 
 more are introduced into the circuit in order to increase 
 the resistance. We shall see in the Fifth Part, which is de- 
 voted to the study of the sources of electricity, how easily 
 by means of the rheostat we may arrive at the determination 
 of electro-motive forces.* 
 
 The rheostat A (fig. 182.), which is intended for circuits 
 
 Fig. 182. 
 
 wherein the resistance is comparatively feeble, is a cylinder, 
 a, of very dry wood, upon the surface of which a helical 
 groove is cut; a thick copper wire is wound round the cy- 
 linder, filling the groove and forming as it were the thread of 
 
 * M. RumkoriF is now constructing, in Paris, rheostats in which a grooved 
 glass cylinder is used in place of the wooden one, and which affords much 
 more security in the employment of the instrument. 
 
90 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 a screw. Immediately over the cylinder, and parallel with its 
 axis, is placed a triangular bar of metal, b, carrying a rider, c; 
 to this rider is attached a spring, d, which is constantly 
 pressing against the spirals of the copper wire, yielding to all 
 the little inequalities. One end of the metallic helix is at- 
 tached to a brass ring, e, against which passes a spring that 
 is in communication, by means of a connecting screw, with 
 one end of the circuit ; the other end of the circuit is re- 
 tained by a similar screw, which is also in metallic connec- 
 tion with the triangular bar of metal. On turning the 
 handle, b, the cylinder is rotated on its axis, in either one or 
 other direction, and the rider, c, guided by the copper wire, 
 slides along the bar, advancing or receding according as 
 the cylinder rotates to the right or to the left. As the rider 
 comes in contact with a different point of the copper wire, a 
 different resistance is introduced into the circuit, consisting 
 of that portion alone of the wire which is comprised between 
 the rider and the end that is in communication with the 
 spring. The cylinder of the instrument constructed by Mr. 
 Wheatstone is 10J inches in length, and 3^ inches in diameter. 
 The wire is of copper T ^th of an inch in diameter ; it makes 
 108 coils round the cylinder. The dimensions of the instru- 
 ment, as well as that of the wire, may be modified according 
 to the limits of the variable resistance that we propose 
 introducing into the circuit, and according to the degree of 
 accuracy with which we purpose measuring these variations. 
 We must not quit this subject without adding that M. Jacobi, 
 who has deeply studied the means of measuring electric cur- 
 rents, has proposed to philosophers to reduce the instrument 
 wherewith they are in the habit of measuring resistances to 
 the same unit, which should be the resistance of a copper wire 
 1 metre (3-28 ft.) in length, and 1 millimetre (-039 in.) in 
 diameter; but as all coppers are not identical, it would be 
 necessary to choose arbitrarily any wire, and send it from 
 one philosopher to another. M. Jacobi has already endea- 
 voured to realise this. Perhaps the best method would be 
 to employ mercury as the standard of resistance for the con- 
 struction of rheostats, or agometers, as M. Jacobi calls them. 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 91 
 
 Mercury in fact has the advantage of being able, by means 
 of distillation, to be reduced to a state of great purity, and 
 consequently to be always identical with itself; on account of 
 its being liquid, it has not, like wire, the inconvenience of 
 possessing a variable molecular structure. The only further 
 precaution and this is by no means difficult is to give it 
 constantly the same dimensions. M. Jacobi has moreover 
 himself already constructed an agometer with mercury ; and 
 he appears to have succeeded in measuring resistances, by 
 means of this apparatus, with a precision which permits of the 
 probable error being diminished to the hundred thousandth 
 part of the total resistance. 
 
 Electric Conductibility of Solids and Liquids. 
 
 We have seen that there is no perfect conductor, but that 
 all bodies present a greater or less resistance to the propaga- 
 tion of electricity. We have considered, as possessing what 
 we call electric conductibility, those bodies which afford to 
 electricity a propagation sufficiently rapid to give rise to the 
 dynamic condition, as detected by the action upon the mag- 
 netised needle. Thus, while resistance to the propagation of 
 electricity would be a general property of bodies, conducti- 
 bility, as we understand it, would belong to only a certain 
 number among them. This is not saying that all substances, 
 even the most insulating, are unable to transmit more or less 
 electricity; but it requires for those that we call insulators, 
 such as glass, the resins, gutta-percha, oils, atmospheric 
 air, an electric source of a very great intensity. And even 
 with the most energetic source a flash of lightning, for 
 example these substances do not transmit electricity under 
 the form which constitutes what we have termed the dynamic 
 state; but they propagate it either too slowly to act upon the 
 magnetised needle, or too instantaneously, by themselves 
 breaking under the action of the discharge, for a current, 
 properly so called, to occur. 
 
 The research that must for the present engage our attention 
 is confined merely to bodies possessed of electric conducti- 
 
92 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 bility, such as we have been defining it. This conductibility, 
 which, as we have seen, is never absolute, varies, as we have 
 demonstrated, with the dimensions of bodies; but it varies 
 also with their nature, and with different physical circum- 
 stances. These are the influences that we desire to examine, 
 and even to measure, so as to give as accurate a Table as 
 possible of the relative degrees of conductibility of different 
 substances, both solid and liquid, as well as the variations 
 that occur in their conducting powers from changes in their 
 physical constitution, and especially in their temperature. 
 
 The determination of the specific conductibility of different 
 bodies is not a problem easy of solution. Its solution depends 
 upon very delicate principles, and requires apparatus pos- 
 sessed at once of a great sensibility and of extreme precision. 
 In order to arrive at its solution, it would be necessary to 
 have a constant source of electricity, so that the tension of the 
 two electricities should remain in it constantly the same, and 
 also to have an accurate means of measuring the quantity 
 of electricity that is circulating in the dynamic state, in a 
 given time, through any conductor. Then, in order to es- 
 tablish a comparison, we should endeavour to obtain the 
 quantity of electricity that traverses in the unit of time an 
 infinitely thin section of each body; and we should divide 
 it by the surface of the section, which would give the quantity 
 of electricity that traverses in the unit of time the unit of 
 surface. 
 
 The principle of this method is altogether the same as 
 that upon which the process employed for the determination 
 of conductibility for heat is founded. Now, if we study 
 closely what takes place during the propagation of electricity 
 through a conducting body, we find this assimilation per- 
 fectly legitimate, as is proved by the recent experiments 
 of Kohlrausch, which we will give briefly. 
 
 The poles of a constant voltaic pair, such as a Daniell's 
 pair, are connected by a very fine and tolerably long wire, 
 which is bent in zigzag, so that the sides of the angles 
 formed by the zigzags shall be all of the same length. A point, 
 a, of the conducting wire is placed in communication with 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 93 
 
 the ground; and then a point, b, of the wire, taken at a 
 certain distance from a, on the side of the positive pole, 
 is put into communication with a sensitive condenser ; and 
 after this a point, V, taken at the same distance from , 
 but on the side of the negative pole. The same tension 
 is obtained; only that of the point b is positive, and that 
 of the point b' ', negative : the two tensions go on increasing 
 in proportion as the points b and V are taken further from a. 
 If the two poles are united by two wires of the same nature 
 (silver for instance), of the same length, but of different 
 diameters, and soldered end to end so as to form only 
 one continuous wire, the electric tension increases in each 
 of the wires in the same progression, setting out from their 
 point of contact, which is made to communicate with the 
 ground; only the absolute tensions in each of the wires 
 are the inverse of the sections. When, instead of two 
 wires of the same nature, we take two of different natures, 
 but of the same diameter, for instance, one wire of German 
 silver, and one of copper, so that the former presents a 
 great resistance to the current, and the latter a much less, it 
 is found that the absolute intensities at the ends of each 
 wire are proportional to their respective resistances, as 
 determined by means of the rheostat, which we have de- 
 scribed in the preceding paragraph. 
 
 The same results are obtained on making use of a 
 liquid conductor. A trough full of sulphate of copper, 
 in which a plate of copper is immersed, contains a porous 
 cell, filled with sulphate of zinc, with a plate of zinc im- 
 mersed. The two plates are connected by a wire. The 
 trough is divided into equal parts ; and we plunge 
 into the liquid, in different places, two copper wires, the 
 one communicating with the earth, and the other with the 
 upper plate of the condenser. We find, as we had done with 
 the metallic conductor, on either side of the point that is 
 in communication with the earth, equal positive and negative 
 tensions. We may even prove in this case (which we are 
 unable to do with a solid conductor), that the tension is 
 the same in all points of the transverse section ; which 
 
94 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 confirms the law, that we have laid down in the preceding 
 paragraph, of the uniform distribution of dynamic electricity 
 throughout the whole mass of a homogeneous conductor. 
 It is necessary in these experiments, that the wires which 
 are employed for sounding be covered along their whole 
 length, except at their very end, with a varnish of gum-lac, 
 so as to take the electricity only at the actual point with 
 which this extremity is in contact. It follows, therefore, 
 from these experiments that, even in the best conductors, 
 the resistance to the propagation of electricity is of such 
 magnitude that, between two consecutive transverse sec- 
 tions, there is a difference of electric tension, the stratum 
 nearest to the electric source having a higher tension than 
 that which is more distant. It is this corresponding differ- 
 ence for different conductors, at the same distance between 
 two strata taken in each, that Ohm calls the electric fall; 
 and the preceding experiments show that this fall is directly 
 proportional to the specific resistance of the metals and 
 inversely to their sections. 
 
 We may even by means of these laws, and with a simple 
 calculation, determine the electroscopic state of each point 
 of a circuit. Let e, for example, be the electro-motive force 
 put into play in the circuit, I the reduced length of the 
 circuit, and I' the reduced length also of the conductor 
 that separates a point a, of the circuit from the point, where 
 
 the electro-motive force is acting ; we obtain e' the electro- 
 
 gr 
 scopic state of the point a, equal to^e ; which signifies that, 
 
 in order to obtain the tension of a point, we must multiply 
 the electro-motive force by the relation that exists between 
 the reduced length of the part of the circuit confined between 
 the point in question and the point connected with the 
 ground, and the reduced length of the entire circuit. Ex- 
 periment completely verifies this formula, as M. Kohlrausch 
 has further proved, by uniting the zinc and copper plates 
 of the last experiment by a long and very fine wire, bent 
 into a zigzag. He has determined the electric tension of the 
 different points of this wire and of the solution of sulphate 
 
CHAP. I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 95 
 
 of copper which in this, as in the preceding case, formed 
 part of the circuit. The negative pole communicated 
 with the ground; and the different points touched were, first, 
 three points taken on the conjunctive wire at increasing 
 distances from the zinc plate or negative pole, then the 
 point of contact of the copper plate with the conjunctive 
 wire, then three points taken in the sulphate of copper, at 
 2-02, at 4 '02, and at 8 inches from the same copper plate. The 
 following is a Table of the calculated and the observed tensions, 
 placed opposite to the respective values of the resistances or 
 the reduced lengths, determined by the rheostat for the parts 
 of the circuit comprised between the negative pole and 
 the point that is touched : 
 
 Points touched. 
 
 Tensions calculated. 
 
 Tensions observed. 
 
 a. 118-5 
 
 0-93 
 
 0-85 
 
 b. 237 
 
 1-86 
 
 1-85 
 
 c. 355-5 
 
 2-89 
 
 2-69 
 
 d. 474 
 
 3-73 
 
 3-70 
 
 e. 610-3 
 
 4-80 
 
 5-03 
 
 /. 745-3 
 
 5-86 
 
 5-99 
 
 g. 879 
 
 6-90 
 
 6-93 
 
 A. 1014 
 
 7-98 
 
 L 7-96 
 
 We may therefore consider each transverse layer of an 
 homogeneous conductor as charged with different quantities 
 of electricity on its two faces, but spread uniformly on each 
 of them ; quantities which, for a constant electro-motive 
 source, differ in proportion as the resistance of the layer 
 to the propagation of electricity is greater. The deter- 
 mination of this difference for layers of the same extent, 
 belonging to conductors of a different nature, would give 
 the measure of their resistance, and consequently of their 
 electric conductibility. But this process, which is very 
 difficult of application, would not, after all, be susceptible 
 of very rigorous accuracy. However, the analysis by 
 which we have been led to it enables us to employ for 
 it another process that is more practical and more delicate, 
 which we will explain presently. 
 
96 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 If we compare the results that we have just obtained, with 
 the considerations that we have laid down, both at the com- 
 mencement of this chapter, as well as previously, on the 
 manner in which the propagation of electricity is brought 
 about, by the polarisation of consecutive particles, we may 
 conclude from this that the resistance to conductibility is 
 nothing more than the sum of the resistances opposed by the 
 successive particles to their electric polarisation, and to the 
 neutralisation of their contrary electricities. Each particle 
 or physical molecule possesses, as it were, a greater or less coer- 
 citive or insulating force, which opposes the separation of the 
 two electricities from each other. Then, when this separation 
 has been brought about, there exists a resistance to the reunion 
 of the contrary electricities of two consecutive particles, either 
 on account of their greater or less mutual distance, or on account 
 of the greater or less constraining power of their very nature. 
 Now, in order to there being propagation of electricity, it is 
 necessary that the resistance to separation and the resistance 
 to reunion be equally surmounted. The former depends on 
 the very nature of the particles ; the latter depends both on 
 their nature and on their mode of aggregation. It is by 
 taking account at the same time of these two very different 
 elements, that we are able to explain that the same exterior 
 circumstance for example, the elevation of temperature 
 may in certain cases favour, and in other cases diminish, con- 
 ductibility, according as it acts upon the particles themselves, 
 or upon their relative positions. The electric state of the 
 particles of a slender filament may be compared with that of 
 a succession of Leyden jars, or rather of spangled panes, 
 which all become charged mutually by induction, except the 
 first and the last, which are respectively in direct communi- 
 cation with a source of positive and with a source of negative 
 electricity. Having arrived at a certain degree of tension, 
 the opposite coatings of the consecutive jars or panes discharge 
 upon each other. There arises from this a general discharge 
 of a uniform intensity throughout the system, and an excess 
 of electricity upon each jar or pane, which increases onward 
 to the extreme panes ; an excess that is positive for those 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 97 
 
 which are on the side of the positive source, and negative for 
 those which are turned on the side of the negative source. 
 The intensity of this excess must depend upon the greater or 
 less degree of resistance that the contrary electricities of the 
 opposite armatures find presented to their reunion ; and the 
 more considerable it is, the less powerful is the discharge or 
 the current. This succession of charges and discharges, 
 which, in a series of Ley den jars, requires a certain time for 
 bringing it about, occurs instantaneously in a series of 
 particles ; and this it is which causes the current to be con- 
 tinuous, and the state of tension of the different molecules to 
 be constant, conformably with the observations of M. Kohl- 
 rausch. 
 
 It is probable that the effects of heat, of light, and of the 
 physiological shocks that almost always attend upon the 
 transmission of dynamic electricity, except in the cases where 
 the resistance is very feeble, are intimately connected with 
 the two causes of resistance, that we have pointed out. With 
 regard to chemical decompositions, they must depend essen- 
 tially upon the arrangement that the polarisation of the 
 particles brings about, in the mode of grouping of the atoms 
 of which they are composed, and in the disturbances that the 
 discharges, which follow polarisation, introduce into this ar- 
 rangement. 
 
 We ought to mention, that the manner in which we have 
 been regarding electric conductibility differs notably from 
 Mr. Faraday's mode of viewing it; who, setting out from 
 the principle that the space by which the particles of bodies 
 are separated is not a conductor, because, if it were otherwise, 
 space being everywhere identical, all bodies ought equally to 
 be conductors, deduced from it a conclusion, that is contrary 
 to the atomic theory. In fact, regarding continuity as an 
 essential condition of electric conductibility, and consequently 
 considering as indispensable that intermolecular space is a 
 conductor, since it is the only continuous part of a body, he 
 had concluded that the atomic theory is false, because it leads 
 us to admit at the same time that this space must be a con- 
 ductor and that it must not be one. For our part, it is to 
 
 VOL. II. H 
 
98 TRANSMISSION OF ELECTRICITY. PART iv 
 
 the molecule alone that we attribute the property of being 
 more or less conducteous or insulating; conductibility is 
 nothing more than the result of the greater or less facility 
 possessed by the consecutive particles of polarising each 
 other through the space by which they are separated, and 
 which is necessarily insulating. We are thus enabled to 
 reconcile, in the most satisfactory manner, the phenomena of 
 electric conductibility with the atomic theory, which is so 
 firmly established by the study of chemical and physical 
 phenomena. 
 
 After these preliminary notions, which have appeared to 
 us indispensable for enabling us to acquire a just idea of 
 electric conductibility, we will pass on to the description of 
 the processes most fitted for determining accurately the con- 
 ducting power of different solid and liquid bodies. 
 
 Priestley, and after him Harris and Riess, have proposed 
 to determine the conducting power of the different metals, by 
 making the same electric discharge pass through rods or 
 wires of the same diameter and the same length, but of 
 different natures, and deducing their relative conductibility 
 from the greater or less degree of increase in temperature that 
 they underwent. Wilkinson adopted the same method, but 
 by substituting an electric current for the discharge. This 
 mode of determination depends upon the principle that the 
 degree of increase of temperature communicated to a wire bv 
 the passage of a given quantity of electricity is inversely as its 
 electric conductibility, a principle which cannot be admitted 
 a priori; for it cannot be proved until we have a direct 
 means of determining conductibility; and, consequently, it 
 cannot be employed for the determination of it. 
 
 The same objection is applicable to Christie's method, 
 founded upon the principle that the intensity of induction 
 currents is proportional, all other circumstances remaining the 
 same, to the conducting power of the substance, that is the 
 subject of the induction. Faraday had, in fact, remarked, at 
 the very outset of his discovery of induction, that induced 
 currents developed in helices made with wires of the same 
 diameter and the same length, but of different natures, have 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 99 
 
 an intensity that is greater in proportion as the conducting 
 power of the wires is greater. But here, again, in the em- 
 ployment of this method for determining conductivity, we 
 have a vicious circle, which prevents our employing it for 
 this purpose. 
 
 Davy made use of a more direct method, which led him to 
 results that have been in great part confirmed by more exact 
 methods. He took wires of different metals, of the same 
 length and of the same diameter, and examined the power 
 that was possessed by each of them for discharging voltaic 
 ,pairs. In order to prove whether a wire entirely discharged 
 several pairs, he added two other silver wires to the two poles 
 of the pile, and made them plunge into conducting water, 
 which was decomposed, if all the current did not pass by the 
 principal wire ; the absence of all liberation of gas was the 
 sign that this wire brought about the entire discharge. 
 However, in virtue of its tendency to distribution, the current 
 must always in a certain proportion pass through the water ; 
 too small, it is true, to cause the decomposition to be sensible. 
 Notwithstanding the imperfections of this process, Davy had 
 succeeded in establishing directly the two general laws of 
 conductibility, namely, that conducting powers are in inverse 
 ratio to the lengths, and in direct ratio to the sections of the 
 wires, that conduct the electricity. 
 
 M. Becquerel, sen., was the first to adopt a more accurate 
 process ; which consists in employing the differential galva- 
 nometer, and which enabled him to guard against the effects 
 of variations in the intensity of the electric current. He 
 obliged the current to divide itself between the two wires of 
 the galvanometer in such a manner, that each of its two 
 portions travelled in an inverse direction, and maintained the 
 magnetised needle at zero, when they were equal. By intro- 
 ducing into these two partial circuits wires of different natures, 
 and of the same diameter, he was always able, by shortening 
 or by lengthening them, to bring back the needle to zero, and 
 thus to determine what lengths of the wires were equivalent 
 in conductibility. In this manner he had also verified the 
 
 H 2 
 
100 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 laws that Davy had already found approximately, and had 
 determined the relative conductive powers of different metals. 
 
 M. Pouillet had more recently adopted an analogous 
 method, with this difference, that he employed two per- 
 fectly equal sources of electricity, the currents of which 
 passed in contrary directions in the two wires of the 
 differential galvanometer; a platinum wire served as the 
 standard wire ; with the conducting power of which he com- 
 pared that of the wire under examination, giving to it such a 
 length as reduced its current as much as the interposition of 
 the experimental wire reduced the current that was com- 
 pelled to traverse it. 
 
 The numerical results obtained by M. Pouillet, with regard 
 to the conducting powers of the different metals, do not 
 agree with those of M. Becquerel, which may be traceable 
 to certain differences in molecular constitution, and in the 
 degree of purity of the specimens submitted to experiment, 
 circumstances, which exercise a great influence over electric 
 conductibility, as was demonstrated by M. E. Becquerel, who 
 has lately taken up this question, and applied much accuracy 
 to its study. 
 
 He also employed the differential galvanometer ; but he 
 took care to introduce into its construction the precaution 
 pointed out by Poggendorff of twisting the two galvano- 
 meter wires around each other, in order that, if the two 
 equal currents pass in an inverse direction in the instrument, 
 their action shall be entirely the same, and that the needle 
 may remain perfectly at zero. M. E. Becquerel also made 
 use of Wheatstone's rheostat, the wire of which, and to which 
 the desired length can be given, forms constantly part of one 
 of the circuits of the differential galvanometer, whilst the 
 wire, w T hose conducting power is in question, forms part of 
 the other. The toothed wheel of the rheostat contains 108 
 divisions, and the tenth part of each division can^be estimated ; 
 so that the circumference of one of the spirals of the helix, 
 being 9*27 in., the lengthening or shortening of the brass wire 
 of the instrument may be measured to the y^ Q part of 9*27 in., 
 or to about '008 in. The wire whose conducting power is the 
 
CHAP. I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 101 
 
 subject of inquiry is stretched between two clips of copper, 
 
 attached to two standards, placed 
 at such a distance apart, that 
 the length of the wire is 4-92 
 feet. A very solid copper rod 
 is firmly fixed above the wire, 
 and parallel to its length ; upon 
 this rod, which is graduated, a 
 copper standard slides tightly, 
 which by the aid of a screw 
 may be fixed in any given 
 position. The upper extremity 
 of this standard is formed of a 
 thick clip, which holds the wire 
 in one of its points ; so that, on 
 causing the standard to traverse 
 along the rod, any length is 
 placed in the circuit, and is 
 measured with great accuracy. 
 The conductibility of the rod, 
 in respect to that of the wire, may 
 be neglected, in consequence of 
 its great dimensions. The form 
 of the apparatus, complete, is 
 given in Jig. 183. H n' is the 
 differential galvanometer; F F' 
 the voltaic pair employed in the 
 experiment; E E' the rheostat, 
 with its handle M, by which 
 motion is communicated to the 
 two cylinders, one being of 
 copper, and the other of wood, 
 so that the wire is wound around 
 one, while it is unwound from 
 the other ; R R' the two standards 
 carrying the clips A A', between 
 which the experimental wire is 
 strained ; a b the divided copper 
 n 3 
 
 Fig. 183. 
 
102 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 rod ; and e c the metal standard, which slides firmly along 
 this rod, so as to place the length c A of the experimental 
 wire in one of the partial circuits. The current, setting out 
 from c, divides between the two conductors c D and c o, so that 
 the first part passes through the wire of the rheostat D D', 
 and thence goes on by the conductor D' N x to traverse one of 
 the wires of the galvanometer; the second part goes 
 through the conductors o P, o P' , o P", to arrive hence by the 
 standard e c at the experimental wire E A, and then to 
 travel, by means of A N, to the second wire of the galva- 
 nometer ; then the two currents, after having traversed in 
 contrary directions the two wires of the differential galvano- 
 meter, unite at G, and find there the conductor G z, which 
 completes the circuit. 
 
 M. E, Becquerel first verified, by means of this apparatus, 
 the law already indicated, that the conducting power is in 
 inverse ratio to the length, and in direct ratio to the section 
 of the wire. 
 
 A First Table contains experiments made at the tem- 
 perature of 60 with an iron wire 0*012 in. in diameter, 
 and of variable length. The* first column indicates, by the 
 position of the clip C e s the variable lengths of the wire ; the 
 second, the number of divisions of the rheostat which 
 present resistances equal to those of the corresponding lengths 
 of the iron wires ; the third, the relation between these two 
 quantities. Now, this relation being constant, it follows that 
 the resistance, brought about by the introduction of the iron 
 wire into the circuit, increases just proportionately to the 
 length of this wire ; or, which comes to the same thing, that 
 its conductibility is inversely as its length. 
 
 The following is the table : 
 
 Position of the clip C e, on the 
 divided rule or the length 
 of the iron wire. 
 
 Divisions of the toothed 
 wheel, or length of the 
 standard wire. 
 
 Relation between the corre- 
 sponding lengths of the 
 two wires. 
 
 Cent. 
 
 
 
 20 
 
 162-6 
 
 8-13 
 
 40 
 
 325-2 
 
 8-13 
 
 60 
 
 485-0 
 
 8-08 
 
 80 
 
 643-3 
 
 8-04 
 
 100 
 
 805-6 
 
 8-06 
 
CHAP. I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 103 
 
 A Second Table contains the experiments made with two 
 iron wires of different diameters. For one metre of length a 
 resistance is obtained, which is represented in the following 
 Table: . 
 
 Resistance in divi. 
 sions of the 
 rheostat. 
 
 Diameters of the 
 wire. 
 
 Squares of the 
 diameters. 
 
 Product of the squares 
 of the diameters by 
 the resistances. 
 
 157-08 
 928-65 
 
 0-7370 
 0-3037 
 
 05322 
 0-0922 
 
 85-717 
 85-622 
 
 Thus, the increase of resistance, caused by the introduction 
 into the circuit of an iron wire of a certain length, is to that 
 produced by the introduction of a wire of the same length, 
 but of a different diameter, inversely as the squares of 
 the two diameters. 
 
 After these preliminary experiments come those which 
 are made with wires of different metals, the diameters of 
 which must be very accurately measured. But since some 
 wires, when they come out of the drawplate, are hardened, 
 but not all, and since hardening influences conductibility, as 
 M. Pouillet has observed, it is of importance to anneal them, 
 in order that all may be as much as possible in the same 
 molecular conditions. The difference in respect to conduc- 
 tibility, between an annealed wire and the same wire unan- 
 iiealed is really very sensible, as may be seen by the follow- 
 ing Table : 
 
 Wires of the dia- 
 meter of O.mm 3. 
 
 Resistances 
 unannealed. 
 
 Resistances 
 annealed. 
 
 Conducting 
 powers un- 
 aunealed. 
 
 Conducting 
 powers 
 annealed. 
 
 Relation of con- 
 ductibility of 
 annealed and un- 
 annealed metal. 
 
 Pure silver 
 
 123-509 
 
 115-416 
 
 93-448 
 
 100-000 
 
 1-0701 
 
 Pure copper 
 
 119-559 
 
 126-222 
 
 89-084 
 
 91-439 
 
 1-0264 
 
 Pure gold - 
 
 179-260 
 
 176-320 
 
 64-385 
 
 65-458 
 
 1-0166 
 
 Iron - 
 
 951 098 
 
 942-046 
 
 12-124 
 
 12-246 
 
 1-0101 
 
 Platina 
 
 1435-158 
 
 1416-007 
 
 8-042 
 
 8-147 
 
 1-0130 
 
 We should mention, that in this Table the resistance, and 
 consequently the conductibility of the wires, is reduced to 
 what it would be by supposing them all to be of the same 
 
 B 4 
 
104 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 diameter; we have also compared all the conductivities with 
 that of annealed silver, which is the best conductor of all 
 
 Temperature, as well as hardening, influences in a notable 
 manner the conductibility of metals. In order to study this 
 influence, M. Becquerel winds the wire that is to be expe- 
 rimented upon, around a glass tube in such a manner, that 
 the spirals of the helix which it forms are well insulated 
 from each other; he then attaches the two ends to two great 
 studs of copper, whose very good conductibility does not 
 sensibly vary, in respect to that of the wire itself, under the 
 influence of the temperature to which it is exposed. He 
 places the tube mounted with its wire in an oil-bath, which 
 he gradually raises from to 100 (32 to 257 Fah.), and 
 which he in like manner cools down from 100 to 0; he 
 then determines the variations of conductibility of the 
 wire by means of the rheostat. This variation follows in a 
 very regular manner in the same metal that of the tempera- 
 ture, to which it is in general proportional; but it differs 
 much from one metal to the other, and is not in relation with 
 its absolute conductibility. We may discover this from the 
 following Table, which contains the relative conducting powers 
 of different metals at and at 100. The order is much the 
 same, except for lead and platinum, which change places ; but 
 the numerical relations, which indicate their relative conducti- 
 bility are notably altered, except for copper, cadmium, and 
 zinc. 
 
 Substances. 
 
 Conducting 
 powers at 0. 
 
 Conducting powers at 
 100, compared with 
 silver at 0. 
 
 Relation of con- 
 ducting powers 
 at 1000. 
 
 Pure silver, annealed 
 
 100 
 
 71-316 
 
 100 
 
 Pure copper, annealed 
 
 91-519 
 
 64-919 
 
 91-30 
 
 Pure gold, annealed 
 
 64-960 
 
 48-489 
 
 67-992 
 
 Cadmium 
 
 24-579 
 
 17-506 
 
 24-547 
 
 Zinc - 
 
 24-063 
 
 17-596 
 
 24-673 
 
 Tin 
 
 14-014 
 
 8-657 
 
 12-139 
 
 Iron, annealed 
 
 12-350 
 
 8-587 
 
 11-760 
 
 Lead - 
 
 8-277 
 
 5-764 
 
 8-078 
 
 Platinum, annealed 
 
 7-933 
 
 6-688 
 
 9-378 
 
 Mercury 
 
 1-7387 
 
 1-5749 
 
 2-2083 
 
CHAP. I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 105 
 
 It is unfortunate that M. E. Becquerel has not investigated 
 the influence of elevation of temperature upon metals above 
 100. Happily M. Lenz has determined this* as high as 200 
 (480 Fah.) The following is the table of the results 
 that he obtained: 
 
 
 AtO 
 
 At 100 
 
 At 200 
 
 Silver - 
 
 136-25 
 
 94-45 
 
 68-72 
 
 Copper - - 
 
 100-00 
 
 73-00 
 
 54-82 
 
 Gold - 
 
 79-79 
 
 65-20 
 
 5449 
 
 Tin 
 
 30-84 
 
 20-44 
 
 14-78 
 
 Brass - 
 
 29-33 
 
 24-78 
 
 21-45 
 
 Iron - 
 
 1774 
 
 10-87 
 
 7-00 
 
 Lead .... 
 
 14-62 
 
 9-61 
 
 6'76 
 
 Platinum - 
 
 14-16 
 
 10-93 
 
 9-00 
 
 This Table, the numerical elements of which differ but 
 little from that of M. Becquerel, confirms the remark that 
 we have already made with regard to the influence exercised 
 by temperature, not only over the absolute conductibility, 
 but also over the relative conductibility of metals. Thus 
 we see the conducting power of gold, which at is only 
 J of that of copper, becomes equal to it at 200; brass, 
 which at is inferior to tin, becomes superior to it at 100, 
 and still more so at 200; finally, platinum, which at is in- 
 ferior to lead and iron, becomes superior to them at 100 and 
 at 200 : the most fusible and evidently the metals that vary 
 most rapidly in the scale of conductibility under the influence 
 of an elevated temperature ; a proof of the influence of mole- 
 cular constitution over this property of bodies. 
 
 Besides the solid substances that we have mentioned, there 
 are some others whose conducting power has been determined. 
 Still calling the conducting power of copper 100, Lenz found 
 
 Antimony 
 
 Mercury 
 
 Bismuth 
 
 - 8-9 
 
 - 4-7 
 
 - 2-6; 
 
 but he does not point out the influence of elevation of tempe- 
 rature upon the conductibility of these metals. 
 
106 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 Palladium is one of the metals, concerning which the ex- 
 periments of various philosophers have given the least con- 
 cordant results. Thus, whilst Pouillet found that it is the 
 best conductor of all the metals, E. Becquerel and Riess 
 place it after silver, copper, gold, cadmium, zinc, and tin. 
 These divergences are probably due to certain differences 
 in the degree of purity of the specimens submitted to experi- 
 ment. 
 
 The electric conductibility of carbon has never been de- 
 termined with precision. This is due to the differences that 
 it presents, from diamond, which is completely insulating, to 
 graphite and plumbago, which conduct very well. Mr. Kemp 
 has pointed out the very great influence of elevation of tempera- 
 ture over the conducting power of wood carbon, which it in- 
 creases considerably. But this influence, which is the reverse 
 of that exercised over metal, differs also from it in its being 
 permanent; that is to say, that it is the fact of having been 
 exposed to a very high temperature which renders wood 
 carbon a better conductor. Thus, M. Violette, in his recent 
 researches on wood carbons, found that fragments of the car- 
 bon of elder wood, prepared at the temperature of 1500, are 
 better and more equable conductors than the graphite that is 
 taken out of gas retorts. We shall, however, return to this 
 subject when we are describing the voltaic arc, that is ob- 
 tained with two carbon points. 
 
 The conductibility of metals, for electricity as we said at the 
 beginning, is a phenomenon that is intimately related to their 
 conductibility for heat. We have a direct proof of this in the 
 fact observed by Prof. Forbes as much as twenty years ago, 
 that the order of the conductibility of metals is the same for 
 heat as for electricity. The following Table was drawn out 
 by MM. Wiedemann and Franz, as the result of fresh re- 
 searches that were made by them upon the conducting power 
 of metals for heat, which gives evidence of this relationship 
 in a remarkable manner. 
 
CITAr. I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 107 
 
 Names of metals. 
 
 Cond'jctibility for electricity. 
 
 Conductibility 
 
 
 Riess. 
 
 Becquerel . 
 
 Lenz. 
 
 
 Silver 
 
 100 
 
 100 
 
 100 
 
 100 
 
 Copper 
 Gold- 
 
 667 
 59-0 
 
 91-5 
 64-9 
 
 73-3 
 
 58-5 
 
 73-6 
 53-2 
 
 Brass 
 
 18-4 
 
 
 
 21-5 
 
 23-6 
 
 Tin - 
 
 10-0 
 
 14-0 
 
 226 
 
 14-5 
 
 Iron - 
 
 12-0 
 
 12-35 
 
 13-0 
 
 11-9 
 
 Lead 
 
 7-0 
 
 8-27 
 
 107 
 
 8'5 
 
 Platinum 
 
 105 
 
 7-93 
 
 10-3 
 
 6-4 
 
 German silver - 
 
 5-9 
 
 
 
 
 
 6-3 
 
 Bismuth - 
 
 
 
 5> 
 
 1-9 
 
 1-8 
 
 Finally, there exists a great number of mineral substances 
 which are able to transmit an electric current, but whose 
 rank or numerical co-efficient of conductibility we have not 
 been able to determine. MM. Henrici and Hanemann, on 
 the one hand, and M. Wartman on the other, have made 
 numerous experiments on this subject. The latter philo- 
 sopher examined 319 species of minerals; 252 of which he 
 found to be insulators, and consequently only 67 conductors. 
 The difficulty of reducing these substances to the same 
 dimensions, and even of giving to them geometric volumes 
 susceptible of being exactly estimated, renders it an im- 
 possibility to determine their relations of conductibility, still 
 less the variations of conductibility which may be manifested 
 in the same mineral, for example, according as the electricity 
 is propagated in one direction or the other. Moreover, 
 there is nothing absolute in the conducting property ; for 
 between all the minerals, that are the best conductors and 
 those which are the best insulators, there are all the interme- 
 diate degrees. We shall prove this further on, in the para- 
 graph in which we shall be engaged upon the propagation of 
 electricity in bodies that are bad conductors. 
 
 The determination of the conducting power of liquids 
 has been obtained by following the same process as for solids ; 
 we have merely to pay regard to two circumstances, which 
 do not occur when operating upon solids. The first is the 
 resistance to passage, that occurs in the transmission of the 
 
108 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 electric current at the surface of contact of the liquid and 
 the metal electrodes, a resistance altogether independent 
 of the electric conductivity properly so called of the liquid ; 
 the second is the alteration that very rapidly occurs to the 
 liquid that is submitted to experiment, in consequence of 
 the chemical decomposition which it undergoes. In order 
 to obviate this latter inconvenience, it is necessary to operate 
 as rapidly as possible, and to arrange the apparatus in such 
 a manner that the substances liberated by decomposition 
 do not alter the liquid. With this view, we endeavour to 
 absorb them, if they are gaseous, by the substance itself 
 of the electrodes, when it is possible, as with oxygen ; or 
 to allow them to deposit, if they are solid, in the portion 
 of the liquid which is at the bottom of the vessel, and which 
 we take care not to include in the circuit. 
 
 It is a more difficult matter to obviate the former incon- 
 venience. For this purpose, M. E. Becquerel adopts a 
 process which is merely a modification of that proposed by 
 Mr. Wheatstone, and which we have employed in order to 
 prove that with liquids, as well as with solids, the resistance 
 to conductibility is proportional to the length of the con- 
 ducting column. But, instead of a single tube, M. E. Bec- 
 querel employs two, so that he may employ the differential 
 galvanometer, as he had done with solids ; and in each of 
 these tubes are two platinum electrodes, one fixed and the 
 other movable like a piston, which permits of the column 
 of liquid being lengthened or shortened at pleasure. 
 
 The apparatus is represented mfig* 184. A B and A' B' are 
 two test glasses with feet, about 1| in. or 2 in, in diameter 
 and 1 1 in. in height. They rest in holes countersunk in 
 a very level base -board M N. Into these glasses descend 
 two cylindrical tubes a b } a' b', supported above by corks, and 
 retained at 1^ in. from the bottom of these same glasses ; they 
 have the same axes with the glasses. These tubes are 
 exactly '846 in. in interior diameter, measured by the 
 weight of a column of water of a certain height. In these 
 tubes, which are placed vertically, circular plates of platinum 
 E E' are able to be moved upwards and downwards ; they 
 
CHAP. I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 109 
 
 are horizontal, and of a somewhat smaller diameter than 
 that of these tubes, and attached to platinum wires soldered 
 
 iv i 
 
 Fig. 184. 
 
 into glass tubes F E, F' E'. Plates of different metals, D I, 
 D' Z', according to the experiments, are placed horizontally 
 at the bottom of the glasses, at the lower part of the tubes 
 a b, a' V. These plates are attached to wires of the same 
 metal, which pass into tubes D c, D' (/. The tube E F is 
 attached to a stem G F, communicating with a rack- work, 
 so that the disc E may be raised or lowered by means of 
 this rack-work ; and we are enabled by means of the vernier 
 T to learn to about T n in. or even less, the amount of 
 variation in the position of E in the tube. The other similar 
 plate E' is raised or lowered by means of the tube F' E', 
 which passes tightly in the cork A'. 
 
 These arrangements being made, if we plac3 the liquid by 
 means of which we propose operating in the glasses, and send 
 a current between the plate E and the plate D L, by raising 
 or lowering E, we shall introduce into or withdraw from 
 the circuit a column of liquid having the same diameter 
 as the tube a b, and having for length the elevation or 
 
110 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 lowering of the plate. The liquid comprised between the 
 glass and the interior tube is not in the circuit. We have 
 thus arranged the apparatus in such a manner that the 
 products formed around the positive plate fall to the 
 bottom of the glass, and do not alter the conductibility of 
 the liquid that is placed within the tube a b. The wires 
 c D, c' D' are to be connected together by being plunged 
 into a cup p, filled with mercury; and by this means 
 they are put in communication with the positive pole of 
 one or more pairs. The negative pole is attached to the point 
 G, at the junction of the two ends of the galvanometer wire. 
 The two other ends N and N' of these same wires are attached 
 to the extremities s, s', which are in communication with 
 the circular plates E, E' ; N is directly attached; N' com- 
 municates by means of two cups R, Q, and by the copper 
 u G F of the rack-work. We therefore perceive that the 
 two circuits P c' E' F' s', p c E F s, in which are the 
 two liquid columns E' ~D' } E D, takes the place of the 
 circuits F' o C A N, F' E' N', of fig. 183., which are 
 all metal. If therefore we pass a current from one, two, 
 four, or more pairs, similar to the pair F F', of jig. 183. 
 the current will divide between the two circuits, the plates 
 E, E' being at the top of the tubes ; the needle of the 
 galvanometer will be deflected a little to the right or to 
 the left, for the two circuits are not at the first trial identical 
 in conductibility; then, by means of the rack-work o H, E 
 is raised or lowered until the needle is brought back to 
 zero. Generally speaking, except under particular cir- 
 cumstances, which will be referred to hereafter, it will 
 remain there ; so that by raising or lowering E 1 mm (^ in.), 
 the needle is deflected to the right or to the left of zero. 
 When once the zero is attained, the two circuits are identical 
 in conductibility ; the copper wire v, that makes communi- 
 cation between the cups G and R, is taken away. And in 
 its place are substituted helices of platinum or of copper 
 wire of a known length ; the needle of the galvanometer 
 is immediately driven in a direction which indicates that 
 the circuit p c E F s presents a resistance greater in 
 proportion to the wire that is substituted in place of v. 
 
CHAP. I. PROPAGATION OF ELECTRICITT. Ill 
 
 If \ve then lower the plate E, with the rack-work O, 
 the needle will return to zero ; and when it shall have 
 arrived at that point, and is maintained there, we must notice 
 how far the plate has descended. Then the length of a 
 column of liquid, having for its diameter that of the tube 
 a by and for its length the course of the plate E, will be 
 equal in resistance to the wire placed between R and Q, 
 in the place of v. This resistance will be independent of 
 the resistance to the passage from liquids into solids; for 
 the sections are identical in the two experiments, as in 
 Wheatstone's apparatus, and the currents are reduced to 
 an equality. Only in this case we make the variation 
 in the height of the liquid column employed, in order to 
 find the value in resistance of the helix placed on v; and 
 this is the converse of Wheatstone's process. It is necessary 
 to employ several helices, according to the liquids that are 
 made use of. 
 
 If the liquid under examination contains a metallic salt that 
 is decomposed by the current, it is then in most cases essential 
 to employ for the lower positives plates D L, D' I/, plates 
 of the same nature as the metal in solution ; for the salt 
 that is decomposed by the current is formed again at the 
 positive pole. If this metal cannot be obtained in plates, 
 an oxidisable metal must be taken; the salt that is formed 
 remaining at the bottom of the vessel, does not enter into 
 the tube a b, and in the course of the experiment does 
 not derange the measure of the conducting power. We must, 
 then, take care that no liberation of gas occurs upon D L 
 and D' i/. Since the metal deposites upon E and E', there 
 is no counter current, and the needle of the galvanometer is 
 retained at zero; so that we obtain the resistance with great 
 precision. 
 
 If a liquid is employed that is not a solution of a metallic 
 salt, we must in this case always employ as positive plates 
 oxidisable metals, in order to obviate the liberation of gas 
 at the bottom of the glass ; and must operate with the most 
 feeble current that we can possibly employ, so that very little 
 gas may be liberated at E and E' : these plates are a little en- 
 
112 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 closed, so that the hydrogen shall not remain adhering; but, 
 notwithstanding these precautions, the needle of the galva- 
 nometer is not fixed at zero, it oscillates a little to the right and 
 left; and we take the position wherein the oscillations on 
 each side have the same amplitude. However, under these 
 circumstances the error does not exceed j 1 ^ in the length of 
 the liquid column. In all cases we must repeat this opera- 
 tion many times, in order to be sure that we arrive at the 
 same numbers. 
 
 M. Becquerel's experiments were at first directed to the 
 influence exercised upon the conductibility of different saline 
 solutions by the greater or less quantity of water, that is 
 contained in them ; thus, on making use of a helix containing 
 9 '84 feet of platinum wire, he operated upon three solutions 
 of sulphate of copper, and at a temperature of 9-25 
 (52*8 Fah.), the one saturated, the second containing 1 the 
 third ^ of sulphate in volume. 
 
 The following Table gives the lengths of liquid columns 
 for each solution equivalent to 9'84 feet of platinum wire, 
 which enables us to deduce their conducting powers, that of 
 silver being 100,000,000. 
 
 Solutions. 
 
 Sulphate of copper 
 contained. 
 
 Length of liquid 
 columns. 
 
 Conducting powers. 
 
 Saturated - 
 
 1 
 
 375 in. 
 
 5-42 
 
 Diluted, so that its 
 
 
 
 
 volume is double 
 
 1 
 
 2-41 
 
 347 
 
 Diluted, so that its 
 
 
 
 
 volume is quad- 
 
 
 
 
 ruple 
 
 1 
 4 
 
 1-44 
 
 2-08 
 
 M. Pouillet had found by Mr. Wheatstone's method a 
 result for sulphate of copper very near to that of M. Bec- 
 querel. He had obtained for this salt a conducting power 
 sixteen million of times more feeble than that of copper. 
 Now, the conducting power of copper being y 9 ^ that of 
 silver, we see that the number 5*42 obtained by Becquerel 
 is very near to that of M. Pouillet. 
 
 Similar experiments were made by M. E. Becquerel 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 113 
 
 upon bichloride of copper, nitrate of copper, chloride of sodium, 
 and sulphate of zinc at different degrees of concentration. 
 He has remarked that in some salts, such as nitrate of copper, 
 and sulphate of zinc, the conducting power increases in pro- 
 portion as the solution is diluted up to a certain limit, at 
 which it attains a maximum; it then diminishes again, so 
 that we can obtain a very dilute solution, that has the same 
 conducting power as a very concentrated solution. About 
 twenty-five years ago I made the same observation in respect 
 to sulphuric acid, which is a better conductor when mixed 
 with a certain proportion of water than when more concen- 
 trated or more diluted ; and what is very remarkable is, that 
 the best conducting solution of sulphuric acid is precisely 
 that which exerts the most active chemical action upon oxi- 
 disable metals, such as zinc, iron, &c. &c. 
 
 M. Matteucci arrived at a similar result by means of a 
 process that we will describe at the end of this paragraph, 
 when relating other experiments of the same philosopher. 
 The following is the Table of the conducting powers of sul- 
 phuric acid in different states of density, taking as unity 
 the conducting power of this acid at the density of 1*259. 
 
 Densities of the acid. 
 
 Conducting powers. 
 
 1-030 
 
 0-301 
 
 1-066 
 
 0-682 
 
 1-100 
 
 0-760 
 
 143 
 
 0-935 
 
 259 
 
 1-000 
 
 340 
 
 0-951 
 
 384 
 
 0-850 
 
 482 
 
 0-622 
 
 1-667 
 
 0-344 
 
 Nitric and hydrochloric acids have also each of them a 
 maximum of conductibility at a certain state of density ; 
 thus, according to M. Matteucci, nitric acid at 1*315 of 
 density conducts better than that which has a greater or 
 less degree of density. Hydrochloric acid at a density of 
 1*186 does not conduct so well as at 1*162; and conducts 
 
 VOL. II. I 
 
1.14 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 better at 1-114 than at 1-076. However, with these two 
 acids the effects are less decided than with sulphuric acid. 
 
 There is therefore an evident relation between the electric 
 conductibility of liquids and their chemical properties. This 
 is a point to which we shall return when occupied with the 
 electro-chemical decomposition of liquids. The following, 
 however, is a tolerably accurate Table of the conducting 
 powers of certain liquids : 
 
 Substances. 
 
 Densities. 
 
 Temperature. 
 
 Conducting 
 powers. 
 
 Pure silver - 
 
 
 
 o-oo 
 
 100,000,000 
 
 Water saturated with 
 
 
 
 
 sulphate of copper 
 
 1-1707 
 
 9 -25 
 
 5-42 
 
 Water saturated with 
 
 
 
 
 chloride of sodium at 
 
 
 
 
 9-50 
 
 
 
 13 -40 
 
 31-52 
 
 Water saturated with 
 
 
 
 
 nitrate of copper 
 
 1-6008 
 
 13 -00 
 
 89-95 
 
 Water saturated with 
 
 
 
 
 sulphate of zinc 
 
 1-4410 
 
 14 '40 
 
 5-77 
 
 250 grms. of water, and 
 
 
 
 
 30 of iodide of potas- 
 
 
 
 
 sium ... 
 
 in 
 
 12 -50 
 
 11-20 
 
 220 cent. cub. of water, 
 
 
 
 
 and 20 of sulphuric 
 
 
 
 
 acid with 1 atom of 
 
 
 
 
 water ... 
 
 
 
 19 -00 
 
 88-68 
 
 Nitric acid of commerce 
 
 
 
 
 at 36 
 
 )) 
 
 13 -10 
 
 97-77 
 
 30 grms. of protochlo- 
 
 
 
 
 ride of antimony, 120 
 
 
 
 
 cent. cub. water, and 
 
 
 
 
 100 cent. cub. hydro- 
 
 
 
 
 chloric acid 
 
 
 
 15 -00 
 
 112-01 
 
 We should notice, that the saturated solution of nitrate of 
 copper, when diluted with water so as to occupy a double volume, 
 has a conducting power which is almost double, 17*073 instead 
 of 8*995 ; and sulphate of zinc, under the same conditions, 
 has a conducting power of 7 '13 instead of 5 '7 7. This is also 
 the maximum of conductibility for these two saline solutions. 
 
 The influence of temperature is very sensible upon the con- 
 ducting power of liquids for electricity ; but this influence 
 here exerts an action contrary to that which it exercises over 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 115 
 
 metals; namely, elevation of temperature increases instead 
 of diminishes the conducting power of liquids. This fact had 
 been pointed out by M. Marianini in 1826, who had noticed 
 that the intensity of the current of a pair was increased by 
 heating the liquid of this pair ; but here the effect was com- 
 plex, because it might be equally well traced to an increase 
 produced by heat in the electromotive action of the metals of 
 the pair, as to an increase in the electric conductibility of the 
 liquid. More recently MM. E. Becquerel and Hankel have 
 proved in a direct manner that the elevation of temperature 
 does actually increase the conducting power of liquids. M. E. 
 Becquerel for this purpose employed the same means that had 
 served him for measuring the actual conductibility of liquids ; 
 and the following are the results, that he obtained with three 
 liquids. The conducting power of each of them being con- 
 sidered as unity, the conductibility for an increase of tem- 
 perature of one degree increased ; 
 
 For saturated solution of sulphate of copper - - 0-0286 
 
 For diluted solution of sulphate of zinc - - 0'0223 
 
 For nitric acid of commerce 0'0263 
 
 Which shows for each of these liquids an increase of more 
 than T n of its conductibility for one degree of elevation of 
 temperature. 
 
 M. Hankel's experiments were made according to a method 
 very similar to that of M. E. Becquerel, by means of a dif- 
 ferential galvanometer ; between the two wires of which a 
 current, produced by two or three pairs of Daniell's, is so 
 divided as to traverse them in opposite directions. In the circuit 
 of one of the wires was included the liquid, that is the subject 
 of the experiment, placed in a U tube ; and in the circuit of 
 the other helices of iron wire, the resistance of which was 
 exactly known, and the lengths of which were varied until 
 they presented a resistance equal to that of the liquid column, 
 which occurred when the needle remained at at the 
 moment when the entire circuit was closed. M. Hankel 
 took the precaution never to allow the current to pass for 
 more than a very short instant ; so that he might prevent the 
 
 I 2 
 
116 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 polarisation of the electrodes, and also the elevation of tem- 
 perature, that arises from the passage of the current, from in- 
 troducing disturbances into the results. He found by this 
 method, that the conductibility of a concentrated solution 
 of sulphate of copper increases on being heated from 
 to 83, about in the relation of 1 to 3*6; that of a 
 concentrated solution of nitrate of copper in the relation 
 of 1 to 3; that of a concentrated solution of sulphate of 
 zinc in the relation of 1 to 5*7. These results are notably 
 more considerable than those obtained by M. E. Becquerel, 
 as may be easily proved by multiplying the latter by 83, the 
 number of degrees between which M. Hankel operated. 
 This difference is probably due to M. Hankel's employing for 
 electrodes plates of copper in solutions of copper, and of zinc 
 in solutions of zinc, instead of platinum wires, as M. E. 
 Becquerel had done. It followed from this, that the action of 
 heat influenced the intensity of the transmitted current ; not 
 only by increasing the conductibility of the liquid, but by 
 facilitating the passage of the electricity by means of the 
 solution of the plates in this liquid ; the effect was therefore 
 complex, which proves that M. Becquerel's results represent 
 better the special influence of temperature, over the con- 
 ductibility proper of the liquid. 
 
 In these phenomena the influence of the electrodes, that 
 is, of the metals by which the current is transmitted into the 
 liquid, is indeed very great ; so that, as I have remarked, we 
 have merely to heat powerfully a platinum electrode, without 
 sensibly raising the temperature of the liquid, in order to fa- 
 cilitate in a very notable manner the transmission of a current, 
 and to raise, for instance, its intensity, as shown by a galvano- 
 meter, from 12 to 30; but what is very curious is, that this 
 result is obtained only when the heated electrode is the ne- 
 gative one ; the heating of the positive electrode has no influ- 
 ence. This effect is due, as we shall see, to a chemical action 
 facilitated by heat, that destroys the polarisation of the 
 electrode; which polarisation contributes to diminish the 
 intensitv of the transmitted current. 
 
 M. Vorselmann de Heer, after having confirmed the results 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 117 
 
 that I had obtained, showed that we have merely to move 
 violently the negative electrode in order to make a current 
 rise from 34 to 40 ; whilst the moving of the positive elec- 
 trode scarcely produces any change in the force of the current. 
 These effects, as M. Beetz has very well demonstrated, are 
 due to either the action of heat, or the mere mechanical 
 motion destroying in certain cases the polarisation of the 
 electrodes, which contributes to diminish the intensity of the 
 transmitted current. We shall return to this important point 
 when we have studied the cause of the polarisation of the 
 electrodes, which is the deposition upon their surface of ele- 
 ments arising from the chemical decomposition of the liquids. 
 
 Heat exercises another kind of influence over the con- 
 ductibility of bodies ; it is to convert into conductors, by 
 making them pass into a liquid state, a considerable number 
 of compound bodies which in their solid state were incapable 
 of transmitting a current, or transmitted it in a very imper- 
 fect manner. This important discovery is due to Faraday. 
 
 The following is the list of the principal substances, that 
 he has found susceptible of becoming conductors, when they 
 are liquefied by heat from being insulators, when in a solid 
 state. 
 
 1st. Ice, or congealed water. 
 
 2nd. Among oxides, that of potassium, the protoxide of 
 lead and that of antimony, the oxide of bismuth, and glass 
 of antimony. 
 
 3rd. The chlorides of potassium, of sodium, of barium, of 
 strontium, of magnesium, of manganese, of zinc, of lead, of 
 antimony, of silver, and the protochlorides of tin and copper. 
 
 4th. The iodides of potassium, of zinc, of lead, the proti- 
 odide of tin, and the periodide of mercury. 
 
 5th. The sulphurets of potassium and of antimony. 
 
 6th. The chlorate of potash, many nitrates, sulphates, 
 &c., &c. 
 
 Among the bodies in which igneous fusion does not 
 develope conducting power we may mention, besides sulphur, 
 phosphorus, camphor, &c., the periodide of tin, the sulphurets 
 of arsenic (orpiment and realgar), &c. Melted glass, especially 
 
 I 3 
 
118 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 flint-glass, becomes a conductor when raised to a high 
 temperature. 
 
 What is very remarkable is, that the mere softening of a 
 body by heat is not sufficient, in general, except in certain 
 exceptional cases, to render it* a conductor; it is necessary 
 for it to become completely liquid ; which would prove that 
 the effect is less due to the elevation of temperature than to 
 the liquefaction of the body. Mr. Faraday observed this, 
 particularly with borate of lead. 
 
 We need scarcely state that Faraday, in all his experi- 
 ments, determined conductibility by the faculty, either 
 possessed or acquired by a body, of transmitting a current 
 capable of acting upon the magnetised needle, or of producing 
 decomposition. We shall see in the following paragraph, 
 that in respect to imperfect conductors, in which the pro- 
 pagation of electricity occurs slowly, the mode of observation 
 is different. 
 
 It is probable that this effect of heat is due to the circum- 
 stance, that the transmission of the current cannot take place 
 in compound bodies unless they are at the same time decom- 
 posed; and that decomposition itself can be effected only 
 while they are liquid. However, Faraday thought he 
 had found some bodies such, for example, as periodide of 
 mercury, which, although insulating when solid, become 
 conductors when they are liquid, without undergoing, in 
 appearance at least, any sensible decomposition. He also 
 found that sulphuret of silver and fluoride of lead, which at 
 the ordinary temperature are insulators, become conductors 
 by the mere elevation of temperature, without the necessity 
 of passing into the liquid state. When once melted, they 
 conduct electricity as well as metals do, and do not appear 
 to undergo decomposition. When they become solid again, 
 and have been brought back to their original temperature, 
 they again become insulators ; which seems to prove that their 
 chemical nature has not been altered by heat. Glass also 
 exhibits the same conditions. However, it is still a contro- 
 verted question, which will be discussed in the Chapter on 
 electro-chemical decompositions, namely, whether a compound 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 119 
 
 body is able to conduct electricity, if not entirely, at least in 
 part, after the manner of simple bodies, without undergoing 
 decomposition. 
 
 Then, also, we shall study the influence of water, which, 
 although a very bad conductor in itself, is able in certain 
 cases to convert into conductors, by admixture with them, 
 not only the solid bodies that it dissolves, but liquids which 
 are very insulating, such as bromine, melted iodine, and 
 liquefied chlorine. There is evidently in this action of water, 
 as well as in that of igneous liquefaction, a facility supplied 
 for electro-chemical decomposition, and, consequently, more 
 a chemical than a physical effect. Moreover, without now 
 insisting upon this subject, I may find a proof of it in the 
 observation that I had made in 1837, and which M. E. Bee- 
 querel has confirmed, as we have already seen above, that 
 mercury, although liquid, loses by heating a notable part of its 
 conducting power ; contrary to what happens with all liquids, 
 which, instead of being simple bodies, are compound sub- 
 stances. 
 
 Before terminating, we will again mention the important 
 results obtained by M. Matteucci, who has submitted to expe- 
 riment a great number of combinations, which he was enabled 
 to obtain in a state of purity, and which satisfied the double 
 condition of being anhydrous and fusible. A voltameter 
 was placed in the principal circuit, which was subdivided 
 into two ; one containing a second voltameter similar to the 
 first, the other the compound substance in a state of igneous 
 fusion. If the indication of the second voltameter was the 
 same as that of the first, it was a proof that the melted 
 substance w r as not conducteous ; if, on the contrary, this 
 indication was less or null, it might be concluded that a 
 portion or the whole of the current passed through the body 
 that was the subject of the experiment. It is by this pro- 
 cess that M. Matteucci had obtained the results that we have 
 related above, on the conducting powers of acids at various 
 degrees of concentration. In a state of fusion, the protoxide 
 and the iodide of lead, the chloride of silver, the protochloride 
 of copper, the sulphurets of antimony, and of potassium, the 
 
 i 4 
 
120 TRANSMISSION OF ELECTRICITY. PART IV' 
 
 nitrates of potash and of silver, conducted the whole of the 
 current, and do not allow of any portion passing through the 
 voltameter; then, in their order of conductibility, come chlo- 
 ride of lead, iodide of potassium, the chlorides of sodium, of 
 calcium, and of zinc, the bi-iodide and the protochloride of 
 mercury, the chloride of antimony, and the protochloride of 
 tin. The bichlorides of tin and of antimony caused the 
 current to pass entirely into the secondary voltameter. 
 Aqueous solutions of these combinations, in as concentrated 
 a state as possible, were then compared with the same bodies 
 in the state of igneous fusion ; and it was found that all the 
 current passed into the melted combination, even when the 
 solution was heated. However, there is a very evident 
 relation between the conductibility of a solution and that 
 possessed by the body, that had been dissolved, when in the 
 state of fusion; then, in order that two aqueous solutions 
 shall have the same conductibility, it is necessary that the 
 one whose compound when in a state of fusion is the worse 
 conductor, should be more concentrated. This consequence 
 seems clearly to prove, that in the aqueous solutions of certain 
 compound bodies, whose conductibility when in a state of 
 fusion is great, the current is conducted by the dissolved 
 body, and that the only function of the water, like that of 
 heat, is to impart to it the liquid state essential to electro- 
 chemical decomposition. 
 
 Another very important observation of M. Matteucci's is, 
 that certain bodies, which do not conduct when in a state of 
 fusion, such as the bichlorides that we have mentioned above, 
 acquire this property when they are dissolved in water ; pro- 
 bably because the presence of water facilitates their decom- 
 position. In like manner the chlorides of antimony, and the 
 protochloride of tin, which are very bad conductors when in 
 a state of igneous fusion, are much better when they form in 
 water very concentrated solutions. It is evident that in all 
 these phenomena there are secondary chemical actions, which 
 the passage of the current brings about and facilitates, and 
 which cause these effects to be very complex. 
 
 We may, therefore, sum up this paragraph by saying ; 1st, 
 
CHAP. 1. PROPAGATION OF ELECTRICITY. 121 
 
 That metals and carbon have a conductibility proper, which 
 varies with their nature and with their molecular state; 2nd, 
 That elevation of temperature diminishes in all of them their 
 conducting power, in a proportion which is variable for each 
 with their nature and their molecular condition ; 3rd, That 
 solid compound bodies, which are insulators at the ordinary 
 temperature, become conductors on being heated, but that 
 the greater number acquire this property only when they 
 are heated sufficiently to pass into the liquid state ; 4th, 
 That for aqueous solutions, the conducting power varies 
 with their degree of concentration, the most concentrated 
 being generally, unless in certain exceptional cases, the best 
 conductors, and that this power generally increases with the 
 elevation of temperature; 5th, That the differences which 
 exist between simple and compound bodies, as far as the in- 
 fluence of heat is concerned, seems to indicate that their con- 
 ductibility, or what comes to the same thing, their mode of 
 propagating electricity, is not completely identical, which is 
 due probably to the circumstance that in compound bodies 
 the transmission of the electric current is either always ac- 
 companied by a molecular change, or more frequently, if not 
 always, by a chemical decomposition ; 6th, It follows from 
 this last circumstance, that the subject of the electric con- 
 ductibility of compound bodies cannot be completely dis- 
 cussed, except by studying electro-chemical decompositions, 
 which form the subject of a distinct Chapter in this Fourth 
 Part. 
 
 Propagation of Electricity in Imperfect Solid and Liquid 
 
 Conductors. 
 
 When in the First Part of this Treatise we gave the list of 
 conducting and insulating bodies*, we were careful to remark 
 that conductibility is not an absolute property ; namely, that 
 we cannot class bodies into two categories, one of which 
 shall consist of perfect conductors, and the other of perfect 
 insulators. We have been engaged in the preceding para- 
 
 * Vol. I p. 8. 
 
122 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 graph with those which are sufficiently good conductors to be 
 able to transmit voltaic electricity in a continuous and rapid 
 manner ; a property that is made manifest by the dynamic 
 effects of the current. We will now go on in this paragraph 
 to study the propagation of electricity in bodies of which 
 several are regarded as insulators, or which at least conduct 
 electricity too imperfectly to be able, unless under certain 
 exceptional circumstances, to transmit a current properly so 
 called. 
 
 Priestley had long ago remarked that ice, glass when heated 
 or when pounded, the flame of a candle, and a great number 
 of mineral substances, are able to transmit the discharge of a 
 Ley den jar, or even that of the charged conductor of an 
 electrical machine. Coulomb, in his admirable works on the 
 slow loss of electricity, was satisfied that cylinders made of 
 substances apparently the best insulators, such as glass, 
 sealing-wax, and gum-lac itself, transmit difficultly it is true, 
 but in a sensible manner, the electricity accumulated upon the 
 conductor of an electrical machine with which they are placed 
 in contact by one of their extremities. This may be proved 
 either by the loss of electricity suffered by the conductor, or 
 by the electric action that these insulating substances become 
 capable of exerting, which proves that they are impregnated 
 with electricity. However, Coulomb found, that when the 
 intensity of the electricity is not very strong, a thread of 
 gum-lac of gj in. in diameter about 2 in. in length is sufficient 
 to insulate completely a cork ball in. in diameter. But, as 
 we see, this insulating property is not absolute ; for Coulomb 
 himself observed, that the degree of electric reaction at which 
 very fine cylindrical supports commence to insulate is, from 
 the same state of the air, proportional to the square root of 
 their length. In order to ascertain the permeability of all 
 substances that transmit electricity imperfectly, it is necessary 
 to determine $]ie intensity of the electric reaction at which 
 insulation commences for threads of the same length and the 
 same diameter, but of different natures. By this means 
 Coulomb found that the value of this reaction is ten times 
 greater for a thread of gum-lac than for one of silk. 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 123 
 
 Riess has submitted to experiment a certain number of sub- 
 stances, in order to determine whether they are conductors or 
 not. By conductor he designated a body that instantaneously 
 takes away the electricity from a charged electroscope with 
 which it is put into contact; by imperfect conductor, that 
 which does not carry it away until after an interval of several 
 seconds; and by non -conductors, that which at the end of 
 some minutes has not in a sensible manner modified the di- 
 vergence of the gold-leaves of the instrument. The last dis- 
 tinction is rather arbitrary. He has thus found that a cylinder 
 of selenium three or four-tenths of an inch in diameter, and ^ 
 in. or 1 in. in length, instantly carried off the electricity of an 
 electroscope with which it was placed in contact; but that 
 when drawn into a fine wire by the flame of a lamp, it was as 
 good an insulator as a thread of gum-lac. Selenium belongs 
 therefore to non-conducting bodies, and friction easily renders 
 it electrical, provided its surface be very smooth. Iodine is 
 an imperfect conductor; cylinders ^ an inch in diameter, 
 and of various lengths, discharge an electroscope in a second, 
 but cannot transmit a voltaic current. Aluminium and 
 beryllium in powder, rammed into glass tubes terminated by 
 metal points, very quickly discharge electricity from the 
 electroscope ; but Riess satisfactorily proved that these two 
 substances owe this property merely to the presence of con- 
 densed water ; for by drying them for half an hour in 
 porcelain crucibles at the temperature of 212, they become 
 non-conductors. Beryllium is even so good an insulator, that 
 a layer of less than ^ in. in thickness does not alter the di- 
 vergence of the electroscope ; with aluminium, in order to 
 obtain the same result, it is necessary that the layer be at 
 least J in. thick.* 
 
 This last observation shows how difficult it is, when ex- 
 perimenting with bodies which are only imperfect conductors, 
 to avoid the different causes, that may lead to erroneous 
 
 * M. Deville has found that aluminium, to which he has succeeded in giving 
 the consistency of the ordinary metals, is an excellent conductor of electricity, 
 and almost as good as silver. It is probable that its imperfect conductibility was 
 due to the particular condition in which it occurred in M. Kiess's experiments. 
 
124 TRANSMISSION OF ELECTRICITY. PART iv- 
 
 
 
 results. M. Karsten points out one that is also calculated 
 to explain the contradictory conclusions to which many 
 philosophers have arrived who have been engaged upon this 
 subject; it is the different manner of preparing the bodies 
 that are the subject of experiment. Thus, being desirous of 
 determining the conducting power of the sulphurets of the 
 different metals, he remarked that sulphuret of antimony in 
 the state of powder is a perfect conductor ; whilst, when it 
 has been melted and cooled in a mould, it becomes an in- 
 sulator. It is true that it is then covered with a vitrified 
 film, which envelopes a crystalline core ; whilst, when the 
 cooling occurs very slowly, the whole mass acquires the 
 crystalline texture, and comports itself as a conductor. But, 
 on the other hand, sulphuret of antimony produced by the 
 moist process is a perfect insulator. It is the same with the 
 sulphurets of cadmium and of zinc ; but prepared by the dry 
 process they are conductors. The sulphurets of tin, copper, 
 lead, bismuth, and iron are always conductors, by whatever 
 process they may have been prepared ; the black sulphuret 
 of mercury is a good conductor, whilst cinnabar conducts very 
 feebly ; finally, the sulphurets of gold and of silver prepared 
 by the moist process are conductors. 
 
 There also exist certain liquids which, although regarded 
 as insulators, are in fact nothing less than imperfect con- 
 ductors ; such, for example, are the different kinds of oils, 
 which in this respect present among themselves very remark- 
 able differences. M. Rousseau, who was the first to observe 
 these differences, used for this purpose an apparatus of his 
 own invention ; which consists of a horizontal needle movable 
 on a pivot, by means of which communication may be made 
 with one of the poles of a dry pile, while one of its ends is 
 very near to a fixed ball communicating also with the same 
 pole.* If communication is made by a body that is more 
 or less a conductor, the needle is driven from its normal. 
 
 * For his movable needle M. Rousseau employs a magnetised needle, so 
 that it might always return to the same position when no action was occurring ; 
 but an unmagnetised needle, one of copper, for instance, accomplishes the 
 object equally well, and gives a more sensible result. 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 125 
 
 position; after having accomplished a few oscillations, it 
 assumes a position of equilibrium that is dependent on the 
 force of the pile, which may be considered as being constant 
 for the same pile for a long time. Now, in order to employ 
 this apparatus for investigating different degrees of con- 
 ductibility, we have merely to place in the course that must 
 be traversed by the electric fluid the different bodies which 
 we propose subjecting to experiment, with the precaution of 
 arranging that the thickness to be traversed by the electricity 
 shall be always equal; if the passage of the quantity of 
 electricity necessary for producing the greatest deviation is 
 not instantaneous, the time that will be required by the 
 needle in order to arrive at its stable position may be taken 
 as the measure of the degree of conductibility of the compound 
 substance. In order to submit liquids to this kind of test, 
 M. Rousseau places them in small metal vessels, which 
 communicate by their foot with the needle and the ball ; then 
 he plunges into the liquid one end of a wire, partly covered 
 with gum-lac, in order that the same surface of metal may 
 always be in contact with the liquid ; he then measures the 
 duration of the movement of the needle, setting out from the 
 moment when communication is established by the other end 
 of the wire with one of the poles of the pile, whilst the other 
 pole is in communication with the ground. 
 
 In operating with different oils, M. Rousseau observed 
 this very curious fact, that olive oil possesses very inferior 
 conductibility to that of all other vegetable or animal oils. 
 Thus, in order to produce a certain deviation, everything 
 being similar in other respects, it required 40' for olive oil, 
 and only 27" for oil of poppies. By merely adding to olive 
 oil a hundredth part only of another species of oil, the term 
 required for producing the same effect was reduced from 40' 
 to 10'. Solid fats do not conduct so well as animal oils; 
 which is due, as may be proved in a direct manner, to the 
 greater proportion of stearine in the former than in the latter. 
 M. Rousseau was unable to detect any difference in the con- 
 ducting property of spirituous, aqueous, acid, alkaline, or 
 neutral liquids ; for with these various substances the time 
 
126 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 required by the needle in order to attain its maximum of de- 
 viation, is too short to enable us to appreciate any inequalities 
 of duration. But these inequalities are very sensible, when 
 we subject to this test resin, gum-lac, or sulphur ; substances 
 which are found to be much better insulators than silk, 
 crystal, and common glass. It would be easy to modify M. 
 Rousseau's apparatus, so as to render it susceptible of in- 
 dicating differences between bodies which are less distant 
 from each other in respect to conductibility ; but in all cases 
 it would only give the order of conducting power, more or 
 less imperfect of bodies ; and never their relations of conduc- 
 tibility. 
 
 Before pursuing the explanation of the experiments that 
 have been made upon the various degrees of conductibility 
 of imperfect conductors, let us devote a short time to the 
 manner, in which the propagation of electricity takes place. 
 We have already given* Mr. Faraday's experiments and 
 theories on this subject, in connection with his experiments 
 on dialectric bodies, as well as the researches of Harris and 
 Matteucci. Faraday's fundamental idea is that the propaga- 
 tion of electricity in bodies, that are more or less insulators, 
 is brought about by the polarisation of the successive mole- 
 cules ; and that each body possesses in this respect a specific 
 power that is peculiarly its own. Matteucci had already 
 confirmed this theory by his remarkable experiment with 
 superposed plates of mica, which became polarised, that is to 
 say, they acquired on each of their faces a different electricity, 
 when they are interposed between two armatures highly 
 charged with contrary electricities ; but he has further de- 
 monstrated, by direct experiments, that molecular electrisation 
 is developed in different degrees in different insulating bodies. 
 Thus he made a small pendulum oscillate, to which he had 
 given electric charges of greater or less intensity, before three 
 spheres of very great diameter, in comparison with that of 
 the electrised ball. The three spheres, placed successively 
 at the same distance from the electrised pendulum (first, at 
 
 * Vol. I. p. 1 39. and the following pages. 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 127 
 
 a distance of 4 in., then of about 5 in.), were a sphere of lead, 
 one of sulphur, and one of resin. The mean duration of 
 20 oscillations, at a distance of 4 in., with a certain electric 
 intensity, was, for the sphere of lead, 24^", for that of 
 sulphur,. 30 J", for that of resin, 32 J" ; with another intensity 
 and at a distance of about 5 in., these numbers were different, 
 but their relations remained almost the same ; which gives for 
 the mean of the numbers, that represent the relation of the 
 forces, 
 
 Sphere of lead - - - ! 
 
 Sulphur - - 0-6072 
 
 Resin .... 0-4800 
 
 Thus at a distance spheres of a different nature experience 
 a different influence from the electricity of the pendulum ; but 
 it is independent, in regard to its relative intensity, of the 
 energy of the electric charge. 
 
 When in contact these differences are more sensible. In 
 order to estimate them, M. Matteucci employed plates and 
 cylinders made of different insulating substances, which he 
 touches successively with an electrised metal ball held by 
 an insulating handle, or with a cylinder of gum-lac electrised 
 by friction ; he then brings the plate or cylinder, that has 
 been touched, in front of a small electric pendulum. If the 
 body that has electrised is an insulator, the point of the 
 plate or cylinder that is touched is found charged with a con- 
 trary electricity to that of the electrised body, and around 
 this point with similar electricity. If the body that has 
 electrised is a conductor, the insulating plate or cylinder is 
 soon found to be charged with the same electricity as this 
 body, provided the insulating substance is not of a large 
 mass, and that the contact has not been maintained longer 
 than a brief moment ; in which case the touched points have 
 a contrary electricity to that. of the electrised conductor. 
 
 Furthermore, the propagation of electricity in an insulating 
 body may be easily proved by direct experiment. For this 
 purpose we have merely to electrise a cylinder of stearic 
 acid by means of the prime conductor of the machine ; if it 
 
] 28 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 is rubbed with woollen cloth, signs of negative electricity are 
 obtained; but, in order to obtain the re-appearance of the 
 signs of positive electricity that had been communicated to 
 it by the electrical machine, and which has become propagated 
 in its interior, we have merely to melt the surface, or to wash 
 it in sulphuric ether. 
 
 The laws of this propagation have been the subject of long 
 and delicate researches on the part of M. Matteucci. By 
 operating with the balance of Coulomb and after the mov- 
 able ball had receded about 30 from the fixed ball by intro- 
 ducing an insulating plate, which he placed in contact with this 
 ball he deduced, by the determination of the distance between 
 the two balls, the facility with which the insulating plate had 
 taken away electricity from the fixed ball, and, consequently, 
 its degree of aptitude in propagating electricity. He took the 
 precaution of allowing contact to remain in each experiment 
 for five minutes ; and he estimated by the diminution of the 
 angle of torsion, after the insulating plate had been removed, 
 the quantity of electricity that it had taken away from the 
 fixed ball. The experiments were made by varying the 
 initial charge of the ball and the extent and thickness of the 
 insulating plate, and by operating for the most part with plates 
 of sulphur; but sometimes also with plates of gum-lac, glass, 
 and mica. In each experiment a note was made of the initial 
 electric force, of the electric force during the contact of the 
 insulating plate, and, finally, of the residual force ; namely, 
 that which remained after a contact of five minutes. During 
 these five minutes, the loss of electricity by the air was abso- 
 lutely insensible. 
 
 The results of the numerous experiments, made in this 
 manner by M. Matteucci, do not lead to very simple laws ; 
 but the results are not the less curious. Thus, the quantity 
 of electricity taken from the ball by the insulating substance 
 is proportionately greater as the electric charge is stronger ; 
 it is in like manner more considerable in proportion as the 
 insulating plate is thinner and less extended ; which is due to 
 the effect being concentrated on a smaller number of points, 
 and being consequently proportionately greater. It follows, 
 
CHAP. I. PROPAGATION OF ELECTEICITY. 129 
 
 that the passage of electricity from a metal ball to an insu- 
 lating body occurs the more easily in proportion as the latter 
 is thinner, and presents to the ball the smallest number of 
 points that do not touch it; so that an electrised metal 
 ball would lose the smallest possible quantity of electricity 
 when resting on a very thick and very extended insulating 
 disc ; and that, on the contrary, the greatest loss of electricity 
 would occur on reducing the insulating body to a very slender 
 and very short stem.* 
 
 If the insulating discs, whatever their nature be, are 
 covered with a thin sheet of tin-foil on one of their faces, 
 whilst the other is in contact with the movable electrised 
 ball, we find that the electric force of the ball diminishes 
 much more, both during and after this contact, than when the 
 insulating disc is not coated : these results seem to demonstrate 
 the penetration of contrary electric charges, that takes place 
 in the two faces of the insulating disc, the one by contact, 
 the other by induction a penetration, which may easily be 
 proved directly. For this purpose, we have merely to take 
 a cubical piece of spermaceti, and to place it between two 
 coatings, so as to constitute a magic pane, which is charged 
 feebly but tediously. Then, by means of plates of glass, the 
 piece of spermaceti is to be divided into several fragments, 
 which are found to be charged to a certain depth with positive 
 electricity on the side of the positive coating, and with nega- 
 tive electricity on the side of the negative coating. If in 
 place of spermaceti, we employ plates of mica superposed on 
 each other, instead of having contrary electric states on the 
 opposite faces of each of them, providing a powerful electric 
 force is employed and allowed to act for a long time, we end 
 by finding the same electricity upon both faces of the same 
 plate, going from the outer plates toward the middle ; namely, 
 positive electricity upon the plates that are on one side, and 
 negative upon those which are on the other. 
 
 M. Matteucci concludes from these experiments, and from 
 
 * This result agrees with Coulomb's observation, that, in order to produce 
 a perfect insulator, a thin stem should be longer in proportion as the substance 
 of which it is made is a less efficient insulator. 
 
 VOL. II. K 
 
130 TRANSMISSION OF ELECTRICITY, PART iv. 
 
 others that we have already * mentioned that the difference 
 observed by Faraday and Harris, between different substances 
 with regard to their faculty for modifying the electric charge 
 of the magic pane, between the two coatings of which they 
 are placed, is not due to their specific inductive power, but 
 simply to differences in the propagation of electricity, either 
 at their surface or at a very small depth in their interior : a 
 proof that the electric molecular states may be destroyed in 
 insulating bodies, and electricity may be propagated in them 
 as in conductors, and that insulating power consists merely of 
 the greater or less resistance to the successive establishment 
 and destruction of the molecular electric states. We may 
 also remark that this molecular electrisation is developed and 
 ceases in insulating bodies at the very moment when the 
 presence of the electrised body commences or ceases. 
 
 It is a very remarkable fact that negative electricity is 
 propagated more readily than positive, both on the surface and 
 in the interior of insulating bodies. The experiment is made by 
 charging balls, sometimes with negative, sometimes with positive 
 electricity, and by comparing the results obtained, on placing 
 in each case the movable ball in contact with the uncoated 
 surface of the insulating plate, the coated surface being in 
 communication with the ground. The differences are very de- 
 cided ; the diminution of the electric force during contact, and 
 of the force that remains after contact, is greater for negative 
 than for positive electricity, in the relation of double to single. 
 The difference is not so great, although it is still sensible, 
 when the insulating plates are not coated ; but it is more 
 considerable in proportion as the electric charge is stronger. 
 It is evident that to this different property of the two electri- 
 cities is to be traced the cause of the Lichtenberg f figures, 
 in which positive electricity is propagated on an insulating 
 surface in ramifications, consequently, in compacted filaments, 
 distributed unequally over this surface, whilst negative elec- 
 tricity is propagated uniformly in radii equally distributed 
 around the electrised point. 
 
 * Vol. I. p. 152. f Vol. I. p. in. 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 131 
 
 We may further add, that differences of temperature, even 
 the slightest, produce a considerable variation in the insulating 
 power of bodies ; but these variations do not follow the same 
 progressions in different substances. Thus, with very strong 
 electric charges, sulphur up to 68 is not so good an insulator 
 as gum-lac ; the reverse is the case beyond 68. In order to 
 determine accurately the difference in the two cases, two 
 cubes of 2 '3 6 in. on each side are taken, the one of sulphur, 
 the other of gum-lac ; each of these cubes is cut through the 
 middle, and a spherical cavity is made in its centre of the 
 size of the movable ball, which lodges in it as in a mould. 
 These cubes being well-dried, the ball is placed in them for 
 a few seconds : it is found that the loss of electricity at 56*8 
 being j T in air, it is J T in gum-lac, and ^ in sulphur ; and 
 at 95, ^T in gum-lac, and ^ in sulphur. 
 
 We must not confound this influence of heat with that 
 which consists in removing from the surface of certain bodies, 
 such as glass and mica, a thin layer of moisture, which 
 renders them slightly conductors. In this case the elevation 
 of temperature increases their insulating power. But a more 
 powerful heating diminishes it ; glass, resin, and wax, become 
 conductors at a temperature sufficient to soften them, and 
 still more so, when they are reduced to the state of liquid. 
 Glass in a state of fusion is even able to conduct a very 
 feeble current, so as to act upon the galvanometer. It is 
 true that under these conditions, it probably experiences an 
 alteration in its chemical constitution, which may explain the 
 modifications brought about in its insulating power; the 
 same thing also occurs when its surface has been radiated by 
 electric discharges ; indeed, it may be seen that the rays are 
 much better conductors than the rest of the surface, which 
 has not been altered by the passage of discharges. However, 
 a simple modification in the arrangement of the particles is 
 amply sufficient, without any chemical alteration, to account 
 for the changes that may occur in the conductibility of 
 bodies that are imperfect conductors ; and we find a remark- 
 able proof of this in the conducting properties of crystals, 
 
 K 2 
 
132 TKANSMISSION OF ELECTRICITY. PART ir. 
 
 which have been studied with great care, successively by M. 
 Wiedemann, and by M. de Senarmont. 
 
 The former of these philosophers, in pursuing these in- 
 vestigations, made use of powder of lycopodium or minium, 
 with which he powdered over the surface of the body sub- 
 mitted to experiment ; he then touches a point of this surface 
 with the point of an insulated needle, by means of which he 
 communicated positive electricity from a Leyden jar. The 
 light powder is dispersed all around the point, by the effect of 
 the repulsion exercised upon it by the points of the surface, 
 that have received the electricity. When the body powdered 
 upon is a plate of glass, a circular figure is obtained around 
 the point, traversed by rays similar to the Lichtenberg figures. 
 When, instead of glass, a pallet of gypsum is employed, the 
 powder is no longer dispersed in a uniform manner in all 
 directions. Two principal directions are noticed which 
 are diametrically opposite, and along which the dispersion 
 occurs with more force; this gives rise to an elliptical 
 surface, whose axes are to each other as 2 or 3 is to 1. 
 The great axis of this ellipses forms a right angle with the 
 principal crystallographic axis, which proves that electricity 
 is more easily distributed in a direction perpendicular to the 
 principal axis, than in any other direction. The same 
 phenomenon is presented with many other crystals, such as 
 celestine, quartz, acetates of lime and copper, which are all 
 positive. On the other hand, with negative crystalline 
 substances, such as arragonite, tourmaline, and Iceland 
 spar, the axis of the ellipse, formed by the electric dispersion 
 of the powder, is parallel to the crystallographic axis. These 
 opposite results seem to indicate, that the direction of best 
 electric conductibility is also that in which light is pro- 
 pagated relatively with most rapidity. 
 
 M. de Senarmont, who had already discovered the unequal 
 conductibility of crystals for heat in different directions, had 
 arrived at the same time as M. Wiedemann * at analogous 
 
 * The researches of M. Wiedemann appeared a short time before those of 
 M. de Senarmont ; but the processes of the two philosophers, although their 
 results generally agree, are very different. 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 133 
 
 results, as far as the conducting power for electricity is con- 
 cerned. M. de Senarmont covers the surface of bad con- 
 ducting bodies with a sheet of tin -foil, forming as it were a 
 metal envelope around the body ; he takes care to perforate 
 this envelope with a perfectly circular hole, which exposes a 
 part of the natural surface. An insulated metal point, 
 placed in the centre of the opening, perpendicular to the 
 surface itself of the bad conducting body, is the way by 
 which the electricity is introduced. The electricity cannot 
 escape, except by traversing toward the circumference, and 
 passing over a non-conducting space; it has, therefore, to 
 overcome resistances, the evidence of which is manifested by 
 luminous phenomena. As every thing is symmetrical, the 
 electricity that enters at the centre of the circle, is attracted 
 equally on all sides by the conducting circumference, and 
 cannot be led in greater proportion in one direction than in 
 the other, except by differences in superficial conductibility. 
 There is an advantage in operating in rarefied air, because 
 the phenomenon is in this way well regulated ; it is true that 
 the continuous escape of electricity does not, in this case, leave 
 any permanent traces ; but it is manifested in darkness by a 
 light, which renders all the peculiarities of the phenomenon 
 visible during its continuance. 
 
 Experiments conducted in this manner show that upon 
 homogeneous matters, or upon crystals of the regular system, 
 electricity spreads circularly around the central point, and 
 covers the surface of the circle with a uniform light ; it is the 
 same with crystals of the prismatic system, with a square and 
 rhombohedral base, but only when the face is normal to the 
 axis of symmetry. In all other cases, namely, on the faces 
 parallel and inclined to the axis of symmetry of crystals of 
 this system, on any face whatever, as well as with crystals 
 of other systems, there exists a direction of principal con- 
 ductibility. In such cases, we see plainly the light escaping 
 freely from the centre in two opposite directions, and thus 
 forming a luminous diameter, which assumes a fixed direc- 
 tion, or spreads a little into a fan, and balances itself by 
 a few slight oscillations on the right and left of its true 
 
 K 3 
 
134 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 direction. The direction is more stable, when a certain 
 tension is allowed to the air; sometimes, even in this case, 
 brilliant and instantaneous sparks intermingle with the per- 
 manent violet light ; and, if the surface has been powdered 
 with flowers of sulphur, the sparks leave upon this powder 
 the trace of the rectilinear course which they have traversed. 
 
 The results obtained by M. de Senarmont show that, 
 when the face of the crystal contains in its plane one or two 
 axes of symmetry, the direction of maximum conductibility is 
 perpendicular or parallel to these axes ; but that, in other 
 cases, namely when the face contains no axes of symmetry in 
 its plane, this direction cannot be anticipated a priori; it 
 must be determined by experiment, and does not necessarily 
 coincide either with the directions of the axes of optical 
 elasticity, or with the directions of the axes of thermic con- 
 ductibility. However, the analogies that are presented by 
 the optical, calorific, magnetic and electric properties of 
 crystals, which we have previously entered into*, and the 
 influence exercised over these properties by the equal or 
 unequal axes of symmetry, are of a nature to demonstrate 
 that they are connected with a common cause, namely, 
 molecular arrangement, and to show the importance of this 
 cause in the phenomena that are now engaging our attention. 
 M. Knoblauch has on his part actually demonstrated the 
 influence of crystalline form over induced electricity, by 
 observing that crystals, suspended between the contrary 
 poles of two dry piles, assume a determinate direction, 
 which is due to the mode in which their particles are 
 grouped. 
 
 We may further add that M. de Senarmont, as well as 
 M. Wiedemann, has remarked a very decided difference 
 between positive and negative electricity, with regard to 
 their mode of action in experiments relating to the super- 
 ficial conductibilty of crystals. The results are, however, 
 very confused and variable, when negative electricity is made 
 to enter by the point ; they are well determined with positive 
 
 * Vol. I. p. 515. 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 135 
 
 electricity alone. We shall return to these differences pre- 
 sented by the two electricities ; but we must first point out 
 one, which was only apparent, and has admitted of explana- 
 tion by the ordinary and known effects of the electric 
 current. 
 
 Ermann thought he had found in a particular class of imper- 
 fect conductors, which he had called unipolar, the property of 
 more easily transmitting one of the electricities than the other. 
 Into a piece of very dry soap, he introduced two wires com- 
 municating respectively with one of the poles of a voltaic 
 pile ; the two poles preserved their tension ; but if the soap 
 was touched with a conducting body, the negative pole 
 was discharged, whilst the positive pole acquired the max- 
 imum of tension that it possesses when, with the pile in an 
 insulated state, the negative pole is put into communication 
 with the ground. Ermann had discovered the same pro- 
 perty in dried white of egg, and in the flame of phosphorus ; 
 he had also noticed it in the flames of hydrogen, of alcohol and 
 of hydro-carbon bodies in general ; but with this difference, 
 that it is the positive pole that is discharged by these flames, 
 whilst the negative pole acquires its highest tension. The 
 former had consequently been designated negative unipolar, 
 the latter positive unipolar, bodies. This classification, in 
 addition to its having been too absolute in its character, had the 
 further defect of being based upon an erroneous interpretation 
 of the experiments. Indeed, Ohm has demonstrated that the 
 cause of the phenomenon observed by Ermann does not reside 
 in any property of the substance interposed between the 
 poles of the pile, but is due to the effect produced in it, 
 as soon as the circuit is closed, by the current that traverses 
 it. This effect consists of the decomposition of the soap, 
 the stearic or oleic acid of which is carried to the positive 
 pole, whilst the soda goes to the negative ; these acids being 
 of an insulating nature, as soon as they have covered the 
 wire upon which they are deposited, the electricity of the 
 pole with which this wire is in communication, namely, the 
 positive, can no longer pass in the soap, whilst the negative 
 continues to be transmitted in it and escapes thence into the 
 
 K 4 
 
136 TRANSMISSION OF ELECTRICITY. PART IT. 
 
 ground. Thus the negative pole of the pile is discharged, whilst 
 the positive maintains its tension. This very natural inter- 
 pretation of Ermann's experiment is found to be confirmed 
 by a great number of facts. Indeed, we have merely to put 
 the wire that came from the positive pole into communication 
 with the negative pole, and which consequently is covered 
 with the coat of acid, and we insulate the negative electricity 
 as had been the case with the positive. In order to succeed 
 in these experiments, it is necessary to have a powerful pile ; 
 for, unless this is done, the products of decomposition occur 
 in so small a quantity that they cannot interpose any obstacle 
 to the circulation of the current. 
 
 With regard to the unipolarity of hydrogenous flames, 
 it is probably due to the voltaic decomposition of the vapour 
 of water formed during combustion, a decomposition that 
 determines upon the surface of the negative wire the deposit 
 of an insulating film of hydrogen ; whence it follows that 
 the positive electricity alone is able to pass away into the 
 ground by means of the wire placed in the flame. We shall 
 elsewhere return to the phenomena connected with the con- 
 ducting powers of flames in the following paragraph, which 
 is devoted to the propagation of electricity in elastic fluids. 
 
 Concentrated sulphuric acid, when placed under the same 
 conditions as soap and flames, is a negative unipolar conductor 
 which arises from the formation on the positive wire of in- 
 soluble and non-conducting sulphate ; but the effect varies 
 with the nature of the wires immersed in the acid ; inasmuch 
 as some form more soluble and better conducting sulphates, 
 than are formed by the others. Finally, all this class of pheno- 
 mena is nothing more than the result of the secondary actions, 
 which always accompany the transmission of electricity 
 through conductors, capable of being decomposed ; and under 
 this view, it loses much of its theoretic importance, and enters 
 into the category of the numerous facts due to the same cause, 
 and which we shall study in the Chapter on electro-chemical 
 decompositions.* 
 
 * In what we have been saying upon unipolar conductors, we have not men- 
 tioned some experiments of Ermann's, relative to the reciprocal insulating and 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 137 
 
 Hitherto, while engaged with imperfect solid and liquid con- 
 ductors, we have spoken only of the slow and gradual propaga- 
 tion of electricity that can be brought about in them ; but these 
 conductors are able to transmit electricity, according to a very 
 different mode, namely, suddenly and instantaneously. This 
 mode of transmission in such bodies is attended by a rupture 
 in their molecular equilibrium, which is manifested under 
 different forms, but which always occurs ; it is also fre- 
 quently attended by luminous, calorific, and chemical effects; 
 but the production of these effects is not a necessary condition 
 of the transmission of electricity : we shall study these effects 
 in the sequel, in the Chapters that are appropriated to them, 
 whilst the molecular phenomena being connected with the 
 very mode of propagation in question, we cannot separate the 
 study of them from that of this mode of propagation. 
 
 When a thin plate of glass or mica is placed between the 
 two extremities of the rods of a discharger, it is, as we have 
 already seen, pierced with a hole, by the discharge of an 
 electric battery ; it is the same with a piece of dry wood, 
 which is split and broken into a thousand fragments, that are 
 dispersed about in all directions. The edges of the hole, 
 when glass or mica is employed, become opaque ; we perceive 
 that the molecular condition of the substance has been altered. 
 If the two extremities of the rods of the discharger are placed 
 at some little distance apart, but on the same side, on the 
 surface of a plate of glass, the discharge occurs by means of 
 a spark, which passes over this surface, leaving upon it traces, 
 that cannot be obliterated, of the route it has followed. On 
 hard glass, and rock crystal, these traces are pale, of a dull 
 grey, and perfectly resist under the nail, as if the polish of the 
 surface had been altered by rubbing it with coarse sand. 
 On soft glass, mica, and delicate crystals, the traces, left by 
 
 conducting action which the incandesceent platinum of Davy's aphlogistic lamp 
 exercises over the two electricities. These phenomena, in which it was at first 
 thought that proofs were found in favour of Franklin's theory of a single 
 electricity, are very complex ; and depend essentially upon the production of 
 electricity, which accompanies the slow combustion that takes place in the 
 aphlogistic lamp. The study of these phenomena must therefore be postponed, 
 until we are engaged with the different sources of electricity. 
 
138 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the discharge, present a different aspect : they seem to indi- 
 cate that the matter has undergone a chemical change to a 
 certain depth, a change that gives rise to the electric figures, 
 observed by Riess, and by other philosophers ; this chemical 
 change almost always accompanies the mechanical effect ; for 
 the traces that are presented by the hardest glass upon its 
 surface after the discharge, are slightly alkaline, as may easily 
 be proved by rubbing them with paper reddened by litmus. 
 
 We have already quoted the experiment of the card, which, 
 when it has been pierced by the discharge, presents bosses on 
 both sides, and the hole of which is always opposite to the 
 negative point, when the two points are not opposite to each 
 other ; which is due, as we shall see, to the unequal pressure 
 experienced by the two electricities on the part of the air. 
 
 When the discharge traverses liquids, if they are imperfect 
 conductors, or rather insulators, such as olive oil, sulphuric 
 ether, and essence of turpentine, there is always a mechanical 
 effect, accompanied by a spark. The vessel in which these 
 liquids are contained, is frequently broken by the effect of 
 even a moderate discharge : thus if it is of wood, it may be 
 violently overturned by a spark, that is the length of -^ of an 
 inch ; in order that it shall be broken, the spark must be a 
 little more powerful. Singer succeeded in breaking into 
 many fragments tubes of glass, whose sides were more than 
 f in. in thickness, by passing a discharge through a column 
 of liquid, with which the tubes were filled ; it is true that 
 care was taken to close hermetically the extremities, by 
 which the wires for transmitting the discharge had been in- 
 troduced. The same effect is produced, when the tube is 
 filled with a good conducting liquid, as mercury for instance, 
 or sulphuric acid; but in this case the tube must be capillary 
 and the length of the liquid column must not be too con- 
 siderable. Morgan has remarked that with concentrated sul- 
 phuric acid, and a tube xgin. in diameter, the greatest length, 
 at which the breaking and luminous explosion can occur at 
 the same time, is about 19^ in. 
 
 The passage of discharge through bad-conducting liquids, 
 such as oils and essences, raises their temperature, and pro- 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 139 
 
 duces in them a deposit of carbon, arising from their de- 
 composition ; and in the end, their conducting power is 
 slightly increased. This is probably an effect of the high 
 temperature of the spark, rather than of the electricity 
 itself; this we shall endeavour to investigate further on. 
 Morgan, who was the first to observe this fact, also remarked 
 that among liquids the oils are they which allow the discharge 
 to pass the least easily, whilst alcohol and water, especially 
 when heated, transmit it much better, so that in the latter 
 instance it ceases to be luminous. 
 
 Moreover, the explosive effect of the discharge through 
 conducting bodies occurs equally, whether they be solid or 
 liquid, like mercury. Thus when a piece of very thin gold 
 leaf is placed between two plates of glass, the upper of Which 
 is loaded with a weight, the gold is reduced to powder, and 
 the plates are often broken in pieces.* la like manner, a 
 very thin iron wire, one or two inches in length, when tra- 
 versed by a discharge, that reduces it to powder, is capable 
 of breaking into a thousand fragments a glass tube of about 
 tj an inch across, in the interior of which it is placed ; and 
 these fragments are projected afar ; care must be taken to 
 introduce the discharge by means of two thick wires, each of 
 which enters one end of the tube, and which are connected 
 by the iron wire. If care is taken to surround this wire by 
 a piece of paper, the paper is torn, but the glass is not at all 
 damaged. The action is infinitely more violent, when the 
 wire is surrounded by water or oil ; this arises from liquids, 
 which are incompressible or nearly so, transmitting in a 
 much more complete and instantaneous manner than air, 
 the pressure to which they are subjected. Pistol barrels 
 may be split by filling them with water or oil, and taking the 
 precaution of placing within the liquid, a thin band of lead, 
 that is pulverised by the discharge. 
 
 In all cases, where the body that is traversed by the 
 discharge is metallic, there is a great development of heat. 
 
 * We have already mentioned this experiment of the gold leaf, but under a 
 slightly different form. See Vol. I. p. 121. 
 
140 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 Is it to a sudden vaporisation, produced by this heat, that 
 the mechanical effects we have been studying may be traced? 
 This might be possible in the case of mercury; but this 
 interpretation of the phenomenon becomes more difficult in 
 the case of gold, and especially in that of iron. It would 
 therefore seem that, independently of the heat which it 
 developes, the discharge would produce, even in very good 
 conducting bodies, when it meets with resistance, a mechanical 
 rupture, and, as it were a kind of very energetic sudden 
 expansion. However, this point deserves a very attentive 
 examination : we reserve it until we shall be engaged upon 
 the calorific effects of discharges, which are altogether con- 
 nected with their mechanical effects, as Reiss has so well 
 demonstrated. 
 
 In conclusion, all the phenomena presented by the pro- 
 pagation of electricity in imperfect conductors, whether it be 
 slow or instantaneous, manifest the intimate connection 
 existing between this propagation and the molecular condition 
 of bodies. In the cases wherein the propagation is slow, 
 every thing that modifies the molecular state has an influence 
 upon it, as crystallisation, liquefaction, or the mere elevation 
 of temperature. In the case, wherein the propagation is 
 instantaneous, the molecular state is influenced by it. It is 
 therefore very probable, that the sensible difference in this 
 respect, existing between good and" imperfect conductors, is 
 due to the polarity of the atoms, which we have already 
 established, being much more sensible in these latter. 
 Indeed, the very imperfection of their conducting powers 
 prevents the contrary electricities produced at their poles, 
 namely, at the extremities of their axis, from uniting by their 
 surface so easily as in the case of those bodies which are 
 endowed with good conductibility ; a polar state of the 
 particles is the result of this, which compels them to 
 change their position so as to arrange themselves in a manner 
 harmonising w r ith the two electricities, between which they 
 are placed ; whilst conducting particles only undergo the 
 effect of induction, or of the artificial and not natural polari- 
 sation, that we have admitted in order to explain the manner 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 141 
 
 in which electricity is propagated in conducting bodies. We 
 shall see many other proofs of this pre-existing polarity of 
 the particles of non-conducting bodies, when we are engaged 
 upon the development of electricity, to which these bodies 
 give rise by the effect of the raising of their temperature. 
 
 Propagation of Electricity in Elastic Fluids. 
 
 Gases, when they are very dry, and especially atmospheric 
 air, pass for being perfectly insulating bodies : however, they 
 are capable of propagating electricity, more or less easily, it 
 is true, according to their nature, and according to the 
 conditions in which they happen to be placed. 
 
 Coulomb had long ago endeavoured to measure the loss of 
 electricity, experienced by a well insulated electrised body, 
 by means of the contact of the air. He had succeeded in 
 eliminating the cause of loss that might arise from the in- 
 sulating support, by employing as an insulator, a thread of 
 gum-lac of Q l j in. in diameter and about two in. in length, 
 and giving to the insulated body, which was a ball of elder- 
 pith about ^ in. in diameter, an electricity, that was not very 
 powerful. This ball was placed in the torsion balance opposite 
 to a movable ball, in like manner well insulated, since the 
 needle by which it was sustained was also a fine cylinder of 
 gum-lac ; this movable ball possessed the same electricity. 
 The loss of electricity, brought about by the contact of the 
 air, became sensible by the gradual diminution of the re- 
 pulsive force of the balls, which was measured by the 
 diminution of the force of torsion necessary to maintain them 
 at the same distance from each other, at 20 for instance. 
 It was easy with a seconds' watch to determine exactly the 
 relation existing between a certain diminution of the repulsive 
 force, and the time necessary for producing this diminution. 
 By comparing this diminution with the mean repulsive force 
 between two consecutive experiments, Coulomb found a 
 fraction, which expressed the proportion of the electric force 
 of the two balls lost during a minute, at any moment. In 
 the tables that Coulomb has given of these results, we find 
 
142 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 that this fraction varies from r y to ^ : we also remark that 
 for the same day and the same state of the air, the weakening 
 of the electricity in a very short time is proportionate to its 
 intensity ; and that it varies according to a law difficult of 
 determination, with the hygrometric state of the air. The 
 nature of the substance of which the balls are made, does 
 not appear to cause any influence on the loss of electricity, 
 by the contact of the air. It is the same with their form, 
 provided it is not angular, a case as we know, in which 
 electricity escapes from the body in an irregular manner. 
 Coulomb found also that there was no difference between 
 the two electricities, with regard to intensity and to the laws 
 of their loss by contact with the air. 
 
 Faraday, in his researches on dialectric bodies, setting out, 
 as we have seen, from the principle, that the communication 
 of electricity is made by the polarisation of successive 
 molecules, had submitted to experiment various gases and air 
 in different states of density, by making use of the apparatus 
 that we have described *, and which is intended to determine 
 the specific inductive power of bodies. It consists, as 
 may be remembered, of two veritable Ley den jars, perfectly 
 similar, in which the insulating substances, interposed 
 between the coatings, are those whose inductive powers are 
 about to be compared. The learned English philosopher, 
 by operating in this way, was unable to detect any sensible 
 difference in this respect between the various gases and air, 
 more or less rarefied, and more or less heated. Only, in these 
 experiments, we must take care to avoid raising the electric 
 tension to the point at which discharge would occur. 
 
 M. Matteucci has taken up the subject of the propagation 
 of electricity in gaseous bodies; and has succeeded in determin- 
 ing its laws by a numerous series of experiments, made 
 with great care. For measuring the electric forces, he made 
 use of several Coulomb's balances, furnished with torsion 
 threads of different lengths and diameters, according to the 
 electric forces with which he was operating. Instead of 
 employing, as Coulomb had done, balls of elder-pith, which 
 
 * See Vol. I. p. 135.,^. 67. 
 
CHAP. I. TKOPAGATION OF ELECTRICITY. 143 
 
 possess the inconvenience of becoming a little insulating 
 in very dry air, he preferred employing balls of the same 
 dimensions, but made with a very thin plate of silver gilt. 
 In other respects, the experiments were conducted in the 
 same manner ; except that the ball affixed to the insulating 
 stem, and which acts upon the movable ball, is withdrawn from 
 the balance in order to be placed under different conditions 
 which exert an influence, in one direction or the other, over 
 the loss of its electricity ; it is then brought back to the 
 balance at the end of a certain time, which is always the 
 same, in order that the loss it has suffered may be deter- 
 mined. The air of the interior of the balance is as dry 
 as possible, so that we may conclude that the loss ex- 
 perienced by the ball of the balance in ten minutes is very 
 small, and always the same for all the experiments. 
 
 The following are the results to which this mode of experi- 
 menting has lead : 
 
 1st. The loss of electricity by the contact of the air is 
 not increased by the agitation of the air ; on the contrary, 
 the loss of electricity in the agitated air is less than that 
 which occurs in the air at rest. This result, singular as 
 it apparently is, is easily explained if we take into account 
 the time which may probably be required, for the particles 
 to become polarised, and thus to transmit the electricity of 
 the body with which they are in contact. 
 
 2nd. The loss of electricity that a body experiences, by 
 the contact of the air, is influenced by the bodies that 
 are in its presence, and varies with the electric state of 
 these bodies. Thus the smallest loss occurs, when the 
 electrised body is in presence of a body, which possesses 
 an electricity contrary to its own ; it is more considerable 
 when the body in presence is not electrised, and is in com- 
 munication with the ground, and especially when the two 
 bodies have the same electricity. In order to perform those 
 experiments, the electrised ball, that is withdrawn from 
 the balance, is placed for ten minutes either so that it 
 is insulated in the air, or in presence of an insulated metal 
 sphere, charged sometimes with the same, at other times with 
 
144 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 the contrary electricity, or in the centre of a metal sphere 
 in communication with the ground. 
 
 The following is the Table of the experiments made in this 
 manner, in air having the same temperature and the same 
 degree of humidity. 
 
 Number of the 
 
 Distance of 
 
 Torsion of the 
 
 After ten 
 
 Distance of 
 
 Torsion of the 
 
 Experiments. 
 
 the Balls. 
 
 Micrometer. 
 
 Minutes. 
 
 the Balls. , 
 
 Micrometer. 
 
 1 
 
 20 
 
 188 
 
 10 
 
 20 
 
 105 
 
 2 
 
 20 
 
 188 
 
 10 
 
 20 
 
 136 
 
 3 
 
 20 
 
 188 
 
 10 
 
 20 
 
 96 
 
 4 
 
 20 
 
 188 
 
 10 
 
 20 
 
 164 
 
 5 
 
 20 
 
 188 
 
 10 
 
 20 
 
 85 
 
 6 
 
 20 
 
 188 
 
 10 
 
 20 
 
 162 
 
 7 
 
 20 
 
 198 
 
 10 
 
 20 
 
 131 
 
 8 
 
 20 
 
 198 
 
 10 
 
 20 
 
 169 
 
 9 
 
 20 
 
 102 
 
 10 
 
 20 
 
 25 
 
 10 
 
 20 
 
 102 
 
 10 
 
 20 
 
 67 
 
 We have merely to compare together the results given 
 in the preceding Table, and we shall have the demon- 
 stration of this proposition. In the first experiment, the ball 
 was left in the air for ten minutes ; and in the second it 
 was placed for the same length of time, in the centre of 
 a hollow sphere of metal, which was in communication with 
 the ground. This sphere was 4 inches in diameter, and 
 the ball was introduced through an aperture of 1 inch. 
 In the third experiment, the ball remained for ten minutes 
 in presence of an insulated metal ball | in. in diameter. The 
 centres of the two balls were at a distance of 4f in. In 
 this experiment, the two balls possessed the same electricity ; 
 whilst, in the fourth, the large ball was charged with a 
 contrary electricity to that of the ball of the balance. In 
 the fifth and sixth experiment, the operations were of the 
 same kind as in the third and fourth. In the seventh 
 experiment, the ball of the balance was in the air ; whilst 
 in the eighth the ball was in the centre of the metal sphere. 
 In the ninth and tenth experiments, the operations were 
 conducted in the same manner. 
 
 3rd. The loss of electricity in pure gases, deprived as 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 145 
 
 much as possible of aqueous vapours, is independent of its 
 intensity, and is consequently constant, at least for quantities 
 of electricity comprised within certain limits. This law 
 differs from that found by Coulomb, when operating in air 
 more or less moist, and which consisted in this loss, in a 
 given time, being always in the same proportion of the total 
 quantity of electricity. It was by taking every possible 
 precaution to operate in air and in gases, perfectly dried by 
 means of phosphoric acid, and by multiplying the experiments 
 made, either according to Coulomb's method, or according 
 to a method slightly differing, that Matteucci has obtained the 
 loss of electricity in a minute, that is, in the unity of time. 
 We shall not introduce here the tables of the results, which 
 show that, notwithstanding the differences, that are in every 
 respect small, and that are inevitably due to errors of experi- 
 ment, the loss of electricity is constant. The experiments 
 were made by means of the two electrised balls, the repulsive 
 force of which was measured, either by bringing them to the 
 same distance, according to the process of Coulomb, or by 
 holding them at a variable distance. In this latter case, 
 the loss is found to be greater, when the distance is less, which 
 agrees with the second law found above. 
 
 4th. The loss of electricity is the same in air, in hydro- 
 gen, and in carbonic acid gas, all being very dry, and taken at 
 the same temperature and at the same pressure. The experi- 
 ments that have led to this result were made at temperatures 
 varying from46'4to 51-8; days were selected, in which the 
 atmosphere was very dry ; a vacuum was made in the globe 
 of the balance, care being taken on each occasion of opera- 
 ting with a new gas, to renew the phosphoric acid, that is 
 placed in it, and then to inject the gas by introducing it very 
 slowly through a Liebig's tube, filled with concentrated sul- 
 phuric acid. 
 
 5th. The loss of electricity, which, in dry and pure 
 gases, is in general the same for positive as for negative elec- 
 tricity, becomes more rapid for negative than for positive 
 electricity, when the electric charges are very strong. This 
 important proposition, which had already been pointed out 
 
 VOL. II. L 
 
146 
 
 TRANSMISSION OF ELECTRICITY. 
 
 rATtT IV. 
 
 by Belli, and which confirms other facts relating to discharges, 
 that we shall study presently, is established by a series of ex- 
 periments, made by electrising the two balls of the balance, 
 sometimes with positive, sometimes with negative electricity. 
 We wait till the movable needle stops at a certain number of 
 degrees, 1 5 for instance, and the time is then noted by a chro- 
 nometer ; then at the end of a certain time, ten minutes for 
 instance, which is the interval of time between the two obser- 
 vations, the thread is very slowly untwisted through the 
 number of degrees necessary for bringing the needle back to 
 15. The following Table shows how much the torsion required 
 to be diminished under the same circumstances for negative 
 as well as for positive electricity ; whence it may be con- 
 cluded, that for comparatively high electric charges, the loss 
 in air was much greater for negative than for positive elec- 
 tricity. 
 
 Torsion and Arc of Repulsion. 
 
 
 Torsion and Arc of Repulsion. 
 
 Positive Electricity. 
 
 Positive Electricity. 
 
 140 + 15 
 117 +15 
 90 +15 
 35 +15 
 
 127 +15 
 107 +15 
 75 +15 
 27 +15 
 
 Negative Electricity. 
 
 A fter Ten 
 Minutes. 
 
 Negative Electricity. 
 
 140 + 15 
 117 +15 
 90 +15 
 35 +15 
 
 
 90 + 15 
 66 +15 
 60 +15 
 12 +15 
 
 6th. The loss of electricity in dry air increases with 
 the temperature. The experiments intended for the esta- 
 blishment of this law can only be made within very 
 restricted limits of temperature, between 32 and 64-4 ; for 
 even above 58, the elevation of temperature diminishes the 
 insulating property of stems of gum-lac itself. However, 
 even within these limits, the influence of temperature over 
 the insulating power of very dry air is very sensible. Thus 
 at 64'4 the loss of the electricity of the insulated ball was 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 147 
 
 Tjy ; whilst at 32 it was only ^| T , that is to say, only the 
 half. 
 
 7th. The loss of electricity in dry air diminishes 
 with the diminution of the density of the air. Thus the di- 
 vergence of an electroscope in rarefied air, at "118 inches of 
 pressure, was the same at the end of two days as at the com- 
 mencement of the experiment ; which could not possibly be 
 obtained with air of a greater density. This experiment 
 seems plainly to prove that the electricity escapes by the par- 
 ticles themselves of the air ; for, the less there are of them, the 
 less rapid is the escape. We have only to remark that the ab- 
 solute quantity of electricity that can remain, on the surface of 
 an insulated conducting body, without escaping in the state of 
 tension, is much less when the air is rarefied than when it is 
 under a higher pressure. M. Matteucci concludes from this, 
 that in a perfect vacuum there would be no electricity retained 
 on the surface of the conducting body ; we shall see, further 
 on, the extent to which this conclusion may be admitted. 
 
 8th. The loss of electricity in air taken at a constant 
 temperature and pressure, increases with the quantity of 
 vapour of water contained in this air ; but not, as Coulomb 
 had imagined, according to a simple law. It is only in air that 
 contains very great quantities of the vapour of water, that 
 the loss is found approximately proportional to the tension or 
 to the quantity of vapour of water, whatever the temperature 
 may be. A very remarkable thing is, that the presence, in very 
 dry air of other vapours, such as those of camphor, of certain 
 essential oils, and even of sulphuric ether, exert no influence 
 over the loss of electricity. 
 
 M. Matteucci, in the important work, by which he was led 
 to the results that we have been relating, had endeavoured to 
 determine the influence that may be exerted over the loss 
 of electricity by the nature of the electrised body. Like 
 Coulomb, he had not found any difference in this respect 
 between metal balls or discs, or gum-lac balls or discs ; sub- 
 ject, however, to one condition, which is, that gum-lac must 
 be electrised by the spark from a machine ; for, if it is elec- 
 trised by friction, there is a constant difference, which is very 
 
 L 2 
 
148 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 probably due to the electricity, instead of being upon the 
 surface, as in the former case, penetrating more deeply, and 
 consequently not being able to escape so easily. 
 
 After having studied the laws of slow propagation, or loss 
 of electricity in gases, let us now turn our attention to those 
 to which is subjected the rapid propagation, that may be 
 brought about, either by discharges, or in a continuous manner 
 under the form of a current. 
 
 It is well known that when the conductor, charged with 
 one or other of the two electricities, is terminated in a point, 
 this electricity escapes with facility into the air. This pro- 
 perty of points, to which we have already directed attention, 
 is founded upon the great density that electricity acquires at 
 points, in virtue of the laws of its distribution. It may be 
 diminished or even annulled, if the point is placed in the 
 interior of a hollow conductor; for example, if a point, 
 which is fixed upon an insulated and electrised metal disc, is 
 situated in the middle and in the axis of a hollow metal 
 cylinder more elevated than itself, and which itself rests upon 
 the disc. When once the electricity is accumulated at the 
 point, it escapes, and is propagated by determining in the 
 air a very violent mechanical movement, which is pro- 
 bably due to the repulsion exercised by the point upon the 
 particles of air in contact with it, to which it has commu- 
 nicated its electricity. Bodies in combustion, and especially 
 flames, exercise the same effect as points. If, for instance, 
 two metal discs are placed one beneath the other, the lower 
 communicating with the pole of a dry pile, by which it is 
 electrised, and the upper with an electroscope, we have 
 merely to place in the former a fragment of German tinder in 
 a state of incandescence, in order that the electroscope, which 
 is connected with the latter, shall diverge violently. The 
 German tinder therefore, in this case, acts like a point, for 
 its effect, like that of the point, may be annulled, by sur- 
 rounding it with a hollow cylinder ; and this proves that it 
 is not the smoke that carries away the electricity, for it con- 
 tinues to rise as at the first in a thick column towards the 
 upper disc. The influence of incandescent German tinder 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 149 
 
 is as much felt in discharging the lower disc, as in charging 
 the upper. It acts in an equal degree from above down- 
 wards, as from below upwards. 
 
 Riess has made a great number of experiments on this sub- 
 ject, by employing a cotton wick, and lighted tapers ; but in 
 order to escape from the disturbing influence of the smoke, 
 he found it preferable to employ a preparation of saltpetre 
 and carbon, united together with astringent gum, so as to 
 make tapers of about an inch in length. He has thus proved 
 the influence of conducting envelopes, which prevent the in- 
 candescent body from discharging the electricity of the disc 
 upon which it rests, and of charging the disc that is near to 
 it; and he has established in a decided manner, the complete 
 analogy that exists between the mode of action of these 
 bodies and that of points. It is therefore not by means of 
 the products of their combustion, that incandescent bodies 
 exercise their conducting property, but in virtue of the par- 
 ticular state of their surface, which comports itself as if it 
 were covered with very fine points. Moreover, the action 
 of very short, but very perfect points is proved by an old ex- 
 periment, in which the discharge of an electrised conductor 
 is brought about by presenting to it at a distance a piece 
 of tinder made from the fungus of an oak, without there 
 being even any need of lighting it ; which is due to the very 
 fine and almost invisible points, with which the whole sur- 
 face of this species of tinder is covered. The existence of 
 similar points in a body in combustion is easily proved ; they 
 are continuously destroyed and renewed. 
 
 In bodies, the combustion of which produce a flame, it is 
 the small filaments of vapour and the points of carbon that 
 conduct the electricity, as may be proved by remarking that 
 the flame does not lose its conducting property by being 
 surrounded by a metal tube, as occurs when the incandes- 
 cent body loses its electricity by the effect of the points 
 with which it is covered. We may, in a very simple experi- 
 ment, even see the action of these two conducting portions 
 of the flame succeed each other visibly. If a wax taper, that 
 is burning actively, be suddenly extinguished, the vapour 
 
 L 3 
 
150 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 contained by the flame is seen to act for a few seconds as a 
 conductor, then the wick, impregnated with melted wax, 
 ceases to act; so that the smoke no longer exerts any influ- 
 ence over the electrised body, when brought near to it. But 
 when the wax ceases to reach the wick, the latter becomes 
 incandescent, and then the small points of carbon that are 
 formed there conduct electricity for a brief moment. 
 
 The property of bodies in combustion of conducting elec- 
 tricity may serve two important purposes ; the first, to remove 
 from an insulating body its electricity, by moving about it 
 a small spirit flame or the point of a lighted taper ; the 
 second, to increase the sensibility of an electroscope intended 
 for detecting a distant electricity, by placing upon it a lighted 
 body, which has the power of drawing off electricity at a 
 still greater distance than a point. 
 
 In all that we have said in respect to bodies in combustion, 
 we have paid no regard to the nature of the electricity em- 
 ployed : their conductibility is, in fact, the same for both elec- 
 tricities, providing the combustion is active and perfect, and 
 that when German tinder and carbon are employed, the pre- 
 caution is taken of frequently clearing from them their 
 ashes. If these precautions are not taken, it is frequently 
 perceived that one of the electricities is more easily con- 
 ducted than the other, which is due to electricity being deve- 
 loped in the very act- itself of combustion. It is not until 
 we shall be occupied with the actual sources of electricity 
 that we shall be able to estimate the amount of influence in 
 the conducting power of flames, that may be due to the 
 liberation of electricity, which accompany their production. 
 
 When electricity escapes by a point, we have seen that 
 this escape is accompanied by a movement of the air, which 
 is similar to that of a slight breath, and which has been 
 called the electric wind. This wind may be rendered sen- 
 sible by being directed against the flame of a taper, against 
 the wings of a small mill of paper, which it causes to turn, 
 or against the powder of licopodium placed upon water, 
 which it drives before it. It is to this agitation of the air, or 
 rather to the repulsion exercised by the electric current, 
 which traverses it, upon that of the point whence it escapes 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 151 
 
 that the rotation, as we have seen, of the electric mill is due. 
 Indeed, in rarefied air this movement does not occur ; and 
 we have thus merely to place the mill in the middle of a 
 vessel, whose sides, which are very near to it, are charged 
 with the same electricity as that which is transmitted to it, 
 and the rotation at once ceases. The electric wind favours 
 the cooling and vaporisation of liquids. This had been long 
 ago remarked by several philosophers ; but it was Peltier 
 who proved it in a positive manner. With this view, he had 
 placed at a distance of six or seven inches above a platinum 
 vessel filled with water, a ball of metal or bundle of wires 
 terminating in a point. The water having been heated about 
 156 or 194, visible vapours commenced arising from the sur- 
 face, but this cloud of vapour became much more consider- 
 able, as soon as electricity from a machine was introduced to 
 the points. A sensitive thermometer, placed in the water, 
 indicated also by its falling an increase in the quantity of 
 vapour formed. The phenomenon was not simply due to the 
 renewal of the air on the surface of the heated liquid: Peltier 
 satisfied himself upon this point, by artificially renewing the 
 air over this surface, by means of a ventilator; the effect was 
 always less considerable than that produced by the electric 
 wind. 
 
 The rapid transmission of electricity through imperfect 
 conductors, such as the air, evidently tends to make the par- 
 ticles recede from each other ; this is very well seen when the 
 luminous brush, that is composed of diverging filaments, 
 formed of the small particles rendered luminous by the pas- 
 sage of electricity, is studied in the dark. This same tendency 
 is also observed in the case in which the imperfect conductors 
 are liquid. Thus Faraday noticed that by making the elec- 
 tricity, arising from the conductor of an electric machine, 
 pass into sealing-wax, rendered fluid by heat, very fine fila- 
 ments are detached from it, which cover a piece of paper placed 
 beneath, like fine wool. A drop of gum-water suspended 
 at the extremity of a rod, by which electricity reaches it, re- 
 solves itself into detached threads, when plunged into essence 
 of turpentine, itself placed in a vessel, the metal bottom of 
 
152 TRANSMISSION OF ELECTRICITY. PART iv 
 
 which allows of the escape of the electricity. A drop of 
 mercury or of chloride of calcium elongates itself and becomes 
 pointed, and minute drops are detached from it, which are 
 drawn by the electricity into the air, wherein the experi- 
 ment is made. By employing a drop of gum-water, very 
 various phenomena are observed, according to the force of the 
 electricity that reaches it. At first the drop is transformed 
 into a cone ; then, in proportion as the electricity increases in 
 intensity, a part of the liquid is seen to be drawn onward, the 
 rest becomes more pointed and acquires a rugged surface, 
 with the noise peculiar to electric brushes ; finally, with a 
 more powerful electrisation, a more considerable portion of 
 the liquid is drawn onward, the remaining drop elongates 
 itself and draws back by fits, forming a very luminous brush. 
 When negative electricity is made to reach the drop of gum- 
 water, the cone that is formed is larger than with positive. 
 
 An old experiment, of the same kind as the preceding, and 
 which is due to Nollet, consists in placing water in a metal 
 funnel, furnished with a few capillary openings, and com- 
 municating with the electric conductor. The water passes 
 through merely in isolated drops and in a rounded form ; 
 whilst, as soon as the funnel is electrised, it comes out in very 
 fine and continuous diverging jets, which are luminous in the 
 dark. 
 
 More frequently, instead of occurring in a slow and con- 
 tinuous manner, the rapid propagation of electricity through 
 air and gases, occurs in an instantaneous and sudden manner 
 by discharges. The distance at which this discharge can 
 occur, and which is termed the explosive distance or limit, for 
 the same intensity of electric discharge, depends upon the 
 density and nature of the aeriform medium. Harris has found, 
 by various experiments, that the quantities of electricity, 
 necessary for traversing a given interval, vary in a simple 
 ratio with the density of the air, and that consequently the 
 explosive limit in rarefied air is inversely as the density of the 
 air; from which it follows that the same discharge can 
 traverse an interval of air of double the length, when the 
 density of the air has been reduced one half. If air contained 
 in a close vessel is heated even to 300, no variation occurs in 
 
CHAP. I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 153 
 
 the explosive limit ; whilst if the vessel is allowed to be open, 
 it is sensibly increased ; which proves that it is not the pressure 
 of the electric fluid, but the number of particles, which is the 
 determining cause of the greater or less difficulty experienced 
 by the electric charge in traversing it. Knockenhauer, by a 
 series of experiments in which, leaving the explosive distance 
 constant, he determined the density of the electricity, necessary 
 for obtaining the electric discharge in different degrees of 
 density of the air, found that these two densities were almost 
 proportional to each other ; a result that was also obtained 
 by Masson, by means of a slightly different method. 
 
 But of all philosophers, Riess is the one who has made the 
 most conscientious study of this subject. We shall defer to 
 a final note the detailed exposition of the methods and calcula- 
 tions by which Riess succeeded in establishing the laws that 
 regulate the discharge of electric batteries* ; we shall confine 
 ourselves for the present to giving the formula, by which he 
 expressses the value of the explosive limit. This formula is 
 
 d = b -, b being the explosive distance for the charge taken 
 
 as unity, d, the explosive distance for the quantity q, of elec- 
 tricity, and s, the size of the surface of the battery, upon 
 which the electricity is accumulated, or the number of jars, 
 of which the battery is composed. In 
 order to demonstrate by experiment the 
 accuracy of the formula, Riess employs 
 an apparatus, which he named spark-mi- 
 crometer ; and which consists (Fig. 185.) of 
 two vertical insulated metal rods, each 
 terminated by a ball ; one of the rods is 
 fixed, the other is moved by means of a 
 micrometer screw, which allows of the 
 exact measurement of the distance, to 
 which the two balls must be brought in 
 respect of each other, in order that the 
 discharge shall occur between them. 
 
 Fig. 185. 
 
 * Vide the final note C. 
 
154 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 One of the balls of the instrument communicates by a wire 
 with the inner, the other with the outer coating, which is also 
 put in communication with an electrometer. In a first ex- 
 periment, the balls of the micrometer were at a distance d = 
 J I ; that is, the distance 1 in the following Table ; the 
 battery composed of s jars was charged until the dis- 
 charge occurred, and the electrometer indicated the value 
 of the quantity q, of the electricity employed. The value 
 of the constant b, was thus found, which gave q = 0-833 
 s d. Now, the following Table gives for the different values 
 of d, and s, the corresponding values of q, observed directly 
 and calculated according to this formula. 
 
 d. 
 
 2s. 
 
 35. 
 
 4s. 
 
 5s. 
 
 Obs. 
 
 q- 
 
 Calc. 
 
 <7- 
 Obs. 
 
 Cfic. 
 
 <7- 
 Obs. 
 
 <& 
 
 9' 
 
 Obs. 
 
 cS., 
 
 1 
 
 
 
 3-0 
 
 i | 
 
 2-25 
 
 3-5 
 
 3-3 
 
 4-3 
 
 4-2 
 
 2 
 
 3' 
 
 3-3 
 
 5-5 
 
 5-0 
 
 7-0 
 
 67 
 
 8-5 
 
 8-3 
 
 3 
 
 4*6 
 
 5-0 
 
 70 
 
 75 
 
 10-1 
 
 10-0 
 
 12-5 
 
 12-5 
 
 4 
 
 6-4 
 
 67 
 
 10-3 
 
 10-0 
 
 135 
 
 13-3 
 
 16-0 
 
 167 
 
 5 
 
 7-5 
 
 8-3 
 
 " 
 
 
 
 16-0 
 
 167 
 
 " 
 
 
 
 The agreement of calculation with observation very well 
 shows the accuracy of the formula. It is evident that, 
 when once the constant b is given and without recourse to the 
 electrometer, we are able to determine very exactly, by 
 means of this formula, the quantity of electricity, with which 
 the battery is charged, provided we know the number of 
 jars or the surface s, of the battery, and the striking 
 distance d } furnished by the spark-micrometer. 
 
 Experiments, made with different gases, had shown Doe- 
 berainer that the explosive distance is less in proportion as 
 the gas itself possesses greater density. Schaffautl had 
 found, in hydrogen compressed and heated to 536 in a close 
 vessel, that this distance was greater than in ordinary air, 
 the pressure of which however was twenty-seven times less. 
 
 These differences between the various gases had already 
 been pointed out by Morgan at the end of the last century. 
 
CHAP. I, 
 
 PROPAGATION OF ELECTRICITY. 
 
 155 
 
 He had remarked the relation that exists between the ex- 
 plosive distance and the charge of the battery ; and that, for 
 a given charge, hydrogen furnishes the greatest explosive 
 distance, and muriatic acid gas the least. Faraday, not very 
 long ago, took up the study that had been touched upon by 
 Morgan: his method, without being rigorous, led to approxi- 
 mate results, which, if they do not present a mathematical 
 precision, at least enable us to classify the different gases 
 into the order of their permeability by the electric discharge. 
 The conductor of an electrical machine must be put into 
 communication with an apparatus, consisting of two metal 
 balls, between which the spark must pass, when traversing 
 ordinary air, and at the same time with a similar apparatus 
 placed in the interior of a receiver, in which a vacuum 
 can be made, and into which various gases can be introduced 
 (Fig. 186.). The two balls of the apparatus, that are placed 
 
 Fig. 186. 
 
 within the receiver, are at a constant distance of 0*62 in. from 
 each other, whilst the mutual distance of the two balls that 
 are placed in the air, can be diminished or increased, so that 
 the electric spark passes by one or other of the two paths 
 that are open to it, or is divided equally between them. 
 
156 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 Faraday, by introducing the gases successively into the re- 
 ceiver, determined for each what was the smallest distance at 
 which the two balls that are situated in the air, could be 
 placed in respect of each other, in order that the spark 
 should still prefer to traverse the gas, and not the air ; and 
 also the greatest distance that could be given to them with- 
 out the spark ceasing to pass through the air, in preference 
 to the gas. Between these two distances, the spark must divide 
 itself between the air and the gas ; by taking the mean of 
 this, we obtain for each gas the value of the explosive dis- 
 tance in the air, equivalent to that of the gas ; which is always 
 at 0*62 in. Since, on the other hand, the quantities of electri- 
 city, that pass in the air between the balls, are proportional 
 to the distances of these balls, we are enabled to discover, by 
 means of these distances, the quantity of electricity that is 
 necessary, in order to traverse the same explosive distance in 
 each gas. By this process it is found that, under the same 
 pressure and at the same temperature, this quantity is 
 greatest for hydrochloric acid gas, and least for hydrogen; 
 so that with the same quantity of electricity, the spark would be 
 longest in hydrogen, and shortest in hydrochloric acid gas, 
 a result in conformity with what had been discovered by 
 Morgan. 
 
 The gases, that were subjected to experiment, had all 
 been carefully dried, and were all at the same temperature 
 and under the atmospheric pressure. The following is, for 
 instance, a table in which at the side of each gas is indicated 
 the mean explosive distance of the two balls in air, equivalent 
 to the constant explosive distance of the gases.* 
 
 Hydrochloric acid - - - 1-105 
 
 defiant gas - - 0750 
 
 Ordinary air - - 0'695 f 
 
 * The distances are expressed in inches and fractions of an inch, and the 
 constant distance of the two balls in the receivers, into which the gases were 
 successively introduced, was 0'62 in. 
 
 f It does not appear to me that this result can be admitted ; for the explosive 
 distance for air in the receivers should be equal to that of air out of the re- 
 ceivers, namely, % 62 in. ; for it is the same air under the same pressure and the 
 same temperature. 
 
CHAP. I. rilOPAGATION OF ELECTRICITY. 157 
 
 Carbonic acid gas ----- 0'640 
 
 Nitrogen ... _ 0615 
 
 Oxygen - ... _ Q-505 
 
 Oil gas - - ... 0-490 
 
 Hydrogen ...--. 0*370 
 
 In Faraday's experiments, the two balls that are put into 
 communication with the conductor of the electrical machine, 
 and placed one in the gas and the other in the air, were 
 of the same size, but had a diameter of about one-half less 
 than that of their two corresponding balls, that were in com- 
 munication with the ground. It followed from this, that 
 if the conductor of the machine were charged with negative 
 instead of being with positive electricity, as in the above ex- 
 periments, the explosive distances in the air, equivalent to 
 those of each of the gases, were all a little less ; but the order 
 of the gases was not altered by the change, except that the 
 difference between hydrochloric acid and olefiant gas became 
 almost null. 
 
 The experiments that we have described, as Faraday him- 
 self has remarked, are far from possessing the accuracy 
 that would be necessary before any great importance could 
 be attached to the numbers of the above Table ; for unexpected 
 circumstances very frequently cause them to vary through 
 very considerable limits ; thus a little dust, a little more or a 
 little less moisture in the air, would modify the direction and 
 the length of the spark, under conditions apparently the same. 
 Nevertheless, these two important facts are deduced from the 
 inspection of the Table: the first is that, under the same 
 pressure, and at the same temperature, the various gases re- 
 quire different changes of electricity, in order to be traversed 
 by the spark through a path of the same length ; the second, 
 that these differences are not simply due to the density of the 
 gas, but also to its nature ; since olefiant gas, less dense than 
 oxygen, and especially than carbonic acid, requires a stronger 
 charge. We have only to regret that the difference of the 
 diameter of the balls has introduced an extraneous element 
 into the study itself of the phenomenon, which is thus found 
 to be a little complex. 
 
158 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 "We see, from what has gone before, that, as far as the 
 propagation of electricity in gases is concerned, a distinction 
 must be made between the case of slow propagation or loss, 
 and that of rapid propagation or discharge. In the former 
 case, indeed, the density of the gas or the number of its 
 particles, is a circumstance favourable to the propagation ; 
 and the nature of the gas has little or no influence. In the 
 latter, the density of the gas, on the contrary, is an unfavour- 
 able circumstance, and the nature of the gas has a very 
 decided influence. Moreover, in the latter case there is a 
 movement, an agitation in the air, which indicates that its 
 displacement is necessary to the propagation ; and that con- 
 sequently, far from facilitating, its presence opposes it. 
 The same things happen when rapid propagation occurs 
 under the form of a continuous current, instead of being 
 brought about by discharges. M. Colladon and myself have 
 satisfied ourselves upon this point, by causing static elec- 
 tricity accumulated and constantly restored upon an insu- 
 lated conductor, to pass in the form of a current, according 
 to the plan contrived by M. Colladon himself*, through 
 common air, taken at different state of density, temperature, 
 and humidity. We employed a glass globe about 9 in. in 
 diameter, fitted up with two necks, in the same diameter. 
 We passed through one of the necks an insulated metal 
 rod, terminated in the interior of the globe by a platinum 
 ball, and communicating exteriorly with the electrised con- 
 ductor ; the other neck was traversed by a similar rod, but 
 terminated interiorly by a platinum point maintained at 
 about ijr in. distance from the ball, and extending exteriorly 
 to one end of the well-insulated wire of a galvanometer, the 
 other end of which was in communication with the ground. 
 By operating carefully we were satisfied that in air rarefied 
 to ^j or T J in., the needle of the galvanometer experienced 
 as strong a deviation when the platinum point and ball 
 were at a distance of 2 in. as when they were in contact 
 with each other ; the deviation was 55 in both cases, whilst 
 
 * Vol. I. p. 328. 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 159 
 
 it was only 35 in air under the pressure of 28 '29 in. In 
 another experiment, the air having been rarefied and heated 
 to 122, the deviation was 57, whilst it was only 24 with 
 air under the pressure of 28 '7 in., at the same temperature. 
 The distance of the ball and point in this case was 5 in. If 
 the interior of the globe was saturated with aqueous vapour 
 the air in it being very rarefied, the transmission of elec- 
 tricity occurred less easily in it than in very rarefied but 
 dry air. In fact, the globe being heated as before to 86, 
 a deviation of 55 was obtained, the point and the ball being 
 at a distance of 2 in., and 60, when they were in contact ; 
 whilst in very rarefied air, heated but dry, the deviation 
 was exactly the same, whether the ball and point were in 
 contact or not. 
 
 M. E. Becquerel obtained much more complete and re- 
 markable results, by transmitting the current of one or more 
 pairs through different gases. His apparatus consisted of 
 a platinum tube, drawn through the draw-plate and without 
 any soldering, 25J- in. in length, and j- in. in internal dia- 
 meter, sufficiently thick for a vacuum to be made within 
 it without its being compressed out of shape, even when a 
 portion of its length was raised to a red-white temperature. 
 The tube passed through a furnace, and was so arranged 
 that it could be brought to a red heat along an extent of 
 7^ in. It was terminated at its two extremities by plugs 
 containing glass tubes, which allowed of the introduction 
 into the platinum tube of various gases, and of their being 
 rarefied by means of the air-pump. A platinum wire, that 
 traversed one of the plugs, served as one electrode, the tube 
 itself serving as the other electrode. In some cases, M. E. 
 Becquerel used for electrodes insulated platinum wires, 
 which passed without touching each other, in the middle 
 of a porcelain tube heated to redness. Every precaution 
 was taken that the supports and the various adjustments 
 should not be exposed to variations of temperature, which 
 might have modified their insulating power, so that the gas 
 alone and the electrodes were subjected to these variations 
 in these different experiments. The experiments were made 
 
160 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 by passing the current, produced by one or more of Grove's 
 pairs, along the wire of a sensitive galvanometer, and through 
 the gas placed in the tube. The circuit also contained a 
 rheostat, consisting of a liquid column of very small dia- 
 meter, which might be lengthened or shortened by thrusting 
 a platinum wire, that serves as an electrode, to a greater or 
 less depth into a graduated tube, in which the column is 
 contained ; this liquid was distilled water holding in solution 
 variable proportions of sulphate of copper, according to the 
 experiments, and the other electrode was a plate of metal 
 placed at the base of the column, and in communication with 
 it. When wishing to operate, we begin, by removing from 
 the circuit the gas that is the subject of experiment, and 
 giving to the liquid column of the rheostat such a length 
 that the needle of the galvanometer should be deflected to 
 20, for instance ; then, without changing anything, the gas 
 was replaced into the circuit, and the end of the platinum 
 wire of the rheostat was lowered until, by diminishing the 
 resistance of the liquid column, as much as that of the 
 circuit had been increased by the introduction of the gas, 
 the deflection of the needle was brought back to what it 
 had been, namely to 20. The intensity of the current 
 evidently remaining constant, the length of the liquid 
 column, comprised between the two portions of the extremity 
 of the platinum wire, was equivalent to the resistance of 
 gas contained in the tube, increased by the resistance to 
 passage of the two electrodes, that transmitted the current 
 into the gas. 
 
 By means of this apparatus, M. E. Becquerel has esta- 
 blished several important facts. He first satisfied himself, 
 that the propagation of the current through the gas could 
 not take place before the latter had attained to red-heat ; but 
 that, setting out from this point, the resistance of the gas 
 diminished progressively, in proportion as the temperature 
 was raised ; and that this diminution was very rapid, when 
 the tube was strongly heated to red- white. All gases 
 present the same property, although in different degrees. 
 When the tube and wire are used for transmitting the current 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 101 
 
 into the gas, it is found that the transmission is more easy 
 when the tube, that is to say, the more extended electrode, is 
 negative, and the wire positive, than in the converse case.* 
 With two parallel and insulated platinum wires for elec- 
 trodes, there is no difference ; and the transmission occurs 
 with an equal facility, whether the current goes in one direction 
 or in the other. On employing these two wires, placed at 
 y 1 ^ in. from each other, it is found that the resistance of air 
 heated to redness, is thirty thousand times greater than that of 
 watery containing a ten-thousandth part of sulphate of copper 
 in solution. This resistance includes that which is due to the 
 passage of the electricity from the electrodes into the gas, 
 independently of that due to the passage through the gas itself. 
 In order to prove the influence of the elastic force of gases 
 upon their resistance to the passage of electricity, we have 
 merely to rarefy the air or gas contained in the platinum 
 tube, taking care to maintain the tube at red-heat. The fol- 
 lowing is the result of an experiment, made with the current 
 of a single pair, transmitted through air maintained at red- 
 heat, but gradually rarefied to the pressure of '078 in. of 
 mercury ; the needle of the galvanometer was brought back 
 to the constant deflection of 25, by means of the rheostat. 
 
 Elastic force. 
 
 Resistance. 
 
 Ordinary Pressure. 
 5-38 
 
 20-9 
 7-1 
 
 1-59 
 
 4-8 
 
 078 
 
 3-8 
 
 Even in the case of the greatest rarefaction, there still 
 exists a very appreciable resistance between the two platinum 
 electrodes, which is superior to y 1 ^ of the resistance, presented 
 
 * Mr. Andrews, in studying the conducting power of flames and heated air 
 for electricity, had already found that air, heated to redness by an Argand lamp, 
 conducted the current of a pole of twenty pairs, only when the positive pole 
 was in communication with the platinum wire, placed within the heated air, and 
 the negative with the brass tube of the lamp, near the orifice from which the 
 flame came out ; in the converse case, the current did not pas? ; the trans- 
 mission of the current was detected by means of the decomposition of iodide of 
 potassium. 
 
 VOL. II. M 
 
162 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 by heated air, at the same temperature and the ordinary 
 pressure. 
 
 A fact, worthy of especial notice, is that the temperature, 
 at which a gas begins to transmit the voltaic current is the 
 same, whether the gas is rarefied or maintained at the 
 ordinary pressure; it requires as elevated a temperature in 
 the one as in the other case ; but, when once this temperature 
 is attained, which is that of nascent red, the differences be- 
 come sensible with the variations of pressure. 
 
 The gases may be classified as follows, into the order of 
 the resistance they present to the current at red-white 
 temperature, under the pressure of the atmosphere, the 
 electrodes being of platinum, and the resistance of the air 
 being taken as unity : 
 
 Hydrogen (resistance comprised between 0'3 and 0'4). 
 
 Proto-carbonated hydrogen. 
 
 Oxygen (resistance comprised between 0*4 and 07). 
 
 Chlorine (resistance not exceeding 0*9). 
 
 Protoxide of nitrogen, and nitrogen (resistance very different from that 
 
 of air). 
 
 Carbonic acid (resistance comprised between 1*2 and 2). 
 Vapour of water (resistance greater than the air). 
 
 Heat, like rarefaction, acts upon all gases so as to diminish 
 their resistance to the transmission of electricity, but this 
 diminution is not equal for all; in proportion as they are 
 heated and rarefied, the relations that express their resistance 
 to the passage of the current, unceasingly tend to approximate 
 to unity. When the pressure of about y 1 ^ in. of mercury is 
 attained, all gaseous substances transmit the current equally 
 well, provided their temperature is the same. Heat acts in the 
 same direction as diminution of pressure; but it possesses 
 manifestly an action peculiar to itself, since at the ordinary 
 temperature, in the most perfect vacuum that can be pro- 
 duced, there is no appreciable transmission of electricity, 
 whilst at red-heat, electricity is able to traverse a gas, even 
 when it is not rarefied. 
 
 The resistance presented by gases, under their different 
 conditions of temperature and rarefaction, to the transmission 
 of electricity, varies with the number of pairs and with the 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 163 
 
 intensity of the current, produced by the same number of 
 pairs. The study that M. E. Becquerel has made of these 
 anomalies, would seem to demonstrate that they are due to 
 resistances, experienced by the current in passing from the 
 electrodes into the gases, which are variable, according to its 
 intensity. 
 
 M. E. BecquerePs experiments are of a nature to confirm 
 the remark that we have already made, upon the difference 
 existing in the action of gaseous substances, between the case 
 of slow loss and that of rapid propagation of electricity. We 
 even see that the influence of the density and of the nature of 
 the gas is almost the same, whether the rapid propagation 
 occurs by discharge or by current; with regard to that of 
 temperature, it has not been studied in the case of discharges ; 
 it is very probable that it would lead to results, analogous to 
 those which have been obtained for the case of currents. 
 
 It appears to us, therefore, to follow, from all this collection 
 of researches, that the function of air and of gases is ex- 
 clusively negative, in connection with the rapid propagation 
 of electricity; whilst it is positive when slow propagation or 
 loss is in question. In this latter case, the particles of the 
 gas are polarised by the electricity of the body that is placed 
 in the midst of them ; and they discharge the body, and dis- 
 charge each other successively, more or less slowly, accord- 
 ing to certain circumstances, in the same manner as takes 
 place with particles of imperfect conductors, whether solid or 
 liquid. Thus the conditions of the phenomenon are the 
 same, whether the bodies, by means of which the slow loss is 
 brought about, are gaseous, liquid, or solid. It is, however, 
 possible that in gaseous bodies, the propagation of electricity 
 is brought about by a slight movement or displacement of 
 the particles, as occurs in the propagation of heat. 
 
 If the propagation is rapid, the tendency of the two 
 electricities to unite is opposed by the presence of the in- 
 sulating particles, whether the medium be gaseous, solid or 
 liquid. This reunion, that is to say, the discharge or 
 current, can take place therefore only when the particles 
 are separated; hence the breaking of solid bodies, the 
 
 M 2 
 
164 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 movement and agitation of the particles in liquids and in 
 gases ; hence also the differences between different substances 
 in regard to their facility of allowing the discharge to pass ; 
 the gases, whose particles are more mobile, allow it more 
 readily to pass, and among them there are also differences due 
 to their difference of mobility, which is not in relation with 
 their specific gravity. The influence of rarefaction becomes 
 no less easy of comprehension, when the particle of gas is 
 no longer a more or less imperfect conductor, but an obstacle 
 to the transmission of electricity. Finally, the effect of tem- 
 perature is equally explicable, if we confine our attention 
 to considering it in the solid electrodes, charged with the 
 contrary electricities, and not in the gases, where it may be 
 considered as null, since it is the same whether the gas be 
 at its ordinary density, or be rarefied so as not to counter- 
 balance more than '078 in. of mercury. 
 
 An important fact, that must also be referred to, before 
 leaving the subject of the propagation of electricity in gases, 
 is the difference existing between positive and negative 
 electricity, with regard to their respective facility of bringing 
 about discharges, under similar circumstances. We have 
 directed attention to this difference, as far as concerns slow 
 propagation, when relating Matteucci's experiments. Belli 
 had, however, before Matteucci, observed that, for equal 
 tensions, negative electricity dissipates itself more promptly 
 than positive, the state of the atmosphere and the arrange- 
 ment of the apparatus being exactly the same ; he operated 
 by means of a quadrant electrometer, the balls of which took 
 10' 2" to descend from 200 to 10, when they were charged 
 with positive electricity, and only 4' 30", when charged with 
 negative. With regard to rapid transmission or discharge, 
 we have long been acquainted with the remarkable difference 
 presented by the light, which accompanies it in the form of 
 a spark, according as the electrised surface, from which it 
 proceeds is positive or negative. But, independently of this 
 appearance, which we shall study when directing our 
 attention to the electric light, there is a more general fact 
 established by Faraday, concerning the discharge itself. 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 165 
 
 We remark, first, that, when the discharge occurs through 
 air, between two balls of unequal size, the spark is much 
 longer when the smaller of the balls is the positive, and the 
 larger the negative, than in the reverse case : thus, in the 
 former case, it could attain to eight or twelve inches in length, 
 and in the latter to *8 or 1*2. There is also an important dif- 
 ference in the length of the spark, according as the balls 
 receive the electricity directly from the source, that is to say 
 are inducteous, or as they receive it by induction, that is to say 
 are induced. Thus the spark is twice as long, when the 
 smaller ball is rendered positive directly, as it is when it is so 
 by induction ; an analogous difference, although not so great 
 in amount, may be observed, when the ball is negative instead 
 of positive. 
 
 In order fairly to determine the different degrees of tension 
 or electric charge, that are acquired by the small balls, before 
 the discharge occurs, according as they are positive or 
 negative, the following apparatus (Jig. 187.), may be employed, 
 consisting of two metal forks, L and R, each terminated by 
 balls of different diameters ; the balls A and D, are two inches 
 in diameter, and the balls B and C, 0-2 in. ; the distance 
 between each of the large and small balls on the same fork is 
 about -94 inches ; the two forks being movable, the intervals 
 n and o, may be varied ; one of the forks is placed in com- 
 
 Fig. 187. 
 
 munication with the source of electricity, and the other with 
 the ground. The intervals n and o, being each one inch, and 
 the balls A and B, being positive and inducteous, the discharge 
 occurs at n, and more frequently with a brush ; the same 
 balls being still inducteous, but negative, the discharge still 
 occurs at ?i, but always with a brush. Here the advantage is 
 in favour of the small inducing ball, whether it be positive or 
 negative; but if the interval n is made '86 in., and the inter- 
 val *62 in., the discharge also occurs between the two inter- 
 si 3 
 
166 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 vals, when A and B are inducteous and positive ; when they 
 are negative, the discharge occurs in greater proportion at n, 
 which seems to prove that the small ball discharges itself 
 more easily when it is negative than when positive. This ex- 
 periment, and others of the same kind, led Faraday to admit 
 that, of two equally conducting surfaces, placed in air, and 
 electrised to the same degree, the one that is negative dis- 
 charges itself at a little lower tension than does the one that is 
 positive ; and that, when the discharge occurs, it passes in 
 stronger proportion from the positive to the negative surface, 
 than from the negative to the positive. 
 
 These different effects are very probably due to the na- 
 ture of the interposed dielectric body, which is in this instance 
 common air, and to the manner in which its particles are 
 polarised ; what proves this is that they vary with the gases, 
 that are placed in the course of the discharge. Faraday, in 
 order to study the influence of different gases, arranged the 
 apparatus of Fig. 187. so that the two forks might be in a 
 receiver, into which the gas was introduced, and that each 
 pair of balls might be in communication exteriorly to the 
 receiver, as in Fig. 186., either with a source of electricity or 
 with the ground. Upon operating in the same manner as 
 with air, namely, by rendering A and B, sometimes positive 
 inductors, at other times negative inductors it is found that 
 the small negative ball has a decided superiority over the po- 
 sitive ball, for determining the discharge in olefiant and in 
 carbonic acid gas, whilst in nitrogen and hydrogen it is the 
 reverse. 
 
 The phenomena upon which our attention has been 
 engaged, are therefore intimately connected with the manner 
 in which the propagation of electricity occurs in elastic fluids, 
 and consequently with the effects that accompany their pro- 
 pagation ; we shall also have occasion to return to this in the 
 following Chapters, which are devoted to the study of these 
 effects. They are to be traced to the same cause, to which 
 the differences observed by M. E. Becquerel in the facility of 
 the transmission of the electric current through "gases are 
 due, according as the positive electricity arrives by the pla- 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 167 
 
 tinum wire or tube. Finally, when we are studying the 
 phenomena of decomposition, that accompany the passage of 
 dynamic electricity through liquids, we shall see effects of the 
 movement and transport of the liquids themselves, from the 
 positive to the negative pole, which further indicate a disparity 
 in the mode of action of the two electricities. 
 
 General considerations on the mode of the transmission of elec- 
 tricity, in bodies and in vacuo ; and on certain molecular phe- 
 nomena, that are its result. 
 
 The study, that we have made of the propagation of elec- 
 tricity through solid, liquid, and gaseous bodies, and through 
 good, and also imperfect conductors, naturally leads us to 
 distinguish two modes of transmission. The first occurs by 
 the intervention of bodies, from molecules to molecules, 
 and more or less rapidly, according to the degree of con- 
 ductibility of these bodies and molecules ; this is what, with 
 Faraday, we have called conduction, and which is always ac- 
 companied by molecular induction. All bodies may therefore 
 be considered as conductors ; those which we call insulators 
 being merely conductors to so feeble a degree, that they do 
 not permit of a propagation of electricity of sufficient ra- 
 pidity to admit of the production of a current ; there is 
 merely slow loss. The mode of transmission by conduction 
 may be attended by calorific and chemical effects ; in the 
 latter case, it constitutes the mode by electrolysis, which is 
 only a particular case, but which Faraday, however, regards 
 as a distinct mode. The second mode occurs at a distance ; 
 it is the result of the tendency that is possessed by the two 
 electricities of uniting by virtue of their mutual attraction; 
 and it is brought about the more easily, in proportion as the 
 medium, necessarily an insulator, that is interposed between the 
 two solid conductors, the positive and the negative, contains a 
 smaller number of material particles. The most favourable 
 medium, therefore, for this mode would be a perfect vacuum ; 
 and all experiments seem to demonstrate this. But it by no 
 means follows from this that vacuum is a conductor ; for 
 
 M 4 
 
168 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 eonductibilitj supposes a succession of material particles, by 
 which the electricity is propagated; but we are here dis- 
 cussing the transmission to a distance, without the inter- 
 vention of contiguous particles. Vacuum, therefore, in 
 this case plays merely a negative part, that is to say, it is the 
 condition of space, most favourable to the reunion of the two 
 electricities at a distance, because it contains no matter that 
 is opposed to this ;. but it does not itself conduct, as we are 
 about to prove. 
 
 How is this reunion of the electricities from a distance 
 brought about ? Is it simply through the ether, and by its in- 
 tervention ? or does it always occur by the intervention of 
 very fine particles, detached from the electrodes, charged with 
 the contrary electricities and transported from one to the 
 other ? Faraday equally admits the two modes : he calls the 
 former disruptive discharge, because it is brought about by 
 the violent displacement of the particles of the ambient me- 
 dium, producing light under different forms ; and the latter he 
 calls discharge by convection or transport, because the discharge 
 occurs by means of particles transported, differing from con- 
 duction, in which the material particles undergo no sensible 
 movement. I should be disposed to believe that these two 
 modes constitute but one, and that even in the cases where 
 the discharge is least violent, there occurs on the small scale 
 what is found on the large in the phenomena of the voltaic 
 arc, namely, a true transport of very finely divided molecules. 
 All the conditions, such as the heating of the electrodes, the 
 rarefaction of gaseous media, that favour transmission, are of 
 a nature to facilitate disintegration by electricity, and the 
 transport of small particles appertaining to the electrodes. It 
 is true that it seems difficult to conceive that the electricity of 
 a single pair is able, as M. Becquerel has remarked, to have 
 sufficient intensity to be transmitted in this manner ; but this 
 objection is not peremptory ; for we shall see many other ex- 
 amples, in which the electricity of a single pair is able, when 
 circumstances are favourable, to produce effects that com- 
 monly require a pile of many pairs. But, in M. Becquerel's 
 experiments, the high temperature to which the electrodes are 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 169 
 
 brought, and their great approximation, must singularly facili- 
 tate the production of the effect that we have been pointing 
 out. Further, we cannot conveniently treat the important 
 question that we have raised, until we are in the Chapters, in 
 which we shall be occupied with the calorific and luminous 
 effects of electricity ; we shall then be able to examine 
 whether we must admit that the two electricities are able to 
 unite at a distance, without the intervention of material par- 
 ticles, or whether this reunion always requires necessarily 
 the presence, 'either of continuous matter, which constitute 
 conduction, or of particles, transported between two bodies, 
 charged with the contrary electrisation, which would reduce 
 the different modes of discharge to two alone. And it would 
 even not be impossible for these two modes not essentially to 
 differ from each other. In fact, what is conduction, if it is 
 not a succession of discharges that occur from molecules to 
 molecules, at infinitely small distances, instead of being 
 brought about between bodies of certain dimensions, at 
 distances of finite extent ? Moreover, in conduction, the dis- 
 charge occurs through molecular vacuum, and consequently, 
 whether on account of this circumstance, or of the small dis- 
 tances by which the molecules are separated, it is not neces- 
 sary that the electricity should possess any great intensity, in 
 order that it may be transmitted. We may also simply ask 
 if the molecular discharges occur, merely by the intervention 
 of the interposed ether, or if there is a very minute transport 
 of matter from one particle to another? This question, 
 which is precisely the same as the one that we have raised 
 for discharges that are brought about at finite distances, 
 cannot be suitably discussed, until we are studying the effects 
 that are produced upon bodies by the passage of electricity. 
 However, we may even in this place remark that the mole- 
 cular alteration, experienced by solid conductors, that have 
 served a long time for the transmission of the current, and 
 which has been pointed out by M. Peltier ; and the chemical 
 decompositions, that accompany this transmission in liquids, 
 would rather seem favourable to the idea of atomic and mole- 
 cular movement. 
 
170 TRANSMISSION OF ELECTRICITY. PART. iv. 
 
 Thus then, to sum up. There might be only one mode of 
 propagation of dynamic electricity, namely, by discharges, 
 occurring either from molecules to molecules, or at distances 
 infinitely small, or from bodies to bodies at finite distances, 
 succeeding each other, sometimes in a manner sufficiently 
 rapid to constitute the current, sometimes too slowly to 
 assume this form. The only question that would remain for 
 solution would be to ascertain whether these discharges 
 always occur by the intervention of material particles, 
 or whether they can equally occur by the intervention of the 
 ether, and without the presence of ponderable substances. 
 This is the question that we shall be called upon to examine 
 in the subsequent Chapters of this Fourth Part, when we shall 
 be engaged with the effects of the propagation of electricity, 
 after having confined ourselves in the present Chapter to pro- 
 secuting a general study, that shall be as complete as possible, 
 of this propagation itself. 
 
 We have now to give direct proofs of the non-conductibility 
 of vacuum, that we have admitted in what has gone before. 
 These proofs are very difficult to obtain, because it is im- 
 possible to deprive space entirely of all ponderable matter ; 
 there always remains in the vacuum of the air-pump, and 
 even in the barometric vacuum, a certain quantity of vapours. 
 However, by filling with mercury that has been well boiled, 
 a tube closed at one end, and which is plunged by its open 
 part into a cup, also filled with mercury, we are enabled to 
 obtain at the top of the tube a very empty space, by rarefying 
 the air above the mercury of the cup, which causes the 
 column of mercury contained in the tube to descend. By 
 surrounding the empty part of the tube with a metallic 
 coating, and electrising it as if it were a Ley den jar, Morgan 
 first saw the electric light in the interior ; and which seemed 
 to prove that vacuum was a conductor, and that it conducted 
 like an inner coating. But by taking the precaution 
 thoroughly to dry the mercury and the tube, he no longer 
 obtained any effect ; and he was able to prove that, on 
 electrising the exterior envelope, no trace of electricity was 
 developed in the interior. Erman, after having inserted a 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 171 
 
 platinum wire in the top of a barometric tube, and having 
 made in it as perfect a vacuum as possible, by having the 
 mercury well boiled, satisfied himself, by means of an elec- 
 troscope, placed in communication with the insulated mercury 
 of the barometric reservoir, that electricity which he caused 
 to enter the platinum wire, did not arrive at the electroscope, 
 and, consequently, did not traverse the empty space 6jin. in 
 length, comprised between this wire and the top of the 
 column of mercury. Davy, on his part, had proved, by 
 means of a small electroscope, attached to a platinum wire, 
 which itself was fixed, as in the preceding experiment, at the 
 top of a tube empty of air, and resting by its base on mercury, 
 that the balls of this electroscope diverged, when the end of 
 the platinum wire, with which they were in communication, 
 was electrised exteriorly. This divergence, however, would 
 not have taken place, if the electricity had been able to pro- 
 pagate itself through empty space. We have already seen * 
 that Harris and Becquerel have also maintained for several 
 days, the divergence of the gold leaves of an electroscope, by 
 placing it under a receiver, in which the air had been rarefied 
 as much as was possible, by means of the air-pump. Riess 
 made the same observation ; he even remarked that the 
 divergence of an electroscope, which had descended from 
 51 in. to '35 in., at the end of 55 minutes in the air of a 
 receiver, remained the same, namely, at *51 in. for 68 minutes, 
 when the air had been rarefied, until it could support only 
 39 in. of mercury. It is merely necessary, in order to the 
 maintenance of this divergence, that the electrised body 
 placed in the vacuum, should be at a sufficiently great 
 distance from every conducting body communicating with the 
 ground ; otherwise the electricity is dissipated, and a bluish 
 light is perceived between the electrised body and the neigh- 
 bouring conductor. 
 
 We may, therefore, admit that an electrised body, sur- 
 rounded on every side by a perfect vacuum, would always 
 preserve its electricity, provided it was at a sufficient distance 
 
 * Vol. I. i>. 131. 
 
172 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 from every other body, so that it could not discharge upon 
 it, a distance necessarily dependent upon the intensity of 
 its electricity. It follows from this that electricity remains 
 upon the surface of conducting bodies, so long as it is not 
 carried away by the contact of particles, that are more or 
 less conductors, or by the attraction exercised upon it by the 
 contrary electricity of a neighbouring body. We here find a 
 confirmation of the objections that we had raised against the 
 property, that had long been attributed to atmospheric 
 pressure, regarding it as the cause that maintains electricity 
 upon the surface of conducting bodies. 
 
 Before terminating this paragraph, we have still to speak 
 of certain phenomena that are connected with this action, by 
 virtue of which, electricity, in propagating itself, and pro- 
 bably in order to propagate itself, displaces, disaggregates, 
 and frequently transports the particles of bodies ; in a word, 
 alters their molecular state. These phenomena are numerous 
 and various ; and, although they almost always accompany 
 the other effects of the transmission of electricity through 
 bodies, they must be studied in a distinct manner, because 
 they are to a certain extent independent of it, and are some- 
 times distinct from it, and because they are connected in a 
 more intimate manner with the very mode of the propagation 
 of this agent. 
 
 M. Fusinieri has proved in an evident manner, by a great 
 number of experiments, the transport of metallic molecules 
 that takes place from one conductor to another, when the 
 discharge of a Leyden jar, or even the simple spark of an 
 electrical machine, is made to pass between these two con- 
 ductors. Thus, particles of silver are transported upon 
 copper, and are even able to penetrate it ; and reciprocally, 
 copper is transported upon silver. Among the experiments, 
 which prove that disaggregated metallic particles are able, 
 under the influence of the electric discharge, to penetrate 
 another metal, without being arrested by it, we will cite the 
 following. A disc of silver, well cleaned, of the thickness of 
 a sheet of cardboard, and about 3 Jin. in diameter, is placed 
 in contact by its centre with a gold ball *58 in. in diameter, 
 
CHAP i. PROPAGATION OF ELECTRICITY. 173 
 
 which itself communicates with one of the coatings of a battery 
 composed of two large Leyden jars ; the other coating com- 
 municates with a silver ball, which is brought near enough 
 to the disc for a spark to pass between them. When several 
 discharges have been made to pass in this way, a beautiful 
 spot of gold, or a very thin plate of this metal, is observed 
 upon the surface of the silver disc, from which the spark pro- 
 ceeded, the formation of which requires that gold shall have 
 traversed the silver, without having mixed with it : on the 
 other surface of the silver, and precisely at its point of 
 contact with the gold, a small circular cavity is found, which 
 seems to present certain traces of fusion. We also observe 
 that silver has been transported upon the gold ; but it does 
 not extend so well as the gold, which is of all metals the one 
 that forms the largest, and, consequently, the thinnest spot, 
 probably on account of its great ductility. 
 
 But the most remarkable effects of this kind are those ob- 
 served by Karsten, and by several other philosophers, and 
 designated by the name of electric figures or images. They 
 must not be confounded with the figures or designs, that may 
 be formed by electrising certain points of insulating plates, 
 and then powdering them with certain powders or dusts, 
 which reproduce the figures that had been traced with elec- 
 tricity. Such are M. Lichtenberg's figures in which the 
 powder itself is electrised, which makes the images come out 
 better, and enables us to distinguish those that are traced 
 with positive, and those that are traced with negative electri- 
 city. Such are also the figures that are obtained by covering 
 a plate with a non-electrised insulating powder, and moving 
 normally over the plate the point of a metal rod, held in 
 communication with the knob of a charged Leyden jar. In 
 this manner, a portion of the electricity passes to the plate, 
 another to the powder, so that the marks designed by 
 the point and the powder are similarly electrised, and 
 the figure is thus traced by lines, from which the powder is 
 cleared away. It is by this means that Wiedeinann, as we 
 have seen *, proved the difference of conductibility, presented 
 
 * Vol. H.p. 132. 
 
174 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 by certain crystals, according as electricity is propagated in 
 one direction or another. These figures also furnish very 
 characteristic differences between positive and negative elec- 
 tricity ; and we shall return to this, when we are studying 
 these differences, and are occupied with the electric light. 
 For the present our attention is to be occupied with electric 
 images of another kind, namely with those that are due, not 
 to a simple attraction, exercised upon pulverulent substances, 
 by electricity that remains adhering, according to certain 
 directions, to insulating plates, but to a permanent molecular 
 modification, produced in conducting bodies, as well as in 
 non-conductors, by the effect of the passage of the electricity. 
 
 Moser had discovered in 1842, the remarkable fact that, if 
 two bodies are in contact, or very near together, they impress 
 their image upon each other. Thus we have merely to place 
 a medal or a piece of money upon a highly polished metal plate, 
 and to leave it there for some time (about twenty minutes), 
 in order that this plate may preserve the impression of the 
 medal or the piece of money. The effect, in this case, is not 
 very marked, but it becomes much more sensible, if the plate 
 is exposed to the vapour of mercury or to the vapour of water, 
 such as is produced by the breath, these vapours condensing 
 themselves, so as clearly to designate the outlines of the image. 
 If the plate is of silver and has been iodised, a much more dis- 
 tinct image is obtained. What is remarkable is, that these ex- 
 periments succeed as well in perfect darkness, and during the 
 night, as under the influence of light. So that Moser had 
 attributed this class of phenomena to a peculiar action of the 
 most refrangible dark rays, setting out from the principle that 
 all bodies radiate light, even in complete darkness ; and he 
 considered this action to consist in modifying the substances 
 in such a manner that, after having been subjected to it, they 
 condense various vapours, otherwise than they would but for 
 this ; the discovery of Daguerre being only a particular case of 
 this general action. 
 
 Karsten succeeded, a short time after Moser's discovery, in 
 producing similar figures, under analogous circumstances, 
 making use of electricity. He placed a piece of money on a 
 
CRAP i. PROPAGATION OF ELECTRICITY. 175 
 
 glass plate, which was itself resting upon a plate of metal ; 
 he then passed some electric sparks upon the money, which 
 were discharged upon the metal plate, by passing round the 
 glass plate. At the end of a hundred turns of the electrical 
 machine, the piece of money was removed, and on breathing 
 upon the glass plate, which had apparently suffered no 
 alteration, the entire impression of the piece was seen to re- 
 appear with its most minute details. By employing thin 
 plates of glass, a great number may be superposed upon each 
 other, and we then obtain figures of the medal upon each of 
 them, feeble it is true, and which become less and less dis- 
 tinct ; but which are, however, always to be recognised. In 
 general, the figure is more defined, in proportion as the species 
 of Ley den jar, formed by the association of the medal and the 
 metal plate, discharges itself more frequently and in a spon- 
 taneous and continuous manner, so as to produce as it were a 
 glory radiating around the piece of money. 
 
 The effect that we have been describing is in no way due 
 to traces of electricity remaining adhering to the glass plate, 
 after the spark has been passed. This may be easily proved 
 by rubbing the plate with a piece of stuff, or by leaving it 
 exposed for some time to the air, which causes all the elec- 
 tricity to disappear; and yet the figure remains with the 
 same distinctness ; it is even a matter of some difficulty to 
 cause it to disappear, by heating and then blowing upon it. 
 But the strongest proof is, that the same figure may be re- 
 produced upon plates of polished metal, a case in which it is 
 impossible to admit that there is any electricity adhering. 
 In order to succeed well, the electricity must be prevented 
 passing too rapidly from the piece of money to the metal 
 plate, that is to receive the impression of it ; and for this 
 purpose, it is necessary, instead of placing them immediately 
 in contact, to separate them by a thin plate of glass, or which 
 is better still, by a thin plate of mica. We thus obtain 
 readily, after fifteen or twenty turns of the plate of the 
 machine, or in ten or fifteen seconds, a figure of extraordi- 
 nary distinctness. The thinner the body is, and consequently, 
 the more perfectly the two contrary electricities are disguised, 
 
176 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 the greater is the distinctness as well as the rapidity with 
 which the figure is formed. We may vary the nature of the 
 plate, that is intended to receive the images, as well as the 
 objects themselves, whose figures we desire to obtain. Kars- 
 ten employed indifferently coins and medals, of various 
 metals, seals, engraved stones, &c. ; however, the most decided 
 results, are those that are obtained with various pieces of coin, on 
 account of the uniformity of the impression. With regard to 
 the plates, the best conducting bodies are the best : and, when 
 using a plate of silver, similar to that which is used for da- 
 guerreotype, there is obtained upon this plate, after a consider- 
 able number of turns of the machine, a very visible impression 
 of the medal and of the sheet of mica, even without there 
 being any necessity of causing them to appear by means of 
 vapours. After a thousand turns of the machine, the entire 
 figure was produced upon the plate, as if it had been done by 
 aquafortis ; and it presented a brownish colour. 
 
 The phenomena observed by Karsten have a great resem- 
 blance to those discovered by Moser, although they are 
 produced in a very different manner. The modifications 
 experienced by the surfaces that receive the impression of 
 medals and of other objects, appear in both cases to be of the 
 same nature ; but what this nature is, is the question that 
 presents itself. 
 
 Riess had already remarked, before Karsten's experiments, 
 that figures may be produced upon plates of glass and mica, 
 by means of electric discharges or of simple sparks, that is to 
 say, traces, ramified designs may be determined upon the 
 surface of these plates, which become visible if breath be pro- 
 jected upon them, and which, on this account, he had termed 
 roric figures. On closely examining pieces of mica, he 
 satisfied himself that a plate of this substance, when exposed 
 to a puff of breath, or held over water in a state of evapo- 
 ration, becomes covered with a deposit of minute drops, which 
 do not form a continuous film ; whilst this film is continuous 
 and perfectly transparent, instead of being disturbed, if the 
 surface of mica is new, and has not been already exposed to 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 17? 
 
 the air.* We might suppose that the renewed surface is not 
 covered with water ; on the contrary, however, it is because 
 it has a great affinity for water, that it condenses it in a con- 
 tinuous film ; which is proved both by the great electric 
 conductibility that it acquires, and by the inspection that may 
 be made of it by means of the microscope, which at the same 
 time reveals these urinate insulated drops upon the parts, where 
 the surface is not new. On the other hand, on exposing it to 
 the action of drying substances, or to that of vacuum, the 
 surface becomes insulating, in consequence of the disappear- 
 ance of the thin film of water. The difference between the 
 old and the new surface of mica, is due to there being formed 
 upon the former a film of foreign matter from the deposit of 
 various substances, principally organic, that occur suspended 
 in the atmosphere, a film, that has not had time to form 
 upon the renewed surface. It is the presence of this slightly 
 fatty film, that constrains the water to deposit itself under the 
 form of drops, instead of forming a continuous deposit. 
 
 The action of the discharge of sparks would therefore con- 
 sist in driving away the foreign film, wherever the electricity 
 has passed ; and the difference in the manner in which the 
 breath arranges itself, where this film exists, and at the spots 
 whence it has disappeared, would thus render the traces of the 
 electricity visible. However, the surface of mica, like that 
 of glass, may itself be modified to a tolerable depth by the 
 effect of the discharges, as we have already seen, which ex- 
 plains the persistency of the figures, which sometimes remain 
 for several years. 
 
 Returning to Karsten's electric figures, it should be noticed 
 that there are two series of discharges, those which occur in 
 one direction, when the model, that is placed upon the insu- 
 lating plate, is charged ; and those which occur, when 
 the electricity of the model, and that of the lower plate, neu- 
 tralise each other. Now, as these two effects succeed each 
 other very rapidly, there results a removal of the foreign film 
 
 * The surface of a plate of mica is easily renewed, by detaching a thin plan- 
 from it with the blade of a penknife. 
 
 VOL. II. N 
 
178 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 from the parts of the insulating plate corresponding to the 
 points, that are nearest together, and consequently the most 
 salient of the model. We may even render this effect sen- 
 sible, by substituting for this lower metal plate, a very smooth 
 surface of resin ; and the image of the model is discovered by 
 means of a fine powder that is deposited, where the electricity 
 has left its traces. The image produced on the metal plate 
 is in like manner due to the removal of a foreign film, analo- 
 gous to that with which the mica is covered, a removal that 
 occurs wherever the discharges have passed. This is proved 
 by the influence of polish, which consists, less in purifying 
 the metal than in clothing its surface with a perfectly uniform 
 foreign substance. This is also proved by M. Fizeau's expe- 
 riment, in which a platinum plate, after having been very 
 well polished with cotton impregnated with a mixture of 
 putty powder and alcohol, gave excellent images, and no 
 longer gave any, after having been purified by incandescence 
 and its successive immersion in acid water and in pure water, 
 until it was able to inflame hydrogen gas. Moreover, Kar- 
 sten, on inspecting with the microscope the images, that are 
 produced by the breath upon a metallic surface, very plainly 
 recognised that they arise from the deposit of a very thin 
 and continuous film of water, which occurs at the points, from 
 which the foreign deposits have been removed. He has also 
 proved that the image that has been determined upon a brass 
 plate is reproduced upon it by a deposit of copper, when the 
 plate is plunged into a solution of sulphate of copper, as 
 negative electrode ; a proof that the traces of the image cor- 
 responded upon the brass surface with the points, from which 
 the foreign film had been removed. 
 
 For the same reason it is that the plates of mica, upon which 
 the reproduction of the image occurs best, are those whose 
 surface is very old, and which have not been renewed for 
 a long time, either by electricity or by mechanical action. 
 
 However, it seems impossible for us to explain, in every 
 case, the formation of electric figures, only by the part attri- 
 buted to this organic film, that exists on the surface of bodies, 
 especially when these figures are visible immediately, as well 
 
CHAP. r. PROPAGATION OF ELECTRICITY. 179 
 
 upon insulating plates as upon plates of metal, without the as- 
 sistance of vapour. We are obliged to admit that a true mole- 
 cular modification is brought about upon the surfaces ; and 
 the proof is, that the images are not merely superficial and 
 transitory, but they penetrate sometimes to a tolerable depth, 
 and are very durable. Now, it is very probable that in 
 Karsten's experiments, the molecular polarisation, expe- 
 rienced by the insulating substance, that is placed between 
 the two metal plates, must be accompanied by a change 
 in the position of the particles, at the places where the 
 electric action is the strongest, namely in the points, corre- 
 sponding to the most salient parts of the object in relief. 
 In like manner, when the discharges occur, the particles 
 of the lower metal plate must, in the points, where they are 
 nearest to the relief, also undergo a molecular change, the 
 effect of which is a superficial alteration, very slight, it is 
 true, but nevertheless sensible. It might also happen that, in 
 certain cases, the prolonged passage of successive electric 
 discharges, would be attended with certain electro-chemical 
 effects, and in particular with an oxidation in the parts of 
 the metal surfaces, that are the nearest to the salient points 
 of the medal. 
 
 With regard to Moser's figures, they seem to me to 
 have the same origin as Karsten's, as we have said above. 
 The appearance and the properties of these two sorts of 
 images are so very similar, that it would be difficult to 
 attribute them to different causes. Moser's images cannot be 
 formed upon a plate of metal through a plate of mica ; is it 
 necessary that the plate and the object, if not in contact, shall 
 at least be at a very small distance apart, circumstances, that 
 are altogether unfavourable to the hypothesis, that the figures 
 are produced by an invisible radiation. That which proves 
 that electricity seems to play a part in their production, is 
 that, according to Karsten's observation, if a piece of silver 
 is placed upon a brass plate, care being taken to place them 
 in communication, by means of a band of copper placed all 
 round on the exterior, an excellent image is obtained ; whilst 
 the image is very bad, when the precaution has not been 
 
 N 2 
 
180 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 taken of attaching the band of copper. In the former case, 
 we have a true pair, in which the air, more or less moist, 
 interposed between the brass plate and the piece of silver, 
 plays the part of a liquid conductor ; whence it follows that 
 . the surface of the brass must be oxidised in all the points 
 where it has not been in contact with the piece. In the 
 latter case, the neutralisation of the electricities occurring by 
 the points of contact of the plate and the piece, the effect must 
 be more confused, than when it is brought about regularly, 
 by the intervention of the copper plate, by which the two 
 metal plates are connected. 
 
 The necessity of an interposed film of air, for the pro- 
 duction of Moser's images, has been proved by Knorr, 
 who has demonstrated that, in very pure water, deprived 
 also of air, as in vacuo, the images are either not formed 
 at all, or very difficultly. This fact is favourable to the 
 explanation, that we have been giving.; but it is not the 
 less a difficult matter to explain the formation of Moser's 
 images, when the two metal plates do not touch. However, 
 it is not impossible that, at the necessarily small distance 
 at which these plates are placed in reference to each other, 
 the electricity, developed upon one of them, by the action 
 of the moist air, being condensed by the influence of the 
 other plate, may be capable of producing sufficient effects 
 to determine the formation of the images. We shall see 
 in the Part, that is devoted to the sources of electricity, some 
 examples of the liberation of electricity, under similar con- 
 ditions. 
 
 We shall not detain ourselves with the other explanations, 
 that have been attempted to be given of Moser's images, 
 especially those of Hunt and of Knorr, who attribute them to 
 a caloric cause ; and, according to Knorr, to a reciprocal trans- 
 mission of heat between the plate and the object. This latter 
 philosopher, indeed, on heating the plates, obtains images, 
 which he terms thermographic, and which are evidently due to 
 an oxidation ; since they cannot be produced with plates of 
 platinum and gold. The action of heat consists especially in 
 manifesting pre-existent differences in the molecular state of a 
 
CHAP, I. PROPAGATION OP ELECTRICITY. 181 
 
 metal surface, probably because these differences determine in 
 it corresponding differences in the oxidation, that is suffered 
 by this surface, through elevation of temperature. Thus 
 heat causes the reappearance of the effaced image of a 
 daguerreotype, and the vanished impression of a piece of 
 money, the well-polished surface allowing no sign or any 
 figure to be visible. In all these cases, the heat does not 
 determine the formation of the image, but simply renders its 
 manifestation sensible. 
 
 Without entering into further details upon this interesting 
 subject, which has been the object of the researches of very 
 many philosophers *, we sum up by stating our opinion 
 that the formation of the image is in every case an electrical 
 effect, due to the influence that the transmission of electricity 
 exercises over the molecular state of bodies, either by dis- 
 persing the particles, when they oppose an obstacle to it, 
 or by physically or mechanically modifying them, when 
 they allow a passage to it. We rest, 1st, upon the fact, 
 that the most certain and efficacious manner of obtaining 
 the figures under all forms is to employ electric discharges ; 
 2ndly, upon the circumstance that, in all cases, in which the 
 figures are produced, without the direct intervention of elec- 
 tricity, the conditions most favourable to this production 
 are at the same time those that are equally so to a liberation 
 of electricity. 
 
 We shall not here speak of the other figures or images, 
 that may be produced by means of electricity, such as 
 Priestley's rings, and those of Nobili, seeing that the former 
 are due to the heat, that is the attendant of the electric 
 spark, and that the latter are the effect of an electro-chemical 
 decomposition ; the study of these will naturally, therefore, 
 find its place in the two following Chapters, which are 
 devoted to the calorific and chemical effects of electricity in 
 motion. 
 
 * We regret, in particular, not to speak of M. Masson's researches, as well as 
 those of M. Morren, which are, however, of a nature to confirm the ideas, that 
 we have put forth, in respect to the cause of these phenomena. 
 
 N 3 
 
182 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 Velocity of the Propagation of Electricity. 
 
 Immediately after the discovery of the Ley den jar, the 
 prodigious rapidity with which the electric discharge is pro- 
 pagated, was proved, both hy making it pass through a 
 numerous file of men, who all held each other by the hand, 
 as well as by transmitting it through a length of two miles, 
 in the Thames, a space which it traversed instantaneously. 
 The most accurate experiment was that made by Watson, on 
 the 5th of August, 1748. The arc, for connecting the two 
 coatings of aLeyden jar, was formed by an iron wire 12,276 
 feet in length, sustained in the open air by insulating supports 
 of dry wood, and so arranged that its two extremities and its 
 middle were in the same chamber with the Leyden jar and 
 the electrical machine. The wire was interrupted midway 
 in its length, and this solution of continuity was occupied 
 by the body of the observer, who held in his hands the two 
 ends of wire, separated by this interruption. At the moment 
 of the discharge, the observer saw the spark that escaped 
 between one end of the wire, and the inner coating of the 
 jar, at the same time that he felt the shock, produced by this 
 discharge; and he was never able to perceive the smallest in- 
 terval between the two sensations ; from which he concluded 
 that the rapidity of the propagation through the wire is not 
 measurable. 
 
 A long time after these first essays, in 1834, Wheatstone 
 took up the examination of this question, according to a very 
 ingenious process, applicable also to a great number of other 
 researches. This process is founded upon the effects of the 
 reflection of a distant luminous point, by a plane circular 
 mirror, traversed by a horizontal axis, situated in its plane 
 and passing through its centre, around which it turns with 
 very great rapidity (Jig. 188.). E is the mirror, fixed to the 
 horizontal axis G F, carried by the two brass supports I and 
 H. The image of the luminous point, according to the law 
 of reflection., describes an arc of a number of degrees double 
 of that described by the mirror in the same time ; that is, in 
 the time employed by the mirror, to pass from the position 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 183 
 
 in which the image of the luminous point has been visible to 
 the eye at rest of the observer, to that in which it ceases to 
 
 Fig. 188. 
 
 be so. If the duration of the light of the point is less than 
 that of the time employed by the mirrors to pass from one 
 of these positions to the other, the luminous arc will not 
 have the length we have just assigned to it, in supposing 
 this light permanent. If even this duration were nothing, 
 and it could happen that the light should be completely 
 instantaneous, the arc would be reduced to a point. Now, 
 when the luminous point is an electric spark, arising from a 
 discharge, produced in air between two conductors, the 
 image, which is effectively nothing more than a point for a 
 velocity of the mirror of 50 turns per second, becomes an 
 arc for a greater velocity, a proof that the light of the spark 
 has a certain duration. If we determined this velocity of the 
 mirror, that is to say, the number of turns it makes in a 
 second, we should be able, by measuring with a divided circle 
 the number of degrees occupied by the image, to determine 
 the time of the duration of the light, produced by the electric 
 discharge, or, which comes to the same thing, the time of the 
 duration of this discharge. Thus, Wheatstone, having found 
 this arc to be 24 for a rotation of the mirror of 800 turns per 
 
 second, concluded from this a duration of - = 
 
 of a second. Indeed, during the time in which the mirror, 
 while turning, traverses 360, the image in it of the luminous 
 point traverses 720 ; now, as the mirror makes 800 turns 
 
 N 4 
 
184 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 in the second, the image traverses 720 x 800, namely, 
 576,000 in a second ; but as it has itself 24 of length, it must 
 
 94. 1 
 
 have endured for the time expressed by 576Q00 or 24000' 
 
 Thus, the first result obtained by Wheatstone is that the 
 discharge, which produces the electric spark, is not com- 
 pletely instantaneous ; but that it has a duration, excessively 
 short, it is true, susceptible, however, of being estimated. 
 
 This point being established, the following is the process 
 adopted by the English philosopher, for determining the 
 duration of the propagation in a good conductor, such as a wire. 
 
 He constructed an apparatus, 
 which he called a spark-board 
 {Jig- 189.), which consists of a 
 wooden disc, upon which are 
 placed, in the same horizontal 
 line, six copper balls, combined 
 in such a manner, that the 
 same electric discharge may 
 give rise to three sparks. Thus 
 the ball, from which the wire 
 No. 1. comes, communicates 
 directly with the inner coating of the jar, whose discharge, 
 passing to the next ball, goes from this ball by the wire 2, 
 which is connected with the wire 3, to the third ball ; thence 
 it passes to the fourth ball, whose wire 4 leads it to the ball 
 of wire 5, so that it may pass onward to the ball, whose wire 
 6 is in communication with the outer coating of the jar. 
 The balls of each of the three systems are only T ^ in. apart 
 from each other, and this constitutes the distance of the path 
 for each of the three sparks ; the circular spark-plate is 3 J in. 
 in diameter. Now the wires 2 and 3, as well as the wires 4 
 and 5, instead of being placed in immediate communication, are 
 respectively united by a copper wire y 1 ^ in. in diameter, and % 
 of a mile in length, which makes a total length of J a mile 
 between the ball 2 and the ball 5, a length interrupted in its 
 middle by the balls Nos. 3. and 4. Thus the discharge, pro- 
 ducing in the course three sparks, supposing it sets out from 
 
CHAP. I. 
 
 PROPAGATION OF ELECTRICITY. 
 
 185 
 
 the inner coating, has to traverse a copper wire ^ of a mile 
 in length, between the first and second spark, and a copper 
 wire of J of a mile also in length between the second and 
 third. If the velocity of propagation in these long con- 
 ductors is appreciable, the appearance of the three sparks 
 should not be simultaneous ; now, experiment shows that 
 the spark at the middle is retarded, as compared with that of 
 the two extremes, a proof, therefore, that the propagation of 
 electricity is not instantaneous, and that it occurs from the 
 extremities of the conductor by which the two coatings are 
 connected, towards its middle. 
 
 The following is the manner in which Wheatstone ar- 
 ranges the experiment, in order to obtain this result, and to 
 measure the velocity of the propagation. 
 
 The apparatus of Jig. 188. is placed at the extremity of a 
 mahogany plank (jig. 190.), upon which there is a wheel K, 
 
 Fig. 190. 
 
 which communicates its motion to the axis, by means of 
 a cord, passing in grooves, hollowed in the circumference of 
 both pieces. In Wheatstone's apparatus, the system of 
 wheels was so arranged that the axis carrying the mirror 
 should have made 1800 revolutions for one of the wheel, if 
 there had been no retardation, arising from the slipping of the 
 
186 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 cord. A discharger o P is in communication by its extremity 
 with the inner coating of a Ley den jar, which is constantly 
 electrised by means of an electrical machine ; the outer 
 coating of the same jar communicates with the wire No. 1. 
 of the spark-plate, and the wire No. 6. abuts against an en- 
 largement of the brass support, upon which the axis of the 
 mirror turns. The same axis carries an arm Q (fig. 188.), 
 which turns with it, and which, at each revolution, is brought 
 opposite to the knob of the discharger ; this brings about the 
 discharge, which, being transmitted through the circuit, 
 passes between the two balls of the discharger, the distance of 
 which is regulated for this purpose, then from the extremity 
 of its stem P to the knob of the arm Q, and thence through the 
 axis of the mirror to the spark-plate, where the eye perceives 
 the three sparks. The plate itself is placed vertically at the 
 distance of 9 '84 ft. from the mirror, and in such a manner 
 that the latter is upon the same level as the horizontal line 
 upon which the three sparks are situated. The arm Q is so 
 arranged that the discharge occurs, and that consequently the 
 sparks appear, at the moment, when the mirror makes an 
 angle of 45 with the horizon, which causes the eye of the 
 observer, placed on the side of I, looking directly from above 
 downward, to see the images of the three sparks, reflected 
 upon a horizontal plane. A flat glass may be placed above the 
 mirror, so as to prevent the eye approaching too near to the 
 mirror. In order the better to regulate the instant of the 
 discharges, which ought to occur at the moment when the 
 mirror is inclined 45, a plate of mica s is interposed, 
 pierced with a very small horizontal opening, parallel to the 
 axis of the discharger, which confines the possibility of the 
 discharge within very narrow limits. Thus, whatever be 
 the rapidity, with which the mirror moves, the sparks are 
 generally in the field of view. 
 
 It is a matter of great importance, as may be supposed, to 
 determine accurately the velocity of the rotation of the axis, 
 that carries the mirror. Mr. Wheatstone arrived at this 
 first, by calculating the pitch of sound, produced by the suc- 
 cession of blows received by a little band of paper or card> 
 
CHAP. 1. PROPAGATION OF ELECTRICITY. 187 
 
 attached to the arm Q, which, at each revolution of the axis, 
 experiences a blow. When the machine had its maximum 
 velocity, a sol sharp of the fourth octave was obtained, which 
 corresponded to 800 revolutions of the mirror per second. 
 More recently, Mr. Wheatstone has succeeded in furnishing 
 the instrument with a counter for registering the number of 
 rotations. It is true that the increase of resistance to motion, 
 which arises from this addition, prevents the mirror executing 
 more than 600 revolutions per second. 
 
 In operating by means of the apparatus, arranged as we 
 have been pointing out, as soon as the velocity of the mirror 
 exceeds a certain limit, the three sparks are seen to be elon- 
 gated into three parallel lines, which are longer in proportion 
 as the movement is more rapid. These lines are arcs of the 
 circle, the centres of which are situated on the axis of the 
 mirror ; the greatest amplitude, they have been found 
 to attain, was 24, which, at 800 revolutions of the mirror 
 per second, corresponds to a duration of the spark of 
 2?reny f a second, as we have seen. With regard to the re- 
 lative position of the three images, when the velocity is yet 
 feeble, their extreme points appear to be exactly in the same 
 vertical, and present this appearance ^ ~ ; but, as soon 
 
 as the velocity becomes considerable, if the mirror is turning 
 from left to right, in respect of the observer, placed at I, the 
 lines assume this appearance "EEiiEEEEIIL > and, if it turns 
 from right to left, they assume this appearance ZIEEElEEEiEr""' > 
 which indicates equally in both cases that the middle spark 
 appeared after the two extreme ones, and that it disappeared 
 also after them. Indeed, in the former case, the mirror having 
 passed the 45 on the side of the vertical, when the middle 
 spark shows itself, it is clear that the commencement of its 
 image must be found in arrear of the commencement of those 
 of the other two sparks, which have appeared at the moment, 
 when the mirror was at 45 ; this must be the reverse in the 
 case, when the mirror turns from right to left. Mr. Wheatstone 
 has succeeded in estimating, approximately to half a degree, the 
 amount, by which the middle image is in arrear or in advance 
 of the other two. This arc of a half degree corresponds to a 
 
188 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 f 2x360xl600 = 1152000 f a SecOnd; the 
 space traversed in this portion of a second being \ of a 
 mile, or 1320 feet, which gives a velocity of 288,000 miles per 
 second. This, then, would be the velocity of the propagation 
 of electricity in a copper wire, a velocity superior to that of 
 light in planetary space, which is only of the above. 
 
 Wheatstone's experiment proves, moreover, that in a wire 
 which communicates, by its extremities, with the coatings of 
 a Leyden jar, the electric derangement is propagated from the 
 two ends of the wire with an equal velocity, and endures for 
 a certain time, very short, it is true, but yet appreciable, in 
 order to arrive at the middle of the circuit. We shall return 
 hereafter, when engaged with the electric light, to certain 
 experiments of Wheatstone's, which have reference to the 
 duration of the spark. 
 
 Recent researches on the velocity of electricity, made with 
 voltaic currents, transmitted through telegraph wires, have 
 given very different results to those obtained by Wheat- 
 stone with ordinary electricity. Thus, Mr. Walker of Wash- 
 ington had found that this velocity, in an iron wire | in. in 
 diameter, was 18,760 miles per second, and Mr. Mitchell had 
 found 28,526, both velocities being very much lower than 
 the 288,000, that had been found by Wheatstone. 
 
 More recently, Mr. Gould took advantage of a colossal 
 voltaic circuit of 1045 miles, established between the station 
 of Seaton, at the north of the Capitol of Washington, and the 
 town of Saint-Louis, with several intermediate stations, as 
 Pittsburg, Cincinnati, in order to determine the velocity of the 
 propagation of the current, according to a method altogether 
 different ; and he found 12,851 miles per secondhand 15,830 
 in using only the experiments, made at a lower temperature 
 than that of the congelation of water, the insulation not being 
 sufficient at higher temperatures. Mr. Gould's method con- 
 sisted in having a pencil fitted to a piece of soft iron, which, 
 when resting on a white paper wound round a cylinder, to 
 which a uniform rotatory motion is applied, by means of a 
 clock movement, makes a regular mark upon it. The piece of 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 189 
 
 soft iron is attracted by the poles of an electro-magnet, 
 surrounded by a wire, one end of which is Jed to the scape- 
 wheel of a seconds pendulum. This wheel periodically 
 interrupts the circuit which, by the action of the electro- 
 magnet upon the armature, produces intermittences of at- 
 traction, which are interpreted by the equal and equidistant 
 interruptions of the tracing upon the paper. A similar 
 apparatus being arranged in each of the consecutive stations, 
 they are all actuated by a single electric current, which 
 traverses their common circuit. Mr. Gould first satisfied 
 himself that the difference of the intervals between the 
 marks at the different stations corresponded well with their 
 distance from the place at which the signal was given, and 
 that it was proportional to the time consumed by the current, 
 in traversing double* the distance between the stations. By 
 thus comparing the registers of each station, including that 
 from which the current set out, he arrived at the result 
 that we have indicated. 
 
 MM. Fizeau and Gonelle had obtained very different results, 
 by operating in a still different manner. The principle of their 
 method consisted in interrupting a current at very limited 
 intervals of time, and simultaneously in two points of a long 
 conductor, very distant from each other. These interruptions 
 were brought about, by means of a wheel, carrying 'upon its 
 circumference a number of equal divisions alternately in 
 wood and metal, like the rheotomes, that we have already 
 described f ; these apparatus could be easily arranged in such 
 a manner, that the circuit could be interrupted at two or 
 at several places, and the interruptions should be perfectly 
 simultaneous, wherever they occurred. A galvanometer, 
 placed in the circuit, received by this arrangement only 
 discontinuous currents ; nevertheless, when the interruptions 
 succeeded each other rapidly, the needle of the instrument 
 was deviated in a stable manner, as if the current had been 
 
 * Double, on account of the necessity of the current to return to the point of 
 departure. 
 
 f Vol. I. p. 301. (fit). 130.), and p. 302. (fig. 131.), p. 398. (fig. 153.) 
 
190 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 continuous. Only the amplitude of the deviations varied 
 with the number of interruptions, that occurred in a given 
 time, and obtained a maximum for a certain number of inter- 
 ruptions, in the same time, that it acquired a minimum for 
 another. If the propagation of the current in a long con- 
 ductor is instantaneous, it is clear that the fact that the 
 circuit suffers simultaneous interruptions at the two extremi- 
 ties of this conductor, should in no way change the devia- 
 tion of the galvanometer, which remains the same as if there 
 had been interruptions only in one point of the circuit. But, 
 if the propagation requires a certain time, for its being 
 brought about, it can no longer be the same, seeing that at 
 the same moment when the interruption takes place at the 
 point of departure of the current, it occurs also at the other ex- 
 tremity of the conductor, at which this same current has not 
 yet arrived. When, therefore, it arrives there, it no longer 
 finds the interrupter in the same position, and the devia- 
 tion of the galvanometer there suffers a diminution. It 
 follows from this, that the velocity of the propagation must 
 give rise to periodical changes in the deviations, corresponding 
 to greater and greater velocities of the rheotomes ; and that 
 consequently, from these changes, we might be able to deduce 
 the velocity itself. MM. Fizeau and Gonelle did this, 
 using for their experiment the telegraph wires from Paris 
 to Rouen and from Paris to Amiens. The two wires of 
 each of these lines might be connected, the former at Rouen, 
 the latter at Amiens ; they thus presented a length of 195 miles 
 for the Amiens line, and 179 miles for that of Rouen. By 
 operating according to the method, that we have been point- 
 ing out, by means of these long conductors, of which one was 
 of iron and the other of copper, the two philosophers arrived 
 at the conclusion that the velocity of the propagation of 
 electricity is independent of the intensity of the current and 
 of the section of the conductor, but not of its nature, and 
 that it is 62,130 miles per second in an iron wire, and 
 111,834 miles in one of copper. Mr. Latimer Clark had 
 already observed, by operating with piles, whose number 
 varied from 31 to 500, and upon a length of wire of 768 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 191 
 
 miles, that the currents are propagated with the same velo- 
 city, whatever their intensity may be. 
 
 It was by means of Mr. Walker's astronomical observations 
 in America that he satisfied himself, as we have seen, that 
 the voltaic current requires an appreciable time for pro- 
 pagating itself in a long conductor. By employing the 
 current for the determination of the difference of longitude 
 between two stations, he proved that this propagation is 
 not instantaneous ; thus between Philadelphia and Cambridge, 
 calculation showed that the current, setting out from one 
 of these towns, at the moment of the passage of a star, 
 did not arrive at the other at the same instant, and that it 
 was necessary to take account of the time that had elapsed, 
 which in this instance was ~ of a second, for the determina- 
 tion of the difference of longitude. The comparison of 
 several observations made between the three stations of 
 Washington, Philadelphia and Cambridge, led Mr. Walker 
 to a velocity of 18,639 miles per second. Mr. Mitchell, of the 
 Observatory of Cincinnati, as the result of numerous trials 
 upon the telegraph line, extending from Cincinnati to Pitts- 
 burg, had found by the same method 28,331 miles per second. 
 Finally, the astronomers of the observatories of Edinburgh 
 and Greenwich obtained only 7600 ; and those of the ob- 
 servatories of Greenwich and Brussels only 2700, namely 
 a hundred times less than Mr. Wheatstone. We should 
 mention that, in this latter case, the copper wire for establish- 
 ing the communication between Greenwich and Brussels, was, 
 for a great part of the distance, submerged in the sea. 
 
 The following is a Table which, by summing up the deter- 
 minations, made according to the different methods, of the 
 velocity of the propagation of electricity, expresses clearly 
 the great differences, that exist in this respect between the 
 results obtained by the different observers. 
 
192 
 
 TRANSMISSION OP ELECTRICITY. 
 
 Names of the Observers. 
 
 Nature of the 
 Wire. 
 
 Velocity in Miles 
 per Second. 
 
 Wheatstone 
 
 Copper. 
 
 288,000 
 
 Fizeau and Gonelle 
 
 
 
 111,834 
 
 Idem 
 
 Iron. 
 
 62,130 
 
 Mitchell 
 
 
 
 28,331 
 
 Walker 
 
 
 
 18,639 
 
 Gould 
 
 
 
 15,830 
 
 Astronomers of Greenwich and Edin 
 
 
 
 burgh 
 Astronomers of Greenwich and Brussels. 
 
 Copper. 
 )> 
 
 7,600 
 2,700 
 
 It is to Faraday we are indebted for having found the 
 causes of these enormous differences, and for having shown 
 that the numerical results, contained in the above Table, 
 do not depend simply on the velocity of the propagation 
 of electricity ; but depend also upon a phenomenon of an 
 entirely different nature. In his first researches upon the 
 propagation of electricity in bad conducting bodies, Faraday 
 had already remarked, when speaking of Wheatstone's ex- 
 periment, that the velocity of the discharge may greatly 
 vary, according to the tension or intensity of the first im- 
 pulsive force. He even added that the retardation of the 
 mean spark, in relation to the extreme sparks, would pro- 
 bably become more sensible if the two extremities of the 
 wire, by which the discharge was transmitted, were in direct 
 communication with two large insulated metal surfaces ; 
 and especially if these two large surfaces were, one the inner 
 and the other the outer coating of a Ley den jar. Now, the 
 learned English philosopher has latterly confirmed the accu- 
 racy of his conjecture by means of direct experiments, made 
 with telegraphic wires covered with gutta percha, intended 
 for the establishment of submarine and subterranean lines. 
 Having procured two hundred coils of these wires, each 
 half a mile in length, he suspended them to a series of barges, 
 ranged in a canal, so that each coil was plunged entirely 
 in the water, with the exception of a, short length of wire 
 at each of the ends. He then connected end to end 
 the extremities of the wires of each coil, deprived of their 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 193 
 
 insulating envelope, so as to constitute a single wire of 200 
 miles in length ; and he connected one of the ends of this 
 long wire with one of the poles of a battery, placing in the 
 circuit a very sensitive galvanometer. The battery was 
 composed of 360 pairs of zinc and copper, charged with 
 acidulated water; it was perfectly insulated, and com- 
 municated with the ground only by its other pole. At 
 the moment, when communication was cut off between 
 the pile and the long wire, a very strong shock was felt, 
 on touching either end of the long wire ; this shock was 
 of such duration, that it might be decomposed, by touching the 
 wire for an instant only each time, into some forty successive 
 shocks. If, instead of touching one of the ends of the wire, 
 it was put into communication with one of the ends of the 
 galvanometer, the other end of which was connected with 
 the ground, the needle was powerfully deflected, and the 
 effect was still sensible, when the experiment was not made 
 till half an hour after the communication between the wire 
 and the pile had been interrupted. 
 
 It is evident that this result is due to the formation of a 
 Leyden jar of enormous size, by means of the long wire, 
 the envelope by which it is insulated, and the liquid con- 
 ductor, by which it is surrounded; which must consequently 
 be charged by a considerable quantity of electricity, when its 
 inner coating, which is the wire, is in communication with 
 a source of electricity, even when this electric source is of 
 feeble tension, as one of the poles of the pile.* In the expe- 
 riment we have mentioned, the copper wire being ^ in. in 
 diameter, and the coating of gutta percha -J- in. in thickness, 
 it follows that the inner coating of the Leyden jar, formed 
 by the long wire plunged in the water, presented a surface 
 of 8300 sq. ft. in extent, and the outer coating 33,000. 
 Moreover, the phenomenon is naturally more decided, in pro- 
 portion as the pile has greater tension, and is consequently 
 
 * Volta, immediately after the discovery of the pile, had shown that a Leyden 
 jar might be charged by putting its inner coating in communication with one 
 of the poles of the pile, the other pole being put in communication with the 
 ground. 
 
 VOL. II. O 
 
194 TBANSMISSION OF ELECTRICITY. PART iv. 
 
 composed of a greater number of pairs, the surface of the 
 pairs, on the contrary, being a matter of indifference. 
 
 It is very curious to see the galvanometer, that is in the 
 circuit, strongly deviated at the moment when one of the 
 ends of the long wire is put into communication with one of 
 the poles of the pile, even when the wire is insulated ; this 
 effect is evidently due to the passage of the electricity, by 
 which the inner coating of this kind of jar is charged. In 
 like manner, at the moment when communication with the 
 pile is cut off, a strong deviation is obtained in the contrary 
 direction, provided the end of the galvanometer, that is not in 
 communication with the end of the long wire, is in commu- 
 nication with the ground. This latter deviation manifests 
 the discharge, as the former indicated the charge. 
 
 The effects that we have been describing had already been 
 observed by Siemens by means of the subterranean telegraphic 
 wires, established in Prussia. He had noticed in these wires, 
 provided they were well insulated, the establishment of the in- 
 stantaneous currents of charge and discharge, that we have 
 been pointing out; the former taking place at the moment when 
 one of the extremities of the long wire was placed in commu- 
 nication with one of the poles of a pile; and the latter, at the 
 moment when this communication ceased, and when a con- 
 ductor, in communication with the ground, was substituted for 
 the pile. In analysing this phenomenon, M. Siemens had well 
 discerned the true cause ; he had recognised in the copper 
 wire the inner coating of a Ley den jar, of which the moist 
 ground was the outer coating, and the gutta percha coating, 
 the insulating layer. 
 
 To the facts that we have been stating, Faraday added 
 another that is still more curious, and which is, however, the 
 consequence of the same principle. He made use of four 
 subterranean wires, each of about 375 miles in length, which 
 are established between London and Manchester; at the 
 Manchester station, he connected together the ends of the 
 first and second wire, and those of the third and fourth. At 
 the London station, he placed one of the ends of the gal- 
 vanometer wire, in communication with the end of the first 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 1 95 
 
 wire ; the other end of the galvanometer being fixed to the 
 pole of a batter y, that had its other pole in communication with 
 the ground ; by the wire of a second galvanometer, he con- 
 nected the ends of the second and third wires ; and, finally, he 
 attached a third galvanometer, communicating also with the 
 ground, at the end of the fourth wire. At the moment when 
 this circuit was closed, the needle of the first galvanometer 
 was immediately deflected, that of the second was not so un- 
 til after a sensible interval, and that of the third a little later 
 still, about two seconds after that of the first. The com- 
 munication of the first galvanometer with the pile was inter- 
 rupted ; the needle of this galvanometer immediately returned 
 to zero; that of the second did not begin to displace itself 
 until a short time after ; and that of the third, later still. On 
 making and breaking this communication, at sufficiently near 
 intervals, we are able, so to speak, to produce in the wire 
 successive electrical waves, so that the three galvanometers 
 are traversed at the same instant by three different waves. 
 And if, after having suppressed the communication of 
 the first galvanometer with the pile, this galvanometer is 
 made to communicate with the earth, the electricity with 
 which the wire is charged, discharges itself simultaneously 
 by its two extremities ; so that the first and third galvano- 
 meters are deflected at the same time in opposite directions. 
 
 When, instead of subterranean wires, Faraday made use of 
 wires, freely suspended in the air, the effects were very little 
 marked ; all three galvanometers were deflected and returned 
 to rest almost at the same instant. In this case there was no 
 Ley den jar, for there was no outer coating, and consequently 
 no possible lateral induction. Thus, this induction, as we have 
 seen above, is able to retard by two seconds the propagation of 
 the electric wave in subterranean wires 1,500 miles in length; a 
 propagation, which is instantaneous in a wire of the same length, 
 insulated in the air. However, even when the wire is not 
 plunged in water, or placed in the moist ground, it may happen 
 that the proximity of the ground, when it is very near, or 
 the presence of neighbouring conductors, such as a conducting 
 
 o 2 
 
196 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 wall, may determine a lateral induction, much less powerful, 
 it is true, but still susceptible of retarding more or less the 
 propagation of electricity. It is to this circumstance, which 
 varies according to the arrangement of the telegraphic wires, 
 that may in a great measure be attributed the considerable 
 differences, that we have remarked in the results obtained 
 by different observers, on the velocity of the propagation of 
 electricity; differences so great that, in the above Table, 
 the first number is the centuple of the last. It is true that 
 the experiment, that had given this last result, was made 
 with a wire immersed in water, for the greater part of its 
 length ; while that which had furnished the first, was made 
 with wires stretched parallel and at a sufficient distance from 
 each other and from the ground, and connected alternately 
 end to end, so as to form but one continuous wire, bent 
 several times upon itself. However, in this case, there 
 was still a slight induction, brought about by the walls 
 and the floor of the room, in which the wires were stretched ; 
 perhaps also of the wires upon each other * ; which explains 
 the small retardation, experienced by the middle spark in 
 respect to the two extreme sparks. 
 
 It follows, therefore, from Faraday's labours, that the 
 experiments, by which the velocity of the propagation of 
 electricity had been supposed to have been measured, are 
 by no means conclusive. They were, in fact, founded upon 
 a false analogy which had been attempted to be made 
 between electricity and the radiating agents, as light and 
 heat. The propagation of electricity is of an entirely dif- 
 ferent nature; it evidently results from a modification, 
 impressed upon the ponderable matter, interposed between 
 the two electric principles; a modification, that may be 
 compared with that, experienced by a series of ivory 
 balls, which transmit the motion, that is received by 
 the first, or like an elastic body, that propagates sound; 
 which causes the velocity of the propagation necessarily 
 
 * The actual distance apart of these wires was, six inches ; and they might 
 consequently influence each other. 
 
CHAP. I. PROPAGATION OF ELECTRICITY. 197 
 
 to vary with the bodies, upon which it is exercised, and 
 with the circumstances under which they are placed, as 
 was observed by MM. Fizeau and Gonelle. It seems to 
 us that it must also vary, at least in the value that is 
 given to it, with the nature of the effects, by which the 
 electricity indicates its presence. It follows, of course, 
 that we are here speaking only of the rapid propagation 
 of electricity ; for slow propagation is a phenomenon of 
 quite another kind; and it is not with this that we are 
 now engaged. 
 
 Mr. Wheatstone has added some new facts to those which 
 had been observed by Faraday, taking advantage for this of a 
 cable, 110 miles in length, containing six copper wires -Jg- in. 
 in diameter, each covered with an insulating coat of gutta 
 percha of ^ in. The whole was covered with twelve strong 
 iron wires, wound spirally, which formed a metallic jacket of 
 J- in. in thickness. The cable was coiled into a spiral in a dry 
 pit in a yard, and one of its extremities extended into the in- 
 terior of a room. The ends of the six wires might be united 
 so as to cause the current to pass in the same direction 
 through the six wires, added end to end, or else through some 
 of them only. 
 
 The first experiments, made by Mr. Wheatstone, showed 
 him that the iron jacket of the compound conductor gave rise 
 to the same phenomena of induction, as Faraday had ob- 
 tained by plunging the insulated wire into water. Also, the 
 wire 660 miles in length was charged with positive or 
 negative electricity, on placing one of its extremities in 
 contact with the positive or negative pole of the pile, whilst 
 its other extremity was insulated ; but it was nevertheless 
 necessary that the other pole of the pile should be in 
 comu ainicatioii with the ground. However, if this pole 
 was placed in contact with the extremity of a second wire, 
 whose other extremity was insulated, the two wires were in 
 like manner charged. The movement of the galvanometers, 
 either during the charge, or during the discharge of the wires 
 was such as Faraday has indicated. The following experiment 
 
 o 3 
 
198 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 renders very evident the successive mode of the propagation 
 of electricity. 
 
 The two extremities of the 660 miles of wire being placed 
 in contact, each with one of the poles of the battery, when 
 one of the extremities previously detached was again at- 
 tached to the pole, the galvanometers placed at the extremities 
 of the wire, and consequently at equal distances from 
 the poles, were influenced immediately and simultaneously, 
 whilst those which were in the middle of the wire were not 
 set in motion until afterwards. When the circuit was inter- 
 rupted in the middle of the wire, on establishing contact, the 
 influence of the current was first felt on the central galvano- 
 meter, that is to say, on the most distant from the pile ; then 
 afterwards upon those which were towards the poles. 
 
 The following now is an experiment, which shows well that 
 the long wire acts as a considerable conductor, in which the 
 electricity is dispersed, similar in this respect to the terrestrial 
 globe, except that, with the wire, the size of the induction 
 being limited, the current ceases, as soon as the charge 
 is complete. One of the poles of the pile is placed in com- 
 munication with the ground, whilst the other is in contact 
 with one of the extremities of the wire, whose other extremity 
 is insulated ; increasing lengths are given to this wire, and a 
 sensitive galvanometer, placed between the pole and the wire, 
 gives induction of a current, stronger in proportion as the 
 length of the wire is greater, as is shown in the following 
 Table, which contains the deviations of the needle, corre- 
 sponding to the different lengths of the wire : 
 
 miles 
 
 110 6* 
 
 220 12 
 
 330 18 
 
 440 231 
 
 550 28 
 
 660 31 
 
 On placing the galvanometer at different distances from 
 the "pile, the wire having always the same length, it was 
 found that the deviation went on diminishing, setting out 
 
CHAP. i. PROPAGATION OF ELECTRICITY. 199 
 
 from the point, where it is immediately in contact with the 
 pole, to that in which it is at the very end of the 660 miles 
 of wire, being in this latter case null. The intensity of the 
 current appeared to depend solely upon the length of the 
 wire that is added to that extremity of the galvanometer, 
 which is not in communication with the pole, and to be 
 entirely independent of the length of that which separates 
 the other extremity of the galvanometer from the pole. This 
 result proves that, whatever be the length of the insulated 
 wire, connected with the pole of a pile, it is charged in its 
 whole length with the same degree of tension ; so that if 
 another insulated wire is added to its free extremity, the 
 latter presents the same phenomenon as if it had been placed 
 in immediate contact with the pole of the pile. From this, 
 therefore, we may conceive that when we place the extremity 
 of a galvanometer, whose other extremity is attached to one 
 of the poles of a pile, in communication with the terrestrial 
 globe, the latter may be considered as an indefinite conductor, 
 and then we obtain the maximum intensity, and an indefinite 
 duration of the current. 
 
 The researches of Mr. Faraday, and of Mr. Wheatstone, 
 show us, that the propagation of electricity is made, as it 
 were, by a series of waves, analogous to those by which sound 
 is propagated.* It is not, therefore, astonishing that the 
 velocity of the propagation varies with the bodies through 
 
 * The experiments of Mr. Latimer Clark, which we have given above (p. 190. ) 
 while they show that the velocity of the propagation of the current is the same, what- 
 ever the tension of the pile may be, furnish a very strong proof in favour of the 
 analogy that we admit between the mode of propagation of electricity, and that of 
 sounds, which are propagated in the same medium with the same velocity, even 
 when they are more or less sharp, or more or less intense. This had been 
 remarked by M. Melloni, at whose request Mr. Latimer Clark had undertaken the 
 important experiment, of which we have made knownthe results. The learned 
 Italian philosopher had also observed, that the retardation in the velocity of the 
 current, experienced in subterranean wires, by the effect of lateral induction, 
 must be the same, and that consequently the absolute velocity must also be the 
 same, whatever may be the tension of the pile ; and this because the portion of 
 electricity that is diverted upon the side of the coating of the wire, by the 
 effect of the induction (which produces the retardation) being retained there 
 by a force arising from this electricity itself, it must necessarily vary in propor- 
 tion to its intensity, and consequently produce a retardation, that is always the 
 same. 
 
 o 4 
 
200 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 which it takes place, as has been observed by MM. Fizeau 
 and Gonelle.* 
 
 We shall not terminate this subject, without remarking 
 the still more intimate connection that the new experiments, 
 of which we have been speaking, contribute in establishing 
 between static and dynamic electricity. We have long 
 known, thanks to the researches of Mr. Colladon, that a 
 current may be produced, capable of acting upon the galvano- 
 meter, on drawing off by a point the static electricity 
 accumulated upon an insulated conductor. We now see the 
 converse, namely, that on introducing a current into an 
 insulated conductor, it may be charged with static electricity. 
 The dynamic state, like the static state, are therefore merely 
 two forms, variable with the arrangement of the apparatus 
 and of the experiments, under which one and the same agent 
 is presented. 
 
 * More recent experiments, made by MM. Guillemin and Burnouf, on the 
 velocity of the transmission of electricity in telegraph wires, have given for the 
 velocity in an iron wire 111,847 miles per second, a velocity a little more con- 
 siderable than that found also for iron by MM. Fizeau and Gonelle. MM. 
 Guillemin and Burnouf operated between Foix and Thoulouse on a line formed 
 by two parallel iron wires '15 in. in diameter, and 51 miles in length, which 
 made, enjoining them end to end, a total length of 102 miles. Their process 
 consisted in placing one of the ends of the wire in contact with one of the poles 
 of a pile, whose other pole communicated with the ground, whilst the other end 
 of the same wire was in contact with one of the extremities of a galvanometer 
 whose other extremity communicated with the ground. Toothed wheels esta- 
 blished and interrupted, a greater or less number of times per second, the con- 
 tact of the two ends of the wire respectively with the pole of the pile and the 
 galvanometer ; the contacts and non-contacts were simultaneous at both these 
 ends. If the propagation of the current was instantaneous, its "transmission 
 should always have taken place ; but if it required a certain time for traversing 
 102 miles, we are able by turning- the wheels with a continually increasing 
 rapidity, to obtain a velocity such, that the current, that sets out from the pole 
 at the moment in which the contact takes place, does not arrive at the galvano- 
 meter at the other end until the moment when this contact no longer takes place, 
 the galvanometer is then no longer affected, and the interval of time that has 
 passed between the instant of contact and that of non-contact is that, which the 
 current has employed for traversing the wire 102 jniles in length. MM. 
 Guillemin and Burnouf employed four toothed wheels instead of two, two of 
 these four being necessary for discharging the wire at its two ends, in the in- 
 terval of the two successive contacts with the pole of the pile, and acting 
 alternately with .the two former, by causing the two extremities of the wire to 
 communicate with the ground. We should further remark, that we never 
 succeed in having an entirely null deviation in the galvanometer ; but merely a 
 minimum deviation, which is due to an effect of L induction, arising from the 
 proximity of the two wires, whose union forms the total circuit ; but this cir- 
 cumstance changes nothing in the results, providing care is taken to observe 
 the velocity i>f the toothed wheels, that corresponds to the minimum deviation. 
 
CHAP. ii. PROPAGATION OF ELECTRICITY. 201 
 
 In terminating this paragraph and this Chapter, we cannot 
 retrain from remarking by anticipation, in order to justify 
 the extent \ve have given to it, how much the general and at 
 the same time the detailed study, that we have made of 
 the propagation of electricity, will facilitate what we are 
 about to advance of the phenomena, to which this propagation 
 gives rise.* 
 
 * List of the principal works relating to the subjects treated upon in this 
 Chapter. 
 
 De la Hive. Distribution and laws of the propagation of dynamic electricity. 
 Memoire de la Soc. de Phys. et d'Hist. Nat. de Geneve, t. iii. p. 109. Annales 
 de Ch. et de Phys. t. xxviii. p. 190. Influence of heat upon electric conducti- 
 bility. Bill. univ. t. vii. p. 388. 
 
 Kirchoff. Laws of distribution in a metal plate. Annales de Ch. et de 
 Phys. (new series), t. xl. pp. 115. and 327.; t. xli. p. 496. 
 
 Fechner. Experimental laws of the intensity of currents, in a closed circuit. 
 1 vol. in 4to. Leipsic, 1831. 
 
 Pouillet. Idem. Comptes rendus de f Academic des Sciences de Paris, t. vi. 
 ( 1 837 ) p. 267. TraiU de Physique. 
 
 Wheatstone. Rheostat and electrical instruments. Annales de Ch. et de 
 Phys. ("new series) t. x. p. 257. Velocity of electricity. Philosophical Trans- 
 actions of the Royal Society of London (1836) part ii. p. 583. ; and Archives 
 de rElectricite, t. ii. p. 35. 
 
 Jacobi. Standard of resistance. Comptes rendus de I' Academic des Sciences 
 de Paris, t. xxxiii. (1851) p. 280. 
 
 Matteucci. Propagation of dynamic electricity in liquids. Annales de 
 Chim. et de Phys. t. Ixiii. p. 256.; and t. Ixvi. p. 22 5. Conductibility. Annales 
 de Ch. et de Phys. (new series) t. xv. p. 498. Propagation in bad conductors. 
 Annales de Ch. et de Phys. (new series) t. xxvii. p. 133.; and t. xxviii. p. 385. 
 
 Marianini. Propagation in liquids. Annales de Ch. et de Phys. t. xxxiii. 
 p. 141.; and t. xlii. p. 131? 
 
 Ohm. Laws of the propagation of currents. Archives de FElectricite, t. i. 
 p. 30. 
 
 Kohlrausch. Mode of propagation of the current. Arch, des Sciences phys. 
 t. xxii. p. 105. 
 
 E. Bccquerel. Conductibility of solids and liquids. Annales de Ch. et de 
 Phys. (new series) t. xvii. p. 262.; and t. xx. p. 53. Conductibility of gases. 
 Idem. t. xxxix. p. 355. 
 
 Lenz. Conductibility of certain bodies. Bibl. Univ. (1838) t. xvii. p. 38. 
 Idem. Conductibility at different temperatures. Annales de Ch. et de Phys. 
 t. xxxix. p. 355. 
 
 Wartmann. Conductibility of mineral substances. Memoire de la Soc. de 
 Phys. 'et d'Hist. Nat. de Geneve, t. xxiii. (1st part). Arch, des Sciences phys. 
 t. xxii. p. 84. 
 
 Hanke'l. Influence of heat on the Conductibility of liquids. Arch, des 
 Sciences phys. t. vi. p. 66. 
 
 Riess. Electric Conductibility of certain solid bodies, and of non-conducting 
 bodies. Arch, de F Electric ite, t. Ii. pp. 91. and 177. Explosive distance. Idem. 
 t. i. pp. 206. and 425. Electric images. Arch, des Sciences phys. t. i. p. 425. 
 
 Vorsellmann de Heer. Influence of heat on electrodes. Arch, de F Electricite", 
 t. i. p. 589. 
 
 Beetz. Same subject. Arch, des Sc. phys. t. xiii. p. 282. 
 
202 TRANSMISSION OF ELECTRICITY, PART iv. 
 
 Karsten. Conductibility of sulphurets. Arch, des Sc. phys. t. v. p. 350.- 
 Electric figures. Arch, de FElectricite, t. iii. p. 310.; and t. iv.'p. 457. 
 
 Rousseau. Apparatus for imperfect conductivity. Annales de Ch. et de Phys. 
 t. xxv. p. 393. 
 
 Wiedemann. Conductibility of crystals. Arch, des Sc. phys. t. xxii. p. 44." 
 
 De Senarmont. Same subject. Annales de Ch. et de Phys. (new series) t. 
 xxviii. p 257. 
 
 Knoblauch. Direction of crystals between two electric poles. Annales des 
 Sc. phys. t. xix. p. 214. 
 
 Ermann, Unipolar conductors. Ann. de Ch. t. Ixi. p. 113.; and Annales de 
 Ch. et de Phys. t. xxv. p. 298. 
 
 Peltier. Vaporization favoured by electricity. Annales de Ch. et de Phys. 
 t. Ixxv. p. 330. Molecular modifications of conductors. Comptes rendus de 
 V Academic des Sciences, t. xx. (1845) p. 62.; and Arch, des Sc. phys t. v. 
 p. 182. 
 
 Andrews. Conductibility of Flames. Bibl. Univ. t. vi. (1836) p. 158. 
 
 Belli. -- Difference between the velocity of the dispersion of the two electri- 
 cities. Bibl Univ. t. xxiii. (1838) p. 196. 
 
 Morgan. Conductibility of vacuum and propagation in imperfect con- 
 ductors. Bibl. Brit. t. ii. p. 119.; and t. xii. p. 3. 
 
 Yarn's. Electric influence of rarefied air. Bibl. Univ. t. xvii. (1838) p. 
 195. ; and Philosophical Transactions (1834) part ii.) p. 203. 
 
 Davy. Conductibility of vacuum. Annales de Ch. et de Phys., t. xx. p. 
 168. 
 
 Fusinieri. Transport of solid substances by discharges. Archives de I'Elec- 
 tricite, t. iii. p. 597.; and t. v. p. 516. 
 
 Moser. Images. Comptes rendus de I'Acad. des Sciences, t. xv. (1842) pp. 
 119.448. 855. and 1201. 
 
 Knorr. Electric images. Arch de T Electricite, t. v. p. 115. 
 
 Hunt. Same subject. Idem. t. v. p. 5. 
 
 Morren. Same subject. Comptes rendus de I'Acad. des Sc. t. xvi. pp. 1078. 
 and 1303. ; and t. xvii. p. 87. 
 
 Masson. Same subject. Idem. t. xvi. pp. 762. and 1652.; and Arch, de 
 V Electricite, t. iii. p. 445. 
 
 Walker and Gould. Velocity of electricity. Ann. des Sc. Phys. t. xix. 
 p. 303. 
 
 Fizeau and Gonelle. Same subject. Comptes rertdus de I'Acad. des Sc. t. 
 xxx. p. 137.; and Arch, des Sc. phys. t xiv. p. 212. 
 
 Faraday. Electric conductivity, discharges, &c. " Collection of Memoirs 
 extracted from the Phil. Trans, from 1832 to 1838. in 1 vol. 8vo. Induction 
 exercised by propagation in long wires. Arch, des Sc. phys. t. xxv. p. 209. 
 
 Becquerel, sen. Conductibility. Ann. de Ch. et de Phys. t. xxxii. p. 420. 
 Traite de VElectricite. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 203 
 
 CHAP. II. 
 
 CALORIFIC AND LUMINOUS EFFECTS OF DYNAMIC 
 ELECTRICITY. 
 
 Forms and Conditions under which Heat and Light are produced 
 by Dynamic Electricity. 
 
 WE have already made mention of the property, possessed 
 by electricity in motion, of giving rise, during its trans- 
 mission, to heat and light. We have even described calorific 
 voltameters, founded upon the heat, that is developed by the 
 electric current, while traversing a fine wire.* We have 
 already explained some of the phenomena of heat and light, 
 that are produced by electric discharges, under the form 
 of sparks or of incandescence, and of the fusion of metals. f 
 We are now called upon to study more closely this class 
 of facts, to examine their details, and to search out their 
 laws. 
 
 The heat and light that accompany the reunion of the two 
 electricities, or the condition that we have designated by 
 the name of dynamic electricity, present themselves under 
 very various forms. The most simple and most direct is the 
 elevation of temperature that results in a conductor, from the 
 passage of dynamic electricity, either continuous as a current, 
 or instantaneous as a discharge. This elevation of temperature 
 is the more considerable for the same conductor in proportion 
 as this conductor has less dimensions, and consequently as 
 it presents greater resistance to the transmission of electricity, 
 and a less volume to the action of the liberated heat. It 
 also varies with the nature of the conductors ; but it occurs 
 in all, as well in liquids as in solids, only in different degrees, 
 according to their nature and their dimensions. 
 
 * Vol. L p. 32. and following pages. 
 f Vol. I. p. 119. and following pages. 
 
204 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 A second form, under which electric heat and light are 
 manifested, is that which has been designated under the 
 name of electric spark and voltaic arc. It differs from the 
 former at the very outset, inasmuch as it always of 
 necessity gives rise at once to light and heat; whilst the 
 former produces obscure heat, and does not develope light 
 until the heat becomes sufficiently intense to render the 
 conductor incandescent. The latter form differs further 
 from the former, inasmuch as the luminous and calorific 
 phenomena are manifested by the passage of dynamic 
 electricity, not through a continuous conductor, but between 
 two conductors, charged with the contrary electricities, 
 placed at a greater or less distance from each other, and 
 separated by an insulating medium or a bad conductor, such 
 as vacuum, an elastic fluid, or a liquid. The spark differs 
 from the voltaic arc, with which in other respects it has 
 many relations, in that it is the result of the instantaneous 
 reunion of the two electricities ; whilst the arc is produced 
 by their continuous reunion ; so that the arc may be regarded 
 as composed of a series of sparks, succeeding each other 
 very rapidly. The spark is generally produced by the 
 discharges of electrical machines and Leyden jars, in the 
 phenomenon, that we have called explosion ; whilst the 
 arc is manifested between two conductors, communicating 
 each with one of the poles of a voltaic pile. However, the 
 real identity that exists, notwithstanding the difference in 
 appearance, between the spark and the arc, may be easily 
 proved by employing, for their production, inductive currents, 
 which are equally suitable for the manifestation of them 
 both. A character common equally to the spark and the 
 arc, is the transport of ponderable matters, which is always 
 the companion of their manifestation. 
 
 Under whichever of the two forms the liberation of the 
 light and heat produced by electricity is manifested, there 
 exists, for one as well as for the other, one condition neces- 
 sary to their manifestation : it is that dynamic electricity, 
 in its transmission, meets with a resistance, and that it is 
 in the points of a given circuit, where this resistance is the 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 205 
 
 greatest, that the heat and light are most intense. This first 
 condition leads to a second : it is that the electrical ap- 
 paratus may liberate electricities, endowed with a tension 
 sufficient to overcome the resistance of the medium, through 
 which their reunion is to be brought about. 
 
 In the examination that we are about to make of the 
 phenomena, which we have been merely pointing out, we 
 shall then commence with those that are manifested under the 
 former form : namely, in the case in which the propagation 
 of electricity occurs through a continuous conductor ; we 
 shall then pass on to those, that occur when the conductor is 
 interrupted (electric spark and voltaic arc); we shall then 
 terminate this Chapter, by a more special study of the electric 
 light and its properties. 
 
 Calorific Effects, produced by the Passage of Dynamic Elec- 
 tricity through good Conductors. 
 
 It was not until after science had been put in possession of 
 the Ley den jar, that the effect could be studied of the heat 
 produced by electric discharges through good conductors. 
 Franklin, by these discharges, succeeded in melting thin 
 leaves of metal ; Beccaria and especially Priestley, succeeded 
 in the same manner in making wires incandescent, and even 
 in melting them. Priestley had even made a very important 
 observation, the accuracy of which was confirmed by all 
 subsequent experiments ; namely, that if the discharge of a 
 powerful battery is passed through two successive wires, 
 connected with each other end to end, of the same length 
 and the same diameter, but of a different nature, only one of 
 them is melted and dispersed, and this is always the one, 
 that is the worst conductor of the two. Thus, of two wires, 
 the one of iron and the other of copper, it is the iron, that is 
 totally dispersed by the explosion, whilst the copper remains 
 intact ; of two wires, the one of copper, the other of silver, it 
 is the copper, that is dispersed ; and it is the silver, when the 
 second wire is of gold, instead of copper. 
 
 Cuthberson, when operating in the air upon wires of 
 
206 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 different metals 10^ in. in length, and with a battery, whose 
 inner coatings presented a surface of about 32 square feet, had 
 obtained the following results : 
 
 Name of the Metals. 
 
 Diameter of the 
 Wires.* 
 
 Charge in Grains of 
 the Electrometer. 
 
 Colours of the Metal Dust 
 collected. 
 
 Lead wire 
 
 A 
 
 20 
 
 Rather deep grey. 
 
 Tin - 
 
 T& 
 
 30 
 
 Almost white. 
 
 Zinc - 
 
 A 
 
 45 
 
 55 55 
 
 Iron 
 
 ifc 
 
 35 
 
 Reddish brown. 
 
 Copper 
 
 Tier 
 
 35 
 
 Brown, tending to 
 purple. 
 
 Platinum 
 
 lio 
 
 35 
 
 Black. 
 
 Silver 
 
 Tib 
 
 48 
 
 5> 
 
 Gold 
 
 Tin 
 
 40 
 
 Brownish purple. 
 
 * The diameters are estimated in fractions of English inches. 
 
 By measuring, on the one hand, the charge of the battery, 
 by means of an electrometer*, and, on the other hand, the 
 calorific action produced by the discharge, taking as a unit 
 of measure the length of iron wire of a given diameter melted, 
 Cuthberson found that the calorific action was almost pro- 
 portional to the square of the charge of the battery for certain 
 lengths of wires ; this law, which was merely glanced at by 
 Cuthberson, who had only very imperfect means of observa- 
 tion, was rigorously established by Riess, as we shall see, 
 presently, not for fusion, but even for the heating of wires. 
 
 With the great machine at the Teyler museum at Harlaem, 
 Van Marum succeeded in melting an iron wire 52 ft. in 
 length ; and, by operating with wires of a different nature, 
 but of the same diameters, he had found that the length he was 
 able to melt with the same charge was greatest for lead, then 
 for tin, iron, gold, &c. When the experiments take place in 
 the air, the wires are not only heated and melted, but are 
 also burned, if they are of an oxidisable metal. Priestley had 
 already made the remark, although he had not at that time 
 
 * The weight-electrometer, employed by Cuthberson, is similar to the dis- 
 charging electrometer, by the same philosopher (Vol. I. p. 1 18.), in which a 
 small travelling weight may be placed at different distances from the axis of the 
 apparatus, along one of the stems, which is divided so as to determine the 
 discharge, only when a certain intensity of electricity is attained. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 207 
 
 just notions of combustion ; he had in particular observed that 
 when iron wire is melted by the electric explosion, brilliant 
 sparks are dispersed around the room in all sorts of directions, 
 which is a sign of combustion. With steel wires, when the 
 charge of the battery is not sufficient to melt them, their 
 surface is seen to be covered with various colours, correspond- 
 ing with the degrees of oxidation, they have undergone. 
 Platinum and gold do not oxidise; but are simply melted 
 and volatilised. In nitrogen, or in hydrogen, the other 
 metals, by the effect of a discharge that disperses them, are 
 simply reduced into a fine powder, not oxidised. 
 
 All the experiments, that we have been quoting, are made 
 by means of the dischargers described Vol. I. p. 118. ; and in 
 globes, furnished with copper rods, which served to transmit 
 the discharge to the wires, when the experiments were made 
 in other media, than in ordinary air. 
 
 Very quickly after the discovery of the voltaic pile, it was 
 observed that the passage of the electric current through wires 
 was able, as well as the transmissior of discharges, to heat 
 them, to render them incandescent and to melt them ; and that 
 very intense phenomena of deflagration were obtained, in the 
 same manner, with very thin sheets of metal, such as gold 
 leaf. Cuthberson pointed out several important differences, 
 between the effect of the current and that of discharges. 
 Thus, besides the duration of ignition, that occurs in the former 
 case and not in the latter, there is a further difference between 
 the two modes, namely, that with charges there is produced 
 an explosion, that disperses the wires and reduces them into 
 powder, whilst nothing similar occurs with the current. 
 
 Foureroy, Vanquelin, and Thenard were the first to remark 
 that voltaic piles with large surfaces, although they have no 
 greater tension for a given number of pairs, than have those 
 with small surfaces, developed much more heat than the latter, 
 in wires placed between their poles. Davy, on his part, found 
 that, with a pile having large plates, water could immedi 
 ately be raised to a state of ebullition by plunging into it an 
 iron wire, two feet long, and ^ in. in diameter, placed 
 between the poles of this pile. The wire itself was able 
 
208 
 
 TRANSMISSION OF ELECTRICITY. 
 
 to become red-white for a length of three or four inches. He 
 had previously been the first to succeed in making red-hot 
 and burning steel wires, thin leaves of tin, zinc, copper, 
 silver, and gold. Each of these metals in burning gives forth 
 a flame of a different colour, accompanied by a species of cre- 
 pitation, and a remarkable kind of hissing. Zinc gives a blue 
 flame; tin, a purple; lead, a yellow with a violet border; 
 copper, a green accompanied with vivid sparks ; silver, white 
 in the centre, and green at the edges ; gold, a brilliant yellow. 
 All these metals oxidise in this deflagration ; gold, in parti- 
 cular, passes into the state of brown oxide. Platinum alone, 
 reduced into leaves as thin as possible, attains to white-red, 
 melts, scintillates at its edges, but does not pass into the state 
 of oxide. 
 
 In order to make these experiments 
 conveniently, it is necessary to have a 
 small ladder, composed of two small 
 vertical metal rods, fixed on a wooden 
 base, and connected by thick brass wires, 
 situated parallel and one above the 
 other, at a distance of three or four 
 inches (fig. 191.). Leaves of metal are 
 suspended to ladders of this kind, so that 
 the leaves of the same nature are sus- 
 Fig. 191. pended to the same wire ; then, after 
 
 having put the metal ladder in communication with one of the 
 poles of the pile, the other is connected with a brass ball, or 
 what is still better, with one of platinum, fixed at the end of a 
 handle of wood or glass. The ball is then made to touch 
 successively each of the thin leaves, and its deflagration and 
 combustion is brought about by thus placing it in the voltaic 
 circuit. In this manner, the phenomena of each metal leaf 
 may be very well studied separately. 
 
 Children subsequently observed, on a large scale, and in 
 a detailed manner, the calorific effects of dynamic electricity 
 in good conductors. This philosopher made use of a battery, 
 of 25 pairs of copper and zinc, each plate of which pre- 
 sented a surface of 62 square feet, and charged with acidu- 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 209 
 
 lated water. He commenced by interposing between 
 the poles of this pile wires associated in pairs, so as to form 
 a single conductor, composed of two lengths of wire of dif- 
 ferent natures, but of the same length and the same diameter ; 
 the worst conductor became heated, and even red, whilst 
 the other remained cold ; thus, on forming a metal chain of 
 three wires of platinum, and three of silver alternately, all 
 the platinum wires were seen to become incandescent, whilst 
 those of silver were not so. This result is similar to that, 
 which Priestley had obtained, when employing discharges in 
 place of currents. Another experiment of Children's, which 
 was suggested to him by Wollaston, consists in placing 
 parallel to each other, in the circuit, two platinum wires 
 of the same length ; but one of them being -Jj in. in dia- 
 meter, and the other only ^ in. ; the thickest of the two 
 wires is seen to become red, whilst when the two wires are 
 united, one following the other, it is the reverse, namely, the 
 finer wire that becomes red. In the latter case, as they 
 form part of the same circuit, it is not astonishing that the 
 finer, which presents the greater resistance to the current, 
 becomes the more heated ; with regard to the former case, 
 the larger, transmitting the greater proportion of electri- 
 city, and having a cooling surface in proportion to its 
 volume, less than that of the finer wire, is the one that 
 should acquire the more elevated temperature. Children, by 
 means of his powerful apparatus, had succeeded in raising to 
 incandescence and even to fusion very large and tolerably 
 long platinum wires ; one of them was in. in diameter, 
 and 2f feet in length ; but all these effects have since been 
 obtained on a very much larger scale by Grove's and 
 Bunsen's battery. 
 
 The most convenient apparatus for producing the different 
 phenomena of the incandescence of wires, that we have been 
 describing, consists (jig. 192.), of two brass rods, fixed upon 
 a small table, and each placed in communication, by a bind- 
 ing screw, one with the positive, the other with the negative 
 pole of the pile. One of the rods carries binding screws, 
 in which are affixed, by one of their ends, the various 
 
 VOL. II. P 
 
210 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 wires that are proposed to be placed in this circuit ; the other 
 end of each of these wires is wound round a metal peg, 
 
 which is itself fixed in a hole 
 pierced in the second rod at the 
 same height as the correspond- 
 ing binding screw of the first rod, 
 so that the wire, when stretched, 
 should be perfectly horizontal. 
 Now, in order to prevent the 
 w ires being all at the same time 
 in the circuit, below each of the 
 holes of the second column, a 
 second similar hole is found, but 
 coated interiorily with an insu- 
 lating layer of wax, glass, or ivory. Into these holes the plugs 
 are inserted, to which are attached the wires, that are not re- 
 quired to be placed in the circuit, leaving that, or those, that 
 are required to be heated by the passage of the current, in 
 the metal holes. In this manner, we are able to see succes- 
 sively the effect of the transmission of the same current in 
 all the various wires, some homogeneous, others composed 
 of pieces, alternately of one kind and of another, some 
 larger, others finer; or to study this same effect simulta- 
 neously upon two wires placed parallel in the circuit ; for 
 example, a fine and a large platinum wire, two wires of 
 the same diameter and length, one of platinum, and the other 
 of silver. 
 
 Whilst Children was observing on so large a scale the 
 phenomena of voltaic ignition, Wollaston succeeded in 
 heating to redness a very fine platinum wire ^Joo m> * n 
 diameter*, by means of a single small pair of zinc and copper 
 of 1 sq. in. of surface. 
 
 * It is known that Wollaston procured these very fine wires, by placing a 
 fine platinum wire in the axis of a cylinder of silver, and drawing the cylinder 
 through a draw plate into as fine a wire as possible. One end of it is then 
 taken and bent into the form of a U ; the wire, with the exception of its two 
 extremities, is then plunged for a few minutes into nitric acid ; the silver dis- 
 solves, and there only remains the platinum of extreme fineness. The ends of 
 this wire, which have retained their silver envelope, serve for rendering it 
 sensible to the eye and the touch. 
 
CHAP. ir. EFFECTS OF DYNAMIC ELECTRICITY. 211 
 
 Metals and solid conducting bodies are not the only bodies 
 that are heated by the effect of the passage of the electric 
 current. Liquids also experience a considerable elevation of 
 temperature ; Davy had already proved this, in his experi- 
 ments on the decomposition of water and of saline solutions, by 
 dynamic electricity. Having placed in the circuit of a battery 
 of a hundred pairs having small surfaces, two cones of gold, 
 filled with distilled water and connected by a skein of asbestos, 
 he placed a thermometer in each of the cones; he then 
 added to the water of the positive cone a drop of solution of 
 sulphate of potass; decomposition commenced, and was 
 followed by an elevation of temperature, which became 
 sufficient in two or three minutes to cause the water to 
 enter into a state of ebullition. With a solution of nitrate of 
 ammonia, the liberated heat rose so high, that it entirely 
 evaporated the water in three or four minutes. Oersted 
 subsequently observed, that in a column of water, traversed 
 by the current, the elevation of temperature is more con- 
 siderable at the positive pole (36. 9) than at the negative 
 (32.4), but that it is greatest (41.4 F.) in the middle. I 
 arrived at the same result as Oersted; but I, at the same 
 time, had observed that the development of heat in the interior 
 of a liquid mass, placed between the two poles of a pile, may 
 be considerably augmented by dividing it into several com- 
 partments, by porous diaphragms made of bladder or gold- 
 beater's skin. It is found that the temperature is higher in 
 the middle compartments than in those of the extremities,- and 
 that in each compartment it is about 4 higher in the 
 portion of the liquid in contact with the diaphragm of bladder 
 than in the rest. If the same current is made to pass suc- 
 cessively through a continuous liquid in a glass tube of a 
 certain diameter, and a certain length, and through a skein 
 of cotton of the same length and diameter as the tube, the 
 temperature of the liquid contained in the tube, is seen to 
 remain stationary, whilst that in the skein of cotton rises 
 considerably, which is due to the cells of cotton, wherein 
 the liquid is lodged, forming so many small compart- 
 ments, separated from each other by diaphragms, which 
 
 p 2 
 
212 TRANSMISSION OF ELECTRICITY. PAKT iv. 
 
 the electricity is obliged to traverse. For the same reason 
 stalk of a fleshy plant, which is a liquid conductor separated 
 into a multitude of small cells by non-metallic diaphragms, 
 becomes heated until the water it contains enters into a state 
 of ebullition when, by means of two platinum points, it is 
 placed in the circuit of a rather strong pile. Liquids are 
 at all times placed in the voltaic circuit by means of wires or 
 small plates of platinum, in order not to complicate the 
 results by the chemical action exerted upon the surfaces of 
 the electrodes, by the solutions, in which they are immersed. 
 
 Different liquids, placed in the route of the same current, 
 present the same phenomena as metal conductors : namely, 
 those which conduct least are heated most. By arranging in 
 the same voltaic circuit, one after the other, several similar 
 capsules, each filled with an equal quantity of water, or of 
 different saline and acid solutions, connected two and two, by 
 arcs of platinum, it is seen that the one in which pure water 
 is contained, becomes heated 18 or 20 above the temperature 
 of the surrounding air, whilst the others are scarcely heated. 
 If the capsule filled with water is removed, the cell, among 
 those that remain, which contains the worst conducting liquid, 
 is always the one that becomes most heated. 
 
 All these experiments appear to point out in a decided 
 manner that in liquids as in solids, the development of heat, 
 produced by the passage of the electric current, arises from 
 the resistance experienced by this current ; since, wherever 
 this resistance is greatest, there also is the elevation of tem- 
 perature more considerable. This general law finds its 
 further confirmation in several facts of another nature, that 
 I have had the opportunity of observing, and to the most 
 important of which I shall confine myself to relating. 
 
 The heat developed in equal quantities of similar con- 
 ducting liquids, traversed successively by the same current, is 
 more considerable in proportion as the electrodes present, both 
 by their dimensions and their nature, greater resistance to 
 the current, their distances remaining the same. By employ- 
 ing, instead of continuous currents, currents rendered dis- 
 continuous by means of a rheotome or a commutator placed 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 213 
 
 in the circuit*, a less elevated temperature is obtained in 
 the liquid into which the discontinuous currents are guided 
 alternately in contrary directions, than in that in which 
 they are constantly guided in the same direction; but, as 
 we shall see, in the Chapter upon electro-chemical decompo- 
 sitions, the transmission of electricity experiences much less 
 resistance in the former case than in the latter. In order to 
 make this experiment, we place consecutively two perfectly 
 similar systems of liquid conductors, which are united and 
 placed in the circuit by small plates of platinum ; then, 
 in the same circuit, we also place a fine platinum wire plunged 
 into a given quantity of water, in which is placed the bulb of 
 a sensitive thermometer. The same quantity of electricity f 
 is made to pass in this succession of conductors, for the same 
 time ; and it is found that the sum of the quantities of heat, 
 developed in the two liquid systems and in the platinum wire, 
 is sensibly the same, whether the current be continuous or 
 be discontinuous, and guided constantly in the same direction 
 in the two systems ; or finally, if it be discontinuous 
 and guided in one of the systems, always in the same 
 direction, and in the other alternately in contrary directions. 
 Only in this case, the first system is heated more than the 
 second, as we have said, and there is also more heat developed 
 in the platinum wire. 
 
 It is very curious to see the liquid system, in which, 
 the current always travelling in the same direction, there 
 is a liberation of gas, become more heated than that wherein, 
 on account of the alternately contrary direction of the 
 current, there is no gas.J This result would appear to 
 
 * For the description of these apparatus, see Vol. I. p. 300. fig. 130.; and 
 p. 398-9. fig. 153. 
 
 f That the same quantity of electricity has passed in each case, is made 
 certain by placing in the circuit, but so that the discontinuous current always 
 traverses it in the same direction, a chemical voltameter (Vol. I. p. 33.), and by 
 stopping the experiment when the same volume of gas has been liberated. 
 
 J The absence of the production of gas is only apparent. It is due to the 
 oxygen and hydrogen, which arise from the decomposition of the water, suc- 
 ceeding each other very rapidly on the surface of the same electrodes, on 
 account of the alternately contrary directions of the currents ; and there is a 
 recomposition of the water, at the same time as a decomposition. 
 
 p 3 
 
214 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 indicate that the formation of the gases does not diminish 
 the quantity of heat liberated in a liquid by the current, 
 which would depend only upon the resistance, that is ex- 
 perienced by the electricity. However, we have seen 
 that in water, decomposed by the electro-chemical process, 
 the elevation of temperature is less at the two poles, at 
 which the two gases, oxygen and hydrogen are liberated, 
 than it is between them; and that at the negative pole, 
 where the liberation of gas (hydrogen) is greatest, it is 
 most feeble. These differences would seem to demons- 
 trate well that the formation of the gases is not without 
 some influence ; the more so as, when the column of water 
 is traversed by discontinuous currents, guided alternately 
 in contrary directions, a case in which this formation does 
 not occur, all these differences disappear and the distribution 
 of temperature in the liquid becomes perfectly uniform. 
 We shall return to this important point, when we shall have 
 studied the chemical effects of dynamic electricity. 
 
 After this rapid review of the principal results, obtained 
 by the philosophers who have turned their attention to the 
 calorific effects, brought about by dynamic electricity in 
 its passage through good conductors, it remains for us 
 to discuss the more precise laws which vigorous researches 
 have enabled us to establish. 
 
 Laws ivJiich regulate the Calorific Effects of Discharges in good 
 
 Conductors. 
 
 In order to study more closely the calorific effects of 
 discharges, Harris and Riess both employed the air- 
 thermometer, the bulb of which is traversed by a wire, 
 which, in transmitting the discharge, is heated it to a quantity 
 that is measured by the movement of the thermometric 
 index. This apparatus, which we have described in the 
 first part of the work *, in order to be able to furnish exact 
 and comparable results, requires much care in its construc- 
 
 * Vol. I. p. 33. fig. 20. 
 
CHAP. ir. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 215 
 
 tion ; and it is probably to the imperfection of the one 
 employed by Harris, that we must attribute the inaccuracy 
 of some of the conclusions, that he deduced from his ex- 
 periments. Harris, indeed, had thought he was able to es- 
 tablish that the calorific effects of an electric discharge, 
 brought about through wires, depended only upon the 
 quantity of electricity, and that consequently it is the same 
 whatever be the tension of the electricity in the battery, 
 provided the total quantity remains the same ; a law which, 
 as Riess has demonstrated, is not accurate. On the other 
 hand, Harris succeeded in measuring very accurately the 
 relation that exists between the quantity of heat, liberated 
 by a wire and its electric resistance, by the effect of the 
 transmission of the same quantity of electricity. The 
 following is the Table that he gave of these relations : 
 
 Metals. 
 
 Heating. 
 
 Resistance. 
 
 Silver 
 
 6 
 
 1 
 
 Copper 
 Gold - 
 
 6 
 9 
 
 1 
 
 H 
 
 Zinc - 
 
 18 
 
 3 
 
 Platinum - 
 
 30 
 
 5 
 
 Iron - 
 
 30 
 
 5 
 
 Tin - 
 
 36 
 
 6 
 
 Lead - 
 
 72 
 
 12 
 
 It follows, as is manifest from the Table, that the heating 
 is exactly proportional to the resistance, or, which comes to 
 the same thing, is the reverse of the electric conductibility. 
 
 Riess, by the very special care, introduced into the con- 
 struction of his electric thermometer, and by the very large 
 number, as well as the scrupulous accuracy of his experi- 
 ments, succeeded in establishing with remarkable precision 
 the laws of the phenomena with which we are engaged. In 
 announcing these laws, we shall endeavour to describe the 
 processes that were followed by this skilful philosopher in 
 order to arrive at them ; at the same time regretting that 
 the limits which are imposed upon us do not permit of our 
 entering into so many details as we should have desired. 
 
 P 4 
 
216 TRANSMISSION OF ELECTRICITY. TART TV. 
 
 The electric thermometer is composed of a glass tube 
 I7f in. in length, bent at right angles, at its two ends, one of 
 which is terminated by a glass globe, 3f in. in diameter, the 
 other by a cylindrical vessel 2f in. in height, by f in. in 
 diameter (Jig. 193.). The tube furnished with a scale divided 
 
 Fig. 193. 
 
 arbitrarily, is fixed on a wooden plank, attached by hinges to 
 a horizontal base, so as to have facilities for being inclined at 
 pleasure, in respect to the horizon, and for being adjusted in 
 the position that is given to it, by means of a divided metal 
 arc, and a binding screw. Coloured sulphuric acid, diluted 
 with alcohol, is poured into the cylindrical vessel. The 
 globe of the thermometer is perforated in three places, two 
 of which are diametrically opposed to each other. Metal 
 sockets cemented in these two openings, are closed hermet- 
 ically by covers that are screwed upon them. The third 
 opening is furnished with a piece of perforated metal, which 
 is closed by means of a metal plug ; it allows of the introduction 
 into the tube of a liquid column of the given length. Into the 
 two sockets there enter with friction two cylinders, about 2 jin. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 217 
 
 in length, by 2 in. in diameter, furnished at their outer end 
 with a screw. At their inner end there is a cone, which is 
 fixed to it by means of a screw ; the base of each of the two 
 cones is cut open, and into these clefts is introduced by its two 
 ends the platinum wire, whose elevation of temperature we de- 
 sire to determine. A rod of metal, that is easily passed through 
 the globe is employed for introducing the platinum wire which 
 it draws along ; after the rod has been removed, the wire is 
 strained by means of the screws. The covers of the sockets 
 and the platinum wire are placed in the circuit of the battery 
 by means of thick brass wires ; the platinum wire on being 
 heated by the discharge, expands the air in the globe and 
 drives the liquid from the tube into the reservoir. The 
 instrument is more sensitive, for given conditions, in propor- 
 tion as the inclination of the tube towards the horizon is 
 greater. In estimating the heating of the wire, the cooling of 
 the air caused by the sides of the globe during the time, which 
 is generally very short, of the falling of the liquid, is neglected; 
 the surface, however, of the globe is surrounded by a very 
 thin envelope of gutta-percha, covered with tinned plate, so 
 as to prevent the variations of temperature that might arise 
 from external causes. Now, by means of a formula founded 
 upon the laws of heat, the increase of temperature that has been 
 experienced by the wire is deduced from the space traversed 
 by the liquid, estimated in linear divisions (lines or milli- 
 metres).* After having finished one experiment, the globe 
 is opened, and the wire is allowed to cool ; the metal plug is 
 then gently replaced. If the cooling has been complete, the 
 liquid, after having descended a certain quantity in the tube, 
 stops ; if not, it begins to rise again. We must take care not 
 to select initial temperatures, too much differing from each 
 other, in the experiments that are to be compared ; for the 
 heating of a platinum wire depends, in a certain measure, on 
 its primitive temperature, and of which no account can be 
 taken ; hence the great importance of this temperature being 
 at all times very nearly the same. In Riess's experiments 
 it was about 60. 
 
 * For the establishment of this formula, and its application to certain cases, 
 see note C. at the end. 
 
2L8 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 In order to establish the relation that exists between the 
 force of a discharge and its calorific effects, we must in the 
 
 outset have a means of 
 measuring the quantity of 
 electricity, with which a 
 battery is charged. For this 
 purpose we employ the elec- 
 trometric jar (Jig. 194.), which 
 is a Ley den jar, whose metal 
 rod, that communicates with 
 the inner coating, is furnished 
 with two balls, one, the lower 
 of the two, intended to be put 
 into communication with the 
 outer coating of the battery, 
 which is carefully insulated, 
 the other, the upper one, 
 placed opposite to a perfectly 
 similar ball, situated at the 
 same height, and affixed to a 
 rod, that can be moved by means of a micrometric screw ; so 
 that the two balls may be approximated to a distance, measur- 
 able with great precision. This latter ball, being insulated, 
 is put into communication with the outer coating of the jar, 
 by means of a platinum wire of a little more than a yard in 
 length and ^ J-^ in. in diameter, twisted round a tube, so as to 
 render the discharges that occur between the balls* less 
 sharp, and thus to diminish the alterations that their surface 
 undergoes, which ought to be well polished. It is in fact 
 necessary that these balls, which ought to be of copper, should 
 be well rounded and polished, in order that the discharge 
 between the outer and inner coating of the jar may always 
 occur with the same quantity of electricity. The jar rests 
 upon a metal foot, the communication of which with the 
 ground is made as perfect as possible. 
 
 194 - 
 
 * It will not do to employ a longer and thinner wire ; for the discharges, 
 which are to be counted, would not then be sufficiently strong or distinct. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 219 
 
 Now, in order to use the electrometric jar, the outer 
 coating of the battery, which has been carefully insulated, 
 must be put into communication with its inner coating ; the 
 electricity of this outer coating, which is driven into the jar, is 
 of the same name as that with which the battery is charged, and 
 it is proportional to it*; so that, in measuring one, the measure 
 of the other is obtained. Now, as soon as the electrometric jar 
 is charged with a determinate quantity of electricity, a dis- 
 charge is brought about between the two balls ; the number of 
 discharges then serve as a measure of the quantity of electricity 
 introduced into the battery. In order that these discharges 
 shall correspond with equal quantities of electricity, it is ne- 
 cessary that the communication between the outer coating of 
 the battery, and the inner coating of the jar shall be well es- 
 tablished and continuous, and that the rotation of the glass 
 plate of the electrical machine, by which the battery is 
 charged, shall occur with as uniform a velocity as possible. 
 Care must also be taken to bring the balls of the electro- 
 metric jar very close together, so that the discharges may 
 occur with very inconsiderable quantities of electricity, which 
 renders the application of the principle, that serves as the 
 basis of this means of measuring, more accurate. The size q, 
 that expresses the quantity of electricity with which the 
 battery is charged, has therefore for a unit the quantity of 
 electricity which, being conducted into the battery, produces 
 a discharge of the electrometric jar; but as this unit is very 
 feeble when the two balls of the jar are placed, for instance 
 at a distance of ? y n. apart, we take for a unit the quantity 
 of electricity, that corresponds to two discharges. 
 
 Besides the quantity of electricity, it is essential to know 
 its density, which depends upon the extent s of the inner 
 coating of the battery, or, which comes to the same thing, of 
 the number of equal jars of which the battery is composed. 
 
 * The method is based upon the principle of condensed electricities (Vol. 
 I. p. 530.) ; namely, that if the quantity 1 of electricity arriving at the battery 
 developing m, in the outer coating, gives rise to a discharge of the electro- 
 metric jar, u discharges, arising from u m of electricity in the outer coating, 
 correspond to the quantity u, of electricity, arriving at the battery. 
 
220 
 
 TRANSMISSION OF ELECTRICITY. 
 
 For the same quantity of electricity, this density is the 
 inverse of the said extent or number, so that it may be ex- 
 pressed by the fraction -. The density may be determined 
 
 s 
 
 directly, by means of a weight-electrometer {fiy. 195.) formed 
 
 O 
 
 Fig. 195. 
 
 of a rod of glass 13 inches in length, furnished at its centre 
 with an arrangement of two pivots which rest upon two agate 
 planes, like the beam of a balance. At one end of this rod 
 is fixed the scale-pan of a balance ; at the other, a hollow 
 metal ball f in. in diameter. The beam would naturally 
 have a horizontal direction ; it is so placed that the ball by 
 which it is terminated, shall be immediately beneath a rather 
 larger ball, that is in communication, by means of a good 
 conductor, with the inner coating of the battery, and shall at 
 the same time be in contact with it. Into the scale-pan is 
 placed a weight p, and the battery is charged, until the fixed 
 ball repels that of the weight-electrometer, which was in 
 contact with it. The number of discharges of the electro- 
 metric jar indicates what was the quantity of electricity 
 necessary to bring about this repulsion, and consequently, to be 
 in equilibrium with the weight p. But the repulsive effect is 
 proportionate to the electric reactions or densities of the two 
 
 balls, which are the same, namely for each ; we have there- 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 221 
 
 fore : p = a f ~ ) , a being a constant quantity; whence we de- 
 \ s / 
 
 duce q=sb Vp, b being a constant equal to 
 
 Va 
 
 By taking 
 
 the mean of all the calculated values, we find 5 = 2.236. 
 Then comparing the values of q, calculated by this formula, 
 with its observed values, we find them in perfect accordance ; 
 which proves that the density is very exactly expressed, by 
 
 making it equal to . This same weight-electrometer may 
 
 s 
 
 serve as a discharging-apparatus, with a slight modification 
 in its construction, which consists in placing the movable ball 
 between two fixed balls, one communicating with the outer, 
 the other with the inner coating of the battery, so that the 
 movable ball, which is itself in communication, by means of 
 the movable metal rod, with the outer coating, is repelled by 
 one of the fixed balls and attracted by the other, to the 
 distance necessary for the discharge to occur.* (Fig. 196.) 
 
 Fig. 196. 
 
 * These pieces of apparatus, with some slight modifications, are the same as 
 those described in Vol. I. p. 118. 
 
222 
 
 TRANSMISSION OF ELECTRICITY. 
 
 Now, in order to operate, the battery, the discharging 
 apparatus, the electrometric jar, and the electric thermometer 
 are so arranged, that the discharge, whose power is measured 
 by the jar, traverses the wire of the thermometer. The 
 universal discharger (Jig. 197.), is also placed in the circuit, 
 
 Fig. 197. 
 
 in order that other wires, besides the one that is heated in 
 the thermometer, may be introduced. Care is taken to 
 count the numbers of discharges of the electrometric jar, 
 until the moment when the charge of the 
 battery attains to the point required, in 
 order that the discharger shall act. It 
 is better in very delicate experiments to 
 employ a discharger (fig. 198.) which is 
 made to act in a direct way, by drawing 
 a silk cord, attached to the arm of the 
 lever, when the battery has been charged 
 with the necessary quantity of electricity. 
 
 The experiments were made with a bat- 
 tery, whose number of jars varied from 2 
 to 25, each jar presenting about \~ sq. 
 ft. of surface. The quantity of electricity 
 accumulated in the battery was indicated 
 by the number of sparks of an electro- 
 metric jar, the balls of which were one line distant from each 
 other. The numbers given by the electric thermometer are 
 in perfect accordance with those, which would be given by 
 
 the formula T = b , in which T expresses the elevation 
 
 Fig. 198. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 of temperature, experienced by the wire of the thermometer, 
 q, the quantity of electricty, s, the surface of the battery, and 
 b, a constant, that depends upon the electric thermometer. 
 Hence is deduced the law that the elevation of temperatures 
 experienced by a ivire, placed in the circuit of the discharge of a 
 battery, is proportional to the product of the quantity of electri- 
 city by the density = q x ; or, which comes to the same 
 
 thing, to the square of the quantity of electricity accumulated in 
 the battery, divided by the extent of the battery. 
 
 Now the question is to determine the influence of the di- 
 mensions of the wire upon its heating, the circuit of the 
 battery remaining constant. With this view, platinum 
 wires of different lengths, coiled into helices, are successively 
 introduced into the globe of the electric thermometer, and a 
 battery is employed, consisting of 5 of the jars of 1-J sq. ft. of 
 surface. By an extensive series of experiments the heating 
 of each wire corresponding to different values of q is found, 
 whence is deduced the value of this heating for q = 1 and 
 s = 1, The following is the Table of this value for different 
 lengths of wire. 
 
 Lengths of Wire. Heating of Wire. 
 
 11 in. 0-238 
 
 8i 0-228 
 
 6 0-239 
 
 3f 0-237 
 
 It follows from this, that the heating, that a platinum wire 
 undergoes by the electric discharge, is independent of its 
 length. To arrive at this result, care must be taken, when 
 operating with shorter wires than the first, to introduce into 
 the circuit a similar wire, but of such a length that the sum 
 of the two wires placed at the same time in the circuit 
 shall be always the same. In this way, there is no difference 
 in the resistance opposed to the discharge, nor yet in its 
 duration, for each experiment ; if this precaution is not taken, 
 the longest wire becomes a little less heated, because there 
 operates on the time of the discharge, a greater retardation 
 than that resulting from the interposition of the short wire 
 
224 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 unless we at the same time compensate for the difference by 
 the means we have just pointed out. It is the same for the 
 determination of the law relating to the influence of the 
 diameters of the wires ; it is necessary, in this case, to 
 operate with two wires of different diameters ; one of which 
 is placed in the thermometer, and the other elsewhere in the 
 circuit; then, after certain experiments made in this way, 
 the respective places of the two wires are changed, and fresh 
 experiments are made. The resistance of the circuit thus 
 remains the same, in each series of experiments, which causes 
 the time of the discharge to remain the same for each of the 
 wires, whose heating we desire to determine. In this manner 
 by comparing the wires two and two, we find : 
 
 Radius of the Wire in Lines.* Heating. 
 
 0-029690 0-1588 
 
 0-023012 -3194 
 
 0-058304 -0592 
 
 0-036170 -3775 
 
 If the values of the heatings are compared with those 
 of the radii, it is found that they are inversely as the fourth 
 powers of these radii. This law would give, in fact, for 
 the heating of the first wire, calculated according to that of 
 the second, O155 instead of 0*158 ; and for that of the third, 
 calculated according to that of the fourth, 0-0589 instead 
 of 0'0592.f The differences between the result of calcula- 
 tion and that of observations may be altogether neglected 
 in such experiments as these. We may, therefore, consider 
 the following law as being well established : When the same 
 quantity of electricity, completely discharged in the same interval 
 of time, traverses wires of the same nature, but of different 
 diameters, each wire experiences an elevation of temperature, 
 independent of its length, and inversely proportional to the fourth 
 power of its radius. 
 
 This law proves to us first, that each wire receives, by 
 
 * These radii have been determined with very great care, under a compound 
 microscope of a magnifying power of 190, by aid of a micrometer, that de- 
 tected the ten-thousandth part of an inch. 
 
 f These calculations were made by means of logarithms. 
 
CHAP. IT. EFFECTS OF DYNAMIC ELECTRICITY. 225 
 
 the same discharge, a quantity of heat proportional to 
 its length ; or, in other words, that each of its points is 
 equally heated; which might in the outset appear reason- 
 able, for there is always in the circuit a wire of a constant 
 length, of which a portion only of greater or less length is 
 contained within the globe of the electric thermometer, which 
 is heated in proportion to the length of this portion. The 
 law shows us, in the second place, that the wire receives 
 by the discharge a quantity of heat that is in inverse ratio 
 to the square of its radius, which is a proof that the influence 
 of its size does not consist simply of the fact that, as the 
 mass of wire to be heated being more considerable, there 
 must result to it a less temperature ; but also of this, that 
 by the effect of its larger diameter, the electricity, in tra- 
 versing it, deposits in it an absolute quantity of heat less 
 in amount ; the two influences, each depending separately on 
 the volume of the wire, their combined action must be 
 proportional to the square of the section, or to the fourth 
 power of the diameter. 
 
 In the law that we have been putting forth, the quantity 
 of electricity transmitted is always the same in the same 
 time : we have now to determine the influence that is 
 exerted on the heating of an invariable wire, by a difference 
 in this quantity, or, which comes to the same thing, the 
 variable dimensions of another wire placed in the same 
 circuit, the length and diameter of which are made to vary. 
 Experiments demonstrate that the heating of the invariable 
 wire is inversely as the length of the added wire and in 
 proportion to the square of its radius : now, this is exactly 
 the law which regulates the electric conductibility of the 
 wire; whence we may conclude that the heating of the 
 invariable wire is inversely as the resistance which the 
 discharge encounters, or reciprocally in proportion to 
 its duration. This last conclusion is deduced from the 
 observation which demonstrates, that the more we increase 
 the resistance that is encountered by the discharge, by 
 introducing into its circuit either a very long wire, or a tube 
 filled with water, or a small cylinder of moist wood, the 
 
 VOL. II. Q 
 
226 TRANSMISSION OF ELECTRICITY. FART iv. 
 
 less is the wire heated ; it ends even by no longer becoming 
 heated at all, and a very great quantity of electricity may 
 traverse it without in any way affecting the liquid indicator 
 of the thermometer. But then the discharge is no longer 
 instantaneous ; it lasts for an appreciable interval of time ; 
 and if we suppose that the retardation it undergoes is pro- 
 portional to the resistance of the conductor introduced ; and 
 consequently, in the case of an homogeneous wire, to its 
 length, we find that the values of the heating, calculated 
 according to a formula based upon this supposition, are 
 perfectly in accordance with the observed values. The 
 same accordance exists between calculation and observation, 
 when wires are introduced, whose diameter and not length 
 is variable ; if indeed we admit that the retardation is 
 inversely as the square of the radius, which enables us to lay 
 down the law, as follows : 
 
 The heating of a wire by an electric discharge is reciprocally 
 proportional to the duration of the discharge; the retardation, 
 that the discharge encounters by the insertion of a wire in the cir- 
 cuit) 'being itself in direct ratio to the length of the wire, and in 
 inverse ratio to the square of its radius. 
 
 By uniting in one all the laws that we have been establish- 
 ing, we are led to the following more general one : 
 
 The elevation of temperature of the normal section of an ho- 
 mogeneous wire inserted in the circuit of a battery is in inverse 
 ratio of the fourth power of its radius., and in direct ratio of the 
 quantity of electricity accumulated, divided by the time of the 
 
 discharge : T = x -, a being a constant, that depends on the 
 
 nature of the wire, r the radius of the wire, q the quantity of 
 electricity, and z the time of the discharge.* We see that 
 
 * When a very fine wire is introduced into the electric thermometer, and the 
 charge of the battery is gradually increased, diminishing at the same time the 
 number of jars, it is observed, even when the total quantity of electricity does 
 not change, that the heating of the wire goes on increasing, and that the wire 
 itself suffers deflections and finishes by being altogether crimpled, a defor- 
 mation that cannot be made entirely to disappear, except by incandescence 
 and polishing. This increase of effect produced by the same quantity of 
 electricity, but of increasing density it is true, can only be attributed to an 
 increase in the rapidity of the discharge, and the most simple supposition to 
 
CUAP. IT. EFFECTS OF DYNAMIC ELECTRICITY. 227 
 
 the length of wire enters neither into the law nor into the 
 formula; which is a consequence of the law, relative to 
 length, which we established further back ; since, as we have 
 remarked, the influence of length is not felt, except on the 
 duration of the discharge, of which z is the expression. The 
 formula, that gives the value z, includes the length of the 
 wire introduced into the circuit ; but this formula, which is a 
 little complicated, does not give for z a value o, when the length 
 of wire becomes o. This result, which is a little odd at first 
 sight, is explained, however, when we reflect that the circuit 
 is not composed of wires only, but of the points of connection 
 of these wires, which subsist always ; so that the time 
 given by the formula, when the wire is reduced to a length of 
 o, is that which the discharge requires for traversing the in- 
 variable parts of the apparatus, and the junction pieces by 
 which they are connected together ; it is this time which is 
 taken for unity. 
 
 The heating of a wire is also influenced by interruptions 
 in a circuit, such as those which result from the interposition 
 of a stratum of air, of a sheet of paper of a greater or less 
 thickness, or of a plate of glass or mica between the two ex- 
 tremities of the discharger, between which the discharge 
 must pass ; and experiments lead to the following results : 
 the electric discharge heats the wire that it traverses less, in pro- 
 portion as the electricity must pass over a greater obstacle before 
 the discharge sets out. We are not here referring to an ob- 
 stacle that retards the discharge continuously, which would 
 
 admit is, that the time of the discharge is inversely proportional to the density of 
 the electricity. By calling y the density, determined by the tension balance of the 
 weight-electrometers, if the quantity I of electricity is discharged in the time 
 
 the quantity q will be in the time -^ ; consequently 2, the time of the dis- 
 charge of the battery, is proportional to -2.. But we have seen that y 
 
 y 
 
 the density, is equal to 2- therefore, z = i will be equal to a x L. = s. 
 s y ^ q 
 
 Whence it follows, that in the formula T = b, 2-, we may put z in place of s, 
 and express T = b . . 
 
228 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 constitute a bad conductor ; but to an obstacle which, so long 
 as it is not surmounted, renders all transmission of electricity 
 impossible. But, as the heating depends at once upon the 
 quantity of electricity and upon its velocity, and as the 
 quantity is not sensibly diminished by the presence of 
 the obstacle, we must hence conclude that the obstacle, 
 although it is surmounted, increases the duration of the 
 discharge. 
 
 Finally, an important circumstance, to which we must 
 have regard in the heating of a wire by the discharge, is the 
 influence of inductive currents, which may be developed in 
 conductors that are near those which are traversed by the dis- 
 charge. Riess has made a very detailed study of this influence 
 also, by placing in the circuit a connecting wire coiled into a 
 spiral, and near this spiral another wire independent of the 
 battery, coiled also into a spiral, or simply a thin plate of tin, 
 interposed between two plates of glass. The effect of this 
 exterior conductor upon the calorific power of the discharge 
 is felt only so long as its conductibility is inferior to that of 
 the connecting wire ; and experience shows that then the dis- 
 charge is more retarded, and consequently the heating of the 
 thermometric wire is less in proportion as the conductibility of 
 the exterior circuit is less. However, the diminution in the 
 heating in the principal circuit, which results from the 
 increase in the resistance that is presented by the closed 
 secondary circuit, has a limit to which we arrive by increasing 
 the length of a german silver wire, for instance, which forms 
 part of this circuit. The two similar spirals, both formed of a 
 copper wire "058 in. in diameter, and 166 in. in length, one 
 of which forms part of the principal circuit, the other of the 
 secondary circuit, are placed at 1 1 in. from each other ; the 
 german silver wire that connects the two extremities of this 
 second spiral is 374 in. in length ; the heating experiences a 
 diminution of 52 per cent. : this is the maximum of diminution. 
 For more considerable lengths, the heating approaches to 
 what it was at the first ; and, when the german silver wire is 
 about 623 ft. in length, the diminution of heating is not more 
 than 13 per cent. The diminution of heating depends not 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 229 
 
 only upon the conductibility of the secondary circuit ; it is 
 also very much influenced by that of the principal circuit, 
 and particularly by the resistance that is opposed to the 
 passage of electricity by the platinum wire of the thermometer, 
 on account of its tenacity. Thus, if we pass the discharge 
 through a shorter and larger platinum wire which is placed 
 in the axis of the helix of a Breguet's thermometer, it is 
 found, by means of the indications of this thermometer, that 
 the diminution of the heating may attain, under the influence 
 of the secondary circuit, to 86 per cent, of the primitive 
 effect that was obtained, when the secondary circuit was not 
 in existence, or was not closed. 
 
 In all these experiments, the secondary circuit acts merely 
 in consequence of its conducting properties ; for exactly the 
 same effects are obtained by substituting for the german silver 
 wire one of platinum, that opposes the same obstacle to the 
 passage of the electricity. 
 
 The preceding facts confirm what we have said respecting 
 the duration of the discharge. In fact, the current produced 
 by induction in the secondary wire, although a little in arrear 
 in respect to the commencement of the discharge, neverthe- 
 less reacts upon a portion of this discharge, retards its move- 
 ment, and consequently diminishes its heating power. The 
 prolongation of the circuit has the double effect, in the first 
 place, of retarding the induced current, and by that increasing 
 its reaction upon the principal wire ; in the second place, of 
 weakening this current, and on the other hand of diminishing 
 the same reaction. At first, the former effect predominates, 
 and the reaction is seen to be increased ; but the secondary 
 current is soon so much weakened that its influence disap- 
 pears more and more until it becomes null for a certain 
 length ; which is equivalent to a complete interruption of the 
 circuit. However, we shall not insist further upon this 
 particular point, which is connected with the properties of in- 
 duced currents, a subject that we have already discussed in 
 detail *, and to which we have reverted in this place only on 
 
 * Vol. I. p. 403. and following pages. 
 Q 3 
 
230 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 account of its showing to us, under another form, the remark- 
 able influence of the duration or the velocity of the trans- 
 mission of electricity upon its calorific power. 
 
 Finally, we shall not dwell longer upon a class of pheno- 
 mena which show, under another form, the remarkable in- 
 fluence, that is exerted upon the heating by the density and the 
 duration of the discharges. These are the calorific effects, 
 that are obtained with Franklin's batteries, which consist of 
 a series of Leyden jars, placed in communication one with 
 the other, so that the knob of the first communicates with the 
 conductor of the electrical machine, the knob of the second 
 with the outer coating of the first, and so on.* The heating 
 of the wire produced by the discharge of a battery of this 
 kind, led Riess, at the end of a great number of experiments, 
 to remarkable results, in respect of density, possessed by the 
 electricity in the various jars of which it is composed, and of 
 the influence of the density.f 
 
 After having set forth the general laws which regulate the 
 heating brought about by discharges in good conductors, it 
 remains for us to examine what is the influence upon this 
 heating, of the particular nature of these conductors, which in 
 our experiments are wires. It is to Riess we are also indebted 
 for having, by his very numerous and accurate experiments, 
 determined this influence. This determination was made for 
 each wire by means of two experiments : in one, the wire sub- 
 mitted to the test, for example a wire of lead, was placed 
 in the circuit of the discharge, in which was also included the 
 platinum wire of the electric thermometer ; in the other, the 
 leaden wire was in the thermometer, and the platinum wire 
 of the thermometer in the circuit. Hence it was easy by 
 means of the laws already established, and by taking account 
 of the diameters of the two wires, to deduce the heating of 
 the leaden wire, in comparison with that of platinum ; the 
 operation was carried on in the same way for each of the 
 other wires, and the following Table was obtained : 
 
 * Vide Vol. I. p. 115. fig. 58. 
 
 | Vide the final note D, for the details relative to the laws of the heating of 
 wires by electric discharge. 
 
CHAP. II. 
 
 EFFECTS OF DYNAMIC ELECTRICITY. 
 
 231 
 
 Metals. 
 
 Force of Retard- 
 ation. 
 
 Power of 
 Heating. 
 
 Quantities of Heat 
 liberated. 
 
 Silver 
 
 0-1043 
 
 0-1267 
 
 0-1120 
 
 Copper 
 Gold 
 
 0-1552 
 0-1746 
 
 0-1133 
 0-2112 
 
 01447 
 0-1847 
 
 Cadmium - 
 
 0-4047 
 
 
 
 Brass 
 
 0-5602 
 
 0-3861 
 
 0-5616 
 
 Palladium - 
 
 0-8535 
 
 
 
 Iron 
 
 0-8789 
 
 0-7080 
 
 0-9148 
 
 Platinum - 
 
 1-0000 
 
 1-0000 
 
 1-0000 
 
 Tin - 
 
 1-0530 
 
 1 -5700 
 
 0-8917 
 
 Nickel 
 
 1-1800 
 
 0-8727 
 
 1-1820 
 
 Lead 
 
 1 5030 
 
 2-8760 
 
 1-4550 
 
 The comparison that may be made between the two kinds 
 of values for the same metal, that are contained in the first 
 two columns of the above Table, shows that there is no 
 direct relation between them. But we arrive at a more 
 satisfactory result, by transforming the numbers of the second 
 column, which express the relative elevations of temperature, 
 into relative quantities of heat. For this purpose we must 
 multiply each of these values by the specific heat and densitv 
 of the metal to which it refers, and divide the product by the 
 product of the specific heat and density of platinum, which is 
 always taken as unity. We thus obtain the relative quanti- 
 ties of heat developed by the electric discharge in each metal, 
 that developed in platinum being taken as unity ; the third 
 column of the above Table contains these values. We see 
 that they differ very little from the numbers that express the 
 force of retardation, so that this force and the quantity of 
 heat developed in a metal may be regarded as proportional to 
 each other ; and when the first of these two values has been 
 determined for a metal, which is always an easy matter, we 
 may readily deduce from it the second, and consequently the 
 power of heating of the metals. The following is the general 
 rule : 
 
 TJie relative power of the electric heating of a metal is found, 
 by dividing its force of electric retardation by its specific heat and 
 by its density. 
 
 It follows, from the combination of all these various laws, 
 
 Q 4 
 
232 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 that we may express, by a general formula, the quantity of 
 heat liberated in each of the wires, which, connected end to 
 end, compose a chain through which the electric discharge 
 passes. This formula leads to the following principle. 
 
 In wires of any metal, connected in succession one to the other, 
 and which serve at the same time to discharge an electric battery, 
 quantities of heat are liberated, which are exactly proportional 
 to the retardations that each of these wires taken separately would 
 produce in any electric discharge. This general principle and 
 the formula that has led to it, are equally applicable to the 
 most simple case, that of a single wire placed in the circuit ; 
 and we thus obtain the quantity of heat liberated in the wire. 
 
 If the wires, that are placed successively one after the 
 other in the circuit of the battery, are of the same diameter, 
 and lengths are given to them that are in the inverse ratio of 
 their force of retardation, the formula indicates the same 
 quantity of heat from each of them, provided the accumu- 
 lation of electricity in the battery is the same. Thus, sup- 
 posing that an electric battery is discharged successively with 
 wires of the same diameter and different natures, whose 
 lengths are for each metal inversely as its force of retar- 
 dation, and represented consequently by the numbers of the 
 Table, that follows, namely, for instance, 148.7 inches for the 
 silver wire, 88-8 for the gold wire, 15-5 for the platinum 
 wire, we shall, it is true, find that all these wires, by the 
 effect of the dischaige, suffer very different elevations of 
 temperature ; but that if we suppose them surrounded by ice 
 during the experiment, they will have melted, in order to 
 return to their primitive temperature, exactly the same quan- 
 tity ; that is to say, the total quantity of heat liberated in each 
 of them would have been the same ; which explains why their 
 temperature is more elevated in proportion as they are 
 shorter. 
 
 Table of the inverse values of the force of retardation, this 
 force being 100 for copper. 
 
 Silver - - 1487 
 
 Copper - - 100- 
 
 Gold ------ 88-87 
 
CHAP. li. EFFECTS OF DYNAMIC ELECTRICITY. 233 
 
 Cadmium - - 38-35 
 
 Brass - - - - 2770 
 
 Palladium - - 18-18 
 
 Iron - 17-66 
 
 Platinum - - - -15-52 
 
 Tin - 14-70 
 
 Nickel - - 13-15 
 
 Lead - 10-31 
 
 Laws of the calorific effects, produced by the passage of con- 
 tinuous currents through good conductors. 
 
 The results obtained by Riess have had the valuable 
 advantage of determining in a rigorous manner this depend- 
 ence, which long before his time had been recognised to exist 
 between the calorific effects of dynamic electricity on the one 
 hand, and the quantity and velocity of this electricity on the 
 other. It was while studying the calorific powers of the 
 voltaic current that this dependence was discovered, without 
 its laws, however, having been exactly established. Thus I 
 had already shown in 1830 that the reason for which a pile 
 with large surfaces, composed of numerous pairs, was pre- 
 ferable to a pile formed of a great number of pairs of less 
 surfaces, for the development of heat in wires placed in their 
 circuit, was that the current in the former case had a greater 
 velocity, and that it was necessary, in order that the calorific 
 effect should be at its maximum, that the resistance of the 
 pile should not exceed that of the wire placed between its 
 poles. More recently I showed that the calorific effect 
 diminished with the intensity or velocity of the electricity in 
 a much greater proportion than this intensity or this velocity. 
 For this purpose, having placed the helix of a Breguet's ther- 
 mometer* in the circuit of a pile of 8 pairs of zinc and copper, 
 each presenting a surface of 41 sq. ft., and which were 
 charged with a mixture of 40 parts water, 2 of sulphuric, and 
 1 of nitric acid, I passed the current through a certain extent 
 of concentrated nitric acid, placed in a prismatic glass trough 
 and which might be separated into two or more compartments 
 
 * Vol. I. p. 33,ji(j. 21. 
 
234 
 
 TRANSMISSION OF ELECTRICITY. 
 
 by means of platinum diaphragms. A magnetic galva- 
 nometer constructed with stout wire was also in the circuit. 
 The following are the results : 
 
 Number of Diaphragms. 
 
 Magnetic Galvanometer. 
 
 Calorific Voltameter. 
 
 1 
 
 85 
 
 312 
 
 2 
 
 84 
 
 170 
 
 3 
 
 83 
 
 115 
 
 4 
 
 75 
 
 12 
 
 5 
 
 40 
 
 
 
 6 
 
 37 
 
 
 
 By interposing into the circuit a chemical instead of a 
 magnetic voltameter, the following results are obtained : - 
 
 Number of Diaphragms. 
 
 Chemical Voltameter.* 
 
 Calorific Voltameter. 
 
 o 
 
 
 5" 
 
 38 
 
 1 
 
 
 25 
 
 3 
 
 * The number of seconds indicates 
 for obtaining a given quantity of gas ; 
 the current. 
 
 , for the chemical voltameter, the time necessary 
 it is therefore inversely as the chemical power of 
 
 Thus the reduction of the calorific effect to y 1 ^ corresponds 
 to a reduction of only of the chemical effect. By sup- 
 posing, therefore, that either the magnetic effect or the chemi- 
 cal effect are in a simple relation with the intensity and the 
 velocity of the current, we see in what greater proportion the 
 calorific effect diminishes or increases with this intensity or 
 this velocity. 
 
 Before going further, let us observe that there is in the ca- 
 lorific effects of dynamic electricity an important distinction 
 to be made between the case of discharges and that of conti- 
 nuous currents. In the former, the velocity, for a given 
 quantity of electricity, depends only upon the conductors that 
 form the arc for joining over the battery, and upon the 
 extent of its surface ; in the latter, it further depends upon 
 the very construction of the producing apparatus. And, in 
 fact, when this apparatus is a voltaic pile, the latter forms a 
 part of the circuit traversed by the current ; as well as the 
 wire that is heated, and nil the conductors by which the two 
 ends of this wire are connected with the poles ; whilst with a 
 
EFFECTS OF DYNAMIC ELECTRICITY. 
 
 235 
 
 battery of Leyden jars the same is not the case. Another 
 difference, which renders all comparison difficult, is that the 
 discharge must be instantaneous, whilst the current has 
 a certain duration, such that the slow escape of the same 
 quantity of electricity does not produce the same calorific 
 effect, as when this electricity, instead of coming from a pile, 
 is derived from an electric machine or a Leyden battery.* 
 Nevertheless, as we are about to see, some of the laws 
 by which calorific phenomena are regulated, when they are 
 produced by a continuous current, are the same as for the 
 case in which they derive their origin from discharges. 
 This is derived from the researches of three philosophers, 
 Joule, Lenz, and E. Becquerel. 
 
 Joule measures the quantities of electricity by a tangent 
 galvanometer, which he places in the circuit ; he then trans- 
 mits the current through a copper wire, which he passes into 
 a glass tube, and then twists in a helix around this tube, 
 which is itself placed in a vessel containing a certain quan- 
 tity of water. The following is then the Table of the 
 results : 
 
 Deviation of the 
 Galvanometer. 
 
 Quantities of dy- 
 namic Electricity.* 
 
 Heating of 
 Water in half 
 an Hour. 
 
 Relations between the 
 Squares of the Quantities of 
 Electricity of Column No. 2. 
 
 16 
 31* 
 55 
 57f 
 
 54i 
 
 0-43 Q 
 -92 
 2 -35 
 2 -61 
 2 '73 
 
 3 
 19-4 
 23- 
 25- 
 
 2-9 
 18-8 
 23-2 
 25-4 
 
 * M. Jonle takos for the unit of measure of the quantity of dynamic electricity a quantity 
 capable of decomposing a hundred grains of water per hour ; it is produced by a current 
 capable of deflecting his galvanometer, 35-5. It is this unit that M. Joule calls Q. 
 
 The experiment prolonged for an hour gave a result in 
 accordance with that contained in this Table ; which proves 
 that the heat, liberated by the current in its passage through 
 the wire, is truly proportional to the square of the electric 
 intensity. On the other hand, certain experiments made 
 with wires of different natures, namely a copper wire, an 
 
 * We shall return to these differences when engaged upon the incandescence 
 of wires, on phenomena in which they are especially sensible. 
 
236 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 iron wire and a filament of mercury, contained in a twisted 
 glass tube, had proved to M. Joule that the same current 
 transmitted through two of these different conductors, placed 
 one after the other, produced quantities of heat which were 
 for the copper wire, compared with the iron wire, 5-5: 6; 
 and for the copper wire, compared with the filament of mer- 
 cury, as 2*9 : 4*4. These relations were precisely those 
 which direct experiment shows to exist between the electric 
 resistances of the conductors employed. Whence may be 
 deduced the following general law, that when a current of 
 voltaic electricity is propagated along a metal conductor, the 
 caloric liberated in a given time is proportional to the resistance 
 of the conductor, multiplied by the square of the electric intensity. 
 
 M. E. Becquerel perfected Joule's method, by taking ac- 
 count of the cooling that had occurred during the continuance 
 of the experiment, and by employing for this purpose a 
 calorimeter, in the waters of which were plunged a very 
 sensitive thermometer, and a wire twisted into a spiral, which 
 was traversed by the current.* The quantity of electricity 
 was here measured by the quantity of gas liberated per 
 minute in a voltameter, which was brought to and to '04 
 in. of pressure : this quantity was made to vary by producing 
 the current from a greater or less number of pairs of a con- 
 stant force. 
 
 Three principal experiments have been made according to 
 this method : one with a copper wire, a yard in length and 
 017 in. in diameter; the second with a platinum wire 17 ^ in. 
 in length, and '009 in. in diameter; and the third with a 
 platinum wire 2-78 ft. in length, and '039 in. in diameter. 
 Each of these wires was twisted into a helix around a glass 
 tube. If, in each of the three series of experiments, we 
 divide the quantities of heat, measured by means of the 
 calorimeter, by the square of the corresponding quantities of 
 electricity, measured by means of a chemical voltameter, we 
 obtain as quotients numbers that are very little different from 
 
 * This method, in which account is taken of the heat lost by cooling during 
 the continuance of the experiment, is the same as that which La Roche and 
 Berard adopted for the determination of the specific heat of gases. 
 
CHAP. II. 
 
 EFFECTS OF DYNAMIC ELECTRICITY. 
 
 237 
 
 each other, for each of the experiments of the same series, 
 numbers whose mean is for the first series, composed of six 
 experiments, 0*0340 ; for the second series, composed of five 
 experiments, 0'1844; and for the third series, composed of 
 four experiments, 3-143. These results prove, first, that the 
 quantity of heat liberated by the passage of the current is 
 proportional to the square of the quantity of electricity that 
 passes ; moreover, the three numbers above being the ex- 
 pression of the quantity of heat liberated by the passage of 
 the same quantity of electricity, it is easy to recognise that 
 they are in the direct ratio of the resistance that is presented 
 by the three wires to the transmission of the current. In 
 fact, the following is a comparative Table of the quantities of 
 heat liberated, deduced both from experiment and from cal- 
 culation based upon this hypothesis : 
 
 Wires. 
 
 By Experiment. 
 
 By Calculation 
 
 Fine platinum wire 
 Thick 
 Copper wire - 
 
 3-14^ 
 0-187 
 0-034 
 
 3-143 
 0-177 
 0-038 
 
 Finally, Lenz arrived at the same results as Joule and E. 
 Becquerel, by placing the wire, that is heated by the current, 
 in spirits of wine, a still more imperfect conductor than pure 
 water, which gives greater assurance that no portion of the 
 current traverses the liquid, and which consequently is 
 transmitted entirely through the wire ; a certainty that is 
 not attained with water. In Jig. 199. B 
 represents the glass stopper of a jar, 
 filled with spirits of wine ; this stopper 
 is pierced by two holes, which allow of 
 the introduction of two thick metal 
 conductors, that are placed at s, in com- 
 munication with the poles of a pile ; and 
 the inner ends of which are united by a 
 fine wire coiled into a helix, which is 
 to be heated by the current. A tangent- 
 galvanometer and a rheostat, intro- 
 
 Fly. 199. 
 
238 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 duced into the circuit, serve to measure the current and to 
 reduce its force to the standard desired in each experiment. 
 The following Table contains the results of sixteen experiments 
 made with three wires of german silver of different thick- 
 nesses, with wire of platinum, of iron, and of copper. 
 
 Nature of the Wires. 
 
 Force of the 
 Curreut. 
 
 Time of heating 
 Spirit of wine 1. 
 
 Resistance of the 
 Wire to Conduc- 
 tibility. 
 
 German silver, 
 
 
 
 
 No. 1. 
 
 6-93 
 
 1-349 
 
 93-50 
 
 do. 
 
 10-53 
 
 0-571 
 
 93-63 
 
 do. 
 
 1430 
 
 0-300 
 
 9394 
 
 German silver, 
 
 
 
 
 No. 2. 
 
 10-53 
 
 0-920 
 
 58-76 
 
 do. 
 
 14-30 
 
 0-481 
 
 58-64 
 
 do. 
 
 18-32 
 
 0-288 
 
 5901 
 
 do. 
 
 14-30 
 
 0-457 
 
 60-16 
 
 German silver, 
 
 
 
 
 No. 3. 
 
 . 18-32 
 
 0-384 1 
 
 44-59 
 
 Platinum 
 
 14-30 
 
 0-555 
 
 50-45 
 
 do. 
 
 1832 
 
 0-325 
 
 51-41 
 
 Iron - 
 
 22-69 
 
 0-435 
 
 24-92 
 
 Copper 
 
 18-32 
 
 1-301 
 
 13-90 
 
 do. 
 
 22-69 
 
 0-385 
 
 13-90 
 
 do. 
 
 27-52 
 
 0-575 
 
 13-92 
 
 do. 
 
 32-98 
 
 0-381 
 
 14-01 
 
 do. 
 
 27-52 
 
 0-544 
 
 14-31 
 
 According to this Table, we perceive that, for each wire, 
 the resistance to conductibility increases slightly with the 
 force of the current, or rather with its heating ; which ought 
 to be the case, since elevation of temperature diminishes 
 the electric conductibility of metals. 
 
 It is easy to deduce, from the number contained in the 
 above Table, the different laws of the heating of wires by 
 the electric current. First we see that the time t, employed 
 by two different wires, traversed by the same current, for 
 heating the same quantity of spirit of wine 1, is the inverse 
 of the resistance I, to conductibility of these two wires; 
 and consequently that the heating itself is proportional to 
 this resistance. In fact, we have t x I constant in all the 
 experiments made with a current of the same force. The 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 239 
 
 following are the values of this product for different 
 currents : 
 
 With the current of 10-53. 
 
 First german silver wire - tl= 53-46 
 
 Second ... *Z = 54'06 
 
 With the current of 14-30. 
 
 First german silver wire ... tl= 28-18 
 
 Second ... tl= 28-11 
 
 Third - *Z = 27'49 
 
 Platinum wire ... tl= 28*00 
 
 In like manner, we shall find 1 1 constant in four experi- 
 ments with the current of 18 '35 ; and in two with the current 
 of 22-69. The small differences between the values of t I 
 in each case arise only from the inevitable errors of experi- 
 ment. 
 
 The numbers of the Table show also that the heating is 
 proportional to the square of the force of the current ; or, 
 which comes to the same thing, that this square is the in- 
 verse of the time t of the heating of 1 ; namely, that s 2 t is 
 constant for each of the six wires, employed successively 
 in the experiments. The slight differences that are pre- 
 sented between the value s 2 t, for each wire, are due to 
 the fact that the more rapid the heating is, the less is the 
 loss of heat arising from cooling ; so that t is necessarily 
 smaller than it would be in the case wherein the current 
 is more powerful. Thus, if we take for example the ex- 
 periments made with the first wire of german silver, 
 we find for s 2 t the following values : 1st, 64*8 ; 2nd, 
 63'3; and 3rd, 61*3, which, as we see, go on diminishing. 
 It is the same for the different values of s 2 t with each 
 of the five other wires. In order that these values should 
 be quite equal with each of the wires, it would be ne- 
 cessary to take account of these differences in the influence 
 of cooling. 
 
 Whatever be the case, we shall always find the two same 
 laws ; namely, that the heating is proportional, 1st, to the 
 resistance of the wire to conductibility ; 2nd, to the square 
 
240 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 of the force of the current. These two laws combined ought 
 to give as constant, in all the experiments of the above Table, 
 the product s 2 t I, since t is the inverse of the heating. 
 Now, the products s 2 1 I, deduced from the number fur- 
 nished by the sixteen experiments of the Table are sensibly 
 equal, and their mean value is 5856. 
 
 The induction currents, engendered by rotation before 
 the poles of a magnet of an armature of soft iron surrounded 
 by a wire, present, with regard to their calorific effects, 
 the same laws as the currents of discharge and voltaic 
 currents. Joule has also demonstrated, by plunging into 
 water, furnished with a thermometer, the soft iron armature 
 and the bobbins of wire with which it is surrounded, that the 
 heat developed in the wires themselves of the bobbins is 
 proportional to the square of the intensity of the current. 
 
 A third law to be added to the two others is that, what- 
 ever be the length of a conducting wire, if it transmit the 
 same quantity of electricity in the same time, the elevation 
 of the temperature of each of its points is the same. Only 
 if its length increases, the source of the current must be 
 rendered more energetic, in order that the same quantity 
 of electricity shall pass in the same time ; so that the devia- 
 tion of a galvanometer remains the same. This law was 
 proved for the first time by Peltier, and confirmed by E. 
 Becquerel. 
 
 The three laws that we have established for a continuous 
 current are the same as those which Riess had found for the 
 case of the discharge *, however, there is between these two 
 modes of heating by electricity an important difference, 
 which renders all comparison between them very difficult ; it 
 is the duration of the former, and the instantaneity of the 
 latter. It would be in vain to accumulate on a battery a 
 quantity of electricity equal to the whole of that which pro- 
 
 * M. E. Becquerel had thought he had found that, for currents as well as 
 for discharges, the elevation of temperature is in inverse ratio of the fourth 
 power of the radius of the wire ; but this law does not yet appear to us to be 
 sufficiently firmly established to enable of its being admitted. We shall see this 
 hereafter. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 241 
 
 duces a current capable of heating a wire for a minute; 
 yet on making this electricity gradually pass away for the 
 period of a minute, the same amount of heating would 
 not be produced. We know besides that, in the instanta- 
 neous discharge, the same quantity of electricity produces a 
 calorific effect, that varies with the surface of the battery. 
 The cause of these differences lies in the nature, so different 
 itself, of the two sources of electricity, as we shall see, when 
 we shall have studied these sources. 
 
 An important point in the researches that have been 
 engaging our attention, is to know what the influence is of 
 the heating itself, that the wire undergoes, upon the resist- 
 ance that it opposes to the electric current. We have, in 
 fact, seen that this resistance increases with the elevation of 
 temperature due to an exterior cause ; now, here the heating 
 arises from the resistance of the wire ; and, on the other hand, 
 this resistance increases with the heating: where is the 
 limit, and how is equilibrium established ? 
 
 This question has been treated in detail, and resolved by 
 means of a great number of experiments, by M. Romney Robin- 
 son. The instruments of which he made use are, a galvano- 
 meter, a rheostat, and a very sensitive pyrometer, of the 
 nature of the one we have described*, and by means 
 of which he was able to appreciate the variations of temper- 
 ature of a wire, especially of one of platinum. The following 
 is a Table of the results obtained with a platinum wire '078 
 in. in diameter, and a pile composed of a greater or less num- 
 ber of pairs. The force of the current is deduced from the 
 indications of the galvanometer, the current taken for unity 
 being that which producing on the galvanometer a deviation 
 of 45, liberates in a voltameter 6*57 cub. in. of gas in five 
 minutes. The pyrometer gives the temperature of the wire. 
 
 * Vol. I. p. 32.,/fy. 19. 
 
 VOL. II. 
 
242 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART iv. 
 
 Force of the Current. 
 
 Temperature of the Wire, 
 
 Resistances of the Wire in 
 turns of the Rheostat. 
 
 0-809 
 
 289-7 
 
 305-5 
 
 0-858 
 
 319-9 
 
 3208 
 
 0957 
 
 559-3 
 
 385-2 
 
 168 
 
 930-9 
 
 497-9 
 
 214 
 
 1020-6 
 
 523-8 
 
 357 
 
 1215-0 
 
 591-6 
 
 404 
 
 13387 
 
 643-8 
 
 515 
 
 1447-0 
 
 666-4 
 
 538 
 
 1545-6 
 
 706-2 
 
 794 
 
 1761-9 
 
 734-4 
 
 2-089 
 
 1966-4 
 
 793-9 
 
 2-200 
 
 2116-0 
 
 840-5 
 
 2-222 
 
 2166-2 
 
 827-8 
 
 2-318 
 
 2461-6 
 
 898-2 
 
 It is curious to see how the resistance increases in a rapid 
 progression with the temperature ; for at 289 0< 7 it is equi- 
 valent to 305 '5 degrees of the rheostat; and at 2461'6, to 
 898-2. 
 
 On placing the pyrometer in vacuum, the increase of 
 resistance with the temperature is the same, only the force 
 of the current, necessary to produce the same temperature, 
 is a little less, because the absence of the surrounding air 
 diminishes the cooling. 
 
 The following is a Table of similar experiments made 
 with a wire of '157 in. in diameter. We should remark that 
 the eighth experiment was made by plunging the pyrometer 
 into diluted alcohol, so that the temperature of the wire 
 could not rise above that of the boiling of this liquid, namely, 
 207 Fahr., nearly that of the boiling of water. 
 
 Force of the Current. 
 
 Temperature of the Wire 
 in degrees Fahr. 
 
 Resistances in Degrees of 
 the Rheostat. 
 
 1-522 
 
 365-9 
 
 127-8 
 
 2-020 
 
 481-3 
 
 144-9 
 
 2-411 
 
 719-6 
 
 169-0 
 
 2-758 
 
 10207 
 
 212-0 
 
 3-226 
 
 1310-4 
 
 2387 
 
 3-699 
 
 1518-0 
 
 270-1 
 
 4-352 
 
 1883-9 
 
 318-6 
 
 9-548 
 
 2078-0 
 
 393-8 
 
 4-821 
 
 22067 
 
 346-0 
 
 5-230 
 
 2355-1 
 
 351-4 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 243 
 
 The eighth experiment, included in this Table, demon- 
 strates, that the increase of resistance is not due to the in- 
 crease of the intensity of the current, since the current there 
 is six times stronger than in the first experiment, and the 
 wire presents less resistance ; but that it arises from the 
 elevation of temperature, which on account of the surround- 
 ing alcohol, is much less in this case. It even appears to be 
 very exactly proportional to this elevation of temperature, 
 whether for a platinum wire, or for one of copper, these two 
 metals being the only ones upon which Mr. Robinson has 
 operated, because they are the only ones whose co-efficient 
 of dilatation for high temperatures has been determined.* 
 
 The very considerable increase of resistance, which ac- 
 companies that of temperature in a wire, gives rise to the 
 question, to know whether the calorific effect of the 
 current, which we have seen to be proportional to the resist- 
 ance that it encounters, is proportional to this resistance, in 
 such sort that the wire possesses it before having been heated, 
 or to this resistance such as it exists, when the wire has 
 attained the temperature that is imparted to it by the passage 
 of the electricity. Mr. Robinson solved the question by en- 
 closing a platinum wire w (fig. 200.) in a 
 first glass vessel B, placed itself in a se- 
 cond A, filled with water; the wire is 
 placed in the circuit by means of the con- 
 ductors c, which receive the poles of the 
 pile. The wire w is first surrounded by 
 air ; the current that traverses it, heats it 
 gHHLJfc?!, vei T powerfully,, and its resistance in- 
 1 creases accordingly ; its heat is all em- 
 j ployed in heating the glass envelopes and 
 the water placed between them. In one 
 experiment, the quantity of water being 
 5^ cub. in. a current of a force equal to 3-527, raised the tem- 
 
 * Mr. Robinson made use of the co-efficients of dilatation given by Dulong 
 and Petit ; but he was not able to make use of the one which they have given 
 for iron, this metal being too oxidizable for its dilatation to be accurately ap- 
 preciated at high temperatures. 
 
 R 2 
 
244 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 perature of the water from 72 to 77*5 Fahr,. being trans- 
 mitted for twelve minutes; the resistance of the wire was 
 equivalent to 257*6 of the rheostat; the wire was red-white, 
 and its temperature must have been about 1500. After 
 having allowed the apparatus to cool, a portion of the water 
 was allowed to pass from the exterior into the interior vessel, 
 so as to fill it completely. The current is then transmitted, 
 which is brought to the force of 3*558, almost the same as 
 before, by placing in the circuit an additional resistance of 
 165*6 of the rheostat. The temperature rose only 2*97 
 instead of 5*5, and the increase of resistance of the wire was 
 only 89 of the rheostat, instead of 257*6. If, in this latter 
 case, we still operate with the same current, but without in- 
 troducing any additional resistance into the circuit, its force 
 is then 6*045 ; the thermometer rises to 83 2 Fahr., and the 
 increase of resistance is equal to 94*5 of the rheostat. The 
 force of the current, which has almost doubled in this case, 
 compensates and more than compensates the effect of the di- 
 minution of resistance ; whilst in the second case, the current 
 having preserved the same intensity as the former, the heating 
 is nevertheless much less ; because the resistance is not so 
 great, the wire being prevented by the water in which it is 
 plunged from acquiring the high temperature, which it had 
 in the former experiment. It follows therefore from this 
 that the true law of the heating of the wire by a current is, 
 that the heat liberated is proportional to the square of the in- 
 tensity of the current, and to the actual resistance of the wire, 
 (namely, that which results from its heating). 
 
 The researches of Mr. Robinson show us that, when a wire 
 is heated by a voltaic current, its resistance to the passage 
 of this current gradually increases until the fusion of the wire 
 takes place, and that this increase is very exactly proportional 
 to that of the temperature. It is therefore important to 
 researches in which we intend to have exact measures of 
 currents, by means of the rheostat, to take account of this 
 cause in the variation of the resistance. 
 
 We may further remark that it is perhaps a matter of 
 difficulty to explain the great increase of resistance, of which 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY, 245 
 
 we have given the numerical value, solely by the effect of the 
 little increase of the distance of the particles, which arises 
 from the elevation of temperature. Mr. Robinson found the 
 cause bearing very little relation to the effect ; he prefers at- 
 tributing the phenomenon to the direct action of heat. How- 
 ever, the great elevation of temperature, experienced by the 
 wires, producing in them a dilatation in proportion always 
 more considerable, as they are more highly heated, it would 
 not be astonishing that the increase of distance of their par- 
 ticles, that follows from this, joined to the modifications 
 that the propagation of the current itself experiences, were 
 sufficient to account for the increase of their resistance, 
 without being obliged to recur to a direct intervention of 
 heat, as we shall see in a subsequent paragraph. 
 
 The heating that is experienced by the wire, by the effect 
 of the current which traverses it, while increasing the resist- 
 ance that it opposes to the passage of this current, must 
 therefore, in diminishing at the same time its intensity, favour 
 its calorific effect ; a double result, of which one is the con- 
 verse of the other, that terminates by determining a state of 
 equilibrium between them. But, if by an exterior cause, we 
 cool one part of the wire that is red by the current, the other 
 portion immediately becomes much more incandescent, and 
 may even melt or burn ; because in diminishing by cooling the 
 resistance of a portion of the circuit, we increase the total 
 intensity of the current that is traversing it. Davy was the 
 first to observe this, by giving to his experiment a very 
 striking form, which consisted in placing a piece of ice upon a 
 portion of platinum wire made red by the current, which in- 
 creased considerably and immediately the incandescence of the 
 rest of the wire. In like manner, when this wire was made 
 red by the current along its whole length, he had merely to 
 heat a portion of it to red-white by means of a lamp, in 
 order that the rest should become cold. 
 
 This influence of the causes of exterior cooling, upon the 
 phenomenon of the incandescence of wires, gives rise, in 
 some cases, to effects that are very inconsistent apparently, 
 but which, nevertheless, enter into the general laws that we 
 
 R 3 
 
246 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 have laid down : Thus it is well known that a platinum 
 wire becomes red much more easily, and along a much 
 greater length, in vaccuo than in air ; which may be easily 
 verified, by means of the apparatus of Jig 201. which consists 
 
 H 
 
 Fig. 201. 
 
 of a tube terminated at one end by a pair of brass nippers, 
 to which one end of the wire is fixed, and at the other by a 
 collar of leathers, in which passes a metal rod, that slides 
 along the wire, so as to place a greater or less portion of it 
 in the circuit. The nippers and the rod communicate ex- 
 teriorly each with one of the poles of a pile. In proportion 
 as the air is rarefied in the tube, and as vacuum is ap- 
 proached, we perceive that a greater length of wire may be 
 made red. 
 
 But if, instead of having a single wire, there are two suc- 
 cessive wires, perfectly similar in respe t o their dimensions 
 and their nature, separated from each other by a thick con- 
 ductor, then the cooling influence of the surrounding medium, 
 produce effects that are singularly complex, and which 
 Grove was the first to point out and to study with care. 
 The apparatus that was employed by this learned English 
 philosopher, consists (fig. 202.), of two glass tubes, about ^ in. 
 
 y 
 
 Fig. 202. 
 
 in diameter, and about 1 J in. in length, closed by plugs tra- 
 versed by small copper rods, to which are attached fine pla- 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 247 
 
 tinum wires, coiled into a helix, y 1 ^ in. in diameter, and 
 about 4 in. in length, when uncoiled ; one of the tubes is filled 
 with oxygen, the other with hydrogen, and they are plunged 
 into two similar distinct vessels, each containing about 
 3 J oz. of water. A thermometer is placed in each vessel ; 
 and the wires are connected so as to form a continuous 
 circuit. A current, produced by a pile of eight pairs of 
 Grove's, each presenting a surface of eight square inches, 
 traverses them successively ; and the platinum wire placed in 
 the tube, which contains the oxygen, is seen to become red- 
 white, whilst that which is in the hydrogen tube is not 
 heated in a visible manner. Hitherto the phenomenon does 
 not appear extraordinary; since we know that the cooling 
 influence of hydrogen is comparatively much greater than that 
 of the other gases. But what is singular is, that the tempera- 
 ture of the water is raised very unequally in the two vessels. 
 Thus, in one experiment it rose in the vessel where the 
 hydrogen tube was, from 60 to 70 ; and in that in which 
 was the tube filled with oxygen, from 60 to 81, namely, 
 double the number of degrees ; analogous differences, but not 
 so considerable, are obtained with other gases. The following 
 is the number of degrees, to which water becomes heated, by 
 surrounding the platinum wire successively with different 
 gases, an<J associating it each time with a similar platinum 
 wire, surrounded by hydrogen. 
 
 Hydrogen 10- 
 
 Sulphuretted Hydrogen 10'8 
 
 Olefiant gas 16 '5 
 
 Carbonic acid - - - - -19 '8 
 
 Oxide of Carbon 19 '8 
 
 Oxygen - 21 . 
 
 Nitrogen - 21 -6 
 
 It follows from this Table that the tube in which is the gas, 
 whose cooling power is most considerable, hydrogen, is the 
 one that imparts the least heat to the water with which it is 
 surrounded. Thus, not only is platinum wire unable to 
 preserve so high a temperature in this as in the gases, which 
 is not astonishing, seeing that it is surrounded by a medium 
 
 R 4 
 
248 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 endowed with a greater amount of cooling power; but it 
 moreover receives from the current a less heat, as is proved 
 by the temperature of the water, which in each case absorbs 
 all this heat. 
 
 Whence arises this latter effect ? Is it that the gases ex- 
 ercise a conducting power, proper, but different for each, 
 which would cause a greater or a less proportion of the 
 current to traverse them instead of to pass entirely by the 
 wire ? But the study that we made in the preceding Chapter, 
 of the electric conductibility of the gases, does not allow us 
 to adopt this explanation. 
 
 It is to Clausius that we are indebted for having found 
 the true cause of this anomaly, which is due to the wire's 
 becoming a better conductor in cooling ; hence the current, 
 in traversing it, meeting with a less amount of resistance, 
 developes in it less heat. Thus the hydrogen, in Grove's 
 experiments, plays the same part as the ice in Davy's ; it 
 cools the platinum wire more than another gas does ; by this 
 it renders it a better conductor, consequently, less susceptiole 
 of being heated by the current, whilst at the same time it 
 facilitates the transmission of this current ; and in thus in- 
 creasing its intensity, contributes to the more considerable 
 heating of the wire placed in the other gas. 
 
 It follows from this that the more considerable the cooling 
 power exerted by a gas, the more conductive it will render 
 the platinum wire, at the same time it will diminish the 
 elevation of temperature, which is produced in it by the 
 passage of the current. Mr. Grove himself found this to be 
 the case, by placing in the voltaic circuit, with a chemical 
 voltameter, the platinum wire, surrounded successively by 
 each of the gases. The following is a Table of the results : 
 
 Gas surrounding the Wire. 
 
 Quantity of Gas liberated 
 per Minute. 
 
 Hydrogen 
 Olefiant gas 
 
 138-6 
 126-0 
 
 Oxide of carbon 
 
 118-8 
 
 Carbonic acid - 
 
 118-8 
 
 Oxygen - 
 
 117-0 
 
 Nitrogen 
 
 115-0 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 249 
 
 The order of the gases in this Table is perfectly the same 
 as in the Table in which is contained the cooling power of 
 each gas upon the platinum wire. 
 
 The laws that regulate the liberation of heat by the passage 
 of the current through wires, is equally applicable to the 
 case of liquid conductors, as M. E. Becquerel demonstrated, 
 making use successively of two solutions, the one of sulphate 
 of copper, the other of sulphate of zinc.* He took the pre- 
 caution to use as electrodes, in the former case, copper wires, 
 in the latter, zinc wires, so as to avoid chemical changes in 
 the liquid, during the continuance of the experiment. A ther- 
 mometer, plunged into the liquid, indicated its temperature, 
 and a chemical voltameter placed in the circuit, measured 
 the intensity of the current. - Every precaution was observed, 
 as with the wires, to take account of the cooling of the liquid, 
 which was contained in a platinum crucible. The following 
 are the quotients, for each solution, that are obtained by 
 dividing the number which represents the quantity of heat 
 liberated in each experiment, by the square of the number, 
 that represents the corresponding intensity of the current : 
 
 Experiments. 
 
 Sulphate of Copper. 
 
 Sulphate of Zinc. 
 
 1st. Experiment 
 2nd do. 
 3rd do. 
 4th do. 
 
 0-2158 
 0-2205 
 0-2032 
 
 0-4280 
 0-3025 
 0-3190 
 0-4123 
 
 Means 
 
 0-2132 
 
 0-3654 
 
 The very sensible equality of these quotients, in each series 
 of experiments, notwithstanding several deviations, due to 
 the difficulties of the experiment, especially sensible with 
 sulphate of zinc, very well shows that for the same liquid, the 
 quantity of heat is proportional to the square of the intensity of 
 the current. 
 
 By comparing the electric resistance of the two solutions 
 with that of a platinum wire taken as a standard, we find 
 
 Each solution contained 60 grs. of sulphate in 300 grs. of water- 
 
250 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 this relation equal to 0*0261 for the solution of sulphate 
 of copper, and to 0*0320 for that of sulphate of zinc. 
 But, from the experiments, the standard wire possesses a 
 conductibility, such that for a current capable of giving 
 061 cub. in. of gas per minute, the quantity of heat li- 
 berated would be 10*027. Therefore, if the law of pro- 
 portionality of the heat liberated to the resistance is true 
 for liquids, as for solids, we shall find the quantity equal, 
 for sulphate of copper, to 10*027 X 0-0261 = 0-26; for sulphate 
 of zinc, to 10*027 x 0*032 = 0*32. By experiments, we 
 obtained 0*21 and 0*36. 
 
 The tolerably large differences, which are here mani- 
 fested between the results of calculation and those of ex- 
 periment, may be due to the chemical effects that necessarily 
 occur at the surface of the electrodes, even when we have 
 chosen the latter, so as to annul these effects as much as 
 possible. Also, when engaged with liquids that undergo a 
 real chemical alteration by the effect of decomposition, we 
 must necessarily take account of these effects ; for this 
 decomposition is always brought about by absorbing the heat 
 necessary for the new molecular equilibrium, a heat con- 
 stantly less than that which is liberated by the effect of 
 the resistance of the body to the passage of electricity, which 
 is thus found diminished from the former, which we shall 
 endeavour to estimate in the following Chapter. 
 
 It is not only in the liquid conductor interposed between 
 the poles of the pile, but also in that in which the pairs 
 are plunged, that we may verify the accuracy of the laws, 
 that we have been stating. Mr. Joule has, in fact, proved that 
 the heat developed in a given time in each pair by voltaic 
 action alone, is proportional to the resistance of conductibility 
 of this pair, multiplied by the square of the intensity of the 
 electric current. From this law, combined with the pre- 
 ceding, the general principle is deduced that the heat, that is 
 developed in any part of the circuit, is proportional to the 
 square of the force of the current, multiplied by the re- 
 sistance of this part of the circuit. If the law is exact for a 
 part of the circuit, it must, according to the very just re- 
 mark of M. Poggendorff, be applicable to the whole of the 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 251 
 
 circuit, including the pile. Hence the greater part of the 
 differences that we have described (p. 240.), as existing be- 
 tween the voltaic pile and the electric battery, with regard 
 to their calorific action. Mr. Joule has deduced also certain 
 conclusions from the general law, which he has verified by 
 experiment, of the relations that exist between the heat 
 liberated by the entire circuit, and the chemical actions 
 that occur in the circuit, both exteriorly to the pairs, and 
 in the pairs themselves. The explanation of these researches 
 cannot conveniently be given, until after having completed 
 the study of the chemical effects of the current. 
 
 I must, however, before terminating this paragraph, make 
 mention yet of an important principle, that I made known 
 in 1843, and which M. Favre has recently confirmed by 
 more direct experiments. This principle consists in the fact 
 that the sum of the quantities of heat liberated by a given 
 current, in the metal conductor, by which the poles of a pair 
 are connected, and in the pair itself, is constant ; only ac- 
 cording to the thickness of the wire that serves as a con- 
 ductor, it is sometimes one, and sometimes the other, of 
 these two quantities that is the more considerable. A very 
 simple method of making the experiment is to employ a pair 
 of platinum and distilled zinc or cadmium with very pure and 
 concentrated nitric acid for the liquid ; and to unite the two 
 metals by a platinum wire of greater or less thickness, which 
 is entirely plunged into a capsule, similar to that in which 
 the pair is contained, and filled with the same quantity 01 
 nitric acid. We observe carefully, with two very sensitive 
 thermometers, the elevation of temperature of the acid in 
 each of the two capsules ; and we find that their sum, at 
 the end of a given time, is always constant, the one being 
 sometimes more, sometimes less considerable than the other. 
 We may in like manner plunge the platinum wire by which 
 the two metals of the pair are connected into the same liquid as 
 the pair itself, and we see that for the same time, the eleva- 
 tion of temperature of this liquid is always the same, what- 
 ever be the thickness of the platinum wire. In both modes 
 of operating, it is necessary to solder to the platinum and 
 
252 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 and to the zinc or cadmium of the pair a rod of platinum 
 of such thickness that it cannot become heated ; by means 
 of these two rods, the platinum wire of variable dimensions 
 is placed in the circuit. 
 
 M. Favre employed a calorimeter similar to the one he had 
 used in the beautiful experiments that he had made in con- 
 junction with M. Silbermann, upon the heat liberated in 
 different chemical actions, in order to confirm and to extend 
 the principle that I have just stated. He also made use of 
 a single zinc -platinum pair, and water acidulated with one- 
 twentieth sulphuric acid ; and he interposed successively in 
 the circuit platinum wires of variable length and of different 
 diameters. He always found that for 500 grs. of zinc 
 dissolved, a total quantity of heat developed, equal to 18,137 
 units of heat, but distributed differently between the pairs 
 and the platinum wire, according to the dimensions of this 
 latter. But this quantity of heat is precisely that which is 
 liberated by the mere solution of 500 grs. of zinc in acid- 
 ulated water, by the effect of the different chemical actions 
 that occur in it, whether the sulphate of zinc be formed by 
 a transmission of electricity through a large wire, which 
 offers no resistance to the current, or is formed directly 
 without electricity transmitted ; in this latter case, the 
 quantity of heat was 18,444 instead of 18,137, which is 
 evidently due merely to certain errors of experiment. M. 
 Favre concludes from this that the heat developed by the re- 
 sistance to the passage of electricity in the conductors of the 
 pile, is a simple subtraction made from the total heat produced 
 by the chemical actions that occur in the pair or pairs ; and 
 that it is rigorously complementary to that which remains 
 confined there, so as to form a sum equal to the total heat 
 corresponding only to the chemical reactions, independently 
 of the whole electricity transmitted. 
 
 It would follow from M. Favre's law that, like as all 
 chemical actions do not produce the same quantity of heat, so 
 also the same quantity of dynamic electricity might also 
 produce very different calorific effects, according to the 
 nature of the chemical action which might have given rise to 
 

 CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 253 
 
 it. M. Botto had already demonstrated this in some re- 
 searches, in which he endeavoured to compare together the 
 quantities of heat, liberated by the electricity derived from 
 pairs of a different nature. We shall return to this subject, 
 and to the different labours to which it has given rise, 
 when we are engaged with the production of electricity by 
 chemical actions. We shall content ourselves for the present 
 with observing, that this very important element of the vol- 
 taic current, namely, the nature of the action that gives 
 rise to it, or, which comes to the same thing, the nature 
 of electro-motive force, plays, in the production of calo- 
 rific effects, a part analogous to that of the density of elec- 
 tricity in the liberation of the heat brought about by electric 
 discharges. This very just remark of Riess's, reveals to us 
 that it is necessary, in like manner as we distinguish in 
 discharges the density of the quantity, to distinguish in 
 currents the intensity that would correspond to the density of 
 the quantity : the study of the chemical effects of electricity 
 will demonstrate to us this also. 
 
 Incandescence and Fusion of Metals by Dynamic Electricity; 
 and the Molecular Effects with which they are attended. 
 
 We have confined ourselves in the two preceding para- 
 graphs, to searching out the laws that regulate the simple 
 heating of wires by dynamic electricity, without occupying 
 ourselves with the changes, either permanent or transitory, in 
 their appearance, which accompany this heating, when the 
 electricity passes a certain degree of intensity. We have 
 already made mention of these effects, both in the second 
 paragraph of this Chapter, as well as in the fourth paragraph 
 of the preceding. They consist essentially in incandescence, 
 fusion, vaporization, as well as in inflexion, rupture, and other 
 molecular modifications, which the wire suffers, by the 
 passage of electric discharges, relatively more powerful than 
 those which produce simple heating. The facts of this order 
 are indeed essentially produced by discharges rather than by 
 electric currents, being the result of a sudden and very in- 
 
254 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 tense action, rather than of a me derate but continuous action ; 
 powerful currents, however, are in certain cases, able to ma- 
 nifest them. It is from Riess that we shall derive the greater 
 portion of the details, that we shall give in the study upon 
 which we are about to enter. 
 
 The first mechanical effect, that a thin wire experiences, 
 when traversed by the discharge, consists of a sensible shock 
 and of the formation of grey thick vapour, composed of 
 metal particles detached from its surface. Sparks are 
 at the same time manifested at the points of attachment 
 of the wire with the conductors, intended for placing it 
 in the arc, by which the circuit of the battery is closed ; 
 these sparks arise from the metal particles, a little larger 
 than the former, which are torn off from the points of 
 attachment, and which scintillate in becoming incandescent. 
 The shaking is more sensible as the wire is more mobile ; 
 and, with regard to the sparks, they are more brilliant with 
 platinum and palladium than with silver and brass ; and 
 there a*e none with copper. The scintillation even of the 
 sparks depends at once on the tenacity of the metal and on 
 its degree of oxidizability ; also, there is none with silver, 
 whilst with iron it is very powerful. The formation of 
 the cloud of vapour is a phenomenon much more constant ; 
 but its intensity varies, not only from one wire to the other, 
 but also in the same wire from the state of its surface. 
 Thus a platinum wire, which has been well polished, care- 
 fully adjusted, and hermetically secured to its points of 
 connection, requires a more powerful discharge than another 
 similar wire, but which is not under the same conditions, 
 in order to manifest the phenomena, that we have been 
 pointing out. By gradually augmenting the force of the 
 discharge, an alteration is observed in the physical state 
 of the wire, which becomes persistent ; it is an inflection 
 that is at first manifested only as a diminution of polish 
 in one point of the surface, and which ends by becoming 
 more and more sensible, and by transforming itself into 
 a very appreciable angle with sides some tenth of an inch 
 or so in length. This angle is generally very obtuse, often 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 255 
 
 110. It is equally manifested in wires of platinum, iron, 
 and copper, even when they have considerable diameters. 
 Its formation is more difficult, when the wire is strongly 
 stretched ; its place is then frequently supplied by a simple 
 slight notch or by a tearing of the wire itself, which occurs 
 where the inflexion would have been formed, if the wire 
 had been able to yield. The undulating appearance, that 
 is presented by the wires, when they have been raised 
 several times in succession to a state of incandescence, 
 by repeated discharges, is due to the formation of several 
 of these angles, which modify each other in this manner. 
 
 To these inflexions we may evidently trace the shortening 
 of wires, which have suffered a great number of discharges, 
 and which Nairn and Van Marum had long ago pointed out, 
 the former having succeeded, by means of fifteen powerful 
 and successive discharges, in making an iron wire, that was 
 10*6 in. in length and y 1 ^ in diameter, *78 in. shorter; the 
 latter having, by a single discharge, made an iron wire 25^ 
 in. in length, *31 in. shorter. Riess has actually shown 
 that a platinum wire 6-8 in. in length, which had suffered 
 a shortening of '46 in. by the effect of discharges, returned, 
 within about *07 in. of its primitive length, by being simply 
 drawn between the fingers; he satisfied himself that this 
 apparent shortening is always due to the inflexions which, in 
 certain cases, escape a superficial observation. 
 
 M. E. Becquerel had equally observed that, whether in 
 air or in vacuo, wires of platinum and of silver, of a very 
 small diameter, shorten and become undulated, under the 
 action of one or of several discharges ; and that this effect 
 increases with the number of the discharges. 
 
 The incandescence of wires is subject to the same laws 
 as the simple heating : Riess has demonstrated this by placing 
 in the closing arc an electric thermometer, furnished with 
 a wire, sufficiently strong not to undergo mechanical altera- 
 tion, but to suffer a simple heating by the effect of the 
 discharge, whose intensity it serves to measure. Thus, in 
 seeking to determine the quantity of electricity and the 
 number of jars, necessary for bringing a platinum wire of 
 
256 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 a given dimension to a state of incandescence visible by 
 daylight, it is found that in order that the heating, indi- 
 cated by the electric thermometer, and the incandescence 
 shall remain the same, it is necessary that the product 
 of the quantity of electricity by its density shall be constant. 
 
 o 
 
 In the experiments made by Riess, this product - was at a 
 
 mean 31, q being the quantity of electricity, and - its 
 
 s 
 
 density; it follows from this that, knowing this product 31, we 
 may determine, for any number s l of jars, the quantity of elec- 
 tricity q, necessary to render the same platinum wire incan- 
 
 <7 2 
 descent. In fact, it is necessary to have - = 31 or q= A/ 31$. 
 
 The following is a Table of the comparative results of 
 calculation and observation, as Eiess obtained them : 
 
 Number of jars - -23 4 5 7 
 
 Calculated value of quantity 7'9 9'6 11 12-4 14'7 
 Observed 8 10 11 12 14 
 
 It is remarkable that the observed values agree so well 
 with the calculated values, in the appreciation of a pheno- 
 menon, in which the sensibility of the eye plays so important 
 a part. 
 
 The force of the discharge, necessary for the production of 
 incandescence is, as for simple heating, independent of the 
 length of the wire, and proportional to the fourth power of 
 its radius. In order to demonstrate the accuracy of the former 
 law, we take first a platinum wire 1*37 in. in length, and find 
 that, in order to render it incandescent, a discharge is required 
 determining in the electric thermometer a heating equal to 8, 
 produced itself by 4 jars, with a quantity of electricity q = 12, 
 or by 7 jars with q = 15, which comes to the same thing, 
 according to the preceding law. With a wire five times 
 longer, namely 6 '85 in., we require, it is true, with 4 jars, a 
 quantity of electricity q = 22, but producing on the thermo- 
 meter the same heating, 8, which proves that the force of the 
 discharge has remained the same. 
 
CHAP. IT. EFFECTS OF DYNAMIC ELECTRICITY. 257 
 
 The second law results from experiments made with five 
 wires of different diameters, placed successively with the 
 electric thermometer in the same closing arc. By calcu- 
 lating, according to the law, what ought to be the force of 
 the discharge, or, which comes to the same thing, the tempe- 
 rature indicated by the electric thermometer, in order to 
 produce the incandescence of each of the five wires, and by 
 comparing the result of calculation with that of observation, 
 the following Table is found: 
 
 
 Temperature of the Electric Thermometer. 
 
 
 Observed. 
 
 Calculated. 
 
 0-00157 in. 
 
 1-2 
 
 1-3 
 
 0-00184 
 
 2-7 
 
 2-3 
 
 0-00231 
 
 5-8 
 
 5-4 
 
 0-00255 
 
 8.1 
 
 8-0 
 
 0-00353 
 
 31-0 
 
 32-4 
 
 When the object is to compare the electric charges ne- 
 cessary for producing the incandescence of the divers metals, 
 the experiment is much more difficult ; because the colour of 
 the metal, its greater or less facility of oxidising, render the 
 observation uncertain. However, Riess succeeded, by the 
 same method as the above, in determining for wires of the 
 same diameter, but of different natures, the force of discharge 
 necessary, in order to render them incandescent. The 
 following are the results, that he obtained with the metals of 
 commerce, and consequently those, whose chemical purity 
 cannot be guaranteed. 
 
 Iron - -0*816 
 
 German silver - - 0-950 
 
 Platinum - 1 '000 
 
 Palladium 1-070 
 
 Brass ------ 2'590 
 
 Silver - - 4'980 
 
 Copper - 5-950 
 
 We plainly see that, in order to produce the same incan- 
 descence in each wire, the force of the discharge must be 
 
 VOL. II. S 
 
258 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 greater, in proportion as the resistance to the passage of 
 electricity is less ; a result similar to what we had obtained 
 for heating, and which had for a long time been proved, as 
 we have remarked, by a great number of philosophers, both 
 for the incandescence produced by discharges, and for that, 
 which is brought about by the electric current. But, in- 
 dependently of this cause, the specific heat of the metal, and 
 its density, must exert an influence, which might be accurately 
 estimated, if we could be certain that incandescence com- 
 menced for the different metals at the same temperature. In 
 this case, indeed, we ought to obtain the same quotient by 
 dividing the product, formed of the force of the discharge 
 necessary for each metal, in order to become incandescent, 
 multiplied by its electric resistance, by the product of its spe- 
 cific heat and its density ; and this is what does not take 
 place. This is due to other circumstances, exercising an in- 
 fluence over the incandescence, such, especially as the 
 greater or less facility, with which the metals absorb the 
 oxygen of the air. We cannot therefore attach a great 
 theoretical importance to the results included in the above 
 Table. 
 
 It remains, therefore, for us to study the phenomena of 
 tearing, of fusion, and of pulverisation, which succeed to an 
 incandescence, brought about by a charge too powerful for 
 the wire to be able to remain intact or to suffer merely 
 simple inflexions ; these are effects partly calorific and partly 
 mechanical, which it is important to analyse well, in order 
 to form a correct idea of this order of phenomena. 
 
 When we gradually increase the quantity of electricity, 
 necessary for the production of the simple incandescence of 
 the wire, we at first obtain a very vivid incandescence, then 
 the wire becomes very white, and finally it breaks into two 
 or into several fragments ; the aspect of these fragments 
 shows that it is rather a tearing than a fusion that is brought 
 about. The difference between the intensity of the discharge, 
 which simply produces incandescence, and that of the discharge 
 that produces the tearing, varies with the nature of the 
 metals; it is great with platinum and palladium, smaller 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 259 
 
 with copper, silver, and iron, and very feeble with brass. It 
 is much less for a metal, that has already suffered the dis- 
 charge, than for that, which suffers it for the first time. In 
 order to examine the state of the fragments, we must place 
 the wire in a glass tube ; we sometimes perceive the 
 fragments to become soldered one to the other ; but they 
 present no trace of fusion at their extremities, which are 
 pointed, as if the wire had been broken, by a force that 
 would have drawn it in the direction of its length. In order 
 to avoid these superficial fusions, we must employ a more 
 powerful discharge. Thus in a bell-glass 7^ in. in height, 
 and 5f in. in width, a battery of five jars rendered a plati- 
 num wire 1*68 in. in length, and 0-00279 in. in radius, in- 
 candescent with a quantity of electricity equal to 12 ; and 
 broke it into several fragments with a quantity equal to 1 7 ; 
 whilst a copper wire, under the same conditions, required 
 23 of electricity, in order to become incandescent, and 27 in 
 order to be torn. The metals, that enter easily into fusion, 
 such as wires of tin and of cadmium, are torn without passing 
 through incandescence. 
 
 If we exceed the force of discharge, that tears the wire, 
 we succeed in melting it, at the same time breaking it into a 
 large number of fragments. Thus, a platinum wire similar 
 to that, which had been torn by the quantity of electricity 
 equal to 17, was broken and partially melted, with a quantity 
 equal to 20. Wires of silver and of tin experience the same 
 effect. But, in order to obtain a complete fusion, more 
 powerful discharges are necessary. The wire is then re- 
 duced into perfectly round small balls ; this is easily observed 
 with wires of platinum and silver; for a copper wire 1/41 in. 
 in length, and 0*0022 in. in radius, a battery of six jars 
 raises it to incandescence with a quantity of electricity 
 equal to 25 ; and, with a quantity equal to 30 only, it divides 
 it into an infinite number of small and scarcely perceptible 
 balls. The difference between the quantities of electricity is 
 very small; this is probably due to the circumstance that, 
 with easily oxidisable metals, the temperature is increased 
 by the presence of the oxygen of the air ; it thus adds a che- 
 
 s 2 
 
260 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 mical heating to the electric heating. This effect is especi- 
 ally sensible with iron, which often melts under the influence 
 of discharges, that could only have produced a moderate 
 amount of heating. Incandescence in this case does not cease 
 immediately after the discharge has taken place, as commonly 
 happens, but the wire attains to white incandescence, and 
 melts into drops, which spurt in scintillating. 
 
 Fusion is therefore a very complex phenomenon ; so that 
 it is impossible to establish for each kind of metal the force 
 of discharge, necessary for melting it ; the more so because, 
 as Van Marum has observed, all the electricity of the 
 battery is not employed in bringing about the fusion, and 
 that there remains a residue in the battery itself, which is 
 sometimes very considerable. This effect, which Riess has 
 studied with care, is due to the electricity producing the 
 disorganisation of the wire, in an instant too short to allow 
 time for its passage entire. It is very curious that the re- 
 sidual after the reduction of a wire into fragments, is 0*23 
 of the whole of the electricity, that was in the battery ; 
 whilst it is only 0*15, namely less considerable, after the 
 simple explosive discharge through air. 
 
 We have seen that the first effect of the discharge upon a 
 wire is the formation of a small cloud of vapours, which 
 proceed from the particles detached from the surface. With 
 a sufficiently powerful discharge, we are able to reduce even 
 the whole mass of the wire into a similar vapour. A platinum 
 wire, subjected to the discharge of five jars, became incan- 
 descent with q = 13, melted into small globules with q = 17, 
 and disappeared with a brilliant light, leaving the tube, 
 within which it was enclosed, covered with a grey film, that 
 might easily be removed. In the open air, the vapour 
 collected upon a plate of copper presented grey and blackish 
 spots, which appeared to be formed of metal fragments, of 
 various forms and sizes, and which presented no traces of fusion. 
 The pulverisation, therefore, is very distinct from fusion ; and 
 what proves this is that tin, which requires for its melting 
 a less charge than cadmium, requires a greater, in order to 
 its becoming pulverised. In general, in the open air, the 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 261 
 
 pulverised metal is at the same time oxidised : we may collect 
 very visible traces of this, by placing upon a sheet of white 
 paper, the wire that is to be pulverised, and, if we desire to 
 obtain traces of the metal itself, and not of its oxide, we have 
 merely to pulverise it in a bell-glass, where there is nitrogen 
 or very rarefied air. We must take care in these experiments 
 to stretch the wires well, placing them between two sheets of 
 paper. 
 
 To sum up, if we follow the series of effects, that are pro- 
 duced by discharges of increasing intensity, we find that 
 the wire begins by heating, that it suffers a shaking, then 
 inflexions, that it becomes incandescent, that it is torn from 
 the pincers in which it was fixed, that it is broken into 
 fragments, melted, and finally pulverised. The calorific and 
 mechanical effect, are thus found mingled together, in a 
 manner not only to succeed each other alternately, but also 
 to be found simultaneously in several cases. Thus the incan- 
 descence of a wire never occurs, without there being at the 
 same time inflexions, and it is rare that a fusion is obtained, 
 without there being at the same time a rupture of the wire 
 into fragments. The pulverisation, likewise, is always 
 attended by a great elevation of temperature, as is proved by 
 the oxidisation of the metallic powders. This association of 
 the two species of effects leads to the presumption that they 
 are connected by a mutual dependence. And, indeed, it is 
 easy to prove that incandescence and fusion are not a simple 
 effect of the liberation of heat by the discharge, following the 
 laws established by experiment ; for this heat, the intensity 
 of which may be calculated by knowing the force of the 
 discharge, would be far from sufficient to produce incan- 
 descence and fusion. There is, therefore, in the production 
 of these two phenomena, a direct effect of electricity, in- 
 dependently of the indirect action which it exercises in the 
 production of heat. Riess estimates that this double mode 
 of action is due to the transmission of the charge being 
 brought about, in a manner altogether different, for the 
 production of the heating of the wire, from that in which it 
 takes place in order to cause mechanical effects, in the 
 
 s 3 
 
262 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 number of which must be placed incandescence and fusion. 
 We shall return to the mechanism itself of the discharge, 
 when we shall have studied its calorific and luminous 
 effects, in its passage through imperfect conductors.* 
 
 This mechanism appears, in certain points, to differ from 
 that of the voltaic current, which would only possess the 
 mode of transmission, proper for the development of heat; 
 for, with this current, the phenomena of incandescence and 
 fusion, appear to be nothing more than a simple consequence 
 of an increase of heating ; and no such mechanical effects as 
 rupture and pulverisation are observed. However, we may 
 notice in wires, that have suffered incandescence, an alteration 
 at their surface of the same kind as that which we have 
 called inflexion. This alteration is even more profound ; for 
 wires, that have been rendered incandescent by the passage 
 of a powerful voltaic current, become more brittle, and seem 
 to undergo a modification in their molecular structure. I 
 have often observed this with platinum wire, a proof that this 
 is not an effect of oxidisation. 
 
 There exist, also, in the calorific and luminous effects, 
 produced by piles of high tension through imperfect con- 
 ductors, particular phenomena, which equally denote a kind 
 of mechanical action, exercised by currents, analogous, up to a 
 certain point, to that of discharges. Finally, for the effects 
 of the incandescence of wires by the current, we should 
 have to prosecute a study, analogous to that, which was 
 made by Riess for discharges; and perhaps we might 
 find more varied results and more detailed laws than those 
 which we have stated wherein we treated upon this subject. 
 
 Calorific and luminous Effects of Discharges through imperfect 
 
 Conductors. 
 
 After having studied the luminous, and principally 
 calorific effects of dynamic electricity, when it is transmitted 
 through good conductors, it remains for us to turn our 
 
 * Grove has also observed a remarkable shortening in leaden wires after 
 having once conducted the electric current. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 263 
 
 attention to the same effects, when the conductor is imperfect. 
 This imperfect conductor may be solid, liquid, or gaseous ; 
 but it is more particularly in the two latter cases, and espe- 
 cially in the last, that the phenomenon, at the same time 
 calorific and luminous, that accompanies either the electric 
 discharge, or the passage of a current, is manifested. We 
 shall, in the study of the phenomenon, distinguish the case, 
 in which it is produced by discharge, the one which is 
 now about to engage our attention, and the case, in which 
 it is produced by current, to which we shall consecrate the 
 following paragraph. 
 
 In general, the luminous appearance, that accompanies 
 the electric discharge through an imperfect conductor, we 
 call the electric spark. This appearance is presented under 
 very various forms, according to the physical state, and 
 the nature, either of the medium, in which it is manifested, 
 or of the good conductors, commonly metallic, between 
 which the discharge is brought about. In the common air, 
 and with conductors in the form of balls and made of brass, 
 the spark has the form of a line of a white colour, with a 
 slight reddish tinge at its two extremities. If the discharge 
 is powerful, the spark is long, and formed of broken and 
 slightly curved lines. With good electrical machines, and 
 without the assistance of Leyden jars, we may obtain sparks 
 of a foot in length, very white and very brilliant, in which 
 the zig-zag form is very decided. This form is evidently 
 due to a condensation of the air, which being brought about 
 in the direction of the discharge, obliges it to deviate laterally, 
 but in no way modifies its point of departure and its point of 
 arrival. 
 
 We may increase the luminous effect of the spark, by 
 means of spangled tubes, which are glass tubes, upon which 
 are glued in a spiral form little lozenges of tinfoil, the 
 points of which are very near to each other. At their 
 extremities, are fixed balls of metal, which are in communi- 
 cation with the lozenges next to them ; one of the balls is 
 held in the hand ; and, on drawing sparks from an electrical 
 machine with the other, sparks are seen to dart at the 
 
 8 4 
 
264 TRANSMISSION OF ELECTRICITY PART iv. 
 
 same time between all the points ; but the light ceases to be 
 so vivid } and it acquires a reddish tint, which it owes in part 
 to the form, and in part to the nature, of the little lozenges. 
 
 Before investigating the properties of the spark, and in 
 particular its luminous properties, we must analyse the 
 circumstances, that exert an influence over its form, and 
 in general over its appearance. These circumstances are 
 chiefly the intensity of the discharge, which gives rise to 
 it, then the form of the conductors between which it escapes, 
 and the nature of the medium, that it traverses. The nature 
 of the conductors, between which it moves, may modify its 
 colour, but not its form. 
 
 In atmospheric air, under the ordinary pressure, the 
 electric spark often acquires the form of a brush. This 
 form is presented, when the electricity of a 
 machine escapes by an angular part of its 
 conductor (Jig. 203.), or escapes from a 
 conductor, surrounded by a piece of cloth or 
 Fig. 203. s i|]^ covered with metallic powder. At its 
 point of escape, the spark presents only a line ; but it very 
 quickly ramifies into a bundle of small sparkling filaments. 
 With a good electrical machine, it is sufficient to fix upon 
 its conductor a long metal rod, a quarter of an inch or so 
 in diameter, terminated by a little ball some f in. in 
 diameter, in order to see a beautiful brush dart from the 
 ball (jig. 204.), when the machine is put 
 into action. If a smaller ball is employed, 
 still having the same electrical machine, the 
 brush is more feeble, and the sound, that 
 accompanies it, although less decided, is 
 more continuous. With smaller balls, or 
 with conductors, terminated in fine points, 
 the brushes diminish still more, and the 
 sound becomes scarcely perceptible. When 
 the sound ceases, the light changes in appear- 
 ance, and becomes continuous, like a glow, 
 instead of appearing like a succession of 
 small points of very vivid light. 
 
CHAP. n. EFFECTS OF DYNAMIC ELECTRICITY. 265 
 
 The brush seems, therefore, according to Faraday, who has 
 made a very special study of it, to be the result of a succes- 
 sion of little discharges between the conductor, and the suc- 
 cessive particles of air, polarised by induction. This would 
 explain the production of the sound. Wheatstone, indeed, 
 showed, by means of his turning mirror *, that the brush, al- 
 though it seems to be continuous, consists of successive and 
 intermittent discharges. Faraday justly regarded this phe- 
 nomenon as the result of the discharge, that occurs through 
 air, between the extremity of the electrised conductor and a 
 neighbouring body, in the absence of the walls of the apart- 
 ment, electrised by induction. The interposed air is polarised, 
 as every other di-electric body would be ; and as the filaments 
 of air converge toward the point of the conductor, from 
 which the brush sets out, it is in the neighbourhood of this 
 point that their polarity is the strongest. So that, when this 
 polarity becomes sufficiently powerful for discharge to 
 take place, the filaments of air are luminous only in their part 
 that is nearest to the point, from which the brush originates, 
 where they are most concentrated. Further on, there is 
 indeed a succession of discharges, but the filaments being 
 more divergent, the intensity is more feeble ; there are only 
 obscure discharges without light. The inductive influence of 
 neighbouring bodies is so necessary for the production of the 
 phenomenon, that, when the electrical machine is feeble, we 
 have merely, in order to give rise to the brush, to bring the 
 hand or a conducting body near, in order to bring it about, 
 and to give it a form and a direction, which vary with the 
 
 * We have seen that Wheatstone succeeded, by means of the reflection pro- 
 duced by a mirror, that turns around an axis with very great rapidity, in 
 seizing the slightest differences of time, between luminous appearances, that 
 seem to be simultaneous (vide p. 182.). By the same method, he assured 
 himself of the instantaneity of the light of the spark, the image of which is 
 not changed by the movement of the mirror, whilst that of the brush is elon- 
 gated in the direction of the movement ; which proves that the discharges 
 of which it is constituted, endure for a certain time, appreciable by the move- 
 ment of the mirror. At the same time, the successive sparks, that constitute 
 the bundle, which is itself placed on the prolongation of the axis of the 
 turning mirror, being each reflected by a different part of the mirror, present 
 themselves as if arranged at regular distances in a circle, a proof of their dis- 
 continuity. 
 
266 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 position of the conductor (figs. 205, 206, 207.), so as to 
 demonstrate that it is really the result of the discharge, that 
 is brought about between the two conductors. 
 
 Fig. 205. 
 
 f 
 
 \ 
 
 Fig. 206. V > 
 
 Fig. 207. 
 
 In the preceding experiments, the electricity of the con- 
 ductor, whence the brush originated, was constantly positive ; 
 ^ if the conductor, terminated in a point, is charged with 
 X negative electricity, then we see appearing upon it, a 
 simple luminous point, or rather, as it were, a little lu- 
 minous star. But we may nevertheless obtain a brush 
 with negative electricity, by using, instead of a point, 
 a conducting rod terminated by a rounded form. 
 Only the brush is much shorter (fig. 208.), and the 
 -,. ^ succession of discharges, of which it is composed, is 
 much more rapid (seven or eight times) than in the 
 case of positive electricity, as is indicated by the sound that 
 accompanies it. 
 
 Another very remarkable difference may be observed, when 
 the rounded end of a wire, that is held in the hand, is brought 
 near to the negative brush : this extremity becomes positive 
 by induction, and shows, even at the distance of 7 or 8 in., a 
 brilliant glow, without any change having yet occurred to the 
 negative brush ; but at a less distance, the sound of the nega- 
 tive brush becomes more acute, which indicates a more rapid 
 succession of the small discharges, of which it is composed ; 
 
I 
 
 CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 267 
 
 at a still less distance, a positive brush shows itself at the ex- 
 tremity of the induced conductor, but, 
 ; at the same time, the negative is con- 
 tracted ; and, both of them are seen 
 simultaneously with a very different 
 appearance (Jig. 209.). By employing 
 as an induced conductor a rather fine 
 wire, we are able to obtain, at a 
 certain distance, two brushes, one 
 positive, the other negative, perfectly 
 similar and giving sounds in unison. 
 
 To conclude, the negative conductor comports itself like a 
 positive conductor, the electricity of which has less tension, 
 which is in accordance with the remark that we have already 
 made in the First Chapter of this Fourth Part *, that negative 
 electricity discharges itself in air, at a lower tension than 
 that which is necessary for positive. Faraday had proved 
 this fact, which had already been pointed out by Belli and 
 several other philosophers, by causing, as we have saidf, the 
 discharges to occur between balls of different dimensions, and 
 by studying the formation of the brushes on the inducing 
 and the induced balls, both positive and negative. We shall 
 see further on, that this phenomenon is due to a more general 
 difference, which exists between the properties of positive 
 electricity and those of negative, when they both, in order to 
 neutralise each other, come out from a conductor, in which 
 they are accumulated. But we have first to study the effect 
 of the nature of the surrounding medium upon the form and 
 the appearance of the spark. 
 
 When the spark is produced in a space, wherein the air 
 is rarefied, it is seen to subdivide, to become feeble, and to 
 acquire a reddish tinge. In a tube two or three yards 
 long, and in which a vacuum has been made, or at least 
 in which the air has been rarefied as much as possible, 
 the spark produces a magnificent reddish violet glow, which 
 fills it entirely, and which seems to circulate interiorly in 
 the form of a helix, which is probably due to the conducting 
 influence of the film of moisture adhering to the glass. The 
 
 * Vol. II. p. 166. t Vol. II. p. 166. 
 
268 
 
 TRANSMISSION OF ELECTRICITY. 
 
 spark is transmitted through the tube by means of two metal 
 ferules, placed at is extremities, and terminated exteriorly, 
 one by a ball, that communicates with the machine, whence 
 the spark is derived, and the other by a stop-cock, which 
 allows of vacuums being made in the tube, and which is 
 made to communicate with the ground. We may also ob- 
 serve the luminous effects of electricity, by means of the 
 electric egg, which is a glass vessel of an ovoid form, at one 
 of the extremities of which is adapted a tube, with a stop- 
 cock, 'and at the other a rod with a knob, passing into a collar 
 of leathers (jig. 210.). The air is rarefied more or less, by 
 
 Fig. 210. 
 
 Fig. 211. 
 
 screwing the tube on the plate of an air-pump ; in proportion 
 as the air is rarefied, the knob of the movable rod may be 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 269 
 
 withdrawn further from that of the fixed rod, adjusted to 
 the stop-cock ; and the spark as it becomes longer, loses its 
 vivacity, acquires a reddish violet colour, and is subdivided 
 into a multitude of elliptic jets. This is a true brush, of the 
 kind given in fig. 205., very long, and composed of ramifi- 
 cations very large and distant from each other, sometimes as 
 much as half an inch or more. 
 
 However, when the discharge is very strong, such as results 
 from a powerful battery, we obtain in vacua, a light as vivid 
 and as brilliant as in air. If the light is generally feeble 
 and diffused in vacua, it is due to the discharge being en- 
 abled to take place under a far less amount of tension than in 
 air, which enables the electrical machine, with which one of 
 the knobs of the electric egg is put in communication, to give 
 off its electricity in proportion as it is developed : it is no 
 longer the same, if we accumulate the electricity by means 
 of a battery, so as to transmit the whole of it at once. 
 
 Finally, we may obtain the spark in the barometric vacuum, 
 by means of a tube bent into the form of a siphon, and forming 
 a double barometer (Jig. 211.) : the electric spark is made to 
 pass from one cup to the other, by obliging it thus to traverse 
 the two columns of mercury, and the empty space by which 
 they are separated. The spark fills this space with a diffused 
 violet light; it requires a very feeble electric tension, in 
 order that the phenomenon may take place. 
 
 Davy made a special study of the electric light in vacua, 
 or rather in spaces filled with vapours of different kinds, He 
 operated by means of a bent tube, 
 having one branch closed and longer 
 than the other (Jig. 212.). A plati- 
 num wire was cemented in the extre- 
 mity of the closed branch, so that one 
 part was outside and the other within. 
 The closed branch was filled with 
 mercury, very much purified and 
 freed of air and of aqueous vapours ; 
 vacuum was then made in the open 
 branch, which was furnished with a 
 Fig. 212. stop-cock at its extremity. An empty 
 
270 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 space, of greater or less extent, is thus formed at the top of 
 the closed branch. The spark of a machine, or, still better, 
 that of a Ley den jar, traversed this space, and produced in it 
 a luminous effect ; but this effect was much increased, by 
 gradually heating the mercury to a state of ebullition ; the light 
 was then of a green colour, the brilliancy of which was most 
 striking. In proportion as the temperature was lowered, the 
 colour lost its vivacity ; and at 29 F. the light was so feeble 
 that it could only be perceived in the most profound darkness. 
 A small quantity of air, introduced into the mercurial vacuum 
 caused the colours to change from green to sea-green, 
 then to blue and to purple. By substituting the fusible 
 alloy of bismuth and tin, in place of the mercury, a yellow 
 and very pale light was obtained ; with pure olive oil and 
 liquid chloride of antimony, the boiling temperature of which 
 was not far from that of mercury, Davy obtained a light 
 rather more brilliant than that which arose from the electri- 
 city, liberated in the mercurial vacuum ; it was of a red 
 colour tending to purple with oil, and of a pure white 
 with chloride of antimony. We may add that, when the 
 temperature is very low, it requires a very strong discharge, 
 in order that it may be transmitted through the barometric 
 vacuum. These experiments of Davy's show the important 
 part played in the production of the electric light, by the bodies 
 between which the discharges pass, and the particles, that are 
 very probably detached from them, by this discharge itself. 
 
 The spark changes also in appearance if, instead of trans- 
 mitting it through the air or through an empty space, it is made 
 to pass into different gaseous media. In nitrogen, the sparks 
 are more brilliant than in air, and are especially accompanied 
 by a very remarkable sound ; in oxygen, they are whiter than 
 in nitrogen or in air, but not so brilliant ; in hydrogen, 
 their colour is crimson ; in dry hydrochloric gas, the spark is 
 always white ; and these differences are doubtless due to the 
 greater or less facility, with which the different gases allow of 
 the passage of the discharge, as we have seen in the preceding 
 chapter.* Faraday, to whom we are indebted for these 
 * Vol. II. p. 161. 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 271 
 
 various observations, has also remarked that the electric 
 spark may be equally obtained in various liquids, such as 
 essence of turpentine, olive oil, resin, melted glass, and in 
 water itself, &c. 
 
 The brush also, like the spark, varies in appearance, with 
 the different media, in which it is produced. We have seen, 
 by the experiment of the electric egg, that, in rarefied air, it 
 is extremely brilliant, and is composed of very elongated 
 branches. It is the same in all the gases ; as soon as they are 
 rarefied, the spark is gradually converted into a brush, which 
 becomes more and more considerable and ramified in a distinct 
 manner, until, at a certain degree of rarefaction, the brushes, 
 that arise from the positive and negative conductors, unite, so 
 as to form together a continuous luminous jet. The pheno- 
 menon varies with the size of the vessel, the degree of rare- 
 faction, and the force of the spark, that is given by the 
 machine. If we now examine the appearance of the brushes 
 in the different gases, we find that in oxygen they are very 
 compressed, and in general much more feeble than in air. 
 The reverse is the case in nitrogen ; this gas is the one in 
 which they are most luminous, and in rarified nitrogen, in 
 particular, they are magnificent. In hydrogen, they are much 
 less brilliant than in nitrogen, but more than in oxygen ; their 
 colour is of a greenish grey. In oxide of carbon and in car- 
 bonic acid gas, they are difficult of production ; they are short 
 and their light is feeble. In hydrochloric acid gas, the brush 
 is still more difficult to be obtained under ordinary pressures. 
 By gradually increasing the distance between the two 
 rounded extremities of the conductors, between which the 
 discharge occurs in this gas, the sparks cease, and at a dis- 
 tance of f in. between these extremities, the discharge occurs 
 without spark and noise ; it is probable that in this case an 
 electrolytic discharge is brought about, namely an electro-che- 
 mical decomposition of the gas ; which we shall see in the 
 following Chapter. 
 
 The brush is not only observed in air and in the gases, 
 but also in more dense media. Faraday succeeded in pro- 
 ducing it in essence of turpentine, by plunging into it the 
 
272 TRANSMISSION OF ELECTRICITY. PARTIV. 
 
 end of a wire, placed in a glass tube, the liquid itself being 
 in a metal vessel. The brush was very small, and was 
 obtained with difficulty ; its ramifications were not numerous, 
 and diverged much from each other ; and a very dark chamber 
 was necessary for observing it, so feeble were its ramifications. 
 A very remarkable thing is that, whilst the medium, in which 
 it is propagated, may singularly modify the brush, the nature 
 of the body, from which it originates, does not seem to exercise 
 over it any other influence than that which arises from the 
 greater or less degree, with which this body, according to its 
 conductibility, facilitates the discharge of the machine. It 
 is the same with the negative brush ; but the latter, like the 
 positive, suffers very decided effects on the part of the 
 medium, in which it is produced. Thus the rarefaction of 
 the air facilitates its development still more than it facilitates 
 that of the positive. The superiority of the positive brush 
 over the negative, which is already very considerable in air, 
 is still greater in nitrogen. In hydrogen, on the contrary, 
 the positive brush loses a portion of its superiority, whilst the 
 negative is but little or not at all affected. Finally, in oxygen, 
 carbonic acid, and hydrochloric acid, all difference disappears 
 between the two brushes, so that it is a very difficult matter 
 to distinguish them from each other. 
 
 There exists, also, besides the spark and the brush, a 
 peculiar form, under which the light produced by the dis- 
 charge is manifested, and which we will designate under the 
 name of glow. It is manifested when we diminish the surface 
 of the ball and of the rod, that are in communication with the 
 machine ; the brushes then disappear, and their place is 
 supplied by a continuous phosphorescent glow, which covers 
 the entire end of the wire. This luminous form appears to 
 arise from the rapidity with which the discharge is renewed ; 
 for, by increasing the force of the machine and the rarefaction 
 of the air, we favour its production. 
 
 The glow is obtained with much more difficulty with 
 negative, than with positive electricity ; in order to produce 
 it, it is necessary to rarefy the air, and, by adjusting the two 
 balls to a suitable distance, we are able to obtain upon the 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 273 
 
 negative ball a glow, which covers it entirely, and equally 
 well when it is inducing as when induced. We perceive the 
 two balls, and a tolerably long portion of the two rods by 
 which they are carried, covered with this electric light. 
 
 The glow presents itself equally in all the gases. Faraday 
 thought he had obtained it in essence of turpentine, but very 
 feeble and scarcely visible ; it is accompanied in the air by a 
 puff of air coming in general from the luminous part, but 
 sometimes also directed towards it. Thus it is probably due 
 to a very rapid charge or discharge of the air, by which the 
 conductor is surrounded, and which remains adhering to it, 
 even in the most perfect vacuum. This air, by virtue of the 
 electricity that it acquires and loses, assumes a regular 
 movement, and gives rise to a continuous glow, without there 
 being any appearance of agitation. In proof of this explana- 
 tion, Faraday quotes an experiment, in which he succeeded 
 in converting a brush into a simple glow, by facilitating the 
 formation of a current of air at the extremity of the con- 
 ductor, when the brush was produced. In like manner, by 
 interfering with the current of air, a simple glow may be 
 changed into a brush. It is easy to follow the transition from 
 the glow to the brush, and from the brush to the spark. Every 
 thing that tends to facilitate the charge of the air by the 
 electrised conductor, and to preserve to this conductor its 
 same tension, notwithstanding the discharge, contributes to 
 produce the glow ; whilst circumstances that prevent the air 
 or other gases from becoming charged with electricity, and 
 which favour the accumulation of electricity upon the con- 
 ductor, determine intermittent discharges, under the form of 
 brushes and sparks. Thus the condensation of the air, the 
 neighbourhood of the hand or of any conducting surface, 
 acting by induction, the gradual approximation of a ball, 
 intended to receive the discharge, provoke the cessation of 
 the glow, and its change into a brush or a spark. In con- 
 clusion, the continuity of the discharge produces the glow, 
 the discontinuity produces the brush, and the spark when it 
 becomes more decided. 
 
 It frequently happens that, in its passage through a 
 
 VOL. II. T 
 
274 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 transparent medium^ the electric discharge is not luminous 
 throughout : this is what Faraday called the dark discharge. 
 Thus, if we separate from each other two metal rods, 
 between the extremities of which the discharge is passing 
 in rarefied air, a continuous glow is perceived upon the 
 end of the negative rod, whilst the positive extremity remains 
 altogether dark* In proportion as the distance increases, 
 a train of purple or of white light appears at the extremity 
 of the positive rod, and advances directly on the negative 
 rod; it elongates itself, but yet without ever joining the 
 negative glow, so that there is always between them a small 
 obscure space (Jig. 213.). This space, which is about y 1 ^ in. 
 
 Fig. 213. 
 
 or less in width, remains invariable in its extent, and 
 in its position, with regard to the negative point; the 
 negative glow no longer changes whilst the purple light 
 of the positive point is seen to lengthen or to shorten, 
 in proportion as the distance of the two points is made to 
 vary. An effect of the same kind is presented in all the 
 gases ; only according to the nature of the gases, the ends 
 of the two rods must be withdrawn to a greater or less 
 distance from each, in order to obtain the dark discharge. 
 In general, the position of the dark space is constant ; and 
 we may satisfy ourselves, by carefully examining the phe- 
 nomenon, that this space exists between the positive and the 
 negative glow, even when it is a difficult matter to observe 
 it, on account of the concave form of the former glow, and 
 the convex form of the latter. This experiment shows that 
 the discharge may be transmitted through a gas, without 
 necessarily rendering it luminous. 
 
 Faraday, who has much studied this question, considers 
 that the dark discharge occurs at a very feeble tension ; and 
 that, after it has commenced, the light is the consequence 
 of the greater quantity of electricity that is forced along 
 
CHAP ii. EFFECTS OF DYNAMIC ELECTRICITY. 275 
 
 the same route, finding in this direction a more easy 
 passage. 
 
 We may obtain the discharge under the form of the glow, 
 and the dark discharge, in a very decided manner, by the 
 sparks, that are produced by induction apparatus, especially 
 by RumkorfFs.* We have merely to connect the two 
 ends of the induced wire respectively with the balls of the 
 apparatus, called the electric egg(/%r. 2 10.) in order to obtain, 
 on rarefying the air, glows in all their beauty around the 
 two balls, with certain differences, however, at the negative 
 and at the positive ball. M. Rumkorff, who has repeated with 
 variations the experiments of MM. Masson and Breguet, 
 has remarked that the light which surrounds the negative 
 ball and rod, is violet ; and that which is around the positive 
 ball is a fiery red, and that it extends toward the negative 
 ball. There dart also from the two balls certain sparks more 
 white and distinct from the glows which probably arise, 
 as we shall see, from the metallic particles, detached from 
 the balls. Mr. Gassiot has observed that, when the vacuum 
 is well made, half of the negative ball is surrounded by a 
 brilliant blue flame ; whilst there escapes from the positive 
 ball a line of brilliant red light; but there is between 
 the red line and the blue flame a space completely dark. 
 
 M. Quet, on his part, has discovered that the double 
 light, which emanates from the two balls, is composed of 
 a succession of brilliant strata, entirely separated from each 
 other by dark strata; and that it is as it were stratified. 
 In order fairly to observe this phenomenon of stratification, 
 we merely require the presence, in the vacuum made in 
 the electric egg, of a very small quantity of alcohol f, essence 
 of turpentine, sulphuret of carbon, or oil of naphtha. By 
 causing the induction current of Rumkorff's machine to 
 pass between the balls, we observe a multitude of brilliant 
 strata, separated by dark strata, forming as it were a 
 
 * Vol. I. p. 389. fig. 150. 
 
 f M. Kumkorff was the first to obtain this phenomenon of stratification, by 
 placing for a few moments over an open jar filled with alcohol, the opening of 
 the electric egg, before making the vacuum in it. 
 
 T 2 
 
276 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 pile of electric light between the two poles. The stratification 
 is more decided in the red light of the positive pole, than in 
 the violet of the negative; but the number of alternately 
 dark and brilliant strata is less considerable. It is moreover 
 easy to prove that the light of the positive pole is separated 
 from that of the negative by a dark stratum, which may 
 be rendered more or less thick, according to the perfection 
 of the vacuum, and the nature of the vapour that it 
 contains. 
 
 The light in these experiments does not possess a con- 
 tinuous duration ; it consists, indeed, in a series of discharges 
 that succeed each other with rapidity. This gives rise to an 
 oscillating movement of the luminous strata, which renders 
 the observations a little difficult. In order to avoid this in- 
 convenience, M. Quet manipulated with his hand the little 
 magnetic hammer of Rumkorff's apparatus, and at each 
 movement an emission of vivid light is obtained, but 
 which endures only for an instant ; the entire succession of 
 strata, alternately brilliant and dark, are thus marked out in 
 a very distinct form; by renewing this manipulation at 
 pleasure, the details of the phenomenon may be easily 
 studied. 
 
 The colour of the light varies with the nature of the 
 vapours that are contained in the vacuum ; with that of 
 essence of turpentine we obtain, at the positive pole, a 
 beautiful white and phosphorescent light, the stratification 
 of which occurs by flat strata, but of unequal thicknesses ; 
 with the vapour of fluoride of silicium, a yellow light is ob- 
 tained at the negative pole. If the two balls are brought very 
 near to each other, one or other of the two lights is at last 
 made to disappear; this depends upon the nature of the 
 vacuum; in the vacuum where there remains only very 
 rarefied air, it is the red light of the positive pole that dis- 
 appears completely ; the violet of the negative remains alone. 
 
 This last phenomenon is precisely the same as that de- 
 scribed by Faraday under the name of the dark discharge. 
 We have indeed just seen that, when the spark is produced 
 in rarefied air, and between two conductors very near together, 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 277 
 
 the negative conductor alone is surrounded by a blue glow 
 and the positive conductor remains dark, whilst in the atmo- 
 sphere, the two conductors appear equally luminous. Elec- 
 tricity is therefore discharged from the positive conductor, 
 without producing light, as well with induction currents as 
 with the electricity of an ordinary machine. 
 
 Previously, however, to M. Quet, M. Neef, on observing 
 with a microscope the passage of an induction current 
 between a platinum point and an oscillating plate of the 
 same metal, by means of an apparatus similar to the one we 
 have already described*, had recognised that the negative 
 electrode alone was luminous. He thought he might con- 
 clude from this observation that the electric spark engenders, 
 at the negative electrode, light without heat, and at the 
 positive, heat without light. We shall return hereafter to 
 the labours of M. Neef: we will confine ourselves for the 
 present to remarking that it is still the same phenomenon of 
 the dark discharge, with this very important difference alone, 
 that it occurs in air instead of in vacuo. M. Riess has suc- 
 ceeded in demonstrating that the difference is more apparent 
 than real ; because, when the sparks succeed each other very 
 rapidly, in a very contracted space, the air is promptly rarefied 
 between the electrodes. Indeed, by varying at pleasure the 
 distance by which the point and plate of platinum are sepa- 
 rated, Riess remarked that, when the distance is rather great, 
 the spark presents no particular appearance ; there is a con- 
 tinuous luminous arc at each spark between the plate and 
 the point; by diminishing the distance, we obtain sparks 
 more and more numerous and nearer together ; finally, at a 
 shorter distance still, the spark loses all its brilliancy, and at 
 the same time a bright blue light is shown at the surface of 
 the negative electrode alone. We perceive within this blue 
 light, on observing it by means of the microscope, a certain 
 number of very brilliant white points ; which appear to be 
 particles of incandescent platinum, detached by the discharge; 
 and this is confirmed by the state of roughness, presented by 
 
 * Vol. I. p. 387.^?. 149. 
 T 3 
 
278 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the surface of the platinum plate, after having been used for 
 some time in these experiments. We may add that Mr. 
 Gassiot observed, when employing as electrodes two platinum 
 wires T J n in. apart, that the negative wire becomes fiery red, 
 whilst the positive remains cold ; in this case, the discharge 
 is very rapid and continuous. This effect would be the 
 reverse of that pointed out by M. Neef, and contrary to what 
 occurs with ordinary currents. These oppositions may 
 be due to the difficulty there is in distinguishing fairly, in 
 induction currents, the positive from the negative pole. Nor 
 must we lose sight of the fact that electro-chemical effects 
 occur, arising from the decomposition of the gases, or rarefied 
 vapours, that are traversed by the discharges, which may 
 contribute to the appearances presented by the light. We shall 
 explain these in the following Chapter. 
 
 After having studied the electric spark, the manner in 
 which it arises, and the different forms that it assumes, it 
 would remain for us to examine its various properties ; but 
 we shall return to this examination in the eighth paragraph, in 
 order to make it comparatively with that of the voltaic arc ; 
 and thus to be able, when appreciating the differences that 
 characterise these two forms of the same phenomenon, to 
 trace them to their common cause. We shall confine ourselves 
 here to saying a few words on the calorific effects of the 
 spark, of which we have already had examples, in the inflam- 
 mation of combustible bodies, and especially in the experiment 
 of Yolta's pistol. Chemistry derives great advantage from 
 this property of the electric spark, in order to bring about the 
 combination of gaseous mixtures. They are introduced into a 
 glass tube, with very strong sides, and graduated : this tube, 
 closed at one end, rests by its open end in a water-bath, filled 
 with water, or, still better, with mercury. Two metal points, 
 generally platinum, penetrate interiorly into the upper part of 
 the tube, into the sides of which they are hermetically sealed, so 
 as to allow between them an interval of at the most not more 
 than JQ in. ; in order to cause the spark to dart through the 
 gaseous mixture, the metal points are put in communication, 
 by their outer extremity, with the coatings of a Leyden jar ; 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 279 
 
 the fire is thus conveyed into the interior of the tube, without 
 there being any need to heat it exteriorly. The same effect 
 may be produced by the incandescence of a fine platinum 
 wire, by means of a current : a proof that the combination is 
 altogether due to the heat liberated, as well in the spark as 
 in the wire ; and that it is not an immediate effect of elec- 
 tricity. Moreover, we shall study, more in detail, the che- 
 mical effects of the spark in the following Chapter. 
 
 We have further proofs of the heat of the spark, from the 
 traces it leaves upon the conductors, between which it 
 escapes. Priestley, who discovered them, had remarked that 
 they are circular, and that they are formed upon metal plates, 
 that receive the spark that comes from a pointed conductor, 
 situated at a distance of y 1 ^ in. Nobili, who studied them 
 with care upon different metals, showed that they are due to 
 internal heat, and even to a commencement of fusion, that is 
 experienced by the metals. The circular form which they 
 assume, is connected with the similar form of the brush, and 
 is due to the dissemination of the electric filaments. 
 
 Notwithstanding these evident proofs of the high temperature 
 of the spark, M. E. Becquerel was unable to discover in it any 
 traces of radiant heat, which is chiefly due to its instantaneity. 
 On this account also it is that it is unable, under ordinary 
 conditions, to inflame certain very combustible bodies, which, 
 like gunpowder, require, for ignition, the application of heat 
 for a time, that must not be too short. But we may succeed 
 in producing this inflammation, by compelling the discharge 
 to pass through an imperfect conductor, which diminishes its 
 rapidity, and so increases the duration of the spark ; for 
 example, through a string moistened with water. With a 
 glass tube 6^ in. in length, and 3 in. in diameter, closed at 
 its two ends by corks, through which wires are passed, in 
 order to conduct the discharge into the liquid, with which the 
 interior of the tube is filled, we notice that, if this liquid 
 is pure water or ether, we must charge a jar of 1} sq. ft. in 
 surface, to 60 of the electrometer, to order to inflame the 
 powder by the discharge of the jar; and to 30 only, if the 
 liquid is alcohol ; and that with acids, the inflammation no 
 
 T 4 
 
280 TRANSMISSION OF ELECTKICITY. PART iv. 
 
 longer occurs, even when it is charged as high as 80. The 
 differences are due to the fact, that the spark, in order to 
 produce its effect, must possess at the same time a certain 
 intensity and a certain duration, elements the converse of 
 each other; and the relative value of which depends on the 
 greater or less conductibility of the liquids. 
 
 Independently of light and heat, the electric spark deve- 
 lopes in certain bodies, while traversing them, phosphores- 
 cence, namely, the property of appearing luminous in the 
 dark, even when they were not so previously. Of all 
 bodies, calcined oyster shells are they which most easily be- 
 come phosphorescent, when they have been placed in the 
 route of the electric discharge. However, many other sub- 
 stances, such as fluor spar, diamond, white marble, enjoy the 
 same property of becoming phosphorescent, after the action 
 of several discharges. However, the light alone of the sparks 
 is able to produce the same effect, without its being neces- 
 sary for the discharge to traverse the bodies ; a property that 
 we shall study in the eighth paragraph, when we shall be 
 occupied with the electric light ; of which we shall see that 
 phosphorescence, after all, is only a particular case. 
 
 Calorific and luminous Effects of Electric Currents through 
 imperfect Conductors* Voltaic Arc. 
 
 Voltaic electricity, like that of the machines, is able to 
 give rise to electric sparks ; but in general these sparks are 
 manifested when we put into contact, or, which is better, 
 when we separate the wires or the metal plates, that are in 
 communication with the two poles of the pile : it is more a 
 phenomenon of voltaic ignition, than a veritable electric 
 spark ; it appears to arise from the heating that is suffered by 
 the two points in contact of the wires, on account of the 
 greater resistance which the current encounters, in this part 
 of the circuit. Indeed, when we unite end to end, attaching 
 them by simple hooks to each other, several wires, it is 
 always at their points of contact that incandescence is first 
 manifested, in order to its propagation thence into the re- 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 281 
 
 maining part of the wires. We have already spoken, in the 
 second paragraph, of the phenomena of ignition or of defla- 
 gration, that are presented by the various metals : we will 
 simply add, that the production of voltaic sparks is accom- 
 panied by a crackling, very similar to that of electric sparks, 
 and that it occurs in rarefied as well as in common air, only with 
 certain differences of appearance among oxidisable metals, 
 that are due to combustion being in them less vivid. 
 
 Davy was the first who succeeded in obtaining voltaic 
 sparks in liquids, by completing the circuit, by means of two 
 small pieces of carbon. Bright sparks were seen to spurt, and 
 there was at the same time an abundant production of gas. 
 The extremities of the carbon appeared of a red white, even 
 some time after contact. The liquid was indifferently water, 
 fixed or volatile oils, ether, alcohol, nitric acid, sulphuric 
 acid ; the gases that were produced in this action varied with 
 the nature of the liquids. It was a decomposition, arising 
 more from the indirect action of the heat liberated at the 
 point of contact of the two charcoal points, than from the de- 
 composing action of the current, which scarcely traversed the 
 liquid, seeing that the two pieces of carbon were in contact. 
 In the following Chapter we shall return to the chemical 
 effects of the voltaic spark, which must not be confounded 
 with the direct decomposing action of the current. 
 
 M. Marianini, long after Davy's time, studied the production 
 of voltaic sparks in liquids, but he operated under very different 
 conditions. It was by using a very feeble pile, and a tube in 
 the form of an inverted syphon, in which there was mercury, 
 that rose in two columns in the vertical branches of the tube 
 without filling them. Into one of the tubes was thrust a 
 wire that was in communication with one of the poles of the 
 pile ; in the other, the wire communicating with the other 
 pole was thrust into a liquid, such as water, or any other, 
 placed above the bed of mercury. The thickness of the 
 liquid stratum that the spark might traverse was very small, 
 j 1 ^ in. at most ; its production was facilitated by a particular 
 oscillatory motion that was suffered by the mercury, at the 
 moment when the circuit is closed ; and this motion, by con- 
 
282 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 tinuing, produced a succession of sparks. The nature of the 
 wires, by which the circuit is closed, is without influence 
 over the phenomenon. It is not the same in respect to the 
 nature of the liquid, within which the sparks spurt. It is 
 the worst conductors that generally favour their production. 
 We are able to make them appear even through oil, by 
 taking care to thrust in the wire, as far as to contact with 
 the mercury, and then sharply to draw it out : it is at this 
 moment that the spark occurs, traversing the thin stratum 
 of oil. By raising the wire thus, and lowering it until it is 
 made to touch the mercury, a spark is every time obtained. 
 With water and alcohol, the effects are similar; only the 
 production of the spark in oil is accompanied by a peculiar 
 noise, that does not occur with the other two liquids. M. 
 Marianini had also noticed that the colour of the sparks is 
 the same in liquids as in the air, and that the circumstances 
 most favourable to their production are also the same in both 
 cases ; that thus they are more easily manifested between two 
 carbon points, than between two metallic points. 
 
 Independently of these small sparks, which are more or 
 less discontinuous, and are only manifested at contact or at 
 very small distances *, voltaic electricity is able to give rise 
 to a luminous phenomenon of the same kind, but much more 
 remarkable, both on account of its intensity and its continuity. 
 This is the phenomenon of the voltaic arc, discovered by 
 Davy. 
 
 In order to obtain it, the illustrious philosopher made use 
 of a pile of 2000 pairs of zinc and copper, each having 32 
 square in. of surface, thus presenting a total surface of 
 128,000 square in., charged with acidulated water. Having 
 terminated the conductors, that were attached to each of the 
 two poles, with pieces of charcoal about an inch in length 
 and in. in diameter, he placed their ends, which were 
 trimmed to a point, at the distance of about -^ in. apart, and 
 he perceived a brilliant spark appear, at the same time the 
 
 * Mr. Gassiot, by means of a pile of 3500 small pairs of copper and zinc, 
 charged with pure water, obtained between two brass discs, only s ' a in. apart, 
 a series of sparks similar to those of the electrical machine. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 283 
 
 charcoals became incandescent through half their length. 
 He succeeded in separating the charcoals to the distance of 
 more than 4 in. from each other, without causing the phe- 
 nomenon to cease, which was manifested as a continuous 
 bundle of fire, passing from one of the charcoal points to the 
 other, in the form of an arc, convex above, probably on 
 account of the ascending current of hot air. When any sub- 
 stance was introduced into this arc, it became incandescent ; 
 platinum melted in it like wax in the flame of a candle; 
 sapphire, magnesia, lime, all the most refractory substances, 
 entered into fusion. Fragments of diamond, points of carbon 
 and of plumbago, disappeared rapidly, and seemed to evaporate 
 in this focus, without appearing to undergo previous fusion. 
 
 In order to produce this phenomenon, an apparatus 
 (fig. 214.) is employed, in which two metal rods, movable in 
 
 Fig. 214. 
 
 the horizontal direction like those of the universal discharger, 
 are carried on two vertical insulating supports ; the rods are 
 each furnished with pincers, for receiving the charcoal points, 
 and are respectively put into communication by means of 
 conductors, with the poles of the pile. Handles of glass or 
 wood, permit of the two charcoal points being withdrawn or 
 approximated at pleasure in respect to each other. When 
 we desire to produce the voltaic arc in vacuo or in very 
 rarefied air, we make use of an apparatus (fig. 215.), formed 
 of a glass globe, into which penetrate, through collars of 
 leather, placed on the same horizontal diameter, the two rods 
 furnished with charcoal points. A stop-cock, fixed to the 
 metal tube, that serves as the support to the globe, enables us 
 
284 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 to produce and to maintain in it very rarefied air ; and at 
 pleasure to introduce into it different gases, under greater or 
 less degrees of pressure. 
 
 \ 
 
 Fig. 215. 
 
 Davy had already remarked, that the phenomenon of the 
 voltaic arc is produced in vacuo, as well as, and even better 
 than, in air ; a .proof that the combustion, with which it is 
 attended in air, is not the cause of the heat and light that 
 are there developed. He even succeeded, by separating the 
 points, in giving the arc in vacuo a length of 6 or 7 in., 
 namely, almost the double of what it presented in air: 
 furthermore, the light was quite as vivid, and the heat quite 
 as great : for the carbon was powerfully incandescent ; 
 platinum wire melted with a brilliant scinctillation, and fell 
 in globules to the bottom of the globe. 
 
 A long time after Davy's brilliant experiments, Professor 
 Sillimann, on repeating it with Dr. Hare's pile of cylindrical 
 pairs, called by him a deflagrator, observed some very re- 
 markable molecular phenomena. He placed plumbago in 
 communication with the positive pole, and a piece of well- 
 baked carbon, with the negative pole. Globules of melted 
 plumbago were soon perceived; and also a hemispherical 
 excavation on the plumbago itself: whilst the carbon was 
 elongated on the side of the plumbago, and the black matter, 
 that was accumulated there, presented the appearance of 
 fusion, not into globules, but into striated fibres. This 
 
CHAP. IT. EFFECTS OF DYNAMIC ELECTRICITY. 285 
 
 matter evidently owed its origin to the plumbago of the 
 positive pole, which had been transported in the state of 
 vapour to the negative pole. On interchanging the poles, 
 very few globules were seen to be formed upon the plum- 
 bago, and none upon the carbon ; but this latter was rapidly 
 hollowed ; the plumbago, on the contrary, was elongated by 
 the matter that accumulated at its extremity ; and which, 
 when seen by means of the microscope, presented an aggre- 
 gation of little spheres, with the character of a perfect fu- 
 sion, and with a decided metallic brilliancy. The spheres 
 seemed to be formed by the condensation of a white vapour, 
 similar to that of the oxides arising from the combustion of 
 different metals. The globules themselves, when powerfully 
 heated in oxygen gas, gave carbonic acid, and a residuum of 
 iron, attractive to the magnet. Mr. Sillimann thought he 
 found some analogy between these melted carbonaceous sub- 
 stances and the diamond ; but the globules in question scratch 
 glass alone, are attractive to the magnet, and do not expe- 
 rience any alteration in oxygen at the highest temperature ; 
 whilst ordinary diamond is not attractive, scratches all bodies, 
 and burns in the air at a red heat. It is therefore very pro- 
 bable that the former are due to the nature of the ashes 
 arising from the iron contained in the plumbago.* 
 
 With regard to the passage of matter from one pole to the 
 other, M. Sillimann observed it very well. By protecting his 
 eyes with a green glass, he distinctly saw the matter pass under 
 different forms to the negative pole, and collect there as dust 
 would have done, that had been driven by the wind ; he also 
 noticed at the positive pole, a species of trepidation, produced 
 as if by the impulsion of an elastic fluid striking against the 
 opposite pole. I have myself observed this latter phenomenon 
 
 * Nevertheless, M. Despretz succeeded, by employing for a negative elec- 
 trode a sort of nippers, formed of fine platinum wires, and a fragment of very 
 pure carbon for the positive electrode, in obtaining, by the formation of the arc 
 between these two electrodes, some very brilliant points at the extremities of 
 the platinum wires, which, when seen by the lamp used by jewellers, presented 
 all the appearance of small fragments of diamond. He also succeeded in pro- 
 curing similar fragments, by substituting a liquid hydro-carbon for the solid 
 carbon. We shall return to this when we are engaged with the chemical effects 
 of dynamic electricity. 
 
286 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 without having need of a very powerful pile ; a Grove's pile, 
 of ten pairs, is sufficient. The two carbon points must be 
 fixed to two metal rods, bent into a horse-shoe, and suffi- 
 ciently elastic that the two points may be in contact by their 
 two extremities, without there being the least pressure of one 
 against the other. Immediately the current is established, 
 the light darts between the points, and a rapid series of, as it 
 were, small detonations, is heard, which, in their communi- 
 cation from the carbon to the metal, make the latter vibrate, 
 so as to produce a sound, and even to render the vibrations 
 sensible to the touch. This noise arises neither from the 
 electrical attractions and repulsions, nor from a friction, that 
 might occur between the points ; for it is the same with the 
 softest carbon, as the carbon of poplar, as it is with two points 
 of the hardest carbon, such as that collected from gas- 
 retorts. It is a species of regular crackling, that occurs 
 among the molecules of carbon, traversed by the current, and 
 is connected with the rending off, and the transport of these 
 molecules. This noise is no longer heard, when spongy pla- 
 tinum is substituted for the carbon points ; although there is 
 in this case, as with carbon, a transport, of which I have con- 
 vinced myself, of particles, from the positive to the negative 
 pole. These particles, by their association, form, as it were, 
 species of ramifications, which the high temperature pro- 
 duced by the current, renders incandescent, and consolidates 
 by fusion, so that they may be easily detached, without their 
 form being altered. 
 
 By this last example, we perceive that the voltaic arc may 
 be produced, not only between two points of carbon, but also 
 between two metal conductors, such as spongy platinum ; it 
 is not even necessary that the metal be in the state of sponge. 
 Thus it may be established between two points of forged 
 platinum ; but then it is not so long, and it requires a more 
 powerful pile for its production. 
 
 The appearance and the length of the arc vary considera- 
 bly, with the nature of the electrodes between which it is 
 manifested. Thus with wood charcoal well burnt and 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 287 
 
 quenched in water*, the light is much more vivid, and is 
 moreover whiter than with coke ; but this carbon requires a 
 pile of a somewhat higher tension. Daniell, with a pile of 
 seventy pairs, copper and zinc, charged with sulphate of 
 copper and water, acidulated with sulphuric acid, obtained a 
 very brilliant arc either with two points of this carbon, or 
 with one point of carbon, and one of platinum. M. Despretz, 
 in a series of beautiful experiments, made with a very 
 powerful pile, had found very variable lengths for the arc, ac- 
 cording to the number and arrangement of the Bunsen pairs, 
 which were the kind employed by him. He produced the 
 arc in air ; enclosing it however within a glass cage, having 
 observed that the agitation of the air greatly deranges it. 
 He affixed the carbon points, which were of coke properly 
 prepared, to the extremity of rods of copper of j- in. in 
 diameter : the arc was vertical. The following are the lengths : 
 25 pairs, 1 in. ; 100 in parallel series of 100, 7^ in.; 24 series 
 of 25, *45 in. ; the 600, in succession one after the other, 
 6^ in, ; pole -f below 2 in. ; pole + above 3 in. M. Despretz 
 always observed certain obscure parts in the arc. Finally, 
 he made some curious observations on the very powerful 
 soldering, that occurs between the carbon rods, of which the 
 arc is formed when they are placed in contact ; especially 
 between those, that have been prepared by calcining sugar- 
 candy. 
 
 In general, in order to obtain the arc, we must commence 
 by putting the two points into contact ; then, when the point 
 of contact has become incandescent, the two electrodes are 
 gradually drawn apart. However, Daniell succeeded in de- 
 termining the arc, without previously placing the electrodes 
 in contact, simply by passing between them a powerful 
 electric spark. This is the cause that, with piles of very 
 high tension, which are able to give a spark at a distance, 
 the arc is obtained between two points, without there being 
 any need of their being made to touch. 
 
 * Wood charcoal, quenched in mercury, is sometimes employed ; with 
 carbon of this kind, the arc may be produced with a much less powerful pile, 
 but its light is less brilliant ; and there is a formation of vapours of mercury 
 that disturb the phenomenon. 
 
288 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 Fizeau and Foucault, when operating with a pile of eighty 
 Bunsen's pairs,, one of the electrodes of which was carbon, 
 and the other a metal rod of silver or of platinum, remarked 
 differences in the length of the arc and in its duration, ac- 
 cording as the metal or the carbon communicated with the 
 negative or the positive pole. 
 
 Mr. Grove had already observed that the length of the 
 arc and its brilliancy depended upon the nature of the metals 
 between which it is produced, the two electrodes being in 
 each case of the same metal. The following is the order in 
 which he classed them, in this relation, commencing by those 
 which give the longest and most brilliant arc, and supposing 
 that the phenomenon occurs in the air: potassium, sodium, 
 zinc, mercury, iron, tin, lead, antimony, bismuth, copper, 
 silver, gold, and platinum. Mr. Grove had also remarked 
 that a part of the substance, whence the luminous arc escapes, 
 is projected from the positive to the negative pole, and that it 
 is in the state of metallic powder, if the ambient medium is 
 vacuum, hydrogen, or nitrogen, and in the state of oxide, in 
 oxygen or in air. 
 
 However, the fact of the transport of molecules from the 
 positive to the negative pole is not so general as had long 
 been supposed. M. Van Breda, when operating in vacuo, 
 and determining the voltaic arc, without previously placing 
 the electrodes in contact, but by means of a powerful electric 
 discharge, has obtained a transport equally in both directions, 
 cording to the relative nature of the two metals between 
 which the arc passes. With two balls of iron, he found that 
 after the experiment, the positive ball had lost 4f grs. and 
 the negative, instead of having gained, had also lost nearly a 
 grain. With an iron ball, and a cone of coke, prepared like 
 the coke that is employed in the Bunsen piles, the iron lost 
 very nearly the same amount, whether it was positive or ne- 
 gative ; and the coke lost more in the former than in the 
 latter case. An experiment, which proves clearly that an 
 emanation of particles may take place equally from both 
 poles, although more powerfully from the positive to the ne- 
 gative than from the negative to the positive, consists in 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 289 
 
 placing between two copper balls, serving as electrodes, a 
 thick and insulated plate of iron. The experiment is made 
 in vacuo, and the arc is brought about by an electric dis- 
 charge. The positive ball gains in weight about a grain, 
 and the negative 5J grs. They are both covered with mole- 
 cules of iron, which are derived from the plate. It seems 
 therefore that matter is repelled at the same time from 
 both poles ; or rather that there exists a repulsion among the 
 metal particles that conduct the current.* 
 
 I have myself studied the formation of the voltaic arc, 
 by employing electrodes of different metals, either both cut 
 into points, or one alone in a point, the other having the 
 form of a plate. In order to measure carefully the length 
 of the arc, I employed two apparatus, one for measuring 
 it in the air, the other for measuring it in vacuo, or in 
 different gases. This latter apparatus might, in strictness, 
 have served both purposes ; but I preferred to have one 
 in which the arc might be produced in the open air. 
 
 The first apparatus (fig. 216.) consists of a groove, 
 
 Fig. 216. 
 
 carrying on one of its sides a linear division, in which there 
 slides truly with friction, a metal support, that carries a 
 
 * We have clearly seen from Ampere's laws, Vol. I. p. 223., that all portions 
 of the same current repel each other ; and that this repulsion, which is mani- 
 fested under the form of a simple movement, when a part of the current is 
 mobile, ought to be able to give rise to a separation or disaggregation of par- 
 ticles, when the conductor, not being mobile in any of its parts, the current is 
 very energetic. 
 
 VOL. II. U 
 
290 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 pair of horizontal nippers, to which may be adjusted con- 
 ducting points of different natures ; a micrometer- screw 
 enables us to measure, with great accuracy, the quantity 
 by which the support, and consequently the point, that it 
 carries, is made to advance or to recede. At one end of the 
 groove is a fixed metal support, to which is adapted either 
 a similar point to the former, or a conducting plate, so that 
 the arc may be made to pass either between two points or 
 between a point and a plate. The divisions of the micro- 
 meter-screw enable us very accurately to measure the 
 distance between the two points or between the point and the 
 plate ; and consequently the length of the arc. The second 
 apparatus (Jig 217.) consists of a bell-glass, that is placed 
 upon the table of an air-pump, in order to rarefy the air, 
 and when required to introduce into it any gas, by means 
 
 of a stop-cock adapted to the 
 mounting, which being situated 
 above the bell, carries itself a collar 
 of leathers, that is traversed by a 
 metal rod, at the end of which is a 
 binding screw, for receiving a metal 
 point. This rod may be lowered 
 or raised to an amount, which may 
 be very accurately measured by 
 means of a circular division traced 
 upon the circumference of a disc, 
 that moves with the piece provided 
 for raising or lowering the rack- 
 work, with which the rod is fur- 
 nished. A fixed metal support is 
 placed at the bottom of the bell- 
 glass; it carries either a vertical 
 point, or a horizontal plate, so that 
 the arc may be established with 
 this apparatus, as with the pre- 
 ceding one, either between two points 
 or between a point and a plate. 
 
 Having taken for one of the 
 electrodes a plate of platinum, I 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 291 
 
 employed successively for the second electrode points of 
 different natures. With a platinum point, the arc is very 
 short, especially if the point is the negative electrode. In 
 air rarefied to about y 1 ^ in., the point could not be separated 
 more than y in. without the arc breaking. The experiment 
 was made with a Grove's pile of fifty pairs, feebly charged. 
 With the same pile, powerfully charged, there was formed 
 upon the platinum plate, employed always as the positive 
 electrode, a perfectly circular bluish spot; it was also 
 formed in air under the ordinary pressure, but it had then 
 a diameter one half less. In hydrogen, it is not formed 
 at all, a proof that its production is the result of an oxida- 
 tion. When the platinum plate is used as negative electrode, 
 it is also covered with a circular spot ; but this spot is 
 formed of a heap of small grains of platinum, and remains 
 white ; like the blue, it is much larger in rarefied, than in 
 ordinary air. With regard to the platinum point, it very 
 rapidly becomes highly incandescent, when it is positive; 
 its extremity enters into fusion, and finishes by falling upon 
 the plate, forming there a perfectly spherical globule ; 
 whilst when it is negative, it is but little heated and does 
 not melt ; on the other hand, the plate, which is then 
 positive, becomes red-white, and runs a risk of being 
 perforated, unless it is very thick. When a point of coke 
 is substituted for the platinum point, the plate remaining 
 still platinum and positive, we obtain an arc of double the 
 length of the one, that had been obtained with the platinum 
 point. The arc itself, instead of presenting, as before, a 
 cone of light, having its base on the plate and its summit 
 on the point, is composed of a bundle of luminous jets, starting 
 from different points of the plate to impinge upon different 
 points of the coke ; finally, the heat developed upon the 
 platinum plate is so much more considerable, that the plate 
 is rapidly melted and perforated. The pile, in these ex- 
 periments, is exactly of the same force as when the point 
 is of platinum, instead of being of coke. By this we plainly 
 perceive the very great influence that is exercised by the 
 negative electrode, whose function is far from being purely 
 
 u 2 
 
292 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 passive ; for we have merely to change its nature, in order 
 to modify in a very notable manner all the details of the 
 phenomenon. When the coke is positive and the platinum 
 plate negative, the arc is not so long, especially in air, in 
 which it is sensibly shorter than in vacuo ; but the coke 
 point is considerably heated, and becomes rapidly incan- 
 descent in its whole extent. 
 
 By employing successively for electrodes iron, copper, 
 silver, and german-silver, we observe, when one of the 
 electrodes is a point, and the other a plate of the same metal, 
 that the point is incandescent throughout its length, if it is 
 positive, and that it is heated at its extremities alone, if it is 
 negative. With regard to the plates, they present very 
 decided cavities, surrounded by coloured circles, when they 
 have been employed as positive electrodes in rarefied air. 
 With mercury taken as one of the electrodes, the luminous 
 effect is of the most brilliant kind ; the mercury is in a state 
 of extreme agitation, rising into the form of a cone, when it is 
 positive, and presenting a cavity below the positive point, 
 when it is negative. 
 
 A point worthy of notice is the difference that exists in 
 the temperature that is acquired by the two points, between 
 which the voltaic arc is formed, according as they are of the 
 same or of a different nature. When they are of the same 
 nature, it is always the positive point that alone becomes in- 
 candescent in all its extent ; if they are of a different nature, 
 it is the least conducteous that is heated, as well when it is 
 negative as when positive. Thus if the positive point is 
 silver and the negative platinum, it is the latter that becomes 
 incandescent, and the silver is much less heated. Things 
 happen, therefore, as they do in a circuit completely closed : 
 it is the portions of the circuit, that present the greatest 
 resistance to the current, that are most heated ; first the 
 portion that forms the arc itself, then the metal that is the 
 worse conductor. But, when the conductors on each side of 
 the arc are identical, the heating, instead of being uniform, 
 is much more considerable for the positive side ; a phe- 
 nomenon which, in connection with the disaggregation that 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECT1UC1TY. 293 
 
 occurs upon the same side, seems to indicate that the positive 
 electrode suffers, on the part of the current, a much more 
 energetic action than the negative. 
 
 M. Matteucci, by plunging for a certain time the two 
 points, between which the arc is established, into masses 
 of water separated, and taken at the same temperature, 
 found that the difference of temperature between the two 
 points is greater, according as they are formed of a material 
 that is less conducteous, and more easy of dis aggregation. 
 But, what is very curious, is that, in hydrogen gas, the 
 difference becomes very small, which is probably due to the 
 same cause that diminishes the heat of a platinum wire 
 traversed by the current, when this wire is surrounded by 
 hydrogen, namely, to the cooling power of this gas, which 
 increases the conductibility of the part of the circuit that is 
 plunged into it. Moreover, this unequal heating may take 
 place by the simple contact of the two conductors, only the 
 difference is greater when the contact is less intimate ; it is 
 diminished by pressing the two conductors strongly against 
 each other : on the other hand, it is augmented by covering 
 one of the surfaces in contact with a slight film of oxide, of 
 graphite, or of carbon powder ; the formation of the arc is 
 further facilitated by artificially heating the positive elec- 
 trode. 
 
 M. Tyrtow, by employing mercury as one of the electrodes, 
 and making use of -wires of different kinds for the other, 
 remarked that, whenever the mercury is negative and the 
 wire positive, the latter becomes red-hot and melts when its 
 extremity is placed in contact with the mercury ; whilst 
 when the wire is negative, and the mercury positive, at the 
 moment of contact some bluish sparks are alone apparent, 
 but the mercury then undergoes a powerful evaporation. 
 Similar experiments have been made by various philosophers, 
 by substituting decomposable liquids for mercury ; but then 
 the luminous and calorific effects are complicated by electro- 
 chemical phenomena ; but we postpone the study of these to 
 the following Chapter. 
 
 u 3 
 
294 TKANSMISSION OF ELECTEICITY. PART iv. 
 
 It is also to the difference of temperature of the two elec- 
 trodes, that Mr. Gassiot's curious experiment must be at- 
 tributed, in which, when placing two wires across, for 
 instance copper wires, that are in communication with the 
 poles of a powerful pile, the positive wire is perceived to 
 become red for a distance of a couple of inches beyond the 
 crossing point, even till fusion occurs ; whilst the negative is 
 incandescent only in the portion traversed by the current. 
 It is evident that in this instance, there is at the point of con- 
 tact, a commencement of the formation of the voltaic arc, the 
 more so as, on separating the wires a little from each other, 
 the arc appeared between them. The positive conductor is 
 here the positive electrode of the arc ; and, in this capacity, it 
 becomes much more heated than the negative, which causes 
 it to become incandescent, not only in the portion that is 
 traversed by the current, but even to a small distance beyond 
 this portion. 
 
 As M. Matteucci observed, the arc is generally composed 
 of a central part almost cylindrical, whose bases rest upon 
 the polar extremities, and which shines with a white and very 
 intense light ; this part is enveloped in a more rare luminous 
 matter, of a spheroidal form, the colour of which changes 
 with the nature of the points whence the arc emanates, and 
 with that of the medium that it traverses. The central part 
 is composed of a matter, in which the electric current is pro- 
 pagated, as in a liquid conductor ; for proof of this, we have 
 merely to thrust into it the fine ends of two platinum wires, 
 coming from two glass tubes, and fixed to the extremities of 
 a galvanometer. At the moment when the platinum wires 
 arrive at the central part of the luminous arc, the elevation of 
 the deviation of the needle of the galvanometer indicates the 
 presence of a powerful derived current. Furthermore, we 
 have merely to introduce a voltameter into the circuit of the 
 voltaic arc, to have evidence that the current is propagated in 
 it in a continuous manner. We are even able, by the indica- 
 tions of the voltameter, to estimate the resistance opposed by 
 the arcs produced with points of different natures, placed at 
 variable distances. Thus, when operating with a pile of 60 
 
< HAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 295 
 
 pairs of Grove's, it is found that the current, by its passage in 
 the voltameter for 60 seconds, liberates in it quantities of gas 
 equal to 3-4, 2-6, and 2-3 cubic inches, for distances, between 
 the points of coke in the arc, corresponding to '07, *11 and 
 15 in. With two points of silver, which alter less promptly 
 than those of carbon, 3'6 cubic inches of gas is obtained, at a 
 distance of *11 in. between the points, and 2-8 cubic inches at 
 a distance of *23 in. With points of different metals, forming 
 luminous arcs of *11 in. in length, there is found in the volta- 
 meter, after passing the current through it for 60 seconds, 
 1-4 cub. in., if the points are of copper; 1-5 cub. in. if they 
 are of brass ; 1 -6 cub. in. if they are of iron ; 1 -7 cub. in. if 
 they are of coke; 2-1 cub. in. if they are of zinc; 2 '7 cub. 
 in. if they are of tin. When the points touch and there is no 
 arc, 2*8 cub. in. are obtained. It evidently follows from this 
 that the conductibility proper of the arc depends, less upon 
 the conductibility of the metals of which the points are 
 formed, than upon their facility of melting and disaggregating, 
 and consequently upon the quantity of matter that disappears 
 in the experiment. 
 
 If a metal plate is placed between the two points, so as to 
 be situated in the middle of the arc, the formation of which is 
 excited by an electric spark, we notice that the central part of 
 the plate commences by entering into fusion, and globules 
 dart from both sides, towards the points, at the same time 
 that similar globules dart from the points towards the plate ; 
 the inner part of the arc, which gives it the spheroidal form, 
 appears to be produced by the still more divided matter, that 
 is the result of the destruction and combustion of these 
 globules ; when the arc is produced in a liquid, this matter is 
 not seen to be volatized and divided, seeing that it is dispersed 
 n the liquid ; the central part alone is perceived, which, on 
 the other hand, is less distinct with carbon points, on account 
 of their great facility of disaggregating. 
 
 It would seem that the formation of the arc is the result of 
 the contrary electrical states, that are possessed by the polar 
 extremities before the circuit is closed, which may be inani- 
 
 u 4 
 
296 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 fested by an attraction and a spark *, and which subsisting 
 when the arc is once formed, determine at a certain distance, 
 that is always very small, between the points a series of 
 sparks and a chain of molten matter, or of incandescent par- 
 ticles, detached from the pole. The same phenomenon ought, 
 indeed, to exist in all parts of the circuit, since it is thus that 
 the propagation of the current takes place ; but it produces 
 mechanical effects in the portion of this circuit, similar 
 to those in which the voltaic arc is manifested, and in which 
 the resistance is greater and the distance of the particles more 
 considerable. 
 
 The spheroidal form of the arc is the result, like the phe- 
 nomenon that is produced with the spark of the machine in 
 the experiment of the electric egg, of the mutual repulsion of 
 the parts detached from the same polar extremity, joined to 
 the attraction exercised over them by the other pole. We 
 may even see, by passing a series of sparks between two 
 metal points plunged into essence of turpentine, that holds 
 in suspension very fine particles of cork or carbon, that these 
 particles group themselves between these points ; forming a 
 mass of a spheroidal form, composed of filaments that go from 
 one point to the other, and each of which is formed by a 
 chain of these molecules, between which small sparks pass. 
 We have already seen in the first Chapter of this Part, that 
 the distribution of currents in a liquid conducting mass seems 
 to take place under the form of filaments abutting on the two 
 poles, and forming between them a spheroid. We shall see 
 new proofs of this, when we are occupied with the chemical 
 effects of the current. 
 
 A phenomenon that is of a nature to confirm what we 
 
 * Mr. Gassiot, as we have seen, had obtained with a pile of 3500 pairs of 
 zinc, copper, and water, at the polar extremities, electrical charges of such 
 strength, as to give for several days in succession, sparks passing at a distance 
 of Jg in. and succeeding each other very rapidly. M. Matteucci, by connecting 
 the poles of a Grove's pile of fifty to sixty pairs, with two brass rods, each carry - 
 ing at its extremity a sheet of gold-leaf, perceived an attraction to be manifested 
 between these leaves at a distance of an inch or so ; and, if these two leaves 
 are made very short and are brought very near together, they are seen to be 
 attracted at the moment when the arc closes the circuit ; at the same time a 
 spark passes, and the luminous arc is generally established. 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 297 
 
 have been saying on the nature of the voltaic arc is the in- 
 fluence that is exercised upon it by magnetism. Arago had 
 suspected this influence immediately after CErsted's disco- 
 very ; Davy proved it soon after, by bringing a powerful 
 magnet near a voltaic arc formed by two carbon points, and 
 from 1 to 4 in. in length, according to the degree of rare- 
 faction of the surrounding air. The arc or luminous column 
 was attracted or repelled with a rotatory movement, accord- 
 ing to the position of the pole of the magnet, and the 
 direction of the current. The action was more energetic, 
 when the air through which the arc was produced was more 
 rarefied, and consequently the arc itself was more extended. 
 
 By employing an electro-magnet instead of a magnet, the 
 effect is much more decided, and the arc may even be broken, 
 by causing a too powerful attraction or repulsion to break the 
 chain of particles, that establish the communication between 
 the two poles, and that constitute the movable conductor, 
 upon which the magnetic force is acting. M. Quet, having 
 produced a vertical voltaic arc, perpendicularly between the 
 two vertical polar faces of an electro-magnet, saw this arc 
 transform itself into a horizontal dart, like that which is pro- 
 duced by blowing upon a flame with a blow-pipe. This dart 
 may attain a length eight or ten times greater than the arc 
 1 or 1J in. in length, for example when the latter is only -J- in. 
 Particles of carbon are seen to be projected by the action of 
 the electro-magnet, in the direction of the dart, when the 
 carbons are incandescent on the side of the points themselves 
 from which the arc emanates. The change of direction 
 of the dart, when the direction of the current or the poles of 
 the electro-magnet are changed, plainly indicates that this 
 effect is due to the repulsive action of one of the magnetic 
 poles, combined with the attractive action of the other, upon 
 the current that is transmitted by the arc. This is confirmed 
 by the convex form that it assumes in the direction of the 
 dart, when the poles of the electro-magnet are too far off" to 
 allow of the dart itself being formed. We may add that its 
 formation is attended by a peculiar whizzing, which lasts as 
 
298 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 long as the dart ; and that at the moment when it ceases, 
 there is produced a very powerful detonation.* 
 
 I had already noticed, before M. Quet, this double noise, 
 in a detailed study that I had made of the action of mag- 
 netism upon the voltaic arc ; and I had shown that it is 
 connected with the molecular modifications that this action 
 brings upon the matter itself of this arc. I had at first 
 remarked that if two rods of soft iron, serving as electrodes, 
 are each placed in a bobbin, formed of a thick copper wire, 
 the voltaic arc, that occurs between these two points, ceases 
 at the moment when the iron rods are magnetised, by passing 
 a powerful current into the bobbins; and that it recom- 
 mences, if we take care to interrupt this current before 
 the points have become cold. The arc itself cannot be es- 
 tablished between two points of iron when they are magnetised, 
 except when they are much nearer ; and its appearance 
 is quite different. The particles that are formed seem to 
 detach themselves, not without difficulty, from the electrodes ; 
 sparks dart with noise in all directions; whilst formerly 
 there was a very vivid light without spark and noise, 
 accompanied by the transport of a liquid mass, which was 
 brought about with the greatest facility. The phenomenon 
 takes place in the same manner whether the two rods of iron 
 present at their ends, between which the luminous arc passes, 
 the same or different magnetic poles. We must also remark 
 that the positive electrode produces, when powerfully mag- 
 netised, at the moment when the arc is established between 
 it and a negative electrode of any nature, a sharp hissing, 
 altogether similar to what occurs to steam in locomotives ; 
 the noise ceases immediately with the magnetisation. 
 
 In order the better to study this kind of effect, it is 
 preferable to employ a powerful electro-magnet. I did 
 this and placed upon one of its polar surfaces a metal plate, 
 and vertically over it a metal point so as to establish the 
 voltaic arc between them. The plate and point being both 
 
 * This detonation is often very powerful, also, in induction sparks, which are 
 veritable instantaneous voltaic arcs. 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 299 
 
 of platinum, and the plate being positive, as soon as the 
 electro-magnet is magnetised, whilst the arc is in existence, 
 a very sharp hissing is heard ; and it is necessary to bring 
 the point very near to the plate in order that the arc 
 may continue. If the plate is negative and the point positive, 
 the arc can no longer maintain its vertical position; it is 
 projected towards the edges of the plate and is immediately 
 broken ; every time its rupture occurs, it is attended by a 
 dry and instantaneous noise, similar to the discharge of a 
 Ley den jar. 
 
 The same effects are observed, by employing a plate and 
 point of any metal, provided the plate and point are of the 
 same metal, and that the latter is not too fusible. Copper, 
 and especially silver, present a remarkable peculiarity; it 
 is that the plate preserves on its surface the impression of 
 the action that it suffers under the influence of the electro- 
 magnet. Thus, when it is positive, the portion of the surface 
 that is. beneath the negative point presents a spot in the 
 form of a helix, which seems to indicate that the melted 
 metal in this portion underwent a gyratory motion around 
 a centre, at the same time that it is raised in the form of 
 a cone. The helical curve is, moreover, in its whole length 
 bordered by small ramifications, perfectly similar to the 
 brushes that are developed by the traces of positive elec- 
 tricity, that comes from the knob of a Ley den jar. When 
 the plate is negative and the point positive, the traces 
 are very different ; there is a circle of a very small diameter 
 from which arises a line, more or less curved, that forms 
 a species of tail to the comet, of which the small circle 
 would be the nucleus; the direction of the tail depends 
 upon the direction in which the arc has been projected. 
 
 On producing the arc between two points, very near to 
 the electro-magnet, between its two poles for example, we 
 may easily bring about either the sharp hissing or the series 
 of detonations ; the latter are even sometimes so strong as to 
 resemble distant discharges of musketry ; it is merely neces- 
 sary that the electro-magnet be very powerful, and the 
 current by which the arc is produced, very intense. With 
 
300 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 a point of platinum, and one of copper, the hissing is obtained, 
 when the platinum is positive, and the detonations, when the 
 copper is positive. This is due to platinum becoming much 
 more heated than copper when positive. It is easy to prove 
 that, in order to obtain the hissing, it is necessary that the 
 positive electrode attain a temperature, capable of making it 
 undergo a commencement of liquefaction ; if this is not the 
 case, we obtain merely detonations : I have satisfied myself of 
 this, by numerous experiments made with different metals. 
 In order to obtain the hissing, the precaution must be taken 
 of maintaining the arc as continuous as possible, when once 
 the positive electrode is well incandescent ; whilst, in order to 
 obtain detonations, one of the electrodes must be held in the 
 hand, and the arc must be established and interrupted 
 frequently, taking care that the temperature of the points 
 does not rise too much. These results appear to point out 
 to us that the hissing is due to the transport of the matter of 
 the positive electrode, more or less liquefied, whilst the 
 detonations arise from the tearing off of these same particles, 
 when the substance that is disaggregated is not highly 
 heated. But what is very extraordinary, is, that this hissing 
 and these detonations take place only when the arc is under 
 the action of the magnet. Can it be simply the effect of the 
 attractive and repulsive action of the currents of the magnet 
 upon the series of particles which, forming the arc, constitute 
 a conductor, more or less mobile, traversed by the current ? 
 Can it be the result of a modification, brought about by the 
 influence of the electro-magnet upon the molecular con- 
 stitution of the electrodes? I am rather disposed to think 
 that, under the powerful influence of the electro-magnet, the 
 molecules which transmit the current, in forming the electric 
 chain, assume forced positions, due to electro-dynamic action ; 
 and that the hissing is the result of this constraint, impressed 
 upon the molecules that come off from the electrodes, whilst 
 the detonation is the effect of their return to their state of 
 molecular equilibrium. The following experiments appear 
 to me of a nature to corroborate this opinion, at the same 
 time they seem to confirm the ideas, which we have put 
 
CHAP, IT. EFFECTS OF DYNAMIC ELECTRICITY. 301 
 
 forth in the preceding Chapter, upon the mode of propagation 
 of the electric current. 
 
 If we place in the axial, or equatorial, or intermediate 
 direction, above the poles of a powerfully magnetised electro- 
 magnet, prismatic bars of tin, zinc, lead, and bismuth of } in. 
 square, and about 20 in. in length, and cause a discontinuous 
 current to traverse them, derived from a pile of from 5 to 10 
 pairs of Grove's, we hear very distinctly a sound composed 
 of a series of blows, corresponding to the interruptions of the 
 current. They give out no perceptible sound, so long as the 
 electro-magnet is not magnetised. The same effect is pro- 
 duced with rods of copper, silver, and platinum. Tubes of all 
 these same metals give out still more decided sounds than solid 
 cylinders ; wires wound in a helix around a wooden cylinder, 
 vibrate in like manner ; a wire of lead, arranged in this 
 manner, is able in particular to give out a very powerful 
 sound. An ordinary magnet produces the same effect as an 
 electro-magnet. It is the same with a helix, traversed by a 
 powerful continuous current, in the axis of which is placed 
 the bar, the tube, or the wire, through which the discon- 
 tinuous current is transmitted. With a double helix, formed 
 of two thick copper wires, covered with silk and wound 
 one exteriorly to the other, we obtain a sound of remarkable 
 intensity, by causing the continuous current to pass through 
 the exterior wire, and the discontinuous through the interior ; 
 in the converse case, the sound is much more feeble, which 
 is due to the magnetic action of a current in a helix, being 
 almost null exteriorly, whilst it is very energetic interiorly. 
 
 The effects, that we have been describing, cannot be at- 
 tributed to a dilatation, arising from a heating brought about 
 by the current, since they take place with conductors of too 
 large dimensions, and with too feeble a current, for us to 
 admit that there is the slightest elevation of temperature. 
 Moreover the sound is produced only so long as the electro- 
 magnet is acting at the same time that the current is being 
 transmitted. Neither can we admit that the production of 
 the sound is the result of a mechanical flexion, occasioned by 
 the attractive or the repulsive action of the electro-magnet 
 
302 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 upon the conductor traversed by the current : the dimensions 
 of this conductor exclude this interpretation, which more- 
 over cannot be reconciled with the fact that bodies so little 
 elastic as lead and well-burnt vegetable carbon give rise to 
 the same phenomenon, as does a column of mercury, con- 
 tained in a glass tube, an inch in diameter, and 10 in. in 
 length.* All these phenomena appear to me to be the 
 result of the action of the electro-magnet upon the small 
 voltaic arcs, that occur from molecules to molecules, in the 
 interior of a conducting body, traversed by an electric 
 current. When the electro-magnet acts upon all the visible 
 voltaic arcs, it is not necessary, in order to the production 
 of the sound, to render the current discontinuous ; because 
 it is already so of itself, the arc being formed of a series of 
 discharges, that succeed each other more or less rapidly. 
 It is not the same, when the current traverses good con- 
 ductors, such as metal rods; it is then necessary to render 
 it discontinuous, in order that the particles may have 
 time to recover their natural position between the passage of 
 two successive currents, and may thus acquire an oscillatory 
 movement around this position, a necessary condition, in 
 order that the action of the electro-magnet may determine a 
 sound, and which is found fulfilled naturally with the lu- 
 minous voltaic arc. 
 
 In fine, the oscillatory motion and the production of sound, 
 which is it consequence, appear to me to be a molecular 
 phenomenon, arising from the conflict established between 
 the position, which the action of the magnet tends to impress 
 upon the molecules, that form the electric chain, and that 
 which the particles possess naturally. This conflict, very 
 apparent to the eye, as well as to the ear, when it takes 
 place in the particles, of which the luminous arc is composed, 
 becomes sensible by sound alone, when it occurs with 
 molecular arcs, or discharges that take place from particles 
 
 When mercury is placed in an open trough, at the same time that a sound 
 is heard, a particular vibratory motion is seen on its surface, very different 
 from the gyratory motion that it manifests under the influence of the poles of a 
 magnet, when traversed by a continuous current. 
 
CHAP, ii EFFECTS OF DYNAMIC ELECTRICITY. 303 
 
 to particles. But, except in its magnitude, it is no less an 
 analogous phenomenon ; which confirms, as we have already 
 remarked, the idea which we have already laid down that 
 the propagation of the current takes place in conductors by 
 a series of discharges from molecules to molecules, similar to 
 those which are brought about at finite distances between 
 two conductors, and which we have just been studying, 
 under the name of voltaic arcs. 
 
 \ 
 
 General Considerations on Electric Heat and Light. Special 
 Properties of this Light. 
 
 The study that we have been making of the electric spark 
 and the voltaic arc, have demonstrated to us that, under these 
 two forms, the production of light and heat by electricity is 
 connected in a remarkable manner with the motion of the par- 
 ticles of bodies. On the other hand, the recent researches of 
 Joule, of Clausius, and of Thomson have led philosophers to 
 regard heat as resulting from a rotatory motion of the par- 
 ticles about an axis ; and we have ourselves considered this 
 hypothesis as calculated to explain the polarity of atoms.* 
 Might it not then be possible that the cause of the heat, and 
 consequently the light, that are generated by the reunion of 
 the two electricities, brought about under the form of dis- 
 charge or current, may be not in the fact itself of this re- 
 union, but in an increase of molecular motion, that might 
 result from the transmission of electricity ? This motion, it is 
 true, is not apparent in the phenomenon of the heating, and 
 the incandescence of good conductors, such as wires, as it is 
 in the spark and in the voltaic arc. However, it is mani- 
 fested, even in this case, by the molecular modifications which 
 are experienced by the wires that have been rendered incan- 
 descent by the effect of discharges. f Moreover, it would 
 
 * Vol. II. p. 48. 
 
 f An experiment which would seem to have demonstrated that the heat liberated 
 by the current is due to a motion having a certain direction, was that in which 
 attempts were made to pass at the same time through the same wire, in di- 
 rections contrary to each other, two energetic currents of the same intensity, 
 and each capable separately of making that wire red-hot. It was found that, 
 
304 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 seem to. us that the best proof, in favour of the existence of 
 this motion, independently of the production itself of the heat, 
 exists in the general fact of the sounds that are given out, 
 and consequently of the vibrations that are experienced, by 
 all conductors which transmit discontinuous currents, when 
 placed under the influence of powerful electro-magnets. 
 
 With regard to the theory that attributes the liberation of 
 heat and light in a direct manner to the reunion itself of the two 
 electricities, we find an objection against its generality, in the 
 important fact, discovered by Peltier, proved and studied by 
 several other philosophers, that this reunion sometimes produces 
 a reduction of temperature. Peltier had demonstrated this 
 curious property of the current, by placing in the interior of the 
 bulb of an air thermoscope, instead of a platinum wire as in 
 Riess's apparatus (fig. 193. p. 216.), a rod y 1 ^ in. in diameter, 
 consisting of two small cylinders, one of bismuth, the other of 
 antimony, applied end to end against each other, so that their 
 surface of contact was almost at the centre of the bulb. He 
 found that the electric current of a single pair, transmitted 
 through the rod, reduced the temperature of the point of contact 
 thirty- seven divisions, when it was going from bismuth to 
 antimony, and raised it about forty-five when travelling 
 from antimony to bismuth. Lenz justly remarked that the 
 effect of the cooling is diminished in the manner in which 
 Peltier operated, by the heating that the passage of the 
 current determines in the bar itself of bismuth, as indeed he 
 proved. In order to avoid this inconvenience, he soldered one 
 after the other two quadrangular bars of bismuth and anti- 
 mony, each 4^ in. in length, and having a transverse section 
 
 under these circumstances, the wire remained perfectly cold ; a proof, it was 
 thought, that the two motions, guided in opposite directions, neutralised each 
 other. But it is easy to see that in this mode of operating, the wire, instead of 
 being traversed by two opposite currents, is not traversed by either. In fact, 
 the experiment is reduced to this ; namely, that when two piles are connected 
 by their opposite poles, so as to form a complete circuit, a wire which unites the 
 two conductors, establishing communications between the poles, is not traversed 
 by any current ; which must be the case ; since scarcely even would a feeble 
 derived current be transmitted by the wire. The experiment, therefore, is in no 
 way conclusive, in favour of the existence of a molecular motion, but it is not 
 contrary to it 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 305 
 
 of -38 sq. in. he then, at the point of soldering, pierced a hole, 
 into which he introduced the bulb of a small thermometer, 
 taking care entirely to fill with iron filings the upper part of 
 the hole, that remained empty. By passing through this 
 metal rod the current of a simple pair of zinc and platinum 
 of about 155 sq. in. surface, he found that the thermometer 
 fell 7*2, when the current was going from the bismuth to 
 the antimony; and that, on the contrary, it rose several 
 degrees, when the current was travelling from the antimony 
 to the bismuth. Having filled the hole of the soldering with 
 water, and having covered the rod, except at the soldering 
 point, with melting snow, so that the temperature of all the 
 apparatus, including the water, was maintained at 32 Fahr., he 
 succeeded in freezing the water contained in the hole, and ev<m 
 in lowering its temperature to 24 Fahr., bj causing the current 
 to pass from the bismuth to the antimony for five minutes. 
 Without the passage of the current, the water did not freeze ; 
 and its temperature was maintained merely at 32 Fahr. 
 
 The curious phenomenon that we have just been pointing 
 out is connected with a more general fact, namely, the vari- 
 ation of temperature that is brought about by the passage of 
 an electric current at the point of contact of two hetero- 
 geneous conductors, soldered end to end. M. Peltier ob- 
 served that, for the greater part of the metals, the elevation 
 of temperature is always much greater at the point of 
 contact of two wires, when the current passes from the 
 worse to the better conductor, than in the reverse case ; and 
 the difference may become such that, in certain cases, in- 
 stead of an elevation there is a fall of temperature, as we have 
 remarked; but then two conditions are necessary in order 
 to obtain this latter phenomenon, the first, that one of the 
 metals, at least, shall be crystalline ; the second, that the trans- 
 mitted current shall have a feeble intensity. 
 
 M. Frankenheim, who made a profound study of these 
 phenomena, justly distinguished this variation of temperature, 
 which takes place at the limit of the two conductors, and 
 which he names secondary, from that which occurs in the 
 whole circuit. The former depends upon the direction of the 
 
 VOL. II. X 
 
306 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 current, whilst the latter is independent of it ; it is propor- 
 tional to the simple intensity of the current, whilst the latter 
 is proportional to the square of this intensity. 
 
 Moreover, the effects, for the first time observed by 
 Peltier, are connected with a phenomenon that we have not yet 
 studied, that of the production of thermo-electric currents, 
 which are developed by heating and cooling alternately the 
 points of contact of small heterogeneous metal rods, soldered 
 end to end, one after the other, so as to form an entire 
 metal circuit. In fact, on heating the point of contact of a 
 bar of antimony an'd a bar of bismuth, a current is deter- 
 mined, which travels directly from the bismuth to the anti- 
 mony ; and on cooling it, a current is obtained which travels 
 in like manner directly from the antimony to the bismuth ; 
 that is to say, that the current produced by these variations 
 of temperature, has a direction precisely contrary to that of 
 the current that would produce these same variations. This 
 opposition seems therefore to indicate that the exterior 
 current, that is introduced into the rod composed of two 
 metals, produces in them a molecular motion, acting in a 
 contrary direction to that which is determined in them by 
 heat, and hence arises the fall of temperature, which is so 
 difficult of explanation otherwise. But it is only in the 
 Fifth Part, devoted to the sources of electricity, and parti- 
 cularly in the Chapter, wherein we shall treat more specially 
 of the development of electricity by heat, that we shall be 
 enabled to return, when studying it more profoundly, to the 
 phenomenon that we have been pointing out, and which has 
 been the object of the labours of a great number of philo- 
 sophers. What we have said of it, however, suffices to 
 justify the double assertion that we have put forth above, 
 namely, that the heat liberated by the transmission of dy- 
 namic electricity is not due to the reunion of the two 
 electricities, but that it must rather be attributed to a 
 molecular motion, the production of which, or at least the 
 increase, is brought about by this reunion. Therefore we 
 conceive that, in the case of crystallised bodies, in which the 
 molecules are retained by forces that do not allow of their 
 immediately acquiring, under the influence of the current, a 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 307 
 
 position that places the direction of their natural rotation in 
 harmony with that of the rotation, which the current tends to 
 impress upon them, these two directions may be contrary in 
 such a manner, that the passage of the current counteracts the 
 motion, and that, far from increasing the velocity, it dimi- 
 nishes it, which, according to the present theories upon heat, 
 lowers instead of elevates temperature. It is no longer the 
 same, when the current, becoming more powerful, the mole- 
 cular forces ought to yield to it, and no longer oppose 
 the particles acquiring the position which it tends to impress 
 upom them, a position which they occupy without conflict 
 in non-crystallised bodies and in liquids. 
 
 These molecular motions, which are so perceptible in the 
 voltaic arc, exist no less in the spark, although they are less 
 sensible in it. We have seen the proof of this in the trans- 
 port of particles, that is brought about by the electric spark ; 
 and in the formation of Priestley's rings. Thus the electric 
 spark, like the arc, is the result of a very rapid motion, im- 
 pressed upon material particles, and which is accompanied by 
 a powerful heat and light; but its excessively short dura- 
 tion renders the perception of these phenomena much more 
 difficult than in the arc, which is permanent. Is not the 
 light of the spark alone due to the incandescence of the small 
 solid particles, detached from the conductor, and of the ambient 
 gaseous molecules ; or rather, might it not in part arise also 
 from a disturbance, impressed directly upon the ether by the 
 motion of the electricity ? It would appear to me a difficult 
 matter to admit that electricity might act directly upon the 
 ether, so as to produce in it luminous undulations ; for there 
 is no electric light in perfect vacuum, except that which arises 
 from the incandescence of the particles detached from the con- 
 ductors by the discharge ; and this light always manifests itself 
 every where, when there are material particles in a space that 
 contains but few of them. Thus in the long tube, in which 
 perfect vacuum has been made, the electric light is seen to 
 travel along the interior surface of the glass tube, to which 
 air or vapour always remain adhering. I have even suc- 
 ceeded in showing, in a striking manner, the presence of a 
 
 x 2 
 
308 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 ponderable substance, where there is electric light, even in 
 apparently the most perfect vacuum. The following is the 
 description of an experiment, which, although made with a 
 view of explaining auroras boreales, as will be seen hereafter, 
 proves well the principle that I have just laid down. 
 
 I introduced into a globe of glass 12 or 15 in. in diameter 
 (Jig. 218.), by one of the two opposite necks with which it is 
 
 Fig. 218. 
 
 furnished, a rod of soft iron about % in. in diameter, so that 
 one of its extremities abuts nearly to the centre of the globe, 
 and the other comes out through the tube, and passes 
 beyond it. The iron rod is covered along its whole extent, 
 except at its extremities, with a very thick insulating coat, 
 formed first of gum-lac, then of a glass tube itself covered 
 with gum-lac, then of a second glass tube, and finally of a 
 very smooth coat of wax ; the insulating coating should be, in 
 all, f in. in thickness, which gives a diameter of about 1^ in. to 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 309 
 
 the bar thus covered. A ring of copper surrounds the bar 
 above the insulating coating in the portion nearest to the 
 neck, but in the interior of the globe. This ring may be 
 placed in communication with an electric source exterior to 
 the bar, by means of a wire carefully insulated, which tra- 
 verses the neck and terminates exteriorly by a hook. A 
 stop-cock, fixed to the second neck of the globe, allows of a 
 vacuum to be made in it. When the air is sufficiently rare- 
 fied in it, the hook is put into communication with the con- 
 ductor of an electrical machine, and the exterior extremity of 
 the soft iron rod with the ground, so that the electricity 
 forms in the interior of the globe a luminous brush, more or 
 less irregular, which originates at the ring and abuts upon 
 the upper extremity of the soft iron. But at the moment 
 when the exterior extremity of this iron is placed upon the 
 pole of a powerful electro-magnet, the electric light assumes 
 a very different aspect. Instead of coming out indifferently 
 from different points of the upper surface of the iron cy- 
 linder, it comes out equally from all points of the circum- 
 ference of this surface, so as to form round it, as it were, a 
 continuous luminous ring. This is not all : this ring pos- 
 sesses a rotatory motion around the magnetised cylinder, 
 sometimes in one direction, sometimes in the other, according 
 to the direction of the electric current, and the direction of 
 the magnetisation. Finally, more brilliant jets seem to come 
 out from this luminous circumference, without being con- 
 founded with the rest of the brush. As soon as the mag- 
 netisation ceases, the luminous phenomenon becomes what it 
 was before, and as it generally is in the experiment known 
 under the name of the electric egg. 
 
 Is it not evident that these luminous jets, which obey the 
 action of the magnet, like movable conductors, are, in this 
 case, as well as in that of the voltaic arc, composed of 
 material particles traversed by the discharge ? I am disposed 
 to admit that these particles, are gaseous, and that they arise 
 from the film of air remaining adherent, notwithstanding the 
 vacuum at the upper surface of the cylinder of iron, out of 
 which the electric jet comes, that draws them with it so as to 
 
 x 3 
 
310 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 form the brush, which, as we have seen, is composed of small 
 filaments of air. Moreover, the violet light of these gaseous 
 filaments, traversed by the discharge, differs notably from the 
 white and much more vivid light of the solid particles detached 
 from conductors, which are found in a greater or less pro- 
 portion in the midst of the electric light. There exists, 
 between these two appearances, almost the same difference as 
 is observed between the pale light of the flame of pure 
 hydrogen or of alcohol, and that of this same flame when 
 small particles of carbon, or a thin plate of platinum are 
 introduced into it, which become incandescent. 
 
 However, M. Neef, who made a particular study of the 
 electric light, is disposed to think that the light of the bluish 
 colour, which is manifested around conductors charged with 
 electricity, arises from a species of gaseous atmosphere, with 
 which every metal in the solid state is surrounded, and which 
 is rendered visible by the electricity, where it acts with the 
 greatest intensity. The presence of this metallic atmosphere 
 would explain the changes of colour, which the light un- 
 dergoes, with the nature of the metals, between which the 
 induction spark passes. M. Neef had observed it with zinc, 
 which gives a blue light, and copper, which gives a green 
 one. M. Matteucci made the same observation with points 
 of zinc, copper, and gold. However, M. Neef recognised 
 that, with frictional electricity, which has much more tension, 
 the air and elastic fluids may become luminous, which 
 explains why the different gases produce light of a dif- 
 ferent colour. It is very probable that it is the same with 
 the light of the induction spark ; and that the differences that 
 are presented in its colour, according to the metals between 
 which it is manifested, are due to the mixture of incandescent 
 metallic particles with gaseous particles equally luminous. 
 
 We have already spoken in a former paragraph, at p. 277., 
 of the interesting labours of Neef, who was the first to apply 
 successfully the microscope to the study of the luminous 
 phenomena of electricity, by carefully examining, with the 
 assistance of this instrument, all the peculiarities of the in- 
 duction spark. This philosopher had thought he might be 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 311 
 
 able to distinguish the two poles, in respect to their calorific 
 and luminous properties, attributing to the positive pole the 
 liberation of heat, the reduction into dust, and the volatisation 
 of the substance of the electrode ; and to the negative pole, 
 the production of primary light, namely, of the light that 
 does not arise from an increase of temperature. The ex- 
 istence of this light, which he terms cold flames, appears to 
 M. Neef very distinct from that which results from the in- 
 candescence and combustion of the solid particles, detached 
 from the electrodes ; and he considers it as being of the 
 same nature as phosphoric light, which, in like manner, seems 
 not to be endowed with heat ; this light is, therefore, ac- 
 cording to him, independent of heat, whilst the secondary 
 light is due to the heat which, arising from the positive pole, 
 produces incandescence and transports to the negative pole 
 particles of the positive electrode, when it acquires a certain 
 degree of intensity ; "the heat and light are then confounded, 
 but not in their origin. It is by diminishing sufficiently 
 the intensity of the induction spark that we succeed in 
 obtaining light at the negative electrode alone ; and for this 
 purpose M. Neef makes use of a small disc and a 
 platinum point, between which he made this spark to pass 
 by means of a similar apparatus to that of Jig. 149 *, the 
 force of which he might diminish at pleasure.f According 
 as the induction current is in one or the other direction, it is 
 at one time the point, at another time the disc, that is illumi- 
 nated with a violet light, whilst the opposite electrode remains 
 dark. Riess, as we have seen, has shown that Neefs 
 luminous phenomenon is analogous to that of Faraday's dark 
 discharge ; and that it may in like manner be produced by 
 means of a powerful induction current, transmitted in rare- 
 fied air between two balls, of which one, the negative, is 
 luminous, and the other, the positive, remains dark. He 
 
 * Vol. I. p. 387. 
 
 f The most simple means of causing the intensity of the induction current 
 to vary, is to introduce into its circuit a small column of water placed in a tube 
 in which are inserted two metal points, that may be brought more or less near, 
 and so that the course of the current through the water may have more or 
 less length ; he called the apparatus a moderator. 
 
 x 4 
 
312 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 has shown that with a less rarefaction, the positive pole 
 becomes also luminous, which proves that the liberation of 
 light is not an exclusive property of the negative pole. 
 
 Neef 's idea of connecting the liberation of light and heat 
 with the nature of the polarity, negative or positive, does not 
 therefore appear to us to have any foundation ; the more so 
 as there is no longer any polarity, as soon as there is any 
 discharge or current ; and as heat and light are developed, 
 only so long as there is electricity in motion. However, 
 there are two facts well demonstrated : the first, that, as 
 soon as there is transmission of a discharge or an electric 
 current through a bad conductor, the positive electrode 
 suffers an increase of temperature and a mechanical disag- 
 gregation, which is not suffered in the same degree by the 
 negative ; the second, that the emission of light is not always 
 identical at the two electrodes, and that, according to the 
 circumstances which accompany the transmission of elec- 
 tricity, it is more powerful at the positive, than at the negative 
 electrode. I am disposed to think that these differences are 
 due essentially to the nature of the medium interposed 
 between the electrodes, as well as to the nature and form of 
 the electrodes themselves, which is also the result of experi- 
 ments made with the voltaic arc. Perhaps also, in certain 
 cases, the chemical alterations, that occur to the medium tra- 
 versed by the electricity, are not altogether foreign to these 
 effects. But before seeking further for the explanation, let 
 us endeavour to study, better than we have hitherto done, 
 the electric light itself, its special properties and its effects : 
 we shall find in this study a means of investigating its nature 
 better, and of better explaining its various appearances. 
 
 Very soon after the discovery of the voltaic arc, it had 
 been remarked that, both in respect to its intensity and 
 to its other properties, this light had much resemblance to 
 solar light. Brande had shown that it determines im- 
 mediately the combination of chlorine and hydrogen : I had 
 myself observed that a daguerreotype impression might 
 be obtained of a plaster bust, illuminated by this light. 
 I had also proved that it presents no trace of polarisation ; 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 313 
 
 another analogy with the rays of the sun. Subsequently, 
 MM. Fizeau and Foucault, on comparing the two lights, 
 either with each other or with that which is produced 
 by oxygen and hydrogen gas projected upon lime, had 
 confirmed this analogy ; for they found that, both in re- 
 spect to their chemical action upon an iodized daguerreo- 
 type plate, as well as in that of their simple luminous action, 
 estimated by the comparison of the images received upon 
 a translucid screen, the intensity of the light of the carbon 
 points, produced by 46 Bunsen's pairs, is to that of solar light 
 as 1:4; and even as 1:2-5, with three parallel series, 
 namely, with forty-six pairs of triple surface ; whilst the in- 
 tensity of the light of oxygen and hydrogen gas is to that of the 
 voltaic light as 1 : 35 or as 1 : 56, with the 46 pairs having 
 large surface. We therefore see how much nearer the 
 electric light approximates to solar light, than does that 
 which is produced by the combustion of the gaseous mixture. 
 One very remarkable thing is, that we arrive at the same 
 result, both in respect to optical intensities as well as 
 chemical intensities ; which proves that these two intensities 
 are in the same relation. I should add that the voltaic 
 light, submitted to experiment, was furnished by the ex- 
 tremity of the positive electrode, which appears to be the 
 most brilliant portion of the arc formed by two carbon 
 points. M. Despretz, in his researches on the voltaic arc, 
 has fairly proved that, if the arc increases in length with 
 the number of pairs, arranged in series, the intensity of its 
 light, having passed a certain limit, does not follow the same 
 progression, but increases with the surface. Thus, beyond 100 
 pairs the intensity does not sensibly increase, if we augment 
 the number of pairs in series even up to 600, whilst the 
 arc becomes six or seven times longer ; but if we arrange the 
 600 pairs in six parallel series, so as to have 100 pairs of a 
 large surface, then the intensity of the light increases almost 
 proportionately to this surface. 
 
 Casselmann, in operating with carbon points, prepared 
 like the carbon of the Bnnsen's piles, but which had been 
 plunged in a solution, either of nitrate of strontian or nitric 
 acid, &c., had found that these points produce a light much 
 
314 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 more equal and more permanent, than that which had been 
 obtained with pure carbon : only it is differently coloured, 
 according to the nature of the solution, into which the carbon 
 points have been plunged 
 
 The following is a Table, which contains the degree of in- 
 tensity of the light for each arc, with the force of the corre- 
 sponding current, measured by means of a tangent galvano- 
 meter, placed in the same circuit of which the arc forms part. 
 The luminous intensity is compared with that of a stearine 
 taper taken as unity. 
 
 
 Distance of the 
 Points. 
 
 Force of the 
 Current. 
 
 Intensity of 
 the Light. 
 
 Pure Carbon - 
 
 !-019 in. 
 176 - 
 
 - 
 
 f 95 
 
 68 
 
 f 932 
 1 139 
 
 Carbon plunged into nitrate of 
 
 019 - 
 
 
 [120 
 
 J 353 
 
 strontian - 
 
 265 - 
 
 
 88 
 
 I 274 
 
 Carbon plunged into chloride 
 
 039 - 
 
 
 f 80 
 
 f 624 
 
 of zinc - 
 
 196 - 
 
 
 67 
 
 I 129 
 
 Carbon, with borax in sul- 
 
 j -058 - 
 
 
 r 72 
 
 /1171 
 
 phuric acid 
 
 1 -196 - 
 
 
 [ 64 
 
 I 145 
 
 These results are only approximate, on account of the mo- 
 bility of the light of the incandescent extremities of the 
 points, that contribute for the most part to the vivid light of 
 the arc. However, compared with others, in which the light 
 had been rendered more steady by means of the action of a 
 magnet, which imparted to it a determinate direction, it is 
 found that the luminous intensity increases in a progression 
 a little more rapid than the force of the current. 
 
 M. Masson, who has made a very particular study of the 
 electric light, directed his attention principally to that which 
 is manifested by the spark; he produced it, in his experi- 
 ments, by the discharges of a condenser, with plates of glass 
 covered on each of their faces with a thin sheet of tin-foil. 
 The instrument intended for these experiments, and which he 
 called an electric photometer, is constructed upon the following 
 principles : A disc of paper, upon which black and white 
 sectors of equal dimensions have been traced, moving with 
 sufficient rapidity, appears of a uniform and greyish tint, if it is 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 315 
 
 illuminated with a permanent white light. This well-known 
 phenomenon is due to the persistence of the sensation. When, 
 instead of a fixed light, we employ an instantaneous light for 
 illuminating the sectors, the disc appears as if it were fixed, 
 the sectors not having been able sensibly to change place 
 during the existence of the light. The eye in this case per- 
 ceiving, and with great distinctness, all the details of the 
 disc, we already acquire a notion of its extreme sensibility, 
 and of the rapidity with which the perception of objects is 
 exercised, and our judgment of their nature is formed. If 
 the disc, illuminated by a permanent light, is suddenly il- 
 luminated by an instantaneous light, an electric spark, for 
 example, we shall see the sectors appear again, for a certain 
 intensity of this latter. If the instantaneous light is succes- 
 sively reduced, a period arrives when the sectors will dis- 
 appear and the disc will appear illuminated of a uniform tint. 
 In this case, the instantaneous light is a fraction of the per- 
 manent light, variable with the eye of the operator, but in- 
 variable for the same eye, the circumstances of vision re- 
 maining the same. In fact, on account of the persistence of 
 the sensation, the place, that a black sector occupies not re- 
 flecting the light of the spark, has entirely preserved the 
 primitive illumination ; that which is occupied by a white 
 sector, sends to the eye as much light as the former, plus the 
 light due to the spark. When the intensity of this latter 
 shall represent the limit of sensibility of the eye of the ob- 
 server, the disc will appear uniformly illuminated. The 
 relation between the intensities of the illuminations of the 
 black and white sectors at the moment when they cease to 
 be distinguishable, may vary, as we shall see further on, from 
 7o ^0 ii~o> according to the sensibility of the eye of the ob- 
 server. With regard to the relation between the intensity of 
 the light of the spark and that of the fixed light, it depends 
 upon the dimensions of the black and white sectors. If the 
 sectors are equal, and it is the case in these experiments, 
 the relation between the instantaneous and the fixed light is 
 the half of that found by experiment. In fact, let us suppose 
 that the sensibility of the eye is ^ 5 when the sectors dis- 
 
316 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 appears the relation between the electric light and the fixed 
 light is only y^ of the illumination that would be produced 
 by the fixed light upon a perfectly white disc ; because the 
 disc in motion sends to us only the half of the light, that it 
 would reflect if it were in a state of rest and perfectly white. 
 The intensity of the electric light, given by experiment, 
 would be only y^- of the fixed light, if the black surface were 
 two-thirds of the white surface. 
 
 The apparatus necessary to the experiments are an electric 
 machine, condensers, a micrometer for measuring the explosive 
 distances of the spark, conductors of peculiar form and 
 nature, the apparatus intended to contain the permanent 
 light, and finally the photometer. The condensers are flat 
 and formed of plates of glass, covered on each of their faces 
 with a thin sheet of tin-foil, which enables us easily to 
 measure their surface and their thickness, and to estimate 
 their degree of homogeneity. The fixed light is produced by 
 a very good Carcel lamp, the illuminating power of which 
 may be rendered constant for two or three hours. The lamp 
 (fig. 219.) is contained within a wooden box blackened, 
 similar to that of a phantasmagoria; and this system is 
 movable upon a grooved road furnished with a division in 
 millimetres ( ~j in.), which, by means of a vertical point COr- 
 
 Fiy. 219. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 317 
 
 responding with the centre of the flame, measures its distance 
 
 from the illuminated disc. The 
 photometric apparatus is essentially 
 constituted of a disc of thick paper 
 {fig. 220.) 3 in. in diameter, upon 
 which have been traced sixty 
 sectors, alternately black and white, 
 and of the same dimensions ; the 
 disc is cemented upon a copper 
 support, fixed by a socket to the 
 principal axis of a clock-movement, 
 contained in a box ; by the aid of a 
 
 detent, we are enabled to arrest or to set in motion the disc, 
 
 the velocity of which can attain to a maximum of from 200 
 
 to 250 turns per second. 
 
 The apparatus complete is represented in vertical projection 
 
 Fig. 220. 
 
 Fig. 221. 
 
 (fig. 221.); M N, is the partition that separates the darkroom, 
 in which the apparatus is placed, from the room, in which are 
 the electrical machine and the condenser, the discharge of 
 which arrives by the brass conductors v and v% sustained in 
 
318 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the centre of glass tubes K H, and K' H', by corks covered with 
 an insulating coating. The armatures of the condensers commu- 
 nicate by metal conductors, v G and v' G', with columns of mer- 
 cury, contained in grooves, L L and i/ L', hollowed in wooden 
 cylinders and varnished within side with black sealing-wax. 
 These conductors, like all the others attached to the apparatus 
 placed in the dark apartment, are covered with varnish of dead 
 black, so as to avoid all reflection. The rods V G, and v' G', 
 amalgamated on all the points that plunge into the mercury, 
 abut at opposite extremities of the canals L L, I/ i/, so that 
 the circuit traversed by the current remains constant. The cy- 
 linder I/ I/ is insulated upon glass legs, covered with a coat 
 of blackened gum-lac ; L L is fixed to the support that receives 
 the apparatus from which the spark passes. This wooden 
 support, constructed like the fixed piece of a planing machine, 
 is marked by the letters Q Q; it is placed upon a table, 
 firmly fixed to the wall or to the floor ; it carries on one of 
 its faces a division in millimetres, which is not visible, be- 
 cause it is traced upon a horizontal rod, and perpendicular to 
 the plane of the figure. The apparatus, that is the seat of 
 the spark, is movable upon Q Q, and may be brought, by 
 means of a Vaucansin endless chain and a handle, to different 
 distances from the photometer. The piece carrying the 
 spark is composed of a plank , b, supporting two vertical 
 rods, one of glass, a 7, the other of copper, b B. At I is in- 
 variably fixed, by a binding screw, a metal conductor, 
 plunging at co into the mercury ; this conductor is terminated 
 at T/ by a ball screwed on. Another conductor, T s, carrying 
 also a ball, T, screwed to it, is set in motion by means of a 
 micrometer screw, R s, giving half a millimetre (j 1 ^ in.) The 
 communication with the ground is established by the con- 
 ductor, S b 9 Y, L, of which the part Y, L, plunges into the 
 groove of mercury L L. The supports, o o, fixed upon the 
 table by binding screws, carry a groove, which enables us to 
 establish parallelism between the trenches L and I/. The 
 centre of the disc, that of the flame of the lamp, and the 
 spark, are contained in a same horizontal plane. The eye of 
 the observer looks at the disc through a tube, blackened in- 
 
CHAP. II. EFFECTS OF DYNAMIC ELECTRICITY. 319 
 
 teriorly and exteriorly, having its axis perpendicular to the 
 plane of the disc ; this tube contains diaphragms, which allow 
 of the eye seeing the sectors alone. The Carcel lamp, with 
 its box, is placed behind the eye of the observer, so as to 
 illuminate the disc upon the horizontal support, when the 
 box that contains it, moves along the division. 
 
 After various preliminary essays, which proved to him the 
 accuracy and the sensibility of his apparatus, M. Masson 
 found that the intensity of the electric light, produced by 
 discharges, depended upon the following elements : 1st, the 
 distance of the explosion ; 2nd, the surface of the condensers ; 
 3rd, the thickness of the condensers ; 4th, the nature, and 
 consequently the condensing power, of the condensers ; 5th, 
 the conductibility of the circuit ; 6th, the nature of the me- 
 dium in which the explosion is produced ; 7th, the nature of 
 the poles, or electrodes, between which the spark passes. He 
 established, moreover, the following laws : 
 
 FIRST LAW. TJie intensity of the electric light varies in the 
 inverse ratio of the square of the distances of this light from the 
 surfaces illuminated. 
 
 SECOND LAW. Tlie intensity of the electric light varies pro- 
 portionately to the surfaces of the condensers, and in the inverse 
 ratio of their thickness. 
 
 THIRD LAW. Tlie intensity of the electric light increases pro- 
 portionately to the squares of the distances of the explosion. 
 
 These are general laws, and independent of the other 
 elements, which influence only the absolute intensity of the 
 electric light. It is very remarkable that, upon comparing 
 the results of M. Masson with those of Riess, we find that the 
 same laws regulate the development of light and that of 
 heat, in such sort that the same formulae are applicable to 
 them ; and that we may lay down as a principle, that the 
 quantities of heat are proportional to the quantities of light. 
 
 We cannot here introduce all the details of the numerous 
 experiments, by means of which M. Masson has obtained the 
 laws that we have just laid down, any more than those which he 
 has made in order to study the influence of the conductibility 
 
320 
 
 TRANSMISSION OP ELECTRICITY. 
 
 PART IV. 
 
 of the circuit, and the explosive distance of the different ga- 
 seous and liquid substances.* We shall confine ourselves to 
 transcribing two of the Tables, that contain the results relating 
 to the influence exercised over the intensity of the electric 
 light, by the nature of the electrodes, which will at the same 
 time give the idea of the manner in which this skilful 
 French philosopher operated in his researches. 
 
 He employed successively for electrodes, balls of metal of 
 different natures, being about *15 in. in diameter; at each 
 change of metal, the position of the vernier, corresponding 
 to the contact of the spheres, was determined by bringing the 
 balls towards each other, until a small spark, produced by 
 the electric machine, was seen to disappear between them ; then 
 designating the explosive distance by x, that of the spark from 
 the photometer by Y, and that of the lamp by z, the results 
 are obtained that are contained in the two following Tables ; 
 the first of which gives x, z and Y, being constants, and the 
 second Y, x and z being constants. In the two series of expe- 
 riments, the surface of the condenser was 70-J- square feet. 
 
 Z = 21-22 in. Y = 24-91 in. 
 
 Metals. 
 
 X. 
 
 Mean. 
 
 Iron - 
 
 2141 in. 
 
 2161 in. 
 
 2161 in. 
 
 2154 in. 
 
 Copper 
 
 2078 
 
 2059 
 
 2082 
 
 2073 
 
 Brass 
 
 2067 
 
 2043 
 
 2035 
 
 2048 
 
 Tin - 
 
 1917 
 
 1925 
 
 1921 
 
 1921 
 
 Zinc - 
 
 1921 
 
 1909 
 
 1913 
 
 1914 
 
 Lead 
 
 1650 
 
 1623 
 
 1419 
 
 1630 
 
 Z = 21 -22 in. X= -236 in. 
 
 Metals. 
 
 Y. 
 
 Mean. 
 
 Copper 
 
 2959 in. 
 
 2955 in. 
 
 2955 in. 
 
 2956 in. 
 
 Brass 
 
 2971 
 
 2975 
 
 2971 
 
 2972 
 
 Iron - 
 
 3002 
 
 2982 
 
 2990 
 
 2962 
 
 Tin - 
 
 3073 
 
 3081 
 
 3077 
 
 3077 
 
 Lead 
 
 3120 
 
 3140 
 
 3128 
 
 3129 
 
 Zinc 
 
 3136 
 
 3128 
 
 3132 
 
 3132 
 
 * We have already treated upon this point in Chapter I. p. 15 6. et seg. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 321 
 
 In classing the metals, according to the increase which 
 they are able to produce in the intensity of the spark, we 
 obtain the following order : 
 
 First Table. Second Table. 
 
 Iron. Copper. 
 
 Copper. Brass. 
 
 Brass. Iron. 
 
 Tin. Tin. 
 
 Zinc. Lead. 
 
 Lead. Zinc. 
 
 We see from this classification, that the metals form two 
 distinct groups, between which there exists a very notable 
 difference of action, whilst it is very slight between the metals 
 of the same group. These groups comprise : the one copper, 
 iron, and brass ; and the other, tin, zinc, and lead. Now, this 
 classification is the same as that which would have been ob- 
 tained, by taking into account the tenacity of these metals ; 
 those which possess the least tenacity giving a more vivid 
 light than those which possess more. As, on the other hand, 
 the inspection with a lens of the balls that have been used for 
 the production of numerous sparks, shows that they are deeply 
 altered at the points of explosion, especially those of tin, zinc, 
 and lead, we are forcibly led to recognise that the luminous 
 phenomenon is due to the effects of tearing away, which vary 
 with the tenacity of the metals and not with their fusibility; 
 since metals having very different points of fusion present the 
 same intensity to the photometer.* Moreover this order is also 
 that which M. Matteucci had found, by classifying the metals 
 according to the conductibility of the arc to which they give 
 rise. Experiments made successively with brass balls, whose 
 surfaces were smooth or rough, tinned or amalgamated, in 
 demonstrating that it is the surface of the metal, and not its 
 conductibility proper, that exercises an influence over the 
 intensity of the light, confirm that this intensity increases 
 
 * M. Riess had already shown that the effect of pulverisation, which the metals 
 equally undergo by discharges, does not depend upon a fusion, but is the di- 
 rect result of a molecular disaggregation, brought about by the passage of the 
 electricity, which must necessarily, under the same circumstances, vary with 
 the tenacity. 
 
 VOL. II. Y 
 
322 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 when the metals are easily transported by the discharge. 
 But it is also possible, as we shall shortly see, that the nature 
 itself of the particles transported, contributes its part to the 
 effect observed. 
 
 This influence of the nature of the particles is especially sen- 
 sible, when we study the spectra formed by the passage through 
 a prism of the light of electric sparks. Wollaston, and es- 
 pecially Frauenhofer, had already found that the spectrum 
 of the electric light differs from that of other artificial lights, 
 and from solar light, by the presence of many very clear rays, 
 of which one in particular, which is situated in the green, 
 is of a clearness almost brilliant in comparison with the rest 
 of the spectrum. Mr. Wheatstone having studied the pheno- 
 menon, by employing different metals for electrodes, had re- 
 marked that the brilliant rays differ in number and in position, 
 according to the metal employed ; and that, when the spark 
 occurs between balls of different metals, or made of different 
 alloys, the brilliant rays belonging to each of the two metals are 
 seen simultaneously. The learned English philosopher had 
 operated with the electric light produced either by piles, by 
 induction machines, or by ordinary electrical machines. M. 
 Despretz and M. Foucault have recently made a more complete 
 examination of the spectrum of the voltaic arc. The former 
 has found that the brilliant rays of the arc, produced between 
 two carbon points, are fixed, and independent of the intensity 
 of the current ; for he satisfied himself that, on passing from 
 100 elements to 600, arranged either consecutively or in 
 parallel series of 100, a yellow or blue ray brought into coin- 
 cidence with the wire of the telescope remains perfectly in 
 the same place. The latter philosopher, M. Foucault, 
 having observed, in this same spectrum, a double line 
 situated at the limit of yellow and orange, recalling to mind, 
 by its form and its situation, the ray D of the solar spectrum, 
 wished to know whether it corresponded with it, and for 
 this purpose he caused a solar image, formed by a con- 
 verging lens, to fall upon the arc itself, which enabled him to 
 observe, superposed upon each other, the electric and the 
 solar spectra: he thus satisfied himself that the double 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 323 
 
 brilliant line of the arc did coincide with the double black 
 line of the solar light. This ray D is found in arcs formed by 
 other matters; and when we employ as electrodes metals which 
 do not cause it to appear without difficulty, such as iron and 
 copper, it may be made to revive with great intensity by 
 touching them with potassium or sodium. By making the 
 spectra of different arcs concur with that of solar light, we 
 find that the rays possess all the shades, that are assigned to 
 them by their refrangibility ; but what is most striking is, 
 that among these rays, there are some that possess an ab- 
 solute intensity, enormously superior to that of the corre- 
 sponding solar ray. Thus, in the arc of the silver, a green 
 ray is found of a dazzling brilliancy, a veritable source of 
 simple light, and which may be rendered as intense as may 
 be desired. 
 
 The philosopher, who studied with the greatest care and 
 in the most complete manner, the spectra of electric light, 
 is also M. Masson, who employed for this study both the 
 light of the spark produced by the discharge of condensers, 
 as well as that of the voltaic arc. He found in the spectrum 
 of the electric spark, developed in the air, all the colours of 
 the solar spectrum *, and he found that the brilliant rays 
 by which it is marked, are quite of the same colour as the 
 part of the spectrum of the same refrangibility ; although 
 sometimes, when they have too much brilliancy, they appear 
 like white light upon a coloured ground. Moreover, by 
 increasing the intensity of the spark, the rays are rendered 
 decidedly more brilliant and vivid, but neither their position 
 nor their number is changed, as M. Despretz, and M. Fou- 
 cault had already remarked, for the rays of the spectrum of 
 the arc. We are also able, by an increase of intensity, to ex- 
 tend the violet, which is always the most feeble in the spectrum 
 of the electric light, but we are never able to extend the 
 spectrum on the side of the red ; a property similar to that 
 which had been recognised by M. Matthiessen, in the spectrum 
 
 * He also proved, as I had already done, but in a more complete manner, 
 that the light of the arc itself never presents any trace of polarisation. 
 
 Y 2 
 
324 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 of solar light, to which, as we see, both by this example, as 
 well as by that which precedes, the electric light has a great 
 resemblance. 
 
 The most important part of the researches of M. Masson 
 is that which concerns the modifications that occur in the 
 distribution of the rays, when the nature of the metals, 
 between which the spark passes, is changed. He has proved 
 that these rays differ in number and in intensity ; but that there 
 are, nevertheless, a certain number of common rays, that is to 
 say, rays that remain the same in all spectra, which indicates 
 the measure of their deviation, which is every where similar, 
 whilst the deviations of the others are very different. The 
 values of these deviations have been carefully determined by 
 M. Masson, for a very great number of rays in spectra 
 produced by the spark, in cases where the electrodes were 
 made of the following substances : carbon, cadmium, antimony, 
 bismuth, lead, tin, iron, and copper. These numbers may 
 some day, perhaps, serve to establish the proper function of 
 the nature of the particles in the production of the light ; for 
 the present, they demonstrate, by the simple fact that they 
 differ from each other, the existence of the function. We 
 shall not refer to them here, we shall content ourselves with 
 a few remarks. Carbon (fig. 222.) gives in the violet many 
 very brilliant, but very fine rays ; at the end of the violet, 
 they are separated by intervals absolutely dark, considering 
 the feebleness of the light. Cadmium (fig. 223.) is, of all 
 the metals tried, the one that gives the most beautiful and 
 the best defined spectrum ; it is especially remarkable by 
 very brilliant green and blue rays. The spectrum of antimony 
 (fig. 224.) is marked by a multitude of very brilliant rays, 
 much more numerous than in the spectrum of the other 
 metals. That of zinc (fig. 225.) contains a very character- 
 istic apple-green ; it is very curious that it differs so much 
 from that of cadmium. Copper gives a spectrum remarkable 
 for the number of fine and brilliant rays of blue and violet ; 
 those of tin and of iron, of bismuth and of lead, present 
 nothing in particular, except the extent of the violet, and the 
 number of very confused rays that are included in that colour. 
 
CHAP. IT. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 325 
 
 CARBON. 
 
 CADMIUM. 
 
 Fig. 224. 
 
 V k> 
 
 k 
 
 fc 
 
 Or & 
 
 Red. 
 
 Orange. 
 
 Green. 
 BIue. 
 
 Fig. 223. 
 
 ZINC. 
 
 Limit Line. 
 
 Red. 
 Orange. 
 
 Yellow. 
 
 Ray in th 
 Limit. 
 
 Green. 
 Green. 
 
 Blue. 
 Blue. 
 
 Indigo. 
 
 Fig. 225. 
 
 Instead of the spark, we may employ as electric light, 
 that which is produced in the voltaic arc ; and we obtain 
 with electrodes of different natures spectra perfectly similar 
 to those given by the spark in each case. If the pile that is 
 
 Y 3 
 
326 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 employed is tolerably strong (50 to 100 pairs of Bunsen's) 
 magnificent spectra are obtained, which are projected upon 
 screens, like the solar spectrum, which they rival in brilliancy. 
 Only, in order to make these experiments, a fixidity must be 
 given to the light of the voltaic arc, which it does not 
 possess naturally. With this view, we employ an apparatus 
 which, by means of the combination of a mechanical force and 
 of the attraction exercised by an electro-magnet upon a piece 
 of soft iron, connected with the system, brings towards each 
 other the points which are employed as electrodes, as soon 
 as they are too far apart for the arc to be enabled to be es- 
 tablished between them, without however allowing them to 
 come into contact, which would cause it to disappear. 
 
 Many philosophers have devised and constructed ap- 
 paratus founded upon this principle: in the list of these 
 apparatus, that of M. Duboscq appears to us one of the most 
 satisfactory; it is essentially intended to produce the arc 
 between two carbon points ; but it is equally well adapted to 
 the production of arcs obtained from electrodes of any nature. 
 
 The folio wing is a brief description of it. {Fig. 226.) The 
 two carbons, between which the light is developed, burn in 
 contact with the air, and shorten at each instant ; a mecha- 
 nism is consequently necessary, which brings them near to 
 each other, proportionally to the progress of the combustion ; 
 and, since the positive carbon suffers a more rapid consump- 
 tion than the negative, it must travel more rapidly in face of 
 this latter ; and this in a relation, which varies with the 
 thickness and the nature of the carbon. The mechanism 
 must satisfy all these exigencies. The two carbons are 
 unceasingly solicited towards each other ; the lower carbon by 
 a spiral spring, that causes it to rise, and the upper carbon by 
 its weight, which causes it to descend. The same axis is 
 common to them. 
 
 The galvanic current is produced by a Bunsen's pile, of 
 from 40 to 50 elements ; it arrives at the two carbons, as in 
 apparatus already known, passing through a hollow electro- 
 magnet, concealed in the column of the instrument. When 
 the two carbons are in contact, the circuit is closed, the 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 327 
 
 Fig. 226. 
 
 electro-magnet attracts a soft iron, placed at the extremity of 
 a lever, which is in gear with an endless screw. An antago- 
 
 Y 4 
 
328 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 nist spring tends always to unwind the screw, as soon as a 
 separation is produced between the two carbons ; if it is a 
 little considerable, the current no longer passes, the action of 
 the spring again becomes predominant, the screw is unwound 
 and the carbons approach each other, until the current, again 
 commencing to pass between the two carbons, the motion that 
 drew them toward each other, is relaxed in proportion to the 
 return of the predominance of the electricity over the spring ; 
 the combustion of the carbons, again increases their distance, 
 and with it the superior action of the spring : hence follows 
 again the predominance of the spring, and so on. These are 
 alternatives of action and reaction, in which at one time 
 the spring, at another time the electricity, has the predo- 
 minance. On an axis, common to the two carbons, are two 
 pullies ; one, the diameter of which may be varied at pleasure, 
 communicates by a cord with the rod that carries the lower 
 carbon, which corresponds with the positive pole of the pile ; 
 the other, of invariable diameter, is in connection with the 
 upper or negative carbon. The diameter of the pulley, 
 capable of varying proportionately to the using of the carbon, 
 with which it is in communication, may be increased from 
 3 to 5. The object of this arrangement is to preserve the 
 luminous point at a convenient level, whatever may be the 
 thickness or the nature of the carbons. It is only necessary 
 to know that at each change of kind or volume of the carbon, 
 the diameter of the pulley must be made to vary. This 
 variation results from that of a movable drum, communicating 
 with six levers, articulated near the centre of the sphere ; the 
 movable extremity of the six arms of the lever carries a small 
 pin, which slides in cylindrical slits. These slits are oblique 
 in respect of the sphere ; they form inclined planes. A spiral 
 spring always rests upon the extremity of the levers ; so that, 
 if the inclined planes are turned towards the right, the six 
 levers bend towards the centre, and diminish the diameter. 
 If, on the contrary, they are turned towards the left, the 
 diameter increases, and with it the velocity of the translation 
 of the carbon, which communicates with the pulley (vide P', 
 p", and p"' ,fig. 226.). We may notice, in passing, that this 
 
CHAP. ii. EFFECTS OF DYXAMIC ELECTRICITY. 329 
 
 apparatus is marvellously adapted to the production of all the 
 experiments of optics, even the most delicate ; and that, in this 
 respect, it advantageously supplies the place of solar light. 
 We shall moreover have occasion to speak of it again, when 
 we are occupied with the applications of electricity, and in 
 particular of illumination. 
 
 In the experiments made with the voltaic arc, the spectrum 
 presents no brilliant ray, when the light emanates from the 
 solid part of the carbon in incandescence. This result 
 is in accordance with what is obtained, upon heating to 
 redness a platinum wire, the spectrum of which, in like 
 manner, presents no brilliant ray.* Neither do we notice any 
 in the spectra arising from the light of a voltaic arc, produced 
 between two charcoal points, plunged either in pure water, or 
 in essence of turpentine, or in alcohol ; but if we take for 
 electrodes in alcohol, balls of brass, instead of carbon points, 
 the spectrum presents magnificent brilliant rays ; we then 
 remark that the metal has been melted, since the third part 
 of the balls has disappeared, and the liquid has become filled 
 with a black matter, which is probably very finely divided 
 oxide of the metal ; whilst, when the electrodes are of car- 
 bon, the liquid retains its transparency, which proves that 
 there has been no transport of particles ; whence it follows 
 that there were no rays. This absence of transport is very 
 sensible in alcohol, in which the same luminous intensity may 
 be obtained for a long time, by preserving the same distance 
 to the carbons. We may add that the spectrum of the light, 
 arising from the electric sparks produced in liquids, in like 
 manner presents no brilliant rays ; perhaps, with more power- 
 ful discharges, which might produce a transport of the 
 matter of the electrodes, some might be obtained. 
 
 It would be very interesting to study the influence exer- 
 cised over the spectrum of the light of the electric spark 
 by a change in the nature or in the density of the gaseous 
 medium, in which it is produced, an influence which, as we 
 
 * This absence of rays in this case, proved by M. Masson, resulted already 
 implicitly from Mr. Draper's very interesting researches upon the luminous and 
 calorilic intensities of a platinum wire heated progressively by the current. 
 
330 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 have seen, is so great over the form and the colour of this 
 spark. M. Masson, who has also made some experiments 
 upon this particular point, has found that the rarefaction 
 of the air diminishes the intensity of the colours, so as 
 almost to make them disappear; but that it, in no way, 
 changes, either their number, or the position of the brilliant 
 rays, which appear more feeble, it is true, upon a ground 
 absolutely dark. 
 
 In hydrogen, the spectrum of the spark presents the same 
 appearances as in rarefied air. The colours of the spectrum 
 are not distinguishable ; and, upon a dark ground, are per- 
 ceived very feeble brilliant rays. We know that the spark 
 itself in hydrogen possesses a very feeble reddish purple 
 light, absolutely similar to that which is obtained in rarefied 
 air. However, if we desire to obtain the spark in hydrogen, 
 we require, for the same explosive distance, the same 
 quantity of electricity as in air under the same pressure ; 
 and the discharge has the same intensity in both cases. 
 The difference in the two lights, which causes that of hydro- 
 gen to become similar to that of rarefied air, can therefore 
 be only due to the molecules of hydrogen giving a less vivid 
 light than those of air under the action of the same dis- 
 charge; and to the particles detached from the electrode 
 suffering a less powerful incandescence in the former gas than 
 in the latter.* 
 
 The detailed study that we have been making of the 
 electric light, confirms all that we have said on the mode of 
 the propagation of electricity, in stating that it could only 
 occur by the intervention of ponderable matter. Masson 
 indeed satisfied himself that the barometric vacuum cannot 
 conduct a current or a discharge, unless the tension of the 
 electricity is considerable, namely, is sufficient to detach 
 some minutely divided particles from the electrodes. With 
 regard to the light, it is produced by a current or a 
 discharge which, propagating itself by the intervention 
 of ponderable matter, heats it in the same manner and 
 
 * There are evidently particles detached in hydrogen, as in rarefied air, since 
 the spectrum presents rays as well in the one as in the other. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 331 
 
 according to the same laws as a voltaic current heats wires 
 and renders them luminous. The state of bodies (solid, 
 liquid, or gaseous) in no way modifies, the general laws 
 of electro-dynamic action : Savary had already demonstrated 
 this, in obtaining exactly the same degree of magnetisation 
 for steel needles, placed some above a tube, in which Boyle's 
 vacuum had been made, others above a metal conductor 
 of the same diameter as the tube, each forming part of the 
 same circuit traversed by a discharge. 
 
 With regard to the light itself, it always possesses the 
 same properties, whatever be the means employed for pro- 
 ducing it; and all the phenomena, that we have been 
 studying, confirm us in the opinion that it really arises from 
 the incandescence of the particles of the medium, which is 
 traversed by the discharge or the electric current, and from 
 that of the particles, which are detached from the electrodes, 
 the presence of which determines the rays of the spectrum, 
 that vary with their nature. It would be interesting to 
 study with care the heat, that accompanies this light, in 
 the various cases, in which it is produced. We have seen 
 that, in the case of the voltaic arc, wherein the transport 
 of incandescent particles is considerable and continuous, the 
 temperature is very elevated. But, when the spark is 
 in question, E. Becquerel has demonstrated that the radiant 
 heat is null or very feeble, which is for the most part due 
 to its shortness of duration ; for we know that it has never- 
 theless a calorific power sufficiently great to determine the com- 
 bination of the gases, hydrogen and oxygen, for example 
 when it is transmitted between two platinum points in a 
 eudiometer, filled with a detonating mixture. But, even in 
 this case, it is necessary that the discharge be sufficiently 
 powerful to detach and to carry along particles from the 
 metal points between which it takes place, as is indicated 
 by the vivid and white light of the spark, and as is proved 
 by the condition of the points, when they have been for some 
 time employed in the experiments. Otherwise, the simple 
 lights, that result from the mere incandescence of the gaseous 
 medium do not liberate any sensible radiant heat, although, 
 
332 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 with very delicate apparatus, we ought necessarily to detect 
 a little. 
 
 The electric light enjoys one other remarkable property, 
 namely, that of exciting phosphorescence in bodies that are 
 susceptible of it. This property is independent of that pos- 
 sessed by the discharge of producing the same effect. Indeed, 
 if we introduce fragments of calcined oyster-shells into small 
 glass tubes, hermetically sealed, and themselves placed in 
 other larger tubes, and pass a great number of electric dis- 
 charges over the exterior surface of these tubes, the fragments 
 become phosphorescent on their being heated ; the light of 
 the voltaic arc produces the same phenomenon, but in a less 
 degree. Its effect is due to the electric light, and not to the 
 direct influence of the electricity ; since on enclosing the 
 same phosphoric substance within tubes of red, yellow and 
 deep blue glass, Seebeck has remarked that at the moment 
 when the three tubes are exposed to the light of the discharge, 
 it is only the substance in the blue tube that becomes 
 luminous; which proves that the blue glass is the one that 
 allows those of the phosphogenic rays of electric light to pass, 
 as it allows those of solar light to pass. MM. Becquerel and 
 Biot have made a very great number of experiments, in order 
 to study the influence of different screens over the transmission 
 of radiation, arising from the spark that produces phospho- 
 rescence, and they have found that it was very distinct from 
 luminous radiation. It is the same with the phosphorescence 
 produced by solar rays ; and of these, the rays that produce 
 it are the most refrangible of the spectrum, whilst the others, 
 such as the red rays, not only do not produce, but they even 
 destroy it. The phosphogenic rays of solar light, and those of 
 electric light, are therefore very nearly the same, and probably 
 also the same as the chemical rays. The phosphogenic pro- 
 perty of electric light is therefore entirely connected with its 
 chemical property, which we have already proved ; and we 
 must in no way confound it with the property possessed by 
 electricity when acting directly upon bodies, of rendering them 
 phosphorescent, or of disturbing their chemical state. 
 
CHAP. ii. EFFECTS OF DYNAMIC ELECTRICITY. 333 
 
 Moreover, the light of phosphorescent bodies has so great 
 a relation, in its different tints and in its intensity, to the light 
 which is in certain cases developed by electricity, that it is 
 very difficult not to impute to it an identity of origin. Phos- 
 phorescence is therefore very probably a light resulting from 
 small electric discharges, which are brought about through 
 the air adhering to the surface of bodies, that are endowed 
 with this property ; and what renders this hypothesis more 
 probable is that, besides the similitude of appearance, we ob- 
 serve that all the means and all the circumstances that produce 
 and favour the development of phosphorescence, are the same 
 that produce and favour the liberation of electricity, as we 
 shall have occasion to see, when we shall be studying the 
 sources of electricity ; and it is especially that the process 
 most suited for rendering bodies phosphorescent, is to let them 
 be traversed by an electric discharge ; and consequently to 
 impart to them directly that electricity, which the other pro- 
 cesses develope in them only indirectly. 
 
 To sum up, we may conclude from all the facts that we 
 have explained in this Chapter, 1st. That the production 
 of electric heat and light cannot take place without the es- 
 tablishment of a closed circuit, all the parts of which ex- 
 ercise the same exterior electro-dynamic action, conformably 
 with Ohm's laws ; 2nd, that this production takes place in 
 the points of the circuit, where the electricity in motion 
 (whether discharge or current) experiences the greatest re- 
 sistance ; 3rd, that the parts of the conductors, which limit 
 the portions of the circuit, where the resistance is greatest, 
 and where consequently the heat and light arise, undergo 
 calorific, luminous, and molecular modifications, which depend 
 at the same time upon their proper nature, and upon that of 
 the electricity, (positive or negative,) of which they are the 
 electrodes : 4th, that these modifications seem to indicate 
 that the movement of rotation of the particles, whose accele- 
 ration, produced by the transmission of electricity, is the pro- 
 bable cause of electric light and heat, is influenced either by 
 the nature itself of the substances, or by the direction of 
 the discharge or of the current ; which determine, in the 
 
334 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 case of the spark and of the arc, a movement of transmission 
 over and above that of rotation.* 
 
 * List of the principal works relating to the subjects treated upon in this 
 Chapter. 
 
 Cuthberson. Incandescence of wires by the discharge. Bibl. Brit. t. xxxix. 
 p. 111. 
 
 Van Marum. Idem. Bibl. Brit. t. Ivi. p. 210. 
 
 Fourcroy. Vauquelin and Thenard. Incandescence by the pile. Ann. de 
 Chim. t. xxix. p. 103. 
 
 Children^ Calorific effects of a powerful pile. Bibl. Univ. (1816) t. i. 
 p. 109. 
 
 Davy. Calorific effects of the pile. Bibl. Brit. t. xx. p. 318.; t. xxxiv. p. 
 397., and t. xxxv. p. 170. Voltaic arc. Bibl. Brit. t. liii. p. 225. Phil. 
 Trans, of 1821 (Part II.), p. 425. Sparks in vacuo. Ann. de Chim. et dePhys. 
 (1822) t. xx. p. 168. 
 
 De la Rive. Heat in liquids. Arch, de I* Elect, t. ii. p. 501., and t. Hi. p. 
 175. Heating power of the current. Ann. de Chim. et de Phys. t. xl. p. 371., 
 and t. lii. p. 147. Voltaic arc. Arch, de VElect. t. i. p. 262., and Arch, des 
 Sc. Phys. t. iv. p. 345. 
 
 Riess. Electric thermometer ; Laws of heating. Bibl. Univ. (1839) t. 
 xxii. p. 367.; Ann. de Chim. et de Phys. t. lix. p. 113., and t. Ixxiv. p. 158. 
 Arch, del 'Elect, t. i.p. 555. Arch, des Sc. Phys. t. i. p. 196., and t. xvii. p. 48. 
 Ann. der Physik pass, and Traite de V Elect, par frottement. 
 
 Harris. Heating of wires by the discharge. Phil Trans. (1834.) 
 
 Joule. Laws of heating by currents. Arch, de V Elect, t. ii. p. 54. and t. iv. 
 p. 483. 
 
 E. Becquerel. Idem. Ann. de Chim. et de Phys. (N. S.) t. ix. p. 21. 
 Phosphorescence and radiation of the spark Bibl. Univ. t. xx. p. 344. 
 and 394. 
 
 Lenz. Idem. Ann. der Physik t. lix. p. 203. and 467., and t. Ii. p. 18. 
 Cold by the current. Bibl. Univ. (N. S.) t. xvii. p. 387. 
 
 Peltier. Heat and cold produced by the current. Ann. de Chim. et de 
 Phys. t. Ixvi. p. 371. 
 
 Robinson. Influence of the medium upon the heating. Trans, of the Irish 
 Academy, vol. xxii. (Part I.) p. 3. 
 
 Grove. Idem. Arch, des Sc. Phys. t. ix. p. 140. and t. xii. p. 165. In- 
 candescence and deflagration. Bibl. Univ. (1839) t. v. p. 18. and 122.; t.xxv. 
 p. 426. and t, xxix. p. 387. 
 
 Clausius. Idem. Arch, des Sc. Phys. t. xxii. p. 269. 
 
 Favre. Heat liberated in the pile. Ann. de Chim. et de Phys. (N. S.) t. xl. 
 p. 393. 
 
 Faraday. Light and appearance of the spark. Phil. Trans. Collection of 
 Memoirs, and Bibl. Univ. t. xvii. p. 178. 
 
 Quet. Stratification of the induction spark. Comptes rendus de V Academic 
 des Sc. t. xxxv. p. 949. Influence of the magnet upon the voltaic arc. Idem. 
 
 Neef. Electric light and heat. Arch, des Sc. Phys. t. i. p. 30., and t. iii. 
 p. 391. 
 
 Marianini. Sparks in liquids. Bibl. Univ. (1843), t. xlvii. p. 253. 
 
 Sillimann. Voltaic arc. Ann. de Chim. et de Phys. t. xxiv. p. 216. 
 
 Despretz. Voltaic arc. Comptes rendus de VAcad. des Set. t. xxx. p. 367., 
 and t. xxxi. p. 418. Formation of the diamond. Cornpte rendu de VAcad. 
 des Sc. t. xxxvii. (5th and 19th Sept. 1853.) 
 
 Van Breda. Voltaic arc. C. JR. de VAcad. des Sc. t. xxviii. p. 426., and 
 Arch, des Sc. Phys. t. iii. p. 32. 
 
 MatteuccL Idem. Arch, des Sc. Phys. t. xii. p. 5., t. xiii. p. 223., and t. 
 xvii. p. 205., and Ann. de Chim. et de Phys. (N. S.) t. xxxvii. p. 44. 
 
CHAP. ir. EFFECTS OF DYNAMIC ELECTRICITY. 335 
 
 Daniel!. Idem. Arch, de TElcctr. t. i. p. 492. 
 
 (liitisiot. Heating of the positive wire. Bill. Univ. t. xviil p. 369. 
 
 Fizeau and Foucault. Electric light. Arch, de VElectr. t. iv. p. 311. 
 
 Foucault. Idem. Arch, des Sc. Phys. t. x. p. 222. 
 
 Masson. Electric photometry. Ann. de Chirn, et de Phys. (N. S.) t. xiv. 
 p. 129. t. xxx. p. 5., and t. xxxi. p. 295. 
 
 Wheatstone. Rays of the electric spectrum. Traite de Phys. de JBecquerel, 
 t. ii. p. 127. 
 
 Duboscq. Electric regulator. Comptes rendus de I'Acad. de Sc. t. xxxi. 
 p. 807. 
 
 Becquerel. Electric heat and light ; phosphorescence. Traite deFElectriciie 
 and Traite de Physique. 
 
 Draper. Light of an incandescent platinum wire. Phil. Mag. vol. xxx. p. 
 345. (1847). 
 
 Viard. Heat in wires by the current. C. R. de TAcad. des Sc. t. xxxix. 
 p. 904.* 
 
 * M. Viard has verified directly by experiment the explanation given by Clausius of the 
 effect of the ambient medium upon the heat developed by the current in wires. He has 
 shown, by the introduction of a rheostat into the circuit, that the heat developed is always prc- 
 poriional to the real resistance that exists, at the moment of the passage of the current, as IVIr. 
 Robinson had already proved (p. 242.) ; so that the presence of a less cooling gas, by increasing 
 the resistance of the wire that it surrounds, causes the current to develope in it more heat. 
 But if, upon shortening the wire of the rheostat, the resistance is rendered equal to what it was 
 when the wire was surrounded with the more cooling gas, then the quantity of heat liberated 
 by the current, is the same as it was in this latter case. 
 
336 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 CHAP. III. 
 
 CHEMICAL EFFECTS OF DYNAMIC ELECTRICITY. 
 
 Decompositions brought about by the Voltaic Current. 
 
 NICHOLSON and Carlisle, a short time after Volta had con- 
 structed his pile, succeeded in decomposing water, by 
 plunging into it two wires, of which one was in communication 
 with the positive pole, and the other with the negative pole. 
 The two wires were of brass ; the one, that was in communi- 
 cation with the + pole gave off no gas, but underwent 
 oxidation, whilst the one that was in communication with 
 the pole liberated hydrogen. The production of the gas 
 was the more abundant, in proportion as the two wires were 
 nearer together. These observers remarked besides, that 
 the decomposition of water not only takes place between the 
 two poles of the pile, but also between the metals of two 
 consecutive pairs, separated by the humid conductor. 
 Finally, they succeeded as easily in obtaining oxygen as 
 hydrogen, by substituting platinum wires for the copper 
 wires, that established communication between the water 
 and the poles of the pile. The two gases may be collected 
 separately, if the precaution be taken of placing over each 
 wire a tube filled with water, at the top of which the gas 
 that is liberated, naturally arranges itself; it is necessary 
 that the two tubes should not touch the bottom of the vessel, 
 in order that the two wires may really be plunged into the 
 same water.* 
 
 Cruikshanks was the first who obtained an effect by 
 plunging into separate vessels each of the poles of the pile, 
 which were silver wires, and uniting at the same time the 
 
 * See Vol. I. p. 31. fig. IS. 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 337 
 
 two vessels by another silver wire ; he perceived hydrogen 
 to be liberated from the wire, that was in communication 
 with the pole of the pile, whilst the end of the wire, that 
 was plunged in the same vessel, was attacked. The other 
 end of this same wire, which was plunged into the second 
 vessel, liberated hydrogen ; and finally, the wire, that was 
 in communication with the + pole, was attacked. The same 
 philosopher, having plunged two silver wires into a diluted 
 solution of nitrate of silver in ammonia, obtained at the 
 negative wire, first an abundant production of gas, then 
 filaments, which were recognised as being metallic silver. 
 The silver wire, that was in communication with the 
 positive pole, gave forth little or no gas, seeing that it 
 was attacked. With copper wires, plunging in an ammo.- 
 niacal solution of copper, Cruikshanks obtained metallic 
 copper around the negative wire : the liquid lost its colour 
 and became similar to distilled water, the copper having 
 been all precipitated. 
 
 Without dwelling upon other of Cruikshanks's experiments, 
 of the same kind, nor upon that of Henry on the decompo- 
 sition of ammonia, we will add that Davy obtained similar 
 results, but upon a greater scale, with a pile of 110 pairs, 
 which enabled him to prove that if, instead of connecting 
 by a wire the vessels full of water, into which are plunged 
 two gold wires, that communicate respectively with the poles 
 of the pile, communication is established by a piece of fresh 
 muscle or by a vegetable fibre, the gases are liberated at 
 the end of the polar wires, hydrogen at the negative wire, and 
 oxygen at the positive. It is the same if the communication 
 between the vessels is established by the intervention of the 
 human body, which can easily be done by plunging into them 
 a finger of each hand. There is no gaseous liberation at the 
 extremities of the fibre or of the fingers, that are immersed 
 in the water of the respective vessels, as there is when it is 
 a wire by which they are connected. Davy further re* 
 marked, that if, by means of muscular fibres, the respective 
 poles of the pile are made to communicate with a vessel 
 filled with water, and the two vessels are connected together 
 
 VOL. II. Z 
 
338 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 by a silver wire, a liberation of hydrogen is obtained at the 
 extremity of the wire, that is plunged into the positive vessel, 
 and an oxidation at the extremity, that is plunged into the 
 negative vessel. 
 
 In all these experiments, the gases oxygen and hydrogen 
 are not always quite pure ; but they are more or less mixed 
 with the nitrogen that arises from the atmospheric air dis- 
 solved in the water ; however, by taking many precautions, 
 and employing only wires that are not susceptible of oxidation, 
 such as gold wires, Davy found that the gases oxygen and 
 hydrogen were truly liberated in the proportion that con- 
 stitutes water. 
 
 Many philosophers had thought they perceived the forma- 
 tion of new bodies ; and in particular that of a peculiar acid 
 in the action of the pile upon certain liquids ; but Davy, 
 taking up anew the entire subject, succeeded, after a series 
 of laborious researches, in establishing, upon perfectly sound 
 bases, the true chemical power of voltaic electricity. He 
 was desirous, above all, to prove that, in electro-chemical de- 
 compositions, there were never any other elements liberated 
 at each of the poles, than those contained in the bodies, sub- 
 mitted to the action of the voltaic electricity. Upon operating 
 with vessels of various substances, agate, wax, Carrara 
 marble and glass, he clearly found alkalies at the negative 
 and acids at the positive pole; but he satisfied himself that 
 these acids and alkalies were derived from the substances 
 themselves of the vessels, which the water was enabled to 
 dissolve, especially under the influence of electricity. It 
 might even be seen, when much soda had been obtained in 
 a vessel of glass, that the latter had been strongly attacked, 
 at its point of contact with the wire. Having yet observed 
 traces of acid and of alkali with gold vessels, Davy satisfied 
 himself that these elements were derived from a small 
 quantity of salt, remaining in solution even in distilled 
 water; and having succeeded in perfectly depriving this 
 water of it, there was no longer any trace of acid or of alkali ; 
 except in some cases, where there was a little ammonia at 
 the negative pole and nitric acid at the positive, the formation 
 
CHAP. ill. EFFECTS OF DYNAMIC ELECTRICITY. 339 
 
 of which was evidently due to the combination of hydrogen 
 and oxygen, in the nascent state, with the nitrogen, dissolved 
 in the water. Indeed, on placing the water, submitted to 
 decomposition, in vacuo, and still better in hydrogen, there 
 was no longer at the two poles anything besides perfectly 
 pure oxygen and hydrogen. 
 
 Thus it is well established that dynamic electricity, acting 
 upon bodies susceptible of being decomposed, produces no 
 new elements, but that it liberates them from the substances 
 exposed to its action, at the same time that it facilitates, by 
 their liberation in the nascent state, their combination with 
 other elements present. It is very remarkable that, under 
 the action of a powerful electricity, substances, apparently 
 the most insoluble, may be decomposed ; this is proved by a 
 great number of Davy's experiments upon glass, upon 
 marble, upon the sulphates of strontian and baryta, employed 
 as vessels filled with water. 
 
 Dynamic electricity not only liberates the elements by 
 separating them, but it transports them, a characteristic 
 that appertains to this mode of decomposition alone. This 
 has been long since established by Berzelius and Hizinger. 
 By operating with wires of different metals, and upon so- 
 lutions of various natures, either separated or mixed, some- 
 times different, at other times similar, at the respective poles, 
 they succeeded in satisfactorily proving this power of trans- 
 port, which accompanies the decomposing power of the 
 voltaic pile. In order to place the different liquids in 
 contact with the respective polar wires, they employed a 
 syphon, the branches of which, closed by corks fitted into 
 their extremities, and traversed by the wires, were filled to 
 about two thirds of their height, one by a liquid, such as 
 sulphate of potash, the other by another liquid, such as 
 muriate of ammonia. The upper part of the syphon con- 
 tained distilled water, in order to put the two liquids into 
 communication ; it was pierced at its summit by several 
 holes, intended to allow the gases to pass out. They had 
 concluded from all their experiments that, when electricity 
 traverses a liquid, the principles that it contains are se- 
 
 z 2 
 
340 TRANSMISSION OF ELECTRICITY. TART iv. 
 
 parated ; that oxygen and acids are transported to the 
 positive pole, hydrogen, the alkalies, the earths, and bases 
 in general, to the negative ; and this, as well when the saline 
 solutions, into which the wires that come from the respective 
 poles are plunged, are heterogeneous, as when they are 
 similar. The numerous results to which they had arrived, 
 had also demonstrated to them the influence over the energy 
 of the decomposition, of the extent of contact of the polar 
 wires with the liquid ; and the part that is played in the 
 production of the effects observed, by the affinity of the 
 elements of these liquids for the substance of the wires, as 
 Well as their reciprocal affinity, when several different liquids 
 are submitted at the same time to the decomposing action. 
 
 But it is Davy, who, by the accuracy and the number of 
 his experiments, has completely analysed this property of 
 transport, possessed by dynamic electricity, and which must 
 not be confounded with that, which we have already described 
 in the preceding Chapter ; for it is manifested only with de- 
 composition. In order to study this phenomenon well, it is ne- 
 cessary to make use of cups or tubes of glass, in which are 
 placed the liquids that are required to be traversed by the 
 current ; into each of these cups, when there are two (fig. 227.), 
 or into the extreme cups, when there are more than two 
 (%. 228.), are plunged the platinum wires or plates, that 
 communicate, one with the + pole the other with the pole of 
 
 Fig. 227. Fig. 228. 
 
 the pile ; then the liquids of the cups are connected one with 
 the other by means of hanks of cotton or asbestos, well satu- 
 rated with water (fig. 229.), or by tubes in the form of a 
 syphon, filled with very pure water (fig. 227, 228.). When we 
 desire to collect the gases that are liberated, each of the polar 
 wires is surrounded by a tube, closed above and open below, 
 which is filled with the same liquid, as that contained in 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 341 
 
 the vessel into which it is plunged ; and the two vessels are 
 connected (fig. 230.). If, when making use of two cups, 
 
 Fig. 229. Fig. 230. 
 
 distilled water is placed in one, and a saline solution in the 
 other, the base or the acid passes into the distilled water, ac- 
 cording as the metal conductor, that is plunged into it, is the 
 negative or the positive. Care must be taken always to 
 maintain the level of the distilled water higher than that of 
 the solution, in order that no part of the latter shall pass into 
 the water. On taking this precaution, we may satisfy our- 
 selves, for example, with sulphate of magnesia, that no 
 pure magnesia passes into the distilled water, when this 
 water is in communication with the negative pole, and that 
 there is no trace of sulphuric acid, since a salt of baryta 
 produces no precipitation. 
 
 In order to discover how far this property of transport ex- 
 tends, it is necessary to employ at least three cups (Jig. 229.) 
 the saline solution is placed in one of the two extreme cups, 
 distilled water in the other, and a reagent in the intermediate 
 cup. If this reagent is water coloured blue by tincture of 
 litmus, on pouring a solution of sulphate of potash into the 
 negative cup, the coloured water is not seen to be reddened 
 by the passage of the sulphuric acid ; but the first impression 
 of redness is shown only at the extremity of the hank of 
 amianthus, which makes communication between the coloured 
 water and the positive vessel, namely, on the side most distant 
 from the vessel from which the sulphuric acid comes. The 
 
 z 3 
 
342 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 same thing takes place for alkali, when, the saline solution 
 being placed in the positive vessel, it is transported to the 
 negative pole. It is even easy to demonstrate that this 
 colouration of blue water into red by acid, into green by alkali, 
 only arises from the diffusion of the acid, which is all carried 
 around the positive wire, and of the alkali, which is all 
 carried around the negative wire. For this purpose, we 
 have merely to employ, as I have done, a large tube, 
 divided into three equal compartments, by two diaphragms 
 of bladder, which allow the current to pass, without permit- 
 ting the liquids to mix : these three compartments fulfil the 
 office of the three cups above mentioned. 
 
 The experiment, that we have just related, shows there- 
 fore that, under the influence of the current which transports 
 them, acid and alkali lose the property of changing the colour 
 of vegetable blue. In order to learn to what point their 
 chemical activity is neutralised, we must substitute for the 
 coloured waters of the intermediate cup, liquid substances, 
 that have more or less affinity for the acid or the base, that 
 are transported, and be satisfied whether they are arrested in 
 their passage by these substances. By this method, we 
 prove that a solution of ammonia, of soda, of potash, or of 
 lime, does not arrest, either sulphuric, nitric, or hydrochloric 
 acids, which continue to present themselves in the distilled 
 water of the positive cup, when salts of these acids in solution 
 have been placed in the negative cup. If the saline solu- 
 tions are placed in the positive cup, their bases are seen to 
 present themselves in the distilled water of the negative cup, 
 through acids, placed in the intermediate cup. It requires a 
 tolerably long time (twenty-four to forty-eight hours), for these 
 effects to be manifested in a very decided manner ; and it is 
 necessary, from time to time, to remove and to wash in pure 
 water the hanks of amianthus, by which communication 
 is established between the cups. The pile must be composed 
 of a very considerable number of pairs, which depends 
 also upon the kind of pile that is employed ; but it is easy 
 to determine in each case the number of pairs necessary for 
 the manifestation of the effect, because there are always some 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 343 
 
 bubbles of gas, which, by being liberated at the polar wires, 
 indicate the moment when the current is sufficiently powerful 
 to pass. 
 
 There are, however, some cases, in which the substance 
 transported is arrested by that which it traverses ; sulphuric 
 acid, for example, cannot traverse solutions of strontian and 
 baryta; and these two bases in their turn cannot traverse 
 sulphuric acid. Thus if we place a solution of sulphate of 
 potash in the negative cup, distilled water in the positive, and 
 a saturated solution of baryta between the two, we do not 
 obtain, even at the end of thirty hours, and with a pile of 150 
 pairs, any appreciable portion of acid in the distilled water ; 
 but there is formed, in the intermediate vessel, much sulphate 
 of baryta. Thus again, a solution of hydrochlorate of baryta 
 being placed in the positive cup, sulphate of potash in the in- 
 termediate cup, potash is soon seen to appear in the distilled 
 water, that is in the negative cup ; and an abundant preci- 
 pitate of sulphate of baryta is formed in the middle vessel. 
 If the intermediate solution is sulphate of silver, hydro- 
 chlorate of baryta being placed on the negative side, sul- 
 phuric acid is seen to appear in the distilled water of the 
 positive side, and an abundant precipitate of chloride of silver 
 to be formed in the silver solution. 
 
 The experiments, that precede, show therefore that the 
 neutralising power of the current has a limit, which depends 
 upon the degree of affinity of the substance transported, for 
 that which is contained in the solution that it traverses ; that, 
 for example, sulphuric acid is able to traverse a solution of 
 potash, of soda, &c., without being arrested; but that it is 
 arrested by a solution of baryta, because it forms with it an 
 insoluble compound. They show therefore that an exchange 
 may take place of base or acid, between the current of the 
 solution that it is traversing, in such a manner that the 
 current may yield to this solution the acid or the base that it 
 was carrying, and take in its place the acid or the base of the 
 salt dissolved. 
 
 An analogous phenomenon, and one of no less importance 
 
 z 4 
 
344 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 for the theory of electro-chemical decompositions, is, that 
 certain bases, that are little or not at all soluble, such as 
 magnesia, and several metallic oxides, arising from saline 
 solutions, placed in the positive cup, are very well able to 
 pass into the negative cup, filled with distilled water, if the two 
 cups communicate only by a hank of amianthus ; but if there 
 is interposed between them a vessel of pure water, still estab- 
 lishing, by means of hanks of amianthus, the communication 
 between this vessel and the other two, then the particles 
 transported fall to the bottom of the intermediate vessel, and 
 do not go to the negative vessel. 
 
 Hitherto we have spoken only of the decomposition of 
 salts and of water, but Davy found that water is not the only 
 binary compound that the passage of electricity is able to 
 separate into its elements, that acids and oxides are also 
 decomposable ; and he thus succeeded in demonstrating that 
 potash, soda, and the different earths are nothing more than 
 oxides, the metal of which he succeeded in obtaining. 
 Having taken a piece of pure potash, which had been for 
 some moments exposed to the air, so as to become a conductor 
 on its surface, on account of the moisture that it had attracted, 
 he placed it upon an isolated plate of platinum, put into 
 communication with the negative pole of a powerful voltaic 
 pile of 250 pairs ; he then touched the upper surface of the 
 piece with a platinum point, communicating with the positive 
 pole. There was liberated around the wire a great quantity 
 of gas, which was recognised to be pure oxygen ; and then 
 were discovered, at the lower part of the potash, some 
 small globules which had a brilliant metallic lustre, but 
 which were not long in becoming tarnished, and covered 
 with a white coating, that formed upon their surface. These 
 globules decomposed water with great vivacity, liberating 
 hydrogen, and oxidising with development of heat and light. 
 In dry air they only became covered with a film of oxide 
 which, for want of humidity to dissolve it, remained upon 
 the surface, protecting the interior of the substance against 
 the action of the oxygen. 
 
 A piece of soda presented exactly the same phenomena ; 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 345 
 
 only it required a pile a little more powerful, in order to 
 obtain the metallic globules ; and the latter were themselves 
 less rapidly oxidised in the air. 
 
 After having proved that potash and soda are therefore 
 oxides of two metals, which he named potassium and sodium, 
 Davy succeeded in obtaining a tolerably large quantity 
 of them, by collecting them, in proportion as they were 
 formed, in recently distilled oil of naphtha, which is without 
 action upon them, and in which they are preserved perfectly 
 intact. These two substances have all the properties of 
 metals ; and they have their brilliancy, presenting an aspect 
 very similar to that of polished silver. They conduct heat 
 and electricity; they melt, potassium at 168, and sodium 
 not under 180^; they crystallise and become brittle at 32. 
 Their density is less than that of water.* These two metals 
 easily amalgamate with mercury, and it is even a means 
 of extracting them from their oxides : a globule of mercury 
 is placed upon a piece of potash or of soda, itself placed upon a 
 platinum plate, which communicates with the positive pole ; 
 then a platinum point is thrust into the globule, which is con- 
 nected with the negative pole of the pile. The alkaline metal 
 is then easily extracted from its amalgam by distillation 
 conducted in oil of naphtha, and the little globules obtained 
 either in this manner, or directly, are converted into a 
 single button by fusion conducted also under oil of naphtha. 
 
 Davy subsequently extended his discovery to other com- 
 pounds ; and, thanks to his labours and to those of some other 
 chemists, it was demonstrated that all the earths and fixed 
 alkalies were metallic oxides, whose bases were more or less 
 easily extracted, first by means of the decomposing force 
 of dynamic electricity, afterwards by purely chemical 
 processes. We shall have occasion to compare the two 
 modes in the Chapters of the Part, which are devoted 
 to applications, whose subject will be the employment of 
 electricity for the extraction of metals. 
 
 The fundamental phenomena of the electro-chemical de- 
 
 * That of potassium is 0'865 ; and that of sodium 0'972. 
 
346 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 compositions, that we have been describing, suffice for the 
 present to enable us to lay down certain general principles. 
 First, they prove to us that electro-chemical decomposition 
 is a phenomenon of dynamic elctricity, and not a pheno- 
 menon of static electricity. Indeed, everything that favours 
 the passage of the current, facilitates decomposition. Gay- 
 Lussac and Thenard succeeded in demonstrating this in their 
 physico-chemical researches. They have proved that the 
 quantity of gas liberated in the decomposition of water, very 
 feeble when the water is pure, increases with the quantity of 
 salt or acid dissolved in it, and consequently with its degree of 
 conductibility ; that it is also, up to a certain limit, greater in 
 proportion as the surface of contact increases between the 
 liquid and the polar conductors. The elevation of temperature 
 which increases the conductibility of the liquid, facilitates its 
 decomposition. All these results, therefore, show that it is im- 
 possible to attribute the decomposition of bodies to an attrac- 
 tion, exercised by the two poles over the constituent 
 molecules ; the one set positive, the other negative, and which 
 would be analogous to ordinary electric attractions and 
 repulsions. 
 
 Another well-established point is, that the portion of the 
 liquid, which is decomposed, is only that which is in contact 
 with the polar conductors, whether it be the same or dif- 
 ferent at the two poles, as the researches of Hizinger and 
 Berzelius have proved. The intermediate liquids, when 
 they are separated from each other and from the polar 
 liquids, merely by porous diaphragms, or humid conductors, 
 do not undergo any alteration in their composition, save in 
 the exceptional cases that we have pointed out above, ac- 
 cording to Davy. In like manner, it is upon the surface of 
 the metals which serve as poles, that the liberated elements 
 are deposited, as is proved by simple inspection, when gaseous 
 and solid elements are in question, and by the employment 
 of tests, in the case of liquid elements. As a proof that the 
 halves of the liquid interposed between the poles are in two 
 opposite states of electric tension, the elegant experiment is 
 quoted ; that a saline solution, sulphate of soda, for example, 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 347 
 
 coloured blue, placed in a u tube (Jig. 231.) becomes 
 half coloured red, and half green, when placed 
 in the circuit of the pile, by means of two 
 platinum wires. But this double colouration 
 is only the effect of the diffusion of the acid 
 and the alkali, which, liberated at each of 
 the poles, spread gradually in the surround- 
 ing parts of the liquid. I have proved this 
 by placing the saline solution in a vessel 
 separated into three compartments by two bladders, which 
 prevent the solutions contained in each of the compartments 
 from mixing, at the same time allowing the current to 
 traverse them. However long may have been the duration 
 of the decomposition, the colour of the liquid contained in the 
 middle cell has not been altered, whilst the liquids contained 
 in the two extreme cells, into which the two poles were 
 plunged, have entirely changed their colour. 
 
 We have seen that if we have in succession several vessels, 
 filled with acidulated water or a saline solution, and if, instead 
 of connecting them by humid conductors, they are made to 
 communicate with each other by metallic arcs, we then 
 obtain, in each vessel separately, a decomposition exactly the 
 same as would have taken place, had the liquid of this vessel 
 been alone in the circuit. Thus, we shall obtain in the two 
 tubes of each of the three vessels of fig. 232., which are 
 filled with acidulated water, oxygen and hydrogen in the pro- 
 portion that constitutes water, the oxygen being in the tubes 
 
 Fig. 232. 
 
 Fig. 233. 
 
318 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 turned towards the side of the positive pole, and the hydrogen 
 in those turned to the side of the negative pole. So also, if 
 we have a series of u tubes (fig. 233.), filled with a saline so- 
 lution coloured blue, and connected by platinum wires, bent in 
 the form of an arc, and plunging by one of their ends into 
 one of the tubes, and by the other into the following, whilst 
 the two extreme branches communicate by platinum wires, 
 one with the positive, the other with the negative pole of the 
 pile, we perceive the solution become coloured red in all those 
 branches of the tube, that are turned to the side of the posi- 
 tive pole, including that into which this pole is plunged, and 
 coloured green in all those that are turned to the side of the 
 negative pole, including that which communicates immediately 
 with that pole. We have merely to change the place of the 
 two poles, to perceive all the red and the green parts of the 
 liquid repass first to blue, then those that were red pass 
 to green, and those that were green pass to red. 
 
 An important point to notice is, that when saline solutions 
 are decomposed, there is at the same time a gaseous liberation 
 at the poles, which seems to indicate a simultaneous decom- 
 position of water. However, there is an important difference 
 to be made in this respect between the salts, whose base is 
 manifested in a state of oxide at the negative pole, and those 
 in which it appears in the revived metallic state ; in this latter 
 case there is, as in the former, a liberation of oxygen with the 
 acid at the positive pole, but there is no hydrogen at the ne- 
 gative pole, as if this gas were employed in reducing the 
 oxide, which forms the base of the salt. We shall see here- 
 after what actually takes place in this case. For the 
 present, we shall confine ourselves to remarking that the re- 
 vived metal is manifested sometimes in the state of plates ad- 
 hering to the surface of the conductor that is employed for a 
 pole, sometimes in a state of powder, sometimes in the 
 crystalline state, or forming remarkable aborizations. One 
 of the most elegant is that which is obtained by employing 
 acetate of lead, and into the middle of a vessel that contains 
 this solution, thrusting a platinum wire in communication with 
 the negative pole of a pile, the other pole of which also com- 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 349 
 
 municates with the liquid, by means of a wire or plate that is 
 immersed towards the edge of the vessel. If the current is 
 not too strong, the aborizations are slowly formed, and in a 
 very brilliant manner, whilst with a very energetic current 
 they are confused. The force of the current, indeed, as we 
 shall see, as well as the nature itself of the salt, submitted 
 to the decomposing action of the electricity, has an influ- 
 ence over the structure of the deposits, that occur in this 
 case. 
 
 Before extending further the study of the phenomena of 
 decomposition, and the research of the precise laws by which 
 they are regulated, we think it useful to make known here, 
 the ingenious manner in which Grotthus succeeded in ex- 
 plaining them. Setting out from the principle laid down by 
 Davy, and afterwards admitted by Berzelius and by Ampere, 
 that the constituent atoms of bodies are, some electro-positive 
 and others electro-negative, and that it is in virtue of the 
 mutual attraction of the electro-positive and the electro- 
 negative elements, that chemical combination is brought 
 about, he explained in the following manner what takes place in 
 the electro-chemical decomposition of any compound water 
 for example. As soon as a filament of water is placed in 
 the circuit, it is polarised, as we have seen every conductor 
 must be, when interposed between the poles * ; but hydrogen 
 being a body eminently positive, the molecules of hydrogen 
 of each particle of water turn on the side of the negative 
 pole, and the molecules of oxygen, which is eminently 
 negative, on the side of the positive polef (Jig. 234.). The 
 current passes, that is to say, there is a discharge of the con- 
 secutive molecules between each other, and of the two 
 extreme molecules with the poles. It follows from this that 
 the negative oxygen of the molecule of water No. 1., which 
 is in contact with the positive pole P, is liberated 
 against the pole of which the electricity is combined with its 
 negative electricity, and that the positive hydrogen of the 
 
 * Vol. IT. p. 63. 
 
 f In each molecule of water the particle of hydrogen is clear, and that of 
 oxygen shaded. 
 
350 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 molecule No. 6., in contact with the negative pole, is liberated 
 in like manner against this pole ; now the hydrogen of the 
 
 d 9 
 
 -* - 
 
 J%. 234. 
 
 molecule of water No. 1. combines with the oxygen of the 
 molecule No. 2., the hydrogen of No. 2. with the oxygen of 
 No. 3., and so on to the last particle. In other words, the 
 discharge that is brought about between the consecutive 
 molecules of water, in order to constitute the current, drawing 
 all the hydrogens of the pole -f to the pole and all the 
 oxygens of the pole to the pole + ,it liberates the hydrogen 
 of the molecule in contact with the pole, and at the same 
 time compels all the oxygens and hydrogens of the inter- 
 mediate particles to combine together to re-form water. The 
 second series of particles of fig. 234. represents these new 
 particles of water. What the first passage brings about, the 
 second passage brings about in like manner, namely, that the 
 particles are polarised anew, and consequently must all make 
 a semi-revolution in order that the oxygens may be turned on 
 the side of the -f pole, and the hydrogens on the side of the 
 pole, as represented by the third series of particles of fig. 
 234. ; then decomposition takes place, as well as the exchange 
 of the constituent parts, between each of these particles, with 
 liberation of gas at the extreme particles, and so on as long 
 as the current is transmitted. We therefore see, since there 
 is only oxygen at the + pole, and hydrogen at the pole, 
 that we are no longer embarrassed to explain what becomes of 
 the hydrogen of the particle in contact with the positive pole, 
 and the oxygen of that which is in contact with the negative 
 pole. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 351 
 
 The explanation that we have been giving, taking water 
 for the example, is equally well applicable to the decom- 
 position of every compound body. In the case in which the 
 solution interposed between the poles is not homogeneous, but 
 is composed of two or three different solutions, the exchange 
 takes place in a similar manner. Thus, if the positive pole 
 is in contact with a solution of nitrate of potash, and the 
 negative with a solution of sulphate of soda, the sulphuric 
 acid of the last particle of the sulphate, and the potash of 
 the first particle of the nitrate combine, liberating a molecule 
 of soda at the pole, and one of nitric acid at the + pole ; 
 then this particle of sulphuric acid combines with a second 
 of potash, liberating a second particle of soda at the pole, 
 a second of nitric acid at the -f pole, until finally the sul- 
 phuric acid comes also to the 4- pole, and the potash to the 
 pole; and that, conformably with the observations of 
 Berzelius and of Hizinger, we have both acids at the + pole, 
 and both bases at the pole. If there is a third solution 
 between the two, it is also by the way of decomposition and 
 combination that the passage of the current and the transport 
 of particles takes place. Only if the compound momentarily 
 formed is insoluble, then, as we have seen, its elements are 
 no longer transported to the two poles, and are replaced by 
 those, which have not formed an insoluble compound. Thus, 
 if the interposed solution is hydrochlorate of baryta, sul- 
 phuric acid forming with baryta an insoluble compound, the 
 sulphate of baryta is precipitated to the bottom of the inter- 
 mediate vessel, and its place at the + pole is supplied by 
 hydrochloric acid. In like manner if the salt, placed at the 
 positive pole, is nitrate of silver, and that placed in the 
 middle is hydrochlorate of soda, the silver, which forms with 
 hydrochloric acid an insoluble body, is precipitated, and soda 
 is liberated in its place at the negative pole. 
 
 We shall see further on, that this theory very well explains 
 the general facts as well as the secondary phenomena, which 
 the more profound study that we shall make of electro- 
 chemical decompositions will enable us to to discover. We 
 merely remark in this place, that we do not admit the dis- 
 
352 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 tinction of the elements of bodies into electro-positive and 
 electro-negative, as it has been in general formularised, a 
 distinction that cannot be maintained in face of the fact, that 
 the same body may comport itself according to the combina- 
 tion into which it enters, sometimes as electro-positive at 
 other times as electro-negative ; for example, chlorine, which 
 goes to the + pole, when it is combined with hydrogen in 
 hydrochloric acid, and to the pole, when combined with 
 oxygen in the chloric acids. The property in question can, 
 therefore, be only relative ; and it consists in this, that as 
 soon as the current traverses a compound liquid conductor, 
 it polarises the molecules of this liquid in such a way that 
 among their elements, some become charged with negative 
 electricity and others with" positive, the same element being 
 able, according to that with which it is combined, to become 
 charged equally with one or with the other. We shall 
 endeavour, when we are occupied with the electricity li- 
 berated in chemical actions, and consequently with the more 
 intimate relations, that exist between these two kinds of 
 force, to show that this property may easily be reconciled 
 with the hypothesis that we have previously made ; namely, 
 that the atoms of bodies all possess a natural polarity. 
 
 Laws of Electro-chemical Decompositions. Definite Action of 
 the Current. 
 
 It had long been thought that the presence of water was 
 necessary, in order that a liquid body might be decomposed 
 by the electric current. It had even been remarked as a 
 very curious fact, that water, which, when it is pure, is very 
 difficultly decomposed, being itself a very bad conductor of 
 electricity, may, by dissolving them, render such bodies as 
 sulphuric, sulphurous and other acids, conductors, which do 
 not of themselves conduct electricity at all, or in a very 
 trifling degree. Davy had, however, already observed, that 
 we may employ, as liquid conductors for charging piles, 
 such salts as chlorate of potash in a state of fusion ; but he 
 had always considered the presence of water as necessary in 
 
CHAP, in, EFFECTS OF DYNAMIC ELECTRICITY. 353 
 
 the liquid, placed between the poles in order to be decom- 
 posed. It is Faraday, who, having succeeded in transmitting 
 currents, even of a feeble intensity, through chlorides and salts, 
 brought to the state of fusion by the action of a high tem- 
 perature, has at the same time shown that these bodies were 
 decomposed by the currents into their elements, some of 
 which were carried to the positive pole, the others to the 
 negative. Thus, on placing some of these solutions in fusion 
 in small glass tubes in the form of a u, and introducing into 
 each of the branches a platinum wire, in order to transmit 
 the current through the substance, he found, with iodides 
 and chlorides of lead, silver, &c., iodine and chlorine at 
 the positive pole, and lead, silver, in a word the metal 
 revived at the negative pole. But it is necessary, in order 
 that the decomposition may take place, that the bodies lique- 
 fied by heat shall become conductors by the fact of this 
 change of state, in order that the current may be able to 
 pass. Now, there are a great number of bodies, such as sul- 
 phurets, perchlorides, as well as many organic substances, 
 which do not become conductors on being liquefied, and 
 which, consequently, are not decomposed. The reverse is 
 equally true, namely, that every compound body, which be- 
 comes a conductor by liquefaction, is decomposed by the 
 current; the exceptions to this rule, which Faraday cites, 
 being only apparent, as we shall soon see. There is, there- 
 fore, a great difference between simple conductibility, which 
 we may call physical, and the conductibility, accompanied 
 by electro-chemical decomposition. The former, which is 
 peculiar to elementary solid and liquid bodies, such as 
 mercury and the melted metals*, diminishes by the effect of 
 elevation of temperature, as we have seen as well in the case 
 of liquids as in that of solids ; the latter, which belongs to 
 
 * Inglis and Palmieri had thought that melted iodine is a conductor of 
 electricity ; but Beetz satisfied himself, by very accurate experiments, that 
 the slight traces of conductibility, presented by iodine in a state of fusion, are 
 due to its mixture with a small portion of hydriodic acid, which is decom- 
 posed by the current. Furthermore, bromine, liquid chlorine, melted sulphur, 
 selenium, and phosphorus are not conductors, so that among elementary bodies, 
 there are only the metals and carbon that conduct electricity. 
 VOL. II. A A 
 
354 TRANSMISSION OF ELECTRICITY. PART iv- 
 
 compound liquid bodies, increases, on the contrary, with the 
 heating, which favours decomposition. It follows from this 
 that it seems almost to be a consequence of this decomposition, 
 or that it is at least intimately connected with it, so as to form 
 with it but one and the same phenomenon. However, 
 Faraday and some philosophers think that compound liquids 
 may conduct a sensible portion, however small, of electricity, 
 without becoming decomposed ; and may consequently possess 
 a certain degree of physical conductibility. We shall ex- 
 amine in the sequel, when we shall have well studied the 
 phenomena, that attend upon decomposition, and shall have 
 determined its laws, the extent to which this opinion is well 
 founded. 
 
 We see, therefore, that every compound body, a conductor 
 of electricity, may be decomposed by the passage of the 
 current, when it is in a liquid state, whether it may have 
 been brought to this state either by solution in water or by 
 fusion. We are now about to investigate the more precise 
 laws, according to which this decomposition is brought about; 
 and, in order to render our labour more easy, we shall adopt 
 the terms introduced by Faraday into this part of the science. 
 Thus, chemical decomposition, brought about by electricity, 
 we shall call electrolysis, to distinguish it from analysis, which 
 is decomposition brought about by purely chemical means, 
 and from which it differs by very decided characteristics. 
 Bodies susceptible of being decomposed by the electro- 
 chemical way, we shall term electrolytes. Finally, we shall 
 retain the name of electrodes to the conductors, that 
 establish communication between the poles of the pile and 
 the electrolyte.* 
 
 The first law that we encounter, and which was established 
 by Faraday, is that the decomposing action of a current is 
 
 * Mr. Faraday calls the positive electrode the anode, and the negative the 
 cathode ; in like manner he designated as anions those elements of the elec- 
 trolyte, that are liberated at the positive pole, and as cathions those that are 
 liberated at the negative pole ; giving the name of tons to these two classes of 
 elements. We shall not make use of these various denominations, which do 
 not seem to be indispensable, whilst those we have adopted are eminently 
 useful. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 355 
 
 constant for a given quantity of electricity. Thus, if we 
 have several voltameters, placed one after the other so as to 
 be traversed by the same current for the same time, it is 
 found that the quantity of oxygen and of hydrogen gas 
 liberated in each is similar, even though the conducting 
 solutions and the size of the electrodes differ from one volta- 
 meter to the other. These solutions may be acid, alkaline, 
 or saline ; they may be more or less diluted ; and notwith- 
 standing they give the same quantity of gas, when they are 
 traversed by the same current for the same time. With 
 regard to the electrodes, it is necessary that they be of 
 platinum, and so arranged that the gases have the shortest 
 possible course to take in the liquid, that always dissolves 
 more or less, which gives rise to the risk of making us 
 suppose differences in the quantity of gas liberated. Care 
 must also be taken, especially when the electrodes present 
 a large surface of contact with the liquids, not to leave the 
 gaseous mixture of oxygen and hydrogen in contact with 
 the platinum electrodes ; because platinum, by its mere con- 
 tact with this mixture, brings about the combination of the 
 two gases. It is even better to collect the gases separately, 
 and to measure one of them, the hydrogen for example, 
 which dissolves less easily ; this is what Faraday, in general, 
 did. We shall see in the fourth paragraph, when occupied 
 with the influence exercised by the electrodes upon the 
 electrolysis, the errors that may arise from the neglect of the 
 precautions that we have been pointing out. 
 
 Thus then, when all the gas is collected, that arises 
 from the decomposition of the acidulated or saline water, 
 and when no secondary effect, as happens with certain 
 solutions, disguises any portion, we obtain in the volume 
 of this gas an exact measure of the quantity of electricity 
 that passes; on which account it is that Faraday termed 
 the apparatus founded upon this principle a voltameter. 
 This is so true that, if we reduce this electricity to one-half, 
 by placing two perfectly similar voltameters parallel to each 
 other, the current divides itself equally between them, and 
 liberates in each of them a quantity of gas, that is exactly 
 
 A A 2 
 
356 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the half of what is liberated in a third voltameter, placed 
 in the circuit in such a manner as to be traversed by the 
 current entire. If there exists any difference of conducti- 
 bility between the two parallel voltameters, because one 
 of them has larger electrodes, or contains a more acid 
 solution, the quantities of gas liberated in each are no longer 
 the same, but their sum is always equal to the quantity 
 of gas liberated in the single voltameter. M. Matteucci 
 demonstrated this very satisfactorily. 
 
 But it is not only upon aqueous solutions, in which the 
 water alone is decomposed, that the chemical power of an 
 electric current is always proportional to the absolute 
 quantity of electricity transmitted : this same property exists 
 for all electrolytes ; whence it necessarily follows that, when 
 a like current traverses for the same time two or many 
 compound bodies, that is to say electrolytes, it must neces- 
 sarily in each of them separate their elements in a quantity 
 proportional to their chemical equivalents.* This beautiful 
 law was established by Faraday, by a great number of 
 experiments. Thus he arranged one after the other, in 
 the same circuit, a voltameter and a tube filled with proto- 
 chloride of tin, placed in a glass tube into which penetrated 
 two platinum wires, and retained in a state of fusion by a 
 spirit lamp. One of the platinum wires that were plunged 
 in the protochloride communicated with the negative pole of 
 the pile, the other with one of the electrodes of the voltameter, 
 the second electrode of which led to the positive pole. After 
 having allowed the decomposition to go on for some time, 
 it was interrupted ; then was carefully weighed the platinum 
 wire covered with tin, whose weight had previously been 
 
 * We understand" by chemical equivalents the relative weights of the 
 elements, that enter into the composition of a body. Thus the equivalent of 
 hydrogen is 12-50, that of oxygen being 100, whence it follows that the equi- 
 valent of water is 1 12-50, which signifies that 1 00 grains of oxygen combine with 
 12-50 of hydrogen to make 112*50 of water. The equivalent of tin is 735"29, 
 and that of chlorine 442*65 ; whence it follows that 735-29 of tin combine with 
 442-65 of chlorine to form 1177-94 of chloride of tin. In like manner, 100 of 
 oxygen combine with 735-29 of tin, in order to make 835-29 of oxide of tin ; 
 and 442-65 of chlorine make, with 12-50 of hydrogen, 455-15 of hydrochloric 
 acid. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTEICITY. 357 
 
 determined ; this weight gave 3^ grs. as the weight of the 
 tin, arising from decomposition; the weight of the water 
 decomposed, estimated from the gaseous volume measured 
 with care in the voltameter, was found to be about O49 grs ; 
 whichgives 735 for the equivalent of the tin, thatof water being 
 112, a number that is indeed the truth. The protochloride 
 of tin, that remains after the operation, is perfectly pure, in 
 such a way that it is evident there has been liberated at the 
 positive pole a quantity of chloride equivalent to that of 
 the metallic tin carried to the negative electrode. Only 
 the secondary actions, such as that of chlorine upon the 
 reduced metal, when the two electrodes are very near to 
 each other, sometimes render the weight of the reduced 
 metal too feeble. With the iodides, which are equally 
 decomposed in the state of fusion, the same inconvenience 
 is presented, on account of the formation of periodides at 
 the positive electrode. In general, many precautions are 
 necessary, and a particular choice of electrolytes, in order 
 that the laws may be manifested in a very distinct manner, 
 without being disturbed by secondary effects. 
 
 In order to make it come out well, Faraday endeavoured 
 to place several different electrolytes one after the other on the 
 route of the current, for example, acidulated water in the vol- 
 tameter, protochloride of tin, and chloride of lead ; and he ob- 
 tained quantities of tin, lead, chlorine, oxygen, and hydrogen 
 equivalent to each other. It is evident, in this case, that it is 
 the worst conducting of the electrolytes, that determines the 
 total effect, an effect which is the same in all. 
 
 Thus we may regard as completely established that the 
 chemical action of electricity is definite, and that the same 
 quantity of electricity, or the same electric current, decomposes 
 chemically equivalent quantities of all the bodies, that it traverses : 
 whence it follows that the weights of the elements, which it 
 separates in these electrolytes, are all, in respect to each other, 
 as the chemical equivalents of these elements. 
 
 The law that we have just established must be general ; 
 but when we endeavour to prove it for the case of com- 
 pound bodies, others than binary, and for that in which these 
 
 A A 3 
 
358 TRANSMISSION OF ELECTRICITY. PART IT. 
 
 compounds are themselves dissolved in an electrolyte, such 
 as water, we encounter very great difficulties, one of the 
 chief of which is the formation of secondary products, 
 which we have frequently some difficulty in distinguishing 
 from the direct products of decomposition. Thus, when 
 we wish to decompose a solution of ammonia, in which the 
 precaution has been taken of dissolving sulphate of ammonia, 
 in order to render it a better conductor, we obtain very 
 pure nitrogen at the positive electrode, and hydrogen at the 
 negative, in the proportion of 3 or 4 volumes of hydrogen to 
 1 of nitrogen. It seems to follow from this that the ammonia 
 alone has been decomposed ; and yet, if we place a voltameter 
 in the same circuit, we find that hydrogen is liberated in it 
 in exactly the same quantity as in the ammoniacal solution ; 
 which seems to prove that, in the latter, the water alone 
 has been decomposed, and that the nitrogen, which is 
 manifested at the positive electrode, is merely the secondary 
 result of the action upon the ammonia of the nascent oxygen, 
 arising from the decomposition of the water ; much more as 
 this nitrogen is frequently mixed with a little oxygen, and 
 as its proportion varies with the greater or less degree of 
 concentration of the solution.* Thus again if we decompose 
 nitric acid, which is a very good conductor, we obtain 
 oxygen at the positive electrode, and there is no gas at the 
 negative; but we find there nitrous acid and deutoxide of 
 nitrogen, which, by dissolving, render the acid yellow or 
 red : is this effect the result of the direct decomposition of 
 the nitric acid into oxygen and nitrous acid, or deutoxide 
 of nitrogen ? or rather the decomposition of the water con- 
 tained in the acid, the oxygen of which appears at the 
 positive electrode, whilst the hydrogen deoxidizes in part 
 the acid, at the negative electrode ? What would seem fa- 
 vourable to the second hypothesis is that, if nitric acid is 
 
 * We should be rather disposed to admit that it is the hydrated sulphate of 
 ammonia that is decomposed, since while the hydrogen of the ammonia and that 
 of the water are liberated at the negative electrode, sulphuric acid, the ni- 
 trogen of the ammonia, and the oxygen of the water go the positive electrode, 
 and that there perhaps the nascent oxygen decomposes a part of the free 
 ammonia of the solution. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 359 
 
 dissolved in an equal volume of water or more, we obtain 
 on the negative electrode a gaseous liberation, the quantity of 
 which varies according to the differences in the strength of 
 the acid, or in the force of the current ; and, on placing a 
 voltameter in the same circuit, we find that oxygen is libe- 
 rated equally in both solutions, which seems to prove that in 
 the acid, as in the voltameter, water alone is decomposed. 
 However, these conclusions of Faraday's, as we shall see, are 
 not altogether accurate. According to the same author, 
 sulphuric acid is not directly electrolysable ; but in certain 
 cases, sulphur is deposited at the negative electrode, by the 
 reaction of the hydrogen, arising from the decomposition of 
 the water. Hydrochloric acid, on the other hand, suffers a 
 direct and definite decomposition, as do also hydriodic, hy- 
 drobromic, and hydrocyanic acids ; this follows from the 
 comparison of the hydrogen, liberated by the electrolysis, 
 with the hydrogen liberated in a voltameter, placed in the 
 same circuit. 
 
 But what is especially important to study is that which 
 takes place in the decomposition of a saline solution. We 
 have seen that with salts, having alkaline or earthy bases,, we 
 obtain oxygen and acid at the same time, at the positive 
 pole, hydrogen and alkali at the negative, whence it seems to 
 follow, that the water and the salt are both decomposed at 
 the same time. Mr. Daniell, who made numerous experi- 
 ments on this subject, first satisfied himself that the decompo- 
 sition of one equivalent of water is accompanied by that of 
 an exact equivalent of the saline solution. In order to arrive 
 at this result, he had divided a voltameter, by means of a 
 porous partition, into two equal compartments, one of which 
 contained the positive and the other the' negative electrode, 
 and both of which were filled with a solution of sulphate of 
 soda, which covered the electrodes. The gases hydrogen 
 and oxygen, arising from electrolysation, were separately 
 collected and measured with care ; then, after having allowed 
 the experiment to continue for a sufficiently long time, he 
 determined exactly the quantity of free acid, that was found 
 in the positive compartment, and that of alkali which was in 
 
 A A 4 
 
360 TRANSMISSION OF ELECTRICITY. PART IT. 
 
 the negative ; and he thus found that there was an equivalent 
 of each at the same time that there was an equivalent of 
 water decomposed. He had previously assured himself that 
 the porous partition, although it allowed the current to pass, 
 did not suffer the liquids to mix. The same experiment was 
 repeated, by placing in the circuit an ordinary voltameter, 
 charged with a solution of sulphuric acid, the electrodes of 
 which were of the same dimensions as those of the voltameter 
 of two divisions, filled with sulphate of soda. Now, the 
 quantities of gas liberated in the two voltameters were 
 sensibly equal ; and there was found besides in that, in which 
 the sulphate of soda was placed, the same quantity of free 
 acid and alkali. Thus, if we admit that the current decom- 
 poses, at the same time, the water and the sulphate of soda, 
 we arrive at the extraordinary conclusion that the same cur- 
 rent, which separates only one equivalent of oxygen from one 
 of hydrogen, in one of the voltameters, is able to separate in 
 the same time in the other, one equivalent of oxygen from one 
 equivalent of hydrogen, and one equivalent of sulphuric acid 
 from one equivalent of soda. What is curious is, that the 
 temperature of the liquid rises considerably in the vessel in 
 which the sulphate of soda is placed, and very little in that 
 in which is the acid solution. The results were the same, on 
 substituting nitrate of potash for sulphate of soda. By sub- 
 stituting in the preceding experiments, sulphuric acid diluted 
 with water for sulphate of soda in the cell with double com- 
 partments, Daniell established a very decided transport of 
 acid to the positive electrode ; and he found that there passed 
 about the fourth of an equivalent of acid for an entire equiv- 
 alent of water decomposed. Faraday had previously ob- 
 tained a result very nearly similar, except a little more 
 powerful. 
 
 It remained therefore to discover how the current acted in 
 the double decomposition of an equivalent of water and of 
 salt. For this purpose, Daniell devised to place in the same 
 circuit, in which the voltameter with the double cell, charged 
 with a saturated solution of sulphate of soda, was situated, 
 some chloride of lead, retained in fusion in a tube by means 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 361 
 
 of a spirit lamp ; a platinum wire served as a negative electrode 
 to the chloride and a small rod of plumbago as positive 
 electrode. Now, the platinum wire, which weighed before 
 the experiment 5'44 grs. attained to a weight of 27'1 grs., 
 which makes for the lead alone, that formed a very distinct 
 button, adhering to the wire, a weight of 21-66 grs. In the 
 voltameter there had occurred decomposition at once of a 
 quantity of water and of a quantity of sulphate of soda, 
 equivalent, each separately, to the weight of chloride of lead 
 decomposed. This experiment therefore shows to us clearly 
 that we cannot admit that there has been at the same time 
 direct electrolysation of an equivalent of water and of an 
 equivalent of salt by the same force, that electrolyses an 
 equivalent of chloride of lead. To the support of this con- 
 clusion, we will note also the following fact, that, if we take 
 a plate of tin for positive electrode in the voltameter with 
 double cells, and charge this voltameter with a solution of 
 chloride of sodium and place it in the circuit, still with the 
 chloride of lead, we find that the loss in weight of the tin, 
 which is attacked by the chloride, and the volume of hydrogen 
 liberated at the negative platinum electrode, to which the 
 soda is also carried, represent the decomposition of a quantity 
 of chloride of sodium exactly equivalent to the quantity of 
 chloride of lead decomposed. The only manner for ac- 
 counting for this result is to admit that the dissolved chloride 
 
 S 
 
 of sodium is alone decomposed, that the chloride is ab- 
 sorbed by the tin, and that the sodium being carried to the 
 negative electrode reacts upon the water, oxidises, liberating 
 its equivalent of hydrogen, which is nothing more than a 
 secondary product, due to an effect purely chemical, and not 
 to the direct electrolysation of the water. 
 
 We are thus led to regard as a fundamental principle that 
 the electric force, which we measure by its definite action, in 
 any point of the circuit, cannot decompose more than an 
 equivalent proportion in another point of the same circuit ; 
 so that the current which we have measured, by its electro- 
 lysation upon the chloride of lead, cannot be at the same time 
 sufficient to electrolyse one equivalent of chloride of sodium, 
 
362 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 and one equivalent of water in the same voltameter between 
 the same electrodes. It follows, from this manner of regard- 
 ing it, that, in the decomposition of the dissolved sulphate of 
 soda, we must admit that the sulphate in like manner is alone 
 decomposed and not the water ; that the oxygen of the oxide 
 of sodium goes with the sulphuric acid to the positive 
 electrode, where it is liberated, whilst the sodium is carried to 
 the negative electrode, where it decomposes the water, and 
 becomes soda, liberating its equivalent of hydrogen, which in 
 like manner is nothing more than a secondary product. 
 With salts, whose metallic base, such as lead or copper, 
 is incapable of decomposing water at ordinary temperatures, 
 the pure metal is found deposited at the negative electrode. 
 This deposit is a direct effect of decomposition, and it is not 
 due, as has long been assumed, to the reduction of the oxide, 
 by the hydrogen arising from the electrolysation of the water, 
 which would have occurred at the same time as that of the 
 salt. Direct experiments made, by substituting, for solution 
 of sulphate of soda, that of sulphate of copper in the circuit, 
 in which there is melted chloride of lead, confirm this ex- 
 planation, which is completely in accordance with the ideas 
 of Davy and Dulong on the composition of salts, which they 
 regard as binary compounds, analogous to the chlorides. 
 Thus, like as chloride of sodium is a compound of one 
 equivalent of chlorine and one equivalent of sodium, a 
 sulphate of soda is a compound of one equivalent of oxy- 
 sulphion, and one equivalent of sodium, an equivalent of 
 oxysulphion being formed of one equivalent of oxygen and 
 one equivalent of sulphuric acid. We see, therefore, that 
 according to DanielPs experiments, Faraday's ideas on se- 
 condary actions, due to the direct decomposition of water in 
 solutions, must be modified, as we have anticipated. 
 
 We have now established, with Faraday, the law of the 
 definite action of the current, and with Daniell, that of the 
 immediate decomposition of salts, dissolved in water. Now, 
 before seeing whether Faraday's law extends to all classes 
 of compounds, and whether, in particular, it is applicable to 
 those in the decomposition of which there enters more than 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 363 
 
 one equivalent of one of the constituent elements, we shall 
 turn our attention to considering how decomposition is 
 brought about, when two or more electrolytes are mixed. 
 
 M. Matteucci was the first, after Faraday, who by numerous 
 labours followed out this class of researches. After having 
 demonstrated that the law of this definite action of the 
 current governs, as veil the chemical action that takes 
 place in the interior of the pile between the pairs, as that 
 which takes place between the poles, an important point for 
 the theory of the pile, he had proved that the electrolysis of 
 combinations of oxides with acids gives the same equivalent of 
 metal, as that of the oxides themselves, as well when these 
 combinations are dissolved in water, as when they are 
 liquefied by heat : this agrees with the results obtained at a 
 later period by Daniell. 
 
 Indeed, setting out from the law discovered by Faraday, 
 that oxides, chlorides, iodides, and binary combinations in 
 general, are decomposed into their equivalents, M. Matteucci 
 had wished to determine what would take place, when these 
 combinations were of the second order, namely salts. Con- 
 sequently, he had submitted successively to the action of the 
 current acetate of lead, both melted and dissolved, taking 
 care to place at the same time in the circuit a voltameter 
 with acidulated water. For '366 cubic inches of mixed 
 gases, which correspond to '049 grains of water decomposed, 
 he obtained *58 grains of lead at the negative electrode, as 
 well in melted as in dissolved acetate, which corresponds to 
 1287, the equivalent of lead, a number very near to that, 
 which is adopted by chemists. He had made the same experi- 
 ment upon nitrate of silver, and he had found for '366 cubic 
 inches of gaseous mixture in the voltameter, '60 grains of silver, 
 which corresponds to 1356 for the equivalent of silver; melted 
 and dissolved nitrate gave the same results. Neutral borate 
 of lead melted gave for *366 cubic inches of the mixture, *58 
 grains of lead at the negative electrode, as the acetate had 
 done. 
 
 The reduced metal is not, therefore, the effect of a secondary 
 action, arising from the decomposition of water; it is evident 
 
364 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 that salts are decomposed directly, as well when they are 
 brought to the liquid state by their solution in water, as 
 when they are brought to it by the effect of heat. The dif- 
 ference, therefore, that exists between an oxide and a salt, is 
 that, whilst for both equally there is an equivalent of metal 
 transported to the negative electrode, there is for the salt an 
 equivalent of acid transported to the positive electrode with 
 an equivalent of oxygen. M. Matteucci perfectly satisfied 
 himself of this, by taking as electrolytes, neutral benzoates, 
 of potash, lime, zinc, lead, and silver, which are all more or 
 less soluble in water, whilst benzoic acid itself is insoluble. 
 This acid might therefore be easily collected at the positive 
 electrode upon filtering-papers, then properly washed and 
 dried. It was weighed, and for its weight was obtained a 
 number very nearly equal to its equivalent, which could 
 easily be proved by collecting and measuring the other 
 products of the decomposition, namely, the oxygen and _ the 
 base of the salt ; only a small quantity of benzoic acid disap- 
 peared by the fact of the water dissolving a little of it ; so the 
 number obtained was slightly lower than the equivalent. 
 
 M. Matteucci has, in like manner, extended Faraday's law 
 to the case of the mixture of two electrolytes, by showing 
 that they are both decomposed ; the sum of the quantities of 
 each of them, that are decomposed, is equivalent to the 
 quantity that is obtained, by decomposing a single one, by a 
 current of the same force and of the same duration, which 
 proves that in this case also, the chemical action of the 
 current is definite. With regard to the proportion of each 
 of the electrolytes that is decomposed, it depends upon their 
 nature, and upon the proportion itself in which they enter 
 into the mixture. Thus, with solutions a little diluted of 
 hydro-chloric and hydriodic acids, of chlorides and of iodides, 
 these compounds alone were decomposed, whilst the water 
 was also, when its proportion in the solution, together with 
 the force of the currents, was increased. 
 
 M. Becquerel, senior, who had also turned his attention to 
 the decomposition of mixtures, had thought he had discovered 
 in it a means of measuring affinities. Having mixed to- 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 365 
 
 gether nitrate of silver, and nitrate of copper, in a proportion 
 such that there were the same number of equivalents of each, he 
 had observed that the nitrate of silver alone was decomposed ; 
 in like manner, in a similar mixture of nitrate of lead and 
 nitrate of copper, the nitrate of copper alone was decomposed. 
 But if in the mixture the proportion of that one of the two 
 nitrates which had not been decomposed, was increased, there 
 arrived a moment when it also was decomposed. Thus, on 
 operating upon a solution which contains one equivalent of 
 nitrate of silver, equal to 1'54 grs., it was necessary to add 
 67 equivalents of nitrate of copper, in order that there might 
 be at the negative electrode a metallic precipitate, composed 
 of one equivalent of each of the two metals. M. Becquerel 
 hence deduced the conclusion, that the current is then divided 
 into two perfectly equal parts, between the two nitrates, be- 
 cause there is produced on each of them the same chemical 
 effect ; and that it overcomes in them equal resistances, which 
 are the affinities existing between the constituent parts of the 
 two salts. It is by increasing the mass, that is to say the 
 number of the particles, exposed to the action of the current, 
 of that one of the nitrates which is the least decomposable, 
 that we arrive at this equality of electrolytic effects ; whence 
 M. Becquerel concluded, that we ought to find in the relation 
 of the masses necessary, in order to there being an equivalent 
 of each decomposed, the measure of the forces, that unite the 
 oxygen and the nitric acid to an equivalent of silver and of 
 copper. We cannot conform to this conclusion ; because, 
 without denying that affinity may play a part in the result 
 obtained, it is incontestible that the relative conductibility of 
 the two mixed nitrates acts a much larger part in it; and that 
 these two properties seem to be independent of each other. 
 
 The influence of conductibility in the phenomena observed 
 by M. Becquerel, is found to be confirmed by the researches 
 that M. Matteucci has also made, but following a different 
 method, in order to discover the relation that may exist 
 between the electrolysation of certain combinations, and the 
 chemical affinity of the elements of which they are formed. 
 
366 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 We have already seen * that he had succeeded in showing 
 that all the compounds which, melted and anhydrous, 
 conduct the current better than water, are always better 
 conductors than their aqueous solutions, even the most 
 concentrated ; and that, in order that two aqueous solutions 
 of two compounds shall have the same conductibility, it is 
 necessary that the one, whose compound is the worst conductor 
 in the state of fusion, should be the most concentrated. Now 
 on operating in the same manner, he found that that which is 
 true for conductibility, is true also for electrolysation. Thus, 
 if two voltameters are placed parallel in the same circuit as 
 an ordinary voltameter with acidulated water, it is found, for 
 example, that one equivalent of nitrate of silver on the one 
 part, and four equivalents of nitrate of lead on the other part, 
 added to 100 grs. of water, give two solutions equally elec- 
 trolysable ; we have for '732 cub. in. of gaseous mixture in 
 the principal voltameter '617 grs. of lead, and *585 grs. of 
 silver in each of the other two. In like manner, it requires 
 2 J equivalents of nitrate of copper, and 1 of nitrate of silver, 
 in order to obtain two liquids equally electrolysable. In all 
 cases, it follows, as a matter of course, that the sum of the 
 equivalents of the two metals is equal to the equivalent of 
 hydrogen liberated in the principal voltameter, which is 
 always placed in the circuit. We see that the proportions 
 found by M. Matteucci are very different from those of 
 M. Becquerel, which proves that the mutual action of the 
 two mixed salts exercises an influence over the result. The 
 solvent has also an influence, although the body dissolved 
 is alone decomposed : two solutions of nitrate of silver of 
 the same density, one in alcohol and the other in water, 
 the former containing consequently much more nitrate 
 than the latter, being each placed in one of the partial 
 voltameters, give, the former, '877 grs. of silver, the latter, 
 .862 grs., numbers almost equal, and the sum of which 
 corresponds to 1'09 cub. in. of the gaseous mixtures, arising 
 from the decomposition of water, in the principal voltameter. 
 
 * Vol. II. p. 119. and following. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 367 
 
 The two solutions are therefore equally electrolysable ; and 
 yet they contain in the same volume very different quantities 
 of nitrate of silver, which is the cause of their having the 
 same density. 
 
 In order to compare the electrolysation of different com- 
 pounds, M. Matteucci always proceeds in the same manner, 
 namely, by placing in the circuit a principal voltameter, filled 
 with water, acidulated with sulphuric acid to the maximum of 
 conductibility (1*232 of density) ; then, in succession, parallel 
 to each other, so that the current may divide equally between 
 them, a second voltameter similar to the former, and the dis- 
 solved or melted substance, that is the subject of the experi- 
 ment. When this substance is protoxide or iodide of lead, 
 chloride or nitrate of silver, it transmits all the current, and 
 none passes through the secondary voltameter ; with chloride 
 or acetate of lead, there is a decomposition in the secondary 
 voltameter, more powerful with the acetate than with 
 the chloride, which would indicate that it is less electro- 
 lysable. By substituting melted acetate of lead for the 
 secondary voltameter, he found with oxide of lead, placed 
 parallel, for '732 cubic in. of gaseous mixture in the 
 principle voltameter, '138 to '154 grs. in the acetate, and 
 924 grs. in the oxide; with nitrate of silver, '061 grs. of 
 lead in the acetate, and 1'07 grs. in the nitrate. Thus free 
 oxide of lead is more electrolysable than the same oxide 
 combined with the acid ; and nitrate of silver is still more so. 
 By comparing successively the chlorides of lead and silver 
 with the acetate, he found *154 grs. of lead in the acetate, 
 and consequently about '924 grs. in the chloride ; whilst with 
 chloride of silver, the acetate is not decomposed. Iodide of 
 lead gives very nearly the same result as the chloride and the 
 oxide, which proves that certain compounds are equally elec- 
 trolysable. On the other hand, if we place parallel with ace- 
 tate of lead protochloride of tin, we always obtain for '732 
 cubic in. of the gaseous mixture in the principle voltameter, 
 985 grs. of lead in the acetate, and scarcely -046 grs. of tin 
 in the protochloride. 
 
 M. Matteucci concluded from all these facts, that com- 
 pounds more easily allow themselves to be decomposed, 
 
368 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 as the chemical affinity by which their elements are united 
 is less powerful, which is the converse of Faraday's opinion, 
 who considers, on the contrary, that the most electroly- 
 sable compounds are those whose elements have the greatest 
 affinity. With regard to ourselves, we are able to see, 
 in these various phenomena, nothing more than the result 
 of the greater or less resistance, which the various liquids 
 present to the transmission of the current and consequently 
 to their electrolysation ; properties, the relationship of which 
 is ignored, if indeed it has any existence ; it is even a point, 
 upon which conjecture differs altogether, since we see that 
 Faraday and Matteucci have in this respect diametrically oppo- 
 site opinions. However, it would seem that combinations, such 
 as pure water, whose elements have the greatest affinity for 
 each other, would indeed be those that have the least con- 
 ducting power, and which are consequently the least electro- 
 lysable. 
 
 Another question, that here presents itself, is to ascertain 
 whether the compounds formed by the combination of one 
 equivalent with two or several equivalents are decomposable, 
 like those which result from the combination of one equiva- 
 lent with a single equivalent; and in the case in which 
 they might be decomposable, what is the law by which 
 their electrolysation is governed. Two philosophers, MM. 
 Matteucci and Becquerel, have equally studied this important 
 point. 
 
 Mr. Faraday had thought that compound salts, decompo- 
 sable by the current, were those that are formed of the com- 
 bination of one equivalent of one element with a single 
 equivalent of another ; not that they are all necessarily so, 
 since there are several, such as the chloride of sulphur, the 
 protochloride of phosphorus, that of carbon, which are 
 not so, not being conductors ; but Faraday allowed that 
 they alone would have been susceptible of being electrolysed, 
 whilst the compounds, formed of one equivalent with two 
 or several equivalents, would be neither conductors nor 
 electrolysable ; two alone would be conductors exceptionably, 
 periodide and perchloride of mercury ; but, although con- 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 369 
 
 ducting the current, they would not be decomposed by it. M. 
 Matteucci, in examining this point more closely, has succeeded 
 notwithstanding in decomposing combinations, into which 
 there enter more than two equivalents. The bodies, to 
 which his experiments have been directed, were proto- 
 chloride of antimony and the two chlorides of copper. 
 The first could be placed in a state of fusion in the circuit 
 with a voltameter ; and experiment gave a liberation of 
 chlorine at the positive electrode, and "123 grs. of antimony 
 at the negative, for a gaseous liberation of *366 cub. in. 
 in the voltameter, which corresponds to *079 grs. of water 
 decomposed.* Now these '123 grs. of antimony represent 
 only a third the number, that is the equivalent of that metal, 
 for one equivalent of water decomposed. With regard to the 
 two chlorides of copper, as they attacked the electrodes of gold 
 and platinum, it was necessary to dissolve them in water; 
 very concentrated solutions of them were made, and he was 
 able to establish, by comparing their electrolysis with that 
 of the water of the voltameter, that they were truly decom- 
 posed directly, the more so -as there was only chlorine, and 
 no oxygen, at the positive electrode. At the negative elec- 
 trode was obtained one equivalent of copper, with the pro- 
 tochloride, but only half an equivalent with the bichloride. 
 
 M. E. Becquerel, by operating upon the dissolved chlorides, 
 both that of antimony, as well as that of copper, has obtained 
 for the latter the same result as did M. Matteucci ; but for the 
 former, he has found there was deposited on the negative elec- 
 trode f of the equivalent of antimony. He attributed the great 
 difference, that exists between his result and that of Matteucci, 
 to the fact, that, in the experiments of this latter philosopher, 
 the chlorine attacks and redissolves a part of the antimony. 
 In order to be secure from this inconvenience, M. E. Becquerel 
 arranged his apparatus so as to place the two electrodes in 
 two different vessels filled with the same solution, causing the 
 
 * In a subsequent experiment, M. Matteucci found, for '576 cub. in. of 
 gaseous mixture in the voltameter, *208 grs. of antimony. He also sometimes 
 arrived at a higher number ; and he discovered that fresh experiments are 
 necessary, in order satisfactorily to establish the law of the decomposition of 
 this body, so difficult of electrolisation by direct means. 
 
 VOL. II. B B 
 
370 
 
 TRANSMISSION OP ELECTRICITY. 
 
 PART IV. 
 
 two liquids to communicate by means of a little syphon, 
 which is charged when the vessels are filled. In the annexed 
 figure (235.), the two glasses are placed upon the plate of 
 an air pump, and covered with a receiver, furnished with 
 a stop-cock and pierced with two openings, which allow 
 
 Fig. 235. 
 
 of the introduction by each of a wire into the receiver, 
 so as to place the decomposing plates in the circuit by 
 means of two small cups filled with mercury. The ne- 
 gative electrode is of platinum, and the positive may be of 
 different metals. The apparatus communicates with a volta- 
 meter placed outside the receiver ; for the latter is used for 
 making a vacuum in order to protect the electrolytic liquids, 
 which are alterable in the air, and to place them within 
 another gaseous medium. In the case in which melted and 
 not dissolved chlorides are operated upon, this apparatus 
 cannot be employed ; for it is necessary to retain the two 
 electrodes in the middle of the mass, and to operate rapidly. 
 The following are two experiments, made in this manner by 
 M. E. Becquerel : 
 
 Gas liberated in a Volta- 
 meter at & 30 in. 
 
 Weight of Water de- 
 composed. 
 
 Antimony at the Negative 
 Electrode. 
 
 2-989 cub. in. 
 5-561 
 
 331 grs. 
 755 
 
 i 
 
 1-63 grs. 
 3-58 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 371 
 
 Now, the equivalent of antimony is 806-45, that of water 
 being 112-5 ; in order that an equivalent of antimony should 
 be deposited, it would be necessary that there should be at 
 
 806-45 
 the negative pole in the first experiment -331 x 1 10.5 = 
 
 2-372 grs. ; and in the second '755 x H2-5 = 5 ' 4 ^ 2 & rs - 
 
 If we take of these two numbers, we find 1-581 grs., and 
 3-608 grs. ; the numbers nearly given by the experiment. 
 
 The experiments that precede, as well as those made upon 
 several other chlorides, both simple and compound, such as 
 the bichloride of tin and the perchloride of iron, have led 
 M. E. Becquerel to admit that, for an equivalent of water de- 
 composed, or, which comes to the same thing, for one equiva- 
 lent of electricity employed, it is always one equivalent of 
 chlorine that is disengaged at the positive electrode, and con- 
 sequently a corresponding quantity of base at the negative 
 electrode. This is the reason why, with the chlorides of 
 silver, tin, iron, there is one equivalent of metal for one 
 equivalent of chlorine ; the same with the bichloride of copper, 
 all the chlorides containing one equivalent of chlorine, and 
 one equivalent of metal ; but with the protochloride of copper, 
 which contains two equivalents of copper for one of chlorine, 
 there are two equivalents at the negative electrode for one 
 of chlorine at the positive ; with perchloride of iron, and per- 
 chloride of antimony, each of which contains two equivalents 
 of metal for three of chlorine, or, which comes to the same 
 thing, f of an equivalent of metal for one of chlorine, we 
 obtain at the negative electrode only -f- of the equivalent of 
 metal, for one equivalent of chlorine at the positive. 
 
 M. E. Becquerel thought he might be able to extend the 
 law that he had found for the chlorides, to the iodides and 
 the bromides, as well as to oxides and to salts, so that there 
 is always one equivalent of the acid element (composed, in the 
 case of salts, of one equivalent of oxygen, and one equivalent 
 of acid), which goes to the positive electrode, and one corre- 
 sponding quantity of base to the negative. It was by operating 
 upon the salts of lead, such as the nitrates, the nitrites, and 
 
 B B 2 
 
372 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the hyponitrites, that he proved the existence of the law for 
 salts ; he has also verified it with two salts of copper, sub- 
 mitted to the action of the same current, and one of which, 
 the hyposulphite of the protoxide of copper, gave '8162 grains 
 of copper at the negative electrode, whilst the nitrate of bi- 
 oxide of copper, placed in the same circuit, gave only "4004 
 grains, that is to say, one-half less : he obtained the same 
 result with the protoxide and bioxide of copper, dissolved in 
 ammonia. 
 
 We ought to bear in mind, that, notwithstanding the labours 
 of MM. Matteucci and E. Becquerel, there is much to be 
 done in order to discover the exact mode of the action of 
 electricity upon compounds, into the formation of which 
 more than two equivalents enter ; unfortunately, the number 
 of these compounds, which are conductors and susceptible of 
 being electrolysed, is very inconsiderable. There are even 
 some among those that M. E. Becquerel employed, which, 
 like the bichloride of tin, do not conduct the current, even 
 when they are melted ; and although in the state of solution 
 they become conductors, this can only be on account of their 
 having undergone some alteration, in combining with water. 
 We are not therefore very certain that these chlorides are 
 decomposed directly, and that -there do not happen some of 
 those secondary actions, which are so difficult of detection, 
 and which disturb the simplicity of the results. M. E. Bec- 
 querel himself points out some examples, in the decomposition 
 of numerous acetates of lead, which is almost always the 
 result of a secondary effect. 
 
 We shall terminate this paragraph by returning to a point 
 upon which all the philosophers, who have directed their 
 attention to electrolysis, as well MM. Matteucci and E. 
 Becquerel, as Mr. Daniell, are agreed, namely, the manner 
 of regarding the decomposition of salts and of acidulated 
 water. With regard to that of salts we have already shown, 
 that it is the metal and not the oxide, except in certain ex- 
 ceptional cases, which we shall examine in the following 
 paragraph, that is transported to the negative electrode. It 
 is thus explained, why, when salts are decomposed, whose 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 373 
 
 oxides are not soluble, such as those of magnesia and zinc, 
 by placing their solutions at the positive electrode, and 
 making them communicate by a moist conductor with dis - 
 tilled water, into which the negative electrode is plunged, it 
 is found that the magnesia and the oxide of zinc are arrested 
 at their entrance into the distilled water, where they remain 
 in suspension, instead of going on to the negative electrode. 
 It is clear that magnesium and zinc, which in their saline 
 solutions were transported from the -f pole to the pole, 
 exchanging, according to the theory of Grotthus, from 
 molecule to molecule, their oxygen and their acid, so as 
 always to form a soluble salt, on arriving at the water, find 
 nothing more than oxygen without acid ; it is therefore no 
 longer a salt but an oxide that is formed ; and as this oxide 
 is not soluble, it goes on no further ; it is then the hydrogen 
 of the first molecule of water, that has met the magnesium or 
 the zinc, which travels in their place by way of exchange 
 from molecule to molecule as far as the negative electrode. 
 Suppose, for example (Jig* 236.), six consecutive molecules 
 
 4 f <r t 
 
 + - 
 
 Fig. 236. 
 
 of which Nos. 1, 2, and 3. (sulphate of magnesia) are composed 
 of 4_ equivalents of oxygen, I equivalent of sulphur, and 1 
 equivalent of magnesium *, and the Nos. 4, 5, and 6. (water) 
 are composed of the oxygen equivalent, and the hydrogen 
 equivalent : the current passes, polarises them, and decom- 
 poses them. The 4 equivalents of oxygen and the equivalent 
 of sulphur of the molecule No. 1., are liberated under the 
 
 * The white circle and the semicircles represent magnesium and hydrogen; 
 the grey, oxygen ; and the black, sulphur. 
 
 B B 3 
 
374 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 form of sulphuric acid and oxygen at the positive electrode, 
 and the equivalent of hydrogen of the molecule No. 6. at the 
 negative electrode. The magnesium of No. 1. combines with 
 the oxy-sulphion of No. 2., the magnesium of No. 2. with the 
 oxy-sulphion of No. 3., the magnesium of No. 3. with the 
 oxygen of No. 4., the hydrogen of No. 4. with the oxygen of 
 No. 5,, and the hydrogen of No. 5. with the oxygen of No. 6. 
 There are then, therefore, no more than five molecules, the 
 third of which, oxide of magnesium, remains suspended in 
 the liquid. The lower series of molecules of fig. 236. repre- 
 sents these molecules at the moment of the exchange of their 
 constituent parts, and before they have been polarised anew 
 by the current, as they are in the upper series. If the oxide 
 is soluble, like that of sodium or potassium, the phenomenon 
 takes place in the same manner, only the potassium and the 
 sodium dissolve, in proportion as they arrive in the water ; 
 but it is very easy to prove that it is at the points of contact 
 between the saline solution and the water, and not at the 
 electrode, that they are first deposited. 
 
 M. E. Becquerel has explained in a very ingenious manner, 
 by the same theory, the mode in which the decomposition of 
 oxygenated water is brought about : a very interesting experi- 
 ment, that he has made by placing oxygenated water in a small 
 glass, and taking as a positive electrode a platinum wire, which 
 passes into a glass tube closed by a spirit lamp, so that the 
 very fine end of the wire is alone employed to decompose the 
 liquid ; there is then placed over the wire a small graduated 
 receiver, and the oxygen alone is collected. An ordinary 
 water voltameter is at the same time placed in the circuit. 
 The following is the comparative result of two experiments: 
 
 OXYGENATED WATER. ORDINARY WATER. 
 
 Gas liberated. Gas liberated. 
 
 1st Exp. 18-5 oxygen. 9'3 oxygen. 
 
 18 -6 hydrogen. 
 2nd Exp. 26 oxygen. 13*2 oxygen. 
 
 24-3 hydrogen. 
 
 We perceive that, in the oxygenated water, there is libe- 
 rated double as much oxygen, at the positive electrode, as in 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 375 
 
 ordinary water. At first sight this result seems in opposition 
 to the law established by M. E. Becquerel for the electrolysis 
 of multiple compounds, in virtue of which there is always one 
 equivalent of oxygen, chlorine, or acid for one equivalent of 
 electricity or of water decomposed ; now, we find two in the 
 oxygenated water, instead of one. But, if we regard the 
 oxygenated water, as we have done, for saline solutions, as 
 the combination of one equivalent of water with one 
 equivalent of oxygen, the equivalent of oxygen accompanying 
 the place of acid, the base, which is the hydrogen, goes to the 
 negative electrode, whilst the two equivalents of oxygen, one 
 of which occupies the place of the oxide, go to the positive 
 electrode. The same thing takes place here as with acidu- 
 lated water, which may be regarded as an hydrate of 
 sulphuric acid ; for example, the hydrogen of this hydrate 
 being deposited at the negative electrode, whilst its oxygen 
 and acid are liberated at the positive. This is demonstrated 
 by the numerous experiments made upon this subject, by 
 various philosophers, and especially by Daniell and by 
 Miller.* 
 
 Apparent Exceptions to the Laws of Electrolysis, and Confirma- 
 tion of these Laws. 
 
 We have been establishing the law of the definite chemical 
 action of the current, which consists in this, that a same 
 quantity, namely, one equivalent of electricity, always de- 
 composes one equivalent of an electrolyte. We have seen 
 that this law, which is general, when the combination sub- 
 mitted to electrolysis is composed of only two equivalents, 
 must necessarily be modified in the cases, in which there enter 
 into the compound more than one equivalent of one of its 
 elements. We have noticed that, notwithstanding the labours 
 of MM. Matteucci and E. Becquerel, a fresh examination is 
 still necessary, in order to recognise all the modifications 
 which the law must undergo in this case, and which are 
 
 * For further details see the final note E. 
 
 B B 4 
 
376 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 probably different in the various compounds with multiple 
 proportions. 
 
 If we set out with the idea laid down in the outset by 
 Faraday that the current, which acts in electrolyses, is only 
 the chemical force put into circulation and transported integrally 
 from one point to another, under the form of current and acting 
 at a distance instead of acting only at contact, the law of electro- 
 chemical equivalents is a necessary and rigorous consequence 
 of this ; for the same chemical force must decompose every- 
 where an equivalent of the compound body. However, this 
 law is frequently disguised by a crowd of circumstances, in 
 the midst of which it becomes so difficult a matter to discern it, 
 that its generality has been placed in doubt. Thus it has 
 been thought that, among compound bodies, there were some 
 which might conduct the current, after the fashion of metals, 
 without being decomposed ; we have been led to admit that, 
 in a great number of cases of electrolysis, the two poles pos- 
 sessed an unequal power of decomposing and of transport ; 
 in a word, many anomalies and exceptions to the electrolytic 
 law have been pointed out. But, in studying them, we are 
 about to show that they are only apparent, and that they may 
 all be explained, by taking account of the secondary actions, 
 that arise from the liberation of the elements which, in a 
 nascent state, have a chemical activity altogether peculiar, 
 and form modifications that are constantly accruing, to the very 
 nature of this electrolyte, which, consequently, cannot remain 
 identical, by the operation of new substances, arising either 
 directly or indirectly from the electrolysis. It is especially 
 to the variations of conductibility which occur in the different 
 parts of the electrolytes of this appearance, that the principal 
 apparent anomalies are due. 
 
 Faraday was himself the first to indicate, as forming an 
 exception to the electrolytic law, that he had discovered 
 certain compounds, such as sulphuret of silver, and bi-iodide 
 of mercury, as capable of conducting the current, when their 
 temperature was raised, without being decomposed. These 
 exceptions, and others also of the same kind, have disappeared, 
 thanks to the researches of M. HittorfF, and of M. Beetz. 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 377 
 
 The former has found that sulphuret of silver is decomposed, 
 even at the ordinary temperature*: there forms, at the negative 
 electrode, a brilliant spot of metallic silver, which always re- 
 mains very small, because the sulphur, deposited upon the 
 positive electrode, is not long in arresting the current, at 
 least when this electrode is neither silver nor another metal, 
 capable of combining with sulphur. If the operations are 
 carried on at a high temperature, the sulphuret becomes as 
 good a conductor as a metal ; and yet, even after an experi- 
 ment of long duration, there is but a small quantity of sul- 
 phuret decomposed ; and the reduced silver is far from being 
 equivalent to the hydrogen released in a voltameter placed 
 in the same circuit. This is due to the circumstance that the 
 silver, reduced to the metallic state by electrolysis, finishes 
 by establishing between the two electrodes a communication, 
 by which the current passes entire. It is true that the in- 
 crease of conductibility disappears, when the sulphuret returns 
 to the ordinary temperature ; but this effect is due to the 
 rupture of metallic communication by the cooling of the mass ; 
 it is indeed impossible to admit that the sulphuret can, at an 
 elevated temperature, transmit the current without being de- 
 composed ; for, if we take as a positive electrode, a plate of 
 zinc, or of any other metal that is not able to combine with 
 sulphur, some sulphur is always deposited upon this electrode, 
 whatever be the temperature at which the experiment is 
 made ; the sulphuret of silver, therefore, never ceases to be 
 decomposable by the current, and the great increase of con- 
 ductibility, that it presents at high temperatures, when the 
 positive electrode is of silver or of platinum, is merely due 
 to the establishment of a direct metallic communication 
 between the two electrodes. The sub-sulphuret of copper 
 and the protosulplmret of tin present the same phenomena 
 as the sulphuret of silver. M. Hittorff, in operating on the 
 
 * Faraday himself, in pointing out the fact that the simple elevation of 
 temperature, arising from the passage of the current, was sufficient to increase 
 the conductibility of sulphuret of silver, observed that there is formed at the 
 positive electrode, a slight deposit (of sulphur), which prevents the transmission 
 of the current, and which can only be attributed to the electro-chemical de-> 
 composition of the sulphuret. 
 
378 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 first of these sulplmrets sheltered from contact with the air, 
 has observed that its conductivity increased rapidly in pro- 
 portion as its temperature was raised ; and he recognised that 
 when the current has traversed it for a certain time, there is 
 some free copper at the negative electrode, and that the 
 sulphur liberated at the positive, has caused the sub-sulphuret 
 to pass into the state of mono-sulphuret. The formation of 
 this mono-sulphuret, which is a conductor, and the manner 
 in which the copper is deposited upon the negative electrode 
 in slender filaments, which advance towards the positive, 
 notably diminish the length of the column of sulphuret, 
 really traversed by the current, and explain the considerable 
 increase of conductibility that is manifested, and that is de- 
 stroyed only in part, when we return to the ordinary tem- 
 perature. 
 
 M. Beetz, on his part, has proved, as M. Hittorff had 
 done for sulphuret of silver, that the bi-iodide of mercury is 
 decomposed by the current, as soon as it is capable of trans- 
 mitting it. With this view, after having purified this com- 
 pound by a double sublimation, he introduced it into a glass 
 tube which he had dried, and the two ends of which he had 
 closed at the lamp, after having introduced into it two pla- 
 tinum wires, in order to place the bi-iodide in the circuit, in 
 which he had also placed a galvanometer, having a single 
 needle that was not very sensitive, and a voltameter charged 
 with a salt of silver. The bi-iodide was heated in a sand- 
 bath ; at 212, it began to become a conductor. At the same 
 time that it acquired the yellow colour, and experienced a 
 commencement of fusion, traces of decomposition became 
 sensible by the property, which the platinum electrodes ac- 
 quire of themselves, giving rise to a current, a property 
 termed polarisation, and of which we shall speak in the 
 following paragraph. The bi-iodide having become altogether 
 liquid, M. Beetz caused a current to pass through it for 
 fourteen hours, taking care to maintain the same temperature ; 
 during the whole of this time, the needle of the galvanometer 
 maintained the same deviation, and at the termination of this 
 experiment, 0*162 grs. of silver were found reduced in the 
 
CHAP. HI. EFFECTS OF DYNAMIC ELECTRICITY. 379 
 
 voltameter. However, the tube that contained the bi-iodide 
 having been broken, no trace of mercury was perceived at 
 the negative wire; but the mass had become black around 
 the positive wire ; and upon throwing some fragments of it upon 
 paper impregnated with starch, the appearance was mani- 
 fested of the violet colour, which indicated the presence of 
 pure iodine, whilst proto-ioduret was found at the negative 
 electrode. It was a difficult matter to determine accurately 
 the proportion of iodine liberated ; however, M. Beetz was 
 enabled to judge approximately that it was lower than what 
 it ought to have been according to the quantity of silver re- 
 duced in the voltameter ; which is probably due to the fact, 
 that a part of the iodine recombines with the proto-iodide 
 that always exists mixed with the bi-iodide, and even with 
 that which is produced by electrolysis. The fluoride of lead 
 had been also quoted by Faraday as an example of compound 
 bodies, that may become very good conductors by simple 
 elevation of temperature, even before being melted, and 
 without undergoing decomposition. M. Beetz has proved 
 in a positive manner, that this compound is electrolysed as 
 soon as the current traverses it. Indeed, the platinum 
 plates, that are employed to place it in the circuit, are 
 polarised as with the bi-iodide ; and, in proportion as it enters 
 into fusion, bubbles of colourless gas are seen to be given 
 off at the positive electrode, which is at the same time power- 
 fully attacked, and a greyish mass, which is an alloy of lead 
 and platinum, is formed at the negative. The needle of the 
 galvanometer, that is placed in the circuit, retains the same 
 deviation during the whole time that the electrolysation of 
 the fluoride is going on ; and the quantity of silver, reduced 
 in the voltameter, compared with the weight of lead obtained, 
 indicates that the fluoride of lead obeys the law of electro- 
 chemical equivalents. 
 
 We have already mentioned in the First Chapter, the pro- 
 perty possessed by glass of becoming a conductor, when heated. 
 M. Beetz assured himself, in operating on glasses of different 
 qualities, and especially on Fuchs' soluble glass, that they be- 
 come conductors between 392* and 428, and that the platinum 
 
380 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 wires, by means of which they are placed in the circuit, are 
 powerfully polarised, which proves the existence of electroly- 
 sis. We shall see hereafter still more direct proof of this 
 decomposition in the use M. Buff has made of melted glass 
 as a liquid conductor interposed between the pairs of a pile. 
 
 But of all the anomalies, that are presented by the pheno- 
 mena of electrolysis, those which have most attracted the 
 attention of philosophers, and which at first sight have pre- 
 sented the greatest appearance of escaping the general laws, 
 that regulate this mode of action, is the inequality respec- 
 tively in the production of the elements, which are trans- 
 ported to the two electrodes, that, in many cases at least, 
 the two portions of the electrolyte, in which each of the 
 electrodes are plunged, seem to possess. MM. Daniell and 
 Miller were the first who observed, by employing the appa- 
 ratus composed of two cells, separated by a membrane, and 
 filled one with acidulated water, the other with a solution of 
 sulphate of copper, or sulphate of zinc, that when the positive 
 electrode plunges into the solution of sulphate, and the nega- 
 tive into acidulated water, oxygen and hydrogen are alone 
 obtained as the products of decomposition ; whilst, on changing 
 the place of the electrodes, oxygen is obtained at the positive 
 electrode, and metal at the negative; in both cases, one 
 equivalent of sulphuric acid is found with the oxygen at the 
 positive electrode. If the two cells are equally filled with 
 sulphate of copper or of zinc, we can easily prove, by 
 analysing after the experiment the liquids contained in each 
 cell, that all the copper or zinc, deposited at the negative 
 electrode, arises only from the sulphate contained in the cell 
 into which this electrode is plunged. 
 
 Among the experiments of Daniell and Miller we will 
 in addition quote those, in which sulphate of potash and 
 sulphate of magnesia, having been placed successively in the 
 positive cell, only ^ of an equivalent of potassium, and T ^ of 
 that of magnesium are obtained. Alumina, magnesia, or 
 oxide of copper do not render themselves in any proportions 
 at the negative electrode, plunged in an acid solution, 
 when they form with potash a double sulphate, the solu- 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 381 
 
 tion of which is placed in communication with the positive 
 electrode. 
 
 In all the phenomena that we have been describing, the 
 membrane, by which the vessel is divided into two compart- 
 ments, has no influence over the results ; so that its place may 
 be supplied by a simple syphon tube filled with liquid, by 
 which communication is established between the two compart- 
 ments, positive and negative. It was by employing an analo- 
 gous mode of communication, that M. Pouillet operated, when 
 he found an anomaly of. the same kind, as those which we 
 have been describing, in the decomposition of chloride of 
 gold. He placed the solution of this chloride in a series of 
 
 u tubes, the lower parts of which 
 being narrower, did not allow of 
 the liquids, with which the two 
 parallel branches were filled, 
 mixing easily (Fig. 237.). On 
 uniting the liquid columns of the to 
 successive tubes by platinum wires, 
 and causing the extreme columns 
 
 Fig. 237. . , . i i 
 
 communicate, the one with the po- 
 sitive electrode, the other with the negative, he has remarked 
 that, when the current had passed for a certain time, all the 
 negative branches of the tubes were less coloured than the 
 positive, that gold was deposited at the negative wire with- 
 out any trace of the liberation of hydrogen, and that chlorine 
 was liberated without oxygen around the positive wire. It 
 was easy to prove that, whilst the liquid of the positive 
 branch contained as much chloride of gold as at the be- 
 ginning of the experiment, that of the negative branch had 
 lost a quantity precisely corresponding to the weight of the 
 gold deposited. It would seem to follow from this, that the 
 decomposing power belongs exclusively to the negative elec- 
 trode. 
 
 M. Hittorff arrived at a still more general result, by show- 
 ing that the proportion of metal, reduced by electrolysation, 
 which is furnished respectively by the part of the liquid in 
 contact with the negative electrode and by that, in which the 
 
382 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 positive is plunged, remains the same for a same solution, 
 whatever may be the force of the current, but varies with 
 the nature and degree of concentration of this solution. The 
 apparatus that he employed, like that of Daniell's, is composed 
 of a cylindrical glass vessel, separated into two compartments, 
 not by a porous diaphragm, but by a disc of glass of a dia- 
 meter less than that of the vessel ; so that there remains 
 between the edge of this disc and the inner side of the vessel 
 a liquid stratum, which the current is able to traverse. 
 The whole vessel is filled with the same solution, the positive 
 electrode plunging into one of the compartments, and the ne- 
 gative into the other ; the apparatus is so arranged that 
 it may be separated into two pieces, corresponding to the two 
 compartments, and by means of a glass plate that may be in- 
 troduced between them, it is easy to preserve the liquids con- 
 tained in each without their mixing. The cylindrical vessel 
 is placed vertically ; the positive electrode lodged in its 
 lower part, is in each case made of the same metal that serves 
 as the base of the salt submitted to electrolysation ; the ne- 
 gative is of silver, and has the form of a little cone, the 
 summit of which is upward, in order the better to retain the 
 metallic deposit. After each experiment, this deposit is 
 weighed ; the weight of metal lost by the portion of liquid 
 contained in the negative compartment is then determined ; 
 this second weight is deducted from the former, which gives 
 the quantity of metal furnished by the positive compartment, 
 that has been transported from the positive electrode to the 
 negative. The relation between this quantity and the total 
 quantity of metal deposited, indicates the proportion of metal 
 transported. 
 
 The following, then, are the results obtained with solutions 
 of copper, of various degrees of density : 
 
 Density 
 of the 
 Solution. 
 
 Quantity of 
 Sulphate of Copper 
 in respect to Water. 
 
 Proportion of 
 Copper 
 
 transported. 
 
 1-0521 
 1-0553 
 1-0254 
 
 1 sulph. cop. to 6*35 water. 
 1 ' 18-08 
 1 3967 
 
 27-6 per cent. 
 34-5 
 35 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 383 
 
 He operated in the same manner upon solutions of acetate, 
 nitrate, and sulphate of silver, and found at the end of a great 
 number of experiments made with much care, that the pro- 
 portion transported from the negative electrode to the positive 
 was for 
 
 The acetate - ... 62-6 per cent. 
 The sulphate .... 44-6 
 The nitrate .... 47'4 
 
 It is to be remarked that, although the absolute quantities 
 were sometimes very different from one experiment to the 
 other, the relations varied very little from those indicated 
 above, which are the means of the results obtained for each 
 salt. The duration of the experiment was not always the 
 same ; but there resulted no appreciable change in the 
 value of the relations found. When the metal, in its 
 deposite at the negative electrode, is accompanied by a 
 liberation of hydrogen, we may be certain that a part at 
 least of this metal is in a state of oxide : M. Hittorff verified 
 this by employing for an electrolyte a very neutral solution 
 of sulphate of iron : the weight of iron deposited at the 
 negative electrode is found superior to that which should 
 be the result, in virtue of the law of the equivalents of the 
 decomposition of nitrate of silver, placed in the same circuit ; 
 indeed, on precipitating the deposite of iron by ammonia, 
 after having dissolved it in aqua regia, which weighed 
 21-043 grs., it is found that iron properly so called entered 
 into this weight only as 14*737 grs., a number very little 
 different from 14-729 grs. calculated according to the equi- 
 valent of silver, deposited by the same current. 
 
 A still more important fact to notice is that, when nitrate 
 of silver is dissolved in alcohol, instead of being in water, 
 which renders it a much worse conductor, and causes the 
 operation to last a much longer time, only 43 per cent, of 
 silver is found transported from the positive electrode to the 
 negative, instead of 47 per cent. 
 
 The various facts, that we just related, do not, in our 
 opinion, prove any difference of power in the poles, as M. 
 
384 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 Pouillet thinks, nor, as MM. Daniell and Hittorff seem 
 to presume, a faculty of transport variable with the nature 
 of the combination, subjected to electrolysation, and de- 
 pendent to a certain point upon the affinity, by which these 
 elements are united. They are merely the effect of the 
 non-homogeneity of the liquids submitted to experiment ; 
 whence it arises that the current not only decomposes the 
 salt dissolved, but decomposes also the more or less acidu- 
 lated water, that is found in the solution. M. d' Almeida 
 has, indeed, shown that, in the electrolysation of a dissolved 
 salt, the deposite of metal, of copper, for example, at the 
 negative electrode, may arise from two sources ; either from 
 the direct electrolysis of the salt, or from a secondary action, 
 namely, the reduction brought about by means of the nascent 
 hydrogen, due to the decomposition of the water. If the 
 solution is perfectly neutral, and especially if it remains 
 neutral during the whole course of the experiment, the 
 metal deposited at the negative electrode, arises almost 
 entirely from the direct decomposition of the salt ; if the so- 
 lution is acidulated, the nascent hydrogen is the principal 
 cause of the reduction of the salt. 
 
 M. d'Almeida has verified the accuracy of his general rule 
 by operating upon solutions of nitrate of silver and of copper, 
 sulphate of copper, of silver, and of zinc ; only there is a very 
 great difficulty in maintaining a solution neutral, during the 
 whole continuance of the electrolysis. The solution sub- 
 mitted to experiment, for example, a neutral solution of 
 nitrate of silver, is placed in two distinct vessels, which com- 
 municate together by a very small opening, as in M. Pouillet's 
 tubes (Jig. 237.). In one of the vessels is plunged a plate of 
 platinum, serving as the negative electrode ; in the other a 
 plate of silver, which is the positive electrode. The current 
 passes for twenty-eight hours; at the end of that time, 
 2*156 grs. of silver is found deposited at the negative electrode; 
 and analysis shows that 1*124 grs. of these 2*156 grs. arise 
 from the solution that surrounds the electrode, and 1*032 grs. 
 from the other vessel ; in this case, the solution is as neutral 
 as possible, and it is kept in this state by the positive silver 
 
cn-vr. in. EFFECTS OF DYNAMIC ELECTRICITY. 385 
 
 electrode, which combines in proportion as the nitric acid is 
 carried to it. If the solution is slightly acid, we find that the 
 2*156 grs. deposited at the negative electrode, have been entirely 
 taken from the solution placed in the vessel in which this 
 electrode was plunged. It is evident that, in the former 
 case, the decomposition of the nitrate of silver is brought 
 about almost entirely by the way of electrolysis ; since, as 
 should take place by this mode, according to Grotthus's 
 theory, the elements deposited at the two electrodes have 
 been furnished equally by the parts of the solution in contact 
 with each of them. In the latter case, on the contrary, the 
 acidulated water that is in the solution being more con- 
 ducteous than the nitrate, it is that which is decomposed; 
 and its nascent hydrogen produces the reduction of the salt 
 at the negative electrode, which is the cause of the reduced 
 metal being furnished only by the liquid in contact with 
 that electrode. M. d' Almeida, indeed, satisfied himself in a 
 direct manner that the acidulated water, as it is found in the 
 solution of the nitrate, conducted the electric current better 
 than this solution in a state of neutrality. 
 
 The same thing takes place in all the experiments, that we 
 have quoted in this paragraph, and especially in those of 
 M. Pouillet and of M. Hittorff. Thus, in the former, it is 
 the hydrochloric acid, that is always found in the solution of 
 chloride of gold, which is decomposed rather than the chloride, 
 which is a worse conductor; chlorine is liberated at the 
 positive electrode, and the gold of the chloride that surrounds 
 the negative electrode is reduced by the nascent hydrogen. 
 There results from this reduction the constant formation of 
 hydrochloric acid, which thus supplies the place of what is 
 decomposed. 
 
 In M. Hittorffs experiments the effects observed are 
 mixed ; a part of the reduced metal is derived from the 
 direct electrolysis of the salt, and the other from the reduction 
 by hydrogen, due to the decomposition of the acid water 
 contained in the solutions of the metallic salts, which are 
 so rarely and with so much difficulty neutral. What proves 
 the accuracy of this explanation is, that the more diluted the 
 
 VOL. II. C C 
 
386 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 solution of copper is, the greater becomes the proportion of 
 copper reduced directly to electrolysis ; because the strength 
 of the acidulated water is diminished. It is by no means 
 certain that, although the positive electrode may be of copper 
 in a salt of copper, and of silver in a salt of silver, that the 
 acid accumulated around this electrode is all neutralised by 
 the metal ; it is, on the contrary, probable that some remains 
 in the solution in the free state ; and then it is the acidulated 
 water that is decomposed, and its hydrogen contributes in 
 part to the reduction of the metal. Indeed, as is proved by 
 the numerical results recorded above, the proportion of 
 sulphate of silver decomposed by direct electrolysis is less 
 than that of nitrate, which is almost entirely decomposed in 
 this manner ; because the sulphuric acid, liberated at the 
 positive electrode, escapes in a greater quantity than the 
 nitric, from combination with the silver. The only very 
 singular fact is that, with acetate of silver, the proportion of 
 silver, furnished by the positive compartment, is more con- 
 siderable than that which is furnished by the negative itself. 
 It is probable that there is here some mixture of the liquids 
 contained in the two compartments ; that, in particular, there 
 passes from the positive electrode to the negative a small 
 quantity, which thus increases the proportion of the salt of 
 silver, that is found in the negative compartment. This 
 mixture must arise essentially from the difference of density 
 of the liquids, and perhaps also from a mechanical transport, 
 which occurs in a sensible manner only when the liquid is 
 an imperfect conductor, which is the case here, and which 
 causes the experiment to last twice as long as with solutions 
 of nitrate and sulphate. Moreover, this double origin of the 
 metal, deposited at the negative electrode, in the electrolysis 
 of salts, is recognised in the appearance itself of the deposit, 
 which is very different, according as the metal arises from 
 electrolysis or from reduction by hydrogen. This is easily 
 to be proved, by making use of solutions more or less acid, 
 and more or less exhausted of sulphate of copper and of 
 nitrate of silver. Thus Mr. Smee saw, on decomposing 
 sulphate of copper, by means of a current of two pairs, the 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 387 
 
 first deposit of copper to be brilliant, united, and ductile ; this 
 it is which arose exclusively from electrolysation. The 
 second was a little brittle ; it is because there was already a 
 little mixture of copper, arising from electrolysis and of that 
 reduced by hydrogen. Finally, the third was like sand ; then 
 spongy ; there was scarcely anything besides copper reduced 
 by hydrogen ; and ac last the gaseous hydrogen finished by 
 appearing. The liquor evidently contained scarcely any more 
 sulphate, and was become too acid, and yet the positive elec- 
 trode was of copper. We shall return to this subject, and 
 especially to Mr. Smee's work, when engaged with the 
 metallurgic applications of electricity, for which these ques- 
 tions possess great importance, as may be understood from the 
 example of copper that we have just given. 
 
 However, we will remark further that the explanation, by 
 which M. d' Almeida accounts so well for this apparent ine- 
 quality of electrolysation around the two electrodes, is equally 
 applicable, as he has himself observed, to the case of alkaline 
 and earthy salts as it is to that of metallic salts, and that it 
 finds in this fact a remarkable confirmation. Thus, if after 
 having poured equal quantities of nitrate of potash into the two 
 vessels of the preceding experiments, he renders the solution 
 acid into which the positive electrode plunges, he finds that, 
 after the decomposition, there has been only a feeble propor- 
 tion of this part of the solution decomposed, the current 
 having passed by preference through the acidulated water ; it 
 is, on the contrary, in the negative vessel that the decompo- 
 sition of the salt has been the most feeble, if the solution of 
 this vessel has been rendered strongly alkaline. Now, what is 
 done artificially is brought about naturally by the electrolysis 
 itself of the salt, which renders the positive solution acid, and 
 the negative alkaline ; but as, in general, the acid of dissolved 
 salts (nitrates, sulphates) is a much better conductor than 
 their bases, soda, potash, &c., it follows that the salt should 
 undergo and it does actually undergo a less abundant de- 
 composition in the parts of the solution in which the positive 
 electrode is, which is that wherein the acid is liberated. But if 
 
 c c 2 
 
388 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the salt remains neutral during the whole continuance of the 
 experiment, the positive and negative solutions furnish 
 equally their part toward the electrolysing action. In 
 order to obtain this neutrality, M. d' Almeida, if he was ope- 
 rating, for example, upon sulphate of potash, poured before- 
 hand some potash into the positive vessel, and some sulphuric 
 acid in equivalent quantity into the negative, with equal 
 volumes of saline solution ; he then allowed the decompo- 
 sition to continue until the quantities of acid and of base, in- 
 troduced at the outset, were in excess on the opposite sides to 
 those into which they had been poured. By this process 
 each of the sections is alkaline for the half of the experiment, 
 and acid during the other half. The influence of the acid and 
 of the alkali is therefore equally exercised on both sides at 
 the moment when the decomposition is stopped ; it is as if the 
 solution had remained neutral all the time. 
 
 It would be useless now to return to the numerous experi- 
 ments made by Daniell and Miller, with the diaphragm ap- 
 paratus upon the decompositions of earthy and alkaline salts, 
 the phosphates in particular. We shall confine ourselves to 
 remarking that they are all favourable to the theory, that we 
 have given upon the composition of salts, and in particular to 
 that of Graham on the phosphates, in which he considers water 
 to play the part of a base ; and with respect to the different pro- 
 portions furnished by the two compartments in the products of 
 electrolysis, the explanation of M. d' Almeida is perfectly well 
 applicable. 
 
 The study that we have been making of the forms, so 
 various and sometimes apparently so complex, under which 
 electro-chemical decomposition is presented, at the same time 
 that they enable us to trace these forms to the simple laws of 
 Davy and of Faraday, no less point out to us the difficulty 
 there is in discovering these laws in the midst of so many 
 causes of perturbation. Thus, it is necessary to guard 
 against the action of these causes, in order to establish on 
 solid bases the generality of the law of the definite action of 
 the current, which has been denied by several philosophers. 
 This has been done successively by M. Buff and M. 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 389 
 
 Soret, in researches conducted with remarkable care and 
 precision. 
 
 M. Buff has especially in view to verify the accuracy of 
 the electrolytic law in cases of very feeble currents, and 
 consequently of very prolonged actions cases in which de- 
 composition is often hardly apparent, and in which consequently 
 it requires much time in order to discover it and to appreciate 
 its effect, which is the cause why several philosophers have 
 not only contested the existence of the law, but even that of 
 electrolysis, when the electricity transmitted does not attain 
 to a certain degree of intensity. M. Buff's first object was 
 to determine the relation of the electrolytic action to the force 
 of the current. 
 
 The liquid submitted to decomposition was a neutral so- 
 lution of nitrate of silver of perfect purity. Two plates of 
 silver were plunged into it, so that, under the influence of the 
 current, silver was detached from one, which passed and 
 arranged itself at the other. He employed in these ex- 
 periments a DanielPs pair, so as to preserve a force almost 
 constant for several days. He caused the force of the 
 current to vary by introducing into the circuit wires of 
 variable length, which served at the same time as wires to 
 galvanometer-multipliers, so that by means of the deviation 
 produced upon the needles, the degree of constancy of the 
 current might be determined. The wires were two in 
 number ; and according as they were placed in the circuit 
 one after the other, or as one alone was there, or as both 
 were arranged parallel to each other, three currents were ob- 
 tained, the relative energy of which may be represented by 
 1, 2, and 4. The resistance of the wires was so great that 
 the resistance of the pile, together with that of the decompo- 
 sition trough, might be set at a small fraction. It follows 
 from the table of experiments made to a great amount, that 
 the weight of the deposit of silver was always proportional 
 to the force and to the duration of the current. M. Buff 
 also placed in the circuit of the constant pair two successive 
 troughs, filled with the same solution of silver ; the two re- 
 sistance wires were adjusted end to end ; the electrodes, to 
 
 c c 3 
 
390 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the number of four, were thin plates of silver. The current 
 remained in action, without interruption, for about nine 
 days namely, 12,539 minutes. At the end of this time, 
 there were found : 
 
 In the 1st trough. In the 2nd trough. 
 
 Loss of weight of the positive plate 4-111 grs. 4-121 grs. 
 
 Increase of the negative - 4'105 4-117 
 
 The solution of silver contained '385 grs. of neutral solution 
 of nitrate of silver in *061 cub. in. : a more diluted solution, 
 which contained only '154 grs. to '061 cub. in. was placed in 
 succession with the former. At the end of fifty-one and a 
 half hours, the negative silver plate had increased in weight 
 1-919 grs. in the more concentrated solution, and 1*912 grs. 
 in the more diluted. Thus the fact that, whether the solution 
 be more or less diluted, it exercises no influence over the 
 electrolytic law. 
 
 On substituting pure water for one of the solutions of 
 silver, there was obtained, at the end of four days, or 5470 
 minutes, an increase of '369 grs. at the negative plate, which 
 plunges in the solution of silver, and a film of oxide of silver 
 on the positive plate of silver plunged in the water, which, 
 when carefully removed, indicated a loss of '369 grs. in 
 weight by this plate. Thus the effect of the electrolysation 
 of water, even by very feeble currents, is similar to that of 
 the electrolysation of the solution of silver ; and yet we should 
 have thought from appearances that the water was not de- 
 composed. It is the same with water slightly acidulated 
 with sulphuric acid. 
 
 Finally, the electrolysation of sulphate of copper presented 
 to M. Buff a perfectly satisfactory agreement with that of the 
 nitrate of silver, provided the solution was perfectly pure, 
 and deprived of all excess of acid. It is, therefore, well 
 established by M. Buff's experiments, that it may be proved 
 that even the most feeble currents, if their action is suffi- 
 ciently prolonged, decompose electrolytic liquids, according 
 to Faraday's law of definite action; and that it does not 
 appear that they traverse these liquids, even in the smallest 
 proportion, without decomposing them. 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 391 
 
 Upon salts of copper, both pure or mixed with others, M. 
 Soret has also verified Faraday's law. He began by pre- 
 paring these salts, so as to have them as pure and as neutral 
 as possible, by a series of successive crystallisations and 
 solutions. He produced his decompositions by placing his 
 solutions in tubes, and by using for electrodes wires of pla- 
 tinum from -0154 to *0231 in. in diameter. His current 
 was produced by Bunsen's piles, of from two to five pairs 
 feebly charged. When he considered that the action had 
 been sufficiently prolonged, he removed the electrodes covered 
 with copper, plunged them for a certain time in distilled 
 water, in order to wash them, then dried them rapidly with 
 blotting paper, and weighed them ; he then dissolved the 
 deposit of copper in nitric acid, and again weighed the pla- 
 tinum wires, in order to obtain the weight of copper depo- 
 sited. It is necessary, in order to obtain good results, that 
 the deposit of copper should be united and compact, other- 
 wise there is a risk lest a portion of the copper may not be 
 detached, or not oxidised. M. Soret found no advantage in 
 employing copper, instead of platinum, for the positive elec- 
 trode ; the solution of this copper not occurring always in a 
 normal manner, and delicate experiments not having pointed 
 out to him any sensible differences in the quantity of copper 
 deposited, according as the solution was neutral or acid.* 
 Indeed, three experiments furnish the following results : 
 
 * M. Jacobi, as the result of numerous experiments, and by employing 
 copper electrodes, had given up employing the decomposition of sulphate of 
 copper, for determining the intensity of the current, on account of the nu- 
 merous anomalies, that had been presented to him by this decomposition. 
 Thus, on comparing together the weights of copper lost on one side and reduced 
 on the other, he found, in a series of experiments, 7*4962 of copper lost for 7^1743 
 of copper reduced, which makes a difference of 4*5 per cent. M. Jacobi re- 
 cognised himself that this anomaly is due to the experiments having been 
 made with the sulphate of copper of commerce, which is not pure; this ex- 
 planation is found amply justified by the results obtained by M. Soret on 
 employing sulphate of copper chemically pure. Indeed, in this case, it is of 
 little importance whether the solution becomes acid or remains neutral, the 
 quantity of copper deposited upon the negative electrode necessarily remaining 
 the same for the same current, whether it arises from direct electrolysis or from 
 reduction by hydrogen. 
 
 c C 4 
 
392 TRANSMISSION OF ELECTRICITY. PlRTiv. 
 
 Weight of Copper deposited in Sulphate of Copper. 
 
 Differences. 
 
 1st Exp. 
 2nd 
 3rd 
 
 Neutral. 
 
 2-5685 grs. 
 -2-0897 
 5-1895 
 
 Acid. 
 2-5700 grs. 
 2-0927 
 5-1926 
 
 + 0-0015 
 + 0-0030 
 -j- 0-0031 
 
 After having verified, by numerous trials, that, under 
 identical circumstances, two perfectly similar solutions of 
 sulphate of copper give deposits, equal within three or four 
 thousandths of a grain, he found that it was the same for two 
 solutions, the one saturated, the other diluted. But if the 
 two solutions, still being similar, are at different temperatures 
 the one at 68, and the other at 212, for example, this 
 latter gives a sensibly less deposit, which is due, as may be 
 proved in a direct manner, to the dissolving action of sul- 
 phate of copper at 212, even though neutral, upon metallic 
 copper. 
 
 Nitrate, phosphate, and acetate of copper were placed, 
 concurrently with sulphate, in the circuit; each of these 
 solutions in each case gave the same deposit of copper at the 
 negative electrode as the sulphate did. The differences in 
 weights of from 1 to 3 grs., and even to 6 or 8 grs., were at 
 a mean 0*003 grs., sometimes in one direction, sometimes in 
 another, and never exceeded 0'006 grs., except in a single 
 case, in which the difference rose to 0*009 grs. It was 
 necessary not to prolong the action with the nitrate too 
 much, so as to avoid liberating too much nitric acid, this 
 acid soon exercising a dissolving action upon the copper 
 deposited ; and it is necessary that the acetate be very con- 
 centrated, the deposit of copper, without this precaution, not 
 being compact, and the differences being too great. 
 
 Sulphate of copper and sulphate of potash, mixed in equal 
 volumes, form a solution, which gives the same deposit as 
 pure sulphate of copper. The bichromate of potash mixed 
 with sulphate of copper forms no deposit, but merely gives 
 a liberation of gas. The mixture of sulphate of copper and 
 borate of soda gives a deposit of copper, but this deposit is 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 393 
 
 alwciys a little more considerable than those obtained simul- 
 taneously in pure sulphate of copper; and the differences 
 are too great -046 to '107 grs. to be able to be attributed 
 to errors of experiment. Moreover, the deposit is never 
 compact ; and it also appears a little oxidised, which it owes 
 to its slightly spongeous form. The sulphate of protoxide of 
 iron, mixed with sulphate of copper, sensibly diminishes the 
 deposit of copper ; which is due chiefly to the copper's dis- 
 solving to a maximum in the sulphate of iron, and in there 
 being always formed a certain quantity of this sulphate, when 
 the sulphate of the protoxide of iron is allowed to be exposed 
 to the air, a formation that must be facilitated by the 
 liberation of oxygen and of free acid, that accompanies electro- 
 lysis. The sulphate of manganese produces the same effect 
 as the sulphate of protoxide of iron. The nitrate of cobalt, 
 the sulphates of zinc and of cadmium, in no way alter the 
 weight of the deposit of copper ; and no trace is found in 
 this deposit, of cobalt, zinc or cadmium, which plainly proves 
 that copper alone is deposited. The following is the Table of 
 comparative results obtained by the passage of the same 
 current in a saturated solution of sulphate of copper, serving 
 as the term of comparison, and in another solution. (See 
 Table on next page.) 
 
 We may therefore conclude, from these last experiments, 
 that the law of electro-chemical equivalents is found to be 
 justified within the limits of errors of observation ; and that, 
 if there is a proportion of electricity that traverses the liquid 
 without producing decomposition, it can only be a very small 
 fraction, s^th at least, of this total quantity of electricity 
 transmitted ; indeed, if it were g-^th, or less, the differences 
 that would result from it would be smaller than the errors 
 of observation. 
 
394 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 Influence of the Electrodes upon Electro-chemical Decomposition. 
 
 There exists yet another circumstance, which, independ- 
 ently of its proper and distinct effect, plays also an important 
 
 NAME OF THE SOLUTION 
 compared with 
 SULPHATE OF COPPER. 
 
 Weight of Copper 
 deposited in 
 
 Difference. 
 
 Sulphate of 
 .Copper in 
 Saturation. 
 
 The Solution 
 inscribed in th 
 1st Column. 
 
 
 grs. 
 
 grs. 
 
 
 Sulphate of Copper diluted by 
 
 
 
 
 | its volume of water 
 
 5-2373 
 
 5-2466 
 
 + 0-0092 
 
 Sulphate of Copper diluted by 1 
 
 
 
 
 volume of water - 
 
 2-7584 
 
 2-7522 
 
 0-0061 
 
 Sulphate of Copper diluted by 1 
 
 
 
 
 volume of water ... 
 
 5-1261 
 
 5-1200 
 
 - 0-0061 
 
 Sulphate of Copper diluted by 1 
 
 
 
 
 volume of water - 
 
 3-9801 
 
 3-9848 
 
 -I- 0-0046 
 
 Concentrated Nitrate of Copper - 
 
 4-3832 
 
 4-3817 
 
 0-0015 
 
 Concentrated Nitrate of Copper - 
 
 7-5480 
 
 7-5649 
 
 0-0030 
 
 Concentrated Nitrate of Copper - 
 
 1-9537 
 
 1-9445 
 
 - 0-0092 
 
 Phosphate of Copper dissolved in 
 
 
 
 
 Phosphoric Acid - 
 
 2-7878 
 
 2-7940 
 
 + 0-0061 
 
 Phosphate of Copper dissolved in 
 Phosphoric Acid - 
 
 1-8642 
 
 1-8688 
 
 0-0046 
 
 Phosphate of Copper dissolved in 
 Phosphoric Acid - 
 
 2-1453 
 
 2-1437 
 
 0-0015 
 
 Acetate of Copper - 
 
 1-3004 
 
 1-2929 
 
 0-0015 
 
 Acetate of Copper - 
 
 1-2464 
 
 1-2495 
 
 + 0-0030 
 
 Mixture of Sulphate of Copper 
 
 
 
 
 and Sulphate of Potash - 
 
 3-1507 
 
 3-1492 
 
 - 0-0015 
 
 Mixture of Sulphate of Copper 
 
 
 
 
 and Sulphate of Potash - 
 
 1-8456 
 
 1-8518 
 
 + 0-0061 
 
 Mixture of Sulphate of Copper 
 
 
 
 
 and Nitrate of Cobalt - 
 
 1-3484 
 
 1-3720 
 
 0-0048 
 
 Mixture of Sulphate of Copper 
 
 
 
 
 and Nitrate of Cobalt - 
 
 1-2881 
 
 1-2896 
 
 -|- 0-0015 
 
 Mixture of Sulphate of Copper 
 
 
 
 
 and Sulphate of Zinc 
 
 2-0964 
 
 2-2477 
 
 + 0-1513 
 
 Mixture of Sulphate of Copper 
 
 
 
 
 and Sulphate of Zinc 
 
 1-5584 
 
 1-5614 
 
 + 0-0030 
 
 Mixture of Sulphate of Copper 
 
 
 
 
 and Sulphate of Cadmium 
 
 1-9769 
 
 1-9800 
 
 + 0030 
 
 part in those which we have been enumerating I would 
 speak of the nature, the form, and the physical state of the 
 electrodes, which establish communication between the poles 
 of the pile and the liquid to be decomposed. 
 
 We have already seen that there always exists, in the passage 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 395 
 
 of the current from a solid conductor into a liquid, a resistance 
 independent of the conductivity proper of the solid body 
 and of the liquid. This resistance is manifested in a very 
 decided manner, when a liquid conductor is separated into 
 two parts by a thin plate of metal, or when two liquid con- 
 ductors, placed in two distinct vessels, into which each of the 
 electrodes are immersed, are connected by a metallic arc. On 
 placing a galvanometer and a voltameter in the circuit, it is 
 easy to prove that, the more the metal of which the plate or 
 the metal arc is made is attackable by the liquids in contact 
 with them, the less is the resistance. It also varies with the 
 relative nature of the metal and of the liquids ; even when the 
 metal is not attackable by either of the liquids. Thus with 
 platinum plates employed, whether as electrodes, or for esta- 
 blishing communications between two or several successive 
 vessels, the resistance is much less with concentrated nitric 
 acid than with hydrochloric, less with hydrochloric than 
 with sulphuric ; it is more considerable with diluted nitric 
 acid than with concentrated, whilst it is the reverse with 
 sulphuric acid : saline solutions, those of potash and ammonia, 
 present almost the same resistance. The intensity of the 
 current exercises an influence not only over the absolute 
 resistance, but also over the relative resistance of two liquids ; 
 thus, when the current is powerful, the resistance to passage 
 is less for hydrochloric acid than for nitric acid ; it is the 
 reverse when the current is feeble. In order to obtain full 
 assurance that these differences depend upon variations in 
 the resistances to passage, and not in the conductibility of the 
 liquid, we make use of several glasses four, for example, 
 filled with liquid ; they are connected by arcs of platinum, 
 whilst the platinum electrodes are immersed in the two ex- 
 treme vessels. It is very curious to perceive that, on 
 varying the number of glasses, and consequently that of the 
 alternations or passages from a solid to a liquid conductor, 
 and reciprocally, we are able to render the same system of 
 metallic-liquid conductors more or less conductors at one 
 time than at another, which is simply due to our modifying 
 the general intensity of the current, by a variation in the 
 number of alternations. Such is the case, as we have said 
 
396 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 with hydrochloric and with nitric acids. Thus, in making 
 of these two acids, two perfectly similar systems, each com- 
 municating with one of the wires of a differential galva- 
 nometer, there is found, on compelling the current to divide 
 itself between them, 48 in favour of the hydrochloric acid, 
 when there is only one alternation ; and 15 in favour of the 
 nitric acid when there are five. But, in the former case, 
 the intensity of the current transmitted by one of the systems 
 alone was 75, in the latter 30. The same result is obtained 
 with two platinum electrodes, employed either in nitric acid 
 or in hydrochloric ; and by causing the intensity of the current 
 to vary by means of a pile of greater or less force. 
 
 The resistance to passage diminishes with the increase of 
 the surface of contact of the liquid and the solid conductors ; 
 but it is proved that the greatest intensity of the current, 
 which results from he increase of the surface of contact, 
 increases in a greater relation than the surface itself when 
 the current is feeble, and in a less relation when the current 
 possesses a certain degree of intensity, this degree being 
 dependant on the relative nature of the solid and liquid 
 conductors. 
 
 Before entering further into this order of phenomena, it is 
 necessary to seek after the cause. Now, it is entirely in the 
 chemical decomposition brought about by the current upon 
 this liquid in contact with the solid conductor that it has its 
 origin. In order to have a good representation of this part 
 played by the electrode in electrolysis, we must have regard, 
 as Faraday does, to the whole of the circuit, and to that 
 power, of which we have already spoken, possessed by the 
 current of transporting the force of affinity, that is ordinarily 
 exercised at infinitely small distances. Now, their force 
 originates at the electrodes, one of which attracts oxygen 
 and the acid elements, and the other hydrogen and the basic 
 elements. 
 
 Two circumstances may favour the exercise of the force, 
 and consequently the passage of the current : viz., the facility 
 possessed by the electrolyte itself of being decomposed, and 
 the very affinity of the substance of which the electrode is 
 
CHAP in. EFFECTS OF DYNAMIC ELECTRICITY. 397 
 
 composed for that element of the electrolyte which the 
 current tends to liberate upon its surface.* Thus, with 
 electrodes of platinum, concentrated nitric acid will offer 
 less resistance to the passage than dilute sulphuric or than 
 hydrochloric acid, because it is more easily decomposed than 
 the other two acids. But, on the other hand, as platinum has 
 an affinity for chlorine, it may be that this circumstance out- 
 weighs the former, since experiment shows us that this takes 
 place for a certain intensity of current. This effect is still 
 much more sensible when we employ for positive electrodes 
 oxidisable metals, such as iron, zinc, &c., and for negative 
 electrodes, peroxides that have a great affinity for hydrogen, 
 such as the peroxide of lead, with which the platinum plate 
 may be covered. It is evident that the oxygen and hydrogen, 
 for example, are attracted with much more force the one in 
 one direction, the other in the other, when the action of the 
 current is added to the affinity of the electrode. But the 
 manner in which this influence of the nature of the electrodes 
 is made most sensible is, in facilitating or in preventing the 
 deposit, which is always in a greater or less degree formed 
 upon the surface of each of them, and which is the most decided 
 cause of the resistance to passage. Thus, it is easy to see, in 
 the electrolysis of acidulated water with platinum electrodes, 
 that there remains a thin film of oxygen adherent to the 
 surface of the positive electrode, and a similar one of hydrogen 
 to the surface of the negative electrode ; these two films, by 
 preventing the immediate contact of the electrodes with the 
 liquid, lessen the facility of passage of the current, at the 
 same time diminishing its intensity, as we shall see, by pro- 
 ducing a secondary current, determined in a direction con- 
 trary to that of the principal current. It is no longer the 
 same when the electrode, combining with the oxygen, forms 
 a soluble oxide, or when, like the peroxide of lead, it absorbs 
 the hydrogen, allowing of the combination of this gas with 
 
 * We arc here speaking only of the passage of the current at the surface of 
 contact of the electrode and the liquid, and not through the liquid itself, the 
 latter passage depending upon the conductibility of the liquid, a property 
 whose relation with elcctrolysution has not yet been determined. 
 
398 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 one part of its own oxygen. With regard to the existence 
 of these deposits, the nature of which varies with that of the 
 electrolyte, it may be proved either directly or indirectly, by 
 a peculiar property which they impart to the electrodes. 
 Let us examine in succession these two modes of demon- 
 strating their presence. 
 
 The attentive examination of the electrodes enables us 
 very quickly to discover upon their surface, when they have 
 been employed for electrolysis, the deposits, even the gaseous 
 ones, that remain adhering to them. In this way we discover 
 that even the most feeble current, such as that of a single 
 pair, cannot traverse an electrolyte acidulated water, for ex- 
 ample, without decomposing it. The gaseous deposit is 
 sometimes so little apparent, even with the microscope, that, 
 in order to render it sensible, it is necessary to place the ap- 
 paratus in which the decomposition takes place, in vacuo ; 
 and then the bubbles of gas are seen to detach themselves 
 from the surface of the platinum electrodes, and the galvano- 
 meter that is in the circuit suffers a greater deviation, a proof 
 that the gaseous film was the cause of 'the resistance to 
 passage. When the deposit is solid, it is an easier matter 
 to see it ; and it commonly forms, in consequence of its little 
 thickness, very brilliant coloured films, analogous to the 
 colours of thin plates. M. Nobili, who discovered them, and 
 called them by the name of electro-chemical appearances, 
 made a very particular study of them. In order to obtain 
 them, he arranges horizontally a plate of platinum or of 
 silver, or even of steel, at the bottom of a flat vessel. He 
 covers it with a thin layer of an electrolytic solution. Then 
 he plunges vertically into the liquid over the plate a fine point 
 of platinum, so that it shall be only j^th or ^th of an inch 
 in distance from this plate. The point and plate serve alter- 
 nately as positive and negative electrodes. One of the 
 most beautiful appearances is that which is obtained upon 
 the positive electrode with acetate of lead. It is altogether 
 similar to Newton's coloured rings and quite as brilliant ; it is 
 due to a very thin deposit of peroxide of lead, a substance 
 which, like the acids, is transported to the positive pole. The 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 399 
 
 action must not be prolonged too much, nor must too power- 
 ful a current be employed, for fear that, the deposit becoming 
 too thick, the colours should disappear. The appearances are 
 in general more brilliant on the positive electrode ; ^however, 
 very decided ones may be obtained on the negative by em- 
 ploying a more energetic current, and mixing together two or 
 three solutions. In order to have the power of more readily 
 comparing the positive and negative appearances, it is well to 
 produce them at the same time upon the same plate. Nobili 
 did this by arranging above the plate A B, two fine platinum 
 wires, each communicating with one of the poles of the pile N P 
 (Jig. 238.). The current came out from the point P, pene- 
 
 Fig. 238. 
 
 trated into the plate at n, then came out from the plate at p, 
 beneath the second point N, into which it entered in order to 
 complete its circuit. The result was the production of a ne- 
 gative appearance at n, and a positive one at p. But if these 
 appearances were produced so as to be too near to each 
 other, they were frequently deformed, as if they were mutu- 
 ally repelled, and expanded exteriorly. This deformity 
 ceased to take place as soon as a thin screen of glass 
 was placed between the two points, so as to prevent all direct 
 communication between the two parts of the liquid that 
 cover the portions of the plate upon which the appearances 
 are formed. It was, therefore, evidently due to this, that, 
 when there was no glass screen, it happened that, among these 
 currents which disseminate in filaments throughout the liquid 
 between the two points that serve as poles, those which should 
 
400 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 have formed the interior contour of the coloured rings tra- 
 versed directly from one point to the other in the liquid ex- 
 clusively, instead of passing in a part of their course through 
 the plate, and this on account of the resistance to passage 
 that it .offers to them. It is not the same for the exterior 
 filaments, which would have a longer course to take through 
 the liquid ; thus they traverse the plate because, notwith- 
 standing the resistance to passage, this second path offers to them 
 a more easy transmission. When the screen is there, there 
 is no longer a choice, and all the currents are almost compelled 
 to pass through the plate, which causes the appearance to be 
 no longer deformed. We see by this example that the form 
 and position of the electro-chemical appearances may serve, in 
 a very useful manner, to follow this mode of the propagation 
 of currents in a liquid. 
 
 Returning to the appearances themselves, we shall add 
 that, among the most beautiful are found those which are 
 obtained at the positive electrode, on decomposing animal or 
 vegetable organic substances, which induced Nobili to see in 
 this the cause of the colouration of plants, and particularly 
 of flowers. With regard to the deposits that arise from the 
 electrolysis of inorganic compounds, they have been the 
 subject of a profound examination, not only on the part of 
 Nobili, but also on the part of M. Becquerel. We shall have 
 occasion to return to the results obtained by these two skilful 
 physicists, when engaged upon the chemical applications of 
 electricity. It would be useless in this place to enter into 
 further details, for it is easy to conceive the innumerable 
 variety of effects that may be obtained by employing different 
 solutions, either pure or mixed, by raising or lowering their 
 temperature, by producing the deposits upon plates, sus- 
 ceptible or not of being attacked by the elements liberated. 
 We may simply add that the production of electro- chemical 
 appearances has been the subject of an experimental and 
 theoretical study, both on the part of M. E. Becquerel, who 
 thought that it was subject to a very simple law, analogous 
 to that which governs Newton's coloured rings, as well as on 
 the part of MM. Dubois-Reymond, and Beetz, who have 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 401 
 
 demonstrated that the phenomenon was more complex, and 
 that it depended besides on several circumstances connected 
 with Ohm's laws. 
 
 Let us now pass on to the indirect mode, by which the 
 presence of the deposits is indicated. It consists in the pro- 
 perty that they impart to the electrodes of giving rise to an 
 electric current, by acquiring what is called secondary 
 polarity ; for example, two platinum plates that have been 
 employed one as positive electrode, the other as negative 
 in acidulated water, become capable of forming a voltaic pair, 
 in which the former plate plays the part of the negative 
 metal, such as copper or platinum, and the latter that of the 
 positive metal, as zinc. This couple produces a current, 
 that acts upon the galvanometer and upon the chemical or 
 calorific voltameters : it is true that it is never very strongj 
 and that its action has only a very short duration. When 
 the principal current has traversed several homogeneous 
 diaphragms or arcs, employed for connecting several liquid 
 compartments one with the other, the secondary polarities, 
 that are acquired by these diaphragms or arcs, make of them 
 a veritable pile, named a secondary pile, and the action also 
 of which never has a long duration. It is not necessary, 
 in order to the establishment of the current, that the liquid 
 conductor in which the polarised metals are plunged should 
 be the same as that whose electrolysation has polarised them 
 a proof that this current does indeed arise from the metals, 
 and consequently from the deposits, which have taken place 
 on their surface. The same results are obtained, and with 
 even a more decided degree of intensity, by the decompo- 
 sition of saline solutions. All these secondary currents are 
 due to the chemical reaction of the liquid, in which the 
 plates are plunged, upon the deposits with which their surfaces 
 are covered ; and what proves this is, that the same effects 
 are obtained by bringing about the deposits in a direct 
 manner, instead of employing for this purpose the action of 
 a current.* We shall study with care the formation of these 
 
 * For example, we have merely, as M. Matteucci was the first (o remark, to 
 place two very clean platinum plates, the one iu oxygen, the other in hydrogen, 
 VOL. II. D D 
 
402 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 currents in the Chapter devoted to the production of elec- 
 tricity by chemical actions, of which they are a particular 
 case. Let us simply remark further, that the polarisation, or 
 rather the secondary polarities that are acquired by the 
 electrodes, whenever they have transmitted dynamic elec- 
 tricity, however feeble or instantaneous it may be, are the 
 most sensible indication of the formation of deposits on their 
 surface, and consequently of the existence of electrolysis. 
 
 Is the resistance to passage simply due to the polarisation 
 of the electrodes, or is it also due to the fact itself of the 
 change of conductor ? This question has been for a long 
 time controverted. Fechner and Poggendorff have main- 
 tained that the two causes equally contribute to the phenom- 
 enon, against Ohm, who was the first to establish that the 
 simple fact of the passage of the current from the solid con- 
 ductor into the liquid does not generate resistance, and that 
 the latter is merely an effect of the polarisation of the metals. 
 Fechner had actually demonstrated, by very accurate mea- 
 surements, in his fine work published in 1831*, that, in 
 a closed voltaic circuit, in which an electrolyte is in- 
 cluded, but without intermediate plates, the total resistance 
 is always greater than are the resistances of the metal and 
 the liquid taken together, which proves the existence of the 
 resistance to passage ; but he had not examined the cause of 
 this resistance, and he confined himself to pointing it out, 
 as had been done by Marianini and myself, in indicating the 
 circumstances that cause it to vary, such as the nature of 
 the metals and of the liquids, and such also as the size of the 
 metal surface immersed in the liquid and the force of the 
 current two influences which are in the inverse ratio to 
 it. It is true that Fechner, replying more recently to 
 Ohm's observations, had thought he was able to establish, 
 by considerations deduced from the resistance to passage, 
 which exists in the pile, changing with time, and from its 
 increasing constantly in proportion as the intensity of the 
 
 in order to obtain a very decided current upon afterwards plunging the two 
 plates into acidulated water. 
 
 * Maussbestimmungen iiber die Galwanischc-Kette, Leipsig, 1831. 
 
CUAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 403 
 
 current diminishes, the conclusion that there exists, inde- 
 pendently of the effect due to polarisation, a positive resis- 
 tance for the current when it traverses conductors alternately 
 liquid and solid. But this kind of argument is not conclu- 
 sive ; because the effect of the polarisation of the electrodes 
 being essentially to create a contrary current to that which 
 is transmitted, and by this to diminish the intensity of the 
 latter, it would be necessary, in order accurately to appre- 
 ciate the influence of this polarisation, to know the exact 
 relation that exists between the secondary current, to which 
 it gives rise, and the primitive current, which itself has 
 produced it; and this relation is not known, or at least 
 cannot be determined in a precise manner. 
 
 The only mode of resolving the question is to demonstrate 
 that there is no resistance to passage when there is no 
 polarisation of the electrodes. Now, in order to obtain this ab- 
 sence of all polarisation, still transmitting the current through 
 the electrolyte, it is necessary to employ instantaneous 
 currents, of equal intensity, sent alternately in contrary 
 directions, and succeeding each other with sufficient rapidity 
 for the polarisation determined by the first to be annulled 
 by the inverse polarisation, that is produced by the following 
 one ; that, for example, oxygen and hydrogen, brought 
 alternately by the electrolysis of water upon the metal 
 surface, may succeed each other with sufficient rapidity to 
 recombine, without being liberated in the gaseous state or 
 remaining adhering to the metal. 
 
 I was the first to point out a fact, which indicated the 
 possibility of this neutralisation of polarisation, by employing 
 the alternate induction currents, produced by a Saxton's 
 machine, and by transmitting them through an acid solution 
 placed in the circuit by means of two platinum plates of a 
 surface equal to that of the section of the liquid, which was 
 itself placed in a primitive trough with a section of -62 sq. 
 in. and 3 '93 in. in length. Not only was no gaseous 
 liberation manifested upon the electrodes, but, on placing a 
 platinum plate as a diaphragm at the middle of the liquid, 
 the intensity of the transmitted currents was not diminished ; 
 
 D D 2 
 
404 TRANSMISSION OF ELECTRICITY. PART iv 
 
 and although this plate received successively upon each of 
 its faces the oxygen and hydrogen arising from the decompo- 
 sition of the water, no gas was seen to appear. The intensity 
 of the currents was measured by a calorific voltameter placed 
 in the circuit, or the helix of a Breguet's* thermometer, or a 
 fine platinum wire, which traversed the bulb of an air 
 thermoscope. 
 
 Poggendorff and Yorsellmann de Heer, on repeating and 
 varying my experiments, had arrived at contradictory results 
 the former having thought he had found a resistance to 
 passage, independent of the polarisation of the electrodes ; and 
 the latter having observed it to disappear as soon as this 
 polarisation ceased to exist. Both of them employed in- 
 duction currents produced by Saxton's machine. M. Poggen- 
 dorff measured the intensity of the currents, by means of two 
 air thermometers, the bulb of which, being larger in one 
 than in the other, was traversed by a fine platinum wire; 
 he placed a metallic diaphragm in the middle of a rectangular 
 box filled with the conducting liquid, so that the two parts 
 of the liquid, separated by the diaphragm, could not commu- 
 nicate together ; finally, he measured the resistance which the 
 current suffered by the interposition of the diaphragm, by 
 comparing it with that of a German silver wire '007 in. in 
 diameter. We may add, that M. Poggendorff was careful to 
 turn the Saxton machine at all times with the same velocity, so 
 as to have fifteen alternate currents per second. A great num- 
 ber of experiments, made with platinum, copper, and iron 
 plates, placed in the same circumstances, sometimes in dilute 
 sulphuric acid, at other times in a solution of hydrochlorate 
 of soda, gave him for platinum a resistance more than double 
 that for copper, and more than quadruple that for iron. M. 
 Poggendorff remarked that, independently of the nature of 
 the liquid and of the metal, the state of the surface of the 
 latter influences in a very notable manner the resistance to 
 passage, as well as did elevation of temperature, which di- 
 minishes it in a very considerable quantity. This diminution 
 
 * Vol. I. fig. 21. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 405 
 
 must not be confounded with that, which is produced by heat 
 in the resistance of conductibility of the liquid itself, which, 
 as Ohm has demonstrated, is independent of the electrodes. 
 Thus, with a diaphragm of platinum in diluted sulphuric acid 
 at the temperature of 6286, the calorific voltameter rose 74 
 divisions; and it rose about 110 divisions when the tempe- 
 rature of the liquid was raised to from 167 to 194. If the 
 temperature of the metal is raised to red heat, as in Leiden- 
 frost's well-known experiment, then no current is trans- 
 mitted a proof that there is no contact between the liquid 
 and the metal. 
 
 M. Vorsellmann de Heer, in order to show that the resistance 
 to passage is due to the polarisation of the electrodes, employed 
 two galvanometers, one of which, the least sensitive, measured 
 the direct current transmitted ; and the other, the more de- 
 licate, the current arising from the polarisation of the elec- 
 trodes. Now, the intensity of one of these two currents was 
 the inverse of that of the other a proof therefore that the 
 polarisation was the cause that diminished the principal 
 current, and that produced consequently the resistance to 
 passage. M. Vorsellmann employed only a single instan- 
 taneous current, always of the same intensity namely, that 
 which was produced by a semi-revolution of the armature of 
 a Saxton's machine a circumstance that enabled him to em- 
 ploy the magnetic galvanometer for measuring it. The elec- 
 trodes were plates of platinum, of copper, or of iron, very 
 homogeneous; and the liquid water acidulated by a little 
 sulphuric acid. 
 
 Lenz, who in like manner employed only a single instan- 
 taneous current, had always found a resistance to passage, 
 which is not astonishing, since he in this manner always 
 brought about a polarisation of the electrodes. When 
 we desire to demonstrate that there is no resistance to pas- 
 sage properly so called, we must succeed in nullifying it, by 
 removing the causes that give rise to it, or at least in attenu- 
 ating it, by diminishing the effect of these causes. I succeeded 
 in accomplishing this before even the researches of MM. Pog- 
 gendorff and Vorsellmann de Heer, by using, in place of iu- 
 
 D D 3 
 
406 TRANSMISSION OF ELECTRICITY. PART IT 
 
 stantaneous or of a continuous current, a series of currents 
 determined alternately in contrary directions. I produced 
 these currents, not only by means of Saxton's induction 
 apparatus, but also by rendering the currents produced by 
 a DanielPs pile of ten pairs instantaneous and alternate, by 
 means of one of the rheotomes or commutators, that I have 
 described in the first volume.* I first satisfied myself, by 
 placing in the circuit a capsule of platinum, containing a 
 layer of concentrated nitric acid \ or { in. in thickness, the 
 upper surface of which was in contact with a disc also of 
 platinum, that the discontinuous and alternate currents were 
 conducted as well, whether they traversed the layer of nitric 
 acid, or whether, by putting into contact the platinum cap- 
 sule and disc, they were not compelled to traverse this layer. 
 It was no longer the same when the currents were guided 
 all in the same direction a proof that the diminution of 
 intensity, which they suffered in this latter case, was due to 
 the polarisation of the two surfaces of platinum. The calo- 
 rific voltameter that I employed in this experiment was not 
 very sensitive ; it is the one founded on the measure of the 
 dilatation experienced by a platinum wire that is traversed 
 by the current.f With this same voltameter and two platinum 
 plates of 7*59 sq. in. of surface, plunged at a distance of 
 39 in. from each other in sulphuric acid diluted with nine 
 times its volume of water, I proved that, when the current 
 was continuous and gas was liberated upon the two plates, 
 the instrument went from to 17, and that it went to 20, 
 as soon as the communicator placed in the circuit was put 
 in motion, and the current was thus rendered discontinuous 
 and alternate. On the other hand, if, by substituting in the 
 circuit for the liquid conductor a platinum wire of a resis- 
 tance almost equal, so that the voltameter went from to 
 20 by the effect of the continuous current, I rendered this 
 current discontinuous and alternate, the instrument indicated 
 no more than 17. Thus this latter form diminishes in fact 
 
 * Vol. I. pp. 295. 398. 
 f Vol. I. p. 32. fig. 19. 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 407 
 
 the effect of the current ; and if it increases it, when there is 
 a liquid conductor in the circuit, it is because it annuls or 
 diminishes the resistance to passage. The following also are 
 the results of experiments made with diaphragms of different 
 nietals, placed vertically in a glass trough 6 in. in length, and 
 1 in. in width and depth, so as to divide the liquid conductor 
 (sulphuric acid diluted with nine times its volume of water), 
 into two, three, or four compartments, without any direct 
 communication between them ; the liquid was placed in the 
 circuit, by means of two platinum plates inserted at the ends 
 of the trough, The calorific voltameter is in this case an air 
 thermoscope, the bulb of which, placed at the top of the tube, 
 is traversed by a fine platinum wire ; it carries an arbitrary 
 division in millimetres (- in.), which goes from the bottom, 
 upward. 
 
 Continuous Current. Alternate Current. 
 
 With a. platinum diaphragm - - 68 mm 54mm 
 
 Without diaphragm - ... 48 48 
 
 Difference - ~2CT If 
 
 With three copper diaphragms - - 144 128 
 
 Without diaphragm - - - . - 133 126 
 
 Difference - TT 2 
 
 With three tin diaphragms - - - 127 106 
 
 Without diaphragm ... - 115 K)6 
 
 Difference - 12~ ~0~ 
 
 Thus, for each kind of diaphragm, the resistance to passage 
 is much less with alternate currents than with direct currents, 
 and it ends by becoming null with diaphragms of tin. We 
 may also annihilate it with copper diaphragms when the 
 latter have already served for several similar experiments, 
 their surfaces then presenting a pulverulent aspect, which 
 indicates that they have undergone a series of oxidations and 
 of reductions. We succeed in rendering it almost insensible 
 with diaphragms of platinum by employing a solution of 
 hydrochlorate of ammonia, which causes the platinum to be 
 alternately attacked and reduced by hydrochloric acid. We 
 obtain the same result with dilute sulphuric acid, when we 
 
 D D 4 
 
408 TRANSMISSION OF ELECTRICITY. PART IT. 
 
 employ for electrodes, the capsule and plate of platinum of 
 which I have made mention above. On interposing between 
 this capsule and disc a capsule of lesser diameter, we in no 
 way modify the intensity of the alternate currents, which are 
 transmitted equally well, whether the capsule be there or 
 not, and whether it be of platinum, of copper, or of tin. 
 However, this result is obtained with the platinum capsule 
 only when the experiment has continued for a sufficient time 
 to modify its surface ; whilst, with the other two, it takes 
 place immediately. 
 
 In order to succeed well in these latter experiments, it is 
 necessary to employ the Saxton's machine, because we can 
 cause the currents, that are determined alternately in con- 
 trary directions, to succeed each other with greater rapidity. 
 Thus, in my latter experiments there were at least 40 per 
 second. In the first there were only 27 ; and it is not sur- 
 prising that, in those of Poggendorff, where there were only 
 15, the resistance to passage had never been completely an- 
 nihilated. 
 
 It is evident, from what has gone before, that the cause 
 which produces resistance to the passage from a solid con- 
 ductor into a liquid, is the deposit upon the metallic surface 
 of the electrode of the foreign substance, arising from elec- 
 trolysis, whether the resistance due to this deposit be only 
 passive, by the effect of the inferior communication between 
 the liquid and the metal ; or be active also, by the creation 
 of a contrary current, due to the polarisation of the metallic 
 surfaces. In every case, in order to annihilate the resistance 
 to passage, it is necessary to prevent the formation of the 
 deposit, or to destroy it immediately it is formed. It is this 
 that is accomplished with the alternate currents, which, suc- 
 ceeding each other very rapidly, carry successively oxygen 
 and hydrogen upon the same surface in an interval of time 
 sufficiently short for them to be able to combine before be- 
 coming liberated. However, the aspect of the metal surfaces, 
 that have for some little time transmitted these currents 
 shows that there has not been simply a deposit of oxygen, but 
 an oxidation, immediately followed by a reduction by hy- 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 409 
 
 drogen. Platinum itself becomes at last covered by a black 
 powder, which is finely divided platinum, the production of 
 which can only be explained by a series of oxidations and 
 reductions, which this metal must have undergone. We 
 shall see that oxygen, in the nascent state, is usually able to 
 become capable of combining directly with platinum.* 
 
 We do not always obtain the disappearance of the deposit 
 with alternate currents, and we can sometimes obtain it with 
 continuous currents. Thus, as an example of the former 
 case, I will cite lead, which, employed as a diaphragm, is 
 covered by alternate currents upon both its surfaces, with a 
 coating of white oxide, which is not reduced, whilst this 
 coating is formed upon a single surface alone, when the 
 current is continuous ; whence it follows that, contrary to what 
 takes place with other diaphragms, the current is less 
 weakened by the interposed plate of lead when it is con- 
 tinuous than when it is discontinuous and alternate. As an 
 example of the second case, I will cite nitric acid, which, in 
 contact with the negative platinum electrode, renders its 
 resistance to passage almost null, by preventing upon the 
 surface of platinum the deposit of hydrogen, which it absorbs 
 in proportion as it is produced, becoming converted into 
 nitrous acid. I will again cite the fact, which I have already 
 pointed out in the First Chapter of this Fourth Part, that we 
 have merely to heat or to shake the negative platinum elec- 
 trode plunged in an acid solution, in order to attenuate 
 notably the resistance to passage, even by a continuous 
 current, M. Beetz satisfied himself by direct experiments 
 that this heating and shaking diminish proportionally more the 
 polarisation of the negative than that of the positive electrode, 
 especially when the current has but little intensity, a case, 
 in which is easily manifested the preponderant influence of 
 
 * The formation of the black powder of platinum is also observed when a 
 powerful current has been transmitted for a long time continuously through a 
 voltameter with plates or wires of platinum, charged with sulphuric acid diluted 
 with nine times its volume of water. This powder is deposited at the bottom of 
 the vessel, and evidently arises from a series of oxidations and reductions 
 which the surface of the negative electrode suffers, under the alternate influence 
 of the oxygen dissolved in. the liquid uud of the hydrogen that is liberated. 
 
410 TRANSMISSION OP ELECTRICITY. PART IT. 
 
 the shaking and heating of the negative electrodes over the 
 facility of the current's being transmitted. 
 
 The part played by platinum as an electrode is very re- 
 markable ; for, although it passes for being not oxidisable, we 
 see it comport itself like the metals that are so, but in a 
 feeble degree. Thus the black powder, that is formed upon 
 the platinum wires, that have been employed for a long time 
 as electrodes to alternate currents in a solution of nitric or 
 sulphuric acid, indicates that these wires have undergone a 
 series of oxidations and of reductions, which is further proved 
 by the condition of their surface, when the powder has been 
 removed which from polish, as it was, has become covered with 
 roughness. Gold and palladium present the same phenomena 
 as platinum, but more promptly : gold becomes covered with 
 a greenish pellicle ; palladium with a layer of bluish black. 
 These layers are, in like manner, formed by the pure metal, 
 but very divided ; for the burnisher renders to them, as to 
 the black powder of platinum, the metallic brilliancy ; and 
 when introduced into the explosive mixture, the three powders 
 equally cause it to detonate : only it is necessary for that of 
 gold to raise the temperature to 122. 
 
 For wires of platinum, as for wires of gold, the quantity 
 of gas liberated goes on diminishing, in proportion as the 
 pulverulent layer is formed ; and at the same time the 
 current transmitted increases in intensity, as is shown by the 
 indications of the calorific voltameters. Thus, with platinum 
 wires in water, acidulated to a tenth, at the end of one 
 minute, the helix of the voltameter * marked 27, and the 
 gas liberated was *427 cub. in. ; and at the end of seventeen 
 minutes, the helix marked 40, and the liberated gas was 
 in all about 2-74 cub. in., and only -061 cub. in. in the 
 seventeenth minute. The wires were then entirely covered 
 with the black powder, and the gaseous mixture detonated 
 without leaving any residuum a proof that the oxygen 
 and hydrogen existed in it in the proportion, that forms 
 water. With gold wires there is sometimes, after the 
 
 * Vol. I. fig. 21. p. 33. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 411 
 
 detonation, a slight residuum of hydrogen, which rises from 
 the gold being slightly oxidised ; this fact explains why the 
 currents pass a little more easily, as is proved by the indi- 
 cation of the helix of the voltameter, which at the end of ten 
 minutes marks as much as 46. 
 
 The condition of the surface of the platinum exercises 
 an influence over its facility of being disaggregated. Wires 
 7 in., and even 13 in., in length, whether straight or 
 coiled into a helix, are very quickly covered with the black 
 powder when, being plunged into water with one-tenth 
 sulphuric acid, they serve as electrodes to induction currents, 
 that succeed each other at the rate of 40 per minute. 
 The operation is much longer and more difficult for plates ; 
 and the gases recombine at their surfaces a long time before 
 any traces of divided platinum are perceived. With spongy 
 platinum serving as electrodes, there is never any gaseous 
 liberation, and the temperature of the calorific voltameter 
 placed in the circuit is higher ; in general, this temperature 
 attains its maximum in all cases as soon as there ceases 
 to be a liberation of gas.* The heating of the liquid, which 
 increases the intensity of the current, when the wires being 
 no longer blackened, there is a production of gas, exercises 
 almost no influence when, the black layer being formed, all 
 gaseous liberation disappears. 
 
 The property that we have been recognising in platinum, 
 of bringing about the combination of the gases arising from 
 electrolysis, in proportion as they are liberated alternately 
 upon its surface, must evidently be the same as that in 
 virtue of which this metal causes the detonation, on being 
 introduced into it, of a mixture of oxygen and hydrogen 
 made in the proportions that constitute water, as was dis- 
 covered by Doebereiner. We may remark, first, that the 
 conditions, which render platinum susceptible of inflaming 
 the detonating mixture, are the same as those, that favour 
 its disaggregation in electrolysis, namely, the absence from 
 
 * We must not confound the temperature of the calorific voltameter placed 
 in the circuit with that of the liquid decomposed, which is altogether inde- 
 pendent of it. 
 
412 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 the surface of all foreign matter whatever, the roughness 
 that it presents, &c. Faraday has even remarked, that 
 the mere fact of having served as an electrode in an acid 
 solution renders a platinum plate eminently fitted to bring 
 about the combination of oxygen and hydrogen. This is not 
 all ; the proof that, in Doebereiner's experiment, there is a 
 succession of alternate oxidations and reductions is, that a 
 -platinum wire, well cleaned and coiled into a helix, employed, 
 instead of spongy platinum, for inflaming hydrogen in the 
 air, soon acquires a greyish pulverulent surface, which is 
 due to the disaggregation of the metal. In order to facilitate 
 the operation, it is necessary slightly to heat the platinum 
 wire, by letting it be traversed by an electric current of 
 feeble intensity, and directing upon the helix a current of 
 hydrogen mixed with atmospheric air, by means of a stop-cock 
 with two openings. The same disaggregation is observed 
 in a platinum wire, that has been used for Davy's aphlogistic 
 lamp. We have merely then to coil into a helix a platinum 
 wire Y^-Q in. in diameter, and to place it upon a spirit lamp, 
 after having carefully washed it, first in nitric acid, then several 
 times in distilled water, so as to have it dry and sheltered from 
 dust. The lamp is lighted, so that the wire becomes red ; 
 and when it is red, the flame is extinguished : it then remains 
 incandescent by the effect of the vapour of alcohol. If 
 the experiment is allowed to continue for twenty-four and 
 even forty-eight hours, the wire, which was perfectly smooth, 
 presents, at the end of this time, a pulverulent surface, due 
 to disaggregated platinum a proof that the phenomenon 
 of the aphlogistic lamp consists also of a series of oxidations 
 and reductions, due to the alternate action of the oxygen 
 of the air, and of the vapour of alcohol. I have greatly 
 varied this experiment. I have employed very pure alcohol, 
 wicks of amianthus instead of cotton wicks, and have 
 always observed the same result. I have besides remarked, 
 that the wires whose surface is thus disaggregated, are much 
 superior to others for making the experiment of the aphlo- 
 gistic lamp succeed. 
 
 The phenomena, that are presented by platinum, as well 
 
CIIAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 413 
 
 in this case as in that of electrolysis, are altogether similar 
 to those, which take place with other more or less oxidisable 
 metals, such as gold, silver, and copper, when exposed to the 
 action of the flame of a spirit lamp phenomena, which 
 Dr. Henry has so well studied. These metals, and especially 
 copper, are very rapidly reduced to powder, by the suc- 
 cession of alternate oxidations and reductions which they 
 undergo.* 
 
 Let us now return to phenomena of electrolysis properly 
 so called, and see how the property, which we have been 
 recognising in platinum, and studying, may account to us for 
 the anomalies, that have induced several physicists to conceive 
 that the laws, by which chemical decompositions are regu- 
 lated were at fault, and consequently were not general. 
 
 I had made a series of experiments, in which I employed 
 for electrodes plates and wires of platinum perfectly purified, 
 but of different dimensions, and as an electrolytic liquid very 
 pure sulphuric acid, diluted with nine times its volume of 
 acidulated water. The platinum plates were cleaned ac- 
 cording to the process pointed out by Faraday, which consists 
 in making them red-'hot, and rubbing them with a piece 
 of potash whilst they are incandescent, and then plunging 
 them into boiling sulphuric acid, and afterwards washing 
 / them in distilled water, constantly renewed. The 
 platinum wires were cleaned in like manner, and 
 inserted in glass tubes closed by the spirit lamp 
 (Jig. 239.), so as to present only a very small surface 
 of contact with the liquid. The plate was bent into 
 a spiral, and placed under a graduated tube filled with 
 acidulated water, and intended for collecting all the 
 l39 ' gas that is liberated. The wire was introduced into a 
 similar tube plunged into the same liquid. The communications 
 
 * The various decompositions and combinations, that are brought about by 
 platinum, especially in the state of sponge, and which have been attributed to 
 
 catalytic force those especially that have been observed by M. Kuhlmaun 
 
 appear to me to be capable of being very easily explained, by admitting an oxi- 
 dation of platinum immediately followed by its reduction. We cannot, in fact, 
 obtain these various phenomena, except so long as oxygen is present under 
 one form or another. 
 
414 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 of the plates and wire with the respective poles of the pile were 
 established by means of platinum wires 
 covered with glass tubes, so as to have no 
 points of contact with the liquid (jig. 240.). 
 The following is the result of some of 
 these experiments : 
 
 Negative plate - - 6 cub. in. of hydrogen. 
 
 Positive wire - - 3 of oxygen. 
 
 Negative wire - - 2-5 of hydrogen. 
 
 Positive plate - - '97 of oxygen. 
 
 There is wanting *28 cub. in. of oxygen, 
 which has been taken up by the plate. 
 \ In the following experiment, the plate was 
 
 3 placed immediately in communication 
 
 Fig. 240. with the positive pole, before having been 
 
 with the negative : 
 
 Negative wire - 1'22 cub. in. of hydrogen. 
 
 Positive plate - - '48 of oxygen. 
 
 13 cub. in. of oxygen taken by the plate is wanting. The 
 poles were changed : 
 
 Negative plate - '94 cub. in. of hydrogen. 
 
 Positive wire - - - '61 of oxygen. 
 
 28 cub. in. of hydrogen are wanting namely, almost 
 double and, consequently, about the equivalent of the oxygen 
 that had disappeared. 
 
 The following is another experiment, in which the plate, 
 after having been thoroughly cleansed, was put into com- 
 munication first with the positive pole : 
 
 Negative wire - - 1'22 cub. in. of hydrogen. 
 
 Positive plate - '36 of oxygen. 
 
 25 cub. in. of oxygen is wanting. On changing the 
 poles : 
 
 Negative plate - '85 cub. in. of hydrogen. 
 
 Positive wire - - - *61 of oxygen. 
 
 37 cub. in. of hydrogen is wanting. There should have 
 been a deficiency of *48 cub. in., in order to represent the 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 415 
 
 equivalent of oxygen that has been taken up by the plate 
 in the previous experiment. In general, it is rarely that we 
 recover all the oxygen, that the plate has taken up, either 
 because the liquid dissolves some of it, or because there is 
 also a formation of oxygenated water, as we are about to 
 see. The oxygen that is recovered, and that is equivalent 
 to the missing hydrogen, is that which remains upon the 
 surface of the platinum. 
 
 Spongy platinum, and a long platinum wire covered with the 
 black powder, conduct themselves like the cleansed plate 
 namely, they absorb a large proportion of oxygen. In two suc- 
 cessive experiments, the long platinum wire gave only 5 mea- 
 sures of oxygen against 20 of hydrogen, liberated on the short 
 wire : 5 of oxygen were therefore wanting ; 4 were recovered 
 by changing the poles, for we had then no more than 12 
 hydrogen against 10 oxygen a proof that 8 hydrogen had 
 been absorbed. 
 
 Sometimes it would seem that a small portion of the oxide 
 of platinum is dissolved, when the surface of the platinum, 
 upon which it is formed is pulverulent, as when the acid is 
 concentrated on boiling. 
 
 We have said that a portion of the gas is dissolved in the 
 electrolytic liquid. But this solution is far from being the 
 cause of the alterations in the proportions of gases liberated ; 
 indeed, when two platinum electrodes do not change functions, 
 and always continue to be, one the positive electrode, and 
 the other the negative, we find, after we have made allow- 
 ance for the oxygen, that is absorbed by the former at the 
 commencement, that the gases finish by being liberated in 
 the proportions that constitute water, even when the electro- 
 lytic liquid is renewed around the surface of the two 
 platinums. Moreover, the secondary polarities that are 
 acquired by the platinum plates, and which they preserve 
 entire, on being transported into another liquid, are a proof, 
 that the gases have remained adhering to their surface at 
 least, the oxygen ; for it might be that the property acquired 
 by the negative plate is less due to the gas remaining 
 adhering to its surface than to the state of purity, to which 
 
416 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 it has been brought by the liberation of the hydrogen, that 
 takes place upon it. We shall see this when, in the study of 
 the sources of electricity, we are engaged with the currents 
 produced by secondary polarities. With regard to the ad- 
 herence of the oxygen, we have seen that it cannot be simply 
 physical, as several physicists have admitted, but that it 
 is rather a phenomenon of that superficial oxidation of which 
 chemistry presents us with a great number of examples ; 
 since we are unable to explain the disaggregation of the rnetal, 
 if a series of oxidations and reductions are not brought about. 
 Moreover, we shall see further on, that in these cases the 
 oxygen is in a peculiar state, which renders it more sus- 
 ceptible of attacking the platinum.* 
 
 The details, into which we have been entering, enable us 
 now to explain the numerous anomalies that have presented 
 themselves to several physicists, in the employment of volta- 
 meters with plates and wires of platinum. Faraday had 
 already pointed out the errors that might be committed 
 in making use of this instrument, and the precautions 
 to be taken in order to avoid them. More recently Mr. 
 Gassiott made several experiments with three voltameters, 
 
 * M. Schoenbein indeed has maintained that there has been no oxidation 
 either of platinum or gold , but that there has been simply an adherence of 
 oxygen to the surface of the metal. He supported his opinion on the facts, 
 that the appearance of the metal does not change, that it does not lose a fraction 
 of its weight at all in proportion to what it ought to lose, when the supposed 
 layer of oxide is removed. Finally, he explains the disaggregation of the 
 electrodes by a mechanical transport of particles analogous to that which takes 
 place in the experiment with charcoal points. To these objections we may 
 reply, first, that there is no transport of particles, since, on taking for electrodes 
 a wire of gold and a wire of platinum, we never find the divided gold except 
 upon the gold wire, and the divided platinum except upon the platinum wire ; 
 moreover, the conditions favourable to the production of the pulverulent layer 
 are precisely the converse of those which physical disaggregation would require 
 namely, the absence of decomposition of the liquid, and a higk electric tension. 
 With regard to the appearance of the oxidised metal, it is true, especially in the 
 case of platinum, that it differs but little from that of the pure metal ; but it is 
 the same with many other metals, when we are concerned with only a thin film 
 of the sub-oxide, which, for the white metals especially, merely tarnishes their 
 surface. Finally, it is well known by all chemists that their platinum crucibles 
 end by being altered by the action of boiling nitric and sulphuric acids. We 
 may even see, by leaving a morsel of spongy platinum for some days in a 
 vessel filled with perfectly pure nitric acid, and hermetically sealed, that this 
 acid acquires a colour which indicates the presence of nitrous acid, and con- 
 sequently the oxidation of the platinum at the expense of the oxygen of the 
 nitric acid. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 4 17 
 
 whose electrodes were wires and plates of platinum of 
 different dimensions, and which he filled either with distilled 
 water, or with a solution of sulphuric acid. On placing them 
 one after the other in the circuit, he remarked that the one with 
 short wires always gave a proportion of gas a little higher than 
 the other two. M. Poggendorff in order to collect the gases 
 separately, and in order at the same time not to diminish too 
 much the force of the current, by thrusting the glass tubes 
 that collect them down into the electrolytic liquid, contrived a 
 voltameter, in which the two graduated tubes that collect one 
 the oxygen, the other, of double the section, the hydrogen, are 
 prolonged below by a cylinder of porous clay ; the two cylin- 
 ders are fixed vertically at the bottom of a glass vessel filled 
 with acidulated water, and the platinum electrodes are sealed 
 to the bottom of the vessel so as to penetrate, one into one 
 of the porous cylinders, the other into the other ; and they 
 come out exteriorly, in order to be placed in communication 
 with the poles of the pile. In this manner, not only are 
 the gases prevented from mixing, but the mixture of the 
 liquids is also avoided, which, in contact with each of the elec- 
 trodes, hold more or less in solution a portion of the hydrogen 
 and especially of the oxygen ; and there is thus no recompo- 
 sition between these two gases. 
 
 This last precaution is the more necessary, as M. Jacobi 
 has in fact remarked that the recomposition of the mixed gases 
 takes place, even when the platinum electrodes do not come out 
 of the liquid, as soon as there is above them a tube filled with 
 the gaseous mixture, which is probably dissolved in proportion 
 as that which is already beneath them disappears under the 
 influence of the platinum, to re-form water. If the acids 
 employed are very pure, and the electrodes perfectly clean, at 
 the end of some hours, the combination is entirely brought 
 about, and there remains no gas; the recomposition takes 
 place still more rapidly when the surface of the platinum is 
 pulverulent. 
 
 Temperature appears to diminish this facility of the gases 
 liberated in the voltameters combining. This explains why M. 
 Soret, on taking two voltameters perfectly similar, placed one 
 
 VOL. II. E E 
 
418 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 after the other for the same time in the same circuit, but one 
 remaining cold and the other heated in a boiling vapour 
 bath, constantly found that the heated one liberated a little 
 greater proportion of gas. As soon as he allowed it to cool, the 
 difference disappeared ; the latter was constantly 2 J per cent. 
 In these experiments, the cold voltameter was kept in a mixture 
 of ice and sea- salt. M. Soret determined the proportion of 
 gaseous mixture, either by measuring it directly, or by dosing 
 the hydrogen, as in an organic analysis ; and by the two pro- 
 cesses he arrived at the same result. 
 
 The difference, that we have just been pointing out, may be 
 due to two causes ; first, to the fact that oxygen, liberated at a 
 low temperature, combines more easily with hydrogen, which 
 causes the recomposition of the gases to be greater ; then, to 
 a formation of a bi-oxide of hydrogen, which does not take 
 place at an elevated temperature. M. Meidinger has indeed 
 observed, on employing for electrodes platinum plates 1*5 in. 
 in length by 1*29 in. in width, and a solution of sulphuric acid 
 of a density of 1 '3, that the proportion of oxygen liberated is 
 inferior to that of hydrogen at the ordinary temperature, 
 and is slightly superior to it at an elevated temperature. 
 This influence of temperature is the more marked, as the 
 electric current is more intense. The hydrogen remains in 
 general tolerably constant, as well when the acid solution is 
 more or less diluted, as when its temperature is caused to 
 vary ; it is the quantity of oxygen that is generally less as 
 the solution is more concentrated and colder. M. Meidinger 
 had concluded from these various observations that, in the elec- 
 trolysis of acidulated water, there is formed bi-oxide of hy- 
 drogen at the positive electrode. This conclusion is found to 
 be confirmed by the fact that the acid solution acquires the 
 property of decomposing iodide of potassium, a property pos- 
 sessed by oxygenated water; as well as by the faculty, 
 possessed by the positive electrode, of liberating pure oxygen 
 when, after having allowed the decomposition of the dilute 
 acid to go on for a long time, this electrode is left in the 
 liquid ; but which it loses, as soon as it is transported into 
 another liquid. Now, as we know that platinum, which has 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 419 
 
 served as a positive electrode for decomposing acidulated 
 water, decomposes oxygenated water by its contact with it, this 
 experiment is a proof of the presence of this compound in the 
 liquid. We may moreover further prove it by heating the 
 acidulated water; we then see an abundant liberation of 
 oxygen arising from the decomposition of the oxygenated 
 water, and this water loses by this the property of reacting 
 upon iodide of potassium. M. Meidinger has remarked also 
 that the oxygenated water, by diffusing itself in the electro- 
 lytic liquid, is able to react upon the hydrogen, liberated at 
 the negative electrode, especially when this electrode has a 
 large surface. Thus two identical voltameters having been 
 filled, one with perfectly pure acidulated water, the other with 
 electrolysed water, namely, charged with oxygenated water, 
 only 14*27 cub. in. of hydrogen were found in the latter 
 voltameter, whilst there were 14'64 in the former. It was 
 merely necessary to introduce the platinum plate, which has 
 been employed as a positive electrode, into the liquid in the 
 tube, in which the hydrogen is liberated, in order to see the 
 volume of gas gradually diminish, in consequence of the 
 action exercised upon it, under the influence of the platinum, 
 by the oxygenated water formed during electrolysis. We 
 may add, that a low temperature and a small dimension of 
 the positive electrode favour this formation of oxygenated 
 water. 
 
 It follows, from the analysis that we have been making, and 
 in particular from the labours of M. Meidinger, that, in order 
 to obtain exact results with the voltameter, it is necessary 
 to measure the hydrogen arising from electrolysis, and not 
 the oxygen or the gaseous mixture; that we should employ, 
 especially for liberating hydrogen, electrodes with small 
 surfaces ; that we must take this precaution of changing the 
 acidulated water of the voltameter after each experiment, or 
 at least of heating it so as to relieve it of all the oxygenated 
 water, that it may contain. 
 
 Without detaining ourselves with other experiments of the 
 same kind, we shall confine ourselves to relating, in addition, 
 those by which M. Despretz, by operating on a large scale 
 
 E E 2 
 
420 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 with voltameters having platinum wires, and water either 
 distilled or acidulated to various degrees with sulphuric acid, 
 found that the quantity of gas liberated in each was, at least 
 within a hundredth part, always the same, when they were 
 placed in the same circuit for the same time. The volta- 
 meters that M. Despretz employed, had as electrodes pla- 
 tinum wires *47 in. distant from each other ; he had commenced 
 by filling three of them with water, acidulated to ^ -$, and 
 Y-J-O with sulphuric acid. In 8 minutes he obtained in each, 
 with 12 Bunsen's pairs, 1'09 cubic inches of gas. On re- 
 placing the water that contained -j-J-g- of sulphuric acid by 
 distilled water, he obtained with 300 Bunsen's pairs *903 
 cubic inches in each voltameter, except in that filled with 
 distilled water, where there was a volume a little more con- 
 siderable. The mean of four experiments, made with only 
 two voltameters, filled the one with pure water, the other with 
 acidulated water, gave him in 45 minutes '6127 cubic inches 
 in the pure water, and *6156 cubic inches in the acidulated 
 water. It is true that the temperature of the distilled water 
 rises considerably, even to twenty times more than that of 
 water, which contains only -joVo f sulphuric acid. This 
 explains why the gaseous volume in it is slightly more con- 
 siderable, the gas not being able to dissolve so easily in it. 
 Moreover the decomposition of distilled water presents other 
 peculiarities; all the water (more than 61 cubic inches in 
 M. Despretz's experiments) became frothy and whitish, 
 which is due to the great dissemination of the gaseous mole- 
 cules, whilst water acidulated to 20 \ 09 as well as to ^ remains 
 perfectly transparent, and the liberation of the gas in it is 
 only manifested at the extremity of the wires, under the form 
 of a circle of bubbles ; this remarkable difference, is due to the 
 great resistance which the current encounters in its trans- 
 mission through pure water, obliging it in this case to diffuse 
 itself, and to pass by all the points of contact of the surface 
 of the wire and of the liquid. 
 
 Whatever may be the case, we see therefore that in taking 
 account of all these causes, which may disturb the manifest- 
 ation of Faraday's law, and in endeavouring to avoid them, 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 421 
 
 this law is still found exact in the decomposition of pure 
 water, as in that of acidulated water, and in the decompo- 
 sition of saline solutions.* 
 
 We have seen that the chemical affinity of the substance, 
 of which the electrodes are made, for one or other of the 
 elements of the electrolyte, is able to facilitate its decomposi- 
 tion, and consequently the passage of the current. This 
 property lias been applied with great success by M. Bec- 
 querel to the production of various compounds, arising from 
 the combination of the electrode with one of the elements 
 liberated by the current, compounds which he has suc- 
 ceeded in obtaining in the crystalline state, by employing 
 only very small electric forces, that is to say, that of a single 
 pair. He has in like manner obtained very remarkable 
 
 * M. Foucault thought he had found a proof of the existence of the physical 
 conductivity of liquids, in the fact that of two voltameters with platinum 
 plates, placed in the same circuit, and charged one with distilled water, the other 
 with water acidulated with ^ of sulphuric acid, the former, in the same time, 
 gave only -061 cuh. in. of gas, and the latter -61 cub. in. But this difference, 
 in every case much too great, is due to the electrodes in each voltameter 
 being formed of a bundle of platinum plates well arranged, maintained at per- 
 haps T go in. from each other, and, by an arrangement of conductors, brought 
 into electric states, alternately opposed. It followed from this arrangement, 
 first, that the oxygen and hydrogen, being very near at the moment of their 
 liberation, ought to recombine with each other, the more easily as they are 
 disseminated over the entire surface of the electrodes, in distilled water, on 
 account of its imperfect conductibility, as we have just seen in the case of M. 
 Despretz's experiments. But, further, this same imperfect conductibility of 
 water, joined to the very great approximation of the platinum plates, alternately 
 positive and negative, caused the greater proportion of the t\vo electricities to 
 reunite between these plates under the form of the voltaic arc, and not electro- 
 lytically, as takes place through air and through liquid non-conducting bodies. 
 We have in fact seen that M. Despretz, on operating so as to avoid these 
 disturbing effects, has found that distilled water, like acidulated water, obeyed 
 Faraday's law of equivalents. 
 
 To these indirect proofs in favour of the opinion that electrolytic liquids do 
 not possess a physical conductibility analogous to that of solids, but that they 
 can only propagate currents while being decomposed, a new and more direct 
 proof has just been added ; Mr. Faraday having proved the possibility of 
 producing, by the action of an electro-magnet, an inductive current in a long 
 column of acidulated water, contained in a tube of gutta percha, coiled as a 
 helix around the electro-magnet. MM. Logeman and Van Breda have ob- 
 served that the platinum plates or wires, by which this current is collected, 
 are polarised ; which proves that the acidulated water has been decomposed 
 by the induced current. Now, if the propagation of the current can be brought 
 about in an electrolytic liquid by way of physical conductibility, it must be in 
 the case of a current induced in the liquid by an exterior current ; and yet, 
 even in this case, the propagation is accompanied by a decomposition. 
 
 E E 3 
 
422 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 secondary products by employing compound electrodes, and 
 bringing about the combination of the elements, liberated by 
 the current with one of the elements of this compound 
 electrode. In a word, he has turned to account the chemical 
 reactions that may arise from the liberation by the current 
 of a body in the nascent state upon the surface of contact of 
 a solid and a liquid. 
 
 It is not only by employing electrodes susceptible of 
 entering into combination with the elements of the electro- 
 lytic liquid, or of being decomposed by them, that their de- 
 composition may be facilitated. Grove, E. Becquerel, and 
 Schoenbein have succeeded in obtaining the same result, 
 still retaining electrodes of platinum, but dissolving in the liquid 
 substances, which had affinity for one or other of its ele- 
 ments. Thus Grove has obtained, with the current of a single 
 pair, the decomposition of water, by arranging the platinum 
 positive electrode so that the portion that came out of the 
 water was placed in a tube filled with hydrogen, which was 
 itself in contact with the electrolysed acidulated water. The 
 decomposition was facilitated by the affinity that hydrogen, 
 under the influence of platinum, exercises over the oxygen 
 of the water. E. Becquerel has succeeded, in like manner, in 
 decomposing water by a feeble current, by dissolving in 
 it either substances greedy of hydrogen, such as chlorine, 
 bromine, and iodine, bi-chloride of copper, or salts whose 
 bases are able to peroxidise, such as sulphate of peroxide of 
 iron, which tends without ceasing to take oxygen from bodies 
 that contain it. On placing in the same circuit a volta- 
 meter with ordinary acidulated water, and these various 
 solutions, we obtain in the solutions proportions of oxygen and 
 hydrogen variable with each of them, and even with the 
 rapidity of decomposition, in consequence of the greater or 
 less facility with which the oxygen or hydrogen combine 
 with the substances dissolved. M. E. Becquerel found, on 
 employing spongy platinum and gold for one of the electrodes, 
 the other being a plate of platinum, that decomposition was 
 facilitated, but that a great proportion of the gas was absorbed 
 by that electrode which was made with the sponge. This is 
 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 423 
 
 always a consequence of divided platinum. M. Schoenbein 
 had already employed spongy platinum as the positive elec- 
 trode for combining the oxygen, arising from the water con- 
 tained in alcohol, with this latter substance, and thus 
 forming a more oxygenated product. He had in like manner 
 succeeded in obtaining a more easy decomposition, by em- 
 ploying as negative electrodes sponges of platinum, that had 
 been plunged into gaseous chlorine or bromine, and which 
 thus exercised a powerful affinity over the hydrogen. The 
 same effect is produced, and even in a higher degree, by taking 
 as a negative electrode a plate of platinum, covered with 
 a layer of peroxide of lead, the oxygen of which combines with 
 the liberated hydrogen. All these facts, and I omit many of 
 the same kind show to us the intimate relation that connects 
 ordinary chemical affinity with the chemical force of the 
 current, which, as Faraday judiciously remarks, is merely 
 the same force transported to a distance, instead of being 
 exercised only in contact. And indeed, we see, by all that 
 precedes, how its action is facilitated, when it finds the con- 
 currence of that of affinity. We shall complete the demon- 
 stration of the intimate connection, that exists between these 
 two forces, when we shall be engaged with chemical action 
 considered as a source of electricity. 
 
 There are, however, some cases that seem to form an ex- 
 ception to the general rule, that we have been laying down. 
 It is that of certain metals which, when employed in a feeble 
 degree of oxidation as positive electrodes, do not allow 
 the current to pass ; such is iron, when, as Schoenbein has ob- 
 served, it is in the state called passive, a state in which it is 
 no longer attacked by acids, and is found modified in a very 
 extraordinary manner, in its chemical properties, by the effect 
 of the presence upon its surface of a film of a peculiar sub- 
 oxide. Such again is copper, which, as Mr. Grove has ob- 
 served, oxidises and gradually dissolves, when it serves as a 
 positive electrode, in diluted sulphuric acid, to a current of 
 moderate force, but which ceases to be dissolved, and stops 
 the transmission of the current, when the latter becomes 
 very strong, which is also due to the formation of a particular 
 
424 TRANSMISSION OF ELECTRICITY. PART iv 
 
 oxide, which cannot combine with the acid. All these ano- 
 malies are rather phenomena purely chemical than electro- 
 chemical phenomena ; for they are due to the impossibility of 
 certain oxides combining with acids, in order to form salts, 
 either because they contain too much oxygen, or because they 
 contain too little. 
 
 Movements produced in electrolytic Liquids by the Passage of 
 the Current. 
 
 The movements that are the effect of the passage of the 
 current through electrolytic liquids, are of two kinds. Those 
 of the first kind are the evident result of the decomposition 
 of the liquid, and of the chemical reaction of the elements 
 separated ; those of the second are manifested by a transport 
 through a porous diaphragm of a part of the liquid, and they 
 seem to be rather a mechanical than an electrolytic effect. 
 However, even in this case, it is not enough that the liquid 
 be a conductor, as mercury would be ; it must also be an elec- 
 trolyte. We shall see to what extent this circumstance may 
 throw light upon the phenomenon. 
 
 Davy was the first to observe that globules of mercury, 
 placed between the two poles of a pile at the bottom of a 
 vessel, filled with a solution which the current decomposes, 
 elongate on the side of the negative pole, manifesting a pecu- 
 liar trembling. Herschell made a detailed study of this kind 
 of action, with which Serullas had previously been occupied, 
 connecting it with the movements, that arise from certain che- 
 mical phenomena. Finally, Nobili has more recently, by new 
 researches, completed the labours of Herschell, and found the 
 true signification of this order of facts. 
 
 Herschell had placed at the bottom of a vessel very pure 
 mercury, covered with a layer of concentrated sulphuric acid 
 about *4 in. in thickness ; and he transmitted through this 
 acid a current of a feebly charged pile. Immediately the 
 current circulates, the acid is seen to undergo a rapid rota- 
 tory motion, due to a mechanical current that is established 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 425 
 
 between the two electrodes and which traverse directly 
 the mercury ; the particles of the acid, contiguous to the 
 mercury, are those which move with the greatest rapidity. 
 It is in the mercury that the cause of the movement resides ; 
 and we have the proof of this in the fact that we have merely 
 to moisten with sulphuric acid the surface of the mercury 
 and the vessel in which it is contained, in order to obtain 
 a very rapid rotatory motion of this metal, employing this 
 same film of acid for establishing the current. We should 
 add that, when the globule of mercury is of considerable 
 thickness, it experiences a continual tendency to elongate 
 or to radiate toward the negative pole ; and when it is very 
 near to it, it reaches it and amalgamates with it. If it is 
 small, its whole mass is set in motion with a very great 
 rapidity, as if it were attracted by the negative wire. This 
 apparent attraction is frequently very energetic, the globule 
 moving with a great vivacity toward the negative wire, 
 to which it adheres as soon as it comes into contact with 
 it. The same effects may be obtained by substituting for 
 sulphuric acid other electrolytic liquids, such as acids more 
 or less concentrated, saline solutions of various kinds ; but 
 the intensity of the movement varies with the nature of the 
 liquid. The mercury must in all cases be very pure ; and 
 there are generally observed currents, more or less violent, 
 which radiate from the point nearest to the negative pole. 
 With certain liquids, and especially the nitrates, there is 
 also formed a current radiating from the positive pole, which, 
 in some cases, even surpasses the other. These two currents 
 coexist in the mercury, and in consequence of their action, 
 there is formed in the globule of mercury a zone of equili- 
 brium nearer to one pole than to the other, according as 
 the current is more or less violent. On operating by means 
 of an energetic pile, and with a great quantity of mercury, 
 placed below very diluted solutions, we perceive in almost 
 all cases these counter-currents, which come from the posi- 
 tive pole, especially if care is taken to keep this pole near 
 and the negative pole far from the globule of mercury. 
 
 The experiments may be varied, by placing one of the 
 
426 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART iv. 
 
 poles immediately in contact with the mercury, whilst the 
 other is alone plunged into the electrolytic liquid. Very 
 sensible currents are obtained, which radiate from the pole 
 placed in this latter liquid : when it is the positive pole 
 that is in contact with the mercury, these currents are less 
 sensible on account of the promptitude with which the 
 surface of the metal oxidises; but, by the agitations of the 
 mercury, we detect the existence of currents beneath the 
 film of oxide : moreover, on preventing the oxidation by a 
 few drops of weak nitric acid, we see the currents established 
 in this case as well as in the other. 
 
 The influence of this formation of an oxidised film over *the 
 movements, seems at once to show that these effects are not 
 the simple result of a mechanical action, but that an electro- 
 chemical phenomenon also takes place in them. This con- 
 sequence, confirmed by other experiments of Herschell him- 
 self, to which we shall return, was completely confirmed by 
 the analysis that Nobili made of these phenomena, con- 
 necting them with the formation of electro-chemical appear- 
 ances. The learned Italian confines himself to substituting, 
 in the apparatus that we have described *, for the metal plate 
 a surface A B (fig. 241.), of very pure mercury, two or three 
 
 Fig. 241. 
 
 inches in diameter, which he covered with a solution of 
 
 sulphate of soda, forming a layer about a quarter of an inch 
 
 * Vol. II. p. 399. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 427 
 
 in thickness, into which are plunged two platinum points, in 
 communication with the pole of a pile of moderate force, so 
 as merely to leave between them and the surface of the 
 mercury as small an interval as possible. The formation of 
 two systems of currents is immediately perceived, terminated 
 by limits that correspond with the shape of the ordinary 
 electro-chemical appearances. These limits consist of two 
 lines ri, n' y n", and p' } p', p", on oval bands, within which 
 the mercury is a little more depressed than it is without : the 
 former is formed above the negative point, and the latter 
 above the positive. In the middle, at o, o, the mercury 
 presents one or two lines, where its surface appears to be agi- 
 tated as by the conflict of two opposite currents, a circum- 
 stance which, joined to those that we have already mentioned, 
 clearly proves that the seat of the movement is at the surface 
 of the mercury, and that the electrolytic solution merely 
 follows the movement, impressed upon the particles of this 
 metal. There is almost always formed at p a little oxide, 
 which is carried by the currents outside toward the border, 
 where it more or less accumulates ; then it expands toward 
 the negative side, which absorbs and reduces it, when the 
 currents on this side are weakened to the point of no longer 
 preventing its expansion. The negative currents disappear 
 at the same time as the oval n, n/ n' 9 as soon as the film of 
 oxide is thrust by the positive currents beyond their ordinary 
 limits. We have merely to oppose an obstacle to the ex- 
 pansion of this film, by means of a small plate of glass thrust 
 in at o, o, to the surface of the mercury, in order to see the 
 currents maintain themselves at n, and the film of oxide in- 
 crease at p 9 so as to acquire sufficient consistence to destroy 
 the positive currents; but, if the plate is removed before the 
 oxidation is well advanced, the pellicle of oxide is seen to break 
 into several fragments, the innermost of which expand toward 
 the negative side, where they are absorbed and reduced, 
 which weakens the negative currents, and at the same time 
 revives the positive. 
 
 When other solutions are substituted for the solution of 
 sulphate of soda, we obtain, according to the nature of the 
 
428 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 solutions, either the two systems of radiating currents, or 
 simply a single one ; sometimes one, at other times the other. 
 The cause of these differences is due to the circumstance 
 that the elements which become deposited upon the secondary 
 poles, formed by the mercury, cover its surface with a thin 
 film, or leave it clear of all apparent deposit. Thus, there are 
 no negative currents with solutions of salts with a base of 
 copper, silver, tin, or bismuth, because the bases are reduced 
 upon the mercury, and present to the eye films more or less 
 consistent; whilst these same currents are very active with 
 solutions of alkaline or earthy salts, the metals of which, in 
 depositing, leave the mercury equally liquid and brilliant. 
 The positive currents are in like manner wanting, whenever 
 oxygen and acids are deposited in thin films upon the surface 
 of the mercury ; whence it follows that the currents may be 
 said to be formed, only where the films, that bring about the 
 electro-chemical appearances, are wanting. 
 
 The superposed liquids only follow the movement im- 
 pressed upon the molecules of mercury. It is necessary, there- 
 fore, in order to appreciate the rapidity of their displacement, to 
 take account of the degree of mobility that they possess upon 
 the surface of this metal ; but we must not forget that the 
 vivacity of the movements of the mercury itself is due to 
 the nature of these liquids, since it is an effect of their de- 
 composition. Sulphuric acid, the drops of which, as we 
 know, extend over mercury with an extraordinary rapidity, 
 is of all the one that possesses the property in question in 
 the most eminent degree. The most feeble electric force, 
 such as that resulting from a pair formed by the mercury 
 itself, the sulphuric acid, and an iron wire plunged into it, 
 is sufficient to bring about the phenomenon.* 
 
 * The following is the process adopted by M. Nobili. He plunges a drop of 
 mercury into a bath of sulphuric acid, and touches it towards its edge with the 
 extremity of an iron wire ; the drop immediately contracts and ceases to touch 
 the iron ; then, resuming its natural form, it comes anew to meet the iron 
 point, to contract and again to expand ; thus continuing an alternate motion 
 of contraction and dilatation so long as the voltaic action of the three elements 
 of the pair continues, namely, mercury, iron, acid. This result is only effec- 
 tively obtained by employing iron or other easily oxidisable metals : the con- 
 tact of gold or of platinum does not produce any effect. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 429 
 
 The experiment may be made under a very remarkable 
 form, and which requires only a very feeble pile. We take 
 a mass of mercury, to which we endeavour to give a very 
 circular form of about an inch in diameter, and cover it 
 with a very limpid alkaline solution. A platinum point, 
 communicating with the negative pole of the pile, is placed 
 above the centre of the drop of mercury so as to touch its 
 surface slightly ; a second similar point, to which the positive 
 pole is connected, is plunged into the solution over the 
 figure of the mercury, at a distance of nearly half an inch 
 from its outer edge. As soon as the circuit is established 
 the mercury flattens notably, and appears under the form 
 of a star, with four blunt points, one of which reaches and 
 touches the positive wire ; immediately this contact takes 
 place the mercury returns upon itself, rising toward the 
 negative point, which it touches afresh, then it flattens, and 
 so on in succession. In its return movement, the circular 
 drop again presents itself under the aspect of a star, the 
 obtuse points of which are found where the intermediate 
 spaces of the former were. 
 
 The effects, that we have been describing, already tolerably 
 complex, become still more so, when the mercury is alloyed 
 with a very oxidisable metal. Sodium, in particular, by its 
 amalgamation with mercury, brings about still more decided 
 movements than other metals of the same kind, although all 
 those that are oxidisable possess more or less the same property. 
 Herschell and Nobili have successively studied with care this 
 influence of metals, which had moreover been already pointed 
 out by Ermann, Pfaff, and Serullas ; this latter chemist had 
 observed it directly, without the assistance of the pile. He 
 had endeavoured to analyse the singular gyratory motions 
 acquired by the alloys of potassium with different metals, 
 when they float in small fragments upon mercury under water ; 
 those produced by the alloys of potassium and bismuth had 
 appeared to him particularly energetic and durable. 
 
 It is evident that, in the experiments of Herschell and 
 Nobili, which we are about briefly to relate, the effects due 
 to the presence of sodium or of similar metals, derived from 
 
430 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 electrolysis, are only secondary, since they may be obtained 
 by alloying the mercury directly with these metals ; but as 
 they combine with the more direct effects of the current, 
 they must be analysed, in order that we may give a good 
 account of these latter. 
 
 The most simple manner of manifesting this order of phe- 
 nomena consists in plunging in mercury (fig. 242.), when 
 
 Fig. 242. 
 
 it is covered with sulphate of soda, the negative point, so as 
 to have at n n r ri f a single negative point above the positive 
 point. This simple immersion revives the negative cur- 
 rents, due essentially to the liberation of sodium, which 
 unites with the mercury ; a contact of a minute is sufficient to 
 charge the amalgam with as much sodium as is necessary 
 for producing the following effects. At the moment when 
 the negative point is withdrawn from the mercury, the posi- 
 tive currents are seen to disappear around the point p ; on the 
 contrary, a system of currents is observed which converges 
 rapidly, from all points of the circumference of the mercury, 
 towards the centre. These currents have different velocities 
 which inflect the spot at A; the latter has in front of it a line or 
 band m m m more or less vivid, which advances towards the 
 point n in proportion as the motion diminishes, and ends by 
 forming the dotted oval around this latter point, when, the 
 sodium being all oxidised, the phenomenon returns to its 
 primitive state. 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 431 
 
 The essential point, that was remarked by Herschell and 
 confirmed by Nobili, is the inversion of the motion at the spot 
 of the positive currents, produced by the presence of the sodium 
 in the mercury. M. Nobili attributed it to the circumstance 
 that the sodium, which has a powerful tendency to unite with 
 the oxygen and acids, that are found in a nascent state at p p f 
 and p", travels rapidly thither, and thus brings about a very 
 rapid system of current, directly opposed to the radiation, that 
 takes place when the mercury, being deprived of this emi- 
 nently oxidisable metal, has nothing else to do than to pro- 
 pagate from the centre to the circumference the impulse, 
 which it receives from the oxygen and the acids liberated. 
 
 Whilst a part of the sodium arrives from all sides to be 
 converted into alkali, under the influence of the oxygen, the 
 mercury itself receives at n n and n" another part of the 
 sodium, which produces the ordinary negative currents ; but, 
 on account of the movements brought about by the sodium 
 already present, the ordinary shape of the negative appear- 
 ance is deformed and elongated to the extent of being trans- 
 ported from the interior side to m m m, which at the same 
 time causes the other depression p p f p" to incline notably 
 towards A. The latter rises and re-forms itself around 
 its centre in proportion as the motion is weakened by the loss 
 of sodium, that is suffered by the amalgam. When the oval 
 reappears around the point n, it is a sign that the oxygen of 
 the positive spot has no longer any sodium to oxidise ; it then 
 attacks the mercury and covers it again with a film, which 
 soon prevents all movement. 
 
 We shall not insist upon the effects, that are obtained by 
 plunging into amalgams, covered with an electrolytic solution, 
 a wire of copper or of platinum, because these are effects of 
 the same kind as the preceding, seeing that thus a voltaic 
 pair is produced ; nor shall we dwell upon the numerous ex- 
 periments of Herschell, made with various amalgams and dif- 
 ferent solutions, because they are the same phenomena, and 
 with nearly the same intensity. We shall confine ourselves 
 to two remarks. The first consists in pointing out this curious 
 property of a very oxidisable metal, amalgamated with mer- 
 
432 TRANSMISSION OF ELECTRICITY. PART iw 
 
 cury, of travelling, under the influence of this current, to the 
 place, where it finds oxygen and an acid, with which it can 
 combine. We shall return to this when occupied with 
 the electricity, liberated in voltaic pairs, of which one of the 
 elements is an amalgam. The second remark is, that the 
 movement of the mercury in the ordinary case is evidently due 
 to the absorption, that it exercises over the elements, that are 
 deposited upon its surface by electrolysis ; not only over oxy- 
 gen on the one hand, and over sodium and other metallic 
 bases on the other hand, but also over hydrogen, of which we 
 shall see proofs further on. And indeed, as soon as these ele- 
 ments cease to be absorbed, but remain upon the surface, the 
 movement ceases. With regard to the movements themselves, 
 they are not a mechanical effect of the current, analogous to 
 the electro-dynamic phenomena of repulsion and attraction ; 
 for the strongest magnets do not modify them, whilst, as 
 we know, they bring about energetic rotations upon mercury, 
 which simply transmits currents, without the intervention of 
 any electrolytic liquid. These movements, therefore, are the 
 results of purely chemical actions; they are analogous 
 to those which are produced in a host of combinations, in 
 which the bodies are mobile, either on account of their being 
 liquids, or, although solids, on account of their floating upon a 
 liquid, as sodium and potassium, or being able to glide along a 
 smooth plane, as globules of tin or iron in ignition. The 
 effect of the current in the phenomena, that have been en- 
 gaging our attention, is simply to impress a direction upon 
 these movements, because it impresses one upon the chemical 
 action, by transporting by electrolysis, into determinate 
 points, the elements among which it is exercised. 
 
 The movements of mercury, again, may be produced in a 
 remarkable manner, by means of a succession of instanta- 
 neous currents, determined alternately in contrary directions, 
 such as those obtained by induction with Saxton's machine. 
 One of the ends of the induced wire is put into communica- 
 tion with mercury placed in a cylindrical capsule, and the 
 other, with a platinum point, plunged in an electrolytic solu- 
 tion, such as sulphuric acid, diluted with nine times its 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 433 
 
 volume of water, which covers the surface of the mercury, so 
 as to be -^ or ^ of an inch distant from it, and to correspond 
 with its centre. As soon as the currents pass, the mercury is 
 seen to be agitated, and to assume a vibratory motion with 
 undulations, setting out from the centre, and the circular, 
 elliptical, or polygonal form of which depends upon the shape 
 of the vessel. 
 
 A very curious effect also is obtained, by placing mercury 
 in a tube, bent into the form of an inverted syphon, and 
 making one of the vertical columns communicate with the 
 negative pole of a pile, whilst the positive is plunged in an 
 electrolytic solution, which covers the summit of the other ; a 
 depression is produced in this latter column and conse- 
 quently a difference of level, between the two columns of 
 mercury, which is greater or less according to the intensity 
 of the current.* It would seem that there is in this case a 
 phenomenon analogous to what is presented by the voltaic 
 arc, when mercury is taken for the negative electrode ; how- 
 ever, as the effect is able to be produced by a very feeble 
 current, it is probable that it is, like the preceding, purely 
 electro-chemical. 
 
 I will not dwell further upon the class of effects, that I 
 have just described, and to which a greater degree of im- 
 portance had generally been assigned, than they really merit. 
 They may at the most be considered as connected with the 
 part played by mercury in electro-chemical phenomena ; a 
 
 * Gerboin, in 1801, was the first to point out these movements. He operated 
 with a tube bent in a U form, 01 an inverted siphon ; the tube was filled with 
 mercury to half the height of its vertical branches ; the surface of the mercury 
 at the summit of each column was covered with a stratum of water, into which 
 were plunged two wires, that communicated respectively with the poles of the 
 pile. It is especially on the surface of that column of mercury which, being 
 beneath the positive pole received the hydrogen arising from the decomposition 
 of the water, that he perceived movements, which were manifested by the ten- 
 dency of small light bodies thrown into it, to move from within outwards upon 
 the surface of the tube. But, if the positive point were made to touch the 
 mercury, the movement of the small light bodies immediately took place in the 
 contrary direction, namely, from the circumference to the centre ; the mercury 
 appeared also to be depressed beneath the positive point, when this point was 
 very near to it. 
 
 No effect took place upon the surface of the mercury, placed beneath the 
 negative point ; it was merely oxidised. 
 
 VOL. II. F F 
 
434 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 very singular part, it is true, in cases of amalgamation, and 
 to which, as I have said, we shall have occasion to return, but 
 which is, nevertheless, of very limited interest, in consequence 
 of its special character. 
 
 The second species of movement, that we have pointed 
 out at the commencement of this paragraph, consists of a 
 transport, that is brought about through a porous diaphragm 
 of a liquid traversed by the current. Porret, who was the 
 first to observe it, made the experiment by separating a cup 
 into two compartments, by means of a diaphragm of bladder, 
 and placing common water in each, with the positive pole of 
 a pile in one of the two, and the negative in the other. At 
 the end of a short time, the water is seen to pass through the 
 bladder, the resistance of which it surmounts, from the posi- 
 tive compartment into the negative, where it retains itself 
 at a more elevated level. The phenomenon is very decided, 
 only so long as the liquid is an imperfect conductor, like 
 unto pure water ; with acidulated water it no longer takes 
 place. M. Becquerel has obtained a phenomenon of the same 
 kind with two tubes half-filled with clay and with water ; the 
 lower mouths of which, being closed by plugs pierced with 
 small holes, were plunged into water, whilst the interior 
 liquids of each tube were placed respectively in communica- 
 tion with each of the poles of a pile, by means of platinum 
 plates. The clay was driven from the tube, into which the 
 positive pole was thrust and not from the other. 
 
 It follows, from these experiments, that there is a very de- 
 cided tendency of a liquid, traversed by a current, to travel 
 from the positive pole towards the negative, provided it 
 presents a certain resistance to the passage of the current. M. 
 Wiedemann succeeded, after very accurate researches, in 
 discovering the laws of this phenomenon. In a first series of 
 observations, his object was to determine the relation of the 
 intensity of the voltaic current to the quantity of liquid, 
 transported in a given time. The liquid was contained in a 
 large glass vessel h h (Jig. 243.), and in a cylinder of 
 porous clay, a, occupying the middle of the great vessel. 
 Upon the cylinder of clay was cemented a bell-glass c, the 
 neck of which allowed of the passage of a vertical tube 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 435 
 
 Fig. 243. 
 
 furnished with a lateral escape-tube e e. At the interior 
 
 and the exterior of the clay 
 cylinder were placed two 
 platinum plates g and i, 
 coiled into a cylinder, each 
 of them communicating 
 with vertical wires f and 
 k, that might be placed in 
 communication with the 
 poles of the pile. The 
 small opening, through 
 which the wire / traversed 
 the bell-glass c, was herme- 
 tically closed with mastic; 
 the adaptation of the vertical tube d to the neck was 
 sufficiently perfect to render the escape of the liquid im- 
 possible. The cylinder of porous clay had been immersed 
 for a long time in diluted hydrochloric acid, before being 
 used for the experiment ; it was thus freed from all soluble 
 matters, that it might contain. 
 
 As soon as the current was established in the direction 
 indicated in the figure, the liquid rose in the tube d s and 
 was not long before it passed out by the lateral tube e y when 
 the level had in a slight degree surpassed the orifice of this 
 tube ; the flask I was for receiving the liquid that ran over. 
 The phenomenon was the result principally of an action 
 proper to the current, but there were also some secondary 
 causes, the influence of which it was essential to estimate and 
 to eliminate. 
 
 One might at first have feared that the pressure, resulting 
 from the elevation of the level in the tube d, might tend to 
 counteract the phenomenon, and to diminish the quantity of 
 liquid transported through the porous cylinder ; but a direct 
 experiment showed that there was no foundation for this 
 fear. The apparatus was filled with water, so as to establish 
 in the tube d an elevation of level, equal to the elevation 
 observed ; and the experiment was left to itself for several 
 hours, without making any current pass. The level having 
 
 F F 2 
 
436 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 remained invariable, it was concluded that the pressure 
 exercised was not sufficiently powerful to cause any appre- 
 ciable quantity of water to pass through the diaphragm. 
 
 At the commencement of the experiment, the elevation 
 and the escape of the liquid were due in part to the bubbles 
 of hydrogen liberated upon the negative plate, which came 
 and lodged themselves in the various parts of the apparatus ; 
 but, at the end of a few moments, the accumulation of gas 
 attained its maximum, and the new bubbles formed were 
 liberated incessantly by the tube d. Then alone were the 
 observations commenced. Evidently nothing similar took 
 place when metallic solutions were experimented upon. 
 
 Finally, if the experiment continued for a long time, the 
 intensity of the current remaining constant, the quantity of 
 liquid, escaped in a given time, underwent a little increase. 
 At the same time, the liquid, placed within the interior of 
 the porous cylinder, was disturbed by the presence of very 
 fine particles of the material of the cylinder. These particles 
 were evidently torn off by the liquid from the pores of the 
 diaphragm ; these pores must therefore have become larger, 
 and hence arose the increase, that was observed of the liquid 
 current. 
 
 The current was produced by a DanielPs pile, and 
 measured by a tangent- compass, or by a galvanometer, com- 
 pared directly with the compass. 
 
 The two following tables demonstrate, in an evident 
 manner, that the quantities of liquid, transported in equal times, 
 are proportional to the intensities of the currents. 
 I. DISTILLED WATER. 
 
 Quantity g of Liquid 
 transported. 
 
 Intensity z of the 
 Current. 
 
 Relation ^. 
 
 grs. 
 
 
 
 1777 
 
 14-4 
 
 1-23 
 
 13-26 
 
 10-8 
 
 1-23 
 
 10-59 
 
 8-3 
 
 1-27 
 
 7-46 
 
 6-0 
 
 1-24 
 
 5-89 
 
 4-8 
 
 1-23 
 
 4-47 
 
 3-6 
 
 1-24 
 
 3-38 
 
 2-9 
 
 1-17 
 
 
 
 Mean 1'23 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 437 
 
 II. SULPHATE OP COPPER. 
 
 9- 
 
 i. 
 
 f 
 
 grs. 
 
 
 
 2-48 
 
 10-6 
 
 0-234 
 
 2-32 
 
 10-1 
 
 0-230 
 
 2-26 
 
 98 
 
 0-231 
 
 2-11 
 
 9-3 
 
 0-226 
 
 1-49 
 
 6-5 
 
 0-229 
 
 1-25 
 
 5-35 
 
 0-233 
 
 
 
 Mean 0-230 
 
 M. Wiedemann has also found, on covering successively 
 various portions of the surface of the cylinder with a coating 
 impermiable to the liquid, and a non- conductor of electricity, 
 then by gradually diminishing its thickness, that the quantities 
 of liquid, transported by a galvanic current, through a porous 
 partition, are independent of the extent of this partition and 
 of its thickness. He found no law, by which the quantity 
 transported is connected with the resistance of the liquid ; 
 but he has remarked, as I had observed in 1825, that very 
 good conducting liquids, such as diluted sulphuric acid, are 
 not transported in any appreciable proportion. 
 
 The experiments, that have just been described, were 
 subject to a very grave objection ; in fact, they only mea- 
 sured a complex phenomenon, produced by the combination 
 of two causes, altogether different, namely, the action 
 proper of the current, and the friction of the liquid in the 
 pores of the diaphragm. This latter cause evidently allowed 
 of no comparability being established between the experi- 
 ments relative to different liquids. On this account, M. 
 Wiedemann has sought for a mode of experimenting, which 
 was independent of this disturbing action ; and he caught the 
 idea of measuring the hydrostatic pressure, that could cause 
 the phenomenon of transport to disappear ; and which con- 
 sequently would form an equilibrium with the action proper 
 
 F F 3 
 
438 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 of the current. The apparatus previously described was 
 consequently modified. The capillary tube 
 e, was placed in communication with a small 
 mercury manometer e, p, m (fig. 244.), and 
 the upper extremity of the vertical tube e 
 (Jig. 243.), was hermetically sealed after the 
 introduction of the liquid. Under these con- 
 ditions, the passage of the current, instead of 
 producing a constant escape of the liquid, 
 brought about a displacement of the mercury 
 in the manometer ; and this displacement was 
 stopped, when the pressure, due to the dif- 
 ference of level of the manometer in the two 
 Fig. 244, branches, was sufficiently powerful to cause 
 a quantity of liquid, equal to that, which the voltaic 
 current would draw along, to repass at each instant through 
 the pores of the cylinder. It is evident that it was necessary 
 to avoid, in this arrangement of the apparatus, all liberation 
 of gas in the tube d ; and, consequently, that we ought to 
 confine our experimenting to solutions of metallic salts. 
 Pure water, or water simply acidulated, or solutions of 
 alkaline salts, are not admissible in this kind of experiment. 
 
 Numerous experiments upon solutions, variously concen- 
 trated, of sulphate of copper, led to the following law : - 
 
 The heights to which the mercury rises, in the manometer, are 
 proportional to the intensity of the current, in inverse ratio to the 
 surface, and in direct ratio to the thickness of the porous diaphragm. 
 These results agree perfectly well with those of experi- 
 ments upon the quantities of liquid transported, if we take 
 into account the laws of the escape of liquids, by capillary tubes, 
 as they have been determined by MM. Hagen and Poisseuille. 
 We know, in fact, that the quantities of liquid, which escape 
 in equal times by very narrow capillary tubes, are propor- 
 tional to the pressure and in inverse ratio to the length of the 
 tubes. Now, a porous diaphragm may be compared to a 
 system of capillary tubes, the number of which is evidently 
 proportional to the superficial extent of the diaphragm, and 
 the length proportional to the thickness. The quantities 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 439 
 
 of liquid, transported by the voltaic current, being propor- 
 tional to the intensity of this current and independent of 
 the thickness of the diaphragm, the pressures capable of 
 producing in an inverse direction the transport of an equal 
 quantity of liquid, must be proportional to the intensity of 
 the current, and to the thickness of the diaphragm. The in- 
 fluence of the superficial extent of the diaphragm is no less 
 evident; the pressure, that brings about the passage of a 
 given quantity of liquid through a system of equal capil- 
 lary tubes, must be in inverse ratio to the numbers of these 
 tubes. 
 
 Finally, the influence of the nature of the liquid is mani- 
 fested in a very simple manner in this second class of experi- 
 ments. The height of the mercury in the manometer is pro- 
 portional to the electric resistance of the liquid. At least we 
 may conclude this from a series of observations, relative 
 to solutions of sulphate of copper, into which the current was 
 introduced by copper electrodes, so as to avoid all polarisation. 
 These observations are summed up in the following Table : 
 
 Proportion of 
 crystallised Sulphate 
 for 100 parts of 
 the Solution. 
 
 Electric Resistance 
 of the Solution. 
 
 Relation of the 
 height of the Mer- 
 cury to the Intensity 
 of the Current. 
 
 Quotients of the 
 Numbers of 
 the 3rd Col. by those 
 of the 2nd. 
 
 1625 
 9-22 
 6-6 
 3-4 
 1-3 
 
 180 
 27-0 
 32-5 
 55-5 
 
 100-0 
 
 1-35 
 
 1-98 
 2-44 
 379 
 6-80 
 
 0-0750 
 0-0733 
 0-0750 
 0-0683 
 0-0680 
 
 
 
 
 Mean 0719 
 
 The constant approximation of the number of the fourth 
 column is a satisfactory proof of the accuracy of the law. 
 In summing up all these laws we may say, that the force, with 
 which a voltaic current tends to transport a liquid through a 
 porous partition from the positive towards the negative pole, is 
 measured l>y a pressure, which is directly proportional to the in- 
 tensity of the current, to the electric resistance of the liquid, and 
 
 r F 4 
 
440 TRANSMISSION OF ELECTRICITY. PART IV. 
 
 to the thickness of the partition, and inversely proportional to the 
 surface of the partition. 
 
 M. Wiedemann remarks, that the simple laws, to which he 
 has found the mechanical actions of the current to be 
 subjected, are the same as those that have been assigned by 
 Ohm for the distribution of electricity in a closed circuit. 
 But, the question that presents itself here is to know whether 
 these mechanical actions are indeed the direct effect of the 
 current, or whether they are not an indirect consequence of an 
 electrolytic phenomenon. This latter opinion, which had 
 already been put forward by M. Raoult, at the end of experi- 
 ments, more or less doubtful, was taken up by Mr. Graham, 
 who considers that, like as in the decomposition of acidulated 
 water, one equivalent of sulphuric acid goes with the oxygen 
 to the positive electrode, whilst one equivalent of hydrogen is 
 liberated at the negative ; so, in the decomposition of pure 
 water, a basic radical composed of several atoms of water, and 
 of one equivalent of hydrogen, goes to the negative electrode, 
 whilst the equivalent of oxygen is liberated at the positive. 
 This manner of viewing the phenomenon would suppose that 
 water, when under the influence of an electric current, by 
 which it is polarised, would assume a peculiar chemical con- 
 stitution, in virtue of which a considerable, but yet variable 
 number of atoms of water, would be associated together 
 to constitute one molecule of liquid water, of which one atom 
 of oxygen would form the negative or acid radical, ana- 
 logous to chlorine, remaining apart ; whilst all the other atoms 
 would form a basic or positive radical, containing definitively 
 one equivalent of hydrogen, which is not neutralised, and 
 which gives to it basic affinity, as takes place in many organic 
 radicals. Now, it is this voluminous basic radical, which is 
 transported in the electric decomposition of pure water, and is 
 decomposed into gaseous hydrogen and into water at the nega- 
 tive electrode, producing that accumulation of water which 
 is observed ; at the same time oxygen is liberated alone at the 
 positive electrode. The porous diaphragm is necessary 
 for giving evidence of this accumulation of water at the nega- 
 tive electrode, in order to prevent the liquid regaining its 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 441 
 
 level, as was necessary in DanielPs experiments, to give evi- 
 dence of the accumulation of acid at the positive electrode, in the 
 decomposition of acidulated water. The analogy is still more 
 complete when a voltameter, with acidulated water, is placed in 
 the same circuit in which the partitioned apparatus is situated, 
 full of ordinary water. I satisfied myself that the quantity 
 of gas liberated in this latter apparatus is exactly equal 
 to that, which is liberated in the voltameter. Now, if there 
 were in the fact of the transport of the water a mechanical 
 labour, independent of electrolysis, it ought to find its equiva- 
 lent in a more abundant decomposition of water in the volta- 
 meter ; which does not take place, whence it would seem to 
 follow, that in the two apparatus there are simply two equiva- 
 lent chemical effects ; one, the decomposition of acidulated 
 water with oxygen and acid at the positive electrode, and 
 hydrogen at the negative ; and the other, the decomposition 
 of pure water with oxygen at the positive electrode and of 
 water and basic hydrogen at the negative. 
 
 The hypothetic constitution, that water would assume 
 under the influence of electric polarity, would present nothing 
 astonishing ; for, like as a molecule of oxygen, or of any other 
 simple body, is composed of a group of chemical atoms more 
 or less numerous, nothing prevents our supposing that a 
 molecule of water is composed of a group of chemical atoms 
 of water (each composed of 1 chemical atom of oxygen, and 
 2 of hydrogen) more or less numerous. In this group one 
 atom of oxygen is detached by the passage of the current, 
 whilst the other atoms of the water, with the two atoms of 
 hydrogen, form a similar group with the atom of oxygen of 
 the group or of the following molecule, according to the 
 theory of Grotthus, as far as the negative electrode, where 
 they finally become free. 
 
 Mr. Graham, applying the same ideas to ordinary en- 
 dosmose, sees, in this class of phenomena, an effect of elec- 
 tricity produced by chemical action, that the liquids between 
 which the porous substance is interposed, exercise upon this 
 substance itself ; he gives the name of osmotic force to this 
 particular form, which electric force so produced assumes ; 
 
442 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 he thus explains why the phenomenon is much more frequent 
 and more decided with animal membranes, than with porous 
 earths. It is not the same when, the endosmose being 
 electric, the electricity is furnished to the liquids directly by 
 an exterior source ; a case, in which the nature of this 
 porous diaphragm has no other influence than that resulting 
 from the greater or less facility, with which it allows the 
 electric current to pass. We shall return to this subject 
 when we shall be treating of the electricity developed by 
 chemical actions, the endosmose of which would in this theory 
 be simply a remarkable manifestation ; we shall then ex- 
 amine to what point Mr. Graham's ideas may be reconciled 
 with the laws found by M. Wiedemann and with the facts, 
 which seem to prove that endosmose may take place, without 
 any apparent chemical action. 
 
 We shall not terminate this paragraph without referring 
 to Mr. Napier's experiments on electric endosmose, which, 
 although they are not contrary to the manner in which Prof. 
 Graham views this phenomenon, nevertheless demonstrate 
 the necessity there is of studying it still more closely, than 
 has been done by the celebrated English chemist. One of 
 the most remarkable consists, in placing the two electrodes of 
 a pile, each in a porous vessel, filled, the one, in which the 
 positive electrode is plunged, with hydrochloric acid, and 
 the one, in which the negative electrode is plunged, with 
 pure water ; the two porous vessels being themselves plunged 
 in pure water. When the current has passed for several 
 hours, a little hydrochloric acid is found in the intermediate 
 water, but not a trace in the negative vessel ; in which, on 
 the contrary, the quantity of liquid has sensibly augmented 
 at the expense of the exterior water. On changing the 
 places of the electrodes, the distilled water is seen to pass 
 from the positive cell into the intermediate vessel, and the 
 acid, which communicates with the negative electrode, expe- 
 riences no change ; endosmose, as in the preceding case, only 
 taking place between the vessels filled with pure water. 
 There is indeed a chemical decomposition, but it is very 
 feeble. -It is not necessary, in order to produce electric 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 443 
 
 endosmose, that the current should be very strong, provided 
 that it be sufficiently prolonged. Mr. Napier has succeeded, 
 with the current of a single pair, the zinc and copper of which 
 were plunged into two compartments, separated by a porous 
 diaphragm, and each filled with distilled water, in making a 
 volume of water of about 2lbs. weight pass from the positive 
 compartment to the negative at the end of forty days ; the 
 current indicated only 3 on a very sensitive galvanometer, 
 placed in the circuit ; and with regard to the decomposition 
 of the water, it was evident, since at the end of the forty 
 days the zinc had lost 38-J grs., which represents the quan- 
 tity oxidised during the course of the experiment. 
 
 Chemical Effects of ordinary Electricity, and of the Electric 
 
 Spark. 
 
 A long time before the discovery of the decomposition of 
 water by the voltaic pile, physicists had succeeded in pro- 
 ducing chemical effects,, by the electricity of electrical 
 machines. I do not speak of the effects of oxidation, that 
 accompany the incandescence of metals, by electric dis- 
 charges, observed by Van Marum and by others; because 
 electricity, in this case, contributes to it only indirectly, by 
 heating the wires. But, in 1790, Paetz and Van Troostwik 
 had decomposed water into its constituent gases, by causing 
 the electric spark to arrive, by means of a very fine gold 
 wire, into the interior of a glass tube, filled with water, and 
 causing it to come out, by means of a second similar wire, 
 also immersed in the water, at some distance from the former, 
 and communicating with the ground. It requires a very 
 powerful discharge to bring about the decomposition, and the 
 employment of a Leyden jar is necessary ; but, in order not 
 to have a discharge that breaks the tube, the two gold wires 
 are placed apart, so that their ends shall be about an inch and 
 a half distant from each other ; little sparks are then made to 
 pass between them, the force of which is gradually increased, 
 bv approximating, little by little, a conductor, which com- 
 municates with one of the wires, towards the outer coating of 
 the Leyden jar, until very small bubbles of gas are seen to rise 
 
444 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 in the water of the tube. As soon as the necessary power of 
 electricity has been discovered, the two gold wires are brought 
 near to each other, so as to obtain in the dark a small glow 
 of about Jj- of an inch at their extremities, immersed in the 
 water. This distance is the most favourable ; for, if the 
 wires are brought nearer together, the spark passes from one 
 wire to the other through the water, and breaks the tube. 
 The passage of 500 sparks produces a considerable quantity 
 of gas, which inflames, leaving only a small residue, by the 
 passage of the spark. This residue arises from the air, that 
 had remained dissolved in the water ; it is no longer presented 
 when the experiment has been made four or five times suc- 
 cessively with the same water. 
 
 Cuthbertson and Pearson also succeeded, by means of 
 a very great number of discharges, in extracting from water a 
 small quantity of the mixed gases, oxygen and hydrogen. 
 But the philosopher, who obtained the most decided effects 
 of chemical decomposition by means of ordinary electricity, 
 was Wollaston, who, in 1801, a short time after the decom- 
 position of water by the pile, showed that, without a Ley den jar, 
 and without even powerful electrical machines, we may 
 succeed in approaching as closely as possible to the conditions 
 under which we operate with the voltaic pile. He devised 
 the plan of introducing a gold wire into a capillary tube, 
 giving to it as sharp a point as possible ; then, after having 
 heated the tube to the extent of causing it to adhere to the 
 point and to cover the latter in all parts, he ground it down 
 gradually, until he was able, with a lens, to discover the ex- 
 tremity of the gold wire.* On passing through the water 
 electric sparks, drawn from the conductor of the machine, by 
 wires thus enveloped, he succeeded in the decomposition, by 
 means of sparks of y 1 ^ of an inch in length, with a point, 
 that was not more than a j^o ^ an mc ^ * n diameter. 
 
 If this diameter is still further diminished, a continuous 
 liberation may be obtained of small gaseous bubbles, merely 
 establishing complete contact between the wire and the con- 
 
 * The same process is equally applicable to platinum wires; we have em- 
 ployed it for obtaining electrodes that should present the smallest possible 
 point of contact with the liquids (fig. 239.). 
 
CHAP, in. EFFECTS OF DYNAMIC ELECTRICITY. 445 
 
 ductor of the machine, without producing any visible spark 
 between them. Two currents of gas may be obtained in 
 like manner, by causing the electricity to pass from the two 
 sides of the water, at the same time, by means of fine points, 
 of which one communicates with the positive conductor, and 
 the other with the negative conductor of the machine. How- 
 ever, the phenomenon, notwithstanding the similarity of ap- 
 pearance, does not take place in the same manner as with the 
 pile; for each wire liberates at the same time oxygen and 
 hydrogen, instead of producing them separately. 
 
 Wollaston had, however, succeeded in decomposing salts, 
 by ordinary electricity, as by the pile ; thus, having plunged 
 two silver wires, covered with wax, except at their very ex- 
 tremities, into a solution of sulphate of copper, and having made 
 one of the wires communicate with the positive conductor 
 and the other with the negative of an electrical machine, he 
 obtained, at the end of a hundred revolutions of the machine, 
 a deposit of metallic copper at the negative wire, whilst the 
 positive wire presented nothing similar. In like manner, hav- 
 ing passed a current of sparks between two very fine gold points 
 placed at the distance of an inch from each other on a card 
 coloured with a strong tincture of litmus, he remarked, after 
 a very small number of turns of the machine, a very visible 
 red spot, around the positive wire ; on placing the negative 
 wire near the same spot, it was soon seen to regain its colour. 
 
 Wollaston's experiments fairly demonstrate the decom- 
 posing power of the electricity of ordinary machines ; but 
 they still allow of certain doubts as to the nature of the 
 mode of decomposition. Is it a simple decomposition? or is 
 this decomposition accompanied by the transport of elements, 
 which characterises the effect of the current and which we 
 have named electrolysis ? 
 
 M. Bonijol, it is true, had succeeded in decomposing water 
 electrolytically, by means of atmospheric electricity, by em- 
 ploying an apparatus with fine points, with which he had 
 also decomposed it by means of ordinary electricity. He 
 drew off atmospheric electricity by the intervention of a point 
 placed at the extremity of an insulating rod, and commu- 
 
446 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 nicating, by a very fine wire, with the apparatus in which 
 the decomposition is brought about. The same philosopher 
 had also succeeded in decomposing solid potash and chloride 
 of silver, by placing them in a very narrow tube, and causing 
 them to be traversed by a series of electric sparks, brought 
 into the tube, by means of two wires, one communicating 
 with the conductor of the machine and the other with the 
 ground ; at the end of five or ten minutes there was found 
 in the tube either potassium, which took fire, in proportion 
 as it was reduced, or sodium. But, neither in this case, 
 could it be proved whether the decomposition was electro- 
 lytic or not. 
 
 Faraday, after having confirmed the accuracy of those 
 experiments of Wollaston's which are favourable to electro- 
 lytic decomposition, succeeded in demonstrating it in a much 
 more evident manner. He took for this purpose a glass 
 plate, upon which he applied two pieces of tin-foil a and b 
 . 245.), which he placed in communication, by means of 
 
 Fig. 245. 
 
 insulated wires c and d, one with the positive conductor of 
 an electrical machine, and the other with the negative con- 
 ductor, or with a discharging apparatus * ; from each of these 
 plates of tin was led a fine platinum wire, well in contact with 
 them, and abutting, one at p, the other at n, forming thus a 
 positive and a negative pole. A drop of sulphate of copper, 
 having been placed upon the glass plate, so that the points 
 p and n might plunge into it, there was precipitated, after 
 twenty turns of the machine, so much copper at n, that 
 the wire appeared to be entire copper ; no spark passed. 
 
 * We have already pointed out in Vol. I. that Faraday means, by dis- 
 charging apparatus, a system of conductors, such as the pipes employed in 
 conveying gas for illumination, which communicate in a perfect manner with 
 the ground. 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 447 
 
 Iodide of potassium, mixed with starch, very rapidly gave 
 off free iodine at p. 
 
 The last mode of operating for experiments of this kind, 
 is to moisten a piece of filtering paper with the solution, that 
 is required to be decomposed, and to place it between the two 
 points p and n. Thus the paper saturated with a solution of 
 iodide of potassium in starch, is seen to become blue at 
 p, after the machine has been turned scarcely half a turn ; 
 this is the most sensitive chemical test, that it is possible to 
 find. A piece of litmus paper, saturated with sulphate of 
 soda, immediately becomes red at p, whilst turmeric paper, 
 moistened in like manner, becomes red at n, by the effect of 
 the liberation of alkali. The effects of voltaic electricity may 
 be still better imitated by arranging (fig. 246.), one after the 
 
 Fig. 246. 
 
 other, upon the glass plate, several small pieces of paper, half 
 litmus and half turmeric, moistened with sulphate of soda, 
 and connecting them by metal conductors of platinum, r, and 
 s, so that the extremities n, of these wires, and of the extreme 
 wire t, which communicates with the negative conductor, 
 shall be in contact with the turmeric paper, and as the ex- 
 tremities p, of the same wire and of the extreme wire m, 
 which communicates with the positive conductor, shall be in 
 contact with the litmus paper, the points r ands, resting upon 
 the glass. After several turns of the machine, we see, from 
 the colour assumed by the paper, that acid is liberated at all 
 the points p, and alkali at all the points n. 
 
 It is necessary, in all these experiments, to take care 
 to avoid the passage of the spark over the moistened papers ; 
 because it is affected by the nitric acid, the formation of which 
 
448 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 is brought about by the spark, by producing the combination 
 of the nitrogen and oxygen of the air. 
 
 The same effects may be obtained by employing only 
 a single conductor conveying one of the electricities to one of 
 the ends of the moistened papers, and causing the other end 
 to communicate with the ground, or simply with the air, by 
 means of a linen or hempen thread of any desired length, 
 moistened with the same solution as the paper, and suspended 
 by silk threads, so as to be insulated. The point where the 
 metallic extremity of the conductor terminates, manifests the 
 liberation of acid or of alkali, according to the nature of the 
 electricity that reaches it. A single metal pole is able, 
 therefore, to produce decomposition, and to receive one of the 
 elements, whilst the other is liberated somewhere at the op- 
 posite extremity of the liquid conductor ; for example, against 
 the air, which may itself serve as a pole or electrode. 
 Faraday quotes several experiments, which proves the reality 
 of this latter supposition. Thus, a piece of turmeric paper 
 a, and a piece of litmus paper b (fig. 247.), having been 
 
 Fig. 247. 
 
 moistened in a solution of sulphate of soda, were placed on 
 wax between two needles p and n, which were in communi- 
 cation, one with the conductor of the machine, by means of 
 a wire, and the other with the discharging apparatus; the 
 interval between each point and the extremity of the cor- 
 responding paper band was about -J an inch ; the point p 
 was opposite to the litmus paper, and the point n to the 
 turmeric paper. As soon as the machine was touched, decom- 
 position took place ; the extremity b manifested the acid re- 
 action, and the extremity a the alkaline re-action ; which in- 
 dicates that the positive electricity arrives from the point p, 
 through the air to b, where it penetrates into the moistened 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 449 
 
 paper, and the negative, in like manner, from the point n to a. 
 In this case the air, on both sides equally, fills the office of 
 electrode ; a result, which can only be obtained by means of 
 ordinary electricity, which is alone capable of traversing so 
 imperfect a conductor as the air. We may give to this last 
 experiment a still more striking form, and which assimilates it to 
 the analogous experiments that are made with the voltaic pile, 
 by placing (fig. 248.) a series of small bands of litmus and tur- 
 
 <*> f 
 
 Fig. 248. 
 
 meric paper a b, moistened with a solution of sulphate of soda, 
 and arranged at a certain distance from each other, on a plate of 
 glass between metal points p and n, through which positive 
 and negative electricity arrive. All the points of the litmus, 
 as well as those of the turmeric paper, are reddened ; which 
 proves that the small layers of air, interposed between the 
 bands of paper, fill the office of conductors and electrodes, as 
 did the wires in Jig. 245. 
 
 The results, which precede, are perfectly in accordance 
 with the theory, that we have given of electrolysis. The 
 elements of an electrolyte, separated by the current, and which 
 are transported by way of successive decomposition and re- 
 composition, arrange themselves at the place where they no 
 longer find an element, with which they can combine ; gene- 
 rally it is against the surface of a metal that the deposit takes 
 place ; but, we have seen that, in many cases, it may take 
 place against the surface of a liquid, as, for example, in the 
 case of the decomposition of sulphate of magnesia, in which the 
 magnesia stops against the water, placed between the sulphate 
 and the negative pole, and does not reach this pole. It is 
 not then astonishing that the acid of the sulphate of soda, on the 
 one hand, and its alkali, on the other, stop against the surface 
 of the layer of air, interposed between the bands of papers 
 
 VOL. II. G G 
 
450 TKANSMISSION OF ELECTRICITY. PART iv. 
 
 and the positive and negative poles ; since they can neither 
 combine with the oxygen nor with the nitrogen of this air. 
 
 But if, as Faraday has proved, ordinary electricity is able 
 to bring about electrolytic decomposition, after the manner 
 of the current of the pile, it is no less true, that it also pro- 
 duces decomposition without transport of elements; for ex- 
 ample, in Wollaston's experiments on the decomposition of 
 water. However, we ought to add, that Davy had succeeded 
 in separating the two constituent gases of water, by plunging 
 into it the very fine extremity of a platinum wire, which re- 
 ceived the electricity of an electrical machine, and by causing 
 this electricity to be dissipated in the air, by means of fila- 
 ments of cotton ; he collected, as it seems, the oxygen and 
 hydrogen gases separate, but he does not say where that gas 
 was arranged, which was not liberated by the platinum wire. 
 This very doubtful experiment is the only one in which there 
 had been success in obtaining the gases separate, in the de- 
 composition of water, by ordinary electricity ; in all others, 
 they were obtained mixed. The explanation of this fact is con- 
 nected with the necessity there is of distinguishing, in decom- 
 positions, brought about by ordinary electricity, those which re- 
 sult from the regular and continuous transmission of electricity, 
 from those which are due to the calorific effect of the 
 spark, acting on the molecules of the liquid, in contact with 
 the wire from which it escapes. The two modes may present 
 themselves simultaneously and in proportions, which depend 
 on the circumstances of the experiment, more favourable to 
 one than to the other. The electrolytic mode is favoured by 
 the very pointed forms of the electrodes, which allow of a 
 continuous escape of electricity, similar to a current ; but it is 
 necessary, in addition, that the liquid be a good conductor; 
 this is why it takes place with saline or acid solutions. The 
 non-electrolytic mode is especially presented, when the liquids 
 are imperfect conductors, such as distilled water, or even 
 when they are almost totally insulating, as alcohol and the 
 oils. 
 
 We have already seen that Morgan had decomposed al- 
 cohol and the oils, by causing electric discharges to pass 
 
CHAP. ill. EFFECTS OF DYNAMIC ELECTRICITY. 451 
 
 through them.* We have also seen that Davy had succeeded, 
 by means of the voltaic spark, produced between two carbon 
 points, plunging in various liquids, in decomposing these 
 liquids, whether they were conductors or not; a proof that the 
 decomposition was not, at least in a great number of the cases, 
 electrolytic, but rather an effect of the heat, liberated between 
 the points. M. Melly has examined more closely this mode 
 of decomposition. He made use of a tube, closed below by 
 means of a cork, through which penetrated a wire, placed by 
 its outer extremity, in communication with one of the poles of 
 a Grove's pile of five or six pairs, and in this tube, filled with 
 the liquid, submitted to experiment, plunged another smaller 
 tube, filled with the same liquid, but closed above by means 
 of a cork, also traversed by a wire, communicating with the 
 other pole of the pile. Contact could be made or broken with 
 the hand, between the extremities of the two wires plunged 
 in the liquid ; and at each rupture a spark was produced. It 
 is easy to obtain more than a hundred of these sparks per 
 minute, as soon as the hand is accustomed to this backward 
 and forward motion. Moreover, by means of a small lever 
 put in communication with a toothed wheel, that is set in mo- 
 tion by the hand, we may very easily bring about the making 
 and breaking of contact between the two wires; we may 
 even place the toothed wheel in the liquid, as well as a little 
 metal spring, which presses constantly on the circumference; 
 this spring communicates with one of the poles, the axis of 
 the wheel with the other, and we thus obtain, on turning the 
 wheel, a series of sparks, the number of which depends both 
 upon that of its teeth, and upon the velocity with which 
 it is made to rotate, f By these various processes, M. Melly has 
 succeeded in decomposing olive oil, essence of turpentine, 
 sulphuric ether, absolute alcohol, alchohol at 36, ordinary 
 naphtha, pure naphtha, sulphuret of carbon, chloride of 
 sulphur, and distilled water, substances, not one of which 
 could be decomposed electroly tically by the current of the pile 
 employed for producing the spark. 
 
 * Vol. II. p. 139. 
 
 f Vide Vol. I. p. 302., ./fy. 131., a wheel similar to that in question. 
 
 G G 2 
 
452 TRANSMISSION OF ELECTRICITY. PART IT. 
 
 Two different facts are observed in general, in these ex- 
 periments : the production of a vapour saturated with the 
 liquid, when it is tolerably volatile, and its decomposition. 
 Essence of turpentine does not sensibly vaporise, but there 
 is seen in it a liberation of large gaseous bubbles, which are 
 a mixture of hydrogen and carburetted hydrogen, and a 
 deposit of carbon, which remains in suspension in the liquid ; 
 olive oil and naphtha give very similar results to that, which 
 is obtained with essence of turpentine. Alcohol, and espe- 
 cially ether, produce a considerable liberation of bubbles of 
 vapour, in addition of those of gas, which, having arrived at 
 the top of the tube, condense gradually by the cooling of the 
 apparatus. The deposit of carbon is very feeble. Sulphuret 
 of carbon gives no gas ; chloride of sulphur gives off a little, 
 In these two liquids, the wires, which are of copper, become 
 grey by the formation of a sulphuret, and carbon in lamina? 
 of a brilliant grey remains in suspension in the former, whilst 
 a little sulphur of a dirty yellow is found in the latter. 
 Distilled water, perfectly pure, and deprived with great 
 care of air, gives rise to a pulverulent deposit, which is 
 protoxide of copper, and to a gaseous liberation, composed for 
 three-fourths of a mixture of oxygen and hydrogen, and for 
 one-fourth of pure hydrogen ; probably equivalent to the 
 oxygen of the protoxide of copper. By substituting platinum 
 wires for copper wires in the distilled water experiment, 
 scarcely any gas is obtained, but a very abundant deposit of 
 a black powder, which is nothing else than very divided 
 platinum, as* may easily be proved. This experiment de- 
 monstrates that, under the influence of the heat of the voltaic 
 spark, platinum has been alternately oxidised and reduced 
 by the hydrogen of the water, which consequently has been 
 decomposed in the same manner as the vapour of alcohol or 
 ether is decomposed in the aphlogistic lamp, by the heat of 
 incandescent platinum. Between two fragments of coke, ob- 
 tained from the gas-works, a spark is obtained, which decom- 
 poses distilled water very well, with production of hydrogen 
 and of a little carbonic acid, the greater part of this acid re- 
 maining dissolved in the water. 
 
CHAP. nr. EFFECTS OF DYNAMIC ELECTRICITY. 453 
 
 Iii all these experiments, the induction spark may be ad- 
 vantageously substituted for the spark of the pile ; which pro- 
 duces the same effect, with a much less considerable number of 
 voltaic pairs ; one alone is sufficient with a good induction 
 apparatus. However, the effects are more complex, because 
 the induction currents frequently act upon the liquid electrolyt- 
 ically, at the same time as they decompose it by the spark. 
 This explains the anomalous results that Grove has obtained, 
 on decomposing, by means of the induction currents of 
 RuhmkorfFs apparatus *, distilled water, or water slightly 
 or powerfully acidulated. The electrodes were very fine 
 platinum wires, sealed into glass tubes, so that their ex- 
 tremity was embedded in the very end of the tube, without 
 passing beyond it. The gaseous product, accumulated 
 around each point, was a mixture of oxygen and hydrogen, 
 with an excess sometimes of one, sometimes of the other gas ; 
 however, when the gaseous mixtures, accumulated around 
 each of the two electrodes, were put together, there was 
 found, after having caused them to detonate, an excess of 
 hydrogen, if the water contains a very feeble quantity of 
 sulphuric acid, and an excess of oxygen if it contains more 
 than the proportion that gives it its maximum of conduct- 
 tibility. When it contains exactly this proportion, there is 
 scarcely any excess of either one gas or the other. We must 
 also remark, that the gaseous volumes are never equal on 
 both electrodes ; it is sometimes at one, sometimes at the 
 other, that they are more considerable. If, instead of a point, 
 we take a plate of platinum for one of the electrodes, there 
 is no sensible liberation of gas around the plate, whilst there 
 is some around the other electrode, which has remained a 
 point, as when they were both points. All these effects are 
 of the same kind as those which we have described in a pre- 
 ceding paragraph, with this difference, that, independently 
 of the presence of alternate currents, which act electrolyti- 
 cally, carrying at once oxygen and hydrogen to each of 
 the electrodes, where they undergo a partial, and sometimes 
 
 * Vide Vol. I. p. 355. 
 
 G G 3 
 
454 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 even a total recomposition, as with the plate, the intervention 
 of the spark, which, with M. Ruhmkorff s apparatus, is very 
 powerful, still further complicates the results. 
 
 It is probable that the excess of hydrogen, observed 
 in certain cases, is due to the formation of a little oxygenated 
 water, like as that of the oxygen, which occurs when the 
 acidulated water is concentrated, is equally due to the forma- 
 tion of a secondary product, such as sulphuretted hydrogen. 
 The observation, that was made by Mr. Grove, that a 
 blackish powder is deposited, which is divided platinum, 
 when the discharge of RuhmkorfPs apparatus has been 
 allowed to pass for a great number of hours (thirty to forty), 
 not consecutive, by means of a plate and a point serving as 
 electrodes, through the vapours of water arising from distilled 
 water placed in vacuo, is a proof of the alternate decompo- 
 sition and recomposition of water. 
 
 Thus, as M. Masson justly remarks, at the end of certain 
 researches, also made with RuhmkorfFs apparatus, all these 
 results, as well as those, which he himself obtained, confirm 
 the distinction, that we have established between polar or 
 electrolytic decomposition, and calorific decomposition. This 
 philosopher has observed that the decomposition is much more 
 abundant, where the electrode is luminous, for example, at the 
 negative and at that which is terminated in a point, when 
 the other has the form of a ball, because the two modes of 
 decomposition are found united. He quotes several examples 
 of the second mode of decomposition, which he has studied, 
 as M. Melly had already done, by operating upon non con- 
 ducting substances. M. Quet, who has made experiments 
 of the same kind as those of M. Masson and Mr. Grove, 
 remarks, that the platinum wire and the glass, by which 
 it is surrounded, are altered and fused, after having been 
 employed for the decomposition of water with Ruhmkorff's 
 apparatus. 
 
 It was of importance to prove in a direct manner the exis- 
 tence of calorific decomposition, for it might always be 
 suspected that it was really an effect of electricity and not 
 of the heat liberated by this electricity. It is to Mr. Grove 
 
CHAP, in. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 455 
 
 we are indebted for having demonstrated that decomposition 
 in the case, wherein it is not electrolytic, is truly due to the 
 action of heat. At first he succeeded, after various trials, 
 in decomposing water, by igniting to redness, by means of 
 an electric current, a platinum wire, inserted at the bottom 
 of a tube filled with water and contracted immediately over 
 the wire, so as to allow only the space strictly necessary for 
 the vapour formed by the heat of the wire to ascend, and for 
 the water to redescend (Jig. 249.). 
 
 Fig. 249. 
 
 Two pairs were sufficient, in order, after the expulsion of the 
 air, that the water may be seen to boil and the wire to 
 become incandescent, in the midst of the vapour ; then 
 small gaseous bubbles are seen to separate and to ascend 
 to the top of the tube, whence they are led, by means of 
 its bent end, under a bell-glass; the phenomenon does 
 not take place in a continuous manner, but only by 
 jerks. The gas is a mixture of hydrogen and oxygen. It 
 is evident that the decomposition of the water is truly an 
 effect of the heat of the wire and not of the current, that 
 traverses it ; for this current is incapable of being trans- 
 mitted through distilled water, and no effect is obtained 
 upon separating the platinum wire at its middle, and upon 
 vaporising the water, by means of the flame of a spirit-lamp, 
 applied exteriorly ; whilst, on vaporising in the same 
 manner, if the wire is continuous and the current is tra- 
 versing it, we bring about tne formation of a bubble of gas, 
 by filling the tube with water well distilled, and carefully 
 freed of air (fig. 250.). Only the bubble must be transferred 
 to another vessel in order to obtain a second. We are not 
 
 G G 4 
 
456 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 able, even when the incandescence has been maintained for a 
 long time, to increase the volume of the gaseous mixture 
 
 beyond a very limited quantity, 
 which is probably due to the fact 
 that, remaining thus in contact 
 with the platinum wire, it de- 
 tonates and re-forms water. In 
 the experiment of fig. 248. it 
 was not the same, because the 
 gaseous bubbles escaped out of 
 the tube, in proportion to their 
 
 formation. Moreover the mode of operating of Jig. 250. 
 excludes all idea of electrolytic decomposition, since the in- 
 candescent platinum wire is not in contact with the water, 
 but only with a non-conducteous atmosphere of dry vapour. 
 
 After these various essays, Mr. Grove, wishing to exclude 
 the employment of the electric current, even as a source of 
 heat, procured a tube of silver 9J in. in length, with a 
 diameter of about \ an inch ; at the upper extremity of 
 which was soldered a head of platinum, furnished with a 
 small tube, also of platinum, soldered and closed with gold 
 (Jig. 251.). The apparatus was filled with water, properly 
 
 prepared, and the latter was 
 then subjected to boiling, in 
 order to expel the air, adhering 
 to the sides. The tube was 
 then inverted and heated at its 
 upper extremity by the flame 
 of a blowpipe ; upon inverting 
 it under water, a small bubble 
 of detonating gas was col- 
 lected. With a globule of pla- 
 tinum, that was melted at the 
 
 Fig. 251. 
 
 extremity of a large wire, the decomposition of water was 
 likewise brought about by plunging it in, at the moment, 
 when it attains to the state of fusion. But, in order to ob- 
 tain a continuous liberation of gas from the body of the water, 
 submitted to the sole action of heat, Grove constructed the 
 
CH4P. m. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 457 
 
 following apparatus (Jig. 252.), in which a and b are two 
 tubes of silver, 3J in. in length, and -f^ in. in diameter, 
 soldered by two platinum cups to a narrower tube, also of 
 
 Fig. 252. 
 
 platinum. The tube a is closed at its extremity, and the 
 bent glass tube d is adjusted, by means of a band of bladder, 
 to the extremity of the tube b. The whole is filled with 
 water, deprived of air, and after having, by means of heat, 
 brought about the expulsion of the air from the tube a, the 
 extremity of the glass tube is plunged into a cup of boiling 
 water. The tube b is first heated, by means of a spirit lamp, 
 and then the tube a, to complete ebullition ; the jet of a gas 
 blowpipe is immediately directed upon the junction tube of 
 platinum. When the temperature has attained as nearly as 
 possible to the fusing point of platinum, gas is liberated at 
 the same time as vapour, so as to fill the apparatus and 
 even to come out of it ; it is then collected in a test-tube. 
 It is for -^ a mixture of oxygen and hydrogen in the pro- 
 portions that form water; the residue is nitrogen, with a 
 little oxygen, which is derived from the air, dissolved in 
 the water. 
 
 Thus, under the influence of incandescent platinum, heat 
 alone, without any electric influence, is able to decompose 
 water. This phenomenon cannot be attributed to the catalytic 
 force of platinum ; since this force, on the contrary, far from 
 producing decomposition, would bring about combination ; it 
 is therefore a veritable direct effect of heat. 
 
458 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 The action of electric heat upon gases thus presents some 
 curious phenomena, which it is of importance to study. This 
 also Mr. Grove did, by placing various gaseous substances, 
 successively in a similar tube to that of Jig. 249. and rendering 
 the platinum wire, which traverses the upper part of the 
 tube, incandescent by means of a voltaic current. The expe- 
 riments were made sometimes over water, at other times over 
 mercury. Oxygen, nitrogen, hydrogen, carbonic acid, under- 
 went no sensible alteration. Bioxide of nitrogen collected 
 over distilled water, contracted to one-third its initial volume ; 
 the residue was nitrogen ; and nitric acid was found in solu- 
 tion in the water. The protoxide of nitrogen was decom- 
 posed into nitrogen and oxygen, increasing by 0*35 of its 
 primitive volume. Ammonia doubled in volume, the water 
 no longer absorbed it, it was decomposed into its three parts of 
 hydrogen and one of nitrogen. Olefiant gas suffered a slight 
 contraction of volume, accompanied by a feeble deposit of 
 carbon ; but the decomposition of the gas was not complete. 
 Chlorine and cyanogen gave thick white clouds, which 
 arose probably from their action upon platinum. 
 
 A long time before Grove, philosophers had succeeded 
 in decomposing gases by the electric spark ; but, in showing 
 that the same effect is produced by incandescent platinum, 
 Grove has proved that it is truly to the heat of the spark, and 
 not to its being electric, that the phenomenon is due. The 
 protoxide and deutoxide of nitrogen, as well as ammonia, 
 are decomposed by the spark, as well as by incandescent 
 platinum; but the spark decomposes also sulphuretted and 
 phosphuretted hydrogen ; the volume of the hydrogen does 
 not change, but sulphur and phosphorus are deposited. Car- 
 buretted hydrogen and hydrochloric acid gases are also 
 decomposed ; with carbonic acid, an increase of volume is 
 observed, and the formation of a little oxide of carbon, but 
 the decomposition is never complete. 
 
 A very remarkable thing is, that this same electric spark, 
 which decomposes compound gases, when traversing them, 
 brings about, in like manner, the combination of elementary 
 gases. The apparatus, that is employed for producing these 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 
 
 459 
 
 combinations, is the same as that, by means of which decom- 
 position is produced. It is a glass tube, the 
 sides of which must be very strong, j- in. in 
 thickness (Jig. 253.), closed at its summit, and 
 open at its other extremity ; it must be pierced, 
 in the portion, near to the summit, with two 
 small holes, through which two wires of pla- 
 tinum or copper are introduced, which are her- 
 metically sealed in them. The inner extremities 
 of the two wires are opposite to each other, 
 leaving between them an interval of -fa or ^ 
 of an inch ; between them the spark is made to 
 pass, by causing the outer extremities of the 
 wires to communicate, one with the inner coating, 
 the other with the outer coating, of a Leyden 
 jar. The tube is generally filled with mercury 
 rather than with water, on account of the solu- 
 Fig. 253. bl e gases ; then the gases are passed in, whose 
 combination is required to be brought about, care being taken 
 not to introduce sufficient to drive out all the mercury, of 
 which an inch or more must always be left at the bottom of 
 the tube ; the latter is plunged by its base in a small cup 
 in which some mercury is placed, that ascends in its interior 
 when the combination of the gases has brought about a 
 diminution of volume in the gaseous mass, as most commonly 
 happens. 
 
 The combination, that is brought about most easily, by 
 means of the electric spark, is that of two volumes of hydro- 
 gen and one volume of oxygen ; it is attended by a violent 
 detonation, which risks breaking the glass tube, if it is not 
 very strong, and the mercury rises rapidly to the top of the 
 tube, to fill the space that had become void by the condensa- 
 tion of the vapour of water, formed by the combination of 
 the two gases. So that the mixture of oxygen and hydrogen, 
 in the proportions that form water, is called explosive 
 mixture. If one of the gases is in excess, it does not prevent 
 the combination, which is always brought about between two 
 volumes of hydrogen and one volume of oxygen, with an 
 
460 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 excess of the gas, that is found in too high a proportion in 
 the mixture. However, the gas in excess must not exceed 
 seven times the volume of the explosive mixture, if it is 
 hydrogen, and twelve times, if it is oxygen ; there is then 
 no combination. In like manner, if there are more than 
 ten volumes of atmospheric air mixed with one volume of 
 the explosive mixture, the latter does not detonate, under 
 the action of the electric spark. This negative influence of 
 the presence of a third gas is general ; but the proportion 
 of the gas, necessary for preventing the combination of the 
 oxygen and hydrogen, varies according to its nature. It is 
 probable that this effect is due to the cooling action, exercised 
 upon the spark by the considerable quantity of the gas, in 
 the midst of which, the explosive mixture is, as it were, 
 drowned ; such at least is the case, when the gas in excess 
 is hydrogen, oxygen, or atmospheric air. But it may also 
 happen that this gas itself exerts an action over the oxygen 
 or hydrogen of the mixture; and, in that case, it requires 
 a much less proportion in order to arrest the explosion ; this 
 takes place with hydrochloric acid gas, with sulphurous acid 
 gas, and with ammonia. 
 
 We should remark, indeed, that in the phenomenon of the 
 combination of oxygen and hydrogen, by the electric spark, 
 the heat of the spark, in bringing about the combination of 
 the first gaseous molecules, that it meets, becomes thus in its 
 turn itself the cause of a great development of heat, which 
 produces the combination of the other molecules, and so on ; 
 in such sort, that this combination is, so to speak, instanta- 
 neous ; a phenomenon, which may consequently be attributed 
 to the great heat, that attends the combination of oxygen and 
 hydrogen. But, when other gases are in question, such as 
 nitrogen and oxygen, for example, which produce but little 
 heat by their combination, a very great number of sparks are 
 necessary in order to their combination, because each spark 
 only brings about the combination of these molecules of the 
 two gases, that it meets directly. Priestley, and after him 
 Cavendish, had observed this, who were the first to succeed 
 in forming nitric acid, by passing a series of electric sparks 
 
CHAP, in. EFFECTS OF DYNAMIC ELECTRICITY. 461 
 
 through atmospheric air. In order to make this experiment, 
 it is necessary to use a bent glass tube (Jig. 254.) about an 
 
 inch in diameter, filled with mer- 
 cury, except in its upper bent part, 
 in which a little atmospheric air is 
 left, and plunging by its two ex- 
 tremities into separate glass vessels 
 also containing mercury. The 
 mercury of one of the vessels is 
 ^^ put in communication with the 
 
 Fig. 254. 
 
 ground, and that of the other is 
 attached to the conductor of an electric machine ; by means 
 of which a current of sparks is made to pass through the air 
 situated in the upper part of the tube. In proportion as the 
 volume of the air diminishes, fresh is introduced. Cavendish, 
 after having operated with this apparatus for a fortnight, 
 half an hour each day, found that the oxygen and nitrogen 
 had combined, in the proportion of seven volumes of oxygen 
 and three of nitrogen, to produce nitric acid ; the presence of 
 which could besides be easily detected, either by its action 
 upon blue vegetable tincture, or by the formation of nitrate 
 of potash, when a solution of potash was introduced into the 
 tube. 
 
 The combination of chlorine and hydrogen in equal volumes 
 to form hydrochloric acid, was in like manner brought about, 
 by the electric spark ; the combination is immediate, as with 
 the explosive mixture, and is attended by a powerful detona- 
 tion. 
 
 Simple gases are not the only ones that form combinations 
 when an electric spark is made to pass through their mixture ; 
 new combinations may also be brought about between a com- 
 pound gas and a simple one. The following is a table, that 
 contains some of the most important results, obtained in this 
 
 manner : 
 
 f2 vols. carbonic 
 2 vols. oxide of carbon and 1 vol. oxygen, give -j , 
 
 r2 vols. oxide of 
 
 protocarburetted hydrogen and 2 oxygen, 4 carbon and 2 
 
 I vols. hydrogen. 
 
462 TRANSMISSION OF ELECTRICITY. PART TV. 
 
 { 8 vols. hydrochlo- 
 ric acid; a de- 
 posit of carbon. 
 4 vols. carbonic 
 
 c^ vois. caroomc 
 bicarbonated hydrogen and 6 oxygen, I add . a deposit 
 
 I of water. 
 
 {2 vols. carbonic 
 acid ; 1 vol. ni- 
 trogen. 
 
 r2 vols. carb. ac- 
 
 1 vol. nitrogen. 
 2 hydrocyanic acid and 2^ oxygen, j and a s i ight dc _ 
 
 v. posit of water. 
 
 We see, by what precedes, that the same cause, which 
 brings about the decomposition of a compound gas, may 
 produce a new combination, when this compound gas is in 
 presence of another. One of the phenomena is a consequence 
 of the other in this sense, that the electric spark in dis- 
 tributing by its passage the chemical equilibrium of one gas, 
 facilitates consequently the formation of an entirely new 
 compound. The property of the spark, or rather of the 
 heat, that it introduces into the midst of the gaseous par- 
 ticles, is therefore to distribute the chemical equilibrium, pro- 
 bably by impressing upon the atoms, according to the theory 
 that we have already on one or two occasions laid down, a 
 more rapid motion of rotation than that, which they possess 
 at the ordinary temperature. 
 
 It is easy to prove that the property possessed by the 
 spark of bringing about combinations as well as decompo- 
 sitions, is indeed due to heat ; we have merely in the appa- 
 ratus (fig* 254.) to substitute for the two platinum points a 
 fine and continuous wire of the same metal, which traverses 
 the tube ; on raising it to red heat, by means of an electric 
 current, the same effects of combination are obtained as with 
 the spark. 
 
 A circumstance that influences this facility, with which 
 gases combine by the effect of the electric spark, is their 
 density. Grotthus has found that a mixture of chlorine and 
 hydrogen no longer detonates, when it is reduced by rare- 
 faction to a sixth of its density. This rarefaction must be 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 4C3 
 
 extended beyond the sixth of its density, in order to make a, 
 mixture of hydrogen and oxygen lose its detonating faculty. 
 Rarefaction resulting from elevation of temperature, produces 
 similar effects, which proves that increase of temperature 
 does not compensate for the weakness that results, in the 
 mutual action of the particles, from their greater mutual 
 separation. It would be quite otherwise, if, on heating the 
 gases, they were prevented from expanding, so that their 
 elastic force alone and not their volume, could increase ; it 
 is very probable, that in this case the action of the electric 
 spark, for bringing about their combination, would be faci- 
 litated. Experiments of this kind have never been made ; 
 they deserve to be attempted. 
 
 Independently of the chemical effects, that are produced 
 by electricity indirectly upon gases by the heat, which it 
 causes to penetrate into their particles, Mr. Grove has found 
 that it is able to bring about more direct ones, and which 
 seem, to a certain extent, to be electrolytic. It is by em- 
 ploying the induction currents, produced by RuhmkorfFs * 
 instrument, that he arrived at the interesting results, that 
 we are about to describe. The experiments were made by 
 means of an apparatus similar to that of Jig. 218. A plate 
 of silver was placed upon the support of the bell-glass, and a 
 steel needle was fixed at the extremity of the stem, at a 
 distance of about yL- of an inch from the plate. The induction 
 current was transmitted from the plate to the needle ; the 
 medium was air, rarefied to about '707 in., mixed with hy- 
 drogen and a little vapour of water ; there was seen to be 
 formed upon the plate, when it was positive, a circular spot 
 of oxide of silver, presenting successively yellow, orange, or 
 blue tints. The direction of the current being reversed, the 
 spot disappeared, and the silver again became perfectly clean ; 
 the place that the spot had occupied, might, however, still be 
 distinguished. In rarefied air, without mixture of hydrogen, 
 oxidation took place, whatever was the direction of the 
 current, but it was more rapid, when the plate was positive. 
 In pure rarefied hydrogen, no oxidation took place, but the 
 
 * Vol. I. p. 389. fig. 150. 
 
464 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 surface of the plate finished by becoming slightly unpolished. 
 Nitrogen conducted itself like hydrogen ; when it was per- 
 fectly pure, there was no trace of oxidation : but, as soon as 
 it was mixed with a little oxygen, then the plate, when it 
 was positive, began to oxidise. For the steel needle were 
 substituted wires of copper, silver, and platinum, without the 
 phenomena being sensibly modified. On substituting for the 
 silver plate, plates of bismuth, lead, tin, zinc, and iron, 
 similar effects were obtained, except as concerns intensity. 
 Platinum alone experienced no effect. 
 
 In order better to study the formation of the spots, Mr. 
 Grove, after a few trials, operated, as in the preceding ex- 
 periments, with a rarefied atmosphere, formed of a mixture 
 of one volume of oxygen and four of hydrogen. The plate 
 was rendered positive, and the lower extremity of the steel 
 needle was brought to distances from the plate, successively 
 equal to ^ in. -j in. y 1 -^ in. -^ in. ; and thus were obtained 
 successively the appearances a, b, c, d, and e, of fig. 255. 
 
 * 
 
 Fig. 255. 
 
 The colour of the central spot was greenish yellow in the 
 centre and greenish blue on the edges ; then came a ring of 
 silver, not oxidised ; then a circular crimson-red ring, tending 
 toward orange on its inner border, and towards deep purple 
 on its outer border. Sometimes in the middle of the central 
 spot, a small circular space was seen, where the silver ap- 
 peared perfectly bright (fig. 255. appearances/ and g\ and 
 which was produced, when the plate was negative ; this small 
 space was surrounded by a dark and badly defined aureola. 
 The spots h and i are derived, the first from the discharge 
 transmitted by a platinum wire, enclosed in a glass tube, 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 465 
 
 after the manner of Wollaston, described above ; the second, 
 from the discharge transmitted by a steel needle ; the silver 
 plate was positive; the distances, traversed by the dis- 
 charges, were T ^- in. ; the receiver contained a mixture of 
 one volume of oxygen and five of hydrogen, under a pressure 
 of -471 in. Finally, the appearance k, is the result of an 
 experiment in which a copper wire -/j in. in diameter had 
 been fixed with wax in a horizontal position at - in. above 
 the silver plate ; the extremity of the platinum wire was 
 itself -g- 1 ^ in. above the copper wire. It is seen that the 
 interposition of the copper wire has divided the spot into two 
 equal portions, separated by an interval, that remained 
 clear. 
 
 The phenomena described by Mr. Grove are analogous 
 in part to those, which I had observed on operating in the 
 same manner, but by means of a pile of high tension * ; only 
 they are more numerous and more varied ; however, I had 
 remarked the formation of the circular blue spot, even upon 
 a plate of platinum in rarefied air, and its non-appearance 
 in an atmosphere of hydrogen. All these effects appear to me 
 to arise essentially from the high temperature, which the points 
 of the metal conductors suffer, from which the positive elec- 
 tricity comes out, joined to the greater oxidising property 
 which the passage of the discharge developes in oxygen, and 
 the study of which forms the subject of the following para- 
 graph. With regard to the effects of reduction by hydrogen, 
 they are also easy of comprehension ; what is least so is to 
 discover why in an atmosphere of hydrogen and oxygen, 
 in which this latter gas is in a small proportion, the plate 
 oxidises, only so long as it is positive, and not when it is 
 negative. When oxygen is more abundant, it oxidises as 
 well as in atmospheric air. Is it that, under the influence 
 of discharges, the oxygen and hydrogen acquired, by the 
 effect of a peculiar polarisation, a tendency to betake them- 
 selves, one to the positive electrode, the other to the negative ? 
 Mr. Grove would be disposed to admit this opinion, and 
 
 * Vol. II. p. 291. 
 VOL. II. H H 
 
466 TRANSMISSION OP ELECTRICITY. PART IT. 
 
 to recognise consequently in gases a species of electro-chemical 
 polarity. I presume rather that the difference of tempera- 
 ture, that is manifested between the two electrodes, joined 
 to the property, that is acquired by oxygen, may explain 
 these oxidations and reductions, that we so frequently see in 
 chemistry to succeed each other easily, by the effect of the 
 slightest variation of temperature. 
 
 Mr. Grove has made one other important observation; 
 it is that, when the experiments, which he has described, 
 are made in certain vapours, such as those of phosphorus 
 and others, the electric light is seen to be striped with 
 transverse dark bands ; only care must be taken to place 
 the needle at about an inch from the plate. This pheno- 
 menon is altogether identical with that, which has been 
 studied by M. Quet, and of which we have spoken in the 
 preceding Chapter.* Up to what point is it connected with a 
 chemical effect, exercised upon the atmosphere of vapours by 
 the discharge, either indirectly by heat, or directly by elec- 
 trolysis ? This is impossible to say, in the present state of 
 the science. What is very remarkable is this coincidence 
 between the formation of rings alternately brilliant and dark, 
 upon the surface of the electrodes, and the appearance in 
 the atmosphere of vapours, of bands, in like manner, alter- 
 nately luminous and obscure ; which would seem to indicate, 
 equally in both cases, a kind of effect of interference, and 
 consequently a connection between the two sorts of pheno- 
 mena. 
 
 We shall not terminate this paragraph, without saying a 
 few words on a mixed phenomenon, which is due at once 
 to the chemical and to the calorific effects of dynamic 
 electricity ; I refer to the incandescence of wires that serve as 
 electrodes, in liquids and in elastic fluids. Hare was the first 
 to observe it in a very striking manner, by plunging into a 
 solution of chloride of calcium, an iron wire as a negative 
 electrode, and a finer platinum wire as a positive electrode ; 
 the latter melted into globules ; on changing the places of the 
 
 * Vol. II. p. 275. 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 467 
 
 wires, the phenomenon did not occur. Mackrell obtained 
 effects of the same kind with wires of different natures 
 plunged into diluted sulphuric acid. He succeeded in raising 
 to a red heat in the liquid, iron and copper wires two inches 
 in length ; the effect depended upon the position of the wire 
 in respect to the positive or negative pole, and on the fact, 
 that one of the two was immersed first or second. When the 
 two electrodes were formed of plates of platinum, the positive 
 electrode was greatly heated and presented from time to time 
 along its section a bluish light ; when the negative electrode 
 was placed last in contact with the liquid, it gave no light, 
 but produced small explosions. 
 
 Grove made some interesting experiments upon this subject 
 with an enormous battery of 500 pairs, which Mr. Gassiot had 
 had constructed. A platinum plate, forming the positive elec- 
 trode of the battery, was plunged into a cup of distilled water, 
 the temperature of which had been raised. The negative 
 electrode, 'formed of a platinum wire, was brought near, so as 
 to touch the surface of the water for an instant, and was 
 immediately drawn back to a distance of about \ in. as soon 
 as the discharge had taken place ; the extremity of the wire 
 entered into fusion, and the melted platinum remained, as it 
 were, suspended in the middle of the surrounding air, giving 
 off an intense light, throwing out sparks in directions contrary 
 to that of the water, and was not detached from the wire, 
 until it was shaken off. The water in a state of vapour was 
 decomposed, for the positive electrode liberated gases ; and 
 the molecular action exercised upon the negative platinum 
 altogether resembled the currents, that are observed upon the 
 surface of mercury, when it is rendered negative in an electro- 
 lyte. However, as the gases produced were not collected, it 
 is impossible to decide whether the decomposition is a veri- 
 table electrolysis or simply an effect of the high temperature 
 of the platinum ; which latter appears the more probable. 
 
 M. Quet, on his part, has succeeded, by means of a pile of 
 forty large Bunsen's pairs, in obtaining a vivid light upon 
 platinum electrodes, by decomposing water, either acidulated, 
 or holding potash in solution. The platinum wire is not in- 
 
 H H 2 
 
468 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 candescent, but surrounded as it were with a sheath of light, 
 which seems to separate it from the neighbouring water. 
 In diluted sulphuric acid, the light of the negative electrode 
 is violet and that of the positive is red ; in solution of potash, 
 that of the negative electrode has a beautiful rose tint. 
 When the luminous phenomenon is produced, the decomposi- 
 tion of the water, which was very vivid, is much reduced ; it is 
 revived, as soon as the illumination ceases. The negative elec- 
 trode is in general the one, that is the more easily illuminated. 
 With a comparatively feeble pile, we obtain, by cautiously 
 bringing near to the surface of the liquid, in which the positive 
 electrode is plunged, the extremity of a platinum rod serving 
 as the negative electrode, a violet light around this extremity 
 with a slight noise of crepitation ; it is essential that the rod 
 shall merely touch the liquid, or shall dip into it only -j of 
 an inch. 
 
 Latterly, again, M. Van der Willigen, in operating with 
 diluted and concentrated sulphuric acid, or with solutions 
 of chloride of sodium, sulphate of potash, &c., has remarked 
 the influence that may be exercised on the calorific or 
 luminous effect, manifested by one of the electrodes, by the 
 fact that it is plunged first or last ; he was able to satisfy 
 himself that these very complex phenomena, in which wires 
 sometimes became incandescent, sometimes are simply sur- 
 rounded by a luminous aureola, are due to its happening 
 that, in certain cases, they are not in contact with the liquid, 
 or account of their elevated temperature, which gives to the 
 surrounding liquid the spheroidal state. In other cases, the 
 products of decomposition themselves suffer an incandescence 
 or a combustion, which imparts to the light a particular tint. 
 Finally, the heat itself combines with the electrolysing action, 
 in order to decompose the liquid conductor, what may itself, 
 as well as a solid conductor, form the electrode of a voltaic 
 arc. Moreover, all these effects would have need of being 
 analysed with much more care than has been devoted to them, 
 in order that we may be enabled fairly to distinguish the part 
 of the influence, which is due to the chemical action of the 
 current, from that which is exercised by the heat itself, 
 
CHAP. m. EFFECTS OF DYNAMIC ELECTRICITY. 469 
 
 that is developed bj the current, whether in producing the 
 arc or in heating wires ; it would appear very probable 
 that we should not find in it any peculiarity, that was not 
 the consequence, easy to be anticipated, of the phenomena, 
 that we have described, either in this or in the preceding 
 Chapter. 
 
 Production and Properties of Ozone* 
 
 Before terminating the study of the chemical effects of 
 dynamic electricity, it is necessary to devote a few moments 
 to the examination of one of the most remarkable ; I refer to 
 the odour, half sulphurous, half phosphoric, which accompanies 
 the liberation of electricity in the air, by ordinary electrical 
 machines, and which is found at the positive electrode, when 
 water is decomposed, by means of a powerful electric current. 
 It is to M. Schcenbein that we are indebted, by his profound 
 studies upon this particular point, which had escaped the atten- 
 tion of physicists, for having put them in the way, which 
 has led them to discover the nature itself of this phenomenon. 
 
 Priestley, Cavendish, and Van Marum had plainly re- 
 marked that gases undergo considerable modifications, con- 
 sequent on the passage of electric sparks, and, in particular, 
 they had pointed out, as we have said, the formation of nitric 
 acid, when the gas was a mixture of oxygen and nitrogen, 
 such as is presented by the atmospheric air. Yan Marum, 
 however, by causing a succession of electric sparks to pass 
 in a tube full of oxygen, 5 J inches in length, between a metal 
 conductor, situated at the top of the tube, and a mercury 
 bath, situated at the lower part, had remarked that the 
 gas had acquired a very powerful odour, which he stated 
 was that of the electrical machine. Moreover, on operating 
 with a narrow and shorter tube, he remarked, that the 
 mercury was powerfully oxidised at its surface, and that 
 the volume of oxygen had diminished ; but these effects 
 might be attributed to the formation of nitric acid, seeing 
 that nothing proved that the oxygen was very pure and that 
 it contained no nitrogen. 
 
 M. Schoenbein, sixty years subsequently, being desirous 
 
 H H 3 
 
470 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 of explaining the cause of the odour, that accompanies the 
 voltaic decomposition of water, observed that this odour 
 is manifested at the positive electrode, only so long as this 
 electrode was not oxidisable, namely, when it was platinum 
 or gold. He proved that the odour still exists, when the 
 mixed gases are collected; and that it may be preserved 
 as long as we please, when the oxygen, or the mixture of 
 oxygen and hydrogen, that possesses it, is enclosed in well- 
 stoppered bottles. All electrolytes are not equally adapted 
 to developing the odorous principle; distilled water and 
 solutions of acids or of oxygenated salts liberate it easily ; 
 but it is not the same with concentrated nitric acid, and with 
 solutions of chlorides, bromides, iodides, nor with that of the 
 sulphate of protoxide of iron. In order to cause the odour 
 to disappear, we have merely to throw into the flask, in 
 which the gas impregnated with it is contained, a few pinches 
 of powdered charcoal, filings of iron, zinc, tin, lead, or arsenic, 
 as well as of bismuth or antimony in powder, or even a few 
 d"ops of mercury. The same effect is produced by small 
 quantities of aqueous solutions of the chlorides of iron or tin, 
 of sulphate of protoxide of iron, or of a few drops of nitrous 
 acid. Mere elevation of temperature produce the same 
 effect ; and so the odour is not developed when the 
 electrolytic liquid is heated, even when, as I have observed, 
 it is the current, by which the decomposition is brought 
 about, that heats it. I have also remarked, that although 
 generally a powerful pile is necessary in order that the odour, 
 attending on electrolysis, may be manifested, it may be 
 obtained with a very feeble current, on the precaution being 
 observed of taking for the positive electrode, in acidulated 
 water, a platinum wire inserted in a glass tube, according to 
 Wollaston's method (fig. 239., p. 413). 
 
 An important property of the gas, inpregnated with the 
 odour, and which it ceases to possess, as soon as this odour is 
 removed from it, is the faculty it possesses, of polarising 
 negatively wires or plates of platinum or gold, that are placed 
 in it, namely, of impressing upon them, on being plunged 
 into conducting water with a similar wire or plate, but which 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 471 
 
 has not been in contact with the odorous principle, the 
 property of developing an electric current, of which they are 
 the negative element. 
 
 Schoenbein has observed that the same property might be 
 given to platinum and to gold, by receiving on very clean 
 plates of one or other of these two metals, the electricity 
 emanating from the blunt extremity of a wire, in communi- 
 cation with the conductors of an electrical machine, and 
 placed at a distance of about an inch from the plates. It 
 is of little consequence whether it is one or other of the 
 electricities, that comes out from the conductor; the effect 
 upon the plate is the same, but the phenomenon is not mani- 
 fested, if, the metal being in direct communication with the 
 conductor, the electricity comes out from the plate, instead 
 of being received by it. Platinum and gold immediately 
 lose their polarity under the action of heat, or if they are 
 plunged for a few moments in an atmosphere of hydrogen ; 
 only, in this latter case, these metals may acquire an opposite 
 polarity, when they are left too long in the hydrogen. 
 
 The odour always attends the polarisation of the me ' 
 thus, no odour nor polarisation is observed when the p< 
 from which the electricity comes out, are heated or are sur- 
 rounded by a layer of water ; it is sufficient even to envelope 
 the metal point with a little piece of cloth, moistened with dis- 
 tilled water, in order to prevent the production of the odour. 
 
 These first observations already establish a great analogy 
 between the odorous principle, developed in the electrolysis of 
 water, and that which is produced by the electricity of ordinary 
 machines ; it also appears probable that it is identical with 
 that which is manifested in clouds, and particularly in the 
 neighbourhood where a lightning flash had occurred. It is, 
 moreover, evident that it is gaseous, and that it is a product 
 of the action of electricity upon the ambient medium, which 
 can be only oxygen, nitrogen, or the vapour of water ; with M. 
 Schoenbein, we will call it ozone, without anticipating for the 
 moment anything as to its chemical nature, simply on account 
 of the peculiar and very decided odour, that it possesses. 
 
 Led by analogies deduced from the odour, M. Schoenbein 
 
472 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 discovered a chemical method of preparing ozone. This 
 method consisted in placing a piece of phosphorus in a vessel, 
 filled with common air. If the temperature is sufficiently 
 elevated for the phosphorus to become luminous, the air of 
 the flask soon acquires an odour of ozone, very distinct from 
 that of phosphorus, or rather from the phosphoric acid, that is 
 liberated at the commencement. This air presents the same 
 phenomena as if it had been submitted to the action of 
 electricity, namely, that the platinum and gold plates are 
 polarised negatively, and that it loses its properties, when 
 filings of iron or of another oxidisable metal, are agitated 
 in it. Phosphorus, in pure and very dry oxygen, in which 
 it does not become luminous, does not produce ozone ; it is 
 necessary, for this production, that it be phosphorescent ; 
 and, for this purpose, that it be placed in a mixture of oxygen 
 and nitrogen, and at a temperature which is not too low. 
 
 Independently of these fundamental properties, ozone, 
 whatever be the manner in which it is prepared, possesses 
 a great number of others, of which the following are the 
 principal. It acts upon vegetable colours, like chlorine; 
 namely, it destroys and bleaches coloured papers, that are 
 plunged into gases that contain it. And this takes place 
 equally whether the ozone has a chemical or an electric 
 origin ; and whether this electric origin arises from electro- 
 lysis, from the action of the electrical machine, or from 
 atmospheric electricity. It is the same with all the chemical 
 effects of ozone, and in particular with one of the most re- 
 markable, namely, with the action that it exercises over 
 iodide of potassium, which absorbs it, liberating iodine, which 
 is rendered sensible by the change of colour. In effect, if 
 starch paste is mixed with a small quantity of a solution of 
 iodide of potassium, and a slip of paper is plunged into it, a 
 test is obtained for ozone, which greatly surpasses in delicacy 
 the best galvanometer, or the most delicate sense of smell. 
 A quantity of ozone, too feeble for polarising a metal in a 
 sensible manner, or for being detected by the smell, is yet 
 sufficient to make the test-paper blue in a decided manner. 
 
 We cannot follow M. Schoenbein in the detailed study, that 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 473 
 
 he has made of the various chemical reactions of ozone, both 
 upon inorganic substances, as well as upon organic com- 
 pounds. Without entering into further details, we may merely 
 say that ozone, in a general manner, always comports itself, 
 and more particularly in respect to compound gases and to 
 simple bodies, absolutely like chlorine or bromine. 
 
 Iodide of potassium enables us to discover the most feeble 
 traces of ozone in the atmospheric air. We have merely to 
 suspend in the open air little slips of filtering paper moistened 
 with a mixture of the iodide and starch, and commonly, at the 
 end of a few minutes, they are seen to become blue, whilst they 
 are not at all coloured in vessels hermetically sealed and filled 
 with air. Ozone is also found in the water of a storm ; for 
 this water imports itself exactly like distilled water, in which 
 ozone has been dissolved. It is simply necessary, in these two 
 cases, in order to liberate the ozone, to pour a little sulphuric 
 acid into the water ; it immediately colours blue the paste of 
 iodine and starch. It would appear that ozone forms with pure 
 water a compound, which is destroyed by the presence of 
 sulphuric acid. We can exactly communicate all the proper- 
 ties of the water of a storm to distilled water, placed in a cup 
 and put into communication with the ground, whilst it is ex- 
 posed to the action of an energetic electric brush, and which 
 diffuses a powerful odour. It is necessary that this exposure 
 should endure for at least half an hour, in order that the 
 water may be sufficiently ozonised. 
 
 Without dwelling upon the divers hypotheses, thathave been 
 advanced upon the nature of ozone, we shall pass on at once to 
 the experiments of M. Marignac, which have been the first to 
 solve the question in a peremptory manner. This learned 
 chemist has first demonstrated that the presence of nitrogen was 
 not, as M. Schoenbein had at first thought, indispensable to the 
 production of ozone. In effect, on decomposing water, aci- 
 dulated with sulphuric acid, in an apparatus accurately pre- 
 serving vacuum, and into which no trace of air could enter, 
 after the experiment had gone on for several days, and the 
 fourth part of the water had been decomposed, the odour of 
 ozone was the same as at the first instant ; it was merely ne- 
 
474 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 cessary to take the precaution of retaining the flask, in which 
 the decomposition takes place, at a low temperature.* Further- 
 more, M. Marignac has found that the most convenient method 
 of obtaining ozone consists in directing a current of air, by 
 means of a gasometer, through a tube, about a yard long and 
 a quarter of an inch in diameter, containing in its length a 
 series of sticks of phosphorus. He has proved, by means of 
 this apparatus, that neither pure oxygen nor nitrogen produces 
 ozone ; but that oxygen mixed, not only with nitrogen, but 
 even with carbonic acid and with hydrogen, developes it. 
 "Perfectly dry atmospheric air does not liberate any ; the 
 phosphorus, in this case, is covered with a white crust, and 
 does not become phosphorescent ; now, its phosphorescence is 
 a condition necessary, in order to there being a production of 
 ozone. 
 
 M. Marignac, on submitting ozone to different tests, re- 
 marked, first, that it is destroyed in passing through a tube 
 heated to 600 or 700 ; that it undergoes no alteration on the 
 part of water, concentrated sulphuric acid, ammonia, and 
 baryta water ; but it is absorbed with the greatest facility by 
 dissolved iodide of potassium ; the liquor becomes yellow ; 
 a portion of iodine is set at liberty, and drawn on by the 
 current of air. When all the iodide is decomposed, the odour 
 of ozone appears, and the liquor again becomes colourless, and 
 contains nothing besides iodate of potassium, mixed with a 
 little carbonate. Metals, in like manner, absorb ozone ; thus 
 on making ozonised air pass through a small tube 4 or 5 in. 
 in length, filled with pure and porous silver, it is found that 
 this air completely loses its odour and its properties, and that 
 
 * M. Soret more recently has found that the quantity of ozone obtained by 
 the electrolisation of acidulated water, increased in a very great proportion 
 with the reduction of temperature. Thus, on surrounding the voltameter with 
 a frigorific mixture of ice and sea-salt, and, still better, chloride of sodium, the 
 gas that escaped from it was so much ozonised, that it attacked and rapidly 
 pierced the caoutchouc tubes, which connected the drying tubes, that it had to 
 traverse. On dosing the ozone by means of a known solution of arsenious 
 acid, which, like chlorine, possesses the property of transforming it into arsenic 
 acid, M. Soret has found a proportion of ozone rising to nearly 0-005 of the 
 volume of oxygen, by cooling the voltameter sufficiently for the temperature 
 to be still 19 '4 at the end of the experiment; this same proportion was at 
 most 003, when the voltameter was not cooled. 
 
CIIAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 475 
 
 the silver is transformed into a matter, which has all the 
 characteristics of oxide of silver ; but the presence of moisture 
 is indispensable. If the ozonised air is completely dried, 
 by its passage through several tubes, filled with pumice-stone 
 impregnated with sulphuric acid, it attacks neither silver 
 nor copper, nor even zinc, and it no longer loses its odour. 
 
 These experiments, and others besides, no longer allow 
 us to chose between two hypotheses on the nature of ozone ; 
 one, that it is a new compound of hydrogen and oxygen, 
 susceptible of being transformed with great facility into 
 oxygen and water, and capable of giving off its oxygen to a 
 great number of bodies ; the other, that it is only a peculiar 
 modification of oxygen, in consequence of which this gas 
 acquires, with a peculiar odour, the property of combining 
 with bodies, upon which it is without action in its ordinary 
 state. This last hypothesis is the one that M. Marignac 
 and I were led to admit, as the result of experiments, in 
 which we endeavoured to expose to electric discharges various 
 gases, that we caused to arrive successively in a glass tube 
 6 in. in length, and -| in. in diameter, communicating on one 
 side with the apparatus, intended to produce the current 
 of gas, that we were desirous of studying, and on the other 
 with a flask, in which we might examine the properties 
 which these gases had acquired. Two platinum wires 
 penetrated by the extremities of the glass tube, and ter- 
 minated in its interior at nearly half an inch from each other. 
 One of these wires was placed in communication with the 
 ground, the other with the conductor of the machine ; it was 
 a matter of indifference whether the charge was made by a 
 succession of sparks, or by a continuous and invisible current. 
 The formation of ozone was easily detected, by means of its 
 odour, and its action on paper impregnated with starch mixed 
 with iodide of potassium. Now, the experiment made with 
 ordinary air, perfectly dried, gave a development of ozone, as 
 great as when the air was moist ; ozone was in like manner 
 developed with the greatest facility in oxygen perfectly pure 
 and dry ; such as is extracted from chlorate of potash purified 
 and previously melted. No ozone was formed in pure carbonic 
 
476 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 acid gas, whether dry or moist, but some was produced, 
 as soon as a very small quantity of air or of oxygen was 
 mixed with the carbonic acid. 
 
 M. Schoenbein, as the result of fresh researches, has him- 
 self come to adopt the opinion, to which M. Marignac and I 
 had been led, that ozone is only a modification of oxygen, by 
 which its chemical affinities are exalted ; for renouncing the 
 opinion that it is a peroxide of hydrogen, he dwelt especially 
 upon the fact that a mass of ozonised air, on traversing a 
 tube heated to near 600, is de-ozonised, without production 
 of water. He also demonstrated that, treated by an alkali, 
 ozonised air always produces a nitrate, on account of the 
 facility that oxygen, in the state of ozone, possesses of com- 
 bining with nitrogen. 
 
 MM. Fremy and E. Becquerel have also, as the result 
 of long and rigorous researches, succeeded in demonstrating 
 that ozone is an allotropic modification of oxygen, due to 
 electricity. In order to obtain ozone, they have employed suc- 
 cessively the decomposition of water by electric currents; 
 the action upon air and upon oxygen of sparks, obtained by 
 the breaking of a voltaic circuit ; of those produced by an 
 induction apparatus ; and, finally, of those, drawn from 
 ordinary electrical machines. The first method produced 
 too little ozone. Voltaic sparks are accompanied by a liberation 
 of heat, which destroys the ozone, in proportion as it is pro- 
 duced ; it is the same, although in a less degree, with the 
 induction sparks ; they were, therefore, compelled to renounce 
 these methods of obtaining ozone, in order to recur to the 
 action of the sparks of ordinary machines. Both philosophers 
 recognised that oxygen, whatever be the source, whence it 
 is derived, is susceptible of being ozonised ; and that oxygen, 
 which has been de-ozonised, by traversing iodide of potassium, 
 may again be ozonised. But the most important, among the 
 points, which they have established, is that a given quantity 
 of oxygen may be entirely converted into ozone ; and that if, 
 in the previous experiments, they had never succeeded in 
 ozonising more than a portion of the gas, submitted to experl 
 ment,it is that probably the electric spark, by its calorific action, 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 477 
 
 destroyed in great part the effect of the ozonisation, that it had 
 produced upon the oxygen. In order to avoid this incon- 
 venience, it was necessary to absorb the ozone, in proportion 
 as it was formed ; with this view some pure oxygen was 
 introduced into a eudiometric tube, itself placed upon a 
 solution of iodide of potassium ; the gas was subjected to the 
 action of electric sparks passing between platinum wires 
 fixed at the top of the tube; there were several similar 
 tubes, the diameters of which were -^ in., and the length 
 nearly 5 in. ; the sparks were about in. in length. The 
 oxvgen was absorbed in a regular manner by the action 
 of the electric sparks ; after three hours of electrisation, the 
 liquid had risen f in. in the interior of the tube ; the absorp- 
 tion was in general proportional to the time of electrisation ; 
 on continuing the experiment for a sufficiently long time, 
 the oxygen might be made to be completely absorbed by the 
 iodide of potassium. A very curious result was obtained, by 
 causing the same quantity of electricity to pass in two tubes 
 placed one after the other, and similar in every respect, 
 except that, by the arrangement of the platinum wires, 
 the sparks were an inch in length in one, and only -- in. in 
 the other ; after three hours of electrisation, the absorption 
 of oxygen in the former was double what it was in the latter, 
 which proves that, for a like quantity of electricity, which 
 traverses a similar mass of gas, a long spark produces more 
 effect than a shorter one.* A plate of silver, introduced 
 into a eudiometric tube placed over water and filled with 
 pure oxygen, absorbed the electrised oxygen, like iodide 
 of potassium, but more slowly than it ; and the absorption 
 took place until the complete disappearance of all the gas. 
 Mercury, under the influence of moisture, has produced the 
 same effect, and is in like manner oxidised. 
 
 Amid the multiplied experiments of MM. Fremy and E. 
 Becquerel, we will in addition cite the following ; in which, 
 having introduced pure oxygen into narrow tubes, one con- 
 
 * Might it not be possible that this result is clue both to the fact that the 
 long spark acts in the same time upon a great number of particles, and that, 
 on the other hand, it developes less heat than the short one? 
 
478 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 taining moist iodide of potassium, and the other a small plate 
 of silver covered with moisture, they caused a series of 
 electric sparks to pass into the interior of these tubes, 
 after having closed them at the lamp, at their two extre- 
 mities. The tube containing the moist silver was electrised 
 for four days, at the rate of six hours per day, "namely, 
 for twenty-four hours in all ; the plate was covered with 
 oxide of silver ; and on then breaking one of the extremities 
 of the tube under water, an absorption was proved equal to 
 two-thirds of the volume of oxygen, submitted to experiment. 
 The absorption was total in the second tube, containing the 
 iodide of potassium ; even, after eighteen hours of electrisa- 
 tion, the spark, which had much brilliancy, was scarcely 
 visible ; a proof that the vacuum in the tube was nearly com- 
 plete ; after forty- eight hours, the tube having been broken 
 at one of its extremities under water, the latter immediately 
 rushed into it, and totally filled it. 
 
 It, therefore, appears now to be well established, that elec- 
 tricity, in acting upon oxygen, impresses upon it properties, 
 which it did not possess before being electrised, and which 
 are manifested by a peculiar odour, and by an exaltation in 
 its chemical activity. It is very probable that the action of 
 phosphorus is also an electric action, arising from a liberation 
 of electricity, which must accompany the combination of a 
 part of the oxygen with this body, and which is manifested by 
 its phosphorescence. 
 
 With regard to the nature of the action, that electricity 
 exercises over oxygen, in order to ozonise it, this is still a 
 mystery ; it might not be impossible that it consists in in- 
 sulating the atoms of oxygen from each other, which in 
 the ordinary state might be grouped so as to form 
 molecules, composed of a greater or less number of these atoms. 
 We could conceive that thus insulated, the atoms might 
 have a greater chemical activity, than when they are 
 agglomerated. This might be the nascent state. This property 
 of oxygen of forming molecules composed of atoms grouped 
 together, might very well be reconciled with the magnetic 
 virtue possessed by this gas, and which it is alone in 
 
CHAP. in. EFFECTS OF DYNAMIC ELECTRICITY. 479 
 
 possessing.* But it is premature to venture upon hypotheses, 
 on which experiment alone can decide ; and to which, more- 
 over, we shall be called again to direct our attention in the 
 sequel. 
 
 We shall confine ourselves to pointing out two rocks upon 
 which physicists have fallen and run the risk of falling, who 
 have been occupied with ozone ; one is, in believing that they 
 see in it a nitrous compound, which is due to the difficulty 
 there is in excluding the presence of nitrogen, which in effect 
 is itself sufficient to bring about the formation of such 
 a compound ; the other, is in believing that ozone is an 
 oxide of hydrogen on account of this water, which oxygen, 
 although perfectly dried, may still deposit on being de- 
 ozonised. M. Baumert had thought he might even conclude 
 from this a difference between ozone, obtained by the electro- 
 lysation of water, and that which is derived from the electro- 
 lysation of oxygen by sparks, admitting that the latter is 
 indeed an allotropic modification of oxygen, but that the 
 former is an oxide of hydrogen. However, it is easy to 
 explain the presence of a small quantity of moisture in the 
 oxygen, that is derived from the electrolysation of water, by 
 the facility with which hydrogen may mix with it, and con- 
 sequently form water, especially when it is thought that the 
 production in question is of merely 0*07 grs. of water, in 
 operations that have continued without interruption, one, six, 
 the other, eight days. 
 
 We must not dwell upon the consequences that result 
 from the production and the properties of ozone in the electro- 
 chemical decomposition of substances, of which oxygen is one 
 of the elements. We shall point out one alone, which is 
 perhaps the most important, namely, the formation of oxy- 
 genated water, in the electrolysis of acidulated water, and, 
 consequently, of the inaccuracy that results from it in the 
 indications of chemical voltameters. M. Meidinger has 
 studied the circumstances which facilitate this formation in 
 facilitating that of ozone ; it is first the degree of concentra- 
 
 * Vol. I. p. 468. and following. 
 
480 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 tion of the acidulated water ; with sulphuric acid of the 
 density 1 *4, he obtained in 6 minutes 245 measures of hy- 
 drogen for 87 of oxygen; whilst with acid of only 1-07 of 
 density he obtained in 19 minutes the required proportions 
 of 244 hydrogen, and 122 oxygen. Then there is the form 
 of the positive electrode ; on taking for this electrode a wire, 
 instead of a plate of platinum, he obtained only 40 measures 
 oxygen for 253 of hydrogen. Then there is finally the force 
 of the current and the reduction of temperature ; two circum- 
 stances that very notably diminish the proportion of oxygen in 
 relation to that of hydrogen. This greater or less diminution 
 in the required quantity of oxygen is accompanied by an 
 odour of ozone, which indicates the production of this body ; 
 but it is easy to prove, on examining the liquid, that the 
 greater part of the liberated ozone has been employed to 
 form the bioxide of hydrogen, which is found in the state of 
 solution in the electrolytic liquid. The presence of this bi- 
 oxide renders this liquid very unfitted for using in volta- 
 metric experiments ; for it then gives a less proportion of 
 hydrogen, than that which is liberated in another voltameter, 
 charged with a liquid that has not been used, and that is 
 placed in the same circuit. It is therefore necessary to change 
 the liquid of the voltameter, when it has been used for a 
 certain time, or carefully to boil it, in order to expel the bi- 
 oxide of hydrogen. In general, if we desire that the indica- 
 tions of the voltameter shall be exact, namely, that the gases 
 shall be truly liberated in the rigorous proportions, it is 
 necessary, in order to avoid the production of ozone, to 
 make use of a water rather feebly acidulated (!! in density), 
 to cause the hydrogen to be liberated on a wire, and the oxy- 
 gen on a plate of platinum which must not be too small.* 
 
 * List of the principal works relating to the subjects treated of in this 
 Chapter. 
 
 Nicholson and Carlisle. Decomposition of water. Bibl. Brit. t. xv. p. 11. 
 
 Cruikshanks. Decomposition of salts. Bibl Brit. t. xv. p. 23. 
 
 Davy. Chemical power of voltaic electricity, &c. Bibl. Brit. t. xxxi v. 
 pp. 16. and 397.; t. xxxvi. p. 391.; t. xxxix, p. 3.; t. xli. p. 33. Ann. de Ch. 
 t. Ixii. p. 172.; t. Ixviii. p. 203.; t. Ixx. pp. 189. and 225. 
 
 Gay-Lussac and Thenard. Causes that facilitate electro-chemical decom- 
 
CHAP. m. BIBLIOGRAPHY. 481 
 
 positions. Phyaico- chemical Researches, 2nd vol. in 8vo. (Paris, 1811) ; Ann. 
 de Ch. t. Ixxxiv. and Ixxix. 
 
 Hizinger and Berzelius. Transport in electro-chemical decompositions. 
 Ann de Ch. t. li. p. 167. 
 
 Grotthus, Theory of electro-chemical decomposition. Ann. de Ch. t. Iviii. 
 p. 54. Influence of density upon explosive mixtures. Idem. t. Ixxxii. p. 34. 
 
 Faraday. Conditions necessary for electrolysis ; electrolytic law. Experi- 
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 1834.) Bibl. Univ. t. lv. pp. 20. and 394.; t. Ivii. p. 305.; t. Iviii. p. 263. 
 
 Daniell. Mode of decomposition of saline solutions. Bibl. Univ. (new 
 series, 1839) t. xxiv. p. 386. Arch, de tElectr. t. i. p. 694. ; and t. iv. p. 259. 
 
 Matteucci. Chemical action of electricity. Laws of the decomposition of 
 mixtures, of compound multiples, &c. Bibl. Univ. t. Iviii. p. 23. Bibl. Univ. 
 (new series) t. xx. p. 159.; t. xxi. p. 153.; t. xxiv. p. 352.; t. xxvi. p. 380.; 
 t. xxviii. p. 410. (1830 1840). Arch, de VElectr. t. i. p. 340. Ann. de Ch. 
 et de Phys. t. xlv. p 322.; and t. Iviii. p. 75. 
 
 Becquerel, sen. Decompositions of mixtures, measure of affinities, &c. 
 Comptes rendus de VAcad. des Sc. t. x. p. 671. Treatise on Electricity and 
 Magnetism. 
 
 E. Becquerel.- Decomposition of compound multiples. Ann. de Ch. et de 
 Phys. (new series) t. xi. pp. 162. and 257. Decomposition of oxygenated water. 
 Comptes rendus de VAcad. des Sc. t. xviii. p. 862, Influence of dissolved gases 
 upon the electrolysation of water. Arch, de VElectr. t. i. p. 281. 
 
 Hittorff. Decomposition of the sulphurets. Ann. de. Ch. et de Phys. (new 
 series) t. xxxiv. p. 124.- Unequal transport at the two poles. Ann. der Physik. 
 t. Ixxxix. (No. 6. of 1853.) 
 
 Beetz. Decomposition of the iodide of mercury, of glass, &c. Ann. der 
 Physik, t. xc. p. 492. (No. 7. of 1854.) 
 
 Pouillet. Unequal electro -chemical power of the two poles. Comptes rendus 
 de fAcad. des Sc. de Paris, t. xx. p. 1544. 
 
 Almeida. Explanation of anomalies in electrolysis. Comptes rendus de 
 de lAcad. des Sc. de Paris, t. xxxviii. p. 682. 
 
 Buff. Confirmation of Faraday's electrolytic law. Arch, des Sc. Phys. 
 t. xxii. p. 344. and t. xxv. p. 65. 
 
 Soret. Idem. Arch, des Sc. Phys. t. xxv. p. 175. and t. xxvii. p. 113. 
 Ozone, t. xxv. p. 263. 
 
 De la Rive. Resistance to passage from a solid conductor to a liquid con- 
 ductor, and oxidation of platinum. Ann. de Ch. et de Phys. t. xxxvii. p. 215. 
 Arch, de TElectr. t. i. p. 175. and p. 333. Arch, des Sc. Phys. t. i. p. 373. 
 
 Nobili. Electro-chemical appearances &c. Bibl. Univ. t. xxiii. p. 312. ; 
 t. xxxiv. p. 194.; t. xxxv. p. 261.; t. xxxvi. p. 3.; t. xxxvii. p. 174.; and 
 t. Ivi. p. 150. Ann. de Ch. et. de Phys. t. xxxiv. p. 286. and 419. 
 
 Poggendorff. Resistance to passage. Arch, de VElectr. t. i. p. 497. 
 
 Vorsellman de Herr. Idem. Arch, de VElectr. t. i. pp. 539. and 581. 
 
 Lenz. Idem. Arch, de VEkctr. t. i. p. 177. Ann. der Physik. t. xlviii. 
 p. 385. 
 
 Meidinger. Formation of oxide of hydrogen in the electrolysation of water. 
 Arch, des Sc. Phys. t. xxv. p. 170. Ann. der Ch. und Phar. t. Ixxxviii. p. 57. 
 
 Despretz. Verification of Faraday's law in the electrolysation of water. 
 Comptes rendus de FAcad. des Sc. de Paris of May 22. 1854, t. xxxviii. 
 
 Schcenbein. Influence of dissolved gases on the electrolysis of Water Arch, 
 de TElectr. t. ii. p. 241. Ozone. Bibl. Univ. (new series), t. xxv., (1840) 
 p 342. Arch, de VEectr. t. iii. p. 295.; t. iv. p. 333.; t. v. pp. 11. 333. and 556. 
 
 Herschel. Movement of mercury by the electric current. Ann. de Ch, et 
 de Phys. t. xxviii. p 280. 
 
 Serullas. Movements of alloys of potassium, &c. Ann. de Ch. et de Phys. 
 t. xxxiv. p. 192. 
 
 Porret. Electro -chemical transport of water. Ann. de Ch. et de Phys. 
 t. 11. p. 137. 
 
 VOL. II. I I 
 
482 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 Wiedemann. Laws of the transport of liquids through diaphragms. Ann. 
 de Ch. et de Phys. (new series), t. xxxvii. p. 242. Arch, des Sc. Phys. t. xxiii. 
 p. 184. 
 
 Graham. Electric endosmose. Arch, des Sc. Phys. t. xxvii. p. 37. 
 
 Napier. Idem. Arch, de VElectr. t. v. p. 459. Arch, des Sc. Phys. t. ii. 
 p. 345. and t iv. p. 68. 
 
 Paetz and Van Troostwik. Decomposition of water by the electric spark. 
 Ann. de Ch. t. v. p. 276. 
 
 Pearson. Idem. Ann. de Ch. t. xxvii. p. 161. 
 
 Van Marum. Idem. Ann. de Ch. et de Phys. i. xli. p. 77. 
 
 Wottaston. Idem. Ann. de Ch. et de Phys. t. xvi. p. 45. 
 
 Bonijol. Decompositions brought about by ordinary electricity. Bill, 
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 Melly. Chemical decomposition by the voltaic spark. Arch, de VElectr. 
 t. i. p. 297. 
 
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 Masson. Chemical effects of inductive electricity. Comptes rendus de 
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 Quet. Idem. Incandescence of electrodes. Comptes rendus de VAcad. 
 des Sc. t. xxxvi. p. 1012. 
 
 Mackrell Incandescence of electrodes. Arch, de VElectr. t. i. p. 1575. 
 
 Van der Willigen. Idem. Arch des Sc. Phys. t. xxvii. p. 312. 
 
 Marignac. Ozone. Arch, de TElectr. t. v. p. 5. 
 
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 Beaumert. Idem. Arch des Sc. Phys. t. xxiv. p. 381. 
 
CHAP. TV. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 483 
 
 CHAP. IV. 
 
 PHYSIOLOGICAL EFFECTS OF DYNAMIC ELECTRICITY. 
 
 Nature of the Effects that are exercised upon Organised 
 Bodies by Dynamic Electricity. 
 
 WE have seen that a frog, properly prepared, suffers a 
 shock, when it is traversed by even a very feeble electric 
 current. Even, before this experiment of Galvani's, it was 
 known that electricity exercises a special action over organised 
 bodies, both vegetable as well as animal ; the electricity 
 furnished by electrical machines, had even been employed 
 as a curative means in cases of paralysis ; but it is chiefly 
 since the discovery of the pile, that we have been enabled to 
 study with more precision the physiological action of dy- 
 namic electricity. This study is very difficult and delicate, 
 as is everything touching on physiology, on account of the 
 ignorance in which we still are, as to the mode of action 
 of the vital force, which presides over all phenomena of this 
 kind. Furthermore: does this electricity act in a direct 
 manner? or does it only exercise an indirect action, by 
 bringing about calorific and chemical effects, which might 
 themselves be the causes of the phenomena observed ? And, 
 in effect, when traversing organised bodies, it necessarily 
 produces in them heat, and chemical decompositions ; in 
 degrees, it is true, more or less sensible, but yet for the most 
 part appreciable. Now, this heat and these decompositions, 
 may themselves give rise to effects, which might erroneously 
 be attributed to the direct action of electricity. Thus Davy, 
 having submitted a laurel leaf to the action of a pile of 150 
 pairs, employing it to connect together two vessels filled with 
 pure water, into each of which was immersed one of the 
 
 x i 2 
 
484 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 electrodes. This leaf assumed the same appearance as if it 
 had been exposed to a temperature of 500 or 600; it 
 became brown, and was even shrivelled ; the green colouring 
 matter, as well as resin, alkali, and lime, had been transported 
 into the negative vessel, whilst the positive contained a clear 
 liquid, that had the odour of the peach blossom, which was 
 hydrocyanic acid. A plant of mint, also employed as a 
 conductor, gave, after a prolonged action, results of the same 
 kind ; but, if the action does not continue too long, the plant 
 is able to recover its original state. It is evident that the 
 electric current acts upon vegetable and animal matters, as 
 upon electrolytes, and that it must necessarily, at the end of 
 a certain time, bring about the disorganisation of the organised 
 body, as would every other calorific or chemical action. 
 
 In the same manner may be explained the apparent in- 
 fluence of electricity upon germination and fermentation. It 
 follows, from the numerous trials, that have been made upon 
 the former point, that static electricity exercises no influence 
 over germination, as Ingenhouz had very well demonstrated, 
 by showing that the errors into which we had fallen in this 
 respect were due to our not having had regard to important 
 circumstances, such as the presence of water, of light, &c. 
 With regard to the influence of dynamic electricity, which is 
 real in some cases, it is easy to prove that it arises from an 
 indirect action, namely, from that, which is exercised by the 
 products of decomposition, and in particular by that of 
 oxygen and the acids, on the one hand, hydrogen and the 
 alkalis, on the other hand, upon seeds placed at one or the 
 other pole, whether in the water, or in moist earth. Thus, 
 whilst oxygen facilitates germination toward the positive 
 electrode, it also very frequently happens that the acid, 
 which is equally liberated at this electrode, produces the 
 contrary effect, by destroying the seed, whilst it is seen to 
 grow at the negative electrode, where an alkaline base is 
 accumulated; this is the result of the numerous researches 
 upon this subject by M. Becquerel and M. Matteucci. But 
 it is not impossible, as we shall see in the Fifth Part, that 
 the electricity developed, even in the act of germination, plays 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 485 
 
 a part, secondary it is true, in this physiological phenomenon. 
 It is the same with the fermentation that M. Gay-Lussac 
 succeeded in bringing about in the juice of the grape, pre- 
 served protected from the air, by plunging into it two pla- 
 tinum wires, communicating respectively with the poles of a 
 powerful pile; it is evident that oxygen, due to electrolytic 
 action, was the cause of the fermentation, since nothing more 
 was necessary than to introduce a small portion of this gas, in 
 order to bring about the production of the phenomenon, which 
 cannot commence in a medium in which there is no oxygen. 
 Finally, the coagulation of albumen around the negative 
 electrode, observed by M. Lasaigne, is also the result of the 
 presence at this electrode of acids, arising from the decom- 
 position of certain salts. 
 
 We shall not, therefore, dwell longer upon these indirect 
 effects of the electric current, we shall confine ourselves to two 
 remarks; first, that we must take it into account, when 
 occupied with the direct effects, and when especially we 
 arrive at the study of the electricity itself, produced by 
 actions either purely physiological, or chemico-physiological ; 
 secondly, that the chemical influence of dynamic electricity 
 upon the organic products would in itself be the subject of a 
 very interesting study, on account of the characters peculiar 
 to this kind of compounds, which cause them to differ in so 
 decided a manner from inorganic compounds, on account of 
 the life that has presided over their formation. Unfor- 
 tunately, the number of researches hitherto made on this 
 particular point, which is more in the jurisdiction of organic 
 chemistry than of electricity, is very limited; we shall 
 endeavour to make known the small number of results, that 
 have been obtained, when we shall be occupied with electro- 
 chemical applications. 
 
 Let us, therefore, now pass on to the phenomena them- 
 selves, to which the direct action of electricity upon organised 
 bodies gives rise. Vegetables, although much less excitable 
 than animals, are yet so within certain limits. Thus, either 
 the Mimosa sensitiva or the Mimosa pudica present movements, 
 when the electric current is made to pass through their 
 
 113 
 
486 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 branches and leaves, by means of small plates of lead or tin, 
 with which they are covered, in some parts of their surface. 
 The simple communication of the coatings together, without 
 the intervention of the pile, is not sufficient ; but, with the 
 passage of electricity we see, in the Mimosa pudica especially, 
 a minute after the establishment of the current, the leaves, 
 especially those that are coated, bend upon their branches ; 
 then the same effect is produced successively upon other 
 leaves here and there, in several parts of the plant. Giulio, 
 to whom we are indebted for these experiments, has found 
 that, in the Mimosa asperata, in which the natural irritability 
 is less decided, the irritability produced by electricity upon 
 its knots, its leaves, and its petals, is much less than upon 
 the other two species of mimosa. The Hedysarum gyrans } and 
 other plants, remarkable by the movements, that are pre- 
 sented by their follicles, suffer no influence on the part of 
 - dynamic electricity. 
 
 We therefore perceive that the physiological action of this 
 agent upon the vegetable kingdom is of very little im- 
 portance; or at least that our knowledge in this respect is 
 very limited. However, there exists yet one plant, upon 
 which very remarkable effects of electricity have been ob- 
 served, it is the char a, which, as we know, presents a very 
 curious physiological phenomenon, namely, a circular move- 
 ment of the globules and of the lymph ; these globules, 
 directed from below upwards, descend again the moment they 
 encounter a knot, which opposes their motion, in order to re- 
 ascend, and so on ; on taking away the diaphragm, which 
 forms the knot, the globules escape by the opening, and dis- 
 seminate themselves in the water. MM. Dutrochet and 
 Becquerel, on causing an electric current of greater or less 
 force to pass in a stem of the chara, sometimes from above 
 downwards, sometimes from below upwards, have remarked 
 that this transmission produces in the first instance, a torpor 
 in the movement of the globules, the intensity of which 
 depends upon the force of the current, and which is in- 
 dependent of its direction, but which is the same on ascending 
 and descending motions. When the motion of the lymph has 
 been arrested, it recommences gradually, without the current 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 487 
 
 ceasing to pass, and it recovers the velocity which it had 
 primitively ; the duration of the stoppage depends upon the 
 intensity of the current ; it may extend to several hours, if 
 this intensity is sufficiently great ; but the passage of the 
 electricity produces no disorganisation in the plant, since a 
 repose of greater or less duration restores to it its natural 
 faculties. Elevation of temperature produces upon the 
 chara effects analogous to those of the passage of the cur- 
 rent. Setting out from 32, the circulation of the chara is 
 accelerated in proportion as the temperature rises ; at 65 or 
 66, it is very rapid ; it diminishes to 80, where it is very 
 much reduced; it then again increases to 113, when it ceases 
 entirely, or it is not able to recommence, the plant under- 
 going at this temperature a disorganisation, which destroys 
 the rotatory movement of the globules. We may therefore 
 believe that it is to the heat, which it developes in traversing 
 the chara, that the current owes its effect ; but it never 
 produces acceleration, as the augmentation of temperature 
 brings about ; and, on the other hand, heat does not produce 
 a stopping, like that which takes place with electricity trans- 
 mitted. It therefore appears more probable, that the in- 
 fluence of the current upon the circulation of the chara arises 
 from the new arrangement, which it compels the molecules of 
 the vegetable to assume, by polarising them; a polarisation 
 which, when it is followed by a very powerful decomposition, 
 may disorganise the vegetable ; but against which, however, 
 the vital forces, that produce circulation, contend with 
 sufficient advantage, that the organic molecules, deranged 
 from their natural position of equilibrium, are able to re- 
 cover their primitive properties. The action, by which the 
 rotatory motion is brought about, overpowering that of the 
 current, the latter continues to pass without disturbing the 
 motion ; but the conflict ceases, when the current possesses 
 a sufficient intensity ; on the other hand, the vital forces, after 
 having made efforts, which, moment by moment, exhaust 
 them, recover their faculties, after a certain time of repose, 
 when once they cease to be exposed to the action of electricity. 
 Wo therefore see, that there are very notable differences 
 
 114 
 
488 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 between heat and the current, in respect to the manner 
 in which their action is exerted, which enables us to con- 
 clude that electricity acts in this class of phenomena in a 
 manner that is peculiar to itself. 
 
 But it is chiefly upon animals that the direct action of 
 electricity has been proved and studied. The most striking 
 manner of demonstrating this is to prepare a frog after 
 Galvani's plan (fig. 256. ) 3 by cutting it in the middle of the 
 
 Fig. 256. 
 
 body ; then, after having rapidly skinned it, the point of a 
 pair of scissors is passed beneath the two lumbar nerves, that 
 appear like white threads on each side of the vertebral 
 column ; the two or three lower vertebra? are removed, and 
 thus the lumbar nerves are laid bare ; they thus form the 
 only link, which now connects the lower limbs with the su- 
 perior vertebras. If now the frog is suspended to an insu- 
 lated conducting wire, by means of its nerves, and that, by 
 touching the lower limbs with another conductor, a slight 
 discharge or a feeble electric current is made to pass from the 
 nerves to the muscles, the limbs of the frog are seen to un- 
 dergo a sudden and extremely sharp contraction. The 
 experiment may, in like manner, be made by placing the 
 legs of the frog each in a separate glass, filled with water 
 (fig. 257.) ; and by plunging into one of the glasses the zinc, and 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 489 
 
 into the other the copper of a small pair, the frog immediately 
 undergoes a contraction of so great violence that it is com- 
 
 Fig. 257. 
 
 monly thrown from one glass into the other, or even from 
 both glasses altogether. It is not necessary in order to ob- 
 tain the contraction, to place the nerves and muscles in the 
 circuit ; it is merely necessary to cause the current to pass 
 in a part, even a very short part of the nerves, for the muscles 
 to contract ; moreover, every existing action, exercised upon 
 the nerve, produces an effect of the same kind. 
 
 But it is not upon the frog alone that the physiological 
 action of the current has been studied. Galvani himself, and 
 Aldini, nearly sixty years ago, produced contractions upon 
 the head of an ox, recently killed, by introducing into one of 
 its ears a wire in communication with one of the poles of 
 the pile, and into the nostrils a wire in communication with 
 the other pole. The eyes were immediately seen to open, 
 the ears to shake, the tongue to move, and the nostrils to 
 dilate; similar results were obtained upon divers animals. 
 More recently, in 1818, Dr. Ure, on having endeavoured to 
 to subject the body of a man who had been hanged, imme- 
 diately after the execution, to the action of the current of a 
 pile of 270 pairs of copper and zinc, of sixteen square inches 
 of surface, and charged with water slightly acidulated with 
 sulphuric and nitric acids, obtained some remarkable results. 
 One of the electrodes of the pile, by means of an incision, was 
 placed in contact with the spinal marrow, whilst the other 
 was applied to the sciatic nerve, which had also been laid 
 bare ; immediately all the limbs of the body were agitated 
 
490 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 by convulsive movements ; on making the second conductor 
 move from the hip to the heel, the knee having been pre- 
 viously bent, the leg was thrown out with such violence that 
 it very nearly overthrew one of the assistants, w r ho endea- 
 voured in vain to prevent the extension. Other experiments 
 made upon different parts of the body, produced contractions 
 more or less violent in different organs, and especially in the 
 diaphragm, to which they succeeded in giving a momentary 
 movement, analogous to that which it possessed during life, 
 thus bringing about a species of powerful and laboured re- 
 spiration. 
 
 Humboldt who, from the origin of Galvani's discovery, 
 had occupied himself upon this subject with much care, 
 after various researches made upon animals, and to which 
 we shall return, was desirous of studying the physiological 
 action of electricity upon himself. Having applied blisters 
 to each of the deltoid muscles, he placed upon one of his 
 wounds a plate of silver and upon the other a plate of zinc, 
 and, connecting the two plates by a wire, he established a 
 pair, the current of which contracted alternately the muscles 
 of the shoulder and of the neck, with a sensation of powerful 
 smarting immediately that the bladder, formed by the blister, 
 was open. 
 
 In order to experience the effect of the current upon one's 
 own body, we have merely to plunge each of the hands 
 into a vessel filled with salt water, communicating, one with 
 the positive, the other with the negative pole, of a pile of some 
 thirty pairs feebly charged; we immediately experience a 
 shock which extends to the wrist or to the elbow, according 
 to the intensity of the discharge. When the current passes 
 for a certain time, and we hold in each hand a moistened 
 metal cylinder sufficiently large to fill it entirely, we suffer 
 a disagreeable sensation, analogous to trembling. If several 
 persons take hold of each other's hands, the shock is ex- 
 perienced by all at the same time in a sensible manner, 
 especially if the number of persons is not very considerable. 
 The human body is not in effect a very good conductor. 
 This is proved by the very exact experiments made by 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 491 
 
 Lenz with one of Nobili's multiplying galvanometers, by 
 means of the inductive current of a Clark's machine, of 
 which the following are the details. 
 
 The resistance is first determined of the entire circuit, 
 composed of the induced wire, of the wire of the multiplier, 
 and of the wires that are used for putting the multiplier 
 in the circuit ; and it is taken for unity : then an individual 
 is interposed in the circuit, by causing him to plunge one 
 or several fingers of each hand into two vessels, filled with 
 a conducting liquid, which are themselves placed in com- 
 munication with the extremities of the induced wire. The 
 force of the current is alternately measured with and without 
 the interposition of the human body, and a very exact mean 
 is thus obtained of the effect of resistance, produced by 
 this interposition. Thus, on employing for a conducting 
 liquid, water acidulated with y^- of sulphuric acid, it is 
 found that the resistance, produced by the body of a man 
 forty- three years of age, is thirty-four times the resistance 
 taken for unity, when he plunges only one finger in each 
 vessel, and only six times when he plunges the entire hand. 
 The resistance is the more feeble, in proportion as the liquid 
 is more acid, and consequently a better conductor ; we, 
 therefore, see by this, that the resistance exists chiefly in 
 the passage of the current from the liquid into the body, 
 and reciprocally ; and that its cause consequently is in the 
 epidermis. In effect, the immersed hand having accidentally 
 received in one experiment a slight scratch, the resistance 
 fell from 6*06 to 4*81, although the circumstances were 
 in other respects perfectly the same.* Mercury, substituted 
 for acidulated water, increases instead of diminishes the 
 resistance, probably because it does not moisten the skin 
 like the acid solution. 
 
 Resistance varies a little with the individuals submitted 
 to experiment ; it is in general much more considerable with 
 
 * No one who has occasionally handled voltaic piles, is ignorant how much 
 the smallest scratch on a part of the hand, when it happens to come into con- 
 tact with one of the electrodes, facilitates the production of the disagreeable 
 -fixation, arising from the passage of the current in the limbs. 
 
492 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 children or with young persons than with more aged people. 
 It is probable that this is due to differences in the surface 
 of the fingers immersed; since the resistances differ less, 
 when it is the entire hand, that is plunged, than when it 
 is only one or two fingers. It would also seem that the 
 right hand presents more resistance than the left hand, 
 which may be due to the greater use that is made of it. 
 
 In order to compare the numerous results, that he has ob- 
 tained with a known resistance, Lenz endeavoured, by the pro- 
 cesses described*, to reduce the resistance of his circuit, not 
 including the interposed human body, to that of a copper wire 
 039 in. in thickness ; and he found that it was equivalent to 
 a length of this wire of 43,823 ft., which makes the mean 
 of the resistances presented by the different individuals, to 
 the number of six, submitted to experiment, equivalent to 
 300,203 ft. M. Pouillet had found this resistance equal to 
 that of a copper wire, still of *039 in. in diameter, but of 
 174,240 ft. in length, which makes a resistance of about one- 
 half less ; it is true that the hands were moistened and 
 plunged into mercury, into which abutted the conducting 
 wires of the current, which explains why the resistance was 
 less considerable ; but the same philosopher has observed that, 
 if the current passes from one finger to another of the same 
 hand, the fingers being moistened and plunged into mercury 
 as far as the half or the third of the first joint, it is weak- 
 ened seven times more, namely, as much as if it had traversed 
 1,219,680 ft. of copper wire. M. Pouillet, in these experi- 
 ments, made use of a pile of twelve pairs of Wollaston's, and 
 of a multiplier of 240 times, furnished with a very sensible 
 magnetised needle. 
 
 More recently M. Masson has studied the physiological effect 
 of discontinuous currents ; he made use of a toothed-wheel 
 to render the currents discontinuous, which traversed a long 
 helix, in the interior of which was introduced a cylinder 
 of soft iron, in order to render them more intense. He has 
 remarked that, on placing a certain interval between each 
 
 * Vol. II. p. so. 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 493 
 
 shock, shocks are felt that can be with difficulty endured ; 
 on increasing the velocity of the wheel, a time arrives when 
 the muscles suffer an involuntary contraction, we can no 
 longer relinquish the handles, that are held in the hands 
 for transmitting the current through the body ; the pain 
 becomes insupportable, the arms writhe of themselves ; and on 
 increasing the intensity of the pile, the pain becomes so great 
 that we faint away, unless the experiment be immediately 
 terminated. On turning more rapidly, the pain diminishes, 
 the contractions are less powerful, there remains only a 
 numbness, which, with a certain velocity, itself finally dis- 
 appears. This limit is not the same for all individuals ; it 
 varies in like manner with the intensity of the current. M. 
 Masson, on applying a greater or less rapid succession of these 
 electric shocks to very healthy cats, very promptly caused 
 their death, which was accompanied by a stiffness of the 
 limbs, similar to what the animal would have manifested, a 
 fortnight after a natural death. 
 
 We shall return to the effects, observed by M. Masson, and 
 in particular upon a property, which he has found to appertain 
 to the induced current, that of only affecting the points of the 
 body touched by the electrodes, when we are occupied with 
 the applications of electricity as a curative means. We 
 shall defer also to this part of our work many important 
 details on the specific action of dynamic electricity upon the 
 nervous and muscular system, as well as the description of 
 various apparatus, contrived for producing currents intended 
 for physiological applications, such as NeePs stunning wheel, 
 of which they are only modifications ; nor shall we pause to 
 describe here the numerous researches of various physio- 
 logists upon the speciality of electric action, in regard to 
 its physiological functions, because the results have been 
 contested, and because, further, it is not until we have com- 
 pleted the theoretical study of electricity, and in particular of 
 animal electricity, that we shall be able to discern in what this 
 speciality may consist. We shall confine ourselves to calling 
 to mind that Ritter had thought that the electricity of the 
 positive pole increases the vital forces, whilst that of the ne- 
 
494 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 gative diminishes them ; that the former swells the parts of 
 the body which it touches, and fortifies the pulse of the hand, 
 whilst the latter reduces it. He had also thought he saw a dif- 
 ferent influence of the two poles upon vision, and upon the 
 senses of taste and smell. All these effects, and many others 
 besides, were evidently due either to the chemical or the colo- 
 rific action of dynamic electricity, and not to a static action of 
 the electricity of each pole. Wassali, Julio, Rossi, and Fowler, 
 at the end of a great number of experiments upon the bodies 
 of criminals after their execution, thought they found a 
 specific action of electricity upon the heart and upon other 
 muscles, such as those of the stomach and the intestines. 
 Volta and Aldini had constantly denied the existence of this 
 kind of action. Finally, Dr. Wilson Philipp, on making upon 
 rabbits the section of the nerves of the eighth pair, had 
 thought he might substitute an electric current for the action 
 of these nerves upon digestion. Others had gone further, 
 advancing that nervous influence is only an action, analogous 
 to that of electricity. They had even attempted to substitute 
 for this influence in secretions an electric current, acting di- 
 rectly upon the secreting organs. But all these results pre- 
 sented merely a false resemblance to those, which are brought 
 about by the vital force, transmitted by the intervention of the 
 nerves, as has been proved by a more deep and more detailed 
 examination. We shall leave aside, therefore, all these 
 researches, in order to study in a more precise and more sci- 
 entific manner, with the different philosophers, who have 
 been engaged with it, the real action of the electric current 
 upon the different parts of the body of animals, of the frog 
 in particular, confining ourselves to stating the positive facts, 
 that multiplied experiments have placed beyond all kind of 
 doubt. However, this study itself can be complete only 
 when, entering in our Sixth Part upon physiological action, 
 considered as a source of electricity, we may be able to esti- 
 mate the share of influence, in the phenomena that are 
 brought about by the application of an exterior and artificial 
 electricity, that is exercised by the natural electricity, which 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 495 
 
 the animal possesses, and which is connected with its physio- 
 logical functions. 
 
 Fundamental Analysis of the Action of the Ekctric Current 
 upon Animals. 
 
 The action of the electric current upon animals is mani- 
 fested distinctively only under two forms : pain, the percep- 
 tion of which can be indicated distinctively by man alone ; 
 muscular contraction, which is sensible with all animals, by 
 the movements that are its result, and which may even be 
 manifested for a longer or shorter time after they have ceased 
 to live. It consists of a shortening of the fibres, of which 
 the muscle is composed, attended by an increase in their dia- 
 meter, without any change taking place in the volume of the 
 muscle itself. M. Matteucci demonstrated this, by placing a 
 torpedo and a frog, prepared after Galvani's method, in a 
 vessel filled with water and closed with a cork, traversed by 
 a narrow tube, in which the liquid rises ; an electric current 
 is directed into the vessel by means of two insulated wires ; 
 and although the torpedo and the frog suffer powerful con- 
 tractions, the level of this liquid column in the tube is not seen 
 to undergo the least change. 
 
 We shall not dwell here on the details relative to the 
 structure of the muscle, and on the hypotheses that have 
 been formed of the manner, in which its construction is 
 brought about ; we shall confine ourselves to adding, that the 
 cause, which determines it in the animal in the normal state, 
 is the influence that is transmitted by the nerves, which is 
 designated by the name of nervous force.* The collection 
 of these nerves constitutes the cerebro-spinal nervous system, 
 which is principally composed of an infinite number of rami- 
 fications, disseminated in the body of the animal, uniting 
 in one central mass, which forms the brain and the spinal 
 
 * We designedly exclude the term nervous Jluid, which is sometimes em- 
 ployed, because it rests upon an hypothesis, with respect to the nature of 
 nervous force, which nothing justifies. 
 
496 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 marrow.* If we cut one of these ramifications in a living 
 animal, and touch it with a red-hot iron, or a piece of potash, 
 or if we wound or pull in any manner the portion of this 
 nerve, that remains in communication with the cerehro-spinal 
 axis, the animal gives signs of pain. On producing these 
 same irritations below the section, the signs of pain are not 
 manifested; and we merely perceive contractions in the 
 muscles, among which the irritated nerve ramifies. When 
 these excitations are administered to the intact nerve, pain 
 and contraction are simultaneously produced. Instead of 
 cutting the nerve, we may tie it, which produces the same 
 effect as the cutting ; but, if we tie it in two points, and irritate 
 it in the portion comprised between the two ligatures, neither 
 pain nor excitation is produced. The nerve, therefore, has 
 the office of transmitting the action of the stimulant applied 
 to it, either to the brain, when it produces a sensation, or to 
 the muscles, when it brings about a contraction. The 
 modern discoveries of physiologists have demonstrated that, 
 among the nerves, there are a certain number, which, on 
 being excited, produce, some, muscular contraction alone, 
 others pain alone. We may add, that a bundle of nerves is 
 composed of a great number of filaments, all capable of trans- 
 mitting separately the action by which they are excited with- 
 out the filaments, with which the one excited is in contact, 
 taking part in it. With regard to the actual nature of the 
 nerves, we will confine ourselves to remarking, that it is a 
 fatty matter contained in small cylindrical canals, of a firmer 
 consistence, and which are termed neuriloema, without entering 
 tor the present into further details on their physical and 
 chemical constitution, which have formed the subject of the 
 researches of a great number of physiologists. 
 
 The causes capable of developing in nerves the nervous 
 force, which, by propagating itself to the muscles, produces 
 
 * Besides the cerebro-spinal nervous system, there exists a second, the gan- 
 glion nervous system, composed of ramifications, distributed principally in the 
 apparatus of organic life, which, notwithstanding its numerous relations to the 
 former, yet gives rise to neither motions nor sensations, when it is irritated. 
 We shall not trouble ourselves with this system, in the researches, that form, 
 the subject of the present paragraph. 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 497 
 
 in them contraction, are first and above all the will, then 
 mechanical actions, chemical actions, heat, and finally elect- 
 tricity ; but electricity in its mode of action, differs from the 
 other exterior agents, by characteristics that are peculiar to 
 itself , and which give it in this respect a much greater relative 
 importance, by approximating its effect to that of the agent, 
 which the will calls into action. The following are the 
 principal characteristics, whose existence we are about to 
 establish : the electric current is the only irritant that is able 
 to excite sometimes contraction, at other times sensation, ac- 
 cording to the direction in which it traverses a nerve ; the 
 electric current does not produce any of the phenomena, 
 which result from the excitability of the nerve, when it 
 traverses it perpendicularly to its length; it brings about 
 neither contraction nor sensation, when its action upon the 
 nerve is prolonged ; it alone is able to modify the excitability 
 of the nerve, even to destroy it, if it circulates in a certain 
 direction ; and to preserve or even to increase it, if guided in 
 the converse direction ; finally, it alone, among irritating agents, 
 is able to revive for a long time the excitability of nerves, 
 when it is very much enfeebled in respect to other stimulants. 
 We have already related, in the preceding paragraph, 
 Galvani's fundamental experiment, and his manner of pre- 
 paring the frog. Volta and Fowler had remarked, on re- 
 peating and varying this experiment, that the same contrac- 
 tions as the frog suffers at the moment when the current 
 is established, are renewed at the moment when this current 
 ceases to traverse it. This fact studied successively by 
 Valli, Rumford, and Pfaff, had been attributed by Volta to 
 a species of rebounding, which is experienced by the current 
 at the moment of the breaking of the circuit, by the in- 
 stantaneous obstacle that it encounters ; as would be the case 
 with a fluid, which, while travelling in a canal, would recede 
 and move in an opposite direction, should it be suddenly 
 arrested. Marianini, who has carefully studied this phe- 
 nomenon, has not succeeded in proving the existence of 
 Volta's hypothetical counter- current, when employing either 
 a galvanometer or the sensation exercised by the current upon 
 
 VOL. II. K K 
 
498 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 the tongue ; he has therefore conceived that, on removing 
 the communications by which the current is transmitted 
 from a pile, no opposed current is originated. It is therefore 
 to the single fact, that it ceases to be traversed by the current, 
 that the frog owes the second contraction, which it suffers ; 
 and the proof is, that for producing it we have merely to 
 connect by an arc of metal the two conductors which 
 establish communication between the two poles of the pile 
 and the frog. Its contraction is brought about, on thus de- 
 riving, by a better conductor, the current that continues to 
 traverse in a circuit of which the animal, it is true, no longer 
 forms a part. However, Marianini has shown, that the con- 
 traction which takes place at the moment of the irruption of 
 the current, and that which takes place at the moment of its 
 cessation, have not the same intensity ; at least, when the frog 
 has lost its excitability, one or other of them is the more 
 powerful, according to the direction in which the current is 
 travelling, in respect to the nervous ramifications. In order 
 well to appreciate this difference, a frog must be prepared so 
 that the thighs are attached to the trunk by the lumbar 
 nerves alone (fig. 258.). The trunk is placed in a cup filled 
 
 Fig. 258. 
 
 with water, which communicates with one of the poles, and 
 the two thighs in another cup, in communication with 
 the other pole. If the positive pole is in the cup in which 
 the trunk is placed, and the negative in that in which the 
 thighs are, the frog contracts every time the circuit is closed, 
 and not when it is opened ; on changing the poles, the effects 
 are converse. The result proves that, in order for contrac- 
 tion to take place, when the circuit is closed, it is necessary 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 499 
 
 for the current to travel in the direction of the ramification 
 of the nerves ; and that, in order to its taking place, when 
 it is opened, it is necessary for the current to travel in a 
 contrary direction to the ramification. We shall term direct 
 current the one that travels in the former direction, and 
 inverse the one that travels in the latter. 
 
 The same phenomenon is manifested when the experiment 
 is made with a frog prepared as above, but arranged so 
 that one of the thighs plunges in one of the glasses, and the 
 other in the other (Jig. 259.). The frog, as we know, leaps out 
 
 Fig. 259. 
 
 of the glasses when one of the poles of the pile is plunged 
 into each ; but if we forcibly retain it in its place, we at 
 first perceive contractions in both legs, as well on opening as 
 on closing the circuit. By continuing to operate, a time 
 arrives when, the excitability of the animal being diminished, 
 a single limb contracts, when the circuit is closed ; it is the 
 one in which the current is direct; and, on the contrary, 
 when it is interrupted, the contraction takes place in the 
 other limb, namely, in that which is traversed by the inverse 
 current. 
 
 This important fact, well analysed and established by Ma- 
 rianini, had been in part recognised by Volta, by Lehot and 
 by Bellinghieri ; who had not, however, remarked the essential 
 point, which M. Marianini was the first to point out, that in 
 the case of the inverse current there is contraction, when the 
 current is interrupted, even when there is none when it is 
 established. We may add, that with two frogs placed in the 
 
 K K 2 
 
500 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 circuit, one after the other, so that their two trunks are 
 plunged into the same vessel, the thighs of the one commu- 
 nicating with the positive pole, and those of the other with 
 the negative, the one that is traversed by the direct current, 
 and not the other that is traversed by the inverse current, is 
 seen to tremble at the establishment of the circuit ; whilst at 
 the rupture of the circuit it is the latter and not the former 
 that trembles. 
 
 M. Marianini has further observed that, when electricity 
 acts immediately upon the muscles, contractions take place, 
 only at the instant, when the circuit is closed, whatever be, 
 in other respects, the direction of the current ; whereas he is 
 led to distinguish these latter, which he terms idiopathic, 
 from those which are derived from the action, exercised by 
 the electric current upon the nerves, that preside over the 
 movement of the same muscles, and which he terms sympa- 
 thetic. We have just seen, that they take place only at the 
 establishment of the circuit and not at its rupture, if the 
 current is direct ; and only at its rupture, and not at its 
 establishment, if it is the reverse. But in the two cases, in 
 which there is no contraction, might there not have been 
 a sensation, at least if the animal is living ? Marianini con- 
 ceived he had established this, on operating on a frog, whose 
 posterior limbs remained attached to the body only by the 
 two crural nerves, and by placing these limbs united toge- 
 ther in communication with one of the poles, whilst one of 
 the anterior legs, the right, communicated with the other pole. 
 If the current entered into the nerves in the direction of 
 their ramification, the frog agitated the inferior extremities, 
 at the moment when the circuit was closed, and at the moment 
 when it was interrupted, it uttered a prolonged cry, with the 
 full force of its lungs, and at the same time raised itself with 
 contortions upon its anterior limbs, without agitating the 
 inferior. If the current penetrated the nerves in the direc- 
 tion contrary to their ramification, it was when the communi- 
 cations were established that the frog uttered its cry, accom- 
 panied with contortions ; and that it repeated it, if the circuit 
 was left closed for some time ; and, when it was interrupted, 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 501 
 
 the posterior extremities were agitated, and the animal 
 ceased to cry and to present contortions. 
 
 M. Marianini quotes a curious experiment in support of 
 the distinction, that he has established between idiopathic 
 and sympathetic contractions, and of the difference of effects 
 of the current in the case in which, when circulating in the 
 nerves, it traverses them in the direction of their ramifica- 
 tion or in the contrary direction. It consists simply in placing 
 the right hand in communication with one of the poles of 
 the pile, the positive for example, and the left with the 
 other, the negative ; every time the circuit is closed, a con- 
 traction is felt in both arms, but stronger in the left than in 
 the right ; if the current is made to pass in the contrary di- 
 rection, it is the right that suffers the more powerful contrac- 
 tion. An analogous effect is obtained, on making one of 
 the poles communicate with the arm and the other with the 
 foot. The contraction is more powerful in the limb in which 
 the current circulates in the direction of the ramification of the 
 nerves ; because it is at the same time sympathetic and idio- 
 pathic, than in the other limb, in which it is only idiopathic. 
 It would appear that, among individuals sensible to the effects 
 of electricity, the shock is, in the latter case, accompanied by 
 a peculiar sensation, which does not take place in the former 
 case, in which it is more violent. 
 
 M. Nobili, as the result of a very complete analysis of the 
 phenomena, described by Marianini, succeeded in distinguish- 
 ing five periods in the degree of irritability of the frog ; the 
 first, in which there is contraction with the direct and with 
 the inverse current, whether the circuit is established, or 
 opened ; the second, in which there are no longer any con- 
 tractions, when the inverse current is established ; the third, 
 when the contractions also cease with the rupture of the 
 direct current ; the fourth, when the contractions, due to the 
 establishment of the direct current, alone remain ; finally, 
 the fifth, in which there are no longer contractions in any 
 case. It is clear that it is always necessary to operate 
 with the same voltaic arc, for all the limits would be thrown 
 back, if the force of the current was more considerable. In 
 
 K K 3 
 
502 TRANSMISSION OF ELECTRICITY. PART iv 
 
 all these experiments, M. Nobili operated upon the nerve 
 alone, by applying to the extremities of the insulated crural 
 nerve the two ends of the voltaic arc, taking good care not 
 to touch the muscle. 
 
 Whilst the current is circulating, there are no sensible 
 contractions, which does not prove that there is not a certain 
 effect produced upon the nerve by the current. Volta had 
 already remarked that a frog, left for half an hour in the 
 circuit of a pile, no longer contracts under the action of the 
 same current ; whilst it suffers a very lively agitation, if it 
 is exposed to the action of an inverse current. We see plainly 
 by this, that the continuous action of a current does not disor- 
 ganise the nerve, but that it alters it, however, to a certain de- 
 gree, by placing it in a different state from its natural state ; if 
 the action has endured a short time, the nerve has not become 
 habituated to its new state, so that, when the current ceases, 
 it immediately recovers its natural condition, and a new in- 
 vasion of the current brings about the same effects. But 
 when, by the duration of the action, it is accustomed to its 
 new state, it may remain in it for a longer or a shorter time, 
 even when the cause that has produced upon it this alteration 
 no longer exists. Thus if, after having suspended the current 
 for a moment, it is made to act anew, it produces no effect, 
 because it finds the nerve still in the condition which it tends 
 to produce in it. It is no longer the same, when the direc- 
 tion of the current is changed; the more the nerve has 
 become accustomed to the effects of this first current, the less 
 easily will it support the action of the second. Experiment 
 does not teach in what the modifications consist, which the 
 nerve suffers under the action of the direct and inverse cur- 
 rents ; it only points out to us that one of the modifications 
 is very different from the other ; M. Nobili calls one direct 
 alteration, it is that, which is produced by the direct current; 
 and the other, which is produced by the inverse current, 
 inverse alteration. 
 
 The animal may therefore be found in three states; the 
 natural state, before the current passes, the state of direct 
 alteration, and the state of inverse alteration. In order that 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 503 
 
 there shall be a shock, two conditions are necessary ; the first, 
 that the nerve shall pass from one state to the other ; the 
 second, that this state shall take place rapidly. M. Marianini 
 had, in fact, remarked, that if the passage from one state to 
 the other, namely, the establishment, or the rupture of the 
 current takes place slowly and gradually, the shock is null, 
 or very feeble. The transition from one state to the other 
 brings about a shock ; and, as there are four possible tran- 
 sitions, there are four shocks, of which two are compara- 
 tively more feeble in comparison with two other stronger ones, 
 which endure for a longer time. The following is the actual 
 order, in which they disappear : the more feeble, which be- 
 longs to the inverse current, at the moment when it is es- 
 tablished ; the less feeble, which is due to the direct current 
 at the moment when it is interrupted; the less powerful, which 
 is due to the inverse current at the moment when it is inter- 
 rupted ; the more powerful, which is due to the direct current, 
 at the moment when it is established. 
 
 In the first period of great excitability, the differences 
 between the four contractions are too small to be able to 
 be detected. In order to explain what takes place in the 
 others, M. Nobili supposes that the nerve possesses a struc- 
 ture, which renders it fit for propagating certain movements 
 in the direction of its ramifications ; whence it follows that 
 the direct current, acting upon the nerve in the direction of its 
 fibres, produces in it a contraction, whilst the inverse current, 
 acting in a contrary direction, does not produce any, or only 
 produces one, when the nerve being very irritable, is capable, 
 like an elastic cord, of propagating the motion that it receives 
 in two directions, but with more intensity, however, in that 
 direction, according to which the force is acting. If the cir- 
 culation of the direct current tends to alter the structure of 
 the nerve in the direction of its fibres, and in that of its 
 ramifications, that of the inverse current tends to alter it in 
 the opposite direction, which causes that, for the same inten- 
 sity of current, the former alteration will give to the nerve a 
 less forced condition than the latter. It will follow from this, 
 that the interruption of the current ought to produce a less 
 
 K K 4 
 
504 TRANSMISSION OP ELECTRICITY. PART iv. 
 
 violent shock, in the case of the direct current, than in the 
 case of the inverse current, which constrains the nerve into a 
 state further from that which is natural to it. 
 
 Such, in brief, are M. Nobili's ideas, which, even though 
 they cannot be admitted under the too explicit form, that he 
 has given to them, are not the less founded, as we shall see, 
 upon the truth. We may further add, that the law of con- 
 tractions, such as he has formularised it, varies with the force 
 of the current, and that, in particular, powerful currents are 
 proportionately more active, when the circuit is interrupted, 
 than when it is closed ; and that the reverse is the case for 
 feeble currents ; which is due to the greater alteration that is 
 produced by the former in the nerves. Furthermore, M. 
 Nobili has recognised that his law of contractions is not mo- 
 dified, by the presence of the muscles in the circuit ; and, in 
 fact, the same effects are obtained, by placing the frog in such 
 a manner, that the current passes from the crural nerve into its 
 lower limbs, as when it passes in a portion of the nerve only. 
 But, it is no longer the same if the current traverses the 
 muscles alone : the shock then takes place only when the 
 circuit is closed, and we no longer observe those which were 
 produced, when it was interrupted, seeing that they were due 
 to the alteration of the nerve, that was traversed by the current. 
 
 We should in this place revert for a moment, to one of the 
 phenomena, that we have described in passing, but which 
 merits a deeper examination ; it is that, to which philosophers 
 have agreed to give the name of voltaic alternatives, on 
 account of Yolta, who was the first to observe it. We have 
 seen that this celebrated philosopher, having placed astride, 
 on two glasses of water, placed in the circuit of the pile 
 (fig. 257.), a frog recently killed and prepared, according to 
 Galvani's method, remarked that, if the circuit had remained 
 constantly closed for half an hour, the legs of the animal no 
 longer contracted, when the circuit was opened and when it 
 was closed. But, on making a current pass in a direction, 
 contrary to the former, the circuit could be neither opened nor 
 closed, without the contractions being renewed each time. 
 If the current was again made to act for half an hour, the 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. ' 505 
 
 muscles lost in this second state all their contractability, but 
 they regained it, upon recovering their former position. On 
 thus bringing about changes, from half-hour to half-hour, and 
 even more frequently, we are able for an entire day and even 
 longer, to annihilate or to revive at pleasure the natural ex- 
 citability of the muscles of the animal. 
 
 The weakening, that is suffered in the frog's property of 
 contracting is the more considerable, as the current is more 
 powerful; but although in general it may contract anew, 
 under the action of a more intense current, yet its sensibi- 
 lity is found to be enfeebled. M. Marianini has very well 
 demonstrated this, by means of two perfectly similar frogs, 
 prepared in the same manner, and at the same time, of which 
 one had been left at rest, whilst the other had been subjected 
 to the action of the current of forty pairs. The operation had 
 lasted for half an hour; at the end of a second half-hour 
 the former frog was still sensible to the current of a single 
 pair, almost as much as at the commencement, whilst the 
 latter remained motionless under the action of two pairs. If 
 the animal is living, the vital force repairs the damage done 
 to the organs of motion by the current. M. Marianini sa- 
 tisfied himself of this, by passing the electric current of sixty 
 pairs, from one of the legs of the living frog to the other, by 
 means of two bands of lead. It was merely necessary for it 
 to obtain some relaxation, when its muscular contractions 
 have been enfeebled, under the action of the current, in order 
 that, regaining its primitive strength, its contractions may re- 
 cover their vigour, without its being necessary to subject it 
 to the action of a contrary current. This repairing principle 
 does not entirely cease with life ; it subsists, at least in part, 
 for some time after death ; however, it is in the living animal, 
 that it acts with the greatest energy. 
 
 This weakening of the excitability of the nerves is prin- 
 cipally manifested in the portion that is traversed by the 
 current, as Matteucci proved on applying the current to a 
 portion of the nerve, more distant from the brain than was 
 that upon which he had operated for a sufficient time to cause 
 the contractions to cease; the contractions are immediately 
 
506 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 seen to reappear, as also the same phenomena as before. On 
 following out these experiments, so as to act upon portions of 
 the nerve, still more distant from the brain, the same effects 
 are still obtained. If the animal is living, we find, on the 
 other hand, that the signs of pain which it manifests, when a 
 current traverses its nerves, are revived, if we act upon 
 parts more and more near to the brain, in proportion as its 
 vivacity diminishes by the prolonged passage of the current. 
 In both cases equally, it is always the excitability of the 
 nerves that is enfeebled by this passage. This experiment 
 is important, in that it shows that the phenomena of voltaic 
 alternatives cannot be attributed, as was done by Marianini, 
 to the fact that a part of the electricity which enters into 
 the organs of motion, remains there for some time, and 
 accumulates more and more, until, by a tendency to flow 
 back, it opposes the current, that arrives at the same organs, 
 so that the action of this current becomes null, or excites 
 feebler contractions, than at the commencement of the ex- 
 periment. Besides, there is nothing that demonstrates this 
 arrest of electricity, which would be, as it were, a species of 
 polarisation of the extreme parts of the portions of the frog, 
 placed in the circuit. We therefore see, as Nobili has so 
 clearly explained, that the electric current brings about in 
 the portion of the nerve that it traverses, an alteration, 
 which is stronger in proportion as its passage is more pro- 
 longed; an alteration, that renders the nerve incapable of 
 transmitting the action of a current, acting in the same 
 direction, and which is only able to disappear by the passage 
 of a current, guided in a contrary direction, or by a rest of 
 some duration, until, by repeated actions, the nerve has lost 
 all excitability. What is the nature of this alteration ? It 
 is probable that it is connected with the state, into which the 
 transmission of the current reduces the nerve ; a state which, 
 by analogy with what takes place in all other cases, must be 
 a polarisation of the molecules, alternating with molecular 
 discharges. We conceive that so long as the nerve has 
 sufficient vitality, it reacts as soon as the current ceases, in 
 order that the molecules may recover their natural position ; 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 507 
 
 but a moment may arrive when this reaction, no longer 
 taking place, a current guided in the opposite direction, is 
 necessary, in order to bring it about. 
 
 An important fact, observed by Matteucci, comes to the 
 support of our manner of regarding it. This learned philo- 
 sopher has observed that the tying of a nerve, for example, the 
 crural nerve of a rabbit, produces the same effect, as would 
 have been brought about by the prolonged passage of the 
 current in the part of the nerve, comprised between the two 
 ligatures. Thus, if the current is made to pass below the 
 ligature, the contractions of the leg are observed ; and if it is 
 made to pass above, there is no longer any contraction, but 
 there are signs of pain, because there is communication with 
 the brain, without an intermediate ligature. It is necessary, 
 in order to perform this experiment well, to take care to 
 insulate the nerve from the moist parts, by which it is sur- 
 rounded, and properly to tighten the ligature ; without this 
 precaution, a portion of the current is able to pass above or 
 below the ligature, and to interfere with the results. It must 
 be remarked, that the ligature does not intercept the current, 
 but weakens its effects ; so that, if one of the poles is placed 
 above and the other below the ligature, the phenomena are 
 the same, as if there was no ligature, but only more feeble. 
 For all these experiments, the best plan is to^ employ the frog, 
 prepared in the usual manner, and to suspend it by its nerve 
 
 (fig. 255.). 
 
 One of the characteristics, whereby the most marked dif- 
 ference is established, between the physiological action of 
 electricity and that of other agents, is the connection that 
 exists between the direction of the propagation of the current 
 and the direction of the nerves and of their ramifications. 
 We have already even remarked that the electric current does 
 not produce any of the effects due to the excitability of the 
 nerves, when it is transmitted transversely to this nerve. The 
 following is the method whereby Matteucci has demonstrated 
 this important point. Two frogs' legs are prepared and sepa- 
 rated ( fig. 260.), so that their nervous filaments cross each 
 other at right angles; one of the nerves is cut, so that the 
 
508 
 
 TRANSMISSION OF ELECTRICITY. 
 
 PART IV. 
 
 Fig. 260. 
 
 two extremities of the section made are at a distance of 
 about | in. from each other, and only | in. from the nerve 
 
 of the other leg, which 
 passes across the section ; a 
 drop of distilled water esta- 
 blishes a communication 
 between the two sections of 
 the cut nerve. The points 
 a and b of the cut nerve are 
 then touched with the poles 
 of a pile composed of a very 
 great number of pairs ; the 
 current traverses, not only 
 the water, but the interposed 
 nerve ; nevertheless, the leg, 
 to which this nerve apper- 
 tains, suffers no effect, whilst the other suffers violent con- 
 tractions. However, if the pile is still more powerful, we end 
 by perceiving some contractions in the leg, whose nerve is tra- 
 versed transversely by the current ; but they are much more 
 feeble than in the other leg. 
 
 Among the multiplied researches of which the physiological 
 action of the current has been the subject, we shall confine 
 ourselves to pointing out in this place a few, either on 
 account of their importance, or because we shall not have oc- 
 casion to return to them, as to others, when engaged with 
 animal electricity. 
 
 One of those, which we have in view, is the de- 
 termination, that M. Matteucci has endeavoured to 
 make, of the relation, that exists between the quantity of 
 electricity transmitted and the contraction excited by this 
 quantity of electricity in a nerve of an animal, either living 
 or killed as recently as possible. The apparatus that he 
 employed consists principally of a solid brass rod, AB,^y. 261., 
 fixed upon a wooden base, and in which there slide at right 
 angles two pieces of metal c and D, which can be fixed in 
 different points by binding-screws. The piece c carries the 
 clip E, into which is introduced and pressed with three 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 509 
 
 screws the pieces of the spinal marrow of the prepared frog. 
 The other piece F, in the form of a fork, is arranged so as to 
 
 Fig. 261. 
 
 have two holes at its two extremities, into which is introduced 
 and by which is regulated a very fine wire. This wire G is 
 terminated at the one end by a hook, which is fixed in the 
 paw of the frog ; at the other it is attached to a silk thread, 
 which is wound over this little pulley I. On this same pulley 
 is coiled, in the contrary direction, another silk thread, to 
 which is attached a little leaden weight o. The axis of the 
 pulley carries a species of double index, P Q, which has the 
 form of a semi-circle. The axis is fixed upon two pivots, 
 which may be brought to greater or less distances from each 
 other. One of these pivots is at the centre of the circle R s, 
 
510 TRANSMISSION OF ELECTRICITY, PART iv. 
 
 which carries a division. In this same pivot is introduced a 
 long and very light ivory needle T v, and which turns with 
 the least possible friction. It is not difficult to conceive the 
 use of this ivory index. In effect, if this index is carried into 
 contact with the other, which has the form of a semicircle 
 P Q, and which is fixed upon the axis of the pulley, it will 
 occur that, on turning this pulley, the ivory index will be 
 also pushed, and it will stop at the point to which it has 
 arrived, even when the pulley shall have been brought back 
 to its position by the little weight. It is necessary to mention 
 that, without this ivory index, it would have been impossible 
 to judge of the extent of the movement of the pulley, pro- 
 duced by the contraction, on account of its very short du- 
 ration. The weight employed was 9^ grains. It is sufficient 
 for the limb to return to its position, the contraction having 
 ceased ; a heavier weight would have strained the nerve too 
 much. The following is the method by which the current is 
 made to pass. It is always a half-frog, whose muscles and 
 pelvis bone have been removed, that is the subject of experi- 
 ment. The half-frog is thus reduced to a piece of spinal 
 marrow, which is pressed in the clip E, to the nervous fila- 
 ment, and to the thigh and leg only, the paws having been 
 cut away. The wire hook G is introduced between the bone 
 and the tendon Achilles. Finally, a gilt steel needle is inserted 
 into the muscles of the thigh, as near as possible to the in- 
 sertion of the nerve ; to this needle is soldered a copper wire 
 K, very thin and covered with silk, which is fixed to a piece 
 of ivory E. It is clear that, in order to cause the current to 
 traverse the nerve, we have merely to touch with the poles 
 of the pile the rod A B, in any point, and the wire K, that is 
 soldered to the steel needle. 
 
 Now, in order to operate, it is necessary to pass an electric 
 current, or a certain discharge of the Ley den jar, through 
 a certain length of the nerve of the frog ; the electro- 
 physiological effect is the contraction of the limb, which, in a 
 certain time, rises to a certain height. But the difficulty is, to 
 cause quantities of electricity to pass, that shall be in given 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 511 
 
 relations to each other, so as to compare them with the cor- 
 responding electro-physiological effect. At first it is necessary 
 to employ a very feeble current, so that the effects shall 
 not be all at their maximum; the current of one pair, 
 even reduced by its passage through water, is sufficient ; 
 then, in order to cause, sometimes the half, at other times 
 the third or the fourth, of the electricity to pass in the same 
 nerve, M. Matteucci interposed between the pincers and 
 the thigh one, two, or three nerves, as similar as possible, 
 both in respect to each other, as well as in respect to the 
 nerve, that is the subject of the experiment : and admitting 
 as approximately true that the half of the current passes 
 in each of the nerves, when there are two, the third, when 
 there are three, and so on, he was enabled to reduce, 
 into the desired proportion, the current, that passes by the 
 principal nerve.* The following is one of the numerous 
 experiments, that M. Matteucci has made in this manner : - 
 
 Number of nerves. Degrees of contraction. 
 
 1 26 
 
 2 14 
 
 3 8 
 
 Although, in general, the results differ very notably among 
 themselves, which is inevitable in this class of experiments, 
 M. Matteucci thought he was able to conclude from them 
 that the physiological effect is proportional to the intensity of 
 the electric current. 
 
 However, it is not probable that this class of action 
 can be subjected to very precise laws; and a German 
 philosopher, who has gone through great and important 
 labours on this subject, M. Du Bois-Reymond, has thought 
 he was able to establish the following fundamental law, 
 as governing electric excitation ; namely, that the motor 
 nerves are not excited by the absolute largeness of the density^ 
 
 * It is true that, on increasing the number of nerves, the total current must 
 increase ; but, as the nerves are very imperfect conductors, this increase is not 
 considerable. 
 
 f M. Du Bois-Reymond, designates by the name of density of the current in 
 
512 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 of the current, but by the variations that occur in the sum of this 
 density from one instant to the other ; the excitation, caused by 
 these changes, being greater in proportion as they take place 
 more rapidly, or as they are more considerable in a given time. 
 Now, this law, established by numerous experiments, cannot 
 be reconciled with that of M, Matteucci. We may, as M. Du 
 Bois-Reymond has done, represent, in each case, these effects 
 by two curves, in which the abscissae represent the time, and 
 the ordinates represent, in one of the curves, the density 
 of the current in the nerve and in the other the value of 
 the excitation ; but these are merely very approximative 
 results. A very curious case is that, in which the excita 
 tion is produced by a series of successive discharges, which 
 follow each other very rapidly ; for example, by means of 
 an apparatus, like Masson's toothed-wheel, which interrupts 
 and re-establishes the current in a very rapid manner. The 
 effect of such a series of discharges is to produce a tetanic 
 contraction of the muscles ; as Volta was the first to observe, 
 and as Nobili afterwards pointed out more in detail.* In 
 experiments upon animal electricity, we are often called 
 upon to bring about in this way tetanus in the limbs of an 
 animal. 
 
 We shall not terminate what relates to the action of the 
 electric current upon the nerves, without saying a few words 
 upon the application, that has been made of it for the 
 construction of a physiological galvanoscope. Although the 
 magnetic galvanometer-multiplier has become, especially 
 with the perfection that Du Bois-Reymond has introduced 
 into its construction f, an instrument, eminently suited to the 
 perception and to the measurement of currents, due to animal 
 electricity, there are, nevertheless, cases, in which its employ- 
 ment is insufficient, and even presents inconveniences. In 
 this case, we may advantageously employ the physiological 
 
 a section of the circuit, the quotient of the intensity of the current, divided by 
 the size of the section of the conductor. 
 
 * It is an effect of this kind, that is experienced in Masson's experiment, of 
 which we have spoken in the preceding paragraph. 
 
 f Vide Vol. I, p. 331. 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 513 
 
 > 
 
 Fig. 262. 
 
 galvanoscope, which Nobili was the first to use, 
 employing the frog, prepared after the manner 
 of Galvani (Jig. 256.). Matteucci and Du Bois- 
 Reymond have found that it was preferable, in- 
 stead of employing, like Nobili, the entire frog, 
 simply to detach a thigh furnished with its 
 nerve, which may be placed in a varnished tube, 
 in order well to insulate it (Jig. 262.), so as to 
 allow only the portion of the nerve to stand out 
 which we desire to insert in the circuit, that is 
 the subject of the experiment. It is in effect a 
 matter of importance to be assured that neither 
 the current proper of the thigh, nor any current 
 other than that which is being studied, shall 
 traverse this nerve. The contraction of the 
 thigh indicates the passage of a current in the 
 nerve ; but only at the moment, when this passage 
 commences and finishes, which prevents this 
 galvanoscope from indicating whether the dis- 
 charge is instantaneous or continuous. 
 
 Among other applications that have been made of the phy- 
 siological galvanoscope, we shall only point out one, which is 
 due to M. Du Bois-Reymond, and which consists in show- 
 ing the development of dynamic electricity, that may take 
 place by the induction, brought about by means of a 
 magnet, or of a current in a circuit, that is not closed, such 
 as a wire. We have merely to place a galvanoscopic frog 
 at each of the extremities of this wire, in order to see them 
 contract, as soon as the current or the inducing magnet is 
 brought near, providing we at the same time touch it with the 
 fingers, in order to determine the passage of the induced 
 current. It is sufficient to touch merely one of the frogs, for 
 the other also to contract, if they are sufficiently sensible. 
 We can also obtain an effect upon the frog by touching with 
 its nerve an imperfect conductor, such as a moist thread, 
 which unites the two extremities of the open induced circuit ; 
 but, for this purpose, it is necessary that the frog be not insu- 
 lated, and that its nerve touches the thread, near one of the ends 
 VOL. II. L L 
 
514 TRANSMISSION OF ELECTRICITY. PART iv. 
 
 of the induced wire ; and, if it is not very sensible, it suffers 
 contractions only when the end near which the nerve is, is that 
 by which the positive electricity arrives. A nerve may be 
 substituted for the moist thread, so that contractions may be 
 excited in the galvanoscopic frog simply by making an 
 induced current pass through the portion of the nerve, that 
 is above a ligature, which may give rise to errors in the 
 study of animal electricity, if great attention is not paid 
 to it. 
 
 This last species of action approximates closely in that 
 which Matteucci has described under the name of induced 
 contraction, with this difference, that, in this latter case, the 
 nerve of the electroscopic frog is affected, not by an electric 
 current, but by its contact with the nerve of another frog ; 
 an effect, that is due, as we shall see, to the electricity, which 
 probably circulates in this nerve. Moreover, it is only 
 when we shall have studied animal electricity considered 
 itself as a source of electricity, that we shall be enabled 
 to have more just and more complete notions of the 
 physiological action of electricity in general, the effects 
 of which are necessarily complicated with those that are 
 due to the electricity proper of the animal. 
 
 In all that precedes we have been only occupied with the 
 effects that result from the passage of dynamic electricity, either 
 through the nerves alone, or through the nerves and muscles at 
 the same time, when the discharge or the current traverse the 
 animal in its entire length. It remains for us to say a few words 
 upon the action of the current on isolated muscular fibre. This 
 research is very difficult, because, even when we have removed 
 from a muscle all the nervous filaments that are visible, it is a 
 difficult matter for no trace of the nervous substance to remain; 
 nevertheless, by taking all the necessary precautions, we are 
 enabled to arrive at results that are tolerably exact. Thus, 
 on causing the current of a pile of thirty or forty pairs 
 to pass through the pectoral muscle of a pigeon, deprived as 
 well as is possible of its nerves, we may show that the mus- 
 cular fibres contract, when a circuit is closed, and when it is 
 opened ; and this, whatever be the direction of the current, 
 
CHAP. iv. PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 515 
 
 relatively to that of the fibres. These contractions cease 
 during the passage of the current ; but they reappear, although 
 more feeble, when, after having interrupted the circuit, it is 
 re-established ; at least whenever the former passage has not 
 been too prolonged ; in which case, the contractions can no 
 longer be produced. 
 
 The effects that we have been pointing out, can only be 
 due to the direct action of the current upon the muscular 
 fibre; for even though there should remain some nervous 
 filaments in the muscle, since the nervous matter is much less 
 conducteous, about four times less than muscular matter, it 
 is essentially the latter, that is traversed by the electricity.* 
 M. Matteucci, to whom we are indebted for these observa- 
 tions, has, moreover, proved directly that no part of the 
 current passes through the small nervous filaments, when 
 it traverses the muscle ; for this purpose he takes the muscle 
 of the leg of a rabbit, or of a dog, that has been dead a suf- 
 ficiently long time for all muscular irritability to have dis- 
 appeared ; he then makes in this muscle an incision, and in- 
 troduces into it the nerve of a very sensible galvanoscopic 
 frog (jig. 262.), so that it may be well covered with the muscle. 
 As soon as the contractions, that are manifested in the frog, 
 at the first moment, have ceased, he causes the current of a 
 pile of from twenty to thirty pairs to pass through the mass 
 of the muscle, by applying the electrodes upon different points 
 
 * In order to determine the relative conductibility of nerves and muscles, 
 M. Matteucci took from a rabbit recently killed, a sufficiently long piece of the 
 sciatic nerve, a layer of the cerebral substance, and a piece of muscle, removed 
 from the thigh. He reduced these substances to slices of the same thickness, as 
 nearly as possible, and he placed them one after the other on an insulating 
 plane ; then he caused the current of a pile of twelve pairs to pass through 
 this chain of animal substances. He then touched, with the platinum ex- 
 tremities of a sensible galvanometer, sometimes one, sometimes the other of the 
 animal substances, the two wires being always held at the same distance ; and 
 he thus obtained deviations, produced by derived currents, drawn under the 
 same circumstances, from the three substances mentioned. He also made the 
 experiment in another manner, by causing the distance of the two platinum 
 wires to vary, so as to obtain a derived current of the same intensity by ope- 
 rating upon the three substances. The derived current, in the former case, is 
 the more powerful as the substance is a worse conductor ; thus, it is more 
 feeble with the muscle than with the nerve, and with the nerve than with the 
 cerebral substance ; whence it follows, that this substance conducts a little less 
 well than the nerve, and the latter about four times less than the muscle. 
 
 L L 2 
 
516 TRANSMISSION OP ELECTRICITY. FART iv. 
 
 of this mass ; and although this energetic current traverses 
 the muscle in all directions, the frog undergoes no contrac- 
 tion, nevertheless, its nerve is contained in this muscle, and 
 forms almost one integrant part of it. Care must be taken to 
 employ a muscle, whose irritability is extinguished; for 
 without this, the frog suffers contractions, which are due to 
 the phenomena of induced contraction, with which we shall be 
 occupied in the sequel. 
 
 Returning to the contraction excited directly upon the 
 muscles, we will further remark that, when it takes place 
 by the effect of the discharge of aLeyden jar, it occasions in 
 the muscle a persistent deadly stiffness, accompanied by a 
 shortening; this is an effect similar to that, which Nobili, 
 Masson, and Matteucci have successively obtained by causing 
 a discontinuous current to pass through the nerve of an 
 animal, which brings about a veritable tetanus ; a tetanus 
 that may be made to cease, either by the passage of a current 
 the inverse of that, by which it has been produced, or by di- 
 viding the nerve, that communicates with the tetanised limb. 
 
 We shall here terminate what we have to say for the 
 present on the physiological effects of electricity; we shall 
 return to many of the points that we have omitted ; such in 
 particular as the influence upon the effects of electricity, of 
 poisons, and of narcotics previously administered to the 
 animals, as well as upon the analysis of the sensations that 
 are produced in men by the passage of dynamic electricity in 
 different parts of their organs. These subjects, as well as 
 other analogous ones, will naturally find their place in the 
 chapter of this Treatise, which will be devoted to the 
 Therapeutic Applications of Electricity ; and they can 
 then be treated in a much more complete manner, because 
 we shall have studied, what we have not yet done, 
 the phenomena relative to the production of electricity by 
 physiological actions, which are designated under the name 
 of animal electricity.* 
 
 * List of the principal works relating to the subjects treated upon in this 
 Chapter. 
 
 Davy. Electro-chemical decomposition of organic substances. Ann. de 
 Chin. t. Ixiii. pp. 223. 255- and 261. 
 
CHAP. iv. BIBLIOGRAPHY. 517 
 
 Gay-Lussac. Effects of electricity upon the fermentation of must. Ann. 
 de Chim. t. Ixxvi. p. 257. 
 
 BecquereL Application of electro- chemical forces to vegetable physiology. 
 Ann. de Chim. ct de Phys. t. Hi. p. 57. 
 
 Matteucci. Influence of electricity upon germination. Ann. de Chim. et de 
 /'///AS. (new series) t. ii. p. 403. Electro- physiological researches. Ann. de 
 Chim. et de Phys. (new series) t. ii. p. 403.; t. xix. p. 52. ; t. xxiii. p. 241. 
 Phil. Trans, of the Royal Soc. London, 1846-7-9 and 1850. Treatise on the 
 Electro -physiological Phenomena of Animals. Paris, 1844, in 8vo. with plates. 
 
 Dutrochet and Becquerel Influence of electricity upon the circulation of the 
 chara. Bill Univ. (new series.) t. xii. p 394. (1837.) 
 
 Lassaigne. Precipitation of albumen at the positive pole. Ann. de Chim. et 
 de Phys. t. xx. p. 97. 
 
 Galvani. Resume of his electro-physiological works. Ann. de Chim. et de 
 Phys. t. xxv. p. 58. 
 
 Humboldt. Irritation caused by metals upon animals. Ann.de Chim. t. xxii. 
 p. 51. 
 
 Ure. Electric experiments upon a corpse. Ann. de Chim. et de Phys. 
 t. xiv. p. 337. 
 
 Lenz. Electric conductibility of the human body. Arch, de T Elect, t. iii. 
 p. 534. 
 
 Pouillet. Idem. Compte rendu de TAcademie des Sciences, t. iv. p. 791. 
 
 Masson. Physiological effects of discontinuous currents. Ann. de Chim. et 
 de Phys. t. Ixvi. p. 5. 
 
 Philipps. Action of the current replacing that of tho nerves. Ann. de 
 Chim. et de Phys. t. xxii. p. 216. 
 
 Volta Animal electricity, Ann. de Chim t. xxiii. p. 276. and t. xxix. 
 p. 91. 
 
 Marianini Various memoirs relative to the physiological action of the 
 current. Ann. de Chim. et de Phys. t. xl. p. 225. ; t. xliii. p. 320.; t. Ivi. 
 p. 387. 
 
 Nobili. Idem. Ann. de Chim. et de Phys. t. xxxviii. p. 225. ; t. xliv. p. 60. 
 
 Du Bois-Reymond. Idem. Ann. der Physik. passim. Untersuchungen uber 
 thierische Ekctricitat. Berlin, 1848, t. i. 
 
 L L 3 
 
518 
 
 PAKT V. 
 
 SOURCES OF ELECTRICITY. 
 CHAPTER I. 
 
 ELECTRICITY PRODUCED BY THE ACTION OF HEAT. 
 
 Development of Electricity by Calorific Action in bad 
 Conductors. 
 
 AFTER having studied the properties of electricity, both in 
 respect to the general laws, to which it is subjected in its 
 different forms, as well as in respect to the effects that it pro- 
 duces in bodies, while traversing them, it remains for us 
 to examine the various means, by which it is brought into 
 being. The sources of electricity are of three kinds, action 
 of heat, mechanical action, and chemical actions. We 
 are about to examine summarily these different sources, 
 in endeavouring to discover the laws, that regulate the 
 development of the electricity, to which they give rise ; 
 then, after having studied them, we shall seek for what 
 they have in common, and for the general principles, by 
 which they are connected with each other, at the same time 
 that we shall introduce certain phenomena, in which there is 
 production of electricity, without apparent cause. We shall 
 commence this study by the action of heat, considered as a 
 source of electricity ; seeing that, of the three sources, it is 
 the one which is the least complex. We shall not occupy 
 ourselves in this Part with the natural sources of electricity, 
 which will form the subject of our study in the Sixth Part of 
 this work. 
 
 The influence of heat upon electricity was noticed from 
 the earliest times, when attention was directed to electrical 
 phenomena ; it was very speedily noticed that elevation of 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 519 
 
 temperature facilitated the liberation of electricity, produced 
 by friction in glass and insulating bodies, as we shall see 
 in the following Chapter. Furthermore, elevation of tem- 
 perature is sufficient of itself, without any other action, to 
 render bodies electrical, which were not so. This property, 
 proved for the first time, in tourmaline, was recognised to 
 belong to other crystals, and has received the name of pyro- 
 electricity, in order to distinguish it from thermo-electricity, a 
 denomination that has been reserved to the collection of elec- 
 trical phenomena, developed by heat in conducting bodies, 
 and which will form the subject of the following paragraphs. 
 Pliny had already spoken of a hard, violet or deep-red 
 stone, which, when heated in the sun, or rubbed with the 
 fingers, attracts small light bodies. At the end of the 
 seventeenth century, some Dutch merchants brought from 
 the island of Ceylon a stone, to which naturalists had given 
 the name of tournamal or ashes-attractor ; and which, when 
 placed upon hot ashes, attracted them, and immediately 
 repelled them, whilst it manifested no similar phenomena 
 upon cold ashes ; this mineral was the tourmaline. ^Epinus, 
 having had in his hands, in 1757, two polished tourmalines, 
 intended for setting in a ring, was the first to make a series 
 of experiments ; which established in a precise manner the 
 laws of the development of electricity by heat in this 
 crystal. He first proved the presence of free electricity in 
 the heated tourmaline, by the attraction and repulsion, that 
 it exercises successively, upon a light body, suspended by a 
 silk thread ; he even drew from it a spark, visible in the 
 dark; but, the most important observation that he made, 
 was that of the simultaneous presence of the two electricities 
 in the same tourmaline, one of them being confined in one 
 part of the crystal, and the other in another; these two 
 parts, constituting the two opposed electric poles of the tour- 
 maline. jEpinus had thought he was able further to lay 
 down, as a general rule, that the electric poles, in the un- 
 equally heated tourmaline, are contrary to what they are in 
 the equally heated tourmaline; he had had, on this point, 
 some contests with Wilson ; and, in general, there remained 
 
 L L 4 
 
520 SOURCES OF ELECTRICITY. PART v. 
 
 many anomalies to explain, when Canton succeeded in dis- 
 covering an important principle, by means of which it was 
 easy to explain all the apparent contradictions, that existed 
 among philosophers, upon this subject. This principle is, 
 that it is not the absolute temperature, but the change of 
 temperature, that renders the tourmaline electric ; and that 
 the electricity of each of its poles varies, according as this 
 change is a heating or a cooling. More recently Bergmann 
 took up Canton's important observation, and analysed with 
 much clearness the various electric phases of the tourmaline, 
 which he explained in a very satisfactory manner. Thus, a 
 tourmaline, placed in a medium, the temperature of which it 
 possesses, is not electrical. Transported into a colder me- 
 dium, to which it abandons its heat, it acquires two contrary 
 electric poles; a state, which again ceases, when the tour- 
 maline has acquired the temperature of the medium. On 
 being brought back into the former medium, the tourmaline 
 again becomes heated, and regains its electric poles ; but with 
 contrary signs to those of the former poles, the pole that was 
 positive during the heating, becoming negative during the 
 cooling, and reciprocally. This law is not only true for the 
 crystal as a whole, but also for each of its parts separately ; 
 so that if the two poles are so arranged that, one is 
 heated while the other is cooled, they have the same elec- 
 tricity at the same time. 
 
 To sum up, the electric state of the tourmaline may vary 
 in six ways, namely, if we call A and B, the two poles : 
 
 A positive, and B negative. 
 
 A negative, and B positive. 
 
 A and B positive. 
 
 A and B negative. 
 
 A positive, and B not electric. 
 
 A not electric, and B negative. 
 
 The first state having been observed, when the tourmaline 
 has been transferred from a cold into a warm medium ; the 
 second is observed when, after having plunged the crystal 
 into a warm liquid, it is allowed to cool, after having been 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 521 
 
 withdrawn from it. The third state is obtained by holding 
 the extremity B, for half a minute in the flame of a lamp or 
 a taper ; because, as soon as it is withdrawn, B cools, and A, 
 on the contrary, becomes heated by conductibility ; but when 
 once A has acquired the highest temperature, to which it can 
 attain, it cools and becomes negative, whilst B remains posi- 
 tive. The fourth state is obtained in the same manner as 
 the third, by heating A instead of B. In order to bring 
 about the fifth and the sixth, we have merely to place the 
 crystal upon an insulated sheet of iron, maintained at a con- 
 stant temperature, by means of a hot fire, and to cover the 
 upper face with a cold piece of metal. The face, that rests 
 upon the plate of hot sheet-iron, preserves a constant tempe- 
 rature, and possesses no electricity ; whilst the other, which 
 receives heat by conductibility, becomes electric, either posi- 
 tively or negatively, according as it is the face A, or the 
 face B. 
 
 Bergmann has further demonstrated that the quantities of 
 positive and negative electricity, developed in the crystal, are 
 exactly in the same proportion ; he has, in fact, proved that an 
 insulated metal vessel filled with hot water, does not become 
 electric, when a tourmaline is plunged into it; a proof that 
 the two contrary electricities, which it acquires, neutralise 
 each other, and that, consequently, they are equal. 
 
 We are indebted also to Canton for a very important 
 observation ; it is that, when we operate no longer upon 
 flat tourmalines, like those, which are employed as stones 
 or rings, but upon elongated tourmalines, whose poles are 
 at the distance of f in. at least from each other, we find, 
 on breaking the stone into, for instance, two or three frag- 
 ments, that each of them has two poles, like the entire crystal, 
 and that the extremities of the fragments, that were in 
 contact, before the rupture, present contrary poles. The 
 mechanical division of a pyro-electric crystal may be carried 
 on as far as we please, without causing the contrary elec- 
 tricities of each fragment to disappear. Brewster, having 
 reduced a tourmaline into very fine powder, observed that 
 this powder remained attached to a glass plate, upon which 
 
522 SOURCES OF ELECTRICITY. PART v. 
 
 he had placed it, as soon as he heated the plate ; and that the 
 small grains, when they were shaken, agglomerated into 
 globules ; a property, that disappeared, as soon as the elevation 
 of temperature ceased to take place. Seen under the micro- 
 scope, this impalpable powder presents small angular frag- 
 ments, which, like the entire crystal, are endowed with electric 
 poles, as soon as they are subjected to a change of tem- 
 perature. 
 
 When a tourmaline is placed so that its lower and its upper 
 extremity are the places of the two electric poles, every ver- 
 tical line that joins these two poles, is termed the electric axis 
 of the crystal. A plane, that cuts the crystal perpendicularly 
 to the axis, determines two faces, which equally become con- 
 trary poles, either one to the other, or to that, which already 
 existed upon the other face of the same fragment. Under 
 this relation, the tourmaline may be compared, either to a 
 magnet, in Colombo's theory*, or, still better, to a dry pile f ; 
 which when it is divided into two, in any part of its length, 
 always presents two opposite poles. The analogy is so com- 
 plete, that, with a dry pile, all the phenomena, presented by 
 the tourmaline, may be imitated. Thus, if two dry piles are 
 applied one against the other, by their similar poles, we have, 
 at the other two free poles, the same electricity, in the same 
 manner, as we have the same electricity at the two extre- 
 mities of the tourmaline, if one of them is subjected to an 
 elevation and the other to a reduction of temperature. Wilke, 
 having heated a tourmaline on one side with the solar rays, 
 concentrated in the focus of a lens, found negative elec- 
 tricity at the two poles, and positive at the middle. 
 
 In order to observe the different electric phenomena, that 
 are presented by the tourmaline, we may place it, as Bec- 
 querel did, in a little stirrup of paper, suspended at the 
 extremity of a thread of the cocoon, fixed vertically in a glass 
 cylinder, itself placed upon a plate of metal, the temperature 
 of which is raised (Jig. 263.) ; in proportion as the interior of 
 the vessel is heated, the temperature of the tourmaline rises ; 
 
 * Vol. I. p. 194. /#. 78. 
 t Vol. I. p. 52. 
 
CHAP. I., ELECTRICITY PRODUCED BY HEAT. 523 
 
 and immediately that it becomes electric, we have merely to 
 present to it a body feebly electrised, in order to observe the 
 
 Fig. 263. 
 
 attractions and repulsions. In order the better to seize upon 
 the changes of polarity in the tourmaline, which are some- 
 times very brief, we must place in the interior of the bell- 
 glass, and at a little distance from each extremity of the 
 crystal, two vertical metal rods, which communicate respec- 
 tively with one of the poles of a dry pile ; immediately that 
 the tourmaline becomes electric, it places itself between the 
 two rods, the contrary poles facing ; it is thus easy to prove 
 its electric state and the nature of its poles.* 
 
 * A very curious fact, which M. Becquerel has proved by means of the same 
 apparatus, is the electric polarity, that may be acquired by a body, a bad 
 conductor, placed under the same circumstances, as the tourmaline, when an 
 electrised body is brought near to it. Thus, if we place in the paper stirrup a 
 small tube of a glass, that is not very hygrometric, about ^ in. in diameter, and 
 about an inch in length, and present to it a rod of electrised gum-lac, it is 
 attracted, in consequence of the decomposition of its natural electricity. On 
 raising the temperature to 86, the tube acquires electric polarity, which dis- 
 appears as soon as the electrised rod of gum-lac is removed ; but, if we cause 
 this polarity to occur at the moment when, after having extinguished the 
 
524 SOURCES OF ELECTRICITY. <>ART v. 
 
 Riess and the German philosophers, who have been much 
 occupied with pyro-electric phenomena, have adopted a de- 
 nomination, which appears to us very happily chosen, for 
 distinguishing the two poles of the tourmaline, and of pyro- 
 electric crystals in general, from each other. He calls that 
 the analogous pole, for .which the sign, that represents the 
 variation of temperature, and the nature of the electricity, 
 are similar ; and antilogous pole, that for which these signs 
 are contrary. Thus, the analogous pole is that which is 
 electrised + when there is elevation of temperature, and 
 when there is reduction ; and the antilogous, that which 
 presents the opposite phenomena. It is very easy to deter- 
 mine, by means of an ordinary electroscope, the electric nature 
 of the two poles ; but it is less easy to find their exact 
 position, as well as that of the electric axis. The natural, or 
 artificial faces, by which the crystal is bounded, frequently 
 cut its axis under acute or obtuse angles ; and then we have, 
 not the poles themselves, but places which are near to them, 
 and which are frequently limited by edges or angles, where 
 the electricity, developed at the poles, is accumulated. It 
 results from this, that very frequently the points where the 
 indication of the electroscope discloses the largest amount of 
 electricity, are only places favourable to the accumulation of 
 electricity; and that they are frequently very near to the 
 electric pole, and not this pole itself. Sometimes deforma- 
 tions and fissures, due to the alteration of the crystal, become 
 the origin of a particular distribution of electricity, which 
 might give rise to errors, as to the place of the poles and of 
 the axis. Thus, unless we find by chance faces perpendicular 
 to this axis, it is necessary, in order to determine its position, 
 to refer to crystallographical or optical measurements. 
 
 Tourmaline is not the only pyro-electric crystal. Canton 
 had already found the same property in the topaz of Brazil ; 
 Brard, in axinite ; Haiiy, in boracite, scolezite, titanite, &c. ; 
 
 lamp, the polarity commences, it endures for a longer or shorter period, even 
 when the electric source, by which it had been produced, has disappeared. 
 We have merely to heat again the medium, in which the small glass tube is, in 
 order that the polarity may disappear. 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 525 
 
 Brewster, in mesolite, quartz, and in some artificial crystals. 
 The electric phenomena are manifested in an almost similar 
 manner, in all these crystals ; thus their detailed study would 
 not present any interest, if there did not exist an intimate 
 connection between the form of the crystals and their elec- 
 tric polarity. Haliy was the first to point this out. He had 
 remarked that the crystallised mineral substances, which 
 present pyro-electric phenomena, are those, the crystals of 
 which deviate from the laws of symmetry ; namely, whose 
 corresponding opposed parts are not similar by the number, 
 the arrangement, and the form, of their faces ; the summit, 
 that is most furnished with facets, being that which gives 
 positive electricity by cooling. More recently, this observa- 
 tion has been confirmed and studied by Kohler, by Hankel, 
 by Rose, and by Riess. All pyro-electric crystals have for 
 their polar faces a form, that is due to the combination of a 
 homo-hedric form, with a hemi-hedric form. We know that 
 the homo-hedric and hemi-hedric forms themselves result from 
 the combination of two simple forms ; in such a manner that, 
 for the first, all the faces of one of the forms are combined 
 with all those of the other ; whilst, for the second, half of 
 the faces of one of the forms are wanting. We have a very 
 simple example of this in the combination of the cube with 
 the octohedron ; in the homo-hedric state, this combination 
 presents a cube, the eight angles of which are truncated, 
 whilst, in its hemi-hedric state, it represents a cube, the four 
 angles of which alone are truncated, alternating with perfect 
 angles. Now, in this case, the combination of the homo- 
 hedric with the hemi-hedric form, which produces the polar 
 face of a pyro-electric crystal, engenders a tetrahedron, by 
 the reunion of the four faces, which have taken the place of 
 the angles of the cube. But, if it is necessary, in order that 
 a crystal may be pyro-electric, that it shall have hemi-hedric 
 polar forms, it does not necessarily follow from this that all 
 those which have these forms are pyro-electric. 
 
 When we desire to study the pyro-electricity of various 
 crystals, which have not all, as the tourmaline may have, 
 an elongated form, we cannot employ Becquerel's process, 
 
526 SOURCES OF ELECTRICITY. PART v. 
 
 described above (fig. 263.). We then make use advanta- 
 geously of a dry-pile electroscope, furnished with a gold-leaf, 
 which is carried by a rod in the form of a truncated cone, 
 the upper surface of which receives the electric face of the 
 crystal. It is necessary to pay great attention, so as to 
 avoid all friction, on placing the crystal down ; for, without 
 this precaution, negative signs are frequently obtained, which 
 are due to the friction of its faces. The crystal is taken 
 with pincers, lined with cork, which must be covered with 
 tin-foil, to prevent its retaining electricity. In order to 
 collect the electric signs, that accompany the cooling of the 
 crystal, the precaution is taken of heating it in a porcelain 
 crucible filled with leaden shot, as fine as possible, which 
 is placed in communication with the ground, by means of 
 a conductor, in order to cause the electricity to disappear 
 that is produced by the heating, and which might remain 
 adhering to the surface of the crystal. It is left plunged 
 in the shot for a longer or shorter time, according to its 
 mass, in order that it may acquire the temperature, indicated 
 by the thermometer, which is also placed in it. In order to 
 cause the electricity to disappear, which may be developed 
 upon its surface by the friction, that it suffers from the 
 shot, at the moment, when it is withdrawn from it, the 
 precaution must be taken of causing it to pass rapidly 
 through a spirit-flame. 
 
 In general, the experiments are better made, by observing 
 the electricity, that is liberated during the cooling, than that, 
 which results from the heating, seeing that the heating can 
 never be brought about with so much regularity as the 
 cooling ; however, the results obtained may be controlled, by 
 heating with a spirit-lamp one of the extremities of the 
 crystal, whilst the other is in communication with the elec- 
 troscope. But we are not able in this way to determine 
 the position of the electric poles, we merely obtain informa- 
 tion, as to the nature of their electricity. 
 
 If we now apply the experimental processes, that we have 
 been describing, to the study of the pyro-electricity of 
 various crystals, we arrive at some interesting results, of 
 
CHAP. I. 
 
 ELECTRICITY PRODUCED BY HEAT. 
 
 527 
 
 Fig. 264. 
 
 which we shall confine ourselves to pointing out the most 
 important. 
 
 The tourmaline, for the most part, as- 
 sumes the form of a nine-sided prism (fig. 
 264.) ; produced either by a three-sided 
 prism, whose edges have two small faces, 
 or by a six-sided prism, the three edges of 
 which are each replaced by a face. The 
 extremities of the prism are formed by 
 three faces of the principal rhombohedron, 
 or simply by the faces of the fundamental 
 prism of three tables. The faces of the 
 principal rhombohedron rest at one of the 
 extremities of the crystal upon the faces, 
 and at the other extremity upon the edges 
 of the three-sided prism. The former of these extremities 
 is the analogous electric pole, the latter the antilogous pole ; 
 the lateral edges of the prism represent the direction of the 
 axis. Sometimes the principal rhombohedron is wanting ; 
 but its position may be appreciated from the other ter- 
 minal faces. The intensity of the electricity, in the same 
 conditions of temperature, varies with each specimen of the 
 crystal ; it is in general greater in tourmalines of clear 
 colours and pure and transparent mass; however, very 
 electric tourmalines are sometimes found among those that 
 are black and not transparent. The dimensions of the 
 crystal also influence the energy of its electric properties, the 
 thicker and the longer being those in which this energy is 
 the greatest.* The tourmaline in general gives only electro- 
 statical effects. However, Du Bois-Reymond succeeded 
 in obtaining an electric current by pressing between two 
 plates of platinum, communicating with the ends of the wire 
 of a galvanometer, the two poles of a black tourmaline an 
 
 * However, M. Becqucrel has remarked, that the fragments obtained by the 
 rupture of a rather long, but thin tourmaline, are more powerfully electric than 
 the entire tourmaline was. He has even found one tourmaline which, not 
 being electric, gave, on being divided into two, fragments thai manifested de- 
 cided signs of electricity. 
 
528 SOURCES OF ELECTRICITY. PART v. 
 
 inch in length, by J of an inch in thickness, which he heated 
 with a spirit-flame ; the deviation of the galvanometer took 
 place in a contrary direction when, instead of heating the 
 tourmaline, it was cooled by moistening it with sulphuric ether. 
 The current came from the analogous pole during the 
 heating, and from the antilogous pole during the cooling. 
 It is probable that this tourmaline was of a more conduc- 
 teous nature ; which occurs with opaque tourmalines, that 
 contain some metallic oxides, the presence of which is probably 
 also the cause of their less aptitude to become charged with 
 static electricity. 
 
 Mr. Forbes, who made a great number of experiments upon 
 this subject, found a crystal of tourmaline, the structure of 
 which appeared regular to the sight, but which possessed the 
 extraordinary property of presenting, on cooling, a positive 
 electric pole at each of its extremities. But he observed that 
 the central portion of the crystal possessed an excess of 
 negative electricity. Everything leads to the belief that this 
 crystal was a mascle, namely, a crystal formed of two others, 
 attached together by the symmetrical faces, which possess 
 consequently the same electric polarity. Mr. Forbes, in the 
 numerous specimens, that he has examined, found, contrary 
 to M. Becquerel, that, in general, the longest pieces of tour- 
 maline are those which give the most intense electric signs, 
 for an equal section ; but there does not appear to exist any 
 relation between the length and the intensity. 
 
 Silicate of zinc is one of the most perfectly electric crystals ; 
 the slightest change of temperature is sufficient to render its 
 electricity sensible. Its analogous pole is the only one, that 
 is perfectly crystallised; the antilogous pole is in general 
 truncated, and very rarely presents natural faces, seeing that 
 the increase of the crystal is brought about by this ex- 
 tremity. Moreover, the two polar extremities, as in all 
 electric crystals, have a different crystallisation. The pre- 
 mature form of silicate of zinc is a rectangular octohedron ; 
 but it presents itself in hexahedral prisms with dihedral 
 summits. 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 529 
 
 Scolezite (silicate of lime and alumina*) presents itself 
 under the form of crystals grouped together so as to possess 
 only one extremity regularly crystallised, which is pyrtr 
 electric and forms the antilogous pole, whilst the analogous 
 pole would be at the free extremity, and where the rami- 
 fications converge ; but the crystallised bundle resolves 
 itself more frequently, at the point of convergence, into a 
 compacted fibrous mass, which is not electric, and which 
 becomes so only at the place, where the crystallised needles 
 may be distinguished fairly formed ; its electric axis is 
 confounded with its crystalline axis. Scolezite, which is very 
 easily electrisable, is still more so, as Sir D. Brewster has 
 remarked, even when heat, by removing from it its water of 
 crystallisation, has converted it into a white powder ; which 
 proves that it is to the particles alone of the crystals, and not 
 to their mass, that the pyro-electricity appertains. It fre- 
 quently happens that the crystals of scolezite, being mascles, 
 the extremities, that have opposite poles, are connected, and 
 there is no sensible development of electricity by heat ; but, 
 if one of the crystals, which form the mascle, is removed by 
 polishing, the other is always electric. 
 
 Axinite (silicate of lime and aluminaf ) is feebly electrical. 
 It is necessary to heat it up to 248, in order to obtains signs 
 of electricity ; and certain specimens even, although very 
 
 * Composition of scolezite : 
 
 Silica - - 4625 
 
 Alumina - - 24-82 
 
 Lime - 14-20 
 
 Soda - - - 0-39 
 
 Water - 13-64 
 
 99-30 
 
 f Axinite contains less alumina and more lime than scolezite. The fol- 
 lowing is its composition : 
 
 Silica - 43-686 
 
 Alumina - - 15*630 
 
 Lime - 20*670 
 
 Ferric oxide - 9*450 
 
 Manganic oxide - - 3'050 
 
 Magnesia - - 1*700 
 
 Potassa - 0*640 
 
 Boric acid - - 5*610 
 
 100*436 
 VOL. II. M M 
 
530 SOURCE OF ELECTRICITY. PARTY. 
 
 well crystallised, sometimes do not give any. In general , 
 the antilogous poles are more energetic than the analogous. 
 It would seem that axinite is formed of two crystals, in 
 which the electrical axes have an opposite direction. 
 
 Boradte (borated magnesia) is powerfully electric. It pos- 
 sesses four electric axes ; the four antilogous poles are upon 
 the brilliant faces of the tetrahedron, and the four analogous 
 poles upon the angles of the cube; for boracite presents 
 itself to us under the form of a cube, modified, for the most 
 part, on the edges and on the solid angles ; so that these latter 
 completely derogate from the law of symmetry. Reduced into 
 powder, boracite is still electric, although we are unable, by 
 the microscope, to discover crystalline forms in the grains of 
 the powder that it forms. Boracite seems to present an ex- 
 ception to the general law, that opposite electricities are ma- 
 nifested at the same pole, only so long as there is an inversion 
 in the march of the temperature. In fact, on heating bora- 
 cite in leaden shot with all possible precautions, we see the 
 antilogous pole, for instance, constantly give negative electri- 
 city with a temperature ascending up to 400 ; it then gives 
 positive from 400 to 493 ; with a descending temperature, 
 it gives negative from 460 to 413, and returns to its normal 
 state, giving positive below 413. This exception is probably 
 only apparent, seeing that it is manifested the more easily, in 
 proportion as the mass of the crystal is less homogeneous. A 
 difference in the structure of the envelope of the crystal, and 
 in that of its nucleus, is necessarily accompanied by a differ- 
 ence in conductibility for heat, and in the development of the 
 electricity of each of the two parts. As soon as the boracite 
 is taken out of the crucible in which it has been heated, in 
 order to expose it to the air, the surface is easily cooled, and 
 covers a nucleus still hot ; so that the electroscope should 
 indicate the difference between two opposite electricities ; 
 namely, that of the envelope, which receives heat from the 
 central nucleus, and that of this nucleus, which is cooling. 
 Negative electricity comes from the nucleus ; also, in order 
 that the electricity which comes from the envelope may pre- 
 ponderate, it is necessary to heat the latter very powerfully. 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 531 
 
 It may happen that the electroscope manifests no electricity, 
 as takes place also after the most powerful heating for tour- 
 maline, axinite, and topaz ; which is due, equally in all these 
 crystals, to the electricity of the nucleus being disguised, at 
 the commencement, by that of the envelope, which is of a 
 contrary nature. Now, it is found that this latter may pre- 
 ponderate over the former in boracite, on account of the par- 
 ticular structure of the crystal, and its facility of becoming 
 electric. 
 
 Rhodizite greatly resembles boracite, in respect to its form, 
 and its manner of being in its electric relation; so that we need 
 not occupy ourselves with it. 
 
 Prehnite (silicate of lime and alumina*) presents in its pyro- 
 electricity a peculiar character ; it is, that its two electrical 
 axes are turned towards each other, in such a manner, that the 
 analogous poles are confounded into a single one, whilst the 
 antilogous are distinct ; which causes the crystal to be tripolar. 
 Thus the little diagonal of the base gives the direction of the 
 two axes ; the common analogous pole of which is in the 
 middle of this line, whilst the two antilogous poles are at its 
 extremities ; and this is the case for the entire mass of the 
 crystal. It follows from this, that the lateral edges of the 
 truncated base possess antilogous electricity in all their 
 extent, whilst the analogous electricity is found in the middle 
 of the face. The crystals, whose electric poles are thus 
 arranged, are called centri-polar. 
 
 The topaz (fluosilicate of alumina f ) is a crystal of the 
 
 * The following is its composition, which differs notably from that of scole- 
 zite and axinite : 
 
 Silica - - 44-10 
 
 Alumina - - 24-26 
 
 Lime - - 26'43 
 
 Protoxide of iron - 074 
 
 Water - - 4-18 
 
 99 71 
 
 There are some varieties which contain less lime, and more protoxide of iron, 
 f The following is the composition of the topaz : 
 
 Silica ..... 34-36 
 Alumina - - - 57'74 
 
 Fluoric acid - - 777 
 
 99-87 
 
 M M 2 
 
532 SOURCE OF ELECTRICITY. PART v. 
 
 same kind ; it also possesses two electrical axes in the di- 
 rection of the shorter diagonal of the base of the prism. The 
 two analogous poles are in the middle of the short diagonal; 
 the two antilogous poles are in the truncated lateral edges, 
 A topaz, that might have a complete form, namely, that of a 
 prism with four faces, with pointed extremities of four tables, 
 would not be electrical at its two extremities ; but the anti- 
 logous electricity would be presented on the lateral truncated 
 edges, in all their extent ; and thence would rapidly diminish 
 on the lateral faces, and would disappear toward the sharp 
 lateral edges, as well as upon the edges themselves. There 
 would not be any analogous electricity on the whole surface 
 of the crystal ; it would all be interiorly. But, in fact 
 topazes deviate much from this normal character. On 
 altering a sharp lateral edge, we provoke the presence oi 
 analogous electricity ; the terminal edges themselves receive 
 electricity from the electric points, that are nearest to them ; 
 and the terminal point, when it is truncated, which is the 
 common case, liberates a feeble analogous electricity. Il 
 follows from this, that the distribution of the analogous and 
 antilogous electricities is singularly modified in the topaz, 
 either by natural irregularities in its crystalline state, or bj 
 those that are brought about by artificial ruptures. 
 
 Mr. Forbes, who has studied the pyro-electricity of the 
 topaz and of boracite, has found, as M. Becquerel had before 
 remarked, that the intensity of the electricity attains its 
 maximum, when the velocity of the cooling has become com- 
 paratively more feeble. He has observed, in particular, thai 
 topaz possesses the property of preserving its electricity for 
 long time after the temperature has ceased to suffer changes, 
 This effect depends simply upon the conductibility of the 
 stone ; for we may very well conceive, that it might happer 
 that the crystal, becoming a worse conductor, in proportior 
 as the heat diminishes, the recomposition of the two electri- 
 cities requires more time for being brought about. Thus, 
 having obtained a deviation of 115 of the needle of Cou- 
 lomb's torsion electrometer, on presenting to it a crystal oi 
 tourmaline, a few instants after it has become electric b;y 
 heat, at the end of 20" the deviation was scarcely diminished : 
 
CHAP. i. ELECTHICITY PRODUCED BY HEAT. 533 
 
 at the end of 40" it was still 95 ; at the end of 60", 85. 
 After several hours, the metal was still powerfully electric. 
 Mr. Forbes has obtained similar results with several other 
 crystals ; it appeared to him, from his researches, that, in all 
 minerals, the difficulty which the two electricities experience 
 in separating, and consequently in recornbining, increases 
 with their mass ; hence it follows that thin crystals are more 
 easily electrical by heat, but remain so for a shorter time. 
 
 Titanite, heavy spar, and rock crystal give, in some cases, 
 signs of pyro-electricity ; but these signs are not at all re- 
 gular ; and we have not yet succeeded in determining the 
 electric axes of these crystals. 
 
 A very great number of crystals, besides those of which 
 we have spoken, have been carefully examined by MM. 
 Rose and Riess, and have not manifested any traces of pyro- 
 electricity ; but these negative results are not entirely con- 
 clusive. Indeed, among pyro-electric crystals, we frequently 
 find specimens that are not so ; either in consequence of some 
 cause that increases their interior conductibility, or by a mode 
 of groupment of their integrant molecules, which disguises 
 the electric state that is developed in these molecules by the 
 movement of heat. It may therefore happen that, among 
 the crystals which have not hitherto appeared to be pyro- 
 electric, specimens occur that are of a nature to be so. 
 
 Independently of natural crystals, many artificial ones are 
 found, which are also pyro-electric. One of the principal is 
 strui'ite, w r hich is an ammoniacal phosphate of magnesia, formed 
 by the prolonged decomposition of animal matters. The 
 struvite is a vertical rhombohedric prism, terminated at one 
 of its extremities by a plane surface, and at the other by the 
 faces of a transverse prism. It has a single electrical axis, 
 which is in the direction of the vertical prism ; the analogous 
 pole is at the right terminal face, and the antilogous is at the 
 edge of the transverse prism of the other face. The crystal 
 becomes easily electrical ; the heat of the hand is sufficient 
 to render the electricity of its two poles sensible. 
 
 Besides the crystals that we have just named, three others, 
 also artificial, among all those that Brewster has studied, 
 
 M M 3 
 
534 SOURCE OF ELECTRICITY. PART v. 
 
 have been generally recognised as pyro-electric ; these are 
 sugar, and the two racemic acids. Care must be had not to 
 take the ordinary racemic acid, for it is very little pyro- 
 electric ; whilst uvic acid, which, in its chemical relations, 
 is similar to it, is very powerfully so. This is due, as M. 
 Pasteur has demonstrated, to racemic acid being formed of 
 two acids chemically identical, but which are dissymmetrical 
 in their molecular relation ; one causing the plane of polar- 
 isation to turn to the right, and the other causing it to turn to 
 the left. Now, these two acids, the former of which is iden- 
 tical with uvic acid, are equally endowed with a very power- 
 ful pyro-electricity ; they have a single electrical axis in the 
 short diagonal of the base of the prism. 
 
 To sum up : it follows, from the detailed study, that we 
 have been making of the pyro-electricity of crystals, that this 
 phenomenon is much more general than has been supposed ; 
 but that it takes place only, so long as the substance is in 
 the crystalline state ; and that it requires for its manifestation 
 a dissymmetry in this state. We may add, that the property, 
 which gives rise to the phenomenon, belongs not to the mass, 
 but to each molecule of the crystal ; that it is very probably 
 due to the manner, in which the atoms are grouped, in order 
 to form the integrant molecule, and to the rupture of electric 
 equilibrium, which is imparted to this molecule by the motion 
 of heat. 
 
 M. Becquerel conceives, also, that there is brought about 
 by heat in crystals a dilatation, that separates the planes of 
 cleavage ; which produces a liberation of electricity analogous 
 to that which takes place in cleavage, as we shall see in the 
 following Chapter. Indeed, when a topaz is split in the di- 
 rection, perpendicular to the axis, the two separated faces are 
 found to be in two different electrical states ; so that we are 
 able to conceive heat as operating a species of cleavage, and 
 liberating the two electricities, which would seem to be dis- 
 guised before the rupture. 
 
 We shall, however, return, after having studied the electric 
 effects of heat in conducting bodies, to this remarkable influ- 
 
CHAP I. ELECTRICITY PRODUCED BY HEAT. 535 
 
 ence of the arrangement of particles in pyro- and thermo- 
 electric phenomena. 
 
 Liberation of Electricity by Calorific Action in good Conducting 
 Bodies. Thermo-electric Curren ts. 
 
 M. Seebeck discovered, in 1823, that an electric current 
 may be brought about in a circuit entirely metallic, by 
 simply establishing a difference of temperature between one 
 point of this circuit and the others. The first experiment was 
 made by forming, by means of a bar of bismuth s s, and a 
 plate of copper s c s, soldered end to end, a kind of arc 
 (fig. 265.) ; in the interior of which, a mag- 
 netised needle a b, rested by its cap upon a 
 point. The apparatus being placed in the 
 direction of the magnetic meridian, in order 
 that the needle, freely suspended, might be 
 parallel to the two pieces of metal between 
 which it was placed, it was merely necessary 
 slightly to heat with a spirit-lamp one of the 
 points of soldering, in order to obtain in the whole of the cir- 
 cuit an electric current, the presence of which was detected 
 by a distinct deviation of the needle. The direction of the 
 deviation, and consequently of the current, changed, accord- 
 ing as it was one or the other of the two solderings, that was 
 heated ; it changed likewise when, instead of being heated, 
 the same soldering was cooled. It is therefore necessary to 
 establish a difference of temperature between the two solder- 
 ings, in order that a current may be established ; if they are 
 exactly at the same temperature, there is no effect. 
 
 Seebeck gives the name of thermo-electric to this current, 
 and to the pair, by which it is generated, in order to distin- 
 guish it from the current, and from the hydro-electric pair, 
 otherwise called voltaic current and pair. 
 
 Seebeck further remarks that, on substituting a bar of an- 
 timony for the bar of bismuth, but taking care still to retain 
 the plate of copper, the direction of the current becomes in- 
 verse, under the same circumstances, from what it was in the 
 
 M M 4 
 
536 SOURCE OF ELECTRICITY. PART v. 
 
 former case ; thus, with copper and bismuth, the current is 
 directed from the bismuth to the copper through the heated 
 point, and consequently from the copper to the bismuth 
 through the point not heated ; and with copper and antimony 
 it is directed from the copper to the antimony in the part 
 heated, and from the antimony to the copper in the part not 
 heated. Also, in order to obtain the greatest effect, it is 
 necessary to form the thermo-electric pair of a bar of bis- 
 muth (fig. 266.), in the form of an arc s c s', 
 the two extremities of which rest upon the 
 two extremities of a bar of antimony s s'. For 
 the needle of the former apparatus is substi- 
 tuted an astatic needle, the axis of which 
 passes freely through an opening made in 
 the middle of the plate of bismuth. When 
 the apparatus has been arranged in the 
 magnetic meridian, we have merely to pinch between the 
 fingers the two metals, at one of their points of contact, in 
 order to bring about between this point and the other, a dif- 
 ference of temperature, capable of causing the needle to de- 
 viate several degrees. 
 
 Seebeck further succeeded in producing thermo-electric 
 currents, by composing the two parts of the pair of a same 
 metal ; but he only succeeded with metals that have a very 
 decided crystalline texture, which establishes a difference of 
 homogeneity between their different parts ; or with two 
 portions of the same metal, rendered directly heterogeneous, 
 such as two pieces of steel, one soft, the other tempered. 
 
 Taking up this last part of Seebeck's researches, various 
 philosophers succeeded in producing thermo-electric currents 
 in homogeneous bodies. Yelin showed that, we have merely 
 to heat one of the extremities of a bar of bismuth, in order 
 to act upon a magnetised needle, on placing it parallel above 
 or below this needle ; the direction of the deviation varies 
 according as the hot or the cold extremity of the bar of 
 bismuth is brought near to the needle ; the same results are 
 obtained for each of the extremities of the bar, when it is 
 heated at its middle, and when its extremities are retained 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 537 
 
 cold. Yelin farther recognised, that the thermo-electric 
 action of metal bars depends upon the form, that has been 
 given to them by casting, and upon the manner in which 
 they have been cooled in their different parts, which enables 
 us to detect a relation between crystallisation, or generally 
 between the molecular constitution of metals, and this class 
 of properties. It is evident that the difference of temperature, 
 between the various points of these large metallic masses, 
 determines the production of currents upon their surface, 
 which act upon the needle in a manner analogous to the in- 
 duction currents, that are produced upon a disc, or upon a 
 rod of metal, by approaching to it a magnet. Only the 
 thermo-electric currents are not instantaneous, like those of 
 induction. With regard to the direction of these electric 
 currents, it is evidently connected with the direction of the 
 propagation of the heat, and with the form and internal 
 texture of the metals, submitted to experiment. 
 
 Mr. Sturgeon obtained more precise results with cylindri- 
 cal and conical bars, either of bismuth or antimony. The 
 currents were, in general, directed from the hot to the cold 
 part, at least in cones, whose base was heated or cooled. 
 In cylinders, the distribution of the current was very regular. 
 On heating uniformly one of the extremities of a cylinder of 
 antimony, two neutral lines were found determined on the 
 surface by a plane passing through the axis of the cylinder, 
 and currents were directed along others generated from the 
 cylinder. Mr. Sturgeon also made a great number of ex- 
 periments on homogeneous rectangles and rings of metal; 
 but, before explaining them, we must speak of the important 
 results, that M. Becquerel had long previously obtained. 
 
 M. Becquerel's process is altogether different from those 
 employed by Seebeck and by the philosophers, of whom we 
 have spoken. He operated, by means .of a multiplier, taking 
 care to use one with a thick and short wire, in order that the 
 thermo-electric currents, produced in a circuit all metallic, 
 shall not encounter too great a resistance, in their course 
 through the wire of the instrument. Having coiled into a 
 spiral the two ends of the copper wire of the multiplier, he 
 
538 SOURCE OF ELECTRICITY. PART v. 
 
 showed that, in order to produce a current, nothing more was 
 needed than to heat one of these ends in a spirit-lamp, and 
 to touch it with the other, that remained cold ; on separating 
 the two spirals, and renewing the contact at each oscillation 
 of the needle of the instrument, very considerable deviations 
 were obtained. Wires of platinum and of silver give rise to 
 the same phenomenon as the copper wire, except as regards 
 intensity, which varies with the metal employed ; thus, with 
 platinum, one of the spirals must be raised to cherry red, 
 the other remaining at the ordinary temperature ; whilst with 
 copper wire, it is not necessary to heat it beyond nascent red, 
 in order to obtain a very sensible current. M. Becquerel, 
 in his first experiments, had constructed with each of the 
 wires submitted to experiment, a complete galvanometer- 
 multiplier; but this is not necessary; we have merely to fix 
 at each of the extremities of the copper wire of an ordinary 
 galvanometer, a piece of the wire upon which we desire to 
 operate, using the precaution of taking these ends of sufficient 
 length, that the heat may not propagate in a sensible manner, 
 as far as the point, where they are in contact with the wire 
 of the galvanometer. We may add that, in the preceding 
 experiments, the current was directed from the heated ex- 
 tremity to the extremity that remained cold, through their 
 point of contact; and consequently from the cold to the 
 heated, through the wire of the galvanometer. 
 
 It would seem, from what precedes, that it would be suffi- 
 cient to connect by a wire the two ends of a galvanometer and 
 to heat this wire in any point of its length, in order to obtain 
 an electric current. Now, M. Becquerel has remarked that, 
 whatever be the nature of the connecting wire, no effect is 
 obtained, on operating in this way, at least if the wire is 
 sufficiently long, and the heated point at a sufficient distance 
 for the heat not to arrive as far as its points of contact with 
 the wire of the galvanometer. But if, without disturbing 
 the homogeneity of a platinum wire a b c (fig. 267.), we 
 make a knot, or better still, coil it into a spiral at o, in a part 
 of its length, at the same time producing no point of dis- 
 continuity, and apply the focus of heat, at a short distance 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 539 
 
 from this spiral, a continuous current is obtained directed 
 from the side of the swelling, setting out from the heated 
 
 ' 
 
 Fig. 267. 
 
 point, which is probably due to the small mass being heated 
 at the expense of the heat, transmitted by the portion / i of 
 the wire, that separates it from the focus. It is very evident 
 that if a distance/ i =fi', is taken at i and i' 9 the movement of 
 the heat cannot be the same on account of the mass o, and the 
 current must arise from the difference of these two movements. 
 Palladium comports itself in the same manner as platinum: a 
 gold wire does not produce any effect ; a silver produces but 
 a very feeble effect ; as is also the case with a copper wire. 
 A continuous current, however, may be obtained by uniting 
 the extremities of the galvanometer with a copper wire, that 
 is cut in two, and the free ends of which are united, by means 
 
 of two hooks, passed one into the 
 other (fig. 268.). The spirit-lamp 
 is placed on the right or on the 
 left of the junction point, at b, for 
 example; and a current is ob- 
 tained, which follows the direc- 
 tion a b c, which is probably due to the propagation of heat 
 taking place more easily, in this direction, than in the other. 
 This explanation appears the more plausible, as the oxidation 
 of the copper wire, at the point of junction of the two ends, 
 which is a consequence of the heat that arrives there, in- 
 creases the intensity of the current, by diminishing the 
 facility of the propagation of heat, in this part of the circle. 
 
 Led on by these experiments, and by others of the same kind, 
 M. Becquerel admits, as a fundamental principle, that the pro- 
 pagation of heat in a metal in a wire a a' a" a' ff (fig. 269.), 
 for example is always attended by a liberation of electricity ; 
 a liberation that consists in this, that the first particle a, which 
 
540 SOURCE OF ELECTRICITY. PART v. 
 
 is in contact with a source of heat b, takes from this source 
 the positive electricity, leaving to it the negative ; that, in its 
 
 o'o'o'o 
 
 M' et," of" a,"" 
 Fig. 269. 
 
 turn, the second particle a', on becoming heated, takes in like 
 manner positive electricity from the first up to the last a'", 
 which is thus found charged with positive electricity. This 
 propagation is naturally made by means of the electric polari- 
 sation of the successive particles, and by a series of decom- 
 positions and recompositions of the contrary electricities of 
 these consecutive particles, in such a manner that there is no 
 free electricity, except at the two extremities ; thus, if we 
 touch the incandescent end, namely, the particle a, with a con- 
 ducting body, sufficiently large not to be sensibly heated, we 
 take away its positive electricity, the negative of takes the 
 positive from a', and so on to the particle a f " ', which is found 
 to retain negative only. 
 
 M. Becquerel has endeavoured to prove directly this prin- 
 ciple, by means of the following experiment. He introduces 
 a platinum wire a b (fig. 270.), into a glass tube, closed by 
 
 Fig. 270. 
 
 the lamp at one of its extremities, and makes the free end 
 communicate with the plate of a condenser; he then coils 
 around the closed end of the tube another platinum wire a' b', 
 the free extremity of which communicates with the ground ; 
 he heats powerfully the end of the tube, and then the interior 
 wire transmits to the condenser a very sensible charge of 
 positive electricity. 
 
 In order to explain this production of electricity, M. 
 Becquerel observes that the glass tube, becoming a conductor 
 by means of its elevated temperature, the positive electricity 
 of the exterior wire traverses the glass and is conducted to 
 
CHAP. T. ELECTRICITY PRODUCED BY HEAT. 541 
 
 the condenser by the interior wire ; the latter, it is true, ought 
 to produce an inverse effect ; but, being less heated, the effect 
 of the former, to which the flame of the lamp is applied 
 directly, preponderates over that of the latter ; if the two wires 
 were equally heated, there would be no effect at all. We 
 may remark, that the negative electricity of the exterior wire 
 is carried to its cold extremity ; and thence into the ground, 
 with which it communicates. 
 
 The interpretation that we have just given of M. Bec- 
 querel's experiment is subject to many objections. M. 
 Gaugain has shown that the employment of the spirit-lamp 
 may give rise to electro-chemical currents ; and, even sup- 
 posing that we succeed, as M. Leroux has done, in avoiding 
 the production of these currents, we cannot protect ourselves 
 from the electricity that may arise from the action upon the 
 platinum of the melted or of the less heated glass. What- 
 ever may be the case, setting out from the principle that the 
 propagation of heat is accompanied by a liberation of electri- 
 city in each metal, M. Becquerel hence concludes that, when 
 we heat in any point of its length, a perfectly homogeneous 
 wire, by which the two ends of a galvanometer are connected, 
 there should be established, setting out from the heated point, 
 two currents perfectly equal, travelling one to its right, the 
 other to its left, and returning to their point of departure, after 
 having traversed the galvanometer ; these two equal currents 
 being guided in contrary directions, their action ought to be 
 null, as demonstrated by experiment. But, provided the ho- 
 mogeneity of the wires be disturbed on one side or on the other, 
 it follows that one of the two thermo-electric currents becomes 
 more powerful or more feeble than the other ; and their differ- 
 ence is detected by the deviation of the galvanometer. A very 
 small matter is sufficient to disturb this homogeneity ; according 
 to M. Becquerel, a simple, but very slight increase of mass is 
 sufficient; a difference in the molecular state, a feeble alteration 
 in chemical purity is, in like manner, sufficient. M. Becquerel 
 attributes the influence of the non-homogeneity to its bringing 
 about a difference in the manner, in which the heat is propa- 
 gated ; a difference which, according to him, is sufficient to es- 
 
542 SOURCE OF ELECTRICITY. PARTY. 
 
 tablish one between the two currents. We shall see, further 
 on, that it is in the non-homogeneity itself, and not in the 
 influence, that it exerts over the propagation of heat, that we 
 must seek for the cause, which makes one of the currents 
 to be stronger or more feeble than the other. 
 
 But, of all methods, the most efficacious for destroying ho- 
 mogeneity, is to substitute for the single wire, by which the 
 two ends of the galvanometer are connected, a wire composed 
 of two pieces of wire of a different nature, but united me- 
 tallically together. On heating their point of contact, we 
 obtain at the galvanometer a current, which is the difference 
 of the currents that each of them would separately produce, 
 each wire being at the same time the conductor of the 
 current liberated by the other. In other words, the intensity 
 of a thermo-electric current is equal to the difference of the 
 thermo-electric actions, produced in each metal by the same 
 temperature ; so that if we call P iron, the thermo-electric 
 power of iron, and P copper, that of copper, the intensity of the 
 current, when the iron-copper soldering is raised to a certain 
 temperature, ought to be equal to P iron P copper, or to P 
 copper P iron, according as it might be the thermo-electric 
 power of the iron or that of the copper, which should be 
 most considerable. In this case, that we have just pointed 
 out, is included Seebeck's primitive experiment of the 
 thermo-electric pair, bismuth and copper. M. Becquerel, 
 on forming similar pairs with various metals, and raising 
 the temperature of their point of contact, has obtained in the 
 galvanometer currents, which led him to arrange these 
 metals in the following order, with regard to their thermo- 
 electric properties : bismuth, platinum, lead, tin, copper, gold, 
 silver, zinc, iron, and antimony. In this Table each metal is 
 positive in respect to that which precedes it, namely, that pla- 
 tinum, for example, acquires positive electricity from bismuth, 
 which causes the current to go from the platinum to the 
 bismuth, through the wire of the galvanometer, from the 
 bismuth to the platinum, through the heated point. But it is 
 preferable to represent the phenomenon, as we have done 
 higher up, namely, setting out from the principle that each of 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 543 
 
 the two metals, heated at their point of contact, gives rise 
 to an independent current, which goes for each, from the 
 heated point to the cold extremity, through the other metal. 
 According to this, the order of the metals, in the above 
 table, would be that of their thermo-electric powers, and the 
 effect observed would be due to the difference of intensity of 
 the thermo-electric powers of the two metals in contact. 
 
 This order differs a little, for some of the intermediate 
 metals, from that which had been established by M. Yelin, 
 and more recently by M. Nobili : but, more than this, these 
 two physicists have remarked that, for some metals, such as 
 antimony in particular, the thermo-electric power is converse 
 of that of the others ; in other words, in these metals the 
 current, instead of being directed, as in all the others, from the 
 heated extremity to the cold, through the entire circuit, 
 is directed from the cold to the hot; so that, when one 
 of them forms a pair with another metal of the series, the 
 two currents that arise from the heating of the point of 
 contact, instead of traversing the wire of the galvanometer, 
 in contrary directions, traverse it in the same direction, and 
 consequently are added together, which renders the pairs 
 thus formed much more powerful ; this is what takes place 
 especially with the bismuth and antimony pairs. 
 
 Another anomaly, observed by M. Becquerel, is the 
 change that takes place in the direction of the current in 
 certain pairs, when the temperature is raised beyond a 
 certain limit. Thus, in an iron and copper circuit, the 
 current goes from the copper to the iron, through the heated 
 point, so long as the temperature does not exceed a certain 
 degree, about 572; under the action of a higher tem- 
 perature, the current changes in direction, and goes from the 
 iron to the copper. The same change takes place, but at 
 a lower temperature, with pairs of zinc and silver, and 
 zinc and gold ; the current which, for less elevated tem- 
 peratures, went from the silver and the gold to the zinc, 
 goes, beyond 212, from the zinc to the silver and the gold. 
 
 We will now see the mode, adopted by M. Becquerel, 
 for determining the relative thermo-electric power of each 
 
544 
 
 SOURCE OF ELECTRICITY. 
 
 PART V. 
 
 metal. In order to render the comparison between metals 
 possible, it would be absolutely necessary to place them 
 under the same conditions ; and consequently not only to 
 reduce them to wires of the same diameter and the same 
 length, but also to place them all in the same circuit, so 
 as to avoid the differences of conductibility, which might 
 influence the intensity of the currents, independently of the 
 thermo-electric power. With this in view, M. Becquerel 
 carefully soldered, end to end, eight wires of different metals 
 of 3*5- th. of an inch in diameter, and about 8 in. in length ; 
 then {fig. 271.) he placed this chain in communication by 
 
 Fig. 271. 
 
 its extremities with the ends of the galvanometer. All the 
 solderings were maintained at 32, except that upon which 
 the experiment was made, which was gradually heated up to 
 68. By operating thus upon each of the soldering suc- 
 cessively he obtained the following results : 
 
 SOLDERINGS HEATED. 
 
 DEVIATIONS. 
 
 INTENSITY of THE 
 CURRENT.* 
 
 Iron Tin 
 
 36-5 
 
 31-24 
 
 Copper Platinum 
 Iron Copper 
 Silver Copper 
 Iron Silver 
 
 16-0 
 34-5 
 4-0 
 33-0 
 
 8-55 
 27-96 
 2-00 
 16-20 
 
 Iron Platinum - 
 
 39-0 
 
 36'07 
 
 Copper Tin 
 Zinc Copper 
 Silver Gold 
 
 7-0 
 2-0 
 
 ro 
 
 3-50 
 1-00 
 0-50 
 
 * These intensities were deduced from the deviations, by means of a table, drawn out em- 
 pirically, which gave the relations between the extents of the deviations, and the correspond- 
 ing intensities of the currents. 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 545 
 
 In order to interpret the results contained in this Table, it 
 is necessary to bear in mind, from what we have said above, 
 that the intensity of the current of each pair is the difference 
 between the intensities of the currents, to which each of the 
 two metals of the pair would give rise separately ; or, which 
 comes to the same thing, that the intensities given in the 
 Table represent the difference of the thermo-electric powers 
 of the two metals, that compose the pair whose point of 
 contact is heated. This important point has been established 
 directly by M. Becquerel, by means of the following experi- 
 ment. 
 
 For this purpose, the circuit of fig. 271. is employed, in 
 which iron and copper are first in contact at the point a, 
 and separated everywhere else, at the solderings b and c, 
 d and e, f and g, by wires of platinum, gold, and tin. The 
 experiments are commenced by raising fhe soldering a to 
 122, whilst all the others are maintained at 32; the intensity 
 of the current is then observed; then, after having suc- 
 cessively raised to 122 the solderings b and c, d and 0,/and 
 g, all the others being equally maintained at 32. Under 
 these different circumstances, the currents have always the 
 same intensity ; so that iron and copper, when they are 
 in contact, or are separated by other metals, give rise to 
 a current, whose intensity is the same ; this current, conse- 
 quently, depends on the temperature alone of the two extreme 
 points. 
 
 Returning to the above Table, M. Becquerel deduced 
 from it the thermo-electric power of the metals, setting out 
 from the principle, that the metal, which takes positive elec- 
 tricity from the other at the point of contact, is the one whose 
 thermo-electric power is the more powerful. Thus, in the 
 iron copper pair, the current goes from the iron to the 
 copper through the entire circuit, and consequently, from the 
 copper to the iron through their heated point of contact ; it 
 is therefore the iron that acquires positive electricity from 
 the copper, and it has (still according to M. Becquerel) a 
 higher thermo-electric power. But, in our opinion, the 
 reverse should be the case ; for, the thermo-electric current 
 
 VOL. II. N N 
 
 
546 SOURCES OF ELECTRICITY. PART v. 
 
 of the iron ought to go from its heated to its cold extremity, 
 through the entire circuit, and that of the copper the same. 
 But the definitive current, detected by the galvanometer 
 travelling in the direction of the current of the copper, indi- 
 cates that it is the latter, which is the more powerful. 
 
 Whatever the case may be, by reasoning with M. Bec- 
 querel, we obtain 27*96 = p iron p copper, and 36*07 = 
 p iron p, platinum. If we subtract the former expression 
 from the latter, we obtain : p copper,^ p platinum = 8*11 ; 
 now, the Table gives, for the value of this expression, drawn 
 directly from experiment, 8-55, a number that is very little 
 different. In like manner, p iron p tin = 31 '24, and p 
 copper p tin = 3 -50 ; whence p iron p copper = 27 '74, 
 in place of 27 '96, which is given by experiment. If, there- 
 fore, we designate by x the thermo-electric power of iron at 
 68, we shall have 
 
 p iron = x 
 
 ^silver = x 26-20 
 
 p gold = x 2670 
 
 p zinc = x\ 26-96 
 
 p copper = x 27-96 
 
 p tin = x 34-24 
 
 p platinum = x 36'00 
 
 Iron is positive in respect to each of the metals of the 
 series ; it is therefore, according to M. Becquerel, its current 
 that determines the direction of the current, which results 
 from the thermo-electric pair, that it forms with each of 
 these metals ; it follows, therefore, from this, that its thermo- 
 electric power is superior to that of the other metals, and 
 that consequently x is greater than 36. With regard to the 
 absolute value of x, it can only be determined indirectly, and 
 by way of hypothesis. M. Becquerel remarks that when, 
 among the calorific properties, we seek for those that are 
 sensibly the same for the different metals, such as gold, 
 silver and zinc, which have the same thermo-electric power, 
 we scarcely see anything but their radiating power ; indeed, 
 it is neither the conducting power, nor the specific heat. If, 
 therefore, we suppose that the thermo-electric powers are 
 
CHAP. I. ELECTRICITY PRODUCED BY IIEAT. 547 
 
 proportional to the radiating powers, we are able, on com- 
 paring, under these two relations, iron and gold, whose radi- 
 ating powers are as 15 : 12, to establish the following pro- 
 portion, 
 
 x : a; 2670=15 : 12 
 
 which gives 
 
 x or p iron= 133-50. 
 
 The thermo electric powers of the other metals are easily 
 deduced from this; and thus we have p silver = 107'30, 
 p tin = 102-26, and p platinum = 97'50. 
 
 But, independently of the uncertainty that reigns over the 
 accuracy of the hypothesis, which has given us the value of 
 x, the thermo-electric powers, calculated, as we have just 
 done, would only be true under the conditions of temperature 
 and conductibility of circuit, which we have employed for 
 establishing them. M. Becquerel succeeded in relieving 
 himself from these two elements, by remarking, that the in- 
 tensities, found directly by experiment, and which give the 
 difference of the thermo-electric powers, such as p iron p 
 copper, are proportional to the conducting powers of the 
 circuit, and to the temperature ; which he verified directly 
 by experiment, forming circuits composed of two metals 
 alone, and causing the temperature to vary within certain 
 limits, without, however, passing beyond 122. Setting out 
 from these acquired points, he was able to represent the 
 thermo-electric powers of the metals by numbers, independent 
 both of the conductibility of the circuit, of which they form 
 part, and of the quantity of heat, that is propagated in them. 
 
 If, as we believe, we must invert the order of thermo-elec- 
 tric powers, namely, regard, as having the strongest powers, 
 that one of the two soldered metals, in which the current 
 travels from the heated to the cold extremity, through the 
 entire circuit, we have in the Table, that gives the value of 
 p iron, p silver, &c. 
 
 
 p silver =26-20 x 
 p gold = 2670 x 
 
 and so on. We must then admit that the thermo-electric 
 
 N N 2 
 
548 SOURCES OF ELECTRICITY. PART v. 
 
 powers are no longer directly but inversely proportional to 
 the radiating powers, and instead of the proportion, 
 
 x: x -26-70 =15 : 12 
 we have 
 
 x: 26-70 x = 12 : 15 
 
 Whence is deduced, 
 
 x or p iron= 12 
 
 And consequently p silver = 14*20, p copper = 14*70, p 
 tin = 22-24, p platinum = 24. 
 
 As we have just explained, M. Becquerel, in connecting 
 the production of thermo-electric currents with the propaga- 
 tion of heat, considers thermo-electricity as a direct effect of 
 heat, modified simply by the special conditions of the body, 
 that transmits the calorific flux. The experiments, in the 
 limits within which these have been made, seem to favour this 
 opinion ; and, in any case, they show, at least, for the metals, 
 which have been the subject of them, and for the tempera- 
 tures to which they have been exposed, that the thermo- 
 electric power of a pair is really the difference of the 
 thermo-electric powers of the two metals, of which it is 
 formed, or else their sum, if these thermo-electric powers are 
 the converse of each other, as is the case with the pair of 
 bismuth and antimony, for example. This simple and im- 
 portant law is not necessarily connected with the hypothesis, 
 which attributes the development of the thermo-electric 
 power to the propagation of heat; it can be sustained, 
 whatever be the cause of this development. Let us therefore 
 endeavour, by new facts, to obtain an accurate idea of this 
 cause. 
 
 We shall not, however, terminate this paragraph without de- 
 scribing also two elegant pieces of apparatus of Mr. Cumming's, 
 founded upon the development of thermo-electric currents. 
 The first is a simple rectangle (fig. 272.). The three sides of 
 
 1 
 
 __" 1 
 
 c 
 
 
 4. 
 
 Fig, 272. 
 
CUAP. I. 
 
 ELECTRICITY PRODUCED BY HEAT. 
 
 549 
 
 \e 
 
 winch a b, b c, and c d, are formed of silver wires, and the 
 
 fourth A B of a platinum wire. 
 This rectangle is suspended 
 at e, in such a manner that 
 the platinum is situated 
 below. If we heat one of 
 the points of junction, or A, 
 and present to one of the 
 sides, to the side c d, for ex- 
 ample, a magnet n s, the rect- 
 angle is immediately seen to 
 obey the attractive or repulsive 
 action of the magnet, upon 
 the current that circulates in 
 c d from c to d. The metal- 
 lic circuit may be suspended 
 upon the magnet itself (fig. 
 273.), so as to allow it, by 
 bending the platinum wire A 
 B c, to turn around the mag- 
 netic pole, which in fact takes 
 place, as soon as we heat, by 
 means of a lamp, the point c, 
 
 Fig. 273. 
 
 which in each revolution of the circuit passes above the 
 flame. 
 
 Relation between Thermo-electricity and the Molecular Structure 
 
 of Bodies. 
 
 The influence, exercised by the molecular structure of 
 bodies over thermo-electric phenomena, follows already from 
 the fact, that one of the conditions essential for the develop- 
 ment of thermo-electricity, is that the heated body shall be 
 solid. Thus, M. Matteucci succeeded in demonstrating that 
 the contact of hot mercury with cold mercury produces no 
 thermo-electric current ; that, consequently, contrary to the 
 opinion of many philosophers, mercury cannot become 
 thermo-electric. He had at first obtained this negative 
 
 N N 3 
 
550 SOURCES OF ELECTRICITY. PART v. 
 
 result, by having three consecutive capsules filled with 
 mercury connected by two syphons, filled also with the 
 same liquid. The two extremes were made to communicate 
 with the ends of the wire of the galvanometer; then, after 
 having removed one of the syphons, the mercury of the in- 
 termediate capsule alone is heated ; the syphon, filled with 
 mercury, is immediately replaced, and a contact is thus 
 established between a large mass of heated mercury and the 
 cold mercury of the syphon, without the galvanometer detect- 
 ing any current, excepting a few very irregular and slight 
 movements of the needle, which arise from the heating of one 
 or other of the two wires of the galvanometer by the effect 
 of the passage of heated mercury, which always more or less 
 takes place to one or other of the two extreme capsules. 
 
 Certain objections having been raised against this process 
 by M. Vorsselmann de Heer and by M. Peltier, M. Matteucci 
 adopted another method, which led him to the same result. 
 It consists in taking an earthen crucible, at the bottom of 
 which are cemented two bent glass tubes ; the crucible is 
 separated into two compartments by a diaphragm, formed of 
 a slice of wood, which slides into a groove, and which conse- 
 quently may be removed at pleasure. The two tubes are, in 
 the outset, filled with mercury, and the two ends of the 
 galvanometer are plunged into them. Then, into one of 
 the compartments is poured mercury cooled down to 14, 
 and into the other mercury at 356. ,The diaphragm is then 
 removed, by sliding it out of the groove. An immediate 
 contact is thus brought about between the hot and the cold 
 mercury, exactly as Nobili and Becquerel had operated to 
 show the production of thermo-electric currents with wires, 
 and yet no deviation of the needle is obtained, although the 
 galvanometer is constructed, so as to be as sensible as possible 
 of thermo-electric currents. 
 
 What has led several physicists to think that mercury might 
 give thermo-electric currents is, that it is a very difficult 
 matter to avoid the contact of the heated mercury with the 
 wires of the galvanometer. But nothing more is necessary, 
 as M. Matteucci has demonstrated, than to plunge two homo 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 551 
 
 geneous, as well as heterogeneous wires into two masses of 
 mercury, which communicate together by means of a syphon, 
 filled with mercury, and of which one is hot and the other 
 cold, in order to obtain a thermo-electric current, which goes 
 from the hot to the cold metal in the wire of the galvanometer, 
 with the greater part of the metals, such as antimony, plati- 
 num, copper, zinc, iron, and even with carbon ; bismuth alone 
 forms an exception. If the surfaces of the metal are well 
 polished, a current is obtained, that goes from the cold to the 
 hot bismuth, instead of going, as with the others, from the hot 
 to the cold, whatever may be the difference of the tempera- 
 ture of the two masses of mercury. Bismuth gives a current, 
 that goes, on the contrary, from the hot metal to the cold if, 
 instead of establishing the circuit through the mercury, the 
 metal, heated at the spirit-lamp, is placed upon the metal, 
 that remained cold ; antimony and platinum, on their part, 
 give in this case a current that goes from the cold to the hot, 
 instead of travelling from the hot to the cold, as when they 
 were immersed in mercury. Copper, zinc, iron, and carbon, 
 do not change, at least when they do not suffer any alteration 
 by the action of the air ; for, if the copper is oxidised, the 
 direction of the current is reversed, even when the circuit is 
 established through mercury. Iron, although oxidised, does 
 not vary in the direction of the current, that it produces. 
 
 M. Gaugain, in some recent experiments, has confirmed, 
 in part, and modified in certain points, the results obtained 
 by M. Matteucci. He operated very simply by placing the 
 two wires, submitted to experiment, in relation with a galva- 
 nometer ; he connected their free ends, by placing them one 
 upon the other ; he then heated in turn each of the wires, 
 by means of a spirit-lamp, placed near the point of junction ; 
 and he observed the direction of deviation, corresponding to 
 each of the two positions of the source of heat. The wires 
 in these experiments were all about ^V of an inch in diameter, 
 and were annealed. With wires of copper, and of iron, the 
 current travels from the cold wire to the hot one, if the 
 surfaces of contact are very metallic. If these surfaces are 
 oxidised or carbonated, the current goes from the hot wire 
 
 N N 4 
 
552 SOURCES OF ELECTRICITY. PART v. 
 
 to the cold. With silver and with zinc wires, the results are 
 the reverse. 
 
 On operating upon circuits formed of two wires of a dif- 
 ferent nature, M. Gaugain found a very much greater number 
 still of irregularities. The duration of the current depends 
 not only upon the fact that the two wires have between them 
 a metallic contact, or that they be separated by a film of 
 oxide or of carburet ; but also on the absolute temperature, 
 to which they are exposed. This current varies even ac- 
 cording as, in the case of metallic contact, the wires are 
 strongly pressed one against the other, or only touch each 
 other lightly; it is clear that the change, when it takes 
 place in this latter case, is due to there being formed, by the 
 effect of the heat, a slight film of oxide upon the surface of 
 contact of one of the metals. Thus all the phenomena 
 enters into the two categories; either immediate metallic 
 contact, or a film either of oxide or of carburet, interposed 
 between the two metals. Then, instead of a single pair, we 
 have two forms of it, the former of one of the metals and 
 of the film of oxide, the latter of the same film of oxide and 
 of the other metal ; and the effect observed is only the dif- 
 ference of the effects due to each pair separately. In support 
 of this explanation, M. Gaugain quotes the fact of a thin 
 plate of platinum, which, being interposed between two silver 
 wires, changes the direction of the current, which travels 
 from the cold to the hot, instead of travelling from the hot 
 to the cold, as had taken place, when the two silver wires 
 were in immediate contact. 
 
 M. Gaugain's experiments, like those of M. Matteucci, 
 show to us that thermo-electric phenomena are less simple 
 than MM. Becquerel and Nobili had supposed. The re- 
 searches of Yelin and of Sturgeon had already proved the 
 very great influence that is exercised over the result, by the 
 molecular state of the body, in which the heat is propagated. 
 Thus Sturgeon had found, on making frames or rings of bis- 
 muth and antimony, that there are, in these frames, points 
 which, when heated, produce currents ; and others, which 
 develope none. He had called these neutral points. These 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 553 
 
 points have this characteristic, that, if the metal on their right 
 is heated, a current is obtained in the opposite direction to that, 
 which is obtained when it is heated to their left. M. Matteucci 
 satisfied himself that the neutral point is found as well for 
 antimony as for bismuth, in the portion of one of the sides 
 of the frame, which corresponds to the point by which the 
 metal had run into the mould, whereby its form was given to 
 it ; which seem to indicate that the corresponding section is, 
 as it were, the surface of contact of the two portions of the 
 frame, that it separates. With regard to the absolute direction 
 of the current, it travels in the bismuth from the cold to the 
 hot part through the section of contact ; and, in antimony, it 
 follows a converse direction. "When the frame of bismuth, 
 or of antimony, is allowed to cool slowly in the mould, neutral 
 points are obtained, wherever there is a boss, namely, 
 wherever the inferior liquid matter has raised up the crust. 
 M. Matteucci, who has made a great number of researches 
 upon this subject, adds the important remark, that the matter, 
 in all the neutral points, presents a crystallisation different 
 from that of the rest of the metal. 
 
 We shall not dwell upon M. Yorsselmann de Heer's ex- 
 periments, who, by operating with bismuth and with antimony, 
 has seen the current go, in the same metal, sometimes from 
 the hot to the cold metal, sometimes from the cold to the hot ; 
 variations which he thought he might attribute to the greater 
 or less differences of temperature between the two bars placed 
 in contact. All these irregularities are due to the crystalline 
 state of the substances, as has been demonstrated successively 
 by M. Svanberg, M. Frantz, and M. Matteucci himself. 
 
 M. Svanberg, following up Faraday's researches upon the 
 magneto -crystalline power of bismuth and of antimony, and 
 the observation of this philosopher upon the existence in these 
 crystals of a plane of cleavage, endowed with greater 
 brilliancy than the others, procured bars of bismuth and of 
 antimony, some of which had their length, perpendicular to 
 this plane of cleavage, like Faraday's magno-crystallic axis*; 
 
 * Vol. I. p. 484. 
 
654 SOURCES OF ELECTRICITY. PART v. 
 
 whilst the length of the others coincided with the intersection 
 of this plane of cleavage, endowed with the greatest brilliancy, 
 and of another, whose brilliancy does not greatly yield to that 
 of the former. The former bars are more negative and the 
 latter more positive in the thermo-electric series, than any 
 other bar that might be formed of the same metal. M. S van- 
 berg has made the important remark, that, for antimony, as 
 well as for bismuth, if the two bars placed in contact are 
 those whose length is perpendicular to the plane of principal 
 cleavage, the current goes from the cold metal to the hot, 
 whilst if they are those whose length is parallel to the inter- 
 section of the two planes of cleavage, the current goes from 
 the cold metal to the hot. No inversion of current is ob- 
 tained, on moving the difference of temperature between the 
 two extremities placed in contact. It follows, therefore, from 
 this, that the differences observed, with regard to the direction 
 of the current, and the changes that this deviation frequently 
 undergoes, are due in bismuth and in antimony to their crys- 
 talline state, and to the position of the planes of cleavage of 
 the specimen submitted to experiment, in relation to the 
 point of contact of the hot and the cold metal. 
 
 M. Frantz has studied the influence of the position of the 
 principal plane of cleavage on the thermo-electric powers of 
 cubical specimens of bismuth and antimony. These specimens 
 of the volume of about '06 cub. in., were so cut, that in each 
 the direction of the principal plane of cleavage was either 
 parallel to two of the faces, or formed an angle of 30 with one 
 of the faces, and consequently of 60 with the other. By 
 this means, two cubes may be placed, one against the other, 
 so that their planes of cleavage are parallel, or are inclined 
 in respect to each other, 30 or 60. In order to operate, 
 M. Frantz placed the cubes between plates of polished glass 
 firmly fixed ; and he made them communicate with the wires 
 of the multiplier by means of small columns of copper, in the 
 form of a square prism. A cylinder of glass, that has been 
 heated in a sand-bath, is placed exactly on the line of contact 
 of the cubes submitted to experiment, which enables us to 
 heat this line to a constant temperature, and one easv of 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 555 
 
 measurements. By means of a lever, suitably arranged, which 
 is loaded with weights, in greater or less amount, the cubes are 
 pressed against each other, so as to render their contact more 
 intimate. The pressure, in M. Frantz's experiments, was 
 generally 16^ Ibs. 
 
 The two cubes, placed between the columns of copper, were 
 first two cubes of bismuth; they were so arranged that their 
 planes of cleavage had a uniform and vertical direction, per- 
 pendicular to the line, that joins the two columns of copper 
 between which they were placed. On heating their line of 
 contact, no current is developed, except certain slight irre- 
 gular currents, due to the perfect non-homogeneity of the 
 internal structure of the metal. If we place cubes, so cut, 
 that the plane of cleavage is inclined 30 to the horizon, a 
 current is obtained of 34 5' on heating their line of contact ; 
 if the plane of cleavage is inclined 60, the deviation is not 
 more than 19 7'; the deviations are exactly of the same 
 value, but in a contrary direction, when the plane of cleavage 
 is lowered in a similar manner, toward the second column of 
 copper instead of being so toward the first. Finally, if the 
 cubes are so placed, that in both the principal plane of 
 cleavage forms the same angle with the vertical plane, there 
 is no current. Neither is there any when the principal planes 
 of cleavage, being placed in an axial direction, form together 
 an angle of 90 ; but a mean deviation of 45 is obtained, when 
 the cubes are placed one against the other, so that the prin- 
 cipal plane of cleavage of one is in an axial position, and that 
 of the other in an equatorial position. 
 
 It follows, from M. Frantz's experiments, that, in every 
 piece of bismuth, cut in the same manner, the inclination of 
 the plane of cleavage indicates the direction of the positive 
 current, developed by the heating of the metal ; and that, 
 when we heat the place of contact of two different pieces, 
 whose principal planes of cleavage are inclined one in re- 
 spect to the other, there is developed a current, that always 
 goes from the direction which is equatorial for this current, 
 and with the more facility, in proportion as the angle, formed 
 by the principal planes of cleavage, is greater. 
 
 Antimony, which also possesses a principal plane of cleavage 
 
556 SOURCES OF ELECTRICITY. PART v. 
 
 altogether predominant, presents the same phenomena as bis- 
 muth. On pressing against each other two cubes of antimony, 
 so that their principal planes of cleavage are in the same 
 position, no current is obtained, when their surface of con- 
 tact is heated up to 212; but a deviation of 12 4' is brought 
 about on arranging the cubes, so that the plane of cleavage 
 of one is in an axial position, and that of the other in an equa- 
 torial. In this case, the current also travels from the cube, 
 whose plane of cleavage occupies the equatorial position in 
 respect to the surface of contact to that, whose plane of 
 cleavage occupies the axial position. 
 
 If cubes made of various other metals are successively 
 placed in contact, either with the cube of bismuth, or with 
 that of antimony, thermo-electric currents are obtained, whose 
 intensity presents considerable differences, according as the 
 plane of cleavage of the bismuth or of the antimony is placed 
 axiallyor equatorially,in respect to the surface of contact, which 
 is always the heated part. The current is twice as strong with 
 equatorial bismuth as with axial bismuth, when combined 
 with iron, lead, zinc, German silver, brass, silver, copper, and 
 tin ; it is the reverse when antimony is substituted for bismuth. 
 The only exception is that presented by steel. With this 
 metal, the current is more powerful when the bismuth is axial, 
 than when it is equatorial ; with antimony, steel comports 
 itself like the other metals. We must not forget that, in the 
 combinations of bismuth with the other metals, the current 
 goes from the bismuth to the metal, through the heated 
 surface of contact, whilst it goes from the metal to the 
 antimony, when this latter is substituted for the bismuth. 
 
 The following, moreover, is the order, in which the metallic 
 cubes, submitted to experiment, may be ranged so that each 
 gives, for a temperature of 212, a positive current with the 
 following: bismuth (plane of cleavage equatorial), German 
 silver, brass, tin, copper, silver, zinc, lead, steel, iron, antimony 
 (plane of cleavage equatorial), antimony (plane of cleavage 
 axial). 
 
 M. Matteucci has lately verified the experiments of MM. 
 Svanberg and Frantz, in a complete manner. He procured 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 557 
 
 tolerably long rods of bismuth, having throughout their 
 length the cleavage parallel or perpendicular to the length, 
 by allowing a stratum of pure bismuth from f inch to 1 inch 
 in thickness, to cool very slowly in a large earthen plate ; he 
 called the former equatorial, and the latter axial, founded 
 upon the position of equilibrium, assumed by the rods between 
 the poles of an electro-magnet, and which very well manifests 
 their uniform structure. He found that, with two axial 
 rods, the thermo-electric current is directed from the heated 
 rod to the other in the surface of contact, and that with the 
 equatorial rods the current has an opposite direction. On 
 heating the line of contact of an axial rod and an equatorial 
 rod, a thermo-electric current is obtained, which goes from 
 the former to the latter at the surface of contact. In order 
 to facilitate the experiments, it is necessary to take two cubes 
 of crystallised bismuth, whose two faces are parallel to the 
 principal plane of cleavage. These two cubes are held in 
 contact, by being pressed between two copper rods, which 
 screw horizontally and which lead to the galvanometer ; it is 
 essential to take care to maintain the contact between the 
 rods and the cubes at a constant temperature, and to raise 
 the temperature of the line of contact of the two cubes, bv 
 touching it with a rod of heated glass. In order to obtain 
 the results described, nothing more is necessary than to make 
 each cube perform quarters of a revolution. 
 
 It is evident that the influence of the planes of cleavage in 
 these phenomena is due, as in those of diamagnetism and in 
 many others, to the molecules being nearer, in the direction 
 of these planes, than in a direction perpendicular ; and the 
 proof is that Matteucci has succeeded in developing by 
 compression in bismuth thermo-electric properties, similar to 
 those, which crystallisation imparts to this metal. The same 
 philosopher has observed that compression is in like manner 
 able to bring about in bismuth differences of conductibility, 
 as well for electricity as for heat, analogous to those, which 
 result from the natural arrangement of the planes of cleavage. 
 Thus equatorial rods of bismuth conduct electricity and heat 
 better than do axial rods ; in like manner, the conductibility 
 
558 SOURCES OP ELECTRICITY. PART r. 
 
 for electricity and for heat is greater parallel to the direction, 
 according to which the bismuth has been compressed, than 
 perpendicularly to this direction. 
 
 M. Matteucci, in order to demonstrate the influence of 
 molecular structure over thermo-electric phenomena, satisfied 
 himself, as he had done for mercury, that there is no thermo- 
 electric current developed in the contact of melted bismuth 
 with a layer of bismuth also melted, but more heated than 
 the former. Yet, of two columns of the same length and the 
 same diameter, one of melted bismuth, the other of solid, the 
 former conducts electricity better than the latter ; it is not 
 therefore to the differences of electric conductibility that the 
 production of thermo-electricity is due. 
 
 It there follows, therefore, from all the facts, that we have 
 been enumerating, the demonstration of the very great in- 
 fluence, that is exercised over thermo-electric phenomena, by 
 the molecular constitution of bodies. This influence had 
 already been proved in 1844 by M. Mousson, in a series of 
 experiments, by which he had demonstrated that, in a homo- 
 geneous wire, the slightest difference in the molecular equi- 
 librium of its different parts, is sufficient to bring about a 
 current, by the application of heat to one of its points ; whilst 
 when the wire is in a perfect state of molecular homogeneity, 
 no current is developed by heating any single point whatever, 
 providing this state of homogeneity is not destroyed by the 
 very application of heat, as takes place with an unannealed 
 wire, and not with one already annealed. The current, that 
 follows from the differences in the molecular state, varies in 
 direction and in intensity with the different metals. In 
 copper and in iron, it goes from the parts that are the more 
 elastic, to those which are the more ductile ; in brass, the 
 reverse is the case. M. Mousson, independently of these 
 general results, had recognised that other circumstances, 
 difficult of determination, exert an influence over the direction 
 and the intensity of the current. 
 
 M. Magnus has latterly taken up this same question ; and 
 he has arrived at results, that appear to us to determine in a 
 very precise manner, the nature of thermo-electric pheno- 
 mena, and their intimate connection with molecular changes. 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 559 
 
 Only, in order not to alter the molecular state of the wire, no 
 higher temperature must be employed than 212 for heating 
 it ; and care must be taken that the two portions, where it is 
 in communication with the galvanometer, shall have exactly 
 the same temperature. 
 
 The first point to be established is to learn whether the 
 development of the current, that results in a homogeneous 
 wire, from an increase of volume arising from a knot, as 
 M. Becquerel was the first to obtain, or from an increase of 
 diameter in a portion of the length of the wire, is due to the 
 difference of the propagation of heat that takes place, when 
 the wire is heated near to the point, or at the point itself, 
 where its volume changes, or to an alteration in its molecular 
 state, produced by the act that has brought about this change 
 of volume. Many experiments have demonstrated that it 
 was to this latter cause, and not to the former, that the pro- 
 duction of the current must be attributed ; we will quote the 
 following, which appears to us the most direct and the most 
 demonstrative. A thick brass wire a yard in length, and 
 nearly ^ in. in diameter (Jig. 274.), was made thin near to its 
 
 Fig. 274. 
 
 middle, so as along a length of 6 in. to preserve a diameter of 
 only ^g- of an inch. On heating one of the points, where the 
 diameter varied suddenly, there was no current. This im- 
 portant experiment, varied in many ways, always gave the 
 same negative result. On the other hand, if a very thin film 
 of copper is deposited by the voltaic process upon a German 
 silver wire, the wire, when heated at the point, where the film 
 of copper terminates, developes a very strong current. An 
 analogous effect is produced by a thin film of oxide, when it 
 covers the surface of a metal. It is not to a modification in 
 the radiating power of the metal, that the effect of these films 
 may be attributed ; for, on modifying this power directly by 
 the superposition of non-conducting films, the same result is 
 not obtained. 
 
560 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 Thus, it appears well proved, that in a homogeneous metal, 
 it is not from an inequality in the quantities of heat propa- 
 gated in the two contrary directions, setting out from the 
 heated part, that the production of the thermo-electric 
 current depends ; since the difference of volumes is not 
 sufficient of itself alone to generate these currents ; but that 
 a difference in the molecular state is essentially necessary, 
 as well, when the volumes are different, as when they are 
 equal. M. Magnus further satisfied himself that unannealing 
 or annealing does not sensibly modify the internal conducti- 
 bility of a large wire of brass or of German silver ; and that 
 consequently the thermo-electric currents, which are developed 
 in a wire, of which one part is annealed and the other not, 
 cannot be attributed to an inequality in the quantity of heat 
 propagated in one of its parts and in the other. 
 
 Now, the following are the results obtained by M. Magnus 
 upon wires drawn out to - of an inch in diameter and 6 ft. in 
 length, and annealed on a length of only 25 \ in. raising each of 
 them to the temperature of 2 1 2 at the point of separation of the 
 annealed and the unannealed portion. In the following Table, 
 the direction of the current is indicated as going from one 
 part of the wire to the other, through the heated point. 
 
 Metal. 
 
 Direction of the Current. 
 
 Deviation. 
 
 Brass - 
 
 From the annealed to the unan- 
 
 
 
 nealed part. 
 
 55 
 
 Silver* 
 
 Id. 
 
 46 
 
 Steel - 
 
 Id. 
 
 
 Silver at 750 of 
 
 
 45 
 
 fineness 
 
 Id. 
 
 40 
 
 Cadmium 
 
 Id. 
 
 25 
 
 Copper 
 Gold, No. l.f 
 
 Id. 
 Id. 
 
 18 
 10 
 
 Platinum 
 
 Id. 
 
 5 
 
 Gold, No. 2.J 
 
 Id. 
 
 2 
 
 German silver 
 
 From the unannealed to the an- 
 
 
 
 nealed part. 
 
 34 
 
 Zinc - 
 
 Id. 
 
 32 
 
 Tin - 
 
 Id. 
 
 30 
 
 Iron - 
 
 Id. 
 
 4 
 
 Lead - 
 
 Doubtful. 
 
 
 
 * Containing 0-0087 of copper. 
 f Containing 0-0097 of copper, and prepared with Prussian gold Fredericks, 
 j Containing O'OOll of silver and prepared.with Dutch ducats. 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 561 
 
 The effects may be increased in the following manner : an 
 unannealed wire is taken, and various portions of it, equal in 
 respect to each other, and separated by equal portions, 
 are annealed ; it is wound upon a frame, the circumference 
 of which is equal to double the length of an annealed part, 
 so that the points of separation of the annealed and the 
 
 unannealed parts, are found al- 
 ternately on the two opposite 
 sides of the frame. On heating 
 all the points, situated on the 
 same side, currents are brought 
 
 , about in the same direction, 
 
 which are all added together. 
 The experiment may be arranged, for example, as i^Jig. 275. 
 Finally, M. Magnus has further endeavoured to determine 
 the direction and the intensity of the current, produced 
 by the contact of two wires of the same nature, perfectly 
 homogeneous, but raised to unequal temperatures, 46 and 
 212, and then 46 and 482, for certain wires only. In the 
 experiments, the wires were either both unannealed or both 
 annealed, or one annealed and the other unannealed. With 
 wires of German silver, fine silver, copper, and tin, the 
 current goes from the cold metal to the hot, by the surface 
 of contact, whether they are both unannealed or annealed ; 
 it goes from the hot to the cold with wires of zinc, platinum, 
 gold, cadmium, brass, and silver of the standard of 0-750. 
 When one of the wires is unannealed and the other annealed, 
 the direction of the currrent is very variable with the nature 
 of the metals. Iron and steel do not give constant results 
 in this mode of experimenting. 
 
 The apparatus, by means of which the operations are 
 conducted, is a cylindrical vessel of tinned iron 4 in. in height 
 and 2| in. in diameter (Jig. 276.). At an inch above the 
 bottom are four openings , b, c, and d, through which pass 
 four horizontal tubes, penetrating into the interior, as far as 
 a vertical tube g. One of the wires, submitted to experiment, 
 is stretched along the axis of the tubes a and b ; as soon as 
 the wire is heated to 212, by means of a lamp, which 
 VOL. II. O O 
 
562 
 
 SOURCES OF ELECTRICITY. 
 
 PART V, 
 
 brings to this temperature the water, with which the vessel is 
 
 filled, the second wire is stretched 
 in the axis of the tubes c and d ; 
 then, by means of a cylinder of wood, 
 movable with gentle friction, in the 
 vertical tube g, the two wires are 
 pressed against a piece of wood 
 /, fixed below their point of cross- 
 ing in the tube g. In order that 
 the pressure may be the same in 
 all the experiments, it is produced 
 by means of a leaden weight p, 
 placed above the wooden cylinder. 
 In order to operate at a tem- 
 perature of 482, a slightly dif- 
 ferent apparatus was employed. 
 We may further add, that M. 
 Magnus has entirely confirmed the 
 result already obtained by M. Matteucci, namely, that no current 
 is developed in the contact of hot mercury and cold. The 
 following is his mode of operating. Two glass tubes A c, and 
 B D, of the form represented in Jig. 277., were filled with mer- 
 
 276> 
 
 Fig. 277. 
 
 cury ; the extremities A and B of the two masses of mercury, 
 were placed in communication with the galvanometer, by pla- 
 tinum wires, which traversed cork plugs, that were thrust in, 
 as far as the surface of the mercury. The mercury of the en- 
 largement c being heated, the drawn-out extremity D of the tube 
 B D, retained at the ordinary temperature, was thrust into it. 
 In another experiment, the extremity D was heated, and it 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 563 
 
 was plunged into the mass C, that remained cold ; there was 
 no trace of current. The columns of mercury in other respects 
 had remained perfectly continuous, since they allowed the 
 thermo-electric current, developed in the other parts of the 
 circuit, to circulate. 
 
 To sum up : it appears to us now to be well established 
 that, in thermo-electric phenomena, the cause of the currents 
 exists, not in the fact itself of the propagation of the heat, 
 but in the molecular effects, that accompany this propagation. 
 Also, when the two portions of a body are perfectly homo- 
 geneous, to the left and to the right of the heated point, the 
 molecular effects, produced by this heat being identical, two 
 currents are the result, which, being called upon to traverse 
 the same circuit, must be equal at the same time that they are 
 contrary ; but the slightest difference in the chemical nature, 
 or in the molecular constitution of these two portions, brings 
 about an intensity, greater in one of the currents than in the 
 other, and consequently produces an effect, that is detected 
 by the galvanometer. With regard to the relation, which 
 M. Becquerel thought he had discovered between the thermo- 
 electric power of metals and their radiating power for heat, 
 it may be applied up to a certain point, in considering that 
 these two powers are equally connected with the molecular 
 state of bodies, as we proved for the former power, and as M. 
 Melloni did for the latter. 
 
 We shall endeavour, further on, and when we shall have 
 been more advanced in the study of the sources of electricity, 
 to see how the connection may be explained, that exists 
 between the production of electricity and the molecular effects, 
 that accompany the propagation of heat. 
 
 TJiermo-electric Piles and application of Thermo-electricity to the 
 Measurement of Temperatures. 
 
 A short time after Seebeck's discovery, Fourrier and 
 CErsted conceived the idea of connecting several thermo- 
 electric pairs, by soldering alternately together, a series of 
 bars of bismuth and antimony, and heating the alternate 
 
 002 
 
564 SOURCES OF ELECTRICITY. PART v. 
 
 solderings, so as always to leave one -cold between two hot 
 ones. A magnetised needle, placed simply upon one of the bars 
 of this circuit, to which a polygonal form had been given, ex- 
 perienced a decided deviation. The same result is obtained by 
 maintaining the alternate solderings at 32, by means of melting 
 ice, those which are not cooling, to be considered as if heated, 
 in respect to the others. The effect upon the needle is very 
 considerable, when cooling and heating are combined ; namely, 
 when all the even solderings, for instance, are surrounded 
 with melting ice, and all the odd ones are heated with a spirit- 
 lamp. The two learned philosophers increased the number of 
 their alternate bars of bismuth and antimony, so as to have as 
 many as twenty-two of each kind. They remarked, that the total 
 effect, exercised upon the needle by this compound circuit, 
 is much inferior to the sum of the isolated effects, that' is ex^ 
 erted by each of the simple circuits, of which it is formed ; but 
 if, without changing the length of the compound circuit, only a 
 portion of the pairs are put into a state of activity, by not 
 heating or cooling all the alternate solderings, then a less 
 effect is obtained : and we are enabled to discover that the 
 intensity of the current is proportional to the number of the 
 elements, that are in action. On the other hand, with 
 perfectly similar pairs, placed under the same conditions of 
 temperature, and confined so as to form piles of eight and 
 sixteen and of thirty-two elements, currents of the same 
 intensity are obtained, whatever be the number of the pairs 
 of the pile. A single pair produces, in like manner, a current 
 of the same intensity. It follows from this, that in a pile of 
 sixteen pairs, the current of each pair is only the sixteenth 
 part of that, which each of the pairs taken separately would 
 produce ; and that, if only a single pair of this pile is put 
 into action, the current of the pile is only the sixteenth of that 
 which would be developed by this pair isolated, when it should 
 be forming a circuit of itself alone. 
 
 These results, already pointed out by Fourrier and 
 M. (Ersted, have been confirmed and perfectly well explained 
 by M. Pouillet, as the result of researches as accurate as they 
 were ample. They come in support of the laws that we have 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 565 
 
 already established in the First Chapter of the Fourth Part *, 
 upon the intensity of currents in closed circuits ; and, in par- 
 ticular, of this fundamental law, that the intensity of a current 
 is in inverse ratio of the length of the circuit that it traverses. 
 And, in effect, if, on the other hand, in a thermo-electric pile, 
 the intensity of the current is proportional to the number of 
 pairs put into action, and that, on the other hand, this same 
 intensity is inversely as the length of the circuit, and conse- 
 quently of the same number of pairs, it must follow, that 
 whatever be their number, provided the pairs be perfectly 
 identical, and form a circuit completely closed, without the 
 intervention of any other conductors, the force of the current 
 will be independent of the number of pairs, 
 
 It was by actually employing thermo-electric currents that 
 M. Pouillet succeeded in establishing the general laws, which 
 regulate the propagation of electric currents in good conductors ; 
 laws, which Ohm and Fechner, on their part, had discovered 
 by employing ordinary voltaic or hydro-electric currents. 
 Thermo-electric currents have the advantage, for this class of 
 researches, of being more regular and more constant, and of 
 requiring for their development only a circuit, that is per- 
 fectly metallic, and consequently not exposed to the dis- 
 turbances that are introduced by the alternation of solid and 
 liquid conductors; but they present the inconvenience of 
 having a very limited intensity. 
 
 In order to get at the laws relating to the influence exerted 
 over the intensity of the current, by the length and the section 
 of the circuit, M. Pouillet employed two pairs, perfectly simi- 
 lar, and each formed by a cylinder of bismuth (Jigs. 278, and 
 279.), at the two extremities of which is soldered a copper 
 wire of about a yard in length ; one of the solderings of each 
 pair was maintained at 32, and the other at 2 1 2 ; then their 
 circuit was closed by wires of any kind. We are thus able 
 to prove, by means of a differential galvanometer, whose two 
 wires are traversed in contrary directions, by the currents 
 of these two pairs, that these currents are perfectly equal. 
 
 * Vol. II. p. 65. 
 
 003 
 
566 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 Then, in order to demonstrate that their intensity is in inverse 
 ratio to the length of the circuit, two similar wires are taken 
 
 Fig. 278. 
 
 Fig. 279. 
 
 in order to form the circuits of the two pairs ; but, for one of 
 the pairs, the wire is only 8 yds. in length, whilst for the 
 other it is 98 yds.; which gives for the former a total length 
 of 10 yds. and one of 100 yds.' for the latter. With the 
 circuit of 10 yds. two turns are made upon the frame of 
 the multiplier, and twenty turns with that of 100 yds. ; then, 
 on making the currents pass in the reverse direction, the 
 needle remains motionless. Therefore the current of the 
 circuit ten times longer is ten times weaker ; since it is ne- 
 cessary for it to act, by a number of turns ten times greater, 
 in order to compensate the effect of the current of the circuit, 
 that is ten times shorter. It is by a similar process that 
 Pouillet has proved that the intensity is proportional to the 
 section, either by closing one of the circuits by three or four 
 similar wires, or by taking a thicker wire, one portion of which 
 has been drawn into a fine wire, in order to be quite sure of the 
 homogeneity of the metal, or by laminating a wire, in order to 
 show that the extent of the surface has no influence, provided 
 that the volume remains the same. In these experiments, the 
 resistance of the bismuth bar may be neglected, on account 
 of the great diameter and the small length of this bar, com- 
 pared with the diameter and the length of the copper wire. 
 
 The laws to which we have just directed attention, joined to 
 others that we have established in the First Chapter of the 
 Fourth Part, enable us to determine the arrangement, that is 
 most suitable to give to a multiplier, in order that it shall 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 567 
 
 have the greatest sensibility in measuring thermo-electric 
 currents. All depends upon the length, and consequently 
 upon the resistance, possessed by the thermo-electric circuit. 
 Suppose, for example, that it is equal to that of a copper wire 
 100 yds. in length and ^-Q i n - i n diameter, if we place in the 
 circuit a multiplier, the wire of which has this length and this 
 diameter, we reduce the intensity of the current one-half, but we 
 have around the frame of the multiplier a very great number 
 of turns, which will be very near together and which will act 
 powerfully upon the needles. If a length of only 10 yds. is 
 given to the wire, the intensity of the current will be reduced 
 to only -J-J- of its primitive intensity, instead of being reduced 
 to the half; but also with the 10 yds. ten times fewer turns will 
 be made than with the 100; and it is evident that 100 turns, 
 each of which acts with an intensity of half, will produce upon 
 the needles much more effect than ten, each of which acts with 
 an intensity of |-J; in the former case the intensity is 50, in 
 the latter 1 -ff ) or about 9. If the wire of the galvanometer 
 multiplier was larger, still remaining of the same length, if 
 for example it was -^j in. in diameter, its interposition in 
 the circuit would cause almost no change in the intensity cf 
 the current, as may be easily perceived; also a much more 
 considerable effect upon the needles would be the result; but, 
 however, it is necessary to observe that, although the number 
 of turns remains the same, the greater thickness of the wire 
 causes them to be more distant from the needles, and to act 
 consequently less powerfully upon them. It is important, 
 therefore, in the construction of the galvanometer multiplier, 
 intended for the measuring of thermo-electric currents, care- 
 fully to estimate these various elements, and to know how to 
 turn them to account. In general, the wires of these gal- 
 vanometers ought to be thick and short, especially when the 
 current has itself very little length, and presents consequently 
 very little resistance to the current. We may add that, if 
 it is in our power to reduce the length of the circuit at our 
 pleasure, the multiplier no longer multiplies ; for, supposing 
 that the resistance of the thermo-electric pair may be neg- 
 lected, it is evident that, with a wire of a nature and di- 
 
568 SOURCES OF ELECTRICITY. PART v. 
 
 arneter, so arranged, as to have ten turns on the multiplier, 
 it is necessary to give to the wire a tenfold length, which 
 reduces the intensity to its tenth part ; so that we lose as much 
 as we gain, since a single turn would have ten times more power 
 than each of the ten. Thus, more effect is obtained with the 
 antimony and bismuth pair of fig. 266., by making it act 
 directly upon the magnetised needle, than by interposing in its 
 circuit a galvanometer multiplier. 
 
 We may easily conceive, from what has gone before, that 
 the interposition in the thermo-electric current of conductors, 
 that present a very great resistance to the current, such as 
 very fine wires, liquids or the human body must singu- 
 larly enfeeble this current. Also, in order to produce with a 
 pile some of the effects, that require a very great electric 
 tension, such as chemical effects, for example, we are obliged 
 to increase the resistance of the pile itself, by constructing 
 it of a very great number of pairs, and by employing, in 
 order to form these pairs, metals, that are as bad conductors 
 as possible. By increasing the number of pairs, we do not 
 increase the force of the current, as we have seen, but we 
 greatly diminish the weakening that this current will under- 
 go by the interposition in the circuit of an imperfect con- 
 ductor. It was by this means that Botto has succeeded in 
 decomposing water slightly acidulated, by the current of a 
 thermo-electric pile, formed of 120 pieces of platinum wire 
 each an inch in length, andy^ in. in diameter, alternating with 
 an equal number of pieces of soft iron of the same dimensions. 
 The chain formed by the succession of these 240 pieces 
 of wire, was coiled round a wooden ruler about 20 in. in 
 length ; so that the odd points of contact were on one side 
 of the ruler and the even on the other side, at about j- in. 
 distance from the former, which were heated with a spirit- 
 lamp of the same length as the ruler. 
 
 M. Poggendorff has also contrived a thermo-electric com- 
 bination, which cannot, it is true, be subjected to so elevated 
 a temperature as that of the iron and platinum, but which is 
 nevertheless almost as efficacious, at the same time that it is 
 much more economical; he obtains it, by substituting for pla- 
 
CHAP. r. 
 
 ELECTRICITY PRODUCED BY HEAT. 
 
 569 
 
 tinum German silver, which is a metal eminently positive in 
 the thermo-electric series ; for it immediately follows bismuth, 
 and goes before platinum. At equal temperatures and 
 for the same number of pairs, the German silver and iron pile 
 has a greater electro-motive force than the platinum and iron 
 pile ; as Poggendorff has proved by a direct comparison, 
 made by means of a differential galvanometer. In this pile, 
 the wires may be arranged, one after the other, along a right 
 
 line (fig. 280.), or disposed in a zigzag (fig. 281.), or even 
 in a cluster (fig. 282.), in order that a change of temperature 
 
 Fig. 281. 
 
 LJ Li U LJ 
 Fig. 282. 
 
 may more easily be effected between the even and the odd 
 points of contact. In all these figures, the shaded lines 
 iudicate the German silver wires, and the plain lines the 
 iron wires. The tension of the electricity, at the two ex- 
 tremities of this pile, increases with the number of pairs and 
 with the difference of temperature, that is established be- 
 tween the even and odd solderings. Kohlrausch constructed 
 one formed of 769 pairs, and consequently presenting 769 
 odd points of contact, and the same number of even. Each 
 pair was formed of an iron wire about 2^ in. in length, and 
 ^ in. in diameter, and of a narrow band of German silver ; 
 the solderings were made with tin ; the pairs were fixed 
 in wax, and small bands of wood served to maintain them 
 in a suitable position. The pile was terminated, at its two 
 
570 SOURCES OF ELECTRICITY. PART v. 
 
 extremities, by iron wires situated in the upper part of the 
 cluster, upon which might be adjusted a dish, filled with 
 melting ice or snow, whilst the lower part was tightly 
 enclosed in a box of cast-iron, that was plunged into water. 
 When placed in communication with the condenser, by one 
 or other of its extremities, the pile does not become charged 
 until the water has been heated by a spirit-lamp ; positive elec- 
 tricity is then obtained at the extremity B, the odd points 
 of soldering being those that were heated, and negative at 
 the extremity A. Precise measure, taken by means of the 
 electric balance, showed that the electric tension of each 
 of the poles, increasing with the number of pairs, was 0*79 
 with 349, 1-18 with 420, and 1-97 with 769. 
 
 With a thermo-electric pile of bars of bismuth and an- 
 timony, constructed in the same manner, but in which there 
 were only twenty pairs, and the bars of which are three or 
 four inches in length by about ^ in. in diameter, currents are 
 obtained, which are very suitable for producing effects of 
 induction ; and can give powerful sparks, when made to pass 
 through a thick wire or a metallic ribbon, coiled into a spiral. 
 Only it is necessary, in order to produce greater effects, 
 to substitute for the hot water a plate of sheet-iron, which is 
 heated by the lamp. 
 
 The thermo-electric pile, as may be imagined from the 
 description we have given of it, is not an instrument of a 
 nature to be very useful for the production of electric 
 currents, except in certain particular cases, in which we are 
 more concerned in studying the effects of dynamic electricity, 
 than in determining the laws of its propagation. But it may 
 render to science services of another kind, in furnishing it 
 with a more sensitive means, than any other that is known, 
 of appreciating differences of temperature. For this important 
 application of thermo-electricity, we are indebted to M. 
 Nobili. He first constructed a thermo-electric pile, formed 
 of six pairs of bismuth and antimony, arranged in crowns, 
 and placed in the interior of a cylindrical box, so that the 
 odd points of contact were in the upper part, and the even, 
 being placed below, were concealed at the bottom of the 
 
CUAP. I. ELECTRICITY PUODUCED BY HEAT. 571 
 
 box, and surrounded with a bed of mastic, rising to about 
 a quarter of an inch only below the odd points of contact. 
 The extremities of the pile were soldered to two attached 
 pieces of copper, which, coming out of the box, served to 
 put the pile in communication with the extremities of a 
 galvanometer-multiplier having two needles. M. Nobili, 
 having placed the thermo-electric box under a receiver 
 of the air-pump, on rarefying the air, obtained a cooling, 
 which, being felt immediately at the upper points of contact 
 not surrounded with mastic, produced a very decided 
 current ; he was thus able to assure himself that the sensi- 
 bility of his thermo-multiplier was fifteen or twenty times 
 greater than that of Breguet's metallic thermometers. Various 
 improvements were introduced by MM. Nobili and Melloni 
 into the original apparatus of the former; and these two 
 philosophers succeeded, by means of their thermo-multiplier, 
 in discovering the presence of heat in insects, in phosphores- 
 cent bodies, in a word, in a great number of cases, in which 
 we had not previously been able to suspect it. But it is 
 essentially to Melloni, that we are indebted, by the precau- 
 tions he has introduced into the construction of the thermo- 
 electric pile, for having made it one of the most valuable 
 instruments of experimental physics. 
 
 M. Melloni's pile is composed of fifty small and very slender 
 bars of bismuth and antimony, of about 1 or 2 in. in length, 
 soldered one to the other, so that the bars of bismuth alternated 
 with those of antimony, as represented in^. 283., and so 
 arranged as to form a small, solid, and compact cluster (Jig* 
 284.), by means of insulating mastic, that filled the vacan- 
 
 Fig. 283. Fig. 284. 
 
 cies, left between themselves by the bars, which must 
 touch only at the solderings. The two extreme bars of the 
 
572 SOUKCES OF ELECTRICITY. PART v. 
 
 chain, one of bismuth, the other of antimony, communicate, 
 by means of two copper wires, rather large, but very short, 
 one at the stud .r, and the other at the stud y, which thus 
 form the two poles of the pile, that are placed in communi- 
 cation with the two extremities of the wire of a multiplier. 
 The two studs pass through a piece of ivory, fixed upon a 
 metal ring, which embraces the thermo-electric pile, and 
 may, by means of a piece attached, furnished with a hinge 
 allow of the axis of the pile to be placed in all desired direc- 
 tions. Care must be taken to blacken the terminal faces of 
 the pile ; and we must cover with a well-polished metal 
 shield, which envelopes, without touching it, the face, that we 
 desire to retain at an ambient temperature; whilst the other, 
 being uncovered, is exposed to the sources of heat or of cold. 
 The sensibility of this apparatus is such, that if the uncovered 
 face of the pile is turned toward a person placed even at a 
 distance of twenty-five feet, the deviation of the magnetised 
 needle, detects the emanation of radiant caloric. 
 
 In order that the galvanometer-multiplier, adapted to the 
 pile, should be as sensitive as possible, it would be necessary 
 to know the length of wire of this galvanometer, equivalent 
 in conductibility to the circuit itself of the pile, and to deduce 
 from this the number of turns, necessary to be given to the 
 instrument ; but, by simple trials, Melloni succeeded in finding 
 the galvanometer-multiplier, which best fulfilled the end. 
 The copper wire, as pure as possible, is of a diameter of -^ 
 of an inch, and seven or eight yards in length ; it makes forty 
 convolutions around the frame; its coils are symmetrically 
 arranged on one side, and the other of the mean line to a 
 width of 1 j in. ; the needles, being well selected, and carefully 
 magnetised and compensated, are connected together, by 
 means of two fine copper wires, twisted together and delicately 
 suspended to a filament from the cocoon. Thus constituted, 
 the thermo-multiplier is of extreme sensibility, although at 
 first sight it seems that the intervention of the wire of the 
 galvanometer ought to diminish the intensity of the current ; 
 but this very slight diminution, in consequence of the 
 smallness of the length and the size of the diameter of the 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 573 
 
 wire on the one hand, and the considerable number, as well 
 as the small dimensions of the bars of bismuth and antimony 
 on the other hand, is more than compensated, as we have 
 already seen, by the increase of effect, that results from the 
 number of turns, that act upon the magnetised needles. It 
 is also to be remarked, that the very considerable number of 
 thermo-electric pairs, of which the pile is composed, possesses 
 the double advantage of enabling a greater surface to be 
 presented to the action of the heat, and to render effective 
 the intervention of the multiplier ; the interposition of which, 
 if there had been but a single pair, would have too much 
 weakened the current. 
 
 In order to make use of the instrument in the measurement 
 of temperatures, M. Melloni first proved, by a comparison 
 with ordinary thermometers, that, with piles of bismuth and 
 antimony, the intensity of the current is proportional to the 
 difference of temperature of the solderings ; then he succeeded, 
 by causing the amount of heat to vary by a known quantity, 
 in establishing the relation which connects the intensities of 
 the current with the deviations of the needle, measured by 
 means of a circular division, made with great care.* In M. 
 Melloni's apparatus, the intensity is exactly proportional to 
 the deviation, up to 20 ; for more considerable deviations, a 
 table of ten columns, drawn up empirically, gives the in- 
 tensities corresponding to the deviations observed: but, in 
 order to obtain more accuracy, we should endeavour, as M. 
 Melloni succeeded in doing, not to obtain deviations, that 
 sensibly surpass 30. 
 
 M. Pouillet has also applied thermo-electricity to the mea- 
 surement of temperatures, by constructing an instrument 
 which, under the name of magnetic pyrometer, could measure 
 all temperatures, from the greatest degree of cold, to the 
 highest degree of heat. The instrument comprises two 
 
 * M. Melloni distinguishes the impulsive deviation and the definitive deviation; 
 namely, the maximum distance, that the needle attains by its first motion of 
 impulse, and the distance where it stops after a series of oscillations ; he seized 
 the constant relations, which exist between them, and which enable our de- 
 ducing one from the other, when a table has been previously drawn up of 
 these relations for each apparatus. 
 
574 
 
 SOURCES OF ELECTRICITY. 
 
 Fig. 285. 
 
 distinct pieces ; namely, a galvanometer or sine- 
 compass, formed with a copper ribbon about 
 f in. in length*, and the thermo-electric appa- 
 ratus itself. This latter (fig. 285.) is composed 
 of a tube of iron or rather of a gun-barrel a b, 
 and of a platinum wire, that comes from the 
 middle c, of the breech at the bottom, being in- 
 corporated with the mass of the iron ; it tra- 
 verses the axis of the tube, so as to arrive at the 
 piece of copper x ; from the annular breech d, 
 proceeds a second platinum wire, which is sol- 
 dered to the piece of copper ; the second wire 
 is maintained by a badly conducting body in the 
 middle of the opening of the annular breech d, 
 so that it cannot touch it ; /, is a piece of wood, 
 fixed upon the end of the tube, and intended 
 to carry to the two pieces of copper x and y. 
 The communication between the multiplier and 
 the pyrometer properly so called is established 
 by means of two copper wires of about -^ of 
 an inch in diameter, which abut on one side at 
 the pieces x and y of the pyrometer, and on the 
 other side at the extremities of the ribbon, of which 
 the multiplier is composed. 
 
 M. Pouillet has graduated his instrument by 
 comparison with an air pyrometer ; but the 
 intensity of the current is far from being pro- 
 portional to the temperature; at least with the 
 platinum and iron pair. It is not the same with 
 a bismuth and copper pair ; experiments made 
 comparatively with an air pyrometer and an alcohol 
 thermometer have shown that the intensity of the 
 current of this pair, measured by the sine-galva- 
 nometer, is well proportional to the temperature, 
 between 212 to 108-4. The low temperatures 
 were obtained, by means of the paste of ether 
 and carbonic acid, into which one of the solderings 
 * Vol. I. p. 335. 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 575 
 
 of the pair was plunged, whilst the other was in melting ice. 
 The thermo-electric pyrometer gives 41 for the tempera- 
 ture of the coagulation of mercury, which agrees with the 
 indications of the air thermometer. 
 
 The question of the relations that exist between the in- 
 sensities of thermo-electric currents, and the corresponding 
 temperatures, had been already discussed by M. Becquerel, 
 as we have already seen in the paragraph commencing at 
 p. 535. ; nevertheless, notwithstanding these researches and 
 those of M. Pouillet, there was something still to be desired, 
 in regard to the confidence, that might be attached to the 
 employment of the thermo-electric properties of metals, for 
 the accurate measurement of temperature. This induced 
 M. Regnault to study carefully, in his researches upon heat, 
 this thermo-electric process, according to a method very 
 different from those, which had been hitherto employed, and 
 which led him to important results. 
 
 He first constructed a bismuth and antimony pair, formed 
 of two bars A B c D (Jig. 286.), obtained by casting, and 
 
 which, being perfectly similar, are juxtaposed in all their 
 extent, being separated by a thin plate of ivory, which does 
 not permit of their touching, except at the extremities A and 
 D, where the two solderings are situated. The apparatus is 
 divided, so that the wire of a galvanometer may be introduced 
 into the circuit. This pair, the vertical branches of which are 
 4-J in. in length, whilst the horizontal branch is 7f in., is the 
 normal pair, to which all the other thermo-electric pairs must 
 
576 SOURCES OF ELECTRICITY. PARTY. 
 
 be referred ; but it must be employed only for Yather low 
 
 temperatures, which do not exceed 86. 
 
 The pair, intended for high temperatures, is formed of 
 
 an iron and a platinum wire ^V f an mcn i n diameter, 
 
 the extremities of which are soldered to silver ; the iron 
 
 wire E and F (fig. 287.), is about 
 j TI 31 in. in length ; and the two pla- 
 
 tinum wires E c, and F d, are 
 attached near to the iron wire 
 from which they are separated by 
 an insulating envelope ; in the 
 
 Fig. 287. , 
 
 lower part, the wires are sepa~ 
 
 rated by a plate of thin glass ; they are terminated by two 
 pieces of brass attached, which allow of the galvanometric 
 wire being introduced into the circuit. 
 
 The galvanometer, that is employed is a very sensitive 
 differential galvanometer, one of the wires of which is intro- 
 duced into the bismuth and antimony circuit and the other 
 into the iron and platinum circuit. The normal pair, 
 bismuth and antimony, is so arranged, that the two solderings 
 plunge into two vessels filled with water at different tem- 
 peratures, and separated from each other by a screen ; two 
 thermometers, very accurate and rigorously compared, give 
 the temperature, in which each of the solderings is placed. 
 The solderings E and F, of the iron and platinum pairs, are 
 maintained in glass tubes filled with fine oil, that does not 
 contain any oxygen ; one of the tubes is placed in a boiler 
 full of oil with a mercury thermometer ranging from 32 
 to 662; the other, which contains the second soldering, is 
 maintained at a constant temperature, by means of melting ice, 
 or in a large water bath, beside the mercury thermometer. 
 
 The apparatus being then arranged, -if the soldering F, 
 of the iron platinum pair, is raised to a temperature, measured 
 by the thermometer, of the oil-bath, a current results, which 
 deflects the needle of the galvanometer ; but on raising to 
 the necessary quantity, the temperature of one of the sol- 
 derings of the bismuth and antimony pair, a second current 
 is obtained, which, moving in a contrary direction to the 
 former, neutralises its effects, and brings back the needle 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 577 
 
 to 0. A ' note is made of the temperatures indicated by 
 the two thermometers at the moments of neutralisation. 
 The difference of temperature, that produces upon the bis- 
 muth and antimony pair a current, capable of neutralising 
 that, which is produced by a certain difference of temperature 
 upon the iron and platinum pair, is much less than this latter ; 
 for the latter being 212 the former is only 43 7. 
 
 By raising the oil bath to different temperatures, currents 
 are obtained in the iron and platinum pair which produce 
 equilibrium on the galvanometer, with the currents produced 
 in the bismuth and antimony pair, by corresponding differ- 
 ences of temperature. A table can therefore be drawn out 
 in which are inscribed, on the one side, the differences of tem- 
 perature T' T, T" T, T'" T, of the iron and platinum 
 pair, measured by the air thermometer, and on the other the 
 differences of temperature if t, t" t, t" t, of the bismuth 
 and antimony pair. If we desire to measure an elevated tem- 
 perature with the iron and platinum pair, we have merely to 
 seek for the temperature, " t, which produces equilibrium 
 with it, and the bismuth and antimony pair, and in the table 
 is found the corresponding temperature T" T, on the iron 
 and platinum pair. It is necessary, in order that the results 
 may be exact, that the two pairs remain constantly perfectly 
 comparable. Now, a very great number of experiments 
 have shown to M. Regnault, that this is not always the case, 
 and that the variations are probably due to changes, that 
 are brought about in the molecular state of the metals, at 
 the place of the solderings. They are felt especially in 
 the iron and platinum pair ; for the bismuth and antimony 
 pair gives very constant results, when the temperature 
 of the solderings is made to vary within limits, which were 
 not exceeded in the comparative experiments, namely, from 
 59 to 86. Between these limits a difference of temperature 
 of 1'8, produced upon the galvanometer sensibly the same 
 deviation of 17, whatever might be their absolute temperature; 
 but which is very curious, and very contrary to the generally 
 received opinion, is, that an increase of 1*8 in the difference 
 of temperature of the two solderings of the bismuth and anti- 
 
 VOL. II. P P 
 
578 SOURCES OF ELECTRICITY. PARTY. 
 
 mony pair, produces an increase in the current the more 
 feeble, as the difference of temperature is greater, even 
 within the limits of 59 to 86. It is easy to verify the result 
 by opposing to the thermo-electric current in the differential 
 galvanometer, so as to produce with it equilibrium, a very 
 constant and very feeble hydro -electric current, the force of 
 which is gradually augmented, in proportion as the tempera- 
 ture of one of the solderings of the bismuth and antimony 
 pair is raised. Equilibrium being established, the difference 
 of temperature between the two solderings is increased by 
 l-8 ; and for this increase, a deviation is obtained, which is 
 less in proportion as this difference was already greater. 
 
 M. Regnault had made several trials with pairs formed of 
 wires, other than those of iron and platinum ; but the iron and 
 platinum pair is much the more regular, and the one, whose 
 thermo-electric intensity diminishes the least with the eleva- 
 tion of temperature ; it is not the same with an iron and 
 copper pair ; thus, the sensibility of this pair becomes com- 
 pletely null at 564 ; then, if the temperature is raised higher, 
 the needle, which had remained stationary from 446 to 500 
 retrograde, and the intensity of the current, far from in- 
 creasing with the temperature, diminishes. This change of 
 direction in the course of the current of the iron and copper 
 pair, at a certain temperature, had already been observed, as 
 we have mentioned, by M. Becquerel. 
 
 The researches of M. Regnault show us the difficulty there 
 is in employing thermo-electric currents for the exact mea- 
 surement of temperatures ; and there is nothing astonish- 
 ing in this, When once it is well established, as we have seen 
 that these currents are not due to a simple difference in the 
 facility with which the heat is propagated, but rather to the 
 molecular changes, which are always more or less irregular, 
 and which accompany this propagation. 
 
 However, if the thermo-multiplier cannot take the place 
 of the thermometer for accuracy, in the measurement of 
 temperatures, it may be advantageously employed in many 
 cases, in which thermometers, even the most sensible, are 
 neither sufficiently prompt, nor sufficiently delicate to detect 
 sudden and inconsiderable changes of temperature, as in 
 
CHAP, I. ELECTRICITY PRODUCED BY HEAT. 579 
 
 Melloni's experiments upon radiant heat. MM. Becquerel 
 and Breschct have also made a happy application of thermo- 
 electricity for the measurement of the temperatures of the 
 organic tissues of the body of man and of animals, by con- 
 structing mixed metallic needles of a diameter of less than 
 a twentieth of an inch, which they introduce by the pro- 
 cess of acupuncture into an organic tissue. It is necessary 
 to have two needles, each composed of two very fine wires, 
 one of copper, the other of steel, soldered together by one 
 of their ends. The solderings of one of the mixed needles 
 is placed in a medium, the temperature of which remains 
 constant during the continuance of the experiment; the 
 soldering of the other mixed needle is introduced into the 
 tissue, whose temperature we desire to measure. The free 
 ends of the steel of the two needles are placed in communi- 
 cation by a steel wire, whilst the free ends of the copper are 
 connected by the wire of a galvanometer. When the two 
 solderings have the same temperature, the needle of the 
 galvanometer is not deflected; but the slightest difference 
 of temperature, if it is only a tenth of a degree, is sufficient 
 to produce a deviation, the direction and the extent of which 
 serve to give exactly the value of this difference ; and conse- 
 quently the temperature of one of the media, when that of 
 the other, which is constant, is known. Different observations 
 made by placing the solderings of one of the thermo-electric 
 needles in the mouth, and the other, for example, in the biceps 
 muscle of a young man, have given a deviation of 4 in 
 favour of the mouth, which corresponded, after previous 
 experiments made on the temperature of the mouth, to 9 7 -8 8 
 for this latter, and only 97'16 for that of the biceps muscle. 
 M. Peltier's thermo-electric pincers is also constructed upon 
 the same principle. It consists of two very slender pairs of 
 bismuth and antimony A and B (Jig. 288.) ; these two pairs 
 are connected one with the other by a copper wire, which 
 unites the antimony a' of the upper pair with the bismuth b' 9 
 of the lower pair ; and by copper wires D and E, which, com- 
 municating with the wire of the galvanometer, complete 
 the circuit between the upper bismuth b" 9 and the lower 
 
 P p 2 
 
580 
 
 SOURCES OP ELECTRICITY. 
 
 antimony a"; F and H' are the free and soldered extremities 
 of each of the pairs which form the jaws of the pincers ; 
 which may, by means of a spring, be applied one against 
 
 Fig. 288. 
 
 the other, or against a small portion of a wire or a metallic 
 bar, the temperature of which at a given moment is required 
 
 to be known. In Jig. 288. the 
 two jaws may be applied against 
 the point of contact F, of a bar of 
 antimony A, and a bar of bis- 
 muth B, which are traversed by 
 the current of a pair P, the con- 
 ductors of which arrive at J. and 
 K. It was by this means that 
 M. Peltier proved that, according 
 to the direction of the current, 
 which passes from the antimony 
 to the bismuth, there is produc- 
 tion of heat or production of 
 cold.* Thus he obtained in the 
 galvanometer G, of the thermo- 
 electric pincers 37 when the 
 current went from the bismuth 
 
 i 
 
 Fig. 289. 
 
 * Vol. II. p. 364. 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 581 
 
 to the antimony and + 45, namely, a deviation of 45 in 
 the other direction, which indicated a heating instead of a 
 cooling, when the current went from the antimony to the 
 bismuth. In order to place this result free from all ob- 
 jection, M. Peltier confirmed it, as we have seen, by passing 
 through the bulb of an air-thermometer (Jig. 289.), a 
 bar of antimony and bismuth, whose soldering S, was at 
 the middle of the bulb. The current of a hydro-electric 
 pair, arriving at the junction of the two bars by the 
 conductors / and g, according to the direction in which 
 it was travelling, caused the column of coloured alcohol, 
 which was maintained in the capillary tube, and which served 
 as an index, to rise or fall. 
 
 Comparison between the Calorific Efects of the Current, and 
 Thermo-electric Phenomena. Attempt at a Theory. 
 
 We have already remarked, that in the section of Chapter 
 II. of this Volume, commencing at p. 303., the remarkable 
 relation, that exists between the change of temperature, pro- 
 duced by a current, in passing from one metal into another, 
 and the electric effects, that are brought about by a change 
 of temperature, at the point of contact of these two same metals. 
 Peltier, who was the first to direct attention to this subject, 
 had thought that he was able to establish, almost as a general 
 rule, that the greatest elevation of temperature took place, 
 when the current passes from the inferior into the better 
 conductor ; and that the reverse is the case, when the current 
 changes its direction. Thus, when the current passes from 
 an iron wire into one of zinc, the temperature rises 86, and 
 when it passes from zinc into iron, only 55*4 ; when it passes 
 from zinc to copper, the elevation of temperature is 68; it 
 is not more than 5 7 "2, when it passes from copper to zinc. 
 With the other metals, as we have seen, it is not merely a less 
 elevation of temperature, but a notable depression, that is 
 obtained, on changing the direction of the current. This takes 
 place especially with bismuth and antimony, either when 
 they are combined together, or when each of them is com- 
 
 p p 3 
 
582 SOURCES OF ELECTRICITY. PART v. 
 
 bined separately with another metal. Thus, a plate of bismuth, 
 soldered between two plates of copper, gives, with a current 
 going from the copper to the bismuth, -f 20 *, and with a 
 current going from the bismuth to the copper, 10. A plate 
 of antimony, under the same circumstances, gives - 5 with a 
 current that goes from the copper to the antimony, and + 10 
 with a current that goes from the antimony to the copper. 
 This causes the maximum of effect to take place, when the 
 plate of bismuth and that of antimony are soldered together ; 
 for, in this case, we have, in fact, 37, when the current goes 
 from, the bismuth to the antimony, and +45, when it goes 
 from the antimony to the bismuth. 
 
 These results can be obtained, only so long as the current 
 is not too powerful ; if its intensity is gradually increased, 
 we arrive, first, at having neither elevation nor reduction of 
 temperature at the soldering, which is cooled ; then comes an 
 elevation of temperature, always less than that, which is 
 manifested, when the current changes its direction. 
 
 The remarkable effect that takes place with bismuth, shows 
 that Peltier's law is far from being general, for it would be 
 necessary to admit, in order to include this in it, that bismuth 
 is a much better conductor than all the metals, which is far 
 from being the case ; moreover, antimony and bismuth, which, 
 by their combination, give the maximum of effect, are very 
 near to each other, in the order of their electric conducti- 
 bility. These phenomena therefore, are probably due to the 
 crystalline state of these metals ; and it is very probable, that 
 it is also to differences in their molecular structure, the other 
 metals are indebted for the differences of temperature, that 
 are brought about by the current at their point of junction, 
 according as it is established in one direction or in the other. 
 It is only over the heat, that is developed in all the length of 
 a homogeneous wire, that the resistance of the metal to the 
 transmission of electricity, exercises an influence, which we 
 have recognised, and even determined. But we must take 
 
 * These degrees are those of the galvanometer-multipliers, connected with 
 the thermo-electric pincers described above, which presses between its two jaws 
 the point of contact of the two metals soldered together. 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 583 
 
 care to distinguish, as we have already mentioned, that 
 Frankenheim had done * this calorific effect from the 
 variations of temperature tkat take place at the points of 
 contact of the two heterogeneous metals, that are traversed 
 by a current. These are two phenomena of a very different 
 order, and in no degree subject to the same laws ; it is some- 
 times a difficult matter to unravel the part of each of these 
 in the result observed, but they are not the less distinct. 
 
 Another proof that the latter phenomenon is essentially 
 connected with the molecular state of the bodies, is the 
 intimate relation that it presents with the production of thermo- 
 electric currents, which we have seen to be an effect of the 
 molecular modifications, produced in bodies where it takes 
 place, by the propagation of heat. Indeed, the elevation of 
 temperature, that is developed at the point of contact of a bar 
 of bismuth and copper, when the current passes from the 
 copper to the bismuth, itself produces a counter current, 
 which goes directly from the bismuth to the copper. In like 
 manner, the reduction of temperature, that takes place when 
 the current passes from the bismuth to the copper, produces 
 a counter-current, which goes from the copper to the bismuth. 
 We may even remark, that these counter-currents should 
 diminish, slightly, it is true, the initial current, that produces 
 the elevation or the reduction of temperature. Thus, there- 
 fore, there is an intimate connection between the cause that 
 produces the thermo-electric current, by an elevation or a 
 reduction of temperature, at the point of contact of the two 
 metals, and the cause which determines, by the passage of an 
 exterior current, a reduction or an elevation of temperature, 
 at the point of contact of these two same metals. 
 
 M. Frankenheim, guided by this class of considerations, 
 made a numerous series of experiments, employing Peltier's 
 cross apparatus, which consists of two bars of bismuth and 
 antimony crossed one upon the other and soldered at their 
 middle. Two of the extremities of this cross are placed in 
 communication with the poles of a pile, and the two others 
 
 * Vol. II. p. 305. 
 P P 4 
 
584 SOURCES OP ELECTRICITY. PART v. 
 
 with the ends of the wire of a galvanometer. It follows from 
 this combination, that the heat or cold, developed by the elec- 
 tricity at the point of soldering, produces a thermo-electric 
 current, which cause the needle of the galvanometer to deflect. 
 By employing a tangent-galvanometer, and a rheostat for 
 measuring and regulating the intensity of the voltaic current, 
 Frankenheim recognised that the elevation of temperature, 
 produced at the point of contact, which he terms secondary, 
 is proportional to the intensity of the current, whilst the eleva- 
 tion of the primary temperature, that takes place in the entire 
 conductor, by the effect of its resistance, is proportional to the 
 square of the intensity of the current. Thus this latter tem- 
 perature varies in a very decided manner, with the thickness 
 of the metallic bars, whilst the secondary temperature is 
 almost independent of this thickness. On this account it is 
 that, in order to escape the influence of the former, and to 
 study well the effect of the latter, it is better to employ thick 
 bars to form the cross, rather than thin bars, which in addition 
 give less constant results, because their defect of homogeneity 
 exerts an influence proportionally more considerable. 
 
 M. Frankenheim, by employing metallic bars of different 
 natures, has well proved that the secondary temperature does 
 not depend, as M. Peltier had supposed, upon the conductibi- 
 lity of the metals, but on their thermo-electric property. He 
 has even found, that the various metals, in their aptitude for 
 engendering secondary heat, follow the same order as in the 
 production of thermo-electric currents, in such sort that 
 bismuth and antimony are at the extremities of the series, and 
 copper in the middle. Now, as the secondary heat produces 
 thermo-electricity, it follows that, if we have two combina- 
 tions, the thermo-electric powers of which = m : n, we shall 
 also have, that the variations of secondary temperature, pro- 
 duced by the same current, that traverses them both, shall 
 be to each other = m : n. But, if the differences of tempera- 
 ture at the points of soldering were the same for the two 
 combinations, we should have, that the intensities of their 
 thermo-electric currents should be to each other = m : n. 
 Now, these differences of temperature, instead of being equal, 
 being themselves = in : n, it necessarily follows that the in- 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 585 
 
 tensities of the two thermo-electric currents are to each other 
 = m 2 : n 2 . This important law has been verified by M. Frank- 
 enheim who has also studied the reaction that the secondary 
 current, which is produced by the heating or the cooling at 
 the point of soldering, must exercise over the current of the 
 pile itself. No reduction from this cause happens to that 
 current, if the interposition of one metal in the circuit formed 
 of another determines at its two points of contact, two equal 
 and contrary currents ; such is the case, for example, of the 
 interposition of a bar of bismuth between two conductors of 
 copper, where the secondary heat produces an equal heating 
 at the two points of contact ; and consequently developes two 
 equal thermo-electric currents moving in contrary directions, 
 which annihilate each other. But, if by the effect of the 
 secondary action, there is a heating at one of the points of 
 contact, and a cooling at the other, these two thermo-elec- 
 tric currents are added together, and the principal currents 
 (that of the pile) suffers a diminution, which is equal to 
 double the intensity of the current produced by the bismuth 
 and copper pair. Perhaps it is to the action of these secon- 
 dary currents, the converse of the principal current, that may 
 be attributed the apparent differences of conductibility of 
 metals, that seem identical. A slight difference in the mo- 
 lecular state and the existence, for example, of small crystals 
 in the texture of a metal, is sufficient for the passage of elec- 
 tricity from one of these metals into another, arranged in a 
 divergent direction, to give rise to a thermo-electric current. 
 On this account it is that galvanoplastic copper, of coarser 
 grain, diminishes less the intensity of the current than melted 
 copper of finer grain, which presents to the current a greater 
 number of passages from one small crystal to another. The 
 same effect is presented with other metals ; and especially 
 with carbonised iron, in which the molecules of carbon are 
 intimately mixed with those of iron. 
 
 It is also to a reaction, produced by the secondary current 
 upon the principal current, that we must attribute the 
 curious results, obtained by M. Wartmann on the diather- 
 inansy of metals ; M. Wartmann thus designates the faculty 
 possessed by two metals, of allowing the passage from one 
 
586 SOURCES OF ELECTRICITY. PARTY. 
 
 to the other, when they are in contact, of an electric current, 
 the intensity of which is appreciated by its calorific effect 
 upon the helix of a Breguet's thermometer, placed in its 
 circuit. The current itself was produced by a single pair of 
 copper and amalgamated zinc, plunged into acidulated water. 
 A very great number of experiments have shown that pairs, 
 formed of two metals not soldered, present great differences 
 in the property they possess of allowing the passage of the 
 current, appreciated always by its calorific effect, according 
 to the direction of this current itself; but that these dif- 
 ferences exist especially when one of the metals at least of 
 the pair, is of a crystalline texture, whilst they are null, 
 when the pairs contain only ductile metals. This result 
 indicates very clearly, that the diminution of intensity of the 
 principal current arises from the thermo-electric current 
 developed by the secondary heat that is produced by the 
 passage of electricity at the point of contact of the two 
 metals of the pair ; a heat, which itself varies in intensity 
 according as the principal current passes from the first to the 
 second or from the second to the first. 
 
 M. Frankenheim, on plunging into a water-bath the point 
 of soldering of a cross of iron and copper, succeeded in deter- 
 mining the temperature, which produces directly in this com- 
 bination a thermo-electric current, equal in intensity to that, 
 which is developed by the secondary heat liberated by a voltaic 
 current of known power. Thus, he found that, for a current 
 of 45, at his tangent- galvanometer, this temperature is 68, 
 and that consequently the secondary heat, produced at the 
 point of soldering, should also be 68. 
 
 We shall not at present dwell upon the theoretical ideas of 
 M. Frankenheim, who estimates that, in a thermo-electric 
 chain, of which all the points of soldering have a uniform 
 temperature, there exist, by the effect of this temperature, 
 equal and contrary currents, that neutralise each other ; that 
 nothing more is needed than an inequality of temperature 
 between certain points of solderings, in order to bring about 
 the superiority of one or of several currents moving in one 
 direction, over those moving in the other. In this point of 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 587 
 
 view, the veritable electricity of contact would be, that pro- 
 duced by the metals in the order of their thermo-electricity, 
 and not in the order of their voltaic tension. We shall 
 return to this point, when we shall have completed the study 
 of electric sources. For the present we shall confine our- 
 selves to proving the fact, already well established by M. 
 Frankenheim, of the intimate connection, that exists between 
 the secondary temperature, developed at the point of contact 
 of two metals, by the passage of an electric current, and the 
 thermo-electric power of these metals. Now, as it is well 
 proved by the experiments of Svanberg, Frantz, Matteucci, 
 and Magnus, that thermo-electricity depends upon the 
 molecular constitution of bodies, and that it is a result of the 
 disturbance, produced in this constitution, by the movement 
 of heat, it follows that the secondary changes of temperature 
 brought about in the point of contact of two heterogeneous 
 conductors by the passage of the current, are equally depen- 
 dent on this molecular constitution, and on the disturbance 
 produced in it by the current. 
 
 If we now collate, one with the other, all the phenomena, 
 by which heat and electricity are linked together, we every- 
 where see molecular influence become manifest. The pro- 
 duction of the primary heat, that results from the passage 
 of the current through a conductor, that presents to it a 
 resistance, is evidently due to the molecular movements, that 
 are brought about by this passage, movements, whose ex- 
 istence becomes visible, providing there is a solution of con- 
 tinuity in the conductor, as in the experiment of the voltaic 
 arc, and which is no less sensible in continuous con- 
 ductors, by the alteration, that these conductors undergo, in 
 their molecular state, when they have transmitted a current 
 for any length of time.* We have just proved that the 
 production of secondary heat at the points of contact, which 
 
 * Very recently, a young Swiss philosopher, M. Dufour, of Lausanne, has 
 demonstrated that the prolonged passage of a current produced hy a single 
 pair, is able to bring about such a change in a copper wire that, even after the 
 passage of this current has ceased, the tenacity of this wire has diminished by 
 more than a fourth from its former tenacity. M. Adie has in like manner 
 noticed a remarkable molecular change, which is produced at the point of 
 contact of thermo-electric pairs, that have been for a long time ill action. 
 
588 SOURCES OF ELECTRICITY. PART v. 
 
 generates thermo-electricity, is also eminently dependent 
 upon molecular structure. But the difficult point for solution 
 is to determine the laws, by which molecular movements are 
 connected, either with electricity or with heat. For this 
 determination, it would be necessary to operate with con- 
 ducting bodies, as with those which are not so, upon perfectly 
 regular and determinate crystals, and not upon amorphous 
 masses, formed of metals, more or less irregularly agglo- 
 merated. We have explained the attempts, made by Svanberg 
 and Frantz, in this direction ; but they are still insufficient. 
 Whatever may be the case, it is evident that the electric 
 effects which are produced by the movement of heat in 
 crystals, are exactly of the same order as those which are 
 produced in metals by this movement ; and that the difference 
 in the mode of the manifestation of electricity is due to the 
 difference of conductibility. 
 
 Now, if we return to the idea, which we have put forth, 
 that atoms have an electric polarity, which they owe to a 
 more or less rapid motion of rotation around an axis, if, 
 conformably to the present mechanical theories of heat, we 
 admit that heat increases this motion of rotation, and exalts 
 consequently, at the same time, the electric polarity, we may, 
 in a very satisfactory manner, account for what takes place 
 in electro-calorific phenomena. We have already said, the 
 passage of the current, by increasing the polarity of the atoms, 
 should exalt their velocity of rotation, and raise the tem- 
 perature ; in its turn, the propagation of heat increases their 
 velocity of rotation, and should increase their electric polarity. 
 If, in this latter case, the atoms are perfectly free to move 
 in all directions, no exterior electric effect ought to take place ; 
 because the polar electricities of the atoms mutually neutralise 
 each other, whether they be exalted or not by heat, since 
 there is never more electricity of one kind, than of the other, 
 whatever their absolute intensity may be ; this is the state 
 of things, in liquids and in very ductile metals. But, if the 
 atoms are grouped, so as to give to the body a more or less 
 crystalline structure, that is to 'say, not uniform in all 
 directions, it ought to follow that, when the heat, in its pro- 
 
CH\P. r. ELECTRICITY PRODUCED BY HEAT. 589 
 
 pagation, exalts the electric polarity of certain atoms, the 
 latter, not being susceptible of moving freely, and consequently 
 of assuming an arrangement, which restores electric equi- 
 librium, the integrant molecule, which they form, is found to 
 have an electric polarity in a certain direction, and a contrary 
 polarity in the other. All the pyro-electric phenomena of 
 crystals, show, in fact, that the appearance of positive elec- 
 tricity, in one place, and negative in another, is due to the dif- 
 ference of molecular structure. With regard to the fact that 
 the two electricities change places, when cooling succeeds to 
 heating, it is due to the manner in which the atoms of the 
 molecule become grouped, according as they receive or emit 
 heat, namely, according as they are more or less warm, and 
 consequently endowed with a greater or less powerful electric 
 polarity. We shall return to this particular point, which 
 requires to be cleared up, when we shall have completed the 
 examination of all the causes, that give rise to the liberation 
 of electricity. 
 
 The thermo-electric properties of metals, connected, like 
 those of crystals, with molecular structure, are manifested 
 under the form of a current on account of conductibility ; but 
 they arise equally from the polar state of each integrant mo- 
 lecule ; a state, exalted by heat, and which produces an ex- 
 terior effect, only so long as there is a movement of the heat, 
 namely, a difference of temperature between the consecutive 
 molecules. The fundamental principle in all this class of 
 phenomena, as well for conducting bodies, as for insulators, 
 is, that the electric state, which is acquired by the mass, is 
 only the result of the electric state of each of the integrant 
 molecules of this mass ; whence follows, according to the 
 manner, in which these molecules are arranged, in respect to 
 each other, different electric manifestations. 
 
 With regard to the phenomena of secondary temperature, 
 that is brought about by a current in passing from one metal 
 to the other, their connection with the thermo-electric property 
 of the two metals in contact shows that they are dependent, 
 like this property, on the molecular constitution of the bodies, 
 and on the disturbances, that the passage of the current brings 
 
SOURCES OP ELECTRICITY. PART v. 
 
 in them. We have already remarked* that, if we set 
 om the hypothesis, that atoms are endowed with a rapid 
 _._ . n of rotation around an axis, a cause at once of their 
 temperature and of their electric polarity, it may happen 
 that this natural polarity is in accordance or discordance with 
 the artificial polarity, that is brought about by the passage of 
 the current. In the former case, the motion should be ac- 
 celerated and the temperature should rise, whilst in the latter 
 it falls, and the motion of rotation should diminish. But it 
 is necessary, in order that these differences may be sensible, 
 that the current shall not be too powerful ; for, however little 
 intensity it may have, the rotation impressed upon the atoms 
 by artificial polarity predominates too much over that, which 
 produces natural polarity, for their being in every case an 
 acceleration of motion and consequently always heat, only a 
 little more or a little less considerable, according as the 
 polarities accord or differ. 
 
 Peltier's experiments and those of Frankenheim are alto- 
 gether in accordance with this mode of explaining this class 
 of phenomena. Thus, according to Peltier, when the current 
 passes from iron to zinc, the temperature rises 86; when it 
 passes from zinc to iron, only 55*4 ; when it passes from zinc 
 to copper it rises 78*8 ; and when it is from copper to zinc 
 14. But the difference is much more marked, when the two 
 metals in contact, or one at least of the two, has a very de- 
 cided crystalline structure. Thus, a plate of bismuth, sol- 
 dered to a plate of copper, gives, with a current of an in- 
 creasing intensity, directed from the bismuth to the copper, 
 the following results : 
 
 Intensity of the Current. 
 
 15 27'5 
 
 20 23 -9 
 
 28 23 -9 
 
 30 32 -0 
 
 35 39 -3 
 
 If the current is directed from the copper to the bismuth, 
 
 * Vol. I. pp. 303. and following pages. 
 
CHAP. I. ELECTRICITY PRODUCED BY HEAT. 591 
 
 there is obtained at the point of contact a temperature, which 
 increases from 10 to 50, in proportion as the intensity of the 
 current is increased. It is evident that, as far as to a current 
 of an intensity of 30, the effect of the passage of the electri- 
 city is a diminution of the natural rotatory movement of the 
 atoms, since there is a reduction of temperature; but, 
 setting out from this intensity of 30, the rotatory movement, 
 impressed upon the atoms by the current is sufficiently 
 powerful to compensate and more than compensate this dimi- 
 nution. A plate of antimony soldered to a plate of copper, 
 presents a converse phenomenon ; the reduction of tempera- 
 ture takes place, when the current passes from the copper to 
 the antimony ; and the elevation, when it passes from the 
 antimony to the copper. This is the cause of the associa- 
 tion of antimony and bismuth producing the maximum of 
 effect. 
 
 But, without entering upon any hypothesis upon the cause 
 of the atomic polarity, and of the temperature, we may yet 
 find a great analogy between electro-thermic phenomena and 
 those presented simply by heat. M. Clausius has shown this 
 in a theoretic work upon the application of the mechanic 
 theory of heat to thermo-electric phenomena, which, being 
 connected with the loftiest notions of rational mechanics and 
 of analysis, can find no place in a work of the nature of the 
 present. We shall confine ourselves to pointing out, as a 
 consequence of this work, the analogy that its author esta- 
 blishes between a thermic chain and a machine moved by 
 heat. Setting out from the experimental fact that, on the one 
 hand, in a thermo-electric pair of bismuth and antimony, the 
 current passes at the heated point of contact from the bismuth 
 to the antimony, and at the cooled point of contact from the 
 antimony to the bismuth, and that, on the other hand, an ex- 
 terior current, which traverses the pair, annihilates heat in 
 the former direction, and produces it in the latter, he con- 
 cludes that the point of contact maintained hot corresponds 
 with the heated part of the caloric machine, and the point of 
 contact maintained cold, with the condenser. Then, applying 
 Carnot's law to these considerations, he deduces from it 
 
592 SOURCES OP ELECTRICITY. PARTY. 
 
 the correspondence between the electric states and the vari- 
 ations of temperature. 
 
 It appears to us, that we may compare what takes place 
 in this case with what transpires with an elastic fluid. If it 
 is heated, it produces a mechanical work by its increase of 
 elasticity ; but, if it produces this mechanical work by its 
 simple dilatation, it cools by absorbing a quantity of heat 
 equivalent to this work. In like manner, if we heat the point 
 of contact of the two metals, a molecular mechanical work 
 is produced, which determines a current ; but, if this same 
 current is produced otherwise than by heating, this production 
 brings about a molecular work, which absorbs heat, and 
 consequently occasions a cooling. The converse would be 
 equally true ; and interesting consequences might be drawn 
 from this comparison of the two cases, of that in which 
 there is a heating, and of that in which there is a cooling, 
 . according to the nature of the work, that accompanies the 
 passage of the current. 
 
 Clausius remarks further, that thermo-electric effects not 
 only take place at the points of contact of the different 
 substances, but that an electric current produces different 
 thermic effects in the same metal, according as it travels 
 from the hot to the cold, or from the cold to the hot ; which 
 is the same as saying that, in the interior of a same 
 metal whose different portions are found to be at different 
 temperatures, the heat has the tendency of propelling the 
 electricity in a determinate direction, as well as in two 
 metals in contact. We may add that he considers justly, as 
 we ourselves have done, the manifestation of the electric 
 state in the interior of a same metal, not as a direct effect, 
 but merely as a secondary effect, of the differences of tem- 
 perature ; that is to say, as the result of a change produced 
 by the heat in the molecular state. In favour of this opinion 
 he quotes both the experiments of Magnus, and those which 
 demonstrate, that the thermo-electric currents, that are 
 brought about in a bar of a same metal, are due to differences 
 of crystallisation in its interior. 
 
 In support of this mode of viewing it, we may further 
 
CHAP. i. ELECTRICITY PRODUCED BY HEAT. 593 
 
 quote Mr. Thomson, who has been much occupied in the 
 application of the mechanical theory of heat to the thermo- 
 electric phenomena, that are presented by crystallised metals, 
 and who arrived by comparison with what takes place in 
 other phenomena, to the conclusion that pressure or tension 
 must develope in a homogeneous metallic mass the thermo-elec- 
 tric properties of crystals. Thus, he has found that a copper 
 wire, stretched by means of a weight, presents, in respect to 
 the same wire not stretched, thermo-electric relations exactly 
 similar to those, which Svanberg has established between a 
 bar, cut in a crystal of bismuth or antimony perpendicularly 
 to the axis, and a bar cut in the direction of this axis. If, 
 therefore, in one part of the circuit, the copper wire is 
 stretched by a considerable weignt, the other parts of the 
 wire remaining in their natural state, and if one of the ex- 
 tremities of the stretched part is heated, there is established 
 a current from the stretched part to the part not stretched 
 through the heated point of junction ; and if the wire is 
 stretched and unstretched alternately on the two sides of the 
 heated part, the current is instantaneously reversed at each 
 of these alternations of tension. 
 
 It remains, therefore, evident to us that the propagation 
 of heat is merely a means of bringing about the molecular 
 changes that give rise to the electric manifestations ; as the 
 propagation of electricity is, in its turn, only a means of 
 producing disturbances in the state of the particles, which 
 bring on a rupture in the equilibrium of temperature. We 
 shall endeavour further on to penetrate more deeply into the 
 nature of these changes and perturbations which, as we have 
 already said, are only modifications, brought about in the 
 natural rotatory movement, and in the relative position of 
 the atoms, whence flows equally the phenomena, that are 
 presented by bodies, as well under the electric and magnetic 
 relations, as under the chemical relations.* 
 
 * List of the principal works relating to the subjects treated upon in this 
 Chapter. 
 
 Becquerel Electricity of the tourmaline, &c. Ann. de Chim. et de Phys. 
 t. xxxvii. pp. 5 and 355. Thermo-electric currents. Idem. t. xxiii. p. 131., and 
 t. xxxi. p. 371. ; t. xxxvii. p. 328., and t. xli. p. 353. 
 
 VOL. II. Q g 
 
594 SOURCES OF ELECTRICITY. PART v. 
 
 Brewster. Pyro-electric minerals. Ann. de Chirn. et de Phys t, xxviii. 
 p. 161. 
 
 Haiiy. Idem. Ann. de Chim. et de Phys. t. i. p. 447. 
 
 Riess and Rose. Pyro-electricity of minerals. Arch, de VElectricite, t. iii. 
 p. 585. 
 
 Forbes. Idem. Transactions of the Royal Society of Edinburgh, t. xiii. 
 (1832). 
 
 Seebeck. Thermo-electric currents. Ann. de Chim. et de Phys. t. xxii. 
 p. 199. 
 
 Yelin. Idem. Bibl. Univ. (1823) t. xxiii. p. 38., and t. xxiv. p. 253. 
 
 Sturgeon. Idem. Bibl. Univ. (1831) t. xlvii. p. 351., and t. xlviii. p. 1. 
 
 Cumming. Thermo-electric relation. Bibl. Umv. (1824) t. xxv. p. 108. 
 
 Matteucci. Various thermo-electric experiments. Bibl. Univ. (new series) 
 t, xii. p. 211. ; t. xiii. p. 199. ; t. xv. p. 187. ; t. xviii. p. 353. ; and t. xviii. 
 p. 410. Arch, de fElectricite, t. ii. p. 227., and t. iii. p. 666. Comptes rendus 
 de V Academic des Sciences (1855), t. xl. p. 541. 
 
 Vorsselmann de Heer. Thermo-electric currents of mercury. Arch, de 
 V Electricite^ t. i. p. 581. 
 
 Gaugain. Thermo-electric currents. Arch, des Sc. Phys. (Bibl. Univ.) 
 t. xxiii. p. 69. 
 
 Svanberg. Influence of crystallisation upon thermo-electric currents. 
 Comptes rendus de TAcad. des Sciences, of August 19. 1850 ; and Arch- des 
 Sc. Phys. t. xv. p. 128. 
 
 Frantz. Idem. Ann. der Physik, t. Ixxxiii. p. 374. ; and Arch, des Sc. Phys. 
 (Bibl. Univ.) t. xviii. p. 297. 
 
 Mousson. Influence of the molecular state upon thermo-electric currents. 
 Arch, de VElectricite, t. iv. p. 5. 
 
 Magnus. Idem. Ann. de Chim. et de Phys. (new series) t. xxxiv. p. 105. 
 
 Fourrier and Oersted. Thermo-electric pile. Ann. de Chim. et de Phys. 
 t. xxii. pp, 201. and 373. 
 
 Pouillet. Theory of the thermo-electric pile and measure of temperatures. 
 Traite de Physique. Comptes rendus de I'Acad. des Sciences, t. iii. p. 782., and 
 t. iv. p. 785. 
 
 Botto. Thermo-electric pile of great resistance. Bibl. Univ. (1832) t. li. 
 p. 337. 
 
 Poggendorff. Idem. Bibl. Univ. (new series, 1840) t. xxx. p. 215. Ann. de 
 Chim. et de Phys. t. Ixxv. p. 333. 
 
 Nobili. Thermo-electric currents. Bibl. Univ. (1828) t. xxxvii. p. 119. 
 Application of the thermo-electric pile to the measure of temperatures. Bibl. 
 Univ. (1830) t. xliv. p. 225., and t. Ivii. (1834) p. 1. 
 
 Melloni. Idem. Ann. de Chim. et de Phys. t. xlviii. p. 198., and t. liii. 
 p. 5. 
 
 Regnault. Idem Arch des Sc. Phys. {Bibl. Univ.) t. xi. p. 265. ; and 
 Memoires de I'Acad. des Sciences de Paris. 
 
 Becquerel and Breschet. Idem. Ann. de Chim. et de Phys. t. lix. p, 113. 
 
 Peltier. Thermo-electric pincers, and cold produced by the electric current. 
 Ann. de Chim. et de Phys. t. Ivi. p. 371., and t. Ixxi. p. 225. 
 
 Wartmann. Electric dia-thermansy. Arch, de rElectricite, t. i. p. 74. 
 
 Frankenheim. Kelations between electro-calorific and thermo-electric phe- 
 nomena. Ann. der Physik, t. xci. 
 
 Clausius. Application of the mechanical theory of heat to thermo-electric 
 phenomena. Ann. der Physik, t. xc. 
 
 Thomson. Considerations upon thermo-electric currents. Arch, des Sc. 
 Phys. (Bibl. Univ.) t. xxvii. p. 51., and p. 347. 
 
CHAP. n. ELECTRICITY BY MECHANICAL ACTIONS. 595 
 
 CHAP. II. 
 
 ELECTRICITY PRODUCED BY MECHANICAL ACTIONS. 
 
 Development of Electricity by the Friction of insulating solid 
 
 Bodies. 
 
 WE have already seen that, of all the methods of developing 
 electricity, friction is the one, that was most anciently known. 
 If, in many cases, it seems to be the most energetic source, this 
 is because we must not confound the electricity collected with 
 the electricity produced. This remark applies equally to 
 all the sources of electricity. In fact, whilst the production 
 of electricity is an instantaneous effect, its collection requires 
 a comparatively enormous time, especially when static elec- 
 tricity is in question. Thus, for example, after having 
 rubbed a body, it is necessary to place it in communication 
 with the instrument intended to detect the electricity, that it 
 has acquired ; and during the interval of time, that separates 
 the two operations, many circumstances may notably diminish 
 the electric signs, and even cause them entirely to disappear ; 
 such is the imperfection in the insulating property of the body 
 and of the supports, the contact of the surrounding media 
 and of the air especially. And it is not in the friction of 
 non-conducting bodies that the difference between the elec- 
 tricity collected and the electricity produced, is the greatest ; 
 we shall see, on the contrary, that if we wished, for example, 
 to conclude from the electric signs manifested by the friction 
 of two bodies, compared with those that are produced in many 
 cases by chemical actions, the superiority of the former mode 
 of action over the latter case in the development of electricity, 
 we should run the risk of falling into grave errors. Another 
 important remark to make, and which is equally applicable 
 to all the other sources of electricity, but the importance 
 of which is greater, when mechanical actions are in question, 
 in which one only of the electricities is collected, is that one 
 
 Q Q 2 
 
596 SOURCES OF ELECTRICITY. PART v. 
 
 of the electricities is never liberated, without the other being 
 equally so, and in the same proportion. This law, laid down 
 for the first time by Wilke, is general, and the apparent 
 exceptions, that it presents, yield before a more attentive 
 examination of the facts. Thus Bergmann had remarked, 
 that two goose feathers, rubbed against each other, were both 
 raised to a positive state ; and Faraday, that two bands of 
 flannel, rubbed against each other, cross-wise, were both 
 made negative. In these experiments, there is evidently 
 a disapearance by friction of a very thin superficial stratum 
 of the two substances in contact, which carries with it, the 
 contrary electricity to that, which remains upon the bodies. 
 Moreover, the apparent exception, of which we have just 
 been speaking, is never presented, except in the friction of 
 two similar bodies. 
 
 Let us now enter upon the study of the electric pheno- 
 mena, that accompany friction. With this view, it is necessary 
 to distinguish two species of friction : the one which we may 
 call rolling, in which, as in the case of the two cylinders of a 
 flatting-machine, the same point of a surface is touched by 
 only one point of the other, without coming into contact with 
 a second ; and the friction of sliding, in which, on the con- 
 trary, each point of a surface is successively in contact with 
 several points of the other. We shall have this latter in view 
 at all times, when we shall not state the contrary. When the 
 two surfaces, that are rubbed against each other, are unequal, 
 we call the larger one rubbed, and the smaller rubbing ; it is 
 consequently the one, each point of which is most rubbed. 
 There is also central friction ; which is that which is obtained by 
 placing two discs of the same size in rotation in a contrary 
 direction, around a common axis, taking care that they are in 
 contact. When the rubbed bodies are two species of a same 
 substance, such as resin, glass, flannel, silk, velvet, cork, &c., 
 we remark that, save the rare exceptions, which we have 
 pointed out above, one of the pieces acquires positive electricity 
 and the other negative ; this is easily proved, by means of 
 the dry-pile electroscope. Bergmann has observed that, when 
 two bands of glass are so rubbed, that all the parts of the one 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 597 
 
 pass only over one part of the other, the rubbed one is 
 negative and the rubbing one positive ; the reverse is the case 
 if the rubbed band is hot. Two plates of glass of the same 
 size held by handles, and rubbed one against the other, from 
 above downwards, present an identical state ; in each, the 
 upper half is positive, and the lower half negative. Two 
 ribbons, rubbed one against the other transversely, like the 
 two plates, are, the rubber negative, and the rubbed positive ; 
 it is the converse of the glass ; an old ribbon, rubbed against 
 a new one, is also negative. Heat tends to give to the 
 ribbon, to which it is applied, the negative property. It 
 is probable that it is to the greater heating, that the rubber 
 ribbon must be negative. A very remarkable thing is that, 
 if a cylinder of glass is covered with a substance, and is 
 rubbed with a similar substance, it is always, whatever be 
 the circumstances, that accompany the rubbing, the one that 
 covers the cylinder, that is positive. 
 
 We shall not insist upon the effects of friction, in the case 
 in which the rubbed substances are similar, but differently 
 coloured ; for, at bottom, the substances are not exactly 
 similar, since they contain a different colouring principle ; we 
 shall pass therefore immediately to the case of the friction, 
 brought about between dissimilar substances. We cannot do 
 better than relate, upon this point, the interesting experiments 
 of Coulomb, such as M. Biot, who has extracted them from a 
 manuscript of this clever philosopher, has consigned them to 
 his Treatise on Experimental and Mathematical Physics, A 
 band of paper, in its natural state, being charged with the 
 moisture of the air, acquires by friction only a feeble degree 
 of electricity. But if it is dried and heated, against whatever 
 body it is then rubbed, it will give sensible signs of electricity. 
 A band of paper, heated and rubbed against a stuff of white 
 wool, always acquires negative electricity. This same band, 
 rubbed against metal, always acquires negative electricity, 
 provided the metal has not a great degree of polish. In this 
 case, it sometimes gives very feeble signs of positive electri- 
 city. The band of paper, being dried and heated, if it is 
 rubbed against a stuff of white silk, gives signs of negative 
 
 Q Q 3 
 
598 SOURCES OF ELECTRICITY. PART v. 
 
 electricity ; but when the heat is passed away, it gives more 
 frequently very feeble signs of positive electricity. The 
 band of paper, heated and rubbed against a stuff of black 
 silk, new and of a good tint, gives signs of positive electricity. 
 The band of paper, heated and rubbed against a black stuff, 
 half worn out, acquires, when it is still hot, a negative electri- 
 city ; some instants after, when rubbed anew, it gives no sign 
 of electricity ; but when rubbed again, some instants after, it 
 gives signs of positive electricity. A ribbon of white silk, 
 heated and rubbed against metal, always gives signs of nega- 
 tive electricity. On allowing it to cool, and rubbing it afresh, 
 if the metal, against which it is rubbed, is not too polished, 
 it will continue to give signs of negative electricity ; but if 
 the metal has a very great degree of polish, it will give 
 very feeble signs of positive electricity. Thus, for example, 
 our cooled ribbon being rubbed against a gilt or silvered 
 paper, which has a very great polish, will always acquire po- 
 sitive electricity ; but, if the ribbon is heated, it will always 
 give signs of negative electricity. It will, in like manner, 
 always give signs of negative electricity, whether it is heated 
 or not, when it is rubbed against the edge of a vessel, or 
 against a metal body, that shall not have a great degree of 
 polish, or even against a piece of tinsel ; but if it is rubbed 
 against a part of the vessel that is very polished, it will then 
 acquire positive electricity. A black ribbon, heated or not, 
 but silky and of a good tint, being rubbed against a polished 
 or an unpolished metal, always gives signs of negative electri- 
 city. When the ribbon is a little silky, and the tint is feeble 
 it sometimes gives signs of positive electricity, in the same cases 
 as does white ribbon. A white silk ribbon, heated or not, and 
 rubbed against a black stuff of a good tint, always gives signs 
 of positive electricity ; but if the black stuff against which 
 the white ribbon is rubbed, is worn, and the white ribbon is 
 heated, it will give signs of negative electricity; and, on 
 cooling, it will again give signs of positive electricity. A silk 
 stuff, agitated in the air with a rapid movement, always ac- 
 quires negative electricity ; so that the friction of the air 
 against silk gives to the air a positive electricity. A white 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 599 
 
 ribbon of wool produces almost the same electric phenomena 
 as a silk ribbon and a band of paper ; if it is rubbed without 
 heating it, or after it is cooled, against a very polished metal 
 surface, such as gilded or silvered paper, or even against 
 the side of a vessel of very polished metal, it will give signs 
 of positive electricity ; if the woollen ribbon is heated 
 before it is rubbed, it will in all cases gives signs of 
 negative electricity ; it will give the same signs of negative 
 electricity, if it is rubbed, without causing it to be heated, 
 against a metal surface, which does not possess a very great 
 degree of polish. 
 
 A ribbon of silk, a band of paper, a ribbon of wool, rubbed 
 against a skin, retaining its hair, such as a fox's tail, or a very 
 dry cat's skin, always acquire negative electricity, and in a 
 greater degree than against every other species of rubber. 
 It is known that skins, retaining their hairs, rubbed on the 
 hairy side upon a conducting body, always acquire positive 
 electricity. 
 
 All the peculiarities of these bodies seem to be able to be 
 comprehended under one general principle, which is as 
 follows : 
 
 When the surface of two bodies are rubbed together, that 
 one whose integrant particles are less separated from each 
 other, and which make less excursions around their natural 
 positions of equilibrium, appear, for this very reason, more 
 disposed to acquire positive electricity ; this tendency increases 
 if the surface undergoes a transitory compression. Recipro- 
 cally, that one of the two surfaces, the particles of which are 
 found to be more separated by the roughness of the other, 
 or by any other cause whatever, is, for this very reason, more 
 disposed to acquire negative electricity. This tendency 
 increases if the surface undergoes a veritable dilatation. The 
 more powerful this opposition of circumstances is, the more 
 energetic is the development of electricity upon the two 
 surfaces. It weakens in proportion as their state becomes 
 more similar. A perfect equality, could such exist, would 
 render it null. 
 
 Thus, when a solid and dry animal or vegetable substance 
 
 Q Q 4 
 
600 SOURCES OF ELECTRICITY. PART y. 
 
 is rubbed against a metal surface, that possesses roughness, 
 it gives signs of negative electricity ; this is the case in 
 which its molecules are separated. When it is rubbed 
 against a very polished metal, which alters its surface but 
 little, or the effect of which is confined to compressing it by 
 parts, without separating individually the particles, of which 
 it is composed, it gives no signs of electricity, or it gives signs 
 of positive electricity. Heat, dilating the pores of bodies, acts 
 upon their surface as would a rougher rubber. It disposes it, 
 therefore, to acquire negative electricity. 
 
 When the hairs of a cat's skin are rubbed against a polished 
 or an unpolished metal surface, they can only yield to its 
 shock and close one upon the other ; but they are in this 
 way compressed all in a piece, without any vibration of their 
 particles. They are thus arranged in a manner eminently 
 favourable for acquiring positive electricity ; which, indeed, 
 they are seen to acquire, since the metal, after the friction, 
 is always found to have negative electricity. But, if these 
 same hairs are employed to form the tissue of a stuff, which 
 will require that they be crowded, compacted and pressed upon 
 each other, then, if they are rubbed against an unpolished 
 metal surface, they will not only be pressed and compacted 
 as before ; they will, on the contrary, be separated and torn 
 by the asperities of this surface. Thus, they must acquire 
 negative electricity, as, indeed, they are seen to acquire, 
 except in the case, in which the metal surface against which 
 they are rubbed has a certain degree of polish. 
 
 In general, when one of the rubbed bodies is a tissue of 
 animal or vegetable fibres, pressed one against the other, as 
 a silk ribbon, a woollen stuff, or a piece of dry paper, the 
 best rubber must be that, the tissues of which can produce 
 only a general and transitory compression. Thus experience 
 teaches that, in this case, nothing is preferable to a skin 
 retaining its hair. 
 
 But, when animal or vegetable substances, rubbed against 
 each other, both expand in the friction, the species of elec- 
 tricity, that is acquired by each of them, depends upon the 
 greater or less enlargement that its pores receive ; and then 
 the slightest modifications, in the state of one or other surface, 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 601 
 
 may bring about opposite results. For example, when a 
 white silk stuff is rubbed against a piece of dry paper, the 
 silk generally acquires negative electricity. It would, 
 therefore, appear to have then more tendency for this species 
 of electricity. But, if we begin by opening the pores of the 
 paper, by heating it, this preparation renders it more apt in 
 its turn to acquire negative electricity ; and the silk, rubbed 
 against it, becomes positive. This faculty, which heat had 
 exalted, diminishes in proportion as the paper cools, and as 
 its pores are compacted. A moment arrives, when it is 
 merely equal to that of the silk. At this epoch, the friction 
 of these two bodies produces no sensible sign of electricity. 
 When this instant is passed, the band of paper continuing to 
 become cool, and its pores to be compacted, its tendency to 
 acquire negative electricity is still weakened, whilst that of 
 the white silk remains the same. Then this latter, being no 
 longer counterbalanced by the state of the band of paper, 
 it will frequently happen that the silk will acquire a negative 
 electricity, and will consequently give to the paper a positive 
 electricity. 
 
 The same considerations may be applied to a stuff of white 
 silk, rubbed against a stuff of black silk. Whether the black 
 dye gives roughness to the surface of stuffs of silk or wool, 
 so that, in rubbing them, their pores are found to be further 
 separated, than those of stuffs that are not dyed, or else the 
 reunion of the colouring particles with the silk increases, 
 under the same degree of friction and dilatation, the tendency 
 of acquiring negative electricity, it is a fact that a stuff of 
 new black silk of a good tint, being rubbed against a ribbon of 
 white silk, always acquires this species of electricity. But 
 when the black stuff is worn and its colour faded, if the 
 pores of the white ribbon are dilated by heat, it acquires in 
 its turn for negative electricity a greater tendency than the 
 black stuff; and, consequently, it renders it positive. This 
 disposition, as may be expected, vanishes with the accidental 
 cause that produced it, and the cold white ribbon acquires 
 anew positive electricity. The black dye produces upon 
 wool the same effect as upon silk. A drj white ribbon, 
 rubbed against a white woollen stuff, always gives signs of 
 
602 SOURCES OF ELECTRICITY. PART v. 
 
 negative electricity, but against woollen stuff dyed black, it 
 gives signs of positive electricity. 
 
 Very dry woods are all negative, when they are rubbed 
 with wax ; but when they are rubbed one against the other, 
 it is in general the denser that are negative, and the lighter, 
 positive ; thus ebony is negative with all the other woods. 
 
 Among non-conducting substances, the one the study of 
 which, as far as regards the electricity, that is developed in 
 it by friction, is the most important, and has been the subject 
 of most labour, is undoubtedly glass, which presents, in this 
 respect, remarkable peculiarities, due to the numerous vari- 
 ations of the state of its surfaces and of its small degree of 
 homogeneity. 
 
 The electric properties of glass are indeed intimately con- 
 nected with the state of its surface ; when this surface is new, 
 that is to say, when the glass has been recently made, it is not 
 powerfully electric; which causes it to be unfit for the con- 
 struction of electrical machines. This absence of electric 
 virtue is due to its conductibility ; but they both disappear 
 with time. Polished and old glass is positive with the 
 greater portion of bodies ; whilst dull or ground glass is ne- 
 gative, when rubbed with wool, feathers, wood, paper and the 
 hand, bodies with which polished glass is itself negative. 
 But dull glass is positive, like polished glass, with wax, 
 sulphur, the metals, &c. It follows consequently that, when 
 polished and unpolished glass are rubbed against each other, 
 the former is positive and the latter negative. Although, in 
 general, the variable state of the surface of glass may be 
 recognised by differences in its conducting powers, there are 
 however cases in the which it is not so. There exists, ac- 
 cording to Henrici, differences in the electric power of the 
 surface of glass, which can neither be perceived by sight, nor 
 be demonstrated by a change in the conducting power. 
 Such is the case with the two halves of a rod of glass, one of 
 which has been exposed to the flame of a spirit lamp, and the 
 other of which has remained untouched. The half, that has 
 been heated, is found to be powerfully negative, when it is 
 rubbed with wax or with leather, whilst the other is positive. 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 603 
 
 A very prolonged or very active friction, the immersion in 
 alcohol, or in a solution of potash, restores its positive virtue 
 to the glass, which had lost it ; however, if it is not made to 
 undergo any operation of this kind, it may preserve for days 
 and weeks its negative property. Rock crystal, under the 
 same circumstances, suffers the same alteration as glass in its 
 electric properties. 
 
 We may even render glass susceptible of acquiring negative 
 electricity when rubbed, by plunging it into an acid, and 
 allowing it to dry, after having previously washed it in 
 distilled water. The immersion in an alkali does not produce 
 the same effect. 
 
 It is evident that the action of flame consists in bringing 
 about an alteration in the state of the surface, since mecha- 
 nical means destroy the effect of this action. It is not a result 
 of the direct action of heat ; for rods of glass that are ex- 
 posed to the same temperature, care being taken to enclose 
 them in tubes of metal, so as to prevent them being in im- 
 mediate contact with the flame, do not suffer any modification 
 in their electric properties. Neither is it an effect of the 
 action, exerted upon the glass by the products of combustion, 
 such especially as the vapour of water on carbonic acid ; for 
 upon allowing these products, already formed, to act at a 
 high temperature, the same result is not obtained. It is 
 therefore probable that it is in the act itself of their formation 
 upon the surface of the glass, that they have an action upon 
 this surface. 
 
 Moreover, it is not only in its electric properties that 
 glass suffers an alteration, by the modification of the surface. 
 Lcevell and Liebig have demonstrated that a rod of glass is 
 able to lose, by its being heated, the property that it possesses 
 in its natural state, of causing a saturated solution of 
 sulphate of soda, into which it is plunged, instantaneously 
 to crystallise. This same solution crystallises immediately 
 it is placed in contact with a part of the glass rod, that 
 has not been heated. The part of the rod that has become 
 inactive, may remain several days in this state ; the im- 
 mersion in water, followed by its drying in air, does not 
 
604 SOURCES OF ELECTRICITY. PART v. 
 
 suffice to restore to it its activity; for this purpose it is 
 necessary that it be exposed for some time to the open air. 
 
 Among the substances in which the electricity, developed 
 by friction, has been studied with care, we may cite a great 
 number of minerals, upon which Haiiy has made numerous 
 experiments. This learned mineralogist rubbed each specimen 
 with a woollen stuff, in order to determine whether it become 
 positive or negative by this friction ; and he thought he 
 found that the electric characters, proper to each of the 
 classes into which he grouped the minerals under the rela- 
 tion, were connected with physical properties common to all 
 the species, comprised in the same class. However, he re- 
 cognised that many circumstances, such as the transparency 
 and the asperity of the surface, bring about modifications in 
 the electric character of the same mineral species. These 
 variations are in general due to the circumstance that the 
 weakening of transparency is due either to a mixture of an 
 heterogeneous matter interposed accidentally in the substance, 
 or to a derangement of structure, which causes a nebulous 
 aspect ; modifications which bring about, as well as the loss 
 of polish of the surface, a diminution in the insulating 
 property of the body. Thus, for example, the variety of car- 
 bonate of lime called Iceland spa, is transparent, very insu- 
 lating and positive, whilst the transparency disappears, at the 
 same time as the insulating property and the positive elec- 
 tricity in the saccharoidal variety (statuary marble), which is 
 negative. Thus, even quartz and topaz, which, in the state 
 of limpid crystals, are insulating and positive, become con- 
 ductors and negative, when the surface is dull and rough ; 
 but when polish is restored little by little to these frag- 
 ments, they recover by degrees the intermediate state?, 
 through which they had passed, and end by entirely regaining 
 their primitive properties in the hands of the lapidary. The 
 state of the surfaces has so great an influence over the nature 
 of the electricity, liberated in the friction of badly conducting 
 bodies, that Haiiy has found a crystallised mineral substance, 
 which he has named disthene, which acquires with the same 
 rubbers positive electricity on certain faces, and negative on 
 
on A p. IT. ELECTRICITY BY MECHANICAL ACTIONS. 605 
 
 others, without our being able to discover apparent differences 
 between them. 
 
 Before drawing out the series of bodies, ranged in the 
 order of the nature of the electricity, that they liberate, on 
 being rubbed against each other, we must occupy ourselves 
 with the case, in which one of the rubbed bodies, being 
 always an imperfect conductor, the other is a good conductor, 
 such as a metal. Cavallo, Wilson, Haliy have made a great 
 number of researches on this particular point. Cavallo had 
 found that almost all the metals became negative, on being 
 rubbed with the greater part of bodies, even with sealing 
 wax. More recently, Faraday had confirmed this result with 
 iron, copper, brass> silver, and platinum ; upon thirteen sub- 
 stances with which he had rubbed them, he had only found 
 sulphur, that renders them positive. Hauy had observed, 
 when rubbed with wax, that silver, lead, bismuth, zinc, and 
 brass are positive, whilst platinum, palladium, gold, nickel, 
 iron, tin, arsenic, and antimony are negative. 
 
 The difference, that is remarked between these various 
 results, is due to the fact that, when one of the rubbed 
 bodies is very hard, in relation to the other, as a metal in 
 relation to wax, it frequently happens that the softer is 
 scratched by the harder ; and that this latter indicates by 
 the electroscope, not its own electricity, but that of the thin 
 film of the substance that it removes. I have pointed out 
 this cause of error, in endeavouring to take it into account in 
 order to explain the anomalies that are presented by electri- 
 city developed in metals, rubbed with imperfect conductors ; 
 and I have succeeded in demonstrating in this way, what is 
 indeed the true nature of that electricity. 
 
 We have merely to place a piece of metal upon the plate 
 of a gold-leaf electroscope, and to rub it delicately with the 
 fingers, in order to bring about a considerable divergence of 
 the gold leaves, without even having need of the assistance 
 of the condenser, it is merely necessary that the fingers be 
 very dry ; in order that the experiment shall succeed well, 
 care is taken to hold with a well insulating glass tube, the 
 piece of metal, in order that it shall not slip, when being 
 
606 SOURCES OF ELECTRICITY. PART v. 
 
 rubbed. The rubbed metals do not all acquire the same 
 electricity in this operation ; thus, antimony is negative, and 
 bismuth positive. If we employ, as rubbing bodies, ivory, 
 horn, cork, and various species of wood, it is found that 
 rhodium, platinum, palladium, gold, tellurium, cobalt, and 
 nickel, acquire negative electricity ; whilst silver, copper, 
 brass, and tin, which are in general also negative, sometimes 
 show themselves positive, especially tin ; antimony, although 
 the most powerfully negative of all, is, however, sometimes 
 positive ; iron and zinc are sometimes positive, sometimes 
 negative ; finally, lead and bismuth are constantly positive. 
 But if we take the precaution of rubbing the metal upon a 
 sharp edge in very dry air, with wood very well dried, and 
 very clean, it always acquires negative electricity, on the other 
 hand, when the rubbed surface is great, and the rubber is 
 moved along its whole extent, the metal becomes in general 
 positive, especially if it is rubbed with cork. Elevation of 
 temperature and moisture favour the liberation of positive 
 electricity in metals, that are easily oxidisable. It is evident 
 that these anomalies are due to the fact, that in air, and 
 especially in moist and hot air, the surface of the majority of 
 metals is covered with a slight film of oxide, that the rubber 
 removes, which causes it to be no longer between the sub- 
 stance of the rubber (finger, wood, cork) and the metal, but 
 rather between the film of oxide, that covers this rubber 
 and the metal, that the friction takes place ; so that, in this 
 case, the metal acquires positive electricity, its oxide being 
 charged with negative. But, if we operate upon a part of 
 the surface well cleaned, and whence it is easy to remove 
 immediately the film of oxide, as a sharp edge, then the 
 metal always acquires negative electricity, whatever its 
 nature may be. With cork and caoutchouc, positive electri- 
 city is more easily obtained upon metal, than with wood ; 
 because the friction, being more gentle, the film of oxide is 
 removed more equally, and remains better adhering to the 
 surface of the rubbing body. 
 
 The development of electricity by the friction of non- 
 conducting bodies and metallic substances has been turned to 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 607 
 
 account, in the employment of an amalgam, with which the 
 cushions of electrical machines, intended to serve as rubbers 
 to the glass, are covered. These amalgams are amalgams of 
 tin, of zinc, and of tin and zinc together; sometimes still more 
 complicated amalgams are employed, and even a metallic 
 combination, as mosaic gold (deuto-sulphuret of tin). Wol- 
 laston had thought that the considerable influence, which the 
 presence of these metallic compounds exercises over the liber- 
 ation of electricity, was due to a chemical action ; namely, 
 to the oxidation, that these compounds suffer in atmospheric 
 air. In support of this opinion, he had quoted the fact that, 
 on substituting carbonic-acid gas for atmospheric air around 
 the plate and rubbers of the electrical machine, no more 
 electricity is possible. But Gay-Lussac remarked that this 
 absence of electricity was due to the hygrometric water, of 
 which it is a difficult matter to deprive the carbonic-acid gas, 
 and he succeeded in obtaining electricity with very oxidisable 
 amalgams in an atmosphere of well-dried carbonic acid. 
 
 M. Peclet has taken up these experiments, speaking of the 
 principle, that the gas is able to act in two manners, when 
 electricity is developed by friction, either as intervening in 
 the production of this electricity, or as a more or less con- 
 ducting body. After having proved, by delicate experiments, 
 made by means of Coulomb's balance, by a process analogous 
 to that which we have already described *, the equality of 
 the conducting faculties of well-dried air and carbonic- acid 
 gas, he arranged an electrical apparatus, consisting of glass 
 cylinder and rubbers, coated with mosaic gold, so that it might 
 be placed entire under a receiver, furnished with a stuffing-box, 
 traversed by a metal rod, that could, by means of gear-work, 
 communicate to the cylinder of glass the rotatory motion, 
 that was imparted to it exteriorly, by means of a handle. 
 Upon operating on the air of the receiver, previously dried 
 for twelve hours by chloride of calcium, then upon carbonic 
 acid, introduced into the receiver in place of the air, after 
 having been completely dried, he found that the indications 
 
 * Vol. II. pp. 142. and the following. 
 
608 SOURCES OF ELECTRICITY. PART v. 
 
 of an interior electroscope, which communicated by a copper 
 wire, passed through the receiver, with a set of metal points, 
 placed opposite and very near to the cylinder of glass, were 
 exactly the same for both gases, provided they were equally 
 dry. As an objection might be raised, that there remained, 
 in these experiments, a small quantity of air, mixed with the 
 carbonic acid, M. Peclet operated successively upon air, upon 
 hydrogen, and upon carbonic acid, taking care, for these two 
 latter gases, to make no experiment until after the receiver had 
 been emptied and filled six times successively with the same 
 gas, so that there might be a certainty of the purity of the 
 gas. The results were always the same. Thus, it remains 
 satisfactorily proved that, in the production of electricity by 
 friction, the action of the air upon the more or less oxidisable 
 portions of the rubbers, exercises no influence. 
 
 Among the substances eminently electrical, we ought also 
 to mention Schoenbein's gun-cotton, which, hard and fila- 
 mentous, is a perfect insulator and negative with all known 
 bodies. Collodion, which is obtained in a thin pellicle by 
 causing a solution of gun-cotton in sulphuric ether to 
 evaporate, and which has been extended upon a surface of 
 glass, is also electric in the highest degree and negative, 
 except with gun-cotton, with which it is positive. If fine 
 unsized paper is plunged, according to the process of 
 Pelouze, into a mixture of sulphuric acid and fuming nitric 
 acid, and is then washed in abundance of water, it assumes a 
 yellowish and translucid appearance, similar to parchment, 
 and acquires powerfully electric properties; for we have 
 merely, when several sheets of paper thus prepared are 
 superposed, to rub the upper one with the hand, in order 
 that they may remain adherent to each other, when the first 
 is raised, and that in separating they may give bright sparks. 
 This paper is positive with gun-cotton and collodion, and is 
 negative with all other substances. Its electric power is so 
 considerable, that powerful sparks may be drawn from it, 
 accompanied by a liberation of ozone. M. Schoenbein, who 
 was the first to remark the powerful electric properties of 
 this paper, proposed to employ it in the construction of 
 
CHAP. H. ELECTRICITY BY MECHANICAL ACTIONS. 609 
 
 electrical machines, which consequently would have been 
 without glass. Moreover, it is observed that, in the fabrication 
 of ordinary paper, there is a continuous liberation of electric 
 sparks, when, in order to dry it, the paper, still in state of 
 pulp, is made to slide along metal cylinders heated interiorly 
 by steam. 
 
 M. Colladon has also remarked that, in spinning machines, 
 the operation, to which the filaments of cotton are subjected, 
 which are compressed, drawn out, and twisted, in order to form 
 threads, by causing them to slide over the metal surfaces, by 
 which they are guided, liberates much electricity. The 
 cotton threads are charged with negative electricity, and the 
 machines acquire positive. It follows from this that, when 
 the air is dry, the machines on the one hand, and the 
 filaments of cotton on the other, preserve their electricity, 
 that the corners and culminant points of the machines attract 
 the small filaments of cotton, that are flying in the apartment, 
 which deranges the operation of spinning, which is also 
 hindered by the electric state of the filaments of cotton, 
 which, by favouring their separation, their disaggregation, 
 thus occasions a more frequent breaking of the threads. It 
 has been also observed at New York, in houses constructed 
 with very dry materials, that the mere friction of the soles 
 of the shoes against the woollen carpets, with which the floors 
 are covered whereon a person walks, liberates sufficient 
 electricity, for this person to be charged with it in an in- 
 convenient manner, seeing that as soon as he brings his hand 
 or himself near to a conducting body, a spark escapes, which 
 is frequently very disagreeable. 
 
 Before pursuing the study of the electricity, liberated by 
 friction, we ought to give here the series of bodies classed 
 according to the nature of the electricity, which they acquire, 
 upon being rubbed successively against each other ; but this 
 series is established with difficulty, because of the difficulty 
 of taking account of all the circumstances which influence 
 the nature of the electricity that is acquired by each body. 
 The following, however, is a tolerably exact Table of the 
 principal substances, arranged one after the other, in such an 
 
 VOL. II. R R 
 
610 SOURCES OF ELECTRICITY. PARTY. 
 
 order that each is positive with the one that follows, and 
 negative with that which precedes : 
 
 Cat-skin, diamond, flannel, ivory, rock-crystal, wool, glass, 
 cotton, linen, white silk, the dry hand, wood, sealing-wax, glue, 
 amber, sulphur, caoutchouc, gutta-percha*, prepared paper, 
 collodion, gun-cotton. 
 
 The analysis that we have been giving of the electrical 
 effects, due to friction, demonstrates clearly that these effects 
 are really due exclusively to the molecular movements, that 
 are brought about by this mechanical action ; but it is of 
 importance to define a little better its nature, and to investi- 
 gate the circumstances, that may render it more or less effi- 
 cacious. M. Peclet has done this in a remarkable work, in 
 which he has studied successively the influence of velocity, 
 pressure, extent of the surfaces of contact, the state of the 
 surface of bodies, their thickness and their nature. The 
 electrical machine, employed by M. Peclet, was a glass cy- 
 linder machine, in which the rubber is placed upon the most 
 elevated point of the cylinders ; the pressure is produced by 
 weights arranged upon the rubber ; the cylinder is rounded 
 and polished throughout, in order to avoid inequalities of 
 friction ; the electricity is collected by a metal comb, which 
 communicates directly, by means of a copper wire covered 
 with waxed silk, with a pendulum electrometer, the arrange- 
 ment of which enables us to follow exactly the variations of 
 tension that ensue, when the circumstances of the friction are 
 modified. The first experiments had for their object to de- 
 termine the influence of the duration of the friction upon the 
 intensity of the electricity developed ; it follows from all those 
 which have been made with a very great number of bodies 
 employed as rubbers, such as bare paper, paper covered with 
 a thin foil of copper, tin, silver, and gold, tin-foil, and various 
 stuffs of wool, silk, cotton, waxed silk, leather, &c., that the 
 deviation of the electrometer goes on constantly increasing, 
 for a certain time, after which it remains sensibly constant, 
 
 * Gutta percha is especially insulating at its surface ; for it conducts 
 tolerably well in the interior of its mass. 
 
CHAP, ii. ELECTRICITY BY MECHANICAL ACTIONS. 611 
 
 whatever, in other respects, the velocity may be, provided 
 this velocity does not change. The permanence of the de- 
 viation is sometimes established, after the first minute ; at 
 other times, it requires a much longer period, even as much 
 as seven minutes. This gradual and more or less rapid in- 
 crease is due to several causes, in particular to the change of 
 form, that happens to the surface of the rubber, during the 
 first instants of the friction. 
 
 After the influence of time, that of the velocity is of im- 
 portance to know. A very great number of experiments, 
 made with rubbers of different kinds, and in favourable at- 
 mospheric circumstances, namely, when the air is very dry, 
 have shown that the velocity with which the friction takes 
 place is without influence over the quantity of the electricity 
 developed ; and that the pendulum of the electrometer 
 preserves the same deviation for velocities of rotation of the 
 glass cylinder, increasing from 1 to 8 ; and this equally for 
 great and small pressures of the rubbers. When the air is 
 moist the deviation increases a little with the velocity from 
 1 to 2 only ; it is equally to be remarked, that permanence is 
 not maintained, when the velocities are very small ; the devi- 
 ation then diminishes with the velocity, and this the more, 
 as the air is moister; which arises, as is easily compre- 
 hended, from the loss of the electricity being proportionately 
 more rapid ; and the equilibrium between this loss and the pro- 
 duction is established at a lower limit. There are, besides, 
 some substances which, when employed as rubbers, produce 
 deviations that increase with the velocity ; such, for example, 
 are silk plush, cotton cloth, linen cloth, &c. These anoma- 
 lies are evidently due to the neutralisation of the electricity 
 of the glass cylinder by the asperities of the rubber, beyond 
 the points of contact, a neutralisation which must be less in 
 proportion as the velocity is greater. To satisfy oneself on 
 this we have merely to follow the motion, that the electricity 
 imparts to the filaments of the surface of the rubbers, and es- 
 pecially to observe in darkness the luminous points, by which 
 they are terminated. This influence must be greater, in pro- 
 portion as the body is a better conductor, and as the filaments 
 
 R R 2 
 
612 SOURCES OF ELECTRICITY. PART v. 
 
 of its surface are longer and more flexible ; this indeed is 
 what we observe, when we employ comparatively stuffs of silk 
 and of cotton, or linen cloth of the same structure. Further- 
 more, we may at pleasure produce or cause to disappear on 
 certain bodies the anomalies in question, by rendering the part 
 of the rubber, that is beyond the contact, either smooth or 
 plushy. The imperfect conductibility of the rubber by pre- 
 venting the immediate escape of the electricity, that is de- 
 veloped upon it by friction, may exercise an influence in the 
 contrary direction to the preceding, and dimmish, with the 
 velocity, the electric tension, which the cylinder of glass should 
 acquire, one part of the electricity of which is taken up in 
 this case by that of the contrary name, which the rubber 
 retains for too long a period. Velocity is not only without 
 influence, if care is taken to eliminate all the causes of error, 
 over the maximum of electric tension, which is acquired by 
 the cylinder of rubbed glass, but it never exercises any over 
 the absolute quantity of electricity that is produced. It is 
 easy to prove this, by placing a metal ball, communicating 
 with the ground at such a distance from the conductor 
 of the machine, that a spark is manifested at every 
 turn, the movement being uniform. If the velocity is 
 changed, the spark passes at each turn, whatever this 
 velocity may be. Now, the discharge of the conductor, 
 always taking place under the same tension, it is evident 
 that the cylinder always furnishes the same quantity of electri- 
 city at each rotation, and that consequently, in a same time, 
 the quantity of electricity produced is in proportion to the 
 velocity, namely, to the number of rotations. This result is 
 not, like the preceding, absolutely true, except for rubbers, 
 which conduct electricity well, such as metals, paper, leather ; 
 for badly conducting bodies, the discharges are only mani- 
 fested for a number of turns, which must be more considerable 
 in proportion as the velocity is greater ; this is easy of com- 
 prehension, from what we have said above. 
 
 To sum up, we see that velocity is without influence over 
 the development of electricity, and that the anomalies, which 
 are sometimes observed, arise from the humidity of the air, 
 the asperity of the surfaces, or the imperfect conductibility of 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 613 
 
 the bodies ; and it is probable also, that for excessively great 
 velocities, the liberation of heat which accompanies the fric- 
 tion would be a cause of disturbance. 
 
 A very great number of experiments have demonstrated that 
 pressure is also without any influence over the tension of the 
 electricity developed. It follows, from an attentive examina- 
 tion of the facts, that the law, which consists in the deviations 
 of the electroscope being independent of the dead pressure 
 exercised upon the rubber, subsists also, when we consider 
 the pressures, experienced by the points actually in contact ; 
 that is to say, that these points always suffer an increase of 
 pressure, corresponding to that of the load, notwithstanding 
 the increase of their number. Some anomalies presented 
 with certain bodies, are due to the heat, that is developed 
 by the friction. M. Peclet satisfied himself of this in a 
 direct manner. 
 
 Neither does the length of the rubber, that is to say, the 
 extent of the surface rubbed, exert any influence over the 
 deviation of the balls of the electroscope ; but it is not the 
 same with the curvature of the rubber beyond the contact 
 which has a real influence over the quantity of electricity ; a 
 quantity, which diminishes in a very sensible manner with 
 the radius of curvature. This fact, which is presented only 
 when the rubber is a conducting body, evidently depends 
 upon the phenomena, that are developed at the moment of 
 the separation of the two surfaces. There is always, in this 
 instant, a recomposition of a certain proportion of the contrary 
 electricities, that the two bodies had acquired by the contact, 
 and which become free immediately on the separation. We 
 can even recognise it, by observing in darkness luminous 
 traces at the extremity of the cushion. Moreover, we 
 easily conceive the influence of curvature, such as is mani- 
 fested in these experiments, by remarking that the rubber 
 must acquire, under the action of the electricity of the 
 cylinder, a tension increasing in proportion as the curvature 
 diminishes, and which must necessarily increase the quantity 
 of the two electrical principles, that recompose. 
 
 The thickness, whether of the rubber, or of the glass 
 
 R R 3 
 
614 SOURCES OF ELECTRICITY. PART v. 
 
 rubbed, has very little influence over the results, at least 
 beyond certain limits. It is only necessary to have regard, as 
 far as concerns glass, to the fact that, when it is hollow as a 
 tube, instead of being solid as a rod, the interior moisture ex- 
 ercises an influence, which it would be wrong to attribute 
 to the difference of thickness. 
 
 We have seen, that two species of friction may be distin- 
 guished, that of sliding, and that of rolling. In order to compare 
 the effects of the two modes, M. Peclet employed a hollow 
 copper cylinder, furnished at its surface with several leathers, 
 for the purpose of enabling it to be applied accurately upon 
 the glass cylinder of the electrical machine, on a certain ex*- 
 tent. By means of weights, the pressure of this rubber against 
 the glass might be made to vary. On rendering the cylinder 
 immovable, the friction of ordinary sliding was produced ; 
 on allowing it to be free to roll around its axis, the friction 
 of rolling was obtained. In this latter case, the rolling 
 cylinder tends, on account of the inequalities of its surface, 
 to separate itself from the glass cylinder ; and this the more 
 in proportion as the velocity of rotation is greater. In order 
 to obviate this inconvenience, the best means is to employ 
 the hands, in order to maintain the rolling cylinder upon 
 the glass. We thus observe that the influence of velocity 
 and pressure, in this mode of friction, as in the other, is null. 
 With regard to the comparison of the effects, produced by 
 the two modes of friction, experiment demonstrates that paper, 
 skin, and metals, or their alloys, produce the same quantity 
 of electricity, by the friction of sliding and by that of rolling. 
 The differences, that are observed with other bodies, are due 
 to accessory circumstances, such as filaments which, acting 
 differently in one case and in the other, are able to draw off 
 the electricity. Regard must also be had to an important 
 difference between the two modes of friction; it is that, 
 in rolling, there is continuous adhesion or pressure ; and that, 
 in friction by sliding, there is not. 
 
 Finally, it follows, from certain observations of M. Peclet's, 
 that heat, as well as the roughness of the surface of bodies, 
 produces a negative tendency ; and that the heat, liberated 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 615 
 
 by the friction itself, always tends to give a tension more 
 negative or less positive to that one of the two bodies, which 
 is the least good conductor of caloric ; results entirely 
 conformable to those, which Coulomb had previously ob- 
 tained, and which we have related above. 
 
 We shall terminate this paragraph by completing, by 
 means of the data, that have been furnished to us by the 
 study, which we have just been making, the description and 
 the theory of electric machines, founded upon the liberation 
 of electricity by friction, which we have hitherto merely 
 sketched out at the commencement of this treatise.* 
 
 We have already remarked that every species of glass 
 is not equally suitable for forming the disc of a machine. 
 Soft glasses and hard glasses, when recently prepared, and 
 when friction has rendered their surface scratchy, have a 
 conducting faculty, which notably diminishes their electric 
 power. The most suitable glass is not that which is most 
 transparent, but that which presents on its surface small 
 brilliant points (of silicic acid). The metallic oxides, that 
 are found mixed with glass, and which impart to it a blue, 
 green, or black tint, have not generally any fatal influence, 
 except in the case in which the oxide is that of manganese, 
 which gives a violet colour to the glass. However, it is 
 very rare that it is the mass itself of the glass that is con- 
 ducteous ; the conductibility is rather superficial, and has 
 its source in the hydroscopic nature of the surface. 
 
 Circumstances being the same, a disc of glass has an elec- 
 tric virtue greater, in proportion as it is thinner; which 
 is due to this, that the two surfaces of the disc being elec- 
 trised with the same electricity, the two electric strata, by 
 virtue of their mutual repulsion, have more density in pro- 
 portion as they are nearer, and as, consequently, the thick- 
 ness of the disc is less. M. Riess mentions an excellent elec- 
 trical machine, the glass disc of which is scarcely y 1 ^ in. in 
 thickness. It would not be prudent, on account of its fra- 
 gility, to go below this limit. 
 
 The glass disc, after having been rubbed, passes between 
 
 * Vide Vol. I. p. 19. and following pages. 
 R B 4 
 
616 SOURCES OP ELECTRICITY. PART v- 
 
 the points of two metal jaws, forming part of the insulated 
 conductor, and which embrace the edge of the disc at the ex- 
 tremities of its horizontal or vertical diameter. The propriety 
 of acting in this way, in order to draw off the electricity from 
 the two faces of the glass, is not perfectly established ; for, if 
 we seem to gain in a direct manner a greater absorption of elec- 
 tricity, on the other hand, we should obtain by acting only upon 
 one of the faces, an electricity endowed with a greater inten- 
 sity upon this face by the repulsive influence of the electricity 
 of the other. However, except in certain particular cases, it 
 is preferable to draw off the electricity at the same time from 
 both faces. It is of importance to be able to vary the distance 
 between the glass disc and the portion of the conductor, that 
 draws off the electricity, because this distance must differ 
 both with the nature of the glass, as well as 
 with the greater or less density, with which 
 we desire that the electricity accumulated 
 upon the conductor, may be endowed. For 
 obtaining these variations of distances, we 
 may employ the system contrived by 
 Oertling (fig. 290.). 
 
 The cushions must have a perfect com- 
 munication with the ground, if we desire 
 1^290. to obtain a powerful electricity upon the 
 disc. With regard to their width, if on the 
 one hand it increases the extent of the rubbed surface, it has 
 the inconvenience on the other hand, when it exceeds certain 
 limits, of causing the disc to lose a part of the electricity, 
 that it had acquired, by increasing its surface of contact with 
 a conducting body. There is, therefore, a happy medium to 
 be maintained, which depends upon the nature of the glass ; 
 the length of the cushion should not, in general, exceed two 
 inches. Care must be taken to avoid, in the construction of 
 rubbers, all points or sharp edges, which might possess the 
 inconvenience of drawing off, and consequently of diminishing 
 the electricity of the disc. It is toward the edge of the 
 cushion, where the disc of glass abandons it, after having 
 been rubbed, that the greatest risk arises of encountering a 
 communication which might cause a portion of the electricity 
 
CHAP. II. ELECTKICITY BY MECHANICAL ACTIONS. 
 
 617 
 
 to be lost. On this account it is that at this point are placed 
 extensions of well insulating silk, which cover the disc, 
 nearly as far as the conductors, in order to protect its electri- 
 city against loss, arising from the action of the air. As we 
 have said, the leather of the cushions is covered with mosaic 
 gold, or with an amalgam formed of tin and zinc melted 
 together in equal proportions, with an addition of two parts 
 of mercury. The whole, after having been agitated in 
 a flask, is pounded in a mortar into a fine powder. Before 
 spreading the amalgam upon the cushions, they are slightly 
 rubbed with a few small pieces of cacao butter. A well 
 amalgamated cushion preserves its electric activity for a long 
 time, provided that the precaution be taken, of frequently 
 removing the dust, which the glass plate accumulates 
 upon it. Care must, likewise, be taken, before placing a 
 second layer of amalgam upon the cushions, entirely to 
 remove the old one. The glass plate, when it has been 
 soiled by the amalgam, must also be cleaned, from time 
 to time ; and for this purpose, sulphuric ether is employed. 
 
 These are the principal precautions that must be taken, in 
 order to obtain good electrical machines. We shall terminate 
 
 Fig. 291. 
 
618 SOURCES OF ELECTRICITY. PART v. 
 
 this paragraph by representing two such; one a cylinder 
 machine (fig. 291.), and the other a plate machine (Jig. 292.), 
 constructed with all imaginable care. Although, as we have 
 seen, the rapidity of the friction in no degree influences the 
 
 Fig. 292. 
 
 quantity of electricity produced, yet we must not turn the 
 glass too slowly, in order not to give the electricity time to 
 be lost between the moment, when it has been produced by 
 the friction brought about by the cushions, and that, in which 
 it is discharged by the conductors. The velocity of rotation 
 is especially necessary with the cylinder machine, in which 
 there is only one rubber, and in which, consequently, a toler- 
 ably long interval of time elapses between the moment of the 
 development of the electricity by the friction of the glass, and 
 that, in which it is drawn off by the insulated conductor. 
 
 Liberation of Electricity in the Friction of Bodies in Powder, of 
 Liquids, and of Gases. Hydro -electric Machine. 
 
 When a body in powder is driven by a pair of bellows, the 
 friction that it exercises against the end itself of the bellows, 
 
CHAP. II. ELECTRICITY BY MECHANICAL ACTIONS. 619 
 
 against an inclined plate that it encounters, or against a sieve 
 or a stuff that it traverses, is sufficient to develope electricity. 
 Bennet made the curious remark, that chalk in powder, 
 blown by a bellows against the plate of the electroscope, gives 
 positive electricity if the plate is about 5 in. from the bellows, 
 and negative, if it is about 6 in. This is due to the chalk 
 suffering two frictions ; one against the tube of the bellows, 
 which renders it positive, and the other against the plate of 
 the electroscope, which renders this latter negative. Accord- 
 ing to the distance, it is one or other of the two electricities, 
 that has the superiority. Ice in powder, and snow well dried, 
 blown by a bellows, give strong signs of electricity. When 
 metal filings are made to slide along a smooth plate of metal, 
 electric signs are obtained, on account of the feeble conduc- 
 tibility of the filings. M. Becquerel, who made a very parti- 
 cular study of this mode of the liberation of electricity, 
 has observed that, when the filings of a metal are projected 
 upon a plate of the same metal, the latter acquires positive 
 electricity, and the filings negative; the effect is the more 
 marked, as the filings are finer, and the blow more rapid. If 
 the plate and the filings are not of the same metal, the effect 
 of the division of the metal is complicated by that, which is 
 due to the developement of voltaic electricity that takes 
 place at the contact of the two heterogeneous metals. Thus 
 copper filings are negative with plates of zinc, lead, tin, iron, 
 bismuth, and antimony ; zinc filings, on the other hand, are 
 positive with plates of platinum, gold, silver, copper, and tin ; 
 they are negative with plates of zinc, bismuth, antimony, and 
 iron; metallic oxides, as well as their sulphurets, reduced into 
 powder, are negative, in respect to their metals. We must 
 avoid the powders being too fine ; for they attach themselves 
 to the surface and prevent the friction of the portions, that 
 come afterwards. 
 
 These effects are evidently connected with the force of ag- 
 gregation, and, consequently, with the molecular constitution 
 of bodies ; hence, they present many anomalies, connected 
 precisely with those which are presented by this constitution 
 itself. Thus we see that antimony, which owes probably to its 
 mode of crystallisation the special character, that it plays in 
 
620 SOURCES OF ELECTRICITY. PART v. 
 
 phenomena of this class, is negative, when in a plate, in re- 
 spect to its filings, whilst it is the reverse for other metals. 
 Heat, in general, increases the intensity of the effects, acting 
 as does generally the division of parts. In certain cases, such, 
 for example, as that in which the filings are of zinc, and in 
 which the plates are but little oxidisable, namely, platinum 
 gold, silver, or copper, the elevation of temperature pro- 
 duces an inversion in the nature of the electric signs, zinc 
 being negative instead of positive. 
 
 Independently of the experiments that we have been relating, 
 there are also a very great number of others, both more ancient, 
 as well as more recent, upon the electric effects, produced by 
 bodies in powder. Thus the electricity has been studied, 
 that is, acquired by different species of powder transmitted 
 through sieves, made w T ith tissues of various organic sub- 
 stances. It has been remarked that, in general, the solid acids, 
 as well as earths reduced into powder, acquire negative elec- 
 tricity, when thus sifted. The electricity developed by the 
 friction of powders one against the other has also been studied. 
 Thus it has been proved that sealing-wax in powder, rubbed 
 with powdered sulphur, is positive, and that the powdered 
 sulphur is negative ; whilst the two powders equally are ne- 
 gative, when they are rubbed each separately with linen 
 cloth. It is by means of the Lichtenberg figures that the 
 nature of the electricity of each powder is easily proved. We 
 shall relate further on some of Faraday's experiments upon 
 the electricity developed by the friction of bodies in powder, 
 by means of an apparatus similar to that which he employed in 
 the study of electricity liberated by the friction of liquids and 
 of elastic fluids. We must first occupy ourselves with this 
 latter point. 
 
 For a long time the experiments that had been made in 
 order to obtain electric signs by the friction of liquids had 
 been fruitless, except in the case in which the liquid was 
 mercury. Yolta had in vain employed oil : and he had 
 considered the liquid state as unfavourable to the manifes- 
 tation of these phenomena. However, on making use of 
 liquids, reduced to the state of very divided globules, both 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 621 
 
 insulated as well as mixed with a current of air, very decided 
 electrical effects are obtained by their friction against solid 
 bodies; thus ether, alcohol and liquid resins, projected against 
 ground glass, render it very positive. A liberation of light 
 has also been noticed in the sudden escape of very compressed 
 air from the vessel, in which it is contained ; many experi- 
 ments, made by discharging air-guns, have given a similar 
 result. But the direct proof has never been obtained that 
 the light had an electric origin. However, Wilson had suc- 
 ceeded in electrising tourmaline, glass, and amber, by di- 
 recting against these substances a current of air coming from 
 a blacksmith's bellows. Henley and Lichtemberg had elec- 
 trised amber and sealing-wax, by means of the air driven 
 from an ordinary bellows ; but the latter of these two phi- 
 losophers had obtained no effect with the metals. In like 
 manner, Yolta had obtained no effect, on turning metals 
 rapidly in the air, whilst he had detected some feeble effect, 
 on operating in the same way with insulating bodies. Marx, 
 on his side, had not been able to electrise glass any more 
 than the metals by their friction against the air. More 
 recently Faraday has explained perfectly these contradictory 
 results by showing that solid bodies, such as wood, sulphur 
 and the metals, cannot be electrised by their friction against 
 very dry air ; but are so only at such times as the air contains 
 water or some other liquid. 
 
 We have said that, of all liquids, the one whose friction 
 against solids gives the most decided signs of electricity, is 
 mercury. Dessaignes, who made a great number of experi- 
 ments upon this subject, had found a great difference between 
 different substances, in regard to their faculty of being 
 electrised by a simple immersion in mercury. Thus amber, 
 sulphur, sealing-wax, and glass do not become electric by 
 this simple immersion ; in order to their becoming so, it is 
 necessary that they be a little hotter than the mercury, and 
 that the immersion be sudden, so as to produce a shock ; 
 whilst with paper, cotton, the particles of which suffer very 
 easily a derangement of position, a slight shaking, such as 
 arises from slow immersion, is sufficient for a liberation of 
 
622 SOURCES OF ELECTRICITY. PART v. 
 
 electricity to take place. Moreover, the results obtained by 
 Dessaignes are so complex, that we shall not dwell upon 
 them longer, on account of the difficulty of distinguishing 
 fairly the different causes that concur in their production. 
 
 M. Perego has taken up the study of the facts, observed 
 by Dessaignes, justly observing that this latter philosopher 
 was wrong in directing his attention only to the electricity 
 acquired by the body, that was plunged into the mercury, 
 and not at all to that which is acquired by this metal. In 
 order to obtain this latter, he pours a little mercury into a 
 footed glass, and by means of an iron wire puts it in com- 
 munication with an electroscope ; he then plunges into the 
 mercury, by one of its extremities, the substance that he 
 desires to test, holding it between his fingers by its other 
 extremity. So long as the substance remains plunged in the 
 mercury, there is no electric sign, but signs are perceived 
 at the moment when we commence to withdraw it ; they 
 become more intense, in proportion as the part withdrawn 
 becomes more considerable; they are at their maximum at the 
 moment, when the body ceases to be in contact with the 
 mercury. The electricity, that is acquired by the mercury 
 is positive, when the substance that is immersed is of an 
 organic nature, such as paper, linen, wool, cloth, silk, 
 sarsnet, quills, and felt ; it is especially very powerful with 
 the last four substances. The mercury is in general negative, 
 when the immersed substances are mineral, such as rock- 
 crystal, sulphur, glass, &c. ; however, there are exceptions. 
 We may add, that amber and sealing-wax render mercury 
 very powerfully positive. Temperature modifies in some 
 bodies only, and not in all, the nature of the electricity with 
 which the mercury is charged. The precaution must be 
 taken in these experiments of well discharging the mercury 
 between two successive experiments^; for, without this, there 
 would be a risk of retaining electricity, probably on account 
 of the glass, which being covered exteriorly with a slight 
 coat of moisture, constitutes a veritable Ley den jar, of which 
 the mercury is the inner coating, and the moist film the 
 outer. 
 
CHAP. II. ELECTRICITY BY MECHANICAL ACTIONS. 623 
 
 In these experiments felt gives so great a quantity of 
 electricity to the mercury, that sparks may be drawn from it. 
 It is the same with feathers ; we have merely to take six or 
 seven between the fingers, and to plunge their feathered 
 ends into the mercury to the bottom of the vessel, in order 
 that the mercury may give a spark on their being withdrawn. 
 In like manner a considerable liberation of electricity is 
 obtained, by projecting against the side of the glass, the 
 bottom of which still retains mercury in communication 
 with the electroscope by means of an iron wire, a jet of 
 mercury, arising from a mass of mercury, contained in 
 another footed glass. The experiment succeeds better, when 
 the precaution is taken of previously heating the glass, in 
 order to drive off all the humidity. Furthermore, we may 
 prove the powerful liberation of electricity, that follows from 
 the friction of mercury against glass, by observing the light, 
 that is manifested at the top of a barometer, whose column 
 of mercury is made to move slightly, or in a closed glass 
 tube, deprived of air, which contains a little mercury, and 
 which is shaken, so as to make it traverse briskly the in- 
 terior of the tube from one end to the other. 
 
 We now come to the great liberation of electricity that 
 may be produced by the friction of water, against solid 
 bodies, a liberation, which serves as the basis of the hydro- 
 electric machine. The production of electricity by this 
 machine was discovered before the cause was known ; and it 
 was even attributed to a cause totally different from the true 
 one. It was Mr. Armstrong who first observed it in the 
 manufactory of Sighill, near Newcastle. A mechanic, having 
 one day accidentally placed one of his hands in the jet of steam 
 from a high-pressure boiler, whilst the other was occupied in 
 adjusting a weight on the lever of the valve, was very much 
 surprised to see a brilliant spark pass between the lever and 
 his hand ; and at the same time to feel in his arms a violent 
 shock. He obtained the same effect upon touching any part 
 of the boiler, or any piece of metal in communication with it, 
 Mr. Armstrong carefully analysed all these effects ; he proved 
 in this sudden expansion of steam, the production of a power- 
 
624 SOURCES OP ELECTRICITY. PART v. 
 
 fid positive electricity, with which the steam was charged ; 
 he did not at first find any negative electricity in the body 
 itself of the boiler, which was due to its not being insulated ; 
 for subsequently, on insulating it, he obtained decided signs. 
 Many other philosophers took up and varied Armstrong's 
 experiments ; but setting out as he did, from the principle 
 that the liberation of the electricity was due to the expansion 
 of the steam, an erroneous principle, as we are about to see, 
 they added nothing very important to the researches of the 
 first observer. M. Peltier alone took advantage of it to 
 make some curious experiments, which we shall describe 
 further on, upon the electricity that accompanies the vapour- 
 isation of water, saturated with different salts, thinking that 
 he saw in this, according to certain results described by 
 Armstrong, the course of the electricity, liberated with the 
 boilers. 
 
 It is to Mr. Faraday, that we are indebted for having 
 discovered and well established the nature of this cause, as 
 the result of an experimental analysis, remarkable, as are all 
 those which the illustrious philosopher has produced. His 
 apparatus consisted of a simple cylindrical boiler, insulated 
 upon three blocks of lac, and furnished with a jet 4^- in. in 
 length (Jig. 293.), which carried at its extremity a large stop- 
 
 Fig. 293. 
 
 cock, and a hollow metal sphere of a capacity of 32 cubic 
 inches. This sphere, called a steam-globe, was pierced with 
 another opening, to which were adapted the apparatus, of 
 various forms, intended to be employed for the escape of the 
 steam. These pieces were very small, in respect to the globe, 
 and to the tube by which it was put into communication 
 
CHAP. ir. ELECTRICITY BY MECHANICAL ACTIONS. 
 
 625 
 
 with the boiler ; so that the globe and the tube might be con- 
 sidered as forming part of the boiler, and the pieces themselves 
 might present to the escape of the steam a sufficient obstacle 
 to occasion a considerable friction. One of the pieces (Jig. 
 294.) consisted of a metal tube shaped into a funnel, and of a 
 
 Fig. 294. 
 
 Fig. 295. 
 
 cone, which a screw caused to advance more or less into the 
 funnel, so that the steam in escaping rubbed against the cone; 
 moreover, this cone might be insulated, or be placed in elec- 
 tric communication with the funnel and the boiler. Another 
 piece (Jig. 295.) consisted of a tube, furnished with a stop- 
 cock, and a feeding channel fixed above this tube, which 
 allowed of the introduction of any other liquid into the 
 current of steam, so that it was drawn on with it. Finally, 
 a last piece (fig. 296.) contained a small cylindrical chamber 
 
 c, intended to receive different 
 liquids, so that the steam, in 
 coining out of the steam-globe^ 
 should become mixed, on en- 
 tering into this chamber, more 
 
 Fig. 296. 
 
 or less with the liquid that was contained in it, and then 
 come and rub against the cone or any other piece, that 
 might be adapted to it. The experiments were all made 
 with steam, whose elastic force varied between -J- and -f of an 
 atmosphere, without ever having exceeded this latter pressure. 
 The electricity of the boiler was detected either by means of 
 a gold-leaf electroscope, or by means of a discharging electro- 
 meter. In order to observe the electricity of the steam, it 
 was necessary to make the latter pass through an insulated 
 
 VOL. II. S S 
 
626 SOURCES OF ELECTRICITY. PART v. 
 
 tube, furnished interiorly with diaphragms of metallic gauze, 
 or by placing in the course of the vapour wires or plates 
 of a conducting substance. In general it is the electricity 
 acquired by the boiler, that Mr. Faraday always collected. 
 
 First it is easy to prove that the electricity produced is 
 due neither to vaporisation nor to condensation. For this 
 purpose, we have merely suddenly to remove the valve, 
 when the steam is found under its highest tension, and no 
 electricity at all is produced, although the vaporisation is 
 considerable. We may in like manner demonstrate that the 
 issue of steam alone is not sufficient for developing electricity ; 
 but that the presence of water in a liquid state is necessary. 
 Thus so long as the steam-globe is empty of water, and is 
 able to collect that, which results from the condensation of 
 the steam, that arrives in it at the first moments of the 
 operation, the steam in escaping produces no electricity ; but 
 as soon as the globe is sufficiently filled for the rest of the 
 water, that condenses in it, to be drawn on by the steam, much 
 electricity is liberated. The electricity, therefore, is entirely 
 due to the friction of the particles of w r ater, which the steam 
 draws on, against the solid sides of the conduits or against 
 the obstacles, as the cones (fig. 294.), which are intentionally 
 opposed to it. Only it is necessary that it be pure ; it has 
 merely to contain in solution a proportion of a salt or of an 
 acid, which renders it a better conductor, in order that all 
 electrical effect shall disappear. This result is evidently due 
 to the fact that, when the water becomes a better conductor, 
 the two electricities liberated at the time of its friction 
 against the solid bodies, of which one remains in this body 
 and the other passes into the water itself, immediately recom- 
 bine. In order to prove this important fact, we have merely 
 to place in the steam-globe a small crystal of a salt, 
 such as sulphate of soda, or a small drop of sulphuric 
 acid, which mingles with the water that is drawn on by 
 the steam : there is no longer any liberation of electricity ; 
 and, after having removed these substances, as soon as 
 distilled water is replaced in the steam-globe, the liberation 
 recommences. 
 
CHAP. II. ELECTRICITY BY MECHANICAL ACTIONS. 627 
 
 Iii order to determine the influence of the substance 
 against which the water is rubbed, cones (Jig. 294.), of 
 various kinds, which can be insulated at pleasure, must be 
 employed. Cones of copper; boxwood, beech, ivory, sulphur, 
 caoutchouc, varnished leather, &c., have been successively 
 employed ; they all became negative, whilst the jet of steam 
 acquired positive electricity. A very great number of other 
 substances, taken in the state of wires or of simple fragments, 
 were held to the jet of steam by means of an insulator, and 
 placed, at the same time, in connection with a gold-leaf electro- 
 scope ; all were negative in different degrees, degrees due, 
 in great part probably to their conducting power, which 
 would more or less facilitate the recomposition of the two 
 electricities. 
 
 There are some substances, such as ivory, which develope 
 very little electricity by the friction of water ; also when the 
 steam is made to pass through an ivory tube, the boiler is 
 scarcely charged with electricity, and the current of steam is 
 no longer sensibly electrical. This proves, still better than all 
 the rest, that it is not vaporisation that produces the elec- 
 tricity. Moreover, this neutral jet serves for studying the 
 effects of substances in wires or fragments, that are placed 
 in it; and it is with a similar jet that we operated above. 
 
 Water, therefore, always acquires positive electricity in its 
 friction against solid bodies. It was interesting to investigate 
 the effect that would be produced by substances, other than 
 water, by causing their particles to be transported by a 
 current of steam. On making use of the apparatus (fig* 295.) 
 and filling the chamber, that surmounts the stop-cock, with 
 essence of turpentine, so as to be able to introduce it at plea- 
 sure into the passage of the steam, it is found, on allowing this 
 essence to penetrate, that the electricity of the boiler, which 
 was negative, when the vapour of water alone passed, becomes 
 immediately positive, as soon as the jet of vapour is able to 
 draw in particles of essence of turpentine ; and the jet it- 
 self, from having previously been positive, becomes negative. 
 On closing the stop-cock that gave issue to the essence, at the 
 end of a few instants, things returned to their normal state, 
 
 s s 2 
 
628 SOURCES OF ELECTRICITY. PART v. 
 
 because the steam soon drove away the particles of es- 
 sence that had remained, and which are no longer renewed. 
 The different species of oils and dissolved resins give the 
 same results. Some liquids, such particularly as naphtha, 
 give variable results, which are probably due to their being 
 able to adhere to the rubbed body, and thus to change its 
 nature ; whilst it is necessary that they should be carried on 
 by the current of steam. 
 
 It is very remarkable that, even in a very small quan- 
 tity, oil, essence of turpentine, and dissolved resin are able 
 to exchange the exciting power of water, which is due to the 
 globules of water being probably covered, by the effect of 
 the agitation of the mass, with a superficial film of these 
 substances, in the same manner as a drop of oil, placed upon 
 water, spreads immediately over the whole surface, forming 
 upon it a pellicle. But this facility of the globules of water 
 for thus covering themselves with an oily pellicle, depends 
 upon their purity. Thus the pellicle of oil is no longer able 
 to remain upon the surface of an alkaline water, which 
 dissolves it, whilst the pellicle of essence of turpentine 
 remains there. 
 
 After this study of the influence of steam, which had 
 showed to him that it exercises no effect by itself, but merely 
 because it is a mechanical agent, which draws along the 
 particles, by which the friction is exerted, Faraday under- 
 took some experiments upon compressed air, employing a 
 powerful copper vessel of a capacity of 46 cub. in., furnished 
 with two stop-cocks ; one serving for the entry of the air, 
 and the other for its escape. When the air had not been 
 dried, and it was allowed to escape suddenly against the cone 
 of copper or wood, it rendered this cone negative ; an effect 
 due evidently to the particles of water, condensed by the 
 cold, arising from the dilatation of the air. These particles, 
 moreover, were visible in the fog that appeared, and in the 
 moisture, that covered the surface of the wood and the metal. 
 But with air perfectly dry, no effect was obtained ; a proof 
 that neither air alone nor steam alone is capable of elec- 
 trising bodies by friction. 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 629 
 
 On adapting the apparatus (fig. 296.) to the reservoir in 
 which the air is condensed, we are able, by placing in the box 
 c these different substances, to prove the effect which they 
 produce on being drawn onward by the current of air ; it is 
 thus that sulphur in powder renders negative the cone of 
 metal, that of wood, and that of sulphur; that resin in 
 powder renders the cone of metal negative, but that of 
 wood positive ; that starch renders wood negative ; that 
 flint in very fine powder renders metal and wood powerfully 
 positive. It is very curious that sulphur and flint in powder 
 acquire contrary electrical states to those which these two 
 substances assume when they are in mass ; at least, when the 
 friction takes place by means of the strong impulse, that is 
 impressed upon them by the current of air that drags them 
 onward. However, it would be necessary to make many 
 experiments upon this subject, although it follows evidently 
 from the statement that we have been making, that there 
 is no electricity developed by friction, except so long as the 
 rubbed bodies are both solid, or one solid and and the other 
 liquid, and that the friction of gaseous particles against solids 
 does not liberate any electricity. 
 
 Before terminating this paragraph, let us add, that 
 Armstrong's discovery has given rise to the construction of 
 a very powerful electric machine, which has been termed 
 hydro-electric^ and of which it remains for us to give the 
 summary description. 
 
 This machine is composed of an insulated steam boiler 
 a (fig. 297.)j of a refrigerating box b, of three escape- tubes 
 c, and of a conductor d. 
 
 The boiler is about 32 in. in length and 15 in. in diameter ; 
 it has a fireplace within it ; / is the furnace door ; g, the 
 chimney ; it is generally heated with charcoal ; it is insulated 
 upon the four glass pillars v, which are themselves carried 
 upon a frame with wheels u ; s is the safely-valve ; r, the 
 cock to give escape to the steam, and to put the apparatus 
 in operation ; when it is opened the steam passes first into 
 the tube t, and thence is distributed into three small tubes, 
 which traverse in a right line the refrigerating box, and 
 
 s s 3 
 
630 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 arrive at the escape-jet, by which each of these tubes is 
 terminated. 
 
 Fig. 297. 
 
 The refrigerating box b, contains water at the ordinary 
 temperature ; but its level is not altogether high enough for 
 touching the steam tubes ; only wicks of cotton placed upon 
 these tubes, and plunging by their two extremities into the 
 water of the box are moistened by capillarity, and thus cool 
 to a certain extent both the tubes and the steam, to which 
 they give passage. The vapours, that are produced in the 
 box, escape into the chimney by the tube g. 
 
 The escape-jet is the essential piece ; on the construction 
 of this depends the electric power of the machine. After 
 various experiments Mr. Armstong decided upon the ar- 
 rangement, that is repre- 
 sented in (fig. 298.). Near 
 its extremity, the steam-tube 
 is enlarged into a cone ; and 
 into this cone is introduced 
 a piece, composed of the 
 
 Fig. sue. 
 
CUAP. ir. ELECTRICITY BY MECHANICAL ACTIONS. 631 
 
 truncated cone of partridge wood p, the little base of which 
 forms part with the metal piece m. The steam arriving 
 directly against the metal, is broken ; it is forced to gain the 
 cleft ; and there, being broken anew, in order to pass into the 
 orifice of suitable size, which is in the axis of the truncated 
 cone of partridge wood ; the screwed ring n merely serves to 
 hold the escape-jet firmly. 
 
 On traversing the box, b, the cooling has produced a few 
 fine drops of water, which are carried on by the steam ; and 
 it is the friction of these drops against the partridge-wood, 
 which developes the electricity, as has been demonstrated 
 to us by the analysis, that Mr. Faraday has made of these 
 phenomena. Thus the drops of water compose the rubbing 
 body, the sides of the jet the rubbed body, and the steam 
 is only the agent or motor, which brings about a rapid 
 friction. 
 
 The conductor d has the form that is represented in the 
 figure : it takes the electricity from the steam ; it is itself in- 
 sulated, and it is upon the ball k that the spark is seen to be 
 drawn. 
 
 Another escape-tube x y, is also seen, which is intended 
 for introducing various pulverulent substances into the path 
 of the steam, in order to study their influence upon the 
 nature and the quantity of the electricity produced, as Faraday 
 has done. 
 
 That which especially distinguishes hydro-electric machines 
 from ordinary machines is the great quantity of electricity 
 of high tension, which they produce. A little boiler, con- 
 taining only 2196 cub. in. of water, is able to give four or 
 five sparks of 5 or 6 in. in length per second. Large boilers 
 give results, four or five times more powerful. In certain 
 respects, these machines seem to unite the advantages of 
 ordinary machines of high tension, and those of voltaic appa- 
 ratus, the effects of which depend principally upon the 
 quantity of electricity developed at each instant. In opposi- 
 tion to these advantages, hydro-electric machines possess the 
 inconvenience of being inapplicable to daily use, since they 
 require, in order to give sure and energetic effects, particular 
 
 S 6 4 
 
632 SOURCES OF ELECTRICITY. PART v. 
 
 preparation and care. It is true, that atmospheric circum- 
 stances do not influence them to the same degree as they do 
 ordinary electrical machines ; on the contrary, the heat, that 
 emanates from the furnace and from the boiler renders the 
 glass supports very insulating; and, when charcoal deprived 
 of moisture is used as the fuel, even prevent the escape of 
 electricity by the current of heated air, arising from the 
 combustion. But, on the other hand, in order to raise the 
 steam to the requisite pressure of five or six atmospheres, the 
 heating is obliged to be maintained for several hours ; it is 
 necessary to remove all the impurities from the interior of the 
 apparatus, by causing it previously to heat a solution of 
 potash, which is allowed to escape through the tubes ; then 
 by washing it with very clean rain water. Moreover, it is 
 well to renew by a stroke of the file the internal condition 
 of the wooden tubes, the superficial texture of which is 
 softened and deteriorated by the hot steam. Finally, in 
 order to obtain powerful effects, it has been found advan- 
 tageous to maintain the boiler for several days in action, 
 changing and preparing it each day afresh. 
 
 Liberation of Electricity in the Friction of two good Conducting 
 
 Bodies. 
 
 The friction of two good conducting bodies is not able to 
 give rise to the liberation of electricity in a state of tension. 
 One of the bodies might in vain acquire by the friction 
 positive electricity, and the other negative, since no sign of 
 either of the two electricities would be perceptible. Indeed, 
 the two rubbed bodies can never be separated with sufficient 
 promptness from each other, without the immediate recom- 
 position of the two electric principles, accumulated separately 
 upon each of them, having previously taken place. In order 
 to make manifest the development of electricity, that ac- 
 companies the friction of two good conducting bodies, such as 
 two metals, it is necessary to employ the process devised by 
 M. Becquerel. To each end of a multiplier is soldered, by a 
 short wire, a plate of a different metal ; each end is passed 
 into a cork stopper, grooved so as to contain within it the 
 
CHAP. IT. ELECTRICITY BY MECHANICAL ACTIONS. 633 
 
 soldering and a part of the plate ; the latter is cemented into 
 the cork, by means of which it is held, so as not to be heated 
 by the contact of the hand ; and that, on passing simply one 
 of the plates upon the other, no effect is produced, on account 
 of the equality of temperature. But as soon as they are made 
 to slide slightly with friction one upon the other, each of 
 them acquires a contrary electricity ; the recomposition of 
 which, being able in part to be brought about by the inter- 
 vention of the wire of the multiplier, gives rise to an electric 
 current. The following is a Table of the different bodies, 
 classed in an order such, that each of them is negative in 
 respect to those which follow it, and positive in respect 
 to those which precede it.* Bismuth, palladium, platinum, 
 lead, tin, nickel, cobalt, copper, gold, silver, iridium, zinc, 
 iron, cadmium, arsenic, antimony, anthrar cite, peroxide of man* 
 ganese. We are immediately struck, on casting the eye upon 
 this Table, that the order of the metals is exactly the same 
 as that of their thermo-electric power; and yet it is easy 
 to prove that the elevation of temperature, that may result 
 from friction, is not the cause of the electricity that is liber- 
 ated. Indeed, if we employ two cylinders of 4 in. in length, 
 one of iron the other of copper, and rub them, so that the 
 same points of the former continually traverse the whole 
 surface of the latter, these points become more heated than 
 the latter surface ; and yet we obtain the same electric 
 current, with regard to direction or intensity, as in the 
 converse case, in which the surface of the former metal was 
 rubbed with the same points of the latter. Thus, the greater 
 or less amount of heat liberated does not exercise any in- 
 fluence over the phenomenon. The essential point for ob- 
 taining the greatest possible quantity of electricity is to sepa- 
 rate the rubbed parts as promptly as possible, still maintaining 
 the contact, so as to prevent the greater proportion of the two 
 electricities from recombining immediately, without passing 
 through the wire of the galvanometer. 
 
 * This manner of classing the metals indicates that the current produced 
 by two metals, such as bismuth and antimony, rubbed together, goes from the 
 one that is placed second in order (antimony) to the one that is first, through 
 the wire of the galvanometer, or from the first to the second, through their 
 point of contact. 
 
634 SOURCES OF ELECTRICITY. PART v. 
 
 M. Gaugain had thought he had found, in the almost 
 entire equality, that he has observed between the intensity 
 of the electricity, developed by friction, and that of the elec- 
 tricity developed under the same circumstances by an ele- 
 vation of temperature equal to that, which is brought about 
 by this friction, a proof that the electric current is due, 
 equally in both cases, to the heating, and that the friction 
 acts only indirectly in producing this heating. But, since it 
 has been well proved that heat does not itself act in the pro- 
 duction of thermo-electric currents, except by the molecular 
 changes that it brings about, it is much more natural to see 
 in friction a direct means of producing these changes. With 
 regard to the equality of effect observed by M. Gaugain, it 
 arises from the fact that electric currents, being due to the 
 arrangement and the relative nature of the particles of the 
 bodies in contact, their intensity must be the same, whatever 
 be the cause, that is acting upon these bodies, provided that 
 it acts with the same power, and that the bodies remain the 
 same. 
 
 The following is in addition another experiment of M. 
 Peltier's, which demonstrates that the slightest change in 
 the position of equilibrium of the particles of a closed 
 metallic circuit, is sufficient to produce a current, and con- 
 sequently to disturb the equilibrium of the electric forces. 
 A large circle is formed with an unannealed copper-wire, 
 placed in connection with a galvanometer multiplier of short 
 wire ; care is taken to sustain this circle at certain distances 
 by supports ; it is then placed alternately in the magnetic 
 meridian, in a plane perpendicular to this meridian, or in an 
 intermediate position, so that we may be able to take ac- 
 count of the inductive action of terrestrial magnetism. The 
 equilibrium of temperature being well established, one part 
 of the wire is raised or lowered ; flexions are then formed, 
 which cannot take place without a displacement of particles, 
 and consequently without there being an electric current. 
 It sometimes happens that there is no effect produced ; this 
 probably takes place, when there are developed two equal 
 currents, determined in contrary directions on each side of 
 
CHAP. II. ELECTRICITY BY MECHANICAL ACTIONS. 635 
 
 the strained point. When this circumstance is presented, some 
 portions on one side of the arc must be hardened, by means 
 of percussion and torsion, or rather they should be again an- 
 nealed. This cause of inequality is sufficient to give rise to 
 the current, by the simple flexion of the wire. The currents 
 cannot be attributed to terrestrial induction, since they are 
 manifested, whatever be the position of the circuit, in respect 
 to the magnetic meridian. With regard to the direction of 
 the current, it is due to differences in the molecular state, of 
 which it is impossible to take account. Moreover, we need 
 derange this molecular state of bodies so little, in order to 
 disturb their electric equilibrium, that we may obtain a 
 current of variable direction by simply rubbing the wire 
 against the fingers or with a piece of cloth ; we may also 
 excite it by drawing it through the draw-plate, after having 
 taken the precaution of placing its two ends in communication 
 with the wire of a galvanometer-multiplier. 
 
 More recently, Mr. Sullivan has also succeeded in ob- 
 taining a slight deviation of the needle of a multiplier, by 
 connecting the extremities of the wire of the instrument by 
 a wire formed of two consecutive pieces, the one of brass, 
 the other of iron, which he caused to vibrate, after having 
 strained it, so as to cause it to give out a musical sound. 
 The current ceased immediately with the vibration, a proof 
 that the heat, which might have been liberated during the 
 vibration, in no way concurred in the phenomena, since it 
 would not probably have disappeared instantaneously. With 
 a bar of antimony, soldered to a bar of bismuth, so as to 
 form in all a bar of 10 in. in length, by J- in. in width, and 
 ^ in. in thickness, the effect is decided ; for putting the bar 
 into a state of vibration, we have merely to strike it with a 
 piece of iron, a file for example. The amplitude of the 
 deviations, or the intensity of the current developed, appeared 
 to depend upon the manner, in which the vibrations are 
 propagated along the wire. It is not necessary that the bar 
 be composed of two metals of a different nature, in order to 
 obtain an electric current by vibration ; it is enough that its 
 texture be not homogeneous. Thus a sensible effect is 
 
636 SOURCES OF ELECTRICITY. PART v. 
 
 obtained with a bar of iron, of which one portion is of hard 
 and crystallised iron, and the other of soft and fibrous iron. 
 These results demonstrate, in an evident manner, the direct 
 influence of molecular movements upon the production of 
 electricity. 
 
 Finally, the experiments of M. Ermann show well the 
 relation, and arising from this, the independence, that exist 
 between friction and heat in the production of electric 
 currents. This philosopher has found, by combining different 
 groups of metal, so as to make of them thermo-electric pairs, 
 that a friction, exercised at their point of contact, produces 
 the same effect as an addition of heat applied to the same 
 point ; that is to say, it brings about a current, if the tempera- 
 ture of the point of contact is the same as that of the ambient 
 medium, and increases the intensity of the current already 
 existing, if this temperature is more elevated. This effect, 
 which Ermann calls tri bo- thermic, is similar neither to that 
 of the heat of conductibility, nor to that of radiant heat. Its 
 production, when friction commences, and its disappearance 
 when it ceases, are entirely independent of the duration of 
 the action, that gives rise to it. The German philosopher 
 seems to believe that these phenomena are due to a peculiar 
 species of molecular vibration, excited exclusively in the 
 points rubbed, and spreading in the conducting medium, 
 as instantaneously as electricity does. 
 
 Liberation of Electricity in Mechanical Actions, other than 
 
 Friction. 
 
 Friction is not the only mechanical action, that is a source 
 of electricity. Every cause, that brings about a molecular 
 movement in a solid body, produces it. Thus we have merely 
 to cut by a cutting body, to file, or to scrape different bodies, 
 such as gum-lac, sulphur, resin, wax, suet, chocolate, &c., in 
 order that the fragments, in falling upon an electroscope, may 
 charge it with electricity, and even give sparks ; and the 
 fragments detached are positive, Very slight differences 
 in the mode of disaggregation are sufficient to cause the 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 637 
 
 nature of the electricity to vary. Thus, with a knife not 
 sharpened, heated beech-wood gives positive fragments, and 
 it gives negative, when cold ; with a sharp knife, the frag- 
 ments are negative, equally in both cases. In like manner, 
 when we scrape sealing-wax with metal plates well-sharpened, 
 the detached parts are negative, whilst they are positive 
 when the cutter is dull. The number of facts in detail, 
 described by different experimentalists, upon this subject, is 
 so considerable, that we need merely state a few of them in 
 order to comprehend their importance, the more so as they 
 are not yet attached to any general law. We shall confine 
 ourselves, therefore, to insisting on the production of electri- 
 city in a very remarkable species of disaggregation, that 
 which takes place in the cleavage of crystals. It is to M. 
 Becquerel also that we are indebted, for the analysis of the 
 mode of the liberation of electricity. 
 
 When a plate of mica is cleaved rapidly in darkness, a 
 feeble phosphoric light is always perceived, the cause of 
 which has been a mystery, until the experiment had been 
 made of fixing an insulating rod to each of the opposite faces 
 of this plate, in order to be able to separate the two faces and 
 to present them to an electroscope. It is then found that each 
 of the separated faces possesses an excess of the contrary 
 electricity, the intensity of which is the greater, as the sepa- 
 ration has been more rapid. This phenomenon always taking 
 place, however thin the plate of mica may be, we may con- 
 clude from it, that it would be produced even to the limit, 
 namely, if it were possible to separate the two molecules from 
 each other. These facts prove two things : 
 
 1st. That the molecules possess at least two faces endowed 
 with different faculties ; for, without this, we do not see why 
 one of the plates gives one electricity and the other the con- 
 trary electricity; 2nd. That each of the faces manifests elec- 
 tric polarity, at the moment, when the force of aggregation 
 is destroyed. Chemical actions, as we shall prove, lead to 
 the same consequences. 
 
 Mica is not the only substance, that possesses the electric 
 property of cleavage ; we shall find it in the leafy talc of 
 
638 SOURCES OF ELECTRICITY. PART v. 
 
 St. Gothard, as well as in all crystalline substances, classed 
 amongst bad or middling conducting bodies. We may 
 therefore lay down as a principle that, whenever two mole- 
 cules in contact are separated, each of them carries away 
 an excess of contrary electricity, provided always that the 
 bodies, to which they belong, are not such good conductors, 
 that the recomposition of the two electricities, that have 
 become free, immediately follows their separation. 
 
 In order to succeed in these experiments, we must remove 
 from the crystals the film of hygrometric water, that generally 
 remains adhering to their surface, and must convey the 
 separated parts rapidly to the electroscope. 
 
 Two plates of mica, detached from the same crystal, being 
 brought to each other and slightly pressed until they are 
 made to adhere, come from the compression, each with the 
 electric state, which it possessed at the instant of cleavage. 
 The effect is particularly marked, when we slightly raise the 
 temperature of that plate, which possessed negative electri- 
 city, in coming from cleavage. 
 
 It is easy to explain now, why we are unable to collect 
 free electricity, when we bruise in an agate mortar crystals 
 of substances, that conduct electricity badly, for there is an 
 immediate recomposition of the two contrary electricities, 
 liberated on two contiguous laminse. It is for the same reason 
 that no electrical effect is obtained, when we break bodies 
 crystallised irregularly or formed of parts grouped con- 
 fusedly, as tubes of glass, rods of gum-lac, &c. &c. In like 
 manner, we perceive why no sign of free electricity is ob- 
 served in the cleavage of a crystal, that is a conductor of elec- 
 tricity, as galena, pyrites and others, seeing that the velocity 
 of the separation can never be sufficiently great to prevent 
 the recomposition of the two electricities, at the moment 
 when they are separated. In the absence of free electricity 
 we might prove the presence of this agent, by means of the 
 electrical effects of movement ; with this view, the crystal 
 ought to be placed in communication by two points with the 
 ends of the wire of a galvanometer. It is infinitely probable 
 that, on cleaving the crystal rapidly, the two electricities, 
 
CHAP. II. ELECTRICITY BY MECHANICAL ACTIONS. 639 
 
 arising from the destruction of the molecular attraction, 
 by following the wire in order to recombine, might produce a 
 current, that would react upon the magnetised needle. 
 
 The electric effects, that are obtained in the solidification 
 of melted bodies, are due, like the preceding, to a disaggrega- 
 tion ; namely, to the destruction of the molecular attraction 
 between two substances, whether homogeneous or heteroge- 
 neous. Thus, if we pour into a conical glass previously 
 heated, some sulphur in fusion, and plunge a glass tube into 
 it before it is cold, it is found after the solidification, when we 
 raise the cone of sulphur, that the glass vessel possesses an 
 excess of negative electricity and the sulphur an excess of 
 positive. Chocolate and phosphoric acid, after their solidifi- 
 cation in a glass, give out similar effects. M. Gay-Lussac has 
 remarked, that the adherence of bodies together first, and 
 then their separation by the inequality of their contraction, 
 as takes place between glass and sulphur, are conditions in- 
 dispensable, in order to obtain electricity after the fusion and 
 the solidification of a body. Thus metals, which do not 
 comply with these conditions, manifest no trace of it, after 
 their solidification in glass. M. Gay-Lussac concludes, from 
 these observations, and from some others also, that congelation, 
 or solidification, is in no degree, as had been supposed, a 
 source of electricity, but that it is merely a means of pro- 
 ducing, in certain cases, a molecular disaggregation, which is 
 itself the cause of the electricity liberated. 
 
 M. Boettiger has arrived at the same conclusion as Gay- 
 Lussac, by bringing to the state of fusion in a platinum crucible 
 double sulphate of copper and potash. He has not observed 
 the least trace of electricity during the act of crystallisation ; 
 but the crucible manifested signs of positive electricity, as 
 soon as the salt contracted with crackling, and detaching 
 itself from the metal. It follows from all these experiments, 
 that it requires a violent separation of the melted mass from 
 the sides of the vessel, that contains it, in order to there being 
 a liberation of electricity. 
 
 It is evident to the electricity that accompanies every 
 change in the relative position of particles, that the luminous 
 
64:0 SOURCES OF ELECTRICITY. PART v. 
 
 phenomena are due, which are manifested in the crystallisation 
 of certain bodies, and of which M. Henri Rose has made a 
 very particular study. Arsenious acid is the first substance, 
 upon which a phosphorescence has been observed, when it 
 passes from the vitreous into the opaque state in crystallising. 
 M. Rose has extended the observation to the sulphates of 
 potash and of soda, and to other salts also. But, he has re- 
 marked, that the light, which accompanies the crystallisation, 
 depends greatly upon the circumstances, under which this 
 crystallisation takes place, and in particular upon the medium 
 in which the salt is dissolved ; which, in fact, influences the 
 relative position of the particles. 
 
 The simple separation of the particles, such as takes place 
 in compressed elastic bodies, at the moment when the pressure 
 ceases, may also be accompanied by a development of elec- 
 tricity, without its being necessary that a disaggregation 
 should take place. Thus Libes was the first to observe, that 
 on laying upon a disc of wood covered with silk coated with 
 a layer of elastic resin, a disc of brass fixed to a glass handle 
 with the precaution of not allowing it to suffer any friction, 
 if the gummed silk is slightly pressed, the metal disc acquires 
 a very considerable excess of negative electricity ; the effects 
 are the reverse on pressing with friction ; discs of silver, 
 zinc, &c., have presented similar effects. This difference be- 
 tween the effects of pressure or those of friction is most 
 remarkable, and has not admitted hitherto of explanation, 
 except by supposing that the approximation of the particles 
 liberates the opposite electricity to that which is liberated 
 by their separation. 
 
 More recently, Haiiy found, that a crystal of Iceland spar, 
 and of some other mineral substances, enjoy the property of 
 becoming electric by the simple pressure of the fingers ; but 
 this property is not so limited as he thought : for, as M. Bec- 
 querel has proved, it belongs to all bodies, even to those that 
 are good conductors, provided they are insulated. In order 
 to put the fact in evidence, small discs are formed of the 
 substances, that we desire to try, of a small fraction of an inch 
 in thickness, which are fitted to handles, that are perfectly 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 641 
 
 insulating ; one handle is taken in each hand, and the discs 
 are pressed against each other ; after having withdrawn them 
 from contact, they are presented to the tinsel disc of Cou- 
 lomb's electroscope, previously electrised ; it is then found 
 that the two bodies possess a contrary electricity, provided 
 however that the body is a bad conductor ; cork and caou- 
 tchouc pressed against each other gives, the former positive, 
 the latter negative, electricity. 
 
 Crystallised mineral substances, having a vitreous aspect, 
 such as sulphate of lime, fluate of lime, sulphate of baryta, 
 acquire positive electricity, when pressed with the disc of cork. 
 Fruits, such as the orange, pressed by a disc of the same 
 nature, communicate to it on the contrary an excess of positive 
 electricity ; in proportion as the fruit is dried and loses its 
 electricity, the faculty of electrising is diminished. Many 
 causes tend to modify the liberation of electricity by pressure ; 
 the first is the greater or less conductibility of the bodies. 
 If, for example, we employ a disc of elder- pith, and a disc of 
 metal, no effect is produced ; and it is the same at all times, 
 when the pressed substances are conductors of electricity. 
 It appears that, at the moment when the pressure is exerted, 
 there is formed a new state of equilibrium between the two 
 electricities, which compose the natural electricity of the 
 molecules in contact ; so long as the pressure lasts, these two 
 electricities are disguised one by the other; thus, notwith- 
 standing their reciprocal attraction, and their tendency to 
 pass from one body into the other, there is found in pressure 
 a force, that neutralises these two actions. When the bodies 
 are good conductors, from the moment that a diminution of 
 pressure takes place, the two electricities recombine in- 
 stantaneously, whatever be the velocity of the separation ; 
 whilst, when one of the two is not a good conductor, a 
 diminution of pressure does not immediately bring about this 
 recomposition, which requires more or less time for its ac- 
 complishment, according to the degree of conductibility of 
 the two pressed bodies. The following experiment renders 
 evident the influence of the velocity of separation in the 
 electrical effects of pressure. Press a disc of cork upon an 
 
 VOL. II. T T 
 
642 SOURCES OF ELECTRICITY. PART v. 
 
 orange, and then withdraw it quickly, it carries with it a 
 very considerable excess of positive electricity ; but, if it is 
 withdrawn but slowly, this excess is found to go on diminish- 
 ing ; and if the velocity of separation is very slow, it becomes 
 scarcely sensible. 
 
 Heat modifies the phenomena of pressure. If we take a 
 very dry cork stopper, and cut it in half with a cutting 
 instrument, pressing the two separated parts against each 
 other, very commonly they each acquire an excess of contrary 
 electricity ; but it also frequently happens that they are not 
 electrised. If the temperature of one of the two discs is 
 raised a few degrees, that of the other remaining constant, 
 it is found that the heated part takes from the other negative 
 electricity. Two pieces of Iceland spar, at the same tem- 
 perature, are not electrised by pressure; but a very slight 
 difference of temperature suffices to give them this faculty. 
 At equal temperatures, the two discs of cork owe their 
 electric faculties of pressure only to a difference in the state 
 of their surface; the one, that possesses the most asperities, 
 always acquires negative electricity from the other. The 
 state of surfaces in badly conducting bodies, also influence 
 their conducting quality ; for Iceland spar, which is ranged 
 amongst the worst conducting bodies (since it preserves for 
 several entire weeks the electricity, that has been communi- 
 cated to it), becomes a sufficiently good conductor, when its 
 polish has been removed, for its being necessary to insulate 
 it, if we desire it to preserve its electricity. The asperities, 
 therefore, not only determine the electricity that a badly 
 conducting body must acquire ; but they modify also its 
 electric conductibility. 
 
 In order to measure the electric effects of pressure, we 
 require an apparatus, that enables us to vary at pleasure the 
 causes that influence their production. Experiments prove 
 that the intensities increase proportionately to the pressures, 
 for pressures that do not exceed 22 Ibs. Does this law ex- 
 tend to higher pressures ? It is a difficult matter to reply to 
 this question. We have seen that M. Peclet had under- 
 taken certain researches in this respect, with a view parti- 
 
CHAP, ii, ELECTRICITY BY MECHANICAL ACTIONS. 643 
 
 cularly of determining the influence of pressure, of velocity, 
 &c., on the liberation of electricity in friction; but the 
 results that he obtained, can in no way be applied to the 
 present case. M. Becquerel thinks that it is possible, that 
 the quantity of electricity which each body acquires, whilst 
 it is compressed, is dependent on the degree of attraction, 
 that the molecules of the surfaces exercise over each 
 other ; but as we are not able to appreciate the relations, 
 existing between attraction and pressure, or the greater or 
 less approximation of the molecules it is impossible to de- 
 termine the relations between the corresponding quantities 
 of electricity. The difficulty of separating instantaneously 
 the two compressed bodies, without passing through suc- 
 cessive intermediate pressure, renders the determination, so 
 to speak, impossible, of the relations in question. 
 
 One might perhaps be led to believe that the heat, liberated 
 in pressure, is the cause of the development of the electricity ; 
 the following experiment, due to M. Becquerel, proves the 
 contrary, at the same time that it shows the influence of the 
 approximation of tlie molecules, in order to increase the liber- 
 ation of electricity, when we come to separate the bodies. 
 Two bodies being found under the action of a certain pres- 
 sure, if we wish to diminish the latter one-half, the effect of 
 the pressure lost subsists for a time, the duration of which 
 depends upon the degree of conductibility ; so that, if we im- 
 mediately withdraw these bodies from compression, each of 
 the two carries with it an excess of contrary electricity, 
 greater than that which is due to the pressure remaining. 
 Now, instead of separating the bodies, when the pressure has 
 been diminished, we restore that which had been taken away, 
 and repeat this mode of action several times. A plate of 
 Iceland spar and a very thin disc of cork, have given, for 
 example, the following results. These two bodies being at 
 first under the pressure of 8f Ibs., the latter was reduced 
 one-half, without deranging the contact; and one minute 
 after they were separated ; the electric tension of each disc 
 was represented by 170: if the separation had taken place 
 during the pressure of 8 f- Ibs., the tension would have been 
 
 T T 2 
 
644 SOURCES OF ELECTRICITY. PART v. 
 
 250; and during the pressure of 4-f- Ibs. 125, the half of the 
 preceding : it is seen therefore that, in the first case, the 
 effect produced by the pressure, that has been lost, still sub- 
 sists in part. Instead of separating the bodies, when the 
 pressure has been reduced from 8-f- to 4-| Ibs., we restore to 
 it the pressure that has been taken away, and repeat several 
 times this alternate play of simple pressure and double pres- 
 sure. We find, finally, that the cork disc never possesses 
 more than the intensity 250, corresponding to the strongest 
 pressure. 
 
 Among molecular actions, there is one that M. Becquerel 
 had thought to be a source of electricity; it is capillary 
 action : but he recognised that the electricity, liberated in 
 capillary phenomena, might be due to numerous effects, that 
 accompany the production of these phenomena, such as the 
 friction of the liquids against the sides of the capillary spaces ; 
 to the chemical action that takes place in certain cases, such 
 as that, in which an electric current is obtained, by the pene- 
 tration of an acid into the pores of spongy platinum, &c. 
 
 To sum up, we are able to establish as a rigorous prin- 
 ciple demonstrated by experiment, that not only friction, 
 but that every mechanical action which disturbs molecular 
 equilibrium, by deranging from their natural positions the 
 particles of a body, becomes a cause of the production of 
 electricity ; electricity, the manifestation of which is more 
 or less sensible, according to the various conditions under 
 which the bodies subjected to these mechanical actions are 
 found. 
 
 General Considerations on the Liberation of Electricity by Me- 
 chanical Actions ; and on its Relations with the Liberation of 
 Heat. 
 
 We have established in the paragraphs that precede the 
 general principle, that every disturbance impressed upon a 
 body, from which arises a derangement in the state of its 
 molecular equilibrium, is accompanied by a production of 
 electricity, which is manifested more or less easily, according 
 
CHAP. II. ELECTRICITY BY MECHANICAL ACTIONS. 645 
 
 to the conditions of conductibility, and of the physical consti- 
 tution of the bodies disturbed. We have related the expe- 
 riments of various philosophers, which show the great ana- 
 logy that exists between mechanical actions and the action of 
 heat, in the development of electricity ; and which lead us 
 to recognise, that the circumstance, which determines the 
 nature, as well as the intensity of the electricity, is much 
 more the body submitted to the action, than the action itself. 
 This then is one motive more for admitting that the parti- 
 cles are, as we have already frequently said, endowed with 
 an electric polarity, which in the natural state is disguised 
 by the equilibrium, that is established between the equal 
 and contrary polarities of all the particles of a same body. 
 Mechanical action, like heat, comes and disturbs this equi- 
 librium, either by changing the relative position of the par- 
 ticles, or else by destroying the uniformity of their natural 
 movements of rotation; conditions, both of them necessary 
 for equilibrium. Mechanical action does more ; by disag- 
 gregating in certain cases the particles, it insulates them, 
 and then it allows of the manifestation of their electric pola- 
 rity ; this is especially sensible in crystallised substances, 
 in which the poles have a similar position on the same face 
 of cleavage. On this account it is that, when a plate of 
 mica is cleaved, we liberate on one of the faces the positive 
 electricity of all the particles of this face ; and on the other, 
 consequently, the negative electricity of all its particles 
 equally. 
 
 The production of an electric current, such as Peltier has 
 obtained, by imparting a movement of vibration to a portion 
 of a conductor, forming part of a closed circuit, can only be 
 explained, by admitting that this vibrating action allows of 
 the particles, that are subjected to it, to arrange themselves, 
 according to their polarity, a similar effect to that, which 
 would be produced by the passage of an artificial current ; 
 and to give rise to a current, by the mere fact of this ar- 
 rangement. This polarity, moreover, has been rendered evi- 
 dent, in an altogether remarkable manner, by M. Volpicelli. 
 The manner of operating of the learned Italian consists in 
 
 T T 3 
 
646 SOURCES OF ELECTRICITY. PART v. 
 
 bringing about in a metal rod a vibration, that is communi- 
 cated to an insulating resinous stratum, with which one of 
 the extremities of this rod is covered. It is by causing to 
 slide, sometimes in one direction, sometimes in a contrary 
 direction, against an insulated metal ring, the metal rod, 
 in the part not covered by an insulating stratum, that 
 vibrations are produced in it, in order to be propagated from 
 it into the resinous stratum. It is observed that, when the 
 portion, covered with this stratum, is that, which is in ad- 
 vance, in the progressive movements, impressed upon the 
 rod, it is with negative electricity, that the metal part of this 
 latter is charged; a proof that this electricity is also that 
 which the interior surface of the insulating stratum acquires. 
 When the movement takes plate in the other direction, 
 positive electricity takes the place of negative. In each of 
 the two cases, we may be sure, that the exterior surface 
 of the insulating stratum acquires a contrary electricity to 
 that, with which the interior surface is charged. For 
 proving this, we have merely to cover the stratum with a 
 small metal ring, which is thus insulated from the rod, with 
 which it has no metallic communication. A very fine wire 
 insulated in the air, establishes communication between this 
 ring and an electroscope ; in like manner, communication is 
 established between the electroscope and the metal part of 
 the rod. When we desire to collect the electricity of the 
 exterior surface of the insulating stratum, it is preferable 
 to make the metal rod the support, that carries the ring, 
 against which it rubs, communicate with the ground. 
 
 We may equally cover both extremities of the rod with an 
 insulating stratum, and cause it to slide by holding it in the 
 hand in a portion of its length, where the metal surface is 
 exposed. We observe that, in each excursion of the rod, 
 the electricity of the external surface of the insulating 
 stratum is negative at the extremity that is in advance 
 in the movement imparted, and positive at the extremity, 
 that is in arrear. This experiment demonstrates well, that 
 the direction according to which the longitudinal vibration 
 that is impressed upon the rod is propagated, influences the 
 
CHAP. ii. ELECTRICITY BY MECHANICAL ACTIONS. 647 
 
 polarity, that is manifested by the molecules of the insulating 
 substance, to which this vibration is communicated. 
 
 Certain experiments, made with rods of various metals, 
 seem to establish differences between them in regard to their 
 faculty of developing, by the transmission of the vibrations, 
 which they suffer, polarity under the insulating stratum. 
 Iron and steel are in this respect very inferior to brass and 
 silver. It is likewise disadvantageous that the metal ring, 
 upon which the rod slides, should present roughness ; it is 
 necessary that the two surfaces, rubbed against each other, 
 should be well polished. A dry and cold atmosphere greatly 
 contributes to the success of the experiments. All possible 
 precautions must be taken that no electricity shall be liberated 
 in the contact of the hands and the insulating strata. Care 
 must also be taken before operating, to remove the thin film 
 of moisture, which almost always covers the insulating 
 substance. 
 
 M. Volpicelli has also found that, on substituting at the 
 extremities of the metal rod a stratum of sulphur for the 
 stratum of resin, the same results are obtained. If we 
 cover the extremities of the rod with tubes of glass, effects 
 are also obtained, similar to those which are produced by 
 rods all of glass ; that is to say, a polarity the inverse 
 of that, which is manifested by resin and sulphur. Finally, 
 when a rod entirely of resin or sulphur is employed, it is 
 remarked that if, on passing upon the ring, by which it is 
 rubbed, it abandons a small portion of its substance, which 
 very often happens, especially in hot weather, a polarity 
 is always developed, but which is overthrown ; it again 
 becomes what it had been previously, if the support is 
 changed. It is very curious, in this case, to see the polarity 
 gradually reduced, become null, and then change its nature. 
 This peculiar phenomenon is never presented with rods of 
 glass, which indeed cannot be disaggregated. An important 
 fact is, that the experiments of M. Volpicelli succeed as well 
 and even better in vacuo than in air, proof that the elec- 
 tricity of the air is not regarded. 
 
 It is very remarkable that the polarity is developed in a 
 
 T T 4 
 
648 SOURCES OF ELECTRICITY. PART v. 
 
 much more decided manner in rods of glass than in those of 
 resin and sulphur, which in fact do not vibrate nearly so 
 well as the former. Let us finally add that, on covering 
 with various substances the support, upon which the friction 
 of the rod is brought about, we in no degree alter the di- 
 rection of the polarity which depends entirely upon the di- 
 rection in which the excursion of the rod takes place. This 
 is a proof that the phenomenon is actually the result of a 
 longitudinal vibration, impressed upon the rod and not of 
 the friction, that it undergoes, in passing upon the support. 
 
 It would, therefore, seem to result, from the researches of 
 M. Volpicelli, that the vibration impressed upon an insulating 
 substance, by the intervention of a vibrating rod, would 
 permit the molecules of this substance so to arrange them- 
 selves, as to constitute a polar chain, perpendicular to the 
 thickness of the stratum, and presenting consequently at its 
 two extremities contrary electricities. The direction of the 
 vibration would influence the direction in which the poles 
 of each of the particles would be turned. A mechanical 
 action would therefore produce here an effect altogether 
 analogous to a caloric action. 
 
 Thus we see heat and mechanical actions, capable of deter- 
 mining in bodies an identical electric state, which surprises us 
 less, since philosophers, as we have already remarked, have 
 been led by facts of quite another order to what has been 
 called the mechanical theory of heat. But previously to this 
 Becquerel had pointed out the analogy, that exists between 
 the effects of heat and the electric effects, produced by 
 friction. In studying them comparatively, he had succeeded 
 in demonstrating that, when bodies are of the same nature, 
 but bad conductors of heat, and differ from each other only in 
 the state of their surface, the surface that is heated most 
 acquires negative electricity, and that which is heated least, 
 positive. This important principle will serve us further on, 
 concurrently with others, to which we shall be led by 
 the study of chemical action, considered as a source of elec- 
 tricity, to establish certain differences between the properties 
 
CHAP. IT. ELECTRICITY BY MECHANICAL ACTIONS. 649 
 
 and action of the positive pole, and those of the negative pole 
 of each particle. For if, the intensities being equal, there did 
 not exist in the exterior power of one of the poles, compared 
 with that of the other, a certain difference, there are a great 
 number of facts in electro-chemical phenomena, that would 
 be inexplicable; which we shall show in endeavouring to 
 establish directly the proofs of this difference, after having 
 completed the study of the artificial sources of electricity.* 
 
 * List of the principal works, relating to the subjects treated upon, in this 
 Chapter : 
 
 Biot. Friction of imperfect conductors. Traite de Phys. experimentale et 
 mathematique, t. ii. p. 354. 
 
 Heintz. Peculiar electric state of glass. Ann. de I Elect, t. iii. p. 551., and 
 Ann. de Chim. t. lix. p. 305. 
 
 Loevel. Properties of glass. Ann. de Chim. et de Phys. t. xxix. p. 110. 
 Hatiy. Electricity by the friction of minerals. Ann. de Chim. et de Phys. 
 t. viii. p. 383. Electricity by pressure. Idem. t. v. p. 95. 
 
 De la Rive. Electricity by the friction of metals. Bibl. Univ. t. lix. p. 13. 
 Peclet. Influence of chemical action null in electricity by friction. Ann. 
 de Chim. et de Phys. t. Ixxi. p. 83. Laws of electricity by friction. Idem. 
 t.lvii.p 337. 
 
 Schoenbein. Electric paper. Arch, des Sc. phys. t. ii. p. 156. 
 Becquerel. Electricity by the friction of metals either in mass or in 
 powder. Ann. de Chim. et de Phys. t. xxxviii. p. 113. Electricity by 
 the pressure and the cleavage of crystals. Idem. t. xxii. p. 5. ; t. xxxvi. 
 p. 265. Electricity produced by capillary actions. Idem. t. xxiv. p. 337. 
 Comparison between the electricity and the heat liberated by friction. Idem. 
 t. Ixx. p. 324. 
 
 Colladon. Mechanical effects in wire-drawing, and of the electricity liber- 
 ated by friction. Bibl Univ. (1836) t. i. p. 362. 
 
 Dessaigne. Electricity by immersion in mercury. Ann. de Ch. et de Phys. 
 t. ii. p. 59. 
 
 Perego. Idem. Arch, de T Elect, t. ii p. 395. 
 
 Armstrong. Liberation of electricity by the expansion of steam. Arch, de 
 VElect. t. i. p. 145. 
 
 Peltier. Electricity of steam at high pressure. Idem. t. i. p. 474. 
 Faraday. Electricity liberated by the friction of water, and other liquids 
 and powders. Idem. t. iii. p. 369. ; and Ann. de Chim. etdePhys. (new series) 
 t. x. p. 88. 
 
 Gaugain. Electricity developed by the friction of two metals. Comptes 
 rendus de FAcad. des Sc. de Paris, t. xxxvi. p. 541. ; and Arch, des Sc. phys. 
 t. xxii. p. 381. 
 
 Peltier Current produced in a conducting wire, by a molecular derange- 
 ment. Ann. de Chim. et de Phys. t. Ix. p. 261. 
 
 Sullivan. Currents produced by the vibration of metals. Arch, de T Elect. 
 t. x. p. 480. 
 
 Ermann. Influence of friction upon thermo-electric effects. Arch, de 
 f Elect, t. v. p. 477. 
 
 H.Rose. Light that accompanies crystallisation. Ann. de Pogg. t. Iii. 
 p. 443. 
 
650 SOURCES OF ELECTRICITY. PART v. 
 
 Gay-Lussac. Electricity produced by the separation of adhering bodies. 
 Ann. de Chim. et de Phys. t. viii. p. 161. 
 
 Volpicelli. Electrostatic polarity. Comptes rendus de VAcad. des Sc. de 
 Paris, t. xxxviii. (May 15. 1854); Arch, des Sc. phys. et natur. (Bibl. Univ.) 
 t. xxviiL p 265. 
 
 Riess. Various details on electricity by friction. TraitedeVElcctricite par 
 Frottement, t. ii. p. 362. and following pages. 
 
 Priestley. Relation of old experiments on electricity by friction. History 
 of Electricity, 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 651 
 
 CHAP. III. 
 ELECTRICITY PRODUCED BY CHEMICAL ACTIONS. 
 
 Production of Electricity by the Chemical Action of Liquids 
 upon Solids ; Voltaic Pair and Pile. 
 
 EVERY chemical action is accompanied by a disturbance in 
 the state of equilibrium of the molecules of a body, and 
 must, consequently, be a cause of the liberation of electricity ; 
 it is even the most powerful of all, although it does not 
 always seem to be so. This is due to the facility, with which 
 the two electricities tend for the most part to recompose im- 
 mediately. Thus it is necessary, in this mode of production, 
 to distinguish, as in the others, the electricity produced from 
 the electricity collected. 
 
 Lavoisier and Laplace had long ago endeavoured, with the 
 aid of a condenser, to obtain signs of the electricity of tension, 
 by the action upon zinc of diluted sulphuric acid ; more re- 
 cently Fabroni, Wollaston, and Parrot had attributed to the 
 chemical actions that liquids exercise upon metals, the pro- 
 duction of the electricity in the voltaic pile ; but it is only 
 since the discovery of the galvanometer-multiplier, that we 
 have succeeded in proving, by direct and conclusive experi- 
 ments, that every chemical action gives rise to an electric 
 current. It was in 1823 that GErsted remarked, that if to the 
 extremities of a galvanometer are fixed two pieces of the 
 same metal, such as two plates of zinc, and they are plunged 
 one after the other into a diluted acid, a deviation of the 
 needle is observed, which indicates the production of an elec- 
 tric current. Becquerel found subsequently that a current 
 is in like manner determined, by plunging into an acid or 
 alkaline solution, the two ends of the copper wire of a galva- 
 nometer ; but, in order that the 'current may take place, it is 
 necessary that the liquid exercise a chemical action over the 
 
652 SOURCES OF ELECTRICITY. PART v. 
 
 immersed part of the wire. The same philosopher observed 
 moreover that the direction of the current appeared to 
 depend upon the one of the two ends of this wire, that was 
 most sharply attacked ; and that thus, it was from the one, 
 that was last plunged in, which had the most points of contact 
 with the liquid, that the current or positive electricity set 
 out, in order to go into the liquid to traverse it ; then to 
 come to the other end, and to return to the first, by traversing 
 the wire of the instrument. Yelin, at about the same period, 
 published a series of experiments, made upon a great number 
 of metals, from which it followed that, in plunging two pieces 
 of the same metal into various acid and alkaline liquids, 
 currents were observed, whose direction and intensity 
 appeared to depend upon that of the pieces, that had been 
 first immersed, and upon the relative nature of the liquid 
 and the metal. 
 
 A great number of philosophers soon came, and added 
 numerous proofs, either direct or indirect, to those which 
 we have been indicating, in order to demonstrate, in a 
 peremptory manner, that every chemical action gives rise to 
 electricity, which is manifested either in the static state or 
 that of tension, or in the dynamic state or that of current. 
 
 In order to establish some order in the study, that we are 
 about to make of this electric source, we shall examine the 
 liberation of electricity, to which it gives rise, by taking 
 successively the various forms, under which chemical action 
 may occur. This action may be that of a liquid upon a 
 solid, that of two solutions upon each other, that of gases 
 acting upon solids or liquids, under certain conditions ; to 
 these three forms, we shall add that, which constitutes the 
 phenomenon of combustion, which we shall study separately, 
 on account of the particular character, that is peculiar to it. 
 We shall commence by the form, that we have first pointed 
 out ; namely, the action of a liquid upon a solid ; this will be 
 the subject of the present paragraph. This mode of the 
 production of electricity is the most remarkable of all, both 
 in itself, and because it is the cause of the electric power of 
 the voltaic pile. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 653 
 
 But before endeavouring to enter upon the study, it is 
 necessary to indicate a serious difficulty, that it presents. It 
 had long been admitted, and many philosophers still admit, 
 that the contact of two solid and heterogeneous conducting 
 bodies is a source of electricity ; one of the bodies, by the 
 mere fact of their contact being put into a positive state, and 
 the other into a negative. Now, as in order to collect the 
 electricity produced in chemical action, it is most frequently 
 necessary to place in contact two solid conductors of different 
 natures, they have wished to attribute to this contact, and 
 not to chemical action, the production of electricity. How- 
 ever, we shall show that, in this case, it is chemical action, 
 that is the veritable source of the electricity ; and that 
 contact is merely a condition, most frequently necessary, but 
 not always indispensable to the manifestation of the electric 
 signs, which it is of itself incapable of developing ; for we 
 shall see that this manifestation is able to take place by the 
 effect of the chemical action alone without contact. Finally, 
 we shall devote a paragraph of this Chapter to the more 
 special study of all the facts, that have been alleged in 
 favour of the contact theory, we shall endeavour to demon- 
 strate, that they are easy of explanation without its being 
 necessary to admit this theory, but that they are a conse- 
 quence of the various modes of action, that produce electri- 
 city; we shall in this same Chapter, examine the various 
 electro-chemical theories, explaining that, which appears to 
 us best in accordance with the phenomena, in the actual 
 state of the science. Let us now come to the object itself 
 of this paragraph. 
 
 In order to analyse well the electric effects, that result 
 from the chemical action of liquids upon solid bodies, we 
 must commence by operating with the condensing electroscope. 
 M. Becquerel, who was the first to make experiments in 
 this manner, placed upon the plate of a condenser a metal 
 capsule filled with a liquid ; he then plunged into this liquid 
 the extremity of a metal plate, the other end of which he 
 held between his fingers. According to the relative nature 
 of the two metals and of the liquid, interposed between them, 
 
654 SOURCES OP ELECTRICITY. PART v. 
 
 he found upon the plate of the condenser, sometimes positive, 
 sometimes negative electricity. If the capsule was of pla- 
 tinum, whatever was the nature of the liquid and that of 
 the metal, held between the fingers, the electroscope always 
 indicated that the capsule had acquired positive electricity. 
 With a capsule of copper, the signs were sometimes positive, 
 sometimes negative, according as the metal, plunged into the 
 liquid, was more or less attacked by this liquid itself. It 
 was the same with a capsule of wood, filled with water, 
 and in immediate contact with the upper plate of the con- 
 denser ; the water, the capsule and consequently the plate 
 acquired positive electricity when there is plunged in a 
 plate more oxidisable than the brass of the condenser ; the 
 plate acquired negative electricity with plates less oxidisable 
 than itself. All these results are very well explained, by 
 setting out from the principle that, when a liquid attacks a 
 metal, the liquid is charged with positive and the metal 
 with negative electricity. When the experiments are made 
 with the platinum capsule, there is chemical action only 
 upon the plate of metal, that is plunged into the liquid, 
 if at least the latter exercises no action upon the platinum ; 
 the liquid is thus charged with positive electricity, which 
 spreads itself into the platinum, and thence upon the plate of 
 the condenser, whilst the negative electricity comes out by 
 the fingers, with which the metal is held. If the capsule, 
 instead of being of platinum, is made of a metal attackable 
 by the liquid, there are then two actions ; that of the liquid 
 upon the metal of the capsule, and that of the same liquid 
 upon the metal plate, that is plunged into it. In virtue of 
 the former action, the capsule is charged with negative elec- 
 tricity and the positive is dispersed into the liquid, whence it 
 tends to come out by the metal plate, which communicates by 
 means of the fingers with the ground ; by virtue of the latter, 
 this plate acquires negative electricity, which goes from it 
 into the ground, whilst the positive electricity is dispersed 
 into the liquid, and passes hence into the capsule, in order to 
 affect the condenser. In virtue of this double action, the 
 latter ought to receive at the same time negative and posi- 
 tive electricity, and according as these two electricities have 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 655 
 
 an equal or a different intensity, it gives electric signs either 
 null, negative, or positive. The first case is realised, when 
 the plate plunged in is of the same nature as the capsule ; the 
 second, when the metal of the capsule is more attacked than 
 that of the plate ; and the third, when it is the metal of the 
 plate, that is more attacked than that of the capsule. 
 
 In order to avoid attributing the effects obtained, either in 
 whole or in part, to the contact of the capsule with the plate 
 of the condenser, it is necessary that the latter should be of 
 the same metal as the capsule; of platinum if the latter is of 
 platinum, of copper if it is of copper, of zinc if it is of zinc. 
 The phenomena transpire exactly in the same manner. More- 
 over, in all these experiments we may employ a condenser, 
 the plate of which is of copper, carefully gilded, or of very 
 smooth glass, covered with a thin film of gold. We then 
 employ a platinum capsule, in order to place in it the liquid, 
 so that, still being insulated, we can place it in metallic com- 
 munication* with one of the plates of the condenser, after 
 having been satisfied that no electricity is developed in its 
 contact with the plate. Then the various metallic plates, 
 attackable by this liquid, are plunged successively into it, 
 holding them by the fingers. 
 
 We shall quote also an experiment of Matteucci's, who 
 demonstrates, in the most direct manner, the liberation of 
 electricity, that accompanies the chemical action of a liquid 
 upon a metal, in a case in which there is no possibility of 
 causing an effect, due to the contact of two different metals, 
 to intervene. To one of the plates of a condenser of copper 
 is united by means of a wire, also of copper, a large plate of 
 this metal, which is made to descend and to plunge into the 
 water of a well, sustaining it with a silken cord ; the other 
 plate of the condenser communicates with the ground. After 
 a few moments of contact, the condenser is found charged 
 with negative electricity. If a small quantity of sulphuric 
 or hydrochloric acid is poured into the water of the well, the 
 electric signs are still more decided. When the plate, instead 
 
 * For this purpose we employ a rod of platinum, or of gilded brass, held by 
 an insulating handle. 
 
656 SOURCES OF ELECTRICITY. PART v. 
 
 of being plunged into the water of the well, is placed in 
 the liquid of a large well insulated receiver, there are no 
 longer any signs of tension, providing that no communication 
 is made by the hand, or any conducting body between the 
 water of the receiver and the ground. What M. Matteucci 
 did with copper, may be done with all the other metals, 
 taking care that the plate plunged into the water, the wire 
 that touches the plate of the condenser, and this plate itself, 
 shall be of the same metal. But electric signs are obtained, 
 only so long as the metal plate is susceptible of being attacked 
 chemically by the liquid in which it is plunged. 
 
 A German philosopher, M. Karsten, had already made, 
 before M. Matteucci, a great number of experiments, which 
 demonstrate the accuracy of the principles, that we have laid 
 down, although he has interpreted them differently, by seeing 
 in them the proof of a development of electricity in the 
 contact of solid and liquid bodies ; but the facts observed by 
 M. Karsten lead to a precisely contrary conclusion. He 
 operates with wires of zinc, of copper, of silver, and of platinum, 
 coiled into a helix at one of their extremities, which plunges 
 into an acid, alkaline or saline solution, and communicating 
 by the other with one of the plates of a condenser. If the 
 wire and the plate are of zinc, the latter is charged with 
 negative electricity. When two wires are plunged at the 
 same time into the liquid without touching, for example, a 
 wire of zinc and one of copper, the zinc wire, when put in 
 contact with the plate of the condenser, is charged with 
 negative electricity, and the copper wire with positive ; and 
 this, whatever the metal may be, of which the condenser is 
 made. It follows, as a matter of course, that the result is 
 the same, when a wire of silver or of platinum is substi- 
 tuted for the copper wire; but, if we place together in 
 the same liquid, always without touching, a wire of copper 
 and one of platinum, it is the copper that gives negative 
 electricity to the condenser, and the platinum positive. 
 All these results are perfectly in accordance with the funda- 
 mental principle, that we have established, namely, that in the 
 chemical action of a liquid upon a metal, the metal is charged 
 
CHAP in. ELECTRICITY BY CHEMICAL ACTIONS. 657 
 
 with negative electricity and the liquid with positive, which 
 is taken from the liquid by the less oxidisable metal, that 
 is plunged into it. We shall return, in our last paragraph, 
 to certain other experiments of M. Karsten's, which would 
 seem at first sight favourable to the opinion that contact also, 
 independently of chemical action, would be a source of elec- 
 tricity by itself. 
 
 The electric signs, that are obtained in the experiments, 
 that we have just related, are in general very feeble ; it re- 
 quires for their manifestation a very sensitive electroscope 
 and condenser. They have not the least relation in the world, 
 as far as intensity is concerned, to the vivacity of the chemical 
 action, that gives rise to them ; in such sort, that one of the 
 most energetic among these actions that of diluted sulphuric 
 acid upon zinc does not give a manifestation of electricity, 
 sensibly stronger than that which results from the simple 
 oxidation of zinc by water. This apparent anomaly is due 
 to a principle, that we have related at the commencement of 
 this Chapter, that of the immediate recomposition of the 
 two electricities, carried by the chemical action, one into the 
 metal, the other into the liquid. The metal and the liquid, 
 being both very good conductors, these two electricities tend 
 to reunite directly upon the surface, when their separation 
 has taken place*, instead of going, one to escape to the 
 ground and the other to act upon the condenser. There is 
 a very feeble proportion, which escapes from this immediate 
 neutralisation, and it is this, which is detected by the in- 
 struments. It is therefore necessary to take great care to 
 distinguish, in the production of electricity by chemical 
 actions, as we have done for other sources, the electricity 
 collected, from that produced. Thus, for example, it is to 
 the circumstance that the immediate recomposition is much 
 less easy, that we must attribute this fact, that the che- 
 mical action, which results upon zinc from the simple moisture 
 
 * We shall see further on, that it is not at the same points of this surface, 
 where the liberation of electricity is made, that the recomposition is brought 
 about ; so that the latter especially takes place, when this surface is not 
 homogeneous. 
 
 VOL. II. U U 
 
658 SOURCES or ELECTRICITY. PART v. 
 
 of the hand, with which it is made to communicate with 
 the ground, often gives more decided electrical signs than 
 those which result from the action of acidulated water upon 
 this same metal. And yet the total quantity of electricity 
 produced is much less in the former case, than in the latter. 
 
 But the most simple manner of diminishing the proportion 
 of the two electricities, which recompose in proportion as 
 they are liberated, is to cause the liquid to evaporate at the 
 moment when it has just produced the chemical action. A 
 capsule of an oxidisable metal is heated ; then a few drops of 
 water are poured into it, either pure or slightly acidulated ; 
 the water attacks the heated metal, and is at the same time 
 evaporated, so that the positive electricity is carried off by 
 the steam, and is unable to reunite with the negative, which 
 passes from the metal to the electroscope, the gold leaves 
 of which it makes to diverge powerfully, without the inter- 
 vention of a condenser being necessary. If the quantity 
 of liquid injected into the capsule is too considerable to be 
 entirely evaporated, there is almost no electrical effect, be- 
 cause the two electricities are able to recompose, the positive 
 not being carried away by the steam. 
 
 The electric effects that are obtained by the means, that 
 we have been pointing out, had already been observed by 
 Volta, and by De Saussure ; and they had been attributed, by 
 these illustrious philosophers, to the evaporation itself of the 
 liquid. But it is easy to prove that this evaporation is not 
 the real cause of the phenomenon, by making use of a very 
 clean platinum capsule, heated to redness, and injecting into 
 it either water or a liquid incapable, like water, of attacking 
 the platinum and of being itself decomposed by the action of 
 the heat. No electrical sign is then obtained, as M. Pouillet 
 was the first to observe. However, if the capsule is not wide-* 
 mouthed, it sometimes happens that it is charged with nega- 
 tive electricity, which arises, as has been observed, from the 
 friction against the sides of the platinum of the globules of 
 water, that are carried on by the steam. There is also a 
 production of electricity, if the water holds a salt in solution, 
 or if the liquid suffers an alteration, by contact with the hot 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 659 
 
 platinum. This effect, as we shall see in the following para- 
 graph, is in some cases simply a mechanical effect, and in the 
 greater number, an effect truly chemical, arising from the 
 decomposition of the solution. M. Matteucci has succeeded 
 in rendering sensible, under the same form, the electricity, 
 due to oxidisation, without having occasion to heat the metal 
 previously. He places at the bottom of the platinum capsule 
 a small piece of potassium, which he bruises, in order to 
 extend it and to make it adhere to the surface of the pla- 
 tinum ; then, after having placed the capsule in communication 
 with the condenser, he causes a drop of water to fall upon 
 the potassium, the latter is decomposed with inflammation of 
 hydrogen ; as soon as the flame of the hydrogen has ceased, 
 he raises the plate of the condenser, and it is found that the 
 capsule has communicated to it negative electricity, whilst 
 the hydrogen and the vapour of water formed by its com- 
 bustion, have carried off the positive. 
 
 Some philosophers had attributed the electric signs, even in 
 the case, in which the capsule is oxidisable, to the friction 
 against the sides of the little liquid drops, drawn on by the 
 vapour. M. Buff has arranged the experiment so as to de- 
 monstrate categorically, that the effect does indeed arise 
 from the action of the liquid upon the metal. With this view 
 he has enclosed the liquid in a glass retort, heated by a spirit 
 lamp, in order thus to avoid all influence of the electricity of 
 the flame. A wire, enveloped in a glass tube, which preserves 
 it from contact with the vapour, plunges by one extremity 
 into the liquid, and by the other, communicates with one of 
 the plates of a condenser- electroscope. At the opening of 
 the retort is placed a well insulated plate of platinum, that 
 the vapour, on being liberated, may encounter it, and which 
 communicates with the second plate of the condenser, or with 
 the ground, this plate in this case also communicating with 
 the ground. The heating of the liquid and the slow evapora- 
 tion that results from it, are accompanied by a very sensible 
 charge of the condenser ; but this charge does not take 
 place if, still leaving the plate of platinum, we withdraw the 
 wire, that plunges into the liquid, a proof that the simple 
 
 u u 2 
 
660 SOURCES OF ELECTRICITY. PART v. 
 
 evaporation of a liquid does not produce electricity. More- 
 over, the force of the charge depends both upon the nature 
 of the liquid as well as upon that of the wire, that is plunged 
 into it. The plates of the condenser being of gilded copper 
 and the liquid ordinary spring water, a negative charge is 
 obtained, on plunging a zinc wire into the water. On substi- 
 tuting successively copper and silver for the zinc, we have 
 still negative signs ; but of an intensity more and more feeble. 
 The experiments of Buff are very analogous to those of 
 Karsten, with this difference, that the electric signs are much 
 more decided, on account of the evaporation of the liquid, 
 which, in carrying away the positive electricity, diminishes 
 the proportion of the two electricities, that recombine in an 
 immediate manner. We shall return also to some of Buff's 
 experiments, which, like those of Karsten, would seem, when 
 not examined closely, favourable to the theory of contact. 
 
 It follows, from what has gone before, that it is a very 
 difficult matter to obtain by chemical action, manifestations of 
 static electricity of any decided intensity. It is not the same 
 for the manifestations that take place under the dynamic or 
 current form, chemical action being of all sources, that which 
 produces them with the greatest energy, because we are en- 
 abled in great part to avoid the influence of immediate recom- 
 position. Indeed, we plunge into a vessel, filled with acidu- 
 lated water, a plate of an oxidisable metal, such as zinc for 
 example ; then, we unite it out of the liquid, by a wire that 
 is soldered to it, to a plate of platinum plunged in the same 
 liquid; then, the positive electricity, that is acquired by 
 the liquid, from the effect of the chemical action, is able to 
 unite to the negative that the attacked metal has retained, by 
 traversing the platinum plate, and the wire, 
 by which this plate is united to ' 1 ( n 1 
 (fig. 299.). A great proportion of the two 
 electricities is neutralised in this manner, 
 instead of taking place immediately at the 
 surface of contact of the liquid and the at- 
 tacked metal, and it thus gives rise to an 
 electric current, which is detected by its 
 action upon a magnetised needle, placed in 
 
CHAP. ill. ELECTRICITY BY CHEMICAL ACTIONS. 661 
 
 the vicinity of the conducting wire, by means of which the 
 two metals are united ; a wire, which may be that of a gal- 
 vanometer. 
 
 This association of two metals, or of two solid conducting 
 bodies, communicating metallically together and placed in a 
 liquid, also a conductor which attacks one of them exclusively, 
 or at least more than the other, is termed a voltaic pair.* It 
 is not necessary that the chemical action shall be absolutely 
 null upon one of the metals ; for the production of an electric 
 current, it is sufficient for the action to be more powerful upon 
 one than upon the other. We may also regard the two 
 metals as separately giving rise to two electric currents, one 
 of which, that arising from the metal most attacked, is more 
 intense, and the other, that arising from the metal least 
 attacked, is more feeble, each of the two metals serving as a 
 conductor to the current of, the other. The current col- 
 lected is then the difference between the two partial unequal 
 currents ; it would be altogether null, if these two partial 
 currents were absolutely equal ; a condition almost impossible 
 to be realised, even by employing two 
 metals, as similar as possible with regard to 
 their nature and the extent of their surface. 
 Fig. 300. represents the case of these two par- 
 tial currents, guided in contrary directions ; 
 the greater arrow indicates the direction 
 of the definitive current, resulting from the 
 difference of the two partial currents. We 
 see that it is the metal most attacked, the 
 zinc for example, that determines the direc- 
 tion of the definitive current; a current that comes from 
 this metal, to direct itself through the liquid to the metal 
 least attacked (the copper), and from this metal to the 
 former through the conductor, by which they are connected 
 exteriorly. 
 
 * In the pile the two metals of the same pair plunge indeed into the same 
 liquid, but are not united metallically together ; one of them is united to the 
 metal of^the following pair, and the other to the metal of the preceding pair ; 
 in Volta's theory, we call a pair the union of two metals connected metallically 
 together, even when they plunge into two different liquid compartments 
 
 u u 3 
 
662 SOURCES OF ELECTRICITY. PART v. 
 
 We shall continue, as is done in the contact theory, to 
 call that metal of the pair positive, which, being most 
 attacked, determines the direction of the current ; and negative 
 the metal least attacked, or not attacked at all, which serves 
 only as a conductor to the definitive current. Only we must 
 not lose sight of the fact, that positive electricity, instead of 
 coming out by the positive metal or the one most attacked, 
 conies out by the other, after having traversed the liquid ; 
 and that consequently it is negative, that comes out of the 
 metal most attacked. The word positive, as far as we are 
 concerned, will only indicate that the metal thus named, is 
 the one which determines the direction of the current.* 
 
 Before occupying ourselves with the circumstances, which 
 influence the intensity of the electricity liberated in a voltaic 
 pair, and with the means of augmenting it, it is necessary 
 to prove that the chemical action, which accompanies the 
 production of the current, to which it gives rise, is really the 
 cause of it. 
 
 I had already demonstrated, in 1828, by making use of 
 a very delicate galvanometer, that a pair, formed of two 
 plates, one of gold, the other of platinum, does not develope 
 any current, when it is plunged in perfectly pure nitric acid, 
 but we have merely to pour a drop of hydro-chloric acid 
 into the nitric acid, in order to obtain a very decided current, 
 directed from the gold to the platinum through the liquid. 
 There is no difference between the two cases, except that, in 
 the former, there is no chemical action, either upon one or 
 upon the other of the two metals ; whilst, in the latter, the 
 gold is attacked, and the platinum is not, or is less attacked. 
 
 * We have found it more convenient not to change the denomination, em- 
 ployed from the beginning ; even when it is now proved that it is from the 
 metal called positive, that exteriorly to the pair, the negative electricity comes 
 out ; and from the metal, called negative, that positive electricity, in like 
 manner, comes out. But this is no contradiction, seeing that, in the chemical 
 theory, the point of departure of the two electricities is at the surface of the 
 contact of the metal attacked and of the exciting liquid ; and that we may con- 
 sider the positive electricity as corning out from the metal attacked, to go into the 
 liquid, &c. Moreover, we understand the words positive and negative in a sense 
 independent of electricity ; that is to say, in the absolute sense of the supe- 
 riority of the positive body'over the negative, with regard to their electro-motive 
 powers. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 663 
 
 In order that this experiment may succeed well, we must 
 employ gold and platinum, prepared with great care, so 
 that they may be free from all alloy ; and care must be 
 taken that their surface is very clean. M. Becquerel had 
 already obtained the same result as I had, by fixing to the 
 extremities of the galvanometer two gold wires, plunged 
 into nitric acid ; he obtained thus no effect ; but, upon 
 adding a very small quantity of hydrochloric acid, near the 
 immersed part of one of the two wires, the magnetised needle 
 immediately detected by its deviation the production of a 
 current, directed through the liquid from the end attacked 
 to the one not attacked. 
 
 To this fundamental fact, I have added several others, 
 namely, that a pair of platinum and palladium, inactive in 
 diluted sulphuric acid, becomes active, as soon as we pour 
 into the solution a few drops of nitric acid, which bring 
 about a chemical action upon the palladium ; it is the same 
 with a pair of rhodium and platinum, the action of which is 
 null in pure nitric acid, and which gives a current in aqua 
 reyia, which attacks the platinum. 
 
 This is not all : after having shown, that there is no current 
 when in a pair there is no chemical action on the part of the 
 liquid, neither upon one or the other of the two metals of the 
 pair, I had shown that the direction of the current changes 
 in a same pair, when we substitute for the liquid, that attacks 
 the first more than the second of the two metals, a liquid 
 which attacks the second more than the first. Among the 
 numerous examples of these inversions that I had found, I 
 will cite that one, in which the two liquids employed are as 
 little different as possible from each other, since the one is 
 concentrated nitric acid, and the other diluted nitric acid. 
 The Table that follows is composed of two columns, in which 
 are inscribed, one below the other, the same metals, in an 
 order such, that each metal determines the direction of the 
 current, when it forms a pair with each of those which 
 precede it, or is positive in respect to them. The metals of 
 the first column are plunged into concentrated nitric acid, 
 those of the second into diluted nitric acid. Now, the order 
 
 u u 4 
 
664 SOURCES OF ELECTRICITY. PART v. 
 
 of the metals is not similar in the two columns, because the 
 chemical action of the concentrated nitric acid upon the dif- 
 ferent metals is not the same as that of the diluted acid ; but 
 in each, it is always the metal that is most attacked, which 
 determines the direction of the current. 
 
 Concentrated Nitric Acid. Diluted Nitric Acid. 
 
 Rusty iron. Silver. 
 
 Silver. Copper. 
 
 Mercury. Rusty iron. 
 
 Lead. Iron. 
 
 Copper. Lead. 
 
 Iron. Mercury. 
 
 Zinc. Tin. 
 
 Tin. Zinc. 
 
 If the liberation of electricity was due to the contact of 
 the two metals, the direction of the current would be in- 
 dependent of the nature of the liquid, interposed between 
 them ; and consequently the order of the metals would be 
 the same in both columns. There should also have been a 
 production of a current in the case that we have quoted 
 above, in which, nevertheless, there was none, so long as 
 there was no chemical action apparent. 
 
 Faraday, who has made a very numerous series of experi- 
 ments upon this subject, has generalised the result, to which I 
 had arrived, by showing that, in order to excite a current in a 
 pair, it is necessary for the liquid to be an electrolyte, and that 
 the more this electrolyte exercises a chemical action over one or 
 other of the two metals of the pair, the direction of the current 
 always depends upon that one of the two metals, that is most 
 attacked. In order to anticipate the objection, that the ab- 
 sence of current might arise from the imperfect conductibility 
 of the electrolytic liquid employed, he made use of such 
 liquids only as conduct the current of a thermo-electric 
 pair of bismuth and antimony ; namely, of sulphuret of potas- 
 sium, of nitrous acid, of pure nitric acid, of concentrated sulphuric 
 acid, and of a concentrated solution of potash. These three 
 latter liquids conduct less than the first two. He operated by 
 placing the electrolytic liquid in two glasses, each communi- 
 cating by means of a plate of platinum with the extremities of 
 the galvanometer ; he then connected the two glasses by an arc 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 665 
 
 p q, formed of the two metals of the pair, that he was desirous 
 of testing ; these two metals being united metallically at m 9 
 by wires of the same nature as each of them (jig. 301.). 
 
 Fig. 301. 
 
 With sulphuret of potassium, the current was null, on 
 plunging into it successively pairs of iron and platinum, of 
 iron and gold, of iron and palladium, of nickel and gold, 
 of nickel and palladium, of platinum and gold, of pla- 
 tinum and palladium ; which is on account of no chemical 
 action taking place in these various combinations. It is 
 sufficient however to heat the point of contact ra, of the two 
 metals of the pair, of which the arc is formed, in order to 
 obtain a thermo-electric current, which causes the needle of 
 the galvanometer to deviate from 50 to 60. 
 
 In these experiments it frequently happens that there is 
 a production of a slight current, at the moment of the im- 
 mersion of the plates of the pair in the vessels filled with 
 the liquid; with the platinum and iron pair, the current 
 sets out from the platinum ; but Faraday satisfied himself 
 that this effect is due to the iron being sometimes slightly ox- 
 idised ; in like manner, we have merely to withdraw one of the 
 plates from the liquid, and to expose it for a moment to the air, 
 in order to obtain a current, which lasts for a few moments 
 only when it is plunged in again. These different causes of 
 disturbance are sensible, on account of the excellent con- 
 ducting power of the liquid employed, and of the sensibility 
 of the apparatus ; but they disappear, if the precaution is 
 taken of not destroying the plates of the pair, when once 
 they are plunged into the solution, and the whole then 
 acquires a natural and perfectly regular state. M. Ohm, who 
 
666 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 has subjected to a very particular examination, this case 
 of the iron and platinum pair in sulphuret of potassium, 
 attributes the nullity of effect to the almost instantaneous 
 formation of a thin film of sulphuret of iron upon the surface 
 of this metal, as soon as it is immersed. 
 
 Hydrated nitrous acid, the mixture of nitric and nitrous 
 acids, a concentrated solution of potash, are equally inactive 
 with a great number of pairs. Silver and platinum, which 
 gives a powerful current with the most slightly acid solution, 
 gives none with the solution of potash ; it is sufficient, how- 
 ever, slightly to heat their point of contact, in order to have 
 a- very decided current, due to thermo-electricity. 
 
 It is useless now to remark that, when with these same 
 liquids, we make use of pairs, that give rise to a current, we 
 may always prove the existence of the chemical action upon 
 one of the metals of the pair. But when the liquid is 
 sulphuret of potassium, there is a production of a sulphuret, 
 that forms upon the metal attacked sometimes a non-con- 
 ducting film, as upon cadmium and tin, consequently im- 
 permeable to the current ; sometimes, on the other hand, a 
 conducting film, but not soluble, which in like manner stops 
 the current, because the chemical action ceases, as with lead 
 and bismuth ; sometimes a non-conducting but soluble film, 
 as with zinc, which allows the current to continue to exist. 
 
 A very curious phenomenon, also observed by Faraday, 
 is the inversion that takes place in the direction of the 
 current of the copper and silver pair, plunged into the 
 solution of sulphuret. The copper is at first the one, from 
 which the current sets out, and the silver is not tarnished ; 
 then the action ceases, and it is the silver that gives rise to 
 the current, and which is covered with the sulphuret, whilst 
 the film, that had been formed upon the copper, is dissolved ; 
 a few moments after, the copper again becomes positive, and 
 thus the direction of the current and the chemical action 
 change simultaneously several times in succession. More- 
 over, Faraday has found a great number of examples of 
 inversion in the direction of the current produced by the 
 same pair, according to the liquid into which it is plunged ; 
 so that he has completely confirmed the principle, that I had 
 
CHAP. III. 
 
 ELECTRICITY BY CHEMICAL ACTIONS. 
 
 667 
 
 established ; namely, that the voltaic series of metals is not 
 absolute, but that it depends upon the nature of the liquid 
 employed as an exciter. The following is a Table, that 
 contains the results of experiments made with seven liquids 
 and ten different metals ; and which is composed of seven 
 columns, in each of which the metals are ranged in an order, 
 variable with the liquid employed. Each metal is marked 
 by a number, which indicates the order in which it ought to 
 be placed, if the liquid employed is a diluted acid, the 
 direction of the current being always such that the metal, 
 that follows, is the one that determines the direction of the 
 current, when it forms a pair with one of those, that 
 precede : 
 
 Diluted 
 Nitric 
 Acid. 
 
 Diluted 
 Sulphuric 
 Acid. 
 
 Hydrochloric 
 ' Acid. 
 
 Concentrated 
 Nitric 
 Acid. 
 
 Solution of 
 caustic 
 Potash. 
 
 Colourless 
 Hydrosulphuref 
 ofPotih. 
 
 Yellow Hydro- 
 sulphuret of 
 Potash. 
 
 1. Silver. 
 
 1. Silver. 
 
 3. Anti- 
 
 5. Nickel. 
 
 I. Silver. 
 
 6. I on. 
 
 6. Iron. 
 
 2. Copper. 
 
 2. Copper. 
 
 mony. 
 
 1. Si ver. 
 
 5. Nickel. 
 
 5. Nickel. 
 
 5. Nickel. 
 
 3. Anti- 
 
 3. Anti- 
 
 1. Silver. 
 
 3. Anti- 
 
 2. Copper. 
 
 4. Bismuth. 
 
 4. Bismuth. 
 
 mony 
 
 monv. 
 
 5. Nickel- 
 
 mony. 
 
 G. Iron. 
 
 8. Lead. 
 
 3. Antimony. 
 
 4. Bis- 
 
 4. Bis- 
 
 4. Bis- 
 
 2. Copper. 
 
 4. Bis- 
 
 1. Silver. 
 
 8. Lead. 
 
 muth. 
 
 muth. 
 
 muth. 
 
 4. Bis- 
 
 muth. 
 
 3. Antimony. 
 
 1. Silver. 
 
 5, Nicke . 
 
 5. Nickel. 
 
 2. Copper. 
 
 muth. 
 
 8 Lead. 
 
 7. Tin. 
 
 7. Tin. 
 
 6 Iron. 
 
 6. Iron. 
 
 6. Iron. 
 
 6. Iron. 
 
 3. Anti- 
 
 2. Copper. 
 
 9. Cadmium. 
 
 7. Tin. 
 
 8. Lead. 
 
 8. Lead. 
 
 7. Tin. 
 
 mony. 
 
 10. Zinc. 
 
 2. Copper. 
 
 8. Lead. 
 
 7. Tin. 
 
 7. Tin. 
 
 8. Lead. 
 
 9. Cadmi- 
 
 9. Cadmium. 
 
 10. Zinc. 
 
 9. Cadmi- 
 
 9. Cadm - 
 
 9. Cadmi- 
 
 10. Zinc. 
 
 um. 
 
 
 
 um. 
 
 urn. 2 
 
 um, 
 
 9. Cadmi- 
 
 7. Tin. 
 
 
 
 10. Zinc. 
 
 10. Zinc. 
 
 10. Zinc. 
 
 um. 
 
 10. Zinc. 
 
 
 
 
 
 i 
 
 
 
 
 Mr. Faraday has also made a very great number of experi- 
 ments in exciting a chemical action, and consequently an elec- 
 tric current, by means of heat applied to one of the metals 
 of a pair ; he has more particularly examined the case, in 
 which the pair, being formed of the two similar metals, one 
 of the two is heated, and not the other, at the moment of 
 plunging into the liquid. It is clear that a difference arises in 
 the chemical action of the liquid upon the two metals ; but 
 these are complex effects, because the liquid frequently suffers 
 itself a chemical alteration by the action of the heat; and regard 
 must be had to the thermo-electric current, which frequently 
 takes place in this case ; we shall not, therefore, for the present, 
 dwell upon this, as we must return to the subject further on. 
 
 But an essential point, established by Mr. Faraday, upon 
 which we must insist, is the possibility of obtaining a current 
 capable of itself producing a chemical decomposition, with a 
 
668 
 
 SOURCES OP ELECTRICITY. 
 
 single metal submitted to chemical action, without the 
 intervention consequently of a metallic contact between two 
 heterogeneous metals. In order to obtained this result, a 
 plate of platinum b is plunged into acidulated water (Jig. 302.), 
 
 Fig. 302. 
 
 Fig. 303. 
 
 and a plate of zinc a c, bent horizontally in the part exterior 
 to the liquid ; a piece of litmus paper, moistened with a 
 solution of iodide of potassium, is placed upon the zinc plate 
 at x, and the end of a platinum wire s, soldered to the plate 
 of the same metal, is also placed in contact with this paper. 
 The iodide is immediately decomposed, which shows that the 
 current, that produces this decomposition, results only from 
 the chemical actions upon the zinc ; for there is no metallic 
 contact between the zinc and the platinum. A solution 
 of potash, substituted for the acid solution, produces the same 
 effect. If we introduce into the circuit the wire of a multi- 
 plier g (Jig. 308.)*, the needle is immediately deviated, as 
 well in the former as in the latter case. Mr. Faraday has 
 obtained a very great number of similar results, in submitting 
 several electrolytes to the decomposing action of the current, 
 produced by various metals plunged into different liquids, 
 into which also a plate of platinum was plunged, intended to 
 connect the exciting liquid with the liquid to be decomposed, 
 as in the experiments that we have just related, without there 
 having been contact between the two metals. The following 
 is a Table of these results, in which are inscribed in the same 
 
 * In fig. 303. a platinum wire is soldered to the zinc z, and this wire is 
 united to that which sets out from the platinum, by means of the paper c, 
 moistened with the electrolytic solution. This is the apparatus that has been 
 employed in the experiments, whose results are contained in the following 
 Table. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 669 
 
 horizontal line the four substances comprised in the circuits ; 
 viz., 1st, the metal attacked ; 2nd, the exciting liquid ; 3rd, 
 the metal not attacked or less attacked, which serves as a con- 
 ductor ; 4th, the electrolytic liquid, that is decomposed. 
 
 Iron. 
 
 Diluted nitric 
 
 Platinum. 
 
 Sulphuret of po- 
 
 Decided cur- 
 
 
 acid. 
 
 
 tassium. 
 
 rent. 
 
 Jf 
 
 n 
 
 99 
 
 Red nitric acid. 
 
 >9 
 
 99 
 
 99 
 
 n 
 
 Strong pale nitric 
 
 Tolerable. 
 
 
 
 
 acid. 
 
 
 99 
 
 9 
 
 M 
 
 Green nitrous 
 
 Very ener- 
 
 
 
 
 acid. 
 
 getic. 
 
 99 
 
 
 
 99 
 
 Iodide of potas- 
 
 Decided cur- 
 
 
 
 
 sium. 
 
 rent. 
 
 > 
 
 Diluted sulphuric 
 
 9 
 
 Sulphuret of po- 
 
 99 
 
 
 acid. 
 
 
 tassium. 
 
 
 M 
 
 n 
 
 99 
 
 Red nitric acid. 
 
 Tolerable. 
 
 99 
 
 Muriatic acid. 
 
 99 
 
 Green nitrous 
 
 Very ener- 
 
 
 
 
 acid. 
 
 getic. 
 
 H 
 
 Diluted 
 
 9 
 
 Red nitric acid. 
 
 Tolerable. 
 
 n 
 
 M 
 
 9> 
 
 Sulphuret of po- 
 
 99 
 
 
 
 
 tassium. 
 
 
 9 
 
 Solution of salt. 
 
 99 
 
 Green nitrous 
 
 Very ener- 
 
 
 
 
 acid. 
 
 getic. 
 
 99 
 
 Ordinary water. 
 
 
 >9 
 
 Tolerable. 
 
 Zinc. 
 
 Diluted nitric 
 
 99 
 
 Iodide of potas- 
 
 99 
 
 
 acid. 
 
 
 sium. 
 
 
 99 
 
 Muriatic acid. 
 
 99 
 
 99 
 
 99 
 
 Cadmi- 
 
 Diluted nitric 
 
 99 
 
 9> 
 
 99 
 
 um. 
 
 acid. 
 
 
 
 
 M 
 
 Muriatic acid. 
 
 99 
 
 99 
 
 99 
 
 Lead. 
 
 Diluted nitric 
 
 99 
 
 99 
 
 99 
 
 
 acid. 
 
 
 
 
 99 
 
 Muriatic acid. 
 
 9 
 
 99 
 
 99 
 
 Copper. 
 
 Diluted nitric 
 
 
 99 
 
 99 
 
 
 acid. 
 
 
 
 
 99 
 
 Muriatic acid. 
 
 99 
 
 99 
 
 99 
 
 Lead. 
 
 Strong sulphuric 
 
 Iron. 
 
 Diluted sulphuric 
 
 Strong. 
 
 
 acid. 
 
 
 acid. 
 
 
 Tin. 
 
 n 
 
 99 
 
 99 
 
 99 
 
 Copper. 
 
 Sulphuret of po- 
 
 9) 
 
 Diluted nitric 
 
 Energetic. 
 
 
 tassium. 
 
 
 acid. 
 
 
 99 
 
 99 
 
 99 
 
 Iodide of potas- 
 
 99 
 
 
 
 
 sium. 
 
 
 99 
 
 Strong nitric acid. 
 
 99 
 
 Diluted nitric 
 
 Very ener- 
 
 
 
 
 acid. 
 
 getic. 
 
 > 
 
 
 
 99 
 
 Iodide of potas- 
 
 99 
 
 
 
 
 sium. 
 
 
 Silver. 
 
 99 
 
 99 
 
 Diluted nitric 
 
 Strong. 
 
 
 
 
 acid. 
 
 
 99 
 
 
 
 99 
 
 Iodide of potas- 
 
 Tolerable. 
 
 
 
 
 sium. 
 
 
 99 
 
 Sulphuret of po- 
 
 
 
 Diluted nitric 
 
 Strong. 
 
 
 tassium. 
 
 
 acid. 
 
 
 Tin. 
 
 Strong sulphuric 
 
 Copper. 
 
 Diluted sulphuric 
 
 >9 
 
 
 acid. 
 
 
 acid. 
 
 
670 SOURCES OF ELECTRICITY. PART v. 
 
 Several philosophers, and especially Davy, had already 
 shown that voltaic batteries might be formed with a single 
 metal and two liquids ; but they had never constructed a 
 single pair, and the nature especially of these phenomena had 
 never been elucidated. 
 
 In the Table, that we have transcribed above, we may 
 remark, that the exciting liquid varies with the electrolytic- 
 liquid to be decomposed. Indeed, in order that decomposi- 
 tion may take place, it is necessary that the action of the 
 former liquid upon the zinc should be more powerful than 
 that of the latter, in order that the current, that results from 
 it, may preponderate over the affinities of the electrolytic 
 liquid and modify them. Thus we are unable to decompose 
 water acidulated with sulphuric acid by means of a zinc and 
 platinum pair, plunged into a similar acidulated water, whilst 
 we decompose a solution of iodide of potassium and of melted 
 chloride of silver. 
 
 A solution of soda, of hydrochloric acid, of nitrate of silver, 
 melted iodide, and chloride of lead, resist this decomposing 
 force ; but they are decomposed if we add to the diluted 
 sulphuric acid, which serves as the exciting liquid, a little 
 nitric acid, which increases the chemical power of this liquid 
 upon the zinc. 
 
 But we have already remarked, in reference to electricity 
 liberated under the form of tension, that there was no relation 
 between the vivacity of the chemical action, and the intensity 
 of the electric signs to which it gives rise. The same obser- 
 vation is applicable to the electricity, produced under the 
 form of current ; it is rather the nature of the chemical 
 action, than its vivacity, which influences the intensity of 
 the electric manifestation. It does not follow from this, that 
 the quantity of electricity liberated is not in relation with 
 the quantity of chemical action, which takes place ; on the 
 contrary, we shall see further on, that these two quanti- 
 ties are exactly proportional to each other ; but the faculty 
 which this electricity possesses of surmounting a certain 
 resistance, or what Faraday has called its intensity, a quality 
 which must not be confoimded with quantity, varies with the 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 671 
 
 nature of the chemical action, that takes place upon the 
 attackable metal of the pair. We may further remark, that 
 the greater or less proportion of the two electricities, that are 
 immediately recomposed on the surface of the attacked metal, 
 must necessarily be the inverse of that, which is transmitted 
 through the circuit; and consequently with a given pair, must 
 vary with the resistance of this circuit. However, this imme- 
 diate neutralisation of the two electric principles, which Mr. 
 Faraday has called local action, is due to another cause, that 
 we must endeavour to analyse. 
 
 I had already remarked, as long ago as 1830, that perfectly 
 pure distilled zinc, when plunged into diluted sulphuric 
 acid, is scarcely attacked, especially in the first moments of 
 its immersion, and even when the action has lasted for a to- 
 lerably long time, gives rise to only a small number of bubbles 
 of hydrogen ; whilst the ordinary zinc of commerce, placed 
 under the same circumstances, produces an enormous quantity 
 of hydrogen, which is liberated with effervescence. However, 
 when united voltaically with platinum, the former zinc gives, 
 for equal surfaces, a more powerful current, and consequently 
 liberates more hydrogen on the platinum than the latter. The 
 cause of this difference is due to the zinc of commerce always 
 containing a small portion of cadmium and especially of iron, 
 as is proved by chemical analysis. In fact, we have merely to 
 mix directly a tenth or even less of iron in very fine powder, 
 with distilled zinc, to render it capable of liberating as much 
 and even more hydrogen than the zinc of commerce, when 
 plunged into acidulated water. The phenomenon is therefore 
 evidently electro-chemical ; and what further proves it is, 
 that the solution of sulphuric acid, which gives with zinc in 
 which there is some iron, as with the zinc of commerce, the 
 most abundant gaseous liberation, is the same as that, which 
 has the most powerful conducting power for electricity ; 
 namely, the solution of the density, 1'259. 
 
 It is therefore evident that there is established upon the 
 surface of zinc, which contains particles, either of iron or of 
 a metal less oxidisable than zinc itself, currents arising 
 from the numerous pairs, that are formed by the particles of 
 
672 SOURCES OF ELECTRICITY. PART v. 
 
 iron with the particles of zinc, that touch them. These 
 currents decompose the water, that they traverse ; the zinc 
 oxidises and is dissolved in the state of sulphate ; and the 
 hydrogen is liberated, wherever there are some portions of 
 iron in contact with the liquid. Mr. Sturgeon, on examining 
 closely the surface of a plate of zinc, plunged in diluted 
 sulphuric acid, proved the existence in it of these negative 
 poles, which frequently changed their place during the con- 
 tinuance of the chemical action, on account of the deposition 
 of oxide, of the texture of the metal, &c. The points, which 
 serve as negative poles, suffering no alteration, we perceive 
 why a plate of zinc becomes roughened after a long im- 
 mersion in a liquid, that attacks it. Iron is not the only 
 metal, whose presence in zinc produces this effect; copper, 
 lead and even tin and cadmium, all less oxidisable than 
 zinc, in like manner but in a less degree determine it; 
 especially the two latter. We may even, by implanting 
 artificially upon the surface of a piece of distilled zinc, a 
 multitude of small points of platinum, produce a very con- 
 siderable gaseous liberation, which takes place at the 
 extremities of these points, when all these little pairs are 
 plunged into the solution of sulphuric acid.* The same 
 effect is produced upon cadmium, which, when pure and in- 
 sulated, enjoys the same property as distilled zinc. 
 
 We may give to ordinary zinc the same property as dis- 
 tilled zinc, of being but little attacked, when plunged into 
 water acidulated with sulphuric acid; for this purpose, we 
 have merely to amalgamate its surface, an operation easily 
 
 * It is to a similar cause, that we may attribute the influence that, according 
 to the observations of M. E. Millon, is exercised over the decomposition of water 
 by zinc, by the presence in the acid or saline solution, in which the zinc is 
 plunged, of small quantities of a metallic salt. Thus, the addition of a little 
 bichloride of platinum to the diluted sulphuric acid causes a plate of zinc to 
 lose in weight 66^ grs., in the same time in which a similar plate in the same 
 acid pure, would lose only grs. It is evident, that a precipitation takes place 
 of a little platinum upon certain points of the surface of the zinc, from which 
 results the formation of voltaic pairs. And indeed the intensity of the effect 
 varies with the nature of the metallic solution, and consequently of the metal 
 deposited ; thus, it is more powerful with bichloride of platinum than with 
 sulphate of copper. Tin and iron present analogous phenomena to those 
 offered by zinc. We may remark, that although all the effects observed by 
 M.E. Millon cannot be explained exactly in the same manner, they are yet 
 all due to electro-chemical causes. 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 673 
 
 done ; for we have merely to rub the surface of the zinc 
 with a rag, impregnated with a solution of sulphuric acid, in 
 order to clean it, spreading mercury at the same time over 
 this surface. Placed in contact with a plate of ordinary zinc 
 in the acid solution, the plate of amalgamated zinc forms, 
 like distilled zinc, a pair, of which it is also the oxidisable 
 element ; although, when it is isolated, it is scarcely attacked 
 at all by the solution. But if we make it communicate with 
 a wire or a plate of platinum, its zinc is rapidly dissolved, 
 with a powerful liberation of hydrogen upon the platinum. 
 Exactly the same effect takes place with distilled zinc. It is 
 evident that this similitude of effects is due to the fact that 
 the washing with diluted sulphuric acid, and the amalgamation 
 that follows, causes to disappear from the surface of the 
 zinc of commerce, all the impurities that are found mixed with 
 it, such in particular as the small molecules of iron. In truth, 
 there is brought about a true solution of pure zinc in the 
 mercury, which covers as a liquid film the surface of the 
 plate of zinc. Now, pure zinc, alloyed with mercury, can no 
 more be attacked than isolated pure zinc can; for the mercury 
 in this case does not form pairs with the molecules of zinc, 
 as the particles of iron, that are simply disseminated in the 
 metal and not alloyed with it, would do ; the mercury here 
 plays the part of a simple solvent. Only, as soon as, by its 
 contact with the platinum, the amalgamated zinc forms a 
 pair, the attraction of the mercury by the zinc is no longer 
 more powerful than the cohesion, which retains the particles 
 of simply distilled zinc to each other, in order to prevent the 
 acidulated water from oxidising and dissolving the metal 
 in this case as in the other. Faraday, who has made a 
 great number of experiments upon this subject, has found 
 that two plates of amalgamated zinc, placed each separately 
 in a test-tube, filled with a solution of sulphuric acid, one of 
 which was insulated, whilst the other was in contact with a 
 plate of platinum, in the same time the former had scarcely 
 lost any part of its weight, liberating very little hydrogen, 
 whilst the latter had lost several grains, liberating an equi- 
 valent quantity of hydrogen upon the platinum. 
 
 VOL. II. X X 
 
674 SOURCES OF ELECTRICITY. PART v. 
 
 But a much more Important question presents itself here : 
 how comes it that amalgamated zinc, or distilled zinc, which 
 comes to the same thing, which are but little or not at all 
 attacked by acidulated water, are so powerfully so, when 
 they are united, by means of a conductor, with a metal that 
 is but little or not at all oxidisable, plunged into the same 
 liquid, and then give rise to a much more powerful current, 
 than that which is produced, under the same circumstances, 
 by the zinc of commerce so powerfully attacked ? 
 
 We may first remark that the action, which the latter zinc 
 suffers, cannot contribute to the formation of the current of 
 the pair, since it arises simply from the superficial currents 
 produced by the molecular pairs, currents, that do not 
 traverse the circuit. On the contrary, these currents, which 
 consume zinc uselessly, diminish greatly the force of the 
 principal current of the pair ; and on this account it is that, 
 for equal surfaces, a plate of amalgamated or of distilled zinc 
 gives a more energetic current than a plate of the zinc of 
 commerce ; and is positive, in respect to this latter, when it 
 forms a pair with it. 
 
 This point being established, we are able to consider, as a 
 principle demonstrated by experiment, that a particle of zinc 
 perfectly pure, presenting no trace of oxidation, is incapable 
 of decomposing water, when it is placed isolately in a solu- 
 tion of sulphuric acid.* But if it is put in contact with a less 
 oxidisable particle than itself, being a conductor, such as a 
 particle of platinum, of iron, of copper, or even with a particle 
 of its own oxide, the water is decomposed, and an electric 
 current is produced. This current is, in this case, mole- 
 cular ; but its circuit is of a finite size, when, instead of two 
 molecules, there are two wires or two plates in contact and 
 forming an arc, which are in the same liquid. The production 
 of the current is simultaneous with the chemical action ; it 
 is neither anterior nor posterior to it ; it is not posterior to it, 
 since there is no chemical action, without the formation of a 
 pair ; it is not anterior to it, since the current can be esta- 
 
 * M. d' Almeida, has lately confirmed this principle, by preparing, by the 
 galvanoplastic method, zinc as pure as possible. The plate showed itself un- 
 attackable in sulphuric acid, diluted with only nine times its volume of water j 
 and it required several hours for dissolving it in boiling acid. 
 
CHAP. III. 
 
 ELECTRICITY BY CHEMICAL ACTIONS. 
 
 675 
 
 blishcd only so long as the voltaic pair is charged with an 
 electrolytic liquid, susceptible of attacking one of its metals, 
 and not with any electrolytic liquid, however good a con- 
 ductor it may be, as has been super-abundantly proved by 
 the numerous experiments, that we have reported above. 
 
 It is to M. Schoenbein, who has found several voltaic com- 
 binations, in which chemical action does not pre-exist, as re- 
 gards voltaic action, that we are indebted for the first idea of 
 the theory, which accounts for these phenomena ; a theory, 
 which approximates much more closely to the manner in which 
 Faraday regards them, and which is in accordance with what 
 we have laid down on the electro-molecular constitution of 
 bodies. 
 
 We will suppose, in what follows, that zinc and water are 
 the matters in question ; it is clear that the same would be the 
 case for every metal and for every electrolytic liquid, of which 
 one of the elements is susceptible of combining with this 
 metal. When the zinc z is plunged into the water (fig. 304.), 
 
 -> 
 
 Fig. 304. 
 
 its molecules polarise each of the molecules of water, that 
 touch it ; these polarise the following ; and so on, in such a 
 manner, that there set out from the surface of the zinc as 
 many filaments of molecules of water polarised, as there are 
 points to the surface. Each of the molecules of these filaments 
 presents its negative oxygen on the side of the zinc, and its 
 positive hydrogen, on the other side ; whilst the molecule of 
 zinc has its positive electricity on the side, where it is in con- 
 tact with the molecule of water, and its negative on the other. 
 
 x X 2 
 
676 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 This state of polarisation or tension ceases only at the moment 
 when, on causing the zinc z and the water to communicate 
 with the ground, or with the plates of a condenser, which 
 comes to the same thing, an escape is given to the negative 
 electricity of the zinc, as well as to the positive of those par- 
 ticles of the water, that are in contact with the conductor, 
 which may be the hand of the observer, or a plate of platinum 
 P, which discharges them* {fig. 305.). At the same instant 
 
 Fig. 305. 
 
 the oxygen of the particle of water in contact with the zinc, 
 combines with it, giving rise to a neutralisation of their two 
 contrary electricities ; the hydrogen of this first particle of 
 water combines with the oxygen of the second ; and so on to 
 the hydrogen of the particle in contact with the conductor P, 
 which is liberated at the surface of this conductor. The 
 same theory is applicable to the case of zinc, that contains 
 heterogeneous substances, such as particles of iron. We may 
 see (fig. 306.) the local currents, that are established upon 
 the surface of the zinc, and which, setting out from the mo- 
 lecules of zinc, nearest to the particles of iron r, abut upon 
 them, and here liberate hydrogen. 
 
 There are therefore four distinct but simultaneous phe- 
 nomena, when we plunge into a vessel filled with water a plate 
 of zinc, placed in communication with the plate of a condenser, 
 
 * The dotted line 4- , represents a wire which unites the zinc and the pla- 
 tinum ; the only difference between this case and the one upon which we are 
 occupied, is that there is a continuous current instead of a succession of dis- 
 charges ; the oxidation also of the zinc and the polarisation of the platinum are 
 obtained much more promptly. 
 
CIAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 677 
 
 and a plate of platinum in communication' with the other 
 plate of the same condenser, or with the ground: 1st, negative 
 change, given to the plate that communicates 
 with the zinc ; 2nd, oxidation of the surface 
 of the zinc ; 3rd, liberation of hydrogen at 
 the surface of the platinum; 4th, escape of 
 positive electricity into the ground or into the 
 plate, which communicates with the platinum. 
 / The quantity of chemical action, that cor- 
 responds to each charge of the condenser, is 
 infinitely feeble ; but on bringing about a 
 great number of successive discharges, we 
 end by perceiving the oxidation of the zinc, 
 from the loss which it undergoes, but espe- 
 cially the presence of hydrogen, in that the 
 plate of platinum is polarised. I have suc- 
 ceeded in proving this polarisation, by plung- 
 i ^W | j n g i n to acidulated water two perfectly similar 
 
 plates of platinum, and assuring myself by 
 means of a very sensitive galvanometer, that 
 they gave rise to no current ; then I plunged 
 into the liquid a plate of zinc, which I placed 
 Fig. .306. in communication with one of the plates of the 
 condenser, whilst I caused one of the plates 
 of platinum a to communicate with the other plate of the 
 condenser, or with the ground, taking care that the second 
 plate b remained insulated. After having thus discharged 
 and recharged the condenser several times in succession, I 
 connected respectively the two platinum plates with the two 
 ends of the galvanometer, and I obtained a current, the direc- 
 tion of which indicated that the platinum plate a had been 
 positively polarised, and consequently covered with a thin film 
 of hydrogen. If it is the plate b, that communicates with the 
 ground, or with the second plate of the condenser, and the plate 
 a, that is insulated, it is the plate b, that is polarised positively.* 
 
 * This experiment, which I have several times repeated, always with success, 
 proves that there can be no production, even of electricity of tension, in a 
 voltaic pair, without there being a corresponding chemical action. I have 
 succeeded, by making it under a slightly different form, in explaining a fact, 
 
 x x 3 
 
678 SOURCES OF ELECTRICITY. PART v. 
 
 When the zinc is not pure the particles of the surface, 
 where there is iron on any other substance less oxidisable than 
 zinc, produce the same effect as platinum. The polarised 
 filaments of water abut upon these points (fig. 306.), and 
 there is there a liberation of hydrogen. It is these molecular 
 currents, that constitute local action. It is probable that the 
 
 that M. Foucault had observed, and which he had conceived to be altogether 
 favourable to the idea that liquids have for electricity a physical conductibility 
 analogous to that of metals, independently of their electrolytic conductibility. 
 The following is this fact : 
 
 In a rectangular trough are arranged vertically, and at the equal distances 
 of fin., eleven copper plates, enveloped with gold-beaters' skin or with filtering 
 paper ; on the edges of the box is placed a cross piece of wood, carrying six 
 plates of amalgamated zinc, which are intercalated among the coppers. All 
 these plates, copper and zinc, are separated, and communicate together 
 only by the acidulated liquid, which is poured into the trough, and the level 
 of which rises very little above the free edge of the copper plates ; the 
 zincs alone emerge by narrow prolongations, by which they are connected to 
 their common support : finally, the two extreme coppers are placed in commu- 
 nication by the wire of a galvanometer. When the zincs occupy the middles of 
 the cells, the galvanometer remains at ; but, as soon as the transverse piece 
 suffers a displacement, in one direction or in to the other, the zincs are all 
 brought together to the same side ; and the result is a current, which goes 
 from the coppers that are nearest to the zincs in the interior of the trough ; and, 
 consequently, from the most distant copper to that which is the nearest to it, 
 outside of the trough. Now, it was easy for me to prove that this effect is only 
 due to the fact, that these coppers are all polarised positively upon those of 
 their faces, that are turned on the side of the nearest zinc. Indeed, if I take two 
 plates of copper, or better still, two plates of platinum, and plunge them into 
 the two extremities of a well insulated glass trough, filled with water very slightly 
 acidulated, taking care that the conducting wires that come from these plates, 
 are held by insulating handles, I obtain no current in the galvanometer, on 
 making it communicate with these conducting wires when the plates are not 
 polarised, even Avhen I plunge between them a plate of zinc, also held by an 
 insulating handle, whether I place the plate exactly between the two plates of 
 platinum, or place it very near to one or to the other. If I cause the zinc plate 
 to communicate with the ground, as well as the two plates of platinum, I have 
 not yet any sensible current, so long as I place the zinc plate very accurately 
 in the middle ; but if I bring the zinc toward one of the platinum plates, I ob- 
 tain one, in which this plate is positive. It is evident that, in this case, the 
 negative electricity of the zinc, being discharged into the ground, the positive 
 of the liquid escapes by the platinum plate that is nearest, liberating upon its 
 surface the hydrogen, that arises from the electrolytic decomposition of the 
 water. This slight film of hydrogen, by polarising the plate, renders it positive 
 in respect to the more distant plate, which, on account of the greater extent of 
 liquid, by which the zinc is separated from it, has not been able to serve for 
 the discharge. In order to render the phenomenon more sensible, it is neces- 
 sary to envelope the zinc in filtering paper, in order to be able to bring it as 
 close as possible in the liquid, to one or other of the platinum plates, still avoid- 
 ing metallic contact. It is a remarkable thing to see that it is merely neces- 
 sary for the zinc plate or the two platinum plates to be insulated, in order to 
 there being no longer any trace of current ; only, it is essential to be sure, 
 before each experiment, that the platinum plates are not polarised, and con- 
 sequently do not act upon the galvanometer, when they are alone in the liquid. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 679 
 
 chemical action, in many cases, of a liquid upon a metal, 
 is brought about in this way ; for when we are able to 
 preserve the surface of a metal from all impurity, we have 
 no chemical action, except with eminently oxidisable bodies, 
 such as potassium. 
 
 We conceive that, when the zinc is sufficiently pure, 
 either because it is distilled or by the effect of amalgamation, 
 for no local action to take place, the number of particles 
 which, for equal surfaces, serve for efficacious action, is much 
 more great; which explains the superiority of pure over 
 ordinary zinc, which we have mentioned above. This dif- 
 ference, very sensible for dynamic effects, is little or nothing 
 for the effects of tension, which require but very little 
 chemical action. This explains an apparent anomaly observed 
 a long time ago by MM. Ampere and Becquerel, but pointed 
 out latterly under a different and more striking form by 
 M. Matteucci, from whom we borrow it. A plate of amal- 
 gamated zinc with a surface of sq. in. is plunged into water 
 slightly acidulated by sulphuric acid, and a plate of pla- 
 tinum in a similar solution separated from the former by 
 merely a porous diaphragm. The former plate is in com- 
 munication with the condenser ; it gives no sign of tension, 
 before the latter communicates with the ground; but, as 
 soon as this communication is established, the gold leaves 
 of the electroscope indicate a divergence of 10. On re- 
 peating the experiment several times the same divergence 
 is obtained ; then, a platinum wire, which is in contact with 
 the zinc plate, is plunged into the compartment, in which the 
 platinum plate is ; hydrogen is immediately liberated upon 
 this wire, and yet the signs of tension are the same as before. 
 Now, nothing else has been done than what a little local 
 action would do ; namely, a part of the zinc of the plate 
 has been employed to produce a current, which results from 
 the addition of the platinum wire ; but more zinc remains 
 than is necessary to supply the tension, and we should have 
 the proof of this in the powerful current, that would be 
 produced, notwithstanding the presence of the platinum wire, 
 if the zinc was connected metallically with the platinum 
 
 x X 4 
 
680 SOURCES OF ELECTRICITY. PART v. 
 
 plate. The result is the same, except with regard to the 
 electric signs, which from negative becomes positive, when the 
 platinum plate is made to communicate with the condenser, and 
 the zinc plate, still united to the liquid, by the platinum 
 wire, that is soldered to it, is made to communicate with the 
 ground. 
 
 In the theory, that we have been laying down, we have 
 admitted that the conductor, associated with the zinc, was alto- 
 gether inactive, that it was a plate of platinum. Things go 
 on in the same manner if it is attackable by the liquid, if it is 
 a plate of copper, or of iron for example ; only the polarisa- 
 tion of the liquid, brought about by the zinc, is diminished in 
 intensity by the force of the contrary polarisation, which is 
 brought about by the chemical affinity of the oxygen of the 
 water for the copper or for the iron. If the two polarisations 
 are perfectly equal, it is clear that one destroys the other. But 
 it may happen that the conducting substance associated with 
 the zinc, instead of having affinity for oxygen, may have it 
 for the hydrogen of the water, then the polarising force of the 
 zinc upon the liquid filament, interposed between the conductor 
 and itself, far from being diminished, is on the contrary 
 increased ; and the current acquires by this a much greater 
 intensity. This happens, when the platinum plate is covered 
 with a film of peroxide of lead, a substance whose affinity 
 for the hydrogen of the water is very great, on account of 
 its tendency to be de-oxidised. The negative electricity of the 
 zinc plate, and the positive, that is acquired by the platinum 
 plate, become much more powerful, as is proved by the charge 
 of the condenser. I have even succeeded in obtaining by this 
 combination a pair, capable of actively decomposing water 
 acidulated by sulphuric acid in a voltameter with platinum 
 wires. The peroxide, brought to the state of a dry and fine 
 powder, is carefully rammed into a porous trough of unglazed 
 porcelain, such as those, which are used in the Grove's piles. 
 A thin plate of platinum is placed in the middle of the 
 trough, so that it is completely enveloped by peroxide. 
 This plate carries an appendix, to which is soldered a con- 
 ducting wire. The porous trough, filled with peroxide and 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. C8l 
 
 a plate of amalgamated zinc, are plunged into a saline or 
 acid solution ; then the plates of zinc and platinum are made 
 respectively to communicate with the two wires of a volta- 
 meter ; by this means as much as f- cub. in. of the mixed 
 gases are obtained in a minute, whilst with a similar 
 Grove's pair, except that nitric acid is substituted for the 
 peroxide of lead, a scarcely sensible decomposition is pro- 
 duced. Only, the effect is enfeebled at the end of a few 
 moments, by the infiltration of a little sulphate of zinc into 
 the peroxide and by the deoxidation of the peroxide itself. 
 It is reduced more rapidly, and is much less intense, when 
 peroxide of manganese is substituted for peroxide of lead, 
 as I have proved. Yet in this case* ^- cub. in. of gaseous 
 mixture is obtained per second. 
 
 The tendency of the peroxides of lead and of manganese 
 to deoxidise, borrowing hydrogen from the water, is so 
 powerful, that we are able to obtain, both in the state of ten- 
 sion and in the state of current, very decided electric signs, 
 by plunging into an acid solution, and even into pure water, 
 a plate of platinum and these peroxides, either in pieces, or in 
 the state of powder, spread upon a sheet of platinum ; Schcen- 
 bein was the first to remark this. The polarity is here brought 
 about by the negative element of the pair ; the platinum 
 plate gives to the condenser negative electricity, whilst the 
 peroxide communicates to it positive electricity, and the cur- 
 rent travels in a conductor, that unites these two substances 
 exteriorly to the liquid, from the peroxide to the platinum; 
 but this current can only be detected by its action upon the 
 galvanometer ; it is unable to traverse a voltameter of acidu- 
 lated water, being incapable of decomposing water. Acid 
 solutions, and especially those of hydrochloric acid, render 
 the current much more energetic by facilitating deoxidation ; 
 M. Matteucci, by plunging into hydrochloric acid a platinum 
 wire, covered with peroxide of lead, and a gold wire, 
 forming a pair, obtained a very strong current, and the 
 
 * The surface of the platinum plate was about 15 in. square ; that of the 
 zinc was double, the plate of this latter metal being bent, iu order to surround 
 the porous trough, as iu Grove's pile. 
 
682 SOURCES OF ELECTRICITY. PART v. 
 
 formation of a chloride of gold. There was no effect, when 
 Uie platinum was not covered with the peroxide. If a piece 
 'of chromate of potash is substituted for the peroxide, a 
 current is obtained of a very remarkable intensity, especially 
 on employing as a liquid, interposed between the chromate 
 and the platinum, hydrochloric or nitric acid ; we know that 
 there is a deoxidation of chromate of potash. M. Poggendorff 
 has likewise observed, that a plate of copper, whose surface 
 is oxidised, facilitates, like peroxide of lead, the production 
 of the current, when it forms a pair with zinc in diluted 
 sulphuric acid. 
 
 M. Becquerel had previously to myself obtained electric 
 currents with a pair of platinum and peroxide of manganese ; 
 but he used only pure water, and did not employ other 
 peroxides ; he found that the effect is manifested, under the 
 form of a species of discharge which requires, in order to its 
 renewal, that the circuit be interrupted for several moments, 
 and which is the more intense in proportion as this inter- 
 ruption has endured for a longer time. This result is pro- 
 bably due to the imperfect electric conductibility of the liquid 
 employed, and the feeble chemical action, that it exercises. 
 M. Becquerel had also produced effects of tension on the 
 condenser, by touching it with a platinum plate, upon which 
 was placed peroxide of manganese, held between the fingers ; 
 we shall see that this is due to the same cause. 
 
 M. Munck, on comparing in this respect various negative 
 substances, had obtained the following results, which show 
 the superiority of the peroxides, by causing the various sub- 
 stances, whose names follow, to communicate with the 
 copper condenser, by means of a moistened paper, and which 
 he touched with a plate of zinc, held between his fingers : 
 
 Zinc placed in contact * ith Degrees of negative tension. 
 
 Copper - 4 
 
 Silver - - - - -41 
 
 Carbon - - - 4f 
 
 Gold - - - - - 5 
 
 Black sulphuret of mercury - - 5 
 
 Pyrites - 6 
 
 Peroxide of manganese- - - 6 
 
 Peroxide of lead - - - . 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 683 
 
 As we shall see further on, the moisture of the hand per- 
 forms for the zinc the part of water and tends consequently 
 to give to it negative electricity, whilst the positive goes into 
 the ground by the body of the observer. Copper, silver, 
 carbon and gold only play the part of conductors, whilst 
 the action of the moist paper upon the latter substances of 
 the Table, adds its effect to that of the oxidation of the zinc, 
 since this action tends to give to the paper, and conseqnently 
 to the condenser, negative electricity. Moreover, we shall 
 return to these rather complex phenomena, when we shall be 
 examining the question of the development of electricity by 
 contact. 
 
 It follows, from what precedes, that the production of 
 electricity in a voltaic pair is only a manifestation, producing 
 itself under a different form, of the electricity, that always 
 accompanies a chemical action. Only under this form the 
 electricity becomes perceptible directly; whilst, in the 
 ordinary form, which we have designated under the name 
 of local action, it is so only indirectly. Chemical affinity 
 cannot therefore be exerted without there being at the same 
 time a production of electricity, sometimes perceptible, at 
 other times not perceptible. More than this : the formation 
 of a pair, that facilitates the perception of electricity, favours 
 in many cases the exercise of chemical affinity, particularly 
 in the case, in which the homogeneity of the solid substance, 
 exposed to the chemical action of a liquid, does not allow of 
 the establishment of superficial molecular currents. It is by 
 taking advantage of the new power, that is thus acquired 
 by chemical affinity, and which he was the first to point out, 
 that M. Becquerel succeeded in producing a great number of 
 compounds hitherto unknown, and in obtaining in the crys- 
 talline state many substances, which they had never suc- 
 ceeded in crystallising before him. This order of facts, 
 which is one of the most elegant applications of electricity to 
 chemistry, will find its place in the Part of this Treatise 
 which is devoted to Applications. 
 
 We may further remark, before quitting this subject, that 
 metallic precipitations, such as those which are obtained in 
 
684 SOURCES OF ELECTRICITY. PART v. 
 
 the tinning of pins, or in plunging a plate of iron into a 
 solution of sulphate of copper, are like the liberation of hy- 
 drogen by the action of diluted sulphuric acid upon the zinc 
 of commerce, only an electro-chemical effect, due to molecular 
 currents, that constitute what we have called local action. 
 A plate of iron plunged into sulphate of copper almost 
 always presents upon its surface one or two points slightly 
 oxidised, where there are several flaws, perhaps some particles 
 of carbon; this defect of homogeneity immediately brings 
 about a small first current, which decomposes the sulphate ; 
 a Ittle copper is immediately deposited ; and then the action 
 becomes only the more easy, until almost the whole of the 
 surface of iron is covered with copper. It has in fact been 
 remarked that, if this surface is perfectly homogeneous, 
 which is difficult to obtain, the precipitation of copper no 
 longer takes place. The important labours of Bucholz and 
 Grotthus, and the more recent ones of Fischer and Breslau 
 upon this subject, and in particular upon metallic vegetations, 
 completely confirm the electro-chemical origin of this order 
 of facts, the details of which enter into purely chemical phe- 
 nomena, since the question is nothing more than the exercise 
 of affinity. However, we shall be called to return to this, 
 when we are engaged on the applications of electricity to 
 chemistry. 
 
 It is also to a similar electro-chemical cause that we must 
 attribute the important fact, observed for the first time by 
 Davy, that a metal, copper for example, may be protected 
 against the corrosion exerted upon it by an acid or a saline 
 solution, such as sea-water, by associating it voltaically with 
 a more oxidisable metal, such as zinc. There is produced 
 between the zinc, soldered or applied to the copper, and the 
 copper itself, a current that decomposes the water, and de- 
 posits its hydrogen against the copper surface ; hydrogen, that 
 prevents oxidation or destroys it in proportion as it takes 
 place. In this latter case, which is very frequently presented, 
 the copper finishes by becoming covered with a pulverulent 
 powder. If the solution contain salts with an insoluble 
 base, or one but little soluble, as is the case of sea-water, the 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 685 
 
 copper is soon seen to be covered with a basic earthy deposit.* 
 It had been for a moment thought that the simple contact 
 of copper or iron with a more oxidisable metal, such as zinc, 
 would render them inattackable, because it constitutes them 
 into a particular electrical state ; but M. Schcenbein has de- 
 monstrated, by a numerous series of experiments, that iron 
 and copper oxidise in air, in water and in a saline solution, as 
 well when they are in contact with zinc, as when they are 
 not so, if there is no electric current ; but that, as soon as 
 there is one established, the negative metal, namely, the one 
 that receives the hydrogen, is no longer oxidised. The forma- 
 tion of a deposit, arising from the decomposition of the so- 
 lution, explains also the fact observed by M. Yan Beck, that 
 a copper vessel filled with sea-water, after having been for 
 forty-seven days connected voltaically, by means of a platinum 
 wire, with a plate of iron, plunged into the same liquid, and 
 having been thus preserved from all oxidation, continued to 
 be so when the platinum wire that connected the copper to 
 the iron had been broken; but the sea- water having been 
 changed, which evidently caused the preservate film, deposited 
 on the surface of the copper, to disappear, the latter recom- 
 menced to oxidise. 
 
 After having well established the theory of the voltaic pair, 
 it remains for us to show how the intensity of the electricity 
 to which it gives rise, may be reinforced. In order to render 
 the explanation we are about to give more clear, we will de- 
 signate, under the name of electro-motive force of a pair,, the 
 force with which the molecules of the electrolytic liquid, which 
 enters into the formation of this pair, are polarised ; a force, 
 which depends, when the negative element of the pair is in- 
 active (platinum and zinc), on the affinity alone of the positive 
 element for one of the elements of the liquid ; which depends, 
 on the contrary, upon the affinity that is possessed for the other 
 element of the liquid, by the negative element of the pair, 
 when it is this which is active, and when the positive is not 
 (platinum and peroxide of lead) ; and, finally, which depends 
 
 * The formation of this deposit has unfortunately rendered Davy's process, 
 Inapplicable to the preservation of the copper, that covers ships exteriorly. 
 
686 SOURCES OF ELECTRICITY. PART v. 
 
 upon the two affinities equally, when both the elements of the 
 pair are active (zinc and peroxide of lead). Our definition of 
 electro-motive force is very different from that which is given 
 to it in Volta's theory, in which under this denomination is 
 designated the force, with which it is supposed that, in the 
 contact of two heterogeneous bodies (platinum and zinc), one 
 is constituted into the negative state, and the other into the 
 positive. 
 
 The electro-motive force of a pair, depending upon the affi- 
 nity of its two elements for those of the electrolytic liquid, 
 we may conceive that it must vary with the nature of these 
 two elements, and with that of the liquid ; whence there re- 
 sults a very considerable number of possible voltaic combina- 
 tions. ' We will point out, at the end of this Chapter, the 
 methods, that have been employed for measuring this force, 
 and the application of them, that has been made to the 
 measurement of the power of the different voltaic pairs. We 
 shall endeavour to see, at the same time, to what point we are 
 able, in the measuring of electro-motive force, to find a means 
 of measuring the power itself of affinity. For the present, 
 we shall confine ourselves to explaining how, a pair being 
 given, we are able to increase its electro-motive force. For 
 this exposition, we shall take as a type the most simple pair, 
 namely, a pair formed of a plate of amalgamated zinc, and a 
 plate of platinum, each with a surface of about 15| sq. in. 
 plunged into water acidulated with sulphuric acid. We 
 will suppose the liquid placed in a well-insulated glass 
 vessel, and the two metal plates each furnished with an 
 appendix of the same metal also well insulated (fig. 305.). 
 
 The electro-motive power of this pair may be appreciated 
 either by the condensing electrometer, the electricity with 
 which each of the metals of which it is composed being 
 collected in the static state, or by a rheostat, this same elec- 
 tricity being manifested in the dynamic state, by its action 
 upon a magnetic galvanometer. In order to increase the 
 electro-motive force of the pair, that is to say, in order to have 
 a greater tension detected by the electrometer, or a greater 
 resistance surmounted in the rheostat, with the same devia- 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 687 
 
 tion of the galvanometer, it will be sufficient to place in suc- 
 cession to this former pair a second similar one, so that the 
 platinum appendix of the former is in contact with the zinc 
 appendix of the latter, and consequently that the zinc appen- 
 dix of the former and the platinum appendix of the latter are 
 insulated. On making these two appendices communicate re- 
 spectively with the two plates of the condenser we shall have 
 a tension the double of that, which we had with a single pair, 
 and in making them communicate together by the wire of the 
 galvanometer and by that of the rheostat, so as to close the 
 circuit, we shall produce a current, that will surmount a re- 
 sistance the double of that which the current of a single pair 
 would have surmounted. "With three pairs, arranged in like 
 manner, one after the other, the tension in the static state will 
 be triple ; and the resistance surmounted in the dynamic 
 state, will be triple also ; and so on, in such sort that for n 
 pairs the tension and the resistance would be n times greater.* 
 Now it is easy to comprehend why the addition of a 
 second pair doubles the force, that polarises the successive 
 molecule of the liquid, as well as that with which their 
 combinations and recompositions are brought about, why 
 the addition of a third triples it, of a fourth quadruples it, 
 and so on. Let us take the case of two pairs voltaically 
 united, as we have pointed out above. If the zinc of the 
 second pair did not exercise any action, that polarised its 
 liquid, this zinc, in communication with the platinum of the 
 first, would receive and would transmit to the liquid molecules 
 in contact with it, a polarity equal to that, which it had 
 received from the platinum ; that is to say, that the first 
 molecule of the water would have its negative oxygen, 
 turned towards the + of the platinum and the liquid of each 
 of the two pairs would be polarised in the same manner 
 (fig. 307.). But the zinc of the second pair exercises upon 
 
 * We shall see, in a following paragraph, that the proportionality between the 
 tension possessed in the static state, by the electricity produced by a certain 
 electro-motive force, is proportional to the resistance, that it is able to surmount 
 in the dynamic state. With regard to the relation, that exists between this 
 tension or this resistance on the one hand, and the number of pairs on the other, 
 we cannot appreciate the point, up to which it is rigorously exact, until \ve 
 shall have been enabled to know, and consecpacntly to eliminate, the circum- 
 stances that tend to disguise it. 
 
688 
 
 SOURCES OF ELECTRICITY. 
 
 its liquid a polarising action, similar to that of the first. 
 These two actions are evidently added to each other, since 
 
 P 
 
 9 
 
 6 
 
 Fig. 307. 
 
 they take place in the same direction. Moreover, in its turn, 
 the polarising action of this zinc is transmitted to the pla- 
 tinum of the first pair, with which it is in contact, and thence 
 to the liquid and to the zinc of this pair, so that the two 
 pairs have equally their electro-motive force doubled. In the 
 same manner will be explained why the addition of a third 
 pair will triple the polarising force ; and consequently the 
 electro-motive force of the three pairs equally ; and why 
 if there are n pairs these forces will be rendered n times 
 greater. 
 
 Thus, when we have an insulated pile, composed of any 
 given number of similar pairs, at the moment when its two 
 poles are made to communicate with the two plates of a con- 
 denser, or with the ground, a chemical action is brought about, 
 which is accompanied by a liberation of electricity. If the pile 
 is composed of a very great number of pairs, the electro-mo- 
 tive force becomes sufficiently powerful for the chemical action 
 to take place even when the poles remain insulated ; thus, on 
 making each of them communicate with an electroscope, we 
 obtain, without the assistance of a condenser, the divergence 
 of the gold leaves. The electric tension, that is acquired by 
 each pole, depends, not only upon the intensity of the electro- 
 motive force, but upon the more or less imperfect conductibility 
 of the pile itself. Indeed, the two electricities accumulated 
 respectively at each of the poles tend to reunite by the pile 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 689 
 
 itself, which separates them, and which plays the part of a 
 simple conductor. Experiment, in fact, teaches us that this re- 
 union is brought about here, as in an ordinary conductor*; that 
 is to say, that, setting out from, the two poles, where they 
 have their maximum of tension, each of the two electricities 
 goes on diminishing in force to the middle of the pile, where 
 the electric state is zero. The contrary electricities, with 
 which the two halves of the pile are charged, are not able 
 to reach the intermediate pairs, since there is always, in each 
 of them, a neutralisation of the two electric principles ; they 
 come evidently from the extremities, or the poles of the pile, 
 where they are constantly renewed. The tension of the two 
 poles would be the greatest possible if we could reconcile, 
 with a great electro -motive force, a very imperfect conducti- 
 bility of the pile ; this is realised with dry piles, as we shall 
 see in the paragraph devoted to the study of that species of pile. 
 In a series of experiments, that I had undertaken with 
 piles charged either with pure water or with saline or acid 
 solutions, I satisfied myself that, in order to obtain the 
 maximum tension, it required a time long in proportion as 
 the liquid was a less good conductor; and that it was in- 
 stantaneously obtained with very good conducting liquids, 
 such as acids diluted with water. Mr. Gassiotf, in a series 
 of very remarkable researches made with his water-battery, 
 composed of 3520 pairs of zinc and copper, perfectly well 
 insulated, arrived thence at results, perfectly in accordance 
 with the theory, that we have been laying down. He con- 
 cluded, from his experiments, that the static effects of the 
 pile exist previous to the closing of the circuit ; and that 
 this latter may be closed, when the tension is powerful, by 
 a succession of sparks, which are established between two 
 polar metallic surfaces, very near to each other. He has 
 also observed that, in a pile, such as the water pile, in which 
 the chemical action is not exercised without difficulty, the 
 tension is produced but slowly ; but he succeeded in proving 
 
 * For the manner in which electricity is distributed in a conductor that con- 
 nects the two poles of a pile, vide Vol. II. p. 94. and following pages. 
 
 f Mr. Gassiot was assisted in his researches by Mr. C. V. Walker, who 
 is well known for his works on electro-chemistry. 
 
 VOL. II. Y Y 
 
690 SOURCES OF ELECTRICITY. PART v. 
 
 plainly that the static effects, as well as the dynamic effects, 
 can be produced only so long as the chemical elements, 
 which enter into the formation of the pile, are susceptible 
 of combining together chemically. He likewise found that 
 the more the mutual affinity of these elements is powerful, 
 the less necessary it is, in order to produce great effects of 
 tension, that the number of pairs be considerable. Thus he 
 obtained with a pile composed of 100 well insulated Grove's 
 pairs a tension at the two poles, as decided as with the water 
 pile of 3520 pairs ; and, in particular, sparks between two 
 discs of copper each placed in communication with one of the 
 poles, and placed at a distance ofy-oVo ^ an * ncn fr m eacn 
 other.* 
 
 It remains therefore well established that, in a pile, or 
 in a pair, all manifestation of electric signs, as well under 
 the static as under the dynamic form, is accompanied by a 
 corresponding chemical action. This action is excessively 
 feeble for a single discharge ; but it becomes sensible, when 
 a succession of discharges are brought about, as was done 
 by Gassiot, by producing a series of sparks between the two 
 poles of the water pile. It is especially sensible, when, con- 
 necting the poles of the pile by a good conductor, the succes- 
 sion of discharges are caused to be brought about with suffi- 
 cient rapidity for constituting the current. We are then able 
 not only to detect, but even to measure exactly, this chemical 
 action ; and it is found at once the same in each pair, and 
 equivalent for each of the pairs, to what it is, exteriorly to 
 the pile, in an electrolyte placed between the poles. It is 
 this that we have still to demonstrate, in order to complete 
 the exposition of our theory. 
 
 It is at first very evident that, in a single pair, zinc and 
 
 * Mr. Gassiot even succeeded in obtaining signs of tension, by means of a very 
 sensitive gold-leaf electroscope, with a single pair of Grove's, well insulated. 
 The foundation of the difficulty that is encountered in obtaining very marked 
 signs of electricity, arises from the pairs not being sufficiently well insulated, 
 which is not at all times easy, especially when we are concerned with piles, 
 charged like Grove's, with acids. Also it is by means of a peculiar construction, 
 and by employing glass vessels alone, for containing the acid solution, that 
 Gassiot succeeded in obtaining with 100 pairs of Grove's, the same effect as 
 with his water battery. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 691 
 
 platinum, the quantity of hydrogen, liberated upon the 
 platinum, must be exactly equivalent to the loss in weight of 
 the zinc, at least if there is no local action upon this metal ; 
 if there is any, we must take account of the hydrogen 
 liberated on the surface of the zinc. Faraday, by accurate 
 measurements and weights, has proved this essential point. 
 If, instead of a pair, we have a pile, composed of a series of 
 pairs, amalgamated * zinc and platinum, so arranged that the 
 hydrogen gas, liberated by the platinum, can be exactly 
 measured, and the zinc can easily be removed for weigh- 
 ing, we find that the quantity of hydrogen is exactly the 
 same in each pair, and in a voltameter placed in the circuit, 
 and that it is at the same time equivalent to the zinc con- 
 sumed, that consequently the latter is also to the oxygen of 
 the voltameter. 
 
 In order to make this last experiment well, each pair 
 . 308.) is constructed by means of a glass bottle, filled 
 
 Fig. 308. 
 
 with a solution of very pure sulphuric acid. This bottle is 
 
 The zinc must be well amalgamated, in order to avoid all local action. 
 
 Y Y 2 
 
692 
 
 SOURCES OF ELECTRICITY. 
 
 PART V 
 
 pierced by three openings; one in the centre, closed by a 
 glass stopper, by which the liquid is introduced ; the other 
 two on each side of the central one, one serving to introduce 
 the amalgamated zinc, the other intended to receive very 
 tightly a graduated tube, open below, and closed above, 
 which is filled with liquid, and in which is placed a wire or 
 a plate of platinum, the upper extremity of which comes out 
 through the top of the tube, terminating by a clip or by a 
 small metal cup, filled with mercury. Several similar pairs 
 are arranged one after the other, care being taken that the 
 wires, soldered to the zincs, arrive at the platinum of each 
 consecutive pair. The circuit is then closed with any con- 
 ductor, for example, with a voltameter ; and when the action 
 has lasted for some time, the hydrogen gas is measured in 
 each pair, and in the voltameter, and the zincs 
 are weighed. The accuracy of the law, that 
 we have laid down, is thus proved. In order 
 to prove it with a single pair, we have merely 
 (fig. 309.) to make the zinc and platinum of 
 the same pair communicate. 
 
 Any electrolyte, such as a metallic salt, may 
 be substituted in the circuit for the acidu- 
 lated water of the voltameter ; and we always 
 find that the reduced metal is equivalent to 
 the hydrogen of each pair. We may also add 
 that the law of equivalents for the pairs of a 
 pile had been pointed out for the first time, 
 after that Faraday had proved it for single 
 ones, by M. Matteucci, who had proved it, 
 by employing salts of copper and silver for de- 
 termining the electro- chemical equivalents. 
 
 Thus then, when the poles of a pile are con- 
 nected by an electrolyte, the quantity of effect 
 produced in this electrolyte is equivalent to 
 the chemical action, or to the chemical expense, that takes 
 place in each pair. If the pile has, for example, ten pairs, 
 ten equivalents of zinc must be consumed, in order to de- 
 compose one equivalent of water; twenty, when there are 
 
 Fig. 309. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 693 
 
 twenty pairs. It would seem, therefore, much more ad- 
 vantageous to employ only one or two pairs ; since, in order 
 to produce the same effect, we should expend twenty or ten 
 times less zinc. But, besides that the decomposition would 
 be much less rapid, which would present grave inconveniences 
 in many cases, there are a great number of electrolytes, 
 which can be decomposed only so long as the current 
 possesses a certain intensity ; or, which comes to the same 
 thing, that the electro-motive force possesses a certain power, 
 which can only be given to it by multiplying the number 
 of pairs. It is the same for the resistances, that are to be 
 surmounted. Thus, when a current is called upon to tra- 
 verse a very long telegraphic wire, it is necessary for it to 
 be produced by a pile of numerous pairs (which occasions a 
 greater expense of zinc) ; because, if it were produced by 
 only one or two pairs, it would not have sufficient intensity 
 to overcome the resistance of the wire. 
 
 However, there exists a manner of increasing the electro- 
 motive force of a pair, and consequently the intensity of its cur- 
 rent, without its being necessary to add to it a second or a third 
 pair ; it is to cause it to be traversed by an induction current, 
 guided in the same direction as the current itself of the pair. 
 This induction current which, when alone, would decompose 
 water, adds its effect to that of the pair, increasing its polarising 
 force, and facilitating the decomposition and recomposition of 
 the successive molecules of the water. I have already de- 
 scribed an apparatus, that I have constructed for this object* 
 in which it is the pair itself that produces the induced current, 
 the effect of which must be to increase its own force ; and I 
 have shown that a pair, which could not decompose water in 
 a sensible manner, becomes by this artifice capable of giving 
 to a voltameter of platinum wires, charged with sulphuric acid 
 to a tenth, as much as three cubic inches of mixed gases per 
 minute. It is true that no economy of zinc is produced ; for, 
 besides that which is consumed at the moment, when the current 
 circulates through the voltameter, and which is equivalent to 
 
 * Vol. I. p. 385. fig. 148. 
 T Y 3 
 
694 SOURCES OF ELECTRICITY. PARTY. 
 
 the water decomposed, a certain quantity is expended at the 
 moment when the current of the pair, instead of traversing 
 the voltameter, passes through the wire of the bobbin, in order 
 to produce the magnetisation, which gives rise to the induction. 
 This expense might be avoided by developing the induction by 
 means of a magnet; but then a mechanical force would be ne- 
 cessary, in order to bring about the rotation of the induction 
 apparatus. This would, it is true, be more economical, since 
 we should only expend a quantity of zinc, equivalent to the 
 chemical effect obtained ; but in a mechanical point of view, 
 we should always have need of a force, equivalent in its 
 effect, although of a very different nature to that which the zinc, 
 that had been economised, might have produced. Moreover, 
 more time would be necessary, in order to obtain the same 
 chemical result. 
 
 To sum up, it follows from the analysis, that we have been 
 making, that the law of electro-chemical equivalents dis- 
 covered by Faraday, and which we have laid down at first, 
 as far as it concerns the decomposition of electrolytes placed 
 in the circuit exterior to the pile *, is general, and is equally 
 well applied to what takes place in the interior itself of the 
 pile as on the outside. We may therefore consider the circuit 
 of a pile, when it is closed, as a system of conductors united 
 end to end, in the series of which the current circulates in a 
 manner perfectly uniform and identical ; circulation, which 
 is brought about by a succession of polarisations and recompo- 
 sitions of the contrary electricities of the consecutive mole- 
 cules, in such sort that this operation is accompanied by a 
 liberation of heat when it encounters a certain resistance, and 
 of chemical decompositions, when the molecules are compound. 
 But all these effects are equivalent in all the parts of a 
 same circuit, the pile included ; we have just proved it, as far 
 as chemical effects are concerned, and we have already seen 
 that it was the same for the effects of heatf 
 
 It would remain for us to examine what the influence is of 
 the number of the pairs upon the effects, that require a great 
 
 * Vol. II. p. 352 and following pages, 
 f Vol. II. p. 250. 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 695 
 
 rapidity in the circulation of the current, such as the effects 
 of heat, as well as the modification that is produced in a pile, 
 by the introduction of one or more pairs more powerful or 
 more feeble than the others, or simply that of homogeneous 
 metallic diaphragms, or inactive pairs. The influence of these 
 circumstances, and of several others, which it is useless to 
 enumerate here, depend upon causes which we cannot ap- 
 preciate until after we have finished the study of the liber- 
 ation of electricity in the different forms under which chemical 
 action is exerted. It is not until the end of this Chapter, that 
 we shall be able to appreciate them. This we shall do in the 
 paragraph, in which we shall compare the different species of 
 piles with each other, with regard to their powers, considered 
 under different relations. We shall then see also the part 
 played by the extent of the surface of the pairs ; a part, more- 
 over, that may be easily comprehended even now; for the 
 size of the surface, being able to influence only the quantity 
 of chemical action, exerted in a given time, it can in no way 
 modify the electro-motive force of the pair or the pile, nor 
 consequently the faculty of the current produced for surmount- 
 ing this resistance. We may remark merely, that this resist- 
 ance, when it exceeds a certain point, itself limits the quan- 
 tity of efficacious chemical action by the quantity of electri- 
 city that can be transmitted in a given time, and consequently 
 renders useless an augmentation of the surface beyond a certain 
 size ; a size which is itself in relation with that of the re- 
 sistance. 
 
 Production of Electricity by the Chemical Action of Solutions upon 
 
 each other. 
 
 M. Becquerel is the first philosopher, who has shown that, 
 on causing two solutions, that are conductors of electricity, to 
 act upon each other, and which are capable of mutually 
 exercising a chemical action upon each other, however 
 feeble it may be, an electric manifestation is obtained under 
 the form of a current. In order to observe this effect, the two 
 extremities of a good galvanometer are made to communicate 
 
 Y Y 4 
 
696 SOURCES OP ELECTRICITY. PART v. 
 
 (fig. 310.) respectively with two plates of very well cleaned 
 platinum, which are plunged, one into a glass d, filled with 
 
 Fig. 310. 
 
 nitric acid, the other into a glass c, filled with a solution of 
 potash, for example ; the two liquids are then connected by 
 a skein of cotton p m q, or better still of amianthus moistened 
 by water slightly acid or salt. There is immediately a pro- 
 duction of a current, which goes from the potash to the acid 
 through the skein ; and consequently from the platinum plate, 
 which is plunged into the acid, to that which is plunged into the 
 potash, through the galvanometer. Davy having attributed 
 the production of electricity, in the experiment that we have 
 been relating, to the contact of the platinum with the nitric 
 acid on the one side, and with the potash on the other, M. 
 Nobili showed, contrary to the result obtained by Davy, 
 who had employed too sensitive a galvanometer, that a 
 decided current may be obtained by avoiding the contact 
 of the platinum with the acid and the alkali. In order 
 therefore to escape this objection, it is necessary slightly to 
 modify the arrangement of this experiment of M. Becquerel's ; 
 in consequence, the two platinum plates of the galvanometer 
 are made to plunge into two capsules, both filled with a solution 
 of nitrate of potash ; then, by means of a skein of amianthus, 
 the two capsules are made to communicate respectively, one 
 with the nitric acid, the other with the solution of potash ; 
 the acid and the potash being also placed in communication 
 by means of a similar skein, a current analogous to the pre- 
 ceding is obtained, but more feeble, on account of the imper- 
 fect conductibility of the nitrate of potash, and of a particular 
 influence, that results from the contact of the nitric acid 
 with the negative plate of platinum, of which we shall speak 
 further on. MM. Nobili and Becquerel have also sue- 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 697 
 
 ceeded in obtaining this current, by substituting a piece of 
 caustic potash for the solution of potash: the former, on 
 plunging the piece of potash into the acid, after having fixed 
 it to the extremity of the skein of cotton, the other extremity 
 of which plunges into one of the vessels filled with nitrate of 
 potash ; the latter, by taking a platinum spoon, filled with 
 nitric acid, and plunging into it the potash, held by platinum 
 pincers, the spoon and the pincers being placed respectively 
 in communication with the two ends of the galvanometer 
 wire. 
 
 In order to avoid every objection, M. Becquerel has like- 
 wise operated, in another manner, by which the contact of 
 the platinum with the different substances is also avoided. 
 He plunges the two platinum plates of the galvanometer into 
 two glasses, each of them filled in like manner with nitric 
 acid; then, he causes them to communicate by means of a skein 
 of cotton saturated with water, and about four inches in length, 
 taking the precaution, on account of its length, of supporting 
 it by a glass tube ; about the middle of this skein, a drop 
 of acid and a drop of dissolved potash are placed gently with 
 a tube beside each other. So long as the two drops are 
 separated, there is no effect ; but at the instant when their 
 reunion takes place, there is the production of an electric 
 current, going directly from the potash to the acid, and from 
 the acid to the potash, through the circuit. By substituting 
 other acids for nitric acid, the results are the same ; but 
 more or less decided, according to the energy of the chemical 
 action, and the conductibility of the liquids. 
 
 Instead of water, we may employ a saturated solution 
 of nitrate of potash, or of any other salt, such as sulphate of 
 soda, for moistening the skein of cotton or amianthus. In 
 this case, the acid and the alkali, in which the extremities 
 of the skein are plunged, exercise upon them chemical 
 actions, which give rise to currents, more feeble than that 
 which results from the action of the acid and the alkali upon 
 each other, but moving in the same direction. These 
 partial currents are the only ones, that are manifested at the 
 very moment, when the union of the acid and the alkali is 
 
698 . SOURCES OF ELECTRICITY. PART v. 
 
 brought about by means of the skein. Thus the effect is more 
 feeble ; but, at the end of a few moments, if the skein is not 
 too long, there is an infiltration of the acid and the alkali, 
 which, finishing by meeting each other, combine in con- 
 siderably strengthening the current. Thus nitric acid and 
 potash, united by a skein impregnated by sulphate of soda, 
 having at the commencement given a constant deviation of 
 only 4 or 5, at the end of a few moments, give an equally 
 constant current of 20, which corresponds with a force at 
 least eight or ten times greater. The former deviation 
 was evidently the results of currents, arising from the respec- 
 tive chemical actions of the acid and the alkali upon the 
 sulphate of soda of the skein ; and the latter, from the 
 additions to these currents of that which would be produced 
 by the direct action of the acid upon the alkali. The 
 current due to the action exercised over the solution, with 
 which the skein is impregnated, vary with the nature of this 
 solution and of the liquids, into which the extremities of this 
 skein are plunged. Still more decided effects are obtained, 
 by moistening the skein with the solution of a salt, the acid 
 and the base of which are the same as the acids and bases of 
 the solutions into which its extremities are plunged; for 
 example, a solution of nitrate of potash with nitric acid and 
 potash ; which proves that, even, in this case, there is still a 
 chemical action, probably due to the effect of the mass or to 
 the degree of concentration of the solutions. 
 
 The chemical action of acids upon acids may in like 
 
 manner give rise to electric 
 currents. Thus, if we pour into 
 one of the branches of a tube 
 bent into a U {fig* 311.) some 
 concentrated sulphuric acid, 
 and, into the other, some nitric 
 acid, so that the two liquids 
 touch at m, without mixing, 
 Fig. 3n. which is easily obtained, on 
 
 account of their difference of density, on plunging the pla- 
 tinum extremities a and b of the galvanometer respectively, 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 699 
 
 into the two acids, a current is obtained, which goes 
 directly from the nitric acid d, to the sulphuric c, the former 
 acid playing the part of base in respect to the latter. Phos- 
 phoric acid produces with nitric acid the same effect as 
 sulphuric ; and, opposed to sulphuric, plays the same part as 
 sulphuric opposed to nitric. 
 
 The following is the order, in which the various conducting 
 solutions may be placed, so that each shall be negative in 
 respect to those which follow, and positive with those, which 
 precede * : 
 
 Phosphoric acid, sulphuric acid, nitric acid, hydrochloric acid, 
 acetic acid, nitrous acid, saline solutions, alkaline solutions. 
 
 There are however cases in which saline solutions are 
 negative with certain acids, and positive with certain bases ; 
 but these are exceptions, which are due to the circumstance, 
 that the phenomenon is complex. We may remark that, 
 in general, water plays the part of a base with acids, and of 
 an acid with bases. It is probably on account of the con- 
 siderable affinity that phosphoric and sulphuric acids have 
 for it, whence it follows that they take it from other solutions, 
 that we must attribute the fact that these acids are at the 
 head of liquids in the above Table. 
 
 We may add that, in order to study thus the currents that 
 arise from the mutual action of various solutions, it is pre- 
 ferable to have recourse to the first mode of operating 
 (Jig. 310.), by connecting the two liquids, into which the two 
 platinum plates are plunged, by a skein of amianthus. It is 
 necessary, at the same time, before each experiment, always 
 to take the precaution of well cleaning the platinum plates 
 by heating them to redness, then placing them in boiling 
 nitric acid, and finally washing them in distilled water ; 
 then, having done this, we assure ourselves, by plunging 
 them into the same liquid, into nitric acid for example, that 
 
 * We always call that body (liquid in this case) positive, whence the cur- 
 rents or positive electricity sets out, in order to go directly to that, which acts 
 chemically upon it, and from the latter to return to the former, through the 
 galvanometer. 
 
698 . SOURCES OF ELECTRICITY. PART v. 
 
 brought about by means of the skein. Thus the effect is more 
 feeble ; but, at the end of a few moments, if the skein is not 
 too long, there is an infiltration of the acid and the alkali, 
 which, finishing by meeting each other, combine in con- 
 siderably strengthening the current. Thus nitric acid and 
 potash, united by a skein impregnated by sulphate of soda, 
 having at the commencement given a constant deviation of 
 only 4 or 5, at the end of a few moments, give an equally 
 constant current of 20, which corresponds with a force at 
 least eight or ten times greater. The former deviation 
 was evidently the results of currents, arising from the respec- 
 tive chemical actions of the acid and the alkali upon the 
 sulphate of soda of the skein ; and the latter, from the 
 additions to these currents of that which would be produced 
 by the direct action of the acid upon the alkali. The 
 current due to the action exercised over the solution, with 
 which the skein is impregnated, vary with the nature of this 
 solution and of the liquids, into which the extremities of this 
 skein are plunged. Still more decided effects are obtained, 
 by moistening the skein with the solution of a salt, the acid 
 and the base of which are the same as the acids and bases of 
 the solutions into which its extremities are plunged; for 
 example, a solution of nitrate of potash with nitric acid and 
 potash ; which proves that, even, in this case, there is still a 
 chemical action, probably due to the effect of the mass or to 
 the degree of concentration of the solutions. 
 
 The chemical action of acids upon acids may in like 
 
 manner give rise to electric 
 currents. Thus, if we pour into 
 one of the branches of a tube 
 bent into a U (Jig. 311.) some 
 concentrated sulphuric acid, 
 and, into the other, some nitric 
 acid, so that the two liquids 
 touch at m, without mixing, 
 which is easily obtained, on 
 account of their difference of density, on plunging the pla- 
 tinum extremities a and b of the galvanometer respectively, 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 699 
 
 into the two acids, a current is obtained, which goes 
 directly from the nitric acid d, to the sulphuric c, the former 
 acid playing the part of base in respect to the latter. Phos- 
 phoric acid produces with nitric acid the same effect as 
 sulphuric ; and, opposed to sulphuric, plays the same part as 
 sulphuric opposed to nitric. 
 
 The following is the order, in which the various conducting 
 solutions may be placed, so that each shall be negative in 
 respect to those which follow, and positive with those, which 
 precede * : 
 
 Phosphoric acid, sulphuric acid, nitric acid, hydrochloric acid, 
 acetic acid, nitrous acid, saline solutions, alkaline solutions. 
 
 There are however cases in which saline solutions are 
 negative with certain acids, and positive with certain bases ; 
 but these are exceptions, which are due to the circumstance, 
 that the phenomenon is complex. We may remark that, 
 in general, water plays the part of a base with acids, and of 
 an acid with bases. It is probably on account of the con- 
 siderable affinity that phosphoric and sulphuric acids have 
 for it, whence it follows that they take it from other solutions, 
 that we must attribute the fact that these acids are at the 
 head of liquids in the above Table. 
 
 We may add that, in order to study thus the currents that 
 arise from the mutual action of various solutions, it is pre- 
 ferable to have recourse to the first mode of operating 
 (fig. 310.), by connecting the two liquids, into which the two 
 platinum plates are plunged, by a skein of amianthus. It is 
 necessary, at the same time, before each experiment, always 
 to take the precaution of well cleaning the platinum plates 
 by heating them to redness, then placing them in boiling 
 nitric acid, and finally washing them in distilled water ; 
 then, having done this, we assure ourselves, by plunging 
 them into the same liquid, into nitric acid for example, that 
 
 * We always call that body (liquid in this case) positive, whence the cur- 
 vents or positive electricity sets out, in order to go directly to that, which acts 
 chemically upon it, and from the latter to return to the former, through the 
 galvanometer. 
 
700 SOURCES OF ELECTRICITY. PART v. 
 
 they produce no currents ; which proves that their surface 
 is quite clean. Notwithstanding this precaution, it always 
 happens that, as soon as a current has been produced, by a 
 chemical action, however slight it may be, the plates of 
 platinum are polarised by the effect of gaseous or other de- 
 posits, arising from the chemical effects of the current upon 
 the liquids, that it traverses ; and that this polarity, which 
 we have termed secondary, tends to produce a current, the 
 converse of that, which has produced it. It follows from this 
 that the intensity of the principal current is powerfully re- 
 duced by it, and sometimes even, to such an extent, that the 
 current is no longer sensible. 
 
 In order to avoid this grave inconvenience, M. Becquerel 
 has devised an apparatus, which he calls a depolariser, and 
 which consists of an arrangement of conductors, which are 
 caused to fulfil the office of rheotomes or of commutators. 
 By this artifice, which, by means of a rotatory motion, com- 
 bined with a downward and an upward motion, causes each of 
 the .plates of platinum to come at once out of the solution, in 
 which it is plunged, in order to plunge it into the other, these 
 plates are placed alternately in communication with one and 
 with the other of the two solutions, still remaining connected 
 respectively with the same end of the galvanometer, which 
 causes the deviation of the needle always to take place in the 
 same direction. In this manner, the current, due to the 
 polarisation of the plates, is added to that which is due to 
 the chemical reaction of the two liquids, in place of diminish- 
 ing or destroying it. If the interrupting apparatus travels 
 rapidly, and the current that is produced by the action of 
 the two solutions, is constant, the deviation of the needle 
 suffers no variation, whilst the platinum plates are in motion. 
 
 With the depolarising apparatus, we are able to discover 
 sources of electricity in the slightest chemical actions, such 
 as those, for example, that are produced by the reaction of 
 distilled water, upon various solutions. Thus, on placing 
 between the two glasses, in which the two platinum plates of 
 the depolarising apparatus are plunged, a succession of four 
 skeins of cotton, placed in contact one after the other, the 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 701 
 
 first and last of which are impregnated with distilled water, 
 whilst the second is impregnated with water saturated with 
 subcarbonate of soda, and the third with water saturated 
 with bicarbonate of soda, a current is obtained in this 
 circuit, which goes directly from the subcarbonate to the 
 water. This current is the difference between currents 
 going in contrary directions ; indeed, between the water and 
 the subcarbonate, there is a current going from the saline 
 solution to the water ; between the bicarbonate and the water, 
 it goes from the water to the bicarbonate ; and between the 
 bicarbonate and the subcarbonate, it goes from the bi- 
 carbonate to the subcarbonate. Experiment shows that the 
 sum of the two latter, the inverse of the former, is less power- 
 ful than it. 
 
 It is to an effect of the same kind that must be attributed 
 the development of electricity obtained by M. Foucault 
 in the following series of moist conductors in contact : 
 water, sulphuric acid, potash, water, sulphuric acid, potash, 
 water, fyc. There are three chemical actions, which give 
 three currents, directed, 1st, water and sulphuric acid, from 
 the water to the acid ; 2nd, sulphuric acid and potash, from 
 the potash to the acid ; 3rd, potash and water, from the pot- 
 ash to the water. M. Foucault's experiments only demon- 
 strate, that the first and third currents, moving in the same 
 direction, overpower the second, moving in the contrary 
 direction ; and cannot furnish the proof, as this philosopher 
 had believed, of a physical conductibility proper to liquids. 
 
 We can therefore form piles composed simply of two 
 liquids, reacting upon each other, and of a single metal, 
 serving as the arc of communication between the different 
 liquids of two consecutive pairs. The liquids, intended to 
 act upon each other, are generally separated by a porous dia- 
 phragm, either of earth or of an organic tissue. There are 
 cases, in which the difference of density between the two 
 liquids enables of their being placed in contact, by simply 
 superposing one upon the other, as we have seen above, 
 when we showed the action of nitric acid and even of diluted 
 sulphuric acid upon concentrated sulphuric acid. It is by 
 
702 SOURCES OF ELECTRICITY. PARTY. 
 
 operating in the same manner that Berzelius had constructed 
 a pile, in which a certain number of glass cups , b, c, d 
 (Jig. 312.), were half filled with a concentrated solution of 
 hjdrochlorate of lime, and half with a stratum of diluted nitric 
 
 Fig. 312. 
 
 acid, which, being lighter, did not mix with the saline solu- 
 tion. Arcs of copper c, c', c", c'", terminated at their ex- 
 tremities by little pieces of zinc z, z', z" ', /", were employed 
 for connecting the cups ; being arranged in such a manner, 
 that the zinc extremity of each plunged entirely into the 
 solution of hydrochlorate of lime, and the copper extremity 
 into the upper stratum of acid in the following cup. In this 
 pile, the zinc, although feebly attacked, is positive in respect 
 to the copper, which suffers a very active chemical action 
 on the part of the acid ; and the more so, as soon as the 
 circuit is closed, the zincs which had remained perfectly clean 
 and brilliant in the saline solution, lose their brilliancy and 
 become oxidised, whilst the coppers cease to be attacked. Al- 
 though, in the chemical theory of the pile, as we have laid it 
 down, this experiment is not an objection against that theory, 
 since it is the nature much more than the vivacity of the 
 chemical action, which determines the direction of the 
 current, yet the effect in this case is especially due to the 
 mutual chemical action of the two liquids ; and the oxidation 
 of the zinc, as well as the reduction of the oxidised copper, 
 are only the results of the transmission through these metals 
 of the current, arising from this action. Indeed, the same 
 current is obtained by substituting homogeneous arcs of zinc, 
 copper, or platinum for the metallic arcs zinc and copper : 
 only the current is more powerful with arcs of zinc than w r>1 
 
CHAP. in. ELECTRICITY BY CHRM1CAL ACTIONS. 703 
 
 arcs of copper or of platinum, and even than with the hetero- 
 geneous arcs of copper and zinc ; which arises from its ex- 
 periencing a much greater facility of passing from a liquid 
 into a metal, in proportion as this metal is more oxidisable. 
 
 M. Nobili, who was one of the first, who made a detailed 
 study of the currents, produced by the action of solutions 
 upon each other, by employing either a galvanometer or a 
 frog as a galvanoscopc, had obtained electrical effects by 
 causing acids to act upon salts, formed with the same acids, 
 such as sulphuric acid upon sulphates, nitric acid upon ni- 
 trates, &c. In the double decompositions, the current is more 
 frequently null, or at least very feeble. 
 
 Among the methods that have been proposed for deter- 
 mining the electricity developed in the chemical reaction of 
 two liquids upon each other, we shall in addition point out 
 that of M. Mousson, which consists in taking two discs, of 
 about two inches in diameter, of platinum and silver, which he 
 puts in metallic communication with the two ends of the wire 
 of a galvanometer. He then applies respectively on these two 
 discs, two discs of the same diameter, of unsized paper, mois- 
 tened with the liquids, upon which he desires to operate ; the 
 two discs are then approximated parallelly, and are placed with 
 pressure against each other. The deviation of the needle 
 immediately indicates the existence and the intensity of the 
 current. Although the galvanometer employed by M. 
 Mousson was by no means sensitive, the effects observed 
 were very decisive. Thus, with nitric acid and potash, the 
 needle flew round and round several times ; with potash and 
 nitrate of potash, it deviated to nearly 80 ; but in this case 
 the effect is due to the reaction of the potash upon the water, 
 which, it is true, when produced directly, gives only a devia- 
 tion of from 25 to 30, on account of the defect of conducti- 
 bility : ammonia and pure water give 30 ; nitric acid and 
 water 90. Sulphuric and hydrochloric acids present nu- 
 merous anomalies in the electricity, that results from their 
 action upon water, and even upon certain other solutions ; 
 which is probably due for the former to the effects of the heat 
 liberated, and for the latter to the circumstance that the 
 
706 SOURCES OF ELECTRICITY. FART v. 
 
 several days, as long as the pair acts. The effect is easy of 
 explanation ; the circulation of electricity due to the reaction 
 of the two liquids, is established in the pair itself; the current 
 sets out from the plate P, traverses the two liquids to go to 
 the plate N, and to return exteriorly from N to P ; the water of 
 the solution of potash is decomposed, the oxygen is liberated 
 on the plate P, and the hydrogen is transported into the 
 nitric acid. The latter absorbs the nascent hydrogen, and is 
 gradually coloured, in consequence of the presence of nitrous 
 vapours. 
 
 The pair devised by M, Becquerel is the first with a con- 
 stant current that had been constructed. This circumstance 
 is due to the plates not being polarised, because the nitrate 
 of potash that is formed is immediately decomposed by the 
 current, and the acid and alkali, transported one to the plate P, 
 the other to the plate N, are found in contact, the former 
 with the potash, the latter with the nitric acid, which causes 
 them to combine immediately and not to remain upon the 
 plates. We may strengthen this pair considerably by substi- 
 tuting for the platinum plate that is plunged into the potash, 
 a plate of amalgamated zinc ; this plate, by seizing upon the 
 oxygen, produces a current, which is added to the former. 
 By means of this pair, thus modified, a powerful decomposi- 
 tion is obtained of acidulated water, placed in a voltameter 
 with platinum wires. We may also connect voltaically, one 
 after the other, several of Becquerel's pairs, so as to obtain a 
 very powerful pile. 
 
 The oxygen-gas pile has been the subject of examination 
 to several physicists, both in regard to its effects, and in 
 respect to the nature of the action, which gives rise to the 
 electricity, that it liberates. Thus M. Jacobi has succeeded 
 in decomposing iodide of potassium by interposing it ex- 
 teriorly between fyvo platinum wires, soldered respectively 
 to two plates of the same metals, plunged, one in nitric acid, 
 and the other potash. He did not succeed in decomposing 
 sulphate of copper in the like manner. He has not found 
 in M. Becquerel's pair a dynamic activity in relation with its 
 chemical activity, when using, in order to appreciate the 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 707 
 
 force of its current, the action upon the magnetised needle, 
 or the magnetisation of soft iron. M. Fechner, on the other 
 side, had made a great number of experiments, with a view of 
 proving that the development of electricity in Becquerel's 
 pile was due to the respective contact of the platinum plates 
 with the acid and with the potash. He operated, by means 
 of four successive glasses, the two extreme ones of which 
 were simply filled in general with a conducting solution 
 of nitrate of potash, and the two middle with two solu- 
 tions, intended for acting upon each other, in particular 
 nitric acid and potash. He also called the two extreme 
 glasses conductors, and the two intermediate, producers. The 
 experiments of Fechner had been directed not only upon 
 nitric acid and potash, but also upon a great number of 
 other liquids. He had even substituted plates of other 
 metals for platinum plates, which complicated the results, by 
 making the action of the liquids upon the plates intervene 
 between the mutual action of the two liquids, producers of 
 electricity ; an action, which we have studied in the 
 preceding paragraph. As far as concerns more particu- 
 larly Becquerel's pile, Fechner had demonstrated that, in 
 order that the effect of this pile may be energetic, it was 
 necessary for the platinum to be in contact with the nitric 
 acid, and that it lost almost all its force, when the experi- 
 ment was so arranged, that the plates of platinum were plunged 
 into two vessels, filled with nitrate of potash, respectively 
 connected, by means of moist conductors, with the nitric 
 acid and the potash, which still act chemically upon each 
 other. Latterly Matteucci has taken up this subject, and 
 while still confirming the fact, pointed out by Fechner, 
 he arrived at some very interesting results upon the electric 
 effects, that arise from the mutual action of various solutions 
 upon each other. 
 
 After certain experiments upon the intensity of the current, 
 obtained by the action of different acids upon potash, and 
 upon certain oxides, and having recognised that the employ- 
 ment of nitric acid is always preferable, he has demonstrated, 
 as Fechner had done, the considerable influence that is 
 
 z z 2 
 
708 SOURCES OF ELECTRICITY. PARTY. 
 
 exercised over the intensity of the current by the fact, that 
 the nitric acid is in contact with the platinum, and he has 
 succeeded in finding voltaic combinations of two liquids 
 capable of producing still more powerful effects than Bec- 
 querel's pile. The following is the arrangement, that he 
 has adopted for making these various experiments : - one of 
 the liquids is contained in a glass bottle, into which is 
 plunged a cylindrical vessel of porous earth, which is filled 
 with the other liquid ; two platinum plates about an inch 
 wide, and four inches high, connected together by a metal clip, 
 plunged into the two liquids. M. Matteucci has also, in cer- 
 tain cases, placed both the liquids in two porous cylinders, 
 both plunged into sulphuric acid, diluted with eight or ten 
 times its volume of water. It was thus that he satisfied himself 
 that the current was almost as powerful, even when the potash 
 and nitric acid were not immediately in contact, but were both 
 in contact with the sulphuric acid, provided that the nitric 
 acid was always well in contact with the platinum. The 
 electric current was measured by the deviation of the needle 
 of the comparable galvanometer of Nobili, and by the 
 quantity of acidulated water, decomposed in a voltameter, 
 the platinum wires of which were ^ in. in diameter and 1 
 in. in length. In some the current was measured by the 
 weight of copper deposited upon the negative electrode, which 
 was in this case a platinum plate, similar to that employed 
 in the pile. 
 
 M. Matteucci's experiments had essentially for their object 
 the study, not only of simple pairs, but of piles, formed of 
 pairs of two liquids, as M. BecquerePs oxygen pair. The 
 liquids, successively tried, were, on the one hand, as attacked 
 bodies, concentrated solutions of caustic potash, protosulphate 
 of iron, sulphate of potash, hyposulphite of soda, penta- 
 sulphuret of potassium, monosulphuret of potassium* ; on the 
 other hand, as attacking bodies, pure and concentrated nitric 
 acid, a concentrated solution of chromic acid, a solution 
 
 * The monosulphuret is obtained by saturating with sulph-hydric acid, one 
 part of potash, and mixing it with one part, remaining in a state of caustic 
 potash, With regard to the pentasulphuret, it is prepared by boiling a con- 
 centrated solution of caustic potash with an excess of sulphur. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 709 
 
 of sulphuric acid, diluted with nine times its volume of 
 water. 
 
 M. Matteucci first satisfied himself that a single pair of 
 pentasulphuret of potassium and nitric acid decomposed 
 water in the voltameter and produced a constant deviation of 
 70 or 76 in the galvanometer. A very distinct spark may 
 likewise be obtained with this pair, by interrupting the 
 circuit through mercury. The monosulphuret of potassium, 
 placed in lieu of the pentasulphuret, gives the same effects, 
 with the simple difference that the action is more constant. 
 The two sulphurets of potassium also form with sulphuric 
 acid, pairs less powerful it is true, than with nitric acid ; 
 but then we see the hydrogen liberated around the plate, 
 that is plunged into the acid. We may increase the force of 
 these pairs by covering the platinum plate, that is plunged 
 into the acidulated water, with a coating of peroxide of lead ; 
 but then we cease to see the hydrogen liberated. A pair 
 formed with a concentrated solution of hyposulphate of soda 
 and nitric acid, or chromic acid, decomposes water, and gives 
 a constant deviation of 40 to 45. By substituting for the 
 acids water rendered- conducteous by means of a little sea- 
 salt, the electric effects that are obtained, are scarcely sensible 
 with the different solutions, indicated above. 
 
 M. Matteucci was not content with studying the effect of a 
 single pair ; he formed with these pairs piles, the power of 
 which he measured. These various piles, composed of twelve 
 pairs, were at first two piles, one nitric acid and potash, the 
 other nitric acid and pentasulphuret of potassium. This 
 latter is the most powerful of all those which can be formed 
 with two liquids. Indeed, it gave a fixed deviation of 75, 
 and 4-J- cub. in. of mixed gases ; whilst that with nitric acid 
 and potash, gave only -67 cub. in. in five minutes, and a de- 
 viation of only 46 to 48. A Grove's pile, also of twelve pairs, 
 liberated in the same voltameter, 8 cub. in. of the gaseous 
 mixture ; that is to say, not quite the double of that which 
 was given by the nitric acid and pentasulphuret pile. On 
 interposing between the nitric acid and pentasulphuret, con- 
 tained in two porous cylinders, a layer of diluted sulphuric acid, 
 
 z z 3 
 
710 SOURCES OF ELECTRICITY. PARTY. 
 
 the effects of this pile are in no way changed. A pile of twelve 
 pairs, each of which was formed of a saturated solution of 
 sulphurous acid and nitric acid, contained in porous cylinders, 
 plunged at the same time in the sulphuric acid solution, gave 
 from 40 to 45 of deviation, and '36 cub. in. of the mixed 
 gases in five minutes. The effects were very nearly the 
 same on substituting, for the sulphurous acid solution, that 
 of sulphate of potash. Finally, with twelve pairs, formed 
 of nitric acid and a concentrated solution of the sulphate of 
 protoxide of iron, a fixed deviation is obtained of 16, and 
 4*88 cub. in. of the gaseous mixture in five minutes. 
 
 M. Matteucci succeeded in proving that the liberation of 
 electricity, which takes place in piles of two liquids, is 
 independent of the metallic arc ; and this, by employing, 
 for connecting these liquids, the nervous filament of the 
 galvanoscopic frog, by means of two glass tubes, filled with 
 sand, rammed down and moistened with a solution of sea- 
 salt or pure water, communicating on the one hand with two 
 different points of the nervous filament, and on the other with 
 the two liquids of the pairs. 
 
 The inspection of the liquids, after the circuits of the dif- 
 ferent piles has been closed for a certain time, shows, more- 
 over, in an evident manner, the presence of an oxidising 
 chemical action, or a liberation of oxygen around the positive 
 platinum plate ; and a deoxidising action, or liberation of 
 hydrogen around the negative.* 
 
 Finally, in order to demonstrate well the" chemical origin of 
 the electricity developed in the piles of two liquids, M. Mat- 
 teucci endeavoured to measure at the same time the electro- 
 chemical effects, produced in the pairs of a pile in action, and 
 that which takes place in the voltameter, wherewith the circuit 
 is closed. With the pile of twelve pairs, nitric acid and potash, 
 he always found the quantity of oxygen a little less in the in- 
 terior of the pile than in the voltameter, especially when the 
 action was slow, and the surface of the plate, in contact with 
 
 * We must not forget that we call that plate positive, whence the current 
 sets out, in order to go into the liquid ; and thence to the other plate, which 
 we term negative, although it is the one, whence the current seems to go, in 
 order to traverse the circuit. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 711 
 
 the potash, was considerable. It is possible that this differ- 
 ence is due either to the formation of a bioxide of potassium, 
 or to an action of the oxygen upon the platinum, in presence 
 of the potash. Perhaps, in these actions might be found the 
 cause of the evident influence that the contact of the platinum 
 with the potash exercises over the intensity of the current, 
 produced by this pile. With a pile of twelve pairs of diluted 
 sulphuric acid, and monosulphuret of potassium, the quantity 
 of hydrogen, collected in the acid, was exactly the same as 
 that furnished by the voltameter. With a pile of twelve pairs 
 of monosulphuret of potassium and sulphate of copper, the 
 law of equivalents is found equally verified. Thus the 
 quantity of copper, deposited upon two platinum plates, 
 taken, one in one of the pairs, the other in a voltameter, filled 
 with a solution of sulphate of copper, is found to be almost 
 exactly the same. In one experiment it was 14*68 grains, 
 on the negative plate of one of the pairs, and 14 '64 grains on 
 the negative electrode of the voltameter. 
 
 It is more difficult to collect and to measure the oxygen, 
 liberated in the interior of the pile ; however, M. Matteuccj 
 has succeeded in this, by forming a pile with pairs, composed 
 of a solution of sulphurous acid, and a solution of nitrate of 
 silver, containing ten parts of water by weight for one of 
 nitrate. After having, by a comparative experiment, esti- 
 mated the quantity of sulphuric acid, that is formed by the 
 oxygen of the air, he was able, by dosing it by means of 
 baryta, to determine exactly the proportion of this acid, 
 that is produced in the sulphurous acid, by the oxygen 
 itself, that arises from the action of the pile. After several 
 essays, and by taking various precautions, he arrived at 
 results that were very satisfactory for their accuracy. Thus 
 having obtained 7*27 grains of silver, deposited upon the 
 negative plate, he found, on taking account of the sulphuric 
 acid, formed by the oxygen of the air, that the quantity of 
 this acid, corresponding to the silver reduced, was 2*73 grains, 
 instead of being 2*69 grains, which would be exactly the 
 equivalent of the silver obtained. The difference between these 
 two numbers is so small, that we may well regard it as demon- 
 
 z z 4 
 
712 SOURCES OF ELECTRICITY. PARTY. 
 
 strated that the quantity of oxygen which, arising from the 
 decomposition of the water in the pairs, combines with the 
 sulphurous acid, is equivalent to the quantity of silver that is 
 decomposed in the pile. We may also remark that, in the 
 pairs, into which nitric acid enters, such as that with nitric 
 acid and potash, it is not only the action of the nitric acid 
 upon the potash, which determines the current, but especially 
 the presence of nitric acid around the platinum plate ; since, 
 provided this presence is maintained, almost as much effect is 
 obtained by interposing a solution of sulphuric acid between 
 the nitric acid and the potash ; and that, on the contrary, the 
 intensity of the current becomes very feeble on placing the 
 sulphuric acid in contact with the platinum, and the nitric 
 acid between it and the potash. These results are easy of 
 comprehension in the theory, that we have given of the pro- 
 duction of electricity in a voltaic pair. The action of nitric 
 acid, like that of sulphuric acid upon potash, produces a cur- 
 rent, in which the acid acquires positive and the alkali, 
 negative electricity. These two electricities are immediately 
 united upon the surface itself of contact of the two liquids, in 
 proportion as they are separated ; but if the circuit is closed, 
 by means of a metallic arc, these two electricities are able to 
 neutralise each other by traversing the circuit; however, 
 they cannot do this, except by decomposing the water of the 
 solutions, and in particular that of the potash. Now, this 
 decomposition is excessively facilitated by the presence at the 
 negative electrode of a body, that easily abandons its oxygen, 
 such as nitric acid ; and which thus plays, in this case, the 
 same part, that we have seen played by the peroxide of lead 
 in a zinc and platinum pair. The acid, like the peroxide, on 
 being deoxidised by means of the hydrogen of the decomposed 
 water, adds further to the force of the current. It is easy to 
 understand that the sulphuric acid, around the platinum 
 plate, cannot produce the same effect. 
 
 We have hitherto spoken only of the electrical effects, 
 that accompany the mutual chemical actions of two solutions; 
 but this is not the only action, that a solution may suffer. 
 Thus, it may be decomposed, without the intervention of a 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 713 
 
 second solution being necessary. This is what happens, for 
 example, when water, which holds a foreign body in solution, 
 is made to evaporate in a heated crucible. M. Pouillet, who 
 was the first to make this species of observation, employed 
 a capsule, and even with more advantage a thick plate of 
 platinum slightly hollowed, which he caused to communicate, 
 after having heated it to redness, with the lower plate of a 
 condenser, by means of a rod, soldered to this plate. After 
 having satisfied himself that the evaporation of pure water 
 did not liberate electricity, he poured successively, into the 
 crucible, some drops of a solution, acid, basic, or saline. He 
 observed that, with a solution of strontian, the capsule, at the 
 moment of the evaporation, preserved the positive electricity, 
 whilst the vapour carried off the negative ; it was the same 
 with other alkaline solutions. Ammonia alone presents a 
 converse effect, because, being more volatile than water, it 
 carries off the positive electricity, and leaves to the water, 
 and consequently to the capsule, the negative electricity. 
 With acid solutions, on the other hand, it is the water that 
 is positive and the acid acquires negative electricity. With 
 a solution of sea-salt it is the same. It therefore appears, 
 from these various researches, that the electric effects, in 
 chemical decompositions, are the reverse of those that take 
 place in combinations. It is, moreover, what we had already 
 remarked, in making a pair with a plate of platinum and 
 peroxide of manganese, or peroxide of lead, plunged into 
 acidulated water. The decomposition of the peroxide pro- 
 duces a current, which goes in the converse direction to that 
 which would result from the oxidation of the metal. We 
 may further prove the accuracy of this principle by projecting 
 solid bicarbonate of soda, into the platinum capsule, heated 
 to redness. This salt is decomposed, by allowing the carbonic 
 acid to escape, which carries off the negative electricity, 
 whilst the capsule acquires a powerful excess of positive 
 electricity. 
 
 M. Peltier, who has studied this subject carefully, remarks 
 that electricity is not produced in the experiments, that we 
 have been relating, in all the phases of the evaporation, but 
 
714 SOURCES OF ELECTRICITY. PARTY. 
 
 only at the moment when the liquid, quitting the spheroidal 
 state, suffers a species of crepitation. He concludes from this 
 that electricity is liberated only at the moment, in which a 
 chemical decomposition takes place, arising from the segrega- 
 tion of the combined water, and not during the separation of 
 the superabundant water. 
 
 M. Gaugain is rather disposed to see in these various phe- 
 nomena the result of the friction against the sides of the cru- 
 cible, of the particles of water, projected at the moment of 
 decrepitation. His opinion is based upon the fact that slow 
 evaporation, which is moreover accompanied also by a 
 chemical decomposition, does not produce any effect, and, 
 moreover, upon the fact, that the electricity developed in this 
 kind of action does not communicate instantaneously to the 
 condenser the maximum of charge, that it carries off, which 
 would be the case, if an electric source, having its principle 
 in chemical action, were the matter in question ; on the 
 contrary, the quantity of electricity increases up to a certain 
 limit with the duration of the action ; and has an invariable 
 value, independent of the extent of the surfaces of the 
 condenser, as is the case for friction ; whilst, when chemical 
 action is in question, not only is the charge instantaneous, 
 as we have just said, but it increases indefinitely with the 
 surface of the condenser employed. It was by operating upon 
 a solution of sea-salt, that M. Gaugain made these observa- 
 tions. It would not appear that the electricity produced, can 
 be due to the friction of the particles of salt against the 
 surface of the platinum ; for direct experiment made by 
 blowing dry sea-salt in powder against the sides of a platinum 
 crucible, heated to redness, has shown that this crucible was 
 charged with positive and not with negative electricity. It 
 would then be only to the friction of the water, that the 
 effect must be due. But then, why should not distilled water 
 produce it equally ? and why should it take place as well 
 in a wide-mouthed capsule, as in a narrow one, whilst there 
 is electricity, liberated by the friction of pure water, in the 
 latter case only, and not in the former ? 
 
 We are therefore disposed to believe that, an electric 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 715 
 
 effect is indeed produced in chemical segregations, in like 
 manner as there is one in combinations, and that, if its ma- 
 nifestation does not in general take place, except when the 
 evaporation is very rapid, this is due, as we have already had 
 occasion to remark in the preceding paragraph, to the fact 
 that in this way we better avoid the immediate recomposition 
 of the two electricities. 
 
 It is also to the decompositions of solutions, that we must in 
 very great part attribute the electric effects, that are obtained 
 by plunging into a liquid two platinum wires, connected to the 
 two ends of a galvanometer, and of which one has been heated 
 to redness, whilst the other has remained cold. Every time 
 that the heated wire takes from the liquid positive electricity, 
 or, which comes to the same thing, plays in the pair the part 
 of negative metal, the electricity arises from the decomposition 
 of the solution, and the wire plays the same part, that was 
 played by the platinum capsule in the preceding experiments ; 
 whilst, when it acquires negative electricity, or conducts 
 itself as the positive metal, it is probable that the electricity 
 arises from a chemical action, exercised upon it by the solu- 
 tion. This is in fact the conclusion, that may be drawn from 
 the experiments, made upon this by M. Henrici. Thus, he has 
 found that whether with hydrochloric acid, or with a solution 
 of potash, the heated wire does acquire negative electricity; a 
 proof that it is attacked, which should actually have taken 
 place in this case. With sulphuric and nitric acids, either 
 concentrated or diluted, the heated platinum wire acquires on 
 the contrary positive electricity, because these are solutions, 
 that are decomposed under the influence of the heat of the 
 platinum. 
 
 To sum up, the electrical effects, that accompany the che- 
 mical actions in which the bodies submitted to these actions 
 are liquids, enter in a general manner into the laws, which 
 regulate the chemical actions, in which one of the bodies is a 
 solid and the other a liquid. However, in order to collect 
 the electricity produced in these actions, we must necessarily 
 employ a solid body as a conductor ; it follows that, whatever 
 precaution may be taken in order that this body may be in- 
 
716 SOURCES OF ELECTRICITY. PART v. 
 
 active, by choosing it among the unattackable metals, such as 
 platinum, it is not always possible to avoid its active inter- 
 vention, which, in these cases, render the phenomena more 
 complex. This is what in particular necessarily follows 
 from the circumstance that unattackable metallic plates, as 
 well as those which are attackable, acquire a secondary pola- 
 rity, by the mere fact that they have transmitted the currents 
 developed in liquids. We are about to see, in the follow- 
 ing paragraph, which is devoted to the study of this polarity, 
 how we may take account of it. 
 
 Production of Electricity in the Chemical Action of Liquids upon 
 the thin Films with which solid Surfaces are covered. Second- 
 ary Polarities ; Gas Pile ; passive Iron. 
 
 Hitter had observed that, on forming a pile of discs of the 
 same metal, alternately with moist card, this apparatus, in- 
 active of itself, becomes capable of giving similar effects to 
 those of the ordinary pile, when it has been interposed for a 
 few moments in a voltaic circuit. The action of this pile, 
 which Ritter had called secondary, was the more powerful, as 
 the current, which had charged it, was more energetic, and as 
 the surface of the metallic discs, employed in its construction, 
 was more considerable, and as the liquid with which the 
 papers were moistened was a better conductor. But this 
 action was not permanent ; it ceased when the pile had acted 
 for a few moments. Volta, having examined Ritter's secon- 
 dary piles, declared that the ordinary pile did not transmit 
 to them any charge, but that their effect was due to this 
 circumstance, that the electric current, in traversing them, 
 decomposed the liquid, interposed between the discs of homo- 
 geneous metal, and covered the surface of each of these discs, 
 with two different solutions, one acid, the other alkaline, when 
 the liquid employed was a saline solution, most frequently the 
 case. This opinion of Volta has been completely confirmed by 
 ulterior researches, and especially by the detailed analysis, that 
 Marianini has made of Ritter's secondary piles. The learned 
 Italian philosopher has demonstrated that it is not as Ritter 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 717 
 
 had conceived, to the difficulty which they oppose to the 
 passage of electricity, that secondary piles owe their electro- 
 motive power, since the more easily they transmit the current 
 of the active pile, the more powerfully and easily they are 
 charged. He has equally proved that the cause of the elec- 
 tricity, that is liberated in secondary piles, is entirely in the 
 alterations that are suffered by the surfaces of the metallic 
 parts, in the portions, in which they are in contact with the 
 moist conductors, since we may turn round and even change 
 these latter, without destroying or even diminishing the power 
 of these piles. Only this alteration is not due, as Marianini 
 seems to think, to a physical modification, that the metallic 
 surfaces might have suffered, but to a simple formation of de- 
 posits arising from the decomposing action, exercised by the 
 transmitted current, upon the liquid of the secondary pile : 
 deposits which, by the chemical action, that is exercised upon 
 them by the liquid, are the origin of the electricity liber- 
 ated. 
 
 We may further add (in order not to be called upon to 
 return to this point, which is however of little importance, 
 except, as we shall see, as far as it concerns the influence, 
 that it exercises upon the force of the voltaic pile), that the 
 best arrangement to be given to secondary piles consists in 
 uniting a series of vessels, filled with a conducting solution, 
 saline for example, by homogeneous arcs, of copper, and even of 
 gold or platinum (Jig. 314.); then, when a current, which should 
 
 Fig. 314. 
 
 have more intensity, in proportion as the number of inactive 
 pairs is more considerable, is transmitted through the system 
 of inactive pairs, the secondary pile is found to have ac- 
 quired an electric charge. It gives signs of tension at its 
 two extremities, and a current, capable of acting upon the 
 
718 SOURCES OF ELECTRICITY. PART v. 
 
 needle, of producing heat, and even a spark, and of decom- 
 posing water. Only the nature of the electricity, accumulated 
 at its two poles, as well as the direction of the current that 
 is established when these poles are united, indicates that 
 these extremities have acquired contrary electricities to those 
 of the poles of the voltaic pile, with which they have been 
 placed in communication. This is an evident consequence 
 of the nature of the deposits, which the initial current has 
 determined upon each part of the metallic arc, and of the 
 direction of the current, to which the chemical action of the 
 liquid upon these respective deposits gives rise. 
 
 In order well to analyse this order of phenomena, we must 
 begin by studying it upon a single secondary pair, and 
 not upon an entire pile. With this view two plates of the 
 same metal are plunged into a vessel, filled with a conducting 
 liquid ; it is preferable to employ platinum, in order to avoid 
 the direct chemical reaction of the liquid upon the metal 
 itself. The current of a voltaic pile is made to pass for 
 some time through the liquid, employing as electrodes plates 
 of metal ; then, after having interrupted the current, the plates 
 are put into communication with a galvanometer, and a 
 powerful current is immediately observed, which lasts for 
 some instants, and the direction of which is the reverse of 
 that which had been transmitted. This current is termed 
 secondary, in opposition to that which had charged the 
 apparatus, and which is termed primary ; and we designate, 
 as we have already seen, under the name Q secondary polarity, 
 the property, which the metal plates have acquired, in trans- 
 mitting the primary current. 
 
 Whenever the electrolytic liquid is a saline solution, the cur- 
 rent produced by the secondary polarities is easy of explana- 
 tion, as M. Becquerel had first clearly demonstrated ; in fact, 
 there is deposited upon the surface of the negative electrode, 
 a film of alkali, and upon that of the positive electrode a 
 film of acid, which, by the action, that is exercised upon 
 them by the solution, ought to produce a current directed 
 from the alkali to the acid in the liquid ; and, consequently, 
 from the plate, that had served as a positive electrode, to 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 719 
 
 that which had served as negative electrode, in the wire of 
 the galvanometer, by which they are united. We can 
 produce the same current without employing the electrolytic, 
 solution ; but by simply plunging one of the plates into an 
 acid, and the other into an alkali, and then placing them in a 
 conducting solution, after having united them with the two 
 ends of a galvanometric wire. 
 
 It was less easy to explain the cause of the secondary current 
 developed when the electrodes which have acquired polarity 
 are simply plunged into pure or acidulated water ; and 
 when, consequently, the deposit, with which they are covered, 
 can be only oxygen or hydrogen. I had already, in 1826, 
 proved the existence of secondary polarities upon platinum 
 plates or wires, when the solution is only water, slightly 
 acidulated with sulphuric acid. I had attributed them to a 
 particular state of polarity, which the electrodes themselves 
 might have contracted under the influence of the current; 
 but M. Becquerel having demonstrated that, when the 
 circuit is all metallic, the phenomenon no longer takes place, 
 and the electrodes present it merely in the parts of their 
 surface, that have been in contact with the electrolytic 
 liquids, it would become natural to see its cause, in the 
 deposit of small gaseous films upon the part of the electrodes, 
 where the liberation of the gases, that arise from decomposition, 
 has been brought about. It was M. Matteucci, who first 
 confirmed this explanation by direct experiments made with 
 very pure water. He assured himself that the polarities 
 remain upon the platinum plates for a very long time, 
 that they may be destroyed by heating these plates to red- 
 ness, and that a single plate was sufficient for exciting the 
 current, when employed with another, which has not been 
 used as an electrode ; but yet, in this case, the plate upon 
 which the hydrogen is deposited, gives a more decided effect 
 than that, upon which the deposit has been oxygen. 
 
 In order to show that there is actually a film of hydrogen, 
 adhering to a plate which has been used as a negative elec- 
 trode, and one of oxygen to a plate, which has been used 
 as a positive electrode, M. Matteucci introduced the former 
 
720 SOURCES OF ELECTRICITY. PART v. 
 
 into a small graduated receiver filled with oxygen, and the 
 latter into a similar receiver filled with hydrogen. In each 
 of the receivers, there was a diminution of volume, which can 
 only arise from the combination of the oxygen and hydrogen 
 contained in the two receivers, respectively with the hydrogen 
 and oxygen remaining adhering to the plates. In one experi- 
 ment the diminution was *024 cub. in. in the oxygen and '012 
 cub. in. in the hydrogen. We may call to mind that I obtained 
 a similar result on reversing the direction of the current in 
 the electrolytic decomposition of acidulated water ; and by 
 showing that the quantities of gas liberated are less than 
 they ought to be, when we take as a negative electrode the 
 plate, that has served as positive electrode and reciprocally.* 
 Moreover, M. Matteucci has equally succeeded in this case 
 as he had done in the case of alkaline and acid deposits, in 
 demonstrating, by a direct experiment, that the current is 
 indeed due to films of hydrogen and oxygen, that are deter- 
 mined by the electrolytic decomposition of the water. With 
 this view, he placed platinum plates in very pure hydrogen 
 and oxygen ; then, after having drawn them out and united 
 them to the wire of a galvanometer, he plunged them into 
 distilled water, and obtained deviations, that amounted to as 
 much as 90. The current always goes in the liquid from 
 the plate, which has been in the hydrogen, to that which has 
 been in the oxygen. The films of gas obtained in this manner 
 are as adherent as those, which are determined by electrolytic 
 decomposition ; it is only necessary to leave the plates in the 
 gases for about ten minutes, in order to obtain the maximum 
 effect. A current can also be obtained by employing only 
 one plate, which has been plunged in hydrogen or in oxygen, 
 and uniting it with another, which has not been placed in con- 
 tact with any gas. In these experiments, it is necessary to em- 
 ploy plates of platinum or of gold, and to be assured, before 
 imparting to them the secondary polarity, that they do not of 
 themselves produce any current. 
 
 M. Schoenbein, in the numerous researches, that he has 
 
 * Vitte above, Vol. II. p. 414. 
 
. in. ELECTRICITY BY CHEMICAL ACTIONS. 721 
 
 maae upon this subject has remarked that, if we separate 
 into two compartments by a porous partition, the vessel 
 in which distilled water is electrolytically decomposed, 
 a very decided current is obtained by plunging into the 
 water of each of these compartments a plate of platinum, 
 that has not been used as an electrode ; and he satisfied 
 himself that this property appertains to the water of the 
 compartment, in which the hydrogen is liberated; for, it 
 subsists, when this water is transported into another vessel, 
 or is in contact by the intervention of another membrane 
 with water chemically pure. The water, in which the 
 oxygen had been liberated, does not possess the same pro- 
 perty. This arises therefore evidently from the hydrogen 
 dissolved in the water ; and, in fact, for developing it, we 
 have merely to cause hydrogen to dissolve artificially in pure 
 water without having need to employ for this purpose electro- 
 lytic decomposition. It is indispensable, in order to succeed, 
 that the metallic plate, which plunges in the hydrogenated 
 water, be of platinum ; that which plunges in water, whether 
 oxygenated or pure, may be indifferently platinum, gold or 
 even silver. The current always travels directly from the 
 water, in which the hydrogen is dissolved, to the water that 
 is in contact with the former by the intervention of the porous 
 partition. M. Schoenbein % has also observed that water, in 
 which oxygen has been made to dissolve, either directly or 
 by transmitting into it a current, the positive electrode of 
 which is in contact with it, is completely inactive with 
 ordinary water, even in the case, in which the circuit is 
 closed by plates of platinum, that plunge into the two liquids ; 
 yet platinum and gold, that have been employed as positive 
 electrodes in water, acquire thus a very decided secondary 
 polarity, a polarity, that is not imparted to them by their 
 simple contact with oxygen, contrary to what had been 
 observed by M. Matteucci. M. Schoenbein thinks with justice 
 that this negative polarity is communicated to the platinum 
 and the gold by a film of ozone or ozonised oxygen, which is 
 deposited upon their surface ; for, he is able to impart the 
 same property to these metals by simply plunging them for 
 VOL. II. 3 A 
 
722 SOURCES OF ELECTRICITY. PART v. 
 
 several moments in air, ozonised by means of phosphorus. 
 Water that is agitated in a large flask, filled with ozonised 
 air, with pure water and plates of platinum, that have not 
 been polarised, gives a current, that goes from the pure 
 water to the ozonised water. The phenomenon takes place 
 as in the case, in which the water holds in solution chlorine, 
 bromine or iodine ; substances, which, like ozone, impart to 
 platinum and gold, when they form a deposit on their surface, 
 negative polarity. In general, as M. Schoenbein was the first 
 to observe, platinum plunged into water, which holds in 
 solution chlorine, bromine, iodine or even ozone, comports it- 
 self opposite platinum which is plunged into pure water, sepa- 
 rated from the former by asimple porous partitionas aperoxide 
 (peroxide of lead), which might form a pair with a plate of 
 platinum in ordinary or slightly acidulated water. It would 
 seem at first sight that platinum plunged into the solutions, 
 that we have been naming, ought on the contrary to have 
 comported itself as a positive metal, on account of the che- 
 mical action, that it must suffer on their part. But the 
 phenomenon is altogether different ; under the influence of 
 platinum, chlorine, bromine, iodine decompose water as a 
 peroxide does ; and it is easy to see that the electrolytic chain 
 is then established, so that the current travels in the liquid 
 from the platinum plate, that is plunged in the pure water, 
 to that which is plunged in the solution, all the hydrogens of 
 the molecules of water being turned on the side of the latter, 
 and the oxygens on the side of the other. Ozonised oxygen, 
 comports itself like chlorine, bromine and iodine ; whilst it 
 is not the same with ordinary oxygen, which is due to the 
 circumstance that the former decomposes water under the 
 influence of platinum, and not the latter. In this general 
 property is found the explanation of the fact, observed by 
 several philosophers, that the solution of chlorine, bromine, 
 and even iodine facilitates the production of electricity in a pair, 
 that is plunged in these solutions, as well as the decomposition 
 of water, in which these substances are dissolved. Indeed, 
 it is a chemical force, which is added to that of the negative 
 metal of the pair, or of the negative electricity of the pile, in 
 order to separate the hydrogen from its oxygen, in each of 
 
CHAP. ill. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 '23 
 
 the molecules of the filament of water, which is already 
 polarised by the positive metal of the pair, or by the positive 
 electricity of the pile. 
 
 Mr. Grove has analysed with great care the phenomena, 
 that are engaging our attention, and has drawn from them the 
 most remarkable consequences. He was the first to show 
 that the action of hydrogen and oxygen upon water, under 
 the influence of platinum, is able to give rise to a constant 
 current, and not only to currents of a more or less short 
 duration. With this view, he took two tubes, closed at their 
 upper part, and each containing a platinum plate, able to 
 communicate exteriorly by means of pieces g and g f attached 
 (fig. 315.). He filled these tubes with acidulated water; he 
 then introduced hydrogen into one, and oxygen into the 
 other, taking care that the platinum plate was 
 plunged, half in the gas, and half in the liquid ; 
 the two tubes being then placed in communi- 
 cation, by means of a solution of sulphuric 
 acid, in which they plunged by their lower 
 part. A constant and decided current was ob- 
 tained by connecting the two platinum plates 
 by the wire of a galvanometer. It is neces- 
 sary for these plates to have been previously 
 well cleaned. The tubes may be filled with 
 the desired gases by causing a voltaic cur- 
 Fig. 315. rent of sufficient force to pass through the 
 liquid, to which the plates serve as electrodes. If the pre- 
 caution is taken of allowing the metallic communication 
 between the plates of platinum to subsist for a long time 
 successively, by which the current is maintained, w r e gradually 
 perceive the oxygen and hydrogen diminish in the two tubes, 
 in the proportion of one volume of oxygen for two of hy- 
 drogen. 
 
 Mr. Grove having recognised that the action can take 
 place only at the place where the liquid, the gas, and the 
 metal are in contact, endeavoured to obtain as great a surface 
 of action as possible. With this view, he employed plates of 
 platinum platinised, that is, covered with a thin pulverulent 
 
 3 A 2 
 
724 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 film of platinum, according to the process of Mr. Smee.* The 
 first experiments were made with platinum wires instead of 
 plates ; and having connected fifty similar pairs voltaically, so 
 that the wire plunged in the hydrogen of the one, communi- 
 cated with the wire plunged in the oxygen of the other, he 
 succeeded in obtaining a pile, the poles of which caused a 
 gold-leaf electroscope to diverge. These same poles, when they 
 were terminated by charcoal points, gave between them a 
 spark visible in open day. The pile produced a shock, that 
 might be felt by five persons connected together, could decom- 
 pose iodide of potassium, hydrochloric acid, water acidulated 
 with sulphuric acid ; acted on the magnetised needle, &c. The 
 effects were the same, whether the pile was charged with 
 oxygen and hydrogen, arising from the electrolytic decom- 
 position of water, as with oxygen and hydrogen, prepared by 
 purely chemical processes. This new pile or battery, was 
 termed by Mr. Grove the gas pile or battery ; and he gave 
 to it various forms ; the last at which he stopped, appears to 
 us the most convenient. 
 
 The following is the description of it : 
 
 Each cell is formed (fig. 316.) of a 
 glass bottle a with three necks, similar 
 to the bottles of fig. 308. which we 
 have used in the construction of the 
 pile, for the purpose of establishing the 
 law of equivalents in the interior itself 
 of the pile. A glass stopper b closed 
 the centre neck; tubes o and h are 
 accurately adjusted in the other two 
 openings by means of collars of glass, 
 which form part with these tubes, and 
 which are ground exteriorly with emery, 
 as is the stopper of the opening ; each 
 tube contains a plate of platinised pla- 
 Fig.316. tinum, not quite so long as the tube, 
 
 * This process consists in employing the plates of platinum, that are to be 
 platinised, as negative electrodes in a solution of chloride of platinum ; they 
 are soon covered with a deposit of pure platinum, but in the state of great 
 division. 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 725 
 
 which is terminated above by a thick platinum wire ; this 
 wire traverses the top of the tube, into which it is hermetically 
 sealed, and carries a small copper cup, that is filled with mer- 
 cury *, which, by means of bent wires, serves to establish com- 
 munication between the successive pairs, as is seen in Jig. 317. 
 
 Fig. 317. 
 
 In order to introduce the acidulated water into the tubes 
 we begin by completely filling the bottle, and then turn it 
 over, taking care to retain with the fingers, the glass stopper 
 and the tubes ; the latter being below, are soon filled with the 
 liquid, especially if care is taken to shake it a little in order 
 to drive out the air. Finally, the gases are introduced into 
 each tube, either by means of a bent tube, which communi- 
 cates with the receiver where the gas is ; or (which is more 
 convenient) by bringing about, by means of an ordinary pile, 
 the decomposition of the water in each bottle. As only one- 
 half less oxygen is required than hydrogen, one of the tubes is 
 narrower than the other, and care must be taken to introduce 
 the oxygen into this latter. Moreover, the tubes are carefully 
 graduated, so as to be able to measure the gaseous volumes. 
 The advantage of this arrangement of the gas pile is, first, 
 that, by plunging the bottle into the pneumatic trough, we 
 are enabled to detach each tube, in order to measure and to 
 examine the gas, that it contains ; moreover, .as the interior 
 
 * Small metal clips may be advantageously substituted for the cups. 
 3 A 
 
726 SOURCES OF ELECTRICITY. PARTY. 
 
 of the bottle is perfectly impermeable to air, and finally being 
 exclusively composed of glass and platinum, it can contain 
 electrolytic liquids of every kind, even the most corrosive. 
 
 A single pair of the gas pile, constructed according to the 
 description, that we have just given of it, is sufficient for de- 
 composing iodide of potassium ; only four are necessary for 
 decomposing the acidulated water of the voltameter. With 
 two pairs the decomposition is brought about with sufficient 
 rapidity to produce, in one experiment, at the end of thirty-six 
 hours, 2 cubic inches of the gaseous mixture in the voltameter ; 
 at the same time, the liquid mounted in each of the hydrogen 
 gas tubes of the pile, 1*46 cubic inches, and in each of the 
 oxygen, -67 cubic inches, which makes in all 2-12 cubic inches 
 that have disappeared in each pair ; a quantity almost ex- 
 actly equivalent to that, which had been liberated in the volta- 
 meter. Frequently, a little more hydrogen disappeared in 
 the pairs, than the quantity equivalent to that of the oxygen 
 absorbed, which is due to the combination, that is brought 
 about, under the influence of the platinum, between the hydro- 
 gen that is in the tube, and the oxygen dissolved in the 
 water. This species of local action takes place equally, 
 whether the pair forms part of the voltaic circuit, or is not in 
 action. 
 
 In order to demonstrate the accuracy of this explanation, 
 it is necessary to drive out as much as possible from the acid 
 solution, all the air that is dissolved in it ; and for this 
 purpose we have merely, after having caused this solution to 
 boil well, to place the trough and the two tubes, that contain 
 it, for twenty-four or forty- eight hours, in vacuum. After- 
 wards, by means of a voltaic current, one of the tubes 
 is filled with oxygen, and the other with hydrogen ; then, 
 after having left the apparatus for two or three weeks, without 
 touching it, the volume of hydrogen is still found to have 
 diminished a little, but much less than when the air has not 
 been driven -out. The volume of oxygen has not changed. 
 On the other hand, another cell is taken, and, far from driving 
 the air from it, as little liquid as possible is put into it, only 
 as much as is necessary for the tubes to dip into the bed of 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 727 
 
 liquid by their lower extremities ; the rest of the bottle 
 is filled with atmospheric air, but the air does not communi- 
 cate with the external air, the bottle being hermetically 
 closed. At the end of about a fortnight, it may be proved 
 that the hydrogen has considerably diminished ; in one expe- 
 riment it diminished 1*95 cubic inches; and, if we introduce 
 into the cell at the moment when it is opened a lighted taper, 
 it is seen to be immediately extinguished, because nothing 
 remains but nitrogen in the upper part of the bottle, and the 
 oxygen of this air has been absorbed gradually by the 
 liquid, in order to come and combine with the hydrogen. 
 Thus, hydrogen, under the influence of platinum, combines 
 with the oxygen, dissolved in the liquid with which this hy- 
 drogen and platinum are in contact ; and the liquid, taking 
 up oxygen, in proportion as its own disappears, is thus able to 
 remove it gradually and almost entirely from the atmospheric 
 air, that is in contact with it.* Mr. Grove has succeeded in 
 obtaining, by this action alone, a tolerably energetic current, 
 by suppressing the oxygen in the gas pile, and replacing it 
 simply by acidulated water ; its effect is at first almost 
 as powerful as that of the pile in which are the two gases 
 equally; but the action diminishes rapidly, whilst it is constant 
 in the other. 
 
 M. Schoenbein attributes the liberation of electricity 
 in Grove's gas pile to the hydrogen, and consequently to 
 the chemical action, that takes place between it and the 
 acidulated water ; he considers that the oxygen, in contact 
 with the platinum, has no other effect than to depolarise 
 
 * Mr. Grove has endeavoured to apply this property to the eudiometric de- 
 termination of the quantity of oxygen, that is contained in the air. With this 
 view, he places in a narrow trough, in which there is some diluted sulphuric 
 acid, two narrow tubes, six or seven inches in length, filled with atmospheric air. 
 These tubes carry a graduation. In one of the tubes is placed a plate of pla- 
 tinised platinum, which is placed in metallic communication with a similar 
 plate, placed in a tube full of hydrogen gas, which plunges into the same vessel; 
 the other tube, full of air, serves only to determine how much is dissolved, 
 during the continuance of the experiment. In one experiment, which had 
 lasted two days, the liquid had mounted twenty-two divisions in the former 
 tube, and one in the latter ; which gives twenty-one per cent, for the quantity 
 of oxygen that is found in a certain quantity of air. At the end of several 
 days, the result had not changed. 
 
 3 A 4 
 
728 SOURCES OF ELECTRICITY. PART v. 
 
 those plates upon which the voltaic action, so long as the pile 
 is in action, constantly brings hydrogen ; which then, instead 
 of remaining in a thin film upon the metal, is carried off by 
 the oxygen that is found there, by combining with it. It 
 should necessarily follow from this, that the effect of the pile 
 is no longer weakened, as when the hydrogen remains 
 adhering to the platinum. But, even admitting the reality of 
 effect, pointed out by M. Schoenbein, can we not say that the 
 chemical combination of the oxygen with the nascent hydro- 
 gen, at the same time, that it depolarises the platinum, contri- 
 butes to the production of electricity, as does the peroxide of 
 lead, which covers the platinum in the zinc and platinum 
 pairs, as we have seen above ? Moreover, the presence of the 
 oxygen is necessary for the production of the current. Thus, 
 Mr. Grove has satisfied himself that, in the pile, in which 
 solution of sulphuric acid is substituted for it, there is no 
 effect produced if (the pairs, being placed in an atmosphere 
 of nitrogen) there can be no oxygen dissolved in the liquid. 
 He has also shown that an active pile may be equally formed 
 with one or other of the two gaseous elements, either by sub- 
 stituting for the oxygen an electrolyte, that has great affinity 
 for hydrogen, such as nitric acid ; or by substituting for the 
 hydrogen an electrolyte that has much affinity for oxygen, 
 such as protosulphate of iron. It is true that the nitric acid 
 and hydrogen pile is more powerful, and especially more 
 constant than that of oxygen and protosulphate of iron ; but 
 this is due to the nature of the chemical action, and to the cir- 
 cumstance, that a great part of the protosulphate passes into 
 the state of sulphate of peroxide, by the direct effect of the 
 oxygen of the air ; which diminishes the action of the oxygen 
 of the pile. 
 
 We may therefore regard the two gases as both of 
 them contributing directly to the voltaic effect in the gas 
 pile. With regard to the theory of this pile, it is exactly 
 the same as that, which we have laid down for piles, in 
 which metals are the active elements. The hydrogen, ad- 
 hering to the surface of the platinum in the line of contact 
 between the surface and the liquid, polarises the filaments of 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 729 
 
 this liquid, so that the negative oxygens of all that their par- 
 ticles are turned on its side, and the positive hydrogens on 
 the other ; the oxygen, adhering to the surface of the second 
 platinum, produces upon the same filaments an analogous 
 effect, which is added to the former, since it acts in the 
 same direction. When the two platinum plates are united 
 metallically, the free negative electricity of the plate, which 
 is in contact with the hydrogen, unites with the positive of 
 that, which is in contact with the oxygen, the decomposition 
 and recomposition of the successive molecules of the filaments 
 is brought about ; and at the same time that the oxygen of 
 one of the extreme molecules combines with the hydrogen, 
 adhering to the platinum, the hydrogen of the other ex- 
 treme molecule combines with the oxygen, adhering to the 
 other platinum. We may add, in support of the theory, 
 that we have been laying down, that Mr. Grove has demon- 
 strated by direct experiments that the active part in the gas 
 pile are the portions of platinum which in each tube are at the 
 level of the liquid in proportion as it rises in the tube ; and 
 these are in fact the only parts where contact can at the 
 same time take place between the liquid and the gas, adher- 
 ing to the platinum.* 
 
 This affinity at a distance, as Faraday has so well charac- 
 terised it, which is exercised by the intervention of the 
 liquid molecules interposed on the one side, and of the metal 
 arc, which connects them on the other side, between the 
 hydrogen and oxygen, that are separated by the liquid, may 
 take place at distances infinitely small, and constitute, as in 
 ordinary voltaic pairs, local action. This happens when the 
 
 * However, it follows from an observation of M. Jacobi's, confirmed by 
 M. Poggendorff, that the combination of oxygen and hydrogen, under the influ- 
 ence of platinum, may take place, even when these gases are not immediately 
 in contact with the liquid, and are separated from it by the electrolytic 
 liquid. Thus M. Poggendorff, having liberated 3'4 cub. in. mixed gas in 
 a voltameter of plates newly platinised, having taken care that the plates 
 should always remain below the level of the liquid, he observed that the re- 
 \ absorption of the gases took place with immense rapidity; such, that in a few 
 \moments several tenths of a cubic inch had disappeared ; the i'e- absorption is 
 K?en relaxed, but, it ends by being completely accomplished. It follows from 
 th\s fact, that combination does not take place exclusively at the spot, that 
 Mr. Grove has assigned to it ; a circumstance, however, of no great im- 
 portance. 
 
730 SOURCES OF ELECTRICITY. PART v. 
 
 liquid in contact with the hydrogen contains dissolved oxygen. 
 The molecules of water, polarised by the hydrogen that ad- 
 heres to the platinum, in the portion wherein the platinum 
 is at the level of the surface of the liquid, find oxygen upon 
 the platinum beneath this surface. There is immediately a 
 small molecular circuit formed. It is not therefore the dis- 
 solved oxygen, that combines directly with the free hydro- 
 gen, but this oxygen serves to form an active circuit, 
 analogous to that, which takes place in the ordinary pair, 
 with the simple difference that it is molecular and that the 
 metallic arc, that enters into its formation, is only a small 
 portion of the surface of the platinum, placed in the hydro- 
 gen tube ; it is, in like manner, the oxygen, adhering to the 
 platinum plate, placed in the solution of sulphuric acid, 
 which serves for the production of the current, when this 
 solution is substituted for the oxygen in the tubes. This 
 oxygen is useless when, instead of a solution of sulphuric 
 acid, we take nitric acid, which parts so easily with its 
 oxygen, that its employment is preferable for the force of 
 the pile to that of oxygen itself. Indeed, three pairs are, 
 in this case, sufficient for decomposing water, whilst it 
 requires four with the oxygen-gas pile. The peroxide of 
 lead produces a still greater effect ; a single pair, hydrogen 
 and platinum, covered with peroxide of lead, easily de- 
 composes water. We may add that, in the gas pile, the 
 oxygen, instead of being simply adherent, is very probably 
 combined with the platinum, so as to form an oxide easily 
 reducible. This results, from an examination of all the cir- 
 cumstances, that facilitate the action of the apparatus, such 
 in particular as the pulverulent state of the platinum, and 
 which is in other respects in accordance with the facts, that 
 we have already related in favour of the oxidation of pla- 
 tinum.* 
 
 Grove's gas pile presents to us a striking example, and I 
 may say a pointed one, of Faraday's law of equivalents. 
 We see the combination of one equivalent of hydrogen and one 
 equivalent of oxygen produce a current, capable of decompos- 
 
 * Vol. II. p. 416. 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 731 
 
 ing one equivalent of water ; that is to say, a quantity of 
 water precisely equal to that, the formation of which has 
 given rise to this current. At first sight, we do not conceive 
 that the force, which produces the formation of water, would 
 be sufficient to surmount the force, by which its constituent 
 molecules are already united. It is easy to reply to this 
 objection as far as concerns the decomposition of water in the 
 voltameter ; for a decomposition cannot take place, except so 
 long as there is more than one pair, four at least, and until 
 consequently we have quadrupled, conformably to the theory 
 of the pile, the decomposing force. If the question is in 
 reference to a single pair, the platinum plates of which are 
 united metallically, the objection is more specious, and it has 
 been proposed by Mr. Grove itself. However, we must 
 remark, that each molecule of the filaments of water, inter- 
 posed between the two plates of the pair, is subjected to two 
 decomposing forces, which act in the same direction ; the one, 
 which draws oxygen from the side of the platinum plate, 
 where the hydrogen is ; the other, which draws hydrogen from 
 the side of the platinum plate, where the oxygen is. What 
 one of these actions cannot do, when it is alone, as is proved 
 by experiment *, the two united bring about ; for if we 
 take one of the molecules of water in the filament, it is easy 
 to see that the affinity of its hydrogen for its oxygen is com- 
 bated at once by the force with which its hydrogen is at- 
 tracted by the oxygen of the following molecule, and by that 
 with which its oxygen is attracted by the hydrogen of the 
 preceding molecule, and so on for all the others. 
 
 Mr. Grove has made a very great number of experiments 
 upon the gas pile by substituting other gaseous substances for the 
 oxygen and hydrogen, either separately or simultaneously. 
 The experiments have all given results perfectly conformable 
 to the theory, that we have laid down. Thus, nitrogen put 
 in place either of the oxygen or the hydrogen, produced no 
 effect. The peroxide of nitrogen, associated with oxygen, in li ke 
 
 * Indeed, no current is ever obtained, and, consequently, no decomposition 
 of the electrolyte with a single pair, when the hydrogen is suppressed, the 
 oxygen alone being left, or when, leaving only the hydrogen, care is taken to 
 drive out all the oxygen, that might be found dissolved in the liquid. 
 
732 SOURCES OP ELECTRICITY. PART V. 
 
 manner, produced no sensible effect ; it was not the same with 
 the deutoxide, which gives a slight current with oxygen; and 
 diminishes when the circuit has been a long time closed, in 
 the proportion of four volumes of deutoxide for one of oxygen. 
 Associated with hydrogen, the two gases produce a decided 
 current ; the volume of deutoxide diminishes one half, and the 
 gaseous residue is nitrogen; the volume then increases gra- 
 dually by the addition of hydrogen. The protoxide does not 
 undergo any change of volume, but its chemical change is 
 detected by the absorption of the hydrogen, that forms the pair 
 with it. Olefiant gas seems to give a continuous, but very 
 feeble current, with oxygen. The gases that appear to be the 
 most efficacious, are, on the one hand, oxygen and chlorine; 
 and on the other hydrogen and oxide of carbon. Chlorine and 
 hydrogen form so powerful a combination, that two pairs are 
 sufficient to decompose water in the voltameter ; chlorine and 
 oxide of carbon likewise produce considerable effects, although 
 less energetic than chlorine and hydrogen. But, the extreme 
 solubility of chlorine renders its employment by no means 
 satisfactory for the production of a current of some duration. 
 Oxygen and oxide of carbon are of the four combinations 
 that may be made with the four gases, indicated above, 
 that which has the least energy ; however, a pile of ten 
 pairs thus charged, decomposes iodide of potassium, and a 
 little water of the voltameter. 
 
 Mr. Grove, having proved that nitrogen was inactive, en- 
 deavoured to employ it as a solvent of some bodies, such as 
 phosphorus and sulphur. With this view, after having filled 
 with nitrogen, one of the tubes of the pair, and the other with 
 oxygen, he introduced phosphorus or sulphur into the nitrogen 
 by means of a rod terminated by a small cup, in which he 
 lodged the substance. The pair thus formed {fig. 318.) 
 gave a powerful current; only when the body introduced 
 was sulphur, it was necessary to raise the temperature, 
 which was done by means of a simple iron ring, furnished 
 with a handle, which was passed over the tube containing 
 the sulphur and the nitrogen, after having sufficiently heated 
 it to bring the sulphur to the liquid state. In these ex- 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 733 
 
 periments, it is the vapours of phosphorus and those of 
 sulphur, which, lodged in the inactive nitrogen, play the part, 
 that the hydrogen played in the gas pile, 
 and combine at a distance, under the influ- 
 ence of the platinum, as this gas did, by the 
 intervention of the electrolytic liquid, with 
 the oxygen, contained in the other tube. 
 Piles of ten pairs, charged with oxygen 
 and the vapour of phosphorus, decompose 
 water; and it is found, on weighing the 
 phosphorus, before and after the experiment, 
 which is made to endure longer in proportion 
 as the exterior temperature is lower; and 
 by measuring, in like manner, the volume 
 of oxygen, that this gas and the phosphorus 
 have diminished almost in an equal propor- 
 tion to that of their equivalent, and the 
 equivalent of water, decomposed by the current. 
 
 It is, therefore, now well established, by Mr. Grove's re- 
 searches, that the action of elastic fluids in their contact with 
 an electrolytic liquid may, under the influence of platinum, 
 develope an electric current ; and that this electro-chemical 
 action is subject to the same laws as the others, and in par- 
 ticular to the law of equivalents. With regard to the force 
 of this action, it depends not only upon the nature of the gas 
 and of the electrolytic liquid, but also on that of the metals, 
 whose presence determines the chemical action. The same 
 metal varies in this respect with the nature of its surface. 
 Thus, M. Poggendorff has remarked that well-polished plates 
 of platinum may acquire a maximum of polarisation, superior 
 to that of platinised plates ; but that the maximum is more 
 rapidly attained with these latter, and that it varies less by 
 the change of the force of the current, that produces the 
 polarisation, than that of polished plates. Indeed, the cur- 
 rent produced by the films of gas, with which the surfaces 
 of the electrodes are covered, that have been employed for 
 decomposition, and which have thus acquired secondary po- 
 larities, varies with the force of the current, that has pro- 
 
734: SOURCES OF ELECTRICITY. PART v. 
 
 duced these polarities. We shall see this in the paragraph, 
 that we shall devote to the measure of electromotive forces, 
 in explaining how we have succeeded in determining that of the 
 gases in the different circumstances under which they are 
 found, in the same manner as that of solids has been deter- 
 mined ; we shall equally see the importance that is presented 
 by this determination in the appreciation of the electro-motive 
 force of piles, and in that of the influence that is exercised 
 over the force by the interposition in piles of inactive pairs ; 
 for, the secondary polarities, that are acquired by metals, which 
 have formed part of a current, are almost always due to 
 gaseous films deposited on their surface by the current, and 
 consequently, their influence, which tends to produce a con- 
 trary effect to that of the current, which has given rise to 
 them, cannot be exactly estimated, so long as we are unac- 
 quainted with the electro-motive force of gases.* 
 
 However, we may at this time explain the influence of 
 certain causes upon the diminution of the resistance, that is 
 presented to the transmission of the current, by the electrodes, 
 that serve for the decomposition of acidulated water in the 
 voltameters. Thus, when water is decomposed with a single 
 nitric acid pair, and even with a peroxide .of lead pair, the 
 action is very quickly arrested or extremely enfeebled by the 
 effect of the polarisation of the electrodes, which exercise an 
 electro-motive force, opposed to that of the pairs. Now, in 
 order to give to it all its primitive vivacity, we have merely 
 to change the direction of the current in the voltameter; 
 because then we cause the two electro-motive forces to act in 
 the same direction. But soon the new polarisation, that the 
 electrodes acquire, weakens the current anew; so that, in 
 order to restore to it afresh its power, it is necessary again 
 
 * It may happen that, in certain gases, the power of a film of gas upon the 
 surface of a metal, instead of diminishing, increases the electro-motive force of 
 this metal ; thus, as M. Buff has observed, when we have caused a thin film of 
 hydrogen to deposit upon the surface of zinc, by employing it as a negative 
 electrode in the decomposition of water, this plate becomes powerfully positive 
 in respect to another similar one, that has not been placed under the same con- 
 ditions ; which is proved either by the charge, which they give to the con- 
 denser, or by the direction of the current, which they produce, when forming 
 a pair. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 735 
 
 to change its direction. By bringing about therefore these 
 alternations in the direction of the current, we easily obtain 
 a tolerably powerful decomposition of water in the voltameter. 
 by means of a single pair. We may employ a commutator 
 moved by the action itself, by imparting to it the necessary 
 movement, by means of an electro-magnet, placed in the 
 circuit, and which is so arranged that, when its power dimi- 
 nishes by the weakening itself of the current, its armature, in 
 detaching itself, causes the commutator to act. Mr. Grove 
 found an advantage by interposing between the pair and the 
 voltameter two large plates of platinum, plunging into diluted 
 sulphuric acid, which, without liberating visible gas, are po- 
 larised by the current. It is upon these plates that the com- 
 mutator acts, so that it is their electro-motive force that is 
 added to that of the current, which causes the latter to travel 
 always in the same direction, in the voltameter properly so 
 called. Three experiments made with a single nitric acid 
 pair gave in the same time in the voltameter, 
 
 Cub. in. 
 
 Without platinum plates interposed. 146 
 With plates interposed - - 0*097 
 
 With plates and commutator - 0'225 
 
 The increase of effects, due to what Mr. Grove calls vol- 
 taic reaction, is therefore very sensible. 
 
 Among the causes that dimmish the resistance to passage 
 in a voltameter, we have pointed out* the heating and shaking 
 of the electrodes, and more particularly of the negative elec- 
 trode. M. Beetz has succeeded in demonstrating that the 
 effect of these two actions is due to the fact, that they diminish 
 or destroy the polarisation of the electrodes. He has re- 
 marked that, when the current is feeble, the destruction or 
 diminution of polarisation by heating is, as I had already ob- 
 served, more sensible for the negative electrode ; but that it 
 becomes the same for both, when the current is powerful ; 
 which is due to the circumstance that the electro- motive 
 force of the electrode, polarised by the hydrogen, is very su- 
 
 * Vol. II. pp. 74. and 409. 
 
736 SOURCES OF ELECTRICITY. PART v. 
 
 perior to that of the electrode polarised by oxygen ; whence it 
 follows, that the difference between them, in this respect, 
 must be more sensible with the current, and consequently the 
 two polarisations are feeble. Moreover, the influence of tem- 
 perature over the polarisation of the electrodes must vary, not 
 only with the force of the current, but with the nature of the 
 electrodes themselves, and of the electrolytic liquids placed 
 between them. 
 
 It remains for us, therefore, before terminating this para- 
 graph, to treat upon some points, that are connected with it. 
 We must first mention a new class of gaseous pairs, dis- 
 covered by M. Gaugain, when making some researches 
 on thermo-electricity, and which we have already pointed 
 out in passing. The most simple of these pairs is that 
 which is obtained by putting in presence of each other at 
 an elevated temperature two tubes of glass which contain, 
 one air, the other the vapour of alcohol. M. Gaugain 
 has succeeded in producing with these pairs, which may be 
 arranged end to end, so as to form a true pile, all the effects 
 of ordinary hydro-electric pairs. He recognised that the 
 nature of the wires, that are employed for placing the glass 
 tabes into communication, either with the ground or with the 
 condenser, does not influence the results, and that these wires 
 consequently play merely the part of simple conductors. By 
 forming a series of gaseous pairs with air, oxygen, nitrogen, 
 carbonic acid, hydrogen, vapours of water, alcohol or ether, 
 M. Gaugain found those alone to be active, in which one of 
 the two elements was air or oxygen, and the other one of the 
 elastic fluids, differing from these two gases. He took care to 
 stop the tube with glass at both ends, when he filled it with 
 an elastic fluid, other than air, or one of the vapours. He is 
 disposed to conclude, from his researches, that the electricity 
 arises simply from an action, that is exercised between the 
 oxygen and the glass, that is brought to a state of fusion ; and 
 that the second elastic fluid plays only the part of a simple 
 conductor. We should be rather disposed to believe, still 
 admitting the action of the oxygen upon the melted glass, 
 that the phenomena observed by M. Gaugain enter altogether 
 
 * Vol. II. p. 423. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 737 
 
 into those of Grove's gas pile, witli this difference, that the 
 electrolytic liquid, which separates the two elastic fluids, is 
 melted glass, instead of being a solution of sulphuric acid ; 
 now, that melted glass can serve as an electrolytic liquid, 
 is what Buff's recent experiments demonstrate, who not 
 only has obtained its decomposition by a voltaic current, but 
 has even succeeded in employing it in this quality in the con- 
 struction of a pile. 
 
 Another point upon which we have yet to speak, is the 
 property discovered by M. E. Becquerel that hydrogen pos- 
 sesses under the influence of platinum, of bringing about 
 the reduction of a solution of chloride of gold ; which 
 neither hydrogen alone, nor platinum alone, are capable of 
 reducing. 
 
 A small test tube, about T ^ of an inch in diameter, filled 
 with hydrogen gas, is placed in a vessel, containing a solution 
 of chloride of gold, so that it plunges into it by its open extre- 
 mity. At the end of some days, if the temperature has not 
 sensibly varied, the level of the chloride of gold in the in- 
 terior of the tube, remained very nearly the same ; but if a 
 platinum wire is introduced below the test tube, so that the 
 wire is situated in part plunged in the hydrogen gas, and in 
 part plunged by its other extremity in the chloride of gold, we 
 then see the volume of gas to diminish in the interior, and 
 even at the end of a certain time to disappear entirely, if the 
 platinum wire goes to the top of the tube, At the same time 
 that the hydrogen disappears metallic gold is precipitated 
 upon the portion of the platinum wire, that plunges in the 
 metallic solution. This action is manifested in closed tubes, 
 and in which there is no trace of atmospheric air ; the effect 
 is not due to the action of the liquid upon the platinum, since 
 platinum alone does not exert it, and no trace of platinum re- 
 mains in the solution after the operation. If a gold wire is 
 substituted for that of platinum, the reduction of the chloride 
 in the hydrogen no longer takes place. This effect is evi- 
 dently the result of a local action, that is to say, of a mo- 
 lecular current, which sets out from the particles of hydrogen, 
 adhering to the surface of the platinum, at the spot where 
 
 VOL. ii. SB 
 
738 SOURCES OF ELECTRICITY. PART v. 
 
 this metal touches the surface of the solution of chloride of 
 gold, traverses a small film of this solution, goes and abuts 
 on the part of the platinum, which, being plunged into it, is 
 no longer covered with hydrogen, and deposits gold upon it. 
 The affinity of hydrogen for chlorine is here sufficient of 
 itself alone to bring about the formation of the voltaic cir- 
 cuit ; and consequently the electrolysation of the solution. 
 
 Finally, it remains to us to speak of a phenomenon, that 
 we have al-ready mentioned in passing * ; and which consists of 
 that peculiar state, that iron is able to acquire, by virtue 
 of which it becomes unattackable by acids, and is able to 
 play in many cases the part of platinum ; a state which M. 
 Schoenbein, who has made a very special study of it, has de- 
 signated under the name of passivity, calling the iron that is 
 possessed of it, passive iron. 
 
 Bergmann and Kirwan bad already remarked that iron, 
 employed for precipitating silver from its solution, loses this 
 property at the end of a certain time ; Keir showed that the 
 iron employed can no longer precipitate silver, not only from 
 the solution, in which it has been already plunged, but from 
 any other. Braconnot having remarked that concentrated 
 nitric acid does not attack iron, Herschel examined this 
 subject nearer; he observed that soft and cleaned iron, 
 plunged into nitric acid of 1*4, begins by getting brown ; then 
 it produces an effervescence, during which the liquid becomes 
 red ; all action soon ceases, and the iron has acquired the 
 property of being no longer attacked ; a slight friction does 
 not remove from it this property ; but it loses it, if it is 
 rubbed too powerfully ; it also loses it, if it is touched in an 
 electrolytic liquid with an oxidisable metal. Iron, in this 
 state, is able to resist the action of a very strong acid. 
 But, of all philosophers, M. Schoenbein is the one, who 
 has made the most detailed study of this subject ; there- 
 fore it is his works, that will essentially direct us. 
 
 When one of the extremities of an iron wire is heated to 
 redness, and, after its cooling, is plunged into nitric acid 
 pf 1*35 of density, this extremity suffers no action on the part 
 
 * Vol II. p. 423. 
 
CHAP. ITT. ELECTRICITY BY CHEMICAL ACTIONS. 739 
 
 of the acid, whilst the same acid acts energetically upon the 
 extremity of the iron wire, that is not heated. A passive or 
 inactive iron wire is able to render passive one, that is not 
 so. It is sufficient for this purpose to place them in nitric 
 acid of 1*35 of density, after having placed them in contact, 
 taking care to introduce the passive iron first ; the two wires 
 then equally suffer no chemical action ; it is the same, when 
 they are separated. We may even render an iron wire 
 passive, which already is suffering a vivid action in nitric 
 acid, by plunging into the acid circuit an iron wire that is 
 already passive, and placing the two wires in contact by their 
 extremities, that are out of the liquid. Platinum, carbon, and 
 all unoxidisable metals, are able as well as iron, already 
 passive, to give by their contact passivity to an iron wire, 
 which does not possess it. A pair of iron and platinum, en- 
 tirely plunged in nitric acid, does not give any effect, when 
 the acid is gradually heated, except when the acid begins to 
 enter into ebullition ; the iron is then attacked, and is not long 
 in being dissolved. 
 
 Passive iron may remain a long time, thirty days and more, 
 in nitric acid, without losing its property of not being 
 attacked; it preserves it, when it is well drawn from the 
 acid, even when it is exposed to the air, or is plunged into 
 pure water, or into ammonia; but as soon as its surface 
 is rubbed, it becomes active again. 
 
 A passive iron wire enjoys all the properties of a platinum 
 wire ; thus it may be used as a positive electrode in a pile 
 in any acid solution, both sulphuric and nitric, and oxygen 
 is liberated upon it in the desired proportion ; whilst the 
 liberation of hydrogen takes place at the negative electrode, 
 which is platinum. Thus again, like platinum, it no longer 
 precipitates copper, and the oxidisable metals, from their re- 
 spective solutions ; a property, to which we shall return in 
 the Chapter of the Seventh Part, which will be devoted to 
 the chemical applications of electricity. When the pile is a 
 simple one, composed of a single pair, if a wire of passive 
 iron is employed as a positive electrode, whilst a platinum 
 wire is its negative electrode, there is no decomposition, on 
 
 3 B 2 
 
740 SOURCES OF ELECTRICITY. PART v. 
 
 plunging the two wires in a solution of sulphuric acid ; whilst 
 there is a powerful liberation of hydrogen around the pla- 
 tinum wire, when ordinary iron or oxidisable metal is taken 
 for the other electrode. We may in like manner momentarily 
 produce this liberation of hydrogen, by placing for a moment 
 in contact in the liquid passive iron, which forms the pair 
 iron and platinum with an oxidisable metal, such as zinc, tin, 
 copper, and even silver ; but the liberation of gas that then 
 takes place upon the platinum, endures for a few seconds 
 only. 
 
 We may even render an iron wire passive, by employing 
 it in water acidulated with sulphuric acid as the positive 
 electrode of a powerful current, produced by a single pair, 
 and the negative electrode of which is of platinum. The 
 decomposition of water no longer takes place in a sensible 
 manner ; but if we touch for an instant the iron electrode with 
 that of platinum in the liquid itself, the decomposition takes 
 place vividly, <is soon as they are separated from each other, 
 to cease an instant after. The same effect is produced by 
 touching the iron with an oxidisable metal in the same 
 liquid. But the most curious fact is that, if we unite, exterior 
 to the liquid, the two wires, that serve as electrodes, by a 
 copper wire, a very momentary liberation of hydrogen is 
 then obtained, as in the preceding case, at the moment when 
 the copper wire, by which the two electrodes were united, is 
 removed. The copper wire must not be more than two or 
 three inches in length, and about ^ in. in diameter. When 
 it is longer or thinner, a liberation of hydrogen is obtained 
 during the same time that is employed for uniting the elec- 
 trodes ; and this liberation increases in proportion as the 
 wire is elongated, until it is a little more than five yards in 
 length. At the moment when the copper wire is removed, 
 which established communication between the electrodes, the 
 liberation of hydrogen becomes much more active than it was, 
 while the communication existed ; but it does not last long, 
 and the decomposition stops. When the copper wire is ex- 
 cessively long, in such sort that it does not probably transmit 
 more than a very minute proportion of the current, things 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 741 
 
 take place, as if the electrodes were not united by a conducting 
 communication. 
 
 All these effects, and many others into the details of which 
 it is impossible for us to enter, and which, for the greater 
 part, have been observed by M. Schoenbein, are evidently 
 due to the property, that is possessed by iron of covering 
 itself with a pellicle of oxide, which renders it unattackable 
 by certain acids. It thus enters into the phenomena of 
 secondary polarities, which are equally due to deposits, 
 brought about upon the surface of metals. Faraday, who 
 was the first to put forth this opinion, remarks that in fact 
 all circumstances, that are proper for rendering iron passive, 
 are those which must bring about the formation of this 
 superficial film of oxide ; such are its heating, its voltaic 
 combination in an electrolytic liquid with a non-oxidisable 
 metal. It would appear that this film of oxide cannot form 
 salts with acids ; and consequently has no tendency to 
 combine with them ; which would explain why they do not 
 attack iron, that is covered with it, which conducts itself either 
 chemically or voltaically, as platinum. Thus, we have seen, 
 that acidulated water cannot be decomposed with the current 
 of an ordinary simple pair, if the two electrodes are of pla- 
 tinum ; for this purpose, it is necessary that the positive metal 
 be attackable by the electrolytic liquid. Now, passive iron 
 wire not being attackable, decomposition does not take place, 
 if it is employed as a positive electrode. But, if this iron 
 is united voltaically in the liquid with an oxidisable metal 
 such as zinc, a liberation of hydrogen is brought about 
 upon its surface, which must deoxidise it, and consequently 
 restore its ordinary chemical activity. It is easy to ex- 
 plain, in the same manner, M. Schoenbein's curious experi- 
 ment which we have related above. When the powerful 
 current has traversed the acid solution by means of two elec- 
 trodes, the negative one being of platinum, and the positive 
 one of iron, the latter has become passive by the first liber- 
 ation of oxygen, that has taken place upon its surface, and 
 the decomposition is stopped. The two electrodes were then 
 united by a thick and short copper wire, that is to say, by a 
 
 3 B 3 
 
742 SOURCES OF ELECTRICITY. PART v. 
 
 very good conductor ; this wire served at the same time to con- 
 duct the current and to form a pair between the two electrodes ; 
 this pair, when formed, has destroyed the passivity of the iron, 
 and the water has been decomposed ; but when the conductor 
 is suppressed, the current begins to pass again between the 
 two electrodes, water is decomposed at the first moment, the 
 iron then becomes passive again, &c. If the copper wire, 
 by which the electrodes are connected, is too long, the phe- 
 nomenon no longer takes place, because the wire becomes 
 too bad a conductor, either to derive the current, which 
 continues to pass in great part between the electrodes, or to 
 permit the latter to form a current sufficiently active, in con- 
 sequence of the imperfect communication, that is established 
 between them; that which proves that this influence of 
 length concerns only the diminution that it occasions in the 
 conductibility of the wire, is that the same result is obtained 
 on making use of a short and thin wire of a badly conducting 
 metal, such as iron or platinum. 
 
 We might perhaps ask how, when forming a pair with iron 
 and platinum, that have served as electrodes, we may restore 
 to the iron its activity, as we do by placing it in contact 
 with an oxidisable metal in the liquid; this is due to the 
 circumstance that platinum plays the same part, that zinc 
 or any other oxidisable metal would have played, by the 
 effect of the polarisation that has been imparted to it by 
 the same current, that has rendered the iron passive. This 
 current, in carrying to the iron the oxygen that has determined 
 the formation of the film of oxide, to which the passivity is 
 due, has developed upon the platinum an equivalent film 
 of hydrogen ; whence it follows, that this metal, afterwards 
 in contact with the positive iron, becomes the positive ele- 
 ment of the pair, which liberates upon the platinum, by de- 
 composing the water, oxygen, which depolarises it, and 
 upon the iron, hydrogen, which deoxidises the surface of this 
 metal, and thus restore to it its chemical activity. 
 
 M. Martens had attributed the passivity of iron to a phy- 
 sical modification, that this metal would have undergone, of 
 a nature to change its voltaic relations; M. Schcenbein, 
 still considering that this modification consists only in an 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 743 
 
 alteration, imparted to the iron, as far as concerns its chemical 
 properties, did not seem to presume that this alteration arises 
 from the formation of a peculiar oxide. It is to M. Beetz, 
 that we are indebted, for having placed beyond doubt the ex- 
 istence of this film of oxide in iron rendered passive ; he has 
 demonstrated, contrary to M. Martens, that the blue colour, 
 which is acquired by iron, when heated, is due to the forma- 
 tion of a slight film of oxide ; and he has shown that, if 
 this film is sometimes formed in hydrogen at a red heat, it is 
 due to the decomposition of the water that is contained in 
 this gas *; so that if we succeed in having the gas perfectly 
 dry and perfectly pure, colouration no longer takes place, 
 even at a very high temperature. 
 
 M. Beetz satisfied himself, by heating an iron wire in a 
 metallic bath, taking care to prevent the wire from retaining 
 a film of air adhering to its surface, that this wire is not 
 passive, and that it is even positive, when it forms a pair 
 with a very polished iron wire. He has demonstrated, by 
 multiplied experiments, made with great care, that it is 
 sufficient to rub or to wash in an acid an iron wire, that 
 has been rendered passive by the action of heat or by that 
 of nitric acid, in order to destroy its passivity; because 
 we thus remove from it the pellicle of oxide, to- which this 
 passivity is due. It is easy to explain, by the formation 
 or the reduction of this film of oxide, all the various 
 phenomena that are presented by iron, with regard to 
 its chemical passivity and activity, when it is employed as 
 an electrode in an electrolytic liquid. It is thus that when 
 a pair is formed in nitric acid of 1/40, with an ordinary 
 iron wire and a passive iron wire, the latter renders the 
 former passive, as a platinum wire would have done, by 
 determining a current, that slightly oxidises it, whilst it is 
 itself deoxidised. It then becomes active in its turn; and 
 it is the latter that has been rendered passive ; the phe- 
 nomenon begins again, the two wires having thus changed 
 
 * This very colouration, that iron assumes at a very high temperature in 
 hydrogen gas, disappears at a less elevated temperature, by the reduction whkh 
 the hydrogen causes the film of oxide to suffer. 
 
 3 is 4 
 
744 SOURCES OF ELECTRICITY. VART v. 
 
 parts, and it can be renewed indefinitely in the same 
 manner. 
 
 Bismuth, nickel, and cobalt are susceptible of becoming 
 passive, like iron, either by the effect of heat, or by the 
 effect of their employment as positive electrodes in the 
 electrolytic decomposition of acidulated waters. Mr. Andrews, 
 who was the first to demonstrate the passivity of bismuth, 
 obtained it by placing this metal in contact with platinum in 
 nitric acid of the density of 1 -40 ; it is merely necessary, in 
 order to procure a passive surface of bismuth, to fill a copper 
 tube with bismuth in fusion, and to make a section in the 
 button thus cooled; plunged into nitric acid of 1'40, this 
 section is not attacked. It is evident that the passivity 
 in this case, as in that of iron, is due to the formation of 
 a thin film of oxide upon the surface of the metals ; a 
 film which is formed even upon bismuth, at the ordinary 
 temperature, as is proved by the coloured tints of this 
 metal. M. Beetz had already proved the passivity of 
 nickel; it has been confirmed by M. Nickles, who has 
 also established it for cobalt. He has found that, in order 
 that the passive state of these two metals may be stable, 
 it is not sufficient to plunge them in nitric acid of 1 '40 ; 
 that they must be blued in the spirit-lamp or upon a char- 
 coal fire, and be plunged while still glowing into this acid. 
 
 It is therefore evident that passivity is only a phenomenon, 
 purely electro-chemical, arising from the impossibility, in 
 which the oxides of certain metals are found, when they are 
 only at a feeble degree of oxidation, of forming salts with 
 nitric or sulphuric acid. It follows, from this defect of affi- 
 nity, that the metals in question cannot form voltaic pairs 
 with platinum ; a new proof, as M. Schoenbein remarks, of 
 the part played by chemical affinity in the production of vol- 
 taic electricity, and a new argument consequently against 
 the contact theory. Regarded in this manner, passivity is 
 nothing more than the effect of the presence of a thin film of 
 an heterogeneous substance (a pellicle of oxide) upon the 
 surface of a metal ; which justifies the place we have given 
 to the study of it in this paragraph. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 745 
 
 A last electrical phenomenon, that arises from the deposit 
 of very thin heterogeneous films upon the surface of metals, is 
 that of the production of electric currents by the action of light 
 upon these deposits, when they are of a peculiar nature. M. E. 
 Becquerel has in fact obtained very decided electric currents 
 by bringing about chemical actions, by means of light upon 
 metallic plates of platinum ; for example, those covered with 
 an impressionable film, such as a film of chloride, iodide or 
 bromide of silver. A plate thus prepared is plunged into 
 acidulated water with another plate also of platinum, but 
 whose surface is perfectly clean ; and they are made to com- 
 municate each with the two ends of a galvanometer. As 
 soon as a ray of light is made to act upon the impressionable 
 film, an electric current is brought about, in which the 
 plate covered with this film, acquires positive electricity, as 
 peroxide of lead would have done; an affect due to the com- 
 bination with the hydrogen of the water, under the influence 
 of light, of the chlorine, bromine or iodine of the film, with 
 which the platinum plate is covered; and consequently to the 
 chemical decomposition of this film. M. E. Becquerel has taken 
 advantage of this property for constructing, under the name 
 of electro-chemical actinometer, an apparatus which enables 
 him to appreciate with the greatest sensibility, the energy 
 with which the rays of light act upon a chemical combina- 
 tion, and consequently of comparing, under this relation, the 
 rays of various refrangibility and the modifications, that are 
 imparted to them, by their passage through screens of 
 various natures. The solution in which the two plates are 
 plunged, is a diluted solution of sulphate of soda ; the two 
 plates are of silver ; the one is cleansed, and has a very clean 
 surface ; the other is covered with a film of a particular sub- 
 chloride of silver, which is violet, and which, of all impres- 
 sionable films, is the one, that is the best, because it gives 
 to the galvanometer an electric effect, that bears a relation 
 to the chemical action produced.* It has, moreover, the 
 
 * This sub-chloride is produced by employing the silver plate, upon the 
 surface of which we desire it to be found, as positive electrode, in hydrochloric 
 acid ; care must be taken to employ a current of only a feeble intensity. 
 
746 SOURCES OF ELECTRICITY. PART v. 
 
 property of receiving coloured impressions on the part of 
 all the luminous rays equally ; and moreover to acquire of 
 itself a tint, similar to that of the ray, that has acted upon 
 it : it is a kind of inorganic retina. We cannot here enter 
 into the details of the construction and preparation of M. 
 Becquerel's apparatus, and of the different parts, of which 
 it is composed, nor yet into the exposition of the results 
 that he has obtained by employing it ; this would be going 
 beyond the limits that we have assigned to ourselves, seeing 
 that the properties of light would be in question and not 
 those of electricity ; for it is here only the means employed 
 to obtain an apparatus, intended for quite another class of 
 studies. 
 
 Production of Electricity in Combustion ; and by the combined 
 Action of Heat and Chemical Affinity. 
 
 When once it is well proved that every chemical action 
 gives rise to electricity, it is evident that combustion, which 
 is one of the most decided of chemical actions, must also 
 liberate it. The study of the electric state of flame has at- 
 tracted the attention of philosophers from the very earliest 
 time, that electricity was the object of attention. It is 
 especially under the relation that it exercises over bodies 
 already electrised, by drawing off from them their electricity, 
 and becoming charged with it, that flame has been regarded. 
 Dufay, Winkler, Watson, Franklin, Priestley had already 
 made many experiments upon this power of flame. Hum- 
 boldt had not found in this respect differences between dif- 
 ferent species of flames, such as those of an oil wick, a taper, 
 phosphorus, hydrogen, and sulphur. He attributed the 
 action of the flame to the conductibility of the various sub- 
 stances, that emanate from it, such as carbonaceous parti- 
 cles, vapour of water, carbonic acid, &c. Volta, who was 
 greatly occupied on this subject, thought that the property of 
 flame of discharging electrised bodies, was due to the current 
 of air, that it brings about, and to the circumstance, that at 
 the same time it renders the air a conductor, by heating 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 747 
 
 and rarefying it. We have seen* that Riess, after having ana- 
 lysed with great care the faculty of flames and substances 
 in combustion, such as carbon, of drawing off electricity 
 from bodies that are charged with it, had demonstrated that 
 they act like a multitude of small points ; but, for this pur- 
 pose, it is necessary that the filaments of vapour, which are 
 formed in combustion, as well as the molecules that play the 
 part of points, shall be of a conducting nature such for 
 example, is the case with the vapour of water, and with 
 particles of carbon. 
 
 In studying the conducting power of bodies in combustion, 
 it was not long before it was seen that it presents anomalies. 
 Thus, it had been remarked that carbon, when its combustion 
 is moderated, discharges unequally positive and negative 
 electricity, and that it is the same with Davy's aphlogistic 
 lamp f ; which is not due, as Ermann had thought, to a pe- 
 culiar property of incandescent platinum wire, but rather to 
 the points of vapour, which arise from this wire. It is posi- 
 tive electricity that Davy's lamp transmits better to a con- 
 ductor in contact, whilst it is negative, which is most easily 
 communicated, under the same circumstances, by a point of 
 carbon in combustion. We are about to see that this ine- 
 quality of action in the conducting property for the two 
 electricities in these two cases is only apparent, and is due to 
 the circumstance, that in one and in the other, there is an 
 actual production of electricity by the effect of combustion. 
 
 Volta had already made evident the electricity liberated in 
 the combustion of carbon, by using, for bringing about this 
 combustion, only a feeble current of air, in order that it might 
 not be too energetic ; for, without this precaution, the electric 
 signs were scarcely sensible. But it was M. Pouillet, who 
 was the first to prove, by decisive experiments, the production 
 of electricity in the combustion, either of carbon or of hy- 
 drogen. He found, conformably to what takes place in the 
 
 * Vide Vol. II. p. 149. 
 
 ' f It is known that, in Davy's aphlogistic lamp, a platinum wire, coiled into a 
 helix, is retained incandescent by the vapour of alcohol, which burns on its 
 surface ; a phenomenon, which is due, as we have, seen above at p. 412. to a 
 series of oxidations and reductions, that the platinum wire undergoes. 
 
748 SOURCES OF ELECTKICITV. PARTY. 
 
 development of electricity by chemical actions, that the carbon 
 is charged with negative electricity, and the carbonic acid, that 
 escapes from it, with positive electricity. In order to obtain 
 this result, he cut into a cylinder a piece of good conducting 
 carbon ; then, after having lighted one of its extremities, he 
 placed it by the other end upon a plate of metal in commu- 
 nication with the upper plate of a condenser ; he then blowed 
 upon the carbon, by means of a bladder, filled with air, in 
 order to retain the combustion in its upper part alone ; the 
 lower plate being placed in communication with the ground, 
 he succeeded in charging the upper with negative electricity. 
 In order to collect the positive electricity with which the 
 carbonic acid is charged, it is necessary to place the carbon 
 cylinder at a little distance below the plate of metal, that 
 communicates with the plate of the condenser, taking care 
 to place it itself in communication with the ground. The car- 
 bonic acid yields its electricity to the plate, in proportion as 
 it rises against its surface. In the combustion of hydrogen, 
 the oxygen is electrised positively, and the hydrogen nega- 
 tively. In order to collect the negative electricity of the 
 hydrogen, a metal tube, which is put in communication with 
 the condenser, is adapted to the bladder, that contains it, and 
 at the extremity of which the gas is lighted ; or rather a long 
 platinum wire is adjusted to the plate of the condenser, the 
 extremity of which is coiled into a narrow spiral, which is 
 plunged carefully and entirely into the interior of the flame. 
 The positive electricity of the oxygen is collected by pre- 
 senting the same platinum spiral at some distance from the 
 flame ; it is necessary to take the precaution of giving it a 
 greater diameter than that of the flame, so that it may envelope 
 it. It may even take, at a distance -jL of an inch or so, the 
 positive electricity, with which the surrounding air is also 
 charged. It is more probable that it is the vapour of water, 
 and not the oxygen, which, in the combustion of hydrogen, 
 acquires positive electricity, as the carbonic acid acquired 
 it, in the combustion of carbon. 
 
 The electric phenomena, that accompany combustion, are 
 less simple than would appear, according to the results ob- 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 749 
 
 tained by M. Pouillet ;.it is especially in the electricity, that 
 is liberated by flame, that these anomalies are sensible. M. 
 Hankel satisfied himself, by means of a platinum plate, placed 
 above the flame of a spirit lamp, that the latter is charged 
 with positive electricity, provided the lamp is in communica- 
 tion with the ground : it is necessary for the lamp to be of 
 metal ; if it is of glass, a platinum wire is placed at the bottom 
 of the wick, or in the alcohol, and which is put into com- 
 munication with the ground. The negative electricity is 
 collected by putting into communication with the condenser, 
 either this wire or the lamp, and placing the platinum plate, 
 that is above the flame, in communication with the ground ; 
 these conditions are indispensable, in order to obtain electric 
 signs. By taking, as with a species of gauge, by means of 
 platinum wires buried in glass tubes, and the extremity of 
 which alone is bare, electricity from the different parts of the 
 flame, M. Hankel found the tensions very different. With a 
 small flame of hydrogen gas, coming out from a brass stop- 
 cock, which is in communication with the ground, he obtained 
 signs of positive electricity, which went on increasing in 
 intensity, in proportion as the platinum that drew it off, 
 approached the extremity of the flame, and which was at its 
 maximum at the extremity itself. The effects were similar, 
 only the electricity was of a contrary nature, when the pla- 
 tinum plate communicated with the ground, and the stop- 
 cock with the condenser. 
 
 Besides signs of tension, M. Hankel obtained electric 
 currents, by causing the wire of a galvanometer to communi- 
 cate on the one part with a lamp, on the other part with a 
 plate of platinum, placed above the flame ; the current was 
 directed in the flame from above downwards. It is necessary, 
 in this case, in order to the currents being a little powerful, 
 that the combustion shall have as much vivacity as possible. 
 This is the reason why the platinum plate must be held, 
 not horizontally, but a little inclined above the flame. The 
 presence of metal is not indispensable for the success of the 
 experiment ; a moist conductor, even the moistened hand, 
 may be substituted for it. In order to be satisfied as to the 
 
750 SOURCES OF ELECTRICITY. PART v. 
 
 part, which a variation in the conductibility of the flame itself, 
 may take in the intensity of the current, M. Hank el introduced 
 into the circuit the current of a small pair, in such a manner, 
 that it was led in a direction contrary to that of the current 
 of the flame ; the first current being constant, it was easy to 
 prove, from variations in the effect observed, that the in- 
 tensity of the latter did increase with the extent and the 
 vivacity of the combustion. A very extraordinary fact, ob- 
 served by M. Hankel, is that the flame of hydrogen gives 
 results precisely contrary to those of the flame of alcohol, 
 whether we study its electric state by means of the con- 
 denser, or prove it by means of the galvanometer ; thus the 
 current travels from below upward in the hydrogen flame, 
 when the circuit is closed, instead of travelling from above 
 downwards, as with the flame of alcohol. 
 
 Becquerel, who already, before the researches of Pouillet, 
 had studied the electric state of the flame of alcohol and of 
 that of hydrogen, had arrived at believing that the pheno- 
 mena of combustion is not the only cause of the electricity 
 liberated. He had remarked that conducting wires or plates 
 acquire negative or positive electricity, which they communi- 
 cate to the flame, according to the degree of temperature, which 
 they acquire, on being heated by it ; he had concluded from 
 this that flame exercises an electro-motive action upon the bo- 
 dies, that enter into contact with it, and that consequently me- 
 tallic plates or wires, that are plunged into it, do not play simply 
 the part of conductors. M. Hankel's experiments are not of 
 a nature completely to refute this idea, since this philosopher 
 is still obliged, in order to collect the electricity, to place 
 the flame in contact with heterogeneous bodies, even when 
 these are, instead of metals, moist conductors or the hand. 
 
 M. Buff, who has made a very particular study of the 
 electric nature of flame, arrived at a similar result. After 
 having proved by delicate experiments that air, hydrogen, 
 carbonic acid, and the vapour of water, are very bad con- 
 ductors up to 752, he has succeeded, by heating them to a still 
 more elevated temperature, in causing them to be traversed 
 by the current of two DanielPs pairs ; he has found more- 
 
CHAP. Hi. ELECTRICITY BV CHEMICAL ACTIONS. 751 
 
 over, that these gaseous bodies, when they are at a very elevated 
 temperature, may develope electricity in other conducting 
 bodies, both solid and gaseous, placed in contact with them. 
 But he has constantly observed, on plunging the two ends 
 of the platinum of the galvanometer into the different parts 
 of the flame, that the current went from the most heated 
 wire to that, which was least so ; whence he has concluded 
 that the effect was due to a thermo-electric current. 
 
 However, when he employed the condenser, Buff has ob- 
 tained positive electricity on touching with a platinum wire 
 in communication with the condenser, the exterior part of 
 the flame, and with the negative, penetrating into its interior 
 part ; this result is independent of the temperature of the 
 wires, which would give a contrary effect, of a nature to 
 diminish the intensity of that which is observed. The bodies 
 of lamps, when they are of metal, draw off the negative 
 electricity from the interior part of the flame, if they are put 
 into communication with the ground ; whilst every conductor, 
 such as a plate of metal, moist wood, or even the moistened 
 hand, draws off the positive electricity from the exterior 
 part. If with an alcohol lamp, we obtain an effect contrary 
 to that which is obtained \vith hydrogen, as Hankel has 
 observed, this is due, as Buff has also proved, to the cir- 
 cumstance that the metallic conductor is in contact with the 
 wick, and consequently is found moistened with alcohol ; it 
 is then the thermo-electric effect of the metal which pre- 
 dominates, the wire that is covered with alcohol being neces- 
 sarily less hot than the other. Also, instead of touching 
 with the wick the wire that is introduced into the interior of 
 the flame, as soon as it is raised a little higher, it is no longer 
 seen to produce the exceptional fact. Thus then w r e may 
 regard it as established that every flame, that of a spirit- 
 lamp as well as that of an oil lamp, or that of hydrogen, 
 disperses into the exterior air, by which it is surrounded, 
 positive electricity, as soon as the negative electricity 
 from the interior is conducted to the ground. All these 
 phenomena, according to M. Buff, are thermo-electric effects, 
 in which the gases and vapours, are as much acting 
 
752 SOURCES OF ELECTRICITY. PART v. 
 
 bodies as metals are ; they have not consequently any re- 
 lation with the chemical phenomena of combustion ; also, 
 this philosopher lays it down as a principle that, when a 
 thermo-electric circuit is closed with air, hydrogen or the 
 vapour of alcohol, carbon or metal, an electric current is 
 developed, which moves through the air, from the hotter 
 place of contact to the less hot. 
 
 The researches of M. Buff, like those of M. Hankel, leave 
 therefore the question still undecided of knowing whether 
 the electricity that is obtained, on introducing solid bodies 
 into flames, has a purely thermo-electric origin, or whether it 
 depends, if not in totality, at least in part upon the phenome- 
 non of combustion. Mr. Grove has endeavoured to solve it 
 in the following manner. He employs two platinum wires, 
 six inches in length, and about -^ in. in diameter, which are 
 botli coiled into helices at one of their extremities, whilst they 
 communicate by their other extremity, by means of an insu- 
 lated copper wire, with the wire of a sensitive galvanometer ; 
 one of the small helices is placed entirely in the yellow part 
 of the flame of a spirit lamp, submitted to the action of the 
 blowpipe, very near to the summit of the blue cone, and the 
 other helix is arranged near to the orifice of the air current, 
 at the base of the blue cone, or root of the flame ; the two 
 helices are at a distance of about two inches from each other. 
 The helix that is in the full flame arrives at the red-white 
 state of incandescence, the other, which is at the origin of 
 the flame, is only cherry-red. The galvanometer indicates a 
 deviation of 6, the helix that is, near the orifice playing the 
 part of the zinc or the positive metal, in this species of pair, 
 in respect to the other, which plays the part of negative 
 metal. 
 
 It is easy to prove that the effect observed is not due to a 
 thermo-electric current developed at the points of junction of 
 the wires of platinum and copper ; for it is not altered, when 
 only one of these points of junction is heated by a spirit 
 lamp. Moreover, the slight thermo-electric current, that 
 may be thus obtained, travels in a contrary direction to the 
 current in question, which may be clearly proved; and 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 70S 
 
 moreover the thermo-electric current requires, in order to 
 be collected, a short wire galvanometer, whilst a long wire 
 galvanometer is necessary for the other. Nor Is it a thermo- 
 electric current, due to the unequal heating of the two plati- 
 num helices ; for, the helix, that is in the yellow plume, may be 
 withdrawn, so that it is less heated than that which is at the 
 base of the flame, without changing with this the direction of 
 the current. If the helix, that is at the base of the flame, be 
 brought beside that, which is toward the summit, the devia- 
 tion of the galvanometer diminishes; but it preserves its di- 
 rection until the wires have become very near ; a case, in 
 which the current of the flame gives place to the thermo-elec- 
 tric current, the direction of which depends upon which of the 
 two helices is most heated. 
 
 Wires of zinc, iron, copper were substituted for one of 
 the platinum wires ; the current equally took place, but more 
 powerfully, when the oxidisable wires were in the full flame 
 and the platinum wires at the base of the flame, than in the 
 reverse case. This difference is probably due to the circum- 
 stance that, the oxidisable wire being thicker, they produced, 
 when they were in the full flame, an effect of cooling, which 
 facilitated the development of a tlier mo- electric current, 
 moving in the same direction as the current proper of the 
 flame. 
 
 We may obtain a much more decided effect by uniting the 
 simultaneous action of these two currents. Mr. Grove has 
 obtained this, by forming with a platinum plate a small cone 
 of a little more than j- of an inch in depth, and of as much 
 in width, and substituting this little cone, suspended in 
 a platinum ring, for the helix placed in the full flame; 
 the other helix being still at the base of the flame. The small 
 cone must be filled with water ; and the water is renewed by 
 pouring it in drop by drop from a pipette. Mr, Grove has 
 thus succeeded in obtaining a deviation of the galvanometer, 
 of 20, and even of 30, the direction of which was the same 
 as that of the deviation, that had been obtained in his former 
 experiment. When the cone full of water was placed at the 
 
 VOL. II. 3 C 
 
754 SOURCES OF ELECTRICITY. PART v. 
 
 base of the flame and the helix above, the deviation was not 
 more than 5. 
 
 Mr. Grove concludes from his researches, that there exists 
 in flame a true voltaic current, that is completely independent 
 of thermo-electricity, which leads him to regard this current 
 as the result of the production of electricity, which takes place 
 in the phenomenon of combustion, as is proved by the experi- 
 ment, by which M. Pouillet charges a condenser with negative 
 electricity, by causing a piece of carbon to burn upon its sur- 
 face. In the experiments, that precede, the platinum, that is 
 at the base of the flame, where chemical action commences, 
 plays the part of the zinc of the pair ; and the platinum which 
 is above, where the combustion, and consequently the chemical 
 action is terminated, the part of the negative metal or con- 
 ductor. 
 
 The cause why this current proper, due to combustion, 
 could be observed by Mr. Grove in a manner very distinct 
 from the thermo-electric current, is that the employment 
 of the blowpipe, by giving to the flame a very determinate 
 direction, readily separates the portions, in which the com- 
 bustion operates from those in which it is operated, whilst in 
 ordinary flames, these portions are mingled, and circulate in a 
 confused manner one among the other. 
 
 M. Becquerel, notwithstanding Mr. Grove's experiments, 
 has persisted in not seeing, as did Buff, in the electric currents 
 liberated in flame, anything else than thermo-electric effects. 
 He remarks that, if one of the ends of the platinum is plunged 
 into the alcohol of the lamp, maintained at 32 by melting ice, 
 and that fixed to the other extremity of the galvanometer 
 is a cylinder of platinum also filled with ice, no current is 
 obtained, on placing this cylinder in the interior of the flame, 
 until the ice which it contains, being melted, the cylinder 
 is able to become heated, a proof that the current is 
 thermo-electric. That is true in this case ; but it does not 
 follow from this, that an electro-chemical current may 
 not exist, when, instead of placing the platinum plate or 
 wire in the alcohol, it is placed in the flame at its very base ; 
 a condition necessary, in order that this current may be 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 755 
 
 established, as we are about to see. M. Becquerel places still 
 symmetrically the two platinum spirals s and s', in the same 
 ^ F horizontal section of the flame F, of a spirit- 
 
 lamp L {fig. 3 1 9.), so as to attain red tem- 
 perature ; and in this case there is no 
 current ; but if, by means of a second 
 lamp and the blowpipe, one of the spirals 
 is heated to red-white, a current is pro- 
 Fig. 319. duced, which goes from the cherry-red spiral 
 
 to the red-white spiral. The current has therefore a direc- 
 tion the inverse of that which it possesses, when one of the 
 spirals is in alcohol at the ordinary temperature, whilst the 
 other is in the flame, with a temperature, which does not 
 exceed incandescence ; which would prove that the thermo- 
 electric properties of platinum would change at elevated 
 temperatures. Another manner of proving the same result 
 consists in placing the two spirals, held by means of two 
 supports, which permit of their being raised up or brought 
 down (fig. 320.), one at the visible extremity s' of the flame 
 
 Fig. 320. 
 
 F, the other at its base s, in its blue part, and at a distance 
 of an inch from the former. There is produced a current 
 which goes from below upwards in the flame ; on successively 
 raising the lower spiral to a distance of an eighth of an inch 
 or so from the upper, the current increases in intensity ; and 
 this augmentation is still more considerable if the upper 
 spiral is heated with a second lamp and a blowpipe. The 
 fact that there is no current when the two spirals, being 
 placed in the exterior envelope of the flame, are at the 
 
 3 C 2 
 
756 SOURCES OF ELECTRICITY. PART v. 
 
 same temperature, and we have merely to heat one of them 
 powerfully, without changing their place, in order to obtain 
 a current, leads M. Becquerel to conclude that the current 
 is thermo-electric, and that it must be the same as that, 
 which is obtained with the two unequally heated spirals, placed 
 one at the summit, the other at the base of 'the flame ; the 
 more so as the positive state of the one, that is at the summit, 
 s increased by heating it more. But in his manner of bringing 
 about the heating, M. Becquerel introduces a great modifica- 
 tion into the experiment, by introducing the action of a 
 second flame, which may play another part than that of simply 
 heating the spiral. 
 
 We therefore believe that, notwithstanding the ingenious 
 experiments of M. Becquerel, we must admit, with Mr. 
 Grove, that there are two currents in the flame; one thermo- 
 electric, the other due to a chemical action. With regard to 
 this latter, M. Matteucci appears to us to have found its 
 veritable cause.* When a flame of alcohol or of hydrogen, 
 which comes to the same thing, is in question, the following 
 is what takes place : one of the plates is in contact with the 
 oxygen of the ambient air, the other with the hydrogen ; 
 these two plates are separated by a film of aqueous vapour 
 formed by combustion; we have thus therefore, a veritable gas 
 pile like that of Grove, with this difference, that the elec- 
 trolyte here is vapour of water. The direction of the current 
 is perfectly in accordance with this explanation ; and we see 
 why M. Becquerel obtains no effect by placing one of his 
 spirals in alcohol, or placing them both in contact with the 
 exterior part of the flame, and consequently with the oxygen. 
 When he heats one of them with the dart of tlie blowpipe, 
 it is evident that he places it in contact, no longer with the 
 
 * M. Matteucci, in his researches on the electricity of flame, commences by 
 determining the electric conductibility of different flames, by employing them 
 for transmitting the current of two Daniell pairs, by means of two platinum 
 wires. When the wires are not more than about T ' a of an inch distant in the 
 flame of a lamp with a double current of air. he perceives that the flame begins 
 to be conducteous, probably by a cause similar to that which causes the current 
 to be transmitted through the gases elevated to a high temperature in the ex- 
 periments of M. E. Becquerel (p. 160.). The flames of wax and of stearic acid 
 are sensibly more conducteous than those of alcohol, if we take care to prevent 
 the formation upon the platinum wires of a film of black matter, which pre- 
 vents the transmission of the current. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 757 
 
 air, and consequently with oxygen, but rather with hydrogen 
 or the vapour of alcohol of the new flame ; it must therefore 
 render it positive, as indeed actually take place. In support 
 of his explanation, M. Matteucci cites a great number of 
 experiments, at first those by which he has proved, by means 
 of a platinum spiral, that he causes to communicate with the 
 condenser, that no electric sign is obtained by directing 
 upon it different parts of a well insulated flame of hydrogen ; 
 whilst if by still holding it plunged in the flame of hydrogen, 
 a similar one is placed in communication with the ground, 
 at an inch or an inch and a half above it, marked and 
 constant signs of negative electricity are found in the elec- 
 troscope, analogous to those, which would be given by a 
 plate in contact with hydrogen in one of Grove's gas pairs, 
 the other plate of which would be in contact with the 
 oxygen and would communicate with the ground. By 
 causing the latter spiral to communicate with the con- 
 denser, and the former with the ground, decided signs of 
 positive electricity are obtained. If spirals of blackened, 
 or platinated platinum are employed, the effects are the 
 same, only more powerful. By substituting oxidisable 
 metals for the platinum plates, less distinct electric signs 
 are obtained ; and the phenomena become complex, because 
 a part of the electricity liberated must arise from the de- 
 composition of the vapour of water by these metals, heated 
 to redness. In support of the analogy, which he esta- 
 blishes between the phenomenon of the electricity of flame, 
 and that of the electricity, produced in a gas pair, M. 
 Matteucci cites an experiment, in which he has obtained 
 very strong signs of electric tension, by placing two plates of 
 platinised platinum, one in hydrogen, the other in oxygen, 
 the two gases being enclosed in two bell-glasses inverted in the 
 same trough, which was itself filled with water, either pure or 
 slightly acidulated, into which the two plates partly plunged. 
 In order to prove the existence of secondary polarities in 
 the platinum wires, that plunge into the different parts of the 
 flame, M. Matteucci places two platinum wires, so- that they may 
 be in contact, one with the interior of the flame of a spirit-lamp, 
 
 3 c 3 
 
758 SOURCES OP ELECTRICITY. PART v. 
 
 and the other with its surface or with its point ; the deviation 
 of the galvanometer indicates that the current goes in the flame 
 from the base to the point. The flame is extinguished ; the 
 wires are allowed to cool; the circuit is then closed with 
 water ; a very strong current is obtained, moving in the same 
 direction, as that which was obtained, before the water had 
 been substituted for the flame. These two currents are 
 therefore evidently due to the same cause ; and, if the former 
 is more feeble, it is due to the imperfect conductibility of the 
 flame, or rather of the vapour of water, which suffers elec- 
 trolytic decomposition on the part of the hydrogen and the 
 oxygen, adhering respectively to the two plates of platinum, 
 between which this vapour is interposed. 
 
 Mr. Grove, still admitting the ideas of M. Matteucci, on 
 the origin of the electro-chemical current of flame, does 
 not think that it is the water in the state of vapour, that 
 plays the part of an electrolyte, but rather the flame itself, 
 which would form an electro-chemical chain, in which each 
 particle of the carbon or the hydrogen would combine with 
 the neighbouring particle of oxygen, and so on, bringing 
 about a series of combinations and decompositions, with excess 
 of oxygen at one of the extremities of the flame, and excess of 
 carbonated hydrogen at the other. However, nothing proves 
 that vapour of water at a high temperature cannot suffer an 
 electrolytic decomposition ; the phenomena of the electro-che- 
 mical polarity of gases discovered by Grove himself, that we 
 have described above*, are altogether as legitimately favour- 
 able to this supposition, as we shall see further on, as are other 
 facts relative to the part played by the vapour of water in the 
 production of the electric phenomena, attributed to contact, 
 and in its conducting property for electricity. 
 
 M. Matteucci explains in an analogous manner the origin 
 of the electricity, that is liberated in the combustion of 
 carbon ; he remarks with justice, that the form and position of 
 the carbon are indifferent to the success of the experiment, 
 which M. Gaugain has confirmed f : but he adds, what is 
 
 * Vol. II. p. 464. and following pages. 
 
 f M. Gaugain finds that he succeeds very well in charging; a condenser with 
 negative electricity, by means of the combustion of carbon, by taking care to 
 
CHAP. in. v ELECTRICITY BY CHEMICAL ACTIONS. 759 
 
 equally exact, that, in order for the experiment to succeed, it 
 is necessary that the air be moist ; moreover, in ordinary 
 carbon, there is always hydrogen, which burns with the 
 carbon itself; and consequently there is formation of water. 
 This water is decomposed by the incandescent carbon, as it 
 would be by a heated iron crucible, into which it might be 
 projected ; and by its decomposition it must render the carbon 
 negative, whilst the hydrogen and carbonic acid carry off 
 the positive electricity. The point upon which the learned 
 Italian insists, in favour of his theory, is that it is impossible 
 to find signs of electricity in the combustion of pure carbon 
 in dry oxygen gas, no more than in that of the metals, such 
 as iron and zinc ; whence he concludes that, in order to there 
 being a development of electricity, the decomposition of an 
 electrolyte is necessary, and that the simple combination of 
 two elements is not sufficient. We shall examine further on 
 the extent to which this opinion is founded. 
 
 Before terminating this paragraph, we shall say a few 
 words upon a particular class of currents, that M. Becquerel 
 has designated under the name of pyro-electric, and which 
 are also, like those of flame, due to the combined action of heat 
 carried to a high degree, and to chemical affinity. These 
 currents are produced whenever metallic substances are in 
 contact with vitreous substances in the state of igneous 
 fusion, or at any rate softened by heat. If, into a furnace 
 filled with glowing coals, is introduced a rod of soft iron and 
 one of copper, each in connection with one of the extremities 
 of a galvanometer, no current is obtained ; whilst one is 
 obtained, if the copper rod is enveloped in a glass-tube, 
 provided that the temperature is raised to the point of 
 fusion of this glass. The current increases in intensity in 
 proportion as it is heated, setting out from the point where 
 the glass softens ; then, when the point of fusion is arrived 
 at, the current attains its maximum and remains constant. 
 
 select a very good conducting piece of carbon, then to light it ; and, after 
 having placed it in communication with the plate of the condenser, to place at 
 about ^ in. from the lighted surface a spiral of platinum, or any other conductor 
 that is made to communicate with the ground. At the commencement it is 
 necessary for some time to excite the combustion with a pair of bellows. 
 
 3 c 4 
 
760 SOURCES OF ELECTRICITY. PART v. 
 
 The current goes from the iron to the copper through the 
 carbon and the glass. The iron oxidises and the copper 
 remains intact, as would have taken place in a hydro-electric 
 pair. 
 
 The liberation of the electricity has therefore a purely 
 chemical origin, merely excited by heat ; for if, when the 
 glass which surrounds the copper, being partially melted, it 
 happens that this metal touches the iron, there is no longer 
 any effect, contrary to which would happen, if the current 
 were thermo-electric. A similar effect is obtained by sub- 
 stituting for the iron a piece of gas-carbon cut into a cy- 
 linder, which suffers a veritable combustion. 
 
 In order to obtain more decided, and more durable effects, 
 M. Becquerel places in an earthen crucible a plate of copper, 
 which he covers with powdered glass, into which he causes 
 a rod of iron to penetrate ; he then places the crucible in a 
 reverberating furnace. He succeeded equally well in pro- 
 ducing a strong and constant current, by introducing two 
 long rods, one of iron, the other of copper, into a crucible 
 filled with pounded glass, to which he adds O25 of carbonate 
 of soda, in order to facilitate fusion. Although other 
 vitreous substances may play the same part as glass, the 
 latter has appeared preferable in all the trials that have been 
 made. 
 
 M. Buff, on his part, at the end of experiments upon the 
 conductibility of heated glass, succeeded in constructing a 
 pile, in which the electrolytic liquid is replaced by glass. 
 He placed one above the other, and in the same order, discs 
 of gilded brass, discs of cleaned zinc, and thin plates of glass ; 
 he then attached platinum wires to the first disc and to that 
 which covered the tenth plate of glass ; the pile thus formed 
 was an inch and a half in height. The plates were pressed 
 against each other, so as to be able to be subjected to the 
 current of hot air of an argand lamp. This pile, at the end 
 of a little time, was able to produce a divergence of j- of an 
 inch in the gold-leaf electroscope. When the discs were 
 heated, a contact of a few seconds produced a divergence of 
 at least an inch and a half. A similar pile, and which had 
 
CHAP Hi. ELECTRICITY BY CHEMICAL ACTIONS. 761 
 
 been frequently used, had lost nothing of its primitive elec- 
 tro-motive force, at the end of five months. 
 
 Applications of the preceding Principles to the Construction and 
 to the Theory of the different Voltaic, Piles. 
 
 We have established in a general manner the theory of 
 the voltaic pile in the first paragraph ; but we were not 
 able, before having completed the study of the liberation of 
 electricity in the various forms that chemical actions assume, 
 to appreciate all the causes, that may influence the power 
 of this apparatus, nor indicate the modifications, by which 
 they may be increased. Now that this study is complete, it 
 is easy for us to make a detailed analysis of all that takes 
 place in a circuit of which the pile forms a part, and to find 
 the means of giving to its action all the energy, of which it 
 is susceptible. 
 
 A closed voltaic circuit may be regarded, as we have 
 already remarked, as a system of conductors, in which the 
 electricity is propagated by a series of decompositions and 
 recompositions of the electricities of their consecutive mole- 
 cules. These decompositions and recompositions of the elec- 
 tricities are accompanied, in the electrolytic liquids, that are 
 used for charging the pairs of the pile, and in those which 
 are found in the voltameters, when there are any in the cir- 
 cuit, by the decomposition and recomposition of the mole- 
 cules themselves. The action is the same or equivalent in 
 each pair and in the voltameter, as is proved by experiment ; 
 and the only difference is, that the pair contains one or two 
 bodies, which, by virtue of the chemical affinity for the 
 elements of the liquid, with which it is charged, determine 
 the formation of the polar chain, which continues in the 
 voltameter, only because the polarity is transmitted into it 
 by the intervention of the electrodes and metallic conductors 
 by means of which they communicate with the pair. We 
 may therefore consider voltameters as inactive pairs intro- 
 duced into the circuit, and we should remark, that their in- 
 troduction weakens the current, not only because it occasions 
 one resistance more, as the introduction of any additional 
 
762 SOURCES OF ELECTRICITY. PAHT v. 
 
 conductor would do; but because it creates an electro- 
 motive force, contrary to that of the voltaic pair or pile 
 itself. Indeed, as soon as a voltameter or inactive pair is 
 interposed in the circuit, the decomposition of the liquid, 
 with which it is charged, brings about a secondary polarity, 
 upon the surfaces of each of its electrodes; polarities, the 
 effect of which is to produce a current, moving in a direction 
 contrary to that which has determined them. It is therefore 
 an electro-motive force, created by the action itself of the 
 current, which must be deducted from the electro-motive 
 force of the pair or the pile, when we desire to recognise 
 the real electro-motive force of the current, that traverses 
 the circuit. 
 
 But it is not only in the voltameters, that this contrary 
 electro-motive force is developed; it is also produced in 
 the pairs themselves, when the circuit is closed for a few 
 moments. Indeed, in each pair there is an active metal, ge- 
 nerally zinc, and an inactive metal, platinum or copper ; 
 while the circuit is closed, the zinc oxidises ; it then dissolves 
 to the state of sulphate, supposing that the exciting liquid is 
 a solution of sulphuric acid, at least so long as the liquid is 
 still acid, and is not saturated with the sulphate ; but the 
 platinum or copper, becoming covered either with hydrogen 
 or with zinc or oxide of zinc, arising from the decomposition 
 first of the acidulated water, then of the dissolved sulphate. 
 Now, these deposits impress upon the metal upon which they 
 take place a secondary polarity, the effect of which is to 
 give rise to a current, moving in a direction contrary to that 
 of the current, that would be produced by the action of. 
 the zinc upon the liquid, and consequently would notably 
 diminish this latter. As these secondary polarities are pro- 
 duced equally upon the inactive metal of each pair, they are 
 added to each other, as the electro-motive actions of the zincs 
 are added ; and the latter, in certain cases, may be sufficiently 
 reduced as to end by becoming null. Then the pile no longer 
 exerts action ; this happens to piles that have been for some 
 time in action, as all experimenters have recognised ; among 
 whom we will cite M. Marianini, who has made a series of the 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 763 
 
 experiments upon the weakening that voltaic piles suffer, whilst 
 their circuit is closed during a longer or shorter time ; and 
 upon the time during which their circuit must be left open, in 
 order that they may recover the whole or part of the force, 
 that they have lost. In general, it is in the first moments, 
 when the circuit has just been closed or opened, that the 
 diminution or increase of power is the most decided ; then a 
 moment arrives, when the power of the pile no longer di- 
 minishes or increases, a very important fact, and one which 
 would have placed M. Marianini in the way of the cause of 
 the phenomena, that he had observed ; in that the weakening 
 takes place in a pile, only so long as its circuit is closed ; and 
 that it is even sufficient that its poles be not well insulated, 
 in order to its being manifested. It varies with the nature 
 of the pairs, and principally with that of the inactive metal. 
 M. Marianini has remarked that it had also taken place with 
 dry piles, the poles of which were united by a band of lead. 
 Two Zamboni's piles of 1500 pairs each, having had their 
 poles thus united, at the end of a minute their tension, mea- 
 sured by the divergence of the leaves of the electroscope, was 
 seen to descend from 14 to 6 ; and at the end of 20 minutes 
 to 2. The circuit having been opened at the end of 21 
 minutes, the tension had returned to 14. Repeated and 
 rapid contacts produce the same effect as a continuous com- 
 munication. Finally, it is easy to restore to a pile the force 
 that it had lost, by causing it to be traversed by the current 
 of another pile, but guided in a direction contrary to its 
 own. All these effects are a natural consequence of the po- 
 larisation, that is brought about upon the inactive plates of 
 the pair by the deposits arising from the electrolytic decom- 
 position of their liquid ; deposits, which disappear at least 
 in part, by the dissolving action of the liquid, when the 
 circuit is open, and which are still better destroyed by the 
 formation of deposits of a contrary nature, that are deter- 
 mined by an inverse current, transmitted through the pile. 
 It is easy to satisfy oneself of the accuracy of this explanation 
 by closely examining these plates, and employing them for 
 forming pairs with plates similar, but which have not been 
 
764 SOURCES OF ELECTRICITY. PART v. 
 
 used ; they play all the parts of the positive metal, in respect 
 to these latter. 
 
 The effect that is produced upon the current of a pile, 
 by the interposition of metallic diaphragms or inactive pairs, 
 between its pairs, is due to the same cause as that, which 
 arises from the polarisation of the inactive metals, or the 
 plates of a voltameter ; a voltameter being, as we have said, 
 itself merely an inactive pair, interposed between the two 
 metals of an active pair. Also the influence of the nature of 
 the substances, of which the inactive pairs are made, explains 
 very well the diminution, which their interposition causes 
 the current to undergo, being in relation to the facility which 
 they possess of retaining the deposits that are formed upon 
 their surface ; thus those upon which the liquid exercises a 
 chemical action, scarcely stop the current at all, because the 
 deposits are dissolved, in proportion as they are formed. 
 Moreover, we have already demonstrated that here was the 
 veritable cause of the resistance to passage, by experiments, 
 by means of which we have proved that this resistance is 
 weakened, and becomes even null, when we employ alternate 
 currents, succeeding each other very rapidly, with which the 
 formation of the deposits is impossible.* 
 
 One of the causes that most contribute to diminish the 
 secondary polarity of the inactive plates of the pairs of which 
 a pile in action is composed, is the presence of oxygen. As 
 far back as 1801, Pepys, and more recently Biot and Cuvier 
 had shown, by placing a column-pile surmounted by a 
 bell-glass, that there was absorption of oxygen, if the poles 
 of the pile were united ; and that in vacuo or in nitrogen, 
 the current of this pile was greatly weakened. This influence 
 of oxygen had been attributed to the circumstance, that its 
 presence facilitates the oxidation of the attackable metal of 
 the pair; but latterly, Mr. Adie, and after him M. Viard, 
 have demonstrated, by accurate and numerous experiments, 
 that it is by its action upon the negative or inactive plate of 
 the pair, that the oxygen exerts its influence. Thus, when 
 
 * Vol. II. p. 402. and following. 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 765 
 
 two plates of the same metal are placed, one in boiled water, 
 and the other in water, that contains oxygen in solution, the 
 two liquids being separated by a porous partition, it is always 
 the latter plate, that is negative, in regard to the former. 
 This result, in accordance with those, which we have seen 
 to have been already obtained by Matteucci and by Grove, 
 explains in the same manner that the establishment of the 
 current in the gas pile, the polarisation of the successive mole- 
 cules of the liquid, and their decomposition and recomposition, 
 are facilitated by the presence of oxygen upon one of the 
 plates, which determines the direction of the polarisation, and 
 consequently that of the current. But the influence of oxygen 
 is much more marked, when the pairs are formed of two 
 different metals ; this M. Viard has proved with various voltaic 
 combinations, such as zinc with platinum, silver, copper, and 
 iron ; iron with platinum, silver, and copper ; copper with plati- 
 num and silver ; and finally, silver with platinum. Different 
 liquids were employed for electrolytes, care being taken, in 
 each case, to place them in two compartments, one of which 
 contained the liquid, deprived as much as possible of oxygen, 
 whilst the other contained the same liquid aerated with oxygen. 
 The experiments were made in the same manner as when the 
 plates were homogeneous, that is to say, by plunging one of 
 the plates into the liquid deprived of air, and the other into 
 the aerated liquid ; it was always the presence of the oxygen 
 on the negative plate, which increased the force of the 
 current ; an increase due evidently to the absence of 
 secondary polarity for this plate, on account of the absorp- 
 tion brought about by the oxygen for the nascent hydrogen, 
 in proportion as it is liberated upon its surface by the 
 current. 
 
 In order to measure and compare the absorption of the 
 oxygen that takes place in pairs of different natures, M. 
 Viard combined his apparatus, so that the electrolyte might 
 be screened from contact with the air ; then, placing above 
 each of the elements of the pair, a small graduated bell- 
 glass, filled with oxygen, he was able to determine the ab- 
 sorptions, both in the case, in which the circuit was closed, 
 
766 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 and in that in which it remained open. The pairs, successively 
 submitted to experiment, were zinc platinum, zinc-silvery zinc- 
 copper, and zinc-iron pairs ; the electrolytes were successively, 
 with each pair, pure water, solutions of sulphate of potash, and 
 of chloride of sodium; the experiments lasted from twenty to 
 twenty-five days with pure water, and only sixteen hours 
 with the other liquids. The following is the result of the 
 absorption, measured by the elevation of the liquid, in the 
 tube filled with oxygen, for two of the pairs, chosen at the 
 two extremities of the scale : 
 
 Electrolyte. 
 
 ZINC-PLATINUM. 
 
 ZINC-IRON. 
 
 Closed 
 circuit. 
 
 Open 
 circuit. 
 
 Closed 
 circuit. 
 
 Open 
 circuit. 
 
 Water 
 Sulphate of potash - 
 Chloride of sodium - 
 
 18-0 
 33-5 
 9 -0 
 
 3-0 
 0-5 
 0-5 
 
 14-0 
 16-0 
 14-0 
 
 12-0 
 8-0 
 
 7-5 
 
 We see that the difference between the absorption, when 
 the circuit is closed, and the absorption, when it is open, 
 is greater with saline solutions than with pure water ; it is 
 the more considerable, as well as the absorption itself, as the 
 negative plate is less oxidisable. The absoption does not 
 take place at the negative plate only, but it equally takes 
 place at the positive, with this difference, that it remains 
 then sensibly the same, whether the circuit of the pairs is 
 open or closed. The absorption at the negative plate must 
 depend upon the intensity of the current; it also varies with 
 the nature of the pair and with that of the electrolyte. With 
 a zinc-iron pair, charged with pure water, and which conse- 
 quently is very feeble, the opening of the circuit has no 
 influence over the absorption, the latter taking place almost 
 exclusively upon the positive plate, whilst with a zinc- 
 platinum pair, charged with a solution of sulphate of potash, 
 and the current of which is very powerful, which permits 
 of a very short experiment, the absorption is considerable, 
 when the circuit is closed, and almost null when it is 
 
CHAP. in. EJLECTRICITY BY CHEMICAL ACTIONS. 7G7 
 
 opened, seeing that then it is taking place upon the positive 
 plate alone. 
 
 It follows therefore from all that precedes, that the cause of 
 the sudden and great reduction, which voltaic piles suffer, 
 when their circuit has been closed for some moments, is not 
 so much the diminution in the exciting faculty of the liquid 
 with which they are charged, that is to say, in the energy 
 of the chemical action exercised upon the oxidisable metal, 
 as the creation of a contrary polarity upon the negative 
 or inactive metal, by the effect of deposits arising from 
 the electrolytic decomposition of the liquid, principally of 
 hydrogen. 
 
 Let us now see how, setting out from these principles, we 
 may be able to give a satisfactory explanation of the pro- 
 perties, that characterise each species of pile, and more 
 particularly the constant current piles. We shall not re- 
 turn to the details of the construction of the diverse voltaic 
 piles ; details, which we have set forth in the Second Chapter 
 of our First Part ; we will regard them as known in the * 
 analysis, that we are about to make of the circumstances, that 
 influence the power of these apparatus. 
 
 The first column-piles *, as well as those in the wooden 
 troughs, the couronne des tosses, the trough of pipe-clay or of 
 copper f, are, as may be remembered, composed of zinc- 
 copper pairs, charged with a single liquid, namely, an acid 
 or saline solution. All present the inconvenience of becoming 
 very rapidly enfeebled when their circuit is closed, by the 
 effect of the polarisation of their negative plates. This 
 inconvenience is reduced, either by taking as an exciting 
 liquid a solution of sulphuric acid, in which a little nitric 
 acid is mixed, or in giving to the negative plates a much 
 greater surface than to the positive. These two modifica- 
 tions, introduced into the first modes employed for charging 
 and constructing the pile, had been introduced empirically, 
 experience having pointed out the advantages of them ; now, 
 it is easy to comprehend the utility of this, by remarking, 
 
 * Vol. I. p. so. (fig. 17.), 
 
 f Vol. I. p. 36. (Jig. 25.) ; p. 37. (Jig, 26.); p. 38. (fig. 27.) ; p. 39. (Jiys. 26. 
 and 29.) ; and p. 40. (figs. 30. and 31.). 
 
768 SOURCES OF ELECTRICITY. PART v. 
 
 that the presence of nitric acid in the exciting liquid facili- 
 tates the partial solution of the deposit upon the negative 
 plate, and that the extent, given to this plate, diminishes on 
 each part of its surface the quantity of this deposit. 
 
 To these perfections, Faraday had added some others ; he 
 had, as Dr. Hare had first * pointed out in his calorimeter, 
 approximated the zinc and the negative metal (copper or pla- 
 tinum) as near as possible to each other, contenting himself 
 with separating the two metals, in order to avoid all contact 
 between them, by a sheet of paper. Moreover, as in 
 Wollaston's pile f , the copper goes around the zinc, and a 
 piece of wood or cork prevents the lower part of the copper 
 from touching the lower edge of the zinc plate. Not only 
 are the zincs very near to the coppers in each pair, but 
 the pairs themselves are also very near together ; and their 
 coppers are also preserved from metallic contact by several 
 sheets of paper. But the greatest modification introduced 
 by Faraday is to plunge the whole pile into the same liquid, 
 and not each pair into a separate cell. Without doubt, the 
 effect is a little enfeebled ; because a part of the electricities 
 is recomposed through the liquid, which bathes equally all 
 the pairs ; but this recomposition is very feeble in respect to 
 that which takes place through the conductor, that unites the 
 two poles of the pile, provided that the exciting liquid is not 
 too acid a solution, and consequently too conducting. Ex- 
 periment has shown that there was no sensible difference, as 
 far as concerns the incandescence of wires, which requires 
 the employment of good conductors, between two piles of 
 forty pairs exactly similar, except that in one the exciting 
 liquid was in cells separated for each pair, and that in the 
 other it was in a single trough. Moreover, the employment 
 of this pile is very convenient, seeing that nothing is more 
 easy than to immerse and to withdraw promptly the metal 
 pairs, which causes very little zinc to be consumed, and the 
 pile to occupy very little space, on account of the proximity 
 of the plates of which it is formed. As the zinc plates are 
 
 * Vol. I. p. 40. (fig. so.). 
 
 t Vol. I. p. 39. (fig. 28.). 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 769 
 
 very thin, they may be made of rolled zinc, which is very 
 superior to cast zinc. MM. Young and Munch have mo- 
 dified Farada}r's pile by substituting amalgamated zinc for 
 the ordinary zinc, and so arranging it, that each zinc is always 
 situated between two surfaces of the same copper; the whole 
 combined so as to occupy the least possible space, so that in 
 Munch's pile fifty pairs occupy scarcely a length of twelve 
 inches. 
 
 Smee's pile, like that of Faraday, is also a pile in which 
 there is only one liquid interposed between the metals of 
 the pairs, but the zinc in it is amalgamated, which avoids 
 all local action, and the negative element is covered with 
 a film of finely divided platinum, as are the platinised 
 platinum plates of Grove's gas pile. This latter circumstance 
 facilitates singularly the liberation of the hydrogen, and con- 
 sequently the development of the electro-motive force of the 
 pair, by diminishing or almost entirely annihilating the se- 
 condary polarity of the negative metal. Thus a same plate 
 of amalgamated zinc, placed successively in contact in diluted 
 acid, with platinised platinum and polished platinum, heated 
 to drive off the air from its surface, liberates in one minute 
 for the former five times as much hydrogen gas as for the 
 latter. All the other effects of the current are increased in 
 the same proportion. Mr, Smee, in his pile, places the pla- 
 tinised plate between the two vertical faces of a plate of amal- 
 gamated zinc, as in Grove's nitric-acid pile ; but as there are 
 neither two liquids, nor any porous cell, he greatly approx- 
 imates the two faces of the zinc, by giving to his pairs the 
 form of those of the Wollaston pile.* The platinised plati- 
 num plate may, without inconvenience, have only f of the 
 size of the faces of the zinc plate. 
 
 Smee's pile is generally charged with a solution of 1 part 
 sulphuric acid for 7 of water. Its effect is much more con- 
 stant than might have been expected from a pile of a single 
 liquid ; and with an equal number of pairs of equal surfaces, 
 it possesses a very superior effect to that of a DanielPs with 
 sulphate of copper. Smee, as a motive of economy, employs, 
 
 * Vol. I. p. 39. (fig. 28.) 
 VOL. II. 3 D 
 
770 SOURCES OF ELECTRICITY. PART v. 
 
 in his pile, platinised silver, instead of platinum ; but silver, 
 on account of its polish, submits badly to the operation of 
 platinising. On this account, M. Boquillon has devised the 
 employment of a plate of copper, upon which he first deposits 
 a coat of copper, so that it is rough and covered with aspe- 
 rities ; he then covers this first coat with a coating of silver, 
 which participates in the same superficial state; and it is 
 upon this film of silver that he finally deposits pulverulent 
 platinum, which, by adhering to it, gives to the plate in 
 the highest degree the property of liberating hydrogen freely. 
 
 M. Poggendorff has also succeeded in giving to pairs, 
 formed of a plate of amalgamated zinc and a plate of copper, 
 plunged into diluted sulphuric acid, a remarkable force and 
 constancy, by covering the copper plate with a pulverulent 
 coat of copper, similar to that of platinum, with which Smee 
 covers his negative plates. 
 
 But the surest manner of avoiding all polarity upon the 
 negative plate is to plunge it into a liquid, which absorbs the 
 hydrogen at the moment when, and in proportion as it is 
 liberated *, and which also prevents a deposit of zinc or 
 oxide of zinc upon this plate, arising from the electrolytic 
 decomposition of the salt, which is formed in the action upon 
 the amalgamated zinc of the liquid, which attacks it. Daniell 
 was the first to conceive the idea of this perfection by making 
 application to the construction of the pairs of a voltaic pile 
 of the electro-chemical effects, that take place in two liquids, 
 separated by a porous membrane, and which M. Becquerel 
 had already discovered and described. This philosopher had 
 in fact already observed, both in his oxygen-gas pile, as well 
 as in a pair formed of two plates, one of zinc, the other of 
 copper, plunged into two distinct compartments, filled with 
 various exciting liquids and separated by a diaphragm of 
 gold-beaters' skin, that much more constant currents may be 
 obtained than when a single liquid is employed. Thus he 
 had obtained a rather strong and tolerably constant current, 
 
 * Another advantage of the absorption of the hydrogen is to avoid the me- 
 chanical obstacle, that the appearance of the bubbles of gas opposes to the free 
 circulation of the current 
 
CHAP. III. 
 
 ELECTRICITY BY CHEMICAL ACTIONS. 
 
 771 
 
 by putting nitrate of copper into the cell where the copper 
 was, and sulphate of zinc into that where the zinc was ; with 
 sulphuric acid very much diluted with water in both cells 
 equally, and a few drops of nitric acid in the copper cell, he 
 had succeeded in producing a rather constant effect, due to 
 the action of the nitric acid, as we have already remarked, 
 when speaking of the advantage that he had recognised when 
 charging old piles with a solution of sulphuric acid containing 
 a little nitric acid. 
 
 Daniell has then contrived to construct a pair, and con- 
 sequently a pile, in which, still leaving the zinc in a solution 
 of sulphuric acid or of common salt, he plunges the copper 
 into a concentrated solution of sulphate of copper ; the two 
 liquids are separated by a porous diaphragm, made of an 
 organic substance, such as bladder, gold-beaters' skin, close- 
 woven cloth, or wood, or simply formed of unglazed and un- 
 varnished earth. We have already given the description of 
 this pile.* We shall therefore confine ourselves to producing 
 here (Jig. 321.) a sulphate of copper pair^ 
 such as Daniell constructed originally. A 
 B is a cylinder of copper, which serves at 
 the same time as vessel and as negative 
 metal ; the two bases of this cylinder are 
 pierced, at E F and at a b, by two circular 
 openings, to which is strongly attached by 
 its two extremities a tube of porous mem- 
 brane, which is nothing more than the in- 
 testine of an ox, properly prepared, in the 
 interior of which is placed a cylinder of 
 amalgamated zinc, c d. From the lower opening to the 
 centre of a b, there comes out a syphon tube c f g, intended to 
 give escape to the liquid contained in the membranous cylinder, 
 when fresh is added to it. Care must be taken to maintain 
 at the top of the solution of sulphate of copper some crystals 
 of this salt, in order that it may always remain as concen- 
 trated as possible. Notwithstanding certain advantages, that 
 this mode of construction might at first seem to present, the 
 * Vol. I. P . 42. 
 
 3 D 2 
 
 Fig. 321. 
 
772 SOURCES OF ELECTRICITY. PART v. 
 
 system, that we have described in our First Volume, is very 
 generally preferred.* 
 
 Darnell's pile, like all other in which the zinc is amalgamated, 
 presents the advantage that there is no chemical action when 
 it is not working ; but that which characterises it essentially 
 is that its effect is constant, because the copper does not po- 
 larise. Indeed, when the current is closed, the hydrogen 
 that results from the decomposition of the acidulated water 
 upon the surface of the zinc, meeting the sulphate of copper 
 beyond the porous membranes, combines with the oxygen of 
 the first molecule of this sulphate, so that it is the sulphate 
 that is now decomposed f, and that it is its copper which 
 goes and deposits itself, forming a thin film of copper upon 
 the copper of the pair ; the latter therefore is not altered, and 
 consequently not polarised. It is true, that when the solution 
 of sulphate, being a little exhausted, has become tolerably 
 acid, it is then the acidulated water, and no longer the 
 sulphate, that is decomposed; whence it follows, that hydrogen 
 is liberated upon the surface of the copper ; but so long as there 
 remains any sulphate in the solution, this sulphate is reduced 
 by the nascent hydrogen, and it is still a deposit of copper, 
 that is obtained ; only it is granulous, instead of being united, 
 brilliant, and ductile, which already diminishes a little the 
 force of the current : then, when the solution is entirely ex- 
 hausted, hydrogen is deposited upon the copper itself, and 
 then the current loses its constancy. On this account it is 
 of great importance to maintain the solution of sulphate of 
 copper, as much as possible in the state of saturation. The 
 useful effect in the Daniell's pile is entirely in the action of 
 the zinc upon the exciting liquid, by which it is bathed ; for 
 copper exercises no sensible action upon its sulphate, as is 
 proved by experiment; the decomposition of this sulphate 
 cannot therefore be an electric source ; but simply the effect 
 
 * There is an advantage in the Daniell's pile, in which the copper and the 
 sulphate of copper are always placed exteriorly, in giving to the zinc cylinders, 
 that plunge into the porous tubes, filled with a solution of sulphuric acid, the 
 form of hollow cylinders, instead of that of solid cylinders, in order that they 
 may present more surface to the action of the liquid. 
 
 f Vide Vol. II. p. 386. 
 
CHAP. III. 
 
 ELECTRICITY BY CHEMICAL ACTIONS. 
 
 773 
 
 of the current produced by the reunion of the two electricities 
 liberated upon the zinc ; an effect, which, by the deposit of 
 copper, that it occasions, produces the constancy of the 
 apparatus.* 
 
 M. Buff has introduced into the Darnell's pile a modifica- 
 tion that gives to it a remarkable constancy, and one, that 
 is very precious for researches, which, without requiring a 
 great force of current, requires that this force shall remain as 
 constant as possible for a tolerably long time. This modifi- 
 cation consists in constantly renewing the sulphate of copper, 
 and at the same time causing the amalgamated zinc to bring 
 itself in its liquid, only in proportion as it is used, which is 
 obtained by means of a counterpoise. 
 
 Things do not take place exactly in the same manner, 
 with the Grove's pile, in which nitric acid is substituted 
 for the sulphate of copper, and consequently platinum for the 
 copper (Jig. 322.). Besides, the nitric acid, being a much 
 
 + / 
 
 Fig. 322. 
 
 better conductor than the solution of sulphate of copper, the 
 current is more easily transmitted, it is probable that in this 
 case the facility with which the nitric acid abandons its 
 
 * See Vol. I. p. 43. {fig. 32.) In fig. 34. the zinc and platinum are con- 
 nected metallically by a thin plate of brass, furnished with hooks and screws, 
 so as to form a clip. In fig. 33. of VoL I. they are simply united by a clip of 
 
 wood or of cork. 
 
 3 D 3 
 
774 SOURCES OF ELECTRICITY. PART r. 
 
 oxygen, tends to decompose the acidulated water, by taking 
 from it its hydrogen ; it is sufficient indeed to plunge into a 
 solution of sulphuric acid two plates of platinum, after having 
 taken the precaution of first moistening one of them with a 
 film of nitric acid, to obtain a powerful current, in which the 
 latter plays the part of the negative metal. Thus then not 
 only does the nitric acid, in preventing by its contact with 
 the platinum plate the deposit of nascent hydrogen and con- 
 sequently secondary polarity, render the current constant, 
 but at the same time it contributes to increase its intensity, 
 as does peroxide of lead and substances in general, which 
 contain much oxygen. A real inconvenience of Grove's 
 nitric-acid pile is, that its constancy does not last long ; if its 
 circuit is closed for a few moments in succession without inter- 
 ruption, providing the conductor that connects its poles is good, 
 nitrous vapours are seen to escape from the porous vessels in 
 which the nitric acid is contained ; this acid itself changes 
 colour, and becomes boiling, and it is then necessary to stop 
 the action of the pile. This inconvenience may be mitigated 
 by mixing a little concentrated sulphuric acid (one-half or 
 one- third) with the nitric acid, or even taking, instead of 
 nitric acid at 1'40, nitric acid mixed with one-half of water. 
 But the current loses in intensity what it gains in constancy, 
 especially if the latter means is employed ; for with the 
 former, which is much preferable, the force is not sensibly di- 
 minished. It has even been proposed to substitute peroxide 
 of manganese, mixed with concentrated sulphuric acid, for 
 the nitric acid ; but satisfactory results are not obtained by 
 the process. 
 
 Bunsen's pile, in which carbon is substituted for platinum * 
 
 * Vol. I. p. 46. (fig 34. and fig. 35). M. Silliman employs as carbon, in 
 Bunsen's pile, natural plumbago, or artificial plumbago, such as that of which 
 crucibles are made. Mere pieces of coke, well selected, may also be advan- 
 tageously employed. 
 
 The following, however, is M. Bunsen's mode of preparing his carbons : An 
 intimate mixture is first prepared, of one part of pitcoal (by weight), and two parts 
 of coke, in impalpable powder. This mixture is introduced into a cylindrical mould 
 of sheet iron, in the centre of which is placed a small roll of card ]th of an inch 
 in diameter, so as to form in the carbon an internal cavity, and facilitate the 
 liberation of the gases during calcination. Thus filled with the mixture of 
 carbon, and closed by means of a movable cover, well adjusted, the iron 
 mould is heated to redness, until all liberation of gas has ceased. After this 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 775 
 
 (fig. 323.) does not present, in the same degree, the incon- 
 venience, that we have been pointing out in Grove's pile. This 
 
 Fig. 323. 
 
 is due to the circumstance that carbon, not being so good 
 a conductor as platinum, the current that results from the 
 closing of the circuit is less violent. However, at the end 
 of a certain time, only a little longer, which is due also to 
 the circumstance that the mass of acid in it is generally more 
 considerable, nitrous vapours are seen to rise, and the acid 
 to enter into ebullition. It is also necessary to take the 
 precaution of not introducing pure nitric acid, but rather to 
 mix it with water. We may even content ourselves with 
 plunging the carbons, when they have sojourned a long time 
 in nitric acid, in a solution of sulphuric acid, with which the 
 porous tubes are filled. The nitric acid, with which the 
 carbons are impregnated, suffices for a tolerably long time to 
 
 calcination, the carbon is easily withdrawn from the mould in a compact form, 
 cylindrical like the mould, very hard, and susceptible of submitting to the action 
 of the file and the saw without breaking. The lathe may give to these cylinders 
 the suitable form. This being done, it is well to steep several times over the 
 cylinders of carbon in a concentrated solution of molasses, and to submit them 
 to a fresh calcination as intense as possible. Many elements may be cal- 
 cined together in a large earthen or iron crucible, the interstices being filled 
 with pulverised coke. 
 
 Finally, before plunging the carbon into the nitric acid, it is indispensable to 
 cover with a film of melted wax the neck, upon which is adapted the metallic 
 ring, or rod intended for establishing the necessary communication between 
 the carbon and the zinc, in order to prevent the acid from coming and corroding 
 the metal by the effect of capillarity. After each experiment, the nitric acid 
 may remain without inconvenience in contact with the carbons. The cell con- 
 taining the sulphuric acid must, on the contrary, be removed, emptied, and 
 washed in plenty of water, as well also as the zinc cylinder. 
 
 3 D 4 
 
776 SOURCES OP ELECTRICITY. PART v. 
 
 increase the power and to maintain the constancy of the 
 pairs.* 
 
 This property of carbon has served me for constructing 
 a pile in which oxygen itself may, up to a certain point, be 
 substituted for nitric acid. I introduced 
 (jig. 324.) into a porous tube, in the centre 
 of which is a platinum wire, carbon well 
 baked, and consequently a good conductor, 
 reduced into an impalpable powder. I took 
 care to ram it well ; then I placed the porous 
 tube thus filled in the interior of a cylinder 
 of amalgamated zinc, which is itself plunged 
 in the solution of sulphuric acid. A pile of 
 eight or ten pairs, constructed in this manner, 
 and the zinc cylinders of which were only 2 in. in height and 
 1^ in. in diameter, gave me for eight days, without inter- 
 ruption, a decomposition of acidulated water, not very strong, 
 about y 1 ^ of a cub. in. per minute, but very constant. The 
 hydrogen which would have polarised the carbon in each pair 
 disappears, by its combination, in the nascent state with the 
 oxygen, that the carbon retains in its pores, and which it takes 
 from the atmospheric air. When the pile is weakened, a 
 few drops of nitric acid poured upon the upper face of the 
 rammed cylinder of carbon, revives it for a tolerably long 
 
 * M. Callan has had the idea of substituting lead for the platinum and the carbon 
 in Grove's and Bunsen's piles ; and he has obtained very satisfactory results. 
 But he has found great advantage in covering the leaden plate with a slight 
 film of platinum or of gold, by means of the chlorides of these two metals. It 
 is evident that there would be a great economy in employing for Grove's piles 
 plates of copper, or lead platinised, intead of plates of platinum. M. Schcen- 
 bein had also the idea of employing, as a negative metal, passive iron, and as a 
 positive metal ordinary iron, the former being in contact with nitric acid, and 
 the latter with the solution of sulphuric acid. It is very curious to see the 
 same metal, iron, play at the same time the part of negative and of positive metal. 
 However, in this latter relation, amalgamated zinc is very preferable ; but hollow 
 cylinders of cast iron, the inner side of which has been rendered passive, may 
 very well serve, at the same time, as negative metals of the pair, and as vessels 
 into which the nitric acid is placed ; then the porous tube, filled with the so- 
 lution of sulphuric acid, into which the iron, or rather the amalgamated zinc, is 
 plunged. I have for a long time advantageously used piles thus constructed. 
 
 Mr. Callan has also latterly made Use of cast iron for constructing with 
 amalgamated zinc, a single liquid pile, charged with a mixture of sulphuric 
 acid and a saline solution. He has obtained very good effects from this ar- 
 rangement. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 777 
 
 time. But a moment arrives at which the sulphate of zinc, 
 having penetrated into the powder of carbon, it is necessary 
 to dismount the pile, in order to wash the powder in plenty of 
 water, or, which is more simple, to change it. I have found, 
 that we might in this pile substitute with advantage, for the 
 platinum wires, small cylinders of carbon, of about -i-th of an 
 in. in diameter, prepared like those that are used in the 
 Bunsen's piles, taking care to place them in the axis of the 
 porous tubes, before surrounding them with the powder of 
 carbon, and planting in them a copper wire, intended for 
 establishing communication. 
 
 Wheatstone, as we shall see in a moment, has successfully 
 employed, in his researches, pairs in which there is only 
 one liquid, but avoiding the immediate contact of the positive 
 metal with this liquid. This metal is dissolved in mercury, so 
 as to form a liquid amalgam ; the amalgam itself is placed in 
 a small porous tube (fig. 324.), and the tube is plunged in 
 the solution, that bathes the negative metal ; sulphate of cop- 
 per, if this negative metal is copper ; chloride of platinum, if 
 this metal is platinum. A wire of copper or of platinum is 
 plunged into the amalgam, in order to draw off the negative 
 electricity. The chemical affinity, that is exerted upon the 
 oxygen, or upon the chlorine of the solution, by the positive 
 metal, the zinc for example, dissolved in the mercury, is suf- 
 ficient to bring about the production of a current, which 
 is tolerably constant * ; less however than in piles of two 
 liquids ; for a little metallic copper is soon perceived in the 
 amalgam, against the interior side of the porous tube, when 
 the solution is sulphate of copper, which is due to the local 
 action of the zinc upon the sulphate, which reduces a little 
 copper. 
 
 In all two-liquid piles, and even frequently in those, 
 in which there is but one liquid, we are therefore led to em- 
 ploy diaphragms or porous tubes, which, while preventing 
 the mixture of the substances that they separate, allow, by 
 their being moistened, of the electric communication being 
 
 * It is necessary, that the salt in solution be a salt whose base is the same 
 metal as the negative metal of the pair, in order that the voltaic current, in 
 decomposing it, may not alter the nature of the surface of this negative metal. 
 
778 SOURCES OF ELECTRICITY. PART v. 
 
 established between them. These diaphragms, as we have 
 seen, are of different species ; and it is not useless, before ter- 
 minating that, which concerns the details of the construction 
 of the different piles, to say a few words upon them. 
 
 Goldbeaters' skin and bladder, on account of their little 
 thickness, are the diaphragms, that oppose the least resistance 
 to the passage of the current ; but chemical agents promptly 
 destroy them, and they possess the inconvenience of facili- 
 tating too much the endosmose of the liquids, which on this 
 account cannot remain long separated. Also this species of 
 diaphragms, which may be good in certain experiments of de- 
 licate researches, must be rejected in the construction of piles 
 in common use. Leather and tanned skin possess the same in- 
 conveniences, but in a less degree ; however, the preparation, 
 which they must be made to undergo, sometimes alters them 
 so much, as to render them unfit for the service for which they 
 are intended. Sail-cloth is better, seeing that it has only a 
 feeble degree of endosmose on neutral solutions ; it is necessary, 
 when the form of a bag is given to them, that the seam be made 
 with a thread covered with pitch. Paper or pasteboard, tarred, 
 a little permeable to liquids, is a tolerably good diaphragm ; 
 the tar prevents the paper from dispersing in the water. But, 
 in fact, of organic diaphragms, those which are made of thin 
 wood are perhaps preferable to all. Thus, for Daniell's pile, 
 hollow cylinders of lime wood, with very thin sides, have con- 
 stantly given me very good results. It is necessary to take 
 the precaution, in order to remove the resinous matters which 
 are found in the wood, especially when it is pine that is em- 
 ployed, to plunge them for a long time in boiling alkaline 
 water ; then they must be preserved, when not in use, in 
 water slightly acidulated ; otherwise they shrink and split 
 in drying, which renders them unfit for the object in view. 
 
 Inorganic diaphragms are generally of clay, or, better still, 
 of kaolin ; this latter, deprived of carbonate of lime, forms in 
 the state of paste a diaphragm, to which much thickness can 
 be given, which is advantageous for avoiding endosmose, pro- 
 vided that it is well saturated with a good conducting liquid, 
 and that it is not too closely pressed. But it is especially 
 under the form of vessels, either prismatic as in Grove's piles, 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 779 
 
 or cylindrical as in those of Bunsen, that inorganic diaphragms 
 are serviceable. They are made in general of unglazed porce- 
 lain, but they present more resistance than half-baked earth 
 and than crucibles. These latter are very convenient, because 
 they may be easily procured ; only it is necessary to diminish 
 with the file the thickness of their sides, which generally is too 
 considerable. Care must be taken to wash frequently all these 
 diaphragms, in order to remove the salts which, penetrating 
 and crystallising in their interior, end by causing the sides 
 to burst, We must also watch that these diaphragms contain 
 neither carbon, pyrites, or other substances of a metallic 
 origin, which, being conducteous, might establish between 
 the two liquids, that are separated by the diaphragm, a com- 
 munication of quite another nature to that which we have in 
 view; that is to say, a metallic communication, which would 
 bring about an electro- chemical decomposition: it is to the 
 presence of these heterogeneous substances, that may be at- 
 tributed the appearance, that sometimes occurs on the surface 
 of the diaphgrams of reduced metallic deposits. Organic sub- 
 sances do not present the same degree of inconvenience, but 
 they possess that of producing of themselves the reduction of 
 certain metals, when they plunge into their solutions. To 
 sum up ; in practice, it is to diaphragms of unglazed porcelain 
 that the preference has been given, although they present 
 more resistance than others to the passage of the current. 
 
 We shall not here dwell upon the description of some other 
 piles, more or less constant, such as those, in which the 
 moist conductor is simply the earth, whether the two metals of 
 the pair are implanted in the moist ground, as Bain, Loomis, 
 and others have done, or they are placed in a vessel filled 
 with earth, which is watered with hydrochlorate of ammonia, 
 as in the Bagration* pile. These different piles having been 
 
 * This pile produces a current of an astonishing constancy, which arises 
 either from the reduction of the hydrogen upon the copper, by the compound 
 that the ammoniacal salt forms upon this metal, or by the absorption of the 
 hydrogen by the earth itself, which moreover fills the office of a diaphragm, and 
 thus prevents a deposit of zinc upon the copper. It is well not to place the 
 two plates of the pair too near to each other, and to plunge the plate of copper, 
 before placing it in the earth, in a solution of ammoniacal salt, allowing it to 
 dry, until a greenish film is formed upon the surface. 
 
780 SOURCES OF ELECTRICITY. PART v. 
 
 constructed with a view to applications, the description of 
 them will naturally find its place when we shall be speaking 
 of those applications, to which they relate. We shall, for a 
 like reason, return to them in a subsequent paragraph of this 
 Chapter, in which we shall be treating the question of 
 contact, the theory of dry piles, of which we have already 
 given the description.* 
 
 But if, in respect to form, we have nothing to add, as we 
 have said, either in this paragraph, or in the fifth of the 
 Fourth Chapter of our First Partf, it is far from being the 
 same, in regard to the nature of the solid and liquid sub- 
 stances, which constitute the pairs ; but this important point 
 is about to be treated in detail in the following paragraph, 
 devoted to the measurement of electro-motive forces, and to 
 the comparison, in respect to their power, of the different 
 voltaic combinations with each other. 
 
 However, before entering upon this important subject, we 
 have still to mention a process very different from those 
 which precede, in order to maintain and to increase the 
 power of piles by destroying secondary polarities ; it is that, 
 which has very recently been devised by M. E. Becquerel, 
 and which, if it has not all the practical tendency, which one 
 might perhaps have been prepared to expect, is not without its 
 interest in a theoretical point of view. The process consists 
 in giving to the pairs of a pile a tolerably rapid motion in 
 the liquid, by which they are bathed. Thus, M. E. Bec- 
 querel has obtained with a single platinum and amalga- 
 mated zinc pair, a very sensible increase, by the fact of the 
 movement. This pair at rest in a solution of sulphate of soda, 
 half-saturated, would give to a galvanometer, that was not 
 very sensitive, a deviation of 8 ; when it was put into motion, 
 the deviation went as far as 20. This effect is evidently 
 due to the circumstance that the motion depolarises the plate 
 of platinum ; however, there is an advantage in moving also 
 the zinc plate, because the liquid films that bathe its surface 
 are thus charged. If a solution of sulphuric acid is substi- 
 
 * Vol.' I. p. 53. f Vol. I. p. 36. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 781 
 
 tuted for that of sulphate of soda, the effect of the movement 
 is much less decided, on account of the abundant liberation 
 of hydrogen upon the platinum; but it becomes more so when 
 well powdered carbon is placed in the diluted sulphuric acid, 
 so as to make of it a paste. This paste facilitates the de- 
 polarisation of the platinum by absorbing tfte hydrogen, at 
 the same time that it removes it by its mechanical action of 
 friction. 
 
 The following is an experiment, that gives the idea of the 
 effect, that the depolarisation of the negative metal of the 
 pairs of a pile may produce, when brought about by means 
 of movement. M. E. Becquerel has arranged a small volta- 
 taic pile of ten pairs formed of discs of amalgamated zinc, and 
 of copper 4 inches in diameter, carried by an axis, so as to 
 be able to be set in motion by the aid of a handle. Their sur- 
 face was parallel, and at a distance of j-th of an inch, and they 
 plunged into troughs in which might be placed a liquid or 
 a pasty mass, so that their circumference might penetrate at 
 a depth of only about J an inch beneath the surface of the 
 liquid. Two copper conductors were carried upon two copper 
 basins, soldered to the two discs of each pair fixed on the 
 axis, so that, from the motion of the discs themselves, one 
 of each of them always plunged in the liquid, and the two 
 discs might be made to communicate together. 
 
 The pile of ten pairs was employed for decomposing water, 
 and the hydrogen at the negative electrode, was measured by 
 the aid of a measure graduated to the tenth of a cubic centi- 
 metre (-006 cub. in.). 
 
 Liquid contained in the Cells 
 of the Pile. 
 
 State of the 
 Discs. 
 
 Volume of Hydrogen in 
 Cent, liberated in 20'. 
 
 Water saturated with sul- "1 
 
 Rest 
 
 6-25 
 
 phate of soda 
 
 Motion - 
 
 4675 
 
 Carbon of coke reduced to 1 
 
 
 
 a liquid paste by water, 
 
 Rest 
 
 21-00 
 
 acidulated by sulphuric 
 
 Motion - 
 
 136-00 
 
 acid to T ^ - 
 
 
 
 We see that, in consequence of the movement, the effect 
 of the pile has been seven times more considerable. 
 
782 SOURCES OF ELECTRICITY. PART T. 
 
 It follows however from the researches of M. E. Becquerel, 
 that movement, independently of the depolarisation that it 
 brings about, is a means of liberating electricity ; thus, of 
 two plates of zinc plunged into a same solution, that which is 
 in motion becomes negative in respect of that in rest, which 
 remains positive*; it is the same with other oxidisable metals ; 
 with those which are not so, or are less so, it is the reverse. 
 Thus, whether we operate in distilled water, or we employ 
 an acid or a saline solution in a pair composed of two similar 
 elements, platinum or carbon, for example, it is the movable 
 one, that is positive in respect to the fixed ; that is to say, 
 which plays in respect to it, the part of attacked metal. In the 
 former case, it is evident that the contact established by the 
 motion between one of the elements of the pair and the 
 oxygen of the air, tends to depolarise it, by taking from it 
 the hydrogen adhering to its surface, and consequently to 
 render it negative ; in the latter, it is possible that the oxygen 
 which the movable element takes from the air, aids the 
 liquid into which this element is then plunged, in exercising 
 upon it a chemical action, which gives rise to a feeble 
 current, of which the galvanometer detects the existence. It 
 may also happen that the simple friction, which follows a rather 
 active agitation of this element in the liquid, may be a source 
 of this electricity. However if, on the other hand, the presence 
 of the powder of carbon increases the effect, whilst that of 
 sand in the liquid does not increase it, it is difficult to see in 
 this the effects of friction. We should be rather disposed to 
 attribute all these phenomena, which are a little complicated, 
 to small chemical reactions, which result from the introduc- 
 tion of air into the liquid under the influence of solid bodies 
 in movement. They would be of the same order as those 
 which M. Becquerel sen. had already for a long time 
 studied ; such in particular as this curious fact, that when 
 the two ends of the wire of a galvanometer are terminated 
 by two platinum plates, plunging into distilled water, and 
 which are not polarised, if one of them is withdrawn from the 
 water, and is immediately plunged into it again, it determines 
 ?i current, in which it is positive in respect to the other. 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 783 
 
 Measure of the relative Electro-motive Force of different Voltaic 
 
 Combinations. 
 
 We have seen*, that the intensity of a current may be re- 
 
 E 
 
 presented by the formula I = - , E being the sum of the elec- 
 
 it 
 
 tro-motive forces; that is to say, the producers of electricity, 
 which are in action in an electric circuit, and R, the sum of 
 the resistances, which this circuit presents to the circulation 
 of the current. We have subsequently denned the electro- 
 motive force of a hydro-electric pair, the force with which 
 the liquid molecules that enter into the formation of this 
 pair, are polarised by virtue of chemical affinity. f For the 
 present, we will confine ourselves to designating under this 
 name, without making any hypothesis as to its nature, the 
 force that produces the electricity in a voltaic circuit, 
 abstraction being made of the resistance, that this circuit 
 presents. Electro-motive force may therefore be measured, 
 either by the intensity of the current to which it gives rise, 
 multiplied by the resistance of the circuit, E = I x R ; or by 
 the static tension of the extremities of the hydro-electric 
 system, the circuit being open. Indeed, from what we have 
 established above if, the tension of a pair or of a voltaic pile, 
 being only one discharge or one element of a current, since it 
 is always accompanied by a corresponding chemical action, 
 there should be no difference with regard to electro-motive 
 force between the two forms of its manifestation ; only, as 
 the velocity with which the electricity is propagated does not 
 exert upon the intensity of its tension (since there is an ac- 
 cumulation of electricity) the same influence as upon that of 
 the current, resistance does not play the same part in the ex- 
 pression of one or of the other intensity. We shall see further 
 on, that we may arrive at exactly the same values, for the ex- 
 pression of the electro-motive force, relative to the different 
 voltaic combinations, in estimating it, either by the intensity 
 of the current, or by that of the tension, to which these com- 
 
 Vol. II. p. 78. f Vol. IL p. 685. 
 
 Vol. II. pp. 676-7. 
 
784 SOURCES OF ELECTRICITY. PART v. 
 
 binations give rise. But as the processes founded upon the 
 estimation of the intensity of the current are of much more 
 easy execution, and more susceptible of accuracy, it is to 
 those, that we shall attach the preference. 
 
 The former of these processes is that pointed out by Ohm 
 himself, and which consists in measuring the intensities of the 
 current produced by a same source of electricity, by intro- 
 ducing into its circuit, by the side of the invariable resistance, 
 due to the nature itself of the circuit, two variable resistances ; 
 it is easy to conclude from the comparison of these two in- 
 tensities, the electro-motive force of the source. Let, in fact, 
 
 (i=. - , J and (i * )> <? being the electro-motive force, 
 
 r the invariable resistance, I and I' the two additional resist- 
 ances *, and i and i' the corresponding intensities of the 
 current, measured by the sine or tangent galvanometer, we 
 
 have, by equating the two values of e, r + 1 = -. 7 ( I' I) ; 
 
 * V s N. 
 
 whence e = - r , ( I' 1), by substituting for r+l its value 
 
 in the value of the aforesaid i. This value of e is given in a 
 function of the difference of the lengths of the wire, or of 
 the additional resistances, that the current surmounts in its 
 circulation. 
 
 If we were able to vary the electro-motive force, instead 
 of the resistance, by a known quantity, we should in like 
 manner obtain the value of this force ; but this process, 
 which might be practicable for thermo electric circuits, in 
 which a simple elevation of temperature is sufficient to change 
 this force, is not so for voltaic as hydro-electric combinations, 
 in which we are unable to modify the electro-motive force, 
 without introducing at the same time a change in the re- 
 sistance. 
 
 A second process, employed by Fechner, consists, for com- 
 paring two electro -motive forces, in connecting two different 
 pairs whose electro-motive forces are e and ef ; so that their 
 
 * The resistances are measured by the lengths of wire, as we have explained 
 Vol. II. pp. 80. and 86. 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 785 
 
 currents travel, first in the same direction, then in contrary 
 directions, then in measuring the sum s, and the difference d 
 of the intensities of their respective currents. We obtain in 
 
 e-\-e' e d e s-t-d , 
 
 fact s = ? , and d= ->; whence -,= _*/ by equating 
 
 the two values of r + /. We suppose in this process, that the 
 intensity of the current is proportional to the sum or to the 
 difference of the two electro-motive forces ; which follows 
 from the principles, that we have laid down in our First 
 Chapter, and which is moreover in accordance with experi- 
 ment, as we are about to see. With regard to the resistance 
 of the voltaic combination, which follows from the union of 
 the two pairs, it is evidently the sum of the resistances of 
 each of the two pairs in particular, in whatever manner they 
 may be united. 
 
 A third process, likewise practised by Fechner, rests upon 
 the principle that, if the resistances are equal, the electro- 
 motive forces are to each other as the intensities of the 
 currents ; a consequence of the formula, that expresses these 
 intensities. We arrive at this equality of resistances, by 
 adding in the circuit of each of the pairs to their respective 
 resistances r and r', a very great resistance R, in respect to 
 which the other two may be regarded as infinitely small. 
 
 We may then consider, in the two expressions i= 
 
 e ' 
 
 and i' = -; 7, the resistances r + R and / + R' as sensibly- 
 equal, whence we deduce 
 
 e: e f = i: i'. 
 
 In order to apply this method, M. Fechner employs a gal- 
 vanometer with a very long wire, the introduction of which 
 into the circuit of the pair determines this resistance R, in- 
 finitely great in respect to the resistances r and /. 
 
 We may add that, in order to measure the intensity of the 
 current, M. Fechner employs the method of oscillations of a 
 magnetised needle, placed in the neighbourhood of the conduc- 
 
 VOL. II. 3 E 
 
786 SOURCES OF ELECTRICITY. PARTY. 
 
 tor which transmits the current, a method put in practice for 
 the first time by MM. Biot and Savart.* 
 
 M. Poggendorff has made the very just remark, that the 
 application of the three processes, that we have just described, 
 to cases of voltaic combinations, with a non-constant force, 
 and in which, as we have seen, the intensity of the current 
 goes on rapidly diminishing, at least when the circuits arc 
 closed, renders all measuring of this current difficult. This 
 is not all ; supposing even, that we attain to a state of the 
 current sufficiently constant to enable us to measure it, wo 
 shall recognise in the principle itself of the processes a very 
 strong objection against the accuracy of the results, that we 
 desire to deduce from them. Indeed, if we endeavour to 
 determine by the first method, that of Ohm, the electro- 
 motive force e, we find for the expression of this force a 
 value greater in proportion as the absolute resistance is more 
 considerable, which is due to the circumstance, that the pair 
 is weakened so much the less rapidly as the circuit, of which 
 it forms part, is a less conductor ; the disturbing causes, such 
 in particular as the polarisation of the negative metal, having 
 so much the less power. The absolute resistance r varies 
 likewise, for the same reason. We therefore conceive that 
 the process is altogether illusory, since the two quantities 
 supposed constant in the formula e and r, vary with the 
 additional resistances I and I' , that are introduced. It is 
 true, that this variation of the two quantities e and r, is less 
 considerable, in proportion as the total resistance is greater ; 
 it is on this account that Fechner has been able to obtain 
 very exact results by the application of the third method, even 
 in the case of currents of non-constant force. M. Poggon- 
 dorff has moreover proposed for the determination of the 
 electro-motive force of these currents, a much more exaet 
 method, which is founded upon a rigorous principle. It rests 
 upon the theory of compound circuits; that is, circuits 
 formed by the union of two or more pairs, in which wo 
 admit, as follows from the experiments of Fechner, Ponillet, 
 and Poggendorff himself, and, as we have reported above, that 
 
 * Vol. I. p. 216. 
 
CHAP. Hi. ELECTRICITY BY CHEMICAL ACTIONS. 787 
 
 the electro-motive force of a compound circuit is the sum or 
 the difference of the electro-motive forces of the simple circuits, 
 of which it is composed, and that its resistance is, in like manner, 
 the sum of the resistances of the simple circuits. M. Poggen- 
 dorfPs method requires the employment of a pair of constant 
 force, such as a Grove's pair, the electro-motive force of 
 which has been determined by one of the three preceding 
 processes, which are applicable in this case ; and we compen- 
 sate, by means of the current of the pair, that of the pair of 
 non-constant force, whose electro-motive force we desire to 
 determine ; on this account it is, that this method has re- 
 ceived from its author the name of compensation method. In 
 the application of his method M. Poggendorff employs two 
 processes, the second of which has the advantage over the 
 first of not requiring a perfect and very prolonged constancy, 
 of the pair with constant force, a condition generally 
 difficult of realisation, and of not imposing the necessity of 
 knowing beforehand the two elements e and r, of this pair.* 
 However, as it is nevertheless of importance, even in the 
 employment of the second process, to know how to determine 
 the electro -motive force of a pair with constant force ; and 
 since moreover this determination is at once the most simple 
 and the most important in practice, it is by this that we shall 
 commence, making use for this purpose of a fifth method, 
 which is that of Wheatstone. 
 
 Mr. Wheatstone first remarks, that if in a circuit the 
 electro-motive force and the resistance are increased in the 
 same ratio, the intensity of the current does not change; 
 
 P Yl P 
 
 thus i = - = . It follows from this, that a single voltaic 
 r nr 
 
 pair, or a pair composed of any number of similar pairs ought 
 to give rise to currents of the same intensity, provided that 
 each pair is introduced with its own resistance, without 
 interposing any additional resistance. Every new resistance 
 interposed diminishes the force of the current, but its effect 
 is in proportion less, as it is smaller in respect to the total 
 
 * See, for the details of PoggendorfFs method, the final Note F., which is 
 devoted to the more mathematical explanation of the different methods. 
 
 3 E 2 
 
788 SOURCES OF ELECTRICITY. PART r. 
 
 resistance of the circuit ; whence it follows that if, into two 
 circuits, which produce currents of equal force, but in which 
 the resistances and consequently the electro-motive forces 
 are very different, the same resistance is introduced, the 
 intensities of the two currents will be weakened in very 
 different proportions also. This is why the same resistance, 
 that arising, for example, from the introduction of a volta- 
 meter, weakens in a much more considerable proportion the 
 
 intensity i= of the current arising from a single pair, 
 
 "7? P 
 
 than the intensity i = arising from the current of a cir- 
 cuit of n pairs, placed in series. These principles, which flow 
 from what we have already said above, and in particular 
 in the First Chapter of our Fourth Part*, explain why it 
 is necessary to employ a series of pairs, in proportion more 
 numerous as the resistance, that the current encounters, is 
 more considerable. 
 
 After having related the principles, which precede, let us 
 see the application, that Wheatstone has made of them. In 
 order to avoid having to measure the variable intensities 
 of the currents, either by sine or by tangent galvanometers, 
 or by the number of oscillations of a magnetised needle, 
 measures scarcely susceptible of a rigorous accuracy, he in- 
 troduces into the circuit, instead of constant resistances, vari- 
 able resistances, thus bringing back to equality the currents 
 produced in the circuits, whose electro-motive force is com- 
 pared ; he then concludes from the total of the additional 
 resistance, introduced in each case, in order to pass from a 
 certain deviation, always the same, of the needle of the galva- 
 nometer, 45 for example, to another deviation of 40, always 
 the same also, the relative values of the electro-motive forces, 
 and of the resistances of the circuit, according to the par- 
 ticular conditions of the experiment. It is by no means 
 necessary, in this method, to know the forces corresponding 
 to the deviation of the needle. 
 
 Mr. Wheatstone, in order to introduce into the circuit a 
 
 * Vol. II. pp. 77. and following pagei. 
 
CHAP. III. 
 
 ELECTRICITY BY CHEMICAL ACTIONS. 
 
 789 
 
 variable resistance, employs the rheostat of which we have 
 already given a detailed description.* The copper wire 
 of the instrument being interposed in the circuit, we have 
 merely to elongate or to shorten it by a quantity, that may 
 be measured with the greatest accuracy, in order to add to 
 or to withdraw a resistance, which is expressed in lengths of 
 this wire. When the object is to measure resistances too 
 great for the introduction of the entire wire of the rheostat, 
 although it may be very long, to be able to bring back the 
 current, so as to deviate the needle of the galvanometer no 
 more than the desired quantity of 45 for example, resistance 
 bobbins are introduced into the circuit, which are arranged 
 beside the rheostat, as is indicated in the figure, so that we 
 are able to interpose a greater or less number of them. We 
 thus succeed in reducing the current to the intensity of 45, 
 by completing, by means of the rheostat, what is wanting to 
 the added resistance, in order to attain exactly to this devia- 
 tion, a resistance, moreover, which it is not necessary to 
 know, since the object we have to measure is simply the 
 length of the wire of the rheostat, which is necessary to be 
 added, in order that the current may pass in each case from 
 the intensity of 45 to that of 40. 
 
 Now, let i = -, i having been brought to produce 45 on 
 * Vol. II. p. 88. (Jig. 181.) ; we reproduce the figure here. 
 
790 SOURCES OF ELECTRICITY. PART v. 
 
 the galvanometer with the pair whose electro-motive force is e, 
 and its resistance r ; let / be the reduced length of the wire of 
 the rheostat that it is necessary to add to r, in order that i shall 
 become i' } and not produce more than 40 on the galvanometer. 
 
 We have i' = j ; let there now be another voltaic combina- 
 tion, the electro-motive force of which is ef = n e. In order 
 that its current may have only the intensity ^producing 45, 
 it is necessary that the resistance be r' = n r, which will be 
 obtained by means of the resistance bobbins ; we shall have, in 
 
 fact, i or - ; but, in order to bring back i to be no more 
 r n r 
 
 than i' 9 namely 40, it is necessary that the additional re- 
 sistance, or the added length of the wire of the rheostat, be 
 
 I' = nl- 9 for since we have i = , in order to obtain 
 
 n r 
 
 = i' or = r , it is evidently necessary that I' 
 
 n r + I' r + I 3 J 
 
 be equal to n L Now, n is the relation of the two electro- 
 motive forces e and e' ; we see that it is the same as that of 
 the two quantities I and I ', with which it is necessary to 
 elongate the wire of the rheostat, in order to cause the 
 currents of the two pairs, whose electro-motive forces are e 
 and d , to pass from 45 to 40 ; its determination is therefore 
 very easy. In the application that we are about to make of 
 this process to the determination of the electro-motive forces 
 of the different voltaic combinations, we shall content our- 
 selves, in order to express the added lengths of the wire of 
 the rheostat, to indicate the number of turns which this wire 
 has been unrolled, each turn corresponding to a length of 
 3 '46 inches. 
 
 Three pairs, differing only by their dimensions, each com- 
 posed of a liquid amalgam of zinc placed in a cylindrical 
 porous cell, which is plunged into a vessel, filled with a solu- 
 tion of sulphate of copper, in which is also immersed a hollow 
 copper cylinder, were successively placed in a circuit, 
 of which the rheostat formed part. All three equally 
 required thirty turns of the rheostat, in order that their 
 
HAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 791 
 
 current might be brought from 45 to 40. One however 
 was 2 in. high, and 1J in. in diameter; the second 3^ 
 in. high, and 2 in. in diameter ; the third 6 in. high, and 
 2-| in. in diameter. Thus the electro-motive force is entirely 
 independent of the size of the surfaces of the pairs : this is a 
 consequence of the nature of this force, as we have already 
 remarked. 
 
 It is not the same with the influence of the number of 
 pairs. It is easy to prove that the electro-motive force 
 increases proportionably to this number, conformably to 
 theory. Thus, with a circuit formed successively of 1, 2, 3, 
 4, and 5 similar pairs of the smallest of those which we have 
 just now employed, we find that, in order to bring the current 
 from 45 to 40, it requires, 
 
 With 1 pair - - 30 turns. 
 
 2 - 61 
 
 3 - - 91 
 
 4 - - 120 
 
 5 - - 150 
 
 We see therefore that, except for the case of two and of 
 three pairs, in which there is a slight difference, arising from 
 a small error of experiment, the law is verified exactly. 
 
 If we now pass to the determination of the electro-motive 
 force of pairs of different kinds, we find first a very remark, 
 able result ; it is that, when we confine ourselves to changing 
 in the pair, amalgam of zinc, sulphate of copper, and copper, 
 the sulphate, providing it is still a salt of copper, substituting 
 for it the acetate, the protochloride, the nitrate, or the ammo- 
 niacal sulphate, we obtain the same electro-motive forces, 
 except as far as concerns the nitrate, which gives a variable 
 result, probably on account of the action of the nitric acid 
 upon the mercury. Another curious fact is, that neither does 
 the proportion of zinc in the liquid amalgam appear to affect 
 the electro-motive force of the pair, only the action does not 
 last so long a time. In fine, it is a result altogether similar 
 to that which has shown us, that the influence upon the electro- 
 motive force of the extent of the surface of contact between 
 the metals of the pair and the liquid with which it is charged, 
 
 3 E 4 
 
792 
 
 SOURCES OF ELECTRICITY. 
 
 PART T. 
 
 is altogether null. The quantity of zinc dissolved in the 
 amalgam determines the number of points of the surface of 
 this amalgam, susceptible of being attacked by the liquid ; it 
 produces, therefore, in varying, the same effect as an increase 
 or a diminution in the surface of the same amalgam, that is 
 to say, a null effect upon the electro-motive force ; the latter 
 being in fact only the property possessed by the current of 
 surmounting a given resistance, it must be the same for each 
 point or each molecule of the surface attacked ; with regard 
 to the absolute quantity of electricity that passes, it is clear 
 that it varies with the number of points attacked ; but it is 
 not this that we are measuring here. 
 
 The greatest electro-motive force that can be possessed by 
 a voltaic pair, composed of two metals and one interposed 
 liquid, is obtained when the liquid is a solution of a salt, 
 having the negative metal for a base. In fact, in this manner 
 we avoid the deposit upon this metal of heterogeneous matters, 
 which, by polarising it, notably reduce the electro-motive 
 force. Thus, on substituting in the pair, amalgam of zinc, 
 sulphate of copper and copper, diluted sulphuric acid for 
 the sulphate, we obtain only twenty turns of the rheostat, 
 instead of thirty, for the expression of the electro-motive force. 
 In like manner, if we substitute in a pair, amalgamated zinc, 
 chloride of platinum, platinum, diluted sulphuric acid for the 
 chloride, we obtain no more than twenty-seven turns, instead 
 of forty. The following is, moreover, a Table of the electro- 
 motive forces of different pairs : 
 
 Amalgam of 
 
 
 
 Turns. 
 
 Zinc - 
 
 diluted sulphuric acid 
 
 copper - 
 
 20 
 
 > 
 
 
 
 platinum 
 
 27 
 
 > 
 j 
 
 sulphate of copper - 
 chloride of platinum 
 
 copper - 
 platinum 
 
 30 
 40 
 
 > 
 
 diluted sulphuric acid 
 
 
 
 peroxide of manganese 
 peroxide of lead 
 
 54 
 
 68 
 
 Potassium - 
 
 sulphate of zinc 
 
 zinc ... 
 
 29 
 
 5 
 }} 
 
 sulphate of copper - 
 chloride of platinum 
 
 copper - 
 platinum 
 
 59 
 69 
 
 
 diluted sulphuric acid 
 
 peroxide of manganese 
 
 84 
 
 ) 
 
 
 
 peroxide of lead 
 
 98 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 793 
 
 An important point, for the theory of the pile, which Mr. 
 Wheatstone has been able to verify by means of his method, is 
 that, if we take three metals, in their electro-motive order, the 
 electro-motive force of a pair formed of the two extreme 
 metals is equivalent to the .sum of the electro-motive forces of 
 the two pairs, formed of the consecutive metals. Thus, with 
 
 Amalgam of potassium, sulphate of zinc, amalgam of zinc, 29 turns. 
 zinc, sulphate of copper, copper - - 30 
 
 potassium, 
 
 Amalgam of potassium, sulphate of zinc, amalgam of zinc, 29 turns. 
 zinc, chloride of platinum, platinum - - 40 
 
 potassium, - 69 
 
 In both examples the electro-motive force, deduced from 
 reasoning, is found to be exactly equivalent to that furnished 
 by experiment. 
 
 We may remark, in passing, the great electro-motive force 
 of potassium, as well as that of sodium, which is scarcely less, 
 which is due to their powerful affinity for oxygen, and to the 
 facility with which consequently they decompose water.* 
 
 A sixth method, under the name of method of opposition, has 
 been proposed by M. Jules Regnault, for the determination of 
 electro-motive forces ; it has been likewise employed by 
 Gaugain. It is based upon this principle, demonstrated by 
 experiment, that if two pairs composed of the same solid and 
 liquid elements are opposed to each other, that is to say, so 
 arranged that, when they form a circuit, the positive element 
 
 * M. Goodman has found, that the most convenient manner of employing 
 potassium in the formation of a voltaic pair, consists in placing it at the bottom 
 of a tube, closed by a membrane, and to place this membrane in contact by its 
 lower part, with the surface of the acidulated water, which covers a horizontal 
 plate of platinum. A drop of mercury, placed upon the membrane, serves to 
 retain the surface of potassium, exposed to the action of the acidulated water, 
 always amalgamated ; and oil of naphtha, with which the tube is filled, preserves 
 it in all the rest of its surface from the oxidising action of the air. A copper 
 wire, planted in the piece of potassium, permits of closing the circuit. If a 
 solution of sulphate of copper, is substituted for that of sulphuric acid, the cur- 
 rent is more constant, but more feeble. A pair thus constructed, powerfully 
 decomposes acidulated water, placed in a voltameter with platinum wires ; 12 
 ranged in series gives almost as much tension as Gassiot's 3520 water pairs, 
 and Grove's 100, provided they are well insulated ; a single one produces a 
 slight divergence of the gold leaves of the electroscope. According to Henrici, 
 the amalgam of sodium has an electro-motive force, almost as great as that of 
 potassium. 
 
794 SOURCES OF ELECTRICITY. PARP Y. 
 
 of the first is joined to the positive element of the second, 
 and their two negative elements communicate in like manner, 
 there is not the least current in the system. But, if the two 
 pairs differ, there is a circulation of a current in the circuit : 
 and the direction of this current is .determined by that of the 
 current, which arises from the pair, whose electro-motive 
 force is greater. Mr. Faraday, in his researches on the 
 chemical origin of voltaic electricity, quotes a great number 
 of experiments, by which this principle is established. The 
 most natural manner of interpreting it is to admit that, in the 
 former case, equilibrium arises from the circumstance that 
 the opposed electro-motive forces are equal ; then in fact, the 
 tendency to polarisation of all the parts of the circuit, as well 
 solid as liquid, being exerted with exactly the same power, but 
 in two opposite directions, its effect must be null. It is as if 
 the two pairs of fig. 307. p. 688. were so arranged, that the 
 zinc of the first communicated with the zinc and not with the 
 platinum of the second, their electro-motive force, instead of 
 becoming double, would become null. In the latter case, 
 the electro-motive force being unequal, the intensity of the 
 current must be proportional to the difference of the electro- 
 motive force of the two pairs. With regard to the resistances 
 that the current must surmount, they are the same, in what- 
 ever manner the pairs are arranged, so that we have i = 
 
 n _ f/ n O* 
 
 >, - and -, being the respective intensities of the two pairs 
 
 that are opposed. If the opposition of the two pairs anni- 
 hilates the current, that is to say, renders i equal to 0, we 
 must necessarily conclude from it that e' = e. 
 
 The same reasoning applies to the pairs in series, that 
 
 constitute piles. Thus we obtain I = -r-j- , n being the 
 
 R -f-[R 
 
 number of pairs of the first pile, e the electro-motive force of 
 each of them and R the sum of their resistances, n' and ef 
 and R' being the corresponding values for the second pile. If 
 I is null, we have n e n' e' ; and if e' is made= 1, namely, if 
 we take for unity the electro-motive force of the more feeble 
 pair, we obtain, supposing also n= 1, e=n', that is to say, that 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 795 
 
 the electro-motive force of the stronger pair is equal to n f times 
 the electro-motive force that has been taken for unity, n f being 
 the number of the more feeble pairs, which make equilibrium 
 with the single stronger pair.* The reasoning, that we have 
 just made, is based upon the principle, that we have demon- 
 strated by experiment, namely, that the electro-motive force 
 is proportional in a circuit, composed of many pairs, to the 
 number of these pairs arranged in series. It is equally accu- 
 rate, whether currents do not circulate, when the electro-motive 
 forces are equal, or whether they circulate simultaneously, but 
 in a contrary direction, so as to annihilate each other in their 
 common circuit, as we have supposed in the First Section of 
 this Chapter ; a supposition, moreover, that the analysis of the 
 phenomena had led us to abandon, in order to admit that, which 
 we have just now pronounced for the first time. 
 
 Before speaking of the applications that M. J. Regnault 
 has made of his method to the determination of the electro- 
 motive force of some voltaic combinations, it is important 
 to fix for a moment our attention upon a point, with which 
 we have not yet been occupied, it is the choice of a unit, 
 to which the various electro-motive forces may be referred, 
 or with which they may be compared. This unit must be 
 an electro-motive force. M. J. Regnault takes for this unit 
 the electro-motive force of a thermo-electric pair, bismuth 
 and copper, for a difference of 32 and 212 between the 
 solderings. Then, making use of a thermo-electric series com- 
 posed of sixty similar pairs, taking care that the solderings of 
 the even and of the odd rank remain at temperatures sensibly 
 fixed during the continuance of the experiments, he seeks 
 to know how many of these pairs must be employed in order 
 to produce equilibrium to a pair, whose electro-motive force 
 we desire to determine. It is thus, that the current of a 
 pair, zinc in sulphate of zinc, and cadmium in sulphate of 
 cadmium, is found to be counterbalanced by the thermo-elec- 
 
 * It seems to us, that it may frequently happen that n is not equal to 1, 
 although less than n' ; then, when we have found the number of pairs of each 
 species, that must be placed in series, in order that their opposition may pro- 
 duce equilibrium, we have n e == n', whence e = 
 
796 SOURCES OF ELECTRICITY. PART v. 
 
 trie current of fifty-five pairs, bismuth and copper, the 
 solderings of which present differences of 32 to 212. But 
 this pair being one of those, whose electro-motive force is the 
 most feeble, it would be necessary to multiply for others in 
 an enormous proportion the number of thermo-electric pairs. 
 Thus, M. J. Regnault proposes to take, for an auxiliary pair, 
 that of zinc-cadmium, the two metals plunging in their 
 respective sulphates, which is endowed with a remarkable 
 constancy ; it is with this that the others are compared, re- 
 membering that its electro-motive force is equal to fifty-five 
 times that, which is taken for the unit. 
 
 Mr. Wheatstone had likewise determined, by his method, 
 the relation that exists between the electro-motive force of a 
 thermo-electric pair, bismuth and copper, the solderings 
 of which were respectively at the temperatures of 32 and 212, 
 and that of the pair, amalgam of zinc, sulphate of copper and 
 copper ; and he had found that, whilst it required for bringing 
 back the deviation of the needle with the former from 10 to 
 5 *, only'eight times of the rheostat, it required 757 with the 
 latter; which established between the two electro-motive 
 forces the relation of 1 to 94-6. M. Pouillet, by an entirely 
 different method, of which we shall speak presently, had 
 found the relation 1 to 94. M. J. Regnault has found a 
 very different relation; namely, that of 1 to 153 ; which he 
 attributes to the circumstance, that in Mr. Wheatstone's pair 
 a difference in the nature of the porous diaphragm, which it 
 is difficult to have indentical, may considerably modify the 
 electro-motive force, as has been demonstrated to him by 
 the experimental comparison that he has made between a 
 Daniell's t pair, the diaphragm of which was of unglazed 
 porcelain, and a Wheatstone's pair, with diaphragms of 
 different natures, f Moreover, this influence of the nature 
 
 * The thermo-electric current was too feeble to cause the needle of the gal- 
 vanometer to deviate from 45 to 40, as in the preceding experiments ; it 
 was necessary, in the comparison of this current with that of the hydro-electric 
 current, to have recourse to the deviation from 10 to 5 only. 
 
 f The difference of the two electro-motive forces was deduced from the op- 
 position of the two pairs ; it was found 3 units in favour of the Daniell's pair, 
 when the two pairs had each a diaphragm of unglazed porcelain ; but it was 
 successively 26, 44, and 103 in favour of the Wheatstone pair, when the dia- 
 phragm of this latter were pipe-clay, bladder, beech. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 797 
 
 of the porous diaphragm upon the electro-motive force is no 
 longer sensible in the piles of two liquids, as M. J. Regnault 
 has further proved with two different pairs, the one zinc- 
 cadmium, with sulphate of zinc and sulphate of cadmium ; 
 the other Daniell's zinc-copper, with sulphate of zinc and 
 sulphate of copper ; he always found that the electro- 
 motive force of the former was equal to 55 times that of 
 the thermo-electric pair, taken for unity, and that of the 
 latter to 175 times this unit, whatever diaphragm was em- 
 ployed in the two pairs, unglazed porcelain, pipe-clay, 
 bladders, and different species of wood. 
 
 With regard to the unit chosen by M. Regnault, which 
 is the same as M. Pouillet has also adapted, it appears to 
 me to present two inconveniences ; the first, of being unable 
 to be found always exactly the same * ; the other, of being 
 led into an electro-motive force of an entirely different 
 species, in regard to its intensity and its origin, from that 
 of hydro-electric pairs. It would seem to us that it would 
 be preferable to adopt for these latter a unit, taken among 
 the electro- motive forces of hydro-electric pairs, chosing one 
 of those, which would give the most constant current. 
 Moreover, M. J. Regnault has plainly seen this, for it is 
 finally to the electro-motive force of the pair, zinc -cad- 
 mium, sulphate of zinc, and sulphate of cadmium, that he 
 has compared that of divers hydro-electric pairs. 
 
 M. J. Regnault has confirmed, for potassium and for zinc, 
 by making use of his method, the fact pointed out by Mr. 
 Wheatstone, that the proportion of positive metal, contained 
 in the liquid amalgam, does not appear to affect the electro- 
 motive force of a voltaic pair of which it forms part. Thus, 
 he has found the electro-motive force of a pair, amalgam 
 of zinc-copper, charged with sulphate of zinc and sulphate of 
 copper, equal to 178 of these units, whether there was -j 1 ^, 
 -j^, or -5-^0 of zinc dissolved in the mercury. In like manner 
 he has found this force equal to 416, whether there was 
 
 * M. J. Regnault has recognised this inconvenience ; thus, he has been oc- 
 cupied in. searching for the means of giving to the current produced, by a greater 
 or less number of consecutive thermo-electric pairs, the greatest possible con- 
 stancy ; but we are not satisfied that he has succeeded. 
 
798 SOURCES OF ELECTRICITY. PART v. 
 
 To or TJO o f potassium dissolved in the mercury with a 
 pair, liquid amalgam of potassium and platinum, charged 
 with chloride of sodium and chloride of platinum. The result 
 is, within certain limits, the same, as far as the degree of the 
 solution in which the positive metal is plunged, is concerned. 
 M. Regnault has found that this degree may vary from I 
 to yVo* without the electro-motive force of the voltaic com- 
 bination being sensibly disturbed. We must not lose sight, 
 in this case, as in that of the amalgam of zinc, that the 
 question here is not of the quantity of electricity produced 
 in a given time, but of the faculty of this electricity of sur- 
 mounting a certain resistance. 
 
 M. J. Regnault, who, like Mr. Wheatstone, has applied his 
 method to the determination of the electro- motive forces of 
 certain voltaic combinations, has found in general, in the 
 small number of cases that he has studied, that the electro- 
 motive force does not very sensibly change in a pair of two 
 metals, which plunge each into a saline solution, with the 
 nature of this solution, provided that it has for a base the 
 same metal, that is immersed in it. However, there are 
 many exceptions to this law, which would seem to be tolerably 
 true only when the metals, which form the pairs, are very 
 far from each other in the electro-motive series, such as zinc 
 and copper, or zinc and platinum. 
 
 We have seen above, that M. Poggendorff had proposed 
 a method, in regard to the case of pairs of non-constant force, 
 in order to be able to escape the influence of the polarisation 
 of the negative metal, which occasions so prompt an alteration 
 in the electro-motive force of these pairs. But a great 
 number of philosophers have sought to appreciate this in- 
 fluence directly, by determining the electro-motive force of 
 the pairs, formed by polarised metals, that is to say, by metals, 
 whose surface is covered with those thin deposits, which 
 imparts to them secondary polarity. 
 
 Wheatstone, in his work upon electro-motive forces, had 
 made an important remark upon this subject, namely, that 
 the electro-motive force, contrary to that of a voltaic circuit, 
 which arises from the interposition in this circuit of a volta- 
 meter with platinum electrodes, charged with a solution of 
 
CHAP. III. 
 
 ELECTRICITY BY CHEMICAL ACTIONS. 
 
 799 
 
 sulphuric acid, is constant ; that is to say, is the same, what- 
 ever be the force of the current. In order to obtain this 
 result, Wheatstone placed the same voltameter successively 
 in four circuits, composed of 3, of 4, of 5, and of 6 of his 
 pairs ; and he determined in each the electro-motive force 
 u-ithout and with the voltameter ; then, deducting the number 
 of turns, which expressed the latter, from that which ex- 
 pressed the former, he obtained a difference always the same, 
 which was the expression of the contrary electro-motive 
 force exerted by the electrodes of the voltameter. The fol- 
 lowing is the Table of the experiments : 
 
 No. 
 
 Without 
 Voltameter. 
 
 With 
 Voltameter. 
 
 Difference, or Electro- 
 motive Force of the 
 Voltameter. 
 
 3 pairs. 
 4 
 5 
 6 
 
 90 
 120 
 150 
 180 
 
 21 
 50 
 79 
 109 
 
 69 
 70 
 71 
 71 
 
 Mean 70 
 
 Thus, the electro-motive force, due to the polarisation of 
 the platinum electrodes of the voltameter, may be regarded 
 sensibly as constant and equal to 70, which causes it to be, 
 to that of a single pair, as 70 is to 30, or as 7 is to 3 ; and 
 which establishes between these two forces the relation of 
 2 -3 3 to 1. On this account it is that at least 3 pairs, con- 
 stituting a voltaic combination of an electro-motive force of 
 90, are necessary, in order to decompose water with the 
 voltameter. 
 
 M. Svanberg, after having found with a Daniell's pile 
 almost the same relation, namely, that of 2 '20, in place of 
 2 '3 3, between the electro-motive force of the polarised elec- 
 trodes P, and that of a pair E, satisfied himself that there is 
 polarisation only on the surface upon which the gas is 
 liberated. He operated, as Wheatstone had done, with a 
 rheostat. He first placed in the circuit of three Daniell's 
 pairs, instead of the voltameter, a copper-platinum pair, 
 the copper plunging in a solution of sulphate of copper, 
 
800 SOURCES OF ELECTRICITY. PART v. 
 
 and the platinum in a solution of sulphuric acid ; the latter 
 serving as positive electrode. By supposing that this alone 
 is polarised, and calling this force of polarisation p, and the 
 electro-motive force of the pair itself, copper-platinum e t which 
 acts in a contrary direction to that of the pile, E being 
 that of one of the DanielPs pairs, we have, 
 
 If now we introduce into the circuit of four DanielPs pairs 
 the copper-platinum pair, so that the copper is positive elec- 
 trode, and the platinum negative, receiving the hydrogen, 
 we find, by experiment, on remarking that in this case the 
 electro-motive force of the copper-platinum pair must be 
 added, instead of being deducted, and calling the force of 
 polarisation of the negative platinum p', 
 
 - = 50-03. 
 
 But 3 E=42-79 by experiment; whence E= 14-26; and 
 consequently 4 E = 57*05 ; which gives, 
 
 p +e =24-78 
 /-e = 7-02 
 
 whence p +^' = 31-80 
 and+= 2-16. 
 
 E 
 
 T> 
 
 But we had found - =2-20; therefore we have p+p' 
 
 E 
 = P. 
 
 The result shows us, therefore, that there is no polarisation 
 except on the electrode, where the gas is liberated ; that, con- 
 sequently, in the former case, there is none upon the copper ; 
 which, serving as negative electrode in sulphate of copper, 
 simply covers itself with revived copper ; and that neither is 
 there any in the latter case, in which the copper, serving as 
 positive electrode in diluted sulphuric acid, oxidises and 
 dissolves. The platinum plate is therefore the only one 
 polarised in the two cases ; in the former, by the oxygen, 
 which gives to it a force of polarisation p 20-03, and in 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 801 
 
 the latter by the hydrogen, which gives to it a force 
 j/ = ll-77. 
 
 M. Svanberg has endeavoured to determine the force of 
 polarisation of hydrogen, when it is liberated upon copper ; 
 but he has found that it was very variable with the degree 
 of polish of the surface of the metal. Thus it was only 
 1'96 when the surface of the copper was granulous, and 12 
 when this surface was perfectly polished, that is to say, equal 
 to the polarising force of hydrogen upon a polished surface 
 of platinum. 
 
 MM. Lenz and Saweljev, in a considerable work upon the 
 electro-motive force, developed by the polarisation of the plates 
 of the electrodes, have generalised Svanberg's result, and 
 they have arrived at the following laws : 1st. The polarisa- 
 tion of the plates, that are employed as electrodes, takes place 
 only so long as gases are liberated upon their surface. 2nd. 
 The polarisation that results from the decomposition of a liquid 
 between two electrodes is the sum of the polarisation produced 
 upon each electrode. 3rd. The polarisation and the electro- 
 motive forces, in each cell of the circuit, where decomposition 
 takes place, are summed up, algebraically speaking, that is to 
 say, each with its sign depending upon the direction, in which 
 it acts. 4th. We may range in order all the various com- 
 binations of a metal with a liquid, under the relation of their 
 electro-motive forces, in a series, in which each is positive in 
 respect to that which precedes; and the resulting electro- 
 motive forces being able to be expressed by numbers, such that 
 those, which would result from the reunion of any two com- 
 binations, are represented by the difference of the two corre- 
 sponding numbers. 5th. To the experimental demonstration 
 of these four laws are attached two Tables, one of which gives 
 the values of the secondary polarities of certain metals in 
 oxygen and in hydrogen, and the other that of the electro- 
 motive forces of different metals in their contact with different 
 liquids, eliminating the contrary element of polarisation. In 
 these two Tables the unit is altogether arbitrary; since 
 
 * One would be surprised to see the polarising force of oxygen superior to 
 that of hydrogen, contraiy to what Grove had found with his gas pile ; but 
 it is necessary to remark, that here the oxygen arises from the decomposition 
 of water, and that it is ozonised. 
 
 VOL. II. 3 F 
 
802 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 it depends upon the particular instrument, that has been em- 
 ployed in the determinations ; but as it is a question of rela- 
 tions only, it possesses no inconvenience.* 
 FIRST TABLE. 
 
 I 
 
 : Polarisation. 
 
 In Units of the 
 Rheostat. 
 
 Platinum in oxygen 
 chlorine 
 
 2-49 
 
 o-oo 
 
 48-8 
 
 oo-o 
 
 Graphite in oxygen 
 
 1-33 
 
 26-0 
 
 Gold 
 
 271 
 
 51-1 
 
 Platinum in hydrogen - 
 
 3-67 
 
 71-9 
 
 Zinc , 
 
 0-90 
 
 17-6 
 
 Copper , 
 
 2-30 
 
 45-0 
 
 Tin , 
 
 1-55 
 
 30-4 
 
 Iron , 
 
 0-48 
 
 9'4 
 
 Mercury , 
 
 4-37 
 
 85-6 
 
 Copper in oxygen 
 
 0-69 
 
 13-5 
 
 SECOND TABLE. 
 
 
 Electro-motive 
 Forces, 
 
 In Units of the 
 Rheostat. 
 
 Platinum in hydrochloric acid 
 
 0-26 
 
 5-1 
 
 sulphuric acid 
 
 0-02 
 
 0-4 
 
 acetic acid - 
 
 o-oo 
 
 o-o 
 
 Graphite in nitric acid - 
 
 0-01 
 
 0-2 
 
 Gold^ M< - 
 
 0-06 
 
 1-2 
 
 Gold in sulphuric acid - 
 
 0-25 
 
 4-9 
 
 Mercury - 
 
 0-70 
 
 13-7 
 
 acetate of protoxide 
 
 
 
 of copper 
 
 0-79 
 
 15-5 
 
 Platinum in a solution of potash 
 Pure copper in sulphuric acid 
 
 1-20 
 1-39 
 
 23-5 
 27-2 
 
 Slightly oxidised 
 
 1-75 
 
 34-3 
 
 Copper in sulphate of copper - 
 Gold in a solution of potash - 
 
 2-00 
 2-31 
 
 39-2 
 45-2 
 
 Tin in hydrochloric acid 
 
 2-38 
 
 46-4 
 
 Iron 
 
 275 
 
 53-9 
 
 Graphite in potash 
 
 2-84 
 
 55-0 
 
 Iron in sulphuric acid - 
 
 2-92 
 
 57-2 
 
 Tin 
 
 2-95 
 
 57-8 
 
 Copper in a solution of potash 
 
 3-10 
 
 60-7 j 
 
 Tin 
 
 3-94 
 
 77-2 
 
 Zinc in diluted nitric acid 
 
 4-01 
 
 79*2 
 
 hydrochloric acid 
 
 4-07 
 
 79-9 
 
 sulphuric acid - 
 
 4-17 
 
 81-9 
 
 Iron in a solution of potash - 
 
 4-65 
 
 91-1 
 
 Zinc 
 
 5-48 
 
 107-4 
 
 * The unit of the current was, that which deviated the needle of the galva- 
 nometer 1 ; the unit of resistance, that of 1 turn of the rheostat ; the unit of 
 electro-motive force, that which produced with the resistance 1, the current 1. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 803 
 
 The method employed by MM. Lenz and Saweljev 
 consisted in having two liquids, separated by a porous 
 diaphragm, into each of which was plunged a metal plate, 
 serving as an electrode; a multiplier and a rheostat, or 
 agometer, as these philosophers call it, being with the decom- 
 position cell introduced into the circuit of a DanielPs pile. 
 The needle of the galvanometer was brought, by means of 
 the rheostat, first to a certain degree of deviation, then to 
 another ; then the same operation was performed, simply re- 
 moving the decomposition cell from the circuit ; the whole 
 repeated several times, in order to obtain exact means ; and, 
 from the comparison of the results, the contrary electro- 
 motive force exerted by the decomposition cell was deduced, 
 and consequently the polarisation of its plates. It is thus, as 
 we are about to see, that the Tables above have been drawn 
 out. 
 
 Admitting that the polarisation is produced simply by the 
 liberation of the gas, in order to determine the polarisation of 
 each electrode in particular, in the case of the decomposition 
 of water by platinum electrodes, we begin by determining it in 
 the case, in which the two platinum plates are plunged into 
 nitric acid ; because there is then no liberation of hydrogen at 
 the negative electrode : we obtain the value of the polarisation, 
 due to the oxygen, which is found equal to 2*48 ; then, going 
 through the same operation by plunging the platinum plates 
 into diluted sulphuric acid, we obtain a polarisation, equal to 
 5*46, which is the sum of the polarisations, due respectively 
 to the oxygen and the hydrogen, since there is a liberation of 
 gas upon both the electrodes. In order to obtain the latter, 
 that due to the hydrogen, we have only to deduct 2-65 
 from 5*46, which gives 3 for its value. But this value changes 
 with the metals, upon which the hydrogen is deposited. Thus, 
 with amalgamated zinc, it is only 1*00; with copper, 2-15 
 with tin, 1-45; with iron, O33, &c. These numbers differ 
 but little from those of the Table, which are more exact, 
 seeing that they have been obtained at the end of more nu- 
 merous and more varied experiments. 
 
 With regard to the Table of the electro-motive forces of 
 
 3 F 2 
 
804 SOURCES OF ELECTRICITY. PART v. 
 
 metals in various liquids without polarisation taking place, it 
 has been likewise drawn out, either by means of direct obser- 
 vations or by deducting from the observations, in which polari- 
 sation intervenes, the effect due to this polarisation, which 
 had been determined directly. 
 
 M. Beetz, who has also been occupied with the electro- 
 motive force of gases, has employed a method altogether 
 different from, and much more direct than that of MM. Lenz 
 and Saweljev ; he has applied quite simply Poggendorff's pro- 
 cess of compensation to Grove's gas pile, charging it suc- 
 cessively with various gaseous substances, and employing a 
 zinc-platinum pair of Grove's in order to establish compensa- 
 tion. He took great precaution in the preparation of the 
 platinums, of the gas pile and of this pile in general, in which 
 he took care to introduce only very pure gases, after having 
 driven out all the air from the solution of sulphuric acid, 
 with which the tubes were filled, that were about to receive 
 the gaseous substances. The following is the Table of the 
 electro-motive forces developed by associating with hydrogen, 
 which was always in one of the tubes, the various substances 
 the names of which follow, and among which M. Beetz in- 
 troduced two solids, namely, platinum without gas in imme- 
 diate contact with the liquid, and platinum covered with 
 copper ; it is very remarkable, that the order, in which the 
 various substances are ranged, with regard to their electro- 
 motive force, is exactly the same as that which Grove had 
 found. 
 
 Names of the Substances. Electro-motive Forces. 
 
 Chlorine - - 31'49 
 
 Bromine - - 27'97 
 
 Oxygen - - 23-98 
 
 Oxide of nitrogen . - 21-33 
 
 Cyanogen 21*16 
 
 Carbonic acid - - 20-97 
 
 Oxide of nitrogen - - 20-52 
 
 Iron - 20-50 
 
 Platinum - - 20' 13 
 
 Sulphuret of carbon - 19'60 
 
 Olefiantgas - - 18'36 
 
CHIP. in. ELECTRICITY BY CHEMICAL ACTIONS; 805 
 
 Names of the Substances. Electro-motive Forces. 
 
 Phosphorus - 16 '06 
 
 Oxide of carbon - 13-02 
 
 Copper - - 3-82 
 
 Sulphuretted hydrogen - - 3-05 
 
 Hydrogen - - O'OO 
 
 Beetz's experiments have shown that, conformably to Mr. 
 Grove's opinion, oxygen contributes in a direct manner to 
 the development of the current in the oxygen-hydrogen pile ; 
 since, when hydrogen is associated with oxygen, the electro- 
 motive force is 23-98, whilst it is no more than 20-13, when 
 it is united with platinum, which gives 3-85 for the electro- 
 motive force of platinum covered with oxygen. This is not 
 an effect due to the depolarising action of oxygen, since the 
 circuit remains closed for an instant only. It is to the former 
 cause that must be attributed the fact, likewise observed by 
 M. Beetz, and already pointed out, as we have seen, by M. 
 Poggendorff, that platinum plates, provided they are well 
 cleaned, give as much effect as when they are platinised, 
 which is due to their not having time to become polarised ; 
 now, it is their faculty of polarising much more powerfully 
 than platinised plates, which gives to them a great inferiority 
 when the circuit remains for a long time closed. 
 
 The influence, that is exerted in general over the pheno- 
 mena of this order by the nature of the solid substance, upon 
 the surface of which the gaseous film is found, arises from 
 the fact that this surface is never entirely covered by the 
 gas, and that there are always some points of contact between 
 it and the liquid. If the immersed plates could be entirely 
 insulated from the liquid by the gases, with which they are 
 enveloped, the chemical nature of the metallic masses would 
 be altogether indifferent. When the plates are covered with 
 gas by means of electrolytic decomposition, they are so in a 
 much more complete manner than by any other means ; but 
 they are never sufficiently so, even when the maximum of 
 polarisation has been imparted to them, for the nature of 
 the metal to play no part. However, the electro-motive 
 power developed by this means, instead of being 24, as 
 M. Beetz had found it, by means of oxygen and hydrogen 
 
 3 v 8 
 
806 SOURCES OF ELECTRICITY. PART v. 
 
 introduced into the tubes, is, according to M. Poggendorff, 
 55 when the platinum plates possess their metallic bril- 
 liancy, and 40 when they are platinised. Still recogni- 
 sing that the oxygen and hydrogen, which arrive on the 
 surface of the platinum by the electrolytic way, form upon 
 it much more continuous deposits, we believe that this 
 enormous difference is due especially to the fact, that the 
 oxygen, when it is produced in this manner, is ozonised ; a 
 circumstance, that considerably augments its electro-motive 
 force, as we have seen it do. 
 
 There is a point upon which M. Beetz does not agree 
 with MM. Lenz and Saweljev ; it is that which concerns the 
 electro-motive force of chlorine which these philosophers had 
 found to be null, which is probably due to the fact that the 
 platinum, in their experiments, was attacked by the chlorine, 
 and formed a chloride, which was dissolved. M. Beetz, in 
 numerous and laborious researches, which we regret being 
 unable to report here a little more in detail, has constantly 
 found, both in operating directly upon gaseous chlorine, 
 as well as in depositing chlorine upon platinum by the 
 electrolytic decomposition of the chlorides, or of hydro- 
 chloric acid, numbers very near to each other, 10*27 and 
 1 1 '0, for the force of polarisation of platinum-chlorine ; he has 
 likewise found, for that of platinum- hydrogen, 19 '08 ; which, 
 added to the former, produces about 30 ; a number a little 
 lower only than that, furnished by direct observation, made 
 with the gas pile, hydrogen and chlorine. On decomposing 
 iodides and bromides, M. Beetz was able likewise to deter- 
 mine the electro-motive force of iodine and bromine, which 
 he found to be for the former, 3-36, the latter 6-96, that of 
 chlorine being 10*10. 
 
 It evidently follows from the analysis, that we have just 
 been making of the works, relative to the electro-motive 
 force of gases, that the numerical determinations leave still 
 some uncertainty in respect to the influence that is exerted 
 upon the force of the current by the nature of the solid 
 substance, that establishes contact between the gas and the 
 liquid, and by the manner, in which the deposifc has been 
 brought about. 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 807 
 
 A point upon which philosophers are not in accordance, 
 is the relation, that exists between the secondary polarities, 
 acquired by the plates, that have been employed as electrodes 
 to a current in an electrolytic liquid, and the intensity of this 
 current. We have seen that, according to Wheatstone, the 
 energy of the secondary polarities would be constant and in- 
 dependent of the intensity of the current. M. Poggendorff 
 has arrived at a different result, and he has found that this 
 energy increases with the intensity of the current, and in a 
 the manner more sensible in proportion as the latter has a less 
 absolute force. He operates with a pile of two Grove's pairs, 
 the electro-motive power of which he first determines when 
 it is alone, then when a voltameter is introduced in it, that is 
 an inactive pair of two platinum plates, plunged in diluted 
 sulphuric acid. Then, causing the length of the wire of 
 the rheostat, which is placed in the circuit, to vary, he 
 notices what are the corresponding variations that are 
 suffered by the electro-motive force of the new circuit, 
 which is equal to the difference between the primitive elec- 
 tro-motive force of the two Grove's pairs, and the contrary 
 one, that results from the secondary polarities acquired 
 by the two plates of platinum. Now, if this latter is 
 constant, the former being evidently so, their difference 
 ought to be so also, which is not the case, as is proved by 
 the following Table, in which I expresses the length of the 
 wire of the rheostat, i the intensity of the current, measured 
 by the sine-galvanometer, E' the electro-motive force of the 
 circuit, andp, the electro-motive force, arising from the se- 
 condary polarities acquired by the plates ; p is obtained by 
 deducting E' from E, the electro -motive force of the circuit, 
 before the introduction of the inactive pair of platinum, which 
 is found equal to 46 '85, on commencing the experiments, and 
 to 46*53, on finishing, which proves the constancy of the pile. 
 With regard to the total resistance of the circuit, includ- 
 ing the wire of the sine-galvanometer, it was 8*78 before 
 the introduction of the inactive pair, and 12*79 when once 
 the pair is introduced. 
 
 3 F 4 
 
808 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 I. 
 
 t. 
 
 E'.* 
 
 p- 
 
 6 
 
 8 
 
 80-15"} 
 62-58 J 
 
 18-51 
 
 28-18 
 
 10 
 
 54-17 
 
 18-50 
 
 28-19 
 
 20 
 
 34-56 
 
 18-77 
 
 27-92 
 
 40 
 
 21-17 
 
 19-16 
 
 27-53 
 
 80 
 
 12-14 
 
 19*66 
 
 27-03 
 
 160 
 
 6-42 
 
 20-16 
 
 26-53 
 
 340-87 
 
 3-27 
 
 21-28 
 
 25-41 
 
 80 
 
 12-80 
 
 19-50 
 
 27-19 
 
 40 
 
 21-11 
 
 19-08 
 
 27-61 
 
 20 
 
 34-12 
 
 18-43 
 
 28-26 
 
 10 
 
 53-39 
 
 1836 
 
 28-33 
 
 8 
 
 61-27 
 
 18-26 
 
 28-43 
 
 6 
 
 76-41 
 
 18-28 
 
 28-41 
 
 We may remark however, that the differences observed 
 by M. Poggendorff between the different values of p, are 
 not very great, and may be due to the inconstancy, that is 
 always more or less presented by the secondary polarity of 
 the positive electrode, on account of the presence at this 
 electrode of a greater or less proportion of ozonised oxygen. 
 
 M, Poggendorff has applied the determination of secondary 
 polarities to the evaluation of the total resistance that is 
 exercised upon a current by the current, produced by a 
 more feeble pair, placed in the circuit of the stronger, but in 
 a contrary direction. He has thus found that a simple pair, 
 zinc-platinum, or zinc-copper, in a solution of sulphuric acid, 
 interposed in this manner in the circuit of a pile of three 
 pairs of Grove's, so that the hydrogen is deposited upon 
 the zinc and the oxygen upon the platinum or the copper, 
 exercised a force of resistance, which was exactly the sum 
 of its electro-motive force proper, and that arising from the 
 secondary polarities of the two plates. 
 
 The principle thus enables us to estimate the electro- 
 motive forces of pairs of non-constant force, when once we 
 
 * The first value of E' was deduced from the two intensities, 80-15 and 
 62-58, by means of Ohm's method, which was allowable, in consideration 
 of the small interval of time, that had elapsed between the two consecutive ex- 
 periments. 
 
CHAP. ill. ELECTRICITY BY CHEMICAL ACTIONS. 809 
 
 know the electro-motive forces developed by the secondary 
 polarities, that it is necessary, in this case, to deduct from 
 those which are furnished by experiment, in order to obtain 
 the electro-motive force of the pairs themselves, before their 
 plates have been polarised. It is by this means that MM. 
 Lenz and Saweljev had drawn out the Second Table, that 
 we have reported above, and which contains the electro- 
 motive forces of the metals, plunged in divers liquids. 
 M. Poggendorff remarks moreover with reason that, for 
 the determination of the electro-motive forces of the pairs of 
 non-constant force, his method of compensation has the ad- 
 vantage of being more direct and more exact. 
 
 This method of M. PoggendorfFs, which we have merely 
 pointed out, and which we have developed in the Note F, has 
 enabled its author to throw light upon many points that are 
 still obscure, relative to the influence of certain causes on the 
 electro-motive force. Thus we had observed that, when the 
 resistance is not very great, the current of a zinc and iron 
 pair, plunging in a diluted acid, exceeds that of a zinc and 
 copper pair, placed under the same circumstances, although 
 iron is more positive than copper, and can form with it a 
 pair in which it is the positive metal. This result is evidently 
 due to the effect of secondary polarity, which is more con- 
 siderable upon copper than upon iron. In order to prove it, 
 it is enough to employ PoggendorfPs method of compensations, 
 which does not allow of the currents being established, and 
 which thus causes us to escape secondary polarities ; in order 
 to obtain the compensation, a Grove's pair is employed, whose 
 electro-motive force is 22 '882, and its resistance proper 5 '47 
 units of length of a German silver wire ; and the following 
 numbers are obtained for the electro-motive forces E of the 
 pairs, whose resistance r has been determined in each case, 
 and which are plunged into a mixture of 1 part of sulphuric 
 acid, and 16 parts of water.* 
 
 * The unit to which E is referred is altogether arbitrary ; it depends on 
 the pair, which is employed for establishing compensation ; but its absolute 
 value has no importance for the objects we have in view. 
 
810 SOURCES OF ELECTRICITY. PARTY. 
 
 Pairs. 
 
 r. 
 
 E. 
 
 Amalgamated zinc, copper j)> 
 iron 
 Iron/ copper - - - - 
 
 52-68 
 16.59 
 12-34 
 
 13-792 
 7-399 
 6-000 
 
 Thus we see, that at all times when we do not permit the 
 current to enter into activity, which is the case in the me- 
 thod of compensation, the electro-motive force of the zinc- 
 copper pair is greater than that of the zinc-iron pair. There 
 is likewise found for pairs of non-constant force, the law 
 already pointed out by Mr. Wheatstone, namely, that, if we 
 have two pairs, the electro-motive force of a third, formed of 
 the two extreme metals of the former, is equivalent to the 
 sum of the electro-motive forces of the two pairs, formed of 
 the consecutive metals.* In fact, upon adding 7*399 and 
 6-000 in the Table above, we find 13*399, a number very 
 near to 13-792. 
 
 After this detailed examination of the different methods 
 employed, accompanied by some of the results obtained, we 
 ought to indicate the electro-motive forces of the various 
 voltaic combinations; but among the determinations that 
 have been made we shall confine ourselves to quoting those 
 which appear to us the best and the most important. 
 
 PoggendorfF had the idea of substituting, in the Grove's 
 and Bunsen's piles, for the nitric acid, chromic acid, which 
 also contains much oxygen, and which abandons it easily. 
 The solution that he employed is composed of a mixture of 
 three parts by weight of acid chromate of potash, four of 
 concentrated sulphuric acid, and eighteen of water. He 
 plunged successively into this liquid, a Bunsen's carbon, 
 platinum, and copper, the other element of the pair being 
 amalgamated zinc, placed in a mixture of nine parts by 
 weight of water and one of concentrated sulphuric acid ; a 
 vessel of porous clay separated the two liquids. The follow- 
 ing is the result of three comparative experiments : 
 
 * Vol. II. p. 793 
 
CHAP. in. 
 
 ELECTRICITY BY CHEMICAL ACTIONS. 
 
 811 
 
 
 Resistance of 
 the Pair. 
 
 Electro-motive 
 Force. 
 
 Bunsen's pair - 
 
 'nitric acid - - 
 chromic acid - - 
 
 6-30 
 12-28 
 
 21-06 
 21-61 
 
 Grove's pair 
 
 nitric acid - - 
 chromic acid - - 
 
 5-04 
 8-30 
 
 21-29 
 13-42 
 
 Daniell's pair 
 
 sulphate of copper 
 chromic acid - - 
 
 14-72 
 6-34 
 
 13-63 
 13-20 
 
 We see that, with platinum, the force in the pah>in which 
 there is chromic acid, is scarcely the two-thirds of what it is 
 with nitric acid even but little concentrated ; for the nitric 
 acid which was employed was of a density of 1'30. With 
 carbon the electro-motive force is the same with both acids ; 
 but, besides that it is not very constant with chromic acid, the 
 resistance of the pair with this acid is almost twice as great 
 as with nitric acid. There is therefore no advantage in sub- 
 stituting chromic acid for nitric acid, although we thus avoid 
 the nitrous vapour. 
 
 The following, for instance, are some determinations of 
 electro-motive forces carefully made for the pairs most in use. 
 We give for each only the means of several experiments. 
 The electro-motive forces have been calculated by means of the 
 
 -i ./ E i . i . , ,i I* i 
 
 -, which give E = ^ *T^YJ * and 
 
 i' being determined by the tangent galvanometer, which was 
 placed in the circuit ; the length I of the additional wire 
 varied from to 75 yards. 
 
 formulas i ~ and i f = 
 
 R R + 
 
 Grove's pair 
 Bunsen's pair 
 
 
 Daniell's pair 
 Smee's pair 
 Wollaston's pair 
 
 (Deloeuil) 
 (Stohrer) 
 
 E. 
 
 829 
 
 - 839 
 
 - 777 
 
 - 470 
 
 - 210 
 
 - 208 
 
 R has also been determined for each pair by eliminating 
 E ; but this element was very variable. However, it is to be 
 remarked, that it is much less for piles with a single liquid, 
 in which there is not any porous diaphragm. 
 
812 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 The following is also a determination made by M. Jacobi, 
 according to a method founded upon the principle of derived 
 currents, and in which, as in Wheatstone's method, the needle 
 is brought back to the same degree of deviation in each case. 
 He has found by four observations perfectly in accordance, 
 that, if the electro-motive force of a DanielPs pair is ex- 
 pressed by 21-042, that of a Grove's pair is by 35-201 ; a 
 relation, which is not very far that, which may be deduced 
 from the.Table, that precedes. 
 
 Mr. Joule has determined the electro-motive force of a 
 great number of voltaic combinations by Fechner's process ; 
 namely, by introducing into the circuit a galvanometer, the 
 resistance of which is very great, 300 times at least that of 
 each pair, in order that this latter may disappear before the 
 former, so that the electro -motive force may be regarded as 
 proportional to the intensity of the current. The following 
 are some of the results : 
 
 Platinum 
 
 Nitric acid 
 
 Dissolved potash 
 
 Amalgam of po- 
 
 
 
 
 
 tassium - 
 
 302 
 
 > 
 
 
 
 9 
 
 Amalgam of zinc 
 
 231 
 
 9 
 
 ti 
 
 M 
 
 Iron - 
 
 169 
 
 99 
 
 
 99 
 
 Copper 
 
 120 
 
 
 
 n 
 
 }> 
 
 Silver 
 
 66 
 
 99 
 
 9 
 
 9 
 
 Platinum - 
 
 31 
 
 99 
 
 99 
 
 Solution of ordi- 
 
 
 
 
 
 nary salt 
 
 Amalgam of zinc 
 
 198 
 
 99 
 
 n 
 
 9 
 
 Iron - 
 
 146 
 
 99 
 
 99 
 
 n 
 
 Copper 
 
 116 
 
 w 
 
 99 
 
 9 
 
 Silver 
 
 95 
 
 n 
 
 
 99 
 
 Platinum - 
 
 55 
 
 9 
 
 9* 
 
 Diluted sulphuric 
 
 
 
 
 
 acid 
 
 Amalgam of zinc 
 
 187 
 
 9 
 
 M 
 
 
 
 Iron - 
 
 140 
 
 tt 
 
 9 
 
 
 
 Copper 
 
 91 
 
 n 
 
 ) 
 
 
 
 Silver 
 
 53 
 
 
 9 
 
 99 
 
 Platinum - 
 
 37 
 
 99 
 
 Peroxide of lead 
 
 
 
 
 
 with sulphuric 
 
 
 
 
 
 acid 
 
 Dissolved potash 
 
 Amalgam of zinc 
 
 277 
 
 
 
 9 
 
 99 
 
 Iron - 
 
 177 
 
 Mr. Joule thinks that we may conclude, from the Table of 
 electro-motive forces, that he has determined, and certain alone 
 of which we have above related, that the difference between the 
 electro-motive forces of two positive metals, plunged into a 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 813 
 
 similar solution, is a constant quantity, whatever may be the 
 changes that the negative elements of the pair are made to 
 undergo. 
 
 As we see, the number of voltaic combinations whose elec- 
 tro-motive force has been determined is already very con- 
 siderable ; unfortunately, these determinations are not made 
 after the same methods, nor upon the same plan ; nevertheless, 
 they are sufficient, in the practical point of view, and they 
 may even also furnish, as we shall see in our last paragraph, 
 some valuable data upon the relations that exist between 
 chemical and electrical forces. An essential point in the theo- 
 retic relation which they enable us. even now to establish 
 is the perfectly exact proportionality that exists between 
 the electro- motive force deduced from the intensity of the 
 current and that concluded from the energy of the static 
 tension, when the circuit is open instead of being closed. 
 This proportionality is a natural consequence of the prin- 
 ciple that we have established, by laying our foundation upon 
 experiment ; namely, that, when the condenser is charged^ by 
 means of a pair, a discharge is obtained, which is a veritable 
 elementary current.* Hence the electro-motive force of 
 this element of the current must be the same as that of the 
 current itself, whatever be the duration of this latter. It is 
 M. Kohlrausch who, by accurate experiments, of which we 
 are about to give the details, has established this important 
 law. 
 
 M. Kohlrausch employed one of Dellmann's electroscopes, 
 furnished with a condenser. Dellmann's electroscope is only 
 a sort of torsion balance, the very delicate construction of 
 which, permits of the measurement of very small forces. 
 The condenser employed by M. Kohlrausch, was arranged in 
 a particular manner, in order to avoid the various causes of 
 error, which the employment of this instrument too fre- 
 quently introduces. It was formed of two brass plates, about 
 6 in. in diameter and -^th of an inch in thickness, each 
 suspended by three silken cords ; the cords that sustain the 
 upper plate, about a foot in length, were attached to a 
 
 * Vol. II. p. 677. 
 
814 SOURCES OF ELECTRICITY. PARTY. 
 
 moveable piece, which permitted of the two plates being 
 separated or brought near to each other at pleasure. The 
 lower plate was covered with a very thin film of gum-lac 
 varnish, and presented at three points near to its edges three 
 small columns of gum-lac ; the upper plate rested upon these 
 columns, when it was required to make the experiment ; and 
 was varnished at only the three corresponding points. In 
 consequence of this arrangement, the distance of the plates and 
 the condensing force remained constant during the whole con- 
 tinuance of the experiments ; the mode of suspension caused 
 the disappearance of the disturbances, that are so frequently 
 produced by electricity, which always ends by accumulating 
 upon the glass supports of the ordinary condensers. The 
 lower plate played the part of the condensing plate, and 
 communicated in general with the ground ; the upper plate 
 played the part of the collecting plate, and in order to make 
 it communicate with the electroscope, it was merely necessary 
 to raise it until it was made to touch a wire F, which led to 
 the, electroscope ; the height of this wire was maintained 
 constant, throughout the continuance of the experiments. 
 
 In order to charge this apparatus, he proceeded in the fol- 
 lowing manner : 
 
 First. The upper plate was raised as far as to the wire F, 
 and, touching the wire F with another wire, that communicated 
 with the ground, the condenser and the electroscope were at 
 the same time discharged. 
 
 Second. The communication of the lower plate with the 
 ground was cut off. 
 
 Third. The upper plate was brought down upon the 
 lower plate ; and the electroscope was at the same time ad- 
 justed. 
 
 Fourth. By the movement of a mechanism, which it is 
 useless to describe, the two plates were placed in relation 
 with the two poles of the voltaic pair, that was being 
 studied. 
 
 Fifth. The communications established between the plates 
 and the poles of the voltaic pair, were cut off; and the com- 
 munication of the lower plate was established with the ground. 
 
CHAP. ill. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 815 
 
 Sixth. The plate was raised until in contact with the 
 wire F ; and the charge of the electroscope was measured. 
 
 In all this series of operations, great care was taken never to 
 touch the metallic pieces of the apparatus with the fingers, the 
 moisture of which might have caused an electro-motive action. 
 
 The electro-motive forces were determined by Wheatstone's 
 method, founded upon the employment of the galvanometer 
 and the rheostat. This measure was repeated four or five 
 times before the application of the condenser, and four or five 
 times after. The differences of the individual observations did 
 not in general exceed -fa of the mean value. The condenser 
 was itself applied twice to each pole ; and the mean was taken 
 of the four tensions thus determined as equal to the true tension 
 of the pair. In each case, there was observed the initial im- 
 pulse communicated to the needle of Dellmann's electroscope 
 and the torsion necessary to maintain this needle at 36 from 
 the fixed line; the initial impulse or the square-root of the 
 torsion might equally serve to measure the electric tension. 
 
 The following Table contains the results of the ex- 
 periments : E designates in it the electro-motive force, T 
 the tension, measured by the initial impulse, T' the tension 
 measured by the square-root of the torsion. In order 
 to render the comparison of the results more easy, the 
 observed values of T and T', were multiplied by factors, such 
 that the electro-motive force of the first voltaic pair inscribed 
 in the Table, was expressed exactly by the same number as 
 the two corresponding values of T and of T'. 
 
 Nature of the Pairs. 
 
 E. 
 
 T. 
 
 T'. 
 
 Zinc, sulphate of zinc, nitric acid of 1 '357 
 
 
 
 
 of density, platinum - 
 
 28'22 
 
 28-22 
 
 28-22 
 
 Zinc, sulphate of zinc, nitric acid of 1 '2 13 
 
 
 
 
 of density, platinum - - - 
 
 28-43 
 
 27-77 
 
 27-75 
 
 Zinc, sulphate of zinc, nitric acid of 1 '2 13 
 
 
 
 
 of density, carbon - 
 
 26-29 
 
 26-15 
 
 26-19 
 
 Zinc, sulphate of zinc, sulphate of copper, 
 
 
 
 
 copper (Daniell's pair) 
 
 18-81 
 
 18-88 
 
 19-06 
 
 Silver, cyanuret of potassium, sea-salt, 
 
 
 
 
 sulphate of copper, copper 
 
 14-08 
 
 14-27 
 
 14-29 
 
 The same pair at the end of some 
 
 
 
 
 time - - ... 
 
 13-67 
 
 13-94 
 
 13-8-2 
 
 The same pair at the end of a longer 
 
 
 
 
 time - ... 
 
 12-35 
 
 12-36 
 
 12-36 
 
816 SOURCES OF ELECTRICITY. PART v, 
 
 We must remark, that the rigorous accuracy with which the 
 electro-motive force, measured by the intensity of the current, 
 is proportional to that deduced from the energy of the 
 tension, is due to the circumstance that the pairs are two- 
 liquid pairs ; for otherwise the tension, estimated after the 
 circulation of the current, would not be the same as that which 
 is observed before the circulation, on account of the secondary 
 polarity, that would have been acquired by the negative ele- 
 ment of the pair. 
 
 After having been engaged in all that concerns the electro- 
 motive force of a single pair, and having pointed out the 
 means of comparing in this respect the various pairs one with 
 the other, it remains for us to point out the laws, which 
 connect the electro-motive force of an assemblage of several 
 pairs in series, constituting a pile, with that of the pairs of 
 which it is composed. We have already seen that Wheat- 
 stone had established, by an experiment, the very simple 
 law that, when the pairs are similar, the electro-motive force 
 of the pile is for a pile of n pairs n e, e being the electro-motive 
 force of one pair, and the resistance n r, r being the resistance 
 
 of one pair ; so that I = ^ =z~ = i, i being the intensity of 
 n T T 
 
 the current of the pile, and i that of one of its pairs. But 
 this result is not verified, except so long as each pair with 
 its resistance is introduced into the pile. Thus if, after 
 having taken the intensity of the current of one pair with the 
 sine-galvanometer, we take that of the current of a pile of n 
 pairs, confining ourselves to introducing into its circuit the 
 same sine-galvanometer, we shall find a much greater in- 
 tensity. In order to find the same, it is necessary that each 
 of the pairs which, by their union compose the pile, enters 
 into its formation with a resistance equal to that which their 
 circuit would offer, when the sine-galvanometer formed part 
 of it. Then, the intensity of the current of n pairs in series 
 is equal to that of one alone. In fact, we have for a single 
 
 pair i= e > I being the resistance of the galvanometer; 
 
 T -f- I 
 
 and for n pairs we have I = - , if we place only the same 
 
CHAP. in. ELECTRICITY KY CHEMICAL ACTIONS. 817 
 
 galvanometer in the circuit of the n pairs; whilst, if we place 
 each pair, adding to it the resistance l % we have I = - =i. 
 
 This important principle, that each pair enters into the 
 formation of the pile with its electro-motive force and its 
 resistance, the other pairs not being to be considered in re- 
 spect to it, except as simple conductors, has been experiment- 
 ally demonstrated by Fechner and by Pouillet. M. Pouillet, 
 as we have already seen, had at first expressed the resistance 
 of a pair by the length of a copper wire, presenting an equi- 
 valent resistance, and which he called reduced length ; he had 
 then found, on elongating this wire, that, conformably to the 
 laws, which regulate the intensity of a current, this intensity, 
 measured by the tangent-galvanometer, was in inverse ratio 
 to the length of the circuit. Then, after having determined 
 the individual intensity, that is to say, the electro-motive 
 force, and the resistance proper of a certain number of pairs, 
 he united them in series ; and, having measured the intensity 
 of the current, produced by this pile, he had found the result 
 of experiment perfectly in accordance with that of cal- 
 culation. 
 
 Thus generally, we are able to express the intensity of 
 the current of a pile, composed of different pairs, by the 
 formula : 
 
 - 
 
 Since, for the pair, whose electro-motive force is e, the 
 intensity of its current, when once it forms part of the pile, is 
 
 tne P air e '> tne i^ensity is 
 So on *" or ^ ie rest * 
 
 ~ r 4- / 4- /' 4- / 
 
 Poggendorff has verified the accuracy of this law, for 
 the case of two pairs, one Grove's, the other DanielPs, united 
 in series, the electro-motive force and the individual resist- 
 ance of which he had determined. 
 
 VOL. II. 3 G 
 
818 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 
 lectro-motive 
 Force. 
 
 Resistance. 
 
 Grove's pair 
 Darnell's pair 
 
 Piles formed by the 
 two pairs in series 
 
 f calculation 
 \ experiment 
 
 25-79 
 15-87 
 
 508 
 1373 
 
 41-66 
 41-62 
 
 18-81 
 18-91 
 
 In the case, in which two or more pairs being in series, 
 one of them is so arranged that its current must travel in a 
 contrary direction to that of the others, it must affect its 
 electro-motive force with the sign , in the general ex- 
 pression of the intensity ; but there is nothing to change in 
 the denominator ; the resistances suffering, by this inversion, 
 no modification. However, this theoretic result is not ex- 
 actly verified by experiment, except in the particular case, 
 in which the intensity of the current is equal to ; because 
 there is an equality between the electro-motive forces that 
 act in one direction and those that act in the contrary direc- 
 tion. In the other cases, for example, when a Grove's pair 
 is opposed to a Daniell's pair, the stronger current, that of 
 the Grove's pair, acts upon the more feeble pair, the Da- 
 niell's, and modifies it, by oxidising its copper, and bringing 
 about a reduction upon its zinc, so as to diminish its electro- 
 motive force. The definitive current, that results from the 
 difference of the other two, is thus found to be more powerful 
 than theory indicates, and it goes on increasing in proportion 
 as the experiment continues, even when the pairs separated 
 gave previously a current of constant force.* 
 
 It is therefore only in the case, in which the two opposed 
 electrical forces are equal, that the intensity of the current 
 is, conformably with theory, completely null, whatever in 
 
 * It follows very evidently from this, that when two pairs are opposed to 
 each other, there is no transmission in the circuit of two contrary currents, hut 
 rather of a single one, that is produced by the difference between the force, with 
 which one of the pairs polarises the different successive parts of the circuit, and 
 that with which the other pair exercises the same polarisation. If these two 
 forces are equal, the different parts of the circuit are not polarised ; and there 
 is no current at all. If things happened otherwise, the current of the more 
 feeble pair, in traversing the stronger, ought to reduce it, as it is itself reduced 
 by the current of the stronger pair. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 819 
 
 other respects the resistances may be. Thus, if we oppose 
 to each other two similar pairs, Grove's, DanielPs, Smee's, 
 no matter what their nature, in one of which the metals have 
 a very great surface, whilst the other has them with a very 
 small one, a null current is obtained, although each of these 
 pairs is able separately to produce very different effects. In 
 fact, if we call the resistance of that with large surface r, 
 that of the small surface, much greater according to the law 
 of sections, will be R ; but the electro-motive forces, which 
 depend only upon the nature of the solid and liquid elements, 
 which are the same in both pairs, are equally e for both of 
 them ; so that, even although we shall have for the former 
 
 a, 
 
 * = - much greater than i' = of the latter, we shall however 
 
 V R 
 
 > p 
 
 have I = = 0, when they shall be united, by opposing 
 
 one to the other. 
 
 It follows from this that, if in a pile composed of a certain 
 number of pairs in series perfectly similar to each other, we 
 increase the dimensions of one or of several among them, 
 without in any way changing their nature, we in no way 
 modify the electro-motive force of the pile, which is always 
 the sum of the individual electro-motive forces of each pair ; 
 but we increase the force of the current or the quantity of 
 electricity, that passes in a given time, because the total 
 resistance of the circuit is diminished, by diminishing those 
 of the pairs, whose dimensions have been increased. This 
 may be verified with the pile of fig. 308.*, in which the 
 hydrogen is collected, that is liberated at the negative element 
 of each of its pairs. When the surface of one of the pairs is 
 increased, more hydrogen is liberated upon the platinums, 
 but always the same quantity upon each of them, according 
 to the law of equivalents ; the chemical work becomes simply 
 more powerful upon the smaller zinc, than it was when the 
 two zincs were equal. The reverse takes place when, in- 
 stead of increasing, we diminish the dimensions of the second 
 pair. 
 
 * Vol. II. p. 691. 
 3 G 2 
 
820 SOURCES OF ELECTRICITY. PART v. 
 
 Mr. Daniell, who made a great number of experiments 
 upon piles composed of a greater or less number of pairs, 
 measuring the volumes of the gases liberated, experiments, 
 the results of which were perfectly in accordance with those 
 that are indicated by theory, remarked that, when we confine 
 ourselves to modifying the dimension of the amalgamated 
 zinc in a pair, without introducing any other change into 
 this pair, the intensity of the current is not sensibly altered ; 
 because we in no way change the resistance of the pair, 
 which depends essentially on the dimensions of the liquid 
 conductor, and on those of the negative metal. 
 
 We have already seen that the greater or less considerable 
 number of pairs, of which a pile is composed, only serves for 
 giving to a same voltaic combination a greater or less electro- 
 motive force ; indeed, it follows, from all that precedes, that 
 the number of pairs of which a pile must be composed, 
 in order to obtain a given electro- motive force, is the 
 converse of the electro-motive force of the voltaic combina- 
 tion employed. But, when once the circuit is closed, the 
 quantity of electricity that circulates in it, is the same 
 as that which is produced by a single pair of this same 
 circuit, and is measured by the chemical action that takes 
 place in this pair, that is to say, by the consumption of the 
 positive metal which, in the entire circuit, is in a direct 
 relation with the number of pairs, and consequently, the in- 
 verse of the electro-motive force. There would therefore be 
 a great economy in finding voltaic combinations, the electro- 
 motive forces and the resistances, of which were such, that 
 a single pair, or at least a small number, produce the same 
 effect as several. Such, for example, would be the combina- 
 tion, amalgam of potassium, diluted sulphuric acid, and per- 
 oxide of lead, which, according to Wheatstone, has the same 
 electro-motive force as a series of five pairs, amalgam 
 of zinc, diluted sulphuric acid and copper. But this com- 
 bination, as well as others of the same kind, is expensive ; 
 so that we prefer to make use of those, in which zine is 
 employed, even although it is necessary to multiply the 
 number of pairs. However, in this case, an important 
 question presents itself ; it is to know, two metallic surfaces 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 821 
 
 being given, amalgamated zinc and platinum, into how 
 many pairs we must divide them, in order to construct a pile 
 which may produce, with a given resistance, the maximum of 
 effect ; which, for example, may decompose the maximum of 
 water in a given voltameter, or produce the maximum of heat 
 in a wire of a given resistance. The quantity of chemical 
 action remains constant, since the total metallic surface, 
 that is attacked, does not change; only, the fewer pairs 
 there are, the more of useful effect will there be. M. Pog- 
 gendorff has solved this question in a very simple manner. 
 Calling I the exterior resistance which we are concerned 
 in surmounting, he remarks, that we have always for 
 
 one pairi 7; and, for n similar pairs, I = ,. 
 
 r + I n r -f I 
 
 Now, if we seek to know what value n ought to have, in 
 order that I shall be a maximum, we find that it is necessary 
 for it to be such that I = n r ; that is to say, that the intensity 
 of the current is at its maximum, when the total interior re- 
 sistance of the pile n r is equal to that, which it is necessary 
 for the current to surmount exteriorly.* Hence, n is deduced 
 by determining r and /, by means of the rheostat. It follows 
 
 g 
 
 from this, that the maximum value of I is I = - ; conse- 
 quently, that the maximum of exterior useful effect, that a vol- 
 taic pile may produce, is the half of the maximum intensity 
 that its current or that of one of its pairs may attain, when 
 there is no exterior resistance. 
 
 If we desire to compare two piles, with regard to their 
 maximum of useful effect, we have only to determine in each 
 of them the maximum of intensity of the current of one of 
 the pairs, of which it is composed ; the relation of these 
 maximums is. the same as that, which is sought for. Indeed, 
 for one this maximum is, 
 
 e e' 
 
 i = , for the other i' = , ; 
 
 I e r' 
 
 or -> = -j . - . 
 i' ef r 
 
 * Vide final Note G. 
 3 G 3 
 
822 SOURCES OF ELECTRICITY. PART Y. 
 
 But the maximum intensity of the current of one pair of 
 the former pile is i = - ; and, for the latter, i' = - > . Now, 
 
 This result of theory is altogether in accordance with that 
 which had been given to me, in 1830, by an experiment 
 founded upon the simple reasoning that, in order to obtain 
 the maximum effect, it is necessary that the number of pairs 
 shall be such that the current should circulate in the pile 
 neither more nor less rapidly than in the conductor that 
 unites its poles, that consequently the resistance of the pile 
 should be equal to that of the conductor.* 
 
 It would remain for us, in order to complete what we 
 have to say of piles, to show that, -as for a single pair, their 
 electro-motive force estimated by the tension of the elec- 
 tricity, that is in the static state at each of their poles when 
 (the circuit being open) the poles are well insulated, is exactly 
 proportional to that which is furnished by the measures of 
 the electricity in the dynamic state. Now, this is what 
 follows from the first labours made by Volta, then by 
 Coulomb and by Biot, upon the electric tension of voltaic 
 piles which philosophers, setting out from the contact theory, 
 have always found to be proportional to the number of the 
 pairs, as we shall see in the following paragraph, in which we 
 shall be occupied with this theory. Moreover, this result, 
 which has been further verified with the new piles, is com- 
 pletely independent of this theory, as is proved by the ana- 
 lysis, that we have just made, and is in accordance with 
 that which Kohlrausch has attained with a single pair. 
 
 Before completing this paragraph, in which we have 
 treated upon one of the most important questions of electricity, 
 it is impossible for us not to remark that, if the theory of 
 electro-motive force in general and of the voltaic pile in 
 particular does not leave much to be desired, it is not the 
 same with the experimental determinations of the electro- 
 motive forces and of the resistances of the various voltaic 
 combinations which, except for some few, present but little 
 * Vide above, Vol. II. p. 233. 
 
CHAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 823 
 
 accordance among the results. This is due to the diversity 
 of the methods employed, to the influence of certain dis- 
 turbing causes, which we do not always know how to avoid, 
 and finally, to the circumstances that the greater part of the 
 processes are founded upon the employment of the rheostat ; 
 an instrument which possesses the inconvenience that the 
 wire, which is its essential part, is not always perfectly homo- 
 geneous, and which, consequently, for equal lengths of this 
 wire, does not always correspond to equal resistances. 
 
 Another cause of confusion in this subject is the absence of 
 a unit adopted by all philosophers, in order to refer all elec- 
 tro-motive forces to it. Perhaps, in this respect, that which 
 would be best, would be to adopt the means proposed by 
 Weber, at the conclusion of the beautiful works executed in 
 common with Gauss, in order to obtain an absolute measure 
 of electric currents. This means consists in causing the 
 current, that we desire to measure, to pass through a thick 
 ring of copper placed in the magnetic meridian, and the re- 
 sistance of which may be considered as null, in respect to 
 that of the other parts of the circuit, in which it is placed ; 
 then, the deviation is observed of a small magnetised needle 
 placed in the centre of this circle. If the diameter of the 
 circle exceeds six or eight times the length of the needle, the 
 intensity of the current is found in a manner altogether in- 
 dependent of the dimensions of the apparatus, and of the 
 intensity of the magnetism of the needle, by multiplying the 
 tangent of the observed angle of deviation <, by the radius of 
 the circle R, and by the absolute intensity of the horizontal 
 component of terrestrial magnetism at the point of observa- 
 tion T, and by dividing the whole by 2 TT ; which gives the 
 
 T> y rp 
 
 formula -^ tang. <. M. Bunsen, who has employed 
 
 this manner of measuring, in order to compare the electro- 
 motive forces of his pairs with those of other pairs, had found, 
 for Marbourg T = 1'88. We shall return, when we shall be 
 occupied with terrestrial magnetism, to this method, which 
 has the advantage of taking in nature, that is to say, in ter- 
 restrial magnetism, the unit of which we have need. 
 
 3 G 4 
 
824 SOURCES OF ELECTRICITY. PART v. 
 
 We have said that M. Pouillet had sought for it in the 
 current produced by a thermo-electric pair, copper and 
 bismutn, the solderings of which were at 32 and at 212. 
 In order to compare this current with that of a simple hydro- 
 electric pair, copper and zinc in acidulated water, he had 
 at first estimated the resistance of this thermo-electric circuit, 
 and found it equal to that of a copper wire 164 ft. in length, 
 and 0-039 in. in diameter. Then, in order to obtain a same 
 deviation of 16 in the galvanometer with a hydro-electric 
 pile composed of twelve pairs, he had found that the total 
 resistance of the circuit ought to be equal to that of a plati- 
 num wire of 590-5 ft. in length, itself equivalent to that of a 
 copper wire of 0-039 in. in diameter, but 316,072 ft. in length. 
 It is easy to conclude from this, that the intensity of the 
 current produced by the twelve pairs of the hydro-electric 
 pile is 1127 times that of the current of the thermo-electric 
 pair ; which establishes between the electro-motive force of 
 this pair and that of a single pair of the pile the relation of 1 
 to 94, very near to that of 1 to 94-6 found by Wheatstone. 
 
 But it was not sufficient to have a common measure for 
 currents. M. Pouillet also wished to satisfy himself directly 
 of the accuracy of the principle that, for equal electro-motive 
 forces the intensity of a current measured by its effect, that 
 is to say, the deviation of the needle of a galvanometer is 
 actually proportional to the quantity of electricity trans- 
 mitted. With this view he placed in the circuit of a 
 current, that traversed a sine -galvanometer, a wheel, the 
 circumference of which, smooth like the border of a disc, 
 presents intervals alternately of metal and of wood, these 
 species of teeth, or of conducting and non-conducting surfaces 
 being equal to each other. This wheel, carried upon a me- 
 tallic axis, which communicates with the metallic teeth of 
 the circumference, is able to receive an extremely rapid rota- 
 tory motion. One of the poles of the pile communicates with 
 the axis, the other with the wire of the sine-galvanometer, 
 which is terminated by a small tongue, that presses a little 
 against the circumference of the wheel. During rest, when the 
 tongue touches a metal tooth, the current passes entire, and 
 we have, for instance, a deviation of 90 ; when it touches a 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 825 
 
 wooden tooth, the current no longer passes. But, on giving a 
 rotatory motion to the wheel, if this motion is slow, we first 
 see the needle oscillate; then, in proportion as it is accelerated, 
 the oscillations diminish in amplitude, and we arrive at a 
 certain velocity, for which the needle remains perfectly fixed. 
 Setting out from this point, we may increase the velocity in- 
 definitely without the needle ceasing to be motionless and 
 to mark the same deviation. In the same experiment, in 
 which the deviation was 60 when the disc was at rest, a 
 fixed deviation was obtained of 25 45', as well when the 
 wheel made five turns per minute, as when it made twenty per 
 second. But the sine of 60, being double of that of 25 45', 
 it follows that, by the motion, the force of the current was 
 reduced one-half. Now, what has been done in this experi- 
 ment, except reducing by one-half the time during which a 
 current passes ? and its force has thus been reduced likewise 
 to the half. On the other hand, it is evident that the quan- 
 tity of electricity, that passes in a circuit, is proportional to 
 the time ; then, a half quantity of electricity produces a half 
 effect ; and it is very true that the quantity of electricity 
 which constitutes a current is proportional to the force of 
 this current measured by the deviation, that it exercises 
 over the needle of a galvanometer. 
 
 This same law is verified by taking, as we have demon- 
 strated might be done, in order to deduce from it the 
 quantity of electricity, the quantity of chemical action, that 
 corresponds to it ; for example, the quantity of water, or 
 of sulphate of copper decomposed, and placing a sine or a 
 tangent galvanometer in the circuit. We may even esta- 
 blish a relation between these two manners of measuring 
 the quantity of electricity, and thus to estimate, in units of 
 currents, that which is required for the decomposition of a 
 certain weight of water, one grain, for example. M. Pouillet 
 did this by operating in the following manner : 
 
 He commences by determining, in lengths of copper wire, 
 the resistances of the pile, of the liquid submitted to decom- 
 position, and of all the other conductors ; then, the moment 
 is noted, when the voltameter, that is placed in the circuit, 
 commences the liberation of gas. The deviation of the 
 
826 
 
 SOURCES OF ELECTRICITY. 
 
 PART V. 
 
 needle of the galvanometer, which remains constant, is ob- 
 served ; and the experiment is allowed to go on until a 
 convenient volume of hydrogen is obtained, which is the 
 only one of the two gases that is collected, for more accuracy, 
 in order to avoid the recomposition of the gaseous mixtures. 
 The following Table shows that the product of the time 
 necessary for obtaining the same volume of hydrogen by 
 the force of the current is a constant number ; and this, 
 whatever the cause may be, that makes the force of the 
 current to vary, as well when it is the degree of conducti- 
 bility of the liquid to be decomposed, or the nature of the 
 electrodes, as when it is the power of the pile. It follows, 
 therefore, from this (since, according to the law that we have 
 just established, the quantity of electricity is proportional to 
 the force of the current), that the quantity of electricity that 
 is required for the decomposition of a certain weight of water 
 is always the same, whether the water be more or less con- 
 ducteous, or the operation lasts consequently a longer or a 
 shorter time. 
 
 The following is the Table : 
 
 
 Metal 
 
 
 Deviation 
 
 
 
 of the 
 
 Time 
 
 of the 
 
 Product 
 
 
 Electrodes. 
 
 for 2 
 
 Galvanometer. 
 
 of the 
 
 Liquid. 
 
 
 cub. c. 
 
 
 Intensit 
 
 
 
 
 of Hy- 
 
 
 
 by i he 
 
 
 Positive. 
 
 Nega- 
 tive. 
 
 drogen. 
 
 Angle. 
 
 Sine. 
 
 Time. 
 
 Distilled water "I 
 with sulphu- [ 
 ric acid -J 
 
 Platinum 
 
 55 
 
 55 
 55 
 
 498" 
 501 
 
 550' 
 5 40 
 
 0-1016 
 0-0987 
 
 50-60 
 50-54 
 
 Former liquid ~j 
 
 
 
 
 
 
 
 diluted with 
 
 55 
 
 55 
 
 725 
 
 4 
 
 0-0697 
 
 50-53 
 
 one volume > 
 of distilled 
 water - J 
 
 55 
 55 
 
 55 
 55 
 
 728 
 919 
 
 4 
 3 10 
 
 0-0697 
 0-0552 
 
 5074 
 50-73 
 
 { 
 
 55 
 
 55 
 
 417 
 
 6 50 
 
 0-1190 
 
 49-62 
 
 
 55 
 
 I 
 
 55 
 
 423 
 
 6 45 
 
 0-1175 
 
 49-70 
 
 Ordinary water ' 
 with sul- { 
 phuric acid 
 
 Copper - 
 
 55 
 
 55 
 
 Zinc - 
 
 55 
 55 
 55 
 55 
 
 251 
 
 247 
 247 
 239 
 
 11 20 
 11 30 
 11 30 
 12 
 
 0-1965 
 0-1994 
 0-1994 
 0-2080 
 
 49-32 
 
 49-25 
 49-25 ' 
 49-71 
 
 
 5) 
 
 55 
 
 258 
 
 11 
 
 0-1908 
 
 4922 
 
 [ 
 
 Platinum 
 
 55 
 
 684 
 
 4 10 
 
 0-0724 
 
 49-50 
 
 'Diluted sulphu- 
 
 
 
 
 
 
 
 ric acid - 
 
 55 
 
 55 
 
 77 
 
 40 
 
 0-6428 
 
 49-50 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS, 827 
 
 Now, in order to obtain the measure of the quantity of 
 electricity, it is necessary to know that the total resistance of 
 the circuit, in the first two experiments of the Table, was 
 equivalent to that of 183,631 ft. of copper wire of '039 in. 
 in diameter, of which 385 ft. are for the resistance of 
 the pile and the sine-galvanometer, and 183,246 ft. for that 
 of the liquid subjected to decomposition. With regard to 
 the intensity of the current, it was 2665 times that of the 
 thermo-electric sources taken for a unit, the circuit of which 
 presents a resistance equal to that of 65*6 ft. of the same 
 copper wire. Now, with this force of the current, there was 
 obtained 2 cub. c. of hydrogen in 500"; and, as a gramme 
 (1543 grs. troy) of water contains 1241'61 cub. c. of hy- 
 drogen, there would be required, in order to bring about the 
 decomposition, a quantity of electricitv represented by 
 
 2665 x ml 2 61C ' C -= 1654-445; 
 
 namely, equal to more than 1600 times that which passes 
 during 500" in the source taken as unity; and if we take the 
 minute for the unit of time, we find that the quantity of 
 electricity necessary for decomposing a gramme of water, is 
 13,787 times the quantity of electricity that passes in one 
 minute in a bismuth and copper circuit, whose total resistance 
 is equal to that of a copper wire of -039 in. in diameter and 
 65 -6 ft. in length, and the solderings of which have a dif- 
 ference of 180 in temperature. And this number is always 
 the same, whether the gramme of water belongs to a 
 solution that is a good or a bad conductor, and whether it 
 is decomposed by a powerful or a feeble pile.* 
 
 * M. Weber has likewise determined the absolute quantity of electricity ne- 
 cessary for decomposing a certain weight of water, by taking for a unit the 
 quantity of electricity, that must pass in the unit of time (a second), through the 
 transverse section of a conductor, which represents the unit of surface, in order 
 to produce at a distance effects identical with those, that are produced by the 
 quantity of magnetism that serves as the unit of measure. It is necessary, then, 
 to observe the magnetic effect of an electric current, during the same time that 
 it decomposes a certain quantity of Avater. We have already seen above, how 
 Weber compares this magnetic effect with that of the terrestrial magnetism, at the 
 place of observation. Unfortunately, Weber's results are not comparable with 
 thos e of Pouillet, the relation btween the different units adopted by these two 
 philosophers not having beene determined. The number found by Weber for 
 the electro-chemical equivalent of water is 0-00936. He obtains it by dividing 
 
828 SOURCES OF ELECTRICITY. PART v. 
 
 It is probable, as we shall see in the last paragraph of 
 this Chapter, that the quantity of electricity necessary for 
 decomposing a gramme of water, is equal to that which is 
 produced by its decomposition brought about by an ordi- 
 nary chemical action, which explains the power of this 
 mode of production of electricity. 
 
 Electricity of Contact. Dry Piles. 
 
 We have already more than once made allusion to the 
 contact theory, in which the production of electricity in the 
 voltaic pile is attributed to the contact of two heterogeneous 
 solid bodies, that form part of two consecutive pairs, which, 
 in this theory, themselves constitute the pair.* We have 
 already cited a great number of facts of a nature to demon- 
 strate that contact in itself alone is not sufficient for liberating 
 electricity, but that it requires, besides an action, an action 
 which, in the pile, is a chemical action. However, there are 
 still a certain number of phenomena that seem at first sight 
 incapable of explanation, except by admitting that, of itself, 
 the contact of two heterogeneous bodies does determine, in- 
 dependently of all action, a development of electricity ; the 
 production of electricity in dry piles is of this number. It 
 is these facts, that we are about to examine, in treating upon 
 the general question of the electricity of contact. 
 
 We have already called to mind Galvani's fundamental 
 experiment | 5 in which a frog properly prepared is made to 
 undergo a sharp commotion by touching its lumbar nerve 
 laid bare with the extremity of a wire, of copper for example, 
 and the muscles of its thighs in like manner laid bare, with 
 the extremity of a wire of a different metal, such as iron ; 
 these two metals themselves touching by their other extre- 
 
 the quantity of decomposed water, expressed in millegrammes (-0154 grs. TV), 
 by the absolute quantity of corresponding electricity ; estimated by means of 
 the formula, that we have given above. In his experiments, the quantity of 
 water decomposed was as a mean 14 m. grs. ('2156 grs. T.), and the absolute 
 quantity of electricity, 1 500 also is a mean. The duration of each experiment 
 was about 1200 seconds. 
 
 * In the chemical theory the pair is formed of the metals, that plunge into 
 the same liquid (see note of p. 661.). 
 
 f Vol. I. p. 29. (fig. 16.) 
 
CHAP. in. ELECTRICITY DY CHEMICAL ACTIONS. 829 
 
 mity. Another more ancient experiment, devised by Sulzer, 
 consists in placing the tongue between two discs of metal, 
 different in their nature, one silver the other zinc, for example ; 
 then in establishing a metallic contact between them by 
 allowing them to touch exteriorly, still leaving the tongue 
 between the two discs. At the moment of contact a sharp 
 taste is experienced, and there is the sensation of an instan- 
 taneous light, if the eyes are kept closed. This double effect, 
 as well as the shock imparted to the frog, are electrical phe- 
 nomena, since they can be produced in an identical manner 
 by the direct action of electricity. Now, what is the cause 
 of this production of electricity ? It is, according to Volta, 
 in the contact of the two heterogeneous metals ; and the frog 
 in the former experiment, the tongue in the latter, merely 
 serve for the transmission of the electricities liberated, and 
 for detecting their presence ; that is to say, that they play no 
 other part than that of conductors and electroscopes. 
 
 Volta then admits, that it is at the contact of two solid 
 conductors, that the electro-motive force is developed; a 
 force in virtue of which one of the bodies is raised into a 
 positive state, and the other into a negative state ; the two 
 electricities, positive and negative, being necessarily equal in 
 such sort that, if one is represented by + e, the other is by 
 e, -f e and e, being added, making 0. With regard to the 
 value of e s or which comes to the same thing, of the differ- 
 ence between the electric states of the two bodies, it depends 
 upon their relative nature ; but it is the same whatever be 
 the absolute electric charge of each of them. Thus if, in 
 their contact, two plates, one of zinc, the other of copper, ac- 
 quire, the former e of positive electricity, the latter e of nega- 
 tive electricity, the difference between the electric states of 
 the two plates will be 2 e, each of the electricities being 
 affected by its sign. If the quantity of electricity with which 
 the zinc is charged goes on to increase so as to be n e, that 
 of the copper in contact with the zinc is then found to be 
 (n 2) 6, so that the difference is always 2 e. This second 
 principle enables Yolta to explain the accumulation of elec- 
 tricity in the pile. Indeed, let there be a certain number 
 of pairs formed each of two superposed discs, one of copper 
 
830 SOURCES OF ELECTRICITY. PART V. 
 
 below, the other of zinc above ; in each pair the copper has 
 ( e) and the zinc ( + e) ; but, if the copper communicates with 
 the ground, its electricity is and that of the zinc is + 2 e. 
 Let us place these various pairs one above the other in such a 
 manner, that the copper is always below the zinc ; and let us 
 separate the zinc of the lower pair from the copper of the 
 upper pair by a disc of moist cloth or card, which while 
 preventing metallic contact between the two metals, be- 
 longing to two different pairs, nevertheless allows the elec- 
 tricity of the first to pass to the second ; we shall thus con- 
 struct the column pile.* It will follow from this, that the 
 copper of the second pair, instead of possessing an electric 
 state 0, will have the same electric state 2 e as the zinc of the 
 first, and the zinc of the second will then have -f 4 e of elec- 
 tricity, by virtue of the electro-motive force, that is exerted 
 by its contact with its copper. This 4 e will be also the 
 electric state of the copper of the third pair, the zinc of 
 which will then have + 6 e of electricity ; and, if there are n 
 pairs, the zinc of the last will have + 2 n e of electricity, the 
 copper of the first, which communicates with the ground, 
 having 0. The pile in this case is charged with positive 
 electricity only, the latter going on increasing from the base 
 to the summit ; it would only be charged with negative elec- 
 tricity, if the pairs had been placed in an inverse order, the 
 zincs being below the coppers. If the two extremities or 
 poles of the pile are both insulated, the distribution of the 
 electricity takes place differently ; one of the halves of the 
 pile is found to be charged with negative electricity, and the 
 other with positive. This calculation of this distribution is 
 easily made, setting out from the same principles, and calling 
 to mind that the sum of the free electricities, taken with 
 their sign, both positive as well as negative, must always 
 be equal to 0, since none has escaped away into the ground. f 
 * Vol. I. p. so. (fig. 17.) 
 
 f The following is this calculation for the case of 8 pairs ; let x be the elec- 
 tricity of the first copper, 2 e being always the difference between the electric 
 states of a copper and a zinc in contact : 
 
 1st copper - - - - x 
 
 1st zinc - - - - - x + 2 e 
 
 2nd copper - - - - x + 2 e 
 
 2nd zinc - - - - x + 4 e 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 831 
 
 The direct observation made by Volta, then subsequently 
 by Coulomb and by Biot, confirms in a very approximate 
 manner the distribution of electricity in a pile, such as is 
 deduced from this theory. But it is remarkable, that this 
 distribution is exactly the same as that which we have 
 seen to be the consequence of an entirely different hypo- 
 thesis on the nature of the electro-motive force. This in fact 
 must be the case ; for that which separates the partisans of 
 the chemical theory from those of the contact theory is the 
 cause and the seat itself of the electro-motive force, but not 
 the manner of regarding the mode of accumulation of the 
 electro-motive forces of the different pairs ; a point, upon 
 which they are in accord. The only difference is, that, in the 
 chemical theory, we merely add to each other the electro- 
 motive forces of the different successive pairs, which must 
 necessarily take place ; whilst, in the contact theory, it is 
 necessary to introduce an hypothesis which it is difficult to 
 verify directly ; it is that the difference between the electric 
 states of the two metals in contact is always the same, 
 whatever be the absolute quantity of electricity with which 
 these two metals are charged. 
 
 As we may see, in the voltaic theory, the liquids with 
 which the pile is charged play the part merely of conductors ; 
 they are in no way electro-motors, the origin of the electricity 
 being entirely in the two metals of the pairs. Without 
 dwelling upon the indirect objections against this manner of 
 explaining the production of electricity in the pile, such as 
 the very intimate relation that unites the quantity of elec- 
 tricity liberated with the quantity of chemical action pro- 
 duced, the necessity that the liquids should have a che- 
 
 3rd copper - - - - x + 4 e 
 3rd zinc - - - - - x + 6 e 
 4th copper - - - - x + 6 e 
 4th zinc - - - - - x + 8 e 
 Sum of the electricities =0 = 8a:+32e 
 Whence - - - - x = 4 e 
 
 This value of x being known, the electric charge of each disc is very easily 
 found. Thus, that of the first copper being 4 e of negative electricity, that of 
 the fourth zinc is 4 e of positive electricity, that of the second zinc, and of the 
 third copper is 0, &c. 
 
832 SOURCES OF ELECTRICITY. PART v. 
 
 mical relation with one at least of the elements of the pair, 
 in order that there may be an electric effect, simple con- 
 ductibility not being sufficient *, points upon which we 
 have already treated in detail, and to which it is useless 
 to return, we shall confine ourselves to insisting upon two 
 peremptory difficulties, that appear to us to be presented by 
 the voltaic theory of the pile. 
 
 The first is the impossibility of drawing out a scale of the 
 electro -motive power of solid conducting bodies. Yolta had 
 thought he had succeeded in drawing out one, in which 
 each body was negative in its contact with those which 
 followed, and positive^! th those which preceded. But this 
 scale was true, only so long as the conductor interposed 
 between the metals of the pair, was water or moist air ; it 
 expressed merely the greater or less facility of each body for 
 decomposing water or for being oxidised under the combined 
 influence of oxygen and of water. It was no longer exact, 
 as soon as, instead of water, a concentrated acid, such as 
 nitric acid, a dissolved sulphuret, such as sulphuret of potas- 
 sium, a melted chloride, &c., was taken for a moist con- 
 ductor. In one word, the order of the electro-motive powers 
 always changes with the nature of the chemical reaction, 
 that takes place between the metals of the pair and the 
 liquid with which the pile is charged. Marianini and several 
 other philosophers have endeavoured to reply to this objec- 
 tion, by pretending that the decomposition, brought about 
 in the liquid, that separates the pairs, by the electricity 
 that is produced by contact in these pairs, in depositing 
 upon the surface of their metals foreign bodies, alters 
 their electro-motive faculty. But if things pass thus, the 
 nature of the electricity, taken by each metal of the pair, or 
 which comes to the same thing, the direction of the current 
 in the pile, ought to be the same at the first moment, what- 
 
 * Indeed, it follows, from the numerous experiments of Mr. Faraday in par- 
 ticular, that pairs formed of two different metals in contact are inactive even 
 when they are plunged into the best conducting liquid, if this liquid is incapable 
 of exercising a chemical action upon one or other of the metals of the pair ; such 
 are a pair of iron and platinum in a solution of sulphuret of potassium, a pair 
 cf iron and copper iii a solution of potash, &c. 
 
HAP. m. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 aver the liquid might be, since it could only depend upon 
 the relative nature of the two metals. Now, it is not so ; 
 otherwise the change in the polarity of the metals of the 
 pair takes place even when their surface is not altered, the 
 compound, that is formed, being dissolved in proportion to its 
 formation. Davy had already remarked the difference that 
 exists in the direction of the current, according as the liquid 
 conductor of a same pile is an acid solution or a liquid sul- 
 phuret. I have myself found a great number of similar 
 Bxamples ; and Faraday has so multiplied them, that it is im- 
 possible to see anything else in Volta's scale, as we have said, 
 than a classification of the metals, according to their degree 
 of affinity for oxygen. 
 
 The second objection is the production of electricity in a 
 single pair, without there being contact between the two 
 metals, of which it is composed. We have quoted many ex- 
 amples of them, such in particular as that of a plate of zinc 
 and a plate of platinum, which, plunged in acidulated water, 
 decompose iodide of potassium, that is placed between the two 
 plates at the place where they should have touched metalli- 
 cally, in order to produce electricity, according to the contact 
 theory.* We are able, in experiments of this kind, to add this 
 no less curious one of the production of the electric spark at 
 the moment when contact is established between the two 
 elements of a single pair. We are even able to render the 
 spark very powerful by plunging into diluted sulphuric acid, 
 two large cylindrical surfaces of copper, between which 
 is placed one of amalgamated zinc, and connecting the zinc 
 and the copper by means of two copper wires, which are 
 respectively soldered to them ; at' the moment when, one 
 being plunged into mercury, the other is plunged in, there is 
 a sharp spark ; the state of electric tension existed, therefore, 
 evidently before the contact df the two metals ; for, but for 
 this, there could not possibly have been production of elec- 
 tricity, nor consequently of spark at the moment of the 
 establishment of the contact; there could only have been 
 one at the rupture. 
 
 * Vol. II. p. 668. 
 VOL. II. 3 H 
 
834 SOURCES or ELECTRICITY. 
 
 PART 
 
 In the face of all these facts and of others of the same kind 
 with which electro-chemistry abounds, the partisans of the 
 contact theory not being able to deny the electro-motive 
 action of liquids in the voltaic pile, have come to extending 
 Volta's principle to the contact of liquids and solids ; and even 
 to admit that there is more electricity developed in the con- 
 tact of solids and liquids than in that of solids with each other. 
 Fechner, Karsten, Buff and Peclet have in particular done 
 this, dwelling upon their own experiments and upon others 
 made previously by M. Becquerel. We have already spoken 
 of Becquerel's experiments, as well as of those of Karsten 
 and Buff, in which the electricity liberated by plunging dif- 
 ferent solid substances into various liquids, is collected with the 
 condenser. We have seen that they were included in the 
 liberation of electricity which accompanies chemical actions. 
 However, we shall return to them in a moment, at the 
 same time that we shall speak of those of M. Peclet and of 
 some others, the results of which do not at first sight seem 
 in accordance with the laws, that regulate the chemical 
 production of electricity. We ought first to examine the 
 important question, to know, if there is or not an elec- 
 trical effect, resulting from the simple contact of two solid 
 bodies. 
 
 Volta was not content with establishing this principle in- 
 directly, in thus explaining both Galvani's experiment as well 
 as that of Sulzer, and also the development of electricity in 
 his pile. He had endeavoured to prove it by direct experi- 
 ments. The following are the three modes of operating 
 which he had devised, and which have been employed after 
 him. Equally in all, a condenser is employed, the copper 
 plates of which ought to be well gilded, in order to be pro- 
 tected against all oxidising action of the moist air. 
 
 The first mode consists in holding between the fingers, which 
 must be moist, in order to be conductors, a plate of zinc sol- 
 dered to a plate of copper, with which one of the plates of the 
 condenser is touched*, the other being placed in communication 
 
 * We may touch directly with the plate of zinc the plate of the condenser, 
 the latter serving as negative metal. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 835 
 
 with the ground. The touched plate is found to be charged 
 with negative electricity, the positive which the zinc has ac- 
 quired by its contact with the copper having passed into the 
 ground. We may in like manner place a moist conductor, such 
 as moistened paper, upon the plate of the condensers, and touch 
 it with the zinc, whilst we hold the plate of copper soldered 
 to the zinc ; the plate is then charged with positive electricity, 
 whilst the negative goes into the ground. It is easy to see that 
 these experiments are as well reconciled with the chemical 
 theory as with that of contact, if we have regard to the che- 
 mical action, that is exercised upon the zinc, either by the 
 moisture of the hand, or by that of the moist conductor. 
 
 The second mode of operating consists in having two in- 
 sulated discs, one of zinc, the other of copper, and placing 
 them in contact ; then, in separating them, and in carrying 
 one of them to the condenser, discharging the other ; after 
 having repeated this series of operations several times we 
 end, when the experiment has succeeded, which is very 
 rarely, in accumulating upon the plate of the condenser, 
 positive electricity, when it has been touched with the disc of 
 zinc, and with negative, when it has been touched with the 
 disc of copper. 
 
 The third mode, which has many relations with the second, 
 but which in general succeeds better, being less capricious, 
 consists in taking for plates of the condenser two discs of 
 a different nature, one of copper for example, and the other 
 of zinc, then in connecting them by means of a small metallic 
 arc, held by an insulating handle. This reunion being 
 accomplished and the arc removed, we find that the disc of 
 copper is charged with negative electricity, and that of zinc 
 with positive electricity. We should remark that, although 
 they may be superposed, the two discs have no other 
 metallic contact together than that which is brought about 
 by means of the insulated arc, on account of the layer of 
 varnish by which they are separated. 
 
 In the two latter modes of operation, we cannot, as in the 
 former, explain the production of electricity by the chemical 
 
 3 H 2 
 
836 SOURCES OF ELECTRICITY. PARTY. 
 
 action of a liquid upon one or other of the metals in contact, 
 since there is no liquid present. We are then obliged, in the 
 chemical theory, to have recourse to the chemical action of 
 the moist air. We see then how we may explain in this 
 manner the liberation of electricity, that takes place in the 
 third mode. We shall return again to the second. It is at 
 first easy to prove the necessity there is, in order to obtain 
 an electric effect, that the surface of one of the metals at 
 least shall be in contact with the air, or with an elastic fluid, 
 in default of a liquid. Pfaff and Fechner have indeed found 
 that, on placing the two plates of the condenser in vacuo or 
 in very dry oxygen, there was still an effect ; but we know 
 how difficult a matter it is, not to say an impossible one, to 
 get free in this way of all aqueous vapours. The most sure 
 means of avoiding all contact between the zinc and the 
 aqueous vapour is to cover its outer surface with a layer of 
 very thick varnish, after having taken the precaution of 
 soldering to the zinc a small rod of platinum, which permits 
 of the establishment of metallic communication between it 
 and the disc of copper. If the layer of varnish is sufficiently 
 thick, that the access of air or of moisture to the metallic 
 surface cannot take place in any point, it is in vain to establish 
 metallic communication between the disc of zinc and the 
 disc of copper, or to touch the platinum soldered to the zinc 
 with the finger, making the copper disc likewise communicate 
 with the ground ; no electric sign is obtained ; nevertheless, 
 according to the contact theory, the zinc ought to be charged 
 with positive electricity and the copper with negative. More 
 than this ; this disc of zinc thus varnished, having become 
 inactive, is able to serve as plate of the condenser as a plate 
 of gilded brass, when the platinum rod, which is soldered to 
 it, is placed in communication with an electric source ; which 
 proves that it is not for want of sensibility, that it manifests 
 no electric signs, when it is placed in contact with the copper. 
 Neither can we say that it is the contact with the zinc of the 
 gum-lac, of which the varnish is made, that modifies its 
 electric state ; since the gum-lac is insulating, and since more- 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 837 
 
 over the film of varnish similar, except that it is thinner, 
 which is upon its lower surface, does not modify it.* 
 
 Another proof of the necessity of this contact between the 
 surface of the zinc and the air or the surrounding moisture, 
 is that no electric sign is obtained on covering the entire 
 surface of the disc of zinc with a film of copper or still better 
 of gold. In other words, a plate made of gilded zinc becomes 
 altogether inactive. However, on touching the exterior sur- 
 face of this plate with the finger, I give escape into the 
 ground to the negative electricity with which the gold is 
 charged in its contact with the zinc, whilst the positive of the 
 zinc is disguised and condensed by the effect of the negative 
 electricity of the second plate of the condenser, which com- 
 municates with the ground. There ought therefore to be a 
 charge of positive electricity in the plate of gilded zinc, and 
 yet there is in it absolutely no electric sign. Care must be 
 taken that the film of gold, with which the surface of the zinc 
 is covered, shall be sufficiently thick to present no solution of 
 continuity, that permits the moist air to have access, even in 
 a point, to the surface of the zinc. 
 
 The necessity of an immediate contact between the surface 
 of the oxidisable metal and the more or less moist sur- 
 rounding air being well demonstrated, let us see how we may 
 explain the production of electricity in the chemical theory. 
 Let us take the case in which it is a disc of zinc, that forms 
 one of the plates of the condenser ; it would be the same for 
 every other metal, susceptible of oxidising. This disc polar- 
 ises the molecules of the film of moisture in contact with its 
 surface, as a plate of zinc polarises the molecules of water in 
 which it is immersed. At the moment when the zinc is 
 placed in contact with the copper disc of the condenser a pair 
 is constituted, a discharge is brought about, the negative elec- 
 
 * M. Pcclet claims to have still obtained electric signs, on covering the 
 surface of the zinc with several layers of gum- lac varnish ; but we cannot be 
 assured that the air has not had access, as far as the metal, by some solutions 
 of continuity, until the layer is sufficiently thick for the zinc to be no longer 
 visible. It is not necessary to increase the thickness of the layer of varnish, 
 that is upon the condensing surface of the plate, because the air has not access 
 to it, and, by increasing this thickness, we diminish the sensibility of the con- 
 denser. 
 
 r> H 3 
 
838 SOURCES OF ELECTRICITY. PART v* 
 
 tricity passes from the zinc into the copper in contact, the 
 zinc oxidises, and the positive electricity, having become free 
 being no longer able to escape, since the medium in which it 
 is liberated, instead of being, as in the case of a true voltaic 
 pair, liquid and a conductor, is gaseous and insulating, re- 
 mains at the very surface of the zinc, where it is con- 
 densed by the negative, that has passed into the copper 
 disc. Hence it happens that, on separating the two plates of 
 the condenser, we find positive electricity accumulated upon 
 the zinc, and negative upon the copper. 
 
 This explanation, which includes in a very simple manner 
 in the chemical theory the development of electricity, that 
 takes place in the case, in which we have just been occupied, 
 rests upon the supposition that one of the metals of which the 
 discs of the condenser are made, oxidises in the moist air, 
 and that this oxidation developes sufficient electricity to charge 
 the instrument. With regard to the first point, it is easy to 
 prove, we have merely to leave for a greater or less length 
 of time a metal whose surface is very polished in contact 
 with air even in appearance very dry, in order to perceive 
 that this surface is tarnished, and this, even when very slightly 
 oxidisable metals are in question, such as copper and silver. 
 With regard to the second, it follows, from the experiments 
 of Faraday and of Becquerel, made in an entirely different, 
 manner, and which we shall relate in the following paragraph 
 that the proportion in which it suffices that a metal shall ox- 
 idise, in order to liberate a quantity of electricity, capable of 
 charging a condenser, is infinitely small, since the decompo- 
 sition of a single milligramme (-015 grs. T.) of water re- 
 sulting from the oxidation of a quantity of metal equivalent 
 to about '06 grs. T. for the zinc, produces sufficient electricity 
 to charge 20,000 times a magic pane, the coated surfaces of 
 which still exceed a square yard, so that each charge shall 
 give a spark -393 in. in length, the oxidation of -015 grs. T. 
 of zinc, would therefore charge it only 5,000 times. Now, 
 in order to charge a condenser without sensible spark, 
 but only in a manmer to cause the gold leaves of the elec- 
 troscope to diverge, the pov^o o tn P art f ^ e charge, that 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 gives a spark of -3937 in., would suffice ; consequently, the 
 oxidation of -000015 gr. of zinc would produce sufficient elec- 
 tricity to charge the condenser 5,000 times. Hence we may 
 comprehend how difficult a matter it is to avoid the very 
 feeble oxidation, that is sufficient to produce the electricity, 
 that is detected by a condenser. We may further remark, 
 that the extent of the metallic surface, that is in contact with 
 the oxidising medium, exercises no influence over the charge 
 of the condenser, which depends, as we have seen, only upon 
 the intensity of the electro-motive force, which arises from 
 the mutual action of this medium and the metal : this ex- 
 plains why it needs but a few points of this surface to be in 
 contact with the medium, in order that the condenser may be 
 charged. 
 
 We may further add, that even although the positive metal 
 should not be susceptible of oxidising in the open air, in its 
 natural state, the fact that it is united metallically to^another 
 metal, which forms the second plate of the condenser, of 
 which it is itself the first, facilitates its oxidation, exactly in 
 the same manner as it is facilitated when this metal, plunged 
 in an electrolytic liquid, is united metallically with a metal 
 less attackable, which plunges into the same liquid.* The 
 only difference is, that there is merely a single discharge, 
 instead of a continuous current ; but we have proved that 
 this in no way changes the nature of the phenomena that 
 take place. f 
 
 It is useless now to quote the numerous experiments by 
 which Fechner, Pfaff, Belli, and so many others have en- 
 deavoured to demonstrate the truth of Volta's theory by 
 means of the third manner of operating, which we have 
 analysed ; since the result of these experiments is not in 
 
 * Vol. II. p. 676. 
 
 f It would be very interesting to combine an apparatus, that enables us to 
 charge and to discharge very rapidly and a great number of times consecu- 
 tively a condenser, of which one of the plates should be of very polished zinc ; 
 and to see if the plate would not be more oxidised than a similar plate left quite 
 insulated in the same medium. Moreover, the great rapidity with which the 
 metals, such as iron, oxidise in the air, when they are in contact with a less 
 oxidisiihle metal, such as lead or copper, allow of no doubt upon the result of 
 the experiment. 
 
 3 H 4 
 
840 SOURCES OF ELECTRICITY. PART v. 
 
 opposition to the chemical theory, as we have just demon- 
 strated. We shall dwell only upon certain facts which seem 
 to conform to it less easily. 
 
 M. Peltier, having taken for plates of a condenser, a disc 
 of gold and a disc of platinum, and having made them com- 
 municate by means of an insulated platinum wire, found that 
 the former was charged with positive electricity, and the 
 latter with negative electricity. Having then prepared four 
 glass discs, one covered with platinum foil, the second with 
 gold leaf, the third with silver leaf, and the fourth with tin 
 foil, he employed them, by combining them one with the other, 
 two and two, as plates of a condenser ; and he found, on placing 
 them in communication with a same source of electricity, 
 that some are more easily charged with negative electricity 
 than others ; whence he concludes, that there exists between 
 the metals a difference with regard to their faculty of coercing 
 the same electricity. Thus the four metals tried ought to 
 be placed in the following order, with regard to their faculty 
 of coercing negative electricity : platinum, silver, gold and 
 tin. M. Peltier had also concluded from his researches that, 
 in their state of natural equilibrium, the metals possess 
 different quantities of electricity, whether positive or negative, 
 according to their nature ; and that it is to this electricity, 
 inherent in the particles of the metals, and which is in- 
 separable from them, that the electric effects of contact 
 would be due, in which no trace of chemical action is per- 
 ceived. But it is easy to see that all the effects observed by 
 M. Peltier are due to an opposition between the electro- 
 motive forces of the sources, with which the condenser is 
 charged, and that which arises from the contact of the moist 
 air with the metals of which the plates of the condenser are 
 made. Nevertheless, the fact of the negative charge, that is 
 acquired by the platinum disc in its contact with the disc of 
 gold, deserves to fix for a moment our attention. 
 
 M. Becquerel has obtained the same result as Peltier ; but, 
 on the other side, on employing a condenser made of two 
 plates of platinum, he observed no electric sign, on touching 
 one of the plates with a plate of gold, held in one hand, and 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 841 
 
 touching the other plate with a finger moistened with distilled 
 water. In the case observed by M. Peltier, and verified by M. 
 Becquerel, it is not therefore the contact of the gold and the 
 platinum, that determines the electric charge. We are in- 
 debted to M. E. Becquerel for an experiment, which has put 
 us in the way to the true explanation of the fact in question. 
 A condenser, whose two plates are of platinum, gives no sign 
 on the electroscope, when they are touched with the finger ; 
 but if one of the plates is removed, and is plunged for a few 
 moments in hydrogen, we find, after having replaced it, and 
 having established metallic communication between the two 
 plates, that the one, which has been in the hydrogen, is 
 charged with positive electricity, and the other with negative. 
 This effect lasts for some time, then diminishes little by little, 
 in consequence of the plates remaining in the atmospheric air. 
 At each new immersion of the plate in hydrogen, the same 
 result is obtained. 
 
 This double property of platinum being sometimes positive, 
 sometimes negative, according as its surface is covered with 
 hydrogen or oxygen *, is due without any doubt to the 
 faculty that is possessed by this metal of bringing about the 
 combination of oxygen and hydrogen by its contact with 
 these gases, and even the decomposition of water, as in 
 Grove's gas pile, when it is in contact with one of these 
 gases and water. The disc covered with hydrogen behaves, 
 therefore, as a positive disc of zinc, that might form one 
 of the plates of the condenser, the other being a disc of 
 ordinary platinum. The platinum disc, that has not been 
 plunged in hydrogen, but simply in atmospheric air, condenses 
 at its surface oxygen, as we have established f ; whether this 
 gas forms a slight film of oxide, or remains in the gaseous 
 state upon the surface of the platinum, is of little importance ; 
 in every case, it acts under the influence of the platinum upon 
 the aqueous vapour in contact with it, and decomposes it ; it is 
 an effect of secondary polarity, analogous also to that, which 
 takes place in the gas-pile. It should follow from this, that 
 
 * We say oxygen, although it is in reality atmospheric air ; but this comes 
 to the same thing. 
 
 f Vol. II. p. 415. and the following. 
 
842 SOURCES OF ELECTRICITY. PART v. 
 
 the platinum disc, when it is placed in contact with a disc 
 of gold, these two discs, forming the plates of a condenser, 
 ought to give to this disc positive electricity, and retain the 
 negative. If the plates of the condenser are both similar 
 discs of platinum, and both of them consequently covered 
 with oxygen, there is no effect. The contact of a plate 
 of gold, that is held between the fingers, with one of the 
 discs, ought no longer to give rise to any electric sign, if our 
 explanation is exact, since the two platinum discs are always 
 identical ; now, this is precisely what arises contrary to what 
 ought to take place, if contact were the cause of the electri- 
 city, liberated in the case, in which the two discs are one of 
 gold, and the other of platinum. If the quantity of chemical 
 action is very feeble, let us not, on the other hand, lose sight 
 of how infinitely small is the quantity of electricity necessary 
 for charging the condenser. 
 
 It is to a cause of the same kind that must be attributed 
 the development of electricity, that takes place in the contact 
 of platinum, or of gold and of peroxides, such as that of lead 
 or of manganese. It is sufficient, in order to prove that it is 
 not an effect of contact, to place between the disc of the con- 
 denser and the peroxide a plate of thin wood, and still suffi- 
 ciently conducteous, although dried ; then, on touching the 
 peroxide with the moist finger, or with a piece of paper 
 steeped in an acid or an alkaline solution, the plate of the con- 
 denser is charged with positive electricity. It is charged 
 with negative on interposing between it and the peroxide 
 moistened paper, and on touching it with the piece of dry 
 wood, that is held between the fingers. Thus, in the chemical 
 action that is exerted by the peroxide of manganese, or that 
 of lead upon moist bodies, the positive electricity remains in 
 the peroxide, from which it passes into solid and conducting 
 bodies in contact with it, whilst the negative passes into the 
 moist bodies. The dynamic effects, to which the immersion 
 of a peroxide and a plate of platinum, fixed respectively to 
 the two extremities of a galvanometer, into pure water, 
 or still better into acidulated water, gives rise, are altogether 
 in accordance with the facts that we have been just describing, 
 
CHAP. ill. ELECTRICITY BY CHEMICAL ACTIONS. 843 
 
 as it results, as we have seen *, from the researches that M. 
 Becquerel and myself have made upon this subject. Mr. 
 Faraday has likewise arrived at the same conclusion, by 
 showing that bodies extremely charged with oxygen, such as 
 the peroxides, very freely exercise chemical actions, especially 
 when they form, as in the cases, which have just engaged our 
 attention, one of the elements of a pair. With regard to the 
 platinum, we know that, even when the quantity of oxygen 
 condensed upon its surface is very feeble, it always behaves 
 in all phenomena of this order as a body quite ready to part 
 with its oxygen.f 
 
 It appears to us, therefore, well established that, in the 
 contact of two solid bodies, the electricity developed is not 
 due to the fact of this contact; since, when we succeed 
 in avoiding all chemical action, which is very difficult, it is 
 true, there is no electric sign, even when all the conditions 
 necessary to there being one in the contact theory are united. 
 It is clear that we must also avoid the other actions, that may 
 give rise to electricity, such as calorific and mechanical 
 actions. Indeed, we have seen, when engaged with thermo- 
 electricity, that the contact of a hot and of a cold body produces 
 an electric current ; but this effect is in no degree due to the 
 contact, which is here, as in the electricity engaged by chemi- 
 cal actions, only a manner of permitting the electricity, de- 
 veloped by the molecular changes that accompany the 
 propagation of heat to manifest themselves. We must like- 
 wise avoid, in the contact of bodies, the mechanical actions, 
 which, in themselves producing electricity, may give rise to 
 errors ; it is especially when we operate according to the 
 second mode pointed out by Volta, by placing in contact discs 
 held by insulating handles, that this precaution is necessary, 
 as we are about to see, when occupying ourselves with this 
 mode.J 
 
 Vol. II. p. 681. 
 
 t Vol. II. p. 415. and following pages. 
 
 j However, we must also have regard to this cause of error, when we ope- 
 rate according to the first mode, by holding between the fingers the bodies that 
 are placed in contact with one of the plates of the condenser. We know in 
 fact that the very slightest friction, exercised upon this body by the fingers, 
 especially when they are dry, is sufficient to liberate a very considerable quan- 
 ity (sec above, p. 605.) 
 
844 SOURCES OF ELECTRICITY. PART v. 
 
 The mode in question consists therefore of placing in 
 contact several times in succession an insulated disc of zinc 
 and one of copper, each time bringing one of them to the 
 condenser, whilst the other is discharged. Fechner has re- 
 marked that, if one of the two discs, that of zinc for example, 
 is fixed to an electroscope, and the other, that of copper, is 
 placed above, as the second plate of a condenser, but without 
 an insulating stratum, a very sensible positive electricity is 
 obtained on the electroscope on raising the copper disc, whilst 
 when they are in contact, there are no sensible electrical signs, 
 even when the copper communicates with the ground. Pfaff and 
 Peclet attribute this effect to the fact, that the two discs, not 
 being very smooth, they are in contact only in certain points, 
 and that every where else they are separated by a stratum of air, 
 which fills the office of insulating stratum, so that there is a 
 condenser. M. Peclet has observed several facts which have 
 proved to him that discs in contact may behave as air con- 
 densers ; he has remarked that, if they are very smooth, so 
 that there is difficulty in separating them, a proof that there 
 is no film of air interposed, there is no electricity developed, 
 whilst there is a notable production if their surfaces are 
 ground with emery and deformed so as to be no longer smooth. 
 MM. Fechner and Buff cannot agree with the explanation of 
 Pfaff and Peclet ; they are rather disposed to admit, on the 
 contrary, that it is especially at the points of contact that the 
 accumulation and condensation of the electricity are the most 
 considerable, Fechner having remarked, contrary to Peclet, 
 that the electricities are condensed more in proportion as the 
 two faces are polished. But these differences possess little 
 importance in opposition to the fact observed by Mr. Grove, 
 namely, that the experiment of the two discs succeeds equally 
 well, even when there is no metallic contact between the 
 discs, which he obtains by placing between them a thin ring 
 of card, which does not prevent of their approaching as 
 much as possible toward each other, but still avoiding 
 metallic contact. We have thus a true condenser with a 
 plate of air for insulating stratum, only we make neither of 
 the two discs communicate with the ground, which makes it 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 845 
 
 necessary for them to be brought several times to each other 
 in order to charge a true condenser. It is of little import- 
 ance therefore whether the discs act as condensers ; as we are, 
 however, inclined to believe in the experiments of Fechner 
 and Peclet, the cause of the liberation is not the less the 
 same as in the experiments made with condensers, the plates 
 of which are of two different metals ; we have therefore no 
 need to return to it. 
 
 But, as we have said, it is important, in this mode of oper- 
 ating, to avoid mechanical actions and particularly friction, 
 which may give rise to grave errors upon the origin of the 
 electricity liberated. M. Becquerel has shown this, on 
 repeating the experiments from which Davy had thought he 
 could conclude that metals could acquire positive electricity 
 in their contact with the acids, and negative electricity in 
 their contact with the alkalies; the acids and the alkalies 
 acquiring contrary electricities to those of the metals. Davy 
 operated with solid acids and alkalies, such as oxalic acid, 
 succinic acid, and boracic acid, dry lime, magnesia or 
 strontian ; the metals were copper, zinc, tin, held by insulating 
 handles. These facts, from which Davy had thought he 
 could deduce important consequences on the nature of the 
 electricity inherent to acids and to bases, were only effects of 
 friction, as Becquerel has proved. He has adapted to a very 
 sensitive electroscope a condenser formed of discs of platinum; 
 he never obtained any effect on placing upon one of the 
 plates of the condenser a piece of very dry lime held between 
 the fingers, and on touching the other plate also with the 
 finger. He then placed the piece of lime upon a plank of 
 very dry wood, then he carefully placed upon it without 
 exciting friction, a copper disc held by an insulating handle ; 
 he withdrew it, then placed it in contact with one of the 
 plates of the condenser, touching the other with the finger. 
 On repeating similar contacts a certain number of times, he 
 never obtained any electric charge ; but if, instead of placing 
 the disc of copper upon the lime with precaution, it is placed 
 with friction, we succeed in charging the condenser after a 
 small number of contacts; the entire charge is the more 
 
846 
 
 SOURCES OF ELP:CTRICITY. 
 
 marked as the friction has been stronger ; the lime acquires 
 positive electricity, and the metals negative. On substituting 
 for the lime one of the acids above mentioned, a charge of 
 electricity is in like manner obtained by friction and not by 
 simple contact ; in this case, the metal acquires positive elec- 
 tricity, and the acid negative. It is therefore well demon- 
 strated, that the results obtained by Davy are due to electric 
 effects of friction, and not to Volta's electro-motive action. 
 
 The analysis, that we have been making of the electric 
 effects, that are manifested in the contact of two solid bodies, 
 confirms the conclusion that we have drawn from facts of 
 quite another order ; namely, that, in a voltaic pair, the origin 
 of the electricity is not in the contact of the two metals, of 
 which the pair is formed. It is therefore in the action, that 
 takes place at the contact of the liquid and the metals. The 
 following is an interesting experiment of Peltier's, which 
 shows in an evident manner where the seat of the origin of 
 the electricity is situated in a pair. 
 
 The extremities of a zinc and copper pair (fig. 325.) are 
 
 Fig. 325. 
 
 plunged into two vessels, separated and well insulated, and filled 
 with the same liquid. The end of a platinum wire d is first im- 
 mersed in the vessel A, that has received the zinc, and the other 
 end of the wire communicates with the ground. By means of 
 another platinum wire e, which is held insulated by a handle of 
 gum-lac/, the zinc, the copper and the liquid of the vessel B, that 
 has received the copper, are placed successively in communica- 
 tion with one of the condensing plates g of an electrometer h. 
 According to this arrangement the liquid is unable to possess 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 847 
 
 free electricity, since it communicates with the ground ; 
 neither ought the zinc to possess any, since the electro-motive 
 force, according to the theory of Volta, is at the contact of 
 the zinc and the copper. It is not thus that the distribution 
 is brought about ; the liquid of the vessel A is neutral ; but 
 the zinc, the copper, and the liquid B are negative in the 
 same degree. The end d, of the platinum wire communicating 
 with the ground, is then placed in the vessel B, and the copper, 
 the zinc and the liquid of the vessel A, which is then insulated, 
 are interrupted in the same manner, by means of the insulated 
 platinum wire e. The liquid of B is necessarily neutral, as 
 well as the copper that is plunged into it ; but it is the same 
 with the zinc, which is equally neutral : the water alone of 
 the vessel A is positive. This experiment proves, therefore, 
 that the electricity is not produced at the contact of the two 
 metals ; but rather at the contact between the acidulated 
 liquid A, and the portion of zinc that is immersed in it. 
 
 The partisans of the contact theory have therefore been 
 led to establish that it is in the contact of liquids and solids 
 that the principal source of electricity resides; but still 
 without recognising that the chemical action, which takes 
 place between the solid and the liquid was the cause of the 
 electricity liberated, admitting that it is simply its effect. 
 Numerous experiments have been made upon the production 
 of electricity, that takes place in the contact of solids and 
 liquids; we have already cited those of Becquerel, which are 
 the most ancient, and those of Karsten and Buff. We may 
 call to mind that those of Becquerel consisted in placing 
 upon the plate of the condenser a metal capsule, what was 
 filled with different liquids, into which various metals held 
 between the fingers were plunged. When the capsule was 
 of platinum, whatever was the metal employed, and whatever 
 was the solution, acid or alkaline, the liquid was always 
 charged with positive electricity, which passed through the 
 platinum capsule, and charged the condenser. When the 
 capsule was of copper, it acquired positive electricity, if (the 
 solution being acid or alkaline) the plunged metals were 
 zinc or iron ; it acquired negative if, in the same solutions, 
 
848 SOURCES OF ELECTRICITY. PARTY. 
 
 the immersed metals were platinum, gold, or silver. All 
 these effects are perfectly in accordance with the chemical 
 theory. With regard to the effects observed by M. Karsten, 
 they also enter into the same theory ; but we shall not dwell 
 upon those which (of the same kind as the results obtained 
 by Becquerel) have already equally been the subject of our 
 examination; the others have been obtained by combining 
 the electricity produced by the immersion of zinc and copper 
 pairs in liquids more or less acid, with that developed upon 
 condensers, of which one of the plates was zinc, and the 
 other copper. Effects of a more or less complex character 
 are the result of this, the explanation of which is easily 
 found by means of the principles that we have established 
 in what precedes ; and upon which consequently it is useless 
 for us to insist. We may only remark, that the electro- 
 motive or polarising force, which arises from the contact of 
 a metal, as zinc with the simple vapour of water, is able to 
 contend against that, which arises from the contact of the 
 same metal with pure water, but is inferior to that which is 
 manifested when the water is acid, alkaline, or saline. This 
 important principle must not be lost sight of when we are 
 endeavouring to reconcile with the chemical theory facts, 
 such as some of those observed by Karsten, which have 
 frequently been put forward as contrary to this theory. 
 
 Among the philosophers who have been much occupied 
 with the electricity liberated in the contact of solids and 
 liquids, we have cited M. Peclet. This philosopher operated 
 either with an ordinary condenser, or, for cases in which 
 the electricity was feeble, with his multiplier-condenser, that 
 we have described.* He touched the upper plate with the 
 metal, and collected the electricity of the lower, so that the 
 electricity given by the metal, was of a contrary sign to that 
 which had been collected. In order to have the action of the 
 same liquid upon the metal, he took each metal between his 
 fingers, after having moistened them with each of the liquids 
 successively. The following is a Table, that contains the 
 results of his experiments. We have chosen it among all 
 Vol. I. p. 107. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 
 
 849 
 
 those, which have been drawn out on this same subject, by 
 various philosophers, as the most exact and the most com- 
 plete. 
 
 
 g 
 
 a 
 
 | 
 
 j 
 
 a 
 
 H 
 
 | 
 
 | 
 
 J 
 
 } 
 
 1 
 
 I 
 
 1 
 
 I 
 
 1 
 
 1 
 
 Pure water. - 
 
 +26 
 
 +26 
 
 + 17-5 
 
 + 15 
 
 + 11-5 
 
 +87 
 
 +7-3 
 
 +7-3 
 
 + 10 
 
 
 
 
 
 -15 
 
 Diluted sulphuric 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 acid - - - 
 
 +27 
 
 +27 
 
 + 14 
 
 416 
 
 + 13 
 
 +7 
 
 + 4 
 
 +2-5 
 
 +3 
 
 ,, 
 
 -fi 
 
 -4 
 
 ~3 
 
 -20 
 
 Diluted nitric acid 
 
 +26 
 
 +21 
 
 + 13 
 
 + 12 
 
 + 8 
 
 
 + 1 
 
 
 +0-5 
 
 -2 
 
 -4 
 
 -4 
 
 -3 
 
 -21 
 
 Hydro-chloric acid 
 
 + 26 
 
 + 20 
 
 + 3 
 
 + 12 
 
 + 11 
 
 +5 
 
 + 5 
 
 +5 
 
 +6 
 
 -3 
 
 > 
 
 -0-3 
 
 -4 
 
 -21 
 
 Aqua regia - 
 
 +27 
 
 + 16 
 
 + 15 
 
 
 + 12 
 
 +6 
 
 + 3 
 
 +3 
 
 + 4 
 
 + 2 
 
 -4 
 
 -4 
 
 -4 
 
 -19 
 
 Solution of potash 
 Ammonia 
 
 +30 
 
 +38 
 
 + 28 
 +26 
 
 +24 
 
 + 22 
 
 + 28 
 
 + 22 
 
 + 195 
 + 13 
 
 +21 : 
 + 16 
 
 * 1-7 
 
 + 10-5 
 
 -11-r 
 + 11-5 
 
 + 10 
 +8 
 
 +35 
 +3-5 
 
 +5 
 +4 
 
 + 5 
 +4 
 
 + 4 
 +3 
 
 -7 
 -4 
 
 Sulph-hydrate of 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 potash 
 
 +30 
 
 +35 
 
 + 17-5 
 
 +24 
 
 + 17-5 
 
 +20 
 
 + 18 
 
 +22-5 
 
 + 20 
 
 +22'5 
 
 + 17 
 
 + 17 
 
 + 13 
 
 +5 
 
 Solution of sea-salt 
 
 + 2" 
 
 +22 
 
 + 14 
 
 + 15 
 
 + 15 
 
 +7 
 
 + 6 
 
 +6 
 
 +6 
 
 + 2-5 
 
 M 
 
 -4 
 
 -2 
 
 -13 
 
 Alcohol 
 
 + 26 
 
 + 22 
 
 + 135 
 
 + 13-5 
 
 + 6-0 
 
 +7 
 
 + 4 
 
 +5 
 
 +3 
 
 M 
 
 
 
 M 
 
 N 
 
 -9-15 
 
 Olive oil 
 
 + 35 
 
 + 125 
 
 + 20 
 
 +0 
 
 + 9 
 
 4-10 
 
 + 7'5 
 
 + 7'5 
 
 +5 
 
 
 
 
 
 -10 
 
 Oil of naphtha 
 
 +24 
 
 + 12-5 
 
 + 13-5 
 
 + 14-5 
 
 + 10 
 
 +7'5 
 
 + 9 
 
 +3'5 
 
 +4'5 
 
 
 
 " 
 
 
 
 " 
 
 -11 
 
 We see from this Table that in general, save rare excep- 
 tions, the electricity collected was always positive, which 
 indicates that that given by the metal to the condenser was 
 negative, and that consequently this metal was attacked by 
 the liquid, with which the fingers were moistened. The 
 peroxide of manganese alone presents an exception ; but this 
 is due, as we have said, to the fact that the chemical action 
 which takes place in its contact with liquids is a deoxidation ; 
 and consequently ought to produce an electricity, contrary to 
 that which results from oxidation.* Silver, platinum, gold, 
 and carbon, also gave with acidulated water, electric signs, 
 contrary to those which would have been produced had their 
 oxidation taken place ; these signs are, it is true, very feeble ; 
 and the assistance of a multiplier-condenser was necessary in 
 order to collect them. They are evidently the result of the 
 action that is exercised upon the fingers themselves by the 
 slightly acid liquid with which they are moistened, an 
 action which is not counterbalanced, in the case in which the 
 
 * There is only one case in which the peroxide of manganese transmits nega- 
 tive electricity to the upper plate, and consequently positive to the lower ; it 
 is that in which it is in contact with sulf-hydrate of potash. This is due to the 
 particular nature of the chemical action, which takes place in this case, an action 
 probably very complicated, because there is at the same time a decomposition 
 of the peroxide and of the sulf-hydrate. 
 
 VOL. II. 3 I 
 
850 SOURCES OF ELECTRICITY. PART v. 
 
 metals are but little or not at all oxidizable, by that which 
 these metals themselves suffer. The positive electricity, 
 taken by the acidulated water in its action upon the finger, 
 is transmitted by the intervention of the metal to the upper 
 plate of the condenser, and charges the lower with negative 
 electricity, as is shown by experiment. 
 
 The effects obtained with alcohol and especially with olive 
 oil and with oil of naphtha, appear at the first moment sur- 
 prising, considering the nature of these substances ; but it is 
 evident that they do not moisten the fingers sufficiently to 
 form an insulating film ; but for this there would be no 
 electric signs, since there would be no communication with 
 the ground ; the oils form probably with the alkaline trans- 
 piration, with which the fingers are in general moistened, 
 a compound that is a conductor, and that acts upon the 
 metals ; an action, which is very far from being null, as 
 we are every day assured, by observing the metallic rusts 
 that are impregnated with oil. 
 
 Let us remark in passing, that in the electric effects of 
 contact, we should have done wrong, when such feeble 
 electric signs are in question, not to have taken sufficient 
 account of the electricity that results from the chemical 
 action upon and by the fingers, that are employed in the 
 experiments. We have already remarked the important 
 part that is played by this action in the development of the 
 electricity, that is obtained on touching a condenser by a 
 metal, held between the fingers ; we have just seen in 
 Peclet's experiments the effect that results from the action 
 upon the fingers of certain liquids. We shall see hereafter, 
 when occupying ourselves with animal electricity, how im- 
 portant it is to have regard to this cause of production of 
 electricity, if we would avoid falling into grave errors. 
 
 We have said that M. Buff has also made numerous 
 researches upon the electricity developed in the contact of 
 metals and of liquids. We have already spoken of effects 
 of this nature, which he had obtained in the experiments, 
 wherein he had demonstrated that evaporation is not itself a 
 source of electricity ; but that it serves merely to render 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 851 
 
 more perceptible, by the conducting faculty of the vapour 
 formed, the electricity liberated by the action of a liquid 
 upon a metal. Like Karsten, he had remarked that, on 
 collecting the negative electricity arising from a zinc wire, 
 immersed in the liquid, with a zinc condenser, he obtained 
 less effect than when the conductor was of copper ; which is 
 due, as we have said, to the opposition of the two electro- 
 motive forces, exerted one by the solution upon the zinc, 
 that is immersed in it, and the other by the moist air upon 
 the plate of zinc. On placing successively, upon condensers 
 made of various metals, liquids of various natures, he had 
 obtained results analogous to those of Becquerel and of 
 Peclet ; and he had deduced from them consequences, alto- 
 gether in opposition to the law of the voltaic series of electric 
 tensions. He had been thus led to connect the electro-motive 
 force with the chemical affinity of the metal for the radical 
 of the compound liquid, with which it is in contact ; and con- 
 sequently to see in the development of voltaic electricity, 
 a chemical phenomenon and not a simple effect of contact. 
 
 To sum up, it seems to us to result from the numerous 
 researches, that have been made upon the cause of voltaic 
 electricity ; researches of which we have been enabled to 
 give only a summary extract; that, in order that this 
 electricity may be developed as well under the static as 
 under the dynamic form, it is necessary that there shall be 
 a chemical relation between the bodies in contact, a relation 
 such that one of them is able to enter into combination with 
 the other, or at least with one of the elements of the other. 
 
 It remains for us now to demonstrate that dry piles are 
 not an exception to this principle, and that it is truly 
 chemical action, and not contact, as has been pretended, 
 which is the origin of their electric power. 
 
 We have already described summarily dry piles * ; we 
 may add to what we have already said upon this subject, 
 that the fundamental idea of dry piles rested upon the 
 voltaic theory of the pile. It was hoped there might be 
 found, for separating the pairs, a conductor at the same time 
 
 * Vol. I. p. 52. 
 3 I 2 
 
852 SOURCES OF ELECTRICITY. PART v. 
 
 not a liquid, and not an electro-motor, in such sort that the 
 pile might have continually given electricity, without 
 sensibly altering ; it was, to speak frankly, seeking to 
 realise the idea of perpetual motion, to hope to produce a 
 constant force by a simple arrangement of substances without 
 corresponding expense or work. The results have also been 
 as poor as the principle was vicious. Piles have been 
 obtained, the power of which was able to last for a very 
 long time, still however having a limit ; but it was at the 
 same time very restricted ; since these piles gave only the 
 effects of tension, and were incapable of producing currents, 
 save in certain exceptional cases. 
 
 The first dry pile was constructed by Behrens in 1805 ; it 
 was composed of eighty pairs of zinc, copper and gilded 
 paper; Deluc in 1810 made several attempts of the same 
 kind, and succeeded in uniting 800 pairs, formed with discs 
 even of tinned iron and of gilded paper ; the tinned iron and 
 the gilding of the paper formed the two metals of the pair, 
 and the paper was its moist conductor. This pile caused the 
 leaves of an electroscope to diverge powerfully at its poles. 
 Finally, Zamboni in 1812, constructed the dry pile according 
 to the mode, which has been generally adopted, namely, by 
 forming it of the super-position of a very great number 
 of discs, made of paper, covered on one of their sides with a 
 thin layer of tin, and on the other with a layer of peroxide of 
 manganese in fine powder, fixed upon the paper by honey or 
 starch paste. A pile formed of 2000 pairs of this kind gives 
 small sparks, is able to charge a Leyden jar, &c. With simi- 
 lar piles placed vertically, one beside the other, at a little dis- 
 tance apart, and so that their opposite poles are facing, a 
 continuous backward and forward motion may be imparted to 
 a small insulated pendulum, that oscillates between the two 
 contrary poles. All dry piles, we have said, lose their power 
 with time ; but those which last longest, at the same time 
 being less powerful than those of Zamboni, are piles con- 
 structed with superposed discs of Dutch-silver paper, and 
 Dutch-gold paper. We must stick together by the surface, 
 where the paper is bare, the discs of different species, so that 
 on super-posing them, we have, for example, Dutch-gold, 
 
CHAP. III. ELECTRICITY BY CHEMICAL ACTIONS. 853 
 
 paper, Dutch-silver, Dutch-gold, paper, and so on, taking 
 care always to observe the same order. The discs are 
 attached together by means of cords made of a very pure 
 silk, so that it may be very insulating, and well impregnated 
 with varnish ; we may also elevate the pile between varnished 
 rods of glass, and press it by means of a screw en- 
 closing it in tubes of varnished glass, of which the bottom 
 whereon the first disc rests is metallic, whilst the last disc is 
 pressed by a metallic screw, terminated exteriorly by 
 a ball. The size of the discs influences the velocity 
 with which the pile is charged; but is without influ- 
 ence upon the tension of its poles. M. Riess, with four 
 piles of this kind, each of 2,230 pairs of an inch in dia- 
 meter, obtained as a mean, on placing them one beside 
 the other, so that their contrary poles were opposite, ninety- 
 six small sparks of -0049 in. in length, per minute. Four 
 months after they had been constructed, they gave no more 
 than forty-eight sparks per minute. Jager and Singer, who 
 have been much occupied with dry piles, had succeeded not 
 only in producing by their means, powerful movements of 
 attraction and repulsion, as well as sparks, but also in 
 charging Ley den jars ; however, they had not succeeded in 
 obtaining chemical decompositions, nor effects of deviation on 
 the magnetised needle or contractions of the frog properly 
 prepared. However, Dubois-Reymond has obtained these 
 last two kinds of effect with a pile of 1800 discs, similar 
 moreover to those which Riess employed. It was necessary 
 that the frog should be freshly prepared ; and with regard to 
 the multiplier, it was of 24,160 turns, and it indicated a de- 
 viation of only a few degrees. Riess, on his side, has decom- 
 posed iodide of potassium, sulphate of soda, and nitrate of 
 baryta, with an old dry pile of small dimensions. 
 
 M. Peltier, and more recently M. Delezenne have easily 
 obtained the decomposition of water, by means of dry piles, by 
 giving to their discs a large surface, so as thus to diminish the 
 resistance. M. Delezenne, in particular, employed piles of 2000 
 pairs, each pair being a rectangle of 12J in. in length by 7 in. 
 in width. The pairs of these piles were of paper, tinned on 
 
 3 i 3 
 
854 SOURCES OF ELECTRICITY. PART v. 
 
 one side, and covered on its other face with peroxide of man- 
 ganese, rubbed in gelatine in fusion. If the number of pairs 
 is too considerable, sparks are obtained ; but, according to 
 Peltier, there are no calorific effects, nor decompositions ; 
 however, Delezenne has easily decomposed water with piles of 
 2600 and of 4000 pairs. The same philosopher has made 
 a great number of experiments, in order to demonstrate the 
 necessity that the paper of the discs should not be too dry ; 
 he moistened them with salt water, so as to obtain the 
 presence of the salt, which on maintaining their moisture, in- 
 creased their electric power ; he then powerfully dried the 
 piles by placing them in ovens which at first increased 
 their power, probably on account of the fusion of the 
 gelatine glue, but which afterwards greatly reduced it, 
 the glue having become solid again, by the effect of the ab- 
 sence of moisture. Finally, he saw that in order to maintain 
 a tolerably considerable power in the pile, it was necessary 
 from time to time to renew the stratum of peroxide of man- 
 ganese which was evidently deoxidised, and he perceived that 
 the tinned face was slightly oxidised. 
 
 All observers have agreed in recognising that moisture is 
 necessary, in order to preserve to dry piles their activity. 
 An experiment of Ermann's, confirmed by Jager and by 
 Parrot, proves this in an evident manner. A very active 
 dry pile, having been placed in a vessel, the air of which 
 had been completely dried by chloride of calcium, entirely 
 lost its force in a few hours, and recovered it again in the 
 moist air. Parrot made a great number of experiments, in 
 which the dry piles were rendered alternately inactive or 
 active, accordingly as they were placed in dried or in moist 
 air. However we must not conclude from the fact of 
 moisture being indispensable to the dry pile, in order to pro- 
 duce its electric effect, that it is in very moist air that this 
 effect is the most powerful ; for there is then a defect of insu- 
 lation, which militates against electric manifestations. 
 
 We may add that Jager has constructed dry piles, by in- 
 terposing between the metal layers in contact layers of resin 
 or of silk ; but these piles are only a series of condensers, 
 which have no relation with the pile properly so called, 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 855 
 
 and for the action of which the moisture of the air is 
 nevertheless always necessary. 
 
 Watkins succeeded also in constructing a dry pile with a 
 single metal, presenting it is true two different surfaces. 
 It is composed of 60 or 80 plates of zinc of about 4 
 square inches of surface, cleaned and polished on one of 
 their faces and not on the other. They are fixed in a 
 wooden trough, parallel to each other, at only J^- of an 
 inch distant from each other, the polished faces being all 
 turned on the same side. The two extremities or poles of 
 this pile give very decided signs of electric tension, of a 
 nature to indicate that the polished face plays the part of 
 positive metal, and the unpolished that of negative metal. 
 The humidity of the air favours the development of elec- 
 tricity in this pile, in which the thin stratum of air, by which 
 the plates are separated, plays the part of moist conductor, 
 like the paper in the ordinary dry piles, which is perfectly in 
 accordance with the manner in which we have explained the 
 liberation of electricity in condensers, of which one of the 
 plates is of zinc and the other of copper, or of zinc covered 
 with a layer of varnish, sufficiently thick for the air not to 
 be able to penetrate as far as its surface. 
 
 It is not necessary to insist long, in order to show that dry 
 piles are all equally apparatus, in which the development of 
 the electricity is due to a chemical action exercised by the 
 paper, as by the moist air upon the substances, whose union 
 constitutes the pairs. With regard to the nature of the 
 effects, that they are susceptible of producing, it depends 
 especially upon the very considerable resistance to conducti- 
 bility, that is presented by these piles, even more than upon 
 their electro-motive forces, which are tolerably energetic. 
 These piles have a certain relation to water piles, such as 
 that of Gassiot's of 3520 pairs, which have much tension, 
 but do not give very considerable dynamic effects, on 
 account of the great resistance which they present to the 
 circulation of the current. Now, as we have seen, Gassiot 
 has very well established the chemical theory of his water- 
 pile ; and in like manner as the presence of moisture is 
 
 3 I 4 
 
856 SOURCES OF ELECTRICITY. PARTY 
 
 necessary to the dry pile in order to its being in action, so 
 also the presence of air or rather of oxygen is indispensable 
 to the water-pile ; because like as dry air is not able to act 
 chemically on the majority of the metals, so also water 
 deprived of oxygen is equally without action ; a proof, 
 equally in both cases, of the necessity of a chemical action. 
 
 Relations between Electricity and Chemical Actions. Electro- 
 chemical Theories. 
 
 Let us consider a voltaic pile, the closed circuit of which 
 includes a voltameter ; suppose that this pile is fig. 308., so 
 constructed, that we collect the hydrogen liberated at each 
 pair, and are able to estimate the quantity of zinc oxidised. 
 Two orders of phenomena are presented to us in this circuit ; 
 an equivalent chemical action exercised wherever there is a 
 liquid conductor susceptible of being decomposed, a pro- 
 duction of electricity, which is manifested exteriorly by the 
 influence, that is exercised upon a magnetised needle by all 
 the parts of the circuit. The arrangement given to the va- 
 rious metallic and liquid parts of which the pile is composed, 
 permit at the same time of the exercise of affinity, and of 
 the production of electricity, that accompanies it. It is 
 evident that the origin of these two forces is in the surface 
 of contact of the zincs, and the liquid, and that the equi- 
 valent chemical action, which takes place in the voltameter, 
 is only the result of the action at a distance of affinity. 
 Indeed, when once all the parts of the circuit, the solids as 
 well as the liquids, are polarised by the combined action of 
 all the zincs upon the electrolytic liquid by which they are 
 bathed, it is necessary, in order that the discharge may take 
 place, and that the water may be decomposed between the 
 metals of each pair, that it be also decomposed between the 
 two platinum electrodes of the voltameter; otherwise the 
 circuit would not be closed. But then, there is a resistance 
 to be overcome, since of themselves the two electrodes are 
 without action upon the liquid of the voltameter. This re- 
 sistance is surmounted by the electromotive force, the 
 intensity of which depends upon the relative nature of the 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 857 
 
 liquids and metals of the pair, and on the number of these 
 pairs. It is true that it varies also for a same electro-motive 
 force, with the nature of the metal of which the electrodes 
 of the voltameter are made. It is clear that if the positive 
 electrode is of zinc, the negative remaining of platinum, not 
 only is there no longer any resistance, but there is an in- 
 crease in the electro-motive force, since there is one pair 
 more. If the electrodes are both of zinc, or of a similar 
 oxidisable metal, it seems that the resistance ought to be the 
 same as with platinum electrodes, because the two zincs 
 tend to polarise the electrolytic liquid in contrary directions 
 with a same intensity ; and that consequently, their effect, 
 in respect to the facility introduced for the decomposition of 
 the liquid, is annihilated. However, things do not take place 
 in this way, and this is due to the circumstance that the 
 oxygen, which is liberated at the positive electrode, instead 
 of forming, as upon the platinum, an adhering film, which 
 hinders the passage of the current and produces a secondary 
 polarity, combines with the metal of the electrode, forming an 
 oxide, which is dissolved. With regard to the hydrogen, that 
 is liberated at the negative electrode, it is in general likewise 
 absorbed by the reduction of this electrode, which is most 
 commonly oxidised, or by its combination, under the influence 
 of the electrode, with the dissolved oxygen. However it is 
 principally at the positive electrode that the advantage is felt, 
 for the propagation of the current in the circuit, of taking for 
 this electrode, a substance, capable of combining with the 
 element of the electrolytic liquid that is liberated, forming 
 with it a compound soluble in this liquid. 
 
 There is, therefore, in a voltaic circuit, of which the volta- 
 meter forms part, decomposition of water in each of the 
 pairs and in the voltameter. These two orders of decompo- 
 sition are equally the result of the affinity for oxygen of the 
 positive metal of the pair. If this affinity is very powerful, 
 as that of potassium or of sodium, a single pair, amalgam 
 of potassium, and water acidulated with sulphuric acid, is 
 sufficient to decompose the acidulated water of the pair, and 
 the same water placed between two platinum electrodes ; 
 
858 SOURCES OF ELECTRICITY. PART v. 
 
 indeed, affinity, according to the arrangement of the circuit, 
 can be exercised only so long as the liquid of the pair, and 
 that of the voltameter are both decomposed. If it is less 
 powerful, as is the case when, instead of potassium, we have 
 zinc, then we must add to that, which is exercised by one pair, 
 that of a second or of a third, in order to decompose 
 the liquid of the voltameter. If we suppose, therefore, what 
 appears from all the experiments probable, that in a pair 
 wherein there is only one active metal, the electro-motive 
 force is proportional to the affinity of this metal, for one 
 of the elements of the electrolytic liquid of the pair *, we 
 shall have in the number of pairs necessary for overcoming a 
 given affinity (that of the oxygen and hydrogen of a water, 
 always acidulated to a same degree,) a very exact expression 
 of the force of affinity. 
 
 It is to be remarked that the voltaic combination must 
 always be of such a nature that, when the two metals of the 
 pair are united by a metallic conductor, the liquid by which 
 they are separated, is decomposed by the affinity of one of its 
 elements for one of the metals ; otherwise we should in vain 
 add any number to each other, we should never obtain 
 either current or decomposition of water in the voltameter. 
 It is important that the liquid, with which the voltameter is 
 charged, shall be always entirely the same ; for if it changed in 
 such a manner as to be more or less easy of decomposition, we 
 understand that the comparison between the different voltaic 
 combinations in respect to electro- motive force, and conse- 
 quently to affinity, would be impossible. It is necessary also 
 that in the pairs themselves, one of the metals should always 
 be inactive ; for otherwise the results would become complex. 
 Thus, with pairs, copper and zinc in diluted sulphuric acid, 
 we should have the measure, not of the affinity of oxygen 
 for zinc, but of the difference between the affinity of oxygen 
 for zinc, and that of oxygen for copper. With pairs of 
 platinum covered with peroxide of lead and zinc in diluted 
 sulphuric acid, we should have the means of the sum of the 
 
 * We must not forget, indeed, that the electro-motive force of a voltaic com- 
 bination, is proportional to the number of pairs, that are formed with this com- 
 bination. 
 
CHAP. in. ELECTRICITY BT CHEMICAL ACTIONS. 859 
 
 affinity of oxygen for zinc and of hydrogen, for the oxygen of 
 the peroxide. 
 
 Mr. Cooke has endeavoured to apply the method that we 
 have just been explaining; only, he measured the electro- 
 motive force of each voltaic combination, by placing in the 
 circuit of which it formed part, a tube filled with sulphate of 
 copper, the liquid column of which might be lengthened or 
 shortened so as, by means of this variable resistance, to 
 cause each combination to produce the same effect upon a 
 galvanometer, placed in the same circuit. The electro- 
 motive force, and consequently the affinity, was deduced from 
 the comparison of the lengths of the liquid column in each 
 case, according to Ohm's laws. Mr. Cooke, on taking 
 various precautions in order to take account of the polari- 
 sation of the plate of platinum of the pair, has obtained the 
 following numbers for the expression of the relative force of 
 affinity of the various metals for oxygen in rain water, 
 taking for unity the electro-motive force 'of a zinc- copper 
 pair in the same rain-water, a force which represents the 
 difference between the affinities of the zinc, and of copper for 
 oxygen : 
 
 Zinc-copper - - - = 1 
 
 Potassium .... 3-13 
 
 Sodium - 2-91 
 
 Zinc - ... 2-23 
 
 Iron - 1-85 
 
 Tin - 175 
 
 Lead - 170 
 
 Bismuth - P29 
 
 Antimony .... 1*29 
 
 Copper - - 1-25 
 
 Silver ..... 0-83 
 
 Mr. Cooke has likewise found for the expression of the 
 affinity of oxygen for hydrogen, the number 2-36 ; we may 
 be astonished that this number is higher than that, which ex- 
 presses the affinity of oxygen for zinc ; and that nevertheless 
 zinc decomposes water. But we must remark that perfectly 
 pure zinc does not decompose distilled water deprived of 
 oxygen : and that consequently Mr. Cooke's results is not in 
 
860 SOURCES OF ELECTRICITY. PART v. 
 
 opposition to that, which results from the examination of the 
 chemical reactions of zinc upon water. 
 
 We should not however attach too great confidence to the 
 numbers found by Mr. Cooke, although the order in which 
 the metals are arranged appears to us to represent well their 
 degree of affinity for oxygen ; while still believing the prin- 
 ciple true, upon which his method is founded, there are yet 
 many points to be made clear and data to be determined, 
 )efore our being able to deduce from the numbers, that 
 xpress in a tolerably exact manner, the relations of affinity 
 f the different bodies in respect to each other. 
 
 One of the most essential among these points is to know 
 u what condition it is necessary that the chemical action be 
 exercised, in order to their being productive of electricity. 
 When water is decomposed by the action of zinc, two phe- 
 nomena are brought about, one the decomposition of the 
 water itself, the other the oxidation of the zinc. Now, some 
 philosophers, and M. Matteucci among others, pretend it is in 
 the former of these phenomena only that there is liberation 
 of electricity, and not in the latter. He relates that Davy 
 had never been able to obtain the least sign of electricity, 
 on causing iron or carbon to burn in very dry oxygen : he has 
 himself proved the accuracy of this negative result, both in 
 his experiments upon the electricity liberated in combus- 
 tion of which we have spoken *, as well as in burning iron 
 and zinc in oxygen, as in combining different metals with 
 gaseous chlorine. He did not obtain in either case electric 
 effects. He has moreover found that on causing chlorine, 
 bromine, or iodine, to act directly upon the positive metal of 
 a pair, zinc for example, plunged in a liquid, separated by a 
 porous diaphragm from the liquid, in which the negative metal 
 is plunged, the force of the current is in no way increased, 
 although the zinc is attacked by the chlorine, bromine, or 
 iodine. It is not the same as we know, if the chlorine, 
 bromine, or iodine, is found in the liquid of the negative 
 metal, because then the decomposition of the water is facili- 
 tated. In like manner as the combination of the two free 
 
 * Page 746. and the following pages. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 661 
 
 elements does not produce electric signs, so also the decom- 
 position of a binary compound, without their being a recom- 
 bination of one of its elements, does not produce any, accord- 
 ing to M. Matteucci. Thus, oxide, as well as bi- oxide of 
 silver, peroxide of lead and chloride of gold, projected upon 
 a platinum crucible powerfully heated and in communication 
 with the condenser, have not produced electricity ; neither the 
 element that remained in the crucible, nor that which 
 escaped from it, were found electrised. From these facts and 
 others of the same kind, M. Matteucci had thought he 
 might conclude that the combination of a simple metalloid 
 body with a metal does not produce electricity, neither in the 
 dynamic nor in the static state ; that consequently in the pairs 
 of the pile, the electric effect is due to the metalloid form- 
 ing part of a combination before combining with one of the 
 metals of the pair. 
 
 M. Becquerel does not share in M. Matteucci's manner 
 of seeing it : he thinks that the results, negative in the case 
 of the combustion of different bodies, is due to the circum- 
 stance, that the ambient medium being insulating, the elec- 
 tricities produced in chemical action cannot propagate 
 themselves as they can when this medium is a liquid; and 
 that they then recombine in proportion as they are developed, 
 so that they are not perceptible. He has further shown 
 that an iodide or a chloride solution increases the intensity 
 of the current of a pair, as well when it is found in the 
 compartment, in which the zinc of the pair is, as when it 
 is placed in that where the copper is : the solutions tried, 
 whether in the natural state, or in the iodide or chloride 
 state, were a solution of nitrate of potash and a solution of 
 potash. It does not appear to us, that these latter experi- 
 ments invalidate M. Matteucci's conclusions ; for nothing 
 proves to us, that the iodine or the chlorine of the solutions 
 acts directly upon the zinc ; it rather appears to us probable 
 that they facilitate its oxidation by aiding the decomposition 
 of the water of the solutions. 
 
 The point upon which M. Becquerel seems to me to be 
 right, is when he affirms that the simple combination of an 
 
862 SOURCES OF ELECTRICITY. PART v, 
 
 oxide and an acid produces electricity, as he has proved in 
 his numerous experiments upon the mutual action of two 
 solutions separated from each other by a porous membrane, 
 and in particular in his very remarkable pair, potash and 
 nitric acid. We know, indeed, and we have proved, that we 
 must not go and seek for the cause of the electricity, that is 
 developed, elsewhere than in the chemical action of the two 
 solutions upon each other, we ought even to add that this 
 action contributes to the liberation of electricity in the two- 
 liquid piles. Thus, there is no doubt that, when we have a pair, 
 zinc, sulphate of zinc, and copper, sulphate of copper, 
 the mutual action of the two sulphates separated from each 
 other by the porous diaphragm, does contribute to the total 
 effect. If we have not taken this into consideration, it is 
 because we have taken the effect of the pair in its totality, 
 and because also the electricity developed in this action is 
 feeble, comparatively to that, which results from the 
 oxidation of the zinc by the decomposition of the water. 
 
 Admitting therefore that the combination of an oxide 
 with an acid produces electricity, we do not however see 
 in this fact an objection against Matteuccl's principle. In- 
 deed, this combination is perhaps brought about in a less 
 simple manner than is supposed; for my own part, I am 
 disposed to believe that it is preceded or accompanied by a 
 decomposition. We know in fact that, in the decomposition 
 of salts, the element that goes to the negative electrode is 
 not the oxide, but the metal of the oxide, sodium, for 
 example, if a salt of soda is in question ; and that the element 
 which goes to the positive electrode, is not the acid alone, 
 but a compound of the acid, and the oxygen of the base. 
 Now, this proves to us that very probably in the combina- 
 tion of an acid and a base, there is a decomposition, perhaps 
 of the base, perhaps of the water of the solution, the oxygen of 
 which is carried to the acid, whilst its hydrogen takes posses- 
 sion of the oxygen of the base, whose metal combines with the 
 oxygenated acid. In this action a phenomenon must take 
 place analogous to that which occurs in the formation of 
 chlorides by the action of hydro-chloric acid upon the oxides ; 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 863 
 
 for it is very evident, that in electrolytic decompositions, 
 all salts behave like chlorides in which the chlorine is 
 replaced by an oxysulpliion, if the acid is a sulphuric acid ; 
 or by similar compounds, if other acids are in question.* 
 
 We may add, that as a result of fresh researches in which 
 M. Becquerel, by means of his depolarising apparatus, of 
 which we have spoken above, has been able to guard 
 against the causes of errors arising from the secondary 
 polarities of the metals that are used as electrodes in the solu- 
 tions, he has arrived at some general results upon the elec- 
 tricity produced in chemical actions, which confirm those that 
 he had already obtained, and which we have already stated 
 in our preceding paragraphs ; he agrees with Matteucci on 
 the point that, in the combination of a metal with dry oxy- 
 gen, chlorine, iodine, and bromine, there is no production of 
 electricity, which he attributes to the non-conductibility of 
 one of the two bodies present ; however, he admits that com- 
 bustion developes electricity, and that the combustible body 
 liberates negative electricity, whilst the burners liberate posi- 
 tive ; yet, in this case, one of the bodies, the burner, is not 
 a conductor. Finally, he observes, that water in its com- 
 bination with the acids, comports itself as a base, that is to 
 say, acquires negative electricity, whilst with bases it comports 
 itself as an acid, and acquires positive electricity. 
 
 In fine, the question upon which we are engaged, of 
 knowing in what case chemical action developes electricity, 
 cannot be solved until we shall be better acquainted with 
 the manner in which chemical action itself is brought about 
 and when we shall know how to measure it ; moreover, it 
 is probable that the two questions are so connected, that one 
 can only be solved at the same time as the other. A fact, 
 which proves to us the state of ignorance in which we still 
 are as to the manner itself, in which chemical actions are 
 brought about, is that which relates to one of the most 
 simple actions, namely, that of the simple oxidation of 
 metals in atmospheric air. According to M. Bonsdorff, no 
 metal oxidises in air perfectly dry, and deprived of carbonic 
 
 * It is proved by the example of the cyanides that compound bodies may 
 play exactly the same part as chlorine, iodine, or bromine. 
 
864 SOURCES OF ELECTRICITY. PART v. 
 
 acid, not even potassium and sodium ; he goes so far as to 
 affirm that in air moist, but well deprived of carbonic acid, 
 not any of the known metals oxidise, save arsenic and lead. 
 However this may be, the former of these two facts, which 
 appears to us well established, shows therefore that the 
 oxidation of a metal in the air is not the simple result of the 
 direct combination of this metal with oxygen ; a more com- 
 plex phenomenon takes place here, namely, a voltaic action, 
 the metal decomposing the water by a local voltaic action, 
 aided by the presence of the dissolved oxygen, which acts 
 upon the hydrogen of this water ; the presence of carbonic 
 acid facilitates the action, by rendering the water more con- 
 ducteous. We will not contest that with the aid of heat, 
 there may not be, in some cases, direct combination of oxygen 
 with the metal ; but these cases, which are exceptional, do 
 not prevent the oxidation being ordinarily, brought about 
 as we have been explaining 
 
 Another important point in electro-chemical phenomena, 
 upon which philosophers are not agreed, is to know whether 
 compound bodies are able to propagate electricity without 
 decomposing, in the manner of simple elementary bodies, such 
 as the metals. We have already discussed the question, both 
 in reference to the experiments upon which is founded the 
 law of electro- chemical equivalents*, as well as incidentally 
 in showing that we have never been able to observe any 
 transmission of an electric current through water, without 
 the electrodes being polarised, a proof that the water is 
 decomposed ; and we have had the opportunity of giving 
 an explanation of the numerous and ingenious experiments, 
 by which M. Foucault had thought he was able to establish 
 this physical conductibility of liquids. We think therefore, 
 that, in the present state of the science, and in face of the 
 known facts, we are compelled to admit that the molecular 
 propagation of electricity in liquid bodies cannot be brought 
 about without being accompanied, in compound liquids, with 
 electrolytic decomposition. We shall not contest that pro- 
 
 * Vol. II. pp. 424. 677. and 701. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 865 
 
 pagation may take place in a liquid, especially if it is a bad 
 conductor, by a discharge between the electrodes, analogous 
 to that which constitutes the electric spark or the voltaic 
 arc, and in which the liquid plays only a passive part, that 
 of an obstacle to the establishment of this discharge ; it then 
 frequently happens that the liquid itself is decomposed by the 
 heat of the spark ; but this fact is in no degree in opposition 
 to the principle that, when the propagation takes place mole- 
 cularly, there is electrolytic decomposition of the liquid. 
 
 Among the numerous questions which are still to be solved 
 on the subject, upon which we are occupied, one of the most 
 important would be to know what the relation is that con- 
 nects the force of affinity with the electric effect, that is gene - 
 rated by the action of this force. Some attempts have been 
 made in this respect : we have made allusion to it in the 
 section commencing at p. 783. ; we think we ought to 
 dwell upon it for one moment longer, although its result is 
 very uncertain and very limited ; for it only concerns the 
 affinity of oxygen and hydrogen. We have already seen that 
 Wheatstone and Pouillet had succeeded in comparing the 
 current, which results from the decomposition of a certain 
 quantity of water, with that which is produced by a thermo- 
 electric pair of a given power; but their result, although 
 demonstrating the great superiority of the electro-chemical 
 current over the thermo-electric current, gave no idea of the 
 absolute quantity of the electricity liberated for the produc- 
 tion of the former. Faraday and Becquerel have succes- 
 sively endeavoured to obtain the value of this quantity. 
 
 Faraday observed that the current, necessary for decom- 
 posing a grain of acidulated water, is sufficient for main- 
 taining at a red heat, during the same time that he employed 
 for decomposing the water, namely 3 minutes, 45 seconds, a 
 platinum wire of y^o-th of an inch in diameter. Now, he 
 estimates that the quantity of electricity, which it would be 
 necessary to employ, in order to produce the same effect, 
 would be that furnished by 800,000 charges of a battery 
 of Leyden jars, composed of 8 jars, of 8 inches in height, 
 and 7J inches in diameter, charged with 30 turns of the 
 
 VOL. IT. 3 K 
 
8f)0 HOIlltCK.S OK I<;M:<:TIM<:iTY. I-AKT v. 
 
 plate of ri. powerful electrical machine. If such is the 
 c . pression of tin-. <piantify of elect ricil y c<|ui valent to that 
 vvliich is necessary for decomposing :i "rain of water, this 
 e\pre ssion is also thai of the ,|uanfify of electricity, thai. 
 is liberated by the combination of the ^uantilies ol' oxy"<-ii 
 :ni(l hydrogen necessary lor producing a. "rain of water ; 
 MII enormous <|ii;ml,il y , ;is wo sec. 
 
 M. I'x-cciuci'cl has found, \>y an <'iil.irrly dill't-rciil. method, 
 .1 n- nil. l.lia.1. is nol, vci'y I'ji.r i-cniovc(| from lli;il. of Karaday. 
 I !< lir:;t. dclcrniincd l.lic- lofcc ol' l.hr cun-cnl,, i.h:il is developed 
 l>y I he secondary polarities cn<'Tndcrcd ujion plates ol ^<>I<1, 
 which servo a,s clcc.t.rodcs in disl.ilh-d water to discliar"c:, f 
 Leyd<-n jars ; IK- has found thai, for discharges vvliich are nol, 
 very considerable, t,he current , and consefjiK'ntly the polarities, 
 which give rise to it, are proportional to the explosive distam -, 
 
 and conseijnently l.n 1.1 le (juanf it.y of elect.ricify, l.ha I, passes in the 
 water, in which the "old plates are plunged. Then, he de- 
 termined the secondary polarities on the same gold plates hoth 
 in distilled water, by means of a current arising from a very 
 feehlc pail' formed of an amah>;am of /inc. placed in a, porous 
 
 tube, and of a platinum wire plunged in distilled water, lie 
 satisfied himself I hat. I he polarities sic<juirod are proportional 
 to the time, diirni" which the current is transmitted, pro- 
 vided this time is vory short. Thus, for a duration of \" he 
 found that the polarised plates e;ave a current of 10"'7.'5, and, 
 for a duration of O"-. r ), a, current of f>"'.'.'i, that, is to say, one- 
 half less powerful. In order to compare the electricity of 
 
 the discharge with that, of the current, he commenced by de- 
 terminin;'; with run- the intensity of the current, due to the, 
 polarities produced by the discharges; and he found that 
 this current produced upon the galvanometer a, mean devi- 
 ation of 17*97. Jlo then substituted the current of the pair 
 for the discharge of the battery, and he found that this 
 
 current in pa .r \" brought about a polarity upon the 
 
 plates, producing l()"-. r ><) of deviation. Setliii"; out from the 
 principle, t hat , I he polarities or iho chemical actions, by which 
 they have been produced, are proportional to the ojuaniiiios 
 of electricity in motion, he deduced from it, thai the quantity 
 of electricity formed in \" by the pair, is to that of the dis- 
 
. IMP. .... Ill* I I'M | | y \:\ < III MM'.U A< TIONM 
 
 rharjje ftfl IC-f.O : 17'!)7 or :is O-jrj : 1. Now, by :i uccessioii 
 of delicate experiment s, i\I. lle.-qiieivl succeeded in determin 
 in; 1 l IK\V iniicli decomposed water the current of tin- pan 
 
 acini!- for i" oorreipoodad i he Um mooteded i findm" 
 
 that, in order lo dec< unpo . :i "i .mi in- ( I . I :; "i- ) 0f Wfttftf j 
 :i quantity <>!' dec! rieity w;is requii <<!, equivalent lo wlial 
 \voul<l !>< i'urnislicd |>y ,0 1 ,, r >H(;/10() <liscli:ir;'cs of a |):i!l.-i\ 
 li:i\in |ii:ir<- IIH-UV f I !)()()!> yurds.) ol' Hiirl':ic-. 'I'lii 
 
 luiiiilicr is n-ducrd to ^O,0(i,'J, I-'ifj when llic ohwfgfl !' lli' 
 l.atlcry is at it ni:i MI.IIII.I. Oil ivdiicin^ l':ir:id:iy's iv.nll |. 
 tlic s.-inic conditions, we find ^1^.00,1,01. Tlic, dill<T< m-c i 
 very inc.on id'-r;il.l- lor -\ |<-riin<-nts of this nal.nn-. \V- m:iy 
 n.in-liidi- I'roin this, adoptin;- tin- nmnd iiiiinli-r of 
 for on<- .'jr.'iininc, lliat, in ord<-r l,o d<M-oni|)o -.; n 
 milligramme C-OI.. if water, l,li-r- art; rcf|iiir-d ^0,()()<> 
 
 di <-|i;ir "--i oi' a battery, \>r<- , iiliii;^ a surl'acc nf OIK* Sf|ii:ir- 
 inctr<-, or tli<- di .f|iar;.'- of :ui clccli'ic j.:mc, thai, would Ji:i -. 
 a surface of about, five acres. Now, it is tJiis same quantity 
 of eleetricity, that must !>< |>rolnc.(Ml \>y l.he decou.po'.ilioii of 
 .din", milligramme oi' water, brought about by chemical 
 means; and, if it were accumulated, so as to di.cliar;"- il < II 
 Ian- 0:1 ly, and not in a successive; manner in proportion 
 production, it would be capable of producin;> the t-ft'< <! ; 
 of a flash of li;ditniii"-. It J, not lieocHKary to attach too "re;ii 
 an importance to 1 he num<-rical values found by Karaday and 
 I*ec(ju. i':l ; but there, follows from their researches .-m im- 
 portant r< -suit c, >n (iinied by I'.'llj.-r, namely } JOW very small 
 i-. the quantity of chemical action ne<:<:ssary for the production 
 of a ;/rc;it elect ric jiowcr. 
 
 lint of all the relations, by which e|i-nii-:il aflinity is COH- 
 jiected with UK; elect/ icily that it .n-nerates, J.h- mo ! 
 portant is tliat which is established |,, ], , ,, the two form .,1 
 th- ;i me loj'ce, by the production of llic heal which ace, )M) - 
 p:mi-.s tin-in. We have already made mention of lln- j 
 
 of Mr. Joule and of those of M. Kaviv, on tin'-; 
 riibject; and I have also <j noted the experiment, by wliic.h I 
 liad IQCeeadad in demon Iralin" lh<: erpiality, thai 
 e the rjuaiitity of heat ee,, ; ruted directly by 
 
 5 K 2 
 
868 
 
 SOURCES OF ELECTRICITY. 
 
 PART v. 
 
 action and that which is produced by the current to which 
 this same chemical action gives rise.* We are now able to 
 return with more details to this class of phenomena, which 
 we had discussed only incidentally, being unable to investi- 
 gate them deeply, before we had been occupied with electro- 
 chemical actions. 
 
 Mr. Joule, after having established, as we have seen, the 
 laws of the liberation of heat, by the passage of the electric 
 current through liquids, had been led to admit that the heat 
 developed by chemical reactions, without electricity being 
 collected, is the same as that, which is produced by these re- 
 actions under the form of electric current, so that the heat 
 in both cases would be due to the resistance to electric con- 
 ductibility. The learned English philosopher has first proved 
 that the quantities of heat, liberated by the combustion of the 
 equivalent of bodies, are proportional to their affinities for 
 gaseous oxygen : he arrived at this result, by seeking for the 
 measure of these affinities in the action of the electric current, 
 and by taking account of the modifications produced in its 
 intensity, by the physical state of the elements of the com- 
 binations, that are formed in the pairs whence the current is 
 derived. He has determined for potassium, zinc, iron, 
 copper and hydrogen, the heat produced by the direct com- 
 bination of these bodies in gaseous oxygen, according to a 
 process analogous to that of Dulong; he then estimated the 
 heat produced by the oxidation of the same substances in 
 the production of the voltaic current; he thus finds the 
 following numbers as expression of the degrees which one 
 equivalent of each body raises, by its oxidation, the tempera- 
 ture of one pound of water, in the case of direct combustion, 
 and in that of the oxidation with electricity collected. 
 
 
 Direct 
 Oxidation. 
 
 Voltaic 
 Oxidation. 
 
 Voltaic 
 Oxidation 
 corrected. 
 
 Potassium ... 
 
 17-60 
 
 21-17 
 
 
 Zinc .... 
 
 11 -03 
 
 13 -83 
 
 11-01 
 
 Iron - 
 
 9 -48 
 
 12 -36 
 
 8 -06 
 
 Copper - 
 Hydrogen - 
 
 5 -18 
 8 -36 
 
 9-97 
 10-47 
 
 5 -97 
 10 -40 
 
 Vol. II. p. 250., and folio-wing page. 
 
CHAP. HI, ELECTRICITY BY CHEMICAL ACTIONS. 869 
 
 In order to obtain the corrected results contained in the 
 third column, Mr. Joule remarks that, in oxidation by the 
 moist way, which is accompanied by the production of a 
 voltaic current, there are three forces, namely ; the affinity of 
 oxygen for the base of the oxide ; that of the oxide for 
 sulphuric acid (supposing that it is in a solution of sulphuric 
 acid that the oxidation takes place) ; and finally, that of the 
 water for the sulphuric acid ; by eliminating the last two 
 forces, which may be estimated directly, the numbers 
 contained in the third column are found, which very 
 nearly approximate to those of the first, except for iron, and 
 for hydrogen, which is due to causes easily appreciable. 
 
 M. Favre, as we have already remarked, when occupied 
 with the calorific effects of electricity, has established, by 
 numerous and exact experiments, the truth of the principle, 
 that I had advanced, on founding it upon a single experi- 
 ment, and to which Mr. Joule had also arrived by another 
 method; namely, that the heat, confined in the liquid 
 of the pair, and that which arises from the resistance of the 
 metallic circuit, whatever it may be, are always comple- 
 mentary to each other. M. Favre has further demonstrated, 
 what Mr. Joule had only glanced at, that we always find 
 in the liquid of the pair, and in the interpolar arc the 
 sum total of the heat, which the chemical action put into 
 play in this pair, would alone be capable of developing. 
 We are unable to reproduce in detail the experiments of 
 M. Favre ; we shall merely call to mind that they were 
 made according to the same method which was employed 
 both by himself and by M. Silbermann in their great work 
 on the measure of the quantities of heat liberated in chemical 
 actions, and with a similar mercury calorimeter, but con- 
 structed upon a larger scale than the former. M. Favre 
 has first measured the quantity of heat liberated in the pair, 
 when the circuit was formed by a copper wire sufficiently 
 thick for there being no appreciable calorific effect developed 
 in consequence of resistance to conductibility : a wire about 
 a twelfth of an inch in diameter and about a foot at most 
 in length fulfilled the desired condition. He then substi- 
 
 3 K 3 
 
870 SOURCES OF ELECTRICITY. PART v. 
 
 tuted for this wire platinum wires of variable diameters and 
 lengths, susceptible of being more or less heated ; and by 
 combining his apparatus so that the total heat, as well that 
 of the wire as that of the pair, might be received by the 
 calorimeter, he obtained with these variable wires, for the 
 measure of the total quantity of heat, numbers very little 
 different from each other, and the mean of which is 18,124 
 units of heat. The number obtained with the copper 
 wire, which was not heated, is 18,137 ; this number re- 
 presents the quantity of heat liberated by the chemical action 
 corresponding to the liberation of 15*43 grains of hydrogen, 
 or to the equivalent of 509*19 grs. of zinc dissolved, with 
 transmission of electricity through a wire, which offers 
 no resistance to the current. From the experiments made 
 by M. Favre in common with M. Silbermann, the number 
 that expresses the heat, liberated by the formation of 
 sulphate of zinc without electricity transmitted, is 18,444, 
 which, although slightly greater, yet approaches sufficiently 
 near to the other two to enable us to conclude from it the 
 accuracy of the principle that we have laid down. 
 
 M. Favre remarks with justice, that the law, which he has 
 established, enables us to demonstrate that it is not the 
 oxidation alone of the metal, that developes the current 
 in a voltaic pair, but that the solution of the formed oxide 
 in the acid contributes also to this production. Indeed, 
 if we admit that the quantity of heat, which is produced 
 in virtue of chemical actions in a voltaic pair, zinc and 
 platinum plunged in a solution of sulphuric acid, is re- 
 presented by A 4- B D, A being the heat liberated 
 by the formation of an equivalent of anhydrous oxide 
 of zinc, B the heat liberated by the combination of this oxide 
 with the diluted sulphuric acid, and D the calorific equi- 
 valent of the w r ater, namely, the heat absorbed by the 
 decomposition of an equivalent of water, and consequently 
 liberated by its formation ; we shall have, according to 
 the direct experiments of MM. Favre and Silbermann, A = 
 42,451 ; B = 10,455 and D = 34,462; whence A -f B- 
 D = 18,444, a number very near to 18,137, the veritable 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 871 
 
 heat liberated. If we admit that tins heat is equal to only 
 A D, we have 7,989, a very different number from 18,137. 
 It is therefore very evident that the oxidation alone of the 
 zinc is not sufficient to account for the effects generated by 
 the current. 
 
 It is by setting out from considerations of the same kind 
 that M. Favre seeks to explain, why we are unable to 
 decompose water in a voltameter, when we arrange but one 
 single pair, zinc and platinum plunged in water acidulated 
 by sulphuric acid, whilst this decomposition is able to take 
 place with a single Grove's pair, in which the platinum is 
 surrounded with nitric acid. He remarks that the heat, 
 necessary for establishing hydrogen in the free state in the 
 voltameter, that is to say, for decomposing water, is not 
 found in the chemical reactions that take place in the 
 former pair, whilst it is found in those which take place 
 in the latter. In fact, in the former pair this quantity 
 of heat is A + B D = 18,444 units, as we have seen ; 
 whilst the decomposition of water absorbs 34,462. In 
 the latter pair, there is no liberation of hydrogen ; conse- 
 quently there no necessity of deducting D from A -f B, 
 which causes that the liberated heat must be 52,906 
 units; but it is in reality only 46,021, because the chemical 
 segregation of the oxygen from the nitric acid absorbs 
 6,885 units of heat by equivalent, which are taken from the 
 heat liberated by the sulphatation of the zinc, and which 
 must consequently be deducted from 52,906. But in 
 all cases 46,021 greatly exceeds 34,462, the number 
 of units of heat necessary to the decomposition of water 
 in the voltameter. 
 
 As we see, M. Favre sets out from the principle that the 
 voltaic heat is merely a borrowing made from the heat libe- 
 rated in the chemical action that produces the current : that 
 consequently, in a closed circuit the total quantity of heat 
 is constant for a same quantity of chemical action ; and that, 
 by distributing itself in different manners, according to the 
 nature of the circuit, it suffers a simple displacement. The 
 learned French philosopher is thus led to admit an instan- 
 
 3 K 4 
 
872 SOURCES OF ELECTRICITY. PART v. 
 
 f aneous transport of heat, in the latent state it is true, which is 
 able to traverse a conductor without raising its temperature, 
 a transport, which is made from molecule to molecule in 
 the water placed in the circuit, in proportion as the successive 
 molecules are decomposed and recomposed by the exchange 
 which is made between them of the gaseous elements of 
 which they are constituted. He estimates that we may thus 
 better account for the effects, that are observed in electro- 
 chemical decompositions, and consequently for the theory of 
 the pile ; but, still being led to believe that we may include 
 the effects produced by the currents of the pile under two 
 orders of manifestation, the former of which might be con- 
 sidered as due to currents of latent heat, and the latter to 
 currents of transmitted affinity, he recognised that they arise, 
 as well as the electricity itself, from the same source, namely, 
 from chemical action. 
 
 Still admitting, with M. Favre, the intimate connection 
 that exists between the quantities of heat liberated in the 
 different parts of a circuit, we cannot consider them as 
 simple displacements of that which is produced in the pair ; 
 we are rather disposed to attribute them to the distribution, 
 variable with the nature of the circuit, of the force which 
 arises from the exercise of affinity in the pair. But, before 
 developing our thought, we ought, in order to complete the 
 exposition of the subject on which we are occupied, to say 
 a few words upon the more recent researches of M. J. 
 Regnault which appear to us to accord with the opinion 
 of M. Favre. 
 
 M. J. Regnault, setting out from an experiment, by which 
 M. Favre finds that the heat liberated by the oxidation of 
 the equivalent of amalgamated zinc, is superior by 352 units 
 to that which is liberated by the oxidation of the equivalent 
 of pure zinc, concludes from it that this difference is due to 
 the fact that in the amalgam, the zinc being liquid, it is not 
 obliged, as when it is solid, to absorb heat in its transforma- 
 tion into sulphate, an absorption which diminishes, in the 
 same degree, that which is produced by chemical combination. 
 The 352 units represent then the quantity of heat become 
 
CHAP. III. ELECTRICITY BY CHEMICAL ACTIONS. 873 
 
 latent in amalgamated zinc ; and which is found again under 
 the form of electricity in the excess of electromotive force, 
 that is presented by amalgamated zinc over pure zinc. This 
 transformation of heat into electro-motive force does not 
 seem to us necessary in order to explain the influence of the 
 amalgamation, which appears to us to be simply due to the 
 fact that affinity is more easily exercised between the acidu- 
 lated water and the zinc, when the latter is dissolved ; since 
 there is no longer any cohesion to overcome, a similar phe- 
 nomenon to that which is presented by the greater proportion 
 of chemical actions. The same cause, namely, the more easy 
 exercise of affinity, appears to us equally to explain the 
 greater development of heat, that accompanies the oxidation 
 of zinc, when, instead of being solid, it is amalgamated. 
 
 Moreover we shall not contest that the liberated heat 
 and the electro-motive force march together, without 
 being altogether the cause, each of the other; since they 
 appear to us equally to depend, with regard to their 
 intensity, upon that of the affinity, which gives rise to them 
 both. M. J. Regnault remarks, in fact, that the relation 
 between the heats liberated in a Grove's pair and in a DanielPs 
 pair, is the same as that of the electro-motive forces of these 
 two pairs, namely, is equal to about 1*731. Mr. Wood, as 
 the result of experiments upon the heat, liberated by the 
 oxidation in water of different metals, had previous to this 
 found that the order of these metals, classed according to the 
 quantity of heat to which their oxidation gives rise, is ex- 
 actly the same as that which is furnished by the comparison 
 of the electro-motive forces that arise from their combination 
 with oxygen. However, the question upon which we are 
 occupied, would require still further researches in order to its 
 being completely solved. 
 
 However it may be, it appears to us to be well demon- 
 strated that there is an intimate relation between chemical 
 affinity on the one hand, and the heat, as well as the elec- 
 tricity that it liberates on the other hand ; and that it is in 
 the determination of the quantities of heat developed and the 
 electro-motive forces generated, that we shall be able to find the 
 
874 SOURCES OF ELECTRICITY. PART v. 
 
 most exact measure of affinities. It is not until such a work 
 as this shall have been accomplished, that it will be possible 
 to found upon bases in any degree solid an electro-chemical 
 theory. However, I shall endeavour for the present to put 
 forth briefly upon this point certain ideas, which appear to 
 be more in accordance with the facts actually established, 
 than the hypothesis, with which we have hitherto been con- 
 tented, still recognising that it is impossible, in the present 
 state of science, to give a completely satisfactory theory. 
 
 We have already called attention to the two electro- che- 
 mical theories, that have been proposed, one by Berzelius, 
 the other by Ampere * ; the former based upon the hypothesis 
 that all atoms have two electric poles of a contrary nature ; 
 the latter, on the hypothesis that all atoms have a natural 
 electricity, some positive, others negative. We have ob- 
 served that the latter theory possesses the grave inconveni- 
 ence of dividing bodies into two distinct categories, the one 
 electro-positive, the other, electro-negative; whilst it is 
 evident that their electric property has nothing absolute, 
 since the same body plays sometimes the part of electro- 
 positive, sometimes that of electro-negative, according to 
 the body with which it is combined. This objection 
 is with us an objection of principle, to which it is im- 
 possible to reply, notwithstanding the ingenious artifices, 
 by means of which endeavours have been made to refute it. 
 The former theory, that of Berzelius, appears to us to 
 present less objections in its principle, than in the manner, 
 in which its author regards it in its details, and makes appli- 
 cation of it. We have already demonstrated all the im- 
 probability that is presented by the hypothesis of Berzelius, 
 that the atoms, while having two electric poles, become 
 unipolar as soon as they combine, namely, that they retain 
 only one of their electricities on combining, and abandon the 
 other. We are moreover about to see that this hypothesis 
 is not necessary in order to explain electro-chemical phe- 
 nomena, which may be very well reconciled with the exist- 
 ence of a permanent polarity of the atoms. We have 
 
 * Vol. II. p. 48. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 875 
 
 already sought to explain, by means of this polarity, mag- 
 netic and diamagnetic phenomena ; we are now about to 
 endeavour to show that it accounts also very well for electro- 
 chemical phenomena. 
 
 The principle from which we set out is, that every atom 
 lias two electric poles, contrary, but of the same force ; is 
 it to a movement of rotation upon itself, or to another 
 cause, that this polarity is due ? This is of little importance ; 
 it is with us a primitive fact. One atom differs from another 
 atom, with regard to its polarity, only inasmuch as one of 
 them has a more powerful polarity than the other, but, in 
 the same atom, the two electric poles are always of the same 
 force. When two insulated atoms are brought near to each 
 other, they attract each other by their opposite poles ; but, 
 as they are spherical, they can come into contact only by 
 one of the poles of the former, and by the contrary pole of 
 the latter : will it be indifferently the positive or the negative 
 pole of the former, that will come into contact with the 
 negative or positive pole of the latter ? We shall be obliged 
 to admit a principle, which it appears to us is able to be 
 founded upon a great number of facts : that is to say that, 
 when the two atoms are free and insulated, it is always the 
 positive pole of that which has the stronger polarity, that 
 unites with the negative pole of that which has the more 
 feeble polarity. If they have the same force of polarity, 
 there is no reason why they should unite by two of their 
 contrary poles, rather than by the other two. Then they are 
 not attracted by their poles ; but they simply obey the mo- 
 lecular attraction, due to the effect of their mass ; this is the 
 case of homogeneous atoms, the attraction of which con- 
 stitutes cohesion ; whilst, when the atoms are heterogeneous, 
 they are attracted by their opposite poles, they then obey 
 chemical affinity. 
 
 Chemical affinity is therefore the result of the attraction of 
 two different atoms by their contrary poles ; but it is exerted 
 in such a manner, that the positive pole of the more power- 
 fully polar is united with the negative pole of that which is 
 less powerfully so. The compound atom, that results from 
 
876 SOUHCES OF ELECTRICITY. PART v. 
 
 the union of the two elementary atoms, has equally two poles, 
 that is to say, the negative of the more powerful atom, and 
 the positive of the more feeble one ; these two poles are 
 equal, because the excess of the more powerful over the more 
 feeble of those which are united, serves to neutralise a cor- 
 responding part of the electricity of the free pole of the more 
 powerful ; the compound atom is therefore found under the 
 same conditions as the free atom, and enjoys the same pro- 
 perties. Thus, on supposing that oxygen is that one of the 
 simple substances, which has the more powerful polarity, an 
 atom of oxygen will unite with one of sulphur, so that its 
 positive pole is adhering to the negative of the sulphur ; it 
 will be the same for the union of one atom of oxygen with 
 two atoms of hydrogen. An atom of chlorine will unite 
 with hydrogen in the same manner as oxygen ; whilst it will 
 unite with an atom of oxygen in such a manner, that it will 
 be the positive pole of the oxygen, that will be united to the 
 negative pole of chlorine ; thus, it will be by its positive pole 
 that chlorine will unite with hydrogen, and by its negative 
 that it will unite with oxygen. 
 
 A compound atom, when it is insulated, has therefore, 
 like the simple atom, two contrary and equal poles ; the 
 electricities of these two poles unite by the surface itself of 
 this atom, in the same manner as we have admitted that it 
 takes place for the simple atom.* But, if we place the 
 compound atom between two contrary polarities, between 
 the two poles of a pile for example, this atom is immediately 
 so arranged that its + pole is turned on the negative side of 
 the pile, and its pole on the positive side of the same pile ; 
 when water therefore is the subject under consideration, it is 
 the atoms of hydrogen, that are turned with their positive pole 
 on the side of the negative pole of the pile, and the atoms of 
 oxygen on the side of the positive pole. The polarisation of 
 the molecules of electrolytic liquids, which always precedes 
 their decomposition, is therefore a consequence of their 
 natural polarity. Now, if the electric power is sufficient, 
 
 * FiWeVoLILp. 49../K7. 177. 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 877 
 
 the positive electricity of the positive electrode attracts the 
 free negative of the first molecule of water, and thus deter- 
 mines the separation of the oxygen, which abandons its hy- 
 drogen to the oxygen of the following molecules of water, and 
 so on. The difference between the natural state of a liquid and 
 its state of electric, polarisation, consists therefore of this, 
 that, in the former state, the molecules left to themselves are 
 in a complete electric equilibrium, the equal and contrary 
 electricities with which their two poles are endowed, unite by 
 their surface ; whilst, in the latter state, the electric equilibrium 
 is broken, the contrary electricities no longer uniting by the 
 surface of the molecules, whose positive poles are all turned 
 on the side of the negative of the pile, and the negative on 
 the side of the positive of the pile. This state of polarisation 
 is followed by electrolysis ; that is to say, by the separation of 
 the constituent atoms of each particle, and their combination 
 with the contrary atoms of the following or the preceding 
 particles, except for those of the extreme particles, which 
 are liberated at the surface of the electrodes. Only we 
 should remark that, at the moment when the atoms of oxy- 
 gen and hydrogen of two consecutive particles become free, 
 they must turn round, so that it is the + pole of the oxygen, 
 that combines with the pole of the hydrogen, and not the 
 + pole of the hydrogen, that combines with the pole of 
 the oxygen ; since this turning round and combination being 
 once brought about, polarisation recommences.* 
 
 All electrolytic decompositions are explained in the same 
 manner. We shall give a few examples only of them. 
 Thus the molecules of a solution of sulphuric acid may be 
 considered as formed of a molecule of sulphuric acid, the 
 4- pole of which has attracted the pole of the molecule of 
 water united with that of the acid ; but the -f pole of the 
 molecule of sulphuric acid belongs to the sulphur, the pole 
 of the molecule of water belongs to the oxygen ; so that, 
 when the molecules of the solution are decomposed, after 
 having been polarised, it is not astonishing that the atom of 
 
 * See for the necessity of this turning, p. 351. of Vol. II. 
 
878 SOURCES OF ELECTRICITY. PART v. 
 
 oxygen travels with the molecule of sulphuric acid, separa- 
 ting itself from the atoms of hydrogen, and forming what we 
 have called an oxy-sulphion. It will be the same when, for the 
 hydrogen is substituted a metallic base, such as sodium or 
 copper, with the difference that, at the negative electrode 
 sodium decomposes water, whilst copper is deposited there 
 in the metallic state. The mode of the electrolytic decom- 
 position of non-binary compounds, must depend upon the 
 manner in which combination is brought about between the 
 various atoms, that enter into their formation, and conse- 
 quently upon the degree of affinity, or relative electric 
 polarity of these divers atoms. It is therefore in studying 
 the phenomena that accompany combination, and in parti- 
 cular in measuring the electro-motive force and the heat, 
 that are developed in it, that we may be enabled to render 
 an account of the manner in which these various atoms are 
 grouped and are separated in decomposition. With regard 
 to binary compounds, their decomposition is easily explained, 
 in the same manner as that of water ; thus, in that of hy- 
 drochloric acid, the chlorine comports itself as does oxygen 
 when water is the subject in hand ; it is the same with other 
 chlorides, with sulphurets, with cyanurets, as with the 
 oxides. In the decomposition of chloric, sulphuric acids, &c., 
 chlorine, sulphur, &c., no longer comport themselves like 
 oxygen, but like hydrogen. All these results are the evident 
 consequences of our theory. 
 
 The formation of compounds is at first sight more difficult 
 of explanation in this theory than their decomposition ; not 
 in the case of binary compounds, the elements of which being 
 free combine according to the mode that we have described 
 above ; but in the case, in which the formation of one compound 
 does not take place, except by the decomposition of another. 
 However we then consider that the same theory may explain 
 in a satisfactory manner what takes place. 
 
 In order to fix our ideas, let us suppose a plate of zinc, 
 plunged into a solution of sulphuric acid ; the first effect of 
 the presence of the metal in the liquid should be to destroy 
 the electric equilibrium of the particles of the solution in 
 
CHAP. III. ELECTRICITY BY CHEMICAL ACTIONS. 879 
 
 contact with it * ; hence the negative electricity of the oxygen 
 and the positive of the hydrogen of each of these particles 
 become free ; but as the former is much more powerful than 
 the latter, since oxygen is much more powerfully polar than 
 hydrogen, it is it which acts upon the metal, by attracting 
 the + pole of its particle, and by thus polarising it; in its turn 
 the free positive electricity of the hydrogen of the particle of 
 water acts upon the following molecule of the solution and po- 
 larises it, destroying also its electric equilibrium, so that its 
 negative oxygen is turned on the side of the particle in contact 
 with the zinc and so on. In this way is established that polar 
 state, which we have admitted to be the first effect of the con- 
 tact of a metal with the electrolytic liquid, and which must take 
 place with every body that is a conductor of electricity, even 
 when it is not followed by the chemical action that gives rise to 
 a new compound. With regard to this chemical action, which 
 consists in the decomposition of the liquid and the combina- 
 
 * The contact of a conducting body, must indeed prevent the recomposition 
 of the free electricities of the combined atoms, which took place by the exterior 
 surface of these atoms ; it follows from this, that the atom of oxygen, which is 
 combined, is thus found to have its negative electricity entirely free, whilst a 
 part of its positive is disguised by the atom of hydrogen ; on this account, it is 
 that it comes and adheres to the metal by its negative pole. It is probable that 
 the catalytic property of platinum and of some other substances is due to the 
 same cause. When molecules of oxygen and hydrogen are in very intimate 
 contact with platinum, the electricities of their respective poles cease to be re- 
 composed by the surface itself of the atoms ; the atoms of oxygen then adhere 
 at their positive poles with the surface of the platinum ; those of hydrogen 
 adhere to it by their negative poles ; and then the free poles of the atoms of 
 oxygen and hydrogen are alternated, being of a contrary nature ; hence results 
 the combination of the atoms of these two gases, accompanied by a small 
 electric discharge through the platinum, and a liberation of heat. The elec- 
 tricity that traverses the platinum, cannot be collected directly, on account of 
 the infinitely small distance of the atoms, whose electricities are thus combined. 
 The adhesion of gases to the surface of metals is probably due in great part 
 indeed to their electric polarity ; it is a phenomenon analogous to that of the 
 polarisation that is exerted upon a molecule of a liquid by a metal plate that is 
 plunged into it. We therefore conceive why, whether for obtaining a powerful 
 adhesion, or for producing the catalytic effect, it is necessary that the metallic 
 surface be very clean, and that if it is very much divided, its power is in- 
 creased. We equally conceive why this surface must not itself combine power- 
 fully with oxygen, since then the latter could no longer combine with the 
 hydrogen ; we say powerfully, because the adhesion of oxygen to platinum for 
 example, is truly a chemical combination ; since it is the result of electric 
 polarity and not of simple molecular attraction ; and we have an experimental 
 proof that it is a combination in the fact of the disaggrcgation of the surface of 
 platinum, which has been employed during a certain time for bringing about 
 the combination of oxygen and hydrogen, by the effect of its catalytic power. 
 
880 SOURCES OF ELECTRICITY. PART v. 
 
 tion of one of its elements with the metal, it takes place 
 generally, as we have seen, only when the electric chain can 
 be formed, whether by the effect of a want of homogeneity in 
 the metallic surface itself, or by the effect of its contact with 
 another substance, constituting with it a voltaic pair. How- 
 ever, it may happen that with certain bodies, such as those 
 whose polar state differs greatly from that of oxygen (very 
 oxidisable metals), the chemical action, which follows the es- 
 tablishment of the polar state, may take place without the 
 circuit being formed, as also with metals, that are very little 
 oxidisable, it does not take place even when it is formed. 
 We conceive that the explanation which we have been giving 
 is easily applicable to all cases analogous to that which we 
 have taken for an example, to those in particular, in which 
 the solution is a chloride, a sulphuret, a cyanide, and not 
 only a combination of oxygen, and in which the compounds 
 formed are consequently in like manner chlorides, sulphurets, 
 cyanurets, &c. 
 
 Thus, all chemical actions of the kind of those of which 
 we have been speaking are electro- chemical actions, in all 
 respects similar, save that they are local, to those which take 
 place in a voltaic pair. It is not therefore astonishing that 
 the quantity of heat, which accompanies their exercise, is ex- 
 actly the same ; that this exercise takes place in one or other 
 of the two forms, when the quantity and nature of the che- 
 mical action are the same.* 
 
 * In speaking of the experiments of Faraday and of Becquerel, for determin- 
 ing the quantity of electricity that is liberated in a certain chemical action, such 
 as the oxidation of zinc, we have said that Peltier had succeeded on his part, 
 by a very different process, in showing how prodigious is the quantity of elec- 
 tricity, that is developed by the effect of the most feeble chemical action. Al- 
 though M. Peltier's results are not perfectly in accordance with those of the 
 two learned philosophers whom we have named, they nevertheless confirm the 
 accuracy of the principle, that they have established. Indeed, according to M. 
 Peltier, we require merely the oxidation of one hundred and fifty-one billioniemes 
 of a milligramme of zinc (O' m e- 0000000151 =0-000000000233 grs. Troy) in 
 order to produce a dynamic electricity, capable of causing the needle of a 
 sensitive galvanometer to deviate 1 ; and the oxidation of the tenth of the two 
 thousand one hundred and thirty-six quatrillioniemes of a milligramme of zinc ; 
 (0- m s -000000000002 136 =0-00000000000003297 grs. Troy) to produce a static 
 electricity capable of causing the needle of M. Peltier's electrometer to diverge 
 1. 
 
CHAP. iir. ELECTRICITY BY CHEMICAL ACTIONS. 881 
 
 Returning to the chemical action that two simple bodies, 
 neither of which form part of any combination, exercise 
 upon each other, it is necessary, in order to its being brought 
 about, that the approximation between the atoms shall 
 be sufficiently great for the + pole of the more powerfully 
 polarised to attract the pole of that, which is less so. 
 Heat, by exalting polarity, is able to facilitate combination. 
 In the case in which one of the simple bodies is oxygen, we 
 conceive that its ozonisation, which appears to consist of 
 disaggregating the molecules, gives to the atoms, by in- 
 sulating them, all their polarity, and thus increases the 
 oxidising power of this gas. We know likewise that the 
 oxidising action is much facilitated by the presence of 
 aqueous vapour; this fact, which is constant, is evidently 
 due to the phenomena then becoming electro-chemical ; the 
 vapour of water is polarised by the metal, as water itself is ; 
 and the affinity of the oxygen for the hydrogen of the aqueous 
 particles favours their electrolyzation, and consequently the 
 oxidation of the metal, which takes place at the expense of 
 the oxygen of these particles, whilst the gaseous oxygen 
 re-forms water with their hydrogen. 
 
 There is no doubt that every chemical action, which is not 
 a simple combination of two isolated elements, but in which 
 there is at the same time decomposition and production 
 of a new compound, is, as we have already remarked, a 
 very complex phenomenon ; and that the atoms of bodies 
 are grouped in a manner very different from that, in which 
 they were grouped before the action. These changes in 
 their mode of grouping cannot be brought about without 
 there being a great disturbance in their movement, which 
 brings about the elevation of temperature, with which the 
 production of chemical action is always accompanied. Now, 
 this elevation is the more powerful, in proportion as the 
 affinity, that determines the chemical action, is more 
 energetic, and as, consequently, the disturbance is greater. 
 The very intimate relation that unites the quantity of 
 heat produced with the affinity on the one hand, and the 
 affinity with the electro-motive force on the other hand, 
 
 VOL. II. 3 L 
 
882 SOURCES OF ELECTRICITY. PART v. 
 
 is very favourable to the hypothesis by which, attributing 
 affinity to the natural electric polarity of the atoms, we 
 make the polarity depend on a movement of rotation of the 
 atoms upon themselves. Indeed,, in the mechanical theory 
 of heat, temperature must depend upon the rapidity of this 
 movement of rotation, which itself must influence the energy 
 of electric polarity. 
 
 We shall not dwell for the present further upon this 
 altogether theoretical subject, seeing that, in the present 
 state of science, we are still in want of facts in sufficient 
 numbers to justify or to invalidate our hypothesis. We 
 shall not conceal the objections, that may be opposed to 
 it, namely, in particular, the difficulty of conceiving that a 
 simple difference in the electric polarity of the atoms is 
 able to explain affinity ; the necessity of admitting in this 
 hypothesis that it is always the positive pole of the atom, 
 whose polarity is the more powerful, that attracts the 
 negative of that, whose polarity is the more feeble ; and 
 never the negative of the former, that attracts the positive 
 of the latter, at least when they are free and not combined ; 
 finally, if the rotation of the atoms upon themselves is the 
 cause of their polarity, and at the same time that of their 
 temperature, how comes it that different atoms, having conse- 
 quently a different polarity, or a different movement of rota- 
 tion, may have the same temperature ? 
 
 Still recognising the force of the objections, that we have 
 been presenting, we are yet able to reply to them in part. 
 First, it appears to us that the polarity of the atom, is one of 
 the principles best established by the whole of the facts, which 
 constitute the science of electricity ; the phenomena of 
 electro-dynamic and electro-static induction, those of thermo- 
 electricity, whether in insulating bodies or in conducting 
 bodies, the facts relative to the liberation of electricity by 
 friction, are almost impossible of explanation, if we do not 
 admit this principle. And the principle once admitted, we 
 can conceive no other difference between two atoms in this 
 respect, unless it is that one has a more powerful electric 
 polarity than the other. Hence the very intimate connection, 
 that exists between chemical affinity and electricity, leads 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 883 
 
 necessarily, in the exercise of the former, to cause it to play 
 a part in the polarity of the atom. We conceive, however, 
 that this polarity, and consequently the action that it ex- 
 ercises, may be modified by the mode of the aggregation of 
 the atoms ; by their degree of insulation, arid by their tem- 
 perature ; but it is not the less very probable that it is the 
 cause of the tendency of two atoms to combine chemically ; 
 a combination which, consisting in the neutralisation of the 
 contrary electricities of the two poles, that come into contact, 
 liberates at the same time the contrary electricities also of 
 the two more distant poles. But, when once the combination 
 has taken place, the compound atom has but two poles, as the 
 simple atom had, as we have explained. Now, I grant 
 it, the hypothesis that consists in laying down as a principle, 
 that it is always by the positive pole of the more powerfully 
 polar atom, and by the negative of that which is less so, that 
 the attraction of the two atoms takes place, would have 
 need of being proved. However, the greater expansive force 
 of positive electricity, compared with that of negative at 
 equal tensions, which is established by so great a number of 
 phenomena, gives to our hypothesis a certain degree of pro- 
 bability. Moreover, I do not despair that we may succeed in 
 demonstrating it more directly. 
 
 If ever, as I hope, I succeed in obtaining this demon- 
 stration as the result of the electro-chemical researches, in 
 which I am at this moment engaged, and which must form the 
 subject of a special work, I shall endeavour at the same time 
 to insist more than I can here do upon the theoretical re- 
 lations, that may also be established between heat and 
 electrical and chemical effects. I shall then be able to reply 
 to the last of the objections, that I have just now laid down. 
 For the present, I shall confine myself to remarking that, 
 in the mechanical theory of heat, regard must be had, not 
 only to the greater or less velocity of the movement of 
 rotation of the atom, but also to its mass ; and that if, for a 
 same atom, the quantity of heat increases with this velocity, 
 it does not follow that for two atoms having different masses, 
 a same velocity of rotation is necessary, in order to their 
 
 3 L 2 
 
884 SOURCES OF ELECTRICITY. PART v. 
 
 having the same temperature. And what is true for isolated 
 atoms is more so for molecules, formed by the aggregation 
 of a greater or less number of atoms, upon which the in- 
 fluence of the mass is much more sensible ; since aggregation 
 itself results from the attraction due to the mass of the atoms. 
 This question, as it is easy to perceive, touches the most 
 delicate points of analytic mechanics ; and it is not until we 
 shall have succeeded in formularising a good mechanical 
 theory of heat, that we shall be able to solve it in a satis- 
 factory manner. 
 
 To sum up : we consider that we may, in a general 
 manner and without risk of hazarding too much, distinguish 
 chemical affinity from physical or molecular attraction, by 
 admitting that chemical affinity is the attraction of atoms, 
 operating by their contrary electric poles which come into 
 contact, so that two atoms make no more than a single one, 
 the polarity of which is a function of the polarities of the 
 elementary atoms, whilst physical attraction results from the 
 mutual attractive action that the atoms exercise over each 
 other in virtue of their masses. This last attraction is never 
 able to produce contact ; because from the action, that is 
 exerted upon the ether, which envelopes the atom in rota- 
 tion, arises a repulsive force, the intensity of which increases 
 in proportion as the space, which separates the atoms, that 
 are attracted, from each other, goes on diminishing. It is 
 this repulsive force, that increases with the rapidity of the 
 rotation of the atom, and consequently with its temperature. 
 
 The distinction, that we have been establishing between 
 chemical affinity and physical attraction appears to us to 
 have, among other advantages, that of well characterising the 
 distinctive features of these two forms of attraction. In the 
 former, there is always electricity liberated, and liberation of 
 heat, as well as the formation of a compound, which has no 
 longer any physical relation with its constituent elements : 
 now this must result from the manner in which we suppose 
 that affinity is exercised, and in particular from the fact that 
 the compojiind atom, when once it is formed, acquires an 
 electric polarity or a movement of rotation upon its axis, 
 
CHAP. in. ELECTRICITY BY CHEMICAL ACTIONS. 885 
 
 which is proper to it, and which is no longer the movement 
 of rotation of either one or the other of the constituent 
 atoms. In the latter, that is to say, physical attraction, the 
 atoms, in grouping themselves by virtue of the attraction 
 of their masses, donotcome into contact, cannot consequently 
 produce electrical effects ; they retain their proper movement 
 of rotation upon themselves, which constitute their individu- 
 ality. There may even here be some liberation of heat by 
 the effect of the approximation of the atoms, as there is ab- 
 sorption by the fact of their separation ; but these are pheno- 
 mena altogether physical, and which are connected with the 
 mechanical work, that takes place in molecular action. 
 
 We shall not terminate this paragraph without quoting in 
 support of the hypothesis of the polarity of atoms, a very 
 recent experiment of M. Foucault's, who has succeeded, by 
 giving a very rapid motion of rotation between the poles of 
 a powerful electro-magnet to a metal body of a rounded form, 
 in producing in this body a strong heat. This elevation of 
 temperature very probably arises from the successive and 
 very rapid displacements, that the particles of bodies in ro- 
 tation undergo, by the effect of the influence of the electo- 
 magnet, displacements themselves due to the fact that, in 
 virtue of their polarity, the atoms are grouped under this 
 influence in directions parallel to those of the currents of the 
 electro -magnet, so as to give rise to induction currents- 
 Moreover, we shall have occasion, at the end of the Third 
 Volume, to return to this subject in an Appendix, that we 
 shall devote to the works that have recently been done on 
 magnetism and on dia-magnetism ; we shall then endeavour 
 to complete the theory, that we have just been sketching out, 
 and which we had already in part set forth in the present 
 volume.* 
 
 * Vol. II. p. 49., and following pages. 
 
 List of the principal works relative to the subjects treated upon in this 
 Chapter. 
 
 Oersted. Electricity produced by chemical actions. Ann. de Chim. et de 
 Phys. t. xxii. p. 358. 
 
 Becquerel. Electric effects produced in chemical actions. Ann. de Chim. et 
 de Phys. t. xxiii. p. 152., and 244. ; t xxiv. p. 192., and t. xxv. p. 405.; t. 
 xxvi. p. 176.; t. xxvii. p. 5. Electric effects in the contact of liquids and metals. 
 
 3 L 3 
 
886 BIBLIOGRAPHY. 
 
 t. xxvii. p. 29. Simultaneous static and dynamic effects, (B. and Ampere), 
 t. xxviii. p. 16. Electric effect of oxygenated water, t. xxxv. p. 113.; t. xli. 
 p. 5.; t. Ix. p. 164. Electric effect in the contact of water and of some crys- 
 talline substances. Pyro-electric currents. Arch, des Sc. Phys., (Bibl. Univ.) 
 t. xxvi. p. 173. Electro-chemical theory. Ann. de Chim. et de Phys. (New 
 Series) t. xxvii p. 5. Electricity in chemical actions. Idem. t. xlii. p. 385. 
 Quantity of electricity associated with particles. Comptes rendus de VAcad. des 
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 for the works of M. Becquerel, the Ann. de Chim. et de Phys. passim , and his 
 two Treatises on Electricity. 
 
 Matteucci. Interior chemical action of the pile equivalent to the exterior 
 action. Bibl. Univ. t. Iviii. (1835.) p. 23. and following pages. Production of 
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 t. xxviii. p. 410. Production of voltaic electricity. Arch, de FElectricite, t. iv. 
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 Electricity by combustion. Arch, des Sc. Phys. (Bibl. Univ.) t. xxvii. p. 235. 
 
 Karsten. Electricity in the contact of metals and liquids. Bibl Univ. 
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 Pouillet. Electricity in combustion, &c. Ann.de Chim. et de Phys. t. xxxv. 
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 t. iii. p. 566. 
 
 De la Rive. Chemical action, source of electricity. Ann. de Chim. et de 
 Phys. t. xxxvii. p. 225. ; t. xxxix. p. 297. ; t. Ixi. p. 38. ; Bibl Univ. (1836) 
 t. iii. p. 375. ; t. iv. p. 152. and 359 Action of sulphuric acid upon zinc. 
 Ann. de Chim. et de Phys. t. xliii. p. 425. Chemical action of a single pair. 
 Arch, de VElectricite, t. iii. p. 175. Electricity due to deoxidation. Bibl. 
 Univ. (1836) t. i. p. 151. Pile of rammed carbon. Arch, des Sc. Phys. (Bibl. 
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 tricite (1840 to 1845), and the Arch, des Sc. Phys. (Bibl. Univ.) 
 
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 365. Electro-chemical effects. Idem. (1839), t. xxiii. p. 189. Passivity of 
 iron, bismuth, &c. Idem. t. iii. p. 377.; t. v. p. 177. and 397.; t. ix. p. 41 ; 
 Arch, de VElectricite, t. xi. p. 267. 286. 509. and 513. Oxy- hydrogen pile. 
 Idem. t. iii. p. 69.; t. iv. p. 56. Pile with electro-chemical effects. Idem. 
 t. xxiii. (1339), p. 189. 
 
 Faraday. Chemical origin of voltaic electricity. Arch, de T Electricite, t. 1. 
 p. 93. and 142. Quantity of electricity in the decomposition of water. Bibl 
 Univ. t. Iviii. (1835) p. 305. Chemical theory of the pile. Bibl Univ. (1835) 
 t. Iviii. p. 263. ; Bibl Univ. (1840) t. xxvii/p. 192. ; Philosophical Transactions 
 of the Royal Society of London; and P/iil. Mag. passim. 
 
 Poggendorff. Electro-motive forces ; relations between electric action and 
 chemical action. Arch, de I' Electricite, t. i. p. 168. ; t. ii. p 5. and 196. ; t. iii. 
 p. 117. 124. and 134. ; t. iv. p. 285. ; Arch, des Sc. Phys. t. iv. p. 399. Force 
 of a non-constant pile. Ann. de Chim. et de Phys. (New Series), t. vii. p. 87. 
 Laws of galvanic polarization. Idem. t. xx. p. 217. Annalen der PJiysik 
 und Chimie, passim. 
 
 Gassiot. Large water battery, and theory of the pile. Arch. deV Electricity 
 t. iv. p. 242. Arch, des Sc. Phys. t. iii. p. 41. Philosophical Transactions of 
 the Royal Society of London, 1844. 
 
 Nobili. Electricity produced by the chemical action of solutions Bibl. 
 Univ. (1829) t. xxxvii. p. 10. ; t. Ivi. (1834), p. 150. 
 
BIBLIOGRAPHY. 887 
 
 Peltier. Action of solutions. Institut. vol. v. p. 159. (No. 210). Quan 
 tity of electricity by the oxidation of a grain of zinc. Idem. t. Ixvii. p. 412. 
 
 Fechner. Becquerel's oxygen pile. Ann. der Physik. t. xlviii. p. 1. 
 
 Jacobi. Idem. Bill. Univ. (1838), t. xiv. p. 171. Constants of the pile, 
 Arch, de t Electricite, t. ii. p. 575. Kecomposition of the gas in the voltameter. 
 Ann. de Ckitn. et de Phys. (New Series), t. xxv. p. 215. 
 
 Gaugain. Gaseous pairs. Comptes Rendus de VAcad. des Sciences; 
 (October, 1853) and Arch, des Sc. Phys. (Bibl. Univ.} t. xxiv. p. 274. 
 Electricity in combustion. Arch, des Sc. Phys. (Bibl. Univ.} t. xxvi. p. 67. 
 and 240. 
 
 Marianini. Secondary piles. Ann. de Chim. et de Phys. t. xxxviii. p. 5. 
 Voltaic piles, Idem. t. xxxviii. p. 337. and 442. Idem. t. xlv. p. 118. 
 
 Grove. Gas pile. Arch, de VElectricite, t. iii. p. 489. Voltaic reaction. 
 Idem. t.iv. p. 148. Idem. Arch, des Sc. Phys. (Bibl. Univ.} t. ii. p. 354. 
 Electricity of flame. Idem. t. xvii. p. 240. and t. xxv. p. 276. Phil. Trans. 
 of the Royal Society of London ; and Phil. Mag. passim. 
 
 Beetz. Passive iron. Arch, de F Electricity t. iv. p. 509. Electro-motive 
 power of gases. Arch, des Sc. Phys. (Bibl. Univ.} t. xii. p. 285. 
 
 Nickles. Passivity of cobalt and nickel. Arch, des Sc. Phys. (Bibl. Univ.} 
 t. xxiv. p. 79. 
 
 E. Becquerel. Electro-chemical properties of hydrogen. Ann. de Chim. et 
 de Phys. (New Series} t. xxxvii. p. 385. Influence of gases upon the electricity 
 of contact. Arch, des Sc. Phys. (Bibl. Univ.} t. ii. p. 59. Electric effects due 
 to the movement of pairs. Ann. de Chim. et de Phys. (New Series} t. xliv. 
 p. 401. 
 
 Mousson. Passive iron. Bibl. Univ. t. v. (1836) p. 165. Electricity in 
 the action of solutions. Bibl. Univ. t. xxi. (1839) p. 170. 
 
 Riess. Electricity by combustion. Arch, de V Electricity t. v. p. 91. 
 
 Hankel.Idem. Arch, des Sc. Phys. (Bibl Univ.} t. xvii. p. 5. 
 
 Viard. Influence of oxygen on the pile. Ann. de Chim. et de Phys., (New 
 Series} t. xxxvi. p. 129. and t. xlii. p. 5. 
 
 Daniell. Voltaic combinations. Arch, de T Electricity t. iii. p. 623. 
 
 Smee. Platinised silver pile. Bibl. Univ. t. xxvii. (1840), p. 186. and 
 p. 386. 
 
 SiUiman. Carbon pile. Arch, de V Electricity t. iii. p. 649. 
 
 Bunsen. Voltaic pile and preparation of carbon. Ann. de Chim. et de Phys. 
 (New Series} t. viii. p. 28 
 
 Callan. Idem. Arch, des Sc. Phys. (Bibl. Univ.} t. vi. p. 47. Idem. t. 
 xxix. p. 162. 
 
 Wheatstone. Electro-motive forces. Ann. de Chim. et de Phys.t. x. p. 257. 
 Phil. Trans, of the Royal Society of London, (1843). 
 
 Goodmann. Pile with potassium. Arch, des Sc. Phys. (Bibl. Univ.} t. ix. 
 p. 305. 
 
 J. Regnault. Electro-motive forces. Ann. de Chim. et de Phys. (New 
 Series}, t. xliv. p. 453. 
 
 Svanberg. Polarising force of hydrogen. Arch, des Sc. Phys. (Bibl. Univ.} 
 t. iv. p. 296. 
 
 Lenz and Saweljev Electro-motive power of gases. Ann. de Chim. et de 
 Phys. (New Series) t. xx. p. 184. 
 
 Kohlrausch. Relations between electro-motive force and tension. Ann. de 
 Chim. et de Phys. (New Series} t. xli. p. 357. 
 
 Joule Voltaic combinations. Arch, de I" Electricite, t. iv. p. 269 Elec- 
 tric origin of chemical heat. Ann. de Chim. et de Phys. (New Series} t. xvi. 
 j). 474. 
 
 W Volta. Electricity of contact. Ann. de Chim. t. xxix. p. 91. ; t. xl. p. 217. 
 and t. xli. p. 3. 65. and 106. 
 
 Biot. Idem. Traite de Physique experimental et mathematique. Paris, 1816. 
 
 Peclet. Idem. Ann. de Chim. et de Phys. (New Scries}, t. ii. p. 233. 
 
 Zamboni. Dry piles. Ann. de Chim. et de Phys. t. ii. p. 190., and t. xxix. 
 p. 198. Bibl Univ. (1837) t. viii. p. 189. 
 
 3 L 4 
 
888 BIBLIOGRAPHY. 
 
 Delezenne. Idem. Arch, de T 'Electricity, t. v. p. 67. 
 
 Cooke. Affinity and electro-motive force. Arch, des Sc. Phys. (Bibl. Univ.) 
 t. xvii. p. 322 
 
 Favre. Relations between heat, affinity and electro-motive force. Ann. 
 de Chim. et de Phys. (New Series), t. xl. p. 193. 
 
 Wood. Heat developed by oxidation. Arch, des Sc. Phys. (Bibl. Univ.) 
 t. xxii. p. 82. 
 
 Bonsdorff. Oxidation in air. Bibl. Univ. t xviii. (1838), p. 373. 
 
 Foucault. Heat developed by magnetic influence upon a body in movement. 
 Comptes Rendus de TAcad. des Sciences, t. xli. p. 450. (17th Sept. 1855.) 
 
 NOTE X. (p. 69.) 
 
 THE following is a List of the principal works relative to the 
 subjects treated on in the Second and Third Parts of this Treatise, 
 which are contained in the First Volume ; and in the Appendix at 
 the commencement of the present Volume. 
 
 PART II. 
 Chap. V. (Vol. I. p. 124.) 
 
 1st. The memoirs of Mr. Faraday, on the induction of ordinary electricity, 
 communicated to the Royal Society of London in 1837 and 1838. Philoso- 
 phical Transactions of the Royal Society of London, 1838. 
 
 2nd. The memoirs of M. Matteucci on the polarisation of plates of mica, and 
 on the propagation of electricity in solid bodies. Bibliothe*que Unwerselle, 
 Arch, des Sc. Phys., Geneva, 1846, t. ii. p. 371. Ann. de Chim. et de Phys., 
 Paris, 1849, t. xxvii. p 133. 
 
 PART III. 
 Chap. I. (Vol. I. p. 156.) 
 
 1st. Scoresby Ann. de Chim.et de Phys. (Paris, 1838) t. Ixix. p. 106 
 2nd. Nobili. Bibl. Univ. de Geneve, t. Ivi. p. 82., and the following pages. 
 3rd. Barlow. Bibl. Univ. t. xxxiv. p. 188. 
 
 Chap. II. (Vol. I. p. 211.) 
 
 Oersted. Ann. de Chim. et de Phys. t. xiv. (1820) p. 417.; and Bibl. Univ. 
 t. xiv. p. 274., and xv. p. 137. 
 
 Ampere. Ann. de. Chim. et de Phys. t. xv. xvi. xviii. xx. xxii. xxvi. xxix. 
 xxx. and xxxvii.; and Bibl. Univ. t. xvi. xvii. xix. xx. and xxrii. (Years 
 1820 to 1828.) Theory of electro-dynamical phenomena, 1 vol. in 4to. Paris, 
 November, 1826. 
 
 G. De la Rive.T. xvi. p. 201., xvii. p. 188., xviii. p. 269. 
 
 Davy. Ann. de Chim. etdePhys. t. xxv. 1824) p. 64. ; and Bibl. Univ.t. xxv. 
 p. 98. 
 
 Faraday. Ann. de Chim, et de Phys. t. xviii. (1821) p. 337. 
 
 Savary. Ann. de Ghim. et de Phys. t. xxii. (1823) p. 91., and xxiii. 
 p. 413. 
 
 Marsh. Bibl Univ. t. xx. (1822) p. 258. 
 
BIBLIOGRAPHY. 889 
 
 A. De la Rive. - Bibl Univ. t. xxi. (1812) p. 29., and Ann.de Chim. et de 
 Phys. t. xxi. p. 24. 
 
 Weber. Ann. der Physik, t. Ixxiii. (1848) p. 193. 
 
 Chap. III. (Vol. I. p. 278.) 
 
 Arago. Magnetism by currents and electric discharges. Ann. de Chim.etde 
 Pliys. t. xv. (1820) pp. 82. 93 and 393. 
 
 Davy. Magnetisation of a still needle. Bibl. Univ. t. xvii. p. 191. 
 
 Nobili. Magnetisation by a flat spiral. Bibl. Univ. t. xxvii. p. 174. 
 
 Savary. Magnetisation. Ann. de Chim. et de Phys. t. xxxiv. (1827) p. 5. 
 
 Abria. Magnetisation by currents. Ann. de Chim. et de Phys. (3rd series) 
 t. i. (1841) p. 385. 
 
 Delesse. Magnetism of rocks. Arch, des Sc. Phys. t. x. p. 207. 
 
 Holl. Magnetisation of soft iron by currents. Ann. de Chim. et de Phys. 
 t. 1. (1832) p. 32., and t. Ivi. (1834) p. 222. 
 
 Alexandre. Influence of heat upon magnetisation by currents. Arch, de 
 TElect. t. iii. p. 658. 
 
 Froment. Magnetic instrument with a vibrating plate. Bibl. Univ., Arch, 
 des Sc. Phys. t. iv. p. 294. 
 
 Nickles. Construction of electro-magnets. Ann. de Chim. et de Phys. (3rd 
 series) t. xxxvii. p. 399. 
 
 Page. Sound produced by magnetisation. Bibl. Univ. (new series) t. ii. 
 (1839) p. 398. 
 
 Delezenne Idem. t. xvi. (1841) p. 406. 
 
 Liphaus and Quetelet. Magnetisation of iron by currents. Ann. de Chim. et 
 de Phys. t. 1. (1832) p. 331. 
 
 Marrian. Sound by magnetisation. Arch, de T Elect, t. v. p. 195. 
 
 Beatson. Sound by the transmitted current. Idem. t. v. p. 197. 
 
 Idem. Expansion of iron by the passage of the current. Bibl. Univ. Arch, 
 des Sc. Phys. t. ii. p. 113. 
 
 De la Rive. Sounds produced in iron by magnetisation and transmitted 
 currents ; and molecular phenomena. Ann. de Chim. et de Phys. (3rd series) 
 t. xvi. p. 93., andt. xxvi. p. 158. Arch, de T Elect, t. v. p. 200. Bibl.Univ., Arch, 
 des Sc. Phys. t. ix. pp. 193. and 265. 
 
 Wertheim. Sounds produced by magnetisation and influence of molecular 
 actions. Ann. de Chim. et de Phys. (3rd series) t. xxiii. p. 302. Comptes Ren- 
 dus de FAcad. des Sc. t. xxiii. p. 336.;~and Bibl, Univ., Arch, des Sc. Phys. 
 t. xxi. p. 223. 
 
 Guillemin. Influence of magnetisation on soft iron. Comptes Rendus des 
 Sc. de PAcad. des Sc. (1846) t. xxii. p. 264. 
 
 Joule, Influence of magnetisation on the dimensions of iron. Bibl. Univ., 
 Arch, des Sc. Phys. t. iv. p. 398., and t. v. p. 51. 
 
 Grove. Arrangement of particles by magnetisation, and heat produced 
 Bibl. Univ., Arch, des Sc. Phys. t. x. p. 182., and t. xi. p. 210. 
 
 Maggi. Influence of magnetisation upon the conductibility of iron for 
 heat. Bibl. Univ. Arch., des Sc. Phys. t. xiv. p. 132. 
 
 Marianini Influence of molecular action upon magnetisation. Ann. dc 
 Chim. et de Phys. (3rd series) t. xiii. p. 237., and t. xvi. pp. 430. and 448. 
 
890 BIBLIOGRAPHY. 
 
 Matteucci. Magnetisation by the current. Bib!. Univ., Arch, des Sc. Phys. 
 t. v. p. 55. 
 
 Wartmann. Sounds produced by the electric current. Bibl. Univ., Arch, 
 des Sc. Phys. t. i. p. 419. 
 
 Chap. IV. (Vol. I. p. 322.) 
 
 Schweiger. Galvanometer-multiplier. Bibl. Univ. t. xvi. (1821) p. 197. 
 
 Nobili. Idem. Bibl. Univ. t.xxix.'(1825) p. 119.,t. xxxvii. (1828.) p. 10.; 
 Ann. de Chim. et de Phys. t. xliii. (1830) p. 146. 
 
 Becquerel. Ann. de Chim. et de Phys. t. xxiv. (1823) p. 337., and t. xxxii. 
 (1829) p. 420. Electro -dynamic balance. Ann. de Chim. et de Phys. t. Ixvi- 
 (1837) p. 84. 
 
 De la Hive. Sine-galvanometer. Mem. de la Soc. de Phys. et d'Hist. Nat. 
 de Geneve, t. iii. (1st part) p. 117. (1824). 
 
 Pouillet. Sine and tangent-galvanometer. Compte Rendu de I'Acad. des 
 Sc. t. xx. p. .; and Traite de Phys. et de Meteor. 
 
 Poggendorff. Comparable galvanometer. Ann. der Physik, t. Ivii. ; and 
 Ann. de Chim. et de Phys. (3rd series) t. viii. (1843), p. 115. 
 
 Lenz. Comparable galvanometer. Ann. der Physik, t. lix. 
 
 Weber. Idem. Idem. t. Iv. 
 
 Despretz. Tangent-galvanometer or compass. Compte Rendu de I'Acad. 
 des Sc. t. xxxv. p. 449. 
 
 Gaugain. Tangent-galvanometer or compass. Compte Rendu de I'Acad. 
 des Sc. t. xxxvi. p. 191. 
 
 Bravais. Ann. de Chim. et de Phys. (3rd Series) t. xxxviii. (1853) p. 301. 
 
 Ritchie. Torsion-galvanometer. Bibl. Univ. t. xlvi. (1831) p. 9. 
 
 Melloni Comparable galvanometers. Ann. de Chim. et de Phys. t. liii. 
 
 (1833) p. 1. 
 
 Peltier. Comparable galvanometers. Ann. de Chim. et de Phys. t. Ixxi. 
 (1839) p. 225. 
 
 Chap. V. (Vol. I. p. 347, and App. Vol. II. p. 1.) 
 
 Arago. Magnetism by rotation. Ann. de Chim. et de Phys., t. xxvii. (1825) 
 p. 363., t. xxviii. (1825) p. 325.; and t. xxxii. (1827) p. 213. 
 
 Babbage and Herschel. Idem. Bibl. Univ. t. xxix. (1825) p. 354. 
 
 Harris. Idem. Bibl. Univ. t. xlvii. (1831) p. 134. 
 
 Christie. Idem. Bibl. Univ. t. xxix (1825) p. 254. 
 
 Ampere and Colladon. Idem. Mem. de I'Acad. des Sc. (1827), and Bulletin 
 de Ferrussac, i. vi. (1826) p. 211. 
 
 Haldat. Idem. Ann. de Chim. et de Phys. t. xxxix. (1828) p. 232., and 
 t. Ixvii. (1838) p. 203. 
 
 Barlow. Idem. Bibl Univ. t. xxxiv. (1827) p. 188. 
 
 Poisson Idem. Ann. de Chim. et de Phys. t. xxxii. (1826) p. 225. 
 
 Faraday. Induction currents. Philosophical Transactions of 1832 and 
 1833 ; Bibl. Univ. t. xlix. (1832) p. 341., and lix. (1835) p. 128. ; Ann. de 
 Chim. etde Phys. 1. 1. (1832) pp. 5. and 113., and t. li. (1831) p. 404. 
 
 Henry. Extra currents and induction of various orders. Arch, de I' Elect. 
 t. ii. p. 350., and t. iii. p. 484. Ann. de Chim. et de Phys. (new series) t. iii. 
 p. 394. 
 
BIBLIOGRAPHY. 891 
 
 Breguet and Masson. Induction. Ann. de Chim. et de Phys. (new series) 
 t. iv. p. 129. 
 
 Masson. Induction of a current upon itself. Ann. de Chim. et de Phys. 
 t. Ivi. p. 5. 
 
 Nobili and Antinoni Idem. Ann de Chim. et de Phys. t. xlviii. (1832) p. 
 412. 
 
 Matteucci. Magnetism of rotation. Arch, des Sc. Phys. et Nat. t. xxiii. 
 p. 39. Induction by discharges. Ann. de Chirn.et dePhys. (new series) t. iv. 
 p. 153., and Arch, de I 'Elect, t. v. p. 530. 
 
 Pixii. Magneto -electric machine. Ann. de Chim. et de Phys. (1832) p. 76 
 
 Marianini. Induction by discharges. Ann. de Chim. et de Phys. (new 
 series) t. x. p. 491., and t. xi. p. 385. 
 
 Riess. Idem. Ann. de Chim. et de Phys. t. Ixxiv. (1840) p. 158. ; Arch, de 
 TElect. 
 
 Verdet. Idem. Ann. de Chim. et de Phys. (new series) t. xxiv. p. 377. 
 
 Knochenhauer. Idem. Ann. de Chim. et de Phys. (new series) t. xvii. p. 130. 
 
 Dove. Various influences of induction. Ann. de Chim. et de Phys. (new 
 series) t. iv. p. 336. ; Arch, de I" Elect, t. ii. pp. 290. 315. and 338., t. iii. pp. 49. 
 and 63., t. iv. p. 331. 
 
 Lenz. Theory of induction and properties of induced currents. Ann. de 
 Poggendorff, t. xxxi. (of the new series, 1834) p. 483., t. xxxiv. p. 385., and 
 t. xlviii. p. 385. 
 
 Weber. Unipolar induction and theory. Arch, de T Elect, t. v. p. 441.; 
 Electro-dynamische Maasbestimmengen (Leipsig, 1846). 
 
 Palmieri,. Induction by terrestrial magnetism. Arch, de T Elect, t. iii. p. 
 341 ., t. iv. p. 172., and t. v. p. 181. ; Ann. de Chim. et de Phys. (new series) 
 t. viii. p. 503. 
 
 Abria. Induction of various orders and by discharges. Ann. de Chim. et 
 de Phys. (new series) t. iii. p. 5., and t. vii. p. 462. 
 
 Ampere. Action of a current and a magnet. Ann. de Chim. et de Phys* 
 
 t. xxxvii Induction currents. Ann. de Chim. et de Phys. t. xlviii. (1831) 
 
 p. 405. (1828) p. 113. 
 
 Prevvst, Professor. Theory of the action of currents. Bibl. Univ. t. xxi. 
 (1821) p. 178. 
 
 Wartmann. Laws of induction. Ann. de Chim. et de Phys. (new series) 
 t. xix. pp. 257. 281. and 385., t. xxii. p. 5. 
 
 A. De la Rive. Induced currents. Bibl Univ. t. ix. (1838) p. 408. ; 
 Arch, de t Elect, t. i. p. : 175., and t. iii. p. 159. ; Ann. de Chim. et de Phys. 
 (new series) t. viii. p. 36. ; Mem. de la Soc. de Phys. et de Hist. Nat de Geneve, 
 t. viii. p. 191., t. ix. p. 163., and t. xi. p. 225. ; Arch, des Sc. Phys. et Nat. 
 t. i. (1846) p. 373. 
 
 Chap. VI. (VoL I. p. 441., and App. Vol. II. p. 1.) 
 
 Lallemand. Attraction and repulsion of induced currents. Ann. de Chim. 
 et de Phys. (new series) t. xxii. p. 19. 
 
 Coulomb. Effects of magnetism on all bodies. Journ. de Phys. t. liv. 
 (1802). 
 
 Becquerel. Transverse magnestism. Ann. de Chim. et de Phys. t. xxv. 
 (IW4) p. 269., and t. xxxvi. (1827) p. 337. 
 
892 BIBLIOGRAPHY. 
 
 Arago. Oscillations of the needle upon non-conducting substances. Ann. 
 de Chim. et de Phys. t. xxxii. (1826) p. 21. 
 
 Lebaillif. Repulsion of the needle hy bismuth and antimony. Bibl. Univ. 
 (1829) t. xl. p. 83. 
 
 Faraday. Diamagnetism. Arch, des Sc. Phys. (et Bibl. Univ.) t. ii. pp. 
 42. and 145., t. ix. p. 141., t. xvi. pp. 52. and 89., t. x. and xvii. p. 
 105. Magneto-crystalline phenomena, Idem. t. xii. p. 89. Lines of force of 
 the magnetic field. Idem. xvi. pp. 129. and 182., t. xix. p. 54., and t. xx. 
 p. 141. Action of magnetism on polarised light. Idem. t. i. pp. 70. and 305., 
 andt. iii. p. 338. Trans. Phil. (1846, 1848, 1850, 1851, and 1852), Phil. 
 Mag. (Sept. and Nov. 1846.) 
 
 Weber. Diamagnetic polarity. Ann. der Physik, t. Ixxiii. (1848) p. 241., 
 and t. Ixxxvii. (1852). 
 
 Poggendorff. Diamagnetic polarity. Ann. der Phys. t. Ixxiii. p. 475. 
 (1848). 
 
 Wiedemann Circular magnetic polarisation. Ann. der Physik (1850 
 
 and 1852), and Arch, des Sc. Phys. (Bibl Univ.) t. xvii. p. 47- 
 
 E. Becquerel. Action of magnetism upon all bodies. Ann. de Chim. et de 
 Phys. (new series) t, xvii. p. 449., and t. xxviii. p. 253. 
 
 Plucker. Determination of the magnetic and diamagnetic power of bodies 
 Magneto-crystalline phenomena. Ann. de Chim. et de Phys. t. xxix. 
 (new series) p. 129. ; Arch, des Sc. Phys. (Bibl. Univ.) t. xi. p. 196. ; t. xviii. 
 p. 146., and t. xix. p. 102. 
 
 Reich. Idem. Arch, des Sc. Phys. (Bibl. Univ.) t. xi. p. 41. 
 
 Verdet. Diamagnetic induction. Ann. de Chim. et de Phys. (new series) t. 
 xxxi. p. 187. 
 
 Tyndall and Knoblauch. Magneto-crystalline phenomena. Arch, des Sc. 
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 Matteucci. Diamagnetism, action on polarised light, and magneto-crys- 
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 Arch, des Sc. Phys. t. xxii. p. 24., and t. xxiv. p. 68. 
 
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 Berlin Idem. Ann. de Chim. etde Phys. t. xxii. (new series) p. 5. 
 
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NOTES 
 
 RELATIVE TO 
 
 MATHEMATICAL DEVELOPMENTS 
 
 OP 
 CERTAIN PARTICULAR POINTS. 
 
 NOTE A. (p. 69.) 
 
 Note relative to the Propagation of Electricity. 
 
 WE have said that M. Kirchoff had endeavoured to determine the 
 laws of the propagation of electricity in other cases than that of 
 linear propagation, and in particular in that of a conducting plate. 
 It is impossible for us to reproduce in this note M. Kirchoff 's com- 
 plete work ; we shall content ourselves with explaining the course 
 that he has pursued ; and, with showing how, on setting out from 
 the principles established by Ohm (principles which Ohm himself 
 has applied to the linear propagation of electricity), he has suc- 
 ceeded in determining the stationary state, that is acquired by 
 electric tensions at the different points of a conducting plate, placed 
 in the circuit of a pile ; and how the results deduced from these 
 calculations have been enabled to be verified experimentally. 
 
 M. Kirchoff admits, according to Ohm, that if, between two ele- 
 ments infinitely near of a same linear conductor, there is a differ- 
 ence of tension (which is necessarily infinitely small), there con- 
 stantly passes from one of these elements to the other a quantity of 
 electricity proportional to the difference of the tensions, to the 
 section of the conductor, to the co-efficient of conductibility, and in- 
 versely proportional to the distance of the two elements. These 
 principles, which are the same as those that we have already 
 
894 NOTES. 
 
 established for linear propagation, being once admitted, the 
 following is M. KirchofTs method of applying calculation to them. 
 
 The place of the points, at which the tension has a same deter- 
 mined value, forms in general a curve, which enjoys the property 
 of being normal to each of its points in the direction, according 
 to which the electricity is propagated; since it follows imme- 
 diately from the principle laid down above, that there is no 
 movement of electricity from one point to another of this curve. 
 According to this, the corresponding strata of equal tension will 
 lead with certainty to the complete knowledge of the propagation 
 of electricity. Now, in order to arrive at the equations of these 
 curves, we must first find the expression of the tension u, in 
 any point of the plate in the function of the co-ordinates of 
 this point ; and the equation, that will be obtained, on making 
 this function of the co-ordinates equal to a constant, will be the 
 equation of one curve of equal tension for a determined tension ; all 
 the others will be obtained in the same manner, by causing the 
 constant to vary. 
 
 We shall not follow M. Kirchoff into the calculations by means 
 of which he determines the expression of the- quantity of electri- 
 city that passes in the unit of time through any element of a 
 curve ; but we shall confine ourselves to remarking that, for this 
 purpose he considers two curves of equal tension infinitely near, 
 and on these curves two elements comprised between the same 
 normals; the parallelepiped, that has for its base the rectangle 
 comprised between the two elements and the two normals, and 
 for its height the thickness of the plate, being capable of being 
 assimilated to a linear conductor ; since the electricity is propa- 
 gated in it only parallel to the normals. He thus succeeded in 
 finding the equation of curves of equal tension ; and this equation 
 showed him that these curves are curves, whose centres are situ- 
 ated on the line that joins the points A and A' of the plate on 
 which the two electrodes abut in a situation such that the ex- 
 tremities of the diameter of each curve are situated harmonically 
 in relation to the points A A'. 
 
 M. Kirchoff has verified the conclusions of theory by numerous 
 experiments. He has first determined the form of the lines of 
 equal tension on a circular plate, communicating by two points of 
 its form with the electrodes of a pile. The plate was touched at 
 the extremities with the wire of a galvanometer ; and the relative 
 positions were determined, which it was necessary to give to 
 
NOTES. 895 
 
 these two extremities, in order to produce no deviation upon the 
 needle of the galvanometer ; in this case, the two points of 
 contact belong to a curve of equal tension ; and this curve had 
 truly the form and the position that was assigned to it by theory. 
 M. Kirchoff has also found a complete agreement between the 
 numerical expression of electric tension, which he had succeeded 
 in determining, and the results obtained at the end of a series of 
 experiments, in which the difference of the tensions of two points 
 taken on the plate, was neutralised by the electro-motive force of 
 a thermo-electric pair, which served to measure this difference. 
 Finally, M. Kirchoff has further verified the accuracy of his 
 theory by measuring the deviations of a small magnetised needle, 
 suspended at a very small distance above the various points of the 
 disc still placed in the circuit, and by comparing them with those 
 which he had succeeded in determining theoretically.* 
 
 NOTE B. (p. 86.) 
 Note relative to derived Currents. 
 
 WE have defined what we understand by primitive current, 
 principal current, partial current, and derived current. It re- 
 mains for us to give their values, which are easily deduced from 
 Ohm's laws. Calling the intensity of the primitive current i, that 
 of the principal current i', those of the partial and of the derived 
 currents i and i' the resistance or the reduced length of the 
 portions of the circuit, corresponding to the principal, the partial, 
 and the derived currents, L, I and /' ; calling E the electro- motive 
 force, and bearing in mind that the two circuits / and /' may be 
 
 7 /' 
 
 replaced by a single one, whose resistance is equal to^ - we shall 
 
 have, as we demonstrated (p. 78.) i' = t-fi'. 
 ' E 
 
 Moreover, as the portions of rrents, that pass through 
 
 two conductors, which abut at the same points of junction, are 
 in the inverse ratio of the resistances of these conductors, we 
 have 
 
 * A more complete idea may be formed of M. KirchofFs researches, by con- 
 sulting the detailed and very well arranged extracts, that M. Verdet has given 
 of the theoretic calculations and labours of the learned German philosopher in 
 the Annalesde Chim. et de Phys. t. xl. pp. 115. and 327. There will be found 
 also (t. xl. p. 236.) an extract of the researches of M. Smaasen on the same 
 subject. 
 
896 NOTES. 
 
 We deduce from this i = ^- ;"and substituting for i + *'=i', 
 
 L -|- t 
 
 the value of i', we have i = . ., //x ; and in like manner 
 
 Mr. Wheatstone has applied the theory of derived currents to 
 the construction of several apparatuses, the detailed description 
 of which is found in the Memoir, published by the learned Eng- 
 lish philosopher in The Philosophical Transactions of the Royal 
 Society of London, 2nd part, 1843. We shall confine ourselves 
 here to stating summarily the object and the principle of the two 
 most important of these instruments, having already made known 
 the rheostat in the body of the work. 
 
 The object of the first instrument is to measure small resistances 
 too feeble to be determined by the rheostat ; and this by means 
 of a differential apparatus. With this view, four similar con- 
 ducting wires are arranged in a lozenge, the precaution being 
 taken of providing a solution of continuity in the two, that are 
 adjacent at one of the obtuse angles of the lozenge. The two 
 electrodes are placed at the two acute angles, and the two ex- 
 tremities of a galvanometer at the two obtuse angles of the 
 lozenge. If the four conducting wires were all continuous, as 
 they are, and perfectly similar, there would be established in the 
 wire of the galvanometer two currents, equal, but moving in 
 contrary directions ; so that the needle would remain at rest. If 
 now, by filling up the solution of continuity of one of the wires, 
 we introduce an unknown resistance, the current that traverses 
 it, is more feeble than the other ; and equilibrium is established 
 by filling up the solution of continuity of the other wire by a 
 known resistance, which is rendered equal to the unknown re- 
 sistance, and which serves consequently as its measure. The 
 partial current is thus rendered equal to the derived current. 
 
 The object of the second apparatus, to the construction of which 
 Mr. Wheatstone has applied the properties of derived currents, is 
 to determine with accuracy the deviation of the needle of the 
 galvanometer, that corresponds to a current of an intensity, 
 which is in a certain relation the half, for example, with that 
 of the current, which has produced a given deviation. The fol- 
 lowing are the principles upon which the arrangement of the 
 instrument rests. " If a wire of the same length, thickness, and 
 
NOTES. 897 
 
 conductibility, as that of the galvanometer, be placed so as 1o 
 divert a portion of the current from it, it is obvious that one-half 
 of the current will pass through the galvanometer wire, and the 
 other half through the diverting path. Though it simplifies the 
 consideration to suppose the extra wire to have the same length, 
 diameter, and conducting power, it is easy to see that the same 
 result follows if the two wires present the same resistance, which 
 they do whenever s'c'l = scl'. If the added wire produced no 
 alteration in the intensity of the principal current, one- half of the 
 former force would act upon the galvanometer ; but this is not the 
 case, the addition of the wire produces the same effect as doubling 
 the section of the galvanometer wire would do, and the total 
 resistance of the circuit is therefore diminished. If the strength 
 of the original current, when it passes wholly through the galvan- 
 
 ometer = - - (r being the resistance of the galvanometer wire, 
 and R all the other resistances in the circuit), - will be the 
 
 strength of the principal current when the extra wire is added ; 
 if now an additional resistance = ~, that is to say a wire, whose 
 
 resistance is equal to half that of the galvanometer wire, be 
 added to the principal portion of the circuit, the intensity will be 
 
 p 
 
 again - , and the force, acting on the galvanometer will be 
 
 exactly half what it was at first." 
 
 We will further cite, among the numerous applications, which 
 Wheatstone has made of the properties of derived currents, 
 that, by means of which he succeeded in measuring currents of a 
 considerable intensity by means of a very sensitive galvanometer, 
 which would be impossible if the galvanometer was simply placed 
 in the circuit of these currents. With regard to other applications, 
 and to the details of the construction of the apparatus, we refer 
 those who desire to know them, to Wheatstone's original Memoirs 
 entitled " An Account of several new Instruments and Processes 
 for determining the Constants of a Voltaic Circuit" Phil. Trans. 
 Part II. 1843. 
 
 " When a galvanometer is employed to measure the force of a 
 current, its wire is usually interposed in the circuit. But it is 
 impossible, in this way, to make use of the same galvanometer to 
 
 VOL. II. 3 M 
 
898 NOTES. 
 
 measure the force of the current in circuits of different kinds. 
 A galvanometer with numerous coils of thin wire adds a very 
 considerable resistance to a circuit, in which the electro- motive 
 force is great and the resistance small ; while, on the other hand, 
 a galvanometer with a short thick wire will give scarcely any 
 indication in a circuit, in which the resistance is very great, 
 though the electro-motive force may be considerable. Besides, a 
 delicate galvanometer is incapable of indicating energetic forces. 
 
 " But, by the following simple means, the same delicate gal- 
 vanometer may be employed to measure forces of every degree of 
 energy, and in all kinds of circuits, without introducing any 
 inconvenient resistance into them. 
 
 " If the current be caused to pass simultaneously through two 
 paths, one being the wire of the galvanometer, and the other an- 
 other wire connected with its two ends, the current will be divided 
 in the inverse proportion to the resistances of the two paths. 
 The action upon the needle of the galvanometer may hereby, 
 by employing different wires to divert a portion of the 
 current, be reduced to any degree. If the proportionate forces 
 are known for the galvanometer without the reducing wire, 
 they will remain equally proportionate, whatever the resistance 
 of the latter may be ; but measures made with the same instru- 
 ment, with different reducing wires applied, will not be comparable 
 unless the changed resistance of the galvanometer thus modified be 
 taken into account. 
 
 " But strictly comparable measures may be obtained, if the 
 precaution be taken of adding to the principal portion of the 
 circuit, a resistance which will compensate for the diminution of 
 resistance, occasioned by placing the reducing wire. Let g be the 
 reduced length of the galvanometer wire, and n g that of the 
 reducing wire. The force of the current in the principal portion 
 of the circuit will be to that in the galvanometer wire as 
 
 1 : -. The resistance to be added to the principal portion 
 
 of the circuit, in order to maintain the current the same as when 
 
 no reducing wire is added, is ff ,. 
 
 n + 1 
 
 " When the measures of energetic currents are required to be 
 determined by means of a delicate galvanometer, it is sufficient 
 to attach its two ends to two points of the conducting wire. The 
 distance between these points must remain the same in all com- 
 parative experiments, but the absolute deviations of the needle 
 
NOTES. 899 
 
 will be greater as these points are further from each other. In 
 the case of the circuit of a powerful electro-magnetic engine, or of 
 a volta-typing apparatus, the diminution of resistance occasioned 
 by connecting the galvanometer wire in the manner above de- 
 scribed is so trifling, that it would be useless to take it into 
 account, and the compensation above alluded to is therefore 
 unnecessary." Ibid. pp. 322 -3. 
 
 NOTE C. (pp. 153. and 217.) 
 
 
 
 Note relative to the Laws of the Discharges of Electric Batteries. 
 
 THE following is the method whereby Riess has succeeded in 
 establishing the law of the proportionality of the explosive dis- 
 tance of the discharge to the density of the electricity accumulated 
 upon the conductor, whence the spark comes out ; a law which he 
 
 expresses by the formula d = b . ^ ; d expressing the distance, at 
 
 s 
 
 which the discharge takes place, or the explosive distance ; q, 
 the absolute quantity of accumulated electricity ; s, the surface 
 
 of the conductor (the relation ? being thus the mean density of 
 
 s 
 
 the electricity) ; and finally b being a constant. We have 
 already seen that Riess' experiments, by means of the spark- 
 micrometer, determine this constant b, and give a remarkable 
 verification of the law, such that, on setting out from the 
 value found for 6, which is 0-833, we may make use of the above 
 formula in order to deduce from it q, when we know d and b. 
 But it remains for us to know the method, that has been fol- 
 lowed by Riess, in order to establish the law. This consists in 
 causing the distance of the discs of a condenser to vary ; and 
 in measuring by means of the torsion-balance the density of 
 the free electricity upon the inducing plate. Tables are thus 
 constructed, in which the distances of the plates, and the cor- 
 responding densities are placed opposite to each other. In a 
 second series of experiments, the distances of the discs were 
 made to pass through the same values as in the former series ; 
 and by measuring the explosive distances by means of the spark- 
 micrometer, new Tables were obtained, wherein the distances of 
 the plates, and the corresponding explosive distances, were placed 
 opposite to each other. Hence nothing further remains than to 
 
 3 il 2 
 
900 
 
 NOTES. 
 
 prove that there exists approximately between the densities the 
 same relations as between the explosive distances. 
 
 The condensing apparatus is composed of two discs of brass, 
 supported vertically upon insulating feet, and of which one 
 the condenser is so arranged as to slide along a graduated rule, 
 the divisions of which indicate the respective distances of the 
 two discs. To the outer surface of the collector is fixed normally 
 a conducting wire, terminated by a ball ; it is the electric density 
 of this sphere, which serves as a measure to that of the plate ; the 
 determination of this density is then made with a small proof-ball, 
 which is placed at t>f the torsion-balance ; the relation of the 
 torsions gives the relation of the densities, which vary with the 
 distance of the discs.* Riess takes for a unit the electric density 
 of the collector for an infinite distance from the condenser ; that is 
 to say, when the latter is no longer acting. 
 
 Distances of the 
 
 
 
 
 
 
 
 
 
 discs - - oo 
 
 50 
 
 20 
 
 15 
 
 10 
 
 5 
 
 4 
 
 3 
 
 2 
 
 Density - - 1 
 
 0-897 
 
 0-683 
 
 0-595 
 
 0-492 
 
 0-335 
 
 0-186 
 
 0-135 
 
 0-173 
 
 This measure of the explosive distances was made by means of 
 the spark-micrometer, the fixed ball of which communicates with 
 the sphere of the collector, and its movable ball with the ground. 
 The following is a Table, corresponding to the preceding one, and 
 in which the unit of explosive distance is that which is found for 
 an infinite distance of the discs ; that is to say, for a distance at 
 which they no longer have any influence over each other. 
 
 Distances of the discs oo 
 Explosive distances - 1 
 
 50 
 0914 
 
 20 
 0-687 
 
 10 
 0-451 
 
 5 
 0-272 
 
 2 
 0-105 
 
 We see, on comparing the two Tables, that the numerical results 
 agree better in proportion as the distance of the discs is greater ; 
 which is doubtless due to the induction of the movable ball upon 
 the fixed one ; an induction, the energy of which increases very 
 
 * We must, in fact, mention, that the operation is commenced by charging the 
 collecting disc, when it is beyond the influence of the condensing disc, with all 
 the electricity that can be transmitted to it by the source with which it is in 
 Communication ; the collector is then gradually brought near, so as constantly 
 to diminish the quantity of free electricity, which must indeed become less in 
 proportion as the discs are nearer to each other : the total quantity of electricity 
 always remaining constant. It is this free quantity, whose density and 
 explosive distance are compared. 
 
NOTES. 901 
 
 rapidly when the two balls approximate. It is by means of a great 
 number of experiments analogous to these, whose results are con- 
 tained in the above Tables, that Riess arrived at the important law 
 that the explosive distance in a point of the collecting disc is pro- 
 portional to the electric density in this point. 
 
 NOTE D. (p. 230.) 
 
 Note relative to the Formula relating to the Electric Thermometer 
 and to the Laws of Heating by Electric Discharges. 
 
 RIESS has established the formula, which, in the electric thermo- 
 meter, gives the temperature of the wire traversed by the discharge, 
 or by the electric current, when the falling of the liquid has 
 been determined in the thermometric tube. Let T be the tem- 
 perature of the wire, that is required to be determined, at the 
 moment when the current passes ; the heating of the wire raises 
 the temperature of the air of the globe, and causes it to pass from 
 
 t to t'. Its elastic force consequently increases, and from p 
 
 / -I . ./ 
 
 becomes p' ; p / being determined from the relation = Z 
 
 p \+at 
 
 or p' p = P y in which a is the co-efficient of the 
 1 , 
 
 a 
 
 dilatation of the air, and p, the barometric pressure observed at 
 the moment of the experiment, which we will designate by b. 
 Let 6 be the number of divisions traversed by the liquid (the 
 unit employed by Riess is the line) ; let ^ be the angle of the 
 graduated tube with the vertical ; 6 cos. is the height of the 
 column of liquid displaced by the elastic force of the air of the 
 
 globe ; and cos -9 j s tj ie height of this column reduced into mer- 
 u 
 
 cury ; fy -f- '-^- would therefore be the value of p', if no 
 
 account was taken of the change of volume of the air ; now, let 
 K be the primitive volume of the air expressed in cubic lines, let 
 d be the section of the tube, the relation of the two volumes 
 occupied by the same mass of air will be 
 K fr 
 
 3 M 3 
 
902 NOTES. 
 
 We have therefore/ = ( b + 6 cos ' ^ . (\ + |^ by sub- 
 \ u ) \ k ) 
 
 stituting for p and p' their values in the first equation ; and, by 
 co-ordinating in respect to 0, we arrive at the following equation : 
 
 6" + ( bu +k\- l^L* . y- '> = 0; 
 
 \ COS. (j> ) COS. (f> 1 
 
 a 
 
 which, on placing - = e, gives 
 cos. <f> 
 
 7, i ~ J, t, 
 
 The development of the expression, which is under the 
 radical, when k is very great in respect to the other quantities 
 that enter into it, which is the case here, gives an excessively 
 convergent series, the first two terms of which are amply 
 sufficient for all the values of (? 1\ that may be presented 
 in experiments. We have thus for the very simple expression 
 
 0= ^A_ - .tf-fl.m 
 
 We have now to express the elevation of the temperature of 
 the wire in a function of the elevation of temperature of the 
 air of the globe. And it is in this part of his calculation that 
 Riess neglects the action of the glass envelope upon the air 
 that it contains ; but we have already said that this action may 
 be entirely neglected ; for the descending of the liquid takes place 
 in a very short time, and the difference of temperatures of the 
 envelope and of the air is always extremely feeble. Let then 
 M be the mass of the wire, that traverses the globe ; c its specific 
 heat ; m and c the same elements for the air. When equilibrium 
 of temperatures is established, we have necessarily the following 
 relation 
 
 (T f) M c = (t' i) m c ; whence 
 
 M C 
 
 Riess rere for m substitutes ** -, calling u the mass of air, 
 
 1 -j- a t 
 
 that would fill the same volume of the globe at the temperature 
 of (32 Fah.), and under the pressure of 1 line. 
 
 By thus making the value of t and of b enter into the expression 
 of m he finally succeeds in being able to compare together the 
 
NOTES. 903 
 
 experiments, in which these elements are no longer the same. 
 We have therefore 
 
 ^ bc +Q (2) 
 c (1 + a t) ) 
 
 On now eliminating (if t) between the equations (1) and (2) 
 we arrive at the following relation : 
 
 According to which we see that the elevation of temperature 
 of the wire is proportional to 0, provided that t and b are 
 constant. 
 
 But it is moreover easy to find the expression of the errors 
 that are committed in making use of the formula (3) in this case, 
 in which t and b sensibly vary. Indeed, on differenting the equa- 
 tion (3) in respect to b, and in respect to t, we have : 
 
 [ -Expressions according to which it is easy to see that the in- 
 evitable error of experiment would greatly exceed these cor- 
 rections. 
 
 Indeed, in the unfavourable case, in which a platinum wire of 
 0'" in diameter, and 5'" in length, might be placed in the globe, 
 we should have : 1st, If the barometric height varied from 360 to 
 
 d d = 0-000355 d b 
 for a variation of temperature from 15 to 15 -f- d t ; 
 
 d d = 0-0000095 d t. 
 
 It is by means of the electric thermometers, of which we have 
 been giving the formula, that Bless has established the different 
 laws relative to the development of heat brought about by electric 
 discharges through wires. We have put forth in the body of the 
 work the principal of these laws ; we shall not return to them, 
 contenting ourselves with referring those of our readers, who 
 might desire to have further details, to the Treatise on the Electri- 
 city of Friction by Kiess Die Zehre von der Reibaugs Electricitaty 
 von P. S. Riess: Berlin, 1853. 
 
 3 M 4 
 
904 NOTES. 
 
 NOTE E. (p. 375.) 
 
 Note relative to the Electrolytic Decomposition of Complex 
 Compounds. 
 
 WE shall here, by giving the summary of the numerous important 
 experiments of MM. Daniell and Miller, complete the details on the 
 electrolysis of secondary compounds, which we have not given, on 
 account of their extent, in the body of the work. We refer, for 
 the description of the experiments themselves, to the Memoir of 
 these two English philosophers, entitled, On the Electrolysis of se- 
 condary Compounds, inserted in the Philosophical Transactions of 
 the Royal Society of London, Part I. for 1844. 
 
 We shall confine ourselves to remarking that the experiments 
 were made by means of an apparatus with three cells separated 
 by two diaphragms of bladder, and so arranged that the gases 
 might be collected, which were liberated in the two extreme cells 
 at the surface of the two platinum electrodes, that plunged into 
 them. A voltameter with acidulated water was always in the 
 circuit, in order to measure the equivalent of electric force. 
 The three cells were filled either with the same liquid or with 
 different liquids. The experiments were made upon the different 
 phosphates, arseniates, arsenites, sulphates, sulphites and hyposul- 
 phites ; upon the various ferro-cyanurets of potassium, upon 
 the double salts of copper and potash, magnesia and potash, &c. 
 The following are, word for word, the conclusions, that the 
 authors have deduced from their researches. 
 
 " In every instance the definite action of the electric current 
 is maintained ; and its passage through a compound liquid 
 conductor is always marked by the disengagement at the 
 platinode of hydrogen or the metallic element, or else of a group 
 of substances, like ammonium, constituting an equivalent com- 
 pound ; and the simultaneous disengagement at the zincode of the 
 non -metallic element, or a group of substances of iso-electric 
 powers. Of such electrolytes it may be convenient to distinguish 
 the following classes : 
 
 " 1st. An electrolyte may consist of simple ions, and then must 
 be constituted of a single equivalent of a metal (or H) for its 
 cation, and a single equivalent of a non-metallic element for its 
 anion ; as K, i; AG, CL ; &c. ; they may be termed simple elec- 
 trolytes. 
 
 " 2nd. An electrolyte may consist of a compound cation, a single 
 
NOTES. 905 
 
 equivalent of which must take the place of a metal ; and a single 
 equivalent of a simple non-metallic anion, as NH 4 , c/. Organic 
 alkalies probably form compound cations of this nature, and when 
 their salts are electrolysed, hydrogen is always disengaged with 
 them at the platinode, as with ammonia : these and the following 
 we may call complex electrolytes. 
 
 " 3rd. An electrolyte may consist of a compound anion, a single 
 equivalent of which would take the place of the simple non- 
 metallic anion, with a single equivalent of a simple cation, a metal 
 (or H), as H, NC 2 ; K, so 4 ; NA, NO 6 . 
 
 " 4th. An electrolyte may consist of a single equivalent of a 
 compound cation, and a single equivalent of a compound anion, 
 as NH 4 , so 4 . 
 
 " These four cases may be included in the term Monobasic Elec- 
 trolytes, as a single equivalent of force (measured by the volta- 
 meter) would electrolyse single equivalents of the electrolytes. 
 
 " 5th. An electrolyte may also consist of two or more equivalents 
 of a metallic cation or (H), or of single equivalents of two or more 
 metallic cations or (H) ; when the anion must consist of a single 
 equivalent of a compound ion, as (K 2 FE CY 3 ). This compound 
 ion, in the case of the oxysalt, contains the so-called anhydrous 
 acid in combination with as many equivalents of oxygen as there 
 are of metallic cations (or H) in the compounds, as (NA 3 , P 2 , o 5 , O 3 ). 
 In this case as many equivalents of force will be required for the 
 electrolysis of one equivalent of the electrolyte as there are equi- 
 valents of metal (or n) in the cation. They may be denominated 
 Polybasic Electrolytes. 
 
 " In these compound anions and cations, it would appear that the 
 oxygen which travels with the acid group, and the hydrogen 
 which is evolved with the alkaline group, must be connected with 
 the other elements whilst under the influence of the current in a 
 manner differing from that in which the latter are combined 
 together ; for we have found that in most cases this connection is 
 immediately dissolved upon their escape from the electric influence, 
 whilst in some others their apparent permanent combination is 
 only the effect of secondary action, where the oxygen is capable 
 of forming a chemical compound of a higher degree of oxygenation 
 and, like other secondary actions of a similar nature, is variable in 
 its amount. 
 
 " The disengagement of the cation and anion of an electrolyte 
 in equivalent proportions is not always effected, as is commonly 
 represented, by their simultaneous transfer in opposite directions 
 
906 NOTES. 
 
 to their respective electrodes, in the exact proportion of half an 
 equivalent of each ; but is sometimes brought about by the 
 transfer of a whole equivalent of the an ion to the zincode, whereby 
 a whole equivalent of the cation is left uncornbined at the pla- 
 tinode ; or by transfer of unequivalent portions of each in opposite 
 directions, making however together a whole equivalent of matter 
 transferred to one electrode or the other ; or speaking more cor- 
 rectly, by the transfer of a quantity of matter capable of exerting 
 one equivalent of chemical force, so that when the anion transferred 
 to the zincode exceeds half an equivalent, the cation transferred 
 to the platinode is in an equal proportion less than half an equi- 
 valent, and vice versa ; the anion and cation set free being always 
 in equivalent proportions. We have, however, in no case ob- 
 served the transfer of a whole equivalent of the cation to the 
 exclusion of the anion." 
 
 MM. Daniell and Miller have seen in the results of their ex- 
 periments a serious objection against the molecular theories of 
 electrolysis, such as they were formularised by Grotthus and 
 by Daniell himself, and such as we have ourselves explained 
 them. We think, on the contrary, that all the anomalies or apparent 
 exceptions to these theories, that may be presented by the facts, 
 observed by the English philosophers, are very well explained, if 
 we have regard to the very just observation of M. D' Almeida 
 that, in the electrolysis of solutions, account must be taken of the 
 conducting powers of the different parts of the mixture that 
 forms the solution, in such sort that it is the most conducteous 
 that are electrolysed ; and that the substances, which show them- 
 selves at the electrodes, are often secondary products. (For 
 further details on the researches of M. D' Almeida, see his original 
 memoirs, Arch, des Sc. Phys. (Bibl. Univ.) t. xxix. p. 5., the 
 principal results of which we have given in the body of the work, 
 p, 384. and following pages.) 
 
 NOTE F. (p. 787.) 
 
 Note relative to M. Poggendorff's Method for the Determination 
 of the Electro-motive Force of a non-constant Current. 
 
 M. POGGENDORFF'S method differs essentially from all others, in 
 that it measures, not the current itself, but the tendency to the for- 
 mation of the current : now, as in currents of non-constant force, it 
 is the action of the current itself, which gives rise to the disturbing 
 
NOTES. 907 
 
 causes that destroy its constancy, it is evident that these causes 
 cease to exist from the moment that the current does not enter 
 into activity. The question, then, is to compensate the current of 
 non-constant force by a current of constant force, and to deduce 
 from the nature of the latter, the electro-motive forces of the 
 former ; we cannot, it is true, create hydro-electric currents, 
 whose electro-motive forces have determinate values ; but we are 
 able, when once we have a like force of a constant nature, to deter- 
 mine any aliquot part of it, and to employ it in this compen- 
 sation. 
 
 Let A be the pair of constant force ; B, the pair of non-constant 
 force ; the two positive electrodes are joined together at the 
 point P, the two negative electrodes at the point N ; and these 
 two points of junction are united by the conductor o ; let us con- 
 sider the following quantities : 
 
 IN O A B 
 
 Electro-motive force K K' K" 
 
 Resistance r r' r" 
 
 When A alone acts i i' i'' 1 
 
 B ,, i 2 i v 2 z" 2 \ Intensities of the currents. 
 
 A and B act / /' I 1 '} 
 
 According to the principle that the current produced by each 
 pair are added, or are deducted, according to their direction, 
 without interfering with each other, we obtain the following 
 equations. 
 
 I = i + i 1 
 I/ = ," _ Z y 2 I 
 
 I=i 2 -i?> J 
 
 (i.) 
 
 The laws of derived currents give the two following relations, 
 supposing that the pair A is alone in action ; i 1 = i + i" and 
 i r == i" r" = h" ; h f designating any one of these two products. 
 
 _ _ 
 
 From these two equations we deduce h' = i' \ \ ; in 
 
 which 1-f -JL is the resistance of the conducting system, formed 
 
 by o, and the pair B ; h" therefore represents the electro -motive 
 force in that system, whence the relative results i" r' + h' = K', 
 which expresses that the electro-motive force of the circuit is 
 equal to the sum of the electro-motive force of the different 
 longitudinal parts of this circuit. 
 
 From these three relations, we deduce the values of z, i', and 
 
908 NOTES. 
 
 i", and, for the sake of abbreviation, making s = 3 - + ~, 
 
 _ 
 I - _ - _ _. 
 
 r s r r's r 
 
 We find, in the same manner, the value of e' 2 , i' 2) and i" 2 , sup- 
 posing that the pair B is alone in action. 
 The equations (1) now become 
 
 ,_ t f^(sr'-i) K" 
 ~77\ r' 7^ 
 _ t (TL" (sr" -i) K 
 
 -""" 
 
 Let us now suppose that the intensity of the current in the pair 
 B is null, i" = O ; which gives K" = f K'(!); substituting 
 
 this value of K" in the other two equations, we find 1 = 1' = 
 
 K' 
 ,, and this relation, compared with the preceding, gives K"= 
 
 r I (2). 
 
 Thus, by means of a galvanometer, placed in the circuit of the 
 pair B, we prove that, at each moment, we have i" = o ; and we 
 will make use of the relations (1) and (2) in order to determine 
 K", which is the electro-motive force of these two non-constant 
 pairs. M. PoggendorfF, on applying each of these two formulas, 
 has been led to the two following processes. 
 
 First Process. Let B be an ordinary pair, zinc and copper with 
 a single liquid ; we chose for A a pair of constant and conside- 
 rable force, for example, Grove's pair. We cause the zinc plates 
 of both pairs to communicate by means of a conducting wire a, 
 and the zinc of B to communicate with the platinum of A by means 
 of the wire b ; finally, this same platinum plate is joined by the 
 wire c, with the copper of the other pair ; the wire c includes a 
 very sensitive galvanometer. 
 
 In this state of things the wire a and the liquids at A give the 
 resistance r ; the wire b, the resistance r ; and, when these two 
 resistances have a certain relation with each other, there is no 
 current in the wire c, nor, consequently, in the pair B ; we arrive 
 at this result, by modifying little by little the length of tne wire b, 
 until the needle of the galvanometer no longer deviates from ; 
 
NOTES. 909 
 
 and, taking care, after each approximation, to leave the circuit B 
 open for a certain time, in order to cause all force of polarisation 
 to disappear. When once equilibrium is well established, M. 
 Poggendorff measures the resistance of b with the greatest accu- 
 racy; the elements of the Grove's pair have been determined by 
 the ordinary processes ; and K" is found by the formula K" = 
 
 - K'. M. Poggendorff has obtained a verification of this 
 r + r' 
 
 method by measuring the electro-motive force of a pair of Darnell's 
 already obtained by Ohm's process. 
 
 r Grove K' =25*886 K' ,..,,.,_ 
 Ohm's method [ Daniell K " = 15'435 K* " 
 
 ( ft 
 
 Method of compensation | r 
 
 K' 
 52-6g ^ = 1-668. 
 
 Second Process. The two pairs are arranged precisely in the 
 same mechanical manner ; only it is necessary to introduce into 
 the wire b a galvanometer ; when we have proved that the current 
 in the wire c is annulled, we measure the resistance of b, and the 
 intensity of the current, that is found in it ; if we make use of a 
 sine-compass, calling a the angle of deviation, we have for E." : 
 K" = r sine a. 
 
 This process has this advantage over the former, a containing 
 implicitly K' and T* ; even when these elements come to vary in the 
 interval of the successive experiments, they always enter into the 
 calculation with their initial values, since the measure of a is made 
 at each experiment ; in the first process, it is necessary in this case 
 to determine from time to time the electro -motive force, and the 
 resistance of the non-constant pair, which is always a very long 
 operation. M. Poggendorff, in comparing his two processes, has 
 shown that they agree within a great degree of accuracy. 
 
 NOTE G. (p. 821.) 
 
 Note Relative to the Mathematical Theory of the Pile. 
 
 WE have established in the First Chapter of our Fourth Part, 
 as one of the general laws of the propagation of electricity, that 
 the intensity of a current in a closed circuit is proportional to the 
 algebraic sum of the electro-motive forces, that are developed by 
 any cause in the different parts of this circuit (a force being 
 taken with its signs). This law, which Ohm was the first to put 
 
910 NOTES. 
 
 forth with this mathematical rigour, in deducing it from a priori 
 considerations, has been experimentally verified both by Fechner 
 and by Pouillet for hydro-electric and thermo-electric circuits. 
 But, in its generality, the law is applicable to every species of 
 circuits, as well as to those, that we have been pointing out ; and 
 in particular to the circuits in which the electro-motive force is 
 developed by the inductive action, that is exerted upon them in 
 one of their portions of greater or less length by the approach of 
 a magnet or of a closed electric circuit. It is, therefore, inde- 
 pendent of the nature of the electro-motive force ; and, conse- 
 quently, also, of every species of hypothesis, that may be made as 
 to this nature. We may have a closed circuit without there being 
 any current that is circulating in it ; such is the case in a thermo- 
 electric circuit, all the parts of which are at the same temperature ; 
 of a circuit intended for induction, before it has been sub- 
 mitted to the inducing action ; these circuits possess a force of 
 resistance, which they always oppose equally to every current 
 that may traverse them, whether this current is derived, either 
 from an electro-motive force, that is exterior to them, or from an 
 electro-motive force, that is excited in one or in several of their 
 parts, for example, on heating the odd points of contact of the 
 heterogeneous portions of the circuit, or on determining upon a 
 certain part of this circuit an inductive action. We find, in 
 Pouillet's Traite de Physique*, the detailed exposition of the ex- 
 periment, and very simple calculations by means of which this 
 learned philosopher has succeeded in establishing the general 
 formula of the intensity of a pile composed of any number of 
 pairs, whose individual intensity and resistance are given. We 
 have, moreover, already demonstrated the accuracy of this 
 formula on many occasions ; we may, therefore, employ it either 
 to solve the question of knowing how we may discover or obtain 
 the maximum intensity of a pile. In order to arrive at the so- 
 lution, we follow the method pointed out by Poggendorff, and the 
 results of what we have already made known in the body of this 
 work (p. 821. and following pages). 
 
 We have i = ,, calling e the electro-motive force of a pair, 
 
 r the resistance of this pair (essential resistance and constant of 
 the circuit) /, the accessory and variable resistance exterior to the 
 pair. If we designate by m, the maximum of intensity of the 
 
 * Elements de Physique et de Meteorologie, par M. Pouillet. Sixth edition ; 
 Paris, 1853, vol. i. p. 631. and following pages. 
 
NOTES. 911 
 
 current, we have m =-. We may approach this maximum, 
 
 which takes place when /=0, either by diminishing as much as 
 possible the resistance /, (by employing a very good conductor for 
 closing the circuit) or by rendering n as great as possible, namely, 
 by increasing, as much as possible, the number of pairs of which 
 the pile is formed. In this manner I disappears before n r, in the 
 
 n e e 
 
 general expression - - ana we nave i=-=m. 
 
 If we have a second circuit, whose elements, corresponding 
 to those of the former, are e 1 , r', V and i' we have, in a general 
 manner, the following expression for the relation of the two 
 circuits : 
 
 i~~ e 1 r+l 
 If we suppose / /', let us then make / ; then, l=- ; we have, 
 
 first 
 
 i, P ^ i P 
 
 in the former case, -. = - , and in the latter -7 = ->. The 
 i 1 e' r i 1 e' 
 
 limit is the relation of the maximum current, since m=- and 
 
 e ' 
 
 m'= t . The second limit is the relation of the electro-motive 
 r 
 
 force. These two limits are themselves in respect to each other 
 inversely as the essential resistances of the two circuits. 
 
 The relation of the maximum currents enables us to solve the 
 question of knowing how we may obtain the maximum of useful 
 effect in various cases. We shall confine ourselves here to the 
 most interesting limit of these cases, that of which we have 
 given the solution in the body of the work, without giving 
 its demonstration. The following is this case: Two metallic 
 surfaces (amalgamated zinc and platinum, for example) being 
 given, how many pairs must be made of them in order to ob- 
 tain a pile, that shall produce the maximum of effect in a me- 
 chanical or calorific voltameter, placed in its circuit? The distance 
 that is to exist between the plates of the pairs, and the liquid or 
 liquids, that are to be employed for charging the pile, are also 
 given. 
 
 The chemical effect of the current being proportional to its 
 intensity, and its calorific effect to the square of its intensity, the 
 useful effect will be in this case the greatest possible when the 
 intensity of the current shall be a maximum. Let, therefore, / be 
 
912 NOTES. 
 
 the resistance of the voltameter, as well chemical as calorific ; 
 which may always be represented by that of a wire of a certain 
 nature and of given dimensions ; X, the resistance of the liquid, 
 that enters into the formation of this pile, for a unit of section and 
 for a length equal to the distance between the plates of each pair, 
 v the size of the surface to be given to each plate, and s the size 
 of one of the two given metal surfaces, which are equal to each 
 
 other. In the general expression i= - we have /*=-, since 
 
 the resistance of the pair must be directly proportional to that of 
 the liquid, and inversely to its section. We have, on the other 
 
 hand,w -, which gives r = . Substituting for r its value in 
 a * 
 
 the expression of i, we have, i = -^ ; so that the intensity of 
 
 n \-\-sl- 
 
 the current is expressed in a function of the only variable n. 
 
 We have, therefore, nothing more than to decide what is the 
 value of n, that will render this expression a maximum, and 
 for this purpose, we must make its derived value equal to ; 
 which gives e s (n 2 \ + s l)2n 2 X e s = ; whence we deduce 
 
 , 
 = or/ = = 
 
 A i 
 
 n\ 
 since r= . 
 
 Thus, as we have stated in the text (p 821.), the intensity of the 
 current, that produces the maximum of effect, takes place, when 
 the number of the pairs is such that the interior resistance of the 
 pile is equal to that, which the current must surmount exteriorly 
 in one or other of the two voltameters. We have consequently 
 for the value of the maximum of useful effect 
 
 n e _ e 
 ~~27. 
 
 ENl* OF THE SECOND VOLUME. 
 
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