ES3 D31 LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class K f A MANUAL OF ELECTRICITY. PAET I. ELECTEICITT AND GALVANISM. ELECTRICITY. See Page 216. GALVANISM. See Page 311. MANUAL ELECTRICITY: INCLUDING GALVANISM, MAGNETISM, DIAMAGNETISM, ELECTRO-DYNAMICS, MAGNETO-ELECTRICITY, AND THE ELECTRIC TELEGRAPH. BY HENRY M. NOAD, PH. D., F.R.S., F.C.S, LECTURER ON CHEMISTRY AT ST. GEORGE'S HOSPITAL, AUTHOR OP "CHEMICAL MANIPULATION AND ANALYSIS," ETC. FOURTH EDITION. ILLUSTRATED WITH FIVE HUNDEED WOOD ENGRAVINGS. LONDON : LOCKWOOD & CO,, STATIONERS' HALL COURT. 1859. The Proprietors reserve to themselves the right of Translation. PREFACE. THE favourable manner in which the former editions of the Author's " Lectures on Electricity" have been received by the public (the third Edition having long been out of print) ; and the repeated demands on the publishers for copies, which they have been unable to supply, have induced him to bestow some care and labour oh the preparation of the work, the first part of which is now presented to the public. The sciences of Elec- tricity and Magnetism have, of late years, progressed with such gigantic strides, and the discovery of Diamagnetism has opened a new field of research, from which already, such abundant har- vests have been gathered, that it was no longer possible to com- press within the limits of a single volume, (without expanding it to an inconvenient size) such an account of the present state of Electrical and Magnetic science as the Author proposed to him- self to convey. In the present volume the subjects discussed are Electricity, Frictional, and Yoltaic ; Thermo-Electricity, and Electro-physiology. In the Second Part, which is in active pre- paration, and which will, it is hoped, be ready in the early part of the ensuing year, it is proposed to attempt a popular ac- count of Magnetism, Diamagnetism, and Electro-dynamics, in- cluding a description of the principal Electric Telegraphs. In the course of the entire work the Author has received much valuable assistance : he wishes particularly to acknow- ledge the obligations he is under to Mr. Faraday, and to Sir VI PEEP ACE. William Snow Harris; the former has, with his well-known courtesy, been ever ready with his kind explanations, and the latter was good enough to give him an opportunity of witness- ing those beautiful experimental demonstrations of the laws of electrical attraction, repulsion, and accumulation, which are described in chapters ii. and y. and which, having seen and assisted in, he is able to record with the greater satisfaction and confidence. From his late lamented and esteemed friend, Andrew Crosse Esq., the Author has, from time to time, received much valuable information; nor must he omit to return his thanks to Professor Tyndall, for his kind promptness in placing in his hands his recent beautiful and elaborate memoirs. The Author wishes in conclusion to observe, that notwith- standing the care and attention he has bestowed on his work, no one can be more sensible than himself to its numerous im- perfections ; he hopes, however, that it contains no substantial mistakes, and that its. errors, whatever they may be, are those rather of omission than of commission. Medical School of St. George's Hospital, October, 1855. CONTENTS. CHAPTER I. STATICAL OR PRICTIONAL ELECTRICITY. Page Historical sketch Observations of the ancient philosophers Re- searches of Gilbert, Boyle, Otto Guericke, Newton, Hawksbee, Wall, Gray, Wheeler, Dufaye, Boze, Winkler, Muschenbroek, Cuneus, Kleist, Watson, Bevis, Wilson, Franklin, Dalibard, Canton, Beccaria, (Epinus, Wilke, Lymner, Cavendish, Coulomb, La Place, Biot, Poisson, Lavoisier, Volta, Saussure 1 CHAPTER II. PHENOMENA OP PRICTIONAL ELECTRICITY. Attraction and repulsion Positive and negative conditions Con- ductors and non-conductors Electroscopes and Electrometers Pyro- Electricity of minerals Laws of Electrical attraction and repulsion 16 CHAPTER III. PHENOMENA OP FRICTION AL ELECTRICITY (Continued). Induction, Distribution, Condensers, and Multipliers . . . .43 CHAPTER IV. THE ELECTRICAL MACHINE. Various forms of the glass Electrical machine the steam Electric machine Various forms of the disruptive discharge . . .68 CHAPTER V. ACCUMULATED ELECTRICITY. The Leyden phial and battery Laws of accumulated Electricity Specific inductive capacity Lateral discharge Physiological and chemical effects of frictional Electricity 108 Vlll CONTENTS. CHAPTER VI. ATMOSPHERIC ELECTRICITY. Page Exploring wires Electrical kites Electrical observations at the Observatories of Kew and Brussels - Lightning and thunder Lightning conductors Tornadoes and waterspouts The aurora borealis Induction of atmospheric Electricity in the wires of the Electric telegraph Electric phenomena of the submerged Electric telegraph wire 169 CHAPTER VII. GALVANIC OR VOLTAIC ELECTRICITY. Various forms of the galvanic or voltaic battery Law of Ohm Wheatstone's application The Rheostat 246 CHAPTER VIII. EFFECTS OF THE VOLTAIC CURRENT. Luminous, thermal, magnetic, and physiological phenomena . . 307 CHAPTER IX. EFFECTS OF THE VOLTAIC CURRENT (Continued). Chemical phenomena 350 CHAPTER X. ELECTRO-PHYSIOLOGY. Historical notice Recent researches of Matteucci and Du Bois Raymond Electric fishes The torpedo The gymnotus The silurus Electricity of plants 420 CHAPTER XI. THERMO-ELECTRICITY . 484 CHAPTER XII. THEORY OP THE VOLTAIC PILE ..... ... 497 CONTENTS OF PART II. CHAPTER XIII. MAGNETISM. Tage Historical sketch Researches of Gilbert, Halley, Graham, Epinus, Coulomb, Humboldt, Hansteen, Barlow, Morichini, Somerville, Dalton, Cavallo, Brewster, Babbage, Herschel, Harris, Faraday . 523 CHAPTER XIV. MAGNETISM (Continued). General Facts and Principles Duality of the Magnetic Force Mag- netic Curves Haldet's Magnetic Figures ..... 547 CHAPTER XV. MAGNETISM (Continued). Methods of making artificial magnets Processes of Knight, Scoresby, Duhamel, Michel}, Canton, Epinus, Coulomb, Barlow, Elias Circumstances which affect the energy of artificial magnets Laws of magnetic combinations Useful application of the magnetic powers Laws of magnetic force . . . . . . .561 CHAPTER XVI. MAGNETISM (Continued). Terrestrial ] Magnetism Magnetical instruments The land compass The mariner's compass The Admiralty compass Harris's com- pass Local attraction in ships Scoresby 's investigations The dipping needle The variation compass The declination magnet The horizontal force galvanometer The vertical force galva- nometer . . .... 584 CHAPTER XVII. 'MAGNETISM (Continued). Magnetical observations Humboldt's researches The declination of the horizontal needle Isogoiiic lines Periodic variations Sabine's researches The inclination of the needle The magnetic equator Terrestrial magnetic intensity Magnetic storms Theory of terrestrial Magnetism . . .611 1V CONTENTS. CHAPTER XVIII. ELECTRO-MAGNETISM. Oersted's discovery Affections of the needle and electrified wire Manual actions and reactions De la Hive's floating ring Mutual actions of parallel electrical currents Laws of angular currents Sinuous currents, solenoids Galvanometers Faraday's researches Electro-magnetic relations Electro-magnets and electro-mag- netic engines . . . . . . . . . . . 641 CHAPTER XIX. MAGNETO-ELECTRICITY. Electro - dynamic and Magneto -electric induction Terrestrial Magneto-electric induction Faraday's researches The Magneto- electric machine Secondary currents Electro-magnetic coil machines The induction coils of Ruhmkorff and Hearder . . 690 CHAPTER XX. THE ELECTRIC TELEGRAPH. History Lesage Lomond Reiser Salva Ronalds Soemmering Ampere Gauss and Weber Steinhei Morse Alexander Cooke and Wheatstone The five-needle telegraph The single- needle telegraph The double-needle telegraph The earth circuit The magneto-electric telegraph Henley Bright The French telegraph Froment Electro-magnetic clocks Bain Shepherd . 747 CHAPTER XXI. DIAMAGNETISM. Action of Magnetism on light Action of magnets on the metals Action of magnets on air and gases The Magne-crystallic force Diamagnetic polarity The Polymagnet Diamagnetic con- ditions of flames and gases Magnetic conducting power Atmospheric Ma.gnetism 804 CHAPTER XXII. MAGNETIC HYPOTHESES. Notions of the Ancients Theories of Descartes and Epinus Ampere's electro-dynamic theory Faraday's researches Lines of magnetic force The moving wire as an examiner of magnetic forces Magnetic "polarity" Physical character of the lines of magnetic force Places of no magnetic action Faraday's view of the con- dition of a magnet .......... 858 MANUAL ELECTRICITY, GALVANISM, &c STATICAL OE FEICTIONAL ELECTEICITY. CHAPTEE I. Historical Sketch Observations of the ancient philosophers Researches of Gilbert, Boyle, Otto Guericke, Newton, Hawksbee, Wall, Gray, Wheeler, Dufaye, Boze, Winkler, Muschenbroek, Cuneus, Kleist, Watson, Bevis, Wilson, Franklin, Dalibard, Canton, Beccaria, CEpinus, Wilke, Lymner, Cavendish, Coulomb, La Place, Biot, Poisson, Lavoisier, Volta, Saussure. (1) THEEE is perhaps no branch of Experimental Philosophy which is so popular with all classes and ages as Electricity. The reasons are obvious. It is a science, the general laws of which are susceptible of pleasing demonstration, and its phenomena, from the striking and ocular manner in which they are presented, are calculated to arrest the attention and become fixed on the mind more powerfully than those of any other science. To this may be added its connexion with the most sublime and awful of the agencies of nature ; its secret and hidden influence in pro- moting at one time the decomposition of bodies, and at another time their re-formation : at one time, in its current form, causing the elements of water to separate, and exhibiting them in the form of gases ; and at another time, in its condensed form, causing these same gases to re-unite and become again identified with water : now, in its current form, exhi- biting the most wonderful and sometimes terrible effects on the muscles and limbs of dead animals ; and now, in its condensed form, moving with a velocity that is beyond conception through the living body, and communicating a shock through fifty or a thousand persons at the same instant : now exhibiting its mighty powers in the fearful thunder-storm ; and now, controlled by the ingenuity of man, made the medium for the interchange of thought, and acting as his truthful messenger over land and sea through distances as yet unbounded. With such varied subjects 2 STATICAL OB, PEICTIONAL ELECTEICITY. for contemplation and admiration, it is no wonder if Electricity should be a favourite and a fascinating study. (2) Common, or Statical Electricity, with which we shall first be engaged, although occupying so prominent a place in modern science, cannot be said to date its entrance into physics before the beginning of the eighteenth century. Thales of Miletus, who lived 600 years before the Christian era, is said to have been the first to describe the property possessed by amber to attract and repel light substances when rubbed. In the writings of Theophrastus (B.C. 321), and of Pliny (A.D. 70), the same observations are recorded, and they also speak of the lapis lyncurius, supposed to be the same with the modern tourmaline, as possessing similar properties. The power possessed by the torpedo of paralyzing the muscles, and the use which the fish makes of its power for securing its prey, are mentioned by Pliny, and Aristotle, G-alen, and Oppian ; and the occasional emission of sparks from the human body, when submitted to friction, is alluded to by Eustathius (A.D. 415) in his Commentary on the Iliad of Homer. No attempt to explain any of these phenomena was made by the writers who narrated them. (3) In the year 1600, Dr. Gilbert, of Colchester, in a work on Mag- netism, mentioned several new facts attributable to electrical agency, and enumerated a variety of substances which enjoyed equally with amber the property of attracting not only light substances, such as feathers and straws, but even stones and metals. Dr. Gilbert also investigated the conditions under which this property was acquired ; he found*that when the wind blew from the north and east, and was dry, the body was excited in about ten minutes after friction commenced, but that when it was in the south, and the air moist, it was difficult and sometimes impossible to excite it at all. (4) Boyle, and his contemporary, Otto Guericke, occupied themselves with similar experiments. The latter constructed an electrical machine of a globe of sulphur, and with it discovered electric light, and the fact that a light body when once attracted by an excited electric, was repelled by it, and was incapable of a second attraction until it had been touched by some other body. Newton substituted a globe of glass for one of sulphur, using as a rubber the palm of his hand ; he also was the first to show that Electricity may be excited on the side of a disc of glass opposite to the side which was rubbed. Hawksbee also used a glass globe, and made several observations on the light emitted by various bodies by submitting them to friction, without however being at all aware that it was occasioned by Electricity. Dr. "Wall compared the light and crackling which attended the friction of amber to lightning and thunder. (5) The true foundation of Electricity as a science was laid by HISTORICAL SKETCH. 3 Stephen Gray (A.D. 17201736). This indefatigable experimentalist first showed that Electricity could bo excited by the friction of feathers, hair, silk, linen, woollen, paper, leather, wood, parchment, and gold- beaters' skin; he next discovered the communication of Electricity from excited bodies to bodies incapable of excitation at distances of several hundred feet, and the conducting power of fluids and of the human body; he demonstrated that electric attraction is not proportioned to the mass of matter in a body but to the extent of its surface. In conjunction with Wheeler he discovered the insulating power of silk, resin, hair, glass, and some other substances. He discovered likewise the fact, though not the principle, of induction, and was on the threshold of the discovery of the two opposite Electricities, an honour reserved for his French contemporary, Dufaye. (6) This sagacious philosopher re-produced in a more definite form the principles of attraction and repulsion, previously announced by Otto Gruericke. He showed that all bodies, whether solid or fluid, could be electrified by an excited tube, provided they were insulated ; but his great discovery was that of the two distinct kinds of Electricity, one of which, from the circumstance of its being developed by the friction of glass, rock crystal, precious stones, &c., he called vitreoiis ; and the other, from its development by the frictipn of amber, copal, gum-lac, &c., he termed resinous. He showed that bodies having the same kind of Electricity repel each other, but attract bodies charged with Electricity of the other kind ; and he proposed that test of the Electricity of any given substance which has ever since his time been adhered to, viz., to charge the suspended light substance with a known species of Electricity, and then to bring near it the body to be examined. If the suspended substance was repelled, the Electricity of both bodies was the same ; if attracted, it was different. It is probable, however, that the honour of this capital discovery must be shared between Dufaye and White who was associated with Gray in many of his experiments. (7) About this time two important additions were made to the electrical machine used by Newton and Hawksbee, viz., that of a prime conductor, consisting of an iron tube suspended by silken strings, introduced by Boze of Wittemberg, and that of a cushion as a substitute for the hand for applying friction suggested by Winkler, of Leipsic. With these improvements the spark from the machine was made to inflame spirits, oil, phosphorus, and several other inflammable substances. (8) It was in the years 1745 and 1746, that those celebrated experi- ments, which drew for many succeeding years the almost exclusive attention of men of science to the new subject, and which led the way to the introduction of the Leyden phial, were made by Kleist, Mus- chenbroek, and Cuneus. Professor Muschenbroek and his associates, B 2 4 STATICAL OR FBICTIOtfAL ELECTRICITY. having observed that electrified bodies exposed to the atmosphere speedily lost their eleQtric virtue, conceived the idea of surrounding them with an insulating substance, by which they thought that their electric power might be preserved for a longer time. "Water contained in a glass bottle was accordingly electrified, but no remarkable results were obtained, till one of the party who was holding the bottle attempted to disengage the wire communicating with the prime conductor of a powerful machine; the consequence was, that he received a shock, which, though slight com- pared with such as are now frequently taken for amusement from the Leyden phial, his fright magnified and exaggerated in an amusing manner. Von Kleist appears to have been the real discoverer of the Leyden phial, though his account of his experiments was so obscurely worded that none of the electricians who repeated them were for some time able to verify his results. The following is an extract from his letter to Dr, Lieberkuhn, of Berlin, dated November 4, 1745, and communicated by him to the Berlin Academy: "When a nail, or a piece of brass wire, is put into a small apothecary's phial and electrified, remarkable eifects follow ; but the phial must be very dry or warm ; I commonly rub it over beforehand with a finger, on which I put some pounded chalk. If a little mercury, or a few drops of spirits of wine, be put into it, the experi- ment succeeds the better. As soon as this phial and nail are removed from the electrifying glass, or the prime conductor to which it hath been exposed is taken away, it throws out a pencil of flame so long that, with this burning machine in my hand, I have taken about sixty steps in walking about my room ; when it is electrified strongly, I can take it into another room, a*id then fire spirits of wine with it. If while it is elec- trifying I put my finger or a piece of gold which I hold in my hand to the nail, I receive a shock which stuns my arms and shoulders." In describing the effect produced on himself by taking the shock from a thin glass bowl, Muschenbroek stated, in a letter to "Reaumur, that " he felt himself struck in his arms, shoulders, and breast, so that he lost his breath, and was two days before he recovered from the effects of the blow and the terror," adding, " he would not take a second shock for the kingdom of France." Boze, on the other hand, seems to have coveted electrical martyrdom, for he is said to have expressed a wish to die by the electric shock, that the account of his death might furnish an article for the Memoirs of the French Academy of Sciences. Mr. Allamand, on taking a shock, declared " that he lost the use of his breath for some minutes, and then felt so intense a pain along his right arm, that he feared per- manent injury from it." Winkler stated that the first time he underwent the experiment, " he suffered great convulsions through his body ; that it put his blood into agitation ; that he feared an ardent fever, and was obliged to have recourse to cooling medicines ! ' ' The lady of this pro- HISTOBICAL SKETCH. '5 fessor took the shock twice, and was rendered so weak by it that she could hardly walk. The third time it gave her bleeding at the nose, Such was the alarm with which these early electricians were struck, by a sensation which thousands have since experienced in a much more powerful manner without the slightest inconvenience. It serves to show how cautious we should be in receiving the first accounts of extraordinary discoveries, where the imagination is likely to be affected. (9) After the first feelings of astonishment were somewhat abated, the circumstances which influenced the force of the shock were examined. Muschenbroek observed that the success of the experiment was impaired if the glass was wet on the outer surface. Dr. Watson showed that the shock might be transmitted through the bodies of several men touching each other, and that the force of the charge depended on the extent of the external surface of the glass in contact with the hand of the operator. Dr. Bevis proved that tin-foil might be substituted successfully for the hand outside and for the water inside the jar ; he coated panes of glass in this way, and found that they would receive and retain a charge ; and lastly, Dr. Watson coated large jars inside and outside with tin-foil, and thus constructed what is now known as the Ley den phial. (10) In repeating the experiments with the Ley den phial, Mr. Wilson, of Dublin, discovered the lateral shock, having observed that a person standing near the circuit through which the shock is transmitted would sustain a shock, if he were only in contact with or even placed very near any part of the circuit. Many experiments were also made to determine the distance through which the electric shock could be transmitted. Dr. Watson took a prominent part in these investigations. In July, 1747, he conveyed the electric shock across the River Thames, at West- minster Bridge, and a few days after he caused it to make a circuit of two miles at the New River, at Stoke Newington ; a circuit of four miles, two of wire and two of dry ground, was accomplished in August ; and in the same month he satisfied himself and his friends that " the velocity of the electric matter, in passing through a wire 12,276 feet in length, was instantaneous." Dr. Watson also distinguished himself by some beautiful experiments on electric light. He was the first to demonstrate the passage of Elec- tricity through a vacuum. He caused the spark from his conductor to pass in the form of coruscations of a bright silver hue through an exhausted tube three feet in length, and he discharged a jar through a vacuum interval often inches in the form of a "mass of very bright embo- died fire." These experiments were repeated and varied by Smeaton, Canton, and Wilson. (11) It was in the year 1747 that, in consequence of a communication from Mr. Peter Collinson, a Fellow of the Royal Society of London, to 6 STATICAL OE TRICTIOtfAL ELECTBICITY. the Literary Society of Philadelphia, Franklin first directed his attention to Electricity ; and from that period till 1754 his experiments and observ- ations were embodied in a series of letters, which were afterwards collected and published. "Nothing," says Priestley, "was ever written upon the subject of Electricity, which was more generally read and admired in all parts of Europe, than these letters. It is not easy to say whether we are most pleased with the simplicity and perspicuity with which they are written, the modesty with which the author proposes every hypothesis of his own, or the noble frankness with which he relates his mistakes when they were corrected by subsequent experiments.'* The opinion adopted by Franklin with respect to the nature of Elec- tricity differed from that previously submitted by Dufaye. His hypo- thesis was as follows : All bodies in their natural state are charged with a certain quantity of Electricity, in each body this quantity being of definite amount. This quantity of Electricity is maintained in equili- brium upon the body by an attraction which the particles of the body have for it, and does not therefore exert any attraction for other bodies. But a body may be invested with more or less Electricity than satisfies its attraction. If it possess more, it is ready to give up the surplus to any body which has less, or to share it with any body in its natural state; if it have less, it is ready to take from any body in its natural state a part of its Electricity, so that each will have less than its natural amount. A body having more than its natural quantity is elec- trified positively or plus, and one which has less is electrified negatively or minus. One electric fluid only is thus supposed to exist, and all elec- trical phenomena are referable either to its accumulation in bodies in quantities more than their natural share, or to its being withdrawn from them, so as to leave them minus their proper portion. Electrical excess then represents the vitreous, and electrical deficiency the resinous Electricities of Dufaye : and hence the terms positive and negative, for vitreous and resinous. (12) In applying this theory to the case of a charged Leyden jar, the inner coating of tin-foil is supposed to have received more than its natural quantity of Electricity, and is therefore electrified positively or plus, while the outer coating, having had its ordinary quantity of Electricity diminished, is electrified negatively or minus, "When the j ar is discharged, the superabundant or plus Electricity of the inside is transferred by the conducting body to the defective or minus Electricity of the outside ; Eranklin demonstrated by various experiments that the inside and outside coatings are really charged with opposite Electricity, and that during the process of charging exactly as much Electricity is added on one side as is subtracted from the other, and he was thus enabled to offer a satisfactory explanation of what had been previously observed by other HISTOEICAL SKETCH. 7 electricians, viz.: that a jar could not be charged if its external coating were insulated ; but though a single jar could not be charged unless its outer coating were in communication with the earth, Franklin showed that a series of jars may be all charged at once by " suspending them on the prime conductor, one hanging on the tail of the other, and a wire from the last to the floor." With the jars thus charged he constructed a battery by separating them, and then putting their insides and outsides in metallic communication. (13) Another capital discovery of Franklin's related to the place where the Electricity resides in the charged Leyden phial. Having charged a jar he removed the wire by which the Electricity was conveyed from the machine, and poured out the water which served as the inner coating, he found both to be free from Electricity; nevertheless, on pouring fresh water into the jar, he obtained a shock on grasping the outside of the jar in one hand and touching the water with the other. He next laid two metallic plates on a pane of glass and charged it from the machine ; on removing the plates he could detect no Electricity in them, but on presenting his finger to the surface of the glass that had been covered with the metal he observed small sparks ; he then replaced the metallic plates, and on touching each at the same time he received a shock. From these experiments he drew the conclusion, that it was upon the glass that the Electricity was deposited, and that the conducting coatings " served only like the armature of the loadstone to unite the forces of the several parts, and bring them at once to any point desired." (14) But the discovery which immortalized the American philosopher, is that in which he connected Electricity with that terrific agent that has so often convulsed the physical world, and which led him to a means of dis- arming the fury of the lightning flash, and of converting it into a useful element. The similarity between lightning and the electric spark had been suggested by Hawksbee, "Wall, and particularly by the Abbe Nollet, who, in the fourth volume of his Lemons de Physique, publishedtowards the close of the year 1748, thus expresses himself; " If any one should undertake to prove as a clear consequence of the phenomenon, that thunder is in the hands of nature what Electricity is in ours, that those wonders which we dispose at our pleasure are only imitations on a small scale of those grand effects which terrify us, and that both depend on the same me- chanical agents, if it were made manifest that a cloud prepared by the effects of the wind, by heat, by a mixture of exhalations, &c., is in relation to a terrestrial object what an electrified body is in relation to a body near it not electrified, I confess that this idea well supported would please me much; and to support it how numerous and specious are. the reasons which present themselves to a mind conversant with Electricity. The universality of the electric matter, the readiness of its actions, its instru- 8 STATICAL OB FBICTIONAL ELECTEICITT. mentality and its activity in giving fire to other bodies, its property of striking bodies externally and internally, even to their smallest parts (the remarkable example we have of this effect even in the Leyden jar experi- ment, the idea which we might truly adopt in supposing a greater degree of electric power), all these points of analogy which I have been for some time meditating, begin to make me believe that one might, by taking Electricity for the model, form to one's self in regard to thunder and light- ning more perfect and more probable ideas than hitherto proposed." (15) There does not appear to be any published suggestion of Franklin's relative to the identity of lightning and Electricity bearing so early a date as the volume of Nollet's from which the above extract is taken. His letter to Mr. Collinson, in which he gives his reasons for considering them to be the same physical agent, bears no date, but appears to have been written in 1749 or 1750, as he refers to it in a subsequent letter to the same gentleman in 1753, as his former paper, written in 1747, and enlarged and sent to England in 1749. He says, " "When a gun-barrel in electrical experiments has but little electrical fire in it, you must approach it very near with your knuckle before you can draw a spark. Give it more fire, and it will give a spark at a greater distance. Two gun-barrels united, and as highly electrified, will give a spark at a still greater distance. But if two gun-barrels electrified will strike at two inches distance and make a loud snap, at what a great distance may ten thousand acres of electrified cloud strike and give its fire, and how loud must be that crack ! " He next states the analogies which afford presumptive evidence of the identity of lightning and Electricity. The electrical spark is zig-zag and not straight ; so is lightning. Pointed bodies attract Electricity; lightning strikes mountains, trees, spires, masts, chimneys. When different paths are offered to the escape of Electricity, it chooses the best conductor ; so does lightning. Electricity fires combustibles; so does lightning. Electricity fuses metals; lightning does the same. Lightning rends bad conductors when it strikes them ; so does Electricity when rendered sufficiently strong. Lightning reverses the poles of a magnet; Electricity has the same effect. A stroke of lightning, when it does not kill, often produces blindness ; Franklin rendered a pigeon blind by a stroke of Electricity intended to kill it. Lightning destroys animal Hfe ; the American philosopher killed a turkey and a hen by electrical shocks. (16) It was in the June of 1752, that Franklin made his memorable experiment of raising a kite into a thunder-cloud, and of drawing from it sparks with which Leyden jars were charged, and the usual electrical experiments performed. A month earlier, it appears that a French electrician, M. Dalibard, following the minute and circumstantial HISTOEICAL SKETCH. 9 directions given by Franklin in his letters to Mr. Collinsoii, obtained sparks from an apparatus prepared at Marly-la- Ville : and an attempt has lately been made by M. Arago to claim for this philosopher, and Nollet, the honour of having established the identity of lightning and Electricity : it is clear, however, that the just right belongs to Franklin ; for although this eminent electrician was a month later in his capital experiment than Dalibard, it w r as nevertheless at his suggestion, and on his principles, that the arrangements of the Frenchman were made ; and indeed, if the honour of the discovery is to be given to the individual who first obtained sparks from an atmospheric apparatus, it belongs neither to Dalibard nor to .Franklin, but to an old retired soldier and carpenter, named Coiffier, who was employed by Dalibard to assist him in his experiments, and who actually first drew a spark from the apparatus when the cure was absent. (17) The following is the account transmitted to us of Franklin's bold experiment : " He prepared his kite by making a small cross of two light strips of cedar, the arms of sufficient length to extend to the four corners of a large silk handkerchief stretched upon them ; to the extremities of the arms of the cross he tied the corners of the hand- kerchief. This being properly supplied with a tail, loop, and string, could be raised in the air like a common paper kite, and being made of silk was more capable of bearing rain and wind. To the upright arm of the cross was attached an iron point, the lower end of which was in contact with the String by which the kite was raised, which was a hempen cord. At the lower extremity of this cord, near the observer, a key was fastened: and in order to intercept the Electricity in its descent and prevent it from reaching the person who held the kite, a silk ribbon was tied to the ring of the key, and continued to the hand by which the kite was held." " Furnished with this apparatus, on the approach of a storm, he went out upon the commons near Philadelphia, accompanied by his son, to whom alone he communicated his intentions, well knowing the ridicule which would have attended the report of such an attempt, should it prove to be unsuccessful. Having raised the kite, he placed himself under a shed, that the ribbon by which it was held might be kept dry, as it would become a conductor of Electricity when wetted by rain, and so fail to afford that protection for which it was provided. A cloud, apparently charged with thunder, soon passed directly over the kite. He observed the hempen cord ; but no bristling of its fibres was apparent, such as was wont to take place when it was electrified. He presented his knuckle to the key, but not the smallest spark was perceptible. The agony of his expectation and suspense can be adequately felt by those only who have entered into the spirit of such experimental researches. 10 STATICAL OE TEICTIONAL ELECTEICITT. After the lapse of some time lie saw that the fibres of the cord near the key bristled, and stood on end. He presented his knuckle to the key and received a strong bright spark. It was lightning. The discovery was complete, and Franklin felt that he was immortal." A shower now fell, and wetting the cord of the kite, improved its conducting power. Sparks in rapid succession were drawn from the key ; a Ley den jar was charged by it, and a shock given ; and in fine, all the experiments which were wont to be made by Electricity were re-produced, identical in all their concomitant circumstances. (18) Franklin afterwards raised an insulated metallic rod from one end of his house, and attached to it a chime of bells, which, by ringing, gave notice of the electrical state of the apparatus ; and having succeeded in drawing the electric fire from the clouds, he immediately conceived the idea of protecting buildings from lightning by erecting on their highest parts pointed iron wires, or conductors, communicating with the ground. The Electricity of a hovering cloud could thus be carried off" slowly and silently ; and if the cloud were highly charged, the electric fire would strike in preference the elevated conductors. (19) These interesting experiments were eagerly repeated in almost every civilized country, with variable success. In France a grand result was obtained by M. de Romas : he constructed a kite seven feet high, which he raised to the height of 550 feet by a string, having a fine wire interwoven through its whole length. On the 26th of August, 1756, flashes of fire, ten feet long and an inch in diameter, were given oft from the conductor. In the year 1753, a fatal catastrophe from incautious experiments upon atmospheric Electricity, occurred to Professor Hichmann, of St. Petersburg ; he had erected an apparatus in the air, making a metallic communication between it and his study, where he provided means for repeating Franklin's experiments : while engaged in describing to his engraver, Solokow, the nature of the apparatus, a thunder-clap was heard, louder and more violent than any which had been remembered at St. Petersburg. Richinann stooped towards the Electrometer to observe the force of the Electricity, and " as he stood in that posture, a great white and bluish fire appeared between the rod of the Electrometer and his head. At the same time a sort of steam or vapour arose, which entirely benumbed the engraver, and made him sink on the ground." Several parts of the apparatus were broken in pieces and scattered about : the doors of the room were torn from their hinges, and the house shaken in every part. The wife of the professor, alarmed by the shock, ran to the room, and found her husband sitting on a chest, which happened to be behind him when he was struck, and leaning against the wall. He appeared to have been instantly struck dead ; a red spot was found on his forehead, his shoe was burst open, and a part HISTOEICAL SKETCH. 11 of his Waistcoat singed ; Solokow was at the same time struck senseless. This dreadful accident was occasioned by the neglect on the part of Richmann to provide an arrangement by which the apparatus, when too strongly electrified, might discharge itself into the earth, a precaution that cannot be too strongly urged upon all who attempt experiments in atmospheric Electricity. (20) The labours of Canton and Beccaria in the field of electrical science stand next in chronological order. The principal discovery of the former was the fact that vitreous substances do not always afford positive Electricity by friction, but that either kind of Electricity may be developed at will in the same glass tube. This he illustrated by drawing a rubber over a tube, one half of which was roughened and the other half polished ; the rough part was charged with negative, and the smooth part with positive Electricity. He found also that a glass tube, the surface of which had been made rough by grinding, possessed positive Electricity when excited with oiled silk, but negative when excited with new flannel. Canton also made the useful practical discovery that the exciting power of a rubber may be greatly increased by covering its surface with an amalgam of mercury and tin. This electrician was the first also to demonstrate that air is capable of receiving Electricity by communication. In a paper read at the Royal Society, December 6th, 1753, he announced that the common air of a room might be electrified to a considerable degree, so as not to part with its Electricity for some time. His Electrometer consisted of a pair of dry elder pith-balls suspended by threads of the finest linen. These were contained in a narrow box with a sliding cover, and so disposed that, by holding the box by the extremity of the cover, the balls would hang freely from a pin in the inside. He describes the following method of communicating Electricity to air. " Take a charged phial in one hand, and a lighted candle insulated in the other ; and going into any room, bring the wire of the phial very near to the flame of the candle, and hold it there about half a minute, then carry the phial and candle out of the room, and return with the pith-balls suspended and held at arms' length. The balls will begin to separate on entering the room, and will stand an inch and a half or two inches apart, when brought near the middle of it." Priestley's History of Electricity, p. 196. With Canton also originated those remarkable experiments on in- duction, or as he expressed it, " relating to bodies immerged in electric atmospheres," which afterwards led Wilke and CEpinus to the method of charging a plate of air like a plate of glass, and to make the most perfect imitation of the phenomena of thunder and lightning. (21) The electrical researches of Eeccaria bear evidence to his extra- ordinary acuteness and accuracy. He was the first philosopher who 12 STATICAL OB FBICTIONAL ELECTRICITY. diligently investigated and described the phenomena of a thunder-storm. His account of the circumstances attendant on this majestic spectacle will be given in the proper place. He first showed that the polarity of a needle was determined by the direction in which the electric current passed through it, and that therefore magnetic polarity may be employed to test the species of Electricity with which a thunder-cloud is charged. By extending this analogy to the earth itself, he conjectured that terrestrial magnetism was like that of the needle magnetized by Franklin and Dalibard, the mere effects of permanent currents of natural Electricity established and maintained upon its surface by various physical causes. He alludes to the vast quantity of the electric fluid circulating between different parts of the atmosphere, particularly in storms. " Of such fluid," he says, " I think that some portion is constantly passing through all bodies situate on the earth, especially those which are metallic and ferruginous ; and I imagine that it must be those currents which impress on fire-irons and other similar things the power which they are known to acquire of directing themselves according to the magnetic meridian when they are properly balanced." The grand discovery of Oersted is in this paragraph distinctly foreshadowed. (22) Beccaria's Treatise on Atmospheric Electricity was published in 1753, at Turin, and his " Lettere dell' Ettricismo " at Bologna, in 1758. The latter contain the results of many important investigations. He showed that water is a very imperfect conductor of Electricity ; that its conducting power is proportional to its quantity, and that a small quantity of water opposes a powerful resistance to the electric fluid. By discharging shocks through wires placed very near to each other in a tube full of water, he succeeded in making the spark visible in that fluid, and sometimes burst the tubes. He proved (in conjunction with Canton) that a volume of air in a quiescent state might be charged with Electricity ; that the Electricity of an electrified body is diminished by that of the air, and that the air parts with its Electricity very slowly. Beccaria also decomposed sulphuret of mercury by the electric spark and reduced several metals from their oxides; and he seems to have been the first to have noticed the bubbles of gas which rose from water when the electric spark was transmitted through it, though he formed no theory respecting the phenomenon. (23) The property possessed by certain minerals of becoming electric by heat appears to have been one of the first electrical phenomena that engaged the attention of (Epinus, who, in 1736, published an account of some experiments, in which he showed that for the develop- ment of the attractive powers of the tourmaline, a temperature between 99^ and 212 Fahrenheit, was requisite. A more important discovery, HISTOEICAL SKETCH. 13 due to- this German philosopher (in conjunction with Wilke), was that a plate of air could be charged in a similar manner to a plate of glass, "by suspending a board covered with tin-foil over another of equal size in communication with the earth, and giving it a charge of positive Electricity. This experiment was suggested by some remarkable ones of Canton's and Franklin's, in which the grand principle of induction was first clearly demonstrated, and the result led, in Yolta's hands, to the discoveries of those useful instruments of electrical research, the Mectrophorus and the Condenser. In the year 1759, (Epinus published, at St. Petersburg, a new theory of Electricity, founded on the follow- ing principles : 1. The particles of the electric fluid repel each other with a force decreasing as the distance increases. 2. The particles of the electric fluid attract the particles of all bodies, and are attracted by them with a force obeying the same law. 3. The electric fluid exists in the pores of bodies, and while it moves without any obstruction in non-electrics, such as metals, water, &c., it moves with extreme difficulty in electrics, such as glass, resin, &c. 4. Electrical phenomena are produced either by the transference of the fluid from a body containing more, to another containing less of it, or fr,om its attraction and repulsion when no transference takes place. (Epinus presented Franklin's theory in a mathematical dress, and showed that, to reconcile it with mathematical statement, it was necessary to assume that between the matter composing the masses of different bodies there exists a mutually repulsive force, acting at sensible distances. (24) A series of experiments, illustrative of the mutual attraction of bodies dissimilarly electrified, was published by Mr. Robert Lymner, in 1759. In pulling off his stockings in the evening he had remarked occasionally a crackling noise, accompanied by the emission of sparks. He noticed that this phenomenon did not occur with white silk stockings, neither did it take place when two black or two white stockings were put on the same leg ; but when a black and a white stocking were put on the one over the other, powerful signs of electrical excitement were manifested on pulling them off, and each showed the entire shape of the leg, and at a distance of a foot and a half they rushed to meet each other, and remained stuck together with such tenacity that a force of several ounces weight was required to separate them. He was also enabled to communicate a charge of positive or negative Electricity to a Ley den jar, according as the wire was presented to the Hack or white stocking. In consequence of these experiments Lymner was induced to adopt a modification of Dufaye's theory, and to maintain that of two distinct 14 STATICAL OB FBICTIONAL ELECTRICITY. fluids not independent of each other, as Dufaye supposed them to be, but co-existent, and by counteracting each other producing all the phenomena of Electricity. He assumed that every body contained in its natural state equal quantities of these fluids : that when positively electrified a body does not contain a larger share of electric matter, but a larger portion of one of the active powers, and when negatively electrified a larger portion of the other, and not, as Franklin's theory supposes, an actual deficiency of electric matter. Lymner did not make any extensive application of his theory, and it did not. therefore, at the time it was proposed, excite much attention. (25) The names of Cavendish and Coulomb occur at this period of our history. The former distinguished physicist undertook a mathe- matical investigation of electrical phenomena, and arrived at results nearly similar to those of GEpinus, with whose researches on the subject he was quite unacquainted. Cavendish also made some valuable experiments on the relative conducting powers of different substances. He found that the electric fluid experiences as much resistance in passing through a column of water one inch long as it does in passing through an iron wire, of the same diameter, 400,000,000 inches long ; that water, containing in solution one part of salt, conducts 100 times better than fresh water ; and that a saturated solution of sea-salt conducts 720 times better than fresh water. He also determined that the quantity of Electricity in coated glass of a certain area increased with the thinness of the glass, and that in different coated plates the quantity was as the area of the coated surface directly, and as the thickness of the glass inversely. By means of the electric spark, Cavendish succeeded in decomposing atmospheric air, and in the month of December, 1787, aided by Grilpin, he demonstrated experimentally to the Royal Society, the formation of nitric acid, by exploding a mixture of seven measures of oxygen gas with three measures of nitrogen. "Whether the discovery of the composition of water by transmitting an electric spark through a mixture of oxygen and hydrogen gases can be justly claimed by Cavendish is a disputed question.* (26) The researches of Coulomb form an epoch in the history of electrical science, laying as they did the foundations of Electro-statics. By means of his balance of torsion he proved, 1st, that, like gravity, the electrical forces vary inversely as the sqiiave of the distance ; 2nd, that excited bodies when insulated gradually lose their Electricity from two causes, from the surrounding atmosphere being never free from * See Lardner " On the Steam Engine," seventh edition, p. 303 ; see also Arago's " Historical Eloge of James Watt," translated by Muirhead, p. 95, et seq., and the Historical Note by Lord Brougham, appended to the same. HISTORICAL SKETCH. 15 conducting particles, and from the incapacity of the best insulators to retain the whole quantity of Electricity with which any body may be charged, there being no substance known altogether impervious to Electricity. Coulomb determined the effect of both of these causes. Adopting the hypothesis of two fluids, this able philosopher investigated experimentally and theoretically the distribution of Electricity on the surface of bodies. He determined the law of its distribution between two conducting bodies in contact, and measured its density. He measured, also, the distribution of the fluid on the surface of a cylinder, and satisfactorily illustrated the doctrine of points, which formed so prominent a part of the researches of Eranklin. Coulomb's experi- ments on the dissipation of Electricity were also important. He found that the momentary dissipation was proportional to the degree of Electricity at the time, and that when the Electricity was moderate its dissipation was not altered in bodies of different kinds or shapes. The temperature and pressure of the atmosphere did not produce any sensible change, but the dissipation was nearly proportional to the cube of the quantity of moisture in the air. He found that a thread of gum-lac was the most perfect of all insulators, insulating ten times better than a dry silk thread, and he found also that the dissipation of Electricity along insulators was chiefly owing to adhering moisture, but in some measure also to a slight conducting power. (27) The phenomena of Electricity having, by the labours of Coulomb, been brought within the pale of mixed mathematics, the investigation was pursued by La Place, Biot, and Poisson. The former illustrious mathematician investigated the distribution of Electricity on the surface of ellipsoids of revolution, and he showed that the thickness of the coating of the fluid at the pole was to its thickness at the equator as the equatorial is to the polar diameter, or, what is the same thing, that the repulsive force of the fluid, or its tension at the pole, is to that at the equator as the polar is to the equatorial axis. This examination was extended by Biot to spheroids differing little from a sphere, whatever may be the irregularity of their figure. He likewise de- termined, analytically, that the losses of Electricity form a geometrical progression when the two surfaces of a jar or plate of coated glass are discharged by successive contacts ; and he found that the same law regulates the discharge when a series of jars or plates are placed in communication with each other. It is, however, to Poisson that we are chiefly indebted for having brought the phenomena of Electricity under the dominion of analysis, and placed it on the same level as the more exact sciences. He took as the basis of his investigations, the theory of two fluids, proposed by Lymner and Dufaye, with such modifications and additions as were suggested by the researches of 16 STATICAL OB PRICTIONAL ELECTRICITY. Coulomb. He deduced theorems for determining the distribution of the electric fluid on the surfaces of two conducting spheres, when they are placed in contact or at any given distance, the truth of which had been established, experimentally, by Coulomb, before the theorems themselves had been investigated. On bodies of elongated forms, or those which have edges, corners, or points, it is shown as a consequence of the theory of two fluids, that the electric fluid accumulates in greater depths about the edges, corners, or points, than in other places. Its expansive force being, therefore, greater at such parts than else- where, exceeds the atmospheric pressure and escapes, while at other parts of the surface it is retained. (28) The Electricity developed during the passage of bodies from the solid or fluid to the gaseous state, was made the subject of a series of experiments, towards the conclusion of the last century, by La Place, Lavoisier, Yolta, and Saussure. The bodies which were to be evaporated or dissolved were placed upon an insulating stand, and made to communicate, by a chain or wire, with a Volta's condenser. When sulphuric acid, diluted with three parts of w T ater, was poured upon iron filings, inflammable air was disengaged with brisk effer- vescence, and at the end of a few minutes the condenser was so highly charged as to yield a strong spark of negative Electricity. Similar results were obtained when charcoal was burnt on a chafing dish, or when fixed air or nitrous gas was generated from powdered chalk by means of sulphuric and nitrous acids. These experiments pointed L to natural evaporation as the cause of the disturbance of the general electrical equilibrium of the globe, giving a surplus of positive Elec- tricity to the air and leaving the earth surcharged with negative fluid. The subject engaged particularly the attention of Volta, who was at that time occupied in the investigation of the electric state of the air. In the course of his experiments this distinguished philosopher had availed himself of the power of flame to attract Electricity, and having found that when a taper was placed on the point of his con- ductor, his Electrometer gave signs of a far larger quantity of Elec- tricity than when it was away, he suggested that the force of storms might be much mitigated by lighting enormous fires on elevated situations, the air being thereby robbed of its Electricity. It does not appear that Volta ever carried this design into effect, though it was suggested by Arago that the conjecture might be tested in Staffordshire, and other English counties which abound in iron furnaces. (29) Having thus briefly sketched the prominent features in the history of Statical Electricity up to the period of the commencement of the present century, we proceed to a popular investigation of the phenomena as they are at present understood. PRIMARY PHENOMENA. 17 CHAPTEE II. Primary phenomena of frictional Electricity Attraction and repulsion Positive and negative conditions Conductors and non-conductors Electroscopes and Electro- meters Pyro-Electricity of minerals Laws of electrical attraction and repulsion. (30) Primary phenomena. For illustrating the fundamental pheno- mena of Electricity we can employ no materials either simpler or better than those used by Stephen Gray in 1730. 1. If a stout glass tube, about an inch in diameter and 18 or 20 inches long, be made dry and warm, and then briskly rubbed for a few seconds with a dry soft silk handkerchief, or better with a piece of oiled silk the rough side of which has been smeared over with " mosaic gold," and then held near a pith-ball suspended by a long silk thread, the ball will be attracted, and after adhering to the glass for a short time, will be repelled to a considerable distance, nor will it be again attracted until it has touched some body in conducting communication with the earth, and thus given up the Electricity which it had acquired from the tube ; or until, by remaining undisturbed for some time, it has lost it by dissi- pation into the atmosphere. 2. If a stick of common sealing-wax be rubbed with a piece of dry flannel, or if a piece of gutta percha such as is used for the soles of shoes be lightly rubbed on the sleeve of the coat, and if either be brought near the pith-ball while under the influence of the Electricity from the glass, it will attract it powerfully, but soon repel it, when the excited glass will again attract it, and the ball may thus be kept for some time vibrating between the two substances. Fig. i. 3. If two pith-balls be suspended by two silk threads and excited either by the glass or by the resin, it will be observed on removing the exciting material, that the balls no longer fall into the vertical position, but stand apart at a greater or less angle, apparently repel- ling one another as shown in Fig. 1; the balls have thus acquired properties relatively to each other, similar to those which the glass and single ball exhibited after contact in the preceding experiment. 4. If the pith-balls be suspended by thin metallic wires, or threads, or if the silk filaments be moistened, it will be found impossible to excite 18 STATICAL OB FEICTIOKAL ELECTRICITY. them permanently ; for the moment the glass, resin, or gutta percha is removed, they return to their original condition. In order to make these interesting phenomena visible at a considerable distance, the pith-balls may be advantageously re-placed by skeleton globes made by gumming together cross strips of common writing paper ; these globes may be two or three inches in diameter, and if the paper be smoothly and evenly cut, they will retain an electrical charge for a long time. (31) Prom these simple experiments we learn several important elec- trical facts : 1. That vitreous substances, such as glass, become electrical by being rubbed with certain other substances. 2. That in this state they attract light bodies. 3. That having once attracted they afterwards repel them. 4. That resinous substances, such as sealing-wax, and gutta percha, are also capable of receiving electrical excitation by being rubbed. 5. That they also attract and then repel light bodies. 6. That though excited glass and excited resin agree in their property of attracting light matter, the property called forth by friction in each is different, for one attracts what the other repels, and vice versa. 7. That bodies charged with the same kind of Electricity exhibit a disposition to repel each other. 8. That in order that they shall retain for any length of time the Electricity communicated to them, they must be insulated from the earth. 9. That silk is a substance which possesses this power of insulation. 10. That metals and a film of water do not possess this power. (32) But certain other phenomena attend the excitation of glass and resin : e.g. if either be rubbed briskly in the dark while dry and warm, a stream of light will be perceived, a slight crackling noise will be heard, and if the hand or face be held near, a sensation similar to that felt on touching a cobweb will be experienced. (33) The difference which in the foregoing experiments we perceived between bodies such as silk, glass, and gutta percha, and others, such as cotton, thread, and metal, arises from the circumstance that the former class of substances conducts Electricity very badly, while the latter offers a ready passage to the same. On this account bodies have been divided into two great groups conductors and non-conductors ; an arrangement useful and sufficiently correct for general purposes, though the recent researches of Faraday and others have shown us, that as there are in reality no substances which can strictly be called perfect conductors of Electricity, so there are none which absolutely refuse a passage to this agent. Conductors and non-conductors (so called) differ only in the degree of their conducting and insulating power ; and all known sub- GUTTA PEKCHA AS AN INSULATOR. 19 stances may be regarded as links of the same chain, at one end of which may be placed the best conductor and at the other the best insulator. (34) Gutta percha as an insulator is equal to shell-lac. It is also an excellent substance for the excitement of negative Electricity, and might probably be used instead of a plate of glass in the construction of an electrical machine. As it comes from the manufacturer it is not however all equally good, but by warming a piece which is found to con- duct, in a current of hot air, and by stretching and doubling it up, and kneading it for some time between the fingers, it becomes as good an insulator as the best. Faraday found that after a piece of gutta percha had been soaked in water for four days, it insulated as well as ever after being wiped and exposed for a few hours to the air. He found this substance very useful in his experiments in. the form of sheet, or rod, or filament. Thus, being tough and flexible when cold, as well as soft when hot, it serves better than shell-lac in many cases where the brittleness of the latter is an inconvenience. It makes very good handles for carriers of Electricity in experiments on induction, not being liable to fracture : in the form of a thin band or string it makes an excellent insulating suspender ; a piece of it in sheet makes a most convenient insulating basis for anything placed on it.. It forms good insulating plugs for the stems of gold-leaf Electrometers when they pass through sheltering tubes ; and larger plugs supply good insulating feet, for extemporary electrical arrangements ; cylinders of it, half an inch or more in diameter, have great stiffness, and form excellent insulating pillars. In reference to its power for exciting negative Electricity, Faraday observes that it is hardly possible to take one of the soles sold by the shoemakers out of paper or into the hand without exciting it to such a degree, as to open the leaves of an Electrometer one or more inches ; or, if it be un electrified, the slightest passage over the hand or face, the clothes, or almost any other substance, gives it an electric state. Some of the gutta percha is sold in very thin sheets resembling in general appearance oiled silk ; and if a strip of this be drawn through the fingers, it is so electric as to adhere to the hand or attract pieces of paper. (35) Mr. Barlow (Phil Mag., vol. xxxvii. 1850, p. 428,) observes, that if a sheet of about four or five feet superficial area be laid on a surface, or held against the wall of a room, and rubbed with the hand or a silk hand- kerchief, and then carefully removed by the extreme edges, and held suspended in the air, it will give off a brush-like spark of several inches in length to the knob of any conducting surface presented to it ; a similar effect may be produced by causing the sheet of gutta percha to be passed once over one, or between two rubbing surfaces, but in order to obtain the best effect the hand should pass over the rubbing surface at an angle of c 2 20 STATICAL OB FBICTIONAL ELECTRICITY. about 10, a greater or less angle being, according to Mr. Barlow's experiments, less favourable to the development of Electricity ; the effect is also much increased by applying a second rubber of silk or horse-hair outside the strip ; the quantity of Electricity developed increasing with the surface of the gutta percha. Grutta percha may be excited both positively and negatively. If a strip about two inches wide and two feet long be laid on a surface and rubbed, the two extremities when suspended in the air repel each other, and the Electricity is resinous ; but if the strip be folded double and rubbed, the upper side exhibits resinous and the lower side vitreous Electricity, and the two extremities attract each other. (36) Among good conducting substances may be classed all metals, charcoal, strong acid, water, steam, smoke, and all vegetable and animal substances containing water ; while among the more or less perfect insulators may be included, gutta percha, shell-lac, amber, resins, sulphur, glass, different transparent gems, silk, feathers, air, and all dry gases, gun cotton, and organic substances perfectly free from water, &c. A substance belonging to the first class when placed upon one in the second list, is said to be insulated from the earth. Atmospheric air must, it is clear, be ranked among the most perfect non-conducting bodies, for if it gave a free passage to Electricity, the electrical effects excited on the surface of any body surrounded with it would quickly disappear, and no permanent charge could be communicated: but this is contrary to experience. "Water, on the other hand, whether in the liquid or vaporous form, being a conductor, though of an order very inferior to that of the metals, affects in a very important manner all electrical experiments, as it is constantly present in the atmosphere in greater or less quantity, hence one of the reasons why electrical experi- ments are made with more facility, and the desired effects produced with more certainty and success in cold and -dry weather, when the atmosphere holds but little aqueous vapour suspended in it; another injurious tendency of the watery vapour in the atmosphere is, that which it has to become deposited on the surfaces of bodies, thereby destroying their insulating power. The insulating supports of elec- trical apparatus are usually made of glass on which moisture is very readily deposited ; they should therefore be coated with a thin layer of gum-lac dissolved in spirits of wine, or for delicate experiments be made altogether of shell-lac, or gutta percha. (37) The nature of conduction has received much elucidation from the beautiful experiments of Faraday (Phil. Trans. 1833). He found that though the insulating power of ice was not effective with Electricity of exalted intensity, yet that the thinnest film was sufficient to obstruct altogether the circulation of Electricity in a very powerful galvanic CONDUCTION. 21 battery ; chloride of lead, chloride of silver, sulphuret of antimony, and a great number of other salts possessed the same property, that, namely, of stopping completely the transmission of the electrical current while solid, but allowing its ready passage when liquefied. Other bodies, such as sulphur, phosphorus, orpiment, realgar, spermaceti^ sugar, shell-lac, &c., refused a passage to the current, whether liquid or solid. Faraday gives the following conditions of electric conduction in bodies, which, though they apply chiefly to voltaic Electricity (under which division of our subject we shall further consider them), are yet true within certain limits for ordinary Electricity. 1. All bodies from metals to lac and gases conduct Electricity in the same manner, but in very different degrees. 2. Conducting power is in some bodies powerfully increased by heat, and in others diminished; yet without our perceiving any accompanying electrical difference either in the bodies, or in the changes occasioned by the Electricity conducted. 3. There are many bodies which insulate Electricity of low intensity, when solid, but conduct it very freely when fluid, and are then decom- posed by it. 4. But there are many fluid bodies which do not sensibly conduct Electricity of this low intensity; there are some which conduct it and are not decomposed, nor is fluidity essential to decomposition. 5. There is but one substance (periodide of mercury) which, insulating a voltaic current when solid and conducting it when fluid, is not decom- posed in the latter case. 6. There is no electrical distinction of conduction which can as yet be drawn between bodies supposed to be elementary and those known to be compounds. (38) In a subsequent paper (Phil. Trans. 1835), Faraday expresses his conviction that insulation and conduction depend upon the same molecular action of the dielectrics concerned, are only extreme degrees of one common condition or effect, and in any sufficient mathematical theory of Electricity must be taken as cases of the same kind ; they are the same in principle and action, except that in conduction an effect common to both is raised to the highest degree, whereas in insulation it occurs in the best cases only in an almost insensible quantity. The beauti- ful experiments of "Wheatstone have shown that even in metals time enters as an element into the conditions of conduction, affording therefore a proof of retardation ; and Faraday has been able to trace the progress of conduction as it were step by step through masses of spermaceti, glass, and shell-lac, acknowledged insulators ; but retardation is in the latter case insulation, and there seems no reason for refusing the same relation to the same exhibition of force in metals. 22 STATICAL OR FKICTIONAL ELECTRICITY. (39) In the following list the bodies are arranged in their order of conducting power, according to the present state of knowledge on the subject, and though probably not absolutely correct, it will serve to show how insensibly conductors and non-conductors merge into each other. All the metals. "Well burnt charcoal. Plumbago. Concentrated acids. Powdered charcoal. Dilute acids. Saline solutions. Metallic ores. Animal fluids. Sea water. Spring water. Rain water. Ice above 13 Fahr. Snow. Living vegetables. Living animals. Flame smoke. Steam. Salts soluble in water. Rarefied air. Vapour of alcohol. Yapour of ether. Moist earth and stones. Powdered glass. Flowers of sulphur. Dry metallic oxides. Oils, the heaviest the best. Ashes of vegetable bodies. Ashes of animal bodies. Many transparent crystals dry. Ice below 13 Fahr. Phosphorus. Lime. Dry chalk. Native carbonate of barytes. Lycopodium. Caoutchouc. Camphor. Some siliceous and argillaceous stones. Dry marble. Porcelain. Dry vegetable bodies. Baked wood. Dry gases and air. Leather. Parchment. Dry paper. Feathers. Hair Wool. Dyed silk. Bleached silk. Raw silk. Transparent gems. Diamond. Mica. All vitrifications. Glass. Jet. Wax. Sulphur. Eesins . Amber. Shell-lac. Grutta percha. (40) Opposite Electricities. We have seen that excited resin and excited glass, though they both attract light substances, exhibit each a different kind of force. Hence the name of resinous Electricity as OPPOSITE ELECTRICITIES. 23 applied to the former, and of vitreous as applied to the latter. These terms are, however, very objectionable, implying, as they do, that when vitreous bodies are excited they are always electrified with one species of Electricity, and that when resinous bodies are excited they are always electrified with the other. But this is by no means the case ; for example : 1. When a glass rod is rubbed with a woollen cloth, it repels a pith-ball which it has once attracted : but if the cloth be presented, it will be found to attract the excited ball. We hence conclude, that as the glass was vitreously electrified, the woollen cloth must be resinously electrified. 2. When a stick of sealing-wax is rubbed with a woollen cloth, it repels a pith-ball which it has once attracted; but if the cloth be presented it will be found to attract the excited ball. Hence, by a similar reasoning, we are led to the inference that the cloth is mtreously electrified. 3. When a piece of polished glass is rubbed, first with a woollen cloth and then with the fur of a cat, and examined after each excitation by a pith-ball, it is found in the first case vitreous, and in the second resinous. A woollen cloth and a piece of glass may thus be made to exhibit both kinds of Electricity ; the terms vitreous and resinous do not therefore convey to the mind a proper impression of the nature of the two forces. (41) The terms positive and negative, though they take their origin in a theory of Electricity which is not now recognized as compatible with observed phenomena, are less objectionable, and have accordingly partially superseded the other terms. Positive Electricity, then, is that which is produced upon polished glass when rubbed with a woollen cloth ; and negative Electricity is that which is produced upon a stick of sealing-wax when rubbed. One kind of Electricity cannot be produced without the other; and of two substances which by mutual friction excite Electricity, one is invariably positive, and the other negative, after the friction. (42) If two persons stand on two stools with glass legs, and one strike the other two or three times with a well-dried cat's fur, he that strikes will have his body charged positively, and he that is struck will be electrified negatively. A spark may, in fact, be sometimes obtained from the face of either, by a person in contact with the earth. There is no substance so easily excited as the fur of a cat ; and most persons are aware of the fact, that if in dry weather the hand be passed briskly over the back of a living cat, the hairs will frequently bristle, and be attracted by the hand, and sometimes a crackling noise will be heard, and a spark obtained. These effects are occasionaly observed with the 24 STATICAL OR ERICTIONAL ELECTRICITY. human hair, which, when clean, dry, and free from grease, is electrified with great facility by friction, and this is especially the case with fair hair which is in general fine and pliable. Even in damp weather, if a person stand on an insulating stool, and connect himself with a con- denser connected with a gold leaf Electroscope, and any one standing on the floor draw a comb rapidly through his hair, on drawing back the uninsulated plate of the condenser, the gold leaves of the Electroscope will diverge with positive Electricity ; if the person using the comb stand on the stool and connect himself with the condenser, as he combs the gold leaves will open with negative Electricity. In dry weather the condenser is not required for this experiment. (43) The following table given by Singer (Elements of Electricity, p. 33), on the authority of Cavallo, exhibits these effects between a variety of substances. By friction with Every substance with which it has hitherto been tried. Every substance hitherto tried except the back of a cat. Dry oiled silk, sulphur, metals. Woollen cloth, quills, wood, paper, sealing wax, white wax, the human hand. Amber, blast of air from bellows. Diamonds, the human hand. Metals, silk, loadstone, leather, hand, paper, baked wood. Other finer furs. Black silk, metals, black cloth. Paper, hand, hair, weasel's skin. Sealing wax. Hare, weasel, and ferret fur, loadstone, brass, silver, iron, hand, white silk. Some metals. Hair, weasel, and ferret fur, hand, leather, woollen cloth, paper, some metals. Silk. Flannel. Singer found- that sealing-wax is rendered negative by friction with iron, steel, plumbago, lead, and bismuth ; and he remarks that in order to arrive at an accurate conclusion, many repetitions of each experiment are necessary, as the least difference in the conditions will occasion singular varieties of result ; for example, positive Electricity may be excited in one stick of sealing wax and negative in another, if the former have its surface scratched and the latter be perfectly smooth. (44) Electroscopic Apparatus. -Instruments for indicating the pre- Is rendered The back of a cat Positive Smooth glass J Positive j f Positive Rough glass 1 Negative j Tourmaline Hare's skin White silk ( Positive ( Negative f Positive J [Negative ( Positive f Negative ( Positive Black silk | Negative j ( Positive Sealing wax | Negative j Baked wood ( Positive ( Negative ELECTROSCOPIC APPARATUS. 25 sence and kind of Electricity are called Electroscopes; those by which its quality under various conditions is measured, are called Electrometers. Various forms have been given to both classes of instruments, the necessary conditions being that they should be very light, and be capable of moving on the application of the smallest force. A pith-ball, or a paper skeleton globe suspended by a silk thread is, in many cases, sufficient to detect the presence and species of Electricity on a body. It may first be charged by touching it with an excited glass rod, and the body to be examined, then brought near it, if it attract the ball, its Electricity is negative, if it repel it, it is positive; if it have no effect on the ball it is not electrified, or at least not sufficiently so to produce a force strong enough to overcome the rigidity of the silk string. A more delicate test is a strip of Dutch metal attached to a slip of paper, and suspended from a stick of sealing wax. (45) The Electroscope of Gilbert and Haiiy consisted of a light metallic needle, terminated at each end by a light pith-ball covered with gold leaf, and supported horizontally by a cap at its centre on a fine point. The attractive and repulsive action of any electrified body presented to one of the balls being indicated by the move- ments of the needle. Canton's Electroscope consisted of a pair of pith-balls suspended by fine linen threads (20), which Cavallo modified and made portable by fitting it up, as shown in Fig. 3, where B shows the instrument in a state of action. "When it is ' unloosed, the end B, carrying the pith- Fi 3 balls, is screwed off, and the balls are put ^^ into the glass tube A, which serves for a handle. This glass case is three inches long and three-tenths of an inch wide, and half of it is covered with sealing wax. A cork, tapering at both ends, is made to fit the mouth of the tube, and to one end are fixed two fine silver wires, carrying two small cones [of dry elder pith. The case of the Electrometer C, encloses at one end a piece of amber for giving negative Electricity, and at the other end a piece of ivory insulated upon a piece of amber, for giving positive Electricity to the balls when rubbed with a piece of woollen. (46) An excellent arrangement of the balanced needle Electroscope 26 STATICAL OB FRICTIONAL ELECTEICITY. :Fi g . 4. o .is shown in Fig. 4. It consists of a short bent brass wire, A, B, C, to either end of which is fixed a reed, so as to form arms of un- equal length. The longer arm carries, at its extremity, a disc of gilt paper, D, about half an inch in diameter, and the shorter arm a small metallic ball, E. The whole is balanced on a finely pointed wire, supported on a rod of varnished glass. The arms are elongated or contracted, and the balance thus adjusted by sliding the reeds upon the wire. The disc, D, is electrified either positively or negatively, and the body, the nature of the Electricity of which is to be examined, is presented to it. If we desire merely to detect the presence of Electricity by its attractive force, we uniiisulate the needle by hanging a metallic wire from the pointed rod of support, and then present the excited substance to the disc D. (47) A still more delicate Electroscope, and one which retains its charge for a long time, even under unfavourable circumstances, such for instance, as in a crowded room, is made by suspending from a Fig. 5. wooden frame, by a fine silk or glass filament, C (Fig. 5), a delicate rod of lac, D, carrying at one of its ends a gilt paper disc, B. This disc, in its natural state, will be attracted by any electrified body, but if a charge of positive or negative Elec- tricity be previously given to it, it will be attracted or repelled, in accordance with electrical laws ; and as its indications are visible at considerable distances, it is a form of Electroscope well adapted for the lecture room. A stick of lac, carrying at one end a gilt paper disc, forms a very convenient apparatus for conveying small charges of Electricity from one body to another ; the paper should be smoothly gilt and the edges free from asperities. (48) Fig. 6 represents Sir William Snow Harris's Electroscope, which acts on the principle of divergence. A small elliptical ring of metal, a, is attached obliquely to a small brass rod, a b, by the intervention of a short tube of brass at a : the rod a b terminates in a brass ball, b, and is insulated through the substance of the wood ball, n. Two arms of brass, r r,_ are fixed vertically in opposite directions on the extremities of the long diameter of the ring, and terminate in small balls ; and in the direction of the shorter diameter within the ring there ELECTEOSCOPIC APPARATUS. 27 is a delicate axis set on extremely fine points : this axis carries, by means of short vertical pins, two light reeds of straw, s s, terminating in balls of pith, and constituting a long index, correspond- ing in length to the fixed arms above- mentioned. The index thus circumstanced is sus- ceptible of an extremely minute force ; its tendency to a vertical position is regulated by small sliders of straw, move- able with sufficient friction on either side of the axis. To mark the angular position of the index in any given case, there is a narrow graduated ring of card-board or ivory placed behind it. The graduated circle is sup- ported on a transverse rod of glass by the intervention of wood caps, and is sus- tained by means of the brass tube, a, in which the glass rod is fixed. The whole is insulated on a long rod of glass, A, by means of wood caps terminating in spherical ends. In this arrangement, as is evident, the index diverges from the fixed arms whenever an electrical charge is communicated to the ball &, as shown in the lower figure. The instrument is occasionally placed out of the vertical position at any required angle by means of a joint at m, and all the insulating portions are carefully varnished with a solution of shell-lac in alcohol. This instrument is, to a certain extent, an Electrometer, as well as an Electroscope, but its applications are, as Sir "W. Harris observes, very limited, for though the amount of divergence does increase with the quantity of Electricity in operation, we are not able to ascertain the ratio of increase because of the diminishing force of repulsion as the divergence increases. (49) But the most elegant and the most generally useful of this class of instruments is the gold leaf Electrometer, invented by the Rev. Mr. Bennett, and improved by Mr. Singer. The original instru- ment is shown in Fig. 7, and is thus described by its author. "It consists of two slips of gold leaf suspended in a glass. The foot may be 28 STATICAL OR FRICTIO^AL ELECTRICITY. Fi ]^ a cylinder of brass, supported on a glass stand, and furnished with a pith-ball Electroscope, and let e be an excited glass tube. On approaching this tube within about six inches distant from J, the pith-balls will instantly separate, indicating the presence of free Elec- tricity. Now, in this case the electric e has not been brought sufficiently near to the conducting body to communicate to it a portion of Electricity, and the moment that it is removed to a considerable distance the balls fall together, and appear unelectrified ; 44 STATICAL OE PEICTIONAL ELECTEICITT. Fig. 15. on approaching e to d the balls again diverge, and so on. The fact is, this is a case of what is termed induction, the positive Electricity of e decomposes the neutral and latent combination in d a c, attracting the negative towards d, and repelling the positive towards e, and the balls consequently diverge, being positively electrified. On removing e the force which separated the two Electricities in d a c is removed, the separated elements re-unite, neutrality is restored, and the pith- balls fall together. The Electricity of e induces a change in the electric state of d c. In Kg. 15, suppose s s' to be two metallic insulated spheres, and a a an insulated metallic conductor ; suppose s to be strongly charged with positive, and s' with negative Electricity, and placed in the position re- presented in the figure. If a a be examined by means of an Electrometer, it will be found that the only part which is free from Electricity is the centre o, that half of the conductor extending from o to a is electrified negatively, and that half extending from o to a is electrified positively. The intensities of the opposite electricities at the extremities will be found to be equal, and at any points equally distant from the centre, as p p , the depths of the electric fluid will be equal, and the electric state of each half may be correctly represented by the ordinates p m, p m of two branches of a curve which are precisely similar and equal. Fig. 16. In Fig. 16, suppose A A' to be a conductor, and the curves of the circles E/ E.' those branches the ordinates of which represent the densities of the Electricity induced upon it by the spheres s s (Tig. lo) ; by gradually removing these in an equal manner, the curves will become less and less concave, and the ordinates correctly re- present the diminished density. But if the spheres be made to approach the conductor, the accumulation of Electricity towards the ex- tremities will be increased, and the curve representing the electrical densities will take the form shown in the lower figure. These results strongly favour the idea of the existence of two electric fluids, uniformly distribute^, in equal proportions over a body in its natural state, and the conductor comports itself exactly as it theoretically should do when charged with equal quantities of the contrary electricities. INDUCTION. 45 (72) We have seen that a rod of excited glass, when approached to one extremity of an insulated conductor, causes the pith-balls, suspended from the other end, to diverge. Now, on examining the conductor, it is found that the end nearest the positively excited electric has become negative, and the opposite end positive, while an intermediate zone is neutral and unelectrified. An examination of the electrical condition of a conductor while under the influence of induction, may be made in an easy and satisfactory manner by the apparatus shown in Fig. 17. Fig. 17. Let A be a cylindrical conductor five or six inches long and about three inches in diameter, and let 5 and c be two thin metallic discs, each insulated and of such a size as to fit accurately the ends of the conductor, so that, when in their places, the whole system may represent one conducting surface. Now, having given a metallic ball a charge of positive Electricity, suspend it by a silk thread, at a distance of about two inches from the cylinder. Next remove the disc, I, by its insulating handle, and test its electrical condition, it will be found to be negative; then remove and examine c, it will be found to be positive. Again, let two metallic cylinders, I c, d e, Fig. 18, be placed within an inch or more of each other in a right line ; 5 c must be insulated, but the end e of d e may be connected with the earth by a wire ; let feathers or light pith-balls be suspended by linen threads from Z> c and d; on now bringing an excited glass tube, 46 STATICAL OB FEICTIOlSrAL ELECTEICITT. a, within three or four inches of ft c, the feather or ball hanging from b will be attracted, at the same time those suspended from c and d will rush together. Let P JX", Fig. 19, be two hemispheres of wood, covered with tin-foil, Fig. 19. mounted on rods of varnished glass, and standing on wooden feet, so that they may be placed in contact N with each other, as shown in Fig. 19 ; while thus in contact approach them with an excited glass rod, and then remove it, the hemispheres will not be found to have acquired any electrical charge. Now vary the experiment by separating the two hemispheres ; while under the influence of the excited electric, and on examining them by the Electroscope, Fig. 8, each will be found electrified, that nearest the glass rod with negative, and the other with positive Electricity. It is scarcely necessary to say that in the separation of the hemispheres from each other, care must be taken to preserve their insulated condition. (73) By the following striking experiment the operation of the electric force at a distance may be made manifest in a large room. Arrange a long insulated cylindrical conductor, with one extremity about a quarter of an inch from a jet from which a gentle stream of gas is escaping, approach suddenly towards the other end a well-excited glass tube, the gas will seldom fail to become inflamed; whilst the excited tube is still in the immediate vicinity of the conductor extin- guish the flame, then suddenly withdraw the tube, and the gas will generally be re-inflamed. (74) From these experiments it appears that the electrical disturb- ance of a neutral body by the proximity of an electrified body is only of a temporary nature, all signs of excitement disappear immediately the charged body is removed. Let us, however, introduce a little variation into the conditions of the experiments. Whilst the conductor, ' Fig. 14, is under the influence of the excited glass, let it be touched with the finger, the pith-balls will instantly collapse, because the positive Electricity with which they were divergent has acquired through the finger, from the earth, a corresponding supply of negative Electricity ; the natural negative Electricity, however, of the conductor is still retained at the opposite extremity by the attractive influence of the glass. On now removing, first the finger, and then the glass tube, the pith-balls will again open, and will remain divergent, because the natural negative Electricity of the conductor being relieved from the inducing influence of the glass tube, will now become expanded over the whole conductor the pith-balls are now diverging with negative Electricity. INDUCTION THE ELECTROPHORTJS. 47 (75) It is precisely in this way that we communicate a permanent charge to the gold leaf Electroscope. If a positive charge is required, an excited stick of wax is ap- proached to the cap of the instrument, which is then touched with the finger; again insulated, and the wax immediately removed. To communicate a negative charge, an excited tube of glass is substituted for the wax, and the manipulations are the same as before. The instrument with Singer's improvement, Eig. 8, will, when dry and warm, retain a charge thus given to it for several hours, but certain pre- cautions necessary to be observed in interpreting its indications are thus described by Faraday (Chem. Ulanip., p. 437) : " Suppose it is desired to ascertain the kind of Electricity by which the leaves of the Electroscope are diverged, we may employ either a stick of excited wax or a tube of excited glass ; the divergence will increase if due to Electricity of the same kind as that of the electric approached, but will diminish if of the opposite kind ; but in applying these excited rods some pre- caution is required. They must be excited at such a distance from the instrument as to have no influence over it, and their effect on the leaves watched as they are gradually approached towards the cap. It is the first effect that indicates the kind of Electricity in the instrument, and not any stronger one, for, although if the repulsion be increased from the first no nearer approach will cause a collapse to take place, except the actual discharge of the leaves against the sides of the glass ; yet where collapse is the first effect it may soon be completed, and repulsion afterwards occasioned from a too near approach of the strongly excited tube. It is, therefore, the first visible effect that occurs as the test rod is made to approach from a distance, that indicates the nature of the Electricity ; and when this effect is observed, the rod should not be brought nearer, so as permanently to disturb the state of the Electro- scope, but should be removed to a distance, and again approached for the purpose of repeating and verifying the preceding observation. The instrument will thus undergo no permanent change in its Electricity, remaining, after a good experiment, in the same state as at first." (76) A very instructive and useful instrument, depending on inductive action, is the Electrophorus, Eig. 20. It consists of three parts a cake of resinous matter, composed of shell-lac, ten parts ; common resin, three parts ; white wax, two parts ; Venice turpentine, two parts ; pitch, half a part ; or, as Pfaff recommends, resin, eight parts ; gum lac, one part ; Venice turpentine, one part ; the materials are melted at a gentle heat ; a conducting plate or sole, which is a circular metallic plate with a rim about a quarter of an inch deep round the edge, into which the compo- sition is poured, and a cover which is of metal, provided with a glass handle. 48 STATICAL OE FEICTIONAL ELECTEICITY. Fig. 20. To use it, the resinous plate is excited by holding it in the hand in a slanting direction, and striking it briskly several times with a piece of dry warm fur or flannel, or with a warm silk handkerchief; the cover is then laid on, and on removing it by its insulating handle, it is found to have acquired a feeble charge of negative Electricity by the contact. Let the metallic plate be re-placed, and uninsulated by touching it with the finger, and on again lifting it by its handle, it will be found to give a strong spark of positive Electricity. The process may be repeated an unlimited number of times without any fresh excitation of the plate being required, and indeed after being once excited, a spark may be obtained from it during many weeks, if kept in a dry place, since the resin acts solely by its inductive influence on the combined Electricities actually present in the plate. (77) It will not be difficult at once to comprehend this. When the metallic plate is placed on the excited resin, its contact with it is, on account of the inequalities on the surface of the latter, very imperfect. It is therefore in a condition analogous to that of a con- ductor, under the influence of an electrified surface, its lower surface becoming positive, and its upper surface negative, by induction. "When it is removed from the resin the separated Electricities re-unite ; but when the plate is uninsulated, while in contact with the resin, the repelled negative Electricity is neutralised by a corresponding quantity of positive Electricity from the earth, and the plate becomes positively charged. It is thus clear that the Electricity of the moveable plate is derived not in the way of cliarge from the resin, but is the result of the process of induction. The figure represents Mr. John Phillips' s modification of the Electro- phorus, the object of which is to avoid the trouble and tediousness of THE ELECTROPHORUS. 49 establishing a communication between, the insulated cover and the earth, by means of the finger, when electrical accumulation, or sparks in rapid succession, is the object. Three methods are proposed : the first consists in raising from the metallic basis above the edge of the resin, a brass ball and wire, to which the edge of the cover, or a brass ball upon it, may be applied ; this method is stated to act very well, especially with small covers, which can with ease and certainty be directed to any particular point of the sole. The second is to fix a narrow slip of tin-foil 5, quite across the surface of the resinous plate, and unite it at each end with the metallic basis. This construction answers perfectly and instantaneously, and is very convenient with large circles, the covers of which, though uneven, will then be sure to touch some conducting point. The third method is to perforate the resinous plate quite through to the metallic basis, at the centre, and any other points, and at all those points to insert brass wires, c, c, c, with their tops level with the resin. The latter of these methods is preferred, and Mr. Phillips describes an instrument constructed on this principle, with a cast-iron basis 20*5 inches in diameter, resinous surface 19' 75 .inches, and cover. 16*25 inches, which yields loud and flashing sparks two inches long, and speedily charges considerable jars. The cover can be easily. charged from fifty to one hundred times in a minute by merely setting it down and lifting it up, as fast as the operator chooses, or as the hand can work. In charging a jar or plate, one knob of the connecting rod is placed near the insulated surface of the jar, and the other some inches above the cover, which is alternately lifted up and set down, and the jar is thus very quickly charged. A very useful modification of the Electrophorus of Volta is made by coating a thin pane of glass on one side with tin-foil to within about two inches of the edge, placing it with the coated, side on the table ; the other side is to be excited by friction by a piece of silk covered with amalgam, then carefully lifting the glass by one corner, place it on a badly conducting surface, as a smooth table, or the cover of a book, with, the uncoated side downwards. Touch the tin-foil with the finger, then carefully elevate the plate with one corner, and a vivid spark will dart from the coating to any conducting body near it : re-place the plate, touch it, again elevate it, and a second spark will be produced. By this means an electric Leyden jar may speedily be charged. This modifi- cation of the Electrophorus, or Electrolasmus, as it is called by its inventor, Dr. Golding Bird, is a very useful instrument in the chemical laboratory. (78) It was by an apparatus constructed on the principles of the Electrophorus that Earaday succeeded in, demonstrating that induction is essentially a physical action, occurring between contiguous B 50 STATICAL OR TRICTIONAL ELECTRICITY. particles, never talcing place at a distance without polarizing the mole- cules of the intervening dielectric, "When an excited glass tube is brought near an insulated conductor in which the electric equilibrium is shown to be disturbed by the divergence of pith-balls, we are not to suppose that the disturbance is occasioned by an action at a distance: for it has been shown by Faraday that the intervening dielectric air has its particles arranged in a manner analogous to those of the conductor, by the inducing influence of the glass tube. The theory of induction depending upon an action between contiguous molecules, is supported by the fact which would otherwise be totally inexplicable, that a slender rod of glass or resin, when excited by friction and placed in contact with an insulated sphere of metal, is capable of decomposing the Electricity of the latter by induction most completely, even at the point of the ball equi-distant from the rod, and consequently, incapable of being connected with it in a right line : so that it must either be concluded that induction is exerted in curved lines, or propagated through the intervention of contiguous particles. Now as no radiant simple force can act in curved lines, except under the coercing influence of a second force, we are almost compelled to adopt the view of -induction acting through the medium of contiguous particles. The apparatus employed by Faraday is shown in Figs. 21 and 22. It consists of a shell-lac Electrophorus, on the top of which is placed a brass ball; the charge on the surface of which is examined by the Fig. 21. carrier ball of Coulomb's Electrometer (56). It was always found to be positive. When contact was made at the under part of the ball, as at (d) Fig. 21, the measured degree of force was 512; when in a line with its equator, as at (c), 270; and when at the top of the ball, as at (6), 130. Now, ' the two first charges are of such a nature as might be ex- fa^filllPli pected from an inductive action in straight lines ; but the last is clearly an action of induction in a curved line, for during no part of the process could the carrier ball be con- nected in a straight line with any part of the inducing shell- lac. Indeed, when the carrier ball was placed by Faraday not in contact with the inducteous body at all, as at (e), it was found to be charged to a higher degree than when it had been in contact ; and at (a) it was affected in the highest degree, having a result above 1000. When a disc or hemisphere of metal was employed, as in Fig. 22, no charge couM be given to the carrier when placed on its centre ; but when placed considerably above the same spot, a charge was obtained, and this even when a thin film of gold leaf-was employed ; INDUCTION. 51 at (i) the force was 112, at (Jc) 108, at (Z) 65, at (m) 35 ; the inductive force gradually diminishing to this point. But on raising the carrier to (n), the charge increased to 87; and on raising it still higher, to (0), it still further increased to 105. At a higher point still (p), the charge decreased to 98, and continued to diminish for more elevated positions. (79) On reflecting upon these beautiful experimental re- sults, it seems impossible to resist the conclusion that induction is not through the metal, but through the air, in curved lines, and that it is an action of the contiguous particles of the insulating body thrown into a state of polarity and tension, and capable of communicating their forces in all directions. We must, in consequence of these decisive experiments, therefore, take a new view of the electric force, and instead of considering the electric fluid to be confined to the surfaces of the bodies by the mechanical pressure of the non-conducting air, which was the opinion previously entertained, we must consider the force originating or appearing at a certain place to be propagated to, and sustained at, a distance, through the intervention of the contiguous particles of the air, each of which becomes polarized, as in the case of insulating conducting masses, and appears in the inducteous body as a force of the same kind, exactly equal in amount, but opposite in its direction and tendencies. Thus, suppose P, Fig. 23, to be a positively charged Fig. 23. >0 O (* 3 3 f (i^ (ii r& (j nb f& v_^ body, and N P a previously neutral body at a distance, the action at P is transferred to N P, through the medium of intervening molecules, each of which becomes eleetro-jTolar, or disposed in an alternate series of positive and negative poles, as indicated by the series of black and white hemispheres. Again, let three insulated metallic spheres, A, B, C, be placed in a line, Fig. 24. P N ABC and not in contact; let A be electrified positively, and then C uninsulated; under these circumstances B will acquire the negative state at the surface E 2 52 STATICAL OB FEICTIOXAL ELECTRICITY. towards A, and the positive state at the surface furthest from it, and C will be charged negatively. The ball B will be in what is called a polar- ized condition, . e plates ; and as the quantity of Electricity is as the square roots of the forces, it appears that the direct induced force is inversely as the distance. The distances between the plates being constant and the quantity of Electricity being varied, it was found that the induced force was as the exciting Electricity directly and as the distance in- versely. When A' B' was insulated, then the direct induction was no longer, as before, in a simple inverse ratio of the distances, but in the inverse ratio of the square roots of the distances. The amounts of reflected induction of A' B' on A B were next ascertained ; they were STATICAL OR FRICTIONAL ELECTRICITY. distances between the plates, while, when A' B' was insulated, the variation was as before, in the inverse ratio of the square roots of the distances. (92) The original condenser of Yolta was constructed as represented in Eig. 33. It consisted of two circular metallic discs, the surfaces of which were covered with a thin and uniform coating of amber varnish ; the lower disc, B, was supported on a metallic stand, B B, the upper disc, A, called the collector, was provided with an insulating handle, and a short wire terminating in a metallic ball, E. The body, the Electricity of which was to be investigated, was brought into contact with E, the Electricity thus com- municated to A, acting by induction through the thin non-conductor on B, confined the Elec- tricity of the opposite kind, repelling its similar Electricity ; at the same time B, being in perfect electrical communication with the earth, had a constant supply of neutral Electricity conveyed to it, which in its turn underwent a similar decomposition. This process lasted until the condenser had received the full charge answering to its surface. The collector, A, being suddenly raised by its glass handle, taking care to keep it parallel to the base, the Electricity accumulated upon it could be transferred to an Electroscope for examination. The plates may be placed vertically, and if made a foot or more in diameter are very efficient and powerful. It is usual, however, to attach them at once to the gold leaf Electrometer, in the manner shown in Pig. 34, where a Fig. 34. represents the collecting plate and b the condenser, the brass stem of which is attached to a hinge, by means of which it can be rapidly approached to and with- drawn from a, in metallic connection with the Electroscope. Sometimes the collect- ing plate is screwed on the top of the Electroscope, the condensing plate resting upon it, and in communication with the earth, and occasionally the whole instru- ment is inclosed in a glass case, a vessel of quicklime being also inclosed to preserve the glass from hygrometric moisture. (93) An electrical condenser of remarkable delicacy was invented by M. Peclet, and is. thus described by him (Annales de Chimie et de Physique, May, 1840). The apparatus consists of three gilded plates i ^ PECLET S CONDENSER. 65 stand, furnished with adjusting screws, an eye-piece, and a portion of a divided circle. It is shown in Fig. 35. The inferior plate, a, Fig. 35. d is metallically connected with the gold leaves, as in ordinary condensers, and is varnished on its upper surface alone. The plate 5, which is placed above, is furnished with an insulating handle, d ; it is varnished on both sides but not at its circumference ; finally, the plate c is pierced at its centre by an orifice, through which passes the handle attached to the plate #; it is furnished with a cylinder of glass, e, serving to raise it, and is only varnished on its lower surface. These three plates are of ground glass, gilt, and then covered with many layers of gum-lac varnish. The lower plate, a, is in metallic connection with the two gold leaves, r, s, which are thin, narrow, parallel, and arranged as in ordinary condensers ; these leaves are placed within a glass shade, large enough to allow the gold leaves to separate to their fullest extent without touching it. On the bottom of the case are fixed two plates of copper, t, o, destined to increase by their in- fluence the divergence of the leaves, their height being so adjusted that the gold leaves may not, at any time, touch them. At the bottom of the shade is placed a box, containing chloride of calcium, to dry the air ; the shade rests on a stand furnished with screws, by means of which the apparatus is rendered vertical. At one of the extremities of this stand, h, is a rod, supporting a circular plate, i, pierced at its centre with a very small hole ; the other extremity is furnished with a section of a circle, &, divided into degrees ; the heights of this 66 STATICAL OB, FBICTIOtfAL ELECTEICITY. graduated piece and that of the centre of the plate i are so adjusted that the line which joins the two centres is horizontal, and also passes through the upper extremities of the gold leaves. The instrument is used in the following manner : the upper plate is touched with a metal held in the hand, and the edge of the second plate with the finger ; the contacts are broken, the upper plate is removed and the lowest touched; the upper plate is then returned, and the same series of operations is several times repeated ; finally, the two upper plates are removed by means of the rod d ; the gold leaves diverge to a degree greater in proportion to the number of operations. The rationale of the operation is this: when the upper plate is touched by a metal held in the hand and the second with the finger, everything takes place as in the common condenser, the two plates become charged with the contrary Electricities, but disguised. "When the first plate is removed these Electricities become free ; but if the third plate is touched with the finger, the latter becomes charged and disguises the charge of the second ; if then the first plate is restored to its place the second will be charged anew, and the charge may be made to pass in the same manner to the third. It is evident that if the Electricity of the upper plate did not dissipate itself it would suffice to touch it but once with the metal held in the hand ; but to avoid the influence of that loss it is better to touch it at each operation. To give an idea of the condensing power of this instrument the following results are mentioned. When the upper disc was touched with an iron wire twice, thrice, four, five, and six times, the divergence of the gold leaves amounted to 9f , 20, 25, 31, 41, and 88. When the experiment was made with a platinum wire, freed from all ex- traneous substances upon its surface by exposure to a red heat, and held in the hand after it had been washed with distilled water, a single contact indicated only a feeble divergence, but after three contacts it rose to 15, and after twenty it amounted to 53. This experimental demonstration of the existence of an electro-motory force between platinum and gold, and which had previously been wanting, was also obtained by M. Peclet with an ordinary condenser, the sensitiveness of which was carried to the utmost limits. It appears, from M. Peclet's experiments with the double as well as the single condenser, that all metals are positive with regard to gold, and that in this respect their relative order is as follows, zinc, lead, tin, bismuth, antimony, iron, silver, and platinum. Bismuth, antimony, and iron behave so like each other that their order in the series could be made out in no other way than by a very frequent repetition of the experiment. (94) Of the various instruments that have been termed " multipliers ' ' CATALLO'S MULTIPLIER. C7 and "doublers" we shall only describe the multiplier of Cavallo, it being very uncertain how far the indications of these instruments are to be relied on, as, from their extreme sensibility, they are liable to induce a low state of excitation during the manipulations performed with them, and thus to lead to equivocal results. Cavallo's multiplier is shown in Fig. 36. It consists of four metallic plates, A, B, C, D. The disc A is insulated on a glass pillar rising from the wooden base ; B is also supported on a glass pillar fixed in a lever, E F, moving on a pivot, E ; C is supported by a glass pillar standing on the base ; and Fig. 36. D rises from a slider, Gr, and is uninsulated ; by means of this slider C and B may be approached to and withdrawn from each other. At the back of B is fixed a metallic wire, H, which touches the metallic pillar, K, when the distance between A and B amounts to about the twentieth of an inch. The apparatus is used thus : the body whoso Electricity is to be examined is brought into contact with A, and B being, by the wire H, in communication, through K, with the earth, acts as a condenser, and becomes charged with the contrary Electricity. The lever, E F, is now moved to the position indicated by the dotted lines, and the contact between the wire, H, and the pillar, K, being broken, the Electricity of the condenser, B, is prevented from escaping to the earth, but is partly transferred to C, with which, by the motion of the lever, E F, it is brought into contact. But the uninsulated disc, D, acts as a condenser to C, and the consequence is, that nearly the whole of the charge on B is attracted to C : the lever is now restored to its former position and the process repeated, and may be continued until C becomes so charged with Electricity, that it can receive no more of the fluid from B ; B is finally removed from A. 2 08 STATICAL OE FBICTIONAL ELECTEICITT. CHAPTER IV. THE ELECTEICAL MACHINE. Various forms of the glass electrical machine The steam-electric machine Different forms of the disruptive discharge. (95) Electrical machines. The first apparatus that was constructed for the exhibition of electrical phenomena, to which the name of electrical machine was given, was the globe of sulphur used by Boyle and Otto Gruerieke (4), with which they discovered electric light. The substi- tution of glass for sulphur was made by Newton, the rubbers employed in both cases being the hand of the operator. That important part ol the machine called the prime conductor was first introduced by Boze, (7), it consisted of an iron tube suspended by silken strings ; and the substitution of a cushion for applying friction in the place of the hand, was first made by Winkler. Various were the forms now given to the electrical machine, for descriptions of many of which the curious reader is referred to Priestley's compendious History of Electricity, 1769. Dr. Watson's machine consisted of four globes turned by the same multiplying wheel, the Electricity being collected by one common con- ductor, and Dr. Priestley seems to have been the first electrician who employed a conductor supported by an insulating pillar. It was a hollow vessel of polished copper in the form of a pear. The insulating support was of baked wood, which was preferred to glass as being a better insu- lator and less brittle. The conductor received its " fire " by means of a long arched wire, or rod of very soft brass, easily bent into any shape, and raised higher or lower as the globe required, and it terminated in an open ring, in which were hung some sharp-pointed wires playing lightly on the globe when in motion. The rubber consisted of a hollow piece of copper filled with horse-hair, and covered with basil skin ; on it was laid an amalgam made by rubbing together mercury and thin pieces of lead or tin-foil on the palm of the hand, and then mixing it into a paste with a little tallow. The electric was a glass globe with a single neck enclosed in a deep brass cap, mounted in a frame of baked wood and turned by a large multiplying wheel. The battery employed by Priestley consisted of sixty-four flint green glass jars, each ten inches long and two inches and a half in diameter ; the coated part of each THE CYLINDER ELECTRICAL MACHINE. was half a square foot ; the whole battery contained thirty-two square feet. (96) The electrical machines now constructed are exceedingly elegant pieces of philosophical apparatus, though they differ in form and arrangement almost as widely as the somewhat clumsy machines of the older electricians. There are two kinds of electrical machines in general use, the cylindrical and the plate machine. The former is shown in Fig. 37. It consists p- ^ of a hollow cylinder of glass, supported on brass bearings, which revolve in upright pieces of wood attached to a rectangular base ; a cushion of leather stuffed with horse- hair, and fixed to a pillar of glass, furnished with a screw to regulate the degree of pressure on the cylinder ; a cylinder of metal or wood covered with tin-foil, mounted on a glass stand, and termi- nated on one side by a series of points to draw the Electricity from the glass, and on the other side by a brass ball. In order to keep the rubber and conductor warm and dry, Mr. Eonalds suggested in 1823 to support them on hollow glass tubes underneath which small lamps are placed. A more uniform temperature may however be obtained by placing underneath the cylinder a plate of metal about 6 inches square, and keeping it heated by an argand lamp. A flap of oiled silk is attached to the rubber to prevent the dissipation of the Electricity from the surface of the cylinder before it reaches the points. On turning the cylinder, the friction of the cushion occasions the evolution of Electricity, but the production is not sufficiently rapid or abundant without the aid of a more effective exciter, which experience has shown to be a metallic substance. The surface of the leather cushion is therefore smeared with certain amalgams of metals, which thus become the real rubbers. The amalgam employed by Canton consisted of two parts of mercury and one of tin, with the addition of a little chalk. Singer proposed a compound of two parts by weight of zinc, and one of tin ; and Pfister a mixture of two parts tin, three zinc, and four mercury, with which in a fluid state six parts by weight of mercury are mixed, and the whole shaken in an iron, or thick wooden box, until it cools. It is then reduced to a fine powder in a mortar, sifted through muslin, and mixed 70 STATICAL OB FKICTIONAL ELECTEICITT. with lard in sufficient quantity to reduce it to the consistency of paste. This preparation should be spread cleanly over the surface of the cushion, up to the line formed by the junction of the silk flap with the cushion ; but care should be taken that the amalgam should not be extended to the silk flap. It is necessary occasionally to wipe the cushion, flap, and cylinder, to cleanse them from the dust which the Electricity evolved upon the cylinder always attracts in a greater or less quantity. It is found that from this cause a very rapid accumula- tion of dirt takes place on the cylinder, which appears in black spots and lines upon its surface. As this obstructs the action of the machine it should be constantly removed, which may be done by applying to the cylinder, as it evolves, a rag wetted with spirits of wine. The pro- duction of Electricity is greatly promoted by applying to the cylinder with the hand a piece of soft leather, five or six inches square, covered with amalgam. This is in fact equivalent to giving a temporary enlargement to the cushion. Peschel states (^Elements of Physics, vol. iii. p. 32), that the most effectual method of using amalgam is to spread it pretty thickly on the cushion itself, and then to cover it with a piece of silk, so that the amalgam may not be in actual contact with the glass : a sufficient quantity will work through the silk when the glass presses against it. By this arrangement the inconvenience of smearing the glass is avoided. One important qualification of the rubber is, that the surface on which the amalgam is placed, should carry off as quickly and as completely as possible, the Electricity excited. To effect this, a piece of copper, or tin-foil, the same size as the cushion, is laid immediately under the surface coated with amalgam. If, however, the cushion is stuffed with metal filings instead of with horse-hair, this arrangement is not necessary. If the surface of the amalgam be covered with finely powdered mosaic gold, increased effects are said to be produced; but attention must be paid to the purity of this substance, or it may be inert or even injurious. According to Masson {Archives de V Electricite, Sept. 1845), mosaic gold (bisulphuret of tin) sometimes contains as much as fifty per cent, of sal ammoniac, the hygrometric and conductric properties of which completely destroy its electric action. Before employing it, therefore, it should be reduced to a powder, and washed on a filter until it no longer gives any indications of the presence of sal ammoniac : it should then be carefully dried and employed in powder upon heated paper. Masson thinks that the bisulphuret of tin does not undergo decomposition, but that it becomes electrized by simple friction. The use of the oiled silk flap is to prevent the dissipation of the Electricity evolved on the glass by contact with the air; it is thus THE PLATE ELECTRICAL MACHINE. 71 retained on the cylinder till it encounters the points of the prime con- ductor, by which it is rapidly drawn off. It is usual to cover with a varnish of gum lac those parts of the glass beyond the ends of the rubber, with a view of preventing the escape of the Electricity through the metallic caps at the extremities of the cylinder, and the inside of the flap is also sometimes coated with a resinous cement consisting of four parts of Venice turpentine, one part of resin, and one of bees' wax, boiled together for about two hours in an earthen pipkin over a slow fire. (97) When the cylindrical machine is arranged for the development of either positive or negative Electricity, the conductor is placed with its length parallel to the cylinder, and the points project from its side, as in the machine shown in the figure. The negative conductor sup- ports the rubber, and receives from it the negative Electricity not by induction, as is the case with the positive conductor, but by communi- cation. If it be required to accumulate positive Electricity, a chain must be carried from the negative conductor (which of course is insu- lated) to the ground ; if, on the other hand, negative Electricity be required, then the conductor must be put in communication with the earth, and the rubber insulated. We shall return to the consideration of this presently. Fig. 38. (98) The Plate Electrical Machine is shown in Fig. 38. It consists of 72 STATICAL OK FRICTIOtfAL ELECTRICITY. a circular plate of thick glass, revolving vertically by means of a winch between two uprights : two pairs of rubbers, formed of slips of elastic wood covered with leather, and furnished with silk flaps, are placed a< two equi-distant portions of the plate on which their pressure may b increased or diminished by means of brass screws. The prime con- ductor consists of hollow brass, supported horizontally from one of the uprights ; its arms, where they approach the plate, being furnished with points. (99) "With respect to the merits of these two forms of the electrical machine, it is difficult to decide to which to give the preference. For an equal surface of glass the Plate appears to be the most powerful ; it is not, however, so easily arranged for negative Electricity, in consequence of the uninsulated state of the rubbers, though several ingenious methods of obviating this inconvenience have been lately devised. Fig. 39. (1) (100) One of the best forms of the Plate Machine is that invented by Mr. C. "Woodward, President of the Islington Literary and Scientific Institution. Fig. 39 represents the one in that Institution, presented to THE PLATE ELECTRICAL MACHINE. 73 Fig. 40. (2) the members by the above-mentioned gentleman. The plate, which is two feet in diameter, is fixed in the ordinary manner, between two uprights, to the top and bottom of which are attached the rubbers. The two conductors, A B, insulated on stout glass pillars, are fixed at each end of the mahogany board on which the whole is mounted, and con- nected together by a brass arm C, which is supported in the centre by a glass pillar E ; from these points project and collect the Electricity from both sides of the plate. This machine possesses the following advan- tages : the insulation is exceedingly good ; it occupies but very little room on the lecture table ; and readily exhibits positive and negative Electricity : for this latter purpose, it is arranged as follows, and the annexed cut will render it perfectly intelligible. The right-hand conductor B, together with the brass arm and support, are removed, and the plate being turned a quarter of a circle, the upper rubber D is brought down on the glass pillar E, and a brass ball Gr screwed into it. We have now a positive and negative conductor ; and although the machine possesses, of course, but half its original power, it is sufficient for all pur- poses of experiment. Instead of one, this machine is readily mounted with two plates, which work equally well, and it then becomes an exceedingly powerful instrument, occupying scarcely any more space. Mr. "Woodward strongly recommends the covering the glass pillars y and also that part of the plate between the spindle and the rubbers, with sealing-wax varnish, stating that it very much increases the power of the machine. (101) In Sturgeon's Annals of Electricity, &c. for September, 1841, two useful modifications of the cylinder and plate machine are de- scribed and lithographed. The principal feature in which the arrange- ment of Mr. Goodman's cylinders differs from those of the usual con- struction, consists in their being supplied with two rubbers, mounted on glass rods placed parallel to each other on opposite sides of the cylinder, and connected together by means of a brass tube bent twice at right angles. This brass tube rises several inches above the top of the cylinder, so as to be out of the way of the prime conductor, which is so contrived as to answer at the same time for a support for one of the pivots on which the cylinder revolves. Two arms proceed from the upper and lower portion of this upright conductor, passing parallel to, and above 74 STATICAL OB FBICTIONAL ELECTRICITY. and below the cylinder, from which a number of points project to receive the fluid accumulated by the excitation of the rubbers, and brought round by the rotation of the cylinder. To prevent dissipation of the fluid from the extremities of the arms, each is made to terminate in a lacquered glass ball. Machines arranged in this manner are stated by the inventor to possess the desirable qualities of strength and en- durance, and for equal surfaces to be twice as powerful as when only one rubber is employed. Mr. G-oodman arranges the rubbers of his plate machine in a similar manner, that is, parallel to each other, and supported by glass pillars on either side of the periphery of the plate, as in the cylinder machine, one end of the axis (of lacquered glass) turns in an insulated conductor pro- vided with horizontal arms carrying points. For common purposes, and where extreme cheapness is desirable, the plate may be made of common window-glass, to the centre of which two wood-turned convex caps may be cemented without any perforation of the plate, and the axle is completed by cementing a glass rod to the centre of each cap. The cement recommended by Mr. Goodman, is equal parts of resin and bees' wax, made sufficiently thick by the addition of red-ochre. The cost of a plate of fifteen inches in diameter is about two shillings, or half a crown. (102) Van Marum in conjunction with Mr. Cuthbertson constructed an electrical machine of extraordinary power, towards the end of the last century. It consisted of two circular plates of French glass, each sixty-five inches in diameter, fixed upon the same axis and excited by four pairs of cushions each nearly sixteen inches in length. A single spark from this machine melted a leaf of gold; a thread became attracted at the distance of thirty-eight feet, and a pointed wire exhibited the appearance of a luminous star at a distance of twenty-eight feet from the conductor. A magnificent machine, somewhat on Van Marum' s principle, has lately been constructed for the Eoyal Panopticon of Science and Art in Leicester Square. The plate of this machine is ten feet in diameter, it is turned by steam power, and excited by three pairs of rubbers, each pair nearly three feet in length. The conductor, which is pear-shaped on Priestley's plan, is six feet long and four feet in diameter in its widest part. When well L excited, sparks from fifteen to eighteen inches in length, and of remarkable brilliancy and volume, may be drawn from the terminal ball of the conductor; the discharge through a vacuous tube seven feet long, exhibits a continuous stream of splendid purple light, and it charges to saturation a battery of thirty-six jars, presenting 108 square feet of coated glass, in less than a minute. (103) Sir William Harris's elegant machine is shown in Fig. 41. HARRIS S PLATE ELECTRICAL MACHINE. 75 The plate A A, about three feet in diameter, is mounted on a metallic axis resting on two horizontal supporters of mahogany, which are by four vertical mahogany columns, fixed themselves x sustained Fig. 4!. upon a firm frame as a base. The whole apparatus rests on the four legs, B C D P, and these again rest upon another steady frame provided with three levelling screws, Gr H I, for securing it in a horizontal position. The rubbers are insulated on the glass pillars, K K, one on either side of the horizontal diameter of the plate. L M N is the positive conductor projecting in a vertical position in front of the plate, while the negative conductor, P, passes in a curvilinear direction behind, and connects the rubbers of each side. The glass plate is turned by an insulated handle, immediately in front of which is placed a short index, which is fixed to the axis, and which moves over a graduated circle attached to the horizontal part of the frame, and through the centre of which the axis passes. In this manner the number of revolutions of the plate may be accurately registered. In order to strengthen the centre of the plate, two smaller plates are cemented to each side by varnish, and a small stop is inserted into the axis to prevent the pressure from increasing beyond a certain point. 76 STATICAL OB FEICTIONAL ELECTBICITY. Fi g- 42. When the machine is used for ordinary purposes, the conductors, as, shown in Pig. 42, are employed, but when it is required to accumulate Electricity, the conductors should have the smallest extent possible. They are thus formed of small straight tubes, as shown in Fig. 42, and its extremities terminate in balls of varnished wood, through the substance of which the metallic commu- nicators pass. To prevent the flaps from being drag- ged over the plate in turning, they are retained in their places by cords of silk attached to them, passing round fixed supports. The machine used by Faraday, in his famous researches, is somewhat in construction similar to Harris's ; the plate is fifty inches in diameter, the metallic surface of the conductor in contact with the air is about 1422 square inches ; when in good excitation one revolution of the plate will give ten or twelve sparks from the conductor, each an inch in length. Sparks or flashes from ten to fourteen inches in length may easily be drawn from the conductors. (104) It is by no means immaterial what kind of glass is employed in the construction of the plates or cylinders of electrical machines. Priestley, who made many experiments on this subject, came to the con- clusion " that common bottle metal is fittest for the purpose of ex- citation," in consequence (as he rightly supposed) of the hardness of the metal and its exquisite polish. Harris recommends the flinty kind of plate-glass of most perfect manufacture, and very highly polished. Common window-glass is admirably adapted to the purposes of electrical excitation. Sir "William constructed a machine of two feet in diameter, by cementing together two plates of window glass with black sealing- wax, and he states that it had most remarkable power. The softer kinds of glass and those in which the alkalies predominate are very inferior, and some kinds cannot be excited at all in consequence of their remark- able conducting power. (105) The eminent electrical properties of gutta percha (35) would suggest the employment of this substance as a negative electric for elec- trical machines. Mr. Barlow (Phil. Mag. vol. xxxvii. p. 428) describes an GUTTA PEECHA ELECTBICAL MACHINE. 77 apparatus of this kind, consisting of a band of thin sheet gutta-percha about four inches wide, which is made to pass round two wooden rollers fitting them very tightly, and rubbed by four brushes of bristles placed outside the band and opposite to the axis of each roller. The machine is provided with a curved brass conductor similar in form to the con- ductors of plate-glass machines : under favourable circumstances this machine acts very well ; but Mr. Barlow finds it much affected by the weather, and he thinks that although gutta-percha is capable of producing a large amount of Electricity, a modification must be effected in the con- struction of the machine before it can take its place as a useful instrument. (106) At the concluding stage of the manufacture of paper, viz., when it leaves the glazing or polishing iron rollers, and accumulates in a finished state on a final wooden roller, powerful electrical phenomena are frequently developed ; the Electricity is negative. Messrs. Arm- strong {Elect. Mag. vol. i., p. 459), Hankel (Poggendorf } s Annalen, vol. xxxi., p. 477), and Walker (Elect. Mag. vol. ii., p. 120), have studied the conditions under which this electrical excitement takes place. The electrized condition of the paper becomes perceptible immediately after the sheet quits the last glazing roller ; and when a person's hand is presented, either to the roll of finished paper, or to any part of the sheet between the roll and the glazing rollers, sparks are emitted by the paper which sometimes reach to a distance of several inches, and when the interior of the room is darkened, the workmen frequently see sparks darting through a space of eight or ten inches between the surface of the roll and the iron work of the machine. By means of a collector, consisting of a row of metallic points insulated by a glass handle, Mr. Armstrong charged Leyden jars, but the quantity of Electricity evolved was not so great as appearances led him to expect. Dr. Hankel found that the heat of the last steam roller exercised great influence, the elec- trical phenomena being much stronger the more the heat of the last steam roller was increased, becoming in fact frequently so strong that very loud sparks darted from the paper to the last smoothing roller, by which jars could readily be charged. In Mr. Elliot's mill, near Chesham, Bucks, sparks from ten to twelve inches long have been obtained from the wooden roller round which the paper is collected ; the greatest effects were produced by a thin brown paper manufactured for Terry's " poor man's plaster." Walker found this paper to be quite free from Electricity previous to its undergoing the final act of pressure between the polishing rollers. The cause of electrical excitement is the pressure and withdrawal of pressure (amounting in fact to friction), which the paper undergoes in its passage through the roller. (107) A similar production of Electricity has for many years been noticed in Mr. Macintosh's manufactory at Glasgow, on tearing asunder 78 STATICAL OB FRICTIONAL ELECTRICITY. the well known waterproof- cloth which is stuck together by means of a solution of India-rubber in coal tar (JEdin. Phil, Jour. vol. x., p. 185), It has also been noticed by Mr. Marsh, during the grinding of newly roasted coffee in an iron coffee mill (Ann. of Elect, vol. viii., p. 124), Powerful electrical phenomena have likewise been observed in cotton mills, arising from the friction of the bands or straps over the rollers bj which the machinery is put in motion ; and lastly, strong electrical sparks have been obtained, where neither friction nor pressure has intervened to produce electrical excitement, as for instance during the drying of dyed or bleached goods, which, according to Mr. Napier (Elect Mag. vol. i., p. 500), become sometimes so highly excited that sparks visible in daylight, will be given off to an individual passing close to them Pieces mordanted with acetate of alumina and dried at a great heat, art often highly charged with Electricity, and if the hand be suddenly drawi along the piece, _ a complete shower of fire is observed with a sharj crackling noise accompanied by a slight shock. Mr. Buchanan relates (Phil. Mag. N. S. vol. i., p. 581), that in a factory at Glasgow, th( accumulation of Electricity in one room in particular, in which was * large cast-iron lathe, shears, and other machinery driven with grea 1 velocity by leather belts, was so great that it was necessary, in order t< protect the workmen from unpleasant shocks, to connect the machinery by means of a copper wire with the iron columns of the building ; anc that when a break in the wire of - f of an inch was made, the inter mediate space was constantly luminous, and even at J of an inch th< succession of sparks was very rapid. The Electricity was positive. (108) Scientific men are not agreed as to the modus agendi of th< amalgam applied to the rubber of the electrical machine. It seemi pretty clear that the oxidation of the amalgam by the friction employee is essential to the increased excitation ; for the development of Electri city does not appear to be increased when amalgams of difficultly oxi dizable metals, such as gold, are employed ; and Dr. "Wollaston coul< not succeed in obtaining any signs of free Electricity from a machim worked in an atmosphere of pure carbonic acid. The bisulphuret o tin (aurum musivum) may be employed instead of amalgam ; by th< friction it probably becomes partially decomposed into bisulphate of tin as iron pyrites is into sulphate of iron. The chemical influence o friction, indeed, is more energetic than is usually supposed : even sili ceous minerals, as mesotype, basalt, and feldspar, become partly decom posed, giving up a portion of their alkali in a free state. (109) The theory of the action of the electrical machine flows imme diately from the principles of induction already illustrated (79) ; ; brief recapitulation may, however, be useful. On turning the handl of the cylinder, or plate, the Electricity naturally present in the rubbe EXPERIMENTS WITH THE ELECTBICAL MACHINE. 79 becomes decomposed, its positive adhering to the surface of the glass, and its negative to the rubber : the positive electric portions of the glass coming, during its revolution, opposite to the points on the conductor, act powerfully by induction on the natural Electricities of the conductor, attracting the negative, which being accumulated in a state of tension at the points, darts off" towards the cylinder, to meet the positive fluid, and thus re-constitute the neutral compound. The con- sequence of this is, that the conductor is left powerfully positive, not, it must particularly be understood, ly acquiring Electricity from the revolving glass, but by having given up its own negative fluid to the latter. The rubber is left in a proportionately negative state, and con- sequently, after revolving the glass for a few minutes, can develop no more free positive Electricity, provided it is insulated : on this account, it is necessary to make it communicate with the earth for the purpose of obtaining a sufficient supply of positive Electricity to neutralize its negative state. In very dry weather, it is necessary to connect the rubber with the moist earth by means of a good conductor ; and it is advisable, if possible, to establish a metallic connexion with metallic water pipes. (110) The subjoined experiments will serve to familiarize the student with the principles and action of the electrical machine. 'Ex. 1. See that the machine is in good working order, the cylinder or plate being free from dirt and black spots (96), and perfectly dry and warm : wipe it well with a piece of warm flannel, and then with an old silk handkerchief. Take care that the insulating glass stands are clean and dry, and see that the rubber is uniformly but not too thickly covered with amalgam (96). All these particulars being duly attended to, turn the handle, and present the knuckle of the other hand to the prime conductor ; a vivid spark will pass between them accompanied by a sharp, snapping sound. It is usual to speak of this spark as the positive spark, a term which does not, however, convey a correct idea of its nature ; for it is not to be regarded as arising from the mere passage of free Electricity, but as the union of the two electric fluids, and the consequent discharge of the electrified body. According to the prin- ciples of induction (70 et seq.) the positively electrified prime conductor induces an opposite state in any conducting substance approaching it, and when this state has amounted to one of sufficient tension, tlie negative Electricity rushes towards the positive of the prime conductor, constituting the neutral combination. It is this neutralization, or discharge of the electric state of the conductor, which constitutes the electric spark ; and it is the same with the sparks from an excited glass tube, and from the cover of an Electrophorus (76) : all cases of discharge must be preceded by induction (82). In order to obtain 80 STATICAL OB FEICTIONAL ELECTEICITT. long sparks from the prime conductor the operator must commence by taking short ones, and gradually lengthen them to their maximum. Long sparks in the open air are always crooked ; this arises from the condensation of the air immediately before the spark in consequence of the immense velocity with which it moves ; a resistance is thereby set up in the line in which it was moving, so that it changes its course, again condenses the air, and is again turned aside ; and this alternate deflection produces a zig-zag appearance. Short sparks are either quite straight or slightly curved, sometimes broken and irregular. IB Fig. 43. condensed air the light is white and brilliant ; in rarefied air divided and faint, and in highly rarefied air purplish. For these experiments the simple appa- ratus shown in Pig. 43 may be employed, consisting oi a glass globe about four inches in diameter, provided at each end with a brass cap to one of which a stop- cock is screwed with a wire and ball projecting into the globe, and through the other a similar wire slide* through a collar of leather, so that the balls may b< set at any required distance from each other in the globe. The apparatus may be exhausted of air by th< air-pump ; or the air may be condensed in it by t condensing syringe. The effect of different gasei may likewise be studied with this apparatus. Ex. 2. Continue to turn the cylinder or plate, keeping the knuckL steadily held towards the prime conductor. The sparks will decreas< in brilliancy, intensity, and frequency, and after some time no mor< will be obtained. Now establish a good metallic communicatioi between the rubber and the earth, and the sparks will be obtaine< uninterruptedly, and undiminished in intensity. Ex. 3. B/emove the conductor from its position in front of the glass and having darkened the room, revolve the cylinder or plate ; a seriei of bright sparks will be observed to pass round the surface of the glass exhibiting a very beautiful appearance. Let an assistant next take i needle in his hand, and approach its point towards, but at a considerabl< distance from, the revolving glass. While at the distance of severa feet, it will be seen to be tipped with luminous matter, illustrating in i simple manner the striking influence of points, and their use on th< prime conductor. Ex. 4. E/emove the ball from the end of the conductor disclosing a rounded blunt wire ; put the conductor in its place, and turning the machine briskly, attempt to draw sparks from the body of th< conductor with the knuckle, you will find that you will obtain verj feeble and powerless ones, but you will perceive a beautiful luminous EXPERIMENTS WITH THE ELECTRICAL MACHINE. 81 appearance proceeding from the end of the wire, and on holding the hand near it, a sensation like that pro- duced by a gentle stream of wind will be experienced. Notice attentively the appearance of the luminous matter at the points at the two opposite ends of the conductor : that on the points immediately opposed to the revolving glass will resemble small stars, and that on the wire at the end of the conductor will resemble a brush or pencil. The appearance of each will be found to be not unlike Fig. 44. The same lumi- nous appearances will be perceived if a pointed wire be held at a short distance from the conductor and rubber, both being insulated, the brush or pencil appearing on the wire held towards the rubber, and the star on the wire presented towards the conductor. "We shall return to the consideration of this electric light presently. Ex. 5. Connect the rubber and conductor together by a wire : on revolving the glass, no signs of Electricity will be obtained from either : but if the machine be extremely energetic, the wire will appear surrounded with a lambent flame, otherwise the electric fluids will traverse, and the discharge take place invisibly along the wire. But if the conductor be interrupted, vivid sparks will appear at each rupture of continuity, arising from inductive action, and consequently discharge taking place at every one of these spots. Ex. 6. The last experiment proves that the charges on the conductor and rubber are exactly equal : that they are in opposite electrical states may be proved by suspending from each some light substances, as feathers or pith-balls, which will strongly attract each other when the machine is put in action. Ex. 7. Place several strips of paper upon the end of a long rod in connexion with the prime conductor, in the centre of a large apartment, they will open out equally, like radii from the centre of a sphere ; but on approximating a conducting body to them in their Fig. 45. charged state, they will incline towards it from the concen- tration of the force upon its nearer surface. This is illustrated by the ridiculous figure of a head of hair, Fig. 45, and is a common electrical ex- periment. When electrified, the hair stands on end; and each fibre, as if in a state of repulsion from its neighbour, is attracted by, and radiates towards, the point which is nearest to it in the oppositely induced state. Ex. 8. Paste some strips of tin-foil on a plate of glass having 82 STATICAL OB FEICTIONAL ELECTEICITY. 46. portions cut out, so that the space represents letters, as shown in Fig. 46 ; or draw a serpentine line on the glass with varnish, and place on it metallic spangles ahout one- tenth of an inch apart ; or stick the spangles in a spiral direction on a glass tube : in each case lines of fire, occasioned by sparks passing apparently at the same moment through all the spaces, will be Fig. 47. observed on connecting the first piece of foil with the conductor, and the last with the ground. Fig. 47 represents a little apparatus invented by Mr. Barker for exhibiting the revolution of a spotted tube. It is made of a glass tube, blown smooth and round at one end, and open at the other: it should be about ten inches long, and three quarters of an inch in diameter. A ball or a piece of smooth tin-foil is fixed at the upper closed end, and the usual spots of tin-foil carried in a spiral form to the lower open end. A cap, either of wood or brass, is cemented on the outside of the lower end of the tube, and a strip of foil placed round it. From this ring four wires project outwards, having their points bent at right angles. The tube is then set on an upright wire which passes upwards into the tube to its top, and this wire is then set on an insulated stand, and brought near the prime conductor. It can thus revolve with great ease. J3x. 9. Provide a stool with glass legs, Fig. 48, and having wiped it clean and dry, let a person stand upon it, holding in his hand a chain or wire communicating with the prime conductor : on setting the machine in action, sparks of fire may be drawn from any part of his person ; he becomes, indeed, for the time, a part of the conductor, and is strongly electrified, although without feeling any alteration in himself. If he hold in his hand a silver spoon containing some warm spirits of wine, another person may set it on fire by touch- ing it quickly with his finger. Ex. 10. By employing the little arrangement shown in Fig. 49, cold spirits of wine may be fired. Place it so that the ball a can receive sparks from the prime conductor : pour spirits of wine into the cup e Fig. 48. EXPEEIMENTS WITH THE ELECTBICAL MACHINE. Fig. 50. till the bottom is just covered : place the cup Fig. 49. under the wire d, then turn the machine, and the sparks that are received by a will fly from the wire through the spirits to the cup, and generally set it on fire. Ex. 11. The phenomena of attraction and repulsion are well illustrated by the apparatus known as the electric bells, Fig. 50. They are to be suspended from the prime conductor by means of the hook : the two outer bells are suspended by brass chains, while the central, with the two clappers, hang from silken strings : the middle bell is connected with the earth by a wire or chain : on turning the cylinder, the two outside bells become positively electrified, and by induction the central one becomes negative, a luminous discharge taking place between them, if the Electricity be in too high a state of tension. But if the cylinder be slowly revolved, the little brass clappers will become alternately attracted and repelled by the outermost and inner bells, producing a constant ringing as long as the machine is worked. Fig. 51 shows an admirable contrivance for illustrating electrical attraction and repulsion. Three or four glass balls, made as light as Fig. 51. possible, are supported on an insulated glass plate, on the under part of which strips of tin-foil are so pasted as to form a broad circle or border near the margin, and four radii to that circle ; on the upper part of the plate is a flat brass ring supported on small glass pillars, so as to have its inner edge immediately over the exterior edge of the tin-foil. The brass ring being in communication with the prime conductor and the G 2 STATICAL OR FBICTIOffAL ELECTRICITY. tin-foil with the rubbers of the machine, the ring and foil will be oppo- sitely electrified. The glass balls being attracted by the ring, become positively electrified in the part which comes in contact with it. Thus electrified, they will be attracted by the foil, and communicating the charge, return to the ring to undergo another change. Different parts undergo in succession these changes, and the various evolutions of the balls are very striking and curious. Fig. 52. Ex. 12. The current of air which accompa- nies the discharge of Electricity from points is pleasingly shown by a variety of toys. Pig. 52 exhibits a little arrangement usually called the electrical planetarium. It is connected with the prime conductor by means of a chain, and when the machine is set in action the currents of air discharged from points inserted at a and b re-act on the wires of the appa- ratus, and it begins to move, gradually acquiring a very rapid horizontal motion, c b round the point a, and a d round the point e. Fig. 53. Pig. 53 represents a model of a water-mill for grinding corn. A is the wheel, B the cog-wheel on its axis, C the trundle, D the running mill- stone on the top of the axis of the trundle. To set it in motion place it near the prime conductor, in which is inserted a crooked wire terminating in a sharp point. Let this point be di- rected to the uppermost side of the wheel A. On putting the machine in motion, the current of air attending the Electricity which issues from the point will turn the wheel, and, conse- quently, all the other working parts of the mill. Ex. 13. Pill a phial with oil, pass through the cork a copper wire bent ear its lower end at right angles, so that its point may press against the inside of the glass, and suspend it by the upper end of the wire from the prime conductor. From the machine the point of the wire in the phial will assume a high state of positive electric tension : bring towards it a brass knob, or the knuckle; induction, and consequent discharge, will take place through the sides of the glass, which will become perforated by a round hole. EXPERIMENTS WITH THE ELECTRICAL MACHINE. 85 J3x. 14. By the following beautiful experiment, the resistance to induction and discharge offered by a dielectric medium, such as atmo- spheric air, is shown. A glass tube A, Eig. 54, two feet in length, is furnished at either end with a brass ball projecting into its interior, and carefully exhausted of its air by means of a good air-pump : on con- necting the end B with the prime conductor, and the end B' with the Fig. 54. Fig. 55. earth, when the machine is turned, B becomes positive, and induces a contrary state on the ball B', induction taking place with facility in consequence of the atmospheric air being removed (or rather highly rarefied), and is followed by a discharge of the two Electricities in the form of a beautiful blue light, filling the whole tube, and closely re- sembling the aurora borealis. Ex. 15. Attraction and repulsion are amusingly shown by suspending a brass plate, Eig. 55, from the prime conductor, and setting under it a sliding stand, on which is laid a little bran or sand, or little figures made of pith : on turning the machine the bran or. sand is attracted and repelled by the upper plate with such rapidity that the motion is almost imperceptible, and appears like a white cloud between the plates, and the little figures appear to be animated, dance, and exhibit very singular motions, dependent on inductive action. Ex. 16. Fig. 56 represents a small pail with a spout near the bottom, in which is a hole just large enough to let the water out by drops ; it is to be filled with water and made fast to the prime conductor : on turning the machine, the water which before descended from the spout in small drops only, will fly from it in a stream, which in the dark appears like a stream of fire ; or a sponge saturated with water may be suspended from the prime conductor, when the same phenomenon will be observed, which is referable to the mutual repulsive property of similarly electrified particles. Ex. 17. Let the tumbler A, Fig. 57, be wiped thoroughly dry, warmed, and the inside charged by holding it in such a direction that a wire pro- ceeding from the prime conductor of a machine in action shall touch it successively in nearly every part ; then invert it over a number of pith- balls ; they will be attracted and repelled backwards and forwards, and effect the discharge of the Electricity which induces from the interior Fig. 56. 86 STATICAL OR TBICTIOtfAL ELECTEICITT. Fig. 58. \ Fig. 57. towards the plate. They will then remain at rest ; but if the Electricity which has been disengaged on the outside towards surrounding objects be removed by a touch of the hand, a fresh portion will be set free on the interior, and the attraction and repulsion of the balls will again take place, and thus for many times successively the action will be renewea until the glass eturns to its natural state. Ex. 18. Fig. 58 is another amusing philosophical toy. It is called the electrical swing, and acts, as will be immediately perceived, upon the principle of attraction and repulsion. The insulated brass ball A is connected with the prime conductor, while the opposite ball B communicates with the earth. The light figure represented as sitting on a silken cord is first drawn towards A, where it receives a charge which it dis- charges on B, and thus is kept swinging between the two balls. Ex. 19. Fig. 59 represents two hollow brass balls, about three quarters of an inch in di- ameter, insulated on separate glass pillars, by which they are supported at a distance of about two inches from each other ; the upper part of each ball is hollowed into a cup, into which a small piece of phosphorus is to be put. A small, candle has its flame situated midway between the balls, one of which is connected with the positive, and the other with the negative conductor of a powerful machine. When the balls are electrified, the flame is agitated, and, inclining towards the one which is negative, soon heats it sufficiently to set fire to the phosphorus it contains, whilst the positive ball remains perfectly cold, and its phosphorus unmelted. On reversing the connexions of the balls with the machine, the phosphorus in the other ball will now be heated, and will inflame. Ex. 20. To a wire proceeding from the prime conductor, attach a piece of sealing-wax ; put the machine in action, no effect will be produced on the wax : now soften the end by the flame of a spirit lamp, and while the machine is in action, present a card to the hot wax, and it will be perceived that a considerable quantity of melted wax has been blown off from the wire, and, in the form of fine, soft, flexible Fig. 59. ELECTRICITY OF EFFLUENT STEAM. 87 Fig. 60. filaments, lias collected on the surface of the card, exhibiting a very- curious appearance. This experiment is interesting, as proving that the mechanical condition of bodies has an influence on their relation to Electricity. The sealing-wax, when cold, stands high amongst non- conductors ; but when the physical condition of its atoms is disturbed by heat, it becomes a conductor. Ex. 21. With the apparatus shown in Fig. 60 some exquisitely beautiful electrical experiments may be made. The balls in the receiver, which may be 12 or 14 inches high and 6 or 7 inches in diameter, are set opposite to each other at the distance of about four or six inches. The receiver is accurately exhausted, and then screwed on the transfer plate, which is connected by a wire with the negative conductor, the upper ball being con- nected with the positive. On turning the machine a current of beautiful light will pass from the positive to the negative ball on which it breaks and divides into a luminous atmosphere entirely sur- rounding the lower ball and stem, and conveying in a very striking manner the idea of a fluid run- ning over the surface of a resisting solid which it cannot enter with facility. No appearance of light occurs on the positive ball but the straight lumi- nous line that passes from it ; but if it be rendered negative, and the lower ball positive, these effects are reversed. If the lower ball and wire be altogether removed, and if the upper wire be made to terminate in a point instead of a ball, then on, 'turning the machine and exhausting the air, the small brush of light which first makes its appearance on the point gradually enlarges, varying in appearance and becoming more diffused as the air becomes more rarefied, until at length the whole of the receiver is filled with a beautiful and varying light, producing an effect which is pleasing in the highest degree. (Singer) (111) Electricity of effluent steam. Under the head of frictional Electricity must be included this very remarkable source of electrical de- velopment, which in the hands of Messrs. Faraday, Armstrong, Ibbetson, and others, has led to the construction of electrical machines compared to which even the most powerful glass machines hitherto constructed are but as pigmies. The first account we have of an observation on the Electricity of a jet of steam while issuing from a boiler is contained in a letter addressed 88 STATICAL OB EEICTIONAL ELECTRICITY. to Professor Earaday, by H. S. Armstrong, Esq. (Phil. Mag. vol. xvii.) It appears that the phenomenon was first noticed by the engine-man entrusted with the care of a steam engine at Sedgehill, about six miles from Newcastle : it happened that the cement, by which the safety-valve was secured to the boiler had a crack in it, and through this fissure a copious horizontal jet of steam continually issued. Soon after this took place, the engine-man having one of his hands accidentally immersed in the issuing steam, presented the other to the lever of the valve, with the view of adjusting the weight, when he was greatly surprised by the ap- pearance of a brilliant spark, which passed between the lever and his hand, and was accompanied by a violent wrench in his arms, wholly unlike what he had ever experienced before. The same effect was repeated when he attempted to touch any part of the boiler, or any iron work con- nected with it, provided his other hand was exposed to the steam. He next found that while he held one hand in the jet of steam, he communi- cated a shock to every person whom he touched with the other, whether such person was in contact with the boiler, or merely standing on the brickwork which supported it ; but that a person touching the boiler, received a much stronger shock than one who merely stood on the bricks. (112) In following up these experiments, Mr. Armstrong provided himself with a brass plate having a copper wire attached to it, which terminated in a round brass knob. "When this plate was held in the steam, by means of an insulated handle, and the brass knob brought within about a quarter of an inch from the boiler, the number of sparks which passed in a minute was from sixty to seventy, and when the knob was advanced about one-sixteenth of an inch nearer to the boiler the stream of Electricity became quite continuous. The greatest distance between the knob and the boiler, at which a spark would pass from one to the other, was fully an inch. A Florence flask, coated with brass filings on both surfaces, was charged to such a degree with the sparks from the knob, as to cause a spontaneous discharge through the glass, and several robust men received a severe shock from a small Leyden jar charged by the same process. The strength of the sparks was quite as great when the knob was presented to any conductor communicating with the ground, as when it was held to the boiler. (113) A long and well-conducted series of experiments was made by Mr. Armstrong, on the Electricity evolved under these peculiar circum- stances.* By standing on an insulated stool, and holding with one * See L. and E. Phil. Mag. vol. xvii. pp. 370, 452; vol. xviii. pp. 50, 133, 328 ; vol. xix. p. 25 ; vol. xx. p. 5 ; vol. xxii. p. 1. See also papers on the same subject by ELECTRICITY OF EFFLUENT STEAM. 89 hand a light iron rod immediately above the safety-valve of a locomotive engine, while the steam was freely escaping, and then advancing the other hand towards any conducting body, he obtained sparks of an inch in length ; when the rod was held five or six feet above the valve, the length of the sparks was two inches ; ' and when a bunch of pointed wires, attached to the rod, was held points downwards in the issuing steam, sparks four inches long were drawn from a round knob, on the opposite extremity of the iron rod. On insulating the boiler, large and brilliant negative sparks an inch long were drawn from it the Elec- tricity of the steam being positive. (114) A small boiler was constructed by Mr. Armstrong it was arranged on a stove which was insulated ; when the rate of evaporation was about a gallon in an hour, and the pressure in the boiler 100 Ibs. on the square inch, by connecting the knob of a Leyden phial with the boiler or stove, he was able to give it a charge, and he found that Elec- tricity could be collected in much greater abundance from the evapo- rating vessel than from the issuing steam. The Electricity of the steam was generally positive, that of the insulated boiler being negative ; occa- sionally, however, these conditions were reversed, and after the boiler had been in use for some time, positive Electricity rarely appeared in the jet, even when circumstances were most favourable to its development. No alteration was effected by washing out the boiler with water, but when it was washed with solution of potash or soda, the positive condition of the steam jet was restored, and by dissolving a little potash in the water from which the steam was generated, the quantity of Electricity was amazingly increased ; on the other hand, when a small quantity of nitric acid, or nitrate of copper, was added to the water, the Electricity of the steam became negative. (115) Subsequent experiments led Mr. Armstrong to the conclusion that the excitation of Electricity takes place at the point where the steam is subjected to friction ; and, in a paper subsequently read before the Royal Society by Professor Faraday, it was shown that the steam itself has nothing to do with the phenomenon. By means of a suitable apparatus, Faraday found that Electricity is never excited by the passage of pure steam, and is manifested only when water is at the same time present ; and hence he concludes that it is altogether the effect of the friction of globules of water against the sides of the opening, or against the substances opposed to its passage, as the water is rapidly moved onwards by the current of steam. Accordingly, it was found to "be increased in quantity by increasing the pressure and impelling force of Mr. Pattinson, vol. xvii. pp. 375, 457; and by Dr. Schafhaeutl, vol. xvii. p. 449; vol. xviii. pp. 14, 95, 265. 90 STATICAL OB, FBICTIONAL ELECTRICITY the steam. The immediate effect of this friction was, in all cases, to render the steam or water positive, and the solids, of whatever nature they might be, negative. In certain circumstances, however, as when a wire is placed in the current of steam, at some distance from the orifice whence it has issued,' the solid exhibits the positive Electricity already acquired by the steam, and of which it is then merely the recipient and the conductor. In like manner the results may be greatly modified by the shape, the nature, and the temperature of the passage through which the steam is forced. Heat, by preventing the condensation of the steam into water, likewise prevents the evolution of Electricity, which again speedily appears by cooling the passages, so as to restore the water which is necessary for the production of that eifect. The phenomena of the evolution of Electricity, in these circumstances, are dependent also on the quality of the fluid in motion, more especially in relation, to its con- ducting power. Water will not excite Electricity unless it be pure : the addition of any soluble salt or acid, even in minute quantity, is sufficient to destroy this property. The addition of oil of turpentine, on the other hand, occasions the development of Electricity of an opposite kind to that which is excited by water ; and this Faraday explains, by the particles and minute globules of the water having each received a coating of oil, in the form of a thin film, so that the friction takes place only between that external film and the solids, along the surface of which the globules are carried. A similar but more permanent effect is produced by the presence of olive oil, which is not, like oil of turpentine, subject to rapid dissipation. Similar results were obtained when a stream of compressed air was substituted for steam in these ex- periments. When moisture was present, the solid exhibited negative, and the stream of air positive Electricity ; but when the air was perfectly dry, no Electricity of any kind was apparent. (116) Mr. Armstrong subsequently (Phil. Mag. vol. xxii. p. 1) confirmed the conclusion, that the excitation of Electricity takes place at the point where the steam is subjected to friction, and described several improvements in his apparatus by which the energy of the effects was amazingly increased. By means of a boiler furnished with a stop cock and discharging jet of peculiar construction, he produced effects upwards of seven times greater than those from n plate electrical machine of three feet in diameter, worked at the rate of seventy revolutions per minute. This boiler was a wrought iron cylinder, with rounded ends, and measured three feet six inches in length, and one foot six inches in diameter. It rested on an iron frame, containing the fire, and the whole apparatus was supported on glass legs to insulate it. It was found much more convenient and effectual to collect Electricity from the boiler than from the steam cloud, but, in order to obtain the highest effect from the THE HYDRO-ELECTRIC MACHINE. 91 boiler, the Electricity of the steam must be carried to the earth by means of proper conductors. (117) In Mr. Pattinson's experiments on one of the locomotive engines belonging to the Newcastle and Carlisle Eailway, sparks four inches long were given off from the person of an individual standing on an insulating stool, and holding a copper rod, terminated by sharp- pointed wires, in the current of steam, blowing forcibly out of the safety-valve at a pressure of 521bs. per inch. The Electricity was ascertained to be positive. It is certainly, as Mr. Pattinson observes, a novel and curious light in which to view the splendid locomotive engine in its rapid passage along the railway line, viz., that of an enormous electrical machine, the steam analogous to the glass plate of an ordi- nary machine, and the boiler to the rubber; while torrents of Electricity might continually be collected, by properly disposing conductors in the escaping steam. (118) Shortly after these experiments were made the directors of the Polytechnic Institution determined on constructing a machine on a large scale for the purpose of producing Electricity by the escape of steam, and under the superintendence of Mr. Armstrong, assisted by Captain Ibbetson, the "Hydro-Electric Machine" was finished and placed in the theatre of the institution, where by its extraordinary power it soon excited the astonishment of all who beheld it. The machine consists of a cylindrical-shaped boiler, similar in form to a steam-engine boiler, constructed of iron plate -f- inch thick ; its extreme length is 7 feet 6 inches, 1 foot of which being occupied by the smoke chamber, makes the actual length of the boiler only 6 feet 6 inches ; its diameter is 3 feet 6 inches. The furnace and ash-hole are both within the boiler ; when it is required entirely to exclude the light a metal screen is readily placed over these; by the side of the door is the water-gauge and feed-valve. On the top of the boiler, and running nearly its entire length, are forty-six bent iron tubes, terminating in jets having peculiar shaped apertures, and formed of partridge wood, which experience has shown Mr. Armstrong to be the best for the purpose ; from these the steam issues the tubes spring from one common pipe, which is divided in the middle and communi- cates with the boiler by two elbows: by this contrivance the steam is admitted either to the whole or part of the tubes, the steam being shut off or admitted by raising or lowering the two lever handles placed in the front of the boiler. Between the two elbows is placed the safety- valve for regulating the pressure, and outside them on one side is a cap covering a jet employed for illustrating a certain mechanical action of a jet of steam, and on the other a loaded valve for liberating the steam when approaching its maximum degree of pressure. At the further 92 STATICAL OB FBICTIONAL ELECTRICITY. extremity of the boiler is the funnel-pipe or chimney, so contrived that, by the aid of pulleys and a balance weight, the upper part can be raised and made to slide into itself (similar to a telescope), so as to leave the boiler entirely insulated. To prevent as much as possible the radiation of heat, the boiler is cased in wood, and the whole is supported on six stout glass legs 3| inches diameter, and 3 feet long. In front of the jets, and covering the flue for conveying away the steam, is placed a long zinc box, in which are fixed four rows of metallic points for the purpose of collecting the Electricity from the ejected vapour, and thus prevent its returning to restore the equilibrium of the boiler the box is so contrived that it can be drawn out or in, so as to bring the points nearer or further from the jets of steam ; the mouth or opening can also be rendered wider or narrower : by these contrivances the power and intensity of the spark is greatly modified. A ball and socket-joint, furnished with a long conducting rod, has been added to the machine, so that by its aid the Electricity can be readily conveyed to the different pieces of apparatus used to exhibit various phenomena. The pressure at which the machine is usually worked is GOlbs. on the square inch. As it is now fully established that the Electricity of the hydro-electric machine is occasioned by the friction of the particles of water (115), the latter may be regarded as the glass plate of the common electrical machine, the partridge wood as the rubber, and the steam as the rubbing power. The Electricity produced by this engine is not so remarkable for its high intensity as for its enormous quantity. The maximum spark obtained by Mr. Armstrong in the open air was 22 inches ; the extreme length under present circumstances has been 12 or 14 inches ; but the large battery belonging to the Polytechnic Institution, exposing nearly 80 feet of coated glass which, under favourable circumstances, was charged by the large plate machine 7 feet in diameter in about 50 seconds, is commonly charged by the hydro-electric engine in 6 or 8 seconds. The sparks which pass between the boiler and a conductor are exceedingly dense in appearance : and, especially when short, more resemble the discharge from a coated surface than from a prime con- ductor. They not only ignite gunpowder, but even inflame paper and wood shavings when placed in their course between two points. In the 151st number of the Philosophical Magazine, a series of electrolytic experiments made with this machine are described by Mr. Armstrong: true polar decomposition of water was effected in the clearest and most decisive manner, not only in one tube, but in ten different vessels arranged in series, and filled respectively with dis- tilled water, water acidified with sulphuric acid, solution of sulphate of soda, tinged blue and red, solution of sulphate of magnesia, &c.. EXPEKIMENTS WITH THE HYDBO-ELECTEIC MACHINE. 93 &c., and tlie gases were obtained in sufficient quantities for examina- tion. The following curious experiments are likewise described : two glass vessels containing pure water were connected together by means of wet cotton ; on causing the electric current to pass through the glasses, the water rose above its original level in the vessel containing the negative pole, and subsided below it in that which contained the positive pole, indicating the transmission of water in the direction of a current flowing from the positive to the negative wire. Two wine glasses were then filled nearly to the edge with distilled water, and placed about 4-10ths of an inch from each other, being connected together by a wet silk thread of sufficient length to allow a portion of it to be coiled up in each glass. The negative wire, or that which communicated with the boiler, was inserted in one glass, and the positive wire, or that which communicated with the ground, was placed in the other. The machine being then put in action, the following singular effects presented themselves : 1st,- A slender column of water, inclosing the silk thread in its centre, was instantly formed between the two glasses, and the silk thread began to move from the negative towards the positive pole, and was quickly all drawn over and deposited in the positive glass. 2nd, The column of water after this continued for a few seconds suspended between the glasses as before, but without the support of the thread ; and when it broke the Electricity passed in sparks. 3rd, When one end of the silk thread was made fast in the negative glass the water diminished in the positive glass and increased in the negative one, showing apparently that the motion of the thread, when free to move, was in the reverse direction of the current of water. 4th, By scattering some particles of dust upon the surface of the water, it was soon perceived by their motions that there were two opposite currents passing between the glasses, which, judging from the action upon the silk thread in the centre of the column, as well as from other less striking indications, were concluded to be concentric, the inner one flowing from negative to positive, and the outer one from positive to negative. Sometimes that which was assumed to be the outer current was not carried over into the negative glass, but trickled down outside of the positive one ; and then the water, instead of accumulating as before in the negative glass, diminished both in it, and in the positive glass. 5th, After many unsuccessful attempts Mr. Armstrong succeeded in causing the water to pass between the glasses, without the intervention of a thread for a period of several minutes, at the end of which time he could not perceive that any material variation had taken place in the 94 STATICAL OE FBICTIONAL ELECTRICITY. quantity of water contained in either glass. It appeared therefore, that the two currents were nearly, if not exactly equal, while the inner one was not retarded by the friction of the thread. Mr. Armstrong like- wise succeeded in coating a small silver coin with copper ; in deflecting the needle of a galvanometer, between 20 and 30 ; and in making an electro-magnet by means of the Electricity from this novel machine. (119) Extraordinary as is the power of the Polytechnic machine, it was afterwards entirely eclipsed by a similar apparatus constructed at Newcastle under the direction of Mr. Armstrong, and sent out to the United States of America. In the arrangement of this machine, the boiler of which is not larger than that at the Polytechnic Institution, Mr. Armstrong introduced certain improvements suggested by the working of the latter, and which had reference to those parts of the apparatus more immediately concerned in the production of the Elec- tricity, viz., " the escape apertures and the condensing pipes" It was found to be a matter of extreme nicety so to adjust the quantity of water deposited in the condensing pipes as to obtain the maximum excitation of Electricity. If on the one hand there be an excess of water, then two results will ensue, each tending to lessen the Elec- tricity produced. 1. The mean density of the issuing current of steam and water is increased, which causes the velocity of efflux and consequent energy of the friction to be diminished; and 2. The ejected steam cloud is rendered so good a conductor by the excess of moisture that a large proportion of the Electricity manifested in the cloud retrocedes to the boiler, and neutralizes a corresponding propor- tion of the opposite element. On the other hand, if the quantity of water be too small, then, although each particle of water may be excited to the fullest extent, the effect is rendered deficient in consequence of the insufficient number of aqueous particles which undergo excitation. In the Polytechnic arrangement the condensation of the steam in the tubes is effected by contact of the external air, and when the density of the steam, in the boiler is diminished rapidly they do not cool down with sufficient rapidity to condense the requisite quantity of water. To remedy this defect in the American machine, Mr. Armstrong adopted a method of condensing by the application of cold water : a number of cotton threads were suspended from each condensing pipe into a trough of water from which by capillary attraction just as much water was lifted as was required for the cooling of the pipe, since it was easy by increas- ing or diminishing the quantity of cotton to increase or diminish the supply of cold water ; and this method of keeping ' down the tempe- rature proved so effective that two or three times the number of jets that were before used could now be employed. The number in the American machine was 140, ranged in two horizontal rows, one above THE AMERICAN 'HTDKO-ELECTEIC MACHINE. 95 the other, on the same side of the machine. The sparks obtained, though not longer than those upon the London machine when it stood in the open air, succeeded each other with three or four times the rapidity, and even under unfavourable circumstances charged a Leyden battery consisting of thirty-six jars, containing thirty-three feet of coated surface, to the utmost degree that the battery would bear, upwards of sixty times in a minute, being equivalent to charging nearly 2000 feet of coated surface in one minute, which is at least twenty times greater than the utmost effect that could be obtained from the largest glass electrical machine ever constructed. (120) The action of the hydro-electric machine is greatly influenced by the nature of the water from which the steam is generated, which should be as pure as possible in order that no impurities should pass from the boiler to the steam passages. It is indeed perfectly surprising how extremely small an admixture of some substances has the effect of re- versing the electrical state of the boiler and steam cloud. When a piece of cotton was steeped in a solution of acetate of lead, and inserted in the con- densing pipe, Mr. Armstrong found that the Electricity of the steam, which in general was positive, was changed to negative. Again, when the conductingpipe is of brass instead of iron the steam cloud is positively elec- trified the same as in ordinary cases ; but if the pipe previously to being used has been immersed in very dilute nitric acid, then negative Electricity instead of positive will be evolved by the steam cloud, notwithstanding that the pipe may have been washed with clean water subsequently to its immersion in the acid, nor does the pipe re-gain the condition necessary for the production of a powerful development of positive Electricity in the steam, till it has been thoroughly washed out with an alkaline solution. Mr. Armstrong found also that the effects were singularly influenced by the material of which the condensing pipe is formed ; thus, glass, lead, tin, copper, and iron, are each effective in a different degree, the variation, as he believes, being in all these cases due to minute quantities of extraneous matter acquired by the condensed water acting chemically or mechanically upon the material of the pipes. (121) Messrs. Watson and Lambert of Newcastle, who built both the Polytechnic and the American machines, construct "hydro-electric machines " of all sizes ; they are mounted on carriages so as to be readily moved about, and they constitute very elegant pieces of electrical appa- ratus. One of these machines is shown in Pig. 61. The boiler is 2 feet 6 inches in length, and 1 foot 2 inches in diameter : A is the door of the fire-place; B C, the conductor for collecting Electricity from the steam ; B, a glass insulating stem ; C, the collecting points ; D, the escape tubes and jets ; E, the condensing vessel enclosing the iron pipes by which the steam is conveyed to the jets. The lower part 96 STATICAL OE FBICTIONAL ELECTEICITI, Fig. 61. of the condensing vessel contains water which nearly reaches the lower side of the steam pipes ; from the latter are suspended filaments of cotton, which dip into the water, and by capillary action raise just sufficient to cause, by its action on the pipes, a condensation of the passing steam into the requisite quantity of water for rubbing against the jet. E Gr is the cock for letting off the steam ; H, the chimney ; I I, the insulating glass pillars ; K K, the frame moving on castors ; a a, the water gauge ',fe, condensing pipes for showing the effect of impreg- nating the ejected water with extraneous substances, and for exhibiting two jets of steam simultaneously issuing from the boiler in opposite states of Electricity ; 5, the cock for introducing extraneous matter ; c d, cocks for admitting steam to the pipes ; g, the safety-valve ; h, the escape pipe for the vapour of the condensing tube. The fuel is charcoal. When in good working order a machine of the above size will produce, according to the makers, as much Electricity as three 30-inch plate glass machines. THE STEAM-ELECTRIC MACHINE. 97 Mr. "Walker (Elect. Mag. vol. i. p. 126) describes certain experi- ments which were made in order to contrast the effects of the great Polytechnic hydro-electric and glass electric machines, the plate of the latter being seven feet in diameter. On placing the large battery on an insulating stool between the prime conductor and the boiler, and connecting the inner coating with the former, and the outer with the latter, he several times failed in communicating a charge : on reversing connexions it was accomplished more readily, though in far longer time than would have been required by the boiler alone. Again, when the aurora obtained by passing the Electricity from the prime conductor through an exhausted tube 4 or 5 feet in length, was contrasted with that produced from the Electricity of the boiler passing through the same tube, the latter was, by many degrees, more brilliant ; but when the boiler was connected with one end of the tube, as it stood on an insulating stool, and the prime con- ductor with the other, the brilliancy greatly diminished. It was at first thought that if the earth in its normal condition could supply to the boiler Electricity equivalent to the production of a certain effect in a certain time, the prime conductor in its positively charged state would produce a greater effect. The actual diminution of effect was, however, on consideration connected with known laws, for, as the maximum supply of positive Electricity which the conductor could furnish was at most not a fourth of that required by the negative boiler, and as the supply from the earth was unlimited, the whole equilibrium was restored in the one case and only a portion of it in the other. (122) Peltier (Z' Institut, Aug. 7, 1844) does not adopt the theory that friction is the cause of -the wonderful development of Electricitj in the hydro-electric machine ; he refers it to chemical decomposition, Every chemical action produces an electrical phenomenon, and every solution however diluted it might be, being a chemical combination, it follows that in the act of evaporation above a solution, the combined element, by separating, produces the converse chemical action, that o'f decomposition, and hence an electrica^ phenomenon with signs con- trary to the act of combination. The reason why electrical phenomena are not manifested during slow evaporation, or even during the boiling of water under simple atmospheric pressure, is, according to -. Peltier, that the vapour is not separated with sufficient suddenness from the rest of the liquid, to carry away and retain the Electricity of the chemical action of its separation, the neutralization by return being made with too much facility in the moist atmosphere touching the surface of the liquid. A boiler is but another means of obtaining vapour at high tension, as it suddenly separates from the liquid ; but H 98 STATICAL OR FRICTIONAL ELECTRICITY. the form which we are obliged to give it is very much opposed to the free liberation of the Electricity, so that we obtain comparatively very small quantities of what is really produced* The quantities depend not only on the internal pressure, but also on the jets, which oppose or facilitate the neutralization by return. Hence it is, that powerful locomotives have been seen to present but feeble elec- trical results, while a small boiler may give them on a considerable scale ; when a saline solution is projected into a red-hot platina capsule, it becomes insulated from the vessel, and its evaporation goes on slowly, the temperature of the liquid never reaching the boiling point of water. As however, the concentration proceeds, particles of saline matter become deposited on the sides of the vessel, and establish partial contacts between the liquid and the metal, these particles of liquid are thus suddenly transformed into elastic vapour, the tension of which is proportionate to the tempe- rature at which it has been formed, and it is this vapour alone that preserves the Electricity due to its passage from the liquid to the gaseous state. The higher the temperature of the capsule, the greater the quantity of Electricity preserved : below 230 Fah. Peltier obtained no signs of Electricity. When in this experiment pure water is substituted for the saline solution, no Electricity is obtained, because no contact takes place between the liquid and the metal, until the temperature of the latter has descended to about 230, the evaporation then goes on too slowly to place an insulating space between the vapour, and the liquid, and the electric phenome- non is completed by returning to a state of neutralization, by means of the conductibility of the column of vapour. To obtain Electricity from high pressure boilers, the conditions are, 1st, an internal pres- sure of several atmospheres ; 2nd, that the vapour snail be accom- panied by a projection of water; and Peltier's view is; that the Electricity is not brought out from the boiler by the escaping vapour, but that it arises from the vapour of the drops of water that are projected at a high, temperature, a portion of which is imme- diately vaporized. r (123) Some interesting experiments are related by Peltier in illus- tration of his view. By elevating an Electrometer immediately underneath the column of vapour, given off by a locomotive engine in motion, he found that the electrical signs were more consider- able as the rapidity of the train increased, they diminished as the velocity diminished, and when the train was near stopping, all signs of Electricity disappeared. This he explains by referring the elec- trical phenomena to the quick separation of the liquid and vapour at the moment of its formation ; when the train was moving quickly DISRUPTIVE DISCHABGE. 09 the column of vapour was rapidly broken up into particles ; as the velocity diminished, the column became more united, and there was therefore less electrical development. The more rare the globular vapour, the greater the signs of positive Electricity ; the Electricity of an opaque column was on the contrary negative : it was noticed also, that the condensation of the vapour on the ball of the Electroscope suddenly changed the Electricity from positive to negative, and that while the head of the column of vapour was positive the tail was negative, the intermediate portions alternating from positive to negative according to the velocity of the train, the quantity of the prevailing vapours, the rapidity of the evaporation, and the state of the sky. (124) Disruptive discharge. "We will now inquire a little more minutely into the nature of electric discharge, which has been made byParadaythe subject of close investigation (Experimental Researches, 13th and 14th series). The discharge which takes place between two conducting surfaces is termed disruptive : it is the limit of the influence which the intervening air or dielectric exerts in resisting discharge : all the effects prior to it are inductive (82), and it consequently measures the conservative power of the dielectric. It occurs not when all the. particles have attained to a certain degree of tension; but when that particle which is most affected has been exalted to the subvert- ing or turning point, all must then give way, since they are linked together, as it were, by the influence of the constraining force, and the breaking down of one particle must, of necessitv, cause the whole barrier to be overturned. In every case, the particles, amongst and across which the discharge suddenly breaks, are displaced the path of the spark depending upon the degree of tension acquired by the particles in the line of discharge. (125) The spark may be considered then, as a discharge, or lower- ing of the polarized inductive state of many dielectric particles by a particular action of a few of the particles occupying a very small and limited space : all the previously polarized particles returning to their first or normal condition in the inverse order in which they left it, and uniting their powers meanwhile, to produce, or rather to continue, the discharge effect in the place where the subversion of force first occurred. We have given this explanation in the words employed by Faraday, that no misconception of his meaning may arise. He is of opinion that a peculiar temporary state is assumed by the particles situated where discharge occurs ; that they have all the surrounding forces thrown upon them in succession, and that they are not merely pushed apart ; that the whole terminates by a discharge of the powers H 2 100 STATICAL OK FBICTIONAL ELECTEICITT. by some, as yet, unknown operation, the ultimate effect being exactly as if a metallic wire had been put into the place of the discharging particles. (126) The electric spark presents different appearances when taken in different elastic media. In air, they have, when obtained with brass balls, a well-known intense light, and bluish colour, with frequently faint or dark parts in their course, when the quantity of Electricity passing is not great. In nitrogen they are very beautiful, having the same general appearance as in air, but more colour, of a purple or bluish character ; and Faraday thought that they were remarkably sonorous. In oxygen they are whiter, but not so brilli- ant as in common air. In hydrogen they are of a fine crimson colour, and have very little sound in consequence of the physical condition of the gas. In carbonic acid gas they have the same general appear- ance as in air, but are remarkably irregular. Sparks can be obtained under similar circumstances, much longer than in air, the gas show- ing a singular readiness to pass the discharge. In muriatic acid gas, when dry, they are nearly white, and always bright throughout. In coal gas they are sometimes green and sometimes red, and occasion- ally one part is green and another red. Black parts also occur very suddenly in the line of the spark, i. e. they are not connected by any dull part with bright portions, but the two seem to join directly one with the other. It is the impression of Faraday that these varieties of character are due to a direct relation of the electric powers to the particles of the dielectric through which the discharge occurs, and are not the mere results of a casual ignition, or a secondary kind of action of the Electricity upon the particles which it finds in its course and thrusts aside in its passage. It was remarked by M. Eusinieri, that when a spark takes place between a surface of silver and another of copper, a portion of silver is carried to the copper, and of copper to the silver ; and Dr. Priestley observed, that if a metallic chain be laid upon a sheet of paper, or a plate of glass, and a strong discharge sent through it, spots will be produced upon it of the size and colour of each link, parts of which will be found to be fused into the substance of the glass. (127) The Electrical Brush. The phenomenon of the electrical brush has been shown by Professor "Wheatstone to consist of succes- sive intermitting discharges, although it appears continuous. If an insulated conductor, connected with the positive conductor of an electrical machine, have a metallic rod 0*3 of an inch in diameter, projecting from it outwards from the machine, and terminated by a rounded end or small ball, it will generally give good brushes ; or if DISKUPTIYE DISCHABGE. 101 the machine be not in good action, then many ways of assisting the formation of the brush may be resorted to ; thus, the hand, or any large conducting surface, may be approached towards the termination to increase the inductive force ; or the termination may be smaller, and of badly conducting matter, as wood : or sparks may be taken between the prime conductor and the secondary conductor, to which the termination giving brushes belongs ; or, (which gives to the brushes exceedingly fine characters and great magnitude,) the air around the termination may be rarefied, more or less, either by heat or the air-pump, the former favourable circumstances being also continued. When obtained by a powerful machine, or a ball about 0'7 of an inch in diameter at the end of a long brass rod, attached to the positive prime conductor, it has the general appearance, as to form, represented in Eig. 62. A short * conical yi gt 62. bright part or root appears at the middle part of the ball, projecting directly from it, which at a little distance from the ball breaks out suddenly into a wide brush of pale ramifications, having a quivering motion, and being accompanied at the same time with a low dull chattering sound. The general brush is resolvable into a number of indi- vidual brushes, each of which is the result of a single discharge each is instantaneous in its exist- ence, and each appeared to Faraday to have the conical root complete. The sound is due to the recurrence of the noise of each separate discharge, which, happening at intervals nearly equal, under ordinary circumstances causes a definite note to be heard, which, rising in pitch with the increased rapidity and regularity of the intermitting discharges, gives a ready and accurate measure of the intervals, and so may be used in any case when the discharge is heard, even though the appearances may not be seen, to determine the element of time. (128) The brush is, in reality, a discharge between a bad, or a non-conductor, and either a conductor or another non-conductor. It is explained by Earaday on the principles of induction, which, taking place between the end of an electrified rod and the walls of a room, across the dielectric air, polarizes the particles of air ; those which are nearest to the end of the wire being most polarized, and those situated in sections across the lines of inductive force towards the walls being least polarized. In consequence of this state, the par- ticle of air at the end of the wire is at a tension that will immediately terminate in discharge, while in those even only a few inches off the tension is still beneath that point. "When the discharge takes place, 102 STATICAL OB, FEICTIONAL ELECTRICITY. the particle of air in the immediate vicinity of the rod .instantane- ously resumes its polarized state, the wire itself regaining its electri- cal state by induction ; the polarized particle of air exerts a distinct inductive act towards the further particles, and thus a progressive discharge from particle to particle takes place. The difference between the brush discharge and the spark is, that in the former discharge begins at the root (127), and extending itself in succession to all parts of the single brush, continues to go on at the root and the previously-formed parts, until the whole brush is complete ; then, by the fall in intensity and power at the conductor, it ceases at once in all parts, to be renewed when that power has risen again to a sufficient degree ; but in the latter, the particles in the line of discharge being, from the circumstances, nearly alike in their inten- sity of polarization, suffer discharge so nearly at the same moment as to make the time quite insensible to us. Mr. "Wheatstone found that the Irush generally had a sensible duration, but he could detect no such effect in the spark. (129) According to Faraday, the brush may be considered as a spark to air ; a diffusion of electric force to matter, not by conduction, but by disruptive discharge ; a dilute spark, which, passing to very badly conducting matter, frequently discharges but a small portion of the power stored up in the conductor : for as the air charged re- acts on the conductor, whilst the conductor, by loss of Electricity, sinks in its force, the discharge quickly ceases, until, by the dispersion of the charged air, and the renewal of the excited con- ditions of the conductor, circumstances have risen up to their first effective condition, again to cause discharge, and again to fall and rise. (130) By making a small ball positive by a good electrical machine with a large prime conductor, and approaching a large uninsulated discharging ball towards it, very beautiful variations from the spark to the brush may be obtained. In Fig. 62 the general appearance of a good brush is exhibited ; but if the hand, a ball, or any knobbed conductor be brought near, the extremities of the coruscations turn towards it and each other, and the whole assumes various forms, ac- cording to circumstances, as shown in Pigs. 63, 64, 65. The curvature of these ramifications illustrates, in a beautiful manner, the curved form of the lines of inductive force existing previous to discharge, in the same manner as iron filings strewed on a sheet of paper placed over a magnet represent magnetic curves ; and the phenomena are con- sidered by Faraday as constituting additional and powerful testimony in favour of induction through dielectrics in curved lines (78), and of the lateral relation of these lines by an effect equivalent to a repulsion producing divergence, or, as in the cases figured, the bulging form. DISRUPTIVE DISCHAEGE: THE BfiUSH. 103 Fig. 63. Fig. 64, Fig. 65, (131) Discharge in the form of a brush is favoured by rarefaction of the .air, in the same manner and for the same reason as discharge in the form of a spark. It may be obtained not only in air and gases, but also in much denser media. Faraday procured it in oil of turpen- tine, but it was small, and produced with difficulty. He also found that, like the spark, the brush has specific characters in different gases, indicating a relation to the particles of these bodies, even in a stronger degree than the spark. In nitrogen, brushes were obtained with far greater facility than in any other gas ; and when the gas was rarefied, they were exceedingly fine in form, light, and colour; in oxygen, on the other hand, they were very poor. (132) The peculiar characters of nitrogen in relation to the electric discharge must, Earaday observes, have an important influence over the form and even the occurrence of lightning, being that gas which most readily produces coruscations, and by them extends discharge to a greater distance than any other gas tried, it is also that which con- stitutes four-fifths of our atmosphere ; and as in atmospheric electrical phenomena, one, and sometimes both the inductive forces are resident on the particles of the air, which, though probably affected as to con- ducting power by the aqueous particles in it, cannot be considered as a good conductor ; so the peculiar power possessed by*nitrogen to originate and effect discharge in the form of a brush or of ramifications, has probably an important relation to its electrical service in nature, 104 STATICAL OR ERICTIONAL ELECTRICITY. as it most seriously affects the character arid condition of the discharge when made. (133) The characters of the luminous appearances at the ends of wires charged positively and negatively are represented in Pig. 44. Faraday has paid considerable attention to the difference of discharge at the positive and negative conducting surfaces. According to his observations, the effect varies exceedingly under different circum- stances. It is only with bad conductors, or metallic conductors charged intermittingly, or otherwise controlled by collateral induction, that the brush and star are to be distinctly distinguished : for if metallic points project freely into the air, the positive and negative lights differ very little in appearance, and the difference can be observed only upon close examination. If a metallic wire with a rounded termination in free air, be used to produce the brushy dis- charge, then the brushes obtained when the wire is charged negatively are very poor and small by comparison with those pro- duced when the charge is positive : or, if a large metal ball connected with the electrical machine be charged positively, and a fine uninsu- lated point be gradually brought towards it, a star appears on the point when at a considerable distance, which, though it becomes brighter, does not change its form of a star until it is close up to the ball ; whereas, if the ball be charged negatively, the point at a con- siderable distance has a star on it as before ; but when brought nearer, (within about 1 \ inch,) a brush forms on it, extending to the negative ball ; and when still nearer, (at i of an inch distance,) the brush ceases, and bright sparks pass. (134) The successive discharges from a rounded metallic rod O3 of an inch in diameter, projecting into air when charged negatively, are very rapid in their recurrence, being seven or eight times more numerous in the same period than those produced when the rod is charged positively to an equal degree ; but each brush carries off far less electric force in the former case than in the latter. Faraday also perceived a very important variation of the relative forms and conditions of the positive and negative brush, by varying the dielec- tric in which they were produced. The difference, indeed, was so great, as to point out a specific relation of this form of discharge to the particular gas in which it takes place, and opposing the idea that gases are but obstructions to the discharge, acting one like another, and merely in proportion to their pressure. Generally speaking, when two similar small conducting surfaces equally placed in air, are electrified, one positively and the other negatively, that which is negative can discharge to the air at a tension a little lower than that required for the positive ball, and when discharge does take place, DISRUPTIVE DISCHARGE : GLOW. 105 much more passes at each time from the positive than from the negative surface. (135) Glow discharge. When a fine point is used to produce disruptive discharge from a positively charged conductor, the brush gives place to a quiet phosphorescent continuous glow, covering the whole of the end of the wire, and extending a small distance into the air. Occasionally this glow takes the place of the brush, when a rounded wire 0'3 of an inch in diameter is used, and the finer the point the more readily is it produced: thus, diminution of the charging surface produces it : increase of power in the machine tends to it, and it is surprisingly favoured by rarefaction of the air. A brass ball 2^ inches in diameter, when made positively inductric (82) in an air-pump receiver, becomes covered with a glow over an area of two inches in diameter, when the pressure is reduced to 4'4 inches of mercury. By a little adjustment, Faraday succeeded in covering the ball all over with this light ; using a brass ball 1*25 inches in diameter, and making it inducteously positive by an inductric negative point, the phenomena at high degrees of rarefaction were exceedingly beautiful. The glow came over the positive ball, and gradually increased in brightness, until it was at last very luminous, and it stood up like a low flame, half an inch or more in height. On touching the sides of the glass jar, this lambent flame was affected, assumed a ring form, like a crown on the top of the ball, appeared flexible, and revolved with a comparatively slow motion, i. e., about four or five times in a second. (136) The glow is always accompanied by a wind proceeding either directly out from the glowing part, or directly towards it. Faraday was unable to analyse it into visible elementary intermitting dis- charges, nor could he obtain the other evidence of intermitting action namely, an audible sound (127). It is difficult to produce it at common pressures with negative wires, even on fine points, though in rarefied air the negative glow can easily be obtained. (137) All the effects tend to show that glow is due to a continuous charge or discharge of air ; in the former case being accompanied by a current from, and in the latter case by one to, the place of the glow. As the surrounding air comes up to the charged conductor, on attaining that spot at which the tension of the particles is raised to the sufficient degree, it becomes charged, and then moves off by the joint action of the forces to which it is subject, and at the same time that it makes way for other particles to come and be charged in turn, actually helps to form that current by which they are brought into the necessary position. Thus, through the regularity of the forces, a constant and quiet result is produced, and that result is, the 106 STATICAL OR FEICTIOtfAL ELECTEICITY. charging of successive portions of air, the production of a current and of a continuous glow. (138) By aiding the formation of a current at its extremity, the brush at the termination of a rod may be made to produce a glow, and on the other hand by affecting the current of air, by sheltering the point from the approach of air, it is not difficult to convert the glow into brushes. The glow is assisted by those circumstances which tend to facilitate the charge of the air by the excited con- ductor, the brush by those which tend to resist the charge of the same ; and those which favour intermitting discharge in a more exalted degree favour the production of the spark. Thus the transi- tion from the one to the other may be established in various ways : by rarefying the air, by removing large conducting surfaces from the neighbourhood of a glowing termination, or by presenting a sharp point towards it, we help to sustain the glow ; and by condensing the^ neighbourhood of a discharging ball, or by presenting the hand gradually towards it, we convert the glow into the brush or (139) Before proceeding further, it may be useful to give a general summary of the views of Faraday relating to induction. His theory is not intended to offer anything new as to the nature of the electric force or forces, but only as to their distribution. It undertakes to state how the powers are arranged, to trace them in their general relations to the particles of matter, to determine their general laws, and the specific differences which occur under these laws. (140) The theory assumes : 1. That all the particles, whether of insulating or conducting matter, are, as wholes, conductors. 2. That not being in their normal state polar, they can become so by the influence of neighbouring charged particles, the polar state being developed at the instant, exactly as in an insulating conducting mass consisting of many particles. 3. That the particles when polarized are in a forced state, and tend to return to their normal or natural condition. 4. That being, as wholes, conductors, they can readily be charged either bodily or polarly. 5. That particles whixjh, being contiguous, are also in the line of inductive action, can communicate or transfer their polar forces to one another more or less readily. 6. That those doing so less readily require the polar forces to be raised to a higher degree before this transference or communication takes place. 7. That the ready communication of forces between contiguous INDUCTION. 107 particles constitutes conduction, and the difficult communication insulation; conductors and insulators being bodies whose particles naturally possess the property of communicating their respective forces, easily or with difficulty ; having these differences just as they have differences of any other natural property. 8. That ordinary induction is the effect resulting from the action of matter charged with excited or free Electricity, upon insulating matter, tending to produce in it an equal amount of the contrary state. 9. That it can do this only by polarizing .the particles contiguous to it, which perform this office to the next, and these again to those beyond ; and that thus the action is propagated from the excited body to the next conducting mass, and these render the contrary force evident, in consequence of the effect of communication which supervenes in the conducting mass, upon the polarization of the particles of that body. 10. That therefore induction can only take place through or across insulators : that induction is insulation, it being the necessary con- sequence of the" state of the particles, and the mode in which the influence of electrical forces is transferred or transmitted through or across each insulating medium. 108 STATICAL OK FRICTIONAL ELECTRICITY. CHAPTER V. . / The Leyden phial arid battery Laws of accumulated Electricity Specific inductive capacity Lateral discharge Physiological and chemical effects of frictional Electricity. (141) Accumulation, of Electricity. The Leyden Phial. In a previous chapter (89) it has been shown that a higher charge may be communicated to the gold leaf Electroscope while under the influence of a second plate not insulated. To illustrate this property of the second plate we have only to bring it as close as possible, without touching, to the inductric plate, and communicate a charge to the latter ; then, on removing the second plate, the accumulation which has been effected will be indicated by an expansion of the gold leaves considerably beyond the original amount. This divergence of the gold leaves is to be considered as occasioned by the attraction in opposite directions of the oppositely electrified inducteous bodies. (142) When an excited glass tube is brought near to the cap of the Electroscope, the second plate (connected with the earth) being close to it, the gold leaves do not open nearly so much as if the second plate were not there, because induction taking place through the intervening plate of air to the nearest body, viz. the inducteous or second plate, the Electricity of the same kind as that of the cap of the instrument, becomes diffused over the earth (89) ; but when the second plate is removed, the leaves diverge much more than if it had not been there, because they have received a higher charge. Now, in this case, the intervening air has received a higher polar tension, which it will be understood, arises entirely from the close proximity of the charged body to a conductor to the earth : the thinner the intervening stratum of air, the higher the degree of polar tension that can be attained, and the rise of force is limited by the mobility of the particles of the air, in consequence of which the equilibrium is restored. either silently or by a spark. (143) If, instead of a plate or stratum of air, we employ a solid dielectric, such as glass, the tension which may be assumed is limited only by its cohesive force. Thus, if we place a plate of glass between two circular pieces of tin, insulated, and connect one plate with the prime conductor of an electrical machine, we shall have an * TENSION" AND INTENSITY. 109 arrangement precisely similar to the condenser (Fig. 33), except that the intervening dielectric will be glass instead of air: on connecting the other plate with the earth to destroy its polar state, and working the machine, the particles of the glass will become powerfully polarized ; and if, instead of connecting one of the plates with the earth, we touch it from time to time with the knuckle, a series of sparks will be obtained, occasioned by the repulsion of the positive Electricity naturally present in the tin plate, by induction through the glass from the opposite plate electrified by the machine. After a time these will cease, and on removing the wire connecting the plate with the prime conductor, it will be charged with positive, while the other plate will be charged with negative Electricity, both in a high state of tension. If now both plates are connected by means of a curved wire, discharge results, attended with a vivid flash and a loud snap. (144) The same effects will be produced by coating either side of a pane of glass with tin-foil, leaving about \\ inch all round uncovered, and it is quite clear that the surfaces of dielectrics and conductors may be arranged in different forms without impairing the effects. Glass jars or bottles are found much more convenient in practice than squares of coated glass ; and the quantity of Electricity which may be accumulated depends upon the extent of the coated surface ; its intensity on the thinness of the glass. (145) It may be as well here to state the meaning we attach to the words tension and intensity; terms in constant use, but respecting which some confusion appears to exist in the writings of many electricians. We are disposed to adopt the views of Harris (PHI. Trans., 1834), according to which, intensity in common Electricity should be limited to the indications of an Electrometer employed to determine by certain known laws of its relationsto an accumulated charge, the quantity accumulated, or any other elec- trical element required to be known. Thus, by the use of certain instruments, it is found that with a quadruple attractive force there is twice the quantity of Electricity accumulated (60), and so on, the surface remaining the same ; again, with a double extent qf surface, the same quantity is accumulated as before, when only, one-fourth the force is indicated by the Electrometer.* The relations of the indications of the quadrant Electrometer, or of any other Electro- meter, to the quantity accumulated, &c. &c., Harris considers as coming under the term intensity ; for they show, at the same time, * See Harris's papers in the Transactions of the Royal Society for 1836, Part 2; and for 1809, Part 2. 110 STATICAL OR FRICTIONAL ELECTEICITT. the force of the charge upon surrounding bodies. Tension, Harris applies to the actual force of a charge to break down any non- conducting or dielectric medium between two terminating electrified planes. For example, take a coated pane of glass, and charge it in the usual way ; then the absolute force exerted by the charge in the intervening glass the force exerted by the polarized particles of the glass to get out of their constrained state, may be expressed by the term tension ; and there would be no contradiction or superfluity of terms to talk of the intensity of the tension in this sense. (146) The sum of the matter appears to' be this : tension applies to the particles of the electric agency itself, to a force, in short, such as Faraday has shown to exist in the polarized state of particles of matter, to unfetter themselves, as it were ; whereas intensity applies "to the attractive forces between the terminating plates which are the boundaries of the system, as when a plane, counterpoised at the end of a beam, is caused to descend upon another plane beneath it, by electrical attraction, the weight in the scale pan requisite to balance this force is the intensity between the planes ; whereas the tension of the charge between them refers to the polarized particles of the dielectric medium, that is, to the force, whatever it be, by which they endeavour to return to their primitive state. Now, the attraction between the planes may be conceived to be the result of the induction sustained by the particles of the dielectric between them, the force of which may be called intensity ; and this may differ from the re-active force in the polarized particles themselves, that is, the force they exert to return to their primitive state. It may be also that this last force is in proportion to the quantity of disturbance in the particles, or in proportion to the quantity of Electricity deve- loped in the terminating planes or .coatings; whilst the intensity, or fores of attraction between the coatings, supposing them free to move, might be as the square of the quantity of Electricity. (147) It is very justly observed by Harris, that it would be almost as well perhaps if the term tension were banished from common Electricity altogether, as being too hypothetical a word for our present knowledge of Electricity, inasmuch as it is essentially applicable to some species of elastic force. Now, we do not know whether Electricity be a force of this kind or not. The term intensity is not open to this objection, because it simply expresses the energy or degree of power with which a particular force operates, be that force what it may. (148) Glass jars, coated on each side with tin-foil, are well known by the name of Ley den phials, from their having been ilrst con- THE LEYDEK PHIAL. Ill structed by Musclienbroek and his friends at Ley den (8). In practice it is found impossible to diminish the thickness of the glass beyond a certain extent, as the constrained position of its polarized particles is apt to rise so high as to destroy its cohesive force, and the charge breaks its way through the glass. Fig. 66 represents a Leyden phial of the usual construction, with the discharging rod furnished with a glass handle in the position in' Fig. 66. which it is placed, in the a^ct of dis- charging the jar by establishing a metallic communication between the outer and inner metallic coatings. The wire which passes through the varnished mahogany cover of the jar, is terminated at one end* by a brass ball, and at the other by a chain reaching to the bottom of the jar. (149) To charge the Leyden phial, its knob should be held about half an inch from the prime conductor, the hand grasping the outer coating. A series of sparks take place between the knob and the conductor, which continue for some time and then cease. The jar is now charged, its inside containing positive, and its outside negative Electricity, their union being prevented by the interposed glass. If the jar be very thin, and the tension of the Electricity considerable, discharge frequently takes place through the glass, which thus becomes perforated and useless ; or, if the metallic coatings extend too near the mouth of the jar, the discharge is very apt to pass over the uncoated surface in the form of a bluish lambent brush of flame, constituting a spontaneous discharge. But if neither of these acci- dents occur, still the jar as thus constructed cannot be kept charged long, neutralization taking place more or less rapidly by the con- ducting substances present in the surrounding atmosphere. It is advisable to varnish the glass above the coating with a solution of gum lac in alcohol, or with the common spirit varnish of the shops, taking care to warm the jars before and after its application. (150.) In Eig. 66 the Leyden phial is represented as undergoing discharge by an instrument for the purpose ; it is not, however, advisable to discharge large phials by placing one of the balls of the discharging rod against its side in this manner, there being some risk of breaking them by the explosion, especially if the glass be thin. The best plan is to place the phial upon a sheet of tin-foil considerably larger than the bottom of the jar, to place the lower 112 STATICAL OB FRICTIONAL ELECTKICITT. ball of the discharging rod upon the metal, and then to bring the other ball quickly within the striking distance of the knob of the jar ; by this method the Electricity becomes diffused over a larger surface, and is not concentrated to a single point of the glass, the risk of fracture of which is necessarily diminished in consequence. (151) When narrow-mouthed jars or bottles, as the common sixteen ounce phials of white glass (which from their thinness form excellent electric jars), are used, some persons coat them internally with brass filings instead of tin-foil, on account of the difficulty o'f applying the latter to their interior ; for this purpose some thin glue should be poured into them, and the bottle turned slowly round until its inner surface is covered to about three inches from the mouth. Brass filings are then put in, and the bottle well shaken, so that they may be diffused equally ov^r its surface ; on inverting it, those which are in excess will fall out, and the bottle will be left tolerably well coated internally. This method, however, rarely answers well ; a better one is, to melt equal parts of lead and tin, and whilst fused, to add quicksilver enough to keep the whole fluid whilst warm, and in this condition to pour it into the bottle, turning the latter round and round in various ways till the whole of the inside is covered with amalgam. A little bismuth keeps the whole fluid at a lower temperature. This plan answers very well for coating Fig. 67. internally large green glass carboys, though no experimentalist is advised to go to the trouble of fitting up these vessels, as they generally prove useless, probably on account of the im- perfection of the dielectric. (152) By the construction shown in Pig. 67 the influence of external causes in. dissipating the charge of a Leyderi jar may to a consider- able extent be prevented. The jar is coated with tin-foil as usual, but a glass tube lined internally to rather more than half its length from the bottom, and surmounted with a brass cap, is cemented firmly into the wooden cover. A communication is established between the brass cap and the internal coating by a small brass wire passing loosely through it, and ter- minating in a small knob. This wire touches the inside of the glass tube. The jar is charged in the usual manner : the wire may then be removed by inverting the jar ; the internal coat- THE LEYDEN PHIAL. 113 ing is thus cut off from contact with the external air, and the dissipation of the charge prevented. Jars thus arranged have been known to retain their charge for days, and even for weeks. In Fig. 68 a good method of fitting up the Leyden Fig. 68. phial is shown : the wire communicating with the interior coating passes through a glass tube extend- ing above and below the cover about six inches. The cover is thus insulated from the inside coating, dust is excluded, and a greater stability is given to the wire. Thus arranged, the jar will retain its charge much longer than on the usual plan. It was contrived by Mr. Barker. (153) The arrangement of the Eev. F. Lockey, by which the fracture of large jars is almost with certainty prevented, is shown in Fig. 69. The wire, instead of communicating with the interior coating by means of a metallic chain, screws into the bar of wood a, which is covered with tin-foil, the sides of which press lightly against the inner coating of the jar ; two slender pieces of wood, b, c, also covered with tin-foil, are mor- ticed into the bar a, and kept in place by a brass pin at d ; the other extremities press against the sides of the jar close to the bottom : wide-mouthed jars should be employed, and if they slope towards the bottom, the firmer can the bar a be fixed : no covers are required. The advantage of this arrangement will be imme- diately perceived ; there being a metallic communication between the knob and four different points of the inner coating, the force of the discharge is divided into four parts, and not only is the risk of fracture decreased thereby, but a complete discharge of the jar is ensured. A curious fact connected with the fracture of jars, first noticed by Priestley (History, p. 611), and afterwards confirmed by Bachhoffner (Elect. Mag., vol. i. p. 282), is, that though a ready passage for restoring the electrical equilibrium is opened by the bursting of the jar, the transmission of the charge takes place through the appro- priated circuit without any apparent loss of power. Bachhoffner refers the occasional bursting of jars to an unequal arrangement of particles in certain parts of the glass, whereby the assumption of the polarized state is impeded, so that at these parts more or less time may be requisite to effect an equal degree of polarized intensity STATICAL OB ERICTIONAL ELECTRICITY. Fig. 70. corresponding to the other portions of the jar, and in like manner during discharge more or less time would be necessary to effect their restoration to the natural state. (154) Sir "William Harris fits up his jars as seen in Eig. 70. The mouths are open, and the charge is conveyed to the bottom of the jar by a copper tube, G H, three-eighths of an inch in diameter. This tube terminates in a ball, E, of baked wood, and is kept in its place by a convenient foot firmly cemented to the bottom of the jar, which is previously covered with a circle of pasted paper leaving a central portion of the coating free, for the perfect contact of the charging rod, Gr H, which passes through the centre of the foot as shown by the dotted lines in the figure. "When the jars are either employed singly, or are united so as to form a battery (77), they should be placed on a con- ducting base supported by short columns of glass, or some other insulating substance, so that the whole can be insulated if necessary. In order to allow the jars to be charged and discharged with precision, Harris connects them with what he calls two centres of action, A and B, Eig. 71. The first of these, A, consists of a brass ball which slides with friction on a metallic rod, A D, so as to admit of its being placed at any required height. This ball has a number of holes perforated in its circumference to receive the point of the rod or rods which connect it with the jar or jars. The rod, A B, which supports this ball, may be either insulated on a separate foot, and connected with the prime conductor, or it may be inserted directly into it. The second centre of action consists of a larger ball of metal, B, attached to a firm foot, and placed on the same conducting base with the jar so as to be perfectly connected with it. When the first centre of action, A, requires to have a separate insulation, the insu- lating glass rod is screwed immediately into the lower ball, B, and sustains the metallic rod above described by the intervention of a ball of baked wood, D, the opposite end of the rod terminating in a similar ball, C, through the 71. TELOCITY OF ELECTRICITY. 115 substance of which the conducting communication with the machine passes when it is placed on a separate foot. All the metallic con- nections should be covered with sealing-wax except at the points of junction, and the wooden balls and different insulations should be carefully varnished. (Encycl. Brit., art. Electricity.) (155) The discharge of the jar is the passage of the electrical forces in their primary state of activity, from a state of tension, into their secondary condition, known as the electrical current. The velocity with which this is effected is so enormous, that it may be regarded as momentary. Nevertheless, the rate at which the forces travel has been measured by Professor Wheatstone, and shown to exceed that of light itself. (Phil. Trans. 1834.) Light is about eight minutes thirteen seconds in passing from the sun to the earth, so that it may be considered as moving at the rate of one hundred and ninety-two thousand miles in a second, per- forming the tour of the world in about the same time that it requires to wink with our eye-lids, and in much less than a swift runner occupies in taking a single stride. The sun is ninety-five millions of miles from the earth, and almost a million times larger : the sun being 882,000 miles in diameter, and the earth 8,400 miles. Yet its magnitude, as viewed from the earth, scarcely exceeds that of the moon, which is not more than one-fourth the diameter of our globe, being 2,160 miles in diameter. Such, however, is the velocity of light, that a flash of it from the sun would be seen in little more than eight minutes after its emission ; whereas the sound evolved at the same time (supposing a medium like air capable of conveying sound between the sun and the earth), would not reach us in less than fourteen years and thirty-seven days, and a cannon ball, proceeding with its greatest speed, in not less than twenty years. (156) The velocity of Electricity is so great, that the most rapid motion that can be produced by art appears to be actual rest when compared with it. A wheel, revolving with a rapidity sufficient to render its spokes invisible, when illuminated by a flash of Electricity, is seen for an instant with all its spokes distinct, as if it were in a state of absolute repose ; because, however rapid the rotation may be, the light has come and already ceased before the wheel has had time to turn through a sensible space ; insects on the wing appear fixed in the air ; vibrating strings are seen at rest in their deflected positions ; and a rapid succession of drops of water, appearing to the eye a continuous stream, is seen to be what it really is. The following experiment was made by Wheatstone : A circular piece of pasteboard was divided into three sections, one of which was painted T 9, 116 STATICAL OB FRICTIONAL ELECTRICITY. blue, another yellow, and a third red ; on causing the disc to revolve rapidly it appeared white, because a sun-beam consists of a mixture of these colours, and the rapidity of the motion caused the distinction of colours to be lost to the eye : but the instant the pasteboard was illuminated by the electric spark, it seemed to stand still, and each colour was as distinct as if the disc were at rest. By a beautiful application of this principle, Wheatstone contrived an apparatus by which he has demonstrated that the light of the electric discharge does not last the millionth part of a second of time. His plan was to view the image of a spark reflected from a plane mirror, which, by means of a train of wheels, was kept in rapid rotation on a horizontal axis. The number of revolutions performed by the mirror was ascertained by means of the sound of a siren connected with it, and still more successfully by that of an arm striking against a card, to be 800 in a second, during which time the image of a stationary point would describe 1,600 circles ; and the elongation of the spark through half a degree, a quantity obviously visible, and equal to one inch, seen at the distance of ten feet, would indicate that it exists 1,152,000th part of a second. A jar was dis- charged through a copper wire half a mile in length, interrupted both in the middle and also at its two extremities, so as to give three distinct sparks. The deviation of half a degree between the two extreme sparks would indicate a velocity of 576,000 miles in a second. This estimated velocity is on the supposition that the Electricity passes from one end of the wire to the other ; if however the two fluids in one theory, or the disturbance of equilibrium in the other, travel simultaneously from the two ends of the wire, the two external sparks will keep their relative positions, the middle one alone being deflected ; and the velocity measured will be only one- half that in the former case, viz. 288,000 miles in a second. (157) The following were the results actually obtained. In all cases, when the velocity of the mirror exceeded a certain limit, the three sparks were elongated into three parallel lines, and the lengths became greater as the velocity of the mirror was increased. The greatest elongation observed was about 24, indicating a duration of about the 24,000th part of a second. The lines did not always commence at the same places : sometimes they appeared immediately below the eye, sometimes to the right, at other times to the left, and occasionally they were out of view altogether. This indetermination was owing to the arm not always taking the spark at the same distance from the discharger, several discharges were therefore re- quired to be made before the eye could distinctly observe the appearances. When the velocity was low, the terminating points VELOCITY OF ELECTRICITY. 117 appeared to be exactly in the same vertical line, but when the velocity was considerable and the mirror revolved towards the right, the lines assumed this appearance : EEEEEEE I when it revolved towards the left, they appeared thus : = in no case were they seen thus : ~ :==== ~ ~ or thus : : ~ a's re- quired by the hypothesis of a single fluid. The spark board was 10 feet from the mirror, and the duration between the extreme sparks and the middle one could not have exceeded one-half of a degree. The general conclusions drawn from the experiments were : 1st. That the velocity of Electricity through a copper wire exceeds that of light through the planetary space. 2nd. That the disturbance of the electric equilibrium in a wire communicating at its extremities with the two coatings of a charged jar, travels with equal velocity from the two ends of the wire, and occurs latest in the middle of the circuit. 3rd. That the light of Electricity in a state of high tension has less duration than the millionth part of a second; and 4th. That the eye is capable of perceiving objects distinctly, which are presented to it during the same interval of time. (158) The quantity of Electricity accumulated in a jar or battery may be roughly estimated by the number of turns of the machine, or more correctly by the unit jar (Fig. 96) ; its intensity may be approx- imately determined by the amount of repulsion between any two moveable bodies under its influence, or rather by the amount of their opposite attractions by surrounding bodies under their inductive influence. In Fig. 72 is shown the quadrant electrometer, invented -pig. 72. by Henley for this purpose. It consists of a graduated semicircle of ivory fixed to a rod of wood d. From the centre of a descends a light index, terminating in a pith- ball, and readily moveable on a pin. To use it, it is removed from its stand and screwed upon the jar or battery, the charge of which it is intended to indicate : as it increases, the pith-ball moves from its centre of suspension, and measures the intensity upon the graduated semicircle. (159) When a series of explosions from a Leyden phial is required for any particular purpose, it is useful to have a contrivance by which the discharges can be effected without the interference of the operator. Fig. 73 represents the apparatus of Mr. Lane for this purpose, a is the prime conductor of an electrical machine ; b the jar, on the wire communicating with the interior of which is fixed the arm of varnished glass c, on the end of this is cemented the brass knob D ; through this ball the wire f d slides, so that the ball 118 STATICAL OB FRICTIOISTAL ELECTEICITY. Fig. 73. d may be brought to any required distance from the knob of the jar e. A simple inspection of the figure will show how this discharging electrometer acts, and how, by increasing or lessening the dis- tance between d and e, the strength of the charge may be regulated. (160) Another useful instrument is the balance electrometer of Cuthbertson, shown in Fig. 74. A B is a wooden stand, about eighteen inches long and six broad, in which are fixed two glass supports d e, mounted with brass balls ; under the ball d is a brass hook : the ball b is made of two hemispheres, the under one being fixed to the brass mounting, and the upper one turned with a groove to shut upon it, so that it can be taken off at pleasure : it is screwed to a brass tube about four inches long, fitted on to the top of e ; from its lower end proceeds an arm carrying the piece fc, being two hollow balls and a tube, which together makes nearly the same length as that fitted on to e : g h, is a straight brass wire, with a knife-edged centre in the middle, placed a little below the centre of gravity, and equally balanced with a hollow brass ball at each end, the centre or axis resting upon a proper shaped piece of brass fixed in the inside of the ball b; that part of the hemisphere towards h is cut open to Fig. 74. Jc permit that end of the balance to descend till it touches d> and the upper hemisphere b is also cut open : the arm g is divided into sixty grains, and furnished with a slider, to be set at the number of grains THE UNIVERSAL DISCHARGER. 119 the experiment requires: k is a common Henley's Electrometer screwed upon the top of I. The slider is placed loosely on the arm ff, so that as soon as g h is out of the horizontal position it slides forward towards /, and the ascending continues with an accelerated motion till Ji strikes d. Now suppose the instrument to be applied to a jar as in the figure ; a metallic communication by a wire or chain is established between c and the inside of the jar, Tc is screwed upon 5 with its index point- ing towards h, the increase of the charge in the jar is thus shown : suppose the slider to be set at fifteen grains, it will cause g to rest upon /with a pressure equal to that weight : as the charge increases in the jar the balls/ and g become more and more repulsive of each other ; and when the force of this repulsion is sufficient to raise fifteen grains, the ball g rises, the slider moves towards &, and the ball h, coming rapidly into contact with d, discharges the jar, and as the force of the repulsion depends upon the intensity of the charge, the weight it has to overcome affords a measure of this intensity, and enables the experimenter to regulate the amount. (161) A very useful piece of appa- Fig. 75. ratus for directing with precision the charge of a jar or battery, is Henley's Universal Discharger, Fig. 75 ; it consists of a wooden stand with a socket fixed in its centre, to which may be occasionally adapted a small table having a piece of ivory (which is a non-conductor) inlaid on its surface. The table may be raised and kept at the proper height by means of a screw s. Two glass pillars P P are cemented into the wooden stand. On the top of each of these pillars is fitted a brass cap having a ring E/ attached to it, containing a joint moving both vertically and horizontally, and carrying on its upper part a spring tube admitting a brass rod to slide through it. Each of these rods is terminated at one end either by a ball a b screwed on a point, or by a pair of brass forceps, and is furnished at the other extremity with a ring or handle of solid glass. The body through which the charge is intended to be sent, is placed on the table, and the sliding rods, which are moveable in every direction, are then by means of the handles brought in contact with the opposite sides, and one of the brass caps being connected with the outside of the jar or battery, the other may be brought into communication with the inner coatings by means of the common discharging rod, Fig. 67. For some experiments it is more convenient to fix the substance on 120 STATICAL OB FEICTIOtfAL ELECTRICITY. which the experiment is to be made in a mahogany frame F, consist- ing of two small boards which can be pressed together by screws, and which may then be substituted for the table. In either of these ways the charge can be directed through any part of the substance, with the greatest accuracy. (162) When several jars are electrically united together, the arrangement is called an Electrical Battery. Fig. 76 represents such an apparatus. It consists of fifteen jars, the inside coatings of all of which are metallically connected by brass rods, and the bottom of the box in which they stand, being lined with tin-foil, secures a con- tinuous conducting surface for the exterior coatiffgs. The battery is shown with a Cuthbertson's Balance Electrometer, and an apparatus Tor striking metallic oxides attached. It is charged in the same Fig. 76. manner as a sijgle jar, by connecting the metallic rods in communi- cation with the inside coatings with the prime conductor, as shown in the figure ; the metallic lining of the box being in good conduct- ing communication either with the negative conductor or with a good discharging train. This does not seem, however, to be the best method of arranging a battery. The jars, according to Harris's experience, should be disposed round a common centre (Fig. 77), that centre being in communication with the prime conductor. As THE LEYDEN BATTERY. 121 shown in the figure, the central insulated rod C D is in direct com- munication with the prime conductor, the remaining jars being connected with each other. Harris found the difference .between the two modes of arrangement to be considerable, and in a battery of five jars, each containing five square feet of coated surface, to amount to one fifth of the entire accumulation. Fig. (163) By thus multiplying the number of jars we have it in our power to accumulate Electricity to an extent limited only by the charging power employed. A prodigious apparatus was constructed towards the end of the last century by Cuthbertson for the Ty- lerian Society at Haerlem. It consisted of one hundred jars of five and a half square feet each, so that the total amount of coated surface was five hundred and fifty square feet. This battery, when charged with Van Marum's large machine (102), produced the most astonishing effects. It magnetized large steel bars, rent in pieces blocks of box-wood four inches square ; melted into red hot globules iron wires 25 feet in length and T ioth of an inch in diameter, and dissipated in a cloud of blue smoke tin wires 8 inches long and -oth of an inch in diameter. The management of large electrical batteries demands considerable caution, as the discharge of a far smaller extent of coated surface than that just described, through the body of the operator, would be attended with serious conse- 122 STATICAL OK FEICTIONAL ELECTRICITY. queiices : by employing, however, the balance electrometer of Cuth- bertson (Fig. 74), or the simple apparatus invented by Harris, and shown in Tig. 95, p. 137, all danger may be avoided. (164) The extent of charge which a jar or battery is capable of receiving may be considerably augmented by moistening the interior. It was noticed by Mr. Brooke (Cuthbertson' s Electricity, p. 169) that a coated jar would take a higher charge when dirty than when clean, and in 1792 Cuthbertson made the casual discovery that a fresh coated jar, the inside of which was a little damp, would take a higher charge than it could do after it had been coated for some time and was quite dry. This observation induced him to make a series of experiments. He found that a battery composed of fifteen jars, and containing seventeen square feet of coated glass which on a very dry day in March (1796) could only, be made to ignite eighteen inches of iron wire, took a charge which ignited sixty inches when he breathed into each jar through a glass tube. He first thought he had thus obtained a method of making one battery perform the func- tions of three, but his subsequent experiments on the fusion of wires by various quantities of Electricity at the same intensity, led him to the conclusion that the increase of eifect was equivalent to the addition of six jars. A jar containing 168 square inches of coating, made very dry, and arranged with his balance electrometer and eight inches of watch pendulum wire, included in the circuit in the manner shown in Eig. 76, was found to discharge spontaneously without affecting the separation of the balls g f, when the slider was set at thirty ; but when the inside of the jar was moistened by breathing into it no spontaneous explosion occurred, but the discharge took place through the electrometer, and the wire was fused into balls. (165) The tendency of jars to spontaneous explosion when very clean and dry, may be diminished without moistening their insides, by pasting a slip of writing paper, about an inch broad, on the inner surface of the jar, so as to cover th.e uncoated interval to the height of half an inch above the upper edge of the inner coating. The action of this and of the other means that have been employed for the same purpose, consists, according to Singer (Elements of Elec- tricity, p. 135), in a gradual diminution of the intensity of the charge at that part from which it has the greatest tendency to explode, by an extension of the charged surface through the medium of an imperfect conductor. The height of the uncoated rim of small jars 'should, according to the same authority, be about two or two and a half inches ; with larger jars a rim of three inches will be sufficient if they are fitted up with an interior paper band. Singer also recommends to interpose a thickness of writing paper between the coating and the glass, which may easily be effected by pasting EXPERIMENTS WITH THE LEYDEN PHIAL. 123 the tin-foil first on paper, and afterwards applying this combined coating to the glass. The metallic coatings are thus placed at a greater distance from each other, and the chance of fracture is diminished. But jars thus fitted up, though they admit ofc a much greater quantity of Electricity being disposed on them than other jars without paper, have not for equal quantities of Electricity the same amount of action, the intensity of the Electricity being much less. A thin jar will, with the same amount of attractive force, ignite more wire than a thick one. (166) A few experiments illustrative of various phenomena connected with the charge and discharge of coated glass may here be introduced. Experiments with the Ley den phial and battery. Ex. 1. Fix to the outside coating of the jar, a } Fig. 78, exposing about a square foot of coated surface, a curved Fig. 78. wire 5, terminated by a metallic ball c, rising to the same height as the knob of the jar d ; charge the jar, and suspend midway between c and d, by a silken thread, a small ball of cork or elder pith. The ball will immediately be at- tracted by d, then repelled to c, again attracted, and again repelled, and this will continue for a considerable time : when the motion has ceased, apply the discharging rod to the jar, no spark or snap will result, proving that the phial has been gradually discharged by the pith or cork ball, the motion of which from d to c likewise proving the opposite electrical states of the outer and inner coatings. Ex. 2. Place the jar A, Fig. 79, on the insulating stand B, and attempt to charge it from the prime conductor, you will find it impossible ; now apply the knuckle to the outside coating, and continue to turn the machine : for every spark that enters, the jar, one will pass between the outside coating and the knuckle, and on applying the discharging rod, the jar will be found to have received a charge. Instead of the knuckle, the knob of a second uninsulated jar C, may be applied as in Fig. 79, loth jars will receive a charge. This experiment was made by Franklin in confirmation of his theory that when a iar is charged it contains in realitv no Fig. 79. 124 STATICAL OB FEICTIONAL ELECTKICITY. more Electricity than it did before, and that during the act of charging the same quantity of "fire" was thrown out of one side of the glass as was thrown on the other side from the conductor of the machine. In order to demonstrate this still more conclusively he arranged a series of jars, as shown in Fig. 80, taking care to Fig. 80. establish a good connection between the outside of the last jar and the earth, and he found that " the fluid that was driven out by the first would be received by the second, and what was driven out of the second would be received by the third, &c. A great number of jars could therefore be charged with the same labour as one, but not equally high, as every bottle in the series receives the new lire and loses its old with some reluctance, or rather gives some small resistance to the charging, and this circumstance in a number of bottles becomes more equal to the charging power, and so repels the fire back again on the globe sooner than a single bottle will do." (Franklin's Letters, p. 12.) This method of charging a series of jars, by giving a direct charge to the first only, is called charging by cascade. The jars may be separated and discharged singly, or they may be so connected as to produce one discharge the force of which shall be equal to the sum of all the separate ones. For this purpose they are placed upright on one common conducting basis, and their interior coatings connected metallically together : the whole series may then be discharged precisely in the same manner as a single jar. In fact, the arrangement then becomes an ordinary electrical battery. Mr. I. Baggs, in a communication to the Royal Society (Jan. 13th, 1818), describes a method of charging and placing jars by which a disruptive spark (124) of unusual length and brilliancy is easily produced. The jars are charged separately and to the same degree of intensity, then quickly placed in series of positive and negative surfaces, very near, but not so as to touch. Ex. 3. The following experiment furnishes another beautiful illus- tration of the theory of the Leyden jar. It is called the luminous or diamond jar. The figure represents a jar the coatings of which are made up of fifty-five squares of tin-foil 1 inch square, and each perforated with a hole - x \ths of an inch in diameter, and pasted in five EXPERIMENTS WITH THE LEYDEN PHIAL. 125 Fig. 81. m:$): .!* ' : *. -* ' .' A < t( i rows inside and outside of the jar. The diagonals of the square pieces are placed horizontal and vertical, and their points or angles are separated by about -Ath of an inch. The rows of the tin-foil squares are similarly placed on the inside of the jar, except that their horizontal points nearly touch one another at the centres of the cir- cular holes of the outer squares. During the charging of the jar the sparks are seen jumping from one metallic surface to the other ; and when the jar is discharged every part of the jar within the boundaries of the metallic spangles becomes momentarily illu- minated, and presenting in a darkened room an exceedingly brilliant appearance. ,Ex. 4. Provide a jar the exterior coating of which is moveable (it may be made of thin tin plate) ; charge this jar in the usual manner, and then place it on an insulating stand : touch the knob from time to time with a conducting body ; the whole charge will thus ultimately be removed, and the glass will be brought to its natural state : now charge the jar again, remove the outer coating, and re-place it on the insulating stand ; in this state it will retain its charge for an indefinite period. The reason of this is, that the wire by which the charge is communicated to the interior coating, being left attached to it, induction does not take place solely through the glass to the opposite coating, but is partly directed, through the air, to surrounding conductors : this portion is usually called free charge, and on removing this, by touching the knob with a conducting body, a corresponding portion of free charge, of the opposite kind, makes its appearance on the outside coating, owing to the induction which is now at liberty to direct itself from that part to surrounding objects. But when the exterior coating is removed the induction is determined entirely through the glass, and the charge on one side is sustained by an exactly equal quantity of the contrary Electricity on the other: all interference with surrounding objects is thus cut off. Ex. 5. Provide ajar with both coatings moveable (the jar for this purpose must be as wide at the mouth as at the bottom) : let the wire communicating with the interior coating pass through a glass tube, by which it may be removed from the jar without touching the metal : charge the jar in the usual manner, then withdraw the inside coating ; and having set it aside invert the jar upon some badly con- 126 STATICAL OB FRICTIOtfAL ELECTRICITY. ducting body, such as the table-cloth, and remove the exterior coating ; then, on applying the discharging rod to the two coatings, no spark or explosion will take place, and they may be taken in the hands without producing any shock, proving them to be quite free from any electrical charge : now re-place the coatings on the jar, and complete the circuit with the discharging rod : both spark and explosion will result, proving that the charge of the Leyden jar is dependent on the dielectric glass, and that the only use of the coatings is to furnish a ready means of communication between the charged particles. Ex. 6. Place a charged jar on an insulated stand, and make a com- munication between the interior coating and the electric bells, Fig. 50 : they will remain at rest until the outside of the jar is connected with the earth, when the clappers will be set in active motion : thus, by touching the exterior coating from time to time with the finger, the bells may be made to ring at pleasure. Ex. 7. Place some gunpowder on the ivory slip of the table of the universal discharger, Fig. 75, and having unscrewed the balls a b, insert the points of the wires into the powder about half an inch apart : on passing an explosion from the Leyden phial through the powderjftt will be scattered in all directions but not ignited, an effect occasioned, probably, by the enormous velocity (288,000 miles in a second, according to Wheatstone's experiments) with which Elec- tricity travels, not allowing sufficient time to produce the effects of combustion ; that this is the reason is rendered apparent by Ex. 8. In which some loose gunpowder is placed in the ivory Fig. 82. mortar, Fig. 82, and the circuit interrupted by ten or twelve inches of water in a porcelain basin : under these circumstances the gun- powder is fired on discharging the jar. EXPERIMENTS WITH THE LEYDEN PHIAL. 127 Fig. 83 represents Mr. Sturgeon's apparatus for firing gunpowder. The powder is placed in the wooden cup A, either dry or made up into a pyra- midical form with a little water. The brass ball b, which moves on a joint, is brought immediately over it, the chains c d, being connected with the outer and inner surfaces of a Ley den jar. The dis- charge takes place, and the powder is cf inflamed. Ex. 9. Tie some tow loosely round one of the knobs of the dis- charging rod, and dip it in powdered resin : place the naked knob in contact with the outside of a charged jar, and bring the other quickly in contact with the ball a : discharge will take place, and the resin will burst into a flame. Ex. 10. Place a thick card or some leaves of a book against the outer costing of a Ley den jar, or between the knobs of the universal discharger: pass the explosion,. the discharge will pass through the paper or card, and perforate it, producing a burr or protrusion in both directions, as though the force producing it had acted from the centre of the thickness of the card outwards ; a strong and peculiar odour is at the same time developed. Ex. 11. Drill two holes in the ends of a piece of wood half an inch long and a quarter of an inch thick : insert two wires in the holes, so that the ends within the wood may be rather less than a quarter of an inch distant from each other : pass a strong charge through the wires, and the wood will split with violence. Stones may be split in a similar manner. Ex. 12. Hang two curved wires, provided Fig. 84. with a knob at each end, in a wine-glass nearly full of water, so that the knobs shall be about half an inch asunder : connect a, Fig. 84, with the outer coating of a charged jar, and 5 with the inner coating, by means of the discharging rod ; when the explosion takes plass the glass will be broken with great violence. Ex. 13. Eemove the press from the universal discharger, and place a lighted candle in the socket : unscrew the balls, and arrange the points of the wires a little above the top of the wick of the candle, and about one inch apart : charge a jar, and having blown out the candle, make the connections between the outer and inner coating: the jar will discharge itself through the smoke of the candle, and re-light it. 128 STATICAL OB FEICTIONAL ELECTRICITY. Ex. 14. Adjust the candle so that the flame shall be exactly on a level with the two points of the discharging wires : set the point of the wire which is to communicate with the interior coating of the jar at the distance of one inch and a half from the flame, snuff the wick of the candle very low, and complete the circuit : the jar will discharge itself slowly and put out the candle. Ex. 15. Eernove the candle, and screw the table into the socket of the universal discharger : place a lump of sugar on the ivory slip, and having screwed the brass balls on the discharging wires, bring the surface of the sugar to nearly the same height as the centre of the balls. Fix Lane's discharging electrometer, Pig. 73, on the Ley den phial, and interpose the universal discharger between the chain f and the outside coating of the jar : darken the room, and turn the electrical machine. When the jar is charged sufficiently high, it will discharge itself over the surface of the sugar, illuminat- ing it, and the light will continue for some time. If five or six eggs be arranged in a straight line, and in contact with each other, they will be rendered luminous by passing a small charge through them. Ex. 16. Place a little model of a brass cannon on a circular brass plate fixed on the top of a Leyden phial instead of the ball, as shown in Fig. 85 : connect the square piece of brass a with the exterior coating, and arrange it at the distance of about half an inch from the mouth of the cannon : bring the knob b of the cannon in contact with the prime conductor, and hold a card between the mouth of the cannon and the brass plate a, so that it shall not touch either : when the jar has received a sufficient charge, the explosion will pass, and the card will be per- forated, as in experiment 10. Ex. 17. Colour a card with vermilion, unscrew the balls from the universal discharger, and place the points on opposite sides of the card, one about half an inch -above the other; discharge ajar through the card, it will be perforated at the point opposite to the wire con- nected with the negative side of the jar; a zig-zag black line of reduced mercury will be found extending from the point where the positive wire touches the card to the place of perforation. This curious result arises from the great facility with which positive Electricity passes through air, as compared to negative; and on repeating the experiment in vaeuo, the perforation always takes place at a point intermediate between the two wires. Ex. 18. To the knob of a large jar A, Fig. 86, screw a small EXPEEIMEKTS WITH THE LEYDEST JAR. 129 Fig. 86. metallic stage C, on which place a small jar B ; charge the large jar in the usual manner : the small jar, though it will not be charged in the usual acceptation of the term, will nevertheless be in a state of polarization ; and on bringing one ball of the discharging rod in contact with the exterior coating of the large jar, and the other in contact with the knob of the small jar, a flash and report will result, arising from the neutralization of a portion of the negative Electricity of the outside surface of A, by a corresponding portion of positive Electricity from the interior of B : both jars will now be charged, the inner surface of A and the outer surface of B being positive, and the outer surface of A and the inner surface of B negative ; and both jars may be discharged together, by con- necting the inside of B by means of a wire or chain with the outside of A, and bringing one knob of the discharging rod in contact with this wire or chain, and the other on the stage C, on which the small jar stands. If the large jar A be first discharged in the usual manner, by bringing one knob of the discharging rod in contact with its outside coating, and the other within striking distance of the stage C, a second charge will be communicated to it, by the electro- polar influence of the small jar, the moment that the discharging rod is removed ; and a second small explosion will take place on applying the discharging rod, after which both jars will be reduced nearly to a state of neutrality. Ex. 19. Fill the bent glass tube, c d, Fig. 87, with resin, or sealing- wax, then introduce two wires, a b, through its ends, so that they may touch the resin and penetrate a little Fig. 7. way into it: let a person hold the tube over a clear fire by the silk string e, so as to melt the resin, and at the same time connect the wires with the interior and exterior coatings of a charged jar : while the resin is solid, the discharge cannot c take place through it, but as it melts it becomes a conductor, and then the discharge passes freely. Ex. 20. The sudden rarefaction which air undergoes during the passage of the electric spark through it, is well shown by an apparatus invented by Mr. Kinnersley, of Philadelphia, and shown in Fig. 88. It consists of a glass tube ten inches long and two inches in diameter, closed air-tight at both its ends by two brass caps : a small glass tube, open at both ends, the lower one bent at a right angle, passes through the bottom cap, and enters the water contained in the 130 STATICAL OE FRICTIONAL ELECTBICITY. Fig. 88. lower portion of the large tube. Through the middle of each of the brass caps a wire is intro- duced, terminating in a brass knob within the tube, and capable of sliding through the caps, so as to be placed at any distance from each other. If the two knobs be brought into contact, and a Ley den jar discharged through the wires, the air within the tube undergoes no change in volume : but if the knobs are placed at some distance from each other when the jar is discharged, a spark passes from one knob to the other : the consequence is a sudden rarefaction of the air in the tube, shown by the water instantaneously rising to the top of the small tube, and then suddenly subsiding ; after which it gradually sinks to the bottom of the tube, the air slowly recovering its original volume. Ex. 21. Fig. 89 represents two small electric jars, coated as usual, externally, and provided with valves to withdraw the air from them by means of an air-pump. After the exhaustion, brass balls are Fig. 89. screwed on the necks of the jars over the valves. Erom'the brass caps wires proceed a few inches within the phials, terminating in blunt points. A jar fitted up in this manner may be charged and discharged like a common Leyden phial, induction taking place with great facility through highly rarefied air. When charged and discharged in a dark room, the extremity of the wire in the inside becomes beautifully illuminated with a star or pencil of rays (as shown in the figure), according as the Electricity happens to be positive or negative. This experiment is -known as the Leyden vacuum. Ex. 22. One of the most beautiful experiments in Electricity is that called (though most improperly) the " falling star :" it is produced by transmitting a considerable electrical accumulation through an ex- hausted receiver. Singer, in his excellent " Elements of Electricity," recommends a glass tube, five feet in length and | of an inch in diameter, capped with brass at each extremity. When such a tube is exhausted, no ordinary Electricity will pass through it in any other than a diffused state ; but by employing the charge of a very large jar, intensely charged, a brilliant flash is obtained through the whole length of the tube. The metallic termination in the tube should be a very small and well polished ball ; and if care be taken to have the brass caps well rounded, and the air within the tube not too much attenuated, the experiment will rarely fail. If the tube be six feet long, it may be four inches in EXPERIMENTS WITH THE LEYDEN" JAB. 131 diameter, and a jar having five square feet of coating should be employed. An assistant should work the pump, and the operator should occasionally try to pass the charge down ; when at a certain degree of exhaustion,, it does so in a brilliant line of white light. Ex. 23. Fig. 90 represents an apparatus for showing the explosion of gunpowder by Fig. 90. Electricity. It is generally made seven or eight inches long, and nearly the same height to the top of the roof; the side, and that half of the roof next the eye, are omitted in the figure, that the inside may be more conveniently seen. The sides, back, and front of the house are joined to the bottom by hinges ; the roof is divided into two parts, which are also fastened by hinges to the sides : the building is kept together by a ridge fixed half way on one side of the roof, so that when the building is put together it holds it in its place. Within the house there is a brass tube 1J inch long, and f- of an inch in diameter, screwed on to a pedestal of wood, which goes through about one- eighth of an inch, the other end by means of a chain has a communi- cation to the hook d ; at the other side of the tube, a piece of ivory, one inch long, is screwed, with a small hole for a wire to slide into. To use this apparatus, fill the brass tube a with gunpowder, and ram the wire & a small way into the ivory tube ; then connect the hook G with the bottom of a large jar, interposing a dish of water as in Pig. 82 : charge the jar, and form a communication from the hook d to the knob ; discharge will take place, the gunpowder will explode, throwing asunder the roof, upon which the sides, front, and back will fall down, without, however, undergoing any damage. The apparatus may be placed on the -pi 91 ground, or on a table out of doors, communication being established with the Leyden phial within by means of insulated wires. Ex. 24. Fig. 91 exhibits a piece of apparatus for showing in an amusing manner the power of the electric discharge to cause the ele- ments of water, viz., oxygen and 132 STATICAL OB FBICTIOtfAL ELECTRICITY. hydrogen, to enter into combination. The metallic wire which passes through the touch-hole of the small brass cannon is insulated from the metal by a hollow tube of ivory : this wire reaches nearly but not quite across the bore of the barrel. The cannon is charged in the following manner: the mixture of the oxygen and hydrogen gas being ready in a 4 or 6 oz. stoppered bottle, the cannon is filled with sand, and being held close to the mouth of the bottle, the stopper is removed, and the sand from the cannon entering, the gas at the same moment ascending occupies its place. The mouth of the cannon is closed by a cork, which is projected to a considerable distance by the force of the explosion. A single inspection of the figure will show the manner of passing the electric discharge. Ex. 25, The following experiment is exceedingly beautiful, and highly interesting, as demonstrating the opposite electric states of a charged jar. Make the resinous cake of an electrophorus dry and warm : draw lines on it with the knob of a positively charged jar, and sift over these places a mixture of sulphur and red-lead ; on inclining the plate to allow the excess of the powder to fall off, every line marked by the knob of the jar will be observed covered with the sulphur, whilst the minium will be dispersed. On wiping the plate, and drawing figures with the outside of the jar, the sulphur will be dispersed, and the minium collected in a very elegant manner on the lines described by the outside of the jar. The rationale of this experiment is as follows : the sulphur and red- lead, by the friction to which they have been exposed, are brought into opposite electrical states, the sulphur is rendered negative, and the red-lead positive, so that when the mixture is made to fall on surfaces possessing one or the other Electricity in a free state, the sulphur will be collected on the positive, and the minium on the negative portions of the plate, according to the well-known law of electric attraction. This experi- ment may be varied by tracing various lines at pleasure on a smooth plate of glass, with the knob of a jar, charged first with positive and then with negative Electricity : on gently dusting the surface with the mixture of sulphur and red-lead, a series of red and yellow outlines will be formed. This experiment is known as " Lichtenberg's figures." The mechanical effects, and calorific phenomena accompanying the discharge of an electric battery, are exemplified in the following experiments. Ex. 26. Between the boards of the press of the universal dis- charger (Fig. 75) lay a piece of stout plate-glass, and send a powerful charge through it, the glass will not only be broken into fragments, but a portion even reduced to an impalpable powder. Ex. 27. Lay a fine iron chain, about two feet long, upon a sheet EXPEBIMENTS WITH THE LEYDEN JAB. 133 of white paper, and transmit a charge from six or eight square feet of coated surface through it : on removing the chain, its outline will be observed marked upon the paper with a deep stain at each link, indeed, if this charge is sufficiently powerful, the paper is frequently burnt through. Ex. 28. Place a slip of tin-foil, or of gold leaf, between two pieces of paper, allowing the ends to project, and press the whole firmly together between the boards of the press of the universal discharger ; transmit the shock of a battery through it, the metals will be com- pletely oxidized ; if gold leaf be the metal employed, the paper will be found stained of a deep purple hue. Ex. 29. If a piece of paper be laid on the table of the discharger, and a powerful shock directed through it, it will be torn in pieces. The electrical battery is exhibited in Fig. 76, in the arrangement for fusing metallic wires, and converting them into oxides, and in Fig. 74 a large jar is represented in the experiment of fusing fine iron wire, a wire being substituted in place of the chain at c. The best material for this purpose is the finest flattened steel, sold at the watchmakers' tool shops, under the name of watch-pendulum wire. It does not require a large extent of coated surface merely to fuse metallic wires, provided they are sufficiently thin ; but to effect their oxidation, large batteries are necessary. Fig. 92 represents a useful appa- ratus for deflagrating metallic wires, invented by Professor Hare. Two brass plates s s, are' fixed in a pe- destal by a bolt N, about which they have a circular motion. On one of the plates a glass column C is cemented, surmounted by a forceps F ; at the corresponding plate there is a brass rod It, furnished also with a forceps. Between this forceps and that at F the wire through which the electric charge is to be sent is stretched; it may be of various lengths, according to the angle which the plates s s make with each other. The bottom of the pedestal is in communication with the exterior coating of a jar or battery which is charged from the prime conductor B, and with which it is allowed to remain in communication. JSTow, it is obvious that in this case, touching the conductor is equivalent to touching the inner Fig. 92. 134 STATICAL OE PEICTIONAL ELECTEICITT. coating of the battery. However, by causing one of the knobs of the discharger D to be in contact with the insulated forceps F, and approximating the other knob to the prime conductor, the charge will pass through the wire W. The oxides of metals produced by sending powerful electric dis- charges through fine wires, and which may be preserved by stretch- ing them about -^ of an inch above sheets of white paper, are exceedingly beautiful : the wires disappear with a brilliant flash, and the paper is found marked as described below (from Singer's Elec- tricity), though no description can convey an adequate idea of the beauty of the impressions. Gold wire Silver Platinum Copper Iron Tin Zinc Lead Diameter. Colour of the Oxides on paper. T !ir of an inch purple and brown. grey, brown, and green. grey and light brown. green, yellow, and brown. light brown. yellow and grey. dark brown. ? brown and blue grey. TST purple and brown. -riir TSTT T!TT Brass Ex. 30. By the following experiment it will be proved that Elec- tricity exerts an agency directly the reverse of the above, viz., that of restoring to the metallic state oxide of tin. If a portion of this oxide be enclosed in a glass tube, and a succession of strong explosions directed through it, the glass will after a time be found stained with metallic tin; and ver- milion may be resolyed into mercury and sulphur, by .the charge of a moderate sized jar. Ux. 31. The equality of two Electricities disposed on the inner and outer surfaces of the Leyden jar was proved by Franklin's experiment (Ex. 1). The following beautiful illustration by Bichman is likewise full of instruction on this point. Let a plate of coated glass, S, be placed vertically on a stand, and let two pith-ball electroscopes, p n, be attached to the coatings. Bring the coating P into contact with the prime conductor, the coat- ing N being in good conducting communica- EICHMAN'S EXPERIMENT. 135 tion with the ground. As the charging proceeds the ball p will be repelled by the free Electricity of P, while the ball n retains its original position. On allowing the apparatus to remain undisturbed for some time, the free Electricity of P will be gradually dissipated, and the ball p will drop into its original position. Now charge the plate again, and immediately cut off the communication between N and the ground. The ball p will slowly descend towards P as before, but at the same time n will begin to rise, and by the time p has reached the position #, n will have risen to 5, the angle between the balls being about the same as at first. Both balls will then slowly sink till the charge is lost by dissipation. If during the descent of the balls we touch N", the ball n will suddenly sink, and p will as suddenly rise by an equal amount. On removing the finger from N, p will fall and n will rise to nearly their former places, and the slow descent of both will again recommence. The same thing will happen if we touch P, p will fall down close to the plate, and n will rise, and so on; and these alternate touchings of the coatings may be repeated a great many times before the plate is discharged. In order to understand this beautiful experiment it must be remembered that as long as N is in communication with the ground it cannot retain any free Electricity, and, therefore, under these circumstances the ball n can never be repelled ; but as the free Elec- tricity on P is dissipated a corresponding portion of the opposite Electricity must be liberated from N, and escape to the earth, and this action must go on till the entire charge is lost. But when both surfaces are insulated, as the free Electricity of P is absorbed by the atmosphere, a corresponding quantity of the opposite Electricity is liberated as before from N ; but as it cannot now escape to the earth it becomes free Electricity, and repels the electroscope n. But this free Electricity becomes gradually absorbed by the air, and thus the entire charge is after a time dissipated. (167) The arrangement of Electricity on a charged surface is strikingly shown by the following experiment introduced by Faraday. A cylinder of gauze wire is placed on a plate of shell-lac ; over it, but not resting on the lac, is placed another similar but larger gauze cylinder. These cylinders correspond with the coatings of a Leyden jar, the glass of which is represented by the intervening dielectric air : a small charge of Electricity is conveyed from the prime conductor of an electrical machine to the inner cylinder by means of a brass ball suspended by a silk thread. On now touching the inner coating of the inner cylinder with a disc of gilt paper insulated by a stick of lac, and then examining its condition by the torsion Electrometer, it is found to be neutral ; but on passing the proof plane between the 136 STATICAL OB ERICTIONAL ELECTEICITT. two cylinders, and touching the outer coating of the inner one, it brings away a charge of positive Electricity. In like manner, on touching the outer coating of the outer cylinder no Electricity is obtained ; but from the inner coating a negative charge is transferred to the disc, which is rendered sensible by bringing the latter into contact with the electroscope. These are simple consequences of Earaday's theory of static in- duction, (78, et seq.) The same general principles may be illustrated with a common Leyden phial, thus : let the jar (the outer coating of which is a little higher than the inner) be charged, and its ball and rod immediately removed by an insulating thread of white silk : now apply a carrier ball to either the inside or the outside coating ; no signs of Electricity will be obtained, the two forces leing entirely engaged to each other ly induction through the glass. Now insulate the jar, and restore the ball and rod. Under these circumstances induction will take place through the air towards external objects, the tension of the polarized glass will fall, and the parts projecting above the jar will give electrical indications and charge the carrier ; at the same time the outside coating will be found in the opposite electrical state, and inductric towards external surrounding objects, because a part of the force previously directed inwards will now be at liberty. The charge upon an insulated conductor in the middle of a room is, according to Earaday's views, in the same relation to the walls of that room as the charge upon the inner coating of a Levden jar is to the outer coating of the same jar, one is not more free or dissimulated than the other ; and when we sometimes make Electricity appear where it was not evident before, as in the above experiment upon the outside of a charged jar, when after insulating it we touch the inner coating, it is only because we divert more or less of the inductive force from one direction into another, for not the slightest change is in such circumstances impressed upon the cha- racter or action of the force, and the terms, "free charge" and " dissimulated Electricity" convey therefore erroneous notions if they are meant to imply any difference as to the mode or kind of action (Ex. Eesear. 1682 1684). Harris entertains similar views : a coated jar, he says (Phil. Trans. 1834), may be considered as a sort of compound conductor in which the controlling effect of the insu- lated coating in respect of the electrometer is greatly increased by its proximity to the other in a free state, hence a much greater quantity may be accumulated on a given extent of surface with the same intensity. " The difference between electrical accumulation on coated glass and that on simple conductors is only in degree of effect, the laws incidental to the electrified substance remain the same." LAWS OP ELECTEICAL ACCUMULATION. 137 (168) Laws of electrical accumulation. These have been mi- nutely and successfully studied by Harris, the results of whose investigations are given in the Transactions of the Plymouth Institu- tion, and in the Transactions of the Royal Society, 1834, 1836, 1839. The following is a brief resume of some of his conclusions : 1. Precisely the same charge accumulates on a coated surface whether we suppose the opposite coating to be insulated and con- nected with one of the conductors of the Fig. 94. machine, or whether it be in a freely unin- sulated state, or whether it operate through an intervening jar. In order to measure the force and extent of electrical accu- mulations, he employed an instrument which he calls the Electro-Thermometer, Pig. 94. It consists of an air thermome- ter through the bulb of which there is stretched, air tight, a fine platinum wire ; the bulb is screwed, also air tight, on a small open vessel containing a coloured liquid, and soldered at the extremity of a long bent glass tube, to which is adapted a graduated scale : the fluid is adjusted to the zero of the scale by a small screw valve at the top of the bulb. When an electrical accumulation is passed through the platinum, wire it becomes more or less heated, expanding the air, and forcing the coloured fluid up the vertical tube, the height to which it ascends being measured on the scale. The delicacy of this instrument depends on the size of the platinum wire, which for ordinary purposes may be from the -s^th to the rth of an inch in diameter, and about 3 inches in length, corresponding with the dia- meter of the ball. The height to which the fluid rises is as the square of the quantity of Electricity discharged. Fig. 95. 138 STATICAL OR FBICTIONAL ELECTRICITY. Eor transmitting the explosion through the wire the simple appa- ratus, shown in Eig. 95, was contrived, c is a brass ball supported on a rod of varnished glass passing through the mahogany ball f, supported on the glass pillar g. The ball c has a hole drilled verti- cally through its centre, so as to admit of the wire d, carrying at its lower end the discharging ball d, passing freely through it. The wire d has two or three small holes drilled in it by which it can be supported at a given height on the ball c, by means of a pointed bent wire attached to a hinge joint at n, and provided with an insulating handle. The ball c is in direct communication with the inside coating of the jar or battery, and the ball b, insulated on a stout pillar of glass, is connected in any required way with the outside coating. To effect the discharge the bent brass wire is liberated by a light touch of the glass handle, upon which the balls d and b come sharply into contact, transmitting the accumulation in a certain and invariable way without leaving any residuum in the battery. (169) A jar containing about five square feet of coated surface was charged with four turns of the machine, and then dis- charged through the Thermo-Electrometer : the fluid rose nine degrees. The jar was now placed on an insulating stand, and its external coating connected by a wire with the internal coating of a second and precisely similar jar, uninsulated and provided with a Lane's discharging Electrometer (Eig. 73). The Electro-Thermo- meter was likewise included in the circuit. After four turns of the machine the second jar discharged, and the fluid rose as before nine degrees. The small residuum in the second jar being removed (the first jar retaining its charge), the machine was again put in motion ; after four turns the discharge of the second jar again took place, and the fluid again rose nine degrees. When the second jar was much smaller than the first, the explosion took place at about each turn of the plate till the large insulated jar was fully charged ; and, as in both cases, the second jars were charged from the outer coating of the first, their explosions may be taken as fair measures of the relative quantities of Electricity communicated by the machine ; and * as these explosions correspond to equal numbers of revolutions, it follows that the accumulation in the insulated jar must have pro- ceeded by equal increments, and consequently that equal quantities of Electricity were thrown on at each time. When several jars were substituted for the single jar, each being carefully insulated, the results were the same ; and when two equal and similar jars were insulated, and one connected with the positive and the other with the negative conductor, their outer coatings being joined by a metallic rod, the effects of the accumulation in either system, THE UNIT JAB. 139 estimated as before at given intervals, were precisely similar, and corresponded to an equal number of turns of the plate, proving that the respective quantities which continued to accumulate in the opposite system after each discharge, must have been also precisely similar. (170) Prom these experiments it appears : 1. That equal quanti- ties of Electricity are given off at each revolution of the plate to an uncharged surface, or to a surface charged to any degree short of saturation. 2. That a coated surface receives equal quantities in equal times, and that the number of revolutions of the machine is a fair measure of the relative quantities of Electricity, all other things remaining the same. 3. That the explosions of a second jar charged from the outer coatings of the first, are proportional to the quantity of Electricity thrown on the inner coating. The quantity of Electri- city may therefore be easily and correctly estimated by the number of explosions. (171) In accordance with these principles, Sir "Win. Harris con- structed his Unit Jar, a little apparatus which he found of the greatest service to him in his subsequent investigations. It consists of a small jar, K, exposing about six square inches of coated surface, Fig. 96. inverted on a brass rod fixed to the conductor of the machine, or otherwise sustained on a separate insulation ; and the jar or battery to be charged is connected with its outer surface through the inter- vention of the brass ball 5, as seen in Fig. 97. In this arrange- ment Electricity is continually supplied to the jar, and the amount 140 STATICAL OR FBICTIONAL ELECTEICITY. of accumulation accurately measured by the number of charges which the unit jar has received, the charges being determinable by means of the discharging balls n ri. By increasing or diminishing the distance betwf^-n the discharging balls, the value of the unit may be rendered as great or as small as we please. Hence, if the balls be securely fixed, and the distance between their points of discharge accurately measured by means of a micrometer screw and index at S, comparative quantities may be always estimated and restored from time to time with a great degree of accuracy. (Phil. Trans. 1834, p 217.) (172) Much difference of opinion has existed amongst electricians as to whether this instrument is really a true measure of the quantity of Electricity thrown into a Leyden jar. The late Mr. Sturgeon (who was an excellent practical electrician), observes {Lectures on Electricity, p. 227) : " After the first discharge has taken place, the resistance of the jar J (Fig. 97) against the Fig. 97. reception of fluid from the outside of the unit jar is increased, and the discharging intensity will be accomplished by a less quantity of fluid than at first ; and this second discharge of the unit jar throws a still less proportion of the diminished quantity into J than in the previous discharge ; and thus it is that each succeeding charge requires less and less fluid for ths discharging intensity, and a corresponding disproportion enters the jar J. When the intensity of J becomes considerable, the unit jar will be nearly choked up, and incapable of receiving any but a very trifling quantity of fluid." Although however it is doubtless true that at each successive dis- charge of the unit jar when measuring into a jar or battery, the THE UNIT JAR. 141 outside of the unit jar becomes more and more charged, it seems clear that its inner surface must be also proportionately more charged each time before the balls connected with the coatings can have the relations requisite for discharge brought on ; and in the discharge it is not the whole of the Electricity which passes, but just that portion which brings the inside and outside into equilibrium ; and this will be the same quantity for every discharge. The jar is therefore a true measure as long as the circumstances of position, &c., are not altered. On this subject Professor Faraday has favoured us with the following remarks, which we gladly insert, as they seem to dispose satisfactorily of the whole question. After describing some experiments relating to the resistance or' back action, he says : " The same difference will in every case exist between the balls n n\ Fig. 96, when a spark is ready to pass. Thus, suppose the unit jar has about one tenth of the electric capacity of the large jar J, Fig. 97, and that being charged up to its discharging point, it contains ten of positive Electricity ; then these ten will pass on into the large jar as a discharge spark, and none will remain within the unit jar. Now, the conductor of the machine, the outside of the unit jar, and the ball and wire of the large jar, will all appear positive to a carrier ball. But when the machine is turned, although a rise in positive condition will gradually take place on all the surfaces, still the mutual relation of n and ri to each other will be the same as before, and the mutual relation of the inner and outer coating of the unit jar will be to each other absolutely as before; for no external relation can alter their mutual relation, though it may affect the outer coatings, both of the large jar and of the unit jar. So the machine must exert a higher charging power than before, which is shown by placing an Electro- meter on its conductor ; and when ten units have been thrown into J, then, if after the eleventh the machine conductor be discharged, the jar J will be discharged back between n and n\ because of the re-action backwards. Still, whenever a spark does pass from n to n\ the Electricity passing must be equal ; because the inductive relations of the coatings to each other through the glass, and the like relations of the balls n n' to each other, remain absolutely the same. This is, as I think, a rigid consequence of the principles of inductive action." (173) The free action of an electrical accumulation is estimated by the interval it can break through, and is directly proportional to the quantity of Electricity. Experiment : Two similar jars, each containing five square feet of surface, being connected together, and with a Lane's discharging Electrometer (Fig. 73), the balls being set at iVth of an inch apart, the discharge took place at the end of two and a lialf turns of the plate ; the interval being doubled, the dis- 142 STATICAL OR FRIOTIONAL ELECTRICITY. charge passed at the end of five turns ; the interval being trebled, at seven turns ; when the interval between the balls amounted to A-ths of an inch, it required ten turns of the machine to produce a discharge. (174) But the free action is inversely proportional to the surface. Experiment: One of the jars in the former experiment being re- moved, the balls being set at -A-ths of an inch, the discharge took place with five turns of the plate ; the second jar being returned to its place, and the balls being set at -A-ths of an inch, the discharge again took place with five turns ; and, on adding two more similar jars and setting the balls at -^th of an inch, or one quarter the first distance, the discharge still took place with five turns. (175) If however as the surface increases the Electricity increases also, in the same ratio, then the discharging interval remains the same; but if as Electricity is increased the surface is diminished, then the discharging interval is directly as the square of the quantity of Electricity. Experiment : The balls of the Electrometer being set at &- ths of an inch, the discharge of a single jar took place with 21 turns; a second similar jar being added, the balls remaining as before, the dis- charge took place with^e turns ; a third jar being added, with seven turns ; two similar jars being used, the interval remaining the same, the discharge took place at five turns ; but when one jar, i. e. half the surface was removed, and the balls set at i-o-ths of an inch, the dis- charge occurred at ten turns. If we represent the quantity of Electricity by Q, the interval by I, and the surface by S, we get the following equation, I = f , from which we get Q = S I, and thus derive another means of estimating the relative quantity of Electri- city thrown upon a given surface, supposing the surface to be either in a divided or an undivided state, and all other things remaining the same.* (176) The want of a correct knowledge of these laws has occa- sioned some uncertainty in electrical inquiries. Thus, in describing some experiments with his steel yard Electrometer (Fig. 74), Cuthbertson assumed (Practical Electricity, p. 175, 178, 179, 180), that when the slider had been set to 15 and 30 so as to measure separate charges, the surface being constant, the corresponding accumulations were in the same ratio, i. e. as 2 : 1 ; whereas, in order to obtain a double accumulation, the slider should be set to 60 instead of 30, since the opposing forces should be to each other as 4:1. It was assumed also by Singer (Elements of Electricity, * In relation to this subject, see also Harris's experiments detailed in chap. ii. LAWS OF ELECTEICAL ACCUMULATION. 143 p. 177), that the same quantity of Electricity will fuse the same length of wire, whether it be disposed on two jars or only on one, but in the experiment on which he relies for the demonstration of this, when the two jars were connected together, the slider of the Electro- meter should have been set at 7i grains instead of at 15 grains, because, as Harris has shown, when the same Electricity is disposed on a double surface, the intensity or free action is reduced to one- fourth ; by setting the slider therefore at 15 grains, Singer nearly doubled the quantity of Electricity accumulated. (177) When the same quantity of Electricity is disposed on the same extent of coated surface, divided into two or more equal parts, there is a gradual loss of power, till at last, when a given amount is disposed on a great number of jars, the effect on the wire of the Thermo-Electrometer becomes altogether insensible. Neither does the effect go on increasing in the same ratio with the quantity of Electricity and the number of jars ; e. g. double the quantity of Electricity disposed on two jars does not produce four times the effect, as it would do if the Electricity in one jar only had been doubled, but only about two and a half times; the differences become more considerable as the number of jars is increased, till at length a limit appears to obtain, in which the advantage derived from an increased quantity becomes neutralized by the opposite effect, and the increased number of jars. (178) The method of estimating the quantity of Electricity in jars and batteries by the fusion of wires as employed by the older electricians, and also to a great extent by Cuthbertson and Singer is very uncertain, since wires may become fused with but little difference in appearance when very different quantities are passed through them (Singer, p. 180) ; besides which, it is very difficult to ascertain with precision the point at which fusion takes place, so that the wire may be just made red hot through the whole length and then drop into balls (Cuthbertson, p. 180). The practice also of moistening the interior of jars by breathing into them, leads to great uncertainty in accurate experiments. It is in fact little more than an ingenious method of increasing the inner coating in such a way as to extend the surface, as to increase the quantity of Electricity, the attractive force of the free action remaining the same. The heating effects however of given quantities of Electricity discharged under the same conditions through a metallic wire are always the same, whatever may have been its previous tension or intensity (145) relating to the conductors on which the accumulation has taken place ; e. g. a given quantity of Electricity accumulated on coated jars always produces the same effect on the wire of the Electro-Thermometer (Fig. 94), 144 STATICAL OE FEICTIOKAL ELECTRICITY. whether accumulated on thick glass or on thin, or on a greater or less extent of surface, the number of jars and the length of the circuit being the same. Harris found, however, that the eifects of given quantities of Electricity discharged through the Electro-Thermometer varied with the resistance, being less with a long circuit than with a short one, and varying in an inverse ratio of the length. (179) By varying the striking distance between the balls of Lane's Electrometer, no variation in the effects on the wire of the Thermometer occurs, even when the striking interval is made very considerable by enclosing the balls in the receiver of an air pump and exhausting the air, so long as the quantity of Electricity remains the same. The effect of exhausting the air however is to facilitate the discharge, e. g. when the density of the air is diminished to one-half, the discharge occurs with one-half of the quantity accumulated ; that is, with one fourth of the intensity or free action, and the distance through which a given accumulation can discharge is in an inverse simple ratio of the density of the air ; e. g. in air of one-half the density, the discharge occurs at twice the distance ; in other words, the resistance of the air is as the square of the density directly. Prom this it would appear that in air highly rarefied, as in the upper egions of the atmosphere, no considerable electrical accumulations can take place; and one of the most beautiful experiments in Electricity is to pass discharges through long distances in rarefied air, by which exact imitations of summer lightnings are produced. (180) The resistance to discharge in air (a non-conductor) is of a different nature to the resistance offered by conducting bodies ; in the former it arises solely from the pressure of non-conducting particles, and when the attractive forces are sufficiently great to overcome the resistance, the discharge pass_es without regard to distance. Harris found also that the restraining power of air is not affected by heat ; the discharge between two balls in an air-tight receiver taking place, with precisely the same quantity of accumu- lation at all temperatures between 50 and 300 Fah. The insulating power of air depends therefore solely on its density, and it would appear also that heat (if material) must be a non-conductor of Electricity, since it does not in the least degree impair the insulating power of air. (181) The supposed conducting power of a vacuum is unphiloso- phical, as a space free from all matter can scarcely be said to have any positive qualities whatever ; the reason an electrified body discharges to a conducting body in vacuo more readily than in air is, because there is less restraining power in consequence of non-con- ducting particles of air. The discharge does not however occur in LAWS OF ELECTRICAL ACCUMULATION. 145 consequence of any tendency of the electric principle to evaporate, but solely because of the removal of the obstructions interposed between the points from, and toward which, the accumulated Electricity tends to flow, and if the density of air could be indefinitely diminished, and the distance between the points of action indefinitely increased, we should in all probability eventually have the same relative electrical state continued without dissipation. (182) Such are some of the important principles of electrical action, established by the researches of this able and indefatigable Elec- trician. A brief recapitulation of the results may be, in conclusion, useful. 1 . An electrical accumulation proceeds by equal increments ; a coated surface receiving equal quantities in equal times, all other things remaining the same, and the quantity of Electricity passing from the outer coating is always proportional to the quantity added to the inner. 2. The quantity of Electricity accumulated may be measured by the revolutions of the plate, or by the explosion of a jar connected with the outer coating. It is as the surface multiplied by the interval the accumulation can pass. When the surface is constant, it is as the interval ; when the interval is constant, it is as the surface. It is also as the surface multiplied by the square root of the free action ; when therefore the surface is constant, it is as the square root of the attractive force. 3. The interval which the accumulation can pass is directly pro- portional to the quantity of Electricity, and inversely proportional to the surface ; it is as the quantity divided by the surface. If the Electricity and surface be either increased or decreased in the same proportion, the interval remains the same. If as the Electricity is increased, the surface be decreased, the interval will be as the square of the quantity of Electricity. 4. The force of electrical attraction varies in the inverse ratio of the squares of the distance between the points of contact of the opposed conductors, supposing the surfaces to be plane and parallel : or otherwise, between two points which fall within the respective hemispheres, at a distance equal to one-fifth of the radius, supposing the opposing surfaces to be parallel. 5. The free action is in direct proportion to the square of the quantity of Electricity, and in inverse proportion to the square of the surface. It is directly as the effect of the explosion on a metallic wire, all other things remaining the same. If the Electricity and surface increase or decrease together, and in the same proportion, the attractive force remains the same. If as the Electricity is 146 STATICAL OB FRICTIONAL ELECTRICITY. increased the surface is decreased, the attractive force is as the fourth power of the quantity of Electricity. 6. The effect of an electrical explosion on a metallic wire depends exclusively on the quantity of Electricity, and is not influenced by the intensity or free action ; it is diminished by accumulating the Elec- tricity on a divided surface ; it is as the square of the quantity of Electricity. It is as the square of the interval which the accumulation can pass ; it is directly as the attractive force and the free action, all other things remaining the same ; it is as the momentum with which the explosion pervades the metal. Fig. 98. (183) Specific inductive capacity. It was with an apparatus constructed on the principles of the Leyden phial, that Faraday succeeded in proving by the most decisive experiments that induction has a particular relation to the different kinds of matter through which it is exerted. A section of this ingenious apparatus is shown in Fig. 98. a a are the two halves of a brass sphere, with an air-tight joint at b, like that of the Magdeburgh hemispheres, made perfectly b flush and smooth inside, so as to present no irregularity ; c is a connecting piece, by which the apparatus is joined to a good stop-cock d, which is itself attached either to the metallic foot e, or to an air-pump. The aperture within the hemisphere at f is very small : g is a brass collar fitted to the upper hemisphere, through which the shell-lac support of the inner ball and its stem passes : h is the inner ball, also of brass ; it screws on to the brass stem ', terminating above by a brass ball B ; 1 1 is a mass of shell-lac, moulded carefully on to i, and serving both to support and insulate it and its balls h B. The shell-lac stem I is fitted into the socket g by a little ordinary resinous cement more fusible than shell-lac applied at m m, in such a way as to give sufficient strength and render the apparatus air-tight there, yet leave as much as possible of the lower part of the shell-lac stem untouched as an insulation between the ball h and the surrounding sphere a a. The ball h has a small aperture at n, so that when the apparatus is exhausted of one gas and filled with another, the ball h may also itself be exhausted and filled, that no variation of the gas in the interval o may occur during the course of an experiment. (184) The diameter of the inner ball is 2'33 inches, and that of the surrounding sphere 3'57 inches. Hence the width of the intervening SPECIFIC INDUCTIVE CAPACITY. 147 space through which the induction is to take place is 62 of an inch . and the extent of this place or plate, i.e. the surface of a medium sphere, may be taken as 27 square inches, a quantity sufficiently large for the comparison of different substances. Great care was taken in finishing well the inducing surfaces of the ball k and sphere a a, and no varnish or lacquer was applied to them, or to any part of the metal of the apparatus. (185) When the instrument was well adjusted, and the shell-lac perfectly sound, its retentive power was found superior to that of Coulomb's Electrometer, i. e. the proportion of loss of power was less. A simple view of its construction shows that the intervening dielectric or insulating medium may be charged at pleasure with either solids, liquids, or gases ; and that it is admirably adapted for investigating the specific inductive capacities of each. (186) Two of these instruments, precisely similar in every respect, were constructed ; and the method of experimenting was (different insulating media being within) to charge one with a Leyden phial, then, after dividing the charge with the other, to observe what the ultimate conditions of each were. For a detailed account of the method of manipulating, and the precautions necessary to obtain accurate results, we must refer to the original paper of the author (Experimental .Researches, Eleventh Series, 118^e seq?.) (187) The question to be solved may be stated thus : suppose a an electrified plate of metal suspended in the air, and 5 and c two exactly similar plates, placed parallel to and on each side of a at equal dis- tances and uninsulated ; a will then induce equally towards b and c. If in this position of the plates some other dielectric than air, as shell-lac, be introduced between a and c, will the induction between them remain the same ? Will the relation of c and I to a be unal- tered notwithstanding the difference of the dielectrics interposed between them ? (JExp. Eesear. 1252.) (188) The first substance submitted to examination was shell-lac, as compared with air. Por this purpose a thick hemispherical cap of shell-lac was introduced into the lower hemisphere of one of the inductive apparatus, so as nearly to fill the lower half of the space between it and the lower ball. The charges were then divided (186), each apparatus being used in turn to receive the first charge before its division by the other ; and as it had previously been ascertained that both the instruments had equal inductive power when air was in both, it was concluded that if any difference resulted from the intro- duction of the shell-lac, a peculiar action in that substance would be proved, and a case of specific inductive influence made out. (189) On making the experiment with all the care and attention T 9 148 STATICAL OR TEICTIONAL ELECTRICITY. that could be bestowed, an extraordinary and unexpected difference appeared, and the conclusion was drawn that the specific inductive capacity of shell-lac as compared with air is as 2 to 1. "With glass a result came out, showing its capacity compared with air to be as T76 to 1 ; and with sulphur a result showing its capacity to be as 2 '24 to 1. With this latter substance the result was considered by Faraday as unexceptionable, it being, when fused, perfectly clear, pellucid, and free from particles of dirt, and being moreover an excellent insulator. (190) Liquids, such as oil of turpentine and naphtha, were next tried ; and though no good results could be obtained, on account of their conducting power, they were nevertheless considered by Fara- day as not inconsistent with the belief, that oil of turpentine, at lea&t, has a specific inductive capacity greater than air. (191) Air was then tried, but no alteration of capacity could be detected on comparing together, rare and dense, hot and cold, or damp and dry : then all the gases were submitted to examination, being compared together in various ways, that no difference might escape detection, and that the sameness of result might stand in full opposition to the contrast of property, composition, and condition, which the gases themselves presented; nevertheless not the least difference in their capacity to favour or admit electrical induction through them could be perceived. (192) During the experiments with shell-lac (188), Faraday first observed the singular phenomenon of the return charge. He found, that, if, after the apparatus had been charged for some time, it was suddenly and perfectly discharged, even the stem having all Electri- city removed from it, it gradually recovered a charge which in nine or ten minutes would rise up to 50 or 60. He charged the appa- ratus with the hemispherical cap of shell-lac in -it, for about forty-five minutes, to above 600 with positive Electricity at the balls h and B, Fig. 98, above and within. It was then discharged, opened, the shell-lac taken out, and its state examined by bringing the carrier ball of Coulomb's Electrometer near it, uri insulating the ball, insulating it, and then observing what charge it had acquired. At first the lac appeared quite free from any charge, but gradually its two surfaces assumed opposite states of Electricity, the concave sur- face, which had been next the inner and positive ball, assuming a positive state ; and the convex surface which had been in contact with the negative coating, acquiring a negative state ; these states gradually increasing in intensity for some time. (193) Glass, spermaceti, and sulphur, were next tried, all of them exhibited the peculiar state after discharge. Faraday also sought to produce it without iud action, and with one electric power, but failed KETITRlf CHARGE. 149 in doing so ; a fact in favour of the inseparability of the two electric forces, and an argument in favour of the dependence of induction upon a polarity of the particles of matter. (194) Earaday was at first inclined to refer these effects to a peculiar masked condition of a certain portion of the forces, but he afterwards traced them to the known principles of electrical action. He took two plates of spermaceti and put them together, so as to form a compound plate, the opposite sides of which were coated with metal. The system was charged, then discharged, insulated, and examined, and found to give no indication to the carrier ball : the plates were then separated, when the metallic linings were found in opposite electrical states. Hence, it is clear that an actual penetra- tion of the charge to some distance within the dielectric, at each of its two surfaces, took place by conduction : so that, to use the ordi- nary phrase, the electric forces sustaining the induction are not upon the metallic surfaces only, but upon and within the dielectric ; also extending to a greater or smaller depth from the metal linings. (195) The following explanation may be offered : Let a plate of shell-lac, six inches square, and half an inch thick, or a similar plate of spermaceti, an inch thick, coated on the sides with tin-foil, as in the Leyden phial, be charged in the usual manner, one side posi- tively and the other negatively. After the lapse of ten minutes, or quarter of an hour, let the plate be discharged and immediately examined ; no Electricity will appear on either surface, but in a short time, upon a second examination, they will appear charged in the same way, though not in the same degree as they were at first. Now, it may be supposed, that under the coercing influence of all the forces concerned, a portion of the positive and negative forces has penetrated and taken up a position within the dielectric, and that consequently, being nearer to each other, the induction of the forces towards each other will be much greater, and that, in an external direction, less than when separated by the whole thickness of the dielectric ; when, however all external induction is neutralized by the discharge, the forces by which the electric charge was driven into the dielectric are at the same time removed, and the penetrated Electricity returns slowly to the exterior metallic coatings, constitut- ing the observed re-charge. According to Earaday, it is the assump- tion for a time, of this charged state of the glass, between the coat- ings of the Leyden jar, which gives origin to a well-known phenome- non, usually referred to the diffusion of Electricity over the uncoated portion of the glass, namely, the residual charge. After a large battery has been charged for some time, and then discharged, it is found that it will spontaneously recover its charge to a very consi- 150 STATICAL OB FBICTIONAL ELECTBICITT. derable extent, and by far the largest portion of this is referred to the return of Electricity in the manner described. (196) The relation of induction to the matter through which it is exerted, is well shown as a class experiment, by the following appa- ratus. Three equal discs of brass are arranged parallel, and at equal distances from each other : the two exteriors are in communication with the ground, the third which is between them is insulated ; a small single leaf Electroscope is suspended equidistant between two brass balls, each of which communicates separately with one of the exterior discs. The middle disc is charged with a certain quantity of Electricity, and the connection of the two exterior discs with the ground is cut off. If the gold leaf is exactly equidistant between the two balls (which is absolutely essential to the success of the experi- ment), it will remain at rest, being equally attracted by each of the balls, which, being in communication with the exterior discs, are equally electrized by induction. As thus arranged, the insulating stratum that separates the three discs is air ; but if for one of these strata one of shell-lac, glass, sulphur, or any other insulator be sub- stituted, the gold leaf immediately diverges, showing that the indu- cing action of the electrized body upon the disc, from which it is separated by the new insulating body, has become greater. This simple method of demonstrating Faraday's great discovery originated with Matteucci. (Meet. Mag. vol. ii. p. 186.) Some of Matteucci' s later experiments gave him results which induced him to doubt the accuracy of the explanation, given by Faraday, of the part played by insulating bodies in the phenomena of induction of static Electricity. He affirms that the insulating power of a body, consists in the greater or less resistance opposed by bodies to the destruction of that molecular polarization, which is always developed in it during the presence of an electric body; that the. differences in insulating plates of different substances are not due to a specific inductive power, but to differences in the propagation of Electricity, either at the surface, or in the interior, of the bodies, and that the Electricity which penetrates into their interiors and which is diffused over their surfaces, returns on the instant to the surface, when it is covered with a metal plate in communication with the ground. The experiments on which he founds these opinions are certainly striking ones. He introduced insulating plates of different substances by means of insulating stems into the case of a Cou- lomb's balance having its two electrized balls divergent, and he found that the ball experienced the same loss of Electricity, whethertouchedby gum-lac, or sulphur, or by glass covered with a coat of gum-lac varnish T$ T of an inch thick ; and by constructing a kind of box of mica, the LATEKAL DISCHABGE. 151 interior surface of which was covered with lac varnish, he compared together air, sulphur, glass, and gum-lac, and found the effects the same in each. (197) Lateral discharge. "When a large jar or battery is discharged by a metallic wire held in the hand, without the protection of an insulating handle, a slight shock is frequently felt in the hand that grasps the wire : and if a large jar be placed on a table, with its knob in contact with the prime conductor, and if a chain be stretched upon the table, with one end nearly touching the outside coating of the jar, by charging the apparatus till it discharges itself voluntarily, a spark is seen to pass between each link of the chain, which thus becomes illuminated, though it forms no part of the circuit. This spark is called the lateral discharge; it is occasioned by a small excess of free Electricity, which distributes itself over a dis- charging surface, when a charged system is discharged or neutralized . It arises from the fact, satisfactorily established by Harris, and acknowledged by Biot, Henry, and others, that the accumulated Electricity is never exactly balanced between the opposed coatings ; so that there will always be an excess of positive or negative Electri- city over the neutralizing quantities themselves, disposed on the coatings of the jar. The existence of this excess of Electricity, either positive or negative, is proved by the fact, that if we charge a jar, allow it to remain insulated, and discharge it gradually, by draw- ing sparks from the knob, and adding them to the outer coating, we can always take ^finite spark from either side alternately, whilst the jar rests on the insulator. If we place a charged jar upon an insulating stand, and discharge it in the usual manner, with a discharging rod, the excess of free Electricity exhibits itself in the form of a spark, at the moment of discharge between any body connected with the outer coating, and another in communication with [the earth : the intensity of the spark depends on the capacity of the jar, being less with a large jar, and greater with a small one ; the quantity of Electricity discharged being the same (Harris). After the discharge, the knob, outer coating, and all bodies connected with the jar, are found in the same electri- cal state, which we may make either positive or negative, by taking a spark either from the knob or coating, previously to discharging the jar. This small quantity of free Electricity may be obtained even when the jar is connected with the earth, provided we seize it before the conductors have time to carry off the residuary accumulation ; it having been proved by Professor "Wheatstone, that some portion of time elapses in the passage of Electricity through wires : the effect, 152 ' STATICAL OB FEICTIONAL ELECTRICITY. however, is greatest when the jar and its appendages are quite insulated. (198) The following experiments convey a good deal of information respecting the nature of the so-called lateral discharge. Ex. 1. Let the jar J. (Fig. 97), be charged positively,. removed. from the machine and insulated ; under this condition discharge it. When discharged, let the electrical state of the knob m, discharging conductor e C, and the outer coating J, be examined ; they will all be found in the same electrical state, which state will be precisely that exhibited by the outer coating and knob, whilst charging, and the small residuary charge will be plus. Ex. 2. Charge the jar as before ; but before discharging it withdraw the free Electricity from the knob. The electrical state of the coating and appendages will now be changed, and the small residuary spark will be minus thus showing that the Electricity of the spark varies with the coatings. Ex. 3. Immediately after the discharge, apply a metallic body to the coating J ; a residuary spark will be thrown off, which spark obviously cannot be caused by any lateral explosion caused by the dis- charging rod. Ex. 4. After this residuary spark has been taken from the outer coating, examine the jar, and it will be found again slightly charged as at first, showing the spark to be merely a residuary accumulation. Ex. 5. Charge a jar, exposing about two square feet of coating, with a given quantity of Electricity, measured by the unit jar u, let a conducting rod terminating in a ball r project from the outer coating, and place near it the electroscope E. Discharge the jar through the rod c c as before, and observe the amount of divergence of the electroscope. Double the capacity of the jar, and again accumu- late and discharge the same quantity. The divergence of the electro- scope will be very considerably decreased : add a second and a third jar to the former, and the effect will be at last scarcely perceptible : connect the jar with the ground, and with a given quantity the spark will vanish altogether. Ex. 6. Accumulate a given quantity as before, and observe the effect of the residuary charge on the electroscope. Let a double, treble, &c., quantity be accumulated and discharged from a double, treble, &c., extent of surface that is to say, for a double quantity employ two similar jars and so on ; the effect will remain the same. These two last experiments prove that the spark is of different degrees of force when the Electricity is discharged from a greater or less extent of surface, whilst double, treble, &c., quantities, when discharged from double, treble, &c., surfaces, give the same spark. LATEEAL DISCHARGE. 153 Now, as no one can doubt but that the effect of a double, &c., quan- tity should be greater than a single, &c., quantity, it is again evident that the spark is not caused by any lateral explosion from the dis- charging rod, it being a well-established law that the same quantity has the same heating effect on wires, whether discharged from a great surface or a small one, from thick glass or thin ; some little allowance being made for the greater number of rods, &c., when the surface is increased by an additional number of jars. The effect, therefore, depends on the jar. Ex. 7. Discharge a jar by means of discharging circuits of dif- ferent dimensions', from a large rod down to a fine wire, which the charge in passing can make red-hot. Observe the effect on the elec- troscope in each case : it will be found nearly the same, being rather less where the tension in the discharging wire is very considerable proving that the tension on the rod is not of any consequence. Ex. 8. Connect the jar with the ground, and place a small quantity of percussion powder enclosed in thin paper between the discharging conductor c, Eig. 97, and a metallic mass placed near it. The powder will not be inflamed even in the case of the discharging conductor becoming red-hot, whereas in passing the slightest spark it inflames directly, which shows that no kind of lateral action arises during the passage of the charge. Ex. 9. Let a circular piece of wood between two and three feet in diameter be covered with tin-foil, placed on a stool, and connected with the earth as shown in -Fig. 99. Let sparks be now taken between the prime conductor and the ball a. Lateral sparks may always be obtained from the wire whenever a con- ductor is approached to it. By connecting a stout cop- per wire with the gas fit- tings of the house, insu- lating it on glass rods at different parts of the room, and drawing sparks from the prime conductor of the large Polytechnic machine by means of a brass ball five inches in diameter attached to the other end of the wire, and held in an assistant's hand by means of a glass rod, Mr. "Walker obtained sparks not only from the gas fittings of the room in which the experiments were made, but also from the burners in the workshops two stories below. It does not, however, require a machine 154 STATICAL OB FBICTIONAL ELECTRICITY. of very great power to exhibit such phenomena ; we have frequently inflamed hydrogen gas from a jet attached to a bladder by directing the stream against a gas pipe in a room adjoining one in which sparks were being drawn from the conductor of a machine the plate of which is 30 inches in diameter.. jEx. 10. The following instructive experiment was arranged by Dr. Bachhoffher. 10 - On a deal board, about two feet square, were past- ed slips of tin-foil a b c, Fig. 100. Sparks were passed from the machine upon a, from which they discharged themselves at d, to the conductor c, and passed along it to B ; but under no circumstances would they pass the spaces x x x, on which was placed percussion powder. The wire B was now removed to the position 'B, connecting it with a good discharging train, and the experimenter took in his hand the wire C, connected with the same pipes, and in the same direction sparks were passed as before at d, and by applying the wire C to any part of the slips of tin-foil, he was enabled to draw off sparks ; but when the wire C was placed in a position similar to that represented by D, touching the tin-foil b at acid, and a similar but smaller cylinder of zinc, which is kept from touching the sides of the copper, by pieces of cork ; both are furnished with wires terminated by caps to contain mercury for the convenience of making and breaking the circuit. The quantity of Electricity set in motion by these simple circles, when on a large scale, is very great, though the intensity is very low. No physiological effects are experienced when the body is included in the circuit, nor is water decomposed ; their heating powers are, however, so great, that they were called by Dr. Hare calorimotors. An arrangement on a very extensive scale was made at the Eoyal Institution, under the direction of Mr. Pepys, Fig. 134<. A sheet of zinc, and one of copper, were coiled round each other, each being sixty feet long and two feet wide : they were kept asunder by the intervention of hair ropes, and suspended over a tub of acid, so that by a pulley, or some other simple contrivance, they could be immersed and removed. About fifty gallons of dilute 252 GALVANIC OB VOLTAIC ELECTRICITY. Fig. 134. acid were required to charge this battery, and when it is stated that a piece of platinum wire may be heated to redness by a pair of plates, only four inches long and two broad, the calorific power of such an arrangement as the above may be imagined to have been immense. The energy of the simple circle depends on the size of the plates, the inten- sity of the chemical action on the oxidable metal, the rapidity of its oxidation, and the speedy removal of the oxide. (333) In order to increase the intensity of the electrical current, with a view to the exhibition of its chemical and physiological effects, we increase the number of the plates ; an arrangement of this sort is called the compound voltaic circle: it was the invention of Volta, and is hence called the voltaic pile. Now, the quantity of Electricity obtained from the voltaic pile is no greater than that from a single pair of plates, it is its intensity alone that is increased ; an important fact which has received much elucidation from the important labours of Faraday. (334) The original instrument of Volta is shown in Pig. 135. It consists of a series of silver and zinc, or of copper and zinc plates, arranged one above another, with moistened flannel or paste- board between each pair. A series of thirty or forty alternations of plates^ four inches square, will cause the gold leaf electroscope to diverge : the zinc end with positive, and the silver end with negative Electricity, a shock will also be felt on touching the extreme plates with the finger, when moistened with water. This latter effect is much increased when the flannel or pasteboard is moist- ened with salt and water; in this case a small spark will be seen on bringing the extreme wires into contact, and water will be decomposed : Irom this we learn that the increase o'f chemical action by the addition of the salt, materially increases the quantity of Electricity set in motion ; but the pile will not in any sensible manner increase the di- vergence of the gold leaves, its intensity, therefore, is not materially augmented. Fig. 135. THE DE.Y PILE. 253 (335) An electric pile was constructed by De Luc, from which much useful information respecting the direction of the electric current in these cases of excitation may be derived. This instrument consists of a number of alternations- of two metals, with paper inter- posed: the elements may be circular discs of thin paper, covered on one side with gold or silver leaf about an inch in diameter, and similar sized pieces of thin zinc foil, so arranged that the order of succession shall be preserved throughout, viz., zinc, silver, paper, zinc, silver, paper, &c. About five hundred pairs of such discs, enclosed in a perfectly dry glass tube, terminated at each end with a brass cap and screw to press the plates tight together, will produce an active column. The late intelligent electrician, Mr. Singer, con- structed a dry pile on a much more extensive scale. It consisted of twenty thousand series of silver, zinc, and double discs of writing- paper : it was capable of diverging with ball electroscopes, and by connecting one extremity of the series with a fine iron wire, and bringing the end of this near the other extremity, a slight layer of varnish being interposed, a succession of bright sparks could be pro- duced, especially when the point of the wire was drawn lightly over the surface. A very thin glass jar, containing fifty square inches of coated surface, charged by ten minutes' contact with the column, had power to fuse one inch of platina wire ToVo of an inch in diameter. It gave a disagreeable shock, felt distinctly in the elbows and shoulders, and by some individuals across the breast. The charge from this jar would perforate thick drawing-paper, but not a card. It did not possess the slightest chemical action, for saline com- pounds tinged with the most delicate vegetable colours underwent no change, even when exposed for some days to its action. (336) On examining the electrical state of the dry electric column, it is found to resemble that of a conductor under induction : in the centre it is neutral, but the ends are in opposite electrical states ; and if one extremity be connected with the earth, the Electricity of the opposite end becomes proper- Fig. 136. tionally increased: the zinc ex- tremity is positive, and the silver or gold extremity negative : as may be proved by laying the column on the caps of two gold leaf electroscopes in the manner shown in Pig. 136, the leaves will diverge with oppositeElectricities: if a communication be made be- tween the instruments by a 25i' GALYASIC OB VOLTAIC ELECTEICITT. metallic wire the divergence of the leaves will cease, but will again be renewed when such communication is broken. It is better to employ, in these experiments, an electroscope in which the gold leaves are suspended singly, as shown in Fig. 137, and so arranged as to Fig. 137. admit of their being brought nearer to or carried further from each other. If in such an instru- ment the leaves are adjusted at a proper distance from each other, and the wire from which one is suspended connected with the zinc end, and the wire from which the other is suspended con- nected with the silver end of the column, a kind of perpetual motion will be kept up between the leaves ; for, being oppositely excited, they will attract each other ; and having by contact neu- tralized each other, they will separate for a moment, and again attract and separate as before. If both silver ends, or both zinc ends of two columns are connected with the two gold leaves a continued repulsion will be kept up between the leaves, they being then similarly electrified. (337) A variety of amusing experiments has been devised, de- pendent upon this curious property of De Luc's column. Thus a small clapper may be kept constantly vibrating between two bells. This was the contrivance of Mr. Forster, who constructed a series of fifteen hundred groups, and by its continued action kept up the vibrations of the pendulum for a very long time. "With twelve hun- dred groups, arranged by Mr. Singer, a perpetual ringing during fourteen months was kept up. We are informed by Mr. Singer, that De Luc had a pendulum which constantly vibrated between two bells for more than two years. A convenient modification of De Luc's column was contrived by Zamboni, by pasting on one side of a sheet of paper finely laminated zinc, and covering the other side with finely powdered black oxide of manganese. On cutting discs out of this prepared paper, and piling them upon each other to the number of 1000, taking care to press them together, a little pile is obtained, capable of diverging the gold leaves of the electrometer to the extent of half an inch. Mr. G-assiot describes (Phil. Trans. 1839) an arrangement which he has constructed, consisting of a series of 10,000 of Zamboni' s piles. "With this arrangement, he charged a Leyden battery to a considerable degree of intensity, and obtained direct sparks of ^o of an inch in length. He ultimately succeeded in obtaining chemical decomposition of a solution of iodide of potas- sium, the iodine appearing at the end composed of the black oxide of manganese. THE WATER BATTERY. 255 (338) Philosophers are divided in opinion respecting the source of the electric charge of the " dry pile," some supposing it due to the contact of the metals, while others trace it to the contact of the zinc with the small portion of moisture which is contained in the paper in its common hygrometric state. It is certain that a degree of mois- ture is indispensable to the action of the instrument ; for the Elec- tricity disappears altogether when the paper discs have lost their humidity by spontaneous evaporation, and the zinc becomes slowly corroded in the course of years ; its charge appears to be altogether one of intensity, and after discharge requiring an interval of time for renewal. It is not improbable that the state of the atmosphere is in some way connected with the phenomenon, for the motion of the pendulum is subject to much occasional irregularity. De Luc and Mr. Hausman both observed that the action of the column was increased when the sun shone on it; but they conceived that the effect was not due to the heat of the sun's rays, because it was found that an instrument put together after the parts had been thoroughly dried by the fire had no power whatever, but that it became effi- cacious after it had been taken to pieces, and its materials had remained exposed all night to the air from which the paper imbibed moisture. Mr. Singer, however, remarks, that the power of the column is increased by a moderate heat, as his apparatus vibrated more strongly in summer than in winter, and the electrical indica- tions were stronger when there was a fire in the room. Care should be taken not to allow the ends of the column to remain for any length of time in contact with a conducting body; for, after such continued communication, a loss of power will be perceived. When, therefore, the instrument is laid by, it should be insulated ; and if it had previously nearly lost its action, it will usually recover it after a rest of a few days. The application of the dry pile to the electro- scope has been already alluded to (52). (339) When a series of some hundred couples of zinc and copper cylinders are arranged voltaically, and charged with common water, a battery is obtained, the Electricity of which is of a high degree of intensity, resembling that of the common electrical machine ; indeed, by connecting the extremities of such an arrangement with the inner and outer coatings of a Ley den battery, it becomes charged so in- stantly that almost continuous discharges may be produced. An extensive series of the water-battery was constructed by Mr. Crosse, and the phenomena which it exhibited were of a very interesting character. It consisted of 2500 pairs of copper and zinc cylinders, most of which were enclosed in glass jars : they were all well insu- lated on glass stands, and were ranged on three long tables, well 256 GALVANIC OB VOLTAIC ELECTEIC1TT. protected from dust and from the light, a situation which expe- rience has shown Mr. Crosse to be most favourable for this peculiar form of the voltaic battery. 340) The following were some of the results obtained from this battery : 30 pairs afforded a slight spark, sufficient to pierce the cuticle of the lip, the hand making the communication being wetted ; 130 pairs opened the gold leaves of the electrometer about half an inch ; 250 pairs caused the gold leaves to strike their sides ; 400 pairs gave a very perceptible stream of Electricity to the dry hand, making the connection between the poles, the light being very visible ; 500 pairs occasioned that part of the dry skin which was brought in contact to be slightly cauterized, more especially at the negative side ; 1200 pairs gave a constant small stream of the fluids, between two wires or two pieces of tin-foil, placed T o -o of an inch apart, such wires or pieces of foil not having been previously brought into contact. This stream, when received by the dry hands, was exceedingly sharp and painful. A pith-ball, i inch in diameter, sus- pended by a silk thread, vibrated constantly between the opposite poles : 1100 pairs produced this latter effect. If the foot of a gold leaf electrometer was connected with one of the poles, and the hand of another person connected with the other pole brought over the cap of the instrument, even when held at several inches' distance, the leaves struck their sides. Again, if the cap of the same elec- trometer was connected with either pole of the battery of 1100 pairs, the opposite pole not being connected with the foot of the instrument, the leaves continued to strike the sides. This latter is a proof of the great waste occasioned by the imperfect insulation of the cylinders. A much more powerful effect would be produced by a superior insu- lation : 1600 pairs of cylinders produced the above effects in a much greater degree. In a tolerably well insulated battery every ad- ditional ten pairs after the first 100 produce an evidently increased effect ; and after 1 000 pairs, the next 100 constitute a much greater addition to their power than one might promiscuously have imagined. "With 1600 pairs the stream between two wires not previously brought into contact was very distinct ; the light, however, was not great ; the stream was of great intensity, but of small diameter. The method adopted by Mr. Crosse for exhibiting this interesting experiment is this : he takes a small glass stick, and ties on it with waxed thread, very securely, two wires of platina, with the two extreme ends ready to be plunged into two cups of mercury connected with the opposite poles of the battery : the two other ends of the wires are brought to the distance of about Toir of an inch from each other. The moment the connexion is made with the poles of the battery, a small stream THE WATER BATTEBY. 257 of fire takes place at the interval between the wires, which may be kept up for many minutes, nor does it appear inclined to cease. This experiment never fails ; though with a much greater number of plates, each pair not being separately insulated, it would never succeed. The light between charcoal points, even with the whole series, was feeble, there was no flame nor even approach to it : the conducting power of the water used in the cells being inadequate to transmit a sufficient current to produce great light and heat, even supposing such current to have been excited. Mr. Crosse has, however, a water battery, consisting of eighty p'airs of very large cylinders, which gives very brilliant sparks between two points of charcoal when rubbed together. (341) When the opposite poles of the 2,400 pairs were connected with the inner and outer coatings of a large electrical battery, containing 73 feet of surface, a continual charge was kept up, each discharge being attended with a loud report, heard at a considerable distance. Each of these discharges pierced stout letter-paper, and fused a considerable length of silver leaf, which it deflagrated most brilliantly, attended with loud snappiugs of light, more than a quarter of an inch in length. Platinum wire was fused at the extremity, and the point of a pen-knife was soon demolished. Light substances were attracted a distance of 'some inches and repelled again : the physiological effects would undoubtedly be exceedingly violent ; we have not, however, heard that any person has yet ventured to experience them. (342) To avoid the trouble of using this large electrical battery, Mr. Crosse constructed one of mica. It is made in the following manner: Seventeen plates of thin mica, each five inches by four, are coated on both sides to within half an inch of the edge with tin-foil, and let into a box lined with glass, with a glass plate between each mica plate. Slips of tin-foil are pasted to each side of each plate of tin-foil, of which all those connected with the lower ones are brought together at the extremities furthest from the plate, and pasted to one end of the interior of the box ; whence, by a tin-foil communication, a connection is made with a brass stem, secured to the outside of the box. This represents what may be called the outer coating of the battery, and is capped with a ball. The remaining strips of tin-foil or those connected with the upper surface of each plate, are brought together at the other end of the interior of the box, and turned back upon the tin-foil or upper part of the top plate. A brass plate, three inches square, is then laid flat upon those combined slips, a cover is fitted on 258 GALVANFC OE YOLTATC ELECTRICITY. the box with screws, and a glass tube carrying a brass stem, passing through it and the cover, is fixed in the centre of the cover : such stem being cut at the lower part into a screw, which passes through a female screw cut in a cap, cemented to the lower end of the glass tube within the cover, pressing on the brass plate. The upper part of the stem passes through a cap on the top of a glass tube, and is terminated with a brass ball, and may be termed the inner coating of the battery. By screwing the stem a perfect contact is made between this ball and all the upper surfaces of the mica plates. The two balls are placed on the same level, and a brass wire of T i>th inch diameter passes horizontally through the ball of the outer coating, cut into a screw to meet a similar one passing through the opposite ball. These wires are furnished with fine platinum points, and can be brought into contact, or made to recede at pleasure. A micrometer screw may be attached. By means of holes made 'in the opposite stems, the mica battery may be connected by wires with the opposite poles of a voltaic battery, and the striking distance accurately measured between the points. (343) The whole arrangement will be understood by inspecting Fig. 138. A, is a sectional view of a dry wooden box, lined with Fig. 138. glass, containing the plates of covered mica, a plate of window-glass being interposed between each. B, strips of tin-foil a quarter of an inch wide, each of which has one end pasted to the tin-foil under each mica plate, and the other end brought to the bottom of the box, and secured together by paste, and attached by a conducting communication of metal to the rod C C. D, similar strips having one end pasted to the tin-foil over each mica plate, and the other ends turned back on the upper part of the upper plate. E, E, a thin brass plate three inches square, placed horizontally on the combined ends of the strip. F, a glass tube, capped at each end, THE WATER BATTERY. 259 passing through the cover of the box Gr. Through this tube passes a brass screw, the lower end of which presses on the brass plate E, E, the upper end bearing the brass ball H. I, a brass ball, capping the stem C, C. Both H and I are pierced by the horizontal wires K, L, placed on the same level, cut into screws ; and having each a platinum point at one end, and a nut at the other. In each of the upright stems immediately under the balls, is a hole drilled to receive the wires of communication M, N. (344) The peculiar merits of this apparatus consist in its com- pactness, and its not being liable to injury from damp. When charged to a certain extent the shock is surprisingly painful, and is equivalent in power to many superficial feet of common coated glass. It is not calculated to be charged to a high intensity, as in such case the thin plates of mica would be pierced. Connected with the water battery, the following results were obtained by Mr. Crosse : three pairs of cylinders produce light : twenty pairs produce a stream of light : 200 pairs produce a stream of scintilla- tions, by drawing fine iron-wire over the lacquered knob of the mica battery : 300 pairs fire gunpowder : 500 pairs give a smart shock to the dry hands : 1200 pairs give a shock not easily borne, felt across the breast anj shoulders, and cause a constant stream of light to pass between two wires % of an inch apart, in an exhausted glass globe of four inches diameter, that globe being faintly but visibly illuminated over the whole of its interior during the experiment : 1600 pairs give a shock perfectly insupportable, which nearly knocked a person down who received it. (345) Shortly after the above account of the performances of his water-battery was published by Mr. Crosse, the author constructed a series of 500 pairs of cylinders, each equal to a five-inch plate ; they were placed in green glass tumblers, insulated with the greatest care, and placed in a cupboard furnished with folding doors, to keep out the dust and to diminish evaporation. This battery, which continued in almost uninterrupted action for upwards of two years, gave very powerful shocks when the terminal wires were grasped with the moistened hands, and when the positive wire was held in one hand, and the dry knuckle brought into contact with the binding- screw attached to the negative, a spark was obtained, and a small blister raised on the cuticle ; a spark was also obtained between the knuckles of two persons touching, respectively, the positive and negative terminations, and bringing their knuckles into contact. This battery had very slight decomposing power: the emission of gas from platinum points in acidulated water was not so great from the whole series of 500 as from 100, and from 100 not so great as H 9 260 GALYA.NIC OB VOLTAIC ELECTRICITY. from 40 ; this was evidently occasioned by the great resistance which the current had to encounter from the bad conducting power of the water with which the battery was charged; a resistance which it could not overcome, and consequently by far the greater portion of the Electricity generated was checked in its passage, while the small quantity that passed was brought to a high state of intensity. The spark obtained on bringing the ends of the terminal wires into contact was small, but brilliant, and when the ends were placed within the flame of a large candle the phenomena were very beautiful, the carbon being deposited in an arborescent form, and with great rapidity on the positive wire : while on the negative wire it was thrown down in much less quantity, though in a more compact form ; occasionally, indeed, filaments started from the latter like the quills on the back of a porcupine. We have seen few more beautiful experiments than this, it was first made by Mr. Gassiot ; the carbon on the positive wire assumes the form of every variety of tree and shrub, some particles starting up into the lengthened form of the poplar, whilst others spread laterally, assuming the appearance of fern : in less than a minute the flame of the candle becomes darkened by the quantity of pre- cipitated solid matter, which, as long as both wires Remain in the flame, goes on increasing. Occasionally the carbon on the wires comes into contact, when a bright spark is seen, and the arbo- rescent appearance for a moment vanishes. "When the finely divided carbon on the wires is brought into contact out of the flame, the epark is exceedingly brilliant, and four or five times as large as the spark from the clean wires, especially when hot; a snap also is heard. (346) Connected with a mica battery (consisting of twenty plates of mica, each four inches square), 100 pairs scintillated iron wire, and gave a pretty strong shock, the whole series gave a brilliant spark, accompanied by a pretty loud snap, and a powerful shock : it caused brilliant scintillations of iron-wire, deflagrated gold, silver and copper leaf, and exploded gunpowder ; it also charged a Leyden battery, containing about twelve square feet of glass, sufficiently high to giye unpleasant shocks. By soldering the terminal wires to two copper plates, about two inches square, and fixing them upright on a turned mahogany frame, under a glass shade, perpetual vibration, of a pith-ball j- of an inch in diameter, suspended by a filament of silk, was kept up rapidly between the plates, placed | of an inch apart. The motion of the ball has been kept up unceasingly for a fortnight and three weeks together. THE WATER BATTERY. 261 (347) A very extensive arrangement of the water battery is described by Mr. Gassiot (Phil. Trans. 1844). It consists of 3520 pairs or series of copper and zinc cylinders, each pair being placed in a separate glass vessel well covered with a coating of lac varnish. The glass cells are placed on slips of glass covered on both sides with a thick coating of lac. The 3520 cells, thus insulated, are placed on forty-four separate oaken boards, also covered with lac varnish, each board carrying 80 cells. The boards or trays slide into a wooden frame, where they are further insulated by resting on pieces of thick plate-glass similarly varnished. Notwithstanding these precautions, the insulation was still imperfect ; nor does perfect insulation seem attainable for any lengthened period when such an extended series is employed.. (348) In describing the results obtained with this gigantic battery, Mr. Grassiot considers the static and the dynamic effects separately. The static. On connecting the copper wires from the extreme cells with the plates a and b of the double electroscope, Fig. 139, the condensing plate p being removed, this instantly produces a con- siderable and steady divergence of the gold leaves ; and on applying the usual tests, the plate #, connected with the copper extremity, gave signs of vitreous, and a connected with the zinc, of resinous Electricity. If a was connected with one extremity of the battery, the other extremity being connected or not with the ground, the same general effects occurred; the divergence of the leaves cor- responded with the connection, and the leaves of b diverged by induction ; if in this state b was touched, and then removed from the influence of a, it was found charged with the opposite Electricity. Fig. 139. (349) The assumption of polar tension by the elements con- stituting the battery before the circuit wax completed was shown not only by the effect on the leaves of the electroscope when placed 262 GALVANIC OE VOLTAIC ELECTEICITT. within two or three inches of either end of the battery, or over any of the terminal cells, but by the production of a spark between the terminal wires through the space of voth o f an inch. When the double electroscope (Fig. 139) was included in the circuit, and the discs a and b closely approximated, the sparks became a stream of fire, which on one occasion were continued uninterruptedly day and night for upwards of five weeks. An experimenter standing on the ground could draw sparks from either terminal. (350) Dynamic Effects. For testing the presence of what is -usually termed the current, two trays containing 160 cells of the battery were removed and most carefully insulated ; a very delicate galvanometer was interposed between the zinc terminal of one tray, and the copper terminal of the other, but not the slightest deflec- tion of the needle took place, neither was there the least indication of the liberation of iodine when a piece of bibulous paper was saturated with iodide of potassium and substituted for the galvano- meter; the inference from which is, that there was no definite chemical action taking place in any cell of the battery, and that the electric or static effects take place before, or independently of, the actual development of the chemical effects. (351) The following instructive experiments were next made : A copper wire attached to the negative end of the battery was connected with the galvanometer, and this with the plate a of the double electroscope '(Fig. 13.9). A platinum wire attached to the positive end rested on a piece of bibulous paper moistened with iodide of potassium, another wire also resting on the paper was connected with the plate I of the electroscope. By a mechanical arrangement the plates could be approximated or separated as required. On approximating the plates so as to permit sparks to pass at intervals of about a second, a tremulous motion was imparted to the needle of the galvanometer, but when they were brought so nearly in contact as to permit the discharges to take place in quick succession, the needle was steadily deflected and iodine freely evolved ; proving that chemical action was taking place in each cell, and that the current is a collection or accumulation of discharges of Elec- tricity of tension. When 320 cells were employed, the greatest care being taken to insure perfect insulation, not the slightest evidence of any chemical action taking place in the cells could be obtained previous to completing the circuit, although there was sufficient intensity to elicit sparks through T ^th of an inch. (352) The following conclusions are deduced by Mr. Gassiot from his experiment with this extraordinary battery. 1st. That the elements constituting the voltaic battery assume polar tension THE COURONNE DES TASSES. 263 before the circuit is complete. 2nd. That this tension when exalted by a series of pairs is such, that sparks will pass between the termi- nals of the battery before their actual contact. 3rd. That these static effects precede and are independent of the completion of the voltaic circuit, as well as of any perceptible development of chemical or dynamic action. 4th. That the current may be regarded as a series of discharges of Electricity of tension succeeding each other with infinite rapidity. 5th. That the rise of tension in a battery occupies a measurable portion of time. 6th. That the static effects elicited from a voltaic series are direct evidence of the first step towards chemical combination or dynamic action. (353) It is easy to see that many inconveniences must attach to the pile of Volta, when the plates are numerous : in addition to the trouble of building it up, it is frequently rendered comparatively inactive by the moisture pressed out of the lower part by the weight of the upper : hence, the substitution of troughs and other arrange- ments. The most simple of these is Volta's " Couronne des tasses," shown in Fig. 140, which consists in a row of small glasses or cups, containing very diluted sul- Fig. 140. phuric acid, in each of which is placed a small plate of copper, about two inches square, and another similar sized plate of zinc, not touching each other, but so constructed that the zinc of the first glass may be in metallic communication with the copper of the second, the zinc of the second with the copper of the third, and so on throughout the series. By this arrangement, when glasses are employed, we can see what is going on in each cell : and if the zinc plates be amalgamated it will be observed that when the wires are connected, and consequently when a current is passing, all the copper surfaces rapidly evolve hydrogen gas, while the solution of the zinc proceeds quietly ; but, that when the connection between the extreme plates is broken, the evolution of gas ceases. Eighteen or twenty pairs of plates will decompose acidulated water rapidly, and thirty will give a distinct shock to the moistened hands. (354) Another arrangement of the plates is shown in Fig. 141, where they are represented as fixed in pairs into a trough of wood : this constitutes Cruickshank's battery. It is very convenient when solution of sulphate of copper is used as the exciting agent, which, as 264 GALVANIC OB VOLTAIC ELECTRICITY. Dr. Fyfe has shown (L. E. Phil. Mag. vol. xi. p. 145), increases the electro-chemical intensity of the electric current, as compared Fig. 141. Fig. 142. with that evolved by dilute sulphuric acid in the proportion of seventy-two to sixteen. An important modification was that sug- gested by the late Dr. Babington, and shown in Fig. 142 : the plates of copper and zinc, usually about four inches square, are united together in pairs by soldering at one point only ; the trough in which they are immersed is made of earthenware, and divided into 10 or 12 equal portions. The plates are attached to a strip of wood, and so arranged that each pair shall enlose a partition between them: by this means the whole set may be lifted at once into or out of the cells ; and thus, while the fluid remains in the trough, the action of the plates may be suspended at pleasure, and when corroded, easily replaced. The piece of wood to which the plates are attached should be well dried, and then varnished, in order to render it a non-conductor of Elec- tricity. When several of these troughs are to be united together, it is necessary to be cautious in their arrangement, as a single trough reversed will very materially diminish the general effect. Care must also be taken to insure perfect communication between the several plates. A battery of two thousand double plates, on this plan, was constructed several years ago for the Royal Institution ; the surface was one hundred and twenty-eight thousand square inches, and its power immense. (355) A great improvement in the construction of voltaic batteries was made by Dr. Wollaston, in 1815. It consisted in doubling the copper plate, so as to oppose it to both surfaces of the zinc, as shown WOLLASTON'S AND HARE'S BATTEB.Y. 265 in Fig. 143. A repre- Fig. 143. sents the bar of wood to which the plates are screwed; B B the zinc plates connected with the copper plates C C C, which are doubled over the zinc plates. Contact of the surfaces is prevented by pieces of wood or cork placed between them. Ten or twelve troughs, on this construction, form a very efficient voltaic battery. It appears, from the experiments of Mr. Christopher Binks (L. Sf IE. Phil. Mag. for July, 1837), that a still further extension of the copper would be attended with a considerable increase of power. He remarks that whatever may be the care taken to procure two plates of zinc of an uniform size and thickness, and however alike the attendant circumstances may be, no two couples will be found to give the same results in the same time when associated with cor- responding copper plates, and acted on by acids in the usual way. While one plate will lose perhaps ten grains ; another, apparently similar, will lose five or six grains ; and another, fifteen or sixteen in the same time : these differences he finds to be independent of accidental differences in the distances of the plates from one another : zinc plates he also finds to lose less the first time of immersion than during the second and third. (356) The arrangement shown in Fig. 144 is that of Professor Hare, of Philadelphia. It combines the advantages of the compound Fig. 144. 266 GALVANIC OR TOLTAIO ELECTRICITY. trough and the calorimotor or deflagrator. A voltaic series fixed in a trough is combined with another trough destitute of plates, and of a capacity sufficient to hold all the acid necessary for an ample charge. The trough containing the series is joined to the other lengthwise, edge to edge ; so that, when the sides of the one are ver- tical, those of the other must be horizontal. The advantage of this is, that by a partial revolution of the two troughs, thus united, upon pivots which support them at the ends, any fluid which may be in one trough must flow into the other, and, reversing the movement, must flow back again. The galvanic series being placed in one of the troughs, and the acid in the other, by a movement such as has been described, the plates may all be instantaneously subjected to the acid or removed from it. The pivots are made of iron, coated with brass or copper, as less liable to oxidizement. A metallic com- munication is made between the coating of the pivots and the galvanic series within. In order to produce a connection between one recipient of this description and another, it is only necessary to allow a pivot of each trough to revolve on one of the two ends of a strap of sheet copper. To connect with the termination of the series the leaden rods (to which are soldered the vices or spring forceps for holding the substances to be exposed to the deflagrating power), one end of each is soldered to a piece of sheet copper. The pieces of copper thus soldered to the leaden rods are then to be placed under the pivots, which are, of course, to be connected with the termination of the series ; the last-mentioned connection is conveniently made by Fig. 145. means of straps of copper, severally soldered to the pivots and the poles of the series, and screwed together by a hand-vice. Each pair consists of a copper and zinc plate, soldered together at the upper edge, where the copper is made to embrace the edge of the zinc. The three remaining edges are made to enter a groove in the wood, TAN MELSEN S BATTEEY. 267 Fig. 146. being secured therein by cement. For each inch in the length of the trough there are three pairs. In the series represented in Fig. 144 there are seven hundred pairs of seven inches by three, and in that shown in Fig. 145, one hundred pairs of fourteen inches by eight. The latter will deflagrate wires too large to be ignited by the former, but is less powerful in producing a jet of flame between two charcoal points, or in giving a shock. Dr. Hare exhibited two of these batteries at the meeting of the British Association at Bristol in 1836. Their power was very great in proportion to their size. (357) A useful ar- rangement of copper and zinc plates for a voltaic battery, the con- trivance of J. A. Van Melsen, of Maestricht, is shown in Fig. 146. The copper soldered to the zinc in each pair envelopes the zinc of the following pair, so as to be exposed to the two surfaces of this plate, but without being in contact with it. It dif- fers from "Wollaston' s pile in having the metallic plates much nearer to each other : they are only about & inch apart, and are maintained thus by small pieces of cork interposed between the plates of zinc and those of copper, whilst the plates of copper of the consecutive elements are separated by squares of glass of the same size as the plates. Fig. 147 repre- sents two elements of the series. All the pairs are placed in a kind of wooden frame, Fig. 148, carefully varnished, in which they are Fig. 147. Fig. 148. 268 GALVANIC OE VOLTAIC ELECTRICITY. easily retained without its being necessary to attach them by screws to a bar of wood, as is the case in the Wollaston combination. This arrangement presents the additional advantage of greatly facilitating the taking to pieces of the elements. The pairs united in the frame are at once immersed into the acidulated liquid contained in the trough : the plates of zinc are carefully amalgamated. Yan Melsen describes a battery* on this plan, which he constructed for the Maestricht University, consisting of 52 pairs, of which the plates of zinc are 6| inches wide, and 7-f- inches high. By its means a platinum wire eV of an inch thick, and 17| inches long, was reduced to incandescence with an extraordinary brilliancy, and fell into seven pieces, at the extremities of which the melted metal arranged itself in globules. A silver wire -gV of an inch thick, and 15 f inches long, became intensely red, and fell into fragments. An iron wire - 2 - - of an inch thick, and 15 f inches long, was speedily brought to the most vivid state of ignition, and was reduced into four pieces, in which, in many places, the melted iron was gathered into large globules. At the period of this latter experiment the battery had already been a long time in action, and was much weakened. When the battery was first excited, in order to produce a spark, the two slips of copper which serve as conductors were brought into contact. The parts in contact became immediately soldered together, so that it was necessary to employ a certain effort to separate them. (358) In a series of papers in the Philosophical Transactions for 1836, Professor Daniell describes his " constant" battery, and the cir- cumstances which led to its adoption. It has been remarked in the former part of this chapter that the evolution of hydrogen gas from the negative metallic surface in the common galvanic battery, greatly interferes with the development of available Electricity, for a considerable portion of the Electricity that is actually generated is probably spent in giving a gaseous form to the hydrogen of the de- composed water. But besides this, Mr. Daniell found that not only were the oxides of copper and zinc reduced by the nascent hydrogen at the moment of its formation, when salts of these metals were pur- posely dissolved in the fluid of the cells of the battery ; but the oxide of zinc itself, formed at the generating plates, was reduced at the con- ducting plates, which became ultimately so incrusted with metallic zinc as entirely to destroy the circulating force. The variations and progressive decline of the power of the ordinary voltaic battery are thus accounted for, since the transfer of the electro-positive metal must eventually cause two zinc surfaces to become opposed to each * Proceedings of the Electrical Society, p. 186. DANIELL'S CONSTANT BATTERY. 269 Fig. 149. WooZ other, the use therefore of the nitric acid in the battery charge is to remove the hydrogen by combination. Since, therefore, the hydro- gen has a two-fold injurious tendency, its absence altogether becomes a desirable object to effect. In a battery constructed by Mr. "War- ren De la Rue, this was done by the employment of sulphate of cop- per as the exciting agent, and in the arrangement of Professor Daniell the same is accomplished, but under circumstances rather different, as will presently appear. Fig. 149 represents a section of one of the cells of Daniell' s ori- ginal "sustaining" or "constant" battery; a b c d is a cylinder of copper, six inches high and three and a half inches wide; it is open at the top a b, but closed at the bottom, except a collar ef, one inch and a half wide, intended for the reception of a cork, into which a glass syphon tube g h ij k is fitted. On the top a b, a copper collar, cor- responding with the one at bottom, rests by two horizontal arms. Pre- viously to fixing the cork syphon tube in its place, a membranous tube, formed of part of the gullet of an ox, is drawn through the lower collar ef, and fastened with twine to the upper, Imno, and when tightly fixed by the cork below, forming an internal cavity to the cell communicating to the syphon tube, in such a way as, that when filled with any liquid to the level m o, any addition causes it to flow ' out at the aperture Jc. In this state, for any number of drops allowed to fall into the top of the cavity, an equal number are dis- charged from the bottom a, at the top of the zinc rod. Various connections of the copper and zinc of the different cells, may be made by means of wires proceeding from one to the other. In the con- struction of this battery, Mr. Daniell availed himself of the power of reducing the surface of the generating plates to a minimum. The effective surface of one of the amalgamated zinc rods, being less than ten square inches, whilst the internal surface of the copper cylinder to which it is opposed is nearly seventy-two inches. His principal objects were to remove out of the circuit the oxide of zinc, (which has been proved to be so injurious to the action of the common battery,) as fast as the solution is formed, and to absorb the hydrogen evolved upon the copper, without the precipitation of any substance that might deteriorate the latter. Port 270 GALVANIC OK VOLTAIC ELECTBICITY. (359) The first is completely effected by the suspension of the zinc rod in the interior membranous cell, into which the fresh acidulated water is allowed slowly to drop, from a funnel suspended over it, and the aperture of which is adjusted for the purpose ; whilst the heavier solution of the oxide is withdrawn from the bottom at an equal rate by the syphon tube. When both the exterior and interior cavities of the cell were charged with the same diluted acid, and connection made between the zinc and the copper, by means of a fine platinum wire, Tov of an i n(J h i n diameter, he found that the wire became red hot, and that the wet membrane presented no obstruction to the passage of the current. The second object is obtained by charging the exterior space sur- rounding the membrane, with a saturated solution of sulphate of copper, instead of diluted acid ; upon completing the circuit the cur- rent passed freely through this solution ; no hydrogen made its ap- pearance on the conducting plate ; but a beautiful pink coating of pure copper was deposited upon it, and thus perpetually renewed its surface. When the whole battery was properly arranged and charged in this manner, no evolution of gas took place from the generating or conducting plates, either before or after the connexions were com- plete ; but when a voltameter was included in the circuit, its action was found to be very energetic. It was also much more steady and permanent than that of the ordinary battery, but still there was a gradual but very slow decline, which Mr. Daniell traced at length to the weakening of the saline solution, by the precipitation of the copper, and consequent decline of its conducting power. (360) To obviate this defect, some solid sulphate of copper was suspended in muslin bags, which just dipped below the surface of the solution in the cylin- ders, which, gradually dissolving as the pre- cipitation proceeded, kept it in a state of saturation. This expedient fully answered the purpose, and Mr. Daniell found the current perfectly steady for six hours together. This arrangement he subsequently improved, by placing the salt in a perforated colander of copper, fixed to the copper collar. Tig. 150 represents a section of this additional arrangement. The colander with its central collar, rests by a small ledge upon the rim of the cylinder. The membrane is drawn through the collar, and turning over its edge is fastened with twine. After this alteration, the effective Fig. 150. DANIELL'S CONSTANT BATTEBY. 271 length of the zinc rods exposed to the action of the acid was found to be no more than four inches and a quarter. (Philosophical Transactions, 1836.) (361) The advantages of this battery over those of the previous construction are very great ; it secures a total absence of any wear in the copper ; it requires no nitric acid, but the substitution of materials of great cheapness, namely, sulphate of copper and oil of vitriol ; it enables us to get rid of all local action, by the facility it affords of applying amalgamated zinc, arid allows the replacement of zinc rods at a very trifling expense ; it secures the total absence of any annoy- ing fumes ; and, lastly, it produces a perfectly equal and steady current of Electricity for many hours together. With a battery of twenty cells arranged in a single series, twelve cubic inches of mixed oxygen and hydrogen gases may be collected from a voltameter in every five minutes of action, and when they are first connected in pairs, and afterwards in a series of ten, the quantity amounts to seventeen cubic inches. Eight inches of pla- tinum wire, T-o-o- of an inch in diameter, may be kept permanently red hot by the same arrangement, and the spark between charcoal points is very large and brilliant. Mr. Daniell even made it the source of the purest oxygen for laboratory purposes. To this end he constructed an oxygen cell, by substituting a plate of platinum for the rod of zinc, enclosing it in the membranous tube, which is closed at the upper end by a glass tube, bent in a proper form to deliver the disengaged gas, under a receiver. In this arrangement the hydrogen is absorbed as before, by the oxide of copper, but the oxygen, to the amount of eighty cubic inches per hour, is given off from the platinum. (362) Eig. 151 represents a single cell of the constant Fig. 151. battery, a cylindrical vessel of porous earth being substi- tuted, for the bladder diaphragm, which proved very inconvenient on account of its becoming rapidly corroded, and pierced by the sharp edges of the crystals of metallic copper, deposited on the copper plate. These porous jars were, it seems, first employed by Mr. Dancer,* of Liverpool, and they are now composed of the thinnest unglazed biscuit ware, a most excellent material. The battery, shown in Fig. 151, consists of a cylinder of copper, containing a tube of biscuit ware, which has a solid rod of zinc supported in its centre ; the cylinder is furnished with a perforated shelf, upon which a supply of crystals of sulphate of copper is placed, so that the battery being once charged, will maintain an equal action for many hours. * Golding Bird's Elements of Natural Philosophy. 272 GALYATaC OH YOLTAIC ELECTEICITT. Fig. 152. Pig. 152 represents a set of six of the above batteries, and Fig. 153 a set of ten large ones, the copper cylinders being eighteen or twenty-one inches high, with zinc rods, and porous earthen tubes in proportion. This forms a powerful voltaic arrangement, evolving eight or ten cubic inches of oxygen and hydrogen gases in the voltameter per minute, and heating to redness twelve or fourteen inches of fine iron wire. A series of thirty cells of the smaller size, six inches high, and three and a half inches in diameter, forms a very efficient battery for the lecture table ; it heats from eighteen inches to two feet of iron- wire, deflagrates mercury most brilliantly, and burns metallic leaves Fig. 153. r -V- vividly. The cells of the sustaining battery must be plentifully supplied with sulphuric acid, without which the power is but feeble. Mr. Daniell recommends a mixture of eight parts of water, and one of oil of vitriol, which has been saturated with sulphate of copper, for the copper cell, the internal tube being filled with the same acid mixture without the copper. The porous cells should be well soaked in dilute sulphuric acid for an hour or two before being used ; and after their removal from the battery they should be repeatedly rinsed, or allowed to soak for some time in warm water, to dissolve out all the metallic salt from their pores. If this be not attended to they will be soon destroyed. DANIELL' s CONSTANT BATTEBY. 273 (363) It was found by Mr. Daniell (Transactions of the Royal Society, May 30th, 1819) that the action of the constant battery is by no means proportional to the surfaces of the conducting hemi- spheres, but approximates to the simple ratio of their diameters ; and hence, he concludes that the circulating force of both simple and compound voltaic circuits increases with the surface of the con- ducting plates surrounding the active centres. On these principles he constructed a constant battery, consisting of seventy cells, in a single series, which gave between charcoal points, separated to a distance of three quarters of an inch, a flame of considerable volume, forming a continuous arch, and emitting radiant heat and light of the greatest intensity. The latter, indeed, proved highly injurious to the eyes of spectators, in which, although they were protected by grey glasses, of double thickness, a state of very active inflammation was induced ; the whole face of Mr. Daniell became scorched and inflamed, as if it had been exposed for many hours to a bright mid- summer's sun. The rays, when reflected from an imperfect parabolic metallic mirror in a lantern, and collected into a focus by a glass lens, readily burnt a hole in a paper at a distance of many feet from their source. The heat was quite intolerable to the hand held near the lantern. Paper steeped in nitrate of silver, and afterwards dried, was speedily turned brown by this light ; and when a piece of fine wire-gauze was held before it, the pattern of the latter appeared in white lines corresponding to the parts which it protected. The phenomenon of the transfer of the charcoal from one electrode to the other, noticed by Dr. Hare, but first observed by Professor Silliman, was abundantly apparent ; taking place from the zincode (or positive pole) to the platinode (or negative pole). The arch of flame between the electrodes was attracted or repelled by the poles of a magnet, according as the one or other pole was held above or below it ; and the repulsion was at times so great as to extinguish the flame. When the flame was drawn from the pole of the magnet itself, including the circuit, it rotated in a beautiful manner. The heating power of this battery was so great as to fuse with the utmost readiness a bar of platinum, one-eighth of an inch square ; and the most infusible metals, Buch as pure rhodium, iridium, titanium, the native alloy of iridium and osmium, and the native ore of platinum, placed in a cavity, scooped out of a piece of hard carbon, freely melted in considerable quantities. (364) Mr. G-assiot afterwards, with the view of ascertaining the possibility of obtaining a spark before the circuit of the voltaic battery is completed, prepared first 160, and then 320 series of the constant battery in half-pint porcelain cells, excited with solutions of 274 GALVANIC OB VOLTAIC ELECTBICITY. sulphate of copper and muriate of soda; but although the effects, after the contact had been completed, were exceedingly brilliant, not the slightest spark could be obtained. He mentions in his paper (Phil. Trans. 1840), that having been present at the experiments of Professor Daniell, above alluded to, he was induced to prepare 100 series of the large constant battery ; but although this powerful apparatus was used under every advantage, and the other effects produced were in every respect in accordance with the extent of the elements employed, still no spark could be obtained until the circuit was completed : even a single fold of a silk handkerchief, or a piece of dry tissue paper, was sufficient to insulate the power of the battery, though after the circuit had been once completed, it fused titanium, and heated sixteen feet four inches of No. 20 platinum wire. (365) Fig. 154 represents a single cell of Mr. $mee's voltaic arrangement, which, considering its advantages to arise from a mechanical help to the evolution of the hydrogen gas, he calls the chemico- mechanical battery. The circumstances which led the author to the construction of this admirable battery, are detailed in a paper inserted in the 16th volume of the L. and E. Phil. Mag. He observes, that " the influence of different conditions of surfaces is a subject which has escaped all experimenters, which is singular, as many must have noticed that in a circuit the greatest quantity of gas is given off at the corners, edges, and points. Following this hint, a piece of spongy platinum, consisting as it does of an infinity of points, was placed in contact with amalgamated zinc, when a most violent action ensued, so that but little doubt could be entertained of its forming a very powerful battery. The fragile nature of this material precludes it from being thus used, and therefore it was determined that another piece of platinum should be coated with the finely divided metal. This experiment was attended with a similar good result, and the energy of the metal thus coated was found to be surprising. After a variety of experi- ments, Mr. Smee found that silver plates were preferable for re- ceiving the precipitated platinum, and he gives the following directions for preparing them : " Each piece of metal is to be placed in water, to which a little dilute sulphuric acid and nitro-muriate of platinum is to be added. A simple current is then to be formed by zinc placed in a porous tube with dilute acid, when, after the lapse of a short time, the metal will be coated with a fine black powder of SMEE 8 CHEMICO-MECHA.IUCA.L BATTERY. 275 metallic platinum. The trouble of this operation is most trifling, only requiring a little time after the arrangement of the apparatus, which takes even less than the description." The cost is about sixpence a plate, of 4 inches each way, or 32 inches of surface. It is necessary to make the surface of the silver rough, by brushing it over with a little strong nitric acid, which gives it instantly a frosted appearance, and after being washed it is ready for the platinizing process ; but the finely divided platinum does not adhere firmly to very smooth metals. (366) The arrangement of the platinized silver battery will be immediately understood from the figure. A piece of the platinized silver has a beam of wood fixed on the top to prevent contact with the zinc, and is furnished with a binding-screw. A strip of stout and well amalgamated zinc, varying from one half to the entire width of the silver, is placed on each side of the wood, and both are held in their place by a binding-screw sufficiently wide to embrace the zincs and the wood. This arrangement is immersed in a jar or glass, con- taining dilute sulphuric acid (1 oil of vitriol and 7 water), and not the slightest effect is produced till a communication is made between the metals, when it instantly hisses and bubbles, and an active voltaic battery is obtained. For intensity effects it may be arranged as an ordinary Wollaston's battery with advantage, as shown in Fig. 155 ; the plates being raised from, and immersed into, the cells by Fig. 155. means of a winding apparatus ; or a series of glass tumblers may be connected together ; 10 or 12 form a very efficient battery, having a very elegant appearance, and well adapted for the lecture table, as the action in each cell may thus be very clearly seen. On account of the rapid removal of the hydrogen gas, there is, in this form of galvanic battery, but little tendency for the zinc to be deposited in a 276 GALVANIC OB YOLTAIC ELECTEICITT. metallic state upon the negative metal; nevertheless, when it is required in action for a long period, it may be advisable to separate the metals by a porous earthenware vessel ; or what answers the purpose equally well, by a thick paper bag, the joinings of which must be effected by shell-lac dissolved in alcohol. By these means the sulphate of zinc is retained on the zinc side of the battery. It may also be arranged as a circular disc battery, or as a Cruickshank, each cell being divided or not by a flat porous diaphragm ; but whatever arrangement is adopted, the closer the zinc is brought to the platinized metal the greater will be the power. In using the chemico-mechanical battery, it is important that no salt of copper, lead, or other base metal, be dropped into the exciting liquid, as by that means there is a chance of getting a deposit on the negative metal, copper in particular is apt to get precipitated, in which case the platinized silver should be immersed in dilute sul- phuric acid, to which a few drops of nitro-muriate of platinum should be previously added, by this process the baser metals are dissolved, and metallic platinum thrown down. The platinized silver battery has become a great favourite with the public; it is simple in its construction, remarkably manageable in its applications, and elegant in its appearance. It is soon set in action, and as quickly cleaned and put aside; and although it has not the constancy of the admirable battery of Daniell, or the won- derful energy of the battery of Grove, it may be kept in active operation for six, eight, ten, or more days, when a sufficiency of acid is supplied to it ; hence, its extensive application in the art of electro- metallurgy. (367) In a paper read before the B/oyal Academy of Sciences of Paris, April 15, 1839, Mr. Grove alludes to the powerful develop- ment of Electricity which would be occasioned by the combination of four elements instead of three ; as, by this means, we should have nearly the sum of chemical affinities instead of their difference. He then describes some experiments which he considers as possessing a high interest, as they prove a well-known chemical phenomenon to depend on Electricity, and thus tighten the link which binds these two sciences ; and they led to the discovery of a voltaic combination much more powerful than any previously known. Gold-leaf is well- known to be unaffected by either nitric or by muriatic acid alone, though in a mixture of the two acids the metal dissolves. Mr. Grove cemented the bowl of a tobacco-pipe (Fig. 156) into the bottom of a wine-glass ; into this he poured pure nitric acid, while the wine-glass was filled with muriatic acid to the same level ; in this latter acid two strips of gold-leaf were allowed to remain for an hour, GROVE S NITRIC ACID BATTERY. 277 at the end of which time they were found as bright as when first immersed. A gold wire was now made to touch the nitric acid and the extremity of one of the strips of gold leaf; this was instantly dissolved while the other strip remained unaltered. Two strips of gold-leaf were afterwards made the electrodes of a single pair of vol- taic metals in muriatic acid; the acid was decomposed, and the positive electrode was dissolved. (368) The action is evidently this : as soon as the electric cur- rent is established, both the acids are decomposed, the hydrogen of the muriatic acid unites with the oxygen of the nitric, and the chlorine attacks the gold. By the test of the galvanometer, the gold which was dissolved was found to represent the zinc of an ordinary voltaic combination; and reasoning on the phenomena, it occurred to Mr. Grove to substitute zinc for the gold ; and on submitting it to the test of experiment, he found that a single pair, composed ol a strip of amalgamated zinc, an inch long and a quarter of an inch wide, a cylinder of platinum, three quarters of an inch high, with a tobacco-pipe bowl, and an egg-cup, readily decomposed acidulated water. This little elementary battery is shown in Fig. 156. He then substituted for the muriatic acid caustic potash, and found the action equally powerful ; then, sulphuric acid, with four or five times its volume of water ; and, although with this the intensity was a little diminished, yet, from its exercising less local action on the zinc, he was eventually induced to give it the preference. Mr. Grove then constructed a small battery, of a circular shape, consisting of seven liqueur glasses and seven pipe bowls : the diameter was four inches, the height one inch and a quarter. This pocket battery gave about a cubic inch of mixed gases in two minutes. Fig. 156. Fig. 157. Fig. 157 represents a single cell of the nitric acid battery, the zinc 278 GALYANIC OB YOLTAIC ELECTEICITT. cylinder Z, open at both ends and divided longitudinally, is plunged into a glass or stoneware vessel containing dilute sulphuric acid, and the platinum plate P, Fig. 158, which is corrugated to give it greater surface, is immersed in a porous cell containing common nitric acid. The sectional diagram, Fig. 159, exhibits the mode of fitting Fig. 159. Fi - 158 - D i up four pairs of zinc and platinum foil plates, as recommended by the inventor. A IB C D is a trough of stoneware or glass, with partitions E E E dividing it into four acid proof cells. The dotted lines represent four porous vessels, of a parallelepiped shape, so much narrower than the cells as to allow the liquid which they contain to be double the volume of that which surrounds them ; the four dark central lines represent the zinc plates, and the five lines which curve under the porous vessels the sheets of platinum foil, which are fixed to the zinc by little clamp screws. Common rolled zinc, about one- thirtieth of an inch thick and well amalgamated, may be employed. On the zinc side, or into the porous vessels, is poured a solution of either muriatic acid diluted with from two to two-and-a-half water, or, if the battery be intended to remain a long time in action, of sulphuric acid, diluted with four to five water ; and on the platinum side, concentrated nitro-sulphuric acid, formed by previous mixture of equal measures of the two acids. The apparatus should be pro- vided with a cover containing lime, to absorb the nitrous vapour. Pig. 160 represents a battery of four cells arranged in series, and the first set of plates, removed from the porcelain trough D, showing very clearly the arrangement. A a is the bent zinc plate, B the insulated platinum plate in its porous cell, C the next platinum plate connected by means of a binding screw with the zinc at a. (369) On the evening of March 13, 1840, Mr. Grove delivered at the Eoyal Institution a lecture on voltaic reaction and polarization, GROVE'S NITRIC ACID BATTERY. Fig. 160. 279 and afterwards exhibited two batteries, constructed as above de- scribed. They were charged some time previously to the lecture and up to the period of its conclusion, remained in perfect inactivity, until the circuit was completed. One of these was arranged as a series of five plates, and contained altogether about four square feet of platinum foil: with this the mixed gases were liberated from water, at the surprising rate of 110 cubic inches per minute. A sheet of platinum, one inch wide and twelve inches long, was heated in the open air through its whole extent, and the usual class of effects was produced in corresponding proportion. "With the other arrangement, consisting of fifty plates, of two inches by four, arranged in single series, a voluminous flame of one inch and a quarter long was exhibited between charcoal points, which showed beauti- fully the magnetic properties of the voltaic arc ; and bars of differ- ent metals were instantly run into globules, and dissipated in oxide. These surprising effects were produced, it must be remembered, by a battery which did not cover a space of sixteen inches square, and was only four inches high. In a paper inserted in the 16th vol. of the L. and E. Phil. Mag., Mr. Grove describes a battery of thirty- six elements, each consisting of a square inch of platinum foil and zinc, and charged with concentrated nitric and diluted sulphuric acid, of each of which it took a pound, so that for the expense of about a shilling he could experiment for eight or nine hours without 280 GALVANIC OR TOLTAIC ELECTRICITY. fresh charge, with a battery which gave between charcoal points an arc of light 0*4 of an inch long. Professor Jacobi states, that he has readily fused iridium, with a nitric acid battery, after it has been at work a whole day. "With airlarrangement of 100 pairs of this bat- tery, the performances are brilliant in the extreme: the flame be- tween charcoal terminals is exceedingly yoluminous, and so brilliant as to be almost insupportable to the naked eye ; upwards of two feet of stout iron wire are heated to whiteness, and ultimately fused, and sulphuret of antimony is decomposed, and the metal brilliantly deflagrated. (370) The following explanation of the superior power of tbis battery is given by Mr. Grove (. and E. Phil. Mag., vol. xv., p. 289). " In the common zinc and copper battery the resulting power is as the affinity of the anion * of the generating electrolyte for zinc, minus its affinity for copper. In the common constant battery, it is as the same affinity plus that of oxygen for hydrogen, minus that of oxygen for copper : in the combination in question, the same order of positive affinities minus that of oxygen for azote. As nitric acid parts with its oxygen more readily than sulphate of copper, resist- ance is lessened, and the power correlatively increased. With regard to the second material question, that of cross precipitation ; in the common combination, zinc is precipitated on the negative metal, and a powerful opposed force created : in the constant battery, copper is precipitated, and the opposition is lessened : in this there is no precipitation, and consequently no counteraction. " If the operation of the battery be watched, the nitric acid changes colour, assuming first a yellow, then a green, then a blue colour, and lastly, becomes aqueous ; after some time nitrous gas, and ultimately hydrogen, is evolved from the surface of the platinum." In the paper from which the above extract is taken, Mr. Grove describes an arrangement of his battery, which, theoretically, should evolve 213 cubic inches of mixed gases per minute, or nearly seven and a half cubic feet per hour ; and, should the period arrive when Electricity shall supersede steam, and become a means of locomotion, the form of battery which he describes would probably be the best that could be devised. The excellent method of economising space, viz., by crimping the negative metal, was proposed by Mr. Spencer, of Liverpool : by this means, in a given space, the surface may be doubled without increasing the mean distance between the metals. (371) A substitution of carbon for platinum in the nitric acid bat- * The terms anion, cation, electrolyte, &c., will be explained in the next chapter. BUNSEN S CAKBON BATTERY. 281 tery was introduced by M. Bunsen {Archives de V Electricite, No. 7, 103 ; Poffff. Ann. vol. lv., p. 265). It had often been attempted to use for this purpose, graphite, and gas carbon, but the excessive cohesion of these substances, the difficulty experienced in working them, and still more the impossibility of making them into pieces of a given form and dimensions, prevented their adoption. Professor Bunsen, however, succeeded in surmounting the difficulty, by heating together in proper proportions, a mixture of well-baked coke and pit coal, both in fine powder. The mixture is heated over a moderate charcoal fire, in sheet iron moulds, or in the form of hollow cylinders, by introducing within the iron mould a cylindrical wooden box, and filling with the mixture the interval existing between the two walls. To render the porous mass compact, it is plunged into a concentrated solution of sugar, and then dried until the sugar has acquired a solid consistence. It is afterwards exposed, for several hours, to the action of a very intense white heat in a covered vessel. If discs are required they are cut out of a cubical block of the prepared carbon, and polished on a plate of grey stone. Bunsen's battery has the cylin- drical form of Daniell's, Fig. 161. Each carbon cylinder carries at Fig. 161. its upper part a collar of copper, carrying a strip of the same metal, by which it can be metallically connected by means of pincers with another metal strap soldered to the zinc cylinder in the adjoining cell; care must, however, be taken that the carbon cylinder is sufficiently high, that the part which carries the copper ring shall rise above the glass vessel, and consequently shall in no way come into contact with the nitric acid. It is difficult, however, to prevent this in consequence of the porosity of the carbon, and the ring must therefore be removed and washed every time the battery is used. The porous earthen cell is placed within the carbon cylinder, in which is contained the zinc element. A modification of this battery 282 GALVANIC OB VOLTAIC ELECTRICITY. was contrived by M. Bonijol (De la Rive's Treatise, vol. i. p. 46, Wal- ker's translation). He employs solid cylinders of carbon, in the tops of which are inserted stout copper rods covered in with a coating of wax, which prevents the nitric acid from ascending as far as the copper. In this arrangement the amalgamated zinc cylinder is outside the carbon, the latter being contained in a porous tube. According to Bunsen's experiments with equal surfaces, the powers of a platinum and carbon battery are nearly equal, and De la Rive says it is constant for a longer time. According to the experiments of MM. Liais and Fleury, the diaphragm of the Bunsen battery may be advantageously suppressed, and when the carbon is porous and impregnated with nitric acid, the conductibility of the pile is in- creased five-fold. To keep the carbon thus saturated with acid, it is surrounded by a glass cylinder, so as to keep an annular space be- tween, which is filled with nitric acid. The two cylinders are fasten- ed together at their lower ends with clay or cement ; this form of the nitric acid battery is much used in Germany and France, but has not found much favour in this country. (372) In the following series, the metals are arranged according to their electrical characters, and in the same relation to each other as zinc has to copper, so that any one of them operates as zinc to all those above it, and the more distant from one another any two metals stand in the series, the greater the galvanic action they will develop. Platinum. Mercury. Tin. Gold. Copper. Iron. Silver. Lead. Zinc. Hence, as we have already seen, a galvanic series of platinum and zinc is more powerful than one of copper and zinc ; and the latter again more powerful than one of lead and zinc, &c. It is not, how- ever, to be understood, that the power of any two metals in the table depends upon the number of intermediate ones, because a series of platinum and iron is much feebler than a series of copper and zinc ; although in the former case there are six intermediate metals, and in the latter there are only three. Charcoal and plumbago stand higher in the scale of electric bodies than platinum, so that a galvanic series of plumbago and zinc is very powerful, as we have just seen. Now, plumbago or graphite is a combination of iron and carbon, and the hint was thrown out by Jacobi,* that by adding more carbon to that which usually enters into the composition of cast-iron, we should probably arrive at a compound whose galvanic properties would be equal to those of platinum. The object may be obtained by a species * See his " Galvanoplastic Art," translated by Mr. Sturgeon, p. 4. 285 of cementation, or by re-melting cast-iron with additional carbon in closed vessels. (373) This high negative character of carbon enables us to under- stand how it is that cast-iron and zinc form so effective a voltaic circle, standing as iron and zinc do immediately next each other in the above series. It was Mr. Sturgeon who first formed a large bat- tery of these metals, (Annals of Electricity, vol. v.) It consisted of 10 cast-iron cylindrical vessels, and the same number of cylinders of amalgamated roDed zinc, with dilute sulphuric acid. The cast-iron vessels were 8 inches high and 3J inches in diameter. The zinc cylinders were the same height as the iron ones, about 2 inches in diameter and open throughout. The iron and zinc cylinders were attached in pairs to each other by means of a stout copper wire. The zinc of one pair was placed in the iron of the next, and so on through- out the series ; contact being prevented by discs of mill-board placed in the bottom parts of the iron vessels. With ten pairs in series, Mr. Sturgeon states, that he usually ob- tained fourteen cubic inches of the mixed gases per minute, and ten and a half cubic inches, when the battery has been in action an hour and a half. On one occasion he states, that he obtained twenty-two cubic inches per minute, fused one inch of copper wire, one-twenty- fifth of an inch in diameter ; kept four inches white hot, and eighteen inches red hot, in broad daylight. Eight inches of watch main- springs were kept red hot, and two inches white hot for several successive minutes. (374) A prodigious battery, probably the largest ever made, in which cast iron was the negative element, was constructed by Dr. Callan (Phil. Mag. vol. xxxiii. 49). It consisted of 300 cast-iron water-tight cells, each containing a porous cell and zinc plate 4 inches square ; 110 cast iron cells, each holding a porous cell and zinc plate 6 inches by 4 ; and 177 cast-iron cells, each containing a porous cell and a zinc plate 6 inches square. The entire battery consisted there- fore of 577 voltaic circles, containing 96 square feet of zinc and about 200 square feet of cast-iron. It was charged by pouring into each cast-iron cell a mixture of twelve parts of concentrated nitric acid, and eleven and a half of double rectified sulphuric acid, and by filling to a proper height each porous cell with dilute nitro-sulphuric acid, consisting of about five parts of sulphuric acid, two of nitric, and forty-five of water. In charging the entire battery, there were used about fourteen gallons of nitric and sixteen of sulphuric acid. (375) The first experiment made with this battery consisted in passing the current through a very large turkey, which was instantly killed, though it afterwards appeared that the whole discharge did 28-1 GALTAKIC OR YOLTAIC ELECT1UCITY. not take place through the body of the bird. In order to give the shock, a piece of tin-foil about four inches square was placed under each wing along the sides of the turkey, which were previously stripped of their feathers, and moistened with dilute acid. The foil was kept in close contact with the skin, by pressing the wings against the sides. The person who held the bird had a very thick cloth between each hand and the wing, in order to save him from the shock. When the discharge took place, the craw of the turkey was burst, and the hay and oats contained within it fell to the ground. When a copper wire in connexion with the negative end of the bat- tery was put in contact with a brass ring, connected with the zinc end a brilliant light was instantly produced. The copper wire was gradually separated from the brass ring, until the arc of light was broken. The greatest length of the arc was about 5 inches. The length of the arc of light between charcoal points could not be deter- mined, in consequence of the rapidity with which the charcoal burned away. At this period of the experiments several of the porous pots burst, and many of the copper slips became disconnected from the zinc cylinders, by the combustion of the solder ; notwithstanding, however, this interruption of the circuit, the arc of light between the coke points was about an inch long, and the heat of the flame defla- grated a file. (376) According to Dr. Callan's experiments a cast iron battery is about fifteen times as powerful as a Wollaston battery of the same size, and nearly as powerful and a half as Grove's, and hence the bat- tery above described is equal in power to a Wollaston battery con- taining more than 1400 square feet of zinc, or more than 13,000 four- inch plates, and to a Grove's containing 140 square feet of platina. The largest copper and zinc battery ever constructed was that made by the order of Napoleon for the Polytechnic school, and which con- tained 600 square feet of zinc ; and the most powerful Grove's, of which an account has been published, does not contain 20 feet of platina. Hence the above battery was more than twice as powerful as the largest Wollaston, and seven times as powerful as the largest Grove's ever constructed. Callan has since (Phil. Mag. Feb. 1854) proposed as the negative element, sheet tin coated with an alloy of lead and tin, in which the proportion of tin is not greater than that of lead, or of lead, tin, and a small quantity of antimony. On tin plates thus coated, dilute sulphuric acid scarcely exerts any action. It may be platinized like sheet silver, or it may be coated with borax, and will then answer nearly as well as if platinized, these plates are far cheaper and more durable than platinized silver. Iron, coated with an alloy of lead and INTENSITY OF THE ZINC-IEON CIECUfT. 285 tin, powerfully resists the action of oxidizing agents, especially if a little antimony be added. (377) This surprising intensity of the zinc-iron circuit is thus ex- plained by Professor Poggendorff (fog. Ann. vol. i. 255). "The intensity of the voltaic circuit depends on two things, electromotive force, and the resistance. It is the quotient from the division of the former by the latter. Now though the electromotive force between zinc and iron is smaller than between zinc and copper, silver, or platinum ; nevertheless the current of the zinc-iron circuit is stronger, because the iron offers less resistance to the transition of the current than copper does. The current, however, possesses less tension than that of the copper circuit ; or, in other words, it is weak- ened by the insertion of a foreign resistance in a greater proportion than that of the copper-zinc ; and it was found that the interposition of a wire of German silver, fifty feet long, weakened the current from the iron- zinc more than that of the copper-zinc ; and further it was supposed, that by a continued increase of the inserted resistance, it would be possible to make the current of the iron circuit, not only as weak, but even weaker than that of the copper circuit. Professor Poggendorff did not, however, succeed practically in effecting this. (378) Mr. Roberts has, however, offered an explanation (L. and E. jPM. Mag. vol. xix. p. 196), which Electricians in this country will probably be inclined to adopt in preference to that given by the learned German, who is one of the most powerful and strenuous sup- porters of the Contact Theory of Galvanism. It is simply, that copper, when immersed in an acidulated solution, does not retain so clean a metallic surface as iron does, when exposed to a like action. When a copper-zinc pair is placed in dilute sulphuric acid, an action takes place upon both the metals, and the balance of their affinities for the acid determines the direction of intensity of the electric cur- rent : but an obstacle to its free circulation arises by the resistance offered to its passage from the acid into the copper, because this metal has in a measure been acted upon by the acid, and its surface partially oxidated : but as the affinity of the base for the acid, under these circumstances, is not sufficient to cause the solution of the oxide, it therefore remains upon the surface of the copper-plate ; and as oxides are worse conductors of Electricity than their metallic bases, we have here a resistance presented by the oxidated surface to the entrance of the electric current into the copper plate. On the other hand, when an iron-zinc pair is immersed in dilute acid, we have also an action on both metals ; but the balance of affinities is here not so much in favour of the zinc, as when it is in combination with copper, and therefore the intensity or electromotive force gene- 286 OR YOLTATC ELECTRICITY. Fig. 162. rated by the iron-zinc, is not so great as in that of the copper-zinc battery : but the quantity circulated by the iron-zinc is greater, be- cause the surface of the iron not only oxidates, as did the copper, but in consequence of its greater affinity for the acid, this oxide becomes dissolved in the liquid, and it is thus removed from the surface of the metal, which remains purely metallic, bright, and far more fitted to conduct Electricity than would be the oxidated surface of a copper plate : it therefore offers less resistance to its entrance, and a larger quantity is thus circulated, although (in consequence of the balance of affinities) in less intensity, or electromotive force, by an iron-zinc than by a copper-zinc galvanic pair. | (379) Mr. Eoberts has introduced a form of battery on the above principles, which, as it has been muoh used for blasting purposes, we shall here describe (Proc. Elect, sec. p. 357). For general purposes it consists of twenty single negative iron, and twenty single positive zinc plates, of six inches square, arranged alternately in a frame of wood, and connected in the following peculiar manner. Let the numbers and z, Eig. 162 represent the zinc, and the letters and i, the iron plates ; let a and & be joined together, and stand free as a double terminal plate or pole, having of course a wire proceeding from them as a conductor ; then join 1 to c, 2 to d, 3 to e, and so on, terminating the other end of the battery by a positive plate, but having both its surfaces opposed to a negative plate, as is the con- dition of 4. In a battery of this construction there is no cross play of Electri- city, because two plates intervene between every positive plate, and the negative plate in metallic connection with it. Its power is very great in consequence of the closeness of the plates one to the other. It is very compact, and the absence of insulating cells renders it very convenient, as it can with no trouble be put into, or taken out of, its Fig. 163. box. The plates are put into a frame made of bars of wood, as in Eig. 163. The plates are kept from touching each other by strips or rods of wood about i or i of an inch square, and long enough to extend from the top to the bottom of each plate, one rod to each side of a plate ; or if the plate be very large, another in the middle. The box containing the exciting liquid (dilute sulphuric acid, one part acid to thirty of water) is put PECULIAR VOLTAIC CONDITION OF IEON. 287 together with white-lead joints, as these are perfectly water-tight. A battery of this construction is found to be far more powerful and constant in its action, than an equal sized one of copper and zinc. (380) While speaking of the electrical properties of iron, we may take the opportunity to detail some peculiar voltaic conditions of that metal. In the L. and E. Phil. Mag,, vols. ix., x., and xi., several papers on this curious subject will be found, by Schoenbein, Earaday, and others ; but we must confine ourselves here to the simple facts, referring to the original papers, for the theoretical explanations offered by the respective authors. If one of the ends of an iron wire be made red hot, and, after cool- ing, be immersed in nitric acid, sp. gr. 1'35, rfeither the end that has been heated, nor any other part of the wire will be affected, whilst acid of this strength is well known to act rather violently upon com- mon iron. By immersing an iron wire in nitric acid of sp. gr. 1*5, it becomes likewise indifferent to the same acid of 1'35. (381) The principal facts that the writer has experimentally verified, and the observations which he has made, in repeating Schoenbein' s experiments, are as follow : 1. It is well known, that when iron wire is immersed in nitric acid, sp. gr. 1-35, it is attacked with violence; but Sir John Herschel was, it seems, the first person who noticed that if the wire was associated with gold or platinum, it was quite inactive in acid of that strength. When an iron wire, one-sixteenth of an inch in diameter, was touched at a given point with platinum, and dipped into nitric acid, sp. gr. 1'37, it was not at all acted upon, but remained, for any length of time, perfectly bright. Once touching it in the acid with the platinum was sufficient to render it inactive when the platinum was removed, as long as it remained in the acid ; but if it were taken out, wiped, and then again immersed, action commenced, but soon again ceased. 2. If the acid was diluted with an equal bulk of water, platinum did not preserve iron wire from its action, even when coiled thickly round it : it appeared, indeed, rather to quicken the action ; but although it did not protect the iron under these circumstances, it did under others which will be mentioned presently. 3. If a wire, having been made inactive by being touched with a piece of platinum, was touched while in the acid with a piece of zinc, or another common iron wire, it was immediately thrown into violent action. Half of a wire, four inches long, was heated to dull redness, the blue tinge was visible through three inches : when the wire was cold, these three inches were quite inactive in nitric acid sp. gr. 1/39, the other end was active ; but when the heated end was made bright by filing, it was rendered active likewise. 288 GALVANIC OE VOLTAIC ELECTRICITY. 4. When an inactive wire and one that was active, were dipped into the same vessel, and made to touch at their parts above the fluid, action was excited in the indifferent wire. A common wire was made to touch an indifferent one, and both dipped into nitric acid, the indifferent one going in first : by this means the common wire was rendered indifferent; not being in the slightest degree acted on by the acid ; the second wire rendered indifferent a third ; the third, a fourth ; and so on. This experiment was found to succeed best with a wire that had been made indifferent by platinum ; but with care, it will answer equally well with a wire that has been made indifferent in the fire, the conditions appearing to be, perfect contact and gradual immersion. When these wires were taken out of the acid, and wiped, they always returned to the active state, but were again made indifferent by repeating the process. 5. A wire, polished very bright, and protected by platinum, was immersed in a solution of nitrate of copper in nitric acid, which acted very strongly on common iron, copper being deposited on the metal ; the protected wire remained, however, bright ; after a few seconds, the platinum was removed the iron became instantly as common iron; but when the platinum was allowed to remain in contact an hour or two, and then removed, the wire was left in the peculiar state, exhibiting the curious phenomenon of a piece of polished iron remaining untarnished in a solution of acid nitrate of copper. The wire thus inactive, on being touched with a piece of common iron was instantaneously rendered active, undergoing rapid solution and becoming covered with a coating of copper. 6. A piece of common wire was bent into the form of a fork, and slipped down an inactive wire into nitric acid, by which it was itself rendered inactive ; now, if another piece of wire was made to touch the fork, before being introduced into the acid, it was rendered itself inactive ; but if it was first thrown into action, and then made to touch either end of the fork, it threw all the wires into action, unless the first wire was one rendered inactive by the fire, in which case it was not thrown into action : the author could not, in this experiment, succeed in making one end of the fork active and the other passive, as described by Schoenbein ; he tried it many times, and in every case every wire was thrown into action, when either was touched in the acid with an active wire. 7. In order to observe the electrical phenomena, a galvanometer was used in the manner described by Faraday ; a platinum wire was connected with one of the cups, and the other end dipped into a glass containing nitric acid, of the above strength ; if now, an iron- wire w r as connected first with the other cup of the galvanometer, and then the other end immersed in the acid, it was inactive, and no deflection PECULIAR VOLTAIC CONDITION OF IRON. 289 of the needle took place ; but if it was first put into the acid, and afterwards connected with the galvanometer, it was active, and the needle was deflected in the same manner as if it had been zinc, i.e., whichever pole of the needle the wire of the galvanometer with which it was joined passed immediately over, moved west. 8. If an inactive wire was in this experiment substituted for the platinum, it acted precisely as platinum, both with regard to its pre- serving action and to the direction of the electrical current produced ; and here it may be observed that a striking proof is by this experi- ment afforded, that voltaic action is due to chemical action, for, when the wires were so arranged that both should be inactive, there was not the slightest electrical current evinced by the galvanometer ; but when either was thrown into action by being touched by a common wire, that wire became instantly as zinc, and the needle was strongly deflected. 9. If the iron- wire had a piece of platinum foil attached to it r the moment the circuit was closed, bubbles of gas made their appearance on the platinum, but none on the iron ; but when the platinum was removed the gas rose rapidly from the iron, which was not, however, thrown into action. 10. "When two glasses were filled with acid, and connected by a compound platinum and iron-wire, all the phenomena which took place in a single glass were observed, and the platinum or inactive wire in one glass exerted a protecting influence on the iron on the other, provided the communication was first made through the gal- vanometer ; a touch from a common wire also threw the iron into action, producing a strong electrical current ; the same was the case with three or four glasses connected by a compound wire. 11. When the acid w r as diluted, so as to have a sp. gr. of 1'2, platinum, as was before observed, could not protect iron from its action, neither when it was connected with the galvanometer did it, if the iron was dipped into the acid first ; but if it was first con- nected with the galvanometer, and then put into the acid, no action whatever took place in any length, of time, even when the platinum was removed ; but it always commenced when the inactive wire was once touched in the acid with a common iron-wire, or with a piece of copper ; but the iron thus made inactive did not as in strong acid possess the power of rendering other wire inactive, but was always thrown into action itself when a piece of common wire was substi- tuted for the platinum, whether it was connected with the galvano- meter first or not : the first wire in this case acted as platinum to the second. 12. "When two cups were employed, and connected by a piece of u 290 GALYANIC OE VOLTAIC ELECTRICITY. bent wire, and so arranged that the iron-wire should be active, on removing the connecting wire, and taking a fresh piece, if it were dipped first into the cup containing the iron- wire, and then the other end brought into the platinum cup, that end was inactive, and there was no passage for the electrical current, the needle of the galvano- meter being quiescent ; but when it was put into an active state the electrical current passed. Here then we have the iron made inactive without any metallic communication with the platinum, and when inactive it is found incapable of conducting, or, at any rate, it obstructs very considerably the passage of an electrical current. 13. If the iron-wire was inactive it was impossible to make either end of the connecting bent wire so, neither could it be, if it were dipped into the platinum cup first ; the action of nitric acid of this strength, viz. 1*2, is not an effervescing action, the iron is slowly dissolved ; when a piece of clean metal is dipped in it, it speedily becomes covered with a brown substance, which is gradually depo- sited, but dissolved by agitation. 14. When iron- wire is made the positive electrode of a galvanic battery, consisting of fifteen or twenty pairs, and dilute nitric, sul- phuric or phosphoric acid the subject of experiment, the negative electrode consisting of a platinum wire, if that pole be first dipped into strong nitric acid, and the circuit closed by a common iron-wire, that wire is immediately inactive, as regards the action of the acid on it, and it behaves precisely as platinum or gold in giving off oxygen from the decomposed water, while the platinum wire becomes sur- rounded with a greenish fluid (nitrous acid) : any other mode of closing the circuit will not answer, and if, while oxygen is given off from the iron-wire, it is once brought into contact with the platinum, it ceases to give off oxygen when separated from it, and will not again do so till exposed to the air. 15". The same phenomena occur with diluted acid, only hydrogen gas is given off in great abundance from the platinum, and as before, when the wires are made to touch in the liquid the iron ceases to perform the office of platinum, and becomes gradually dissolved; exposure to the air, however, brings it again to the peculiar state. 16. Diluted sulphuric and phosphoric acid exhibit similar pheno- mena, but the iron cannot be made inactive in muriatic acid with that or any other voltaic power ; it is always converted into muriate. When diluted nitric acid is employed, and when two cups are con- nected by a common iron-wire, the effects are the same ; and if the connecting wire be removed, and the cups joined by another, in the manner before described, that end in the cup in which the platinum negative electrode was, gives off oxygen, while the other end under- ELECTRICAL CHARACTER OF ALLOTS. 291 goes solution, and the iron-wire which acted the part of the positive electrode gives off oxygen also ; if four cups be employed, a similar result is obtained ; but the quantity of oxygen liberated diminishes as the number of elements increases : if either of the ends of the wires be now touched with a common iron-wire, its peculiar state is destroyed, and it becomes as the other end, while the oxygen it gave off appears to be divided between the two inactive wires ; and if the iron-wire in immediate connection with the battery be made active, and all the others but the middle one made active also, then the middle wire performs the office of the positive electrode. Much more might be said on this curious subject ; the above must, however, suffice here, and those who are anxious to see the matter fully discussed may be referred to the 9th, 10th, and llth volumes of the L. and E. Phil. Mag. A voltaic battery, consisting of zinc and passive iron, or of active and passive iron, in either case excited after the manner of a Grove's battery, was described in a commu- nication from Professor Schoenbein to the London Electrical Society. The power of the arrangement is said to be very great. Its economy is also a matter of importance, and the value of the salt produced (sulph. ferri) is not to be overlooked. (382) The electrical character of an alloy of metals does not, it must be observed, always take a place between bhose metals of which it consists, but more frequently it stands either much higher or much lower in the series. Such is the case with brass, which mostly acts in galvanic arrangements, either quite as well, or even better than copper, which is one of its constituents. (Jacobi.) On the other hand, either amalgamated zinc, or a compound of zinc and quicksilver, acts even better than zinc alone, although quicksilver itself stands high in the galvanic series. A compound is described by Jacobi, which is still better than quicksilver and zinc ; it consists of 38 parts of quicksilver, 22 parts of tin, and 12 parts of zinc. Nevertheless, he observes, in such alloys as these, where too much quicksilver is introduced, the disadvantage is, that they are extremely brittle, and have but little coherence. (383) The inaction of amalgamated zinc in acidulated water is considered by Mr. Grove (L. and E. Phil. Mag., vol. xv. p. 81) as being the effect of polarization; but of one which differs from ordinary cases of polarization, in that the cations of the electrolyte, instead of being precipitated on the negative metal, combine with it, and render it so completely positive, that the current is nullified, and not merely reduced in intensity as in other cases. The experiments made by Mr. Grove, to verify this idea, are curious and striking. u 2 292 GALVANIC OE YOLTAIC ELECTRICITY. 1. Half the surface of a strip of copper was amalgamated and immersed with a strip of zinc in water, acidulated with >th of sulphuric or phosphoric acid ; on making the plates touch there was a rapid evolution of gas from the unamalgamated part of the copper, while only a few detached bubbles appeared on the amalgamated portion. 2. A large globule of mercury was placed in the bottom of a glass of acidulated water, and by means of a copper wire, the whole surface of which was amalgamated, it was made to communicate with one extremity of a galvanometer, while a strip of amalgamated zinc, im- mersed in the same liquid, communicated with the other extremity ; at the instant of communication an energetic current was indicated, which, however, immediately diminished in intensity, and at the end of a few minutes the needle returned to zero : scarcely any gas was evolved, and of the few bubbles which appeared, as much could be Detected on the surface of the zinc as of the mercury. 3. With the same arrangement a strip of platinum, well amal- gamated, was substituted for the mercury. In a few minutes the current became null or very feeble, and if, after the cessation of the current, the zinc was changed for unamalgamated platinum, this latter evolved torrents of hydrogen, and the needle indicated a violent current in a contrary direction. 4. With things arranged as in 2, sulphate of copper was substi- tuted for acidulated water, a constant current was produced, and copper was precipitated on the mercury, as long as crystals of the sulphate were added to the solution. (384) In these experiments it is shown that mercury, which, in its normal state, is well known to be inefficient as the positive metal of a voltaic combination, is in many cases equally inefficient as a nega- tive metal from its faculty of combining with the cations of electro- lytes, which renders it equally positive with the metal with which it is voltaically associated, and the opposed forces neutralize each other. But if, as in 4, the cation of the electrolyte is not of a highly electro-positive character, the zinc (or other associated metals) retains its superior oxidability, and the voltaic current is not arrested. (385) The application of these experiments to the phenomena presented by amalgamated zinc, Mr. Grove thinks evident ; all the heterogeneous metals with which the zinc may be adulterated, and which form minute negative elements, being amalgamated, become by polarization equally positive with the particles of zinc, and conse- quently without the presence of another metal to complete the circuit, all action is arrested as in the case of pure zinc. The fact of amalgamated zinc being positive with respect to common zinc, of LESSOR'S BICHROMATE OF POTASH BATTERY. 293 its precipitating copper from its solutions, and other anomalies, are also explained by these experiments. (386) A form of voltaic battery, the arrangement of Dr. Leeson, in which, instead of sulphate of copper, a solution of bichromate of potash (ten parts water to one of bichromate), is employed as the exciting agent, is shown in Pig. 164. A A is a vertical, and B B a horizontal section of the wooden trough rendered water-tight. It is grooved at the sides, as seen in B B, so as to receive the zinc plates Z Z : between each pair is a groove to receive the flat porous cell, containing the copper plate C. Each zinc plate rests on a piece of zinc, which forms as it were the bottom of a cell : one of each pair of zinc plates, Z, is higher than the other, as seen in the vertical section, for the convenience of forming the connection, which is effected by binding over the copper plate, and attaching it to the tall zinc one by a small binding screw, as seen at e. The trough is charged with acid solution, and the porous cell containing the copper with the solution of bichromate. Each trough contains ten or twelve cells. By having the zinc which surrounds the copper in three pieces, the trouble of binding is avoided, and it is much easier of manipulation. It will be seen by this, that the expensive plan of employing actual partitions between the respective pairs is avoided, each arrangement of zinc forming its own cell. It is scarcely requisite to mention, that the zinc is not of necessity to be accurately fitted in its groove, under the idea of making each cell water-tight, the fallacy of this idea having been long since developed. (387) A beautiful little voltaic battery, and one of great power in which potassium is the positive element, is described by Mr. G-ood- nian, (Memoirs, Manchester Lit. and Phil. Soc. vol. viii.) A wine glass was filled with dilute sulphuric acid, and in this was immersed 294 GALVANIC OB TOLTAIC ELECTEICITT. a plate of platinum just below the surface of the liquid. At the extremity of a short length of glass tubing a piece of membrane was tied, so as to close up its lower end, which was by an appropriate stand so fixed that the membrane or diaphragm should come in contact with the surface of the acidulated water immediately above the immersed plate of platinum. Into this tube was dropped a globule of mercury, which lying upon the membrane would serve to amalgamate and keep in that condition the piece of potassium destined for that situation. The tube was then filled with mineral naphtha, so that the metal could be raised with pleasure into a medium in which it would remain perfectly quiescent, and would only suffer loss when required to do so. The potassium, weighing about half a grain, was now screwed upon the " topped" extremity of a copper wire, upon which a shoulder or button of wood was also screwed, about one-sixteenth of an inch from its extremity, to prevent the wire perforating the potassium too far, and coming itself in contact with the diaphragm. This wire was in metallic communi- cation with the immersed platinum, and for the purpose of raising or depressing the potassium in its cell, a moveable mercury cup formed the medium of communication. From this the potassium hung sus- pended by its wire, upon which a small weight was affixed to insure the continuous contact and close application of this metal to the membrane. With the apparatus thus arranged, it was found that potassium became a very manageable element in a voltaic battery, and on lowering it into contact with the diaphragm a continuous current of 45 to 50 was observed by the aid of an intervening galvanometer. Acidulated distilled water was energetically de- composed by this miniature galvanic battery, and Mr. Goodman even succeeded in producing a sensible and measurable deflection gold leaf with a single cell. (388) A most extraordinary and perfectly novel voltaic battery, in which the active ingredients are gases, was described by Mr. Grove (Phil. Mag. Dec. 1842 ; Phil. Trans, part ii., 1843 ; and part ii. 1845). It consisted originally of a series of 50 pairs of platinized platinum plates, each about a quarter of an inch wide, enclosed in tabes partially filled alternately with oxygen and hydrogen gases, as shown in Fig. 165. The tubes were charged with dilute sulphuric acid, sp. gr. 1*2, and the following effects were produced : 1st. A shock was given which could be felt by five persons joining hands, and which when taken by a single person was painful. 2nd. The needle of a galvanometer was whirled round, and stood at about 60; with one person interposed in the circuit it stood at 40, and was slightly deflected when two were interposed. GROVE'S GAS BATTERY. 295 Fig. 165. 3rd. A brilliant spark visible in broad daylight was given between charcoal points. 4th. Iodide of potassium, hydrochloric acid, and water acidulated with sulphuric acid, were severally decomposed : the gas from the decomposed water was eliminated in sufficient quantity to be collected and detonated. The gases were evolved in the direction denoted in the figure, i. e., as the chemical theory and experience would indicate, the hydrogen travelling in one direction throughout the circuit, and the oxygen in the reverse. It was found that twenty-six pairs were the smallest number which would decompose water, but that four pairs would decompose iodide of potassium. oth. A gold leaf electroscope was notably affected. When the tubes were charged with atmospheric air, no effect was produced, nor was any current determined when the gases employed were carbonic acid and nitrogen, or oxygen and nitrogen: when hydrogen and nitrogen gases were used, a slight effect was observed, which Mr. Grove is inclined to refer to the oxygen absorbed by the liquid when exposed to the air, which, with the hydrogen, would give rise to a current. The voltaic current generated by this battery is attributed by Mr. Grove to chemical synthesis, of an equal but opposite kind, in the alternate tubes, at the points where the liquid, gas, and platinum meet, and the object of covering the platinum with the pulverulent deposit was to increase the number of these points, the liquid being retained upon the surface of the platinum by capillary attraction. Schoenbein considers (Phil. Mag., March, 1843) that the oxygen does not immediately contribute to the production of the current, but that it is produced by the combination of hydrogen with water, a suboxide of hydrogen being formed. In consequence of this opinion, Mr. Grove undertook a searching investigation into the phenomena, and the following are some of his principal results. 296 GALVANIC OR YOLTAIC ELECTRICITY. (389) In order conveniently to examine the gases either after or during an experiment, without changing the liquid in which the tubes are immersed, the form of cell shown in Fig. 166 was adopted. Fig. 166. Fig. 167. i c d e is a parallelepiped glass or stone- ware vessel, such as is commonly used for the outer cells of the nitric acid batteries. The tubes are cemented into pieces of wood a b, a c, and can, with the wood, be separately detached from the trough, as shown in Fig. 167. At the aperture or space a , between the tubes, there is just om for a finger to enter, close the orifice of either tube, and thus detach it from the apparatus. The platinum foil is turned up round the edge of the tube, and brought into connection with a binding-screw screvred into the wood. In Fig. 168 a battery and five cells of this Fig. 168. construction, each containing about 1^ cubic inch, is represented as charged with oxygen and hydrogen, connected with a decomposition of water apparatus. With a battery of 50 of these cells there was but a trifling difference in the rise of the liquid in all the cells, and the rise of gas in the decomposing apparatus was so directly propor- tional that an observer unacquainted with the rationale of the voltaic battery would have said the gases from the exterior cells were con- veyed through the solid wires, and evolved in the voltameter. (390) In order to decide the question whether the points of action were, where the liquid, gas, and platinum met, or whether the gases entered into solution first, and were then electro-synthetically combined by the immersed portion of the platinum, a series of ten cells was constructed in which the Dlatinum reached onlv to half the GROVE'S GAS BATTERY. 297 height of the tubes. This was charged with oxygen and hydrogen, so that the liquid just covered the extremities of the platinum. Here, it is evident that the gases must enter into solution before the platinum could affect them, and the result was that a highly sensitive galvanometer was but slightly affected, but when a little gas was added so as to expose the platinum to a gaseous atmosphere, a con- siderable current was developed, proving that it is at the exposed por- tion of the platinum plate that the real work of the battery is carried on. (391) The analogy of the hydrogen tube to the zinc plate of an ordinary voltaic battery was beautifully shown by arranging a single pair with oxygen and hydrogen, and a second pair with hydrogen in one tube, and dilute sulphuric acid in the other ; the oxygen of the first was metallically connected with the hydrogen of the second, and the hydrogen of the first with the liquid of the second hydrogen gas immediately rose from the platinum. In short, though it required four pairs to decompose water with .immersed platinum elec- trodes, yet the platinum in the atmosphere of hydrogen being analogous to an oxidable anode, one pair was with this assist- ance sufficient to decompose water. The analogy of the gaseous and metallic voltaic batteries was further shown by charging three cells alternately with hydrogen and nitric acid; water was decomposed, the gaseous hydrogen deoxidizing the nitric acid in this arrangement, just as nascent hydrogen does in the metallic battery. A battery of two cells charged with hydrogen and dilute sulphuric acid was powerless in an atmosphere of pure nitrogen, a fact conclusive against the view which regards hydrogen and water as the efficient agents in the gas battery. (392) Mr. Grove describes a series of experiments with other gases : the following is a general account of his results with ten cells charged in series. Oxygen and protoxide of nitrogen No effect on iodide of potassium. Oxygen and deutoxide of ditto . Very slight, soon ceasing. Oxygen and olefiant gas . . Very feeble, but continuous. Oxygen and carbonic oxide . . { Notable effects ; Sli S ht s y m P toms > (^ of decomposing water. Oxygen and chlorine . ( Considerable action at first, ' | scarcely perceptible in 2 4 hours . Chlorine and dilute sulphuric acid About the same. Chlorine and hydrogen . ( PowerM effects - Two cells de " ( composing water. ilorine and carbonic oxide. . ( Go0(L Ten cells decomposing ( water, "hlorine and olefiant gas . . Feeble. 298 GALVANIC OR VOLTAIC ELECTRICITT. The most interesting practical result of Mr. Grove's experiments on the gas battery will probably be its application to eudiometric purposes. " Two narrow cubic inch tubes of seven inches long were carefully graduated into 100 parts. These .were immersed in separate vessels of dilute sulphuric acid, and filled with atmospheric air exactly to the extreme graduation ; the water-mark within the tube was examined when exactly at the same level as the exterior surface of the liquid : folds of paper were used to protect them from the warmth of the hands and thus prevent expansion ; the barometer and thermometer were examined, and every precaution taken for accurate admeasurement. One of these tubes was left empty, in order to ascertain and eliminate from the result the effect of solubility. Into the other was placed a slip of platinized platinum foil, one quarter of an inch wide. This strip of foil was connected by a platinum wire with another strip placed in a tube of hydrogen and inserted in the same vessel. After the circuit had been closed for two days, the liquid was found to have risen in the graduated tube 22 parts out of the 100 ; in the tube placed by its side, it had risen one division. The tubes were allowed to remain several days longer, but no further alteration took place. This analysis gives therefore 21 parts in 100 as the amount of oxygen in a given portion of air." In these experiments, it must be observed that only a single pair of the gas battery can be used, as, if more be employed, the electrolyte is likely to be decomposed, and gas added to the compound. Another useful application of this interesting battery is the means which it affords of obtaining perfectly pure nitrogen. All the oxygen in a given quantity of air may be abstracted, as well as the free oxygen contained in the liquid which confines it, and by subsequently introducing into the tube a little lime water, the trifling quantity of carbonic acid may be removed. With respect to the theory of the gas battery, Mr. Grove says : " Applying the theory of Grotthus to the gas battery, we may suppose that when the circuit is completed at each point of contact of oxygen, water and platinum in the oxygen tube, a molecule of hydrogen leaves its associated molecule of oxygen to unite with one of the free gas ; the oxygen thus thrown off unites with the hydrogen of the adjoining molecule of water, and so on, until the last molecule of oxygen unites with a molecule of the free hydrogen: or we may conversely assume that the action commences in the hydrogen tube." . . . . " There are one or two other theoretical points as to which the gas battery offers ground of interesting speculation; the contact theory is one. If my notion of that theory be correct, I am at a loss GROVE'S GAS BATTEEY. 299 to know how the action of this battery will be found consistent with it, if indeed the contact theory assumes contact as the efficient cause of voltaic action ; but admit that this can only be circulated by chemical action, I see little difference, save in the mere hypothetical expression, between the contact and chemical theories ; any con- clusion which would flow from the one, would likewise be deducible from the other. There is no observed sequence of time in the phenomena, the contact, or completion of the circuit, and the elec- trolytical action are synchronous. If this be the view of contact theorists, the rival theories are mere disputes about terms ; if, how- ever, the contact theory connects with the term contact an idea of force which does or may produce a voltaic current, independently of chemical action, a force without consumption, I cannot but regard it as inconsistent with the whole tenor of voltaic facts and general experience." In a postscript appended to this paper, Mr. Grove details some further experiments, the theory of which seerns at present by no means clear. On repeating the eudiometrical experiment already .described, with an apparatus in which the external air was shut out, it was found, after the expiration of three days, that the volume of gas in the air-tube which had previously contracted had now increased and continued to do so. Mr. Grove at first believed that nitrogen was decomposed; he subsequently, however, found that the increase was due to the addition of hydrogen, and that in order to obtain the effect with certainty two points were essential ; first the exclusion of any notable quantity of atmospheric air from solution ; and secondly, great purity in the hydrogen ; it hence becomes necessary in order to ensure accuracy in eudiometric experiments, either purposely to use common hydrogen, or to employ closed vessels the tubes of which are long and narrow ; and having first charged the tubes with hydrogen and atmospheric air, to allow these to remain in closed circuit until all the oxygen is abstracted, and a little hydrogen added by the electrolytic effect to the residual nitrogen ; then to substitute oxygen for the original hydrogen, which will in its turn abstract hydrogen from the nitrogen, and leave only pure nitrogen. This, Mr. Grove says, he has frequently done with perfect success. The only way at present of accounting for the fact disclosed in these last experiments, appears to be, to regard mixed gases as in a state of feeble chemical union, the effect being produced by the affinity of the nitrogen or carbonic acid for the hydrogen; the affinity of the oxygen of the water being balanced between the 300 GALYANIC OE VOLTA.IC ELECTRICITY. hydrogen in the liquid and that in the tube, would enable the resultant feeble affinity of the nitrogen for hydrogen to prevail. Mr. Grove does not, however, venture a positive opinion ; the fact, as he says, " that gaseous hydrogen should abstract oxygen from "hydrogen without the latter forming any combination, being so novel, that attempted explanation is likely to prove premature." (393) The form of gas battery employed by Mr. Grove in his later experiments, and which possesses the great advantage of entirely preventing the interfering action of the atmosphere, is shown in Fig. 169. In this battery, oxygen and deu- toxide of nitrogen gave a continuous current, and a permanent deflection of the galvano- meter was produced, when a piece of phos- phorus was suspended in the nitrogen tube, the product being phosphorous acid ; and the curious instance was exhibited of the employ- ment of a solid, insoluble non-conductor, and the existence of a continuous voltaic current, and of a true combustion ; the combustible and the "comburant" being at a distance: phosphorus burned by oxygen which is sepa- rated from it by strata, both of water and gas, of indefinite length. A current was likewise produced by sulphur in nitrogen and oxygen, the sulphur being contained in a little capsule of glass that could be heated by a small hoop of iron with a handle as . shown in the figure, the moment the sulphur entered into fusion, the needle of the galva- nometer moved, and it continued deflected during the whole time it remained in the fused state. Various other substances, such as camphor, oil of turpentine, oil of cassia, alcohol, ether, &c., were thus tried, and all produced notable voltaic effects, and a field has thus been laid open for ascertaining the voltaic relations and quantitative electro-chemical combinations of solid and liquid substances, which from their physical characteristics have not hitherto been recognized in lists of the voltaic relations of different substances, and conse- quently formed to a certain extent a blank in the chemical theory of the voltaic pile. (394) Ohm's law. In none of the various forms of the hydro- electric battery do we obtain in the form of a current the whole of the Electricity excited by the chemical action on the positive element. The amount of Electricity realized, or, in other words, the force of the current, is equal to the sum of the electromotive forces, OHM'S LAW. 301 divided by the sum of the resistances in the circuit ; thus, let F denote the actual force of the current, E the electromotive force, and E- the resistance. By the term electromotive force, is to be understood the cause which in a closed circuit originates an electric current, or in an unclosed one gives rise to an electroscopic tension. According to the chemical theory, it is the affinity between the active metal and the element of the liquid compound on which it acts. By the term resistance is signified the obstacle opposed to the passage of the electric current by the bodies through which it has to pass ; it is the inverse of what is usually called their conducting power. (395) The different causes which influence the quantity of Electri- city obtained in a voltaic circuit have been investigated mathematically by Professor Ohm, of Nuremberg ; a translation of whose paper is to be found in Taylor's Scientific Memoirs, vol. ii., and his formulae, which have been verified by the researches of Daniell and Wheat- stone, may be regarded as the basis on which all investigations that have since been made relative to the force of the voltaic current have been founded. (396) By increasing the number of elements of a voltaic series we increase the tension, urging the Electricity forward, but then at the same time we increase the amount of resistance offered by the liquid portion of the circuit ; so that, provided in both cases the circuit be completed by a perfect conductor as a stout copper wire, we obtain precisely the same results in both cases, the electromotive forces and the resistances being increased by an equal amount, for, E n~E E ntt But it is very different when the circuit is closed by an imperfect conductor : for a resistance which might weaken to a considerable T^ m Tf extent -=r- might not sensibly diminish - ^- and in accordance t n C with this we find that when great resistances have to be overcome, it is necessary to increase the number of elements in proportion to those resistances. (397) The resistances to the circulation of available Electricity are of a two-fold character. We have first E., the resistance in the battery cell, which varies directly with the distance between the plates and inversely as the area of the efiicient section of the liquid, and which Daniell has shown to be the mean of that of the opposed faces of the metals ; and we have r, the specific resistance of the 302 GALVANIC OR VOLTAIC ELECTRICITY. conducting wire. The amount of work which a battery is capable of performing may be expressed therefore by the fraction, -P - E - R + r In a single circle closed by a good conductor, the value of r nearly vanishes, and the force of the current is proportional to the super- ficies of the metallic elements. In a compound circle, the following general formula expresses the force of the current when the circuit is completed by a connecting wire : n E n ED rl .'* ~S~ + ~S~ where the other letters signifying the same as before. D = The distance between the plates. S = The section of the plates in contact with this liquid. Z = The length of the conducting wire. S = The section of the same. n = The number of element. This formula leads to the following general law. (Wheatstone, Phil. Trans. 1843.) 1. " The electromotive force of a voltaic circuit varies with the number of the elements, and the nature of the metals and liquids which constitute each element, but is in no degree dependent on the dimensions of any of their parts. 2. " The resistance of each element is directly proportional to the distances of the plates from each other in the liquid, and to the specific resistance of the liquid ; and is also inversely proportional to the surface of the plates in contact with the liquids. 3. " The resistance of the connecting wire of the circuit is directly proportional to its length, and to its specific resistance, and inversely proportional to its action-. " $'4BfcJuLX> - vv* 1 (398) The method employed by the German electricians for measuring the strength of the hydro-electric current, was by ob- serving its effect on the magnetic needle, the force of the current being estimated from the angle of deviation. When the gal- vanometer consists merely of a single stoat copper wire placed immediately under, and parallel to, a common variation needle, the force of the current acting on the needle was determined by Kamtz to be proportional to the product of the sine into the tangent of the angle of declination ; and to save the trouble of making a calculation for each experiment, the following table (Peschel's Elements of Physics] was drawn up by Pohl, from which the proportional force INTENSITY OF THE VOLTAIC CT7BBENT. 303 of any current may be ascertained for any declination given in degrees from 1 to 90. Deflec- tion of Needle. Intensity of Current. Deflec- tion of Needle. Intensity of Current. Deflec- tion of Needle. Intensity of Current. 1 o-oooi 31 0-1016 61 0-5179 2 0-0004 32 0-1087 62 0-6451 3 0-0009 33 0-1161 63 0-5740 4 0-0016 34 0-1238 64 0-6049 5 0-0025 35 0-1328 65 0-6380 6 0-0036 36 0-1402 66 0-6735 7 0-0049 37 0-1489 67 0-7119 8 0-0064 38 0-1579 68 0-7533 9 0-0081 39 0-1673 69 0-7983 10 o-oioo 40 0-1770 * 70 0-8475 11 0-0122 41 0-1872 71 0-9014 12 0-0145 42 0-1978 72 0-9608 13 0-0170 43 0-2088 73 1-0268 14 0-0198 44 0-2202 74 1-1004 15 0-0228 45 0-2321 75 1-1833 16 0-0259 46 0-2445 76 1-2775 17 0-0293 47 0-2574 77 1-3854 18 0-0330 48 0-2709 78 1-5106 19 0-0368 49 0-2850 79 1-6577 20 0-0409 50 0-2997 80 1-8334 21 0-0452 51 0-3150 81 2-0471 22 0-0497 52 0-3313 82 2-3133 23 0-0544 53 0-3479 83 2-6536 24 0-0594 54 0-3653 84 3-1061 25 0-0647 55 0-3840 85 3-7378 26 0-0702 56 0-4035 86 4-6830 27 0-0759 57 0-4239 87 6-2551 28 0-08 1 9 58 0-4455 88 9-6133 29 0-0882 59 0-4683 89 18-8034 30 0-0948 60 0-4924 90 infinite. (399) Ohm determined the intensity of a current by the multi- plier, but instead of measuring the declination of the needle, he observed the amount of torsion of the fine wire by which the needle was suspended, the intensity of the current being proportional to the number of degrees which the torsion index was moved back. Fechner determined the number of oscillations made by the needle of a galvanometer placed in the magnetic meridian under the influence of the current, the conducting wire intersecting the mag- netic meridian at right angles. " The intensities of the currents are inversely as the squares of the times of the vibrations ; or the number of units of time which are required to complete the same number of vibrations." Thus, supposing that the number of vibra- tions made by the needle under the influence of a current a in 10 seconds is made under the influence of another current I in 5 seconds, then a : I = T fc : -,\- = T fo : j f = 25 : 100 =1:4. 304 GALVANIC OB VOLTAIC ELECTBICTTT. Therefore the intensity of the current 5 is four times greater than that of the current a. Pohl, by following the same method of magnetic measurements, arrived at the following law, which was practically verified by Peschel, viz. : " That the intensities of cur- rents of single hydro-electric batteries, in which both electromotors present equal surfaces to the exciting fluid, are, caeteris paribus, as the biquadrate roots of the areas of the surfaces in action ;" from which it follows that to construct a battery, the intensity of whose current shall be double that of another given battery, the exciting surface of the former must be 16 times greater than that of the latter. (400) In their verifications of Ohm's theory, the German and French electricians adopted Fechner's method. They first observed the oscillations of the needle where no extraneous resistance was introduced into the circuit, and they then added a known resistance, and again measured the oscillations. Wheatstone adopted a different method ; instead of constant, he employed variable resistances, bring- ing thereby the currents in the circuits compared to equality, and inferring, from the amount of the resistance measured out between two deviations of the needle, the electro-motive forces and resist- ances of the circuit according to the particular conditions of the experiment. For this purpose he invented an instrument which he calls a rheostat ; it consists essentially of two cylinders, one of wood, on which a spiral groove is cut, and round which is coiled a long wire of very small diameter, and the other of brass ; by means of a handle any part of the wire can be unwound from the wooden cylinder and wound on to the brass. The coils on the wood cylinder being insulated and kept separate from each other by the groove, the current passes through the entire length of the wire coiled upon that cylinder, but the 'coils on the brass cylinder not being insulated, the current passes immediately from the point of the wire, which is in contact with the cylinder, to a spring in metallic communication with the wires of the circuit. The effective part of the length of the wire is therefore the variable portion which is on the wooden cylinder. The cylinders are six inches in length and 1J inch in diameter ; the threads of the screw are 40 to the inch, and the wire is of brass T ^th of an inch in diameter. Very thin and badly conducting metal is employed in order to introduce a greater resist- ance into the circuit ; a scale is placed to measure the number of coils unwound, and the fractions of a coil are determined by an index which is fixed to the axis of one of the cylinders aod points to the divisions of a graduated scale. (401) For measuring very great resistances, as long telegraph WHEATSTOKE'S BHEOSTAT. 305 wires, or imperfectly conducting liquids, Wheatstone employs a series of coils of fine silk covered copper wire about the - 2 -o- of an inch in diameter ; two of these coils are 50 feet in length, the others are respectively 100, 200, 400, and 800 feet in length. The two ends of each coil are attached to short thick wires, fixed to the upper faces of the cylinders, which serve to combine all the coils in one continuous length. On the upper face of each cylinder is a double brass spring, moveable round a centre, so that its ends may rest at pleasure either on the ends of the thick wires united to the circuit, or may be removed from them and rest on the wood. In the latter position, the current of the circuit must pass through the coil, but in the former position the current passes through the spring, and removes the entire resistance of the coil from the circuit. When all the springs rest on the wires, the resistance of the whole series of coils is removed ; but by turning the springs so as to intro- duce different coils into the circuit any multiple of 50 feet up to 1600 may be brought into it. Wheatstone finds that the resistance of the entire 1600 feet is equivalent to 218-880 units of resistance, or feet of the standard wire (diameter -071 of an inch). He also sometimes employs six other coils, each containing 500 yards of wire. The reduced length of this series is above 233 miles of the standard wire, and by combining this series of coils with the preceding, he is able to measure resistances equal to 274^ miles. Eor measuring comparatively small resistances, Wheatstone employs a cylinder 10^ inches in length, and 3^ in diameter, round which is wound 108 coils of a copper wire -A-th of an inch thick, any part of which can, by turning the cylinder, be included in the circuit ; but the thickness, length, and material of the wire may be varied according to the limits of the variable resistance required to be introduced into the circuit, and the degree of accuracy with which these changes are required to be measured. This form of rheostat may be usefully employ/Kl as a regulator of a voltaic current in order to maintain for any required length of time precisely the same degree of force, or to change it in any required proportion. It would serve as a regulator for an electro-magnetic engine. In Yolta-typing operations the advantage of using the rheostat is obvious, by varying it from time to time so as to keep the needle of the galvanometer (which should consist of a single thick plate or wire, making a single convolution) to the same point, a current of any required degree of energy may be maintained without any notable increase or diminution, for any length of time. These two forms of the rheostat are shown in Eigs. 170,171; Pig. 170 being the instrument employed for great re- sistances, and Fig. 171 that used when the resistances are smaller. x 306 GALVANIC OB VOLTAIC ELECTRICITY. Fig. 170. IIIIIIIHHIIillllllllllM Fig. 171, (402) By means of his rheostat, Wheatstone has shown that the number of turns of the cylinder requisite to reduce the needle of the galvanometer from one given degree to another, is an accurate measure of the electromotive force of the circuit. He has also proved that similar voltaic elements of various magnitudes conform- ably to theory, have the same electromotive force ; that the electro- motive force increases exactly in the same proportion as the number of similar elements arranged in series ; and that when an apparatus for decomposing water is placed in the circuit, an electromotive force opposed to that of the battery is called into action, which is constant in its amount, whatever may be the amount of the number of elements of which the battery consists. The electromotive forces of Voltaic elements formed of an amalgam of potassium with zinc, copper, and platinum, a solution of a salt of the electro-negative metal being the interposed liquid, are given : the last combination is one of great electromotive energy, and when a voltameter fc inter- posed in the circuit, it decomposes water abundantly. A still more energetic electromotive force is exhibited by a voltaic element, con- sisting of amalgam of potassium, sulphuric acid, and a plate of platinum covered with a film of peroxide of lead. A series of 10 such elements being equal to 33 of Daniell's, or 50 of Wollaston's cells. EFFECTS OF THE VOLTAIC CUBEEXT. 307 CHAPTEE YIII. EFFECTS OF THE VOLTAIC CUEEENT. Luminous, thermal, magnetic, and physiological phenomena. (403) ON comparing the Electricity of the Voltaic battery with that of the Electrical battery, we find a difference between the two which may be expressed in the three following particulars : 1. The intensity of voltaic Electricity, as compared with statical, is exceed- ingly low : 2. The quantity of Electricity set in motion by the smallest voltaic circle is almost infinitely greater than that from the electrical machine ; indeed, it has been shown by Faraday (lExp. Itesear., 371, et sey.) that two wires one of platinum and one of zinc, each one-eighteenth of an inch in diameter placed five- sixteenths of an inch apart, and immersed to the depth of five-eighths of an inch in acid, consisting of one drop of oil of vitriol and four ounces of distilled water, at a temperature of about 60, and con- nected at the other extremities by a copper wire, eighteen feet long and one-eighteenth of an inch thick, yield as much Electricity in eight beats of a watch, or T-f-o of a minute, as an electrical battery, consisting of fifteen jars, each containing 184 square inches of glass, coated on both sides, and charged by thirty turns of a fifty-inch plate machine : 3. While the discharge of the electrical battery is instan- taneous ; in the voltaic battery a current circulates in an uninter- rupted and continuous stream, although the wire uniting the opposite ends is constantly tending to restore the electric equilibrium. (404) In considering the effects of voltaic Electricity, it will be convenient to do so in relation to these three circumstances, as con- trasting it with ordinary Electricity. In a former chapter it has been shown, that a piece of glass or sealing wax rubbed with flannel, and held near the cap of the gold-leaf electroscope, causes an imme- diate divergence of the leaves ; but the largest calorimotor that has ever been constructed is incapable of producing an equal effect: indeed, it is only by the application of the condenser that any indi- x 2 308 GALVANIC OB VOLTAIC ELECTEICITT. cations of Electricity can be obtained from it ;* but with a battery of many pairs the effect is very distinct, though water be the sole exciting agent, as we have already seen (340) . And it matters not what the size of the plates may be ; pairs of copper and zinc, one quarter of an inch square, being quite as effectual as plates four inches square, numerous alternations being the only requisite. Here then we see a remarkable difference between the simple and the compound voltaic circle, and between quantity and intensity. From the largest calorimotor that was ever constructed, we can obtain no direct shock, and only feeble electro-chemical effects, while thirty or forty pairs of zinc and copper, four inches square, excited by the same acid, will diverge gold leaves, give shocks, and decompose acidulated water very rapidly : in general terms it may be stated, cceteris paribus, that the quantity of the electric current bears a relation to the size of the plates, and the intensity to the number of the alternations. (405) Thermal and luminous phenomena. The wonderful heating powers of an extensive voltaic battery, and the intense light emitted between charcoal points, were noticed in the last chapter (363). In the Proceedings of the Electrical Society (4to. volume), a series of experiments performed with a sulphate of copper battery, consisting of 160 cells, are detailed. The deflagration of mercury is described as most brilliant; and the length of the flame between charcoal points, was three-fourths of an inch. Zinc turnings were speedily deflagrated, and their oxide was seen floating about the room. In these experiments, the following interesting result was first obtained : * With the aid of the electroscope shown in Fig. 172, constructed by Mr. Fig. 172. Gassiot, the Eev. Charles Pritchard (Phil. Trans. 1844) obtained signs of tension in a single cell excited by dilute sulphuric acid with platinum and zinc. A is a glass vessel, the stem of which is well coated with lac ; B B' two copper wires passing through glass tubes and corks ; D D' gilt discs, each about two inches in diameter, attached to the wires ; P a copper plate, with a wire passing through a glass tube ; to the end of the wire is attached a narrow slip of gold leaf L. The discs must be adjusted with care, so as to allow the leaf to be equidistant from each. If B is con- nected by a wire attached to the platinum, and B' to another wire attached to the zinc of a single cell of the nitric acid battery insulated on a plate of lac, and an excited glass rod is approximated very gradually towards the plate P, the gold leaf will be attracted to B', or the disc attached to the zinc; and if excited resin is approximated in a similar manner, the gold is then attracted to B or the disc attached to the platinum. THEEMAL AND LUMINOUS PHENOMENA. 309 When the ends of the main wires were placed across each other (at about one or two inches from their extremities, not touching, but with an intervening stratum of air, the striking distance through which the Electricity passed, producing a brilliant light), that wire connected with the positive end of the battery became red-hot from the point of crossing to its extremity. The corresponding portion of the other wire remained comparatively cold. The wires were removed from the battery : that which had been made the positive was made the negative, and that which had been negative was made positive. The results were still the same : the positive wire becom- ing in all cases heated from its end to the point of crossing, and finally bending beneath its own weight. "When a piece of sulphuret of barium was placed on the table, with one wire resting on it, upon bringing the other to within the striking distance, the portion conti- guous to the wire was fused, but could not be collected. When sulphuret of lead was similarly placed, the metal was released in small quantities, but when sulphuret of antimony was placed in circuit the most brilliant effects were obtained. The negative wire was firmly held on the sulphuret, and the positive brought to within one-eighth of an inch of it, the heat of the flame immediately disen- gaged the elements combined with the metal, and they were dissi- pated in the form of vapour, leaving a small portion of fused metal in a state of intense heat. When the main wires were crossed, and their ends placed in two similar jars, containing distilled water, in about two minutes the water in the positive cell boiled ; that in the other presenting no such appearance. On applying a powerful magnet the flame from the charcoal points obeyed the known laws of electro-magnetism, being attracted or repelled as the case might be, or following the motion of the magnet if the latter was revolved. But when a powerful horse-shoe magnet was held horizontally with its north or marked end uppermost, and the wire from the negative side of the battery firmly pressed on the magnet, the positive wire being brought to within the striking distance, a brilliant circular flame of electrical light was seen to revolve from left to right as the hands of a watch. When the position of the magnet was reversed, the flame revolved from right to left. The appearance of the flame was not unlike that of the brush from the electrical machine received on a large surface, only much more brilliant. (406) The colour of the light which attends the voltaic disruptive discharge varies with the substances between which the discharge passes. If thin metallic leaves be employed, they are deflagrated with considerable brilliancy. The beautiful effects are not, however, owing to the combustion of the metals, though in some cases in- 310 GALVANIC OB YOLTAIC ELECTRICITY. creased by this cause, but arise from a dispersion of their particles analogous to that of the more momentary explosion of the Leyden battery. Gold leaf emits a white light, tinged with blue ; silver, a beautiful emerald green light ; copper, a bluish white light, with red sparks ; lead, a purple ; and zinc, a brilliant white light, tinged with red. The experiments may be performed by fixing a plate of polished tinned iron to one wire of the battery, and taking up a leaf of any metal on the point of the other wire, bringing it in contact with the tin plate. Even under distilled water the disruptive discharge of the voltaic battery takes place in a stream of brilliant light. Fig. 173. Mr. De la Eue has contrived the arrangement, shown in Fig. 173, for submitting metals to the action of the voltaic current. It consists of two brass columns surmounted by a series of holders which move on centres, and any two opposed points are brought into contact by a rack and pinion adjustment. (407) The best method of showing the power of the voltaic current to heat metallic wire, is to roll about eighteen inches of wire into a long spiral, and to place it in the interior of a glass tube, Fig. 174, its ends passing through corks, or attached to screws, so as to be readily con- Fig. 174. nected with the terminal wires of the battery : by this means a high temperature may be communicated to the glass tube, though the wire may not be ignited ; and by immersing it' in a small quantity of water, that fluid may speedily be raised to its boiling point. "When a wire in the voltaic circuit is heated, the temperature frequently rises first, or most at one end ; but it was shown by Faraday that this depends on adventitious circumstances, and is not due to any relation of positive or negative, as respects the current. Faraday has also shown (Experimental Researches, 853, note) that the same quantity of Elec- tricity which, passed in a given time, can heat an inch of platinum wire of a certain diameter red hot, can also heat a hundred, a thousand, or any length of the same wire, to the same degree, provided the cooling circumstances are the same for every part, in all cases. (408) It was Lieut.-G-eneral Pasley who first applied the heating power of the galvanic battery to a useful practical purpose. While engaged in operations on the river Thames, he was written to by Mr. Palmer (Smee's Electro-metallurgy, p. 297), who recommended him DESTRUCTION OF THE BOUND-DOWN CLIFF. 311 to employ the galvanic battery, instead of the long fuse then in use, and after being put in possession of the method of operating, he immediately adopted it, and has since turned it to excellent account in the removal of the wreck of the Royal G-eorge at Spithead, as is well known. (409) The destruction by gunpowder of the Round Down Cliff on the line of the South Eastern Railway, on Thursday, 26th January, 1843, is a splendid example of the successful application of a scientific principle to a great and important practical purpose. In this grand experiment, by a single blast, through the instrumentality of the galvanic battery, 1,000,000 tons of chalk were in less than five minutes detached and removed, and 10,OOOZ. and twelve months' labour saved. The following account is abridged from the Report in the Times newspaper : " The experiment has succeeded to admiration, and as a specimen of engineering skill, confers the highest credit on Mr. Cubitt who planned, and on his colleagues who assisted in carry- ing it into execution. Everybody has heard of the Shakspeare Cliff, it would be superfluous, therefore, to speak of its vast height, were not the next cliff to it on the west somewhat higher : that cliff is Round-Down Cliff, the scene and subject ef this day's operations. It rises to the height of 375 feet above high-water mark, and was, till this afternoon, of a singularly bold and picturesque character. As a projection on this cliff prevented a direct line being taken from the eastern mouth of Abbot's Cliff Tunnel to the western mouth of the Shakspear Tunnel, it was resolved to remove, yesterday, no inconsi- derable portion of it from the rugged base on which it has defied the winds and waves of centuries. Three different galleries and three different shafts connected with them, were constructed in the cliff. The length of the galleries or passages was about 300 feet. At the bottom of each shaft was a chamber 11 feet long, 5 feet high, and 4 feet 6 inches wide. In each of the eastern and western chambers, 5,500 Ibs. of gunpowder were placed, and in the centre chamber 7,500 Ibs., making in the whole, 18,000 Ibs. The gunpowder was in bags, placed in boxes : loose powder was sprinkled over the bags, of which the mouths were opened, and the bursting charges were in the centre of the main charges. The distance of the charges from the face of the cliff was from 60 to 70 feet. It was calculated that the powder, before it could find a vent, must move 100,000 yards of chalk, or 200,000 tons. It was confidently expected that it would move one million. " The following preparations were made to ignite this enormous quantity of powder : At the back of the cliff a wooden shed was 312 GALYAKIO OB YOLTAIC EIECTBICITY. constructed, in which three galvanic batteries were erected. Each battery consisted of 18 Daniell's cylinders, and two common batteries of 20 plates each. To these batteries were attached wires which communicated at the end of the charge by means of a very fine wire of platinum, which the electric current as it passed over it made red hot to fire the powder. The wires, covered with ropes, were spread upon the grass to the top of the cliff, and then falling over it, were carried to the eastern, the centre, and the western chambers. Lieu- tenant Hutchinson, of the Royal Engineers, had the command of the three batteries, and it was arranged that when he fired the centre, Mr. Hodges and Mr. "Wright should simultaneously fire the eastern and western batteries. The wires were each 1000 feet in length, and it was ascertained by experiment that the current will heat platinum wire sufficiently hot to ignite gunpowder to a distance of 2,300 feet of wire. "Exactly at twenty-six minutes past two o'clock, a low, faint, indistinct, indescribable, moaning subterranean rumble was heard, and immediately afterwards the bottom of the cliff began to belly out, and then almost simultaneously about 500 feet in breadth of the summit began gradually but rapidly to sink. There was no roaring explosion, no bursting out of fire, no violent and crashing splitting of rocks, and comparatively speaking very little smoke : for a pro- ceeding of mighty and irrepressible force, it had little or nothing of the appearance of force. The rock seemed as if it had exchanged its solid for a fluid nature, for it glided like a stream into the sea, which was at a distance of 100 yards, perhaps more from its base, filling up several large pools of water which had been left by the receding tide. As the chalk, which crumbled into fragments, flowed into the sea without splash or noise, it discoloured the water around with a dark, thick, inky-looking fluid; and when the sinking mass had finally reached its resting place, a dark brown colour was seen on different parts of it which had not been carried off the land." (410) The circumstance of so little smoke being seen attendant on the combustion of such a prodigious quantity of gunpowder, occa- sioned to many a good deal of surprise, and induced a belief that the whole of the gunpowder had not been fired ; but when we consider that the smoke owes its visibility principally to the solid and finely divided charcoal* which is suspended in it, and that in passing through such an immense mass of limestone, it must have been Jil- * The principal gaseous results of the combustion of gunpowder are carbonic oxide, carbonic acid, nitrogen, and sulphurous acid ; the solid residue consists of carbonate and sulphate of potassa, sulphuret of potassium, and charcoal. COOLING INFLUENCE OF HYDROGEN GAS. 313 tered as it were from this solid matter, our wonder at the absence of smoke on this occasion will cease. (411) It was first pointed out by Mr. Grove (PJiil. Mag. Dec. 1845 ; Phil. Trans. 1847) that there is a striking difference between the heat generated in a platinum wire by a voltaic current according as the wire is immersed in atmospheric air or in other gases. He found, by including a voltameter in the circuit, that the amount of gas yielded by the battery is in some inverse ratio to the heat developed in the wire, and by placing a thermometer at a given distance he further showed that the radiated heat was in a direct ratio with the visible heat. The following remarkable experiment was made. Two glass tubes of precisely the same length and internal diameter were closed with corks at each extremity; through the corks the ends of copper wires penetrated, and joining these were coils of fine platinum wire one-eightieth of an inch in diameter and 3-7 inches long when uncoiled. One tube was filled with oxygen and the other with hydrogen, and the tubes thus prepared were immersed in two separate vessels in all respects similar to each other, and each containing three ounces of water. A thermometer was placed in the water in each vessel, the copper wires were connected so as to form a continuous circuit with a nitric acid battery of eight cells, each cell exposing eight square inches of surface. Upon the circuit being completed, the wire in the tube containing the oxygen rose to a white heat, while that in the hydrogen was not visibly ignited ; the temperature of the water, which at the commencement of the experiment was 60 Fahr. in each vessel, rose in five minutes in the water surrounding the tube of hydrogen from 60 to 70, and in that containing the oxygen from 60 to 81. Here then we have the same quantity of Electricity passing through two similar portions of wire immersed in the same quantity of liquid, and yet in conse- quence of their being surrounded by a thin envelope of different gases, a large portion of the heat which is developed in one portion appears to have been annihilated in the other. Similar experiments were made with other gases, and it was found that hydrogen far exceeded all other gases in its cooling effect on the ignited wire. The following was the order of the gases, both by direct experiment and by testing the intensity' of ignition by the inverse conducting power of the wire as measured by the amount of gas in a voltameter included in the circuit. Cubic inches of gas evolved in Gases surrounding the wire. the voltameter per minute. Hydrogen ....... 7*7 Olefiant gas . . . . . . 7'0 314 GALVANIC OB VOLTAIC ELECTRICITY. Cubic inches of gas evolved in Gasses surrounding the wire. the voltameter per minute. Carbonic oxide ...... 6*6 Carbonic acid . . . . . . 6' 6 Oxygen " .6*5 Nitrogen . 6'4 (412) Experiments were made by Mr. Grove in order to ascertain whether the phenomenon was occasioned by the varying specific heat of the media surrounding the wire, but the results were of a negative character. It then occurred to him that from the recognized analogy in chemical character of hydrogen to the metals, this gas may possibly possess a certain conducting power, and thus divert a portion of the current from the wire. An experiment, however, with a battery of 500 cells of the nitric acid arrangement failed to show the slightest conducting power either in this gas or in atmospheric air. Neither can the cooling effects of different gases be in any way connected with their specific gravities, since carbonic acid on the one hand and hydrogen on the other, produce greater cooling effects than atmo- spheric air ; and olefiant gas, which closely approximates air, and is far removed from hydrogen in specific gravity, much more nearly approximates hydrogen, and is far removed from air in its cooling effect. On the whole, Mr. Grove is inclined to think that although influenced by the fluency of the gas, the phenomenon is mainly due to a molecular action at the surfaces of the ignited body and of the gas. We know that in the recognized effects of radiant heat, the physical state of the surface of the radiating or 'absorbing body exercises a most important influence on the relative velocities of radiation or absorption : thus black and white surfaces are strikingly contra-distinguished in this respect. " Why," he asks, " may not the surface of the gaseous medium contiguous to the radiating substance, exercise a reciprocal influence ? Why may not the surface of hydro- gen be as black, and that of nitrogen as white to the ignited wire ?" Mr. Grove thinks this notion to be more worthy of consideration as it may establish a link of continuity between the cooling effects of different gaseous media, and the mysterious effects of surface in catalytic combinations and decompositions by solids such as platinum. Whatever may ultimately prove to be the real cause of the cooling influence of different gases, it is evident from Mr. Grove's experi- ments, that it is to be referred to some specific action of hydrogen, as the differences of effect of all gases other than hydrogen and its compounds, are quite insignificant when compared with the differences between the hydrogenous and other gases. Mr. Grove (the tendency of whose mind is to make practical applications of the facts disclosed THE VOLTAIC AECH. 315 by science) suggests that the experiments now detailed may ulti- mately find some beneficial applications in solving the problem ot a safety-light for mines . A light which is just able to support itself under the cooling efiect of atmospheric air, would be extin- guished by air mixed with hydrogenous gas ; indeed it is almost impossible to obtain the voltaic arc in hydrogen, though in nitrogen, which is equally incapable of combining with the terminals, it can be obtained without difficulty. (413) Pig. 175 represents the appearance presented by the voltaic Fig. 175. flame between pencils of well-burnt boxwood charcoal, or which answers better, between pencils formed of that plumbago-like sub- stance found lining the interior of long used coal-gas retorts. The arched form of the flame is owing to the ascensional force of the heated air. With respect to the charcoal light, it was noticed by De la Rive, with a Grove's battery of forty pairs (Proc. "Elect. Soc.'), that the luminous arc cannot be obtained between two charcoal points until after' the two points have been in contact, and are heated around this point of contact. "We may then by separating them gradually succeed in having between them a luminous arch an inch or more in length. "Wood charcoal, which, after having been power- fully ignited, has been quenched by means of water, is that which gives the most beautiful light, on account of its con- ducting power being increased. Coke, though it succeeds as well as charcoal, does not give so brilliant and white a light: it is always rather bluish, and sometimes red. The transfer of particles of carbon from the positive to the negative pole, whilst the luminous arch is produced, is evident ; but it is espe- cially sensible in vacuo, Fig. 176. A cavity is observed to be formed in the point of the positive charcoal, pre- senting the appearance of a hollow cone, in which the solid cone, formed by the deposition of particles of carbon, might penetrate almost exactly. The pheno- menon is almost the same in the air, except that the accumulation of carbon 011 the negative point is less, because a portion of the molecules burns in the transfer ; Fig. 176. 316 GALVANIC OE VOLTAIC ELECTRICITY. and the positive point presents only a flat instead of a hollow surface. This latter result probably arises from the combustion of the thin exterior of the hollow cone, which must be formed in air as well as in vacua. It is this more rapid consumption of the positive, than the negative carbon which has hitherto been one of the chief difficulties in the application of the electric light to practical illumination. Many attempts have been made to overcome this difficulty, but the most simple, perfect, and portable apparatus are those invented by M. Jules Duboscq and by M. Deleuil. The object to be attained is the maintenance of the charcoal terminals at a constant distance from each other. The lower or positive carbon is in Duboscq's lamp pressed upwards by a spring, the action of which is regulated by an endless screw set in motion by a lever, which is worked by an electro-magnet ; this electro-magnet, enclosed in the pillar of the lamp, is only active when the circuit is complete, the moment therefore the charcoal terminals become separated, its iron keeper is detached, and the action of the spring, previously restrained by the screw, is put in force, and the carbon terminals are again brought into contact. The light is by this means kept tolerably constant. Deleuil' s regulator Fig. 177. is shown in Pig. 177. The negative carbon 1ST is attached to a metal rod, which slides through the ball D with sufficient friction to remain perma- nent wherever it may be placed: the positive carbon P rises gradually by the operation of the voltaic current itself, so as to preserve a constant interval between N and P. The apparatus by which this is effected is situated beneath the frame of the instrument, and is shown separately in JFig. 178. A lever, A, is attached at one end to the spiral B, the other being retained between the points of two screws, so that the lever itself has freedom of motion vertically, but to a very small extent about the pivot L. E is an electro- magnet round which the battery current circulates. I is a steel spring in contact with one of the teeth of the vertical rod K, which carries the positive carbon P. C is an apparatus for regulating DELEUIL'S ELECTRIC LAMP. 317 the spring B. Suppose now the voltaic current to pass with its full intensity round the electro-magnet E,the armature on the lever will be imme- diately attracted, the resistance of the spiral E will be over- come, that end of the lever will descend, and the rod K will be restrained or trigged by the between the ignited carbon spring I : as the distance P increases, the current circulating round the electro-magnet gradually diminishes, till the force of the spiral It predominates ; that end of the lever now rises, and the spring I forces the rod K upwards, the carbons are thus again brought into contact, the current again circulates round the electro- magnet, the rod K is again restrained, and in this way a series of periodic movements is kept up, the result of which is to keep the carbon terminals constantly within the proper distance for the passage of the disruptive discharge. To preserve the ignited termi- nals from the cooling influence of the external air, they are enclosed in a glass cylinder and a metallic reflector H, which may be removed at pleasure, is placed behind them. Pig. 179 represents the arrangement of Foucault's experiment of Fig. 179, hrowing the image of the carbon terminals during ignition by means f a lens on a screen. It shows in a beautiful manner the gradual Bearing away of the positive and the increase of the negative carbons, -he small globules or specs observed on the charcoal arise from the 318 GALYANIC OR YOLTAIC ELECTEICITT. fusion of the minute quantities of silica contained in the coal. When the voltaic current is thrown on, the negative carbon first becomes luminous, but the light from the positive is afterwards much the most intense, and as this is the terminal which wears away, it should be somewhat thicker than the other. (414) On reflecting on the remarkable difference between the heating effects of the positive and negative wires of the voltaic battery (405), it occurred to Mr. Grove (Phil. Mag. vol. xvi/p. 478) that it might be due to the interposed medium, and that were there any analogy between the state assumed by voltaic electrodes in elastic media, and that which they assume in electrolytes, it would follow that the chemical action at the positive electrode in atmo- spheric air would be more violent than that at the negative, and that if the chemical action were more violent, the heat would necessarily be more intense. By experiments performed with an arrangement of thirty-six pairs of his nitric acid battery, Mr. Grove established the following points : 1. If zinc, mercury, or any oxidable metal constitute the positive electrode, and platinum the negative one, in atmospheric air, while the disruptive discharge is taken between them, a voltameter inclosed in the circuit, yields considerably more gas than with the reverse arrangement. 2. In an oxidating medium, the brilliancy and length of the arc are (with certain conditions) directly as the oxidability of the metals between which the discharge is taken. 3. In an oxidating medium the heat and consumption of metal is incomparably greater at the anode than at the cathode. 4. If the disruptive discharge be taken in dry hydrogen, in azote, or in a vacuum, no difference is observable between the heat and light, whether the metals be oxidable or inoxidable, or whether the oxidable metal constitute the positive or negative electrode. 5. The volume of oxygen absorbed by the disruptive discharge taken between a positive electrode of zinc and a negative one of platinum in a vessel of atmospheric air, is equal to that evolved by a voltameter included in the same circuit. (415) A remarkable analogy between the electrolytic and disrup- tive discharges is here presented, but there are two elements which obtain in the latter which have little or no influence on the former, viz., the volatility and state of aggregation of the conducting body. This was shown remarkably in the case of iron, which in air or in oxygen gave a most brilliant voltaic arc, while in hydrogen, or a vacuum, with the same power, a feeble spark only was perceptible at ANALOGY BETWEEN ELECTEOLTTIC AND DISRUPTIVE DISCHARGE. 319 the moment of disruption. Mercury, on the other hand, gave a tolerably brilliant spark in hydrogen, azote, or a vacuum, and one more nearly approaching to that which it gives in air. (416) It has been established by Faraday, that in electrolysis, a voltaic current can only pass by the derangement of the molecules of matter; that the quantity of the current which passes is directly proportional to the atomic disturbance it occasions : he deduces from this, that the quantity of Electricity united with the atoms of bodies is as their equivalent numbers, or in other words, that the equivalent numbers of different bodies serve as the exponents of the comparative quantities of Electricity associated with them (Experimental He- searches, 518, 524, 732, 783, 836, 839). " Now," observes Mr. Grove, "what takes place in the disruptive discharge? When we see dazzling flame between the terminals of a voltaic battery, do we see Electricity, or do we not rather see matter, detached, as Davy sup- posed, by the mysterious agency of Electricity, and thrown into a state of intense chemical or mechanical action ? Matter is un- doubtedly detached during the disruptive discharge, and this discharge takes its tone and .colour from the matter employed. Now, as this separation is effected by Electricity, Electricity must convey with it either the identical quantity of matter with which it is associated, or more or less ; more it can hardly convey, and if less, some portion of Electricity must pass in an insulated state or unassociated with matter, and some with it." Mr. Grove proceeded to institute some experiments with a view of determining whether the quantity of matter detached by the voltaic disruptive discharge was definite for a definite current, or bore a direct equivalent relation to the quantity electrolyzed in the liquid portions of the same circuit. The great difficulties attending such an inquiry defied accurate results; but sufficient was gathered to afford strong grounds for presumption that the separation of matter in the voltaic arc is definite for a definite quantity of Electricity, and that the all important law of Faraday is capable of much extension ; and uniting this view with the experi- ments of Faraday on the identity of Electricity from different sources, and with those of Fusinieri on the statical electrical discharge, it would follow as a corollary that every disturbance of electrical equili- brium is inseparably connected with an equivalent disturbance of the molecules of matter. (417) In a paper published in the Transactions of the Uoyal Society (Phil. Trans, part i., 1847), De la E/ive has communicated some further researches on the voltaic arc, and on the influence which magnetism exerts on it, and on bodies transmitting interrupted electric currents. The length of the luminous arc has a relation to 320 GALVANIC OR YOLTAIC ELECTEICITT. the greater or less facility with which the substances composing the electrodes possess of being se-gregated, a facility which may depend upon their temperature diminishing their cohesion, upon their tendency to oxidize, upon their molecular state, and, lastly, upon their peculiar nature. Carbon is one of the substances which pro- duces the longest luminous arc, a property which it derives from its molecular condition, which renders it particularly friable. "When a plate of platinum was made the positive electrode to a point of platinum, the negative electrode of a nitric acid battery of fifty pairs in rarefied air, a circular spot presenting the appearance of one of Nobili's coloured rings was formed on the plate, the result evidently of the oxidation of the platinum : it was not so vivid in ordinary air. When the plate was negative, and the point positive, the former became covered with a white circular spot formed of a vast number of minute grains of platinum, which having been raised to a high temperature, remained adhering to the surface. This also was larger in the pneumatic vacuum. With a point of coke negative, and a plate of platinum positive, an arc more than twice as long as before was obtained, and the light, instead of being a cone, was composed of a multitude of luminous jets diverging from different points of the plate, and tending to various parts of the point of coke ; the heat was also much greater, and the platinum plate was soon perforated. With the point of coke positive, and the platinum plate negative, the heat was still very great though the arc was less. With a platinum plate and zinc point the effects were most brilliant, white oxide of the metal being precipitated (in air) upon the platinum plate, and a black deposit in the vacuum of the air pump. An iron point gave in air a deposit of red oxide, and in rarefied air a deposit of black oxide. With a point and plate of copper the arc had a beautiful green colour. When mercury was used the luminous effect was most brilliant, the metal was excessively agitated, rising up in the form of a cone when it was positive, and sinking considerably below the positive point when it was negative. When the arc is formed, it is those parts of the circuit which present the greatest resistance to the current which become the hottest. The metal, which is the worst conductor, is the most strongly heated. When bo^h the conductors are of the same material the development of heat is not uniform, it being much greater on the positive side. With a silver positive and platinum negative point, the latter becomes incandescent, the silver being much less heated ; with two silver or two platinum points the positive one alone becomes incandescent throughout its whole length. In consequence of its good conducting power, a voltaic battery will INFLUENCE OF MAGNETISM ON THE YOLTAIC ARC. 321 heat to redness a greater length of silver wire than of platinum ; nevertheless, if a compound wire be formed of several alternate links of platinum and silver, as shown in Fig. 180, and disposed between the poles of a powerful Fig. 180. battery, the platinum links will become red hot during the passage of the current, while the alternate silver * ^^_ links will remain dark. The charge, which passes freely along the silver, meets with resistance enough in the platinum, to produce ignition. . (418) Influence of magnetism on the voltaic arc. It was first observed by Davy that a powerful magnet acts upon the voltaic arc, as upon a moveable conductor traversed Fig. 182. Fig. 181. by an electric current ; it attracts and repels it, and this attraction and repulsion manifests itself by a change in the form of the arc, which may even become broken by too great an attraction or repulsion. Fig. 181 represents the voltaic flame be- tween two cylinders of plumbago, and BBi~*" Bill Fig. 182 the curved form which it assumes under the influence of a magnetic pole. De la Bive found that an arc cannot be formed between two iron points when they are magnetized, unless they are brought very close, and then, instead of a quick luminous discharge, sparks fly with noise in all directions, as if the transported particles disengaged themselves from the positive electrode with great difficulty. The noise is analo- gous to the sharp, hissing sound of steam issuing from a locomotive, and this is the case whatever may be the nature of the negative electrode. "When a plate of platinum was placed upon one of the poles of a powerful electro-magnet, and a point of the same metal vertically above it, and the voltaic arc produced between the point and the plate, the former being positive and the latter negative, a sharp hissing sound was heard ; when the conditions were reversed the effect was totally different ; the luminous arc no longer maintained its vertical direction when the electro-magnet was charged, but took an oblique direction, as if it had been projected outwards towards the edge of the plate ; it was broken incessantly each time, being accompanied by a sharp and sudden noise similar to the discharge of a Leyden jar. The direction in which the arc was projected depended on that of the current producing it, as likewise ' on the position of the plate on one or other of the two poles. When a copper 322 GALVANIC OB VOLTAIC ELECTRICITY. plate was made the positive electrode on a pole of the electro-magnet, that portion of the surface lying underneath the negative point presented a spot in the form of a helix, as if the metal melted in this locality had undergone a gyratory motion round a centre, at the same time that it was uplifted in the shape of a cone towards the point. The curve of the helix was fringed with tufts similar to those which mark the passage of positive Electricity in a Leyden jar. When the plate was negative, and the point positive, no such marks were produced. With two copper points, the hissing sound was so loud, as to bear a resemblance to distant discharges of musketry, but for this the magnet was required to be very powerful, and the battery power intense. The hissing sound was the result of the easy and continuous transport of matter more or less liquefied from the positive electrode, while the detonations were probably the effect of the resistance opposed by the same matter, to the disintegration of its particles when it was not sufficiently heated. (419) The magnet causes these effects by producing a change in the molecular constitution of the matter of the electrode, or rather in the highly diffused matter which forms the voltaic arc. That the magnet really does exert a molecular modification of the particles of matter subjected to its influence, is proved by the sounds produced when electric currents are sent through metallic bars when placed on the poles of the electro-magnet; bars of iron, tin, zinc, bismuth, and even of lead, emit distinct sounds when traversed by a current from five to ten pairs of the nitric acid battery, while resting on the pole of a powerful magnet ; copper, platinum, and silver bars do the same, and mercury enclosed in a tube of glass emits an intense sound. De la Rive also found that helices of metals were sonorous, as were dilute sulphuric acid, and solution of common salt. It is the opinion of De la Bive that the influence of magnetism on all conducting bodies impresses on them, as long as it lasts, a molecular constitution similar to that which iron and generally all bodies susceptible of magnetism possess naturally. (420) For experiments on the sounds produced in metallic wires by the passage of a voltaic current through or round them, a sounding board may be employed on which the wires or rods are kept in a state of tension, by a weight of nine or ten pounds ; the electric current may be sent through the wires, or through helices of copper wire surrounding but not touching them ; the current must not be continuous, but broken at regular intervals by means of a mechanical contrivance called a commutator. Those metals which are the -worst conductors give the most pronounced effects, but iron far surpasses every other metal, after which comes platinum. The sound given out by a well-annealed iron wire, when it transmits the current, is very CONDUCTING POWEKS OF METALS. 323 strong, greatly resembling the sound of church bells in the distance. De la Eive suggests that it might perhaps be advantageously employed in the electric telegraph. The tone of the sound varies with the velocity with which the discontinuous currents succeed each other when the succession is very rapid, the sound resembles the noise which the wind makes when it blows strongly. (421) The vibratory motion which results from the magnetization and demagnetization of soft iron is shown by the following beautiful experiment. In the interior of a bobbin, or a bottle surrounded with a wire rolled into a helix, are placed some very small discs or filings of iron ; when the discontinuous current traverses the wire of the helix, the discs or filings are seen to be agitated, and to revolve round each other in the most remarkable manner, the filings have the perfect appearance of being in ebullition ; if the current is intense, they dart in the form of jets like so many fountains. The motion of the filings is attended with a noise similar to that of a liquid when it is boiling. (422) The heating power of the voltaic flame is so intense that the most refractory substances succumb to it; platinum, iridium, and titanium, which withstand the heat of the most power- Fig. 183. ful furnace, are readily fused. To exhibit these effects a small cavity is bored in the positive gas coke electrode, which serves as a crucible, Pig. 183 ; into this the metal is placed, and the current is transmitted from a battery of not less than twenty of Grove's or Bun- sen's arrangements, as shown in the figure; the metals are not only fused, but are actually converted into vapour and disappear. (423) The conducting powers of metals, or their capacity for trans- mitting Electricity, have been estimated very differently by different experimenters, as will be seen by the following table, in which the relative lengths of wires which, with equal diameters, conduct the same quantity of Electricity, are expressed in numbers. OHM. BECQUEBEL. C Copper . . 100 Copper Gold . 93-6 Gold . Silver . 73-6 Silver Zinc ^ . . 28-5 Zinc . Platinum . 16-4 Brass Iron . 15-8 Iron . Tin . . 15-5 Platinum Lead . 8'3 Tin . Mercury . . 3-45 Lead . Potassium . 1-33 DAVY. 100 Silver . 109-1 57-4 35-6 Copper Gold . 100- . 72-7 33-3 Lead . 691 28-0 Platinum . . 18-2 17-4 Palladium . 16'4 17-1 Iron . . 14-6 16-8 97 J 2 324 GALVANIC OB, VOLTAIC ELECTEICITY. Silver Copper Gold Tin 'AHB. BEISS. POUTLLET. 136-25 Silver . 148-74 Gold 103-5 100- Copper . 100-00 Copper . 100-0 7979 Gold . 88-87 Platinum 22-5 30-84 Cadmium 38-35 f 15-2 29-33 Brass 27-70 Brass 1234 17-74 14-62 Palladium Iron . ' . 18-18 17-66 Cast Steel J13-0 (20-8 14-16 Platinum . 15-52 T (15-6 Tin . r '.. 14-70 Iron \18-2 Nickel . 13-15 Mercury . 2-6 Lead 10-32 Iron Lead . Platinum Harris gives the following order (Trans. Royal Soc. Edinburgh, 1834) but does not express the relative conducting powers numerically ; silver, copper, zinc, gold, tin, iron, platinum, lead, antimony, mercury, bismuth. His mode of examination was to pass the current from the battery through equal lengths and sizes of the respective wires, his electro-thermometer (Fig. 94) being included in the circuit ; the conducting powers of the metals, which were kept cool by being surrounded with cold water, were estimated by the height to which the liquid rose in the stem of the instrument. By thus experimenting Harris arrived at the following deductions. 1. That for certain and given small forces, the differences in the conducting powers vanish, each metal being equally efficient. 2. The differences in conducting powers become more apparent within a certain limit as the force of the battery increases. 3. The principle arrived at by Mr. Children, that the heat evolved by a metal whilst transmitting a charge is in some inverse ratio of the conducting power, is only true in employing charges within the limit of the transmitting power, and when the force is great, the best conductor i most heated, when less, the inferior conductor. (424) Some other results obtained by Harris with his electro- thermometer are worth recording. The heat excited in a metallic wire by a simple voltaic arrangement is exactly in the inverse ratio of the distance between the plates, and directly as the quantity of metal immersed in the exciting liquid. When the wire is very thin, it is more heated by a feeble current than a thick one, but with an increased power, the thick wire is the most heated, the thin wire being unable to transmit the whole of the power. The influence of heat in diminishing the conducting power of a metal is shown by including a length of about 6 inches in the circuit together with the electro-thermometer, and when the liquid is at its greatest height, heating it by a spirit lamp, the fluid immediately falls, and continues : MAGNETIC PHENOMENA. 325 to descend, as the wire becomes more and more heated ; on removing the lamp, and allowing the wire to cool, the liquid recovers its former elevation ; when, on the contrary, the wire is artificially cooled by pouring ether on it, the effect on the electrometer is increased. A wire that is heated to redness through its entire length by a voltaic battery, may be fused by suddenly dipping a portion of it in cold water, which is the common mode of demonstrating the influence exerted by heat on the conducting power of metals. With, a series of 160 cells of the constant battery, "Walker was unable to heat platinum wire A-th of an inch in diameter, though sixty inches of rio-th of an inch in diameter were made red-hot. But with the same battery arranged in a different manner, thirty-four inches of the thicker, and only twenty-seven of the thinner were heated. The size of the wire heated by a battery depends on the extent of the surface of the electro-motive elements, the length heated depends on the number of the series, the quantity of Electricity remaining the same. This has been verified by Walker, in his experiments with the constant battery above referred to (Trans. Elect. Soc. p. 69), and is precisely what theory would lead us to expect. Paraday found (Ex. Resear. 853, note) that the same quantity of water was decomposed by a battery, whether half-an-inch or eight inches of red-hot wire were included in the circuit, and he observes that a fine wire may even be used as a rough but ready regulator of a voltaic current ; for if it be made part of the circuit, and the larger wires communi- cating with it be shifted nearer to, or further apart, so as to keep the portion of wire in the circuit sensibly at the same temperature, the current passing through it will be nearly uniform. (425) Magnetic phenomena. The influence of magnetism on the voltaic arc has already been alluded to ; the consideration of the mutual relations of the magnetic and electrical forces belongs to another division of our subject, and we only refer to them here for the purpose of describing some instruments which are much used for determining the intensity of hydro-electric currents. These instru- ments are called galvanometers or galvano-multipliers, and are founded on the important discovery of Oersted, made in the year 1819. The fundamental fact observed by this philosopher was, that when a magnetic needle is brought near the connecting medium (whether a metallic wire, or charcoal, or even saline fluids, of a closed voltaic circle), it is immediately deflected from its natural position, and takes up a new one, depending on the relative positions of the needle and wire. If the connecting medium is placed horizontally over the needle, that pole of the latter which is nearest to the negative end of the battery always moves westward ; if it is placed under, the same 326 GALVANIC OR YOLTAIC ELECTEICITT. Fig. 184. pole moves to the east. If the connecting wire is placed parallel with the needle, that is, brought into the same horizontal plane in which the needle was moving, then no motion of the needle in that plane takes place, but a tendency is exhibited in it to move in a vertical circle, the pole nearest the negative side of the battery being depressed when the wire is to the west of it, and elevated when it is placed on the eastern side. If the battery current be sent above and below the needle at the same time, but in oppo- site directions, the deflection is more powerful, for the current traversing the wire above the needle conspires equally with the current passing along the wire below, to deflect the needle from its natural position, and to bring it into a new one, nearer to right angles to the plane of the wire. (426) If, instead of simply passing once over and once under the needle, the conducting wire be caused to make a great number of convolutions, the deflecting power of the current will be propor- tionately increased, and an instrument will be obtained by which very feeble currents may be readily detected. This then is the principle of the galvanometer, the simplest form of which is shown in Pig. 184, but to which, to adapt it to the detection of very minute currents, various forms have been given ; in all the convolutions of Fig. 185. the wire are multiplied, and the lateral transfer of Elec- tricity prevented by coating it with silk or sealing-wax. Fig. 185 is a vertical section of the torsion galvanometer of the late Professor Eitchie. The following is his descrip- tion of its construction: "Take a fine copper wire, and cover it with a thin coating of sealing-wax, roll it about a heated cylinder, an inch or two in diameter, ten, twenty, and any number of times, according to the delicacy of the instrument required. Press together the opposite NOBILl's GALVANOMETER. 327 sides of the circular coil till they become parallel, and about an inch, or an inch and a half long. Fix the coil in a proper sole, and connect the ends of the wires with two small metallic cups, for holding each a drop of mercury. Paste a circular slip of paper, divided into equal parts horizontally, on the upper half of the coil, and having a black line drawn through its centre, and in the same direction with the middle of the coil. Fix a small magnet, made of a common sewing needle, or piece of steel wire, to the lower end of a fine glass thread, while the upper end is securely fixed with sealing- wax in the centre of a moveable index, as in the common torsion balance. The glass thread should be inclosed in a tube of glass, which fits into a disc of thick plate glass, covering the upper side of the wooden box containing the coil and magnetic needle." (PhiL Trans 1830, p. 218.) (427) The sensibility of this instrument is very much increased by neutralizing the magnetic influence of the earth, by employing two needles, which was first done by Professor Gumming of Cambridge, and afterwards on an improved principle by Nobili. The neutralizing needle in his instrument is attached to the principal one ; placing them one above another and parallel to each other, but with their poles in opposite directions. They are fixed by being passed through a straw, suspended from a thread. The distance between the needles is such as to allow the upper coil of the wires to pass between them, an opening being purposely left, by the separa- tion of the wires at the middle of that coil, to allow the middle of the straw to pass freely through it. A graduated circle on which the deviation of the needle is measured, is placed over the wire, on the upper surface of the frame of the instrument, having an aperture in its centre for the free passage of the needle and straw. The whole of this arrangement will be easily understood, by imagining another needle to be suspended to the one above the coil in Fig. 185, moving within the wire, and having its poles turned the reverse of those of the upper needle. The instrument as thus constructed is called the astatic needle galvanometer. In Nobili' s instrument, the frame was twenty-two lines long, twelve wide, and six high. The wire was of copper covered with silk, one-fifth of a line in diameter, and from twenty-nine to thirty feet in length, making seventy -two revolutions round the frame. The needles were twenty-two lines long, three lines wide, a quarter of a line thick, and they were placed on the straw five lines apart from each other. (428) The advantages of Nobili' s instrument consist in the direc- tive force, arising from the influence of the earth's magnetism being nearly balanced, and a double rotatory tendency being given to the 328 GALVANIC OB VOLTAIC ELECTRICITY. needles. The lower needle is acted upon by the sum of the forces of the currents in every part of the coil, and the upper needle is acted upon by the excess of force in the upper current which is nearest to it, which force, of course, acts in a direction the reverse of that in which it acts upon the lower needle, being situated on the opposite side ; but since the poles are also in a reversed position, the rotatory tendency becomes the same in both needles. M. Lebailiff has extended the principle of Nobili's galvanometer, by employing four needles, two within the coil, having their poles similarly situated, and one above, and one below, having their poles reversed. He likewise employs five parallel wires, each sixty feet long for the coil, instead of one length of three hundred feet; by this means the current is divided into five parts, and made to flow through five different channels, with the alleged advantage of increasing the quantity, and diminishing the intensity of the Electricity ; it is not decided whether this is the case, nor is the advantage of employing four needles sufficiently obvious. Pig. 186 represents an elegant modification of Nobili's galva- Fig. 186. nometer. The bobbin is surrounded with some two or three thousand turns of very fine and well-insulated copper wire. The needles are suspended by a single fibre of bleached and baked silk. When the instrument is not in use the upper needle rests on a graduated card, from which it is raised when about to be put in action, by a simple mechanical contrivance, at the top of the glass shade. The axis joining the two needles must be brought exactly in the centre of the card, which is easily effected by means of adjusting screws. The upper needle is brought exactly to zero of the scale by turning the card, by means of a button, under- neath the base of the instrument. A good galvanometer should not make more than two oscillations a minute, and should return exactly to zero. It is almost needless to say, that the table on which it stands should contain no iron, and that all iron vessels should be removed, as far as possible, from its neighbourhood. It is covered with a glass case, to protect it from currents of air. So exquisite a test of the presence of minute quantities of Electricity, is a delicate galvanometer, that, by it, Schoenbein (Pog. Ann. xlv. p. 263) was able to prove a change in the composition of chloride of cobalt, when that salt in solution was changed blue by the action of heat, v. (429) The following illustration of the increase of the power of THE GALVANOMETER. 329 the current by employing the astatic system, is given by Peschell (Elements of Physics, vol. iii. p. 107) : Suppose that the multiplier wire wound 333 times, then the original current would act on the lower needle with a force of 666, and on the upper with a force of 333 times, what it would have possessed had the wire made but a single circuit ; adding both together, with a force 999, or 1000 times as great. Both needles made, with a similar position of their poles, 57 vibrations in a minute, an astatic needle only 9. As the direct- ing force of the earth's magnetism is proportional to the squares of these numbers, in the common needle this force will be 3248, and in the astatic needle 81 ; in the latter therefore it is 40 times less, and by consequence the electric current acts with 40 times the force upon it. The deflecting power of the original current will therefore be increased by this galvanometer 1000 X 40=40,000 times. The two needles in the astatic galvanometer, should be as similar as pos- sible, but not of precisely the same magnetic power, a slight degree of directive force being necessary in the system, otherwise it would remain in equilibrium in all azimuths. The frame on which the wire is wound should not be fixed, but moveable upon an axis, so that by a simple mechanical contrivance it may be brought into any required position with respect to the needles. (430) The sensibility of a galvanometer is judged of by the slow- ness of the oscillations of its magnetic system ; it may be considered sufficiently delicate," if they are at the rate o one a minute : but it not unfrequently happens that either from too strong a current, being sent through the instrument ; from the contiguity of a mag- netic bar ; from the reaction of the magnetism of the two needles ; or from some diiference in their dimensions, and the quality of the steel ; the galvanometer after a time loses a portion of its sensibility. By subjecting the needles to the following treatment, (Matteucci) the original delicacy of the instrument may be restored, but the operation requires considerable care and tact, and it is not an un- usual occurrence, to spend whole days in the arrangement of a galva- nometer for a course of delicate experiments. The first thing to be done is to note carefully the duration of an oscillation, then to ascer- tain which is the weaker of the two needles, for this purpose the upper one is first removed ; if now the system remain in its position, it is clear that the needle removed is more feeble than the other ; if, on the other hand, the needle which remains, returns of itself, it is evident that the needle taken away was the stronger of the two. The weak needle is then re-magnetized by passing a smtill bar magnet a few times along it from end to end, taking especial care not to arrest the motion of the bar or to return it on itself: the needle is 330 GALVANIC OB YOLTAIC ELECTRICITY. then returned to its place, and the duration of an oscillation of the system again determined ; if it has become greater, a proof is obtained that the sensibility of the galvanometer has been increased : should too much magnetism have been given to the needle, a portion must be taken away by reversing the motion of the magnetising bar along it. This is a nice operation and frequently gives a good deal of trouble. (431) It is usual for the maker of a galvanometer to mark on the scale, an indication by which the experimenter is enabled to ascertain from the direction of the deviation of the needle, the direction of the current. For this purpose we find marked on the scale two letters A and B, the same two letters are also marked on the side of the two extremities of the galvanometer. By a first experiment, the operator determines once for all, by means of a single electro-motive element, zinc and copper for instance, to which letter the point of the needle is carried according as the current enters into the wire of the instru- ment by the extremity A or B ; of course in the single voltaic pair the current is from the copper to the zinc. (432) Before commencing a series of experiments, the marked in- dications of the galvanometer should be verified, which may easily be done by plunging the extremities of two wires, platina and copper, into distilled water, and allowing the current of Electricity thereby determined to pass through the instrument, the direction of the current is from the platinum to the copper, through the galvanome- ter. (433) In his researches in electro-physiology, M. Dubois Eeymond employed a galvanometer containing 4560 coils of copper wire, and he has more recently had an apparatus constructed by M. Sauerwald of Berlin, with from 25,000 to 30,000 coils ; with this instrument, be detected the existence of electric currents in nerves and in muscles ; but to fit it for these delicate investigations, it was necessary to make corrections for certain irregularities of action, arising from two causes ; first, from the axes of the needles never being rigorously pa- rallel, in consequence of which the system is never accurately in the meridian; and second, from the impossibility of obtaining copper wire absolutely free from iron, the consequence of which is that the needle never stands exactly at zero. The correction applied by Dubois Eeymond is an improvement of that originally adopted by Nobili, and consists in placing in the interior of the galvanometer, facing the zero, a small magnetized fragment - S V of an inch in length, which com- pensates the disturbing action as long as the needles are near zero, but the action of which is null, as soon as they move through a few degrees. THE SINE GALVANOMETER. 331 (434) The Sine Gralvanometer (Fig. 187), consists of a single magnetized needle surrounded with a coil which is move"able on its axis ; it acts on the principle that the intensity of the current varies as the sine of the angle of deflection, and is applicable rather to the determination of the intensity of strong currents, than to the detec- tion of weak ones. The Fig. 187. instrument is placed in the magnetic meridian, and when the needle is deflected by the current, the coil is turned until it again coincides with the new direction of the needle, the exact paral- lellism of the needle and coil, being determined with the aid of a lens. The number of degrees which it was necessary to turn the coil from the zero point to adjust it to the new position of the needle, is read off" on the graduated scale surrounding the coil. This is the exact measurement of the angle which the needle forms with the magnetic meridian, and also of the intensity of the current, by which the needle has been deviated ; but this is also equal to the horizontal force of terrestrial magnetism, in virtue of which, the needle tends to return to the magnetic meridian, and this being equal to the sine of the angle of deflection, the intensity of the current is of course the same, and its value may be determined by reference to a table of natural sines. (435) Professor Callan's sine galvanometer (Phil. Mag. N. S. vol. vii. p. 73), consists of a mahogany circle 2 feet 4 inches in diameter, and nearly 2 inches thick, in the circumference of which is turned a groove | an inch wide and 3^ inches deep ; of seven concen- tric coils of f of an inch copper wire in the groove, and well insulated from each other ; of a strong frame in which the circle is moveable on an axis and always kept in a vertical position ; and of a compass- box, which, by means of a slide 3 feet long, and at right angles to the circle at its centre, may be moved in a direction perpendicular to the circle to the distance of 3 feet from it, so that the centre of the needle, which is a bar 5% inches long, will always be in the axis of the 3oil, and that the line joining the N. and S. points of the compass- 3ox will be always parallel to the horizontal diameter of the mahogany nrcle and coil. From this description it is evident that (no matter vhere the compass-box is placed on the slide) the needle is parallel o the mahogany circle and coil, or perpendicular to their axis when- ver it points to 0. Hence, if a voltaic current sent through the oil deflect the needle, and if the circle and coil be turned round so 332 GALVANIC On VOLTAIC ELECTRICITY. as to follow the needle until it points to 0, the needle, no matter where it may be placed on the slide, will then be parallel to the coil and perpendicular to its axis. The effective part of the earth's magnetism in impelling the needle to the magnetic meridian is also exerted in the direction of a perpen- dicular to the needle or of the axis of the coil, but opposite to that in which the magnetic force of the coil acts. Since the needle is kept at rest by these two forces acting in opposite directions, they must be equal. But the effective part of the earth's magnetism in impelling the needle to the magnetic meridian varies as the sine of the angle which it makes with the meridian ; therefore the magnetic power of the current flowing through the coil also varies as the sine of the angle which the needle, when it points to 0, makes with the magnetic meridian. If the connection with the battery be broken, the needle will immediately return to the magnetic meridian. The graduated circle of the compass-box will give the number of degrees the needle was deflected from the magnetic meridian. For measuring the angle of deviation, a graduated circle about 13 inches in diameter is used ; it is attached to the upper part of the mahogany circle, and at right angles to it, and to the axis about which it is moveable. "When the current is sent through? coils, the deflection is so great, that only very feeble currents can be measured on the sine galvanometer. When the needle isjn the centre of the coil, this galvanometer, used as a sine instrument, large as is its diameter, is incapable of measuring the power of a current produced by a single circle of the cast iron battery : but by sliding the compass-box and needle 2 or 3 feet from the coil, a current of very great power can be measured. (436) The Tangent Galvanometer (Figs. 188 and 189) consists of a large circle or hoop of copper ribbon covered with silk, fixed verti- Fig. 188. Fig. 189. THE TANQENT GALYANOMETEK. 333 cally upon a graduated circle, exactly in the centre of which is placed, either by suspension by a silk thread, or on a cap resting on a pivot, a very short but intensely magnetized needle. The hoop is placed exactly in the magnetic meridian, and when the current is transmit- ted through it, the needle deviates, and the force of the current is proportional to the tangent of the angle of the needless declination, whence the name given to the instrument. The needle is provided transversely with a long light copper needle by means of which the angle is measured. This instrument is not so sensitive as the sine galvanometer, but is applicable to currents of very high intensity. The tangent of the angle of deflection may be learned, without calcu- lation, by reference to the table of natural tangents. An instrument called the differential galvanometer has been used for the determina- tion of the relative force of two currents. It consists of a galvano- meter with two perfectly similar wires wound round the same frame ; now, if two currents of precisely the same intensity be sent in oppo- site directions through these wires the needle will obviously remain at zero, but if one current be more powerful than the other, the needle will move, indicating the strongest current, and showing by the amplitude of the deviation, by how much, the strongest current exceeds the weakest. (437) Tor the detection of currents of small intensity, such as those produced by thermo-electric action, neither of the galvano- meters above described is adapted, the length and the thinness of the wire opposing too great a degree of resistance to the passage of such feeble forces. The wire for such purposes should make but few turns round the needle, and should be at least -g^th of an inch in thickness, or, as Fechner recommends, should consist of a single strip of copper, and an astatic needle having the freest possible motion. (438) A large and very sensible thermoscopic galvanometer was invented by Dr. Locke, professor of chemistry in the medical college of Ohio, and by him communicated to the Phil. Mag., in August, 1837. The object proposed by Dr. Locke in the invention of this instrument was to construct a thermoscope so large that its indi- cations might be conspicuously seen on the lecture-table by a numerous assembly, and at the same time so delicate as to show extremely small changes of temperature. How far he succeeded, will appear from the following very popular experiment he was in the habit of making with it. By means of the warmth of the finger applied to a single pair of bismuth and copper discs, there was transmitted a sufficient quantity of Electricity to keep an eleven-inch needle weighing an ounce and a half, in a continued 334 GALVANIC OE VOLTAIC ELECTRICITY. revolution, the connexions and reversals being properly made at every half turn. The greater part of this effect was due to the massiveness of the coil which was made of a copper fillet about fifty feet long, one-fourth of an inch wide, and one-eighth of an inch thick, weighing between four and five pounds. This coil was not made in a pile at the diame- ter of the circle in which the needle revolved, but was spread out, the several turns lying side by side and covering almost the whole of that circle above and below. It was wound closely in parallel turns on a circular piece of board eleven and a half inches in diameter, and half an inch in thickness, covering the whole of it except two small opposite segments of about ninety degrees each ; on extracting the board, a cavity of its own shape was left in which the needle was placed. The copper fillet was not covered by silk, or otherwise coated for insulation, but the several turns of it were separated at their ends by veneers of wood just so far as to prevent contact throughout. In the massiveness of the coil this instrument is perhaps peculiar, and by this means it affords a free passage to currents of the most feeble intensity, enabling them to deflect a very heavy needle. The coil was supported on a wooden ring furnished with brass feet and levelling screws, and surrounded by a brass hoop with a flat glass top or cover, in the centre of which was inserted a brass tube for the suspension of the needle by a cocoon filament. The needle was the double astatic one of Nobili, each part being about eleven inches long, one-fourth wide, and one-fortieth in thickness. The lower part played within the coil, and the upper one above it, and the thin white dial placed upon it, thus performing the office of a conspicuous index underneath the glass. For experiments in which large quantities of Electricity are concerned, this instrument is quite unfit : but it is well adapted to show to a class, experiments on radiant heat with Pictet's conjugate reflectors, in which the differential, or air thermo- meter, affords to spectators at a distance but an unsatisfactory indication. For this purpose the electrical element necessary is merely a disc of bismuth as large as a shilling soldered to a corre- sponding one of copper, blackened and erected in the focus of the reflector, while the conductors pass from each disc to the poles of the galvanometer. "With this arrangement the heat of a non- luminous ball at the distance of twelve feet will impel the needle near 180, and if the connexions and reversals are properly made will keep it in continued revolution. (439) We have seen (49) that the lightness and flexibility of gold-leaf have rendered that metal highly valuable to the electrician IREMONGER'S HYDROSTATIC GALVANOMETER. 335 in the construction of instruments for appreciating minute quantities of statical Electricity. The same material, with the addition of a magnet, may be arranged so as to form probably one of the most delicate tests possible, of the existence and direction of a weak galvanic current. A slip of gold leaf is retained in the axis of a glass tube by a metallic forceps at each end, and a strong horse- shoe magnet is fixed with its poles on either side of the middle of the tube ; on causing the electrical current to pass down the gold leaf it will be attracted or repelled, laterally by the poles of the magnet, according as the current is ascending or descending. (Cum- ming's Manual of Electro-dynamics.) (440) Mr. Sturgeon also describes {Lectures on Galvanism, p. 80) an instrument in which a single gold leaf is employed, but instead of a magnet a dry electric pile is used : " A glass phial has its neck cut off and is perforated on its two opposite sides, for the intro- duction of two horizontal wires. These wires are formed into screws and work in box- wood necks which are firmly cemented to the bottle, with their centres directly over the perforations. Through the centre of a wooden cap, cemented to the top of the bottle, passes a brass wire tapped at its upper extremity for the reception of a metallic plate, and from its lower extremity hangs a very narrow slip of gold leaf pointed at its lower end, which reaches just as low as the inner balls of the horizontal wires. The bottle stands upon and is cemented to a boxwood pedestal. Upon two glass pillars fixed to a wooden base is placed horizontally, a dry electric pile, consisting of about one hundred pairs, or rather single pieces of zinc with bright and dull surfaces. The poles of this pile are connected with the two- horizontal wires by thin copper wires." The sensibility of this instrument Mr. Sturgeon states to be very great. A zinc plate about the size of a sixpence being attached to the upper end of the axial wire, on pressing upon it a similar sized copper plate, the pendant leaf leans towards the negative ball, and when the copper is suddenly lifted up, the leaf will strike ; when the plates are reversed the leaf leans towards, and strikes the positive ball. (441) Mr. Iremouger describes (Proceedings of the London Elec- trical Society,) an ingenious galvanometer on hydrostatic principles. ' A small bar magnet is attached to the bottom of an areometer : this ipparatus being so weighted that the ball may float just below the surface of pure water. Over the proof glass, containing the said ireometer, is passed a De la Rive's ring placed rather below the level >f the lower pole of the magnet. Now, on passing a voltaic current hrough the ring, the magnet and areometer are forced downwards : >ut at the same time I accompany this motion by a corresponding 336 GALVANIC OR VOLTAIC ELECTRICITY. movement of the ring, by which means the descent of the floating apparatus is continued till the electro-magnetic forces are in equili- brium with the upward pressure of the liquid. Now, the pressure of liquids being simply as their height, the different degrees of any equally divided scale attached to this instrument, will be of equal value no slight advantage. The delicacy of the instrument will depend on several circumstances, such as the size of the stem of the areometer, the strength of the magnet, and also on the length of wire and number of turns in the ring." Mr. Iremonger gives a detailed account of the method of constructing this instrument, for which, as it could not be well understood without a drawing, the reader is referred to his original paper, in the Proceedings of the Elec- trical Society. (442) Physiological E/ects of Galvanism. The action of galvanic Electricity on the living animal, is the same as that of the common electric current, account being taken of the intensity of the one, and the duration of the other. When any part of the body is caused to form part of the circuit of the voltaic pile, a distinct shock resembling that of a large electrical battery weakly charged, is experienced every time the connection with the extremities is made ; and besides this, if the pile be a large one, a continued aching pain is frequently felt as long as the current is passing through the body, and if the slight- est excoriation or cut happen to be in the path of the currrent, the pain is very severe. The intensity of galvanic Electricity is so low that it requires good conductors for its transmission ; unless, there- fore, the skin be previously moistened, it will not force its way through the badly conducting cuticle, or outer skin. The most effectual mode of receiving the whole force of the battery, is to wet both hands with water, or with a solution of common salt, and to grasp a silver spoon in each, and then to make the connection between the poles of the battery. Another method is to plunge both hands into two separate vessels of water, into which the extremities of the wires from the battery have been immersed. Yolta has remarked, that the pain is of a sharper kind on those sensible parts of the body included in the circuit, which are on the negative side of the pile ; this is particularly remarkable with the water-battery, and the same has been noticed with regard to the pungency of the com- mon electrical spark. (443) It does not require a voltaic pile to exhibit the effects of galvanic Electricity on the animal, whether living or dead. The simple application of a piece of zinc and one of silver to the tongue and lips, frequently gives rise, at the moment of the contact of the metals, to the perception of a luminous flash ; but the most certain PHYSIOLOGICAL EFFECTS. 337 way of obtaining this result, is to press a piece of silver as high as possible between the upper lip and the gums, and to insert a silver probe into the nostrils, while at the same time a piece of zinc is laid upon the tongue, and then to bring the two metals into contact. Another mode is to introduce some tin foil within the eyelid, so as to cover part of the globe of the eye, and place a silver spoon in the mouth, which must then be made to communicate with the tin foil, by a wire of sufficient length ; or, conversely, the foil may be placed on the tongue, and the rounded end of a silver probe applied to the inner corner of the eye, and the contact established as before. This phenomenon is evidently produced by an impression communicated to the retina or optic nerve, and is analogous to the effect of a blow on the eye, which is well known to occasion the sensation of a bright luminous coruscation, totally independent of the actual pre- sence of light. In the like manner the flash from galvanism is felt, whether the eyes are open or closed, or whether the experiment is made in day light or in the dark. If the pupil of the eye is watched by another person when this effect is produced, it will be seen to contract at the moment the metals are brought into contact ; a flash is also perceived the moment the metals are separated from each other. When different metals are applied to different parts of the tongue, and made to touch each other, a peculiar taste is perceived': in order that this experiment should succeed, the tongue must be moist ; the effect is materially diminished if it be previously wiped, and cannot be produced at all if the surface be quite dry. The quality of the metal laid upon the tongue influences the kind of taste which is communicated ; the more oxidable metal giving rise to an acid, and the less oxidable metal to a distinct alkaline taste. Similar differences have been observed by Berzelius, with regard to the sensations excited in the tongue, by common Electricity directed in a stream upon that organ from a pointed conductor; the taste of positive Electricity being acid, and that of negative Electricity caustic and alkaline. (444) If the hind legs of a frog be placed upon a glass plate, and the crural nerve dissected out of one, made to communicate with the other, it will be found on making occasional contacts with the remaining crural nerve, that the limbs of the animal will be agitated at each contact. Aldini, the nephew of the original discoverer of galvanism, produced very powerful muscular contraction, by bringing a part of a warm-blooded and of a cold-blooded animal into contact with each other, as the nerve and muscle of a frog, with the bloody flesh of the neck of a newly decapitated ox, and also by bringing the nerve of one animal into contact with the muscle of another. (445) If a crown piece be laid upon a piece of zinc of larger size, 338 GALVANIC OR VOLTAIC ELECTRICITY. and a living leech be placed upon the silver coin, it suffers no incon- venience as long as it remains in contact with the silver only, but the moment it has stretched itself out and touched the zinc, it suddenly recoils, as if from a violent shock. An earth worm exhibits the same kind of sensitiveness. The convulsive movements excited in the muscles of animals after death, by a powerful galvanic battery, are extremely striking if the power is applied before the muscles have lost their contractility. Thus, if two wires connected with the poles of a battery of a hundred pairs of plates are inserted into the ears of an ox or sheep, when the head is removed from the body of the animal recently killed, very strong actions will be excited in the muscles of the face every time the circuit is completed. The con- vulsions are so general as often to induce a belief that the animal has been restored to life, and that he is enduring the most cruel sufferings. The eyes are seen to open and shut spontaneously ; they roll in their sockets as if again endued with vision ; the pupils are at the same time widely dilated ; the nostrils vibrate as in the act of smelling; and the movements of mastication are imitated by the jaws. The struggles of the limbs of a horse galvanised soon after it has been killed, are so powerful as to require the strength of several persons to restrain them. (446) The following account of some experiments made by Dr. tire on the body of a recently-executed criminal, will serve to convey a tolerably accurate idea of the wonderful physiological effects of this agent, and will be impressive from their conveying the most terrific expressions of human passion and human agony : " The subject of these experiments was a middle-sized, athletic, and extremely muscular man, about thirty years of age. He was suspended from the gallows nearly an hour, and made no convulsive struggle after he dropped; while a thief, who was executed along with him, was violently agitated for a long time. He was brought into the anatomical theatre of our university about ten minutes after he was cut down. His face had a perfectly natural aspect, being neither livid, nor tumefied, and there was no dislocation of the neck. " Dr. Jeffray, the distinguished professor of anatomy, having on the preceding day requested me to perform the galvanic experiments, I sent to his theatre the next morning with this view, my minor voltaic battery, consisting of two hundred and seventy pairs of four- inch plates, with wires of communication, and pointed metallic rods with insulating handles, for the more commodious application of the electric power. About five minutes before the police-officers arrived with the body, the battery was charged with dilute nitro-sulphuric acid, which speedily brought it into a state of intense action. The PHYSIOLOGICAL EFFECTS. 339 dissections were skilfully executed by Mr. Marshall, under the super- intendence of the professor. " Experiment 1. A large incision was made in the nape of the neck just below the occiput ; the posterior half of the atlas vertebra was then removed by bone forceps ; when the spinal marrow was brought into view, a profuse flow of fluid blood gushed from the wound, inundating the floor. A considerable incision was- at the same time made in the left hip, through the great gluteal muscle, so as to bring the sciatic nerve into sight, and a small cut was made in the heel ; from neither of these did any blood flow. The pointed rod connected with one end of the battery was now placed in contact with the spinal marrow, while the other rod was applied to the sciatic nerve ; every muscle of the body was immediately agitated with con- vulsive movements, resembling a violent shuddering from cold. The left side was most powerfully convulsed. On removing the second rod from the hip to the heel, the knee being previously bent, the leg was thrown out with such violence as nearly to overturn one of the assistants, who in vain attempted to prevent its extension. " Experiment 2. The left phrenic nerve was now laid bare at the outer edge of the sternothyroideus muscle, from three to four inches above the clavicle ; the cutaneous incision having been made by the side of the sterno-cleido-mastoideus. Since this nerve is distributed to the diaphragm, and since it communicates with the heart through the eighth pair, it was expected by transmitting the galvanic current along it, that the respiratory process would be renewed. Accord- ingly a small incision having been made under the cartilage of the seventh rib, the point of the one insulating rod was brought into contact with the great head of the diaphragm, while the other point was applied to the phrenic nerve in the neck. This muscle, the main agent of respiration, was immediately contracted, but with less force than was expected. Satisfied from ample experience on the living body, that more powerful effects can be produced by galvanic excitation, by leaving the extreme communicating rod in close contact with the parts to be operated on, while the electric chain or circuit is completed by running the end of the wires along the top of the plates in the last trough of either pole, the other wire being steadily immersed in the last cell of the opposite pole, I had immediate' recourse to this method. The success of it was truly wonderful ; full, nay, laborious breathing, instantly commenced, the chest heaved and fell, the belly protruded, and again collapsed with the relaxing and retiring diaphragm. This process was continued without inter- ruption as long as I continued the electric discharges. In the judg- ment of many scientific friends who witnessed the scene, this respi- 2 z 340 GALYANIC OB VOLTAIC ELECTRICITY. ratory experiment was perhaps the most striking ever made with philosophical apparatus. " Let it also be remembered, that for- full half an hour before this period, the body had been well nigh drained of its blood, and the spinal marrow severely lacerated. No pulsation could be perceived, meanwhile at the heart or wrist ; but it may be supposed that but for the evacuation of blood, the essential stimulus of that organ, this phenomenon might also have occurred. "Experiment 3. The super-orbital nerve was laid bare in the forehead, as it issues through the supra-ciliary foramen in the eye- brow ; the one conducting rod being applied to it, and the other to the heels, most extraordinary grimaces were exhibited every time the electric discharges were made, by running the wire in my hand over the edges of the plates in the last trough, from the two hundred and twentieth to the two hundred and seventieth pair, thus fifty shocks, each greater than the preceding ones, were given in two seconds. Every muscle of his countenance was simultaneously thrown into fearful action ; rage, horror, despair, and anguish, and ghastly smiles united their hideous expression in the murderer's face, surpassing far the wildest representations of a Fuseli or a Kean. At this period several of the spectators were obliged to leave the room from terror or sickness, and one gentleman fainted. "Experiment^. The last galvanic experiment consisted in trans- mitting the electric power from the spinal marrow to the ulnar nerve, as it passes by the internal condyle at the elbow ; the fingers now moved nimbly, like those of a violin performer: an assistant, who tried to close the fist, found the hand to open forcibly in spite of his efforts. When one rod was applied to a slight incision on the top of the forefinger, the first being previously clenched, the fingers extended instantly, and from the convulsive agitation of the arm, he seemed to point to the different spectators, some of whom thought he had come to life. About an hour was spent in these operations." (447) In these experiments the positive wire was always applied to the nerve, and the negative to the muscles ; that this is important, will appear from the following facts : Let the posterior nerve of a frog be prepared for electrization, and let it remain till its voltaic susceptibility is considerably blunted, the crural nerves being connected with a detached portion of the spine ; plunge the limbs into one glass full of water, and the crural nerves, &c. into another glass ; then take a rod of zinc in one hand, and a silver tea-spoon in the other, plunge the former into the water of the limbs' glass, and the latter into the water of the nerves' glass, without touching the frog itself, and gently strike the dry parts of PHYSIOLOGICAL EFFECTS. 341 the metals together ; feeble convulsive movements or mere twitching of the fibres will be perceived at each contact ; reverse now the position of the metal rods, and on renewing the contact between them, very lively convulsions will take place, and if the limbs are skilfully disposed in a narrow conical glass, they will probably spring out to some distance. Or, let an assistant seize in his moistened left hand the spine and nervous cords of the prepared frog, and in his right a silver rod, and let another person lay hold of one of the limbs with his right hand, and a zinc rod in the moist fingers of the left ; on making the contact, feeble convulsive twitching will be perceived as before ; now let the metals be reversed ; on renewing the contact, lively movements will take place, which become very conspicuous ; if one limb be held nearly horizontal, while the other hangs freely down, at each touch of the voltaic pair, the drooping limb will start up and strike the hand of the experimenter. Hence, for the purposes of resuscitating the dormant irritability of the nerves, as Dr. Ure remarks, or the contractility of their subordi- nate muscles, the positive pole must be applied to the former and the negative to the latter. (448) Some interesting researches, on the relation between voltaic Electricity and the Phenomena of Life, were published in the Philo- sophical Transactions by Dr. Wilson Philip. In his earlier researches, he endeavoured to prove that the circula- tion of the blood, and the action of the involuntary muscles, are in- dependent of the nervous influence. In a paper, read in January, 1816, he showed the immediate dependence of the secretory function on the nervous influence. The eighth pair of nerves distributed to the stomach, and subservient to digestion, were divided by incisions in the necks of several rabbits ; after the operation, the parsley which they ate remained without alteration in their stomachs, and the ani- mals, after evincing much difficulty in breathing, appeared to die of suffocation. But when in other rabbits similarly treated, the galva- nic power was distributed along the nerve below its section, to a disc of silver placed closely in contact with the skin of the animal oppo- site to ita stomach, no difficulty of breathing occurred. The voltaic action being kept up for twenty-six hours, the rabbits were then killed, and the parsley was found in as perfectly digested a state as that in healthy rabbits fed at the same time ; and their stomachs evolved the smell peculiar to that of rabbits during digestion. These experiments were several times repeated with similar results. Thus a remarkable analogy is shown to exist between the galvanic energy and the nervous influence, the former of which may be made 342 GALVANIC OE VOLTAIC ELECTRICITY. to supply the place of the latter, so that while under it, the stomach, otherwise inactive, digests food as usual. (449) Dr. Philip was next led to try galvanism as a remedy in asthma. By transmitting its influence from the nape of the neck to the pit of the stomach, he gave decided relief in every* one of twenty- two cases, of which four were in private practice, and eighteen in the Worcester infirmary. The power employed varied from ten to twenty-five pairs. (450) These results of Dr. Philip have since been confirmed by Dr. Clarke Abel, of Brighton (Journ. Sc. ix.) : this gentleman employed, in one of his repetitions of the experiments, a comparatively small, and in the other a considerable, power. In the former, although the galvanism was not of sufficient power to occasion evident digestion of the food, yet the efforts to vomit and the difficulty of breathing, (constant effects of dividing the eighth pair of nerves,) were prevented by it. The symptoms recurred when it was discontinued, but vanished on its re-application. "The respiration of the animal," he observes, " continued quite free during the experiment, except when the disengagement of the nerves from the tin foil, rendered a short suspension of the galvanism necessary, during their re-adjustment. The non-galvanized rabbit wheezed audibly, and made frequent attempts to vomit. In the latter experiment, in which greater power of galvanism was employed, digestion went on, as in Dr. Philip's experiments." (451) It had been suggested by an eminent French physiologist, M. Gallois, that the motion of the heart depends entirely upon the spinal marrow, and immediately ceases when the spinal marrow is re- moved or destroyed. But Dr. Philip rendered rabbits insensible by a blow on the occiput, the spinal marrow and brain were then removed and the respiration kept up by artificial means ; the motion of the heart and circulation were carried on as usual. When spirit of wine or opium was applied to the spinal marrow or brain, the rate of cir- culation was accelerated. These experiments appear to confute the notion of M. Gallois. (452) The general inferences deduced by Dr. Philip from his numerous experiments are, that Voltaic Electricity is capable of effecting the formation of the secreted fluids when applied to the blood, in the same way in which the nervous influence is applied to it ; and that it is capable of occasioning an evolution of caloric from arterial blood, when the lungs are deprived of the nervous influence^ by which their function is impeded, and even destroyed; when diges- tion is interrupted by withdrawing this influence from the stomach, THERAPEUTIC APPLICATIONS. 343 these two vital functions are renewed by exposing them to the influ- ence of a galvanic trough. " Hence," says he, " galvanism seems capable of performing all the functions of the nervous influence, in the economy : but obviously, it cannot excite the functions of animal life, unless when acting on parts endowed with the vital principle" Application of Galvanic Electricity to the treatment of diseases. (453) The following observations on this subject occur in the Cyclopaedia of Practical Medicine, from the pen of Dr. Apjohn: " There are several diseases incident to the human frame, in which the application of galvanism by the hand of a skilful physician, may be, and indeed has been, attended with happy results. In asphyxia, for instance, whether proceeding from strangulation, drowning, narcotic poisons, the inhalation of noxious gases, or simple concussion of the cerebral system, it has been applied with success. In all these cases, the interrupted current that is, a succession of shocks should be resorted to ; the battery should be pretty powerful, and care should be taken that the Electricity be as much as possible confined to the nerves, and that it be sent along them in the direction of their rami- fications. M. G-oudret was the first who proposed galvanism in cases of asphyxia produced by concussion of the brain ; he experimented 011 rabbits, which were to all appearance killed by a few violent blows inflicted upon the back of the head, and succeeded in recovering them perfectly by a succession of shocks continued for half an hour from a battery of thirty couples, and transmitted between the eyes, nose, and meatus auditories externus on the one hand, and different parts of the spine of the animal on the other. The same experiments have been repeated by Majendie, Apjohn, and others with perfect success, and the former states that he has recovered rabbits as- phyxiated by submersion in water for more than a quarter of an hour. In paralytic affections also, which are of a purely functional character, or which do not depend upon organic diseases of the nervous system, or pressure exercised on any part of it, the agency of the pile can be rationally resorted to by the medical practitioner. Under this head may be ranged general or local paralysis, arising from exposure to cold, palsy of the wrists from the absorption of lead, and many varieties of deafness and amaurosis. In all these cases, as the nerves are to be stimulated to increased action, an interrupted current must be employed. In cases of deafness, to submit the auditory nerve to galvanic action, it is sufficient to introduce a wire connected with one of the poles of a battery into the affected ear, 344 GALVANIC OB VOLTAIC ELECTEICITY. and the other wire into the opposite ear, the circuit then being rapidly broken and completed by an assistant. (454) In amaurosis, the galvanic shock may be transmitted at pleasure through the ball of the eye, so as to traverse the retina, or be confined to those twigs of the first branch of the fifth pair of nerves, which ramify on the forehead above the orbit, and upon the state of which alone Majendie has shown that gutta serena often depends. In aphonia, the circuit may be completed through the organs chiefly concerned in the production of the voice, by placing a shilling upon the tongue and touching it with the negative wire of a battery whose other pole is alternately brought into connexion with, and separated from, different parts of the external larynx. (455) The following case of a cure of an epileptic patient by galvanic treatment is related by Dr. Pearson (Revue Medicate, vol. iii. p. 333) . The cuticle having been removed by a blister from the back of the neck and inner side of one knee, those parts were covered with bits of moistened sponge, upon which slips of linen were laid, and over all, discs of silver and copper, the former metal being applied to the neck, the latter to the knee. The discs were then connected by a copper wire and enclosed in a pouch composed of chamois leather, so as to be insulated from adjacent parts. ' This apparatus having been applied for six months, the case was cured. It was found to continue in action for ten or twelve hours, after which it became necessary to clean the plates and renew the pledgets of sponge and linen. (456) Galvanism, in the form of the continued current, has also been strongly recommended by Dr. "Wilson Philip for the treatment of what he denominates habitual asthma. His method is to apply a disc of silver to the nape of the neck, and another to the epigastric region, and then press the positive wire of a galvanic trough, con- sisting of from 8 to 16 pairs of 4 inch plates charged with very dilute muriatic acid, against the former, and the negative wire against the latter : relief usually occurs in from five to fifteen minutes. Another application of the galvanic pile is to the coagulating the blood within an aneurismal tumour ; this is founded on the discovery of Brande, that " when the wires attached to the extremities of the trough are introduced into any animal fluid containing albumen, the latter principle separates at the positive pole in a coagulated state." A case in which a perfect cure of an aneurism of the temporal artery was effected by galvanism, is related by M. Petrequin (Comptes Rendus, Nov. 3, 1845). Two needles were thrust into the tumour, and the power employed was gradually augmented up to 50 pairs. At the end of 12 minutes the throbbing had entirely ceased, and the THERAPEUTIC APPLICATIONS. 345 aneurism with isochronous pulsations was replaced by a solid and indurated tumour. (457) Galvanism has also been applied by M. Pravaz (Revue Medicale, December 1830,) as an eschar otic to wounds caused by the bites of rabid animals. He details several cases in which this practice was successful, in one of which the cauterization was not resorted to until 54 hours after the reception of the bite. The battery he used was of low power, consisting of only two troughs, containing between them but fifty pairs of electromotors. The escTiar was usually detached on the eleventh day, and the cicatrization com- pleted on the seventeenth. (458) A very curious application of the pile was suggested by Prevost and Dumas (Journal de Physiologie, torn. iii. p. 207). Reflecting on its powers of decomposition, it occurred to them that it might be successfully employed for breaking down the materials which compose urinary calculi, and that thus the necessity for one of the most formidable of surgical operations would be obviated. Their idea in fact was to introduce into the bladder a canula containing two platina wires carefully insulated from each other, and whose internal ends should be brought in contact with the stone, while their external extremities were put in connexion with the poles of a powerful battery. Upon the established principles of electro-chemis- try, they expected that it would be resolved into its acids and bases, the former assembling at the- positive, the latter at the negative pole, and that in this way its gradual disintegration would be effected. A preliminary experiment made upon a fusible calculus, placed in a basin of water, and a second upon a stone of the same kind, intro- duced into the bladder of a dog previously injected with tepid water gave encouraging results. The former submitted for 8 hours to the action of a battery composed of 120 pairs, was reduced from 92 to 80 grains, and in 8 additional hours was so disintegrated as to break into small crystalline fragments upon the application of the slightest pressure. The latter underwent similar changes, and they found that no irritating effect whatever was produced upon the bladder, however powerful the battery which they employed. The manipula- tions are however exceedingly dimcult, as may easily be imagined, and the proposal has not hitherto been acted on. (459) Eor the medical application of voltaic Electricity, the old Cruikshank trough may be employed; the exciting agent being dilute sulphuric acid. The mode of application may differ in diffe- rent cases ; when it is to be applied on the surface, the current may be transmitted through the medium of sponges ; or, what is perhaps 346 GALVANIC OR VOLTAIC ELECTRICITY. more convenient, by means of saddles of tain sheet copper covered with thick flannel, and saturated with brine, the surface of the skin being also well moistened with salt and water. It is sometimes, how- ever, desirable to act on parts deeply seated below the surface ; in such cases, the following method of M. Sarlandiere may be adopted: Needles of steel or platinum are introduced, as in the process of acupuncturation, the needles being connected respectively with the two opposite ends or poles of the battery. Becquerel considers this to -be the most efficacious mode of applying Electricity, since it permits the operator to act directly on the diseased part. Several ingenious "electro-voltaic" batteries for physiological purposes have recently been invented. Pulvermacher's modification of the pile consists of a chain formed of a series of gilded copper and zinc wires wound closely together round pieces of porous wood ; to excite it, the wood is immersed in vinegar, a sufficient quantity of which is absorbed to act on the zinc, the elements of the chain are connected by small metallic hooks ; 100 links give a pretty strong shock. Stringfellow's patent pocket battery is an elegant, and, for its size, a surprisingly powerful arrangement.. Each element consists of a strip of zinc about 2<| inches long, round which is wound, as closely as possible, but not in absolute metallic contact, a coil of flattened copper wire forming 30 convolutions. A series of six of these elements when excited with weak acetic acid gives distinct shocks, and decomposes unacidulated water. A set of 22 gives a brilliant park between graphite points, decomposes unacidulated water briskly, and gives pretty smart shocks ; and the power is scarcely impaired, after half an hour's action ; the battery is charged by drawing a small piece of sponge, moistened with distilled vinegar, (one part acetic acid to seven parts of water) several times down the centre on both sides of each fold ; it is then replaced in its case, not longer than a common card-case, and the current applied to any part of the body by means of two small metallic discs attached to either pole of the battery by elastic cords. (460) It was first noticed by Marianini that the force of the shock differs considerably according as the current goes in one direc- tion or another ; thus, if a person grasp two conductors connected with the poles of an extensive voltaic battery in vigorous action, he will experience a much more powerful muscular contraction in the arm which is in communication with the negative, than in that connected with the positive end ; so also, if the current be passed down the arm from the shoulder to the hand, the latter being im- mersed in a basin of salt water, a powerful contraction is experienced ; THERAPEUTIC APPLICATIONS. 347 if, however, the current be passed from the hand to the shoulder, the contractions are much less violent, and the difference is observed most strikingly in paralytic patients. (461) The following explanation of these differences is offered by Marianini : The action of Electricity on the muscles and nerves produces two distinct kinds of contractions ; the first, which he calls idiopatJiic, is the result of the immediate action of the current on the muscles; and the second, which he calls sym- pathetic, arises from the action of Electricity on the nerves which preside over the motions of the muscles. Now, idiopatJiic con- tractions are necessarily produced in whatever direction the current of Electricity passes ; but the occurrence of sympathetic contractions must be governed by the direction of the passing current they can only take place when the Electricity is transmitted in the direction of the ramification of the nerves ; the shocks then, experienced when the current is transmitted from the shoulder to the hand, are more powerful than those passed in the reverse direc- tion, because in the former case the Electricity is transmitted in the direction of the ramifications of the nerves, and in the latter in the contrary direction. These facts, which the researches of Matteucci confirm and illustrate in a satisfactory manner, will serve as a valuable guide to the Electrician in his treatment of cases of paralysis by this form of Electricity. (462) Majendie and Grapengresser have paid much attention to the curative effects of galvanism in amaurosis and deafness ; the same observations, which we made above, respecting the care and ana- tomical knowledge requisite for treating such diseases by frictional Electricity, apply also here, and perhaps even with greater force. Majendie's usual plan was to employ acupuncturation, making the electrical current act directly on the nerves of the orbit of the eye ; and in this way he accomplished some remarkable cures. Grapen- gresser proceeded in a different manner. He introduced into the nose a silver probe connected with the positive end of the battery, and touched the region of the frontal nerve, previously well moistened, with a wire connected with the negative end. In cases of deafness, he used two silver wire conductors, each bent at one end, exactly in the direction of the meatus auditorius, and terminating in a small knob exactly fitting the auditory canal, which was covered with linen and moistened. The current running through the nerves with great rapidity, is communicated to the auditory nerve, and generally occa- sions the sensation either of a loud noise or of a tinkling sound. A feeble power must be employed in these cases, and be continued for only a few minutes at a time ; as a general rule, the operator should 348 GALVANIC OB YOLTAIC ELECTEICITT. in all cases commence with a weak battery, gradually increasing its strength as the case progresses : in cases of paralysis, the battery power required frequently rises to 100 pairs. (463) The observation was made long since by Humboldt, that a a very weak galvanic power was capable of exercising a remarkable influence on the secretions from wounds ; he found that when a simple arc was applied to a blistered surface, the part exposed to the most oxidable metal was more irritated than that to which the negative plate was applied. Dr. Golding Bird has made an ingenious application of this singular fact to the production ofpuriginous sores, in the place of the issue and seton. His plan is the following :^By means of small blisters he raises the skin by effused serum, and having snipped it, he applies to the blister from which a permanent discharge is required a piece of zinc foil, and to the other a piece of silver, the two metals being connected by a wire, and covered with a common water dressing and oiled silk. On raising the zinc-plate after a few hours, the surface of the skin underneath will have assumed a white appearance, as if it had been rubbed with nitrate of silver : in forty-eight hours a decided eschar will appear, which, still keeping on the plates, will, at the end of a few days, begin to separate at the edges. The plates may then be removed ; the surface where the silver was applied will be found to be completely healed. A common poultice may then be applied to the part, and a healthy granulating sore, with well-defined edges, freely discharging pus, will be left. During the whole process, if the patient complains of pain at all, it will always be referred to the silver plate, where, in fact, the blister is rapidly healing ; and not the slightest complaint will be made of the zinc-plate, where the slough is as rapidly forming. (464) Dr. Bird is of opinion, that in this method of forming a sore the escliarotic action is that of the chloride of zinc, which is produced by the chlorine set free, by the galvanic action from the chloride of sodium constituting the saline ingredient of the fluid, effused on the surfaces of the blisters ; and, in illustration of the truth of his theory, he instances the following experiment made by Dr. Babington : The doctor took two slices of muscular flesh, and placed one between two plates of glass, and the other between plates of copper and zinc, binding them together with wire. In the course of a few days, the weather being warm, the flesh between the glasses began to putrefy, and soon afterwards was full of maggots ; while that between the metallic plates remained free from putrescency. A remarkable change had, however, occurred ; for on taking off the plates the side opposite the zinc-plate was hard, as if it had been artificially dried ; while that opposed to the copper had become THERAPEUTIC APPLICATIONS. 3-19 covered with a transparent substance resembling jelly ; in fact, observes' Dr. Bird, the result of the experiment evidently was, that the chloride of sodium existing in the flesh had been decomposed, the zinc had been acted upon, and a dry, hard compound of chloride of zinc and albumen formed on one side of the piece, whilst the soda set free on the other side had become converted into albuminate of soda, in the form of a gelatinous mass. 350 GALVANIC OE YOLTAIC ELECTRIC IT ST. CHAPTEE IX. EFFECTS OF THE HYDKO-ELECTBIC CTJEBENT. (CONTINUED.) Chemical Phenomena. (465) Before entering upon this interesting branch of our subject, it will be necessary that we describe the new terms introduced by Faraday, and state his reasons for adopting them. According to the views of this philosopher (Experimental Researches, 518, 524), elec- tro-chemical decomposition is occasioned by an internal corpuscular action, exerted according to the direction of the electric current, and is due to a force either superadded to, or giving a direction to, the ordinary chemical affinities of the bodies present. He conceives the effects to arise from forces which are internal, relative to the matter under decomposition, and not external, as they might be considered if directly dependent upon the poles. He supposes that the effects are due to a modification, by the electric current, of the chemical affinity of the particles through, or by which, that current is passing, giving them the power of acting more forcibly in one direction than in another, and consequently making them travel by a series of suc- cessive decompositions and recompositions in opposite directions, and, finally, causing their expulsion or exclusion at the boundaries of the body under decomposition, in the direction of the current, and that, in larger or smaller quantities, according as the current is more or less powerful. Fig. 190. Thus, in Fig. 190, the particles L A J^~^) a a cou ^ not De transferred, or ^^^J travel from one pole JST, towards the other P, unless they found particles Fi &- 191 ' of the opposite kind, I I, ready to pass in the opposite direction; for ii} is b ^ virtue of their increased affinity for those particles, combined with their diminished affinity for such as are behind them in their course, that they are urged forward ; and when any one particle a, CHEMICAL PHENOMENA. 331 Fig. 191, arrives at the pole, it is excluded or set free, because the particle b of the opposite kind, with which it was the moment before in combination, has, under the super-inducing influence of the current, a greater attraction for the particle a\ which is before it in its course, than for the particle a, towards which its affinity has been weakened : a may be conceived to be expelled from the compound a b, by the superior attraction of ' for b, that superior attraction belonging to it in consequence of the relative position of #' b and a, to the direction of the axis of electric power superinduced by the current. The electric current is looked upon by Faraday as an axis of power, having contrary forces, exactly equal in amount, in contrary directions. (466) According to Faraday's views (Experimental Researches, 518, 524), then, the determining force is not at the so called poles of the voltaic battery, but within the body under decomposition : to avoid, therefore, confusion and circumlocution, and for the sake of greater precision of expression, he framed the following new terms, some of which have since been generally adopted : What are* called the poles of the voltaic battery are merely the surfaces, or doors by which the Electricity enters into, or passes out of, the substance suffering decomposition ; Faraday hence proposes for them the term electrodes, from iiXsxrgov and odbg a way, meaning thereby, the substance, or surface, whether of air, water, metal, or any other substance, which serves to convey an electric current into, and from, the decomposing matter, and which bounds its extent in that direction. (467) The surfaces at which the electric current enters and leaves a decomposing body, he calls the anode and the cathode ; from ava upwards, and odbf a way, the way which the sun rises; and xara downwards, and 666g a way, the way which the sun sets. The idea being taken from the earth, the magnetism of which is supposed to be due to electric currents, passing round it in a constant direction from east to west, if, therefore, the decomposing body be considered as placed so that "the current passing through it shall be in the same direction, and parallel to that supposed to exist in the earth, then the surfaces at which the Electricity is passing into, and out of, the substance, would have an invariable reference, and exhibit constantly the same relations of powers. The anode is, therefore, that surface at which the electric current enters : it is the negative extremity of the decomposing body ; is where oxygen, chlorine, acids, &c., are evolved; and is against or opposite the positive electrode. The cathode is that surface at which the current leaves the decomposing body, and is its positive extremity : the combustible bodies, metals, alkalies, and bases, are evolved there, and it is in contact with the 352 GALVANIC OB, VOLTAIC ELECTRICITY. negative electrode. Thus, in Fig. 192, if we suppose a current of Electricity traversing a wire in the direction of the darts, and enter- Fig. 192. ing at E, then, on separating fl _ the wires at p, p p" would become" its electrodes : p would be the anelectrode or emitting electrode, and p' the E' catJielectrode, or receiving electrode; E being the wire connected with the last active copper plate, and W the wire connected with the last active zinc plate of a battery ; and if we suppose the chain of small circles to represent the fluid under decomposition, A will be its anode and C its cathode. (468) Compounds directly decomposable by the electric current are called electrolytes, from qXexrgov and X6w to set free, to electro- lyze a body is to decompose it electro-chemically : the elements of an electrolyte are termed ions, from iwv, participle of the verb e/jew, to go ; anions are the itins which make their appearance at the anode, and were formerly termed the electro-negative elements* of the com- pound, and cations are the ions which make their appearance at the cathode, and were termed the electro-positive elements. Thus, chloride of lead is an electrolyte, and when electrolyzed evolves two ions, chlorine and lead, the former being an anion, and the latter a cation : water is an electrolyte, evolving likewise two ions, of which oxygen is the anion, and hydrogen the cation : muriatic acid is like- wise electrolytical, boracic acid, on the other hand, is not. (469) Mr. Daniell proposes further to distinguish the doors by which the current enters and departs, by the terms zincode and platinode, the former being the plate which occupies the position of the generating plate in the battery, and the latter of the conducting plate ; when water is decomposed, therefore the last particle of oxygen gives up its charge to the zincode, and the last particle of hydrogen gives up its charge to the platinode, each passing off in its own elastic form. (470) Eechner, a distinguished champion of the contact theory (323), assumes that the elements of an electrolyte are in opposite electrical conditions, as the result of their contact, the same process being car- ried on between them as between two electromotors when brought into contact : before, therefore, the separation of the elements can take place by the electric current, the attractive force of the positive pole on the negative particle must exceed .the force by which it is united to the positive particle ; a separation being thus effected, and the positive particle being repelled, it combines momentarily with the negative particle of the second link in the chain of electrolytes, which CHEMICAL PHENOMENA. 353 is itself attracted towards the positive pole, but the overpowering action of which quickly again separates it, and thus the influence is regularly transmitted, through the entire stratum of the electrolyte lying between the poles. The same influence which is assumed to emanate from the positive, proceeds also from the negative pole, but it acts on the elements in the contrary direction. In this theory, electrolysis is maintained by the simultaneous and corresponding action of both poles, and the elements of the electrolyte are them- selves, from their contact, exciters of Electricity. (471) The chemical power of the voltaic pile was discovered and described by Messrs. Nicholson and Carlisle, in the year 1800. Water was the first substance decomposed. In 1806, Davy com- municated to the E-oyal Society his celebrated lecture " on some chemical agencies of Electricity," and in 1807, he announced the grand discovery of the decomposition of the fixed alkalies. The years from 1831 to 1840 are marked in science by the publication of the masterly researches of Faraday, in which, much that was before unin- telligible, has not only been explained and enlightened, but a new character has been stamped on electrical, as connected with chemical, science. Of these remarkable essays, it has-been said, that in point of originality of talent and perspicuity, they rank among the first efforts of philosophy of the age, if indeed they do not surpass all others. (472) When water and certain saline solutions are made part of the electric circuit, so that a current of Electricity may pass through them, they are decomposed, that is, they yield up their elements in obedience to certain laws. Water is resolved into oxygen and hydrogen gases, and the acid and alkaline matters of the neutral salts, which it holds in solution, are separated, not in an indiscrimi- nate manner, but the oxygen and acids are always developed at the anode, and the hydrogen and alkaline bases are given off at the cathode. If pure water be submitted to the action of the current, it is decomposed with great difficulty, in consequence of its bad con- ducting power. A greatly increased conducting power is, however, given to it by the addition of salts-, and particularly by sulphuric acid, though that compound is not itself capable of electrolysis. One essential condition of electrolysis is liquidity : and the current of a powerful battery will be completely stopped by a film of ice, not more than one-sixteenth of an inch in thickness.* To decompose acidulated water, it may be confined in a glass tube, sealed hermeti- cally at one extremity, and made part of the electrical circuit by * Faraday's Experimental Researches, 381, et seq. A A 354 (JALTANIC OE VOLTAIC ELECTEICITY. means of gold or platinum wires, or arranged as in Fig. 193, the Fig. 193. wires being about a quarter of an inch apart. "When the tube is about half full of the mixed gases, if a spark from the electrophorus (Fig. 20) be passed between the wires, an explosion will take place ; and if care be taken to prevent any escape, by the expansion, the tube will be re-filled with water, that fluid having been re- produced by the explosion. If two glass re- ceiving tubes be employed, one over either elec- trode, gas will be collected in each; but that in the tube over the cathode will be rather more than double in volume that x>ver the anode, the former being hydrogen and the latter oxygen. Now the hydrogen and oxygen gases are to each other in water exactly as two to one, by volume : and the reason they do not appear precisely in this proportion inthe electrolysis of that fluid, is because oxygen is partially soluble. By referring to Fig. 191 it will be immediately seen how it is that there is no visible transfer of the oxygen and hydrogen : if the electrodes were several inches apart, there would be no appearance of decomposition between them ; the oxygen a, of the atom of water a b' ', under the superinducing in- fluence of the current, is transferred to the hydrogen b of the second atom of water a b : the oxygen of this second atom is in like manner transferred to the hydrogen of a third, and so on till the electrode P is arrived at, against which the oxygen of the last particle is evolved, having nothing to combine with. Fig. 194. (473) Take a syphon-shaped tube, and placing its bent part in a wine glass for support (Fig. 194), or on any convenient stand, fill it with the blue in- fusion of red cabbage ; then put a few crystals of some known salt, such as sulphate of soda, into the tube, and electrize the solution. In a short time the liquid nearest the cathode of the battery will be- come green, indicating the presence of free alkali ; and the liquid nearest the anode will become red, showing that an acid is present : reverse the direction of the current, and the colours will also gradually be reversed. Thus, sulphate of soda is an electrolyte, the anion of which is sulphuric acid and the cation soda ; and in all salts decomposable by the voltaic current, the acid passes to the anode and the base to the cathode. (474) If two glasses be taken, both being filled with the blue infusion, holding in solution sulphate of soda, and an inverted glass tube, in which two platinum wires are sealed, be immersed in each, CHEMICAL PHENOMENA. 355 as shown in Fig. 195, and the two glasses connected together by a glass syphon filled with the liquid ; on electrizing the solution, tt\ it will be found that, notwithstanding they are in separate vessels, the blue liquor will, as before, be turned red and green ; and if the experiment be continued sufficiently long, the alkali of the salt will be found to have passed from P. to N, and the acid from N to P, the acid and alkali appearing to traverse the syphon in opposite directions. It was hence inferred, that under the influence of electrical attraction, the usual chemical affinities are suspended ; but the same explanation which accounted for the phenomenon of the decomposition of water, will serve here : a line of particles of sulphate of soda extend from one electrode to the other; and it is by a series of decompositions and recompositions that the effect is pro- duced. (475) In various experiments of decomposition, the little form of apparatus of which Fig. 196 is a sketch, will be found exceedingly useful. It is a cell of plate glass, made by cementing five pieces together with transparent varnish, and supporting them upon a wooden foot, in which they are fastened. The cell is about five or six inches long, and an inch broad, and may be divided into two parts by the insertion of the temporary diaphragm #, which is a small frame of cane with muslin stretched over it. "When this is in its place, a separate electrode may be introduced on each side of it; they may most conveniently consist of two pieces of thin platinum foil, about four inches long and half an inch broad. To show the evolution of chlorine at the anode or positive pole, fill the glass cell with weak salt and water, acidulated with muriatic acid, and coloured blue by a few drops of the sulphuric solution of indigo ; then introduce the electrodes. In a few minutes the anodic division will be found to lose colour, and will finally become colourless, owing to the separation of chlorine, which by its bleaching powers destroys the blue of the indigo. The presence of uncombined iodine may be demonstrated, by filling the cell with a weak solution of starch, to which a little common salt and iodide of potassium have been added ; then, on passing the electric current through the liquid, the iodine will show itself at tho anode by 356 GALVANIC OB YOLTAIC ELECTRICITY. a beautiful blue colour, it being the property of this singular substance to strike a fine -deep blue colour with starch. (476) Fill the cell with a solution of salt to which a few drops of yellow prussiate of potash have been added ; introduce into each division a plate of iron as an electrode ; the production of a deep blue colour in the anodic division while the liquid in the cathodic com- partment remains colourless, will prove the oxidation and solution of iron at the anode, and the absence of all action at the cathode. In the like manner, pieces of silver and copper, both of which, under ordinary circumstances, are readily attacked by dilute nitric acid, may be made to resist the oxidizing power of that acid by making them the catJielectrodes of a battery. The experiment with copper may be made thus : immerse a strip of the metal for a few minutes in the acid ; then remove it, and add a slight excess of ammonia ; the production of a fine blue colour will announce the presence of copper in solution ; now connect the strip of copper metallically with a similar strip of zinc, and immerse the pair in the acid ; no blue colour will follow the introduction of ammonia into the acid as before, showing the pro- tecting action of the zinc, the more oxidizable metal. This principle has received an important practical application, in the manufacture of which is called galvanized iron. (477) The electro-reduction of the alkaline metals originally accom- plished by Davy, with a battery of 100 pairs of six-inch copper and zinc plates, may be effected with a series of eight or ten cells of the nitric acid arrangement in the following manner : scoop out a cavity in a piece of pure moistened caustic potash or soda, and fill it with mercury : lay the alkali on*a strip of platinum foil connected with the positive pole of the battery, and introduce into the mercury a platinum wire in contact with the negative pole, an amalgam of mercury and potassium or sodium will speedily be formed. In like manner, the ammoniacal amalgam may be formed by pouring a little mercury into a hole scooped in a lump of sal ammoniac and connecting the mercury with the negative, and the moistened sal ammoniac with the positive pole. This is a very striking experiment, the globule of mercury gra- dually increasing in size until it extends far beyond the cavity which first contained it, and the amalgam is produced more readily and copiously, if the mercury be previously combined with a small quantity of potassium or sodium. (478) By m'eans of the little apparatus shown in Tig. 197, Golding Bird (Phil. Trans. 1837) (Nat. Philosophy, p. 372,) obtained amalgams of potassium, sodium, and ammonium, with the feeble current from a single Daniell's pair. A glass cylinder, J, 1*5 inch in diameter and 4 inches in length, is CHEMICAL PHENOMENA. 357 Fig. 197. closed at one end by means of a plug of plaster of Paris O7 inch in thickness the cylinder is fixed by means of corks. Inside o,a cylindrical glass a, about eight inches deep and two inches in diameter; a piece of copper c, six inches long and three inches wide, having a copper con- ducting wire k soldered to it, is loosely coiled up and placed in the small cylinder with the plaster bottom ; a piece of sheet zinc e of equal size is also loosely coiled up and placed in the larger external cylinder, being furnished, like the copper plate, with a conducting wire I. The larger cylindrical glass being then nearly filled with weak brine, and the smaller with a saturated solution of sulphate of copper, the two fluids being prevented from mixing by the plaster of Paris diaphragm, the apparatus is complete, and will continue to give a continuous current of Electricity for some weeks, provided care be taken that the fluids in the two cylinders are maintained at the same level. The decomposing apparatus is the counterpart of the battery itself. It consists of two glass cylinders, one within the other, the smaller one g having a bottom of plaster of Paris fixed into it ; this smaller tube is about half an inch wide and three inches long, and is intended to hold mercury and the metallic solution submitted to experiment ; the external tube /in which it is immersed being filled with a weak solution of common salt. In the latter, a slip of amal- gamated zinc i is immersed for the positive electrode soldered to the wire coming from the positive plate of the battery ; whilst for the negative electrode a slip of platinum foil h, fixed to the wire from the zinc plate of the battery, passes through a cork fixed in the mouth of the smaller tube, and dips into the metallic solution which it contains. In about eight or ten hours the mercury becomes swollen to double its former bulk, and when quickly poured into distilled water evolves hydrogen gas, and the water becomes alkaline. The ammonium amal- gam was most easily obtained ; it had a buttery consistence, and when immersed in water, slowly gave off hydrogen and yielded solution of ammonia. Bird found that the spongy ammoniacal amalgam, though it cannot be kept immersed in water even for a few instants without 358 GALVANIC OB VOLTAIC ELECTRICITY. the formation of ammonia, could nevertheless be preserved for weeks without change, as long as it was connected with the negative pole of the battery ; with the same apparatus Dr. Bird reduced the metals from solutions of chloride or nitrate of iron, copper, tin, zinc, 'bismuth, antimony, lead, and silver. Bismuth, lead, and silver\ were beautifully crystalline ; the latter of dazzling whiteness, and usually under the form of needles. He also obtained silicon, from a solution of chloride of silicon in alcohol. Aluminium and silicium have recently been obtained by weak elec- tric actions by Mr. Goze (Phil. Mag. March 1854 ;) the former was reduced from the chloride, by placing a dilute solution of the salt into a jar and immersing in the liquid a porous earthenware pot containing dilute sulphuric acid ; a plate of amalgamated zinc was plunged into the acid, and a corresponding plate of copper into the chloride, the plates being connected by an arc of copper wire. After some hours the copper plate became covered with a lead-coloured deposit of aluminium, which when burnished, possessed the same degree of whiteness as platinum, and did not appear to tarnish readily by immersion in cold water, or in the atmosphere, but was acted upon by dilute sulphuric and nitric acids. Silicium was reduced from a solution of monosilicate of potash, prepared by fusing one part of silica, with 2 J parts of carbonate of potash ; the same voltaic arrangement was adopted as before, except that a small pair of Smee's batteries was interposed in the circuit ; with a very slow and feeble action of the battery the colour of the deposited metal was much whiter than that of aluminium, closely approximating to that of silver. (479) The following classification of the elementary substances by Berzelius, though not altogether derived from experiment, and there- fore subject to correction and modification, is useful as indicating the electrical tendencies of a large number of bodies. In the list of negative substances, each element is to be considered as negative to all below and positive to all above it in the list, and the same applies to the list of positive substances. The elements are, therefore, nega- tive and positive only in relation to each other. Thus, supposing a compound of oxygen and chlorine to be electrolyzed, the oxygen would go to the positive and the chlorine to the negative electrode ; but if the compound were composed of chlorine and phosphorus, then the chlorine would go to the positive and the phosphorus to the negative electrode. I. ELECTEO-NEGATIYE ELEMENTS. 1. Oxygen. 2. Sulphur. 3. Nitrogen. 4. Chlorine. 5. Iodine. 6. Fluorine. CHEMICAL PHENOMENA. 359 7. Phosphorus. 8. Selenium. 9. Arsenic. 10. Chromium. 11. Molybdenum. 12. Tungsten. 13. Boron. 14. Carbon. 15. Antimony. 16. Tellurium. 17. Columbium. 18. Titanium. 19. Silicon. 20. Osmium. 21. Hydrogen. II. ELECTBO-POSITIYE BODIES. 1. Potassium. 2. Sodium. 3. Lithium. 4. Barium. 5. Strontium. 6. Calcium. * 7. Magnesium. 8. Grlucinum. 9. Yttrium. 10. Aluminium. 11. Zirconium. 12. Manganese. 13. Zinc. 14. Cadmium. 15. Iron. 16. Nickel. 17. Cobalt. 18. Cerium. 19. Lead. 20. Tin. 21. Bismuth. 22. Uranium. 23. Copper. 24. Silver. 25. Mercury. 26. Palladium. 27. Platinum. 28. Ehodium. 29. Iridium. 30. Gold. (480) A substance cannot be transferred in the electric current beyond the point where it ceases to find particles with which it can combine ; and it cannot be too strongly impressed, that electro- chemical decomposition does not depend upon any direct attraction or repulsion exerted by the metallic termina- tions either of the voltaic battery, or of the ordinary electrical machine. The beautiful experiments of Faraday, in which air was shown to act as a pole, have been quoted (213) ; in the following equally beautiful experiments (Faraday's Exp. Researches, 494), the decom- position of sulphate of magnesia against a surface of water, is most satisfactorily shown. (481) A glass basin, four inches in diameter, and four inches deep, had a division of mica, a, Pig. 198, fixed across the upper part, so as to descend one inch and a half below the Fig. 198. 360 GALVANIC OR TOLTAIC ELECTRICITY. edge, and to be perfectly water-tight at the sides. A plate of platinum, 5, three inches wide, was put into the basin on one side of the division a, and retained there by a glass block below, so that any gas produced by it in a future stage of the experiment, should not ascend beyond the mica, and cause currents in the liquid on that side. A strong solution of sulphate of magnesia was carefully poured without splashing into the basin until it rose a little above the lower edge of the mica division a, great care being taken that the glass or mica, on the unoccupied or c side of the division in the figure, should not be moistened by'agitation of the solution above the level to which it rose. A. thin piece of clean cork, well wetted in distilled water, was then carefully and lightly placed on the solution at the c side, and distilled water poured gently on to it, until a stratum, the eighth of an inch in thickness, appeared over the sulphate of magnesia. All was then left for a few minutes, that any solution adhering to the cork might sink away from it, or be removed from the water on which it now floated ; and then more distilled water was added in a similar manner, until it reached nearly to the top of the glass. In this way, solution of the sulphate occupied the lower part of the glass, and also the upper on the right-hand side of the mica ; but on the left-hand side of the division, a stratum of water from c to d, one inch and a half in depth, reposed upon it, the two presenting, when looked through horizontally, a comparatively definite plane of contact. A second platinum pole, e, was arranged so as to be just under the surface of the water, in a position nearly horizontal, a little inclina- tion being given to it, that gas evolved during decomposition might escape. The part immersed was three inches and a half long by one inch wide ; and about seven-eighths of an inch of water intervened between it and the solution of sulphate of magnesia. (482) The latter pole, e, was now connected with the negative end of a voltaic battery, of forty pairs of plates, four inches square ; whilst ^the former pole, b, was connected with the positive end. There was action and gas evolved at both poles ; but, from the inter- vention of the pure water, the decomposition was very feeble, com- pared to what the battery would have effected in an uniform solution. After a while (less than a minute), magnesia also appeared at the negative side. It did not make its appearance at the negative metallic pole, but in the water, at the place where the solution and the water met ; and on looking at it horizontally, it could be there perceived lying in the water upon the solution, not rising more than a fourth of an inch above the latter ; whilst the water between it and the negative pole was perfectly clear. On continuing the action, the bubbles of hydrogen, rising upwards from the negative pole, im- TBANSFER OP ELEMENTS. 361 pressed a circulatory movement on the stratum of water, upwards in the middle, and downwards at the side, which gradually gave an ascend- ing form to the cloud of magnesia in the part just under the pole, having an appearance as if it were there attracted to it ; but this was altogether an eifect of the currents, and did not occur till long after the phenomena looked for were satisfactorily ascertained. (483) After a little while the voltaic communication was broken, and the platinum poles removed with as little agitation as possible from the water and solution, for the purpose of examining the liquid adhering to them. The pole ', the stopper c replaced, and the metre tube refilled, by properly inclining the instru- ment: a second measure of gas is then collected, on re-establishing the circuit, and so on. Fig. 202 is another very useful form of this instrument, to which its in- ventor has given the name of the volta-. electrometer. (492) By a series of experiments made with this apparatus, under a variety of forms, with different sized platinum elec- trodes, and with solutions . of various degrees of strength, it was proved that water, when subjected to the influence of the electric current, is decomposed in a quantity exactly proportionate to the quantity of Electricity which passes through it, whatever may be the variations in the conditions and circumstances under which it may be placed ; and hence, that the instrument may be employed with confidence as an exact measurer of voltaic Electricity. (493) A voltameter, in which the electrodes are tin-plates coated with an alloy of lead and tin, has recently been described by Callan. (Phil. Mag., N. S., vol. vii. p. 73.) The decomposing cell is of wrought-iron about an inch thick, made perfectly air-tight, the top consisting of an iron plate screwed down on an Indian-rubber collar ; fche gases are liberated through a stop-cock screwed on -the top plate. The electrodes are arranged in two ways ; for batteries of low inten- sity, 20 plates each 12 inches by 4 are employed ; they are ranged parallel and separated -iVth of an inch from each other by strips of wood. Ten are connected with one end of the battery, and the other ten with the opposite end. The acting surface, including both sides of each plate, is about 3 square feet. The electrodes for batteries of high intensity, are likewise separated from each other by a non- conductor, but only the two terminal plates are connected with the poles of the battery. The cells are made perfectly water-tight, so that the battery current can only pass from one end of the battery to the other through the interposed plates and fluid. The number of cells should be about ^th of the number of cells in the battery. Thus, for a battery of 12 cast-iron cells, there should be 3 cells or two plates between the two terminal plates ; for a battery of 100 THE VOLTAMETER CALLAN' S EXPERIMENTS. 367 cast-iron cells in series, there may be 25 decomposing cells or 24 interposed plates. The intensity of a battery of 100 cells is 25 times greater than that of 4 cells, therefore the current from it will overcome 25 times the resistance, and will pass through 25 decom- posing cells successively, as freely as a current from a battery of 4 cells will pass through a single decomposing cell, since there is as much of the .mixed gases produced in each of the 25 decomposing cells as in the single cell through which the current from a battery of 4 cells passes. If the current from a battery of 100 cells arranged in one series, were sent through the electrodes as they are commonly arranged, the power of the battery would be exhausted about twice as soon as if the current passed through the electrodes arranged for batteries of high intensity, and the twelfth part of the full decom- posing power of the battery would not be effective. Callan states, however, that it is better not to arrange a large battery in series for decomposing water, but in sets of four, because a faulty cell, or a bad zinc plate, will diminish considerably the power of the entire battery. The fluid used is a solution of an ounce and a quarter, or an ounce of carbonate of potash, soda, or ammonia (the latter best), in a quart of water : if more than an ounce and a quarter be used, the foam will be considerable ; if less than an ounce, the conducting power will not be sufficient. The vessel must be tolerably capacious to allow the foam to accumulate, and the iron vessel in which the electrodes are contained should be coated with an alloy of lead and tin, or lead and antimony, in which the proportions of tin and antimony are small. (494) Callan also describes an apparatus for applying the mixed gases to the production of the lime light for illuminating purposes : it consists of two wrought-iron vessels of unequal size ; the smaller one is about 5^ inches high and 2 inches in diameter, the. sides being an inch thick ; the larger one is about 7 J inches high and 4 inches in diameter, the sides about -f-ths of an inch thick. On the top of the vessel is laid a collar of thick vulcanized Indian-rubber ; an iron plate about f ths of an inch thick is there screwed down to it by iron bolts ; the vessel is thus made air tight : the top of this vessel is connected by an Indian-rubber tube with the bottom of the small one, the bottom is connected by a similar tube with the gas-bag, gas- holder, or voltameter : the two vessels are nearly filled with water : the gas is sent into the bottom of the large one, ascends through the water, passer through the tube to the bottom of the small one, then through the water, and issues from the jet screwed to the top of the small vessel. The two vessels being of unequal size, it is impossible that all the water should be carried out of both at the same time, by 368 GALVANIC OB YOLTAIC ELECTEICITT. the stream of the gases ; and should an explosion occur after the small vessel becomes empty, the flame would be stopped by the water in the large vessel. In each vessel the gases are made to pass through wire gauze or perforated zinc, or through small pieces of porous earthenware, in order to break the. bubbles, and thus prevent the gases from ascending in a continued series of large bubbles. To prevent the water from being driven into the gas-bag or voltameter, an Indian-rubber valve is placed across the hole through which gases enter. This valve opening only inwards, becomes closed by any expansive force acting outwards : no dangerous explosion can con- sequently happen with this apparatus. With a battery of twelve four-inch cast-iron cells, or of four cells, each 6x8 inches, Callan obtained a sufficient amount of gas for the supply of the gas micro scope, dissolving views, &c. ; the lime light was Jth of an inch in diameter and constant. (495) The following observations on the relative practical values of the lime and -coke lights are worth attention, as being the results of .extensive experiments. If the jet of the gas-holder be attached to a stop-cock, by which the gases may be confined for 55 seconds in every minute, and if they are allowed to issue from the jet only for five seconds in each minute, twelve times as much of the gases must pass through the jet in these five seconds, as would pass through it in the same time were the stop-cock always open. Hence, if the gases pro- duced by the battery are ignited for five seconds in each minute as they issue from this jet, and are confined in the voltameter for the remaining 55 seconds, the flame will, when thrown on lime, give a light twelve times as large as one a quarter of an inch in diameter, or one nearly -fths of an inch in diameter. This is effected by means of a stop-cock of peculiar construction, the key of which is worked by clock-work. The expense of such an intermitting light >vould not be great, and it is particularly recommended for light-houses. The constant light seems at present almost impracticable. "When coke is used and the light constant, the battery soon wears out. The coke light is more intense than the lime light, and somewhat less expensive ; but the lime light is much more easily managed than the coke light. To produce a coke light sufficient for all illuminating purposes, 40 cast iron cells, each containing a zinc plate, 2 inches by 4, will suffice. To obtain a lime light of equal illuminating power, a battery containing at least twice as large a surface of zinc will be required. The coke points will require to be changed more frequently than the lime, and there is more reason to fear that the coke light will fail, on account of the destruction of the positive coke point, than that the DEFINITE ELECTRO-CHEMICAL DECOMPOSITION. 369 lime will go out on account of the wearing of the lime. The smallest, and therefore the least expensive, battery by which, by the aid of a good apparatus for adjusting the coke points, a continuous light of great illuminating power can be obtained, Callan found to be 40 cells, in which the zinc plates were 2x4 inches. To produce an equal light from lime, a battery nearly twice the size would be required, the cells being arranged in sets of 4. The most effective method for arranging a cast-iron battery for the decomposition of water, is in sets of four. Callan found that 4 cells produced more than half the quantity of gases yielded by 12 of the same size, and that a battery of 60 cells working in series, produced in a minute, very little more than 4 of the same size. He thinks that there is a certain intensity, above and below which there is a loss of decomposing power, and that in the cast-iron battery when more than 4 cells are employed in series, some of the Electricity passes through the water without meeting the resistance or re-action necessary for decom- position. With a common voltameter, a battery of 500 cast-iron cells arranged in rows of four will produce more than 50 times as much gases as it will when the cells are arranged in series. (496) A detail of one experiment with protochloride of tin (Fara- day 's Experimental Researches, 789), will be sufficient as an example, both of definite electro-chemical decomposition, and of the masterly method of examining the question which was adopted by Faraday. Fig. 203. A piece of platinum wire had one extremity coiled into a small knob ; and, having been carefully weighed, was sealed hermetically into a piece of bottle-glass tube, so that the knob should be at the bottom of the tube within. The tube was suspended by a piece of platinum wire, so that the heat of a spirit-lamp could be applied to it. Ra cently fused protochloride of tin was introduced in sufficient quantity to occupy, when melted, about one-half of the tube. The wire of the tube was connected with a volta-electrometer, which was itself con- nected with the negative end of a voltaic battery ; and a platinum wire connected with the positive end of the same battery was dipped 11 B 370 GALVANIC OB VOLTAIC ELECTRICITY. into the fused chloride in the tube, being however so bent, that it could not by any shake of the hand or apparatus, touch the negative electrode at the bottom of the vessel. The whole arrangement is delineated in Fig. 203. (497) Under these circumstances, the chloride of tin 'was decom- posed; the chlorine evolved at the positive electrode formed bi- chloride of tin, which passed away in fumes ; and the tin evolved at the negative electrode combined with the platinum, forming an alloy fusible at the temperature to which the tube was subjected, and therefore never occasioning metallic communication through the decomposing chloride. "When the experiment had been continued so long as to yield a reasonable quantity of gas in the volta-electrometer, the battery connection was broken, and the positive electrode re- moved, and the tube and remaining chloride allowed to cool. When cold, the tube was broken open, the rest of the chloride and the glass being easily separable from the platinum wire and its button of alloy. The latter, when washed, was then re- weighed, and the increase gave the weight of the tin reduced. (498) The following are the particular results of one experiment : The negative electrode weighed at first 20 grains ; after the experi- ment, it, with the button of alloy, weighed 23 -2 grs. The tin evolved by the electric current at the cathode weighed therefore 3 '2 grains. The quantity of oxygen and hydrogen collected in the volta-electro- meter = 3*85 cubic inches. As 100 cubic inches of oxygen and hydrogen, in the proportions to form water, may be considered as weighing 12-92 grains, the 3'85 cubic inches would weigh 0;49742 of a grain : that being therefore the weight of water decomposed by the same electric current as was able to decompose such weight of proto chloride of tin as could yield 3*2 grains of metal. Now, 0-49742 : 3'2 : : 9 (the equivalent of water) : 57.9, which should therefore be the equivalent of tin, if the experiment had been made without errdr, and if the electro-chemical decomposition is in this case also definite. In some chemical works, 58 is given as the chemical equivalent of tin ; in others, 57"9. Both are so near to the result of the experiment, and the experiment itself is so subject to slight causes of variation, that the numbers leave little doubt of the applicability of the law of definite action in this and all similar cases of decomposition. Chloride of lead was experimented upon in a manner exactly similar, except that plumbago was substituted for platinum, as the positive electrode. The mean of three experiments gave 100' 85 as the equivalent for lead : the chemical equivalent is 103-5, the deficiency being probably attributable to the solution of part of the gas in the volta-electrometer. ELECTRO-CHEMICAL EQUIVALENTS. 371 (499) In some experiments, several substances were placed in succession, and decomposed simultaneously by the same electric current : thus, protochloride of tin, chloride of lead, and water, were acted on at once, the results were in harmony with each other : the tin, lead, chlorine, oxygen and hydrogen evolved being definite in quantity, and electro-chemical equivalents to each other. (500) By these and numerous other experiments, an irresistible mass of evidence was produced to prove the truth of the important proposition, that the chemical power of a current of Electricity is in direct proportion to the absolute quantity of Electricity which passes, which also is not merely true with one substance, as water, but gene- rally with all electrolytic bodies j and farther, that the results obtained with any one substance, do not merely agree amongst them- selves, but also with those obtained from other substances, the whole combining together into one series of definite electro-chemical actions. (501) The following is a summary of certain points respecting electrolytes, ions, and -electro-chemical equivalents, developed by Dr. Faraday, and given in the seventh series of his Experimental E/esearches. (826, et seq.) i. A single ion, that is, one not in combination with another, will have no tendency to pass to either of the electrodes, and will be perfectly indifferent to the passing current, unless it be a compound of more elementary ions, and itself subject to decomposition. Upon this fact is founded much of the proof adduced in favour of the new theory of electro-chemical decomposition put forward in a former series of these Researches. ii. If one ion be combined in right proportions with another strongly opposed to it in its ordinary chemical relations, that is, if an anion be combined with a cathion, then both will travel, the one to the anode, and the other to the cathode of the decomposing body. iii. If therefore an ion pass towards one of the electrodes, another ion must be also passing simultaneously to the other electrode, though, from secondary action, it may not make its appearance. iv. A body decomposable directly by the electric current, that is, an electrolyte, must consist of two ions, and must give them up during the process of decomposition. v. There is but one electrolyte composed of the same two ele- mentary ions, at least such appears to be the fact, dependent upon a law, that only single electro-chemical equivalents of elementary ions can go to the electrodes, and not multiples. vi. A body not decomposable when alone, as boracic acid, is not directly decomposable by the electric current when in combination ; it may act as an ion, going wholly to the anode or cathode : but it B B 2 372 GALVANIC OK YOLTAIO ELECTRICITY. does not give up its elements, except occasionally by chemical action. vii. The nature of the substance of which the electrode is formed, provided it be a conductor, causes no difference in the electro- decomposition, either in kind or in degree ; but it seriously influences, by secondary action, the state in which the ions finally appear. Advantage may be taken of this principle, in combining and collect- ing such ions, as, if evolved in their free state, would be unmanage- able. viii. A substance which, being used as the electrode, can combine altogether with the ion evolved against it, is also an ion, and com- bines in such cases in the quantity represented by its electro- chemical equivalent. All the experiments agree with this view, and it seems, at present, to result as a necessary consequence. Whether in the secondary action that takes place where the ion acts, not upon the matter of the electrode, but upon that which is round it in the liquid, the same consequence follows, will require more extended investigation to determine. ix. Compound ions are not necessarily composed of electro-chemical equivalents of simple ions. For instance sulphuric, phosphoric, and boracic acids, are ions, but not electrolytes, that is, not composed of electro-chemical equivalents of simple ions. x. Electro-chemical equivalents are always consistent, that is, the same number which represents the equivalent of a substance A, when separating from a substance B, will also represent A when separating from a third substance C. Thus 8 is the electro-chemical equivalent of oxygen, whether separating from hydrogen, or tin, or lead ; and 104 is the electro-chemical equivalent of lead, whether separating from oxygen, chlorine, or iodine. xi. Electro-chemical equivalents coincide, or are the same with ordinary chemical equivalents. (502) The theory of definite electro-chemical action led Faraday to the consideration of the absolute quantity of electric force in matter : for although, as he observes, we are utterly ignorant of what an atom really is, we cannot resist forming some idea of a small particle, which represents it to the mind, and there is an immensity of facts which justify us in believing that the atoms of matter are in some way endowed or associated with electrical powers to which they owe their most striking qualities, and amongst them their mutual chemical affinity. Now, to decompose a single grain of acidulated water, an electric current, powerful enough to retain a platinum wire OT of an inch in thickness, red-hot, must be sent through it for three minutes and three quarters, and this quantity of Electricity is SECOND ART EE STILTS. 373 equal to a very powerful flash of lightning : yet the electrical power which holds the elements of a grain of water in combination, or which makes a grain of oxygen and hydrogen, in the right proportions, unite into water when they are made to combine, equals, in all probability? the current required for the separation of that grain of water into its elements again ; and this Earaday has shown to be equal to 800,000 charges of a Ley den battery of fifteen jars, each containing one hundred and eighty-four square inches of glass, coated on both sides : indeed, a beautiful experiment is described by Faraday, in which the chemical action of dilute sulphuric acid on 32'31 parts, or one equiva- lent of amalgamated zinc, in a simple voltaic circle, was shown to be able to evolve such quantity of Electricity in the form of a current, as passing through water could decompose nine parts, or one equivalent of that substance ; thus rendering the proof complete (bearing in mind the definite relations of Electricity), that the Elec- tricity which decomposes, and that which is evolved by the decomposition of, a certain quantity of matter, are alike. (503) Secondary Results : In investigating the action of the voltaic current on chemical compounds, it is important to distinguish carefully between primary and secondary results. When a substance yields, tmcombined and unaltered dt the electrodes, those bodies which have been separated by the electric current, then the results may be considered as primary ; but when any second re-action takes place, by which the substances, which appear at the electrodes, are not those which the immediate decomposition of the compounds would produce, then the results are secondary, although the bodies evolved may be elementary. These secondary results occur in two ways, being sometimes due to the mutual action of the evolved substance on the matter of the electrode, and sometimes to its action on the substances contained in the body itself, under decomposition. Thus, when carbon is made the positive electrode in dilute sulphuric acid, carbonic oxide, and carbonic acid occasionally appear there instead of oxygen : for the latter acting on the matter of the electrode, produces these secondary results. Or if the positive electrode, in a solution of nitrate, or acetate of lead, be platinum, then peroxide of lead appears there equally a secondary result with the former ; but now depending upon an action of the oxygen on a substance in the solution. Again, when ammonia is decomposed by platinum electrodes, nitrogen appears at the anode.; but though an elementary body, it is a secondary result in this case, being derived from the chemical action of the oxygen, elec- trically evolved there upon the ammonia in the surrounding solution. In the same manner, when aqueous solutions of metallic salts are 374 GALYANIO OB TOLTAIC ELECTRICITY. electrolyzed, the metals evolved at tlie cathode, though elements, are always secondary results, and not immediate consequences of the decomposing power of the electric current. (504) By the aid of feeble electric currents, some interesting decompositions and crystallizations were obtained by Becquerel. The following are some of his results :* suboxide of copper in the form of small bright octohedrons of a deep red colour was obtained by filling a tube with solution of nitrate of copper, placing at the bottom some powdered protoxide, and plunging into the liquid a plate of copper. The tube being then hermetically sealed, the crystals made their appearance after about ten days. That part of the plate which was in contact with the protoxide was positive, and the other part negative. If there was excess of protoxide, the solution after a time became colourless. Crystallized protoxide of lead was obtained by placing at the bottom of a tube some pulverized litharge, and pour- ing over it a slightly diluted solution of sub-acetate of lead, then plunging fnto it a plate of -lead which was equally in contact with the litharge ; the tube was then hermetically sealed, and the surface of the plate became gradually covered with small prismatic needles of hydrate of lead. Crystallized oxide of zinc was obtained in the fol- lowing manner: two bottles were* filled, one with a solution of zinc in potash, and the other with a solution of nitrate of copper, a com- munication was established between them by means of a bent tube filled with potter's clay, moistened with a solution of nitrate of potash ; a plate of lead was immersed in the solution of zinc, and a plate of copper in the solution of copper : these two plates were put in metallic communication with each other. The nitrate of copper was decomposed in consequence of the action of the current proceed- ing from the action of the alkali on the lead : the oxygen and the nitric acid were transferred to the plate of lead, and there produced nitrate of potash and oxide of lead, which was dissolved in the alkali. After the experiment had been continued some days, small clear crystals, having the shape of flat prisms, and so disposed as to form rosettes, were found deposited on the plate of lead. Crystallized hydrate of lime was obtained by filling a V shaped tube, the lower part of which was plugged with moist clay with Seine water, which contains sulphate of lime, and passing the current from fifteen elements through the liquid, both the water and the sulphate of lime were decomposed; that in the negative branch became alkaline, and a * Trait^ de Electricite, vol. iii. p. 287, et seq. Taylor's Scientific Memoirs, vol. i. p. 414. Comp. Rend. Feb. 1852. L. and E. Phil. Mag., N. S., vol. iii. p. 235. SECONDARY RESULTS : BECQUEREL' S RESEARCHES. 375 crystalline deposit gradually took place. Chloride of silver was ob- tained, in the form of beautiful translucent octohedrons, by immersing a plate of silver attached by a wire of the same metal to a piece of charcoal, in a tube containing concentrated hydrochloric acid, and nearly closed. The silver attracted and combined with the chlorine, and the hydrogen of the acid formed, with the charcoal, a gaseous compound, which escaped. With a similar arrangement, substituting copper for silver, fine tetrahedral crystals of chloride of copper were formed after a few months' action. Becquerel also succeeded in forming, artificially, by slow electric action, the sulphurets of silver, copper, lead, and tin, in beautifully crystalline forms. (505) More recently the weak actions to which Becquerel' s atten- tion has been more particularly directed, are those which commence as soon as the rocks, the metallic and other substances which occupy veins and beds, come in contact with the mineral waters which rise from all parts of the earth's interior. Time, then, becomes an ele- ment in the growth of the. crystalline substances formed. The following experiments were made : 1. A plate of amalgamated zinc surrounding a copper wire was plunged in a solution of silica in potash. After a fortnight's action, very small, regular, octohedral crystals of hydrate of zinc were formed on the zinc plate ; 2. A lead- copper arrangement was substituted for the zinc copper, anhydrous crystals of oxide of lead were deposited on the lead plate ; 3. Lumps of galena were left for several years in solutions of chloride of sodium and sulphate of copper ; the following products were formed, either on the galena or on the bottom and sides of the vessel : a, chloride of sodium in cubes, cubic octohedrons, and even in octahedrons, having great transparency and very definite forms ; b, chloride of lead, in needles and cubes, slightly yellowish and of a very perfect form ; c, sulphate of lead in cuneiform octohedrons, much modified, precisely resembling the crystalline sulphate of lead of Anglesea; d. chloro. sulphate of lead, in needles ; e. basic chloride of lead in microscopic crystals disseminated here and there throughout the whole product ; f. sulphur et of copper, black, without an appearance of crystallization. The whole of these substances covering the piece of galena gave it the appearance of a specimen from a mineral vein. A voltaic couple formed of a piece of galena surrounded by a platinum wire placed in a saturated solution of common salt and sulphate of copper diluted^ with three volumes of water, give rise to the formation of a consider- able quantity of crystallized chloride of lead in cubes without any other product. Becquerel thinks that these re-actions take place in nature ; rain water, coming into contact with mineral masses and veins formed of 376 GALVANIC OE YOLTAIC ELECTRICITY. metallic combinations, becomes charged with chloride of sodium and sulphate of copper arising from the decomposition of copper pyrites ; the resulting solutions once in contact with galena, re-act upon it weakly, and give rise to the various compounds above described. ' (506) To obtain in a crystalline state sulphur, sulphate, and car- bonate of baryta, the apparatus shown in Tig. 204 was employed. Fig. 204. A., A', A" are three "Wolfe's bottles ; A contains a solution of sul- phate of copper, A' a solution of the substance in the constituent parts of which it is desired to introduce a change, and A" contains water, rendered a conductor by the addition of an acid or common salt. A communicates with A' by means of a bent tube, a I c, filled with potter's clay or plaster of Paris, as suggested by Dr. Golding Bird, moistened with a saline solution, the nature of which depends on the effect intended to be produced in A. A' and A" communi- cate with each other by means of the two platina plates, p p 1 and A and A" communicate by means of a voltaic pair c M z: t t is a safety tube, to indicate internal pressure arising from the disengage- ment of gas. According to this arrangement, the extremity p" of the platina plate is the positive pole of a voltaic apparatus, whose action is slow and continuous when the liquid in A' is a good conductor ; the inten- sity of the electric forces is sufficient to decompose the sulphate of copper in A; from that instant the oxygen proceeds towards a as well as the sulphuric acid, which, in passing into the tube a b c, expels those acids which have a less affinity than itself towards the bases. These acids and the oxygen pass into the liquid A', where their slow re-actions determine the relative changes in the bodies which they BECQTJEREL'S RESEARCHES. 377 find there. On introducing in A' an alcoholic solution of sulpho carbonate of potash, and moistening the clay in the tube ale with a solution of nitre, a crystalline deposit of sulphur and carbonate of potash took place on the platinum plate p" after 24 hours' action, when a solution of sulpho-carbonate of baryta was substituted for sulpho-carbonate of potash, the deposit consisted of crystals of sul- phur, and carbonate, and sulphate of baryta. A' was filled with a solution of sulphite of potash, p p 1 p" being a double plate of copper. The extremity p", which was still the positive pole, attracted the oxygen and the nitric acid, the latter decomposed the sulphite and took possession of the base : the sulphurous acid was carried to the oxide of copper, which was formed at the same time and combined with it. The sulphite of copper combined with the sulphite of pot- ash, and formed a double compound, which' crystallized in beautiful octohedrons, but which was gradually decomposed, and gave place to fine transparent octahedral crystals of sulphite of copper, of a vivid red colour, and with the brilliancy of garnets. (507) By the following arrangement, recommended by Dr. Grolding Bird, fine crystals of copper , of suboxide of copper ', and of oxide of zinc, may be obtained : A glass tube, open at both ends, about half an inch in diameter and three inches in length, is closed at one end by means of a plug of plaster of Paris, about i of an inch in thick- ness. The tube is filled with a moderately diluted solution of nitrate or chloride of copper, and placed inside a cylindrical glass vessel, nearly filled with a weak solution of potash or soda. The leaden leg of a compound lead and copper arc is plunged into the outer cylinder, and the copper leg into the tube. The lead slowly dissolves in the alkaline solution, and electric action is set up ; the current traverses the plaster of Paris partition, and the oxide of copper (precipitated by the slow admixture of the alkaline solution with the copper salt) is reduced partly to the metallic state and partly to suboxide, both of which crystallize on the negative copper leg of the arc. If a solu- tion of oxide of zinc in caustic potash be substituted for the uncorn- bined alkali in the larger vessel, a very elegant deposit of oxide of zinc takes place in about eight or ten days, on the lead or positive plate, while fine crystals of copper and suboxide are deposited on the copper or negative plate. (508) The following experiments were made by Mr. Crosse : 1*. In an oval glass dish, of the capacity of about two quarts, was placed, on the bottom horizontally, a flat piece of clay-slate, a few inches square, with a platinum wire round its middle, and connected with the negative pole of a sulphate of copper lattery of eight pairs of plates. Upon this was placed a piece of mountain limestone, of a 378 GALYAtflC OE YOLTAIC ELECTRICITY. few ounces' weight, round the middle of which passed a platinum wire, connecting it with the positive pole. This stone was prevented from touching the slate below by three small wedges of deal, placed as supports. The glass dish was filled with spring water, and a stream of gas was rising from each wire. After two months' action the negative platinum wire was entirely covered throughout its whole length, under water, with crystalline carbonate of lime, and the positive wire had produced a great effect upon that part of the lime- stone with which it was in contact, having eaten into it so as to form a neck round it. In another month the effects greatly increased, and carbonate of lime began to form rapidly over the whole of the slate, as well as over the greater part of the inner surface of the glass basin. It so happened that the most elevated part of the limestone stood perpendicularly above a part of the negative wire, from which a constant stream of hydrogen gas, in minute bubbles, was playing against the little wall of limestone above it. Exactly where this line of bubbles existed, about half an inch in width, was a line of most beautiful translucent crystals of carbonate of lime upon the lime- stone, and occupying the whole surface of that part of it which was exposed to the current of hydrogen gas. 2. In a glass jar of spring water were placed two pieces of clay slate, and between them a piece of crystallized carbonate of strontia, connected with the positive pole of a sulphate of copper battery, of six pairs of plates, the lower slate being in connection with the negative pole : both slates became thickly covered with pearly-white carbonate of strontia in a botryoidal formation : the glass was also partially covered with stalactitic carbonate of strontia. 3. In a similar jar, carbonate of barytes was positively electrified : the negative wire and a portion of the slate became gradually covered with a beautiful mamillated formation of carbonate of barytes. 4. In a similar jar, sulphate of barytes was positively electrified : the slate was studded with brilliantly transparent crystals of sulphate of barytes. 5. A piece of solid opaque white quartz, suspended in a glass basin, filled with solution of pure carbonate of potash, was kept posi- tively electrified by a similar battery, a similar piece of quartz being in the same manner kept negative. Some small pieces of quartz were placed between the two : after some months' action there was a considerable formation of crystals. (509) Among the results obtained by the author, the following are worthy of being recorded : 1. Two pieces of white marble, placed horizontally in a glass basin, were connected by platinum wires with the positive and nega- 379 tive terminations of a battery of twenty pairs, in glass jars, charged with salt and water. The basin was filled with spring water, : after several months' action the positive marble was cut nearly half through its thickness, and the edges of the negative marble, and the negative side of the basin, were covered with myriads of crystals. A strong smell of chlorine was perceptible, evidently occasioned by the decom- position of the chlorides contained in the water. Mr. Crosse noticed the same in some of his experiments, and there is no doubt, as he remarks, that the small quantity of chlorine thus evolved at the positive pole, lent material assistance to the transference. 2. The positive platinum wire of a similar battery was twisted round a piece of mountain limestone ; the negative wire was attached to a piece of slate : after the lapse of several months the limestone was cut nearly in 'two, and the slate was beautifully studded with crystals of carbonate of lime. 3. To the positive pole of a battery of twenty pairs, charged with salt and water, was attached a crystal of sulphate of barytes. This rested on the bottom of an inverted gallipot, which was placed in a large glass jar filled with spring water. After six months' action the negative side of the gallipot had become studded with beautiful transparent crystals, many of which could be distinctly pronounced to be four-sided and tabular. These crystals rapidly increased, both in size and number, and after twelve months' action the jar itself, and also the slate, were completely covered with crystals. 4. Under similar circumstances (except that instead of a gallipot a small inverted tumbler was employed), a crystal of sulphate of strontia was kept positively electrified ; thare was a similar formation of transparent crystals over the negative side of the inverted jar, and also over the side of the large jar in which the whole was placed. The odour of chlorine was in both these experiments very distinct. 5. The carbonates of barytes and strontia kept positively electri- fied in vessels of spring water, after several months' action, transferred beautiful crystals to the negative side of the basin ; and, in the case of the carbonate of strontia, the negative slate was very thickly studded ; the evolution of chlorine was very evident in both cases. 6. A common large garden flower-pot without a hole in the bottom, was filled with fragments of common red-brick, and placed on two pieces of brick standing in a common salting pan : the pot was kept filled with spring water, the droppings being poured back every morning. Three platinum wires from the positive extremity of a salt-and-water battery, of sixty pairs of cylinders, in three series of twenty pairs each, enveloped two of the pieces of brick, about three inches beneath the surface ; and three silver wires from the negative 380 GALYAtfIC OB YOLTAIC ELECTRICITY. extremity were twisted round two other pieces at the opposite side of the pot. A few days after the commencement of the experiment, a strong odour of chlorine rose from the positive side ; and, after the lapse of several months, there was a large accumulation of carbonate of lime on the negative side of the pot, not only over the fragments of brick, but all over the outside of the pot, and between the bottom of the pot and the crucible under the negative side. "With the aid of a lens, a large accumulation of small crystals of carbonate of lime could be seen between the interstices of the bricks. This experiment is a modified repetition of one of Mr. Crosse's experiments, which was as follows : In a large, common, glazed salting-pan, filled with the spring water of the country, a common red brick was laid horizontally, each end resting on a half brick of the same sort. The two ends of the brick were connected respectively with the positive and negative termi- nations of a sulphate of copper battery, of nine pairs of nine-inch plates : the upper surface of the brick was covered with clear river- sand. At the termination of a quarter of a year, the apparatus was taken apart, and the following observations were made : On attempting to lift the whole brick from the two half bricks that supported it, it was found that while the positive end was easily re- moved from the brick below it, the negative end required some little force to separate it from its support ; and when the two were wrenched asunder, it was observed that they had been partially cemented together by a tolerably large surface of beautiful snow-white crystals of arragonite, thickly studding that part of the brick in groups, the crystals of each radiating from their respective centres. Here and there were formed in some of the little recesses in the brick, elevated groups of needle arragonite, meeting together in a pyramidal form in the centre ; while, in the open spaces between, were some exquisitely-formed crystals of carbonate of lime in cubes, rhomboids, and more particularly in short six-sided prisms, with flat terminations, translucent and opaque, sufficiently large to determine their form without the use of a lens. The positive end of the brick and that which supported it were also covered with crystals, much smaller and apparently of a different nature. On emptying the water from the pan, there was found at its negative end, at the bottom, a very large quantity of snow-white carbonate of lime to the extent of some ounces in weight, in the form of a gritty powder in minute crystals. Three-fourths of the whole interior of the pan were covered with myriads of crystals of carbonate of lime, so firmly adhering to the pan, as not to be separated without the aid of an acid. CEOSSE'S EXPEBIMENTS. 381 (510) Of the action of a weak acid on limestone, when concen- trated at the positive pole, the following pretty application was made by Mr. Crosse : In a saucer, filled with a concentrated solution of nitrate of potash, a flat, polished piece of white marble was placed ; and upon the middle of the marble, a common sovereign, with its reverse in contact with the marble, and having a stout glass rod supported perpen- dicularly on the coin, to keep it in its place. Between the rod and the coin was affixed a platinum wire, which was connected with the positive pole of a sulphate of copper battery, of eight pairs of plates ; while round the marble, but not touching it, was a coil of similar wire connected with the negative pole. The nitric acid was soon separated from the potassa, and attacked the marble in contact with the sovereign ; and, at the expiration of three days, the coin was per- fectly imbedded in the marble. The experiment was then put an end to, and the marble being taken out and inverted, the sovereign fell out of its stony receptacle, leaving a tolerably perfect impression on the marble. A very singular result took place in this experiment : the end of the glass rod which rested on the platinum wire in contact with the coin, chanced to be ground for the length of about two inches, which ground portion at the termination of the experiment became permanently gilded. This was at first referred by Mr Crosse to the presence of a minute portion of chlorine in the solu- tion; the real cause was detected in the course of the following experiments, made some years afterwards and communicated by Mr. Crosse to the chemical section of the British Association, in 1854, in a paper, " On the Apparent Mechanical Action accompanying Electric Transfer." " Experiment the first. I placed a piece of smooth carbonate of lime, of two inches square and half an inch thick, at the bottom of a rather deep saucer, which I nearly filled with dilute pure nitric acid. The preparation of the acid being one-fiftieth part by measure of the distilled water employed, which was one pint. Upon this piece of limestone I placed a sovereign, which weighed 123 grains, and upon the upper surface of the coin I placed one end of a platinum wire, which was connected with the positive pole of a small sustaining sulphate of copper battery. This end of the wire was kept firm on the coin, and the coin on the limestone by a stick of glass, supported vertically. The lower end of the stick was ground, as in my former experiment. Around the square piece of limestone I coiled a second platinum, wire which was connected with the negative pole of the battery. " The action commenced, hydrogen gas being liberated at the latter 382 GALYANIC OB VOLTAIC ELECTEICITT. pole, and carbonic acid gas from that part of the coin in contact with the limestone at the positive pole. I kept this in action for fifty- hours, and then took the apparatus apart. The coin had sunk into the limestone to the depth of half its thickness, and when removed, it left a clean impression on the stone. But the most striking circum- stance was that the carbonic acid gas in its evolutions from the stone, had struck off a portion of the milled edge of the sovereign, leaving it quite smooth at that part, and the pieces broken off had the milled edge remaining on them. Moreover, the evolution of gas carried up a small portion of gold, and gilded the whole of the ground surface of the glass rod. The broken pieces of metal lay around the coin, which when weighed, showed a loss of three grains, which was exactly the weight of the pieces, including the gilding on the glass, which I care- fully removed. It is particularly to be noticed, this was at the positive pole. On testing the fluid, it evinced not a trace of gold or copper, but merely a portion of nitrate of lime. Indeed had either of these metals been in solution, they must have appeared on the negative platinum wire, which was not the case. " Experiment the second. I repeated the former experiment in a different manner, using pure sulphuric acid instead of nitric, and acting on the same sovereign, which now weighed 120 grains. This I placed on a larger piece of marble and kept it pressed firm in its position by a glass weight of larger diameter than the former, and weighing about two pounds. Instead of a saucer I used a glass jar, filling it with one ounce of sulphuric acid and forty-nine of distilled water, so that the pressure of the fluid was of course greater, from the greater depth of the vessel containing it, and resistance to the extrication of the gas was in consequence proportionably greater. I employed a sulphate of copper battery of eight pairs, weakly charged but in good action. This action was continued for ninety hours, and then stopped. The coin weighed 114 grains, having lost six grains, which lay in pieces around it upon the surface of the marble, and which weighed exactly six grains. The glass weight in this experi- ment was not gilded, and the coin had made but little impression on the marble. On examining the sovereign, I found that one portion of its edge had the entire milling completely removed, and that part of the edge was left perfectly smooth, the remaining part of the coin being little if at all acted on. In fact, neither of the flat sides of the coin was at all acted on ; with the exception of a small portion of loth sides which were contiguous to that part of the edge from which the entire milling was removed. The carbonic acid gas which was liberated from the limestone had found an easier vent from under one part of the coin than the other, and from this part it poured THE ELECTRICAL ACARUS. 383 forth in considerable quantity, and by its constant friction broke off small pieces of the coin, which lay in a heap adjoining. I must observe that a very minute quantity of the purple oxide of gold stained a part of the marble. In this latter experiment I placed a glass strip, of three-fourths of an inch wide and some inches in length, upon the two opposite edges of the glass jar containing the dilute acid, and half an inch above the surface of the fluid, as I expected a crystallization of sulphate of lime upon its under surface. I was not disappointed, as the whole of the glass was covered with hundreds of needle crystals of sulphate of lime from one end to the other. The glass strip was placed in a line exactly corresponding to the line of passage of the electric current, one end being over the positive wire, and the other over the negative ; but every one of the crystals was at right angles to the electric current, viz., in the magnetic direction. " In the electric transfer of the earthy carbonates, and probably of many other substances, the mechanical action of the gases evolved at loth poles 'of the voltaic battery is strikingly shown by supporting a piece of clay-slate in a horizontal position, a few inches above each termination; taking care that such piece of clay-slate is somewhat below the surface of the fluid employed. In this way I have obtained crystals of the carbonates of lime, strontia, and baryta, on the under part of the clay-slate, suspended above both the positive and negative terminations of the battery. The deduction I draw from these experiments is, that a constant disturbance of the fluid electrically acted on, is a powerful agent in the formation of minerals, and in modifying the forms of matter. Some persons of high scientific authority have suggested that this power may possibly account for various hitherto unexplained phenomena in nature. It is my intention to pursue this subject in its different bearings." (511) It was in the course of his experiments on electro-crystal- lization, that that extraordinary insect about which so much public curiosity was at the time expended, was first noticed by Mr. Crosse. The following is his account of the experiment in which it first made its appearance : A wooden frame was con- structed, of about two feet in height, con- sisting of four legs proceeding from a shelf at the bottom, supporting another at the top, and containing a third in the middle. A JB, Fig. 205, represents two of the four uprights, or legs, issuing from the base (7, supporting the moveable shelf Fig. 205. 384 GALVANIC OR VOLTAIC ELECTRICITY. D, which shelf is kept in its place by four pins ~E, passing through the four uprights, and may be raised or lowered at pleasure. Each of these shelves was about seven inches square. The upper shelf was pierced with an aperture in which was fixed a funnel of Wedge- wood ware, 6r, within which rested a quart basin, on a circular piece of mahogany placed within the funnel. When this basin was filled with fluid, a strip of flannel, wetted with the same, was suspended over the edge of the basin and inside the funnel, which, acting as a syphon, con- veyed the fluid out of the basin through the funnel in successive drops. The middle shelf of the frame was likewise pierced with an aperture, in which was fixed a smaller funnel of glass, L, containing a piece of somewhat porous red oxide of iron from Vesuvius, J, immediately under the dropping of the upper funnel. This stone was kept con- stantly electrified by means of two platinum wires, M N, on either side of it, connected with the poles of a voltaic battery of nineteen pairs of five-inch zinc and copper plates, excited by water only. The lower shelf supported a wide-mouthed bottle o, to receive the drops as they fell from the second funnel. When the basin was nearly emptied, the fluid was poured back again from the bottle below into the basin above, without disturbing the position of the stone. The fluid with which the basin was filled was made as follows : A piece of black flint was reduced to powder, having been first exposed to a red heat, and quenched in water. Of this powder, two ounces were taken and fused with six ounces of carbonate of potash : the soluble glass formed was dissolved in boiling water, diluted, and hydrochloric acid added to supersaturation, the object being to form, if possible, crystals of silica at one of the poles of the battery. On the four- teenth day from the commencement of the experiment, Mr. Crosse observed, through a lens, a few small whitish excrescences or nipples, projecting from about the mindle of the electrified stone, and nearly under the dropping of the fluid above. On the eighteenth day these projections enlarged, and seven or eight filaments, each of them longer than the excrescence from which it grew, made their appear- ance on each of the nipples. On the twenty-second day these appearances were more elevated and distinct; and on the twenty- sixth day each figure assumed the form of a perfect insect, standing erect on a few bristles which formed its tail. Till this period Mr. Crosse had no notion that these appearances were any other than an incipient mineral formation ; but it was not until the twenty-eighth day, when he plainly perceived these little creatures move their legs, that he felt any surprise. When an attempt was made to detach them from the stone, they immediately died ; but in a few days they separated themselves, and moved about at pleasure. In the course THE ELECTRICAL ACABTJS. 385 of a few weeks about a hundred of them made their appearance on the stone : at first, each of them fixed itself for a considerable time in one spot, appearing to feed by suction, but when a ray of light from the sun was directed upon it, it seemed disturbed, and removed itself to the shaded part of the stone Mr. Crosse adds, " / have never ventured an opinion as to the cause of their birth ; and for a very good reason I was unable to form one. The most simple solution of the problem which occurred to me was, that they arose from ova deposited by insects floating in the atmosphere, and that they might possibly be hatched by the electric action. I next imagined, as others have done, that they might have originated from the water, and consequently made a close examination of several hundred vessels filled with the same water as that which held in solution the silicate of potassa. In none of these vessels could I perceive the trace of an insect of that description. I likewise closely examined the crevices and most Fig. 206. dusty parts of the room with no better success." (512) In subsequent experi- ments, this same insect (which it appears is of the genus acarus, but of a species not hitherto ob- served, and of which a magnified representation -is given in Pig. 206) made its appearance in electrified solutions of nitrate and sulphate of copper ; of sul- phate of iron, and sulphate of zinc ; also on the wires attached to the poles of a battery working in a concentrated solution of silicate of potassa, as shown in Pig. 207 ; also in fluo-silicic acid, in Fig. 207. c Fig. 208. Fig. 209. the arrangement shown in Pig. 208, in which a glass basin is shown partly filled with fluo-silicic acid, to the level 1 : 2, a small porous 386 GALVANIC OB VOLTAIC ELECTRICITY. pan made of the same materials as a garden-pot, partly filled with the same acid to the level 2, with an earthen cover, 3, placed upon it to keep out the light, dust, &c.: 4, a platinum wire connected with the positive pole of the battery, with the other end plunged into the acid in the pan, and twisted round a piece of common quartz ; the platinum wire passes under the cover of the pan : 5, a platinum wire connected with the negative pole of the same battery, with the other end dipping into the basin an inch or two below the fluid, and, as well as the other, twisted round a piece of quartz. After eight months' action, Mr. Crosse perceived two or three insects in their incipient state, appearing on the naked platinum wire at the bottom of the quartz in the glass basin at the negative pole. In Eig. 209 a magnified view is given of the wire, &c., 1 being the platinum wire ; 2, the quartz ; 3, the incipient insects. At the suggestion of Mr. Crosse, some of these experiments were repeated by the late Mr. Weekes, of Sandwich, by passing currents of Electricity through vessels filled with solutions of silicate of potash, under glass receivers inverted over mercury, the greatest possible care being taken to shut out extraneous matter, and in some cases previously filling the receivers with oxygen gas. The general result was, that after an uninterrupted action of upwards of a year, insects made their appear- ance in every respect, perfectly resembling those which occurred in the Broomfield experiments, as the author can testify, having had many opportunities of examining each. In some of Mr. Weekes 's later experiments, the acarus made its appearance in solution of ferrocyanuret of potassium. Similar experiments were made by the author, and were continued for upwards of sixteen months. He did not succeed in obtaining the insects within the bell jars which covered the solutions undergoing electrolysis, but several, precisely similar to those of Grosse and Weekes, were repeatedly found on, and about, the terminal cells of the battery. (513) The following account of some of his more recent experi- ments, in which acari made their appearance, has been kindly com- municated by Mr. Crosse : " I calcined black gun flints, in a crucible, flung them while hot into water ; I then dried and reduced them to powder. Of this powder I took one ounce, to which I added three ounces of car- bonate of potassa, and intimately mixed them. I then projected the whole by separate portions, into a heated crucible, till the whole was in perfect fusion, which fusion I kept up for five hours, increasing the heat until it exceeded that sufficient to melt cast iron. I then removed the crucible and allowed the contents to become solid, which formed into a pale green transparent glass ; Avhile still hot, I THE ELECTRICAL ACABTJS. 387 broke them into pieces. These hot pieces I threw into a vessel of boiling distilled water, which entirely dissolved them, and I took care that the water should be nearly saturated: we will call this silicate of potassa A : and I made use of it, as hereafter described, whilst it was still hot. I had previously prepared an apparatus to act electrically upon this fluid. It consisted of a common tubulated glass retort, supported in a frame contrived to keep it in the same position as when used in distillation. The beak or long end of this retort rested in a small cup of pure mercury, from which proceeded a platinum wire, which passed up through the whole length of the retort, and when it reached the bulb, was bent at right angles, so as nearly to touch the bottom of the bulb. The glass tube, which fitted air tight into the neck of this retort, had a platinum wire passed straight through it, the upper part of which was hermetically sealed into the upper part of the tube, and the lower part of the wire was continued downwards so as nearly to touch the bottom of the bulb. These two platinum wires were thus placed parallel to each other , within the bulb of the retort, and at the distance of about two inches from each other. The wire which passed through the neck was then connected with the positive pole of a small sustaining sulphate of copper battery of six pairs of cylinders ; and the mercury, from which proceeded the longer wire, which passed through the whole length of the retort, was connected with the negative pole. Of course no electric action could take place, until the bulb of the retort was filled more or less with a conducting medium. When all was ready I poured the solution A, still hot, into the bulb of the retort, having tempo- rarily removed the tube in the neck for that purpose, and carefully fitted it again, it being accurately ground so as to fit air-tight. The bulb was about one-half filled with A. As soon as the bulb was filled as related, an electrical action commenced at both wires. Oxygen and hydrogen gases were liberated: the volume of atmospheric air in the retort was soon expelled, and a continual but slow succes- sion of oxi-hydrogen gas bubbles passed through the cup of mercury into which the end of the retort was dipped, which lasted during the whole continuance of the experiment. Every care had been taken to avoid atmospheric contact, and admittance of extraneous matter, and the retort itself had been previously washed with hot alcohol. This apparatus I placed on a shelf, in a dark subterranean cellar, and I examined it carefully every two or three days. After some weeks' action, gelatinous silica collected in some quantity around the end of the positive wire, but I discovered no sign of incipient animal for- mation, until, on the 140th day after the commencement of the expe- riment, I plainly distinguished one fat acarus actively crawling about c o 2 388 GALVANIC OB VOLTAIC ELECTRICITY. within the bulb of the retort, and above the fluid, on the upper part towards the neck. I held a lighted lamp behind the bulb with one hand, and examined every portion of it, by means of a common lens held in my other hand. When first I observed this little creature I thought it might be outside the bulb, and I passed my finger several times over it but no, it was plainly and distinctly within the ~bulb y and was as active as possible. I never saw it again, and in spite of the closest examination and the continuance of the experiment for a whole twelvemonth, I never detected another. And now I found that, in spite of all my caution, I had committed a great error in the per- formance of this experiment, that is, I had omitted to insert within the bulb of the retort, a resting place for these acari, should any appear, for them to dwell upon. I have no doubt but that 'the one I saw, and perhaps others, had fallen down into the fluid and were destroyed. I ground this opinion upon two facts. First, I had observed in former experiments that if I let fall by means of a small camel's hair brush, one of those acari into the fluids, under which he had been born, he was immediately drowned and secondly, my late friend Mr. Weekes, had made similar observations ; moreover, it was not an easy matter to detect all the acari in the bulb of a retort which contained nearly a pint of fluid, by means of a lens with a short focal power. It is strange that in a solution eminently caustic and under an atmospere of oxi-hydro$en gas : one single acarus should have made his appearance. " I shall now make mention of the last experiment I have made in which acari appeared, but which, I should observe, were quite unexpected by me. I had previously been trying some experiments upon sheep's wool, by passing the Electric current from a small sus- taining battery through two porous pots, filled with salt and water, standing on a glass vessel side by side, which vessel was filled with the same fluid. These two porous pots were kept respectively posi- tive and negative by platinum wires, connected with the opposite poles of the battery ; and a small lock of wool was attached to the end of each wire. "When the electric action began, the chlorine of the salt went of course to the positive pole, and the wool there sus- pended was impregnated with it, while at the same time the soda went to the negative pole, and similarly impregnated the wool in that porous pot. At the expiration of three weeks, I removed both locks of wool from their respective pots, and plunged the one just taken from the positive pot, and impregnated with chlorine into the negative pot, where it was, to my surprise, dissolved in an instant. I repeated this with fresh locks of wool, first moistening them in the positive pot, and after a short time, letting them fall into the nega- THE ELECTRICAL ACABTJS. 389 tive, where they were dissolved but more slowly than at first. I continued this till the fluid in the negative pot would dissolve no more wool, after which I removed and filtered it. The solution was of a fine yellow colour, exactly similar in appearance to that of chlo- ride of gold, and it was perfectly transparent. This solution I shall call B. It smelt rather strongly of chlorine, and with it I made the following experiment, with a view to decompose the solution, but not expecting animal, life to appear during the process : I filled a tumbler with B, into which I immersed a small porous pot, filled with the same solution, and kept positive by a platinum wire connected with a small sustaining battery of three pairs of plates. Into this tumbler I let fall a piece of white quartz attached to a platinum wire, and connected with the negative pole of the same battery. This tumbler I placed in a tea saucer, and inverted a glass jar over the tumbler, which rested on the saucer, and the two wires of platinum which conducted the electric current passed between the bottom of the glass jar and the upper surface of the saucer. I made this arrange- ment merely to keep out the dust. This was set in action on June 10th, 1853. Some weeks afterwards, an assemblage of crystalline matter, some of which was perfectly transparent, and some white and opaque, formed upon that part of the negative platinum wire from which the quartz was suspended not that portion which was immersed in B, but that part of the wire which was bent outside the tumbler to enable it to pass under the inverted glass jar in its passage to the negative pole. These crystals increased in size and number for some months, but are now somewhat diminished. It is difficult to describe their form properly ; they are partly four-sided prisms, but curved in various directions, and they appear of small specific gravity. There is a constant faint smell of chlorine proceeding from the small aper- ture between the bottom of the inverted glass and the saucer. The crystals are discernible at some distance without the aid of a lens ; in fact, some of them are occasionally half an inch in length, and occasionally much less, and they vary in size in proportion to the greater or less temperature of the room and the greater or less moisture which exists under the inverted glass jar, and which is occa- sioned by the slower or quicker evaporation of the fluid B in the tum- bler. On the 27th of January, 1854, on examining this apparatus, I distinctly saw one perfect acarus, and some others in different stages, by means of a lens ; but no movement was perceptible in the per- fect insect. I took a drawing of these appearances. A week or two afterwards, I discovered another perfect acarus, but like the former, without motion. Both these aeari, as well as others that afterwards appeared during this experiment, were on the interior of the inverted 390 GALVANIC OB YOLTAIC ELECTRICITY. glass jar which covered the tumbler, and were constantly in an atmosphere impregnated with chlorine, which was continually renewed by the electric action, which was always more or less causing its evolution from the fluid B. The limbs of the perfect acari were extended in a natural position, and they appeared in all respects like living insects, but without motion. Some of my friends who examined them with a lens, fancied they perceived a movement, but I believe this was a mistake, as they remained in their respective situations from the time I first saw them to the present date, February 5th, 1855. This has never occurred to me before. Whether the chlorine prevented their complete animation I cannot say. I must here observe that, although I have seen these acari during many previous experiments, I have never known them to make their appearance before, except during the warmer months of the year, say from April to October, both months inclusive. The least approach of frost has either prevented their birth or destroyed them when living ; but on this occasion the result was entirely different, although the acari were precisely of the same kind as those I usually observed. There are af present three perfect acari, and some incipient ones, and they are perceptible by means of a common lens. This experiment is still continuing, and although the temperature of the situation in which the apparatus is placed, has been for some days past nearly down to the freezing point, not the least alteration is perceptible in the acari. I did expect during the warm months of last summer that they would have been in an active state, but this has not taken place." (514) Among the most interesting of Mr. Crosse's experiments, are those in which he has imitated in a most extraordinary manner, " constant" and "intermittent" springs with the aid of the voltaic battery. The experiments were made in the following manner : 1. A common garden-pot full of moistened pipe-clay was placed in a basin full of water : a platinum wire connected with the negative extremity of a sulphate of copper battery of twelve pairs of plates, each two inches long by one inch wide, was placed three inches deep into the middle of the clay ; and a second platinum wire con- nected with the positive pole, was plunged into the water in the basin, to the same depth. Within a fortnight fissures took place in the clay in contact with the negative wire ; and in six or eight weeks, these fissures filled with water, which was drawn up two inches above the level of the water in the basin. A small pool of water was formed round the negative wire, which at last overflowed and trickled constantly into the basin below. Here, then, was a constant electrical spring. CKOSSE'S EXPEEIMENTS. 391 2. Here the experiment was varied; but the apparatus was precisely similar. In this, both wires were plunged three inches deep into the same pot of moist pipe-clay, at the opposite sides, but about three-quarters of an inch from each side. Within a fortnight, fissures took place at the negative, but none at the positive wire. In a month or six weeks more, these fissures filled with water, which overflowed, and after a day or two ebbed, and then again overflowed, and so on, being apparently acted on by change of weather. Mr. Crosse generally found the spring overflowing when the barometer was very low, and the reverse when it was high. Here then was an electrical intermittent spring, (515) In subsequent experiments, Mr. Crosse found it better to employ porous earthen pots, open at the top and bottom, filled within an inch of the top with pipe-clay kneaded with water to the consistence of putty, and plunged into a basin three platinum wires issuing from one stout wire connected with the negative extremity of the battery, being plunged three inches deep into the clay ; and a group of six platinum wires issuing from one connected with the positive pole, being immersed to the same depth in the water. With this arrangement, if the battery is active, the water will rise in one night half an inch above the surface of the clay in the pot, the lip of which, together with the whole rim, to the depth of an inch, is glazed. Under the lip is placed a small shoot of sheet copper, to convey the water, as it falls drop by drop from the lip, to a graduated glass vessel. In one experiment, Mr. Crosse mixed dilute sulphuric acid with pipe-clay instead of distilled water. Not one drop of water was raised upwards to the negative wire ; but the water in the basin, which was also acidulated with the same acid, was changed to a most beautiful rose-red. In a letter received from Mr. Crosse, addressed to the author, in the beginning of the year 1840, he says : " My two springs the one constant, the other inter- mittent-rare in as good action as ever. The intermittent one over- flows generally when the barometer is somewhat below 29 ; and is generally dry when the barometer is above that point. A row of open porous pitchers being filled with pipe-clay, all their lips turned the same way and all negatively electrified, may yield a succession of drops, which being collected in a shoot, may be used to turn a small water-wheel, thus producing perpetual motion; and provided the power be found equivalent to produce such increased effect, it may be applied in the most important ways. Also, the fissures formed in the clay at the negative pole, may be converted into metallic lodes, by mineralizing the water in the basin with metallic and other solutions : this I have already done" 392 GALYANIC OE YOLTAIC ELECTRICITY. (516) The author's first repetition of these extraordinary experi- ments was not attended with successful results. By employing, however, a salt-and-water battery, of forty pairs, the observations of Mr. Crosse were verified in a most satisfactory manner. After a continued action of about eight weeks, several ounces of water were drawn to the negative wire upwards of three inches above the level of the water in the exterior basin ; and after the lapse of thirteen weeks there was a centinual flow of water over the top and sides of the porous jar, amounting to upwards of an ounce daily. Common river-water was employed to fill the basin and to knead the pipe- clay. The odour of chlorine from the positive wire was very marked. (517) The motion of fluids from the positive to the negative pole of the closed voltaic circuit has more recently been investigated by Wiedemann. (Silliman's Journal, Nov. 1852 ; Phil. Mag., N. S., vol. iv. p. 546.) The apparatus employed by this physicist consisted of a porous earthenware cell, closed at the bottom, and terminated above by a glass bell, firmly cemented to the upper edge of the cylinder. Into the tubulure of the bell a vertical glass tube was fitted, from which a horizontal tube proceeded so as to permit the fluid raised to flow over into an appropriately-placed vessel ; a wire, serving as the negative pole of a battery, passed down through the glass bell into the interior of the porous cylinder, where it termi- nated in a plate of platinum or copper. Outside the porous cylinder another plate of platinum was placed, and connected with the positive pole of the battery. The whole stood in a large glass vessel, which, as well as the interior porous cylinder, was filled with water. The intensity of the current was measured by a galvanometer. As soon as the circuit was closed, the liquid rose in the porous cylinder and flowed out from the horizontal tube into a weighed vessel. The results are summed up by "Wiedemann as follows : 1. The quantity of fluid which flows out in equal times is directly proportional to the strength of the current ; 2. Under otherwise equal conditions, the quantities of fluid flowing out, are independent of the magnitude of the conducting porous surface ; 3. The height to which a galvanic current causes a fluid to rise is directly proportional to the extent of the porous surface ; 4. The force with which an electric tension present upon both sides of a section of any given fluid, urges the fluid from the positive to the negative side, is equivalent to a hydo- static pressure which is directly proportional to that tension. The above laws only hold good for fluids of the same nature. "When different fluids are subjected to the action of the currents, the mechanical action is greatest upon those which oppose the greatest resistance to its passage. SECONDABT BESTJLTS. 393 (518) To return to the consideration of the secondary results of decomposition : it appears that there are two modes by which sub- stances may be decomposed by the voltaic battery ; 1st, by the direct force of the current ; and 2ndly, by the action of bodies which that current may evolve. There are also two modes by which new com- pounds may be formed, i. e. by combination of evolving substances whilst in their nascent state directly with the matter of the elec- trodes ; or else their combination with those bodies, which being contained in, or associated with, the body suffering decomposition, are necessarily present at the anode and cathode. "WTien aqueous solutions of bodies are used, secondary results are exceedingly frequent. They are not, however, confined to aqueous solutions, or cases where water is present. Whenever hydrogen does not appear at the cathode, in an aqueous solution, it always indicates that a secondary action has taken place there. (519) A series of admirable papers, on the electrolysis of secon- dary compounds, was published in the Philosophical Transactions by the late professor Daniell, of King's College. The primary object of these researches was, the determination of the relative proportions of the decompositions both of water and salt, when various saline solu- tions were subjected to the action of the voltaic current, and their relation to the amount of electrolytic force in action, with a view to increase our knowledge of the constitution of saline bodies in general. (520) From an elaborate series of experiments on the sulphates of soda, potash, and ammonia, phosphate of soda, nitrate of potash, &c., it appeared, " that in the electrolysis of a solution of a neutral salt in water, a current which is just sufficient to separate single equiva- lents of oxygen and hydrogen from a mixture of sulphuric acid and water, will separate single equivalents of oxygen and hydrogen from the saline solution, while single equivalents of acid and alkali will make their appearance at the same time at the respective elec- trodes;" and further experiments showed, that whenever dilute sul- phuric acid is used, there is a transfer of acid towards the zincode or anode, the quantity scarcely ever exceeding the proportion of one- fourth of an equivalent, as compared with the hydrogen evolved. Mr. Daniell thought possibly this might be owing to the acid being mechanically carried back to the platinode (cathode), as in all cases there is a mechanical connection of the liquid from the anode to the cathode ; and this is greater in proportion to the inferiority of its conducting power. If, however, this deficiency of acid were owing to the mechanical re-transfer, mechanical means, such as increasing the number of diaphragms, would stop it : the proportion, however, was, even under these circumstances, still maintained. No difference 394 GALVANIC OB VOLTAIC ELECTHICITY. was observed, whether the oxygen was allowed to escape from a platinum anode, or whether it was absorbed by copper or zinc : the metals, of course, being dissolved in proportions equivalent to the hydrogen developed at the cathode. Solution of potash, baryta, or strontia, similarly treated, exhibited a transfer of about one-fourth of an equivalent towards the cathode. (521) In order to remove the ambiguity which might thus possibly be conceived to arise from the employment of dilute sulphuric acid, as the measurer of the electrolytic force, the following arrangement was substituted for the voltameter: a green glass tube (into the bottom of which, as a cathode, was welded a weighed platinum wire) was filled with chloride of lead, maintained in a state of fusion by a spirit-lamp ; the corresponding anode was made of plumbago. At the termination of the experiment, the tube was broken, the wire and adhering button of lead weighed ; and the result showed, that " the same current which is just sufficient to resolve an equivalent of chloride of lead, which is a simple electrolyte unaffected by any asso- ciated composition, into its equivalent ions, produces the apparent phenomena of the re-solution of water into its elements, and at the same time, of an equivalent of sulphate of soda into its proximate principles." (522) Aqueous solutions of the chlorides were next tried, as the simple constitution of this class of salts promised to throw light upon the nature of the electrolysis of secondary compounds. A weighed plate of pure tin was made the anode of a double cell of peculiar construction, which was charged with a strong solution of chloride of sodium, and a tube of fused chloride of lead, as before, included in the circuit. Not a bubble of gas appeared on the tin electrode, and no smell of chlorine was perceptible ; but hydrogen in equivalent proportion to the quantity of tin dissolved, was given off at the cathode ; and the cell contained an equivalent proportion of free soda. One equivalent of lead was reduced in the voltameter tube. Muriate of ammonia treated in the same way, gave precisely similar results, proving it to be " an electrolyte," whose simple anion was chlorine and compound cathion nitrogen, with four equivalents of hydrogen. Its electrolytic symbol, therefore, instead of being (Cl + H) + (N + 3 H) is Cl + (N + 4 H), confirming, in a striking manner, the hypothesis of Berzelius, of the base (N + 4 H) called ammonium. (523) In discussing the results of all these experiments, we must bear in mind the fundamental principle, " that the force which we have measured by its definite action at any one point of a circuit, cannot perform more than an equivalent proportion at any other DANIELL'S KESEAECHES. 395 point of the same circuit." " The sum of the forces which held together any number of ions in a compound electrolyte, could, more- over, only have been equal to the force which held together the elements of a single electrolyte, electrolyzed at the same moment in one circuit." (524) In the electrolysis of the solution of sulphate of soda, and many of the other salts, water seemed to be electrolyzed ; at the same time acid and alkali appeared in equivalent proportion with the oxygen and hydrogen at the respective electrodes. "-We must con- clude," says Mr. Daniell, "from the above-mentioned principle, that the only electrolyte which yielded, was the sulphate of soda, the ions of which were not, however, the acid and alkali of the salt, but an anion, composed of an equivalent of sulphur and four equiva- lents of oxygen, and the metallic cathion, sodium. From the former, sulphuric acid was formed at the anode, by the secondary action and evolution of one equivalent of oxygen ; and from the latter, soda at the cathode, by the secondary action of the metal and the evolution of an equivalent of hydrogen." (525) To avoid circumlocution (but only when speaking of elec- trolytic decomposition), Mr. Daniell proposes to adopt the word ion, introduced by Dr. Faraday, as a general termination, to denote the compounds which in the electrolysis of a salt pass to the anode ; and that they should be specifically distinguished by prefixing the name of the acid slightly modified, as is shown in the following table : Ordinary Chemical Formula. Electrolytic Formula. Sulphate of copper (S + 3 0) + Cu + 0) = S + 4 0) + Cu oxysulphion of copper. Sulphate of soda (S+3 0) + (Na+0) = (S + 4 0)+Na oxysulphion of sodium. Nitrate of potassa (N + 5 0) + (Ka + 0) = (N + 6 0) + Ka oxynitrion of potassium. Phosphateofsoda(P + 3iO) + (]Sra+0) = (P + 440) + Na oxyphosph. of sodium. (526) The following experiments, strongly favouring the above view, were made by Professor Daniell : A small glass bell, with an aperture at top, had its mouth closed, by tying a piece of membrane over it. It was half filled with a dilute solution of caustic potassa, and suspended in a glass vessel, contain- ing a strong neutral solution of sulphate of copper, below the surface of which it just dipped. A platinum electrode, connected with the last zinc rod of a large constant battery of twenty cells, was placed in the solution of potassa ; and another connected with the copper of the first cell was placed in the sulphate of copper immediately under the diaphragm which separated the two solutions. The circuit conducted very readily and the action was very -energetic. Hydro- gen was given off at the cathode in the solution of potassa, and oxygen at the anode in the sulphate of copper. A small quantity of 396 GALVANIC OB VOLTAIC ELECTRICITY. gas was also seen to rise from the surface of the diaphragm. In about ten minutes, the lower surface of the membrane was found beautifully coated with metallic copper, interspersed with oxide of copper of a black colour, and hydrated oxide of copper- of a light blue. The explanation of these phenomena is this In the experi- mental cell we have two electrolytes, separated by a membrane, through both of which the current must pass to complete the circuit. The sulphate of copper is resolved into its compound anion, sulphuric acid -f oxygen-(oxysulphion), and its simple cathion, copper. The oxygen of the former escapes at the zincode, but the copper in its passage to the platinode, is stopped at the surface of the second electrolyte, which, for the present, we may regard as water, improved in its conducting power by potassa. The metal here finds nothing by combining with which it can complete its course ; but, being forced to stop, yields up its charge to the hydrogen of the second electrolyte, which passes on to the cathode, and is evolved. The corresponding oxygen stops also at the diaphragm, giving up its charge to the anion of the sulphate of copper. The copper and oxygen thus meeting at the intermediate point, partly enter into combination, and form the black oxide ; but from the rapidity of the action, there is not time for the whole to combine, and a portion of the copper remains in a metallic state, and a portion of the gaseous oxygen escapes. The precipitation of blue hydrated oxide doubtless arose from the mixing of a small portion of the two solutions. Nitrate of silver, nitrate of lead, proto-sulphate of iron, sulphate of palladium, and proto-nitrate of mercury, were similarly treated, and afforded analogous results, somewhat modified by the nature of the metallic base. Sulphate of magnesia w r as subjected to the same process in hopes of finding magnesium, but magnesia alone was deposited. (527) The theory of ammonium, as proposed by Berzelius, and the hypothesis of Davy, developing the general analogy of all salts, whether derived from oxyacids or hydracids, may, by this evidence, especially when taken in conjunction with the recent researches on the constitution of organic bodies, be considered as almost experi- mentally demonstrated. (528) The bisalts yield results which, at first sight, do not accord with the preceding deductions : a strong solution, for example, of pure crystallized bisulphate of potassa was made, and its neutralizing power carefully ascertained by the alkalimeter. Evaporation and ignition with carbonate of ammonia, gave the quantity of neutral sulphate yielded by a certain measure of the solution. An equal measure was then' placed in each arm of the double diaphragm DANIELL'S RESEARCHES. 397 cell,* and the current passed through till 70*8 cubic inches of mixed gases were collected : half the solutions from the anode and cathode were then separately neutralized, and half evaporated and ignited in the vapour of carbonate of ammonia. It was then found that bhe anode had gained eighteen grains, and the cathode lost nineteen of free acid: of potassa, the anode had lost 9 '9 grains, and the cathode gained an equal quantity. Thus, though the solution conducted very well, not more than one-fifth of an equivalent of the potassa was transferred to the cathode, as compared with the hydrogen evolved ; while half an equivalent of acid was transferred to the anode a whole equivalent of oxygen was evolved. On this experiment Mr. Daniell remarks : " I think we cannot hesitate to admit, that in this case the current divided itself between two electrolytes, that a part was conducted by the neutral sulphate of potassa, and a larger part by the sulphuric acid and water. It is a well known fact, that the voltaic current will divide itself between two or more metallic conductors in inverse pro- portion to the resistance which each may offer to its course : and that it does not in such cases choose alone the path of least resistance. Analogy would lead me to expect a similar division of a current between two electrolytes; but I am not aware whether such a division has ever before been pointed out." * This apparatus, which was found by Daniel very useful in his experiments on the electrolysis of secondary compounds, is shown in Fig. 210, and is thus described by its author (Introduction to Chemical Philosophy, 2nd edit., p. 533) : Fig. 210. A and B are the two halves of a stout glass cylinder, accurately ground so as to fit into two half cylinders, which, when adjusted, cover it entirely. The two rims of the ring are each cut down to a shoulder, to admit of a thin piece of bladder being tied over them to form a kind of drum. At K is a small hole to admit of the cavity being filled with a liquid. D and E are two stout bent tubes, fitted to the two half cylinders, for collecting the gases evolved in the experiments : g and h are two circular platinum electrodes, connected with the battery by the wires i f. The apparatus, when adjusted, forms three compartments, each of which may be filled with the same or a different liquid, and the whole may be supported on a wooden frame. GALVANIC OB VOLTAIC ELECTRICITY. (529) These considerations enable us to explain the apparent anomalies in the electrolysis of diluted sulphuric acid and alkaline solutions alluded to. The results are explained by supposing that the solution is a mixtur.e of two electrolytes : with sulphuric acid, they are H + (S + 4 0) oxysulphion of hydrogen ; (H + 0) water. The current so divides itself, that three equivalents of water are decomposed, and one equivalent of oxysulphion of hydrogen. Analagous changes occur with the alkaline solutions, the alkaline metal passing as usual to the cathode. According to Professor Daniell's view of Faraday's beautiful ex- periments with sulphate of magnesia (481), the first electrolyte was resolved into a compound anion, sulphuric acid + oxygen, which passed to the anode, and the simple cathion magnesium, which on its passage to the cathode was stopped at the surface of the water from not finding any ion, by temporarily combining with which, it could be further transferred according to the laws of electrolysis. At this point, therefore, it gave up its charge to the hydrogen of the water, which passed in the usual manner to the cathode, and the circuit was completed by the decomposition of this second electrolyte. The corresponding oxygen, of course, met the magnesium at the point where it was arrested in its progress, and, combining with it, magnesia was precipitated. This combination of the oxygen and metal is^looked upon by Professor Daniell as a secondary result, due to the local affinity of the elements thus brought into juxta-position, and in no way connected with the primary phenomena of the current, which would have completed its course, whether this combination had taken place or not ; i. e. whether magnesium and oxygen had been separately evolved, or whether magnesia had been formed by the combination of the .two. It also seemed probable that, although in the very slow action of this experiment this combination invariably took place, by varying the experiment so as to evolve metals possess- ing different degrees of affinity for oxygen, and particularly by shortening the time in which the evolution might take place, instances might be found of some portion of the metal escaping this combina- tion, which would thus afford the most incontrovertible proof of the point to be established. Professor Daniell was thus led to the experiment above detailed, (530) Voltaic reduction of ores. M.M. Dechaud and faultier de Claubry in France, and Messrs. Napier, Uitchie, and Crosse in this country, have made metallurgical applications of Becquerel's discovery of the chemical actions determined under the influences of feeble electric currents, and the latter gentlemen have patented their pro- cesses. The following are the data on which the apparatus of the VOLTAIC BEDFCTION OF ORES. 399 French chemists is based : (Gomptes Rendus, June 2, 1843.) If we place upon each other two solutions, the one of sulphate of copper, and the other of sulphate of iron, the former being the densest, place in the sulphate of copper a plate of metal forming the cathode, and in the sulphate of iron a piece of cast iron, and unite the two metals by a conductor, the precipitation of copper immediately commences, and is completed in a longer or shorter space of time, depending on the temperature, or the concentration of the liquids, and on the extent of the metal surfaces. In applying this process to metallurgy, a wooden box lined with lead, or protected by proper varnish, con- tains the sulphate of iron ; an opening above introduces the liquid at a given degree of density, and another below permits the concentrated solution to pass away. Into this are immersed cases formed of a frame the ends and bottom of which are of sheet lead, and the lateral sides of which are furnished with a sheet of pasteboard; a lower opening gives entrance to the saturated solution of sulphate of copper, and another opening higher up, gives exit to the exhausted sulphate. In each case is placed a sheet of lead, between them, and also on the outside of the two extreme cases are plates of cast iron ; distinct conductors affixed to each plate make it communicate with a common conductor placed outside the apparatus. The two solutions are supplied from appropriate reservoirs. The density of the liquids is regulated once for all, and the apparatus goes on working for months together without requiring any kind of care ; at a tempera- ture of 66 Fahr. 1*19 square yards of surface receives 2'2 Ibs. of copper in twenty-four hours. The metal is pure and constant in its physical character. The Committee appointed by the French Academy, consisting of M.M. Berthier, Dumas, and Becquerel, reported favourably upon this process, remarking, however, that it required that the ores to be transformed should be converted entirely into sulphate, in which the whole industrial question consists. (531) The following is an extract from Mr. Ritchie's patent: (sealed October 13th, 1844, enrolled April 10th, 1845 ; Repertory of Patent Inventions, June, 1845.) " The solution of the calcined ore is placed in a rectangular vessel of any required length ; on the upper surface is placed a solution of sulphate of iron to be used as the exciting solution ; thus prepared, the generating plate (a surface of cast iron), is introduced, which is connected by copper or 'other conducting material with a plate of lead or suitable metal, having an equal extent of surface with the cast iron ; and these plates or surfaces so con- nected, being introduced into solutions in the vessels, the copper in the solution will be quickly deposited. It will be found that in the course of working, the solution of sulphate of copper, which at start- 400 GALVANIC OR VOLTAIC ELECTRICITY. ing is a saturated solution, will become at its upper part lighter than lower down, and the patentee prefers that it should be drawn off when it has lost half its copper, and it is evident that the solution of sulphate of iron, which at starting is made by mixing two parts of water with one of saturated solution, will become, at its lower part, of greater specific gravity than the upper part ; and he prefers to draw off the solution when it becomes as dense as the weaker solution which is being drawn off." (532) Mr. Napier's process is thus specified : (Repertory of Patent Inventions, July, 1845.) " I take a large crucible, or other con- venient vessel, made of an electro-conducting material ; those I have used being plumbago (common black lead) ; the inside of this vessel I line all round with a lute of clay, except the bottom, which I leave uncovered ; the luting should be very thin, and laid on in two or three coats, drying slowly between each, so as to prevent cracking. "When the vessel is sufficiently luted and dried, I put therein (with the usual fluxes) the regulus or calcined ore, which, when sulphurets are used, should have been well roasted, so as to drive off as much as possible of the sulphuret ; I then place the vessel with its contents in an ordinary air-furnace, keeping up the heat until the mass is in a state of fusion. In the meantime, I have prepared an ordinary voltaic battery of copper and amalgamated zinc charged with acidulated water, one part sulphuric acid, twenty-five parts water. To the positive wire of this battery I attach an iron rod, having rivetted at right angles to its extremity a flat disc of iron, the disc being a little smaller than the inner circumference of the crucible ; to the negative wire of the battery, I attach a simple rod or bar of iron. The matter in the crucible being in a state of fusion and well fluxed, I place the above-mentioned disc of iron, which will now form the positive pole of -the battery, on the surface of the fused mass, and keep the rod which is connected with the negative pole in contact with the outside of the crucible, the bottom of which thus forms the negative pole. The fused matter now forms a portion of the electric circuit, and the heat being kept up, the metal is gradually reduced and deposited at the bottom of the crucible. The proportions I have found suitable are as follows : Eor every hundred weight of regulus of 30 per cent, of metal, I employ a battery of five pairs of plates, the size of the zinc plates being three feet square, and the copper doubled round the zinc in the usual way. The size of the pole should be smaller than the zinc plates. "With apparatus of these proportions, the time for extracting the metal varies from one to two hours. The metal so extracted may be refined when necessary in the usual way." (533) In the specification of his patent, Mr. Crosse describes his YOLTAIC EEDTJCTION OF ORES. 401 invention as follows: (Eepert. Pat. Invent. N.8. 21, p. 235.) "I cause the ore to be calcined, and then reduced to powder, and I employ an apparatus, consisting of a tub or vessel, which I prefer to be of wood or earthenware ; at the bottom of this vessel I apply a frame of strong platinum wire, of the dimensions of the interior of the vessel ; tKe frame has formed on it reticulate platinum wire-work or netting, with meshes of about an inch each way. The frame and netting is lowered down on, and covers the ore placed on, the bottom of the vessel ; a platinum wire is connected to the frame, and also with the positive pole of a Daniell's battery. The connecting platinum wire is covered with gutta percha when working with cold liquid, and with other non-conductor when the liquid is heated, from the point where it is connected with the frame up to a point above the vessel, so that the fluid within may not come in contact with the wire. The battery which I have employed when acting with a vessel containing about 250 or 300 quarts of diluted acid, consists of twenty pairs of plates, each in a gallon glass vessel, which I fill with a saturated solution of sulphate of copper, and add one twentieth to one-tenth of sulphuric acid. To the negative pole of the battery I affix a copper wire, and to the other end of such wire I (by three or more smaller ones) suspend a basin of wood which is lined on the inside with sheet copper, and I cover this lining with a cover of copper- wire netting, which consists of about one-inch meshes ; the copper lining is in contact with the suspending wires. Into the vessel I put about 230 to 235 quarts of diluted sulphuric acid, using about five quarts of sulphuric acid of commerce to 230 quarts of water; into this liquid I introduce about 151b. of the powder of calcined ore, stirring the fluid as the powder descends. " I have found it desirable that the ores should remain in the dilute acid some three or four days before subjecting the same to electric currents, stirring from time to time ; after which, and immediately after stirring, I introduce the frame of platinum wire, and then the battery being charged, the process of separating the copper will immediately go on, and the copper will be received into the basin in the form of a powder; the process of separating all the copper requires some days, and I have not found that the acid solution requires to be added to, during the process ; the other metals separated from the copper will be in the sediment at the bottom of the vessel, and when the process is completed, or judged to be completed, the liquid is run off with the remaining or sediment matter at the bottom of the vessel, and the vessel is again to be charged. If, on testing the deposited matters, after they have been run off" and allowed to subside, they indicate a material quantity of copper, I again calcine D D 402 GALYANIC OE YOLTAIC ELECTEICITT. them and add them to calcined ores, or a quantity of subsided matter in the vessel may, before being run off from the bottom of the vessel, be tested to ascertain whether it is desirable to carry on the process further thereon. The dilute acid run off from the subsided matters may be used again. I have found it desirable to hpat the liquid during the process as much as conveniently may be done, even up to boiling, and this I have done when using earthenware vessels by means of a sand-bath." (534) Mr. Crosse has also patented a process " for extracting or separating impurities or matters from fermentable, fermented, and other liquids, by electric action." (Rep. Pat. Inven. N.8. 10, 1847, p. 231.) Supposing the liquid to be wine, or cyder, or other ferment- able liquid, he immerses in the cask two porous tubes, the upper part of which comes above the liquid; into one tube he places a cylinder of zinc, and in the other a cylinder or coil of iron, connect- ing the two together by a metallic strip. The tubes are then filled with water ; an electric action is set up in the liquid which is con- tinued till the necessary degree of attenuation has been obtained, when the liquid is removed, casked off, and closed up. He states that this process materially improves the character of the liquid, and tends to prevent its becoming acid. In applying the process to the purification of sea water, he first causes the water to be distilled once, and then operates by electric action as above described ; the impurities of the water are precipitated, and gaseous matter is evolved, and any acid and alkaline properties go to the porous tubes ; the water is thus purified. The same gentleman has likewise patented a process for applying electric or galvanic effects in the pots or vessels in which hides or skins are under process of tanning, for an account of wMch see Repert. Pat. Invent. N.S. 15, 1850, p. 35. (535) Electro-metallurgy. In our historical account of the sul- phate of copper battery of Daniell it was stated, that on completing the circuit, the electrical current passes freely through the metallic solution ; that no hydrogen makes its appearance on the conducting plate, but that a beautiful pink coating of pure copper is deposited on it, and thus perpetually renews its surface. In the discovery of this battery, then, we find the origin of electro-metallurgy; for it appears that in his earlier experiments it was noticed by Mr. Daniell that on removing a piece of the reduced copper from a platinum electrode, scratches on the latter were copied with accuracy on the copper, and Mr. De la Eue, later, in a paper in the Phil. Mag.,* detailing some experiments with a voltaic battery of ordinary con- struction, charged with sulphate of copper, made the observation * Vol. ix. p. 484. ELECTBO-METALLTTBGY. 403 that " the copper plate is covered with a coating of metallic copper, which is continually being deposited ;" and he proceeds to remark, " so perfect is the sheet of copper thus formed, that on being stripped off it has the polish and even a counterpart of every scratch of the plate on which it is deposited." On reading this passage at the present time, when the art of electro -metallurgy is so extensively practised, we can hardly resist a feeling of surprise that the applica- tion of the facts discovered by Daniell and De la Bue did not occur to either of these gentlemen. They were, however, probably too intent on the battery itself to attend to any collateral circumstances, and it was left for Jacobi in Russia, and Spencer in this country, to do so. The process of the former distinguished philosopher was called " Galvanoplastic ;" that of Mr. Spencer, " Electrography" And though it is quite certain that the discovery was made by each, independent of the other, the priority must be given to Jacobi, who states in the preface of his " Gralvanoplastic,"* that it was in the month of February, 1837, while prosecuting his galvanic investiga- tions, that he discovered a striking phenomenon which presented itself in his experiments, and furnished him with perfectly novel views ; and Mr. Spencer, in his pamphlet,t informs us that his first results were obtained in -1838. (536) The description of an original experiment is generally interesting ; it is always so when connected with a subject of much practical importance. "We shall therefore insert Mr. Spencer'? account of his first successful experiment in electrography : J "1 selected a very prominent copper medal. It was placed in a voltaic circuit, and a surface of copper deposited on one of its sides to about the thickness of a shilling. I then proceeded to get the deposition off. In this I experienced some difficulty, but ultimately succeeded. On examination with a lens, every line was as perfect as the coin was from which it was taken. I was then induced to use the same piece again, and let it remain a much longer time in action, that I might have a thicker and more substantial mould, in order to test fairly the strength of the metal. It was accordingly again put in action, and let remain until it had acquired a much thicker coat of the metallic ' deposition ; but on attempting to remove it from the medal, I found I was unable. It had apparently completely adhered to it. I had often practised, with some degree of success, a method of preventing the oxidation of polished steel, by slightly heating it until it would melt fine bees' wax : it was then wiped apparently completely off, but the pores or surfaces of the metal became impregnated with the * Translated from the German edition, by Wm. Sturgeon. t Griffin's Scientific Miscellany, No. iv. p. 33. J See his Pamph. p. 33. D D 2 404. GALVANIC OB YOLTAIC ELECTRICITY. wax. I thought of this method, and applied it to a copper coin. I first heated it, applied wax, and then wiped it off so completely that the sharpness of the coin was not at all interfered with. I proceeded as before, and deposited a thick coating of copper on its surface. Being desirous to take it off, I applied the heat of a spirit-lamp to the back, when a sharp crackling noise took place, and I had the satis- faction of perceiving that the coin was completely loosened. In short, I had a most complete and perfect copper mould of one side of a halfpenny." (537) The first kind of apparatus employed by Mr. Spencer was simply a common tumbler to hold the copper solution, and a gas-glass having one end closed with brown paper, or plaster of Paris, to con- tain the saline solution ; the coin to be copied, and a piece of zinc of equal size, were attached to the extremities of a piece of copper wire. The gas-glass being fixed in the axis of the tumbler, the zinc was placed in it, and the copper wire bent in such a manner as to bring the coin immediately under it in the copper solution. The battery process is subsequently described by Mr. Spencer, but he gives no method of depositing copper on any surface but a metallic one. In Jacobi's pamphlet, however, which was published at St. Petersburg in March, 1840, the use of plumbago, for giving a con- ducting surface to non-metallic substances, and so enabling them to answer all the purposes of metallic originals, is distinctly alluded to. It appears, however, that Mr. Murray has the merit of havdng introduced this discovery into this country ; and the Society of Arts have recorded their sense of its value by presenting this gentleman with a silver medal. The employment of the battery was first suggested by Mr. Mason, who, by connecting a piece of copper with the anode in a second cell, the object to be copied being connected with the cathode, showed that the quality of the copper was much better than when reduced in the single cell apparatus, besides the great advantage that was gained by the unlimited number of opera- Fig. 211. tions that may be going on at the same time. (538) Pig. 211 represents the single cell apparatus. Z is a rod of amalgamated zinc ; m, the mould ; w, the wire joining them ; c, the copper solution ; p, a tube of porous earthenware, containing a solution of acid and water. To put this in action, pour in the copper solution, fill the tube with the acid water, and place it as shown in the figure. Last of all put in the bent wire, having the zinc at one end, and the mould at the other. It is essential that the copper solution be kept saturated, or nearly so ; with which view the ELECTRO-METALLURGY. 405 perforated shelf must be kept well furnished with crystals of sulphate of copper. The mould must not be too small in proportion to the size of the zinc, and the concentrated part of the solution must not be allowed to remain at the bottom, or the copy will be irregular in thickness. Fig. 212 represents the battery apparatus. A is a cell of Daniell's battery (or Smee's may be used) ; B is the decomposition cell, filled Fig. 212. with the dilute acid solution of sulphate of copper ; Zinc ' Tin Platinum Palladium Iron Silver Gold Tin Copper Platinum Iron Lead 486 THEEMO-ELECTEICITT. (686) Many trials have been made to construct thermo-electric piles, that would operate in a manner similar to the admirable instru- ment for which we are indebted to the genius of Yolta. It appears that the labours of MM. Nobili and Melloni were first crowned with the greatest success. These two philosophers constructed conjointly a thermo-electric pile, with which they made some very interesting Fig. 237. experiments on radiant heat. The pile, Tigs. 237, 238, was composed of fifty small bars of bismuth and antimony, placed parallel side by side, forming one prismatic bundle thirty millimetres* long, and some- thing less in diameter. The two terminal faces were blackened. The bars of bismuth, which succeeded alternately to those of antimony, were soldered at their extremities Fig. 238. to the latter metal, and separated at every other part of their surfaces, by some insulating substance, such as silk or paper. The first and last bars had each a copper wire which termi- nated in a peg of the same metal passing through a piece of ivory, fixed in a ring. The space between this ring and the elements of the pile was filled with some insulating substance. The loose extremities of the two wires were con- nected with the ends of the wire of a galvano- meter which indicated by the motion of the needle when the tempera- ture of the farthest face of the pile was above or below that of the other. In Fig. 239 is a representation of this thermo-electric pile, as arranged by Melloni for his experiments on radiant heat : t, a brass cylinder containing the compound bars, having the wires from the Fig. 239. poles connected with the galvanometer, which, as the therino-current * A metre is 39'37 inches; a decimetre 3*9 inches; a centimetre 0'39 inches ; and a millimetre 0'039 inches. THERMOPILES. 487 has but little intensity, should consist of a few coils of pretty stout copper wire. The extremities of the bars at I being exposed to any source of radiant heat, such as the copper cylinder d heated by the lamp I, while the temperature of the other extremity of the bars remains unchanged, a current of Electricity passes through the wires from the poles of the pile and causes the needle of the galvanometer to be deflected. The quantity of Electricity circulating increases in proportion to the difference of the temperature of the two ends ; that is, in proportion to the quantity of heat falling on b, and the effect of this current of Electricity on the needle, or the deviation produced, is proportional to the quantity of Electricity circulating, and con- sequently to the heat itself at least Melloni found this correspond- ence to be exact through the whole are from zero to twenty degrees, when the needle is truly astatic. The deli- cacy of this apparatus is such, that, according to Nobili, it is capable of measuring a differ- ence of temperature of -raW of a degree. (687) Thermo-piles are now constructed by soldering together at their alternate edges bars of antimony and bismuth, with squares of card-board or thick paper intervening to prevent contact, the terminal metals being furnished with wires for the convenience of connection. (688) Fig. 240 is a representation of Locke's convenient form of the thermo- electric battery. It is composed of from 30 to 100 series of bars of antimony and bismuth soldered together at their extremities, and placed in a metallic cylinder which is then filled with plaster of Paris, leaving merely the extremities of the bars exposed. The first bar of bismuth is connected with one mercury cup, and the last antimony bar with the other cup. The instrument is put in action by placing it in a vessel of ice, and then laying the hot iron plate on the top. Fig. 241 is Professor Gumming' s stellar- form thermo-electric composite battery. It is composed of a series of forty pairs of iron and copper wires, formed in radial lines on a circular card-board. The battery is excited by the radiation of a heated body, placed Fig. 240. 488 THEEMO-ELECTEICITT. opposite the central junctions, while, at the same time, the exterior parts of the wire-frame are screened from the influence of the calorific rays by a polished reflecting screw. ? 242 - Pig. 242 is Professor Dove's composite thermo-battery for constant currents. It consists of a horizontal half-cylinder of wood covered with 100 pairs of iron and platinum wires, which touch its periphery in such a manner that all the iron wires are situated in a right-handed ball, the platinum wires in a left- handed spiral. The .elevation of temperature at the junction of the united pairs is effected by the oil or water contained in the oblong trough being heated by a spirit lamp. Fig. 243. Pig- 243 represents Van der Voort's thermo-electric combination, consisting of eighteen pairs of bismuth and anti- mony prismatic rods united alternately by solder, and fixed in a mahogany box by plaster of Paris, leaving the two extremities of the metals exposed to be acted on by unequal temperatures. To use it, the lower end is placed in a freezing mixture, and boiling oil or water is placed on the top. Fig. 244. "Watkins's massive thermo-electric pile is shown in Pig 244. It con- sists of an association of square bismuth and antimony plates, alter- nately soldered together, so as to form a composite battery, mounted in a frame with the upper and lower junctions of the metals exposed. "When either ends are slightly ele- vated or depressed, in regard to temperature, the electric current is established, and with the radiation of red hot iron at one extremity and ice at the other, all the ordinary electric phenomena, such as the spark, heat, electro- magnetic rotations, chemical action, &e., are developed. (689) A very ingenious hygrometer, founded on thermo-electric principles, was invented by Peltier, Pig. 245. It consists of a series of slender bars of antimony TTNTDALL'S EXPERIMENT. 489 and bismuth, arranged alternately in the form of a crown, and metallically united in pairs : the extreme bars are connected by copper wires, with binding screws attached to the stem of the support. A platinum dish containing distilled water is placed on the points of the compound bars. An electrical current is developed by the reduction of temperature, occasioned by the evaporation of the water in the capsule, and the deflection of the galvanometer caused thereby, may be taken as a measure of the rapidity of evaporation, and hence, of the hy groin etric state of the atmosphere. (690) It was discovered by Peltier that heat is absorbed at the sur- face of contact of bismuth and antimony in a compound metallic con- ductor when Electricity traverses it from the bismuth to the antimony, and that heat is generated when the current traverses it in a contrary direction. This is referred to by Joule (Phil. Mag. 1843), as show- ing how it may be proved that when an electrical current is continu- ously produced from a purely thermal source, the quantities of heat evolved electrically in the different homogeneous parts of the circuit are only compensations for a loss from the junctions of the different metals, or that when the effect of the current is entirely thermal, there must be just as much heat emitted from the parts not affected by the source, as taken from the source. Adie (Phil. Mag. vol. v. p. 197,) denies the production of cold under any circumstances by the electrical current, but the following ingenious experiment of Tyndall, who has recently re-investigated the subject (Phil. Mag. vol. iv. 1852, p. 419,) seems quite conclusive on the point : B is a curved bar of bismuth with each end of which a bar of antimony A A is brought into close contact ; in front of the two junctures are chambers hollowed out in cork, and filled with mercury. A current is sent from the cell B in the direction indicated by the arrow ; at M it passes from antimony to bismuth, and at M' from bismuth to antimony. Now, if Peltier's observation be correct, we ought to have the mercury at M warmed, and that at M' cooled, by the passage of the current. After three minutes' circulation, the 490 THEBMO-ELECTEICITY. voltaic circuit was broken, and the thermo-test pair A' B' dipped into M', the consequent deflection was 38 ; and the sense of the deflection proved that at M' heat had been absorbed. The needles were brought quickly to rest at 0, and the test pair was dipped into M, the consequent deflection was 60, and the sense of the deflection proved that at M heat had been generated. The system of bars represented in the figure being imbedded in wood, the junction at M was cooled slowly, and would have taken a quarter of an hour at least to assume the temperature of the atmosphere. The voltaic current was reversed, and three minutes' action not only absorbed all the heat at M, but generated cold sufficient to drive the needle through an arc of 20 on the negative side of 0*. It was shown by Lenz (Pogg. Ann. vol. xliv. p. 341), that if two bars of bismuth and antimony be soldered across each other at right angles, and they be touched with the conducting wires of the battery, so that the positive current will have to pass from the bismuth to the antimony, a cold sufficient to freeze water may be produced ; for if a cavity be excavated at the point of contact, and a drop of water previously cooled to nearly 32 be placed therein, it will rapidly 'become ice. (691) The first account we have of the production of a spark from a thermo-electric apparatus, appears in a communication from Professor Wheatstone to the London and Edinburgh Philosophical Magazine (vol. x. p. 414). The following is the simple statement : The Cav. Antinori, Director of the Museum at Florence, having heard that Professor Linari, of the University of Siena, had succeeded in obtaining the electric spark from the torpedo by means of an electro-dynamic helix and a temporary magnet, conceived that a spark might be obtained by applying the same means to the thermo- electric pile. Appealing to experiment, his anticipations were fully realized. No account of the original investigations of Antinori has reached, we believe, this country, but Professor Linari, to whom he early communicated the results he had obtained, immediately repeated them, and published the following additional observations of his own, in & Indicatore Sanese, No. 50, Dec. 13, 1836. 1. "With an apparatus consisting of temporary magnets and electro- dynamic spirals, the wire of which was five hundred and five feet in length, he obtained a brilliant spark from a thermo-electric pile, of Nobili's construction ; consisting only of twenty-five elements, which was also observed in open day-light. 2. " "With a wire eight feet long, coiled into a simple helix, the spark constantly appeared in the dark, on breaking contact, at every interruption of the current ; with a wire fifteen inches long, he saw SPAEKS FBOM THE THERMOPILE. 491 it seldom, but distinctly ; and with a double pile, even when the wire was only eight inches long. In all the above-mentioned cases, the spark was observed only on breaking contact, however much the length of the wire was diminished. 3. " The pile, consisting merely of these few elements, readily decomposed water, within such restricted limits of temperature as those of ice and boiling water. Short wires were employed, having oxidable extremities ; the hydrogen was sensibly evolved at one of the poles. 4. " A mixture of marine salt moistened with water, and of nitrate of silver, being placed between two horizontal plates of gold, com- municating respectively with the wires of the pile, the latter, after having acted on the mixture, gave evident signs of the appearance of revivified silver on the plate which was next the antimony. 5. " An unmagnetic needle, placed within a close helix, formed by the wire of the circuit, was well magnetised by the current. 6. " Under the action of the same current, the phenomenon of the palpitation of mercury was distinctly observed," (692) The principal results here stated were verified by Professor Wheatstone ; he employed a thermo-electric pile, consisting of thirty- three elements of bismuth and antimony, formed into a cylindrical bundle, three-fourths of an inch in diameter, and one inch and one- fifth in length ; the poles of this pile were connected by means of two thick wires, with a spiral of copper ribbon, fifty feet in length, and one inch and a-half broad, the coils being well insulated by brown paper and silk. One face of the pile was heated by means of a red-hot iron, brought within a short distance of it ; and the other face was kept cool by contact with ice. Two stout wires formed the communication between the poles of the pile and the spiral, and the contact was broken when required in a mercury cup, between one of the extremities of the spiral and one of these wires. "Whenever contact was thus broken, a small lut distinct spark was seen ; it was visible even in day-light. Professors Daniell, Henry, and Bache assisted in the experiments, and were all equally satisfied with the reality of the appearance. At another trial, Professor Wheatstone obtained the spark from the same spiral, connected with a small pile of fifty elements, on which occasion Dr. Earaday and Professor Johnston were present. On connecting two such piles together, so that the similar poles of each were connected with the same wires, the same was seen brighter. (693) Some experiments on the chemical action of the thermo- electric pile, were made anterior to those above described, by Professor 492 THEBMO-ELECTBICITY. Gr. D. Botto, of the university of Turin, with a different arrangement of metals ; his experiments are published in the Bibliotheque Uni- verselle for September, 1832. His thermo-electric apparatus was a metallic wire or chain, consisting of twenty pieces of platinum wire, each one inch in length, and one-hundredth of an inch in diameter, alternating with the same number of pieces of soft iron wire, of the same dimensions. This wire was coiled as a helix round a wooden rule, eighteen inches long, in such a manner that the joints were placed alternately at each side of the rule, being removed from the wood at one side to the distance of four lines. Employing a spirit- lamp of the same length as the helix, and one of Nobili's galvano- meters, a very energetic current was shown to exist; acidulated water was decomposed, and the decomposition was much more abun- dant, when copper instead of platinum poles were used ; in this case, hydrogen only was liberated. The current and decomposition were augmented when the joints were heated more highly. Better effects were obtained with a pile of bismuth and antimony, consisting of one hundred and forty elements, bound together into a parallelepiped, having for its base a square of two inches, three lines, and an inch in height. (694) For developing Electricity of feeble intensity it is always best to employ a flat copper ribbon coil. Mr. Watkins found that he could always show a larger spark with it than with an elongated wire coil and large temporary magnet; and that the snapping noise accompanying the thermo-electric spark was more discernible. Mr. Watkins arranged one of the extremities of his pile of strong sheet copper, cut like a comb, and covered with soft solder ; and when the moveable extremity of the flat coil is passed over the comb, and the thermo-electric pile in action, bright sparks were seen every time the moving part of the coil broke the circuit by leaving a tooth of the comb. With a pile consisting of thirty pairs of bismuth and antimony, one inch and a-half square, and one-eighth thick, with the radiation from red-hot iron at one extremity, and ice at the other, a soft iron electro- magnet under the inductive influence of the Electricity thus generated, supported ninety-eight pounds weight. The same experimentalist states that he has thermo-electric piles in his possession, varying from fifteen to thirty pairs of metallic elements, which give brilliant sparks by simply pouring hot water on one end, while the other end is at the temperature of the atmosphere ; and that sparks are exhibited by the same piles, when the temperature is reduced at one end by the aid of ice, while the other end is at the temperature of the surrounding air. In order to effect the decomposition of water, Mr. Watkins employed a massive thermo-battery, with pairs of bismuth and antimony, a small THERMO-CTJKEENT FBOM FUSED SALTS. 493 apparatus for the decomposition of water, of the ordinary description, and an electro-dynamic heliacal apparatus. The primary coil of wire was ninety feet long, and when-the thermo-electric current simply per- vaded this coil, he did not notice any disengagement of the gases ; but as soon as the contrivance for making and breaking battery-contact was put in action, then an evolution of the gases took place, while at the same time powerful shocks were received from the secondary coil of wire one thousand five hundred feet long. (695) Erom the interesting discovery made by Faraday, of the high conducting power of certain fused salts for voltaic Electricity, Dr. Andrews was led to imagine that thermo-currents may be excited by bringing them into contact with metals, and he succeeded in verifying this conjecture in the following manner : * (696) Having taken two similar wires of platina (such as are used in experiments with the blowpipe), and connected them with the ex- tremities of the copper wire of a delicate galvanometer, he fused a small globule of borax in the flame of a spirit-lamp on the free ex- tremity of one of the platinum wires, and introducing the free extremity of the other wire into the flame, he brought the latter, raised to a higher temperature than the former, into contact with the fused globule ; the needle of the instrument was instantly driven with great violence to the limit of the scale. The direction of the current was from the hotter platinum wire through the fused salt to the colder wire. A per- manent electrical current in the same direction was obtained by simply fusing the globule between the two wires, and applying the flame of the lamp in such a manner, that, at the points of contact with the fused salt, the wires were at different temperatures. (697) Dr. Andrews also succeeded in obtaining chemical decomposi- tions by this peculiar therrno-current. A piece of bibulous paper, exposing on each side a surface of one-fourth of a square inch, was moistened with a solution of the iodide of potassium, and laid on a platinum plate, which was in metallic connexion with one of the platinum wires used in the previous experiments. The extremity of the other platinum wire in contact with the globule, was applied to the surface of the bibulous paper, and the flame of the lamp was so directed, that the latter was the colder of the wires, between which the globule of borax, or carbonate of soda, was fused. The platinum plate in this arrangement, therefore, constituted the negative pole, and the extremity of the wire applied to the bibulous paper the positive pole* Accordingly when the circuit was completed, an abundant * Dr. Andrews found that by using a platinum wire, exposing an extensive surface, as one pole of a voltaic pair, and a fine wire of the same metal as the other, he could effect the decomposition of water ; when, by employing a pair of 494 THEEMO-ELECTKICITT. deposition of iodine occurred beneath the platinum wire. "When a similar wire of platinum was substituted for the plate on the negative side, the effect was either none or scarcely perceptible. (698) Dr. Andrews next formed a compound arrangement, by placing a series of platinum wires on supports, in the same horizontal line, and fusing between their adjacent extremities small globules of borax. The globules and wires were exactly similar to those that are used in blow-pipe experiments. A spirit-lamp was applied to each globule, so as to heat unequally the wires in contact with it ; and the corresponding extremity of each wire being preserved at the higher temperature, the current was transmitted in the same direction through the whole series. By connecting the extremities of four cells of this arrangement with an apparatus for decomposing water, in which the opposite poles consisted of a thick platinum wire, and a guarded platinum point (both being immersed in dilute sulphuric acid), very minute bubbles of gas soon appeared at the guarded point, and slowly separating from it, ascended through the liquid. They were obtained in whichever direction the current was passed, but rather more abundantly when the point was negative and the wire positive. With only two cells, similar bubbles formed in a visible manner on the guarded point, but in such exceedingly small quantity that they did not separate from it. "With an arrangement contain- ing twenty cells, a doubtful sensation was communicated to the tongue, when the poles were applied to it : but no spark was visible, although the current was passed through a helix of copper wire, surrounding a bar of iron, and the contact was broken with great rapidity, by means of a revolving apparatus. It is necessary to observe, however, that the lamps were unprotected, and that it was impossible to render the flames of such a number of spirit-lamps, burning near each other, so steady, as to heat at the same moment, similar platinum plates, or similar fine wires as poles, he could obtain no such result. After the evolution of gas had ceased, he finds that an additional quantity is procurable, either by increasing the surface of the broad pole, or by removing it, and heating it to redness, or by reversing the direction of the current. Dr. Andrews accounts for this, by supposing that when the poles exposed on both sides equal surfaces, the gases were dissolved in the nascent state by the surrounding liquid ; but when the polar surfaces were unequal, the solution of the gas being greatly facilitated by the broader pole, the element of water separated there was dissolved, while the other element was disengaged in the gaseous state at the wire, which served as the opposite pole. In order, therefore, to discover, in case of difficulty, whether an electrical current is capable of decomposing water, or other substances, it is necessary to employ poles, having very unequal surfaces ; and this will be effected in the most perfect manner by opposing a thick wire, or plate of platinum, to one of Wollaston's guarded points (211). DE. ASTDBEWS' EXPEKIMENTS. 495 in the required manner, all the globules and wires. "With an enlarged and more perfect apparatus, Dr. Andrews thinks a spark might be obtained. (699) Hence it appears that an electrical current is always pro- duced when a fused salt, capable of conducting Electricity, is brought into contact with two metals, at different temperatures, and that powerful chemical affinities can be overcome by this current quite independently of chemical action. The direction of the current is not influenced by the nature of the salt or metal, being always from the hotter metal through the fused salt to the colder ; its intensity is inferior to that of the hydro-electric current developed by platinum and zinc plates, but greatly superior to that of the common thermo- electric currents, and is capable of decomposing, with great facility, water and other electrolytes. Dr. Andrews found also that currents were produced before the salt becomes actually fused, but that their direction no longer follows the simple law before enunciated, but varies in the most perplexing manner, being first from the hot metal to the cold, then with an addition of heat, from the cold to the hot ; and again, with a second addition of heat, from the hot to the cold. (See Dr. Andrews' paper, in vol. x., and page 433, of the L. and E. Phil. Mag.) (700) Since the phenomena of thermo-Electricity seem to account, in a satisfactory manner, fort he general distribution of Elec- tricity and magnetism over the earth, the interest attached to this peculiar development of the subtile agent we have been engaged with, is exceedingly great. That the earth may be considered as a great magnet, the phenomena of the dip of the needle sufficiently show : and the facts connected with electro-magnetism lead to the conclu- sion, that, when a magnetic needle is in its natural position of north and south, there exist electrical currents in planes of right angles to the needle descending on its east side, and ascending on its west side ; we must hence suppose that currents of Electricity are con- stantly circulating within the earth, especially near its surface, from east to west, in planes parallel to the magnetic equator. (701) The cause of these electrical currents has been thus ex- plained by Ampere. The earth, during its diurnal motion on its axis from west to east, has its surface successively exposed to the solar rays, in an opposite direction, or from east to west. The surface of the earth, therefore, particularly between the tropics, will be heated and cooled in succession, from east to west, and currents of Electricity on thermo-electric principles will, at the same time, be established in the same direction : now, these currents once established, from east to west, will, of course, .give occasion to the magnetism of the earth 496 THERMO-ELECTRICITY. from north to south. Hence, the magnetic directive power of the earth, in a direction nearly parallel with its axis, is derived from the thermo-electric currents induced in its equatorial regions by the unequal distribution of heat there present, and depending principally on its diurnal motion. The actual existence of these electrical currents has been fully established by the experiments of Pox, Heich, and others, made in mines. It was ascertained, by the former, that by connecting two distant parts in the same vein, with the wires of a galvanometer, that currents of different degrees of intensity run in some cases from east to west, and in others, from west to east. Eeich verified this observation in the mines of Saxony, and he found that the direction of the currents depended on the geographical situation of the place, and on the depth of the station below the surface. THEOET OE THE YOLTAIC PILE. 407 CHAPTEE XII. THE THEOEY OF THE VOLTAIC PILE. (702) Is the proximate cause of the voltaic current the contact of the two dissimilar metals, or is it the action of the oxidizable metal on the water of the acid solution? This question has been the subject of much profound discussion. It has already been stated that the first view of the subject was adopted by Yolta, who, attri- buting the Electricity of the pile to the contact of dissimilar metals, regarded the interposed solutions merely as imperfect conductors, admitting the transfer of Electricity when the circuit was completed; and when incomplete, throwing the whole by induction into an electro-polar state. This view has been adopted and reasoned on, with their peculiar ingenuity, by the Grerinan philosophers ; on the other hand, a powerful mass of evidence has been brought against it by Faraday, and the chemical theory has obtained, in this country at least, almost universal assent. (703) It will be proper, however, to attempt a popular account of the present state of this interesting question. By Davy the electric state of the pile was considered as due partly to the contact of the opposed metals, and partly to the chemical action exerted on them by the liquid. He concluded, to use his own words,* that " chemical and electrical attractions are produced by the same cause ; acting, in one case, on particles, in the other on masses of matter ; and that the same property, under different modifications, is the cause of all the phenomena exhibited by different voltaic combinations." By Dr. "Wollaston the phenomena were referred solely to chemical action ; and he even attributed the Electricity of the common ma- chine to the oxidizement of the amalgam, and found, contrary to the experiments of his great contemporary, that the electrical machine was not active in atmospheres of hydrogen, nitrogen, or carbonic acid. The first suggestion, however, of the chemical origin of voltaic Electricity is to be found in a paper communicated by Fabroni, in 1792, to the Florentine Academy. This philosopher ascribed the convulsions in the limbs of the frog, in the experiments of Gralvani and Volta, to a chemical change made by the contact of one of the * Philosophical Transactions, 1826, p. 389. K K 498 GALVANIC OB VOLTAIC ELECTRICITY. metals with the liquid matter on the parts of the animal body ; to a decomposition of this liquid ; and to the transition of oxygen from a state of combination with it, to combination with the metal. He maintained that the convulsions were chiefly due to the chemical changes, and not to the Electricity incidental to them, which he con- sidered, if operating at all, to do so in a secondary way. Pepys placed a pile in an atmosphere of oxygen, and found that in the course of a night, 200 cubic inches of the gas had been absorbed ; while in an atmosphere of azote, it had no action. MM. Biot and Cuvier also observed the quantity of oxygen absorbed, and inferred from their experiments that, " although, strictly speaking, the evolu- tion of Electricity in the pile was produced by oxidation, the share which this had in producing the effects of the instrument bore no comparison with that which was due to the contact of the metals, the extremities of the series being in communication with the ground." (704) The source of the Electricity of the voltaic pile was made by Faraday the subject of the 8th, 16th, and 17th series of his Experimental Researches. By the arrangement shown in Fig. 247 he succeeded in producing Electricity quite independent of contact. A plate of zinc (Fig. 247) was cleaned and bent in the p^ 247. middle to a right angle ; a piece of platinum, about three inches long and half an inch wide, J, was fas- tened to a platinum wire, and the latter bent as in the figure. These two pieces of metal were arranged as shown in the sketch ; at x a piece of folded bibulous paper, moistened in a solution of iodide of potassium, was placed on the zinc, and was pressed upon by the end of the platinum wire ; when, under these circum- stances, the plates were dipped in the diluted nitric and sulphuric acids, or even in solution of caustic potash, contained in the vessel c, there was an immediate effect at #, the iodide being decomposed, and iodine appearing at the anode, that is, against the end of the platinum wire. As long as the lower ends of the plates remained in the acid, the electric current proceeded, and the de- composition proceeded at x. On removing the end of the wire from place to place on the paper, the effect was evidently very powerful ; and on placing a piece of turmeric paper between the white paper and the zinc, both papers being moistened with a solu- tion of iodide of potassium, alkali was evolved at the cathode against the zinc, in proportion to the evolution of iodine at the anode ; the galvanometer also showed the passage of an electrical current ; and we have thus a simple circle of the same construction and action as THE GET OP THE VOLTAIC PILE. 499 those described in Chapter VII., except in the absence of metallic contact. (705) It is shown by Faraday that metallic contact favours the passage of the electrical current, by diminishing the opposing affini- ties. When an amalgamated zinc plate is dipped into dilute sulphuric acid, the force of chemical affinity exerted between the metal and the fluid is not sufficiently powerful to cause sensible action at the sur- faces of contact, and occasion the decomposition of the water by the oxidation of the metal, though it is sufficient to produce such a condition of Electricity as would produce a current if there were a path open for it ; and that current would complete the conditions necessary, under the circumstances, for the decomposition of water. Now, when the zinc is touched by a piece of platinum, the path required for the Electricity is opened, and it is evident that this must be far more effectual than when the two metals are connected through the medium of an electrolyte ; because a contrary and opposing action to that which is influential in the dilute sulphuric acid is then intro- duced, or at any rate the affinity of the component parts of the electrolyte has to be overcome, since it cannot conduct without decomposition, and this decomposition re-acts upon, and sometimes neutralizes, the forces which tend to produce the current. (706) The mutual dependence and state of the chemical affinities of two distant portions of acting fluids, is well shown in the following experiments : Let P (Fig. 248) be a Fig. 248. plate of platinum, Z a plate of amal- ^ gamated zinc, and y a drop of dilute \E LA BTYE. 509 duced is almost entirely perceived. There is, "however, a slight re- composition ; for the negative tension of an insulated metal is sensibly augmented by giving a translator^ motion to the gas which attacks its surface ; the consequence of which is, that the positive Electricity accumulated in the gas, being removed with it, cannot unite with the negative left in the metal. The principle of the immediate recom- position of the two Electricities applies also to the production of electric currents in a pair. In very lively chemical actions, the larger proportion of the Electricities developed often undergoes this recom- position ; a small part only runs through the whole circuit, especially if it be not a very good conductor, which is the reason that the strongest currents are not always those produced by the most lively chemical actions, and that in a pair, the metal most attacked is not always the positive one ; that is, the one whence the current com- mences. However, the latter case occurs only when each of the two metals of the pair are immersed in different liquids. A single example may be adduced : a plate of zinc is immersed in concentrated sul- phuric acid, and a plate of copper in nitric acid : the two acids are immediately in contact, and the two metallic plates communicate by means of the wire of a galvanometer. In this pair the zinc is positive, though it is much less attacked than the copper, because the two Electricities developed by the action of the sulphuric acid on the zinc, can be more easily reunited by making the tour of the circuit, than by passing from the sulphuric acid to the zinc, and reciprocally ; while, on the contrary, the two Electricities developed by the action of the nitric acid on the copper, reunite immediately with the greatest facility, in consequence of the conductibility of the nitric acid, and the ready passage of the Electricity from that acid to the copper ; while to make the circuit, they would be obliged to traverse the con- centrated sulphuric acid, which is a very imperfect conductor, and pass from the zinc to the acid a very difficult passage. Two cir- cumstances prove the exactitude of this explanation : 1. The same result is obtained in the preceding experiment by substituting a plate of zinc similar to that which is immersed in the sulphuric acid for the plate of copper immersed in the nitric acid. 2. If a capsule of platinum be put upon the plate of a condenser, and filled in suc- cession with nitric acid and concentrated sulphuric acid, and a plate of copper or zinc held between the fingers, be immersed in the former liquid, and a plate of zinc in the latter, a much stronger positive Electricity is obtained in the second case than in the first. (727) In applying these principles to the explanation of the theory of the voltaic pile, De la Rive remarks, that the use of the pile is to 510 GALVANIC OB VOLTAIC ELECTEICITT. facilitate the passage of the current through imperfect conductors, and not to increase the quantity of Electricity ; for the utmost that can be effected by a pile composed of a certain number of similar pairs is to compel all the Electricity produced by only one of its pairs, to pass through the conducting body which connects its poles. The only means of attaining this object is to separate the two metals of a pair by other pairs, as similar to the first as possible. These intermediate pairs, the number of which should correspond to the more or less im- perfect conductibility of the bodies interposed, will each produce as much Electricity as the extreme pairs. But these Electricities do not pass through the conductor, they only compel the Electricities of the extreme pairs to pass through it almost in totality. (728) Let us see how this effect is produced. " We shall take a pile in activity, and suppose that all the pairs of which it is composed are so exactly similar in every respect that the free Electricity on each of them has the same intensity. Let 5 be a pair in the pile taken at hazard, and disposed in such a manner that its zinc is immersed in the same liquid as the copper of the pair a, which precedes it ; and its copper in the same liquid as the zinc of the pair c, which follows it. The chemical action of the liquid upon the zinc of the pair b, developes in it a certain quantity of Electricity ; the portion of this Electricity, which does not undergo immediate recomposition, remains free, and the same for all the pairs, they being similar and symmetrically dis- posed with relation to each other. According to this, the positive Electricity of 6, developed by chemical action, in the liquid in which the copper of a is immersed, neutralizes the negative Electricity of this latter pair, which is equal to it. In the same manner, the nega- tive Electricity of 5, which by chemical action is carried to the zinc, and thence to the copper in contact with the zinc, neutralizes the positive Electricity of c, which also is perfectly equal to it. There remains, then, an excess of free positive Electricity in the liquid in which the zinc of a is immersed, and an excess of free negative Electricity, perfectly equal upon the copper of c. But these free Electricities are"neutralized by the equal and opposite Electricities of the following pairs, with regard to which we may reason in the same manner as for the pairs , 6, c. Thence there results an excess of free positive Electricity at the extremity of the pile, at the side of a ; and an exactly equal excess of negative Electricity at the extremity, situated at the side of 5. Such is found to be the fact, if a commu- nication be established between each of the extremities and an electro- scope : and if they be united by a conductor the two excesses of free Electricity are collected together and form the current. The intensity THEORY OP THE YOLTAIC PILE j DE LA EIYE. 511 of this current, as experiment has proved, ought to be perfectly equal to that of the current which is established in the pile itself between all the pairs." (729) M. de la Rive next proceeds to show how it happens, that though the quantity of free Electricity developed upon each pair of the pile be frequently not mathematically the same, yet the current which traverses a conductor, uniting the two extremities, is still mathematically equal to that which traverses each of the pairs. To establish this important result, instead of soldering the zinc and copper of the same pair to each other, an independent conductor must be fixed to each. By means of these two conductors, a metallic communication is established between the two metals of the pair by the intervention of one of the wires of a double galvanometer, the second wire of which serves as conductor to the current of a second pair of the same pile, or to effect a communication between the two poles. (730) If these two currents are carefully made to pass in contrary directions in each of the wires of the galvanometer, their action on the needle will be always found absolutely null, provided they are mathematically equal. This equality is easily explained. Take the most feeble pair in the pile ; let I be the pair ; the positive Electri- city disengaged by I cannot neutralize all the negative of a ; there will remain then, in the copper of a, an excess of negative Electricity, which will retain, by neutralizing it, an equal quantity of positive ; the result will be, that a, though much stronger than #, can only set at liberty a quantity of positive Electricity equal to that of b. It appears from this analysis, that the current of each pair, and conse- quently the current of the whole pile, should be equal to the current produced by the weakest pair. ISTow experiment fully proves, that if a feeble pair is introduced into a pile composed of energetic pairs, the immediate result is a considerable diminution in the force of the current of the pile, and consequently of the current of each of the other pairs. But this reduction is never sufficient to render this current equal to that which would be developed by the pair intro- duced in an insulated state. Indeed, any pair whatever necessarily produces a greater quantity of Electricity when it is in the circuit than when it is isolated. Prom these valuable remarks we see how necessary it is, in the construction of compound voltaic batteries, to prepare plates as similar as possible, both in size and quality of metal; for of how many pairs soever the arrangement may consist, and how perfect and alike soever all the other pairs may be, the introduction of one smaller or faulty pair will inevitably reduce the power of the battery to that which would result from an equal number of pairs of plates of the size and condition of the feeble pair. 512 GALVANIC OE VOLTAIC ELECTRICITY. (731) The same indefatigable electrician published also in 1836 another essay, embodying a series of experimental arguments against the contact theory. This memoir was afterwards replied to by Fechner, in a paper published in Poggendorf's Annalen,* entitled "Justification of the Contact Theory." "We shall give one or two extracts from each of these memoirs, more, however, with a view of exhibiting specimens of the profundity of thought and skill thrown by both parties into the argument, than with an expectation of enabling any of our readers to form a conclusion respecting these hardly-contested theories. (732) Amongst other important experiments, quoted by Be la Rive, is the following : A piece of potassium or sodium was fixed, in a solid manner, by one of its ends to a platinum forceps, while the other extremity was held by means of a wooden or ivory one. If, after having well brightened it, it is surrounded by very pure oil of naphtha, and the condenser be touched with the end of the platinum forceps, no electrical sign is observable ; while, if the naphtha oil is taken off", and none remain adhering to the metal, this is observed to oxidate rapidly by the contact of the air, and the Electricity indi- cated by the electroscope is of the most lively kind. The condenser is scarcely necessary to render it perceptible. If, sometimes, some indications of Electricity are obtained when the potassium or sodium, is on the oil of naphtha, then a small quantity of humidity has been introduced into the liquid, which had remained adhering to the sur- faces of the two metals, and which exercises on them a chemical action, which it is easy to recognise. Immersed in azote and in hydrogen, the two metals still give rise to a development of Electri- city, proceeding from the action exerted upon them, either by the gas or by the aqueous vapour, from which it is impossible entirely to free them ; and in proof of this chemical action, we see their surfaces lose their metallic brightness and become tarnished very much, as would have taken place in the air. (733) By a variation in the method of performing this experi- ment, Fechner brings it forward as furnishing an argument against the chemical theory. If the potassium be brought into connection with the earth by means of moist wood, then powerful action is pro- duced in the petroleum, arising, according to the chemical theory, from the chemical action produced through the moisture, and, accord- ing to the contact theory, from the increased conducting power of the wood. If the one-half of the bar of wood, which stood in connection with the potassium, was moistened, and the other half air-dried, then no eifect was produced on the condenser, provided the dry half of * Vol. xiii p. 481. THEORY Or THE YOLTAIC PILE ; TECHNEE. 513 the wood was held in the hand ; and this was even the case if the potassium was moistened with acidulated water during the contact, so that a violent chemical action took place, a proof that the non- conducting power of the dried wood is sufficient to explain the nega- tive result. A delicate electrometer was constructed to present the smallest possible surface : it consisted solely of a very thin and short brass wire, which, as the axis of a surrounding gum lac cylinder, traversed the perforated bottom of an inverted drinking-glass, and from which, within the glass, was suspended, between the pole plates of a dry pile, a very small gold leaf, 2J inches long, while the Electricity could be transferred to the prominent end of the brass, without the glass. Into the potassium ball was inserted a thin platinum wire, as short as the convenience of transfer of the Electricity allowed, and the ball itself, for the purpose of increasing its surface, was pressed between two copper plates, which had been soaked in petroleum, as smooth as was possible, without cutting the potassium ball with the platinum wire. Thus, the entire electrometer might have been some- what about double the size of the surfaces of the potassium. The potassium disc, with the upwards-bent platinum wire proceeding from it, was placed in a small glass, and covered with petroleum to about half an inch high, the platinum wire which projected from the petroleum, and which nowhere touched the glass, was discharged on to the electrometer, the glass being held in the hand. The divergence to the side which indicates the negative Electricity followed in this case quite as constantly, evidently, and certainly, as if the potassium had been insulated in the air. It is true, observes Eechner, that when the potassium is brought from the air into the petroleum, the chemical action of the adhering moisture is shown by the gas bubbles which rise from the liquid ; but this development of gas soon ceases, and, twenty-four hours after it had entirely disappeared, the elec- trical signs in the petroleum were of quite the same force as during the development of gas, and even in the air, so that any objection raised on the grounds of chemical action is valueless, and the experi- ment is entirely in favour of the contact theory. (734) Some experiments are described by De la E-ive, in which two similar plates of zinc are furnished with a brass knob soldered to each, the inner surface of one plate, and both exterior and interior surfaces of the other, being covered with lac varnish. When these plates are made sometimes to stand in the place of the plates of a condenser, and sometimes using one of them and another brass plate, it was shown that when entirely protected from the action of the air by means of a layer of varnish, a plate of zinc does not become L L 514 GALVANIC OE YOLTAIC ELECTEICITT. electric in its contact with a brass knob, and, indeed, that it conducts itself as a homogeneous plate of brass ; for when the brass knob was touched with the copper element of a heterogeneous plate, the zinc of which was held in the hand, it became charged with negative Elec- tricity, though, according to the contact, theory all kind of action should have been neutralized, from the opposition of two pairs of plates perfectly similar. (735) These experiments were repeated by Pechner with contrary results. He states, that in order to lay aside the objection which perhaps might be raised respecting the chemical action of the air upon the copper knob, he fixed a platinum wire to it, and then varnished the whole over so as to have the platinum alone exposed. Nevertheless, when the platinum was touched with the finger or with a slip of paper moistened in distilled water, the zinc condensers became quite as well charged with positive Electricity as if it had not been varnished. Becquerel and Peltier arrived at similar results ;* and Pfaif, who states that he repeated De la Rive's experiments quite in accordance with his own statement, always observed the same action of the zinc condensers with as without varnish. (736) The following experiment is produced by Pechner as an experimentum crucis against the chemical theory. Ten pairs of zinc and copper, in every respect as equal to one another as possible, were arranged into a " couronne des tasses," so that half of the said pairs produced a current opposite in its direction to that which was originated by the other half. The exciting fluid used was common water. Such an arrangement being connected with the galvanometer can, according to either of the two theories, have no effect upon the needle, provided everything in the two systems of cells be equal ; muriatic acid was then put into one of the systems, and it was found that in these circumstances the previous equilibrium was in the first instance maintained, but that by degrees the current of the water cells got the ascendancy over the acid system. " According to the contact theory," says Pechner, " the explanation of this experiment is easy." The addition of muriatic acid increases the action only by diminishing the opposition to the conduction present in the circuit, and this diminution is of as great advantage to the Electricity (which is developed by contact in the cells without acid) in its entire circu- lation throughout the circuit, .as to the Electricity of the pairs of plates which are in 'the very acid fluid. " How the result is to be explained according to the chemical theory, I cannot conceive." (737) We think, however, that Schcenbein has given a very satis- * Traite d'ElectricitS, ii. p. 139. THEOET OF THE YOLTAIO PILE; FAEADAY. 515 factory explanation of this experiment on the chemical principle. From the results of various experiments, it appeared that only in a few instances the chemical difference of the exciting fluids contained in the two systems of cells determines a difference of currents produced by the two sets of pairs, and that the general rule is the production of current equilibrium. Now it had been established by De la Hive that the electricities which are set free by chemical action at the two ends of a closed compound circle, unite themselves in two ways : one of which is the pile itself, the other the conductor placed between the poles the quantities of Electricity recombining within each of the two conducting mediums depending upon the peculiar degree of conducting power in each. If in the case in question we consider the acid cells as originating the current and the water cells merely as the medium placed between the poles, it is evident that by far the larger portion of the Electricity developed must be re-united within the pile, and only a small quantity pass through the water cells and through the galvanometer ; but as we know that the water cells also give rise to a current, which, on account of the peculiarity of the arrangement, would be in direction opposite to that excited by the acid cells, it appears from the fact of equi- librium usually taking place, that both currents are generally equal to one another. If ten voltaic pairs be taken, half of them being put into water cells, and the other half into acid ones, and arranged in the usual way, a current is produced much weaker than that which is obtained from five pairs alone placed within the acid fluid. Why (the contact theorist may ask) should this be?. the extent of chemical action in the whole arrangement must be greater than that of only a part ! how then does it happen that the voltaic effect of ten pairs is smaller than that produced by five ? * The answer to this question is too obvious to require further consideration. (738) The celebrated papers of Faraday on the theory of the voltaic pile were read before the Eoyal Society in February and March, 1840. We shall attempt a brief analysis of these memoirs, as they form the most powerful series of experimental arguments that have hitherto been brought together against the contact theory, and are considered by the great majority of electricians, in this country at least, as quite unanswerable. * In the arrangement shown in Fig. 251, the glasses D E are filled with solution of sulphuret of potassium ; P, I, in D, are plates of platinum and iron ; and P, P, in E, plates of platinum ; G- is a galvanometer. Here it will be observed that there are three metallic * See also, in relation to this subject, the experiments with the water battery. 516 GALVAKIC OR YOLTAIC ELECTEICITY. Fig. 251. contacts of platinum and iron, viz., at #, a, and 5; with certain precautions no current passed, though heating either of the junctions at #, J, or x, caused a thermo-current deflecting the galvanometer from 30 to 50 ; and when the tongue or a wet finger was applied at either of the junctions, a strong current passed : contact of platinum and iron therefore in this case produced nothing. Zinc, gold, silver, potassium, and copper, introduced at #, produced no current ; so no electromotive force exists between these metals and platinum and iron. Various other combinations of metals were tried with similar negative results. In green nitrous acid, iron and platinum produced no current ; neither did it in solution of potassium. JX"ow, according to the contact theory, the contact effects between metals and liquids, so far from being balanced, give rise to the phenomena of the pile : it cannot, therefore, be supposed that in the above cases the effects are balanced without straining the point in a most unphilosophical manner. According to the chemical theory, however, the facts admit of very simple explanation : where there is no chemical action there is no current, and a single experiment shows the operator what he is to expect. The contact theory cannot explain why, substituting zinc for iron, a powerful current should be produced in sulphuret of potassium with platinum ; but the chemical theory at once recognizes a chemical action on the zinc, and the same is the case with copper, silver, tin, &c. Many circuits of three substances, all being con- ductors, were next tried, but without establishing anything like electromotive force. (739) To account for the current of the voltaic pile, distinct and important cases ought to be brought forward, and not a case where the current is infinitesimatty small. To account for the phenomena THEOEY OF THE VOLTAIC PILE ; PAEADAY. 517 obtained with sulphuret of potassium, the contact force must be sup- posed to be balanced in some cases (iron and platinum), and not in others (lead and platinum) ; in the latter case, the current ceases when a film of sulphuret has been formed by the chemical action, though the circuit be a good conductor. The case, therefore, will stand thus : Iron platinum . sulphuret of potassium j , , . , , ,, . { Electromotive forces Lead platinum. . sulphuret of potassium j ^ with a film Lead of sulphuret a good con- ductor Electromotive forces , , . , , ( Electromot: platinum . sulph. potas. . . . j balanced< Nothing, therefore, can be predicted by the contact theory regard- ing results. (740) Some active circles excited by the sulphuret of potassium are next examined. Tin and platinum produced a strong current, tin being plus ; after a time the needle returned to 0, the tin becoming invested with a non-conducting sulphuret. The current here could not have been produced by the contact force of the sulphuret, because it happens to be a non-conductor. Lead and platinum produced a strong current which ceased when the lead became invested with sulphuret ; nevertheless, though che- mical action ceased, and, therefore, no current was called forth, the arrangement conducted a feeble the r mo-current exceedingly well, the sulphuret of lead being a conductor : this was an excellent case in point. Lead and gold, lead and palladium, lead and iron, gave similar results. Bismuth with platinum, gold, or palladium, gave active circles, the bismuth being plus ; in less than half an hour the current ceased though the circuit was still an excellent conductor of thermo-cur- rents. Bismuth with iron, nickel, or lead, produced similar results. Copper, associated with any metal chemically inactive in the solution of sulphuret gave a current, which did not come to a close as in the former cases, and for this reason, the sulphuret of copper does not adhere to the metal, but falls from it in scales, exposing a fresh sur- face to the action of the sulphuret of potassium. Antimony, plati- num, and sulphuret of potassium, produced a powerful and perma- nent current, but the sulphuret of antimony does not adhere to this metal, which sufficiently explains the phenomenon, showing it to be dependent on chemical action. Sulphuret of antimony is not a con- ductor. Silver acts like copper ; the current is continuous, and the sulphuret of silver separates from the metal. Sulphuret of silver is a non-conductor. Zinc also gives a permanent current, but sulphuret 518 GALYANIC OR YOLTAIC ELECTRICITY. of zinc is soluble in sulphuret of potassium. Now, sulphuret of zinc is a non-conductor ; how then, in this case, can the current be pro- duced by contact ? All the phenomena with sulphuret of potassium are decidedly unfavourable to the contact theory : with tin and cad- mium, it gives an impermeable non-conducting body ; with lead and bismuth, an impermeable conducting body ; with antimony and silver, it produces a permeable non-conducting body ; with copper, a per- meable conducting body; and with zinc, a soluble non-conducting body. The chemical action and its resulting current are perfectly consistent with all these variations ; but the phenomena can only be explained on the contact theory by making special assumptions to suit each particular case. (741) A series of experiments was then made with different metals in solutions unequally heated, and the results were considered as affording striking proofs of the dependence of the current on chemical action, according perfectly with the known influence of heat, and not cognizable by the theory of contact without fresh assumptions being added to those already composing it. The elec- tric current appeared to be determined, not by the amount of che- mical action which takes place, but by the intensities of the affinities concerned ; and the intensity of currents is exactly proportional to the degree of affinity which reigns between the particles, the com- bination or separation of which produces the currents. (742) The effect of dilution is next examined. In Fig. 252, the Fig. 252. P ar ^ below m is strong acid, and that above diluted, the wires being platinum, and the fluid nitric acid ; drawing the end of the wire B upwards above m, or depressing it from above in downwards, caused great changes in the galvanometer. The wires, silver, iron, lead, tin, cadmium, and zinc, being compared, it was found that the metal in the weaker acid was plus to that in the stronger. The fluids being strong and dilute muriatic acid, and the metals silver, copper, lead, tin, cadmium, and zinc, being compared, the metal in the strongest acid was plus, and the current in most cases powerful. The fluids being strong and dilute solution of caustic potash, with iron, copper, lead, tin, cadmium, and zinc, the metal in the strong solution was positive. Cases occurred also in which metals in acids of a certain strength were negative to the same metals in the same acid, either stronger or weaker. Iron and silver being in the tube C D, Tig. 253, whichever metal was in weak acid was positive to the other in the strong acid ; it was merely requisite to raise the one and lower the other metal to make THEOET OF THE VOLTAIC PILE ; FAEADAY. 519 Fig. 253. either positive at pleasure. Of the metals, silver, aopper, iron, lead, and tin, any one can be made positive or negative to any other, with the exception of silver positive to copper : and such are the won- derful changes that may be brought about by the mere effect of dilution, that the order of these metals may be varied in a hundred different ways by the mere effect of dilution. (743) The same metals in the same acid of the same strength, at the two sides, may be made to change their order thus : Copper and nickel being put into strong nitric acid, the copper will be positive ; in dilute acid the nickel will be positive. Zinc and cad- mium, in strong acid : the cadmium will be positive ; in dilute acid, the zinc strongly positive. An effective battery may be constructed by employing only one metal and one fluid ; thus, if the parts of the tubes at a, Eig. 254, contain strong nitric or sulphuric acid, and Fig. 254. the parts at 5, diluted acid of the same kind, then, by connecting these tubes by. wires, rods, or plates, (c) of one metal only, such as copper, iron, silver, tin, lead, or any of those metals which become positive and negative by difference of dilution in the acid, we have a voltaic arrangement. (744) Where chemical action has been, but diminishes or ceases, the electric current diminishes or ceases also. If a piece of tin be put into strong nitric acid, it will generally exert no action in conse- quence of the film of oxide which is on its surface ; and if two plati- num wires, connected with a galvanometer, be put into the acid, and one of them pressed against the tin, no current will be produced. If now the metal be scratched under the acid, so as to expose a clean surface of metal, chemical action takes place, and a current is pro- duced ; but this is only for a moment, for oxide of tin is soon formed, chemical action ceases, and the current with it. (745) When chemical action changes, the current changes also. If copper and silver be associated in dilute solution of sulphuret of potassium, the copper will be chemically active and positive, and the 520 GALVANIC OB YOLTAIC ELECTEICITT. silver will remain clean until of a sudden the copper will cease to act, and the silver will become instantly covered with sulphuret, showing by that, the commencement of chemical action there ; and the needle of the galvanometer will jump through 180. (746) Where no chemical action occurs, no current is produced ; but a current will occur the moment chemical action commences. This Fig. 255. is well illustrated by the following experiment: In Fig. 255, let both tubes be filled with the same pure, pale, strong nitric acid, and the two platinum wires p p, being connected by a galvanometer, and the wire i, of iron, no current is produced; now, let a drop of water be put in at &, and stir the water and acid together by means of the end of the wire i, chemical action com- mences, nitrous gas is evolved, and the iron wire acquires a positive condition at ~b, producing a powerful current. (747) When the chemical action which either has, or could have produced a current in one direction, is reversed or undone, the current is reversed or undone also. It was shown by Yolta, in 1802, that crystallized oxide of manganese was highly negative to zinc and similar metals, giving, according to his theory, Electricity to the zinc at the point of contact. In 1833, Eecquerel examined this subject, and thought the facts favourable to the theory of contact. Accord- ing, however, to De la Hive, the peroxide is at the time undergoing chemical change and losing oxygen, a change perfectly in accordance with the direction of the current it produces. Peroxide of manganese associated with platinum in green nitrous acid, originates a current, and is minus to the platinum ; but a chemical action is going on, the peroxide giving up oxygen, and converting the nitrous into nitric acid. Peroxide of lead produces similar phenomena in solution of common salt, and in potash it is minus to platinum ; but direct ex- periments show that there is sufficient chemical action to account for fche effects. (748) Faraday concludes his elaborate defence of the chemical theory of galvanism, with the following remarks on the improbable nature of the assumed contact force : " It is assumed that where two dissimilar metals touch, the dissimilar particles act on each other, and induce opposite states ; that the particles can discharge these states one to the other, and yet remain unchanged ; and that while thus plus and minus, they can discharge to particles of like matter with themselves, and so produce a current. But if the acting THEOEY OF THE YOLTAIC PILE ; PAEADA Y. 52 i particles are not changed, it should follow, that the force which causes them to assume a certain state in respect to each other, is unable to make them retain that state, thus denying the equality be- tween cause and effect. If a particle of platinum by contact with a particle of zinc willingly gives off its own Electricity to the zinc, b ecause this, by its presence, tends to make the platinum as sume a negative state, why should the particle of platinum take Electricity from any other particle of platinum behind it, since that would only tend to destroy the very state which the zinc had just forced it into ? This is quite contrary to common induction ; for there a ball, ren- dered negative, not only will not take Electricity from surrounding bodies, but if we force Electricity into it, it will, as it were, be spur- red lack again wth a power equal to that of the inducing body. Or, if it be supposed that the zinc particle, by its inductive action, tends to make the platinum particle positive, and the latter, being in con- nexion with the earth by other platinum particles, calls upon them for Electricity, and so acquires a positive state, why should it dis- charge that state to the zinc the very substance which, making the platinum assume that condition, ought, of course, to be able to sus- tain it ? Or why should not Electricity go from the platinum to the '.zinc, which is as much in contact with it as its neighbouring plati- num particles are ? Or if the zinc particle, in contact with the platinum particle, tends to become positive, why does not Electricity flow to it from the zinc particles behind, as well as from the plati- num V There is no sufficient, probable, or philosophic cause assigned for the assumed action, or reason given why one or other of the con- sequent effects above-mentioned should not take place. The contact theory assumes, that a force which is able to overcome powerful resistance, can arise out of nothing : that without any change in the acting matter, or the consumption of any generating force, a current can be produced, which shall go on for ever against a constant resist- ance, or only be stopped as in the voltaic trough, by the ruins which its exertions have heaped upon its own course. The chemical theory, on the other hand, sets out with a power, the existence of which is pre-proved, and then follows its variations, rarely assuming anything which is not supported by some corresponding simple chemical fact. The contact theory sets out with an assumption to which it adds others, as the cases require, until at last the contact force, instead of being the firm unchangeable thing at first supposed by Volta, is as variable as chemical force itself. Were it otherwise than it is, and were the contact theory true, then the equality of cause and effect must be denied. Then would perpetual motion also be true ; and it would not be difficult, upon the first given case of an electric current M M 522 THE THEORY OF THE VOLTA.TC PILE. by contact alone, to produce an electro-magnetic arrangement, which, as to its principle, would go on producing mechanical effects for ever." (749) It would be difficult to give a satisfactory explanation of the theory of Mr. Grove's gaseous voltaic battery, on the contact hypothesis. " Where," says its ingenious author, " is the contact, if not everywhere ? Is it at the points of junction of the liquid, gas, and platinum? If so, it is there that the chemical action takes place; and as contact is always necessary for chemical action, all chemistry may be referred to contact ; or, upon the theory of a uni- versal plenum, all natural phenomena may be referred to it. Contact may be necessary ; but how can it stand in the relation of a cause, or of a force?" In the opinion of Mr. Grove, the most interesting effect of this extraordinary battery is the fact which it establishes, that gases in combining and acquiring a liquid form, evolve sufficient force to decompose a similar liquid, and cause it to acquire a gaseous form ; for it has been proved, that the gases evolved at the electrodes are exactly equal to the quantity absorbed in each pair of tubes. TJfE END OF PART J. SI ADDON, BROTHERS, AND CO., PRINTERS, CASTLE STREKT, FIN8EURT. MAGNETISM. 523 PART II. MAGNETISM. CHAPTEE XIII, Historical sketch Researches of Gilbert, Halley, Graham, Epinus, Coulomb, Humboldt, Hansteen, Barlow, Morichini, Somerville, Dal ton, Cavallo, Brewster, Babbage, Herschel, Hams, Faraday. (750) ALTHOUGH the attractive power of the loadstone (a ferrugi- nous mineral first discovered in the province of Magnesia in Lydia) appears to have been known among the nations of the west in times of very remote antiquity, and its properties studied even during the Dark Ages, yet its directive power, and that of a needle touched or rubbed with it, was known exclusively to the Chinese. More than a thousand years before our era,* at the obscurely known epoch of Codrus, and the return of the Heraclides to the Peloponnesus, these people employed magnetic cars, on which the figure of a man, whose move- able outstretched arm pointed always to the south, guided them on their way across the vast grassy plains of Tartary ; and in the third century of our era, at least seven hundred years before the introduc- tion of the compass in the European seas, Chinese vessels navigated the Indian ocean with needles pointing to the south. (751) A Neapolitan named Flavio Gioia, who lived in the thirteenth century, has been regarded by many as the inventor of the compass. Dr. Gilbert affirms that Paulus Venetus brought the compass from China to Italy in 1260 ; and Ludi Vestomannus asserts, that about 1500, he saw a pilot in the East Indies, direct his course by a mag- netic needle like those now in use. The variation of the needle was discovered two hundred years before the time of Columbus ; but the variation of the variation, that is, the fact that the variation was not a constant quantity, but varied in different latitudes, was first noticed by the discoverer of America, as appears from the following extract from Irving's " Life and Voyages of Columbus," (vol. i, p. 201 ): " On * Humboldt's " Cosmos," MM* 524 MAGNETISM. 1 the 13th of September, 1492, he perceived about night-fall that the needle, instead of pointing to the north-star, varied about J a point, or between 5 and 6, to the north-west, and still more on the following morning. Struck with this circumstance, he observed it attentively for three days, and found that the variation increased as he advanced. He at first made no mention of this phenomenon, knowing how ready his people were to take alarm; but it soon attracted the attention of the pilots, and filled them with conster- nation. It seemed as if the laws of nature were changing as they advanced, and that they were entering into another world, subject to unknown influences. They apprehended that the compass was about to lose its mysterious virtues ; and without this guide, what was to become of them in a vast and trackless ocean ? Columbus tasked his science and ingenuity for reasons with which to allay their terrors. He told them that the direction of the needle was not to the polar star, but to some fixed and invisible point. The variation was not caused by any failing in the compass, but by the movement of the North star itself, which, like the other heavenly bodies, had its changes and revolutions, and every day described a circle round the pole, The high opinion that the pilots entertained of Columbus, as a pro- found astronomer, gave weight to his theory, and their alarm subsided." (752) That ferruginous substances always possess a greater or less degree of Magnetism, has long been known. One Julius Caesar, a surgeon of Kimini, is said to have first observed the conversion of iror into a magnet. In 1590, he noticed this effect on a bar of iron, which had supported a piece of brick work, on the top of a tower of the church of St. Augustin. The very same fact was observed aboul 1630, by G-assendi, on the cross of the church of St. John, at Aix which had fallen down in consequence of having been struck with lightning. He found the foot of it wasted with rust, and possessing all the properties of a loadstone. (753) In the year 1600, Dr. Gilbert, of Colchester, published s work, entitled " Physiologia Nova, seu Tractatus de Magneti el Corporibus Magneticis," which contains almost everything concerning Magnetism, which was known during the two following centuries He regarded the earth as acting on a magnetized bar, and upon iron like a magnet, the directive power of the needle being produced bj the action of Magnetism of a contrary kind to that which exists al the extremity of the needle directed towards the pole of the globe He gave the name of pole to the extremities of the needle, whicl pointed towards the poles of the earth, conformably to his views o: terrestial Magnetism ; calling the extremity that pointed towards the HISTORICAL SKETCH. 525 north, the south pole of the needle, and that which pointed to the south, the north pole. (754) Newton, Huygens, and Hooke, with some of the other philo- sophers who nourished about the end of the seventeenth century, were occupied to a certain extent with the subject of Magnetism. Some of their observations and discoveries are referred to in a manu- script volume of notes and commentaries, written by David Gregory, in 1693, in a copy of Newton's "Principia," and used by Newton in improving his second edition. Newton had supposed that the law of magnetic action approaches to the inverse triplicate ratio of the dis- tance ; but Gregory did not adopt this opinion, and invalidates the arguments that were used in its support. (755) In ]683 Dr. Edmund Halley published his theory of Mag- netism. He regarded the earth's Magnetism as caused by four poles of attraction, two of them near each pole of the earth ; and he supposes, " that in those parts of the world that lie nearly adjacent to any one of these magnetic poles, the needle is governed thereby, the nearest pole being always predominant over that more remote.' ' He supposes that the magnetic pole, which was, in his time, nearest Britain, was situated near the meridian of the Land's End, and not above 7 from the north pole ; the other north magnetic pole being in the meridian of California, and about 15 from the north pole of the earth. He placed one of the two south poles about 16 from the south pole of the globe, and 95 west from London ; and the other, or the most powerful of the four, about 20 from the south pole, and 120 east of London. (756) In order to account for the change in the variation, Dr. Halley, some years afterwards, added to these reasonable suppositions the very extraordinary one, that our globe was a hollow shell, and that within it a solid globe revolved, in nearly the same time as the outer one, and about the same centre of gravity, and with a fluid medium between them. To this inner globe he assigned two magnetic poles, and to the outer one, other two : and he conceived the change in the variation of the needle to be caused by a want of coincidence in the times of rotation of the inner globe and the external shell. " Now supposing," says he, " such an external sphere, having such a motion, we may solve the two great difficulties in every former hypothesis : for, if this exterior shell of the earth be a magnet, having its poles at a distance from the poles of diurnal rotation, and if the internal nucleus be likewise a magnet, having its poles in two other places, distant also from its axis, and these latter, by a gradual and slow motion, change their places in respect of the external, we may then give a reasonable account of the four magnetic poles, as also of the M M 2 526 MAGNETISM. changes of the needle's variation." From some reasons, which Dr. Halley then states, he concludes " that the two poles of the external globe are fixed in the earth ; and that if the needle were wholly governed by them, the variation would be always the same, with some little irregularities ; but the internal sphere, having such a gradual translation of its poles, influences the needle, and directs it variously, according to the result of the attractive and directive power of each pole, and consequently there must be a period of revo- lution of this internal ball, after which the variation will return as before." (757) Mr. Graham, a celebrated mathematical instrument-maker, in London, discovered in 1722, the daily variation of the needle. "While the needle was advancing by a gradual motion to the westward, Mr. Graham found that its north extremity moved westward during the early part of the day, and returned again in the evening to the east- ward, to the same position which it occupied in the morning, remaining nearly stationary during the night. Mr. Graham at first, ascribed these changes to defects in the form of his needles ; but, by numerous and careful observations, repeated under every variation of the weather, and of the heat and pressure of the atmosphere, he concluded that tjie daily variation was a regular phenomenon of which he could not find the cause. It was generally a maximum, between 10 o'clock A.M., and 4 o'clock P.M. ; and a minimum, between 6 and 7 o'clock P.M. Between the 6th of February, and the 12th of May, 1722, he made a thousand observations in the same place, from which he found that the greatest westerly variation was 14 45', and the least, 13 50'; but in general, it varied between 14 35' and 14, giving 35' for the amount of the daily variation. (75 b) Various speculations respecting the cause of the phenomena of Magnetism, had been hazarded by different authors : but it was reserved for M. Epinus to devise a rational hypothesis, which embraced and explained almost all the phenomena which had been observed by previous authors. This hypothesis, which he has explained at greab length in his " Tentamen Theorise Electricitatis et Magnetismi," published in 1759, may be stated in the following manner : i. In all magnetic bodies there exists a substance which may be called the magnetic fluid, whose particles repel each other with a force inversely as the distance. ii. The particles of this fluid attract the particles of iron, and are attracted by them in return, with a similar force. iii. The particles of iron repel each other, according to the same law. HISTORICAL SKETCH. 527 iv. The magnetic fluid moves through the pores of iron and soft steel with very little obstruction ; but its motion is more and more obstructed as the steel increases in hardness or temper, and it moves with the greatest difficulty in hard-tempered steel and the ores of iron. (759) The method of making artificial magnets, which was practised by the philosophers of the seventeenth century, was a very simple, but a very inefficacious one. It consisted in merely rubbing the steel bar to be magnetized upon one of the poles of a natural or artificial magnet, in a plane at right angles to the line joining the poles of the magnet. Towards the middle of tbe eighteenth century, however, the art of making artificial magnets had excited general attention ; and it is to Dr. Growin Knight, an English physician, that we are indebted for the discovery of a method of making powerful magnets. This method he kept secret from the public, but it was afterwards published by Dr. Wilson. Duhamel, Canton, Michell, Antheaume, Savery, Epinus, Eobison, Coulomb, Biot, Scoresby, and others, made various improvements on this art; for a detailed account of their numerous experiments, the reader is referred to the article on Magnetism, drawn up by Sir David Brewster, for the seventh edition oi the Encyclopedia Britannica. (760) One of the ablest cultivators of the science of Magnetism was the celebrated Coulomb, who, by the application of the principle of torsion, first used by Michell, determined the correct law of magnetic attraction and repulsion. His first object was to deter- mine the law according to which Magnetism is distributed to a magnetic bar. It was of course well known, that the Magnetism in the middle of a bar was imperceptible, and that it increased according to a regular law, and with great rapidity, towards each of the poles. By suspending a small proof needle, with a silk fibre, and causing it to oscillate horizontally opposite different points of a magnetic bar placed vertically, Coulomb computed the part of the effect that was due to terrestrial Magnetism, and the part that was due to the action of the bar ; and in this way he showed the extreme rapidity with which Magnetism is increased towards the poles. (761) In examining the distribution of Electricity in a circular plane, Coulomb found that the thickness of the electric stratum was almost constant from the centre, to within a very small distance of the circumference, when it increased all on a sudden with great rapidity (as has been shown in a previous Chapter.) He conceived that a similar distribution of Magnetism took place in the transverse section of a magnetic bar ; and, by a series of nice experiments with 528 MAGNETISM. the torsion balance (56) he found this to be the ease, and established the important fact that the magnetic power resides on the surface of iron bodies, and is entirely independent of their mass. (762) The effect of temperature on magnets was another subject to which Coulomb directed his powerful mind ; but he did not live to give an account of his experiments, which were published after his death by his friend M. Biot. Coulomb found that the Magnetism of a bar, magnetized to saturation, diminished greatly, by raising its temperature from 12 of Eeaumur to 680, and that when a magnetic bar was tempered at 780, 860, and 950 of Eeaumur, the develop- ment of its Magnetism was gradually increased, being more than double at 900 of what it was at 780. He found also that the directive force of the bar reached its maximum when it was tempered at a bright cherry red heat at 900, and that at a higher temperature the force diminished. (763) Coulomb made many valuable experiments on the best methods of making artificial magnets, and he subjected all the various processes that had previously been employed to the test of accurate measurement. His experiments on the best forms of magnetic needles are equally valuable ; but the most interesting of his researches, and the last to which he devoted his great talents, were those which relate to the action of magnets upon all natural bodies. Hitherto iron, steel, nickel, and cobalt, had been regarded as the only magnetic bodies; but in the year 1802, Coulomb announced to the Institute of France, that all bodies whatever are subject to the magnetic influence, even to such a degree as to be capable of accurate measurement. In order to determine if the phenomena were owing to particles of iron disseminated through the bodies which he subjected to experiment, he tried a needle of silver, purified by cupellation, and another needle of silver alloyed with - 8 ~2~oth part of iron ; and he found that the action of a magnet on the former was 415 times less than upon the latter. Hence, as he had previously shown, that the forces exerted by magnets on needles are proportional to the absolute quantities of iron which they contain, there will be 415 times less iron in the pure than in the impure silver ; and since the latter contained -rio-th part of its weight of iron the first will contain ^isth part of irso-th, or T3- 2 Voifth, or it will contain 132,799 parts of pure silver, and one of iron a quantity of alloy beyond the reach of chemical detection. (764) Amongst the scientific travellers who have contributed to our knowledge of terrestrial Magnetism, Baron Alexander Humboldt was one of the most distinguished. Himself a careful and scientific observer, and possessed of accurate instruments and exact HISTORICAL SKETCH. 529 methods of research, he made numerous observations on the dip and variation of the needle in various parts of the earth, and particularly near the magnetic equator ; and by means of these valuable data, M. Biot was enabled to throw much light on the subject of terrestrial Magnetism, and to deduce a formula which represented the obser- vations with extraordinary accuracy. Professor Krafft, of St. Petersburg, undertook the same inquiry in the year 1809, and after comparing the same observations which were used by Biot with the respective situations of the places where they were obtained, he arrived at the following simple law : " If we suppose a circle circum- scribed about the earth having the two extremities of the magnetic axis for its poles, and if we consider this circle as a magnetic equator, the taugent of the dip of the needle in any magnetic latitude will be equal to double the tangent of this latitude ;" and to this simple law, Biot, upon re-examining his former formula, found that it was reducible. (765) An able work on the Magnetism of the earth was published in 1817, by Professor Hansteen of Christiana; the result of his researches was favourable to that part of Halley's theory, which assumes the existence of four poles and two magnetic axes. He also deduced the law of magnetic action, and showed that " the attractive or repulsive force with which two magnetic particles affect each other, is always directly as their intensities, and inversely as the squares of their mutual distances." And he likewise demonstrated that " the distance from the middle of a magnet being the same, the force opposite the poles, or in the direction of the axis, is double the force in the magnetic equator, Hansteen collected all the observations of value that had been made on the variation of the needle, and from these he proved that there were four points of convergence among the lines of variation, viz., a weaker and a stronger point in the vicinity of each pole of the globe. The strongest poles, N. S., lie almost diametrically opposite to each other, and the same is true of the weaker poles, n., s. These four poles he found to have a regular motion obliquely. The two northern ones, N, n, from west to east, and the two southern ones, S, s, from east to west. The following he found to be their periods of revolution, and their positions in 1830: Time of revolution Long, from round each Lat. Greenwich. pole of the globe. Pole N. . 69 30' N. . . . 87 19' N. . . . 1,740 years. Pole S. . 68 44' S. . . . 131 47' E. . . . 4,609 Pole n. . 85 6' N. . . . 144 17' E. . . . 860 Pole s. . 78 29' S. . . . 137 45' W. . . 1,304 530 MAGNETISM. And on comparing these results with the magnetical observations made by Captain Parry in the Arctic regions in 1819, he found them to differ so little as to give them a high degree of probability, Hansteen showed that the changes in the variation and dip of the needle in both hemispheres, may be well explained by the motion of the four magnetic poles. The same enterprising philosopher, with a view to the determination of the intensity of the earth's Magnetism at different parts of its surface, caused observations on the oscillation of the same needle to be made in every part of Europe, and under- took himself a journey to Siberia for the same purpose. From these observations, he deduced the following law, according to which the magnetic intensity varies with the dip of the needle. Magnetic dip. Magnetic intensity. o . .''' V \ V 1-0 24 . . : ; l : v . 1-1 45 . . V . 1-2 64 . . . . ' 1-3 73 . , . - ;. 1-4 ret v . . ; . 1-5 81 . '. i . ' , . 1-6 86 o ; . . ; 1-7 Hansteen was the first to determine the diurnal variation of the needle. He found that the minimum intensity took place between 10 and 11 A.M., and the maximum between 4 and 5 P.M. (766) In an aerostatic voyage made by Gay Lussac and Biot, in 1804, at the height of nearly 13,000 feet, they were unable to detect any change in the intensity of terrestrial Magnetism. Saussure, however, had found that the intensity was considerably less on the Col du Geant than at Chamouni and Geneva ; the difference in the levels of these places being in the one case, 10,000, and in the other 7,800 feet ; but his observations contradict his conclusions. M. Kupffer has more recently obtained a similar resulb, by obser- vations on Mount Elbrouz ; having found a decrease in intensity in rising 4,500 feet above his first station ; and he explains the result obtained by MM. Gay Lussac and Biot, by supposing that an increase of intensity was produced by a diminution of temperature. Mr. Kenwood, on the other hand, has made observations at the surface of Dolcoath mine ; at 1,320 feet beneath its surface ; and on a hill, at 710 feet above the level of the sea ; without being able to detect any difference in the intensity. To the late Captain Foster we are indebted for many valuable observations on the magnetic intensity, made at Spitzbergen and elsewhere. From these he concluded that HISTORICAL SKETCH, 531 the diurnal change in the horizontal intensity is principally, if not wholly, owing to a small change in the amount of the dip. The maximum took place at about 3h. 30min. A.M., and the minimum at 2h. 47min. P.M. ; its greatest change amounting to -A-rd of its mean value. Captain Foster is of opinion, that these changes have the sun for their primary agent, and that his action is such as to produce a constant inflection of the pole towards the sun during the twenty- four hours ; an idea which had been previously stated by Mr. Christie. (767) About the year 1818, Professor Barlow, of Woolwich, turned his attention to the subject of Magnetism, with a view principally of calculating the effect of ship's guns on the compass. In trying the effect of different iron balls, he was led to the curious facts that there exists round every mass of iron, a great circle inclined to the horizon, at an angle equal to the complement of the dip of the needle ; that the plane of this circle is a plane of no attraction upon a needle whose centre is in that plane ; that if we regard this circle as the magnetic equator, the tangent of deviation of the needle from its north or south pole will be proportional to the rectangle of the sine of the double latitude and cosine of the longitude j that when the distance of the needle is variable, the tangent of deviation will be reciprocally proportional to the cube of the distance, and that all things else being the same, the tangent of deviation will be pro- portional to the cubes of the diameters of the balls, or shells, whatever be their masses, provided their thickness exceeds a certain quantity. Mr. Barlow was, from these discoveries, enabled to invent a most ingenious method of correcting the error of the compass arising from the attraction of all the iron on board ships. This source of error had been noticed by Mr. Wales, Mr. Downie in 1794, and by Captain Flinders ; but it is to Mr. Bain that we owe the distinct establish- ment and explanation of this source* of error. As a hollow shell of iron, about 4 pounds in weight, acts as powerfully at the same distance as a solid iron ball of 200 pounds' weight, Mr, Barlow happily conceived that a plate of 5 or 6 pounds' weight might be made to represent and counteract the amount of the attraction of all the iron on board a vessel ; and, therefore, leave the needle as free to obey the action of terrestrial Magnetism as if there was no iron in the ship at all. After this ingenious contrivance had been submitted to the Admiralty, it was tried in every part of the world ; and even in the regions which surround the magnetic pole, where the compass becomes useless, it never failed to indicate the true magnetic direc- tion, when the connecting plate was properly applied. " Such an 532 MAGNETISM. invention as this," says Captain Parry, " so sound in principle, so easy in application, and so universally beneficial in practice, needs no testimony of mine to establish its merits ; but when I consider the many anxious days and sleepless nights which the uselessness of the compass in these seas had formerly occasioned me, I really should have esteemed it a kind of ingratitude to Mr. Barlow, as well as great injustice to so memorable a discovery, not to have stated, my opinion of its merits, under circumstances so well calculated to put them to a satisfactory trial." For this beautiful invention, the Board of Longitude conferred upon Mr. Barlow the highest reward of five hundred pounds ; and the Emperor of Russia, who was never inatten- tive to the interests of science, sent him a fine gold watch and a rich dress chain for the same contrivance. (768) The late Dr. Morichini, an eminent physician at Rome, first announced it as an experimental fact, that an uiimagnetized needle could be rendered magnetic by the action of the violet rays of the sun. His experiments were successfully repeated by Dr. Carpi, at Rome, and the Marquis Ridolfi, at Florence ; but M. D'Hombre Fionas, at Alais, in France, Professor Configliachi, of Pavia, M. Berard, of Montpelier, failed in obtaining decided magnetic effects from the violet rays. In 1814, Dr. Morichini exhibited the actual experiment to Sir Humphry Davy, and in 1817, Dr. Carpi showed it to Professor Playfair. A few months after Sir Humphry witnessed the experiment, Sir David Brewster met him at Geneva, and learned from him the fact, that he had paid the most diligent attention to one of Morichini's experiments, and that he saw -an unmagnetized needle rendered magnetic by violet light. The following account of the experiment made by Dr. Carpi, was given to Sir David, by Professor Playfair : " The violet light was obtained in the usual manner, by means of a common prism, and was collected into a focus by a lens of sufficient size. The needle was made of soft wire, and was found, upon trial, to possess neither polarity, nor any power of attracting iron filings. It was fixed horizontally upon a support, by means of wax, and in such a direction, as to cut the magnetic meridian at right angles. The focus of violet rays was carried slowly along the needle, proceeding from the centre towards one of the extremities, care being taken never to go back in the same direction, and never to touch the other half of the needle. At the end of half-an-hour after the needle had been exposed to the action of the violet rays, it was carefully examined, and it had acquired neither polarity nor any force of at- traction ; but after continuing the operation 25 minutes longer, when it was taken off and placed on its pivot, it traversed with great HISTOEICAL SKETCH. 533 alacrity, and settled in the direction of the magnetical meridian, with the end over which the rays had passed turned to the north. It also attracted and suspended a fringe of iron filings. The extremity of the needle that was exposed to the action of the violet rays, repelled the north pole of a compass needle. This effect was so distinctly marked, as to leave no doubt in the minds of any who were present, that the needle had received its Magnetism from the action of the violet rays." In this state of the subject, Mrs. Somerville made some simple and well conducted experiments, which seemed to set the question at rest, from the distinct and decided character of the results. A sewing needle, an inch long, and devoid of Magnetism, had one-half of it covered with paper, and the other exposed to the violet rays of the spectrum, 5 feet distant from the prism. In two hours it acquired Magnetism, the exposed end exhibiting north polarity. The indigo rays produced an equal effect, and the Hue and the green the same in a less degree. The yellow, orange, and red rays had no effect even after 3 days' exposure to their action. Pieces of blue watch-spring received a higher Magnetism. When the sun's light fell upon the exposed end through blue-coloured glasses, or through Hue or green riband, the same magnetic effects were produced. The experiments of Mr. Christie, an account of which was read to the Royal Society, a short time before Mrs. Somerville's, confirmed her results to a certain degree, by a different mode of observation. The general opinion seems, however, now to be, that light does not exer- cise any decided effect in producing Magnetism. The experiments of M.M. P. Hies and Moser were made with needles both polished and oxidated, and also with wires half-polished, and polarized as well as common light was made to fall on them in a concentrated state, but no decided effect upon their number of oscillations could be observed ; and they state that they think themselves justly entitled to reject totally a discovery which for seventeen years has at different times dis- turbed science. (769) On 24th February, 1840, the following account of some experi- ments on this subject was laid before the Royal Irish Academy by Mr. G. J. Knox and the Rev. T. Knox : " Having procured several hundred needles, of different lengths and thicknesses, and having ascertained that they were perfectly free from Magnetism, we enve-. loped them in white paper, leaving one of their extreme ends uncovered. Taking advantage of a favourable day for trying experiments upon the chemical ray (known by the few seconds required to blacken chloride of silver), we placed the needles at right angles to the magnetic meri- dian, and exposed them for 2 hours, from 11 till 1 o'clock, to the 534 MA.GNETISM. differently refrangible rays of the sun, under coloured glasses. Those beneath the red, orange, and yellow, showed no trace of Magnetism, while those beneath the blue, green, and violet, exhibited, the two first feeble, but the last strong traces of Magnetism. " To determine how far the oxidating power of the violet ray is concerned in the phenomenon, we exposed to the different coloured light, needles whose extremities had been previously dipped in nitric acid, and found that they became magnetic (the exposed end having been made a north pole) in much shorter time than the others, and that this effect was produced in a slight degree, under the red (when exposed a sufficient length of time), strongly under white glass, and so strong under violet glass, that the effect took place even when the needles were placed in such a position along the magnetic meridian, as would tend to produce, by the earth's influence, a south pole in the exposed extremity. " Conceiving that the inactive state produced in iron (as observed by Schoenbein, 292 et seq.) when plunged into nitric acid, sp. gr. 9-36, or being made the positive pole of a battery, or by any other means, might throw some light upon the nature of the change pro- duced, experiments were instituted to this effect, which showed that no trace of Magnetism couldbetherebyproduced." (See somecurious experiments on the magnetic influence of the lunar spectrum in 20th vol. of Phil. Mag.) (770) A valuable series of observations on the influence of the aurora borealis on the Magnetic needle, was made by Dr. Dalton at Kendall and Keswick, during seven years, from May, 1786, to May, 1793, and has been published in his Meteorological Observations and Essays, which appeared in 1793. During these observations he noticed the effect produced on the magnetic needle, and he was thus led to study the phenomena of the aurora, and to establish, beyond a doubt, the relation of all its phenomena to the magnetic poles and equator. In some cases, however, Dr. Dalton did not observe any perceptible dis- turbance of the needle. (771) Professor Hansteen, who occupied himself extensively with the subject of magnetism, observes, that large extraordinary move- ments of the needle, in which it traverses frequently, with a shivering motion, an arc of several degrees on both sides of its usual position, are seldom, perhaps never exhibited, unless when the aurora borealis is visible, and that this disturbance of the needle seems to operate at the same time in places the most widely separate. (772) Prom the extensive series of accurate observations, made by M. Arago, at Paris, since 1818, the needle was almost invariably HISTORICAL SKETCH. 535 found to be affected by aurorse that were seen in Scotland ; and so striking was the connexion between the two classes of facts, that the existence of the aurora could be inferred from the derangements of the needle. M. Arago has likewise discovered, that early in the morning, often 10 or 12 hours before the aurora is developed in a very distant place, its appearance is announced by a particular form of the curve, which exhibits the diurnal variation of the needle, that is, by the value of the morning and evening maxima of elongation. (773) During the journey of Captain Back to the polar regions, in 1833, 1834, and 1835, he found that the needle was generally affected by the aurora ; and on one occasion the deviation which it produced was 8; he repeatedly observed that when the aurora was concen- trated in individual beams, the needle was powerfully affected ; but that it generally returned to its mean position, when the aurora became generally diffused. On several occasions, the needle waa- restless, and exhibited the vibrating action produced by the aurora, when this motion was not visible ; and Captain Back states that he could not account for this, except by supposing the invisible presence of the aurora in full day. (774) The only metals which were supposed to have a distinct and decided power, and were, therefore, called magnetic metals, are iron, cobalt, and nickel. A needle of the latter metal carefully purified by M. Thenard, was found by Biot to have a magnetic directive power k that of a similar-sized needle of steel. Mr. David Lyon has endeavoured to show that these metals resemble one another, not only in their principal qualities, but in the numerical values of their qualities ; and, he adds, that whilst these three magnetic substances have the values above referred to, near each other, there are no other substances in which the same values come very near, or fall within those of the three magnetic substances. The values to which Mr. Lyon alludes are the following : Specific Atomic Atoms contained gravity. weight. in a given space. Nickel . . 8-27 . . 739-51 . . 1118 Iron ... 7-21 .. 678-43 . . 1062 Cobalt . . 7-8 . . 738 . . . 1057 (775) M. Pouillet, on the other hand, thought that there were five simple magnetic bodies, viz., iron, manganese, nickel, cobalt, and chrome ; and in consequence of having observed some remarkable analogies, between the distance of the atoms of bodies, and their magnetic properties, he was led to suppose that the magnetic limit of different bodies ought to be found at very different temperatures. "I have, indeed," says he, "demonstrated by experiment, first, that 536 MAGNETISM. cobalt never ceases to be magnetic, or rather that its magnetic limit is at a temperature higher than the brightest white heat ; second, that chrome has its magnetic limit a little below the temperature of dark blood-red heat ; third, that nickel has its magnetic limit about 350 centigrade, nearly at the melting point of zinc; and fourth, that manganese has its magnetic limit at the temperature of from 20 to 25. below zero. Experiments on these five magnetic bodies seem to prove, first, that heat acts upon Magnetism only, in conse- quence of the greater or less distance which it occasions between the atoms of bodies ; and second, that all bodies would become magnetic if we could by any action whatever, make their atoms approach within a suitable distance." It was afterwards shown by Faraday that to Pouillet's list of magnetic metate must be added platinum, palladium, osmium, titanium, and cerium ; he has found, moreover, that not only the pure metals, but solutions of their salts are acted on by a powerful electro-magnet in a manner similar to iron. (776) A series of careful experiments was made by Cavallo on the magnetism of brass when hammered. He found that this compound, whether old or new, was made magnetic, when placed between two pieces of card, and hammered, either on an anvil by a hammer, or between two flints. He observes : " It appears that the property of becoming magnetic in brass, by hammering, is rather owing to some peculiar configuration of its parts than to any admixture of iron ; which is confirmed still further, by observing, that Dutch plate brass (which is made, not by melting the copper, but by keeping it at a strong degree of heat, whilst surrounded by lapis calaminaris,) also possesses that property ; at least, such was the case with all the pieces I tried. From this it follows, that when brass is to be used for the construction of instruments wherein a magnetic needle is concerned, as dipping nee'dles, variation compasses, &c., the brass should either be left quite soft, or it should be chosen of such a sort as will not be made magnetic by hammering, which sort, however, does not occur very frequently." (777) These suggestions of M. Cavallo were not attended to as their importance deserved, and there is no doubt that considerable errors have arisen from their neglect. Many examples have indeed occurred in which the errors were detected ; and it is now the in- variable practice of well informed instrument makers, to reject hammered brass bowls for compasses, and to use those which are cast and turned for the purpose. (778) The existence of magnetism in brass, while there was not the least trace of it either in the copper or zinc of which it is com- posed, led philosophers to investigate the effects produced by the HISTORICAL SKETCH. 537 union of different metals, or by their combination with other sub- stances. Iron itself is a simple chemical body. Steel is a com- bination of iron and carbon. The loadstone is a combination of iron and oxygen ; and as no Magnetism is found either in carbon or in - oxygen, we are naturally led to believe, as M. Pouillet has remarked, that the magnetic fluid resides in the substance of the iron, and that it is carried with the atoms of that metal into all the chemical com- binations which they form ; we may, therefore, expect to find magnetic properties in all ferruginous bodies, whether the iron be an accidental or a necessary ingredient ; and indeed cast-iron, plumbago, and the oxides and sulphurets of iron, exert a sensible action on the needle. (779) On the other hand, Dr. Matthew Young found that the smallest admixture of antimony was capable of destroying the polarity of iron ; and M. Seebeck states, that an alloy of one part of iron and four parts of antimony was so completely destitute of magnetic action, that even when put into rotation, it exerted no action on the magnetic needle. The magnetic qualities of nickel (which stands next to iron in magnetic susceptibility, and which is usually found to possess considerable power), are also destroyed by a mixture with it of other metals. Chevenix found that a very small portion of arsenic deprived a mass of nickel, that had previously exhibited a strong magnetic power, of the whole of its Magnetism ; and Dr. Seebeck found that an alloy of two parts of copper with one of nickel was entirely devoid of Magnetism, and on this account he recommends it as well suited for the manufacture of compass boxes, On the other hand, Mr. Hatchett ascertained, that when a large pro- portion of carbon, or sulphur, or phosphorus, was combined with iron, the iron was enabled fully to receive and retain its magnetic properties ; but he, at the same time found, that there was a limit beyond which an excess of any of these three substances rendered the compound wholly incapable of receiving Magnetism. (780) Animal and vegetable substances, after combustion, are said to be attracted by the magnet. The flesh, and particularly the blood, is acted on more powerfully than other parts, and bone less power- fully. Burned vegetables have the same property, and also soot and atmospheric dust ; and M. Cavallo has maintained that brisk chemical effervescences acted upon the magnetic needle. (781) In 1802, the supposition of universal Magnetism was put to the test of rigorous experiment by Coulomb. He employed a glass receiver, from the top of which was suspended, by a silk fibre, the needle of the substance to be examined, about 1 inch long, and -irbth. thick. The receiver was then placed so as to enclose the opposite poles of two powerful bar magnets, each formed of four bars 538 MAGNETISM. of steel tempered to a white heat, and the number of oscillations of the needle between these poles was noted. It was found that all substances whatever, when formed into small needles, turned themselves in the direction of the poles of the magnets, and after a few oscillations, finally settled in that position. When these bodies were moved a very little way out of their position of equilibrium, they immediately began to oscillate round it, the oscillations being always performed more rapidly in the presence of the magnets than when they were removed out of their influence. Gold, silver, brass, wood, and all other sub- stances, whether organic or inorganic, thus obeyed the power of magnets. Hence it was concluded, either that all bodies are suscep- tible of Magnetism, or that they contain minute quantities of iron, or other magnetic metals, which give them their susceptibility. Various other methods have been employed in developing Magnetism in all bodies whatever, since the time of Coulomb ; but we must refer for an account of them to the excellent treatise on Magnetism drawn up for the Encyclopaedia Britannica by Sir D. Brewster. The interesting question of the universal prevalence of Magnetism subsequently derived new interest from the beautiful discovery of M. Arago. This distinguished philosopher conceived the idea of studying the oscilla- tions of a magnetic needle when placed above or near any body whatever. Having suspended a magnetic needle above metal, or even water, and caused it to deviate a certain number of degrees from its position, it began, when left to itself, to oscillate in arcs of less and less amplitude, as if it had bSen placed in a resisting medium ; and what was peculiarly curious in these experiments, this diminution in the amplitude of the oscillations did not alter the number of oscilla- tions which were performed in a given time. Dr. Seebeck found, that in alloying magnetic with non-magnetic substances, he formed com- pounds which exercised no action on the needle. The alloys which had particularly this singular property, were those consisting of four parts of antimony, and one of iron, or two parts of copper, and one of nickel. In these cases the Magnetism of the two ingredients must have been neutralized by their opposite actions. (782) In consequence of these experiments of M. Arago, which were announced at the sitting of the French Institute, on the 22nd of November, 124, and repeated in London, on the 7th of March, 1825, philosophers in every part of Europe turned their attention to the development of Magnetism by rotation. The most important results were obtained by Messrs. Babbage and Herschel. A horse-shoe magnet, which lifted 20 pounds, was made to revolve rapidly round its axis of symmetry, placed vertically with its poles upper- most. A circular disc of copper, 6 inches in diameter, and HISTORICAL SKETCH. 539 of an inch thick, was suspended above the revolving magnet. As soon as the rotation of the magnet commenced, the copper began to turn in the same direction, at first slowly, but afterwards with an increased velocity. When the magnet was made to turn in an opposite direction, the disc of copper changed the direction of its motion also, and exhibited the same phenomena. Metallic plates 10 inches in diameter, and i-inch thick, when interposed between the magnet and the copper disc, did not sensibly modify the results, as M. Arago had observed. Glass produced no effect ; but a sheet of tinned plate iron diminished greatly the influence of the magnet, while two such plates almost destroyed it. They found also that a disc of copper, 10 inches in diameter, and i-inch thick, and revolving with a velocity of 7 revolutions in a second, did not communicate any motion to a similar disc freely suspended above it. (783) Messrs. Babbage and Herschel next sought to determine the effect produced by a solution of continuity in the metallic disc, upon which the revolving magnet acted. For this purpose a disc of lead 12 inches in diameter, and roth of an inch thick, was sus- pended at a given distance from a horse-shoe magnet, revolving with the ordinary rapidity, first in its entire state, and afterwards in the state shown in the annexed figures, the black lines in the direction of the radii being the planes where the lead was cut through. (Figs. 256, 257, 258, 259, 260.) The accelerating forces, represented Fig. 256. Fig. 257. Fig. 258. Fig. 259. Fig. 260. by t a, where s is the number of the revolutions, and t the time em- ployed, are as follow : 540 MAGNETISM. Disc as in Diso as in Disc as in Disc as in Disc as in Fig. 256. Fig. 257. Fig. 258. Fig. 259. Fig. 260. 1258 1047 913 564 432 324 Effects similar, but differing in degree, were obtained with other metals : with soft tinned iron, the cutting produced a very slight diminution of effect, while in copper the same operation reduced the accelerating force in the ratio of 5 to 1. They next tried the effect of filling up the cuts with different metals. A light upper disc suspended at a given distance above a revolving magnet, performed 6 revolutions in 54" 8. "When cut as in Fig. 260. its magnetic action was so weakened, that it took 121" 3, to perform 6 revolutions ; when the right open radial spaces were filled up with tin, its magnetic action was restored to such a degree, that it made 6 revolutions in 57" 3. This fact is very interesting, as tin has less than half the energy of copper. (784) M. Haldat made some very interesting experiments on this subject. He found that every needle, however weak its Mag- netism, obeyed the action of the revolving disc ; but that this action disappeared entirely when its polarity disappeared. He found it impossible to magnetize needles by the action of the revolving disc, however rapid; and in consequence of ascribing this effect to the want of coercitive power, he employed discs of iron and steel, both soft and hardened. A disc of soft iron acted with more energy than one of copper, and with the same velocity, it dragged the needle twice the distance that a disc of brass did. Iron, strongly hammered, acted like soft iron, and was unable to give polarity to a steel needle; but a disc of un- tempered steel, inrth of an inch thick, did not produce any appre- ciable effect on the magnetic needle, which, after a few irregular oscillations, maintained its ordinary position of equilibrium. Hence, he concluded, that the force which acted upon it was in the inverse ratio of the coercitive force. M. Haldat also found, that discs in a state of incandescence exercised the same action as those at the ordinary temperature. (785) Sir "Win. Snow Harris has since shown that several substances not supposed to contain iron, have the power of intercepting the influence of a revolving magnet, contrary to the observations of Messrs. Babbage and Herschel. A circular magnetic disc being delicately balanced on a fine central point by means of a rim of lead, was put into a state of rotation on a small agate cup, at the rate of 600 revolutions in a minute ; and a light ring of tinned iron, also finely balanced on a central pivot, was placed immediately over it at about 4 inches distance, by means of a thin plate of glass, on which its HISTOEICAL SKETCH. 541 pivot rested. When the ring of tinned iron began to move slowly on its pivot by the influence of the magnet revolving below, a large mass of copper about three inches thick, and consisting of plates a foot square, was carefully interposed between the magnet and the iron ring. The interposition of the copper soon sensibly diminished the motion of the iron disc, and at length arrested it altogether. On again withdrawing the copper, the motion of the disc was restored ; and the same effects were repeatedly obtained. In this experiment both the magnet and the disc were enclosed by glass shades, and supported on a firm base. The same effects were produced by a mass of silver and zinc : but when their thickness was considerably diminished by removing the central plates, the motion of the disc was not impeded. A very great thickness of lead was necessary to stop the disc, in consequence, as Sir W. Harris supposes, of its magnetic energy being so much less than that of copper. (786) It was about the period of these researches that Faraday made the capital discovery that a permanent current of Electricity may be produced by ordinary magnets. Fig. 261. represents the form of apparatus employed. Fig. 261. A copper plate mounted on an axis, is furnished with a handle for giving it motion ; w w, are conducting wires, the one retained in perfect metallic contact with the axis, and the other with the circum- ference of the disc. A powerful horse-shoe magnet is then placed so as to allow of the revolution of the disc between its poles, and the wires w w, are connected with the galvanometer, g ; the wire w, is retained on the circumference of the disc, at the point between the poles of the magnet. When this machine is made to revolve from right to left, a current of Electricity from the centre to the circum- s -s 2 542 MAGNETISM. ference is determined in the direction of the arrows, and ^galvano- meter is deflected accordingly. If the revolution of the disc, or the poles of the magnet be reversed, the electric current moves in an opposite direction ; while the plate is at rest, there is no disturbance of the needle of the galvanometer. The same effects are produced when electro-magnets, or coils of wire are substituted for the per- manent magnetic poles ; and when instead of employing a circular disc of metal, a strip of copper plate is placed between the magnetic poles, while two conductors from the galvanometer are held in contact with its edges, a current of Electricity is shown to be produced by simply drawing the slip of metal between the poles of the magnet. (787) The law which governs the evolutions of Electricity by mag- neto-electric induction, is thus illustrated by Faraday.* If in Fig. 262 P N represent a horizontal wire passing by a pig. 262. marked magnetic pole, so that the direction of x , . its motion shall coincide with the curved line proceeding from below upwards ; or if its mo- /[.- tion parallel to itself be in a line tangential to " the curved line, but in the general direction of the-^rows, or if it pass the pole in other direc- tions, but so as to cut the magnetic curves in the same general direc- tion, or on the same side as they would be cut by the wire if moving along the dotted curved line ; then the current of Electricity in the wire is from P to N. If it be carried in the reverse directions, the electric current will be from N to P : or if the wire be in the vertical position P' N', and it be carried in similar directions, coinciding with the dotted horizontal curve so far as to cut the magnetic curves on the same side with it, the current will be from P' to N'. If the wire be considered as a tangent to the curved surface of the cylindrical magnet, and it be carried round that surface into any other position ; or if the magnet itself be revolved on its axis so as to bring any part opposite to the tangential wire ; still if afterwards the wire be moved in the directions indicated, the current of Electricity will be from P to N ; or if it be moved in the opposite direction, from N to P ; so that, as regards the motions of the wire past the pole, they may be reduced to two, directly opposite to each other, one of which produces a current from P to N, and the other from N to P. The same holds true of the unmarked pole of the magnet, except that if it be substituted for the one in the figure, then, as the wires are moved in the direction of the arrows, the current of Electricity would be from N to P, and when they move in the reverse direction, from P to N, * Experimental Researches, 114. HISTORICAL SKETCH. (788) The direction of the current of Electricity which is excited in a metal when moving in the neighbourhood of a magnet is thus shown to depend upon its relation to the magnetic curves. Faraday, with his usual happy method of illustration, has given us this popular expression of it. Let Fig. 263. AB (Fig. 263) represent a cylin- der magnet, A being the marked, and B the unmarked pole ; let P N be a silver knife-blade, resting across the magnet with 7 with its edge upward, and with its marked or notched side toward' the pole A; then in whatever direction or position this knife be moved, edge foremost, either about the marked or unmarked pole, the current of Electricity produced will be from P to IN", provided the intersecting curves pro- ceeding from A, abut upon the notched surface of the knife, and those from B upon the unnotched side ; or if the knife be moved with its back foremost, the current will be from N to P, in every possible position and direction, provided the intersected curves abut on the same surfaces as before. A little model is easily constructed, by using a cylinder of wood for a magnet, a flat piece for the blade, #nd a piece of thread connecting one end of the cylinder with the other, and passing through a hole in the blade for the magnetic curves ; this readily gives the result of any possible direction. (789) From this discovery of Faraday's, then, viz., that when a piece of metal is passed before a single pole, or between the opposite poles of a magnet, electrical currents transverse to the direction of motion, are produced across it, a very satisfactory explanation of the pheno- menon first observed by Arago, and afterwards examined in detail by Babbage, Herschel, and Harris can be given, without having recourse to the supposition of the formation in the revolving copper of a pole of the opposite kind to that approximated, surrounded by a diffuse polarity of the same kind. It is evident that as the plate revolves, in the neighbourhood of the magnet, or vice versa, electrical currents' are produced from the centre to the circumference, or from the cir- cumference to the centre, in the direction of the radii ; and the effect is precisely the same as in the electro-magnetic rotations, Avhich, as we shall hereafter see, are governed by the following law : If a wire P N" (Fig. 264) be connected with the positive and negative ends of a voltaic battery so that the positive Electricity shall pass from P to N, and a marked magnetic pole N, be placed near the wire, between it and the spectator, the pole will move in a direction 544 MAGNETISM. Fig. 264^ tangential to the wire, that is towards the right, and the wire will move tangentially towards the left, according to the direction of the arrows. So also when a plate of metal is made to rotate beneath a magnetic pole (suppose an N pole), a series of currents of Electricity will pass from the centre to & > the circumference of the plate if it is rotating in the direction of the hands of a watch, or from the circumference to the centre if it is rotating in the contrary direction ; and it is at once evident that, according with the above law, both magnet and plate must move in the same direction ; it is also evident why the phenomena cease when the magnet and metal are brought to rest, for then the electrical currents cease. The effects of a solution of the continuity of the disc in the experiments of Babbage and Herschel are likewise readily explained. The question as to the universality of Magnetism has been placed in a new and intensely interesting light by the recent discoveries of Faraday and others relating to diamagnetic action, a full account of which we reserve for a future chapter. (790) With regard to the influence of heat on magnetism, Mr. Christie, from a number of experiments made with the torsion balance, the needle being suspended by a brass wire yi-oth of an inch in diameter, ascertained the following facts : i. Beginning with 3 Fahr. up to 127, the intensity of magnets decreased as their temperature increased. ii. With a certain increment of temperature the decrement of intensity is not constant at all temperatures, but increases as the temperature increases. iii. From a temperature of about 80, the intensity decreases very rapidly as the temperature increases ; so that, if up to this tempera- ture, the differences of the decrements are nearly constant, from this point the differences of the decrements also increase. iv. Beyond the temperature of 100, a portion of the power of the magnet is permanently destroyed. v. On a change of temperature, the most considerable portion of the effect on the intensity of the magnet is produced instantaneously, showing that the magnetic power resides on, or very near the surface. vi. The effects produced on soft iron by changes of temperature, are directly the reverse of those produced on a magnet ; an increase of the temperature causing an increase in the magnetic power of the iron. This was observed between the temperatures of 50 and 100 Fahr. Mr. Christie regards this as a strong argument against HISTORICAL SKETCH. 545 the hypothesis, that the action of iron upon the needle arises from the polarity which it receives from the earth. (791) In the year 1820 Sir David Brewster announced the discovery of two poles of maximum cold on opposite sides of the north pole of the earth, and he was led to entertain the opinion that there might be some connexion between the magnetic poles and those of maximum cold. " Imperfect," says he, " as the analogy is between the iso- thermal and magnetic centres, it is yet too important to be passed over without notice. Their local coincidence is sufficiently remark- able, and it would be to overstep the limits of philosophical caution, to maintain that they have no other connexion but that of accidental locality ; and if we had as many measures of the mean temperature as we have of the variation of the needle, we might determine whether the isothermal poles were fixed or moveable." The connexion between the poles of maximum cold and those to which the iso- dynamical magnetic lines are related was considered as a probable supposition by the late Dr. Dalton. Other philosophers have expressed similar opinions. Dr. Traill says, " The disturbance of the equilibrium of the temperature of our planet by the continual action of the sun's rays on its inter-tropical regions, and by the polar ices, must convert the earth into a vast thermo-magnetic apparatus; and the disturbance of the equilibrium of tempera- ture, even in stony strata, may elicit some degree of Magnetism." Mr. Christie also thinks it not improbable "that difference of temperature may be the primary cause of the polarity of the earth, though its influence may be modified by other circumstances." And in his treatise on " Thermo-Electricity," M. (Eersted remarks, " that the most efficacious excitation of Electricity upon the earth appears to be produced by the sun producing daily evaporation, deoxidation, and heat, all of which excite electrical currents." . . . " Thus the earth seems to have a cons tan t magnetic polarity produced in the course of time by the electrical currents which sur- round it, and a variable Magnetism produced immediately by the same current." (792) Sir Wm. Snow Harris's Memoirs were published in the Transactions of the Koyal Society of Edinburgh for 1827, and in the Philosophical Transactions for 1831. In the first, entitled " Experi- mental Inquiries concerning the Laws of Magnetic Forces," he shows by a beautiful series of experiments, that the magnetic development in masses of iron by induction is, cceteris paribus, directly proportional to the power of the inductive force, and inversely as the distance; and that the forces which magnets develope in a mass of iron at a given distance, within certain limits, may be taken as a fair measure of their 546 MAGNETISM. respective intensities ; he also shows that the absolute force of attrac- tion, exerted between a magnet and a piece of iron, varies with the power of the magnet, and consequently with the force induced in the iron, cceteris paribus ; and that when the force induced in the iron is a constant quantity, while its distance from a temporary or permanent magnet is variable, the absolute force varies with the distance. Sir William made a number of nice experiments on the absolute force of attraction and repulsion between two magnetized bodies, which he found to be in the inverse ratio of the square of the distance. "When in the case of attraction, the magnets however were nearly approxi- mated in relation to their respective intensities, the increments in the forces began to decline, and in some instances at near approxi- mations, the absolute force was in the simple inverse ratio of the distance. In the experiments with the repelling poles, the deviatioiis from the regular force were still more considerable, and what is curious in this case, the force became less and less until the polarity of the weaker magnet appeared to be so counteracted by induction that the repulsion was at length superseded by attraction. The law according to which the forces are developed in different points of the longitudinal magnetic axis between the centre and poles of a magnet he found to vary directly as the square of the distance from the magnetic centre, a law which is uniform in bars of steel regularly hardened and magnetized throughout. This law of distribution is exactly the same as that which had been given by Hansteen. Sir "W. Harris repeated the experiment of Mr. Christie, and found with that philosopher that the oscillations of a magnetic bar were dimi- nished in bright sunshine, but he found all differences to disappear when the needle was made to oscillate in an exhausted receiver, from which it would appear that Mr, Christie's results must have been owing to currents of air. UENEllAL TACTS AND PltliNClRLES. 547 MAGNETISM (CONTINUED). CHAPTER XIV. General Facts and Principles Duality of the Magnetic Force Magnetic Curves Haldat's Magnetic Figures. (793) The native magnet, or natural loadstone, is an ore of iron, consisting chiefly of the two oxides of that metal, together with a small proportion of quartz and alumina. It is usually of a dark grey hue, and has a dull metallic lustre. It is found in considerable masses in the iron mines of Sweden and Norway, and also in different parts of Arabia, China, Siam, and the Philippine Islands. Small loadstones have occasionally been met with among the iron ores of England. The smallest loadstones have generally a greater attractive power, in proportion to their size, than larger ones. They have been found of such a strength, that, though weighing only about 25 grains, they could lift a piece of iron forty-five times heavier than themselves. Sir Isaac Newton had a small specimen, set in a ring, which was capable of lifting 746 grains of iron, or 250 times its own weight ; and it is stated by Cavallo, that he has seen a loadstone which weighed only 6^ grains, which lifted a weight of 300 grains. (794) If we immerse a natural loadstone no matter of what shape in a quantity of clean iron filings, we shall find that there are two points exactly opposite each other, on which the filings are accumu- lated more abundantly than on any other place, assuming the form shown in Fig. 265, the lines di- verging from the ends of the magnet in curves, the centre a, being nearly free from them. These are called its poles ; and if we balance a small needle of iron on a pivot, and bring it near either of these poles, we shall find that it will be attracted towards it ; or, conversely, if we suspend the loadstone by a fine fibre, and bring into the vicinity of its poles, a 548 MAGNETISM. piece of soft iron, it will be drawn towards the iron ; a reciprocal attraction is exerted between them, action and re-action being equal and opposite. The power of the natural magnet is greatly increased by adapting two pieces of flat soft iron to its poles, and enclosing it in a silver or brass case. In Fig. 266 a magnet thus armed, is shown : A is the loadstone ; BB, two pieces of soft iron placed against its opposite poles, the lower ends turning inwards, and fastened by transverse bars of copper, c c, to the brass case which surrounds the sides and' upper part of the stone. In the top of the box is inserted a ring, R, for the purpose of suspending the whole ; and to the lower part of the armature is adapted -a piece of soft iron, with a hook, on which is hung as much weight as the strength of the magnet will bear. (795) When a piece of steel has been rendered magnetic, it exhibits the same properties as the natural loadstone ; and since we are in the possession of a variety of methods of communicating to it this state, the artificial magnet is always employed in experimental inves- tigations. We shall describe some of the most approved methods of magnetizing iron presently : in the meantime, we shall only observe that, for the exhibition of the experiments we shall first have to allude to, the following simple and ready method will be found amply sufficient for communicating to small bars of steel the requi- site degree of -Magnetism. (Scoresby.) Break off sharply with a pair of pliers, about 3 inches of a thick steel knitting needle, and give it several smart blows with a hammer, while its smooth and rounded end rests on the knob of a poker held vertically between, the knees, the poker itself having been previously hammered while in this position. The wire will, by this treatment, become magnetic. The downward end, while under percussion, being a north pole. If the bar to be magnetized be placed between two iron rods (the lower one having been previously Fig. 267. hammered) and the hammer then ap- plied to the top of the pile, increased effects are obtained. If the bar which has been thus treat- ed, be suspended horizontally in a little stirrup of paper or metal by a fibre of silk, (Fig. 267), and if all bodies of a ferruginous nature be removed from its vi- i cinity, it will, after a few oscillations, take GENERAL FACTS AND PRINCIPLES. 549 up a position nearly north and south ; and if it be disturbed from this position, and placed in any other, it will not remain there ; but as soon as it is at liberty to move, it will resume its former position. It will also possess the power of communicating Magnetism to hard steel permanently, and to soft iron temporarily, the degree of strength, of course, depending on its own power, and with respect to the steel, on the time which it is suspended. If two magnetized bars be poised and placed in different positions respecting each other, it will be found that in some cases they appear to be attracted towards each other, while in others they manifest a mutual repulsion. This, however, does not happen capriciously ; the two north poles and the two south poles invariably repel each other ; but the north pole of one magnet always attracts, and is of course attracted by the south pole of the other. An excellent extemporaneous pivot for a needle or bar may be formed by inverting a common precipitating glass on a pivot, and laying the bar on it. The bar may likewise be laid upon the centre of a clean watch-glass, on which, because of the curvature of the glass, it will rest as on a point, and perfect freedom of motion will be obtained by tapping the table near the watch-glass with the knuckle. (796) If the bar thus rendered magnetic be sprinkled over with, or rolled into, fine iron filings, the filings will be observed to adhere to it, in the form of bristling tufts (Fig. 268), but by no means in a uniform manner : at the extremities, e e the iron filaments will be Fig. 268. very long, standing out perpendicularly from the surface. As the centre of the bar is approached they will become shorter, gradually taking up a more and more inclined position, and adhering in smaller and smaller tufts as the central line m m is approached. In the immediate neighbourhood of this line no filings are attracted ; this, therefore, is called the neutral line, and the two halves of the barp p' are called the magnetic poles. Every magnet, natural or artificial, 550 MAGNETISM. possesses essentially this neutral line and these magnetic poles ; it sometimes, however, happens that a magnetized bar possesses more than two poles, two or more poles alternating between those situated at either extremity of the bar. A magnet in this condition is said to have " consecutive poles" (797) In order to communicate Magnetism from a natural or arti- ficial magnet to unmagnetized iron or steel, it is not necessary that the two bodies should be in contact. The communication is effected as perfectly, though more feebly, when the bodies are separated by space. Thus, in Fig. 269, if F i g> 259. the north pole of an artificial steel magnet A, be placed near the extremity S, of a A piece of soft iron _5, the end s, will instantly acquire the properties of a south pole, and the opposite end n, those of a north pole. The opposite poles would have been produced at n and s, if the south pole s, of the magnet A, had been placed near the iron S. In like manner, the iron JB, though only temporarily magnetic, will render another piece of iron C, and this again, another piece D, tem- porarily magnetic, north and south poles being produced at n, s', and n", s". (798) Here we cannot fail to observe a pointed analogy between the phenomena of magnetic attraction and repulsion, and those of electrical. In both there exists the same character of double agen- cies of opposite kind, capable, when separate, of acting with great energy, and being, when combined together, perfectly neutralized, and exhibiting no signs of activity. As there are two electrical, so there are also two magnetic powers ; and both sets of phenomena are governed by the same characteristic laws. So also in the last expe- riment, the Magnetism inherent in JB, 0, Z), is said to be induced by the presence of the real magnet A ; and the phenomena are exactly analogous to the communication of Electricity to unelectrified bodies by induction, the positive state inducing the negative, and the nega- tive the positive, in the parts of a conductor placed in a state of insulation near an electrified body. (799) A simple experiment will satisfactorily show that soft iron possesses magnetic properties, while it remains in the vicinity of a magnet. Let A (Fig. 270) be a magnet, Fig, 270. and K a key, held either horizontally near 1 one of its poles, or near its lower edge. Then if another light piece of iron, such as a small nail, be applied to the other end of the key, the nail will hang from the kev, and will continue to do so while ATTRACTION AND REPULSION. 551 the magnet is slowly withdrawn ; but when it has been removed beyond a certain distance, the nail will drop from the key, because the Magnetism induced on the key becomes at that distance too weak to support the weight of the nail. That this is the real cause of its falling off, may be proved, by taking a still lighter fragment of iron, such as a piece of very slender wire, and applying it to the key. The Magnetism of the key will still be sufficiently strong to support the wire, though it cannot the nail ; and it will continue to support it, even when the magnet is yet further removed ; it at length, how- ever, drops off. If the key be held above a portion of iron filings, they will not be attracted by it; but if the magnet be then brought near the ring ol the key, as in the figure, the iron filings will instantly start up, and be attracted by the key. (800) It has been observed, that in all cases where a magnet at- tracts iron, a reaction takes place, the iron attracting the magnet ; it is the same with a bar of iron on which Magnetism has been induced. It reacts upon the magnet, which induces its Magnetism, and incre&ses its magnetic intensity. Hence, we derive a distinct explanation of the remarkable facts, that a magnet has its power increased by having a bar of iron placed in contact with one of its poles, and that we can gradually add more weight to that which is carried by the magnet, provided we make the addition slowly, and in small quantities, the power of the magnet being increased by the reaction of each separate piece of iron that it is made to carry. These facts enable us to explain the phenomena of magnetic attraction and repulsion. The magnet attracts a piece of iron by inducing an opposite polarity at the end in contact with it ; and the two opposite principles attract each other. In like manner, the north pole of one magnet attracts the south pole of the other ; and the north and south poles repel each other, in consequence of the attraction and repulsion of the opposite and similar principles. The attraction of iron filings is explained in the same way. The particle of iron next the magnet, has Magnetism induced on it, and it becomes a minute magnet, like B, Pig. 269. This particle again makes the next particle a magnet, like C, and so on, the opposite polarity in each particle of the filings attracting one .another, as if they were real magnets. (801) In comparing the amount of the attractive force of two dis- similar poles of two magnets, with the amount of the repulsive force of the two similar poles, it has been found that the former force is considerably greater than the latter. This result is a necessary consequence of the inductive process above described. When the 552 MAGNETISM. two attracting poles are in contact, each magnet tends to increase the power of the other, by developing the opposite magnetic states in the adjacent halves, and thus increasing their mutual attraction. But when the two repelling poles are brought into contact, the action of each half brought into contact,has a tendency to develope in that half, a Magnetism opposite to that which it really possesses, and thus to diminish the two similar principles, and weaken their repulsive power. This injurious influence of opposite poles upon the repulsive power of the magnets in action, is well exhibited when one of the magnets is very powerful, and the other very weak. When the two similar poles are held at a moderate distance, a repulsion is distinctly exhibited ; but when they are brought into contact, the stronger attracts the weaker magnet, an effect which is produced by its actually destroying the similar weak Magnetism in in the half next to it, and inducing in that half the opposite Magnetism, which of course occasions attraction. (802) The law regulating the variation of the intensity of the magnetic forces, both attractive and repulsive at different distances, has been submitted to careful investigation by several eminent mathematicians, and the general result has been it is the same that obtains in Electricity and in gravitation, viz., that the intensity of the force by which magnetic polarities act on each other is inversely as the square of the distance, a law which seems common to all forces emanating in every direction from a central agent. (803) The process of induction is in its operation independent of the relative positions of the magnet and the soft iron. Thus in Fig. 271, let A be the permanent steel Flg ' ' magnet, and B and C pieces of soft v A N iron. The two ends s s will become s south poles, and the opposite ends n n, north poles, under the inducing influence of A ; but C will become more powerfully magnetic than B, 71 because from its inclined position the pole S of the steel bar A begins to exert an inductive influence on n. From this it is evident that the most favourable position in which a bar can be placed for receiving the full inductive influence of both poles is that of Fig. 272. parallelism, as shown in Fig. 272. The effects become somewhat complicated ^ A when the inducing bar is brought either very near, or in contact with, the iron bar n ["' ~\ S i n other positions than the ends. Thus if J * we brinsr the north end of a magnetized INDUCTION. 553 bar opposite the centre of a soft iron rod, the two ends of the rod will become temporarily two north poles, a south pole Fig 273. being induced in the centre. In like manner the star- shaped piece of iron (Fig. 273) will have south poles at s s s s, on bringing the S pole of the bar S opposite its centre. If a circular iron plate be substituted for the star, then every part of its circumference will have a southern polarity. (804) The experiment illustrated in Fig. 274, shows the operation of magnetic induction in a very instructive manner. Fig 274. Several soft iron wires are suspended from the N pole of a strong bar magnet. The wires immediately become temporarily magnetic, their S poles being determined towards the IN" pole of the inducing bar, and their opposite extremities becoming n poles. Both ends have a natural tendency to repel each other, but the S ends are prevented from yielding to their repulsive influences in consequence of their strong adhesion to N. The n poles not being under the influence of this restraining power avoid one another, as represented in Fig. 274. Again, in the following experiment of Cavallo, we have well illustrated the mutual repulsive action of similar poles. Two pieces of soft iron (Fig. 275) are suspended by threads from a ring or hook, so as to have free liberty of motion, on bringing either, say the N pole of a strong bar magnet, at a certain distance below the Fig. 275. wires, the wires become inductively mag- netic, and their similar S poles being determined towards N, a mutual repulsion is set up. If now the magnet A be ap- proached very near to the wires, the repul- sion of the s s ends of the wires gives place to an apparent attraction; this is caused by the stronger attraction of A, for both wires overcoming their own mutual repulsions ; the repulsion of the n ends of the wires is, however, now rendered evi- dent, and the nearer the inducing magnet is brought to the wires the stronger will this repulsion be manifested. On removing A, the wires immediately collapse, and fall into a parallel and vertical position, the Magnetism induced upon them being merely of a temporary nature. When fine steel needles 554 MAGNETISM. are substituted for soft iron wires, it often happens that they acquire a certain amount of permanent Magnetism, in which case they, of course, continue to repel each other after the removal of the magnetic bar. (805) The following experiment of Dr. Robison is likewise instruc- tive as showing the neutralization or destruction of induced Magnet- ism by two equal and opposite magnetic actions. A forked piece of Fig. 276. soft iron, C D E, is suspended by one of its branches from the N 1 pole of the magnetic bar, A B ; if the power of B be pretty strong, it will induce sufficient temporary Magnetism in C D E to enable it to hold in suspension the key K ; but if we now bring into contact with the other branch of the fork the S pole of a second magnetic bar, the key will immediately drop off. The reason is evident : the N pole of B induces a N pole at the lower end E of the fork; hence its power of sustaining the key; but the S pole of A tends to give a southern polarity to the same end, and the two actions mutually destroy or neutralize each other. Again, Fig. 277. suspend any object of soft iron, as a key, from either pole of the magnetic bar A, then gradually slide over A a second similar bar B, taking care that the opposite poles of the two bars shall come into contact when the end of B arrives within a certain distance of A, the key will fall off as if the bar had lost its magnetic power ; this, how- ever, is not the case, for on removing B the key will be again supported. (806) We have seen the close analogy which exists between the phenomena of Electricity and those of Magnetism, as far as relates to the law of action, and the influence of induction, but beyond this point it fails us entirely. No natural or artificial magnet ha& ever been seen with only one pole, or with one kind of Magnetism ; Elec- tricity on the other hand, whether positive or negative, is net only capable of being excited by induction, but it may be actually trans- ferred from one body to another. A body may without difficulty be electrified positively or negatively as has been shown in a previous MAGNETIC CUKVES. 535 chapter (30 42) ; but with Magnetism there is never any transfer of properties, but only the excitation of those which were already inherent in the body operated on. If we examine a magnetized bar, by laying it on a table, covering it with a sheet of white paper, or with a plate of thin glass, and then sifting some fine iron filings over it from a muslin bag, the filings will, on gently tapping the table, be found to arrange themselves round and about the poles of the magnet in a very beautiful manner, forming a succession of curves known as the " magnetic curves," (Eig. 278), or "the curved lines of magnetic Fig. 278. force " (Earaday). On examining these curves, it will be found that the force decreases gradually from the poles towards the centre, or some point intermediate between the two poles, where it vanishes altogether. This is the neutral point, or as it may be called the equator of the magnet. If we break the magnet at this point, we shall not find a north polar Magnetism distributed uniformly over one portion, and a south polar Magnetism over the other, but each half will be a perfect magnet in itself, and if examined by iron filings, will be found to exhibit the " curved lines of magnetic force " as perfectly as the unbroken bar; the same will be the case if the pieces be again broken- other magnets will be formed, each having an equator and two poles ; and in like manner, however numerous and minute the fragments into which a magnet may be divided, each part will be still a complete magnet with two poles and a neutral point. (807) Beautiful visual evidence of the existence of two distinct magnetic forces of their mutual attractions, repulsions, and neutralization are afforded by the phenomena presented when iron filings are submitted to the -influence of the opposite and similar poles of two pairs of magnetic bars. Let the two dissimilar poles of two powerful bars be placed in the same line, about \\ or 2 inches apart, and let the filings be sifted through a sieve on a frame of drawing paper, placed over them, the filings will arrange themselves as shown in Eig. 279, the curved and straight o o 556 MAGNETISM. lines of magnetic force issuing from similar points of each bar joining the two poles, Fig. 279. and showing reciprocal attraction. Then let the two similar poles be placed opposite each other and the filings again sifted over them ; evidence of mutual repulsion will now be obtained, the lines of force being apparently conflicting, as shown in 'Fig. (280.) Fig. 280. It sometimes happens, that either from some peculiarity in the structure of the bar, or from some irregularity in the magnetizing process, a magnet is met with having more than two poles. This curious condition is readily detected by examining the magnetic curves into which iron filings are thrown when sprinkled over the bar. They will be found to be distributed in the manner shown in Fig. 281. A magnetic bar in this condition is said to have consequent or consecutive poles. The fundamental proper ties of the magnetic curves were investigated mathematically by Dr. Eoget (Journal of the Royal Institution, Feb., 1831). He describes them as having the following remarkable SUSTAINING POWEE OF ELECTRO-MAGNETS. 557 Fig. 281. property, viz., that the difference of the cosines of the angles, which lines drawn from any point in the curve to the two poles, make with the axis, taken on the same side, is constant ; and he constructed a system of rulers by which these curves may be mechanically delineated. (808) Sustaining Power of Electro-Magnets. The experiments of Jacobi and Lenz (Pogg. Ann. xlvii., 403) led them to the conclusion that under conditions in other respects similar, the total attraction, i.e., the mutual adherence of two straight cylindrical electro-magnets, or of one electro-magnet and one armature of soft iron, is proportional to the square of the strength of the current ; to this proposition Miiller assents (Ann. rep. Prog. Chem. 1850). According to Barral (Comptes Rendus, xxv. 757), the attraction increases with the weight of the keeper, and reaches its maximum when the electro-magnet and keeper are of equal weight. The experiments of Dub agree with this indica- tion only so far that for a given electro-magnet, and a given diameter of keeper, a certain amount of sustaining power cannot be exceeded. This limit seems to depend more upon the length than on the weight, and to be more slowly attained the greater the strength of the current. He corroborated the result that the single coils contribute more to the development of the magnetic intensity of the poles, the nearer they are to the latter ; and that when the coils are arranged in different systems of equal power, the lifting power, with a constant cur- rent, is proportional to the square of the number of systems in action. The distribution of Magnetism in the polar surfaces of an electro- magnet was determined by Von Koike (Pogg. Ann. Ixxxi., 321). The magnetic force in any given zone of the surface which intersects the axis of the magnet at right angles, is always greater at the edges than upon the surfaces ; in fact, in the case of a large horse-shoe electro- magnet, he found the force almost twice as great at the rim as at the centre. In consequence of the action of the poles upon each other, the weakest point was not found to be at the exact centre, but o o 2 558 MAGNETISM. approached it more and more, the less the two limbs could act inductively upon each other. The method of measurement adopted was that proposed by Pliicker, viz., by determining by means of a balance, the weight necessary to separate a small-pointed iron cylinder from a given point on the surface of the magnet. For all practical purposes the numbers thus obtained may be taken to repre- sent the magnetic intensity of the places tested. The results obtained by Pfaff are the following (Peschel) : 1. The amount of suspensive force is immediately dependent on the intensity of the electric current which circulates about the iron ; and the intensity of the Magnetism excited in the soft iron is exactly proportional to that of the electric current. 2. The intensity of the current continuing the same, the magnet's suspensive force increases with the number of turns made by the wire ; or the total effect of all the coils is equal to the sum of their effects, if taken singly. 3. The attractive force of an electro-magnet increases as the mass of the iron composing it, and this increase is proportional to the dia- meters of the iron cylinders, their lengths being equal. 4. The purer and softer the iron, and the more homogeneous the mass, the stronger the Magnetism it is capable of receiving. 5. The form of the iron influences its suspensive power, cylinders carry greater weights than rectangular bars, and a hollow cylinder, from which a portion has been cut away so as to form a long horse- shoe magnet, when viewed in the direction of its axis, but a very short one if taken, as to its height, is capable of receiving a very great suspensive force ; and lastly, a slight curvature of the polar surface adds considerably to its power. (809) "We are indebted to M. Haldat, of Nancy, for the discovery of magnetic figures analogous to those first produced with Electricity by M. Lichtenberg, and which may easily be exhibited. For this purpose he employs plates of steel, from 8 to 12 inches square, and from -^-th to ith of an inch thick. The plates which he used were of that kind of steel which is used for the manufacture of cuirasses ; so that it did not require to be tempered, being suffi- ciently hard to preserve the Magnetism communicated to it. Figures of any kind may be traced on the surface of the steel plate, either by one magnet or by several combined, and the best form for this pur- pose is that in which the poles are rounded. In this way we may write on a steel plate the name of a friend, or sketch a flower or figure, with the extremity of a magnet. If it is the south pole that we use, all the traces that we make will have north polar magnetism ; and if we shake steel filings on the plate out of a gauze bag, the HALDAT' s MAGNETIC FIGURES. 559 filings will arrange themselves in the empty spaces between the lines traced by the pole of the magnet, and thus represent in vacant steel the name which has been written, or the flower or figure which has been sketched. " These figures," says M. Haldat, " have a perfect resemblance to those which are formed on the surface of non-magnetic plates, viz., wood, card, glass, or paper, under which a magnet is placed. The resemblance between the two sorts of figures, when the magnets and the parts magnetized have the same form, is not only exact iii the whole figure, but likewise in the smallest details. The filings collect at the parts where the Magnetism is most intense, and they arrange themselves in pencils and radii. These curves, and pencils, and rays, so similar at the two poles of the same magnet, have such a resemblance that they do not allow us to distinguish the two parts from one another." (810) In sifting the iron filings upon the steel plate, a general vibration of the plate, by tapping its edge with the ring of a small key, will assist the filings in taking their proper places ; but we must avoid such vibrations as will produce regular acoustic figures, unless we wish, as M. Haldat has found to be practicable, to unite the magnetic with the acoustic figures, which produces very interest- ing and varied forms. In order to remove the Magnetism from the steel plates, they may be heated over charcoal, till they become of the straw-coloured tem- perature ; and to render the repolishing of them unnecessary, M. Haldat tins them, and the temperature at which the tin melts, when it is required to efface the Magnetism, indicates the necessary heat. (811) As the figures traced on the steel are nothing more than magnets of different forms, and are surrounded on all sides with a substance capable of acquiring the Magnetism which may be deve- loped by communication, we might expect, as M. Haldat remarks, that this means of communication between the opposite poles of the magnets would bring them into a neutral state. This, however, is not the case ; and the portion of the metal which surrounds the magnetic figure, performs the part of the armature of a loadstone, and the Magnetism is thus kept up. The figures might be rendered permanent, by covering the steel plate either with a gummy or balsamic solution, which will become hard by exposure to the air ; or with a coating of some easily melted substance which becomes fixed at ordinary temperatures. If we sift the iron filings on the steel plate when covered with such a fluid, the filings will take their magnetic position round the traced lines, and will become fixed by the induration or solidification of the fluid coating. 560 MAGNETISM. Mr. Faraday gives (Ex. Besearches, Series 29), the following process for fixing the designs on the paper : A piece of cartridge paper is well moistened with a solution of one part of gum in three or four of water, by means of a broad camel's hair brush, and after wafting it through the air once or twice to break the bubbles, it is laid carefully on the filings, then covered with ten or twelve folds of equable soft paper ; a board is placed over the paper, and a half- hundred weight on the board for thirty or forty seconds ; or with a large design, the hand should be applied so as to rub with moderate pressure all over the surface equably in one direction. If after that, the paper be taken up, all the filings will be found to adhere to it, and when dry are firmly fixed. If a little solution of red ferro-prus- siate of potash, and a small proportion of tartaric acid is added to the gum water, a yellow tint will be given to the paper, and Prussian blue will be formed under every particle of iron, and then if the filings be removed, the designs still remain recorded. "When the designs are to be preserved in blue only, the gum may be dispensed with. METHODS OE MAKING ARTIFICIAL MAGNETS. 561 MAGNETISM -CONTINUED. CHAPTEE XV. Methods of making artificial magnets Processes of Knight, Scoresby, Duhamel, Michell, Canton, Epinus, Coulomb, Barlow, Elias Circumstances which affect the energy of artificial magnets Laws of magnetic combinations Useful ap- plication of the magnetic powers Laws of magnetic force. (812) Methods of making Artificial Magnets. For the impregnation of small bars or plates, the following simple process will be effectual. Draw the bar (which should be of a well hardened steel, tempered by plunging it at a cherry -red heat into cold water, and afterwards polished) a few times across the poles of an armed natural loadstone, or an artificial horse-shoe magnet, taking care not to remove the bar from either extremity of the inducing magnet, and to terminate the operation when its extremities are equi-distant from either pole of the horse-shoe, that is, when the poles of the latter are as nearly as possible at the centre of the bar. In this position remove it, and it will be found to have acquired all the magnetic power it is capable of receiving. For larger bars, a great variety of processes have been invented. The first of these was that of Mr. Knight. This method which was kept a secret during his lifetime, but which was made public after his death by Mr. "Wilson, consisted in placing the bar to be magnetized, after having tempered it at a cherry -red heat, under the poles N S, (Fig. 282) of two equal magnets. These magnets are then separated .,_ F ,. Fig. 282. in opposite direc- tions, S A, N A, so -^ ^- that the south pole - i ' of the one should pass over the north polar half, B n, of the bar, B, and the north pole, IS", of the other half over the south polar half, B s, of B ; this oper- ation is repeated several times till the magnetization of the bar B is fully developed. (813) This method is modified by Scoresby (Magnetical Investiga- tions, 1839), by placing the bar to be magnetized, above, instead of leneath, the magnets employed in the operation, by which great facility is given for the performance of the requisite manipulations, and for the maximum development of the magnetic condition. The plate to be magnetized is laid flat upon the magnets, so as to extend equally over the surface of both. The bars are then drawn asunder 562 StAGNETISM. till the plate just rests with its extremities in contact with the extreme poles of the magnets, and then it is slid off sideways, and removed to some distance, preserving the parallelism of its position with that of the magnets, till these are restored to the proximity with which the operation commenced. The process is repeated with the other side of the plate in contact with the magnets, and in the case of thin small plates sea compass-needles for instance the condition of saturation is found to be obtained. Usually, however, four strokes are given, two on each side ; and in hard short bars, six or eight strokes are given, partly on the edges. A dozen compass- needles may thus be magnetized to saturation in five or six minutes, and by means of a pair of strong two-feet magnets, compass needles or dipping needles of the usual form, can be brought to their maximum power without removing their agate caps or centres. (814) Soon after the publication of Dr. Knight's method, small bars thus magnetized were distributed all over Europe, and were eagerly sought after by the cultivators of natural philosophy. "When the process, however, was applied to bars of large size, it was found to be defective ; philosophers therefore renewed their efforts to devise methods of greater and more universal efficacy. The next improve- ment was made by M. Duhamel, of the Academy of Sciences, in con- junction with M. Antheaume. The process is represented in Fig. 283. The bars B It to be magnetized, are placed paralled to each other, and have their extremities united Fig. 283. ky ^ WQ pieces, Mm, of soft iron, at right angles to the bars ; two strong magnets, or two bundles of small bar magnets, A A', nay i n g tne i r similar poles to- gether, are placed as in the figure, at an angle of about 90, or inclined at 45 to the bar J?, and then separated from each other, as in Dr. Knight's method ; the same operation is repeated on the other bar B, and continued alternately on both, till the Magnetism is supposed to be completely developed in both bars. When A A are placed on the second bar _B, the disposition of the poles must be reversed ; the pole that was formerly to the right hand being now turned to the left. The two bars _B JB are then turned, so that the undermost faces are uppermost, and the same process carried on as before. The peculiarity of Duhamel's process consists in the employment of the pieces of iron M m, and in the use of bundles of small bars, which are more efficacious than two single ones of the same size. In METHODS OF MAKING ARTIFICIAL BAR MAGNETS. 563 proportion also as the steel bars acquire Magnetism, the connecting pieces participate in the acquisition of a similar power, and serve to retain it in the bars themselves ; just as the Electricity which is imparted to the inner coating of a Leyden jar, is retained by the reciprocal influence of the induced, and contrary Electricity of the outer coating. The Magnetism of the bars is retained by a similar influence, and greater facility is thus afforded to increase its amount, by the subsequent additions it is receiving from the action of the magnets, as they pass along the surface. (815) About the same time that Duhamel was occupied with this subject, Mr. Michell, of Cambridge, and Mr. Canton, were separately engaged in the same inquiry. Mr. Michell published his method in 1750, to which he gave the name of method by double touch. Having joined together, at the distance of ith of an inch, two bundles of strongly magnetized bars, A A (Fig. 284), their opposite poles, JVS, being together, he placed five or more equal steel bars, B' B' B" B" ', c: ~i ,1 . T ^ B" Jl' Tf / ' ft" in the same straight line, and resting the extremity of the bundle of magnets, A A, upon the middle of the central bar, B, he moved them backwards and for- wards throughout the whole length of the line of bars, repeating the operation on each side of the bars,' till the greatest possible effect was produced. By this method Mr. Michell found that the middle steel bars, B B' B', acquired a very high degree of magnetic virtue, and greater than the outer bars, B // B" ; but by placing these last bars in the middle of the series, and repeating the operation, they acquired the same power as the rest. Mr. Michell states that two magnets will, by his process of double touch, communicate as strong a magnetic virtue to a steel bar as a single magnet of five times the strength when used in the process of single touch. The bars A A act with the sum of their powers in developing Magnetism in all parts of the line of the bars between them, and with the differ- ence of their powers in all parts of the line beyond them. The external bars act the same part in this process as the two pieces of soft iron in the method of Duhamel. (816) Mr. Canton placed the bars as in Duhamel' s method, joined by pieces of soft iron. He then applied Michell's method of double touch, and afterwards he separated the two bundles of magnets, A A ; and having inclined them to each other, as in Du- hamel's method, he made them rub upon the bar from the middle to 564 MAGNETISM. Fig. 285. its extremities. The peculiarity of Canton's method is the union of these two processes ; but Coulomb and others are of opinion that the latter part of the process is the only effectual one. (817) In order to make artificial magnets, without the aid either of natural loadstones or artificial magnets, Mr. Canton gives the follow- ing detailed process : He takes six bars of soft, and six of hard steel ; the former being smaller than the latter. The bars of soft steel should be 3 inches long, ith of an inch broad, and aVth thick ; and two pieces of iron must be provided, each having half the length of one of the bars, and the same breadth and thickness. The bars of hard steel should be each 5| inches long, \ an inch broad, and --roths of an inch thick, with two pieces of iron of half the length, and of the same breadth and thickness. All the bars being marked with a line quite round them at one end, take an iron poker and tongs, or two bars of iron (the larger and the older the better), and fixing the poker upright, as in Fig. 285, hold to it with the left hand near the top, P, by a silk thread, one of the soft bars, B, having its marked end downwards; then grasping the tongs, T, with the right hand a little below their middle, and keeping them nearly in a vertical line, let the bar, B, be rubbed with the lower end, L, of the tongs, from the marked end of the bar to its upper end, about ten times on each side of it. By this means the bar, B, will receive as much Magnetism as will enable it to lift a small key at the marked end; and when suspended by its middle, or made to rest on a point, this end will turn to the north, and is called its north pole, the unmarked end being the south pole. When four of the soft steel bars are thus rendered magnetic, the other two, AC,BD, Pig. 286, must be laid parallel to each other, at the distance of about one-fourth of an inch, having their dissimilar poles united by the smallest pieces of iron, A It, C, D. Two of the magnetized bars are then to be placed together, as at G, with their similar poles united, and when separated by a piece of wood, at I, METHODS OF MAKING ARTIFICIAL BAB MAGNETS. 565 they are slid four or five times backwards and forwards along the whole length of the bar, A Q, so that the marked end, F, of Gr is nearest the unmarked end of A G, and vice versa. This operation is carefully re- peated on B D, and on the other sides of both A G and B D. "When this is done, the bars A G &-'+ and D are to be taken up and substituted for the two outer bars of the bundles Gr K-, these last being laid down in the place of the former, and magnetized in a similar manner. This operation must be repeated, till each pair of the soft bars has been magnetized three or four times. When the six soft bars are thus magnetized, they must be formed into two bundles of three each, with their similar poles together, and must be used to magnetize two of the hard bars in the manner already described ; and when they are magnetized, other two of the hard bars must be touched in a similar manner. The soft bars are now to be laid aside, and the remaining two hard bars magnetized by the four hard bars already rendered magnetic ; and when this is done, the operation should be repeated by interchanging the hard bars, till they are impregnated with the greatest degree of per- manent Magnetism which this method is capable of communicating to them. (818) In performing the above operations, which may be completed in about half an hour, the bars A G, B D, and the pieces A B, G D, should be placed in grooves or fixed between pins of wood or brass, to keep them steady during the successive frictions which are applied to them. According to Canton, each of the six artificial magnets thus made, will lift about twenty-eight ounces troy. They should be kept in a wooden box, and placed so that no two poles of the same name may be together, the pieces of iron being placed beside them. (819) The method of " double touch," introduced by Michell and Duhamel, was much improved by Epinus, who substituted magnetic bars for the pieces of soft iron Mm, forming the rectangle (Fig. 283). He then inclined the bundles of magnetic bars which formed his battery, and separating their dissimilar poles by a piece of wood, he passed them backwards along the whole length first of one of the steel bars, and then of the other, taking care to reverse the poles when passing from one bar to the other ; the process was then re- peated on the other sides of the bars. Epinus found that a maximum 566 MAQNETISM. effect was produced when the magnetizing bars were inclined 20 or 30 to the steel bars over which they passed. Scoresby modifies this process by passing a horse-shoe magnetic battery round the whole parallelogram of steel bars in the same direction, terminating at the middle of one of the bars, instead of limiting the manipulations to the extent of the steel bars separately from end to end. For a pair of bars, tempered from end to end, 2 feet in length, 1-5 inch broad, and 0'6 inch thick, two circuits only of the parallelogram on each side of the bars by the large magnets were necessary, and in order to avoid hitching, and to make the magnet pass smoothly, the surfaces of the bars should be slightly oiled. By this modification of Epinus, Scoresby states that he was enabled to obtain one-seventh the additional power in two heavy bars. (820) The following is an account of Coulomb's method of making artificial magnets, which consists of the most efficacious parts of the preceding processes, improved and extended by long experience. The apparatus which he uses consists of fixed and moving bundles of magnets. Each of the fixed bundles consists of ten bars of steel, tempered at a cherry-red heat, their length being about 21 inches, their breadth -A-ths of an inch, and their thickness 1th of an inch. Having rendered them as strongly magnetic as possible, with a natural or artificial magnet, he joined them with their similar poles together, and formed them into two beds of four bars each, these beds being separated by small rectangular parallele- pipeds, m n, of soft iron, projecting beyond their extremities, as Fig. 287. shown in Fig. 287. The moving bundles consist of four bars tempered at a cherry- red heat, each being about 16 inches long, -A-ths of an inch wide, and -roths of an inch thick. "When these bars were magnetized in the same way as the other bars, he united two of them by their width, and two of them by their thickness, so that each bundle was l-A-th inch wide, and -A-ths thick. The bars being separated as before, by pieces of soft iron, Coulomb found that all kinds of steel, provided the quality was good, were capable of receiving the same degree of Magnetism. In order to magnetize a bar, he placed the large fixed bundles, M N", (Fig. 288) in the same straight line, and at a distance of a little less than the length of the bar to be magnetized ; and this bar, B B, was placed as in the figure, so as to rest on the projecting pieces of iron, so that the contact took place only over a length of 1th of an inch : the two moving bundles, A A', having their dissimilar poles separated by a small piece of wood or copper, about ith of an inch wide, between them ; and each being in- METHODS OF MAKING HORSE-SHOE MAGNETS. Fig. 288. 567 clined at an angle of 20 or 30 to the bar, B B'. The united poles of the moving bundles are then moved successively from the centre to each extremity of the bar, B B', so that the number of frictions upon each half of the bar may be equal. When the last friction has been given, the united poles are brought to the middle point of the bar, B B', and then withdrawn perpendicularly. The same operation is then repeated on the other side of the bar, B B'. If we wish to employ the method of Duhamel, we do not require the piece of wood or copper, but have only to separate the bars when the united poles are in the middle of the bar, B B', making each pole pass to the extremity of it. (821) If the pieces composing the moveable magnets have not re- ceived their full power, they will, notwithstanding, communicate to the bars subjected to their action, a greater degree of Magnetism than they possess themselves. "We may therefore now increase their power, by repeating the process on them with the bars which they have themselves impregnated : by so doing three or four times, we shall succeed in effecting their complete saturation. If the bars to be magnetized be very large, Coulomb recommends an increase of the number of the moveable magnets, each of the bars projecting beyond the last, as shown in Eig. 289. Thus Fig. 289. the pole of each, which Coulomb supposes generally to reside at the very extremity of the bar, will come immediately in contact with the bar to be magnetized, when the compound magnet is applied to it with the proper inclination, and the whole will powerfully conspire to produce the same effect. (822) Horse-shoe Magnets. The form of a horse-shoe is generally given to magnetic bars when both poles are wanted to act together, which frequently happens in various experiments ; such as for lifting weights by the force of magnetic attraction, and for magnetizing steel bars by the process of double touch, for which they are exceedingly convenient ; fulfilling in this operation all the purposes of compound magnets. 568 MAGNETISM. (823) The following is the method of making a powerful magnetic battery of the horse-shoe form, recommended by Professor Barlow : " Take bars of steel, 12 inches long, and bend them into a horse- shoe shape, their length being 6 inches, their breadth 1 inch at the curved part, and fths of an inch at their extremities, and their thickness th of an inch. Let them be filed nicely, so as to correspond, and lie flatly upon each other. Then drill two holes Fig. 290. in each, as shown in Eig. 290, and by means of screws, Y V, passing through these holes, let nine horse-shoe bars be bound together. When the heads and ends of the screws are constructed so as to leave the outer surfaces smooth, the mass of bars must be filed as if they were one piece, and the surface made flat and smooth. "When the bars are separated, let them be carefully hardened so as not to warp ; and when they are cleaned and ren- dered bright, but not polished, magnetize them separately in the following manner: When the two extremities of the bar are connected by a piece Pig. 291. of soft iron, M, the Magnetism may be developed in the two halves by Duhamel's method, as in Eig. 283; or, following Epinus, M a strong magnet may be applied to each pole, and their extremities Fig. 292. connected either with a piece of soft iron or another magnet, or two horse-shoe magnets may be applied to each other, as in Eig. 292, uniting the poles which are to be of contrary names. When the magnets are prepared in any of these ways, they are then to be mag- netized with another horse-shoe magnet, by placing its north pole next to what is to be the south pole of one of the horse-shoe bars, and then carrying the moveable magnet round and round, but always in the same direction. In this way, a very high degree of magnetic METHODS OF MAKING HOL?SE-SHOE MAGNETS. 569 virtue may be communicated to each of the nine bars. When this is done, they are to be reunited by the three screws ; and their poles or extremities connected by a piece of soft iron, or lifter, as in Fig. 34, having in its middle a hook, H, for suspending any weight. As the lifting power depends on the accurate contact of the poles of the magnet with the lifter, the extremities should, after hardening, be properly rubbed down with putty on a flat surface. A magnet of this size and form was found by Professor Barlow to suspend forty pounds ; but he afterwards found, that a greater pro- portional power could be obtained by using bars that were long in comparison with their breadth. (824) The following is another simple and efficacious method of muking artificial magnets, which has been successfully practised by Mr. Barlow. Having occasion for thirty-six magnets, 12 inches long, 1^ inch broad, and -^ths of an inch thick, he placed thirty-six bars of steel of these dimensions on a table, so as to form a square, having nine bars on each side, the marked or north pole of each bar being in contact with the unmarked or south pole. At the angular points of the square, the under edges of the bars were brought into contact, and the external opening thus left was filled up by a piece of iron 1^ inch square, and -rs-ths of an inch thick. The horse-shoe magnet described in the preceding section, was set upon one of the bars, so that its north pole was towards the unmarked end of the bar, and was then carried or rubbed along the four sides of the bars, and the operation was continued till the compound magnet had gone twelve times round the square. Without removing the magnet, each bar was turned one by one, so as to bring their lower sides uppermost, and the horse-shoe magnet was made to rub along the four sides of the square other twelve times. The bars were then highly magnetized, and the whole process did not occupy more than half an hour. (825) This last process is the simplest, quickest, and most efficacious of all the methods that have been described ; so that when a person is in possession of one good horse-shoe magnet, consisting of three or four bars joined together, he may afterwards make any number at the same time : indeed, the more the better. In removing the bars from each other after they have undergone the operation, it is ad- visable to place small pieces of soft iron on the poles of each before they are separated ; for it is a fact well known to experimentalists, that a very considerable portion of the power of a bar is lost at the moment of its separation from others that have been impregnated with it ; nor is it possible by any means to secure the whole of the Magnetism that has been given to it. By following the plan recom- 570 MAGNETISM. mended above, however, it will be found that a much larger portion is retained. The whole of the bars become in fact, as one single magnet ; and the act of separation is, of course, analogous to that of fracture. (826) Magnets should, when laid aside, be placed as nearly as pos- sible in the position which they would assume in consequence of the action of terrestrial Magnetism. If this be neglected, in process of time they will become gradually weaker ; and this deterioration is most accelerated when its poles have a position the reverse of the natural one. Under these circumstances indeed, unless the magnet be made of the hardest steel, it will eventually lose the whole of its magnetic power. Two magnets may also very much weaken each other, if they be kept, even for a short time, with their similar poles fronting each other. This will readily be understood from what has been said with regard to magnetic induction. The polarity of the weaker magnet is rapidly impaired, and sometimes actually reversed. All rough and violent treatment of a magnet should also be carefully avoided : every concussion or vibration amongst its particles tends to weaken its power. (827) Horse-shoe magnets should have a short bar of soft iron, adapted to connect the two poles ; and should never be laid by with- out such a piece of iron adhering to them. Bar magnets should be kept in pairs, with their poles turned in contrary directions, and the dissimilar poles on each side connected by a bar of soft iron, so that the whole may form a parallelogram. They should fit into a box when thus arranged, so as to guard against accidental concussion, and to preserve them from the dampness of the atmosphere. They should be polished, not with a view of increasing their Magnetism, but because they are then less liable to contract rust. Both single magnets and needles have their powers not only preserved but increased, by keeping them surrounded with a mass of dry filings of soft iron, each particle of which will react, by its induced Magnetism, upon the point of the magnet to which it adheres, and maintain in that point its primitive magnetic state. (828) The following simple method of magnetizing steel bars was published by M. P. Elias, of Haarlem (Phil. Mag., vol. 25, p. 348). Fig. 293. MAGNETIZING BY THE VOLTAIC BATTEBY. 571 From 23 to 25 feet of well insulated copper wire are wound so as to form a hollow, very short, but very thick, cylinder. A current from a strong voltaic pair is passed through the wire, and the steel bar to be magnetized is placed in the cylinder in which it is moved up and down to the very ends. When the central portion of the steel bar again occupies the cylinder, the circuit is opened, and the bar, which is now perfectly magnetized, is withdrawn. When the bar is curved in the form of a horse-shoe, it is well to close it with its keeper during magnetizing ; and when a straight one, to provide it at top and bottom with a piece of soft iron. The wire employed is ith of an inch in thickness. The voltaic apparatus is a single pair of Grove's (368), which has -|rd of a square foot of active platinum. The resistance which the current meets with in this battery, is equal to that of a clean copper wire, irs-tli of an inch in diameter, and 13 inches long. The hollow cylinder is 1 inch high ; the bore nearly 1J inch in diameter, and the sides 1| inch thick. By means of this process, a steel horse-shoe bar, weighing 34 pounds, was magne- tized to saturation by one single passage through a cylinder, con- structed purposely for the experiment. This mode of magnetizing is nothing more than the double passing of Duhamel or Michell, by means of galvanism ; and far more powerful, easy, and certain. As in the double passing, the opposite poles of the magnet employed must be kept close together, so as to exert successively their greatest action upon each small part of the bar to be magnetized; in like manner the cylinder is made quite short, that each portion of the bar may experience the entire force of the voltaic element. Instead of a helix, Bottger (Pogg. Ann., Ixvii. 115) recommends a band-spiral of copper, which admits of obtaining the required amount of inductive power with the smallest amount of copper. By means of a spiral, weighing 4^- Ibs., 1 millimetre thick, and 20 broad, a 6-lbs. bar of very hard cast steel, when its poles were united with an armature of soft iron, was magnetized to saturation, as completely as it could have been by any known process of communicating permanent Magnetism, merely by passing the spiral once backwards and forwards along the bar. The same bar without the aid of the armature, even if the spiral were passed over it many times, did not assume more than 0*6 of this power. The celebrated Logeman magnets are made according to the method of Elias ; their strength in proportion to the quantity of steel, is unusually great. PoggendorfF describes a small horse-shoe magnet, weighing rather over a pound, which possessed a constant lifting power of 31i Ibs. (829) Circumstances which affect the Energy of Artificial Magnets. p P 572 MAGNETISM. Quality of steel denomination (such as cast steel, shear steel, blister steel, &c.), temper or hardness, mass and form, are stated by Dr. Scoresby (Brit. Assoc., Cork, 1843) to be among the principal. Prom the varying influence of these circumstances, it is impossible to give a general answer to the inquiry as to the best kind and temper of steel bars for permanent magnets. For large compound magnets, the best cast steel made as hard as possible, is the most effective ; for small magnets and thin compass-needless, cast steel, tempered, is the best. The power of a magnet is essentially depen- dent on both quality and hardness. Scoresby has determined experi- mentally, that proportional magnets of similar steel and temper, are not energetic proportionally with their masses ; in other words, that two magnets, one for instance, in all its dimensions being double that of the other, will not exhibit power corresponding with the masses, or in proportion to the cubes of their lengths ; the proportions instead of being as I 3 : 2 3 = 8, would perhaps be found to be as 1 to 5 or 6 only. From this he infers that magnets cannot be advantageously enlarged to an indefinite extent. Scoresby also found that the same condition did not obtain with straight bars and with horse-shoes ; that whereas with the former, in large combinations, extreme hardness is the most effective ; in horse-shoes, the bars must be annealed at a temperature of about 505, to give them their greatest lifting powers. (830) Directive Power -of Magnetized Bars. For ascertaining this point, Coulomb employed his balance of torsion (56). Dr. Scoresby, however, recommends as sufficiently exact for practical purposes generally, the method of deviations. The bars to be examined and compared are laid in a horizontal position, and at right angles to the magnetic meridian, so as to be precisely in the plane of the magnetic equator of the earth, in order that they may receive no inductive influence whatever from terrestrial Magnetism, and thus exhibit only their own actual energy. A compass needle is suspended at a given distance, say five or six times the length of the compass needle, and the tangents of deviation produced by the different bars, provided they are of the same length, afford a satisfactory estimate of their proportional powers. In order to ascertain the relative strength or tenaciousness of mag- netic bars, compass needles, &c., Scoresby first ascertains their direc- tive energy separately, and then binds them up into a bundle with their corresponding poles in contact ; he then takes them apart, and again determines their directive energy. Sometimes the bars have their poles reversed by this treatment. In this way, surprising differences were detected in bars apparently similar. The following DB. SCOBESBY'S INVESTIGATIONS. 573 is an example : 32 large uniform plates of cast steel, tempered throughout their length, of 2 feet long, 1J inch broad, and 042 inch thick, and weighing on an average 2,869 grains, were each magnetized to saturation by his modification of Knight's process. The mean power of deviation on a compass at one length distance as tried separately, was 16 10', the weakest bar causing a deviation of about 15, and the strongest about 18 30'. They were all then placed for a short interval in one fasciculus with their similar poles together, and before being entirely separated, the several plates were alternately changed as to positions, and trans- ferred to different parts of the mass. The whole series being now separately examined again, the average deviating power was found to be reduced to 7 35', but the amount of deterioration suffered by the individual plates was singularly different, some retaining a deviating power of 10, others retaining only from 2 to 4, and some losing their power altogether. Yet these bars were constructed out of the same mass of steel, wrought by the same hand, and tempered pre- cisely alike ; and the manufacturer was probably not at all aware of the difference, nor could he by any decided or satisfactory means, separate the good from the bad. (831) For testing the bars or needles of compasses of uniform, or nearly uniform dimensions, Scoresby employs a powerful, perfectly hard bar-magnet, of length and width corresponding pretty nearly with the dimensions of the plate to be tried. The test magnet he usually employs consists of a rectangular prism of best cast steel, thoroughly hardened throughout the mass, 6 inches in length, and | an inch square. Its power is great, occasioning a deviation of 38 Q to 39 C on a compass at 12 inches, or two lengths distance. When employed for testing, its power is first reduced by laying it on a similar bar with corresponding poles coincident, which brings its deviating power down to about 33 or 34. In this reduced state, the testing of any number of compass needles, or other small bars produces no further deterioration, so that the degree of violence to which each is subjected, may be considered as precisely similar. The bars to be tried after being thoroughly magnetized, are laid in suc- cession upon the test bar, with similar poles in contact. The mere momentary contact of the two sides of the plate is sufficient, care being taken to bring the plate or bar evenly down upon the test magnet, without sliding or friction. The time required for the whole routine of this process, is only about a minute to a minute and a half for each bar ; and the precision of the result is such, that the whole series, though amounting to several dozens, can be satisfac- torily arranged in the order of their relative tenaciousness,or strength, p p 2 574 MAGNETISM. in a numerical succession. The bars best adapted for compasses, are those in which the product of the forces of the original power and the reduced power is greatest. (832) Ratio of Power to Mass. Captain Kater had deduced from his investigations on " the best kinds of steel, and form for a compass needle " that the directive force in needles of nearly the same length and form is as the mass. Scoresby's experiments do not confirm this, but they show on the contrary, that the ratio of augmentation of power diminishes as the thickness increases. The softer the metal, the less its tenacity, and he found an undeviating accession of power, or capacity with the increase of hardness. (833) Steel for Magnetical Instruments. -It results from Dr. Scores- by's experiments that the system prevalently acted on in the construc- tion of magnetical instruments generally, is grounded on an erroneous supposition, as to the capacity of steel of different degrees of hard- ness for the magnetic condition. It was imagined that a moderate hardening of the ends only of bars destined for magnets w r as neces- sary, but this mode of tempering possesses no advantage as to capa- city, whilst it has much disadvantage as to tenaciousness, except in very thin bars. Thus, Scoresby could only give a very weak power to a large bar 3 feet long and 3 inches wide, made out of a flat bar of iron, steeled and tempered at the ends. A moderate hardening of the steel throughout was abundantly proved by Scoresby to be the most efficacious. As a general proposition also it is erroneous to suppose that perfectly hard steel bars, have an inferiority in capacity for the magnetic condition. It was found that in all masses above the weight of 130 grains, perfectly hard steel was superior in capacity to soft steel, in masses above 250 grains' weight, superior to bars tem- pered only at the ends, and above 400 grains, superior to any of the kinds of tempering with which it was compared. Scoresby, moreover, found no difficulty in magnetizing to any degree of energy very hard bars, even when of considerable thickness. (834) The Magnetic Test applicable to the Determination of the Quality of Steel Bars. Dr. Scoresby examined in the state as nearly as possible of raw material, both when soft, and when hardened at a white heat in salt water, bars of common spring steel, single shear steel, double shear, blister, and common cast steel, perfectly similar (as to weight and size), and the results revealed such a relation between the magnetical properties of the several bars, and the respective qualities of their denomination of steel, as to show that the mag- netical properties may be rendered available not only for ascertaining the degrees of carbonization, but for the determination of the essential quality of the iron out of which it may have been manufactured. He DR. SCOHESBT'S INVESTIGATIONS. 575 adds : " It is not perhaps unreasonable to expect, that were all the varieties of magnetic capacity in each denomination of steel, and in each quality as respects the iron out of which the steel is * converted,' experimentally ascertained, a strictly scientific process of testing founded on these principles, might be devised a process which might possibly exhibit results, if not as exact, at least as conclusive in cer- tain most important relations of value in the metal, as are obtained by the beautiful process of assaying." Scoresby found a constant relation between the ductility of iron, and its magnetic capacity. The best iron possesses the highest magnetic quality, and therefore the best steel ; the cast steel for example converted out of the best Swedish iron, such as that known technically, with reference to its mark, as "hoop L" would be expected to possess higher magnetic properties than the cast steel made out of iron of acknowledged inferiority of quality. (835) Construction of Magnetic Batteries By combining the prin- ciple .of the diffusion of energy by the combination of separated plates, with that of the selection by testing of powerful and tena- cious plates, very powerful magnetic batteries may be constructed. When the plates were of a spring temper only, Scoresby found that a limit to the number that could usefully be combined was soon at- tained; but with hard plates, in which the power of sustaining violence was very great, he has constructed magnetic batteries of 15-inch plates, the power of which has gone on efficiently accumulating to the amount of 192, the power being five or six times as great as could possibly be obtained in any extent of combination whatever, in bars of similar length of the usual kind employed. He found it impossible, by the ordinary process, to communicate the full charge of magnetic influence to very hard shear steel, or cast steel bars, or such as were best suited for retaining it, and therefore best for the manufacture of compasses ; but by interposing thin bars of soft iron between the charging poles of the magnet, and the steel to be mag- netized, he could give a remarkably strong charge by a single stroke of the poles of the magnet over the bar, (836) Laws of Magnetic Combinations. The following general results of a long and laborious course of experiments, conducted by the same indefatigable magnetician, are of too high a practical value to be omitted. It was established: 1. That any single bar is proportionally more powerful than two or more corresponding and equal bars. 2. That a combination of magnetic bars is always more powerful than any single bar of precisely the same steel of equal weight. 3. That the absolute gain of power in the combined mass by each additional plate or bar progressively diminishes. 576 MAGNETISM. 4. That, beyond a certain extent, continued additions to a powerful combination of bars is not only not beneficial, but posi- tively injurious. 5. That a certain amount of deterioration ; in the permanent energy of all the bars in combination takes place by every addition of power to the mass. 6. That the measure of tenacity or strength of a plate may be tested by its relative deterioration when combined. 7. That though a weak plate may have its power totally destroyed in a large combination, it may be capable of considerable power and retentiveness of energy in a smaller combination. 8. That besides a permanent deterioration of power, magnetic bars suffer by combination a certain amount of transient deteriora- tion, which they recover on separation. (837) Separation of the Combined Bars by Limited Spaces. The following results were arrived at : 1. That the effect of combination is increased in proportion as the spaces between the plates are enlarged. 2. That by thus preventing the plates from coming into contact, a larger number of plates may be advantageously combined. 3. That in proportion as the density of the mass is thus diminished by separation, the amount of permanent deterioration in the several plates is also diminished. 4. That when separated by discs or blocks, weaker plates can be combined advantageously to a much greater extent than when in contact. 5. That an advantage is gained by a partial separation, such as that in the middle of the plates, but the effect is not so good as when the separation is complete. (838) Hardness and Temper. It was established : 1. That the relative powers of combinations of magnetized plates or bars of steel, as well as those of simple pieces, are greatly affected by differences in the state of the steel, both as to its quality and temper. 2, That various degrees of hardness have an influence on the magnetic capacity and energy of steel, differing both in the nature and quality, in proportion to the magnitude of the masses em- ployed ; so that the kind of tempering which may exhibit superiority with a certain mass, may be greatly inferior in other magnitudes. 3. That though with certain limited masses, partially tempered or slightly hardened bars have a pre-eminence, nevertheless, in fixity or permanence of power, the softer magnets are always inferior. 4. That under certain conditions, and with small combinations, DB. SCOKESBY'S INVESTIGATIONS. 577 an advantage is gained by heating the middle of thoroughly tempered plates, and so softening them. 5. That for all practical uses, the limits of hardness may be con- sidered as comprised between a brittle hardness like that of files, and that of an elastic or spring temper. 6. That in sustaining power, hard bars have a superiority ; and that for heavy bars, the greater the hardness the more powerful the magnet. 7. That in the construction of magnetic batteries, the steel should be similar in quality throughout, and the bars as near the same size as possible. (839) Qualities of Steel. Dr Scoresby ascertained : 1 Q That the magnetic capacity differs in each denomination of hard steel, being the lowest in those kinds susceptible of the greatest hardness. 2 C . That in thin and medium plates made quite hard, shear steel possesses a higher capacity, and exhibits a greater energy in the in- dividual plates, than blister or cast steel, and cast steel the least of all. 3. That the comparative magnetic powers of different denomina- tions of steel change their relation to each other in combination; each denomination under powerful combinations exhibiting a degree of effectiveness, according apparently, to its susceptibility for hardness. 4. That cast steel being capable of the greatest hardness, is as a denomination, most effective in large straight-bar magnets, whether consisting of single massive plates, or of combinations of thin plates. 5. The better the iron out of which the cast steel is made, the better the magnetic properties of the steel ; the harder the steel also, the better for magnets of great energy, but for single thin plates cast steel from Bradford iron is the best. (840) Hard thin plates gain in power by boiling in linseed oil, while medium or thick plates lose by a similar treatment. The tena- ciousness of the magnetic condition is much impaired by annealing large thick straight bars or combinations, but the result is different with thin best cast steel bars. . (841) Although no universal answer can be given to the question What is the best kind of steel, and the best kind of hardness, or mode of tempering for magnetical instruments ? yet the following summary deduced by Scoresby, from his innumerable experiments, may prove very useful to the practical magnetician. Eor all large or massive single and compound magnets of the straight-bar form, the lest cast steel made quite hard ; for horse-shoe 578 MAGNETISM. magnets, if single, cast steel annealed from file hardness at a tem- perature of about 550, or shear steel a little reduced ; and for com- pound horse-shoe magnets, cast steel annealed at 480 to 500, or shear steel perfectly hard : for compass needles, if single and heavy, such as are suited for stormy weather, hard cast steel ; if light or of moderate weight, whether single or compound, the best cast steel annealed at 500 or 550, or hard shear steel, or hard cast steel from Bradford iron ; and for very light needles or other small magnets the best cast steel annealed at the heat of boiling oil. (842) Measure of Permanency. The degree of retentiveness of magnets is directly as the hardness, and inversely as the energy. The loss of energy by time in unprotected magnets is much more consi- derable at first than subsequently. The retentiveness of combina- tions of thin bars is quite equal to that of single massive bars, espe- cially if the plates be separated by a little distance ; and soft magnets if properly protected, are as enduring as hard ; and when the maxi- mum power of a magnet is slightly reduced by unfavourable proximity to another magnet, the resulting energy is still less influenced by time. (843) Cast Iron Magnets. The magnetic capacity and retentiveness of cast iron, though considerable, is greatly inferior to that of pro- perly hardened steel. The better the quality of the cast iron, and the more rapidly the casting is cooled, the more favourable the metal for Magnetism. Scoresby found that good cast iron was quite equal to soft steel for single plates, and much superior for large combina- tions. Hard thin bars of No. 1 pig metal are capable of forming powerful compound bar magnets, quite as strong as solid massive bars of ordinary steel, if only hardened slightly at the ends. Mr. Hearder constructed a compound cast iron horse-shoe magnet, which was capable of lifting 60 Ibs., and the power was very permanent. It was composed of 24 bars of the best pig-iron, as hard as green sand could make them. The bars weighed 3 Ibs. each, the weight of the combined series being about 70 Ibs. The cost of this magnetic battery was not more than twelve or fourteen shillings, whereas a steel magnet of equal power would cost two or three pounds. (844) Useful Applications of the Magnetic Powers. Among these may be mentioned the magnetic steel masks, worn by the Sheffield needle-grinders to arrest the minute particles of steel which are con- stantly flying from the wheel, and which would otherwise enter their lungs. These masks are found, after the day's work, fringed with fine particles of steel a proof of their protecting power. Magnets are also used in paper mills to abstract from the pulp the little par- ticles of iron which arise from the abrasion of the machinery, and LAWS OF MAGNETIC FORCE. 579 which, under the form of peroxide, frequently disfigure the commoner kinds of paper. The attractive power of magnets is also employed for abstracting the filings of iron from among the dust of other metals of a more valuable character. An exceedingly ingenious appli- cation of the magnetic influence to the determination of the thickness of rocks was made by Dr. Scoresby. It is founded on the method of deviations (83), the direction of the needle obeying the same laws, whether the forces act in it merely through an interval of air, or through rock, iron, or other materials. We have seen (830) that the deviations of a small compass needle by the action of a magnet placed in the line of its centre at right angles to the meridian, may be taken as a measure of the force of the magnet ; if, therefore, we determine beforehand the amount of deviations for different distances between the magnetic bar and the compass needle, we can apply the instru- ments to the determination of the thickness of any substance placed between them. The needle is placed on one side of the rock, and the magnetic bar perpendicular to its centre on the other, and the amount of deviation of the former is compared with the table of de- viations deduced from the preliminary experiments. In this way Dr. Scoresby states that he can determine the thickness of 2 or 3 feet of rock to ith of an inch, and that he can measure distances of from 125 to 150 feet with great approximation to truth. He found that neither iron nor ironstone interfered with the results, for on placing the magnets and the needle one each side of a locomotive engine, the effect was not interfered with. The application of this method to mining operations, and especially to tunnelling, is likely to be very valuable. (845) Laws of Magnetic Force. This subject has occupied the attention of many of the most profound mathematicians. Newton inferred " from some rude observations" that the power of a magnet decreases not in the duplicate but almost in the triplicate ratio of the distance. Hawksbee's experiments {Phil. Trans. 1712, vol. xxvii.) gave a law of force which varies as the sesquiduplicate ratio of the distances, and his results were subsequently confirmed by Whisfcon and Taylor (Phil. Trans. 1721). Muschenbroek's researches, made a few years later, led him to the conclusion " that no assignable pro- portion exists between the forces and the distances, whether of attrac- tion or repulsion." Mayer and Martin, who wrote on the subject between the years 1750 and 1760, both came to the conclusion that the true law of the magnetic force is identical with that of gravita- tion, and that in the previous experiments of Hawksbee and others, proper allowance had not been made for the disturbing changes in the magnetic forces so inseparable from the nature of the experi- 580 MAGNETISM. ments. Lambert's researches* (Historic de VAcademie Roy ale des Sciences, Berlin, 1776), which were described by Dr. Robinson as worthy of Newton himself, determined that the action of Magnetism on a magnetic needle, considered as a lever, is proportional to the lines of the angle of obliquity of its direction ; and that hence the effective force which operates in restoring the needle to its meridian when drawn aside from it, is directly as the line of the angle of its deflection. The law of force was found to be the inverse duplicate ratio of the distances. The directive or polar force of a magnet upon a small needle, was shown by Lambert in a subsequent memoir to be " as the absolute force or magnetic intensity of the particles directly, and as the squares of the distances inversely." Lambert's deductions were confirmed twenty years later by Coulomb, by means of his torsion balance, and more recently (about the year 1817), by Pro- fessor Hansteen, of Christiania. (846) Amongst the latest inquiries are those of Sir "W. Snow Harris. (Edirib. Phil. Trans., 1829 ; and Rudimentary Magnetism, Part III.) He first investigates the laws and operation of the elementary forces of induction the essential function of all magnetic development. When a bar of soft iron and a magnetic bar are opposed to each other, the near pole of the latter induces on the near parts of the former, a polarity the reverse of its own, and a polarity of a similar nature on parts at a distance. The temporary polarity of the iron reacts on the magnet by a kind of reflection or reverberation, inducing on it a new temporary polarity of the same character as its own permanent one ; this new force again reacts on the iron, and thus a series of magnetic waves is produced, each becoming weaker until they vanish into rest. Magnetic attractions and repulsions being the results of this inductive reverberation, the study of the laws of the elementary force of induction became necessary as a preliminary to the investigation of the laws of the magnetic force generally. (847) The apparatus employed by Harris was his Hydrostatic Balance, which he found well adapted to the measurement of very small magnetic forces. It appears that there is a limit in respect of the elementary inductive forces, different for different magnets, and varying with the magnetic conditions of the experiment ; but as a general rule, it was concluded, that the elementary force of magnetic induction is as the Magnetism directly, and from the or square root to the | power, or sesquiduplicate ratio of the distance inversely. Applying these results to the explanation of the different laws of * For a full discussion of these profound researches, the reader is referred to Sir Wm. Snow Harris's Rudimentary Magnetism, Part III. HARRIS S INVESTIGATIONS. 581 force, deduced experimentally by Lambert, Coulomb, and others, Harris shows that their seeming contradictions and differences may be reconciled, and that the deduction of Brook Taylor, " that mag- netic attraction as commonly observed, is quicker at greater distances than at small ones, and different for different magnets," is a necessary result of the elementary laws of Magnetism. (848) Law of Force in different Points of a Magnetic Bar. Harris also applied his Hydrostatic Magnetometer to the determination of this problem. The investigation had previously been made by Coulomb, by observing the vibrations of a delicately suspended magnetic needle when brought into various positions, in respect of a long magnetic wire, placed vertically in the magnetic meridian, the dissimilar polarities being opposed to each other. The force due to any given point of the magnetic wire was considered to be propor- tional to the square of the number of vibrations ; the constant and previously determined force, by which the needle vibrated when away from the wire, being deducted. In this way Coulomb obtained as a curve of intensity, a logarithmic curve, the ordinates of which a b c, &c., are in geometrical progression, while the abscissae C a, C 5, Fig. 294. &c., corresponding to these ordinates, are in arithmetical progression, From the many difficulties attending this method of examination, and from the irregular distribution of the Magnetism in the bar, arising from the imperfection of its temper, &e., it is to be doubted whether the true law of intensity is really represented by this peculiar curve. Harris examined the forces at successive points of an accurately divided, powerfully magnetized, and equably tempered bar through a small cylindrical armature of soft iron; the square root of the forces taken in degrees on the graduated arc of the balance being considered to represent very nearly the comparative magnetic development. His results showed that the Magnetism, in different parts of a regularly tempered and magnetized steel bar of uniform texture is directly as the distance from the magnetic centre, 582 MAGNETISM. whilst the reciprocal force between any given point and soft iron, is as the square of the distance from that centre. (849) Law of Magnetic Charge. The amount of Magnetism in a bar of well tempered steel, under a given attractive force, is indepen- dent of the mass of the magnetized body. This, Harris proved by a very beautiful experiment. He placed between the magnet M, Fig 295, and the trial rod, , of his magnetometer a small cylinder of Fig 295. soft iron, AB, into which could be inserted as a core, a closely fitting solid cylinder, a ft, also of iron. The magnet was placed at a con- stant distance below the cylinder, and the attractive forces on the trial rod were measured when the interposed cylinder was hol- low, when its core was in its B place, and when it was drawn out __jD) (as represented by the dotted lines in the figures), so far as to double the extent of the inter- posed surface ; when the joint cylinders were taken together as a mass, and when the interior cylinder was altogether removed, the force was in both cases the same, amounting to 10, but when the core was drawn out so as to extend the surface to the greatest limit, the intensity fell to 5, being diminished one-half. Hence Magnetism, like Electricity, is only influenced by surface, and a hollow steel cylinder may be made to acquire as much magnetic power as a solid cylinder of the same dimensions. (850) In order to determine experimentally the intensity of Mag- netism in respect to the quantity developed, and the extent of surface over which it is dispersed, Harris surrounded a soft iron bar with three distinct and similar coils of wire, which could be connected with three distinct and similar voltaic batteries ; he then examined the attractive forces on the trial cylinder of the magnetometer, when the iron rod was magnetically excited by one, two, and three of the coils ; the batteries being precisely similar, were assumed to develope each when taken singly, the same amount of magnetic force, and it was found on trial that the intensity was very nearly as the square of the quantity of Magnetism, being precisely the same law as that deduced for electrical charge, and therefore to obtain the relative quantity of Magnetism in operation we must take the square roots TYNDAL'S INTESTIGATIO^S. 583 of the respective intensities, the magnetic surface and all other things being the same. "We have no experiments to show whether this law holds good with dissimilar magnetic bodies of variable size and surface, though it is probable that the law of surface is the same with that of Electricity, and that the intensity is as the square of the surface inversely, i e., that the same quantity of Magnetism developed upon a doubled surface would have only |th the intensity. (851) The latest experimental investigation of the laws of Mag- netism is that of Tyndal (Phil. Mag., N. S. vol. i. p. 295). The subjects of his inquiry were : 1st. To determine the general relation between the strength of a magnet, and the mutual attraction of the magnet and a mass of soft iron when both are in contact. 2nd. To determine the same relation, when the magnet and the mass of soft iron are separated by a fixed distance. 3rd. A constant force being applied to the mass of soft iron, in a direction opposed to the pull of the magnet, to determine the con- ditions of equilibrium between this force and Magnetism, when the distance between the magnet and the mass varies. 4th. To determine the general relation between force and distance, *. e., the law according to which the magnetic attraction decreases when the distance is increased. (852) The following are the principal results : 1st. The mutual attraction of a magnet and a sphere of soft iron, when both are in contact, is directly proportional to the strength of the magnet. 2nd. The mutual attraction of a magnet and a sphere of soft iron, when both are separated by a small fixed distance, is directly pro- portional to the square of the strength of the magnet. 3rd. The mutual attraction of a magnet of constant strength, and a sphere of soft iron, is inversely proportional to the distance between the magnet and the sphere. 4th. "When the distance between the magnet and the sphere varies, and a constant force opposed to the pull of the magnet is applied to the latter, to hold this force in equilibrium, the strength of the magnet must vary as the square root of the distance. 584s MAGNETISM. CHAPTEE XVI. MAGNETISM CONTINUED. Terrestrial Magnetism Magnetical instruments The land compass The mari- ner's compass The Admiralty compass Harris's compass Local attraction in ships Scoresby's investigations The dipping needle The variation compass The declination magnet The horizontal force galvanometer The vertical force galvanometer. (853) THE tendency of the magnetized needle or bar to turn nearly to the north and south, when left at liberty to move freely on a pivot, or otherwise suspended so as to allow of freedom of motion in a horizontal plane, is derived from a force supposed to reside naturally in the earth. The earth in fact must be regarded as a magnetic mass, operating on the magnetic needle, precisely in the same way as one magnet operates upon another.* If we communicate Magnetism to a steel bar which in its previous condition had been exactly equipoised when suspended freely from its centre, we shall find that it no longer maintains its horizontal position, but assumes an oblique one, being inclined with its north pole downward at an angle of about 69. If we take this needle to different parts of the earth, we shall find its inclination to be different in different parts, the angle becoming greater and greater as we approach the poles, and less and less as we approach the equatorial regions. (854) The following simple method of constructing a magnetic direction needle is given by Dr. Scoresby (Magnetical Investigations, vol. ii.) Two pieces of watch spring, each 2 inches in length, are slightly heated in the candle, and then coated on the concave side with the wax of a common taper ; the waxed surfaces are then placed * The total magnetic power, or " moment of Magnetism" of the earth, as com- pared with that of a saturated steel bar, 1 pound in weight, is calculated by Gauss to be as 8,464,000,000,000,000,000,000 to 1, which, supposing the magnetic force uniformly distributed,, will be found to amount to about 6 such bars to every cubic yard. TERRESTRIAL MAGNETISM. 585 Fig. 296. together, and the two pieces bound closely together by thread. A fine sewing needle is introduced as an axis between the two plates midway from each extremity. A piece of brass wire of the thicker size employed for the pianoforte, is bent into the form of a staple, the ends being turned up to receive the axis of the bar. The watch-spring needle is adjusted by a minute quantity of sealing- wax, and the centre of gravity adapted to the axis by accurately straightening the plates with the fingers ; on magnetizing the needles, and suspending them by a silk fibre in a large jar, it acts beautifully as an inclination or dipping needle ; any deviation from torsion of the silk may be detected by comparing it with a hori- zontal needle placed at a little distance, and may be avoided by suspending a weight equivalent to that of the needle from the fibre previous to using it. (855) The analogy of the earth to a magnet is beautifully illus- trated, by holding a light and sensitive magnetic needle over different parts of a magnetic bar, laid horizontally on a table. The bar should be about 30 inches long, and powerfully and equally magnetized ; the needle will assume the various positions indicated in Pig. 297. Fig. 29 T. \ \ \ Thus in the magnetic equator of the bar C it will be exactly hori- zontal ; at N and S it will hang vertically, the N pole downwards at S and the S pole downwards at N, between the poles and the equator ; the needle will take up different positions as it is moved along, becoming less and less oblique as it passes from the former to the latter, precisely as it would do if carried from the polar to the 586 MAGNETISM. Fig 298. equatorial regions of the earth ; lor a bar magnet may be en- closed in a light wooden or pasteboard sphere, as shown in Fig. 298, and on passing a short dipping needle over the exterior surface of the globe, from pole to pole, the mag- netic conditions of our planet may be still more strikingly illustrated. (856) "We have seen that when a piece of soft iron is brought into the neighbourhood of a magnet, it acquires by induction temporary magnetic properties; now it has long been known that rods of iron that have been kept for a long time in a fixed position acquire magnetical polarity : this property they have derived from terrestrial magnetic induction. The position most favourable for developing Mag- netism in an iron rod, is that of the dipping needle, and accordingly we find that old kitchen pokers that have been standing for many years nearly in that position have become feeble magnets, their lower ends being JS". poles ; any piece of soft iron however, when held in the position of the dipping needle, is pro tempore a magnet. The fol- io wing experiments of Scoresby are instructive on this point (Magn. Invest, vol. i.). Lay a compass very near the edge of a square table on the E. or W. side of it, so that the direction of the needle is parallel to the proximate side of the table ; adjust the compass with its needle and N. and S. line in correspondence, and holding the kitchen poker horizontally in the direction of the E. and "W. points of the compass, strike it a blow or two with a hammer to neutralize any Magnetism it may have ; the poker whilst held in a vertical posi- tion being now brought within 3 or 4 inches of the compass E. or "W. of its centre, will strongly attract the IN", pole when the upper end is on a level with the compass, and repel the same pole when the lower end is raised to the same level, indicating a southern polarity in the upper, and a northern in the lower. The evanescent character of this induced Magnetism is further shown by placing the knob end of the poker held horizontally, against the edge of the table, with the compass about 3 inches within ; raising the point with one hand, whilst the knob is kept steady against the table with the other (like a ball moving in a socket) ; the JXT. pole of the needle will gradually recede till the poker becomes vertical, and then lowering TEEEESTEIAL MAQKETISM. 587 the point, the N. pole will gradually approach the knob till the poker becomes again vertical, in the direction opposite to its former position ; thus showing that the knob had obtained northern polarity, when the bar was vertical with the knob downward, and southern polarity with the knob upward. By alternately raising and depressing the point of the poker, the needle may be kept in oscillation, and even in un- ceasing rotation if the movements are consistently continued. The point of the poker being down, and the rod in a vertical position, the quantity of magnetic action on the needle diminishes as the poker is brought to a horizontal position ; if the poker be moved in an E. or "W. plane, the action on the needle is nil when it is horizontal ; but if it is moved in a N. or S. plane, and traversed northward of the compass, it will pass beyond the horizontal about 20 before the same neutral effect takes place. The kitchen poker should be used in these experiments, as the parlour poker with a view to polish and firmness is usually steeled. The influence by which the Magnetism of iron bodies is thus spon- taneously elicited, acts in a direction, not like gravitation, perpendi- cular to the earth's surface, but in a direction inclined in the same degree as that of the earth's magnetic action, and the plane of no attraction is at right angles to the line of the dipping needle. (857) Soft iron may even be made to acquire temporary lifting power under the influence of terrestrial magnetic induction ; thus Scoresby found that a piece of annealed iron plate, 15 inches long and 1*5 inch broad, with a smooth and polished end, when held in the position of the dipping needle could support an iron nail weighing 3 grains, and a thicker rod weighing 3,830 grains supported a nail weighing 10 grains ; by combining a dozen such plates some further capabilities were elicited, but by no means corresponding with the increase of mass. By bending a piece of annealed iron plate 15 in- ches long and f-inch wide, reversely at the end, in the form of an architectural ogee, and suspending it by silk fibres, a meridional iron needle was made, that assumed true magnetic direction (though quite free from Magnetism), and was found, moreover, to obey extra- neous influences precisely like a steel magnetic needle. (858) Dr. Scoresby gives (" Magnetical Investigations," vol. iii.) the following general results of a very extensive investigation into the phenomena of terrestrial induction. 1. That true Magnetism is induced in soft iron by terrestrial induction. 2. That in masses of uniform temper and quality, the neutral plane is parallel with a plane at right angles to the dip, and obliquely through, or near to, the centre of gravity. Q Q 588 MAGNETISM. 3. That in spherical and other formed bulky masses, the magnetic axis coincides with that of the earth, the chief energy being ab the extremities of such magnetic axis, and the neutral plane at right angles to the axis in the middle ; but in bars and other elongated forms, the direction of the magnetic forces follows the course of the longitudinal extent of the bars, exhibiting the two polarities in maximum degree, at the opposite ends of the bar, with a neutral plane in the middle. 4. That different kinds of iron, steel, and iron ores, differ in their respective capacities for terrestrial Magnetism ; and that the capacity of each is influenced by its temper, hardness, and mass. 5. That fascicule of thin plates have developed in them a some- what higher power than solid masses of like dimensions, but that a progressive diminution of power attends the combination of plates this being more marked in pure annealed iron than in cast steel. 6. The magnetic energy of a mass of iron under terrestrial in- duction, is the resultant of two antagonistic forces the developing force of the earth, and the tendency of the molecular Magnetism of the metal to a state of neutrality; hence bulky masses of iron receive inferior polarity to elongated masses of equal weight, and hollow shells and solid shots have equal magnetic development ; this, how- ever, is only true in certain special cases, when similar qualities of metal are compared. 7. That the Magnetism terrestrially induced, becomes like that in permanent magnets, so highly concentrated at the extremities of elongated bars or plates of malleable iron, as to yield an attractive power sufficient to lift small portions of iron like a feeble magnet, and a directive power adequate to correct adjustment of position, in a plate duly suspended like the needle of a compass. (859) The effects of percussion and of flexure in communicating Magnetism to soft iron bars while held in a vertical position, is very remarkable, and well worth stating, from its bearing on the important subject of the Magnetism of iron ships. A kitchen poker carefully deprived of Magnetism, by giving it a few smart blows while held horizontally E. and W., affected the compass needle at a given distance, when held vertically, point upwards, 21 ; in the position of the dip, 22. A smart blow with the hammer on the square side of the lower end, increased the upright deflecting power of the knob from 21 to 35 ; six blows increased it to 44, and gave it when in a horizontal position a deflecting power of 26. On inverting the poker, a single blow not only neutralized its previous Magne- tism, but changed the poles to an extent of 19 of deviating power ; and six more blows gave it a horizontal deflecting power of 27. The poker now being held horizontally east and west, a single blow TEEEESTEIAL MAGNETISM. SCOEESBY'S EESEAECHES. 589 reduced its power to 3. The effects were increased when the poker was hammered while held in the position of the dip. (860) The following experiments are instructive as illustrating the effect of percussion and flexure : 1. Lay a small delicate compass needle on a table about 3 inches from the E. or W. side, the needle being adjusted to zero. Hold an iron poker (kitchen) point upwards, and strike it several smart blows on the top with a hammer ; now turn it point down- wards, and bring the knob against the edge of the table near the compass little or no action will take place, because although a little northern polarity will have been communicated to the knob by the percussions, still the position in which the poker is now held will tend to produce in the knob a southern polarity by terrestrial induction, and the one will neutralize the other. Should, however, the N. pole of the compass be attracted, a few more blows with the hammer on the point (point upwards) will destroy this attrac- tion. Whilst now the knob of the poker is on a level with the compass (point downwards), let a smart blow be struck on the top> the needle will start aside or whirl round the N. end, being attracted by the poker as if acted upon by some magical power. 2. Provide two or three plates of thin sheet iron, about 18 inches long, 2 broad, and the thickness of a shilling. After having annealed them by heating them to redness, and allowing them to cool gradually, tie them flat in a bundle in brown paper, one end being marked. Destroy all Magnetism by moderate flexure without permanent bending, the handle being held horizontally E. and W. till there is no action on the needle. Hold the plates verti- cally, marked end downward, and give them a moderate flexure both ways, the marked end will now repel the north pole of the needle, probably 25 or 80. Now bend the plates with the marked end upwards, and the polarity will be reversed. Next hold the plates E. and W., and bend them backwards and forwards ; the polarity will, in all probability, be wholly, or nearly wholly destroyed. Scouring, filing, polishing, or any other process acting on the surface of a piece of iron or soft steel, has a corresponding magne- tizing or demagnetizing tendency with reference to the position of the metal when thus operated on. (861) On this principle, iron rods may be completely deprived of Magnetism. "We have only to strike them a few blows while held in a horizontal position E. and W., testing them from time to time with a compass. For demagnetizing thin plates of iron which might become bent by hammering, the ap plication tfflexure\& quite as effective and much readier. Scoresby magnetized an unannealed piece of iron Q Q 2 590 MAGNETISM. plate, 18 inches long, 1 inch broad, and *12*12 inch thick, as highly as possible, and found that six smart blows with a hammer, while the plate was in an upright position, 1ST. pole upwards, were sufficient to disperse the Magnetism. (862) When steel bars are hammered while held vertically or in the position of the dip, they acquire permanent Magnetism, but the magnetic lifting power is increased 30 to 1 when they are hammered while resting on the top of an iron bar also held vertically. Powerful magnets may thus be formed. Thus, Scoresby took 6 bars of soft steel, and having magnetized them by percussion, 2 of them con- nected at their extremities by two short pieces of soft iron, in the form of a parallelogram, were rubbed with the other 4 bars after Canton's method (816), by which their original power was greatly increased. These being substituted for two of the bars of the operating set, were applied with increasing efficacy to the new parallelogram ; and the latter, after being thus strengthened, became effectively available for the improvement of the third pair of the series. After treating each pair of bars in regular succession, and through several repetitions of the process, the whole of the bars were found to be in a very high degree magnetical, apparently to the extent of their capacity, each pair readily lifting a weight of above 8 ounces. (863) The Land Compass. The needle is placed upon a point in the centre of a brass or wooden box, furnished with a graduated limb, and sometimes the ends of the needle are made to carry a vernier scale in order to bring down the readings to a minute or lower. The box which may be square, round, or octangular, is furnished with two straight edges of brass, or index marks to set to any proposed line, and sometimes with sights, the top being covered with glass to pre- Fig. 298. vent the needle from being dis- turbed by the action of the air. There are also two small pieces of brass, one of them turning on a fixed point, seen in the figure, which is used to check the oscillation of the needle, by pressing upon the upper end ; the ring at the other end of the H| lever is raised till it touches the 1 needle which is thereby rendered W steady ; the lever is then let down, and the needle left to find its proper direction. In the figure the needle is mounted with a card THE MABITTER S COMPASS. 591 divided into points and quarter-points of the compass ; the N. and S. points being made to correspond very exactly with the needle ; in this form the general direction of an object will be known by observing its bearing, which will always arrange itself according to the magnetic meridian of the place of observation. (86-1) The Mariner's Compass. In its ordinary form it consists of a magnetic needle attached to a circular card, the surface of which is divided into the four cardinal points N., S., E., W. ; these again are subdivided into 32 points which are called in nautical lan- guage 'Rhombs^ from the Greek word gs/^jSw, to turn. In the azimuth compass the circle is divided into 360 parts. The position of the needle is usually estimated in terms of the 32 points, but for refined purposes it is found better to estimate the angular deviation of the needle from the line of the magnetic meridian, in degrees and minutes taken in reference to either the N. or S. pole of the card Thus instead of the Ehomb S. W., we say S. 45 W. ; instead of E.N.E., we say N. 6730'E., and so on. The card (Fig. 299) is balanced Fig. 299.. upon a pivot fixed in the bottom of a circular box, and the top of the box is a plate of glass for protecting the needle from the motion of 592 MAGNETISM. the air. In Fig. 300, A B is the compass box, suspended within a larger box P Q, upon two concentric brass circles or gimbals, the outer circles being both fixed by horizontal pivots to the inner circle which carries the compass box ; the two axes upon which the gimbals move being at right angles to each other. The effect of this construction is that the compass box AB, will retain a horizontal position during the motions of the vessel. The instrument Fig. 300. shown in the figure, is the Azimuth Compass; it is fur- nished with sights, GrH, through which any object may be seen, and its angle with the magnetic meri- dian increased. For this purpose, the whole box is hung in detached gimbals, CD, EF, which turn upon a stout vertical pin, seen above S. In this compass the card is divided on its rim into 360 , but the divisions are more frequently placed on a light metallic rim which it carries. The eye is applied to the sight H, which is a slip of brass, containing a narrow slit. The other sight Q-, which is turned towards the object, contains an oblong aperture, along the axis of which is stretched a fine wire, which is made to pass over the object whose angular distance, or azimuth, from the magnetic meridian is to be determined. (865) The questions Which is the best form, and What the best construction of compass needles, have been frequently discussed, and many valuable experiments have been made on the subject; the most important perhaps are those of Captain Kater and Dr. Scoresby. The principal inferences to be drawn from the experiments of the former are the following (Phil. Trans., 1821.) 1. That the best material for compass needles is clock spring, but care must be taken in forming the needle, to expose it as seldom as possible to heat, otherwise its capability of receiving Magnetism will be much diminished. 2. That the best form for a compass needle is a pierced Ehombus Fig. 301. CONSTRUCTION OF COMPASS NEEDLES. 593 in the proportion of about 5 inches in length to 2 inches in width, this form being susceptible of the greatest directive force. 3. That the best mode of tempering a compass needle is first to harden it at a red heat, and then to soften it from the middle to about 1 inch from each end, by exposing it to a heat sufficient to cause the blue colour which arises again to disappear. 4. That in the same plate of steel of the size of a few square inches only, portions are found varying considerably in their capa- bility of receiving Magnetism, though not apparently differing in any other respect. 5. That polishing a needle has no effect on its Magnetism. 6. That the best mode of communicating Magnetism to the needle appears to be by placing it in the magnetic meridian, joining the opposite poles of a pair of bar magnets (the magnets being in the same line), and laying the magnets so joined flat upon the needle with their poles upon its centre ; then having elevated the distant extremities of the magnets, so that they may form an angle of about 2 or 3 with the needle, they are to be drawn from the centre of the needle to its extremities, carefully preserving the same in- clination, and having joined the poles of the magnets at a distance from the needle, the operation is to be performed 10 or 12 times on each surface. 7. That in needles of from 5 to 8 inches in length, their weights being equal, the directive forces are nearly as the lengths. 8. That the directive force does not depend upon the extent of surface, but in needles of nearly the same length and form, is as the mass. 9. That the deviation of a compass needle occasioned by the at- traction of soft iron, depends, as Mr. Barlow has advanced, on extent of surface, and is wholly independent of the mass, except a certain thickness of the iron amounting to about -roths of an inch, which is requisite for the complete development of the attractive energy. (866) The pierced E-hombus was the form of needle used in merchant ships previous to the researches of Dr. Growan Knight in 1750. This form he considered objectionable, as likewise the needle employed at that time in the Navy, which was a single piece of spring tempered steel, broad towards the ends, which were pointed, and tapering towards the middle ; and he proposed as the most advan- tageous form, that of a regular parallelepiped, or straight narrow- edged bar, hardened throughout and suspended upon an agate attached to its under surface, and this kind of needle is now usually employed. 594 MAGNETISM. (867) The general results of Dr. Scoresby's experiments on the magnetical capacities and powers of steel plates adapted for sea compasses, have already been given. The following is a more com- plete resume of his investigations. 1. For single bar needles exceeding in weight 400 to 500 grains, the 6-inch bar, hard cast steel; for lighter needles, the directive energy is improved by annealing. 2. The most energetic cast steel is that from Bradford iron ; next comes shear steel SS, or of hoop L iron ; then blister steel hoop L ; and lastly cast steel hoop L. 3. Thin plates of cast steel for single needles have their mag- netical capacities improved by annealing in oil, at a temperature of from 500 to 550. 4. A great advantage is gained by employing two or more thin plates not in contact, but separated from each other; the plates being either of hard shear steel, or of slightly annealed cast steel. (868) The compass recommended by the Committee of Inquiry appointed by the Admiralty is constructed in accordance with Scoresby's principles. It consists "of 4 compound magnetic bars secured together with a card within a light ring of brass : the card is made of mica, and covered with thin paper, on which the impression of the cardinal points is printed ; the caps are of agate or ruby, and the points of suspension of native alloy ; the bowl is made of copper. It is a beautifully constructed instrument, but costly, and is said to be not very steady at sea. (869) Sir "William Harris's compass, which is also used in the Navy and by the Honourable East India Company, is thus constructed by the patentees, Messrs Lilley and Son, Opticians, Limehouse. The needle is a simple light bar magnet, from 5 to 7 inches in length, turned on its edge, and mounted on an agate centre. It is regularly and accurately formed, hardened and tempered throughout, and previous to being magnetized is nicely balanced in a horizontal position ; in this state two small silver sliders are placed on each arm equally distant from the extremities and centre of the bar. "When the bar is made mag- netic, it is magnetized in such a way, that the centre of the magnetic forces falls in the line of the point of suspension, and any inclination in the direction of the dip is corrected by moving one of the sliders a little towards the centre on one arm, and a little from the centre on the other arm. By this new distribution of the matter, the bar is again brought into a horizontal position, and all undue tendency to an oscillating or swinging motion so far avoided, for there is still as much matter to be moved on one arm of the lever as on the other, whilst the change of the angular inertia of the sliders is so small that HARRIS'S COMPASS. 595 it may, for all practical purposes, be neglected in the calculation. The needle, though light, has considerable magnetic power, lifting at either pole three times its own weight of iron, and producing according to Scoresby's method of deflections, a deviation of 22 at a distance of twice its length from the centre of the trial needle. The needle and card are placed closely within a dense ring of pure copper, the influence of which, as has been already shown (785) is to bring the needle rapidly to rest in its meridian, whenever from any cause it is put into a state of oscillation ; so that the effect of disturbing forces on the card (a very light disc of talc), such as that of a ship's motion at sea, is checked at the instant without the aid of mechanical restraint,* and the needle is thus prevented from moving out of its natural position, at least to any inconvenient extent, by means of an invisible agency, and without any interference with its directive property. This effect of the copper ring in calming the oscillations of the compass, may be immediately seen by attracting the needle aside 90 from its meridian, with a small piece of iron, and allowing it to swing from that point, when it will be ob- served to be rapidly reduced to rest at each swing. Thus in an experiment described by Messrs. Lilley, a needle and card of 7 or 6 inches in diameter, were observed in an open space to make 25 swings and to occupy 200 seconds, in coming to rest from an angle of 90, whereas within a ring of copper, it came to rest in 5 swings and only occupied 40 seconds. The needle point is centrally fixed in a transverse bar placed as a diameter to the ring of copper. Should the point wear, or be damaged from any cause, it may be unscrewed and screwed in the reverse way, the point being a double one. The cap also can be renewed when requisite. The compass kettle is fitted with faces of plate glass, so that the card may be lighted from below or above it. These compasses can be fitted to any bin- nacles, and adapted to any locality of situation on board. When the horizontal position of the card is disturbed by any alteration of dip incidental to a change of latitude, it is to be corrected by moving the silver sliders on the needle. (870) This compass, which has now been in use for some years, appears to fulfil all the conditions requisite to the full practical conditions of the mariner's compass. In the heavy seas about Cape * Sir William Harris has investigated the magnetic conditions of this phe- nomenon (Phil. Trans., 1831), and has shown that the restraining force with a magnet of a given power, is as the quantity of the copper within the sphere of action directly, and as the squares of the distances from the magnetic polar extremity of the needle inversely. 596 MAGNETISM. Horn and the Cape of Good Hope, the card was not found to oscillate more than from i to \ a point each way, and it has been found to be especially steady in steam ships fitted with the screw propeller. (871) The following is the method of testing the compasses intended to be employed in H.M.'s ships, as adopted in the Observa- tory at Woolwich.* Fig. 302. Three pedestals, S N C. (Fig. 302), are firmly fixed in the room, quite independent of the floor, in the line of the magnetic meridian. The pedestal S carries a suspended magnet, which is observed by means of a transit telescope fixed on the centre pedestal, C ; on the pedestal N is placed the compass to be examined. The collimating magnet S consists of a hollow steel cylinder i an inch in diameter and about 6 inches in length, centrally suspended in an appropriate frame by a long silk fibre ; a small lens is fixed in the N. end of the cylinder, and there is an extremely fine scale of 160 divisions traversing it horizontally and right across its centre. The transit on the central pillar C being duly adjusted and directed in the axis of the collimating magnet, its scale is observed to vibrate across fine filaments of spider's web fixed perpendicularly in the tube of the telescope. The magnetic meridian being found by these means, the transit is turned over and directed towards the N. upon a mark painted on a distant wall on a rising ground called Cox Mount ; this mark corresponds to the line of the collimating magnet on pedestal S ; we thus transfer over, as it were, the line of the magnetic me- ridian, as taken in the telescope, upon the compass to be examined, and which is placed on the pedestal N. The needle and card being removed, the compass is so adjusted in position by the appropriate apparatus on which it rests, as to bring the point of suspension of the needle in the line of the telescope, and so bisect it ; this done, * Harris's "Rudimentary Magnetism," Part III., p. 157. LOCAL ATTBA.CTION IN SHIPS. 597 the card is replaced, and its N. pole is made also to coincide with the line of the telescope. Eor the adjustment of the azimuth compasses there is a set of graduated divisions painted on the distant wall, and the vertical line of the telescope is conveyed through the window so as to cut these divisions ; the prism is now adjusted for the zero point of the card, the hair line of the sight vane being directed to the particular division on the wall cut by the vertical line of the telescope. The pivots, caps, and gimbals, and the metal of the compass bowl, &c., are now carefully examined ; also the magnetic power of the needles, which are tested by a standard magnetometer of deviation, so that errors liable to arise in any particular instrument are certain to be detected. (872) Local Attraction. From what has been said respecting the temporary magnetic condition of iron under the influence of terres- trial magnetic induction, it is obvious that the compasses in ships must be subject to derangements from the large masses of iron, guns, anchors, cables, &c., on board. These derangements amount sometimes to 15 or 20, and have exposed the vessel to the most imminent perils ; indeed, there can be little doubt but that some of the most dreadful shipwrecks which are to be found recorded in our naval annals are to be ascribed to this. The loss of H.M.'s ships St. George, of 98 guns ; Defiance, 74 ; and Hero, 74, in the winter of 1811-12, are cases in point. The Hero sailed December 18th, 1811, from Wingo Sound in the Cattegat, and instead of standing well to the westward to compensate for the deviation of the compass and the action of a north-easterly wind, steered directly the compass course for the Downs, the consequence was that she struck the ground in a heavy squall of wind and sleet upon Haak Sand near the Texel Island, and soon went to pieces, all on board, with the exception of eight, perishing. The St. George, which had been dismasted in the Baltic, attempted together with the Defiance to perform the same passage, unfortunately both steering a direct compass course ; both ships went on shore on the western coast of North Jutland ; of the crew of the former only eleven, and of the latter only six men were saved. The number of persons who suffered in these three ships, including the whole of the officers on board, amounted to nearly 2,000, being a greater loss of life in British seamen than has occurred in some of the most splendid battles in which our fleets have been engaged. In iron ships the disturbance is far more serious than in vessels built of wood; it is sometimes indeed so great as to render the compass nearly useless. Messrs. Lilley, for instance, observed in the steam ship Shanghai, one of the vessels of the Peninsular and Oriental Company, 598 MAGNETISM. a deviation, with the ship's head to the S., amounting in the binnacle to 171 34' W., being more than 15 points. (873) A subject of such serious, we may say of such national importance, has demanded the particular attention of scientific men, but although many useful investigations have been made, the problem of compensation for local attraction as regards iron ships is not as yet satisfactorily solved. We have already alluded to Professor Bar- low's " neutralizing or correcting plate," and as this method of com- pensation has, for wooden vessels, proved in practice eminently successful, we will now give a more particular account of the instru- ment (Encycl. JBrit., Art. Magnetism). T is a rod of copper Fig. 303. Fig. 304. 1 J inches in diameter, and E F' two plates of iron about 12 or 13 inches in diameter, and of such a thickness that a square foot of it will weigh about 3 Ibs. avoirdupois; these plates are separated by a circular sheet of card, and pressed against each other at their centre by a screw on the end of the rod T, and at their margins by 3 small screws of iron. The compass C is placed on the top of a wooden box B, and the corrector T, is placed in one of the holes in the side of the box. The adjustment of the plate is made when the ship is lying in a calm bay near the shore ; an observer with a needle and theodolite is placed at some distance from the shore, from which he can per- ceive the ship while she is turning her head in different directions. The compass on board the ship is under the management of another observer, with the same apparatus. At a signal given, the observer determines the angle which his own needle makes with the axis of the telescopes (one being directed to the other), which is called the central line. But as the needle on shore experiences no disturbing action, it is evident that if the needle on ship-board also experience none, the two needles will be parallel, and will form the same angle with the central line. Hence the difference between these two LOCAL ATTEACTION IN IRON SHIPS. 599 aDgles, when they are not the same, is that which is produced by the magnetic action of the iron in the vessel from its compass needle at the instant of observation. The vessel is now made to turn round completely, and a -new observation is made at every azimuth of 10 or 12 degrees ; the value of the deviation produced in all positions of the ship's head upon the compass needle is thus obtained. When this is done, the observer on shore takes away his compass, and replaces it with that of the ship, which he sets on the wooden cage (Fig. 303), having different holes for receiving the axis T of the plate 1?' E. As the box is turned round its axis, it carries along with it the compensator P F', which will affect the needle of the compass C differently in different azimuths ; and by a few trials it may be adjusted by means of the holes of its axis T to produce the very same deviations in the compass as was produced upon it when in the ship by the action of the iron. When it is done, the position of the centres of the plate E l v with regard to the needle is completely marked, and when it is taken on board the ship, and placed in its proper position, the compensator is adjusted on the stand which carries the compass, so as to have exactly the same relative position as it had in the box D. Now since the compensator produces the same effect as the iron on shipboard does, the deviation will be doubled in place of being corrected ; but this furnishes the means of making the correction. If the variation is found to be 36 "W. by the compass without the compensator, and afterwards 40 with the compensator, the difference 40 36=4 shows that the compensator augments the variation 4, and the iron on board the vessel as much. Hence the true variation wiU be 36 4=32, or 4044=32. If the observations with the compensator had given a less result than without it, this would have shown that the action of the iron had diminished the declination, and the difference of the two observations must have been added to the first to have the true declination.* (874) Local Attraction in Iron Ships. It had been noticed by Captain Johnson that an iron ship operates on the compass needle in the same manner as a permanent magnet placed outside the vessel ; this observation induced the Astronomer-Royal to direct his attention to the subject with a view to the discovery of some method of cor- recting the local attraction in iron vessels. The results of his inves- * This method of correcting the compass for local attraction is not, we believe, now adopted in the Koyal Navy. Either tables of errors are constructed for each ship, or the card is distorted so as to correspond with the true magnetic direc- tion of the ship's head, the vessel being swung upon the different points of the compass. 600 MAGNETISM. tigations were communicated to the Eoyal Society, and are published in the Transactions for 1839. The experiments were made on board the iron steam ship Rainbow, and the iron sailing ship Ironsides. For the purpose of ascertaining the laws of the deviation of the compass, four stations were selected in the vessel, about 4 feet above the deck, and at these the deviations of the horizontal com- passes were determined in various positions of the ship's head. All these stations were in the vertical plane, passing through the ship's keel, three being in the after part of the ship, and one near the bow. Observations were also made for determining the horizontal intensity at each of the stations. The deviations of dipping needles at three of these stations were also determined, when the plane of vibration coincided with that of the ship's keel, and also when at right angles to it. The most striking feature in the results as to the disturbance of the horizontal compass at the four stations, was the very great apparent change in the direction of the ship's head as indicated by the compass nearest the stern, corresponding to a small real change in one particular position ; the former change being 97, whereas the latter was only 23 ; and the small amount of disturbance indicated by the compass near the bow. Any attempt to discuss Mr. Airy's elaborate mathematical inves- tigation would be quite foreign to the object of this work. (875) The fundamental supposition of the theory of induced Mag- netism on which he rests his calculations is, that by the action of ter- restrial Magnetism, every particle of iron is converted into a magnet, whose direction is parallel to that of the dipping needle, and whose intensity is proportional to that of terrestrial Magnetism ; the upper end having the property of attracting the N. end of the needle, and the lower end that of repelling it. He deduces the following simple rule for the correction of a compass disturbed by the induced Mag- netism only of the iron in a ship : 1. Determine the position of Barlow's plate with regard to the compass, which will produce the same effect as the iron in the ship. 2. Fix Barlow's plate at the distance and depression determined by the last experiment, but in the opposite azimuth. 3. Mount another mass of iron at the same level as the compass, but on the starboard or larboard side, and determine its position so that the compass points correctly when the ship's head is 1ST.E., S.E., S.W., or N/W. ; then the compass will be correct in all positions of the ship's head, and in all magnetic latitudes. When the disturbing iron of the ship is at the same level as the compass, the correction is stated to be much more simple, it being then only necessary to introduce a single mass of iron at the star- LOCAL ATTBACTION IN IEON SHIPS. 601 board or larboard side, and at the same level as the compass ; but in the construction of the ship, and in the fixing of correctors, no large mass of iron should be placed below the compass. (876) In his experiments on the ship Ironsides, Mr. Airy corrected one of the compasses by a tentative process, which he considers likely to be of the highest value in the correction of compasses of iron ships in general. The ship's head being placed exactly N. as ascertained by a shore compass, a magnet was placed upon the beam from which the compass was suspended, with the direction of its length exactly transverse to the ship's keel ; it was moved upon the beam to various distances, till the compass pointed correctly, and then it was fixed. Then the ship's head was placed exactly E. and another magnet, with its length parallel to the ship's keel, was placed upon the same beam, and moved to different distances till the compass pointed correctly, and then it was fixed. The correction for induced Magnetism was neglected, but there would have been no difficulty in adjusting it by the same process, placing the vessel's head in azimuth 45, or 135, or 225, or 315. The deviations of the compass are caused by two modifications of magnetic power ; the one being the independent Magnetism of the ship which retains, in all positions of the ship, the same magnitude and the same direction relatively to the ship ; the other being the induced Magnetism, of which the force varies in magnitude and direction when the ship's position is changed. In the cases investigated by Mr. Airy, the effect of the former force was found greatly to exceed that of the latter. The most remarkable result, in a scientific view, of Mr. Airy's investigation, is the great intensity of the permanent Magnetism of the malleable iron of which the ship is composed. It appears, how- ever, that almost every plate of rolled iron is intensely magnetic. (877) The Eev. Dr. Scoresby, whose unceasing labours in the service of practical magnetics we have had occasion repeatedly to refer to, has devoted much study to the variation of the compass in iron vessels.* He considers that the adjustment of the compasses of iron ships by fixed permanent magnets is not only delusive but dangerous. Iron becomes magnetic by virtue of the inductive influ- ence of the earth, but its Magnetism might be controlled, altered, or destroyed, by mechanical action (859861). Applying this to the case of iron ships, Dr. Scoresby considers that, in consequence of the percussive action to which the material is exposed while the ships are in course of construction, it becomes as intensely magnetic as it * Vide "Magnetical Investigations," vol. ii. ; also, Reports of the Proceedings of the British Association at Oxford in 1847, and at Liverpool in 1854. 602 MAGNETISM. is possible for malleable iron to do. This augmented Magnetism is not, however, permanent or fixed, but under different circumstances as to the relative deviation of the ship's Magnetism and that of the earth, is easily changeable, and liable necessarily to be changed. Experiments on rolled iron plates of the same kind as those of which ships are generally built, showed that in them the Magnetism was changeable and controllable like that in bar iron under the requisite change of position, by vibratory or percussive action. Dr. Scoresby likewise made experiments on a portion of a plate cut out of the side of a ship recently built, and the results of his observations was to establish the fact that, besides the two denominations of Magnetism ordinarily received, that of simple terrestrial induction, and that of permanent independent Magnetism, there was another denomination corresponding with neither, not being absolutely controllable, like the former, by terrestrial influences, nor capable, like the latter, of resisting all kinds and modes of mechanical violence. To this deno- mination he gives the name of retentive Magnetism. The vibration of a ship in a heavy sea is sufficient to change the original Magnetism developed and augmented in the course of her construction. A great deal will depend on the position in which the ship has been built. If, for instance, she has been built with her head to the JST.E., she will have a certain magnetic distribution, but Avhen she begins to strain with her head to the S.W., that distribution will be- come changed, and the first effect will be to alter the compasses adjusted by fixed magnets. All attempts, therefore, to adjust a tran- sient influence by a permanent one, only aggravate the error which it is sought to overcome, and captains of ships should lose no oppor- tunity of correcting and verifying their compasses whenever the sun or a star is in sight. A compass should likewise be kept aloft, as far as possible from the iron of a ship, as a standard for reference. An- other objection that has been raised to the Astronomer-Soya!' s system is, that the magnetic poles of the compensating magnets are liable to change or vary in their intensity. The Magnetism of iron ships is thus changeable in all its qualities, the most enduring being of a description changeable under severe straining and mechanical violence ; this Scoresby calls " retentive Magnetism" His suggestions are : 1. A standard azimuth compass to be placed on a high pedestal where (on the Admiralty plan) a position of small deviation may be found. 2. A compass at the mast-head for reference will be best of all. 3. The wheel compass required for ships engaged in the home trade, or traversing mainly parallels of latitude, not southward of the MAGNETISM OF IRON SHIPS. 603 Mediterranean, if adjusted with magnets and pieces of iron, may not then be unsafe, where reference may always be had to the standard for verification. 4. No standard compass in great distances. 5. Care in selection of compasses to have ample directive force. His improvement had trebled the directive force weight for weight of the compasses used in the Navy up to 1849 or 1850. 6 Captains should be made to take observations for verifying their compasses by azimuth compasses, stars, position of land, &c. 7. Captains should have a special knowledge for the charge of iron ships ; for here, in addition to the ordinary dangers of naviga- tion, is a new source of error and misguidance, as to which it is most important he should never be thrown off" his guard.* * A most lamentable instance of the loss of an iron ship in consequence of changes in the action of her compasses, occurred in the early part of the year 1854. The circumstances were as follow : The ship, Tayleur, a new vessel bound to Australia, sailed from Liverpool on Thursday, 19th January; she was 1,979 tons burden new measurement, and she had on board 458 passengers the crew and passengers together making a total of 528 persons. She left the Mersey about noon, and the pilot left her between seven and eight o'clock in the evening in a position between Point Lynas and the Skerries. On Friday she encountered very heavy weather, and about eight o'clock on the following morning it was for the first time ascertained that there was any material difference between her compasses. One was near the helmsman, and was the one by which he was steer- ing ; the other was near the mizen mast. Both of these compasses had been adjusted by permanent magnets, so that if the principle of adjustment had been correct, they should not either have changed or differed from each other. Trust- ing to the compass near the helmsman, the captain had the idea firmly impressed upon his mind that he was sailing fairly down almost mid-channel ; at all events, in a good position for navigating the Irish channel. The other compass indicated a difference of about two points ; the captain, however, judging from certain indications which he had noticed previously, assumed that the wheel compass was the correct one. In the course of a few hours about half-past eleven o'clock on the same morning the wind having increased and a heavy sea setting up the channel, the ship made rather a rapid progress, when they came suddenly in sight of land on the lee beam in such a position that there was necessarily a great difficulty in this case (according to the measures pursued), an insurmountable difficulty in avoiding the land. An attempt was made to wear the ship round ; this failed, and then an attempt was made to use the anchors to bring her up. Both the cables snapped on the occasion, and the ship was thus left helpless, driving broadside upon the rocks of Lambay Island. The result was the fearful catastrophe of the loss of about 290 lives ! Inquiries were instituted by the Board of Trade in two departments ; one by means of Captain Walker of the Navy, who ascribed the loss of the vessel to the captain's supposition that the compass by the helm was correct ; the other by means of the Marine Board of Liverpool, who reported that although the captain had given very great attention to the ascertaining of the correctness of his compasses, yet the Tayleur was K B 604 MAGNETISM. (878) To these observations of Dr. Scoresby, Mr. Airy lias made a reply (Athen, is in C exact equilibrium with the rectilinear portion, a b. The combination of a rectilinear with a sinuous cur- rent is called a solenoid. It is a system of circular currents, equal and parallel, formed by twisting a silk- covered copper wire, corkscrew-fashion, back upon itself ; but to make it perfect, the straight part of the wire must be as exactly as possible in the centre of the helix. Thus arranged, when the circuit is tra- versed by a current, the action of the solenoid in the direction of Fig. 330. +A : its length, A B, is destroyed by that of the rectilinear current B C, and the only effect produced is due to the system of circular currents, equal and parallel, moving in a direction perpendicular to its axis. Now, as the action of fixed currents on moveable ones is to bring them into a position parallel to themselves, with their currents moving in the same direction, a solenoid freely suspended on a ver- tical axis should, when acted on by a rectilinear current, range itself its circles parallel to that current. It is accordingly found that Fig. 331. on passing a strong vol- taic current through a solenoid suspended from two mercury cups, as shown in Eig. 331, so as to allow it perfect free- dom of motion round a vertical axis, and passing at the same time under, neath, and parallel to its axis, a rectilinear cur- rent, the solenoid turns taking up a position with its circles itself across that current SINUOUS CURRENTS ; SOLENOIDS. 655 parallel to it. If instead of passing the rectilinear current hori- zontally underneath the solenoid, it be passed vertically and near one end, the latter is either attracted or repelled according as the currents are passing in the same or in opposite directions, through the wire and through the contiguous parts of the solenoid. Two solenoids exhibit towards each other the phenomena of attraction and repulsion in a manner precisely similar to two magnets, and a solenoid is influenced by a magnetic bar precisely as another magnet would be. In short, a solenoid has all the properties of a magnet, and when suspended, as shown in Eig. 331, and traversed by a strong electric current, it will range itself with its axis parallel to the direction of the declination needle. If the solenoid be a right Fig. 332. S'-* AV /"v r\ /~\. /\. /\ f\ 7\ /x 7x ^>*^_ 9 lianded helix, its wire being turned from left to right, then the ex- tremity at which the current enters has the magnetic properties of a N. pole, and the extremity at which it leaves the helix those of a S. pole. If the helix be left-handed, its wire turning from right Fig. 333. to left, then the extremity at which the current enters has the pro- perties of a S. pole, and that at which it leaves the helix has those of a N. pole. When a magnetic bar is broken across, each fragment is itself a perfect magnet, the two A Fi S- 334. t fractured ends having an opposite polarity ; it is precisely the same with a solenoid : sup- pose, for example, A B to represent a sole- noid extending indefinitely on either side of the point m, and traversed by a current in the direction of the arrows, the extremity A is a S. pole, because on looking at the face of this terminal circle the ascending current is observed to be moving from left to right ; suppose now the solenoid to be cut in two at m, the a end will be a S. pole, and the end b a N. pole, because on looking at the face of the terminal circle of the latter, the ascending current is seen to be moving B [| from right to left. It is evident, therefore, that there will be atfcrac- 656 ELECTRO-MAGNETISM. tion between a and 5, and it may be proved moreover that this attraction is, as in the case of magnets, inversely as the square of the distance between a and b, (948) A beautiful exemplification of the mutual attraction of conducting wires carrying voltaic currents moving in the same direction, is aiforded by Eoget's spiral (Fig. 335). It consists of a Fig. 335. loose coil of copper wire, the upper end being either held by a binding screw or suspended by a fibre of silk, and the lower end (which should be amalga- mated) just touching the surface of some mercury in a little cup, communi- cating with the negative electrode of a pretty strong voltaic battery. On making .-a contact between the upper extremity of the spiral and the positive electrode, the coils being all traversed 5= by a current in the same direction, will mutually attract each other ; the entire spiral being hereby shortened, the lower end leaves the mercury, and the .contact with the battery is broken ; the weight of the wire thus causes it again to fall into the mercury, and the passage of the current is restored ; in this way a rapid series of longitudinal vibrations is produced, accompanied by a snapping noise, and a succession of bright sparks. Again, suspend from a horizontal rod two similar compound spirals, each consisting of several layers of insulated copper wire superposed, and send a strong current through each in the same direction ; they will attract each other powerfully, even at a .distance of several inches ; now reverse the direction of the current in one of the spirals, upon which a repulsion equally powerful will be set up between them. It must be borne in mind that in flat spirals as well as in helices, the nature of the mag- netic poles is determined by the direction of the spirals as well as by the direction of the current. In the right-hand spiral (Fig. 836.) the end at which the current enters has the magnetic pro- perties of a N. pole and in the left-hand helix (Fig. 337), the end at which the cur- rent enters has the properties of a S. pole. GALTAKOMETEKS. 657 Fig. 338. (949) Galvanometers. We have already described the construc- tion of the various forms of this valuable instrument (426 et seq.\ and the preceding considerations render it probably unnecessary to add any- thing with reference to the princi- ples on which their action depends. In Fig. 338, is shown the vertical spiral coil, galvanometer described by Dr. Itoget (Library of Useful Knoivledge, Electro-magnetism, No. 44). The needle is suspended from its centre by a fine thread between four vertical spiral coils, the centres of which are brought very near to ^ the poles of the needle. The] same current is made to circulate through all the four spirals, the turns of which are directed so as to produce repulsion of the contiguous pole on the one side, and attraction of the same pole on the other side. In each disc the force acting perpendicularly to the plane of the discs is multiplied in proportion to the number of the circumvolutions of the wire, and the spiral turns being made in the same directions in all the discs, their actions will concur in pro- ducing in the needle a deviation in the same direction, and the total force will be four times that of a single disc. (950) The action of a magnet on a moveable conductor has also been made available as an extremely delicate test of a weak galvanic current. (Cumming's Electro Dynamics.) A slip of gold leaf g (Fig. 339) is retained loosely between two forceps, each termina- ting in a mercury cup or binding screw, for establishing the communications by which the current is transmitted through the leaf. The whole is enclosed in a cylindrical glass case, the middle of Which is placed between the poles of a powerful horse-shoe magnet, so that the gold leaf may be nearly equidistant from them when the circuit is complete. The latter is attracted or repelled laterally by the poles of the magnet according as the current is ascending or descending ; the broad sur- face of the leaf becoming convex towards 658 ELECTBO-MAGKETISH. the magnet in the one case, and concave in the other. This prin- ciple has been adopted by Highton in one of his patented electric telegraphs. (951) Mr. Faraday, whilst making experiments to ascertain the posi- tion of the magnetic needle relative to the connecting wire, was led (Quart. Jour, of Science, xii., p. 74) to some new views of electro- magnetic action. On placing the wire perpendicularly, and bringing the needle towards it to ascertain the attractive and repulsive posi- tions with regard to the wire, he found them to be eight 2 attrac- tive and 2 repulsive for each pole. Thus, allowing the needle to take its natural position across the wire, and then drawing the sup- port away from the wire slowly so as to bring the N. pole, for instance, nearer to it, there was attraction, as was to be expected ; but on continuing to make the end of the needle come nearer to the wire, repulsion took place, though the wire still was on the same side of the needle. If the wire was on the other side of the same pole of the needle, it repelled it when opposite to most parts between the centre of motion and the end ; but there was a small portion at the end where it attracted it. Fig, 340. Fig. 341. Pig. 340 shows the positions of attraction for the N. and S. poles. Tig. 341 the positions of repulsion. (952) On making the wire approach perpendicularly towards one pole of the needle, the pole passed off on one side in that direction which the attraction and repulsion at the extreme point of the pole gave ; but if the wire were continually made to approach the centre of motion by either the one or the other side of the needle, the ten- dency to move in the former direction diminished ; it thus became null, and the needle was quite indifferent to the wire, ultimately the motion was reversed, and the needle powerfully endeavoured to pass the opposite way. From this it was evident that the centre of EARADAY'S RESEARCHES. 659 the active portion of either limb of the needle, or the true pole as it may be called, is not at the extremity of the needle, but may be repre- sented by a point generally in the axis of the needle at some little distance from the end. It was evident also that this point had a tendency to revolve round the wire, and necessarily, therefore, the wire round the point ; and as the same effects in the opposite direc- tion took place with the other pole, it was evident that each pole had the power of acting on the wire by itself, and not as any part of the needle, or as connected with the opposite pole. In Pig. 342, sections of the wire in its different positions to the needle are represented the active poles by two dots ; and the arrow heads show the tendency of the wire in its positions to go round these poles. Fig. 342. OR From these facts it follows that both attraction and repulsion of conducting wires are compound actions ; that there is no attraction between the wire and either pole of the magnet, and that the wire ought to revolve round the magnetic pole, and the magnetic pole round the wire. By the following ingenious apparatus Faraday proved this to be really the case. Into the centre of the bottom of a cup, as in the vertical section, Eig. 343, a copper wire c D, was inserted; a cylin- drical magnet n s, was attached by a thread to the copper wire, c, and the cup was nearly filled with mercury, so that only the X. pole of the magnet projected. A conductor, a 5, was then fixed in the mercury, perpendicularly over c. On connecting the conducting wires with the opposite ends of the battery, a current was transmitted from one wire through the mercury to the other. If the positive current descended, the N. pole of this magnet immediately began to rotate round the wire a b, passing from E. through the S. to "W., i. e., in the direction of the hands of a watch ; but if the current ascended, the line of rotation was reversed. Con- versely, a magnet was fixed in a vessel of mercury, and the conduct- ing wire hung from a hook above it, the end just dipping into 660 ELECTRO-MAGNETISM. Fig. 344. Fig. 345. the fluid ; the electric current being then transmitted through the moveable conductor, Faraday found that the free extremity instantly began to revolve round the pole of the magnet, in a direction similar to the last. A good contrivance for exhibiting this, is shown in Fig. 344. (953) In order to obviate the necessity of employ- ing so much quicksilver, which, by the resistance which it offers to the revolution of the magnet, greatly dimi- nishes the velocity of the rotation, the apparatus in Tig. 345, was devised by Mr. "Watkins. It exhibits the contrary poles of two magnets rotating about two electrified wires. Two flat bar magnets, doubly bent in the middle, and having agate cups fixed at the under part of the bend, by which they are supported upon upright pointed wires, are affixed in the basis of the apparatus, upon which they turn round as upon an axis. Above the agate cups, on the upper part of the bend, small cisterns to hold mercury are also formed. Two circular troughs to contain mercury, are supported upon a stage, affixed to the basis, having holes in their centres, to allow the magnets to pass through them. A bent pointed wire is affixed into the cisterns of each magnet, the ends of which dip into the mer- cury contained in the troughs upon the stage ; and through the sides of the trough, wires are passed, entering into the mercury contained in the troughs, and bearing at their ends other cups to hold mercury. To steady the motion of the magnets, wire loops are affixed to them, which embrace the upright pointed wires on which the magnets rest. A hollow pillar is firmly affixed to the stage, in which a bent wire supporting another cross wire is inserted, and is capable of being raised or lowered, and secured ELECTBO-MAGNETIC KOTATIONS. 661 at any required height by a binding screw. The two ends of the cross wire are bent downwards and pointed, and made to enter the two small cisterns affixed upon the magnets. A third cup to contain mercury is also provided at the top of the cross wire, and a commu- nication being made with the battery by means of uniting wires dipping into the mercury in the cups, the wire from the positive end of the battery being placed in the upper cup, and the wire from the negative end in each of the lower cups, the magnets will begin to rotate in opposite directions, and those directions may be reversed, by changing the situations of the uniting wires. Two batteries should here be employed, in order to make both the magnets revolve with the desired velocity ; and attention must be paid, when using two batteries, that the currents of Electricity flow in the same direc- tion ; otherwise, the phenomena of the revolutions of the magnets in contrary directions will not take place, but they will both revolve in the same direction. (Popular Sketch of Eletro-magnetism, by Francis "Watkins.) (954) Thus it will be seen that the direction of the rotation im- parted by a fixed current to a moveable pole, will be the same as that which the same pole imparts to the same cur- rent. Suppose w (Fig. 346) to represent a sec- tion of a conducting wire, along which a positive Bj current is descending, and n the N. pole of W T ^"" a magnet ; the influence of w on n will be to impel it in the direction of the arrow ; but n will also react on w, and tend to produce in it motion in an opposite direction, as exhibited by the arrow attached to w. Each is supposed to describe a circle round the other, moving in the same direction as the hands of a watch ; and if w and n were at liberty equally to move, they would have a tendency to rotate round the line between them. (955) Ampere first succeeded in effecting the rotation of a mag- net round its own axis. In his original experiment the magnet was allowed to float, without a support, in a vessel of mercury, being kept in a vertical position by a weight of platinum attached to its lower end. The object was to make the electrical current pass through one half of the magnet itself, and then to divert it from its course, and make it pass away in such a direction as that it should not affect the other half. The reason of this is evident : suppose a positive current be made to descend a magnet placed vertically, its JST. pole being uppermost, it would tend to urge that pole round from left to 662 ELECTRO-MAGNETISM. right, but its influence on the S. pole would L be just the reverse, tending to urge it from right to left ; or if two electrical currents be supposed, corresponding to the vitreous and resinous electricities, the tendencies would be the same ; and here it may be as well to mention, that in describing the phenomena of Electro-magnetism, we shall, to avoid tediousness, adopt the language of a single fluid, and suppose, that in the connecting wire of a voltaic battery, the elec- trical current is passing in one stream from the positive to the negative end. (956) In Ampere's experiment, the electric current, after travers- ing the upper half of the magnet, passes into the mercury, and being diffused through it, acts in no sensible degree on the lower half, and does not interfere with the rotation produced by its influence on the upper pole. It is, however, better to carry off the current by a different chan- nel, and this is effected by adopting the form of apparatus, shown in Fig. 347. -Fig* 347. I* i s tnus constructed by Mr. Watkins. A flat bar magnet is supported in a vertical position by an upright metal wire, aflixed in the basis of the ap- paratus, and having a hole in its centre, containing an agate cup, to receive the lower pointed end of the magnet ; its upper end turns in another hole, made in a vertical screw, with a milled head to turn it by, which is passed through a screw hole, made in an arched piece of wire, aflixed to the upper part of the basis. Around the first mentioned vertical wire a cistern to contain mercury is provided ; and another, having a hole in its centre, to allow the magnet to pass through, and revolve within it, near the middle of the magnet. These cisterns have metal wires pro- jecting into them, through their sides, to support cups which contain mercury, to effect the communication with the voltaic battery by means of uniting wires. Into the magnet two small bent and pointed wires are aflixed, the ends of which dip into the mercury contained in the cisterns. When the voltaic circuit is complete, the magnet begins to rotate within the Electricity, which it conducts itself, as it in fact forms part of the circuit ; the rapidity of the revo- lutions of the magnet depending upon the delicacy of the sustaining point, the strength of the magnet, and the power of the battery em- ployed. If it be desired to actuate a large magnet, it is necessary that an addition to the apparatus should be made, by providing a cup, affixed to the vertical screw, to contain mercury, by which contrivance, and by employing an additional battery, a current of Electricity can be ELECTRO-MAGNETIC ROTATIONS. 663 passed from the top of the magnet to its equator ; and. as in the first mentioned case, an opposite current can be passed from its lower end to the equator, an additional force is obtained. The current from the second battery must, of course, be sent along the upper half of the magnet, in a direction contrary to that which passes through the lower pole ; but since the rotatory force is proportional to the power of the voltaic battery employed, it is probable that the second battery would be equally efficacious, if it were employed in increasing the strength of the first by being joined to it. The ends of the wires should be amalgamated, by rubbing them first with nitrate of mercury and then dipping them into the clean metal. (957) Fig. 348 represents an apparatus to exhibit the rotation of a conducting body round its own axis, and is exactly the converse of the last experiment. In the former case, the elec- Fig- 348. trie current was applied in the interior of the mag- net, but here means have been devised for procuring the action of the magnet, from the interior of the conducting body. In the place of the wire, there- fore, a hollow metallic cylinder is employed, in the axis of which the influencing magnet can be placed. Mr. Barlow devised this instrument, and the figure shows the arrangement on a horse-shoe magnet by Mr. "Watkins. A horse-shoe magnet is supported vertically upon a stand, having holes formed in the centres of its ends. Two wooden circular troughs are secured by binding screws upon the arms of the magnet, to contain mercury. Into the holes in the centres of the ends of the magnet, two conical pointed wires are inserted, which are affixed in the middle of two hemispherical cups, united to cylinders, the rims of which are formed into points, which are dipped into the mercury contained in the circular troughs. Upon the top of each hemisphere is placed a small platinum cup to contain mercury. Other cups for holding mercury are supported on the external ends of bent wires, which pass through the sides of the circular troughs into the mercury contained therein. "When a stream of voltaic Electricity is passed through this apparatus by means of connecting wires, placed in the mercury contained in the upper and lower cup, the cylinders commence revolving in oppo- site directions, that cylinder on the N. pole, and down which the current is descending, moving from left to right ; but if the two upper cups be united by a wire, and the lower cups connected with the positive and negative extremities of the voltaic battery, the same stream will traverse both sides of the apparatus, passing up- wards in one cylinder, and downwards in the other ; and the rotations 664 ELECTRO-MAGNETISM. will now, from the contrary influences of the two poles, be in the same direction in both cylinders. (958) Earaday has shown, that the results in this last experi- ment, are the same when the magnet and conductor are united toge- ther ; for on fixing a thin piece of wood on the upper end of a magnet, loaded at its lower extremity with a platinum weight, floating in a vessel of quicksilver, and attaching to the wood an arch of strong wire, the whole apparatus commenced revolving on the transmission of the electric current through it ; on the other hand, when a hollow cylinder of metal was balanced on a vertical axis of wood, and acted on by the poles of a magnet placed outside, the rota- tory force was very feeble. This affords us means of explaining the circumstances of the rotation of a magnet about its own axis, for the explanation of that experiment will very much depend on the course which the current of Electricity is supposed to take in its passage through the magnet. If it be supposed to pass through the interior, along the axis of the magnet, it would then occasion rota- tion by its influence on the parts of the magnet that are situated nearer the surface ; but if the course of the current be supposed to be along the surface, it will itself be influenced by the polarity of those portions of the magnet which lie near the axis, and the rota- tory tendency impressed upon it will produce the rotation of the magnet, which will, of course, be carried along with it. This, it will be seen, corresponds with the rotation of a conducting body round its own axis, a magnet being in the centre ; _and it has been shown above, that the circumstance of the magnet and conductor being immoveably joined makes no difference in the results. (959) Another fact is made apparent by this last experiment, which is, that the electro-magnetic influence of the conductor takes place equally when the electrical current is diffused over a consider- able surface, as when it is concentrated in a single wire ; in the cylinder, every filament of which it is composed may be supposed to conduct its share of the current, and thus contribute towards the general effect. (960) A magnetic needle is found to be influenced by the cmv rent of Electricity that is passing through the voltaic battery from its positive to its negative pole, as well as by the wire that completes the circuit, or in other words, every part of the circuit exhibits the same electro-magnetic properties ; and as action always implies an equal and corresponding re-action, the magnet may be supposed to have a tendency to move the battery, equal to that which the battery lias to move it. This tendency was first actually exhibited by a very ingenious contrivance of Ampere, and which Mr. "Watkins ELECTRO-MAGNETIC ROTATIONS. 665 has applied to each of the poles of a horse-shoe magnet, as shown in Pig. 349. It consists of a horse-shoe magnet, firmly fixed to a stand at its bent part ; its two ends being made round, and having a small hole in the centre of each, at the bottom of which hole, an agate cup is placed, in which pointed wires fixed to the parts presently to be described are made to revolve. A doable cylindrical copper vessel, having a bent metal wire fixed to the top of its innermost cylinder, with a vertical wire pointed at both ends fixed in the middle of that bent wire, is hung upon the upper end of each pole of the magnet, the lower points of the vertical wires of each vessel entering the holes, formed as above described, in the magnet for that purpose. Two hollow cylinders of zinc, each furnished with similar bent wires, having holes made in the under sides of each, are then placed within the double copper vessels ; the holes in the bent wires being hung upon the uppermost pointed ends of the vertical wires before mentioned. Diluted acid being then poured into the space between the copper cylinders, the voltaic action commences, and presents the phenomena of the whole four cylinders revolving upon their axes, the copper vessels revolving in opposite and contrary directions, and the zinc cylinders turning in opposite directions to them : the rapidity of their revolutions depending upon the strength of the acid and the delicacy of their suspension.* (961) Numerous amusing experiments have been devised for ex- hibiting the vibratory tendencies of electrified wires when under the influence of magnets. Fig. 350 represents an arrangement by Mr. Marsh. It con- sists of a slender wire, suspended from a loop and capable of free motion ; its lower end is amalgamated, and dips into a small cistern of mercury ; the cups a and 5 are filled also with mercury, and through them the electrical current is passed down the loose wire ; no motion of this wire is per- ceptible until a horse-shoe magnet is placed in a horizontal position on the basis, with its poles enclosing the wire, when it is in- stantly urged either forwards towards c, or backwards towards d, * The zinc cylinders revolve with great rapidity, but from the superior weight of the copper cylinders when filled with the exciting liquor, it is rarely that a rapid rotation can be exhibited in them. Fig. 350. 666 ELECTEO-MAGNETISM. according to the position of the poles, and the direction of the cur- rent. In either case it is thrown out of the mercury, and the circuit being thus broken, the effect ceases, until the wire falls back again by its own weight into the mercury ; when the current being re-es- tablished, the same influence is again exerted, the phenomenon is repeated, and the wire exhibits a quick succession of vibratory motions. (962) This vibratory motion is easily converted into one of rota- tion by employing a spur wheel, as in Fig. 351. The radii of the Fig. 351. wheel must be so arranged that each ray shall touch the surface of the mer- cury before the preceding ray shall have quitted it. The direction of the motion depends of course on the same circumstances as were before men- tioned. This forms a very brilliant experi- ment when a powerful battery and a strong magnet are employed. The wheel revolves with immense velocity, and streams of sparks of a green colour, arising from the combustion of the copper points of the radii of the wheel, are thrown sometimes over the cups of the instrument. Mr. Sturgeon found that the division of the wheel into rays was not necessary, and that if a circular metallic disc be substituted for the spur wheel, as shown in Eig. 352, it will revolve equally well. In Fig. 352. all these experiments it is im- portant that the ends of the wires and surface of the metals which touchthe mercury should be well amalgamated in order to ensure perfect contact. By altering the direction of the electrical current all the ^_^ vibrations and rotations that ^ have been just described are reversed. (963) Magnetizing Properties of the Voltaic Current. If the wire which connects the two extremities of a voltaic battery be plunged into fine iron filings, a considerable portion will be attracted and will remain attached to the wire as long as the current continues to circulate through it ; on breaking the circuit, the filings will imme- diately drop off. If small steel needles be laid across the wire, they MAGNETIZING POWER OF THE VOLTAIC CURRENT. 667 will also be attracted, and on removing them they will be found to be permanently magnetized. The voltaic current is thus seen to possess the power of decomposing the natural Magnetism of magnetic bodies, in a manner precisely similar to magnets themselves. From what has been already said, it will appear evident that in order to give the current its full efficiency, it should be allowed to pass transversely round the iron or steel ; it should surround it in the form 353. 355. of a helix. Here again we find the polarity given to the needle to depend on the direc- tion of the turns of the helix. If it be a right-handed spiral (Fig. 353), the N. pole is always formed at the end at which the current enters, that is, on the positive side ; if it be a left-handed helix (Fig. 354), the bar acquires at this end, a southern polarity. If the wire be twisted round the tube in such a manner as to form reverse contrary helices following one another,' then the needle is magnetized with "consecutive poles" (807) at the junctions of the helices, each helix acting as if it were alone. If the helix be con- structed in such a manner that it turns alternately from the right to the left, the needle will not be found to have acquired any permanent polarity. The magnetizing power of the voltaic current is exerted instantaneously, the steel bars acquiring the utmost Magnetism they are capable of receiving the moment the circuit is completed. This instantaneous breaking down of the resistance offered by the coer- citive force of the bar is a phenomenon of a very remarkable character. We have in a previous chapter (828) described the application of the helix to the magnetizing of large steel bars by Elias of Haarlem. This method has been compared by Frick (Annual Report of the Progress of Chemistry ,1849), with that of the touch (819), an electro- magnet being used; on the whole he prefers the latter. By employing, however, the band spiral (828) recommended by Bottger, a 6-lb. bar of very hard cast steel was magnetized to satu- xx 668 ELECTRO-MAGNETISM. ration as completely as it could have been by any known process of communicating permanent Magnetism, merely by passing the spiral once backwards and forwards along the bar. (964) Electro- Magnets. When bars of soft iron are submitted to the influence of the voltaic current, they acquire a very high degree of Magnetism, but the coercitive force, that is, the force in a magnetic substance which opposes the separation of the two magnetic fluids, and their recombination when separated, being, in iron, almost inappreciable, the Magnetism is only temporary, the bar returning nearly to its normal state the moment the current ceases to pass through the enveloping helix ; we say nearly to its normal state, because if the iron be not perfectly pure it always retains a certain amount of Magnetism. Eig. 356 shows the ordinary arrangement of the horse-shoe electro-magnet. The copper wire, Fig. 356. which for large bars should be very stout and well co- vered with silk, is wound a a great number of times round the two arms, so as to form two bobbins, A and B. It must turn in the same direction round each bobbin, in order that the two extremities of the bar should acquire opposite po- larities; the S. pole being formed on the side at which the current enters, and the N. pole on the opposite side. The power of the electro-magnet varies with the size of the iron cylinder, with the intensity of the current, and with the length and thickness of the copper wire. With regard to the thickness of the iron bar, the power of the electro -magnet to deflect a magnetic needle, has been found by Dub to be proportional to the square root of the diameter of the cylinder, and its lifting power in proportion to its simple diameter. Instead of coiling the wire round the bobbins in one continuous length, which is known to diminish considerably the influence of the current, it is better that the total length of wire intended to be used should be cut into several portions, each of which, covered with silk or cotton, should be coiled separately on the iron; the ends of all the wires are then collected into two separate parcels, ELECTRO-MAGNETS. 669 and made to communicate with the battery, care being taken that the current shall pass along each wire in the same direction. A powerful bar electro-magnet was constructed' some years ago under the direction of Mr. Faraday, for the magnetic observatory at "Wool- wich. The helix was 27 inches long, by 2f . inches internal diameter ; it had 4 coils of No. 7 copper wire covered with tape ; their lengths being 108 feet 10- inches, 120 feet, 129 feet 7 inches, and 143 feet; in all 501 feet 5< inches ; and they were arranged with bars and clamps so as to admit of using one or more of the helices variously combined. The soft iron core was 28 inches long by 2| inches in diameter, and there were 2 ether cores, each 12 inches by 2f inches, for magne- tizing a steeL bar placed in the coil between them. A horse-shoe electro-magnet of extraordinary power was constructed in the year 1830, for the Faculty of Sciences, at Paris, by M. Pouillet. It con- sisted of two horse-shoes, the ends of the branches of which were presented to each other, .the bands being turned in contrary directions. The superior horse-shoe was fixed in the frame of the apparatus, the inferior being attached to a cross piece which slided in vertical grooves formed in the sides of the frame. To this cross piece a platform was suspended in which weights wre placed, by the effect of which the attraction which united the two horse-shoes was at length overcome. Each horse-shoe was wrapped with 10,000 feet of copper wire, and they were so arranged that the poles of contrary names should be in contact. With a current of moderate intensity, this apparatus sup- ported a weight of many tons. (965) In Sturgeon's Annals of Electricity,, vol. vi., the three fol- lowing electro-magnets are described. The first is the contrivance of Mr. Eichard Roberts ; its peculiarity consists in the great extent of the area of the face, on the surface of which a series of grooves are formed, into which the conducting wire is coiled. The magnet is 2-iV inches thick, and 6f inches square on its face, into which are planed (at equal distances from each other across its surface) 4 grooves, 1J inch deep, and nearly |- of an inch broad. Into these grooves was coiled^ three-fold deep, a bundle of 36 copper wires (No. 18), wrapped with cotton tape, to prevent contact with the iron, the wires having no insulation from each other. The magnet, with the conducting wire, weighed 351bs. The armature was 1| inch thick, and the same size as the magnet on the face ; its weight was 231bs. The upper side of the iron, which constituted the magnet, was formed into an eye or bow, by which the whole was suspended ; and a similar bow was formed on the back of the arma- ture, to which the weight scale was attached. This electro-magnet, x x2 670 ELECTRO-MAGNETISM. when excited by a battery of 8 pairs of Sturgeon's cast iron jars, is reported to have sustained the enormous weight of 2950 Ibs. (Sturgeon's Annals, vol. vi. p. 168), which is nearly double the weight which the author's large magnet, the weight of which is about 1121bs., will sustain with any battery that has been tried. The second is that of Mr. Joseph Radford. Its peculiarities con- sist in the convoluted figure of its face, and in the unusual arrange- ment of its poles, both of which are on the same convoluted strip of iron, one pole occupying the whole length on one edge, and the other the whole length of the opposite edge. Its diameter is 9 inches, and it weighs, with its copper coil, 18 Ibs. 4 oz. The keeper, or armature, weighs 14 Ibs. 4f oz. The depth of the convoluted groove, or recess, is f of an inch, and \ of an inch wide. The width or breadth of the metal between the grooves is J an inch ; the thickness of the magnet is 1 inch at the outside edge, and about f in the centre. When excited by a battery of 12 of Sturgeon's jars, this electro-magnet is stated to have sustained 2500 Ibs. avoirdupois ; it is, therefore, in proportion to its weight, much more powerful than Mr. Eoberts's magnet. The third electro-magnet alluded to (vol. vi. p. 231.) is that of Mr. J. P. Joule, and is shown in Tig. 357. IB are two rings of brass, each Fig. 357. 12 inches in exterior diameter, 2 inches in breadth, and 1 inch in thickness; to each of these, pieces of iron are affixed, by means of the bolt- headed screws, s s, &C.L 24 of these are grooved, and fastened to the upper ring ; 24 are plain, and affixed to the^ lower ring, A bundle, W W, consisting of 16 Fig. 358. copper wires (each of which was 16 feet long, and -^o-th of an inch thick), covered with a double fold of thick cotton tape, was bent in a zig-zag direc- tion about the grooved pieces. Pig. 358 represents the method adopted for giving the electro-magnetic ring a firm and equable suspension : a a are hoops of wrought iron, to each of which 4 bars of the same metal are riveted, and welded together at the other end into a very strong hook. The hoops are bound down to the brass rings by means of copper wires. The weight of the pieces of grooved iron was 7'25 Ibs., and that of the plain pieces 4'550 Ibs ; and when excited by 16 pairs of the cast-iron battery, arranged into a series of 4, a weight of 2710 Ibs. was suspended from the armature, without separating it from the electro- ELECTRO-MAGNETS. 671 magnet ; and Mr. Joule thinks, that by the use of some precautions, which have occurred to him since making his first experiments, the actual power will be very considerably augmented. It has been mentioned that when very soft iron is employed in the construction of the electro-magnet, its Magnetism nearly dis- appears, when the voltaic current ceases to flow through the helix surrounding it. It was, however, discovered by the late Dr. Ritchie, that there are other circumstances which modify the retaining power ; the most remarkable of which is the length of the magnetic circuit. When the electro-magnet is very short, and the poles near each other, the retaining power is exceedingly small ; when the magnet is very long, the retaining power is very great, the reason of which appeared to Dr. Ritchie to be this (L. & E. Phil. Mag. vol. iii. p. 123.) the molecules of the electric fluid, acting on each other with the same force, will obviously return to their natural position most rapidly when the length of the circuit through which the action takes place is diminished. If it be diminished till the coercitive force of the iron be overbalanced by the tendency of the molecules to return to their natural state of equilibrium, from which they have been forced by the action of the conducting wire, the electro-magnet will lose all its retaining power. Another singular fact discovered by Dr. Ritchie was, that a short electro-magnet, though its lifting power be very considerable, is incapable of inducing permanent Magnetism on an unmag- netized horse-shoe of tempered steel ; while an electro-magnet of 4 feet in length, though of no greater lifting power than the small one, is capable of inducing a very considerable permanent effect. It was likewise found by Dr. Ritchie that a bar electro-magnet, 4 feet long, which scarcely retained any power when its connexion with the battery was broken, on being re-connected with it, in the name direction as before, was rapidly converted into a powerful mag- net ; but after being removed, and its wires now connected with the opposite poles, it required a long time to convert it into a magnet of much inferior power, as if the atoms of Electricity, having been first put in motion in one direction, are afterwards more easily turned in that direction than in the contrary. (966) It was first noticed by Professor Page, of Philadelphia, (Silliman's Journal, 1837), that during the act of sudden magnetiza- tion of a bar of iron, a peculiar sound is elicited. This phenomenon has since been studied by Marrian, Joule, Grove, Beatson, and other electricians. The sound is bsst observed by resting the end of a long iron bar, surrounded with a coil of covered copper wire, on a sounding board ; it thus becomes a musical note, and is distinctly 672 ELECTRO-MAGNETISM. audible throughout a large room. It is heard 'both on mag- netizing and demagnetizing the iron, that is, on making and on breaking contact between the coil and the battery ; ; but it is louder in the latter case than in the former. By suspending an iron bar so that it could vibrate freely, and circulating the voltaic current by a wire so as not to touch the bar, and breaking and renewing battery contact rapidly, Mr. Beatson elicited sounds as loud and distinct as those from a small bell ; he found, moreover, that similar though feeble tones were produced by passing an intermitting current from a set of 10 of Smee's battery, through a brass wire A-th of an inch in diameter, stretched across a sounding board, and from an iron wire simply suspended without any tension, with each end dipping into a mercury cup. Professor Page succeeded in producing the various notes in the scale by carefully suspending steel bars within a series of coils, and breaking the galvanic current at the rate of five or six thousand times per minute by a revolving apparatus placed in an adjoining room. These effects are caused by a molecular disturbance of the particles of the metal by the action of the galvanic current, as has been well shown by M. Wertheim (Gomptes Rendus, July 22nd, 1844) . It is strikingly illustrated by an experiment arranged by Mr. Grove, in which a glass tube, open at both ends, but protected along its length with a copper jacket, is filled with water, in which is suspended powdered magnetic oxide of iron. On looking through the tube at distant objects, a considerable portion of the light is intercepted by the heterogeneous arrange- ment of the particles of the oxide ; but on passing a current through a coil placed round the tube, these particles assume a symmetrical character, and much more light is transmitted. Mr. Beatson has shown (Elect. Mag. vol. ii, p. 295) that, at the moment the sound is produced, the metal undergoes a sudden expansion ; in the case of an unannealed iron wire, amounting to about -rsVoth of an inch, and on interrupting the circuit a similar sudden con- traction takes place ; this expansion and contraction is independent of that produced by the heating power of the current, as was proved by the fact of its taking place after the current had developed the total expansion which its heating power was capable of producing. Mr. Beat son also succeeded in eliciting distinct intonations from an iron wire by means of the discharge of a Ley den Jar; and we have frequently successfully repeated the same experiment. (967) An ingenious piece of apparatus was invented by the late Dr. Bitchie for illustrating the induction of Magnetism on soft iron. It is shown in Pig. 359, where a bar of iron is represented covered with a helix of insulated copper wire and mounted horizontally on BCTA.TING ELECTRO-MAGNETS. 673 Fig. 359. a wire, the extremity of which is finely- pointed, so as to allow the bar to rotate freely. The two ends of the helix are bent downwards so as just to dip into a small channel of mercury divided into two parts by a diaphragm of wood; one end of the wire dips into each division of the trough, and a sufficient quantity of mercury is poured into the trough to fill it, without however allowing the two portions to become united ; the mercury in each division will be found to rise a little above the level of the partition by capillary repulsion. It will thus be imme- diately seen that on connecting the two cells of mercury with the two plates of a battery the current must pass through the helix enclosing the iron bar before the circuit can be completed, and that the iron will consequently become for the time magnetic. Now, sup- pose each end of the iron bar to be opposed to the pole of a powerful steel bar magnet, an opposite pole on each side, and suppose the connexions with the battery to be made so that the N. pole of the iron bar is formed opposite to the N. pole of the steel bar, then as a necessary consequence, the opposite end of the iron bar will be a south pole, and will be opposed to the S. pole of the steel bar ; repulsion will accordingly take place on each side, and the iron bar will move through half a revolution. Here the wires of the helix surrounding it pass over the wooden partition, and dipping into the oppo- site cells of mercury, the polarity of the bar becomes reversed and so on, the bar soon revolv- ing with great rapidity in consequence of its polarity being reversed twice during each revo- lution. Sometimes the bar is arranged to rotate vertically as shown in Fig. (360.) (968) In all these pieces of apparatus the employment of mercury is essential. Messrs. Knight have, however, devised a method of arranging the rotating magnet whereby the use of the fluid metal is dispensed with. A round plate of brass is divided by 2 small Fig. 360. Fig. 361. strips of ivory and the wires of the helix are terminated by 2 small metallic rollers which thus pass easily over the brass surface, contact being broken at the proper place by the ivory strips. Fig. 361 exhibits this useful modification of Ritchie's rotating magnet. (969) In Fig. 362 a horse-shoe magnet is represented supported 674 ELECTRO-MAGNETISM. on a tripod stand with levelling screws, in which state it is well adapted for exhibiting the rotation of coils, wires, helices, &c. A A is the magnet, IB the tripod stand, C C two circular wooden cisterns for holding mercury, and capable of being adjusted at any required height by binding screws, E E are two light wire frames, F F two helices, H a Ritchie's rotat- ing magnet ; on the tops of the wire frames and helices are small cups to contain a drop of mercury, G is apiece of brass wire bent twice at right angles and terminated at each end by a fine point to dip into the globules of mercury: it can be raised or depressed without disturbing the general arrangement of the apparatus, as a simple inspection of the figure will show. When the rotating magnet is set in action in this apparatus a loud humming noise and sometimes a loud musical sound is excited by the rapid vibratory motion assumed by the fixed magnet during the rapid revolution of the electro-magnet. This musical sound is best observed when the levelling screws of the tripod are placed on a mahogany table in the middle of a large room. For the electro-magnet H a simple coil of wire may be substituted, the rotation of which will be exceedingly rapid, its faces becoming alternately attracted and repelled by the poles of the magnet. (970) In Sturgeon's Annals of Electricity, vol. iii., p. 426, will be found a description and engraving of an ingenious apparatus for exhibiting the simultaneous rotation in opposite directions of the permanent magnet and the electro-magnet. The current from the voltaic battery instead of going directly to the mercury flood in con- nexion with the electro-magnet, is made to enter two concentric troughs containing mercury, placed immediately under the former, communication between the upper and lower cups being established by means of wires; the electro and permanent magnet may thus be placed on one spindle, and the former being put in motion, it was found that the permanent magnet immediately commenced rotating in an opposite direction. This instrument was the contrivance of Mr. C. W. Collins. (971) Electro-Magnetic Engines. The prodigious force which electro-magnets manifest when excited even by a feeble current, and the power of annulling or reversing it in an instant, might seem to justify a hope of their affording a motive power as energetic and ELECTRO-MAGNETIC ENGINES. 675 more economical than the steam engine. An immense amount of inventive talent has been expended in attempts to realize this hope. These attempts have, however, shown (observes Dr. Robinson), that electro-magnetic engines can scarcely ever be a cheap or a very efficient source of power. Electricity is now known to have a definite mechanical equivalent. The zinc and acid required to produce it are more costly than the coal which will evolve isodynamic heat, and the hitherto contrived methods of converting Electro-magnetism into moving force, involve much more loss than the mechanism of the steam engine does in respect of heat. It may be added that the great magnetic force exists only in contact ; on the least separation of the keeper it decreases rapidly, not merely because magnetic force follows the law of the inverse squares of the distance, but because that separation destroys in a very great degree the actual Magnetism of the magnet. It must, however, be kept in mind, that there are many cases, where economy and intensity are of less consequence than facility of application and convenience, in which therefore the electro-magnetic engines deserves a preference either for industrial purposes, and much more for the work of the experimental physicist, although its action may be more costly. In particular, the absence of all danger, and perfect quiescence when not put in action, and the capability of being moved to any locality where a couple of wires can be led from its battery, deserve special consideration. (972) A series of experiments on the application of Electro-mag- netism as a motive force, is described by Dumont (Comp. Rendus, August, 1851), and the following consequences deduced : 1. The electro-magnetic force, though it cannot yet be compared to the force of steam in the production of great power, either as it regards the absolute amount of power produced, or the expense, may nevertheless, in certain circumstances, be usefully and practically applied. 2. While in the development of great power the electro-magnetic force is very inferior to that of steam, it becomes equal and even superior to it in the production of small forces, which may thus be subdivided, varied, and introduced into trades and occupations using but small capitals, where the absolute amount of mechanical power is of less consequence than the facility of producing it instantaneously and at will. In this point of view the electro-magnetic force assists, as it were, the usefulness of steam in the place of uselessly competing with it. 3 Other things being proportional, electro-magnetic machines, with direct alternating movement, present a great superiority of the power developed, over rotating machines, since, in the first, there are 676 ELECTKO-MAGKNETISM. no components lost, and with the same expense a much more con- siderable power is obtained than with rotating machines. 4 In machines of direct movement the influence of the currents of induction appears less considerable than in rotating machines. (973) To describe in detail all, or the most ingenious even, of the electro-magnetic engines that have been invented during the last eighteen years would involve far too great an expenditure of time and space. We select a few that have been thought by their inven- tors worthy of being patented.* * For the convenience of those who feel inclined to see and examine the de- scriptions of the numerous electro-magnetic machines that have been proposed by different experimentalists, a list of references to the periodicals containing some of the principal ones, is subjoined. . Sturgeon's Electro-magnetic Engine for turning Machinery. " Annals of Elec- tricity," vol. i. p. 75. Jacobi's valuable paper on the application of Electro-magnetism to the moving of machines, with a description of an Electro-magnetic Engine. " Annals of Electricity," vol. i. p. 408 419. Mr. Joule's Electro-magnetic Engine. " Annals of Electricity," vol. ii. p. 122. Mr. Davenport's Electro-magnetic Engine. " Annals of Electricity," vol. ii. p. 257. The Rev. F. Lockey's Electro-magnetic Engine. " Annals of Electricity," vol. iii. p. 14. Dr. Page on Electro-magnetism as a moving power. " Annals of Electricity," vol. iii. p. 554. Mr. Joule's second Engine. " Annals of Electricity,'' vol. iv. p. 203. Mr. Uriah Clarke's Engine. " Annals of Electricity," vol. v. p. 33. Mr. Thomas Wright's Engine. "Annals of Electricity," vol. v. p, 108. Mr. U. Clarke's Electro-magnetic Locomotive Carriage. " Annals of Elec- tricity," vol. v. p. 804. Jacobi on the " Principles of Electro-magnetical Machines." Report of the Meeting of the British Association, Glasgow, September, 1840. "Annals of Elec- tricity," vol. vi. p. 152. (This is a most valuable paper, and is well deserving of attentive study.) Mr. Robert Davidson's Electro-magnetic Locomotive. Engineers' Magazine, &c. Part 14, p. 48. Mr. Taylor's Engine. Mechanics Magazine, vol. xxxii. p. 694. Mr. Watkins's Electro-motive Machine. Phil. Mag., vol. xii. p. 190. An Inquiry into the possibility and advantage of the, application of Electro- magnetism as a moving power, by the Rev. James William M'Gauley. Report of the Proceedings of the British Association for the Advancement of Science, Dublin, 1835. '* Experiments and Observations on the Mechanical Powers of Electro-mag- netisrn : Steam and Horses. By the Rev. Dr. Scoresby. Phil, Mag., vol. xxviii. p. 448. Dr. Kemp's Patent for a new Method of obtaining Motive Power by means of Electro-magnetism. Repertory of Patent Inventions, Feb. 1852. Hansen's Electro-magnetic Engraving Machine. Athenceum, June 17, 1854. A new Electro-magnetic Engine, invented by M. Marie Davy. Comptes Rendus, May 15, 1854; and Phil. Mag., vol. vii. 1854. ELECTRO-MAGNETIC ENGINES. 677 (974) In Silliman^s Journal, for April, 1837, there is a notice of a rotative engine, invented and patented by Mr. Thomas Davenport of Brandon in the county of Rutland, and State of Vermont, United States. The following is a general outline of its construc- tion: The moving part is composed of 2 iron bars, placed hori- zontally, and crossing each other at right angles ; they are covered with insulated copper wire, and sustained by a vertical axis ; proper connexion with the voltaic battery being made in the usual manner. Two semicircles of strongly magnetized steel form an entire circle? interrupted only at the two opposite poles ; and within this circle, which lies horizontally, the galvanized iron cross moves in such a manner, that its iron segments revolve parallel, and very near to the magnetic circle, and in the same plane. Its axis, at its upper end, is fitted by a horizontal cog wheel to another and larger vertical wheel, to whose horizontal axis the weight is attached, and raised by the winding of a rope. By the galvanic connexion, these crosses, and their connected segments are magnetized, acquiring N. and S. polarity at their opposite ends ; and being thus subjected to the attracting and repelling force of the circular fixed magnets a rapid horizontal movement is produced, at the rate of 600 revolutions in a minute, when a large calorimotor is employed. The movement is instantly stopped by breaking the contact with the battery, and then reversed by simply interchanging the connexion of the wires of the battery with those of the machine, when it becomes equally rapid in the opposite direction. Another machine, composed entirely of electro-magnets, both in its fixed and revolving members, is also described. (975) In a subsequent number of the same Journal, it is stated that the proprietors had been engaged in experiments on magnets of different modifications, as well as on the proper distance between the magnetic poles of the circle ; that they had entirely altered the form and arrangement of the magnets, greatly increasing thereby the energy of the machine. The use of magnets in the form of segments of a circle, was discontinued, and horse-shoe formed magnets substituted ; the poles being changed once in every 3| inches of the circle. On this arrangement, a machine with a wheel 7 inches in diameter, elevated 90 Ibs. 1 foot per minute, and per- formed about 1200 revolutions in the same time. It is also stated that the proprietors were engaged in constructing a machine with a motive wheel of about 2 feet in diameter, from which, it was expected, that sufficient power to propel a Napier's printing press (requiring a 2-horse power), would be obtained. (976) In 1838 Captain Taylor obtained a patent for an electro- 678 ELECTRO-MAGNETISM. magnetic engine in the United States ; and on November 2nd, 1839, he patented the same engine in England. In the London Mechanics' Magazine, vol. xxxii. p. 694, there is a full description and drawing of this engine, a working model of which was for some time exhibiting in the Colisseum, in active operation, turning to the wonder and admiration of thousands, articles in wood, ivory, and iron. Referring to the above periodical for a detailed description of this engine, we shall confine ourselves to the peculiar principle of its action, as explained by Mr. Taylor. " The generality of the plans which have been hitherto devised for obtaining a working power from Electro- magnetism, have depended on taking advantage of the change of polarity, of which masses of iron fitted as electro-magnets are susceptible, so as to cause them alternately to attract and repel certain other electro-magnets, brought successively within the sphere of their influence, and thus to produce a continuous rotatory move- ment ; and the failure of these attempts is owing to the difficulty, if not impossibility, of accumulating power by such means. Instead of this, Mr. Taylor employs as his prime movers a series of electro- magnets, which are alternately and almost instantaneously magnetized and demagnetized, without any change of polarity whatever taking place, and certain other masses of iron or electro-magnets, are brought successively under the influence of the said prime movers when in a magnetized state, which latter are demagnetized as soon (or nearly so), and as often as their attractive power ceases to operate with advantage ; or in other, and perhaps plainer words, his invention consists in letting on, or cutting off, a stream of the electric fluid in such alternate, quick, and regular succession, to and from a series of electro-magnets, that they act always attractively or positively only, or with such a preponderance of positive attraction, as to exercise a uniform moving force upon any number of masses of iron or magnets, placed so as to be conveniently acted upon." The power of tho machine constructed on this principle, which was exhibiting at the Colisseum, was small, certainly much below that of a single man. Mr. Henley, however, afterwards constructed a very large engine on the same principle, which did some work, though at an enormous expense, the battery employed containing 13 cwt. of metal. (977) It appears from a letter in the Phil. Mag., (vol. xv. p. 250,) from Professor P. Eorbes, of Aberdeen, and also from a communication from Mr. Robert Davidson to the Mechanics'' Magazine, (vol. xxxii. p. 63,) that the latter individual had anticipated Mr. Taylor in the principle of his machine, having in 1837 employed the electro- magnetic power in producing motion by simply suspending the ELECTRO-MAGNETIC ENGINES. 679 Magnetism without a change of the poles: "so close," says Mr. Davidson, "is the resemblance between Mr. Taylor's machine and one of mine, that, independently of the frame work, I belie Ye the chief differences are, first, that the circumference of Mr. Taylor's revolving disc is composed of alternate parts of copper and ivory, while the circumference of mine is composed of alternate parts of copper and box- wood; and second, that in Mr. Taylor's machine the armatures appear to be sunk to about half their depth in the periphery of the wheel to which they are attached, while in mine they are sunk their whole depth, so as to be flush, with the cylindrical surface." (978) In the Practical Mechanics* and Engineers' Magazine for November, 1842, there is a full account and drawing of a large electro-magnetic locomotive constructed by Mr. Davidson, and tried on the Edinburgh and Glasgow Eailway. The carriage is 16 feet long and 6 feefc broad, and weighs above 5 tons, including batteries, magnets, &c. The electro-magnets are not one solid piece of iron, nor are they rounded behind. Each of the side parts or arms is constructed of 4 plates of soft iron put together, so as to form as it were a box for the sake of lightness. The arms are 25 inches long, and joined together behind by plates of iron. Their rectangular poles measure 8 by 5 inches, and at their nearest points are only about 4 inches asunder. The coils with which they are surrounded do not consist of a single copper wire, but of bundles of wire wrapped round with cloth to insure insulation. According to Mr. Davidson's first arrangement, these magnets were placed so that their poles were nearly in contact with the revolving masses of -iron in their transit ; but so prodigious was the mutual attraction that the means taken to retain the magnets and iron in their assigned position were insufficient. They required to be more firmly secured, and their distances had to be somewhat increased, which perhaps contributed very materially to the failure of the machine, which when put in motion on the rails travelled about 4 miles an hour only, thus exhibiting a power less than that of a single man, who on a level railway could certainly move a carriage of this weight at as great a velocity. (979) In 1838, Professor Jacobi, of St. Petersburg, at the expense of an imperial commission, tried the grand experiment of propelling a boat by the agency of Electro-magnetism. The vessel was a ten-oared shallop, equipped with paddle wheels, to which rotatory motion was communicated by an electro-magnetic engine. The boat was 28 feet long and 7-J- feet in width, and drew 2f feet of water. In general there were 10 or 12 persons on board, and the voyage was continued (on the Neva), during entire days. The 680 ELECTHO-MAGNETISM. difficulty of then managing the batteries, and the imperfect con- struction of the engine were sources of frequent interruption, and could not be well remedied on the spot. After these difficulties were in some degree removed, the professor gives as the result of his experiments, that a battery of 20 square feet of platinum will produce power equivalent to 1 horse : but he hoped to be able to obtain the same power with about half that amount of battery surface. The vessel went at the rate of four miles per hour, which is certainly more than was accomplished by the first little boat that was propelled by the power of steam. In 1839, Jacobi tried a second experiment in the same boat ; the machine, which was the same as that used on the previous occasion, and which occupied little space, was worked by a battery of 64 pairs of platinum plates, each having 36 square inches of surface, and charged according to the plan of Grove with nitric and sulphuric acid. The boat, with a party of 12 or 14 persons on board, went against the stream at the rate of 3 miles an hour. (980) Professor Page, of America, who has greatly distinguished himself by his researches in this department of science, has invented an electro-magnetic engine, the fundamental principle of which is thus described (Silliman's American Journal, Nov. 1850) : " It is well known that when a helix of suitable power is connected with the poles of a battery in action, an iron bar within it will remain held up by the induced Magnetism, although the helix be placed in a vertical position ; and if the bar be partly drawn out of the helix by the .hand, it goes back with a spring when the hand lets go its hold. This power the action of the helix upon the metallic bar within it is the power used in Page's engine. The power, when a single coil is used, has its points of greatest and weakest force, and in this con- dition is objectionable. But by making the coil to consist of a series of short independent helices, which are to be brought into action successively, the metallic rod is made to pass through the coil and back again, with great rapidity and with an equable motion. In all the engines hitherto used there is a loss of power at the instant of the change of current, owing to the production of a secondary cur- rent, moving in the opposite direction, and to this loss is owing the fact that these engines cannot be rendered available. Professor Page had in view the obviating of this difficulty when he commenced his investigations. He exhibited one of his engines of between 4 and 5 horse-power at the Smithsonian Institute, the battery to operate which was contained within the space of 3 cubic feet. It was a reci- procating engine of 2-feet stroke, and the whole, including the battery, weighed about 1 ton. Page states that the consumption of 3 Ibs. of ELECTRO-MAGNETIC ENGINES. 681 zinc a day would produce a 1 horse-power. Joule's estimate is widely different ; he calculates that in an electro-magnetic engine, constructed most favourably to prevent loss of power, the consumption of zinc per 24 hours to produce 1 horse-power is in a Grove's battery 45 Ibs., and in a DanielPs battery 75 Ibs. (981) By an extended application of the force which attracts a mass of iron within an electro-magnetic helix, Hankel also attempted to produce a motive power ; his investigations established the impor- tant practical law " that this force is as the square of the power of the current" Fessel has also described an engine constructed on the same principle (Biblioiheque Universelle de Geneva). His model is formed of two helices placed end to end in a horizontal position. They serve to conduct the current always in the same direction, but in such a way that it traverses alternately each of the two helices, and consequently only one at a time. In the interior of the helices is a bar of iron which is alternately attracted from the one into the other by constantly maintaining the same polarity, and which thus executes a motion backwards and forwards. To the two extremities of the bar are fixed two slender horizontal shanks of brass, which rest upon two pulleys attached to the two extremities of the appara- tus, and which thus support the whole weight of the iron. One of these shanks sets a wheel in motion ; a commutator is moved by an eccentric, by means of a directing rod which is placed so as to be able to make the machine move backwards and forwards as in steam vessels. In his later machines, Fessel has replaced the pulleys by oscillating shanks of metal rod, similar to the oscillating cylinders of steam engines. Fig. 363 represents Fig. 363. a small t working model of an electro- magneto-motive en- gine constructed by Mr. Bain, with some few improvements by the publishers of this work. On to a stout mahogany board are fixed the brass up- rights E E; to these are attached the elec- tro-magnets A , covered with stout wire; through the upper part of these uprights, and above the 682 ELECTRO-MAGNETISM. magnets, the two ends of the steel spindle c work ; this spindle carries about its centre an iron bit, which is alternately attracted by the two magnets A and , but prevented from absolute contact by pieces of paper ; another spindle, m, at right angles with c, and sup- ported by the uprights, h h, carrying at one end the fly-wheel, &, and on the other a small pulley, is cranked in the centre and connected with c by the spring and hook b. At h are seen two brass springs bearing lightly on the spindle, which is divided in the middle by a small piece of ivory, so that one only is in contact at the same time. The connexions are formed thus : one termination of the electro- magnet, A, is connected to one of the upright springs bearing on the spindle, and the other termination to the binding screws seen at the end of the board. The one termination of the electro-magnet is connected with the other spring, and the other extremity to the same binding screw to which one end of A was attached, the remaining binding screw being in connexion by means of a wire with the brass box in which m works. The working of this machine is greatly assisted by two spiral springs fixed underneath the board attached to the moving bit. The whole arrangement performs extremely well, and no doubt if made on a large scale would be very powerful. (982) Mr. Henley gives the following descriptions of two electro- magnetic engines, constructed by him for Mr. Talbot and Professor Wheatstone: " Mr. Talbot' s engine consisted of 6 powerful horse-shoe electro- magnets, placed in a line with their poles upwards ; to each magnet was adapted an armature, to which was affixed a jointed arm ; in the centre of the armature was a hole which was fitted to a 6-throw crank, the throws set at an angle of 60 with each other, the currents acting on the magnets in succession from 1 to 6 ; at the time of breaking at 6 it commences again at 1 : contact is made when the armature is at a small distance from the magnet, and is continued till it reaches it ; at this moment contact is broken and made with the succeeding one ; the connecting rod playing through the hole in the armature allows the crank to pass down ; when it remains stationary on the poles of the magnets a piece of paper prevents adhesion. There is a knob at the end of the connecting rod, by which it lifts the armature in one position, and is pulled in the other. In this machine the magnet acts when the crank is in the very best position, and were it not for the additional friction from the great number of rubbing parts, it would certainly be the best form of machine. On the shaft is mounted an A shaped frame, and at one end carries a heavy fly wheel, and at the other a contact-breaking ELECTBO-HAGNETIC ENGINES. 683 apparatus, which consists of a wheel and 6 levers, the points of which dip in mercury."* The original of Professor Wheatstone's machine consists of a brass ring, within which are placed 8 magnets ; an eccentric wheel revolves within, the longest radius of which passes close to each magnet successively, following the current as it were, which acts on each magnet a little in advance of the wheel ; the break piece, which is stationary, is made of a piece of ivory, into which are let 8 pieces of brass ; the shaft which passes through this without touching, carries a spring which presses on the break piece. The shaft and frame work is in connexion with one pole of the battery, one end of the coil on each magnet, and the other end of each with its corre- sponding piece of brass ; the shaft also carries a fly-wheel and pulley to transfer the power. If there were a hundred magnets, of course the same battery would be sufficient, as they only act one at a time. Mr. Henley has also constructed a machine which works a lathe, it is made with 3 horse-shoe magnets, with their poles upwards, the bent parts crossing each other ; a bolt passes through them and holds them firmly to a base : within the poles revolves a soft iron cross ; one magnet acts at a time, but the cross is attracted con- tinually. The cross is suspended by 4 stout brass columns. At first there were but 2, it was found necessary, however, to add 2 more to resist the strain of the magnets, as the poles are curved, and the cross passes very close : there is a piece of apparatus to stop it immediately it is a lever, which makes contact with one of the magnets independent of the break piece. (983) Electro-motive power has been applied very successfully by M. Gustave Froment of Paris, who has obtained so high a celebrity for the construction of accurate mathematical and astronomical instruments. We had prepared a description of one of the large one- horse-power machines of this ingenious mechanician from the " Elements de Physique " of M. Pouillet ; but having since been informed by the inventor that the description is inaccurate, and moreover that he had been obliged to abandon the use of the machine for giving motion -to his lathes and planing machines, on account of * This engine was 3 feet 6 inches long, and 2 feet 6 inches wide, but its power was not equal to the expectations that were formed of it ; when excited by a Grove's battery, consisting of 4 cells with double plates of zinc 9 inches by 6, platinum plates 9 inches by 5^, excited by diluted sulphuric acid 1 to 4, and con- . centrated nitric acid, Mr. Henley drove with it a lathe in which he turned a gun- metal pulley 5 inches in diameter, but in three quarters of an hour the battery was quite exhausted. This machine, it will be observed, was something more than a model. T Y 684 ELECTBO-MAGNETISM. the great expense of the battery, which amounted to 20 francs per day, we have not thought it worth while to have fresh drawings made of the machine. M. Froment states, however, that for delicate work, such as for giving motion to dividing instruments, polishing apparatus, &c., he finds electro-magnetic power very valuable as a mechanical agent, and constantly employs it in his workshop. (984) Hear tier's Magnetometer. This simple but useful apparatus designed by its author for ascertaining the conditions which modify the development of Magnetism in iron by the action of electrical currents, is shown in Fig. 364. Fig. 364. A B is a strong base of wood, about 4 feet long and 1 foot wide, to which are attached 4 levelling screws. D D are two strong iron uprights, firmly screwed into the base, and connected at the top by a stout iron cross piece E, having a hole in the centre through which passes the screwed tail F, of a strong double suspension hook Q-. Two iron nuts, H H, serve to fix the suspension hook at any height. 1 1 is a light and delicate, but strong steel yard, being graduated on one side to correspond with the distance between the knife edges K and M ; these are respectively 1 and 2 inches apart. Different weights, from 1 oz. to 16 lbs.,are applied on the long. arm, according to the power to be measured. N is a rest to support the long arm of the lever, and is capable of being adjusted to any height by a tightening screw in 685 the hollow socket 0. P is another suspension hook, upon which is hung the connecting piece Q ; which, by means of the long screw B, and swivel hook S, will admit of elongation or contraction without altering the parallelism of the keeper T, of the magnet U U. The magnet is secured to the stand by a lever, which passes through a hole in the fork, and through two iron plates, one above and the other below the stand, the whole being tightened by a screw nut from below. V V are two projecting studs, which serve to support the cylindrical counterpoise weights "W (seen in another part of the figure) which are made of lead cast with a hole in the centre, to allow of their being placed on, over the connecting piece Q, these weights are adjusted so as to exactly balance the long arm of the lever. A variety of magnets, differing in their shape and relative proportions, may be used in the place of N N : an extremely useful arrangement is represented in the figure. U U is a wire rope composed of 24* strands of No. 16 copper wire, each 12 feet long. These are all previously covered with cotton and thickly varnished with sealing wax, so as to render them perfectly independent of each other. They are then twisted together into a rope, by which means every strand bears the same relative position on the magnet. The whole rope is again covered with tape and varnished. It is then coiled upon the magnet, as represented in the figure, the ends being left loose, and numbered by attaching tickets to them. The value of this arrangement will be seen by taking the two extremes of which it is susceptible. First, all the similar ends may be united in one by a binding screw at each end, thus forming one stout conductor, 12 feet long and 24 strands thick ; or they may be united at dissimilar ends, so as to form one continuous length of 288 feet. A great variety of intermediate lengths and thicknesses can of course be formed, or the whole may be divided into independent conductors, carrying separate currents, either coincident or reverse. This arrangement will be found well adapted to determine the laws which govern a great variety of phenomena. For example, let it be required to ascertain the rate at which the magnetic development in iron proceeds, with known additions of exciting power. A small battery is attached to each wire, and the effect of each separately noted. The batteries are then added one after the other, and the difference between the actual and calculated effects can be thus ascertained. Again, the best mode of arranging wire upon a magnet, so as to obtain the greatest amount of power with a given quantity of wire and a battery of given dimensions, may be ascertained by taking any number of strands and uniting them in different lengths and thicknesses. The law of the resistance of wires and its relation to TT2 686 MAGNETO-ELECTKICITY. electro-motive force may be investigated under a great variety of conditions, and the relative value of different voltaic arrangements for electro-magnetic purposes may be correctly examined. The practical magnetist will perceive a great variety of applications, of which the instrument is susceptible, in addition to those already mentioned. (985) The following experiments with this instrument, having for their object to ascertain the rate of magnetic development in iron, by successsive additions of exciting elements of known power, applied through separate and independent coils, have been communicated by Mr. Hearder. The 24 strands of wire upon the electro-magnet were separately tested by the same battery, and each was found to produce the same lifting power; 24 Smee's batteries were employed in separate cells, each having a platinized silver plate of 4 inches square, and 2 amalgamated zinc plates to correspond. The magnetizing power of each battery was first ascertained, and its value noted in Ibs. Each battery had a single wire of the electro magnet appropriated to it, independently of the rest, and in each case the electro-motive force of the battery was less than the resis- tance of the wire, or, in other words, each battery excited more Electricity than the wire would carry. The batteries were numbered, and superadded in succession each to its own wire. The 1st column in the following table gives the distinctive number of the battery wire. The 2nd, the distinctive number of the battery. The 3rd, shows the value or exciting power in Ibs. of each battery. The 4th, the calculated sum of the elements employed; and the 5th shows the actual effect upon the electro magnet : TABLE I. Showing the rate of magnetic development in iron, by successive known increments of exciting voltaic power, applied through separate and independent coils. No. of wire. No. of batter,. 1 1 14| 14J 141 2 2 18i 32f 421 3 3 17i 50 701 4 4 13i 63i 94 5 5 15* 79 llli 6 6 15 941 125 7 7 14 108* 142 HEAEDEE'S MAGNETOMETEE. 687 N o.o fwire . No. otba e ry . Serf SggSS ^jeigM 8 8 181 1271 155 9 9 17| 144 ^ 169 10 10 13 \ 158i 174 11 11 15| I74i 186 12 12 15 189i 195 13 13 141 203| 207 14 14 18 222 218 15 15 I7i 239i 229 16 16 131 252| 236 17 17 15f 2681 238J 18 18 15 2831 2441 19 19 141 298 252 20 20 18i 3161 2561 21 21 I7i 3331 260 22 22 13i 346f 264 23 23 15f 2621 267 24 24 15 377J 271 (986) By this table it appears that, up to a certain point, the in- crease of magnetic power goes on more rapidly than is equivalent to the value of the additional exciting element. Up to 7 elements there appears an average excess of about 31 Ibs., but the proportion which this excess bears to the sum of the elements, appears to diminish rapidly after this point; and when about 12 or 13 are used, the excess almost disappears, and the total weight sustained is nearly equivalent to the united power of the batteries employed. After this point the pro- duction of power bears a decreasing ratio to the power employed, and this diminution of effect becomes more and more considerable towards the end, so that the last 5 elements scarcely produce an increase of effect equivalent to the value of one. Hence, it would appear, that a limit would somewhere be found to the susceptibility of iron to undergo magnetic induction. As the addition of each battery was in effect a mere extension of surface, the intensity of battery being the same, and as each wire presented the same re- sistance, an experiment was afterwards made with 12 voltaic elements, separately applied to 12 wires, and after ascertaining the amount of weight sustained, the 12 silver plates were united by one common conductor on one side, and the 12 zinc plates on the other, so as to make a single pair of twelve times the area, the wires of the electro- magnet still remaining attached, but no alteration of effect was ob- served. Some results analogous to the preceding were obtained from 688 MA&NETO-ELECTSICITY. the following experiments, in which the increase of -surface was effected by immersing a single pair of larger size in acid, by successive equal portions, and connecting an extra wire with it for each successive portion immersed: the results are given in the following table : TABLE II. Showing the rate of ntaglaetic development in wire, by successive and equal additions to the surface of the voltaic element, and corresponding additions to the capacity of the transmitting coil. 1 1 11 11 11 2 2 11 22 25k 3 3 11 ^33 40 4 4 11 44 53 5 5 11 ^55 >6 6 6 11 66 80 This table shews the same kind of difference between the increas- ing ratio of the resulting magnetic power, and that of the sum of the elements employed, estimated according to their individual value. (987) Application of' the Magnetometer to estimate the ^Electro-motive Character of different Voltaic Arrangements. Three voltaic elements were constructed as nearly as possible alike in size and surface. 1st. A Grove's nitric acid battery, consisting of a platinum plate, 4 inches square, immersed in a suitable flat diaphragm, externally to which were a pair of corresponding zinc plates. 2nd. A Daniell's sulphate of copper battery, having a copper plate of 4 inches square, and a diaphragm and zinc plates similar to the 1st. 3rd. A Smee's battery of similar dimensions, but having its zinc plates equidistant with those of the other batteries, in order to place each arrangement under the same conditions, with the exception of the omission of the unnecessary diaphragm. 4th. A 'Smee's battery, with the zinc plates at the ordinary distance from the silver. These batteries were first tested as to the relative quantities of Electricity excited by each, by employing a short helix of large dimensions, consequently opposing little or no resistance, the wires being united so as to form a helix 12 feet long, and 24 wires in thickness. Secondly, they were tested for intensity, by uniting the wires end to end, so as to form a single wire of 288 feet in length, thus opposing great resistance. The results are given in the following table : HEARDER'S MAGNETOMETER. 689 TABLE, showing the comparative power of Grove's, Daniell's, and Smee's batteries, in relation to quantity and intensity. INTENSITY. QUANTITY. Grove . . . .87 Grove . . . .44 Daniell . . . . 43 1 Daniell . . . .12 Smee, JSTo. 1, open . . 27^ Smee, No. 1, open . . 42 Smee, approximated plates 32 Smee, approximated plates . 49 Thus, it appears, that nearly equal quantities of Electricity are excited by equal surfaces of Grove's and Smee's batteries, but that the electro-motive force or intensity of the nitric acid battery is rather more than three times that of Smee's. Daniell's arrangement holds an intermediate position with regard to intensity, but is de- ficient in quantity. 690 MAGKETO-ELECTKICITY. CHAPTEE XIX. MAaNETO-ELECTBICITY. Electro-dynamic and Magneto-electric induction Terrestrial Magneto-electric induction Faraday's Kesearches The Magneto-electric machine Secondary currents Electro-magnetic coil machines The induction coils of Kuhmkorff and Hearder. (988) Electro-dynamic and Magneto-electric Induction. "When a current of Electricity from a single voltaic pair is sent through a metallic wire, it "induces a current of Electricity in a second wire forming a complete circuit and placed parallel to it, both at the moment when contact with the battery is made and when it is broken ; but while the Electricity continues to flow through the first wire, no inductive effect on the second wire can be perceived. The direction of the induced current on breaking battery -contact is the reverse of that on making contact. In the former case it is in the same direction, and in the latter in the reverse of that of the inducing current. By arranging a length of about 200 feet of copper wire in a coil round a block of wood, and a second similar coil, as a spiral, between the coils of the first metallic contact being everywhere pre- vented by twine by connecting the ends of the second coil with a small helix formed round a glass tube in which was placed a common sewing needle, and then causing a current of Electricity from a vol- taic battery to pass through the first coil, Faraday proved that the needle became a magnet, provided it was removed from the helix before battery contact was broken ; if, however, it was allowed to remain, its Magnetism was entirely or very nearly destroyed. If the needle was introduced into the helix after battery contact had been made in the first coil, it acquired no magnetic properties unless it was allowed to remain till battery contact was broken, it then became a magnet, though with its poles in a contrary direction from the first, thus proving that it is only at the moment of making and breaking battery contact that a current of Electricity is induced in the second coil, and that the direction of the inducea current is opposite in the two cases. (989) If, instead of coiling the wires round a block of wood, they are arranged round a ring of iron as shown in Fig. 365, where A and MAGNETO-ELECTRIC INDUCTION. 691 JB represent the compound helices, being separated by about -J- an inch of un- covered iron, a current of Electricity from the battery sent through one helix A, in- duces a current in the second helix J?, much more powerful than when the ar- rangement is made round wood, but only on making and breaking contact as before ; if the battery be large, a minute spark may be perceived between charcoal points fastened to the ends of JB, at the moment of making, and sometimes, though not often, on breaking contact with the battery, but never while a con- tinuous current is passing through A. (990) To prove that the increased inductive power is occasioned by the iron and is not a common effect of metals, an arrangement of helices of copper wire may be wound round a hollow cylinder of thin wood or pasteboard, and the power of the induced current tested first with the helices alone ; then, after inserting a bar of copper, lead, tin, or any other metal except iron, and perhaps nickel, in the axis of the cylinder, no effect beyond that of the helices alone will be found to be produced ; but when a bar of soft iron is inserted, the power of the induced current will be found to be surprisingly increased. (991) By the following beautiful experiment (Ex. Resear., 36, 37), the property of ordinary magnets to induce electrical currents without the intervention of any galvanic arrangement, is clearly demonstrated. A long compound helix wound round a cylinder of pasteboard was connected with a galvanometer by two copper wires, each 5 feet in length ; a soft iron bar was introduced into its axis ; a couple of bar-magnets, each 24 inches long, were arranged with their opposite poles at one end in contact, so as to resemble a horse-shoe magnet, and then contact made between the other poles and the ends of the iron cylinder so as to convert it into a magnet, as shown in Pig. 366. By breaking the magnetic contacts, or reversing them, the Magnetism of the iron cylinder could be destroyed or reversed at pleasure. Upon making magnetic contact, the needle was deflected; continuing the contact, the needle became indifferent and resumed its first position ; on breaking contact it was again deflected, but in the opposite direction ; and then it again became indifferent ; when Fig. 366. the magnetic contacts were reversed, the deflections were reversed. 692 MAGNETO-ELECTEICITY. In order to prove that the induced electrical current was not occa- sioned by any peculiar effect taking place during the formation of the magnet, Faraday made another experiment in which soft iron was rejected, and nothing but a permanent steel magnet employed. The ends of the compound helices being connected with the galvano- meter, either pole of a cylindrical magnet was thrust into the axis, as shown in Fig. 367, the needle of the Fig. 367. galvanometer was immediately deflected, but soon resumed its first position; on with- drawing the magnet a second disturbance of the needle took place, but in an opposite direction. (992) When a powerful magnet is employed, induced electrical currents are evinced by the galvanometer, when the helix with its iron cylinder is brought near, but without touching the magnetic poles ; and by experimenting with the large compound magnet belonging to the Eoyal Society,* Faraday was able to throw the needle of the galvanometer 80 or 90 from its natural position by placing the copper helix without the iron cylinder between the poles ; and by using an armed loadstone capable of lifting about 30 pounds, he succeeded in powerfully convulsing the limbs of a frog by the induced electrical current. (993) Terrestrial Magneto-electric Induction. "When a soft iron bar is held in the direction of the magnetic meridian, and inclined in the position of the dip of the needle, it becomes a temporary magnet, the lower end acquiring the properties of the N. pole ; if the bar be inverted, its polarity is at the same time changed. Faraday took a soft iron cylinder, and having carefully deprived it of all traces of Magnetism by heat, he placed it in the axis of a coil of wire, the ends of which were connected with a galvanometer by wires eight feet long. The coil was held in the line of the dip, and then suddenly inverted ; the needle of the galvanometer was immediately deflected, proving that a current of Electricity was evolved by means of the Magnetism of the globe ; he afterwards succeeded in obtaining indications of Electricity without the iron cylinder; and by causing a circular plate of copper to rotate in a horizontal plane, electric pheno- mena were produced without any other magnet than the earth : when the plate was revolved in the same direction as the hands of a watch * This magnet is composed of about 450 bar magnets, each 15 inches long, 1 inch wide, and \ an inch thick, arranged in a box so as to present at one of its extremities two external poles. It requires a force of nearly 100 pounds to break the contact of an iron cylinder f of an inch in diameter and 12 inches long, put across the poles. It formerly belonged to Dr. Gowin Knight. FABADAY'S RESEARCHES, 693 move, the current of Electricity was from the centre to the circum- ference ; when in the contrary direction, the current was from the circumference to the centre. (994) A new electrical machine was thus formed, diifering re- markably from the common machine in the circumstance of the plate being a most perfect conductor, and in the absolute necessity of a good conducting communication with the earth. "When the plate was revolved in the magnetic meridian no electrical effects were developed, and they became most powerful when the angle formed by the plane of the plate with the dip was 90. It was likewise shown by Faraday that a current of Electricity is produced in a wire by merely moving it from right to left, or from left to right, over a galvanometer, and he states it to be a remarkable consequence of the universality of the magnetic influence of the earth, that scarcely any piece of metal can be moved in contact with others, either at rest or in motion with different velocities or in varying directions, without an electric current existing within them ; further researches likewise proved that the current produced by the magneto-electric induction in bodies, is exactly proportional to, and altogether dependent upon their conducting power. (995) By the aid of the diagram, Fig. 368, the relation between volta-electric and magneto-electric induction may easily be under- stood. Suppose an electrical current to be passing through the middle wire from P to N, this wire is surrounded at every part by magnetic curves, diminishing in intensity according to their distance from the wire, and which in idea may be likened to rings situated in planes perpendicular to the wire, or rather to the electric current within it. The dotted rings may represent the magnetic curves round the wire N P, and if small magnetic needles be placed as tangents to it, they will become arranged as in the figure. But if instead of causing the needles to be influenced by an electric current, Fig. 368. r~ s* - zzr^ f \>s they are acted on by magnets, then in order that they shall take up the same position as before, the magnets must be placed as shown in the figure, the marked and unmarked poles a b above the wire being 694 MAGNETO-ELECTRICITY. in opposite directions to those a' V below it ; in such a position, therefore, the magnetic curves between the poles a b and a b' have the same general direction with the corresponding parts of the ring magnetic curve surrounding the wire N P carrying the electric current. Now if a second wire pnbe brought near the wire carrying the electric current, it will cut an infinity of magnetic curves in the same manner as it would the magnet curves if passed from above downwards between the poles, and the electric current induced in the wire will obviously be the same in both cases ; if the wire p' n be carried up from below, it will pass in the opposite direction between the magnetic poles, but then the magnetic poles themselves are reversed, consequently the induced current is in the same direction as before ; it is also for equally evident reasons in the same direction, if produced by the influence of the curves dependent on the wire. (906) Electric &park from a Magnet. Faraday first obtained a spark from a temporary or electro-magnet in November, 1831 ; but the first person who obtained the spark from a natural or permanent magnet in this country, was Professor Forbes of Edinburgh ; the experiment was made on the 13th of April, 1832, with a powerful natural magnet capable of supporting 170 Ibs., presented to the University of Edinburgh, by Dr. Hope. * The arrangement of the apparatus is shown in Fig. 369. A is the magnet ; a b a cylindrical Fig. 369. collector of soft iron passing through the axis of the helix c, and connecting the poles of the magnet ; accuracy of contact was found to be of considerable importance in the success of the ex- periment, and one side of the cylinder was carefully formed to % a curve of about 2 inches radius for this purpose. Great advantage was found from a mechanical guide not represented in the figure to enable an assistant to bring up the connector rapidly and accurately to the magnet in the dark. The helix c, consisted of about 150 feet of * The first spark was obtained by Professor Forbes on the 30th of March. It appears that the first document giving an account of the excitation of a spark from a permanent magnet, is by Signor Nobili and another dated from the Museum at Florence, lst January, 1832. ELECTRIC SPARK FROM A MAGNET. 695 copper wire, nearly ^.th of an inch in diameter, 1\ inches long, and containing 4 layers in thickness, which were carefully separated by insulating partitions of cloth and sealing-wax. The one termination d e of the wire passed into the bottom of a glass tube h, half filled with mercury, in which the wire terminated, and the purity of the mercurial surface was found to be of great consequence. The other extremity f, of the helical wire com- municated by means of the cup of mercury i, with the iron wire, g, the fine point of which may be brought by the hand into contact with the surface of the mercury in h, and separated from it at the instant when the contact of the connector a 5, with the poles of the magnet is effected. The spark is produced in the tube h. The success of the experiment obviously depended on the syn- chronism of the production of the momentary current by connecting the magnetic poles, and the interruption of the galvanic circuit at the surface of the mercury ; with a little practice, Mr. Forbes was able to produce for many times in succession at least two sparks of a fine green colour from every three successive contacts. (997) The magnetic spark may be produced with great ease and certainty, and with a magnet of moderate strength by employing the little arrangement shown in Eig. 370. It consists merely of a cylinder of soft iron, round the centre of which is wound a few feet of small insulated copper wire ; to one end of Fig. 370. this wire is soldered a small disc of copper which is well amalgamated, the other end is bent up, the point cleaned and amalgamated, and brought into contact with the disc. On laying this cylinder across the poles of the magnet, and then suddenly breaking contact, the point and the disc become separated at the same time, and the spark appears. Another excellent method of showing the spark from a single pole, and which is well adapted for the lecture table, is to mount a strong bar magnet (about 2 feet long) horizontally on a stand, to wind 18 or 20 feet of wire, the ends of which are prepared, as in the last arrangement, round a piece of wood, through which a hole is cut large enough to allow the end of the magnetic bar to work freely ; rapid horizontal motion is then given to the coil by means of a multiplying wheel, and con- tact between the point and disc is broken by the end of the bar striking a small piece of wood loosely placed at one end of the aper- ture in the wood, through which one end of the copper coil passes. A series of sparks which, if the magnet is powerful, are very brilliant, appear with such rapidity as to keep up a constant light. MAGNETO-ELEOTE1CITY. (998) In the fourth volume of the London and Edinburgh Philo- sophical Magazine, page 104, a very simple method of detonating a mixture of oxygen and hydrogen gases by the magneto-electric spark was described by the late Dr. Ritchie. It forms an excellent class experiment. Round the soft iron lifter of a horse-shoe magnet capable of carrying fifteen or twenty pounds, 10 or 12 feet of insulated copper wire are wound. To the ends of the coil 2 thick copper wires are to be soldered in order to form a complete metallic circuit when the lifter is in contact with the poles of the magnet. The magnet is mounted, poles upwards, on a wooden stand, having a pillar with an arm or lever passing through a mortice in the top of it, for the purpose of removing, by a sudden jerk, the lifter from the poles of the magnet. In front of the magnet a glass tube is fixed, having its top closed by a cap of box- wood, through which the copper wires soldered to the extremities of the coil pass, as near air-tight as Fig. 371. possible, into ths glass tube ; the end of one wire being flattened, is bent at right angles and well amalgamated. The other, which is straight, can be brought down or removed from it by means of the lever. The whole ar- rangement will be readily understood by a simple inspection of Fig. 371. The mixed eases are introduced O into the tube G by means of a bent or flexible tube. On giving the lever E a smart blow with the palm of the hand, the iron lifter A B is suddenly removed from the poles of the magnet, a current of Electricity is induced in the coil, contact between the wires in the tube G is broken, a spark appears, and the gases are immediately exploded. (999) The Magneto-electrical Machine. The first magneto-electric machine that is, an instrument by which a continuous and rapid succession of sparks could be obtained from a permanent magnet was invented by M. Hipolyte Pixii, of Paris, and was first made public at the meeting of the Academic des Sciences, on Sept. 3rd, 1832. A description of this invention will be found in the Annales des Chimie, for July, 1832, and a representation of it in Becquerel's THE MAGNETO-ELECTBICAL MACHINE. 697 " Traite de 1'Electricite," vol. iii. "With this machine, furnished with a coil about 3,000feet in length, sparks and strong shocks were obtained ; a gold leaf electrometer was made to diverge, a Leyden jar was weakly charged, and water was decomposed. (1000) At the meeting of the British Association at Cambridge, in June, 1833, Mr. Saxton exhibited his improvement on Pixii's machine, and in the August of the same year, a large instrument on the new construction was placed in the Gallery of Practical Science, in Adelaide Street. With this machine were exhibited- the ignition and fusion of platinum wire, and the excitation of an electro-magnet of soft iron; and in December, 1835, there was added to the instru- ment the double armature, producing at pleasure either the most brilliant sparks and strongest heating power, or the most violent shocks, and effecting chemical decompositions. Saxton's machine differs principally from Pixii's in two respects : first, in M. Pixii's instrument the magnet itself revolves, and not the armature ; and secondly, the interruptions, instead of being produced by the revolu- tion of points, were made by bringing one of the ends of the wire over a cup of mercury, and depending on the jerks given to the instrument by its rotation, for making and breaking the contact with the mercury.* (1001) In the Philosophical Magazine for October, 1836, Mr. E. M. Clarke describes his ingenious arrangement of the magneto-elec- trical machine, in which the battery of magnets is placed in a vertical, instead of a horizontal position, whereby vibration (known to be so injurious to magnets) is materially lessened. Two soft iron arma- tures are employed ; one is covered with 40 yards of thick copper bell wire, and is used for quantity effects, such as igniting platinum wire, magnetizing iron, producing the spark, deflagrating metals, &c. ; and the other, the iron of which is only half the weight of the former, has 1,500 yards of fine insulated copper wire on it, and is used for the exhibition of those effects usually ascribed to intensity, viz., giving the shock, and effecting chemical decompositions. (1002) Saxton's machine as at present constructed is exhibited in Fig. 372. Eigs. 373, 374, 375, 376, 377, 378, show the different arrangements and their application to illustrate various phenomena. The letters in Eig. 372, answer to the same in the other figures. A is a compound horse-shoe magnet, composed of 6 or more bars, and supported on the rests b e, which are screwed firmly on the board * A description and engraving of the machine deposited by Mr. Saxton in the Adelaide Gallery, in August, 1833, will be found in Lond. and Edinb. Phil. Mag., vol. ix. p. 360. MAGNETO-ELECTEICITT. B D ; into the rest e, is screwed the brass pillar c, carrying the large wheel f 9 having a groove in its circumference, and a handle by which it can readily be revolved on its axis ; a spindle passes from one end of the magnet to the other between the poles, and projects beyond them about 3 inches, where it terminates in a screw at h, to which the armatures, to be described immediately, are attached ; at the further extremity is a small pulley, over which a gut band passes, by means of which, and the multiplying wheel /, the armatures can be revolved with great velocity. (1003) The armatures or inductors, as seen at F, are nothing more Fig. 372. Fig. 373. Fig. 374. THE MAGNETO-ELECTRICAL MACHINE. Fig. 375. 699 Fig. 377. than electro-magnets ; two pieces of round iron are attached to a cross piece, into the centre of which the spindle 7i, screws ; round each of these bars is wound in a continuous circuit a quantity of insulated copper wire, one end being soldered to the round disc , the other connected with the copper wire passing through, but insu- lated from it by an ivory ring. By means of the wheel and spindle, each pole of the armature is brought in rapid succession opposite each pole of the magnet, and that as near as possible without abso- lutely touching. The two armatures differ from one another. The one termed the quantity armature is constructed of stout iron, and covered with thick insulated wire. The other, the intensity armature, is constructed of slighter iron, and covered with from 1,000 to 2,000 yards, according to the size of the instrument, of fine insulated wire. The quantity armature is adapted for exhibiting the magnetic spark, inducing Magnetism in soft iron, heating platinum wire, &c. The intensity is best adapted for administering the magnetic shock z z 700 MAGtfETO-ELECTBICITY. (which from only a moderate-sized machine is so powerful, that few will venture to take it a second time), and for effecting chemical decompositions. (1004) The Flood Cup is that part of the instrument to which the different arrangements and apparatus used to illustrate various phenomena, are attached. The one here represented can be used either with or without mercury ; it consists of a square block of wood supported on a stand capable of being raised or lowered to the height required. Two hollows, r and s, are made on the top, into which mercury is put when that medium is required ; the round metal disc i (Fig. 372), revolves in s, and the point A, just dips into r ; the wire fork n, connects the two floods of mercury together. On revolving the armature, contact is continually broken and renewed at the point &, and a brilliant succession of sparks, forming almost a con- tinuous light, is produced. Two pieces of stout brass m, bent at two right angles, are fixed to the sides of the wood block, but insulated from each other ; to these are attached binding screws, which answer in every respect the same purpose as the mercury. (1005) Fig. 373 exhibits a small electro-magnet connected with the apparatus. A small roller u, attached to a spring, presses on the circumference of the metal disc i, at the same time a bent piece of wire is fixed by the binding screw p, into the centre of the copper pin, the terminating wires of the electro-magnet being connected with the binding screws q q. Pig. 374 exhibits the arrangement for heating platinum wire, which is enclosed in a small glass tube. Fig. 375, the arrangement for igniting charcoal points, the break piece z, being screwed to the copper pin, and a wire spring inserted into the binding screw p ; by this means contact is broken and renewed, as with the mercury and points shown in Fig. 372. Fig. 377 illustrates the method of decomposing water. Fig. 376, the combustion of steel by inserting a piece of wire in one of the binding screws q q, and a small file into the other ; on turning the wheel of the machine, and drawing the wire over the surface of the file, brilliant scintillations" are pro- duced. Fig. 378, exhibits the arrangement for administering the magneto-electric shock, w w represent 2 glass cups containing a little acidulated water ; into these the fingers or hands are to be dipped ; a small metal bottom connects them with the binding screws, one of which is connected by a wire with the fork n ; the other is inserted into the centre of the copper pin : on turning the wheel the magneto-electric shock is communicated. (1006) The magneto-electric machine is certainly one of the most beautiful and instructive instruments of modern science ; by it we see exemplified the close connexion between, if not the identity of, THE MAGNETO-ELECTBICAL MACHINE. 701 the electric and magnetic forces ; by it, the same heating, magnetizing, and decomposing powers, the same velocity of motion, the same physiological and the same chemical effects are shown to be common to both ; and let us not forget that it is to the genius and labours ol an English philosopher that we are indebted for the development oi the leading principles on which this beautiful instrument is con- structed. Let us remember that the unfolding of the laws of electro- dynamic and magneto-electric induction was effected by a countryman of our own, and that these brilliant discoveries were not (as many o: the first importance are known to have been) the offspring ol accidental or fortuitous circumstances, but purely the result of, and affording fine illustrations of that method of physical research introduced by the great reformer of philosophy (Lord Bacon), viz., well-founded and well-verified inductions and deductions. (1007) The application of the magneto-electrical machine to the art of electro-plating was made and patented by Mr. J. P. "Woolrich, of Birmingham.* In the 38th volume of the Mechanics' Magazine, page 146, will be found a full and illustrated account of the machine which he employed, and of the method of conducting the process. Mr. "Woolrich made use of sulphite of potash as the solvent for the gold, silver, and copper, with which the articles were plated ; and he gives in his specification a detailed account of the method of preparing the different "liquors." The thickness of the metallic coating to be deposited, depends on the time during which the article is submitted to the operation of the magnetic apparatus and solu- tions ; a thin coating will be deposited in a few seconds, whilst to obtain a thick coating the article must be submitted to the constant operation of the magnet and solution for several hours. The dis- tance at which the poles of the magnet should be placed from the ends of the armature will depend on the superficies of the article to be coated ; the larger the superficies, the nearer must the magnet be placed to the armature ; and the smaller the article, the greater must the distance be increased, the distance being inversely as the super- ficies of the article to be coated. If the surface of the article under the operation of coating becomes, while in connexion with the mag- netic apparatus, of a brownish or darkish appearance, or if gas be evolved from its surface, the distance between the poles of the magnet and the ends of the armature must be increased until the metal contained in the solution is properly deposited, Mr. Woolrich sub- sequently introduced such improvements into the magneto-electric machine, that at the cost of about 15 he was able to construct an * Patent dated August 1st, 1842; Specification enrolled, February 1st, 1843. z z 2 702 MAGKETO-ELECTBICITT. apparatus which was capable of depositing 60 ounces of silver per- week. The magneto-electric machine is now very extensively used in Birmingham as a substitute for the voltaic battery in the operation of electro-plating. A single Saxton's machine will, if kept in con- tinuous revolution, precipitate from 90 to 100 ounces of silver per week from its solutions ; and machines have "been constructed by which 2J ounces of silver per hour have been deposited upon articles properly prepared for this mode of plating (Miller's " Chemical Physics," p. 407). (1008) A very few words will suffice to explain the theory of the magneto-electrical machine, as at present understood. As often as the bent ends of the armatures or inductors F, F, F, Figs. 372, 373, 374, are brought by the rotation of the wheel opposite the poles of the magnet, they become by induction magnetic ; but they cease to be so when they are in the position shown in Fig. 372, viz., at right angles to it. Now, we have seen (991) that at the moment of the induction as well as of the destruction of the Magnetism in an iron bar surrounded by copper wire, currents of Electricity moving, however, in opposite directions, are induced in the wire, if the circuit be complete ; the points k, Fig. 372, are th erefore so arranged that they shall leave the mercury, and thus break the circuit in the wire surrounding the armature F, at the moment that its ends become opposed to the poles of the magnet ; for which purpose they must be placed nearly at right angles to it : the circuit is thus ^broken at the precise moment that a rush or wave of Electricity is determined in the wire, and hence the electrical effects that are obtained. As, however, the currents alternate in opposite directions, we cannot obtain the oxygen and hydrogen gases from decomposed water separately, when the full power of the machine is employed ; but by causing the wire p, Fig. 377, to rub on the break-piece z, instead of on the cylindrical part, one-half of the power of the machine is destroyed, but as the induced electrical current will be in one uniform direction, the usual results of polar decomposition may be obtained. Various methods have been contrived for obtaining a continuous electric current in one uniform direction from the magneto-electric machines : several magnetic batteries are connected together, and the respective armatures are so arranged that each shall in turn become magnetic just before the preceding armature has lost its Magnetism, a current is thus caused to commence in one coil before it has ceased in that one which immediately precedes it. (1009) The laws which regulate the magneto-electric force excited by Magnetism in the induction spirals, have been investigated by SECONBAEY. CUEEENTS. 703 j and his results agree with those which, in conjunction with Jacobi, he had previously found to regulate the intensity of the electro-dynamic force excited by voltaic currents. These laws^are (" Peschel's Elements of Physics," Vol. ii., p. 236) : 1 That the magneto-electric energy excited in an induction spiral by means of Magnetism is equal to the sum of the electro-motive forces of all the individual coils of the wire ; this is in accordance with the fundamental law of Ohm (394). 2 With equally powerful currents the magneto-electric force will be nearly proportional to the number of coils, the thickness of the wire exerting no influence on it ; its intensity will, however, be slightly diminished by increasing the width of the coils. The excitation of the current does not keep pace with the velocity of the rotation, the production and disappearance of the Magnetism in the iron cores requiring a certain time. (1010) Secondary Currents. If a small pair of voltaic plates be moderately excited, and a small short wire used to connect its mercury cups, no spark, or only a very minute one, will be perceived, either on making or breaking contact. As, however, the length of the con- necting wire increases, the spark becomes proportionally brighter, "until, from extreme length, the resistance offered by the metal as a, conductor, begins to interfere with the principal result"* (Faraday's "Ex. Eesearches," 1067.) If two equal lengths of wire be taken, and one made up into a helix, and the other laid out on the floor, and each used to connect the mercury cups of a small battery, very great difference will be observed in the size of the spark afforded by each on breaking contact. Supposing the length of each to be 60 feet, the wire laid on the floor will give a small bright spark, while the wire wound into a helix, will produce a large brilliant spark accom- panied by a snap. Again, to render the fact still more decisive, take 100 feet of covered wire and bend it in the middle, so as to form a double termination, which can be communicated with the electrometer ; wind one-half into a helix, and let the other remain in its extended condition; use these alternately as the connecting wire, and the helix will be found to give by far the strongest spark. (1011) The spark and snap are much increased when a bar of soft iron, or what is better, a bundle of iron wires, are introduced into the axis of the helix; but it is only on breaking contact with the battery that the effect is produced; the reason is, that the iron, magnetized by the power of the continuing current, loses its Magnetism at the moment the current ceases to pass, and in so doing tends to produce an electric current in the wire round it. (1012). These effects are evidently "dependent on some affections of 704 MAGNETO-ELECTRICITY. the current in the conducting wire, and the spark produced Vhen the cups of the electrometer are connected by a short wire, is the only one that can be considered as produced by the direct power of the battery ; that the increase of the spark when the wire is lengthened does not depend on any thing analogous to momentum in the Elec- tricity circulating through it, and consequently producing effects at the instant the current is stopped, is proved by the fact that the same length of wire produces the effects in very different degrees, according as it is simply extended or made into a helix, or forms the circuit of an electro-magnet. How then is it to be accounted for ? The inge- nuity of Faraday has provided an answer. In his ninth series of "Experimental Researches," he has shown, that if a current be established in a wire, and another wire forming a complete circuit be placed parallel to the first, at the moment the current in the first is stopped, it induces a current in the same direction in the second, the first exhibiting then but a feeble spark ; but if the second wire be away, disjunction of the first wire induces a current in itself in the same direction, producing a strong spark. The strong spark in the single long wire, or helix, at the moment of disjunction, is therefore the equivalent of the current which would be produced in a neighbouring wire, if such second current were permitted. Viewing the phenomena, therefore, as the results of the induction of electrical currents, the different effects of short wires, long wires, helices, and electro-magnets, may be compre- hended. If the inductive action of a wire a foot long, upon a collateral wire also a foot in length, be observed, it will be found very small ; but if the same current be sent through a wire 50 feet long, it will induce in a neighbouring wire of 50 feet a far more powerful current at the moment of making or breaking contact, each successive foot of wire adding to the sum of action; and by a parity of reasoning a similar effect should take place when the conducting wire is also that in which the induced current is formed ; hence the reason why a long wire gives a brighter spark on breaking contact than a short one, although it carries much less Electricity. (1013) If the long wire be made into a helix, it will then be still more effective in producing sparks and shocks on breaking contact; for by the mutual inductive action of the convolutions, each aids its neighbour, and will be aided in turn, and the sum of effect will be greatly increased. (1014) The following experiments were made by the author shortly after the publication of Faraday's researches. Two sheets of thin cooper, each 4^ feet long, and 26 inches wide, were cut into ribbons INDUCED CURBETfTS. 705 1 inch wide; all the lengths were soldered together, and formed into a single coil, with list intervening. A continuous coil of copper ribbon, 234 feet long, was thus provided. At the commencement of the coil, and at intervals of 25 feet through its whole length, wires were soldered, which projected about 2 inches, and supported small cups to contain mercury. By this arrangement, the current could be sent through any length of ribbon, from 234 to 25 feet, and by the aid of the mercury cups, the effect produced on one part of the wire by the action of an electrical current sent through any other part could be examined. In describing some of the experiments made with this coil, which seem to bear on the present subject, we shall distinguish the cups by figures, indicating their position on the coil, thus: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. corresponding to 25. 50. 75. 100. 125. 150. 175. 200. 234. feet. Exp. 1. When communication was made with the positive end of a pair of plates, contained in a pint cup, and excited by dilute sulphuric acid, and cup 1, and the wire from the negative end, dipped in succession into 2, 3, &c., to the end of the arrangement, the spark and snap increased in intensity to 4; at 5, it appeared the same, and afterwards went on decreasing to 10, where the spark was not nearly so large, nor was the snap nearly so loud; the maximum effect, therefore, seems to be produced with the battery when the current has traversed between 75 and 100 feet. Exp. 2. When a half-pint battery was employed, no difference in the size of the spark could be perceived in 4, 5, 6, 7, 8 ; but it was larger and brighter in these cups than in 2, 3, and 9 and 10, in which it seemed about the same: with a pair of plates, containing about one-fourth the surface of metal, no difference in the size or appearance of the spark, could be perceived throughout the whole arrangement, after cup 2, being as bright at 10, as at 3. Exp. 3. When a pair of plates, each 2 inches square, was em- ployed, the spark seemed brighter at 9 and 10 than either 4, 5, or 6 ; with a pair 1 inch square, the difference was more marked ; with a pair \ an inch square, it was feeble in 2, 3, 4, after which it went on increasing, and at 10 it was much larger ; with a pair a i of an inch, a slight snap was several times heard accompanying the spark in the last 3 cups ; but the sparks produced in the first 6 cups were decidedly smaller, and less bright. Exp. 4. A pair -J- of an inch square was then tried : sparks were produced in all the cups; feeble in 2, and 3, but in 7, 8, 9, 10, bright; largest and brightest in 10. Exp. 5. Strips of copper and zinc, an-inch long, and -^th of an 706 MAGNETO-ELECTRICITY. inch wide, were immersed in the acidulated liquor, and connected with the coil ; sparks were obtained in all the cups, bright in 8, 9, 10; the strips were then cut in half, and by rapidly breaking contact, sparks were obtained in 5, 6, 7, 8, 9, 10; they could only occasionally be got from 4, and not at all from 2 and 3. The strips were then reduced to about ^th of an inch long, and -^,-th wide ; in 9, and 10, several sparks were obtained, but none could be got from any of the other cups. Exp. 6. A large calorimotor, highly excited with nitrous acid, was then tried ; the brightest and loudest spark was at 2 ; the snap was very loud, and could be distinctly heard in a room, at the bottom of a flight of stairs, the door being shut, and also the door of the room in which the experiments were made ; it was as loud, every time contact was broken, as the explosion from a pint Leyden phial; the sparks were very vivid, and evolved copious fumes of mercury ; these effects rapidly diminished as the connecting wire approached the termination of the coil, and at 8, 9, 10, the sparks were not more brilliant nor louder than those produced by the half- pint battery. Exp. 7. The shock with this apparatus did not increase with the spark : when a brass conductor was grasped by the hand, and kept permanently in 1, and another held in the left hand, and dipped suc- cessively into each of the other cups, in which contact with the battery was rapidly broken by an assistant, the large calorimotor being employed, the following were the results : Exp. 8. The left hand conductor being in cup 2, and contact with the battery broken in it, the shock was very slight ; in 3 it was stronger, and went on increasing to 10, where it was strong enough to be felt at the elbows ; now the spark and snap were most intense in 2, and least in 10 ; hence the shock appears to be inversely as the Exp. 9. The left hand conductor was then dipped into the cup next to that in which contact was broken, being out of the circuit of the current, as for instance in 3, while contact was broken in 2 ; the shock went on increasing, as before, to the end of the arrangement ; it was then kept permanently in 6, while contact was broken in all the other cups ; in 2, 3, 4, the shocks were distinctly felt, and went on increasing to 9. Exp. 10. The current was then passed from 2 to 9, while the conductors were held in 1 and 10, then from 3 to 8, then from 4 to 7, then from 5 to 6, shocks were felt in all cases ; strongest when the current was from 2 to 9, and weakest when from 5 to 6. Exp. 11. The wires from the battery were then connected with 1 EXPERIMENTS WITH THE EIBBON COIL. 707 and 2, and the conductors held in 3 and 4, then in 1 and 3, while the conductors were in 4 and 5, 1 and 4, 5 and 6, &c. ; but no shocks were felt, even when the wires from the battery were in 1 and 8, and the conductors held in 9 and 10. Hasp. 12. Although, however, no shock could be obtained directly from this arrrangement, yet the existence of a secondary current was easily proved by the galvanometer, when the positive wire from the battery was in 1 and contact broken by the negative wire in 2, one wire of the galvanometer being in 3, and the other in 10, the needle was strongly deflected in a direction indicating the passage of a current in the same direction as the inducing current, that is, from 3 to 10. "When the needle had taken up its position, it was retained in it by a pin ; contact was then broken in 2, and the needle was immediately deflected in a contrary direction, showing now the passage of a current from 10 to 3. Exp. 13. By employing a coil apparatus powerful shocks were obtained from the secondary current; the wires from the large calorimotor being in 1 and 2, and the terminal wires of the primary coil in 3 and 10, shocks felt at the elbows occurred every time con- tact was broken, and when this was done rapidly by a revolving wheel, or by Ritchie's rotating magnet, the succession of shocks was almost intolerable ; when one of the wires of the primary coil was dipped in the same cup in which contact with the battery was broken, the shocks were very violent, even with a half-pint battery. "When a wheel was employed to break contact, the scintillations were very brilliant, when it was connected with the first four cups of the coil. The well known optical illusion, of a body in rapid motion appearing stationary, was beautifully shown when the room was darkened, and the large battery used. Without the intervention of the coil, the shocks obtained on breaking contact, by means of a wheel, were not so strong as was expected. The most efficient method in this case was to draw the end of the connecting wire rapidly over the edges of the ribbon, from the centre to the circumference. Exp. 14. Secondary shocks were obtained from the coil imme- diately ; i. e., without the intervention of the coil, by dipping the conductors grasped by the hand, in 10, and the negative cup of the battery, while contact was broken, in 2, 3, 4, 5, 6, 7, 8, and 9 ; in the last three, the shocks were as strong as could be given with any other arrangement of the apparatus, and when the coil was interposed, very severe, even when contact was broken by 2, and a half-pint battery employed. Exp. 15. The wire from the zinc end of the battery was then kept permanently in 10, and contact with the copper end broken in 9, 8, 7, 708 MAGNETO-ELECTRICITY. 6, 5, 4, 3, and 2, the left-hand conductor being in 1, and the right in the positive cup. Shocks were felt in all; slight in 9 and 8, and strong in 4, 3, 2* These results agree very closely with those obtained by Professor Henry, of New Jersey, Princeton, to whom we are indebted for a very elaborate investigation of the phenomena of the induction of galvanic currents, and for the discovery of analogous results in the discharge of ordinary Electricity. (1015) It was found by this experimentalist that when the length of the coil is increased, the battery continuing the same, the defla- grating power decreases, while the intensity of the shock continually increases, but that there is a limit to the increase of the intensity of the shock ; and this takes place when the increased resistance or diminished conduction of the lengthened coil begins to counteract the influence of the increasing length of the current. "When the inten- sity of the battery is increased, the action of the short ribbon coil decreases, but it is surprisingly increased when the length of the coil is increased in proportion. Thus Dr. Henry found that the current from a battery of 10 pairs of Cruickshank's trough, which, when sent through the ribbon, a, b, or c, (Tig. 379) produced scarcely any effect ; when passed through a spool of copper wire -iV of an inch in diameter, and Jive miles long, gave shocks too strong to be taken through the body; and that a battery composed of 6 pieces of copper bell-wire 1J inch long, and an equal number of pieces of zinc of the same size, was capable, through the medium of this long spool, to give shocks at once to twenty-six persons joining hands; though when a simple battery, exposing a zinc surface of If square foot was employed, no shock, or at most a very feeble one only, could be obtained. Fig. 379. (1016) Tig. 379 repre- sents the method by which battery contact was broken and renewed in Professor Henry's experiments : a is the ribbon coil about 100 feet long; d, a rasp, the end of which communicates with the zinc cylinder of the battery through the medium of a cup of mer- cury; one end of the ribbon is placed perma- After these experiments were made, the ribbon was cut down the midde, and 709 nently in tlie cup connected with the copper element, and by drawing the other end smartly over the surface of the rasp, a series of brilliant sparks are produced, and the electrical current through the coil is rapidly broken and renewed. Now on placing coil c, containing about 60 feet of insulated copper ribbon on coil a, a plate of glass being interposed, and sending the electrical current from the battery through a, it was found that as often as the circuit was interrupted, a powerful secondary current was induced in c, and that when the ends of this coil were rubbed together, sparks were produced; when a small coil of wire enclosing a needle was interposed, the needle became magnetic ; when a small horse-shoe of soft iron, surrounded by a coil of wire, was interposed, Magnetism was developed ; when the ends of the coil were attached to a small decomposing apparatus, gas was given off at each pole ; and when the body was interposed, a shock, though a feeble one, was expe- rienced. When, instead of a ribbon coil, a helix containing 2,650 yards of fine insulated wire was placed on coil a, the magnetizing effects disappeared, the sparks were smaller, and the decomposition less ; but the shock even from a single rupture of the battery current was sufficiently powerful to be sent through 56 persons, and was too strong to be received with impunity by a single individual. When a helix containing 1,500 yards of wire i^= of an inch in diameter was placed on coil a, scarcely any effects could be obtained ; nevertheless when the ribbon coil was made into a ring, as shown in 5, (Fig. 379) and the long spool of wire placed in the centre, shocks sufficiently intense to be felt at the shoulder, when passed only through the forefioger and thumb, were obtained, sparks and decomposition were produced, and needles were rendered magnetic. (1017) By these experiments it is proved that the induced current is diminished by increasing the length of the wire, and that the more so in proportion as the size of the wire is diminished ; it is also shown that when a ribbon coil is employed, the induced or secondary current has the properties of one of considerable quantity ', but of moderate intensity: and that when a helix of small copper wire is used, the soldered together so as to form a length of about 460 feet, \ an inch wide, which was insulated and wound as before, into a spiral : the maximum spark, with this arrangement, a pint battery being used, was at about 150 feet; and with a very small voltaic pair, the largest and brightest spark was still at the extremity of the spiral ; on the whole, the effect of dividing the copper ribbon was to diminish the size of the spark, but greatly to increase the intensity of the shock, which, when obtained from the last cup, and the negative end of the battery, was very severe. Water was readily decomposed by the secondary current, developed by this arrangement. 710 MAGNETO-ELECTEICITY, secondary current is one of small quantity, but of great intensity; the difference between the currents induced in the two cases is precisely similar to the difference which we notice between the Electricity from a voltaic battery consisting of a single pair of plates, and that from a voltaic arrangement consisting of a number of pairs in series weakly charged, as from the water battery (339). The fact that the induced current is diminished by a further increase of the wire after a certain length has been attained, is, as Dr. Henry observes, important in the construction of the magneto-electrical machine, since the same effect is produced in the induction of Magnetism. The wire on the inductor of the machine may therefore be of such a length, relative to its diameter, as to produce shocks but no decomposition ; and if the length of the coil be still further increased, the power of giving shocks may also become neutralized, from the increased resistance offered to the induced current by the great length of wire : a good idea of the difference between quantity and intensity may be formed by supposing that in the first there is a large current moving slowly without any or but small resistance, and in the second a small current moving with great velocity, but still having a resistance to overcome. The experiments of Professor Henry, relative to the induction of secondary currents at a distance, are exceedingly striking. By Fig. 380. sending an intermitting current of Electricity through the spiral , (Fig. 3 SO), and placing the helix of thin wire b, over it, a plate of glass ^ - being interposed, shocks may be obtained on grasping the handles attached to the coil. "When a, consisted of about 300 feet of copper ribbon, 1^ inch in width, and &, a helix of copper wire 5 miles long : Dr. Henry found that shocks might be obtained when the coils were four feet apart; and at a distance of 12 inches they were too strong to be taken through the body: the Professor also mentions a very instructive method of exhibiting these astonishing experiments, which we have frequently adopted in the lecture-room, viz., to cause the induction to take place through the partition walls of two rooms, for which purpose a coil, about 100 feet of ribbon, is sus- pended against the wall in one room, while a person in the adjoining room receives the shock by grasping the handles of a helix of about 300 yards of thin wire, and approaching it to the spot opposite to which the cml is suspended. The effect is as if by magic, without a visible cause. It is best produced through a door or thin wooden partition. (1018) When an intermitting electrical current is sent through the INDUCED CURRENTS. HENRY' S EXPERIMENTS. 711 ribbon coil as, (Fig. 381), a secondary current is, as we have seen, induced Fig. 381. in b, placed at a distance above it. Dr. Henry farther ascertained that this induced secondary current, by passing through the coil c, was capable of inducing a current of the third order in the helix d; and that this coil again, by passing through the helix e, induced a current of the fourth order in the coiiy, as was proved by the power possessed by this coil of magnetizing the needle g; he further determined that there existed an alternation in the direction of the currents of the several orders, commencing with the secondary, it was as follows : Primary current ......+ Secondary current . . . . + Current of the third order . . . . Current of the fourth order + Current of the fifth order . . . . From our previous knowledge of this subject, the induction of currents of different orders, of sufficient intensity to give shocks, on; about 300 oscillations of the iron bar can thus be obtained in a minute. The coil is thus arranged : on a reel, with a hollow axis, 3 inches in length, are wound about 60 feet of copper wire, i\th of an inch in diameter, covered with cotton thread for the purpose of insulation, the two ends being connected wiihp p (Fig. 385), so that by means of the binding screws communication may be made by wires with the contact-breaker and battery ; this is the primary coil ; over it a second insulated copper wire, - 8 vth of an inch in diameter, and about 1,500 feet in length, is wound, and the two ends are connected with s s, furnished with binding screws, for forming connexion with wires, for communicating the shock, &c. (1026) The connexion with the battery is best made in the way shown in Pig. 394 r in which R represents a section of the reel, S an end of the short helix connected with the mercury cup in J5, Z the other end of the short helix connected with one plate of the battery, whilst the wire connects the other cup of mercury in H with the other plate of the voltaic couple. When this is properly arranged, a series of induced currents may be obtained from s s, the extremities of the long helix, capable not only of communicating a series of intense shocks, but of exerting powerful electrolytic action; and when a bundle of soft iron wires is inserted in the hollow axis of the reel e, (Fig. 385), the dynamic power of the coil is considerably increased. In this case, indeed, the sparks produced when the ends of the helices round the iron bar E F, leave the mercury, are very- brilliant, accompanied by a loud snapping noise and a vivid combustion of mercury, clouds of the oxide of that metal being copiously evolved. (1027) If the ends P It?, of the long and thin coil are furnished with platinum points, and immersed in water acidulated with sulphuric acid, rapid electrolytic action ensues, torrents of minute bubbles of oxygen and hydrogen gases being evolved. If, instead of water, the points are pressed on paper moistened with iodide of potassium, electrolytic action ensues, iodine and oxide of potassium being separated. Solutions of neutral salts, such as sulphate of potash and soda, chloride of potassium, sodium, antimony, and copper, are also rapidly decomposed. In these experiments, as Dr. Bird remarks, it will be found that the great majority of the electro- positive elements (for example) appear constantly at one termination of the coil, cceteris paribus, but not all, for it must not be forgotten that on making, as well as breaking contact with the electromotor, an induced current takes place in the long coil, though of far weaker 3 A 2 718 MAGNETO-ELECTRICITY. intensity than the latter, to which it is opposed in direction, and consequently in electrolytic effects. (1028) If the brass conducting tubes d $ (Fig. 385), are grasped, even with the unmoisteued hands, the intensity of the rapid succession of shocks will be found intolerable, even when the battery used consists but of two plates, presenting 4 or 5 square inches of surface ; and with pairs of half an inch, the shocks obtained, when contact is rapidly broken (which in this case, is best done by a rotating magnet, motion being communicated by the fingers), are very disagreeable. When the wires at the end of the conducting tubes, d d' are made to touch, small bright sparks are produced ; and if, while the oscilla- ting bar of the contact-breaker is vibrating rapidly, a large pair of plates being employed, a piece of well-burnt charcoal is fixed on one of the terminations, and the other drawn lightly over it, a rapid succession of brilliant sparks is obtained. These sparks depend entirely upon the induced currents, as the fine coil has no connexion with the battery. For the exhibition of this, as well as of the electric light of an energetic arrangement, pencils of that kind of artificial graphite found lining the interior of the iron cylinders used for the distillation of coal in gas manufactories are very far superior to box- wood, or indeed to any other form of charcoal. By connecting the ends of the primary coil of this arrangement with the quantity inductor of the magneto-electrical machine, powerful shocks and strong electrolytic effects are obtained ; the spring must rub on the double break, which in this experiment performs the same office as the contact-breaker; the coil, which, as we have seen, is, when revolving before the magnets a powerful source of Electricity, supplying the place of the voltaic couple. (1029) There are several other forms of the electro-magnetic coil machine, and many other modes of breaking battery- contact with the primary coil. Fig. 386 is a very elegant arrangement; the primary coil con- sists of about 35 feet of insulated copper wire (No. 12), and the secondary of 1,400 feet of silk-covered copper wire (No. 20), battery- contact is broken and renewed by the rotation of the soft iron bar h, which, mounted between two brass pillars, is situated immedi- ately over the axis of the coil, in which is placed a bundle of iron wires ; the electrical ELECTUOMAGtfETIC COIL MACHINES. 719 current from the battery passes through the pillar d, and the axis carrying the iron bar ; and contact is broken and renewed by the point i dipping, as h revolves, into, and out of, the mercury contained in the brass cup g r mounted on the brass pillar a, through which the circuit is completed ; communication with the voltaic battery is made through one pair of the binding screws on the base of the instrument ; and the shocks, electrolytical effects, &c., are obtained from wires attached to the other pair. (1030) Fig. 387 represents another form of the instrument which possesses this advantage over the last, viz., that it does not require mercury. The current from the battery passes from the binding screw p, up the wire a, which terminates in a small disc of iron, arranged Fig. 387. immediately over the bundle of iron wires in the axis of the coil, from which however it is pre- vented from coming immediately into contact, when the machine is not in action, by the horizontal spring by which it is connected with the wire a. The binding screw c, is connected with a wire, the top of which is seen in the figure rising above the coil. On the top of this wire is a horizontal strip of metal tipped with platinum, and with this, by the action of the spring, the disc of iron is kept in contact ; now, when connexion is made with the battery through the wires p and c, the central core of iron wires becomes magnetized, and consequently attracts the disc of iron, thus breaking battery-contact ; the current being shut off, the disc of iron is again raised by the spring, and thus contact is broken and renewed with amazing rapidity. The secondary effects are obtained from the handles attached to p c. this is decidedly the best arrangement of the coil machine, as it is more compact than any other, and dispenses with the use of mercury. (1031) In Pig. 388 is a representation of the Eev. F. Lockey's electro-magnetic coil machine, to which is attached an ap- paratus for producing luminous galvanic rings. The contact-breaker is the curved spring C, which is carried rapidly round by the multiplying wheel and handle d, striking in its course against the notches For medical purposes, Fig. 388. 720 MAGNETO-ELECTRICITY-, in the interior of the metallic circled. This circle must have an odd number of teeth or notches, in order that the ends of the S shaped spring may produce the spark at opposite parts of the ring; when there are 25 or 35 breaks, the resulting ring of sparks is exceedingly beautiful. The diameter of the ring a ft may be about 5 inches ; rings a foot in diameter produce very brilliant effects ; they may be made of different metals, and if corresponding springs be used, 'there will be a different light for each. The rings are secured in the circular rabbet of the square piece of wood, A, by small turn buttons ; one end of the primary coil is in communication with the ring, the other is in connexion with the binding screw e, where one of the battery wires is to be fixed. The spring c has metallic communication with the other pole of the battery by means of its metallic socket, to which a wire is soldered and brought down to another connecting piece symmetrical with JJ to the interval of time elapsing be- tween the making and breaking of the circuit. To secure the rapidity and certainty of the contacts, a metallic plate, J J, is fixed across the band, Gr Gr, carrying 2 screws, the Fig. 411, extremities of which serve to re- gulate the motion of the lever, and to keep it within certain narrow limits just sufficient to secure ex- actness and regularity. The paper is in one continuous length, and is wound lightly round a wooden cy- linder, from which it is afterwards cut into convenient lengths. The operation of the instrument is as -pig. 413. Fig. 412. lever paper follows : Motion is given to the drum or barrel B (Pig. 411) in the direction of the arrow by a weight attached to a cord acting on wheel-work within ; the motion is communicated through a series of intermediate wheels to the cylinder E, between which and the cylinder F the paper passes ; E is kept in close contact with E by means of a spring; S is the steel cylinder underneath which the paper passes, and E is one of the steel points attached to the lever L (Fig. 410) ; the pulley Q receives motion in the direction of the arrow from the pulley E in the centre of the barrel B. It carries on its axis a horizontal arm, H, which is immediately under the lever ; it is bent at D so as to come into contact with the wooden friction-wheel, C, at the point P. This friction-wheel is fixed under the last screw of the machine, and below the lever. From the lever, L, proceeds a 756 THE ELECTRIC TELEGRAPH. strip of metal, A, which traverses the arm, H ; a screw and nut, I, placed at the extremity of the rod serving to lengthen or shorten it. It must act freely at its point of junction with the lever as well as at its point of junction with the screw H ; it also works a hammer, which striking a bell below the platform of the apparatus, warns the operator when a signal is about to be transmitted. Now, as long as the bent arm, H D, is in contact with the friction-wheel, the whole machine is at rest ; but when by the action of the electro-magnet on the lever, the rod A is raised, the weight being no longei restrained, gives motion to the barrel B, and the apparatus is put into action, but is again stopped the instant the bent arm touches the friction- wheel. In this way the operator, both near and at a distance, has perfect control over the instrument. The apparatus or key for opening and shutting the circuit is shown in Pig. 412. A small metallic anvil, E, is secured on a platform, P P ; it is in metallic communication underneath with a copper wire, C ; M is a metal hammer attached to a spring and soldered to the block, B, also in contact with a copper wire, D. Another and better form of key-apparatus is that shown in Fig. 413, the operation of which will be understood by a single inspection. The hammer, L, is prevented from touching the anvil, J, when the telegraph is at rest, by the spring, D, acting on the lever C ; the hammer, B, and the anvil, K, being then in contact : on pressing down the lever, L and J come into contact the voltaic current passes through the telegraph. (1066) The alphabet used with this telegraph is constructed by various combinations of the lines and dots in the following manner : D E F G H L M N P Q U V W X Y Z 345 6 890 Suppose, now, a message has to be transmitted from one station to another, say from Baltimore to Washington, the key of the first operator is at Baltimore, and his register at Washington ; the key of the second operator, on the other hand, is at Washington, and his register at Baltimore. Each has perfect control over his own appa- ratus, and sets the paper to receive his correspondent's message. The apparatus, wires, and batteries being found to be in good order, the Baltimore correspondent commences his communication, and however COOKE AND WHEATSTONE'S FIVE-NEEDLE TELEGRAPH. 757 rapidly and suddenly he establishes in his key the contacts between L and J (Fig. 413) the electro-magnet at Washington becomes excited, its armature attracted, the whole machinery of the telegraph brought into full operation, and the communication stamped on the paper in accordance with the above alphabetical characters. It having, however, been found in practice somewhat difficult to regulate the contacts between the hammer and anvil, so as to give full effect to this notation, Morse has substituted for it another code of signals by which a far greater precision is secured. (1067) Alexander's telegraph, a description of which appeared in the Mechanics' Magazine for November, 1837, consisted of 30 coils and 30 magnetic needles. Each needle carried a screen which con- cealed a letter behind it. On the transmission of the voltaic current through either of the coils (which was effected by pressing down its corresponding key), the needle was moved aside, and the letter on the] dial exposed^to view ; by confining the motion of the needle to one direction only, oscillation was prevented. Mr. Alexander's original instrument was shown at the Great Exhibition of 1851. In Davy's telegraph (1837) the letters or signals were painted on glass, which was illuminated by a lamp placed behind the instrument ; as in Alexander's, the letters were exhibited by the deflection of a mag- netic needle carrying a screen, which, when the telegraph was at rest, concealed them from view. (1068) The first patent of Messrs. Cooke and Wheatstoiie " for improvements in giving signals and sounding alarms at distant places by means of electric cur- rents transmitted through me- tallic circuits," was sealed on the 12th of June, 1837. The telegraph here patented is shown in Fig. 414, and is thus described by Mr. "Wheatstone in his examination before the Parliamentary Committee on Railways : " Upon a dial are arranged 5 magnetic needles in a vertical position ; 20 letters of the al- phabet are marked upon the face of the dial, and the various letters are indicated by the mutual convergence of 2 needles Fig. 4] 4. 758 THE ELECTRIC TELEGBAPH. when they are caused to move. These magnetic needles are acted upon by electrical currents passing through coils of wire placed immediately behind them. Each of the coils forms a portion of a communicating wire which may extend to any distance whatever ; these wires at their termination are connected with an apparatus, K, which may be called a communicator, because by means of it the signals are communicated. It consists of 5 longitudinal, and 2 transverse metal bars, fixed in a wooden frame ; the latter are united to the poles of a voltaic battery, and in the ordinary condition of the instrument, have no metallic communication ^with the longitu- dinal bars which are each immediately connected with a different wire of the line ; on each of these longitudinal bars, 2 stops are placed, forming together 2 parallel rows. When a stop of the upper row is pressed down, the bar upon which it is placed forms metallic communication with the transverse bar below it, which is connected with one of the poles of the battery ; and when one of the stops of the lower row is touched, another of the longitudinal bars forms a metallic communication with the other pole of the voltaic battery ; and the current flows through the 2 wires connected with the longi- tudinal bars to whatever distance they may be extended, passing up one and down the other, provided they be connected together at their opposite extremities, and affecting magnetic needles placed before the coils, which are interposed in the circuit." The 5 galvanometers or multipliers are numbered 1,1; 2,2 ; 3,3; 4,4 ; 5,5 ; and of the terminal wires 5 are represented as passing out of the side of the telegraph case on the left hand, and the other 5 on the right they are numbered 1, 2, 3, 4, 5. The wires of the same number as the multiplier are those which belong to it, and are con- tinuous. Thus the wire 1, on the left hand, proceeds from the first coil of multiplier 1, then to the second coil, and then coming off, passes out of the case, and is numbered 1 on the right hand ; and so on with the other wires. The letters C, J, Q, U, X, Z, are not represented on the dial. Each needle has two motions, one to the right, and the other to the left. For the designation of any of the letters the deflection of two needles is required, but for the numerals one needle only. The letter intended to be noted by the observer is designated in the operation of the telegraph by the joint deflection of two needles pointing by their convergence to the letter. Eor ex- ample in the figure the needles 1 and 4 cut each other by the lines of their joint deflection at the letter V on the dial, which is the letter intended to be observed at the receiving station. In the same manner any other letter may be selected. Suppose the needle 1 to be vertical as needles 2, 3, and 5, then needle 4 only being deflected points to the numeral 4 as the number intended to be signified. COOKE AND WHEATSTONE'S ELECTEO-MAGNETIC TELEGEAPH. 759 A second patent for improvements' on the needle telegraph was specified by Messrs. Cooke and Wheatstone in October, 1838. It relates principally to a method of enabling two intermediate sta- tions to communicate with each other and with either terminus ; and to sounding an alarum by liberating wound-up mechanism by the angular motion of a magnetic needle. (1069) The patent for Messrs. Cooke and Wheat stone's electro- magnetic telegraph bears the date of January 21, 1840. In this apparatus Mr. "Wheatstone availed himself of the property pos- sessed by soft iron of immediately acquiring and losing magnetic properties, by the establishment or interruption of a current in a wire covered with silk with which it is surrounded. To trans- mit all the letters of the alphabet and the figures which may be required in a telegraphic communication, two conducting wires be- tween one station and another, were found sufficient. By means of a commutator, which served to interrupt or establish the circuit at one of the stations, soft iron was magnetized and demagnetized an equal number of times at the other station. The commutator was a wheel turning on its axis, and the circumference of which pre- sented 48 portions alternately conductors, so that for one com- plete revolution of the wheel the current was 24 times inter- rupted and re-established ; a letter of the alphabet corresponded to each of these 24 alternations ; the soft iron at the other station was in like manner magnetized and demagnetized 24 times. This alternate state of the magnetization and non-mag- netization of the soft iron, gave an oscillating motion to a small appendix of soft iron, which communicated a similar motion to a wheel by which each of the twenty-four letters of the alphabet en- graved on the wheel were brought successively before the observer. Care was required to insure an agreement between the letters cor- responding to the alternations of the commutator, and those pro- duced by the alternate movement effected by the magnetization and demagnetization of the electro-magnet. Tho following was the method of working this telegraph : Suppose the commutator placed at A, and the letter A brought to the observer by the electro-mag- net (at each station they agree to arrange the apparatus that the starting point shall be the same), we wish to transmit the letter D ; the commutator must be moved onwards 3 alternations ; B, C, and D, have been successively introduced at the other station, and so on for each of the letters. A large bell which was struck by a piece of iron attracted by the electro-magnet at the moment when the circuit was re-established, served to give the signal. It is evi- dent that in order that the transmission be reciprocal, there must be 760 THE ELECTEIC TELEGEAPH. a double set of apparatus, so that each station may possess those necessary to transmit, and those necessary to receive the communi- cation. (1070) An addition to this was afterwards made and patented by Mr. "Wheatstone, by which the letters were printed instead of their being merely presented to the eye. The following are the means by which this is effected : For the paper disc of the telegraph, on the cir- cumference of which the letters are printed, a thin disc of brass is substituted, cut from the circumference to the centre, so as to form 24 springs, on the extremities of which types or punches are fixed ; this type-wheel is brought into any desired posi- tion just as the paper disc is. The additional part consists of a mechanism, which, acted upon by an electro-magnet, occasions a hammer to strike the punch, brought opposite to it, against a cylin- der, round which are rolled alternately several sheets of thin white paper, and of the blackened paper used in the manifold writing apparatus ; by this means, without presenting any resistance to the type-wheel, several distinct copies of the message transmitted are obtained. The great practical difficulty with this telegraph was that of insuring the synchronism of the movements of discs at the different stations, Fie:. 415. Fig. 416. or if they did not move precisely to- gether, then when B was visible at one sta- tion, A would be in view at another, and thus all would go wrong. It has, there- fore, been entirely abandoned for other and better plans. (1071) Messrs. Wheatstone and COOKE AND WHEATSTONE'S SINGLE-JSEEDLE TELEGRAPH. 761 Cooke's single-needle telegraph, patented May 6th, 1845, is shown in Fig. 415. The essential part of the instrument is composed of a single multiplier, with an indicator fixed vertically on a hori- zontal axis, and moving in front of a dial plate. This indicator may be either a light strip of wood, or a magnetic needle ; if the latter, its poles must be in a reversed position to those of the needle within the bobbin. "When the voltaic current is sent through the coil the needle is deflected to the right or to the left, according to the direction in which the current passes. The alphabet is situated both on the right and the left hand side of the needle ; some letters require 4 movements of the needle, but the last motion which completes the indication of a letter situated on the right hand side is always a movement to the right ; in like manner the last motion which completes the indication of a letter on the left side is always a movement to the left ; for example the letter "W is indicated by 4 motions of the needle, 3 to the left and 1 to the right ; the letter L also is indicated by 4 motions, first to the right, then to the left, then again to the right, and finally to the left. (1072) The code of signals adopted is shown in the following diagram ; and bearing in mind that the deflections of the symbols for each letter commence in the direct ion of the short marks and end with the long ones, it will be seen that the deflec- tions of a single needle may be made to denote all the letters of the alphabet. The numerals are in- scribed on the dial un- derneath the needle, and are indicated by the movements of its lower half; for example the figure 4 is designated by the motion of the lower extremity once to the right and once to the left ; the figure 9 by a movement once to the left and once to the right, and so on. The internal mechanism of the telegraph is exhibited in Fig. 418. B A is the bobbin, in the interior of which is placed either a single magnetic needle, in the form of a rhomboid, H inch long by Iths of an inch broad ; or which Mr. Walker found to be still better, several highly magnetized short needles, firmly secured on either or both sides of a very thin ivory disc. The exterior or index needle is about 3 inches long. The frame of the coil, B, is made of copper, 762 THE ELECTRIC TELEGRAPH. Fig. 418. wood, or ivory ; it is screwed to a plate of varnished copper against the side of the telegraph case. The copper wire surrounding the bobbin A is about TO oth of an inch in diameter, and is well covered with cotton; one end of the wire from the right hand bobbin is in contact with the screw Gr, which, by means of a metallic strap, is connected with the screw G-' secured on the base of the apparatus; the other end of the wire on the left hand bobbin is in contact with another screw, D, sup- ported by a strip of brass which is fixed to the base ; from this brass plate there rises an upright stiif steel spring d, which presses strongly against a point attached to an insulated brass rod, r, screwed against the side of the case ; on the opposite side of this rod is an- other point against which a second stiff steel spring, d', presses ; this spring is attached to a brass plate, E, terminated by a binding screw E' ; E', therefore, is the screw terminal of the wire from the left hand coil. If Gr' and E' be now connected by a wire, "W, the current will flow from GK through Gr into the right hand coil, out from the left hand coil to D, thence through d r d' to E, and from the terminal screw E', round the wire circuit, back to GT ; and if the wire from Gr' proceed up a line of railway, and the wire from E' down the line, the circuit being complete throughout, the needle in the bobbin, A, will be deflected by a current proceeding from any station on the line, and thus signals will be communicated. Battery contact is broken and the direction of the current reversed by the action of the springs d d' in the following manner : B is a box-wood drum, moveable by a handle seen at H, in the front of the base of Fig. 415. Kound either end of this drum are fixed the brass caps and Z ; the caps do not touch each other, a disc of box-wood being between them. Into these caps are screwed the steel projecting pieces C'Z', which become the poles of the battery, the Z' being connected with the zinc end, and C' with the copper, thus : a wire, C, from the copper end of the battery conveys the current, C'C', and a wire from the zinc end along Z, to a steel spring, which touches z, the continuation of the Z end of the box- wood cylinder. Now on moving the drum, by turning the handle, H, THE DOUBLE-NEEDLE TELEGRAPH. 703 Kg. 415, the steel spring d will be raised from its corresponding point on r ; the circuit will thus become broken, but by continuing the motion of the drum, the wire C will come into contact with the spring below it, and thus there will be a battery pole at either end of the drum, and signals will thus be made on the dial, and on all the instruments connected with it. The connexions are made in such a manner, that when the handle is turned to the right the needle moves to the right. The exterior, or indicating needle is always placed with its N. pole upwards ; that within the coil with its N. pole downwards ; so that, in accordance with Oersted's fun- damental law, looking at the face of the instrument, if we see the upper part of the needle moving towards the right, the spectator may be sure that the current is ascending in that half of the wire which is nearest to him. Fig 419. (1073) Messrs. Cooke and Wheatstone's double-needle telegraph now in general use for railway service in this country, is shown in Figs! 3D 764 THE ELECTRIC TELEGRAPH. 419 and 420. On the top of the case is the alarum, A, which is worked by the handle, B. H IT are the handles by which the two needles are manipulated, and S is the " silent apparatus." The internal mecha- nism is precisely similar to that of the single-needle apparatus. The Fig. 444. THE DOUBLE-NEEDLE TELEGRAPH. 765 letters of the alphabet are ranged from left to right, as in therordinary mode of writing, in several lines above and below the points of the needles, the first series, from A to P, being above, and the second series, from R to Y, below. Each letter is indicated by one, two, or three movements. The following is the complete vocabulary and mode of correspondence : A. Two movements towards the left, by the left needle. B. Three movements towards the left, by the left needle. C, and the Fig, 1. Two movements of the left needle, the first to the left, and the second to the right. D, and the Fig. 2. Two movements of the left needle, the first to the right, and the second to the left. E, and the Pig. &. One movement of the left needle to the right. F. Two movements of the left, needle to the right. G-. Three movements of the left needle to the right. H. and the Fig. 4. One movement to the left of the right hand needle. I. Two moyements to the left of the right needle. J is omitted, and replaced by Gr. K. Three movements of the right needle to the left. L, and the Fig. 5. Two movements of the right hand needle, the first to the right, the second to the left. M, and the Fig. 6. Two movements of the right needle, the first to the left, the second to the right. N, and the Fig. 7. One movement of the right needle towards the right. O. Two movements of the right needle to the right. P. Three movements of the right needle to the right. Q is omitted, and K substituted for it. E, and the Fig. 8. A single movement of both needles towards the left. S. Two movements of both needles towards the right. T. Three movements of both needles towards the left. U, and the Fig. &. Two movements of both needles, the first towards the right,, the second towards the left. V and 0. Two movements of both needles, the first to the left, the second to the right. W. One movement of both needles towards the right. X. Two movements of both needles towards the right. Y. Three movements of both needles towards the right. Z is omitted, and replaced by S_ 3 D 2 766 THE ELECTRIC TELEGRAPH. The sign + > indicating the termination of a word, is designated b j a single movement of the left needle towards the left ; the same signal is given when the receiver does not understand his corres- pondent's message. The exhibition of the letter E signifies that he does understand, and to denote the word yes. The signal for E is repeated twice, i. e., two movements of the left needle towards the right are made. (1074) The words "wait," "go on" seen on the right and left side of the bottom of the dial plate are of great importance. Suppose, for example, the London clerk wishes to communicate with his corre- spondent at Dover, and that the latter is at the time engaged, he immediately signals the letter E, thereby intimating that he is not prepared to receive the London message ; when he is at liberty, he directs his needles towards W, which means " go on," and the correspondence begins. It is also absolutely necessary to have a method whereby one station may signify to any individual station on the line that a message is proposed to be sent to it. Suppose, for example, that London wishes to communicate with Tonbridge ; on the dial plate of Pig. 419 will be seen the names of the six stations of one of the groups on the South Eastern Bail way, viz., Eeigate, Tonbridge, Ashford, Folkstone, London, and Dover ; each of these stations is represented by a letter. Thus, London is designated by E, Tonbridge by E, Dover by W, and so on. The London corre- spondent signals E, and at the same time rings the bell at the station at Tonbridge ; the Tonbridge clerk immediately returns the ring at London, thereby intimating that he is at his post. London now signals B, by which Tonbridge knows that it is London that wishes to communicate with him ; he returns the signal E ; London again rings the bell, and the correspondence commences, Tonbridge sig- nalling the letter E after every word if he understands, or the cross + if he does not. The message being finished, London deflects his left hand needle twice to the left ; Tonbridge returns the signal, if he has no reply to make, and proceeds to transmit the message to its destination. The numerals are indicated by certain letters ; the letter H, fol- lowed by a cross +, intimating that figures and not letters are about to be shown. The letter "W interposed between certain figures serves to group them : thus the letters HE "W N might mean 43 7*., or 43 feet 7 inches, &c. Special signals are also devised for special purposes. (1075) The mechanism of the alarum used on the telegraphic line of the South-Eastern Eailway Station is shown in Fig. 421. THE ALARUM. 767 Fig. 421. A is an electro-magnet ; B, an arma- ture of soft iron, which is attracted as often, and as long as, the voltaic current circulates round its bobbin. This arma- ture is prevented from coming into actual contact with the pole of the elec- tro-magnet by means of two little copper studs, tipped with ivory, inserted in its face ; this is necessary, because as soft iron does not lose the whole of its Mag- netism when the battery circuit is broken, permanent adhesion would otherwise en- sue. The armature is mounted on the short arm of a lever, C, carrying at the end of the other arm a short pro- jecting piece 0, which, catching in a stop in the circumference of the wheel d, prevents it from moving. The armature is brought back to its normal position, when the attraction ceases by the small spring./, which presses against the long arm of the lever. Of the clock-work contained in the barrel, only the principal pieces are shown in the figure ; the cog wheel & is connected by a pinion with the cog-wheel a, which works i, and this again gives motion to d, which carries the stop. The anchor escapement g works on the wheel i, and on the axis of the same wheel is placed the double-headed hammer, Ji. On completing the battery circuit, the armature, B, is attracted by the electro-magnet, the long arm of the lever, C, moves to the left, and the wheel d, being then set at liberty, the mainspring in the barrel, which is kept constantly wound up, sets it in motion, and the hammer is instantly put into rapid vibration, striking alternately the opposite sides of the bell, D ; the ringing is kept up as long as the circuit is closed, but the moment it is broken the armature is detached by the spring /, and the catch is again pressed into its place on the wheel d. It is not the voltaic current that rings the bell, but the mainspring in the barrel ; all that the Electricity does is to disengage the catch ; and there is no greater difficulty, therefore, in ringing a large bell than a small one. It is easy to see that this principle may be modified in a variety of ways. (1076) The batteries used to work our English telegraphs are com- posed of amalgamated zinc and copper plates, 4| inches long by 3J inches wide, the zinc being -A-ths of an inch thick. The plates are ce- mented water-tight on to stout teak-wood or oak troughs, each trough being from 15 to 30 inches long, and 5 inches wide, and divided into 768 THE ELECTBIC TELE&EAPH. 1 2 or 24 cells by partitions of slate. The plates connected together by copper slips, are placed across tbe slate partitions, and the cells are filled to within an inch of the top with siliceous sand, which is then saturated with a solution of 1 part of oil of vitriol in 15 parts of water. The numbers of cells used varies according to the distance between the stations : for short groups of 10 or 15 miles, 24 cells are employed, for distances from 40 to 60 miles double that number. The telegraphs on the South Eastern Bailway of 180 miles and 47 stations are worked with 2,200 pairs of plates, and the whole tele- graph system in the United Kingdom employs about 20,000 pairs. ("Walker's " Electric Telegraph Manipulation," p. 9.) According to Mr. Walker's experience, new batteries, when carefully put together, will, with care, do duty for six or eight months, when the work is not very heavy ; and by washing the sand out with a flow of water, and refilling them, they frequently remain on duty ten or twelve months without being re-amalgamated. In America, for the regis- tering telegraphs, Grove's battery is mostly in use, 30 cells of which are required for a distance of 150 miles. They require cleaning and replenishing about once a fortnight. Fig. 422. (1077) The modes of sustaining and insulating telegraphic wires adopted nearly universally in England are represented in Figs. 422 and 423. Wooden posts, from 15 to 30 feet high, are fixed firmly in the ground, at the rate of about 30 a mile ; the upper part of each post is 5 or 6 inches square ; it Fig. 423. carries a wooden arm, which is sepa- rated from the post by discs or rings of brown delf-ware. The arm is secured to the post by an iron bolt and screw. On the face of the wooden arm, 4 hollow double earthenware or glass cones are fas- SUSTAINING POSTS. 769 tened by collars of iron ; through these the wires pass, and are thus effectually insulated. A similar system of wires passes on the oppo- site side of the post, and each post is provided with a small roof of earthenware or slate, on the top of which is a metallic point con- nected with the earth as a preservative against the effects of light- ning. The contrivance for tightening the wires is seen at B. The posts on which this apparatus is placed are much stouter than the ordinary sustaining posts, and they are fixed at intervals of Jth of a mile apart. To the upper part of the post are attached as many iron screws as there are telegraph wires, and each screw carries a winder, consisting of a grooved drum with a wheel and ratchet attached ; the ends of the winder are insulated from the post by discs of earthen- ware ; a and b are two earthenware pulleys, or shackles, each furnished with two hooks insulated from each other. The winding post is thus seen to be out of the circuit, but the metallic continuity of the telegraph wire is secured by a thin wire, c, soldered to the outside of each shackle. The telegraph wire is of iron, about ith of an inch in diameter : it is protected against the corroding action of atmos- pheric air and moisture by being passed through a bath of melted zinc, or galvanized, as it is called ; zinc being more positive than iron, combines first with oxygen ; the wire thus becomes coated with a thin layer of oxide of zinc, which acts as a coat of paint and effec- tually preserves the iron. In the neighbourhood of large towns, where great quantities of coal are daily burned, the sulphurous vapours arising from such fuel and passing over the oxide of zinc covering convert it into sulphate of zinc, which being soluble in water, is immediately melted by the rain and drops off. The wire thus deprived of its insoluble covering soon corrodes. Mr. Highton mentions (" Electric Telegraph," p. 117) that he has seen galvanized iron wires reduced in this way in less than two years from the diameter of ^th of an inch to that of a common sewing needle ; and he suggests that in the neighbourhood of large towns the wires should either be painted and varnished, or entirely cased in gutta percha. (1078) The insulator employed on the " Morse " line from New York to Washington, is simply a glass knob with 2 rings, between which the wire is wrapped. It is said to be very imperfect (Turnbull on the " Electro-magnetic Telegraph," p. 176), the wire losing its insula- tion almost entirely in wet weather, and the instruments working with difficulty upon even the slightest shower. It has been found also, that with this form of insulator, the atmospheric Electricity cracks the glass in two pieces, just as if it had been cut with a diamond. In the " House" line of telegraph (American) the glass cap, which is 770 THE ELECTRIC TELEGRAPH. covered with lac varnish, is screwed into a bell-shaped iron cap, which is filled with much care to the top of the post, and well painted and varnished, the telegraph wire is fastened to the top of the cap by projecting iron points. This plan, though decidedly, superior to Morse's, is objectionable on the score of expense, and very inferior to the method adopted in England. In Germany, the wires are insu- lated by passing through porcelain caps, in the shape of a reversed cup, placed on the summit of the posts, which are thus covered with roofs. It is said to be very perfect. The posts in France are from 20 to 30 feet long, and are driven into the ground to a depth of from 30 to 60 inches, the buried parts being preserved by injection with sulphate of copper. The insulators, which are either bell-shaped or double oblique cones, are, as in England, fixed to the side of the post by screws, and sealed with sulphur in the interior ; the conducting wire passes through a ring support fixed in the interior of the cone, so that the wire only passes on a point sheltered by the mass of the support. When the conducting wires have to pass underground, they are usually made of copper, and are either covered with gutta percha or with cotton saturated with tar, and collected in leaden pipes in groups of three or four ; the leaden pipes are covered with a pitched cord, and the whole placed in an iron pipe. (1079) When the wires have to pass under water, as in the sub- marine telegraphs, great care is required for their insulation and protection. The first wires for the submarine telegraph between England and France were sunk in the British Channel, in August, 1850. The wire was 30 miles long, simply covered with gutta percha, and sunk to the bottom of the sea by leaden weights ; it soon, however, became useless, being cut to pieces by attrition against the rocks. In the September of the following year, a submarine cable was constructed by Messrs. Newall and Co., and on the 18th of October, an electric communication was established between Dover and Calais, a distance of 21 miles. The plan adopted in the manu- facture of this cable was as follows (Highton on the " Electric Tele- graph") : A copper wire, No. 16, was first carefully covered with gutta percha; upon this a second covering was laid the wire was thus thoroughly insulated. Four of these were then bound together with spun- yarn and hemp saturated with tar. This bundle of insu- lated wires with its hempen covering was then surrounded by 10 galvanized iron wires, each wire being -A-ths of an inch in diameter. The insulated wires thus formed the core of a large continuous wire rope (Fig. 424), which was wound into a coil 30 feet in diameter, It was 24 miles long, and weighed 180 tons. THE SUBMARINE CABLE. 771 Fig. 424. (1080) The " paying out" of this enormous cable commenced Sept. 25th, 1851. Steam tugs were placed by the Admiralty at the service of the Company. The Blazer, on which the cable was shipped, was towed from Dover to the South Foreland, and one end of the rope conveyed on to the English shore ; after this, the vessel was towed in the direction of Cape Grinez. The distance between the two coasts is 20 miles, and though to allow for undulations and sinuosities 24 miles of cable had been constructed, the end of the rope was found to fall short of its destination by half a mile ; another mile of cable was made, and spliced to the end of the first ; and on the 18th of October, the communication was found to be perfect. The cost of this cable is said to have been 20,000, and the expenses to the Company to have been no less than 75,000. The success of this experiment stimulated Messrs. ISTewall and Co. to attempt a still greater enterprise, viz., that of connecting telegraphically England and Ireland, by extending a submarine cable between Holyhead on the Welsh, and Howth on the Irish coast. This they effected in June, 1852, but from some unascertained cause (probably from its being too light, the cable enclosing only a single wire, and weighing only one ton a mile the Dover and Calais cable weighing seven tons), after working well for three days, it became imperfect, and a great portion has been taken up. Nothing daunted by this failure, Messrs. Newall and Co. constructed a cable measuring seventy miles in one un- broken length, and with it, on the 6th of May, 1853, the first electric telegraphic communication was established between Belgium and England. This cable contains 6 wires, insulated by gutta percha, and laid into a rope with prepared spun yarn ; it is covered with 12 thick iron wires, of a united strength equal to a strain of 40 to 50 tons more than the proof strain of the chain cable of a first-rate man-of-war (Lardner on the "Electric Telegraph," p. 157). It weighed 7 tons a mile, its total weight being 500 tons ; its cost was 37,000.* The great success which has hitherto attended submarine telegraphing has given rise to a project for the deposition of an * For a graphic illustration of the manner in which this enormous cable was coiled in the hold of the vessel ; also for the way in which it was deposited, see Illustrated London News, May 14, 1853. 772 THE ELECTEIC TELEGBAPH. electric cable across the Atlantic, so as to put the Old "World into instantaneous communication with the new, a distance (between the nearest point of British America and the west coast of Ireland) of about 1,600 miles. Whether the curious phenomenon of the arrest of the Electricity supplied by voltaic battery, and the charging of the submerged or buried wire elsewhere described (310), would inter- fere with the realization of this project is a question which must be left for time and further experience to determine. It should, however, be mentioned that the Magneto-electric Telegraph Com- pany, who have nearly 900 miles of underground wire in operation, report that they sometimes pass their signals, without any difficulty, through 500 miles of underground wire without any break or delay in the circuit. (Lardner on the " Electric Telegraph," p. 172.) (1081) The Earth Circuit. It had long ago been shown by Watson and others (10) that a Leyden phial could be discharged through a circuit, one half of which consisted of moist earth. It appears that Steinheil was the first to employ the earth to act the part of a conducting wire in an electro-telegraphic circuit. The two extremities of the wire of his telegraph, constructed at Munich in 1837, were attached to two copper plates, which were buried in the earth. He attributed the transmission of the current to the direct conductibility of the earth. It was proved on a larger scale in 1841, by Messrs. Cooke and Wheatstone, by experiments on the Blackwall Eailway, that the earth may be employed successfully to replace one half of the conducting wire, or for the return circuit. In fact, they state that so excellent a conductor is the earth, and so little resistance does it offer to the transmission of Electricity, that the same pile will work a much greater distance with a circuit half wire and half earth than when altogether wire. (1082) Whilst prosecuting some experiments with an electro-mag- netic sounding apparatus, in the year 1841, Mr. Bain found that if the conducting wires were not perfectly insulated from the water in which they were immersed, the attractive power of the electro- magnet did not entirely cease when the circuit was broken. With a view of ascertaining the true cause of the phenomenon, Mr. Bain, in conjunction with Lieutenant Wright, made a series of experiments on the Serpentine river in Hyde Park, and after verifying their former observations relative to the remnant of power in the electro- magnet when contact with the battery was broken, the electro- magnet being on one side of the river, and the battery on the other, the wires passing through the river ; and after making other experi- ments, in which the water and the moist earth formed part of th<; circuit, and wire the remainder, it occurred to Mr. Bain, that if THE PHENOMENA OF THE EAETH CIRC PIT. 773 positive metal were attached to one end of the conducting wire, and a negative metal to the other, and if the two metals were then placed in water, or buried in the moist earth while the connecting wire was properly insulated, a current might be generated. This was found to be the case, for when a large surface of copper was placed within Kensington Gardens at the one end of the river, and within Hyde Park at the other end a similar surface of zinc, and the metals con- nected by a wire, in the circuit of which was a galvanometer, a current of considerable intensity was found to be passing. The experiment was next tried on a more extended plan ; a surface of zinc was buried in'the moist earth of Hyde Park, and at rather more than a mile distant, a surface of copper was buried, and the metals were connected by a wire suspended on the railings ; when the plates were large, Mr. Bain not only obtained the usual electro- magnetic eifects in an enhanced degree, but also succeeded in the performance of electrotype operations ; for in the course of a few minutes he coated a half-crown with copper. Subsequent experi- ments showed that if the metals are thus buried, and connecting wires are employed, electrotype depositions may be effected, and electro-magnetic apparatus worked for a great length of time. (1083) Signor Ch. Matteucci made in the year 1844, numerous experiments on the conductibility of the earth for the electric current, (Comptes Eendus, June 3rd, 1844) . He made the current from a single Bunsen's element (371) circulate in a copper wire, 9,281 feet long, and through a bed of earth of the same length; and he found the diminution which occurred in the intensity of the current to be such, that the resistance of the bed of earth must not only be regarded as nothing, but that further, the resistance of the copper wire entering into the mixed circuit must be considered as less than that presented by the same wire when it enters alone into the circuit. Experiments were made to ascertain whether this extraordinary fact was due to the passing of a voltaic current between the buried plates, but on closing the circuit with the earth and the wire without the pile, a deviation not exceeding 1 was obtained, and this shortly disappeared- It then occurred to Matteucci, that an explanation might possibly be given by having recourse to a current derived from Ampere's terres- trial currents. The battery current in the first experiments passed along the wire from E. to W. ; he now reversed the current, causing it to pass from W. to E. ; the deviation of the galvanometer, how- ever, remained the same, as was also the case when the current was caused to pass from N. to S. or from S. to JST. These expe- riments were afterwards repeated on greater lengths at Milan, and their results confirmed Matteucci in the conclusion to which he 774 THE ELECTRIC TELEGBAPH. bad previously arrived, viz., that when a current is transmitted by a circuit composed in parts of a long copper wire and of a long bed of earth, the diminution suffered by this current from the resistance of this mixed circuit, is less than that which it would have suffered by the resistance of the copper wire alone. Matteucci regards the earth as all other conducting bodies, its great volume making up for its inferior conductibility ; he quotes the following experiment (Comptes Rendus, Jan. 12th, 1846), as conclusive against the hypothesis that the two electric charges liberated at the extremities of the pile always find means of diffusing themselves into the earth, w r hich being a universal reservoir, succeeds in neutralizing their charges with its natural fluid, decomposed by the free fluid of the pile. Experiment : The circuit of a pile of 10 Bunsen's elements, was established by plunging the two poles in two wells 160 metres apart ; a galvanometer being in the circuit to ensure the passage of the cur- rent. In this interval were two other wells almost in a straight line with the two extreme wells. The distance between these two wells was 30 metres ; they were distant from the two extreme wells, one, 80 metres, the other, 50. The extremities of a good long ware galvano- meter were plunged into the two intermediate wells : the current was then passed in the long circuit, when a deviation of 35 or 40 was instantly obtained; on reversing the direction of the current in the long circuit, that of the derived current was likewise inverted. This, remarks Matteucci, is precisely what ought to be the case, if we admit that the electric current is transmitted in the ordinary manner, whilst it cannot be conceived under the other hypothesis. (1084) The improbability of the earth's acting as a mere conductor in these cases, is strikingly shown by the following experiments made by M. Breguet, on the telegraph line between Paris and Eouen (Moigno's "Telegraphe Electrique," p. 259,) one of the poles of the Paris battery was soldered to a large metal plate, which was plunged into a well, the other pole communicated with the line wire to Rouen, and was there fastened to a similar metal plate, which was also plunged into a well; the circuit was thus half earth and half metal, or the cir- cuit could be made metallic throughout. Similar arrangements were made at Eouen. Two zinc galvanometers, in every respect similar and working together with great uniformity, were employed to mea- sure the electric forces at the two stations. The mean of twenty-eight experiments showed that when the current was half metal and half earth, the intensity was twice as great as when it was metallic through- out, that is, a circuit of 40 miles earth and 40 miles wire presented the same resistance as a circuit of 40 miles wire ; the earth, in fact, offering no resistance at all. The intensity at Paris, of the current THE PHENOMENA OF THE EAKTH CIECUIT. 775 Fig. 425. transmitted through a copper wire to Rouen, and from Rouen back to Paris, through the earth was 56 8'; that of a current sent and returned through a copper wire 29 1', or nearly one-half. At Rouen, the mean relative intensities were the same being 35 5' and 17 8'. Moigno and Gauss both regard the earth as a reservoir or drain in which the positive Electricity on the one side, and the negative on the other are absorbed and lost. Thus let A (Fig. 425) represent the cell of a voltaic bat- tery, P and IN" being its two poles united by a metallic con- ductor; according to the theory of Am- pere, the Electricity set free at the posi- tive pole, meeting with a resistance in the conducting wire, decomposes the neutral Electricity of the nearest molecule, attracting the negative and repel- ling the positive; the positive fluid of the first attracts the negative Electricity of the second, and repels its positive ; this again acts on the neutral Electricity of the third, and so on, the decomposition pro- ceeding step by step ; the positive Electricity of the last molecule, p, being neutralized by the negative Electricity emanating from the N. pole of the battery. Immediately succeeding the first series of de- compositions is a second series of recompositions, the last negative molecule, n being separated from its associated positive molecule, and thus becoming free, now combines with the positive molecule which precedes it, the negative molecule of which combines with the positive immediately behind it, and so on step by step. Suppose now the metallic circuit to be broken, between two free molecules, + p on the positive side, -j ri on the negative, and that a communi- cation be made with the earth through the metallic plates, B and C. The positive molecule will be brought into contact with an enormous reservoir, into which it will flow without meeting with any resistance ; it will not, therefore, exercise any decomposing action, being in fact simply absorbed. The preceding negative molecule being again set free, will immediately combine with the contiguous positive molecule, and the same will happen at the negative end of the battery. A double series of decompositions and recompositions thus takes place, and this only in one-half of the circuit ; the resistance is consequently reduced one-half, that is, the intensity of the current is doubled. (1085) It must be admitted that there is some difficulty in this theory of the " drinking up" of Electricity by the earth, and that the 776 THE ELECTEIC TELEGRAPH. question is still open to investigation ; but whatever may be the true explanation of this remarkable function of the earth, its discovery has been a great boon to electro-telegraphy, and the fact that the earth absolutely offers no resistance whatever to the circulation of the electrical force, is taken due advantage of on all telegraphic lines. " Of all the miracles of science," observes Lardner (" The Electric Telegraph," p. 123), " surely this is the most marvellous. A stream of electric fluid has its source in the cellars of the Central Electric Telegraph Office, Lothbury, London ; it flows under the streets of the great metropolis ; and, passing on wires suspended over a zigzag series of railways, reaches Edinburgh, where it dips into the earth and diffuses itself upon the buried plate. Prom that it takes flight through the crust of the earth and finds its own way back to the cellars at Lothbury!" But this is not all; though offering less resistance to the circulation of the electrical force than the lest of all conductors, it at the same time acts as the most perfect insulator. Of this the following striking illustration is given by Mr. "Walker (" Electric Telegraph Manipulation," p. 35) : " Ten wires enter the London office, each going to one side of the galvanometer ; the other sides of the galvanometers are connected respectively by ten wires with a long slip of brass, which brass is connected with the water- pipes ; strthat, in point of fact, the wires, notwithstanding all our care and cost to keep them insulated from each other throughout their course along the railway,* are actually one and all clustered together, and connected into one common bundle, as soon as they have passed the galvanometer. Notwithstanding this oneness of the wires, provided all is clear along the line, a current can be sent along any one of the ten, without any portion being distributed among the other nine. Take the case of two wires only as an example. They * The difficulty of obtaining perfect insulation of the wires is one of the greatest impediments to the establishment of telegraphic communication. The difficulty is increased when wires forming short circuits are placed in close proximity to those of long circuits. Under these circumstances, if the wires are not protected by an insulating coating, there is frequently in a damp state of the atmosphere, an escape of Electricity from the long wire to the short one, and a consequent diversion of the Electricity from its intended course ; for although the low inten- sity of voltaic Electricity may in experiments on a limited scale effectually prevent it from passing through a thin stratum of moist air, it must be remem- bered that each iron wire from London to Liverpool exposes a surface of not less than 45,000 square feet, and between several surfaces of that extent only 6 inches apart, a large quantity of Electricity may be transferred and lost. The escape of Electricity from telegraph wires, in the manner now alluded to, was first brought under the notice of telegraphic engineers by Mr. Bakewell. (" Bakewell on Elec- tric Science," p. 157.) LIGHTNING CONDUCTORS. 777 are united, and are joined to the earth wire before they enter the London instrument. They are kept carefully apart from London to Dever, but after passing the Dover instrument, they are again united, and are joined to the earth wire, so that they form a continuous loop ; and yet the current intended for one wire always takes the earth as the return half of the circuit, and no part of it finds its way into the companion wire. But if by any accident the earth wire is divided, the case is widely altered, and the current tells its own tale by its reverse action on the galvanometer, for it now accepts the companion wire, which before it entirely rejected." (1086) The necessity of paying the utmost attention to the insu- lation of the line wire, involves the introduction of a difficulty of another kind, and which has to be carefully guarded against ; that, viz., arising from the action of atmospheric Electricity, both induced, and in the form of direct strokes of lightning. " More damage," observes Mr. Highton ("The Electric Telegraph," p. 11), " is often done to the telegraph in a second by a single thunder storm, than by all the mischievous acts of malicious persons in a whole year." Posts are split in pieces, coils of wire are fused, needles are demagnetized, and permanent Magnetism given to soft iron electro-magnets. In the year 1846, the electric telegraph on the St. Germains Railway was visited by an attack of atmospheric Electricity, the following account of which was communicated by M. Breguet to M. Arago (" Year-Book of Facts," 1848) : " About five o'clock in the afternoon, during a heavy fall of rain, the bells of the electric telegraph at Le Yesitret began to ring, which led the attendant to suppose that he was about to receive a communication. Several letters then made their appearance, but finding they con- veyed no meaning, he was about to make the signal " Not under- stood" when suddenly he heard an explosion, similar to a loud pistol- shot, and at the same time a vivid flash of light was seen to run along the conductors placed against the sides of the shed. The con- ductors were broken into fragments, their edges being fused. The wires of several electro-magnets were also broken, and the attendant who was holding the handle which moves the needle sustained all over the body a violent concussion, and several workmen standing about him also experienced severe shocks." At the other end of the line, at the Paris station, nothing was broken, and nothing remark- able occurred, excepting that several of the bells were heard to ring. At the Oundle station of the London and North-Western Railway considerable mischief was done in 1846, several of the coils being burst open, and the wires fused ; and at the Chilham station, on the South-Eastern Eailway, a flash of lightning destroyed, in August, 778 THE ELECTEIC TELEGEAPH. 1849, the wire of the t bell coil and both the galvanometer coils. In India, which is occasionally visited with storms of lightning such as we never witness in this country, the damage done is often much more severe ; and in America, the disastrous consequences resulting from the same cause, soon after the establishment of the first line of telegraph by Morse, in 1844, rendered it imperatively necessary to devise some means for the protection of the operators and instru- ments. (1087) Numerous forms of lightning conductors have been in- vented and adopted. Actual lightning flashes are warded off by the points visible above the posts (Fig. 421), which are connected with the earth by a wire. Highton's plan, which he states to be so effectual that since its adoption not a coil has been injured, is very simple. He surrounds the wire for 6 or 8 inches before it enters a telegraph instrument with bibulous or blotting paper, and passes it through a deal box lined with tin plate in connexion with the earth ; the box is then filled with iron filings. All high tension Electricity collected by the wires will at once dart through the air in the bibulous paper to the myriads of points in the iron filings, which carry it safely to the earth. Walker's " protector" consists of a small hollow metal cylinder connected with the earth. The line wire in its passage from the railway to the telegraph passes within this cylinder, traversing which, it is first presented to the inner surface in the form of a thick wire furnished with spurs whose points are in the closest possible proximity to the cylinder without being in actual contact ; it is then continued on, and presented as a short coil of very fine wire (finer, in fact, than that of the instrument coils) wound on a bobbin, the outer convolution of the coil being very close to the cylinder. Thus a better means of escape is presented to the lightning than is found in any part of the instrument ; conse- quently it always escapes by this conductor, either by the points or by burning the fine wire. It is found to be perfectly effectual. In Steinheil's method the line wire extending over the station is divided, each end being fastened to a copper plate 6 inches in diameter ; the plates are brought close together, but prevented from touching by a silk cloth ; then coils of wire pass down from the corners of each plate to the telegraph instrument. The galvanic current is thus enabled to pass ; but an atmospheric discharge would break through the small obstacle between the copper plates in preference to passing out of its way through the thin spiral of wire. Since the introduc- tion of this protector in 1846, no derangement of the apparatus is stated to have occurred even with the most vivid flashes of lightning. (1088) On the Brunswick State Telegraphs, the main wire, well THE MAGKETO-ELECTBIC TELEGRAPH. 779 protected by gutta percha, is passsed through pipes underground, and fastened to a copper plate in the telegraph room. From this plate a small insulated wire is extended to the signaling instrument, and through the battery to a second copper plate in connexion with the earth. The two copper plates are screwed together, but insulated from each other by pieces of ivory. The two thin wires, which are covered with silk, are twisted together, but separated near the telegraph appa- ratus, to the screws of which they are attached. The galvanic current passes through the main wire to the first plate, through the thin wire to the apparatus and electro-magnet, through this to the galvanic battery and the second plate, over this by the stronger insulated wire to the ground, making a perfect circuit. But a discharge of atmospheric Electricity would pass between the two copper plates rather than through the long thin wires, and the telegraph apparatus is thus effectually protected. Various forms of lightning protectors are used in America, the simplest and best seems to be that oi Bulkley, which consists of two brass plates with serrated edges, one o which is fixed to a board, the other adjustable by means of a screw to any required proximity to the first; the line wire is connected with the fixed plate, and the moveable one is in communication with the earth ; the plates are brought as near together as possible with- out touching, so that any Electricity of tension may meet with as little resistance as possible in its passage from the line wire to the earth. (1089) Breguet's paratonnerre used on the French telegraph lines, Fig. 426. is shown in Fig. 426. The line wire is con- nected with a very fine iron wire placed in a glass tube, capped at both ends with brass and screwed on to a board. To the side of one of the brass caps is fastened a serrated piece of metal, B; immediately opposite and as close as possible to which is a similar serrated piece of metal, C, in communication with the earth by the wire E, so that if the wire of the line should become charged with atmospheric Electricity, it may discharge itself by these points to the earth ; and in the event of a flash of lightning striking the line wire, the thin iron wire A would be fused, and the telegraph instrument protected. (1090) The Magneto-electric Telegraph. In this instrument, patented by Mr. Henley in 1848, the motions of the needles are actuated by the electric currents momentarily induced in electro-magnetic coils when moved in proximity to the poles of a permanent steel magnet. This 3 E H 780 THE ELECTRIC TELEGRAPH. telegraph is adopted, with certain improvements, by the English and Irish Magnetic Telegraph Company, through a length of line above 2,100 miles; by it messages are now passed between Liverpool and Dublin direct, a distance of about 420 miles; the line of commu- nication extending via Port Patrick and Belfast ; and signals can be interchanged when necessary between London and Dublin, a distance by the wire of 660 miles, .without any break of circuit, or renewal of the magnetic circuit: the whole length of wire in use is about 13,900 miles, of which 6350 miles are laid underground, and about 7,500 above ground. This telegraph, the simplest and the most economical yet invented, merits a detailed description. For the following parti- culars we are indebted to the kindness of Mr. B. Bright, the secretary of the above company. Fig. 427. (1091) The original apparatus of Mr. Henley is shown in Fig. 427. Two compound bar magnets, a a, are fixed parallel to each other, so that their opposite poles are in juxta-position. At each end of the magnets are arranged a pair of electro-magnetic coils, 5 &', which are connected together at the back by a soft iron armature, c ; each pair is attached to a separate axle and finger key, e e ', and are perfectly independent of each other, so that by their motion they can communicate magneto-electric currents to the two line wires, z z. In order to avoid the friction that would ensue on the motion of the coils, if their soft iron centres were in actual contact with the poles of the permanent magnets, the axles upon which the coils are fixe< are so adjusted as to bring the ends of the soft iron cores to withii about the -rVth part of an inch from the magnets. AVhen the sent ing part of the apparatus is at rest, a spring, k, keeps the coils so disposed that the centre of one is before one pole of the magnet, ant the other before the other pole. This answers a double purpose ; th( iron cores and armatures of the coils act as a keeper to the magnets when the apparatus is not in use, and the position at the same time THE MAGNETO-ELECTRIC TELEGRAPH. 781 is such that the maximum of inductive effect is obtained upon the motion of the coils. The finger key attached to the axle, on being depressed, reverses the position of the coils in relation to the poles of the magnets ; the alteration in the polarity of the soft iron cores which thereupon ensues, occasions by induction a revulsion in the electric condition of the convolutions of wire forming the coils, and the current induced flows from one terminal wire of the pair of coils, through the indicating portion of the apparatus, i, in one direction to the earth, and from the other terminal wire in the opposite direction through the line wire. On the return of the finger key to its original position, the polarity of the cores is again reversed, and currents are induced in the opposite direction to those previously generated. The operation of the one current is to deflect, and of the other to bring back to zero the indicating needles of the apparatus, and of the instruments,, at the various stations to which the currents may pass. The motion of the other finger key leads to similar effects being pro- duced in connexion with the other line wire ;. and the combinations of movements of the two indicating needles constitute the alphabet. (1092) The indicating portion of the apparatus consists of a pair of small electro-magnetic coils coupled together by an armature ; the soft iron cores project beyond the coils, and are terminated by semi- circular horns of soft iron. This elongation of the cores was found necessary in order to prolong the polarization of the coil, as the great intensity of the induced current would not occasion during its passage through the coil a sufficient amount of polarity in the iron to move the magnet of the indicating needle unless its effects were, so to speak, thus temporarily fixed. On the return of the finger key to its original position, an amount of residual Magnetism is left in the horns of the indicating coils sufficient to hold the needle in its position at zero when the instrument is at rest. By this arrange- ment what is technically termed a "dead beat" of the needle is produced, and the needle at the same time is in perfect equilibrium upon its axle, conditions which conduce greatly to the rapidity and invariability of the needle's motion, and to the accurate interpreta- tion of the signals. The magnets used to generate the induced cur- rents are tempered in a particular manner, and retain their polarity for years. They are easily remagnetized when required, by bringing their poles for a short time into contact with a powerful electro- magnet. (1093) Recoil Currents from Underground Lines. The Magnetic Telegraph Company have adopted, to a very great extent, the under- ground system. In 1851, they laid a line between Liverpool and Manchester ; they afterwards extended the system from London 3 E 2 782 THE ELECTRIC TELEGRAPH. through Birmingham to Manchester, Liverpool, and the various towns in the Lancashire districts, northwards to Scotland, with a submarine cable linking up underground wires laid to Belfast and Dublin. They have been enabled to accomplish this through the great per- fection to which the insulation of wire by successive coatings of gutta-percha has been brought by Mr. Statham. It was found upon communicating a charge to a great length of underground wire, that after the withdrawal of the excitation (whether galvanic or magnetic Electricity was employed), an electrical recoil immediately took place at the end of the wire to which the current had been previously com- municated. The nature of this phenomenon has been explained by Faraday (316 et seq.) ; its existence was soon found to interfere very materially with the working of telegraphic apparatus, nor does it appear that up to the present time, any adequate remedy as regards the galvanic system has been applied. The nature of the interference will be at once understood, when it is mentioned that, with a letter- printing telegraph, the surplus current has the tendency to carry the machinery on farther, and to make other letters than those intended. "With the chemical and other recording telegraphs, the surplus flow of Electricity will continue nearly a minute, entirely confounding the marks, and representing one letter with the next; and with the needle telegraphs, a beat more is made by the back current than intended with every letter formed.* Another remarkable feature to be noticed in connexion with the underground system, is the small comparative velocity with which the electrical impulse is commu- nicated through each conductor in long circuits. Through a circuit of 480 miles, Messrs. Bright found that the difference of time between the communication of the electrical impulse and its arrival at the other end of the wire, amounted to rather more than a third part of a second, which would give as the rate of transmission of the galvanic or magnetic fluids through such conductors, only about 1,000 miles per second. It has been shown by Faraday (316 et seq.) that this retardation does not arise from any resistance of the conducting medium, but is the consequence of a lateral induction whereby the wire becomes charged statically with Electricity, becomes in fact an immense Leyden arrangement. (1094) On applying the magneto-apparatus above described to the underground system, it was found impossible to work it without making some provision against the effects of the recoil currents, for when the needle had been deflected and brought back to zero, by the two successive currents generated by the instrument, the recoil G. B. Bright, " Shaffner's Telegraph Companion." BBIGHT'S MAGNETO-ELECTRIC TELEGBAPH. 783 current flowing in the opposite direction to the last current sent, again threw the needle over, so that each time a signal was trans- mitted, instead of two beats of the needle being given, three occurred, disorganizing the series of signals employed, and leaving the indicating needles of the sending instrument in such a position as to render the answering signal (given after every word) unintelligible ; for of the two currents employed in sending the answering signal from the other end, only the second showed any effect ; the first serving to keep the needle against the stop pin, where the recoil current had left it. Moreover, the continual recurrence of two currents in one direction, and only one in the other, for each move- ment of the finger-key, a residual excess of one kind of polarity accumulated in the indicating coils ; and thus after a short time, the effects of currents from the other end were neutralized, and the com- munication of signals rendered impossible. As the reciprocality of two instruments working in a circuit together is almost a sine qua non for correct transmission of signals, and constitutes the most valuable feature of excellence in the English system, it was at once seen that if underground wires were to be worked, this difficulty must be overcome. (1095) Messrs. Bright' 's Improved Magnetic Telegraph. It was first sought to obviate the effects of the recoil currents by placing the charged wire into direct connexion with the earth at the instant that the exciting current ceased, so as to prevent the flow of the recoil current" from passing through the indicating apparatus, which was again placed in communication with the line wire when the handle had recovered its place of rest.. It was found, however, that upon extending the line, the time required for the recoil current to discharge itself increased also ; Messrs. Bright then applied another method. The indicating apparatus was altogether disconnected from the action of the sending currents, and only brought into con- nexion with the line wire at their termination. In this plan, instead of shutting off the recoil current it was permitted to pass through the receiving coils at the close of the sending currents, and the con- nexions of the apparatus were so arranged that it conduced to the efficient working of the apparatus by keeping the needles at zero, so as to be in the proper position for receiving signals from the opposite ends of the line. A compensating apparatus was also introduced having for its object : 1st, the obviating the effects of the deflecting currents which continually pass through telegraph wires, more or less, and in different directions, and which arise from variations of terrestrial Magnetism, and during aurora borealis and other atmo- spherical electrical disturbances (311 et seq.) ; and 2nd, the 784 THE ELECTEIC TELEGEAPH. neutralizing any excess of residual Magnetism that might be engendered in the horns of the coils by the recoil current ; this excess varies with the difference in the length of the circuit worked, and requires a constant compensation to ! be maintained. The apparatus consists of a permanent magnet of much greater strength than the magnet within the horns of the indicating coils, fixed upon an axis, at such a distance from the lower pole of the indicating needle, that the poles of the compensating magnet may be made to describe a circle intersecting the lower pole of the indicating magnet, but being in a plane slightly removed from it, so as not actually to come into contact. By an external regulator, the com- pensating magnet can be adjusted, so that the influence of either of its poles can be brought to exercise a definite influence of attraction or repulsion upon the receiving magnet, and upon the soft iron horns of the coils by which it is moved, and thus to negative an excess of polarity in either direction. Since this contrivance has been adopted not the least inconvenience has been suffered from the greatest electro-terrestrial disturbances, even when to such an extent as to deflect a galvanometer needle at right angles; nor does the strongest return current from the most extended circuit impede in the least the efficient transmission of signals. (1096) The magnetic telegraph as thus improved and with which the underground wires are now worked, is shown in Eig. 428 ; Fig. 428. a a, compound horseshoe magnets, formed of steel plates screwed tog. b bj induction coils attached to axles moved by the handles c c BRIGHT' s ACOUSTIC TELEGRAPHIC APPARATUS. 785 one of the wires terminating each pair of induction coils is connected to an insulated metallic cam; the other end of each pair of coils is conducted directly to the earth. c c, the metallic cams ; they are insulated from the axles to which they are attached by ivory plates. ffi two springs connected with the line wires, and resting against the screws of the bearings g g. g g, two bearings, or bridge-pieces, in connexion with the indicating portion of the instrument. h h, the outside of the dial ; i i, the indicating needles moved by magnetic needles inside on the same axles. x x, thumb-screws by which the magnet regulators are adjusted. z z z z adjusting pins between which the needles beat. The internal arrangement of the indicating apparatus is not shown in the figure. When at rest, the spring / is in contact with the bridge-piece g, and the line wire is in direct communication with the indicating part of the instrument, and the electric currents from other stations pass from the line wire through the indicating coils, and thence to the earth, producing in their passage the required signals. When, however, the handle ^is depressed, the metallic cam or stud attached to the axle presses the spring away from the bear- ing g, and the current of Magneto-electricity produced in the induc- tion coils by their change in position, as regards the pole of the permanent magnet, passes direct to the line wire ; this current deflects the needles of other stations from zero. Directly the down- ward motion of the handle is arrested, and during its return to its original position, a current in the opposite direction is induced, and flows through the line wire, bringing the indicating needles of the other stations back to zero, but not affecting its own indicating apparatus, owing to the connexion between the spring and the bearing being still incomplete. The moment the spring is again in contact with the bridge-piece, on the cam setting it at liberty, the line wire, in which a portion of the last current has keen fixed, as it were in transitu, seeks to gain its equilibrium, and the recoil current passes through the indicating portion of the instrument (now in circuit again), and holds the needles to zero, in the proper position to be actuated by currents from the other stations. (1097) Messrs. Bright' 's Acoustic Telegraphic Apparatus. Under the ordinary system of telegraphing, it is necessary to employ a transcriber to write down the words as interpreted from the visual signals, and dictated to him by the receiving operator, whose eyes being fixed on the rapidly moving needles, could not be engaged in conjunction with his hands in writing. It was found that owing to 786 THE ELECTEIC TELEGEAPH. the frequent occurrence of words of nearly similar sound, the tran- scribers sometimes unavoidably misunderstood the meaning of the receiving operator's, and altered the sense of the despatch by writing the wrong word. Such words as "two," "too," "to;" "four," " for ;" " hour," " our," may, for instance, be very easily confounded. Messrs. Bright have sought to remedy this inconvenience by trans- ferring the manifestation of the effects of the current from the eye to the ear. Their apparatus is shown in Figs. 429 and 430. Fig. 429. Fie. 430. a is the bell ; b, the hammer ; ', the muffler to deaden the sound, and stop the vibration after each stroke ; c, the con- tact maker and breaker, by which the local battery is put on and shut off ; d y a fixed muffler ; e, e, Fig. 429, the electro-magnetic coils through which the local current is passed, and which actuates the magnet i, from the axle of which extend arms bearing the hammer and muffler b V. There are usually a pair of these bells together, one bell differing half an octave in tone from the other, and one being fixed to a wooden par- tition, one on one side, and the other on the other side of the operator. From the number of beats, and the difference in tone, the letters and words are formed in the same manner as with the needle telegraph. (1098) Besides the saving in staff and in mistakes, any injury to the eyes of the clerks is prevented, and an appeal is made to an organ far better capable of endurance and accurate interpretation ; and it is found that a greater speed can be attained than by the old plan of telegraphing by needles, and the prompt attention of the operator is at once directed to the instrument, by the sounds given, upon a call being made. It is worthy of note, that while to read by a visible signal a movement of at least the eighth part of an inch is necessary for accuracy, the local current of the acoustic apparatus produces the full sound by the slightest movement, even the T-Hth part FEOME^T'S FEEIS T CH TELEGRAPH. 787 of an inch of the magnet actuated by the primary current proceeding from a distant station. The idea of assisting the telegraphic operator in interpreting visual signals, by releasing the detent of a train of clockwork, and so producing intonation of an alarum to mark out the number and period of the beats of the needle more distinctly, appears to have been suggested in this country about twelve years ago, but practical difficulties at that time prevented its application. A similar plan without, however, the employment of local currents, was pro- posed in Germany in the early days of electro-telegraphing, but it was not successfully carried out. We are informed, however, that some of the most busy circuits in connexion with the English and Irish Magnetic Telegraph Company are now worked by this method at the rate of from 30 to 40 words per minute, received and written down by the same operator. (1099) The following details of the system of underground wires have been kindly furnished by Mr. Bright : It was evident that the integrity of the insulating coatings of gutta percha could not be preserved long without some external protection throughout the length of each line, as the mere compression of the soil, gravel, and stones would at once have injured it, and in opening the roads for repairs, they would experience still further damage ; after discussing the merits of various plans of protection, it was finally decided that the wires throughout towns should be laid in cast iron piping, divided longitudinally, so that the wires might be laid in quickly, without the tedious and injurious operation of drawing them through, as was the case with the old system of street work, where the wires were laid in ordinary gas piping ; and that along the country roads, which were comparatively little liable to disturbance from the construction of sewers or laying of gas or water pipes, the wires should be laid in creasoted wooden troughs, of about 3 inches scantling, cut in long lengths, so as to be little liable to disturbance upon any partial subsidence of the soil, which not unfrequently occurs in districts where mining ope- Fig. 431. rations are carried on. The tops of the troughs are generally protected by fas- tening to them a galvanized iron lid. Eig. 431 shows a section of one of the troughs : m being the trough ; n, the gal- vanized iron lid ; 0, the gutta perchaed wire ; and p, a lapping of tarred yarn. The trough is deposited at a depth of 2 feet from the surface of the road. The iron piping used in towns is about 2J 788 THE ELECTEIC TELEGBAPH. inches in diameter. The lower halves are first laid, socket into socket, in the trench, and the wires are then rapidly reeled off, and deposited in the lower halves from a drum drawn over the trench. The upper halves are then laid on, and attached to the already laid portions by clamps or bolts fastening through ears cast in the sides of the pipes. So well has this mode succeeded that in Liverpool the whole lengths of the streets from Tithebarn railway station to the office in Exchange Street East were laid down in a single night ; and in Manchester, the line of streets from the railway station in Salford to Ducie Street by the Manchester Exchange, in 22 hours. (1100) In the overground system, the wires are arranged upon insulators attached to arms of different lengths, so that if a wire breaks and falls off it does not come into contact with those below, so as to impede the transmission of signals, but falls clear. The insulators are of glass or earthenware, of the form shown (side view and section in Figs. Fig. 432. Fig. 433. 432 and 433). The wires pass through a groove in the top of the insulator, and are secured there by a small peg and lapping of binding wire. (1101) Froment's French alphabetic tele- Fig. 434. FROMEFT'S ALPHABETIC TELEGBAPH. 789 graph shown in Fig. 434 is an exceedingly elegant piece of apparatus. In external form it resembles a small pianoforte without the black keys. There are 28 keys : 26 representing letters, 1 a cross, and I an arrow ; by pressing down any key its corresponding letter is shown on the dial, and at the same time on the dial of a similar apparatus at the distant station. Suppose, for example, the apparatus figured in the text to be at Paris, the current from the pile enters the apparatus at 5 and leaves it at V ; it proceeds thence to the distant station say Rouen where it traverses and works a precisely similar apparatus. (1102) The mechanism of the internal part of the apparatus will be understood from a slight consideration of Figs. 435 and 436. Fig. 435. Fig. 436. -8 Fig 435 is the manipulator, or the instrument for giving signals ; Fig. 436 is the receiver. The current from the battery enters through A, Fig. 435, passes up the brass spring N, which is in contact with the wheel R, and from this through the second notched spring M, out by the wire B, and on along the line wire to the telegraph at the distant station. There the current traverses the bobbin of an electro-magnet, not seen in Fig. 435, but exhibited separately in Fig. 437. This electro-magnet is fixed horizontally at one extremity, Fig. 437. the other being left free to operate on the soft iron armature a, which forms part of a bent lever, moveable round the pin o ; the lever is restored to a vertical position when the elec- tro-magnet is no longer active by the action of the spring r. The moment the electrical current traverses the bobbin, the lever at C is attracted, and the motion is imparted to a second lever d, through the shank i. This second lever is fixed on a horizontal axis, and is united to the fork F. When the current is interrupted the spring pulls back the lever, and 790 THE ELECTEIC TELEGRAPH. thus a step by step movement is given to the fork, which it transmits to the wheel G carrying the index. (1103) The manner in which the battery current is interrupted and renewed will be understood by referring to Fig. 435. The wheel R carries 26 teeth ; on turning it by the button P, while the plate IS" is, from its curved form, in constant contact with the teeth, the plate M, being crooked, has its contacts broken and renewed every time it passes over a tooth, and at the same time the battery current is thrown off and on. Suppose the pointer P is advanced 4 letters, then the current between N and M will be 4 times made and 4 times broken, and the armature of the electro-magnet at the distant station will be 4 times attracted and 4 times pulled back by its spring ; but these 4 attractions will give 4 movements to the wheel Gr, and the pointer will pass over the same number of letters in the dial of Fig. 436, the receiver, as in that of Fig. 435, the mani- pulator. At the top of the case of the instrument is the alarum, which is worked by a special electro-magnet. Referring now to Fig. 434, we see in front of the apparatus a series of 28 ivory keys, the first being marked with a cross, the last with an arrow, and the inter- mediate 26 with the letters of the alphabet ; the first 10 letters carrying also the 10 numerals. Immediately in front of the keys, on a horizontal platform of mahogany, is the dial B and 2 small metal pieces, m n, which are moveable, and which by means of a handle may be brought into contact, m with s or r, and n with y or p. The dial B is the verifier ; its index must always point to the same letter as that last signalled ; if it does not, it shows that the appa- ratus is not in proper working order. "W hen m is in contact with s, the apparatus is in a condition to send signals from Paris to Rouen. When in contact with r, it is in a condition to receive a signal from Rouen to Paris. In like manner when n is in contact with q, the alarum may be sounded at Rouen ; when in contact with ^>, the machinery is in a state to receive a notice from Rouen. (1104) Electro-magnetic Clvclcs. Mr. Bain, who has patented several applications of Electricity to useful purposes, exhibited in the spring of 1841, at the Polytechnic Institution, an electro-mag- netic clock, the principle of which will be clearly understood by an inspection of Figs. 438 and 439. jB, Fig. 438, is a back view of an ordinary clock, with a pendu- lum vibrating seconds; C, a plate of ivory affixed to the frame of the clock, in the middle of which is inserted a slip of brass in connexion with the positive pole of the battery. To the pendulum is attached a very light brass spring, F, in such a manner, that every vibration of the pendulum, brings the free end of the ELECTKO-MAG^ETTC CLOCKS. 791 spring into contact with the strip of brass, thus completing the elec- tric circuit, which is broken as soon as the spring touches the ivory. A series of electric clocks may be connected, by means of the wires, with this clock, and if a voltaic battery be included in the circuit they will all go together. (1105) Fig. 439, is a back view of one of the electric clocks : a is Fig. 438. Fig. 439. an electro-magnet, and 5, its feeder, suspended by a spring pendulum- fashion ; c is a small screw to regulate the distance of the feeder from the electro-magnet. At the lower end of the feeder is jointed a light click lever, d, falling into the teeth of a ratchet wheel e; /is a spring to keep the ratchet wheel steady. When the pendulum of the clock sends an electric current through the conducting wire, the feeder is attracted by the magnet, and the click lever d, takes over 1 tooth of the ratchet wheel ; upon the current being arrested (by the spring F of the pendulum, leaving the slip of brass in the primary clock), the feeder falls back into its former position, and causes the click lever to draw the ratchet wheel 1 tooth forward. The arbor of the ratchet wheel carries the seconds' hand, which is thus taken forward 1 degree every second, corresponding to the vibration of the clock . A pinion on the ratchet arbor gives motion to other simple wheel-work, which carries the minute and hour hands. -"When a large number of clocks is to be worked, the ratchet wheel is placed on the arbor of the minute hand, and is moved every minute instead of every second. An ivory circle, with slips or studs of metal, inserted flush with its face, corresponding to the number of clocks or group of clocks intended to be worked, is fixed on the face of the regulating or primary clock ; in the centre of this circle is placed 792 THE ELECTRIC TELEGRAPH. the arbor of the seconds' hand of the clock, upon which is fixed a slight metal spring with its free end in contact with the ivory circle. The conducting wire from the positive pole of the battery is in con- nexion with the framework of the clock ; every time, therefore, that the seconds' hand passes over a metal stud in the ivory circle, an electric circuit is completed and a current transmitted to the clock or group of clocks in connexion with that particular stud. As the seconds' hand passes over every portion of the circle once in each minute, the whole number of clocks thus connected with the regu- lating clock will be moved forward 1 degree every minute. By this means a large proportion of electric power is saved, for the battery has only a single clock or a small group of clocks to work at the same instant of time. (1106) Mr. Bain has also invented an apparatus for making ordi- nary clocks keep correct time ; also a method of working the electric clock by the deflection of the wire coil. In conjunction with Mr. Barwise, he took out a patent for these inventions, which was sealed 8th January, 1841. On the 28th of March, his clock was exhibited at the Polytechnic Institution. Fig. 440, shows the method adopted by Mr. Bain for working the electric clock by the deflection of the wire coil, instead of the attrac- tive power of the electro-magnet. A is a coil of insulated copper wire, freely suspended on centres. is a compound permanent steel magnet, immoveably fixed within the coil. C G are two spiral Fig. 440. springs, one on each side, for the purpose of conveying the electric current from the stationary conduct- ing wire D, to the moveable coil. F is a click lever attached to the coil. E is a ratchet w r heel fixed upon the minute-hand arbor of the clock, and G a wheel to keep the spring steady. The regulating clock transmits the electric current to the wire coil, upon which the left hand end is instantly depressed, and the clock lever F draws the wheel ~E forward 1 tooth. "When the flow of Electricity from the regulating clock is discontinued, the wire coil resumes its original horizontal position by the action of the spring C. If the clock receives an electric current once in every second, the wheel E is placed on the arbor of the seconds' hand ; but if the Electricity is only transmitted once in each minute, then the wheel JE must be placed on the spindle of the minute hand. EIECTUO-MAGNETIC CLOCKS. 793 Fig. 441. (1107) The llev. F. Lockey's contact-former for the electro-mag- netic clock is shown in Fig. 441. Fig. 1 shows the contact-former entire ; in each figure similar letters refer to similar parts. On the base board A (about 3 by 2 inches) is fixed the circular box or trough S. Fig. 2 exhibits a section of this box- wood trough wherein is turned the channel E R, and the central part, C C, is left as a solid cylinder on which to place rather firmly the glass tube G G. This tube, of which G G in Fig. 2 shows the section, rests on a rim or shoulder just below the rim at .#, which shows the level to which mercury is poured into the channel H JR, for the purpose of closing the bottom of the tube, and preventing all access of dust to its interior. The glass tube is surmounted by an ivory cap, H, Fig. 1, ce- mented thereon ; through the ivory cap pass the two wires I J, furnished with screw con- necting pieces for the pur- pose of uniting them with the p and n wires of the gal- vanic battery. The lower end of these wires terminates in two very thin and flexible copper springs, of which the lower portions are seen in Fig. 2, E F; they are tied together at K, Fig. ] , a piece of ivory being interposed to prevent metallic contact, as well as to place them pa- rallel to each other in the tube; they are tipped with platinum foil at E and F, and one of them is a little longer than the other. The spring F is so set as to have a slight ten- dency to advance towards E, but it is prevented from doing so by the ivory stud D, Fig. 2. Part of the central cylinder C C is sup- posed to be broken away in Fig. 2 to show the lever (formed iron wire No. 18) bent somewhat in the form E C P L, the fulcrum P being beneath the end of the tube, and the part E OP working freely in a slit in the cylinder C C. If this contact-breaker 794 THE ELECTEIC TELEGEAPH. is intended to work an electro-magnetic clock, it is so placed at tlie side of the central or regulating clock, as that the pendulum M N O, just before it swings into a perpendicular position, shall begin to act on the lever at L. During the remaining half of its vibra- tion towards the right hand (in the figure), as well as during the first half of its returning vibration towards the left hand (see Fig. 3) it will maintain contact between the free or platinum ends of the springs IE and F ; during the other two halves of its vibrations, the lever is unacted upon, and the springs returning to their parallelism, contact is broken, and the battery current ceases. Such an instru- ment does not impede the action of the clock to which it is applied ; Mr. Lockey's had been upwards of six months in continuous use, and acting with unfailing accuracy, when the author first saw it.* (1108) Mr. "WTieatstone's electro-magnetic clock, which was exhi- bited and explained at the Eoyal Society, 25th November, 1840, is thus constructed: all the parts employed in a clock for maintaining and regulating the power are entirely dispensed with. It consists simply of a face with its second, minute, and hour hands, and of a train of wheels which communicate motion from the arbor of the seconds' hand to that of the hour hand, in the same manner as in an ordinary clock train; a small electro-magnet is caused to act upon a peculiarly constructed wheel placed on the seconds' arbor, in such a manner that whenever the temporary Magnetism is either produced or des- troyed, the wheel, and consequently the seconds' hand, advance gHfth part of its revolution. On the axis which carries the scape wheel of the primary clock, a small disc of brass is fixed, which is divided on its circumference into 60 equal parts ; each alternate division is then cut out and filled with a piece of wood, so that the circumference consists of 30 regular alternations of wood and metal. An extremely light brass spring, which is screwed to a block of ivory or hard wood, and which has no connexion with the metallic parts of the clock, rests by its free end on the circumference of the disc. A copper wire is fastened to the end of the spring, and proceeds to one end of the wire of the electro-magnet; while another wire attached to the clock frame is continued until it joins the other end of that of the same electro-magnet. A constant voltaic battery, con- sisting of a few elements of very small dimensions, is interposed in any part of the circuit. By this arrangement the circuit is periodically * The cost of working an electro-magnetic clock, according to Mr. Tylee's observations, is under a penny per week, the battery employed being one on Smee's construction, platinized silver, 85 inches square, and the exciting fluid, water with ^V part of sulphuric acid. Such a battery Mr. Tylee finds will work his clock for 14 days without being interfered with. BAIN'S ELECTBO-MAGNETIC PENDULUMS. 795 made and broken, in consequence of the spring resting for one second on a metal division, and the next second on a wooden division. The circuit may be extended to any length, and any number of electro- magnetic instruments may be thus brought into sympathetic action with the standard clock. It is necessary to observe, that the force of the battery and the proportion between the resistances of the electro-magnetic coils and those of the other parts of the circuit, must, in order to produce the maximum effect with the least expenditure of power, be varied to suit each particular case. (1109) The next step in the progress of the invention of electric clocks, was the application of the electric power to work single clocks, so that no winding might be required, and the common clock dispensed with altogether. Mr. Bain's arrangements for effecting this are shown in Figs. 442, 443.* Fig. 442 is a representation of an electric pendulum, suspended from a metal bracket, Ji ; the bracket being firmly fixed to the board AA, which is, in a finished clock, the back of the clock-case. The pendulum-rod is of wood. B the bob of the pendulum, is com- posed of a reel of insulated copper wire, having (merely to improve the appearance) a brass covering ; the ends of the wire are carried up the rod, and terminate in two suspension springs, i and j, which serve the double purpose of suspending the pendulum, and conveying Electricity to and from the wire in the bob B. nn are two brass tubes fixed to the sides of the case, and facing each other, a b c f g is an apparatus called the break, for letting on and cutting off the electric current to and from the wire in the pendulum B, and per- forming the same office for clocks in distant places. Z is a plate of zinc buried in the ground. C is a plate of copper, or what is equally good, a quantity of carbon (common coke or wood charcoal). In private houses and other establishments in town, the ground under- neath the floor of the coal-cellar, or the flags of the area, is a suitable position for sinking the plates, or in any place where free access may be had to the moist soil. In country establishments there will be i no difficulty, as the plates may be sunk as above, or in any part of the garden. D and D 1 , are wires connecting the zinc and carbon with the pendulum. These wires should be entirely insulated, and I for this purpose gutta percha covering is the best material ; thus protected, they may be carried to any distance in any manner most I convenient. The zinc and carbon should be buried in the soil, at east 3 feet deep, and should not be less than 4 feet apart. To mite the wire D with the zinc plate, it must be simply soldered ; 1 )ut in uniting the wire D 1 with the carbon, a piece of platinum wire * History of Electric Clocks, by Alexander Bain. 3, 976 THE ELECTRIC TELEGRAPH. must be soldered to the end of the copper wire, and the other end of the platinum wire tied firmly round a small piece of the carbon, Fig. 442. Fig. 444. e and placed in the centre of the mass. Especial attention must be given to this, as it has been found, in every instance, that if the copper wire come into contact with the carbon it will inevitably corrode. Another plan equally good, is to drill a small hole in a piece of the carbon, and drive in a plug, likewise made of carbon, with the end of the platinum wire. If the plate C be composed of copper, it will simply be necessary to soldef the copper wire to it. The break is composed of two metal standards, a and Z>, fixed to the back of the case j c is a wooden or ivory bar, fixed (but easily move- ELECTRO-MAGNETIC PENDULUMS. 797 able) in the standards, by means of binding screws. On the surface of the end of the wood or ivory bar/^ is inserted a strip of gold, concave on the upper surface, as seen at F, Fig. 444, which is in metallic contact with the standard 5. At the end g, of the bar, is inserted (bound in a metal ring) a small piece of agate, and a piece of gold, both semicircular, represented by Fig. 444 ; the light part being the gold, the dark part the agate, with a shallow groove cut in the surface of each, similar to that in the gold at F, in fig. 444. In the grooved part of the .agate, and perfectly flush with the surface, is inserted a plug of gold. The plug of gold is in metallic con- nexion with the bracket a. The semicircular piece of gold is to form the connexion with other clocks at a distance, f g repre- sents the thin-kneed bar, the ends of which rest and slide freely in the grooves or concave parts already described. H is the regulating \veight, which brings the pendulum to time. The opening in the in- terior of the reel B is large enough to permit the pendulum to vibrate freely, without the liability of touching the tubes n n. The suspension spring j', being connected by a wire with triie carbon, if the end of the kneed bar rest on the gold plug in the agate, the electric circuit will be complete, and the course of the current may be thus described. The current is supposed to begin at the plate of zinc in the ground, thence through the moisture of the earth (a sufficient conductor) to the carbon, then through the wire D l , as shown by the arrows to the spring j, through the spring down a wire, to the coil of insu- lated wire in the bob B, which it permeates, and thence, by the wire 1, to the spring i, to the bracket a of the break, through the gold plug in the agate, to the point g of the bar g f, then through the bar to the bracket 5, and returning by the wire D to the zinc plate, as shown by the arrows. (1110) The mechanism and the means of establishing the galvanic power being thus explained, the manner of its operation remains to be shown. While the Electricity is thus passing, it renders the coil of wire in the bob B magnetic, that is, it gives it all the properties of a magnet with dissimilar poles, JN". and S. In the diagram, the N. pole is to the right hand, and the S. to the left. Now, the permanent magnets having their N. poles inwards next to the coil, it is evident, by the well known law of Magnetism, that the N. pole of the left hand magnet will attract the S. pole of the coil, while at the same instant the N. pole of the right hand magnet will repel the N. pole of the coil, and by these means the pendulum will receive an impetus towards the left. It cannot under these circumstances hang perpendicular, but if the galvanic current is broken (which can be done by sliding the bar gf a little to the left, 798 THE ELECTRIC TELEGEAPH. till the point is off the gold plug), the coil being no longer magnetic, the magnet will have no further effect upon it; the pendulum is therefore free to go back in the contrary direction. The pendulum itself gives motion to the sliding bar, by means of the pin d : which projects from the rod, and acts in the kneed part of the bar. If we now take hold of the pendulum with the hand, and move it to the right, till the point of the bar is on the gold plug, and then let it swing back, it receives an impulse from the magnets, as just explained. When it arrives at the end of its excursion to the left, it will of itself push the sliding bar off the gold plug ; the power will then cease, and it is free to return to the right hand by its own momentum, until it pushes the sliding bar again on to the gold plug- and thereby receiving another impulse, will continue its vibrations, which will increase in length, till the point of the sliding bar is carried beyond the surface of the plug on the right, and partly on to the agate, this action cutting off a great portion of the electric current, and if the vibration further increase in the smallest degree, the power during one vibration is entirely cut off. In this way the pendulum is kept precisely at one given arc of vibration, however variable the electric current may be, provided only that there be always sufficient. It may be here remarked, that the lower the break is placed with reference to the pendulum, the greater will be the accuracy of its vibration. This governing principle of the break is a most important feature in the invention, and is accom? plished without any extra work or friction. For large church clocks an apparatus termed a mutator is employed, which, instead of cutting off the current, changes its direction, so that the pendulum receives its impulse, both from right to left, and left to right, but it has the same governing principle as the break just described. (1111) Fig. 443 is a representation of another pendulum, with, its earth-battery and connecting wires. In this arrangment the perma- nent magnets are in the bob of the pendulum, and the coils of wire are fixed to the case ; or, in other words, the permanent magnets move, and the temporary magnets, viz., the coils of wire d, d, are fixed, b is the pendulum-rod, suspended in the ordinary way by a single steel spring to the bracket a. c c are two semicircular permanent steel magnets, having X. poles pointing to the left, and S. poles pointing to the right, d, d are two oblong coils of insulated copper wire, fixed to the back of the case, the opening in the coils being large enough to allow the bob of the pendulum to move freely without the liability of touch- ing; the break in this case is the same in principle and action as that already explained, but the connecting parts are covered with brass caps to exclude the dust, and the brackets are more ornamental. The BAIN'S ELECTEO-MAGNETIC CLOCKS. 799 action is as follows : When the galvanic current is let on, the coil d attracts the N. poles of the magnets of the pendulum-bob, at the same time the coil d l repels the S. pole ; the pendulum thus gets its impulse to the left, and the current being cut off by the break, as explained in Pig. 442, the pendulum is free to return by its own momentum, and the motion is thus perpetuated. It will be observed that these pendulums are moved not by mechanical means, which involve friction and wear, but by magnetic pow r er, in which there is none of either, and even that power is applied, at the utmost, in every second vibration, though in actual practice it is not in full force more than once in every fifth vibration, the only friction (which is very slight) being the sliding of the \>SLT gf, of the break; it may therefore, be safely inferred that these are the most detached pen- dulums ever yet contriv- Fig. 445. ed. They are regulated to time in the ordinary way, by raising or lowering the weight E, or by rais- ing or lowering the bob itself. (1112) Fig. 455 repre- sents the mechanism Jby which motion is given to the hands ; there are but two wheels in the train, besides the dial-wheels, and as these are moved in the ordinary way, they are not shown in the figure, a a, are the frames, fitted to each other in the usual manner ; fixed to the top of the frames is a cross bar- to which the pendulum may be suspended (Mr. Bain, prefers suspending it as shown in Fig. 455) ; c is the top portion of the pen- dulum-rod, which is sus- pended at d; f is the crutch, shown by two dotted lines, having its axis at e on the same axis is the arm 800 THE ELECTEIC TELEGRAPH. Ji, which carries the click i; k and Z are projections from the inner part of the back frame; these are the bearings of a spindle, which carries the ratchet-wheel at i, and a worm which works into the teeth of the wheel m t the arbor of the wheel projecting through the front frame. The action takes place as follows : the pendulum-rod, in its excursion to the left, comes against the projecting pin y, which is fixed in the lower end of the crutch, and pushes it aside ; this action gives similar motion, through the crutch and axle e, to the arm h and click * : this causes the point of the click to slip oyer one tooth of the rachet-wheel. Now, when the pendulum takes its excursion to the right hand, the crutch follows by means of its own weight (or a small weight attached to it), and the click i pushes the rachet-wheel forward the space of one tooth, the worm gives motion to the wheel m, and this gives motion to the dialwork and hands in the usual manner. (1113) But the electric pendulum does more. It not only gives motion to the clock, or rather indicator, which is in the case with it, by mechanical action, but it lets on currents of Electricity to other clocks or indicators at any distance ; and this important object it accomplishes without any extra wear or tear, and without any friction ; for it will be perceived in the previous explanation of the break, that when the point g of the bar is oif the gold plug which is in connexion with the pendulum, it is moved on to the gold grooved plate which is connected with the distant clocks, thus letting on the current to the pendulum and clocks at a distance alternately. By this arrangement there is a great economizing of electric power, as when the current is cut off from the clocks it is working the pendulum ; when cut off from the pendulum it is working the clocks ; and thus there is no moment when the electric current is not in practical operation. (1114) Pig. 446 represents the mechanism of one of the 'affiliated or companion clocks, a a is a brass plate to which the dial and all parts of the mechanism are fixed ; c c are reels filled with insulated copper wire ; d is a semicircular permanent steel magnet, a similar one being on the other side. These magnets are fixed to an axle by means of arms, poles of the same name being opposite each other, viz., N- to 1ST., and S. to S., and the poles vibrate freely in the interior of the coils. These coils are joined to, and form part of, the electric circuit with the parent clock, and by the transmission of electric currents from thence the magnets, d vibrate in unison with the pendulum. (1115) Having thus obtained uniform motion between the pendulum of the parent clock and the magnets of the affiliated ones, it remains BA.IIT8 ELECTKO-MAGNETIC CLOCKS. Fig. 446. 801 to be shown how motion is given to the hands of the latter, /"is a small frame, fixed on the same axle as the magnets. This frame carries the little click ^, which acts in the teeth of the ratchet- wheel li ; this wheel is carried by the spindle i, on which is a screw or worm working in the teeth of the wheel n more clearly shown in Pig. 447; the axle of this wheel projects through the plate a a, and gives motion to the hands in the ordinary way. I is a straight steel spring to keep the rachet- wheel from going back with the click, k is a bearing for one end of the axle of the wheel n ; the other bearing is in the plate a a. b represents the back of the dial-plate. Mr. Bain tested the correctness of this principle in 1846, by working Fig. 447. a clock at Glasgow, by an electric pendulum in the telegraph station at Edinburgh, a. distance of 46 miles. The two clocks went accu- 802 THE ELECTBIC TELEGRAPH. rately together, the magnet of the companion clock at Glasgow vibrating in unison with the pendulum in Edinburgh. (1116) Shepherd's Electro-Magnetic Clock. In this beautiful apparatus, well known to the frequenters of the Great Exhibition in 1851, Electro-magnetism is the moving power. The pendulum is so arranged as to make and break an electric circuit, and consequently to make and unmake a horse shoe magnet at each vibration. Each time that the magnet is made it attracts an armature, which lifts certain levers ; one of these is concerned in raising a weighted lever and causing it to be held up by a detent or latch ; the magnet is then unmade in consequence of the pendulum breaking the circuit, and the armature is released, when the pendulum lifts the latch, and allows the weighted lever to fall, which in falling strikes the pendu- lum so as to give it an adequate impulse ; then the circuit is again completed, the armature attracted, the levers moved, the weight raised and held up by the detent ; another vibration breaks the circuit, and releases the armature, the pendulum then raises the detent, the weight falls, and in falling, its arm strikes the pendulum, and gives it an impulse, and so on. (1117) But the pendulum at each vibration not only makes and breaks the electric circuit of the battery, which maintains it own action, but also, and simultaneously, that of a second battery, of which the duty is to make and unmake the electro-magnets belonging exclu- sively to the clock or clocks which are upon this circuit. These electro-magnets act upon the extremes of one or more horizontal bar-magnets, so as alternately to attract and repel their opposed poles, and which carry upon their axis the pallets, by the alternating motions of which to the right and the left, the ratchet wheel is pro- pelled onwards at the rate of a tooth each second, and the axis of this ratchet wheel carries the pinion which moves the other wheels of the clock. (1118) The circuit of thehattery connected with the striking part of the clock is only completed once in an hour, and is connected with an electro-magnet, so arranged as by means of a proper lever to pull the ratchet wheel attached to the notched striking wheel 1 tooth forward every 2 seconds, and each tooth is accompanied by a blow on the electro-magnetic bell. The number of blows depends upon the notched wheel, the spaces on the circumference of which are adapted to the number to be struck, and when this is complete, a lever falls into the notch, and so doing cuts off the electric current, which is not re-established through the striking electro-magnet till the next hour, when a peg upon the hour wheel pushes the striking SHEPHEED'S ELECTBO-MAGNETIC CLOCKS. 803 lever forward, so as to cause it to be depressed by a similar peg upon the minute wheel. (1119) Shepherd's clocks are adopted in the extensive warehouse of Mr. Pawson, in St. Paul's Churchyard, where eight dials are maintained in action by an electro-magnetic pendulum in the counting-house ; they are also used at the Greenwich Observatory, at the Tunbridge station of the South Eastern Bail way, &c. ; indeed, the time is pro- bably not far distant when clock power will be applied to all the principal cities and towns in Europe, as water and gas are at the present day. 804 DIAMA.GNETISM. CHAPTER XXI. DIAMAGNETISM. Action of Magnetism on Light Action of Magnets on the Metals Action of Magnets on Air and Gases The Magne-Crystallic Force Diamagnetic Polarity The Polymagnet Diamagnetic Conditions of Flames and Gases Magnetic Conducting Power Atmospheric Magnetism. (1120) Action of Magnetism on Light. On the 27th of Novem- ber, 1845, Professor Faraday communicated to the Royal Society a memoir, in which he made known the interesting fact, that when the "line of magnetic force " (by which he understands that exercise of magnetic power which is exerted in the lines usually called " mag- netic curves ") is made to pass through certain transparent bodies parallel to a ray of polarized light traversing the same body, the ray of polarized light experiences a rotation. The experiment was made in the following manner. A ray of light from an argand lamp polarized by reflection was passed through a Nicol's eye-piece,*' revolving on a horizontal axis. Between the polarizing mirror and the eye-piece the poles of an electro-magnet, each of which would sustain from 28 to 56 pounds, were arranged. The poles were sepa- rated from each other about 2 inches in the direction of the line of the ray, and so placed that, if on the same side of the polarized ray it might pass near them, or if on the contrary side, it might go between them, its direction being always parallel, or nearly so, to the magnetic lines offeree. A piece of silicated Morale of lead glass was placed between the poles, so that the polarized ray should pass through its length. The eye-piece was now turned in such a posi- tion that the image of the ray was invisible. On now causing the electric current from a Grove's battery of 5 cells to circulate the iron, the image of the lamp-flame became visible, and continued so as long as the iron continued magnetic, but on stopping the current, the light instantly disappeared. The force impressed upon the dia- magnetic f was one of rotation, as the light could be extinguished * The arrangement known as " Nicol's prism " consists of a rhombohedron of calcite (doubly refracting spar) split into two wedge-shaped portions by a plane passing through two opposite solid angles, and perpendicular to the principal plane, which passes through the same angles ; the two wedges are cemented together with Canada balsam, which, while it allows one of the doubly refracted rays to be transmitted, banishes the other ray altogether from the field of vision. -J- By " diamagnetic " is meant a body through which lines of magnetic force are passing, the same not being magnetic like iron. _ ACTION OF MAGNETISM ON LIGHT. 805 and again rendered visible by the revolution of the eye-piece to the right or to the left. When the N. pole was nearest the observer, the rotation of the ray was right-handed ; when the S. pole was nearest, it was left-handed. Common magnets acted in the same manner as electro-magnets, though more feebly, (1121) The law of the action is this : " If a magnetic line of force be going from a N. pole, or coming from a S. pole, along the path of a polarized ray, coming to the observer it will rotate that ray to the right-hand." Thus, supposing Fig. 448 Fig. 448. to represent a cylinder of glass, the line /~v "~ ~~"Y ~~~7"\ joining N and S is the magnetic line I 1 4, f I of force, and if a line be traced round v J ' \ J the cylinder with arrow heads on it to represent direction, as in the figure, such a simple model held up before the eye will express the whole of the law, and give every position and consequence of direction resulting from it. The amount of rotation was in pro- portion to the extent of the diamagnetic through which the ray passed, and the power of the rotation was in proportion to the intensity of the magnetic force. The interposition of non- magnetic metals between the poles had no influence on the result ; but iron, by diverting the direction of the lines of force, affected the results materially. That the phenomenon is directly con- nected with the magnetic form of force is proved by the circum- stance, that the brightness of the polarized ray is developed gradually, the iron requiring some little time (a couple of seconds) to acquire its full magnetic intensity after throwing on the current. (1122) All transparent bodies do not possess this power in the same degree, and some have it not at all ; but in those in which it exists, whether solid or liquid, or however opposed in chemical cha- racter, the law of rotation is the same. The best substance is silico- borate of lead ; both flint and crown glass give it, as do water, alcohol, ether, and, in fact, every liquid substance that has been tried ; but Faraday was unable to find the power in rock crystal, Iceland spar, sulphate of baryta, carbonate of soda, or ice. (1123) The following experiment is quoted by Faraday as clearly demonstrating that a ray of light may be electrified, and the electric forces illuminated. A tube was filled with distilled water and intro- duced as a core into a long helix or coil 65 inches long, and contain- ing 1,240 feet of wire ; it was placed in the line of the polarized ray, so that by examination through the eye-piece the image of the lamp- flame produced by the ray could be seen through it. Then the eye- piece was turned until the image of the flame disappeared, and after- wards the current of 10 pairs of plates was sent through the helix ; 806 D1AMAGKETISM. instantly the image of the flame reappeared, and continued as long as the electric current was passing through the helix ; on stopping the current the image disappeared ; the light did not rise gradually as in the case of electro-magnets, but instantly ; when the current was sent round the helix in one direction, the rotation induced upon the ray of light was one way ; when the current was changed, the direction of rotation changed likewise. In this experiment the apparent deflection of the ray of light is by many believed to be occasioned by an alteration in the refracting power of the medium through which the ray passes, and not to an influence exerted directly by Magnetism on the beam of light. (1124) The apparatus shown in Fig. 449, was constructed by Pro- fessor Bottger (Beitrdge zur Physik et Ghemie Drittes If eft, p. 1) for the illustration of these novel phenomena: a is a stand sup- Fig. 449. porting a pair of achromatic Nicol's prisms, g and^ placed horizon- tally ; between these there is placed a brass tube, some 2 or 3 lines in diameter, and from 6 to 8 inches long, closed at both ends by plates of glass ; ft h, the tube, filled with any double refracting fluid, for instance, tartaric acid, oil of turpentine, a solution of sugar candy (ird candy and frds water), &c., &c., is placed in the axis of a hollow helix, which is lined throughout its entire length with a thin cylinder of sheet iron, c ; the projecting terminals of the helix are brought by means of the commutator, d, into connexion with the poles of a Grove's battery of 6 or 7 pairs. On letting the light of an argand lamp, i, pass through the hindermost Mcol's prism, and thus causing a ray of polarized light to traverse the saccharine ACTION OF MAGNETISM ON LIGHT. 807 solution in hi, it will be observed that a certain position may be given to the front moveable prism, g, in which the field is dark ; if, now, by completing the circuit, the galvanic current be caused to traverse the helix c in such a manner that it enters the right-handed helix, where the polarized ray enters the refracting liquid, the longi- tudinal magnetic axis coinciding with the axis of the ray, or in other words, the magnetic N. pole being at 5, and the S. pole at fl, there will instantly be indicated a rotation of the plane of polariza- tion to the left, the field no longer remaining dark, but becoming of a reddish hue, the phenomenon remaining constant as long as the circuit is closed. On inverting the current by means of the com- mutator, so that the IS", pole is brought to h and the S. pole to 5, the plane of polarization becomes inverted to the right, the field at the same time becoming of a bluish green tint. (1125) Taking the natural rotating force of a specimen of oil of turpentine as a standard of comparison, Faraday obtained the follow- ing numbers, a powerful electro-magnet being employed with a con- stant difference of 2| inches between its poles : Oil of turpentine .... 11*8 Heavy glass ..... 6'0 Flint glass 2-8 Eocksalt . ;Y : - . " : .V . 2-2 Water . ; \ ... ' ^ ,~ . TO Alcohol . ,.*:'; .'... : .:.* less than water. Ether .... ,. less than alcohol. the different substances being corrected by calculation to one stan- dard length. That light and the magnetic and electric forces have a direct relation and dependence is further shown by the following experiment :* Place side by side a certain quantity of water in a helix, and a tube containing oil of turpentine. If the oil possesses right hand rotation, pass an electric current through the helix so as to give rotation to the right ; the water in the tube will acquire a rotatory power to the right, and the two liquids will possess the same mode of action. Leaving now the tubes, the helix, and the current in the state just described, pass the polarized ray in the con- trary direction through the tubes, and observe at the opposite extre- mity of the tube. The oil of turpentine will be still seen to turn the ray to the right, but it will not be the same with the water, which will turn the ray to the left ; the rotation being absolutely connected with the direction of the electric current which moves in the circuit, * Faraday, Comptcs fandus, January 16, 1846. 808 DIAMAGtfETISM. and which, seen through this extremity, passes to the left. If, instead of water, oil of turpentine be in the helix, and if the electric cur- rent be sufficiently intense to produce on the luminous ray a rotation equal to that determined by the oil, its rotatory power, observed on a ray passing in a certain direction, will appear double ; while, examined by a ray passing in the contrary direction, it will be reduced to zero. It thus appears, that it is only through the inter- vention of matter that the direct relations of the magnetic force and light become manifest ; that different matters possess the property in different degrees ; and that as the substances between the mag- netic poles, though clearly affected by the magnetic force, are not rendered magnetic in the sense of iron, their molecular condition, while in this state, must be new, and the force must be a new mag- netic force. (1126) The rotatory power superinduced by magnetic action is quite independent of that which the substance possesses of itself. In oil of turpentine, for instance, whichever way a ray of light (polarized) passes through this fluid, it is rotated in the same manner, and rays passing in every possible direction through it simultaneously are all rotated with equal force, and according to one common law of direc- tion, i. e., all right handed, or else all to the left. This is not the case with the rotation superinduced on the same oil of turpentine by the magnetic or electric forces ; it exists only in one direction, that is in a plane perpendicular to the magnetic line, and being limited to this plane, it can be changed in direction by a reversal of the direc- tion of the inducing force. The direction of the rotation produced by the natural state is connected invariably with the direction of the ray of light, but the power to produce it appears to be possessed in every direction, and at all times, by the particles of the fluid ; the direction of the rotation produced by the induced condition is con- nected invariably with the direction of the magnetic line, or the elec- tric current, and the condition is possessed by the particles of matter, but strictly limited by the line or the currents changing and disap- pearing with it. (1127) The General Magnetic Condition of Matter. The first substance submitted by Faraday to the action of the magnetic forces w r as heavy silicated borate of lead glass. A bar of this substance, 2 inches long and \ an inch wide and thick, was suspended centrally between the poles of a powerful electro-magnet ; when the effect of torsion was over, the current was thrown on ; the bar immediately moved, and took up a position across the magnetic line of force (equa- torial).* On being displaced, it returned to it, and this happened * Let N and S, Fig. 450, represent the poles of a horse-shoe magnet looking down GENERAL MAGNETIC CONDITION OE MATTER. 809 many times in succession. The reversal of Fi g 450 the poles of the electro-magnet caused no difference. The bar went by the shortest course to the equatorial position. The power that urged the bar into this position was so thoroughly under command, that it could be either hastened in its course into it, or arrested as it was passing from it, by seasonable contacts at the Yoltaic battery. If the bar was in the direction of the axis, or magnetic line of force, it did not move on making battery contact, neither did it if it was originally in the equatorial position ; but if it was in the least oblique, its obliquity increased till it became equatorial. Here, then, was a magnetic bar pointing E. and ~W. instead of N. and S. (1128) If the bar was suspended nearer to one pole than the other, it was repelled from the nearer pole ; and if it was equidistant from both poles, but in the axial line, that is in the line from pole to pole, it pointed equatorially on being moved a little on either side of the axial line from which it was apparently repelled. If two bars were suspended each near the opposite poles, both were repelled by their respective poles, and thus appeared to attract each other ; so also when two bars were hung equatorially on either side of the axial line, both receded from that line, apparently repelling one another. "When a cube was employed, the effect was repulsion from both poles, and recession from the magnetic axis on either side. The tendency was to move from a stronger to a weaker place of magnetic force, and this is the cause of the pointing of any oblong arrange- ment. "When one or two magnetic poles are active at once, the courses described by the glass form a series of curves, which Faraday calls diamagnetic curves in contradistinction to the lines called mag- netic curves. In these experiments we have magnetic repulsion apparently without polarity. (1129) A very great number of other substances, both solid and liquid, were then submitted to the action of the magnet, the liquids being enclosed in small glass tubes hermetically sealed. The results are given in the following table : upon them; the space between the poles is called "the magnetic field ;" the line, a 6, parallel to which a magnetic body, such as a bar of iron, would take up its position, is called the " axial line ;" the line, c d, at right angles to a b, and parallel to which a diamagnetic body, such as a bar of bismuth would set, is called the ". equatorial line." 810 DIAMAGNETISM. POINTED EQUATORIAL!, Y (DIAMAGKNETIC). Hock crystal. Sulphate of lime. Sulphate of baryta. Sulphate of soda. Sulphate of potassa. Sulphate of magnesia. Alum. Nitric acid. Sulphuric acid. Muriatic acid. / Solution of alka. \ line and earthy | V salts. ) Glass. Muriate of ammonia. Litharge. Chloride of lead. Chloride of sodium, Nitrate of potash. Carbonate of soda. Iceland spar. Oxalate of lead. White arsenic. Iodine. Phosphorus. Sulphur. Besin. Spermaceti. Tartrate of potash and Caffeine. antimony. Tartaric acid. Citric acid. Water. Alcohol. Ether. Sugar. Starch. Gum arabic. Wood. Ivory. Dried mutton. Fresh beef. Cinchona. Margaric acid. Wax from shell lac. Olive oil. Oil of turpentine. Jet. Caoutchouc. Dried beef. Dried blood. Fresh blood. Leather. Apple. Bread. POINTED AXIALLT (MAGNETIC). Paper. Sealing wax. Fluor spar. Peroxide of lead. Plumbago. China ink. 4 Berlin porcelain. Eed lead. Sulphate of zinc. Shell lac. Silkworm gut. Asbestos. Vermilion. Tourmaline. Charcoal. (1130) Phosphorus appears to stand at the head of all diamagnetic substances ; its pointing could be verified between the poles of a common magnet. If a man could be suspended between the poles, he would point equatorially, for all the substances of which be is made possess this property. The reason why blood which contains iron is not magnetic, is, probably, because it is diamagnetic in a greater degree ; and the latter force neutralizes and predominates over the former. By these new facts, forces directly the opposite of those existing in magnetic bodies are proved to have an existence ; for, whereas the latter produce attraction, the former produce repulsion. The former ACTION OF MAGNETS ON THE METALS. 811 cause a body to set in the axial direction, but the latter make it take an equatorial position. (1131) Action of Magnets on the Metals. The metals were exa- mined as to Magnetism by Fig. 451. suspending them in pieces of about 2 inches long in the mag- netic field of the electro-magnet. The apparatus employed by M. Plucker (a philosopher who has followed up these inquiries with great ability and success) is shown in Fig. 451. The electro-magnet a b is surrounded with 4 coils of thick silk-covered copper wire, each wound separately around its 2 branches, and commu- nicating with 2 metallic conduc- tors n n . The current from the battery is thrown on and off, and changed in direction, by means of a commutator c. The poles of the magnet are surmounted by a glass case with a suspension thread, so that different sub- stances may be submitted to the action of the magnet in a still atmosphere, or in atmospheres more or less charged with various vapours and gases. (1132) The following metals, when thus tried, were either not magnetic, or if so, to so small an amount as not to destroy the results of the other force : Antimony. Gold, Tin. Bismuth. Lead. Zinc. Cadmium. Mercury. Copper. Silver. The following were magnetic in the sense of iron : Cobalt. Nickel. Platinum. Titanium. Palladium. Of all the metals, bismuth was found to be the most eminently diamagnetic, excelling in this property even heavy glass and phos- phorus ; and it is, therefore, specially adapted for showing the various phenomena. Its movements were, however, complicated, and demanded careful analysis ; but they all resolved themselves into their 3 G 812 DIAMAGNETISM. simple elementary origin ; the ruling principle being that each par- ticle of the metal tends to go from the stronger to the weaker points of the magnetic field. "When bismuth powder was sprinkled upon paper and laid over the horizontal circular termination of the vertical pole of a bar electro-magnet, it retreated in both directions, inwards and outwards, from a circular line just over the edge of the core, leaving the circle clear, and at the same time showing the tendency of the particles of bismuth to move in all directions from that line ; and when the pole was terminated by a cone, a clear line could be traced through the powder, by drawing the paper on which it was sprinkled over the cone. (1133) Copper (in consequence, as Faraday believes, of its excel- lent conducting power for electric currents) exhibited some remark- able phenomena. When suspended between the poles it first advanced towards the axial line, as if it were magnetic ; it then suddenly stopped, and took up a new position, from which it could only be removed by the application of some force. Even when swinging with considerable momentum, it could be caught up and retained at will. If after the Magnetism had been sustained for two or three seconds the electric current was suddenly stopped, there was instantly a strong action on the bar, and it began to revolve ; on again renewing the current it was again arrested as before. Some other metals, viz., silver, gold, zinc, cadmium, tin, mercury, platinum, palladium, lead, and antimony exhibited in a greater or smaller degree the same phenomena. In, order to form a sufficient idea of the arresting power of these Fig. 452. induced currents, take a lump of solid I copper, approaching to the cubical or globular form, weighing from a J to I a pound, suspend it by a long thread, give it rapid rotation, and then introduce it, while spinning, into the magnetic field of the electro-magnet, its motion will be instantly stopped, and on trying further to spin it whilst in the field it will be found impossible. (1134) Faraday next submitted various metallic salts to the action of the magnet : all salts and compounds containing iron in the "basic part were found to be magnetic both in the form of crystals and when in solution ; yellow and red prussiate of potash were however both diamagnetic ; pure sulphate and chloride of nickel, both in crystals and in solution, were magnetic ; oxide of titanium, oxide of chromium, and chromic acid were magnetic, as were also ACTION OF THE MAGNET OK METALLIC SOLUTIONS. 813 the salts of manganese and chromium ; the compounds of lead, platinum, palladium, and arsenic pointed equatorially, as was also the case with chromate of potash. An interesting set of results was obtained by filling tubes with ferruginous solutions of different degrees of strength, and suspending them in similar ferruginous solutions, also of different degrees of strength, between the poles of the electro-magnet. When the solution in the tube was stronger, or contained more iron than that in the glass in which it was suspended, it pointed axially ; when it was weaker, or contained less iron than that in the glass, it pointed equatorially ; and when the solutions in both tube and glass were of the same degree of strength, the tube was indifferent. Let n, Tigs. 453 and 454, represent a thin Fig. 453. Fig 454. 'lass trough, filled with a solution of 16 grains of crystallized proto- ulphate of iron in each cubic inch of water, the trough being placed Between the poles of a powerful magnet ; let m be an oblong glass rough, containing a solution of 8 grains of proto sulphate of iron to ach cubic inch of water, the latter will set across the magnetic field s in Eig. 454, like a bar of bismuth, because it contains less iron than, he liquid in which it is suspended. Let the exterior trough be filled r ith the weaker solution, and the interior tube with the stronger, the itter will now set as shown in Fig. 453, that is, axially, as it would o in air. Iron and nickel, when heated to a degree far above that squired to render them insensible to an ordinary magnet, still Dinted axially between the poles. By multiplying these experi- .ents the following order of metals in their relation to the magnetic rce was obtained (0 is the medium point or condition of a metal substance indifferent to the magnetic force) : 3 G 2 DIAHAGKETiSM. MAGNETIC. DIAMAGNETIC. Iron. Bismuth. Nickel. Antimony. Cobalt. Zinc. Manganese. Tin. Chromium. Cadmium. Cerium. Sodium. Titanium. Mercury. Palladium. Lead. Platinum. Silver. Osmium. Copper. . Gold. Arsenic. Uranium. Hhodium. Iridium. Tungsten. 0. (1135) Action of Magnets on Air and Gases. Common air, sealed hermetically in a glass tube, and placed between the poles, pointed feebly towards the equatorial position, the effect being due to the glass. "When the air round the tube was rarefied, and finally exhausted as far as possible by a good pump, not the slightest diffe- rence in the pointing of the tube could be observed, neither could there when the tube was surrounded with hydrogen or carbonic acid; there seems, therefore, no difference between dense air and rare air, or between one gas and another. On the other hand, the air tube pointed axially when subjected to the magnetic forces whilst sub- merged in water, alcohol, turpentine, and mercury ; the action of the air in the fluids being the same as the action of a magnetic body in air. Various gases and vapours and a vacuum pointed equatoriatty when surrounded with air, but axially when surrounded with liquids; the equatorial pointing being due to the glass only, but the axial pointing depends upon the relation of the contents of the tube to the surrounding air. It appears, therefore, that gases and vapours occupy a medium position between magnetic and diamagnetic bodies]; and that however marked the diamagnetic character of a body may .be, it loses all traces of this character when it becomes vaporous. Taking air and a vacuum as the neutral point, the following table represents a general list of certain substances in their relation to the magnetic force : ACTION OF MAGNETS ON AIR AND GASES. 815 Iron. Bismuth. Nickel. Phosphorus. Cobalt. Antimony. Manganese. Heavy glass. Palladium. Flint glass. Crown glass. Air and vacuum. Mercury. Platinum. 0. Water. Osmium, Middle of the series. Gold. Alcohol. Ether. Arsenic. (1136) This position, intermediate between magnetic and dia- magnetie bodies taken by air; its exhibiting no change in its relations by rarefaction ; its taking a place exactly in the middle of a great series ; and lastly, the fact that all gases and vapours are alike, seems to point to the fact that air must have a great, and perhaps an active part to play in the physical and terrestrial arrangement of magnetic forces. The whole of these extraordinary discoveries prove that the magnetic force presides over matter as universally as the gravitating, the electric, the chemical, and the cohesive forces, and that substances arrange themselves into two great divisions, the magnetic and the diamagnetic, which are hi the same general anti- thetical relation to each other as positive and negative in Electricity, or as northness and southness in polarity, or as the lines of elec- tric and magnetic forces in magnetic Electricity. Neither was this remarkable power (the diamagnetic), given to bodies for nothing. "It doubtless," says Faraday, "has its appointed office, and that, one, which relates to the whole mass of the globe. For, though the amount of the power appears to be feeble, yet, when it is considered that the crust of the earth is composed of substances of which by far the greater portion belongs to the diamagnetic class, it must not be too hastily assumed that their effect is entirely overruled by the action of the magnetic matters, whilst the great mass of waters and the atmosphere must exert their diamagnetic action uncontrolled." Faraday found that it required more than 48 '6 grains of crystallized protosulphate of iron to neutralize the dia- magnetic power of 10 cubic inches of water, and it is not, therefore, at all unlikely that many of the masses which form the crust of our globe may have an excess of diamagnetic matter and act accordingly. He throws out the notion that it may not hereafter prove impossible to construct an instrument for measuring one of the conditions of terrestrial Magnetism, on the principle that a pound of bismuth or of 816 DIAMAGKETISM. water estimated at the equator, where the magnetic needle does not dip, ought theoretically to weigh less than in latitudes where the dip is considerable, whilst a pound of iron or nickel ought under the same change of circumstances to weigh more. (1137) The Magne-crystallic Force. In his experiments on bismuth, Faraday had noticed some very embarrassing results : e. g., taking at random from a quantity 4 small cast cylinders of the metal, and suspending them horizontally between the poles of the electro- magnet, the first pointed axially\ the second, equatorially ; the third, equatorial in one position, and obliquely equatorial if turned round on its axis 50 or 60 ; the fourth, equatorially and axially under the same treatment ; whilst all of them were repelled by a single magnetic pole, thus showing their strong and well-marked dia- magnetic character. The cause of these variations he succeeded in tracing to the regularly crystalline condition of the metallic cylinder. On suspending between the poles a carefully selected group of crystals of bismuth, and sending the current on, the metal vibrated strongly about a given line, into which at last it settled; and if moved out of that position, it returned when at liberty into it, point- ing with considerable force, with its greatest length axial. The position taken up by the metal had nothing to do with its shape, but was entirely dependent on its crystalline condition, and the eifect occurred with a single pole. Now, bismuth being eminently a dia- magnetic body, and as such tending to pass from a stronger to a weaker place of magnetic force, it would have no tendency to point at all in a field of uniform force (such as between the rounded poles of an electro-magnet) ; the crystalline group, however, does point in such a field, the tendency being that the line joining two opposite solid angles of the crystalline group, should take up an axial position. The impelling force is therefore distinct, both from the magnetic and the diamagnetic, and is called by Faraday the magne-crystallic force. (1138) It was further noticed that the cleavage of the bismuth was not made with equal facility at the four solid angles, and that two, or more frequently one of the planes produced by cleavage were brighter and more perfect than the others. When the crystal was suspended in the magnetic field with its bright plane vertical, it pointed with considerable force with the plane towards either the one or the other magnetic pole, so that the magne-crystallic axis appeared now to be horizontal, and acting with its greatest power ; when, how- ever, the crystal was suspended with its bright plane 'horizontal, so that the magne-crystallic axis was vertical, it did not point at all; the law of action appearing to be, " that the line or axis of magne- crystallic force tends to place itself parallel, or as a tangent to the THE MAGNE-CRYSTALLIC PORCE. 817 magaetic curve or line of magnetic force, passing through the place where the crystal is situated." It does not require very powerful magnets to exhibit these remarkable phenomena; they may be verified with common horseshoes, with a lifting power of under 2 pounds. Neither is bismuth the only metal in which they are observed; Faraday having succeeded in obtaining magne-crystallic action with antimony, arsenic, zinc, titanium, and with the sulphates of nickel and iron. (1139) The most remarkable property of this force is its not possessing a dual or antithetical character, both poles of the crystal having like characters ; but Faraday has shown by the following experiment that a crystal of bismuth is able to re-act upon and affect a magnet at a distance. He suspended a small magnetic needle per- pendicularly by a single cocoon filament, and placed near its lower pole a crystal of bismuth with the magne-crystallic axis in a horizon- tal direction, the whole being left for two or three hours ; the effect was small but distinct, the result being, that if the direction of the magne-crystallic axis made an angle of 10, 20, or 30, with the line from the magnetic pole to the middle of the bismuth crystal, then the pole followed it, tending to bring the two lines into parallelism, and this it did whichever end of the magne-crystallic axis was towards the pole, or whichever side it was inclined to. It thus appears that a ciystal of bismuth is able to react upon and affect a magnet at a distance. This new force Faraday believes to be one induced under the magnetic and electric influences, and not an original force inherent in the crystal; for the crystal can take away nothing from the magnetic fluid, neither is it affected by the earth's Magnetism ; it is, however, a most peculiar one, the body possessing it being moved without having any attractive or repulsive powers. (1140) Whilst engaged in the study of the diamagnetic properties of organic bodies, Pliicker was induced to submit various crystalline bodies to the action of the magnet, and he made the following remarkable discoveries Taylor's " Scientific Memoirs," vol. 5) : " "When any crystal having a single optic axis* is placed between the * In all crystals which possess the property of double refraction, there are one or two directions in which the splitting of the ray does not take place ; these directions are called the axes or the optic axes of the Fig. 455. crystals. Those crystals, the interiors of which pre- sent only oue direction of indivisibility, are called uniaxial ; those with two directions of indivisibility are called Unaxial. As an example of an uuiaxial crystal, Iceland spar may be taken, the primitive form of which is a rhombohedron (Fig. 455), that is, a crystal of this substance, whatever its form may 818 DTAMAGNETISM. two poles of a magnet, this axis is repelled by each of the two poles. If the crystal has two optic axes, each of these two axes is repelled by each of the two poles with the same force. The force which produces this repulsion is independent of the magnetic or dia- magnetie condition of the mass of the crystal ; it diminishes less as the distance from the poles of the magnet increases, than the magnetic or diamagnetic forces emanating from these poles and acting upon the crystal. M. Pliicker suspended a green plate of be, is to be regarded as made up of an infinite number of molecules sym- metrically arranged side by side, each being a rhombohedron. The line a x joining the obtuse summits of one of these rhombohedrous is called its crystal- lographic axis. It has been proved experimentally to be a law without exception that in an uniaxial crystal, the axis of double refraction, or the optic axis, coincides with the crystallographic axis. It has further been found that in some crystals the ray of extraordinary refraction is inclined from the axis, and in others towards it, more than the ordinary ray. The former are said to have a negative axis, the latter a positive. Uniaxial crystals may, therefore, be arranged in two classes, as in the following table (Pouillet's " Elements of Physics ") : NEGATIVE UNIAXIAL CRYSTALS. Iceland spar. Carbonate of lime and magnesia. Carbonate of lime and iron. Tourmaline. Rubellite. Corindon. Sapphire. Ruby. Emerald. Hydrochlorate of lime. Hydrochlorate of strontia. Subphosphate of potash. Sulphate of nickel arid copper. Cinnabar. Mellite. Molybdate of lead. Beryl Apatite. Idocrase (Vesuvian). Wernerite. Mica (certain varieties). Phosphate of lead. Arseniophosphate of lead. Hydrate of strontia. Arseniate of potash. Octohedrite. Prussiate of potash. Phosphate of lime. Arseniate of lead. Arseniate of copper. Nephiline. POSITIVE UNIAXIAL CRYSTALS. Sulphate of potash and iron. Subacetate of copper and lime. Hydrate of magnesia. Ice. Hyposulphate of lime. Dioptase. Red silver. Zircon. Quartz. Oxide of iron. Tungstate of zinc. Stannite. Boracite. Apophylite. It was discovered by Fresnel that in binaxial crystals there is no ordinary properly so called; neither of the rays into which the light becomes resolve obeying the usual law of refraction or the law of sines, as it is termed (the sines the angles of incidence and refraction not being in a constant ratio.) The followii table (Brewster) contains the names of a few binaxial crystals with the inclinatk of their optic axes to each other. THE MAGNE-CBTSTALLIC FOECE PLUCKEH's RESEAKCHES. 819 tourmaline, the longitudinal direction of which corresponded with the direction of its optic axis, between the poles of an electro-magnet in the apparatus shown in Eig. 451, in such a manner that the direc- tion of the thread corresponded with the direction of the optic axis ; the plate being magnetic, arranged itself between the poles, the direction of its breadth coinciding with a straight line connecting the poles, as any other magnetic body of the same form would have done. But when the plate was suspended in such a manner that the direction of its breadth coincided with that of the silk thread, so that the optic axis could now oscillate freely in a horizontal plane, it assumed that position which a diamagnetic body of the same form would have done : i.e., with its axial and longitudinal direction per- pendicular to the line of the apices of the poles. On again sus- pending the plate so that it could oscillate horizontally, it took up the same position as a diamagnetic body of the same form would have done. The direction of its breadth being in the line of the apices of the poles, and its longitudinal and axial direction perpendicular to it. By opening and closing the circuit in each of the three positions of suspension, the tourmaline could be turned round and retained in exactly the opposite position. (1141) Pliicker then took a dark brown crystal, having the form of a six-sided prism, and suspended it between the poles, the latter being so close together that the crystal had just room to oscillate freely. Under these circumstances, the magnetic attraction caused A, Principal Axis, Positive. B, Principal Axis, Negative. Substances. Inclination. Substances. Inclination Sulphate of nickel . 3 to 42 1' Nitrate of potash. 5 20' Biborate of soda 28 42' Carbonate of strontia . 6 56 Sulphate of baryta . 37 42 Talc .... 7 24 Spermaceti .... 37 40 Carbonate of lead 10 35 Henlandite .... 41 40 Mica (certain varieties) 14 Sulphate of soda and magnesia 46 49 Sulphate of magnesia . 37 24 Brazilian topaz 49 50 Carbonate of ammonia . 43 24 Sulphate of strontia. 50 Sulphate of zinc . 44 28 Sulphate of lime 60 Sugar .... 50 Nitrate of silver 62 16 Phosphate cf soda 55 20 Scottish topaz .... 65 Tartrate of potash 71 20 Sulphate of potash . 67 Tartaric acid 79 Potassiotartrate of soda . 80 Uniaxial crystals include all those crystals belonging to the pyramidal and, rhombohedral systems ; Unaxial crystals include those belonging to the prismatic oblique, and anortldc systems.. 820 DTAMAGNETISM. the tourmaline to assume such a position that the axis of the prism, which is also its optic axis, coincided with the line of the apices of the poles. The poles were then gradually separated from each other, and as they receded, the force tending to keep the crystal in its first position became less and less intense, and when their distance amounted to 80 millimetres (about Aths of an inch), the crystal rotated 90, as if it became diamagnetic, so that its axis was now r perpendicular to the line of the apices of the poles. On the further separation of the latter, the force which retained it in the position just described increased, and in this, it continued distinctly to remain after the apices of the poles had been entirely removed. At a sufficient distance from the poles, therefore, the repulsive action overcomes the magnetic attraction. (1142) A crystal of calcareous spar, a decidedly diamagnetic body, was then suspended between the poles, so that its axis should oscil- late horizontally. On charging the magnet, the axis became placed exactly eqitatorially, the crystal assuming a position in which neither a magnetic nor a diamagnetic mass of the same form would have rested when acted upon by the magnetic aud diamagnetic action of the poles of the electro-magnet. Various other magnetic crystals, viz., rock crystal, opaque crystallized quartz, a square octohedron of zircon, two yellowish-green transparent crystals of emerald, a black idocrase, and a large corundum, exhibited the same deportment, as did aUo the following linaxial crystals (crystals having two optic axes), mica, a magnetic body; topaz, sugar, arragouite, nitre, and sulphate of soda diamagnetic bodies. All these, when suspended so that the planes of their two optic axes could oscillate horizontally, took up the equatorial position. (1143) These experiments appeared to PKieker to disclose a rela- tion between the forms of the ultimate particles of matter and the magnetic forces, and to lead to the remarkable result that we can determine crystalline forms by the magnet. He thought, moreover, that they showed the existence of a relation between the forces which are in action during crystallization and the^ magnetic forces. According to Faraday's view, the ne\v force discovered by PJiicker is an optic axis force exerted in the equatorial direction, and therefore existing in a direction at right angles to that which produces the magneto-crystallic phenomena ; both forces, however, have relation to the force conferring the condition of crystalline structure, aud Fara- day is of opinion that they have one common origin and cause. (J144) The more recent experiments of Tyndall and Knoblauch (Phil. Mag., vol. xxxvi. p. 178, and vol. i., N. S., p. 1) lead, however, to a different view of the matter. These physicists have investigated EXPEBIMENTS OF TYNDALL AND KNOBLAUCH. 821 Pliicker's phenomena with great ability. They have shown that the action of a crystal so far from being independent of the Magnetism or Diamagnetism of its mass, as announced by Pliicker, is totally changed by the substitution of a magnetic constituent for a dia- magnetic. In determining whether the optic axis will be repelled or not, their plan was to take a thin rhomb, cloven from the crystal, and having ground it into the shape of a disc, it was suspended between the poles, when, if it belonged to a class whose optical axis is repelled, the line bisecting the acute angles of the rhomb set itself axial, if of the ol'her class, the same line set itself equatorial. Their method of examining crystals was to pound them in an agate mortar, and then to make them into a paste with distilled water, which, when dry, they suspended between the poles. On experi- menting with gutta percha, Messrs. Tyndall and Knoblauch found that a circular disc of this substance always arranged itself with the direction of the fibre axial, and a parallelogram, f-ths of an inch long and | an inch wide, with the fibres crossing it transversely, set stiffly equatorial. This they consider to be owing to the facility with which the magnetic force can act in the direction of the fibre. The same phenomena were produced with ivory, which could be made to stand either axially or equatorially by cutting it in a particular way. They consider that Pliicker's explanation of Earaday's experiment is incorrect, and that the setting of a crystal in the magnetic field is dependent on the amount of magnetic or diamagnetic force in the direction of the lines of cleavages. (1145) The experiments of Messrs. Tyndall and Knoblauch are irreconcilable with Pliicker's statement, that the position of the optic axis is independent of the Magnetism or Diamagnetism of the crystal; nor does their extensive examination of crystalline bodies confirm the law announced by the German philosopher, that " there will be either repulsion or attraction of the optic axes by the poles of the magnet, according to the crystalline structure of the crystal if the crystal is a negative one there will be repulsion, if it is a positive one there will be attraction ;" in some cases they found this law to hold good, but in many others the results were opposed to it. (1116) Messrs. Tyndall and Knoblauch quote the following ex- periment to show that the deportment of crystalline bodies in the magnetic field may be explained without assuming the existence of an " optic axis" force: Take a slice of apple, rather thicker than a penny piece, stick through it, in a direction perpendicular to its flat surface, some bits of iron wire, and hang it in the magnetic field ; it will set itself equatorial, not ly repulsion, but by the attraction of the iron wires. Substitute bits of bismuth wire for the iron, the 822 DIAMAGSETISM. apple will now set axial, not by attraction, but by the repulsion of the bismuth. Now, arrangement is conceivable amongst the par- ticles of a magnetic or a diamagnetic body capable of producing similar effects, and if the magnetic and diamagnetic forces be asso- ciated with the particles of matter, the inference is not unreasonable that the closer these particles are aggregated, the less will be the obstruction offered to the transmission of the respective forces among them. As regards Magnetism, different directions through the same body may represent good and bad conductors in Elec- tricity, the line of preference being that of closest contact among the material particles. If some fine bismuth powder be kneaded into a paste with gum-water, and then s made into a roll, about li inch across, it will point eqiiatorially between the magnetic poles, but if it be squeezed flat it will point axially, even though its length be ten times that of its breadth ; again, if a similar roll be made of pounded carbonate of iron, it will point axially, but after being squeezed, it will recoil violently between the poles, and point equatorially. The cause of these phenomena is evident. The line of closest contact is perpendicular in each case to the surface of the plate, a consequence of the pressure in this direction ; and this perpendicular stands axial or equatorial, , according as the plate is magnetic or diamagnetic. This sort of action must exist in all non-homogeneous masses, and there must be an election of a certain line by the force operating, and this line they call the line of elective polarity. (1147) Messrs. Tyndall and Knoblauch imitated Faraday's expe- riments with crystals of sulphate of iron by substituting for them a model of powdered carbonate of iron with gum-water, made into a paste, and compressed and arranged so that the line of " elective polarity" through the model was perpendicular to the length. With this they obtained corresponding results ; the model, though mag- netic, and strongly attracted by the magnet, actually receded from it when made to stand between the flat-faced poles obliquely. In the same way, by using bismuth powder, they imitated Earaday's experiments with a plate of bismuth. Now, as by reducing the substances to powder, all symmetry of crystalline arrangement is annihilated, and the force among the particles which makes them cohere in regular order, rendered ineffective, it would seem that Magnetism and Diamagnetisin are clearly modified by mechanical arrangement. They enunciate the general principle in the fol- lowing terms : " If the arrangement of the component particles of any ~body, be such as to present different degrees of proximity in different directions, then the line of closest proximity, other circumstances being DIFFERENTIAL MAGNE-CRTSTALLIC FOECE. 823 equal, will be that chosen by the respective forces for the exhibition of their greatest energy. If the mass be magnetic, this line will stand axial; if diamagnetic, equatorial" Both experiment and speculation seem, indeed, to concur in pronouncing the line of closest proximity among the particles to be that in which the magnetic and dia- magnetic forces will exhibit themselves with peculiar energy, thus determining the position of the crystalline mass between the poles. (1148) It had been announced by Pliicker as a law that the magnetic attraction decreases in a quicker ratio than the repulsion of the optic axis. By this law he accounted {jpr the following fact. On setting a small rhomboid of Iceland spar, with its optic axis hori- zontal, between the pointed poles, brought together as closely as pos- sible, it sets equatorially, the optic axis coinciding with the magnetic axis ; on now separating the poles 1- or f of an inch from each other, the rhomboid turns through 90, and sets with its optic axis equa- torial, and its greatest length axial. In the first instance the dia- magnetic force overcame the optic axis force ; in the second the optic axis force was the strongest. Tyndall and Knoblauch imitated these phenomena exactly with a model rhomboid, made by dissolving pure Iceland spar in hydrochloric acid, precipitating by carbonate of ammonia, and making with this precipitate a dough with gum- water, which they squeezed in one direction, so that the line of compression through the model coincided with that which represented the optical axis. Between the near points of the magnet the artificial optical axis stood from point to point ; between the distant points it stood equatorially. They also constructed models of magnetic crystals from emery sand-paper ; some of these, where magnetic layers of emery were perpendicular to its length, acted in the magnetic field pre- cisely like a prism of beryl ; between the near points both stood axial, between the distant points equatorial. Prom these and many similar experiments, these intelligent philosophers came to the con- clusion that both classes of phenomena have a common origin ; and that from the deportment of crystalline bodies between the poles of a magnet, no direct connexion between light and Magnetism can be inferred. (1149) Constancy of Differential JMagne-Crystallic Force in Diffe- rent Media. It had been observed by Faraday in his earlier expe- riments on magne-crystallic action, that with respect to bismuth the relation between the magnetic force in the axial and equatorial directions was unchanged by varying the surrounding medium from water to a solution of sulphate of iron. In his Thirtieth Series of Experimental Researches (Nov. 15th and 25th, 1855), he makes this condition the subject of further and special investigation. The 824 DIAMAQXETISM. method employed to compare the possible variation of force pro- duced by different circumstances, was to suspend the magne-crystal by a torsion fibre or wire, to place it in the magnetic field, to adjust the torsion index so that it should be at zero when the crystal had taken its position of stable equilibrium ; then to put on riylit- Jianded torsion until the crystal had attained the point of unstable equilibrium, or the upsetting point on that side; and after having noticed the torsion required, to reverse the motion, and put on left- lianded force, until the upsetting point on the opposite side was attained. Either of these forces^ minus the deflection, is the measure of the upsetting force, and therefore the sum of these two observations, minus the number of degrees through which the crystal has moved in passing from one upsetting point to the other, may be considered as expressing the force which solicits the crystal to retain its stable position of rest. (1150) The magnet employed was that great one constructed by Logeman, and sent to the Exhibition of 1851. It could sustain a weight of 430 pounds, and is very constant in power. The sliding poles pieces were of square iron, and presented either pomte 1 termina- tions towards each other, or two flat faces 1'7-inch square, which could be brought up to the opposite sides of the troughs or vessels containing the different fluids or media required for the experiments. These vessels were of various sizes and kinds ; but the outer ones were usually of copper, with flat sides, that the pole pieces might bear against them, and be thus preserved in their position during the progress of a single experiment, or a series of comparative results. The torsion suspender was about 24 - 5 inches in length, and was either a fine platinum wire, of which 28'5 inches weighed 1 grain, or a finer wire of silver, or a bundle of cocoon silk fibres. The torsion wire terminated below, by a hook, made out of a flat piece of copper foil, intended to receive on its edge a corresponding hook attached to the object submitted to experiment. The crystal was held by one turn of a fine copper wire which was continued upward for 5'7 inches, and terminated by aflat hook, like that just described. A horizontal bristle was fixed to each loop, and this, by its position, not only showed the place of the crystal beneath, but being retained between moveable stops associated with a horizontal scale, it indicated when the crystal was approaching the upsetting point, and being held within, and governed by the stops, allowed them, through it, to govern the crystal. The balance was enclosed by glass, to obviate the effects of currents of air. (1151) With this apparatus Faraday experimented with lismuth, tourmaline, protocarbonate of iron, and red ferroprussiate of potassa, DIFFERENTIAL MACKSE-CRYSTALLIC FORCE. 825 in various media. With a bismuth crystal, in the form of an octa- gonal prism, suspended perpendicularly between the flat faces of the sliding poles, so that its magnc-crystallic axis was horizontal, the up- setting torsion force in air was 2250 ; in absolute alcohol, 2269 ; in water, 2230 ; and in saturated solution of protosulpliate of iron, 2234. In another experiment at a higher temperature, viz., 160 Fahr., the torsion force in water was 1945, and in melted phosphorus, 1950. With tourmaline the following numbers were obtained, the fine silver torsion wire being employed : water, 1082 ; olive oil, 1085; alcohol, 1081; air, 1079; saturated solution of protosul- phate of iron, 1081. A rough octagonal prism of native protocar- lonate of iron (a highly paramagnetic substance) being suspended between the poles, opened to the full extent of the magnet, viz., 4'7 inches ; the torsion force in water was 542 ; in air, 543 ; and in protosulpliate of iron, 542. Lastly, a crystal of red ferroprus- slate of potash, gave a torsion force in air, 314; and in camphine, 316. (1152) These results point to the conclusion that there is no experimental difference in the proportion of the force developed in different directions in a magne-crystal, by the action of induction, whatever be the nature of the medium surrounding it, and whatever the difference in the paramagnetic and diamagnetic character of the crystals, or the media employed, crystals differing as much as bismuth and carbonate of iron, and media differing as greatly as phosphorus and saturated solution of protosulpliate of iron having been employed. The aptitude of a magne-crystal, when in the mag- netic field, to assume a maximum conductive state in a given direc- tion, makes it similar in action to a permanently magnetized sphere ; and magne-crystals may be employed in experiments to measure mag- netic force just as needles are ; indeed, they are in some points of view philosophically more accurate, being equal in quality in all their parts, taking up precisely the same state under the same induc- tive force ; having no coercitive or retentive faculty, and being inde- pendent of the surrounding medium. (1153) As the setting force of a crystal remains constant for any surrounding medium, the possibility existed of finding a magne- crystal and a medium so related that the attraction and repulsion of the crystal as a whole, should be convertible terms depending upon the position of the crystal in regard to the lines of force. This case Faraday realized with the paramagnetic red ferroprussiate of potassa and a solution of sulphate of iron, and also with the diamagnetic crystal, carbonate of lime, and diluted alcohol. He also sought for a crystal amongst the ferrocarbonates of lime having this relation to 826 DI A MAGNETISM. the assumed natural zero presented by a vacuum, or carbonic acid ; but this case was not realized. (1154) Action of Heat on Magne-crystals. When magne-crystals subjected to the same constant magnetic force, were raised or lowered to different temperatures, it was found that the setting force was affected ; and at all temperatures, from Fahr. upwards, the force diminished as the temperature became higher. Thus the torsion force of a crystal of bismuth at 92 being 175, was at 279 diminished to 82 ; that of a tourmaline, by passing from the temperature of 79 to 289, was so far diminished, that the power at the lower temperature was nearly double that at the higher. A like result occurred with carbonate of iron, and also with compressed bismuth. In all these cases the bodies resumed their first full power on returning to lower temperatures, nor was there any appearance of magnetic charge in any part of the range of observa- tions. Between 32 and 300 the force of bismuth appeared to alter by equal, regular degrees ; but with tourmaline and carbonate of iron the change was greatest for an equal number of degrees at the lower temperatures. At a full red heat, however, both tourmaline and calcareous spar retained a portion of their magne-crystallic force or condition, and so did carbonate of iron up to that temperature at which it was decomposed. A crystal of ferrocarbonate of lime had its magnetic condition absolutely reversed by change of temperature ; at low temperatures the optic axis pointed axially, and at high temperatures equatorially. (1155) Effect of Heat upon the Absolute Magnetic Force of Bodies. At temperatures varying from 30 to 288 the inductive force in iron appears to undergo no change, having obtained and kept its maximum degree ; with nickel there is a diminution of force at the upper temperature, which is in accordance with the general effect of heat ; with cobalt, on the other hand, there was an increase of power with elevation of temperature. Faraday thinks it probable that in passing to lower temperatures than those employed, a particular temperature would be arrived at for nickel and iron, presenting the maximum magnetic induction for each, and below which their inductive force would diminish a view which adds much additional interest to the relation between heat and Magnetism. (1156) Diamagnetic Polarity. By the following experiment, "Weber (Pogg. Ann. Jan., 1848) considers the polarity of bismuth to be proved : A strong horseshoe magnet is laid upon a table in such a position that the line joining its two poles is perpendicular to the magnetic meridian, and to be considered as prolonged on one side ; in that line, and near the magnet, is to be placed a small DIAMAGNETIC POLARITY WEBER. 827 powerful magnetic needle, suspended by a cocoon silk, and on the other side of it, the pole of a bar magnet r in such a position-, and so near, as exactly to counteract the effect of the horseshoe magnet, and leave the needle to point exactly as if both magnets were away. Then a mass of bismuth being placed between the poles is said to react upon the small magnet needle, causing its deflection in a particular direction,, and is supposed to indicate the polarity of the bismuth under the circumstances, as it had no such action when the magnets were away. A piece of iron, in the place of the bismuth, produces a contrary deflection of the needle. This experiment may be variously modified, but in every case the force of the bismuth must be observed upon other magnet poles than those which deter- mine the diamagnetic condition of the bismuth, and they all concur (according to Weber) in confirming the assertion that bismuth con- stantly acts upon such poles in an opposite manner to iron in its place, that it consequently repels where iron attracts, and attracts where iron repels ; in short, that at other magnet poles than those which diamagnetize the bismuth we as frequently observe attractive as repulsive forces of the bismuth. (1157) In order to remove every doubt as to the diamagnetic force being really nothing else than the magnetic fluids, or their equivalents Ampere's currents, Weber proceeded to examine whether, agreeably with the laws of induction discovered by Faraday, an elec- tric current can be induced in a neighbouring conductor by rotating a diamagnetic body under the influence of a powerful magnet. The following was the arrangement adopted : An iron nucleus, 600 milli- metres * in length, coated several times with thick copper wire, was used as the electro-magnet. To the circular terminal surface, 50 millimetres in diameter, of this iron nucleus, was fixed the annular conductor, which consisted of copper wire, 300 metres long, and |rds of a millimetre thick, well spun with silk, and coiled upon wooden cylinders. The space included in this annular conductor, in which the bar of bismuth was to be placed, was 140 millimetres in length, and 15 millimetres in breadth ; the bar of pure precipitated bismuth was somewhat thinner. The extremities of the annular conductor were connected with a commutator, as were also the extremities of the multiplier of a very sensitive galvanometer, the magnet needle of which was provided with a mirror, in which the image of the distant scale was observed by a telescope directed towards it. The galvanometer was, moreover, provided with so effective a damper that it was scarcely possible to observe any vibration of the needle. * 1 millimetre = 0'03937 English inch; 1 metre = 39'37 English inches. 3 H 828 DIAMAGNETISM. Now, whilst a very powerful and constant galvanic current passed through the thick wire of the electro-magnet, the bar of bismuth was withdrawn from the annular conductor, the commutator changed, and the bar of bismuth again inserted, the commutator again changed, and the bar of bismuth withdrawn, &c. During this experiment, continued for about one minute, the state of the galvanometer was read off at intervals of about 10 seconds. A second series of experiments was now made, but with this difference, that the commutator assumed that position, on withdraw- ing the bar of bismuth which it had occupied in the first series on inserting the bismuth, and vice versa. (1158) The results were these : The commutator being in the position A, whilst the bismuth was withdrawn, the galvanometer rose 2*62 ; the commutator being in the position B, whilst the bismuth was withdrawn, the galvanometer fell 2'10. The extreme end of an iron bar being substituted for the bismuth, the induced current was too powerful to be measured ; the direction of the needle could alone be observed. The position of the commutator being A, whilst the iron bar was removed, there was a decrease in the deflection of the galvanometer ; and the position of the commutator being B, there was an increase in the deflection of the needle on removing the iron bar, and these results being exactly the reverse of those obtained with the bismuth, prove, (according to Weber,) the induction of electric currents by the diamagnetization of the bismuth, the direction of these currents being constantly the reverse of those induced by iron under the same circumstances, precisely as it should be if the bismuth contained magnetic fluids, or their equivalents (Ampere's currents,) which are set in motion, or rotated under the influence of powerful magnets in exactly an opposite direction to that of iron. (1159) The apparatus employed by Faraday for the determination of this question is thus described (Phil. Trans., part i., 1850) : " A straight wooden lever, 2 feet in length, was fixed by an axis at one end, and by means of a crank and wheel made to vibrate in a hori- zontal plane, so that its free extremity passed to and fro through about 2 inches. Cylinders of metal, or other substances, 5 j inches long, and f ths of an inch in diameter, were fixed in succession to the end of a brass rod, 2 feet long, which itself was attached at the other end to the moving extremity of the lever, so that the cylinders could be moved to and fro in the direction of their length through a space of 2 inches. A large cylinder electro-magnet was also pre- pared, the iron core of which was 21 inches long and 1*7 inch in diameter ; but one end of this core was made smaller for the length of 1 inch, being in that part only 1 inch in diameter. On to this DIAMAGtfETIC POLARITY FARADAY. 829 reduced part was fixed a hollow helix, consisting of 516 feet of fine covered copper wire ; it was 3 inches long, 2 inches external diameter, and 1 inch internal diameter ; when in its place, 1 inch of the central space was occupied by the reduced end of the electro-magnet core which carried it, and the magnet and helix were both placed concen- tric with the metal cylinder above mentioned, and at such a distance that the latter in its motion would move within the helix, in the direction of its axis approaching to, and receding from the electro- magnet in rapid or slow succession. The least and greatest distances of the moving cylinder from the magnet during the journey, were --th of an inch and 22 inches. The object, of course, was to observe any influence upon the experimental helix of fine wire which the metal cylinders might exert, either whilst moving to or from the magnet, or at different distances from it. " The extremities of the experimental helix wire were connected with a very delicate galvanometer, placed 18 or 20 feet from the machine, so as to be unaffected directly by the electro-magnet ; but a commutator was interposed between them. This commutator was moved by the wooden lever, and as the electric currents which would arrive at it from the experimental helix, in a complete cycle of motion, or to-and-fro action of the metal cylinder, would consist of two con- trary portions, so the office of this commutator was, sometimes to take up these portions in succession, and send them on in one con- sistent current to the galvanometer, and at other times to oppose them and to neutralize their result ; and, therefore, it was made adjustible, so as to change at any period of the time or part of the motion. " With such an arrangement as this, it is known, that however powerful the magnet, and however delicate the other parts of the apparatus, no effect will be produced at the galvanometer as long as the magnet does not change in force, or in its action upon neigh- bouring bodies, or its distance from, or relation to, the experimental helix ; but the introduction of a piece of iron into the helix, or any- thing that can influence, or be influenced by the magnet, can, or ought to show a corresponding influence upon the helix and galvano- meter. ' The apparatus? observes Faraday, ' I should imagine to be almost the same in principle and practice as that of M.Weber, except that it gives me CONTRARY RESULTS.' " To insure steadiness, the machine, the magnet and helix, and the galvanometer stood upon separate tables on a stone floor laid upon the earth, the table carrying the machine being carefully strutted to neighbouring stone work. No iron was employed in any of the moving parts, and great care was taken to prevent the core while in 3 H 2 830 DIAMAGKETISM. motion from disturbing in the least degree the experimental helix and magnet. The magnet was excited by a current from 5 pairs Grove's plates, and was then very powerful. It was observed that on connecting the magnet with the battery, and then the experimental helix with the galvanometer (a very deli- cate instrument by Ruhmkorff), a current appeared at the latter, which continued a varying time, and which seemed to come from the battery. This current, which it was necessary in these delicate investigations to guard against, was traced to the time occupied by the iron core in attaining its maximum magnetic condition. It dis- appeared after the magnet had been excited a short time, and no experiment was proceeded with till it had entirely ceased. (1160) On proceeding to experiment with this apparatus, Faraday found that when magnetic metals were used as cores, and such a velocity given to the machine as to cause five or six approaches and withdrawals of the core in one second, the direction in which the needle of the galvanometer moved was consistent with the effect of a magnetic body ; but when diamagnetic metals were used, the deflec- tion of the needle was in a contrary direction, but the deflection was not the greatest for the most diamagnetic substances ; indeed, the effect with bismuth, antimony, and phosphorus was scarcely appreciable. The effects were proportionate to the conducting power of the substance for Electricity ; and after minutely examining into all the circum- stances, and varying the experiments in many ways, Faraday came to the conclusion that they were due to induced currents moving through the masses of the diamagnetic substances, and not to any polarity correspondent in its general nature (though opposed in its direction) to that of iron. (1161) Kef erring to Reisch's experiments as described by "Weber, according to which both JN". and S. poles, when they act at the same time on the same side of a piece of bismuth, by no means repel it with the sum of the forces which they would individually exert, but only with the difference of these forces ; Faraday says, that he repeated it " carefully and anxiously, but could never obtain the slightest trace of action with the bismuth." He obtained action with the iron, but in those cases the action was far less than if the iron were applied outside between the horse-shoe magnet and the needle, or to the needle alone, the magnets being entirely away ; with weak magnetic substances, he did not find the arrangement at all comparable for readiness of indication or delicacy, with the use of a common or an astatic needle. Faraday also refers to an experiment of Pliicker, which at first seems to indicate strongly the polarity of bismuth or phosphorus. If DIAMAGNETIC POLARITY FARADAY. 831 a bar of either of these substances be suspended horizontally between the poles of the electro-magnet, it will go to the equatorial position with a certain force, passing from stronger to weaker places of action. If a bar of iron of the same size be fixed in the equatorial position, a little below the plane in which the diamagnetic bar is moving, the latter will proceed to the equatorial position with much greater force than before, and this is considered as due to the circumstance that on the side where the iron has N". polarity, the diamagnetic body has S. polarity, and that on the other side the S, polarity of the iron and the N. polarity of the bismuth also coincide. (1162) It is, however (says Faraday), very evident that the lines of magnetic force have been altered sufficiently in their intensity of direction, by the presence of the iron, to account fully for the in- creased effect. For, consider the bar as just leaving the axial posi- tion and going to the equatorial position, at the moment of starting its extremities are in places of stronger magnetic force than before, for it- cannot be doubted for a moment that the iron bar determines more force from pole to pole of the electro-magnet than if it were away. On the other hand, when it has attained the equatorial posi- tion, the extremities are under a much weaker magnetic force than they were subject to in the same places before, for the iron bar determines downwards upon itself much of that force which, when it is not there, exists in the plane occupied by the bismuth. Hence, in passing through 90, the diamagnetic is urged by a much greater difference of intensity of force when the iron is present than when it is away ; and hence, probably, the whole additional effect. . . . The effect does not (Earaday thinks) add anything to the experimental proof of diamagnetic polarity, nor can he find any evidence of such a state either in his own experiments or in those by Weber or B-eisch, and the actions represented or typified by iron, by copper, and by bismuth remain at present distinct. (1163) A series of memoirs have recently been published by Von Feilitsch (JPogg. Ann.), in which he endeavours to prove that dia- magnetic bodies possess a polarity the same as that of iron ; and in this uncertain state of the subject some admirable experiments were undertaken by Dr. Tyndall, the results of which were laid before the Physical section of the British Association at Liverpool in 1854. That the repulsion of a diamagnetic body depends not alone on the magnet operating upon it, but upon the joint action of the magnet and diamagnet, is proved by the fact that the repulsive force increases not simply in proportion to the strength of the magnet, but to the 832 DIAMAG2TETISM. square of the strength.* Tyndall confirms the observation of E/eisch, that the condition, whatever it may be, which is evoked in a bar of bismuth by one magnetic pole is neutralized by the other ; that each pole evokes a condition peculiar to itself, for when a bar of that metal was suspended between the poles of two bar electro-magnets it was repelled when the poles were alike, but remained motionless when the poles were of different names. The most perfect antithesis was observed in all cases between the deportment of a normal dia- magnetic bismuth bar (a bar in which the planes of principal cleavage are parallel to the length of the bar) and a bar of soft iron ; the elec- tric and magnetic forces, which caused a deflection of the former from right to left, produced a deflection of the latter from left to right. The whole of the experiment seemed to justify the presumption, that whatever be the nature of the influences evoked in magnetic bodies by the action of currents or magnets, or of both combined, to an in- fluence of the same nature but antithetical in its manner of distri- bution, the deportment of diamagnetic bodies is to be referred. (1164) The following experiment is described by Tyndall as pointing to the conclusion that, whatever the ideal magnetic distri- bution in iron may be, a precisely opposite distribution occurs in bismuth ; or, in other words, that the diamagnetic force is a polar force, but that the polarity is the reverse of magnetic polarity. Two helices were so placed that the end of the soft iron cores which fitted into them, were about 6 inches apart from centre to centre ; the he- lices were at opposite ends of the plane which touched the ends of the cores. A helix of copper wire was introduced, and within it a bismuth bar, 6J inches long, and four-tenths of an inch in diameter, * This mark of distinction between those bodies which have their power of exhibiting magnetic phenomena conferred upon them by the magnet, and those whose actions are dependent upon some constant property of the mass, was pointed out by Tyndall and Poggendorff in 1851. It may be illustrated thus : Let M represent the Magnetism of either pole of a magnet, and let M' be the Magnetism of the opposite pole of a very hard steel bar, then their mutual attraction at a given unit of distance is expressed by the product MM'. If now the power of the pole of the magnet be increased to n M, the mutual attraction will be n MM', provided, that is, that the steel bar is hard enough to resist magnetization by influence ; hence, when a variable magnetic pole acts on an opposite one of constant power, the attraction is proportional to the strength of the former. But, if instead of a hard steel bar, a piece of soft iron (M') be taken, the Magnetism of which will increase in the same ratio as that of the influencing pole of the magnet, then on increasing the power of the latter from M to n M, the attraction expressed by the product of both will be w 2 MM' ; that is to say, the attraction of a body magnetized by influence, and whose Magnetism varies as the strength of the influencing magnet is proportional to the square of the strength of the latter. DTAMAGISETIC POLARITY TYNDALL. 833 was freely suspended, so that the ends of the bar were opposite to those of the soft iron cores. A current being sent through the helix, if the bismuth bar within it were excited by the current, it was pro- bable that the nature of the excitement would manifest itself in the action of the magnets upon the diamagnetic body. By working deli- cately, the most perfect mastery was obtained over the suspended bismuth : when the current through the helix flowed in a certain direction, the ends of the diamagnetic bar were repelled by the elec- tro-magnets ; when the current flowing through the helix was reversed, the same ends were attracted by the magnet. The same effect was obtained when instead of reversing the helix current, the polarity of the two magnets was reversed. On comparing the deflections with those of soft iron, it was found that they were perfectly antithetical. The exeitement which caused the ends of the iron bar to be attracted, caused the ends of the bismuth bar to be repelled ; while the excite- ment which caused the ends of the iron bar to be repelled, caused those of the bismuth bar to be attracted. (1165) If it be true that the polarity of the bismuth bar is the reverse of magnetic polarity, its two ends must, when the current circulates round it, be in different states ; but if this is the case, then, if we make the two poles acting upon the ends of the bar alike, we ought to have attraction at one end and repulsion at the other ; the result of these opposing actions being that the bar must remain undeflected. Tyndall made this experiment, and the result was in accordance with this conclusion. Two magnets with poles of the same name were brought to bear on a bismuth bar, the direction of the force emanating from the two poles being the same, the repulsion of one end and the attraction of the other tended to deflect the bar ; two other poles of the same name, but of opposite names to the former two, were then caused to act upon the bar, i. e., four magnets were employed the two poles to the left being of the same name, and the two to the right of the opposite quality. The bar was promptly deflected, thus corroborating the view that diamagnetic bodies possess a polarity opposed to magnetic bodies. (1166) In the Bakerian Lecture for 1855, I>r Tyndall reinvesti- gates this interesting subject at great length, and adduces powerful experimental evidence in proof of the duality of diamagnetic excitement and of diamagnetic polarity. In experimenting with bismuth, the question of structure must be particularly attended to, for the " setting" of a bar of that metal between the magnetic poles will depend on the relation of the form of the mass to the planes of crystallization. A bar of bismuth whose planes of principal cleavage are throughout parallel to its length, suspended in the magnetic field 834 DIAMAGKETISM. with the said planes vertical, will set its longest dimension at right angles to the line joining the poles this is the normal department of diamagnetic bodies, and Tyndall, therefore, calls such a bar, a normal diamagnetic bar. On the other hand, a bar of compressed bismuth dust, or a bar of bismuth whose principal planes of crystal- lization are transverse to its length, will set .axial in the magnetic field ; such bars he calls abnormal diamagnetic bars. Again, a bar of iron sets with its longest dimension from pole to pole ; but a bar of compressed carbonate of iron dust, whose shortest dimension coincides with the line of pressure, sets its length equa- torial ; the former may, therefore, be called a normal paramagnetic bar, and the latter an abnormal paramagnetic bar. (1167) The apparatus employed in examining the separate and joint action of a magnet and a voltaic current on these different bars, is shown in Fig. 456. A helix was formed of covered copper wire, Fig. 456. ioth of an inch thick ; the space within the helix was rectangular, and was 1 inch long, O7 vinch high, and 1 inch wide ; the external diameter of the he- lix was 3 inches. Within the rectan- gular space, the body to be examined was suspended by a fibre which descended through a slit in the helix. The latter was placed between the two flat poles of an electro-magnet, and could thus be caused to act upon the bar within it, either alone or in combination with the magnet. When a normal, paramagnetic bar was suspended in this helix, and a current sent through the latter, the bar set its longest horizontal dimension parallel to the axis of the helix, and consequently perpendicular to the coils. An abnormal paramagnetic bar suspended in a similar manner set its longest dimension perpen- dicular ,to the axis of the helix, and consequently parallel to the coils. A normal diamagnetic bar comported itself in the helix precisely as an abnormal paramagnetic bar; and an abnormal diamagnetic bar exactly as a normal paramagnetic bar. (1168) In examining the conjoint action of the magnet and the helix, eight experiments were made with each particular bar; in the first four the magnet was excited first, and after the suspended bar had taken up its position of equilibrium, the ^deflection produced by the passage of a current through the surrounded helix was observed ; in DIAMAQtfETIC POLARITY TYNDALL. 835 the second four experiments the helix \\ as excited first, and when the bar within had taken up its position of equilibrium, the Magnetism was developed and the consequent deflection observed. "We give the results of the eight experiments with the normal paramagnetic bar. N S (Fig. 457) indicate the N. and S. poles of the electro- magnet ; a b is the bar of iron ; the helix within which the bar was suspended is shown in outline around it ; the arrow shows the direc- tion of the current in the upper half of the helix. Fig. 457. Fig. 458. Fig. 459. Fig. 460. 1. Magnet excited first. On exciting the magnet, the paramagnetic bar set itself parallel to the line joining the poles, as shown by the unbroken line a b. On now sending a current through the helix in the direction of the arrow, the bar was deflected towards the position dotted in the figure ; interrupting the current in the helix and per- mitting the magnet to remain excited, the bar returned to its former position ; the current was now sent through the helix in the direc- tion of the arrow (Fig. 458), the consequent deflection was towards the dotted position. In Figs. 459 and 460, all other things remaining the same, the polarity of the magnet was reversed; the deflections of the bar on exciting the helix are shown by the dotted lines. Fig. 461. Fig. 462. Fig. 463. Fig. 464. 2. Helix excited first. On passing the current through the helix the bar immediately set its length parallel to the axis of the helix. On now exciting the magnet so that its polarity was that indicated by Fig. 461, the deflection was towards the dotted position. Inter- 836 DIAMAGNETISM. rupting the current through both magnet and helix, and reversing the current through the latter, the bar came to rest as before, parallel to the axis, On exciting the magnet as in the last case, the deflection was that shown in Eig. 462. Preserving the same current in the helix, and reversing the polarity of the magnet the deflection was that shown in Fig. 463. Preserving the magnet poles as in the last experiment, and reversing the current in the helix the deflection was that shown in Fig. 464. (1169) These experiments were repeated under precisely the same conditions with a normal diamagnetic bar; the deflections were in each of the eight cases the reverse of those indicated in the figures ; they were next repeated with an abnormal paramagnetic bar, made of compressed carbonate of iron dust ; the deflections were in each case the same with those with the normal diamagnetic bar ; and lastly, an abnormal diamagnetic bar, consisting of a prism of bismuth, whose principal planes of crystallization were perpendicular to its length, was tested by a mode of experiment the same as that applied in the other cases, and the deflections were found to agree with those of the normal paramagnetic bar. (1170) For examining the question of the " polarity " of dia- magnetic bodies, the plan adopted by Tyndall was to cause fixed magnets to act upon a moveable bar of bismuth encircled by an electric current, and to note from the deflections of the bar the character of the force acting upon it. The bar was suspended with great delicacy in the axis of a helix of covered copper wire ; opposite to either end of the bar was placed an electro-magnetic spiral, enclosing a core of soft iron. The spirals were so connected Fig. 465. together that the same current excited both, so that the same mag- netic strength was de- veloped in both poles, and by means of a reverser the polarity of the cores could be changed at pleasure; a current reverser was also attached to the helix enclosing the bismuth bar, so that the current from the battery could be caused to flow through DIAMAGTSTETIC POLAKITY TYNDALL. 837 it in either direction. The arrangement will be at once under- stood by an inspection of Fig. 465. A B, the helix enclosing the bismuth bar ; N S, the ends of the cores of the electro- magnets; B', the current reverser of the spirals; B-, the current reverser of the helix. On sending the current through the helix in the direction indicated by the arrow, the magnets being so excited that the pole N. was N. and the pole S., S. ; the bar moved from its position, and came to rest in the dotted position, being manifestly attracted by the magnets. On reversing the poles of the magnets, the bismuth bar instantly loosed from the position it previously occupied, and receded from the poles ; it was now repelled. On now changing the direction of the current through the helix, attraction was again manifested. " In all cases, when the bar was freely moving in any direction under the operation of forces acting upon it, the reversion, either of the current in the helix or the polarity of the cores, arrested the motion; approach was converted into recession, and recession into approach." (1171) Tyndall has more recently (Phil Trans., 1856) again investigated this interesting subject with an apparatus based on different principles, and constructed (from a plan furnished by M. Weber,) by M. Leyser, of Leipsic. The diamagnetic bar, suitably excited, is permitted to act upon an astatic system of steel magnets ; and from the deflections of the system the polarity of the bar is inferred. The instrument consists essentially of 2 spirals of covered copper wire, about 18 inches long, firmly attached to a massive slab of mahogany. The slab is attached by brass bolts to the solid masonry of the Hoyal Institution, so as to have the spirals in a vertical position. Above the spirals is a wooden wheel, with a grooved periphery, and below them a similar one. The wheels are united by an endless string, which communicates motion from one of them to the other. To this string the cylinders submitted to examination, are attached ; and by turning the lower wheel with a suitable key, the cylinders can be caused to move up and down within the spirals. Two steel bar magnets are arranged astatically, connected by a rigid brass junction, and so suspended that the magnets are in a horizontal plane. The two magnets have the two spirals between them, their poles being o'pposite the centres of the spirals. When, therefore, a current is sent through the spirals, it exerts no more action upon the magnets than the central or neu- tral point of a magnet would do. If the bars within the spiral be perfectly central, they also will present these neutral points to the suspended magnets, and hence exert no action upon them. But if the key be so turned that the two ends of the diamagnetic bars shall 838 DIAMAGNETISM. Fig. 466. act upon the magnets, then, if these bars be polar, the intensity and character of their polarity will be indicated by the deflections of the magnets. Hence, we have not only the action of the earth neutralized, but a turning force is brought to bear upon the sus- pended system four times that which would come into play if only a single spiral arid a single pole were made use of. The instrument is enclosed on all sides from external air currents ; the magnets have a mirror attached to them which moves as they move, and which is observed by means of a telescope and scale placed at a distance of about 10 feet from the instrument. (1172) The apparatus, and the working of its various parts, will be understood by reference to Fig. 466 ; B O B' O' is the outline of the rectangular case, the front of which is removed so as to show the apparatus within. D D' are the screw holes by which the box is secured firmly to the wall ; H E IT E' are the copper wire helices wound round 2 brass reels, the upper ends of which protrude from H to Gr and from H' to G' ; W W are the grooved wheels, to the string of which are attached the cylinders, m, n, o, p, of the body to be examined ; Gr Gr' is a cross-bar of brass, through the centre of which the screw, E, passes, from which the astatic arrangement of magnets, S N, is suspended by silk fibres ; the black circle in front of the magnet S N is a mirror, and the rectangle, d a d' a, is the outline of a copper damper, which, owing to the currents induced in it by the motion of the magnets, soon brings the latter to rest, and thus expedites experiment. (1173) When cylinders of bismuth, copper, antimony, heavy glass, marble, and many other substances were submitted to experiment with this apparatus, very marked deflections were produced. We quote one particular experiment performed by Dr. Tyndall in the presence of Pro- fessors Faraday, De la Rive, and Marcet. The bismuth cylinders were 3 inches long and 0'7 of an inch in diameter, and were chemically pure. A current from a single DIAMAGNETIC POLARITY TYNDALL. 839 cell of Grove's battery being caused to circulate in the helices, the cylinders remaining in their centres as in the figure, the cross wire of the telescope cut the number 650 on the scale. Turning the wheel "W so as to raise the cylinder m n and depress the cylinder o p, the magnet promptly moved, and after some oscillations took up a new position of equilibrium the cross wire of the telescope then cutting 670 on the scale. Reversing the motion so as to place the cylinders again central, the former position 650 was assumed ; on turning further in the same direction so as to depress m n and raise o p, the position of equilibrium of the magnet was at the number 630. Hence, by bringing the two ends n and o to bear upon the astatic magnet, the motion was from smaller to greater numbers, the position of rest being then 20 divisions greater than when the bars were central. By bringing the ends m and p to bear upon the mag- net, the motion was from greater to smaller numbers, the position of rest being 20 divisions less than when the bars were central. When the current was caused to flow through the helices in the contrary direction, an opposite result was obtained. The following was the experiment : The bismuth cylinders being in the centres of the helices, the cross wire of the telescope cut the number 482 on the scale. Turning the wheel so as to raise m n and depress o p, the cross wire cut 468 ; reversing the motion so as to place the cylinder again central, the former position of 482 was assumed, and on turning further in the same direction so as to depress m n and raise op, the number became 493. In this case, therefore, the first motion was from greater to smaller numbers, and the last from smaller to greater. (1174) In answer to the objection that has been urged against these experiments, that the deflections are due to induced currents aroused in the bismuth by its mechanical motion up and down within the spiral, Tyndall satisfactorily replies 1st, that the deflection produced is permanent, which could not be the case if the effect were due to induced currents, which vanish instantaneously. 2ndly, if the effect were due to induction, it would be shown in the most exalted degree by the best conductors. Now, antimony is less diamagnetic than bismuth, but it is a better conductor. The deflection produced by it, however, shows that it is its diamagnetic quality, and not its conductive quality which is effective; the amount of deflection being less than that of bismuth. Copper is fifty times a better conductor than bismuth, but its diamagnetic capacity is nearly nil ; it produces no sensible action upon the magnets, which could not possibly be the case were the result due to induction. Both paramagnetic and diamagnetic liquids have been included by 840 DIAMAGNETISM. Tyndall in this examination, and the polarity of both has been established. (1175) TyndaWs Polymagnet. For the exhibition of the various phenomena of Diamagnetism and Electro-magnetism, the apparatus shown in Eig. 467, was devised by Dr. Tyndall. It consists of an Fig. 467. TYNDALL'S POLYMAaNET. 841 arrangement of two horseshoe magnets, a helix of covered copper wire disposed between them, and a suitable means of suspension. The diameter of the soft iron cores is 1/125 inch, and their distance apart from centre to centre 4*85 inches. The diameter of the covered copper wire surrounding the cores is 01 inch, and the weight of it which surrounds each limb of the magnet is 12 pounds. The helix placed between the two electro-magnets has an internal diameter of 1 inch, an external diameter of 8 inches, and measures along its axis 1'15 inch. The diameter of its wire is 0'065 of an inch, and its weight is 6 pounds. It is wound so as to form a double coil, and is held compactly together by radial strips of brass. A simple current reverser is fixed on the base-board of the instrument, which, to preserve a still atmosphere, is surrounded by a glass case. In the figure a bismuth bar is represented as suspended within the helix by several fibres of unspun silk attached to the central rod which passes through the top of the glass case. The bar is 6 inches long and '4 of an inch in diameter. When suspended so as to swing freely within the helix, its ends lie between the movable masses of iron which rest upon the electro-magnetic cores. Eour poles are thus brought simultaneously to bear upon the bar of bismuth, and its action is thereby rendered both prompt and energetic. The two poles to the right of the bar must both be of the same name, and the two to the left of the bar of the opposite quality. If those to the right be both N"., those to the left must be both S., and vice versa. On sending a current from 10 or 15 cells round the helix, and exciting the magnets by a battery of 4 or 5 cells, the current reversers place the deflections of the bar entirely under the control of the experimenter. By changing the direction of the current in the helix by means of its reverser, a change of deflection is produced. The same is effected if the polarity of the magnets be changed by the reverser which belongs to them. All the experiments that are usually made with an upright electro- magnet may be made with this instrument, the various parts of which may with great facility be lifted separately out of the case; and numerous experiments will suggest themselves to those acquainted with what has been done of late years in Diamagnetism.* (1176) Diamagnetic Conditions of Flames and Gases. At the meeting of the Physical section of the Ninth Italian Scientific Congress in Yenice, 21st of September, 1847, a memoir on the Universality of Magnetism was read by Padre Bancalari, Professor of Physics in the * The instrument above described was constructed by Mr. Becker, of Newman Street, and the same ingenious mechanician has recently completed a very perfect and elegant apparatus of a similar nature for Mr. J. Strange. 842 DIAMAGNETISM. Royal University of Grenoa ; and on the 27th of the same month it was announced by the reporter that it had been proved in the presence of several philosophers, " that on the interposition of a flame between the poles of an electro-magnet, it was repulsed at the instant the electric current was closed, to return to the first position the instant it was broken." This experiment was repeated shortly afterwards by Professor Zantedeschi, not at first with satisfactory results, but he afterwards fully confirmed Bancalari's experiments, "having," as he says, "constantly observed repulsion in the act of closing the circle, which lasted the whole time that the Magnetism was kept up, and when in the act of opening the circle, he saw the flame return to its primitive position." (1177) A further study of the phenomena gave Zantedeschi the following results : He found that the phenomenon occurs with con- tacts of both solid and hollow soft iron, showing that the movement of the flame was not attributable to currents of air. 2nd. That the repulsion when it is quite distinct, and the flame quite pure and terminated in a well-shaped top, is accompanied by a depression. 3rd. That, cteteris paribus, the greatest effect takes place when the flame is touching the convex of the magnetic curves indicated by iron filings. 4th. That the action is null, or almost null, when the flame is placed in the centre of the interval which separates the two contacts. 5th. That in the manifestation of the effects it is not necessary for the contacts to be entirely separated. 6th. That there is a certain mass of the keeper pieces which is the most efficacious ; beyond a limit, which can be shown by experi- ment, increase of the mass causes a diminution in the effect. 7th. That the movements of the flame increase with the number of the battery plates. (1178) Faraday repeated Bancalari's experiment with the large electro-magnet belonging to the Eoyal Institution. The two terminal pieces of iron forming the vertical magnetic poles, were each 1'7 inch square and 6 inches long, biit the ends were shaped to a form approaching that of a cone, of which the sides have an angle of about 100, and the axis of which is horizontal, and in the upper surface of the pieces of iron. The apex of each end was rounded nearly a tenth of an inch of the cone being in this way removed. When these terminations are brought near to each other, they give a powerful effect in the magnetic field, and the axial line of magnetic force is of course horizontal, and on a level nearly with the upper surface of the bars. (1179) His results were as follows : DIAMAGNETIC CONDITION OF FLAMES AND GASES. 843 When the flame of a wax taper was held near the axial line but on one side or the other, about one-third of the flame rising above the level of the upper surface of the poles, as soon as the magnetic Fig. 468. Fig. 469. Fig. 470. force was on, the flame was affected, and receded from the axial line, moving equatorially, until it took an inclined position, as if a gentle wind was causing its deflection from the upright position an effect which ceased the instant the Magnetism was removed. The effect was not instantaneous, but rose gradually to a maximum. It ceased very quickly when the Magnetism was removed. The progressive increase is due to the gradual production of currents in the air about the magnetic field, which tend to be, and are formed on the assump- tion of the magnetic conditions in the presence of the flame. When the- flame was placed so as to rise truly across the magnetic axis, the effect of the Magnetism was to compress the flame between the points of the poles, making it recede in the direction of the axial line from the poles towards the middle transverse plane, and also to shorten the top of the flame (Fig. 468). On raising the flame a little more, the effect of the magnetic force was to increase the intensity of the results just described, and the flame actually became of a fish-tail shape disposed across the mag- netic axis (Fig. 469.) (1180) If the flame was raised until about two-thirds of it were 3 i 844 DIAMAONETISM. above the level of the axial line, and the poles approached so near to each other (about O3 of an inch) that they began to cool and compress the part of the flame at the axial line, yet without inter- fering with its rising freely between them, then on rendering the magnet active the flame became more and more compressed and shortened, and as the effects proceeded to a maximum the top at last descended and the flame no more rose between the magnetic poles, but spread out right and left on each side of the axial line producing a double flame with two long tongues (Fig. 470). When the magnet was thrown out of action, the flame resumed its ordinary upright form between the poles at once, being depressed and redivided again by the renewal of the magnetic action. "When a small flame only about ^rd of an inch high was placed between the poles, the magnetic force instantly flattened it into an equatorial disc. (1181) Remarkable results are obtained with the dense stream of smoke rising from a blown -out green wax taper. When the ignited wick is held about an inch below the axial line, the smoke rises vertically in one column until about ^rds of that distance is passed over, and then it divides, going right and left, leaving the space between the poles clear. As the taper is slowly raised, the division of the smoke descends, taking place lower down until it occurs upon the wick at the distance of 0*4 or O5 of an inch below the axial line. If the taper be raised still more, the magnetic effect is so great as not only to divide the stream but to make it descend on each side of the ignited wick, producing a form resembling that of the letter W ; and at the same time the top of the burning wick is greatly brightened by the stream of air that is impelled downwards upon it. In these experiments the magnetic poles were only '25 of an inch apart. Faraday has even succeeded in affecting the smoke from a small spark by a good ordinary magnet. (1182) In searching into the cause of these phenomena Faraday began by examining the effect of heat alone in conducing to the dia- magnetic condition of flame. For the burning taper he substituted a helix of fine platina wire, which could be placed in any position and ignited by a voltaic battery. When the helix was placed directly under the axial line, the hot air rose up between the poles freely, being rendered evident above by a thermometer, or by burning the finger, or even by scorching paper ; but as soon as the magnet was rendered active, the hot air divided into a double stream and was found ascending on the two sides of the axial line ; but a descending current was formed between the poles, flowing downwards DIAMAGNETIC CONDITION OF FLAMES AND GASES. 845 towards the helix and the hot air, which rose and passed off sideways from it. (1183) This experiment showed that hot air is more diamagnetic than cold air, and by the following beautiful experiment Faraday proved that air artificially cooled is with relation to air at the natural temperature actually magnetic. A stream of air was conducted through a tube surrounded by a freezing mixture, and then directed downwards a little on one side of the axial line into a tube contain- ing a delicate air thermometer, which of course immediately fell ; on rendering the magnet active, the thermometer rose, but on bringing the tube under the axial line it again fell, showing that the cold current of air had been drawn inwards or attracted towards the axial line ; i.e., had been rendered magnetic in relation to air at the ordinary temperature. (1184) This extraordinary effect of heat in increasing the dia- magnetic condition of bodies seems to be confined to gases and vapours, Faraday could not detect any distinct increase of the force by heating cylinders of copper and silver to redness. (1185) Common air being thus shown to have a decided magnetic relation, Faraday proceeded to examine other gases and vapours for which he employed the following ingenious apparatus : A "Woulf's bottle was provided, having three apertures a, b, c; into a, a wide tube was fixed descending within the bottle to the bottom, being open above and below ; by this water could be poured into the bottle, and employed to displace the gas previously within it. Aperture 5 was closed with a stopper ; aperture c had an external tube with a stop-cock fixed in it to conduct the gas to any place desired. To expel the gas and send it forward, a cistern of water was placed above the bottle, and its cock so plugged by a splinter of wood, that when fully open, it delivered only 12 cubic inches of fluid in a minute. This stream of water being directed into aperture d, and the cock of tube c open, 12 cubic inches of any gas within the "Woulf s bottle were delivered in a minute of time, and this proportion was found not sufficiently great to deluge the magnetic field. In order to deliver the gas at the magnetic poles, a piece of tube bent at one end nearly to a right angle was held by a clamp in a moveable position, so that its vertical part could be placed anywhere below the axial line ; the aperture of this tube was about th of an inch in diameter. In the horizontal part, near the angle, was placed a piece of bibulous paper, moistened when necessary with strong solution of muriatic acid. If the gas to be employed as a stream was heavier than the surrounding medium, then the glass tube was so bent as to deliver its stream downwards, and over the axial line. 3i2 846 DIAMAGNETISM. (1186) The next point was to detect and trace the course of these streams. This was effected by arranging upon little stands a set of tubes of thin glass, open at both ends, and about the size and length of a finger. These tubes could be readily adjusted at pleasure, either over or under the magnetic poles. When they were over the poles, three tubes were generally used, one over the axial line, and one at each side. When they were under the poles the low end was turned up a little for the purpose of facilitating observation. Now, the gas issuing from the delivering tube had diffused through it a little invisible muriatic acid vapour, and to make it evident into which of the "catch" tubes it passed, a piece of bibulous paper moistened with ammonia was suspended in each, and it was evident at once by the visible fume formed at the top of one of the tubes, whether the gas delivered below passed up the one or the other tube, and which; and yet the gas was perfectly clear and transparent as it passed to the place of magnetic action. To pre- serve the air in a tranquil state, a little sheltering apparatus of mica was built up round the poles. (1187) To try the working of the apparatus, air was sent in ; the stream being directed by the axial line, the fume appeared in the catch tube above, whether the magnet was active or not, just as it should have done. Nitrogen When sent from below upwards, it passed by the axial line into the catch tube above ; but when the magnet was made active a fume appeared in the side tubes as well. The jet was now arranged a little on one side of the axial line, so that without the magnetic action it still went into the middle tube ; on making the magnet active a great portion of it was sent to the side catch tube, thus showing that in relation to atmospheric air nitrogen is at the same temperature diamagnetic. Oxygen When sent from above downwards through air between the poles, it descended vertically, whether the magnet was excited or not ; when it was made to descend on one side of the axial line it was deflected and drawn towards the axial line, thus showing either that in common air oxygen is magnetic, or that it is less diamagnetic than a mixture of oxygen and nitrogen. Hydrogen In spite of its lightness it was deflected, and sent equatorially, proving it to be strongly diamagnetic. Carbonic Acid In air it was diamagnetic; its course was traced by a glass containing lime water placed beneath the lower end of the catch tube. The stream was sent downwards, a little on one side of the axial line, the tube and lime water being placed further out, so DIAMAGNETIC CONDITION OF FLAMES AND GASES. 847 that the gas should fall clear of it when the magnetic power was not on. On rendering the magnet active, the lime water became turbid. This made a beautiful experiment. Carbonic oxide More diamagnetic than carbonic acid. Nitrous oxide Moderately diamagnetic. Nitric oxide Yery slightly diamagnetic. Olefiant gas, coal gas, sulphurous acid gas, muriatic acid gas, hydriodic acid qas,fluosilicon, ammonia, chlorine, iodine, bromine, and cyanogen, were all more or less diamagnetic in air. Of all the vapours and gases tried, oxygen seems to be that which has the least diamagnetic force, and this is the cause of the compara- tively low diamagnetic condition of atmospheric air. (1188) Faraday then surrounded the poles of the magnet with a mica chamber, which could be filled with carbonic acid gas; the former arrangements in respect to the magnetic field, the delivery tube, catch tubes, &c., being preserved, he found air and oxygen passed to the magnetic axis, being, therefore, less diamagnetic than carbonic acid gas. On the other hand : Nitrogen, hydrogen, coal gas, olefiant gas, muriatic acid gas, ammonia, and nitrous oxide passed equatorially, and were all, in a greater or less degree, diamagnetic in relation to carbonic acid. (1189) By covering the poles of the magnet with a French glass shade, similar experiments were made with hydrogen and coal gas with the following results : In coal gas Air passed feebly to the axial line ; oxygen had the appearance of being strongly magnetic, presenting a striking pheno- menon, and nitrogen was clearly diamagnetic. In Hydrogen Air passed feebly to the axial line, nitrogen was strikingly diamagnetic, and oxygen as strikingly magnetic. Nitrous oxide, ammonia, carbonic acid, carbonic oxide, and olefiant gas were diamagnetic. The most striking circumstances in these experiments are the strongly marked diamagnetic character of nitrogen, and the feeble diamagnetic condition of oxygen, standing as it does, in l/his respect, far apart from all other gaseous substances. (1190) Faraday then examined the influence of heat : Sot oxygen was powerfully diamagnetic in an atmosphere of cold oxygen. Hot carbonic acid was diamagnetic to cold carbonic acid. The relation of hot and cold hydrogen could not be ascertained, as Faraday could not succeed in heating the platinum helix which he employed in these experiments by the voltaic battery in an atmosphere of hydrogen, in consequence, as he supposes, of the rapidity with which 848 DIAHAGKETISM. that gas is heated and cooled in comparison with other gases. In short, however, all the experiments went to prove that all gases are more diamagnetic when hot than when cold. (1191) Non-Expansion of Gaseous Bodies by Magnetic Force. Taking common air as a standard, it appears from the preceding experiments that nitrogen and many other gases are strongly diamag- netic in relation to it, whilst oxygen has the appearance of a magnetic body. It appears also that the diamagnetic character of flame is due chiefly to the heated state of the gaseous portions. It occurred to Faraday that if the particles of a diamagnetic gas tended to go from strong to weak places of action, in consequence of the direct and immediate effect of the magnetic power on them, such a gas should tend to become enlarged or expanded in the mag- netic field. On the other hand, if a gas were magnetic, then the force cast upon the particles by the direct and immediate action of the magnetic power upon them, would urge them towards the axis of the magnetic field, and so coinciding with, and being superadded to the pressure of the atmosphere, would tend to cause contraction or diminution of bulk. (1192) A change in the bulk of air in the magnetic field had been observed by Pliicker ; Faraday was, therefore, induced to submit the matter to a minute examination; the result of which was that in none of the gases tried, whether considered as magnetic or diamag- netic bodies, could any alteration in volume be effected by the mag- netic force, whether in fields of equal power, or in places where the power is rapidly diminishing; and this result he considers very important in relation to the true nature of magnetic force, either as existing in, or acting upon the particles of bodies. Faraday made similar experiments with liquids, but with very delicate apparatus and powerful electro-magnets, he was unable to observe any change of volume, neither could the least change be observed in the volume of iron or bismuth, however powerful the magnetic force to which they were submitted, and he could obtain no evidence that the mag- net exerts any direct power of attraction or repulsion on the particles of gases, or that they move in the magnetic field as they are known to do by any such immediate attraction or repulsion. (1193) Differential Magnetic Action of Gases. The cause of the diamagnetic change of place is believed by Faraday to be a differen- tial result depending on the differences of the two portions or masses of matter occupying the magnetic field ; and in the case of gases, the phenomena may be produced and examined in a very useful manner by the employment of soap bubbles. In Faraday's experiments, these bubbles were about J an inch in diameter, and by employing MAGNETIC CHABACTEBS OF OXYGEN, NITBOGEN, AND GASES. 849 recently-prepared cold soap water, and a bent glass tube connected with a bladder and stop-cock, he was able with a little care to blow them of a nearly uniform size and thickness. The gases were exa- mined by placing the bubbles in the angle of a double pole of iron arranged between the poles of the large electro-magnet. "When the bubble was of air, and a power of 20 pairs Fig. 471. of plates employed, it was deflected slightly outwards from the axial line, the deflection being due to the water of the bubble. This deflection served as a correction in experiments with other gases. Nitrogen was driven equatorially with great force, forming a strik- ing experiment when it is considered that this gas constitutes *ths of the atmosphere. Oxygen was pulled inwards towards the axial line with much force, exactly as if it were highly magnetic. Nitrous oxide and olejiant gas were both driven equatorially. The other experiments with gases were quite in accordance with those already described, and all tended to prove that the effect is a differential result of the masses of matter present in the magnetic field. (1194) Magnetic Characters of Oxygen, Nitrogen, and Space. In order to examine the differential action of two gases, tubes the size and shape of fig. 472, of thin flint glass, were filled with the gases and having been sealed up hermetically, they were fastened by means Fig, 472. of sealing wax to loops of thread, by which they were suspended perpendicularly from a torsion balance, so that the middle of each should, when in place, be on a level with the magnetic axis. Now, when so suspended, if the gases are both alike in magnetic or diamagnetic power, their position, will not be altered en the superven- tion of the magnetic force ; but if one gas is more diamagnetic than another, the most diamagnetic will move outwards equatorially, pulling the least diamagnetic inwards, till the two are in such new positions that the forces acting on them are equipoised, and they will assume a position of stable equilibrium. Their relative diamagnetic inten- sities can then be measured by the force required to restore them to their equidistant position from the magnetic axis. (1195) The tubes being filled respectively with oxygen and nitro- 850 DIAMAGNETISM. gen, a most striking effect was observed the moment the magnetic force was thrown into action. The oxygen tube was carried inwards towards the axis, and the nitrogen tube driven outwards on the con- trary side. When the tubes had taken up their new position, the oxygen tube was about ^th of an inch from the iron of the core, and the nitrogen tube fths distant, and ten revolutions of the torsion axis altered only in a slight degree these relative distances. (1196) The effect of rarefaction was 'then tried ; bulbs the size and shape of Fig. 473, were filled with oxygen, and then reduced under Fig. 473. the air pump, so that one tube contained gas at the pressure of one atmosphere ; a second, gas at half an atmosphere, or 15 inches of mercury ; a third, gas at the pressure of 10 inches of mercury ; and a fourth, after being filled with oxygen, was reduced to as good a vacuum as an excellent air-pump could effect. On trying these tubes one against the other, the expanded por- tion was always driven away, the denser gas going inwards ; and when the tube containing gas at one atmosphere pressure was opposed to the vacuum, the former passed axially with such power that it was evidently only the diamagnetic power of the glass tube that prevented it from passing against the iron core, and occupying the centre of the magnetic field. Oxygen, then, .is a very magnetic substance, its magnetic force being in proportion to its density. With nitrogen the differences produced by rarefaction could not be detected, there being no perceptible difference between the tube of gas at one atmosphere pressure, and that reduced as nearly as possible to .a vacuum ; both tubes remained equidistant from the magnetic axis. Nitrogen, then, is neither magnetic nor diamagnetic : it is equivalent to a vacuum. Magnetically considered, it is < like space itself, which may be considered zero. (1197) The lines of magnetic force can traverse pure space just as gravitating force does, and as static electric forces^do ; space, therefore, has a magnetic relation of its own, which will probably, hereafter, be 'found to be of the utmost importance in natural phenomena. The true zero is represented by such bodies as when added to space pro- duce no magnetic or diamagnetic effect. The -term magnetic, Faraday MAGNETIC CONDUCTION. 851 proposes, should be a general one, and include all the phenomena and effects produced by the power, and he proposes that bodies mag- netic in the sense of iron should be called paramagnetic bodies (as placing themselves parallel to the lines of magnetic force), so that the division would stand thus C Paramagnetic. 1 Diamaguetic. (1198) Amongst all the gases hitherto examined, there is nothing that compares with oxygen ; its magnetic power is so great that it makes atmospheric air a magnetic medium of no small power, which must be taken into consideration when experimenting on the diamagnetic condition of other gases. The discovery of the high magnetic condition of oxygen and its variations with variations of temperature and density, suggests an explanation of the cause of the variations of the magnetic force which are now so carefully watched on different parts of the surface of the globe, of the daily and annual variation of the needle, and of the relation between the aurora borealis and the Magnetism of the earth. (1199) Magnetic Conducting Power Atmospheric Magnetism Magnetic Conduction. The remarkable results respecting oxygen. and nitrogen just described, led Faraday to the idea that if bodies possess different degrees of conducting power for Magnetism, that difference may account for all the phenomena, and its further consi- deration may assist in developing the nature of magnetic force. By the term conducting power, he means to convey a general expression of the capability which bodies may possess of effecting the trans- mission of magnetic force, and not to imply anything as to how the process of conduction is carried on ; so that if a medium of a certain degree of conducting power occupy the magnetic field, that body will be displaced if another substance possessed of better conducting power be introduced into the field the result being a differential effect of their difference in conducting power. (1200) In pure space the lines of magnetic force are ^-T-T-^ straight and parallel ; be introduced, the lines are no longer straight, butthere will be a concentration of them on the conduct- ing body, so that the space occupied by the conducting body trans- 852 DIAMAGNETISM. mits more magnetic force than before (Fig. 471 A). If a diamagnetic body be introduced, there will be a divergence of the lines, and the space occupied by the diamagnetic body will transmit less force than before. (Fig. 471 B). The two bodies affect, first, the direction of the lines of force, not only within the space occupied by themselves, but also in the neigh- bouring space ; secondly, the amount of force in any particular part of the space within or near them, and the influence of this disturb- ance is easily made manifest experimentally. A small sphere of iron, exactly equidistant from the iron poles, is in a position of unstable equilibrium, and at such time a great concentration of force takes place through it, and at the iron faces opposite to it, and through the intervening axial spaces. If the iron be a spheroid, its greatest diameter points axially, and the circumstances are more favourable for the concentration of force in the axial line passing through the iron than before. The converse is the case with diamagnetic bodies, which find their place of stable equilibrium in the spot where the posi- tion of paramagnetic bodies is unstable. Their relative and reverse positions in a field of equal magnetic force, may be retained in the mind by conceiving that if a liquid sphere of a paramagnetic con- ductor were in the place of action, and then the magnetic force deve- loped, it would change in form and be prolonged axially, becoming an oblong spheroid, w r hereas, if such a sphere of diamagnetic matter were placed there, it would be extended in an equatorial direction, and become an oblate spheroid. (1201) The mutual action of two portions of paramagnetic matter in a field of equal magnetic force is that of repulsion, and it is pre- cisely the same with two portions of diamagnetic matter. Faraday found that when the lines of power passing across the magnetic field were strengthened by placing in the field a saturated solution of protosulphate of iron, a small moveable cylinder of phosphorus sus- pended in the middle of the magnetic field was distinctly repelled by another piece held close to it. Also, when a piece of phosphorus was suspended in water in a field of equal magnetic force, it was repelled equatorially by another piece of phosphorus, but attracted by a tube filled with a saturated solution of protosulphate of iron. Thus, then, paramagnetic and diamagnetic bodies attract each other equatorially in a mean medium, but each repels bodies of its own kind. (1202) Conduction Polarity. Paramagnetic polarity consists in the convergence of the lines of magnetic force on to two opposed parts of the body, which are to each other in the direction of the magnetic axis. The difference of character of the new poles is at CONDUCTION POLAEITT. 853 these parts very great. Faraday thinks it not improbable that polar attraction or repulsion may exist in oxygen, and in all paramagnetic bodies consistent with the attraction and repulsion of magnets having correspondent poles. Diamagnetic Conduction Polarity is a different matter. It consists in a divergence of the lines of power on to, or a convergence from, the parts which being opposite are in the direction of the magnetic axis. This polarity is to be carefully distinguished from that which depends upon the reversion of the direction of the power ; the latter Faraday considers as a property of the particles of magnetic matter, the former as dependent rather upon the action of the mass ; the latter is an absolute inversion of the direction of the power, the former only a divergence or deflection of it. (1203) Though Faraday speaks of iron as illustrating the action of paramagnetic conductors, he draws an important distinction between the polarity of a magnet and the polarity due to mere con- duction. A permanent magnet has a polarity in itself which is pos- sessed also by its particles, and this polarity is essentially dependent upon the power which the magnet inherently possesses. The polarity of a conductor is simply a consequence of the condensation or expan- sion of the lines of force, and is not due to a determinate arrange- ment of the cause and source of magnetic action. Speaking figura- tively, the difference may be compared to that of a voltaic battery, and the conducting wires or substances which connect its extremities. The stream of force passes through both, but it is the battery which originates it, and also determines its direction ; the wire is only a better or worse conductor, however, by variation of form or quality, it may diffuse, condense, or vary the stream of power. (1204) Applying the idea of conduction to magne-crystallic bodies, Faraday thinks that the special results may be understood by sup- posing that a magne-crystallic body conducts better in the direction of the magne-crystallic axis than in any other direction, and he con- cluded, that if a symmetrical crystal of bismuth were carefully exa- mined in different directions, it would be found to be less diamagnetic when its magne-crystallic axis is parallel to the axis of magnetic force than when it is perpendicular to it. By means of the differential torsion balance, he was able to make the trial, and found the results as he anticipated. With calcareous spar he was not able, with his present balance, to establish any difference ; but concludes that it will prove most diamagnetic when its optic axis, being in a horizontal plane, is placed parallel to the magnetic axis. (1205) The place and position of iron in a field of equal force, is the result of the extraordinary power which it has of transmitting 854 DIAM1GNETISM. the magnetic force across the space which it occupies, and Faraday accepts the converse phenomena as to the place and position of a dia- magnetic body as a proof that it has less power of transmitting the magnetic force than the space it occupies. (1206) Atmospheric Magnetism. The earth may be assumed to be a mighty compound magnet, the lines of force issuing from the northern and southern parts with different corresponding degrees of inclination, and inclining to, and coalescing with each other over the equatorial parts. The atmosphere consists of 4 volumes of nitrogen and 1 volume of oxygen, or by weight of 3J parts of the former and 1 part of the latter. These substances are nearly uniformly mixed throughout, so that as regards their manner of investing the earth, they act magnetically as a single medium ; nor does there seem to be any tendency in the terrestrial magnetic forces to cause their separation, though they differ very strikingly in their constitution as regards this power. As regards the magnetic force nitrogen is a very indifferent body, being neither diamagnetic nor paramagnetic, whether in a dense state or in a rare state, or whether hot or cold. As regards the magnetic force oxygen is highly paramagnetic, increasing in force as its temperature is lowered, and diminishing as its temperature is raised, and these properties it carries into the atmosphere, which becomes therefore a highly magnetic medium, varying however in intensity by alterations in its temperature and density. (1207) Faraday assumes as a type case the existence of two globes of air distinct from the surrounding atmosphere by a difference of temperature or a difference of density ; that one of these globes is colder or denser than the contiguous parts, and that it is in a portion of space which, without it, would present a field of equal magnetic force. The air of such a globe will facilitate the transmission of the magnetic force through the space which it occupies, de- termining more lines of force through it than elsewhere. The disposition of these lines, in respect to the line of the dip of the place will be something like what is represented in Fig. 475, and Fig. 475. ATMOSPHERIC MAGNETISM. 855 consequently the globe will be polarized as a conductor of the para- magnetic class. Hence the intensity of the magnetic force and its direction will vary not only within but without the globe, and these will vary in opposite directions, in different places, under the influence of laws which are perfectly regular and well known. (1208) Now a magnet used as an intensity test will indicate a less intensity at P, because the conducting power of the globe has been increased in consequence of its coldness and density. If on the other hand the globe were warmer or more rarefied than the surrounding space, it would convey less power as being a worse con- ductor, and the magnet would set with greater force, and give an indication of greater intensity both within, and equatorially without the globe. But if changes in the medium can effect the magnet, a magnet ought to make a greater number of vibrations in an atmosphere of nitrogen than in one of oxygen, because these two gases differ naturally in their magnetic relations. (1209) If another typical globe of air be assumed having a higher temperature than the surrounding air, its condition will be that of a diamagnetic conductor, and it will have power Fig. 476. to affect both the intensity and direction of the lines of force in conformity with the action of the former globe, but in the con- trary order, although the conditions of the foregoing typical globes can never actually occur in nature, still the comparison holds in principle, and we may expect that as the sun leaves us on the west some effect correspon- dent to that of the approach of a body of cold air from the east will be produced, which will increase and then diminish, and be followed by another series of effects as the sun rises again and brings warm air with him. (1210) Again, there is more air by weight over a given portion of the surface of the earth at latitudes from 24 to 34, than there is either at higher latitudes or at the equator, and that should cause a difference from the disposition of the lines of force which would exist if there were equality in that respect. The temperature also of the air is greater at the equatorial parts than in latitudes N. and S. of it ; and as an elevation of temperature diminishes the conduct- ing power for Magnetism, so the proportion of force passing through these parts ought to be less, and that passing through the colder parts greater, than if the temperature of the air were at the same mean degree over the whole surface of the globe. 856 DIAMAGNETISM. (1211) Annual and Daily Variation. The effect of the approach and retreat of the suii in his daily course is to produce such variations of changes in the temperature and expansion of the atmosphere, as to influence the lines of force emanating from the earth both in their direction and intensity; the manner in which this influence may be developed, Faraday, by means of figures and descriptions, states, in relation to the annual and daily variation, and the irregular per- turbations of the magnetic force, which he thinks are consequences of it. He then applies the result of the magnetic observations at Hobarton* as a test of the probable truth of the hypothesis, and considers that it affords strong confirmation. The upper or JS". end of the needle there goes W. till about 21 o'clock, whilst the dip increases ; the dip still increasing till noon, the upper end returns rapidly E. as the sun passes by until 2 o'clock the dip then de- creasing, after which the needle goes W. again following the sun. On examining the results at Toronto, corresponding effects were found to occur, when the upper or S. end of the needle was con- sidered, and therefore in accordance with the hypothesis. Faraday also discusses the observations made at Greenwich, Washington, Lake Athabusca, Fort Simpson, and St. Peters- burg, and considers them as adding further confirmation. By the aid of these observations he re-states his principles more minutely, endeavouring to indicate what difference changes in the inclination, declination, place of sun, land, sea, &c. will produce. (1212) Though the sun is the cause of those changes in the atmo- sphere which affect the lines of force on the earth, he is not assumed as the centre of action as regards those lines ; that, is considered to exist somewhere in the atmosphere. It appears to be in the upper regions and not on the surface of the earth, because it increases the dip of places N. and S. of the tropics, which have a certain amount of inclination, as at Hobartou and Toronto, both in summer and winter, but it diminishes the dip at places which are within the tropics, and with little inclination, as at St. Helena. By other kinds of observations it appears to be in advance of the sun. All the phenomena indicate that the sun does not act directly on the needles at different places, but mediately through its effect on the atmosphere. (1213) The probable cause of numerous irregular variations, such as those that are shown in the photographic processes of record at Greenwich and Toronto, are then considered, and Faraday thinks that changes in the lines of magnetic force may be produced by the * "Magnetical and Meteorological Observations. Hobarton, vol. i. 1850." Sabine, Toronto. MAGNETIC POWER OF OXYGEN. 857 varying pressure of the atmosphere, by the occurrence of winds and large currents of air, of rain, and snow ; by the passage of those masses of warm and cold air which the meteorologist recognizes in the atmosphere, by the aurora borealis, &c. He thinks it very possible that masses of air at different temperatures may be moved by the magnetic force of the earth, according to the principles of differential action made manifest in the experiments on warm and cold oxygen, in which case, material as well as potential " magnetic storms " may exist. (1214) Faraday, at the conclusion of this paper (26th Series), again alludes to the wonderful magnetic power of oxygen. It is in the air what iron is in the earth, and its striking contrast with the nitrogen which dilutes it in the atmosphere, impresses the mind, and by the difference, recalls that which also exists between them in relation to static Electricity and the lightning flash. He expresses his convic- tion, that there is much to do with oxygen relative to atmospheric Magnetism ; and he starts the question What is the final purpose in nature of its magnetic condition in the atmosphere, liable as it is to annual and diurnal variations, and to entire loss by entering into combination ? That it has an important purpose to serve is evident, for nothing in nature is superfluous. MAGNETIC HYPOTHESES. CHAPTER XXII. MAGNETIC HYPOTHESES. Notions of the Ancients Theories of Descartes and OEpinus Ampere's electro- dynamic theory Faraday's researches Lines of magnetic force The moving wire as an examiner of magnetic forces Magnetic "polarity" Physical charac- ter of the lines of magnetic force Places of no magnetic action Faraday's view of the condition of a magnet. (1215) THE notions entertained by the ancients respecting the imme- diate source of the power of the magnet, were of the wildest descrip- tion. Thus Thales and Anaxagoras conceived that the magnet was possessed of an immaterial spirit, in obedience to which iron moved and was attracted ; Cornelius Gemma said, that invisible rays pass between the iron and the magnet ; others, that there exists a sympathy between them ; Epicurus supposed that the atoms of the iron were hooked on to those of the magnet ; Plutarch thought that there was an emanation proceeding from the magnet. Cardan said, that iron is attracted because it is cold, and Costeo de Lodi regarded iron as the natural food of the magnet. Then came Descartes, whose theory of vortices was for a long time universally adopted. According to his theory, a rush of subtle matter passes rapidly through the earth from the equator towards each pole. This matter being porous, is not arrested in its passage by ordinary matter, but magnetic sub- stances, in consequence of a peculiarity in their molecular structures oppose a resistance and are hence affected. Moreover, the vortex moves with the greatest facility in one particular direction ; one of its ends being always turned towards the JST. The pores of iron are regarded as valves, which open readily in one direction, but oppose the entrance of any substance in the opposite direction. (1216) The theory of Descartes was adopted by Euler, who in his Letters (translated 1802) has thus set it forth : " Non-magnetic bodies are freely pervaded by the magnetic matter in all directions ; loadstones are pervaded by it in one direction only ; one of the poles being adapted to its admission, the other to its escape. But iron and steel, when rendered magnetic, fulfil this last condition ; when they are not, it may be affirmed that they do not grant a free DESCARTES, EULER, OEPLNUS. 859 transmission to the magnetic matter in any direction." (Vol. II. p. 242.) " You can easily imagine a series of fluids, one always more subtile than another, and which are perfectly blended together. Nature furnishes instances of this. Water, we know, contains in its pores particles of air which are frequently seen discharging them- selves in the form of small bubbles ; air, again, it is equally certain, contains in its pores, a fluid incomparably more subtile, viz., ether, and which, on many occasions, is separated from it, as in Electricity ; and now we see a still further progression, and that ether contains a matter much more subtile than itself the magnetic matter, which may, perhaps, contain in its turn others still more subtile ; at least, this is not impossible. The loadstone, besides a great many pores filled with ether, like all other bodies, contains some still much more narrow, into which the magnetic matter alone can find admission. These pores are disposed in such a manner as to have a communica- tion with each other, and constitute tubes or canals through which the magnetic matter passes from the one extremity to the other. Finally, this matter can be transmitted through these tubes only in one direction, without the possibility of returning in the opposite direc- tion." (P. 244.) .... " As we see nothing that impels the iron towards the loadstone, we say, that the latter attracts it. It cannot be doubted, however, that there is a very subtile, though invisible matter, which produces this effect, by actually impelling the iron towards the loadstone." (Vol. I. p. 214.) " The arrangement assumed by the steel filings leaves no room to, doubt that it is a subtile, invisible matter which runs through the particles of the steel, and disposes them in the direction which we here observe. It is equally clear that this subtile matter pervades the loadstone itself, entering at one of the poles and going out at the other, so as to form by its continual motion round the loadstone a vortex, which re-conducts the subtile matter from one pole to the other, and this motion is without doubt extremely rapid. The nature of the loadstone consists then in a continual vortex which distinguishes it from all other bodies ; and the earth itself, in quality of loadstone, must be surrounded with a similar vortex, acting everywhere on magnetic needles, and making continual efforts to dispose them according to its own direction." (Vol. II. p. 240.) (1216) (Epinus applied the electrical theory of Franklin with great ingenuity to the explanation of the phenomena of Magnetism. The four propositions which his theory includes have been already stated (758). The laws of attraction and repulsion find a satis- factory explanation on this hypothesis, but it fails when applied to the consequences which follow on the division of a magnetic bar ; 3 K 860 MAGNETIC HYPOTHESES. each piece should have a different and distinct polarity, whereas it is well known that each fragment is a bi-polar magnet, and that this is the case, however many may be the number of pieces into which the bar is divided. (Epinus endeavoured to overcome this difficulty by supposing that during the act of fracture the balance of magnetic- force was disturbed, and that a portion of fluid escaped from the overcharged pole, while another portion entered into that which was undercharged. (1217) The theory of two magnetic fluids was first propounded by "Wilke and Brugmann, and afterwards enforced by Coulomb. According to this hypothesis, a magnet is considered as composed of minute invisible particles or filaments of iron, each of which has individually the properties of a separate magnet. It is assumed that there are two distinct fluids the austral and boreal ; and under the influence of either in a free state, the bar of iron or other metal will point to the N. or S. poles of the earth, according to circumstances. It is within these small particles or metallic elements that the dis- placement or separation of the two attractive powers takes place ; and the particles may be the ultimate atoms of the iron. A magnetic bar may, therefore, be represented (as in Pig. 477), as Fig. 477. composed of minute por- tiops, the right-hand ex~ tremities of each of which , possess one species of Magnetism, and the left-hand extremities the other. The shaded ends being supposed to possess boreal, and the light ends austral Magnetism, then the ends of the bar itself, of which these sides of the elementary magnets form the faces, possess respectively boreal and austral Magnetism, and are the boreal and austral poles of the magnet. In ordinary iron, these fluids exist in a combined state, and are, therefore, perfectly latent ; the metal appearing to be destitute of Magnetism. They exist an certain proportions united to each molecule or atom of the metal, and from which they can never be dis- united, the only change which they are capable of undergoing being their decomposition into the separate fluids, one of which in a per- manent magnet is always collected on one, and the other on the opposite side of each molecule. This theory occupied the attention of the great mathematician Poisson, who by applying to it the refinements of modern analysis, succeeded in discovering formulaB which represent numerically all the principal phenomena of the science, even in their minutest details, and which furnish a ready and consistent explanation of the physical mode by which they are produced. {Hoget.} AMPERE'S ELECTRO-DYNAMIC THEORY. 861 (1218) Ampere's Electro-dynamic Theory. Keasoning from the phenomena of the mutual action of magnets and electric currents, Ampere was led to deny the existence of any magnetic fluid as dis- tinct from Electricity, and to consider all magnetic phenomena as the visible effects of invisible electric currents perpetually circulating around the particles of which the magnetic bodies are composed. Each particle or magnetic element is, according to this theory, regarded as constituting a voltaic circuit, and a magnet is composed of an assemblage of parallel filaments, each of which is made up of a series of particles, round which electric currents are circulating in the same direction with reference to the axis of the filament, and moving in planes perpendicular to that axis. In a bar of un- magnetized iron the Electricity is supposed to be in a latent or quiescent state ; that extremity of the magnetic filament in which when uppermost, the positive current is moving in the same direction as the hands of a watch, has the properties of a S. magnetic pole, and vice versa. If the filament be placed horizontally, its N. pole pointing to the N". and its S. pole towards the S., the electric currents circulate on the upper side from ~W. to E., and downwards on the eastern side ; on the under side from E. to "W., and upwards on the western side. Fig. 478. The mutual repulsion of two magnetic poles of the same name, and the attraction of two dissimilar poles, are simple consequences of this hypothesis. It has been shown (944) that there is a repulsive action set up between two wires along which electrical currents are moving in opposite directions, but that when the currents move in the same direction along each wire attraction results. Now it is easy to see (Fig. 479) that when two similar magnetic poles are brought near each other, the hypothetical electric currents are moving in contrary directions at the sides contiguous to each other, and that when two dis- similar poles are approximated (Pig. 480) the currents are flowing in the same direction ; hence repulsion Fig. 479. 3K2 862 MAGNETIC HYPOTHESES. in the former case, and attraction in the latter. The direction in which the currents are supposed to now in every possible position of the magnet, and the mutual relations of these currents, are well realized to the mind by drawing a series of arrow heads round a pair of wooden cylinders, and placing them in various positions relatively to each other. (1219) It follows also as a consequence of this mutual action of Fig. 481. currents, that, viewing a magnet as an assemblage of filaments round each of which electrical currents are circu- lating, the resultant action of the mag- net can only be exerted externally ; for let Fig. 481 represent the section of a cylindrical magnetic bar, and the small included circles some of its filamentary elements, the currents moving round the contiguous sides of any two of these circles, being opposed in direction, neutralize each other, while the currents that pass near the circum- ference are not so compensated by others, and their action is, there- fore, fully exerted on external bodies. Again, the tendency of a magnet and a conducting wire to place themselves at right angles to one another (931 et seq.) is referred by Ampere's theory to the transverse movements of the electric currents in the magnet which act upon the current in the conductor, and are also acted upon by Fig. 482. that current. Thus, let S N represent a magnet, and P N, a wire convey- ing a current of Elec- tricity ; the arrow heads show the direction in which the currents are moving round the mag- net, viz., in planes per- pendicular to its axis ; the wire P N, tends to range itself, therefore, transversely to the axis of the bar, in order that the current moving along it should be parallel to that of the cur- rent in the nearest part of the magnet. Further, the theory happily explains the induction of an opposite polarity in the adjacent end of a piece of soft iron, by a magnetic pole. Thus, let A B (Fig. 483), be the magnet, and C D, the bar of iron, the former has a tendency to AMPERE'S ELECTEO-DYNAMTC THEOKY. 863 Fig. 483. B c excite in the latter a current of Electricity, circulating in the same direction as the currents moving round its own filaments ; but it is evident, that if the current at the end of B revolves, as seen by a spectator looking at that end, from right to left, the current induced at the end of the iron bar C, revolving in the same direction in space, will appear to the spectator, looking at that end, to move from left to right ; and, as the polarity depends upon the direction of the current with respect to the axis at the extremity, the polarity of B will be the reverse of that of C, and the same as that of D, but the polarities C and A, will be the same. Precisely the same conse- quences must follow upon the fracture of a magnetic bar ; each piece becomes a perfect magnet, the polarities of the fractured ends being opposed to each other. (1220) If we bring a magnetic pole opposite the centre of a soft iron rod, the two ends of the latter will acquire a temporary polarity of the same kind with that of the inducing pole ; a polarity of the opposite nature being induced in the centre of the bar (803). This phenomenon is easily explained by Ampere's theory. Thus Fig. 484. suppose the N. pole of the magnet A to be laid on the centre of the bar B C, and at right angles to it, the currents induced in the latter, on the side A C, will be in the direction of the arrow heads, while those induced in the bar, on the side A B, will move the con- trary direction ; but if we examine the ends of our test cylinders (1218), we shall find, that under these circumstances, the arrow heads are pointing in the same direction at each end ; B and C must, therefore, be both N. poles. The parts of B C, however, immediately 864 MAGNETIC HYPOTHESES. under A, will have currents, in opposite directions, induced in them, the point of the bar, therefore, immediately underneath the inducing bar will be a S. pole. (1221) This beautiful theory of Ampere, which is sustained by the highest mathematical investigation, furnishes a satisfactory explana- tion of all the mutual actions of magnets and electric currents, and of magnetic and electro-magnetic phenomena in general ; as applied to these, "it satisfies every condition that is required of a true theory, uniting the character of simplicity in principle, and compre- hensiveness in its application, and possessing this important advan- tage over the theory of tangential forces, viz., that it presents greater facility of mathematical investigation, and for the comparison of the analytical formula? thence obtained, with the results of experiment." (Roget.) The theory, however, as laid down by Ampere, wholly fails to account for diamagnetic actions. To render it at all consistent with these phenomena, it has been assumed, that magnetic and electric force might, in diamagnetic matter, induce currents of Elec- tricity in the reverse direction to those in magnetic matter, or else might induce currents where before there were none ; whereas, in magnetic cases, it was supposed that they only constrained particle currents to assume a particular direction, which before were in all directions. Others, amongst whom is Weber, have made an addition to the hypothetical views of Ampere, viz., that there is Elec- tricity amongst the particles of matter which is not thrown into the form of a current until the magnetic induction comes upon it, but which then assumes the character of current, having a direction the contrary to that of the currents which Ampere supposed to be always circulating round magnetic matter, and so those other matters are rendered diamagnetic. A striking experimental distinction between a magnet and a helix (947) has been pointed out by Faraday (Ex. Res. 3273), viz., " Whereas, an unchangeable magnet can never raise up a piece of soft iron to a state more than equal to its own, as measured by the moving wire (1225), a helix carrying a current can develope in an iron core magnetic lines of force of a hundred or more times as much power as that possessed by itself when measured by the same means." (1222) De la Rive (Notices of the Meetings of the Royal Institution, Yol I. p. 458), distinguishes magnetic action into four kinds or modes, namely, the ordinary, the diamagnetic, the induction of cur- rents, and the rotation of a ray ; and he points out that any accept- able hypothesis ought to account for the four modes of action, and, it may be added, ought to agree with, if not account for, the pheno- DE LA HIVE'S HYPOTHESIS. 865 mena of electro-chemical action also. He conceives that, as regards these modes of action, this hypothetical result may be obtained, and both Ampere's and Weber's views also retained, in the following manner. All the atoms of matter are supposed to be endowed with electrical currents of a like kind, which move about them for ever, without diminution of their force or velocity, being essentially a part of their nature. The direction of these currents for each atom is through one determinate diameter, which may, therefore, be consi- dered as the axis. "When they emerge from the body of the atom they divide in all directions, and running over every part of the surface, converge towards the opposite end of the axis diameter, and, therefore, re-enter the atom to run ever through the same course. The converging and diverging points are, as it were, poles of force. Where the atom* of matter are close or numerous in a given space, the hypothesis then admits that several atoms may conjoin into a ring, so that their central or axial currents may run one into the other, and not return as before over the surface of each atom ; these form the molecules of magnetic matter, and represent Ampere's hypothesis of molecular currents. Where the atoms being fewer in a given space are farther apart, or where, being good conductors, the current runs as freely over the surface as through the axis, then they do not form like groups to the molecules of magnetic matter, but are still considered subject to a species of induction by the action of external magnets and currents, and so give rise to Weber's -reverse currents. The induction of momentary currents and the rotation of a ray are considered by De la B/ive as in conformity with such a supposition of the electric state of the atoms and particles of matter. (1223) "This hypothesis," remarks Faraday, "the most perfect that has been offered, requires large assumptions ; it is necessary in the first place to conceive of the molecules as being flat or disc-like bodies, however numerous the atoms of each may be ; also that the atoms of one molecule do not interfere with or break up the disposition of those of another molecule ; also that electro-chemical action may consist with such a constituted molecule j also that the motive force of each atom current is resident in the axis, and on the other hand that the passage of the current over the surface offers resistance ; for unless there were a difference between the axial and the surface force in one direction or the other, the atoms would have no ten- dency to congregate in molecules." While, however, criticizing these various hypotheses, and considering their rapid succession rather a proof of weakness in this department of physical knowledge than of strength, Faraday fully admits the value, and even the 866 MAGNETIC HYPOTHESES. necessity of hypothesis where rightly used ; meanwhile, he himself proceeds to investigate experimentally, and by a new method, the direction, intensity, and amount of the magnetic forces, and to deduce therefrom new views respecting the condition of the magnet itself, without, however, pretending to convey any clear idea of the physical condition constituting the charged magnetic state, or to explain all the points of difficulty with which this subject is sur- rounded. (1224) Definition of a Line of Magnetic Force. (Phil. Trans., 1852, p. 1.) That line which a very small needle describes when it is so moved in either direction correspondent to its length, that the needle is constantly a tangent to the line of motion ; or that line along which, if a transverse wire be moved in either direction, there is no tendency to the formation of any current in the wire, whilst, if moved in any other direction, there is such a tendency ; or that line which coincides with the direction of the magne-crystallic axis of a crystal of bismuth, which is carried in either direction along it, the direction of these lines about and between ordinary magnets is easily represented in a general manner by the use of iron filings. In using this term " line of force," Faraday intends to express simply the direction of the force in a given place, and not any physical idea or notion of the manner in which the force may be there exerted. (1225) The lines of magnetic force may be recognized either by their action on the magnetic needle, or on a -conducting body moving across them, the former showing its results by attractions and repul- sions, the latter by the production of a current of Electricity (991 et seq.'). That this latter method may be advantageously em- ployed, excellent conductors are required ; that generally used by Earaday was a short copper wire O2 of an inch in thickness. The galvanometer also, instead of including many hundred convolutions of a fine wire, should consist of not more than 48 or 50 inches oi stout wire, disposed in two double coils about the astatic needle, because, although the Electricity produced by the intersection of the lines of magnetic force is abundant in quantity, its intensity is sc low that the fine wire galvanometer oiFers great obstruction to its (1226) The moving wire produces its effect when moving trans versely across the lines of force ; and it determines the direction oi the polarity by the direction of the electric current produced in it during the motion. A natural standard of this polarity may be obtained by referring LINES OF MAGNETIC TORCE. 867 to the lines of force of the earth in the northern hemisphere ; thus, if a person with arms extended move forward in these latitudes, then the direction of the electric current, which ivould tend to be produced in a wire represented ~by the arms, would be from the right hand through the arm and body towards the left. The moving wire may be applied where the needle cannot, to the interior of a magnet, e. g.; and though its sensibility does not approach to that of a magnetic needle, yet the facilities with which it is applied, and the diversity of its possible arrangements, render it as valuable as it is correct a philosophical indication of the presence of magnetic force. (1227) A piece of metal or conducting matter which moves across lines of magnetic force has, or tends to have, a current of Electricity produced in it. Thus : If N represent a magnetic pole, and over Fig. 485. it a circuit be formed of metal of any shape, and which at first is in a posi- tion C ; then if that circuit be moved in one direction into position 1, or in the contrary direction into positions 2, or 3, or 4, or 5 ; or if the first position C, be retained, the pole move to or towards the position n, then an electric current will be produced in the circuit having in every case the same direction, being that marked by the arrows. Reverse motions give currents in the reverse direction. No mere rotation of a bar magnet on its axis produces any induc- tive effect on circuits exterior to it ; in fact, the system of power about the magnet must not be considered as revolving with the magnet any more than the rays of light which emanate from the sun are supposed to revolve with the sun. Therefore, if by a mechanical contrivance a conductor, such as a Fig. 486. loop of wire, be caused to rotate toge- ther with a bar, magnet, no electric cur- rent will be produced by such rotation ; but if the loop be kept stationary while the magnet revolves, a current is produced ; and if the magnet be kept stationary while the loop revolves, a current will also be produced, but in a contrary direction ; that is, the current produced by the direct revolution of the wire is the same as that produced by the reverse revolution of the magnet. (1228) The magnetic forces are distributed in and round a bar- magnet in the simplest and most regular manner, so that any wire or line proceeding from a point in the magnetic equator of the bar so 868 MAGNETIC HYPOTHESES. as to pass through the magnetic axis to a point on the opposite side of the magnetic equator, must intersect all the lines in the plane through which it passes ; and a wire proceeding from the end of the magnet, at the magnetic axis, to a point in the magnetic equator, must intersect curves equal to lialf those of a great plane, however small or great the length of the wire may be. But a wire from pole to pole passing close to the equator has no electric current induced in it when revolved round the magnet, because it intersects half of the external lines of force in a great plane twice in opposite direc- tions. A wire ring, somewhat larger than the magnet, held edgeways at one of the poles, and then turned 90, and carried over the pole to the equator, intersects once, all, or nearly all, the lines of the magnet. (1229) From the results of experiments, Faraday draws the following conclusions : " The amount of magnetic force as shown by its effect in evolving electric currents, is determinate for the same lines of force, whatever the distance of the point or plane at which their power is exerted, is from the magnet. Or, it is the same in any two or more sections of the same lines of force, whatever their form or the distance from the seat of the power may be. "That there is no loss, or destruction, or evanescence, or latent state of the magnetic power by distance. " That the convergence or divergence of the lines of force causes no difference in their amount. "That when a wire is moving in a field of equal magnetic force, and with a uniform motion, the current of Electricity produced is pro- portionate to the time and to the velocity of the motion. " That the quantity of Electricity thrown into a current is directly as the amount of curves intersected." It also appeared from the experiments, that there exist lines of force within the magnet of the same nature, and of equal amount to those without; and every line of force, therefore, at whatever distance it may be taken from the magnet, must be considered as a closed circuit passing in some part of its course through the magnet, and having an equal amount of force in every part of its course. (1230) In experimenting on the currents produced in wires when they cross lines of magnetic force, it was found expedient to employ a galvanometer, the coil of which was replaced by a single convolution of very stout wire, the fine long wire of the coil galvanometer offering too great obstruction to the passage of currents of such feeble intensity. FARADAY'S EESEAECHES. 869 Pig. 487 represents the form of the instrument, the wire O2 of C c Fig. 488. an inch in diameter, passing horizontally Fig. 487. under the lower needle, then between that ^ and the upper needle over the upper, and then again between that and the lower needle, afterwards attached to a stand, and continued for 19 or 20 feet outside >u of the glass cover. ft A more perfect apparatus is shown in Fig. 488, in which the conducting coil is cut out of plates of copper, so as to form a square band 0*2 of an inch in thickness, which passes twice round the vibration-plane of each needle, the length of metal round the needles being 24 inches. The metal must be scrupulously clean, and the metallic connexion perfect throughout; and when observations are about to be taken, the temperature should be uniform, galvano- meters of this construction being remarkably sensible to thermo-electric currents. The wires forming the con- nexions should be of thick copper, and not longer than necessary. (1231) These galvanometers proved Fig. 489. far more sensible than the fine wire instruments ; the mere passage of the ends of the wire soldered together, so as to form a loop once between the poles of a horseshoe magnet (Fig. 489), capable of supporting 40 Ibs., being sufficient to cause a swing of the needle through 90. It was found necessary, however, in order to obtain uniform results, that the wire should be moved with the same velocity, for when it was passed rapidly, a deflection equal to 140 was some- times obtained, whilst a very slow motion gave only 30 or 40 ; but by operating always with the same velocity, and taking the average of several observations, very trustworthy results were obtained. As an illustration of the obstruction offered by thin wires to these magneto-electric currents, when 28 inches of copper wire, 0*045 of an inch in diameter, were interposed in the circuit, the swing of the needle was reduced from 140 to 40, and when this wire was replaced by another, 19'6 inches long and 0'0135 of an inch in diameter, the deflection was reduced to 7 or 8. 870 MAGNETIC HYPOTHESES. In all observations, the swing of the needle was observed and counted as the effect produced, the extent of which may be con- sidered as dependent on the Electricity which passes at the moment through the coil. (1232) Wires of different thicknesses of copper were bent into loops and soldered to the ends of two conducting rods, the other termi- nations of which dipped into the mercurial cups of the galvanometer. The loops were then passed, with uniform velocity, over one of the poles of a horseshoe magnet, capable of sustaining 211bs. The deflection of the needle increased with the thickness of the wire, though not in proportion to the masses of the wires, e. g. O Copper wire, -gV inch thick, deflected the needle, 16 00 Copper wire, & 44*40 Copper wire, i 57'37 (1233) The result of many experiments led to the conclusion : " That the current or amount of Electricity evolved in a wire moving amongst the lines of force, is not simply as the space occupied by its breadth, correspondent to the direction of the line of force, which has relation to the polarity of the power ; nor by that width or diminution of it which includes the number or amount of the lines of force, and which, corresponding to the direction of the motion, has relation to the equatorial condition of the lines ; but is jointly, as the compound ratio of the tw T o, or as the mass of the moving wire. The power acts just as well on the interior portions of the wire as on the exterior or superficial portions, and a central particle, surrounded on all sides by copper, is put in the same relation to the force, as those which being superficial, have" air next them on one side. (1234) When wires of different metals are moved across the lines of force of a magnet, the currents induced in these different bodies are proportional to their electro-conducting power. In repeating these experiments with the thick wire galvanometer, and with loops of wires of the different metals of precisely the same diameter, viz., - 04 of an inch, the following results were obtained : o Copper wire deflected the galvanometer . 63'0 Silver . 61-9 Zinc . 31-5 Tin . 19-1 Iron . 18-0 Platinum . 16'9 Lead . 12-1 FARADAY'S RESEARCHES THE MOVING WIRE. 871 (1235) In these experiments the difference in the results was thought to be mainly due to the difference in the substance of the loops, the conducting part of each system being very good and the same for each ; but on varying the experiments in many ways the conclusion was arrived at : " That the current of Electricity excited in different substances, moving across the lines of magnetic force, appears to be directly as the conducting power of the substances, and has no reference to the magnetic character of the body ; and the amount of lines of force appears to be equal for equal spaces occupied by the different metals, which agrees with the conclusion before arrived at, that, for air, water, bismuth, oxygen, nitrogen, or a vacuum, the lines of force are the same in amount, except that they are more or less concentrated in the substance across which they pass, according as it is more or less competent to conduct or transmit the magnetic force. (1236) What then is the definition of the term magnetic polarity ? As Faraday understands it, it means the opposite and antithetical actions which are manifested at the opposite ends of a portion of a line of force. But if this be so, is it correctly exhibited or indicated in every case by attractions and repulsions? A weak solution of proto- sulphate of iron, if surrounded by water, will in the magnetic field point axially, but if in a stronger solution than itself, it will point eqiiatorially (1134) ; pointing, then, is an effect dependent on media and circumstances. But a wire moving across the magnetic field shows that the lines of force have in all cases the same general polarity ; therefore, in investigations into the nature of the magnetic force, the indications of the moving wire are most valuable. N In a field of equal force a magnetic needle cannot show polarity, as the very fact of pointing implies the disturbance of the equality of arrangement of force ; a moving wire, however, shows the full amount of magnetic power without in the least disturbing the dis- position of the power. (1237) At the conclusion of this paper Faraday again expresses his conviction that the idea of lines of force possesses advantages over the method of representing magnetic forces by centres of action. In a straight wire, for instance, carrying an electric current, it is apparently impossible to represent the magnetic forces by centres of action, whereas the lines of force simply and truly represent them. The moving wire or conductor again, he considers as a very valuable examiner of magnetic forces, as it does not sensibly disturb the forces in the magnetic field, where, however, it indicates the quantity of force independent of tension, and enables us to examine the 872 . MAGNETIC HYPOTHESES. interior of magnets, and thus gain experimental evidence of a nature not otherwise attainable. (1238) The Employment of the Induced Magneto-electric Current as a Test and Measure of Magnetic Forces. The amount of current induced is precisely proportionate to the amount of lines of mag- netic force intersected by the moving wire in which the electric current is generated and appears. "When a compound bar magnet, consisting of two plates, 12 inches Fig. 490. long, 1 inch broad, and O5 a 9 feet long. thick, was introduced once into the loop (Fig. 490) and left there, the current pro- duced at the galvanometer 6 Wire 0-2 inches diameter. was constantly 16. The swing of the needle occupied 13 seconds ; it was possible, therefore, to make three or four observations at the same time in this way : the magnet having been introduced into the loop, the electric current is broken by removing a or b from the mercury cup of the galvanometer, and then the magnet removed, which by this motion does nothing ; the mercury contact is then restored and the magnet again intro- duced into the loop ; by this mode of proceeding two, three, and even four impulses could be given to the needle, and it was found that the deflections were, as near as possible, as 1, 2, 3, and 4 ; thus using only one of the two magnetic bars: One introduction gave . . " *. " . 8'00 Two . .;,:.- i -v,- -.^V ftj; . 1575 Three . ..'-. *. = ^ ; ; ; . . 23-87 Tour . :....., - .. ; :.....' . . 31-66 It appears, therefore, that for small arcs the number of degrees of swing deflection are nearly proportional to the magnetic force which has been brought into action on the moving wire. (1239) Revolving Rectangles and Rings. For experimenting with the magnetic forces of the earth, the form of moving wire employed was in the form of a rectangle or ring, which was caused to rotate, and the currents produced gathered up by a commutator, and sent on to the galvanometer to be measured. The lines of terrestrial magnetic force are inclined at an angle of 69 to the horizontal plane, but as only comparative results w r ere required, the rotating instrument was always placed in the horizontal plane with the axis of rotation perpendicular to the plane of the magnetic meridian. (1240) There is this difference between the magnet and the earth REVOLTING RECTANGLES AND EINGS. 873 in their action on the moving wire. If a loop be passed over a magnet it encloses all the lines of force belonging to it; therefore, the greater the number of convolutions of that loop the greater the amount of Electricity induced. The contrary is the case with regard to the earth's magnetic force; here, the lines of force intersected are as the areas of the moving rect- angles. Twelve feet of wire in one square, intersects the lines of force passing through an area of 9 square feet (the areas enclosed being as the square of the periphery); but if the same length of wire be arranged in a triple circuit, aboub a square of one foot area, it will only intersect the lines due to that area. Large rectangles, are, there- fore, advisable in experimenting on the earth's Magnetism. (1241) Six revolutions of a rectangle of copper wire, 4 feet in length, enclosing, therefore, 1 square foot of area, gave an average swing deflection of 15 0- 66, nine revolutions (from left to right) gave 23*87, nine reverse revolutions 23*27, twelve revolutions gave 31 0< 33, the means of each for one revolution are 2*62, 2 0> 61, and 2 0- 61, results so much in accordance as to give great confidence in this method of investigating magnetic forces. Variations in the arrangement of the rectangle, and in the length of the parts of the wires intersecting the lines of magnetic force, have no influence in altering the result, which being dependent alone on the number of lines of force intersected, is the same when the areas of the rectangles are the same. (1242) When the wires of which the rectangles were made were of different thicknesses, there was a corresponding difference in the twing ; thus, a rectangle of wire O05 inch in diameter gave a mean deflection of 2'61 per revolution, a rectangle of wire O'lO inch in diameter gave a mean deflection of 7'33 per revolution. a rectangle of wire O20 inch in diameter gave a mean deflection of 8 -94 per revolution. "When a delicate RuhmkorfTs galvanometer, the diameter of the wire of which was -riyth of an inch, was employed, great obstruction to the current took place, only a fiftieth part of the current from a thick wire (Ol inch in diameter) rectangle passing through the instrument ; but when the rectangle was made up of four convolu- tions of copper wire (O05 inch in diameter), the mass of wire being the same as before, but its length four times as great, one- fourth or one-fifth part of the current surmounted the obstructions 874 MAGNETIC HYPOTHESES. of the instrument, the current being with the thin wire less in quan- tify, but far higher in intensity, than with the thick. (1243) A rectangle of wire, 0'2 of an inch in diameter, the square of which was 36 inches in the side, and enclosed, therefore, an area of nine square feet, caused in one revolution a swing deflection of upwards of S0*44. Now a rectangle of similar wire having an area of one square foot gave 8 C> 94 per revolution which is very nearly th of 81-44 Ai 9 AA = 9-04 the two numbers are so nearly alike that the experiment may be considered as proving the truth of the statement, " that the magneto-electric current evolved is as the amount of lines of force intersected" Faraday thinks it not unlikely that by improved arrangements, the moving wire may hereafter be applied with advantage to the inves- tigation of the earth's magnetic force in different latitudes and places. The axis of rotation must be perpendicular to the lines of force, i. e. to the dip. (1244) From a correct and close investigation of the disposition and characters of the magnetic force, the magnets should be of hard steel and invariable; when this is the case, Faraday found that the power of a magnetic bar, as indicated by the moving wire, is very little affected by bringing near to it, in favourable or unfavourable positions, other and far more powerful bars ; and from his results he draws the following conclusions : 1. Lines of force of different magnets in favourable positions to each other coalesce. 2. There is no increase of the total force of the lines by this coalescence. 3. The analogy of a magnet with two or more voltaic batteries* associated end to end in one circuit, is perfect. Probably some effect corresponding to intensity in the case of batteries, will be found to exist among magnets. 4. The increase of power upon a magnetic needle, or piece of soft iron, placed between two opposite poles, is caused by the concentra- tion upon it of the lines which were before diffused, and not by the addition of the power represented by the lines of force of one pole to that of the lines of force of the other. There is no more power represented by all the lines of force than before ; and a line of force is not more powerful because it coalesces with a line of force of another magnet. In this respect the analogy with the voltaic pile is also perfect. 5. Coalescence is not the addition of one line of force to another in power, but their union in one common circuit. (1245) Faraday magnetized to saturation a, very hard steel bar, 12 PHYSICAL CHARACTER OF LINES Or MAGNETIC FORCE. 875 inches long, 1 inch broad, and O05 inch thick its power as measured by the moving wire was 6*9. It was now broken into two pieces nearly in the middle ; one-half had a power of 5'94, the other of 5*89. The two pieces placed side by side with poles together as a compound magnet, had a power of 11'06, not much below the sum of the powers of each half ascertained separately, and the loss on each half as compared with the original bar was not greater than was to be expected considering the saturated state of the original magnet. This again is in perfect harmony with the voltaic battery, for it is well known that if a battery of 20 plates be separated into two of 10, or four batteries of 5 pairs, each of the smaller latteries can supply as much dynamic Electricity as the original battery, provided there be no obstruction to the passage of the current. (1246) Physical Character of the Lines of Magnetic Force. Having shown that Equator, magnetic Equivalents, electro-chemical Escharotic, Galvanism as a . Exploring apparatus, Read's . Noads 172 Colladon's .173 Gal- 47 62 187 261 158 159 160 160 344 628 371 345 171 Crosse's Weekes's Eonalds's Greenwich Peltier's 173 179 185 191 192 Falling star ....... \ . .130 Fire-balls, appearances termed . 205 illustrations of the effects of . 206 Fishes, electric .... 463 Flame, generation of a voltaic cur- rent by 418 diamagnetic condition of .842 Fog, remarkable electrical pheno- mena during a . . . .177 Free charge, Faraday and Harris on 136 Frog, galvanoscopic preparation of 427 current proper of . . .436 electric pile cf . , ...>/ .437 Galvanic, or voltaic Electricity , 246 Page Galvanic arrangements . . . 246 circles, simple . . . 247 circles, simple, illustrations of, .... . 249 circles, simple, modifications of . ..-V:,V; < . " . . 251 Galvanic batteries . . .263 Cruickshank's . . ... 264 Babington's . . . 264 Wollaston's . . . .265 Hare's . . . . . 265 Van Melsen's . . .267 Daniell's . . . .269 Smee's 274 Grove's - . , ' . . 276 Bunsen's . . . '. 281 Sturgeon's . . . .283 Callan's . . . .283 Roberts's . v , . 286 Leeson's . . . . 293 Goodman's . . . . 293 Grove's gas .... 295 Galvanism, physiological effects of 336 Galvanometers . . , . 325 Galvanometer, Ritchie's torsion . 326 Nobili's astatic . . . 328 Matteucci on the . . . 329 Du Bois Raymond's . . 330 the sine . . , . 331 Callan's sine . . "' \ .331 tangent . . . . 332 thermoscopic . . . 333 Locke's .... 333 Sturgeon's gold-leaf . .335 Iremonger's hydrostatic . 335 method of judging the sensi- bility of . . . . . 329 Roget's vertical spiral coil . 657 gold-leaf . . v. . . 657 Galvanoscopic frog, preparation of 427 Gas battery, Grove's . . . 295 experiments with . . . 297 as a source of pure nitrogen . 298 theory of . . .298 Gases, electro-chemical, polarity of 415 diamagnetic, condition of .846 Glass, kind best adapted for elec- trical machines . . . .75 specific inductive capacity of 148 Glow discharge . . . .105 Gutta percha, as an insulator . 19 electrical machine . .77 Gymnotus, capture of . . . 472 electric phenomena of . . 475 Hydro-electric machine, made under the superintendence of Messrs. Armstrong and Ibbet- son, for the Polytechnic . . 91 machine, made under the su- perintendence of Messrs. Arm- strong and Ibbetson, for the United States . . . .94 INDEX. 889 Hydro-electric machine, Watson and Lambert's . . . .97 machine, theory of . .97 current, methods of measur- ing the strength of . . .302 Hydrogen ga, cooling influence of 313 Inclination of the needle . . 626 Induced currents, Henry's experi- ments on 708 Reiss's experiments on . .713 Matteucci's apparatus for . 714 phenomena of . . .733 chemical effects of . . 743 therepeutical application of . 743 Induction 43 essentially a physical action . 49 illustrations of the nature of 51 principles of ... 53 importance of, in electrical action 54 Faraday's theory of . .54 summary of Faraday's views relating to . . . .106 static, general principles of . 136 relation of, to the matter through which it is exerted . 150 Matteucci on . . .150 lateral, applied to the pheno- mena of the charging of sub- merged telegraphic wires . . 242 electro-dynamic and magneto - electric 690 terrestrial magneto-electric . 692 spark in air . . . . 733 coil apparatus, experiments with coil apparatus, jars charged by spark in rarefied air 734 737 738 736 741 spark in liquids spark in different vacua spark across secondary con- ductors 742 spark between different metals 742 Inductive forces, Harris's investi- gations relative to . .63 capacity, specific, Faraday on 146 Insulation and conduction, extreme cases of one common condition . 21 Insulators, gutta percha and shell- lac as 19 Ion, meaning of the term . . 351 Iron, peculiar voltaic condition of 287 Isoclinal lines . . . .616 Isodynamic lines . . . .616 Isogonic lines . . . .616 Kite, electrical, examination of the Electricity of the air by . . 180 apparatus for securing safety while experimenting with . .181 242 151 137 374 127 Page Kite, experiments with . . .183 Sturgeon's experiments with 183 Lateral induction applied to the charging of submerged telegraph wires ..... discharge .... Laws of electrical accumulation Lead, protoxyde of, crystallization by electric action sulphuret of, crystallization of, by electric action . . . 375 Leyden battery, mechanical and ca- lorific effects of . . . .132 Leyden jar, luminous or diamond . 125 with moveable coatings . 125 firing gunpowder by . . ] 26 perforating card, by discharge of breaking wine glass, by dis- charge of . . . - . . 127 lighting and extinguishing a candle by 128 decomposition of vermillion by discharge of . . .128 discharging through melted resin 129 with metallic gauge coatings 135 Leyden phial, discovery of, by Kleist . . ... arid battery .... method of constructing charge and discharge of Barker's arrangement of . Lockey's arrangement of fracture of . Harris's arrangement of discharge of . Leyden vacuum .... Light, velocity of . action of Magnetism on Lightning, analogy between, and electric spark .... * and thunder, electrical phe- nomena effects of .... Lightning conductors, arrange- ment of 210 phenomena of . . .204 Arago's classification of . 204 some remarkable appearances of 207 effects of, on buildings . 209 Harris on .... 210 Harris's, conditions of, for safety 211 on the Nelson Monument . 212 on the Great Monument . 212 Harris's, principles of action of . . . . . .213 Harris's, illustrations of action of 213 Harris's, for defending ships 215 4 108 111 111 113 113 113 114 115 130 115 804 196 196 202 900 INDEX. Page Lightning conductors, Harris's sys- tem of 216 for the electric telegraph . 777 Lime, hydrate of, crystallization by electric action . . .374 Loadstone, its attractive power known to the ancients . . 523 Harris's conditions of, for natural, where found . . 547 Luminous or diamond jar . .125 phenomena of the voltaic current 308 Magnets, artificial, old methods of making 527 simple and ready methtid of making 548 artificial, methods of making. 561 Knight's process . . .561 Scoresby's modification of Knight's process . . . 561 Duhamel arid Antheaume's process Michel's process . Canton's process . Epinus's process . Coulomb's process Barlow's process . Elias's process directive power of horse-shoe batteries 562 563 563 565 566 568 57JO 572 568 585 608 analogy of to the earth . declination . rotation of, on its own axis . 662 electro 668 electric spark from . . 694 action of, on the metals. . 811 action of, on air and gases . 814 notions of the ancients re- specting the source of power of . 858 its analogy with an insulated voltaic battery . . . .876 Faraday's view of the condi- tion of a 882 Magne-crystallic force . . .816 differential .... 825 action of heat on the . .826 Magnetic phenomena of voltaic Electricity poles, how found . poles, consecutive . attraction and repulsion induction 325 549 550 549 553 555 curves, fundamental proper- ties of 556 figures 558 test for steel . ._ . .574 batteries, construction of .575 combinations, laws of . .575 powers, useful applications of 578 force, laws of . . .579 force in different points of a bar 581 Page Magnetic charge, laws of . .582 power of the earth . .584 direction needle, simple me- thod of making a ... 585 terrestrial induction . .587 observatories . . .612 observatories at Dublin . 614 poles of the globe . . .617 equator, form and motion of. 629 intensity, terrestrial . 630 storms 634 pole, rotation of, round an electrified wire .... 659 power of the voltaic current . 667 condition of matter . . 808 conducting power . . .851 hypotheses . . . .858 force, definition of a line of . 866 force, physical character of the lines of . . . .875 action, places of no . .880 574 523 Magnetical instruments, steel for . Magnetism, historical sketch of decrease in intensity of, in elevated regions production of, by light . universality of ... influence of heat on 530 532 537 544 general facts and principles of 547 terrestrial . . . .584 induced by percussion and flexure 589 terrestrial, theory of . .636 action of, on light . . .804 atmospheric .... 854 Ampere's electro - dynamic, theoiy of De la Rive's theory of Magneto- electric induction machines machines, Pixii's machines, Clarke's. machines, Saxton's telegraphs 864 690 696 696 697 698 779 currents as tests of magnetic force 872 Magneto-electrical machine, theory of 702 laws of 703 Magueto-Electricity . . . 690 discovery of, by Faraday 541 Magnetometer, horizontal-force . 609 vertical-force . . .609 Hoarder's .... 684 experiments with . .686 Matter, absolute quantity of elec- tric force in .... 372 Metallic wires, sounds produced by the passage of a voltaic cur- rent through .... 322 solutions, action of the mag- net on 813 Metallo-chromes . . . .408 INDEX. 901 Page Metals, colours produced by the deflagration of . . . .134 deflagration of, by the voltaic battery 308 colour of, when deflagrated by the voltaic disruptive discharge . 309 conducting powers of . . 323 Becquerel, Ohm, and Davy on 323 Lenz, Eeiss, Pouillet, and Harris, on 324 action of Magnetism on 811 Mica battery, Crosse's . 257 Mill, electrical . . 84 Minerals, pyro-Electricity of 30 Multiplier, Cavallo's . 67 Multipliers ... 61 Muscular electric pile . 428 electric current, laws of 430 Needle, horizontal declination of 616 variation of, in London. 618 variation of, in Paris . 618 variation of, in Brussels 619 inclination of, in London 626 inclination of, in Paris and Brussels 627 Negative Electricity, meaning of the term 23 Nerves, action of the electric cur- rent on 455 Nitrogen, peculiar characters of, in relation to electric discharge , 103 neutral character of, as regards Magnetism .... 850 Observatories, magnetic . .613 Opposite electricities . . .22 Ores, voltaic, reduction of . . 398 Dechaud and Gaultier de Claubry on . . . .398 Eitchie on . . . .399 Napier on . . . .400 Crosse on . . . 401 Oxide of tin, reduced by the elec- tric discharge . . . .134 Oxygen, magnetic character of .849 its wonderful magnetic power 851 Ozone, properties of . . .410 Schoenbein on . . .410 Baumert on . . . .414 Fremy and Becquerel on .411 quantitative determination of 413 Panopticon, large electrical ma- chine at 74 Paramagnetic bodies . . .851 Paper, Electricity developed during the manufacture of . .77 Physiological effects of statical Electricity . . . .156 effects of Galvanism . .336 Plants, Electricity of . . .481 Platinode, meaning of the term . 352 Page Polarity, diamagnetic . . . 826 Polymagnet, Tyndall's . . .841 Positive Electricity, meaning of the term 23 Protochloride of tin, electro-chemi- cal decomposition of . . .369 Pyro-electricity of minerals . .30 Quadrant electrometer . 117 Repulsion, electrical, general phe- nomena of 17 Residual charge, phenomena of . 149 Resinous substances become electri- cal by friction . . . .18 Return charge, phenomena of .148 Rheostat, Wheatstone's . . 305 Ribbon coil, experiments with . 705 Round-Down Cliff, destruction of, by gunpowder . . . .311 Salts, decomposition of, by voltaic Electricity . . . .354 Sealing-wax spun while hot by Electricity . . . .87 Secondary results . . . .373 results of voltaic decomposi- tion 393 compounds, electrolysis of .393 currents . . . .703 Shell-lac, specific inductive capa- pacity of 148 Silicated borate of lead, Diamag- netism of 810 Silicium, electro-reduction of . . 358 Silver, chlorate of, crystallization by electric action . . . 375 sulphuret of, crystallization by electric action . . . 375 Silurus electricus .... 481 Sine, galvanometer . . .331 Sinuous electrical currents . .653 Solenoids 653 Sounds produced during the_act of magnetization of iron . .671 Space, its magnetic relations . 850 Spark, electric nature of . .99 electric, in different elastic media 100 measurer, Ronalds's . .187 Specific inductive capacity . .146 Spiral electromagnetic, Roget's . 656 Spirits fired by Electricity . .83 Springs, constant and intermittent, imitation of, by voltaic Electri- city 390 Static induction, general princi- ples of, illustrated . . .136 Steel, qualities of, best adapted for magnets . 577 Sulphate of magnesia, decomposi- tion of 359 3 M 902 INDEX. Page Sulphur, specific inductive capa- city of 148 Swing, electrical . . . .86 Tangent galvanometer . . .332 Tayleur, loss of the, from changes in the action of her compasses . 603 Telegraph, electric, history of the 747 Tension and intensity, meaning of the words 109 electrical signs of, in a single cell 308 630 633 634 584 636 Terrestrial magnetic intensity Sabine on Lloyd on ... Terrestrial Magnetism . theory of ... Terrestrial magneto-electric induc- tion 692 Tetraodon electricus . . .481 Therapeutic applications of voltaic Electricity . . . .343 Thermal phenomena of the voltaic current 308 Thermo-electric piles . . . 486 MM. Nobili and Melloni's . 486 Locke's 487 Cumming's .... 487 Dove's . . ... .488 Van der Voort's . . .488 Watkins's . . . .488 Peltier's . . . .488 Tyndall's . . . .489 sparks from .... 491 chemical decomposition by . 491 Thermo-electric series . . . 485 Thermo-Electricity . . . 484 Thermoscopic galvanometer . . 333 Thunder house . . . .131 cloud, structure of . .174 storm, phenomena of . .197 storm, appearance of the heavens during . . . .197 storm, Beccaria's account of . 197 storm, Thomson's description of 198 identical with the snap from the prime conductor . . .200 phenomena of . ... 201 storm, positions of safety during 203 storm, awful effects of . . 207 Tin, sulphuret of, crystallization of by electric action . . .375 Tornadoes, the nature of . .219 Torpedo, Walsh's experiments with 464 anatomical structure of . . 465 electric phenomena of . .466 laws relating to the distribu- tion of Electricity in the body of 468 causes which influence the discharge of . . . .468 * Hunter's engraving of . .471 Trichiarus electricus Tourmaline, pyro-Electricity of Page , 481 . 31 Unit jar 139 Faraday's observations on .141 Vacuum, conducting power of, unphilosophical . . .144 Variation compass . . .608 of the needle . . .618 periodic, of the horizontal needle 622 annual, at Toronto, Hobar- ton, the Cape of Good Hope, and St. Helena . . . .624 Vacuo, electric light in . . .85 Vegetables, their power of con- ducting Electricity . . .158 Vitreous substances become elec- trical by friction . . .18 Volcanic eruptions in the sea, electrical phenomena . .218 Volta-electrometer, Faraday's .366 Callan's . . . .366 Voltaic current, effects of . .307 arc, De la Rive on the . .320 arc, influence of Magnetism on the 321 arc, intense heating power of 323 Electricity, magnetic pheno- mena of 325 Electricity, relation between, . and the phenomena of life . 341 Electricity, therapeutic, appli- cations- of 343 Electricity, chemical pheno- mena of 350 reduction of ores . . .398 current, generation of, by flame. . . . . .418 battery, rotation of, round a magnet 665 current, magnetizing proper- ties of 666 battery for the electric tele- graph 767 Voltaic pile . . . . .252 theory of . . . .497 Faraday on \'. . . 498 Poggendorff on the . . 503 De la Rive on ... 506 Fechneron . . . 513 Faraday on . . .515 Grove on .... 522 Water, decomposition of, by vol- taic Electricity . . .354 decomposition of, by statical Electricity . . . .161 battery, Crosse's . . . 256 battery, Noad's . . .259 Water battery, Gassiot's . . 261 INDEX TO AUTHORITIES. Waterproof cloth, development of Electricity during the manufac- ture 78 Waterspout, fearful ravages com- mitted by . . . .221 Peltier's theory of . . 222 Beechey's description of . 223 Wheel, stellar, rotation of, between magnetic poles 903 Page Zinc oxide, inaction of, in acidu- lated water . . . .291 crystallization by electric action . .374 INDEX TO AUTHORITIES. Page ABEL, DR. CLARKE, his electro- physiological experiments . 342 Airy on the local attraction of the compass in iron ships . 601, 604 Alexander, his electric telegraph . 757 Allainand, his description of the electric shock .... 4 Ampere, his electro-magnetic appa- ratus ...... 645 ---- on the mutual action of paral- lel electrical currents . . 650 -- on the laws of angular cur- rents ...... 651 - his electro-dynamic theory of Magnetism . . . .861 -- Andrews on chemical decom- position by the thermo-current . 493 Apjohn, Dr., on the application of voltaic Electricity to the treat- ment of diseases . . . 343 Arago on the phenomena of light- ning ...... 204 --- on the influence of aurorso on the magnetic needle . . .535 -- on the universality of Mag- netism ..... 538 Aristotle mentions the electrical powers of the torpedo . . 2 Armstrong, his experiments on the Electricity developed during the manufacture of paper . . 77 his experiments on the Elec- tricity of effluent steam 88 Babbage and Herschel on the de- velopment of Magnetism by rotation ..... 539 Babbington, his galvanic battery . 264 Back, Captain, on the influence of aurorae on the magnetic needle . 535 Bachhoffner on the fracture of Ley den jars Bancalari on the diamagnetic con- dition of flame . 113 841 Page Bain, his electro-magnetic en- gine . . . . . .681 his electro-magnetic clocks . 791 his electro-magnetic pendu- lums 795 Barlow, his observations on' the electrical properties of gutta percha 19 his gutta percha electrical machine 77 his magnetical investigations 531 his method of making arti- ficial magnets . . . .568 on the theory of terrestrial Magnetism . . . .638 Baumert on ozone . . .414 Baumgartner on the induction of atmospheric Electricity on the wires of the electric telegraph . 239 Beatson on the sounds produced dxiring the magnetization and demagnetization of iron . . 672 Beech ey, Captain, his description of waterspouts . . . .224 Beccaria, his electrical researches . 12 his description of a thunder- storm 197 Becquerel on the conducting powers of metals' 323 his experiments on electro- crystallizations . . . .374 on slow and weak electric ac- tions 375 his researches on secondary electric actions .... on the Electricity of plants . Bennett, his electroscope . _ . Biot, his mathematical investiga- tion of Electricity his apparatus for illustrating distribution of Electricity his theory of the aurora bore- alis . on the Magnetism of nickel . 376 482 28 15 56 232 535 904 INDEX TO AUTHOETTIES. Bird, Dr. Golding, on some thera- peutic applications of voltaic Electricity .... 348 his apparatus for the electro- reduction of inetals . .357 his experiments on electro- crystallization . . . .377 his electro-magnetic coil ma- chine 716 Birt, his discussion of the electrical observations at Kew . .185 Bohnenberger, his electroscope . 30 Bottger, his apparatus for illus- trating the action of Magnetism on light 806 Botto on the chemical action of the thermo-pile . . . .491 Boyle, his electrical discoveries . 2 Boze introduces prime conductor . 3 his description of the electric shock . . . . . .4 Bregnet, his paratonnere for the electric telegraph . . .779 Brewster, Sir D., his list of pyro- electrical minerals . .31 on the theory of terrestrial Magnetism . . . .636 Bright, his magnetic telegraph . 783 his acoustic telegraph . . 785 Brussels, Koyal Observatory of, Quetelet's experiments at . .194 Buchanan, his observations on the Electricity generated in a factory at Glasgow . . . .78 Buff on the Electricity of plants . 481 Bunsen, his galvanic batteries .281 Caesar, Julius, discovers the con- version of iron into a magnet . 524 Callan, his galvanic batteries . . 283 his sine galvanometer . . 331 his voltameter . . .366 his apparatus for applying the mixed gases to the production of the lime light . . . 367 on the relative practical va- lues of the lime and coke lights 368 his electro-magnetic coil ma- chine 715 Canton, his electrical discoveries . 11 his electroscope . . .25 his method of making artifi- cial magnets .... 563 Cavallo's multiplier . . .67 on the Magnetism of brass . 536 Cavendish, his mathematical inves- tigation of Electricity . .14 his contributions to electrical science 14 his artificial torpedo . . 464 Chenevix on the effect of arsenic in destroying the Magnetism of nickel . 537 Christie on the influence of heat on Magnetism . . . .544 Clarke, Latimer, on the charging of the submerged telegraphic wire . ..... 241 Colladon, his atmospheric explor- ing apparatus . . . .173 Cooke and Wheatstone, their five- needle telegraph . . .757 their electro-magnetic tele- graph ..... 759 their single-needle telegraphs 761 their double-needle telegraphs 763 Columbus discovers the variation of the needle . . . .523 Coulomb lays the foundation of electro-statics . . . .14 his contributions to electri- cal science . . . .15 torsion-balance electrometer 32 his electrical law of attraction and repulsion . . . .34 Faraday's arrangement of .34 determines the law of mag- netic attraction and repulsion . 527 his researches in Magnetism . 528 on the universality of Mag- netism 537 his theory of Magnetism . 860 Crosse, his atmospheric exploring apparatus . . . . .173 his account of the construc- tion of a thunder cloud . . 174 his account of the electric phenomena attending a dense November fog . . . .177 his experiments with a water battery . . . .256 his experiments on electro- crystallization .... 378 on the mechanical action ac- companying electric transfer . 381 on the electrical acarus . .383 his imitation of constant and intermitting springs . . . 390 on the voltaic reduction of ores 401 Cruickshank, his galvanic battery . 264 Gumming, his thermo-pile . .486 Cuthbertson's balance electrometer 118 Dalton, his description of the aurora borealis 226 his galvanic batteries . . 269 on the influence of aurorae on the magnetic needle . . . 534 Daniell, Professor, on the galvanic force 249 his new terms . . .352 on the electrolysis of second- ary compounds .... 393 his electrolytic formula) . 395 his electrolytic apparatus . 397 INDEX TO AUTHORITIES. 905 Page Davenport, his electro-magnetic en- gine 677 Davidson, his electro-magnetic en- gine 679 Davy, Sir H., his plan for protect- ing the copper sheathing of ships 251 on the conducting power of metals 323 on the chemical agencies of of Electricity . . . .362 his electric telegraph . .757 Dochaud and Gaultier de Claubry on the voltaic reduction of ores . 391 Deleuil, his electric lamp . .316 Descartes, his theory of Magnetism 858 De Luc, his dry electric column . 253 De la Rive, his theory of the aurora borealis 234 ou. the voltaic arc . 315, 319 on the theory of the voltaic pile 506 his floating electro-magnetic ring 647 his theory of Magnetism . 865 De la Rue, his apparatus for deflag- rating metals . . . .310 Dove, his thermo-pile . . . 487 Du Bois, Raymond, his galvano- meter 330 his researches in animal Elec- tricity 439 his law of the muscular cur- rent 439 on the production of an elec- tric current by muscular con- traction ..... 462 Dubosq, his electric lamp . .316 Dufaye, his electrical discoveries . 3 Duhamel's process for making arti- ficial magnets . . . .562 Durnont on the application of Electro-Magnetism as a motive force 675 Elias, his method of making artifi- ficial magnets . . . .510 Elkington, his large electro-metal- lurgical establishment . . 407 Epiiius, his method of making arti- ficial magnets .... 565 his theory of Magnetism . 859 Euler, his theory of Magnetism . 859 Eustathius alludes to the occasional emission of sparks from the human body when submitted to friction ..... 2 Faraday, his experiments on con- duction . . . . .21 researches into the nature of induction 50 apparatus for illustrating dis- tribution of Electricity . 58 Page Faraday, his experiments to endea- vour to charge air bodily . .59 his electrical machine . . 76 his experiments on the Elec- tricity of effluent steam . .89 his investigations into the nature of electric discharges . 99 summary of his views relating to induction . . . .106 on specific inductive capacity 146 on the chemical effects of common Electricity . . .163 his views respecting the aurora borealis . . . .236 on subterraneous telegraph wires 241 his new electrical terms . 350 on the electro-decomposition of sulphate of magnesia . . 359 on the electro-decomposition of chloride of silver . . . 360 on definite electro-chemical action 365 his volta-electrometer . .366 on the electro-chemical de- composition of proto-chloride of tin 369 on electro-chemical equiva- lents 371 on the absolute quantity of electric force in matter . . 372 his experiments with the gymnotus ..... 475 on the theory of the voltaic pile 498, 515 on the magnetic metals . 536 his discovery of magneto- electric induction . . .541 his electro - magnetic re- searches 658 on electro-dynamic and mag- neto-electric indue: ion . . 690 on secondary or induced cur- rents 704 on the induction apparatus . 737 on the action of Magnetism on light 804 on the general magnetic con- dition of matter . . 809 on mague-crystallic pheno- mena 817 on diamagnetic polarity . 828 on the diamagnetic condition of flame 842 on atmospheric Magnetism , 854 on lines of magnetic force . 866 Ids researches in Magnetism . 868 Fechner on the theory of the vol- taic pile 513 Flavio Gioia regarded as the in- ventor of the compass . .523 Forbes on the magneto-electric spark 695 906 TO AUTHORITIES. IXDEX TO AUTHORITIES. 90T Page Hawksbee, his electrical experi- ments . . . . .2 on the laws of magnetic force 579 , Hearder, his magnetometer . . 684 j his induction coil . . . 744 Henley, his quadrant electrometer 117 his universal discharger . 119 his electro-magnetic engines . 682 his electro-magnetic coil ma- chine 721 his magnetic telegraph . . 779 Henry, Professor, on the induction of atmospheric Electricity on the wires of the electric telegraph . 238 on induced currents . . 708 Humboldt, his description of the aurora borealis .... 228 his experiments on Galvanism 425 his account of the method of capturing gymnoti . . .472 his researches in terrestrial Magnetism .... 529 on the establishment of mag- netical observatories . . .611 on magnetic storms . . 635 Hunter, his anatomical examina- tion of the torpedo . . .465 Iremonger, his hydrostatic galvano- meter 335 i Jacobi, his discovery of the gal- vano-plastic process . . . 403 his electro-magnetic engine .679 Joule, his electro-magnet . . 670 Kater on the construction of com- pass needles .... 592 Kew Observatory, atmospheric elec- trical observations at . .185 atmospheric electrical discus- sion of 189 i Kinnersley' electric thermometer . 129 | Kleist, the real discoverer of the Ley den phial .... 3 Knight, Dr. Gowin, his method of making artificial magnets . 527, 561 his coil machine for medical 723 534 Knox, G. J. and T., on the mag- netizing power of light Lambert, his niagnetical researches 680 Lane's discharging electrometer . 218 La Place, his mathematical investi- gation of Electricity . . 15 Lavoisier, his electrical experi- ments 16 Leeson, his galvanic battery . 293 Lehot, his contributions to animal Electricity .... 426 Lenz, on the conducting powers of metals . 324 Page Lenz, on the laws of the magneto- electric force Lesage, his electric telegraph . 747 Lichtenberg's figures . .132 Locke, his thermoscopic galvano- meter ..... 333 his thenno-pile . . . 486 Lockey, his electro-magnetic cofl machine . . . . .719 Lottin, his description of aurora boreales .... Lymner, his electrical experi- ments . . . . , 14 Lyon on the Magnetism of nickel and cobalt 535 Magnus, his electro-magnetic cur- rent reverser . . . .646 Marianini on idiopathic and sym- pathetic contractions of "the muscles and nerves . . .347 Majendie on the curative effects of Galvanism in amaurosis . .347 Matteucci on the galvanometer . 329 his electro-physiological re- searches .... on the muscular electric cur- rent 423 his muscular electric pile . 42y on the current proper of the frog 433 on the physiological pheno- mena produced by a muscle dur- ing contraction .... 440 on the influence of the elec- tric current on living or reeentlv killed animals . 443 on the effects of poisons comparison of the effects pro- duced by the electric current and other stimulants on the relation between the electric force, and the unknown force of the nervous system . 457 on the electric phenomena of the torpedo .... 467 his apparatus for the develop- ment induced . . . .714 on the phenomena of the earth circuit 773 Mayer and Marten on the law of magnetic force . . . .579 Melloni and Xobili, their thermo- pile 486 Michel's method of making artificial magnets 553 Morichini on the magne: power of light . . . .532 Morse, his electric telegraph . 754 Muschenbock, his account of the electric shock .... 4 on the laws of magnetic force . . - . " ' j 908 INDEX TO AUTIIOKITIES. 287 378 705 728 328 Page Napier, his observations on the Electricity produced during the drying of bleached goods . . 78 on voltaic reduction of ores . 400 Newton, his electrical discoveries . 2 on the laws of magnetic force 579 Nicholson and Carlisle, their dis- covery of the chemical power of the voltaic pile . . . .353 Noad, his experiments on electro- culture 160 his atmospheric exploring apparatus . . . .172 his experiments with a water battery . . . . 259 on the peculiar voltaic condi- tions of iron .... his experiments on electro- crystallization .... on secondary or induced cur- rents his coil machine for medical use Nobili, his galvanometer . his researches in animal Elec- tricity 426 Nott, his illustration of the aurora borealis 235 (Epinus, his theory of Electricity . 1 3 his theory of Magnetism . 526 Oersted, his discovery of Electro- magnetism . . . 325, 642 Ohm, his law . . . .301 his determination of the in- tensity of the hydro-electric cur- rent 304 on the conducting powers of metals 323 Oppian speaks of the electrical powers of the torpedo . . 2 Otto Guericke, his electrical expe- riments . . . . .2 Page, his electro-magnetic engine . 680 on musical notes produced during the magnetization and demagnetization of iron . .672 Parry, Captain, his description of the aurora borealis . . .227 Pasley, Lieut.-General, his destruc- tion of the Round-Down Cliff . 311 Pattinson, his experiments on the Electricity of effluent eteam . 91 Pearson, Dr., on the treatment of epilepsy by Galvanism . .344 Peclet, his condenser . . 65 Peltier on the theory of the hydro- electric machine . . . 97 his induction electrometer . 192 on the source of astmospheric Electricity 195 on the effects of a tornado . 219 Peltier, his thermo-pile . .488 Petrequin on the cure of aneurism by Galvanism . . . .344 Philip, Dr. Wilson, on the relation between voltaic Electricity and the phenomena of life . .341 on the treatment of asthma by Galvanism . . . .344 Pine, his experiments on electro- vegetation 159 Pliny speaks of the property of amber and of the lapis lyncurius to attract light substances when rubbed 2 Pliicker, his apparatus for illus- trating the phenomena of Dia- magnetism. . . . .811 his researches on magne-crys- tallic phenomena . . .818 Poggendorff on the cause of the intensity of the zinc-iron circuit 285 on the theory of the voltaic pile 503 on Ruhmkorff's induction apparatus .... - 731 Poisson, his mathematical investi- gation of Electricity . . .15 Pouillet, his experiments on electro- vegetation . . . .159 on the conducting powers of metals 324 on the magnetic metals . 535 Pravaz on the application of Galva- nism as an escharotic. . .345 Priestley on the fracture of Leyden jars 113 Pulvermacher, his chain battery . 346 Quet on the induction spark in different vacua . . . .739 Quetelet, his observations with Peltier's induction electrometer 194 Radford, his electro-magnet . .699 Read, his atmospheric exploring apparatus . . . . .171 Reiser, his electric telegraph . 748 Reiss on the conducting powers of metals 324 on induced currents . .713 Richmann killed by atmospheric Electricity 10 his experiments for demon- strating the equality of the Electricity on the two surfaces of the Leyden jar . . . 135 Ritchie, his galvanometer . .326 on the voltaic reduction of ores 399 his rotating electro-magnets . 673 on the magneto-electric spark 696 Ritter, his speculations on Magne- tism and Electricity . . .642 INDEX TO AUTHORITIES. 909 Roberts on the cause of the inten- sity of the zinc-iron circuit . 285 his galvanic battery . .286 his electro-magnet . . 668 Roget, his electro-magnetic spiral 656 his vertical spiral coil galva- nometer . . . . . 657 Romas, his electrical kite experi- ments ..... Ronalds, his atmospheric exploring apparatus . . his atmospheric electrical observations at Kew . his electric telegraph . Ruhmkorff' s induction apparatus . sparks and shocks from commutator of interrupting apparatus of induction apparatus the condenser ..... his induction coil . 10 185 185 748 728 728 729 729 730 742 621 Sabine, his researches in terrestrial Magnetism Salva, his electric telegraph . .748 Sarlandiere on the medical appli- cation of Galvanism . 346 Saussure, his electrical experi- ments Schoenbein on ozone his experiments with the gymuotus Scoresby's method of magnetizing steel bars 561 his magnetical investigations 572 16 409 480 his investigations in terres- trial Magnetism. on the construction of com- pass needles .... on the variation of the com- 587 594 pass in iron vessels . . 601 Seebeck, his discovery of thermo- p:iectricity 484 on the effect of antimony in destroying the polarity of iron . 537 Shepherd, his electro-magnetic clock 802 Singer, his electroscope . . 28 Smee, his galvanic batteries . .274 Soemmeriug, his electric telegraph 751 Somerville, Mrs., on the magneti- zing power of light . . . 533 Spencer, his original experiment in electrography Steinheil, his electric telegraph Stringfellow, his electroscope his pocket battery for medical purposes ..... Sturgeon, his electrical kite experi- ments his observations during a thunder-storm .... his galvanic battery 403 753 30 346 183 184 283 Page Taylor, his electro-magnetic engine 677 Thales first describes the electrical properties of amber ... 2 Theophrastus speaks of the pro- perty of amber and of the lapis lyncurius to attract light sub- stances when rubbed ... 2 Thomson, his description of a thunder-storm . . . .198 Tilland, Captain, on marine volca- noes 218 Tyndall, his thermo-electric experi- ments 489 his investigation of the laws of Magnetism . . . .583 and Knoblauch on mague- crystallic phenomena. . .820 on diamagnetic polarity . 831 his poly -magnet . . .841 Ure, Dr., his experiments on the body of a recently executed criminal 338 Valli, his experiments in electro- physiology . . . 426 Van der Voort, his tliermo-pile . 488 Van Melsen, his galvanic battery . 267 Van Marum, his large electrical machine ...... 74 Van Swinden on the analogy be- tween electric and magnetic forces 641 Volta, his experiments on the Elec- tricity of the globe . . .16 his condenser . . .64 his fundamental experiment. 246 his original pile . . .252 his repetition of Galvaiii's ex- periments . 424 his discovery of the pile . 425 Walker, his experiments on the Electricity developed during the manufacture of paper his experiments with the Poly- technic hydro-electric machine . on the influence of the aurora borealis on the needles of the electric telegraph compares electric light to lightning Walsh, his experiments with the 77 97 240 464 torpedo Wartmann on the Electricity of plants ..... 481 Watkins, his thermo-pile . .488 Watson, his electrical researches . 5 Weber on diamagnetic polarity . 827 We ekes, his experiments on the conducting power of vegetables 158 his experiments on electro- vegetation . . . . . 1 60 3 TST 910 INDEX TO AUTHORITIES. Page Weekes, his atmospheric exploring apparatus 179 Whea,tstone,his experiments on the velocity of Electricity . .115 his rheostat for measuring the resistances of the hydro- electric current .... 305 his electro-magnetic engine . 683 his electro-magnetic clocks . 794 Wheeler, his electrical discoveries . 3 Wilson discovers the lateral shock 5 Winkler introduces the cushion for the electrical machine . . 3 his description of the electric shock 4 Page Wollaston, his galvanic battery . 2r. Noad has made the best use of his time in the interim, and he now gives to the public a volume which is really a valuable compilation of the principal researches in electricity." Literary Gazette. "A work wherein the principles and laws of Electricity are clearly explained and fully developed, and by which an acquaintance with this science is placed within the reach of the most ordinary capacity ; such is the book before us, which amplitude of detail, clearness of definition, easy diction, and avoidance of too abstruse technicality, combine to render com- prehensible as well as useful." Chemist. " These Lectures are written with much perspicuity, vigour, and correct- ness, and the illustrations apt and familiar ; it is a much needed, admirably designed, and carefully executed volume, and we can unhesitatingly characterize it as one of the most excellent text-books that have issued from our London press." British Friend of India Magazine and Indian Review. " The work before us is a new and greatly enlarged edition of the pre- viously published Lectures of the author, with a large accumulation of valuable facts from all the most important works on the subject, so arranged as to give a popular view of this most interesting science. The author has done ample justice to the subject. The Lectures are all arranged in a con- venient number of paragraphs, a plan which greatly facilitates reference. The first lecture commences with an historical sketch of Electricity, and proceeds in an elementary manner through all the gradations of Electricity atmospheric and voltaic, magnetism and electro-magnetism, concluding with magneto-, and thermo-Electricity. The experiments are illustrated by nearly three hundred woodcuts, and from the easy description of their per- formance the work is most valuable for the student and amateur, while it forms a most convenient text-book for the man of science." Mining Journal. " Let our readers imagine magnetism, electro-magnetism, and magneto-, and thermo-Electricity, equally well enriched with new things as well as with the good old standard facts that have borne the test of time, and they have the general character which pervades the whole." Electrical Magazine* " This is a most complete treatise, which does very great credit to the scientific acquirements and to the perseverance of the author. The addi- tions which have been made to our knowlege of Electricity during the last few years, have been so varied and important, that Dr. Noad's attempt to analyze the whole must have been a most arduous one, one which for its accomplishment required all the talent and information he undoubtedly possesses." The Lancet. u To those of our readers who wish for information on the interesting subject of Electrical phenomena, we would refer to Dr. H. M. Noad's- valuable l Lectures on Electricity, Galvanism, : : zi_-j : ' -. : r : i: i; :::vr; .1 _ : . . DEMP5EY, G. D. THE PRACTICAL RAILWAY DOWLIXG, C. H. A SERIES OF METRIC TABLES, in -I -"^'--i iri :.- - ,:.! --:- :--- :: -~-i ontheContiaeBL By C. H. DOWLESS, OK DOWSIXG, TTM. THE TIMBER MERCHANTS A3TD BUILDEKS COMPAXIOX, and Battens, of all BKS, from One to a" - - - -"_ - - .:- 7: 1:- : 17: : :. -.:_ . .'.- 7.,: :: >: .: . _i -.L -.:- . : r - ; . : - -r . . . -e ;.-....- -^ -. --_ - - . ----- :.., :- 1 :-..:.: :-.:'': :-^ : r. . - .: , ~ -.1 - ."i.-ril^ - 1 I :--- -7 --- <;iflrl. :: - ^ :: ii~.' {:''-'- - -'- -- "- -"-;- -= --- -- -- - - - f -.,::. :!:'::.., .: ^.-^-iL_. r-rr L^-:-^I7:.: ;: .- ,.- :. ^; ._ :_ RY MAX'S OWN LAWYER: \ HAXDY BOOK OF THE PRINCIPLES OF LAW AXD EQUITY. By a BJLRKISZKBL Sixth Edition, much enla of 1867 GflBBkn. 12mo, price -fe. Srf. ^sared bound ia cloth. CampriMi^ the Kigbta and Wnags of tile and Commercial Law, Criauaal Law. Parish Law, Cwmtj Couxt Law, Game Lairs, th Laws of body."- JRdUMfs iffajii^r. -"Tbis is vwk wtMckkn IO^)KM WORKS PUBLISHED BY LOCKWOOD & CO. FAIRBAIRN, WM. IRON ; its History, Properties, and Processes of Manufacture. By WILLIAM FAIRBAIRN, C.E., LL.D., F.R.S., &c. With numerous Woodcuts. Demy 8vo, price 9s. cloth. " A scientific work of the first class, whose chief merit lies in bringing the more important facts connected with iron into a small compass, and within the comprehension and the means of all persons engaged in its manufacture, sale, or use." Mechanic's Magazine. GEAHAM, ALEX. J. S. A MANUAL ON EARTHWORK. By ALEX. J. S. GRAHAM, C.E., Resident Engineer, Forest of Dean Central Railway. With numerous Diagrams, 18mo, 2s. 6d. cloth. " We can cordially recommend the work to the notice of our readers." Building News. " As a really handy hook for reference, we know of no work equal to it ; and the Railway Engi- neers and others employed in the measurement and calculation of earthwork will find a great amount of practical information very admirably arranged, and available for general or rough esti- mates, as well as for the more exact calculations required in the Engineers' Offices." Artizan. GRANDY, R. E. THE TIMBER IMPORTER'S, TIMBER MERCHANT'S, and BUILDER'S STANDARD GUIDE. By RICHARD E. GRANDY, 12mo. price 7s. 6d. cloth. Comprising For the Timber Importer and Merchant / An Analysis of Deal Standards, Home and Foreign, with comparative Values and Tabular Arrange- ments for Fixing Nett Landed Cost on Baltic and North American Deals including all intermediate Expenses, Freight, Insurance, Duty, &c. ; also Practical Methods and Examples for Reduction, embracing Solid, Lineal, Numerical and Superficial Quantities, Prices, &c. A Complete Exposition of the Square Timber Trade, North American and Baltic ; with Percentage Differences on String, Caliper, Cubic, and Running Measurements. Also Tabular Matter, with Nett Landed Cost, including all intermediate Expenses, constructed on the data of a progressive Rate for First Cost in Dollars, Currency, or Sterling. American and Baltic Lathwood, Staves, &c., with particulars of Freights, Duties, Expenses, and Measurements, United States Exchange and Canadian Currency ; with Examples, for the Retailer and Huilder : Copious Information, with Tables setting forth Nett Cost of Mate- rial and Workmanship to Builder or Manufacturer on Flooring, Sheeting, Joisting, Skirting; Doors, Windows, Architraves, &c., per Square, Piece, Superficial or Lineal Measurement, Brickwork, Stonework, Excavations, Slating, Tiling, Metal Pillars, Lead, Zinc, Corrugated Iron, Koofing Felt, Cisterns, Painting, Papering, Builders' Ironmongery, &c. "This very useful volume." Builder. 'The tables comprised in this work must afford material assistance to the timber merchant" Mechanic's Magazine. "A vast number of very valuable tables for the timber importer and consumer." Practical Mechanic's Journal. " A handy guide to the timber trade. The information is very complete." Dublin Builder. " Everything it pretends to be : built up gradually, it leads one from a forest to a trenail, and throws in, as a makeweight, a host of material concerning bricks, columns, cisterns, &c. all that the class to whom it appeals requires." English Mechanic. " The only difficulty we have is as to what is NOT in its pages. What we have tested of the contents, taken at random, is invariably correct." Illustrated Builder's Journal. GRANTHAM, JOHN, C.E. and NAVAL ARCHITECT. ON IRON SHIP-BUILDING, with Practical Examples and Details, in twenty-four plates, together with separate text containing Descriptions, Expla- nations, and General Remarks, for the use of Ship-owners and Ship-builders. By JOHN GRANTHAM, C.E., Consulting Engineer and Naval Architect. The plates of the present Work have been prepared, and the subjects drawn, in elevation, plan, and detail, to a scale useful for immediate practice, in a folio size, with figured dimensions, and accompanied by a small Volume of text (which may be had separately). \* A New Edition of this work, very considerably enlarged, with upwards of twenty new plates, making in all nearly forty, is in preparation, and will be ready very shortly. WORKS PUBLISHED BY LOCK WOOD & CO. GREGOKY, Dr. OLINTHUS. MATHEMATICS for PRACTICAL MEN ; being a Common Place Book of Pure and Mixed Mathematics, designed chiefly for the use of Civil Engineers, Architects, and Surveyors. By OLINTHUS GREGORY, LL.D., F.R.A.S. Enlarged by HENRY LAW, Civil Engineer. Fourth Edition, carefully revised and cor- rected by J. R. YOUNG, formerly Professor of Mathematics, Belfast College ; Author of "A Course of Mathematics," &c. With 13 plates, medium 8vo, II. Is. cloth. CONTENTS. PART I. PURE MATHEMATICS. Chapter I. ARITHMETIC. 1. Definition of nota- tion 2. Addition of whole numbers 3. Sub- traction of whole numbers 4. Multiplication of whole numbers 5. Division of whole num- bers proof of the first four rules of arithme- tic 5. Vulgar fractions ; reduction of vulgar fractions : addition and subtraction of vulgar fractions ; multiplication and division of viil- gar fractions 7. Decimal fractions ; reduction of decimals ; addition and subtraction of deci- mals ; multiplication and division of decimals 8. Complex fractions vised in the arts and commerce ; reduction ; addition ; subtraction and multiplication ; division ; duodecimals 9. Powers and roots ; evolution 10. Propor- tion ; rule of three ; determination of ratios 11. Logarithmic arithmetic ; use of the tables ; multiplication and division by logarithms ; proportion, or the rule of three by logarithms ; evolution and involution by logarithms 12. Properties of numbers. Chap. II. ALGEBRA. 1. Definitions and notation 2. Addition and subtraction 3. Multiplica- tion 4. Division 5. Involution 6. Evolution 7. Surds ; reduction ; addition, subtraction, and multiplication ; division, involution, and evolution 8. Simple equations ; extermina- tion ; solution of general problems ; 9. Quad- ratic equations 10. Equations in general 11. Progression ; arithmetical progression ; geo- metrical progression 12. Fractional and nega- tive exponents 13. Logarithms 14. Compu- tation of formula;. Chap. III. GEOMETRY. 1. Definition 2. Of angles and right lines, and their rectangles 3. Of triangles 4. Of quadrilaterals and poly- gons 5. Of the circle, and inscribed and cir- cumscribed figures 0. Of planes and solids 7. Practical Geometry. Chap. IV. MENSURATION. 1. Weights and Mea- sures i. Measures of length ; ii. Measures of surface ; iii. Measures of solidity and capacity ; iv. Measure of weight ; v. Angular measure ; vi. Measure of time ; comparison of English and French weights and measures 2. Mensu- ration of superficies ?,. Mensuration of solids. Chap. V. TRIGONOMETRY. 1. Definitions and trigonometrical formulae 2. Trigonometrical tables 3. General propositions 4. Solution of the cases of plane triangles ; right-angled plane triangles 5. On the application of trigo- nometry to measuring heights and distances ; determination of heights and distances by approximate mechanical methods. Chap. VI. CONIC SECTIONS. 1. Definitions 2. Properties of the ellipse ; problems relating to the ellipse 3. Properties of the hyperbola ; problems relating to the hyperbola 4. Pro- perties of the parabola ; problems relating to the parabola. Chap. VII. PROPERTIES OF CURVES. 1. Defi- nitions 2. The conchoid 3. The cissoid 4. The cycloid and epicycloid 5. The quadratrix 6. The catenary ; tables of relations of cate- narian curves. PART II. MIXED MATHEMATICS. Chapter I. MECHANICS IN GENERAL. Chap. II. STATICS. 1. Statical equilibrium 2. Centre of gravity 3. General application of the principles of statics to the equilibrium of structures ; equilibrium of piers or abutments ; pressure of earth against walls ; thickness of walls ; equilibrium of polygons ; stability of arches ; equilibrium of suspension bridges. Chap. III. DYNAMICS. 1. General definitions 2. On the general laws of uniform and vari- able motion ; motion uniformly accelerated ; motion over a fixed pulley ; motion on inclined planes ; motion of bodies under the action of gravity 3. Motions about a fixed centre, or axis ; centres of oscillation and percussion ; simple and compound pendulums ; centre of gyration, and the principles of rotation ; cen- tral forces ; inquiries connected with rotation and central forces 4. Percussion or collision of bodies in motion 5. On the mechanical powers ; levers ; wheel and axle ; pulley ; inclined plane ; wedge and screw. Chap. IV. HYDROSTATICS. 1. General defini- tions 2. Pressure and equilibrium of non- elastic fluids 3. Floating bodies 4. Specific gravities 5. On capillary attraction. Chap. V. HYDRODYNAMICS. 1. Motion and efflu- ence of liquids 2. Motion of water in conduit pipes and open canals, over weirs, &c. ; veloci- ties of rivers 3. Contrivances to measure the velocity of running waters. Chap. VI. PNEUMATICS. 1. Weight and equili- brium of air and elastic fluids 2. Machines for raising water by the pressure, of the atmosphere 3. Force of the wind. Chap. VII. MECHANICAL AGENTS. 1. Water as a mechanical agent 2. Air as a mechanical agent ; Coulomb's experiments 3. Mecha- nical agents depending upon heat ; the steam engine ; table of uressure and temperature of steam; general description of the mode of action of the steam engine ; theory of the steam engine ; description of the various kinds of engines, and the formulae for calcu- lating their power; practical application of the foregoing formula; 4. Animal strength as a mechanical agent. Chap. VIII. STRENGTH OF MATERIALS. 1. Re- sults of experiments and principles upon which they should be practically applied 2. Strength of materials to resist tensile and crushing strains; strength of columns 3. Elasticity and elongation of bodies subjected to a crushing or tensile strain 4. On the strength of materials subjected to a transverse strain ; longitudinal form of beam of uniform strength ; transverse strength of other materials than cast iron ; the strength of beams according to the manner in which the load is distributed 5. Elasticity of bodies subjected to a transverse strain 6. Strength of materials to resist torsion. APPENDIX OF COPIOUS LOGARITHMIC AND OTHER TABLES, &e. &c. 10 WORKS PUBLISHED BY LOCKWOOD & CO. HASKOLL, W. D., CIVIL ENGINEER. EXAMPLES OF BRIDGE AND VIADUCT CONSTRUCTION OF MASONRY, TIMBER, AND IRON ; consisting of 46 Plates from the Con- tract Drawings or Admeasurements of select Works. By W. DAVIS HASKOLL, C.E. Second Edition, with the addition of 554 Estimates, and the Practice of Setting out Works, with 6 pages of Diagrams. Imp. 4to, price 21. 12s. 6d. half morocco. " One of the very few works extant descending to the level of ordinary routine, and treating on the common every-day practice of the railway engineer. .... A work of the present nature by a man of Mr. Haskoll's experience, must prove invaluable to hundreds. The tables of esti- mates appended to this edition will considerably enhance its value." Engineering, Oct. 18, 1867. HAWKINGS, JAMES. THE TRADESMAN'S GUIDE to SUPERFICIAL MEASUREMENT. Tables calculated from 1 to 200 inches in length, by 1 to 108 inches in breadth. For Architects, Surveyors, Engineers, Timber Merchants, Builders, Carpenters, Upholsterers, Coach Makers, Looking and Crown Glass Dealers, Painters, Stonemasons, &c. By JAMES HAWKINGS. Fcp. 3s. 6d. cloth. HUDSON, K., CIVIL ENGINEER. THE LAND VALUER'S BEST ASSISTANT : being Tables, on a very much improved Plan, for Calculating the Value of Estates. To which are added, Tables for reducing Scotch, Irish, and Provincial Customary Acres to Statute Measure; also, Tables of Square Measure, and of the various Dimensions of an Acre in Perches and Yards, by which the Contents of any Plot of Ground may be ascertained without the expense of a regular Survey ; Miscellaneous Tables, &c. By R. HUDSON, Civil Engineer. New Edition, with Additions and Corrections, price 4s., strongly bound. ( ' This new edition includes tables for ascertaining- the value of leases for any term of years ; and for showing how to layout plots of ground of certain acres in forms, square, round, &c., with valuable rules for ascertaining the probable worth of standing timber to any amount ; and is of incalculable value to the country gentleman and professional man." Farmer'' K Journal. HUMBEB, WM. A COMPLETE and PRACTICAL TREATISE on CAST and WROUGHT IRON BRIDGE CONSTRUCTION, including Iron Foundations. In Three Parts Theoretical, Practical, and Descriptive. 13y WILLIAM HUAIBEE, Assoc. Inst. C.E., and M. Inst. M.E. Second Edition, in 2 Vols. imp. 4to, with 95 Double Plates and 237 pages of Text, price 61. 16s. 6d., half-bound in morocco. "A very valuable contribution to the standard literature of civil engineering. In addition to elevations', plans, and sections, large scale details ure given, which very much enhance the instruc- tive worth of these illustrations. No engineer would willingly be without so valuable a fund of information." Civil Engineer and Architect's Journal. HUMBER, WM. A RECORD OF THE PROGRESS OF MODERN ENGINEERING, 1863; comprising Civil, Mechanical, Marine, Hydraulic, Railway, Bridge, and other Engineering Works. With Essays and Reviews. Edited by WILLIAM HUMBER, Assoc. Inst. C.E., and Memb. Inst. M.E., Author of " A Complete and Practical Treatise on Cast and Wrought Iron Bridge Construction." Imperial 4to. Illustrated with 3G Double Plates, and a Photographic Portrait of John Hawkshaw, Esq., F.R.S., late President of the Institution of Civil Engineers. Price Zl. 3s., half-bound in morocco. "Mr. Humber has now completed his first Annual Volume. It consists of a goodly number of plates of large size, principally relating to railway bridges, roofs, station buildings, and works of a similar character." Artizan, Feb., 1864. . ' ' Handsomely lithographed and printed, it will find favour with many who desire to preserve in a permanent form copies of the plans and specifications prepared for the guidance of the contractors for many important engineering works." Engineer. ** This Work will bo continued annually. WORKS PUBLISHED BY LOCKWOOD & CO. 11 INSTANT RECKONER, THE, Showing the Value of any Quantity of Goods, including Fractional Parts of a Pound Weight, at any price from One Farthing to Twenty Shillings : with an Introduction, embracing copious Notes of Coins, Weights, Measures, and other Commercial and Useful Information ; and an Appendix containing Tables of Interest, Salaries, Commission, &c. 24mo, Is. b'rf. cloth ; or 2s. leather. MURRAY, ANDREW AND ROBERT. SHIP-BUILDING IN IRON AND WOOD. By ANDREW MURRAY, M.I.C.E., Chief Engineer and Inspector of Machinery of H. M.'s Dockyard, Portsmouth; and STEAM SHIPS, by ROBERT MURRAY, C.E., Engineer Surveyor to the Board of Trade. Second Edition, in 1 vol. 4to, with 28 Plates and numerous Woodcuts, price 14s. cloth. " Indispensable in the office of the naval architect." Practical Mechanic's Journal. "Ought to be in the hands of every shipbuilder or shipwright." Sunderland Herald. NOAD, HENRY M., PH.D., F.C.S. A MANUAL OF ELECTRICITY; including Galvanism, Magnetism, Dia- magnetism, Electro-Dynamics, Magno-Electricity, and the Electric Telegraph. By HENRY M. NOAD, PH.D., F.C.S. , Lecturer on Chemistry at St. George's Hospital. Fourth Edition, entirely re-written. Illustrated by 500 woodcuts. In two Parts. Part I. ELECTRICITY and GALVANISM. Part II. MAGNETISM and the ELECTRIC TELEGRAPH. Complete in 1 vol. 8vo, II. 4s. cloth. N.B. THE SECOND PART may be had separately, price 10s. d. cloth. "This publication fully bears out its title of Manual.' It discusses in a satisfactory mann r electricity, frictional and voltaic, thermo-electricity, and electro-physiology. To diffuse correct views of electrical science, to make known the laws by which this mysterious force is regulated, which is the intention of the author, is an important task." Athencmm. "It is worthy of a place in the library of every public institution, and we have no doubt it will be deservedly patronised by the scientific community." Mining Journal. NEVILLE, JOHN. HYDRAULIC TABLES, CO-EFFICIENTS, and FORMULAE for finding the Discharge of Water from Orifices, Notches, Weirs, Pipes, and Rivers, By JOHN NEVILLE, Civil Engineer, M.R.I.A. Second Edition, with Extensive Additions, New Formula), Tables, and General Information on Rain-fall, Catchment-Basins, Drainage, Sewerage, Water Supply for Towns and Mill Power. With numerous Woodcuts, 8vo, 16s. cloth. NORMANDY, A. THE COMMERCIAL HANDBOOK OF CHEMICAL ANALYSIS; or Practical Instructions for the determination of the Intrinsic or Commercial Value of substances used in Manufactures, in Trades, and in the Arts. By A. NORMANDY, Author of " Practical Introduction to Rose's Chemistry," and Editor of Rose's " Treatise of Chemical Analysis." Illustrated with woodcuts. Second and cheaper Edition, post 8vo, 9s. cloth. " We recommend this book to the careful perusal of every one ; it may be truly affirmed to be of universal interest." Medical Times. " The author has produced a volume of surpassing 1 interest, in which he describes the character and properties of 400 different articles of commerce, the substances by which they are too frequently adulterated, and the means of their detection." Mining Journal. PYNE, GEORGE. PRACTICAL RULES ON DRAWING FOR THE OPERATIVE BUILDER AND YOUNG STUDENT IN ARCHITECTURE. By GEORGE PYNE, Author of a Rudimentary Treatise on Perspective for Beginners. With 1 4 plates, 4to, 7s. 3d. boards. CONTEXTS. 1. Practical Rules on Drawing, Outlines. 2. Ditto, the Grecian and Roman Orders. 3. Practical Rules on Drawing, Perspective. 4. Practical Rules 011 Light and Shade. 5. Practical Rules on Colour. ' &c. &c. 12 WORKS PUBLISHED BY LOCKVVOOD & CO. HYDE, EDWARD. A GENERAL TEXT BOOK FOR ARCHITECTS, ENGINEERS, SUR- VEYORS, SOLICITORS, AUCTIONEERS, LAND AGENTS, AND STEWARDS, in all their several and varied professional occupations; and for the assistance and guidance of Country Gentlemen and others engaged in the Transfer, Management, or Improvement of Landed Property. Together with examples of Villas and Country Houses. By EDWARD RYDE, Civil Engineer and Land Surveyor. To which are added several chapters on Agriculture and Landed Property, by Professor DONALDSON, Author of several Works on Agriculture. With numez-ous engravings, in 1 thick vol. 8vo, price II. 8s. cloth. CONTENTS. Chap. I. ARITHMETIC. Chap. II. PLANE AND SOLID GEOMETRY. Chap. III. MENSURATION. Chap. IV. TRIGONOMETRY. Chap. V. CONIC SECTIONS. Chap. VI. LAND MEASURING. Including Table of Decimals of an Arc Table of Land Mea- sure, by dimensions taken in yards. Chap. VII. LAND SURVEYING. 1. Parish and Estate Surveying 2. Trigonometrical Survey ing 3. Traverse Surveying 4. Field Instru- ments the Prismatic Compass; the Box Sextant ; the Theodolite. Chap. VIII. LEVELLING. Levelling Instru- ments. The Spirit Level ; the Y Level ; Troughton's Level; Mr. Gravatt's Level; Levelling Staves Examples in Levelling. Chap. IX. PLOTTING. Embracing, the Circular Protractor the T Square and Semicircular Protractor Plotting Sections. Chap. X. COMPUTATION OF AREAS. The Pedi- ometer the Computing Scale Computing Tables. Chap. XI. COPYING MAPS. Including a de- scription of the Pentagraph. Chap. XII. RAILWAY SURVEYING. 1. Explora- tion and Trial Levels ; Standing Orders -2. Proceedings subsequent to the Passing of the Act; Tables for Setting out Curves; Tables for Setting ovit Slopes ; Tables of Relative Gradients ; Specification of Works to be exe- cuted in the Construction of a Railway ; Form of Tender. Chap. XIII. COLONIAL SURVEYING. Chap. XIV. HYDRAULICS IN CONNECTION WITH DRAINAGE, SEWERAGE, AND WATER SUPPLY with Synopsis of Ryde's Hydraulic Tables Specifications, Iron Pipes and Cast-iron Pipes and Castings ; Stone Ware Drain Pipes ; Pipe Laying, Reservoir. Chap. XV. TIMBER MEASURING. Including Timber Tables, Solid Measure, Unequal Sided Timber ; Superficial Measure. Chap. XVI. ARTIFICERS' WORK. 1. Bricklayers' and Excavators' 2. Slaters' 3. Carpenters' and Joiners' 4. Sawyers' 5. Stonemasons' t>. Plasterers' 7. Ironmongers' 8. Painters' 9. Glaziers' 10. Paper Hangers'. Chap. XVII. VALUATION OF ESTATES. With Tables for the Purchasing of Freehold, Copy- hold, or Leasehold Estates, Annuities, and Advowsons, and for renewing Leases for Terms of Years certain, and for Lives. Chap. XVIII. VALUATION OF TILLAGE AND TENANT RIGHT. With Tables for Measuring and Valuing Hay Ricks. Chap. XIX. VALUATION OF PARISHES. Chap. XX. BUILDERS' PRICES. 1. Carpenters' and Joiners' 2. Masons' 3. Bricklayers' 4. Plasterers' 5. Ironmongers' 6. Drainers' 7. Plumbers' 8. Painters' 9. Paper Hangers' and Decorators' 10. Glaziers' 11. Zinc Workers' 12. Coppersmiths' 13. Wire Workers'. Chap. XXI. DILAPIDATIONS AND NUISANCES. 1. General Definitions 2. Dilapidations by Tenants for Life and Years 3. Ditto by Mort- gagee or Mortgagor 4. Ditto of Party Walls and Fences 5. Ditto of Highways and Bridges 6. Nuisances. Chap. XXII. THE LAW RELATING TO APPRAISERS AND AUCTIONEERS. 1. The Law Relating tu Appraisements 2. The Law of Auction. Chap. XXIII. LANDLORD AND TENANT. 1. Agreements and Leases 2. Notice to Quit 3. Distress L Recovery of Possession. Chap. XXIV. TABLES. Of Natural Sines and Cosines For Reducing Links into Feet Decimals of a Pound Sterling. Chap. XXV. STAMP LAWS. Stamp Duties Customs' Duties. EXAMPLES OF VILLAS AND COUNTRY Hoi SES. ON LANDED PROPERTY. BY PROFESSOR DONALDSON. Chap. I. Landlord and Tenant Their Position and Connections. Chap. II. Lease of Land, Conditions and Re- strictions ; Choice of Tenant, and Assiguati< .11 of the Deed. Chap. III. Cultivation of Land, and Rotation of Crops. Chap. IV. Buildings necessary on Cultivated Lands Dwelling Houses, Farmeries, and Cottages for Labourers. Chap. V. Laying out Farms, Roads, Fences, and Gates. Chap. VI. Plantations, Young and Old Timber. Chap. VII. Meadows and Embankments, Beds of Rivers, Water Courses, and Flooded Grounds, hap. VIII. Land Draining, Opened and Co- vered Plan, Execution, and Arrangement between Landlord and Tenant. Chap. IX. Minerals, Working and Value. Chap. X. Expenses of an Estate Regulations of Disbursements and relation of the appro- priate Expenditures. Chap. XI. Valuation of Landed Property ; of the Soil, of Houses, of Woods, of Minerals, of Manorial Rights, of Royalties, and of Fee Farm Rents. Chap. XII. Land Steward and Farm Bailiff ; Qualifications and Duties. Chap. XIII. Manor Bailiff, Woodreevc, Gar- dener, and Gamekeeper Their Position and Duties. Chap. XIV. Fixed Days of Audit Half- Yearly Payments of Rents Form of Notices, Re- ceipts, and of Cash Books, General Map of Estates, and of each separate Farm Con- cluding Observations. WORKS PUBLISHED BY LOCKWOOD & CO. 13 RICHAKDSON, WM. PACKING-CASE TABLES ; showing the number of Superficial Feet in Boxes or Packing-Cases, from six inches square and upwards. Compiled by WILLIAM RICHARDSON, Accountant, Author of " The Calculator, or, Timber Merchants' and Builders' Guide." Oblong 4to, cloth, price 3s. 6d. " Makers and users of packing-cases. will find these labour-saving tables invaluable. By their aid the number of superficial feet in a case of any dimensions can be ascertained in a moment." RITCHIE, ROBT., C.E. A TREATISE ON VENTILATION, NATURAL AND ARTIFICIAL. By ROBERT RITCHIE, C.E., Associate of the Institution of Civil Engineers, London ; Past Vice-President of the Royal Scottish Society of Arts ; Author of "Rail ways, their Rise, Progress, and Construction ;" " The Farm Engi- neer, with' Remarks on the Ventilation of Farm Buildings," and various Prize Essays on the Ventilation of Factories, Ships, &c., &c. With numerous plates and woodcuts. 8vo, 8s. 6d. cloth. " An interesting and extremely useful volume, in which the subject of ventilation is completely and exhaustively treated." Mining Journal. " This must continue to be for some time the textbook upon one of the chief difficulties of domestic architectural construction and of social hygienics." Lancet. " Will be found exceedingly useful as a book of reference by all those interested in the subject of ventilation, whether applied to public or private buildings, mines, or ships." Artizan. SHEILD, F. W. STRAINS ON STRUCTURES OF IRON WORK ; with Practical Remarks on Iron Construction. Second Edition, with 5 plates. Royal 8vo, price 5s. t cloth. SIMMS, F. W., on LEVELLING. A TREATISE on the PRINCIPLES and PRACTICE OF LEVELLING, showing its application to purposes of Railway and Civil Engineering, in the Construction of Roads, with Mr. TELFORD'S Rules for the same. By FREDERICK W. SIMMS, F.G.S., M. lust. C.E. Fifth edition, revised and corrected with the odditiou of Mr. LAW'S Practical Examples for setting out Railway Curves, and Mr. TRAUTWINE'S Field Practice of Laying out Circular Curves. With 7 plates and numerous woodcuts, Svo, 8s. 6d. cloth. N.B. Trautwine on Laying out Circular Curves may be had separately, price 5s. SIMMS, F. W., ON TUNNELLING. PRACTICAL TUNNELLING ; Explaining in Detail the Setting Out of the Works ; Shaft Sinking and Heading Driving ; ranging the Lines and Levelling under Ground; Sub-Excavating, Timbering, and the Construction of the Brickwork of Tunnels ; with the amount of Labour required for, and the Cost of the Various Portions of the Work. By FREDK. W. SIMMS, F.R.A.S., F.G.S., M. Ins. C.E. Author of " A Treatise on the Principles and Practice of Levelling," &c. &c. Second edition, revised by W. DAVIS HASKOLL, Civil Engineer, Author of " The Engineer's Field Book," &c. &c. With 16 large folding plates, and numerous woodcuts, imperial Svo, II. Is. cloth. SIMMS, F. W. A TREATISE ON THE PRINCIPAL MATHEMATICAL AND DRAWING INSTRUMENTS employed by the Engineer, Architect, and Surveyor. By FREDERICK W. SIMMS, F.G.S., M. Inst. C.E., Author of " Practical Tunnelling,'" &c. &c. Third Edition, with numerous Cuts. 12mo, price 3s. 6d. cloth. STEVENSON, THOS. THE DESIGN AND CONSTRUCTION OF HARBOURS. 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