UC-NRLF 
 
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i vj (,u,rntua wuins vn j. /tcurtmcui unit j:rucncat, science ; 
 AND 
 
 PLACIDO AND JUS TO GENEB, 
 
 Civil Engineers. 
 
 LONDON: 
 
 E. & P. K SPON, 16, BUCKLEBSBIJRY, 
 
 AND ALL BOOKSELLERS. 
 
 OPINIONS OF THE PRESS :- 
 
 "A very useful guide to the Practical Engineer." Civil Engineer <$ Architects' Journal. 
 
 " The object of the Authors seems to have been to afford to the Practical Man the 
 means of investigating for himself the variety of formula from which general rules 
 are deduced ; and the formulae are accompanied and elucidated by practical rules. The 
 problems and examples s^em to have been carefully worked, and we feel satisfied that 
 even well-informed Practical Engineers will derive benefit from the study of a treatise, 
 which appears to be also peculiarly suited to the Student, and the Enquirer." Mining 
 Journal. ^ 
 
 " To the Practical and Scientific Engineer, and to the Assistant Engineer who aspires 
 to pass his examination for Chief, with credit to himself and the service, we can cordially 
 recommend the work." The Nautical Standard. 
 
 " A considerable mass of useful matter is contained in the pages of this book: the 
 association of the Messrs Gener with Mr. Hann in this work was evidently with a view 
 to supply all those practical details which cannot be looked for from the mere theoretic 
 enquirer, but with which actual and constant experience alone can give acquaintance, 
 and iheir labours in this clt'i/ai tment have been attended with considerable success. We 
 may refer especially io a very full and, as far as we know, original investigation of the 
 effects of lap and lead of the Slide, and the pages upon Chimneys.' Mechanics' Magazine. 
 
THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 MRS. PRUDENCE W. KOFOID 
 
 
ELECTRIC SCIENCE; 
 
 ITS HISTORY, PHENOMENA, AND APPLICATIONS. 
 
 F. C. .BAKEWELL, 
 
 AUTHOR OF "NATURAL EVIDENCE OF A FUTURE LIFE," ** PHILOSOPHICAL CONVERSATIONS, 
 
 ESSAYS ON MECHANICAL SCIENCE ; 
 INVENTOR OF THE COPYING ELECTRIC TELEGRAPH, ETC. 
 
 Jllustrateli uritl) upmarts of One fluntircb ttJoob-Cngratmujs, 
 
 LONDON: 
 INGRAM, COOKE, AND CO. 
 
 1853. 
 
PRINTED BY ROBSON, LEVEY, AND FfcANKI/YK, 
 
 Great New Street and Fetter Lane. 
 
PBEPACE. 
 
 THE attention that electricity now commands, by its intimate relations 
 with the other physical sciences and by the important objects to which 
 it is applied, makes it particularly desirable that the student of natural 
 philosophy should have the means of attaining, in a compendious form, a 
 knowledge of the progress of electric science to the present day, and of 
 comprehending its varied phenomena, and the applications of which it has 
 been found capable. With this object in view, the author has endeavoured 
 to set forth clearly, yet concisely, the prominent points in the history of 
 electricity, and to notice and explain all those phenomena which indicate 
 any special attribute of that peculiar force. 
 
 In attempting to comprise all that is important to be known of the 
 history, the phenomena, and the applications of electricity within a single 
 volume, there is considerable risk of producing a mere chronological record 
 and an explanatory catalogue rather than an interesting treatise. When, 
 indeed, it is considered that Priestley's History of Electricity occupies a 
 thick quarto volume though written before the most important sources 
 of electric force had been revealed by Galvani and Yolta, by (Ersted, See- 
 beck, Faraday, and Armstrong it might be supposed that a history which 
 includes those discoveries, and is contained within forty pages, must be 
 only a barren sketch. To afford space for circumstantial illustration and 
 explanatory remarks, attention has been concentrated on the characteristic 
 facts, by the adoption of which course it is hoped that the historical notice 
 of the advancement of electric science will be found interesting as well as 
 instructive. 
 
 As a mere statement of effects would have proved unsatisfactory with- 
 out an explanation of the causes that produce them, such explanations 
 have been given as appeared to the author to afford the clearest insight 
 into the nature of electrical action. Though the Franklinian theory of 
 
 W374419 
 
IV PREFACE. 
 
 the excitement of frictional electricity has been generally adopted, because 
 it is the most simple, and voltaic action has been attributed to chemical 
 agency, theoretical discussions have been avoided as much as possible, 
 lest they might tend to obscure rather than to throw light on the causes 
 of electrical phenomena. In some few instances views have been taken of 
 the action of electric force different from those commonly entertained ; but 
 in such cases the reasons for the departure from received opinions have 
 been fully stated. 
 
 The author is not aware that the many varied inventions for the appli- 
 cation of electric power to the uses of man have been previously described 
 collectively. In noticing them, prominence has been given to those objects 
 that are of the greatest importance ; it having been considered sufficient 
 in appliances of less consequence merely to indicate the mode of operation, 
 and to explain the principles of their action. 
 
 By dividing the consideration of electric science into its history, phe- 
 nomena, and applications, some repetitions have almost unavoidably oc- 
 curred, in order to make each part complete in itself. It is conceived, 
 however, that the advantages attending such an arrangement, by affording 
 a clearer conception of each branch of the subject, more than counter- 
 balance the inconvenience of occasionally going, for a short distance, over 
 the same ground. 
 
 HAVERSTOCK TERRACE, HAMPSTEAD, 
 June 1853. 
 
CONTENTS. 
 
 PART I. 
 
 THE HISTORY OF ELECTRICITY. 
 CHAPTER I. 
 
 PAGE 
 
 First discovery of electric attraction Dr. Gilbert's additions to known elec- 
 trics Curious fallacies of early electricians Invention of the electrical ma- 
 chine Discovery of electric light and repulsion Identity of electricity and 
 lightning suggested Distinction between conducting and non-conducting 
 bodies discovered The two kinds of electricity discovered by Du Fay 
 Sparks from the human body Improvements in electrical machines 
 Igniting power of the electric spark The Ley den jar Extraordinary alarm 
 at the electric shock Exaggerated descriptions of its effects Electrical 
 batteries Dangerous shocks given with them Conducting power of the 
 earth ascertained Franklin's theory of electricity . . . . .9 
 
 CHAPTEK II. 
 
 The identity of lightning and electricity pointed out by Franklin Electricity 
 drawn from the clouds in France Franklin's electric kite Lightning- 
 conductors invented Dangerous experiments with lightning Death of 
 Professor Eichmann Beccaria's experiments on atmospheric electricity 
 Electrical induction discovered The theory of vitreous and resinous 
 electricity revived Measurement of electric forces Inventions of the torsion 
 balance and of the electrophorus Progress of discovery to the end of the 
 eighteenth century .... : V . * "< . 19 
 
 CHAPTER III. 
 
 Discovery of Galvanism, and the circumstances that led to it Galvani's 
 erroneous notions of the exciting cause Volta's investigations Invention 
 of the Voltaic pile Commencement of the science of Voltaic electricity 
 Various Voltaic batteries Theories of their action Investigations by Sir 
 Humphrey Davy Decomposition of the alkalies and earths The experi- 
 ments that led to the discovery founded on a hoax Prodigious Voltaic bat- 
 teries constructed Napoleon Bonaparte's experience of their power Un- 
 successful application of Voltaic electricity by Sir H. Davy . . . .27 
 
 CHAPTER IV. 
 
 Discovery of Electro-magnetism Increase of the force by coils of wire Elec- 
 tro-magnets Tangential action of the force Invention of the Galvano 
 meter Its application to telegraphic purposes Discovery of Magneto-elec- 
 tricity Magneto-electrical machines Thermo-electricity Faraday's ex- 
 perimental researches Introduction of new terms Daniell's constant bat- 
 tery Discovery of the electrotype process Development of electricity 
 from high-pressure steam Present state of electric science . . . .35 
 
VI CONTENTS. 
 
 PAKT II. 
 
 THE PHENOMENA OF ELECTRICITY. 
 CHAPTER V. 
 
 GENERAL PROPERTIES. 
 
 Static and current electricity Electrical excitement by friction Attraction 
 and repulsion Illustrative experiments Electrics and conductors All 
 substances electrics when insulated The opposite kinds of electricity 
 
 Negative and positive electrics changeable Mutual dependence of the 
 two electricities Electrical induction The Electrophorus Influence of 
 conductors on surrounding bodies The Electrometer Various inductive 
 powers of electrics Explanation of all electrical phenomena by induction 
 
 The two theories of electricity . . . 47 
 
 CHAPTER VI. 
 
 DIRECT DEVELOPMENT OF ELECTRICITY. 
 
 Electrical machines; cylinder, plate, and gutta-percha Influence of points 
 Explanation of the cause Electricity confined to exterior surfaces Intensity 
 of machine-excited electricity Inflammation of combustibles by the spark 
 Kesistance of the air Nature of electric discharge Disruptive, brush, and 
 glow discharge Colour of the electric spark * 60 
 
 CHAPTER VII. 
 
 ACCUMULATED ELECTRICITY. 
 
 The Leyden jar Its construction and mode of action the amount of electricity 
 always constant Chain of Leyden jars self-charged The charge in the 
 glass, and not in the coating Charged plate of glass Electrical batteries 
 Intensity of force diminished by extension Residual charge Lateral dis- 
 charge : its cause and effects Distribution of electricity during discharge 
 Universal discharger Lane's discharger Quadrant electrometer . .71 
 
 CHAPTER VIII. 
 
 MISCELLANEOUS PROPERTIES AND EFFECTS. 
 
 The electric shock : its physiological effects Heating power of the electrical 
 battery All electrical effects consequent on resistance The electric light : 
 its instantaneous duration calculated Magnetising and decomposing power 
 of static electricity 78 
 
 CHAPTER IX. 
 
 ATMOSPHERIC ELECTRICITY. 
 
 Beccaria's observations of a thunder-storm Mr. Crosse's apparatus and ex- 
 periments Remarkable phenomena of a thunder-storm Different con- 
 ditions of artificial electricity and lightning Lightning-conductors Sup- 
 posed danger from lateral discharge Various kinds of lightning-conductors 
 Safest place in a thunder-storm Causes of the electrical state of the clouds 
 
 Sheet-lightning and forked-lightning Thunder The aurora borealis . 83 
 
 CHAPTER X. 
 
 ELECTRICITY FROM HIGH-PRESSURE STEAM. 
 
 Steam, an abundant source of electrical excitement Hydro-electrical machine 
 State of the electricity excited by it Combination of quantity and intensity 
 Friction of water the cause of excitement Faraday's experiments on high- 
 pressure steam .* .92 
 
CONTENTS. Vll 
 
 CHAPTER XI. 
 
 EXCITEMENT OF VOLTAIC ELECTRICITY. 
 
 PAGE 
 
 Excitement of electricity by metallic contact and by chemical action Mutual 
 influences of chemical action and electricity Simple Voltaic circle Con- 
 struction of the Voltaic pile Identity of Voltaic and fractional electricity 
 Volta's couronne de tasses Conditions requisite for the excitement of Voltaic 
 electricity Solid and liquid elements of the battery Their actions and re- 
 actions Faraday's hypothesis of conduction through fluids Resistance to 
 the Voltaic current Ohm's formula Local action in batteries Intensity 
 and quantity of electricity considered Their correspondence and difference 95 
 
 CHAPTER XII. 
 
 PHENOMENA OF VOLTAIC ELECTRICITY. 
 
 Different conditions of Frictional and Voltaic electricity The two poles of the 
 battery How to distinguish them Mystification caused by new terms 
 Voltaic action immediate and continuous Its rapid transmission exemplified 
 Resistance of wires to the electric current Heating effects of the Voltaic 
 battery Combustion of carbon Extraordinary physiological effects Con- 
 trivances for giving shocks "Water-batteries Intensity of their action Mr. 
 Crosse's water-battery Cause of the intensity of water-batteries . ? . 109 
 
 CHAPTER XIII. 
 
 SECONDARY CURRENTS. 
 
 The Voltaic current dependent on resistance Induction of secondary currents 
 on making and breaking contact Induction of electricity in a separate wire 
 The direction of secondary currents opposite to primary Faraday's views 
 of the action of induced currents . ' , . 1 1 17 
 
 CHAPTER XIV, 
 
 ELECTRO-CHEMICAL DECOMPOSITION. 
 
 Decomposition of water Transference of the elements through intermediate ves- 
 sels Faraday's hypothesis Infinitesimally small particles acted on Sus- 
 pension of chemical affinity by Voltaic action Supposed identity of chemical 
 affinity and electricity Decomposition of the alkalies Remarkable combus- 
 tion of paper by Voltaic action Decomposition of metallic salts Definite 
 action of electro-chemical force Electro-chemical equivalents Absolute 
 quantity of electricity in bodies The quantity in a grain of water estimated 
 The Voltameter . . ? - - - 120 
 
 CHAPTER xv. 
 
 ELECTRO-MAGNETISM. 
 
 Effect of Voltaic currents on magnetic needles Magnetism induced in the con- 
 ducting wire Directions of deflected magnetic needle by opposite currents 
 Multiplication of effect by coils of wire Galvanometers, their extreme sensi- 
 tiveness Magnetic action of copper wires Polar direction of a wire coil 
 Electro-magnets ; their great power and limited spheres of attraction Ratio 
 of diminution of attractive force Proportionate sizes of wire and iron Eco- 
 nomical effect of long coils Great rapidity of electro-magnetic action Resi- 
 dual power in electro-magnets Medical coil-machines Rotary motion of 
 conducting wires 128 
 
 CHAPTER XVI. 
 
 MAGNETO, THERMO, AND ANIMAL ELECTRICITY. 
 
 Induction of electricity by magnetism Multiplication of effects by motion Mag- 
 neto-electric machines: their powerful effects Magneto-electric spark 
 Decomposition by magneto-electricity Correlation of magnetic and electric 
 forces Development of electricity by heat List of thermo-electrics Ther- 
 mo-electric batteries Indications of temperature by thermo-electricity 
 
viii CONTENTS. 
 
 PAGE 
 
 Animal electricity Electrical organs of the torpedo Identity of animal and 
 voltaic electricity Electrical power of the gymnotus Connexion between 
 nervous influence and electricity 140 
 
 CHAPTER XVII. 
 
 ECONOMICAL APPARATUS. 
 
 Simple form of apparatus for frictional electricity Directions for constructing 
 electrical machines Leyden jars and batteries Electrometers Electro- 
 phorus Universal discharger Voltaic batteries Electro-magnets Gal- 
 vanometers Observations on exciting liquids for Voltaic batteries . . 148 
 
 PAET III. 
 
 THE APPLICATIONS OF ELECTRICITY. 
 CHAPTER XVIII. 
 
 ELECTRIC TELEGRAPHS MEANS OF COMMUNICATING. 
 
 First attempts to transmit messages by electricity Conducting power of the 
 earth Opinions respecting the cause Resistance of long wires to transmis- 
 sion Voltaic currents Modes of making electric communications Difficul- 
 ties of insulation Defects of the present system Submarine telegraphs 
 New plan proposed Prospect of telegraphic communication with America . 153 
 
 CHAPTER XIX. 
 
 ELECTRIC TELEGRAPHS SIGNAL INSTRUMENTS. 
 
 Progress of telegraphic invention Instruments invented by Lomond, Reizen, 
 Soemmering, Ronalds, Ampere, Schilling, Gauss, Steinhil, Alexander, Davy 
 Cooke and Wheats tone's needle telegraph Action of the needle tele- 
 graph Rapidity of transmission Henley's Magneto-electric telegraph 
 Breguet's semaphore 160 
 
 CHAPTER XX. 
 
 ELECTRIC TELEGRAPHS RECORDING INSTRUMENTS. 
 
 Morse's telegraph Modification of it by the Electric Telegraph Company 
 Bain's dotting telegraph Brett's printing telegraph Copying telegraph 
 Mode of transmitting copies of writing Regulation of the instruments 
 Rapidity of the copying process Means of maintaining secrecy . . . 1 67 
 
 CHAPTER XXI. 
 
 ELECTRO-METALLURGY. 
 
 Competing claims to the discovery Deposition of metals from their solutions 
 Its dependence on secondary results Apparent anomaly of deposition in a 
 single cell Formation of moulds Copying medals Reduplication of cop- 
 per-plate engravings Glyphography Electro-plating and gilding . .175 
 
 CHAPTER XXII. 
 
 ELECTRIC CLOCKS. 
 
 First application of electricity to indicate time Bain's self-acting electric clock 
 Means of making and breaking contact Application of mechanical power 
 The earth-battery Shepherd's electro-magnetic clock Independence of the 
 pendulum and its advantages Instantaneous indication of Greenwich tune 
 at distant places 182 
 
 CHAPTER XXIII. 
 
 MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 
 
 The electric light Electro-magnetic engines Blasting rocks Explosion of 
 fire-damp in mines Sounding the sea Determining longitudes Fire 
 alarms Table-moving Harpooning Conclusion . , . . .187 
 
ELECTKIC SCIENCE; 
 
 ITS HISTORY, PHENOMENA, AND APPLICATIONS. 
 
 PART I. 
 
 THE HISTORY OF ELECTRICITY. 
 
 CHAPTER I. 
 
 First discovery of electric attraction Dr. Gilbert's additions to known electrics Curi- 
 ous fallacies of early electricians Invention of the electrical machine Discovery of 
 electric light and repulsion Identity of electricity and lightning suggested Dis- 
 tinction between conducting and non-conducting bodies discovered The two kinds 
 of electricity discovered by Du Fay Sparks from the human body Improvements 
 in electrical machines Igniting power of the electric spark The Leyden jar 
 Extraordinar}'- alarm at the electric shock Exaggerated descriptions of its effects 
 Electrical batteries Dangerous shocks given with them Conducting power of the 
 earth ascertained Dr. Franklin's theory of electricity. 
 
 THERE requires no deep research in the pages of antiquity to trace the rise 
 and progress of the science of electricity. It sprang into being in com- 
 paratively recent times ; and after the first halting-stages of its existence 
 were surmounted, it advanced from infancy to manhood with the rapidity 
 of its own lightning spark j and though not yet arrived at maturity, it has 
 attained a degree of importance scarcely to be equalled by any of the phy- 
 sical sciences. 
 
 Some of the ordinary phenomena of electricity, indeed, attracted ob- 
 servation from the earliest periods. Not to mention lightning and its 
 accompanying thunder, the excitement of sparks by the rubbing of furs 
 must have been noticed, and wondered at, by the nomad tribes who first 
 inhabited the earth. The earliest recorded observation of electrical phe- 
 nomena, however, occurs 600 years before the Christian era. About that 
 time, it is stated that Thales of Miletus, one of the seven sages of Greece, 
 remarked that amber, when rubbed, attracted light bodies to its surface. 
 This seems to have been the extent of his observations ; but the fact af- 
 forded ample matter for speculation. He conceived that amber must 
 possess some inherent living principle, called into action by friction, and 
 that when thus excited it emitted an invisible effluvium, constantly return- 
 ing to itself, and bringing back with it those substances which were not 
 too heavy to resist its adhesive force: The next recorded notice of elec- 
 
 B 
 
10 THE HISTORY OF ELECTRICITY. 
 
 trical attraction is given by Theophrastus, 300 years afterwards. He 
 remarked that the crystal called by him lyncurium, supposed to be 
 tourmalin, attracted light bodies to its surface. 
 
 The shock given by the torpedo is mentioned by Pliny j but that phe- 
 nomenon was not, until the middle of the last century, imagined to have 
 any connection with the attractive properties of amber and tourmalin. 
 Some very remarkable facts are also mentioned by Eustathius, who lived 
 in the fifth century of the Christian era. He states that a freedman of 
 Tiberius was cured of the gout by the shock of the torpedo ; the first 
 known instance of the application of electricity to medical purposes, and, 
 if authentic, much more successful than its application in modern times. 
 Eustathius further relates, that Wolimer, king of the Goths, was able to 
 emit sparks from his body ; and that a certain philosopher, whilst dress- 
 ing and undressing, emitted flashes of light. 
 
 There is a void of nearly 1200 years ere we find any other distinct 
 notice of electrical phenomena. The subject must, however, have attracted 
 attention j for at the beginning of the seventeenth century a book by Dr. 
 Gilbert was published, entitled De Magnete, in which many other sub- 
 stances besides amber and tourmalin are mentioned as having the property 
 of attracting light bodies when rubbed ; but as amber was the substance 
 first noticed to possess that property, its Greek term electron had pre- 
 cedence in giving a name to the infant science of electricity. 
 
 When we consider that previously to the announcement of Dr. Gil- 
 bert's discoveries, the only known electrics were amber, tourmalin, and jet, 
 the accessions he made to the number must be regarded as an important 
 first step in the progress of electricity. He added at least twenty to the 
 list of electrics, including most of the precious stones, glass, sulphur, 
 sealing-wax, and resin ; and he determined that those substances, when 
 rubbed under favourable circumstances, attract not only light floating 
 bodies, but all solid matters whatever, including metals, water, and oil. 
 He observed also that the conditions most favourable to the excitement 
 of the attractive power are, a dry state of the atmosphere, and a brisk and 
 light friction ; whilst moist air and a southerly wind he found to be most 
 prejudicial to the production of electrical effects. 
 
 The deductions of Dr. Gilbert from his experiments were in many in- 
 stances curiously fallacious. In pointing out, for instance, the distinction 
 between magnetic and electric attraction, he affirmed that though magnetic 
 bodies rushed together mutually, it was only the excited electric that 
 exerted any power on the bodies attracted ; and he noticed as a special 
 distinction between magnetism and electricity, that the former repelled as 
 well as attracted, whilst the latter only attracted. 
 
 After the discoveries and investigations of this father of electric 
 science, there was a lapse of about sixty years with scarcely any progress. 
 Mr. Boyle is the next person whose investigations are worth mention. 
 Though he repeated and confirmed former experiments, and devoted much 
 time to the subject, he did little more than add some few to the number 
 of electrics. This philosopher has, indeed, the reputation of being the first 
 who discerned the electric light ; but his notice of it was so indistinct that 
 he can scarcely be said to be the discoverer of the luminous property of 
 electricity. 
 
 Mr. Boyle's theory of electrical attraction was similar to that of Thales; 
 
THE HISTORY OF ELECTRICITY. ll 
 
 Without, however, attempting to assign a cause for the active principle. 
 He conceived that the excited electric emitted a glutinous effluvium which 
 laid hold of small bodies in its progress, and on its return to the electric 
 carried them with it. This theory was advocated by other electricians at 
 the time, and experiments were made, and are recorded in the Philosophi- 
 cal Transactions, which were considered to prove the emission of glutinous 
 particles. 
 
 The most important advances in the science at this time were made 
 by Otto Guericke, burgomaster of Madgeburgh, the inventor of the air- 
 pump, who was contemporary with Mr. Boyle. 
 
 The apparatus with which electricians had experimented till near the 
 end of the seventeenth century was of the most simple kind. A rod or 
 flat surface of glass, resin, or sulphur, rubbed with the hand or with a 
 piece of woollen, was their best means of exciting electricity ; it may 
 therefore be supposed that the quantity at any time under observation 
 was very small. Otto Guericke constructed the first electrical machine. 
 It consisted of a sulphur globe, whirled round on an axis, whilst he held 
 his hand to it to serve as a rubber. Sulphur, it may be remarked, was a 
 favourite electric with early experimenters, as it was imagined that elec- 
 tricity was emitted with the sulphurous effluvium produced by the fric- 
 tion. In the construction of M. Otto Guericke's electrical machine, for 
 example, he cast the sulphur in a glass' globe, and then broke the glass 
 which would have served the purpose better in order to expose the sul- 
 phur to the action of the rubber. With this machine, rude as it was, 
 Otto Guericke excited much greater quantities of electricity than had 
 previously been produced ; and he was thus enabled not only to see 
 flashes of light, but to hear the snapping noise of the electric spark. 
 
 It may seem extraordinary that the most commonly observed pheno- 
 menon of electricity had not been before noticed as a property pertaining 
 to electrical bodies. It should be borne in mind, however, that furs and 
 silks, from the friction of which sparks are so frequently emitted, had not 
 been classed as electrics, and the only property of electricity then known 
 was that of attraction. It was not likely, therefore, until the two pheno- 
 mena of attraction and the emission of light were observed combined in 
 the same substance, that the excitement of sparks by friction should be 
 considered due to electricity. 
 
 On Otto Guericke must also be conferred the honour of having disco- 
 vered the property of electric repulsion. He ascertained that a feather, 
 when attracted to an excited electric, after adhering to it for a short time, 
 is repelled from the surface, and that it will not again approach until it 
 has touched some other body to which it can part with the electricity it 
 contains. He observed, also, that a feather when thus repelled by an ex- 
 cited electric, always keeps the same side presented towards it. As there 
 was a correspondence between this fact and the position of the moon 
 towards the earth, it was assumed that the revolution of the moon round 
 the earth might be caused by electrical attraction and repulsion. 
 
 The discoveries of Sir Isaac Newton, shortly afterwards, dispelled this 
 notion, and so far engaged the attention of scientific inquirers, that elec- 
 tricity for a time remained in abeyance. Newton had, indeed, paid a 
 passing attention to electrical phenomena, but the only addition made by 
 him to the facts before collected was, that electric attraction and repulsion 
 
12 THE HISTORY OF ELECTRICITY. 
 
 penetrate through glass. He made known, for instance, that when a plate 
 of glass is excited on one side, the other side also becomes electrical. 
 
 About the same time that Otto Guericke obtained decisive evidence of 
 the luminous properties of electricity, the fact was made more strikingly 
 manifest by Dr. Wall, who operated with a stick of amber of large dimen- 
 sions. He used a piece of woollen cloth for a rubber, and appears to have 
 been remarkably successful in eliciting by that means a greater amount 
 of electricity than had been excited even with the sulphur-globe of Otto 
 Guericke. 
 
 The first idea of resemblance between electrical phenomena and thunder 
 and lightning was suggested to Dr. Wall by the apparently remote analogy 
 of the crackling sounds and sparks ; and the fact deserves to be recorded 
 in his own words : " From the friction of the amber," he observes, " a pro- 
 digious number of little cracklings were heard, and every one of these 
 produced a little flash of light. And what to me is very surprising, upon 
 its eruption it strikes the finger very sensibly, wheresoever applied, with a 
 push or a puff like wind. The crackling is full as loud as charcoal on fire ; 
 and five or six cracklings or more, according to the quickness of placing 
 the finger, have been produced from one single friction, light always suc- 
 ceeding each of them. This liglit and crackling seems in some degree to 
 represent thunder *andliglitning" 
 
 Little further progress was made for nearly forty years. During that 
 interval, the accumulation of facts and improvements in the apparatus 
 were slow and insignificant. As yet, experimenters had worked without 
 any system, and without in the least comprehending the principles on which 
 the effects they produced depended. It was not until 1729 nearly 130 
 years after the first book on the science had been published that the 
 distinction between conductors and non-conductors of electricity was dis- 
 covered. This important fact was accidentally ascertained by Mr. Stephen 
 Grey, whilst attempting to communicate electricity to a line suspended by 
 threads. His first experiments were unsuccessful, because he suspended 
 the line by threads that conducted the electricity from it nearly as quickly 
 as it entered. It was then suggested by Mr. Wheeler, who assisted at the 
 experiment, that the cause of the escape of the electricity was the thickness 
 of the packthread employed, and he recommended that silken threads 
 should be tried, because being much thinner, it was supposed the electric 
 fluid would not be able to flow through it so readily. Accordingly the silk 
 thread was tried, and with great success. 
 
 So little were the experimenters aware that the difference in the effects 
 was caused by the different conducting properties of the substances em- 
 ployed, and so impressed were they with the notion that success with 
 the silk suspenders was entirely owing to their superior fineness, that they 
 endeavoured to obtain still better results by suspending the line on very 
 fine wires. The total failure of the experiment in this case induced them 
 at length to consider that there must be a difference in the conducting 
 properties of the substances employed. 
 
 The attention of electricians having been thus directed to this subject, 
 light was gradually, though still feebly, thrown on the causes of success and 
 failure in their experiments under different circumstances. Lists of con- 
 ducting and of non-conducting substances were made, when it was found 
 that glass, resin, and all bodies known as electrics, were bad conductors of 
 
THE HISTORY OF ELECTRICITY. 
 
 electricity, and that those in which electricity could not be excited were 
 conductors. In the conducting and non-conducting properties of these 
 substances great difference was soon detected; glass and resin being the 
 worst, and metals the best conductors. 
 
 Nearly contemporaneously with the discovery of the different conduct- 
 ing properties of electrics and non-electrics was the announcement that 
 M. Du Fay, intendant of the French king's gardens, had detected the 
 existence of two distinct kinds of electricity. This, like all the other dis- 
 coveries hitherto made, originated from accidental circumstances. A piece 
 of gold-leaf having been repelled from an excited glass rod, M. Du Fay 
 pursued it with an excited rod of sealing-ivax, expecting that the gold-leaf 
 would be equally repelled by that electric ; but he was astonished to see it, 
 on the contrary, attracted to the wax. On repeating the experiment he 
 found the same result invariably to follow : the gold-leaf when repelled 
 from glass was attracted by resin ; and when repelled from the latter 
 was attracted by glass. Hence M. Du Fay assumed that the electricity 
 excited by the two substances was of different kinds ; and as one was pro- 
 duced from glass, the other from resin, he distinguished them by the 
 names vitreous and resinous electricity. 
 
 It is a curious fact that M. Du Fay, the discoverer of this important 
 property of electricity, afterwards repudiated his own discovery. Subse- 
 quent experiments and consideration induced him to depart from the truth 
 he had developed, and to imagine that the effects observed arose entirely 
 from difference in the degrees of force excited by different electrics ; the 
 more powerful attraction of the one overcoming the feeble repulsion of the 
 other. It is difficult to conceive how he could have thus retrograded from 
 the position he had established ; for supposing the gold-leaf when repelled 
 from the excited glass to have been attracted to the resin by superior 
 electrical force, this superiority of force could not have yielded to the 
 weaker attraction of the glass ; yet the mutual interchange of attractive 
 and repellent power must have been frequently noticed. Other investi- 
 gators, however, confirmed the fact he had discovered and thus singularly 
 renounced ; and the original terms "vitreous" and "resinous" electricity 
 continue to be retained by a majority of electricians. 
 
 One of the experiments devised about this period, which excited great 
 astonishment, and tended to direct the attention of philosophic inquirers 
 to the subject of electricity, was the development of sparks from the 
 human body. Mr. Grey suspended a boy horizontally with hair lines, and 
 communicated electricity to him by means of an excited glass tube, when 
 sparks were then drawn from all parts of the boy's body. This phe- 
 nomenon, depending simply on the fact that the bodies of animals are 
 conductors of electricity in consequence of the fluids they contain, was 
 conceived to be owing, in some mysterious manner, to a connexion between 
 the electric effluvium, as it was called, and the vital principle. M. Du Fay 
 suspended himself in a similar manner for the purpose of experiencing the 
 sensation, and the experiment soon afterwards became the most popular 
 in the range of electrical phenomena, when the more convenient mode 
 of insulation by standing on a cake of resin, or on a glass stool, was 
 introduced. 
 
 About the middle of the 18th century, the investigation of electrical 
 phenomena was undertaken by several scientific inquirers in Germany. 
 
14 THE HISTORY OF ELECTRICITY. 
 
 M. Boze, Professor of Philosophy at Wittemburg, made considerable im- 
 provement in the mode of exciting electricity, by the addition of metal 
 conductors to the revolving glass globes of his machines. In the first 
 instance his conductor was held by a man, insulated by standing on a 
 cake of resin ; but he shortly afterwards adopted the more convenient 
 method of supporting the conductor by means of silk cords ; and to faci- 
 litate the passage of the electricity from the excited globe, he added a 
 number of linen strings to the conductor, which served the purpose, 
 though very imperfectly, of the metal points subsequently used. M. Boze 
 and other experimenters adopted the plan of increasing the quantity of 
 electricity excited, by bringing several globes into action at the same time, 
 and concentrating their power in one conductor. With these instruments 
 they are represented to have produced effects which seem incredible with 
 such imperfect apparatus, and the accounts must be considered to be 
 greatly exaggerated. It is stated, for instance, that by sparks from these 
 electrical machines blood was drawn from the finger; that they produced 
 a sensible shock extending from the head to the feet ; and that they were 
 sufficiently powerful to kill small birds. Even with the improved electrical 
 apparatus of the present day, with the addition of metal points and amal- 
 gamated rubbers, at that time unknown, nothing approaching these effects 
 can be produced by the largest machines. 
 
 Of the experiments performed by the continental philosophers at this 
 period, none excited so much general interest as the setting on fire of in- 
 flammable substances. This was first accomplished by Dr. Ludolph, of 
 Berlin; and the experiment was quickly repeated and improved on in dif- 
 ferent parts of Europe. The inflammation of spirits of wine, of phos- 
 phorus, and even of gunpowder, by an electric spark emitted from the 
 finger of a person insulated by standing on resin, was considered so ex- 
 traordinary, that it not only drew the attention of more men of science 
 to this branch of natural philosophy, but the exhibition of these and other 
 electrical wonders became a very popular public entertainment. 
 
 Quickly following the development of the igniting powers of the electric 
 spark was the discovery of the Ley den phial, the most astonishing of any 
 of electrical phenomena then made known, and which opened an entirely 
 new field for scientific investigation. 
 
 For the honour of being the original discoverer of the Leyden phial 
 there were several claimants ; as is generally the case with important dis- 
 coveries and inventions. It is commonly attributed to M. Cuneus of 
 Leyden, at the beginning of the year 1746, and was, like all antecedent 
 discoveries, the effect of accident, so far, at least, as he was concerned. 
 It occurred to him whilst repeating a well-devised experiment of Professor 
 Muschenbroeck for collecting and confining the " electric effluvium." The 
 professor conceived, if he could impart electricity to a conducting substance 
 entirely surrounded by non-conductors, that it would be thereby prevented 
 from being dissipated, and the force might be concentrated. The most 
 convenient form of trying the experiment appeared to be to electrify 
 water contained in a glass bottle, connection with the conductor of the 
 machine being established by an iron nail passing through the cork into 
 the water. The experiment, however, was not attended with any results 
 to Professor Muschenbrosck. The object he contemplated was, indeed, 
 accomplished, but the accumulation of electricity in the phial was not 
 
THE HISTORY OF ELECTRICITY. 15 
 
 manifested, owing to the want of a conducting surface on the outside by 
 which it could be concentrated. M. Cuneus, in repeating the experiment, 
 happened to grasp the bottle with his hand, which thus served for the 
 requisite conducting surface outside the glass, and when with the other 
 hand he endeavoured to disengage the nail from the conductor of the 
 machine, he was startled by receiving a smart shock through his arms. 
 Professor Muschenbrceck then renewed the experiment, with the advantage 
 of the experience of M. Cuneus, and with equal success. In these expe- 
 riments with the Leyden phial, and for a considerable time afterwards, the 
 bottle was always grasped by the hand, the cause of its producing the 
 effect not being understood. 
 
 Though M. Cuneus acquired the reputation of being the discoverer of 
 the Leyden phial, the claim of M. Von Kleist, dean of the Cathedral of 
 Camin, to be the first discoverer, rests on strong ground. It is stated 
 that he sent an account of the discovery to Dr. Leiberkuhn of Berlin, on 
 the 4th November, 1745. This account, communicated to the Academy 
 of Berlin, and entered among their proceedings, is to the following effect : 
 " When a nail or a piece of thick brass wire is put into a small apothe- 
 cary's phial and electrified, remarkable effects 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 spirit of wine be put into it, the experiment succeeds the better. As 
 soon as this phial and nail are removed from the electrifying glass, or the 
 prime conductor to which it has been exposed is taken away, it throws 
 out a pencil of flame so strong, that with this burning instrument in my 
 hand I have taken above sixty steps in walking about my room. When 
 it is electrified strongly, I can take it into another room, and there fire 
 spirits of wine with it. If, whilst it is electrifying, 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. A tin tube, or a man, placed upon electrics, 
 is electrified much more strongly by this means than in the common way. 
 When I present this phial and nail to a tin tube which I have, fifteen feet 
 long, nothing but experience can make a person believe how strongly it is 
 electrified. Two thin glasses have been broken by the shock. It appears 
 to me very extraordinary that when this phial and nail are in contact with 
 either conducting or non-conducting matter, the strong shock does not 
 follow. I have cemented it to wood, glass, sealing-wax, metal, <fec., which 
 I have electrified without any great effect. The human body, therefore, 
 must contribute something to it. This opinion is confirmed by observing 
 that unless I hold the phial in my hand, I cannot fire spirits of wine 
 with it." 
 
 The foregoing account of M. Von Kleist's experiments clearly shews 
 that he had stumbled on the same discovery as M. Cuneus; and the date 
 is previous to the experiment of the latter. It appears, however, that 
 the dean was not aware of the full importance of grasping the bottle 
 during the experiment, and his description was so vague, that several 
 philosophers to whom he communicated the discovery were unsuccessful 
 in their attempts to repeat the experiments. 
 
 The physiological effects of the Leyden phial were those that naturally 
 excited most attention in the first instance ; and the accounts given by 
 some of the early experimenters of the sensation of the electric shock 
 
16 THE HISTORY OF ELECTRICITY. 
 
 exhibit curious illustrations of the exaggeration caused by the terror of 
 this novel agitation of the nervous system. The small and inefficient ap- 
 paratus experimented with could have produced only very feeble shocks, 
 yet the effects are represented to have been little less than those of a flash 
 of lightning. These exaggerations are the more remarkable, when it is 
 borne in mind that they proceeded from eminent philosophers accustomed 
 calmly to investigate physical phenomena. M. Muschenbrceck, for exam- 
 ple, says in a letter to M. 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. He adds, that 
 he " would not take another shock for the whole kingdom of France." 
 
 M. Allamand, a fellow-professor with M. Muschenbrceck, and who 
 assisted in the experiments which led to the discovery, stated that he lost 
 his breath for some moments after taking the first shock ; and that he felt 
 so intense a pain along his right arm, that he apprehended serious conse- 
 quences from it. Another distinguished electrician, Professor Winckler 
 of Leipsic, said that the first time he tried the experiment his body was 
 greatly convulsed, and that it put his blood into such violent agitation 
 that he was apprehensive of an ardent fever, and was obliged to take re- 
 frigerating medicines. He also felt great heaviness in his head, as if a 
 stone were laid upon it. On two other*occasions he said the shock made 
 Ids nose bleed, to which he had not been previously disposed. 
 
 The astonishing effects of the electric shock were calculated to draw 
 public attention to the subject of electricity more than any previous dis- 
 covery. Every one was anxious to see the effects and to experience the 
 new sensation, notwithstanding the terrible accounts given of it. Travel- 
 ling showmen with their Ley den phials and electrical machines were to 
 be seen in all parts of Europe, who found profitable employment in exhi- 
 biting that and other striking electrical phenomena. NOT were philoso- 
 phers idle in the new field of inquiry which this discovery opened to their 
 investigation. The properties of the Leyden phial were closely examined ' y 
 the conditions requisite to the development of the phenomena were better 
 understood ; and many ingenious, though fallacious, theories were devised 
 for their explanation. The construction of the apparatus was improved 
 by the addition of an outside metallic coating, and jars were substituted 
 for bottles, by which means a metallic lining could be applied also to the 
 inside of the glass. 
 
 Many interesting experiments exemplified still more strongly the 
 powerful and rapid action of electricity. The shock was communicated 
 at the same instant through one hundred and eighty of the French guards, 
 in the presence of the King of France, by joining their hands in a con- 
 nected chain ; the soldier at one end touching the outside of the jar, and 
 the man at the other end touching the wire connected with the inside 
 coating. 
 
 By combining several jars together to form an electrical battery, the 
 force was greatly accumulated ; so as to set fire to all kinds of inflamma- 
 ble substances, to melt fine wires and gold and silver leaf, and to kill 
 small animals. 
 
 Though the feeble shocks of the small phials employed in the early 
 stages of the discovery created such a state of nervous apprehension, 
 and produced, as we are told, such distressing effects, yet within a 
 
THE HISTORY OF ELECTRICITY. 17 
 
 few years of that period we find electricians receiving shocks of really 
 formidable power with remarkable stoicism, and giving similar charges 
 to others, in a manner that would now be considered highly dangerous. 
 Dr. Franklin, the American philosopher, for instance, experimented with 
 glass jars containing six gallons each ; and whilst trying the destructive 
 power of the electric shock on some fowls, he inadvertently received the 
 full charge of two of these very large jars through his arms and body. 
 The effects, as he describes, were " sufficiently severe ;" yet the daring phi- 
 losopher, merely mentions them as shewing that a man can bear without 
 much detriment a shock greater than he had imagined. He said that on 
 receiving the shock, it seemed like a universal blow through the body 
 from head to foot, and was followed by a violent quick trembling in the 
 trunk, which went off gradually in a few seconds. It was some minutes 
 before he could collect his thoughts so as to know what was the matter ; 
 for he did not see the flash, though his eye was on the spot of the prinfe- 
 conductor, from whence it struck the back of his hand ; nor did he hear 
 the crack, though the bystanders said it was a loud one ; nor did he 
 particularly feel the stroke on his hand, though it raised a small swelling 
 there. His arms and the back of his neck felt somewhat numbed the 
 remainder of the evening, and his breast was sore for a week after, as if it 
 had been bruised. 
 
 Electricians of the present day would not venture to repeat such an 
 experiment as the following, of which an account is given by Franklin in 
 a letter dated Philadelphia, 1755. " The knocking down of six men was 
 performed with two of my large jars, not fully charged. I laid one end 
 of my discharging-rod upon the head of the first ; he laid his hand on the 
 head of the second ; the second his hand on the head of the third, and so 
 to the last, who held in his hand the chain that was connected with the 
 outside of the jars. When they were thus placed, I applied the other end 
 of my rod to the prime conductor, and they all dropped together. When 
 they got up, they all declared they had not felt any stroke, and wondered 
 how they came to fall ; nor did any of them either hear the crack or see 
 the light of it. You suppose it a dangerous experiment ; but I had once 
 suffered the same myself, receiving by accident an equal stroke through 
 my head that struck me down without hurting me ; and I had seen a 
 young woman that was about to be electrified through the feet (for some 
 indisposition) receive a greater charge through the head by inadvertently 
 stooping forward to look at the placing of her feet, till her forehead (as 
 she was very tall) came too near my prime conductor : she dropped, but 
 instantly got up again, complaining of nothing. A person so struck sinks 
 down doubled, or folded together as it were, the joints losing their strength 
 and stiffness at once, so that he drops on the spot where he stood instantly, 
 and there is no previous staggering, nor does he ever fall lengthwise. 
 Too great a charge might, indeed, kill a man, but I have not yet seen any 
 one hurt by it. It would certainly, as you observe, be the easiest of all 
 deaths." 
 
 With the powerful batteries employed by Franklin he also succeeded 
 in communicating magnetism to steel needles. This had, indeed, been 
 previously done by others, but not in so satisfactory a manner. 
 
 Numerous experiments were undertaken by Dr. Watson, Lord C. Ca- 
 vendish, and other gentlemen associated with them, for the purpose of 
 
18 THE HISTORY OF ELECTRICITY. 
 
 ascertaining the rapidity of the electric discharge, and the distances it 
 could be transmitted through water and dry ground. In one of these 
 experiments, performed in 1747, an electric discharge was sent across the 
 Thames ; and in another, near Shooter's Hill, the discharge passed instan- 
 taneously through two miles of wire and two miles of dry ground without 
 any perceptible interruption. 
 
 These experiments deserve special notice at the present day, as they 
 established the fact of the conducting property of the earth, which has been 
 turned to such good account in the construction of electric telegraphs. 
 Another fact also intimately bearing on the same subject was ascertained 
 by Signor Beccaria, viz. that water is an imperfect or a good conductor of 
 electricity in proportion to its quantity. This conclusion was drawn from 
 experiments in sending electric discharges through tubes of different sizes 
 filled with water ; when it was found that a charge which passed freely 
 through the larger was obstructed by the smaller tubes. 
 
 Numerous speculations were broached to account for the phenomena 
 of the Leyden phial, but the nature of its action was very imperfectly un- 
 derstood until Dr. Franklin undertook the investigation. It had, indeed, 
 been discovered that a jar could not be charged whilst it was insulated 
 from the earth j but this circumstance, which afforded a clue to the eluci- 
 dation of the phenomena of the Leyden phial, remained a barren fact 
 until it attracted Franklin's observation. He was the first to discover 
 that the electricity on the outside of the jar is of a different kind from 
 that within ; and that in charging a jar, a quantity of electricity is ex- 
 pelled from one side of the glass equal to that introduced on the other. 
 Hence the necessity of supplying a passage to the electricity outside by 
 connecting it with a conducting substance, which had hitherto remained 
 unaccounted for. According to Franklin's view of the condition of a 
 charged Leyden phial, the inside when charged from excited glass is filled 
 with what had been termed vitreous electricity, and the outside is equally 
 charged with electricity of the opposite kind. These electricities having a 
 strong mutual attraction, and being kept asunder only by the resistance 
 offered by the non-conducting glass and surrounding air, instantly rush 
 together when the opposite surfaces are brought in connexion, producing 
 all the phenomena of the Leyden phial, and leaving the glass in its ori- 
 ginal neutral condition. 
 
 Franklin also proved more satisfactorily than had previously been done., 
 that the electric charge is in the glass, and not in the metallic coatings of 
 the jar, which serve merely to conduct, and to concentrate to one point, 
 the electricity spread over the surface of the glass. To illustrate this fact 
 most conclusively, he contrived a jar with loose metallic coatings, that 
 could be removed and changed for others after the jar was charged ; and 
 this change being effected, the amount of electricity was found to be 
 scarcely diminished. 
 
 The simple and beautiful theory of Franklin for explaining the action 
 of the Leyden jar is one of the most important contributions of that phi- 
 losopher to the science of electricity. Amplifying and improving the 
 views that had previously been taken by Dr. Watson, he conceived that 
 the friction of glass and of other electrics does not generate electricity, 
 but that it causes a disturbance of the quantity of the electric fluid pre- 
 existing producing thereby in some bodies an excess and in others a 
 
THE HISTORY OF ELECTRICITY. 19 
 
 deficiency. The terms positive and negative were introduced to designate 
 these states of repletion and want ; and these terms have been generally 
 adopted in this country in speaking of the two kinds of electricity. It 
 will be observed, therefore, that it formed an essential part of this theory 
 to consider the phenomena of electricity as produced entirely by the dis- 
 turbance of the equilibrium of the same ethereal fluid, the particles of 
 which were mutually repulsive. On this principle was explained the 
 effect of bodies similarly electrified repelling each other, and the attraction 
 of the opposite electricities was attributed to the force exerted in attempt- 
 ing to restore the equilibrium. 
 
 The application of this theory to explain the action of the Leyden jar 
 presents a perfectly satisfactory view of the phenomena. When, for ex- 
 ample, the wire connected with the interior coating is brought near the 
 conductor of an electrical machine, an effort is made to part with a portion 
 of its excess of the electric fluid to the jar ; but the latter cannot receive 
 an addition to its natural quantity inside until an equal quantity of that 
 on the outside is expelled by means of some conducting body connected 
 with the earth. The inside thus becomes positively electrified and the 
 outside negatively, and in equal degrees. The resistance offered to the 
 passage of the electric fluid by the uncovered portion of the glass and by 
 the surrounding air, prevents the two electricities from coalescing until 
 the metallic surfaces of the jar are brought sufficiently near, by means of 
 connecting conductors, to enable the attractive powers of the opposite 
 electricities to overcome the interposed resistance. 
 
 The Franklinian theory of electricity is not without difficulties, espe- 
 cially in the explanation of repulsion from bodies electrified negatively ; 
 and the philosophers on the continent have adopted the vitreous and 
 resinous theory of Du Fay. But the great simplicity of Franklin's hypo- 
 thesis, and its accordance with those theories which have been established 
 as affording the most satisfactory explanation of phenomena in other de- 
 partments of science nearly related to electricity, have enabled it to main- 
 tain its ground in this country ; and from the time of the announcement 
 of Franklin's theory much clearer notions of the principles of electrical 
 action were generally entertained. 
 
 CHAPTER II. 
 
 The identity of lightning and electricity pointed out by Franklin Electricity drawn 
 from the clouds in France Franklin's electrical kite Lightning-conductors in- 
 vented Dangerous experiments with lightning Death of Professor Richmann 
 Beccaria's experiments on atmospheric electricity Electrical induction discovered 
 The theory of vitreous and resinous electricity revived Measurement of electric 
 forces Inventions of the torsion balance and of the electrophorus Progress of dis- 
 covery to the end of the eighteenth century. 
 
 WE now approach another important epoch in the history of electricity, 
 in which Dr. Franklin's powers of philosophical research and his fertility 
 of invention are eminently conspicuous. 
 
 The flashing light, and the snapping noise of the electric spark, had 
 
20 THE HISTORY OF ELECTRICITY. 
 
 induced some of the earliest electricians to imagine a similarity between 
 those manifestations of electricity and the phenomena of thunder and 
 lightning. We have previously quoted the remarkable words of Dr. 
 Wall, alluding to this probable identity, at a time when the known facts 
 were so few as to have made the analogy seem merely fanciful. The fur- 
 ther development of electrical force, especially after the discovery of the 
 Leyden phial, enabled experimenters to imitate on a small scale many of 
 the destructive effects of lightning. 
 
 The observations of the Abbe Nollet bear so close a relation to the 
 truth, that they deserve to be recorded, as indications how well prepared 
 philosophers at that time were for the subsequent discovery of Franklin. 
 In his Legons de Physique the Abbe" says : " If any one should take upon 
 him to prove from a well-connected comparison of phenomena, that thun- 
 der is in the hands of nature what electricity is in ours, that the wonders 
 which we now exhibit at our pleasure are minor imitations of those great 
 effects which frighten us, and that the whole depends upon the same me- 
 chanism ; if it is to be demonstrated that a cloud prepared by the action 
 of the winds, by heat, by a mixture of exhalations, &c., is opposite to a 
 terrestrial object ; that this is the electrified body, and at a certain proxi- 
 mity from that which is not, I avow that this idea, if it was well sup- 
 ported, would give me a great deal of pleasure ; and in support of it how 
 many specious reasons present themselves to a man who is well acquainted 
 with electricity ! The universality of the electric matter, the readiness of 
 its action, its inflammability, 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 in the ex- 
 periment of Leyden, the idea which we might truly adopt in supposing 
 a greater degree of electric power, &c. ; all these points of analogy which 
 I have been sometime meditating, begin to make me believe that one 
 might, by taking electricity for the model, form to one's self in relation 
 to thunder and lightning more perfect and more probable ideas than have 
 been hitherto offered." 
 
 !N"o one, however, had devised a means of ascertaining the identity of 
 lightning and electricity until Franklin pointed out the way of drawing 
 electricity from the clouds ; nor would he probably have thought of the 
 means of doing so but for the results of an unsuccessful experiment under- 
 taken by his friend Mr. Hopkinson. That gentleman electrified an iron 
 ball with a needle fixed to it, expecting to draw a stronger spark from 
 the point, as from a kind of focus ; but he was greatly surprised to find 
 that, instead of increasing the intensity of the electricity, the point dissi- 
 pated it altogether. He mentioned the failure of the experiment to Dr. 
 Franklin, who immediately undertook to investigate the cause, and to de- 
 termine the influence of points in attracting electricity. In repeating the 
 experiment, he ascertained not only that the ball could not be electrified 
 when a needle was fastened to it, but that when the needle was removed and 
 the ball was charged with electricity, the charge was silently and speedily 
 withdrawn when a point connected with the earth was presented to it. 
 
 From this effect of points on electrified bodies, Franklin inferred that 
 lightning might also be drawn silently and safely from the clouds by a 
 metallic point fixed at a great elevation, and he awaited with considerable 
 anxiety the completion of a spire at Philadelphia to enable him to try the 
 
p. 21. 
 
 LIGHTNING FIRST DRAWN FROM THE CLOUDS. 
 
THE HISTORY OF ELECTRICITY. 21 
 
 experiment. In the meantime he published the results of his discoveries, 
 and recommended that where opportunities occurred the trial should be 
 made. 
 
 In a letter to Dr. Lining of Charlestown, containing answers to several 
 questions, Dr. Franklin has given the following account of the origin of 
 the idea that led to the grand discovery. " Your question, how I came 
 first to think of proposing the experiment of drawing down the lightning 
 in order to ascertain its sameness with the electric fluid, I cannot better 
 answer than by giving you an extract from the minutes I used to keep of 
 the experiments I made, with memorandums of such as I purposed to- 
 make, the reasons for making them, and the observations that arose upon, 
 them, from which minutes my letters were afterwards drawn. By this 
 extract you will see that the thought was not so much an ' out-of-the-way 
 one/ but that it might have occurred to an electrician. ' Nov. 7, 1749. 
 Electric fluid agrees with lightning in these particulars : 1. giving light ; 
 2. colour of the light ; 3. crooked direction ; 4. swift motion ; 5. being 
 conducted by metals ; 6. crack or noise in exploding ; 7. subsisting in 
 water or ice ; 8. rending bodies it passes through ; 9. destroying ani- 
 mals ; 10. melting metals ; 11. firing inflammable substances; 12. sul- 
 phureous smell. The electric fluid is attracted by points. We do not 
 know whether this property is in lightning, but since they agree in all the 
 particulars in which we can already compare them, is it not probable they 
 agree likewise in this ? Let the experiment be made.' " 
 
 Acting on this suggestion, M. Dalibard and M. Delor erected apparatus 
 for the purpose of collecting electricity from the clouds ; the former at 
 Marly la Ville, about six leagues from Paris, the latter at his residence 
 situated on high ground in Paris itself. M. Dalibard's apparatus consisted 
 of an iron pointed rod forty feet long, the lower end of which was inserted 
 in a sentry-box protected from rain, and on the outside it was fastened 
 to three wooden posts by silk cords also defended from the rain. It was 
 this rod that first attracted electricity from the clouds at a time when, 
 unfortunately, M. Dalibard was not present to witness the realisation of 
 his hopes. He was absent from Marly at the time, and had left the ap- 
 paratus in charge of a joiner named Coiffier. On the 10th of May, 1752, 
 between two and three o'clock in the afternoon, a sudden clap of thunder 
 made Coiffier hurry to his post, and, according to the instructions given 
 him, he presented a phial furnished with a brass wire to the rod, and im- 
 mediately saw a bright spark accompanied by a loud snapping noise. 
 After having taken another spark stronger than the first, he called in the 
 neighbours, and sent for the Cure. The latter ran to the spot with all 
 speed, and his parishioners seeing him running, followed at his heels, ex- 
 pecting that Coiflier had been killed by lightning ; nor were they pre- 
 vented from hastening to the spot, notwithstanding a violent hail-storm. 
 The Cure was equally successful in drawing sparks from the iron rod, and 
 instantly despatched an account of the important event to M. Dalibard. 
 The Cure stated that the sparks were of a blue colour, an inch and a half 
 long, and smelt strongly of sulphur. He drew sparks at least six times 
 in about four minutes, and in the course of these experiments he received 
 a shock in the arm extending above the elbow, which he said left a mark 
 such as might have been made by a blow with the wire on the naked skin. 
 Eight days after the identity of lightning and electricity had been 
 
22 THE HISTORY OF ELECTRICITY. 
 
 proved at Marly, the rod erected by M. Delor, which was ninety-nine feet 
 high, yielded electric sparks ; and the same phenomenon was afterwards 
 exhibited to the French king and to numbers of the nobility. 
 
 In the meantime, Dr. Franklin remained at Philadelphia unconscious 
 of the success which had attended the adoption in France of his suggestion 
 for drawing lightning from the clouds. Becoming impatient to verify his 
 opinion of the identity of lightning, and electricity, it occurred to him that 
 he might establish an electrical connection between a thunder-cloud and 
 the earth by means of a boy's kite, without waiting for the completion of 
 the spire. Accordingly, on the first promising occasion, which occurred 
 in June 1752, a month after the success at Marly, he undertook the 
 experiment. Afraid of being laughed at should the expedient fail, he 
 took his son with him to make it appear that he was merely going for the 
 boy's gratification, to assist in flying the kite. The apparatus consisted 
 of a silk handkerchief attached at the corners to two laths placed cross- 
 wise. The kite thus constructed was able to bear a shower of rain without 
 being injured, and a pointed wire was fixed to it for the attraction of elec- 
 tricity, but there was not any conducting substance in the string, which 
 consisted of common packthread. 
 
 Having raised the kite in the air, he looked anxiously for the result, as 
 some thunder-clouds passed over it, but for some time without any sign of 
 electricity. At length, as he was about despairing of success, he perceived 
 some fibres of the hempen string to stand erect and to avoid one another, 
 just as they would have done if electrified. He then presented his knuckle 
 to a key attached to the string, and to his unutterable delight received a 
 spark. Other sparks succeeded, even whilst the string was dry, and con- 
 sequently a very imperfect conductor ; and when the rain had wetted the 
 string, he drew forth sparks very copiously, with which he charged a Ley- 
 den jar. It must be observed that the key was insulated by a silk string 
 to prevent the electricity from passing through the packthread to the 
 earth. 
 
 Dr. Franklin afterwards erected an iron rod on the top of his own 
 residence, having found the influence of points to extend farther than he 
 had at first imagined, and one end of the rod being conveyed into his 
 study, he was able at his convenience to perform with lightning all the 
 experiments of artificially-excited electricity. That his attention might 
 be drawn to the apparatus whenever lightning was attracted, he attached 
 a set of bells to the rod, which by the attraction of their clappers gave the 
 signal. Sometimes these bells rang so violently as to be heard all over 
 the house. 
 
 The application made by Franklin of his great discovery to the pro- 
 tection of buildings from lightning, was the first practical benefit derived 
 from the science of electricity. He inferred, as points are so efficacious in 
 attracting lightning, that a pointed metallic rod attached to the side of a 
 house, rising some height above it and descending to the earth, would draw 
 off the electricity of a passing thunder-cloud silently, and thus prevent a 
 sudden discharge ; or if a flash of lightning should strike the rod, that the 
 electric fluid would be conducted safely through the metal to the ground. 
 He consequently recommended the attachment of such protecting rods to 
 all exposed buildings, and to the masts of ships. Experience has proved 
 the correctness of his inference, and the value of the suggestion. The 
 
p. 22. 
 
 FRANKLINS KITE EXPERIMENT. 
 
THE HISTORY OP ELECTRICITY. 23 
 
 plan has been extensively adopted, and has been the means of protecting 
 every building and ship to which such conductors have been properly 
 applied. 
 
 Electricians in all parts of the world were anxious to repeat the expe- 
 riment of drawing electricity from the clouds, and many of them received 
 injuries and had narrow escapes from being killed, in consequence of the 
 hazardous manner in which they performed their experiments. No one 
 succeeded in drawing down such large continuous torrents of electric fire 
 as M. de Komas of Nerac, who employed an electrical kite, in the string 
 of which a thin wire was inserted to serve as a better conductor than the 
 hempen string alone. The kite he used was seven feet high and three feet 
 wide, and a tin tube connected with the wire-string was sustained at a 
 short distance from the ground by means of a silk ribbon, which served, 
 when the kite was elevated, to insulate the wire from the operator. In 
 experimenting with this kite, when raised to a height of 600 feet, in Au- 
 gust 1756, the streams of fire issuing from the tin tube were one inch 
 thick, and ten feet long ; and on one occasion a loud explosion was heard 
 and a flash of lightning passed from the tin tube to the earth, making a 
 small hole in the ground. At such times, when the flow of electricity was 
 very abundant, M. de Romas experienced the same sensation over his face 
 as is produced when near the prime conductor of an excited electrical ma- 
 chine, which induced him to retreat and discontinue the experiments, from 
 the dread of receiving a shock. Experience had taught him caution ; for 
 when he first raised his kite, and whilst taking hold of the wire-string, he 
 was struck severely. M. Mormier, a member of the Academy of Sciences, 
 and M. Bertier of Montmorency, were both knocked down by flashes of 
 lightning, whilst taking sparks from their apparatus ; and numerous other 
 persons were more or less injured. 
 
 A fatal warning of the danger of experiments with lightning was 
 given by the death of Professor Richmann of St. Petersburgh, on the 26th 
 of August 1753. He had constructed an instrument which he called an 
 electrical gnomon, to measure the strength of electricity, and was observing 
 the effect of a thunder-cloud on this instrument, accompanied by M. Solo- 
 kow, an engraver. Professor Richmann was standing with his head in- 
 clined towards the gnomon, when M. Solokow, who was close to him, 
 observed, as he expressed it, "a globe of blue fire as large as his fist," 
 dart from the rod of the gnomon towards the Professor's head, which was 
 about a foot distant. This flash caused the instantaneous death of the 
 Professor, and M. Solokow was so much stunned that he could give no 
 particular account of the effects upon himself. He said that there arose a 
 sort of steam or vapour which entirely benumbed him, and made him 
 sink down upon the ground, so that he could not even hear the accompany- 
 ing clap of thunder, which was very loud. The effects of the lightning 
 were very apparent in the room ; the door-case was split through, and 
 the door torn off its hinges and thrown down. 
 
 On examining Professor Richmann's body, a red spot was observed on 
 the forehead, from which some drops of blood issued through the pores, 
 though the skin was not broken. The shoe of the left foot was burst open, 
 and a blue mark was found on that part of the foot; from which appear- 
 ances it was assumed that the lightning entered the head and passed 
 through the body to the foot. The body itself exhibited several red and 
 
24 THE HISTORY OF ELECTRICITY. 
 
 blue spots. With the exception of the left shoe, the dress was uninjured. 
 When the body was opened, twenty-four hours after death, the cranium 
 was without injury, and the brain perfectly sound ; but the transparent 
 pellicles of the windpipe were excessively tender, gave way, and were 
 easily rent. There was some extravasated blood in the cavities below the 
 lungs ; and the throat, the glands, and the thin entrails were all inflamed. 
 The body so rapidly decomposed, that two days after death it could with 
 difficulty be got into the coffin. 
 
 The physiological effect of lightning is exactly the same as that of a 
 shock from a Leyden jar or electrical battery. The author of this work is 
 able to speak from personal experience on this matter, though the shock 
 received by him was too slight to produce any disagreeable consequences. 
 During a severe thunder-storm, accompanied by torrents of rain, he was 
 endeavouring to prevent the overflow of a cistern by stopping up the con- 
 duit-pipe, when an electric shock passed through the right arm, from the 
 wrist that was pressing against the pipe to the elbow that rested on the 
 cistern. The effect was very startling, and induced him to make a quick 
 retreat. A loud clap of thunder immediately followed, indicating that a 
 powerful flash of lightning had struck the house ; but several metal pipes 
 conducted it safely to the ground, and it was so divided by passing through 
 those conductors that but a very small portion of the discharge could 
 have passed through the imperfect connexion formed by the author's arm. 
 
 One of the first objects of scientific experiments on lightning was to 
 determine whether the electricity from the clouds was positive or negative. 
 Franklin found, during all his experiments in the spring of 1753, that the 
 lightning-rod exhibited in every case signs of negative electricity; he 
 therefore concluded, somewhat too hastily, that the clouds are always ne- 
 gatively electrified, and that during thunder-storms it is the earth that 
 strikes into the clouds, and not the clouds into the earth. In a subsequent 
 experiment, however, he found the electricity positive. The observations 
 of other electricians serve to shew that the electrical condition of the 
 clouds frequently varies from negative to positive, and that these changes 
 sometimes occur during the course of the same storm. 
 
 The pointed rod with the accompanying apparatus to detect when a 
 thunder-cloud was passing, were soon found to indicate the presence of 
 electricity, not only when there was no thunder-storm, but when the 
 atmosphere was perfectly clear. Signor Beccaria, especially, made search- 
 ing investigations into the subject, and determined the close connection 
 between electricity and all meteorological phenomena ; nor has much been 
 done in elucidating this mysterious connection since the researches of that 
 distinguished philosopher. 
 
 The discovery of the identity of lightning and electricity may be con- 
 sidered as the culminating-point in the history of electricity during the 
 last century. No very striking discoveries resulted from the researches 
 of the many electricians who were engaged in investigating the new field 
 opened to their researches j nevertheless numerous interesting facts were 
 made known, and considerable light was thrown on the laws that govern 
 the actions of the electric fluid. 
 
 The discovery by Mr. Canton of the property of electrical induction, 
 though not of a character to produce any marked impression at the time, 
 has proved of the utmost consequence in explaining the phenomena of 
 
THE HISTOKY OF ELECTRICITY. 25 
 
 electricity. In the earlier years of the science an obscure notion was 
 entertained of the influence of excited electrics in bodies at a distance 
 from them ; but nothing was actually known of this influence until Mr. 
 Canton proved, by numerous experiments, that an excited electric always 
 induces in other bodies within the sphere of its influence an electrical 
 condition of a kind different from that itself possesses. Mr. Canton found 
 that when he brought an insulated conducting body near to an excited 
 electric, it became electrified so long as it remained there, and that if the 
 electric were positive, that part of the conducting body nearest to it would 
 be negatively electrical, and the more distant part positively. This sym- 
 pathetic state of electricity, he ascertained, continued only whilst in the 
 vicinity of the excited electric, and that on removing the insulated con- 
 ducting body, it returned to its natural state. If, however, whilst under 
 the electrical influence, the part farthest from the electric was touched by 
 a conductor, so as to enable it to throw off the electricity repelled to that 
 end, the body remained in an electrical state after the excited electric was 
 removed. These remarkable phenomena were ascribed by Mr. Canton, 
 and also by Dr. Franklin, who verified the experiments, to the presence of 
 electrical atmospheres round all bodies, which atmospheres were supposed 
 to be mutually repellent. 
 
 M. ^Epinus and Mr. Wilcke, who experimented together with a view 
 to elucidate the cause of the inductive property of electricity, were led to 
 infer that the repelling property exerted at a distance by excited electrics 
 would enable them to charge a space of air included between two con- 
 ducting plates, in the same manner as a plate of glass is charged when 
 coated on both sides with tin-foil. The experiment answered their expec- 
 tations, and succeeded at a distance of several inches between two insu- 
 lated metal discs supported horizontally. When a discharging-rod was 
 connected with the upper and lower plates, a loud discharge, like that of a 
 Ley den jar, instantly took place. 
 
 It may be observed that the property of induction might have been 
 deduced from the action of the Leyden jar, as explained by Franklin ; but 
 until the experiments of Mr. Canton it could not have been inferred that 
 the presence of positive electricity, which on one side of a plate of glass 
 induces a negative state on the other, would also operate at a distance in 
 communicating negative electricity through the non-conducting air. 
 
 Mr. Canton also advanced the progress of electrical science by ascer- 
 taining that the kind of electricity excited by the friction of any given 
 substance may be changed from positive to negative, or the reverse, by 
 using different rubbers, or by altering the surfaces of the electrics. Glass 
 is less susceptible of these changes than other electrics, but its generally- 
 positive state may be converted into negative by employing the back of a 
 cat for the rubber, or by roughening the surface. To Mr. Canton is also 
 due the merit of introducing the application of a metallic amalgam to the 
 rubber, to increase the facility of exciting electricity. 
 
 The opinion which had hitherto been generally entertained, that elec- 
 trical phenomena depended on the presence of one electric fluid, the equi- 
 librium of which was disturbed by friction, was very ably disputed by Mr. 
 Symmers in a communication to the Royal Society in the year 1759. 
 He adduced several experiments which he considered could only be pro- 
 perly explained on the supposition of the existence of two electric fluids, 
 
 c 
 
2/0 THE HISTORY OF ELECTRICITY. 
 
 not indeed independent, but, on the contrary, always co-existent and 
 counteracting each other. This theory closely resembled that of Du Fay, 
 and his terms of vitreous and resinous electricity were adopted by Mr. 
 Symmers, though Du Fay conceived, in opposition to all observed elec- 
 trical facts, that the two electricities were independent of each other, and 
 were never combined. 
 
 The revival of the theory of vitreous and resinous electricity by Mr. 
 Symmers deserves to be noticed in a history of the science, from the cir- 
 cumstance that, though it did not receive much attention at the time, it 
 has been the foundation of the opinion now generally entertained by elec- 
 tricians on the continent, where the theory of two distinct electric fluids 
 has in a great measure supplanted the more simple plus and minus theory 
 of Franklin. A very impartial review of the experiments of Mr. Sym- 
 mers, and of the inferences founded on them, is given by Dr. Priestley,* 
 who, though an advocate of the Franklinian theory, admitted that all the 
 phenomena of electricity might be equally well explained by the suppo- 
 sition of the existence of two distinct fluids as of only one, and that as 
 regards repulsion, the explanation was even more satisfactory. Dr. Priest- 
 ley, however, adhered to the single fluid as the more simple theory, and 
 as presenting closer analogy to what is known of the operations of nature. 
 
 M. ^Epinus and the Hon. Henry Cavendish brought mathematical sci- 
 ence to bear on the phenomena of electricity, and determined some of the 
 laws that govern its attractive and repellent forces. These researches 
 were pursued still more successfully by M. Coulomb in 1785 with the aid 
 of the electrometer he invented, called the torsion-balance, for measuring 
 the force of electrical attraction and repulsion. In that instrument a 
 filament of silk or spun glass serves to suspend horizontally a fine needle 
 of shellac, with a small gilt pith ball fixed at one end. When the ball is 
 repelled by the excited electric whose force is to be determined, the sus- 
 pending filament receives a twist from the mutual repulsion of the pith 
 ball and the ball of the electrified conducting body. The two balls thus 
 mutually repelled are forced together by means of a screw to which the 
 filament of glass is attached, and the degree of torsion or twist produced 
 in the filament by forcing the two balls together is measured by an index. 
 The delicacy of the instrument is so great that a force not exceeding the 
 20,000,000th part of a grain may be indicated. With this sensitive indi- 
 cator of electrical forces, Coulomb deduced the following important laws 
 as governing the electric fluid : that bodies electrified by similar elec- 
 tricities repel each other with a force that diminishes in the same propor- 
 tion as the square of the distance between them is increased ; and that the 
 mutual attraction or repulsion of two electrified bodies is directly propor- 
 tional to the quantity of electricity on the other, and diversely proportional 
 to the square of the distance between them. Coulomb ascertained that 
 electrified bodies, when insulated, gradually lose their electricity by the 
 conduction of the surrounding atmosphere, which is never free from 
 moisture, and by the imperfect insulation afforded even by the best elec- 
 trics. He also determined, in a more decided manner than had previously 
 been done, that electricity is accumulated on the surfaces of conducting 
 bodies only, and never penetrates the interior. 
 
 * History of Electricity, p. 247, 
 
THE HISTORY OF ELECTRICITY. 27 
 
 A few years before the invention of the torsion-balance, the electro* 
 phorus of M. Volta had been added to the apparatus of the electrician. 
 This instrument is principally valuable as exemplifying in a remarkably 
 striking manner the action of induced electricity. When an insulated 
 metal plate is brought into contact with a cake of resin, or with any other 
 flat electric surface when excited, the insulated plate is immediately ren- 
 dered electrical ; but not, as might be supposed, by electricity communicated 
 directly from the resin, but by induction. The two sides of the metal 
 disc become in opposite states of electricity ; that one nearest to the elec- 
 tric being of the contrary kind to that of the electric itself. Supposing a 
 cake of resin to be employed, the metal surface in contact with it is posi- 
 tively electrified, and the other side negatively. If when thus in contact, 
 the finger, or any other conducting body, be brought near the plate, the 
 negative electricity passes off" in a spark, and the plate being then lifted 
 up by the insulating handle, it will be found to be electrified positively j 
 and so strongly that sparks nearly an inch long may be taken from it. 
 In this manner, by a succession of contacts, electricity may be developed 
 sufficient to charge several Ley den jars without sensibly diminishing the 
 electricity of the excited resin. 
 
 The principal remaining incidents in the progress of electric science 
 to the end of the 18th century were the researches of Lavoisier, La Place, 
 and others relative to electrical excitement by the evaporation of fluids^ 
 and by the solution of solids in acid menstrua. In every instance of sud- 
 den change of state, and of rapid chemical action under such circumstances, 
 electricity was developed. These experiments by the French chemists 
 indicated the close connexion between electricity and chemical action, 
 which subsequent investigations have proved to possess a most important 
 bearing on the development of electricity. 
 
 CHAPTER III. 
 
 Discovery of Galvanism, and the circumstances that led to it Galvani's erroneous 
 notions of the exciting cause Volta's investigations Invention of the Voltaic pile 
 Commencement of the science of Voltaic electricity Various Voltaic batteries 
 Theories of their action Investigations by Sir Humphery Davy Decomposition 
 of the alkalies and earths The experiments that led to the discovery founded on a 
 hoax Prodigious Voltaic batteries constructed Napoleon Bonaparte's experience 
 of their power Unsuccessful application of Voltaic electricity by Sir H. Davy. 
 
 As the last century drew to its close, a new era commenced in electric 
 science of far more importance to its development than any of the pre- 
 ceding stages of advancement. The first glimmering of light in the new 
 direction, as in most of the preceding discoveries, arose from fortuitous 
 circumstances j and it is worthy of notice that this discovery was founded 
 on ignorance of the principle on which it depended. 
 
 Galvani, an anatomical professor at Pavia, has the merit of being the 
 originator of that branch of electric science which was for many years 
 termed galvanism. One account of the discovery represents that his at- 
 
28 THE HISTOKY OF ELECTRICITY. 
 
 tention was first directed to the subject by his wife and a pupil, who had 
 observed the limb of a frog convulsed when touched by a knife near to 
 an electrical machine. Madame Galvani is made more conspicuous in the 
 matter by the assertion that she was an invalid, and that the presence of 
 the limbs of frogs in the dissecting-room was owing to her having ordered 
 the frogs as a delicacy for her dinner. It is stated, however, by Galvani, 
 in a work published at Bologna in 1791 for the Institute of Sciences,* that 
 he was dissecting a frog on a table whereon stood an electrical machine, 
 when the limbs suddenly became convulsed by one of his pupils touching 
 the crural nerve with a dissecting-knife. This occurred at the instant that 
 a spark was taken from the conductor of the machine. The experiment 
 was repeated several times, and it was found to answer in all cases when 
 a metal conductor was connected with the nerve, but not otherwise. Gal- 
 vani, who entertained the opinion that muscular action is attributable to 
 electricity, looked on this phenomenon as a confirmation of that opinion, 
 and pursued the inquiry with great zeal. Having tried various experi- 
 ments successfully with the electrical machine, the electrophorus, and other 
 artificial means of exciting electricity, he also tried the effect of atmo- 
 spherical electricity. He attached the legs of frogs and of warm-blooded 
 animals to a pointed conductor fixed at the top of the house, and found 
 that they were violently convulsed by every flash of lightning. Similar 
 effects, though not so strong, were also produced by atmospherical elec- 
 tricity, when there was no thunder-storm. In the prosecution of these 
 researches he suspended some frogs, on metal hooks fixed in the spine, 
 from the iron railings of his garden, and observed the contractions in all 
 states of the weather, when he connected the hook with the iron rails. 
 He therefore supposed that the effect might be produced independently of 
 the atmosphere ; and he found, on experimenting with a frog in his room, 
 that whenever a metallic connection was made between the external muscle 
 and the crural nerve, the limbs became convulsed. As this effect was 
 produced without any apparent external excitement of the electric fluid, 
 Galvani inferred, in accordance with his preconceived hypothesis, that 
 the muscular contraction was caused by animal electricity, that the muscle 
 and the nerve were in the condition of the inside and the outside of a 
 charged Leyden jar, and that the metallic connection merely served the 
 same purpose as a discharging wire, by giving the two electricities the 
 means of combining. 
 
 It has been observed, that had Galvani been more accustomed to elec- 
 trical experiments, he would have paid no attention to the convulsion of 
 the frog's limb, and would have considered it merely as the customary 
 effect of electricity when passed through an animal conductor. The same 
 fact had, indeed, been observed by others, and thus disregarded. But 
 Galvani, impressed with his idea of muscular action being caused by ani- 
 mal electricity, brought the fact prominently forward. The electricians 
 who had observed the same without regard, formed, indeed, more correct 
 notions of the cause than Galvani, but by his endeavour lo establish an 
 error, he was the means of elucidating a most important truth. 
 
 In the meantime, the extraordinary physiological effects produced by 
 such insignificant means gave countenance to Galvani's notion that they 
 
 * Aloysii Galvani de viribus electricitatis in motu muscular! commentarius. 
 
THE HISTORY OF ELECTRICITY. 29 
 
 were produced by animal electricity, and physiologists eagerly seized hold 
 of this assigned cause of vital energy, the agency of the "nervous fluid" 
 being relinquished for that of electricity. Volta, however, manfully com- 
 bated the opinion that the exciting cause resided in the animal fibres, and 
 contended that the muscular contractions produced when the muscle and 
 the nerve were connected by a metal, arose from the contact of the metal 
 itself, and was entirely independent of animal electricity. In support of 
 this opinion was adduced the peculiar sensation occasioned by the contact 
 of a piece of silver with a piece of lead or zinc, when both are placed upon 
 the tongue, a fact which had been noticed by M. Sulzer in 1762, without 
 attracting much attention.* Volta conceived that by combining a series 
 of silver and zinc plates, he should be able to add to the electrical effect 
 by increasing the number of metallic contacts. He therefore piled up a 
 series of plates, consisting of zinc and silver alternately, with interposed 
 pieces of wet cloth, and obtained the expected accumulation of electrical 
 force. 
 
 The results of Volta's important experiments were announced in a 
 letter to Sir Joseph Banks, which was read before the Royal Society on 
 the 26th of June 1800. In that communication M. Volta stated that he 
 had obtained some striking results from electricity excited by the simple 
 mutual contact of different kinds of metals, and even by the contact of 
 other conductors different among themselves, whether liquid or containing 
 some fluid to which they were indebted for their conducting properties. 
 The principal results he stated were, "the construction of an apparatus 
 which resembles, in its power of producing electric shocks and other elec- 
 trical phenomena, the Ley den jar, and still more closely electrical batteries 
 when feebly charged j which operate also without ceasing, and possess a 
 perpetual impulsion." This apparatus consisted of discs of silver and zinc, 
 about one inch diameter, and small discs of card or parchment, moistened 
 with water or with a solution of common salt. The metal discs were piled 
 upon one another alternately, and between every two was applied one of 
 the moistened cards. With a series of tweuty of these pairs of discs, he 
 stated that Cavallo's pith ball electrometer, aided by a condenser, was af- 
 fected to the extent of from 10 to 15 degrees ; that when wires connected 
 with the upper and lower plates of the series were brought together, sparks 
 were emitted ; and that the apparatus would give a shock through the fin- 
 gers. With a series of fifty pairs, the shock, he stated, became so powerful 
 as to reach to the shoulders, and when passed through a single finger, the 
 pain was too great to be borne. Volta, it is probable, exaggerated the 
 effects of this diminutive apparatus, and he evidently mistook the partial 
 combustion of the metallic wires, on making contact, for the electric spark, 
 
 * The following extract from M. Sulzer's writings marks the first dawn of this im- 
 portant discovery : 
 
 " When two pieces of metal, one of lead and the other of silver, are so joined toge- 
 ther that their edges make one surface, a certain sensation will be produced on applying 
 it to the tongue, which comes near to the taste of martial vitriol ; whereas each piece 
 by itself betrays not the slightest trace of that taste. It is not improbable that, by a 
 combination of the two metals, a solution of either of them may have taken place, in 
 consequence of which the dissolved particles penetrate intathe tongue; or we may con- 
 jecture that the combination of these metals occasions a trembling motion in their 
 respective particles, which, exciting the nerves of the tongue, causes that peculiar sensa- 
 tion." Theory of Agreeable and Disagreeable Sensations; Berlin, 1762. 
 
30 THE HISTORY OF ELECTRICITY. 
 
 which can only be produced by a much more numerous and powerful 
 arrangement than Volta employed. 
 
 Volta had been a long time in obtaining the results communicated in 
 his letter to Sir Joseph Banks, and having experienced the inconvenience 
 of the pile, he contrived an arrangement called by him ct, couronne de 
 tasses, in which zinc and copper plates connected together by wires were 
 immersed in different cups containing a solution of common salt. A series 
 of these cups formed a very efficient battery, and he was enabled, as he 
 said, to produce effects which, though considerably less active than a bat- 
 tery of Ley den jars, possessed nevertheless immense power. The close 
 resemblance of the electricity evolved in this manner to that of the torpedo 
 did not fail to strike Volta, who accordingly called his apparatus the 
 organe electrique a/rtificid. 
 
 The discoveries of" Volta, though far surpassing those of Galvani, were 
 at first considered subservient to the purpose of giving greater effect to 
 the experiments of the latter. The increased muscular energy that could 
 thus be given to the limbs of recently killed animals excited amazement 
 and awe, and itinerant lecturers in all parts of the kingdom exhibited these 
 wonders to collected multitudes; nor were charlatans wanting, who by 
 tricks of legerdemain gave a still more marvellous character to the really 
 extraordinary effects of this newly discovered agent. The importance of 
 the exciting power thus became merged in the effects it produced. Because 
 the battery of Volta was at first chiefly employed to illustrate the discovery 
 of Galvani, it received the name of the " Galvanic battery," which it for a 
 long time retained, and the new branch of science founded upon it was 
 still more unjustly termed Galvanism. 
 
 As this new mode of exciting electricity was announced in 1800, we 
 may date from the beginning of the present century the commencement 
 of the science of voltaic electricity. In the early days of this discovery it 
 was not determined whether to consider it as a modification of the electric 
 fluid, or as a distinct agent excited by the contact of metals, though the 
 researches of the most eminent electricians have since established the iden- 
 tity of the two. 
 
 The points of resemblance between the two electricities are, that both 
 produce similar effects on the nerves that contract the muscles and occa- 
 sion the electric shock, which may be communicated through a great num- 
 ber of persons instantaneously ; that the same substances are conductors 
 and non-conductors of both kinds of electricity ; that both possess the 
 power of igniting and heating ; that sparks are emitted by the voltaic 
 battery when great numbers of plates are used to increase the intensity of 
 the force : that the phenomena of attraction and repulsion are common to 
 both, and by both chemical decomposition can be effected. 
 
 The differences between voltaic and frictional electricity consist in the 
 continued duration of the effects of the former, and in the different states 
 of intensity in which they are evolved : voltaic electricity being evolved 
 in great quantity at a low degree of intensity, whilst the quantity of fric- 
 tional electricity excited is comparatively very small, but at a high degree 
 of intensity. These different conditions in which the electricities of the 
 voltaic pile and of the electrical machine are excited, occasion a difference 
 in the phenomena of each. It was not, for example, an easy matter to 
 make an arrangement with frictional electricity for the exhibition of che- 
 
THE HISTORY OF ELECTRICITY. 31 
 
 mical decomposition, nor could the electric spark be readily made to force 
 itself through even the smallest space of air from a voltaic battery. The 
 experiments of Dr. Wollaston, of Sir Humphrey Davy, and more recently 
 of Dr. Faraday, have, however, removed all doubts respecting the power 
 of frictional electricity to effect chemical decomposition ; and Mr. Crosse, 
 with a water battery of 2000 cells, has evolved voltaic electricity possess- 
 ing sufficient tension to force itself in a rapid succession of sparks through 
 a small intervening space of air. 
 
 Numerous attempts were made soon after the announcement of Volta's 
 discovery and invention to improve the form of apparatus, and these en- 
 deavours have been continued with more or less success to the present 
 day, though the arrangement & couronne de tosses, modified and rendered 
 more compact, is still that most frequently adopted. The only marked 
 variations in the principle of construction which require to be noticed in 
 this part of our work, were the increase of the quantity of electricity by 
 enlarging the size of the plates, so as to communicate greater heating power 
 to the battery, and the increased intensity produced by greatly adding to 
 the number of combinations, as in the column of De Luc. The latter 
 arrangement deserves notice also, from the circumstance that no moisture 
 is applied to produce the effects. This apparatus, as improved by Zam- 
 boni, consists of paper, on one side of which is pasted finely laminated 
 zinc, and the other is covered with powdered black oxide of manganese. 
 The paper so prepared is cut into discs about one inch in diameter, which 
 are arranged over one another with the' zinc sides placed in the same 
 direction, and they are enclosed within a glass tube after having been 
 pressed together. This instrument, when it consists of a pile of 10,000 
 discs, exhibits a constant excitement of electricity of considerable intensity. 
 It deflects the gold leaves of the electrometer, yields small sparks, charges 
 a Leyden jar, and attracts and repels light substances in the manner of an 
 excited glass tube. Its action continues without intermission for months, 
 and even for years. A pile consisting of 1000 prepared paper discs may 
 be arranged so as to keep a small pendulum vibrating between its oppo- 
 site poles, and it thus approaches more closely than any other invention 
 to perpetual motion.* 
 
 In this instrument the paper is the substance interposed between each 
 pair of metallic exciters, and though apparently dry, it contains sufficient 
 moisture in all states of the atmosphere to act as a conductor. 
 
 The exciting cause of electricity in the voltaic battery was conceived 
 by Volta to be the contact of dissimilar metals. The liquid wherein the 
 plates are immersed was regarded merely as the conductor of electricity 
 from one pair to another, and the advantage of employing saline solutions 
 in preference to water was attributed to their superior conducting power. 
 This theory was quickly combated by Dr. Wollaston, who ascribed the 
 effect entirely to the chemical action of the solution on the zinc. That 
 opinion was afterwards ably confirmed by Sir Humphrey Davy, who 
 proved, by various experiments, that chemical action is essential to the 
 excitement of voltaic electricity. He shewed, also, that a voltaic battery 
 
 * We ought perhaps to except the German atmospherical clock, shewn at the Great 
 Exhibition, in which the variations in the pressure of the atmosphere were applied as 
 the motive power. 
 
32 THE HISTORY OF ELECTRICITY. 
 
 may be constructed without any metallic element. In November 1801 r 
 he formed a battery of this kind, which consisted of ten pieces of well- 
 burnt charcoal, with nitric acid and water arranged alternately in wine- 
 glasses, which produced all the effects usually obtained from an alternate 
 arrangement of zinc, silver, and water. More recently, Dr. Faraday has 
 shewn, that when the usual elements are employed, voltaic action may be 
 excited without contact of the metals. Notwithstanding these evidences 
 of chemical action, the contact theory continues to be the favourite hypo- 
 thesis with philosophers on the continent, and the action of De Luc's 
 column, without the perceptible presence of any fluid, has given support 
 to their arguments. 
 
 Whether chemical action be, or be not, the exciting cause of voltaic 
 electricity, the agency of that power in disturbing chemical affinities is one 
 of its most remarkable and important characteristics. Nor did this extra- 
 ordinary power long lie dormant. Two months before Volta's communica- 
 tion was read before the Royal Society, Messrs. Nicholson and Carlisle 
 effected the decomposition of water by Volta's apparatus, which had been 
 described in foreign journals ; and Sir Humphrey Davy, improving on 
 these experiments, succeeded in producing the oxygen and hydrogen gases 
 from separate portions of water, in different glasses, connected together by 
 moistened threads. Following up these experiments, he decomposed se- 
 veral compound bodies, and in every case he found that when substances 
 containing sulphur or metal combined with oxygen were operated on, the 
 sulphur and metal appeared at the negative end of the battery, and oxygen 
 at the positive end. He was led to infer from these and similar experi- 
 ments with the voltaic battery on the decomposition of bodies, that elec- 
 trical action is identical with chemical affinity. 
 
 In pursuing his investigations into the nature of the action of the vol- 
 taic battery, Sir Humphrey Davy ascertained that the intensity increases 
 with the number of the plates, and that the quantity of electricity excited 
 is dependent on their size ; a fact which was subsequently verified by Mr. 
 Children, who with a single pair of very large plates of zinc and copper 
 was enabled readily to melt the most infusible metals. 
 
 Armed with such a powerful decomposing agent as the voltaic battery,, 
 numerous chemical experimentalists pursued their researches into the 
 elementary constituents of bodies with great ardour. Dr. Henry decom- 
 posed several of the acids, and resolved ammonia into its proximate ele- 
 ments. Berzelius transferred the elements of neutral salts to their respec- 
 tive poles : the acids being collected at the copper end of the battery, and 
 the alkalies and earths being attached to the zinc terminus. These and 
 various other results were published in the journals, and served to give 
 additional stimulus to electro-chemical investigations. 
 
 Whilst scientific men were anxiously looking for important results 
 from the inquiries thus sedulously pursued, there appeared in the Philoso- 
 phical Journal a letter signed E. Peel, of Cambridge, announcing that, in 
 his experiments on the decomposition of water, he had invariably found 
 the pure water with which he commenced operating impregnated with 
 common salt. This announced generation of salt by the action of the vol- 
 taic battery excited a lively sensation amongst philosophers in most parts 
 of Europe. Some applied themselves to verify the experiment, whilst 
 others speculated on the new light thus thrown on the cause of the sea 
 
THE HISTORY OF ELECTRICITY. 33 
 
 being salt. The announcement was, however, soon afterwards detected to 
 be a hoax, there being no person of the name of Peel at Cambridge. In 
 the meantime, while the concocter of this practical joke was probably 
 enjoying its success, experimentalists had actually obtained the results 
 which he had published as a wildly extravagant notion. It was ascer- 
 tained that distilled water, after having been acted on for some time by 
 a voltaic current, contained in every case an appreciable quantity of salt. 
 This proved a most perplexing discovery. The apparent creation of mat- 
 ter by voltaic action was as difficult to account for, as in later days has- 
 been the apparent creation of living insects by the same agency. Sir 
 Humphrey Davy entered ardently into the investigation, and after a con- 
 tinued series of carefully conducted experiments, he ascertained that the 
 salt or earthy matter eliminated was extracted from the substance of the 
 threads employed, or was owing to the partial decomposition of the glass 
 vessels in which the experiments were conducted. The more careful he 
 was in avoiding these sources of error, the water became more free from 
 saline particles ; and when fibres of pure asbestos were substituted for 
 thread, and agate cups for glass, no trace of alkali or earthy matter was 
 to be detected in the water. 
 
 It was in consequence of these researches, undertaken for the purpose 
 of shewing that the results of the experiments on the Continent were as 
 illusory as the ignis fatuus which lighted the way to them, that Sir 
 Humphrey Davy was led into the course of experiments which terminated 
 in his brilliant discovery of the metallic bases of the alkalies and earths. 
 The circumstance that the origin of one of the most important discoveries 
 in science may be thus traced to the senseless trick of an unknown indi- 
 vidual, presents a remarkable feature among the curiosities of science, and 
 affords ample food for reflection to the speculative philosopher on the eli- 
 mination of valuable truths from falsehood and error. 
 
 It is not strictly within our province to notice the labours of chemical 
 experimentalists ; but the decomposition of the alkalies and earths exhibits 
 such striking examples of the chemical power of voltaic electricity, that 
 the discovery of their bases by its means may be fairly considered to belong 
 to the history of the progress of electric science. 
 
 From the first announcement of the discovery of the voltaic battery, 
 Sir Humphrey Davy foresaw the vast importance of its agency in chemical 
 researches. In a note-book dated August 6th, 1800, he writes : "I cannot 
 close this notice without feeling grateful to M. Volta, Mr. Nicholson, and 
 Mr. Carlisle, whose experience has placed such a wonderful and important 
 instrument of analysis in my power."* In his first Bakerian lecture six 
 years afterwards, he expresses the hope that " the new mode of analysis 
 may lead us to the discovery of the true elements of bodies, if the ma- 
 terials acted on be employed in a certain state of concentration, and the 
 electricity be sufficiently exalted. For, if chemical union be of the nature 
 which I have ventured to suppose, however strong the natural energies of 
 the elements of the bodies may be, yet there is every probability of a limit 
 to their strength ; whereas the powers of our artificial instruments seem 
 capable of indefinite increase."t 
 
 * Memoirs of the Life of Sir Humphrey Davy, Bart., by John Davy, M.D. 
 f Ibid. 
 
34 THE HISTORY OF ELECTRICITY. 
 
 In conformity with the notion of counteracting chemical attraction by 
 electrical agency, he instituted a series of experiments on potass with a 
 view to its decomposition ; the compound nature of the alkalies having 
 been for some time suspected. At first he experienced great difficulty in 
 getting the electric current to act on the potass, which when in a solid 
 state is a non-conductor of electricity, and when acted on in solution the 
 water only was decomposed. The first successful results were obtained 
 by employing fused potass ; inflammable matter was then developed, which 
 burst into flame the instant it was formed. The complete success of the 
 investigation occurred on the 6th of October. The following brief account 
 of the discovery is contained in a manuscript of a lecture delivered at the 
 Koyal Institution. 
 
 " Experiments. Then a piece of potass, moistened, and to my great 
 surprise I found metallic matter formed. 
 
 " Oct. 6th. This matter instantly burnt when it touched water, swam 
 on its surface, reproducing potass. In dry oxygen gas likewise it burnt 
 into perfectly dry potass."* 
 
 " The extreme delight which he felt when he first saw the metallic 
 basis of potass," observes Sir Humphrey Davy's brother, " can only be 
 conceived by those who are familiar with the operations of the laboratory, 
 and the exciting nature of original research ; who can enter into his pre- 
 vious views, and the analogies by which he was guided ; and can compre- 
 hend the vast importance of the discovery in its various relations of che- 
 mical doctrine ; and, perhaps, not least, who can appreciate the workings 
 of a young mind with an avidity for knowledge and glory commensurate ? 
 I have been told that when he saw the minute globules of potassium burst 
 through the crust of the potass, and take fire as they entered the atmo- 
 sphere, he could not contain his joy he actually danced about the room 
 in ecstatic delight, and that some little time was required for him to com- 
 pose himself sufficiently to continue the experiment." 
 
 The battery power employed by Sir Humphrey Davy in effecting this 
 brilliant result consisted of a combination of twenty-four plates of copper 
 and zinc twelve inches square, one hundred plates of six inches, and one 
 hundred and fifty of four inches. As it is a peculiar property of the 
 voltaic battery that the quantity of electricity transmitted by a series of 
 plates is dependent on the size of the smallest plate of the series, it follows 
 that the power thus brought to bear was equal to that of a battery of 274 
 pairs of plates of four inches square. The managers of the Royal Insti- 
 tution afterwards placed at his disposal a voltaic battery of 600 double 
 plates four inches square : and a still larger battery, consisting of 2000 
 plates, was constructed by subscription for his use. 
 
 The important discoveries of Sir Humphrey Davy, by means of the 
 voltaic battery, caused increased attention to be paid to that valuable 
 agent in chemical analysis, and voltaic batteries were made on a larger 
 scale than any that had previously been constructed. It is related that 
 when Napoleon heard of the decomposition of the alkalies by an English 
 philosopher, he angrily questioned the savans of the Paris Institute why 
 the discovery had not been made in France. The excuse alleged was the 
 want of a battery of sufficient power. He immediately commanded one to 
 
 * Memoirs of the Life of Sir Humphrey Davy, Bart., by John Davy, M.D* 
 
THE HISTORY OF ELECTKICITY. 35 
 
 be made; and when completed he went to the Institute to see it. With his 
 usual impetuosity, the Emperor seized hold of the wires, and before he 
 could be checked by the attendant, applied them to his tongue. His 
 imperial majesty was rendered nearly senseless by the shock; and as soon 
 as he recovered from its effects, he walked out of the laboratory with as 
 much composure as he could assume, not requiring further experiments 
 to test the power of the battery ; nor did he ever afterwards allude to the 
 subject.* 
 
 With the powerful voltaic batteries that were then constructed, the 
 course of investigation into the constituent parts of bodies was steadily 
 pursued ; and numerous compound substances yielded up their elements 
 to the decomposing influence. Substances that had resisted the greatest 
 heat of the furnace were readily fused, and even the diamond was burnt 
 in the voltaic arc, and its chemical character was identified with carbon. 
 
 We must not omit to notice the attempt made during this period by 
 Sir H. Davy to practically apply voltaic electricity for the prevention of 
 the corrosion of the copper sheathing on ships. He had ascertained, when 
 two metals in contact are immersed in a saline solution, that whilst an 
 increased action takes place on one of the metals, caused by contact, the 
 action of the solution on the other is diminished. Copper, for example, 
 undergoes corrosion in sea-water ; but when zinc is in contact with it the 
 corrosion of the copper ceases. Sir H. Davy applied this principle to 
 copper sheathing, by protecting it with strips of zinc. The experiment 
 succeeded scientifically by preventing corrosion, but it practically failed ; 
 for the copper thus protected became covered with sea-weed and shell-fish, 
 which do not adhere to the corroded surface. Sir H. Davy was deeply 
 mortified at the failure of this experiment in a practical point of view ; 
 but it has led to the discovery of an alloy of copper that answers the 
 purpose intended very successfully. 
 
 CHAPTER IV. 
 
 Discovery of Electro-magnetism Increase of the force by coils of wire Electro-mag- 
 nets Tangential action of the force Invention of the Galvanometer Its application 
 to telegraphic purposes Discovery of Magneto-electricity Magneto-electrical ma- 
 chines Thermo-electricity Faraday's experimental researches Introduction of 
 new terms Daniell's constant battery Discovery of the electrotype process De- 
 velopment of electricity from high-pressure steam Present state of electric science. 
 
 THOUGH the investigations, conducted with the powerful means at com- 
 mand, elucidated many interesting facts, no striking incident occurred for 
 several years ; and Dr. Bostock, in his History of Galvanism, appears to 
 have considered that discoveries by the agency of the voltaic battery had 
 reached their end. His words are : " It may be conjectured that we have 
 carried the power of the instrument to the utmost extent of which it 
 admits; and it does not appear that we are at present in the way of 
 making any important additions to our knowledge of its effects, or of 
 
 * Dr. Paris's Life of Sir Humphery Davy. 
 
36 THE HISTORY OF ELECTRICITY. 
 
 obtaining any new light on the theory of its action." This was written 
 in 1818j and in the next year a new light almost as brilliant as any of 
 the preceding flashes that had illumined its progress was thrown on elec- 
 tric science by the discovery of electro-magnetism. 
 
 That a close relation subsisted between electricity and magnetism had 
 been known from an early period of its history, and the identity of the two 
 had formed a subject of discussion. 
 
 Franklin and his contemporary electricians had communicated mag- 
 netism to small bars of steel by the charge of an electrical battery ; and 
 the power it exerted in destroying and reversing polarity was also known. 
 
 It may be mentioned, as an indication that the question of the pro- 
 bable identity of magnetism and electricity excited considerable attention, 
 that in 1774 the Electoral Academy of Bavaria proposed as the subject 
 of a prize-essay : " Is there a real and physical analogy between electric 
 and magnetic forces ; and if such analogy exists, in what manner do these 
 forces act on the animal body?" Though the prize was gained by a pro- 
 fessor who maintained that the two powers were essentially distinct from 
 each other, there were not wanting competitors who as strenuously main- 
 tained that the forces were the same, though modified by special circum- 
 stances. The impression, indeed, of the identity of electrity and magnetism 
 continued very strong; and it seems a remarkable omission in the investi- 
 gations of philosophers, especially after the discovery of the voltaic pile, 
 that no well-conducted experiments were undertaken to ascertain more 
 closely the relations between the two forces. 
 
 Professor (Ersted of Copenhagen, to whom the world is indebted for 
 the discovery of this new and practically useful department of science, 
 published a work in 1807, in which he described the analogies between 
 magnetism and electricity, wherein there occurs the following remarkable 
 passage : " In galvanic action the force is more latent than in electricity; 
 and it is still more so in magnetism than in galvanism. It is necessary, 
 therefore, to try whether electricity in its latent state will not affect the 
 magnetic needle." It does not appear, however, that (Ersted actually tried 
 the experiment indicated in his book ; nor does any one else seem to have 
 made the trial, though we now know that the question would have been 
 determined by merely placing a magnetic needle over the wire connected 
 with a voltaic battery. It was not till 1819, twelve years after he had 
 pointed out the way to others, that (Ersted followed the course he had 
 indicated, and by bringing a magnetic needle in the direction of a voltaic 
 current, ascertained that the conducting wire is itself magnetic. He found 
 also that the nature of the conducting medium is immaterial to the result, 
 and that whether the voltaic circuit be compelled through metals or 
 through a fluid, the magnetic needle is equally affected ; being deflected 
 in one direction when placed over the conductor, and in the opposite 
 direction when under it. 
 
 The discovery was no sooner made known than all those who were 
 engaged in scientific researches throughout Europe pursued the inquiry 
 with diligence, and continually elicited additional facts, which bestowed 
 increased importance on this correlative branch of electric science. MM. 
 Ampere and Arago, of the French Academy of Sciences, having discovered 
 that the direction of the magnetic force is tangential to the wire, suc- 
 ceeded in multiplying the power by twisting the conducting wire into 
 
THE HISTORY OP ELECTRICITY. 37 
 
 a spiral coil. In this manner the action of the voltaic current was fre- 
 quently repeated within a small area ; and by adopting this arrangement 
 sufficient magnetic force was obtained to attract iron filings to the coil, 
 and a steel bar placed within it was quickly magnetised. 
 
 In September of the same year that Professor CErsted's discovery was 
 known, M. Arago communicated to the French Academy that the electric 
 current possesses the power of imparting magnetism to iron and steel; and 
 Sir Humphrey Davy ascertained independently the same important fact, 
 though somewhat later. 
 
 It was ascertained that the coil of wire through which the voltaic cur- 
 rent was transmitted in these experiments operated in all respects like a 
 magnet ; but that the action ceased instantaneously when the current was 
 interrupted. The power of the coil was found to be greatly augmented by 
 introducing a bar of iron within it, to which bar magnetic properties were 
 instantly communicated ; but if the iron were pure and soft, those proper- 
 ties ceased the moment that the electric circuit was broken. The nearer 
 the whorls of the coil were brought together without touching, the effect 
 was found to be more concentrated. To prevent the communication of the 
 electricity laterally in the folds of the coil, the wire was insulated ; by 
 varnish in the first instance, and afterwards by winding silk or cotton 
 round it, to prevent metallic contact ; that slight degree of separation 
 being sufficient to prevent the conduction of voltaic electricity. 
 
 The insulation of the wire, trifling as the improvement appears to be, 
 afforded the means of increasing the power of electro-magnetism to a most 
 astonishing degree. Not only could the wire of the coil be twisted close 
 together, but it could be wound upon itself many folds in thickness, each 
 additional layer of wire giving increased magnetic effect. In this manner 
 electro-magnets could be formed with sufficient attractive power to lift 
 upwards of a ton ; yet this attraction, so far exceeding that of any arti- 
 ficial magnet that can be made by other means, ceases the instant that 
 the connexion is broken between the coil of wire surrounding it and the 
 voltaic battery. 
 
 Professor (Ersted having ascertained that the electric current passing 
 through a conducting wire acts on the magnetic needle transversely in 
 every position in which it can be placed, he inferred that the magnetic 
 effect of the electric current is to give a circular motion round the wire. 
 M. Ampere entertained the same view, and proved by experiment that 
 the conducting wires of two galvanic currents, if free to move, would 
 mutually attract each other. Dr. Faraday contrived an ingenious appa- 
 ratus for shewing not only the rotation of a magnet round a conducting 
 wire, but the rotation of a conducting wire round a magnet. This seemed 
 to confirm the previously announced theory of M. Ampere, that magnetism is 
 induced by circular currents round the magnetised bodies ; and it appeared 
 also to introduce an anomaly in the action of moving forces, which are al- 
 ways exerted in straight lines. The apparent anomaly may probably be re- 
 moved by resolving the circular motion, like that of all other bodies moving 
 in curves, into the operation of two forces acting in different directions. 
 
 The communication of rotary motion by electro-magnetism, and the 
 powerful attractive force called into action in electro-magnets, were con- 
 sidered to indicate a new and valuable source of motive power, that could 
 be applied directly to the production of rotary motion. Numerous at- 
 
38 THE HISTORY OF ELECTRICITY. 
 
 tempts were made to apply the power to useful purposes as a substitute 
 for steam, and the notion is not yet abandoned ; though there have been 
 hitherto no practical results that lead us to expect the object will be at- 
 tained. 
 
 A most valuable instrument in conducting researches in voltaic elec- 
 tricity was contrived shortly after the discovery of the magnetic influence 
 of the voltaic battery, and depending on that influence for its action. 
 The low state of tension of voltaic electricity prevents it from being ap- 
 preciable by the ordinary electrometer, excepting when the intensity is 
 increased by the combination of a series of plates. An attempt was made 
 by Mr. Pepys, in the very infancy of voltaic electricity, to obtain an indi- 
 cation of its force by increasing the sensibility of the gold-leaf electrometer; 
 and he so far succeeded that with a pile consisting of a series of eighty 
 pairs of plates, he produced a very decided deflection of the gold leaves, 
 but the instrument afforded no indication of electricity with a much smaller 
 number.* 
 
 The experiment that discovered electro-magnetism, at the same time 
 pointed out the means of measuring its force. The deflection of the mag- 
 netic needle by the conducting wire of the battery afforded a highly 
 sensitive indicator of the excitement of voltaic electricity. When the 
 method of multiplying the force by means of folds of insulated wire 
 twisted into a spiral coil became known, it was quickly made available 
 for giving increased sensibility to the magnetic needle ; and in this manner 
 galvanometers were constructed of such extreme delicacy as to detect the 
 minutest portions of electricity. 
 
 The invention of the galvanometer suggested the application of that 
 instrument to the purpose of communicating telegraphic signals. That 
 plan has, after numerous improvements, attained such a degree of perfec^ 
 tion, that by the varied deflections of two galvanometer-needles communi- 
 cations are transmitted between places hundreds of miles asunder almost 
 as quickly as they can be written down. The idea of employing elec- 
 tricity, though in a different manner, for telegraphic purposes was indeed 
 by no means new. So far back as 1774 a plan was proposed of transmit- 
 ting signals through wires by causing pith balls to be deflected when an 
 electric discharge was made. It was in 1830 that M. Ampere suggested 
 the application of deflected needles, and in 1837 Mr. Alexander of Edin- 
 burgh exhibited in London the first electric telegraph on that principle. 
 The plan was, however, impracticable, as it required a separate magnetic 
 needle and a separate insulated wire for each letter of the alphabet. 
 
 We shall not attempt at present to follow the course of telegraphic 
 invention, which will be fully described when we come to treat of the 
 practical applications of electricity. It is sufficient in this place to observe 
 that since the application in 1837 of M. Ampere's suggestion, there have 
 been at least one hundred patents obtained for different modes of tele- 
 graphic correspondence, most of them based on the same principle, or 
 depending for their action on electro-magnetism ; and that by employing 
 electro-chemical agency, communications may now be instantaneously 
 transmitted with a single connecting wire ten times faster than any one 
 can write. 
 
 * Philosophical Journal, June 1801. 
 
THE HISTORY OF ELECTRICITY. 39 
 
 In pursuing investigations into the phenomena of electricity, Dr. 
 Faraday was led to infer that as a current of electricity induces mag- 
 netism, the magnetic force would induce electricity. Aided by the multi- 
 plying power of the coil, and by the sensitiveness of the galvanometer, he 
 was enabled to prove the correctness of the inference, and to establish the 
 foundation of the branch of electric science termed magneto-electricity. 
 His experiments were conducted in the year 1831, and shortly produced 
 most important results. 
 
 The induction of electricity by magnetism was in the first instance 
 shewn by connecting a hollow coil of wire with a galvanometer, and then 
 inserting within the coil a powerful steel magnet. Whilst the magnet 
 remained in the coil, the galvanometer gave no indication; but on quickly 
 withdrawing the magnet, the needle was instantly deflected. A similar 
 temporary deflection was observed to take place when the magnet was 
 quickly introduced ; and in November of the same year Faraday derived 
 still more complete evidence of induction by eliciting an electric spark. 
 The effect produced by inserting and withdrawing the permanent magnet 
 into and out of the coil of wire was found to be greatly augmented when 
 an electro-magnet was substituted for the permanent steel one, and contact 
 with the voltaic battery was rapidly made and broken. The instant that 
 the iron was rendered magnetic, by making contact with the battery 
 wires, the temporary transmission of electricity took place through the 
 coil of wire which surrounded it; and by making and breaking contact 
 with great rapidity, there was a continuous succession of electrical effects. 
 The electricity thus induced in what is now termed the secondary cwr- 
 rent was ascertained to be of a high degree of intensity, and to pass in a 
 contrary direction to that of the primary current. The phenomena be- 
 came more marked when the length of wire in the coil of the secondary 
 circuit was increased ; so that by adding to its length, a degree of intensity 
 was obtained equal to that of a numerous series of plates of a voltaic 
 battery, though the primary exciting cause which communicated magnetism 
 to the iron was only a single pair. 
 
 By improved mechanical arrangements, the principle of electro-dy- 
 namic induction brought to light by the experiments of Faraday has been 
 made to operate as a most powerful exciter of electricity. Magneto-elec- 
 tric machines have been constructed with permanent steel magnets, that 
 possess the power of the most intense voltaic batteries ; giving shocks 
 that are insupportable, emitting sparks, and operating as active decom- 
 posing agents. The instrument is also capable of being arranged as an 
 exciter of quantity-electricity in a comparatively lower state of intensity, 
 so as to fuse wire, induce magnetism, and exhibit the other phenomena 
 common to the voltaic electricity excited from a pair of plates of large 
 size. This mode of exciting electricity, independently of the friction of 
 electrics or of chemical action, seemed to present the advantage of pro- 
 curing a powerful agent with comparatively little labour and no cost of 
 materials ; and attempts have been consequently made, with considerable 
 success, to apply it to practical purposes, which we shall have subse- 
 quently to notice. 
 
 Though the world is indebted to Faraday for the development of the 
 induction of electricity from steel magnets, the fact that electrical effects 
 could be so elicited had been imperfectly discovered at the beginning of 
 
40 THE HISTORY OF ELECTRICITY. 
 
 the present century ; but it had then no results, and was soon forgotten. 
 The only notice of that discovery which we have been able to find occurs 
 in the Monthly Magazine for April 1802, to this effect : " Galvanism is 
 at present a subject of occupation of all the German philosophers and 
 chemists. At Vienna an important discovery has been announced an arti- 
 ficial magnet, employed instead of Volta's pile, decomposes water equally 
 well as that pile, or the electrical machine, whence it has been concluded 
 that the electric, galvanic, and magnetic fluids are the same." It is cu- 
 rious to observe how thus in the course of time discoveries and inventions 
 that have passed away and been disregarded, because circumstances were 
 not then suited to their development, are revived in later years either by 
 accident or original research and ingenuity, and become important ele- 
 ments in the advance of science and the progress of civilisation. We may 
 notice also, in the preceding announcement, that the fact of the correlative 
 nature of the three forces, which has been established by the persevering 
 investigations of modern philosophers, was anticipated fifty years ago. 
 
 For the purpose of not breaking in upon the outline of the progress of 
 electro-magnetism, we have passed by other discoveries of considerable 
 importance to which it is necessary to revert. 
 
 An additional source of electricity was developed, in the year following 
 the discovery of electro-magnetism, by Dr. Seesbeck, who communicated 
 to the Academy of Berlin that he had succeeded in exciting electricity by 
 the disturbance of temperature. He ascertained that two metals anti- 
 mony and bismuth being the most effective when soldered together at 
 their extremities and then heated at the joints, whilst the other ends 
 are kept cool, produce a decided deflection of the galvanometer. This 
 property of the metals has no reference to their efficiency in voltaic ar- 
 rangements, nor to their powers of conducting electricity. The effects first 
 produced by Dr. Seesbeck were derived from the combination of four bars 
 of antimony and bismuth in the form of a rectangular frame, one corner 
 of which was heated and the other covered with ice. 
 
 Messrs. Nobili and Melloni succeeded in constructing thermo-electric 
 piles by the combination of a series of bars of metal soldered together. 
 With this apparatus most of the ordinary electrical phenomena have been 
 produced, including the appearance of the electric spark, the decompo- 
 sition of water, and the communication of magnetic properties. The 
 quantity of electricity evolved by this means is, however, very small ; and 
 thermo-electricity has yet assumed scarcely any importance ; though some 
 philosophers are disposed to ascribe the magnetism of the earth to thermo- 
 electric currents circulating round the globe. 
 
 Long previous to the discovery of Dr. Seesbeck, the influence of 
 heat in exciting electricity had been ascertained, though the knowledge 
 was then limited to its effects on crystalline bodies. In 1717 M. Lemery 
 exhibited to the French Academy of Sciences a stone, supposed to be 
 tourmalin, which attracted light substances ; and the Duke de Noya per- 
 formed many electrical experiments with that crystalline body ; but it was 
 ./Epinus who first shewed that heat was necessary to produce the pheno- 
 mena. The Abbe* Haiiy, celebrated for his researches in crystallography, 
 found that the electricity of the tourmalin decreased rapidly from the poles 
 of the crystal, and that when broken, each fragment is electrical, and in a 
 similar polar condition. He afterwards discovered that topaz and many 
 
THE HISTORY OF ELECTRICITY. 41 
 
 other crystals of similar conformation exhibit signs of electricity when 
 heated. Sir David Brewster has more recently discovered that the same 
 property extends also to the crystals of many salts. 
 
 The crystalline bodies which could thus be acted on by heat 'were 
 called pyro-electrical. As their phenomena depend on the same exciting 
 cause as that which produces electricity in variably expansive metals, they 
 may be considered as belonging to thermo-electricity ; and we have deferred 
 noticing them till they could be classed together with the crystalline metals 
 that become electrical by heat. 
 
 Professor Faraday commenced in 1832 a series of experimental re- 
 searches into the nature of electro-chemical action, the results of which 
 were published from time to time in the Philosophical Transactions from 
 1833 to 1844, and constitute most valuable contributions to electric science. 
 One important point which these researches tend to prove is, that in the 
 course of electro-chemical decomposition the elementary atoms of the 
 compound substance acted on are transferred from atom to atom of the 
 fluid, in a continuous chain from one pole of the battery to the other; the 
 conduction of voltaic electricity through fluids being thus dependent on a 
 successive series of decompositions and recompositions in opposite direc- 
 tions. Another important point which they may be considered to have 
 established is, the law of definite electro-chemical action; that "for 
 a constant quantity of electricity, whatever the decomposing conductor 
 may be, whether water, saline solutions, acids, fused bodies, &c., the 
 amount of electro-chemical action is also a constant quantity, i. e. would 
 always be equivalent to a standard chemical effect founded upon ordinary 
 chemical affinity."* 
 
 According to the views of Professor Faraday, electro-chemical decom- 
 position is occasioned by " an internal corpuscular action excited according 
 to the direction of the electric current ; and that it is due to a force either 
 superadded to or giving direction to the ordinary chemical affinity of the 
 bodies present." He conceives, therefore, the effects of the decomposition 
 " to arise from forces which are internal relative to the matter under de- 
 composition and not external, as they might be considered if directly 
 dependent upon the poles." 
 
 To express these views of the action and direction of the forces ex- 
 erted during electro-chemical decomposition, Faraday conceived that the 
 terms previously employed were inefficient ; he therefore determined to 
 introduce a nomenclature suitable to the modes of action indicated. He 
 obtained the assistance of two classical friends to aid him in this under- 
 taking, and the result was the application of several Greek terms to denote 
 processes and things which had been long known by other names. It 
 may seem presumptuous to question the propriety of the course adopted 
 by that eminent philosopher, but so strong is our impression of the in- 
 jurious effects of multiplying terms requiring constant explanation, that 
 we venture to express our conviction that it has tended unnecessarily to 
 encumber the study of electricity. 
 
 The nomenclature of every science ought, in our opinion, to be ex- 
 tremely simple, and, if possible, clearly expressive of the character or 
 action of the thing or process designated ; nor do "we perceive any equi- 
 
 * Experimental Researches in Electricity, Tf 505. 
 D 
 
42 THE HISTORY OF ELECTRICITY. 
 
 valent advantage gained by the adoption of the words of a dead language, 
 which often serve no better purpose than to conceal by their unfamiliar 
 sounds absurd, puerile, or questionable designations. The terms previ- 
 ously in use to express the different electrical phenomena and conditions 
 were so various as to afford ample choice to those who entertain differing 
 views of the nature and actions of the electric fluid. There were " plus 
 and minus" " positive and negative," " vitreous and resinous," to express 
 the kinds of electricity excited ; and " electrics," " ideo-electrics," " non- 
 electrics," " conductors," and " non-conductors," to indicate the electrical 
 qualities of different substances. When voltaic electricity gave rise to new 
 terms, the copper or zinc " end " of the battery was an intelligible English 
 expression to denote what those more fond of classic names called " ter- 
 minus, " and which afterwards received the name of " pole. " Posses- 
 sed of this abundance of expressions, we do not conceive that any good 
 purpose is answered by adding to the list a number of Greek words and 
 terminations to express supposed analogies in the action of the voltaic 
 battery. Faraday himself had evidently misgivings on the subject ; for 
 after explaining the meaning of the new terms, he adds : " I do not mean 
 to press them into service more frequently than will be required j for I 
 am fully aware that names are one thing, and science another ;" and he 
 afterwards found it advisable to change some of the terms for " such 
 as were at the same time simple in their nature, clear in their reference, 
 and free from hypothesis."* It is to be wished that he had from the 
 first acted on his own judgment and knowledge, without being guided by 
 his learned friends. 
 
 As it is our intention to present a clear and intelligible view of the 
 science of electricity free from unnecessary technicality, we shall endea- 
 vour to avoid using any portion of the nomenclature constructed by Pro- 
 fessor Faraday's philological friends ; but as those terms will be often met 
 with in other works on the subject, they must not be passed by unnoticed. 
 We therefore adopt the following abbreviated explanation by Mr. Noad : f 
 " What are called the poles of the voltaic battery are merely the sur- 
 faces 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 f/XcKT/oov and 6c)oe, a way, meaning thereby the sub- 
 stance 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. 
 
 " The surfaces at which the electric current enters and leaves a decom- 
 posing body he calls the anode and cathode, from ava, upwards, and bSbg, 
 a way the way which the sun rises; and rara, downwards, and 6c)oe, 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." "The anode is, 
 therefore, that substance 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 
 
 * Experimental Researches in Electricity, vol. i. ^[ 666. 
 f Lectures on Electr.city. 
 
THE HISTORY OP ELECTRICITY. 43 
 
 body ; the combustible bodies, metals, alkalies, and bases are evolved there, 
 and it is in contact with the negative electrode." " Compounds directly de- 
 composable by the electric current are called electrolytes, from ijXeicrpov and 
 Xww, to set free to dectrolyze a body is to decompose it electro-chemically : 
 the elements of an electrolyte are called ions, from iwv, participle of the 
 verb eifjn, to go ; anions are the ions which make their appearance at the 
 anode, and cations are the ions which make their appearance at the 
 cathode, and were termed the electro-positive elements." " 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." 
 
 We have abstained from noticing the many alterations and improve- 
 ments in the form and construction of the voltaic battery that have been 
 introduced since the original discovery by Volta, partly because those 
 which are of practical importance will be afterwards described, and partly 
 also because such improvements are not of a character to produce any 
 notable impression on the course of electrical discovery. The " constant" 
 battery of Professor Daniell, however, invented in 1832, requires to be 
 noticed in this place ; not only from the distinguishing principles of its 
 action, but from its influence on the discovery of the process of electro- 
 metallurgy. 
 
 In the arrangement cb couronne de lasses of Volta, and in all subsequent 
 contrivances for exciting voltaic electricity, the action of the battery dimi- 
 nished rapidly after the first minute. This was attributable to the com- 
 bined causes of the collection of bubbles of hydrogen gas and the reduction 
 of the oxide of zinc on the conducting plate. Professor Daniell, with a 
 view to remove these obstructive effects, separated the fluid in which the 
 zinc plate was immersed from that of the copper by an animal membrane, 
 the interposition of which did not retard the passage of the electricity, 
 whilst it effectually prevented the deposition of zinc on the copper plate. 
 The collection of bubbles of hydrogen gas on that plate still, however, 
 operated against the perfect action of the battery. To remove this impe- 
 diment, the copper plate was immersed in a saturated solution of the 
 sulphate of copper, which was kept separate from the acidulated solution 
 surrounding the zinc plate by the animal membrane. By this arrangement 
 the evolution of hydrogen gas was altogether prevented ; for as quickly as 
 detached from its combination with the oxygen of the fluid menstruum 
 by the chemical action on the zinc surface, it seized on the oxygen of the 
 metallic salt, and the metal before held in solution was deposited on the 
 copper plate of the battery. Both of the previously existing causes of the 
 diminution of the force of the battery were thus removed, and by keeping 
 the solution in a saturated state, the action of the voltaic battery was 
 steadily sustained. This "constant" battery of Professor Daniell has 
 proved a most valuable aid in prosecuting researches and in conducting 
 processes that require the continuance of voltaic action for several days 
 with the same amount of force. 
 
 The deposition of pure metallic copper from the solution of the sul- 
 phate, and the increase in weight of the conducting-plate by the aggrega- 
 tion of particles of copper, could not fail to be observed from the earliest 
 use of the " constant" battery ; and Professor Daniell noticed that on the 
 
44 THE HISTORY OF ELECTRICITY. 
 
 removal of some portion of the deposited copper, the parts detached pre- 
 sented exact copies of the irregularities of the surface of the plate. Mr. 
 De la Kue, who indeed preceded Professor Daniell in the use of a solution 
 of sulphate of copper as the exciting fluid of an ordinary battery, sent 
 a communication to the Philosophical Magazine, published in December 
 1836, in which he mentions particularly the remarkable appearance of the 
 deposited copper : " So perfect," he observes, " is the sheet of copper thus 
 formed, that on being stripped off, it has the polish and even a coun- 
 terpart of every scratch of the plate on which it was deposited." 
 
 We perceive, therefore, how closely Mr. De la Rue had arrived at the 
 discovery of the electrotype process. It was, in fact, the process itself ; 
 conducted, however, without appreciation of its value, and without any 
 idea of its practical application. 
 
 In the earliest period of the history of voltaic electricity, indeed, we find 
 that M. Cruickshanks had observed that metals were " revived" from their 
 solutions at the negative pole of the battery ; and in 1 805 M. Brug- 
 notelli stated that he had " gilt in a complete manner two large silver 
 medals, by bringing them, by means of a steel wire, into communication 
 with the negative pole of a voltaic pile, and keeping them immersed in 
 ammoniuret of gold, newly made and well saturated." It was not, how- 
 ever, till 1839 that any practical application was made of the deposition of 
 metals from their solutions. There are three competitors for the honour 
 of the priority of invention ; but each one has the merit of having origi- 
 nated it about the same time independently of the others. M. Jacobi of 
 St. Petersburgh asserts that he made the application of the process in 
 February 1837; but the first notice of his experiments made known in 
 this country was published in the Athenaeum of May 4, 1839. In 1837, 
 Mr. Spencer of Liverpool had obtained a counterpart of the head and 
 letters reversed of a penny-piece, which he had fortuitously used as a con- 
 ducting-plate in his battery ; and on the week following the publication 
 of the notice of M. Jacobi's experiments, Mr. Spencer gave notice that he 
 should read a paper at the Liverpool Polytechnic Institution, containing 
 the -results of his experiments on the same subject ; but the reading of it 
 was deferred till September. In the mean time, a letter in the MecJianics 
 Magazine, from Mr. Jordan, a printer, gave a full and accurate description 
 of the process. It, however, attracted no attention ; and the matter 
 dropped until Mr. Spencer's paper was read in Liverpool, illustrated with 
 various specimens of electrotypes. 
 
 The first efforts with the electrotype process in this country were limited 
 to obtaining fac-similes of coins and medals. It was endeavoured to be 
 carried out on the Continent on a large scale, by applying it to the manu- 
 facture of all kinds of copper vessels ; but we believe the operation was 
 found more costly than the ordinary mode of fabrication. 
 
 Electro-chemical metallic deposits have been successfully applied to 
 coating natural objects with a film of metal, to the transference and mul- 
 tiplication of elaborately-engraved plates, and even the delicate pictures of 
 the Daguerreotype have been solidified by this means. But the most ex- 
 tensively-useful application of the process has been to silver-plating and to 
 gilding. Electro-plating has been carried to a high state of perfection, 
 and in many respects it possesses considerable advantages over the old 
 modes of operating. Electro-metallurgy is yet, however, in its infancy ; 
 
THE HISTORY OF ELECTRICITY. 45 
 
 and though the experiment of fabricating metallic vessels by means of 
 electro-chemical deposition has hitherto failed as a commercial under- 
 taking, it is not improbable that further improvements especially the 
 discovery of some cheaper means of exciting electricity for practical pur- 
 poses may eventually render it an important branch of manufacturing 
 industry. 
 
 A new and very unexpected source of electricity was discovered in 
 1840 in effluent high-pressure steam. The discovery arose accidentally, 
 owing to the issue of steam from a fissure in the boiler of a steam-engine 
 at Seghill, near Newcastle. The engineer happened to have one hand in 
 the issuing steam, whilst he touched the lever of the valve with the other, 
 and was surprised to see a bright spark, accompanied by an electric shock. 
 The same effect was produced whatever part of the boiler he touched, pro- 
 vided one hand was in the effluent steam. 
 
 Air. Armstrong, to whom the fact was communicated, instituted several 
 experiments with a view to develop the phenomena and ascertain their 
 cause. He obtained sparks four inches in length from the issuing steam, 
 by holding in it a bundle of wires, insulated by a glass rod, or held by a 
 person standing on a glass stool. When the boiler was insulated, the 
 electrical effects were increased, and it was found that more electricity 
 could be drawn from the boiler itself when thus situated, with the steam 
 issuing from it, than was collected by holding a conducting body in the 
 steam. The electricity of the boiler was generally found to be negative, 
 and that of the steam positive. 
 
 One of the extraordinary features of this discovery was the great 
 quantity of electricity evolved. Mr. Armstrong in his experiments with 
 a locomotive boiler produced effects upwards of seven times greater than 
 those from a plate-machine three feet in diameter, working at the rate 
 of seventy revolutions in a minute ; and the apparatus at the Poly- 
 technic Institution, which was constructed purposely for the evolution 
 of electricity from high-pressure steam, produces much more powerful 
 effects. 
 
 The cause of the development of electricity by this means was at first 
 considered to be owing to the capacity of steam for the electric fluid being 
 much greater when in its expanded state than when compressed within 
 the boiler ; and the phenomenon of the excitement of so large an amount 
 of electricity by change of state was thought to afford a satisfactory illus- 
 tration of the generation of atmospheric electricity. This explanation was 
 so simple, and appeared so completely in accordance with the Franklinian 
 theory of electrical excitement, that it seemed to command belief; and we 
 must admit it was with considerable reluctance we felt compelled to 
 abandon it. Professor Faraday undertook to investigate the question ; 
 and by a long series of well-devised and carefully -conducted experi- 
 ments, he appears to have proved very conclusively, that in the evo- 
 lution of electricity the steam acts only a secondary part ; and that the 
 immediate cause of the electrical excitement is the friction of particles of 
 water against the sides of the jet whence the steam issues. In pursuing 
 the experiments with compressed air and gases, as substitutes for steam, 
 the same results were obtained when the tubes and jets contained mois- 
 ture j but no electricity was apparent when the air and gases were dry. 
 
 An apparatus on a small scale for experimenting on the electricity 
 
46 THE HISTORY OF ELECTRICITY. 
 
 evolved by effluent steam is one of the wants of the laboratory ; and 
 without such means of investigation, the subject has not received so much 
 attention as it deserves. The great amount of electricity, of high inten- 
 sity, that can be thus excited, might probably by some more convenient 
 arrangement be rendered practically useful. 
 
 Since the discovery of the evolution of electricity during the emission 
 of high-pressure steam, there has been no marked advance in electric 
 science. The last ten years have, however, been distinguished for nume- 
 rous ingenious applications of electric force, which has been made to 
 subserve almost all kinds of purposes, from the transmission of thought 
 to the performance on musical instruments. 
 
 We have endeavoured in the preceding sketch to note and render 
 intelligible those successive stages of discovery and of inductive investi- 
 gations which have given to electricity, though comparatively a science of 
 recent date, a rank as high, and a character as important and interesting, 
 as that of any other of the physical sciences. Though so much has been 
 done in developing and in practically applying electrical phenomena, much 
 more remains to be accomplished : the field is yet only partially culti- 
 vated. A large tract remains unexplored, in which we anticipate suc- 
 ceeding cultivators will bring to light additional facts as extraordinary as 
 any hitherto discovered. Their labours may remove the veil that at 
 present obscures the nature of the connexion between frictional electricity, 
 voltaism, heat, and the magnetic force; and may elucidate the mysterious 
 influence which electricity is known to exercise on the functions of vi- 
 tality. 
 
PART II. 
 
 THE PHENOMENA OF ELECTRICITY, 
 
 CHAPTER V. 
 
 GENERAL PROPERTIES. 
 
 Static and current Electricity Electrical excitement by friction Attraction and repul- 
 sion Illustrative experiments Electrics and conductors All substances electrics 
 when insulated The opposite kinds of Electricity Negative and positive electrics 
 changeable Mutual dependence of the two Electricities Electrical induction The 
 Electrophorus Influence of conductors on surrounding bodies The Electrometer 
 Various inductive powers of electrics Explanation of all electrical phenomena 
 by induction The two theories of Electricity. 
 
 IN the foregoing outline of the history of electricity we have traced the 
 progress of the science from the first feeble spark to its identification with 
 the lightning's flash; and thence pursuing its course into the vast field 
 which the excitement of electric force by chemical action has opened we 
 have endeavoured to follow its rapid strides since Galvani convulsed the 
 limb of a frog, Volta constructed his wonder-working pile, Davy decom- 
 posed the alkalies and earths, and (Ersted detected magnetism in the elec- 
 tric current, till Faraday, reversing the process, has from magnetism 
 eliminated electric fire. 
 
 We have now to describe more particularly the great variety of elec- 
 trical phenomena, and the means by which they are produced in the 
 present advanced state of the science. In doing this we shall proceed 
 nearly in the same order in which the leading facts presented themselves 
 in our historical sketch ; commencing, in the first place, with the phe- 
 nomena of frictional, or as it is more frequently called "static electricity." 
 The latter term is applied to distinguish the action of the force excited by 
 friction from that of the voltaic battery ; frictional electricity exhibiting 
 itself in a state of equilibrium, and remaining comparatively at rest, ex- 
 cepting during the instant of discharge; whilst voltaic electricity appears 
 to be constantly in motion from one pole of the battery to the other, and 
 has hence been called current electricity. 
 
 The friction of a glass rod or stick of sealing-wax, adopted by the early 
 electricians as their only means of exciting electricity, affords the simplest 
 mode of exhibiting the phenomenon of electrical excitement. A glass 
 tube about two inches in diameter and two feet long answers the purpose 
 
48 THE PHENOMENA OF ELECTRICITY. 
 
 very well. It should be made perfectly dry, and then corked at each end ; 
 and if varnished inside, to prevent the condensation of moisture on the 
 glass, it will be better. A piece of black silk, on which some of the amal- 
 gam of mercury, zinc, and tin, has been spread, forms the best rubber. 
 On rubbing the tube briskly with the silk, after both have been first 
 warmed, electricity will be excited in almost all states of the atmosphere j 
 and when the weather is fine and frosty, loud cracklings will be heard. 
 In the dark, flashes of light will be observed darting from the tube to the 
 hand that holds it ; and on presenting the knuckle within an inch or two 
 of the excited glass, sparks will be emitted, accompanied by a slight tin- 
 gling sensation. 
 
 When a downy feather is held at some distance from the excited tube, 
 the fibres will be attracted towards it, and when liberated, the feather will 
 rush to the glass. In a short time, however, the downy parts will be ob- 
 served to separate from each other, and when the feather is charged with 
 electricity, it will fly off nearly as rapidly as it was attracted. The feather, 
 when thus repelled from the tube, will not again approach until it has 
 parted with its charge of electricity ; and to enable it to do so, it will rush 
 towards the hand or towards the nearest conducting body. If, however, 
 before the feather has had the opportunity of parting with the charge, the 
 excited tube is brought near, it is repelled farther off, and it may in this 
 manner be chased round the room, and kept suspended in the air. 
 
 The feather, when in a charged state, exerts an attractive force on all 
 surrounding bodies equal to that with which it is attracted towards them ; 
 and if a light conducting body were suspended near, they would rush to- 
 wards each other with equal forces, and with velocities inversely propor- 
 tioned to their respective weights. The same law also regulates the 
 repelling force ; and when two light bodies charged with electricity from 
 the glass tube are suspended near to each other, they will be mutually 
 repelled. If two small pieces of cork, for example, or what is still better, 
 two pith balls, are suspended by strings of equal length so as to touch, 
 and they are then charged with electricity from the glass tube, they repel 
 each other and keep apart until they are either touched by a conducting 
 body, or the electricity is gradually discharged into the air. 
 
 The properties of electric attraction and repulsion may be illustrated 
 in a great variety of ways, some of which are extremely amusing. If a 
 number of small figures are cut out in paper, or carved out of pith, and an 
 excited glass rod be held a few inches above them on the table, the figures 
 will immediately commence dancing up and down, assuming a variety of 
 droll positions. A favourite posture, if we may so express it, of these little 
 figures, is that of standing on the head or on one hand, presenting a foot 
 towards the glass, their little frames being agitated all the time with a qui- 
 vering motion. From this position of the figures may be learned the fact 
 that first suggested to Franklin the means of drawing lightning from the 
 clouds. The sharp edges and corners of the paper serve as points to draw 
 off the electricity from the excited glass tube, and each one of the figures in 
 that posture is operating, on a small scale, in the same manner as the 
 lightning-conductor on a church-steeple when a thunder-cloud is passing 
 over it. This action of the edges and points of the paper in drawing off 
 the electricity at a distance, prevents the figures cut out in paper from 
 dancing so energetically as those made of pith, and pith balls act more 
 
GENERAL PROPERTIES. 
 
 49 
 
 fiff. 1. 
 
 briskly than either. The experiment can 
 be shewn better by means of an electrical 
 machine than with the excited tube, by 
 suspending horizontally from the prime 
 conductor a metal disc a few inches above 
 a flat metal surface connected with the earth, 
 on which the figures are placed. By this 
 arrangement the dancers have more space 
 for their lateral gyrations, and sometimes 
 waltz together very laughably. 
 
 Experiments illustrative of electric at- 
 traction and repulsion may be greatly diver- 
 sified when an electrical machine is used, so 
 as to increase the quantity of electricity and 
 to conveniently apply it. Among the appa- 
 ratus commonly employed for exhibiting this 
 property in an amusing manner is a doll's 
 head with long hair. When attached to 
 the prime conductor of the machine, the hairs 
 stand erect, presenting an exaggerated repre- 
 sentation of fright. 
 
 A dry glass tumbler becomes charged by 
 grasping it with the hand and presenting the 
 inside to a point fixed on the conductor. If it 
 be then placed over a number of pith balls on 
 the table, the balls dance up and down with 
 great rapidity, each ball being first attracted to 
 the top or to the sides of the glass, and when 
 charged is repelled or falls on to the table, where 
 it discharges the electricity it has received, and 
 is again attracted to the glass. In this manner 
 the tumbler is gradually discharged of its elec- 
 tricity. The outside of the glass is equally 
 charged with the inside, though negatively, and parts 
 with its electricity to the air or surrounding bodies 
 in proportion to the discharge of the interior surface ; 
 it being one of the laws of statical electricity, that 
 one surface of a non-conducting body cannot be 
 charged without the other, as will be explained more 
 fully when we come to the consideration of the phe- 
 nomena of electric induction and the Ley den jar. 
 
 The bell apparatus, for ringing bells by means 
 of electric attraction and repulsion, is a good illus- 
 tration of those forces. A metal rod, fig. 4, fixed 
 horizontally to the prime conductor of the machine, serves to suspend 
 three or more small bells. When three bells are employed, the two end 
 ones are hung by wires or chains, and the central one is suspended by a 
 silk thread to insulate it from the conductor, though a metallic communi- 
 cation is made from it to the table by a chain. Two small metal clappers 
 are also suspended by insulating silk threads from the horizontal rod. 
 When the machine is put in action, the bells at each end of the rod being 
 
 fig. 2. 
 
 fig. 3. 
 
50 
 
 THE PHENOMENA OF ELECTRICITY. 
 
 fig. 4. 
 
 connected with the conductor by metal connec- 
 tions, become charged with electricity, and at- 
 tract the clappers, which being instantaneously 
 charged are as quickly repelled and attracted to 
 the central bell, connected with the table, at 
 which their electricity is discharged. The clap- 
 pers are then again attracted and strike against 
 the other bells, and by these brisk alternate 
 attractions and repulsions keep ringing as long 
 as the machine is in action. It was by attach- 
 ing a set of bells of this kind to his lightning- 
 conductor, that Dr. Franklin received notice, 
 by their ringing, whenever a thunder-cloud 
 was passing over the apparatus. 
 
 One of the effects of electrical attraction is 
 exemplified in its action on running fluids, 
 causing them to flow more quickly. Let a metallic cup, for 
 example, fig. 5, containing water, and with a small opening at 
 the bottom, be suspended from the prime conductor of an elec- 
 trical machine. If the aperture be so small as to allow the water 
 only to issue by drops when the machine is not in action, the 
 flow will be increased to a stream as soon as the electricity is 
 excited. The water being charged with positive electricity, it 
 is attracted with increased force towards the earth, and that 
 force, added to the attraction of gravitation, produces the more 
 rapid flow. 
 
 The early electricians appear to have had no knowledge of 
 variations in degree of conducting power, nor of electrical ex- 
 citement, in different substances ; but more recent investigations 
 have shewn that conductors and electrics are blended together by such 
 inappreciable degrees, that it is impossible to say to which class some of 
 the intermediate bodies belong. As all substances probably are capable 
 of electrical excitement, they might consequently be all classed in the 
 list of electrics, gutta-percha being at the head, and gold or copper at the 
 bottom. On the other hand, as all substances conduct electricity in vari- 
 ous degrees, they might all come within the class of conductors, in which 
 case the order would be reversed. So different, indeed, is the conducting 
 power of bodies usually considered as conductors of electricity, that water, 
 which is classed as a conductor, offers three million times more resistance 
 to the electric fluid than copper. 
 
 It is a remarkable fact in the conduction of electricity, that imperfect 
 conductors can compensate by quantity for their deficiency in quality. Thus 
 assuming that in equal bodies of copper and water the latter would not 
 conduct more than the three-millionth part of the quantity of electricity in 
 the same time that would pass by the copper, yet by increasing the quan- 
 tity of water in a proportionate degree, the resistance in both cases would 
 be equal. We shall have occasion to shew, indeed, in speaking of electric 
 telegraphs, that when the conducting power of water is brought to operate 
 on an extensive scale, the resistance it offers to the passage of electricity 
 diminishes to an inappreciable quantity. 
 
 The principal conductors of electricity, arranged in the order of their 
 
 fig. 5. 
 
GENEBAL PROPERTIES. 51 
 
 conducting powers, is subjoined. It is difficult, however, to determine 
 how far such a list should extend, since all substances conduct in a greater 
 or less degree. 
 
 Copper. Platinum. Animal fluids. 
 
 Gold. Charcoal. Sea water. 
 
 Silver. Plumbago. Fresh water. 
 
 Mercury. Strong acids. Ice and snow above zero. 
 
 Iron. Soot. Vapour. 
 
 Tin. Metallic ores. Rarefied air. 
 
 Lead. Diluted acids. 
 
 Zinc. Saline solutions. 
 
 We have previously noticed that the best electrics are the worst con- 
 ductors of electricity, and that all substances may be considered to be elec- 
 trics or non-electrics in proportion to the resistance they offer to the 
 conduction of electricity. As gutta-percha offers more resistance to the 
 passage of electricity than any other body, it may consequently be consi- 
 dered the best electric ; and copper, being the best conductor, should be 
 the farthest removed from the condition of electrical excitement. A copper 
 rod may, however, be converted into an electric by insulation ', but when 
 a metal rod is excited by friction, the electricity is discharged at once, 
 when a conducting body is brought near, instead of parting with the elec- 
 tricity by slow degrees, like an excited tube of glass. It seems probable 
 that electricity is always excited by friction under every circumstance, 
 though it is only observable in those substances that have the power of 
 retaining it on their surfaces after being excited. The mere movement 
 of the feet along the carpet is sufficient to excite electricity ; as may be 
 shewn by placing the hand on a delicate electrometer whilst the feet are 
 in motion. 
 
 The experiment which led Du Fay to the discovery that there are two 
 kinds or states of electricity may be easily repeated. Having caused a 
 feather to be repelled from an excited glass tube, excite a stick of sealing- 
 wax, or what is better, a rod of gutta-percha, and the feather which has 
 been repelled by the glass will be attracted by the gutta-percha. Then 
 holding the glass tube in one hand and the gutta-percha in the other, the 
 feather will be alternately attracted and repelled, and with greater force 
 than when a conducting body connected with the earth is brought near 
 to either of the excited electrics and the feather. After a succession of 
 attractions and repulsions, the electricity Df the excited glass and gutta- 
 percha is discharged, the feather having acted as a discharger from one to 
 the other. This experiment clearly shews that the electricity excited in 
 glass, whilst it apparently repels bodies similarly electrified, attracts those 
 that are electrified by wax or gutta-percha. The phenomenon of mutual 
 attraction is shewn more briskly if a piece of gold-leaf or suspended pith 
 ball be substituted for the feather; for the downy fibres of the latter tend 
 to dissipate the electricity quietly from their distended points, and thus 
 prevent the feather from becoming fully charged. 
 
 A still more satisfactory way of exhibiting the different actions of fhe 
 two kinds of electricity is to suspend two pith balls by threads of equal 
 lengths from an insulated metal conductor, as represented in fig. 6 ; c c 
 being the pith balls suspended from one end of the horizontal metal cy- 
 linder A, and insulated from the earth by the glass leg B, fixed into a 
 
52 THE PHENOMENA OF ELECTRICITY. 
 
 wooden base. Touch the end A with 
 an excited glass tube, and the pith balls 
 will separate and will continue apart 
 when the tube is removed, each one 
 being electrified with the electricity 
 of the glass. If an excited stick of 
 sealing-wax be then brought near, the 
 ^. expanded balls will collapse, even be- 
 fore the wax touches A. On remov- 
 ing the excited wax without touching 
 the horizontal rod, the pith balls will 
 fig- e. again separate, and will be in the same 
 
 electrical condition as before. But if 
 
 the excited stick of wax come in contact with the rod, or approach it so 
 near as to transmit a spark, the state of electricity becomes changed, and 
 the balls will then expand with the opposite kind of electricity. When 
 the excited wax is again brought near, the pith balls will expand more 
 widely instead of collapsing, as before, and the excited glass tube, which 
 previously made the balls expand, will now cause them to collapse. 
 
 It appears, therefore, that the electricity communicated to the balls 
 by the excited glass differs essentially in its attractive properties from 
 that communicated by the excited wax ; and Du Fay, who first disco- 
 vered the difference, distinguished the opposite states of electricity by the 
 terms vitreous and resinous. These terms are still retained by those elec- 
 tricians who conceive that there are two electric fluids ; but those who, 
 with Franklin, entertain the opinion that the different attractive actions 
 are occasioned by the plus or minus state of the same electric fluid, call 
 the electricity excited by glass positive, and that excited by resin negative. 
 Shortly after the discovery of the difference of the two electrical con- 
 ditions, all the known electrics were classed according to the kind of 
 electricity each one excited ; but such classification was afterwards found 
 to be very fallacious, for the state of electricity depends, with few excep- 
 tions, on the rubber employed. Even glass and resin, which are con- 
 sidered the types of the two distinct classes of electrics, may be made to 
 interchange their states of electrical excitement; for glass when rubbed 
 with the fur of a cat yields negative electricity, and resin becomes posi- 
 tively electrified when rubbed with metals. The fur of a cat is the only 
 known substance that does not alter its electrical state with whatever it is 
 excited. In the following list of electrics, those which come first excite 
 positive electricity when rubbed with any of those that follow, and are 
 negative when rubbed with those that precede. 
 
 Fur of a cat. Feathers. Silk. 
 
 Polished glass. Wood. Gum lac. 
 
 Woollen cloth. Paper. Rough glass. 
 
 The change of electrical excitement seems to depend more on the na- 
 ture of the surface than on the inherent quality of the electric ; for in the 
 preceding list it will be observed that glass is positive when polished, and 
 is strongly negative when roughened. The following table, given by Ca- 
 vallo as the results of experiments, shews more fully the changes effected 
 by different rubbers. It will be observed, however, that the relative elec- 
 
GENERAL PROPERTIES. 
 
 53 
 
 Substances excited. 
 
 Kind of el 
 Positive 
 Positive 
 Positive 
 
 - Negative 
 
 Positive 
 Negative 
 : Positive 
 Negative 
 ' Positive 
 Negative 
 Positive 
 Negative 
 Positive 
 Negative 
 Positive 
 Negative 
 
 ect 
 
 ricity 
 
 
 Rough glass . . . . " 
 Tourmalin 
 
 Hare-skin ..... 
 
 White silk ..... 
 
 Black silk 
 
 Sealing-wax .... 
 Baked wood .... 
 
 trical conditions do not exactly agree with those mentioned in the fore- 
 going list. 
 
 The rubbers. 
 
 Every substance tried. 
 Every substance but the back of a cat. 
 Dry oiled silk, sulphur, metals. 
 Woollen cloth, paper, wax, the human 
 
 hand. 
 
 Amber, a current of air. 
 Diamond, the human hand. 
 Metals, silk, leather, hand. 
 Finer furs than hare-skin. 
 Black silk, metals. 
 Paper, hand, hair. 
 Sealing-wax. 
 Furs, metals, hand. 
 Metals. 
 
 Furs, hand, leather, cloth. 
 Silk. 
 Flannel 
 
 These facts respecting the change of electrical state from positive to 
 negative are difficult to explain on any known hypothesis. If we adopt 
 the theory of Franklin, and infer that the positively electrified bodies only 
 are the exciters of electricity, then we must assume, in those cases where 
 a change in the kind of electricity is produced by a change of rubber, that 
 the body on which positive electricity is excited is always to be regarded 
 as the electric. Thus when glass which has been positively excited by 
 friction with silk becomes negative by friction with the fur of a cat, it 
 must in the latter case be regarded not as the electric, but as the rubber. 
 The frequent change of state from positive to negative, which we shall 
 have further occasion to notice, presents, indeed, one of those mysteries 
 of electric science of which no satisfactory explanation has hitherto been 
 afforded. 
 
 One of the remarkable features of the two electricities is their depend- 
 ence on each other. Positive electricity cannot be excited without the 
 excitement at the same time of an equal amount of negative electricity, 
 nor can the latter be excited without the evolution of positive electricity. 
 Thus, when a tube of glass held in the hand is rubbed with silk, the hand 
 holding the silk has a quantity of negative electricity communicated to 
 it equal to the positive electricity excited in the glass. In ordinary 
 circumstances the negative electricity is not apparent, because it is con- 
 ducted to the earth as quickly as it is 
 evolved ; but when the person who is ex- 3P 
 citing the glass tube is insulated from the 
 ground, sparks of negative electricity may 
 be taken from any part of his body. Not 
 only is it impossible to excite positive or 
 negative electricity without at the same 
 instant exciting electricity of the opposite 
 kind, but the presence of an excited elec- 
 tric induces in bodies at a distance from 
 it the opposite electrical state. When an 
 excited glass tube is placed at the distance 
 
54 THE PHENOMENA OF ELECTRICITY. 
 
 of a foot from the end p of the horizontal insulated metal cylinder N p, 
 furnished with pith balls at each end, the balls will be immediately dis- 
 tended by the influence of the excited tube, though no electricity is com- 
 municated to them directly from the glass. On the removal of the tube 
 to a greater distance, the balls will collapse, and no trace of electricity 
 can be detected in the rod. But if the finger or any other conducting 
 body touch the end N whilst the balls are distended under the influence of 
 the glass tube near p, and it is withdrawn whilst the influence is exerted, 
 then on removing the tube the balls will remain distended, the rod having 
 received a charge of negative electricity. The electrical state of the rod 
 may be easily tested by bringing the glass tube near it again, when the 
 balls will be seen to collapse on its approach, instead of expanding as at 
 first. 
 
 Having touched the rod to remove the electricity, again bring the 
 excited glass tube near the end p, and whilst the balls are distended under 
 its influence, let an excited stick of sealing-wax be brought near the same 
 end, and the balls will partially collapse ; but if the excited wax approach 
 towards the other end, they will be separated still farther apart. 
 
 In this experiment the approach of the positively excited glass tube 
 towards the insulated rod repels the electricity to the end farthest from 
 the excited tube. The equilibrium of the natural electricity in the rod is 
 thus disturbed, and it exhibits electrical phenomena without in fact having 
 received any charge of electricity. According to the theory of Franklin, 
 the rod has parted with a portion of its natural electricity, which was re- 
 pelled to one end by the excited glass, and it is left in a minus state until 
 it regains its natural quantity from surrounding bodies. 
 
 These simple experiments afford most satisfactory illustrations of the 
 important property of induction ; and they should be, therefore, carefully 
 studied in all their bearings. The fact has been satisfactorily established, 
 that every excited electric induces electricity of an opposite kind in all 
 surrounding bodies ; and that this influence is exerted through the air or 
 any other non-conducting substance with instantaneous rapidity. There 
 is no actual communication of electricity in these cases, but an attractive 
 or repelling action is exerted only so long as the influence of the electric 
 operates. The instantaneous transmission of this inductive force through 
 bodies that offer the most resistance to the conduction of the electric fluid, 
 bears some analogy to the transmission of radiant heat instantaneously 
 through the non-conducting air. How far the influence extends has not 
 been ascertained, but it most probably obeys the same laws as heat and 
 all other radiant forces ; extending indefinitely into space, but diminishing 
 in quantity inversely as the squares of the distance. 
 
 The property of induction is admirably illustrated in a very ingenious 
 and useful apparatus invented by Volta, called the Electrophorus. It 
 consists of a thick flat cake of resinous substance laid upon a sheet of 
 metal. The resinous cake being rubbed with hot flannel, the upper sur- 
 face becomes charged with negative electricity, which induces an equal 
 positive charge on the under surface in contact with the metal plate. A 
 metal disc insulated by a glass handle is then pressed upon the excited 
 resin. As the electricity cannot pass away through the insulating glass 
 handle, the effect of the application of the metal disc on to the excited 
 resin is to induce electricity on the surfaces of the metal, each surface 
 
GENERAL PROPERTIES. 55 
 
 being in an opposite state ; the positive electricity being attracted to the 
 surface nearest the resinous electric, and the negative being repelled to 
 the upper surface. If the disc be pressed upon the resin, and removed 
 without any connexion with the earth, the equilibrium of its two surfaces 
 will be restored as soon as it is lifted from the influence of the electric, 
 and it will exhibit scarcely any sign of having gained electricity by the 
 contact. But if whilst resting on the excited resin, the upper surface be 
 touched, the negative electricity is thereby withdrawn ; and when the 
 disc is lifted away, it remains positively charged, and a strong spark may 
 be taken from it. This operation may be repeated any number of times, 
 for none of the electricity of the excited resin is communicated directly 
 to the disc, which becomes electrical merely by the induction of opposite 
 kinds of electricity on its two surfaces ; the equilibrium of its natural state 
 being disturbed by the attractive force of the excited electric. When a 
 plate of glass is substituted for one of resin, the electricity of the disc of 
 course becomes reversed. The upper surface is then positive whilst under 
 the influence of induction, and on allowing that to escape by communica- 
 tion with the earth, the metal when removed from contact is in the nega- 
 tive state. 
 
 The continued supply of electricity from an 
 electrophorus by a single excitement of the 
 resinous plate renders this instrument occa- 
 sionally very useful in electrical experiments, 
 where a small quantity of electricity only is re- 
 quired, as it is sufficiently powerful to charge a 
 good-sized Leyden jar. Figure 8 represents 
 the apparatus as generally constructed. The 
 cake of resinous matter, A A, is poured on a 
 circular wooden pan, lined with tin-foil ; c is 
 the metal disc, usually made of brass, rounded 
 at the edges; and B is the glass handle for the 
 purpose of insulation. A sheet of gutta- 
 percha might be advantageously substituted for the resin, and a handle of 
 baked wood varnished would serve nearly as well as glass. 
 
 The induction of electricity through glass may be shewn by exciting 
 one side of a thin plate when laid flat on the table. The glass when 
 rubbed with silk becomes positively electrified on its upper surface, and 
 the under surface is at the same time charged with negative electricity. 
 This may be shewn by lifting the glass by the corners and bringing it near 
 the pith balls (fig. 6), after they have been distended by contact with an 
 excited glass tube. It will then be seen that the balls will be distended 
 farther when the upper surface of the pane of glass is presented to them, 
 and that they will collapse on the presentation of the under surface. 
 
 It has been already stated, that in every case of electrical excitement 
 electricity is induced in all surrounding bodies. When an excited glass 
 rod, for instance, is held in the middle of the room, the walls and every 
 thing they enclose are under its influence, though it may be too feeble to 
 be appreciated. The effect of the excited glass is to attract a certain 
 portion of negative electricity towards it, and a mutual attractive force 
 is exerted between the excited glass and every object thus influenced. 
 Many persons are painfully sensitive of the approach of a thunder-storm, 
 
THE PHENOMENA OF ELECTRICITY. 
 
 and often complain that there is "thunder in the air," when no storm 
 succeeds. There can be no doubt that during the passing of a thunder- 
 cloud electricity is induced in all bodies beneath ; and Faraday on this ac- 
 count considers it dangerous to have iron roofs to powder-magazines. 
 Such a roof might have electricity induced in it by the action of the 
 electricity in the cloud, and a spark might pass from the under surface of 
 the roof to the ground. 
 
 The action of that useful instrument, the electrometer, depends for the 
 most part on the induction of electricity. The simplest indicator of elec- 
 trical excitement is the arrangement of two pith balls, already shewn in 
 fig. 6. The weight of the balls, however, and the imperfect conducting 
 character of the suspending string, prevent it from being very sensitive. 
 Bennett's gold-leaf electrometer is a much more delicate instrument. It 
 consists of a wide glass tube, about four inches long, mounted on a metal 
 stand, and covered with a metallic cap. From the inside of the cap there 
 is a small projection, to which two thin strips of gold-leaf are attached. 
 The extreme lightness of the gold-leaf and its great conducting power 
 render it extremely sensitive to the action of small quantities of electricity ; 
 and the delicacy of the instrument is increased by fixing strips of tin-foil 
 on the sides of the tube, opposite to the gold leaves, which are attracted 
 towards them and diverge with very slight electrical excitement. 
 
 Fig. 9 represents the form of this useful indicator 
 A of the presence of electricity. The brass cap A fits 
 
 closely on to the tube B, and from the cap the gold- 
 leaves c c are suspended. Two strips of tin-foil, D r>, 
 are connected with the metallic base, and through it 
 with the earth. 
 
 To increase the sensibility of this electrometer, 
 metal discs, AB, called condensers, are added, one of 
 which is attached to the brass cap, and the other is 
 mounted on a support that is movable by a joint at 
 the bottom, so that it may be removed to the position 
 indicated by the dotted lines in the figure. By the in- 
 duction of electricity on the surface of the movable 
 disc several successive times, and by its reaction on the 
 electrometer, an accumulation of 
 the electric force is effected ; by 
 which means the presence of 
 otherwise inappreciably small 
 quantities of electricity is de- 
 tected. 
 
 This instrument, and others 
 of a similar construction, 
 though called electrometers, do 
 not indicate the quantity of 
 electricity; and the name elec- 
 troscope, which has been re- 
 cently applied to them, is more 
 appropriate to their character. 
 The torsion-balance of Coulomb, which has been previously noticed, 
 measures the electric force exerted, and may therefore with strict pro- 
 
 fig. 9. 
 
 fig. 10. 
 
GENERAL PROPERTIES OF ELECTRICITY. 
 
 57 
 
 priety be called an electrometer. It consists of a 
 fine rod of shellac, c, at each end of which there is 
 a gilded pith ball, the rod and balls being suspended 
 from the centre by a filament of spun-glass a. The 
 ball d is similar to the others, and is also fixed to 
 a rod of shellac, with a corresponding ball at the 
 other end. The latter is called the carrier-ball, 
 as it conveys electricity from the body to be tested 
 to the electrometer. When applied to the excited 
 body under examination, it receives a portion of 
 the electricity, and on being then placed in its 
 position in the instrument, the suspended ball that 
 rests against it is repelled. By turning the screw 
 b the two balls may be brought together ; and the 
 amount of torsion or twist given to the filament 
 of glass, so as to overcome the electrical repul- 
 sion, is measured by a graduated scale. 
 
 The action of electrical induction takes place 
 through all non-conducting bodies, though not with equal facility, the 
 transmission of the influence being readiest through those substances which 
 are the worst conductors of electricity. The term dielectrics has been given 
 to those bodies that permit induction to take place through them ; but it 
 seems to be a useless multiplication of names, since all electrics are also 
 dielectrics. The following has been ascertained experimentally to be the 
 comparative order of the inductive power of the principal electrics : 
 
 SPECIFIC INDUCTIVE CAPACITY. 
 
 Air 1-00 
 
 Resin . . . . 177 
 
 Pitch 1-80 
 
 Wax 1-86 
 
 Glass 1-90 
 
 Sulphur ..." 1-93 
 
 Shellac 1-95 
 
 Though gutta-percha is not included, its inductive capacity is known 
 to be greater than that of any other body. 
 
 An important portion of Faraday's Experimental Researches in Elec- 
 tricity is occupied with investigations respecting the nature of inductive 
 action. He has arrived at the conclusion that induction " is a physical 
 action occurring between contiguous particles, never taking place at a 
 distance without polarising the molecules of the intervening dielectric, 
 causing them to assume a peculiar constrained position, which they retain 
 so long as they are under the coercing influence of the inductive body." 
 According to this view of the question, therefore, all the particles of air, 
 and of every solid non-conductor, must assume a polar arrangement, like 
 the particles of iron-filings when within the sphere of magnetic attraction ; 
 and in this manner act directly, through a chain of contiguous particles, 
 on the bodies in which electricity is induced. 
 
 The property of induction is now adduced to explain every pheno- 
 menon of static electricity ; irrespective of the opposing theories of the 
 two electricities, or of the mode by which inductive action is eflected. 
 The phenomena of attraction and repulsion are thus explained : the two 
 states of electricity being admitted to exert a mutual attraction on each 
 other, the induction of negative electricity by positive, and the reverse, 
 
58 THE PHENOMENA OF ELECTRICITY. 
 
 must necessarily be attributable to an attractive force. The repulsion of 
 bodies similarly electrified is considered to be caused by attractive forces 
 in opposite directions, and not by any operating repulsive power exerted 
 among the particles of such bodies. Two simib Jy electrified pith balls, 
 for example, are supposed to diverge in consequence of each one inducing 
 an opposite state of electricity in surrounding bodies, towards which they 
 are consequently attracted in opposite directions ; the divergence and 
 apparent repulsion from each other being occasioned altogether by at- 
 tractive forces. The existence of a negative force, as repulsion may be 
 regarded, is indeed opposed to the principles which have been established 
 by investigation in other departments of physical science ; and by the 
 hypothesis of inductive action the student of electricity is called upon to 
 dismiss the action of repulsion from operating forces, as the student of 
 chemistry is compelled to deny the existence of cold as a positive pro- 
 perty. It seems questionable, however, whether the term " induction " 
 has not been introduced unnecessarily, since all the phenomena may be 
 regarded as the results of electrical attraction. 
 
 The question whether there are two distinct kinds of electricity, or 
 only one kind which is exhibited in different states of intensity, though 
 interesting in a theoretical point of view, is not essential to the explana- 
 tion of electrical phenomena, which may be almost as readily explained by 
 one hypothesis as by the other. The analogy of those other powers in 
 nature which, though apparently operating as distinct forces, have been 
 proved to consist of only one, as well as the more simple character of the 
 plus and minus theory, incline us strongly in its favour. 
 
 The foundation on which the Franklinian theory rests is thus stated 
 by Dr. Priestley : " According to this theory, all the operations of elec- 
 tricity depend upon one fluid sui generis, extremely subtle and elastic, 
 dispersed through the pores of all bodies ; by which the particles of it are 
 strongly attracted, as they are repelled by one another. When the equi- 
 librium of this fluid in any body is not disturbed, that is, when there is 
 in any body neither more nor less of it than its natural share, or than 
 that quantity which it is capable of retaining by its own attraction, it 
 does not discover itself to our senses by any effect. The action of the 
 rubber upon an electric disturbs this equilibrium, occasioning a deficiency 
 of the fluid in one place and a redundancy of it in another. This equi- 
 librium being forcibly disturbed, the mutual repulsion of the parti- 
 cles of the fluid is necessarily exerted to restore it. If two bodies be 
 both of them overcharged, the electric atmospheres repel each other, 
 and both the bodies recede from one another to places where the fluid is 
 less dense. If both bodies be exhausted of their natural share of this 
 fluid, they are both attracted by the denser fluid existing either in the 
 atmosphere contiguous to them, or in other neighbouring bodies ; which 
 occasions them still to recede from one another as much as when they 
 were overcharged."* 
 
 The statement of the theory of vitreous and resinous electricity we 
 shall also take from Dr. Priestley, who, though an advocate for the sing >- 
 fluid hypothesis, has stated the arguments for and against both with great 
 impartiality : 
 
 * Priestley's History of Electricity. 
 
GENERAL PROPERTIES OF ELECTRICITY. 59 
 
 " Let us suppose, then, that there are two electric fluids which have a 
 strong chemical affinity with each other, at the same time that the par- 
 ticles of each are as strongly repulsive of one another. Let us suppose 
 these two fluids in some measure equally attracted by all bodies, and ex- 
 isting in intimate union in their pores ; and while they continue in this 
 union, to exhibit no mark of their existence. Let us suppose that the fric- 
 tion of any electric produces a separation of these two fluids, causing the 
 vitreous electricity of the rubber to be conveyed to the conductor, and the 
 resinous electricity of the conductor to be conveyed to the rubber. The 
 rubber will then have a double share of the resinous electricity, and the 
 conductor a double share of the vitreous ; so that upon this hypothesis no 
 substance whatever can have a greater or less quantity of electric fluid 
 at different times. The quality of it only can be changed. The two 
 electric fluids being thus separated will begin to shew their respective 
 powers, and their eagerness to rush into reunion with one another. With 
 whichsoever of these fluids a number of bodies are charged, they will repel 
 one another, and they will be attracted by all bodies which have a less 
 share of that particular fluid with which they are loaded ; but will be much 
 more strongly attracted by bodies which are wholly destitute of it, and 
 loaded with the other. In this case they will rush together with great 
 violence. 
 
 " Upon this theory every electric spark consists of both fluids rushing 
 contrary ways and making a double current. When, for instance, I pre- 
 sent my finger to a conductor loaded with vitreous electricity, I discharge 
 a part of the vitreous and return as much of the resinous, which is sup- 
 plied to my body from the earth. Thus both the bodies are unelectrified, 
 the balance of the two powers being perfectly restored." 
 
 Dr. Priestley proceeds to state, with great fairness, the analogies and 
 the facts which may be adduced in support of the two distinct electric 
 fluids. The combination of two caustic and powerfully-active substances, 
 as an alkali and an acid, in the form of a neutral salt, in which the pro- 
 perties of neither of the constituent parts is perceptible, is one of the ana- 
 logies advanced in favour of the vitreous and resinous fluids being com- 
 bined, and rendered perceptible only when their combination is disturbed. 
 
 It appears from the preceding consideration of the properties of the 
 two electricities, that the cause of electrical attraction is the endeavour 
 they make to combine and return to a neutral state. This attractive 
 power, which is extended in the phenomena of induction to considerable 
 distances, seems to afford sufficient explanation of the cause of those phe- 
 nomena, without supposing the exertion of any separate action of induc- 
 tive force. And if we concur in the explanation assigned for the mutual 
 repulsion of negatively- electrified bodies, attractions of the two electricities 
 in opposite directions will supply adequate cause for all the phenomena of 
 repulsion, without the necessity of supposing that there exists any posi- 
 tively active repulsive power in electricities of the same kind. 
 
60 
 
 THE PHENOMENA OF ELECTKICITY. 
 
 CHAPTEE VI. 
 
 DIRECT DEVELOPMENT OF ELECTRICITY. 
 
 Electrical machines ; Cylinder, Plate, and Gutta Percha Influence of points Expla- 
 nation of the cause Electricity confined to surfaces Intensity of machine-excited 
 electricity Inflammation of combustibles by the spark Resistance of the air 
 Nature of electric discharge Disruptive, brush, and glow discharge Colour of 
 the electric spark. 
 
 THE excitement of electricity by friction with the hand is adequate to illus- 
 trate the primary phenomena and elementary properties of the electric 
 fluid ; but for the exhibition of its powerful effects and more complicated 
 actions, it is requisite to employ other apparatus. The quantity excited 
 must be greater in a given time, and means must be provided for collect- 
 ing and accumulating the electricity when excited. 
 
 The electrical machines that were used by Du Fay and Priestley con- 
 sisted of a sulphur globe whirled round on an axis, with the hand ap 
 plied for a rubber. The globes of sulphur were supplanted by cylinders of 
 glass ; and though that form has in a great measure given place to the 
 more powerful plate-machine, the cylinder is so well suited for purposes of 
 general experiment, that it continues to be preferred in cases where no 
 extraordinary power is required. 
 
 Figure 12 represents an approved construction of this kind of electrical 
 
 fig. 12. 
 
 machine. The cylinder a, placed horizontally, is mounted upon sup- 
 ports of glass varnished, to insulate it from the ground. The rubber g 
 consists of a hair-cushion covered with leather, over which is placed a 
 flap of black silk. The cushion is mounted on a glass support, for the 
 purpose of insulation when the exhibition of negative electricity is re- 
 
DIRECT DEVELOPMENT OF ELECTRICITY. 6V 
 
 quired ; and it is adjusted by a screw ra, to regulate the pressure on the 
 cylinder. In the ordinary working of the machine the cushion is con- 
 nected by a chain with the ground, whence the supply of electricity is 
 derived. A hollow brass or tin cylinder h, rounded at each end, and 
 placed at a short distance from the glass cylinder, serves to collect the 
 electricity as it is excited. On the side facing the glass there is a 
 row of metal points which facilitate the collection of electricity ; and 
 to prevent it from passing off to the earth, the metal cylinder, called 
 the prime conductor, is mounted on a varnished glass support k. For 
 the convenience of attaching apparatus to the prime conductor, holes 
 are made on the top and at one end. In some electrical machines a metal 
 cylinder similar to that of the prime conductor is attached to the rubber, 
 as represented in the wood-cut, for the purpose of facilitating experiments 
 with negative electricity. In large cylinder-machines the prime conductor 
 is usually mounted on a separate stand, detached from other parts of the 
 apparatus ; but moderately sized instruments are generally constructed 
 with the conductor attached to the same base as the cylinder, an arrange- 
 ment being contrived to allow of its adjustment at different distances. 
 
 A cylinder electrical machine of about nine inches diameter is suffi- 
 ciently large for ordinary* purposes of experiment. An apparatus of that 
 size will, under favourable circumstances, fully charge a quart Leyden jar 
 with twelve turns of the handle. 
 
 Little need be said in explanation of the action of this machine, which 
 is only a modification of the means of electrical excitement by the friction 
 of a glass tube with the hand. On turning the handle e, friction is produced 
 between the surface of the cylinder and the rubber ; the electrical equi- 
 librium is thereby disturbed, and electricity is excited, which, when the 
 prime conductor is removed, exhibits itself in bright flashes of light round 
 the cylinder. When the points of the prime conductor are presented to 
 the revolving cylinder, the electricity is immediately transferred to it, and 
 it emits sparks to any conducting substance brought near. The electricity 
 thus abundantly excited is supplied from the earth to the rubber, which is 
 continually having its supply drawn from it by the coercive force called 
 into action by friction with the glass. That the electricity is derived from 
 that source is evident from the great diminution of quantity when the 
 metallic connexion between the rubber and the ground is removed. In 
 that insulated state the rubber becomes strongly charged with negative 
 electricity, and sparks pass between it and any conducting body brought 
 near almost as abundantly as from the prime conductor when in full action. 
 
 The rationale of the excitement of electricity by the machine is, ac- 
 cording to the Franklinian theory, very simple. The friction of the glass 
 and silk, by disturbing the electrical equilibrium, deprives the rubber of its 
 natural quantity of electricity, and it is therefore left in a negative state, 
 unless a fresh quantity be continually drawn from the earth to supply its 
 place. The surplus quantity is collected on the prime conductor, which 
 thereby becomes charged with positive electricity. On the hypothesis of 
 two electric fluids, the same frictional action causes the separation of the 
 vitreous from the resinous electricity in the rubber, which therefore re- 
 mains resinously charged; unless there be a connexion with the earth to 
 restore the proportion of vitreous electricity of which the rubber has been 
 deprived. 
 
62 THE PHENOMENA OF ELECTRICITY. 
 
 The electrical excitement of the machine is greatly increased by apply- 
 ing to the rubber a metallic coating consisting of an amalgam of zinc, 
 tin, and mercury. It is prepared by melting together two parts by 
 weight of zinc, and one of tin, with which, whilst in a melted state, six 
 parts by weight of mercury are mixed. The mass is shaken well together 
 till it cools, and it is then pounded finely in a mortar and mixed with lard 
 to the consistence of a paste. The amalgam is spread on the cushion 
 only, care being taken to prevent it from being spread on the silk flap. 
 
 The effect of an amalgam of this kind in increasing the electrical ex- 
 citement is very decided, though some difference of opinion exists as to 
 the principle on which the action depends. It has been imagined that the 
 amalgamated metals are oxydised during the friction with the rubber, and 
 that the electricity is due to chemical action. The more simple explana- 
 tion appears to be, that the coating of metal on the rubber assists in con- 
 ducting the electricity from it. The use of the silk flap is merely to pre- 
 vent the electricity from discharging itself into the air before it reaches the 
 conductor, and it would be unnecessary if the collecting points were brought 
 near the rubber. The adhesion of particles of amalgam to the silk flap 
 is prejudicial to the action of the machine by forming conducting points 
 for the dispersion of the excited electricity. 
 
 fig. 13. 
 
 Plate machines are now much used on account of the greater quantity 
 of electricity that can be excited by that arrangement of the instrument. 
 A disc of glass about a quarter of an inch thick has an axis fixed in its 
 centre, firmly supported by two cheeks of baked wood. On the upper 
 and lower parts of these cheeks four cushions are fixed, to press against 
 
DIRECT DEVELOPMENT OF ELECTRICITY. 
 
 63 
 
 both sides of the glass plate at the top and at the bottom. Small flaps of 
 silk are attached to the cushions to prevent the electricity excited from 
 being dissipated before it arrives at the collecting points of the prime con- 
 ductor. The conductor itself is also fixed to the upright cheeks, but is 
 insulated from them by a horizontal glass support. Rows of points 
 serve to collect the electricity from both sides of the glass plate, at the top 
 and bottom. By this arrangement a much larger surface of glass is ex- 
 posed to friction, and two rubbers can be employed on each side of the 
 plate. The surface exposed to friction in a plate machine with a glass 
 disc of only one foot in diameter is more than double that of a nine-inch 
 cylinder machine. 
 
 The inconvenience of a plate machine, as usually constructed, arises 
 from the imperfect insulation of the rubbers, in consequence of which the 
 negative electricity excited cannot be exhibited. 
 
 An electrical machine in which 
 the exciting surface consisted of 
 gutta-percha was shewn amongst 
 the philosophical instruments at 
 the Great Exhibition. An end- 
 less band of gutta-percha A was 
 stretched over rollers B B placed 
 above each other about two feet 
 apart. The rotation of the upper 
 roller communicated a rapid ver- 
 tical motion to the band of gutta- 
 percha, which was pressed against 
 at the top and bottom by hard 
 hair brushes, c c, that served as 
 rubbers. The electricity was col- 
 lected on each side by a branching 
 conductor D, armed with points, 
 and concentrated in a similar 
 manner to the arrangement of the 
 plate machine. 
 
 Though we have not had an opportunity of trying the effect of this 
 machine, we have heard it very favourably spoken of. It presents some 
 practical advantages that would make it preferable to glass machines, 
 among which must be mentioned its non-liability to fracture, and the su- 
 perior excitability of its surface.* Sheets of gutta-percha may also be 
 attached to discs of wood to serve instead of glass in plate electrical 
 machines. 
 
 With an electrical machine of any of the kinds mentioned, most of the 
 phenomena of electricity can be exhibited in a much more convenient 
 manner than by an excited glass tube, and some of them could scarcely 
 be manifested without the aid of such an apparatus. It is requisite, how- 
 ever, for its due action, that the machine should be placed before the fire 
 for a short time before it is used, to expel the moisture that adheres to 
 the glass and the cushion, and that the insulating glass supports should 
 
 fig. H. 
 
 * The Jurors' Reports of the Great Exhibition, which have been published since 
 the above notice was written, make very favourable mention of this machine. 
 
64 THE PHENOMENA OF ELECTEICITY. 
 
 be rubbed with a warm silk handkerchief. These conditions being 
 attended to, and the rubber being covered with amalgam, the prime 
 conductor will emit sparks several inches in length when the handle is 
 turned rapidly. The action of the apparatus will, however, be considerably 
 influenced by the state of the weather, whatever precautions be taken to 
 keep it dry. On a fine frosty day the sparks emitted will be longer and 
 more abundant than can be obtained when the atmosphere is charged 
 with moisture, because the damp air acts as a conductor in restoring the 
 electrical equilibrium. 
 
 The peculiar influence of points in withdrawing the charge from an 
 electrified body may be readily shewn by fixing a pointed wire to the 
 prime conductor of ^n electrical machine. When the point is attached, 
 the apparatus appears to be deprived of its power of exciting electricity, 
 and but few and very feeble sparks will be emitted. The point, in fact, 
 disperses the electric fluid almost as rapidly as it is excited ; and if the 
 room be darkened, rays of light will be seen issuing from it into the air 
 in the form of a cone, of which the point is the apex, the light being 
 brighter there, and diminishing as the rays expand. When the point is 
 fixed to the insulated rubber charged negatively, the effect is the same 
 in the dispersion of the charge,'but the appearance is that of a star instead 
 of a luminous cone. These different appearances of the electric light at 
 the rubber and at the prime conductor induced Franklin to infer that the 
 latter emitted electricity, and was consequently in a positive state, and 
 that the rubber was negatively electrified the plus and minus hypothesis 
 being assumed. 
 
 On presenting the back of the hand to a metal point fixed on the prime 
 conductor, a sensation similar to that of a small blast of air will be per- 
 ceived ; and several kinds of apparatus have been contrived to exhibit the 
 action of the force, whatever it may be, that issues from or is induced to- 
 wards electrified points. The most simple of these contrivances is the 
 electrical jack, which consists of four light pieces of wire placed cross- 
 wise, and balanced horizontally on a pivot in the centre. The ends of 
 these wires are pointed, and are bent in the direction of a tangent to the 
 circle described by the apparatus during its rotation on its axis. 
 
 When attached to the prime conductor, as 
 represented in fig. 15, and the machine is put in 
 action, the blasts from the bent points cause the 
 air against which they strike to react on the ap- 
 paratus, and to turn it rapidly round ; in the same 
 manner that water or steam issuing from jets simi- 
 larly directed turn water-mills and model steam- 
 engines, on the principle of reaction. 
 
 Another and very curious experiment, which 
 is adduced as proving the emission of some active 
 fig. 15. force from an electrified point, is the following : 
 
 Put a little sealing-wax at the end of the pointed 
 
 wire A, fig. 16, and whilst the machine is in action melt the wax. A 
 thread of sealing-wax finer than a spider's web will then be propelled 
 from the point ; and if a piece of white paper be held near, the convolu- 
 tions of the web-like films, as they overlap each other, produce a remark- 
 able and sometimes a beautiful effect, 
 
DIRECT DEVELOPMENT OF ELECTRICITY. 65 
 
 It might be supposed, if electricity be 
 emitted only from the positive prime con- 
 ductor, and the insulated rubber be elec- 
 trified negatively, by having its natural 
 share of electricity abstracted from it, that 
 there would be no emission from the point 
 fixed to the rubber, but rather an influx 
 towards it. This, however, is not the 
 case; for the phenomena of propelling 
 wheels and projecting sealing-wax fila- 
 ments occur whether the point be positively or negatively electrified. This 
 is one of the difficulties which the advocates of the plus and minus states 
 of electricity have to contend with ; for the phenomena of equal apparent 
 emission from negatively electrified points appears to support the original 
 hypothesis of Du Fay, that there are two distinct electric fluids. To 
 account for the apparent anomaly, it is said that the effect of propulsion 
 is not produced by the emission of negative fluid from the point, but 
 that it is caused by the mutual attractions always subsisting between 
 bodies in opposite states of electricity. The seeming emission of air from 
 points fixed on either of the conductors of the electrical machine is merely 
 a secondary and a mechanical effect produced by the air being put in 
 motion by the continuous discharges from the points. 
 
 The cause why points exert such powerful influence in the discharge 
 of electricity has been explained by the researches of M. Coulomb into the 
 distribution of electricity on the surfaces of bodies of different forms. On 
 a sphere, every part of the surface being equally distant from the centre, 
 the distribution of electricity is equal ; but the more the shape of the body 
 departs from that of a sphere, the more unequally is the electricity dis- 
 tributed. M. Coulomb insulated a metal rod, two inches in diameter and 
 thirty inches long, with hemispherical ends; and having charged it with 
 electricity, he found that at a distance of two inches from the end the 
 electricity was to that in the middle of the rod as 1^ to 1. At one inch 
 from the end the proportion was as If to 1, and at the extreme end it 
 was as 2^y to 1. It appears from the results of his experiments that 
 the intensity of the electrical charge increases in a very rapid proportion 
 towards the edges of an insulated conductor ; that it augments still more at 
 the corners; and that when points project, their extremities concentrate 
 the electricity with great additional intensity. 
 
 By the aid of these experiments, the cause of the escape or discharge 
 of electricity from points may be readily inferred. The non-conduct- 
 ing air which surrounds an electrified body resists the escape of the 
 electricity in proportion to its pressure on the surface, the amount of 
 resistance being in an inverse ratio to the intensity of the electric force. 
 If, therefore, the force be concentrated at a point where the amount of 
 surface-resistance to its escape is reduced to the smallest quantity, the 
 concentrated force meets with comparatively little obstruction, and rapidly 
 rushes towards the surrounding bodies which are exerting an attractive 
 power on the excited electricity. 
 
 One of the many effects of electrical induction is the distribution of 
 static electricity entirely on the surfaces of conductors. The electricity 
 communicated to any substance induces an opposite state of electrical ex- 
 
66 THE PHENOMENA OF ELECTRICITY. 
 
 citement on surrounding bodies, 
 and the mutually attractive in- 
 fluence draws all the electric fluid 
 to the surface. Thus an insulated 
 hollow ball, however thin its sub- 
 stance, will contain a charge of 
 electricity equal to that of a solid 
 fig 17 ball of the same size, all the 
 
 charge being distributed, in either 
 
 case, on the surface alone. An experiment contrived by M. Biot affords 
 a very satisfactory illustration of the distribution of electricity on surfaces. 
 Let a metal globe A, fig. 17, be suspended by a silken cord, and com- 
 municate to it a charge of electricity. Two hemispheres B, B, that will 
 exactly enclose the globe, should be insulated by glass handles, and placed 
 over it when thus charged, so that the exterior surfaces of the hemispheres 
 may become the outside of the globe. Under these circumstances, the 
 whole charge of electricity will be transferred from the globe to the hemi- 
 spheres; and when they are removed by the glass handles, all the electricity 
 of the globe will be discharged, and will be retained on the exterior surfaces 
 of the hemispheres. 
 
 The interior surfaces of hollow vessels have not any electricity dis- 
 tributed on them, because there is no opposing surface on which the elec- 
 tricity of the opposite kind can be induced. The inside of a hollow metal 
 globe, for example, has opposed to it only the metal already charged with 
 electricity of the same kind as its own; consequently, there can be no 
 inductive action on such surface. The absence of electricity from the 
 inside of charged metallic vessels may be shewn by electrifying a metal ice- 
 pail or a pewter pot placed on an insulating stand, and then lowering 
 into it a metal ball suspended by silk, allowing it to touch the inside. 
 When the ball is withdrawn, it will not indicate the least trace of elec- 
 tricity; but if it be then applied to the outside of the metal vessel, it will 
 acquire and carry away a large portion of the charge. 
 
 A more striking exemplification of the diffusion of elec- 
 tricity exclusively on the outsides of vessels is afforded 
 when, instead of a solid metallic vessel, a cylinder formed 
 of wire-gauze is employed. Let the insulated ball B be 
 lowered into the wire-gauze cylinder A, fig 1 8, when elec- 
 trified and mounted on an insulating stand, and it may 
 touch every part of the interior without receiving any por- 
 tion of the electricity with which the exterior surface is 
 charged, though the slightest touch on the other side of 
 the open wire mesh would communicate its electricity to 
 the ball. 
 
 When a wire-gauze cover is placed over an electrometer, 
 it effectually prevents the gold leaves from being affected 
 by excited electrics, and it is customary to cover all deli- 
 cate instruments of the kind with a metallic net, to protect 
 them from injury by too violent action. 
 
 The fact that by increasing the surface of any body 
 charged with electricity the intensity is diminished, was 
 known to Dr. Franklin, who illustrated this absorbing influence of ex- 
 
DIRECT DEVELOPMENT OF ELECTRICITY. 67 
 
 tended surface by electrifying a chain heaped together on an insulating 
 stand, and then drawing part of it upwards by a silk thread. When 
 the surface capable of being surrounded by an electrical atmosphere was 
 thus increased, the intensity of the charge was diminished, and by lowering 
 the chain again the original force was regained. 
 
 Another mode of shew- 
 ing the effect of enlarging 
 the surface is to wind a 
 strip of tinfoil round a 
 small insulated wooden cy- 
 linder, as represented in 
 the annexed woodcut. 
 ^Vhen a charge of electri- 
 city is given to the metal, 
 the pith-balls a, a diverge. 
 Take hold of the small 
 piece of ribbon 5, and draw 
 some of the foil from the 
 cylinder, so as to expose a fig. 19. 
 
 large surface, and the balls 
 
 collapse. On winding the foir again on the cylinder the balls again di- 
 verge. It is evident, therefore, that the quantity of electricity undergoes 
 no change by the altered state of the surfaces, but that the intensity is 
 diminished by the same quantity being diffused over a larger space. The 
 difference in effect produced by expanding or contracting the surface over 
 which a given charge of electricity is diffused will be further noticed when 
 we speak of the electrical battery. 
 
 Though the electrical charge resides on the surfaces of conductors, it 
 does not exist as an atmosphere of electricity around them, as was for- 
 merly imagined ; but it seems to be confined within the external surface. 
 No difference is made in the distribution of electricity on metals when a 
 part or the whole surface is covered with varnish, or even with a thick 
 coat of wax. 
 
 The electricity excited by the electrical machine is in a high state of 
 intensity ; but the quantity is comparatively small. Its concentrated energy 
 enables it to force a passage through the non-conducting air to a greater 
 distance than when collected in much larger quantities in a lower state of 
 intensity; but the physical effects of the long spark emitted are only 
 feeble. They are sufficient however to shew, in addition to the general 
 phenomena of attraction and repulsion which we have noticed, the igniting 
 power of electricity in some of the more inflammable substances. If spirits 
 of wine be warmed in a metal spoon, and 
 a spark from the conductor be made to 
 pass through the spirit, it will be instantly 
 
 set on fire. This experiment appears the ' ' . -| 
 
 more curious when the spark is passed f | I ' ( 
 
 from the finger of a person placed on an 
 insulating-stool. 
 
 Hydrogen gas may also be inflamed 
 by a spark. For performing this experi- fi s- 20 - 
 
 nient in the most efficient manner, an electrical cannon or pistol is con- 
 
68 THE PHENOMENA OF ELECTRICITY. 
 
 structed. It consists of a brass tube, about one inch in diameter and six 
 inches long, closed at one end. A piece of wire a, fig. 20, that is to 
 conduct the electricity through the gas, is introduced into the tube, but is 
 insulated from it by ivory or wood, b. 
 
 The most convenient way of charging the pistol is to attach a tube to 
 a bladder containing an explosive mixture of hydrogen and oxygen gases, 
 to insert it perpendicularly into the mouth of the pistol, and then, by 
 gently squeezing the bladder, to force the gas out. In this way the atmo- 
 spheric air is displaced, and the cannon is charged without wetting the 
 insulating ivory. The open end is then closed with a cork whilst the pistol 
 continues to be held inverted, to prevent the escape of the hydrogen. On 
 taking a spark from the machine through the wire, the gas explodes with 
 a loud report, and propels the cork to a considerable distance. 
 
 In charging the pistol in this manner from a bladder filled with an 
 explosive mixture of hydrogen gas, care should be taken not to allow a 
 lighted candle to be brought near. From neglect of this precaution on one 
 occasion, an accident happened to the author that produced considerable 
 alarm. He was filling a gun-barrel with explosive gas from a bladder 
 held under his arm, when, in consequence of approaching too close to the 
 candle, the contents of the bladder exploded, extinguishing the lights and 
 stunning his arm and side, though it did no serious damage. 
 
 The resistance offered by air to the passage of electricity may be very 
 beautifully illustrated by sparks from the machine. If the air were a con- 
 ductor there could be no manifestation of electrical phenomena, for the 
 equilibrium would be restored as quickly as it was disturbed; but the 
 resistance of the air serves to retain the excited electricity on the surfaces 
 of electrified bodies. When the electricity possesses sufficient intensity to 
 force its way through the resisting air, the discharge is accompanied by a 
 bright spark. If the machine be powerful and in good order, sparks eight 
 or ten inches long may be obtained, which, in overcoming the resistance 
 of the non-conducting medium, are diverted from a straight path and 
 describe a ziz-zag course, resembling a flash of forked lightning. 
 
 That the resistance 
 to the passage of elec- 
 tricity from body to 
 body is caused by 
 
 fig. 21. * ,. ,1 
 
 something more than 
 
 by the intervening space, is proved by the facility with which electrical 
 discharge is effected through vessels exhausted of air. For instance, let a 
 glass tube c, fig. 21, about three inches in diameter and two feet long, be 
 fitted at each end with a brass cap, to which a wire and a brass ball are 
 attached. At the end B there is a screw to fit on to the air-pump, 
 by which the tube may be exhausted. On applying one end to the 
 prime conductor, and the machine is put in action, the electricity passes 
 readily through the partial vacuum, and is. discharged through the tube. 
 When the experiment is performed in the dark, the interior of the tube 
 will be observed to be luminous with beautiful purple-coloured flashes, 
 which present a miniature resemblance to the aurora borealis. 
 
 If the air be gradually admitted whilst the machine continues in action, 
 and the tube be removed a short distance from the conductor, so that 
 sparks may pass between them, the resistance to the electricity will in- 
 
DIRECT DEVELOPMENT OF ELECTRICITY. 69 
 
 crease as the air is admitted, until the sparks can no longer force a pas- 
 sage. At an early stage of the re-admission, when the air is still greatly 
 attenuated, the electric spark will pass through like a ball of light, 
 moving comparatively slowly, so that its form and course may be dis- 
 tinguished. This very interesting experiment, which requires a little 
 address for its perfect development, exemplifies the phenomena of meteors 
 or "falling stars" in the upper regions of the atmosphere, where the air 
 is less rarefied than in the higher fields of space where the aurora cor- 
 uscates. 
 
 Faraday has examined with great care the various kinds of elec- 
 trical discharge, with a view to establish his theory of induction; and he 
 has succeeded in accumulating a great number of interesting facts con- 
 nected with the transmission of electricity through resisting media. Fara- 
 day's theory of induction, as we have before stated, supposes that the 
 particles of non-conducting bodies, when acted on by an electric force, 
 assume a polar state, and form a chain of contiguous particles, each one of 
 which has a positive and negative end. This polarised chain of particles, 
 it is assumed, extends from the excited electric through the air or other 
 non-conducting body, and induces in the nearest conducting body a state 
 of electricity opposite to that of the coercing force. In proportion as the 
 particles of different substances possess the power of communicating elec- 
 tricity to each other, their tendency to assume a polar condition dimin- 
 ishes ; and, on the other hand, the greater the non-conducting property of 
 the particles, the more strongly will they take the polar direction. In 
 other words, induction can only take place across insulating substances, 
 and the inductive action is more or less readily assumed according to the 
 power of conducting electricity. 
 
 Applying this theory to the explanation of electric discharge through 
 resisting media, Faraday assumes that there is a limit to the influence 
 which the intervening chain of polarised particles possesses in retaining 
 the attracting forces apart, and that when any of the contiguous particles 
 have attained their highest degree of polarised exaltation, they can no 
 longer resist the passage of the electric force. Thus 
 when one or more links of the chain are subverted, 
 the two forces cannot be restrained. Every case of 
 discharge is therefore preceded by inductive action 
 which coerces the insulating particles into a polar state, 
 until they are restored to their natural condition by 
 the overpowering attraction of the combining forces. 
 
 The electric spark is considered " as a discharge or 
 lowering of the polarised inductive state of many di- 
 electric particles by a particular action of a few of the 
 particles occupying a very small and limited space, all 
 the previously polarised 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." 
 
 The sudden restoration of the electrical equilibrium 
 by the mutually-attracting forces bursting through the 
 intervening non-con(Jucting space, is termed disruptive discharge. It may 
 
70 
 
 THE PHENOMENA OF ELECTRICITY. 
 
 take place either in the form of a spark or in a series of rapidly-intermit- 
 ting discharges, so near together as to appear continuous. The latter is 
 called the brush discharge (fig. 22), from the form of its luminous corus- 
 cations. 
 
 To produce the brush discharge with effect requires the machine to be 
 in good order, and the intensity of the electricity on the prime conductor 
 to be increased by adding to it a projecting rod with a rounded end. The 
 discharge takes place from the end into the air, or to any conducting body 
 brought near, and it is accompanied with a continuous rushing noise. 
 Professor Wheatstone has proved that the sound is produced by a rapid 
 succession of disruptive discharges, and that the brush of light observable 
 in a darkened room is resolvable into a number of brushes, each 
 of which indicates a separate and instantaneous discharge ; 
 though the discharges are so rapid as to mingle together in 
 one luminous expanding cone, with a bright apex near the 
 discharging conductor. 
 
 The difference in the appearance of the brush discharge 
 from the positive and negative conductors is very observable. 
 The brushes obtained from the negatively-charged conductor 
 (fig. 23) are shorter, and the discharges are more rapid, " being 
 seven or eight times more numerous in the same period than 
 those produced when the rod was charged positively to an equal 
 degree."* 
 
 Another form of discharge is obtained when a fine point, 
 instead of a blunted thick wire, is attached to the prime con- 
 ductor. In that case, the expanding brush accompanied wHh 
 a rushing sound gives place to a small pencil of rays, which 
 1 1 1 produces a steady light. This has obtained the name of the 
 |(/ glow discharge, a, fig. 24. It is probable that even this 
 steady and noiseless discharge may be resolved, like that 
 of the brush, into an innumerable quantity of intermittent 
 discharges, mingled together so intimately as to be sepa- 
 rately indistinguishable. 
 
 When a fine point is attached to the insulated rubber of 
 the machine, the light presents the form of a star, b. 
 
 The light of the electric spark varies as it passes 
 through different media. In air the sparks have that in- 
 tense light and bluish colour which are so well known, and 
 often have faint or dark parts in their course when the 
 quantity of electricity is not great. In nitrogen gas they 
 have more colour of a bluish or purple character; and 
 Faraday considers them remarkably sonorous. In hydrogen, the colour 
 is crimson ; in oxygen, whiter than in nitrogen, and not so brilliant ; in 
 carbonic acid gas similar to air, but with a green tinge, and remarkably 
 irregular ; in coal gas the spark is sometimes green, sometimes red, and 
 occasionally one part green and another red, and the black parts occur 
 very suddenly. These various colours of the spark in different gases are 
 considered by Faraday to be attributable " to a direct relation of the elec- 
 tric powers of the particles of the dielectric through which the discharge 
 
 fig. 23. 
 
 a\ 
 
 fig. 24. 
 
 * Faraday's Experimental Researches. 
 
ACCUMULATED ELECTRICITY. 71 
 
 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."* 
 
 The brush discharge also exhibits peculiar characters in the different 
 gases, the effect in nitrogen being finer in form, light, and colour than 
 in any other gas, and evolving a greater quantity of light. The peculiar 
 character of nitrogen in relation to the electric discharge must, it is sup- 
 posed by Faraday, have an important influence over the form, and even 
 the occurrence of lightning, as that gas, which extends its discharge farther 
 than any other, constitutes four-fifths of the atmosphere. 
 
 CHAPTER VIT. 
 
 ACCUMULATED ELECTRICITY. 
 
 The Leyden jar Its construction and mode of action The amount of electricity 
 always constant Chain of Leyden jars self-charged The charge in the glass, and 
 not in the coating Charged plate of glass Electrical batteries Intensity of force 
 diminished by extension Residual charge Lateral charge : its cause and effects 
 Distribution of electricity during discharge Universal discharger Lane's discharger 
 Quadrant electrometer. 
 
 THE power of accumulating electricity by means of the 
 
 Leyden jar has placed in the hands of electricians a force 
 
 of almost unlimited extent. In our sketch of the history 
 
 of electric science, we have .already adverted to the nature 
 
 of the apparatus. As at present constructed, it consists 
 
 of a thin glass jar A, fig. 25, coated within and without 
 
 with tin-foil, which reaches to about three inches of the 
 
 top. A wooden cover B serves as a support to a straight 
 
 thick brass wire c, that passes through the centre of the 
 
 cover, and has a metallic connexion by a chain or wire 
 
 with the interior coating. This wire rises a few inches 
 
 above the cover, and is surmounted by a hollow brass ball, 
 
 which is screwed on to the top of the wire to prevent the 
 
 dispersion of the electricity from the end. The sizes of the fi s- 25 - 
 
 jars vary from half-a-pint to ten gallons. One holding 
 
 about a pint will give a shock as strong as most persons like to receive. 
 
 To charge a jar with positive electricity, connect its small brass ball 
 with the prime conductor of the machine, and make a connexion between 
 the outside coating and the ground. When fully charged, it will give in- 
 dications of its electrical condition by a muttering sound ; and in the dark, 
 rays of light will be seen issuing from the edges of the tin-foil and from 
 the ball. 
 
 The notion of Muschenbrceck, which led to the discovery of the Leyden 
 jar, was to collect electricity within a phial to prevent its dispersion, and 
 thereby to store up an increased quantity of the electric fluid ; but it is 
 
 * Experimental Researches. 
 
THE PHENOMENA OF ELECTRICITY. 
 
 now ascertained that a jar when highly charged does not contain more 
 electricity than it did before it was applied to the conductor. The effect 
 produced by charging is not to increase the quantity, but only to disturb 
 the natural electricity previously present in a latent state on the inside 
 and outside of the glass. There is injected into the inside, by connexion 
 with the electrical machine, an amount of positive electricity, whilst an 
 equal amount of negative electricity is driven from the outside by the 
 force of electrical induction ; and unless the electricity on the outer surface 
 of the glass can be thus driven off by affording it a connexion with the 
 ground, the inside cannot receive a charge. 
 
 Let a Ley den jar be insulated from the earth by placing it on a glass 
 stand, and it will receive scarcely any electricity from the conductor ; not 
 more than equal to the quantity which can escape from the outside to the 
 
 surrounding air. If the knob of another 
 insulated jar be connected with the ground, 
 and the outside coatings of the two jars be 
 brought near together, sparks will then 
 pass rapidly from the prime conductor to 
 the knob of the first, and they will also pass 
 as rapidly between the outside coatings of 
 the two jars. In this manner both the 
 Ley den jars become charged, and it will be 
 found that they are charged equally, but 
 with electricity of opposite kinds. The 
 first one, that derived its electricity directly 
 from the prime conductor, will be charged 
 positively ; the second, that derived its 
 charge from the electricity escaping from 
 the knob to the ground, will be negative. 
 Place the two jars on the table, and sus- 
 pend between them a pith ball B or other 
 light substance, and it will be attracted alternately from one to the other 
 in rapid vibrations, clearly shewing that the electricity in the two jars is 
 of opposite kinds. 
 
 The phenomena that occur during the charge of a Leyden jar have 
 been adduced as evidence in support of the Franklinian theory of a single 
 electric fluid, the outside being supposed to be in a minus state after part- 
 ing with its natural quantity to the other jar. But the phenomena are 
 explicable also on the hypothesis of two fluids, it being assumed that they 
 are separated from their neutral state by the coercing force of the free 
 electricity communicated to the inside of the jar. 
 
 Franklin attempted to apply practically the charging of one jar from 
 the escaping electricity of another. He inferred, that if a series of insulated 
 jars were arranged with the outside coatings and knobs alternately touch- 
 ing, the coating of the last one being connected with the ground, that by 
 this arrangement the positive electricity expelled from the outside of the 
 first jar would charge the second ; that the electricity from the outside 
 of the second would charge the third positively, and so on to any num- 
 ber ; and that an immense electric force might be thus accumulated from 
 the same quantity of electricity that is required to charge a single jar. 
 Let ABC represent a series of three jars, A and B being mounted on 
 
ACCUMULATED ELECTRICITY. 73 
 
 insulating glass stands. On 
 making connexion from the 
 prime conductor of an electri- 
 cal machine to the knob of A, 
 that jar will be charged posi- 
 tively, and an equal amount of 
 electricity will be expelled from 
 the outside into B, which will 
 also be positively charged. The 
 third jar c will in like manner 
 be charged from the outside 
 of B, and the electricity which 
 was expelled from A, on arriv- 
 ing at the outside of the last 
 jar of the series, will be con- 
 ducted to the earth. fi g . 27. 
 
 To effect the discharge of 
 
 a jar, it is requisite that a connexion be made between the positive elec- 
 tricity within and the negative electricity without, so that the equilibrium 
 may be restored. Now if a metallic connexion be made from the knob of 
 B to the knob of A, there will be a discharge of the first jar only; for 
 though the connexion is made with the knob of B, none of the positive 
 electricity within can be discharged, for it is restrained by the coercing 
 force of the opposite electricity on the outside. If metallic connexion be 
 made between the outside of B and the knob of A, both those jars will be 
 discharged, and the third will remain charged; but by bringing a wire 
 from the outside of c to the knob of A, the three jars will be at once dis- 
 charged. 
 
 We have been led away by the phenomena exhibited in charging the 
 Leyden jar from the consideration of the cause of its accumulating elec- 
 tricity, and discharging the force instantaneously. We have stated that 
 the cause depends on inductive action operating through the substance of 
 the non-conducting glass. Exemplifications of this action through glass 
 have been previously given. It was shewn that a pane of glass when ex- 
 cited by friction on one side, has negative electricity induced on the other, 
 and that a glass tumbler may be charged with electricity by exposing the 
 inside to the influence of an electrified point, whilst the outside is grasped 
 by the hand. The electricity thus collected on the surfaces of the pane of 
 glass and the tumbler is sluggish in its action, and is dissipated by slow 
 degrees, on account of the non-conducting property of the glass surfaces ; 
 but if metal plates be applied on each side of the pane of glass, the elec- 
 tricity is instantly concentrated at any point, and on connecting the two 
 surfaces with a wire, a discharge takes place, exactly as in the Leyden jar. 
 The charged tumbler might also be converted into a Leyden jar by the 
 application of interior and exterior casings of metal foil, to serve as con- 
 ductors, to concentrate at any point the electricity distributed over the 
 surface of the glass. 
 
 To prove most conclusively that the charge of a Leyden jar is retained 
 on the surface of the glass, and not in the metallic coatings, Leyden jars 
 are made with tin inside and outside casings, so contrived that they may 
 be easily removed. A jar of this kind, when charged and placed on an in- 
 
 F 
 
THE PHENOMENA OF ELECTRICITY. 
 
 sulating stand, may have the metal casings removed and others substituted 
 for them ; yet after this change the jar will be found to retain its charge. 
 The metal serves only to conduct the electricity simultaneously from all 
 parts of the glass. 
 
 A plate of glass affords the most 
 convenient mode of illustrating that 
 the electrical charge is retained by 
 the glass and not by the metal. Let 
 a pane of glass A A, fig. 28, about 
 one foot square, be covered on one 
 side with tin-foil, and laid horizon- 
 tally on the table. To the other 
 side apply the insulated metal disc 
 c of an electrophorus ; connect the 
 disc with the prime conductor, and 
 fig- 28. a few turns of the machine will 
 
 charge the glass. Remove the disc 
 
 by the insulating handle B, and it will manifest scarcely any trace of elec- 
 tricity. Let the same or another disc be again applied to the surface of 
 the glass, and on making connexion between the metals on the opposite 
 sides a strong discharge will take place. A movable metal disc might 
 be applied to each surface of the glass with similar results; but the ar- 
 rangement indicated in the figure is more convenient. 
 
 When a more powerful charge of electricity is required than a single 
 jar will retain, several are combined to form an electrical battery. For 
 convenience, the jars are placed in a box with divisions, the bottom being 
 
 fig. 29. 
 
 lined with tin-foil, to make connexion with all the exterior coatings. The 
 knobs of the jars are connected together by wires, as represented in 
 fig. 29 ; and there is a metal hook projecting from the side of the box 
 connected with the tin -foil lining. Thus all the interior and all the outside 
 coatings of the jars are connected; and when communication is made 
 between the prime conductor and any of the knobs of the jars the whole 
 are simultaneously charged. They are also discharged simultaneously by 
 making connexion between the projecting hook and any one of the knobs. 
 
ACCUMULATED ELECTRICITY. 75 
 
 The combination of several small jars is found better than having a 
 smaller number of large ones, because the thickness of the glass necessary 
 in jars of large size obstructs induction through it. By an arrange- 
 ment of many jars, an amount of electric force may be accumulated that 
 would almost equal the destructive power of lightning. The battery used 
 by Faraday in his experiments consisted of fifteen equal jars, coated eight 
 inches upwards from the bottom, and twenty-three inches in circum- 
 ference ; so that each contained 184 square inches of glass coated on 
 both sides, independently of the bottoms of the jars, which were of thicker 
 glass, and contained each about fifty square inches. The total coated 
 surface of the battery consequently comprised 3500 square inches of 
 coated surface. The electrical battery at the Polytechnic Institution 
 exposes a coated surface of nearly eighty square feet. To receive the full 
 charge of such a battery would be instant death. A battery of nine quart 
 jars is sufficient to exhibit the deflagrating effects of electricity on a small 
 scale ; nor would it be safe to receive a shock from a battery of that size. 
 
 It is a fact deserving consideration that the accumulation of quantity 
 diminishes the intensity of electricity. For instance, an electrical machine 
 when in good action will emit sparks four inches long. When a Leyden 
 jar is charged with twelve such sparks, the accumulated electricity will 
 not force its passage through more than a quarter of an inch ; and if the 
 same quantity be distributed among the jars of an electrical battery, the 
 discharge will not take place through the eighth of an inch. The quantity 
 of electricity is in each case the same, but the state of intensity diminishes 
 in proportion to the surface over which it is diffused. The difference 
 between quantity and intensity is still more remarkably manifested in the 
 different conditions of frictional and voltaic electricity, as will be subse- 
 quently noticed. 
 
 One of the peculiar phenomena of the electrical battery is the residual 
 charge. When communication is made between the inside and outside 
 coatings of a battery consisting of several jars, the whole of the electricity 
 is not immediately discharged. On again making connexion between the 
 inside and outside coatings, after a short interval, a second discharge will 
 occur ; which, though comparatively feeble, might occasion a disagreeable 
 shock. The cause of this residual charge is partly attributable to the 
 accumulation of electricity on those parts of the jar just above the metallic 
 coating ; which portions, not being in direct contact with the metal, are 
 not conducted with equal rapidity. Part of the charge also enters into 
 the pores of the glass, and is thus removed from immediate contact with 
 the metal. 
 
 The simplest kind of instrument employed for discharging a Leyden 
 jar or an electrical battery is a thick curved piece of brass wire, fitted 
 with a small ball at each end. One of these balls is applied to the outside 
 coating, and when the other is brought near to the knob of the jar the 
 electricity instantly passes through the wire with a smart snap or report, 
 connexion being thus made between the two charged surfaces of the jar. 
 When, however, a discharger of this kind is employed for an electrical 
 battery a slight shock is felt, owing to what is termed the lateral dis- 
 charge; therefore, to avoid the inconvenience and the danger that might 
 arise from holding the wire in the hand, an insulated wire is generally 
 employed. Its form is represented in fig. 30, as applied in discharging a 
 
76 THE PHENOMENA OF ELECTRICITY. 
 
 Leyden jar. Two thick brass 
 wires a a, of equal lengths, and 
 terminated with brass balls, are 
 jointed together at c for the con- 
 venience of adjustment, and are 
 cemented to a glass handle 6, 
 which serves to insulate the wires 
 from the hand, and prevents the 
 liability of any perceptible portion 
 of the charge being received by 
 the operator. 
 
 There has been much discus- 
 sion among electricians on the 
 
 subject of lateral discharge, in reference more particularly to the safety of 
 lightning-conductors ; we shall therefore notice in this place the cause of 
 the phenomenon. 
 
 It is the case with electricity, <even to a greater extent than with all fluid 
 bodies, that it will discharge itself into every channel that is open to it. 
 Thus, as in a mountain-torrent some portion of the water will deviate 
 from the straight and broad course into circuitous and narrow crevices, so 
 will the highly tensive electric fluid force its passage through every con- 
 ducting medium, even though the course directly open to it appears to 
 offer a free passage. It must be borne in mind, however, that as every 
 water-course offers some obstruction to the current, so does even the best 
 conductor offer resistance to the electric fluid ; some portion of which is 
 consequently diverted through every conducting substance by which it 
 can be transmitted. Thus, when a Ley.den jar is discharged with an insu- 
 lated wire, a small part of the charge passes through the circuitous and 
 comparatively obstructive course offered by the body of the operator, by 
 the floor, and by the table whereon the jar is .placed. In the case of a 
 single jar, the quantity of electricity that passes in that direction is imper- 
 ceptibly small ; but when several jars are combined, the lateral discharge 
 may become unpleasantly strong, especially if the wire of the discharging- 
 rod be not very thick. Even when an insulated discharging-rod is 
 employed, we may infer that some portion of electricity will force its 
 way along the glass; but it is so innnitessimally small as to be inap- 
 preciable. 
 
 Applying the experience and inferences deducible from experiments 
 with the electrical battery to the more powerful effects of lightning, we 
 are led to consider that every flash of lightning must be accompanied by 
 lateral discharge, and that the quantity thus diverted from the direct and 
 easiest path between the clouds and the earth will depend on the amount 
 of resistance which that direct course offers. Therefore, though lateral dis- 
 charge must, to some extent, always occur, it may be rendered entirely 
 innocuous by a sufficiently thick and unbroken lightning-conductor. In the 
 Report of a Committee appointed by the House of Commons to examine 
 the plan produced by Sir William Snow Harris for protecting ships from 
 lightning, several eminent scientific men expressed their opinions that no 
 lateral discharge could occur with uninterrupted conductors of sufficient 
 thickness. These opinions could, however, only have had reference to 
 any possible danger likely to arise from the division of the charge in 
 
ACCUMULATED ELECTRICITY. 
 
 77 
 
 fig. 31. 
 
 other directions ; for it has been satisfactorily proved, that during an elec- 
 tric discharge and the transmission of an electric current, some portions 
 will be diverted into every possible path. 
 
 Reverting to the consideration 
 of the electrical battery and the ap- 
 paratus connected with its applica- 
 tion, we must notice particularly the 
 "universal discharger" as an instru- 
 ment of very general utility in elec- 
 trical experiments. It consists of a 
 wooden base A, into which are in- 
 serted three upright pillars. The 
 two outermost pillars are of glass, 
 for the purpose of insulating the ball- 
 and-socket joints c c, through which 
 brass rods BB slide, so as to bring 
 them to any required distance on the small table 
 D, which is supported on the central pillar E. 
 The table may be raised to any height, and 
 fixed by a screw. The outer coating of the Ley- 
 den jar or battery is connected with one of the 
 rods, and the insulated discharger being con- 
 nected with the other by means of a chain, the 
 charge of the battery is thus very conveniently 
 sent through any substance placed on the table 
 between the ends of the two rods. 
 
 Lane's discharger is frequently very useful 
 in connexion with the preceding instrument, as- 
 it is self-acting, and transmits a succession of 
 charges of regulated power. Fig. 32 will afford 
 a correct idea of the construction of this appa- 
 ratus. A bent glass rod c is attached to the wire of a 
 Leyden jar, and on the top of the bent arm is a brass ball, 
 through which the horizontal wire D slides, so as to regulate 
 the small ball at the end of it to any required distance from 
 the knob of the jar. A wire or chain E connects the hori- 
 zontal wire with the outside of the jar; and in its course 
 may be placed the universal discharger or any substance to be 
 operated on. It is evident from this arrangement that the 
 discharge of the Leyden jar will take place whenever the 
 electricity has attained a degree of intensity sufficient to over- 
 come the resistance of the air in the space between the knob 
 of the jar and the ball of the discharger ; and by the proper 
 regulation of that distance a succession of charges of nearly 
 equal strength may be transmitted without any interference, 
 with the apparatus. This kind of discharger is sometimes 
 attached to the prime conductor of the electrical machine as 
 a more convenient mode of appliance. 
 
 For ascertaining the intensity of charge, an instrument 
 constructed on the principle of the pith-ball electrometer is usually at- 
 tached to the prime conductor. It is called Leslie's quadrant electrometer, 
 
 fig, 32. 
 
 fig. 33. 
 
78 THE PHENOMENA OF ELECTRICITY. 
 
 represented in fig. 33. The pith-ball A, attached to a light but rigid stem 
 c, is suspended from the upright conducting pillar B, and is repelled pro- 
 portionally to the intensity of the electricity in the Leyden jar or battery 
 connected with the prime conductor. The quadrant D is graduated to 
 mark the degree of repulsion, and by this means, and with the aid of 
 Lane's discharger, the intensity of any charge or succession of charges 
 may be known and regulated. 
 
 CHAPTER VIII. 
 
 MISCELLANEOUS PROPERTIES AND EFFECTS. 
 
 The electric shock : its physiological effects Heating power of the electrical battery 
 All electrical effects consequent on resistance The electric light : its instantaneous 
 duration calculated Magnetising and decomposing power of static electricity. 
 
 NEARLY all the properties of accumulated electricity may be exemplified 
 by means of a cylinder machine of nine inches diameter and a battery of 
 nine quart jars, assisted with the accompanying apparatus which we have 
 described. Many of the phenomena we are about to notice require only a 
 single jar for their development. 
 
 The sudden contraction of the muscles by the peculiar action of elec- 
 tricity on the nerves is at all times startling and disagreeable, and when 
 the sensation of the shock was quite novel and the consequences unknown, 
 it was calculated to excite fear, though we now ridicule the exaggerated 
 accounts first given of the sensation. We have already noticed the re- 
 markable effect of a charge sent through the brain, as described by Dr. 
 Franklin in his dangerous-seeming experiments ; but without venturing 
 on such powerful charges as he distributed without fear, the sudden loss of 
 muscular power may be illustrated by sending a comparatively small shock 
 from a single jar through the spine. When a powerful charge is sent 
 through the lungs it is said to cause a violent shout ; and a much smaller 
 charge through the same organ occasions involuntary laughter. The de- 
 rangement of the nerves by the sudden shock has the effect of causing, 
 in nervous persons, continued trembling of the limbs for some time after- 
 wards ; and a frequent repetition of shocks is by no means desirable. 
 
 When the powerful influence exerted by electricity on the nervous 
 system was discovered, great hopes were entertained that it would prove 
 a valuable remedial agent. These hopes have, however, for the most part 
 been disappointed. Several instances, indeed, are recorded of wonderful 
 cures effected by electrical agency, though they seem to have been more 
 dependent on the imagination than on the direct influence of electricity. 
 In cases of chronic rheumatism rapid successions of feeble electric shocks 
 or vibrations have been found to afford relief; but generally speaking 
 the application of electricity to medical purposes has hitherto failed of 
 success, probably from ignorance of the means by which its powers may 
 be rendered serviceable. 
 
 Of the experiments made on living creatures with a view to ascertain* 
 
MISCELLANEOUS PKOPERTIES AND EFFECTS. 79 
 
 the amount of charge sufficient to produce death, those on eels are the 
 most curious. Difficult as it is to deprive them of life by ordinary means, 
 they are killed instantly by a powerful electric charge ; and when such a 
 charge is sent through a part only of the body of an eel, that portion is 
 deprived of life, while the other part continues to exhibit signs of vitality. 
 It has been observed that the bodies of animals killed by electricity very 
 quickly decompose ; and this fact seems to explain what Franklin was 
 inclined to conceive a mere " fancy," when he thought that a turkey killed 
 by electricity ate remarkably tender. 
 
 The fusing power of electricity was known before it was acknowledged 
 to possess the property of imparting heat ; and some of the early elec- 
 tricians entertained the notion that the dissipation of thin leaves of 
 metal by the electrical battery was produced by what was termed " cold 
 fusion." 
 
 Some illustrations of the igniting power of the electric spark have 
 been already mentioned ; but to exhibit the heating effects of electricity 
 on metals, and other less inflammable substances, requires an electrical 
 battery containing a considerable amount of coated surface. 
 
 Let a thin strip of gold, silver, or copper leaf be attached by moisture 
 between the rods of the universal discharger, and connect one of the rods 
 with the outside coatings of the battery-jars. When the battery is fully 
 charged, as indicated by the elevation of the ball of the quadrant elec- 
 trometer, apply one of the knobs of the insulated discharging-rod to the 
 second rod of the universal discharger, and bring the other knob in con- 
 nexion with the inside coatings of the battery-jars. The charge will thug 
 be sent through the strip of metal-leaf, which will be instantly deflagrated. 
 If the metal-leaf be laid upon paper, the part whereon it was placed will 
 be burnt, and traces of metallic oxide will remain. A small length of very 
 fine wire may be deflagrated in the same manner. 
 
 ^ The deflagration of the metal-leaf and of the wire are caused by the 
 resistance they offer to the passage of the electric charge ; for if they be a 
 little thicker, so as to allow the electricity to pass more freely, the metals 
 will be made red hot without being melted. It is, indeed, only by the 
 resistance bodies offer to the passage of accumulated electricity that its 
 presence is manifested. Through metals sufficiently thick to conduct it 
 freely, electricity passes without any sign; but a similar charge sent 
 through an imperfect conductor may produce destructive effects, in conse- 
 quence of the resistance it encounters. This observation applies to all 
 electric action whatsoever. The manifestation of electricity is a proof of 
 resistance offered to its passage ; and when the resistance is decreased the 
 electrical effects are proportionally diminished. 
 
 The following experiment affords a satisfactory illustration of the in- 
 crease of effect by increasing the resistance. Paste a broad strip of tin- 
 foil across a small piece of sheet-glass ; on the top of it place a corre- 
 sponding piece of glass, perfectly dry, and press both together with a 
 weight. The charge of a battery may thus be sent through the tin-foil 
 without any perceptible effect. Cut away a small part of the foil, so as to 
 leave a break in the middle about the sixteenth of an inch. The battery- 
 charge may even then be sent between the glasses without injury, but the 
 electricity will manifest itself by a bright spark at the point of separation 
 in the foil. Increase the interval by cutting away another portion of the 
 
80 
 
 THE PHENOMENA OF ELECTKICITY. 
 
 foil, so that the resistance to the electric fluid may be increased, and on 
 then repeating the discharge the glass will be shivered. 
 
 A piece of apparatus called a " thunder-house," constructed for the 
 purpose of shewing the action of lightning- 
 conductors, illustrates very satisfactorily the 
 effect of interposed resistance to the course of 
 the electric charge. A piece of mahogany 
 about an inch thick is shaped into the form 
 of the gable end of a house, A, fig. 34 ; and 
 there is a small square wooden shutter, D, 
 that may be easily taken out and placed at 
 opposite corners. A strong wire, B c, rises 
 above the chimney, passes down the house 
 and across the shutter to the wire that con- 
 nects with the outside of a large Leyden jar. 
 When the jar is discharged through the wire, 
 in the position represented in the diagram, 
 the shutter retains its place, for the electric 
 fig. 34. circuit is not interrupted ; but if the shutter 
 
 be turned, so that the wire may be in the di- 
 rection marked by the dotted lines, the continuous circuit is broken, 
 and the resistance which the electric fluid meets with in crossing the inter- 
 vening space causes the shutter to be forced out to some distance. 
 
 The discharge of a Leyden jar may be prolonged by interposing an 
 imperfect conductor ; and by thus diminishing the rapidity of the passage 
 of the electric fluid, it will produce effects that its more rapid action ren- 
 ders unattainable. Thus, if a small quantity of gunpowder be laid on the 
 table of the universal discharger, the effects of an ordinary discharge will 
 disperse the powder without igniting it ; but if the metallic circuit be 
 interrupted by a basin of water interposed between two ends of the con- 
 necting wires, the discharge is prolonged by the resistance of the water, 
 and the force, though less energetic, is more effectual in igniting the gun- 
 powder, which then explodes instead of being dispersed. 
 
 Several forms of apparatus have been contrived for exhibiting the elec- 
 tric light. Spangles of tin-foil are pasted on to glass, in various patterns, 
 
 so arranged as to form a continuous 
 line for the passage of the electric 
 fluid. By means of Lane's discharger 
 a continuous stream of small charges 
 is sent through these breaks in the 
 conducting metal-foil, at each of 
 which a brilliant spark appears, re- 
 presenting in vivid lines the device 
 arranged by the disposition of the 
 breaks in the foil. In the dark this 
 exhibition has a very agreeable effect; 
 and when a lengthy device is pat- 
 terned on the glass, the simultaneous appearance of sparks at all the breaks 
 serves to shew, in some degree, the instantaneous character of the electric 
 discharge. In the arrangement of the tin-foil spangles in devices, care 
 must be taken that the sum of the spaces between each is not greater 
 
 fig. 35. 
 
MISCELLANEOUS PROPEKTIES AND EFFECTS. 81 
 
 than the space through which the electricity of the jar will discharge it- 
 self. Sparks from the prime conductor of the electric machine will tra- 
 verse over a much greater space than a discharge from a Leyden jar, but 
 the light is not so intense. A suspended chain also serves to exhibit 
 the brilliancy and instantaneous nature of the electric discharge ; for vivid 
 sparks appear at the junctions of the numerous links ; and when the chain 
 is hung in festoons, luminous tracery is produced. 
 
 The instantaneous duration of the electric spark is shewn in a striking 
 manner by a very ingenious application, by Professor Wheatstone, of one 
 of the properties of vision. The retina of the eye, it is well known, pos- 
 sesses the peculiar property of retaining the impression of an image for 
 the eighth part of a second after the object that produced it is removed. 
 The eighth part of a second may perhaps seem to most persons a duration 
 inappreciably small ; but those accustomed to note time will detect, with 
 the naked eye, a variation of the tenth part of a second in the vibration of 
 a pendulum, and by means of the copying electric telegraph a variation of 
 the thousandth part of a second may be detected and rendered visible. 
 The fact that a lighted stick, when whirled round in the air, appears like 
 a circle of light, proves also that the circle must be completed within the 
 eighth part of a second, otherwise the line of light would appear to be bro- 
 ken ; but as it is, the impression at every part of the circle remains on the 
 retina until the light returns to the same point to renew it ; and thus the 
 circle described by the lighted stick, instead of appearing to be made up of 
 numerous sparks, resembles a continuous ring of light. The same cause 
 also explains why a circular screen containing figures or patterns painted 
 on it becomes a confused mass of colour when turned rapidly round. It 
 may be easily conceived, however, that if only instantaneous sight could 
 be obtained of either of the whirling bodies, it would be seen in its true 
 form ; that is, the lighted stick would appear as a stationary spark, and 
 the figures on the screen would be distinctly visible, and would seem to be 
 stationary, though in reality revolving very rapidly. It is by applying 
 this principle that Professor Wheatstone has determined the duration of 
 the electric spark. A painted screen is turned round rapidly in the dark, 
 and is lighted at intervals by electric sparks from a Leyden jar. The 
 figures on the screen seen by this occasional light appear quite distinct, 
 and to be at rest ; thus proving that the duration of the light must be 
 considerably less than the eighth part of a second. The velocity of the 
 screen's motion is regulated to a known number of revolutions in a second, 
 and by increasing the rapidity a speed is at length attained at which the 
 colours become confused ; even the duration of the*electric spark affording 
 time for the objects to be seen in more than one position. The rapidity 
 of revolution being known, and also the duration of impressions on the 
 retina, the length of time that light is thrown on the screen just before 
 the figures become confused may be estimated ; and thus Professor Wheat- 
 stone has been enabled to prove that the duration of the electric spark is 
 not longer than the millionth part of a second. The electric spark seems, 
 indeed, to be much longer in sight ; but the retention of the light by the 
 retina causes the duration of the impression to remain for the eighth part 
 of a second, though the light itself only lasts the millionth part of that 
 time. A flash of lightning is equally instantaneous, and all objects in 
 motion seen in the night-time by lightning appear to be at rest. Even 
 
82 THE PHENOMENA OF ELECTKICITY. 
 
 a cannon-ball in rapid flight would appear to be motionless in the air. 
 " As quick as lightning " has become a proverbial expression, though few 
 persons are aware how very instantaneous it really is. 
 
 The magnetising and decomposing powers of electricity will be no- 
 ticed more particularly when we come to speak of that modification of 
 the force exhibited in the voltaic battery ; but a few examples of the ex- 
 ercise of those powers by statical electricity will serve to shew that in 
 these, as in all other respects, there is a similarity between the chemically 
 excited and the frictional agent. 
 
 Let a sewing-needle be placed on the table of the universal discharger, 
 so that several charges of the electrical battery may be sent through it 
 in quick succession. This can be most conveniently done by connecting 
 Lane's discharger with the instrument. After the needle has been thus 
 operated on, it will be found to possess magnetic properties, and the effect 
 will be increased if the needle be placed in the magnetic meridian during 
 the experiment. 
 
 The decomposing power of statical electricity may be shewn by pass- 
 ing a succession of electric sparks from the machine through litmus or 
 turmeric paper moistened with a solution of sulphate of soda. The salt is 
 shortly decomposed by the electric agency ; and the acid liberated from the 
 soda will turn the paper red if litmus be used, or if turmeric paper be 
 the re-agent, the alkali separated from the acid will give it a brown stain. 
 The experiment succeeds better when the electricity is directed 
 from the prime conductor to the paper by points, or by some 
 other form of discharge which will cause a constant current of 
 electricity of a lower degree of intensity to act on the salt to be 
 decomposed. 
 
 The decomposition of water may be illustrated by passing a 
 rapid succession of charges from a Leyden jar between the 
 ends of two wires inserted in a glass tube containing water, 
 the ends of the two wires in the water being about half an inch 
 apart. At each discharge small bubbles of hydrogen and oxy- 
 gen gases rise from the ends of the wires in the proportion of 
 two parts of hydrogen to one of oxygen, that being the propor- 
 tion in which the two gases combine in the constitution of 
 water. The gases thus evolved, if mingled together, will ex- 
 plode when a light is brought near ; and if the experiment be 
 conducted with great care, and on a sufficiently large scale, a 
 quantity of water will be formed by the re-union of the gases 
 fig. so. during the explosion, exactly corresponding in weight to that 
 of the water decomposed. 
 
ATMOSPHERIC ELECTRICITY. 8S 
 
 CHAPTER IX. 
 
 ATMOSPHERIC ELECTRICITY. 
 
 Beccaria's observations of a thunder-storm Mr. Crossed apparatus and experiments 
 Remarkable phenomena of a thunder-storm Different conditions of artificial elec- 
 tricity and lightning Lightning-conductors Supposed danger from lateral dis- 
 charge Various kinds of lightning-conductors Safest place in a thunder-storm 
 Causes of the electrical state of the clouds Sheet-lightning and forked- lightning 
 Thunder The aurora borealis. 
 
 THE identity of lightning and electricity was fully proved by Franklin 
 and by the French electricians, who succeeded, by experimenting accord- 
 ing to his directions, in drawing lightning from the clouds. The fact was 
 so completely established by the first experiments on the subject as to 
 leave no doubt that lightning is the effect of electrical discharge between 
 the earth and the clouds ; and the principal object of succeeding investiga- 
 tions has been to determine the peculiar conditions of the electricity of the 
 clouds, the means by which they become charged, the force of the disrup- 
 tive discharge, and the most effectual means of guarding against its effects. 
 Signor Beccaria, of Turin, a contemporary of Franklin's, made a care- 
 ful and very extended series of observations on lightning and atmospheric 
 electricity, which have scarcely been surpassed by those of succeeding elec- 
 tricians. In his experiments he made use of kites and pointed rods, and 
 of a great variety of both at different places. He paid particular attention 
 to the appearances presented by the clouds during thunder-storms, of which 
 the following were the most remarkable : " The first appearance of a 
 thunder-storm is one or more dense clouds increasing very fast in size, 
 and rising into the higher regions of the atmosphere. The lower surface 
 is black and nearly level, but the upper finely arched and well defined. 
 Many of these clouds seem often piled one upon another, all arched in the 
 same manner, but they keep continually uniting, swelling, .and extending 
 their arches. At the time of the formation, or approach of the dense cloud, 
 the atmosphere is generally full of a great number of separate clouds, 
 motionless and of peculiar shapes. All these, on the appearance of the 
 thunder-cloud, draw near towards it and become more uniform in their 
 shapes as they approach, until they coalesce into one uniform mass. When 
 the thunder-cloud has increased to a great size its lower surface is often 
 ragged, particular parts being detached towards the earth, but still con- 
 nected with the rest. Sometimes the lower surface swells into various 
 large protuberances, bending uniformly towards the earth \ and sometimes 
 one entire side of the cloud will have an inclination to the earth, and 
 the extremity will nearly touch the ground. When the eye is under the 
 thunder-cloud, after it has grown large and w T ell-formed, it is seen to sink 
 lower, and darken prodigiously ; at the same time that a number of 
 small clouds are seen in rapid motion driving about in very uncertain 
 directions under it. Whilst these clouds are agitated with the most rapid 
 motions the rain generally falls in the greatest plenty, and if the agitation 
 be exceedingly great, it generally hails. 
 
84 THE PHENOMENA OF ELECTRICITY. 
 
 " While the thunder-cloud is swelling and extending in branches over 
 a large tract of country, the lightning is seen to dart from one part of it 
 to another, and often to illuminate the whole mass. When the cloud has 
 acquired sufficient extent, the lightning strikes between the cloud and the 
 earth in two opposite places, the path of the lightning lying through the 
 whole body of the cloud and its branches. The longer this lightning con- 
 tinues, the rarer does the cloud become, until at length it breaks in dif- 
 ferent places and shews a clear sky. When the thunder-cloud is dispersed, 
 those parts which occupy the upper regions of the atmosphere are equally 
 spread and very thin, and those underneath are black, but also thin ; and 
 they vanish gradually without being driven away by any wind, being dis- 
 solved into invisible vapour."* 
 
 Experiments on a scale of vast magnitude have been for some years 
 past conducted by Mr. Crosse, of Broomfield, near Taunton, a gentleman 
 who, secluded within his own domain, which he has converted into an ex- 
 tensive electrical laboratory, has been endeavouring to dive into the secrets 
 of nature, and to trace the agency of electricity in the construction of rocks, 
 and even in the creation of living creatures. This philosopher collects 
 electricity from the atmosphere by means of what he terms an " exploring 
 wire," which extends for several miles over his grounds. This wire is in- 
 sulated, and is connected with many pointed metal rods, which are sup- 
 ported and insulated on poles fixed to some of the highest trees in his 
 park. These poles are erected in all directions, as far as the eye can 
 reach, and the exploring wire connected with them is made to terminate 
 outside the window of the laboratory. A thick wire communicating with 
 the earth is supported on a pole near to the exploring wire, to serve as a 
 safety conduit for the electricity when it is emitted in such quantities as 
 to become dangerous. When experiments are performed in the laboratory 
 with the accumulated electricity collected by the exploring wire, it is intro- 
 duced through the window by a connecting wire ; convenient arrange- 
 ments being made for applying the force with advantage and for securing 
 the safety of the operator. 
 
 The following is Mr. Crosse's account of the construction of a thunder- 
 cloud, as examined by the exploring wire ; and of his views of the manner 
 in which the electricity is distributed : 
 
 "On the approach of a thunder-cloud to the insulated atmospheric 
 wire, the conductor attached to it gives corresponding signs of electrical 
 action. In fine cloudy weather the atmospheric electricity is invariably 
 positive, increasing in intensity at sun-rise and sun-set, and diminishing at 
 mid-day and mid-night, varying as the evaporation of the moisture in the 
 air ; but when the thunder-cloud (which appears to be formed by an un- 
 usually powerful evaporation, arising either from a scorching sun succeed- 
 ing much wet, or vice versa) draws near, the pith balls suspended from the 
 conductor open wide with either positive or negative electricity ; and when 
 the edge of the cloud is perpendicular to the exploring wire, a slow suc- 
 cession of discharges takes place between the brass ball of the conductor 
 and one of equal size carefully connected with the nearest spot of moist 
 ground. I usually connect a large jar with the conductor, which increases 
 the force, and in some degree regulates the number of the explosions j and 
 
 * Priestley's History of Electricity. 
 
ATMOSPHERIC ELECTRICITY. 85 
 
 the two balls between which the discharges pass can be easily regulated, 
 as to their distance from each other, by a screw. After a certain number 
 of explosions, say of negative electricity, which at first may be nine or ten 
 in a minute, a cessation occurs of some seconds or minutes, as the case 
 may be, when about an equal number of explosions of positive electricity 
 takes place, of similar force to the former, indicating the passage of two 
 oppositely and equally electrified zones of the cloud ; then follows a second 
 zone of negative electricity, occasioning several more discharges in a 
 minute than from either of the first pair of zones ; which rate of increase 
 appears to vary according to the size and power of the cloud. Then occurs 
 another cessation, followed by an equally powerful series of discharges of 
 positive electricity, indicating the passage of a second pair of zones : these 
 in like manner are followed by others, fearfully increasing the rapidity of 
 the discharges, when a regular stream commences, interrupted only by 
 change into the opposite electricities. The intensity of each new pair of 
 zones is greater than that of the former, as may be proved by removing 
 the two balls to a greater distance from each other. When the centre of 
 the cloud is vertical to the wire, the greatest effect consequently takes 
 place, during which the windows rattle in tlieir frames, and the bursts of 
 thunder without and the noise within, every now and then accompanied by 
 a crash of accumulated fluid in the wire striving to get free between the 
 balls, produce the most awful effect, which is not a little increased by the 
 pauses occasioned by the interchange of zones. Great caution must of 
 course be observed during this interval, or the consequences would be 
 fatal. My battery consists of fifty jars, containing 73 feet of surface on 
 one side only. This battery, when fully charged, will perfectly fuse into 
 red hot balls 30 feet of iron wire in one length ; such wire being -^-^ of 
 an inch in diameter. When this battery is connected with 3,000 feet of 
 exploring wire, during a thunder-storm it is charged fully and instanta- 
 neously, and of course as quickly discharged. As I am fearful of destroy- 
 ing my jars, I connect the two opposite coatings of the battery with brass 
 balls one inch in diameter, and placed at such distances from each other as 
 to cause a discharge when the battery receives three-fourths of its charge. 
 When the middle of a thunder-cloud is overhead a crashing stream of 
 discharges takes place between the balls, the effect of which must be wit- 
 nessed to be conceived. 
 
 "As the cloud passes onward, the opposite portions of the zones which 
 first affected the wire come into play, and the effect is weakened with each 
 successive pair till all dies away, and not enough electricity remains in 
 the atmosphere to affect a gold-leaf electrometer. I have remarked that 
 the air is remarkably free of electricity, at least more so than usual, both 
 before and after the passage of one of these Clouds. Sometimes a little 
 previous to a storm, the gold leaves connected with the conductor will 
 for many hours open and shut rapidly, as if they were panting, evidently 
 shewing a great electrical disturbance. 
 
 " It is known to electricians that if an insulated plate, composed of a 
 perfect or of an imperfect conductor, be electrified, the electricity commu- 
 nicated will radiate from the centre to the circumference, increasing in 
 force as the squares of the distance from the centre ; whereas in a thunder- 
 cloud the reverse takes place, as its power diminishes from the centre to 
 the circumference. First a nucleus appears to be formed say of positive 
 
86 THE PHENOMENA OF ELECTRICITY. 
 
 electricity embracing a large portion of the centre of the cloud, round 
 which is a negative zone of equal power with the former ; then follow 
 the other zones in pairs, diminishing in power to the edge of the cloud. 
 Directly below this cloud, according to the laws of inductive electricity, must 
 exist, on the surface of the earth, a nucleus of opposite or negative elec- 
 tricity, with its corresponding zone of positive, and with other zones of 
 electrified surface corresponding in number to those of the cloud above, 
 although each is oppositely electrified. A discharge of the positive nu- 
 cleus above into that of the negative nucleus below, is commonly that 
 which occurs where a flash of lightning is seen ; or from the positive be- 
 low to that of the negative above, as the case may be ; and this discharge 
 may take place according to the laws of electricity through any or all of 
 the surrounding zones, witliout influencing their respective electricities, other- 
 wise than by weakening their force by the removal of a portion of the 
 electric fluid from the central nucleus above to that below ; every successive 
 flash from the cloud to the earth, or from the earth to the cloud, weaken- 
 ing the charge of the plate of air, of which the cloud and the earth form 
 the two opposite coatings."* 
 
 It would appear, therefore, from Mr. Crosse's observations of the phe- 
 nomena of a thunder-storm, that the cloud between which and the earth 
 discharges occur is electrified in concentric rings, each one becoming less 
 intensely charged towards the extremity. As each ring or zone must of 
 course become enlarged as its distance from the centre increases, the quan- 
 tity of electricity in each zone may probably be assumed to be equal ; 
 though to this point Mr. Crosse's observations do not extend. Though 
 the electricity of the atmosphere is in all essential particulars the same as 
 the electricity excited by the machine, the condition in which it exists in 
 a thunder-cloud is different from any that can be artificially produced, in 
 consequence of the magnitude of the scale on which nature operates. The 
 strongest spark emitted from the most powerful electrical machine does 
 not exceed two or three feet in length ; and when numbers of such sparks 
 are accumulated in an electrical battery, so as to imitate, in a feeble 
 manner, the destructive effects of lightning, the charge, when spread over 
 the surface of the glass, will not force its way through more than two 
 inches of resisting air. A discharge between the clouds and the earth will 
 sometimes occur when the thunder-cloud cannot be less than 300 feet above 
 the object struck by lightning ; though the resistance of the intermediate 
 space is no doubt greatly diminished by the moist atmosphere and by rain. 
 The electricity in the clouds immediately before the discharge must conse- 
 quently be of a very high degree of intensity ; and there is ample evidence 
 in the destruction of imperfectly conducting bodies of the immense quantity 
 of electricity concentrated in a flash of lightning. 
 
 A long spark from a powerful electrical machine, severed and zig-zagged 
 by the resistance of the air, nearly resembles in form a flash of forked 
 lightning ; and in speculating on the mode of the action of lightning, the 
 spark of an electrical machine, in consequence of its greater intensity, may 
 "be taken as bearing a closer analogy to it than the disruptive discharge of 
 an electrical battery. In considering, therefore, the disputed question of 
 the best mode of protection from lightning, and the effects of lateral dis- 
 
 * Noad's Lectures on Electricity. 
 
ATMOSPHERIC ELECTRICITY. 87 
 
 charge, we are more likely to arrive at safe conclusions if the character of 
 the discharge from the prime conductor be examined, rather than the more 
 powerful, though less concentrated, discharge of the battery. 
 
 The question in dispute in reference to the lateral discharge is, whether 
 a lightning-conductor, allowed to be of proper thickness, will conduct a 
 disruptive discharge safely from the clouds without danger of injury from 
 the passage of the electricity in other than the direct course. It is ad- 
 duced, as an illustration that there is danger in lightning-conductors, that 
 when a discharge from an electrical machine is conducted to the earth by 
 a very efficient wire, sparks may nevertheless be drawn from the wire at 
 any part of its course, though sparks cannot be drawn when the conduct- 
 ing body is connected with the wire itself. It has hence been inferred, that 
 to render a lightning-conductor perfectly safe, all conducting bodies near 
 it should have a metallic connexion with the rod. It appears, however, 
 that the simplest mode of viewing the subject is to regard every discharge 
 of lightning as distributed among all conducting bodies in the vicinity, 
 forcing its way through every course open to it in quantities proportioned 
 to the facilities offered for its passage. According to this view, we must 
 consider that in every flash of lightning there is not only a lateral dis- 
 charge, but what may be termed a distributive discharge within a definite 
 range. 
 
 The quantity of electricity that finds its way to the earth through 
 these multifarious channels will be proportionate to their relative con- 
 ducting powers. Suppose, for example, that a wire were joined to the 
 lightning-conductor, and continued uninterruptedly to the earth ; as much 
 of the -electric fluid would be conducted through that wire, in proportion 
 to its thickness, as through the main conductor. If, however, the con- 
 tinuity of the wire were interrupted, the resistance occasioned by the 
 imperfect connexion would very materially diminish the quantity of elec- 
 tricity transmitted, though some portion would still pass through the 
 divided wire. We may conceive that, in the same manner, every other 
 substance, however imperfectly it conducts, transmits some portion, though 
 it may be inappreciably small, of the infinitely divided charge. 
 
 The preceding consideration of the question is not calculated to di- 
 minish the value of lightning-conductors ; but it points out the danger of 
 dividing the discharge of lightning in such a manner as to direct a large 
 portion of the electric fluid from its direct course. It was stated by 
 Dr. Faraday, in evidence before the committee of the House of Commons, 
 that a man would be safe even though leaning against the conductor of a 
 ship when struck by lightning; nor is it probable that an appreciable 
 quantity of electricity would pass from the continuous metal rod to find a 
 devious and resisting course elsewhere ; but if the man leaning against the 
 conductor were at the same time to be standing on the iron cable, so as to 
 form part of a metallic connexion with the sea in another course, there 
 can be little doubt he would receive a shock more or less severe. The 
 author's personal experience, as previously mentioned, enables him to 
 speak of the distributive character of the discharge of lightning. When 
 the electric fluid passed through his arm, that limb was sharing the discharge 
 with many other and much better conductors of electricity ; and though 
 the sensible effect extended only from the wrist to the shoulder, a much 
 smaller quantity of electricity must, according to the principle of distributive 
 
88 THE PHENOMENA OF ELECTRICITY. 
 
 discharge, have passed through his body to the support on which he was 
 standing. A serious instance of distributive discharge of lightning oc- 
 curred last summer at Paddington. A row of buildings was struck by 
 lightning, and four men, at work in different homes, were killed. 
 
 There has lately been much variety introduced in the forms of light- 
 ning-conductors. In the early days of their application, electricians 
 questioned whether the elevated portion of the rod should terminate with 
 a metal knob or a point, or whether it should be formed of a non-conduct- 
 ing substance. The point, however, gained the day; as it was rightly 
 considered better to attract the electricity silently and gradually than to 
 trust to the rod only for conducting a disruptive discharge. The notion 
 of tipping the end with a non-conductor was simply absurd. Those who 
 thus attempted to keep off lightning might with equal reason have erected 
 a glass rod instead of a metal one. The opposite principle is now so 
 generally adopted that, with a view to increase the silent attraction of 
 atmospheric electricity to lightning-conductors, it is customary to add 
 several branching points. It may be questioned, however, whether any 
 advantage is gained by more than a single point. 
 
 A recent invention, to which her Majesty's letters patent have been 
 granted, exhibits a curious misconception of the true properties of light- 
 ning-conductors. The patentee terminates his lightning-conductors with 
 a great number of magnetised steel points, conceiving, no doubt, that as 
 there is an intimate connexion between electricity and magnetism, the 
 magnetism of the points would add greatly to their attractive power. As 
 iron and steel do not conduct electricity so readily as copper, the latter 
 metal is the best for the purpose; an4 it is employed by Sir W. Snow 
 Harris in his system of protecting ships from lightning. The greater 
 expense of copper prevents its adoption on buildings, and a proportionally 
 thicker rod of iron coated with zinc, or, as it is commonly called, " galva- 
 nised," answers the purpose very efficiently. 
 
 Buildings to which lightning-conductors are attached, elevated several 
 feet above the highest point, are in little danger during a thunder-storm. 
 In houses not so protected, the place of greatest safety is an under-ground 
 cellar. Those who are alarmed, and yet do not like to descend into the 
 cellar, will do well to lie down on a sofa near the middle of the room, 
 taking care to avoid the proximity of suspended chandeliers, or any other 
 interrupted metallic body. Persons who are exposed out of doors in a 
 thunder-storm should avoid taking shelter under trees ; for though they 
 possess sufficient conducting power to attract lightning, they are not such 
 good conductors as the fluids of the human body, and the electricity will 
 consequently take its course to the earth through the better conductor. 
 
 In the mountain valleys of Savoy, application has been made of pointed 
 rods to draw the electricity silently from the atmosphere for the purpose 
 of protecting the vineyards from the destructive effects of hail, which fre- 
 quently accompanies a thunder-storm. These conductors of electricity, 
 termed paragreles, have been found to answer very effectively. 
 
 There is much variance of opinion respecting the requisite thickness 
 of lightning-conductors. A French commission appointed to determine 
 the question reported that a rod of iron seven-tenths of an inch square is 
 quite sufficient under all circumstances. In the lighthouses and public 
 buildings in this country, rods of copper three-quarters of an inch wide 
 
ATMOSPHERIC ELECTRICITY. 89 
 
 and about a quarter of an inch thick are employed, and as copper conducts 
 electricity seven times better than iron, these conductors are consequently 
 much more efficient than those recommended for adoption in France ; yet 
 several lighthouses so protected were damaged during the thunder-storms 
 of last autumn, and Eddystone lighthouse was considerably damaged by 
 lightning in January last. As the resistance of a metal rod to the con- 
 duction of electricity is greatly increased by its length, a much thinner 
 conductor is sufficient for a dwelling-house than is required for a lofty 
 building. 
 
 Wires will sometimes serve to conduct lightning safely even when so 
 thin as to be melted by its transmission. A remarkable instance of this 
 kind is noticed in the following unpublished letter of Franklin's, which 
 will be read with considerable interest* 
 
 Philadelphia, March 1, 1755. 
 
 SIR, I am but just returned from a long journey, after near six 
 months' absence, and find your favour of September 29, by which have the 
 agreeable advice that you expect to be able to remit me something in 
 Smith's affairs very soon. 
 
 As to the thickness of wire necessary or sufficient to conduct a large 
 quantity of lightning, concerning which you desire my sentiments, you 
 will find something on that head in pages 124 and 125 of the enclosed 
 pamphlet, which please to accept. And I may add, that in my late jour- 
 ney I saw an instance of a very great quantity of lightning conducted by 
 a wire no bigger than a common knitting-needle. 
 
 It was at Newbury, in New England, where the spire of the church- 
 steeple, being seventy foot in height above the belfry, was split all to 
 pieces and thrown about the street in fragments ; from the bell down to 
 the clock, placed in the steeple twenty foot below the bell, there was the 
 small wire above mentioned, which communicated the motion of the clock 
 to the hammer, striking the hour on the bell. 
 
 As far as the wire extended no part of the steeple was hurt by light- 
 ning, nor below the clock as far as the pendulum-rod reached, but from 
 the end of the rod downwards, the lightning rent the steeple surprisingly. 
 The pendulum-rod was about the thickness of a small tobacco-pipe stem, 
 and conducted the whole without damage to its own substance, except 
 that the end where the lightning was accumulated it appeared melted, as 
 much as made a small drop. But the clock-wire was blown all to smoke, 
 and smutted the wall by which it passed in a broad small black track, and 
 also the ceiling under which it was carried horizontally. No more of it 
 was left than about an inch and half next the tail of the hammer, and as 
 much joining to the clock. 
 
 Yet this is observable, that though it was so small as not to be suffi- 
 cient to conduct the quantity with safety to its own substance, yet it did 
 conduct it so as to secure all that part of the building. Excuse this 
 scrawl, which I have not time to copy fair. 
 
 I am, with much respect, Sir, 
 
 Your very humble servant, 
 
 B. FRANKLIN. 
 
 We are indebted to the kindness of Charles Reed, Esq., F.S.A., fer this letter, 
 from his collection of manuscripts. 
 
 G 
 
90 THE PHENOMENA OF ELECTRICITY. 
 
 P.S. I have just been reading a similar instance taken from the 
 Journal des Swvans for 1676, page 113, viz : 
 
 " En 1676, le tonnerre 6crasa le clocher de 1'abbaye de Saint Medard de 
 Soissons ; la foudre se porta a une grande distance le long des fils d'archal 
 qui communiquoient a 1'horloge ; elle fondit ces cordes metalliques sans 
 faire d'autres de"sordres dans tout le trajet." 
 
 To MB. JAMES BIRKIT, Merchant, Antigua, 
 Per CAFT. SNOOK, J. D. C. 
 
 The continuous discharges of the electric fluid during a thunder-storm 
 occur more frequently from cloud to cloud than between the clouds and 
 the earth. These discharges of what are called " sheet-lightning" may often 
 be observed at intervals of only a few seconds apart, and occurring with 
 that rapidity for some hours, varied from time to time by discharges 
 between the clouds and the earth. During a thunder-storm in August 
 last, we noticed a continuous flashing among the clouds, some of the 
 lightning being of the most vivid kind, and darting horizontally like a 
 ball of fire across a considerable expanse of the horizon. 
 
 Several causes have been assigned for the electrical condition of the 
 clouds. The simplest hypothesis appears to be that founded on the plus 
 and minus theory of Franklin, which well explains the varying circum- 
 stances of the accumulations of electricity in the atmosphere, and of its 
 frequent changes from positive to negative. The fact that the natural 
 capacity of a body for electricity varies with changes in the extent of its 
 surface has been already noticed. The capacity of steam and vapour for 
 electricity, therefore, very greatly exceeds that of the water from which 
 the steam is evaporated. Thus, when evaporation takes place from the 
 earth, the vapour is combined with a vast quantity of electricity in a latent 
 state. The condensation of the vapour into clouds diminishes its capacity, 
 and a quantity of electricity is consequently set free, surrounding the 
 particles of mist. As the mist collects into drops, a further amount of 
 electricity is liberated, and the intensity of its condition is increased, 
 though the actual quantity of electric fluid remains the same. On the 
 other hand, when a cloud "melts into air," the capacity of the invisible 
 vapour is greatly enlarged, and it absorbs the free electricity which was 
 previously contained in the cloud. The changes continually taking place 
 in the electrical condition of the clouds may thus be accounted for by the 
 continual changes of state in the condensed vapour. 
 
 That the conversion of water into steam excites electricity during the 
 enlargement of its volume may be readily proved. If a metal cup con- 
 taining water be placed on the top of an electrometer, and a hot cinder be 
 dropped into it, the sudden generation of steam will immediately cause the 
 gold leaves of the electrometer to diverge. The water by increasing in 
 volume has its capacity for electricity increased, and absorbs it from all 
 surrounding bodies, leaving the electrometer in a negative state. 
 
 During evaporation from the surface of the earth, the electrical condi- 
 tion of the vapour may be modified considerably by the comparative ra- 
 pidity or slowness of the process j but it may be assumed that under all 
 circumstances the vapour obtains, at the time of its formation, the quantity 
 of electricity natural to its state of density ; -and that it does not become 
 
ATMOSPHERIC ELECTKICITY. 91 
 
 actively electrical by being plus or minus until it undergoes a change of 
 state when it has risen in the air and become insulated from the earth. 
 
 When the clouds are in such a highly electrical state as to cause a dis- 
 charge between them and the earth through a large intervening space of 
 the resisting air, it might be imagined that one such discharge would neu- 
 tralise the condition of the clouds, and that the thunder-storm would be 
 ended. But it must be borne in mind that the condensed vapour of the 
 clouds is a very imperfect conductor of electricity, and that one cloud, or 
 a portion of a cloud, may have its electricity discharged, whilst another 
 adjoining cloud remains fully charged ; in the same manner that an excited 
 rod of glass emits a succession of discharges to a conducting body brought 
 to different points of its surface. Thus when the electricity of one cloud 
 is discharged whilst the surrounding clouds remain in a highly electrical 
 state, a constant effort is made to restore the equilibrium, and discharges 
 from cloud to cloud, called sheet-lightning, are the consequence. 
 
 The reverberating sound of thunder is produced by the devious course 
 of lightning through the resisting air. The amount of such resistance 
 cannot well be calculated, but as the resistance of the air to the motion of 
 a musket-ball when propelled at the rate of 1600 feet in a second is equal 
 to twenty pounds on the square inch, or to 120 times the weight of the 
 ball, some notion may be formed of the immense resistance encountered 
 by the electric fluid in its instantaneous passage through the air. The 
 first peal of thunder heard arises from the concussion of the air at the 
 nearest point ; therefore, assuming the direction of a flash of lightning to 
 be from the clouds to the earth, the thunder will be first heard from the 
 part where the lightning strikes the ground. The subsequent successive 
 reverberations are occasioned by the comparatively slow progress of sound ; 
 those rumblings of thunder last heard being, in fact, caused by the first 
 impulsive action of lightning on the air. 
 
 We have heard it remarked by Faraday as a curious error of artists in 
 their representations of thunder-storms, that they make the lightning 
 pointed towards the earth. Now, if it were possible to trace the course of 
 a flash of lightning by the eye, the part near the clouds, being the more 
 distant, would appear to be much more pointed than that part which 
 would be seen approaching the earth. 
 
 The phenomena of the aurora borealis and of " falling stars " are attri- 
 butable directly to atmospheric electricity. In the upper regions of the 
 atmosphere electricity is readily conducted, and flashes of electric light 
 are transmitted through the highly rarefied air with little resistance. The 
 experiment of sending flashes of light through an exhausted receiver ex- 
 emplifies, with considerable accuracy, the phenomenon of the aurora, but 
 there are other circumstances connected with it, in reference to the sources 
 of electrical excitement and the conditions in which the electricity is de- 
 veloped, that yet remain undetermined. 
 
92 
 
 THE PHENOMENA OF ELECTKICITY. 
 
 CHAPTER X. 
 
 ELECTRICITY FROM HIGH-PRESSURE STEAM. 
 
 Steam, an abundant source of electrical excitement Hydro-Electrical Machine State 
 of the electricity excited by it Combination of quantity and intensity Friction of 
 water the cause of excitement Faraday's experiments on High-Pressure Steam. 
 
 THE excitement of electricity by the emission of high-pressure steam is 
 the most recently discovered means of disturbing the electrical equili- 
 brium ; and it affords a more abundant supply of electricity of great inten- 
 sity than any other artificial source. 
 
 fig 37. 
 
 The effect is not fully developed unless the steam be raised to a pres- 
 sure of 50 Ibs. on the square inch. The apparatus constructed for exhibi- 
 tion at the Polytechnic Institution is the largest machine of the kind yet 
 made. The boiler A A, fig. 37, is constructed on the same principle as the 
 boilers of locomotive steam-engines ; being perforated longitudinally by 
 tubes, through which the draught of the furnace passes. These tubes serve 
 the double purpose of increasing the generation of steam and of strength- 
 ening the boiler. The length of the boiler is six feet six inches; its 
 diameter, including the furnace, which is in the centre, is three feet six 
 inches. There are forty-six bent tubes, T, at the top for the escape of the 
 steam. These tubes are made of iron, but the jets through which the steam 
 issues are formed of partridge wood j that material having been found by 
 
ELECTRICITY FROM HIGH-PRESSURE STEAM. 93 
 
 experience to give the best results. In front of the jets there are several 
 rows of metallic points, for the purpose of conducting the electricity, as 
 quickly as it is excited, to the earth, and thus to prevent its return to the 
 boiler from which the sparks are taken. The boiler is insulated from the 
 ground by six stout glass pillars, B B B, about three feet high, on which 
 the apparatus rests. 
 
 The pressure of steam commonly used in experimenting with this ap- 
 paratus is 60 Ibs. to the square inch. When in full operation, with steam 
 issuing from the 46 jets, the torrents of electricity evolved bear some 
 resemblance to those described by Mr. Crosse as having poured forth 
 from his exploring wire during a thunder-storm. The electricity excited 
 combines quantity with intensity. Though the sparks emitted are not so 
 long as those from the large plate-electrical machine in the Polytechnic 
 Institution, they are more dense, and approximate to the character of the 
 spark from the discharge of an electrical battery. The length of the 
 sparks that may be taken from the boiler is about fourteen inches, and at 
 the distance of six inches there is a rapid flow of electrical discharges too 
 quick to be counted. The large battery of the institution, comprising 
 84 feet of coated surface, is fully charged in eight seconds ; though requir- 
 ing at least fifty seconds to be charged by the plate-electrical machine in 
 its best action. 
 
 The sparks from this apparatus ignite gunpowder and inflame paper 
 and wood shavings, and by this means also numerous effects of electro- 
 chemical decomposition can be exhibited. 
 
 The excitement of electricity by effluent high-pressure steam appears 
 from the experiments of Dr. Faraday and Mr. Armstrong to be caused by 
 the friction of condensed water against the jet from which the steam 
 issues. It was found that when the jet and the pipe leading to it were 
 heated, so as to prevent the condensation of the steam before it issued forth, 
 scarcely any electrical eflects were produced ; and that they were in- 
 creased by lengthening the pipe, so as to cause greater condensation. It 
 is for this object that the emission pipes of the apparatus at the Polytech- 
 nic Institution are bent so as to allow the water to collect near the aper- 
 tures. 
 
 There are several additional facts tending to confirm the opinion that 
 friction is the cause of the excitement of the electricity thus produced, 
 and not evaporation or mere change of density in the steam. In Faraday's 
 experiments no electricity was excited when the safety-valve was opened 
 wide, and the steam escaped without friction, but when it was allowed to 
 impinge on a cone, electrical effects were directly manifested. Changes in 
 the substance of the jet, or of the material of the cone on which the issu- 
 ing steam impinged, greatly affected not only the quantity of electricity 
 excited, but its character. When distilled water was employed, the boiler 
 was in nearly all cases charged with negative electricity, and the issuing 
 steam was positive ; but by the introduction of oil of turpentine into 
 the jet the boiler became strongly positive and the steam negative. In 
 all cases, however, the issuing steam and the insulated boiler were found 
 to be in opposite states of electricity. 
 
 In the experiments conducted by Faraday with a small apparatus, the 
 pressure of steam never exceeded thirteen inches of mercury, or about six 
 pounds to the square inch, and generally it was not more than five pounds ; 
 
94 THE PHENOMENA OF ELECTRICITY. 
 
 therefore the effects were very feeble compared with those of the hydro- 
 electrical machine at the Polytechnic Institution. In some respects, how- 
 ever, this more feeble excitation of electricity was of advantage, as it af- 
 forded the opportunity of detecting changes of state that would not pro- 
 bably have been noticed under the action of much stronger pressure. It 
 was found, for instance, that electrical effects could only be obtained when 
 distilled water was employed ; for the mixture of any saline salts, or of any 
 soluble substance that improved the conducting power of the fluid, pre- 
 vented its acting as an electric with a low degree of friction. One of the 
 many curious results derived from these experiments is, that water may 
 claim to rank among the first of the positive electrics ; and Faraday con- 
 jectures that further investigation will place it at the head of all substances 
 as a positive electric ; for even glass became negatively electrical when 
 exposed to friction of the emitted steam of pure water. 
 
 With a view to prove still more conclusively that the electricity ex- 
 cited by emission is due to friction and not to expansion, the experiments 
 were repeated with compressed air substituted for steam. Under these 
 circumstances electricity was excited when moisture was supplied to th& 
 jet, but when the air and the emission pipe were dry, no electrical effects. 
 could be detected. 
 
 The excitement of electricity by effluent steam affords a striking illus- 
 tration of one of the numerous ways in which electrical agency operates 
 without our consciousness of its presence. An ordinary locomotive engine 
 generates during every minute of its onward course a force sufficient to 
 destroy instantaneously all the passengers it propels. This force, however, 
 is dissipated as soon as it is created, and it was only by accident that its 
 existence became known. It is the same with nearly all the chemical 
 changes that are taking place around us. Even the burning of a candle, 
 there is reason to believe, puts in action an amount of electricity greater 
 than that of a thunder-cloud, though no means have yet been discovered 
 of preventing the force from being dissipated unperceived. In other che- 
 mical actions, however, less energetic than combustion, the accompanying 
 electricity can not only be detected, but it is developed in quantities, com- 
 pared with which the excitement of it by friction is altogether insignifi- 
 cant. The consideration of the phenomena of the electricity excited by 
 chemical agency, to which we are about to direct attention, constitutes,, 
 indeed, the most important practical branch of electric science. 
 
EXCITEMENT OF VOLTAIC ELECTRICITY. 95 
 
 CHAPTER XL 
 
 EXCITEMENT OP VOLTAIC ELECTRICITY. 
 
 Excitement of electricity by metallic contact and by chemical action Mutual influ- 
 ences of chemical action and electricity Simple Voltaic circle Construction of the 
 Voltaic pile Identity of Voltaic and frictional electricity Volta's couronne de 
 tosses Conditions requisite for the excitement of Voltaic electricity Solid and 
 Liquid elements of the battery Their actions and re-actions Faraday's hypothesis 
 of conduction through fluids Resistance to the Voltaic current Ohm's formula 
 Local action in batteries Intensity and quantity of electricity considered Their 
 correspondence and difference. 
 
 THE discovery by Galvani that muscular contractions are produced by 
 the contact of dissimilar metals, and the rapid successive additions to that 
 discovery by Volta and others, have been already noticed in our intro- 
 ductory sketch of the history of electricity. We shall now proceed to 
 explain more particularly the character and the actions of the force thus 
 generated by chemical action. 
 
 The simplest manifestation of the excitement of a peculiar force by 
 the contact of metals is obtained by placing a piece of zinc under the 
 tongue, and a piece of silver upon it, and then allowing the metals to 
 touch. Before contact, no sensation is perceived beyond the mere pres- 
 sure of the two hard substances against the tongue ; but the instant that 
 contact is made it is accompanied by a strong metallic taste, which con- 
 tinues without intermission. The same sensation will be perceived if, 
 whilst the two metals are kept separated, a metallic connexion be made 
 between them by touching each with a piece of copper wire. 
 
 When a plate of zinc is immersed in diluted sulphuric acid, chemical 
 action immediately commences. The oxygen of the water combines with 
 the metal, and the hydrogen is liberated and exhibits itself in a copious 
 discharge of bubbles of gas j the water being decomposed by the superior 
 affinity of its oxygen for the zinc. The decomposition continues until the 
 sulphuric acid, which greatly facilitates the action, is exhausted by the 
 combination of the sulphur with the zinc, forming, in connexion with the 
 oxygen portion of the decomposed particles of water, soluble sulphate of 
 zinc. This is the ordinary chemical action which takes place during the 
 generation of hydrogen gas for experimental purposes ; the quantity of 
 hydrogen gas evolved being exactly proportionate to the oxygen with 
 which it was previously combined to form water. 
 
 When the surface of the zinc plate is well amalgamated with mercury, 
 the continuous decomposition of the water is prevented. Those particles 
 of fluid only in immediate contact with the metal are decomposed. The 
 hydrogen gas collects in minute bubbles over the surface of the plate ; but 
 they do not attain sufficient size to detach themselves from the metal, and 
 the plate consequently becomes coated with innumerable minute bubbles of 
 hydrogen gas. This gaseous coating protects the metal from being further 
 acted on by the acidulated water j and it would thus remain in the liquid, 
 unchanged, for a length of time. 
 
96 THE PHENOMENA OF ELECTRICITY. 
 
 A piece of sheet copper may be immersed in the same vessel without 
 causing any alteration in the state of things, so long as the metals are 
 kept apart. Bring the copper gradually closer to the zinc until scarcely 
 any perceptible space intervenes, still there will be no action ; but the 
 instant that the metals touch, a brisk action commences. The bubbles 
 on the surface of the zinc are transferred to the copper, and rise rapidly 
 to the top of the fluid ; these are followed by continuous successions of 
 bubbles of gas, all rising from the copper surface, as if the chemical action 
 were taking place with that metal. It is the zinc, however, that is alone 
 attacked, and being deprived of its protecting coating of bubbles, it con- 
 tinues to be converted into sulphate of zinc, until, as in the previous case, 
 the free sulphuric acid is exhausted. 
 
 It is not necessary for the production of this effect that the metals 
 should touch in the fluid. If the lower parts only of the plates be im- 
 mersed, and the upper ends are brought together, the formation of bubbles 
 
 proceeds quite as briskly as when the 
 metals are in contact in the liquid. 
 Neither is it requisite that the cop- 
 per and zinc should be immediately 
 connected. If the lower ends of a 
 copper and of a zinc plate be im- 
 mersed, and the parts out of the fluid 
 be connected with a wire, as in the 
 annexed diagram, the evolution of 
 bubbles from the copper surface will 
 continue, though not so rapidly as 
 before ; the diminution in the action 
 arising from the resistance which the 
 fig. ss. wire offers to the passage of the sti- 
 
 mulating force. 
 
 Preserving the order of arrangement shewn in the figure, let the sizes 
 of the plates be enlarged till the extent of surface immersed amounts to 
 about fifty square inches. The evolution of gas from the larger surfaces will 
 be greater than before, but not in proportion to their increased extent ; for 
 if the thickness of the connecting wire W do not correspond with the in- 
 creased capacity of the plates, the resistance it offers will diminish the 
 effect. Let the wire be reduced to the size of a hair, and another remarkable 
 phenomenon will be observed. The force is then much greater than can 
 be freely transmitted through that thin wire, and it is developed in the 
 form of heat. The wire will become red hot, and, if the action be ener- 
 getic, will even be melted in the act of transmitting from plate to plate 
 the peculiar power by means of which water is decomposed. 
 
 The phenomena of chemical action hitherto noticed bear but little ap- 
 parent relation to those of electricity. The power of decomposing water 
 and of melting metals is, indeed, common to both j but it is exhibited in 
 such different forms, that no argument in favour of the identity of the 
 forces could be founded on those phenomena alone. Volta's pile, however, 
 affords the means of assimilating the force thus evolved very closely to 
 that of electricity. 
 
 If, instead of immersing the zinc and copper plates in a vessel con- 
 taining acidulated water, a piece of cloth soaked in the liquid be inter- 
 
EXCITEMENT OF VOLTAIC ELECTRICITY. 
 
 posed between the inetals, the effect will be nearly the same. The acidu- 
 lated water contained in the cloth acts on the surface of the zinc when a 
 metallic connexion is made with it and the copper, and similar results 
 may be thus attained, though somewhat diminished in effect. 
 
 This arrangement presented a ready means of increasing the series of 
 plates to augment the action of a single pair, of which Volta availed him- 
 self. He constructed a pile consisting of a series of zinc and of silver 
 discs with moistened cloth interposed between each. He commenced with 
 a zinc disc, upon that he placed a silver coin of the same size, on that a 
 circular piece of cloth rather less than the metal discs, having previously 
 soaked it in water slightly acidulated. On the cloth was laid another disc 
 of zinc, then silver, and again cloth, and so on in succession until a pile of 
 fifty series of alternate metal discs and moistened cloths was formed, as 
 represented in fig. 39. To prevent the discs from falling, they were sup- 
 ported by vertical wooden pillars, and a weight was placed on the topto 
 keep them pressed together. 
 
 When the uppermost and lowest of the plates 
 in such an arrangement are touched with mois- 
 tened fingers, a very decided shock is perceived, 
 exactly resembling that from a Ley den jar feebly 
 charged. The shock is, however, different from 
 that of a Leyden jar in the continuity of its effect, 
 for similar shocks are continued in rapid succes- 
 sion as long as the connexion between the plates, 
 through the hand, is maintained. This physiolo- 
 gical effect presents a clear analogy to the shock 
 of the Leyden jar, and different as is the manner 
 of its excitement, and different also as are many 
 of the manifestations of the chemical agent, the 
 accumulation of the force in the Voltaic pile 
 pointed out at once its identity with electricity. 
 Subsequent investigations, more especially the 
 experimental researches of Faraday, have esta- 
 blished this identity in almost every particular. 
 
 The action of the Voltaic pile gradually diminishes from the time it is 
 first put together, until at length the effect appears to cease. This dimi- 
 nution of power is more rapid in proportion to the energy given to the 
 pile in the first instance by the larger quantity of acid mixed with the 
 water. To restore the original energy, it is necessary to decompose the 
 pile, to clean the zinc and copper discs, and to moisten the cloths again. 
 Such an apparatus is therefore attended with much trouble. To obviate 
 it, Volta contrived another arrangement, which he called ct couronne de 
 tosses. He connected a piece of zinc to a piece of copper by soldering to 
 them a short length of bent copper wire. Having procured a number of 
 such connected plates, he put them into a row of glasses containing acidu- 
 lated water, taking care so to dispose them that the zinc and the copper 
 connected together should be in separate glasses, in the manner represented 
 in fig. 40. 
 
 To the copper plate in glass 1, a wire is attached to serve as a con- 
 ductor for forming connexion. In the same glass there is a zinc plate 
 connected with the copper immersed in glass 2. In this manner each 
 
 '.39. 
 
98 THE PHENOMENA OF ELECTRICITY. 
 
 glass contains a zinc and copper plate connected by a wire, which are kept 
 apart in the fluid, and the series may be continued to any extent. By 
 bringing the wire attached to the first plate in connexion with a similar 
 wire soldered to the zinc plate in the last glass of the series, the action 
 immediately commences, and it is more or less intense according to the 
 number of plates. This arrangement is, in many respects, very superior 
 
 fig. 40. 
 
 to the pile. A much larger quantity of fluid can be brought to act on 
 each plate, consequently the effect does not so rapidly diminish ; the plates 
 can be readily removed when the apparatus is not wanted, and the acidu- 
 lated water may remain ready for the immersion of the plates when expe- 
 riments are renewed. 
 
 The arrangement a couronne de tosses as invented by Volta continues, 
 with some modifications for convenience in use, to form the voltaic battery 
 that is most generally employed. A series of this kind, consisting of 100 
 plates of copper and zinc four inches square, will generate electricity in 
 sufficient quantity to exhibit in a powerful manner most of the phenomena 
 of frictional electricity. It is desirable, however, before noticing more 
 particularly the phenomena of the voltaic battery, that we should examine 
 the rationale of its action. 
 
 Reverting to the arrangement of a single pair of plates (fig 38). let us 
 consider the conditions necessary for the excitement of electricity by che- 
 mical action. We observe two metals employed, one of which has a 
 much stronger affinity to oxygen than the other. This dissimilarity in 
 the chemical affinities of the metals will be found in all similar arrange- 
 ments to be essentially necessary for the excitement of electricity ; and 
 the quantity generated will be great or small according to the degree of 
 dissimilarity of the metals in their relations to oxygen. 
 
 The metals that excite electricity by their mutual actions are ranged 
 in the following order ; those placed first acting in reference to those be- 
 neath as copper does to zinc. 
 
 Platinum. Mercury. Tin. 
 
 Gold. Copper. Iron. 
 
 Silver. Lead. Zinc. 
 
 Any two of the foregoing series will constitute what is termed a vol- 
 taic circuit. Thus zinc will excite voltaic action in combination with iron ; 
 iron will take the place of zinc when combined with tin ; and tin will 
 take the place of iron when combined with copper. The energies of these 
 
EXCITEMENT OF VOLTAIC ELECTRICITY. 99 
 
 combinations increase as the metals are more distant from each other in 
 the scale, the most powerful practical combination being zinc and platinum, 
 the most incorrodible of all metals. 
 
 Though two plates are necessary in such an arrangement, only one of 
 them is active in the excitement of electricity, the other plate serving merely 
 as a conductor to collect the force generated. A metal plate is generally 
 used for that purpose, because metals conduct electricity much better than 
 other substances exposing an equal surface to the fluids in which they are 
 immersed ; but other conductors may be used, and when a proportionately 
 larger surface is exposed to compensate for inferior conducting power, 
 they answer as well, and in some instances even better than metal plates. 
 Charcoal has been employed as one of the elements of a voltaic battery ; 
 but the most advantageous is graphite, a very hard substance that is found 
 encrusted within gas retorts. As it is altogether impervious to the action 
 of acids, it may be ranked even above platinum in the scale of non-oxidiz- 
 able bodies ; and though not so good a conductor as that metal, its finely 
 granulated or crystallised texture exposes so large a surface to the fluid, 
 that the conducting power is practically nearly equal to it. 
 
 We have hitherto considered only the solid elements of the voltaic 
 battery. They form, indeed, the most conspicuous parts of the arrange- 
 ment, but they serve merely as the intermediate agents for the development 
 of the electric force. The chemical action that gives rise to the excite- 
 ment of electricity takes place during the decomposition of the liquid in 
 which the plates are immersed. It is essential, therefore, to the formation 
 of an active voltaic arrangement, that the liquid employed should be 
 capable of being decomposed. Water is most conveniently applicable for 
 the purpose. Its elements, oxygen and hydrogen, are separated by the 
 superior affinity of the oxygen for the zinc ; especially when that affinity 
 is heightened by the connexion of the zinc with an incorrodible metal, to 
 which the hydrogen gas of the decomposed molecules of w^ater is attracted. 
 Whether the electricity evolved be the cause or merely the effect of chemi- 
 cal action is at present unknown. In whichever way the phenomenon be 
 regarded, the electricity appears to be excited at the surface of the active 
 plate, thence to be transferred to the conducting plate, and back again 
 through the connecting wire to the zinc, forming what is termed an 
 electric current.* 
 
 Water being a very imperfect conductor, it offers so much resistance 
 to the passage of the electric current that a very small quantity of voltaic 
 electricity can be excited when water alone is employed ; especially when 
 
 * The terms 'electric fluid' and 'electric current,' which are frequently employed 
 in describing electrical phenomena, are calculated to mislead the student into the sup- 
 position that electricity is known to be a fluid, and that it flows in a rapid stream along 
 the wires. Such terms, it should be understood, are founded merely on an assumed ana- 
 logy of the electric force to fluid, bodies. The nature of that force is unknown, and 
 whether its transmission be in the form of a current, or by vibrations, or by any other 
 means, is undetermined. At the meeting of the British Association for the Advancement 
 of Science at Swansea, a discussion arose on the nature of electricity, and Dr. Faraday 
 was called on to give his opinion. He then said, " There was a time when I thought I 
 knew something about the matter; but the longer I live, and the more carefully I study 
 the subject, the more convinced I am of my total ignorance of the nature of electricity.'* 
 After such an avowal from the most eminent electrician of the age, it is almost useless 
 to say that any terms which seem to designate the form of electricity are merely to be 
 considered as convenient conventional expressions. 
 
100 THE PHENOMENA OF ELECTRICITY. 
 
 the plates are at a considerable distance apart. By the addition of an acid 
 or a neutral salt to the water, the conducting power is greatly increased, 
 and the excitement is augmented in a corresponding degree. It is a dis- 
 puted point whether the increased action from the addition of acids arises 
 from the improved conducting power alone, or whether it is to be attri- 
 buted also to the increased affinity of the oxygen to the zinc. The effect 
 is most probably owing to the joint effort of the two forces. 
 
 In the opinion of Faraday, the conduction of electricity through liquids 
 is accompanied by, if it be not owing to, the successive decomposition of 
 the intervening particles. When a copper and zinc plate, for example, 
 are connected together and immersed in diluted acid, the oxygen in the 
 particle of liquid contiguous to the plate enters into combination with the 
 metal, and its equivalent quantity of hydrogen is disengaged. The hy- 
 drogen is not immediately liberated, but is transferred from particle to 
 particle of the liquid in a continuous chain till it reaches the conducting 
 plate, where, not meeting with any more liquid particles to which it can be 
 transferred, it is liberated in the gaseous form. The intervening particles 
 are supposed to undergo temporary decomposition during this transfer 
 from plate to plate, and to assume a polar condition, the oxygen and hy- 
 drogen occupying opposing places in each particle of liquid. 
 
 The annexed diagram (fig. 41) 
 shews, in an exaggerated form, the 
 chain of particles of water through 
 which the decomposing influence is 
 supposed to be transmitted. Voltaic 
 action having been established through 
 water in the vessel A from the zinc 
 plate z to the copper plate at c, the 
 particles between the two metals are 
 thrown into a polar state ; the oxygen 
 fig. 41. of each being directed towards z, and 
 
 the hydrogen towards c. The zinc 
 
 plate absorbs the oxygen of the particle nearest to it, and the liberated 
 hydrogen combines with the oxygen of the next adjoining particle, and 
 in this manner a continuous interchange takes place. According to this 
 view of the conducting power of fluids, no fluid can conduct electricity 
 unless it be capable of being decomposed ; the conduction being necessa- 
 rily accompanied by a train of successively decomposed particles. 
 
 All chemical action is believed to be accompanied by the development 
 of electricity, though in only a very limited number of arrangements can 
 it be observed. It is necessary for the sensible development of the force 
 that the elements of bodies undergoing decomposition should be separated 
 from each other in an imperfectly conducting medium, and be transferred 
 in different directions. These conditions are complied with in a voltaic 
 arrangement of a pair of plates of dissimilar metals, immersed in a decom- 
 posable fluid. The positive and negative electricities, which in ordinary 
 chemical combinations immediately coalesce imperceptibly, are in the vol- 
 taic battery constrained to separate, and in order to reunite must pass 
 along the conducting substances that connect the generating and the con- 
 ducting plates. But even the best voltaic arrangements do not develop the 
 whole of the electric force accompanying chemical decomposition. 
 
EXCITEMENT OF VOLTAIC ELECTRICITY. 101 
 
 The causes that obstruct the development of electricity in a current 
 have been minutely investigated by Professor Ohm, of Nuremburgh, who 
 has reduced them to mathematical formula?. The free development of 
 electricity is opposed, in the first place, by the affinity of the elements of 
 the exciting liquid for each other, tending to resist decomposition ; se- 
 condly, by the imperfect conduction of the fluid itself ; and in the third 
 place, by the resistance of the conducting wires. As the formula? deduced 
 by Professor Ohm from these investigations have received general accep- 
 tance among electricians, it is desirable to put them on record, and we 
 cannot do this in a better manner than by copying the lucid explanation 
 of them by Dr. Golding Bird.* 
 
 << E = electromotive force, equivalent to the affinity of the exciting 
 liquid for the generating metal, and corresponding to the amount of electri- 
 city which would appear in current if all opposing causes were removed. 
 
 " E = resistance opposed to E by the contents of the cell, arising for 
 the most part from the affinity of the elements of the exciting liquid for 
 each other. 
 
 "r = external resistance, arising chiefly from the imperfectly conduct- 
 ing nature of the wires used to convey the current. 
 
 " a = active force, or the amount of electricity which really reaches 
 the end of the conducting wire. 
 
 "The theoretical value of E is diminished materially in practice by 
 the affinity of the conducting plate for the ingredient of the exciting fluid, 
 which tends to combine with the generating plate ; this affinity, however 
 weak, is still seldom absolutely null. The mutual affinity of the separated 
 elements of the fluid evolved at the surfaces of the plates also lessens the 
 intensity of E. 
 
 " The internal resistance, R, varies directly with the distance, D, be- 
 tween the two plates, and is inversely as the area of the section, S, of the 
 exciting liquid. Thus the real resistance is equal to the former divided by 
 the latter, or 
 
 " r, or the external resistance, so far as it is dependent on the conduct- 
 ing wire, varies inversely as the square of the diameter of the wire, S, and 
 directly as its length I, or 
 
 It must be remarked that the foregoing estimate of electrical force and 
 resistances does not take into account the actual loss of electricity by the 
 want of proper direction. The chemical action that converts any given 
 quantity of zinc into a metallic salt develops, with the best arrangement, a 
 given quantity of electricity. Let it be assumed that one ounce of zinc 
 
 * Elements of Natural Philosophy. 
 
102 THE PHENOMENA OF ELECTRICITY. 
 
 will generate an amount of electricity equivalent to 1000; that quantity 
 will not be diminished by the resistances considered by Professor Ohm 
 Those resistances relate exclusively to the time in which a given amount 
 of electricity can be generated, and have no relation to actual loss of 
 electric force. Thus, in a well-constructed voltaic apparatus no more elec- 
 tricity is generated than can flow in a current through the conducting 
 wire. If the resistance to the current be increased by diminishing the 
 thickness of the wire or by adding to its length, the action of the gene- 
 rating-plate is diminished in a corresponding degree, so that if only half 
 the electricity is developed, only half the quantity of zinc is consumed; and 
 to whatever extent the resistances are increased the ounce of zinc will, 
 theoretically at least, produce its equivalent of electricity, though in a 
 longer time. 
 
 In practice, however, an actual loss of electricity does generally occur, 
 arising principally from what is called " local action " in the generating- 
 plate. If a plate of zinc were perfectly pure and homogeneous, no chemical 
 action would ensue when it was immersed in diluted acid. But zinc, as it 
 is commonly procured, contains copper, iron, and other impurities which 
 serve to set up voltaic action over its whole surface when exposed to diluted 
 acids, which cause a rapid decomposition of the liquid. The positive and 
 negative electricities thus generated immediately combine, and are neutra- 
 lised imperceptibly, and thus so much electric force is absolutely lost. 
 This local action is in a great measure, though not entirely, prevented by 
 amalgamating the zinc plates with mercury : this is readily done by first 
 dipping them in diluted sulphuric acid, and then sprinkling a few drops of 
 mercury on the surface and rubbing them over with a cork. The effect of 
 amalgamation is to produce a homogeneous surface, and to protect the zinc 
 from the action of the diluted acid until the affinity of the liquid for the 
 metal is increased by the agency of the conducting plate. 
 
 The electricity generated by a single pair of plates possesses a very 
 low degree of intensity. The quantity is only limited by the size of the 
 plates, but no increase of size alone will add to the intensity of the force. 
 Thus, though a pair of large zinc and copper plates, excited by diluted 
 sulphuric acid, will fuse any of the metals, they cannot decompose a drop 
 of water ; because in the latter case the force is not sufficiently energetic 
 to overcome the resistance of the fluid. 
 
 To increase the intensity of the force it is necessary to form a series of 
 conducting and generating plates on the principle of Volta's arrangement 
 
 a couronne de lasses. 
 
 It will simplify the explanation 
 of the mode of operation to consi- 
 der, in the first place, the combined 
 action of two pairs of plates only. 
 In fig. 42, A and B are two cells, 
 containing diluted sulphuric acid. 
 Into cell A an amalgamated zinc 
 plate z is immersed ; it being con- 
 nected by a wire to a copper plate 
 c in the cell B. No voltaic action 
 would ensue between those two 
 plates ; because, being in separate 
 
EXCITEMENT OF VOLTAIC ELECTRICITY. 103 
 
 cells, the hydrogen element of the particles of water set free at the zinc 
 plate could not be transferred to the copper. But by introducing a second 
 pair of zinc and copper plates z and c' into the cells, the transfer could 
 take place, and the electric current would pass ; first from z to the copper 
 c, thence it would be conducted to the second zinc plate z by the con- 
 necting wire, and from that through the fluid to c, and back again to the 
 first generating plate by the wire, which completes the circuit. 
 
 In tracing the course of the electric current thus established, no notice 
 has been taken of the action of the second zinc plate. If that be con- 
 sidered as inactive, except as a conductor, the quantity of electricity trans- 
 mitted would be very small, owing to the resistance of the imperfectly 
 conducting liquid. But the zinc plate in the second cell is acted on by 
 the diluted acid equally with that in the first; and the effect is to nearly 
 double the energy of the electric current excited by the action of the acid 
 on the first zinc plate. 
 
 The cause of this increased action is easily intelligible, on the suppo- 
 sition that the electricity excited by each zinc plate is carried forward to 
 the next in succession. Thus, for instance, a certain quantity of electricity 
 having been excited by the zinc plate in cell A, it is transferred to the 
 conducting plate c in the same cell ; and if a metallic connexion were made 
 between those two plates, the electricity would be directly returned in a 
 short circuit to z. But as there is no metallic connexion with the zinc, 
 the electricity must pass through the wire to the surface of , which acts 
 as a conducting plate. The action of the acid in the second cell on the 
 zinc excites at the same time a quantity of electricity equal to that it re- 
 ceives from the first plate ; and this accumulated quantity being compressed 
 within the same space is transmitted with redoubled energy through the 
 fluid to the second conducting plate c, and thence by the wire to the first 
 generating-plate z, to restore the electrical equilibrium. 
 
 According to this view of the action of a voltaic battery consisting of 
 two pairs of plates, the electricity excited by the first zinc is transferred to 
 the second, where its force is doubled by the excitement of an equal quan- 
 tity, and both united traverse the wire of the return circuit. On arriving 
 at the first zinc, half the quantity is parted with ; but an equal quantity of 
 fresh electricity is excited, and is carried on to the second zinc, where the 
 same process is repeated ; and thus the electrical equilibrium is continually 
 disturbed and continually restored after traversing the wires that connect 
 the plates at the extreme ends. When greater numbers of zinc and copper 
 plates are united in a series, a similar transference of electricity from plate to 
 plate takes place with a progressively increasing quantity and intensity of 
 force, the action being continued as long as the series remains unbroken, 
 or until the fluid becomes saturated with sulphate of zinc, and further 
 chemical action is prevented. 
 
 It is necessary to state that the preceding explanation of the action of 
 the voltaic battery differs from the view taken of it by Dr. Faraday, and 
 after him by most other writers on the subject. In the opinion of Dr. 
 Faraday, addition to the number of plates in a series occasions no addition 
 to the quantity of electricity generated by the first pair of plates, but 
 merely serves to give increased intensity to that quantity. Thus the most 
 powerful effects produced by a voltaic battery consisting of 1000 pairs of 
 plates are assumed to be caused by the same quantity of electricity that is 
 
104 
 
 THE PHENOMENA OF ELECTRICITY. 
 
 excited by a single pair only of the series : the exalted action in the former 
 case being attributed to an increase of intensity without any addition to 
 quantity. 
 
 This view of the nature of the action of the voltaic battery is sup- 
 ported by numerous ingeniously-contrived and apposite experiments ; * but 
 though fully disposed to pay the highest possible respect to so great an 
 authority as Dr. Faraday, we think he has failed to establish the position 
 that increased intensity is not accompanied by addition to quantity. 
 
 There are many arrangements of voltaic batteries for the development 
 of accumulated electric force in different modes, but they all depend on 
 the same principle. The most compact is Cruikshank's modification of the 
 voltaic pile. Zinc and copper plates of equal size are soldered together, 
 and then cemented into a wooden trough. Each pair of plates is fixed less 
 than half an inch from each other, care being taken that all the zinc and 
 copper surfaces are turned the same way. The compartments between the 
 plates form water-tight cells, into which diluted acid, or other exciting 
 liquid, is poured, A piece of wire is introduced at each end to complete 
 the circuit through any substances to be subjected to the voltaic action. 
 
 fig. 43. 
 
 A series of fifty small double plates may be cemented into a trough 
 two feet and a half long ; and two such batteries, with plates two inches 
 square, will give a rapid succession of smart shocks, and will exhibit most 
 of the phenomena of voltaic electricity. The disadvantages of a battery 
 of this kind are, that the exciting liquid cannot be emptied at the end of 
 each experiment without much trouble, and there is some difficulty in 
 cleaning the plates when they become corroded. By emptying the cells as 
 
 soon as possible and washing them 
 with water, a battery of this con- 
 struction may, however, be kept 
 in order for a considerable time ; 
 and when voltaic electricity of high 
 intensity and small quantity is re- 
 quired, a Cruikshank's battery, with 
 plates about two inches square, is 
 very convenient. 
 
 An arrangement contrived by 
 Dr. Babington affords the advantage 
 of making the plates easily accessi- 
 ble for the purpose of cleaning, and 
 also of removing them from the 
 liquid when the experiment is ended. 
 
 * Experimental Researches. 
 
EXCITEMENT OF VOLTAIC ELECTRICITY. 105 
 
 An earthenware trough is divided by plates of the same material into 
 water-tight compartments about two inches wide, so as to form a number 
 of cells. Each pair of zinc and copper plates is connected by a strip of 
 copper, instead of having their surfaces soldered directly against each other, 
 and the zinc and the copper are placed in separate cells. This arrange- 
 ment, indeed, very closely resembles that d, couronne de tosses of Volta ; 
 but it is more compact, and as all the copper and zinc plates are attached 
 to a piece of wood, they can be readily lifted out of the exciting liquid 
 when not in use. This is a great convenience when a continued series of 
 experiments is conducted at short intervals. As the earthenware trough 
 with fixed divisions is liable to be broken, and is rather difficult to manu- 
 facture, it has been found more convenient to have the cells made sepa- 
 rately, and to enclose them in a wooden case. 
 
 The original form of the trough has been recently very extensively 
 used for the electric telegraph, though made of other materials than earth- 
 enware. Most of the batteries of the Electric Telegraph Company, until 
 very recently, were constructed in wooden troughs, with partitions of slate 
 made water-tight by means of marine glue. These, again, are being sup- 
 planted by troughs made of gutta-percha, which are very much lighter, 
 and the cells can be more effectually prevented from leaking. The plates 
 of these batteries are connected by strips of copper, which are^ bent into 
 arches, so as to admit of each unattached pair of plates being inserted into 
 separate cells. The zinc plates are well amalgamated, and are allowed to 
 remain in the cells day and night, the local action being in a great measure 
 prevented by filling each cell with fine sand, and by using sulphuric acid 
 diluted with about twelve parts of water. A voltaic battery, with sand 
 and diluted sulphuric acid, will continue in good action, with occasional 
 additions of acid, for two months before the zinc plates require to be cleaned 
 or re-amalgamated. The consumption of zinc on the numerous and ex- 
 tended lines of the Electric Telegraph Company is very great, the cost of 
 battery-power amounting to nearly three thousand pounds in a single year. 
 
 Batteries in which graphite is substituted for plates of copper have 
 been introduced by Mr. C. V. Walker in working the electric telegraphs 
 of the South-Eastern Railway Company, and with very good results. One 
 of these batteries of twelve pairs, of which a record was taken, was kept in 
 daily action for ninety-seven weeks without having been washed or having 
 the sand changed. It was supplied with about a dessert-spoonful of acid- 
 water twenty-one times during the 
 period it was in action, and six times 
 with merely warm water. In one in- 
 stance it did duty for seventy-seven 
 days without having been touched.* 
 
 Dr. Wollaston contrived the ar- 
 rangement shewn in fig. 45 for obtain- 
 ing the greatest amount of power from 
 a given surface of zinc. The copper 
 plates c c c are doubled, so as to expose 
 a conducting surface to both sides of 
 the zinc plates, bbb. The plates are fi ^ 45 . 
 
 * Jury Reports of the Great Exhibition. 
 H 
 
106 
 
 THE PHENOMENA OF ELECTRICITY. 
 
 also brought as close together as possible without actual contact. They 
 are secured to a bar of wood, and are kept apart by pieces of cork. With a 
 battery of this kind, consisting of a few pairs of large plates, prodigious 
 heating power is produced, though the intensity of the electricity is too 
 feeble to communicate a shock. 
 
 The battery invented by Professor Daniell, the action of which has 
 been previously noticed,* is constructed on a different principle. It is 
 found in the voltaic arrangements before mentioned, that the zinc and 
 copper plates immersed in the same cell are liable to have their action im- 
 peded, and ultimately altogether arrested, by the transfer of zinc to the 
 copper surface. The action of the conducting plate is also greatly retarded 
 by the accumulation of hydrogen gas ; so much so, indeed, that very fre- 
 quently, after the first minute the battery has been put in action, not more 
 than one-tenth of the original power is obtained. In Professor Daniell's 
 battery the zinc and copper plates are kept apart by means of porous 
 earthenware cells, or by pieces of animal membrane, which, though suffi- 
 cient to prevent the passage of metallic particles, do not materially inter- 
 rupt the voltaic action. 
 
 Fig. 46 shews an arrangement of a single cell of this kind : c is a 
 copper cylindrical vessel, with a binding screw B, soldered to one edge for 
 the purpose of holding a connecting wire. Into this 
 copper cylinder a porous tube D, closed at the bottom, is 
 introduced ; and into the tube is placed a rod of amalga- 
 mated zinc z, with a binding screw at the top. A solu- 
 tion of muriate of soda (common salt) is poured into the 
 porous tube, and the outer copper vessel is nearly filled 
 with a saturated solution of sulphate of copper to which 
 a little sulphuric acid has been added. 
 
 When metallic connexion is made between the rod 
 of zinc and the copper cylinder, active excitement of 
 voltaic electricity occurs. The oxygen of the acid com- 
 bines with the zinc, and the liberated hydrogen passes 
 through the porous cell to the copper. It does not, 
 however, escape in the form of gas, but it enters into 
 combination with the oxygen of the sulphate of copper, 
 and the metal, being thus deprived of its oxygen, becomes 
 " revived," and is deposited in a metallic form on the inner surface of the 
 cylinder. By the continued absorption of hydrogen by the sulphate, and 
 the deposition of copper, a bright conducting surface is maintained ; and 
 this constant renewal of the conducting surface not only increases the 
 intensity of the action, but maintains it with a steadiness that cannot be 
 attained by any of the batteries previously described. 
 
 The constancy of action peculiar to this arrangement has obtained for 
 it the name of the " constant battery." To maintain its constancy, the 
 solution of sulphate of copper should, however, be preserved in a satu- 
 rated state by the addition of crystals of the metallic salt ; and when this 
 precaution is observed, a Daniell's battery will continue in action for 
 several days without much diminution of the original force. A ledge per- 
 forated with holes is generally fixed inside the copper cylinder for holding 
 
 fig. 46. 
 
 * Page 43. 
 
EXCITEMENT OF VOLTAIC ELECTRICITY. 
 
 107 
 
 fig. 47. 
 
 crystals of the sulphate, which gradually dissolve and keep the solution in 
 a saturated state. 
 
 The voltaic arrangement contrived by Mr. 
 Smee deserves special notice from its general uti- 
 lity. The principal differences between it and a 
 battery of Dr. Babington's arrangement consist 
 in the material of the conducting plate and in 
 the mode of placing it. The conducting plate is 
 made of silver-foil platinized ; that is, a thin 
 coat of platinum is deposited on the silver by 
 the electrotype process. The minutely-divided 
 particles of platinum that thus cover and adhere 
 to the silver present a greatly-enlarged surface 
 to liquid in which it is immersed, by which 
 means a smaller-sized plate answers equally with 
 a much larger one of smooth metal. Platinum 
 also being a metal less readily oxidised than cop- 
 per, the effect of the voltaic arrangement is 
 heightened by the greater dissimilarity of the 
 two metals. The platinized silver-foil is fixed in 
 the centre of a wooden frame s, and two zinc 
 plates, z z, well amalgamated, are attached to the 
 upper rim of the frame by a brass clamp, which has a binding-screw con- 
 nected with it. By this arrangement the zinc plates can be very readily 
 removed and cleaned. In this respect a Smee's battery is more conve- 
 nient than any other ; its action also approaches a Daniell's battery in 
 constancy. These are important advantages, which render this form of 
 voltaic battery the best that can be used for general purposes. 
 
 The substitution of graphite for the platinized silver plates promises to 
 be a still further improvement. With graphite conducting plates there is 
 no occasion for the wooden frame. A single zinc plate, with a binding- 
 screw soldered to it, occupies the central place, instead of the platinized 
 foil, and two flat pieces of graphite may be clamped on each side ; care 
 being taken to insulate the zinc from the graphite by small strips of var- 
 nished wood. It will be observed that in this disposition of the apparatus 
 with the graphite, the position of the exciting zinc in reference to the 
 conducting surfaces is transposed, as well as the proportions of each to 
 the other being reversed ; a single plate of zinc being placed between two 
 conducting surfaces instead of the conducting surface being in the centre, 
 with a zinc plate on each side. 
 
 When a battery of great power, and occupying comparatively small 
 space, is required, Mr. Grove's arrangement is commonly employed. The 
 intensity of its action depends on associating two metals the most dissi- 
 milar in their chemical characters, and exposing one of them separately 
 to the strongest exciting acid. This can only be done by using a porous 
 cell, which keeps the zinc from the destructive action of the powerful acids 
 employed, and to which platinum is exposed in a separate compartment. 
 The porous cell which contains the zinc is filled with diluted sulphuric 
 acid, in the proportion of one of acid to four of water ; and the other 
 vessel, with the platinum-foil, contains equal proportions of concen- 
 trated nitric and sulphuric acids. With a battery of this construction 
 
108 THE PHENOMENA OF ELECTRICITY. 
 
 consisting of fifty pairs four inches long by two wide, and which does 
 not occupy more space than eighteen inches square, the most powerful 
 effects may be produced ; metal wires being melted into globules and 
 dissipated in oxides, and a dazzling flame upwards of an inch long pro- 
 duced between charcoal points. 
 
 There are various other arrangements of voltaic batteries, but we have 
 described nearly all those that are constructed on distinctive principles. 
 The object in every case is to obtain from a given quantity of the exciting 
 metal the greatest possible amount of current electricity, without allowing 
 the power to be wasted in other ways. The consumption of a given 
 weight of zinc cannot, by any possible combination, excite more electricity 
 than will decompose a quantity of water equivalent to that which is de- 
 composed by the chemical affinity of the metal for oxygen. Thus sup- 
 posing two grains of water to be decomposed in the generating cell, and 
 eight grains of zinc to be oxidized, the electricity generated during the 
 process cannot be more than sufficient to decompose another two grains of 
 water. The power obtained, even by the best arrangements hitherto con- 
 trived, seldom amounts to so much. By increasing the chemical action of 
 the liquid on the generating plates, the energy of the battery is increased, 
 but most frequently not in proportion to the consumption of zinc. By 
 bringing the plates in the generating cells nearer together, the energy of 
 the battery is also increased, by diminishing the intervening fluid resist- 
 ance ; but this may be attended with waste of power if the plates be 
 brought too close. 
 
 Economy of construction is an important consideration when experi- 
 ments are conducted on a large scale, and this must in general prevent 
 the adoption of platinum. The use of porous cells for the purpose of 
 preventing the deposition of zinc on the conducting plate is very advan- 
 tageous, but the high price at which they are sold in this country limits 
 their use, for after a time the pores become clogged and the vessels require 
 to be replaced. This cannot be done in London at a cost of less than 
 ninepence for each, though small j but the porous vessels which are used in 
 the batteries of the electric telegraphs in India are purchased there at the 
 rate of twenty for one halfpenny. Several contrivances have been adopted 
 to serve the purpose of porous earthenware, such as brown-paper bags, 
 bladder, and sail-cloth, but each has its inconvenience, and there is still 
 wanting some cheap substitute for the earthenware vessels that are now 
 sold at such extravagant prices. 
 
PHENOMENA OF VOLTAIC ELECTRICITY. 109 
 
 CHAPTER XII. 
 
 PHENOMENA OF VOLTAIC ELECTRICITY. 
 
 Different conditions of Fractional and Voltaic electricity The two poles of the battery 
 How to distinguish them Mystification caused by new terms Voltaic action 
 immediate and continuous Its rapid transmission exemplified Resistance of wires 
 to the electric current Heating effects of the Voltaic battery Combustion of car- 
 bon Extraordinary physiological effects Contrivances for giving shocks Water- 
 batteries Intensity of their action Mr. Crosse's water-battery Cause of the inten- 
 sity of water-batteries. 
 
 THE power developed by a numerous series of voltaic elements, though 
 in many respects resembling that of an electrical battery, is in several 
 particulars dissimilar to it. The difference in the phenomena may be 
 attributed chiefly, if not entirely, to the different degrees of intensity in 
 which the two kinds of electricity are excited. Even when the intensity of 
 the voltaic battery is increased by the reduplication of the power fifty times, 
 the electricity has not sufficient energy to pass through the smallest space 
 of resisting air in the form of a spark, nor can it exert an attractive force 
 on light non-conducting bodies. Thus, when the electricity excited by 
 several pairs of large plates has sufficient power to melt metals and to 
 give a strong electric shock, the presence of electricity is not appreciable by 
 the most delicate pith-ball electrometer. But when the elements are in- 
 creased to the number of two or three thousand, as in Mr. Crosse's extra- 
 ordinary water-battery, the intensity of voltaic electricity becomes so far 
 augmented, that a spark will pass between the connecting wires before 
 contact, and the electrometer is very sensibly affected. 
 
 The experiments of Mr. Crosse have supplied all that was wanted to 
 shew the complete identity of the two forces, and to prove that the differ- 
 ence in their modes of action depends alone on the degree of intensity in 
 which they are excited. 
 
 The electricity developed at the opposite ends of a voltaic battery ap- 
 pears to bear the same relation to each end as the electricity of the inside 
 and outside of a charged Leyden jar. One end therefore is considered to 
 be negative, and the other to be positive. If the wires from the termi- 
 nating zinc and copper plates be furnished with platinum points, and 
 inserted into a glass filled with water slightly acidulated to increase its 
 conducting power, the fluid will be decomposed, and bubbles of hydrogen 
 gas will rise from one wire, and bubbles of oxygen gas from the other. 
 It will be found, on collecting the bubbles of gas in separate receivers, that 
 the oxygen is liberated from the wire connected with the copper end 
 of the battery, and the hydrogen from the wire connected with the zinc. 
 In all cases of electro-chemical decomposition it is also found that the ele- 
 ment which collects at the wire from the copper corresponds with that 
 which collects at the positive wire of the electrical machine ; hence it is 
 inferred that the electricity evolved from the wire connected with the 
 copper of a voltaic battery is identical with positive frictional electricity, 
 and that the electric current proceeding from the zinc is negative. The 
 copper and zinc ends of a voltaic battery are, therefore, commonly called 
 
110 THE PHENOMENA OF ELECTRICITY. 
 
 positive and negative " poles ;" the word pole, having been given to the 
 opposite ends from the polar arrangement which, in some instances, ap- 
 pears to be induced by voltaic action. 
 
 It is difficult to avoid confusion in speaking of the opposite poles of a 
 voltaic battery. This difficulty arises partly from the apparent generation 
 of the electric force by the conducting plate, which is in reality inactive ; 
 it is partly to be attributed to the different arrangements of the zinc and 
 copper plates in different batteries ; and it is increased by the various 
 names that have been arbitrarily given to the terminal wires. 
 
 When the electricity of a single pair of zinc and copper plates is con- 
 sidered, it will be observed that though the electricity is excited by the zinc, 
 the electric current proceeds to the copper, and thence is returned by the 
 conducting wire to the zinc. Therefore when the ends of two wires, one 
 from the zinc and one from the copper plate, are inserted into a conducting 
 fluid, the positive electricity will enter from the wire connected with the 
 inactive or negative plate, and at that point the effects of positive electri- 
 city will be produced ; whilst negative effects will be developed at the wire 
 connected with the generating plate. 
 
 The contradiction apparently involved in this statement will disappear, 
 when it is considered that the electric current excited by the zinc always 
 tends towards the copper, which serves to conduct it back again to the 
 generating plate ; and that though the electricity appears to proceed from 
 the copper, that metal operates only as the conductor of the current, which 
 is assumed always to proceed from the copper to the zinc. The same 
 effect takes place when several zinc and copper plates are combined. The 
 wire leading from the copper end of the battery will be positive, because 
 it is conducting the accumulated electricity on its return to the zinc end ; 
 and the other wire will be negative, because it is receiving the flow of 
 electricity, and is consequently in a less highly charged condition. 
 
 In using a voltaic pile or a Cruikshank's battery, mistakes are likely 
 to arise in consequence of the last zinc and copperplates not being active, 
 but merely serving as metallic conductors. In a Cruikshank's battery, 
 for instance, a small cell is generally left at each end without any corre- 
 sponding plate opposite the last zinc and the last copper ; thus, when a 
 conducting wire is introduced at the end where the zinc is the last of the 
 series, it is the same in effect as if the conducting wire were connected to 
 the copper, for the last zinc plate is soldered to the copper only for uni- 
 formity, and is altogether inoperative. It would, indeed, be better if the 
 terminal plates were cemented to the end of the trough with a binding 
 screw attached to hold the wire, and then no confusion from that source 
 would arise. The same observation applies to the voltaic pile, the end 
 plates of which, to avoid mistake, should consist of a single zinc disc and 
 a single copper disc. 
 
 We have before expressed regret at the introduction into electric science 
 of new terms, derived from the vocabulary of a dead language, which serve 
 to mystify, to perplex, and to mislead. The difficulty attending the clear 
 comprehension of the right character of the two ends of the voltaic battery 
 has been by this means increased. To call the extreme copper and zinc 
 plates in a continued series, and the wires connected with them, the ends 
 of the battery, expresses clearly and simply the fact, without giving 
 sanction to any doubtful theory. But the word " end " was not deemed 
 
PHENOMENA OP VOLTAIC ELECTRICITY. Ill 
 
 sufficiently dignified. " Terminals " sounded better, but not being so ge- 
 nerally understood it was no improvement. As the action of a voltaic 
 battery produces in some cases a polar arrangement, the name " poles " 
 was introduced, and the negative and positive pole of a battery have be- 
 come familiar terms. The implied polarization was however objected to, 
 and the word "electrode" has been concocted from the Greek electron, 
 amber, and odos, a way or door, signifying the door into and out of which 
 the electric current passes. As, however, it is questioned by Faraday 
 himself, who sanctioned the term, whether there is any actual entrance and 
 exit of electricity, and whether there is any current whatever, we may 
 be permitted to doubt the appropriateness of the term ; and even if the 
 signification be admitted, we should much prefer its expression by an 
 English word. 
 
 Again, the terms " positive" and " negative" were objected to, as sig- 
 nifying conditions of electricity, of the correctness of which many enter- 
 tain doubts. With a view to improve the nomenclature, the much more 
 objectionable terms " anode " and " cathode " have been introduced, sig- 
 nifying an upward and a downward way, and founded on a fancied re- 
 semblance between the direction of electric currents round the earth, and 
 the rising and setting of the sun. The " anode " is the electrode at which 
 the current enters, the " cathode " the electrode at which the current leaves, 
 the decomposing fluid ; the former being in fact the positive, and the 
 latter the negative end of the battery. 
 
 When the wire from one end of a voltaic battery is connected with 
 the wire from the opposite end, voltaic action instantly commences ; and 
 it as instantaneously ceases when the connexion is interrupted. The 
 rapidity with which the electric circuit may be completed and broken has 
 no ascertained limit ; nor does it appear to be controlled by resistance 
 caused by traversing miles of wire. 
 
 If a number of short lines close together be drawn with varnish or 
 other non-conducting liquid on a smooth metallic surface, and a metal 
 point in connexion with one of the poles of a voltaic battery be drawn 
 rapidly over them, the electric current will pass at every minute interval 
 between the lines, and will be interrupted each time that the lines of var- 
 nish intervene. To prove this experimentally, draw a number of straight 
 strokes with a pen dipped in varnish on a piece of tin-foil A, fig. 48, and 
 connect the foil with the copper end of a small voltaic battery. On to 
 another strip of tin-foil D, con- 
 nected with the zinc end of the 
 battery by the wire z, lay a piece 
 of paper B, that has been soaked in 
 a solution of diluted muriatic acid 
 and prussiate of potass. Bend a 
 steel wire, w, so that each end may 
 be drawn at the same time over 
 the moistened paper and the lines 
 of varnish. By this arrange- 
 ment the electric circuit will be 
 -completed whenever the ends of 
 the bent wire press on the foil and on the paper, and it will be 
 broken as the point passes over the varnish. However rapidly the wire 
 
112 THE PHENOMENA OF ELECTRICITY. 
 
 is drawn across the varnish lines by the hand, the making and breaking 
 of contact will be indicated on the paper by a line of blue dots. If the 
 wire be drawn along very quickly the marks will be more faint, but the 
 presence of electric action and the discontinuance of its action may be 
 perceived, even when the connexion is made and broken one thousand 
 times in a second. 
 
 Though the intensity of voltaic electricity is beyond all calculation 
 less than that of electricity excited by friction, it nevertheless passes along 
 a conducting wire as quickly as the discharge of a Ley den jar. In an 
 experiment performed last autumn before the Court of Directors of the 
 East India Company on Warley Common, a current of voltaic electricity 
 was sent through ten thousand yards of copper wire, and a fuse at one 
 end of the battery was ignited without any perceptible interval of time, 
 as soon as connexion was made between the wires ; the fuse having been 
 introduced near the end of the circuit that the cause and effect might be 
 seen to be instantaneous. In passing through a length of 2000 miles, 
 however, a perceptible interval is observed between making connexion 
 at one end and the resulting effect at the other. 
 
 It is a peculiar property of voltaic electricity, depending on its low 
 degree of intensity, that it will traverse a circuit of 2000 miles rather 
 than make a short circuit by passing through an interval of resisting air, 
 not exceeding the hundredth part of an inch. Frictional and atmospheric 
 electricity, on the contrary, will force a passage across a considerable in- 
 terval, in preference to taking a long circuit through wire ; or at least the 
 greater portion of it will pass through the air, though some part of the 
 charge will in all such cases traverse the wire. The resistance offered by 
 a long thin wire to the passage of intensity electricity resembles in effect 
 that of an imperfect conductor, and if there were no other course through 
 which to force its way, the conduction of a charge of electricity by a long 
 wire would occupy an appreciable time ; as a Leyden jar may be discharged 
 gradually through a wet string. When quantity is combined with in- 
 tensity, the resistance offered by a thin wire occasions its fusion. Instances 
 of this sometimes occur during thunder-storms, by the destruction of the 
 galvanometer-coils of the electric telegraph by lightning. To protect the 
 instruments from such accidents, advantage has been taken of the different 
 modes of conduction by voltaic and frictional electricity, and the coil is 
 protected by a lightning-conductor consisting of a thick piece of brass in 
 which there is a minute interruption, quite sufficient to prevent the voltaic 
 current from being diverted from the long circuit into the short one, but 
 through which the lightning forces a passage in preference to encountering 
 the resistance of the coil. 
 
 The heating effects produced by the concentration of voltaic force in 
 a series of plates may be fully shewn by a battery consisting of ten pairs of 
 plates in Smee's arrangement, each plate being not less than six inches 
 square. With such a battery in good action, all the metals may be burned 
 by attaching strips of the thinnest leaves into which they can be beaten 
 on to a wire connected with one of its poles, and then bringing the wire 
 from the other pole into contact. The metals will thus be deflagrated 
 with a brilliant light, the colours of the flames differing with the metal 
 operated on. Gold burns with a white light, tinged with blue ; silver 
 emits an emerald green light j copper burns with a greenish flame ; the 
 
PHENOMENA OF VOLTAIC ELECTRICITY. 113 
 
 flame of lead is purple ; of zinc, white tinged with red ; and mercury burns 
 with a pure brilliant white light. Short lengths of thin wires are made 
 red hot and melted when stretched between the battery connexions. The 
 lengths that may be thus melted are proportionate to the power of the 
 battery and the thickness of the wire. 
 
 The deflagration of metals by voltaic action, though it apparently 
 takes place immediately on making contact, is not so instantaneous as the 
 deflagration by frictional electricity. The difference in the rapidity of 
 their actions may be shewn by the following experiments. Let equal 
 short lengths of fine wire be covered with silk. First, discharge the con- 
 tents of a battery of combined Leyden jars through the wire. It will be 
 instantly deflagrated, the oxide being dissipated in powder, but the silk 
 thread that covered it will be uninjured. Next, send a momentary current 
 from the voltaic battery through an equal length of the covered wire by 
 making an instantaneous connexion of the poles. The effects will now be 
 the reverse of the former experiment ; for the silk will be destroyed, 
 whilst the wire will remain entire. In the first case the action is so 
 rapid that the particles of metal are dissipated before the silk, a slow 
 conductor of caloric, can be affected by the momentary presence of heat ; 
 in the second experiment, the slower action of the voltaic power has not 
 time, during the short contact, to exert its full power and to melt the wire, 
 though it heats it sufficiently to burn the silk. 
 
 The most brilliant of the phenomena of voltaic electricity is the light 
 evolved between two charcoal points. To exhibit this effect a battery 
 consisting of at least fifty pairs of copper and zinc plates four inches 
 square is required. Two pointed pieces of graphite answer better than 
 wood charcoal. They may be conveniently fixed to the rods of the uni- 
 versal discharger, each rod being, connected with the opposite ends of the 
 
 fig. 49. 
 
 voltaic battery, as shewn in fig. 49. The two points must first be brought 
 into contact ; and the electric current being thus established, the pieces of 
 graphite, after being heated, may be gradually separated from each other, 
 to the distance of an inch and upwards, without breaking the voltaic cir- 
 cuit. The space between the points is occupied by an arch of flame that 
 nearly equals in dazzling brightness the rays of the sun. 
 
 The cause of the phenomenon is not exactly understood. The light is 
 not occasioned by ordinary combustion, for it is equally bright in a vacuum, 
 and may be produced, with diminished intensity, in water. It seems pro- 
 bable that minute particles of carbon become separated from the points, 
 and that their incandescence, under the influence of voltaic action, causes 
 the brilliant light. M. de la Rive has produced a voltaic arch of nearly 
 
114 THE PHENOMENA OF ELECTRICITY. 
 
 equal brilliancy by substituting a finely divided preparation of spongy 
 platinum for charcoal. During the evolution of light from charcoal points 
 there is a transfer of a minute portion of carbon from one to the other. 
 A small hollow cone is made in the piece of charcoal connected with the 
 positive pole of the battery, and on the point of the negatively-connected 
 charcoal a projecting cone is deposited that exactly fits the cavity. The 
 light is accompanied by heat sufficiently intense to fuse any of the metals. 
 
 The intimate relation subsisting between voltaic action and the nervous 
 influence has not latterly excited so much attention as in the early days of 
 the discovery of voltaic electricity. The extraordinary contortions of the 
 limbs on connecting the nerves and muscles of recently killed animals with 
 the poles of a voltaic battery, gave rise to the impression that by the 
 -agency of galvanism the vital functions might be carried on after death. 
 This opinion has been to some extent realised by experiment. Dr. Philip 
 succeeded in maintaining the respiration, the pulsation of the heart, and 
 the circulation of the blood, in rabbits from which the spinal marrow and 
 brain had been removed ; and he inferred from these experiments " the 
 identity of galvanic electricity and nervous influence." 
 
 Some remarkable experiments on the body of a recently-executed mur- 
 derer are recorded by Dr. Ure, who superintended the arrangements. The 
 experiments were conducted in the theatre of anatomy at Glasgow. The 
 body was that of a middle-sized, athletic, and extremely muscular man. 
 He was taken into the theatre about ten minutes after he had been cut 
 down, his face having at the time a perfectly natural aspect, and the neck 
 not dislocated. The voltaic battery put in requisition consisted of 270 
 pairs of plates four inches square. On placing one wire of the battery on 
 the exposed spinal marrow on the neck, and the other on the sciatic near 
 the left hip, " Every muscle of the body was immediately agitated with 
 convulsive movements, resembling a violent shuddering from cold. The 
 left side was most violently convulsed at each renewal of the electric con- 
 tact. On moving the second wire 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." 
 
 In another experiment, directed with the view of renewing the respi- 
 ratory process, " Full, nay, laborious breathing instantly commenced. The 
 chest heaved and fell ; the belly protruded and again collapsed with the 
 relaxed and retiring diaphragm." One of the connecting wires having then 
 been applied to the forehead, the other to the heel, " Every muscle in his 
 countenance was simultaneously thrown into fearful action ; rage, horror, 
 despair, anguish, and ghastly smiles united their hideous expression in the 
 murderer's face. At this period several of the spectators were forced to 
 leave the apartment from terror or sickness, and one gentleman fainted." 
 Dr. Ure was of opinion that if the pulmonary organs had been excited 
 before the spinal marrow had been wounded, the man might have been 
 restored to life. 
 
 To produce physiological effects with the voltaic battery, intensity 
 rather than quantity is required. To communicate an electric shock 
 directly from the battery requires a series of fifty pairs of plates, and even 
 then the shock is only feeble. Even with a series of one hundred pairs 
 the intensity is scarcely sufficient to overcome the resistance of the outer 
 
PHENOMENA OF VOLTAIC ELECTRICITY. 115 
 
 skin, without dipping the hands in acidulated water or an alkaline solution. 
 The effect of the shock is increased when the surface of contact is enlarged 
 by attaching small copper cylinders to the wires ; for by this means the 
 imperfect conduction of voltaic electricity through the skin is compensated 
 by the larger surface exposed to its action ; it being one of the properties 
 of conducting bodies that a bad conductor of voltaic electricity offers no 
 more resistance to an electric current than a good conductor, provided the 
 size of the former be great in proportion to its degree of imperfect 
 conduction. 
 
 A voltaic battery of six large plates, capable of fusing metals with 
 facility, produces no sensible effect when the wires from the opposite poles 
 are held in the hands ; but when they are applied to the more delicate 
 and sensitive substance of the tongue, a very strong and disagreeable sen- 
 sation is experienced. By adding to the intensity of the current the phy- 
 siological effects are greatly increased, even when the quantity of electricity 
 generated by each pair in the series is extremely minute. A water-battery 
 was constructed by Professor Daniell that consisted of 2100 series. The 
 conducting surfaces were formed of pieces of copper tube, about one inch 
 long and three-eighths of an inch in diameter, the generating surfaces 
 being pieces of zinc wire soldered to the copper tubes, and bent so as to 
 enter into the centre of each proximate copper tube without touching it. 
 Small separate cups filled with pure water, into which each copper and 
 zinc element was immersed, completed the arrangement. This Lilliputian 
 battery of numerous elements excited a current of electricity closely ap- 
 proaching in intensity to that of a Leyden jar. It gave shocks, emitted 
 sparks, affected strongly a gold-leaf electrometer, and attracted light 
 substances. 
 
 The direct effects of this battery were almost inappreciable when ap- 
 plied to metals, but they could be multiplied in exactly the same manner 
 as the effect of an electrical machine is increased. An extended coated 
 surface of glass could be continuously charged by this water-battery, and 
 then the quantitive effects were much greater. The charge was commu- 
 nicated to a coated surface of several square feet almost instantaneously. 
 A succession of discharges was obtained to the same extent, but more 
 rapidly, as when the electrical battery was charged by a powerful machine. 
 
 Though the full charge which this water-battery was capable of com- 
 municating was imparted almost instantaneously, there was an appreciable 
 interval between each discharge of the Leyden battery sufficient to indicate 
 that the voltaic action, though apparently immediate, consists of a suc- 
 cession of efforts rapidly following each other. This is particularly the 
 case when the current has to pass through an imperfect conductor, like 
 the human body ; the force seeming to require to be accumulated till it 
 attains sufficient energy to overcome the resistance. When metals form 
 the circuit, the electricity passes as quickly as it is generated, and there is 
 in that case no occasion to increase the intensity by adding to the series of 
 plates. 
 
 A water-battery has been constructed by Mr. Crosse with much larger 
 
 surfaces than those of Professor Daniell, and with the cells more carefully 
 
 insulated. A particular account of it is given by Mr. Noad, who was 
 
 present during many of the experiments.* It consists of 2,500 pairs of 
 
 * Lectures on Electricity. 
 
116 THE PHENOMENA OF ELECTRICITY. 
 
 copper and zinc cylinders, most of which are enclosed in glass jars. They 
 are all well insulated on glass stands, and are ranged on three long tables, 
 well protected from dust and from the light a situation which experience 
 has shewn Mr. Crosse to be most favourable to this peculiar form of the 
 voltaic battery. Thirty pairs afford a slight spark sufficient to pierce the 
 cuticle of the lip, the hand making the communication being wetted ; 130 
 pairs open the gold leaves of the electrometer about half an inch ; 250 pairs 
 cause the gold leaves to strike the sides of the glass ; 400 pairs give a very 
 perceptible stream of electricity to the dry hand ; 500 pairs occasion that 
 part of the dry skin which is brought in contact to be slightly cauterised ; 
 1,200 pairs give a constant small stream of electricity between two wires 
 placed T ^yth of an inch apart, such wires not having been previously 
 brought into contact. This stream, when received by the dry hands, is 
 exceedingly sharp and painful. A pith ball, a quarter of an inch in dia- 
 meter, suspended by a silk thread, will constantly vibrate between the 
 opposite poles. With 1,600 pairs, the stream between the two wires not 
 previously brought into contact is very distinct ; it may be kept up for 
 many minutes, nor does it appear inclined to cease. The light between 
 charcoal points, even with the whole series, is feeble ; there is no flame, or 
 approach to it. When the opposite poles of 2,400 pairs are connected 
 with the inner and outer coatings of an electrical battery containing 
 seventy-three feet of surface, a continual charge is kept up ; each dis- 
 charge being attended with a loud report heard at a considerable distance. 
 Each of these discharges will pierce stout letter-paper, and fuse a consider- 
 able length of silver-leaf, which it deflagrates brilliantly, attended with 
 loud snappings of light more than a quarter of an inch in length. Plati- 
 num wire is fused at the extremity, and the point of a penknife is soon 
 demolished. Light substances are attracted at a distance of some inches, 
 and repelled again. 
 
 The intensity effects of a water-battery may be considered to be con- 
 sequent on the bad conducting power of that fluid. The small quantity of 
 electricity generated by each zinc plate is transmitted from plate to plate to 
 the end of the series, and it is prevented from returning through the liquid in 
 the cells by non-conducting resistance. Thus, though a much less quan- 
 tity of electricity is generated, it is increased by each successive plate in a 
 greater proportionate degree than when a better exciting, and at the same 
 time a better conducting, fluid is employed. The greater degree of inten- 
 sity accumulated in a numerous series of elements makes the insulation of 
 the cells more necessary, which is a point but little attended to in voltaic 
 batteries of few combinations, and excited by diluted acids. 
 
SECONDARY CURRENTS. 9 117 
 
 CHAPTER XIII. 
 
 SECONDARY CURRENTS. 
 
 The Voltaic current dependent on resistance Induction of secondary currents on 
 making and breaking contact Induction of electricity in a separate wire The di- 
 rection of secondary currents opposite to primary Faraday's views of the action of 
 induced currents. 
 
 THE manifestation of the presence of electricity, whether excited by 
 friction or by chemical agency, depends, as we have previously observed, 
 altogether on resistance to its diffusion. Were there no resisting medium 
 there would be no development of electric force, because it would be neu- 
 tralized as quickly as generated by unimpeded conduction. A glass rod 
 cannot be excited by friction unless the air be, partially at least, dry and 
 non-conducting ; whilst, on the other hand, a metal rod may serve as an 
 electric, if the dispersion of the electricity be prevented by insulating the 
 metal on a glass handle, which resists the flow of the electric fluid. It is 
 resistance, also, that in the same manner induces the manifestation of vol- 
 taic electricity. Were it not for the resistance of the fluid in the cells of 
 the battery, which prevents the direct return of the electricity from the 
 conducting plate to the zinc, no voltaic action could be perceived, for the 
 positive and negative electricity would be immediately neutralised. If, 
 for instance, a good conducting medium were established by the introduc- 
 tion of mercury into the bottom of the cells, there would be very energetic 
 chemical action ; there would be the excitement of electricity, but it would 
 be inappreciable, because it would be conducted back to the zinc plate as 
 quickly as generated. It is evident, therefore, that without a resisting 
 medium electricity could not be excited. It is equally true, though not 
 at first so evident, that the exhibition of electric force, when excited, de- 
 pends on the resistance made to its passage through the bodies on which it 
 acts. Lightning passes imperceptibly through a thick metallic rod, but 
 shivers into pieces an imperfectly conducting oak. The voltaic "current 
 also passes through a thick conducting wire without any observable effects ; 
 but when the same current is obstructed by a thinner wire it develops 
 heat. Even in electro-chemical decomposition, it is found that the de- 
 composing effect is diminished when the liquid undergoing decomposition 
 conducts electricity too freely. If, however, the resistance be too great, 
 the electric current is so far retarded as to diminish the action or to prevent 
 it altogether ; and it is difficult in some electro-chemical decompositions 
 to determine how far the effect is increased or diminished by increasing or 
 diminishing the conducting power of the solution. 
 
 The phenomena of induced voltaic currents present some of the most 
 interesting and important facts in electric science. We shall have to 
 notice this inductive action more particularly when considering the phe- 
 nomena of electro-magnetism, but there are some points which come 
 appropriately within the present division of our subject. 
 
 When contact is made and broken with the connecting wires of a single 
 of plates, the wires used being thick and the circuit short, scarcely 
 
118 % THE PHENOMENA OF ELECTRICITY. 
 
 any spark is visible on breaking contact ; but when the current passes 
 through a long wire, a bright spark, accompanied by a snapping noise, 
 will be seen when the contact is suddenly broken. The effect increases to 
 a certain extent with the length of the wire, and if it be twisted into a 
 spiral the spark is more bright and the snapping sound is louder. 
 
 Such a result is directly at variance with the presupposed action of a 
 voltaic current. As the resistance increases with the length of the wire, 
 it might have been confidently predicated that the indications of electric 
 force would decrease with the diminution of the quantity transmitted 
 instead of being in any way increased. The phenomena of this anoma- 
 lous action of the voltaic current in long resisting wires have been in- 
 vestigated by Faraday with the care and ability manifest in all his ex- 
 perimental researches, and he has succeeded in elucidating from them 
 some highly-interesting facts.* It was ascertained that the spark on 
 breaking contact becomes brighter, and the electric development stronger, 
 in proportion to the addition to length of the conducting wire ; until 
 the resistance of the metal as a conductor so far diminishes the quantity 
 of electricity as to interfere with the effect. Having attained the maxi- 
 mum result that mere addition to the length of the wire can give, the 
 effect was much increased by twisting the wire into a spiral. The helix 
 thus formed by coils of well-covered wire allowed the same quantity of 
 electricity to pass as when the wire was straight ; therefore so far as the 
 direct action of the conducting wire was concerned the conditions were 
 the same, though the amount of effect was different. The brightness of 
 the spark and the strength of the shock were still more augmented by the 
 insertion of a bar of soft iron within the coil of covered wire. It was evi- 
 dent, therefore, from these variations in the amount of force, whilst the 
 length of the wire and its resistance to the electric current remained the 
 same, that the increased effect could not be attributed, as was at first con- 
 ceived, to momentum acquired by the electric fluid in its transmission 
 through the wires. 
 
 Another remarkable fact developed in those researches was, that the 
 extra current could be developed in a second and altogether separate wire 
 placed parallel to the first ; and that when the power was thus imparted 
 to the second wire, the primary one, through which the direct action of 
 the battery was communicated, appeared to be no longer specially affected 
 on breaking contact. To produce the current in the second wire it was 
 bent double, so as to form a continuous circuit, and extended alongside 
 the primary wire ; or, what was found still better, the first and second 
 wires, insulated by being covered with cotton or silk, were twisted into a 
 spiral together, and the two ends of the second were brought together to 
 form a circuit. From these and from other facts elicited in the course of 
 his experiments, Faraday arrived at the conclusion that the extraordinary 
 development of electricity is derived from a current induced in the wires 
 at the instant of breaking contact, and which is only momentary in its 
 duration. 
 
 If any further proof were required that the currents thus induced are 
 not dependent on increased energy in the conducting wire, it is afforded 
 by the additional fact, no less curious than any other of these remarkable 
 
 * Experimental Eesearches, series ix. 
 
SECONDARY CURRENTS. 
 
 119 
 
 fig. 50. 
 
 phenomena, that the secondary currents are in the reverse direction of the 
 primary. If, for instance, a voltaic current from the positive to the ne- 
 gative pole be suddenly broken, the induced electricity is of the opposite 
 kind to that which is transmitted through the primary wire directly from 
 the voltaic battery. Thus the electricity induced by breaking contact 
 in the wire from the positive pole is negative, and that induced in the 
 negative wire is positive. 
 
 A simple apparatus contrived by 
 Faraday exhibits most satisfactorily 
 the phenomena of induced currents, 
 and the changes of their directions. 
 A pair of zinc and copper plates, z c, 
 were immersed in diluted acid ; G and 
 E represent cups of mercury, wherein 
 contact was made and broken with 
 the wires A B, which formed a circuit 
 through a long conducting wire ; two 
 wires, N P, were attached to the long 
 circuit, and could be brought into 
 contact at x, or have an apparatus in- 
 terposed there to indicate the direc- 
 tion and force of the induced currents. 
 To produce a spark in the cross-wire 
 junction, apiece of soft iron was placed 
 in a helix at D, and the ends of the 
 cross wires were rubbed lightly to- 
 gether whilst contact was broken at G or E by raising the wires A or B 
 quickly from the mercury. In such circumstances a bright spark passed at 
 x at the moment of breaking contact, none occurring at G or E ; this spark 
 exhibited the luminous passage of the extra current through the cross 
 wires. When there was no contact at x, then the spark appeared in the 
 mercury-cups when contact was broken ; the extra current forcing its 
 way through the cell of the pair of plates. On introducing a fine platinum 
 wire at x no visible effects occurred so long as the contact was continued, 
 but on breaking contact at G or E the fine wire was instantly ignited. 
 Chemical decomposition was also exhibited by the cross-wire current by 
 the introduction into the circuit of a piece of paper moistened with a solu- 
 tion of iodide of potassium ; but the points at which the iodine and the 
 potass appeared were the reverse of those at which they were disengaged 
 by the direct current. This proved that the momentary current induced 
 in the cross wires on breaking contact was in the contrary direction to the 
 primary current. The same fact may be more clearly shewn by the in- 
 troduction into the circuit of the cross wires of a galvanometer, an instru- 
 ment which will be more particularly noticed with electro-magnetic phe- 
 nomena. 
 
 In, addition to the induction of an electric current on breaking con- 
 tact, it has been satisfactorily proved that an extra current is also induced 
 on making contact ; the direction of the secondary current in that case 
 being the same as the primary. In reference to the specific action of 
 these induced currents of electricity Faraday observes : " From the facility 
 of transference to neighbouring wires, and from the effects generally, the 
 
120 THE PHENOMENA OF ELECTRICITY. 
 
 inductive forces appear to be lateral, i. e. exerted in a direction perpendicular 
 to" the direction of the originating and produced currents. There can be no 
 doubt that the current in one part of a wire can act by induction upon 
 other parts of the same wire which are lateral to the first, i. e. in the same 
 vertical section, or in the parts which are more or less oblique to it, just 
 as it can act in producing a current in a neighbouring wire or in a neigh- 
 bouring coil of the same wire. It is this which gives the appearance of 
 the current acting upon itself ; but all the experiments and all analogy 
 tend to shew that the elements (if I may so say) of the currents do not 
 act upon themselves, and so cause the effect in question, but produce it 
 by exciting currents in conducting matter which is lateral to them." He 
 also gives this important opinion : " Notwithstanding that the effects 
 appear only at the making and breaking of contact, I cannot resist the 
 impression that there is some connected and correspondent effect pro- 
 duced by this lateral action of the elements of the electric stream during 
 the time of its continuance." 
 
 CHAPTER XIV. 
 
 ELECTRO-CHEMICAL DECOMPOSITION. 
 
 Decomposition of water Transference of the elements through intermediate vessels 
 Faraday's hypothesis Infinitessimally small particles acted on Suspension of che- 
 mical affinity by Voltaic action Supposed identity of chemical affinity and electri- 
 city Decomposition of the alkalies Remarkable combustion of paper by Voltaic 
 action Decompositio 't me allic s De nte action ofelectro- chemical force 
 Electro-chemical equivalents Absolute 'quantity of electricity in bodies The 
 quantity in a grain of water estimated The Voltameter. 
 
 WE have already noticed that a succession of sparks from an electrical 
 machine, or a succession of discharges from a small Leyden jar, can pro- 
 duce the decomposition of many compound substances; and that in such 
 decompositions certain elements attach themselves to the positive, and 
 others to the negatively electrified wires. These effects, and this pecu- 
 liarity of action, which are observable only on a very limited scale in 
 frictional electricity, are largely and powerfully developed by the voltaic 
 battery. 
 
 The decomposition of water affords one of the simplest and most satis- 
 factory exhibitions of the decomposing power of voltaic electricity. A 
 single pair of plates, when excited by diluted sulphuric acid, is not 
 sufficient to produce the effect. The addition of another pair of plates 
 imparts the required intensity, but only enough to exhibit the phenomena 
 of decomposition in a feeble manner. With a combined series of twelve 
 cells most compound substances may be resolved into their elementary 
 constituents very satisfactorily. When the connecting wires from the op- 
 posite poles of such a battery are inserted into a glass containing acidu- 
 lated water, there will be a copious discharge of gas from each, if the wires 
 are tipped with platinum, the discharge from one of the points j being 
 more copious than from the other. 
 
ELECTRO-CHEMICAL DECOMPOSITION. 
 
 121 
 
 The form of apparatus represented in fig. ol is well adapted for the 
 collection of the products of the decomposition of water. Two glass tubes 
 A, B, closed at the top, are filled with water slightly acidulated, and then 
 inverted in a glass vessel of the same fluid, and held in position by the 
 wooden lid D. To the bottom of the binding screws E, E, thick copper 
 wires are soldered, which are bent under the tubes. The copper wires 
 must be well varnished, excepting at their ends, which should be tipped 
 with platinum. The wires from the battery 
 are connected to the apparatus by the binding 
 screws. When the battery is put in action, 
 a discharge of bubbles of gas takes place 
 from the ends of the two wires, which, rising 
 through the water in the tubes, collect at the 
 top of each. The quantity of gas evolved at 
 the negative conducting surface exceeds that 
 evolved at the positive surface, in the pro- 
 portion of two to one, the former being 
 hydrogen gas and the latter oxygen, in the 
 exact proportions in volume that, when che- 
 mically combined, constitute water. When 
 the positions of the wires connected with the 
 poles of the battery are reversed, the hydro- 
 gen and oxygen are evolved from the oppo- 
 site points ; and under whatever circum- 
 stances the experiment is conducted, it is accompanied with the same 
 result, even when decomposition is effected in separate vessels. 
 
 Let the three glass vessels, 1, 2, 3, containing acidulated water, be 
 arranged as in fig. 52, connected with filaments of wetted thread or asbes- 
 tos b b', and introduce into the two extreme glasses small strips of pla- 
 tinum-foil connected with the opposite poles of a voltaic arrangement. 
 
 fig. 51. 
 
 fig. 52. 
 
 When the voltaic current passes from c the positive surface, to z the nega- 
 tive, oxygen gas will be evolved in No. 3, and hydrogen in No. 1, in the 
 exact proportions that they were liberated when the wires were inserted 
 in the same vessel. Under these circumstances, it will be observed that 
 the hydrogen element of the particle of water decomposed, which is sepa- 
 rated from the association with oxygen at c, must pass through the fila- 
 ments &', through the fluid in the central vessel, through the second fila- 
 ments b, and through the water in glass 1 to z, where it is evolved. No 
 variation in the amount of battery power employed produces any altera- 
 tions in the proportions of the gases evolved : the only difference attend- 
 ing the increase of the electric force is to increase the quantity of the 
 gases evolved, the proportions being in all cases those that combine to- 
 gether to form water. When the experiment is arranged with conducting 
 
122 THE PHENOMENA OF ELECTRICITY. 
 
 surfaces of metals that easily combine with oxygen, hydrogen only is evolved, 
 the oxygen portion of the decomposed water entering into combination 
 with the metal. It is for this reason that, when the two gaseous products 
 of the decomposition are required to be collected, platinum or gold points 
 should be used. 
 
 If we assume that the process of decomposition is strictly limited to 
 the same particle of water, and that the separation of its two elements 
 takes place either at c or z ; that portion of the elemental gas which ap- 
 pears at the other wire must traverse invisibly through the three vessels, 
 must rise through the two bundles of filaments, and descend again, 
 without any portion of it escaping. But according to the view taken by 
 Faraday of voltaic decomposition, as already explained,* the process is 
 not confined to a single particle of the fluid, but each particle in the chain of 
 communication is decomposed. Thus, commencing at c (fig. 41), the particle 
 of water decomposed yields up its oxygen at that point, and the gas rises 
 directly to the surface. The adjoining particle of fluid is also decomposed, 
 but latently, the oxygen separated from that second particle instantly com- 
 bining with the hydrogen liberated from the first, and parting with its 
 own atom of hydrogen to the next particle ; this transfer of the hydrogen ele- 
 ment being continued through all the particles of fluid in succession until 
 it arrives at the other battery termination, where, the series of decomposi- 
 tions being ended, the hydrogen is liberated and rises to the surface as a 
 bubble of gas. According to this hypothesis, which has received very 
 general acceptation, the hydrogen liberated in bubbles at one wire is not 
 the same that was associated with the oxygen evolved at the other pole, 
 but there is a complete cycle of voltaic changes, each particle of fluid in 
 the chain of communication having undergone decomposition and recom- 
 position with different though exactly equal atoms of the same element. 
 
 The particles of water acted on during decomposition are most proba- 
 bly infinitessimally small. A bubble of hydrogen gas the one hundredth 
 part of an inch in diameter is distinctly visible, and one million of such 
 bubbles would be contained in a cubic inch. Assuming the bubbles to 
 constitute an entire cube of gas, fifty of such cubes would weigh only 
 a single grain ; and taking into calculation the oxygen element of the 
 water, the evolution of a bubble of hydrogen gas T ^th of an inch in dia- 
 meter indicates that a particle of water has been decomposed which could 
 not have weighed more than the sixteen-millionth part of a grain. 
 
 The arrangement of the three glass vessels with asbestos connexions 
 (fig. 52) will serve to illustrate, in a still more remarkable manner than 
 the decomposition of water, the peculiarity attending the transfer of the 
 elements of the decomposed body through an intermediate solution. A 
 solution of muriate of soda (common salt) being put into glass 1, a solu- 
 tion of ammonia in 2, and an infusion of litmus in 3, it will be found that 
 the muriatic acid combined with the soda in No. 1 will be transferred 
 through the ammonia without combining, and will be collected in the glass 
 containing the litmus, as will be indicated by colouring it red. In this 
 case, therefore, it will be observed that the acid separated from the salt in 
 No. 1 is conveyed through a solution for which it has, in ordinary circum- 
 stances, a strong chemical affinity ; but under the influence of voltaic elec- 
 tricity the action of chemical affinity appears to be suspended. 
 
 * Page 100. 
 
ELECTRO-CHEMICAL DECOMPOSITION. 123 
 
 In the same manner the elements of numerous other compound sub- 
 stances may be transferred through solutions of alkalies or acids without 
 exhibiting any disposition to combine. This peculiar influence of the 
 electric current is confirmatory of Faraday's hypothesis respecting the 
 mode of electric conduction through fluids. By that hypothesis the appa- 
 rent suspension of chemical affinity in the intermediate vessel is attributed 
 to the continued transfer of the acid from particle to particle of the fluid 
 with which it ultimately combines, no free acid being actually liberated 
 till the chain of connexion is terminated by arriving at the opposite pole 
 of the battery. 
 
 The powerful influence of voltaic electricity in controlling chemical 
 affinities led Sir Humphrey Davy to infer that chemical affinity is itself 
 a modification of electric attraction, and that those bodies which com- 
 bine most energetically possess inherently, and in the greatest degree, 
 positive and negative electricities. Considering, therefore, chemical af- 
 finity and electricity to be identical, he conceived that the voltaic battery 
 would afford the means of separating the most intimately combined 
 elements by overpowering the attractive force with which they are held 
 together. Acting on this opinion, he applied the power to the alkalies, 
 which he and other chemists had predicted to be compound substances. 
 The result of these investigations constitutes one of the greatest triumphs 
 of analytical chemistry ; for by this means those important substances, 
 the earths and alkalies, were discovered to be oxides of peculiar metals, 
 distinct in many of their qualities from any of the metallic bodies pre- 
 viously known. 
 
 The battery power employed by Sir Humphrey Davy was equal to 
 that of 274 pairs of plates four inches square ; but even with this 
 powerful apparatus it was not till after numerous failures that he suc- 
 ceeded in decomposing potass. The difficulty experienced was to bring 
 the voltaic influence to act upon the alkali ; for in a dry state the non- 
 conducting property of the potass stopped the electric current, and when 
 dissolved, the power of the battery was spent in the decomposition of the 
 aqueous solvent. To apply the electric force to the alkali itself, Sir Hum- 
 phrey Davy adopted the expedient of making a crystal of potass transmit 
 a current by the moisture of the breath on its surface. This had the desired 
 effect, and the appearance of a globule of metal (potassium) at the nega- 
 tive pole of the battery was a glorious reward for his intelligent and 
 persevering investigations. 
 
 The decomposition of the alkalies does not, however, require a 
 powerful voltaic arrangement. This fact was experienced by the author 
 in a somewhat annoying manner when experimenting with the copying 
 electric telegraph, the action of which depends on making marks on 
 paper by electro-chemical decomposition. The paper was well moist- 
 ened with a solution of prussiate of potass in diluted nitric acid, and 
 the voltaic current passed through the paper from a steel wire con- 
 nected with the positive pole of the battery. The effect intended to be 
 produced was to decompose the prussiate, and to cause it to combine with 
 the iron of the wire to make a blue mark on the paper. The battery 
 power employed consisted of two troughs of a Cruikshank's arrangement, 
 each containing fifty pairs of plates two inches square. With this battery 
 the paper was not only marked with a deep blue line as the steel wire was 
 
124 THE PHENOMENA OF ELECTRICITY. 
 
 drawn along, but when not moving rapidly it was actually set on fire, for 
 a small bright flame accompanied the steel, and burnt holes through the 
 paper. The cause of this combustion was at first perplexing, as paper 
 cannot be ignited by the direct action of voltaic electricity however 
 powerful. The smell of hydrogen gas shortly resolved all doubt, by indi- 
 cating the combustion of potassium. The voltaic current, small in quan- 
 tity as it was, had decomposed the prussiate-of-potass solution in the 
 paper ; and as quickly as potassium was formed, it was inflamed by com- 
 bining with the oxygen of the aqueous solvent. 
 
 The decomposition of metallic salts by voltaic electricity deserves 
 special consideration, from the circumstance that it forms the basis of the 
 important art of electro-metallurgy, which has already become of great 
 practical utility, and promises to be extended much more generally. 
 
 The processes of electrotyping and electro-gilding will be particularly 
 noticed among the applications of electric science ; we shall now, there- 
 fore, only consider the nature of the action of electricity in producing 
 metallic deposits. 
 
 When a voltaic current is transmitted through a solution of sulphate 
 of copper, the water which holds the metallic salt in solution is the substance 
 decomposed, the deposition of the metal being a secondary result. The 
 hydrogen, disengaged from its particle of water at the conducting surface 
 connected with the positive pole of the battery, on being transferred to the 
 negative surface combines with the oxygen that holds the copper in so- 
 lution, and the metal is deposited. Thus, when small plates of copper 
 connected with the poles of the battery are inserted in the solution, the 
 oxygen liberated from the decomposed water is not evolved, but enters 
 into combination with the copper, and forms with the sulphuric acid a 
 particle of sulphate of copper, which is immediately dissolved. Neither is 
 the hydrogen on reaching the metal plate connected with the negative 
 pole evolved in the form of gas, but it combines with a quantity of oxygen 
 in the metallic solution, equal to the quantity with which it was associated 
 in the original particle of water decomposed, and thus forms a new particle 
 of water ; whilst the copper, held in solution by the oxygen, is deposited 
 over the surface of the metal plate. By the continuation of the process 
 the copper from the positive plate is gradually transferred to the negative 
 plate ; not, it will be observed, by the direct decomposition of the sulphate 
 of copper held in solution, but by the action and reaction of the oxygen and 
 hydrogen liberated from the decomposed water. 
 
 There is great difference in the facility with which different compound 
 substances yield up their elements to the controlling force of voltaic action. 
 Iodide of potass may be decomposed by a single pair of plates feebly 
 charged. Muriatic acid and diluted sulphuric acid may be decomposed 
 with a single pair when the energy is increased by nitric acid, but a com- 
 bination of three or more plates is generally required to produce decom- 
 position in other bodies. This difference in the facility with which dif- 
 ferent bodies may be decomposed by an electric current is attributed to 
 the different intensities of their chemical affinities, those substances whose 
 atoms are held together by the strongest affinities offering greatest resist- 
 ance to the decomposing force. 
 
 The interesting and important fact has been clearly established by 
 Faraday, that electro-chemical force is definite in its action, and that the 
 
ELECTRO-CHEMICAL DECOMPOSITION. 125 
 
 chemical power of a current is in direct proportion to the absolute quan- 
 tity of electricity that passes. The expression of the theory by Faraday 
 is, " that the chemical decomposing action of a current is constant for a 
 constant quantity of electricity, notwithstanding the greatest variations in 
 its sources, in its intensity, in the size of the electrodes used, in the nature 
 of the conductors (or non-conductors) through which it is passed, or in 
 other circumstances."* 
 
 The demonstration of this theory by numerous experiments tends 
 strongly to confirm the opinion that electricity and chemical affinity are 
 the same force differently modified ; for it is found that the amount of 
 decomposing effects in all substances agrees very closely with their chemi- 
 cal equivalents. 
 
 To those not acquainted with the nature of chemical combinations, it 
 may be desirable to state that the elements of bodies always unite in defi- 
 nite proportions ; for instance, eight atoms of oxygen unite with one of 
 hydrogen to form water, and one atom of oxygen combines with five of 
 potassium to constitute potass ; and those elements will not combine in 
 any other proportions. Many elementary substances unite differently to 
 form different substances, but those proportions are always multiples of 
 the first, and for the constitution of any given substance they will only 
 combine in constant definite proportions. For example, if oxygen and 
 hydrogen gases are mingled together in the proportions of ten to one, and 
 then exploded in a close vessel, it will be found that chemical combination 
 has taken effect only between those quantities of the gases required to 
 form water, and that the two portions of oxygen in excess remain in the 
 vessel not affected by the explosion. 
 
 The law by which the combination of elements is regulated in definite 
 proportions to constitute any single substance, is found also to extend re- 
 ciprocally to all substances whatever. The operation of this law is clearly 
 exemplified in the mutual action of acids and alkalies. Thus, six parts of 
 potass neutralise five of sulphuric acid, and four parts only of soda produce 
 the same effect. These proportions of six to four prevail in the relations 
 of potass and soda to all the acids; and this being known, the quantity of 
 either required to saturate any other acid can be ascertained without expe- 
 riment. For instance, as the saturating power of soda for sulphuric acid 
 exceeds that of potass in the inverse proportion of four to six, and it 
 being known that 4-4 parts of potass saturate five of nitric acid, it is easily 
 computed that as6 :4'4 ::4 : 2 93 ; the number 2 93 representing the 
 parts of soda equivalent to potass in saturating nitric acid. The equivalent 
 proportions in which all bodies combine with one another may thus be 
 computed, after having determined experimentally the proportions of one 
 or two combinations. 
 
 The amounts of electric force required to separate the elements of 
 bodies from their combinations correspond in a remarkable manner with 
 the chemical equivalents of the same bodies. For instance, 8 parts by 
 weight of oxygen, which combine with 1 of hydrogen to form water, 
 combine in the proportions of 32 with copper, 58 with tin, and of 103 
 with lead ; and the same amount of electric force that is required to sepa- 
 rate 8 parts of oxygen from water, will, by secondary action, separate 
 
 * Experimental Researches, series vii. 
 
126 THE PHENOMENA OF ELECTRICITY. 
 
 copper, tin, and lead from their solutions in the proportions of 32, 58, and 
 103 ; corresponding with their chemical equivalents. So closely have these 
 numbers been found to agree in numerous experiments, that electricians 
 do not hesitate to apply the more strict results of direct chemical analysis 
 to the correction of the results of electro-chemical decomposition.* In 
 reference to this subject, Faraday observes, " I think I cannot deceive my- 
 self in considering the doctrine of definite electro-chemical action as of the 
 utmost importance. It touches by its facts, more directly and closely 
 than any former fact or set of facts have done, upon the beautiful idea 
 that ordinary chemical affinity is a mere consequence of the electrical 
 attractions of the particles of different kinds of matter ; and it will pro- 
 bably lead us to the means by which we may enlighten that which is at 
 present so obscure, and either fully demonstrate the truth of the idea, or 
 develop that which ought to replace it." 
 
 The discovery of the law of the definite action of electro-chemical force, 
 and that the chemical power of an electric current is in direct proportion 
 to the quantity of electricity that passes, has shewn the way to the deter- 
 mination of the absolute quantities of electricities belonging to different 
 bodies in their natural states. This interesting subject of inquiry is opened 
 by Faraday in the seventh series of his invaluable Experimental Researches 
 in Electricity. " Considering," he observes, " this close and twofold rela- 
 tion, namely, that without decomposition transmission of electricity does 
 not occur, and that for a given definite quantity of electricity passed, an 
 equally definite and constant quantity of water or other matter is decom- 
 posed ; considering also that the agent, which is electricity, is simply em- 
 ployed in overcoming electrical powers employed in the body subjected to 
 its action ; it seems a probable and almost a natural consequence, that the 
 quantity which passes is the equivalent of, and therefore equal to, that of 
 the particles separated ; i. e. that if 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, could be thrown into the form of a current, it would 
 exactly equal the current required for the separation of that grain of water 
 into its elements again." 
 
 The enormous quantity of electric power contained in a single grain of 
 water is exemplified by the following experiment. 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 acidulated water consisting of one drop of oil of 
 vitriol and four ounces of distilled water, and connected at the other ex- 
 tremity by a copper wire eighteen feet long and one-eighteenth of an inch 
 in thickness, yields as much electricity in little more than three seconds of 
 time as a Leyden battery charged by thirty turns of a very powerful elec- 
 trical machine in full action. This quantity, though sufficient if passed 
 at once through the head of a cat to kill it, is evolved by the action of so 
 small a portion of the zinc and water, that the loss of weight sustained 
 by either is inappreciable by the most delicate instruments. 
 
 By continuing the experiment until a grain of water was decomposed, 
 it was ascertained that one grain of water requires for its decomposition a 
 
 * Experimental Researches, series vii. 
 
ELECTRO-CHEMICAL DECOMPOSITION. 
 
 127 
 
 continued current of electricity for three minutes and three quarters, which 
 current must be powerful enough to retain a platinum wire y^th of an 
 inch in thickness red-hot in the air during the whole time. Making a 
 comparison by the loss of weight of zinc oxidised during the action, it 
 appears that 800,000 such charges of a Leyden battery as that referred to 
 would be necessary to supply electricity sufficient to decompose a single 
 grain of water. Thus, " zinc and platinum wires one-eighteenth of an 
 inch in diameter and about half an inch long, dipped into dilute sulphuric 
 acid so weak that it is not sensibly sour to the tongue or scarcely to our 
 most delicate test-papers, will evolve more electricity in one-twentieth of 
 a minute than any man would willingly allow to pass through his body at 
 once. The chemical action of a grain of water upon four grains of zinc 
 can evolve electricity equal in quantity to that of a powerful thunder- 
 storm."* 
 
 In further proof of the high electric condition of the particles of mat- 
 ter, and of the equality of proportions of that belonging to them with 
 that necessary for their separation, Faraday carefully collected the results 
 of the action of an amalgamated zinc plate and a plate of platinum when 
 immersed in diluted sulphuric acid in the proportion of 1 of acid to 30 of 
 water. The quantity of oxygen and hydrogen gases evolved measured 
 18-232 cubic inches ; equal in weight to 2-3535544 grains, which was 
 therefore the weight of the water decomposed. The weight of the zinc 
 plate was diminished 8 - 45 grains ; and 2*3535544 grains, the weight of 
 water decomposed, is to 8-45, the quantity of zinc oxidised, as 9 is to 
 32-31. These numbers correspond with the equivalent numbers of water 
 and zinc ; which shews that for an equivalent of zinc oxidised, an equiva- 
 lent of water was decomposed. 
 
 The decomposing power of electricity has been employed as a mea- 
 surer of the strength of a voltaic current. The fact that the amount of 
 decomposition is proportioned to the quantity of electricity being taken 
 for granted, it is only necessary to measure the quantity of gases evolved 
 from water within a given time, to determine the force of the electric 
 current. Instruments of this kind were contrived by 
 Faraday, and were frequently used by him in his experi- 
 mental researches. Fig. 53 represents the form of the in- 
 strument suitable for general experiments. A graduated 
 tube D, of even bore, is ground or cemented into one of the 
 openings of a two-necked bottle, B. Two platinum wires, 
 pp', are fused into the glass and penetrate within the tube, 
 where they are connected with two small platinum plates. 
 If the bottle be two-thirds full of diluted sulphuric acid, 
 the fluid will fill the tube when the bottle is inverted, and 
 will not flow out when placed upright. An electric cur- 
 rent being then passed through the tube by connexion 
 with the wires p p', the gases evolved against the plates col- 
 lect at the top, and the quantities are measured by the dis- 
 placement of the water. When the instrument is in use 
 the stopper is taken out of the second opening, to allow 
 the enclosed air to escape as the water descends from the 
 tube. 
 
 * Experimental Researches. 
 
 iig. 53, 
 
128 
 
 THE PHENOMENA OF ELECTRICITY. 
 
 CHAPTER XV. 
 
 ELECTRO-MAGNETISM. 
 
 Effect of Voltaic currents on magnetic needles -Magnetism induced in the conducting 
 wire Directions of deflected magnetic needle by opposite currents Multiplication 
 of effect by coils of wire Galvanometers, their extreme sensitiveness Magnetic 
 action of copper wires Polar direction of a wire coil Electro-magnets Their 
 great power and limited spheres of attraction Ratio of diminution of attractive 
 force Proportionate sizes of wire and iron Economical effect of long coils Great 
 rapidity of electro- magnetic action Residual power in electro-magnets Medical 
 coil machines Rotary motion of conducting wires. 
 
 A CURRENT of electricity transmitted by wires from one end of a voltaic 
 battery to the other meets with great resistance, even when passino- 
 through the metals' that are the best conductors. The amount of this 
 resistance, it has been already stated, is proportioned to the square of the 
 diameter ; and it increases rapidly, in some ratio not exactly ascertained, 
 with the length of the conducting wire. The action and reaction that 
 are thus continually in operation during the passing of a voltaic current 
 produce remarkable magnetic effects, which extend to a considerable dis- 
 tance beyond the surfaces of the conductors. 
 
 The influence of frictional electricity in magnetising and demagnet- 
 ising steel needles was known to Franklin and other of the early elec- 
 tricians ; but it was reserved for Professor (Ersted of Copenhagen to 
 discover, in 1819, the much greater magnetising influence of a current of 
 voltaic electricity ; and that that influence is exerted, not by transmitting 
 the current directly through the bar to be magnetised, but by a secondary 
 action m the conducting wire. 
 
 If a thick copper wire c z, connected with the opposite poles of a 
 voltaic battery, be placed over a magnetic needle N s balanced on its 
 centre like the needle of a compass, and in the line of the magnetic me- 
 ridian, the needle will be deflected the instant that the current passes 
 through the wire ; and it will remain deflected from its natural position in 
 a greater or less degree according to the strength of the current. If the 
 current from the copper, or positive, pole of the battery pass from the 
 north to the south pole of the magnetic needle, the deflection will be 
 towards the east; but if the current pass in the opposite direction, the 
 flection of the needle will be towards the west. If the wire be then placed 
 
 below the needle, the action will 
 
 * * ..I be reversed: the north pole of 
 
 the needle, which was deflected 
 to the west when the wire was 
 
 above it, will be deflected to the 
 east. A similar reversal of the 
 fig. 54. deflections of the needle occurs 
 
 when the direction of the electric 
 
 current is changed by reversing the positions of the connecting wires. 
 The conducting wire seems to be endued with polarity at right angles 
 
ELECTRO-MAGNETISM. 
 
 129 
 
 to its axis, as if an infinite number of small magnets were ranged side 
 by side transversely to the direction of the current. The transmission of 
 the electric current, indeed, appears to convert the conducting wire into a 
 compound cylindrical magnet, every point of the surface of the cylinder 
 being a magnetic pole with its opposite pole in the centre of the wire. 
 
 It is not essential that the conductor should be metal. Charcoal, and 
 even acids, will, when conducting a current of electricity, become tem- 
 porary magnets, and deflect the magnetic needle when it is placed parallel 
 to the flow of electricity. The same power is exerted by the battery 
 itself; for if a long magnetic needle be suspended from its centre over the 
 cells of a voltaic arrangement, it will be deflected in the same manner as a 
 needle balanced over a conducting wire. 
 
 As the needle is deflected in opposite directions when the wire is 
 placed above and when it is below, it appears, on the first view, as if the 
 magnetic influence were changed by the al- 
 teration of position ; but the change is in 
 reality only apparent. Let cz, c' z' represent 
 the conducting wire, with the current passing 
 in the direction of the arrows from c to z. The 
 magnetic needle n s is balanced on a pivot 
 fixed to the wire, so that it may be turned 
 round with it ; and being held in a vertical 
 position, and a trifle heavier at one end, it 
 will not be affected by terrestrial magnetism. 
 The wire on the left in the figure shews the 
 north pole of the needle deflected towards the 
 right hand. Turn the wire gradually round 
 until it is brought into the other position, 
 and then the north pole of the needle seems 
 to be deflected in the contrary direction, 
 though in relation to the wire it has re- 
 mained unchanged ; the apparent difference 
 being caused entirely by its being seen from the opposite side. 
 
 Bend the conducting wire zc into the form of a rectangle, and place a 
 balanced magnetic needle in the centre of it, as in fig. 56 ; the end c of 
 the wire being connected with the positive pole of the battery, and the 
 end z with the negative, or zinc end. The effect of this arrangement on 
 the needle will be, in the first place, to deflect N towards the east by the 
 influence of the current from c pass- 
 ing over the needle from north to 
 south. The same current, if it were 
 to return over the needle from s to N, 
 would neutralise its first influence 
 by the change of direction, and would 
 bring the needle back to its original 
 position. But by passing under it, 
 the direction of the current in refer- 
 ence to the needle is reversed, and fi 56 
 the influence is exerted to increase 
 
 the first deflection towards the east, and the force of the current is thus 
 doubled. By bending the wire again in the same manner an additional 
 
 fig. 55. 
 
 II 
 
 3ST. 
 
130 
 
 THE PHENOMENA OF ELECTRICITY. 
 
 effect is produced ; and by numerous reduplications of this kind the in- 
 fluence of the current may be so multiplied, that the needle will be de- 
 flected by a quantity of electricity far too miuute to have any sensible 
 effect if passed over it through a single wire. 
 
 It will, perhaps, render this double action of the voltaic current on the 
 
 1 
 
 fig. 57. 
 
 needle more clear if the same arrangement be placed vertically, as in 
 fig. 57. The electric current from the positive pole of the battery passing 
 from the north to the south pole of the needle, deflects it towards the 
 right hand of a spectator placed in the position of e, and towards the left 
 hand of a spectator at e'. The same current on its return towards z passes 
 from the south to the north pole of the needle ; but as it passes on the 
 opposite side, the return current tends further to deflect the needle in the 
 same direction, and it continues to point to the right hand of the spec- 
 tator at e, and to the left hand of the spectator at e', instead of changing 
 positions as it appears to do in fig. 55, when seen on opposite sides during 
 the passing of a single current. 
 
 The instruments called galvanometers, employed for indicating the 
 presence of a feeble electric current, are constructed on the foregoing prin- 
 ciple ; and as each coil of wire that surrounds the needle seems to increase 
 the effect, it might be supposed that the sensitiveness of such an instru- 
 ment could be indefinitely extended. But there are limits to the length 
 of the wire-coil, beyond which the sensitiveness of the needle is diminished 
 instead of being increased. For instance, the influence of the conducting 
 wire diminishes with its distance from the needle, and that distance 
 becomes greater and greater with each additional superposed coil. With 
 a view to increase the number of spirals as much as possible without 
 lessening the effect by increased distance, very fine wire is used ; which 
 being carefully covered with silk or cotton, to prevent lateral conduction, 
 may be wound on a rectangular bobbin close together, having a space in 
 the middle for the introduction of the magnetic needle. In the galva- 
 nometers employed for the electric telegraph it is customary to wind 
 round the needle about 150 yards of covered wire as fine as a hair. But 
 when such a length of very fine wire is used, the great resistance it offers 
 
ELECTRO- MAGNETISM. 
 
 131 
 
 to the passage of the electric current operates materially against the sen- 
 sitiveness of the instrument, and currents of feeble intensity meet with 
 so much obstruction that the quantity which passes is scarcely appreciable ; 
 the otherwise augmenting effect of the reduplication of the wire being 
 more than counterbalanced by the increased resistance. 
 
 Asa magnetic needle when suspended horizontally is attracted towards 
 the north and south by the magnetism of the earth, it is necessary, when 
 a single needle galvanometer is used, to place the coil in the magnetic 
 meridian parallel to the needle ; but the sensibility of the instrument is 
 diminished by the directive influence of the earth, which tends to prevent 
 the deflection. This defect may, however, be remedied, by attaching to 
 the vertical support of the needle within the coil a second magnetised 
 needle above the coil, with its poles in a reversed position ; so that the di- 
 rective tendency of the one being overcome by that of the other, the 
 needle remains in a neutral state in whatever position it may be placed. 
 This contrivance, which was first applied by Professor Gumming of Cam- 
 bridge, and afterwards improved upon by Chevalier Nobili, has given such 
 increased sensitiveness to the galvanometer that it indicates the presence 
 of the most minute trace of a voltaic current. 
 
 Fig. 58 represents one of the approved forms of this kind of galvano- 
 meter, which has obtained the name of " astatic multiplier." A bent 
 
 fig. 58. 
 
 standard D screwed into the mahogany base M M serves as a support 
 whence the magnetised needles n s, s ri are suspended by a filament of unspun 
 silk or by a human hair. The coil A A is formed of copper wire one-sixtieth 
 of an inch in diameter and two hundred feet long, carefully covered with 
 silk.* The coil is made by binding the wire round a thin wooden frame, 
 the top and bottom of which are about two inches square and half an inch 
 apart. The ends of the wire pass through the base, and are soldered to 
 the binding screws B B. The needles are formed of pieces of thin watch- 
 spring, flattened and strongly magnetised, or fine light sewing needles will 
 answer the purpose. They are fixed on to a piece of straw with their 
 
 Messrs. Watkins and Hill had a very delicate galvanometer at the Great Exhibi- 
 tion, the coil of which contained 230 yards of wire yi^th of an inch in diameter. 
 
132 THE PHENOMENA OF ELECTRICITY. 
 
 poles in opposite directions, the straw being attached vertically to the sus- 
 pending hair. One of the needles is within the coil, the other about a 
 quarter of an inch above it. A circular piece of card divided into 360 is 
 fixed on the top of the coil, the upper needle serving as the index to mark 
 the degrees of deflection. There are screws, not marked in the diagram, 
 for adjusting the card and the needles to their proper positions, and the 
 instrument is covered with a glass shade E E to protect the needle from 
 the influence of currents of air. 
 
 When it is required to examine the development of electricity, con- 
 nexions are made with the binding screws B B, so that the current may 
 pass through the coil and deflect the needle. The intensity of the current 
 is generally as the sine of the angle of deviation. This instrument is so 
 extremely sensitive in its indications of an electric current, that if a drop 
 of water be placed on the top of one of the brass binding screws, and it is 
 touched with a zinc wire connected with the other binding screw, the 
 needle will be deflected. The galvanometer is specially valuable in expe- 
 riments with feeble currents of voltaic electricity, which are altogether in- 
 appreciable either by the gold-leaf electrometer or the voltameter. 
 
 In the preceding illustrations of the magnetic properties of a wire con- 
 ducting an electric current, the peculiarity of the phenomenon is, in some 
 degree, masked by the intervention of the magnetic needle. Other expe- 
 riments shew more directly that the copper wire through which the cur- 
 rent passes is for the time converted into a magnet. 
 
 Twist three feet of covered copper wire, about the thickness of bell-wire, 
 round a pencil, so as to form, when the pencil is withdrawn, a hollow 
 compact coil of wire, in form like a common bell-spring. Support the 
 coil horizontally on a pivot, so that it may turn round freely, and let the 
 wires at the ends dip into concentric cells of mercury, as represented in 
 fig. 59, each cell being connected with one of 
 the poles of a voltaic battery. The instant that 
 the current is sent through the coil it will begin 
 to oscillate, and after a short time will place 
 itself in the magnetic meridian. If a magnet 
 be brought near to either end of the coil, it 
 will be attracted by one of the poles and be 
 repelled by the other, exactly in the same 
 manner as a steel magnet similarly poised. On 
 reversing the connecting wires, so as to send 
 fig . 59. the current through the coil in the contrary 
 
 direction, the magnetic poles will be changed, 
 
 as will be indicated by the turning round of the coil, the end that before 
 pointed to the north being then directed towards the south. 
 
 The direction in which the wire of the coil is twisted also influences the 
 position of the poles. When twisted from right to left, the current from 
 the copper end of the battery will impart different polarity to that which a 
 coil twisted from left to right possesses. That end of the coil at which the 
 positive current is transmitted from left to right always points towards 
 the north. 
 
 If the coil be doubled on itself by continuing to twist the wire in the 
 same direction over the first single spiral, the magnetic properties will be 
 considerably increased ; and they will continue to be increased by adding 
 
ELECTRO-MAGNETISM. 
 
 133 
 
 to the thickness of the coil, until the resistance offered to the current by 
 the increased length of wire counteracts the multiplying tendency of the 
 redoubled wires. The magnetic power of such a coil becomes wonderfully 
 augmented by introducing a bar of soft iron within it. The iron becomes 
 in that case powerfully magnetic the instant that contact is made with the 
 voltaic battery, and the magnetism ceases almost as instantaneously when 
 the electric circuit is broken. 
 
 The electro-magnet thus formed by surrounding a bar of soft iron with 
 covered copper wire owes its magnetic property entirely to the electric cur- 
 rent that circulates round it. The iron seems to act as a conductor and 
 concentrator of the force, and appears to bear the same relation to the coil 
 that the metallic coating does to the glass of a Leyden jar. It may be 
 presumed that the same amount of magnetism is excited when the iron 
 bar is withdrawn from the coil as when it is inserted ; but without it the 
 power is diffused through the wire, and is not concentrated so completely 
 at the poles. Iron possesses almost exclusively the peculiar property of 
 thus conducting and concentrating the magnetic force. Even a steel bar 
 produces scarcely any effect when introduced within the coil, unless the 
 voltaic current proceeds from a combination of several pairs of plates ; and 
 when magnetism is thus imparted to steel, it does not disappear when the 
 voltaic circuit is broken, but the steel bar becomes a permanent magnet. 
 Why iron of all the metals should be thus peculiarly affected,* and why the 
 slight modification it undergoes in being converted into steel should pro- 
 duce such a change in its powers of receiving and retaining magnetism, 
 are at present among the unsolved mysteries of science. 
 
 A bar of soft iron bent into the 
 shape of a horse-shoe, and then co- 
 vered with coils of copper wire 
 twisted upon it in the same direc- 
 tion, constitutes an electro-magnet 
 of the most powerful kind. A 
 straight and flat piece of soft iron 
 N s, sufficiently long to reach across 
 the two ends of the bent bar, is at- 
 tracted towards it with more than 
 double the force that a single bar 
 magnet exerts. 
 
 That the force should be doubled 
 might have been expected, because 
 there are two poles acting on the 
 piece of iron instead of only one. The 
 additional attraction is occasioned 
 by the induction of magnetism in 
 the connecting piece, which is called 
 the keeper or armature of the mag- 
 net. That part of the keeper in connexion with the north pole of the 
 electro-magnet has southern polarity induced in it, and the opposite end 
 becomes a north pole. Thus the keeper, during the time of contact, 
 
 * Of the other metals, nickel possesses magnetic properties in the highest degree, 
 but the power is so feeble as not to deserve notice in this general survey. 
 
134 THE PHENOMENA OF ELECTRICITY. 
 
 becomes a second magnet, and the attractive power exerted between the 
 two is increased almost in the same proportion as if the keeper were a 
 permanent steel magnet. 
 
 An electro-magnet of the horse-shoe shape, half an inch in diameter 
 and five inches long, with three or four spirals of covered wire of the 
 thickness of bell- wire twisted round each limb in the same direction, and 
 excited by only a single pair of plates four inches square, will lift several 
 pounds. 
 
 The magnetic power to be obtained by a current of electricity very 
 far exceeds what can be permanently imparted to steel. An electro-mag- 
 net constructed by Mr. Joule was shewn in the Great Exhibition, 
 capable of lifting a ton weight ; and electro-magnets of larger size have 
 been made that lifted several tons. The most powerful permanent mag- 
 net in the Great Exhibition weighed 101 pounds, and lifted 436 pounds. 
 
 Though the attractive power of an electro-magnet is so enormous when 
 the surfaces of the keeper and of the magnet are in close contact, the 
 sphere of its influence is extremely limited. The thickness of a sheet of 
 paper introduced between them will diminish the power more than one 
 half, and at the distance of half an inch apart scarcely any attraction will 
 be perceptible. The influence of a permanent steel magnet extends con- 
 siderably farther than that of an electro-magnet. The ratio in which the 
 power decreases by distance has not, we believe, been determined; but 
 there is good reason to suppose that magnetism of both kinds obeys the 
 same law as all central radiating forces, and that the diminution is pro- 
 portioned to the square of the distance. 
 
 It may, indeed, appear at first sight irreconcilable with the observed 
 difference in the extent of the influence of permanent and electro magnets, 
 that the ratios of decrease should be alike in each ; but the seeming dis- 
 crepancy vanishes if we suppose the centre of attractive power to be more 
 deeply seated in the steel, which becomes permanently magnetic by some 
 retentive power in its particles combined together as a whole, than in the 
 soft iron, which acts only as a conductor of the magnetic force induced in 
 the copper wire by the electric current. 
 
 Figure 61 represents one of the poles of a permanent bar magnet. 
 Assuming the focus of attraction to be situated at c, a point equally dis- 
 tant from the sides of the bar and from the upper surface, then the lines 
 B c, DC, drawn to that centre, will shew by their radia- 
 tion the ratio of decrease of the magnetic power by dis- 
 tance in the same manner as, if c were the centre of an 
 emanating force, they would indicate its proportionate 
 diminution of energy. For example : let c be one quarter 
 of an inch from the upper surface of the steel bar, and 
 assume the attractive force at the surface to be equal to 
 lift one pound. Then, if the force diminish according to 
 the square of the distance, at a quarter of an inch from 
 the surface, that is at twice the distance from the centre 
 of force, the magnet would lift a quarter of a pound ; at 
 the distance of half an inch it would lift the ninth part of 
 a pound ; and at the distance of three quarters of an inch, 
 that is at four times the distance from the centre of 
 - 6L attraction, it would lift one-sixteenth part of a pound. 
 
ELECTRO-MAGNETISM. 
 
 135 
 
 Let us next consider the effect of the diminution of 
 force in an electro-magnet with a similar ratio of decrease. 
 The centres of attraction are assumed to be on the surface, 
 or, for the sake of calculation, one-hundredth part of an 
 inch beneath it ; the weight that the magnet will lift 
 being one pound, as in the former case. Then, assuming 
 the ratio of decrease to be the same, at three times the 
 distance from the surface that the surface itself is from any 
 of the centres of attraction, the power will be reduced as be- 
 fore to one ounce ; but the measured distance will now be 
 less than the thirty-third part of an inch, instead of three 
 quarters of an inch, for the point whence the ratio of 
 decrease commences is nearly on the surface of the magnet. 
 At the distance of three quarters of an inch the power 
 would be reduced to less than the five-thousandth part of 
 a pound. 
 
 The intensity of electro-magnets, or the spheres of their attractions, 
 increases with the intensity of the voltaic current, and with the number 
 of the coils of wire that surround them. Thus a bar of soft iron a quar- 
 ter of an inch in diameter, covered with numerous coils of fine wire, and 
 excited by a battery of twelve pairs of plates, will have a greater attrac- 
 tive distance than a bar half an inch diameter, with a fewer number 
 of coils of thick wire, and excited by a single pair of large plates, though 
 the latter magnet may sustain a heavier weight when the surfaces are in 
 contact. 
 
 In making an electro-magnet, regard should be had to the relative 
 thicknesses of the soft iron and the wire that is to form the coil. Small 
 bell-wire, number 16 gauge, is suitable for bar-iron half an inch in dia- 
 meter. A rod of about five inches should be bent into the form of a 
 horse-shoe, having each limb of equal length, and the two ends filed per- 
 fectly flat and even. A length of 
 100 feet of wire, carefully covered 
 with cotton, coiled round both limbs 
 in the same direction, either from 
 right to left or left to right, will 
 make a magnet which, when excited 
 by a current from two pairs of plates 
 six inches square, will lift upwards 
 of ten pounds. Mr. Shepherd, the 
 inventor of the gigantic electro- 
 magnetic clock of the Great Exhi- 
 bition, who has had great experience 
 in the construction of electro-mag- 
 nets, adopts a very convenient plan 
 for facilitating the winding of the 
 coils. The wire is not twisted im- 
 mediately upon the iron, but on se- 
 parate short lengths of brass tube of 
 
 sufficient diameter to admit the iron, fig 63. 
 
 which is inserted after the coils have 
 been separately made. By this means the coils of wire may be readily 
 
136 
 
 THE PHENOMENA OF ELECTRICITY. 
 
 wound to any length that is desired. The diagram represents the coils 
 and iron detached from each other. 
 
 A shorter length of thick wire will produce as strong an attractive 
 force as a long coil of thin wire, because though the multiplying effect by 
 the reduplication of the coils is less, it allows a much larger quantity of 
 electricity to pass- The use of the thick wire is, however, attended with 
 a greater loss of battery power. It is an object, in an economical point 
 of view, to extend the length of the coil as far as practicable without di- 
 minution of magnetic force, for by that means an equal amount of power 
 is gained with a feebler current ; the reduplication of the wire compensat- 
 ing by its repeated efforts for the diminished quantity of electricity which 
 will pass in a given time through the greater length of wire. 
 
 To illustrate the advantage 
 gained by numerous coils of 
 wire, let a voltaic current pass 
 through two electro-magnets A, B, 
 joined together in the same cir- 
 cuit ; A being large and covered 
 with a few coils of thick wire, 
 and B a smaller magnet with 
 numerous coils of fine wire. The 
 magnetism of A will be extremely 
 feeble at the same time that B is 
 fig- 64< energetically attractive ; though 
 
 when connected separately with a voltaic battery of a single pair of 
 plates, A may be the stronger magnet of the two. 
 
 The greater consumption of zinc in the battery in imparting magnetism 
 by short coils of thick wire is indicated by the rapid evolution of gas in 
 the cells when the circuit is short, compared with the action when it is 
 transmitted through a long circuit, though the latter is capable of pro- 
 ducing an equal effect by a multiplication of the coils. 
 
 The electro-magnets used for telegraphic purposes, in which great sen- 
 sitiveness is required, with a current very small in quantity but of con- 
 siderable intensity, are made of iron about three-eighths of an inch in dia- 
 meter, coiled round with nearly two hundred yards of extremely fine wire 
 covered with silk. The keepers of these electro-magnets are attached to a 
 slender spring to force them back when the circuit is broken, and they are 
 adjusted to a distance of not more than the tenth of an inch from the 
 magnet. These electro-magnets work briskly through a circuit of up- 
 wards of 400 miles, with a battery consisting of 100 pairs of plates. 
 
 The rapidity with which magnetism is imparted to soft iron on mak- 
 ing contact with a voltaic battery appears to be simultaneous with the 
 transmission of the electric current. An apparatus represented in the 
 annexed diagram is admirably calculated to shew the extreme rapidity of 
 electro-magnetic action. A short bar electro-magnet A is mounted on a 
 wooden stand B. A piece of brass is fixed to the top, which serves for 
 the attachment of a small keeper K to the magnet, and for the support of 
 a bent brass arm c, used for the purpose of applying an adjusting screw s. 
 The keeper is attached to a slender spring, which forces it from the mag- 
 net against the screw when the voltaic current is not passing. One of 
 the poles of the battery v is connected directly with the lower end of the 
 
ELECTRO- MAGNETISM. 
 
 137 
 
 fig. 65. 
 
 coil-wire by the binding screw 
 z, and the other wire N is con- 
 nected with the screw s, against 
 which the keeper presses. The 
 arm c is insulated from the 
 brass to which the keeper is 
 fixed by being screwed into a 
 piece of box-wood, and the other 
 end of the coil of wire is con- 
 nected by the binding screw E 
 with the keeper. By this ar- 
 rangement the electric circuit is 
 completed through the coil, by 
 passing through the bent arm 
 
 and through the keeper. The points of contact should have small pieces 
 of platinum soldered to them to prevent corrosion of the metal, which 
 would otherwise soon stop the action. 
 
 The instant that the keeper is attracted towards the magnet, its con- 
 tact with the screw is broken, and the voltaic current is interrupted. The 
 magnet then ceases to act, the keeper is forced against the screw by the 
 spring, and the contact being again renewed, the electro-magnet is brought 
 into action as before, but to be again instantaneously demagnetised by 
 attracting the keeper. It will be observed, therefore, that the circuit is 
 broken every time that the keeper is attracted by the magnet, and re- 
 newed when forced back against the screw ; and that each movement of 
 the keeper indicates that the iron has been magnetised and demagnetised. 
 When the voltaic battery is put in action, the keeper of the electro-magnet 
 is attracted and forced back again with a rapidity altogether incalculable 
 by the eye ; the vibrations being so rapid as to produce a humming sound, 
 which is more grave or acute according to the rapidity. By turning the 
 screw s, so as to bring the keeper more close to the electro-magnet, the 
 rapidity of the vibrations increases with the increased attraction of the 
 magnet ; and by the musical note thus occasioned, the vibrations of the 
 keeper have been estimated to exceed two hundred in a second. 
 
 Though magnetism can be imparted with this amazing rapidity, the 
 amount of magnetic power is in such cases by no means equal to that 
 which the electro-magnet exerts when tjie contact is of longer duration. 
 Only a given quantity of electricity can be excited by the battery in a 
 given time ; and assuming that it requires chemical action to be con- 
 tinued one-tenth of a second to obtain the full power of the battery, 
 when the contact is made and broken more frequently than the tenth part 
 of a second the quantity of electricity that passes is very considerably 
 less, though the diminution is not proportionate to the shortness of the 
 contact. It appears, indeed, from the result of numerous experiments on 
 this subject made by the author, that the full effect of an electro-magnet, 
 with a coil of thirty yards of thick wire, cannot be obtained more fre- 
 quently than four times in a second. 
 
 When the keeper of a horse-shoe electro-magnet is in contact with the 
 two poles, some magnetic power is retained after the contact is broken ; 
 and to prevent the continuance of the induced magnetism it is requisite 
 to interpose a piece of card or thin leather, so that the keeper and the 
 
138 
 
 THE PHENOMENA OF ELECTRICITY. 
 
 magnet may not touch each ojher. Besides this retention of magnetism 
 by the keeper, the electro-magnet itself retains its power for a short time, 
 if the bar of soft iron be above three or four inches long ; therefore, to 
 ensure rapid action when the contact is made* and broken rapidly, it is 
 desirable that the iron round which the wire is coiled should be as short 
 as possible. 
 
 The self-acting mode of breaking contact, represented in fig. 65, has 
 been applied with great advantage in constructing apparatus for giving 
 shocks by secondary currents of electricity for medical purposes. A great 
 length of very fine covered wire is twisted round the primary coil of thick 
 
 fig. 66. 
 
 wire through which the voltaic current passes ; and each time that contact 
 is broken, a secondary current is induced through the fine wire. Brass 
 handles are soldered to the ends of the second wire to increase the sur- 
 face contact when grasped by the hands, or conducting plates are used 
 when the electricity is transmitted through other parts of. the body. The 
 making and breaking contact by the self-acting vibrations of the keeper 
 produce a rapid succession of shocks, the strength and rapidity of which 
 may be regulated by the adjusting screw. 
 
 Reverting to the deflective action of a conducting wire on a magnetic 
 needle, it will be observed that the action is a tangential one ; that is, the 
 direction of the force is at right angles to the radius of the wire. One 
 pole of the needle is deflected to^the right hand, the other pole to the left 
 hand ; and whatever side of the wire the needle is placed, the same effects 
 take place. Thus, if the conducting wire were surrounded by a number 
 of magnetic needles ranged parallel to it, they would be all deflected in 
 the same manner, evidently shewing that the deflecting force acts tan- 
 gentially at every point of the circumference of the wire. The effect of a 
 tangential force acting on all parts of the circumference is to communi- 
 cate rotary motion to bodies free to move, in the manner that a wheel is 
 turned round by impelling it at the circumference in directions at right 
 angles to its radius. As there cannot be action without reaction, and as 
 hey are always equal and in opposite directions, the tendency of the force 
 exerted by the conducting wire is to cause its rotation about its own axis, 
 and to communicate motion in the opposite direction to the magnets with- 
 in its influence. 
 
 Faraday, who was the first to take this view of the character and 
 
ELECTRO-MAGNETISM. 
 
 139 
 
 tendency of the electro-magnetic force, succeeded in illustrating it most 
 satisfactorily by experiment. To do this, it was necessary to remove the 
 counteraction of one of the poles of the magnet on the other ; for as the 
 south pole of a magnet is deflected in the opposite direction to that of 
 the north pole, the contrary forces, when allowed to operate, completely 
 neutralise each other. The simplest arrangement for producing the ro- 
 tation of a magnet is that shewn in fig. 67. Into the bottom of a wooden 
 cup A, made to contain mercury, is inserted a wire d, 
 to which a bar magnet is attached by a thread. When 
 the cup is filled with mercury, the steel magnet being 
 the lighter rises to the top, and is retained in an up- 
 right position by the thread A thick wire c, connected 
 with the positive pole of a voltaic arrangement, dips into 
 the mercury, but is insulated from it by being covered 
 with cotton and varnished, excepting at the end. When 
 a voltaic current is transmitted through the conducting 
 wire, it influences the north pole of the magnet ; but after 
 communicating with the mercury it is so diffused that 
 the south pole is not affected. By this means the tan- 
 gential force with which the induced magnetism in the 
 conducting wire acts on the north pole is not counter- 
 acted, and the magnet being free to move in a circular 
 direction, begins to rotate round the conducting wire. 
 
 Fig. 68 shews another form of apparatus for illus- 
 trating this remarkable phenomenon. Two long but 
 light magnets N s, N' s', are fixed into a circular piece of 
 wood D, which rests on a pivot B, so as to turn round easily. The con- 
 ducting wire c, from the copper end of the battery, dips into a cup of 
 mercury in the wood, and by means of mercurial connexions the electric 
 current is conducted through the wire z to the negative end without 
 passing near the southern poles of the magnets. The connexion with the 
 battery being completed, the magnets rotate freely round the conducting 
 wire in the direction from left to right, like the hands of a watch. On 
 reversing the battery connexions, so that the positive current may enter 
 
 fig. 67. 
 
 fig. 69. 
 
 fig. 68. 
 
140 THE PHENOMENA OF ELECTRICITY. 
 
 at z and return up the wire to c, the direction of the rotation is changed. 
 A similar change in the direction of the motion also occurs when the 
 position of the poles of the magnets is reversed. 
 
 The rotation of a bar magnet on its own axis may be effected by an 
 arrangement similar in principle to the foregoing. The contrivance 
 originally proposed by M. Ampere is the simplest. The magnet N (fig. 69) 
 is allowed to float in mercury, being kept in a vertical position by a 
 weight of platinum ; and the action of the electric current is confined to 
 one pole of the magnet by insulating the conducting wire c, with the excep- 
 tion of its end, and introducing it vertically into the mercury to the depth 
 of half tjie magnet. The counteraction that would otherwise occur from the 
 other pole is thus prevented, and the magnet rotates slowly on its axis. 
 
 CHAPTER XVI. 
 
 MAGNETO, THERMO, AND ANIMAL ELECTRICITY. 
 
 Induction of electricity by magnetism Multiplication of effects by motion Magneto- 
 electric machines : their powerful eifects Magneto- electric spark Decomposition 
 by magneto-electricity Correlation of magnetic and electric forces Development 
 of electricity by heat List of thermo-electrics Thermo-electric batteries Indica- 
 tions of temperature by thermo-electricity Animal electricity Electrical organs of 
 the torpedo Identity of animal and voltaic electricity Electrical power of the 
 gymnotus Connexion between nervous influence and electricity. 
 
 IT might have been inferred ct priori, from the induction of magnetism by 
 electricity, that electricity could be induced by magnetism. The verification 
 of this inference is one among the many facts for which electric science is 
 indebted to Dr. Faraday. 
 
 The simplest mode of inducing electricity by magnetic action is by an 
 arrangement of permanent magnets and an electro-magnet shewn in the 
 diagram. 
 
 Two long permanent bar-magnets N s, N s are placed in the manner 
 represented, with their opposite poles joined at one end and spread out at 
 
 fig. 70. 
 
 the other ; each of the separated poles being in contact with a bar electro- 
 magnet M, round which there is coiled about 200 feet of covered wire, the 
 60th part of an inch in diameter. The ends of the coil of wire are con- 
 nected with a galvanometer G, placed at such a distance from the magnets 
 as to be beyond their direct influence on the magnetic needle. Whilst the 
 magnets continue thus connected, the galvanometer will not indicate any 
 trace of electricity; but at the instant that contact is broken, a current of 
 electricity is induced in the coil of wire, and the galvanometer is strongly 
 deflected. The effect is, however, only instantaneous, and the needle, after 
 
MAGNETO, THERMO, AND ANIMAL ELECTRICITY. 141 
 
 a few vibrations, returns to its normal position. On making contact again, 
 the galvanometer is again deflected ; but the deflection is in the contrary 
 direction to that on breaking contact, the electricity being equally tem- 
 porary, and being in other respects like that of the secondary currents 
 induced on making and breaking contact with a voltaic battery. The 
 more suddenly contact is made and broken by jerking away either of the 
 magnets, the more powerfully is the galvanometer deflected. 
 
 The current of electricity induced by the arrangement shewn in^ fig. 70 
 is very small in quantity, even when the most powerful magnets are em- 
 ployed ; but the further researches of Faraday led to the discovery of new 
 modes of action, by which the current may be prodigiously increased, and 
 all the effects of a powerful voltaic battery, either of high intensity or of 
 great quantity, may be produced by permanent magnets without any 
 battery whatever. 
 
 Faraday was stimulated to his investigations on this subject by the 
 remarkable phenomenon observed by M. Arago, of the induction of mag- 
 netism by motion in substances not otherwise magnetic. The French phi- 
 losopher discovered that if a copper disc be revolved close to a magnetic 
 needle, it is deflected, and that when a magnet is so suspended that it may 
 rotate in a plane parallel to that of the disc, the magnet tends to follow 
 the motion of the disc ; or if the magnet be revolved, the plate tends to 
 follow its motion, and the effect is so powerful that magnets or discs of 
 many pounds weight may be thus carried round. This effect, M. Arago 
 stated, not only takes place with the metals, but with all substances, solid 
 or liquid, and even with gases. It must be observed, however, that in 
 repeating these experiments, neither Mr. Babbage, Sir John Herschel, nor 
 Dr. Faraday was able to produce the effect with any substances that were 
 not very good conductors of electricity. 
 
 The experiments conducted by Faraday with the view of elucidating 
 these phenomena, led him to the conclusion that whenever a metallic body 
 is put in motion close to a magnet, a current of electricity is induced, 
 which ceases the instant that the motion ceases. As the movement of any 
 metallic body, such as a disc of copper, in close proximity to the poles of 
 a permanent magnet was found to induce a temporary electric current in 
 the metal, Faraday inferred that the effect would be increased if, instead 
 of a copper disc, a coil of covered copper wire round a bar of soft iron were 
 used. This was tried with most satisfactory results ; and other elec- 
 tricians have applied the principle to the construction of magneto-electric 
 machines, that excite torrents of electricity by the rapid rotation, close to 
 the poles of a powerful permanent magnet, of a piece of soft iron sur- 
 rounded by coils of covered copper wire. 
 
 Fig. 7 1 represents a magneto-electric machine. A powerful compound 
 permanent horse-shoe magnet a (composed of several thin plates of steel 
 separately magnetised and bound together,) is fixed in a horizontal posi- 
 tion. The soft iron covered with copper wire c d, by the rotation of which 
 the electricity is induced, resembles a horse-shoe electro-magnet ; but in- 
 stead of being a bent bar of soft iron, it is made of two short straight bars 
 connected together by a cross-piece of soft iron. This form is adopted 
 because it facilitates the winding of the numerous coils of wire, and is 
 more convenient for the mechanical arrangements. When intensity effects 
 are required to be produced, the iron of the rotating electro-magnet, called 
 
142 THE PHENOMENA OF ELECTRICITY. 
 
 the armature, is of small diameter, and about fifteen hundred yards of very 
 fine insulated wire are coiled round both limbs. When quantity effects are 
 wanted, the armature is made of iron of greater diameter, and the coil 
 consists of one-tenth the length of wire about the thickness of bell-wire. 
 The armature is fixed on to a spindle attached to a small grooved wheel 
 that is worked by a band over a larger wheel, by which means very rapid 
 motion may be given to the armature. Wires, through which the induced 
 
 fig. 71. 
 
 electricity is conducted, are connected with each end of the coil of wire 
 round the armature ; and as the latter revolves as closely as possible to, 
 without actually touching, the poles of the magnet, alternate currents of 
 negative and positive electricity are transmitted. Arrangements are made, 
 either by projecting points dipping into mercury, or by springs pressing 
 on interrupted collars of metal, for breaking the circuit of the wire coil 
 the instant that the two ends of the armature come opposite the poles of 
 the magnet ; by which means the rotating electro-magnet becomes mag- 
 netised and demagnetised twice in every revolution, and at each break in 
 the circuit a current of induced electricity is transmitted through the coil. 
 
 When the armature with the long coil of fine wire is used, a succession 
 of very severe shocks passes through the body on communication being 
 made between the wires by grasping two conducting metal cylinders. 
 The decomposition of water, and of all compound bodies that are decom- 
 posable by voltaic electricity, may also be effected, and a rapid current 
 of most brilliant sparks is emitted at the points when contact is broken. 
 With the armature of thicker and shorter wire, the metals may be ignited, 
 and all such effects can be produced as may be obtained from a voltaic 
 combination of a few large-sized plates. The sparks, on breaking' contact, 
 are also brighter, but no shock is given by the quantity armature. 
 
 In these experiments, the parts of the copper with which contact is 
 made and broken should be amalgamated with nitrate of mercury, or by 
 applying a drop of nitric acid, and then rubbing over it a particle of mer- 
 cury. Good contact is essential to the success of all experiments in elec- 
 tro-magnetism, and to ensure it, it is customary to employ mercury, and 
 to amalgamate the connecting points that dip into it. The liquid metal 
 
MAGNETO, THERMO, AND ANIMAL ELECTRICITY. 143 
 
 is, however, apt to be thrown about, and it is attended with other incon- 
 veniences. When solid points of contact are employed they should con- 
 sist of platinum. With the other metals, the ignition of small particles by 
 the secondary current on making and breaking contact forms an oxide of 
 the metal on the points, which, after a short time, interrupts the electric 
 circuit; but platinum, being the most incorrodible of the metals, is not 
 liable to have its surfaces oxidised. 
 
 The quantity of electricity induced by magnetism is proportionate to 
 the power of the magnets employed. In a very large and powerful mag- 
 neto-electrical machine constructed by Mr. Clarke, the magnet battery 
 consists of 106 cast-steel bars, each four feet long, and when combined 
 weighs 156 pounds. With this machine, a cubic inch of gas from the de- 
 composition of water is evolved in one minute and a half, the shocks are 
 too powerful to be received without danger, and the sparks, when the 
 quantity armature is used, are accompanied with a loud snapping noise 
 like the discharge of a Leyden jar. 
 
 The induction of electricity by magnetism alone seems to open an 
 exhaustless source for the supply of electric force without the trouble, the 
 annoyance, and the cost of voltaic batteries ; but hitherto it has not been 
 of much avail. The labour of turning the wheel for the rapid rotation of 
 the armatures, and the irregularity in the force consequent on irregularity 
 of mechanical action, are serious drawbacks to the use of magneto-electric 
 machines as the generators of electricity for experimental purposes. As 
 an economical means of exciting electricity for electro-plating, it was at 
 one time thought to promise great advantage. A patent was obtained for 
 the application of magneto-electricity to that purpose, and Messrs. Elking- 
 ton constructed at their works in Birmingham a very large machine to be 
 worked by steam-power ; but it was not found to answer so well as voltaic 
 electricity, in consequence of the want of continuity and steadiness in the 
 electric current produced. Magneto-electricity has also been applied by 
 Mr. Henley to work a needle telegraph with very good effect, as will be 
 subsequently noticed. 
 
 As electro-magnets are far more powerful than any combination of 
 magnetic steel bars, they have been sometimes used instead of permanent 
 magnets for the induction of magneto-electricity, and with good results ; 
 but the employment of a voltaic battery to induce magnetism, which is 
 afterwards to be applied to induce electricity, complicates the considera- 
 tion of the action, and seems to render it doubtful whether the magnetism 
 excites the electricity or the electricity excites the magnetism. This mu- 
 tual transmutation of the two forces into one another proves, however, in 
 the strongest possible manner, the intimate connexion, if not the identity, 
 of electricity and magnetism. By some hitherto inscrutable modifications 
 of the same common force, it is developed at one moment exerting limited 
 though energetic attractions on steel and iron alone ; at another it is ope- 
 rating on compound substances of every kind, separating their elements 
 from the most intimate combinations ; again, we see it emitting light that 
 rivals the sun in brightness ; now it is carrying lightning-messages through 
 hundreds of miles of wire, rather than force its way through a gossamer 
 web ; and yet again, we see the same force dealing destruction in its 
 course, as it rends a passage through the air from the clouds to the earth. 
 The development of heat being a characteristic phenomenon of an elec- 
 
144 THE PHENOMENA OF ELECTRICITY. 
 
 trie current, it was inferred that heat was also capable of developing 
 electricity. The satisfactory proof of this inference is due to Professor 
 Seebeck, of Berlin ; and though this interesting branch of electric science 
 has yet made no important progress, sufficient has been done to prove 
 that heat, electricity and magnetism, are correlative forces. 
 
 All that is necessary for the development of thermo-electricity is to 
 heat any metallic body irregularly at its extremities. The thermo-electric 
 relations of metals have not, as at present ascertained, any connexion 
 with their relative voltaic or conducting properties. In the following 
 series the combination of the metals at the two extremes produces the 
 strongest electrical effects, the effect of the intermediate metals in the 
 series diminishing as they approach. Those at the top of the list, com- 
 mencing with galsena, are positive to all below. 
 
 1. Galaena. 6. Tin. 12. Zinc. 
 
 2. Bismuth. 7. Lead. 13. Iron. 
 
 3. Mercury. 8. Brass. 14. Arsenic. 
 
 4. Platinum. 9. Gold. 15. Antimony. 
 
 5. Manganese. 10. Copper. 
 
 11. Silver. 
 
 The arrangement shewn in the annexed diagram represents a simple 
 
 thermo-electric circuit that exhibits the phenomena in a very satisfactory 
 
 manner. The rectangle B D represents a frame of metal ; the rectangular 
 
 bar BCD being of bismuth, soldered at the corners B and D to a similar 
 
 rectangular bar of antimony. A magnetic 
 
 IB L ""pi needle M is poised in the centre, and the 
 
 II ?] whole is supported on an elevating stand. On 
 
 ^^^^Hjtebg^^-^ il pply'"^ l R ' at to either of the corners B or D, 
 the magnetic needle is immediately deflected, 
 thus indicating that an electric current is 
 passing through the bars. The quantity of 
 electricity excited is, to a certain point, pro- 
 portionate to the different degrees of tempera- 
 ture communicated to different parts of the 
 same metallic bar, and does not depend on the 
 fig 72> absolute heat. Thus the application of ice will 
 
 produce an electric current as well as the appli- 
 cation of heat ; and by applying ice to one corner and the flame of a spirit- 
 lamp to the other at the same time, the effect is greatly increased. 
 
 The intensity of the thermo-electric current from a single circuit is 
 extremely feeble, and is altogether impeded even by a short length of 
 fine wire ; but it may be greatly increased by multiplying the series, as in 
 the voltaic pile. With a series cf very short and thin bars of bismuth 
 and antimony, having their alternate ends soldered together, and insulated 
 from each other by pieces of thick paper, a very delicate thermometer may 
 be constructed, which indicates, by the deflection of the galvanometer 
 needle, variations of temperature much too minute to be appreciated by 
 iny other indicator of heat. 
 
 By multiplication of the series sparks have been produced, and electro- 
 magnetic effects have been obtained. A vivid spark was elicited by Che- 
 valier Antinori of Florence, on breaking contact ; and Professor Wheat- 
 stone successfully repeated the experiment. He used a thermo-battery of 
 
MAGNETO, THERMO, AND ANIMAL ELECTRICITY. 
 
 145 
 
 thirty pairs of bismuth and antimony, packed into a cylindrical bundle 
 1 *2 inch long and three-quarters of an inch in diameter, with a coil of in- 
 sulated copper ribbon 50 feet long and 1^ inch broad. Mr. Watkins, by 
 using a thermo-electric battery of thirty pairs, each plate being 1*5 inch 
 square and O33 inch thick, and heating one end of the arrangement with 
 a hot iron, whilst the other was kept cool with ice, succeeded in exciting 
 an electro-magnet to such an extent as to support a weight of ninety- 
 eight pounds.* 
 
 M. Mellori and Professor Forbes have made valuable use of thermo- 
 electricity in their researches into the nature of heat, as it affords the most 
 delicate means of detecting variations of temperature. The apparatus of 
 Professor Forbes is represented in fig. 73. The thermo-electric battery 
 A, mounted on its stand, con- 
 sists of thirty-six alternations 
 of bismuth and antimony in 
 very short and thin bars, con- 
 nected at their ends, but insu- 
 lated laterally by paper. The 
 terminal elements of the bat- 
 tery are produced at c, to which 
 thick copper wires connected 
 with the galvanometer G are 
 attached. In his experiments 
 the deflections of the needle 
 were examined through a mag- 
 nifying instrument, so that the 
 least movement might be ob- 
 served. The instrument is so sensitive in its indications that the approach 
 of the hand towards the end of the battery produces a deflection of several 
 degrees. 
 
 Another source of electricity the last we have to notice is derived 
 from the organisation of living animals. There are several fishes which 
 possess the power of giving electrical shocks ; but those best known in 
 this country are the torpedo and the gymnotus. The former is found in 
 the Mediterranean, and along the shores of France and the south of Eng- 
 land. It is a species of ray. The electrical organs lie on each side of the 
 head, and consist of a great number of hexagonal prisms, 'with their bases 
 to one side of the fish and their apices to the other. Upwards of one 
 thousand of these prisms have been counted in a single organ. The 
 power of communicating shocks depends entirely on the nerves of the fish, 
 for its heart may be taken out without diminishing the effect ; but the 
 instant that the nerves are divided the electrical power is lost. The back 
 and the belly are in opposite states of electricity, that of the back being 
 positive, and that of the belly negative; and to receive a shock.it is neces- 
 sary to make a communication between them. 
 
 The accompanying figure shews the fish with part of the skin turned 
 over, so as to expose the right electric organ, which presents the appear- 
 ance of a honeycomb. The mouth is shewn at d ; the ten bronchial 
 
 fig. 73. 
 
 Dr. Golding Bird's Natural Philosophy. 
 
146 
 
 THE PHENOMENA OF ELECTKICITY. 
 
 apertures at e e ; ff the outer margin of the great lateral fin ; g g two 
 smaller fins, and h the tail fin. 
 
 The electrical properties of the gymnotus, or electrical eel, are better 
 known than those of the torpedo, because some living specimens exhibited 
 in London, first in the Adelaide Gallery and now at the Polytechnic In- 
 stitution, have enabled Faraday and other electricians to make experiments 
 with the electricity evolved. The electrical organs are arranged from the 
 head of the fish to the tail on each side of the spine, like a voltaic bat- 
 tery; the end near the head being positive, and the tail negative. The 
 whole power of this living battery is exerted when connexion is made 
 between the head and the tail; and if the communication be made between 
 any intermediate parts, the effect is diminished in the same degree as in a 
 voltaic battery under similar circumstances. On putting small live fish 
 into the water with the gymnotus, the latter forms itself into a circle 
 enclosing the fish, and sends a charge through the water, which instantly 
 stuns its prey. When the hand is held in the water whilst the charge is 
 transmitted, a shock is felt, though not so strong as when the gymnotus is 
 touched at its two extremities. 
 
 fig. 75. 
 
 Fig. 75 represents a gymnotus with the electrical organs laid bare, the 
 skin being turned over on each side. Flat portions and cross divisions 
 appear in parallel lines nearly in the direction of the axis of the body. 
 They consist of thin membranes nearly parallel to each other ; their 
 breadth about the semi-diameter of the body, but of different lengths. In 
 the figure, a represents the head ; b the cavity of the body ; dd the ventral 
 fin ; ee the skin turned back ; //the external muscles of the fin ; gg the 
 
MAGNETO, THERMO, AND ANIMAL ELECTRICITY. 
 
 147 
 
 large electrical organ ; h h the smaller organ. Fig. 76 presents two views 
 of the entire fish. 
 
 fig. 76. 
 
 In a series of experiments with the gymnotus, Faraday clearly esta- 
 blished the identity of its peculiar power with that of voltaic electricity of 
 great intensity. It produces a succession of shocks at short intervals ; it 
 effects electro-chemical decomposition, evolves heat, emits sparks, affects 
 the galvanometer, and renders iron magnetic. An attempt was made to 
 estimate the power of the apparatus, and though the experiments were 
 not very satisfactory, Faraday was led to conclude that a single medium 
 discharge of the gymnotus is at least equal to a Leyden battery of fifteen 
 jars containing 3500 square inches of glass, coated on both sides and 
 highly charged. 
 
 The electrical eel experimented with was forty inches long, but it is 
 found in the rivers and lakes of Venezuela six feet in length. Horses 
 that venture into the pools where the gymnotus abounds are stunned by 
 their shocks and often drowned. Humboldt mentions that on one occa- 
 sion he witnessed about thirty horses and mules driven into a pool oc- 
 cupied by numbers of gymnoti, which glided under the bellies of the 
 animals and discharged through them most violent and repeated shocks. 
 The horses, convulsed and terrified, their manes erect, and their eyes 
 staring with pain and anguish, made unavailing struggles to escape. 
 The electrical energy of the eels, however, became exhausted in less than 
 a quarter of an hour, and those horses that had contrived to keep above 
 water during the attack recovered. 
 
 The power of developing electricity appears to be limited to about 
 eight genera of the known fishes. Frogs and some other animals of low 
 organisation are peculiarly sensitive to the influence of electricity, but it 
 is very questionable whether they possess any voluntary power of its de- 
 velopment. The experiment of the convulsion of the limb of a dead frog 
 by making a communication between a muscle of the leg and a nerve, 
 which has been adduced as a proof of the electricity of frogs, is altogether 
 
148 THE PHENOMENA OF ELECTRICITY. 
 
 distinct from that control of the electrical power which is exercised by the 
 torpedo and gymnotus. 
 
 That there exists some intimate connexion between nervous influence 
 and electricity there is little doubt. Many attempts have been made, and 
 with some success, to prove that the human body generates electricity; 
 and we have heard it publicly asserted, and maintained by ingenious 
 arguments, that the lungs are galvanic batteries which are constantly 
 generating vast supplies of the electric fluid, which are conveyed by the 
 nerves to the brain, and thence distributed to the whole nervous system 
 to stimulate the vital functions. Dr. Golding Bird affirms, that "it is 
 quite indisputable that the human body is always in an electric state, but 
 of the feeblest tension, never exceeding that evolved by the contact of a 
 plate of zinc with a plate of copper. It increases with the irritability of 
 the person, and appears to be greater in the evening than in the morning, 
 and disappearing altogether in very cold weather." * It appears to be also 
 certain that electricity exerts an influence on the germination of seeds, 
 though the experiments hitherto made on this subject have led to no satis- 
 factory results. 
 
 From the mysterious connexion which is known to subsist between 
 electricity and the nervous system, it is but a step to attribute the in- 
 fluence of the imagination, and of other affections of the mind, to electrical 
 causes. On this supposition is founded the belief in mesmerism; which 
 assumes that an invisible electric fluid may be emitted by the power of 
 will from the finger-ends of the operator, and be transfused into the 
 system of the patient. It is not our intention to enter that debatable 
 ground ; we allude to the subject only as it is one of the most notable 
 forms in which the prevailing opinion of the influence of an electric fluid 
 on the vital functions has clothed itself. It is a deeply-interesting question, 
 however, which still remains to be proved, whether the same force which, 
 differently modified, produces electricity, magnetism, and heat, is also to 
 be identified with the immediate stimulus of vitality. 
 
 CHAPTER XVII. 
 
 ECONOMICAL APPAEATUS. 
 
 Simple form of apparatus for frictional electricity Directions for constructing Electri- 
 cal Machines Leyden Jars and Batteries Electrometers Electrophorus Uni- 
 versal Discharger Voltaic Batteries Electro -Magnets Galvanometers Obser- 
 vations on exciting' liquids for Voltaic Batteries. 
 
 THERE are many students strongly inclined to explore the attractive regions 
 of electric science, whose researches might add greatly to the stock of 
 knowledge, and tend to the elucidation of the mysteries in which the rela- 
 tions of electricity to other forces and to the vital principle are shrouded ; but 
 they are deterred from advancing by the cost of the necessary apparatus. 
 We propose, therefore, to assist in removing this obstacle by giving hints 
 
 * Elements of Natural Philosophy, p. 307. 
 
ECONOMICAL APPARATUS. . 149 
 
 for the construction of apparatus which any one possessed of a certain 
 degree of mechanical skill can put together himself. 
 
 Every thing that is absolutely necessary for exhibiting the phenomena 
 of frictional electricity may be provided at the cost of a few shillings, 
 when no great amount of electrical force is required. The author, when 
 a boy, made and experimented with an apparatus of the very simplest kind. 
 His first exciter of electricity was a long bottle of the same shape as those 
 in which eau-de-Cologne is contained, but wider and larger. An old piece 
 of black silk, on which a little aurum musivum was spread, served for the 
 rubber ; and with this bottle, after it had been well dried before the fire, an 
 energetic excitement of positive electricity was obtained by holding it in 
 one hand and rubbing it briskly with the other. For exciting negative 
 electricity a large stick of sealing-wax was used. With the glass electric 
 a Leyden jar, consisting of a large glass tumbler coated inside and out with 
 tin-foil to within an inch of the rim, was fully charged in a quarter of a 
 minute. The discharging-rod was a piece of bent wire ; and an insulated 
 stand was formed of a piece of board mounted on a small phial cemented 
 to the wood with sealing-wax. An electrical machine was afterwards made 
 of equally simple materials. The cylinder was a large phial, into the hol- 
 lowed bottom of which was cemented an axis, shaped with a knife to fit 
 into the hollow at one end, and rounded at the other like a spindle. A 
 rudely-constructed handle was cemented into the neck of the phial, and it 
 was mounted upon two wooden supports fixed into a flat board to serve 
 as the base. The prime conductor was part of the handle of a hair- 
 broom, rounded off at each end and covered with tin-foil. It was mounted 
 on a long narrow phial for its insulating support, and pins were stuck into 
 the wood to collect the electricity. The cushion was supported on a wooden 
 prop, and pressed against the bottom of the small cylinder. With this ma- 
 chine, sparks two inches long could be obtained, and it could fully charge 
 the tumbler Leyden jar with about twenty turns of the handle. 
 
 With an apparatus so rude and costless in its construction, many of 
 the most remarkable phenomena of electricity could be exhibited ; but its 
 diminutive size and rough appearance were scarcely suited for the labo- 
 ratory of an adult experimental philosopher : we notice it merely to shew 
 at what little expense electrical phenomena may be exemplified. We shall 
 now describe a means of providing an apparatus of a better kind, suitable 
 for all experiments with frictional electricity. 
 
 A length of stout glass tube, two feet long and an inch and a half in 
 diameter, which may be purchased at a barometer-maker's for one shilling, 
 serves as an excellent means of exciting electricity by manual friction. It 
 should be varnished inside to prevent the moisture of the atmosphere from 
 condensing and adhering to the glass, and it should be closed at each end 
 with corks. Aurum musivum (sulphuret of tin), a small quantity of which 
 may be purchased at an operative chemist's, serves even better than amal- 
 gam to stimulate the excitement of electricity by alternating friction. 
 
 The glass cylinders for electrical machines may now be purchased of 
 various sizes from the philosophical glass-vendors. One of these, six 
 inches in diameter, fitted into a frame consisting of a wooden base and 
 two uprights made of baked wood, will answer for most purposes very well. 
 The prime conductor may also be of wood, covered with tin-foil ; its insu- 
 lating support being a glass tube about nine inches long, varnished. Pins, 
 
150 THE PHENOMENA OF ELECTRICITY. 
 
 or pieces of brass wire sharpened at both ends, may be stuck into the 
 wood to collect the electricity from the_ excited cylinder. The cushion, 
 with its flap of silk attached, may be supported on an upright of well- 
 baked wood firmly fixed into the wooden base, which will press against 
 the side of the cylinder by the springy nature of the w r ood. A handle may 
 be purchased to cement into the neck of the cylinder, it being of not much 
 consequence whether it be insulated or not. 
 
 Leyden jars may be easily made by coating glass jars with tin-foil in- 
 side and out, the foil being made to adhere by a thin layer of paste. A 
 thick brass wire, to serve for the connexion with the inside coating, 
 should be supported in a firm position in the centre of the jar by a large 
 cork, and a piece of thin wire must be attached to the bottom to make 
 connexion with the inside coating. The object of having thick wire is to 
 prevent the dissipation of electricity, which takes place from points and 
 small surfaces. The end of the wire outside should, for the same reason, 
 be covered with a hollow brass ball. Such balls, with screw-holes for the 
 wires, may be obtained at the philosophical -instrument makers' for three 
 pence each. 
 
 In forming a battery of Leyden jars, they should be fitted into a box 
 about half their height, with partitions inside to prevent the jars from 
 being broken by collisions ; and the bottom of the box should be lined 
 with tin-foil, to form a metallic connexion between the outside coatings. 
 All the wires or knobs connected with the insides of the jars should 
 also be joined together by wire. A battery of six quart jars, sufficient to 
 deflagrate small strips of metal leaf, may thus be constructed at a cost of 
 fourteen shillings. 
 
 An electrometer presents little difficulty. Four inches of glass tube 
 two inches in diameter may be cemented on to a wooden stand, having 
 first pasted two narrow strips of tin-foil one inch and a half long opposite 
 to'.-each other inside on the lower part of the tube. The strips of tin-foil 
 should be connected together, and have also a metallic connexion outside 
 the stand. A cork covered with tin-foil may be fitted into the top of the 
 tube, instead of a metal cover, allowing a small piece of foil to project in 
 the centre inside for the convenient attachment of two strips of gold-leaf. 
 The gold-leaves should reach so far down as to be rather below the strips 
 of foil on the side of the tube, taking care, in pasting them to the cover, 
 that the metallic connexion is not obstructed by the paste or gum. 
 
 In making an electrophorus, recourse may again be had to wood 
 covered with tin-foil, as a substitute for solid metal. Paste a disc of tin- 
 foil nine inches in diameter on a flat board, and over the foil fix a disc of 
 the same size of thick sheet gutta-percha, or pour over it some melted 
 resinous cement, made as flat as possible. The conducting insulated plate 
 may consist of a flat circular piece of wood, smaller than the cake of 
 cement ; the surface being covered with tin-foil, and having attached to 
 the centre of its upper surface a piece of glass tube to serve for the in- 
 sulating handle. 
 
 An universal discharger, insulating stands, and stools may be made by 
 using short lengths of strong glass tube for the insulating supports. Gutta 
 percha will be found a very convenient substance for many smaller parts 
 of apparatus, as it may be easily moulded into form by immersing it in 
 hot water, and no known substance is so good an insulator. By adopting 
 
ECONOMICAL APPARATUS. 151 
 
 the plan thus sketched out, any person, with a little ingenuity and me- 
 chanical skill, may put together a yery complete and sufficiently powerful 
 apparatus for general experiments with frictional electricity, at a cost of 
 less than two pounds. 
 
 Experiments with voltaic electricity, if continued, are more costly, be- 
 cause, in addition to the original expense of the apparatus, there is the 
 constant consumption of the exciting materials. For those experiments, 
 however, which do not require a numerous and powerful combination 
 of plates, voltaic apparatus may be made at even less cost than that for 
 frictional electricity. Zinc plates may be obtained at the metal-ware- 
 houses of various degrees of thickness, and cut into any size required, at 
 the rate of fivepence the pound. It is not desirable to have the plates 
 less than the eighth of an inch thick. They may be readily amalgamated 
 by dipping them for a few seconds into diluted sulphuric acid, to clean 
 the surfaces, and then sprinkling over them some globules of mercury, 
 which may be rubbed on the zinc with the end of a cork. 
 
 The only part of the manipulation in making voltaic batteries that is 
 attended with any difficulty, is the soldering of the metallic connexions. 
 The method of doing it is, however, soon acquired, and with a brazier's 
 small soldering-iron, a little soft solder, and some muriatic acid, the cop- 
 per connexions and the binding screws may be soldered on to zinc plates 
 without much trouble. A voltaic arrangement, consisting of two pairs of 
 zinc and copper plates six inches square, may be fitted up in earthenware 
 cells for four shillings. Such voltaic battery will ignite fine metal wires, 
 decompose water and most other compound substances, powerfully excite 
 electro-magnets, deposit metals from their solutions in the processes of 
 electrotyping and electroplating, and, by inducing secondary currents, give 
 strong electric shocks. 
 
 The large flat earthenware cells cost one shilling each ; therefore it is 
 most economical, when many combinations are required, to divide a long 
 water-tight wooden trough into compartments by cementing into it square 
 pieces of slate or thick glass, about an inch and a half apart. 
 
 Electro-magnets are very readily made. Having obtained from a 
 smith some pieces of best soft bar-iron, bent into the shape of the letter U, 
 wind round each limb a quantity of covered copper wire, observing to twist 
 it round each in the same direction and as evenly as possible, and the 
 magnet is complete. The quantity and thickness of the wire depend on 
 the kind of magnet that is required, as previously explained.* Covered 
 copper wire of the size of thick bell- wire (No. 14), which is the kind 
 generally used for primary magnetic coils, is sold for three shillings the 
 pound. Thirty yards of such wire are sufficient to make a powerful horse- 
 shoe magnet, with iron about half an inch in diameter and five inches 
 long. The wire for inducing secondary currents should be wound upon 
 the primary coil, but separated from it by a piece of silk ; and medical 
 coil-machines for giving shocks by secondary currents require at least 
 1000 yards of very fine covered wire. The finest silk-covered copper wire 
 to be procured is as thin as a human hair. ' Its price is sixteen shillings 
 the pound, and one pound of it contains 18,000 yards. Though wire of 
 this extreme degree of tenuity is much used for secondary circuits and for 
 
 * Page 133. 
 
152 THE PHENOMENA OF ELECTRICITY. 
 
 highly sensitive galvanometers, it is questionable whether a rather thicker 
 wire, that will allow a greater quantity of electricity to pass, is not to 
 be preferred. 
 
 To construct a galvanometer in the easiest way, it will be advisable to 
 purchase a common pocket-compass, which may be procured for two shil- 
 lings. Fix on to the magnetic needle a very thin strip of paper at right 
 angles to it, to serve for the index. Twist across the compass-box a 
 number of turns of fine wire, so that the coil wound round it may be 
 about half an inch wide and about a quarter of an inch in thickness. The 
 galvanometer thus formed should be fitted into a small box open at the 
 top, to enable it to be placed steadily, and through the sides of the box let 
 the wires from each end of the coil project. When used horizontally, the 
 compass should be so adjusted that the coil and the needle may be parallel 
 to each other ; therefore both will then be in the magnetic meridian, the 
 needle being concealed by the coil. When the two ends are connected 
 with any source of voltaic electricity, so that the current may pass through 
 the coil, the needle will be immediately deflected, and the paper index will 
 shew the direction and the amount of the deflexion. Simple galvano- 
 meters of this construction were employed by Dr. O'Shaughnessy on the 
 first telegraphic lines in India, and they were found very efficient instru- 
 ments at a distance of several hundreds of miles. 
 
 The exciting liquid for voltaic batteries most generally used is sul- 
 phuric acid, diluted with water in various proportions. When the zinc 
 plates are well amalgamated, one measure of acid may be diluted with ten 
 of water ; but when the plates become worn a weaker solution is desirable. 
 By this dilution local action is avoided, and the effect is equally powerful j 
 because the zinc when worn exposes a larger surface, and is more easily 
 attacked by the acid. When powerful action is not necessary, it is better 
 to employ a much more diluted acid, in the proportion even of one to forty. 
 Sulphuric acid, when purchased by the pound, is very cheap. A large stop- 
 pered glass bottle, containing ten pounds, may be bought for half-a-crown. 
 Solutions of alum and of salt are good exciters when energetic action is not 
 required. Sulphate of copper is also a good exciter of voltaic electricity ; 
 but when used, the zinc should be placed in a separate porous cell, con- 
 taining diluted acid or a saline solution ; otherwise metallic copper deposits 
 on the zinc, when immersed in the sulphate, and produces counteraction. 
 
 The preceding remarks on the construction of economical apparatus, 
 though not perhaps sufficient as explicit directions, will serve at least as 
 hints to those who desire to exercise their ingenuity or to save expense. 
 When neither motive operates, the student may supply himself with better 
 apparatus than he can hope to make from any of the manufacturers of 
 philosophical instruments. 
 
PAET III. 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 CHAPTER XVIII. 
 
 ELECTRIC TELEGRAPHS MEANS OF COMMUNICATING. 
 
 First attempts to transmit messages by electricity Conducting power of the earth- 
 Opinions respecting the cause Resistance of long wires to transmission Voltaic 
 currents Modes of making electric communications Difficulties of insulation 
 Defects of the present system Submarine telegraphs New plan proposed Pro- 
 spect of telegraphic communication with America. 
 
 THE practical application of electric force to the requirements of civilised 
 life can scarcely be dated beyond fifteen years from the present time ; yet 
 within that short period the power of electricity has been applied, with 
 more or less success, to a vast variety of purposes. The transmission of 
 lightning messages, the working of machinery, the chronicling of time, the 
 lighting of streets, the manufacturing of metal utensils, gilding and plating, 
 even sounding the depths of the sea, and the detection of the midnight 
 burglar, are among the many varied uses to which electricity has been 
 directed. 
 
 The rapid transmission of electric discharges through extended lengths 
 of wire suggested, at a very early period of the history of electricity, the 
 idea of its applicability to telegraphic purposes. The first plan for trans- 
 mitting messages by that means of which there is any record, was that of 
 M. Lesarge, of Geneva, in 1774. The signals were made by pith-ball elec- 
 trometers, placed on insulated wires extended between the places with 
 which communication was to be established. The discharge of a Leyden 
 jar, on being sent through the wire at one end, caused the pith balls to 
 expand on the other. There were as many insulated wires as letters of the 
 alphabet, each one serving to indicate a separate letter; and, as the electric 
 discharge was sent successively through the wires, by noticing those on 
 which the pith balls expanded, the words to be transmitted were spelt. 
 
 Thus we perceive that at least seventy years before any electric tele- 
 graph was in practical operation, a plan for establishing such means of com- 
 munication had been pointed out. Several other modes of making commu- 
 nications by frictional electricity were invented, which will be noticed in the 
 next chapter ; but most of them, like that of Lesarge, required a separate 
 wire for indicating each letter. The discovery of voltaic electricity, and 
 still more that of electro-magnetism, greatly added to the facility of trans- 
 mitting signals ; nevertheless twenty-six wires, one for each letter, were 
 generally considered requisite ; and the difficulty of forming an insulated 
 
 L 
 
154 THE APPLICATIONS OF ELECTRICITY. 
 
 wire connexion through which the voltaic current may be transmitted 
 without loss of power, is still the great difficulty in telegraphic communi- 
 cation, even when two wires only are employed for each instrument. 
 
 Before we describe the various modes that have been invented for 
 transmitting electric messages, it is desirable that we should explain the 
 means of making communication, and shew how the difficulties to be en- 
 countered may be overcome. 
 
 The experiments undertaken in 1747 by Dr. Watson and other Fellows 
 of the Koyal Society, at Shooter's Hill, on the conduction of electricity 
 through wires supported on short posts, not only proved that at a distance 
 of two miles the charge passed instantaneously, but also that the return 
 circuit, of equal length, could be transmitted through the dry ground. In 
 those experiments frictional electricity was employed, the discharge of a 
 Ley den jar having been sent through the circuit. The force of voltaic elec- 
 tricity is comparatively so feeble, that scarcely any sensible current would 
 pass through ground as dry as that purposely selected for its dryness in. 
 Dr. Watson's experiments ; but when plates connected with the two poles- 
 of a voltaic battery are buried in moist earth, the conduction is so perfect, 
 that at a distance of several hundreds of miles no appreciable quantity of 
 voltaic electricity is obstructed by resistance. The honour of the discovery 
 of the conducting power of the earth has been claimed in recent times, 
 though the fact was established by experiment before the close of the last 
 century. 
 
 The " earth-circuit," as it is called, is now made use of in all telegraphic 
 communications, and is of great practical utility, not only because it dimi- 
 nishes the resistance to the electric current, but it effects also a consider- 
 able saving of expense. If wire communication alone were depended upon, 
 it would be necessary to have one wire to conduct the current, and another 
 to convey it back to the battery ; but by introducing large copper plates 
 into the earth at the corresponding stations, the return circuit is completed 
 through the moist ground, and one wire is saved. This saving of wire y 
 which in the case of a single circuit amounts to one-half, is not propor- 
 tionally great when several circuits are employed ; for a single wire will 
 serve for the return circuits of any number that may be used, in the same 
 manner as the earth. 
 
 The annexed diagram will explain more clearly the action of the earth- 
 circuit. The letters A B represent the wires making communications be- 
 
 .77. 
 
 tween the batteries D and E, and the telegraphic instruments i o, at the 
 receiving station. The electricity from the copper end of the battery D 
 would be conducted along A through the instrument I, by the wire K to 
 
ELECTRIC TELEGRAPHS MEANS OF COMMUNICATING. 155 
 
 the earth-plate H. It would be then transmitted through the earth, on. 
 its return to the battery, in the direction of the arrows, to the other earth- 
 plate G, and thence it would find its way to the zinc pole of the battery 
 D, and complete the circuit. In the same manner the electric current 
 from the copper end of the battery E would be transmitted through the 
 wire B, and would complete its circuit also by means of the earth-plate e, 
 and would traverse the course indicated by the arrows, and return to the 
 zinc end of E. Though both electric currents traverse the same wire, from 
 the instruments I o to the earth -plate H, and are thence transmitted 
 through the earth to a single plate G at the transmitting station, there is 
 no mingling of currents, the electric current of each battery being kept as 
 distinct as if separate wires were used both for the transmitted and the 
 return current. It would, indeed, be as impossible for the separate currents 
 transmitted from the two batteries to be mingled together, as it would be 
 for the written contents of two letters enclosed in the same mail-bag to inter- 
 mix. The entire separation of the two currents, when transmitted through 
 the earth, also takes place when a single wire only is used for the returning 
 portion of the circuit. Suppose, for instance, the plates H and G, in- 
 stead of being buried in the earth, were directly connected by an insu- 
 lated wire, the current from each battery would be equally separate ; bat 
 the resistance offered by the wire being very much greater than that of 
 the earth, not nearly so much of the power of the battery would be trans- 
 mitted. 
 
 Pure water is estimated to offer three million times the resistance of 
 copper to the passage of an electric current. It seems, therefore, an 
 anomalous fact, that the moisture of the earth should conduct electricity 
 between two distant points so very much better than metal wires. The fact 
 is, indeed, so contradictory to the known relative proportions of the conduct- 
 ing powers of water and metals, that attempts have been made to explain 
 the phenomenon by assigning other causes than mere conduction. It has 
 been assumed that the earth is a vast reservoir of electricity,* and that the 
 positive current from the battery E, when it enters that reservoir, is at 
 once transferred by some process different from that of conduction to the 
 corresponding plate. 
 
 This opinion has received countenance in quarters that have given it 
 more importance than it would otherwise seem to deserve, especially when 
 it is well known that an imperfect conductor can compensate for its defec- 
 tive state of conduction by increase of volume. Take, for instance, the 
 two metals copper and iron. Iron offers seven times the resistance of cop- 
 per to the passage of an electric current ; but by proportionally increasing 
 the size of the iron wire, a current of electricity will be transmitted 
 through it as readily as through the better conducting metaL In the same 
 manner, by bringing into conducting action a large body of interposed 
 moist earth, the electricity, which would not pass through a small quantity, 
 is transmitted without any apparent resistance when a large sectional area 
 is included between the plates buried in the ground. 
 
 Professor Matteuchi has made numerous experiments with a view to 
 ascertain the amount of resistance offered by the earth to an electric cur- 
 rent, and the mode by which the transfer is effected, the result of which 
 
 * Electric Telegraph Manipulation, by C. V. Walker. 
 
156 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 is decidedly in favour of the opinion that the transmission is produced 
 directly by means of conduction only. " If/' as he observes, " the effect 
 was caused by immediate absorption and reproduction, a mere contact 
 with the earth would be sufficient ; but it is essential that the plates buried 
 in the ground should present a large surface, without which there is a 
 comparatively small quantity of electricity transmitted." The Electric 
 Telegraph Company generally bury a quantity of sulphate of copper with 
 the earth-plates, so as to surround them with a good liquid conductor, 
 which serves, practically, to increase the conducting surfaces that connect 
 the poles of the battery with the earth. 
 
 The resistance of a wire to the passage of an electric current increases 
 with its length, but not in direct proportion. In experiments by Professor 
 Morse, of the United States, when using a battery of 100 pairs of plates, 
 it was found that when the current was transmitted through one mile, one- 
 third of the battery power was lost ; at a distance of two miles, one-half 
 the power was transmitted ; and at a distance of five miles, only one-fifth 
 the quantity of water could be decomposed in the voltameter, compared 
 with the decomposing power of the battery when no length of wire at all 
 was interposed. The resistance proceeded in a diminishing ratio until a 
 distance was attained beyond which there appeared to be little further 
 diminution of the power transmitted. The same result has been observed 
 in the telegraph lines in England. The diminution of the electric current 
 by resistance of the wire is not much greater at a distance of 200 miles 
 than it is at a distance of 100, provided the insulation be very good ; but 
 if the insulation be imperfect, of course the loss of power will increase 
 with the length of the circuit. 
 
 The difficulty of effecting perfect insulation of the wires is the greatest 
 impediment to the establishment of telegraphic communication. The 
 wires are either supported on posts, or they are covered with gutta-percha, 
 and laid in trenches underground. The former plan is generally adopted. 
 The posts are about fourteen feet high, and cross arms of wood D D (fig. 
 
 78), eighteen inches long, are fixed to 
 them cross-wise, about ten inches apart. 
 At each end of the short wooden arm balls 
 of earthenware b b are attached, in the 
 sides of which nicks are made to hold the 
 wire ; and these globes are covered with a 
 cap of galvanised iron, to protect them 
 from the rain, and to prevent the deposi- 
 tion of dew. The earthenware being an 
 imperfect conductor of electricity, insulates 
 the wires from the posts, and prevents the 
 electric current from passing down them 
 to the earth in wet weather. Balls of 
 glass are beginning to be used instead of 
 earthenware, as that substance is a better 
 insulator. Iron wire, one-sixth of an inch 
 in diameter, and galvanised to prevent 
 corrosion, is the kind used in the telegraph 
 lines of this country. As many as thir- 
 teen of these wires are attached to the posts on the North- Western Kail- 
 
 lig. 78. 
 
ELECTRIC TELEGRAPHS MEANS OF COMMUNICATING. 157 
 
 way, near London. Some of them extend to Liverpool and Manchester, 
 some to Glasgow, and some are connected with the intermediate towns. 
 
 By placing wires forming short circuits in close proximity to those of 
 long circuits, the difficulty of insulation on the longer circuits is consider- 
 ably increased. Let D I represent a wire extending from London to Liver- 
 pool, and EO one extending from London to Birmingham, both sup- 
 ported on the same posts within a few inches of each other. In a damp 
 
 fig,79. 
 
 state of the atmosphere, when there is any defect in the insulation of the 
 wires, the electricity in its course along D I will be continual^ passing to 
 the wire E o, as shewn by the dotted lines ; for it can by that means take 
 a shorter return-circuit by passing to the earth-plate of o, and thus return 
 by the plate, which is common to both wires, to the battery of D, instead 
 of traversing the whole of the long circuit to I. In this manner it not 
 unfrequently happens that so much of the electric current is diverted that 
 the telegraph instruments cannot be worked. 
 
 In the opinion of the author, the escape of electricity from the wire is 
 greatly facilitated by the exposure of the wires in such close proximity to 
 each other without any insulating coating. He brought this subject before 
 the notice of the British Association for the Advancement of Science at 
 the two last meetings at Ipswich and Belfast; and in the papers read by 
 him on those occasions he endeavoured'to shew that the greater part of 
 the loss of electricity in damp weather is owing to the communication 
 from wire to wire through the moist atmosphere, and is not occasioned by 
 defective insulation at the posts. In this opinion several telegraphic engi- 
 neers now agree ; and to secure perfect insulation, not affected by rain or 
 fog, it would be necessary to varnish or otherwise insulate the surfaces of 
 the wires. 
 
 It is the opinion of many electricians that the low intensity of voltaic 
 electricity effectually prevents it from passing from wire to wire, even 
 through an atmosphere of fog. This opinion is, however, opposed to sound 
 reasoning on well-established facts ; and though on the small scale in 
 which experiments can be conducted in a laboratory, no appreciable quan- 
 tity of voltaic electricity will pass through the air. such limited means of 
 observation are not to be depended on when the surfaces exposed are very 
 great. 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 six inches apart, there can be little question that a large quantity of 
 the electric power must be transferred and lost when the air is charged 
 with moisture. 
 
 The wires on the telegraph lines in India are thicker, and they are 
 
158 THE APPLICATIONS OF ELECTRICITY. 
 
 placed at a greater elevation than in this country. The stronger wires 
 were found to be necessary to enable them to support the large birds and 
 the monkeys that perched and congregated upon them ; and greater height 
 was required to allow loaded elephants to pass underneath. Dr. O'Shaugh- 
 nessy, the superintendent of the East India Company's lines, has also 
 introduced the plan of making the posts stronger as well as higher, by 
 which means they may be placed at greater distances apart; not more 
 than eight posts being required in a mile. In this country it has been 
 customary to consider the protection of a railway essential to the esta- 
 blishment of telegraph lines. The protection, however, that a railway 
 affords is more imaginary than real; and in India the completion of a 
 system of telegraphic communication over 2000 miles of country will pre- 
 cede the construction of railways. 
 
 When the atmosphere is in an electrical condition, the telegraphic 
 instruments are often disturbed, though no current is transmitted along 
 the wires from the batteries ; and during thunder-storms the wire coils 
 have been destroyed by lightning. To prevent this disturbance by atmo- 
 spheric electricity, lightning-conductors are attached to the posts at certain 
 distances. 
 
 In the underground plan of laying down telegraphic lines, the copper 
 wires are covered with gutta-percha, and are then laid in trenches two feet 
 deep. This plan is found more expensive than the suspension of wires on 
 posts, and it has not, until recently, been adopted in this country, except- 
 ing under special circumstances, such as connecting the wires with the 
 telegraph stations in towns by passing under the streets. In those cases 
 it is usual to protect the wires by enclosing them in iron tubes. In 
 Prussia the underground system was at first generally adopted; but it is 
 giving way to the suspension on posts, as the gutta-percha coating was 
 attacked by vermin when not enclosed in tubes. A successful under- 
 ground line has been recently laid down along the common road from 
 London to Dover, in connexion with the submarine telegraph to Calais, 
 which may perhaps be the means of introducing that method more exten- 
 sively into the telegraph system of England. 
 
 The plan that has been found most successful for submarine telegraphs 
 is to enclose several copper wires, coated separately with gutta-percha, 
 within a hollow wire cable, of which the insulated wires form the core. 
 Cables of this kind, resting on the bed of the English Channel and of the 
 German Ocean, now serve to transmit messages between England and the 
 Continent, and answer the purpose remarkably well. 
 
 Fig. 80 shews the mode of enclosing the wires in their outer casing of 
 
 fig. 80. 
 
 iron. The protruding end c exhibits the copper wires covered with gutta- 
 
ELECTRIC TELEGRAPHS MEANS OF COMMUNICATING. 159 
 
 percha, and twisted spirally ; B is a covering of hempen twine, to form 
 the core ; A the cable of iron wire, and the other end shews a section of 
 the whole. 
 
 The principal objection to that system is its cost. The cable from 
 Dover to Calais, with four thin copper wires enclosed, cost, we understand, 
 
 Copper wire is used for submarine telegraphs, because copper is a 
 much better conductor of electricity than iron; and as a thinner wire 
 answers the purpose of conduction, it may be more easily insulated, and 
 forms a smaller core for the external cable. This mode of forming sub- 
 marine telegraphs is, however, in the author's opinion, open to many 
 objections. All the failures that have occurred in endeavouring to establish 
 submarine telegraphic communication have arisen from the breaking of the 
 wires. The experimental wire across the English Channel broke shortly 
 after the first signal was transmitted ; it was the same with that from 
 Holyhead to Dublin, though protected by a thick wire covering ; and the 
 first wire from Donaghadee to Port Patrick was cut in two by mistake. 
 It seems highly objectionable, therefore, to continue the use of thin copper 
 wire under circumstances which experience has shewn require additional 
 strength. The rejection of thick iron wire, on the ground that it is more 
 difficult to insulate than thin copper of equal conducting power, seems 
 to be not well founded. As iron conducts electricity witb less facility 
 than copper, any defect in the insulating coating will have a less injurious 
 effect than if an equal or a much smaller surface of copper was exposed ; 
 therefore, the difficulty of insulation would not be increased by the use of 
 the stronger and less perfectly-conducting metal. The cable, it is true, 
 would be thicker ; but its strength would be increased in a very much 
 greater proportion, and there would be much less danger of failure. 
 
 In forming a submarine telegraph it would be desirable not to employ 
 many wires, which increase the difficulty of insulation, but to rely rather 
 on increasing the rapidity of transmission by the use of superior instru- 
 ments. The actual number of public messages transmitted by the Electric 
 Telegraph Company between all parts of England and Scotland in the 
 half-year ending in July 1852, amounted to 85,915 ; and that number might 
 be transmitted through a single wire if the most rapid instruments were 
 employed. 
 
 Having succeeded in connecting England with the continent of Europe 
 by submarine telegraph, so as to transmit intelligence instantaneously from 
 London to Brussels and Paris, the problem that remains to be solved is, 
 to effect similar communications with America, the East Indies, and Aus- 
 tralia. It has, even at present, almost resolved itself into a question of 
 money. Such a cable as that which now connects France with England 
 might, by proper arrangements and the aid of a number of steam-ships, 
 be stretched across the Atlantic. The cost of the cable, with the ex- 
 pense of laying it down from the western coast of Ireland to New 
 Brunswick, would not amount to one million pounds sterling ; and for the 
 accomplishment of a great national object, so important to commerce and 
 to our colonial government, the expenditure of one million is scarcely 
 worth consideration as an objection. But if the mode of communication 
 which we have indicated as most suitable for submarine telegraphs were 
 adopted, the cost would not amount to nearly so much, nor would the 
 difficulty of laying down the wire be so great. 
 
160 THE APPLICATIONS OF ELECTRICITY. 
 
 A single wire telegraph between England and America would, in the 
 first instance at least, be amply sufficient. A thick galvanised iron wire 
 or rod, coated with gutta-percha, and that coating protected for some dis- 
 tance by a covering of iron wire, might be constructed at a comparatively 
 small cost, and would be much stronger and form a more efficient con- 
 ductor of electricity than a thin copper wire. Such a telegraph-wire 
 might be laid down between the west of Ireland and America for less than 
 100,OOOZ. It should be remembered, also, that in the depths of the At- 
 lantic, beyond the range of animal or vegetable life, and where no anchors 
 ever reach, the telegraphic wire would be free from the dangers to which 
 it is exposed in shallower seas. There is, indeed, no practical difficulty 
 in extending a telegraph wire to America that may not be easily sur- 
 mounted ; and with the almost certain prospect of instantaneous commu- 
 nication between the old and new world, for one-tenth the cost of build- 
 ing a bridge across the Thames, it cannot be long before that event is 
 realised. 
 
 The extent of telegraphic communication in Great Britain at the pre- 
 sent time is about 3000 miles, in France 2000, Prussia 4000, Austria 
 3000, and in America not less than 15,000. 
 
 CHAPTEK XIX. 
 
 ELECTRIC TELEGRAPHS SIGNAL INSTRUMENTS. 
 
 Progress of telegraphic invention Instruments invented by Lomond, Reizen, Soem- 
 mering, RonaLds, Ampere, Schilling, Gauss, Steinhil, Alexander, Davy Cooke and 
 Wheatstone's needle telegraphs Action of the needle telegraph Rapidity of trans- 
 mission Henley's Magneto-Electric Telegraph Breguet's Semaphore. 
 
 THE form of instrument first contrived by Lesarge, in 1774, for transmit- 
 ting telegraphic messages has been already noticed. In 1787 M. Lomond 
 so far simplified the means of telegraphic communications, as to point out 
 the way of transmitting signals with a single wire. He adopted Lesarge's 
 plan of using a pith-ball electrometer ; and he indicated the letters of the 
 alphabet by the numbers, and the variations in the duration, of the diver- 
 gences of the balls. With this telegraph M. Lomond communicated be- 
 tween different rooms in his house, the force employed being that of an 
 electrical machine. 
 
 Ten years afterwards a very ingenious application of electric light to 
 telegraphic purposes was made by M. Reizen. He pasted on a pane of 
 glass strips of tin-foil with spaces cut out in the form of letters of the 
 alphabet, so that when an electric spark was transmitted through the con- 
 voluted foil, the light at the interstices presented the form of the letter to 
 be indicated. As a means of indicating the signals this mode was perfect, 
 but it required a separate wire for each letter. Several other ingenious 
 contrivances were invented on the continent for the transmission of signals 
 by frictional electricity at the commencement of the present century, but 
 none that deserve special notice in this summary. 
 
 The first known application of voltaic electricity for the transmission 
 
ELECTRIC TELEGRAPHS SIGNAL INSTRUMENTS. 161 
 
 of signals was that of M. Soemmering, in 1809, as announced to the Aca- 
 demy of Sciences of Munich. The bubbles of gas arising from the de- 
 composition of water served to indicate the letters to be transmitted. 
 Thirty-five gold wires were inserted through the bottom of a long narrow 
 glass vessel, half filled with acidulated water. The circuit of the voltaic 
 battery was passed through the water by connecting any two of the wires 
 with the opposite poles of the battery. The instant that connexion was 
 made and the circuit completed, bubbles of hydrogen gas rose from one 
 of the wires, and of oxygen from the other. The hydrogen gas, being in 
 the proportion of twice the volume of the oxygen gas, could be easily dis- 
 tinguished. Every wire signified a letter of the alphabet, and that wire 
 from which the hydrogen was successively evolved was the letter to be 
 noticed. By this means a very efficient mode cf signalling by electro-che- 
 mical decomposition was arranged ; but the practical difficulty of requiring 
 so many wires would, under even more favourable circumstances, have 
 prevented its adoption. By a simple modification of the instrument, how- 
 ever, it may be easily adapted to the transmission of all required signals 
 with a single wire. If two gold wires only were inserted through the bot- 
 tom of the glass vessel, the hydrogen gas might be made to issue from 
 one or the other by reversing the poles of the battery, in the manner now 
 done with the needle telegraph, as will be presently explained. By this 
 means the issue of hydrogen gas from the right-hand wire might signify 
 one letter, and from the left wire another. A repetition of the jets of 
 gas, from either of the wires alternately, might signify other letters ; and 
 thus the whole alphabet might be indicated by a single circuit, in the same 
 manner, and almost with equal facility, as it is now done, by deflecting a 
 magnetic needle to the right hand and to the left. To call attention when 
 a message was to be transmitted, M. Soemmering proposed to liberate a 
 wound-up alarum by means of the evolution of the gas. 
 
 A modification of M. Soemmering' s telegraph, by which all the signals 
 might be transmitted with two voltaic circuits, was, indeed, proposed by 
 M. Schwieger. By his plan the variations of the symbols were caused by 
 employing two batteries of different powers, which consequently evolved 
 different quantities of gas, and also by making varied intervals in the 
 emissions of the gas from the gold wires. 
 
 A very remarkable form of electric telegraph was invented by Mr. 
 Ronalds in 1818, in which, however, he reverted to frictional electricity 
 for the actuating agent. At each corresponding station he had a revolving 
 dial carried round by the seconds-hand of a clock. On this dial the letters 
 of the alphabet were marked, and they were seen in succession through a 
 small aperture, near to which was suspended a pith-ball electrometer. 
 The two dials were made to revolve exactly together, so that when a letter 
 appeared at one aperture the same letter appeared also at the aperture on 
 the corresponding dial. The pith-balls were maintained in a diverging 
 condition during the transmission of a message ; and the instant that the 
 letter required to be indicated came in sight at the transmitting station, 
 the electricity sent through the communicating wire was discharged, and the 
 collapse of the pith-balls directed the attention of the observer to it at the 
 receiving station. In this manner communications could be transmitted 
 with a single wire. The synchronous movement of the two clocks, to en- 
 sure the same letters appearing at the same time at each instrument, was 
 obtained by adjusting them by an electric signal before each message. 
 
162 THE APPLICATIONS OF ELECTEICITY. 
 
 Mr. Ronalds was very persevering in his attempts to perfect his tele- 
 graph, and to bring into notice the advantages of electricity as a means 
 of telegraphic communication. He, at great expense, insulated eight miles 
 of wire in glass tubes on the lawn of his house at Hammersmith, through 
 which the telegraph was worked. He endeavoured to direct the attention 
 of the government to the subject ; but he met rebuff instead of encourage- 
 ment. The government officials told him that telegraphs are of no use in 
 time of peace, and that the semaphore answered all the required purposes ! 
 It is in this manner that attempts at improvement are generally received 
 by persons in authority. They will not give themselves the trouble to 
 investigate the merits of any invention, but wait until it has struggled 
 through all difficulties, and forces itself on their notice. Of the very 
 many useful inventions that are lost in the struggle which inventors have 
 to make, little or nothing is known. In the case of Mr. Ronalds, finding 
 his endeavours to be hopeless, he not long afterwards quitted England, 
 and took no further steps to improve a system then considered by the 
 government of so little value, but which is now, year by year, becoming 
 of more and more importance as means of general communication. 
 
 The discovery of electro-magnetism by Professor (Ersted presented a 
 new means of transmitting signals by voltaic electricity ; and in 1820 M. 
 Ampere laid before the Academy of Sciences a method which he had con- 
 trived for sending messages by the deflection of magnetic needles sur- 
 rounded by coils of wire ; his plan, however, required a separate wire for 
 each symbol. 
 
 The Baron de Schilling made a great practical improvement on the 
 plan of Ampere. He first constructed, at St. Petersburgh, in 1832, a 
 telegraph in which five magnetic needles were employed. By the single 
 deflection of these five needles alternately to the right or to the left, ten 
 primary signals were obtained, without the necessity of two needles being 
 used at the same time. The combination of a few such signals was made 
 to express whole words or sentences. He also invented an alarum. The 
 motion of one of the magnetic needles allowed a weight to fall, and sound 
 an alarm. Another of Baron Schilling's plans, of a later date, was to use 
 only one magnetic needle ; and by counting the deflections to the right or 
 to the left, the letters of the alphabet were indicated.* 
 
 Not long after the discovery of magneto-electricity by Professor Fara- 
 day, Messrs. Gauss and Weber of Gottingen applied the magneto-electric 
 machine to the transmission of messages. They employed only a single 
 needle to make all the symbols, and a telegraph operating on that princi- 
 ple was worked at Gottingen for a distance of a mile and a quarter. 
 
 Dr. Steinheil's telegraph, invented in 1837, presented great advance- 
 ment in the application of electricity to telegraphic purposes. It is spoken 
 of by Mr. Highton as a perfect arrangement, and as one which " may well 
 ut to shame many of the plans afterwards patented in this kingdom." 
 r. Steinheil could either transmit messages by sound or by making per- 
 manent marks on paper. This telegraph consisted of a single circuit, half 
 of it being galvanised wire, the other half the earth, and the stations be- 
 tween which the telegraph worked were twelve miles apart. One or two 
 magnetic needles were employed as required, and they were deflected by 
 
 * The Electric Telegraph, by E. Highton. 
 
 S 
 
ELECTRIC TELEGRAPHS SIGNAL INSTRUMENTS. 163 
 
 magneto-electricity. When it was required to telegraph by sound, the 
 needles struck against either of two bells differently toned. When the 
 message was recorded, the needles were furnished with small tubes holding 
 ink, and by their motions dots were made on paper properly moved in 
 front of them by wound-up mechanism, one needle making dots in one 
 line, and the other needle making dots in a line underneath the former. 
 Not more than four dots were required to make any of the letters, and 
 some were marked by a single dot. The mode of recording on paper the 
 messages transmitted by this means will be rendered more intelligible by 
 the annexed representation of the symbolical alphabet made by the pen- 
 holding needles. 
 
 ABDEFGHCHSCfflKL MINT O PR S TVW Z 
 L AX\ rn""*-, A> J V- - "~VS/ YV\% 
 
 fig. 81. 
 
 Before the year 1837 scarcely any attempt besides that of Mr. Ronalds's 
 had been made in England to improve the electric telegraph; but that 
 year seems to mark the commencement of the direction of inventive genius 
 to the subject in this country, which has since progressed most rapidly. 
 In June 1837 the electric telegraphs of Mr. Alexander and of Mr. Davy 
 were publicly exhibited in London. The former operated by removing 
 screens from before letters of the alphabet. The letters were painted on a 
 frame, and were concealed from sight by small light screens attached to 
 the magnetised needles, the deflection of which, when the voltaic current 
 passed through the coils, successively exposed the letters to view. Mr. 
 Davy's telegraph was constructed on the same principles, but the letters 
 were painted on ground glass illuminated from behind, consequently the 
 letters were more distinguishable. Both these telegraphs required a sepa- 
 rate voltaic circuit for each symbol. It is, indeed, curious to notice in 
 the progress of telegraphic invention, that notwithstanding the impracti- 
 cability of using a telegraph which required so great a number of wires, 
 notwithstanding also that the mode of transmission by one or two wires had 
 been often pointed out, how resolutely each inventor in succession adhered 
 to the appropriation of a separate wire for every symbol to be transmitted. 
 
 In 1837, Professor Wheatstone, who, in conjunction with Mr. Cooke, 
 succeeded in establishing the first working electric telegraph, appeared in 
 the field. The patent taken out by Messrs. Cooke and Wheatstone in 
 1837 was for a needle telegraph, in which the symbols were made with 
 five needles. In the following year the arrangement was simplified so far 
 as to reduce the number of needles to two. That arrangement of the 
 double needle telegraph is the one that continues to be generally used in 
 this country. 
 
 It would occupy far too much space to give an account of all the modifi- 
 cations and improvements in the modes of transmitting messages that have 
 been since introduced. Upwards of fifty patents for electric telegraphs 
 have been obtained in England since the first of Messrs. Cooke and 
 Wheatstone's, and numerous other similar inventions have been patented 
 on the continent and in America ; but it will be sufficient to limit our no- 
 tice to those that possess the most distinguishing features. 
 
164 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 The needle telegraph is simply a delicate galvanometer constructed of 
 numerous coils of the finest copper wire covered with silk. The magnet- 
 ised needle is placed upright, the lower end being slightly heavier, to make 
 it assume a perpendicular position when in its normal state. There are 
 two oblong coils of the fine wire connected together, between which the 
 needle is poised. The object of employing two connected coils instead of 
 a single one, is to allow the axis that carries the needle to pass between. 
 
 fig. 82. 
 
 The diagram exhibits a perspective view of a mounted needle h. 
 The axis is supported within the coil i k, so as to allow the needle to 
 vibrate with the least possible resistance from friction. The needle h is 
 fixed to the end of the axis, and is outside the coil, to serve as an index to 
 denote the deflection of the needle. The poles of the outer needle are in a 
 reversed position to those of the inner one, so that the magnetic action of 
 the coil, when the current passes, tends to deflect them both in the same 
 direction and with increased force. The index is, however, sometimes 
 made of a light strip of wood, but by that means some of the power of the 
 coil is lost. When the voltaic current is sent through the coils the needle 
 is instantly deflected either to the right or to the left, according to the di- 
 rection in which the current passes ; the connexions with the copper and 
 the zinc ends of the battery being so arranged that they may be reversed 
 on moving the working handle either to the right or to the left. 
 
 The arrangements of the instrument to reverse the directions of the 
 voltaic current are rather complicated ; but the principle on which they 
 depend will be readily understood by inspection of fig. 83. The letters D E 
 
ELECTRIC TELEGRAPHS SIGNAL INSTRUMENTS. 165 
 
 represent the communicating wire, in which there is a break at the trans- 
 mitting station. Close to this break is placed a movable piece b d, that 
 slides laterally, and it is connected with the two poles c z of the voltaic 
 battery. The upright wires at b d, each connected with the zinc pole z, are 
 insulated from the wire e, which is connected with the copper pole c. It 
 will be evident, therefore, that if the piece to which these wires are attached 
 be shifted towards the right, the wire e will touch the communicating wire 
 at D, and b will touch E. By these contacts with the two ends of the com- 
 municating wire, the circuit of the voltaic battery will be completed, and 
 an electric current will be transmitted from c to D, in the direction of the 
 arrow, to the earth-plate H, thence to the receiving station, and back again, 
 through the instrument I, to the 
 zinc pole z. The lateral move- 
 ment of the wires connected with 
 the battery to the left will, in the 
 like manner, bring e, which is in 
 connection with the copper pole, 
 to E, and d of the zinc pole to D, 
 and the current will then be sent 
 in the opposite direction, viz. from 
 the copper pole of the battery to 
 E, through the instrument I to 
 the receiving station ; and it will fig . 83> 
 
 return by the earth-plate H to the 
 
 zinc end of the battery. By rapidly changing the positions of the wires 
 from side to side, the voltaic current may be thus reversed several times in 
 one second ; and each reversal of the current will change the direction in 
 which the needle is deflected. 
 
 By the adoption of what is called a code of signals, the deflections of a 
 single needle may be made to denote all the letters of the alphabet. The 
 code at present in use in this country for a single needle -telegraph is shewn 
 in the annexed diagram ; the number of deflections of the needle to the 
 right and left being made to indicate the letters under which the marks are 
 placed. The deflections of the symbols for each letter commence in the 
 direction of the short marks, and end with the long ones. Thus it will be 
 seen, that to indicate the letter D the needle is first deflected once to the 
 right and then once to the left ; whilst two deflections, beginning with one 
 to the left and ending with one to the right, signify the letter R. 
 
 It will be observed that all 
 
 the symbols in the left division -A. B C M !H" O IP 
 
 of the scale commence with a \ \\ \\\ \\\\ / // /// //// 
 
 right-hand deflection and end X XX XXX XXXX I ' " ll/ ///l 
 with the left; whilst those on the D B I A R S T 
 
 right division commence with the \, \, \\. 1 J J/ J// 
 
 left and end with a deflection to 
 
 the right. When the double = * TT V TT 
 
 needle-telegraph is used, the V ^ ^ II / ^1 / 
 
 number of successive deflections | 
 
 requisite to denote all the letters M "u U II II A\ 
 
 of the alphabet are fewer, because, WWW N W \V 
 
 with two needles capable of being fig. 84. 
 
166 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 pointed in both directions, six primary symbols are obtained by a combi- 
 nation of the deflections of the two needles. 
 
 A practical knowledge of the working of the needle instruments is 
 generally acquired within a month. Some of the telegraph clerks have 
 become so expert by continued practice, that they can transmit as many 
 as 150 letters a minute with the double needle instrument. It is, however, 
 much more difficult to read the symbols than to transmit them ; and as 
 the messages must be written down, the rapidity of transmission is prac- 
 tically limited to the speed of writing, which seldom exceeds 100 letters a 
 minute, and that is considerably faster than the average rate of transmission. 
 In the early stages of the progress of the electric telegraph it was con- 
 sidered very important to have the means of calling attention when a mes- 
 sage was to be transmitted, and there were many contrivances for ring- 
 ing bells at the distant stations. The use of alarums has, however, been 
 discontinued at nearly all the stations of the Electric Telegraph Company. 
 ^The sound of the needles striking against the pins fixed in the dial to limit 
 the range of the deflections is generally sufficient to call the attention of 
 the clerks, who are constantly seated near their instruments. When ala- 
 rums are required, bells are sounded by liberating a wound-up mechanism 
 by withdrawing a detent by means of an electro-magnet. 
 
 Fig. 85 represents a front view of a double needle instrument. The 
 handles are held by the clerks, and by moving one or both to the right or 
 to the left one or both of the needles are correspondingly deflected. In 
 transmitting messages in this manner it is customary for the clerk at the 
 receiving instrument to intimate at the end of each word that he under- 
 stands, by giving a single 
 deflection of the left-hand 
 needle to the right ; when 
 he does not understand, and 
 requires the word to be re- 
 peated, he deflects the same 
 needle to the left. 
 
 There have been many 
 patents obtained for modifi- 
 cations of the needle tele- 
 graph ; but they are all 
 identical in principle with 
 the original one of Messrs. 
 Cooke and Wheatstone. One 
 of the objects that it has 
 been the endeavour to at- 
 tain, is a dead beat of the 
 needle without any vibration. 
 It is now the practice to use a piece of lozenge-shaped magnetised steel 
 instead of a needle within the coil, that form having been found to be more 
 sensitive to the action of the voltaic current, and to produce less vibration. 
 One arrangement of the needle telegraph, quite distinct from the fore- 
 going, is the magneto-electric telegraph invented by Mr. Henley. We 
 have already noticed several attempts to apply magneto-electricity to tele- 
 graphic purposes, but that of Mr. Henley is by far the most successful. 
 Two armatures, in close proximity to strong permanent magnets, are made 
 
 fig. 85. 
 
ELECTRIC TELEGRAPHS RECORDING INSTRUMENTS. 167 
 
 to revolve rapidly by striking down projecting levers ; and the revolutions 
 of the armatures induce currents of electricity along the communicating 
 wires, that re-act on the magnetic needles, and cause them to be instantly 
 deflected. 
 
 The electricity generated in this manner is small in quantity, and of 
 comparatively great intensity, therefore more liable to be diverted from 
 the circuit by imperfect insulation. Another difficulty which this form of 
 telegraph has to contend with is, that the current cannot be conveniently 
 reversed, therefore each needle is only deflected in one direction. Two 
 communicating wires are consequently required to obtain the same com- 
 bination of deflections that can be given with a single wire when a voltaic 
 current is transmitted. It is a great advantage of this system that it dis- 
 penses with the use of voltaic batteries, which are very troublesome and 
 expensive ; and it remains a question to be determined by practical expe- 
 rience, whether this advantage is sufficient to counterbalance the objections 
 attending the use of the magneto-electric telegraph. 
 
 The electric telegraph used on all the telegraph lines in France was 
 invented by M. Breguet, and transmits symbols resembling those of the 
 semaphore. Two movable arms attached to the tops of two stationary 
 vertical pillars are made to assume positions at certain angles in the cir- 
 cles they describe, and the combinations of those different positions in 
 the two arms allow of their expressing a great variety of symbols, which 
 correspond exactly with the code of the discarded semaphore. 
 
 We have heard this kind of signal telegraph highly commended, and 
 have seen messages that were transmitted by it at the rate of 120 letters 
 a minute. It possesses the advantage, from the great variety of com- 
 binations of which it is capable, of not requiring successive actions to in- 
 dicate any letter of the alphabet or numeral. The movements are effected 
 by electro-magnets, which give rotary motion to wheels that carry round 
 the arms ; and the accuracy with which it is necessary that the semaphore 
 should be pointed to the required angles renders very nice adjustment of 
 the instruments indispensable. 
 
 CHAPTEE XX. 
 
 ELECTRIC TELEGRAPHS RECORDING INSTRUMENTS. 
 
 Morse's telegraph Modification of it by the Electric Telegraph Company Bain's dot- 
 ting telegraph Brett's printing telegraph Copying telegraph Mode of transmit- 
 ting copies of writing Regulation of the instruments Rapidity of the copying pro- 
 cess Means of maintaining secrecy. 
 
 THE telegraphic instruments we are now about to describe record on 
 paper the messages they transmit ; in other telegraphs the symbols are 
 exhibited for an instant and disappear. Many more errors occur in read- 
 ing the evanescent signals than in the transmission of them ; but as the 
 recording instruments impress what is transmitted, the message may be 
 read at leisure when the whole is completed. 
 
168 THE APPLICATIONS OF ELECTRICITY. 
 
 We have already noticed, in the progress of telegraphic invention, the 
 recording telegraph of Dr. Steinheil, which made dots on paper by means 
 of ink-holders fixed to magnetic needles. That plan, though it has formed 
 the model of several subsequent inventions, was imperfect, because the 
 deflections of the needles were retarded by the weight of the pens, and the 
 marks made were not sufficiently distinct. 
 
 The most successful of the instruments that impress arbitrary symbols 
 on paper is that of Professor Morse of America, invented in 1837, and 
 since considerably improved. The transmitting part of the instrument is 
 of the very simplest kind, and might be carried in the waistcoat-pocket. 
 It consists only of a key, like the key of a musical instrument, which, on 
 being pressed down, makes connexion with the voltaic battery for a 
 shorter or longer duration, according to the time that the finger of the 
 operator is pressed upon it. The receiving instrument is more compli- 
 cated. By means of clock mechanism, a small drum, round which a long 
 strip or ribbon of paper is rolled, is made to revolve. The paper as it is 
 unrolled from the drum passes under a lever attached to the keeper of an 
 electro-magnet, armed with a projecting point. When the electro-mag- 
 net is put into action, the lever is drawn down on the paper, and the 
 point makes an indentation on it. As the paper is continually drawn 
 along, the length of the indentation varies from a mere dot to a long 
 stroke, according to the time that the lever continues to be pressed against 
 the paper ; and by varying the duration of the pressure on the trans- 
 mitting key, dots and strokes are impressed on the paper at the receiving 
 station. Conventional symbolical alphabets have been arranged, by the 
 alternation of the dots and strokes, which, with a little practice, may be 
 easily read. The symbolical alphabet that has been adopted in this coun- 
 try, when a modification of Morse's system is used, is represented in 
 figure 86. 
 
 A. B C !>__ E _JP_ _r_ 3C_ I 
 
 K jL _??__ ?. Q S __ J L. 
 
 T TT IT "W 3Z__ ~S: 25^ 
 
 fig. 86. 
 
 As the mechanical power required to impress marks on the paper is 
 stronger than could well be transmitted directly through the long circuit, 
 a local voltaic battery and magnet are employed to do the work ; and they 
 are brought into action by means of a small electro-magnet, surrounded 
 by a great number of convolutions of very fine wire, that may be actuated 
 by the feeble current transmitted by the communicating wire. This kind 
 of telegraph is extensively used in the United States, and it is also coming 
 into use in Belgium and Germany. 
 
 In the modification of Professor Morse's instruments, as occasionally 
 used by the Electric Telegraph Company, the marks on the paper are 
 made by the agency of electro-chemical decomposition, and not by mecha- 
 nical pressure. The application of electro- chemical decomposition to 
 telegraphic purposes was first adopted by Mr. Davy in 1838. His plan 
 
ELECTRIC TELEGRAPHS RECORDING INSTRUMENTS. 169 
 
 was to moisten paper in a diluted solution of nitric acid and prussiate of 
 potass, and to send a voltaic current from the positive pole of the battery 
 through a steel wire pressing on the paper. By the action of electricity 
 the oxygen of the acid attacks the steel wire, and a deposition of iron is 
 made on the paper, and it is converted into prussian blue by the prussiate 
 of potass. The arrangements of Mr. Davy's recording telegraph need not 
 be described, as they were never made practically available ; but his system 
 of marking paper by electro-chemical agency has been successfully applied 
 to other telegraphs. 
 
 In 1846, Mr. Bain contrived a modification of Professor Morse's system, 
 in which the marks are made by Mr. Davy's process. The transmission of 
 symbols in this telegraph of Mr. Bain's is not effected by a key moved by 
 hand, but metallic contact is made and broken by mechanical means. 
 Apertures are punched in a strip of paper, to correspond with the dots and 
 strokes intended to be impressed on the paper of the receiving instrument. 
 The paper-message when thus prepared is passed rapidly over the peri- 
 phery of a metal wheel, and a brass wire-spring, connected with a voltaic 
 battery, presses on the paper as it passes along. The spring, by pressing 
 through the holes, touches the wheel, which is connected with the other 
 pole of the battery, and thus completes the voltaic circuit, which is again 
 broken when the spring rests on the insulating paper. Mr. Davy's pre- 
 pared paper is applied at the receiving station, and the effect of the action 
 of the two corresponding instruments is to transmit dots and strokes, 
 marked in prussian blue on the paper at the receiving station, agreeing 
 with the smaller and larger holes punched in the strip passed through the 
 transmitting instrument. The annexed diagram represents a piece of the 
 punched paper with the symbols of the word " Bain." 
 
 . 87. 
 
 The rapidity of transmission by this means exceeds that of any other 
 telegraph. As many as 1000 letters a minute have been transmitted from 
 London to Manchester; but the time required for punching the paper 
 preparatory to sending a message is a serious drawback to the general use 
 of the system. 
 
 The Electric Telegraph Company, when they employ any other instru- 
 ment than the needle, use that of Professor Morse, with the substitution of 
 electro-chemical marks for those produced by mechanical pressure. The 
 rate at which messages can be transmitted by means of the key with a 
 single communicating wire is about ninety letters a minute. The transmis- 
 sion, however, requires the utmost attention on the part of the operator, 
 who cannot continue to transmit at that rate for many minutes at a time. 
 
 Among the early inventions of recording telegraphs were some that 
 printed letters from metal types. Professor Wheatstone and Mr. Bain dis- 
 puted for the honour of being the inventor of the first printing electric 
 telegraph ; but their instruments did not attain such a degree of perfection 
 
170 THE APPLICATIONS OF ELECTRICITY. 
 
 as to render them practically useful. Mr. House of America, and subse- 
 quently Mr. Brett, have, however, succeeded in producing printing tele- 
 graphs which work effectively through long circuits. The mechanism is 
 complicated, but the principle on which the action depends may be easily 
 understood. A small wheel, that revolves by the agency of electro-mag- 
 netism, carries on its circumference metal types of each letter of the 
 alphabet, which are inked as the wheel turns round by rubbing on the 
 surface of a small inking roller. At one part of the circumference of the 
 type-wheel there is a ribbon of paper close to the types, and by the pres- 
 sure of the paper against the wheel the letter that is opposite to it is 
 printed. The movement of the type-wheel is regulated by the operator 
 at the transmitting instrument, who, by bringing an index to point on the 
 dial of his instrument to the letter required, it at the same time causes the 
 type-wheel to move round, so as to bring a corresponding letter opposite 
 the paper. A local electro-magnet is then put in action ; by which means the 
 drum on which the paper rests is pressed against the type, and the letter 
 is printed. As each letter is thus printed, the strip of paper is moved 
 onward about a quarter of an inch, to leave a clear space for the next. 
 
 The action of the printing telegraph is rather slow ; but it is worked 
 with a single wire. We have not seen it working faster than at the rate 
 of forty letters a minute ; but we are informed that it can print upwards 
 of sixty letters in that time. One peculiar advantage of Mr. Brett's 
 arrangement is, that the type-wheel is placed in correct position at the 
 end of each transmission; so that if by mistake an error is committed, 
 by printing one letter instead of another, that error is not continued 
 to the next letter, for the type-wheel is adjusted to start from zero be- 
 fore the next movement of the index. All preceding printing tele- 
 graphs were liable to perpetuate errors whenever a single one had been 
 committed. 
 
 The copying-telegraph, of which the author of this work is the in- 
 ventor, transmits copies of the handwriting of correspondents. The 
 advantages of this mode of transmission are, that the communications 
 may be authenticated by the recognised signatures of the parties by whom 
 they are sent, and as the writing received is traced from the original 
 message, there can be no errors of transmission; for every letter and 
 mark made with the pen are transferred exactly to the other instru- 
 ment, however distant. 
 
 The electro-chemical mode of marking the paper, invented by Mr. 
 Davy, is adopted in the copying process. The writing is copied on paper 
 soaked in a solution of prussiate of potass and muriatic acid, a piece of 
 steel wire serving for the pen. The paper is placed round a cylinder 
 about six inches in diameter, and a steel wire, connected with the copper 
 end of the voltaic battery, presses upon it, and is carried slowly along by 
 a screw as the cylinder revolves. By this arrangement, when the voltaic 
 current passes uninterruptedly from the wire through the paper to the 
 cylinder which is connected with the zinc end of the battery, lines are 
 drawn upon it at the same distance apart as the threads of the screw that 
 carry the point. These lines are in fact but one continuous spiral line, 
 commencing at one end of the cylinder and ending at the other. 
 
 The communication to be transmitted is written on tin-foil, with a 
 pen dipped in varnish. Thin sealing-wax varnish, made by dissolving 
 
ELECTRIC TELEGRAPHS RECORDING INSTRUMENTS. 
 
 171 
 
 sealing-wax in spirits of wine, answers the purpose best, as it dries very 
 quickly. The letters thus written form on the conducting metal surface a 
 number of non-conducting marks, sufficient to interrupt the electric current, 
 though the deposit of resinous matter is so slight as not to be perceptible 
 by the touch. 
 
 The message on tin-foil is fixed round a cylinder at the transmitting 
 instrument, which instrument is a counterpart in its mechanical arrange- 
 ments of the receiving one, and either of them may be used to transmit 
 and receive messages. A metal style in connexion with the voltaic battery 
 presses on the tin-foil, and it is carried along by an endless screw as the 
 cylinder revolves, exactly in the same manner as the steel wire that draws 
 lines on the paper on the receiving instrument. The varnish writing, 
 when it interposes between the style and the tin-foil, stops the electric 
 current ; consequently, at every part where the electric current is stopped 
 by the varnish at one instrument, the steel wire ceases to make marks on 
 the paper at the other station. Both instruments are so regulated that 
 the cylinders rotate exactly together, therefore the successive breaks of 
 the electric current by the varnish-letters cause corresponding gaps to be 
 made in the lines on the paper ; and the succession of these lines, with 
 their successive gaps where the letters occur, produces on the paper of the 
 receiving instrument the exact forms of the letters. The letters appear of 
 a white or pale colour on a ground of blue lines, there being about nine or 
 ten lines drawn by the wire to make one line of writing. In the diagram, 
 A shews the writing on tin-foil, from which the copy is made in the form 
 shewn at B. 
 
 It is essential to the correct working of the instruments that the cylin- 
 ders should rotate exactly together. This synchronous movement of the 
 two instruments is effected by means of regulating electro-magnets, aided 
 by a " guide-line" on the transmitting cylinder. 
 
 The moving power of each instrument is gravity, accelerated motion 
 being prevented by a rapidly revolving fan, which produces a very steady 
 movement of the cylinder. The speed may thus be very easily varied by 
 adding or by taking off weight. The " guide-line" consists simply of a 
 strip of paper pasted across the tin-foil at a right angle, as shewn at c. That 
 strip of paper effectually stops the electric current, and leaves a gap of equal 
 breadth in each line drawn on the prepared paper of the receiving instru- 
 ment. If the receiving instrument be moving at exactly the same speed 
 as the transmitting one, these gaps in each line will be in the same relative 
 
172 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 positions, and will fall under each other on the receiving cylinder, making 
 a broad white stripe corresponding with the strip of paper on the trans- 
 mitting cylinder. But if the receiving cylinder be moving faster than the 
 other, the gaps in the lines will not fall under one another, but every one 
 will be farther towards the right hand. By noticing the position of these 
 gaps on the paper, it may be seen exactly how much faster one instrument 
 is going than the other, and weight may be taken off the receiving instru- 
 ment until the gaps form a continuous stripe. In this manner the two 
 instruments may be regulated to move together. It is immaterial at what 
 distance apart they are ; for if they be in the same room, or two hundred 
 miles from each other, the same plan of adjustment must be adopted. 
 
 Supposing the mechanism of the instruments to be very good, and that 
 there were no irregularities on the surfaces of the cylinders, the plan of 
 regulating by means of the guide-line alone would be sufficient for the 
 copying process. Legible writing may, indeed, be obtained in that manner, 
 but not with sufficient accuracy and certainty to be depended on in ordi- 
 nary working operations. To secure the requisite degree of accuracy and 
 certainty, an electro -magnetic regulator is used. This may be brought into 
 action by means of a second communicating wire, or by local action alto- 
 gether ; in the latter case a single wire only is required to work the copy- 
 ing telegraph. When two wires are employed, one of them is used for the 
 electro-magnet that regulates the instruments, the other for transmitting 
 the current that marks the paper by electro-chemical decomposition. The 
 diagram will assist in explaining the mode of regulating the instruments 
 when a separate wire is used for that purpose. 
 
 fig. 89. 
 
 A side view only of the two instruments is given, without their stands 
 or other mechanism than that which appears on the outside of each ; the 
 trains of wheels propelled by the weights being contained within the 
 cheeks A A and B B, and the cylinders being on the opposite sides. The 
 wheel D is fixed to the projecting arbor of a fast-moving wheel next to the 
 fan, and it makes twelve revolutions to one of the cylinder. Two springs 
 e e, insulated from the instruments by being mounted on wood, are con- 
 nected by wires c z to the voltaic battery, and to the electro-magnet M on 
 the other instrument. The other end of the coil of wire round the electro- 
 magnet is fixed to the voltaic battery, so that when the two springs e e 
 touch; the circuit of the battery is completed, and the electro-magnet is 
 
ELECTRIC TELEGRAPHS RECORDING INSTRUMENTS. 
 
 173 
 
 instantly brought into action. This occurs once every revolution of the 
 wheel D, by the projecting part g pressing the two springs together. The 
 wheel E on the instrument A is fixed on to the arbor of a wheel corre- 
 sponding with that of D, and likewise makes twelve revolutions to one 
 revolution of the cylinder. 
 
 The keeper K of the electro-magnet has an arm or lever L added to it, 
 which reaches to the circumference of the wheel E, and, when the keeper is 
 attracted by the magnet, rubs against a projecting part of the circum- 
 ference o, and thus operates as a break to check the motion of the instru- 
 ment. In regulating the instruments to rotate synchronously by these 
 means, a heavier weight is put on A than on B, to cause it to rotate consi- 
 derably faster than the other when the break is not applied. But when 
 both instruments are set in motion, the lever being pulled down each time 
 that the springs are pressed together by the wheel D, the break is thus put 
 in operation just sufficiently to make the movements of the two instru- 
 ments correspond. By this arrangement it will be observed that one 
 instrument regulates the other; and it has it under such complete control, 
 that if the speed of B be diminished, the movement of A will be retarded by 
 the longer continued action of the break, and be made to rotate equally 
 slowly, and even to stop by stopping the motion of B. 
 
 When the instruments are worked at a distance from each other, the 
 electro-magnet M is put into action by a local battery, and the contact is 
 made and broken by an intermediate small electro-magnet, as in Mr. Morse's 
 telegraph. In that manner the copying telegraph has transmitted messages 
 with perfect accuracy from Brighton to London. 
 
 When a single communicating wire only is used, the instruments are 
 regulated independently of each other by means of pendulums. Clock- 
 movements, with pendulums that beat four times in a second, are employed 
 at each instrument. These pendulums at every vibration strike against 
 springs, at each contact with which the electro-magnets which regulate the 
 instruments are brought into action. 
 
 The arrangement of the mode of making and breaking contact by the 
 pendulum will be easily understood by the diagram. The pendulum D is 
 
 fig. 90. 
 
174 THE APPLICATIONS OF ELECTRICITY. 
 
 connected by the wire c to the electro-magnet M. The springs 5 s' are con- 
 nected with the voltaic battery v, from which a wire z connects with the 
 other end of the coil of the electro-magnet. It will be evident, therefore, 
 that when the rod of the pendulum vibrates against s s', the voltaic circuit 
 is completed through the magnet, which is brought into action in regulat- 
 ing the instruments as rapidly as the pendulum beats. Each instrument 
 has its regulating magnet and pendulum, and the regulation of each is 
 thus effected independently, without requiring a second wire. 
 
 The guide-line serves to indicate with the greatest accuracy whether 
 the pendulums at two corresponding stations are beating together ; for if 
 one be vibrating faster than the other, the guide-line on the paper will be 
 slanting instead of perpendicular ; and by means of an adjusting screw to 
 raise or lower the pendulum-bob, the two may be readily adjusted to beat 
 together. In this manner a variation of even the thousandth part of a 
 second may be observed and corrected. 
 
 It may probably be supposed, because the metal style has to pass over 
 each line of writing nine or ten times to complete it, that the copying, 
 process must be necessarily slow ; but it is, on the contrary, the quickest 
 mode of transmission yet invented, with the exception of Mr. Bain's. A 
 cylinder six inches in diameter will hold a length of paper on which one 
 hundred letters of the alphabet may be written in a line. When the 
 instruments are working at their ordinary speed, the cylinder revolves 
 thirty times in a minute ; and allowing ten revolutions to complete each 
 line of writing, the rate of transmission is three hundred letters in a 
 minute. Much greater speed than that has been obtained ; and there is, 
 indeed, no limit to the rapidity of transmission other than the diminishing 
 strength of the mark on the paper when the decomposition is extended 
 over a larger surface. 
 
 One of the advantages which the copying process also possesses is the 
 means it affords of maintaining the secrecy of correspondence. It is now 
 customary for those who wish their communications not to be known to> 
 transmit messages in cypher, by which certain letters or figures have sig- 
 nifications given to them which are only intelligible to the parties corre- 
 sponding. This plan has the serious disadvantage of being very liable to 
 error, because the clerks engaged in transmitting such a message are pur- 
 posely kept in ignorance of the meaning of the symbols they transmit. By 
 the copying telegraph whatever symbols are made on the tin-foil are trans- 
 mitted as accurately as if written in full, for no manipulation whatever i& 
 required, the effect being produced altogether by mechanism. 
 
 There is also a special mode of maintaining secrecy by transmitting 
 the messages impressed on the paper invisibly. If the paper be moistened 
 with diluted acid alone, the iron is deposited on the paper, but no mark 
 whatever is visible, and the paper remains blank until it is brushed over 
 with a solution of prussiate of potash, which instantly renders it legible. 
 In this manner messages written with colourless varnish may be trans- 
 mitted without any one seeing the contents ; that part where the name 
 and address are written being alone rendered legible till the message is 
 delivered to the person for whom it is intended. 
 
 The author trusts he shall be excused for having described thus fully 
 his invention of the copying telegraph. It is very probable that he 
 attaches more importance to it than those not so specially interested may 
 
ELECTRO-METALLURGY. 175 
 
 think that it deserves ; but he has received the assurance of some scientific 
 gentlemen who have been the longest and the most successfully engaged 
 in such undertakings, that the copying of writing is the beau-ideal of tele- 
 graphic communication, and that sooner or later it must supersede all other 
 means of corresponding by electric telegraph. 
 
 CHAPTER XXL 
 
 ELECTRO-IIETALLITRGY. 
 
 Competing claims to the discovery Deposition of medals from their solutions Its de- 
 pendence on secondary results Apparent anomaly of deposition in a single cell 
 Formation of moulds Copying medals Reduplication of copper-plate engravings 
 Glyphography Electro-plating and gilding. 
 
 THE important application of electricity to working in metals is of even 
 more recent date than the invention of the electric telegraph. The fact 
 that metals could be "revived" from their solutions by means of electricity 
 was, indeed, known at the beginning of the present century. In 1805 
 Brugnatelli gilded a large silver medal by connecting it with the negative 
 pole of a voltaic battery, and then immersing it in a solution of ammo- 
 niuret of gold ; but, strange as we now think it, the practical use to 
 which this peculiar action of electricity might be applied did not occur to 
 him. Mr. Spencer of Liverpool claims to be the first who discovered that 
 the deposition of metals by electrical agency might be rendered useful in 
 the arts. He states, that when experimenting in 1837 with a Daniell's 
 battery, he used a penny instead of a plain piece of copper for a pole ; and 
 that on removing the wire which connected the penny with the battery, 
 he pulled off a portion of the deposited copper, which he found to be im- 
 pressed with a counterpart of the head and letters of the coin. Even this 
 did not suggest to Mr. Spencer any useful application, until he accident- 
 ally dropped some varnish on a piece of copper similarly connected with 
 the negative pole, and he observed that no deposition of copper took place 
 on those parts covered by the varnish. It then occurred to him that by 
 covering a sheet of copper with varnish or wax, and cutting a design 
 through it so as to lay bare the metal, the copper would be deposited from 
 the solution of sulphate of copper in the lines of the design cut through 
 the wax, and would adhere to the surface of the plate, producing the figure 
 in relief. 
 
 The statement of the experiments by Mr. Spencer was not made 
 known until 1839, after Professor Jacobi of St. Petersburgh was announced 
 to have made a similar discovery. Indeed, before the account of Mr. 
 Spencer's experiments was published, a letter from Mr. Jordan, a printer, 
 appeared in the Medianics Magazine of May llth, 1839, describing a 
 method of producing copper casts by what is now known as the electro- 
 type process. It appears, therefore, that though Mr. Spencer was the first 
 discoverer, the earliest published notice referred to the discovery of Jacobi, 
 whilst the letter of Mr. Jordan contained the first explanation of the mode 
 
176 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 by which the effects may be produced. It was not, however, till the 
 autumn of the same year, when Mr. Spencer brought the subject before 
 the British Association for the Advancement of Science, and exhibited 
 numerous specimens of electrotype casts and designs, that the attention of 
 the public was directed to this application of electric force. 
 
 It is well observed by Mr. Napier, in his excellent treatise on electro- 
 metallurgy, to which we are much indebted, " In reviewing the rise and 
 progress of any discovery in the arts and sciences, particularly of one con- 
 nected with chemistry, there are two circumstances which almost invariably 
 demand especial notice. The first is, that the discovery has been the result 
 of accidental observation rather than the result of a direct endeavour to 
 make the discovery. The second is, that after the discovery has been made 
 known, it is found that many previously published experiments exhibited 
 results which bore more or less directly upon the subsequent discovery, 
 and which are consequently sometimes cited to detract from the merit of 
 the discoverer, and the originality and value of his discovery." These 
 remarks apply with special force to the art of electro- metallurgy. It is to 
 Mr. Spencer, however, that we are inclined to award the honour of the 
 discovery, and the merit of having brought it into practical operation in 
 this country. 
 
 The deposition of metals in the process of electro-metallurgy has been 
 to be the result of secondary action, arising primarily 
 bion of water in the fluid menstruum. 
 
 ju xx v U*^LrwDAUlVrU V/J. 
 
 previously explained 1 
 from the decompositi< 
 
 fig. 91. 
 
 Let b be a vessel containing a saturated solution of sulphate of copper 
 (blue vitriol), with three circular medals immersed in it and connected 
 with the voltaic battery a by the wires c d, from the copper and zinc plates 
 respectively. An electric current will thus be established from d, which 
 is in connexion with the copper of the battery, to b, and the oxygen of 
 the fluid decomposed will be liberated on the surface of the copper plate 
 e, to which it is attached, and the hydrogen on the medals. But the nas- 
 cent hydrogen, the instant that it is liberated from its association with 
 oxygen in the fluid, and before it can assume a gaseous form, combines 
 with the oxygen that holds the copper in solution, and with it constitutes 
 another particle of water, and the copper is deposited on the medals. 
 
 The deposition of the metal from its solution is the result of a variety 
 of rather complicated chemical actions. The strong affinity of oxygen for 
 the hydrogen, with which it was combined to form water, is first overcome 
 
ELECTRO-METALLURGY. 177 
 
 by the influence of the electric force. The oxygen, liberated at the plate 
 e, immediately enters into combination with the sulphur in the solution 
 to form a fresh particle of sulphuric acid ; the hydrogen, freed from its 
 combination with oxygen, is transferred to the medals, and its affinity for 
 oxygen being greater than that subsisting between the oxygen and the 
 copper held in solution, the hydrogen re-enters into combination with 
 oxygen and forms a fresh particle of water, whilst the copper is set free in 
 its metallic state and is deposited. In all the processes of electro- 
 metallurgy, whether they consist in the depositions of copper or of other 
 metals from their solutions, the same chemical actions and reactions take 
 place ; the hydrogen in every case effects the deposition of the metal by 
 combining with the oxygen which holds the metal in solution at one pole 
 of the battery, after having been separated from an equal particle of oxy- 
 gen at the positive pole. There is, consequently, throughout the process 
 a continual decomposition of water at one pole of the voltaic battery, and 
 a recomposition of exactly the same quantity of water at the other pole. 
 
 One of the simplest illustrations of metallic depo- 
 sition by electro-chemical action is afforded by the 
 following experiment. Put a silver spoon A, fig. 92, 
 into a glass containing a solution of sulphate of copper, 
 and into the same glass insert a piece of zinc z. No 
 change will take place in either metal so long as they 
 are kept apart, but as soon as they touch, copper 
 will be deposited on the spoon, and if it be allowed to 
 remain, the part immersed will be completely coated 
 with copper, which will adhere so firmly that mere 
 rubbing alone will not remove it. The same effect 
 takes place, if instead of bringing the metals into 
 contact in the solution, they are connected externally e g . 92. 
 
 by the wire c. 
 
 The foregoing experiment represents the electrotype process as carried 
 on in a single cell, the metal surface whereon the copper is deposited then 
 forming the conducting plate of the voltaic arrangement by which the 
 electricity is generated. It must be observed that, in this single-cell ar- 
 rangement, the deposition takes place on the conducting plate ; whereas, 
 when the operation is conducted in a separate cell, it is on the plate con- 
 nected with the zinc that the deposition occurs. In order to explain this 
 apparent anomaly, let it be remembered that the metal is always deposited 
 from its solution on the surface into which the electric current enters, and 
 that that is the negative pole of the battery. The electricity excited by 
 the zinc passes through the fluid and enters into the conducting plate ; 
 therefore, when the deposition takes place in the same cell, the metal is 
 deposited on that surface ; but whjsn the electric current is transmitted 
 through a wire into a separate cell, it then proceeds from the conducting 
 plate, that wire becomes the positive pole of the battery, and when intro- 
 duced into the decomposing cell, the electric current passes from it to the 
 metal surface connected with the other, or negative pole, on which accord- 
 ingly the deposit takes place. 
 
 Having, we trust, made the rationale of the electrotype process intelli- 
 gible, it is only necessary to give a general explanation of the modes of 
 operating. Those who desire to pursue the art practically will do well to 
 
178 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 consult the able and compendious treatises on this subject by Mr. Napier, 
 Mr. Smee, and by Mr. C. V. Walker. 
 
 The first application of the electrotype process was to copying ancient 
 coins and medals, and that continues to be the principal use to which it is 
 applied by amateurs. To obtain a fac-simile of a medal, it is necessary in 
 the first place to make a mould, to serve as a matrix for the copper to be 
 deposited upon. This may be done, when circumstances will permit, by 
 obtaining an electrotype directly from the surface of the medal. To do 
 this, the surface whereon the deposition is to take place must be well 
 cleaned, and afterwards smeared over with a minute quantity of sweet oil 
 or with black lead, which is requisite to prevent the deposited copper from 
 adhering. The thinnest possible film of oil should be allowed to remain, 
 and even after the medal has been rubbed with dry cotton-wool, sufficient 
 will adhere to effect separation from the deposit. It is evident that only 
 one face of the medal can be copied at a time, therefore 
 the side not to be operated on must be protected by a 
 covering of wax. The preparation of the medal is com- 
 pleted by twisting a fine wire round the edge for the 
 purpose of suspending it in the copper solution, and of 
 connecting it with a piece of amalgamated zinc. 
 
 The decomposing apparatus may consist of a large 
 preserve jar, fig. 93, to hold the solution of sulphate of 
 copper, and a porous vessel c placed within the jar to 
 contain the zinc. Fill the porous vessel to within a few 
 inches of the top with a mixture of sulphuric acid and 
 water, in the proportion of one of acid to twenty-four of 
 water, taking care that the solution in the jar and the 
 acidulated water in the porous vessel are nearly on the 
 same level. The medal e suspended by the wire is then 
 immersed in the jar, and is connected with the zinc in 
 the porous vessel by the wire a b, as shewn in the diagram. 
 
 This arrangement may be considered as equivalent to a single cell of a 
 Daniell's battery, in which the medal represents the conducting plate. 
 The electric action is established as soon as the zinc and the copper are 
 immersed ; the deposition of the copper on the medal immediately begins, 
 and it is continued as long as the action is maintained. In twenty-four 
 hours the deposited copper will be about the thickness of a card, which is 
 quite sufficient. This coating of copper may be easily separated from the 
 medal, and will be found to present an exact counterpart of it, those parts 
 in relief on the medal being of course presented as sunk in. The mould 
 thus formed is to be treated exactly as the medal, and the copper will be 
 deposited in it, so that when removed the electrotype will be a fac-simile 
 of the medal, with the intaglio and relief corresponding with the original. 
 A mould of this kind will, with care, serve to take many copies. 
 
 A mould made by depositing the copper on the surface is more sharp 
 in its details than moulds taken by other means ; but in many cases, espe- 
 cially with ancient coins, the surfaces cannot be cleaned so as to allow of 
 this mode being adopted, and other means of making the moulds must be 
 found. One of the best plans is to make a cast of the original in fusible 
 metal. A strip of tin is bound round the edge of the coin, about a quar- 
 ter of an inch higher than the highest part. The metal is melted and 
 
 fig. 93. 
 
ELECTRO-METALLURGY. 179 
 
 poured into a small wooden tray, and when cooled into a semi-fluid state, 
 the coin is suddenly pressed upon it and held down till the metal " sets." 
 The fusible metal is made by melting and mixing together tin, lead, and 
 bismuth, in the proportions of two of the latter to one each of the former 
 metals. This alloy melts at a temperature below that of boiling water, 
 therefore it affords great facility for removing the moulds from the deposits 
 in case they should adhere. 
 
 Wax, plaster of Paris, and gutta-percha, are frequently employed for 
 making moulds, especially for large objects. When such substances form 
 the moulds, it is necessary to cover their surfaces with black-lead, bronze- 
 powder, or other conductors of electricity. The discovery that plumbago- 
 will impart a sufficiently good conducting surface to objects that are 
 otherwise incapable of receiving metallic deposits, has afforded great faci- 
 lity in extending the electrotype process. Flowers, leaves, lace, and even 
 insects, may be thus coated with a thin protecting film of metal, which 
 preserves their forms accurately and durably. 
 
 A recent valuable application of the electrotype process is the coating 
 of glass and earthenware vessels, which are thus rendered fire-proof; for 
 the metallic coating quickly distributes the heat equally over the surface, 
 and thus prevents them from breaking, as they otherwise would, by unequal 
 expansion. The surface of the glass or porcelain is first roughened by the 
 fumes of hydro-fluoric acid, and then varnished and black-leaded, to form 
 an adhering and conducting surface for the metallic deposit. 
 
 One of the most delicate operations of the art of electrotyping is that 
 of copying copper-plate engravings. A cast is first made from the plate 
 by electro-chemical action, in the same manner as a mould is taken from 
 a medal. In such a cast all the lines are in relief ; it is requisite, there- 
 fore, to make a second deposit on that surface to obtain a fac-simile with 
 the lines engraved. Nothing shews more clearly the beauty of the elec- 
 trotype process than these transfers of copper-plate engravings. The finest 
 lines are most faithfully copied, and it is impossible to distinguish a 
 print taken from the electrotype from the proof impression of the ori- 
 ginal. 
 
 It was at one time expected that this mode of multiplying copper- 
 plate engravings would supersede engraving on steel plates ; but it has been 
 found in practice, that the copper deposited does not possess sufficient 
 hardness to resist the wear and tear of copper-plate printing. This ob- 
 jection may, however, be overcome ; and there were displayed in the 
 Great Exhibition sheets of copper deposited by electro-chemical decom- 
 position, that appeared to possess the firmness of hammered plates. 
 
 A very successful application of electro-metallurgy to the fine arts is 
 the process called glyphography. It consists in depositing on a plate of 
 copper a design in relief, that may be printed from by the letter-press. 
 The surface of the copper-plate is coated with wax, through which the 
 design is cut sufficiently deep to expose the metal. This plate is then 
 electrotyped, and copper is deposited in all the lines cut through the coat- 
 ing. By this means there is left on the plate, when the wax is removed, 
 a perfect copy of the design in relief, so bold as to be printed from. This 
 is, in fact, the original process invented by Mr. Spencer. The advantage 
 it possesses over wood-engraving is in the facility of shading by " cross 
 hatching," as it is termed, so as to resemble an etching on copper-plate. 
 
180 THE APPLICATIONS OF ELECTRICITY. 
 
 The success or failure of the electrotype process depends very much 
 on the preparation of the copper solution, and on the strength of the vol- 
 taic battery. A saturated solution is not so well adapted for the purpose, 
 as such a solution diluted with one-fourth part of water. To prevent it 
 from becoming too weak by the deposition of metallic copper, some crys- 
 tals of the sulphate are added during the process. 
 
 Mr. Smee determined the laws that regulate the deposition of metals 
 in different states. The strength of the battery, in relation to the strength 
 of the solution, causes the metals to be deposited either as a black pow- 
 der, in a crystalline form, or as a flexible plate. The metals are deposited 
 as a black powder when the current of electricity is so strong that hy- 
 drogen is evolved from the medal or negative plate in the decomposition 
 cell. The crystalline state occurs when there is no evolution of gas and 
 no tendency thereto. The regular deposit takes place when the electric 
 current is stronger in relation to the solution than in the last case, but is 
 not sufficiently strong to cause the evolution of gas. 
 
 The art of electro-metallurgy has been more extensively practised in 
 plating and gilding than in any other way. To appreciate the advantage 
 of the process of electro-plating, it is requisite that the mode of manufac- 
 turing plated articles by the ordinary means should be understood. A 
 thick plate of silver was attached to an ingot of copper, and the metals 
 after being heated were passed through rollers, until they were reduced 
 into a thin sheet of plated copper, the silver being equally spread over the 
 surface. The plated copper was then cut into pieces, punched into the 
 required forms, and soldered together ; the interior being filled with 
 melted lead. Such articles cannot be ornamented by engraving or chas- 
 ing, but by milling and punching only. When the process of electro- 
 plating is used, the articles may be cast, or put together in any con- 
 venient method, and the most elaborate designs may be worked in metal, 
 which, on being afterwards coated with the purest silver, presents an ap- 
 pearance in every respect equal to the finest works in the solid metal. 
 
 The operations for electro-plating differ in several particulars from 
 the ordinary process of the electrotype. The single-cell arrangement 
 which has been described is inapplicable to the deposition of one metal 
 upon another of a different kind. The plan of having a separate battery, 
 with two or more combinations of plates, is indeed necessary even in the 
 deposition of copper upon copper, when the operation is conducted on a 
 large scale, and the electric current has to pass through a considerable re- 
 sisting medium. When a separate battery is employed, the vessel in which 
 the deposition is effected is called the decomposing trough. 
 
 To effect the deposition of silver or gold upon metals that are more 
 easily oxidisable, a peculiar kind of menstruum is required ; for if the 
 silver be held in solution by an acid that will attack the baser metal, no 
 electro-chemical deposition of metallic silver can be effected. The men- 
 struum that is found most suitable for the purpose is a solution of cyanide 
 of potassium. There are various modes of preparing the solution and dis- 
 solving the silver, but the cheapest and best, as recommended by Mr. 
 Napier from practical experience, is to dissolve the silver in a solution of 
 cyanide of potassium, by the action of a voltaic battery. The proportions 
 mentioned are for operation on a large manufacturing scale, but the quan- 
 tities may be reduced according to the requirements of the amateur. The 
 
ELECTRO-METALLURGY. 181 
 
 directions he gives are as follows: "Dissolve 123 ounces of cyanide of 
 potassium in 100 gallons of water ; get one or two flat porous vessels, 
 and place them in this solution to within half an inch of the mouth, and 
 fill them to the same height with the solution ; in these porous vessels 
 place small plates or sheets of iron or copper, and connect them with a 
 zinc terminal of a battery ; in the large solution place a sheet or sheets of 
 silver connected with the copper terminal of the battery. This arrange- 
 ment being made at night, and the power employed being two of Wollas- 
 ton's batteries of five pairs of plates, the zincs seven inches square, it will 
 be found in the morning that there will be dissolved from 60 to 80 ounces 
 of silver from the sheets. The solution is now ready for use, and by ob- 
 serving that the articles to be plated have less surface than the silver 
 plate forming the positive electrode for the first two days, the solution 
 will then have the proper quantity of silver in it." The strength of the 
 solution recommended is that of one ounce of silver to the gallon. 
 
 During the process of plating, the sheets of silver immersed in the 
 solution gradually dissolve as the metal is deposited, and by this means 
 the solution is maintained at the same strength. 
 
 In preparing articles for plating, they must be completely freed from 
 grease by washing in an alkaline ley, and dipped into very diluted nitric 
 acid to remove any traces of oxide. The object is then suspended in the 
 decomposing trough and connected with the negative pole of the bat- 
 tery, the positive pole being connexion with a sheet of silver in the 
 solution. Silver is immediately deposited, and the plating process proceeds 
 as long as the object continues immersed. An ounce and a half of silver 
 to one square foot of surface gives an excellent plating. 
 
 The articles when taken out of the solution are white, the silver being 
 afterwards polished on the parts required to be bright. A bright deposit 
 may, however, be made by adding a little sulphuret of carbon to the solu- 
 tion. When a thin coating of silver is deposited on a bright surface, the 
 silver is also bright ; and in order to obtain a coating of dead silver on a 
 medal, it should have a thin film of copper deposited over its surface be- 
 fore it is immersed in the silver solution, by which means the silver, even 
 when very thin, will be white. 
 
 In operating on a large scale, the decomposing trough is upwards of 
 two yards long, one yard deep, and one yard wide, and contains about 250 
 gallons of the solution. At Messrs. Elkington's establishment at Birming- 
 ham, several of these troughs are in continual use. The silver plates in a 
 single trough expose a surface of nearly thirty square feet, and the articles 
 to be plated are suspended from metal rods that are connected with the 
 positive pole of the battery. The voltaic batteries used by Messrs. El- 
 kington generate large quantities of electricity of low intensity. When 
 we inspected their manufactory, the deposition of each trough was effected 
 by plates the zincs of which were three feet long by eighteen inches wide. 
 Mr. Napier, however, recommends batteries with smaller plates, with 
 several combined in a series, to increase the intensity of the electric cur- 
 rent. 
 
 The operation of electro-gilding very closely resembles that of electro- 
 plating. The gold solution may be prepared by dissolving gold in a solu- 
 tion of cyanide of potassium in the same manner as the silver, but the 
 liquid should be heated. The strength of the gold solution need not ex- 
 
182 THE APPLICATIONS OF ELECTRICITY. 
 
 ceed half an ounce of gold to the gallon, and a sufficiently thick coating of 
 the metal is deposited in two or three minutes. Voltaic batteries of three 
 or four pairs of plates are generally employed for electro-gilding; but if 
 the solution be heated to nearly the boiling-point, a single pair will an- 
 swer the purpose, for the hotter the solution the less the battery power 
 required. 
 
 The method of gilding, before the introduction of the electro-chemical 
 process, was extremely injurious to health. The gold was converted into 
 a thin amalgam with mercury, which was brushed over the surface of the 
 article to be gilt, and exposed to a strong heat to dissipate the mercury. 
 The mercurial fumes produced the most pernicious effects, notwithstanding 
 all the care taken to prevent them ; so much so, indeed, that the average 
 lives of the workmen engaged in gilding by mercury do not exceed 
 thirty-five years. Electro-gilding is also prejudicial to health, though not 
 to the same extent, and the operation should be conducted in a lofty well- 
 ventilated room. 
 
 CHAPTER XXIT. 
 
 ELECTRIC CLOCKS. 
 
 First application of electricity to indicate time Bain's self-acting electric clock 
 Means of making and breaking contact Application of mechanical power The 
 earth battery Shepherd's electro-magnetic clock Independence of the pendulum, 
 and its advantages Instantaneous indication of Greenwich time at distant places. 
 
 THE claim to the invention of electric clocks has been disputed by Profes- 
 sor Wheatstone and by Mr. Bain ; but whatever claim Professor Wheat- 
 stone may have to be the original designer of such application of electric 
 force, to Mr. Bain is unquestionably due the merit of having brought it 
 into practical operation. 
 
 In 1841, Mr. Bain, in conjunction with Mr. Barwise, obtained a patent 
 for the application of electricity to the regulation and movement of clocks. 
 The invention at that time specified had for its principal object the move- 
 ment of several clocks by currents of electricity, transmitted at regular 
 intervals by the agency of a clock of the ordinary construction. The ad- 
 vantage proposed to be gained was, to make any number of clock-dials in 
 a large establishment indicate exact time with one well-made clock, with- 
 out requiring any impelling mechanical power. By a subsequent improve- 
 ment of the invention, each clock was made to move independently by 
 electricity, without any assisting clock to regulate the transmission of the 
 electric current. The arrangement by which the independent regulated 
 movement is obtained will be understood by the annexed figure. 
 
 The bob A of the pendulum A B consists of a hollow coil of covered 
 copper wire. A hollow brass tube c c, about two inches in diameter, 
 passes through the coil, there being sufficient space left for the coil to move 
 to and fro without touching. Within the hollow tube, and on each side 
 of it, are placed permanent bar magnets, with their similar poles presented 
 
ELECTRIC CLOCKS. 
 
 183 
 
 fig. 94. 
 
 towards each other at a distance of about four inches apart. For example, 
 the magnets within the tube on the right hand have their north poles pre- 
 sented to the coil, and those on the left hand have also their north poles 
 presented to it. When an electric current 
 passes through the coil it becomes instantly- 
 magnetic ; the end towards the right, we 
 will suppose, having a south polarity, and 
 that towards the left a north polarity. The 
 coil is consequently immediately attracted 
 towards the right, and is repelled by the 
 magnets on the left, as the pendulum swings 
 in that direction. Before arriving at the end 
 of its vibration, the connexion with the vol- 
 taic battery is broken by the action of the 
 pendulum itself; the magnetic property of 
 the coil instantly ceases, and it descends by 
 the force of gravity. On ascending the other 
 arc of its vibration, contact is again made 
 with the battery, and the electric current is 
 sent through the coil, but in the reverse di- 
 rection ; so that the left-hand end of the coil 
 has south polarity given to it, and the right becomes the north pole. By 
 this reversal of the current the coil is impelled towards the left, and the 
 vibrations of the pendulum are thus maintained for an indefinite time. 
 
 To make and break contact with the wires of the voltaic battery, and 
 to reverse the direction of the electric current, a light sliding frame is car- 
 ried from side to side by the pendulum. The wires e d, from the opposite 
 ends of the hollow coil, are carried up the pendulum-rod. A cross-piece of 
 wood fixed to the clock-case serves as a stage whereon the light movable 
 frame slides, the uprights whereon it rests being gold wires. Inlaid in the 
 stage or cross-piece are studs of gold, connected by wires to the voltaic 
 battery. When the pendulum vibrates towards the right, the movable 
 frame is carried towards the right hand, so that two of the upright gold 
 wires rest on the studs ; by this means connexion is made with the voltaic 
 batter}', and an electric current is transmitted through the coil A. On the 
 returning vibration of the pendulum the movable frame is shifted towards 
 the left, and the electric current is reversed, the polarity of the coil being 
 thus changed at each vibration of the pendulum. 
 
 In ordinary clocks the impelling power of a weight or spring commu- 
 nicates motion to a train of wheels, and the use of the pendulum is to retard 
 and regulate the motion ; but in Mr. Bain's electric clock the movement of 
 the pendulum propels the hands, and the train of wheels is dispensed with. 
 The mode by which the vibrations of the pendulum are applied to propel 
 the hands will be readily understood on inspection of fig. 95. 
 
 An electro-magnet A is fixed on the top of the clock, and an electric 
 current is sent through the coil on each vibration of the pendulum. Each 
 time that the electro-magnet is put into action by these transmissions of 
 electricity, the keeper B, to which the light-jointed click-lever D is attached, 
 is attracted, and falls into a tooth of the ratchet wheel E. When the con- 
 nexion with the battery is broken on the fall of the pendulum, the lever is 
 forced back by the spring at B, and thus advances the wheel the space of 
 
184 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 fig. 95. 
 
 one tooth. A small spring keeps 
 the wheel steady, and prevents it 
 turning back during the next vi- 
 bration ; and by this arrangement 
 the ratchet-wheel is advanced one 
 tooth by two swings of the pendu- 
 lum. Thus, when the wheel con- 
 tains thirty teeth, and the pendu- 
 lum vibrates once a second, the 
 wheel will make one complete 
 revolution every minute. That 
 wheel will therefore constitute the 
 seconds wheel of the clock, and 
 the minute and hour hands may 
 be moved by it, in the same man- 
 ner as in ordinary clocks. 
 
 The voltaic power employed 
 by Mr. Bain in working these 
 
 clocks consists of a large plate of zinc, and a quantity of coke buried 
 in moist ground. Mr. Bain first directed attention to the use that may be 
 made of the moisture of the earth in exciting a very steady current of 
 voltaic electricity. In the earlier experiments he employed a large plate 
 of zinc and a corresponding plate of copper ; but it was afterwards found 
 that coke or charcoal, among which copper wires were introduced to act 
 as conductors, answered the purpose better, because a larger surface is 
 thus exposed to contact with the moisture. On making connexion be- 
 tween the coke and the zinc a current of electricity is established, which, 
 though of very feeble intensity, is sufficiently powerful to keep the pendu- 
 lum of the electric clock in motion. 
 
 It was supposed by Mr. Bain that the electricity thus excited was de- 
 rived directly from the earth, and he attached great importance to the 
 discovery as a new source of obtaining electric power ; but the effect is 
 due only to the moisture of the earth acting on the zinc, and plates of 
 equal size, if immersed in water, would generate an equal amount of elec- 
 tricity as when buried in the ground. In practice, however, there is con- 
 siderable advantage gained by employing an " earth battery," for the action 
 proceeds undisturbedly, and a battery of this kind will continue at work 
 for a year or longer without requiring any attention. 
 
 Objection has been raised to Mr. Bain's clock, that as the pendulum 
 is impelled by the direct action of electro-magnetism, it is liable to be 
 affected by any variation in the power of the voltaic current, and such 
 variations are continually taking place, even in the earth battery. The 
 mode of making contact by the movable piece is also uncertain, and by 
 a slight deposition of dust the connexion may be interrupted. With 
 proper care, however, these clocks will continue to perform well for several 
 months without touching them. 
 
 Mr. Shepherd, whose gigantic electric clock kept time over the central 
 entrance of the Great Exhibition, has effected a considerable improvement 
 by rendering the movement altogether independent of variations in the 
 electric power. In his clocks the vibrations of the pendulum are main- 
 tained by repeated blows of a small spring, the electro-magnetic power 
 
ELECTRIC CLOCKS. 
 
 185 
 
 being employed only to draw back the spring after it has given the blow, 
 so as to be ready to strike again when the pendulum returns. The regu- 
 larity of the movement is still further secured by detaching the pendulum 
 from the mechanism that propels the hands, which are moved forwards by 
 separate electro-magnets. All that the pendulum does is to make and 
 break contact with a voltaic battery by striking against a small spring at 
 every vibration. The instant that contact is made, not only is the impel- 
 ling spring drawn back by an electro-magnet, but other electro-magnets 
 are brought into action alternately, and by their successive altractions 
 propel the seconds-wheel of the clock. By this arrangement the isochro- 
 nous motion of the pendulum is not interfered with by any variation in 
 the power of the battery, nor by the attachment of mechanism of any 
 kind. 
 
 Figure 96 shews Mr. Shepherd's arrangement for making and break- 
 ing contact with the voltaic batteries, and his mode of applying electro- 
 magnetism to propel the mechanism of the clock. A metallic cross-bar 
 A, fixed to the upper part of the pendulum, has two projecting pins of 
 platinum, that dip alternately in cups of mercury in m, as the pendulum 
 vibrates. Wires are carried from each cup of mercury to a separate vol- 
 taic battery, and from the batteries to the electro-magnet B, and thence 
 to the pendulum of the clock. A permanent magnet N s is fixed to 
 the top of the palette D, which is so arranged in respect to the ratchet- 
 wheel E, that it propels it one tooth at each double action. Thus, when 
 the pendulum vibrates to the right, as shewn in the figure, connexion is 
 made through the cup m with the battery cz, and the electro-magnet 
 attracts the north pole N of the permanent magnet, and repels the south 
 pole. The opposite action takes place when the current is reversed, by 
 making connexion through the cup m', and the other battery is brought 
 into play. In this manner the alternate movements are continued, and 
 the ratchet-wheel is regularly propelled. 
 
 A single pendulum will serve to move the hands on the dials of any 
 number of clocks. Such an arrangement has been in operation for some 
 
 N 
 
186 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 BL. 
 
 time at an extensive warehouse in the city. All the dials of a numerous 
 series of clocks are regulated by one pendulum placed in the counting- 
 house, and the wire required to communicate between the pendulum and 
 the dials in different parts of the warehouse is upwards of a quarter of a 
 mile in length. When several clocks are required in one establishment, 
 great advantage is derived by employing electro-magnetism in this man- 
 ner, because the dials of all indicate exactly the same time ; they can be 
 constructed at considerably less cost than good ordinary clocks, and they 
 continue to go without the trouble of winding up. The public clocks of 
 a whole town might thus be propelled, by employing a more powerful vol- 
 taic battery, the movements of all being regulated by a single pendulum. 
 
 In connexion with electric clocks may be mentioned the means of 
 indicating exact time at different places. An arrangement of this kind 
 has been recently completed between the Royal Observatory at Greenwich 
 and the Electric Telegraph Company's office in the Strand. A large ball 
 on the top of the Royal Observatory falls daily, to indicate exact, time at 
 one o'clock, and a similar ball on the top of the Telegraph Office also falls 
 at the same instant ; communication being made between the two places 
 by an insulated telegraph wire. The method by which the descent of the 
 ball in the Strand is effected will be understood 
 on inspection of figure 97. Let A represent a sec- 
 tion of the tube on which the large hollow ball B 
 slides up and down. A jointed lever E, consisting 
 of a piece of soft iron, acts as the keeper of the elec- 
 tro-magnet M, and when resting perpendicularly, a 
 projection on the other side takes hold of a catch 
 D in the straight arm that is fixed to the ball, and 
 thereby holds it in position at the top of the per- 
 pendicular tube. The instant that the ball on the 
 Royal Observatory falls, it makes contact with a 
 voltaic battery in connexion with the wires c z of 
 the electro-magnet M, and brings that magnet into 
 action \ the keeper E is attracted from the catch D, 
 by which the ball is supported, and it thus falls at 
 the same instant as the ball at the Observatory. 
 To prevent concussion, by accelerated velocity 
 during the descent, a plunger attached to the rod 
 that supports the ball is introduced in the tube F, 
 and by compressing the air within, the fall of the 
 ball is sufficiently retarded. 
 
 The arrangements at the Observatory for libe- 
 rating the ball exactly at one o'clock were effected 
 by Mr. Shepherd in the following manner : Three 
 small pairs of springs for making contact, a, b, c, 
 are fixed on the frame of the clock, so that they 
 may be pressed together by projecting pins e,f,g, 
 on the wheels that carry the hour-hand, the minute- 
 hand, and the seconds-hand respectively. The 
 hg.97. wire z connected with the voltaic battery is at- 
 
 tached to the pair of springs c, and when they are 
 pressed together by the pin e, metallic contact is made with the spring 
 
THE ELECTRIC LIGHT. 
 
 187 
 
 fig. 98. 
 
 b, by a connecting wire w. When 
 these springs are pressed together 
 by the pin on the wheel B, con- 
 nexion with the battery is extended 
 to the third pair of springs a, and 
 on contact being made by the pin on 
 the seconds -wheel c, the voltaic cir- 
 cuit is completed through the three 
 springs, and the electric current 
 puts in action an electro-magnet, 
 which withdraws the detent that 
 supports the ball on the top of the 
 Royal Observatory. 
 
 It will be observed that to com- 
 plete the circuit it is necessary that 
 the three contact springs should be 
 pressed together at the same time. 
 As the hour-hand on the first wheel 
 A, which revolves once in twenty-four hours, approaches towards one 
 o'clock, it first presses together the spring d, and as that wheel moves 
 slowly, contact is made for a quarter of an hour or more before the time 
 required. The minute-wheel B next makes contact about half a minute 
 before one o'clock, but no effect is produced until the seconds-wheel c 
 makes contact exactly at one o'clock, and at that instant the voltaic current 
 passes, first to the electro-magnet on the Observatory, and thence to the 
 electro-magnet which liberates the ball on the Telegraph Office in the 
 Strand. The balls are wound up by mechanism at half-past twelve 
 o'clock. It is proposed to extend similar arrangements to different parts 
 of the kingdom, through the telegraph wires j so that correct Greenwich 
 time may be known once every day. 
 
 In the figure some of the wheels in the train of the clock are omitted 
 to avoid confusion ; but it is evident that by this arrangement the voltaic 
 circuit can only be completed once during the revolution of the hour- 
 wheel, however often contact is made with the springs connected with the 
 other wheels. 
 
 CHAPTER XXIII. 
 
 MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 
 
 The electric light Electro- magnetic engines Blasting rocks Explosion of fire-damp 
 in mines Sounding the sea Determining longitudes Fire-alarms Table-moving 
 Harpooning Conclusion. 
 
 THE ELECTRIC LIGHT. 
 
 THE application of electricity to the purposes of illumination was brought 
 prominently into notice about four years since, and then promised to 
 become a most valuable means of lighting streets. The electric light 
 proposed to be employed, though introduced as a new discovery, was 
 
188 THE APPLICATIONS OF ELECTRICITY. 
 
 nothing more than the previously well-known evolution of brilliant lumi- 
 nous rays from charcoal points when exposed to the action of a powerful 
 voltaic battery. The light thus produced almost equals in brilliancy and 
 purity that of the sun; and if means could be found of regulating the 
 action, so as to ensure steadiness and certainty, it would prove a most 
 useful source of illumination. 
 
 Mr. Stait, when proposing to make the electric light available, in- 
 vented a voltaic battery intended to act with great steadiness, and he 
 introduced arrangements for adjusting the charcoal points, which im- 
 provements it was thought would overcome the difficulty ; but though he 
 succeeded in maintaining the light for a short time, it could not be regu- 
 lated with the steadiness and certainty requisite for practical use. 
 
 An ingenious contrivance by Mr. Allman was in the Great Exhibition, 
 of a self-acting adjustment of the charcoal points, so that the distance 
 apart might vary in proportion to the variations in the power of the 
 battery. We have not, however, heard of any practical application of this 
 invention ; and we fear it has not been found to overcome the difficulty. 
 
 Another objection to the application of the electric light, in an eco- 
 nomical point of view, is the cost of generating the electric force. It 
 has been ascertained by experiment that the expense of maintaining the 
 requisite battery power would considerably exceed that of the quantity of 
 gas that would yield an equivalent amount of light. This objection, 
 though it might prevent the electric light from coming into general use, 
 would not prevent its being applied in many cases where the question of 
 cost is an inferior consideration, could the constancy of the light be 
 depended on. 
 
 The impediment to the perfection of the invention, occasioned by the 
 cost of exciting power, will probably be removed by the discovery of 
 some better and cheaper means of exciting voltaic electricity than by the 
 consumption of zinc ; and in that case the electric light may become as 
 common a source of artificial illumination as coal-gas is at the present 
 day. Even in the imperfect state in which the invention now remains, the 
 electric light might, with proper care and attention, be applied with great 
 advantage to many lighthouses on the coast. 
 
 Some recent investigations, by Professor Wartmann of Geneva, into the 
 applicability of the electric light, tend indeed to shew that it may be used 
 to advantage more generally than we have, in the existing state of the 
 invention and in the imperfect condition of the voltaic battery, assumed 
 to be practicable. 
 
 It is asserted that the light emitted from a single pair of charcoal 
 points equals that of 300 large burners ; and that when a powerful voltaic 
 circuit is formed, the charcoal points may be introduced at several parts 
 of the circuit, and thus distribute the light from several points of illlu- 
 mination.* 
 
 ELECTRO-MAGNETIC ENGINES. 
 
 The application of electro-magnetism as a moving power is, like the 
 electric light, also awaiting, for practical purposes, further improvements in 
 the mode of generating voltaic electricity. 
 
 Electro-magnetic engines of various kinds have been constructed, some 
 
 * Philosophical Magazine, January 1853. 
 
ELECTRO-MAGNETIC ENGINES. 
 
 189 
 
 of which have propelled boats and worked printing machines; but the 
 amount of power obtained has been so small compared with the cost of 
 the -voltaic battery, as to render such applications of electricity practically 
 useless as substitutes for steam. The most simple of the various modes 
 by which electro-magnetism may be applied to propel machinery is shewn 
 in the annexed diagram. 
 
 fig. 99. 
 
 The lever A B, jointed at B, is either made of soft iron or it has bars of 
 soft iron fixed on each side to serve as keepers for the electro-magnets 
 E D. The magnets are fixed in inclined positions, as shewn in the figure, 
 so that the keepers on the movable lever may rest on the poles of each 
 alternately, as it is attracted from side to side. 
 
 Two pairs of metal studs ee, hh' are connected respectively with one 
 end of the coils of the electro -magnets and with the voltaic battery that 
 brings them into action. Thus, the wire of magnet D is connected with e, 
 and a wire from the stud e is connected with the battery. A movable 
 piece of metal m slides laterally, and is shifted from side to side by the 
 curved piece n striking against it when the lever A B is in action. When 
 that sliding piece of metal rests upon either pair of studs, it completes the 
 communication with the voltaic battery through the magnet to which the 
 stud is connected. 
 
 In the position of the engine, represented in the figure, the sliding 
 piece is resting against the stud connected with the electro-magnet D, 
 which consequently becomes magnetic and attracts the lever. The instant 
 before the keeper comes in contact with the magnet, the connexions are 
 reversed, by the curved piece n shifting the sliding metal from its contact 
 with e e against the opposite studs ; and by this means the magnet E 
 comes into action, and the lever is attracted towards it. In this manner 
 the lever may be kept in action for an indefinite time. The alternating 
 movement may be converted into rotary motion by means of a crank, in 
 the ordinary manner. 
 
 In some electro-magnetic engines rotary motion is communicated di- 
 rectly to a wheel, without the intervention of a crank, by fixing a number 
 
190 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 of electro-magnets in the circle of rotation close to the periphery of the 
 wheel, into which numerous pieces of soft iron are inlaid. Each electro-* 
 magnet is brought into action in succession by making and breaking 
 contact with the voltaic battery as the wheel revolves ; by this means there 
 is a continuous change in the points of attraction round which the wheel 
 is thus made to rotate. 
 
 One cause why so little power is obtained by electro-magnetic engines 
 of these constructions is the limited sphere of electro-magnetic attraction. 
 In the arrangement of the vibrating arm, for example, the force with 
 which the keeper is attracted is very feeble until it approaches close to 
 the magnet, when the magnetic action must necessarily cease. With a 
 view to overcome this objection, an arrangement has been contrived in 
 which the attractive power of a hollow coil is employed. A model engine 
 of this kind was placed in the Great Exhibition. Its mode of action will 
 be understood by the annexed section. Two hollow coils of covered copper 
 
 fig. 100. 
 
 wire A B are fixed vertically, the coils being connected together as if they 
 formed the helices of an electro-magnet. Inside the coils two hollow 
 cylinders of soft iron ii and ee are introduced. Two plungers c D, formed 
 of soft iron, are mounted on a balance lever F. The ends of the coils are 
 connected with the balance lever in such manner that as each end rises 
 and falls alternately, it reverses the direction of the voltaic current through 
 the coils in a manner similar to that shewn in fig. 99, and thus reverses 
 the poles of magnetic attraction. In the position represented, the plunger D 
 having reached the centre of the coil, where there is no magnetic action, 
 the direction of the electric current is reversed by the lever, and c is then 
 attracted into the hollow coil A. The lever is thus alternately lifted up 
 and down like the beam of a steam-engine, the two hollow coils repre- 
 senting the two cylinders. 
 
 By this means of applying the force of induced magnetism the spt ?re 
 of attraction is very much increased, especially when permanent steel 
 magnets are used as plungers, for it then extends almost to the centre ; and 
 as the attractive power in one of the coils diminishes, the repelling pow-r of 
 the other is correspondingly increased. We have not heard of any prac- 
 tical application of this form of electro-magnetic engine; but it is a new 
 mode of applying the force of electro-magnetism, which promises to be 
 attended with favourable results. 
 

p. 191. 
 
 ROUND DOWN CLIFF BLASTED BY ELECTRICITY. 
 
BLASTING ROCKS. 191 
 
 In the Reports of the Juries of the Great Exhibition an electro-mag- 
 netic engine, invented by Mr. Hjorth of Denmark, is highly spoken of. 
 It operates on the same principle as the engine we have just noticed. It 
 consists of two sets of hollow horse-shoe electric magnets, conical inside, 
 with a corresponding number of solid electro-magnets, which by mutually 
 attracting each other, make a double stroke of four inches in length. The 
 power has been found, by means of a spring-balance, to be about thirty 
 pounds at the commencement of the stroke when the distance of the re- 
 spective poles is about half an inch, decreasing slightly by degrees as the 
 piston enters into the hollow electric magnet.* The Jury state, " we can- 
 not help flattering ourselves that the attainment of this mysterious motive 
 force will soon be followed by the making it available for practical pur- 
 poses." 
 
 BLASTING ROCKS. 
 
 When a voltaic current is transmitted through a thick wire, it is con- 
 ducted so freely that there is no sensible increase of heat. But if a very 
 thin wire be interposed in the circuit, the resistance thus offered to the 
 electric current causes the evolution of heat sufficient to make the wire 
 red-hot. This heating property of the voltaic current has been rendered 
 available in blasting rocks. Thick wires from a voltaic battery containing 
 a series of plates of not less than four inches square are laid down to the 
 spot where the explosion is to take place, and at that point the circuit of 
 thick wire is broken, and a short length of very fine platinum wire is in- 
 troduced. The fine wire is usually inserted in a cartridge of gunpowder, 
 and it is covered over by the powder to be exploded. When every thing 
 is properly arranged and all persons have retired to safe distances, the 
 thick wires are connected with the two poles of the battery, and the pow- 
 der is instantly ignited. 
 
 This plan of blasting rocks is more effectual and more free from danger 
 than the ordinary method of igniting the powder by a fuse, for it some- 
 times happens that the lighted fuse communicates with the powder before 
 the time calculated \ occasionally also it hangs fire, and the men, supposing 
 it to be extinguished, approach the mine and are killed by the unexpected 
 explosion. 
 
 The application of voltaic electricity to the purposes of igniting large 
 charges of powder was first successfully made by Col. Pasley in blowing 
 up the wreck of the Royal George, and it has since been generally em- 
 ployed for submarine explosions. The most remarkable instance of this 
 application of electricity was the removal of an immense mass of the 
 Round Down Cliff at Dover, on the 26th of January, 1843. The cliff was 
 375 feet above high-water mark ; and as a projection of it prevented a di- 
 rect line of the South-Eastern Railway being taken to the mouth of the 
 Shakespeare tunnel, it was resolved to remove the obstruction by blasting. 
 Three different galleries and three shafts connected with them were exca- 
 vated in the chalk rock. The length of the galleries was about 300 feet, 
 and at the bottom of each shaft was a chamber eleven feet long, five feet 
 high, and four feet six inches wide. In these chambers 18,000 pounds of 
 gunpowder were placed in bags, with the mouths open and loose powder 
 scattered over them. The distance of the charges from the face of the 
 * Reports of the Juries, class x. p. 283. 
 
192 THE APPLICATIONS OF ELECTRICITY. 
 
 cliff was about seventy feet. At the back of the cliff a wooden shed was 
 constructed in which three voltaic batteries were arranged. Each combined 
 battery consisted of eighteen of Daniell's cells and two common batteries 
 of twenty pairs of plates each. To these batteries were connected thick 
 wires, covered with cord to insulate them from the ground. The wires 
 were laid upon the grass to the top of the cliff, and then falling over it 
 were carried to the eastern, the central, and the western chambers. The 
 wires were each 1000 feet long, and it was ascertained by experiment that 
 the electric current was sufficient to heat the interposed length of platina 
 wire at a distance of 2300 feet. The powder was divided into three 
 charges, each one being exploded separately by a distinct circuit, it being- 
 arranged that at the instant the central charge was fired, the voltaic cur- 
 rent should also be transmitted through the two other circuits. Flags 
 were fixed at various points on the cliffs to warn people not to approach, 
 and on the top of the Round Down Cliff a larger flag was planted, towards 
 which all eyes were directed as the time appointed for the explosion ap- 
 proached. "At twenty-six minutes past two o'clock," as reported in 
 the Times of the following day, "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 proceeding of mighty and irrepressible force, it had little or 
 nothing of the appearance of force. The rock seemed as if it had ex- 
 changed its solid for a fluid nature, for it glided like a stream into the sea, 
 which was at the distance of 100 yards, perhaps more, from its base." 
 The top of the Round Down Cliff did not fall down on to the beach as 
 might have been expected, but it descended almost perpendicularly, retain- 
 ing its former distinctive character at a lower level than the surrounding 
 cliffs which it before overtopped, as represented in the accompanying 
 engraving. By this blast one million tons of chalk were removed, which 
 would have otherwise required twelve months' labour to cut away. 
 
 EXPLOSION OF FIRE-DAMP IN MINES. 
 
 The same arrangement that is adopted for blasting rocks might be 
 applied, with great effect, to diminish the loss of life occasioned by explo- 
 sions of carburetted hydrogen gas in coal-mines. It is the practice in 
 many mines that are considered to be " fiery," for a man to descend every 
 morning, before the miners go to work, to ascertain whether the passages 
 are in a safe condition. The duty of the "viewer" is to proceed to all the 
 dangerous parts with a safety-lamp, and if he finds from the indications of 
 the flame within the wire gauze that the atmosphere is inflammable, the 
 miners are not allowed to descend until additional means have been taken 
 to ventilate the mine. This duty is sometimes very negligently performed, 
 and in the case of a fatal explosion which occurred last summer, several of 
 the miners accompanied the viewer with unprotected candles, and most of 
 them were killed. 
 
 The trouble and loss of time of this precautionary examination and its 
 accompanying danger might, the author conceives, be saved, by igniting 
 lucifer-matches, or other combustibles, by voltaic electricity in various 
 
SOUNDING THE SEA. 
 
 193 
 
 parts of the mine. This might readily be done at a very trifling cost. A 
 thick insulated wire fixed to the side of the shaft from the mouth of the 
 pit to the farthest part of the workings, and there attached to a copper 
 plate immersed in a pool of water, would serve to conduct the current of 
 electricity, and the return current might be completed by a similar plate 
 of metal buried a few feet deep in the moist earth near to the battery at 
 the pit's mouth. By intercepting the thick wire circuit in those parts 
 usually most dangerous, and introducing a short piece of very fine platina 
 wire, heat sufficient would be evolved at those points, when the circuit was 
 completed through the battery, to ignite lucifer-matches laid upon the fine 
 wires over night. By this means the condition of the mine could be as- 
 certained in an instant, without personal examination. 
 
 There would of course be objections raised to any plan so different 
 from the usual routine, but in the opinion of the author it presents an 
 easy, safe, and practicable mode of testing the safety of coal-mines, which 
 it would be advisable, at all events, to try. 
 
 SOUNDING THE SEA. 
 
 In sounding the sea by "the lead" at great depths, 
 it is difficult to ascertain exactly when the weight strikes 
 the ground. An ingenious contrivance has been in- 
 vented by Mr. Bain for removing the difficulty by em- 
 ploying electrical agency. We are not aware that the 
 invention has yet been brought into use ; but it may be 
 desirable to explain the modus operandi as an illustration 
 of one of the many different ways in which electricity 
 may be applied. 
 
 In fig. 101, A represents a metal spring-hook, the 
 curved end of which c presses against the projection z, 
 when the two points are not kept apart by the weight of 
 the lead, as they are represented to be in the woodcut. 
 The end c is insulated from the other part of the hook 
 by the piece of wood d. A wire g, connected with the 
 end c, proceeds from one of the coils of an electro-mag- 
 net on the deck of the ship ; the wire f proceeds from a 
 voltaic battery to which the other end of the coil of the 
 electro-magnet is attached. By this arrangement it will 
 be perceived that when the points z and c come in con- 
 tact, the electro-magnet will become active; and the 
 keeper, as it is attracted, may strike a bell, or give notice 
 in any other convenient way. This would take place as 
 soon as the lead touched the ground, for its weight would 
 then cease to operate against the action of the spring in 
 keeping the two ends apart ; and by this means the in- 
 stant that the bottom was reached would be made known. 
 
 For the sake of shewing the action more clearly the 
 two wires are represented in the figure as entirely sepa- 
 rated ; but they might be both twisted together round 
 the plumb-line, if care be taken to insulate them from 
 each other by a covering of cotton well varnished. 
 
 1. 101. 
 
194 
 
 THE APPLICATIONS OF ELECTRICITY. 
 
 DETERMINING LONGITUDES. 
 
 Instantaneous communication from place to place, by means of elec- 
 tricity, has been applied to determine the longitude. This was first done 
 in America at great distances apart, and recently in this country; Professor 
 Challis, of Cambridge observatory, having in May last undertaken a series 
 of experiments, in connexion with the Royal Observatory at Greenwich, 
 for that purpose. The principle on which this application of electric force 
 depends is very simple. A telegraphic wire was connected with the ob- 
 servatory at each place, and the instant that the seconds-hand of the clock 
 at Greenwich indicated a given time, a signal was transmitted through the 
 telegraph-wire, and the Cambridge time was directly noted. The difference 
 between the two affords the means of determining the longitude with great 
 exactness, by shewing how much sooner the sun comes to the meridian at 
 Cambridge than at Greenwich. 
 
 FIRE ALARMS. 
 
 Electro-magnetism has been ingeniously applied to sound an alarum 
 in case of fire. The action of the instrument depends on the well-known 
 expansion of mercury by heat. The mercury is contained in a glass bulb 
 similar to the bulb of a thermometer ; and when heated it rises up the 
 tube and touches a wire which is connected with a voltaic battery, and 
 instantly brings into action an electro-magnet. A detent is then withdrawn 
 from a piece of clock-mechanism, and an alarm is thus sounded whenever 
 the room in which the thermometer-instrument is placed becomes heated 
 a few degrees above the ordinary temperature. 
 
 In the accompanying figure A represents the glass bulb ; B c are two 
 
 short tubes communicating with it, into 
 which wires are introduced. The bulb 
 is filled with mercury, and placed in a 
 vertical position, so that when it is ex- 
 panded by heat it will rise up in the 
 tube and touch the wire. The wire at 
 the bottom is connected with the elec- 
 tro-magnet, and that at the top with 
 the voltaic battery ; and in this manner 
 the circuit is completed as soon as the 
 mercury becomes sufficiently expanded 
 to rise as high as the wire c. 
 
 A thermo-electric alarm might at 
 very trifling cost be placed in every 
 room of a house, one voltaic battery 
 and one loud alarum being sufficient for 
 all. In hotels, and in all large esta- 
 blishments, an apparatus of this kind 
 
 would prove a great safeguard, as it would be the means of giving warn- 
 ing of danger before any indication of fire was otherwise perceptible. 
 
 TABLE-MOVING. 
 
 As the alleged phenomena of table-moving, which at present attract 
 much attention, have been generally attributed to electrical agency, it 
 
 fig. 102. 
 
TABLE-MOVING. 1 95 
 
 might be considered an omission in this work if the subject were not no- 
 ticed. We have no hesitation in asserting, that it is absolutely impossible 
 such effects could be produced by the known properties of electricity. 
 Even admitting which we are far from being inclined to do that elec- 
 tricity can be excited by the imposition of hands, and that it could be so 
 excited with unlimited abundance, no acccumulation of electrical force 
 could operate in such a manner on a solid table placed upon the floor. 
 
 Let us consider for a moment the physical circumstances necessary to 
 produce the simplest of the movements stated to occur. To raise a table 
 on one side a few inches from the ground by electrical attraction would, 
 in the first place, require a greater amount of electric force than was ever 
 generated by the most powerful artificial means. Such a concentration 
 of electricity could not fail to exhibit itself by the emission of sparks, by 
 the attraction of all surrounding movable objects, and by the repulsion of 
 any light bodies placed upon the table. No such effects are represented 
 to be exhibited j and we are told that tables move without any previous 
 manifestation of the ordinary phenomena of electrical attraction. It is 
 also irreconcilable with all the known actions of static electricity, to sup- 
 pose that it could be accumulated in quantity and intensity on such an 
 imperfect insulator as a carpet. Even if that were possible, the attrac- 
 tion of the floor, as the nearer object, would greatly surpass that of the 
 ceiling, and would therefore hold the table more firmly to the ground, in- 
 stead of lifting it up. 
 
 If, again, voltaic electricity be the assumed agent, the difficulties are 
 no less insurmountable. Attractive power in that case could only be ob- 
 tained by inducing magnetism. We must suppose, therefore, the exist- 
 ence of some undiscovered property, which can impart an unknown kind 
 of magnetism to wood, that is capable of attracting other similar bodies. 
 But even admitting all this, a cause would still be wanting to account for 
 the magnetised table being attracted to the more distant ceiling instead 
 of to the floor. 
 
 We have only considered the causes necessary to account for the mere 
 raising of a table on one side ; and if the known properties of electricity 
 are unable to produce that simple effect, they would be still less adequate 
 to cause movements at the will of the operators, which, even though en- 
 dowed with vitality and intelligence, a rigid table could not accomplish 
 without assistance. 
 
 In addition to those inventions we have described, there are numerous 
 other applications of electricity ; some of which, however, are of little 
 practical utility, and in other cases the practicability of the applications of 
 the force is too questionable to render it requisite to give special descrip- 
 tions. Among the variety of objects to which electricity has been applied 
 may be mentioned a means of measuring the velocity of cannon-balls, and 
 of other rapidly moving bodies ; a mode of performing on musical in- 
 struments ; the detection of the frauds of omnibus-conductors ; and a 
 plan for catching whales. The last-named invention we have only recently 
 seen noticed, and if feasible, it will certainly afford great advantage to the 
 arctic fishermen. The harpoon is connected by a wire to a voltaic battery, 
 and the instant it strikes a whale it is to communicate a stunning shock 
 that will render the creature powerless. 
 
196 THE APPLICATIONS OF ELECTRICITY. 
 
 It is impossible to conceive limits to the extent to which electric force 
 may be applied by the ingenuity of man as progress continues to be made 
 in the science, and especially when more facile methods of generating elec- 
 tricity are discovered. Its importance as a means of transmitting intel- 
 ligence is becoming daily more appreciated ; and when the electric tele- 
 graph has received the improvements of which it is already capable, it 
 will become a general means of correspondence. The other object to 
 which we look forward at present as most likely to effect important changes 
 in the social condition of mankind is, the application of electricity as a 
 moving power. The practical part of the science is not yet sufficiently 
 advanced to enable us to expect an early approach of this event ; but we 
 feel assured that not many years will have passed before means will be 
 found of employing electric force with great advantage for that purpose ; 
 and when that time arrives, changes will be effected in the means and 
 facilities of locomotion, as great as any that have been introduced by the 
 power of steam. 
 
INDEX. 
 
 ABSOLUTE quantities of electricity, 126. 
 Air, resistance of, to electrical conduction, 
 
 67. 
 
 Alkalies, the decomposition of, 33, 123. 
 Alexander's telegraph, 163. 
 Amalgam, 62. 
 Amber, its attractive properties discovered, 
 
 9. 
 
 Animal electricity, 145. 
 Apparatus, economical, 148. 
 Applications of electricity, 153. 
 Atmospheric electricity, 83. 
 Attraction, electrical, 48. 
 Aurora borealis, 67, 91. 
 Aurum musivum, 149. 
 
 BAIX'S electric clocks, 182. 
 
 telegraph, 169. 
 
 invention for sounding the sea, 192. 
 
 Battery, electrical, 74. 
 
 thermo-electric, 145. 
 
 Beccaria's observations of a thunder-storm, 
 
 83. 
 
 Blasting rocks by electricity, 191. 
 Boyle's theory of electrical attraction, 10. 
 
 CANTON'S discovery of induction, 21. 
 Charcoal, action of voltaic current on, 115. 
 Chemical affinity identical with electrical 
 
 attraction, 123. 
 
 suspension of, 122. 
 
 Clouds, electrical condition of, 90. 
 Coils of wire, multiplying effect of, 130. 
 Conduction through liquids, 100. 
 
 moist earth, 154. 
 
 Conductors, list of, 51. 
 Constant battery, 43, 106. 
 Contact-breaker, self-acting, 137. 
 Cooke and Wheatstone's electric telegraph, 
 
 163. 
 
 Copying electric telegraph, 170. 
 Coulomb's determination of electrical 
 
 laws, 26. 
 
 electrometer, 57. 
 
 Couronne-de-tasses, 98. 
 
 Crosse's account of a thunder-storm, 84. 
 
 water-battery, 115. 
 
 Cuneus's discovery of the Leyden phial, 
 
 14. 
 Currents induced by secondary action, 
 
 119. 
 
 Current, electric, a conventional term, 99. 
 
 DANIELL'S constant battery, 43. 
 
 water-battery, 115. 
 
 Davy's, Sir H., decomposition of the al- 
 kalies, 33. 
 
 sheathing for ships, 35. 
 
 Davy's electric telegraph, 163. 
 Decomposition, electro -chemical, 120. 
 
 of metallic salts, 124, 177. 
 
 of water, 82, 121. 
 
 Definite electro-chemical action, 126. 
 Deflections of magnetic needles, 128. 
 Deposition of metals, causes of, 177. 
 Discharge, brush, 69. 
 
 glow, 70. 
 
 Dischargers, 75. 
 
 Distribution of electricity on surfaces, 65. 
 
 Distributive discharge, 87. 
 
 Du Fay's discovery of two electricities, 13. 
 
 EARTH-battery, 184. 
 Earth-circuit, 154. 
 Electric light, 187. 
 Electrics, list of, 53. 
 
 change of state in, 53. 
 
 Electric clocks, 182. 
 
 18. 
 
 Electric discharge through the ground, 
 Electric shock, effects of, 78. 
 
 its imagined effects, 16.J 
 
 shocks, formidable ones given by 
 
 Franklin, 17. 
 Electric Telegraph Company, their plan 
 
 of insulating, 156. 
 
 batteries used by, 105. 
 
 Electric time- ball, 186. 
 
 Electrical attraction, phenomena of, 48. 
 
 battery, 74. 
 
 induction, 54. 
 
 jack, 64. 
 
 Electrical machine invented, il. 
 
 , cylinder, 60. 
 
 , plate, 62. 
 
 , gutta-percha, 63. 
 
 machines, how to make, 149. 
 
 Electricity, absolute quantity of, 126. 
 
 "in water, 126. 
 
 excitement of, by animal volition, 
 
 145. 
 
198 
 
 INDEX. 
 
 Electricity, excitement of, by chemical ac 
 
 tion, 95. 
 
 effluent steam, 45, 92. 
 
 evaporation, 191. 
 
 friction, 2, 47, 93. 
 
 heat, 40, 144. 
 
 magnetism, 39. 
 
 nature of unknown, 99. 
 
 two kinds of, 51. 
 
 Electro-chemical decomposition, action of, 
 
 41. 
 
 definite, 126. 
 
 Electro-gilding, 181. 
 
 Electro-magnets, 133. 
 
 their limited spheres of attraction, 
 
 135. 
 
 how to make, 152. 
 
 Electro-magnetic engines, 188. 
 Electro-magnetism, its discovery, 35. 
 
 instantaneous communication of, 136. 
 
 Electrometer, 56. 
 
 , Coulomb's, 57 
 
 Electrometers, how to make, 150. 
 Electrophorus, 27, 55, 150. 
 Electro-plating, 180. 
 Electrotype, discovery of, 44, 175. 
 
 process, 176. 
 
 Evaporation, excitement of electricity by, 
 
 191. 
 Exciting liquids for voltaic batteries, 152. 
 
 FALLING stars, 91. 
 
 Faraday's discovery of magneto-electricity, 
 
 39. 
 
 experimental researches, 41. 
 
 experiments with high-pressure steam, 
 
 92. 
 
 new terms, 41. 
 
 Fire-alarms, 194. 
 
 Fire-damp in mines, explosion of, 192. 
 
 Franklin's, an unpublished letter of, 89. 
 
 kite experiment, 22. 
 
 suggestions for drawing lightning from 
 
 the clouds, 21. 
 
 theory of the Leyden jar, 18, 73. 
 
 Franklinian theory of electricity, 58. 
 Friction, excitement of electricity by, 2, 
 
 47, 93. 
 
 GALVANI'S experiments, 27. 
 Galvanometer, invention of, 38. 
 construction of, 130,152. 
 Gilbert's discoveries, 10. 
 Glass, excitement of electricity by, 48, 60. 
 Glyphography, 179. 
 
 Graphite, used for voltaic batteries, 99, 105. 
 Grey's discovery of conductors and non- 
 conductors, 12. 
 Grove's battery, 107. 
 Guericke, Otto, his discoveries, 11. 
 Gutta-percha electrical machines, 63. 
 Gymnotus, 146. 
 
 HEATING power of electricity, 79. 
 
 Henley's magneto-electric telegraph, 166. 
 Human body, electricity of the, 148. 
 Hydrogen gas, evolution of, in voltaic bat- 
 teries, 95. 
 
 INDUCED currents, 119. 
 Induction, electrical, 54, 57. 
 Inductive capacity, 57. 
 Inflammation by the electric spark. 67. 
 Insulation of telegraph wires, 156. 
 Intensity, cause of increase by voltaic bat- 
 teries, 102. 
 Intensity of frictional electricity, 67. 
 
 Jacobi's discovery of electro-metallurgy, 
 
 175. 
 Jordan's electrotype experiments, 175. 
 
 LANE'S discharger, 77. 
 Lateral discharge, 76, 87. 
 Lesarge's electric telegraph, 153. 
 Leslie's quadrant electrometer, 77. 
 Leyden phial, discovery of, 14. 
 
 jar, phenomena of, 71. 
 
 theory of, 73. 
 
 Leyden jars charged in series, 72. 
 
 i how to make, 150. 
 
 Light from charcoal- points, 113. 
 Lightning-conductors, 88. 
 Lightning drawn from the clouds, 21. 
 Local action in voltaic batteries, 102. 
 Lomond's electric telegraph, 160. 
 Loss of electricity in mixed telegraphic 
 circuits, 157. 
 
 MAGNETS, permanent, their spheres of at- 
 traction, 134. 
 Magnetic needles, deflections of, 128. 
 
 properties of voltaic current, 128. 
 
 Magnetising power of electricity, 82. 
 Magneto-electricity, 39, 140. 
 Magneto- electric machine, 141. 
 Medical coil machine, 138. 
 Metals, their relative voltaic powers, 98. 
 Muschenbroeck's experiments, 14. 
 
 NEEDLE telegraph, 164. 
 
 Nervous influence, its connexion with 
 
 electricity, 114, 148. 
 New terms, Faraday's, 41, 110. 
 
 CERSTED'S discovery of electro-magnet- 
 ism, 36. 
 Ohm's formula of resistance, 101. 
 
 PHYSIOLOGICAL effects of electricity, 114. 
 Pistol, electrical, 67. 
 Points, influence of, 64. 
 Poles of a voltaic battery, 110. 
 Porous cells, 106, 108. 
 Priestley's statement of electrical theories, 
 58. ' 
 
 QUADRANT electrometer, 77. 
 
INDEX. 
 
 199 
 
 Quantity of electricity in bodies, 126. 
 
 RAPIDITY of voltaic action, 111. 
 
 Recording telegraph instruments, 167. 
 
 Reizen's electric telegraph, 160. 
 
 Repulsion, the action of, explained, 57. 
 
 Residual charge, 75. 
 
 Resinous electricity, 52. 
 
 Resistance essential to electrical action, 
 
 79,96, 117. 
 
 Resistance of long wire circuits, 156. 
 Resisting media, electrical discharge 
 
 through, 69. 
 Reversing currents, 165. 
 Richmann, Professor, killed by lightning, 
 
 21. 
 
 Ronalds's electric telegraph, 161. 
 Rotation of magnets, 139. 
 
 SCHILLING'S electric telegraph, 162. 
 
 Sealing-wax emitted from points, 64. 
 
 Secrecy of telegraphic correspondence, 1 74. 
 
 Seesbeck's discovery of thermo-electricity, 
 40. 
 
 Secondary currents, 117. 
 
 Sheet-lightning, 90. 
 
 Shepherd's electric clock, 184. 
 
 Signal telegraph instruments, 160. 
 
 Sremmering's electric telegraph, 160. 
 
 Sounding the sea, 193. 
 
 Spark, electric, colours of, 70. 
 
 instantaneous duration of, 81. 
 
 Spencer's electrotype experiments, 175. 
 
 Spiral coils, effect of, 118. 
 
 Static and current electricity, 47. 
 
 Static electricity confined to exterior sur- 
 faces, 66. 
 
 Steinheil's electric telegraph, 162. 
 
 Submarine telegraph wires, 158. 
 
 Submarine telegraphs, new system of, 159. 
 
 Surfaces, influence of, on electrical in- 
 tensity, 67. 
 
 TABLE-moving, 194. 
 
 Tangential direction of deflecting force, 138. 
 
 Telegraph, electric, Bain's, 169. 
 
 Breguet's, 166. 
 
 copying, the, 170. 
 
 Coo'ke and Wheatstone's, 163. 
 
 Lesarge's, 153. 
 
 Lomond's, 160. 
 
 Morse's, 167. 
 
 Reizen's, 160. 
 
 Ronalds's, 161. 
 
 Soammering's, 161. 
 
 Schilling's, 162. 
 
 Steinheil's, 162. 
 
 Alexander's, 163. 
 
 Davy's, 163. 
 
 Henley's, 166. 
 
 Telegraphs, electric, rejected by Govern- 
 ment, 162. 
 
 Telegraph-lines, mode of constructing, 158. 
 Telegraph-wires in India, 158. 
 Telegraphic communication with America 
 
 suggested, 159. 
 
 signals, 163, 165, 168. 
 
 Theories of two electricities, 58. 
 Thermo-electricity, its discovery, 40. 
 Thermo-electric batteries, 145. 
 Thermo-electrics, list of, 144. 
 Thunder, cause of, 91. 
 Thunder-cloud, condition of electricity in. 
 
 86. 
 
 observations of, 83. 
 
 phenomena of, 84. 
 
 Thunder-house, 80. 
 
 Thunder-storms, safest place during, 88. 
 
 Torpedo, 145. 
 
 Transmission of telegraphic messages, rates 
 
 of, 166, 169, 174. 
 
 UNIVERSAL discharger, 77. 
 Ure's galvanic experiments on a dead 
 body, 114. 
 
 VITREOUS electricity, 52. 
 Volta's discoveries, 29. 
 Voltaic action, its rapidity, 111. 
 
 controlling force of, 125. 
 
 conditions necessary for, 100. 
 
 Voltaic battery, heating effects of, 112. 
 
 theories of, 31. 
 
 its decomposing agency, 32. 
 
 Babington's, 104. 
 
 Cruikshank's, 104. 
 
 Daniell's, 43, 106. 
 
 Grove's, J07. 
 
 Smee's, 107. 
 
 Wollaston's, 105. 
 
 positive and negative poles of, 110. 
 
 Voltaic batteries, action of, explained, 102. 
 
 how to make, 151. 
 
 Voltaic electricity conducted by moist 
 
 air, 157. 
 
 identical with frictional, 109. 
 
 its low intensity, 112. 
 
 Voltaic pile, 97. 
 Voltameter, 127. 
 Von Kleist's experiments on accumulated 
 
 electricity, 15. 
 
 WALL'S suggestions respecting lightning, 
 
 Water, decomposition of, 82, 121. 
 
 excitement of electricity by, 93. 
 
 Water- battery, Crosse's, 115. 
 
 Daniell's, 115. 
 
 Water- batteries, cause of their intensity, 
 116. 
 
 ZINC, action of acidulated water on, 95. 
 
 voltaic electricity excited by, definite 
 
 in quantity, 108. 
 Zinc plates, amalgamation of, 102. 
 
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