-NRLF 
 
 M E5E fi57 
 
PRESENTED BY 
 
AN 
 
 ACCOUNT 
 
 j 
 
 / 
 
 HISTORY AND PRESENT STATE 
 
 GALVANISM. 
 
 BY 
 
 JOHN BOSTOCK, M.D. F.R.S. 
 
 MEMBER OF THE GEOLOGICAL SOCIETY ; MEMBER AND LATE PRESIDENT 
 
 OF THE EDINBURGH MEDICAL SOCIETY; MEMBER OF THE LONDON 
 
 MEDICAL AND CHIRURGICAL SOCIETY ; HONORARY MEMBER 
 
 OF THE NEW-YORK HISTORICAL SOCIETY, &C. 
 
 LONDON; 
 
 PRINTED FOR BALDWIN, CRADOCK, AND JOY, 
 PATERNOSTER ROW. 
 
 1818- 
 
' 
 
 
 
 
 . 
 
 C. Baldwin, Printer, 
 New Bridge-street, London. 
 
ADVERTISEMENT. 
 
 THE basis of the following Essay is an ar- 
 ticle that was published in the tenth volume 
 of Dr. Brewster's Encyclopaedia. The commend- 
 ations which it received, wjhile under that form, 
 from those whom I supposed competent to de- 
 cide upon its merits, have induced me to reprint 
 it, although with considerable additions and cor- 
 rections, which will, I hope, render it more deserv- 
 ing of the public favour. My present residence 
 in the metropolis has given me the opportunity of 
 examining several works on galvanism, which I had 
 not before been able to procure, and I have also en- 
 deavoured to profit by the remarks of my scien- 
 tific friends, so as to rectify the inaccuracies into 
 which I had fallen, and to render those parts more 
 perspicuous, which were thought to be obscure. 
 
 Great Coram Street, 
 June 24, 1818. 
 
 218 
 
For a Description of the Plates, see Page 156. 
 
 ERRATA. 
 
 Page 27, line 11, for cocks read corks. 
 Page 28, line 9, for dissolved read decomposed. 
 Page 69, side note, for d read and. 
 
 Page 127, line 10, for effected read affected. 
 
 

 
 ON GALVANISM, 
 
 -' -- 
 
 xjfALYANISM is a branch of natural philoso- 
 phy, entirely of modern origin, which derives its 
 name from Galvani, Professor of Anatomy at Bo- 
 logna. He had the good fortune to make some 
 observations on the electricity of the muscles of 
 frogs, that appeared to him to depend upon a new 
 power in the animal body ; and although it is now 
 generally admitted that he drew an erroneous 
 inference from his observations, yet they led to a 
 train of experiments, which have associated his 
 name with some of the most brilliant discove- 
 ries of modern science. To the supposed new 
 power he gave the name of animal electricity, 
 conceiving it to depend upon something inherent 
 in the animal body itself; but we now regard 
 these effects as produced by minute quantities of 
 the electric fluid, set at liberty by a certain agency 
 of substances upon each other. 
 
 Galvanism may be defined, a series of electrical Definition 
 phenomena, in which the electricity is developed 
 
2 INTRODUCTION. 
 
 without the aid of friction, and where we perceive 
 a chemical action to take place between some of 
 the bodies employed. 
 
 Plan of the In treating upon this science, it will be found 
 convenient to arrange the subject into two divi- 
 sions : in the first I shah* give an historical detail 
 of the discoveries that have been successively made 
 from the time of Galvani's first observation to 
 the present period ; and, in the second place, I 
 shall examine the principal theories and hypotheses 
 that have been formed to explain the phenomena 
 of galvanism. 
 
PART I. 
 
 SECTION I. 
 
 Experiments before the Discovery of the Pile. 
 
 IN reviewing the history of galvanism there are 
 two great eras, which especially arrest our notice, 
 the formation of the pile of Volta in the year 1791 * 
 1800, and the decompositions of the alkalies and 
 earths by Sir H. Davy in 1806 ; these discoveries 
 naturally divide the narrative into three periods, 
 during each of which a particular train of phe- 
 nomena was pursued, and the attention was 
 occupied by a different kind of investigation. 
 
 The original discovery, to which I have already 
 alluded, took place from a singular accident. The 
 wife of Galvani, being in a declining state of 
 health, employed as a restorative, according to 
 the custom of the country, a soup made of frogs. 
 A number of these animals, ready skinned for 
 the purpose of cookery, chanced to lie in his 
 laboratory, on a table near an electrical machine. 
 While the machine was in action, an attendant 
 happened to touch, with the point of a scalpel, the 
 
4 HISTORY OF GALVANISM. 
 
 crural nerve of one of the frogs that was not far 
 from the prime conductor, when it was observed, 
 that the muscles of the limb were instantly 
 thrown into strong convulsions. This experiment 
 was performed in the absence of the Professor, 
 but it was noticed by his lady, who was much 
 struck with the appearance, and communicated it 
 to her husband. He repeated the experiment, 
 varied it in different ways, and perceived that the 
 convulsions only took place when a spark was 
 drawn from the prime conductor, while the nerve 
 of the frog was, at the same time, touched with a 
 substance which was a conductor of electricity. 
 At the time that this accidental discovery was 
 made, Galvani was engaged in a set of experi- 
 ments, the object of which was to prove that 
 muscular motion depends upon electricity ; and 
 it appeared, in a very remarkable manner, to 
 K v confirm his hypothesis ; so that he was induced to 
 
 prosecute the inquiry with redoubled diligence.* 
 prepared When a frog was so placed as to form part of 
 the electric circuit, it was found that an extremely 
 minute quantity of electricity produced contrac- 
 tions in the muscles. If the hind legs were dis- 
 sected from the body, the connexion being kept up 
 by the crural nerves only, and the electric fluid was 
 passed through it in this state, a still more minute 
 quantity was rendered visible ; so that a frog, 
 prepared in this manner, was capable of exhibiting 
 
 * Eloge de Galvani, par Alibert. 
 
HISTORY OF GALVANISM. 5 
 
 very decisive marks of electricity, where none 
 could be detected by Bennet's gold-leaf elec- 
 trometer. 
 
 After employing the electric fluid, as disengaged Discovery 
 from the common machine, Galvani next tried the g a i?LnUm. 
 atmospherical electricity ; and it was in pursuance 
 of this object, that he was first led to observe 
 the effects of galvanism properly so called. Hav* 
 ing suspended a number of frogs by metallic hooks 
 to an iron railing, he found that the limbs were 
 frequently thrown into convulsions, when it did 
 not appear that there was any electricity in the 
 atmosphere. Having duly considered this pheno- 
 menon, he discovered that it did not originate from 
 an extraneous electricity, but that it depended 
 upon the position of the animal, with respect to 
 certain metallic bodies. 
 
 It appeared, that when the muscle and nerve Action of 
 of a frog were each in contact with metallic bodies, 
 and these were also connected by a metal, the 
 contractions were always produced. The effect 
 was considerably increased by arming the nerve 
 with a metallic coating, by which means a larger 
 portion of it was brought into contact with the 
 metal. But the most important of Galvani's dis- 
 coveries was the effect produced by the combina- 
 tion of two metals. Of these combinations the 
 most powerful was that of zinc and silver ; and 
 the most violent convulsions ensued when the 
 nerve was coated with one of these metals, the PLATE i. 
 muscle placed in contact with the other, and the Fts ' 9 * 
 
6 HISTORY OF GALVANISM. 
 
 two metals connected by a conductor of elec- 
 tricity. 
 
 General Galvani's general conclusion from his experi- 
 on * ments was, that the animal body possesses an in- 
 herent electricity of a specific kind, which is con- 
 nected with the nervous system, and conveyed by 
 means of the metals into the muscles, so as to 
 throw them into convulsions. He deduced a theory 
 of muscular motion from his discoveries, according 
 to which the body contains an apparatus analogous 
 to the Leyden phial, its different parts being in 
 different states of electricity, and the metals 
 forming a connexion between them, by which the 
 electricity is equalized. In this application of the 
 new phenomena, Galvani went beyond the limits 
 of correct deduction ; yet he deserves much com- 
 mendation for the perseverance and ingenuity 
 which he exhibited in prosecuting the inquiry. 
 Although the discovery originated, in a consider- 
 able degree, from accident, still it must be re- 
 membered, that it is only men of ability who take 
 advantage of such accidents.* 
 
 Vaiii's let- Galvani had no sooner published an account of 
 ers, 1792. ^ dig^ve^ than the philosophers, in different 
 parts of Europe, entered with eagerness upon the 
 examination /of the new phenomena. Among the 
 earliest writers on the subject were Valli, Fowler, 
 and Volta. The principal object pf Valli's letters f 
 
 * A. Galvani de Viribus Electricitatis in Motu musculari 
 Commentarius. 
 f Journal de Physique, xli. and xlii. 
 
HISTORY OF GALVANISM. 
 
 was to examine how far the opinion of Galvani 
 was correct, respecting the dependence of the new 
 influence upon the nervous fluid, and its identity 
 with electricity. Although much of his reasoning 
 must now be regarded as erroneous, yet still he 
 manifests ingenuity and address in the contrivance 
 of his experiments, and in the inferences which he 
 deduced from them. 
 
 In the following year, Fowler published his 
 Essay on Animal Electricity, which displays con- 
 siderable acuteness, and by which he may be con- 
 sidered as having prepared the way for many of 
 the discoveries of his successors. At the time 
 when he wrote, the question was warmly agitated, 
 whether the phenomena of galvanism could be 
 referred to the electric fluid, or whether they do 
 not rather depend upon some specific agent pecu- 
 liar to the animal body. He accordingly com- 
 mences by the inquiry, " Are the phenomena Are 
 exhibited by the application of certain different electricity 
 metals to animals referable to electricity?" Al- identical ? 
 though he conducts his train of reasoning with 
 much ability, yet he drew the conclusion which 
 we are now enabled to say is not correct. After 
 examining minutely the circumstances which are 
 necessary for the production of the galvanic influ- 
 ence, he finds that it is requisite that there should 
 be two different metals, which are to communicate 
 with each other and with the animal. He con- 
 ceives it necessary that they should be in contact, 
 one with the nerves, and the other with the 
 
g HISTORY OF GALVANISM. 
 
 muscles ; and points out an error into which Valli 
 had fallen in his experiment's, where he thought 
 that the contact of the nerve only is sufficient to 
 cause the contractions : he shows that, in this 
 case, the moisture on the surface of the nerve 
 acted as a conductor of the influence of one of the 
 metals to the fibres of the muscle. 
 
 Supposed Fowler concludes that the galvanic influence is 
 ferent. not referable to electricity, because for the produc- 
 tion of the former the presence of two different 
 metals appears to be necessary, while electricity, as 
 proceeding from the electrical machine, is excited 
 by the action of an electric upon a conductor ; an 
 inference which was correct, according to the state 
 of the science at the time when he wrote. He 
 also endeavours to show that electricity and gal- 
 vanism are not, in all cases, conducted by the same 
 substances, and particularly adduces charcoal, 
 which, although a conductor of electricity, is im- 
 pervious to the galvanic influence. He afterwards 
 made some curious observations upon the effect 
 of galvanism on animals not furnished with dis- 
 tinct limbSj such as worms of various kinds. 
 These animals could not be made to contract ; yet 
 by the nature of their motions, they seemed to be 
 sensible to the impression of the two metals, when 
 they were placed, partly on one, and partly on the 
 other. From these experiments he inferred that 
 animals of this description were furnished with a 
 nervous system, and that the peculiar effect of the 
 metals upon them depended upon the mechanism 
 of their organs of motion. 
 
HISTORY OF GALVANISM. 9 
 
 Fowler afterwards enters upon an interesting Effect on 
 
 , . ,, a* r> i ,1 the volun- 
 
 inquiry respecting the effect of galvanism on the ta r y and in- 
 
 different parts of the body. " What are the re- 
 lations which subsist between the influence dis- 
 covered by Galvani, and the muscles, the nervous, 
 and the vascular systems of animals ? " He found 
 that the contractions were very readily excited in 
 all the muscles which are subservient to the will, 
 but that they were with great difficulty produced 
 in the heart, while he was not able to produce any 
 effect upon the stomach and intestines. He ob- 
 served, that when a part is in a state of inflamma- 
 tion it acquires an additional sensibility to the 
 galvanic stimulus, and he made the curious dis- Effect on 
 co very of the flash of light, which is produced by tongue. *" 
 placing the two metals in contact with the ball of 
 the eye, and then causing them to communicate 
 with each other. Sultzer, a German metaphysical 
 writer, had mentioned several years before, the 
 effect produced on the organ of taste, by applying 
 two metals, one above and the other below the 
 tongue, and then bringing them into contact; 
 but the sensation was ascribed to a peculiar vibra- 
 tion excited by the metals, and conveyed to the 
 tongue. The experiments with the two metals, 
 upon the eye and the tongue, were varied in dif- 
 ferent ways by Professor Robison, an account of 
 which is published at the end of Fowler's Essay. 
 Professor Robison also mentions the sensation of 
 taste which is excited, w~hen the tongue is applied 
 to the edges of a number of plates of zinc and 
 
 8 
 
10 HISTORY OF GALVANISM. 
 
 silver, placed alternately upon each other ; a con- 
 struction which may be regarded as an approxima- 
 tion to the apparatus afterwards discovered by 
 Volta. 
 
 Voita's let- In the same year in which Fowler's Essay was 
 ers, 1793. p^igh^ a verv va l ua ble communication appeared 
 in the Philosophical Transactions of London, from 
 the pen of Professor Volta, of Pavia, in the form 
 of letters to CavaLlo. He gives a luminous ac- 
 count of Galvani's discovery, and adds many cu- 
 rious experiments and observations of his own. 
 He attempted, and with complete success, to 
 overthrow Galvani's opinion, that the animal body 
 bears an analogy to the Leyden phial, its different 
 parts being in opposite states of electricity. He 
 supposed, that for the production of the effect it 
 was essential to have two different metals ; and 
 hence he arrived at the important conclusion, 
 which may be regarded as leading to all his future 
 discoveries, that the muscular contractions are 
 produced by small portions of electricity, that are 
 liberated by the action of the metals upon each 
 other. Another point which Volta established 
 was, that the nerve is the organ on which the 
 galvanic influence immediately acts ; but he found 
 that if a part of a muscle be laid upon two differ- 
 ent metals, and these be made to communicate, a 
 contraction is produced. This probably depends 
 upon the nervous matter that is dispersed through 
 the muscles, and also upon the moisture that is 
 always present, and which serves to conduct the 
 
HISTORY OF GALVANISM. 11 
 
 electricity to all parts of the body. Volta per- 
 formed many experiments, in order to discover 
 what circumstances are favourable to the excita- 
 tion of the contractions, and what parts of the 
 body are the most easily called into action. His 
 observations agree, in almost all respects, with 
 Fowler's, although it is certain that their experi- 
 ments must have been made without concert or 
 communication. He found that snails and worms 
 could not be made to contract ; but that many of 
 the insects, as butterflies and beetles, were subject 
 to the influence of the metals. It appeared from 
 his numerous trials, that those animals alone were 
 sensible to galvanism who are furnished with 
 distinct limbs, having flexor and extensor mus- 
 cles. In the animals of this description, he sup- 
 posed that it was the voluntary muscles alone 
 which are capable of being made to contract. Al- 
 though the heart is a muscle which is easily 
 thrown into powerful action, by chemical or me- 
 chanical stimuli, yet he could never produce any 
 effect upon it by the action of the two metals. 
 Volta made some of the same observations upon 
 the effect of the two metals on the organs of sense 
 as have been mentioned in the account of Fow- 
 ler's Essay. 
 
 In these letters Volta lays down the basis of the Voita's 
 
 . . . theory. 
 
 theory of galvanism, which, with certain modifi- 
 cations, he has since so zealously defended, and 
 which may be regarded as the one that has been 
 most generally received. He argues against the 
 
 6 
 
HISTORY OF GALVANISM. 
 
 doctrine of Galvani, that the animal body has 
 any share in the production of the electricity ; 
 this is thought to be entirely owing to the action 
 of the two metals upon each other; by this action 
 a small quantity of the fluid is liberated, which, 
 by passing through the nerve, causes the muscular 
 fibres connected with it to contract. Thi; action 
 of the metals upon each other is described as one 
 by which their electrical equilibrium is destroyed ; 
 and by establishing a communication between 
 them, their equilibrium is restored. This destruc- 
 tion of equilibrium he speaks of as a new law of 
 electricity discovered by himself; and the animal 
 
 is supposed to have no further concern in it, than 
 as being a peculiarly sensible electrometer, and 
 affording a very delicate test of the presence of 
 this disengaged electricity in its passage from one 
 metal to the other.* 
 
 pa- Dr. Wells wrote an interesting paper on galvan- 
 ism, which was also published in the Philosophical 
 Transactions of London. He proposed three dis- 
 tinct objects of inquiry, which, at the time when 
 he wrote, embraced the points that were the most 
 general subjects of discussion. He first inquires, 
 whether the influence discovered by Galvani de- 
 pends upon any property inherent in the animal 
 body, or peculiar to it : in the second place, he 
 inquires into the conditions that are necessary for 
 its excitement : and, lastly, he examines how far 
 
 * Phil. Trans, for 1793, p. 20, et alibi. 
 
HISTORY OF GALVANISM. 
 
 it ought to be considered as identical with elec- 
 tricity. Dr. Wells coincides in opinion with Volta, 
 that the contractions of the muscles depend upon 
 electricity liberated by some cause, independent of 
 the animal body, and that the moisture which is 
 present in all parts is the immediate cause of the 
 facility with which the effect is produced. He 
 discovered the important fact, that charcoal may 
 be employed, together with one of the metals, 
 for exciting the influence; and also that the 
 influence, when excited, may be conducted by 
 charcoal. He argues at length against the hy- 
 pothesis of Volta, respecting the production of 
 the electricity by the contact of the two metals, 
 and urges as a decisive objection to it, that the 
 moisture which is attached to the animal ought to 
 serve as a conductor, and equalize their electrical 
 condition, without their being absolutely brought 
 into contact. 
 
 Dr. Wells made some curious experiments 
 upon the effects that were produced on the power 
 of the metals and on charcoal by friction ; after 
 this operation he found that one of the substances 
 alone was sufficient to produce the contractions. 
 As it appeared that the friction did not immedi- 
 ately communicate electricity to the body that was 
 rubbed, it must be supposed that some change 
 was brought about in its nature, by which its 
 different parts were enabled to act upon each 
 other in the same manner with two distinct 
 substances. He is decidedly of opinion, that 
 
14 HISTORY OF GALVANISM. 
 
 galvanism is identical with electricity, because 
 
 every substance which is a conductor of one of 
 
 these principles is also a conductor of the other.* 
 
 iiumWdt's An interesting set of experiments was performed 
 
 rn^u" about this time by Humboldt, on the irritability 
 
 1 ^opi 
 
 of the muscular fibre ; the object of which was to 
 prove that this property depends immediately upon 
 a specific proportion of the chemical elements 
 which enter into the composition of the muscle. 
 When certain agents were applied to a muscle, 
 he conceived that its contractile power was in- 
 creased, in consequence of some change that had 
 been effected in its chemical composition, or even 
 that the contractility might be restored after it had 
 been destroyed, while, on the contrary, there were 
 other agents which seemed to be equally powerful 
 in depriving the muscles of their irritability, in 
 consequence of an opposite change in their che- 
 mical constitution. He employed the galvanic 
 influence as a test of the presence of the irritability 
 of the muscle ; and he was led, in the course of 
 his experiments, to inquire into the nature of this 
 influence, and to make many curious observations 
 concerning it, which were derived from a very 
 elaborate train of experimental research. He was 
 induced to form some conclusions very different 
 from those that had been adopted by Galvani, 
 Volta, and the authors that had preceded him, 
 some of which were important additions to our 
 
 * Phil. Trans, for 1795. 
 
HISTORY OF GALVANISM. 15 
 
 knowledge; but with respect to others, we can 
 have no hesitation in pronouncing them to be er- 
 roneous.* 
 
 One of his doctrines, to which this remark Remarks 
 applies, is the opinion that the galvanic influence U) 
 is not electrical, an opinion which he embraced 
 after long deliberation, and, as he supposed, after 
 duly considering all the phenomena, and carefully 
 weighing the arguments on both sides of the ques- 
 tion. As at this period the whole that was known 
 of the effects of galvanism was their action upon 
 the organs of the living body, Humboldt was led 
 to suppose that it was entirely a vital action, or 
 that it depended upon something essentially con- 
 nected with the living body ; he however differed 
 from Galvani and Valli, who regarded it as a 
 proper electrical phenomenon, depending upon 
 electricity evolved from the different parts of the 
 body itself, without the addition of any extrane- 
 ous substance. Humboldt's experiments were 
 brought forward in such a manner, as to im- 
 press upon his readers the idea that they were 
 performed with the most scrupulous regard to 
 accuracy ; yet owing to the novelty of the subject, 
 and no doubt also, in a considerable degree, to the 
 extremely delicate nature of the substances on 
 which he operated, it appears that many of them 
 
 * Ann. de Chim. xxii. 51 ; Journ. de Pbys. xlvi. 465, and 
 xlvii. 65; Experiences sur le Galvanisnie, Traduction par 
 Jadelot, 1799. 
 
HISTORY OF GALVANISM. 
 
 have not been found to succeed in the hands of 
 other experimentalists. One important fact, how- 
 ever, he may be considered as having established, 
 that contractions can be excited in an animal by 
 placing the nerves and the muscles in certain 
 situations with respect to each other, without em- 
 ploying any metallic substance ; a fact which was 
 afterwards brought forward in a very striking 
 manner by Aldini, but which appears still to be 
 involved in a degree of mystery, both as to the 
 nature of the operation itself, and as to the class 
 of physical phenomena to which it ought to be 
 referred. 
 
 Voita's Volta continued to be actively engaged in pro- 
 
 secuting his inquiry into the nature of galvanism, 
 and in perfecting the hypothesis that he had 
 formed, to explain the operation by which it is 
 excited. He now introduced a new principle into 
 his theory, and found it necessary to alter the 
 terms in which he had announced it, particularly 
 with respect to the circumstances requisite for the 
 extrication of the electric influence. He had 
 before stated that two metals were essential to this 
 purpose ; but he now informs us that, provided the 
 substances diifer in their power of conducting 
 electricity, their metallic nature may be dispensed 
 with. He divides conductors into the two classes 
 of the dry and the moist ; the first including 
 metals and charcoal; the latter essentially consist- 
 ing of water, holding various substances in solu^ 
 tion. In order to form a galvanic circuit, it is ne- 
 
HISTORY OF GALVANISM. 17 
 
 cessary that a body from one of these classes be 
 placed between two bodies from the other class ; by 
 this means the equilibrium is destroyed, and it is 
 again restored when the two are united by a con- 
 ductor. The same effects proceed from this ar- 
 rangement as when the equilibrium is destroyed 
 by the contact of the two metals ; but two con- 
 ductors of the same class, whatever be their dif- 
 ference, are not sufficient to form a circuit with- 
 out the intervention of one of the other class. 
 For the purpose of illustrating his theory, he 
 brings forward what he calls an experimen- 
 tum crucis ; he applies the ends of two metal- 
 lic rods, one formed of silver and the other of 
 tin, to the two disks of Nicholson's doubler, and 
 unites their other ends by a moist conductor ; after 
 they have remained for some time in this situation, 
 he finds that the disk in contact with the silver 
 rod indicates the positive electricity, and that in 
 contact with the tin the negative. As was the 
 case in his former paper, he does not attempt to 
 explain the cause of this change in the electric 
 state of the substances, but is satisfied with 
 pointing it out as a matter of fact which he had 
 discovered, and as constituting a well-established, 
 although empirical law of electricity.* 
 
 A very ample and elaborate memoir on the Committee 
 subject of animal electricity was drawn up by a French in- 
 cbmmittee of the French Institute, which, besides JViS te> 
 
 * Ann. de Chim. xxiii. 276. 
 c 
 
18 HISTORY OF GALVANISM. 
 
 examining all the opinions and controversies that 
 existed on the subject, contained an account of a 
 great variety of original experiments. The com- 
 mittee was composed of some of the most cele- 
 brated chemists and natural philosophers of 
 France; Morveau, Fourcroy, Vauquelin, Halle. 
 Coulomb, Sabbatier, Pelletan, and Charles. They 
 arrange the materials of their report under six 
 heads: 1st, They examine the different circum- 
 stances which influence the nature of what they 
 call the animal arc, by which they mean, that 
 part of the galvanic circle which consists of the 
 parts of the animal. They conceive that the 
 animal arc may consist of nerve only; they 
 found that cutting a nerve across did not pre- 
 vent the passage of the influence, provided the 
 cut ends were laid close together, and also that 
 it was transmitted through different parts of the 
 same animal, or even through parts of different 
 animals, provided they were in perfect contact. 
 They observe, that when a nerve is made part of 
 the circle, those muscles are thrown into contrac- 
 tions to which the extremities of the nerve are 
 distributed, not those which are contiguous to the 
 trunk of the nerve. In the %d place, they examine 
 the nature and disposition of what is called the 
 excitatory arc, or the metallic part of the circle. 
 3d, They inquire into the circumstances extrinsic 
 to the composition of both parts of the galvanic 
 circle, but which in any way affect its action, or 
 influence its effects. The 4th head consists of 
 
HISTORY OF GALVANISM. 19 
 
 the means which may be employed for varying, 
 diminishing, or restoring the sensibility of the 
 animal to the galvanic influence. In this part, 
 they mention the effects of immersing the animal 
 in a fluid, or in an unrespirable gas, so as to pro- 
 duce suffocation, when the susceptibility to the 
 galvanic influence was either destroyed or much 
 impaired ; but the effects were very various, and 
 difficult to account for in many cases. The 5th 
 head consists of a comparison between electricity 
 and galvanism ; and the 6th contains a detail of 
 some experiments which were performed by Hum- 
 boldt, and subjected to the inspection of the com- - 
 mittee. These appear to have been substantially 
 the same experiments of which I have already 
 given an account.* 
 
 An ingenious paper was about this time published 
 by Fabroni, of Florence, in which he discusses the 
 question, whether the galvanic phenomena are im- 
 mediately referable to electricity, or whether they 
 ought not rather to be attributed to chemical 
 affinity ? He relates many observations, that he 
 made upon the chemical action of different metals 
 on each other, when placed in contact, and shows, 
 that they were then disposed to oxidate under the 
 same circumstances, except that of being in con- 
 tact, where, if separate, no effect would have 
 been produced. He argues, that the facts stated 
 by Galvani, Volta, and others, which were con- 
 
 * Journal de Physique, xlvii. 392, 441. 
 C 2 
 
20 HISTORY OF GALVANISM. 
 
 ceived by them to prove the electrical nature 
 of the phenomena in question, only went so far 
 as to show, that electricity was concerned in 
 the operation, but did not prove it to be the cause 
 of them ; and he is inclined to regard it rather as 
 the effect. 
 
 Fabroni mentions, among other facts, that mer- 
 cury and tin when pure, and kept distinct from 
 other metals, will remain a long time without tar- 
 nishing ; but when alloyed, or placed in contact 
 with other metals, they soon begin to exhibit signs 
 of oxidation. He remarked, that coins composed of 
 a pure metal were more durable than such as 
 were composed of a mixture of metals. He men- 
 tions the corrosion which takes place, when cop- 
 per roofs are soldered with another metal, and in 
 the copper sheathing of ships when fastened with 
 iron nails. These phenomena are supposed to 
 depend upon a chemical affinity between the me- 
 tals, by which their particles are individually 
 attracted towards each other, while the separa- 
 tion of the particles of the solid metal, which is 
 caused by their tendency to unite, permits the 
 oxygen to act upon them. " These facts," he says, 
 " as well as many others of the same nature, no 
 less common than well known, ought to have 
 proved to philosophers, that the metals, by exer- 
 cising their mutual attractive force, must by 
 the same energy diminish their respective powers 
 of aggregation; that though neither of them 
 separately may be able to attract oxygen from the 
 
HISTORY OF GALVANISM. 
 
 atmosphere, or from water, they may acquire 
 that power by simple mechanical touch, as they 
 pass to new combinations." 
 
 He then relates some experiments which he 
 performed, in order to observe the comparative 
 effect produced, by placing metals first in separate 
 vessels of water, then in the same vessels, but not 
 in contact; and lastly, in the same vessels, and 
 also in contact. In the two former cases there 
 was no change produced, while in the latter there 
 was a considerable degree of oxidation. He after- 
 wards entered upon some speculations on the 
 source of the oxygen, and he found that, by cover- 
 ing the water with a stratum of oil, and thus ex- 
 cluding the atmosphere, the process of oxidation 
 was retarded. This fact he adduces as a powerful 
 argument in favour of the chemical hypothesis. 
 He concludes, that the oxygen in these cases 
 cannot be derived from the water, because, were 
 the water decomposed, there would be a liberation 
 of hydrogen. The effect that is produced on the 
 senses of vision and of taste, he attributes to the 
 formation of new chemical compounds, which act 
 in a peculiar manner upon the organs ; an opinion 
 which may be true, to a certain extent, so far as 
 respects the tongue ; but it is not easy to conceive 
 how it could cause the flash of light which is ex- 
 cited in the eye by the contact of the metals.* 
 
 Fabroni's paper did not appear to excite much 
 
 * Journal de Physique, xlix. 318. 
 
22 HISTORY OF GALVANISM. 
 
 attention at the time when it was published, as it 
 directly opposed the current of popular opinion. 
 But many of the statements have been since veri- 
 fied by succeeding philosophers; and when we 
 consider that it was written before the discovery of 
 the pile, it must be regarded as displaying much 
 sagacity and nice observation. 
 
 In this state the science of galvanism remained 
 until the year 1800. It was generally admitted, 
 that the immediate agent in producing the pheno- 
 mena was the electric fluid, and that the actions 
 exhibited by the animal body depended merely 
 upon its extreme sensibility to small quantities of 
 this fluid. The experiments principally consisted 
 in different combinations of conducting substances 
 with parts of the animal body, composing what 
 was called the galvanic arc or circle. The chemi- 
 cal effects had been little attended to, except by 
 Fabroni ; and his remarks, although truly ingeni- 
 ous, must be regarded rather as the first glance 
 of a series of important facts, than as constituting 
 their complete development. 
 
HISTORY OF GALVANISM. 
 
 SECTION II. 
 
 Experiments from the Discovery of the Pile to 
 the Decomposition of the Alkalies. 
 
 THE second period of the history of galvan- Discovery 
 
 .,, ,, . j. of the pile 
 
 is m commences with the important discovery Dy Voita, 
 made by Volt a, of the instrument which has been 1{ 
 called the galvanic or voltaic pile. Volta, as has 
 been remarked above, adopted the idea, that the 
 action excited by the two metals depended upon 
 an alteration in their respective states of electricity, 
 or in a destruction of its equilibrium. The effect 
 produced by one pair of plates could only be 
 comparatively small ; but he supposed that by 
 interposing- a conductor between several pairs of 
 plates, it might be multiplied and concentrated in 
 an indefinite degree. He accordingly provided a pescrip- 
 number of silver coins, and pieces of zinc of simi- 
 lar dimensions ; these were disposed in pairs, and PLATE i. 
 between each pair was placed a piece of card ' s ' 
 soaked in water ; and thus a pile or column was 
 formed, in which the three substances silver, zinc, 
 arid, water, existed in regular rotation. The effect 
 of the combination fully justified the expectations 
 of the discoverer. All the phenomena that had Effects, 
 been excited by a single pair of metals were far 
 exceeded by those of the pile, while by touching 
 the two ends of it at the same time, it was found 
 
24 HISTORY OF GALVANISM. 
 
 that a distinct shock was felt in the arms. This 
 fully established the opinion that had been formed, 
 and was generally adopted, of the identity of elec- 
 tricity and galvanism; although there were still 
 some circumstances connected with the latter, 
 which appeared not to be completely analogous to 
 the usual operations of the electric fluid. 
 Galvanic He found that forty pairs of the metallic disks, 
 with the proper number of pieces of moistened 
 card interposed, were sufficient to produce a shock, 
 which was very distinctly felt in the hands and 
 arms, and that by increasing the number of pairs, 
 the power of the pile was proportionally aug- 
 mented. In order to produce the full effect, it was 
 found necessary that two pieces of metal, either 
 composing the extremities of the instrument, or 
 in contact with them, should be firmly grasped by 
 the two hands ; and the shock might, in this case, 
 be repeated for any number of times, as long as 
 the pasteboard between the two metals remained 
 sufficiently moist. Volta conceived that the newly 
 invented apparatus was analogous in its action to 
 the electrical organ of the torpedo. 
 
 Couronne He afterwards constructed another apparatus, 
 Fig. 3. ' or rather arranged the component parts of the pile 
 in a different form. It consists of a set of small 
 glasses, placed side by side, and containing water 
 or some saline solution. A number of metallic arcs 
 are then procured, having one end composed of 
 zinc, and the other of silver or copper ; these arcs 
 are inserted into the glasses in a uniform order, 
 
HISTORY OF GALVANISM. 25 
 
 each glass having the zinc leg of one arc, and 
 the copper or silver leg of another arc, immersed 
 in the fluid. The zinc and copper legs are not 
 in contact, and they are always to be disposed in 
 the same situation with respect to each other, i. e. 
 one is to be always at the right hand, and the 
 other at the left. Volta named this apparatus, 
 the couronne des tasses. The operation of both 
 these instruments is precisely the same, and is 
 referred by the author to the new principle, 
 which he conceives he had discovered, by which 
 different metals, when placed in contact, destroy 
 the electric equilibrium, or, as he expresses it, 
 become movers of electricity, producing that elec- 
 tric motion which is supposed to be the primary 
 and essential cause of the galvanic action. 
 
 The experiments which Volta performed with 
 the pile were almost exclusively confined to the 
 animal body; and he seems to have entertained no 
 idea of the important use to which it might be ap- 
 plied, as an instrument of chemical analysis. His 
 attention appears indeed to have been so totally 
 absorbed in the electrical action of the apparatus, 
 that he overlooked its other effects, and only no- 
 ticed, in a very cursory manner, the changes 
 which it induced upon the fluid. It is indeed a 
 little remarkable, that after making so curious a 
 discovery, he should have rested there, and not 
 have proceeded with the further prosecution of 
 the subject. It would be unjust not to acknow- 
 ledge, in the warmest terms, the obligation under 
 
26 HISTORY OF GALVANISM. 
 
 which the scientific world was laid by the discovery 
 of Volta; but, at the same time, it must be ad- 
 mitted, on the other hand, that the benefit of the 
 discovery has been obtained by others.* 
 
 No sooner was the discovery of the galvanic 
 pile announced, than the English experimentalists 
 began their operations w r ith it, and almost at the 
 first trial of its effects made some important and 
 interesting observations. Sir Joseph Banks, on 
 the receipt of the information, having communicated 
 an account of it to his scientific friends, a pile was 
 
 Nicholson's formed by Messrs. Nicholson and Carlisle, with 
 - which tJiey began to repeat the experiments of 
 olta They arranged the su b s tances in the order 
 of silver, zinc, fluid ; silver, zinc, fluid, &c. : an 
 arrangement which it is necessary to attend to, 
 in speaking of what have been called the silver 
 and zinc ends of the apparatus. Volta, it appears, 
 had satisfied himself that the action of the pile 
 was electrical, because it produced the shock ; 
 
 Discovered but Messrs. Nicholson and Carlise applied to it 
 
 -States" t ne instrument caUed the revolving doubler, f and 
 by this means decidedly proved it to be the case : 
 they found, that the silver end was in the negative 
 and the zinc end in the positive state of electricity. 
 
 Decompo- In the course of the experiments, a part of the 
 circuit between the upper and lower ends of the 
 
 P^ e was f rme( i by water, and it was observed that 
 cuit - there was a disengagement of gas at the part 
 
 * Phil. Trans, for 1800. f Phil* Trans, for 1788. 
 
HISTORY OF GALVANISM. 
 
 where the wire came in contact with the fluid. 
 This gas was thought to have the odour of hy- 
 drogen ; and it led them to notice, with more 
 attention, the effect produced by causing the 
 electricity to pass through a tube of water, into 
 the two ends of which wires were inserted, 
 which communicated with the extremities of the 
 pile. I shall relate this very important experi- 
 ment in Mr. Nicholson's own words. " On the 
 2d of May we inserted a brass wire through each 
 of two cocks, inserted in a glass tube of half an 
 inch internal diameter. The tube was filled with 
 New River water, and the distance between the 
 points of the wires in the water was one inch and 
 three quarters. This compound discharger was 
 applied, so that the external ends of its wire were 
 in contact with the two extreme plates of a pile 
 of thirty-six half-crowns, with the correspondent 
 pieces of zinc and pasteboard. A fine stream of 
 minute bubbles immediately began to flow from 
 the point of the lower wire in the tube, which 
 communicated with the silver, and the opposite 
 point of the upper wire became tarnished, first 
 deep orange, and then black. On reversing the 
 tube, the gas came from the other point, which 
 was now lowest, while the upper, in its turn, be- 
 came tarnished and black." " The product of 
 gas, during two hours and a half, was two- 
 thirtieths of a cubic inch. It was then mixed with 
 an equal quantity of common air, and exploded 
 by the application of a lighted waxed thread." 
 
28 HISTORY OF GALVANISM. 
 
 in the body Mr. Nicholson observed, that the same process 
 e * of the decomposition of water is carried on in the 
 body of the pile, as between the two ends of the 
 wire in the interrupted circuit ; the side of the 
 zinc next to the fluid being covered with oxide 
 in two or three days, and the apparatus then ceas- 
 ing to act. It was also observed, that the com- 
 mon salt which had been dissolved in the water 
 was dissolved, for that there was an efflorescence 
 of soda round the margin of the plates. Mr. 
 Nicholson afterwards found that, by using me- 
 tallic plates of considerably more extensive surface, 
 no greater effect was produced in the decomposition 
 of water, or in the violence of the shock ; so that 
 he concludes, " the repetition of the series is of 
 more consequence to this action than the enlarge- 
 ment of the surface." As he proceeded in his ex- 
 periments it was more decidedly ascertained, that 
 the electricity of the silver end was negative, that 
 of the zinc end positive. Although it appeared 
 evident that there had been a decomposition of 
 water effected by the copper wire, yet Mr. Nichol- 
 son determined to render the operation more deci- 
 sive, by employing a metal which was not oxida- 
 Piatina ble. Platina was therefore substituted for the 
 dnced P both c PP er > an( i now g as was disengaged from both 
 hydrogen s id es an d neither of the wires were tarnished. 
 
 and oxy- 
 gen. In a subsequent experiment, the w^ires were so ma- 
 naged, that the gases extricated from each side 
 were kept distinct ; and it was found that they 
 consisted, the one of oxygen, and the other of hy- 
 
 2 
 
HISTORY OF GALVANISM. 29 
 
 drogen, and that they were generated in the 
 proportion necessary to produce water. In some 
 of these experiments the spark was visible.* 
 Every one will be sensible of the important views 
 that were disclosed by the experiments related 
 in this paper, in connexion with those performed 
 by Mr. Cruickshanks of Woolwich, of which an 
 account will be given below. They must be re- 
 garded as leading directly to the wonderful dis- 
 coveries that have been made by means of the gal- 
 vanic apparatus, as well as the theoretical deduc- 
 tions to which it has given rise, and which have 
 produced almost a complete revolution in our ideas 
 of the action of bodies upon each other. 
 
 Cruickshanks confirmed the observations ofcvuick- 
 Nicholson, respecting the actual appearance of p^mentsT 
 sparks and the decomposition of water. This last 
 process he varied in different ways. By employ- 
 ing the interrupted circuit with silver wires, and 
 -passing the influence through water tinged with 
 litmus, he found, that the wire connected with the 
 zinc end of the pile communicated a red tinge to 
 the fluid contiguous to it ; and afterwards, by em- 
 ploying water tinged with Brazil wood, he found 
 that the wire connected with the silver end of the 
 pile produced a deeper shade of colour in the sur- 
 rounding fluid. Hence it appeared, that an acid Acid and 
 was formed in the former, and an alkali in the lat- duced in" 
 ter case. The galvanic influence was passed tbe water ' 
 
 * Nicholson's Journ. 4to. iv. 179. 
 
SO HISTORY OF GALVANISM. 
 
 through the interrupted circuit, in which the 
 tube was filled with the solution of acetate of lead, 
 when it was observed that the lead was sepa- 
 rated in the metallic state, and deposited at the 
 Metais re- end of the silver wire, or the wire connected with 
 metallic so- the silver end of the pile, in the form of fine 
 needles. Experiments were afterwards made upon 
 the solutions of sulphate of copper and nitrate of 
 silver : in this last case, he observes, " the metal 
 shot into fine needles, like crystals articulated or 
 jointed to each other, as in the arbor Diance" 
 He also succeeded in decomposing some of the 
 neutral salts.* 
 
 In a second memoir, Cruickshanks paid more 
 particular attention to the nature of the gases emit- 
 ted in the interrupted circuit to the effects of 
 different kinds of wires and to the influence of 
 the fluid medium upon the decomposition of the 
 Concludes water. Some of his most important conclusions 
 gen is y ai- ~ are, that from the wire connected with the silver 
 te^from 1 '" or c PP er en ^ of the pile, whatever be its compo- 
 ooe wire, s ition, if it terminate in water, the eras emitted is 
 
 from the 
 
 other oxy- chiefly hydrogen ; if it terminate in a metallic 
 wireoxi- solution, the metal is reduced, and is deposited at 
 the end of the wire. When the wire connected 
 with the zinc end is formed of a perfect metal, 
 nearly pure oxygen is disengaged : when of an 
 oxidable metal, it is partly oxidated and partly 
 dissolved, and only a small quantity of oxygen is 
 
 * Nicholson's Journ. 4?to. iv. 187. 
 1 
 
HISTORY OF GALVANISM. 31 
 
 liberated. When fluids contain no oxygen, they Fluids 
 appear to be incapable of transmitting the galvanic oxygen 
 influence; while, on the contrary, it would seem ^Jt! " 
 that it may be transmitted by every one which 
 contains this element.* These views of Cruick- 
 shanks respecting the action of the pile were 
 confirmed by some experiments that were per- 
 formed, about the same time, by Colonel Haldane. 
 He found that the apparatus ceased to act when Haidane's 
 it was immersed in water, or if it was placed in " e nt"~ 
 the vacuum of an air-pump. He found, on the Pile will 
 contrary, that it acted more powerfully in oxygen 
 
 gas, than when confined in an equal bulk of at- 
 mospheric air, while azote had the same effect 
 as a vacuum. These circumstances led him to 
 conceive that its action depended essentially upon 
 the combination of oxygen, which it derives from 
 the atmosphere.f He also made some experi- 
 ments on the series of metals which are the best 
 adapted for producing the galvanic effects, and the 
 relative power which they possess in this respect. 
 
 In the early part of his experiments, Cruick- Trough ap - 
 shanks invented a new manner of disposing the Fig. 5, ' 
 apparatus, which has proved scarcely less im- 
 portant to the interests of science, than its ori- 
 ginal discovery by Volta. I allude to the method 
 of placing the metals horizontally in a frame or 
 trough, with proper intervals for containing the 
 fluid which is intended to act upon them. 
 
 * Nicholson's Journ. 4to. iv. 254. t Ibid, 241, 313. 
 
32 HISTORY OF GALVANISM. 
 
 The power of the pile in decomposing chemical 
 substances being now established, by the experi- 
 ments of Nicholson and Cruickshanks, a new field 
 of investigation was opened, which was ardently 
 entered upon by some of the most distinguished 
 Henry 'sex- among the English chemists. Dr. Henry was 
 among the first who employed the galvanic in- 
 fluence for the purpose of analysis ; he de- 
 composed the sulphuric and nitric acids, and am- 
 monia, and he reduced the oxymuriatic to the 
 Decom- state of muriatic acid ; but as gases do not 
 andlmmo! con duct the galvanic influence, its decompo- 
 nia. sm g power could not be applied to this last body. 
 
 Davy's ex- Sir H. Davy, at an early period of the science, 
 Disengages commenced the career of discovery which he 
 from* wo afterwards brought to so brilliant a termination, 
 portions of He proposed, as a subject of experimental re- 
 search, whether the ends of the wire, in the inter- 
 rupted circuit, would- discharge the two gases, if 
 they were made to terminate in different por- 
 tions of water. They were therefore placed in 
 separate glasses, while the glasses were jnade to 
 communicate by means of the fingers, or a moist 
 substance, and it was found that the oxygen and 
 hydrogen were evolved as usual. He next inquired 
 whether it was necessary for the effect that the 
 wires should be in contact with the ends of the 
 pile; and in order to prove this point, slips of 
 muscular fibre were interposed between the wires 
 and the ends of the pile. The result of this 
 disposition was that the gases were disengaged, 
 
HISTORY OF GALVANISM. 33 
 
 but in a reverse order ; the hydrogen now pro- 
 ceeding from the wire connected with the zinc 
 end of the pile, and the oxygen from the silver 
 or copper wire. 
 
 These experiments, which at the time when New com, 
 they were performed seemed most extraordinary, 
 and almost inexplicable, were succeeded by others 
 equally curious, in which Sir H. Davy produced 
 the galvanic effect, by a new combination of 
 substances. He found that charcoal was capable 
 of conducting the influence and of decomposing 
 water, the copper end giving out hydrogen, hold- 
 ing a little carbon in solution ; the zinc end did 
 not produce any considerable quantity of gas, as 
 the carbonic acid which was produced was ab- 
 sorbed by the water in which the charcoal was 
 immersed. He formed a pile of zinc and charcoal, piieof one 
 which acted with considerable energy ; and he metal * 
 afterwards discovered that a pile may be con- 
 structed of only one metal, with different fluids 
 applied to its two surface?, one of them capable 
 of oxidating the metal, the other of preventing 
 the effect of oxidation, the two fluids being se- 
 parated from each other by water. The series 
 which he employed was metal, diluted nitric acid, 
 water, sulphuret of potash, and then again metal. 
 In a subsequent train of experiments, he proceeded 
 still farther, and composed a pile without any pj] e O f 
 metal, but consisting solely of pieces of charcoal, c ^^ 
 having their opposite surfaces exposed to the ac- metal - 
 
 D 
 
34. HISTORY OF GALVANISM. 
 
 tion of two fluids that bore a different chemical re- 
 lation to them. 
 
 Pile win Sir H. Davy also made some very important 
 with pure observations on the nature of the fluid interposed 
 between the plates of the pile, and the nature of 
 the changes which it experiences. If the water 
 that is employed be perfectly pure, containing no 
 acid, salt, or gas, the apparatus is incapable of 
 acting. He found that its energy was in pro- 
 portion to the rapidity with which the oxidation 
 of the metal advances, and consequently was most 
 energetic when nitric acid was made use of. 
 Strong sulphuric acid, on the contrary, had little 
 effect, because zinc has not the power of decom- 
 posing it ; but if the acid be diluted, the metal was 
 oxidated, and the electricity was evolved. Upon 
 the same principle it appeared, that the sulphu- 
 rets, which cannot act upon the metallic surface, 
 had not the power of exciting the energy of the 
 pile. In pursuance of this opinion, he discovered, 
 that the pile can act in vacuo, if an acid be in- 
 terposed between the plates.* 
 
 Remarks Sir H. Davy's very curious discovery, that the 
 
 Davy's ex. two constituents of water might be obtained sepa- 
 
 nts ' rate from two portions of the /fluid contained in 
 
 different glasses, seemed at variance with all 
 
 former opinions of chemical composition, and gave 
 
 rise to a number of speculations, which although 
 
 * Nicholson's Journ. 4to. iv. 275, 326, 337, 380, 394- ; 
 v. 78, 341 ; and 8vo. i. 144. 
 
HISTORY OF GALVANISM. 35 
 
 many of them sufficiently ingenious and interest- 
 ing at the time when they were proposed, it is 
 not necessary to relate, as they have been entirely 
 superseded by his subsequent discoveries. I may 
 observe, that one of two consequences seemed 
 necessarily to result from it ; either that water, 
 by some kind of combination with the two states 
 of electricity, is convertible into oxygen and hy- 
 drogen ; or that one of these bodies has the power 
 of uniting to other bodies, without apparently 
 affecting their form, and passing silently through 
 them. The earlier discoveries of Sir H. Davy 
 seemed to afford a very powerful support to the 
 chemical hypothesis of Fabroni, and to be equally 
 irreconcileable to that of Volta ; and they appear, 
 when they were first announced, to have been 
 viewed in this light by the discoverer himself, and 
 by the most scientific of his countrymen. 
 
 With respect to the nature of the galvanic in- Theoreti- 
 fluence, or the primary cause of its operation, the s " 
 English philosophers seem at this time to have 
 been nearly unanimous in ascribing it to electri- 
 city. On the Continent, however, where the late 
 discoveries that had been made in this country 
 were little known or imperfectly understood, a 
 considerable difference of opinion still existed on 
 this subject. Of these discussions, which have 
 now entirely lost their interest, it will not be ne- 
 cessary to give any account, but I shall briefly 
 notice an hypothesis which was brought for- 
 wards about this time by Brugnatelli, of Pavia, 
 
 D 2 
 
HISTORY OF GALVANISM. 
 i which, although at present known to be erroneous, 
 
 on electric , . , - 
 
 acid. seemed, in the first instance, to be supported by 
 a considerable body of direct evidence. He sup- 
 posed that the galvanic influence was identical 
 with electricity, but that when it is extricated in 
 contact with water, so as to decompose this fluid, 
 it unites with a portion of its oxygen, and forms a 
 new acid, which he called the electric acid. Like 
 other acids, he conceived that it had the property 
 of combining with bodies and forming various 
 compounds, the properties of which he describes. 
 It might be difficult and little important to trace 
 out, in every instance, the source of Brugnatelli's 
 errors. There can be no doubt that he operated 
 upon impure substances ; it is probable that the acid 
 which he obtained was derived either from small 
 portions of nitric acid which were generated, or 
 of muriatic acid which were liberated in the course 
 of the experiment. 
 
 Woliastoifs Soon after the discovery of the pile, Dr. Wollas- 
 mSS, t( >n turned his attention to the subject of galva- 
 nism, and displayed his accustomed sagacity and 
 penetration in a paper which he presented to the 
 Royal Society. He observes that the energy of 
 the apparatus seems to be in proportion to the 
 tendency which one of the metals has to be acted 
 upon by the interposed fluid. An experiment is 
 related, not very unlike some of those which had 
 been previously performed by Fabroni. If a plate 
 of zinc and a plate of silver be immersed in diluted 
 sulphuric acid, and kept asunder, the silver is not 
 
HISTORY OF GALVANISM. 37 
 
 affected, but the zinc begins to decompose the 
 water, and to evolve hydrogen. If the plates be 
 now placed in contact, the silver discharges hy- 
 drogen, and the zinc continues, as before, to be dis- 
 solved. From these, and other analogous facts, Electricity 
 he concludes, that whenever a metal is dissolved 
 by an acid, electricity is disengaged. He extends 
 this principle to the action of the electrical ma- 
 chine, which he conceives has its power increased 
 by applying an amalgam to the cushion, into the 
 composition of which a metal enters which is rea- 
 dily oxidated. As a further illustration of the same 
 principle, he found the machine will not act when 
 immersed in carbonic acid gas. 
 
 Nicholson had already suggested the opinion, Electricity 
 that the electricity of the pile differs from that " n f 
 of the machine, in consequence of the latter being 
 
 in a state of higher intensity, but in less quantity ; tie intcnsi- 
 the former of course being in greater quantity, but 
 of low intensity. Dr. Wollaston coincided in 
 this idea, and supposed that it might explain the 
 difference between the operation of the two in- 
 struments. It had been long known that water 
 might be decomposed by the electric shock, but 
 v the effect differs from that of the pile, the two 
 gases being separated promiscuously from both 
 ends of the wire, not, as when the pile is employed, 
 the oxygen from one end, and the hydrogen from 
 the other. But Dr. Wollaston succeeded in pro- 
 ducing the galvanic effect on water by common 
 electricity, so as to keep the gases separate This 
 
38 HISTORY OF GALVANISM. 
 
 he accomplished by coating two silver wires, the 
 ends of them only being left exposed. He then 
 connected these wires with the two conductors of 
 the electrical machine, and passed the spark, from 
 one to the other, through a solution of a salt of 
 copper ; the negative wire was found to be covered 
 with a metallic coating, as if it had been con- 
 nected with the copper or silver end of the pile.* 
 Remarks The experiments of Dr. Wollaston, and the 
 
 on Wollas- 
 
 ton's expe- reasoning which he employed concerning them, 
 must be considered as both affording a very im- 
 portant addition to our knowledge of galvanism, 
 and as giving a greater precision to our ideas on 
 the theory of its production, and on the nature of 
 the relation which it bears to common electricity. 
 In the experiment in which the plates of zinc 
 and silver are separately immersed in a diluted 
 acid, we find that the decomposition of the water 
 is effected solely by the zinc ; but that when the 
 metals are connected, the hydrogen is disengaged 
 from the silver. In this case it does not appear 
 that the silver in any way tends to promote the 
 decomposition of the water, but that it merely 
 influences the manner in which its constituent 
 parts are liberated, which, there is every reason to 
 suppose, depends essentially upon the electrical 
 condition of the different parts of the metallic 
 surface. Although Nicholson, by applying his 
 doubler to the two extremities of the pile, may be 
 
 * Phil, Trans, for 1801, p. 4-27. 
 
HISTORY OF GALVANISM. 39 
 
 considered as having shown that the galvanic influ- 
 ence depends upon some modification of electricity, 
 yet the complete identity of the two agents could 
 scarcely be considered as fully proved, until the 
 most remarkable effects of the pile had been imi- 
 tated by the action of the machine. Dr. Wollas- 
 ton's view of the subject has been considered as 
 combining, to a certain extent, the theory of Volta 
 with that of Fabroni ; according to the literal ac- 
 ceptation of the terms, however, it must be re- , 
 garded as favouring the chemical hypothesis, be- 
 cause it contemplates a chemical change as the 
 primary step in the operation, from which all the 
 subsequent effects are ultimately derived. 
 
 A set of experiments was performed about this De&orme' 
 period by Desormes, the object of which was to "cuts"" 
 ascertain the source of the oxygen which com- 
 bines with the plates ; this he conceives did not 
 depend upon the actual decomposition of the 
 water, but upon some change which the water 
 experiences by the union of the negative and po- 
 sitive electricity. The same reasoning was of 
 course applied to the hydrogen, and a similar 
 opinion has been since adopted by other philoso- 
 phers, but it has generally been regarded as a less 
 simple method for accounting for the facts, and as 
 involving more gratuitous suppositions.* 
 
 Professor Trommsdorff discovered that the pile Tromms- 
 
 rt i i dorff burns 
 
 possesses a very powerful effect in burning me- metallic 
 
 leaves. 
 * Ann. de Chim. xxxvii. 284. 
 
40 HISTORY OF GALVANISM. 
 
 tallic leaves. He formed an instrument of large 
 plates of zinc and copper, and fixed gold leaf to 
 the zinc end ; then by bringing it in contact with 
 the silver end, the leaf was rapidly consumed, 
 the process being attended by a beautiful emission 
 of coloured light. Silver, tin, and copper leaves 
 were burned in the same manner, each giving out 
 a brilliant flame tinged by its appropriate colour.* 
 In a subsequent set of experiments he even suc- 
 * ceeded in burning the metals in the different gases 
 which contained no oxygen, but we are not fully 
 informed what was the exact nature of the pro- 
 ducts obtained in this case. Experiments on the 
 combustion of metals were performed about the 
 same time by Fourcroy, Thenard, and Vauquelin, 
 when they observed, that the energy of the shock 
 and the power of decomposition were not increased 
 The effect by the size of the plates, but by the number of 
 the repetitions ; while the same extent of surface, 
 arranged in the form of a few large plates, readily 
 consumed the metallic leaves, but had only a com- 
 paratively small effect on the sensation s.f Four- 
 croy, at this period of the investigation, supposed 
 that the galvanic phenomenona could not be refer- 
 red to the action of electricity ; but this opinion 
 he was afterwards induced to retract. Indeed this 
 point was shortly afterwards established beyond 
 dispute by Mr. Cruickshanks actually charging the 
 
 * Nicholson's Journ. 4to. v. 238. 
 Ann. de Chim. xxxix. 103. 
 
HISTORY OF GALVANISM. 41 
 
 Ley den phial from the pile; and in this way he 
 was able to demonstrate still more clearly than it 
 had been before done, that the extremity of the 
 apparatus which gives out oxygen is in the posi- 
 tive, and that which gives out hydrogen is in the 
 negative state. 
 
 As the opinion of philosophers was generally Van Ma. 
 agreed in respect to the identity of the galvanic pa? e reTec- 
 and electric influences, many speculations were 
 formed as to what constituted the essential differ- 
 ence between the electric fluid, as generated by the 
 pile, and as disengaged by the common machine. In 
 order to elucidate this point, Van Marum, in con- 
 junction with Professor Pfaff, of Reil, entered 
 upon a series of experiments, in which the action 
 of the pile was compared with that of the great 
 Teylerian machine at Haarlem. He succeeded in 
 charging, not only single jars, but whole batteries, 
 by the pile ; and it appeared that they were 
 always charged to the same degree of intensity 
 with that which the pile itself indicated to an elec- 
 trometer placed upon it. He found that the zinc 
 end of the pile communicated positive electricity 
 to the side of the jar or battery with which it was 
 in contact, and the copper end the reverse. No 
 perceptible difference could be experienced between 
 shocks of the same intensity given by a jar or by 
 the battery ; whether they were charged by the 
 pile or by the machine. He observed that the in- 
 tensity of the pile was always the same from the 
 same number of plates, whatever was their size ; 
 
42 HISTORY OF GALVANISM. 
 
 but he perceived Fourcroy's observation to be 
 correct, that it was necessary to employ large 
 plates to burn the metals. He formed a pile of 
 large plates of zinc and copper, and succeeded in 
 Fuses iron fusing iron wires of considerable thickness ; he at 
 wires. at ia l ast even fused a wire of platina. He found that a 
 battery, consisting of 137-i- square feet of coated 
 glass, was charged by a galvanic apparatus to an 
 intensity equal to itself, in l-20th of a second ; a 
 circumstance which proves the amazing velocity 
 of the fluid. He conceived that the energy of the 
 pile was much augmented when it was kept in 
 an insulated state, and likewise when a solution 
 of the muriate of ammonia was interposed between 
 the copper and zinc plates.* 
 
 Action of We have already noticed the discovery of 
 oxidates Cruickshanks, that the pile acted more powerfully 
 in oxygen gas than in the air of the atmosphere ; 
 and an observation the converse of this, was made 
 by Biot and Cuvier, which confirmed the relation 
 between the action of the apparatus and the che- 
 mical state of the fluid in which it is immersed. 
 When the pile was enclosed in a limited quantity 
 of air, they found that, after some time, the air 
 was sensibly deoxidated.f 
 
 state of The discoveries that were made with the gal- 
 vanic pile, especially by the English chemists, 
 completely established some of the most important 
 points which had previously been subjects of doubt 
 
 * Ann. de Chim. xl. 289. f Ibid, xxxix. 24-2, 
 
HISTORY OF GALVANISM. 43 
 
 or controversy. Animal electricity, as produced in 
 the original experiments of Galvani, and after- 
 wards in those of Valli, Fowler, Volta, and others, 
 was now admitted to depend upon nothing adhe- 
 rent in, or attached to, the animal body, but upon 
 an agent, called into action by external causes, and 
 manifesting itself in consequence of the delicate 
 sensibility of the nervous and muscular systems. 
 This agent was now generally recognized as being 
 identical with electricity, conducted by the same 
 substances, possessing the same properties, and, in 
 short, subject to the same physical laws. It was 
 conjectured, that the apparent difference between 
 electricity, as excited by the machine and by the 
 pile, depended upon the different states of intensity 
 in which they exist ; the electricity of the machine 
 being in a much higher state than that of the 
 pile, although this latter is generally disengaged in 
 greater quantity. This may be regarded as the 
 state of the science in 1801 ; from this time, until 
 the grand discovery of Sir II. Davy, which I 
 have marked out as the third era, the attention 
 of the different experimentalists, who devoted 
 themselves to this department of natural philoso- 
 phy, was partly directed to improving or modify- 
 ing the apparatus, and partly to hypothetical dis- 
 cussions, respecting the nature of the action, and 
 its connexion with chemical affinity. 
 
 The effect of the size of the plates in the gal- Blot's ob- 
 vanic pile had been already observed by Fourcroy 
 and others, and was now more particularly noticed 
 
44 HISTORY OF GALVANISM. 
 
 by Biot, who wrote a memoir, the principal object 
 of which was to illustrate the relative action of 
 the different kinds of apparatus, and to discover 
 the cause on which this difference depends. Elec- 
 tricity is known to be discharged by points, and 
 to be retained by extensive surfaces ; and from this 
 circumstance he conceives, that the smaller the 
 plates are, the more rapid will be the circulation 
 of the fluid ; large plates furnish a greater quan- 
 tity of the fluid, but it is less rapid in its motion ; 
 smaller plates, on the contrary, furnish less fluid, 
 but it passes with more rapidity through the 
 different parts of the apparatus. Hence what was 
 spoken of by Nicholson and others, as constituting 
 the intensity of the fluid, is resolved by Biot into 
 Different the velocity of its motion. The different opera- 
 tions of the pile are differently affected by these 
 two properties. The taste, the flash, and the shock, 
 exist nearly in the same degree, and all depend 
 principally upon the velocity ; while the combus- 
 tion of the metals is more influenced by the 
 quantity of the electricity. The electrical attrac- 
 tions also depend upon the quantity of fluid, 
 and are therefore more perceptible when large 
 plates are used. It is observed that a pile com- 
 posed of small plates affords very pungent shocks, 
 but is more quickly exhausted. It was before 
 stated, that Biot had perceived the pile to deoxi- 
 date a portion of the air in which it was confined ; 
 and he now informs us, that the effect was pro- 
 duced more rapidly when the ends of the pile were 
 
HISTORY OF GALVANISM. 45 
 
 made to communicate by intervening wires. The 
 general conclusions with which he sums up this 
 interesting paper, are, that the galvanic fluid re- 
 sembles the electric in the repulsive property of 
 its particles, and that the different phenomena de- 
 pend upon variations in the quantity and velocity 
 of the fluid * 
 
 An elaborate set of experiments was published Lehot's ob- 
 about this period by Lehot, on the direction of J^thed?- 8 
 the galvanic current. This subject had also occu- Recurrent, 
 pied the attention of Biot, and it was generally ad- 
 mitted that its course was from the zinc plate, 
 across the fluid, to the silver or copper plate.f 
 
 A circumstance of some importance 4n our view Erman's 
 of the action of the pile, was pointed out by Erman the name" 
 of Berlin ; he remarks, that the action takes place, of the ex " 
 
 ' treinities. 
 
 not between the metals, but between the metal 
 and the fluid ; therefore, in designating the end 
 of the pile, we should say that the zinc end is the 
 negative, and the copper the positive. Nicholson 
 and Cruickshanks supposed the apparatus to be 
 constructed of copper, zinc, fluid ; but it would be 
 more correct to say, zinc, fluid, copper, as in 
 this arrangement we have the complete circle. :(: 
 A similar remark was made by Priestley, who Priestley's, 
 was at this time performing experiments on gal- 
 vanism in America. He says, that no alteration 
 is produced in the apparatus by whatever metal is 
 
 * Journ. de Phys, liii. 264. f Ibid. Hi. 135. 
 Ibid. liii. 121. 
 
46 HISTORY OF GALVANISM. 
 
 placed at the ends beyond the reach of the fluid. 
 Most of the phenomena of common electricity had 
 been imitated by the electricity of the pile, except 
 
 r.autherot that of attraction ; and Gautherot at length sue- 
 on galvanic ' 
 
 attraction, ceeded in contriving an apparatus for producing 
 this effect. It consisted of two delicate wires, 
 which hung loose from the extremities of the 
 pile; when they were brought near together, a 
 sensible approximation was perceived, and they 
 were found to adhere with a sensible degree of 
 force.* 
 
 Voita de- it does not appear that Volta himself partici- 
 
 fends the 
 
 electrical pated, in any degree, in the various discoveries 
 Sls ' that were made by means of his apparatus, or that 
 he employed any means for improving or altering 
 its original form. He seems to have interested 
 himself solely in defending the hypothesis, which 
 he had proposed to account for its operation, and 
 which indeed may be considered as having led to 
 its construction. His opinion, that the primary 
 action was electrical, and that it depended en- 
 tirely or essentially upon a change in the distri- 
 bution of the electric fluid, had been called in ques- 
 tion by Mr. Nicholson, Dr. Wollaston, and other 
 English chemists, who were more disposed to refer 
 the effects to the chemical action of the fluid inter- 
 posed between the plates in oxidating the metals. 
 Volta, however, still adhered to his first opinion; and, 
 
 in a paper written about this time, he lays it down 
 
 
 
 * Ann. de Chim. xxxix. 205. 
 
HISTORY OF GALVANISM. 47 
 
 as his decided conviction, that the action of one of 
 the metals upon the other is the sole cause of the 
 excitation of the electricity, and that the only 
 use of the interposed fluid is to convey the ex- 
 cited electricity from one pair of plates to the 
 other.* 
 
 Many papers were written on the subject of this Cuthbert- 
 controversy, some of them containing illustrations ri 
 or modifications of the electric hypothesis, while 
 others proceeded entirely upon the opposite opi- 
 nion, endeavouring to prove, either that the phe- 
 nomena could not be explained on this principle, 
 or that the data on which it was attempted to be 
 founded were incorrect. Of this latter description 
 is an examination of the experiments which Volta 
 had himself brought forwards as the basis of his 
 reasoning, by Mr. Cuthbertson, an able practical 
 electrician, who, after repeating the experiments 
 with every precaution, could not obtain the results 
 which had been announced ; a circumstance which 
 he attributes to a defect in Volta's apparatus.f 
 It was about that time that I published the outline 
 ,of a chemical theory of galvanism, which was after- 
 wards given more in detail, the further consi- 
 deration of which will be deferred to the second 
 part of the essay. 
 
 Professor Simon, of Berlin, repeated on a large 
 
 * Nicholson's Journ. 8vo. i. 135. t !*>"* 281. 
 J Ibid. iii. 69 ; and Thomson's Ann. iil 32. 
 
48 HISTORY OF GALVANISM 
 
 scale the experiments of Trommsdorff, on the 
 * combustion of metals by galvanism, and gave a 
 minute account of the different phenomena which 
 were produced during the process.* 
 
 pepys'sgai- By an ingenious alteration in Bennet's electro- 
 Ler ' meter, Mr. Pepys endeavoured to convert it into 
 
 PLATE ii. a galvanometer, and it may be so far entitled to 
 
 ijf' ' ' this appellation as it is calculated to measure ex- 
 tremely minute quantities of electricity, which 
 perhaps could not be made sensible by any other 
 means. He also confirmed the facts which I have 
 already alluded to, that oxygen is absorbed by the 
 pile, that it will not act in azote or in hydrogen, 
 and that it may be excited in vacua, provided an 
 acid be interposed between the plates.f About 
 
 Ritter s ex- this time, Hitter of Jena entered upon his inves- 
 tigation of the galvanic phenomena, and both 
 performed many new experiments, and entered 
 
 supposed very zealously into theoretical discussions. He 
 conceived that he had observed a connexion be- 
 twcen galvanism and magnetism : he says, that if 
 an iron wire be placed in the magnetic meridian, 
 the north pole of the wire is more disposed to be- 
 come oxidated than the south pole ; when the 
 magnetized wire is placed in water, the south 
 pole, on the contrary, is most affected. If similar 
 wires be employed, but not placed in the mag- 
 netic meridian, no difference is to be observed in 
 
 * Ann. de'Chim. xlii.ifc? 
 t Tilloch's Phil, Mag, x. 38. 
 
HISTORY OF GALVANISM. 49 
 
 the oxidation of the two extremities.* It does not, 
 however, appear that these experiments of Ritter 
 have been confirmed by any subsequent observa- 
 tions. 
 
 In the experiments that had been performed 
 on animals, those with cold blood were gene- 
 rally employed, both on account of their being 
 more' convenient for the operation, and from the 
 greater tenacity with which they retain their 
 vitality. It was, however, ascertained, that ani- 
 mals with warm blood were equally susceptible of 
 the influence; and Creve, of Wurtzburg, pro- 
 duced strong contractions in a human leg after am- 
 putation. Vassali-Eandi, in conjunction with his By Vassal*, 
 friends Giulio and Rossi, performed a more ample 
 set of experiments upon the bodies of some cri- 
 minals that were beheaded at Turin. f They paid 
 particular attention to the effect of the galvanic 
 electricity upon the heart and the other involun- 
 tary muscles, a point which had been the subject 
 of much controversy. Volta supposed that the 
 involuntary muscles could not be made to contract ; 
 Fowler however asserts, that contractions were 
 excited in the heart, although with difficulty : 
 Vassali confirmed the observations of Fowler, 
 and extended them to the stomach and intestines ; 
 the same opinion was also maintained by Nysten,f 
 who afterwards published an elaborate treatise on 
 
 * Journ. de Phys. Iv. 235. f Ibid. Iv. 286. 
 Ibid. Iv. 465. 
 
HISTORY OF GALVANISM. 
 
 Aldini. 
 
 Circaud's 
 experi- 
 ments on 
 fibrine. 
 
 the subject.* On the other hand, Aldini, the nephew 
 of Galvani, who now came into notice as an assi- 
 duous experimentalist, asserted that he was unable 
 to act upon the heart. In order to complete our 
 view of the experiments that relate to the action 
 of galvanism on the different parts of the nervous 
 system, I may mention, that Bichat, in his trea- 
 tise on life and death, informs us that he found 
 the nerves which are connected with the great 
 sympathetic, and with the ganglia, those which 
 are distributed to the organs of what he calls the 
 organic f unction s, to be very little acted upon by 
 this stimulus, so as indeed to be almost insensible 
 to it, when compared with its effects upon the 
 nerves which go to the voluntary muscles.f 
 
 Circaud announced a discovery, which, if it 
 were fully confirmed, would prove of great impor- 
 tance in physiology, that the fibrine of the blood, 
 immediately after it leaves the vessels, may be 
 made to contract by the galvanic apparatus. De- 
 lametherie confirms the statement of Circaud, 
 from his own observations ; but the experiment has 
 not succeeded in this country, even although re- 
 peated in the most careful manner ; and when we 
 consider the difficulty and delicacy of the process, 
 we may be allowed, without impeaching the ve- 
 racity of the narrators, to entertain some doubts 
 on the subject. 1 
 
 * Nouvelles Experiences Galvaniques, 1803. 
 f P. 336, et alibi. J Journ. de Phys. Iv. 402. 
 
 9 
 
HISTORY OF GALVANISM. 51 
 
 In the year 1803, Aldini, professor of natural 
 
 philosophy at Bologna, published his Treatise meats. 
 on Galvanism, a work which contains many 
 curious experiments, and also some new theore- 
 tical opinions. The experiments which were the Contrac- 
 
 -. i , j , i . . , i tions in the 
 
 most calculated to produce an impression upon the human 
 
 spectators, were performed on the body of a cri- 
 minal, who was hanged at Newgate, and also on 
 the head and limbs of some of the larger warm- 
 blooded animals. A powerful battery being ap- 
 plied, very strong contractions were excited, the 
 limbs were violently agitated, the eyes opened and 
 shut, the mouth and jaws worked about, and the 
 whole face was thrown into frightful convulsions. 
 These experiments, however, were principally re- 
 markable from the subjects made use of, and the 
 magnitude of the effect : there were others per- 
 formed, really more curious, in which very consi- 
 derable muscular contractions were excited, with- contrac- 
 out the intervention of any metal, or other sub- diSwu'h 
 stance which could be supposed capable of disen- outmetals - 
 gaging the electric fluid. In some cases the effect 
 was produced by bringing into contact the nerve 
 of one animal with the muscle of another, and at 
 other times by employing the nerves and muscles 
 of the same animal. In some of the experiments, 
 there appears to have been the most powerful con- 
 tractions excited, by bringing the parts of a warm 
 and a cold blooded animal into contact with each 
 other. It does not appear, from any expressions 
 in this treatise, whether Aldini considered the 
 
 E 2 
 
52 HISTORY OF GALVANISM. 
 
 animal electricity, as he calls it, to be of a speci- 
 fically different kind from that excited by the pile, 
 or whether he supposes that the different parts of 
 the animal body have the power of generating the 
 same kind of electricity, without the aid of any ex- 
 ternal agent. He, however, deduces from his ex- 
 periments an inference in favour of Galvani's hy- 
 pothesis, of a proper animal electricity inherent in 
 the body, and not requiring the assistance of any 
 external agent for its development. 
 Remarks There are some points respecting" these experi- 
 
 on Aldiui's . , 
 
 experi- ments that require farther explanation. The most 
 obvious conclusion that we should draw from them, 
 would be that which was formed by Aldini him- 
 self, in favour of a proper animal electricity. But 
 if this be the case, they must be regarded as es- 
 sentially different from those of Galvani, where 
 an electricity of the usual kind was certainly ex- 
 cited. Perhaps the most probable supposition is, 
 that the parts of the body, in these experiments, 
 acted in a manner analogous to the pile which 
 was constructed by Sir H. Davy, in which elec- 
 tricity was developed by the action of two different 
 fluids upon carbon. There are, however, many 
 circumstances wanting to render this analogy 
 complete. 
 
 Lagrave'a An important experiment was announced by 
 
 pile Lagrave : he stated, that by placing upon each 
 
 other alternate layers of muscular fibre and of 
 
 brain, separated by a porous body, soaked in salt 
 
 water, a pile was formed which produced the 
 
HISTORY OF GALVANISM. 53 
 
 usual effects of the galvanic apparatus.* The 
 experiment must be of difficult execution, and I 
 believe no one has since attempted to repeat it. 
 Should it be confirmed, it might throw some light 
 upon the experiments of Aldini, and assist in 
 the explanation of those facts where animal elec- 
 tricity seemed to be developed, without the in- 
 tervention of metallic bodies. 
 
 About this time galvanic electricity began to be Galvanism 
 
 . , . j- ii employed 
 
 extensively employed in medicine, especially in in 
 those diseases where common electricity had been 
 previously found useful. It might have been ex- 
 pected that much benefit would have been derived 
 from so powerful an agent, and one which is so 
 easy of application to any part of the body. Our 
 expectations of advantage have, however, been 
 generally disappointed. Flattering accounts of 
 success were indeed published, in different nervous 
 disorders, in paralytic affections, in deafness, in 
 some kinds of blindness, in the recovery of per- 
 sons apparently drowned or suffocated, and even 
 in hydrophobia and insanity. But subsequent 
 trials did not support the credit which the remedy 
 acquired in the first instance ; it gradually fell into 
 disuse, and for several years it was very little em- 
 , ployed as a medical agent, until it was again 
 brought into notice by Dr. Philip, of Worcester. 
 From some pathological opinions which he adopted 
 on the nature of spasmodic asthma, he was in- 
 
 * Journ. de Phys. vol. Ivi. p. 235. 
 
54 HISTORY OF GALVANISM. 
 
 duced to make trial of it in this complaint, and 
 from the report of his first experiments, we have 
 reason to hope that it will prove a powerful remedy 
 for this untraetable disorder.* 
 
 Hitter's Ritter published an account of a curious ap- 
 piie. ' pendage to Volta's pile, which he called the se- 
 condary pile, and which has been since named 
 the pile of Ritter. It is a kind of electric ap- 
 paratus, which may be charged by the voltaic 
 pile, or may be made to retain the electricity that 
 is perpetually flying off from this instrument. He 
 perceived that a body, which had formed part of 
 the galvanic circle in the pile of Volt a, when the 
 pile was removed, became itself electrical ; but it 
 exhibited an electricity opposite to that which it 
 had previously possessed. Thus, if two wires ter- 
 minating in water, and connected with the pile, 
 were discharging one oxygen and the other hy- 
 drogen, when they were removed from it, they 
 would still continue to discharge the gases, but 
 the operation would be reversed. These wires, 
 in this state, may be considered as charged, and if 
 a greater number of similar wires be placed be- 
 tween the ends of the pile, they will all become 
 charged. The nature of the experiment will not 
 be affected, if, instead of wires terminating in 
 water, plates of a single metal be substituted, with 
 Described, wet cards interposed. An instrument will thus be 
 formed, which of itself cannot produce any signs 
 
 * Phil. Trans, for 1817. 
 
HISTORY OF GALVANISM. 55 
 
 of electricity, but which may be rendered electri- 
 cal, by being placed in contact with the primary 
 pile. When the two piles are connected, the 
 action of the ends of each are reversed to each 
 other, and as when they are separated, the ends of 
 the secondary pile are again reversed, consequently 
 the ends of both the piles will now act in the same 
 manner. It is necessary for the pile of Ritter to 
 remain for some time in contact with the pile of 
 Volta, in order that it may be sufficiently charged. 
 It is stated that the chemical effect of Hitter's Effects. 
 pile, that is, its effect in decomposing water, does 
 not bear a regular ratio to its physiological effect, 
 that is, its effect in giving shocks. The author ob- 
 serves, with respect to the voltaic pile, that its 
 tension is the greatest, and it produces the strong- 
 est effects on the sensations, immediately after it 
 is constructed, but that its chemical effects are the 
 most powerful after it has been acting for some 
 hours.* 
 
 Shortly after the publication of the account of Farther ex. 
 the secondary pile, Ritter made a number of expe- 
 riments with the pile of Volta, which are original J 
 and curious. He observed that when a communi- 
 cation was formed between the positive end of the 
 voltaic pile and the earth, the whole instrument 
 became negatively electrified, and when the com- 
 munication was made with the negative end, the 
 instrument became positive. These changes do 
 
 * Journ. de Phys. Ivii. 34?5. 
 
56 HISTORY OF GALVANISM. 
 
 not. however, destroy the chemical action of the 
 pile, which goes on in the same manner as be 
 fore the communication was formed. He supposes 
 that the decomposition of water is effected in con 
 sequence of the positive end disengaging oxygen, 
 and the negative end hydrogen, and that the two 
 ends have also a pendency to dispose metals to 
 unite with oxygen and hydrogen respectively. 
 He says, if the positive end be armed with gold 
 leaf, and the negative with charcoal, and these 
 substances be then brought into contact, the gold 
 will be burned ; but if the position of the sub- 
 stances be reversed, the charcoal will be burned. 
 When the extremities of a pile do not communi- 
 cate, it is said that the action exercised between 
 the different plates is very unequal ; the zinc, 
 which is nearest the positive end, is the most oxi- 
 Different dated. It is also asserted, that if a pile be broken 
 different" into separate parts, by a number of wires in- 
 partsofthe gerte( i between every fifth pair of plates, those 
 wires nearest the positive end will be the most 
 oxidated; while, on the contrary, those wires 
 near the negative end will be less oxidated than 
 if they had been simply plunged in water. Hence 
 he infers, that at the negative end an action has 
 taken place, or a state has been induced, the re- 
 verse of oxidation. He goes so far as to say, that 
 different sensations are excited by the two ends of 
 the pile, the one expanding, and the other con- 
 tracting, the muscular fibre ; the positive end 
 
HISTORY OF GALVANISM. 57 
 
 strengthens the pulse* and produces heat, the ne- 
 gative weakens it, and produces cold *. 
 
 So far as I have been able to learn, few, if any, Remarks 
 of the experiments of Hitter have been repeated, e:rperi- 
 either in Enland or in France; a circumstance 
 
 meuts> 
 
 
 which is not a little remarkable, when we con- 
 sider that many of them are quite original, and 
 would lead to important theoretical deductions. 
 His language and manner of writing are, how- 
 ever, unfortunately obscure ; and he abounds so 
 much in hypothesis, that he has not obtained that 
 degree of attention to which he would seem to be 
 entitled, from his industry and ingenuity. It is 
 scarcely to be supposed that he could have been 
 mistaken respecting the effect of the secondary 
 pile, or that he would have invented a series of 
 facts, the fallacy of which might be so easily de- 
 tected. With respect to the experiments on the 
 voltaic pile, their authority is more doubtful; 
 they seem to have been performed with a manifest 
 view to a particular hypothesis ; some of them are 
 of an indeterminate nature, and we may imagine 
 that many are exaggerated, or even inaccurately 
 stated. 
 
 The attention of the different experimentalists Biot's 
 
 . .,, , . -. .,, ,, . nions re- 
 
 Was still very much occupied with the comparative spec-ting 
 merits of the two hypotheses, the electrical and ^ "^al- 
 chemical ; generally speaking, the English seemed * a o n n ic ac * 
 to* incline to the latter, and the continental writers 
 
 * Journ de Phys. Ivii. 401. 
 
58 HISTORY OF GALVANISM. 
 
 to the former. Biot drew up a candid and ju- 
 dicious memoir, in which he compares the merits of 
 the two opinions, and endeavours to show how far 
 either of them is supported by acknowledged facts. 
 Electricity, he observes, is certainly excited, but it 
 is not certain whether we ought to regard it as 
 cause or effect. He proceeds to inquire whether 
 the action of the pile depends upon the oxidation 
 of one of the metals, upon their electric operation, 
 or upon the two causes in conjunction. The first 
 supposition, he says, is certainly not true, because 
 Volta has proved that metals produce electricity by 
 mere contact, without any oxidation taking place, 
 and his experiments likewise tend to show that 
 the fluid merely performs the part of a conductor, 
 because the electrometer is equally affected whe- 
 ther water or acid be employed; but M. Biot doubts 
 the accuracy of this experiment. It is admitted 
 that the increase of electricity is in proportion to 
 the oxidation of one of the metals ; but this cir- 
 cumstance does not prove that these actions stand 
 to each other in the relation of cause and effect, 
 it only shows that electricity renders bodies more 
 oxidable. He performed a set of comparative ex- 
 periments on the effect of different fluids being 
 interposed between the metals, and by employing 
 the electrical balance as a measure of the quantity 
 of electricity that was liberated, he finds that it 
 is much influenced by the nature of the fluid. The 
 following is supposed to be the order in which the 
 fluids have the power of exciting the action of 
 
HISTORY OF GALVANISM. 
 
 the pile, beginning with those which are the least 
 powerful : water, muriate of soda, muriate of am- 
 monia, hyperoxymuriate of potash, sulphate of 
 alumine, and sulphate of iron. It is remarked, 
 that if the fluids differed in their action merely 
 in consequence of a difference in their conducting 
 power, the same effects should be produced by suf- 
 fering them to remain for a sufficient length of 
 time in contact, but on account of the changes 
 which take place in the state of the pile in other 
 respects it is difficult to ascertain this point. Sub- 
 stances generally have their electrical condition 
 altered when they undergo any change in their 
 state, and therefore the chemical action of the pile 
 will probably develop electricity, as well as the 
 action of the metals upon each other; but the 
 author is disposed to conclude that the effect of 
 the chemical change in the fluids is considerably 
 less than the electrical effect excited by the contact 
 of the metals.* 
 
 In the year 1804, a very valuable memoir 
 was written by Hisinger and Berzelius, which MUS 
 must be regarded as containing the germ of those 
 doctrines, which have since been so extensively 
 developed by Sir Humphry Davy. By passing 
 the galvanic influence through solutions of the 
 different neutral salts, they found that there was 
 a transfer of the acid and alkali to different parts 
 of the apparatus. They formed the general con- 
 
 * Ann. de Chim. xlvii. 1. 
 
60 HISTORY OF GALVANISM. 
 
 elusion, that whenever electricity is sent across a 
 fluid, it disposes its constituents to separate and 
 pass to the two sides respectively ; combustible 
 substances, alkalies, and earths, are attracted to 
 the negative ; acids, oxides, &c. to the positive 
 extremity of the pile. The force of the decom- 
 position they suppose is in the ratio of the 
 quantity of electricity, and that the electricity 
 is in proportion to the surface of metal which 
 is in contact with a moist conductor. The de- 
 composition is also influenced by the affinity 
 of the components of the substance, its power 
 of conducting electricity, and other circum- 
 stances.* 
 
 Supposed Mr. Cruickshanks, among his earliest disco- 
 ofmt!ria ( tTc veries, had observed, that an acid and an alkali 
 5 ' were generated at the two ends of the wires in 
 the interrupted circuit, and this fact had been 
 confirmed by Pfaff,f Brugnatelli,| and other expe- 
 rimentalists. The substances produced were sup- 
 posed to be nitric acid and ammonia; the first 
 originating from the union of oxygen with the 
 azote of air dissolved in the water, the latter from 
 hydrogen combining with the same element. De- 
 sormes also had obtained an acid and an alkali 
 during the decomposition of water; but he thought 
 the acid was the muriatic; and the same result 
 
 * Ann. de Chim. li. 167. 
 
 f Nicholson's Journ. xvii. 362. 
 
 J Journ. de Phys. Ixii. 298 ; Ixjv. 78. 
 
HISTORY OF GALVANISM. 61 
 
 was obtained by Simon.* In these experiments 
 we may conceive that there was a minute portion 
 of common salt contained in the water upon which 
 they operated. It was now, however, announced 
 that muriatic acid and soda were generated by 
 passing the electric current through pure water, 
 where the muriate of soda could not be sus- 
 pected to be present in any part of the apparatus, or 
 in any of the materials employed. In the spring of 
 1805, the following letter was published, purport- 
 ing to be written by Mr. Peel of Cambridge : " I Peel's ex- 
 took about a pint of distilled water, and decom- p 
 posed about one half of it by means of galva- 
 nism ; the other half I evaporated, and found to 
 remain at the bottom of the glass a small quantity 
 of salt, which, upon examination, proved to be 
 muriate of soda. The salt could not have been 
 contained in the water before I made the experi- 
 ment, because I used every precaution to have it 
 free from impurities. I even took the trouble to 
 repeat the same experiment, though a tedious one, 
 and I again obtained the same, result. A friend 
 of mine has just informed me that he has tried 
 my experiment, and has succeeded in procuring 
 the salt."* 
 
 Almost at the same time that this notice was Pacchioni'i 
 published in London, Pacchioni, professor at Pisa, ments. 
 gave an account of some experiments upon the 
 
 * Ann. de Chim. xxxvii. 284; xli. 109. 
 f Tilloch's Phil. Mag. x. 221, 279. 
 
62 HISTORY OF GALVANISM. 
 
 action of galvanism on water, in which he ob- 
 tained results analogous to those stated above. 
 He informs us that when water had been for a 
 long time subjected to the galvanic influence, and 
 had been parting with its oxygen from the ex- 
 tremity of a gold wire, the fluid was found to con- 
 tain a quantity of oxymuriatic acid. From this 
 experiment he drew the following conclusions : 
 oxymuriatic acid is an oxide of hydrogen ; it con- 
 sists of water deprived of part of its oxygen ; mu- 
 riatic acid is water in a still lower degree of oxida- 
 tion; and, of course, hydrogen is susceptible of 
 different degrees of oxidation.* 
 
 Not con. A great degree of attention was excited by 
 e * these experiments, to which the more credit was 
 attached, because they proceeded from sources 
 entirely independent of each other. They were 
 repeated by different experimentalists in this coun- 
 try, and, in some cases, with apparent success. 
 Mr. Sylvester, in particular, obtained traces both 
 of muriatic acid and soda, where proper precautions 
 were supposed to have been taken, to exclude the 
 muriate of soda from every part of the appara- 
 tus. But from facts which have been subse- 
 quently discovered we may conclude, that the sub- 
 stances obtained in these cases were not derived 
 from the decomposition of the water. Pacchioni's 
 experiments are now universally admitted to have 
 been incorrect ; and it appears that no such indi- 
 
 * Edin. Med. Journ. i. 393. 
 
HISTORY OF GALVANISM. 63 
 
 vidual as Mr. Peel could be found in Cam- 
 bridge, so that the letter bearing his name is a 
 complete fabrication. It was not, however, en- 
 tirely without its use : for the minute examination 
 of the effects of galvanic electricity upon water to 
 which it gave rise, may probably be regarded, in 
 some measure, as the immediate cause of Sir H. 
 Davy's most brilliant discoveries. 
 
 An elaborate memoir was written by Erman of 
 Berlin, on the conducting power of different 
 
 bodies, which obtained the prize from the French 
 Institute. His object was to remove some anoma- 
 lies, which appeared to exist in the relation of the 
 galvanic electricity to the different conducting 
 substances. 
 
 He divides all bodies into five classes : 1st, Per- 
 fect non-conductors; 2d, Perfect conductors ; 3d, 
 
 Imperfect conductors; 4th, Positive conductors; 
 and 5th, Negative conductors. The nature of the 
 three first classes requires no explanation; the 
 fourth and fifth class of bodies act as perfect 
 conductors, when applied to either of the two 
 poles separately, but when placed between them, 
 insulate either the positive or negative pole 
 respectively, and do not form a communication 
 between them. The flame of a spirit lamp is Flame a 
 described as a positive conductor ; if it be ap- conductor. 
 plied to each pole separately it conducts the 
 electricity ; but if it be placed between the two 
 poles, it will not form a communication be- 
 tween them, in consequence of its insulating 
 
64 HISTORY OF GALVANISM. 
 
 the negative electricity. Although flame is a 
 conductor of galvanism, it does not conduct it so 
 perfectly as metals. No effect is produced when 
 flame is interposed between the extremities of 
 the pile. Flame is, however, a very different sub- 
 stance according to the body from which it is pro- 
 cured : the above observation refers to the flame 
 of a hydro-carbon on s body. The flame of sul- 
 phur insulates both the poles ; and that of phos- 
 phorus insulates the positive, and conducts the 
 negative influence. Phosphorus must therefore 
 be placed in the fifth class of bodies ; and perfectly 
 dry soap is also a negative conductor. 
 Soapane- The author gives an account of a number of 
 experiments that he performed on this latter sub- 
 stance, many of which are curious and original. 
 Hard soap, when perfectly dry, if applied to either 
 end of the galvanic pile, conducts all the electri- 
 city from that extremity into the ground, and 
 there appears to be no perceptible difference in its 
 action upon the two extremities. If wires be 
 connected with each end, and be made to ter- 
 minate in a prism of hard dry soap, which is 
 kept insulated, the circuit will not be completed ; 
 but if this soap be uninsulated, by establishing a 
 communication with the ground, an electrometer 
 connected with the positive pole manifests a great 
 degree of divergence, while one on the negative 
 pole loses all signs of it. " Consequently," M. 
 Erman observes, " the soap which insulates the 
 positive effect, is a perfect conductor for the ne- 
 
HISTORY OF GALVANISM. 65 
 
 gative." As a proof and illustration of this pro- 
 perty, the author informs us, that " if one finger 
 be applied to the wire of the positive pole, and 
 another finger wetted to the soap, no shock is felt, 
 and the electrometers do not show the least change 
 in their respective divergencies. But if the experi- 
 ment be repeated, by establishing a communication 
 between the positive pole and the soap, with both 
 fingers wetted, a very perceptible shock will be 
 felt, and the two electrometers will arrive at an 
 equal, and a very weak degree of intensity." He 
 proposes the following nomenclature for thes"e Erman's 
 five classes of bodies : 1st, Insulators ; 2d, Per- 
 feet conductors ; 3d, Bipolar imperfect conductors ; 
 4th, Positive unipolar ; and 5th, Negative unipolar 
 bodies.* Although, as we shall afterwards find, 
 Mr. Brande explains the facts upon rather a 
 different principle, yet they are highly impor- 
 tant, and Erman is entitled to much commendation 
 for the skill with which he conducted his ex- 
 periments. 
 
 Morveau suggested an idea, which appears suffi- Morveau's 
 ciently plausible, that the action of galvanism 
 may affect the formation of metallic oxides, and 
 even cause them to assume the particular forms 
 which they occasionally exhibit.f Bucholtz de- 
 tailed a series of experiments which he performed, uigmetai- 
 where a metallic oxide, held in solution by an llc oxides * 
 
 acid, was precipitated in the metallic state by the 
 
 
 
 * Journ, de Phys. Ixiv. 121. f Ann. de Chim. Ixiii. 113. 
 
 F 
 
66 HISTORY OF GALVANISM. 
 
 metal itself. The metallic solution was placed in 
 the bottom of a cylindrical jar, and a stratum of 
 water was carefully spread over it. A slip of the 
 same kind of metal that formed the solution was 
 then placed perpendicularly in both the fluids. 
 The upper part of the metal which was in the 
 water was oxidated, while the lower part in the 
 metallic solution had particles of the reduced metal 
 deposited upon it. The reduction of the oxide 
 was always expedited by whatever promoted the 
 Grotthas's oxidation of the upper part of the metal.* Ex- 
 ments'on periments of an analogous nature were performed 
 Son "**" ky Grotthus, on what he calls the arborization of 
 metals, which, like the circle of actions described 
 by Bucholtz, he attributes to a galvanic operation. 
 In these processes, however, there are two metals 
 concerned ; and he shows that the tree is formed 
 by successive portions of the dissolved oxide being 
 reduced and attached to the solid metal, which, in 
 its turn, becomes oxidated.f I have a little anti- 
 cipated the chronological order in the relation of 
 these last two sets of experiments, in order that 
 the account of the decomposition of the alkalies 
 and earths, which composes the third period of the 
 history of galvanism, might not be interrupted. 
 
 * Ann. de Chim. Ixvi. 266. f Ibid. Ixiii. 5. 
 
HISTORY OF GALVANISM. 67 
 
 SECTION III. 
 
 Decomposition of the Alkalies and Earths. 
 
 
 ABOUT the conclusion of the year 1806, Sir Davy's 
 H. Davy read to the Royal Society of London the 
 
 first of his series of papers on what has been styled 
 the electro-chemical action of bodies, which have 
 been so justly celebrated, no less for the brilliant 
 discoveries of which they give an account, than for 
 the acuteness and sagacity which the author dis- 
 plays in his researches into the most hidden ope- 
 rations of nature. He commences by some Action of 
 remarks on the action of galvanic electricity ffectridty 
 upon water. He notices the experiments in " e p r n 
 which acids and alkalies appear to have been 
 formed in water subjected to the galvanic current ; 
 and he states, that when he employed separate por- 
 tions of water, connected together by slips of 
 bladder, and united by gold wires to the voltaic 
 battery, he obtained nitro-muriatic acid at the 
 positive, and soda at the negative wire. It was, 
 however, conjectured, that the animal matter 
 placed between the two portions of water might 
 contain muriate of soda, and thus afford the sub- 
 stances procured in the experiment ; he therefore, 
 at the suggestion of Dr. Wollaston, substituted 
 asbestos for the slips of bladder. It was also con- 
 
68 HISTORY OF GALVANISM. 
 
 PLATE i. ceived, that when glass vessels were used, the 
 alkali might proceed from a partial decomposition 
 of the glass ; and after trying various other sub- 
 stances, at length conical vessels of gold were 
 employed. With these precautions, and when the 
 water was very carefully prepared, neither acid nor 
 
 Neither alkali were obtained ; and consequently the author 
 
 acid nor . . __ , " . 
 
 alkali concludes that in all those experiments, which 
 generated. were a | ten( j e( j w ^ contrary results, the acid 
 
 and alkali must have proceeded from some ex- 
 traneous source, not having been generated, 
 but evolved, either from something held in solu- 
 tion by the water, or from some of the materials 
 employed in the apparatus. Perfectly pure water, 
 when subjected to the action of electricity, af- 
 fords nothing except oxygen and hydrogen. 
 Decompo- The very powerful action of the galvanic elec- 
 cafthVand tricity, in the decomposition of various earthy and 
 "aits'* 1 saline compounds, as experienced by Sir H. Davy 
 in the researches above-mentioned, offered an ex- 
 tensive field for farther investigation. Hisinger 
 and Berzelius, in the valuable memoir to which 
 I have already referred, noticed the tendency 
 which different bodies possess, to attach them- 
 selves to one of the wires exclusively ; acids and 
 analogous bodies being attracted to the positive, 
 while alkalies, metals, and all inflammables, were 
 attracted to the negative wire. Our author had 
 observed similar phenomena in his own experi- 
 ments, and was induced to make them the more 
 immediate subject of his examination. Acids and 
 
HISTORY OF GALVANISM. 69 
 
 alkalies were found uniformly to observe this 
 order ; and it was perceived, that when sub- 
 stances, not supposed to be soluble in water, 
 formed part of the circuit, they were also de- 
 composed, and their components carried to the 
 positive and negative wires respectively. In this 
 way was effected the decomposition of sulphate of 
 lime, sulphate of strontites, fluate of lime, and 
 sulphate of barytes. It was also perceived, that 
 where small portions of acid and alkaline bodies 
 entered into the composition of solid earths, they 
 might be detected by the galvanic influence, and 
 would be transmitted to their respective wires. 
 In this way, lime and soda were obtained from 
 basalt and from zeolite, potash from lepidolite, &c. 
 In proportion to the solubility of a salt, its de- 
 composition was the more readily accomplished; 
 and when neutral salts were employed, the sepa- 
 ration of the component parts seems to have been 
 quite complete. 
 
 The tendency which different substances pos- Transfer of 
 sess to attach themselves to their appropriate wires, {Jentsof *~ 
 causes them to be transferred across a medium com P unds - 
 which may be interposed. Thus, if muriate of PLATE u. 
 lime be at the positive wire, the lime will pass, '5' 
 for a considerable space, to gain the negative 
 wire, and may be conveyed from one vessel to 
 another along the conducting fibres of the as- 
 bestos. In the same manner, when nitrate of 
 silver was on the positive side, and distilled water 
 on the negative, the silver passed along the trans- 
 
70 HISTORY OF GALVANISM. 
 
 mitting amianthus, so as to cover it with a thin 
 metallic film. When a neutral salt was placed 
 in a vessel between two other vessels of water 
 connected by asbestos, the alkali passed to the ne- 
 gative, and the acid to the positive side : the de- 
 compostion in this case is complete, and the sub- 
 stances produced quite pure. A small vessel of 
 the infusion of litmus was interposed between 
 pure water and the solution of sulphate of potash, 
 and the latter was negatively electrified. The 
 acid passed across to the positive wire, and red- 
 dened the litmus, but the change of colour did 
 not extend beyond the centre ; so that the negative 
 side, although it was transmitting the acid, was 
 not affected by it. An experiment of precisely 
 an opposite kind was performed with the infusion 
 of turmeric, with a similar result ; and afterwards 
 the two operations were combined in the same 
 experiment, so that soda passed through tur- 
 meric, and muriatic acid through litmus, each 
 without changing their colour. 
 Passage of As it appeared that acids and alkalies could 
 
 acids and * * 
 
 alkalies be conveyed through water, without affecting co- 
 louring substances dissolved in it, Sir H. Davy 
 
 next tried whether this power might not extend 
 to other bodies. He accordingly found, that 
 acids could be transmitted through alkalies, and 
 alkalies through acids, to their respective wires, 
 without neutralizing each other; and, in short, 
 that the electrical state which was induced upon 
 a substance, by the contact of the galvanic appa- 
 
HISTORY OF GALVANISM. 71 
 
 ratus, had the power of counteracting, or even 
 changing, the effects of chemical affinity. The General 
 general principle was thus completely established, pn ' 
 that hydrogen, alkalies, and metals, are attracted 
 by the negative, and repelled by the positive end 
 of the pile ; while acids and oxygen are attracted 
 by the positive, and repelled by the negative end. 
 For the production of this effect, it is necessary 
 that there be a conducting chain of particles 
 through the transmitting fluids ; the transfer can- 
 not take place where insoluble compounds are 
 formed, because in this case the new compound is 
 carried out of the sphere of action. 
 
 The establishment of the general principle Effect of 
 mentioned above, suggested some views of the 
 nature of the change produced by electricity, 
 which led to a new train of experiments. Sir 
 H. Davy observes, that many bodies, after being 
 brought into contact, exhibit opposite states when 
 they are separated. When a galvanic combina- 
 tion is formed from an acid, an alkali, and a 
 metal, the alkali appears to acquire, and the acid 
 to part with, a quantity of electricity ; the alkali 
 is therefore rendered positive, and the acid nega- 
 tive, and they will of course have an attraction for 
 each other. He found that when such acids as 
 were capable of being employed in the dry state 
 were touched by metals, and then separated, the 
 acids were rendered negative, and the metals 
 positive; but when the metals were touched by 
 the alkaline earths, the metals became negative. 
 
72 HISTORY OF GALVANISM. 
 
 Hence it may be concluded that acids and alkalies 
 not only exhibit opposite electricities, when they 
 have been in contact with metals, but also when 
 they have been in contact with each other. The 
 attraction of oxygen and acid for the positive, 
 and of hydrogen and alkalies for the negative 
 electricity, is so powerful, as to counteract their 
 usual chemical affinities. 
 
 Relation These considerations induced the author to 
 i enter into some farther speculations respecting the 
 
 city and af- relation between the electricity of bodies and their 
 
 fiuity of 
 
 bodies. chemical affinities. We have seen that chemical 
 affinity is destroyed by giving a body an electri- 
 city different from its natural one, and is, on the 
 contrary, increased by giving it a greater share of 
 its natural electricity. It would farther appear, 
 that all those bodies which possess a chemical 
 affinity for each other are naturally in opposite 
 states of electricity ; and hence we conclude, that 
 by inducing a state of electricity upon any body, 
 contrary to its natural one, its chemical relations 
 may be changed, and that thus we have in our 
 possession an agent of indefinite power for affect- 
 ing the decomposition of substances which had 
 hitherto withstood all our attempts. 
 
 Action of With respect to the action of the voltaic pile, 
 thevoitaic g ir ft Dav y conce i veSj that the fi rst step m t h e 
 
 process is the destruction of the electrical equili- 
 brium, and that the chemical changes tend to 
 restore it to its original state. The saline solution, 
 which is interposed between each pair of plates, is 
 
HISTORY OF GALVANISM. 73 
 
 decomposed, the acid is transferred to the zinc, 
 and the alkali to the copper surface. This tends to 
 restore the equilibrium which is destroyed by the 
 contact of the metallic elements of the pile ; but 
 the solution of the zinc, which then takes place, 
 again alters the electrical condition of the bodies, 
 and maintains the energy of the apparatus. Upon Primary 
 the whole, although it may be supposed that the 6 
 
 chemical changes are an essential part of the pro- 
 cess, they are considered by the author as only of 
 secondary importance; the first step in the pro- 
 cess, and that which immediately gives rise to all 
 the rest, being an electrical effect arising from 
 the action of bodies placed in contact.* 
 
 The uncommon merit of this paper will be a importance 
 sufficient reason for this copious abstract of its pe r thls pa ~ 
 contents. It may be regarded, not only as giving 
 rise to some of the most important experiments 
 and discoveries that have occurred in the history 
 of modern science ; but as leading to the establish- 
 ment of a new train of reasoning, and to a new 
 theory, respecting the action of bodies upon each 
 other, and the connexion which subsists between 
 the different branches of natural philosophy. The 
 general principle being clearly established, the con- 
 sequences were comparatively obvious, and the skill 
 and ingenuity which Sir H. Davy afterwards 
 manifested in the contrivance and execution of 
 the experiments, which are next to be related, 
 
 * Phil. Trans, for 1807, p. I. 
 
74 HISTORY OF GALVANISM. 
 
 although attended by such brilliant results, are 
 really less meritorious than that profound insight 
 into the operations of nature by which they were 
 suggested. Highly, however, as we must appre- 
 ciate the merit of Sir H. Davy, it is proper to 
 remark, that the views suggested by Hisinger 
 and Berzelius must be regarded as leading to the 
 theory that was so amply detailed and so firmly 
 established by our illustrious countryman. 
 Decompo- About a year after the reading of the above 
 paper, Sir H. Davy presented a second to the 
 
 Royal Society, in which he most happily applied 
 his hypothesis to practice, and succeeded in solving 
 the problem, which had so long remained involved 
 in obscurity, respecting the composition of the 
 fixed alkalies. After encountering some difficulties 
 in the arrangements of the operation, the grand 
 object was at length accomplished in the following 
 Relation of manner, "A small piece of pure potash, which 
 menf.* pen had been exposed for a few seconds to the atmo- 
 sphere, so as to give conducting power to the sur- 
 face, was placed upon an insulated disk of pla- 
 tina, connected with the negative side of the 
 battery, of the power of 250 of 6 and 4, in 
 a state of intense activity ; and a platina wire, 
 communicating with the positive side, was brought 
 into contact with the upper surface of the alkali. 
 The whole apparatus was in the open atmosphere. 
 Under these circumstances, a vivid action was soon 
 observed to take place. The potash began to fuse 
 at both its points of electrization. There was a 
 
HISTORY OF GALVANISM. 75 
 
 violent effervescence at the upper surface ; at the 
 lower, or negative surface, there was no liberation 
 of elastic fluid ; but small globules, having a high 
 metallic lustre, and being precisely similar in visi- 
 ble characters to quicksilver, appeared, some of 
 which burst with explosion and bright flame, as 
 soon as they were formed, and others remained, 
 and were merely tarnished, and finally covered by 
 a white film, which formed on their surfaces." 
 
 These globules proved to be the substance of Base of 
 which the author was in search, and were found L'da! 
 to be a peculiar inflammable body, possessed of 
 very singular properties, which constituted the base 
 of potash. By employing a similar kind of pro- 
 cess, a substance was procured from soda, which 
 exhibited properties of an analogous nature, and 
 which was the basis of the mineral, as the former 
 was that of the vegetable alkali. 
 
 The author then proceeded to examine the Proved to 
 properties of these bodies, and by a masterly train b< 
 of experiments, simple yet conclusive, he demon- 
 strated that they are metals ; that they have every 
 quality which is deemed essential to characterize 
 this class of substances, and that the alkalies are 
 oxides of these metals. The theory of the decom- Theory of 
 position of the alkalies, by means of the galvanic the process * 
 apparatus, is sufficiently obvious, and follows as the 
 direct consequence of the facts that had been 
 previously established. In all the decompositions 
 that had been effected by the electrical influence, 
 combustible substances were developed at the 
 
76 HISTORY OF GALVANISM. 
 
 negative wire, while oxygen was produced or 
 evolved by the positive termination. That this 
 was the case with the alkalies, was not only 
 rendered probable by the result of the process, 
 but was afterwards proved by subsequent experi- 
 ments. " When solid potash or soda, in its con- 
 ducting state, was included in glass tubes, fur- 
 nished with electrified platina wires, the new 
 substances were generated at the negative sur- 
 faces ; the gas given out at the other surface, 
 proved by the most delicate examination, to be pure 
 oxygen ; and unless an excess of water was pre- 
 sent, no gas was evolved from the negative 
 surface." 
 Recompo- The experiments by synthesis confirmed the 
 
 sition of . 
 
 theaika- results of those by analysis. The new metallic 
 bodies were converted into potash, by exposure to 
 the air, and it was found that this depended upon 
 the oxygenous part of it. When the globules 
 were placed in contact with oxygen, they com- 
 bined with it, and were covered with an alkaline 
 crust. Sir H. Davy observes very justly, " that 
 in these facts there is the same evidence for the 
 decomposition of potash and soda into oxygen and 
 two peculiar substances, as there is for the decom- 
 position of sulphuric and phosphoric acids and the 
 metallic oxides into oxygen and their respective 
 combustible bases." The two components of the 
 alkalies obey the general law which was laid down 
 in the former paper ; the metallic or combustible 
 base is attracted by the negative extremity of the 
 6 
 
HISTORY OF GALVANISM. 77 
 
 apparatus, and perhaps repelled by the positive ; 
 while the oxygen, which reduces it to the state 
 of an oxide, follows the contrary order. In the 
 recomposition of the alkalies, the substances exert 
 their natural affinities ; according to circumstances, 
 either simple oxidation is produced, or a more 
 rapid combination, attended with the extrication 
 of heat and light. 
 
 Sir H. Davy next proceeded, in an elaborate Properties 
 train of experiments, to ascertain the physical metals, 
 properties of these metals, to which he gave 
 the names of potassium and sodium, and their 
 chemical relations to other bodies. He examined 
 their fusibility, the power which they possess of 
 conducting electricity and caloric, and their speci- 
 fic gravity. He afterwards observed their action 
 on water, the acids, sulphur, phosphorus, the 
 metals, oils, and metallic oxides. It is scarcely 
 necessary to remark, that the examination was 
 conducted with the address and dexterity which 
 characterizes all the operations of this distin- 
 guished experimentalist. A minute detail of the 
 particulars would be foreign to the object of 
 this work, and strictly belongs to the science of 
 chemistry ; galvanism being no farther connected 
 with these bodies, than as the instrument by which 
 they are produced. On this account it will not fall 
 under my province to notice the discussions which 
 ensued respecting the nature of these new metals ; 
 for although it was generally admitted that the 
 substances were the bases of the fixed alkalies, 
 
78 HISTORY OF GALVANISM. 
 
 and were metallic, yet there were some circum- 
 stances in the mode of their formation, which led 
 to the supposition that they were a compound of a 
 metal and hydrogen; but this opinion is now 
 abandoned. 
 Attempts The analogy which exists between the proper- 
 
 to decom- 
 
 pose am- ties of the fixed and the volatile alkalies, led Sir 
 H. Davy to apply his powerful means of decompo- 
 sition to ammonia. The analogy of properties, 
 however, which causes them to be placed in the 
 same class of bodies, seemed to be counteracted by 
 the experiments of Berthollet, who, as is well 
 known, had resolved this latter substance entirely 
 into hydrogen and azote. Accordingly the me- 
 tallic nature of ammonia has not yet been proved ; 
 and although Sir H. Davy, in his earlier experi- 
 ments, conceived that he had procured oxygen 
 from it, and Berzelius obtained a species of amal- 
 gam, by exposing it in contact with mercury to the 
 galvanic influence, yet subsequent experiments by 
 Dr. Henry, and MM. Gay-Lussac and Thenard, 
 appear to explain these appearances on other 
 principles, and to restore the original conclusion, 
 that ammonia is a compound of azote and 
 hydrogen alone.* 
 
 Decompo- Sir H. Davy next turned his attention to the 
 ?he earihs. earths. He found them more difficult to decom- 
 pose than the alkalies, and many arrangements 
 were employed without success. The object was, 
 
 * Phil. Trans, for 1808, p. 1. 
 
HISTORY OF GALVANISM. 79 
 
 however, at length, to a certain degree, accom 
 plished by mixing the earth with a metallic oxide, 
 and placing this in contact with a globule of mer- 
 cury negatively electrified, when an amalgam was 
 formed, consisting of the mercury and the metal 
 of the earth employed. In this way it appeared, 
 that a metallic basis had certainly been obtained 
 from the four alkaline earths, to which the names 
 of barium, calcium, strontium, and magnium, 
 were respectively applied. The remaining earths, 
 silex, alumine, zircon, and glucine, were still 
 more refractory, probably in consequence of their 
 more powerful affinity for oxygen. No decom- 
 position could be effected by the same means - 
 which had been found successful with the alka- 
 line earths ; but it was at length partially accom- 
 plished, by keeping the earth in fusion with pot- 
 ash, inducing upon it positive electricity, and 
 touching it with a negative wire. In this case 
 an amalgam was produced, which probably con- 
 sisted of the metal of the earth employed and pot- 
 assium.* 
 
 The brilliant discoveries of Sir H. Davy, and Confimm- 
 still more the new and powerful agent which he Davy's ex- 
 had introduced into chemistry, could not fail to pen 
 engage the attention of all those who were inte- 
 rested in the progress of the science. Among 
 these, Gay-Lussac and Thenard in France, and 
 Berzelius in Sweden, immediately commenced 
 
 * Phil. Trans, for 1808, p. 333. 
 
80 HISTORY OF GALVANISM. 
 
 their operations in the application of galvanic elec- 
 tricity to the decomposition of bodies, made many 
 important experiments, and brought to light many 
 new facts. The general result was, to afford an 
 ample confirmation of the statements of our illus- 
 trious countryman in their most important parts, 
 although in some particulars they regarded the 
 subject in a different point of view, both as to the 
 mode of accounting for the effects, and the con- 
 sequences which they deduced from them. These 
 discussions, as well as the many new and inte- 
 resting experiments connected with them, which 
 have completely changed the aspect of many 
 branches of chemistry, and have enlarged our 
 knowledge of the nature of bodies far beyond its 
 former limits, it does not belong to my present 
 subject to detail. It will be proper, however, to 
 notice some of the observations that were made 
 by Gay-Lussac and Thenard, on what strictly 
 belongs to galvanism, reserving the consideration 
 of the hypothetical opinions to the second division 
 of the essay. 
 
 Gay-Lm- These sagacious experimentalists point out a 
 distinction, which had not been sufficiently at- 
 
 Bended to, between the electrical and the chemical 
 Difference energy of the pile; actions which are essentially 
 the"iecfri- dissimilar, and which do not exist in the same 
 chemical ratio - Tne 7 state > tnat a comparatively few 
 action. plates, with acid interposed between them, will 
 decompose the alkalies ; while a greater number, 
 with water instead of acid, will not produce this 
 
HISTORY OF GALVANISM. 81 
 
 effect, and will yet exhibit a higher electrical 
 tension. The power of the apparatus was found 
 to be nearly in proportion to the strength of the 
 acid employed ; and some comparative experiments 
 were instituted, for the purpose of comparing the 
 effects of acids, alkalies, and neutral salts. The 
 test which they employed to judge of the quantity 
 of effect produced by the pile, was the amount of 
 gas evolved from a fluid, subjected to the action 
 of the wires connected with its two extremities : 
 this they conceived was a more exact measure 
 of its energy than the different lengths of wire 
 which it was capable of consuming. The general 
 conclusion which they formed respecting the action 
 of the pile was, that its chemical energy depends 
 upon its tension, upon the conducting power of 
 the fluids with which it is charged, and upon the 
 facility of their decomposition. 
 
 When they employed a very powerful battery, shock pro- 
 it was observed that considerable shocks were ^rge bat-* 
 given by it to an individual ; but that in a chain of tery ' 
 four or five persons, it was not felt in the centre ; 
 and in the extremities of the chain, that part of 
 the body received the greatest impression which 
 was nearest to the apparatus. This fact is sup- 
 posed to prove, that the electric fluid Cannot cir- 
 culate through the whole circuit, according to the 
 Franklinean hypothesis. When the battery is put 
 into strong action, its chemical effect, i. e. its 
 power of decomposing water, soon declines, or al- 
 
82 HISTORY OF GALVANISM. 
 
 together ceases, while its electrical tension remains 
 for some time longer unimpaired. 
 
 An interesting train of experiments is next 
 detailed, in which mercury was interposed between 
 the wires, and formed an amalgam with the sub- 
 stance which was intended to be decomposed : an 
 arrangement which we have already pointed out, 
 as having been employed by Sir H. Davy in his 
 decomposition of the proper earths. They repeated 
 the experiments of this philosopher on ammonia, 
 and they formed the amalgam with mercury, 
 which he conceived was composed of this sub- 
 stance with the metallic basis of ammonia; but 
 they differ from him in their idea of its constitu- 
 tion, and suppose that there is no evidence of the 
 existence of the metal of the volatile alkali, al- 
 though the analogy of the fixed alkalies offers so 
 powerful an argument in its favour. But it does 
 not belong to my present subject to give any far- 
 ther account of the chemical effects produced by 
 the apparatus. 
 
 DC LUC'S While Sir H. Davy was pursuing, with so much 
 the pHe, success, his interesting researches into the electro- 
 l09 * chemical action of bodies upon each other, De Luc 
 undertook to investigate the nature of the galvanic 
 pile, and to examine the mode of its operation. 
 After some animadversions upon the hypothesis of 
 the inherent electric energies of bodies, which con- 
 stitute the origin of the train of phenomena that 
 are connected with the pile, he proceeds to dissect 
 
 6 
 
HISTORY OF GALVANISM. 83 
 
 this instrument into three parts. He divides it Dissection 
 into three separate groups, corresponding to what 
 he regards as the three elements of the pile. These 
 elements are the two metals and a fluid. They 
 were first placed with the fluid between the two 
 metals ; then with the fluid in contact with one, PLATE n. 
 and afterwards in contact with the other metal, the 3^4'. ' ' 
 different groups being kept distinct from each other 
 by small wire stands, so as to confine the action to 
 that part alone. When the piles were fitted up in 
 these three different ways, a delicate electrometer 
 was attached to each extremity, and they were also PLATE n. 
 connected by the interrupted wire passing through Fl ' 12 * 
 water. His first set of experiments were made 
 upon the pile in which the groups were arranged First dis- 
 with the fluid between the two metals. By means JJe'jJne?* 
 of the electrometer, he observed which ends of the 
 apparatus were in the positive and negative states 
 respectively ; and he likewise made some new ob- 
 servations on the direction which the electric cur- 
 rent takes in its passage across the water in the 
 interrupted circuit and in the body of the pile 
 itself. His observations agreed with those origin- Observa- 
 ally made by Nicholson, that the extremity of the direction e 
 pile, which is connected with the wire emitting ent he an!T 
 oxygen, is positive, and that the current is directed . n . the P" 
 from this to the wire which emits the hydrogen, negative 
 He informs us, however, that although electrome- 
 ters placed at the extremities, when they are af- 
 fected, indicate the electricity to be in the state , 
 mentioned abov ; yet they are not always both of 
 
84 HISTORY OF GALVANISM. 
 
 them affected, sometimes only the positive electri- 
 city is visible, sometimes only the negative, while 
 at other times both of them are perceptible. He 
 conceives that, from various causes, the electric 
 fluid passes through the apparatus with different 
 velocity at different times, or through its different 
 parts at the same time, so as to produce a partial 
 accumulation or deficiency : it seems to be always 
 retarded when it passes from the point of the wire 
 into water. He observes, that the expressions po- 
 sitive and negative, as applied to the ends of the 
 pile, or to the wires in the interrupted circuit, can 
 only be regarded as comparative terms, because 
 the chemical action of the pile goes on as usual in 
 the decomposition of water, although the whole in- 
 strument be rendered positive or negative, by at- 
 taching it to the prime conductor, or to the rubber 
 of the electrical machine. This experiment is ad- 
 duced to prove, that the action of the pile is not 
 necessarily connected with the electric energy of 
 the substances that enter into its composition. 
 The pile, when dissected in the first way, with the 
 fluid interposed between the two metals, acts in 
 the same manner as if the parts were continuous, 
 except that the effect is rather less powerful. 
 Second dis- De Luc then examined the action of the pile, 
 section. w jj en dissected according to the second arrange- 
 ment, where the metals were placed together, and 
 the wet cloth in contact with the zinc, or the most 
 oxidable of the metals ; the ternary groups being 
 separated from each other by the wire frames. 
 
HISTORY OF GALVANISM. 85 
 
 The extremities of the pile indicated to the elec- 
 trometer the same states of positive and negative, 
 as in the former instance, but no shock was expe- 
 rienced; when the wires of the interrupted circuit 
 were placed in water, although it appeared that 
 there was a communication established through the 
 fluid, yet no decomposition took place, nor did there 
 appear to be the retardation of the electric current 
 upon its entering the fluid, as in the former case. 
 Hence the author concludes, that the electrical and 
 chemical effects originate from different causes, be- 
 cause in this state of the instrument the electrical 
 effects continue, although the chemical effects are 
 suspended. The third dissection of the pile was Third dis- 
 now made, i. . it was divided into ternary groups, se 
 consisting of the metals contiguous to each other, 
 and the wet cloths in contact with the silver ; the 
 groups being separated as before, by wire supports. 
 Here there was no effect perceptible, either electri- 
 cal or chemical. 
 
 In the above experiments, the cloths which were Muriate of 
 employed to retain the fluid were moistened with 
 water : a second set of experiments was now per- 
 formed, in which a strong solution of muriate of 
 soda was employed. The pile, whether moistened 
 with water or the saline solution, had the same ef- 
 fect upon the electrometers, both as to quality and 
 quantity ; but when the salt was used, there was a 
 more powerful effect upon the sensations. He ob- 
 served, that a new shock was experienced every 
 time either of the hands was brought into contact 
 
86 HISTORY OF GALVANISM. 
 
 with the apparatus, or removed from it ; but that 
 no effect took place as long as they remained in 
 contact. When the interrupted circuit was applied 
 between the extremities of the pile, the shock 
 might be felt, but it was rendered less violent; 
 and the chemical effects were diminished, but not 
 suspended, while the contact of the body was pre- 
 served : hence it may be inferred, that the body 
 is about an equally good conductor with water. 
 The retardation of the current appeared to be 
 rather greater in this case, than where the appa- 
 ratus was supplied with pure water. 
 
 The pile was now dissected in the same three 
 ways as before, muriate of soda in solution being 
 employed instead of water. In the first dissec- 
 tion, i. e. with the moistened cloths between the 
 plates, the same electric effects were exhibited 
 by the electrometers, the same shock was felt, and 
 the same chemical effects were produced, only in 
 rather a less degree than in the continuous pile, 
 with muriate of soda. The second and third dis- 
 sections of the pile produced exactly the same ef- 
 fect, as when the same dissections were employed 
 with pure water. 
 
 Hypothesis The author afterwards enters upon a number of 
 speculations respecting the manner in which the 
 circulates through the apparatus, and 
 
 chemical upon the immediate cause of the electrical and 
 
 chemical phenomena. He conceives, that when 
 
 no cause of retardation exists, the electric fluid 
 
 ^circulates so rapidly through the pile, as not to ex- 
 
HISTORY OF GALVANISM. 87 
 
 K. 
 
 hibit any of its effects, or indeed not to indicate its 
 presence ; and that when these are manifested, it 
 always depends upon some retarding cause. The 
 electrical and chemical effects are supposed to ori- 
 ginate from different parts of the pile, or from dif- 
 ferent groups, considered in their relation to th$ 
 parts contiguous to them. The electrical effects 
 consist simply in the combination of the two 
 metals, each pair being separated by a non-metal- 
 lic conductor ; while for the chemical effects, ter- 
 nary groups are necessary, the two metals with a 
 fluid between them. This distinction between the 
 two sets of properties, or the two modes of action, 
 is supposed to be proved by the different effects 
 which are produced by the pile in its three states 
 of dissection. In the pile dissected in the first 
 manner, which indeed may be regarded as equiva- 
 lent to the instrument in the continuous state, 
 both the electrical and chemical action takes 
 place : for here are the two metals, either in con- 
 tact, or connected by the wire frames, for the elec- 
 trical effects ; and for the chemical effects, there 
 are the two metals with the wet cloth interposed. 
 In the pile as dissected in the second manner, there 
 are the binary groups, i. e. the metals in contact, 
 and accordingly they produce the electrical effects ; 
 but we have no chemical effects, because they have 
 no fluid between them. In the third dissection* 
 no effects are produced ; we have not the chemical 
 effects, because the metals have not the wet cloth 
 between them, and we have no electrical effects, 
 
38 HISTORY OF GALVANISM. 
 
 because the zinc has the copper plate on one side, 
 and the wire frame on the other, which have the 
 same electrical relation to the zinc, and therefore 
 counteract each other. 
 
 File of sii- The different effects which seemed to ensue, be- 
 pewter. tween the pile when furnished with pure water, 
 and with the solution of a neutral salt, induced 
 De Luc to examine what connexion existed be- 
 tween the oxidation of the zinc, and the chemical 
 action of the instrument. For this purpose he 
 formed a pile of silver and pewter, the pewter 
 being selected for the experiment, because it has 
 an electrical relation with silver, and is oxidable 
 by muriatic acid, at the same time that it is not 
 much affected by pure water. In the first instance, 
 water was interposed between the plates ; the ex- 
 tremities of the pile, as indicated by the electrome- 
 ter, became electric, the pewter side negative, and 
 the silver positive ; but there was no shock, nor 
 any decomposition of the water in the interrupted 
 circuit. A pile was then formed of such a num- 
 ber of zinc and silver plates, that its electrical 
 energy might be the same with the pewter pile ; 
 but here there was both the shock produced, and 
 the decomposition of water. The pile of pewter 
 and silver was then fitted up with muriatic acid ; 
 and in this case, when the pewter plates became 
 oxidated, the shock and the decomposition of 
 General water were both produced. From these experi- 
 ments, the author deduces the following con- 
 clusions. When the metal is not oxidated, no 
 
HISTORY OF GALVANISM. 89 
 
 chemical effect is produced on the water in the in- 
 terrupted circuit. When the oxidation is pro- 
 duced by means of pure water, there is no shock, 
 although the chemical effects take place ; and 
 lastly, when either of these effects are produced, 
 the current of electricity is retarded in its passage 
 across the water in the interrupted circuit.* 
 
 It was in the prosecution of these experiments, Discovery 
 while he was examining the effect of different t r f iL ! h c e ! Iec " 
 conducting substances placed between the plates, lumn - 
 that De Luc was led to the discovery of the 
 curious instrument, which he named the electric 
 column. It is a pile consisting of a number of 
 disks of zinc and Dutch gilt paper, placed alter- 
 nately upon each other, and included in a glass 
 tube. In order to produce any considerable effect, 
 it is necessary that the instrument should contain 
 several hundred pairs of plates ; when the number 
 amounts to 800 or 1000 it will always affect the 
 electrometer. They are made about two-thirds of 
 an inch in diameter, and are kept in their proper 
 position by rods of glass, coated with sealing wax. 
 The end of the column which is bounded by the 
 zinc plate is found to be in the state of positive 
 electricity ; that bounded by the copper plate, of 
 negative electricity .f 
 
 Different opinions have been entertained re- Remarks 
 specting the nature of this apparatus, whether it OI 
 should be regarded as a galvanic, or simply as an 
 
 ' 
 
 * Nicholson's Journal, xxvi. 1 16, 241. f Ibid. xxvi. 246. 
 
90 HISTORY OF GALVANISM. 
 
 electrical instrument; in other words, whether 
 its primary operation is to produce any chemical 
 change in the metals of which it is composed, or 
 whether it depends merely on the electric action of 
 the bodies upon each other. It has been supposed 
 by some that the phenomena of the electric column 
 originate from a small quantity of moisture, which 
 is still adherent to the paper interposed between 
 the metallic plates ; and experiments have been 
 adduced to prove, that in proportion as the paper 
 is carefully dried, the electric effects are dimi- 
 nished. These observations have not, however, 
 been confirmed, while there are, on the other hand, 
 some circumstances which seem to favour the 
 contrary supposition. The instrument has been 
 known to remain in action for months or even 
 for years, and yet no visible alteration could be 
 perceived on the surface of the metals ; which 
 could scarcely have been the case had any che- 
 mical action existed between the metal and the 
 moisture in the paper. Another circumstance 
 which seems in favour of its being essentially an 
 electrical, rather than a chemical instrument, is 
 the connexion which there appears to be between 
 its action and the electric state of the atmo- 
 sphere. This connexion was perceived by De Luc 
 soon after he had constructed the apparatus, and 
 he made a number of accurate observations upon 
 the subject. Mr. Forster, by a mechanical con- 
 trivance, has adapted a bell to it, which continues 
 to ring with a regular motion in the ordinary 
 
HISTORY OF GALVANISM. 9! 
 
 electric condition of the atmosphere, but ceases or 
 proceeds irregularly when any considerable cjiange 
 occurs in this respect. If the action of the instru- 
 ment were galvanic, or essentially connected with 
 any chemical change in the state of its component 
 parts, it is not probable that the atmospheric elec- 
 tricity would have affected it in so great a degree 
 and in so uniform a manner. 
 
 I shall anticipate a little the chronological order 
 
 of discovery by giving an account in this place of P 
 an instrument, supposed to be analogous to De 
 Luc's, which has been constructed by Professor 
 Zamboni, of Verona. Zamboni's pile, as it was 
 first announced, consisted of disks of silvered paper, 
 to the plain side of which was applied a layer of 
 the black oxide of manganese mixed with honey. 
 In this state it could not literally be entitled to 
 the appellation of a dry pile, but it is said that it 
 has been since constructed upon a less exception- 
 able principle. The most curious property of 
 Zamboni's pile is the degree in which it exhibits 
 the electrical attractions and repulsions. If two of 
 these piles be placed at the distance of four or five 
 inches from each other, and a metallic needle be 
 properly suspended between them, it will be alter- 
 nately attracted by the two piles, so to move be- 
 tween them like a pendulum. This action, we 
 may presume, is certainly electrical ; but the pile of 
 Zamboni appears likewise to have a proper chemi- 
 cal action ; for when it has been confined for some 
 time in a limited portion of air, the air becomes 
 
92 HISTORY OF GALVANISM. 
 
 deoxidated, and the action of the pile ceases. We 
 are nq,t informed whether, in this case, any visible 
 change is produced on the surface of the metals, or 
 whether all access of moisture was very scrupu- 
 lously prevented in the instrument upon which 
 these experiments were made.* 
 
 Hachette The account of De Luc's pile had been published 
 sormes's f r some time, when a claim of priority of inven- 
 plle * tion was made by Hachette, in favour of himself 
 and Desormes, stating that they had formed a dry 
 pile so long back as the year 1803. It is difficult 
 to decide upon the merit of such claims ; but as a 
 general principle it is always proper, in these 
 cases, to adhere to the date of publication, unless 
 they can be substantiated by written documents of 
 unexceptionable authority. In the present instance, 
 however, it would appear, that the original pile, as 
 formed by Hachette and Desormes, is by no means 
 entitled to the appellation of dry, and indeed does 
 not appear to be analogous to De Luc's instrument, 
 for it is described as having been constructed with 
 paste or size between the plates ; and we are ex- 
 pressly told that, in proportion as the moisture 
 was evaporated, the action of the apparatus was 
 diminished.! 
 
 children's While Sir H. Davy and De Luc were thus en- 
 larging our knowledge of the powers of galvanism 
 as a chemical agent, and of the means by which 
 
 * Journ. of Science and the Arts, ii. 161. 
 f Ann. de Chim. et Phys. ii. 76 ; see also Biot in Ann. de 
 Chim. xlvii. 15. 
 
HISTORY OF GALVANISM. 93 
 
 its wonderful effects are accomplished, Mr. Child- 
 ren was advantageously employing himself in im- 
 proving the apparatus. He formed a battery, PLATE t 
 constructed upon the principle employed by Volta, ls ' 
 in the couronne des tasses, according to which the 
 plates are not in contact through the whole of 
 their extent, but are connected only at the top by 
 a metallic conductor, and are then immersed in 
 the cells of a trough. He employed 20 pair of 
 plates, of four feet by two, making in all a sur- 
 face of 92,160 square inches. The fluid that he 
 used was a diluted mixture of nitric and sulphuric 
 acids, the whole quantity being no less than 120 
 gallons. The effect of these large plates was to fuse 
 entirely, in about 20 seconds, 1 8 inches of platina , / 
 
 wire, of one-thirtieth of an inch in diameter, and 
 to render three feet of the same wire red-hot. 
 Charcoal burned with intense brilliancy. It 
 seemed not a little remarkable, considering the 
 powerful effect on platina wires, that the action of 
 this battery on iron wires was comparatively trifling. 
 Of iron wire, one-seventieth of an inch in diameter, 
 it barely fused ten inches, and was not able to ignite 
 three feet. It had not the power of decomposing 
 barytes and other similar substances ; it did not 
 affect Bennet's electrometer ; and it scarcely pro- 
 duced a perceptible shock. 
 
 Mr. Children next formed a battery of 200 pairs c om para- 
 of plates of two inches square, affording a surface 
 of 3,200 inches. With this the alkalies and alka- P lates - 
 line earths were readily decomposed, and a con- 
 
34 HISTORY OF GALVANISM. 
 
 siderable divergence was produced in the gold 
 leaves of the electrometer. From this comparison 
 of the effects of the two batteries, we are led to 
 the conclusion which has been already referred to, 
 that the intensity of the electricity is increased 
 with the number, and the quantity of it with the 
 extent of the metallic plates. Upon this principle, 
 we may explain why the platina wire was acted 
 upon more readily than the iron wire, the more 
 perfect conducting quality of the former presenting 
 no obstacle to the passage of the electricity 
 through it ; while the tendency of the iron to oxi- 
 dation required a greater intensity of the fluid to 
 striking effect its transmission through the wire. In this 
 galvanic paper, the author states, that he has removed one 
 
 Q . t j ie objections that have been urged against the 
 identity of the galvanic and the common electri- 
 city, that the former has no striking distance ; by 
 employing a proper apparatus, he ascertained that 
 the galvanic spark was capable of passing through 
 a certain space between the extremities of two 
 platina wires. 
 
 General Mr. Children's general conclusion is, that " the 
 
 ' absolute effect of a voltaic apparatus is in the 
 
 compound ratio of the number and size of the 
 
 J plates ; the intensity of the electricity being as the 
 
 former, the quantity given out as the latter ; con- 
 sequently, regard must be had in its construction, 
 to the purposes for which it is designed. For ex- 
 periments on perfect conductors, very large plates 
 are to be preferred, a small number of which will 
 
HISTORY OF GALVANISM. 95 
 
 probably be sufficient ; but where the resistance of 
 imperfect conductors is to be overcome, the com- 
 bination must be great, but the size of the plates \s 
 must be small. But if quantity and intensity be 
 both required, then a great number of large plates 
 will be necessary. For general purposes, four 
 inches square will be found to be the most conve- 
 nient size.* 
 
 Mr. Children has since constructed a still larger More pow* 
 and more powerful battery, consisting of 20 pairs ry^isia*" 
 of copper and zinc plates, each plate being six feet 
 by two feet eight inches. It ignited six feet of thick 
 platina wire, and melted platina with great faci- 
 lity ; it also melted iridium and osmium. At the 
 suggestion of Dr. Wollaston, a singular fact was 
 ascertained, that a greater length of thick platina 
 wire was ignited, than of platina wire of a much 
 smaller size.f 
 
 About this time a^battery of very great power Battery at 
 was constructed at the Royal Institution. It institution, 
 consisted of 200 separate parts, each part com- 
 posed of 10 double plates, and each plate con- 
 taining 32 square inches, the whole of the double 
 plates being 2,000, and the whole surface 128,000 / 
 
 square inches. When the whole series was put 
 into action, platina, quartz, sapphire, magnesia, 
 and lime, were all rapidly fused ; while diamond, 
 
 * Phil. Trans, for 1809- p. 32. 
 f Annals of Philosophy, it. 147. 
 
96 HISTORY OF GALVANISM, 
 
 charcoal, and plumbago, in small portions, disap- 
 peared, and seemed completely evaporated. A 
 singularly beautiful effect was produced by placing 
 pieces of charcoal at the two ends of the wires in 
 the interrupted circuit ; when they were brought 
 within the thirtieth or fortieth part of an inch of 
 each other, a bright spark was produced, above 
 half the volume of the charcoal, which was rather 
 more than an inch long, became ignited to 
 whiteness ; and by withdrawing the points from 
 each other, a constant discharge took place through 
 the heated air, in a space equal to at least four 
 
 PLATE ii. inches, producing a most brilliant arch of light ; 
 this light constituted the sphere of activity of the 
 instrument. When the communication between 
 the two wires was made in air so far rarefied as to 
 support only one quarter of an inch of mercury in 
 the barometric gauge of the air-pump, the spark 
 passed through a space of nearly half an inch ; and 
 by withdrawing the points from each other, the 
 
 t electric fluid was discharged through six or seven 
 
 inches, producing a most beautiful coruscation of 
 purple light, while the charcoal itself became in- 
 tensely ignited, and some platina wire attached to 
 it fused with brilliant scintillations, and fell down 
 in large globules. All the effects of chemical de- 
 composition were rapidly and powerfully produced ; 
 various substances submitted to the action of the 
 apparatus were instantly resolved into their ele- 
 mentary gases ; and so intense was the action, that 
 
HISTORY OF GALVANISM. 97 
 
 sparks were produced even in the nitric and sul- 
 phuric acids.* , 
 
 I have given above some account of a paper of Branded 
 Erman's, in which he endeavours to show, that Erman, 
 certain bodies are what he calls Unipolar, that is, 1! 
 that they are conductors of one kind of electricity 
 only. Mr. Brande conceived, that the facts 
 brought forward by Erman might admit of a bet- 
 ter explanation upon a different principle, viz. that 
 some chemical bodies being naturally positive, and 
 others naturally negative, they would be attracted 
 to the surface of the pile in a contrary state to 
 their own, the positive to the negative, and the 
 negative to the positive surface. 
 
 In order to submit his opinion to the test of ex- Experi- 
 periment, Mr. Brande procured two insulated me- m 
 tallic balls, one connected with the prime con- 
 ductor, and the other with the rubber of an electri- 
 cal machine ; and placing between them the differ- 
 ent substances under examination, he observed to 
 which of the balls they were attracted. He found 
 that the flame of a candle, which principally con- 
 sists of carbon and hydrogen, was attracted to the 
 negative ball ; while the flame of phosphorus, 
 which would contain a quantity of phosphoric 
 acid, was attracted to the positive side. Here the 
 bodies seemed to folio w the known laws of electro- 
 chemical attraction, according to the idea of their 
 inherent electrical states; and the other experi- 
 
 f 
 
 * Davy's Elements of Chemical Philosophy, p, 152. 
 H 
 
HISTORY OF GALVANISM. 
 
 Wollas- 
 ton's ele- 
 mentary 
 battery, 
 1815. 
 
 merits which he performed of a similar nature 
 generally tended to the same conclusion. The 
 facts stated in this paper are conceived to be fa- 
 vourable to the hypothesis of Sir H. Davy, respect- 
 ing the natural electricities of bodies, and also, 
 when viewed in connexion with Erman's observa- 
 tions, to afford an additional proof of the identity 
 of electricity and galvanism.* 
 
 Mr. Brande's method of viewing these experi- 
 ments is, I conceive, preferable to that of the 
 author himself, as being more simple, and as in- 
 volving no principle in addition to those which are 
 deduced from other phenomena. In most cases at 
 least it offers a satisfactory explanation of the facts ; 
 and it does not appear, in any instance, to be 
 directly at variance with them. 
 
 Dr. Wollaston constructed a very curious appa- 
 ratus, which he calls an elementary galvanic bat- 
 tery, the object of which is to exhibit the most 
 minute arrangement of electrical substances, by 
 which visible ignition can be produced. The 
 smallest that he has constructed consists of a 
 thimble, without its top, flattened until its sides 
 were about one-fifth of an inch asunder ; a small 
 plate of zinc was then contrived to be fixed within 
 the thimble, but without touching it ; and a pro- 
 per appendage of platina wires was added. The 
 zinc plate was less than three-fourths of an inch 
 square, and even when water was employed that 
 
 * Phil. Trans, for 1814-. 
 
HISTORY OF GALVANISM. 99 
 
 contained only -^ part of sulphuric acid, a platina 
 wire of 3 ' of an inch in diameter, and from 
 ^ to -jV of an mcn m length was readily fused.* 
 In the formation of his minute apparatus, this sa- 
 gacious experimentalist made an observation of 
 great importance in enabling us to produce as 
 much effect as possible from the smaUest quantity 
 of materials. He remarks that the zinc plate 
 should have a counterpart of copper opposed to 
 each side of it ; for in the usual arrangement, 
 although both sides of the zinc are oxidated, that 
 side only is efficient which has a copper surface 
 opposed to it. 
 
 This principle, which Dr. Wollaston had used children's 
 with so much success in his elementary battery, tery. 
 was applied by Mr. Children with proportionate 
 success, to the formation of the most powerful 
 galvanic instrument which has hitherto been con- 
 structed. The plates were six feet long by two 
 feet eight inches, so as to present 32! square feet 
 of surface ; each zinc plate was supended between 
 two copper plates, and they were connected to- 
 gether by lead. Each of these sets or triads of 
 plates was immersed in the separate cell of a trough, 
 which was filled with a properly diluted mixture of 
 the sulphuric and nitric acids, and the plates were 
 all attached to a beam, and so adapted to a coun- 
 terpoise as that they could be readily lifted up 
 out of the trough and again immersed in it at 
 
 * Ann. of Philosophy, vi. 209. 
 H 2 
 
100 HISTORY OF GALVANISM. 
 
 pleasure. The following was the order in which 
 metallic wires were raised to the red heat ; plati- 
 num, iron, gold, copper, zinc, and silver, an order 
 which was conceived to be exactly the reverse of 
 their conducting power ; the places of tin and lead 
 could not be ascertained, because they melted 
 before they became red hot. 
 
 its effects. Among the effects of this powerful apparatus in 
 generating heat, the following are some of the 
 most remarkable. Five feet and a half of plati- 
 num wire, '11 inch in diameter, was raised 
 to a red heat visible in day-light ; the same effect 
 was produced upon 84- inches of platinum wire, 
 *44 inch in diameter, and upon a bar of plati- 
 num 4- inch square, and 2^- inches long. The 
 chemical effects of the apparatus were no less 
 remarkable than its power of extricating caloric. 
 The oxide of molybdenum was easily fused and 
 reduced; the oxide of tungsten was fused and partly 
 reduced; the oxides of uranium, titanium, and 
 cerium were fused, but not reduced ; and the oxide 
 of tantalum was partially fused. The compound 
 ore of iridium and osmium was fused into a 
 globule, and iridium was formed into a globule 
 containing cavities. Box-wood charcoal was in- 
 tensely heated in chlorine and in azote, but in 
 neither case produced any effect. By heating iron 
 in contact with diamond powder, the diamond was 
 consumed ; and the iron was converted into steel. 
 Blue spinell and gadolinite were fused, and zircon 
 from Norway imperfectly so; magnesia was agglu- 
 
HISTORY OF GALVANISM. 101 
 
 tinated ; while ruby, sapphire,, quartz, and silex, 
 were not affected.* 
 
 Since the experiments of Mr. Children, the only 
 addition which the science of galvanism has ac- 
 quired is from Dessaignes, who some time before 1! 
 had made a series of observations on the effects of 
 temperature upon the action of the pile, which he 
 now repeated and extended. He informs us, that 
 the instrument ceases to act if the whole of it be 
 heated to 2121: but that, on the contrary, its action 
 is doubled, if one half of it be heated, while the 
 other is cooled. He farther informs us, that two 
 pieces of metal of the same kind will act, if one of 
 them be heated, while the other is cooled ; and even 
 that the same effect will follow if different parts of 
 the same piece of metal be kept at different tem- 
 peratures. The result of these experiments is 
 probably what we should not previously have ex- 
 pected ; yet they may be explained either upon 
 electrical or chemical principles; as both the elec- 
 trical condition of bodies, and the effect of che- 
 mical re-agents, is materially affected by the degree 
 of temperature to which they are exposed.* 
 
 These experiments will conclude the first part 
 of this essay, containing the history of galvanism. 
 Although it may be somewhat hazardous to form 
 predictions respecting the progress of science, I 
 
 * Phil. Trans, for 1815, p. 363. 
 
 f Journ. de Phys. Ixxiii. 230, 417; Ixxxii. 360 ; Ixxxiii. 194, 
 
102 HISTORY OF GALVANISM. 
 
 may remark, that the impulse which was given, in 
 the first instance, by Galvani's original experi- 
 ments, was revived by Volta's discovery of the 
 pile, and was carried to the highest pitch by Sir 
 H. Davy's application of it to chemical decompo- 
 sition, seems to have, in a great measure, subsided. 
 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 ob- 
 taining any new light upon the theory of its 
 action. 
 

 PART II. 
 
 THEORY OF GALVANISM. 
 
 ACCORDING to the plan which was laid down, General 
 I must now proceed to give an account of the the- 
 ories and hypotheses that have been formed to 
 explain the phenomena of galvanism. I have had 
 occasion to allude to many of these in the course of 
 the historical sketch ; and the reader will, in some 
 degree, have anticipated my opinion respecting 
 them. The subject divides itself into several 
 branches, partly corresponding with the progress 
 of our knowledge of the facts that were gradually 
 developed, and partly depending upon the sup- 
 posed relation of galvanism to the other depart- 
 ments of natural philosophy. 
 
 In this concise view of the science, I shall not Gaivani'g 
 think it necessary to enter into the merits of the h yP othesi - 
 earlier speculations that have been superseded by 
 later discoveries. Of this nature is the original 
 hypothesis of Galvani himself, that the convul- 
 sions which he observed in the muscles of frogs 
 were produced by a new and peculiar agent, re- 
 siding in the body, to which he gave the name of 
 animal electricity. Although there are some few 
 cases which seem to militate against the supposi- 
 
104 THEORY OF GALVANISM. 
 
 tion, it must, upon the whole, be regarded as 
 being decisively proved, that all the phenomena 
 which we style galvanic depend merely upon the 
 action of electricity, modified by the manner in 
 which it is produced or excited. 
 
 what is Hence arises an interesting question, and one 
 which lies at the very foundation of all our future 
 inquiries, How does galvanism differ from common 
 electricity ? This question may refer both to the 
 nature of the phenomena themselves, and to the 
 
 Remarks means employed for their production. We may 
 
 on thedefi- , - , . . Al , 
 
 define galvanism, either by enumerating the spe- 
 cific characteristics of those events which we class 
 together under this title ; or we may show how 
 they have all a reference to each other, from the 
 similarity of the processes that are employed for 
 their development. The definition that was given 
 at the commencement of the essay, may be re- 
 garded as sufficiently correct and comprehensive, 
 without exceeding the limits to which a definition 
 ought to be restricted. It appears to include every 
 action of bodies upon each other which is usually 
 considered as belonging to this particular branch 
 of natural philosophy ; while it excludes those that 
 are, by common consent, referred to a different 
 department. It is, however, in some cases, difficult 
 to draw the exact line of distinction between elec- 
 tricity and galvanism ; and indeed we may doubt 
 whether any precise distinction actually exists. 
 For as it is conceived that they both depend upon 
 the same agent, having merely experienced some 
 
THEORY OF GALVANISM. 105 
 
 modification in its nature, or mode of action, we 
 must conclude, that there may be some intermediate 
 or indeterminate state,, which might be referred to 
 one or the other with almost equal propriety. 
 
 To recur then to the former definition : " Gal- Definition, 
 vanism is a series of electrical phenomena, in 
 which the electricity is developed without the aid 
 of friction, and where we perceive a chemical ac- 
 tion to take place between some of the bodies em- 
 ployed." This definition may perhaps be thought 
 to limit the science too much, and to remove from 
 it many facts which have always been regarded as 
 galvanic. For example, a great number of the 
 original experiments of Galvani himself, and his 
 contemporaries, where contractions were excited 
 in the muscles of animals, by the application 
 of the two metals, many of those of Fowler, 
 and the first set of Volta's experiments, would, 
 according to this definition, be reduced to the 
 effects of common electricity. To this objection we 
 may reply, that wherever moisture comes in con- 
 tact with the zinc, or more oxidable metal, it is not 
 improbable that some chemical action is produced, 
 but that it is very slight, and has therefore not 
 been noticed. If, however, upon a strict examina- 
 tion, it is found not to be the case, and that there 
 is actually no change in the chemical condition of 
 any part of the apparatus, it must be admitted 
 that, according to our present ideas, the phenomena 
 are not to be referred to galvanism. The first un- First pro- 
 equivocal experiments where the chemical effects n 
 
 ments. 
 
106 THEORY OF GALVANISM. 
 
 were observed, and were connected with the elec- 
 trical condition of the substances, are those of 
 Fabroni's ; and it was not until Volta's discovery 
 of the pile, that we were put in possession of a 
 method by which we were enabled to examine, 
 with any degree of accuracy, the relation between 
 these two actions. Even if we find it necessary 
 to conclude that Galvani, although he had the 
 good fortune to have his name associated with a 
 new department of science, did not witness any of 
 the facts to which we now apply the term, the 
 contradiction will be more apparent than real ; and 
 we must not permit the mere circumstance of 
 names to influence our opinion respecting the es- 
 sential nature of things. The present state of our 
 knowledge seems, however, to warrant the conjec- 
 ture, that the action of the two metals on the 
 parts of animals is strictly galvanic, L e. accompa- 
 nied by a chemical action on the metals and the 
 fluids, so as to reduce it within the limits of the 
 proposed definition. 
 
 Difference Waving, however, the farther discussion of this 
 ekaridty point, which indeed can only be decided by experi- 
 nSn galTa ~ ment, we must recur to the question already 
 stated, respecting the essential difference between 
 galvanism and common electricity ; and, conceiv- 
 ing it to be ascertained, that in the production of 
 the former, a chemical action takes place, which 
 is not necessary in the latter, we must next in- 
 quire, in what way this chemical change of the sub- 
 stances imparts to the electricity that particular 
 
THEORY OF GALVANISM. 107 
 
 state or modification which we style galvanic. With 
 respect to the nature of this chemical change, experi- 
 mentalists are generally agreed : as to the metals, 
 it consists in the oxidation of that metal which 
 possesses the strongest attraction for oxygen ; and 
 with respect to the fluid interposed between the 
 rnetals, it consists in its decomposition, the oxygen- 
 ous part being attracted to the most oxidable me- 
 tal, and the alkaline to that which is the least 
 oxidable. Although, as I have already had occa- 
 sion to remark, there are various galvanic combina- 
 tions into which only one metal enters, or even 
 some entirely without metals, yet, as the most 
 powerful and complete circle is that which con- 
 sists of two metals with a fluid interposed, I shall 
 confine my illustrations to this form of the ap- 
 paratus. 
 
 We may consider it as proved by a number of Galvanic 
 experiments, which have been stated in the first onow Po- 
 part of this article, that the electricity, as it is tensit y 
 evolved by the different galvanic combinations, 
 always exists in what has been styled a state of 
 low intensity ; and that, to whatever extent we 
 increase the apparatus, and however powerfully it 
 acts, still the intensity is but little augmented. 
 Unfortunately it is still a doubtful point of theory, > 
 upon what the intensity of electricity depends, or 
 in what it precisely consists. Some writers have Remarks / 
 ascribed it to a greater or less concentration of the n c "* 
 fluid ; some to a difference in the velocity of its sit ?- 
 motion, or in the strength of its affinity for the 
 
108 THEORY OF GALVANISM. 
 
 surrounding bodies ; and others to its containing a 
 greater or less portion of caloric. For the present, 
 we must rest satisfied with admitting the fact of 
 the low intensity, as manifested by the phenomena, 
 without being able to explain its cause ; and we 
 may next proceed to inquire, whether there be any 
 circumstances in the different methods of exciting 
 or producing electricity, by the machine or the pile 
 respectively, which should cause the first to deve- 
 lop the fluid in a higher, and the latter in a lower 
 state of intensity. 
 
 Electricity 'And here, it must be confessed, we have little to 
 by the ma- direct our inquiries but conjecture and uncertain 
 analogy. Of these, however, as being our only 
 guides, we must make the best use that lies in em- 
 power. It is generally agreed, that all bodies pos- 
 sess a certain quantity of electricity, which is said 
 to be natural to them, and which, while it remains 
 undisturbed, manifests no indications of its exist- 
 ence. There are many processes which alter 
 the state of this natural electricity, by which it 
 is extricated from one body, and may be trans- 
 ferred to others in the neighbourhood. But this 
 additional portion, being more than their natural 
 share, seems to be retained by them with difficulty, 
 and is ready to fly off in all directions, in order to 
 restore the equilibrium. This may be considered 
 as descriptive of what occurs in the operation of 
 the common electrical machine, where, by the fric- 
 tion of the rubber against the cylinder, a portion 
 of the electric fluid is carried off from one or both 
 
THEORY OF GALVANISM. 109 
 
 of them, and is transferred to the conductor. From 
 the conductor it may be communicated to a variety 
 of other bodies that are placed within the sphere 
 of its influence ; but, in all these cases, it is re- 
 tained by them for a certain space of time only, 
 and is continually passing off, more or less rapidly , 
 to all the surrounding bodies. 
 
 But besides this temporary transfer from one Electricity 
 body to another, without their undergoing any far- 
 ther alteration, they occasionally experience a more 
 permanent change in their electrical state, when, 
 in consequence of their acquiring different physical 
 and chemical properties, their capacity for electri- 
 city is entirely altered. When their capacity is 
 diminished, a more gradual, but more continued 
 discharge of the electric fluid takes place ; and in 
 this appears to consist the essential action of the 
 pile, as contrasted with that of the machine. In 
 the action of the machine, by which the electric 
 fluid is set at liberty, and transferred from one 
 body to another, no change appears to take place > ' 
 in the substances employed, except the alteration 
 in their respective quantities of electricity. Their 
 attraction for it is neither increased nor dimi- 
 nished ; and, consequently, they have a tendency, 
 the one to lose, and the other to acquire, the elec- 
 tricity which has been thus, as it were, forced into 
 the one, and out of the other. According to the 
 nature of the action by which the electricity is 
 evolved, whether the substances experience any 
 permanent change in their capacity, or whether 
 
HO THEORY OF GALVANISM. 
 
 their equilibrium is merely disturbed in a tempo- 
 rary manner, the state of the fluid appears to be 
 affected, so as to cause a difference in its intensity. 
 The two When we employ the machine, the electricity that 
 
 electrici- , . i 11 i , 
 
 lies com- we procure appears to be in a highly elastic state, 
 pared. ^ s p ar t| c } es are strongly repulsive of each other, 
 and at the same time not disposed to enter into a 
 permanent union with other bodies. The galvanic 
 electricity which we procure from the pile is more 
 readily united to other bodies, and has a tendency 
 to form new combinations with them, which is so 
 powerful as to counteract some of the strongest 
 chemical affinities. At the same time, it exhibits 
 less of what may be called mechanical action : its 
 particles are less repulsive of each other ; its mo- 
 tions appear less rapid ; it causes less commotion in 
 its passage from one body to another ; and although 
 its ultimate effects are more powerful, it seems to 
 act with less violence. The one may be compared 
 to a small quantity of an agent highly concen- 
 trated ; the other to a larger quantity, but in a state 
 of greater dilution. The phenomena of electri- 
 city, as excited by the common machine, depend 
 upon the attraction and repulsion of the electric 
 fluid, and its passage from one body to another ; 
 while the most important actions of galvanic elec- 
 tricity result from the chemical changes that it 
 produces in the composition of bodies. The excita- 
 tion of common electricity is not necessarily at- 
 tended with any permanent alteration in the state 
 of the substances that are employed in producing 
 
THEORY OF GALVANISM. Ill 
 
 it. It is usually developed by the mechanical aid 
 of friction ; and the same apparatus may continue 
 to be employed for an indefinite length of time. 
 Friction, on the contrary, has no effect in the pro- 
 duction of galvanic electricity ; it requires a che- 
 mical change in some part of the apparatus ; and 
 the individual parts which have been employed in 
 generating it acquire new properties, and are^ in- 
 capable of any farther galvanic action. In the 
 above remarks I have proceeded upon the hypo- 
 thesis which is the most generally received in this 
 country, and which I am disposed to consider as 
 the most plausible, that the two electricities differ 
 from each other merely in the relation of quantity. 
 But if the contrary opinion be adopted, which is 
 more current in France, and which has been so 
 elaborately detailed by Biot in his late' treatise, 
 and we regard them as differing in their nature, 
 still it will not essentially affect the reasoning that 
 I have employed, although it may require to be 
 expressed in somewhat different terms. According 
 to this view of the subject, when we employ the 
 common electrical machine, we forcibly alter the 
 proportion in which the vitreous and the resinous 
 electricities naturally exist in the different parts of 
 the apparatus, which have a constant tendency to 
 resume their former condition. In the action of 
 the pile, on the contrary, we alter the capacity of 
 some part of the instrument for one or other of the 
 electricities, and produce a state in which their ba- 
 lance is permanently changed. 
 
112 THEORY OF GALVANISM. 
 
 Action of After these general observations, which, scanty 
 
 the pile. J 
 
 and inconclusive as they are, appear to be all that 
 our present knowledge upon the subject will war- 
 rant, we must proceed to examine more minutely 
 into the nature of the action that is exercised by 
 the galvanic apparatus. From the remarks that 
 have been already made, it will be obvious, that 
 in the operation of the pile there are both electri- 
 cal and chemical phenomena produced ; and it has 
 been a point very warmly contended, which of 
 these is the most essential, or rather which of 
 them is the primary effect, and, consequently, is to 
 be considered as the cause of the other, and of the 
 whole train of actions. Volta, and most of the 
 continental philosophers, support the electrical hy- 
 pothesis ; while there are several distinguished ex- 
 perimentalists in this country who maintain, that 
 the chemical action is the one which gives rise to 
 all the changes that are produced, and therefore 
 constitutes the primary action of the instrument. 
 Voita sup. In all the experiments that were performed with 
 electric * the two metals, previous to the discovery of the 
 hypothesis> pile, with the exception of those of Fabroni, 
 which seem to have been but little attended to, the 
 only point in discussion was, whether the effects 
 were to be referred to the electric fluid, or to a 
 new agent inherent in the animal body. Volta 
 strenuously adopted the opinion, that they de- 
 pended simply upon common electricity ; and ac- 
 counted for them by supposing, that the contact of 
 the two metals had the power of altering the quantity 
 
THEORY OF GALVANISM. 
 
 of electricity which was natural to them, adding a 
 portion of it to the one, and subtracting it from 
 the other respectively. To this power he gave the 
 title of electro-motion; and he spoke of it as a 
 new property, which had not been before noticed, 
 and distinctly claimed to himself the merit of its 
 discovery. He conceived that he might increase Forms the 
 the power of the instrument, or rather concentrate 
 the effect of a number of separate pairs of metal, 
 by interposing between each pair a conducting 
 substance, which, without altering the electric state 
 of the metals, might increase the effect by trans- 
 mitting it through a number of successive stages. 
 Whatever we may think of the hypothesis, the ex- 
 periment to which it gave rise was most fortunate; 
 for it led to the construction of the pile ; an appa- 
 ratus by means of which the most curious and im- 
 portant discoveries have been made in the different 
 departments of natural philosophy. 
 
 Although Volta completed the discovery of the Did not no- 
 pile, and fully ascertained its action on the animal m i ca i ef- 
 body, yet it is not a little remarkable, that he fects * 
 limited his inquiries to this object, and seems to 
 have been totally ignorant of the farther powers of 
 the instrument of which he was possessed. This 
 circumstance must appear the more remarkable, 
 when we recollect that upon the very first em- 
 ployment of it by Nicholson and Carlisle, they 
 perceived its chemical action, and became aware of 
 its importance as an agent in the decomposition of 
 bodies. Cruickshanks, Davy, Wollaston, Henry, and 
 the other English philosophers, farther developed 
 
114 THEORY OF GALVANISM. 
 
 its powers in this respect, which had so completely 
 escaped the notice of Volta, and they were con- 
 sequently led to form a different idea of the mode 
 of its operation. Dr. Wollaston seems to have 
 been the first who decidedly adopted the opinion, 
 that the chemical action of the pile is the primary 
 origin of all the changes which it experiences, and 
 is the cause of the electrical effects ; and the same 
 idea was embraced by Sir H. Davy, although he has 
 since abandoned it for the hypothesis of electric 
 energies. 
 
 An account I must now proceed to examine the two lead- 
 trie hyp 1 "" ing theories of the galvanic action, as exhibited in 
 
 fhe S piie f ^ pile, with more minuteness ; and I shall ^ 
 gin with that of Volta, or the one which sup- 
 poses a change in the electrical condition of the 
 metals to be the primary cause of its operation. 
 This philosopher has given a statement of his opi- 
 nions on the subject, in several letters which he 
 wrote to his friends, and which have been pub- 
 lished in different scientific journals. His first 
 communication was in a letter to Cavallo ; the se- 
 cond toGren;* both written before his discovery of 
 the pile. His original account of this apparatus 
 is contained in a letter to Sir Joseph Banks, in 
 which he explains his ideas respecting its action ; 
 and he afterwards farther developed them in let- 
 ters to Delametherie and to Van Marum.f In 
 
 * Phil. Trans, for 1793 ; Ann. de Chim. xxiii. 276. 
 f Phil. Trans, for 1800; Nicholson's Journal, Svo.i. 135; 
 Ann. fe Chim. 40, 225. 
 
THEORY OF GALVANISM. 115 
 
 some of these papers Volta details his hypothesis 
 at considerable length ; yet, after an attentive 
 examination of them, it appears to me that they 
 are not altogether consistent with each other ; and 
 that, without any intimation of the circumstance, 
 he has, in fact, presented to the world two distinct 
 hypotheses. 
 
 The letter written to Cavallo, of which I have 
 already given some account, is Volta's first essay 
 on the subject of galvanism, and contains an ac- 
 count of Galvani's original discovery, and of the 
 additional experiments which he had himself per- 
 formed by the combination of the two metals. He 
 accounts for all the facts on the principle, that 
 when metals are placed in certain circumstances 
 with respect to each other, there is " a destruction 
 of the equilibrium " of the electricity. This action 
 is stated to consist essentially in two metals, when 
 placed in contact, giving the one to the other a 
 portion of its natural electricity, so that the one 
 becomes positive and the other negative. Some 
 combinations of metals possess this electro-motive 
 faculty much more powerfully than others ; those 
 that Galvani and Volta originally employed were 
 zinc and silver ; and in this case the zinc acquired 
 the electricity and became positive, while the silver 
 lost electricity or became negative. In this paper 
 no other principle is referred to ; and the action is 
 not spoken of as belonging to any class of bodies 
 except the metals. Volta speaks of the principle 
 as a new law of electricity, which had not been 
 
 I 2 
 
THEORY OF GALVANISM. 
 
 before noticed, and decidedly claims to himself the 
 discovery of it. 
 
 In the letter to Delametherie, written after the 
 discovery of the pile, Volta still farther develops 
 his hypothesis, but without altering the ground on 
 which it rests. He describes each pair of metals 
 as the efficient part of the apparatus, and speaks 
 of the fluid that is interposed between them as 
 merely carrying the electricity from one pair to 
 another, without producing any change in it. In 
 his letter to Van Marum, he relates the following 
 fundamental experiment, as it is called : a plate of 
 copper and a plate of zinc are placed in contact 
 with each other, but so that a part of each plate 
 projects beyond the other ; and he finds, that of 
 the parts which thus project, one becomes positive 
 and the other negative. So far all these opinions 
 appear to be consistent with each other ; but in 
 the letter written to Gren, an idea is brought for- 
 ward, which is not noticed in the other essays, and 
 which seems to be essentially different from them. 
 All conductors of electricity are divided into two 
 classes, the dry and the moist ; and electricity is 
 supposed to be always excited, when two con- 
 ductors of either of these classes are placed in con- 
 tact with one conductor of the other class. In this 
 way one metal only would appear to be sufficient 
 for a galvanic combination, provided there be two 
 moist conductors in contact with it. How the 
 fluids act in this case, or what relation they bear 
 to each other and to the metal, we are not exactly 
 
THEORY OF GALVANISM. 117 
 
 informed ; but we may conclude, that it is not 
 from any chemical operation, because in the letter 
 to Delametherie, written four years after that to 
 Gren, it is expressly said, that the fluids have no 
 effect but in transferring the electricity from one 
 metal to another. 
 
 Upon the whole we may conclude, that Volta General 
 conceives the electricity to be excited by the electric hy- 
 metals producing a degree of electro-motion, or by potl 
 destroying the natural equilibrium of the electri- 
 city ; one metal thus becoming positive and the 
 other negative, they each of them exhibit signs of 
 electricity to an electrometer or other similar in- 
 strument. The only use of the fluid is to tranfer 
 the electricity which is excited by one pair of 
 metals to the next pair ; and although a chemical 
 action may take place between the fluid and the 
 metal, this action is merely incidental, and is not 
 essential to the production of the galvanic effects. 
 
 The objections to Volta's hypothesis are very Objections 
 forcible : in the first place, I am disposed to think to 
 that the fundamental position, on which the whole 
 rests, is objectionable. Volta supposes that two voita's 
 metals, as for example, a plate of zinc and one of [!)" " 
 copper, when placed in extensive contact with each 
 other, may become respectively positive and nega- 
 tive. This he endeavours to prove by direct ex- 
 periment ; but it will be found that in none of the 
 cases is the experiment precisely in point. He 
 adduces some facts, where metals were found re- 
 spectively positive and negative, that had been in 
 
118 THEORY OF GALVANISM. 
 
 contact, but were afterwards separated : in one of 
 his experiments the metals never actually touched, 
 but were connected by a moist conductor ; and in 
 the experiment which we have related above, it 
 was only the projecting parts of the plates that 
 could be made to exhibit the opposite electric 
 states. And it appears that a very general mis- 
 conception has prevailed on the subject, and that 
 almost all writers have confounded the state of 
 approximation with that of contact. The experi- 
 ments of Bennet and Cavallo have been adduced 
 as analogous to those of Volta, and Sir H. Davy 
 expressly designates Yolta's hypothesis as an ex- 
 tension or generalization of these experiments, re- 
 marking that Bennet had proved, that bodies 
 brought into contact, and again separated, exhibited 
 different states of electricity.* Volta himself has 
 clearly fallen into the same error ; for in the expe- 
 riments which are related in his letter to Delame- 
 therie, he examined the metals separately, after 
 they had been in contact, and draws his inference 
 from this examination.! Yet these experiments 
 do not apply to the circumstances of the pile, 
 where the metals have an extensive communica- 
 tion with each other, and where, from this circum- 
 stance, it is probable that, while they remain in 
 
 * Phil. Trans, for 1807, p. 32. 
 
 -) Nicholson's Journ. 8vo. i. 136, &c. ; Henry's Elements, 
 i. 248; Murray's Chemistry, i. 581. See also Haiiy, Traite 
 de Physique, ii. 15, &c.; Biot, Traite de Physique, ii. 471 ; 
 and Ann. de Chim. xlvii. 8. 
 
THEORY OF GALVANISM. 119 
 
 contact, or this communication is preserved, they 
 must be in the same state of electricity. An elec- 
 trified body may communicate electricity either by 
 contact or by approximation ; in the first case the 
 electricity is the same with that of the communi- 
 cating body ; in the second, the communicated 
 electricity is of the opposite kind, but it is de- 
 stroyed as soon as the bodies actually come into 
 contact. The experiment of Volta, which comes 
 the most near to the circumstances of the galvanic 
 apparatus, is that mentioned above, where the 
 projecting parts of two metallic disks were found 
 to be in opposite electric states. But this is an 
 experiment of a most delicate nature, and Mr. 
 Cuthbertson, who attempted to repeat it, obtained 
 results contrary to those stated by Volta.* 
 
 But, waving this objection, and admitting that chemical 
 
 , , ., . , . . effects not 
 
 the two metals, while they are in extensive con- accidental, 
 tact, may be in opposite electrical states, it may be 
 objected to Volta's hypothesis, in the second place, 
 that the chemical effects of the pile are not, as he 
 supposes, merely accidental. They seem, on the 
 contrary, to be absolutely essential to its action, 
 for when perfectly pure water is interposed be- 
 tween the metals, or when the apparatus is placed 
 in any situation where it is excluded from obtain- 
 ing a supply 'of oxygen, it ceases to act. The 
 same thing happens when the acid, or other oxi- 
 dating fluid, is all expended ; and in short it may 
 
 * Nicholson's Journ. 8vo. H. 281. 
 
120 THEORY OF GALVANISM. 
 
 be stated, as a general principle, that whatever 
 promotes the action of the fluid upon one of the 
 metals increases the energy of the instrument, and 
 whatever tends to prevent or destroy this action 
 suspends the energy. When considered in this 
 point of view, the experiments of De Luc, on the 
 dissection of the pile, seem to be strongly adverse 
 to the electric hypothesis. In the second distribu- 
 tion of the ternary groups, the two metals are in 
 contact, and therefore any electrical effect might 
 be produced, which would arise from this circum- 
 stance ; there was also the fluid between them, 
 which would serve as a conductor of electricity ; 
 yet because the apparatus was so arranged that 
 this fluid could not act upon the zinc and oxidate 
 it, no proper galvanic effect ensued. 
 
 It is a little remarkable, that notwithstanding 
 the weight of authority to prove that the action of 
 the pile is suspended in vacuo, or in any gas which 
 does not contain oxygen, unless the fluid between 
 the plates contain some saline matter,* Volta, even 
 in a comparatively late period of the inquiry, still 
 continued to deny the fact.f And the same re- 
 mark may apply to what this philosopher says 
 respecting the superior efficacy of saline fluids, 
 which, notwithstanding the experiments of Davy 
 and others, he still perseveres in ascribing simply to 
 their superior conducting power.* And, indeed, 
 
 * Davy, Biot, Van Marum, Pepys, Haldane, &c. 
 f Ann. de Chim. xlii. 281. 
 Nicholson's Journ. 8vo. i. 239. 
 
THEORY OF GALVANISM. 
 
 independently of any experiments performed ex- 
 pressly for the purpose, when we consider how 
 readily pure water transmits the electric fluid, we 
 can scarcely attribute to a deficiency in its con- 
 ducting power the comparatively small effect which 
 it produces in the pile, nor to a mere increase of 
 this conducting power, the vastly greater activity of 
 diluted acids or neutral salts. And if we refer to 
 the principle of the hypothesis, the more we increase 
 the conducting power of the fluids, the less should 
 be the action of the pile. The contact of the 
 metals is supposed to destroy the electrical equili- 
 brium, and the operation of the fluid is to counter- 
 act this disturbance and restore the equilibrium. 
 It must then follow, that the more perfect the 
 conductor, the more completely will the equili- 
 brium be restored, and the less effect will be pro- 
 duced by its destruction. 
 
 It may be urged as an objection to Volta's hy- 
 pothesis, that it does not provide for any absolute 
 increase of the electric power. The two metals, 
 by their contact, become one positive and the other 
 negative; and this is equally the case with each 
 pair ; but the fluid that is interposed between the 
 metals is conceived to restore the equilibrium of 
 the electricity, which has been disturbed by the 
 metals. This is the whole effect of the apparatus ; 
 and we are not informed how any electricity can 
 be actually produced or generated, as it would 
 appear that the nature of the instrument is to 
 cause an electric action in one part, which must 
 be immediately counteracted by another part. 
 
THEORY OF GALVANISM. 
 
 Whatever deficiency of electricity there was in any 
 copper-plate would be instantly supplied by the 
 water communicating the superabundant electricity 
 of the opposite zinc plate, so that the effect of the 
 whole would be reduced simply to the difference 
 between the two extreme plates of copper and 
 zinc. 
 
 The hypothesis may be thus illustrated. C 1 
 and Z 1, by their contact, produce a change in 
 their natural state of electricity; part of what 
 belonged to C 1 is transferred to Z 1, so that C 1 
 becomes negative and Z 1 becomes positive ; and 
 supposing that their natural share of electricity is 
 represented by 100, and that the copper gives T V 
 to the zinc, C 1 and Z 1 will be brought to the 
 states of 90 and 110 repectively. The same 
 alteration in their electrical states will, at the same 
 time, take place in the second pair of plates, C 2 
 and Z 2. The water, which is in contact with 
 C 1 and Z 2 will, however, from its conducting 
 power, have the effect of equalizing the electrical 
 states of these bodies, and will therefore reduce 
 the electricity of Z 1 to 100, and raise that of C 2 
 to the same degree. The electrical state of the 
 four plates will therefore be 90, 100, 100, and 
 110. The third, and every succeeding pair of 
 plates will be acted upon exactly in the same 
 manner with the second ; the electricity of the 
 copper, which was reduced to 90 by the action of 
 the zinc in contact with it, will be brought to 100 
 by sharing a part of the excess which the former 
 zinc plate had acquired. This appears to be all 
 
THEORY OF GALVANISM. 
 
 the change which can be produced upon the ori- 
 ginal hypothesis of Volta ; the only fundamental 
 positions of which are, that the electrical equili- 
 brium of the two metals is destroyed by placing 
 them in contact, and that the water, when inter- 
 posed between the plates, conducts the electricity 
 so as to destroy the equilibrium. In this state of 
 things the apparatus will be nearly inert, at least 
 it will have no more power than that produced by 
 a single pair of plates ; for all the intermediate 
 ones, being in contact with water, will be brought 
 to a state of equilibrium. 
 
 Dr. Wollaston, as I have already remarked, was chemical 
 the first who decidedly pronounced the chemical yp< 
 action of the pile to be the primary cause of its 
 effects ; but in establishing this point, he did not 
 proceed to explain the nature of the operation, or 
 show what was the train of events which contri- 
 buted to the final result. This was attempted by cuthber<- 
 Mr. Cuthbertson, who, in the essay to which I s n o' n s . pl ~ 
 referred above, after pointing out the inaccuracy of 
 the experiments that were brought forward by 
 Volta in favour of the electric hypothesis, offers 
 some observations in support of the contrary opi- 
 nion. He conceives that the chemical action of 
 the interposed fluid upon the zinc alters the elec- 
 tric properties of the metal, and disposes it to part 
 with electricity ; that this evolved electricity can- 
 not enter into the remainder of the zinc which has 
 not been acted upon, because it retains its former 
 electric state, but that it is " propelled forwards 
 
 6 
 
THEORY OF GALVANISM. 
 
 from the zinc, through the menstruum, to the 
 next adjoining copper in the pile or trough." This 
 effect, however, can only happen in a progressive 
 manner, because the fluid is but an imperfect con- 
 ductor ; and to this he ascribes many of the pecu- 
 liar phenomena of the apparatus. Dr. Henry, 
 in a judicious essay, " On the Theories of the 
 Excitement of Galvanic Electricity "* observes, 
 that, " the explanation of Mr. Cuthbertson is un- 
 equivocally a valuable supplement to the theory of 
 Volta, inasmuch as it takes into account the effi- 
 ciency of chemical menstrua." But, as he farther 
 remarks, it is defective, because it does not ex- 
 plain why " the action of the menstruum is chiefly, 
 if not entirely, exerted in oxidizing and dissolving 
 the zinc plates, and why the evolution of hydrogen 
 gas, or of nitrous gas, occurs chiefly at the copper 
 surface." 
 
 The an- The first attempt which I made to explain 
 tne chemical action of the pile, was written 
 about the same time with the above remarks of 
 Mr. Cuthbertson, and may be considered, in some 
 degree, as supplying the deficiency of his hypo- 
 thesis which is noticed by Dr. Henry. I pro- 
 ceeded upon the principle which was laid down by 
 Dr. Wollaston, that electricity is evolved by the 
 oxidation of metals ; and generalized it so far 
 as to conclude, that the electric fluid is always li- 
 berated when an oxidable substance is united to 
 oxygen. In addition to this principle, I proposed 
 
 * Manchester Mem. 2d series, ii. 293. 
 
THEORY OF GALVANISM. 125 
 
 to admit the two following postulates, that the 
 electric fluid has a strong attraction for hydrogen, 
 and that when in passing through a chain of con- 
 ductors, it leaves the oxidable substance to be con- 
 veyed through water, it combines with the hydro- 
 gen, and is again disengaged from it, whenever it 
 again enters into an oxidable substance. I shall 
 again quote from the essay of the same candid 
 and judicious writer, as his account of the hypo- 
 thesis, although concise, is, at the same time, 
 perfectly correct. 
 
 " To the efficiency of the pile, two circum- Henry's ac- 
 stances are essential ; that the electric fluid should 
 be disengaged, and that it be confined and carried Fig. 5. 
 forward in one direction, so as to be concentrated 
 at the end of the apparatus. The first object is 
 fulfilled by the oxidizement of the zinc ; the se- 
 cond, as Dr. Bostock supposes, is effected by the 
 union of the evolved electricity with nascent hy- 
 drogen, and by the attraction of the next copper- 
 plate for electricity. At the surface of this plate, 
 the hydrogen and electricity are supposed to sepa- 
 rate ; the hydrogen to be disengaged in the state 
 of gas, and the electricity to be conveyed onwards 
 to the next zinc plate. Here, being in some de- 
 gree accumulated, it is extricated in larger quan- 
 tity, and in a more concentrated form, than before. 
 By a repetition of the same train of operations, the 
 electric fluid continues to accumulate in each suc- 
 cessive pair ; until, by a sufficient extension of the 
 arrangement, it may be made to exist at the zinc 
 
126 THEORY OF GALVANISM. 
 
 end of the pile, in any assignable degree of force." 
 After an interval of fifteen years, and notwith- 
 standing the succession of brilliant discoveries that 
 have been made during this period, I am not aware 
 of any fact which is adverse to the above hypothe- 
 sis, or any phenomenon which it does not explain. 
 It mvist, however, be confessed that it entirely de- 
 pends upon the assumption of two postulates, for 
 which we have no other proof except the facility 
 with which they explain the phenomena ; yet they 
 are positions which are not in themselves improba- 
 ble, and which do not seem incompatible with our 
 ordinary conceptions on the subject. 
 
 The pile A considerable part of the difficulty which has 
 electrical occurred in forming a theory of the pile, has, I 
 n"cinstnT.~ think, arisen from our not clearly discriminating 
 mem - between its effects in exciting common electricity, 
 and that modification of it which is called galva- 
 nism. I have endeavoured to point out in what 
 respect these two actions differ from each other; 
 and, imperfect as our knowledge is concerning the 
 cause, I conceive that there is an obvious difference 
 in the effect. Now it will appear that the pile, as 
 it is usually constructed, is both an electrical and 
 a galvanic instrument ; and that when we attempt 
 to form a theory of its action, we have two dis- 
 tinct sets of phenomena to explain. The power of 
 producing muscular contraction is an electrical ef- 
 fect, that of decomposing chemical bodies a galva- 
 nic effect ; while that of burning metallic leaves, or 
 igniting wires, probably partakes of both these ac- 
 
THEORY OF GALVANISM. 
 
 tions. That the electric and galvanic effects of 
 the pile bear no proportion to each other, that one 
 may exist in a great degree while the other is 
 scarcely apparent, is rendered evident from the 
 experiments of the late Mr. Singer. In examin- singer's ex- 
 ing the power of different kinds of fluids inter- P< 
 posed between the plates, he observed, that al- 
 though some of the effects were rendered more 
 powerful by employing a solution of salt, yet the 
 electrometer was not more effected than with 
 simple water. He even asserts, that in many 
 trials on a very extensive scale, for example, with 
 1000 pairs of metals, he has " found the electri- 
 cal effects greatest when the chemical effects have 
 been least." He relates other facts of a similar 
 kind, which appear to place this matter beyond all 
 doubt, and to establish a decisive difference be- 
 tween these two operations of the instrument.* 
 
 De Luc's experiments confirm and illustrate this De LUC'S 
 view of the subject ; for they not only show this 
 want of proportion between the two effects, but 
 they enable us to separate them from each other. 
 In his second dissection of the pile, we have a 
 powerful electrical instrument, but one which does 
 not produce galvanic effects ; and the same may 
 be said of his electric column, which exhibits none 
 of the phenomena that we exclusively refer to gal- 
 vanism. On the contrary, some of those combi- 
 nations which have been made by Mr. Children, 
 
 * Singer's Elem. p. 330. 
 
128 THEORY OF GALVANISM. 
 
 and other experimentalists, where a few large 
 plates were employed, and where a diluted acid 
 was interposed between them, may be considered 
 as precisely the reverse of De Luc's column. Here 
 very slight marks of common electricity were ma- 
 nifested, while the most powerful galvanic effects 
 were produced. 
 
 Proper The general conclusion that I should form on 
 
 action of the subject is, that part of the effects usually pro- 
 the pile, (Ceding from the pile are purely electrical, and do 
 not, in any degree, depend upon a chemical change 
 in the state of the metals. I conceive it to be a 
 doubtful point in what way this electrical action is 
 induced, because, for the reasons which have been 
 already given, I do not think that the experiments 
 of Volta, and the others that have been supposed 
 to coincide with them, are applicable to the state 
 of things as they exist in the pile ; nor, if we were 
 to admit them, would they account for the con- 
 tinued evolution of fresh portions of electricity ;* 
 or -explain, why the disturbance of the electric 
 fluid, or the electro-motion, as it is styled, is not 
 counteracted by the conductors that are connected 
 Galvanic with the metals. As to the proper galvanic effects 
 of the pile, I con side rthem to be always immedi- 
 ately caused by the chemical action of the fluid 
 upon the metals ; and that, in proportion to the 
 extent of this action, as depending upon the quan- 
 tity of surface exposed, or the nature of the fluid 
 
 * Davy's Elements of Chemical Philosophy, p. 174. 
 
THEORY OF GALVANISM. 
 
 employed, we obtain the evolution of electricity in 
 greater or less quantity, and in a more or less in- 
 tense state. 
 
 The great discoveries that have been made by Davy's h y - 
 Sir II. Davy, in his application of galvanism to pot 
 chemical decomposition, and the importance which 
 must attach to all his opinions upon the subject, 
 will make us anxious to inquire, what view he 
 takes of the question that has now been discussed. 
 I have already related the experiments which he 
 performed on the chemical action of the pile ; and 
 it appears that he formerly considered it as the pri- 
 mary cause of the phenomena. This opinion, 
 however, he afterwards retracted, and adopted an 
 hypothesis which he conceived might reconcile the 
 doctrine of Volta with the experiments of the 
 English chemists. He supposes, that both electri- 
 cal and chemical actions are necessarily concerned 
 in the production of the effect; that the former 
 are the first in order of time, and that their ten- 
 dency is to disturb the electric equilibrium of the 
 different parts of the apparatus, while the chemi- 
 cal changes operate in restoring this equilibrium. 
 In the farther detail of the hypothesis I shall em- 
 ploy the author's own words. " In the voltaic pile 
 of zinc, copper, and solution of muriate of soda, in 
 what has been called its condition of electrical 
 tension, the communicating plates of copper and 
 zinc are in opposite electrical states. And with 
 regard to electricities of such very low intenMty, 
 water is an insulating body ; every copper plate, 
 
 K 
 
130 THEORY OF GALVANISM. 
 
 consequently, produces by induction an increase of 
 positive electricity upon the opposite zinc plate, and 
 every zinc plate an increase of negative electri- 
 city on the opposite copper plate ; and the inten- 
 sity increases with the number, and the quantity 
 with the extent of the series. 
 
 " When a communication is made between the 
 two extreme points, the opposite electricities tend 
 to annihilate each other ; and if the fluid medium 
 could be a substance incapable of decomposition, 
 the equilibrium, there is every reason to believe, 
 would be restored, and the motion of the electri- 
 city cease. But solution of muriate of soda being 
 composed of two series of elements, possessing op- 
 posite electrical energies, the oxygen and acid are 
 attracted by the zinc, and the hydrogen and alkali 
 by the copper. The balance of power is moment- 
 ary only/, for solution of zinc is formed, and the 
 hydrogen is disengaged. The negative energy of 
 the copper, and the positive energy of the zinc, are 
 consequently again exerted, enfeebled only by the 
 opposing energy of the soda in contact with the 
 copper; and the process of electro-motion conti- 
 nues as long as the chemical changes are capable 
 of being carried on."* 
 
 This hypothesis agrees with that of Volta, in 
 ascribing the train of actions to the electric condi- 
 tion of the metals, yet it differs from it in many 
 
 * Phil. Trans, for 1807, p. 45 : and Elements of Chemical 
 Philosophy, p. 168, et alibi. 
 
THEORY OF GALVANISM. 131 
 
 essential points. It supposes the chemical Decom- 
 position of the interposed fluid to be a necessary, 
 although not the first step in the process. The 
 conducting power of the fluid is, in both cases, 
 taken into account, yet it is regarded in precisely 
 an opposite point of view. According to Volta, 
 the better is the conducting fluid, the more ener- 
 getic is the action of the pile ; while the hypothe- 
 sis of Sir H. Davy seems to require the fluid to 
 possess almost a non-conducting property. 
 
 Some of the late speculations of this illustrious Electric 
 chemist have led him to deviate still farther from el 
 the ordinary hypothesis, not only as it respects gal- 
 vanism, but electricity in general. Those effects 
 which were formerly attributed to a material 
 agent, capable of being added to, or subtracted 
 from a body at pleasure, are now conceived, like 
 gravitation, to be inherent qualities of matter. 
 To these, which are called electric energies, all che- 
 mical decompositions are to be ultimately referred ; 
 for it is supposed, that chemical attraction, in all 
 cases, results from the circumstance of two bodies 
 possessing opposite electric energies, and conse- 
 quently having a strong tendency to unite. By 
 means of the galvanic combinations, we have it in 
 our power to excite the electric state of a body to 
 an indefinite degree, and to induce an electricity 
 contrary to that which is natural to it. 
 
 At the same time, however, that Sir H. Davy 
 conceives this intimate relation to exist between 
 the natural electricity of bodies and their electric 
 
 K 2! 
 
132! THEORY OF GALVANISM. 
 
 attractions, he decidedly states his opinion that 
 they are not absolutely identical. He regards 
 them, on the contrary, as distinct phenomena, pro- 
 duced indeed by the same power, but acting in 
 one case on masses, and in the other on particles. 
 He illustrates his opinion by observing, " that the 
 primary cause of both may be the same, and that 
 the same arrangements of matter, or the same at- 
 tractive powers, which place bodies in the relation 
 of positive and negative, i. e. which render them 
 attractive or each other electrically, and capable of 
 communicating attractive powers to other matter, 
 may likewise render their particles attractive, and 
 enable them to combine, when they have full free- 
 dom of motion." * 
 
 But the farther consideration of the merits of 
 this theory belong rather to electricity than to 
 galvanism strictly so called. To whatever cause 
 we ascribe the electric state of bodies, whether to 
 a material agent distributed through them in dif- 
 ferent quantities, or to some affection of their pri- 
 mary qualities, the states of positive and negative 
 electricity actually exist, and our present business 
 is merely to inquire what relation they bear to 
 the phenomena of the galvanic pile. 
 
 De LUC'S De Luc advances an argument, which he con- 
 objections, ^veg to k e q u i te decisive, against the hypothesis 
 of the natural electric energies of bodies produc- 
 ing the phenomena of the pile, that the whole in- 
 
 * Davy's Elements of Chemical Philosophy,. p. 164- 
 
THEORY OF GALVANISM. 133 
 
 strument may |3e rendered either positive or nega- 
 tive, by connecting it with the conductor or rubber 
 of the electrical machine; and yet its operation is 
 riot in any degree affected. He also contrived an 
 apparatus, in which there were three wires placed 
 between the extremities of the pile, two of them 
 connected with the ends of the pile, and the third 
 in the centre ; the wires having water interposed 
 between them, and electrometers so situated, as to 
 ascertain the electric condition of the w^ires. In 
 the ordinary state of the apparatus, the terminal 
 ing. wires were one positive and the other negative, 
 corresponding to the ends of the pile to which they 
 were attached, while the central wire was neutral ; 
 yet the ends of this neutral wire produced opposite 
 electrical effects, one separating oxygen, and the 
 other hydrogen. By altering the apparatus, the 
 electrical state of the wires was altered ; the cen- 
 tral wire was rendered at one time positive, and 
 afterwards negative, and the state of the termin- r&s?i*iD 
 ating wires was reversed; yet no change took 
 place in the chemical action of the wires, each of 
 them continuing to evolve oxygen and hydrogen 
 as at first, and the two ends of the central wire 
 separating oxygen and hydrogen respectively at 
 its extremities, in the same manner whether the 
 Avire itself was positive, negative, or neutral.* 
 
 Mr. Singer has proposed an objection to Sir H. singer's <rt>, 
 Davy's hypothesis, very similar to this of De Luc. jet 
 
 * Nicholson's Journal, xxvi. 124-, et alibi. 
 
134 THEORY OF GALVANISM. 
 
 PLATE ii. If a number of metallic wires are placed in a line, 
 with their extremities immersed in a fluid, and the 
 whole connected with the pile, each wire will 
 evolve oxygen at one end, and hydrogen at the 
 other. Now, he conceives it impossible that every 
 wire can have an opposite electricity at its two ex- 
 tremities, when it is surrounded by a conducting 
 fluid ; for no metallic body can be made polar, i . e. 
 one end positive and the other negauve, but by the 
 temporary disturbance of the equilibrium of its na- 
 tural electricity ; an event which can only hapjren 
 when they are separated by a non-conducting s lib- 
 stance. But he observes, " No one can maintain, 
 that water, or any saline fluid or acid mixture, is a 
 non-conductor, either of the chemical or electrical 
 effects of the voltaic apparatus; yet the usual che- 
 mical changes produced by voltaic electricity occur 
 at every interruption of the metallic circuit in such 
 fluids."* 
 
 Chemical As I am disposed to think that the electric hy- 
 p thesis, under any of its modifications, is inade- 
 quate to explain the action of the pile, we must 
 substitute in its place the chemical hypothesis, 
 which supposes that the first step of the process 
 consists in the action of the fluid upon one of the 
 metals, and that the electrical, or rather the galva- 
 nic phenomena, depend upon this action. This ac- 
 tion essentially consists in the oxidation of the sur- 
 face of one of the metals, while the opposite sur- 
 
 * Elements, p. 376. 
 
THEORY OF GALVANISM. 135 
 
 face of the other metal is not affected. The posi- 
 tions upon which the chemical hypothesis rests are 
 the following : 1. One of the metals, the zinc for its funda- 
 example, is oxidated, the oxidated part has its ca- tious. p0 
 pacity of electricity diminished, and electricity is 
 consequently evolved : 2. This electricity is re- 
 ceived by the contiguous fluid, and is transmitted 
 by it to the surface of the other metal, the copper, 
 which is not oxidated, and is therefore disposed to 
 receive it, and the whole of the copper plate hence 
 becomes positive : 3. The remaining part of the 
 zinc which is not oxidated remains in its natural 
 state, and therefore, as it relates to the copper, is 
 negative : 4. The elements of the pile, which, ac- 
 cording to the electrical hypothesis, are supposed 
 to be in the order of copper, zinc, fluid, are, ac- 
 cording^to the electric hypothesis, zinc, fluid, copper; 
 the electricity passing from the zinc plate, across 
 the fluid to the copper plate : 5. The action takes 
 place, not between the metals, but between the 
 oxidated surface and the fluid ; no change would 
 therefore be produced by placing a copper plate 
 beyond the first zinc plate, or a zinc plate beyond 
 the last copper plate.* Strictly speaking, it is the 
 zinc end of the apparatus which is negative, and 
 the copper positive. 
 
 The following are the circumstances in which superiority 
 the chemical appears to explain the phenomena of nicaihy- 
 the pile more easily than the electrical hypothesis. p thesis ' 
 It shows why the action of the pile is always in 
 
 * See Lehot, Priestley, Erman, De Luc, &c, 
 
136 THEORY OF GALVANISM. 
 
 proportion to the oxidation of the metallic surface. 
 It satisfactorily explains the progressive increase in 
 the energy of the different parts of the instrument. 
 The first copper plate, in consequence of the elec- 
 tricity which it has acquired from the oxidated 
 part of the zinc, becomes positive, or, to use the nu- 
 merical illustration, is brought to the state of 110. 
 PLATE II. This state it communicates to the contiguous, 
 or second zinc plate, which also becomes 110. 
 The fluid oxidates the surface of the metal here, as 
 in the former case, but a larger quantity of elec- 
 tricity is liberated to the second copper plate, which 
 raises it to 120. According to the chemical hy- 
 pothesis, although one end of the pile becomes 
 highly positive, and is therefore disposed to com- 
 municate a portion of its redundant electricity to 
 the other end, yet this end may be considered as 
 only relatively negative, and there is no part of 
 the apparatus in a neutral state. There is no 
 tendency in any part of the apparatus to restore 
 the equilibrium of the electric fluid which is de- 
 stroyed by the oxidation of the metal. The essen- 
 tial effect is to increase the electricity of one end 
 of the apparatus, and therefore the more powerful 
 is the action of the fluid either in oxidating the 
 metals, or in conveying the electricity to the oppo- 
 site surface, the more powerful will be the effect of 
 the apparatus. This effect does not necessarily 
 depend upon the ends of the pile being united, be- 
 cause the essence of the operation consists in the 
 oxidation of one of the metals. It is, however, to 
 
THEORY OF GALVANISM. 137 
 
 be expected that the effect will be increased 
 when the extremities of the pile are united ; for 
 in this case the electricity will be powerfully at- 
 tracted towards one end of the apparatus, in order 
 to produce an equilibrium with the other end, 
 which is relatively negative. The chemical hypo- 
 thesis is not encumbered with the necessity of a 
 current of electricity from one end of the pile to 
 the other ; it only supposes the passage of the elec- 
 tricity across the interposed fluid in each individual 
 pair of metals. The chemical differs frc-m the elec- 
 trical hypothesis in the material circumstance of the 
 former pointing out a source for the liberation or 
 evolution of electricity, in consequence of a change 
 in the nature of one of these substances, which 
 diminishes its capacity for it, and therefore ren- 
 ders it less disposed than before to retain it. The 
 electrical hypothesis only contemplates an inter- 
 change of electricity between the different parts of. 
 the apparatus, one part merely acquiring what it 
 attracts from the other part, a process by which 
 there can be no absolute production of it. 
 
 The chemical differs very essentially from the Relative 
 electrical hypothesis with respect to the supposed metals/ * 
 state of the contiguous metals ; the electrical sup- 
 poses that they can have different states of electri- 
 city while they are in contact; the chemical takes it 
 for gran ted, that, while they are in contact, their elec- 
 trical states must be similar. The chemical hypo- 
 thesis satisfactorily explains all the facts that have 
 been observed, respecting the necessity of oxygen for 
 
138 THEORY OF GALVANISM. 
 
 the action of the apparatus ; it explains the rea- 
 son why the metals must differ in their degree of 
 oxidability, and why the fluid must be one that 
 will act differently upon the two metals. The 
 Nature of facts that have been noticed respecting the dif- 
 ferent effects of the interposed fluids may be ex- 
 plained by referring to three circumstances, which 
 all coincide with the chemical hypothesis, but 
 which seem to have no relation to any electrical 
 action : 1. That the fluid acts only upon one of 
 the metals : 2. That the surface of one of the me- 
 tals is oxidated with a certain degree of rapidity : 
 3. That the oxide is removed so as to present a 
 fresh surface to the fluid. If acids be employed, 
 those are the best that dissolve the oxide ; or if 
 neutral salts, those which form triple compounds 
 size of the with the oxide which is produced. The chemical 
 hypothesis affords a plausible method of accounting 
 for the different effects of the apparatus, whether 
 we use large or small plates ; for it is not unreason- 
 able to suppose that the electricity will become 
 more intense or concentrated at every successive 
 transmission through a new oxidating surface, 
 while its absolute quantity will depend upon the 
 amount of oxide that is formed. 
 
 Nature of With respect to the experiments of Bennet, and 
 STiieri-' 8 ^ ers f a s i mu<ar kind, which have been adduced 
 meats. m favour of the electrical hypothesis, it is proba- 
 ble that Volta has been mistaken in his application 
 of them, and of the principle to which they should 
 be referred. Instead of supposing, as he does, that 
 
THEORY OF GALVANISM. 139 
 
 all metals are naturally in the same state of elec- 
 tricity, and that, by being placed in contact, a 
 portion is attracted from one to the other, the facts 
 would seem to indicate that the reverse takes 
 place : and that although the electricity of each 
 individual metal is in equilibrio with the atmo- 
 sphere, yet that it is unequal with respect to each 
 other ; that zinc, for example, is negative with res- 
 pect to copper. When they are placed in con- 
 tact, their electricity is equalized; but when they 
 are again separated, the zinc, having acquired a 
 portion of electricity from the copper, becomes po- 
 sitive with relation to the atmosphere; and the 
 copper, for the same reason, negative. 
 
 The electric hypothesis of galvanism being, in Relation of 
 some measure, connected with the views which ^chemical 
 have been lately taken by Sir H. Davy, respecting affimt J- 
 the connexion between electricity and chemical 
 affinity, it may be proper to consider the grounds 
 upon which these opinions rest, and also to inquire 
 how far they affect the present question. Hisin- 
 ger and Berzelius seem to have been the first who 
 distinctly pointed out the property which the two 
 extremities of the pile possess of attracting to 
 themselves different kinds of substances ; and Sir 
 H. Davy, by a masterly train of experiments, 
 afterwards showed that this action was so power- 
 ful, as apparently to counteract the usual effects of 
 chemical affinity. Not only was a solution of a 
 neutral salt, in which the two wires terminated, 
 decomposed, and the acid attracted to the positive, 
 9 
 
140 THEORY OF GALVANISM. 
 
 and the alkali or metal to the negative wire ; but 
 the wires seemed even to possess the power of 
 attaching to themselves the acid and the alkali, 
 when other substances intervened to which they 
 each had a strong affinity. These effects were 
 attributed to the attraction of the positive wire for 
 substances containing oxygen, and of the negative 
 wire for those that contained hydrogen, or any 
 other inflammable ingredient, and Sir H. Davy 
 was induced to infer, that the former class of 
 bodies were naturally in a negative state of elec- 
 tricity, and the latter in a positive state. This 
 conclusion respecting the natural electrical condi- 
 tion of these two classes of bodies he afterwards 
 attempted to substantiate by more direct experi- 
 ments, in which the electrometer indicated the 
 negative electricity, after being in contact with 
 acids, and the positive after being in contact with 
 alkalies.* 
 
 proofs of Two distant sets of facts and experiments have 
 tion. 6 ' been brought into view, those respecting the de- 
 composition and transfer of acids and alkalies by 
 the two extremities of the pile, and those to which 
 the electrometer was applied; it is to the former 
 of these only that the present question has any 
 reference. Before we can form a correct judg- 
 ment concerning them, it will be necessary to 
 attend a little more minutely than has hitherto 
 
 * Phil. Trans, ubi supra; and Elements of Chemical Phil, 
 p. 158, et seq. 
 
THEORY OF GALVANISM. 141 
 
 been done to the electrical state of the water in 
 the interrupted circuit. When water, or any Condition 
 other conductor, is interposed between two sub- water in 
 stances that are in different states of electricity, its 
 first effect is to form a communication between cult 
 them, by means of which their electricities are 
 equalized, the water itself, as well as the two elec- 
 trified bodies, all tending to acquire the same 
 electrical condition. When the two extremities of 
 the pile are connected by the intervention of 
 water, there is, in the first instance, an attempt 
 to produce this equilibrium ; but the equilibrium 
 is no sooner formed than it is again destroyed by 
 the continual generation or evolution of electricity 
 which goes on in the body of the pile. On this 
 account the wire which was originally positive is 
 kept in that state, and the same with respect to 
 the negative wire. But the two wires being im- 
 mersed in water must have a constant tendency to 
 bring the water into the same electrical state with 
 themselves, and will, to a certain degree, accom- 
 plish it ; we may therefore conclude, that the 
 water contiguous to the positive wire is itself posi- 
 tive, and that contiguous to the negative wire 
 negative. These two portions of water must, 
 however, be continually tending to equalize their 
 electrical states with that of the remaining part of 
 the water, and the result will be, that contiguous 
 to the two wires there are two portions of water, 
 in the same, or nearly the same, electrical states 
 with the wires themselves, and that the electricitv 
 
THEORY OF GALVANISM. 
 
 diminishes in the successive portions of water, 
 until at length, in the middle of the vessel, the 
 I fluid is in a neutral state. 
 Decompo- Now if we dissolve a quantity of a neutral salt 
 in this water, we find that the acid particles dif- 
 fuse themselves through the water which is posi- 
 tively electrified, and the alkaline particles through 
 that which is negatively electrified. This is well 
 illustrated in the experiments of Sir H. Davy, 
 where the water was tinged with litmus and tur- 
 meric ; for it was found that the intensity of the 
 effect produced on the colours, and consequently 
 the quantity of acid and alkali contained in the 
 water, was greatest near the wires, and diminished 
 until it arrived at the centre, where the effect 
 ceased. The transfer of the acid to the neigh- 
 bourhood of the positive wire may, therefore, with 
 greater probability, be ascribed to its being at- 
 tracted by the positively electrified water, than to 
 the positive wire itself; for it does not attach itself 
 immediately to the wire, but it diffuses itself 
 through the water, in proportion to the electrical 
 state of its different parts. If we go farther, and 
 inquire why acids are disposed to be transferred 
 to water which is in a state of positive electricity, 
 we may, I think, conjecture, according to Sir H. 
 Davy's hypothesis, that it is owing to the attrac- 
 tion which subsists between oxygenated substances 
 and positive electricity, as the acquisition of this 
 electricity seems to be the only change which the 
 water has experienced. 
 
THEORY OF GALVANISM. 143 
 
 The opinion which is entertained by Dr. Young Young's 
 on this much agitated question, whether the pri- opin 
 mary effect of the pile be chemical or electrical, 
 although not given in a very decided manner, is, 
 I apprehend, favourable to the hypothesis which I 
 have endeavoured to defend, at least so far as re- 
 lates to the connexion between the two operations. 
 He observes, that the phenomena of galvanism are 
 piincipally derived from an inequality in the dis- 
 tribution of the electric fluid, but that it originates 
 from chemical changes. He supposes that this 
 inequality is continued in consequence of the re- 
 sistance which the electric fluid experiences to its 
 motion depending upon the alteration of sub- 
 stances of different kinds, which is conceived to 
 afford a greater resistance to its transmission than 
 would have arisen from any one of the substances 
 singly. He does not venture to determine in 
 what degree the different conducting powers of 
 the elements of the pile contribute to its action ; 
 but he conjectures that the oxidation of metals 
 may produce positive electricity, and that, on the 
 contrary, negative electricity is produced by their 
 combination with sulphur, and that these electric 
 states, when generated, may be communicated to 
 the best conductors that are contiguous to them.* 
 
 In tracing the progress of opinions, it is neces- 
 
 sary to notice the abstruse speculations of Pro- ypot 
 fessor Berzelius, which are indeed not essentially 
 
 * Lectures on Nat. Phil. i. 674. 
 
144 THEORY OF GALVANISM. 
 
 different from those of Sir H. Davy, although, as 
 being- more fully developed, and carried to a 
 greater length, they are perhaps, on this very ac- 
 count, more open to animadversion. He conceives 
 that the atoms of which bodies are composed al- 
 ways possess, what he styles, electric polarity a 
 term which is intended to express that two of 
 their opposite sides possess different states of elec- 
 tricity. Upon the intensity of these opposite elec- 
 tricities the force of chemical affinity depends, 
 which consequently becomes resolved into, or iden- 
 tified with, electric polarity. Each of the poles of 
 bodies possesses an appropriate and specific elec- 
 trical condition ; it may be so precisely balanced as 
 to leave the atom in a neutral state ; but in most 
 cases, the electricity of one pole is greater than 
 that of the other, and thus gives the body, what 
 he terms, a unipolar state, which may be either 
 electro-positive, or electro-negative, according to 
 the predominancy of the positive or negative ex- 
 tremities. It is supposed, however, that bodies 
 may combine together in consequence of their ge- 
 neral electrical intensity, as w r ell as from the at- 
 traction of the different kinds of electricity, for we 
 find that a very powerful affinity may be exercised 
 between bodies that possess the same kind of uni- 
 polarity ; and in this case the electro-chemical pro- 
 perties of the compound become the most intense, 
 because all the energy is conceived to be exercised 
 in one direction, whereas in other cases a kind of 
 neutralization takes place, in which the opposite 
 
THEORY OF GALVANISM. 145 
 
 forces destroy each other. The essential effect of 
 the galvanic pile is conceived to be that of re- 
 storing the particles that are combined together, 
 and in consequence of this combination, have their 
 electric energy partially neutralized, to their ori- 
 ginal state of intensity, or, as the author expresses 
 it, to re-polarize them.* 
 
 If we proceed upon the supposition that electri- Remarks* 
 city is the general cause of chemical affinity, we 
 must admit literally, that the primary action of 
 the pile is electrical, and that the chemical changes 
 which its component parts experience, are to be 
 regarded as an effect, and not as a cause. But 
 this reasoning applies rather to the explanation of 
 chemical affinity in general, than to what respects 
 the galvanic apparatus in particular. It would not 
 be inconsistent to regard a chemical change as the 
 immediate cause of the action of the pile, al- 
 though we might be induced to consider this che- 
 mical change, as well as all other chemical changes, 
 to be dependent upon electricity. The question 
 still remains, what is the first step in the process 
 which constitutes the essential operation of the 
 pile? Does the oxidation of the zinc depend 
 upon any previous disturbance of the electrical 
 condition of the two metals, or does the oxidation 
 of the metal produce a change in its electrical 
 condition ? This view of the subject will reduce 
 
 * Journ. de Phys. Ixxiii. 251 ; Stockholm Mem. for 1812, 
 xxxiii. 166, 223. 
 
 I. 
 
146 THEORY OF GALVANISM. 
 
 it to the same state in which it has already been 
 considered, and will therefore render it unneces- 
 sary to recur to the arguments which have been 
 previously adduced. 
 
 Oersted's An hypothesis, which in its leading features 
 s * seems very similar to that of Professor Berzelius, 
 has been more lately proposed by M. Oersted of 
 Berlin. M. Oersted, in the same manner with 
 Professor Berzelius, resolves chemical affinity into 
 the operation of two forces which are supposed to 
 be identical with the positive and negative electri- 
 cities, and which are also the immediate agents 
 in the production of the phenomena of heat and 
 light. Like Sir H. Davy, he proceeds upon the 
 general principle that chemical substances may 
 be divided into two great classes, according as 
 they possess the positive and negative electricities ; 
 that they are attracted to the end of the pile 
 which is in the contrary state to that which they 
 naturally exhibit, and that the force with which 
 they are attracted is in proportion to the intensity 
 of their positive and negative energy. Upon 
 this hypothesis M. Oersted builds a complete sys- 
 tem of chemical arrangement, classing the various 
 substances according to their supposed positive 
 and negative power, and to the intensity with 
 which they exhibit their respective energies.* 
 Into the merits of this part of the system it is not 
 my business to inquire, as it has no immediate re- 
 
 * Joura. de Phys, Ixxviii. 338. 
 
THEORY OF GALVANISM. 14 
 
 lation to galvanism. As far as respects this parti- 
 cular department of science, it will stand upon the 
 same general grounds with the hypothesis of Da\ r y 
 and Berzelius, although, for the same reason which 
 induced me to prefer the view of the subject 
 which has been taken by the former of these phi- 
 losophers, I conceive that of M. Oersted to be still 
 more objectionable, as by descending into a greater 
 variety of minute details, it becomes more in- 
 volved in difficulties and inconsistencies. 
 
 I have already had occasion to detail the obser- Biot' 
 vations of M. Biot on the two leading theories of nion * 
 galvanism, in which he estimates their respective 
 merits, and appears almost in doubt to which he 
 ought to give the preference ; but in his late 
 learned treatise on naturaj philosophy he decidedly 
 adopts the electric hypothesis. He defines galvan- 
 ism to be electricity by simple contact, and he 
 conceives that electricity is capable of being ex- 
 cited by simple contact in metals and many other 
 substances, and probably indeed in all bodies in 
 nature.* As a proof of this position he refers to 
 Volta's experiment of the zinc and copper disks ; 
 and adapting it to the hypothesis of the two elec- 
 tric fluids, which he assumes in all his specula- 
 tions, he supposes that the zinc acquires the vitre- 
 ous, and the copper the resinous electricity as a 
 consequence of their contact ; and, like Volta, he 
 conceives that this difference in their electric 
 
 * Traite de Physique, ii. 467. 
 L 2 
 
148 THEORY OF GALVANISM. 
 
 states may exist while they actually remain in con- 
 tact. He speaks of the pile under the title of an 
 electro-motive apparatus, which derives its power 
 entirely from the electric action of the two metals; 
 the interposed fluid serving merely as a conduct- 
 ing body, and its chemical action being only 
 incidental. In describing the effect of this instru- 
 ment, the oxygen is stated to proceed from the 
 vitreous and the hydrogen from the resinous pole ; 
 and he proceeds entirely upon the supposition that 
 the effect depends upon the action of the metals 
 on each other, and not upon that of the fluid 
 upon either of the metals. His arguments against 
 the chemical action of the pile may be considered 
 as summed up in the following paragraph, which 
 I give the reader in the author's own words. 
 " The connexion which we observe between the 
 oxidation and the electrical state has induced some 
 distinguished philosophers to suppose that the 
 second was an effect of the first ; and the increase 
 of action which is produced by chemical decom- 
 positions have furnished them with very powerful 
 arguments in favour of this opinion. But it 
 appears to me that the experiments of Volta on 
 the development of electricity which takes 
 place from the contact of insulated metals, can 
 leave no doubt as to the principle; and the 
 less so, because if we join to this the phenomena 
 of the transfer, there is no circumstance in the ex- 
 periments which is not perfectly explained by dif- 
 ferences in the conducting power. If the chemical 
 
THEORY OF GALVANISM. 149 
 
 decompositions acted in any way but as conductors, 
 if they gave electricity to the disks, we ought to 
 perceive this electricity when we insulate the pile, 
 and establish a communication for some time be- 
 tween the poles ; but this is not found to be the 
 case. Besides, if chemical affinity were the prin- 
 ciple of the action, it ought to be exercised in the 
 same manner whether the communication was esta- 
 blished or not between the two poles of the pile, 
 since this circumstance has no influence but upon 
 the circulation of the electricity. But we find, on 
 the contrary, that the decompositions are not car- 
 ried on with any degree of energy in the pile, ex- 
 cept the communication be established ; and when 
 it is not so, if we only employ simple saline solu- 
 tions, which are of themselves incapable of attack- 
 ing the metal, we find that there is either no oxida- 
 tion at all produced, or only a partial and extremely 
 feeble one, such as is capable of being produced by 
 the imperfect communication which is established 
 between the two poles of the pile by the mere 
 contact of the molecules of air, which slowly 
 remove the electricity which is developed at its 
 summit." * 
 
 How far the remarks of M. Biot ought to be 
 regarded as containing any valid objections against 
 the chemical hypothesis, or how far the statements 
 upon which he founds his opinions are agreeable to 
 the facts that are the best established, and that 
 
 . 
 
 * Traite de Physique, ii. 537, 
 
130 THEORY OF GALVANISM. 
 
 rest upon the best authority, those who have at- 
 tended to the subject of galvanism will be able to 
 judge. I shall not think it necessary to enter into 
 any formal refutation of his hypothesis, or of the 
 reasoning by which it is supported, as I do not 
 perceive that he has advanced any thing which has 
 not been already noticed, or that he has adduced 
 any new arguments, in addition to those that had 
 *V been brought forward by Volta himself. 
 
 The opinions which are entertained by M. Haiiy 
 an d by M. Thenard, respecting the immediate 
 cause of the galvanic action, do not materially 
 differ from each other, or from that of M Biot. 
 Like him, they believe in the existence of the two 
 electric fluids, and suppose that when the relative 
 proportion of the two fluids in one body is de- 
 stroyed by the contact or approximation of the 
 metallic plates, the phenomena of galvanism may 
 be produced, so as to refer the whole to an un- 
 equal distribution of the vitreous and resinous 
 electricity. The greater energy of the apparatus 
 when acids or saline solutions are employed instead 
 of water, Thenard, like Volta; ascribes merely to 
 their superior conducting power, and agrees with 
 him also in regarding the chemical changes which 
 take place as not essential to its operation.* 
 
 The last publication on the subject of galva- 
 ' nism which I shall have to notice, is the essay of 
 Mr. Donovan of Dublin, in which, besides many 
 
 * Haiiy, Traite de Physique, ii. 1 to 58 j Thenard, Trait 
 de Chimie, i. 19. 
 
THEORY OF GALVANISM. 151 
 
 ingenious experiments and much valuable informa- 
 tion, we are presented with a new hypothesis, not 
 only of the action of the pile, but even of the 
 nature of the principle which produces the action. 
 Mr. Donovan examines at considerable length the 
 opinion of Volta, offering very much the same kind 
 of objections against it which I had previously 
 urged ;* and he likewise regards the hypothesis of 
 electric energies to be equally inapplicable to the 
 phenomena. He states the following fact, which 
 is assumed as the basis of his hypothesis. " If a 
 piece of zinc and a piece of copper be immersed 
 in dilute nitric acid, but not in contact, they 
 effervesce and dissolve rapidly ; and oxides of zinc 
 and copper are found in the solution. Hence 
 these two metals have an affinity for the oxygen 
 of nitrous acid. If the zinc and copper be 
 brought in contact, and immersed in the dilute 
 acid, both appear to effervesce, but the zinc alone 
 dissolves." f 
 
 The conclusion which the author draws from 
 this fact is, that the copper has lost an affinity for 
 m'tric acid which it before possessed, which affinity 
 appears to be gained by the zinc ; for it must be 
 observed that the zinc dissolves more rapidly than 
 it did in the first instance, and therefore seems to 
 have acquired what the copper has lost. This 
 transfer of affinity from one metal to the other by 
 
 * Ann. of Phil. iii. 32. 
 
 t Essay on Galvanism, p. 274s 
 
THEORY OF GALVANISM. 
 
 their contact forms the foundation of the theory ; 
 it is supposed that all bodies have specific affinities, 
 which are transferable under certain circumstances, 
 and that this interchange depends upon the nature 
 of affinity itself, and is entirely unconnected with 
 any electrical action. He brings forward many 
 experiments to prove that electricity is not in any 
 case the agent which produces the phenomena of 
 galvanism, but that they may all be referred to 
 the principle of transfer. 
 
 A number of experiments are detailed on vari- 
 ous combinations of metals, to prove that the same 
 effect which takes place with respect to zinc and 
 copper may be observed in all similar cases, and 
 hence is deduced the conclusion, that " the princi- 
 ple of transferred electricity is general ; and what- 
 ever may be the attraction of any metal to oxy- 
 gen, that it is always either diminished or increased 
 by the contact of another metal ; the more oxyda- 
 ble metal acquiring the increase, and the less 
 oxydable suffering the diminution." * This hy- 
 pothesis is then applied to all the operations which 
 are usually styled galvanic, such as metallic arbori- 
 zations, the chemical effects of the pile, the effect 
 upon the muscle and nervous fibre, and other phe- 
 nomena which are more related to common elec- 
 Remarks tricity. It must, I think, be admitted that there is 
 Tan's hy " much ingenuity in many parts of Mr. Donovan's 
 reasoning, an d that he has adduced many valuable 
 
 * Essay on Galvanism, p. 285. 
 
THEORY OF GALVANISM 153 
 
 facts in its support, but still the fundamental posi- 
 tion on which the whole rests, the transfer of che- 
 mical affinity, considered as a primary cause, is 
 not easy to comprehend, unless we ascribe it to 
 the agency of some principle that must possess 
 different qu ah' ties from those that we usually as- 
 cribe to chemical affinity. I apprehend that it 
 must be regarded as a verbal, rather than as an 
 actual explanation of the fact, and that, at all 
 events, we ought not to apply it as a means of ex- 
 plaining phenomena, until we have established its 
 existence by some independent evidence. 
 
 With these remarks I shall conclude my account Concluding 
 of the theory of galvanism. It will be perceived, 
 that much discordance of opinion still exists upon 
 the subject, and that some strong objections attach 
 to every hypothesis which has yet been proposed. 
 The most important points to ascertain are, the 
 difference between electricity, as excited by the 
 friction of the common machine, and that modifi- 
 cation of it which is strictly called galvanism. 
 For this purpose, the nature of electric intensity 
 should be further investigated ; for it would appear 
 that if we were able to attach a more precise idea 
 to this term, a considerable insight would be gained 
 into the cause of this difference. Experiments 
 somewhat similar to those of De Luc should be 
 prosecuted, in which the electrical and chemical 
 effects of the pile are separated from each other, 
 and a more accurate measure of the proper galva- 
 nic power should, if possible, be obtained, than any 
 
154 THEORY OF GALVANISM. 
 
 \ 
 of which we are now possessed. The conducting 
 
 power of the fluids concerned in the galvanic appa- 
 ratus should be carefully examined, and the rela- 
 tion of their chemical action to their conducting 
 power should be ascertained. But it is unnecessary 
 to enlarge upon these topics : the rapid succession 
 of discoveries which have been made in this de- 
 partment of science, and the very general atten- 
 tion which it has obtained from the first philoso- 
 phers of the age, afford every reason to expect, 
 that the farther investigation of it will be followed 
 by no less success than that which has hitherto at- 
 tended its progress. 
 
 BESIDES the references which have been made 
 in the course of the essay, the following works 
 and papers deserve to be noticed, either as pre- 
 senting a correct view of the gradual progress of 
 the science, or as containing an abstract of the 
 hypotheses that have been brought forwards at 
 different times. 
 
 PfafTs Dissertation on Animal Electricity, 
 1793. 
 
 Monro on Animal Electricity, 1793. 
 
 Aldini on Animal Electricity, 1794. 
 
 Cavallo on Electricity, vol. iii. 1795. 
 
 Cuvier's Report, Journ. de Phys. Iii, 1801. 
 
 Hachette's Report, Journ. Poly tech. iv.1801. 
 
THEORY OF GALVANISM. 155 
 
 Biot's Report, Ann. de Chim. xli.* 
 
 Reports made by Delametherie, in several vo- 
 lumes of his journal, xli. xlvi. xlviii. 1. liv. 
 
 Sue's History of Galvanism, 1802. 
 
 Cuthbertson's Practical Electricity, 1807. 
 
 Carpue's Introduction to Electricity and Gal- 
 vanism, 1807. 
 
 Conversations on Chemistry, 5th conversation. 
 
 Article " Voltaism" in Rees's Cyclopaedia. 
 
 Article " Galvanisme," in the Diet, des Scien. 
 Med. by Halle and Nysten. 
 
 * This was the report of a commission composed of Laplace, 
 Coulomb, Halle, Monge, Fourcroy, Vauquelin, Pelletan, 
 Charles, Brisson, Sabbatier, Mourveau, and Biot. 
 
 . 
 / 
 
DESCRIPTION OF THE FIGURES. 
 
 PLATE I. 
 
 Fig. 1. The galvanic pile, as originally constructed by 
 Volta, where the letters C, Z, and F denote the plates of 
 copper and zinc, and the pieces of cloth or pasteboard soaked 
 in fluid. The pile has four rods placed round it, to keep it 
 in the perpendicular direction. The lower end was called the 
 copper and the upper the zinc end. 
 
 Fig. 2. When the number of plates is very considerable, 
 Volta divides it into two or more parts, each being connected 
 by slips of metal. In this case, it is essential that the same 
 order of parts be observed from one end to the other, up the 
 first pile, down the second, up the third, and, lastly, down 
 the fourth. 
 
 Fig. 3. This was a modification of the galvanic apparatus, 
 that was formed by Volta, which he called couronne des tasses, 
 where the zinc plates Z and copper plates C are not in con- 
 tact, but are connected by metallic rods, and then immersed 
 in a fluid. 
 
 Fig. 4-. Represents the battery of Mr. Children, which is 
 a combination of the couronne des tasses of Volta and the 
 trough of Cruickshanks. The plates are not in contact, but 
 each pair is connected by slips of metal, and the whole is at- 
 tached to a beam, so as to be lifted out of the cells at plea- 
 sure. The trough and partitions may be formed of either 
 wood or earthenware, and contain the fluid that is to act on 
 the zinc plates. 
 
 Fig. 5. Represents the trough apparatus invented by Mr. 
 Cruickshanks ; the plates of zinc and copper are soldered to- 
 gether, and are then cemented into a wooden frame, leaving 
 intervals between the double plates, to receive the fluid which 
 is intended to act upon the zinc. It is provided with wires at 
 each end, which are in opposite states of electricity, and may 
 be applied to any substance which it is proposed to subject 
 to its influence. 
 
 Fig. 6. Represents the apparatus, which was employed by 
 Sir H. Davy to exhibit the decomposition of salts, and the 
 
DESCRIPTION OF THE FIGURES. 157 
 
 transfer of their constituents, consisting of the three vessels 
 connected by amianthus. 
 
 Fig. 7. Is one of the wire-stands employed by M. De Luc 
 in his dissection of the galvanic pile. 
 
 Fig. 8. Is the apparatus for receiving in separate vessel* 
 the gases which are evolved by the action of galvanism upon 
 water. The two small jars have metallic wires inserted at 
 their upper end, one of which is connected with the positive, 
 and the other with the negative extremity of the pile. They 
 are filled with water and inverted in the same fluid ; and the 
 ends of the wires are so situated, that the gas disengaged from 
 them rises to the top of the jar. 
 
 Fig. 9. Represents the lower limbs of a frog, lying on a 
 plate of metal, while another kind of metal is placed in con- 
 tact with the spinal marrow ; these two metals are then con- 
 nected by a conducting body, and the muscles of the legs are 
 thrown into convulsions. 
 
 Fig. 10. Are the agate cups, connected by amianthus, 
 employed by Sir H. Davy in the decomposition of water; 
 and Fig. 11, are the gold cones in the same set of ex- 
 periments. 
 
 Fig. 12. Represents the apparatus in which the gases dis- 
 engaged from water may be reconverted into water by the 
 electric spark. 
 
 PLATE II. 
 
 Figs. 1, 2, 3, 4. The dissected pile employed by De Luc, 
 to illustrate the mode of its action. The shaded part re- 
 presents the moistened cloths, and the letters C and Z the 
 copper and zinc plates respectively. In Fig. 1, the pile 
 is continuous, in its usual form ; Fig. 2, is the first dissection; 
 Fig. 3, the second; and Fig. 4, the third. 
 
 Fig. 5. Is the author's numerical illustration of the effect 
 of the pile ; the letters point out the nature of the substances, 
 and the figures indicate the increase of power which the 
 electricity acquires by passing along the instrument. 
 
 Fig. 6. Is an experiment of Mr. Singer's, which is supposed 
 to disprove the hypothesis of electric energies. In this appa- 
 ratus each wire will have its ends in the opposite states of 
 electricity, one positive and the othej 1 negative. 
 
158 DESCRIPTION OF THE FIGURES, 
 
 Fig. 7. Represents the apparatus for taking the galvanic 
 spark in gases : it consists of a graduated glass tube, into 
 which two wires are introduced, the one which enters at the 
 side being moveable, and capable of being approached to the 
 other ; according to circumstances, they may be tipped with 
 pieces of charcoal, or the wires may be bare. 
 
 Fig. 8. Is a variation in the form, which may be em- 
 ployed over mercury. These instruments were invented by 
 Sir H. Davy. 
 
 Figs. 9, 10, and 11. Consist of a representation of Mr. 
 Pepys's galvanometer ; Fig. 9, is the apparatus in its complete 
 state, except that the lid is elevated a little above the mouth 
 of the glass cylinder, in order to render the description more 
 perspicuous. The lid is composed of two circular plates of 
 brass, attached to a cork, that fits into the cylinder ; a thin 
 slip of silver is fixed to the lid, the end of which hangs down 
 in the body of the cylinder and has a pair of gold leaves 
 attached to it, and the whole is so contrived as to be capable 
 of being moved nearer to, or farther from, the pieces of zinc, 
 which stand up from the bottom of the cylinder. In Fig. 10, 
 the under sicje of the co^er is seen, and also a section of it, 
 with the slip of silver adapted to it. The pieces of zinc are 
 BO contrived that the parts of them which project upwards 
 from the bottom of the cylinder may be fixed at different 
 distances from each other, by means of a slide and screw, as 
 is represented in Fig. 11. 
 
 Fig. 12. Represents the apparatus employed by M. De 
 Luc to illustrate his theory of the galvanic pile: it con- 
 sists of two piles connected by a metallic rod at the bottom ; 
 between the upper ends is interposed the interrupted wires 
 terminating in water, and to each extremity one of Bennet's 
 electrometers is applied. 
 
 Fig. 13. Represents the apparatus which Sir H. Davy 
 employed for the decomposition of salts, and the transfer of 
 their constituents. 
 
 Fig. 14. Represents the luminous arch of light produced by 
 passing the galvanic influence between two portions of char- 
 coal. 6 
 
INDEX. 
 
 J^ CID and alkali produced by galvanism, 29, 60. 
 Acid, muriatic, said to be generated by galvanism, 60. 
 Affinity, chemical, how connected with electricity, 72, 131, 
 
 139. 
 Aldini's experiments on muscular contraction, 51. 
 
 produces contractions without metals, 51 . 
 
 Alkalies, fixed, decomposition of, 74. 
 Ammonia, attempts made to decompose, 78. 
 
 , Gay-Lussac and Thenard's experiments on, 82. 
 
 Animal arc, remarks on, 18. 
 
 electricity, galvanism so named, 1, 5, 13, 52. 
 
 , modification of common electricity, 9, 
 
 11, 43. 
 
 . pile formed by Lagrave, 52. 
 
 Arborization of metals, experiments on, by Grotthus, 66. 
 
 Battery, elementary, by Wollaston, described, 98. 
 
 , galvanic, described, 92, 95, 99. 
 
 Bennet's experiments, remarks on, 138. 
 
 Berzelius's experiments on the decomposition of bodies, 59. 
 
 i hypothesis of galvanism, 14-3. 
 
 Bichat on the effects of galvanism upon the involuntary mus* 
 
 cles, 50. 
 
 Biot and Cuvier on the effect of the pile upon the air, 42. 
 Biot's observations on the size of the plates, 43. 
 
 . on the theory of galvanism, 44, 147 
 
 Bostock's observations on the action of the pile, 124. 
 Brande's observations on positive and negative bodies, 97- 
 Brugnatelli's experiments, 36. 
 Bucholtz's observations on metallic oxides, 65. 
 
 Carlisle and Nicholson's experiments on the pile, 26. 
 Chemical affinity, how connected with electricity, 72, 131, 
 
 139. 
 and electrical hypothesis of the pile compared, 
 
 135. 
 effects of galvanism first noticed by Fabroni, 19. 
 
160 INDEX, 
 
 Chemical hypothesis of the pile, 134. 
 Circaud's experiments on fibrine, 50. 
 Charcoal employed to form a pile, 33. 
 Children's battery, 92, 95, 99. 
 
 experiments, 93, 95, 100. 
 
 Cruickshanks's experiments, 29. 
 
 invents the trough apparatus, 31. 
 
 Current, galvanic, remarks on, 45, 83. 
 Cuthbertson's experiments, 47. 
 
 - observations on the action of the pile, 123. 
 
 Davy disengages gases from separate portions of water, 32, 
 
 forms new galvanic combinations, 33. 
 
 's experiments on the action of galvanism upon water, 
 
 34, 67. 
 
 _ decomposition of salts, 68. 
 
 , of alkalies and earths, 74, 78. 
 
 's hypothesis of galvanism, 72, 129. 
 
 Definition of galvanism, 1, 104. 
 Delametherie on the contraction of fibrine, 50. 
 De Luc discovers the electric column, 89. 
 
 J s experiments on the pile, 82. 
 
 . hypothesis of its action, 86. 
 
 objections to the hypothesis of electric energies, 
 
 132. 
 Desormes* experiments, 39. 
 
 pile, account of, 92. 
 
 Dessaignes* experiments, 101. 
 Donovan's hypothesis, 150. 
 
 Earths, decomposition of, 78. 
 
 Electric acid, supposed discovery of, 36. 
 
 Electrical and chemical hypothesis of the pile compared, 
 
 110, 136. 
 Electric column described, 89. 
 
 energies, what, 131. 
 
 objections against, 132. 
 intensity, in what it consists, 107. 
 polarity, Berzelius's account of, 144. 
 
INDEX. 161 
 
 Electricity, its relation to chemical affinity, 72, 131, 139. 
 
 of the machine and pile compared, 41, 106, 
 
 110, 128. 
 Erman's remarks on the ends of the pile, 45. 
 
 .- conducting power of bodies, 63. 
 
 Extremities of the pile, gases disengaged by the, 26. 
 
 remarks on their denomination, 45. 
 
 Fabroni on the chemical action of the metals, 19. 
 
 *s observations on the sensations, 21. 
 Fibrine, application of galvanism to, 50. 
 Flash, galvanic, discovery of, 9. 
 Forster's experiments on the electric column, 90. 
 Fourcroy discovers the effect of large plates, 40. 
 Fowler's experiments, 7. 
 
 thinks galvanism not electrical, 8, 
 
 discovers the flash, 9. 
 
 Frog, a delicate electrometer, 4. 
 
 Galvani's discovery, 3. 
 
 hypothesis, 6, 103. 
 
 Galvanic and common electricity compared, 80, 106, 110. - 
 electricity of low intensity, 107. 
 
 pile, discovery of, 23. 
 
 Davy's experiments with, 32. 
 
 , u_ observations on, 72, 129. 
 
 De Luc's observations on, 83. 
 
 __ , Ritter's experiments on, 55. 
 
 theory of, 112. 
 
 shock discovered, 24. 
 
 Galvanism, history of, 3, 
 
 theory of, 103. 
 
 modification of electricity, 106. 
 
 Galvanometer, Pepys's, 48. 
 Gautherot on galvanic attraction, 46. 
 Gay-Lussac's experiments, 80. 
 Grotthus on the arborization of metals, 66, 
 Guyton-Morveau on metallic oxides, 65. 
 
162 INDEX. 
 
 Hachette and Desormes* pile, 92. 
 
 Haldane's experiments, 31. 
 
 Haiiy's opinion respecting galvanism, 150. 
 
 Henry decomposes acids and ammonia, 32. 
 
 's observations upon the action of the pile, 125. 
 
 Hisinger's experiments on the decomposition of bodies, 59- 
 
 Humboldt's experiments, 14. 
 
 Icstitute of France, report by, 17. 
 Institution, Royal, galvanic battery at, 95. 
 Intensity of the galvanic pile, 107. 
 
 , Biot's remarks on, 44. 
 
 Iridium melted by galvanism, 100. 
 
 Lagrave's animal pile, 52. 
 
 Lehot on the galvanic current, 4-5. 
 
 Leyden phial charged by galvanism, 41 . 
 
 Medicine, galvanism employed in, 53. 
 Metallic leaves burned by galvanism, 39, 47. 
 solutions revived by galvanism, 30. 
 Metals, combinations of, produce galvanism, 5. 
 Morveau's experiments on metallic oxides, 65. 
 Muriatic acid supposed to be generated, 60. 
 Muscles involuntary, experiments on, 9, 11, 49. 
 Muscular contraction, experiments on, 4, 8, 10, 14, 19, 24, 
 49,51,81. 
 
 Nerves, how effected by galvanism, 10, 18. 
 Nicholson and Carlisle's experiments, 26. 
 
 *s observations on the size of the plates, 28. 
 Nysten's experiments on the involuntary muscles, 49, 
 
 Oersted's hypothesis of galvanism, 146. 
 
 Osmium melted by galvanism, 100. 
 
 Oxides, metallic, experiments on, 65. 
 
 Oxygen necessary to the action of the pile, 3J, 42. 
 
INDEX. 163 
 
 Pacchioni and Peele's experiments, 61 . 
 
 Pepys's galvanometer, 48. 
 
 PfalPs experiments, 41. 
 
 Philip employs galvanism in asthma, 53. 
 
 Pile, galvanic, discovery of, 23. 
 
 theory of, 114. 
 
 of De Luc described, 89. 
 
 of Hachette and Desormes, 92. 
 
 of Ritter, 54. 
 
 of Zamboni, 91. 
 
 Plates, size of, Biot's remarks on, 43. 
 
 Children's remarks on, 94. 
 Fourcroy's remarks on, 40. 
 Nicholson's remarks on, 28. 
 Platina wire, experiments on, 93, 95. 
 Potassium formed, 75. 
 Priestley's observations on the pile, 45. 
 
 Hitter's experiments on the galvanic pile, 55. 
 
 observations on the connexion of galvanism with 
 
 magnetism, 48. 
 
 secondary pile described, 54. 
 
 Robison's experiments on the sensations, 9. 
 
 Salts, experiments on, by Cruickshanks, 30. 
 
 decomposed by Davy, 68. 
 
 .1 remarks upon the decomposition of, 142. 
 
 Shock produced by the pile, 24. 
 
 , De Luc's observations on, 85. 
 
 Gay-Lussac's observations on, 
 
 81. 
 
 Simon's experiments on the combustion of metals, 47. 
 
 Singer's experiments, 127, 133. 
 
 Soap, Erman's experiments on, 64. 
 
 Soda supposed to be generated by galvanism, 62. 
 
 Sodium formed, 75. 
 
 Sultzer's observations on the taste, 9. 
 
 Sylvester's experiments on the production of acid and al- 
 kali, 62. 
 
164 INDEX. 
 
 Temperature, effect of, upon the pile, 101. 
 Tension, electric, Davy's remarks on, 129. 
 Thenard's experiments, 80. 
 
 opinion on the theory of galvanism, 150. 
 
 Theory of sralvanism, 103. 
 Trommsdorff burns metallic leaves, 39. 
 Trough apparatus described, 31. 
 
 tjnipolar bodies, Erman's remarks on, 63. 
 . Branded remarks on, 97. 
 
 Valli's experiments and hypothesis, 6. 
 
 Van Marum compares electricity and galvanism, 41 .. '^ 
 
 Vassali's experiments on the human body, 49. 
 Volta's experiments, 10, 23. 
 
 theory, 11, 16, 25, 46, 112. 
 
 examined, 114. 
 
 Voltaic pile (see Galvanic pile). 
 
 Water decomposed by galvanism, 26. 
 
 , its state in the interrupted circuit, 141 . 
 
 Wells's experiments, 12. 
 Wollaston's elementary battery, 98. 
 
 experiments on the chemical action of the 
 pile, 36. 
 
 Young's observations on the action of the pile, 143* 
 Zamboni's pile described, 91. 
 
 THE END. 
 
 C Baldwin, Pnnttr, 
 New Bridge-street, London. 
 
Fig I. 
 
 ig 2. 
 
 PigS 
 
 Enarav'S, ~by J~,STr 
 
 ,Hifltiiy of Galvanism- 
 
1 1 
 
 Water 
 
 120 
 
 Z 2 
 
 2LO 
 
 120 
 
 Fig 13. 
 
 T>y J Shary. for IF SoftooTc's History, trfGcdv 
 
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