CHAP. VII., 2.] 



ELECTRICITY VOLTA. 



165 



(746.) 

 Practical 

 jharacter 

 jf Volta's 



.nventioiis. 



(747.) 

 History of 

 the Pile 

 Volta'8 

 sarly pa- 

 pers on 

 galvanism. 



His letters 

 to Cavallo. 



is tested by mixing the latter in known proportions 

 with hydrogen in a close vessel through which an 

 electric spark can be passed. Detonation takes 

 place, and the quantity of gas which has vanished (by 

 conversion into water) measures the amountof ogygen 

 which has combined with hydrogen in the experi- 

 ment. It was for a long period employed as by far 

 the best means of testing the purity of air. 



All the preceding labours of Volta (and I do not in- 

 tend to touch on any minor ones) have evidently an 

 intensely practical character. His aim throughout 

 was to improve the instrumental means of detecting 

 and measuring electricity, and to detect and measure 

 it as it occurred in practice, rather than to form theo- 

 ries of its nature. 1 Even the discovery of galvanism, 

 which vividly excited his interest, only partially di- 

 verted him from his scientific destiny. Volta will 

 indeed be always remembered as the author of the 

 plausible theory of electro-motion, and as having 

 corrected the too exclusive doctrine of G-alvani con- 

 cerning the sources of electric excitement ; but his 

 real claim to immortality is the invention of the Pile. 

 To this part of the history we therefore proceed. 



II. When Galvani announced his discoveries in 

 the Bolognese Transactions in 17 9 1, 2 Volta was 

 Professor of Physics at Pavia, having been appointed 

 to that post in 1774. As has been mentioned in a 

 former section, the announcement of these researches 

 excited the immediate attention of electricians and 

 anatomists in every part of Europe. Of course Italy 

 was not exempted from the general impulse. In that 

 country physiological observations have always been 

 prosecuted with interest and success ; and indeed it 

 has never been deficient in persons of ability, whether 

 in physical or in purely mathematical enquiries, since 

 the very dawn of letters, at which time Italy made so 

 distinguished a figure in literary progress. Volta, 

 Aldini, Valli, and Spallanzani were all, at the time 

 of which I now speak, actively engaged in the 

 pursuit of science; and Galvani's opinion that the 

 commotion of the frog by the connection of the 

 muscle and nerve through a " conducting arc " of 

 metal was due solely to animal electricity, was gene- 

 rally adopted, and by none more cordially than by 

 Volta in a letter and memoirs published in Brug- 

 natelli's Journal early in 1792. These were speedily 

 followed by two letters to Cavallo, dated October of 

 the same year, and communicated to the Royal So- 

 ciety of London, in acknowledgement, as the author 

 states, of the honour recently done him of electing 

 him an Honorary Fellow. The title of this com- 

 munication deserves notice, " Account of some 

 Discoveries made by Mr Galvani of Bologna, with 

 Experiments and Observations on them ;" 3 and 

 also the first sentence (the letters are in French), 



the 



"Le sujet des decouvertes, et des recherches, 

 dont je vais vous entretenir, Monsieur, est Velec- 

 tricite animate." In the course of the paper, how- 

 ever, he distinctly states that whilst he agrees with 

 Galvani in considering that the convulsions of the 

 frog, obtained with homogeneous conductors, are 

 due to a proper animal electricity ( 12, 16), the 

 more powerful effects occasioned by the contact of 

 unlike metals are caused by " common electricity " 

 developed at the junction, and having the nature, not 

 of a discharge, but of a continued stream. He re- 

 peats and modifies Galvani's experiments on animals, 

 cold and warm-blooded, and makes interesting ob- 

 servations on the excitement of the nerves of taste 

 and sight by the contact of unlike metals. The con- 

 clusion of his paper is in opposition to its earlier 

 portion. He expresses a grave doubt whether there 

 be any vital electricity in the matter. 



The induction of Volta was imperfect in this, that (748.) 

 he did not prove that the effects which he attributed v< ? lta re- 

 with great probability to the contact of metals pro- 

 duced any other recognised electric effect than the phy- Medal. 

 siological ones. Galvani had gone very nearly as far. 

 He had even hesitated between the terms animal 

 electricity and electricity of metals ; he had considered 

 the frog as a very sensitive electrometer, exactly as 

 Volta did ; and the manner of so using and applying 

 it is ascribed by the latter in this memoir to Galvani, 

 who having thus invented the instrument which 

 for years served alone to indicate the presence of the 

 new species of electricity and having also described 

 accurately the influence of the heterogeneous metals 

 in aiding the results left to Volta only the credit of 

 the assertion that in some instances the effect was 

 due to the metals themselves, in others to the natural 

 electricity of the animal frame. Under these cir- 

 cumstances, I think that the award of the Copley 

 Medal by the Royal Society to Volta, rather than to 

 Galvani, was a questionable decision : the great va- 

 lue of Volta's paper, at the time, was undoubtedly 

 that it directed the attention of English experimen- 

 ters to Galvani's discoveries, then quite recent and 

 probably imperfectly known. * 



Many publications followed. I shall only notice (749.) 

 that by Dr Fowler of Edinburgh (afterwards of Salis- Robison's 

 bury), which is remarkable as containing a letter by ^J c ^ a " 

 Professor John Robison (335), who first thought of Volta's 

 increasing the effect of heterogeneous contact by using pile. 

 " a number of pieces of zinc made of the size of a shil- 

 ling, and making them up into a rouleau with as 

 many shillings." We have here unquestionably the 

 first idea of the pile, which moreover was actually 

 constructed. This was in May 1793. It was only 

 applied, however, to excite the nerves of the senses. 



In various scattered memoirs, from 1793 to 1796, (750.) 



1 His arguments as to the primary law of electric attractions and repulsions, are wholly inexact. His electrometer was unfitted 

 for such enquiries. 



a Vol. vii. His paper was reprinted separately at Modena in 1792. 3 Philosophical Transactions, 1793. 



4 See the grounds of the award stated by Sir Joseph Banks. Weld, Hist. R. Society, ii., 202. 



