> 
TT |, eee 
ee 
Cuar. VII, § 2.] 
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. 
beseg All the preceding labours of Volta (and I do not in- 
character tend to touch on any minor ones) have evidently an 
of Volta’s intensely practical character. His aim throughout 
inventions. 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. 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 Galvani 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. 
dai, vos . II. When Galvani announced his discoveries in 
the Pip. the Bolognese Transactions in 1791,? Volta was 
—Volta’s Professor of Physics at Pavia, having been appointed 
earlypa- to that post in 1774. As has been mentioned in a 
2 stra 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 are” 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 Jowrnal 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;”* and 
also the first sentence (the letters are in French), 
His letters 
to Cavallo 
ELECTRICITY—VOLTA. 
963 
—Le sujet des découvertes, et des recherches, 
dont je vais vous entretenir, Monsieur, est l’elec- 
tricité animale.” 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 Volta re- 
with great probability to the contact of metals pro- Soler 
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 (PUCR* 
Professor John Robison (335), who first thought of yoita’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, (759.) 
1 His arguments as to the primary law of electric attractions and repulsions, are wholly inexact. His electrometer was unfitted 
for such enquiries, 
2 Vol. vii. His paper was reprinted separately at Modena in 1792. 
3 Phil hical Tr s, 1793. 
4 See the grounds of the award stated by Sir Joseph Banks. Weld, Hist. R. Society, ii., 202, 
