i 
2 
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GALVANISM. 
. published in different scientific journals. His first com- 
munication was in a letter to Cavallo; the second to 
Gren, (Phil. Trans, 1793; Ann. de Chim. xxiii. 276.) : 
- both written before his discovery of the pile. His ori- 
» ginal account of this apparatus is contained in a letter 
_ to Sir Joseph Banks, in which he explains his ideas re- 
specting its action; and. he afterwards farther develo- 
them in letters to Delametherie and to Van Marum, , 
( Phil. Trans..1800 ; Nicholson's Journal, 8vo, i. 135 ; 
Ann. de-Chim, xl. 225.) In some of these papers, Volta 
details his hypothesis at considerable length ; yet, after 
an attentive examination of them, it appears to us that 
-are not altogether consistent with each other ; 
that, without any intimation of the circumstance, 
he has, in fact, given to the world two distinct hypo- 
theses. 
. The letter written to Cavallo, of which we have al- 
ready given some account, is Volta’s first essay on the 
subject of galvanism, and contains an account of Gal- 
vani's original discovery, and of the additional experi- 
ments. which he had himself performed by the combi- 
nation of the two metals. He accounts for all the facts 
on the principle, that when metals are placed in cer- 
tain circumstances with r to each other, there is 
‘¢a destruction.of the equilibriam” of the electricity. 
This action is stated to consist essentially in two me- 
tals, 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 this electro-motive fa- 
culty much more po lly than others; those that 
Galvani and: Volta originally employed were zinc. and 
silver ; and in this case the zinc acquired the electrici- 
ty and became positive, while the silver lost electrici- 
- ty or became-negative. In this paper no other prin- 
is referred to, and the-action is net spoken of as 
belonging to any class of bodies except the metals. 
Volta speaks of the principle as a new law of electrici- 
pe which had not been before noticed, and decidedly 
ims to himself the discovery of it. . 
. In the letter to Delametherie, written after the dis« 
covery of the pile, Volta still farther developes his hy- 
: is, but without altering. the d on which it 
-rests. He describes cach pair of metals as the efficient 
part of the apparatus, and speaks of the fluid that is in- 
terposed between them, as merely carrying the electri- 
city from one pair to another, without. producing. any 
: 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 con- 
tact with other; but so that a‘ part of each plate 
projects beyond the other ; and he finds, that of the 
parts which thus prajects one becomes positive and the 
other negative. far all these opinions appear to be 
eonsistent with each. other ; but in the letter written to 
Gren, an idea is brought forward, 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 
‘ is supposed to be always excited, when two 
conductors 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 
agalvanic combination, provided. there be two moist 
conductors in contact with it. How the fluids act in 
. this case, or what relation bear to each other and 
to the metal, we are not 'y informed ; but we may 
Aonclude, that it is not from any chemical operation, 
»  WOks X. PART I, beaters : 
97 
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 con- General 
ceives the electricity to be excited by the metals pro- 
ducing a degree of electro-motion, or by destroying the 
natural equilibrium of the, electricity ; one metal thus 
becoming positive and the other negative, they each of 
them exhibit signs of electricity to an electrometer or 
other similar instrument. The only use of the fluid is 
to transfer the electricity which is excited by one pair 
of metals to the next pair; and although a chemical ac« 
tion 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 hypothes 
effécts of the pile are, as he supposes, merely inciden- 
tal.. They seem, indeed, absolutely essential to its ac- 
tion, 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 obtaining a 
supply of oxygen, it ceases to act. The same thing 
happens when the acid, or other oxidating fluid, is all 
expended ; and in short it may be stated, that whatever 
romotes 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. It has been urged as an objection: to Volta’s 
hypothesis, 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. Whatever 
deficiency of electricity there was in any copper-plate-: 
would be instantly supplied by the water communica-~ 
ting the superabundant electricity of the opposite zine 
plate, so thatthe effect of the whole would be reduced: 
simply to the difference between the twe extreme plates 
of copper and zinc, A third, and:perhaps a stillstrenger 
argument against the. electric hypothesis, is,. that the- 
fundamental position on which it rests, is itself objec. 
tionable. Volta supposes that two metals, as for ex- 
ample, a plate of zinc-and one of copper, when placed: 
in extensive contact with each other, may become re- 
spectively positive and negative. This he endeavours 
to prove by direct experiment; but it will be found that 
in nene of the cases is the experiment precisely in 
point. He adduces some facts, where metals were 
found respectively positive and negative, that had been 
in 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 ex- 
periment which we have related:above, it was only the 
projecting parts of the plates-that could be made to ex~ 
ibit the opposite electric states. And here we may be 
allowed to entertain some doubt respecting the accu- 
racy of the fact; it is evidently an experiment of a 
most delicate nature, and Mr Cuthbertson, who at- 
tempted: to repeat it, obtained results. contrary to those 
™ 
is are-very. forcible ; Opjections 
in the first place, it.does not appear that the chemical to it. 
