Electromotive Forces in the Voltaic Cell. 155 
Moreover, he started a hypothesis to account for the action, a 
sort of impulsion or attraction of electricity by matter—an 
idea subsequently elaborated by Helmholtz. Fabroni* ob- 
jected to Volta’s explanation of his experiment. He denied 
contact force, and considered that the electricity was developed 
by chemical action. 
Then the fight began, and lasted on and off some half-century. 
On the one side were Volta, Davy, Pfaff, Péclet, Marianini, 
Buff, Fechner, Zamboni, Matteucci, and Kohlrausch. On 
the other were Fabroni, Wollaston, Parrot, Girsted, Ritchie, 
Pouillet, Schénbein, Becquerel, De la Rive, and Faraday. 
It was not all fighting: part of it resulted in a more 
thorough investigation of voltaic phenomena ; and very often 
the original point of dispute was lost sight of, and Volta’s 
fact itself was doubted in the eagerness to disprove Volta’s 
explanation. The experiments of Pfaff and Péclety, however, 
fairly well established the correctness of his observation; and 
Kohlrausch showed how, by means of a Daniell’s cell combined 
with a condenser, to measure Volta forces absolutely, thus in- 
venting a method which has been employed with modifications 
by Hankel, by Gerland, by Clifton, by Ayrton and Perry, by 
Von Zahn, and by most other experimenters on the subjectf. 
* Fabroni, Journal de Physique de l Abbé Romer, xlix. p. 348. 
+ Péclet on the Contact of Good Conductors: Comptes Rendus, 1838, 
p. 980; Poge. Ann. xlvi. 1839, p. 346; Ann. de Chim. 1842 and 1541, 
3 ser. li. p. 233. 
Pfaff, Letter to Gay Lussac: Ann. de Chim. 2 ser. xli. p. 256 (1829).— 
Pfaff: For and against the production of Electricity by Chemical Pro- 
cesses, aS a consequence of some experiments on the H.M.F. of liquids 
and metals: Poge. Ann. xli. 1840, pp. 110 and 197.—Pfaff: Experimen- 
tam crucis in favour of the Contact Theory: Pogg. Ann. lili. 1841, p. 803. 
This crux is on p. 306, and consists in substituting ZnSO, for H,SO, in 
a Grove cell, and showing that the current through a thin wire galvano- 
meter is stronger than before. This, he says, leaves no further shift or 
evasion (Ausflucht) for the chemical theory. It is a fact we have grown 
accustomed to, but it 2s rather surprising, that the E.M.F. given by ZnSO, 
should be even higher than that given by H,SO,. A convenient “‘ Aus- 
flucht” could nevertheless be provided for the chemical theory by pointing 
out that the combustion heat Zn, 2NO, is greater than Zn, SO,—H,SO, 
+2(H,NO,), if indeed the fact be so. Another shift is to talk about 
basic sulphate and the sourness of ZnSO,; another is to use the word 
“ dissociation.” 
{¢ Kohlrausch’s method consisted in bringing the plates of the two 
metals close together, connecting them by a wire for an instant, sepa- 
rating them, and putting one into connection with a Dellman electrometer, 
the other with the earth. The observation is repeated with a Daniell in 
the connecting wire, first one way, then the other. Thus three equations 
are obtained, yf’ ha, D+M/M’=k8, D—M/M'=hy; 
whence me Me Siew” # 
M/M Sets ot ge 
(Pogg. Ann. vols. lxxy. p. 88, lxxxii. pp. 1 and 40, and Ixxxviii. p. 465, 
1851 and 1853.) He gets his results much Jower than later experi- 
menters ; only } a volt for Zn/Cu, and °58 for Zn/Pt, 
M 2 
