ELECTROMOTIVE FOllCES IN THE VOLTAIC CELL. 



465 



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that these views are af,'roed with, thoy may yet servo as links with which 

 to connect tho facts and the multifarious observations thereon. 



1. Tn the course of my reading on the subject, I have found only two 

 ijreat and epoch-making papers, that of Volta in 1801, and that of Sir 

 William Thomson in 1851. Other contributions aro some of tlioni 

 keen, like those of Faraday and Clerk Maxwell ; some of them laborious, 

 like those of Hankel and Ayrton and Perry ; but none contain anything 

 essentially and powerfully new except those two : unless indeed wo 

 include in the subject the immensely important phenomena of Seebock 

 and of Peltier, and Faraday's fundauiental law of electro-chemical decom- 

 position. 



Volta ' showed that when two motals were put into contact and sepa- 

 rated, the insulated ono was charged with electricity sufficient to make 

 gold leaves diverge. He also stated that the contact force between any 

 two metals was independent of intermediate metals, so that tho metals 

 could bo arranged in a delinite numerical series; and ho gave tho flrst 

 .series of the kind — 



/nw,_.Pbw^Sn^^Fe-^^Cu-^^Ag. 



5 1 1 2 l; 



Moreover he started a hypothesis to account for tho action, a sort of im- 

 pulsion or attraction of (ilectricity by matter — an idea subsequently elabo- 

 rated by Helmholtz. Fabroni "^ objected to Volta's explanation of h's ex- 

 jieriment. Ho denied contact force and considered that the electricity 

 was developed by chemical action. 



Then tho Qght began, and lasted on and off some half-century. On 

 the one side were Volta, Davy, PfatF, Peclet, Marianini, Buff, Fechner, 

 Zamboni, Matteucci, and Kohlrausch. On the other wore Fabroni, 

 Wollaston, Parrot, G']rsted, Ritchie, Pouillet, Schcinbein, liecquerel, Do 

 la Hive, and Faradaj'. 



It was not all fighting : part of it resulted in a more thorough investi- 

 gation 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 PfaflF and Peclet,* 

 however, fiiirly well established the correctness of his observation, and 

 Kohlrausch showed how, by mciins of a Daniell's cell combined with a 

 oonden.ser, to measure Volta forces absolutely, thus inventing a method 

 which has been employed with modifications by Hankel, by Gerland, by 



' Volta: (>'rhlcr''s mii'tcrhielt, iv. filC. See .ilso a carefully edited version 

 Aiiiuilrs tir ('him. xl. 1 .'<or.. p 225, 1801. 



^ Fahnmi : Jouriitil dc Physique de Vahhe. liozicr, xlix. .^48. 



' i'Lt'lc't ( 111 t lio contact of good cnnductor.s. — Coiiipfiit lloidus, 1 838, p. 930. — Pogg. 

 Ann. xlvi. 18;!1», p. 34G. Ann. de Clilm. 1842 and 1841, 3 ser. ii. 233. 



I'fatf, letter to Gay Lussac— J/i« de (1itm.2 ser. xli. 23(i, 1829. TfatT.— ' For 

 and ajjainst tho produotion of K. by chemical processes, as a conso<)ucnce of some 

 t'xpcrinieiits on the K.M.F. of liqnids and metals.'— iV)/7y. Anu. xli. 1840, pp. 110 and 

 l'J7. I'fatr — ' K.xperimentnm crucis in favour of tlie contact theory.' — Pogg. liii. 1841, 

 ]!. .W3. This crux is on ]>. 30(5, and consisis in snbstitutinj.' Zn80, for IL.SO^ in a Grove 

 •I'll, and showing' that the current through a thin wire •,'alvanomeicr is stronfrcr than 

 befure. Tiiis, \w says, leaves no further shift or evasion (.Ausllucht) for the chemical 

 theory. It is a fact wo have grown accustomed to, but it i» rather surprising that 

 'lie E..M.F. triven by ZnS04 should be even higher than that given by H^fSOi. A con- 

 venient ' Austiueht ' could novertlieles.s be provided for the chemical theory by pointing 

 nut that the combustion heat Zi ,2N0, is greater than Zn,SO^-II..,SO, + 2(H,N03), if 

 indeod the fact be so. Another shift is to talk about basic sulphate and the sourness 

 oE ZnSO, : another is to use the word ' dissociation.' 



1H81. H H 



