Faraday. 201 



atoms of bodies which are equivalent to each other in their 

 ordinary chemical action, have equal quantities of electricity 

 naturally associated with them. " But," he added, " I must 

 confess I am jealous of the term atom : for though it is very 

 easy to talk of atoms, it is very difficult to form a clear idea 

 of their nature, especially when compound bodies are under 

 consideration." 



These discoveries and ideas tended to confirm Faraday in 

 preferring, among the rival theories of the voltaic cell, that one 

 to which all his antecedents and connexions predisposed him. 

 The controversy between the supporters of Volta's contact 

 hypothesis on the one hand, and the chemical hypothesis of 

 Davy and Wollaston on the other, had now been carried on 

 for a generation without any very decisive result. In Germany 

 and Italy the contact explanation was generally accepted, under 

 the influence of Christian Heiririch Pfaff, of Kiel (b. 1773, 

 d. 1852), and of Ohm, and, among the younger men, of Gustav 

 Theodor Fechner (b. 1801, d. 1887), of Leipzig,* and Stefano 

 Marianini (b. 1790, d. 1866), of Modena. Among French writers 

 De La Eive, of Geneva, was, as we have seen, active in support 

 of the chemical hypothesis; and this side in the dispute had 

 always been favoured by the English philosophers. 



There is no doubt that when two different metals are put 

 in contact, a difference of potential is set up between them 

 without any apparent chemical action ; but while the contact 

 party regarded this as a direct manifestation of a "contact- 

 force " distinct in kind from all other known forces of nature, 



* Johaim Christian Poggendorff (b. 1796, d. 1877), of Berlin, for long the editor 

 of the Annalen der Physik, leaned originally to the chemical side, but in 1838 

 became convinced of the truth of the contact theory, which he afterwards actively 

 defended. Moritz Hermann Jacobi (b. 1801, d. 1874), of Dorpat, is also to be 

 mentioned among its advocates. 



Faraday's first series of investigations on this subject were made in 1834 : 

 Exp, es., series viii. In 1836 De La Kive followed on the same side with his 

 Eccherches sur la Cause de V Electr. Voltaique. The views of Faraday and De La 

 Rive were criticized by Pfaff, Revision der Lehre vom Galvanistntts, Kiel, 1837, and 

 by Fechner, Ann. d. Phys., xlii (1837), p. 481, and xliii (1838), p. 433 : translated 

 Phil. Mag., xiii (1838), pp. 205, 367. Faraday returned to the question in 1840, 

 Exp, Jtes., series xvi and xvii. 



