118 THEORY OF GALVANISM. 



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 experiment which we have related above, it 

 was only the projecting parts of the plates that 

 could be made to exhibit the opposite electric 

 states. And it appears that a very general mis- 

 conception has prevailed on the subject, and that 

 almost all writers have confounded the state of 

 approximation with that of contact. The experi- 

 ments of Bennet and Cavallo have been adduced 

 as analogous to those of Volta, and Sir H. Davy 

 expressly designates Yolta's hypothesis as an ex- 

 tension or generalization of these experiments, re- 

 marking that Bennet had proved, that bodies 

 brought into contact, and again separated, exhibited 

 different states of electricity.* Volta himself has 

 clearly fallen into the same error ; for in the expe- 

 riments which are related in his letter to Delame- 

 therie, he examined the metals separately, after 

 they had been in contact, and draws his inference 

 from this examination.! Yet these experiments 

 do not apply to the circumstances of the pile, 

 where the metals have an extensive communica- 

 tion with each other, and where, from this circum- 

 stance, it is probable that, while they remain in 



* Phil. Trans, for 1807, p. 32. 



-) Nicholson's Journ. 8vo. i. 136, &c. ; Henry's Elements, 

 i. 248; Murray's Chemistry, i. 581. See also Haiiy, Traite 

 de Physique, ii. 15, &c.; Biot, Traite de Physique, ii. 471 ; 

 and Ann. de Chim. xlvii. 8. 



