THEORY OF GALVANISM. 115 



some of these papers Volta details his hypothesis 

 at considerable length ; yet, after an attentive 

 examination of them, it appears to me that they 

 are not altogether consistent with each other ; and 

 that, without any intimation of the circumstance, 

 he has, in fact, presented to the world two distinct 

 hypotheses. 



The letter written to Cavallo, of which I have 

 already given some account, is Volta's first essay 

 on the subject of galvanism, and contains an ac- 

 count of Galvani's original discovery, and of the 

 additional experiments which he had himself per- 

 formed by the combination of the two metals. He 

 accounts for all the facts on the principle, that 

 when metals are placed in certain circumstances 

 with respect to each other, there is " a destruction 

 of the equilibrium " of the electricity. This action 

 is stated to consist essentially in two metals, 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 possess this electro-motive 

 faculty much more powerfully than others ; those 

 that Galvani and Volta originally employed were 

 zinc and silver ; and in this case the zinc acquired 

 the electricity and became positive, while the silver 

 lost electricity or became negative. In this paper 

 no other principle is referred to ; and the action is 

 not spoken of as belonging to any class of bodies 

 except the metals. Volta speaks of the principle 

 as a new law of electricity, which had not been 



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