THEORY OF GALVANISM. 



before noticed, and decidedly claims to himself the 

 discovery of it. 



In the letter to Delametherie, written after the 

 discovery of the pile, Volta still farther develops 

 his hypothesis, but without altering the ground on 

 which it rests. He describes each pair of metals 

 as the efficient part of the apparatus, and speaks 

 of the fluid that is interposed between them as 

 merely carrying the electricity from one pair to 

 another, without producing any change in it. In 

 his letter to Van Marum, he relates the following 

 fundamental experiment, as it is called : a plate of 

 copper and a plate of zinc are placed in contact 

 with each other, but so that a part of each plate 

 projects beyond the other ; and he finds, that of 

 the parts which thus project, one becomes positive 

 and the other negative. So far all these opinions 

 appear to be consistent with each other ; but in 

 the letter written to Gren, an idea is brought for- 

 ward, which is not noticed in the other essays, and 

 which seems to be essentially different from them. 

 All conductors of electricity are divided into two 

 classes, the dry and the moist ; and electricity is 

 supposed to be always excited, when two con- 

 ductors of either of these classes are placed in con- 

 tact with one conductor of the other class. In this 

 way one metal only would appear to be sufficient 

 for a galvanic combination, provided there be two 

 moist conductors in contact with it. How the 

 fluids act in this case, or what relation they bear 

 to each other and to the metal, we are not exactly 



