THEORY OF GALVANISM. 135 



face of the other metal is not affected. The posi- 

 tions upon which the chemical hypothesis rests are 

 the following : 1. One of the metals, the zinc for its funda- 

 example, is oxidated, the oxidated part has its ca- tious. p0 

 pacity of electricity diminished, and electricity is 

 consequently evolved : 2. This electricity is re- 

 ceived by the contiguous fluid, and is transmitted 

 by it to the surface of the other metal, the copper, 

 which is not oxidated, and is therefore disposed to 

 receive it, and the whole of the copper plate hence 

 becomes positive : 3. The remaining part of the 

 zinc which is not oxidated remains in its natural 

 state, and therefore, as it relates to the copper, is 

 negative : 4. The elements of the pile, which, ac- 

 cording to the electrical hypothesis, are supposed 

 to be in the order of copper, zinc, fluid, are, ac- 

 cording^to the electric hypothesis, zinc, fluid, copper; 

 the electricity passing from the zinc plate, across 

 the fluid to the copper plate : 5. The action takes 

 place, not between the metals, but between the 

 oxidated surface and the fluid ; no change would 

 therefore be produced by placing a copper plate 

 beyond the first zinc plate, or a zinc plate beyond 

 the last copper plate.* Strictly speaking, it is the 

 zinc end of the apparatus which is negative, and 

 the copper positive. 



The following are the circumstances in which superiority 

 the chemical appears to explain the phenomena of nicaihy- 

 the pile more easily than the electrical hypothesis. p thesis ' 

 It shows why the action of the pile is always in 



* See Lehot, Priestley, Erman, De Luc, &c, 



