chap, ii.] VOLTAIC PILE. 15 



in a frame. The lower end of the pile Volta showed 

 to be charged with negative, the upper with positive 

 electricity. 



A copper wire is attached to the lower copper and 

 another to the upper zinc. These form the two poles 

 of the pile. On connecting them there is a flow of elec- 

 tricity through the wires. Volta believed the difference 

 of potential causing the current to be due to the con- 

 tact between the zinc and the copper, the moist cloth 

 playing no essential part in the process, but simply 

 acting as a conductor. It soon became evident that 

 the disengagement of electricity in the pile was not 

 due only to the contact between the lower copper disc 

 and the zinc above it, but also to chemical action, due to 

 the presence of the moist cloth between the zinc on one 

 side and the copper on the other, the acid or saline solu- 

 tion of the cloth attacking the copper and zinc unequally. 

 Thus, in the pile as originally constructed by Volta (in 

 which, beginning from below, there is a disc of copper 

 and then of zinc followed by moist cloth and again 

 copper) there is no need for the lowermost copper, 

 which acts merely as a conductor, the actual begin- 

 ning of the pile being at the second disc, viz. the 

 zinc. Similarly at the top of the original pile (which, 

 beginning from above, is as follows : zinc, copper, 

 moist cloth, zinc) it is evident that the copper, cloth, 

 and zinc form the last of the series of which the 

 pile is made, and that, therefore, the topmost zinc, is 

 useless. Thus, beginning from the insulating column 

 of glass the pile would consist of zinc, moistened 

 cloth, copper, zinc, moistened cloth, copper, in regular' 

 order to the top, the lowest disc being zinc, the 

 uppermost copper. The lower part would then be 

 charged with - , the upper with + electricity, and a 

 wire from the last zinc would be the negative pole, 

 one from the top copper the positive. 



Naturally enough the view that the development 



