124 



ELEMENTARY LESSONS ON [CHAP. in. 



where the dissimilar metals touched one another, and 



upon the plates of 

 the condenser the op- 

 posite charges have 

 accumulated. When 

 the upper plate is 

 lifted off the lower 

 one, the capacity of 

 the condenser dimin- 

 ishes enormously, and 

 the small quantity of 

 electricity is now able 

 to raise the potential 

 of the plates to a 

 higher degree, and 

 the gold leaves ac- 

 cordingly expand. 1 



15O. The Voltaic 

 Pile. The second of 

 Volta's proofs was less 



Fig. 68. 



direct, but even more convincing ; and consisted in 

 showing that when a number of such contacts of dis- 

 similar metals could be arranged so as to add their 

 electrical effects together, those effects were more power- 

 ful in proportion to the number of the contacts. With 

 this view he constructed the apparatus known (in honour 

 of the discoverer) as the Voltaic Pile (Fig. 69). It 

 is made by placing a pair of discs of zinc and copper 

 in contact with one another, then laying on the copper 

 disc a piece of flannel or blotting-paper moistened with 

 brine, then another pair of discs of zinc and copper, and 

 so on, each pair of discs in the pile being separated 



1 Formerly, this action was accounted for by saying that the electricity 

 which was "bound" when the plates of the condenser were close together, 

 becomes "free" when the top plate is lifted up; the above is, however, a 

 more scientific and more accurate way of saying the same thing. The 

 student who is unable to reconcile these two ways of stating the matter 

 should read again Articles 47, 48, on pp. 53 to 55. 



