42 ELEMENTS OF STATIC ELECTRICITY. 



The friction of the same rubber is also greater on 

 a substance like sealing-wax, whose surface is soon soft- 

 ened by the heat generated, than on a smooth, hard sub- 

 stance like glass, which is not affected in this way. 



And, as already shown, difference of potential produces 

 attraction, while equality of potential produces repulsion, 

 between bodies. Hence the attraction by the sealing- 

 wax, of the pith ball electrified by the glass, is a neces- 

 sary result of difference of potential ; while its repul- 

 sion by the glass follows from equality of potential. 

 And the same will be true of the ball electrified and re- 

 pelled by the wax and attracted by the glass. 



But if a difference exists in the kind of electricity 

 produced by the different classes of substances, we 

 should expect that difference always to manifest itself 

 whenever one of either class is employed as a generator. 



But this is only true in a general way, to which the 

 exceptions are very numerous ; for it often happens that 

 glass and sealing-wax, or other substances belonging to 

 the different classes, when rubbed with the same rubber, 

 exhibit the same electric qualities. The same result 

 also will often follow \vhere different kinds of rubbers 

 are employed, as silk on one substance and woolen on 

 the other. 



Such results are inconsistent with the theory of two 

 electricities ; but are easily accounted for by a differ- 

 ence, or an equality of potential, which we know is 

 liable to exist. 



Hence, preference must be given to the doctrine of one 

 electricity, originally proposed by Franklin ; simple and 

 plain, like truth itself, and in strict accord with all elec- 

 tric phenomena ; whether pertaining to static electric- 

 ity, or to electricity under other forms. 



