ELECTRIC POTENTIAL. 15 



tricity is from the electrified to the non-electrified ball, 

 that is, from higher to lower potential, the movement 

 of the balls is mutual. 



It will also be noticed that the movement of the non- 

 electrified ball is opposite to that of the electricity. 

 Hence, while electricity moves from higher to lower 

 potential, bodies under its influence may move in either 

 direction. 



We have seen that when the two balls come into 

 contact there is a transfer of electricity from the elec- 

 trified to the non-electrified ball ; equilibrium is estab- 

 lished, and mutual repulsion follows, not only between 

 the balls, but also between them and the electrified 

 sealing-wax. 



So long as a difference of potential exists there is 

 mutual attraction ; but when equilibrium is established 

 there is mutual repulsion. The same results may be 

 produced by numerous similar experiments, in which 

 different substances and different methods may be 

 employed. Hence we deduce the following important 

 principle : 



Electrified bodies at different potentials attract, while 

 those at the same potential repel each other. 



There can be no repulsion unless there is a difference 

 of potential between the electrified bodies and their 

 surroundings. For if the surrounding bodies \vere at 

 the same potential as the electrified bodies, the repul- 

 sion would be neutralized by their reaction. Hence 

 bodies at zero potential can show no repulsion. But in 

 all cases of electrification there is a difference of poten- 

 tial created in the body, either above or below the origi- 

 nal zero. 



Indeed, attraction may account for the apparent 



