564 ELECTRICAL INDUCTION. 



they are charged, positive electricity is communicated 

 to an electrical pendulum with insulating suspension 

 (silk) by touching it with a rubbed glass rod; repeat- 

 ing the experiment, the disc a will be repelled by the 

 pendulum, and the disc b will be attracted ; in other 

 words, a is positively charged and b negatively. 



The experiment being repeated several times, the 

 fact will be established beyond doubt, that if two 

 metallic discs are in contact, and near an electric body, 

 they will become charged with opposite electricities, 

 provided, first, that they are separated by a small dis- 

 tance after the electrical body has been brought near 

 them, and second, that after their contact has ceased 

 the electrical body is removed. If after removal of the 

 excited glass rod the two metallic discs are allowed to 

 touch one another and then tested with the conducting 

 pendulum, neither of them will manifest a trace of 

 electricity. 



These experiments show how two bodies may be 

 charged with opposite electricities, and the last experi- 

 ment proves the important fact that equal quantities of 

 opposite electricities neutralise one another; or in other 

 words, bodies which contain equal quantities of both 

 electricities behave exactly like unelectric bodies. 



No electricity has in these experiments been directly 

 communicated by the glass rod to the discs; the mere 

 approach of the excited glass rod was sufficient to pro- 

 duce opposite electrical states in them, and we are 

 therefore justified in conceiving that each of the discs 

 was in fact, previous to the approach of the glass rod, 

 charged with electricity, but in such a manner as to be 

 incapable of manifesting it; further, that the electricity 



