ELECTRICAL INDUCTION. 565 



with which each disc was charged was of both kinds, 

 each kind being present in equal quantity and both 

 therefore neutralizing one another; finally, that the 

 action of the excited glass rod was nothing else but to 

 effect a separation of the two electricities and to distribute 

 them over the discs in such a manner that by a suit- 

 able mode of procedure each kind of electricity may be 

 rendered manifest. We may, indeed, go a step farther 

 and say, every unelectric body contains both electrici- 

 ties in equal quantities. 



The term ' opposite ' electricities originates solely in 

 the fact that the two electricities neutralise one another 

 in their effects, for a positively charged body behaves 

 exactly like one charged negatively. The algebraical 

 signs 4- E and E being often taken to represent a 

 positive or a negative electric charge respectively, a 

 body in the unelectric or neutral state may in accor- 

 dance with the above conception be designated as con- 

 taining E. 



This action of an electrical body upon neutral bodies 

 at a distance, whereby it ' induces ' in them the elec- 

 trical state, is called electrical induction. The electrical 

 body and its electricity, as in our case the glass rod and 

 its positive charge, are often respectively termed the 

 * inducing body ' and the c inducing electricity,' while 

 either of the electricities separated by induction may be 

 called ' induced electricity.' 



It is not difficult to explain the phenomena observed 

 in the preceding experiments. The approach of an 

 electric body to a neutral one, that is, to a body con- 

 taining both electricities, effects their separation simply 

 because the electricity of the first body attracts that 



