486 INDUCTION. 



either of the conductors, they become electrified with 

 the opposite electricity to it; either receiving a share 

 from the already electrified atmosphere by conduction, 

 or acted upon by the direct inductive influence of the 

 conductor itself: they are then attracted by the con- 

 ductor to which they are in opposition; or, if with- 

 drawn in their electrified state, they will be attracted 

 by any other oppositely charged body. In like 

 manner the hand, if brought near enough to the 

 conductor, receives or gives an electric discharge ; 

 now we have no evidence that a charged conductor 

 can be suddenly discharged unless by the approach of 

 a body oppositely electrified. In the case, therefore, 

 of the electrical machine, it appears that the accu- 

 mulation of electricity in an insulated conductor is 

 always accompanied by the excitement of the contrary 

 electricity in the surrounding atmosphere, and in 

 every conductor placed near the former conductor. 

 It does not seem possible, in this case, to produce one 

 electricity by itself. 



Let us now examine all the other instances which 

 we can obtain, resembling this instance in the given 

 consequent, namely, the evolution of an opposite 

 electricity in the neighbourhood of an electrified body. 

 As one remarkable instance we have the Ley den jar ; 

 and after the splendid experiments of Faraday in 

 complete and final establishment of the substantial 

 identity of magnetism and electricity, we may cite 

 the magnet, both the natural and the electro- magnet, 

 in neither of which is it possible to produce one kind 

 of electricity by itself, or to charge one pole without 

 charging an opposite pole with the contrary electricity 

 at the same time. We cannot have a magnet with 

 one pole : if we break a natural loadstone into a 

 thousand pieces, each piece will have its two oppo- 



