454 INDUCTION. 



they will be attracted by any other oppositely charged body. 

 In like manner the hand, if brought near enough to the con 

 ductor, receives or gives an electric discharge; now we have 

 no evidence that a charged conductor can be suddenly dis 

 charged unless by the approach of a body oppositely electri 

 fied. In the case, therefore, of the electric machine, it appears 

 that the accumulation of electricity in an insulated conductor 

 is always accompanied by the excitement of the contrary elec 

 tricity 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 neigh 

 bourhood of an electrified body. As one remarkable instance 

 we have the Leyden jar; and after the splendid experiments 

 of Faraday in complete and final establishment of the substan 

 tial identity of magnetism and electricity, we may cite the 

 magnet, both the natural and the electro-magnet, in neither of 

 which it is 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 oppositely elec 

 trified poles complete within itself. In the voltaic circuit, 

 again, we cannot have one current without its opposite. In 

 the ordinary electric machine, the glass cylinder or plate, and 

 the rubber, acquire opposite electricities. 



From all these instances, treated by the Method of Agree 

 ment, a general law appears to result. The instances embrace 

 all the known modes in which a body can become charged with 

 electricity ; and in all of them there is found, as a concomitant 

 or consequent, the excitement of the opposite electric state in 

 some other body or bodies. It seems to follow that the two 

 facts are invariably connected, and that the excitement of elec 

 tricity in any body has for one of its necessary conditions the 

 possibility of a simultaneous excitement of the opposite elec 

 tricity in some neighbouring body. 



