ELECTRICITY. 477 



a plate of glass or of iron placed between them, they 

 will still repel each other, as if there was no intervening 

 object. If one is resinously, and the other vitreously 

 electrified, they will attract each other notwithstanding 

 the intervention of the plate. 



3. Theory of the discharge of the electric fluids. Let 

 us suppose two brass balls to be charged, one with the 

 vitreous, and the other with resinous electricity. Let 

 both of them be suspended by silken threads, at the dis- 

 tance of several inches from each other. The silken 

 thread is a non-conductor, the air around the balls is a 

 non-coriductor, and the vitreous electricity of the one 

 ball, and the resinous electricity of the other, though they 

 have a strong tendency to come together, into their origi- 

 nal union, yet they cannot pass through the intervening 

 space, for both balls are surrounded by non-conductors ; 

 or in the technical language, they are insulated. If now, 

 a wire is brought into contact with both the balls, a con- 

 nexion will be formed, for the wire being a conduc- 

 tor, the two fluids can pass across it and thus become 

 united, and diffused in their natural state of union, over 

 both the balls. 



4. Theory of induction of electricity. If a ball vitre- 

 ously electrified and suspended by a silken thread, so as 

 to be insulated, that is, surrounded by non-conductors, IB 

 brought near to the extremity of a brass rod, in its natu- 

 ral state, but suspended by a silken thread, the vitreous 

 electricity of the ball will repel the vitreous electricity 

 which is in the nearest extremity of the rod. This vitre- 

 ous electricitv will pass consequently to the other extremi- 

 ty. The ball, however, besides repelling the iritreous 

 electricity will attract the rtsinons electricity of the rod 

 to the end nearest itself; for it was stated above, that vi- 

 treous electricity attracts the resinous, as well as repels 

 the vitreous. The rod then, through the influence of the 

 ball, will have its resinous electricity collected at the ex- 

 tremity nearest the ball, and its vitreous electricity driven 

 back to the extremity farthest from it. Thus the ball, 

 by its presence merely, will electrify the rod, throwing 

 the two extremities into opposite states. This corres- 

 ponds evidently with the theory, and is always found to 



VOL. i. NO. xx. 42* 



