68 



ELEMENTS OF STATIC ELECTRICITY. 



Fig. 13 Spheres in Contact. 



ELECTRIFIED SPHERES. Let two insulated metal 

 spheres, of equal size and similarly charged, be placed 

 in contact, as represented in Fig. 13. It is evident that 

 either .of them, separately, would fulfill the conditions 



just named; but 

 when placed in con- 

 tact, they must be re- 

 garded as one mass, 

 having its center at 

 the point of contact ; 

 the electric distribu- 

 tion being the same 

 on each. 



Hence the forces 

 of induction and re- 

 pulsion which before acted to remove electricity from 

 the center of the single sphere to the parts most remote 

 from it that is, to the surface now act in the same 

 manner, to remove electricity from this new center to 

 those parts of the mass most remote, that is, to the 

 points A and B, and the surfaces surrounding them. 



There must also be a certain amount of electricity 

 distributed over the entire surface of each sphere ; and 

 there must be repulsion between the surfaces adjacent 

 to the point of contact : so that the charge will be zero 

 at this point, and increase each way toward A and B. 



This may be demonstrated by touching the points 

 A, B, and C with the proof plane, and, after each con- 

 tact, bringing it near the disc of the electroscope ; 

 taking care to discharge it with the finger before mak- 

 ing the next test. 



It will be found that the central point shows scarcely 

 a trace of electricity, while the points A and B are 



