ELECTRICITY IN EQUILIBRIUM. 



different bodies, for receiving electricity, depend much more on 

 flit quant ty of their surfaces, than on their solid cont<-nt> : thus, 

 the conductor of an electrical machine will contain very nearly or 

 quilt- as much electricity if hollow as if solid. 



If two spheres be united by a cylindrical conducting substance, 

 of small dimensions, there will be an equilibrium, when the actions 

 of the redundant fluid in the spheres, on the whole fluid in the 

 cylinder, are equal ; that is, when both the spheres have their 

 surfaces electrified in an equal degree : but if the length of the 

 cylinder is considerable, the fluid within it can only remain at 

 rest when the quantities of redundant fluid are nearly equal m 

 both spheres, and consequently when the density is greater in the 

 smaller. And, for a similar reason, in bodies of irregular forms, 

 the fluid is always most accumulated in the smallest parts; and 

 when a conducting substance is pointed, the fluid becomes so dense 

 at its extremity, as easily to overcome the forces which tend to 

 retain it in its situation. 



In this distribution we find a very charisteristie difference be. 

 tween the pressure of the electric fluid, and the common hydro. 

 static pressure of liquids, or of simple elastic fluids ; for these 

 rxrrt on every surface, similarly situated, a pressure proportionate 

 to its magnitude ; but the electric fluid exerts a pressure on small 

 niul angular surfaces, greater, in proportion to their magnitudes, 

 than the pressure on larger parts : so that if the electric fluid were 

 in general confined to its situation, by the pressure of the atmo. 

 sphere, that pressure might easily be too weak to oppose its escape 

 from any promr-.ent points. It ('oes not appear, however, that 

 this pressure i> (1 e only cause which prevents the escape of the 

 electric fluid , nor is jr. certain that this fluid can pass through a 

 perfect vacuum, although it has not yet been proved, that a body 

 placed in a vacuum is perfectly insulated. Whatever the resist- 

 ance n.ny be, which prevents the dissipation of electricity, it is 

 always the more easily overcome, as the electrified substance is 

 more pointed, and as the point is more prominent; and even the 

 presence of dust is often unfavourable to the success of eh ctncal 

 experiments, on account of the great number of pointed termina- 

 tions which i( affords. 



The getu-ral effect of electrified bodies on euch other, if their 

 bulk is small in comparison with their distance, is, that they are 

 mutually repelled when in similar states of electricity, and at. 



