^6j[ LECTURE LIII. 



its distribution, and the attractive and repulsive effects exhibited by it, under 

 different forms. Supposing a quantity of redundant fluid to exist in a- 

 spherical conducting body, it will be almost wholly collected into a minute 

 space contiguous to the surface, while the internal parts remain but little 

 overcharged. For we may neglect the actions of the portion of fluid which 

 is only occupied in saturating the matter, and also the etlJect of the matter 

 thus neutralised, since the redundant fluid is repelled as much by the one 

 as it is attracted by the other; and we need only to consider the mutual 

 actions of the particles of this superfluous fluid on each other. It may then 

 be shown, in the same manner as it is demonstrated of the force of gravita- 

 tion, that all the spherical strata which are remoter from the centre than any 

 given particle, will have the whole of their action on it annihilated by the 

 balance of their forces, and that the effective repulsion of the interior strata 

 will be the same, as if they were all collected in the centre. This repulsion 

 will, therefore, impel the particles of the fluid towards the surface, as long 

 as it exists, and nothing will impede the condensation of the redundant fluid 

 there, until it is exhausted from the neighbourhood of the centre. In the same 

 manner it may be shown, that if there be a deficiency of fluid, it will be only 

 in the external parts, the central parts remaining always in a state of neu- 

 trality: and since the quantity of electric fluid taken away from a body, in 

 any common experiment, bears but a very small proportion to the whole 

 .that it contains, thedeflciency will also be found in a very small portion of the 

 sphere, next to its surface. And if, instead of being spherical, the body be 

 of any other form, the effects of electricity will still be principally confined 

 to its surface. This proposition was very satisfactorily investigated by Mr. 

 Cavendish; and it was afrerwards more fully shown, by Dr. Gray's experi- 

 ments, that the capacities of different bodies, for receiving electricity, depend 

 much more on the quantity of their surfaces, than on their solid contents: 

 thus, the conductor of an electrical machine will contain very nearly or quite 

 as much electricity if hollow as if solid. 



■ If two spheres be united by a. cylindrical conducting substance of small di- 

 mensions, there will be an equilibuum, when the actions of the redundant 

 fluid in the spheres,on the whole fluid in the cyliuderjare equal; that is, uhtn 

 both the spheres have their surfaces electrified in an equal degree: but if the 

 length of 'the cylinder is consid&iable, the fluid within it.caa only remain at 



