234 PHILOSOPHICAL TRANSACTIONS. [aNNO 1771. 



its shape or situation by the attraction or repulsion of other bodies on it: he also 

 supposes the electric fluid in these bodies to be moveable, but unable to escape, 

 unless when otherwise expressed. As for the matter in all the rest of the 

 universe, he supposes it to be saturated with immoveable fluid. He also sup- 

 poses the electric attraction and repulsion to be inversely as any power of the 

 distance less than the cube, except when otherwise expressed. 



By a canal, he means a slender thread of matter, of such kind that the 

 electric fluid shall be able to move readily along it, but shall not be able to escape 

 from it, except at the ends, where it communicates with other bodies. Thus, 

 when he says that two bodies communicate with each other by a canal, he means 

 that the fluid shall be able to pass readily from one body to the other by that 

 canal. 



' Prop. Q. If any body, at a distance from any over or undercharged body, be 

 overcharged, the fluid within it will be lodged in greater quantity near the surface 

 of the body than near the centre. For, if you suppose it to be spread uniformly 

 all over the body, a particle of fluid in it, near the surface, will be repelled towards 

 the surface by a greater quantity of fluid than that by which it is repelled from 

 it; consequently the fluid will flow towards the surface, and make it denser there: 

 moreover, the particles of fluid close to the surface will be pressed close 

 together; for otherwise, a particle placed so near it, that the quantity of redun- 

 dant fluid between it and the surface should be very small, would move towards 

 it; as the small quantity of redundant fluid between it and the surface would be 

 unable to balance the repulsion of that on the other side. 



From the 4 foregoing problems it seems likely, that if the electric attraction 

 or repulsion is inversely as the square of the distance, almost all the redundant 

 fluid in the body will be lodged close to the surface, and there pressed close toge- 

 ther, and the rest of the body will be saturated. If the repulsion is inversely as 

 some power of the distance between the square and the cube, it is likely that all 

 parts of the body will be overcharged : and if it is inversely as some less power 

 than the square, it is likely that all parts of the body, except those near the 

 surface will be undercharged. 



Corol. For the same reason, if the body is undercharged, the deficiency of 

 fluid will be greater near the surface than near the centre, and the matter near 

 the surface will be entirely deprived of fluid. It is likely too, if the repulsion is 

 inversely as some higher power of the distance than the square, that all parts of 

 the body will be undercharged: if it is inversely as the square, that all parts, 

 except near the surface will be saturated, and if it is inversely as some less power 

 than the square, that all parts, except near the surface, will be overcharged. 



Prop. 10. Let the bodies a and d (fig. 5), communicate with each other, by 

 the canal ef; and let one of them, as d, be overcharged; the other body a will 



