44 First published Paper on FJectricity 



38] Though the four foregoing problems do not immediately tend to 

 explain the phaenomena of electricity, I chose to insert them; partly 

 because they seem worth engaging our attention in themselves ; and partly 

 because they serve, in some measure, to confirm the truth of some of the 

 following propositions, in which I am obliged to make use of a less accurate 

 kind of reasoning. 



39] In the following propositions, I shall always suppose the bodies 

 I speak of to consist of solid matter, confined to the same spot, so as not 

 to be able to alter its shape or situation by the attraction or repulsion of 

 other bodies on it: I shall also suppose 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, I shall suppose it to be 

 saturated with immoveable fluid. I shall also suppose the electric attrac- 

 tion and repulsion to be inversely as any power of the distance less than 

 the cube, except when otherwise expressed. 



40] By a canal, I mean 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 I say that two bodies communicate with each 

 other by a canal, I mean that the fluid shall be able to pass readily from 

 one body to the other by that canal*. 



41] PROP. IX. If any body at a distance from any over or under- 

 charged body be overcharged, the fluid within it will be lodged in greater 

 quantity near the surface of the body than near the center. 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: more- 

 over, 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 redundant 

 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 four 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 together, 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 over- 

 charged: 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. 



* [Note 3, p. 365.] 



