226 PHILOSOPHICAL TRANSACTIONS. [aNNO 1771. 



as the repulsion is supposed to be inversely as some power of the distance less 

 than the cube, a particle may be sensibly affected by the repulsion of a finite 

 quantity of fluid, placed at any finite distance from it. 



Definitim. If the electric fluid in any body, is by any means confined in such 

 manner that it cannot move from one part of the body to the other, Mr. C. 

 calls it immoveable: if it is able to move readily from one part to another, he 

 calls it moveable. 



Prop. 1. — A body overcharged with electric fluid attracts or repels a particle 

 of matter or fluid, and is attracted or repelled by it, with exactly the same force 

 as it would, if the matter in it, together with so much of the fluid as is sufii- 

 cient to saturate it, was taken away, or as if the body consisted only of the 

 redundant fluid in it. In like manner an undercharged body attracts or repels 

 with the same force, as if it consisted only of the redundant matter; the electric 

 fluid, together with so much of the matter as is sufficient to saturate it, being 

 taken away. — This is evident from the definition of saturation. 



Prop. 1. — ^Two over or undercharged bodies attract or repel each other with 

 just the same force that they would, if each body consisted only of the redundant 

 fluid in it, if overcharged, or of the redundant matter in it, if undercharged. — 

 For, let the two bodies be called a and b : by the last proposition, the redundant 

 substance in b impels each particle of fluid and matter in a, and consequently 

 impels the whole body a, with the same force that the whole body b impels it: 

 for the same reason the redundant substance in a impels the redundant substance 

 in B, with the same force that the whole body a impels it. It is shown there- 

 fore, that the whole body b impels t^he whole body a, with the same force that 

 the redundant substance in b impels the whole body a, or with which the whole 

 body A impels the redundant substance in b ; and that the whole body a impels 

 the redundant substance in b, with the same force that the redundant substance 

 in A impels the redundant substance in b. Therefore the whole body b impels 

 the whole body a, with the same force with which the redundant substance in a 

 impels the redundant substance in b, or with which the redundant substance in 

 B impels the redundant substance in a. 



Coral. Let the matter in all the rest of space, except in 2 given bodies, be 

 saturated with immoveable fluid ; and let the fluid in those 2 bodies be also im- 

 moveable. Then, if one of the bodies is saturated, and the other either over or 

 undercharged, they will not at all attract or repel each other. If the bodies are 

 both overcharged, they will repel each other. If they are both undercharged, 

 they will also repel each other. If one is overcharged and the other undercharged, 

 they will attract each other. 



N. B. In this corollary, when Mr. C. calls a body overcharged, he would be 

 understood to mean, that it is overcharged in all parts, or at least no where un- 



