Principles of Saturation 35 



8] COR. If AB is infinitely small, . __ 3 is infinitely great; therefore 



the repulsion of that part of the cone between A and Bb, on A , is infinitely 

 greater than the repulsion of all that beyond it. 



9] LEMMA II. By the same method of reasoning it appears, that if n 

 is equal to 3, the repulsion of the matter between Bb and Dd on a particle 



AD 

 at A, is proportional to the logarithm of -j-^; consequently, the repulsion 



of that part is infinitely small in respect of that between A and Bb, and 

 also infinitely small in respect of that beyond Dd. 



10] LEMMA III. In like manner, if n is less than 3, the repulsion of 

 the part between A and Bb on A is proportional to AB 3 ~": consequently 

 the repulsion of the matter between A and Bb, on A, is infinitely small 

 in respect of that beyond it. 



n] COR. It is easy to see from these three lemmata, that, if the 

 electric attraction and repulsion had been supposed to be inversely as 

 some higher power of the distance than the cube, a particle could not have 

 been sensibly affected by the repulsion of any fluid, except what was 

 placed close to it. If the repulsion was inversely as the cube of the distance, 

 a particle could not be sensibly affected by the repulsion of any finite 

 quantity of fluid, except what was close to it. But 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. 



12] DEF. 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, I call it immoveable: if it is able to move readily from one part 

 to another, I call it moveable. 



13] PROP. I. 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 sufficient to saturate it, was taken away, or as if the body 

 consisted only of the redundant fluid in it. In like manner an under- 

 charged 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. 



f* 



14] PROP. II. 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 



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