252 ' PHILOSOPHICAL TRANSACTIONS. [aNNO 1771. 



repulsion is inversely as the square of the distance. It should also seem from 

 those experiments, that the quantity of redundant or deficient fluid in two bodies, 

 bore very nearly the same proportion to each other, whatever is the shape of the 

 canal by which they are joined, or in whatever direction they are situated in 

 respect of each other. 



Though the above propositions should be found not to hold good, when the 

 bodies are joined by real canals, still it is evident, that in the 22d proposition, if 

 the plates ab and dp are very near together, the quantity of redundant fluid in 

 the plate ab will be many times greater than that in the body h, supposing h to 

 consist of a circular plate of the same size, as ab, and df will be nearly as much 

 undercharged as ab is overcharged. 



Sir Isaac Newton supposes that air consists of particles which repel each other 

 with a force inversely as the distance: but it appears plainly from the foregoing 

 pages, that if the repulsion of the particles was in this ratio and extended indefi- 

 nitely to all distances, they would compose a fluid extremely diffierent from com- 

 mon air. If the repulsion of the particles was inversely as the distance, but 

 extended only to a given very small distance from their centres, they would com- 

 pose a fluid of the same kind as air, in respect of elasticity, except that its density 

 would not be in proportion to its compression : if the distance to which the re- 

 pulsion extends, though very small, is yet many times greater than the distance 

 of the particles from each other, it might be shown, that the density of the fluid 

 would be nearly as the square root of the compression. If the repulsion of the 

 parts extend indefinitely, and was inversely as some higher power of the distance 

 than the cube, the density of the fluid would be as some power of the compres- 

 sion less than 4. The only law of repulsion, Mr. C. can think of, which will 

 agree with experiment, is one which seems not very likely; namely, that the 

 particles repel each other with a force inversely as the distance ; but that, whe- 

 ther the density of the fluid is great or small, the repulsion extends only to the 

 nearest particles : or, what comes to the same thing, that the distance to which 

 the repulsion extends, is very small, and also is not fixed, but varies in propor- 

 tion to the distance of the particles. 



Part II. Containing a Comparison of the Foregoing Theory with Experiment, 



§ 1 . It appears from experiment, that some bodies suffer the electric fluid to 

 pass with great readiness between their pores ; while others will not suffer it to 

 do so without great difficulty; and some hardly suffer it to do so at all. The 

 first sort of bodies are called conductors, the others non-conductors. What 

 this difference in bodies is owing to; Mr. C. does not pretend to explain. It is 

 evident that the electric fluid in non-conductors may be considered as moveable, 

 or answering to the definition given of that term immediately before prop. 1» 



