398 Note 1 8: GaroenduKt early views on electricity 



He then introduces the phrase "degree of electrification" and gives a 

 quantitative definition to it, so that this, the leading idea of his whole research, 

 was fully developed at the early date of the "Thoughts." 



Several expressions which Cavendish freely used in his own notes and 

 journals, but which he avoided in his printed papers, occur in the "Thoughts." 



Thus he speaks of the "compression" or pressure of the electric fluid. 



Besides the "Thoughts," which may be considered as the original form of 

 the introduction to the paper of 1771, there is a mathematical paper corre- 

 sponding to the Propositions and Lemmata of the published paper, but following 

 the earlier form of the theory, in which the forces exerted by ordinary matter 

 are not considered, and referring directly to the " Hypotheses " of the " Thoughts. " 



The first part of this paper is carefully written out, but it gradually becomes 

 more and more unfinished, and at last terminates abruptly, though, as this 

 occurs at the end of a page, we may suppose that the end of the paper has been 

 lost. I think it probable, however, that when Cavendish had advanced so far, he 

 was beginning to see his way to the form of the theory which he finally published, 

 and that he did not care to finish the manuscript of the imperfect theory. 



The general theory of fluids repelling according to any inverse power of the 

 distance is given much more fully than in the paper of 1771, and the remarks 

 [at the beginning] on the constitution of air are very interesting. 



I have therefore printed this paper, but in order to avoid interrupting the 

 reader with a repetition of much of what he has already seen, I have placed it 

 at the end of this Note. 



CAVENDISH'S FIRST MATHEMATICAL THEORY FROM MS. BUNDLE 17. 



Let a fluid whose particles mutually repel each other be spread uniformly 

 through infinite space. Let a be a particle of that fluid; 

 draw the cone baft continued infinitely, and draw the ,j 



section bf$: if the repulsion of the particles is inversely 

 as any higher power of the distance than the cube, the 

 particle a will be repelled with infinitely more force from 



the particles between a and b/3 than from all those situated beyond it, but if 

 their repulsion is inversely as any less power than the cube, then the repulsion 

 of the particles placed beyond bfi is infinitely greater than that of those between 

 a and b/3. 



If the repulsion of the particles is inversely as the n power of the distance, 

 n being greater than 3, it would constitute an elastic fluid of the same nature 

 as air, except that its elasticity would be inversely as the n + 2 power of the 



At I ^ 



distance of the particles, or directly as the - - power of the density of the 

 fluid. 



But if n is equal to, or less than 3, it will form a fluid of a very different 

 kind from air, as will appear from what follows. 



