PROGRESS OF ELECTRICAL THEORV. 27 



a confirmation appeared in a number of the most 

 obvious cases; and to these, Cavendish added others, 

 which, though not obvious, were of such a nature that 

 the calculations, in general difficult or impossible, 

 could in these instances be easily performed; as, for 

 example, cases in which there are plates or globes 

 at the two extremities of a long wire. In all these 

 cases of electrical action, the theory was justified. 

 But in order to give it full confirmation, it was to 

 be considered whether any other facts, not imme- 

 diately assumed in the foundation of the theory, 

 were explained by it ; a circumstance which, as we 

 have seen, gave the final stamp of truth to the 

 theories of astronomy and optics. Now we appear 

 to have such confirmation, in the effect of points, 

 and in the phenomena of the electrical discharge. 

 The theory of neither of these was fully understood 

 by Cavendish, but he made an approach to the 

 true view of them. If one part of a conducting 

 body be a sphere of small radius, the electric fluid 

 upon the surface of this sphere will, it appears by 

 calculation, be more dense, and tend to escape more 

 energetically, in proportion as the radius of the 

 sphere is smaller; and, therefore, if we consider a 

 point as part of the surface of a sphere of imper- 

 ceptible radius, it follows from the theory that the 

 effort of the fluid to escape at that place will be 

 enormous; so that it may easily be supposed to over- 

 come the resisting causes. And the discharge may 

 be explained in nearly the same manner ; for when 



