PROGRESS OF ELECTRICAL THEORY. 29 



matter, the principal facts of excitation and the 

 like receive a tolerably satisfactory explanation. 



The theory of ^Epinus, however, still required to 

 have the law of action of the particles of the fluid 

 determined. If we were to call to mind how mo- 

 mentous an event in physical astronomy was the 

 determination of the law of the cosmical forces, the 

 inverse square of the distance, and were to suppose 

 the importance and difficulty of the analogous step 

 in this case to be of the same kind, this would be to 

 mistake the condition of science at that time. The 

 leading idea, the conception of the possibility of ex- 

 plaining natural phenomena by means of the action 

 of forces, on rigorously mechanical principles, had 

 already been promulgated by Newton, and was, 

 from the first, seen to be peculiarly applicable to 

 electrical phenomena; so that the very material 

 step of clearly proposing the problem, often more 

 important than the solution of it, had already been 

 made. Moreover the confirmation of the truth of the 

 assumed cause in the astronomical case depended 

 on taking the right law ; but the electrical theory 

 could be confirmed, in a general manner at least, 

 without this restriction. Still it was an important 

 discovery that the law of the inverse square pre- 

 vailed in these as well as in cosmical attractions. 



It was impossible not to conjecture beforehand 

 that it would be so. Cavendish had professed in 

 his calculations not to take the exponent of the 

 inverse power, on which the force depended, to be 



