Capacities of bodies of similar forms 141 



the case will be the same with bodies of any other shape ; secondly, that 

 the charge of any thin plate is very nearly the same whatever its thickness 

 may be, provided its thickness is very small in respect of its breadth or 

 smallest diameter ; and there can be no doubt also but what this will hold 

 good in thin plates of any shape, though it was tried only with square 

 ones ; and thirdly, if the plate is square and its thickness is several times 

 less than its side, though not small enough to be disregarded, its charge 

 is equal to that of a very thin square plate whose side exceeds that of the 

 former by about i^ of its thickness. 



This last circumstance seems far from being repugnant to the theory; 

 but as I do not know how to calculate the charge of such a plate within 

 tolerably near limits, I shall not trouble the reader any further about it. 



273] EXP. V. This experiment was made with a view to find what 

 proportion the charges of similar bodies of different sizes bear to each 

 other, and whether it is the same that it ought to be by the theory on a 

 supposition that the electric attraction and repulsion is inversely as the 

 square of the distance, and that the bodies are connected to the jar by 

 which they are electrified by canals of incompressible fluid. It was tried 

 by taking two circular tin plates of 9 inches diameter, and comparing the 

 charge of these two circles together with that of one of twice the diameter. 

 The circles were placed in a vertical situation, and were disposed as in 

 Fig. 18, where the letters D, 8, m, T, M,N, a, A, S and R stand for the 



Fig. 18. 



same things as in Fig. 17. Bb and Cc are the two small circles placed 

 parallel to each other, which, as they are in a vertical situation, appear 

 in the plan as straight lines. Rf and Rg are the wires by which they are 

 electrified, which are bent near /and g so as to enable them to rest on the 

 edges of the circles. Dd is the wire for making a communication between 



