169 



entire surface ; he further gives some new experiments on induction, 

 with a view of proving that when one surface is opposed as it were 

 to itself, as in the case of the interior surface of a sphere, the induc- 

 tive susceptibility of one-half the surface is reduced to zero. The 

 phenomena of what the author calls, after Cavendish, electrical 

 charge, he refers to some peculiar arrangement or disposition of the 

 electrical particles on the surfaces of the several conductors, by which 

 they exhibit a greater or less degree of excitement, as observable by 

 the electrometer. 



The remaining portion of this paper is devoted to the laws and 

 phenomena of electrical attractive force. The attractive force of a 

 given surface ixnder a given charge does not depend on the quantity 

 of electricity, but on the number of attracting points called into 

 operation by what is usually considered as the attracted body. Two 

 circular discs of very light wood, of 5 inches diameter, being care- 

 fully prepared in a lathe, were divided into six concentric rings, 

 including a central plate of about an inch in diameter. The attract- 

 ive force on each pair of rings was determined by means of the 

 electrical balance and carefully noted ; the force was as the several 

 opposed areas ; and when the series was combined into one plate, the 

 force was the sum of the forces of the respective rings; when the 

 attractive forces of circular plates equal in area to the several rings 

 respectively were examined, the force was the same as that exhibited 

 by the two rings whose area was the same ; hence it is inferred that 

 whether the charge operates from the circumference or near the 

 centre, the attractive force is the same. Two rings combined exhibit 

 forces equal to the sum of the forces taken separately ; and when 

 the force is examined between the plates or the several rings and a 

 plane circular area of large and continuous surface, the forces are no 

 greater than that between two plates or rings of equal area. When 

 the distances between the attracting surfaces or the quantities of the 

 electrical accumulation varied, then the force was as the square of the 

 accumulation directly, and as the square of the distances inversely. 



The author extends these experiments to spheres of different 

 diameters. He had shown in a former paper, that, taking the attract- 

 ive force to be as the areas directly, and as the squares of the 



distances inversely, according to the expression F cc v, two points 



