ELECTRICAL MEASUREMENT. 427 



the result agreed within, if I remember rightly, 

 one-half per cent, of Cavendish's measurements. 

 When I mention these cases of the measurement 

 of electrical force by Coulomb and Robinson, which 

 has led to the true law of force and of the 

 measurement of electrostatic capacity, a subject 

 which is the least known generally, and held to be 

 the most difficult, I have said enough to show 

 that we must not in this century claim all the 

 credit of being the founders of electrical measure- 

 ment. 



The other chief method of experimenting 

 in connection with measurement to which I 

 have referred is illustrated also by Cavendish's 

 writings, that is the adjustment to a zero. It is 

 very curious, that while Coulomb and Robinson 

 by direct measurement of a continuously varying 

 quantity discovered the law of the inverse square 

 of the distance, Cavendish, quite independently, 

 pointed out by very subtle mathematical reasoning 

 that the law must either be the inverse square 

 of the distance, or must vary in a determinate 

 manner from the law of the inverse square of the 



