428 POPULAR LECTURES AND ADDRESSES. 



distance if in a certain case, which he defined, 

 either a perfect zero of electric force is observed, 

 or if instead of a perfect zero any particular amount 

 of electric force is observed. It is quite clear from 

 Cavendish's writings that he believed that perfect 

 zero would be found when the experiment should 

 be made, but with a caution characteristic of the 

 man and also proper to his position as an accurate 

 philosopher and mathematician he never would 

 state the law absolutely. He had that scrupulous 

 conscientiousness which prevented him from guess- 

 ing at the conclusion at which no doubt he himself 

 had arrived. His mind was probably a great deal 

 quicker than are many other minds in which the con- 

 clusion is jumped at and given as if it were proved, 

 but he conscientiously avoided stating it as a 

 conclusion, and held it over until exact measure- 

 ment should prove whether or not it was justified 

 by experiment. 



The subject of measurement in this case of the 

 null method pointed out by Cavendish was this. 

 If in the interior of a hollow electrified conductor 

 the electrostatic force upon a small insulated 



