134 Experiments on the Charges of Bodies 



with the same strength when the balls are to separate positively as when 

 they are to separate negatively, as otherwise a small error will arise in 

 finding the required surface of the trial plate. 



254] In all the following experiments I took care to proportion the 

 size of the bodies B and & in such manner that the quantity of redundant 

 fluid in one should not be very different from that in the other, so that, 

 though the deficience of fluid in the trial plate should not be very nearly 

 as the square root of its surface, it would make very little error in the 

 conclusion. 



255] The usual distance of the centers of B and J in these experiments 

 was 83 inches, the distance of B from the vial A 106 inches, and that 

 of T from a 86 inches, and the distance of the two vials about 10 inches*. 

 The usual height of the body B and the trial plate above the ground was 

 50 inches ; they were commonly supported upon pillars such as are repre- 

 sented in Fig. 16, where Ee, Bb and Dd are three upright pillars of baked 



wood about 40 inches long, and ee, 6,8, and d8 are sticks of glass 10 inches 

 long and J inch thick let into the wood, and covered with sealing-wax. 

 ACGF is a piece of board which the pillars are fastened into. The points 

 M, N, R, and S were each supported by a pillar of the same kind, and the 

 point D was supported nearly in the same manner. In some experiments, 

 however, the body B was suspended by silk strings. The wires dD8, rRSs, 

 and mMNn were about T ' T inch thick. 



256] It is well known that the air of a room is easily rendered over- 



or undercharged, in particular if a wire such as rRSs [Fig. 14] is positively 



* [See plan at Art. 265, details at Art. 466, and theory in Note 17.] 



