On the comparison of charges 127 



redundant fluid in B was more or less than sufficient to saturate the re- 

 dundant matter in the trial plate, by making a communication between 

 them by a piece of wire; for if the redundant fluid in B was more than 

 sufficient to saturate the redundant matter in the trial plate, they would 

 both be overcharged after the communication was made between them; 

 if, on the other hand, the redundant fluid in B was not sufficient to saturate 

 the redundant matter in the trial plate, they would be undercharged. 

 Having by these means found what size the trial plate must be made so 

 that the redundant matter in it should be just sufficient to saturate the 

 redundant fluid in B, I tried the body b in the same manner, and if I 

 found that it required the trial plate to be of the same size, in order that 

 the redundant matter in it should be just sufficient to saturate the re- 

 dundant fluid in b, I was well assured that if B and b were successively 

 made to communicate with a third body and positively electrified they 

 would each of them contain the same quantity of fluid, supposing the 

 quantity of redundant fluid in the third body to be the same each time; 

 that is, that the charge of B was equal to that of b. 



Having thus given a general idea of the method I used, I proceed to 

 describe it more particularly. 



239] The trial plates I made use of consisted of two flat tin plates 

 ABCD and abed (Fig. 15), made to slide one upon the other, so that by 



making the side be of one plate extend more or less beyond the side BC 

 of the other it formed a plate of a greater or less size, and which conse- 

 quently contained more or less electricity*. 



240] The apparatus used in making these experiments is represented 

 in Fig. 14, where the parallelogram T represents the trial plate and B one 

 of the bodies to b compared together, each supported on non-conductors. 

 dDS is the wire for making a communication between them, having a 



* [See table for trial plate at Art. 468.] 



