Second method of experiment 1 5 5 



together I prepared two trial plates, which I shall call L and /, not coated 

 as that above described, but in the usual way, namely, with the coatings 

 of the same size on both sides*. 



The first of these plates, or L, was of such a size that when used as 

 a trial plate with the plate B or b on the other side, the quantity of de- 

 ficient fluid in it was rather more than ought to be in order that the pith 

 balls should just separate negatively, and the second plate I was rather 

 greater than it ought to be in order that they should just separate posi- 

 tively. 



I also prepared a sliding plate of the same kind as the trial plate used 

 in the former method, but whose charge was many times less than that 

 of the plate B or b. This sliding plate I placed along with the plate B or b 

 on the side N, and on the other side I placed the trial plate L and found 

 what size it was necessary to give to the coating of the sliding plate in 

 order that the balls should just separate negatively. I then removed the 

 plate B and put b in its room, and found what sized coating it was necessary 

 to give to the sliding plate in order that the balls should separate the same 

 as before. Having done this, I removed the trial plate L and put / in its 

 room, and tried each of the plates B and b as before, finding what coating 

 it was necessary to give to the sliding plate that the balls might just 

 separate positively. 



Having done this, if I found that it required the coating of the sliding 

 plate to be of the same size in order to exhibit the same phenomena in 

 trying the plate B as in trying b, it is plain that the charges of B and b 

 must be both alike, but if I found that it was necessary to give less surface, 

 one square inch for instance, to the coating of the sliding plate in trying B 

 than in trying b, then it is plain that the charge of B exceeds that of b 

 by a quantity equal to that of the charge of the sliding plate when its 

 surface is one square inch, supposing, as is very nearly the case, that the 

 charge of the sliding plate is in proportion to the surface of its upper 

 coating. 



In this way of trying the experiment, it is plain that, in order to 

 determine the proportion which the charges of B and b bear to each other, 

 we must first know what proportion the charge of the sliding plate, when 

 its coating is of a given size, bears to that of B. This I found by finding 

 what sized coating must be given to the sliding plate that its charge should 

 be equal to that of another plate, the proportion of whose charge to that 

 of B I was acquainted with. 



It is plain that, if it is necessary to give one inch less surface to the 

 coating of the sliding plate in trying B than in trying b when the trial 

 plate L is made use of, it will be necessary to make the same difference 

 in the surface of the sliding plate when the trial plate / is made use of, 



* [Art. 457.] 



