

Affect of floor and walls of the room 109 



tnMNn is inversely as the distances of their centers from m, and the increase of the 

 quantity of redundant fluid in the circles Bb and Cc by the attraction of T is in 

 the same proportion. 



Therefore take the point a so that the repulsion of a particle at a on that canal 

 shall be a mean between the repulsions of the same particle thereon when placed 

 at B and C, the charge of T will be increased in the same proportion as it would be 

 by the repulsion of a plate containing as much redundant fluid as the two plates 

 together whose center was a, and the charge of the two circles together will also be 

 increased in the same proportion as that of the circle whose center is a would be 

 thereby. 



192] Consequently, in trying either the large circle or the two small ones, 

 the trial plate must be opened to very nearly the same surface to contain the 

 same charge as them as it must be if they were placed at an infinite distance 

 from the trial plate, and consequently no sensible alteration can be produced 

 in the phsenomena of the experiment by the repulsion and attraction of the 

 circles and trial plate on each other. 



193] Thirdly, for the same reason it appears that as the circles and the trial 

 plate are both at much the same distance from the ground and walls of the room, 

 no sensible alteration can be produced in the experiment by the ground near 

 the circles being rendered undercharged and that near the trial plate over- 

 charged. 



It must be observed, indeed, that the distance of the circles and trial plate 

 from the ground is much less than their distance from each other, and conse- 

 quently the alteration of the charge of the two circles and trial plate produced 

 by this cause will not be so nearly alike as that caused by their attraction and 

 repulsion on each other; but as, on the other hand, the whole alteration of their 

 charge produced by this cause is, I imagine, much less than that produced by 

 the other, I imagine that this cause can hardly have a more sensible effect in 

 the experiment than the preceding. 



194] Fourthly, we have not as yet taken notice that the canals by which 

 the jars A, a communicate with the ground are but short, and meet the ground 

 at no great distance from the jars. 



But it may be shewn by the same kind of reasoning used in Prop. [II, 

 Art. 178], with the help of the second corollary to the preceding proposition, 

 that the quantity of redundant fluid in the circles will bear very nearly the same 

 proportion to that in the positive side of the jar A, whether the canal by which 

 A communicates with the ground is long or short. 



Besides that, if it was possible for this circumstance to make much alteration 

 in the proportion which the redundant fluid in the circles bears to that in A , 

 it would in all probability have very nearly the same effect in trying the two 

 small circles as in trying the large one, so that no sensible alteration can be 

 produced in the experiment from this circumstance. 



It appears, therefore, that none of the above-mentioned circumstances can 

 cause any sensible alteration in this experiment*. 



* [Note 17, p. 394.] 



