I 2 2 Delicacy of the experiment 



consequently the electricity of the pith balls communicated to the globe, 

 they still continued to separate, though but just sensibly. I then repeated 

 the experiment in the same manner, except that the pith balls were 

 negatively electrified in the same degree that they before were positively. 

 They still separated negatively after being brought in contact with the 

 globe, and in the same degree that they before did positively. 



229] It must be observed that if the globe was at all overcharged the 

 pith balls should separate further when they were previously positively 

 electrified than when negatively, as in the first case the pith balls must 

 evidently separate further than they would do if the globe was not over- 

 charged, and in the latter case less. 



Moreover, a much smaller degree of electricity may be perceived in 

 the globe by this manner of trying the experiment than the former, for 

 when the pith balls have already got a sufficient quantity of electricity 

 in them to make them separate, a sensible difference will be produced in 

 their degree of divergence by the addition of a quantity of fluid several 

 times less than what was necessary to make them separate at first. It is 

 plain that this method of trying the experiment is not just, unless the 

 hemispheres are electrified in nearly the same degree when the pith balls 

 are previously electrified positively as when negatively, which was pro- 

 vided for by the electrometer. 



230] In order to find how small a quantity of electricity in the inner 

 globe might have been discovered by this experiment, I took away the 

 hemispheres with their frames, leaving the globe and the pith balls as 

 before. I then took a piece of glass, coated as a Leyden vial, which I 

 knew by experiment contained not more than Jyth of the quantity of 

 redundant fluid on its positive side that the jar by which the hemispheres 

 were electrified did, when both were charged from the same conductor. 



I then electrified this coated plate to the same degree, as shewn by 

 the electrometer, that the jar was in the former experiment, and then 

 separated it from the prime conductor, and communicated its electricity 

 to the jar, which was not at all electrified. Consequently the jar contained 

 only ^th part of the redundant fluid in this experiment that it did in 

 the former, for the coated plate and jar together contained only 5 Vth. an d 

 therefore the jar alone contained only g^th. 



By means of this jar, thus electrified, I electrified the globe in the same 

 manner that the hemispheres were in the former experiment, and im- 

 mediately after the electrifying wire was withdrawn, approached the pith 

 balls. The result was that by previously electrifying the balls, as in the 

 second way of trying the experiment, the electricity of the globe was 

 very manifest, as the balls separated very sensibly more when they were 

 previously electrified positively than when negatively, but the electricity 



