Discharge by points 73 



insulated receives electricity from the air if brought near an overcharged 

 body, and loses some when brought near an undercharged body: and a 

 body insulated and containing its natural quantity of fluid, in some cases, 

 receives, and in others loses electricity, when brought near an over or 

 undercharged body. 



123] 4. The well-known effects of points in causing a quick dis- 

 charge of electricity seem to agree very well with this theory. 



It appears from the 20th proposition, that if two similar bodies of 

 different sizes are placed at a very great distance from each other, and 

 connected by a slender canal, and overcharged, the force with which a 

 particle of fluid placed close to corresponding parts of their surface is 

 repelled from them, is inversely as the corresponding diameters of the 

 bodies. If the distance of the two bodies is small, there is not so much 

 difference in the force with which the particle is repelled by the two bodies ; 

 but still, if the diameters of the two bodies are very different, the particle 

 will be repelled with much more force from the smaller body than from 

 the larger. It is true indeed that a particle placed at a certain distance 

 from the smaller body, will be repelled with less force than if it be placed 

 at the same distance from the greater body; but this distance is, I believe, 

 in most cases pretty considerable; if the bodies are spherical, and the 

 repulsion inversely as the square of the distance, a particle placed at any 

 distance from the surface of the smaller body less than a mean proportional 

 between the radii of the two bodies, will be repelled from it with more 

 force than if it be placed at the same distance from the larger body. 



I think therefore that we may be well assured that if two similar bodies 

 are connected together by a slender canal, and are overcharged, the fluid 

 must escape faster from the smaller body than from an equal surface of 

 the larger; but as the surface of the larger body is greatest, I do not know 

 which body ought to lose most electricity in the same time; and indeed 

 it seems impossible to determine positively from this theory which should, 

 as it depends in great measure on the manner in which the air opposes 

 the entrance of the electric fluid into it. Perhaps in some degrees of 

 electrification the smaller body may lose most, and in others the larger. 



124] Let now ACB (Fig. 18) be a conical point standing on any body 

 DAB, C being the vertex of the cone; and let DAB 

 be overcharged: I imagine that a particle of fluid 

 placed close to the surface of the cone anywhere 

 between b and C, must be repelled with at least as 

 much, if not more, force than it would, if the part 

 AabB of the cone was taken away, and the part aCb Fig. 18. 



connected to DAB by a slender canal; and conse- 

 quently, from what has been said before, it seems reasonable to suppose 

 that the waste of electricity from the end of the cone must be very great 



