254 PHILOSOPHICAL TRANSACTIONS. [anN0 1771. 



of fluid as If it communicated with one of those bodies by a canal of incompres- 

 sible fluid ; all the rest of these bodies must, by that corol., contain the same 

 quantity of fluid as if they communicated with b by canals of incompressible 

 fluid : but yet it is possible that some of those bodies may be overcharged, and 

 others undercharged : for suppose the bodies to be positively electrified, and let 

 an overcharged body d be brought near one of them, that body will become 

 undercharged, provided d is sufficiently overcharged; and yet by the definition 

 it will still be positively electrified in the same degree as before. 



Moreover, if several bodies are insulated and connected together by conduct- 

 ing substances, and one of these bodies is electrified by excited glass, there can 

 be no doubt but they will all be positively electrified ; for if there is no other 

 over or undercharged body placed near any of these bodies, the thing is evident ; 

 and though some of these bodies may, by the approach of a sufficiently over- 

 charged body, be rendered undercharged ; yet he does not see how it is possible 

 to prevent a body placed at an infinite distance, and communicating with them 

 by a canal of incompressible fluid, from being overcharged. In like manner if 

 one of these bodies is electrified by excited sealing wax, they will all be nega- 

 tively electrified. 



It is impossible for any body communicating with the ground to be either 

 positively or negatively electrified ; for the earth, taking the whole together, 

 contains just fluid enough to saturate it, and consists in general of conducting 

 substances; and consequently though it is possible for small parts of the surface 

 of the earth to be rendered over or undercharged, by the approach of electrified 

 clouds, or other causes ; yet the bulk of the earth, and especially the interior 

 parts, must be saturated with electricity. Therefore assume any part of the earth 

 which is itself saturated, and is at a great distance from any over or undercharged 

 part ; any body communicating with the ground, contains as much electricity as 

 if it communicated with this part by a canal of incompressible fluid, and therefore 

 is not at all electrified. 



If any body A, insulated and saturated with electricity, is placed at a great 

 distance from any over or undercharged body, it is plain that it cannot be elec- 

 trified; but if an overcharged body is brought near it, it will be positively elec- 

 trified; for supposing a to communicate with any body b, at an infinite distance, 

 by a canal of incompressible fluid, it is plain that unless b is overcharged, the 

 fluid in the canal could not be in equilibrio, but would run from a to b. For 

 the same reason a body insulated and saturated with fluid, will be negatively elec- 

 trified if placed near an undercharged body. 



§ 1. The phenomena of the attraction and repulsion of electrified bodies seem 

 to agree exactly with the theory ; as will appear by considering the following 

 cases. Case 1. Let two bodies, a and b, both conductors of electricity, and 



