68 First published Paper on Electricity 



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 under- 

 charged, 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. 



105] 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 electrified; but if an overcharged body is brought near it, it 

 will be positively electrified; 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 electrified if placed 

 near an undercharged body. 



106] 2. The phenomena of the attraction and repulsion of electrified 

 bodies seem to agree exactly with the theory; as will appear by con- 

 sidering the following cases. 



107] CASE I. Let two bodies, A and B, both conductors of electricity, 

 and both placed at a great distance from any other electrified bodies, be 

 brought near each other. Let A be insulated, and contain just fluid 

 enough to saturate it; and let B be positively electrified. They will attract 

 each other ; for as B is positively electrified, and at a great distance from 

 any overcharged body, it will be overcharged; therefore, on approaching 

 A and B to each other, some fluid will be driven from that part of A 

 which is nearest to B to the further part: but when the fluid in A was 

 spread uniformly, the repulsion of B on the fluid in A was equal to its 

 attraction on the matter therein; therefore, when some fluid is removed 

 from those parts where the repulsion of B is strongest to those where it 

 is weaker, B will repel the fluid in A with less force than it attracts the 

 matter; and consequently the bodies will attract each other. 



108] CASE II. If we now suppose that the fluid is at liberty to escape 

 from out of A, if it has any disposition to do so, the quantity of fluid in 

 it before the approach of B being still sufficient to saturate it; that is, 

 if A is not insulated and not electrified, B being still positively electrified, 

 they will attract with more force than before: for in this case, not only 

 some fluid will be driven from that part of A which is nearest to B to the 

 opposite part, but also some fluid will be driven out of A. 



