48 First published Paper on Electricity 



that the fluid in the part DB of the canal will be repelled from C, with 

 just a smuch force as in the last proposition; but the fluid in the part 

 BG will not be repelled at all: consequently D will be undercharged, but 

 not so much as in the last proposition. 



53] COR. If ABC is now supposed to be undercharged, it is certain 

 that D will be overcharged, provided the matter near ABC on the outside 

 is saturated with immoveable fluid; and there is great reason to think 

 that it will be so, though the fluid in that matter is moveable. 



54] PROP. XVI. Let AEFB (Fig. 9) be a long cylindric body, and D 

 an undercharged body; and let the 

 quantity of fluid in AEFB be such, that 

 the part near EF shall be saturated. It 



1 ** 



appears from what has been said before, F - 



that the part near AB will be over- 

 charged; and moreover there will be a certain space, as AabB, adjoining 

 to the plane AB, in which the fluid will be pressed close together; and the 

 fluid in that space will press against the plane AB, and will endeavour 

 to escape from it; and by Prop. II the two bodies will attract each other: 

 now I say that the force with which the fluid presses against the plane AB, 

 is very nearly the same with which the two bodies attract each other in 

 the direction EA ; provided that no part of AEFB is undercharged. 



Suppose so much of the fluid in each part of the cylinder as is sufficient 

 to saturate the matter in that part, to become solid; the remainder, or 

 the redundant fluid remaining fluid as before. In this case the pressure 

 against the plane AB must be exactly equal to that with which the two 

 bodies attract each other in the direction EA : for the force with which 

 D attracts that part of the fluid which we supposed to become solid, is 

 exactly equal to that with which it repels the matter in the cylinder ; and 

 the redundant fluid in EabF is at liberty to move, if it had any tendency 

 to do so, without moving the cylinder; so that the only thing which has 

 any tendency to impel the cylinder in the direction EA is the pressure of 

 the redundant fluid in AabB against AB; and as the part near EF is 

 saturated, there is no redundant fluid to press against the plane EF, and 

 thereby to counteract the pressure against AB. Suppose now all the 

 electric fluid in the cylinder to become fluid ; the force with which the 

 two bodies attract each other will remain exactly the same; and the only 

 alteration in the pressure against AB, will be, that that part of the fluid 

 in AabB, which we at first supposed solid and unable to press against 

 the plane, will now be at liberty to press against it; but as the density 

 of the fluid when its particles are pressed close together may be supposed 

 many times greater than when it is no denser than sufficient to saturate 

 the matter in the cylinder, and consequently the quantity ot redundant 

 fluid in AabB many times greater than that which is required to saturate 



