VOL. LXI.'] PHILOSOPHICAL TRANSACTIONS. 257 



Case g. But if one of the bodies, as A, is positively electrified, in a less de- 

 gree than B, then it is possible for the bodies to attract each other; for in this 

 case the force with which b repels the fluid in a may be so great, as to make the 

 body A either entirely undercharged, or at least to make the nearest part of it so 

 much undercharged, that a shall on the whole attract a particle of fluid in b. It 

 may be worth remarking, with regard to this case, that when two bodies, both 

 electrified positively but unequally, attract each other, you may by removing 

 them to a greater distance from each other, cause them to repel ; for as the 

 stronger electrified body repels the fluid in the weaker with less force when re- 

 moved to a greater distance, it will not be able to drive so much fluid out of it, 

 or from the nearer to the farther part, as when placed at a less distance. 



Case 10 and 11. By the same reasoning it appears, that if the two bodies are 

 both negatively electrified in the same degree, they must repel each other : but 

 if they are both negatively electrified in different degrees, it is possible for them 

 to attract each other. 



All these cases are exactly conformable to experiment. 



Case 12. Let two cork balls be suspended by conducting threads, from the 

 same positively electrified body, in such manner, that if they did not repel, they 

 would hang close together: they will both be equally electrified, and will repel 

 each other: let now an overcharged body, more strongly electrified than them, 

 be brought under them ; they will become less overcharged, and will separate 

 less than before : on bringing tlie body still nearer, they will become not at all 

 overcharged, and will not separate at all : and on bringing the body still nearer, 

 they will become undercharged, and will separate again. 



Case 13. Let all the air of a room be overcharged; and let two cork balls be 

 suspended close to each other by conducting threads communicating with the 

 wall. By prop. 15, it is highly probable that the balls will be undercharged; 

 and therefore they should repel each other. 



These last two cases are experiments of Mr. Canton's, and are described in 

 Phil. Trans., 1753, p. 350, where are other experiments of the same kind, all 

 readily explicable by the foregoing theory. 



I have now, says Mr. C, considered all the principal or fundamental cases of 

 electric attractions and repulsions which I can think of; all of which appear to 

 agree perfectly with the theory. 



§ 3. On the cases in which bodies receive electricity from or part with it to 

 the air. 



Ltmma 1. Let the body a, fig. 6, either stand near some over or under- 

 charged body, or at a distance from any. It seems highly probable, that if any 

 part of its surface, as mn, is overcharged, the fluid will endeavour to run out 

 through that part, provided the air adjacent to it is not overcharged. 



VOL. XIII. L L 



