VOL. LXI.] PHILOSOPHICAL TRANSACTIONS. 255 



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 posi- 

 tively 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 farther 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 in it; therefore when some fluid is removed 

 fi-om 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. 



Case 1. 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. It must be observed, that if the repulsion of b on a particle at e, fig. 

 1 9, the farthest part of A, is very small in respect of its repulsion on an equal 

 particle placed at D, the nearest part of a, the two bodies will attract with very 

 nearly the same force, whether a is insulated or not ; but if the repulsion of b, 

 on a particle at e, is very near as great as on one at d, they will attract with very 

 little force if a is insulated. For instance, let a small overcharged ball be 

 brought near one end of a long conductor not electrified ; they will attract with 

 very near the same force, whether the conductor be insulated or not ; but if 

 the conductor be overcharged, and brought near a small unelectrified ball, they 

 will not attract with near so much force, if the ball is insulated, as if it is not. 



Case 3. If we now suppose that A is negatively electrified, and not insulated, 

 it is plain that they will attract with more force than in the last case; as A will be 

 still more undercharged in this case than in the last. 



N. B. In these 3 cases, we have not as yet taken notice of the effect which the 

 body A will have in altering the quantity and disposition of the fluid in b ; but in 

 reality this will make the bodies attract each other with more force than they 

 would otherwise do ; for in each of these cases the body a attracts the fluid in 

 B ; which will cause some fluid to flow from the farther parts of b to the nearer, 

 and will also cause some fluid to flow into it, if it is not insulated, and will con- 

 sequently cause B to act upon a with more force than it would otherwise do. 



Case 4. Let us now suppose that b is negatively electrified; and let a be insu- 

 lated, and contain just fluid enough to saturate it > they will attract each other ; 

 for B will be undercharged ; it will therefore attract the fluid in a, and will cause 



