258 PHILOSOPHICAL TRANSACTIONS. [aNNO 1771. 



For let G be any point in that surface, and p a point within the body, ex- 

 tremely near to it ; it is plain that a particle ,of fluid at p, must be repelled with 

 as much force in one direction as another (otherwise it could not be at rest) un- 

 less all the fluid between p and g is pressed close together, in which case it may 

 be repelled with more force towards g, than it is in the contrary direction : now 

 a particle at g is repelled in the direction pg, i. e. from p to g, by all the redun- 

 dant fluid between p and g ; and a particle at p is repelled by the same fluid in 

 the contrary direction ; so that as the particle at p is repelled with not less force 

 in the direction pg than in the contrary, Mr. C. does not see how a particle at 

 g can help being repelled with more force in that direction than the contrary, 

 unless the air on the outside of the surface mn was more overcharged than the 

 space between p and g. 



In like manner, if any part of the surface is undercharged, the fluid will have 

 a tendency to run in at that part from the air. The truth of this is somewhat 

 confirmed by the 3d problem ; as in all the cases of that problem, the fluid was 

 shown to have a tendency to run out of the spaces ad and eh, at any surface 

 which was overcharged, and to run in at any which was undercharged. 



Corol. 1 . If any body at a distance from other over or undercharged bodies, 

 be positively electrified, the fluid will gradually run out of it from all parts of its 

 surface into the adjoining air ; as it is plain that all parts of the surface of that 

 body will be overcharged : and if the body is negatively electrified, the fluid will 

 gradually run into it at all parts of its surface from the adjoining air. 



Corol. 2. Let the body a, fig. 6, insulated, and containing just fluid enough 

 to saturate it, be brought near the overcharged body b ; that part of the surface 

 of a which is turned towards b will, by prop. 2, be rendered undercharged, and 

 will therefore imbibe electricity from the air ; and at the opposite surface rs, the 

 fluid will run out of the body into the air. 



Corol. 3. If we now suppose that a is not insulated, but communicates with 

 the ground, and consequently that it contained just fluid enough to saturate it 

 before the approach of b, it is plain that the surface mn will be more undercharged 

 than before , and therefore the fluid will run in there with more force than be- 

 fore ; but it can hardly have any disposition to run out at the opposite surface 

 RS ; for if the canal by which a communicates with the ground is placed opposite 

 to B, as in fig. 5, then the fluid will run out through that canal, till it has no 

 longer any tendency to run out at BS; and by the remarks at the end of prop. 

 27, it seems probable that the fluid in a will be nearly in the same quantity, 

 and disposed nearly in the same manner, into whatever part of a the canal is in- 

 serted, by which it communicates with the ground. 



Corol. 4. If B is undercharged, the case will be reversed ; that is, it will run 

 out where it before ran in, and will ran in where it before ran out. 



