[ 6o6 ] 
tide, placed either between them, or on the outfide 
of them, with the fame force as if all the matter of 
thofe fpaces was colleded in the middle plane be- 
tween them. 
It is needlefs mentioning the three cafes in which 
A D is undercharged, as the reader will eafily fupply 
the place. 
Though the four foregoing problems do not im- 
mediately tend to explain the phasnomena of eledri- 
city, I chofe to infert them ; partly becaufe they feem 
worth engaging our attention in themfelves ; and 
partly becaufe they ferve, in fome meafure, to con- 
firm the truth of fbme of the following propofitions, 
in which I am obliged to make ufe of a lefs accurate 
kind of reafoning. 
In the following propofitions, I fliall always fup- 
pofe the bodies I fpeak of to confift of folid matter, 
confined to the fame fpot, fb as not to be able to 
alter its fliape or fituation by the attradlion or re- 
pulfion of other bodies on it : I fiiall alfo fuppofc 
the eledric fluid in thefe bodies to be moveable, but 
unable to efcape, unlefs when otherwife exprefled. 
As for the matter in all the refl: of the univerfe, I 
(hall fuppofe it to be faturated with immoveable 
fluid. I fhall alfo fuppofe the eleblric attradion 
and rcpulfion to be inverfely as any power of the 
diftance lefs than the cube, except when otherwife 
exprefled. 
By a canal, I mean a flender thread of matter, of 
fuch kind that the eledric fluid fliall be able to move 
readily along it, but fliall not be able to efcape from 
it, except at the ends, where it communicates with 
other bodies. Thus, when I fay that two bodies 
com- 
