'[ 67 + 3 
board to’ the other : but whichever of thefe is-tW 
cafe, the experiment is equally conformable to the 
theory. 
It mull be obferved, that a particle of fluid placed 
between the two plates is drawn towards the under- 
charged plate, with a force exceeding that with which 
it would be repelled from the overcharged plate, if 
it was electrified with the fame force, the other plate 
being taken away, nearly in the ratio of twice the 
quantity of redundant fluid actually contained in the 
plate, to that which it would contain, if eleCtrified 
with the fame force by itfelf j fo that, unlefs the plate 
is very weakly eleCtrified, or their diftance is very 
eonfiderable, the fluid will be apt to fly from one to 
the other, in the form of fparks, ' • 
§ 8* Whenever any conducing body as A, com- 
municating with the ground, is brought fufficiently 
near an overcharged body B, the eleCtric fluid is apt. 
to fly through the air from B to A, in the form of a. 
fpark : the way by which this is brought about 
feems to be this.. The fluid placed anywhere be- 
tween the two bodies, is repelled from B towards A, 
and will confequently move flowly through, the air 
from one to the other : now it feems as if this mo- 
tion increafed' the elafticity of the air,, and made.it 
rarer: this will enable the fluid to flow in^a fwifter 
current, which will, ftlll further incroafe the elafti- 
city of the air,, till at laft it is fo^much. rarified, as tO: 
form very little oppofition to the motion of the elec- 
tric fluid, upon which it flies in an uifrntermpted mafs 
frem one body to the other. 
In 
