[ 4^2 ] 
by bringing the power gradually nearer, and then re- 
moving it quickly. 
We may then veryjuflly conclude, that this repara- 
tion of the balls, is occafioned by the expanfive power 
of the electric fluid, or ather> crowding from without , 
and through the air, to enter the bails, and reflore the 
equilibrium . And in like manner that the plus electri- 
city caufes a reparation of the balls in confequence 
of the fame electric fluid, or cether , crowding from 
within to get out of the balls, and palling through 
a like quantity of air, in order to reflore the equili- 
brium ; for the fame medium which appertains to the fur- 
faces of bodies , mufi reff the exit and entrance equally : 
and therefore the one cafe will be always the converfe 
of the other. 
We have feen that on bringing the electrified glafs 
near enough to the wood, the balls are electrified mi- 
nus. If now the circumflances are changed, by 
bringing the fame glafs conjiderably nearer to the wood, 
and much quicker, the balls are electrified plus and 
continue fo for a confiderable time after the glafs is 
removed : which is the ftrongeft confirmation that 
this effect entirely depends upon the ref fiance of the 
wood being overcome, and the electric fluid entering 
the apparatus, by the nearer approach of the glafs. 
There are then two different methods of caufing 
a plus appearance in the balls. The one, we find, de- 
pends upon an actual enterance of the fluid, from the 
glafs, into the wood, 6tc. And the other upon a quan- 
tity of the fluid, originally in the wood, being forced 
* The glafs in this experiment mull not only be brought 
quickly towards the wood, but it mull likewife be removed from 
it as fuddenly. 
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