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from each furface ; and there the light was always 
confidcrably brighter ; infomuch that a gentleman, 
then prefen t, who was unacquainted with experi- 
ments of this kind, defired to know the reafon of 
the three knobs of light appearing on the tops of the 
quickfilver. I mention this circumflance, becaufe 
they were remarkably confpicuous; whereas the thiee 
under furfaces exhibited no fuch appearance, the 
light being rather lefs bright than even in the general 
appearance of the whole illuminated vacuum. 
An electric current, fetting in from the glafs of the 
electrifying machine, and paffing along the tube 
through the quickfilver and vacuum , and fo to the 
earth, muff have caufed thofe bright knobs by means 
of the refinance the fluid met with at the upper fur- 
face of the quickfilver in endeavouring to enter it ; 
becaufe the .appearances were alike on the three up- 
per furfaces, and nothing of the fame kind was feen' 
at the under furfaces. Glafs therefore eledrifies bo- 
dies plus , or, in other words, gives bodies a quan- 
tity of eledric fluid more than they have naturally. 
I am now to acquaint you with the appearances 
that the minus eledricity occafioned. 
Inftead of the glafs cylinder to eledrify with, I 
put a refinous one, preserving the communication, 
and every thing elfe, as in the former experiment. 
In thefe circumftances, the general appearance of 
the light in the vacuum was the fame ; but in this 
experiment the knobs of light were on the under fur- 
faces, and not upon the upper. . 
From the knobs of light being at the under fur- 
faces, and not upon the upper, I concluded that the 
flow of the fluid was the contrary way to that caufed 
by 
