[ s 9 8 3 
filvcr was eledrified minus , and both fides of the 
glafs, with the condudor and balls, plus. 
There are, therefore, certain circumftances under 
which the eledric fluid paffes through glafs ; I repeat 
in certain circumftances , my Lord, becaufe in others, 
for inftance, the Leyden bottle , the fluid does not pafs 
through tiie glals, but eledrifies one flde phis , and 
the other fide minus , as my friend Dr. Franklin 
hath fhewn, in his letters upon eledricity. 
This difference, which is caufed by the vitreous 
eledricity in both cales, may perhaps be explained 
from the furrounding medium *, and the different de- 
grees of the power with which the eledric fluid en- 
deavours to enter a bodv. 
For the rejiftance owing to the furrounding me- 
dium in a polifhed plane, without covering, is not 
overcome, but by bringing the power neat the glafs, 
whereby the glafs is eledrified plus on both lides j 
whereas, when the glafs is properly cove i ed i and the 
power brought upon, it, the covering conduds the 
fluid equally to all the parts on that fide, where it 
accumulates, that is, eledrifies it plus ; whilft the op- 
poflte covering carries oft to the communicating earth 
an equal quantity of the fluid naturally belonging to 
the glafs, that is, eledrifies it minus. . 
The fame glafs, without any covering, will be ren- 
dered minus on both fides, by removing the power to 
a greater diftance, by which it is diminifhed, and the 
quantity of intermediate air, and confequently of tt- 
Jiftance , increafed. 
* See the former paper upon 
Volume, Part I. 
the Tourmalin, p. 329. of this 
The 
