[ 7 s i 1 .. . 
one kind of bodies. electrify pofitively, and the other 
negatively ; that excited glafs throws out the elec- 
tric fire, and excited fulphur drinks it in. But no 
reafoti has yet been afiigned, why vitreous bodies 
fhould receive, and refinous bodies part with this 
fire, by rubbing them. Some perlons indeed, of 
conliderable knowlege in thefe matters, have fup- 
pofed the expanfion of glafs, when heated by fridion, 
to be the caule of its receiving more of the electric 
fluid than its natural fharej but this fuppofition cannot 
be made with regard to bodies of the other fort, fuch 
as fulphur, fealing-wax, &c. which part with it when 
treated in the fame manner. The following experi- 
ments, firfl made at the latter end of December 
1753, and often repeated fince, may perhaps call 
new light on this difficult fubjed. 
Having rubbed 'a glafs tube with a piece of thin 
fheet-lead and flower of emery mixt with water, till 
its tranfparency was entirely deftroyed 3 after making 
it perfedly clean and dry, 1 excited it with new flan- 
nel, and found it ad in all refpeds like excited ful- 
phur or fealing-wax. The eledric fire feems to ilfue 
from the knuckle, or end of the finger, and to fpread 
itfelf on the fur face of this tube, in the beautiful 
manner reprefented at A and B in Fig. 1. Plate 32. 
If this rough or unpoliihed tube, be excited by a 
piece of dry oiled filk (efpecially when rubbed over 
with a little chalk or whiting), it will ad like a 
glafs tube with its natural polilh. And in this cafe, 
the fire appears only at the knuckle, or end of the 
finger ; where it is very much condenfed before it 
enters; as at A and B in Fig. 2* 
But 
