C J °7 ] 
of non-ele&rical Contad * within, the Glafs, and 
the Denfity -f* of the Matter conftituting thofc 
Points, provided this Matter be in its own Na- 
ture a ready Conductor of Electricity. For. this 
Reafon it is prefumed, that fo much of the 
Lead contained in the Shot in the before-mcn- 
tion’d Experiment, only concurred to make the 
electrical Explofion, as touched the internal Surface 
of 
* Bodies having the Power of readily conducting EleCtricity 
feems to depend very little upon their fpecific Gravity limply conft- 
dered : Metals, for Inftance, and Water, are in a great Degree 
Non-eleCtrics, and confequently conduCt EleClricity the belt of 
any Subftances, that have yet fallen under our Notice ; whereas the 
Calces of Metals, though very denfe Bodies, and very greatly more 
fo than Water, prevent in a great Degree the quick Propagation of 
the eledtrical Power. So that a Phial coated within and without 
with Cerufe, /. e. the Calx of Lead, and eleCtrifed, did not, upon the 
Application as ufual of one Hand to the external Surface thereof, 
and touching, the prime Conductor with the other, occafion any 
Shock, or make any Explofion more than the fimple Stroke from 
the prime Conductor. The fame Obfervation holds good with re- 
gard to red Lead, Litharge, and lunar Cauftic or the Calx of Sil- 
ver, none of which fnap, when eleCfrifed. For the fame Reafon, 
Filings of Iron, which are rufty, i. e. have their Surfaces converted 
into a Calx , are much lefs proper to be put in Glaffes to make the 
Experiment of Leyden , than thofe that are not ; inafmuch as thefe 
laft caufe a much louder Explofion than the firft. The making 
ufe of rufty Filings of Iron was the Occafion of my mentioning 
in my Sequel , § XVI. that the Stroke from thefe was lefs than that 
from Water} the contrary of which I afterwards found true, when 
Filings of Iron not rufty were fubftituted. 
f I heretofore, p. n, tsV. of my Sequel , took notice, how 
much the EffeCt of this Experiment depended upon the Quantity 
of non-eleCtric ContaCt upon the Outfide of the Glafs. 
O 2 
