[ 327 ] ' 
finger , and obferved, that both Tides were electrified 
plus. 
When the Tourmalin was put into its natural / fate , 
To as to eleCtrify plus and minus , I gave the fame fide 
another flight rub ; and in this cafe both fides were 
electrified plus. 
Upon repeating thefe two laft experiments with the 
plain fide inftead of the other, the Tourmalin was 
electrified plus on both Tides likewife ; but with this 
difference, that now they were confiderably more 
electrified than before. 
This is a farther argument, that the refiftance is 
lefs on the plain fide than on the convex fide ; and that 
the fluid pa (Jed through the Jlone. 
And becaufe fo flight a friction occafioned fuch a 
fenfible alteration, we are fufliciently cautioned from 
touching the flone at any time, but when the experi- 
ment requires it. The fame caution is to be obferved 
with glafs, amber, filk, &c. 
Thefe experiments put me upon trying the experi- 
ment with the pane of glafs, mentioned in the begin- 
ning of this letter; and, upon finding that the eleftric 
fluid not only pajfled through the glafs, but electrified 
it plus , I had a mind to try, whether I could not elec- 
trify it minus. 
Exp. 2 1. For this purpofe I made ufe of the fame 
glafs, and, when it was a little warmed, I held it 
within two feet of the prime conductor, which was 
oleCtrified plus. By this method, that part of the 
glafs, which was oppofed to the conductor, became 
electrified minus on both fides ; but beyond that, a con- 
fiderable part all round the minus , was electrified plus 
on both (ides. This effeCt is of the fame kind with 
2 that 
