[ 332 ] . , , . . 
Exp. 3 y. Two Tourmalins being rubbed againfl 
each other, one became plus, and the other minus. 
From all which it appears, that fome alteration 
was made in the medium on their furfaces ; otherwife 
thefe oppofite effects could not have been produced : 
and in regard to the fame bodies producing different 
effects, it is not improbable but they may differ in 
degrees of hardnefs, polifh, or of their electrifying 
power. 
Now, as eleCtrics , rubbed againfi eleClrics , occa- 
fioned electrical. appearances, I was encouraged to try 
what would be the effeCt of air, if I rubbed , or rather 
forced, it againff eleCtrics ; for I fuppofed the particles 
of air to be furrounded with a medium of the fame 
kind as groffer bodies, which is the caufe of their 
being fo elaffic. 
Exp. 36. To do this, I only made ufe of a com- 
mon pair of bellows, and having brought the Tourma- 
lin near to the end of the pipe, I found, after it had 
received about twenty blajis , it was electrified plus on 
both fides. 
Air therefore feems to be lefs eleCtric than the 
T mrmalin. 
Exp. 37. Into the place of the Tourmalin I brought 
a pane of glafs, and blew againfl it the fame number 
of times as in the former experiment. When I exa- 
mined both fides, they were electrified plus alfo, but 
lefs than the Tourmalin. 
Exp. 38. Amber, treated in the fame manner, was 
electrified lefs than the glafs. 
Exp. 39. I had recourfe next to a fmith’s bellows. 
The difference thefe occafioned was only a much 
flronger 
