C 333 3 
ftronger electricity in the Tourmalin. Amber was 
ftill weaker than the glafs, and the glafs weaker than 
the Tourmalin . 
Still having in view the medium on the furfaces of 
the particles of air, I confidered, that heat would ra- 
tify it; by which means, air, having its refiftance leff- 
ened, would more readily part with the electric fluid, 
and of confequence eleCtrify more powerfully. 
Exp. 40. The pipe of the bellows being made red- 
hot, I blew againft the Tourmalin twelve times only, 
which was eight blafts lefs than in the former experi- 
ments with cold air. In this experiment likewife the 
Tourmalin was electrified plus on both Tides, but to a 
confiderable degree more, than was done in the 36th 
and 39th experiments. The hot air had the fame 
effedt upon glafs ; but electrified it lefs than th eTour- 
malin : and amber, though, like the other bodies, it 
fuffered an increafe of power by the fame treatment, 
was electrified the leaft of all. 
From the air electrifying more powerfully when it 
is hot, than when cold; and the Tourmalin being elec- 
trified more than glafs, and glafs more than amber, 
as appears by thefe laft experiments, we feem to have 
obtained a proof, that the whole atmofphere is con- 
ftantly promoting a flow of the electric fluid, by the 
alternate changes of heat and cold : and further, that 
air is not only lefs eleCtric than the Tourmalin , but 
lefs than glafs, and even amber. 
Exp. 41. When the Tourmalin had received the 
fame number of blafts againft the plain fide, whilft 
my finger touched the convex fide, it afforded differ- 
ent appearances; for the plain fide was electrified 
plus , and the other minus. After a fhort time, both 
