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Since that time, I find it has been the opinion of 
fome perfons, that this change does not immediately 
depend on the heat, but only confequentially , by eva- 
porating the moifture, which, they fuppofe, returns 
again on the bodies cooling. 
This fuppofition will naturally, at firft view, prefent 
itfelf to every one, who confiders the beginning only 
of thofe experiments ; but I did not think any careful 
obferver, who had repeated them, or confidered all 
the circumftances of them, would have been milled 
by it. 
That you may judge the better of this, I fhall 
mention the circumflances of one of thole experi- 
ments particularly. When a common tobacco-pipe, 
or any other llender body of the like kind, is heated 
red-hot, it conduds the eledric fluid as perfedly as 
when cold : on cooling, it gradually arrives at its 
moll perfed eledric fiate in two minutes j and, in 
lefs than two minutes more,, it entirely lofes its 
eledric property again, though at that time it is not 
cold : it cannot, therefore, in that interval, have 
imbibed a moifture lufticient to have deftroyed its 
eledricity. Nor are any of the fubftances, employed 
in the experiment, of that kind of bodies, which are 
apt fuddenly to draw moifture from the air. 
In confirmation of particular bodies requiring par- 
ticular degrees of heat, to render them eledric or non- 
electric, independent of moifture, I lhall acquaint 
you with a fubftance, which is affeded by heat in an 
oppofite manner to the former inftancesj for the de- 
gree of heat neceflary to render the other fubftances 
eledric, makes this non-eledric. 
• 2 
The 
