C 458 ] 
tricity before it has acquired a fenfible degree of 
heat (i). 
That glafs is a condudor in damp weather, on ac- 
count of the moifture on its furface, is well known ; 
as alfo, that warming it a little will render it a non- 
conductor j and that a great degree of heat will make 
it feem to be a conductor again. Now tobacco-pipe, 
wood, &c. will not only attract the moifture of the 
air to their furfaces, but will alfo abforb it; whence 
they are conductors in dry weather; and require 
more heat than glafs, as well as a longer continuance 
in it, to render them non-conductors. It is remark- 
able, that tobacco-pipe, after it begins to cool, will 
become a condutor again, fooner than moft other 
fubftances, and much fooner than wood. The caufe 
of this appears to me, to be the tobacco-pipe’s ab- 
forbing the moifture of the air fafter than moft other 
(1) I have obferved alfo, that the Tourmalin, Brazil Topaz, 
and Brazil Emerald, will give much ftronger figns of eleCtricity 
while cooling, after they have been held about a minute within 
two inches of an almoft furrounding fire, where the air is a con- 
ductor, than they ever will after heating them in boiling water. 
And if both Tides of either of thofe (tones be equally heated, but 
in a lefs degree than will make the furrounding air a conductor, 
the eleCtricity of each fide, whether plus or minus , will continue 
To, all the time the {tone is both, heating and cooling ; but will 
increafe while it is heating, and decreafe while it is cooling. 
Whereas, if the heat be fufficient to make the furrounding air 
conduCt the eleCtric fluid from the pofitive fide of the ftone to 
the negative fide of it, while heating ; the eleCtricity of each fldc 
will increafe, while the ftone is cooling, and be contrary to 
what it was, while the ftone was heating. See the Philofophical 
TranfaCtions, Vol. LI. p. 403 and 404. 
fubftances* 
