C 459 ] 
fubftances, and much fafter than wood : for the fur- 
faces of tobacco-pipe and wood being wetted, the 
furface of the wood will continue wet much longer 
than the furface of the tobacco-pipe. 
That tobacco pipe does not become a non-con- 
duCtor by a particular degree of heat, without eva- 
porating its moifture, is evident, from the following 
experiments. If three or four inches of one end of a 
tobacco-pipe, of more that a foot in length, be made 
red-hot, without fenfibly heating the other end ; this 
pipe will prove a ready conductor, through the hot 
air furrounding one part of it, and the moifture con- 
tained in the other ; although fome part of it muft 
have the degree of heat of a non-con duCtor. But if 
the whole pipe be made red-hot, and fuflfered to cool, 
till it has only fuperficial moifture enough to make it a 
good conductor ; and then three or four inches of one 
end be again made red-hot, it will become a non- 
conductor. And if a nail be placed at, or near each 
end of a longilh folid piece of any of the abforbent 
bodies above-mentioned, fo that the point of each 
nail may be about half the thicknefs of the body, 
within its furface ; this body, by heat, may be made 
a non-conduCtor externally, or fuperficially, while it 
remains a good conductor internally : for the eleCtric 
fluid will pals readily from one nail to the other, 
through the middle of the body, when it will not 
pafs on its furface ; and even when the internal' parts 
of the body are in an equal degree of heat with the 
external ; as they mull foon be, after it begins to cool. 
But if the fame body be expofed', for a Ihort time, 
to a greater degree of heat than before; or if it be 
kept 
