[ 423 ] 
MISCELLANEOUS ESSAYS. 
Tffay on the Means of confining Heat, and 
directing its Operations. 
From Couut Rumford’s E-ffays, 
vol. 2, chap. 3. 
HAT heat paffes more freely 
through fome bodies than 
others, is a faét very well known; 
but the caufe of this difference in 
the conducting powers of bodies, 
with refpect to heat, has not yet 
been difcovered. 
The utility of giving a wooden 
handle to a tea-pot or coffee-pot of 
metal; or of covering its metallic 
handle with leather, or with wood, 
is well known: but the difference 
_in the conducting powers of various 
bodies with regard to heat, may be 
fhown by a great number of very 
fimple experiments ;—fuch as are 
in the power of every one to make 
at all times and in all places, and 
~almoft without either trouble or 
expence. eee 
{f an iron nail and a pin of wood, 
of the fame form and dimenfions, 
be held fucceffively:in the flame of 
acandle, the difference in the con- 
ducting powers of the metal and of 
st 
wood will manifeft itfelf in a man: 
nerin which there will be no room 
left for doubt. As foon as the end 
of the nail, which is expofed in the 
flame of the candle, begins to be 
heated, the other end of it will 
grow {fo hot as\to render it impoffi- 
ble to hold it in the hand without 
being burnt; but the wood may 
be held any length of time in the 
fame fituation without the leaft in- 
convenience; and, even after it 
has taken fire, it may be held till it 
is almoft entirely confumed; for 
the uninflamed wood will not grow 
hot, and, till the flame actually 
comes in conta¢t with the fingers, 
they will not be burnt. If a {mall 
flip or tube of glafs be held in the 
flame of the candle in the fame 
manner, the end of the glafs by 
which it is held will be found to be 
more heated than the wood, but 
incomparably lefs fo than the pin 
or nail of metal ;—and among all 
the various bodies that can be tried 
in this manner, no two of them 
will be found to give paffage to heat 
through their fubftances with ex- 
actly the fame degree of facility *. 
% To thow the relative conduéting power of the different metals, Doétor Ingen- 
houz contrived a very pretty experiment. :He took equal cylinders of the different 
metals (being ftraight pieces of {tout wire, drawn through the fame hole, and of 
the fame length) and, dipping them into’ melted wax, covered them with a thin 
coating of the wax. He then held one end of each of thefe eylinders in boiling 
water, and obferved how far the coating of wax was melted bythe heat gona yale 
cated through the metal, and with-what celerity the heat pafied « 
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