CALORIC. 
stratum, it makes its way upwards, inde- 
pendently of that conducting power, in 
consequence of the fluidity of the body, 
and the expansion of the heated particles. 
The lowest stratum, as soon as it combines 
with a dose of caloric, becomes specifically 
lighter, and ascends. New particles ap- 
proach the source of heat, condrine with 
caloric in their turn, and are displaced. 
In this manner all the particles come, one 
after another, to the source of heat; of 
course the whole of them are heated in a 
very short time, and the caloric is carried 
almost at once to much greater distances 
in fluids than in any solid whatever. Fluids, 
tlierefore, have the property of carrying or 
transporting caloric ; in consequence of 
which they acquire heat independently al- 
together of any conducting power. 
If we take a bar of iron and a piece of 
stone of equal dimensions, and putting one 
end of each into the fire, apply either ther- 
mometers or our hands to the other, we 
shall find the extremity of the iron sensibly 
hot long before that of the stone. Caloric, 
therefore, is not conducted through all 
bodies with the same celerity and ease. 
Those that allow it to pass with facility, 
are called good conductors ; those through 
which it passes with difficulty, are ca^ed 
bad conductors. 
Metals are the best conductors of caloric 
of all the solids hitherto tried. The con- 
ducting powers of all, however, are not 
equal. Dr. Ingeuhonsz procured cylinders 
of several metals exactly of the same size, 
and having coated them with wax, he 
plunged their ends into hot w^ater, and 
judged of the conducting power of each by 
the length of wax-coating melted. From 
these experiments he concluded, that the 
conducting power of the metals which he 
examined were in the following order: 
Silver, 
Gold, 
Ti*n ^ nearly equal. 
Platinum,) 
Steel f much inferior to the others. 
Lead, ) 
Next to metals, stones seem to be the 
best conductors ; but this property varies 
considerably in different stones. Bricks are 
much worse conductors than most stones. 
Glass seems not to differ much from 
stones in its conducting power : like them, 
it is a bad conductor. This is the reason 
that it is so apt to crack on being suddenly 
heated or cooled. One part of it, receiv- 
ing or parting ivith its caloric before the 
rest, expands or contracts, and destroys 
the cohesion. Next to these, some dried 
woods. 
Charcoal is also a bad conductor : accord- 
ing to the experiments of Morveau, its con- 
ducting pow'cr is to that of fine sand 2 ; 3. 
Feathers, silk, wool, and hair are still worse 
conductors than any of the substances yet 
mentioned. Tliis is the reason that they an- 
swer well for articles of clothing. They do 
not allow the heat of the body to be car- 
ried off by the cold external air. Count 
Romford lias made a very ingenious set of 
experiments on the conducting power of 
these substances. He ascertained that their 
conducting power is inversely as the fine- 
ness of their texture. 
Having in the preceding sections consi- 
dered the nature of caloric, the manner in 
which it moves through other bodies and 
distributes itself among them ; let us now 
examine, in the next place, the effects 
which it produces on other bodies, either 
by entering into them or separating from 
them. The effects w'Hich caloric produces 
on bodies, may be arranged under three 
heads ; namely, changes in bulk ; changes 
in state; and changes in combination. 
It may be laid down as a general rule, to 
which there is no known exception, that 
every addition or abstraction of caloric 
makes a corresponding change in the bulk 
of the body which has been subjected to 
this alteration in the quantity of its heat. 
In general the addition of heat increases 
the bulk of a body, and the abstraction of 
it diminishes its bulk ; but this is not qiii- 
formly the case, though the exceptions are 
not numerous. 
Indeed these exceptions are not only con- 
fined to a very small number of bodies, but 
even in them they do not hold, except at 
certain particular temperatures; while at 
all other temperatures these bodies are in- 
creased in bulk when heated, and diminish- 
ed in bulk by being cooled. We may there- 
fore consider expansion as one of the most 
general effects of heat. It is certainly one 
of the most important, as it has furnished 
us with the means of measuring all the 
others. See Pyrometer. 
Though all bodies are expanded by heat, 
and contracted by cold, and this expansion 
in the same body is always proportional to 
some function of the quantity of caloric add- 
ed or abstracted ; yet the absolute expan- 
sion or contraction has been found to differ 
exceedingly in different bodies. In general, 
the expansion of gaseous bodies is greatest of 
