our, and a most agreeable odour; and it is held 
in great veneration by the Hindoos, and offered 
on the shrines of both Sheva and Vishnoo. Its 
fruit is somewhat similar in appearance to a wal- 
nut; it has a bitterish and somewhat unctuous 
taste; and it yields an odoriferous fixed oil, 
which has the reputation of being an excellent 
external application for rheumatisms, and is 
much used in Travancore for burning in lamps. 
Two other species have been introduced to Bri- 
tain from India, and one from Bourbon; and the 
chief of these is noticed in the article CALABA. 
CALORIC. A name given, in chemistry, to that 
agent which produces the phenomena of heat and 
combustion. It is hypothetically regarded as a 
subtile fluid, the particles of which repel one an- 
other, and are attracted by all other substances. 
It is imponderable, and, by its distribution, in 
various proportions, among the particles of mat- 
ter, gives rise to the three general forms of gas, 
liquids, and solids. The particles of water, by 
losing caloric, have their cohesion so much in- 
creased, that they assume the solid form of ice ; 
by adding caloric, they again become fluid ; and 
by a still further addition, they are converted 
into vapour. 
Caloric exists in two different states—/ree or un- 
combined, and in a state of combination. In the for- 
mer condition, it creates the sensation of heat, and 
produces expansion in other bodies. The power 
which any body has of exciting the sensation of 
heat, and occasioning expansion, is understood by 
the expression of its temperature. This is supposed 
to vary with the quantity of free caloric in a 
given quantity of matter; a high temperature 
being ascribed to the presence of a large quantity 
of free caloric, and a low temperature to that of 
a small quantity. We are ignorant, however, of 
the extremes of temperature, and may compare 
it to a chain, of which a few of the middle links 
only are exposed to our observation, while its 
extremities are concealed from our view. 
The expansion of bodies is one of the most uni- 
versal effects of an increase of temperature. This 
| increase in bulk, however, is not the same in all 
| bodies. The same increase of temperature causes 
liquids to expand more than solids, and aériform 
bodies much more than either. On this princi- 
ple are constructed the various instruments for 
measuring temperature; since the degree of ex- 
pansion produced by caloric bears a sufficient 
proportion to its quantity to afford us the means 
of ascertaining it with tolerable accuracy. Our 
senses, it is obvious, are quite inadequate to 
afford us this information; for we compare our 
sensations of heat, not with any fixed or uniform 
standard, but with those sensations which we 
have had immediately previous. Hence, the 
same portion of water will feel warm to a hand 
removed from contact with snow, and cold to an- 
| other hand which has been heated before the 
fire. To convey precise notions of temperature, 
therefore, we are obliged to describe the degree 
CALORIC. 
of expansion produced in some one body which 
has been previously agreed upon as a standard of 
comparison. The standard most generally adop- 
ted is quicksilver, which is contained in a glass 
ball, terminating a long, narrow tube. This in- 
strument is called a thermometer. If quicksilver, 
or indeed any other substance except the gases, 
suffered equal expansion by equal increments of 
the calorific power, then this instrument would 
be perfect ; but the same increase of bulk is not | 
effected in the same liquid or solid, at all tem- 
peratures, by adding similar quantities of heat ; 
for bodies expand, by equal increments of caloric, 
more in high than in low temperatures, because 
the force opposing expansion is diminished by 
the interposition of caloric between the particles 
of bodies; and, therefore, when equal quantities 
of caloric are added in succession, the last por- | 
tions meet with less resistance to their expansive | 
force than the first. In gases, on the contrary, 
which are destitute of cohesion, equal increments 
of heat appear to be attended with equal aug- 
mentations of bulk. See the article THERMoME- 
TER. 
The tendency to an equilibrium is a characteris- 
tic of free caloric. Any number of different bo- 
dies, unequally heated, when exposed in an apart- 
ment to the same temperature, gradually arrive 
to an equality of temperature. It is in obedience 
to this law, that we experience the sensations of 
heat and cold when we touch bodies which are 
warmer or colder than ourselves. There exists 
much diversity in the rapidity with which differ- 
ent substances abstract caloric when in contact 
with a body in which it is accumulated. Com- | 
mon air and gases abstract it but tardily, while 
wood, stones, and metals acquire it more rapidly. 
According to their power of conducting it off 
under; these circumstances, bodies are divided 
into conductors and non-conductors of caloric ; and, 
in general, the power of conduction varies with 
the densities of bodies. But this tendency of cal- 
oric to an equilibrium is not established solely 
by the agency of intermediate bodies or com- 
munication. A part of it moves through the at- 
mosphere, like light, in right lines, and with im- 
measurable velocity, and has, therefore, been 
called radiant caloric. The comparative quanti- 
ties lost by radiation and by conduction may be 
approximated by observing what time it takes to 
cool any body through the same number of de- 
grees in air and iz vacuo. Thus Dr. Franklin 
imagined he had ascertained that a body, which 
requires five minutes to cool ¢ vacuo, will cool 
in air, through the same number of degrees, in 
two minutes. Count Rumford’s experiments, 
with a Torricellian vacuum, give the proportions 
of five to three. Radiant coloric passes only 
through transparent media, or free space. When, 
in its passage, its rays impinge upon the surface 
of a solid or a liquid substance, they are either 
reflected from it, and thus receive a new direc- 
tion, or they lose their radiant form altogether, 
ira 
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