S. B.

None of the modifications of caloric should properly be called _heat_;
for heat, strictly speaking, is the sensation produced by caloric, on
animated bodies; this word, therefore, in the accurate language of
science, should be confined to express the sensation. But custom has
adapted it likewise to inanimate matter, and we say _the heat of an
oven_, _the heat of the sun_, without any reference to the sensation
which they are capable of exciting.

It was in order to avoid the confusion which arose from thus confounding
the cause and effect, that modern chemists adopted the new word
_caloric_, to denote the principle which produces heat; yet they do not
always, in compliance with their own language, limit the word _heat_ to
the expression of the sensation, since they still frequently employ it
in reference to the other modifications of caloric which are quite
independent of sensation.

CAROLINE.

But you have not yet explained to us what these other modifications of
caloric are.

MRS. B.

Because you are not acquainted with the properties of free caloric, and
you know that we have agreed to proceed with regularity.

One of the most remarkable properties of free caloric is its power of
_dilating_ bodies. This fluid is so extremely subtle, that it enters and
pervades all bodies whatever, forces itself between their particles, and
not only separates them, but frequently drives them asunder to a
considerable distance from each other. It is thus that caloric dilates
or expands a body so as to make it occupy a greater space than it did
before.

EMILY.

The effect it has on bodies, therefore, is directly contrary to that of
the attraction of cohesion; the one draws the particles together, the
other drives them asunder.

MRS. B.

Precisely. There is a continual struggle between the attraction of
aggregation, and the expansive power of caloric; and from the action of
these two opposite forces, result all the various forms of matter, or
degrees of consistence, from the solid, to the liquid and aeriform
state. And accordingly we find that most bodies are capable of passing
from one of these forms to the other, merely in consequence of their
receiving different quantities of caloric.

CAROLINE.

That is very curious; but I think I understand the reason of it. If a
great quantity of caloric is added to a solid body, it introduces itself
between the particles in such a manner as to overcome, in a considerable