a
body in such a manner as to be imperceptible.

MRS. B.

If you lay your hand on a hot body, you feel only the caloric which
leaves it, and enters your hand; for it is impossible that you should be
sensible of that which remains in the body. The thermometer, in the same
manner, is affected only by the free caloric which a body transmits to
it, and not at all by that which it does not part with.

CAROLINE.

I begin to understand it: but I confess that the idea of insensible heat
is so new and strange to me, that it requires some time to render it
familiar.

MRS. B.

Call it insensible caloric, and the difficulty will appear much less
formidable. It is indeed a sort of contradiction to call it heat, when
it is so situated as to be incapable of producing that sensation. Yet
this modification of caloric is commonly called SPECIFIC HEAT.

CAROLINE.

But it certainly would have been more correct to have called it
_specific caloric_.

EMILY.

I do not understand how the term _specific_ applies to this modification
of caloric?

MRS. B.

It expresses the relative quantity of caloric which different _species_
of bodies of the same weight and temperature are capable of containing.
This modification is also frequently called _heat of capacity_, a term
perhaps preferable, as it explains better its own meaning.

You now understand, I suppose, why the milk and chalk required a longer
portion of time than the lead to raise their temperature to that of the
oven?

EMILY.

Yes: the milk and chalk having a greater capacity for caloric than the
lead, a greater proportion of that fluid became insensible in those
bodies: and the more slowly, therefore, their temperature was raised.

CAROLINE.

But might not this difference proceed from the different conducting
powers of heat in these three bodies, since that which is the best
conductor must necessarily attain the temperature of the oven first?

MRS. B.

Very well observed, Caroline. This objection would be insurmountable, if
we could not, by reversing the experiment, prove that the milk, the
chalk, and the lead, actually absorbed different quantities of caloric,
and we know that if the different time they took in heating, proceeded
merely from their different conducting powers, they would each have
acquired an equal quantity of caloric.

CAROLINE.

Certainly. But how can you reverse this experiment?

MRS. B.

It may be done by cooling the several bodies to