ad would always keep its
advantage over the chalk and milk, and would perhaps be boiling before
the others had attained the temperature of the oven. I think you might
as well say that, in the course of time, you and I should be of the same
age?

MRS. B.

Your comparison is not correct, Caroline. As soon as the lead reached
the temperature of the oven, it would remain stationary; for it would
then give out as much heat as it would receive. You should recollect
that the exchange of radiating heat, between two bodies of equal
temperature, is equal: it would be impossible, therefore, for the lead
to accumulate heat after having attained the temperature of the oven;
and that of the chalk and milk therefore would ultimately arrive at the
same standard. Now I fear that this will not hold good with respect to
our ages, and that, as long as I live, I shall never cease to keep my
advantage over you.

EMILY.

I think that I have found a comparison for specific heat, which is very
applicable. Suppose that two men of equal weight and bulk, but who
required different quantities of food to satisfy their appetites, sit
down to dinner, both equally hungry; the one would consume a much
greater quantity of provisions than the other, in order to be equally
satisfied.

MRS. B.

Yes, that is very fair; for the quantity of food necessary to satisfy
their respective appetites, varies in the same manner as the quantity of
caloric requisite to raise equally the temperature of different bodies.

EMILY.

The thermometer, then, affords no indication of the specific heat of
bodies?

MRS. B.

None at all: no more than satiety is a test of the quantity of food
eaten. The thermometer, as I have repeatedly said, can be affected only
by free caloric, which alone raises the temperature of bodies.

But there is another mode of proving the existence of specific heat,
which affords a very satisfactory illustration of that modification.
This, however, I did not enlarge upon before, as I thought it might
appear to you rather complicated. --If you mix two fluids of different
temperatures, let us say the one at 50 degrees, and the other at 100
degrees, of what temperature do you suppose the mixture will be?

CAROLINE.

It will be no doubt the medium between the two, that is to say, 75
degrees.

MRS. B.

That will be the case if the two bodies happen to have the same capacity
for caloric; but if not, a different result will be obtained. Thu