the same degree in an
apparatus adapted to receive and measure the caloric which they give
out. Thus, if you plunge them into three equal quantities of water, each
at the same temperature, you will be able to judge of the relative
quantity of caloric which the three bodies contained, by that, which, in
cooling, they communicated to their respective portions of water: for
the same quantity of caloric which they each absorbed to raise their
temperature, will abandon them in lowering it; and on examining the
three vessels of water, you will find the one in which you immersed the
lead to be the least heated; that which held the chalk will be the next;
and that which contained the milk will be heated the most of all. The
celebrated Lavoisier has invented a machine to estimate, upon this
principle, the specific heat of bodies in a more perfect manner; but I
cannot explain it to you, till you are acquainted with the next
modification of caloric.

EMILY.

The more dense a body is, I suppose, the less is its capacity for
caloric?

MRS. B.

This is not always the case with bodies of different nature; iron, for
instance, contains more specific heat than tin, though it is more dense.
This seems to show that specific heat does hot merely depend upon the
interstices between the particles; but, probably, also upon some
peculiar constitution of the bodies which we do not comprehend.

EMILY.

But, Mrs. B., it would appear to me more proper to compare bodies by
_measure_, rather than by _weight_, in order to estimate their specific
heat. Why, for instance, should we not compare _pints_ of milk, of
chalk, and of lead, rather than _pounds_ of those substances; for equal
weights may be composed of very different quantities?

MRS. B.

You are mistaken, my dear; equal weight must contain equal quantities of
matter; and when we wish to know what is the relative quantity of
caloric, which substances of various kinds are capable of containing
under the same temperature, we must compare equal weights, and not equal
bulks of those substances. Bodies of the same weight may undoubtedly be
of very different dimensions; but that does not change their real
quantity of matter. A pound of feathers does not contain one atom more
than a pound of lead.

CAROLINE.

I have another difficulty to propose. It appears to me, that if the
temperature of the three bodies in the oven did not rise equally, they
would never reach the same degree; the le