m is effected; this you found to be the case
when the marble table cooled your hand, and again when it melted the
ice.

CAROLINE.

This reciprocal radiation surprises me extremely; I thought, from what
you first said, that the hotter bodies alone emitted rays of caloric
which were absorbed by the colder; for it seems unnatural that a hot
body should receive any caloric from a cold one, even though it should
return a greater quantity.

MRS. B.

It may at first appear so, but it is no more extraordinary than that a
candle should send forth rays of light to the sun, which, you know, must
necessarily happen.

CAROLINE.

Well, Mrs. B--, I believe that I must give up the point. But I wish I
could _see_ these rays of caloric; I should then have greater faith in
them.

MRS. B.

Will you give no credit to any sense but that of sight? You may feel the
rays of caloric which you receive from any body of a temperature higher
than your own; the loss of the caloric you part with in return, it is
true, is not perceptible; for as you gain more than you lose, instead of
suffering a diminution, you are really making an acquisition of caloric.
It is, therefore, only when you are parting with it to a body of a lower
temperature, that you are sensible of the sensation of cold, because you
then sustain an absolute loss of caloric.

EMILY.

And in this case we cannot be sensible of the small quantity of heat we
receive in exchange from the colder body, because it serves only to
diminish the loss.

MRS. B.

Very well, indeed, Emily. Professor Pictet, of Geneva, has made some
very interesting experiments, which prove not only that caloric radiates
from all bodies whatever, but that these rays may be reflected,
according to the laws of optics, in the same manner as light. I shall
repeat these experiments before you, having procured mirrors fit for the
purpose; and it will afford us an opportunity of using the differential
thermometer, which is particularly well adapted for these experiments.
--I place an iron bullet, (PLATE III. Fig. 1.) about two inches in
diameter, and heated to a degree not sufficient to render it luminous,
in the focus of this large metallic concave mirror. The rays of heat
which fall on this mirror are reflected, agreeably to the property of
concave mirrors, in a parallel direction, so as to fall on a similar
mirror, which, you see, is placed opposite to the first, at the distance
of about ten feet; thence