ware.

EMILY.

According to these experiments, light-coloured dresses, in cold weather,
should keep us warmer than black clothes, since the latter radiate so
much more than the former.

MRS. B.

And that is actually the case.

EMILY.

This property, of different surfaces to radiate in different degrees,
appears to me to be at variance with the equilibrium of caloric; since
it would imply that those bodies which radiate most, must ultimately
become coldest.

Suppose that we were to vary this experiment, by using two metallic
vessels full of boiling water, the one blackened, the other not; would
not the black one cool the first?

CAROLINE.

True; but when they were both brought down to the temperature of the
room, the interchange of caloric between the canisters and the other
bodies of the room being then equal, their temperatures would remain the
same.

EMILY.

I do not see why that should be the case; for if different surfaces of
the same temperature radiate in different degrees when heated, why
should they not continue to do so when cooled down to the temperature of
the room?

MRS. B.

You have started a difficulty, Emily, which certainly requires
explanation. It is found by experiment that the power of absorption
corresponds with and is proportional to that of radiation; so that under
equal temperatures, bodies compensate for the greater loss they sustain
in consequence of their greater radiation by their greater absorption;
so that if you were to make your experiment in an atmosphere heated like
the canisters, to the temperature of boiling water, though it is true
that the canisters would radiate in different degrees, no change of
temperature would be produced in them, because they would each absorb
caloric in proportion to their respective radiation.

EMILY.

But would not the canisters of boiling water also absorb caloric in
different degrees in a room of the common temperature?

MRS. B.

Undoubtedly they would. But the various bodies in the room would not, at
a lower temperature, furnish either of the canisters with a sufficiency
of caloric to compensate for the loss they undergo; for, suppose the
black canister to absorb 400 rays of caloric, whilst the metallic one
absorbed only 200; yet if the former radiate 800, whilst the latter
radiates only 400, the black canister will be the first cooled down to
the temperature of the room. But from the moment the equilibrium of
temperature has ta