n as they are good radiators of caloric, as it is this quality
which reduces their temperature below that of the atmosphere; hence we
find that little or no dew is deposited on rocks, sand, water; while
grass and living vegetables, to which it is so highly beneficial,
attract it in abundance--another remarkable instance of the wise and
bountiful dispensations of Providence.

EMILY.

And we may again observe it in the abundance of dew in summer, and in
hot climates, when its cooling effects are so much required; but I do
not understand what natural cause increases the dew in hot weather?

MRS. B.

The more caloric the earth receives during the day, the more it will
radiate afterwards, and consequently the more rapidly its temperature
will be reduced in the evening, in comparison to that of the atmosphere.
In the West-Indies especially, where the intense heat of the day is
strongly contrasted with the coolness of the evening, the dew is
prodigiously abundant. During a drought, the dew is less plentiful, as
the earth is not sufficiently supplied with moisture to be able to
saturate the atmosphere.

CAROLINE.

I have often observed, Mrs. B., that when I walk out in frosty weather,
with a veil over my face, my breath freezes upon it. Pray what is the
reason of that?

MRS. B.

It is because the cold air immediately seizes on the caloric of your
breath, and, by robbing it of its solvent, reduces it to a denser fluid,
which is the watery vapour that settles on your veil, and there it
continues parting with its caloric till it is brought down to the
temperature of the atmosphere, and assumes the form of ice.

You may, perhaps, have observed that the breath of animals, or rather
the moisture contained in it, is visible in damp weather, or during a
frost. In the former case, the atmosphere being over-saturated with
moisture, can dissolve no more. In the latter, the cold condenses it
into visible vapour; and for the same reason, the steam arising from
water that is warmer than the atmosphere, becomes visible. Have you
never taken notice of the vapour rising from your hands after having
dipped them into warm water?

CAROLINE.

Frequently, especially in frosty weather.

MRS. B.

We have already observed that pressure is an obstacle to evaporation:
there are liquids that contain so great a quantity of caloric, and whose
particles consequently adhere so slightly together, that they may be
rapidly converted into vapou