posure
to the dew; for it may be deposited on your clothes, and chill you
afterwards by its evaporation from them. Besides, whenever the dew is
copious, there is a chill in the atmosphere which it is not always safe
to encounter.

CAROLINE.

Wind, then, must promote the deposition of dew, by bringing a more rapid
succession of particles of air in contact with the earth, just as it
promotes the cooling of the earth and warming of the atmosphere during
the heat of the day?

MRS. B.

Yes; provided the wind be unattended with clouds, for these
accumulations of moisture not only prevent the free radiation of the
earth towards the upper regions, but themselves radiate towards the
earth; under these circumstances much less dew is formed than on fine
clear nights, when the radiation of the earth passes without obstacle
through the atmosphere to the distant regions of space, whence it
receives no caloric in exchange. The dew continues to be deposited
during the night, and is generally most abundant towards morning, when
the contrast between the temperature of the earth and that of the air is
greatest. After sunrise the equilibrium of temperature between these two
bodies is gradually restored by the solar rays passing freely through
the atmosphere to the earth; and later in the morning the temperature of
the earth gains the ascendency, and gives out caloric to the air by
contact, in the same manner as it receives it from the air during the
night. --Can you tell me, now, why a bottle of wine taken fresh from the
cellar (in summer particularly), will soon be covered with dew; and even
the glasses into which the wine is poured will be moistened with a
similar vapour?

EMILY.

The bottle being colder than the surrounding air, must absorb caloric
from it; the moisture therefore which that air contained becomes
visible, and forms the dew which is deposited on the bottle.

MRS. B.

Very well, Emily. Now, Caroline, can you inform me why, in a warm room,
or close carriage, the contrary effect takes place; that is to say, that
the inside of the windows is covered with vapour?

CAROLINE.

I have heard that it proceeds from the breath of those within the room
or the carriage; and I suppose it is occasioned by the windows which,
being colder than the breath, deprive it of part of its caloric, and by
this means convert it into watery vapour.

MRS. B.

You have both explained it extremely well. Bodies attract dew in
proportio