CAROLINE.
You astonish me! But why, then, is the air so dry in frosty weather, when its temperature is at the lowest?
EMILY.
This, I conjecture, proceeds not so much from the moisture being dissolved, as from its being frozen; is not that the case?
MRS. B.
It is; and the freezing of the watery vapour which the atmospheric heat could not dissolve, produces what is called a hoar frost; for the particles descend in freezing, and attach themselves to whatever they meet with on the surface of the earth.
The tendency of free caloric to an equilibrium, together with its solvent power, are likewise connected with the phenomena of rain, of dew, &c. When moist air of a certain temperature happens to pass through a colder region of the atmosphere, it parts with a portion of its heat to the surrounding air; the quantity of caloric, therefore, which served to keep the water in a state of vapour, being diminished, the watery particles approach each other, and form themselves into drops of water, which being heavier than the atmosphere, descend to the earth. There are also other circumstances, and particularly the variation in the weight of the atmosphere, which may contribute to the formation of rain. This, however, is an intricate subject, into which we cannot more fully enter at present.
EMILY.
In what manner do you account for the formation of dew?
MRS. B.