Note 54 — Chapter VIII · (continued 2)

I may here add, that exactly the reverse is true in the melting of snow and ice. It requires as much heat to convert these solids into fluids, without at all increasing their temperature, as it does to raise the temperature of water from the freezing point, one hundred and forty degrees, or from thirty-two to one hundred and seventy-two degrees, as indicated by the thermometer. This principle is of vast importance to the world, and particularly to the inhabitants of cold countries, where the ground is covered with snow and ice a part or the whole of the year. The transition from the cold of winter to the heat of summer, in some of the northern climates, takes place within a few days. In these climates, also, there are vast accumulations of snow and ice, which, but for this principle, would be converted into water as soon as the temperature of the atmosphere becomes above thirty-two degrees, which would produce a flood sufficient to inundate and destroy the whole country. But the uniform action of this law renders the melting of snow gradual, and no such accident ensues.

A similar law is observed in the conversion of water into vapor, which is of great use in enabling us to cool apartments by sprinkling floors or hanging up moistened cloths. The heat of even a whole city is in like manner greatly moderated by frequently sprinkling the streets. It is on this account that gentle showers in hot weather are so cooling and refreshing.