Dew
a deposition of water from the in the form of minute globules. During heat, but after sunset its supply of the day the earth both absorbs and emits warmth is cut off, while it still continues to radiate heat into the surrounding good radiators, lose after sunset the heat space. Grass, flowers, and foliage being which has previously been absorbed by them, without phere. by them, without receiving any in return, and their temperature consequently falls considerably below that of the atmossubstances the particles of vapor in the here. From the proximity of these cold adjoining air are condensed and deposited on their surfaces in the form of dew, or of hoar-frost where the temperature of the earth is below 32°. When the sky is clouded the heat abstracted from the earth's surface by radiation is restored by the clouds, which, being good radiators, send back an amount of heat equal to what they receive; and a balance of temperature being thus maintained between the earth and the surrounding atmosphere, no dew is formed.
Horizontal surfaces, and those which are exposed to a wide expanse of sky, receive a greater supply of dew than sheltered or oblique surfaces, where circumstances diminish the amount of radiation. The radiation from the earth's surface is one of these happy provisions for the necessities of living beings with which nature everywhere abounds. The heavy dews which fall in tropical regions vegetation, which, but for this supply of are in the highest degree beneficial to moisture, would, in countries where scarcely any rain falls for months, be soon scorched and withered. In cold climates the earth, being cold and sufficiently moist, requires little dew; accordingly the clouds, which are so common in damp and chilly regions, prevent the radiation of heat; the surface is thus preserved warm, and the deposition of dew is, in a great measure, prevented.