Forest Patrols
AERIAL. (See AERONAUTICS: FOREST PATROLS.) FOUR-POWER TREATY. (See WASHINGTON CONFERENCE.) FRANCE. Leygues ministry succeeded (Jan. 16, 1921) by that of Aristide Briand. Premier Briand succeeded by Raymond Poincaré (Jan. 15, 1922).
FROSTS AND FROST PROTECTION.
The term frost, in agricultural usage, means the occurrence of a temperature low enough to kill or injure vegetation.
Such a temperature is usually about the freezing point of water, being being a little under 32° Fahrenheit in the case of ordi- GANDHI plants is acnary fruits and vegetables. The temperature of a plant may be affected by other conditions than the atmospheric temperature considered by itself. Thus a clear, calm night is more conducive to frosts than a moist, disturbed night, since the absence of clouds facilitates the radiation of heat from the earth; evaporation of moisture goes on more rapidly, and the surface of plants is accordingly chilled; while the absence of disturbing winds or breezes allows the colder, heavier layers of air to settle stagnantly to the ground. For the same reason, frosts are more apt to occur in valleys than at points higher up on hillsides, the cold air settling undisturbed in the valley. Moisture in the atmosphere retards evaporation, and thus is one of the preventives of frost. The U. S.
Weather Bureau classifies frosts as light, heavy, and killing. This bureau has made an extensive study of the subject and maintains the most thorough frostprotection service in the world. In addition to the regular publication of frost charts and special forecasts, it distributes warnings by telegraph, by telephone, and, more recently, through the agency of radio broadcasting stations. Frostprotection methods include the covering GANDHI of plants with screens of glass, wood, straw, cloth, or paper; the building of smudge fires to form blankets of smoke, and the artificial charging of the air with moisture or the sprinkling of the leaves and buds of plants themselves to prevent evaporation on clear nights when frosts are threatened. Orchards are especially endangered by frosts, and some are provided with alarm thermometers, which ring a bell at the approach of the danger point. Heaters of various types are used, with the object, primarily, of preventing the settlement of a stagnant layer of cold air on the orchard. In extensive orchards it has been discovered that there are "warm spots" in which the trees are less liable to be injured by frosts, due probably to something in the character of the soil. There are also "thermal belts" or "verdant zones" in orchard regions of mountainous States, where the temperature under ordinary conditions is higher than in belts both below and above. The local prediction of frosts from general weather observations is still uncertain. An extensive study of the subject has been made by the Weather Bureau and published as Supplement 16 of the Monthly Weather Review (1920).
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