Science for beginners . ating and the Winds.—The earths sur-face is heated most near the equator; also wherever there ismost sunshine, and where the land slopes toward the sun,and where there is bare ground, or certain kinds of soil. Thisunequal heating is the chief cause of the winds. Warm air isexpanded and is lighter than cold air. The warm lighter airis then pushed away or crowded upward by the colder heavierair from other places or from above. Those movements of theair are the winds. The greater heating at the equator is the 156 THE WEATHER principal cause of the whole system of earths wi
Science for beginners . ating and the Winds.—The earths sur-face is heated most near the equator; also wherever there ismost sunshine, and where the land slopes toward the sun,and where there is bare ground, or certain kinds of soil. Thisunequal heating is the chief cause of the winds. Warm air isexpanded and is lighter than cold air. The warm lighter airis then pushed away or crowded upward by the colder heavierair from other places or from above. Those movements of theair are the winds. The greater heating at the equator is the 156 THE WEATHER principal cause of the whole system of earths winds (SeeArts 216 and 221). Many other influences help. 167. The Wind and Our Personal Temperature; Why aWindy Day Seems Cool.—The air is usually cooler than ourbodies, and takes away heat from the body. The wind forcesair through the clothing and brings fresh supplies of cold airinto contact with the body to carry away our heat. Theharder the wind blows the faster the body loses its heat andthe colder seems the Fig. 111.—A lath screen. These are usually arranged to roll or slideaside to admit sunshine. Night temperature under this screen aver-aged 4 degrees higher than in an unprotected orchard nearby. To leftof center, in foreground, is seen one type of firepot used in warming theground air. (Illustration by F. A. Carpenter, in Monthly Weatlter Review.) 168. The Lag of Temperature; Afternoon and Night.— While the earth is being warmed by the sun, it is also coolingall the time by radiating heat out into space. During the fore-noon of a clear day the ground receives heat faster than itradiates heat, and our temperature rises. This continuesusually till about 2 or 3 p. m. But the warmer the ground be-comes, the faster it radiates heat. By 2 or 3 p. m. radiation THE ATMOSPHERE AND ITS TEMPERATURE 157 (cooling) usually becomes faster than the warming. At thatmoment the temperature begins to fall. Ordinarily radiation(cooling) continues greater through the remainder o
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