Jacques Wardlaw Redway

“ Temperature and Radiation.—Very dry, clear air permits the sun’s rays to pass readily to the earth with but little perceptible loss—that is, dry, clean air is diathermous to the heat rays that impart the feeling of warmth to living bodies. [4] The heat is in turn absorbed by the earth. Earth temperature at the surface, or to a depth of an inch or two, may be many degrees higher than that of the air. Thus, in desert regions, pieces of metal lying on the ground in the sun become so hot they cannot be held in the hand. ”

“ The line beyond which grass will not grow is determined in part by temperature; it marks the limit beyond which grazing animals cannot thrive, and, with a few exceptions, cannot survive. Conditions of temperature, such as obtain in the temperate zones, stimulate both the bodily and the mental faculties of humanity. [6] Therefore they have resulted in a civilization fundamentally different from that of tropical regions. ”

“ Because of the vertical rays of the sun in equatorial regions, the air is not only warmed to a much higher temperature, but it is also warmed more quickly than in higher latitudes. Being expanded by the greater warmth, it becomes specifically lighter and is pushed upward by the denser cold air which flows in to take its place. The updraught of air flows poleward in upper currents, until it is chilled and descends to the surface again. A part of the descending current continues poleward but a considerable part flows back to tropical regions as a surface wind. ”

“ Air Altitudes and Terrain Altitudes.—The laws and values which apply to vertical altitudes in free air are not applicable to altitudes on the earth’s surface. In general, temperature decreases with altitude, but this is not always true. At various times the temperature of mountain valley floors is lower than that of the foot-hill slopes several hundred feet higher. On very cold, still nights, low spots, such as stream valleys, are almost always colder than higher ground. In regions where late frosts prevail, fruit growers have learned to take advantage of this fact. ”

“ Every species of plant and animal has an optimum temperature at which it thrives most vigorously, and man is no exception. The optimum may vary a little from individual to individual, but not much. It is more likely to vary from one type of activity to another. For physical health among the white race as a whole, the best temperature is an average of 64° F for day and night together. In other words, people’s health and strength are greatest when the temperature drops to about 56° to 6o° at night, and rises to somewhere between 68° and 72° during the middle of the day. ”

“ On dry, winter days, the flagstones of a sidewalk frequently absorb enough heat to melt ice and snow, even though the temperature of the air is as low as 20°; and occasionally side walks and hard-paved streets are slushy with the thermometer scarcely above 25°. ↑ A moist surface, and very moist air as well, does not have a temperture materially higher than the wet-bulb thermometer; a dry surface, or very dry air, acquires a temperature approximating that registered by the black-bulb thermometer. ”

“ One result of the constant parallelism of the earth’s axis is a movement of the belt of vertical rays—the “heat belt”—back and forth, an angular distance of nearly 47 degrees—from the Tropic of Cancer to the Tropic of Capricorn. The polar circles, 23° 27' from each pole, mark the farthest point beyond each pole to which the sun’s rays extend when vertical at a tropic. Another result of the inclination of the earth’s axis is the increasing length of summer days and winter nights as the latitude increases. ”

“ The study of the relations between temperature and vertical altitudes is a matter of great importance in meteorology, and it has been prosecuted diligently during the last quarter of a century in various parts of the United States, Canada, Europe, South America and Africa. ”

“ It seems certain that the air of the stratosphere contains dust a-plenty—both cosmic dust and dust that is hurled into it by volcanic eruptions. If dust is absent, the air of the stratosphere differs from that below it and from space above it. One thing is certain, the radio-activity within the stratosphere indicates the presence of dust particles highly electrified. ”

“ Throughout the greater part of Europe and the United States, westerly winds prevail; in summer they are frequently from the southwest, and in winter mainly from the northwest. The Pacific Coast of the United States receives ocean winds, and the winters are mild; west of the high mountain ranges zero temperatures rarely if ever occur. Along the coast, summer temperatures are never high ”

“ Over areas of moist air a considerable part of the heat of insolation is absorbed in another way. Almost always in such areas there is a considerable water in the form of mist—that is, minute droplets of water. ”

“ Within the temperate zones the longest days vary from 13.5 hours to 24 hours. The possible hours of daily sunshine vary according to month and according to latitude. Polar and tropical circles are the boundaries, not of climatic, but of light zones. The duration of daylight is of great importance; it governs, in no small degree, the maturing of crops, and therefore concerns practically all agricultural industries. In general, the regions of greatest productivity of staple food-stuffs are those in which the summer days are from 14 hours to 16 hours long. ”

“ Many thousand flights have been made by kites, manned balloons, captive balloons, pilot balloons, sounding balloons, airplanes and dirigible airships. At Uccle, Belgium, a pilot balloon reached an altitude of 20.1 miles, or 32,430 meters. Up to an altitude of about 9 miles, temperature and pressure statistics of the air have been obtained for about every thousand feet of altitude ”

“ In the main, these are the daily range, the range of monthly means, and the seasonal range. These are affected in turn by latitude, by altitude above sea level, by the direction of prevailing winds, and by distance from the sea. In a minor way they are also affected by the moisture and the smoke content of the air.
The mean annual temperature of a place varies but little from year to year. In New York City, the range of yearly means has varied about 6 degrees in ninety-seven years. The average of each ten-year period for that time varies but a trifle from the normal of 52°. ”

“ The cooperative observer’s day begins and ends with the time that the maximum thermometer is set—usually from sunset to the following sunset. The daily mean thus established, however, does not differ materially from the true mean. The monthly and the yearly means are sufficiently accurate for practical purposes. ”

“ Note that an inversion of temperature occurs at the altitude of about 12 miles, and at 20 miles the temperature is about 20 degrees higher than at 12 miles. upper layer may be the warmer; indeed, the airman is quite apt to find a higher temperature above than below. Above a height of 2 miles, when the air is moderately still, the fall in temperature is apt to be fairly uniform. At a height varying from nearly 7 to 10 miles the fall in temperature ceases. ”