The most equable temperature on the globe will be found on the high table-lands and pla- teaus of the tropics. Santa Fe de Bogota, in the United States of Colombia, has an average temperature of about 59° F. for all months of the year, and the range for the entire year is less than is often experienced in a single day in some parts of the middle latitudes. But while the ideal temperature may be found on the higher elevations of the tropics, the rain fall is much greater and more continuous than in this country.
The temperature of a place depends chiefly on three conditions,—latitude, elevation and contiguity to large bodies of water. At sea level in the tropies extreme conditions of heat and moisture produce great physical dis comfort. But even under the equator it is pos sible to escape the tropical heat of low levels by, ascending from 4,000 to 6,000 feet. In the economy of nature there is a certain limit be yond which the two extremes, dryness and equability of temperature, cannot coexist; thus we may find a region so deficient in moisture as to satisfy the requirements of the case, but the very lack of moisture is a condition that facilitates radiation and thus contributes to great extremes of temperature. Regions may be found, as on the lower Nile, where there is a lack of rainfall coupled with a high and mod erately uniform temperature. The mean win ter temperature of Cairo, Egypt, is 56° F.; mean summer temperature, 83'; a range from winter to summer of 27°. The mean winter temperature of Phcenix, Ariz., is 52°; mean summer temperature, 87° ; a range of 35°. It is by no means difficult to find a counterpart of the far-famed Egyptian climate in the great Southwest.
The dryness of the air and the clearness of the slcy are the conditions upon which daily ranges of temperature depend; the greater these, the greater the range of temperature from day to night. While a high summer tem perature is characteristic of the Southwest and other portions of the Rocky Mountain plateau, it is a fact that the sensation of heat as ex perienced by animal life there is not accurately measured by the ordinary thermometer. The sensation of temperature which we usually re fer to the condition of the atmosphere depends not only on the temperature of the air, but also on its dryness and the velocity of the wind. The human organism, when perspiring freely, evaporates the moisture of its surface to the dry air of the interior arid regions, and thus lowers its temperature and prevents sunstroke, which, in the more humid regions from the Mississippi Valley eastward, occur in great number with the air temperature much less than obtains in the West.
The meteorological instrument that registers the temperature of evaiporation, and thus in some measure the actual heat felt by the human body, is the wet-bulb thermometer. The latter, as indicated by its name, is simply an ordinary mercurial thermometer whose bulb is wettcd with water at the time of observation.
Effect of Climate on the is the most potent of any factor in the environ ment of races. It is climate and soil, plus heredity and form of government, that produce either vigorous or weak peoples. In this re spect the United States is tuiexcelled by any -othef\region of the world.
Climate, soil and good heredity may pro duce a race large of stature and of great physi cal endurance, but unless such a people exists under a liberal form of government, in which public education is fostered and the arts and sciences taught, it is unable to employ its strength in those lucrative vocations that give a high per capita of wealth. It is weak in de fending itself, either in war or in commerce, against a people of less numerical strength that is liberally educated, skilled and humanely governed.
If we consider the invigorating effect of cold air alone we might expect to find the strongest peoples inside of the Arctic Circle; and if we consider fruitfulness of soil alone we might reasonably expect to find the dominant peoples in the tropics. But the fact is that the greatest human potentiality occurs somewhere between these two extremes. The boundaries cannot be accurately determined by the naming of cer tain parallels of latitude, but a close approxima tion is made to the truth in the statement that the most vigorous people physically and the most resourceful mentally will be found in the regions that produce an abundance of cereal CTOpS.
It is probable that much of the activity that has caused the United States to talce such a commanding place in the world is caused by the invigorating effect of the cold, dry, highly electrified air bf the North Amen can cold wave. These winds have a much greater specific gravity than wann and humid winds, and this condition, added to the force with which they come, scatter and diffuse the befouled air near the surface of the earth. Enough has been said to indicate that climate is nearly as important a part of the environ ment of animal life as it is of the vegetable existence, and that a cortsiderable range of annual temperature, if it be not so great as to limit the production of cereal crops, favors the development of strong races of men.