Rainfall and Natural Sections.— The habitability of a land outside of Arctic regions depends first upon its water supply and sec ondly upon its disposition. The prevailing winds which supply the rainfall of all countries by the ocean vapors they carry blow nearly cast and west, the easterly called specifically "trades,' the westerly "anti-trades." The eastern con tinent has its greatest length in this direction and a great mountain wall on the east; hence much of central Asia lying beyond the reach of vapors remains a permanent desert. America, from its narrowness and its sides being toward these winds, is much more easily supplied. The Great Lakes add to the rainfall in their region; the Gulf of Mexico, as will be demonstrated, turns the whole east centre from a potential desert to a garden; and the only entire deserts are between two arms of the western range in the northern part and some portion of the strip along the western coast of the southern.
In the polar regions the cold and physical conformation make the water supply of little avail. Northern Alaska and northern Canada are flat, spongy moors but half reclaimed from the ocean, with permanently frozen subsoil, thawing slightly in the brief, intense summer (sometimes of and developing a few mosses, grasses and weeds, with dwarfed shrubs and clouds of mosquitoes. (See ALASKA). But the distance southward to which Arctic conditions extend is t.L greater on the eastern coast than the western, owing to the effect of the Rocky Mountain wall in breaking the force of the polar winds, and of the warm ocean vapors ; the latter also make the temperature far more equable. The midwinter Arctic tem perature of 50° and below has no representative on the western coast. The Labrador coast, latitude for latitude, is 20° colder than the Alaskan in mean annual temperature, about 20° against 40° even in the extreme northwest; and its mean midwinter temperature 30° colder, against 5°. Even from the interior to the western coast the isotherms rise astonishingly; that of north Virginia at lat. 40° N. is that of British Columbia at 50°. On the other hand, the range of temperatures is much greater on the east, the temperature rising pretty steadily as we go southward, to 80° mean annual on the Mexican Gulf coast, a range of 60° from semi-Arctic to semi-tropic, while in the corre sponding part of southern California it is only 70°, a range of 30°. The midwinter range is over on the east coast, not above 50 on the west; the midsummer is 40° in the east, not over 20° on the whole coast from southern California to Bering Sea. Much greater ex
tremes still are found in the Cordilleran region, where the mean annual embraces a scale of and the mean midsummer runs from 40° to in southern Arizona and northern Mexico, while the thermometer rises to 120° at times, as at Fort Yuma and similar places.
From about lat. 52° N. to perhaps 44° in the interior and east, the climate, though not quite fatal to civilized energies, is very severe, with winters of seven or eight months and summers at best but short and not always calculable, though rising to 100° and over in waves; with sudden intense "northers" and "blizzards' of intense cold with fine dry snow sometimes par alyzing business activities for days. The dry atmosphere, however, makes it less trying than the damper though somewhat warmer eastern weather; it has developed great cities and popu lous States in the United States and flourish ing communities in Canada above ; and the industrial and intellectual future of the region is as promising as that of any part of the con tinent. There is not much difference between the central and eastern parts in this respect, Duluth and Quebec, Saint Paul and Ottawa, corresponding closely in parallels and nearly in climate. Northwestern Canada and the northern central States of the United States form the great cattle and wheat district of North Amer ica; and this on both sides of the Rockies is the chief timber section. South of this is the great °temperate° section, shading into the semi-tropic by imperceptible degrees, but which in the United States may be roughly divided by the basin of the Ohio. The northern por tion has summers and winters of the same gen eral character as the former, but less intense at either extreme, neither hot waves nor cold waves usually lasting long; the weather damper than in the farther north. It is the chief region of Indian corn and apples, hay and potatoes, etc. The southern half shows the beginnings of tropic elements in the seasons, which are not so much winter and summer as wet and dry; in the luxuriance of vegetation and characteris tically tropic varieties; in the less bracing at mosphere and in the bottom lands its languor ous oppressiveness; in the domestic architecture, where the obvious desire is to escape heat rather than to ward off cold; and in the productions, such as cotton and tobacco, rice and sugar, sweet potatoes, and oranges in the far south.