significance, unless its mineral resources developed unsuspected importance.  In Europe, the absence of mountain barriers across the course of these westerly winds from Norway to central Spain, and the unobstructed avenue offered to them by the Mediterranean Sea during fall and winter, enable all the Atlantic’s mitigating influences of warmth and moisture to penetrate inland, and temper the climate of Europe as far east as St. Petersburg and Constantinople.  Thus several factors have combined to give the western half of Europe an extraordinarily favorable climate.  They have therefore greatly broadened its zone of historical intensity toward the north, pushed it up to the sixtieth parallel, while the corresponding zone in eastern Asia finds its northern limit at the fortieth degree.

[Sidenote:  Rainfall.]

Moisture and warmth are essential to all that life upon which human existence depends.  Hence temperature and rainfall are together the most important natural assets of a country, because of their influence upon its productivity.  The grazing capacity and wheat yield of southern Australia increase almost regularly with every added inch of rainfall.[1419] The map of population for the Empire of India clearly shows that a high degree of density accompanies a high and certain rainfall.  Exceptions occur only where hilly or mountainous tracts offer scant arable areas, or where plains and valleys are sparsely populated owing to political troubles or unhealthiness.  Nearly three-tenths of the population are found crowded together on the one-tenth of India’s level territory which is blessed with a rainfall above the average for the country.[1420] Deserts which yield nothing are purely climatic phenomena.  Steppes which facilitate the historical movement, and forests which block it, are products of scant or ample precipitation.  The zonal distribution of rainfall, with its maxima in the Tropics and the Temperate Zones, and its minima in the trade-wind belts and polar regions, reinforces and emphasizes the influence of temperature in determining certain great cultural and economic zones.

In equatorial regions, which have an abundant rainfall throughout the year, agriculture is directed toward fruits and roots; only in certain districts can it include cereals, and then only rice and maize.  The temperate grains demand some dry summer weeks for their maturity.  Excessive moisture in Ireland has practically excluded wheat-growing, which in England and Scotland also is restricted chiefly to the drier eastern counties.[1421] It thrives, on the other hand, in Manitoba and the Red River region even with a short season of scant rainfall, because this comes in the spring when moisture is most needed.[1422] Most important to man, therefore, is the question how and when the rainfall is distributed, and with what regularity it comes.  Monsoon and trade-wind districts labor under the disadvantage of a wet and dry season, and a variability which brings tragic results, since it easily reduces a barely adequate rainfall to disastrous drought.  These are the lands where wind and weather lord it over man.  If the rains hold off too long, or stop too soon, or withhold even a small portion of their accustomed gift, famine stalks abroad.