ulation 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.

[Sidenote: Temperature and zonal location.]

Temperature, the other important element of climate, depends primarily
upon zonal location, which has far different historical results from
central and peripheral location, continental and insular. It determines
the amount of heat received from the sun, though air and ocean currents
may redistribute that heat within certain limits, and humi