Sweden north of the sixtieth parallel. [See map page 484.]

[Sidenote: Effect of the westerlies.]

Owing to the prevalence of westerly winds in the Temperate Zones and
particularly in the North Temperate Zone, the mean annual temperature is
high on the western face of the northern continents, but drops rapidly
toward the east.[1417] This is especially true of winter temperatures,
which even near the eastern coast show the severity of a continental
climate. Sitka and New York, Trondhjem and Peking have the same mean
January temperatures, though Peking lies in about the latitude of
Madrid, over twenty-three degrees farther south.

Europe's location in the path of the North Atlantic westerlies, swept by
winds from a small and narrow ocean which has been super-heated by the
powerful Gulf Stream, secures for that continent a more equable climate
and milder winters than corresponding latitudes on the western coasts of
North America, whose winds from the wide Pacific are not so warm.[1418]
Moreover, a coastal rampart of mountains from Alaska to Mexico restricts
the beneficial influences of the Pacific climate to a narrow seaboard,
excludes them from the vast interior, which by reason of cold or aridity
or both must forever renounce great economic or historical 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 pop