equatorial margins of the zones the
difference in temperature between summer and winter becomes smaller, and
the transition seasons weaken and even disappear. At the polar margins
the change from winter to summer, and vice versa, is so sudden that
there also the transition seasons disappear.

These seasonal changes are of the greatest importance in the life of
man. The monotonous heat of the tropics and the continued cold of the
polar zones are both depressing. Their tendency is to operate against
man's highest development. The seasonal changes of the temperate zones
stimulate man to activity. They develop him, physically and mentally.
They encourage higher civilization. A cold, stormy winter necessitates
forethought in the preparation during the summer of clothing, food and
shelter. Development must result from such conditions. In the warm,
moist tropics life is too easy; in the cold polar zones it is too hard.
Near the poles, the growing season is too short; in the moist tropics it
is so long that there is little inducement to labour at any special
time. The regularity, and the need, of outdoor work during a part of the
year are important factors in the development of man in the temperate
zones.

_Weather._--An extreme changeableness of the weather, depending on the
succession of cyclones and anticyclones, is another characteristic. For
most of the year, and most of the zone, settled weather is unknown. The
changes are most rapid in the northern portion of the north temperate
zone, especially on the continents, where the cyclones travel fastest.
The nature of these changes depends on the degree of development, the
velocity of progression, the track, and other conditions of the
disturbance which produces them. The particular weather types resulting
from this control give the climates their distinctive character.

The types vary with the season and with the geographical position. They
result from a combination, more or less irregular, of periodic diurnal
elements, under the regular control of the sun; and of non-periodic
cyclonic and anticyclonic elements. In summer, on land, when the
Cyclonic element is weakest and the solar control is the strongest, the
dominant types are associated with the regular changes from day to
night. Daytime cumulus clouds; diurnal variation in wind velocity;
afternoon thunderstorms, with considerable regularity, characterize the
warmest months over the continents and present an analogy wit