Page:Popular Science Monthly Volume 76.djvu/255

Rh zones lies a debatable belt, shifting seasonally. Within it, stormy westerlies and drying trades alternately hold sway. It is known as the "subtropical belt." With prevailingly fair skies, even temperature and moderate rainfall, the subtropical belt is a favored climatic region, where invalids seek health, and an escape from the rigors of a cold winter is found by many who have the time, and the means, to leave their northern homes. The long list of well-known health resorts on the Mediterranean, and the shorter list for southern California—"the American Riviera"—bear witness to the popularity of this subtropical belt.

Seasons in most of the temperate zones are classified according to temperature—not, as in the tropics, by rainfall. The four seasons are important characteristics, especially of the middle latitudes of the north temperate zone. These seasonal changes are of the greatest importance in the life of man. They control his occupations, his crops, his place of residence, to a considerable extent his health.

The north temperate zone embraces so great a variety of climates that no single district can be taken as typical of the whole. Its climate has been called "a crazy quilt of patches." The south temperate zone, on the other hand, may be described as a piece of fairly uniform texture and appearance throughout. This is the effect of the large ocean surface. The whole climatic regime is more uniform than that of the northern zone. The south temperate zone may truly be called "temperate," but our own zone is certainly in the highest degree "intemperate."

Characteristics of the Polar Zones.—The climate of the polar zones gains a peculiar character by reason of the longer or shorter absence of the sun. At the poles themselves, the day and the year are alike. In the Arctic climate, plants must make rapid growth in the short, cool summer. They grow and blossom with great rapidity and luxuriance where the exposure is favorable, and where the water from the melting snow can run off. Over great stretches of the northern plains the surface only is thawed out in the warmer months, and swamps, mosses and lichens are found above eternally frozen ground. In high latitudes, where the exposure is good, snow melts in the sun even when the temperature of the air in the shade is far below freezing. It has been reported that at Assistance Bay, latitude 74.5° north, in March, when the air temperature was about—25°, snow near stones and other dark objects melted in the sun. The temperature in the immediate vicinity of the North Pole is probably a little below—40° in January; below 32° in July and a few degrees below 0° for the average of the year. It may be noted, however, that northeastern Siberia has a January mean temperature which is 20° lower than that at the North Pole in the same month.

For the Antarctic our knowledge is still very fragmentary. The