316 PHYSIOGRAPHY 



(afternoon )rains. In this belt flourish the forests of the Amazon 

 and of middle Africa. 



Along the coasts of tropical lands, the temperature is modified 

 by the daily sea-breezes, as well as by the monsoons. 



The range of temperature in the tropical deserts is considerable. 

 The average annual temperature of the Sahara is about 80 F. The 

 temperature of the warmest month averages about 90 F., and that 

 of the coldest about 70 F. ; the average annual range is therefore 

 relatively slight. But the yearly extremes of temperature are far 

 greater, for the temperature sometimes reaches 120 F., and some- 

 times drops to 50. Great as this range (70) is, it is far less than 

 that of most inland places in the intermediate zones, where extreme 

 ranges of 120 are not uncommon. 



Climate of Intermediate Zones 



The average temperature of the intermediate zones is lower 

 than that of the tropical zone, their annual range of temperature is 

 greater, and their daily range, on the average, less. 



These zones receive from the sun less heat per square mile than 

 lower latitudes, where the rays are more nearly vertical. This 

 explains their lower average temperature. The range of tempera- 

 ture from season to season is greater than in the tropical zone, 

 because of (1) the greater inequality of day and night, and (2) the 

 greater range in the angle of the sun's rays, and therefore greater 

 variation in their heating power. In latitude 45, for example, 

 there are, at the maximum (summer solstice), about 15^ hours of 

 sunshine (and heating) and 8J^ hours of night (and cooling), while 

 at a minimum (winter solstice) there are but 8^ hours of sun- 

 shine, with 15^ hours of night. Not only this, but when the days 

 are longest, the sun's rays are most nearly vertical, so that the heat 

 received in an hour is greatest when the days are longest, and least 

 when they are shortest (Fig. 213). The result is that the summers, 

 even in the latitude of 45, may be very hot, while the winters are 

 very cold. The summer heat, at its maximum, is not less than that 

 of the tropical zone; and the winter cold, at its severest, is frigid. 

 The annual range is greater in the higher latitudes of this zone than 

 in the lower. 



