16 



ANIMAL LIFE IN DESERTS 



warmed very rapidly to a high temperature. The 

 hot surface of the earth then warms the lower layers 

 of the atmosphere by conduction, and produces 

 high air temperatures. At night, on the other hand, 

 there is no blanket of vegetation to hinder loss of 

 heat from the ground. Therefore much of the heat 

 which has accumulated during the day in the 



Fig. 4. 



Xli I II 



IV V VI VII VIII IX X XI Xl> 



40^ 



^ Wadi Haifa. Egypt. Helwan, Egypt 



Babylon, Mesopotamia. 



-Average Monthly Mean Shade Temperatures op Three 

 Places in the Great Pal^la.rctic Desert. 



superficial layers of the soil is radiated into space 

 between sunset and sunrise. 



The monthly average temperatures of certain 

 desert stations are shown graphically in Fig. 4. 

 Two things are apparent : very high temperatures 

 are attained in deserts, higher in fact than are ever 

 reached in many places closer to the Equator, and 

 very wide annual ranges of temperature are char- 



