24 



ANIMAL LIFE IN DESERTS 



of temperature are excessive, and there is little 

 moisture available to increase the humidity of the 

 air when its temperature rises. There is, therefore, 

 a great contrast between the forest type of climate, 

 with a very constant humidity, and the desert type, 

 in which the humidity fluctuates widely in each 

 period of twenty-four hours. 



In point of fact such a range of relative humidity 



Monday -^mt— -Tuesday >f<^- Wednesday-^ 



19 P.!4t r2 24 12 I 







Fig. 7. — Curve obtained from Recording Instrument showing Daily 

 Fluctuation in Relative Humidity at Gizeh, Egypt, 20th-22nd 

 March, 1922. 



The figures on the side of the graph represent percentages of humidity. (C. B. Williams.) 



as is shown in Fig. 7 does not occur from one year's 

 end to another in many tropical forests, yet at 

 Gizeh, Egypt, it is a normal daily occurrence during 

 the summer. The curve of which Fig. 7 is a repro- 

 duction was actually made during the end of March, 

 1922, and shows that the humidity can drop from 

 saturation to 20 per cent, in a few hours. Fig. 8, 

 which shows the daily fluctuation (8 a.m. and 4 p.m.) 



