PRECIPITATION. 



27 



TABLE 6. Mean relative humidity at localities in the desert regions of Tunis, 

 Algeria, and the United States. 



Winter comprises December, January, and February ; spring, March, April, and May ; 

 summer, June, July, and August ; and autumn, September, October, and November^ 



As shown by the above table, the Tunis oases have at all seasons a 

 decidedly more humid atmosphere than those of Algeria. At Yuma 

 the air is drier than at any of the North African localities, except in 

 summer, when Yuma is more humid than Biskra and Ouargla. 

 Comparing the three Tunis localities one with another, we find that 

 at most seasons the humidity is greatest at Gabes, as would be 

 expected from its situation on the coast, and least at Gafsa, which 

 lies in the midst of extremely arid elevated plains and is cut off from 

 the sea by ranges of desert mountains. Tozer in winter is slightly 

 more and in spring little less humid than Gabes, but in summer and 

 autumn it is decidedly drier. All things considered, the humidity at 

 Tozer is surprisingly higher for a locality where the finest kinds of 

 dates are produced. 



PRECIPITATION. 



TABLE 7. Normal precipitation, in inches, at localities in the desert regions of 

 Tunis, Algeria, and the United States. 



The total annual rainfall of the Jerid oases (Tozer and Nefta) is 

 very much less than that of Gabes, on the coast of Tunis, and of 

 Gafsa, which has an elevation of 1,000 feet above sea level. Tozer 



The relation of the rainfall of the Tunis oases to date production is dis- 

 cussed under the heading " Ripening," on pp. 51 and 52 of this bulletin. 

 92 



