26 



AGRICULTURAL EXPLORATIONS IN ALGERIA. 



DESERT REGION. 



TEMPERATURE. 



If we had no other data concerning the climate of the Sahara than 

 the mean annual temperature, we should .suppose it to be a very mild 

 one. The variations from the yearly, monthly, and daily mean.s are, 

 however, enormous. Winter temperatures of 18 F. and summer 

 temperatures of 112° F. are by no means uncommon. The daily 

 range sometimes exceeds S6 degrees. The unshaded soil — sandy or 

 rocky— becomes heated up to 160'^ F. At Biskra, which is by no 

 means extreme in its summer climate, it is said to be possible some- 

 times to cook an egg in the sand. In the Oued Rirh region, on the 

 other hand, ice sometimes forms in winter in the irrigation ditches. 

 Evaporation is imdoubtedly very great, but no accurate records of this 

 phenomenon havQ been kept in the Sahara. 



Table 3. — ifean temperatures (in degrees Fahrenlieil) of localities in the desert region 

 of Algeria, as compared with similar localities in the southwestern United States. 



Of the stations in the Algerian desert comprised in the accompanying 

 table of temperatures, Bou Saada, at an elevation of 2,194 feet, l)elongs 

 rather to the high plateau region, lying north of the mountain chain 

 which forms the boundary of the Sahara. It is in a region, however, 

 where the conditions are entirely desert-like, closely resembling those 

 of the higher western part of the Sahara. The other three stations 

 are in the low eastern part of the Sahara proper. Biskra can hardly 

 be regarded as a typical locality, being just within the limits of the 

 desert, only a few miles south of the mountains which form the north- 

 ern boundary of the Sahara. Biskra is 407 feet above sea level. 

 Tougourt, 120 miles farther south, in the Oued Rirh country, is the 

 center of some 40 oases, where hundreds of thousands of date palms 

 are orown. Its altitude above mean .sea level is 22(5 feet. Ouargla, well 

 into the Sahai-a, 120 miles still farther south, has the .same elevation. 



