106 STEPPES AND DESERTS. 



radiation from the ground, less to the great purity and serenity of 

 the sky (irrigiamento calorifico per la grande serenita di cielo nell' 

 immensa e deserta pianura dell' Africa centrale), than to the pro- 

 found calm, the nightly absence of all movement in the atmosphere. 

 (Consult also, respecting African meteorology, Aime in the Explora- 

 tion de PAlgerie, Physique generale, t. ii. 1846, p. 147.) 



The southern declivity of the Atlas of Morocco sends to the 

 Sahara, in lat. 32, a river, the Quad-Dra (Wady-Dra), which for 

 the greater part of the year is nearly dry, and which Renou (Explor. 

 de FAlg. Hist, et G-eogr., t. viii. pp. 65-78) considers to be a sixth 

 longer than the Rhine. It flows at first from north to south, until, 

 in lat. 29 N. and long. 5 W.,it turns almost at right angles to its 

 former course, runs to the west, and, after passing through the great 

 fresh water Lake of Debaid, enters the sea at Cape Nun, in lat. 28 

 46' N. and long. 11 8' W. This region, which was so celebrated 

 formerly in the history of the Portuguese discoveries of the 15th 

 century, and was afterwards wrapped in profound geographical ob- 

 scurity, is now called on the coast " the country of the Sheikh Bei- 

 rouk" (a chief independent of the Emperor of Morocco). It was 

 explored in the months of July and August 1840, by Captain Count 

 Bouet-Villaumez of the French Navy, by order of his government. 

 From the official Reports and Surveys which have been communi- 

 cated to me in manuscript, it appears evident that the mouth of the 

 Quad-Dra is at present very much stopped up with sand, having an 

 open channel of only about 190 English feet wide. A somewhat 

 more easterly channel in the same mouth is that of the still very 

 little known Saguiel el-Hamra, which comes from the south, and is 

 supposed to have a course of at least 600 geographical miles. One 

 is astonished at the length of these deep, but commonly dry river 

 beds. They are ancient furrows, such as I have seen in the Peruvian 

 Desert at the foot of the Cordilleras, between those mountains and 

 the coast of the Pacific. In Bouet's manuscript ^J&lation de TEx- 

 pe*dition de la Malouine," the mountains which rise J to the north of 

 Cape Nun are estimated at the great elevation of 2800 metres (9185 

 English feet). 



Cape Nun is usually supposed to have been discovered in 1433, 

 by the Knight Gilianez, acting under the command of the cele- 



