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MR. T. HOPKINS ON THE INFLUENCE OP SUN-HEATED LAND 



The accounts which we have of other winds that occasionally 

 blow on the same side of the Sahara represent them as coming 

 from the west, that is, from the desert, and towards the Valley 

 of the Nile. This is so decidedly the prevalent direction of 

 these winds, as to cause them to carry the loose sand of the 

 desert towards the river. It is confidently said that this sand 

 has long been covering the land on the west bank of the river, 

 and converting it into desert. Now if air generally ascended 

 from the desert, such a wind would not exist ; it is therefore 

 also evidence in favour of the non-existence of an ascending 

 aerial current within the desert. 



Another wind is sometimes encountered in this part of the 

 world, which is thus described in a popular Geographical work : 

 " Egypt is liable in spring, for a period of fifty days, to the 

 terrible wind of the desert called the Simoom, which from its 

 intense heat and dryness threatens, when long continued, the 

 extinction of animal life. It seldom, however, continues above 

 three days." This wind is probably caused by a local ascend- 

 ing aerial current, as it raises large masses of the sand of the 

 desert to a considerable height. It is generally accompanied 

 by a thick cloud, which intercepts the light of the sun to 

 such an extent as to bring on darkness like that of the 

 night; there must, therefore, notwithstanding the dryness of 

 the air below, be a considerable amount of condensation of 

 vapour taking place above, in order to produce the cloud. 

 One writer, describing this wind, says — " We knew not 

 where we were, and could not distinguish anything at the 

 distance of a foot. The sand wrapped us in darkness, like 

 a fog, and the sky and the earth seemed confounded and 

 blended together." — Caille.* The precise operating cause 



* It 19 recorded that "in August, J 81 9, a fierce Simoom blew at Bagdad, 

 while the temperature was very high, and a heavy rain falling, an unprecedented 

 event, the whole region was converted into a vast hot steam bath." — Milner, 

 p. 495. And Mr. Richardson, the recent African traveller, describes the sudden 

 descent of a large body of water in what had just before been a dry valley of the 

 Sahara. These are instances of the Simoom evidently producing an atmospheric 

 current which ascended high enough to condense the vapour that was in it, but 

 this does not appear to occur often. 



