VALLEYS AND GREAT LEVELS OF THE EARTH. 



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termed in the poetical language of the Orientals. One chief source of danger arises from 

 the Samoom, a hot southerly wind, which rolls along in suffocating masses the sandy 

 billows, darkening the air, and frequently overwhelming every object in their path. 



Sand S;orm lathe Desert. 



This wind in passing over the desert acquires an extraordinary degree of heat and dryness, 

 and stops respiration at once upon exposure to it. To avoid its effects, the Arabs drop the 

 Kafieh, a handkerchief which they wear upon their heads, so as to cover their faces. If 

 the immediate perils of this fierce burning blast are escaped, it often happens that the water 

 contained in the skins borne by the camels is absorbed ; and in such circumstances, if at too 

 great distance to obtain a fresh supply in time, the whole company fall victims to intolerable 

 thirst. In this way an akkabah or caravan, consisting of 2000 persons and 1800 camels, 

 was cut off in the year 1805. The Sahara is one principal theatre of that singular optical 

 illusion called the " mirage," to which the Arabs apply the more poetical name of the Lake 

 of the Gazelles. This is the appearance of tracts of water in the desert a deception 

 supposed to arise from the reflection which takes place between strata of air of different 

 densities, owing to the radiation of heat from the plains of sand. These mock lakes the 

 " waters that fail," or that have no reality often torment the passenger oppressed with 

 heat and thirst. Major Skinner describes a deception of this kind, the most perfect that 

 could be conceived, which for a time exhilarated the spirits of the party with whom he jour- 

 neyed in the desert, and promised an early resting-place. They had observed a slight 

 mirage two or three times before ; but the one in question surpassed all that could well be 

 fancied. Although aware that these, appearances have often led people astray, he could not 

 bring himself to believe that this was unreal. Even the Arabs were doubtful. The seeming 

 lake was broken in several parts by little islands of sand, which gave strength to the delu- 

 sion. The dromedaries of the sheikhs at length reached its borders, and appeared to have 

 commenced to ford, as they advanced and became more surrounded by the vapour. They 

 seemed to have got into deep water, and to be moving with greater caution. In passing 

 over the sand-banks, their figures were reflected in the water. So convinced was one of 

 the party of its reality, that he dismounted and walked towards the deepest part of it, 

 which was on the right hand. He followed the deceitful lake fora long time, and 

 appeared to be strolling on its banks, his shadow stretching to a great length beyond. 

 There was not a breath of wind ; and the sultriness of the day would have added dread- 



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