670 THE UNIVERSE. 



ing, and advancing as if on wheels. Its overhanging sum- 

 mit is of a brick color, its base deep red and almost black. 

 In proportion as it approaches it drives before it burning 

 effluvia, like the breath of a lime-kiln. Before it reaches us 

 we are covered with its shadow. The sound it makes is like 

 that of a wind passing through a pine forest. So soon as 

 we are in the midst of this hurricane the camels halt, turn 

 their backs, throw themselves down, and lay their heads 

 upon the sand. After the cloud of dust comes a rain of im- 

 perceptible stones, violently hurled about by the wind, and 

 which, if it lasted long, would quickly flay the skin from 

 those parts of the body unprotected by the clothes. This 

 lasted five or six minutes, and was frightful. Then the sky 

 became clear again, and gave the same feeling of sudden 

 change to the eye as a light suddenly brought into a dark 

 place." 



It is in the sand deserts that the phenomenon of the mi- 

 rage takes place most frequently. I was enabled to see it 

 once in all its splendor. 



The captain or reis of our escort had asked leave to stay 

 at a part of the Nile where stood one of his harems, in order 

 to pass the day there with his wives and family. I say one, 

 for he had several, ingeniously established along the river, 

 the scene of the continual voyages which he made. He 

 stopped by successive stages at each of his establishments, 

 in such a way as not to excite the jealousy of any of the 

 sultanas whom he maintained. 



I had profited by this halt to make an excursion into the 

 desert, and had started, when the reis, seeing me in the dis- 

 tance, came with some Arabs of his tribe to beg I would 



