456 PHYSICAL GEOGRAPHY. 



west, whereas in the early part of its action the east end of the chapel had been blown in, 

 which shows the wind then to have been in the east. The hurricanes of New South 

 Wales have been observed to develop the same peculiarity. Mr. Meredith traced the path 

 of one in the centre, and found at the termination a circle plainly shown, in which the 

 trees lay all ways. 



The cause of this rotatory motion of storms remains in obscurity, but it is probably due 

 in part to the same law under which eddies or whirlpools are formed in water, by two 

 currents being obliquely impelled against each other. The great hurricanes may thus be 

 considered identical with the small local whirlwinds, which are common with us in the 

 summer season, carrying upwards and along the dust and loose grass in spiral columns, 

 exhibiting a progressive and rotatory motion. In the region of the sandy deserts these 

 atmospheric whirls transpire upon a great scale, raising up immense quantities of the 

 loose particles in columns to a considerable height, which sweep along with prodigious 

 violence, and have occasionally swallowed up whole caravans in their tremendous 

 vortex. 



' Man mounts on man, on camels camels rush, 



Hosts march on hosts, and nations nations crush, 



Wheeling in air the winged islands fall. 



And one great earthy ocean covers all." 



" One of the largest of these pillars of sand,'' says a modern traveller, Caille, " crossed 

 our camp, overset all the seats, and whirling us about like straws, threw one of us on the 

 other in the utmost confusion. 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 in one. Whilst this frightful tempest 

 lasted we remained stretched on the ground motionless, dying of thirst, burned by the 

 heat of the sand, and buffeted by the wind. We suffered nothing, however, from the sun, 

 whose disk, almost concealed by the clouds of sand, appeared dim and deprived of its rays." 

 Bruce has sketched with spirit several of these desert whirlwinds of which he was an eye- 

 witness : "At one o'clock," he states, " we aligfited among some acacia trees at Waadi 

 el Halboub, having gone twenty-one miles. We were here at once surprised and terrified 

 by a sight, surely one of the most magnificent in the world. In that vast expanse of 

 desert, from W. to N. W. of us, we saw a number of prodigious pillars of sand at different 

 distances, at times moving with great celerity, at others stalking on with a majestic 

 slowness ; at intervals we thought they were coming in a very few minutes to overwhelm 

 us ; and small quantities of sand did actually more than once reach us. Again they 

 would retreat so as to be almost out of sight, their tops reaching to the very clouds. 

 There the tops often separated from the bodies, and these, once disjoined, dispersed in 

 the air, and did not appear more. Sometimes they were broken in the middle, as if 

 struck with large cannon shot. About noon they began to advance with considerable 

 swiftness upon us, the wind being very strong at north. Eleven of them ranged along- 

 side of us about the distance of three miles. The greatest diameter of the largest appeared 

 to me at that distance as if it would measure ten feet. They retired from us with a wind 

 at S. E. leaving an impression upon my mind to which I can give no name, though 

 surely one ingredient in it was fear, with a considerable deal of wonder and astonishment. 

 It was in vain to think of flying ; the swiftest horse, or fastest sailing ship, could be of no 

 use to carry us out of this danger ; and the full persuasion of this ri vetted me as if to the 

 spot where I stood. The same appearance of moving pillars of sand presented themselves 

 to us this day in form and disposition like those we had seen at Waadi Halboub, only 

 they seemed to be more in number and less in size. They came several times in a 

 direction close upon us, that is, I believe, within less than two miles. They began 



