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 rivetted 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 immediately after sun rise like a
thick wood and almost darkened the sun. His rays shining through them
for near an hour, gave them an appearance of pillars of fire. Our people
now became desperate, the Greeks shrieked out and said it was the day of
judgment; Ismael pronounced it to be hell; and the Turcorories, that the
world was on fire." Bruce's Travels, Vol. IV. p. 553,-555.

From this account it would appear, that the eddies of wind were owing to
the long range of broken rocks, which bounded one side of the sandy
desert, and bent the currents of air, which struck against their sides;