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 upward 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 traveler, 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 any thing 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 alighted 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 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 the north. Eleven of them ranged alongside 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 riveted 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 sunrise 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.” The procession of tall columns of dust, the upper end seeming to vanish off, or puff away like light smoke, and the lower apparently touching the earth, is not unusual on the large plains of New South Wales, in dry weather. They move in a perpendicular position, quietly and majestically gliding along one after another, but really so fast that the fleetest horse is unable to keep pace with them. According to Mrs. Meredith, when they are crossing a brook, the lower portion of the dust is lost sight of, and a considerable agitation disturbs the water, but immediately on landing the same appearance is resumed. “As some vanish,” she remarks, “others imperceptibly arise and join the giant waltz; and when I first observed this most singular display, I amused myself by fancying them a new species of genii relaxing from their more laborious avocations, and having a sedate and stately dance all to themselves. When the dance ends, these dusty performers always appear to sit down among the neighboring hills.” To the same class with these rotating and progressing pillars of sand, that singular phenomenon called the waterspout clearly belongs, a whirlwind raising into a columnar mass the waters of the sea, and causing the aqueous vapors in the atmosphere to assume the same form, the two frequently uniting, the whole presenting a magnificent spectacle.
Waterspout.
The Greeks applied the term Prester to the waterspout, which signifies a fiery fluid, from its appearance being generally accompanied with flashes of lightning, and a sulphureous smell, showing the activity of the electrical principle in the air. Lucretius refers to it in the following terms:—
Hence, with much ease, the meteor may we trace