It is said that these furious whirlwinds have occasionally engulfed 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 wingèd islands fall, And one great sandy ocean covers all." Whether this be true or not, there can be no doubt that the spectacle is one of great magnificence, and calculated to inspire the traveller with emotions of awe and dread. Mr. Atkinson describes it as seen by him, on one occasion, when traversing the Mongolian Desert:-- "As we passed," he says,[62] "in the middle of a space sown with innumerable hillocks of sands, we saw about thirty of them suddenly raise themselves around us, lengthen into long elliptical columns, and glide with many a whirl and sweep over the surface of the Desert with the hissings and contortions of gigantic serpents which had awakened at our approach. These spouts, for the phenomenon was no other, varied in diameter; the smallest measured between twenty and thirty feet; a few attained to a hundred; and one, which absorbed in its vortex all that it approached, rose to nearly two hundred. One might have said, on seeing them bending, rising again and crossing one another in space amidst an atmosphere of dust, that they were antediluvian monsters emerging from their geological bed, and returning into the feverish activity of existence. But soon, the atmospheric forces which had raised them beginning to fail, we saw these sand-spouts fall away one after another, and form on the surface of the Desert a number of moving hillocks similar to those from which we had just emerged." * * * * * The poet, invoking the judgment of Heaven on the traitor, would fain doom him to the misery of cherishing hopes that shall never be realized. "May he," cries the minstrel-- "May he, at last, with lips of flame, On the parched desert thirsting die, While lakes that shone in mockery nigh Are fading oft, untouched, untasted."[63] The image here is borrowed from that most singular phenomenon of the Desert, the _Mirage_; an atmospheric illusion due to the refraction of the sun's rays upon the sand, and the intense expansion of the lower strata of the air,--in other words, it arises from the total reflection of the rays of light from the lower surface of a stratum of air. "This occurs when, from any cause, such a stratum of air possesses a higher refractive power than the one immediately below it. Such a condition of the atmosphere causes remote objects to be seen as if reflected in a mirror, or to appear as if suspended in the air. When the effect is confined to apparent elevation, the English sailors call it _looming_; when inverted images are formed, the Italians give it the name of _Fata Morgana_. The Arabs call it _Serab_, or _Suhrab_, the 'Water of the Desert;' and the Hindus, _Tchittram_, or 'the Picture.'"