A peculiarity in the climate of the plateau which deserves to be noticed is the extreme dryness of the atmosphere. In summer the rains which fall are slight, and they are soon absorbed by the thirsty soil. There is a little dew at nights, especially in the vicinity of the few streams; but it disappears with the first hour of sunshine, and the air is left without a particle of moisture. In winter the dryness is equally great; frost taking the place of heat, with the same effect upon the atmosphere. Unhealthy exhalations are thus avoided, and the salubrity of the climate is increased; but the European will sometimes sigh for the soft, balmy airs of his own land, which have come flying over the sea, and seem to bring their wings still dank with the ocean spray. Another peculiarity of this region, produced by the unequal rarefaction of the air over its different portions, is the occurrence, especially in spring and summer, of sudden gusts, hot or cold, which blow with great violence. These gusts are sometimes accompanied with, whirlwinds, which sweep the country in different directions, carrying away with them leaves, branches, stubble, sand, and other light substances, and causing great annoyance to the traveller. They occur chiefly in connection with a change of wind, and are no doubt consequent on the meeting of two opposite currents. Their violence, however, is moderate, compared with that of tropical tornadoes, and it is not often that they do any considerable damage to the crops over which they sweep. One further characteristic of the flat region may be noticed. The intense heat of the summer sun striking on the dry sand or the saline efflorescence of the desert throws the air over them into such a state of quivering undulation as produces the most wonderful and varying effects, distorting the forms of objects, and rendering the most familiar strange and hard to be recognized. A mud bank furrowed by the rain will exhibit the appearance of a magnificent city, with columns, domes, minarets, and pyramids; a few stunted bushes will be transformed into a forest of stately trees; a distant mountain will, in the space of a minute, assume first the appearance of a lofty peak, then swell out at the top, and resemble a mighty mushroom, next split into several parts, and finally settle down into a flat tableland. Occasionally, though not very often that semblance of water is produced which Europeans are are apt to suppose the usual effect of mirage. The images of objects are reflected at their base in an inverted position; the desert seems converted into a vast lake; and the thirsty traveller, advancing towards it, finds himself the victim of an illusion, which is none the less successful because he has been a thousand times forewarned of its deceptive power.