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.

In the mountain range or Zagros and the tracts adjacent to it, the climate, owing to the great differences of elevation, is more varied than in the other parts of the ancient Media.  Severe cold prevails in the higher mountain regions for seven months out of the twelve, while during the remaining five the heat is never more than moderate.  In the low valleys, on the contrary, and in other favored situations, the winters are often milder than on the plateau; while in the summers, if the heat is not greater, at any rate it is more oppressive.  Owing to the abundance of the streams and proximity of the melting snows, the air is moist; and the damp heat, which stagnates in the valleys, broods fever and ague.  Between these extremes of climate and elevation, every variety is to be found; and, except in winter, a few hours’ journey will almost always bring the traveller into a temperate region.