368 UNDULATIONS OF HOT AIR. 



Equinox and blows, at each point, in an opposite 

 direction to the Polar current, or counter trades, which 

 are here passing overhead, as an upper current, in 

 the higher regions of the atmosphere; and with occa- 

 sional intermissions the Simoom continues to blow until 

 the Summer Solstice.* This accounts for the fact that 

 the Simoom (under the name of the " Sirocco "), though 

 of course in a comparatively mild form, invades Southern 

 Europe, and sometimes extends the sphere of its influ- 

 ence for a considerable distance inland it is, for in- 

 stance, occasionally quite distinctly felt all over Spain, 

 as well as at Pau and other places in the South of France, 

 The characteristic features of this wind are, of course, 

 its high temperature and extreme dryness, and in the 

 desert, according to Count D'Escayrac de Lauture, it 

 most generally blows in hot gusts, rather than as a 

 steady breeze; almost as if the plain was being in- 

 undated by undulations of hot air which forms so 

 strongly marked a peculiarity, that the Arabs, who 

 are keen observers of everything connected with the 

 natural phenomena of their desert homes, have a saying 

 "that wind at sea blows horizontally, while that of 

 the desert jumps, and gallops, in excavating the sand. " f 

 It seems highly probable that this undulatory motion 

 of the atmosphere is due to the uprising of waves of 

 heated air, given off from the scorched surface of the 

 sand, and gusts of wind, blowing in this manner, would 

 evidently be likely to put the sand in motion, and carry 

 a certain quantity of it up into the air, which after- 

 wards falls in a rain of sand while the lighter and 



* Le Desert et Le Soudan, par M. Le Comte D'Escayrac de Lauture, 

 1853, pp. 289. 

 t Ibid., p. 46. 



