134 THE ATMOSPHERE AND THE SOIL. 



sented by these edifices with their sun-illuminated walls. Notwith- 

 standing their small dimensions and mean architecture, when thus lit 

 up in glorious radiance, they seem to realize the wonders told in fairy 

 tales of the enchanted palaces of the genii ! 



CHAPTER IV. 



PHENOMENA OF THE DESERT. 



THE desert has its own meteorology ; it is the theatre of peculiar 

 phenomena, which one observes in no other part of the globe. 

 Its climate, at least in the sandy region, is remarkably uniform ; 

 it varies only, according to latitude, in a greater or less elevated 

 thermometrical mean. Hippocrates, the ancient philosopher, rightly 

 called "the Father of Medicine," states the three elements of 

 climate to be, the atmosphere, the soil, and the waters. Throughout 

 the desert these are identically similar, and consequently originate 

 identically similar phenomena. 



The atmosphere, in fact, is everywhere of an almost unchanging 

 purity. It is only in the neighbourhood of mountains that clouds 

 accumulate, to spend themselves at periodical seasons in more or less 

 abundant rains. In the plains it never rains, and during the day no 

 veil is interposed between the earth and the sun's burning glare, nor 

 during the night do any refreshing dews weaken the force of the 

 terrestrial radiation. There result constant alternations of devouring 

 heat while the sun is above the horizon, and of rapid and frequently 

 intense cooling when he has disappeared. 



The soil is everywhere as smooth as " the liquid main." This 

 uniformity contributes, in addition to its silicious, argillaceous, or 

 calcareous character, to render more abrupt the changes of tempera- 

 ture which occur from morning to evening and from evening to morn- 

 ing. In truth, the earth reflects the sun's heat in proportion as it 



