85 



the desert is deeper dyed and warmer lined than 

 any other for the reasons just given. It takes 

 on many tints at different times, dependent 

 upon the thickening of the envelope by heat 

 and dust-diffusing winds. I do not know if it 

 is possible for fine dust to radiate with heat 

 alone ; but certain it is that, without the aid of 

 the wind, there is more dust in the air on hot 

 days than at any other time. When the ther- 

 mometer rises above 100 F., the atmosphere is 

 heavy with it, and the lower strata are dancing 

 and trembling with phantoms of the mirage at 

 every point of the compass. It would seem as 

 though the rising heat took up with it countless 

 small dust-particles and that these were respon- 

 sible for the rosy or golden quality of the air- 

 coloring. 



There is a more positive tinting of the air 

 produced sometimes by high winds. The lighter 

 particles of sand are always being drifted here 

 and there through the aerial regions, and even 

 on still days the whirlwinds are eddying and 

 circling, lifting long columns of dust skyward 

 and then allowing the dust to settle back to 

 earth through the atmosphere. The stronger 

 the wind, and the more of dust and sand, the 

 brighter the coloring. The climax is reached 



Color pro- 

 duced by 

 dust. 



Effect of 

 heat. 



Effect of 

 winds. 



