80 



THE DESEET 



Clear air. 



DuBt 

 particles. 



Hazes, 



the quantities of dust and vapor in the air are 

 comparatively small, the distances that one can 

 see are enormous. A mountain seventy miles 

 away often appears sharp-cuTagainsFjhe_^y, 

 andTat sunseFtEeH1glitsaS3~iEadows upon its 

 side"gi:OoF"only ten miles' distantr~~ '"" ~~' 

 ~ButTi€sert air is iibt quit^ike the plateau 

 air of Wyoming, though one can see through it 

 for many leagues. It is not thickened by moist- 

 ure particles, for its humidity is almost noth- 

 ing ; but the dust particles, carried upward by 

 radiation and the winds, answer a similar pur- 

 pose. They parry the sunshaft, break and color 

 the light, increase the density of the envelope. 

 Dust is always present in the desert air in some 

 degree, and when it is at its maximum with the 

 heat and winds of July, we see the air as a blue, 

 yellow, or pink haze. This haze is not seen so 

 well at noonday as at evening when the snu's 

 rays are streaming through canyons, or at dawn 

 when it lies in the mountain shadows and re- 

 flects the blue sky. Not does it muffle or ob- 

 scure so much as the moisture-laden mists of 

 Holland, but it thickens the air perceptibly and 

 decreases in nieasure the intensity of the light. 

 Yet despite the fact that desert air is dust- 

 laden and must be thickened somewhat, there 



