98 



THE DESERT 



The night 

 sky. 



Slackness 

 of space. 



Bright sky- 

 eolors. 



has darkened still more and has a violet hue 

 about it. The night sky at this altitude is al- 

 most weird in its purples. A deep violet fits 

 up close to the rim of the moon, and the orb 

 itself looks like a silver wafer pasted upon the 

 sky. 



The darkening of the sky continues as the 

 height increases. If one could rise to, say, fifty 

 thousand feet, he would probably see the sun 

 only as a shining point of light, and the firma- 

 ment merely as a blue-black background. The 

 diffusion of light must decrease with the grow- 

 ing thinness of the atmospheric envelope. At 

 what point it would cease and the sky become 

 perfectly black would be difficult to say, but 

 certainly the limit would be reached when our 

 atmosphere practically ceased to exist. Space 

 from necessity must be black except where the 

 straight beams of light stream from the sun and 

 the stars. 



The bright sky-colors, the spectacular effects, 

 are not to be found high up in the blue of the 

 dome. The air in the zenith is too thin, too 

 free from dust, to take deep colorings of red 

 and orange. Those colors belong near the earth, 

 along the horizons where the aerial envelope is 

 dense. The lower strata of atmosphere are in 



