THE BLUE SKY 



49 



into black space, but the color gradations are so 

 subtle that we do not perceive the changes from 

 one to another. Clouds help us somewhat in 

 increasing the feeling of depth, for they are 

 perspective points five or six miles on the way 

 at least. Sometimes a pillar of cumulus will 

 rise in the air thirty thousand feet from base to 

 top, and tracing this upward the eye may see 

 far above it the drift clouds of the stratus, and 

 still higher, like specks upon the blue, the fine- 

 spun fibres of the cirrus. This will give some 

 idea of distance, though it is not entirely satis- 

 factory. The view from Alpine peaks, where 

 we are already twelve thousand feet up, and see 

 still far above us against a violet sky the white 

 spirals of the ice clouds, is not more satisfactory, 

 save that in the thinner and clearer air the feel- 

 ing of space is greater, and the sky becomes 

 more of a blue wilderness than a domed roof. 



We comprehend the breadth and reach of the 

 sky perhaps as little as its depth. Our horizon 

 is an apparent circle as our zenith is an imagin- 

 ary point. The circle is twenty, fifty, or from 

 high ground perhaps seventy miles in diameter, 

 but we always see its outside limit the com- 

 plete circle no matter how vast the view. No- 

 where is the eye so hemmed in, nowhere does 



