THE BLUE SKY 



59 



in its color transitions, they are, perhaps, even 

 less observant of its luminosity or light-diffus- 

 ing power. It is a popular belief that the sky 

 is a screen or veil to the earth, and that its 

 principal reason for existence is that it tempers 

 light to human eyes by obscuring it. And that 

 is partly true. But the blue also receives, dif- 

 fuses, and transmits light. It is luminous, 

 at times scintillant, in small bright points. By 

 long and attentive watching one can actually 

 see these little points of light twisting, curling, 

 falling and disappearing quickly as though 

 they were mere flashings of star dust. And this 

 does not refer to that portion of the blue sky 

 near the sun where shafts of light are thrown 

 down, but to the portions far removed, which 

 are seen, perhaps, when the sun itself is under 

 a cloud. The pure blue throws out more light 

 than we imagine. If a sheet of white paper be 

 held under it, even when the sun is below the 

 horizon and eliminated from the problem, it 

 will appear much lighter than the sky. But is 

 it lighter ? Paper is not a body luminous in 

 itself. All the light there is in it is merely the 

 reflection of what comes from the sky, and a 

 reflection can never be so strong as its original. 

 There is an apparent contradiction just here, 



Luminosity 

 of the blue. 



Sluetky 

 and white 

 paper. 



