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 ascreen 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 
acloud. The pure blue throws ont more light 
than we imagine. Ifa 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, 
Blue sky 
and white 
paper. 
