42 
NATURE FOR ITS OWN SAKE 
Necessary 
conditions 
of the 
colored 
shadow. 
Blue 
shadows 
upon snow. 
in shadow or, at least, an error to suppose 
that it is always apparent to us. There are in- 
fluences, too, such as the local color of the 
ground and the sky reflection, that may neutral- 
ize or utterly destroy the complementary hue. It 
might be thought that a yellow sun at midday 
would produce blue shadows under the green 
maple on the lawn, but as a matter of fact it 
does not. The color of the shadow, whatever 
it may be, is absorbed and lost in the green of 
the lawn upon which it falls. The same tree 
shadow falling on pale-gray clay, or across a 
sandy road, will show blue or lilac at once; 
but Ido not think this is owing necessarily to 
the presence of the complementary hue. It is 
more likely caused by sky reflection, helped 
out, perhaps, by atmospheric reflections from 
the sides. 
The blue shadows upon snow, so common 
in winter, are never seen except under a blue 
sky; and the blner the sky the more apparent 
the blue in the shadow. They are produced 
by sky reflection, and the sky coloring is faintly 
apparent on the snow in full sunlight, but more 
obvious, of course, in the shadow. These blue 
shadows are stronger at sunrise and at sunset 
than at any other time. Under a clouded 
