And in the
vicinity of the sun a good deal of the blue light is reflected back into
space by the finer dust, thus giving a yellowish tinge to that which
reaches us reflected chiefly from the coarse dust of the lower
atmosphere. At sunset and sunrise, however, this last effect is greatly
intensified, owing to the great thickness of the strata of air through
which the light reaches us. The enormous amount of this dust is well
shown by the fact that, then only, we can look full at the sun, even
when the whole sky is free from clouds and there is no apparent mist.
But the sun's rays then reach us after having passed, first, through an
enormous thickness of the higher strata of the air, the minute dust of
which reflects most of the blue rays away from us, leaving the
complementary yellow light to pass on. Then, the somewhat coarser dust
reflects the green rays, leaving a more orange coloured light to pass
on; and finally some of the yellow is reflected, leaving almost pure
red. But owing to the constant presence of air currents, arranging both
the dust and vapour in strata of varying extent and density, and of high
or low clouds, which both absorb and reflect the light in varying
degrees, we see produced all those wondrous combinations of tints and
those gorgeous ever-changing colours, which are a constant source of
admiration and delight to all who have the advantage of an uninterrupted
view to the west, and who are accustomed to watch for these not
unfrequent exhibitions of nature's kaleidoscopic colour-painting.
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