It is for the same reason that the
"Italian skies" are of so rich a blue, because the Mediterranean Sea on
one side and the snowy Alps on the other do not furnish so large a
quantity of atmospheric dust in the lower strata of air as in less
favorably situated countries, thus leaving the blue reflected by the
more uniformly distributed fine dust of the higher strata undiluted. But
these Mediterranean skies are surpassed by those of the central Pacific
ocean, where, owing to the small area of land, the lower atmosphere is
more free from coarse dust than in any other part of the world.
If we look at the sky on a perfectly fine summer's day, we shall find
that the blue colour is the most pure and intense overhead, and when
looking high up in a direction opposite to the sun. Near the horizon it
is always less bright, while in the region immediately around the sun it
is more or less yellow. The reason of this is that near the horizon we
look through a very great thickness of the lower atmosphere, which is
full of the larger dust particles reflecting white light, and this
dilutes the pure blue of the higher atmosphere seen beyond.
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