Oldal 162 [162]
96 LIGHT AND WATER
It w ould be outside the scope of this essay to at¬
tempt to discuss fully and systematically the varied
and complex colour effects seen at sea, but, beyond the
general outline which wehavepresented, atewremarks
on some special features will not be out of place.
The waters of the Mediterranean are rich in colour¬
ing, and will furnish illustration of certain points. At
some distance from land, the churning of the screw
or the foam of the breakers shows an almost pure
blue, but nearer shore (probably owing to contamina¬
tion of some kind) the water assumes a greenish
tinge, which becomes still more marked in the har¬
bours. This brilliant colour, it need hardly be said, is
Dover that often greets us on our return to English
waters from sunnier seas. Looking down into the
clear depths of the Mediterranean, however, the water
often seems to be of a slightly purplish or violet blue,
and does not show any sign of green. Even ona dull
day, when looked at perpendicularly from the deck
or in the near sides of the waves, it still appears of
this beautiful deep ultramarine,—so that the colour
is evidently not due to reflexion from the blue sky,—
whilst the farther sides of the waves, being tilted away
from us, reflect strongly the gray light from the clouds.
The most probable explanation of this difference is
that sea water, in common with many other liquids,
possesses the property of showing a somewhat differ¬
ent colour according as one is looking through a thick
or a thin layer of it." In this case the particles in the
‘ A solution of Prussian blue, with which the sea water was
matched in Threlfall’s experiments, described on page 84, has this
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