Page 163 [163]
COLOURS IN RIPPLED WATER 97
depths give a thick layer, whilst the air bubbles in
the wake, being near the surface, furnish a thin layer
of water; the former appears violet-blue or ultra¬
marine, the latter greenish or cyan-blue.
When at anchor in full sunshine, the colour of the
water is most vividly seen towards midday if the
observer looks over the rail at the sunlit surface close
to his own shadow, for in this position he is looking
straight at the illuminated sides of the floating par¬
ticles (as we do at the illuminated surface of the moon
when at the full), and they therefore reflect more light
to the eye than if the direction of vision differed con¬
siderably from that of illumination. Here the colour
will be more brilliant than in the shadow of the vessel,
where (as explained in the last chapter, page 77)
more of the sky colour and less local colour is seen.
Looking over the other side of the boat, the colour will
not show up so strongly—unless in the dark reflexion
of a boat lying alongside, where, the sky reflexion
being interrupted, the colour of the water is again
very obvious. bj
By the shore there will often be seen a patch of
bright green, where a shelving rock or pebbly beach
property. If two bottles of colourless glass, one large and the other
small, be filled from the same solution of Prussian blue, and placed
against the same white background, the difference, not merely in
shade, but actually in colour, between a thin and a thick layer of
the solution will be seen at once. Indeed, one bottle is sufficient
to show it, the colour varying with the direction in which one looks
through the bottle, or with the strength of the transmitted light.
The paler parts are distinctly green, the darker show no signs of
it; and in the deepest parts, as when looking down on to the
shoulder of the bottle, the violet tinge appears.
H