Stranica 135 [135]
COLOURS IN STILL WATER . 7:
is, however, very obvious in a case like that shown
in the accompanying photograph of boats, taken
from the high edge of the quay at low tide (Plate
XAXAXAIII). Inthe reflexions of the first row of boats
the dirty green of the water is far more apparent than
in the reflexions of the second row, so much so that
the bright stripes of paint on the nearer boats are
almost lost, whilst those on the boats beyond are dis¬
tinctly reproduced. Plate XX XIV is a further illus¬
tration of the same point. In this case the colour of
the water could be plainly seen in the reflexion of
the nearest duck, whilst that of the farthest showed
no sign of it, but looked as white as the duck itself.
It need scarcely be pointed out that, speaking
generally, the “value” of water in the foreground,
the reflected ray is much stronger than the refracted. By rough
experiment the strengths of the reflected and refracted rays are
found to be equal when looking at an angle of about 13° or 14°
with the surface.
If we mix into the water some Prussian blue or other pigment,
we see its colour by means of light (reflected from the bottom of
the basin) which has lost certain rays by absorption during its
passage through the blue water, but, on lowering the eye to the
second position, the colour of the water entirely disappears, and
we see nothing but the reflexion of the white edge of the basin.
We may now vary the first experiment as follows:—take a piece
of bright red paper and hold it upright with its lower edge almost
touching the water on the further side of the basin. The reflexion
of this red paper as seen from the second position is almost
identical in colour and strength with the direct view of it, but, on
slowly raising the head, the blue colour of the water becomes more
and more apparent, until, looking abruptly down on to the surface
of the water, the red has almost entirely disappeared; so that the
reflexion of the red paper seems to change from red through
purple to blue, (See also footnotes, pages 79 and 92.)