Oldal 130 [130]
72 LIGHT AND WATER
from beneath the surface, which latter, proceeding in
this case not from the bottom, but from particles
floating in the water, give merely a general impression
of its “local colour;” and, as before, the more obliquely
we look upon the water, the more the former picture
gains in strength at the expense of the latter.
So that we have this further and more important
condition governing the apparent colour of water.
Given smooth water of a definite colour, with a fixed
proportion of suspended particles, and illuminated toa
certain degree, the apparent strength of colour depends
upon the position of the observer, being greatest on look¬
ong vertically down at the surface and lessening gradu¬
ally as the line of vision strikes the surface more and
more obliquely, the colour due to reflexion gaining in
brilliancy as the local colour dies away. For instance,
when looking very obliquely at a sheet of water in the
distance, the objects beyond are reflected as in a
mirror, the reflexions being practically identical in
colour with the objects themselves, whilst the water
itself appears perfectly colourless.’ Indeed it might
be turned into blood and we should not perceive the
change. The same phenomenon can be observed in
any flat reflecting surface, such as the top of a well¬
polished table. Sitting in a low chair, with the eye
only slightly above the level of the table, one sees the
objects beyond distinctly reflected, and one could not
! On referring to the table in the Note, page 64, it will be seen
that at very oblique incidence water reflects by far the greater part
of the light that falls upon it. At the same time the amount of
refracted light reaching the eye in this position is so small as to
be negligible.