Oldal 119 [119]
COLOURS IN STILL WATER 6s
towards O. The ray OE would then consist of rays
travelling along AO and CO, and—assuming the
water to be still—of these rays alone. It is evident
that only a minute fraction of the light from above
reaches the eye, whilst it receives a very considerable
proportion of the light from below the surface. On
the other hand, by superimposing Figs. 25 (II) and
(IV), we see that when the eye is placed at e, so that
the line of vision, eO, strikes the surface of the water
very obliquely, it receives a large amount of reflected,
and only a small portion.of refracted, light. The sig¬
nificance of this point will soon be apparent.
When light is reflected at the surface of water it
is unchanged in colour, and therefore the " double”
of the objects that we imagined inverted below the
surface of the water in Chapter I, is similar to the
real scene in colour, as well as in form, though, as our
view of this image is a different one to our direct view
of the objects, so we may get in the reflexion different
combinations of colouring or different effects of light
and shade (page 17). But besides the reflexions that
we see on the water, we actually perceive in most
cases and to a certain extent the colour of the water
itself. Let us consider this apart from the reflexions.
How do we get the sensation of colour? We know
that by passing the sun's light through a prism it can
be split up into rays of different wave-lengths, which
produce upon the eye the effects of the different
colours of the rainbow, and that these coloured rays
can be reunited by means of a second prism to form
white light again. So we say that white light is com¬
posed of light of all colours. Any transparent coloured
F