Stranica 54 [54]
30 LIGHT AND WATER
so that unless the ripple is very gentle, the image is
soon lost. The position of the spectator in the figure
(Fig. 12) is so chosen that he can see little but the
near sides and the crests of the waves, and indeed
this is generally the case when one is standing close
to a sheet of water and looking at a gently rippled
surface at a little distance. he line of vision is so
nearly parallel to the level of the water that the far
sides of the waves are out of sight. The objects on
the opposite shore are seen reflected in the crests
of the waves (supposing always that they would be
visible in that part of the water, if smooth) and be¬
tween these glimpses of the image the sky appears
by reflexion on the tilted surfaces. If the water is
much agitated, or if one is looking in a virtually hort¬
zontal direction, as at distant waves from a position
near the level of the lake, one sees nothing but their
near sides, and therefore in all probability only re¬
flected sky light.’
" In any wave-section (as in Figs. 12 or 13) there is of course
only one point on the crest of each wave—z.e., the summit—where
. the normal is vertical, and where a ray would therefore be reflected
as on a horizontal plane. But on either side of this point there is a
short piece of the curve where the normals are nearly vertical, and
which would reflect rays to the eye from points close above or below
the point which is seen reflected in the summit. ‘Thus a conspicuous
white object, such as the side of a house, gives patches or strips of
white light on the crests of the waves.
It is perhaps unnecessary to warn the reader that if he could see
a definite image of any object in the curved side of a wave, it would
be a very distorted one (and in a concave surface an erect, instead
of an inverted, image). As a matter of fact, this is hardly ever
possible, and moreover does not at all concern us in the present
discussion, as we are considering the combined effect of the re¬