Oldal 97 [97]
REFLEXIONS IN RIPPLED WATER :3
Fig. 15, which represents the view of P and its re¬
flexions as seen from Q, we draw through P a hori¬
zontal line,’ we shall get as the reflexions of this line
a succession of pairs of horizontal lines (one pair for
each wave) through the points a and ő, c and d, 7 and
£, / and 2? But, owing to the irregularity of the sur¬
face of the water, and the breaking up of the troughs
by crossing waves into comparatively short depres¬
sions, these different reflexions of a horizontal line
cannot continue in the water as horizontal lines. If
we follow one of the pairs of theoretically horizontal
lines on the side of a wave, we soon come to a place
where the trough assumes such a shape that only one
image, or none, can be formed; so that the two lines
merge into one or vanish completely, perhaps to re¬
appear a little farther on, and instead of two parallel
lines we see a chain of loops or a series of disconnected
rings.°
Such rings are amongst the commonest features of
gently moving water in the foreground of a picture.
The reflexions of a boom or bowsprit, or of any con¬
spicuous horizontal line, often assume this form (see
On the third wave there is only one point at which P can be seen
reflected, viz., E.
! Representing a straight line through P, Fig. 14, at right angles
to the plane of the paper.
? And a single horizontal line through e.
> A cup filled with water is all the apparatus necessary for the
production of “rings.” Let the cup be placed so that a horizontal
bar of the window frame is seen reflected in the still water. If the
water be gently stirred round, its surface will become concave, and
when the rotation has nearly ceased, the reflexion of the window¬
bar in the hollow surface will be seen to take the form of a ring.