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REFLEXIONS IN RIPPLED WATER 33
what takes place in the water. By comparing these
two figures (11b and ric) we see that the position
of F’s reflexion moves backwards and forwards be¬
tween A and D, and that of G between K and C.
In other words, if we could substitute a sheet of
rippled water for our table and mirrors ! the reflexion
of the picture would be prolonged towards us as far
as D, and away from us as far as K. The reflexion
of the wall below would blend with this as far as C,
and every part of the surface nearer than A would
also show light from the wall above or the ceiling.
By prolonging the lines EA in Fig, t1b and ED
in Fig. 11c to f, making Afequal to AF and Df equal
to DF, we get the position of the image of the point
F in each diagram. These are the two extreme posi¬
tions of the image of F, and between these it may be
seen at any intervening position (its normal position
being shown in Fig. 11a) so that, instead of appear¬
ing as a point, it seems to be drawn out into a vertical
line.” Of course, if the water were more strongly
rippled, the position of F s reflexion would lie any¬
where between a point still farther back than A and
:! We assume that the imaginary sheet of water is rippled by waves
(travelling at right angles to the direction of vision) to such a degree
that the greatest inclination of the tangent to the surface at any
point is that of the mirrors in Figs. 11b and r1c, an angle of 5 to
the horizon.
* These points, / in each diagram all lie, of course, in the plane
of reflexion (or incidence), that is, the plane containing all the lines
of vision both before and after reflexion. For the sake of greater
clearness, the intersection of this plane with the ceiling, wall and
floor is shown by a brokenline. In 110, f lies in front of the plane
of the wall; in 11b, behind it.
D