Stranica 61 [61]
OCR
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 between 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 positions 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 appearing 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 anywhere 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
