Stranica 57 [57]
OCR
REFLEXIONS IN RIPPLED WATER 31 Thus we have the well-known effect of a ripple spreading over the water. The image of the hills opposite, a few moments ago so vivid, becomes less and less distinct, being interrupted by minute patches of sky reflexion, while, as the breeze gains in strength, it disappears altogether, and the water gleams with light from sky or cloud. (See Plate IV.) For the reason just given all definite reflexions in water in the far distance vanish entirely with the commencement of the ripple. So far it has been assumed that only the near sides of the waves are in view; but when the breeze is so gentle that the height of the waves is small compared with their length* and one is not standing too low, a certain amount of their farther sides, as in Fig. 13 at a, 6, c, a, e, f, is also seen. In Fig. 11c (page 27) is shown the effect of tilting the mirror away from us, instead of towards us, as before; the lines of vision are now deflected delow flexions in hundreds of minute waves, rather than a single image in any one. For our purpose it is enough to know that light from a given object reaches the eye after reflexion at a certain part of the wave. The ¢circu/ar curves (so drawn for greater convenience) representing the wave forms in this chapter, are only rough approximations to the theoretical wave-form, which is a so-called " harmonic curve ” ey ay SNa or “curve of sines.” It will be noticed that the harmonic curve is much flatter on the sides of the waves than the circular curve. ' The “length” of a wave is the distance from one crest to the next.
