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I. § 8.] |
WATER-WAVES. |
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level-line. The reader will at once observe, on looking along the line of circles from left to right, that each particle occupies in its own orbit a position one-eighth of a revolution behind that of the particle to the left of it.
(1) shows the arrangement of the particles when an interval of time equal to one-eighth of the period of a complete circle-revolution has elapsed from the moment at which they were grouped as in (0).
Similarly (2) represents the state of things after two-eighths of that period, (3) after three-eighths of it, and so on, until in (8), one complete period of revolution having in all elapsed, the particles are necessarily again in the same positions as those shown in group (0).
If now the reader allows his eye to be guided by the oblique dotted lines of the figure, he will readily perceive that the wave A has moved horizontally to the right at each of the above stages and, after the lapse of one complete period of particle-revolution occupies, in (8), the position which the wave B held in (l), i.e. has traversed its own wave-length from left to right. We may express this result generally by saying that while an individual particle performs one complete orbital revolution, the wave advances by one wave-length. This is the fundamental pro- |
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