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II WATER-WAVES. [I. §8.
vertical plane, the longer diameter of the oval being horizontal. From the fact that the difference between the horizontal and vertical diameters of the oval diminished as the depth of the water in creased, the brothers Weber inferred that at the surface of very deep water these diameters would be equal, and the orbits of the particles therefore exact circles.
Fig. 5 shows how a series of particles, by describing fixed circular paths in a vertical plane, cause progressive waves to be transmitted horizontally. At the top of the figure are 17 spots representing as many particles floating at equal distances along a straight line in the undisturbed surface of very deep water indicated by dots in the figure. The equal vertical circles are the paths which the particles are respectively about to describe in the direction in which the hands of a watch move, as indicated by a curved arrow in the figure, and with equal uniform velocities.
(0) represents the state of things at a momment when the group of particles plot out two complete equal waves included by the brackets A and B, each consisting of a crest to the right and trough to the left as marked by the sub-brackets a, a' and b, b' respectively. The horizontal dotted line represents, as before, the section of the undisturbed surface or