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V. § 52.] RATE OF SEGMENTAL VIBRATION. 105 |
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cordingly each point of the tube is displaced through twice as great a distance as if it had been acted on by only one system. The tube thus takes the form indicated by the strong line in the figure. In (2), one set of waves has moved half a pulse-length to the right, and the other the same distance to the left. The two systems are now in complete antagonism, the displacements being equal in amount and opposite in direction at every point. The tube is therefore momentarily in its undisturbed position. In (3), each system has moved through a pulse-length, and the maximum effect is again produced on the tube, but in opposite directions to those of (1). In (4), where the systems have moved through a pulse-length and a half, the tube passes again through its undisturbed position, and, in (5), regains that which it occupied in (l), the systems of waves, meanwhile, having each traversed two pulse-lengths, or one wave-length. Thus the tube executes one complete vibration in the time occupied by a pulse in passing along a length of the tube equal to twice one of its own ventral segments. In other words, the tube's rate of vibration varies as the number of segments into which it is divided. It moves most slowly in the form shown in Fig. 26 with but a single segment; twice as fast in that of Fig. 27, where it is divided into two segments; three times as fast with three segments, and so on. |
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