Page:Popular Science Monthly Volume 13.djvu/179

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WATER-WAVES AND SOUND-WAVES.

—not with uncertain speed, but so regularly that all the waves all round are all parts of circles and of concentric circles.

PSM V13 D179 Wave formation by circular motion.jpg
Fig. 2.—Showing the Formation of Waves by the Circular Motion of Each Particle of Water in a Vertical Plane. Eight positions in each revolution are shown—I. One Particle in Motion.—II. Two Particles in Motion.—III. Three Particles in Motion.—IV. Complete Wave and Motion of its Elements.

Let us drop two stones in at some little distance apart. What happens then? We have two similar systems each working its way outward, to all appearance independently of the other. We get what is represented in Fig. 1.

PSM V13 D179 Graphical observation of a vibrating tuning fork.jpg
Fig. 3.—Graphical Method of observing the Mode of Vibration of a Tuning-Fork.