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CHAPTER VI. |
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ON THE CONNEXION BETWEEN QUALITY AND MODE OF VIBEATION.
70. It was stated on p. 74 that, when a pendulum performs oscillations whose extent is small compared to the length of the pendulum, the period of a vibration is the same for any extent of swing within this limit. We will apply this fact to prove that the prongs of a tuning-fork vibrate in the same mode [§ 11] as a pendulum.
When a sustained simple tone is being transmitted by the air, we may regard it as originated by a tuning-fork of appropriate pitch and size. But we know experimentally that, by suitable bowing, we may elicit from such a fork tones of various degrees of intensity, but having all the same pitch. Here, therefore, though the extent of vibration varies, the period remains constant, which is the pendulum-law. Accordingly the vibrations of a tuning-fork are identical in mode with those of a pendulum. The same thing will hold good of the aerial vibra- |
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