Sound / by John Tyndall.

  • John Tyndall
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: Sound / by John Tyndall. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

    151/494 page 129
    CHLADXIS TONOMETER. would be heard simultaneously. By damping the proper point and imparting the proper shock, we can still further subdivide the rod, as shown in fig. 55. § 3. ChladnVs Tonometer: the Iron Fiddle, Musical Box, and the Kaleidophone. And now let us shorten our rod so as to render its vibrations sonorous. When it is about four inches long it emits a low musical sound on being agitated by a bow. When further shortened, the tone is higher ; and by con- tinuing to shorten the rod, the speed of vibration is augmented, until finally the sound becomes painfully acute. IThese musical vibrations differ only in rapidity from the .grosser oscillations which a moment ago appealed to the eeye. The increase in the rate of vibration here observed is rruled by a definite law: the number of vibrations exe- cuted in a given time is inversely proportional to the I square of the length of the vibrating rod. You hear the t sound of this strip of brass, two inches long, as the fiddle bow is passed over its end. Making the length of the - strip one inch, the sound is the double octave of the last . one ; the rate of vibration is augmented four times. Thus !by doubling the length of the vibrating strip we reduce i its rate of vibration to one-fourth ; by trebling the length we reduce the rate of vibration to one-ninth; by qua- drupling the length we reduce the vibrations to one- sixteenth, and so on. It is plain that by proceeding in this way we should finally reach a length where the vibrations would be sufficiently slow to be counted. Or, beginning with a long strip whose vibrations could be counted, we might, by shortening, not only make the strip sound, but also determine the rates of vibration corresponding to its different tones. Supposing we start with a strip 36 inches long, which vibrates once in a K
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