Sound / by John Tyndall.

  • Tyndall, John, 1820-1893.
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)

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    the bell. On permitting hydrogen to enter the half-filled receiver until it was wholly filled, the sound sank until it was scarcely audible. This result remained an enigma until it received a simple and satisfactory explanation at the hands of Professor Stokes. When a common pendu- lum oscillates, it tends to form a condensation in front and a rarefaction behind. But it is only a tendency; the motion is so slow that the highly elastic air moves away in front before it is sensibly condensed, and fills the space behind before it can become sensibly dilated. Hence sonorous waves or pulses are not generated by the pendu- lum. It requires a certain sharpness of shock to produce the condensation and rarefaction which constitute a wave of sound in air. The more elastic and mobile the gas, the more able will it be to move away in front and to fill the space behind, and thus to oppose the formation of rarefactions and condensations by a vibrating body. Now, hydrogen is much more mobile than air; and hence the production of sonorous waves in it is attended with greater difficulty than in air. A rate of vibration quite competent to produce sound-waves in the one may be wholly incom- petent to produce them in the other. Both calculation and observation prove the correctness of this explanation, to which we shall again refer. At great elevations in the atmosphere sound is sensibly diminished in loudness. De Saussure thought the explo- sion of a pistol at the summit of Mont Blanc to be about equal to that of a common cracker below. I have several times repeated this experiment; first, in default of any- thing better, with a little tin cannon, the torn remnants of which are now before you, and afterwards with pistols. What struck me most was the absence of that density and sharpness in the sound which characterise it at lower elevations. The pistol-shot resembled the explosion of a