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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    prongs of a tuning-fork. After it has been made to vibrate, place a sheet of paper or the blade of a broad knife, with its edge parallel to the axis of the fork, and as near to the fork as may be without touching. If the obstacle be so placed that the section of it is a or P, no effect is produced ; but if it be placed at c, so as to prevent the reciprocating to and fro movement of the air, which tends to abolish the condensations and rarefactions, the sound becomes much stronger. § 2. Laws of Vibrating Strings. Having thus learned how the vibrations of strings are rendered available in music, we have next to investigate the laws of such vibrations. I pluck at its middle point the string b b', fig. 31. The sound heard is the funda- mental or lowest note of the string, to produce which it swings, as a whole, to and fro. By placing a moveable bridge under the middle of the string, and pressing the string against the bridge, it is divided into two equal parts. Plucking either of those at its centre, a musical note is obtained, which many of you recognise as the octave of the fundamental note. In all cases, and with all instruments, the octave of a note is produced by doubling the number of its vibrations. It can, moreover, be proved, both by theory and by the syren, that this half string vibrates with exactly twice the rapidity of the whole. In the same way it can be proved that one-third of the string vibrates with three times the rapidity, producing a note a fifth above the octave, while one-fourth of the string vibrates with four times the rapidity, producing the double octave of the whole string. In general terms, the. number of vibrations is inversely proportional to the length of the string. This is our first law. Again, the more tightly a string is stretched the more rapid is its vibration. When this comparatively slack string is caused to vibrate, you hear its low fundamental