Science and music / [by Sir James Jeans].

  • Jeans, James, 1877-1946.
Date:
1947
Catalogue details

Licence: In copyright

Credit: Science and music / [by Sir James Jeans]. Source: Wellcome Collection.

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    miles a second, is found to be specially suitable for this purpose. Vibrations travel the whole length of a sound¬ board of this material in about a two-thousandth part of a second, so that for low-pitched tones the vibrations are in approximately the same phase ail over the board, and for higher tones the differences of phase are not excessive. Bowed Strings Theories of plucked and struck strings have proved to be comparatively simple; that of a string which is bowed, as in the violin or violoncello, is very much more intricate. A violin-string gives out the same note when it is bowed as when it is plucked, and this shews that the bowing must set up free vibrations of the string. We could not have been sure of this from general principles alone; we might have thought that as the bow provides a continuous stream of energy, it would compel the string to perform “ forced55 vibrations. Such forced vibrations are, in actual fact, ruled out because the force which the bow exerts on the string has no definite periodicity of its own. Helmholtz was able to trace the motion of a violin-string during the bowing process, by attaching a bright bead to it and taking a succession of instantaneous photographs. A more modern method is to make the bowed string per¬ form its vibrations behind a narrow slit, placed at right angles to the string. On looking through this slit, we see only a single point of the string, and when the string is vibrating, this appears to be moving up and down behind the slit. The detailed motion is, of course, too quick to be followed with the eye, but it is easily recorded photo¬ graphically. If a sensitised plate is made to move steadily