HANDBOOK OF ACOUSTICS - online book

A complete view of Acoustical Science & its bearings on music, for musicians & music students.

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124
HAND-BOOK OF ACOUSTICS.
occur through a fall, or by screwing or unscrewing them in and out of resonance boxes.
VlBRATIONS OF PLATES.
Though not of much importance in reference to music, these vibrations are of much interest, on account of the beautiful method by which their forms are analysed. The plates usually employed are constructed of either metal or glass, the metal being usually brass. Any regular shape may be adopted, the most common being the circular and square forms. The plate is firmly fastened at the centre or some other point, to a stand; and the vibrations are best set up, by bowing the edge of the plate with a double-bass bow. The rate of vibration of a circular plate is directly proportional to the thickness, and inversely proportional to the square of the diameter.
A node can be formed at any desired point, by touching that point firmly, while bowing. By thus successively touching various parts of the plate, a variety of notes of different pitches, corre­sponding to its overtones, may be obtained, the plate vibrating
Fig. 64.
differently for each note. About 100 years ago, Chladni discovered the method of rendering these different vibration forms visible, by