HANDBOOK OF ACOUSTICS - online book

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

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90                      HAND-BOOK OF ACOUSTICS.
may be mentioned. The density of the fourth string of the violin is increased in the same way.
The pitch of a string, stretched between two fixed supports, is materially affected by heat, especially if the string be of metal As the metal expands on heating and contracts on cooling, the tension becomes less, and the pitch is lowered in the former case, while the tension becomes greater and the pitch rises, in the latter. Heat also produces a difference in the elasticity of strings which acts in the same direction. Strings of catgut are also affected by moisture, which by swelling the string laterally, tends to shorten it, thus increasing the tension, and raising the pitch.
We pass on now, to discuss the conditions, which determine the quality of the tone produced by a stretched string. A                       b                        r
Fig. 46.
.Fasten one end of an india-rubber tube, about 12 feet long, to the ceiling of a room, and taking the other end in the hand, gently move it backwards and forwards. It is easy after a few trials, to 6et the tube vibrating as a whole (fig. 46A). On moving the hand more quickly the tube will break up into two vibrating segments (fig. 46, B). By still more rapid movements, the tube can be made to vibrate in three (fig. 46, C), four, five, or more segments. Precisely the same results can be obtained, by fastening the tube at both ends, and agitating some intermediate point. The points