Acoustics & Sound For Musicians - Online Book

The Theory Of Sound Which Constitutes The Physical Basis Of The Art Of Music.

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	II. §26.]                       THE SYREN.                                55 the roughness of the surface, a series of irregular vibrations are set up in the materials of the surface, and of the pencil, and by them communicated to the air. The more rapid these vibrations, the shriller is the sound produced. The instrument described below, which is called a Syren,' gives us the means of following up with accuracy the hint just obtained.
	AB is a thin circular disc of metal or card-board, which by means of a multiplying wheel, can be set in rapid uniform rotation in its own plane about a fixed axis through its centre, C. A series of holes (eight in the figure) are punched in the disc at equal distances along a circle having its centre at C. A small tube, ab, is held with one end close to one of the holes. If, while the disc is rotating, we blow steadily and continuously into the tube at a, a certain quantity of air will pass through the disc