The elements of physiological physics The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology elementsofphysio00mgre Year: 1884 Chap. XXXTI.] THE SIREN. 425 The siren of Cagniard de la Tour (Fig. 186) permits the number of vibrations producing sounds of different pitch to be accurately estimated. It consists of a brass air-chamber B, the top of which is perforated with fifteen holes, disposed at regular intervals from one another. Above the perforated lid is a circular plate D, finely pivoted, capable
The elements of physiological physics The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology elementsofphysio00mgre Year: 1884 Chap. XXXTI.] THE SIREN. 425 The siren of Cagniard de la Tour (Fig. 186) permits the number of vibrations producing sounds of different pitch to be accurately estimated. It consists of a brass air-chamber B, the top of which is perforated with fifteen holes, disposed at regular intervals from one another. Above the perforated lid is a circular plate D, finely pivoted, capable of rotation on the centre of the lid, and pierced with an. equal number of holes at dis- tances from one another corresponding to those of the lid of B. In particular positions the holes of the two plates will exactly coincide. B has an inlet tube through which air may be driven into the chamber by a bellows. Now the holes of the lid and rotating plate are not pierced in a straight direction, but obliquely, and those of the plate are in an op- posite direction to those of the lid. Fig. 186 shows the section carried through one hole, by which the nature of the obliquity is seen. There- fore, when air is blown into B, it escapes through the openings in the lid, and then through those of the disc D. But in pnssiiig from lid to disc, the air strikes obliquely on the holes of the latter, and since it is easily movable, causes it to rotate. By a slight turn of D the holes of B are blocked; but the disc rotating farther, the holes again coincide, the Fig. 186.—The Siren.
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