A Dictionary of Music and Musicians/Siren

by William H. Stone

SIREN. This, though not strictly a musical instrument, has rendered such good service to acoustical science that it deserves brief notice: for fuller details the works referred to below must be consulted. 'It consists essentially,' says the most recent writer on mathematical acoustics,^[1] 'of a stiff disc, capable of revolving about its centre, and pierced with one or more sets of holes arranged at equal intervals round the circumference of circles concentric with the disc. A windpipe in connexion with bellows is presented perpendicularly to the disc, its open end being opposite to one of the circles, which contains a set of holes. When the bellows are worked, the stream of air escapes freely if a hole is opposite to the end of the pipe; but otherwise it is obstructed. As the disc turns, puffs of air in succession escape through it, until when the velocity is sufficient, these blend into a note the pitch of which rises continually with the rapid sequence of the puffs. One of the most important facts in the whole science of Acoustics is exemplified by the siren—namely, that the pitch of a note depends upon the period of its vibration. The size and shape of the holes, the force of the wind, and other elements of the problem may be varied; but if the number of puffs in a given time, such as one second, remains unchanged, so does the pitch. We may even dispense with wind altogether, and produce a note by allowing a card to tap against the edges of the holes as they revolve; the pitch will still be the same.'

The Siren may be defined as a wind instrument, in which the successive air-waves are produced not at random or by consonance, but by circular rotatory motion, which is susceptible of accurate adjustment as well as measurement. It was originally invented by Cagniard de la Tour, who made it needlessly complicated by using the force of the wind to drive the rotating disc as well as to produce the required note. For this purpose the speaking holes in the top of the small windchest were pierced in an oblique direction; those in the disc sloping in an opposite diagonal. There was also a counting apparatus attached to the upper part of the main axis, with two dials for registering the number of rotations in a given time. This form has been faithfully reproduced in every manual of Physics up to now.^[2] The name is said to have been somewhat fancifully, and indeed incorrectly, given it from Homer's Sirens, on account of its property of singing under water. It is true that if water be forced through it after the fashion of the Turbine, a buzzing or humming sound is produced. This is, however, of no practical value. The Sirens named in the Odyssey are nowhere accredited with this strange power. Seebeck and others effected material improvements, but the only two which need special notice are the instruments constructed by Helmholtz and Rudolph Kœnig respectively. The former is figured and described in that author's 'Tonempfindungen,'^[3] and consists essentially of two sirens united on a single axis, each disc of which possesses four rows of holes susceptible of being separately opened, thus giving means for producing a large variety of intervals.

The upper windchest, which looks downwards, can be rotated on its feeding-tube so as to bring about varying changes of phase between the two discs. With this instrument Helmholtz succeeded in producing excellent results, using a small electromotor for driving it at an uniform rate.

The Siren of M. Rudolph Kœnig of Paris is a far more imposing instrument. It was made for W. Spottiswoode, Esq., P. R. S., was exhibited by the writer at the British Association meeting at York in 1881, and is now in the physical laboratory of the College of Science at Bristol. It is furnished with more than a dozen rotating discs of different kinds, which fit on to a vertical spindle, above a windchest of large size fitted with a keyboard of eight notes. A strong clockwork actuated by heavy weights forms the motive power, and an ingenious counting apparatus is made not only to record the number of rotations, but also to set going automatically a watch movement, and thus obtain by one motion of the observer's hand the speed of the disc, and the time of the observation. By properly computing the rings of perforations, the harmonic series is given by one disc, and the enharmonic scale by another. Indeed there is hardly any law of musical acoustics which it cannot be made to illustrate.^[4] For purposes of demonstration the siren is excellent, and also for the illustration of perfect musical intervals; but for the accurate determination of absolute pitch it is far inferior to Lissajous's optical method; and still more so to Scheibler's tuning-fork method, described under Tonometer [App. p.793 "for Tonometer read Scheibler"], and to Prof. McLeod's Cycloscope.

[ W. H. S. ]

1. Lord Rayleigh, Theory of Sound, vol. i. p. 5.
2. Deschanel, Nat. Philos. iv. p. 822; Everitt's translation. Ganot's Physics, p. 189; Atkinson's transl.
3. Helmholtz, Sensations of Tone, Ellis's transl. p. 243 et seqq.
4. A description of this Instrument is to be found in Poggendorf's Annalen, and in the Philosophical Magazine, for 1876.