DARBY.
SIRENE.—The Sirene, an instrument for measur ing the number of vibrations of the air, which are re quired to produce a sound, was invented by Baron Cagniard de In Tour. It was made on the principle that if, as is the general opinion, the sound of instru ments is produced by the regular impulses given to the air, by their vibrations, then any mechanical means of striking the air with the same regularity and velocity should also produce sound.
The invention is as follows: A current of air is passed from a bellows by a small orifice, which is covered by a circular plate, moving on a centre, at a little distance on the side of the aperture. Through this plate there is bored a certain number of oblique holes in a circle round the axis, which passes over the orifice of the bellows; and the holes are placed at equal distances from one another. When the plate is made to turn round, which, owing to the holes be ing oblique, may be easily done by the current of air itself, or by mechanical force, the aperture is alter nately open and shut to the passage of the air, by which means a regular succession of blows is given to the outward air, and produces sound similar to the human voice, and varying in the degree of acuteness, according to the velocity of the plate.
In the instrument, in place of one aperture, there are many, which are opened and closed at the same time, by which means its strength is increased, with out the height of the sound being at all interfered with. The instrument is a circular copper box, four inches in diameter, having its upper surface perfo rated with a hundred oblique holes, each a quarter or a line wide, and two lines in length; there is an axis upon which the circular plate moves, on the centre of this surface; this plate is also pierced with 100 holes, similar to those below, and equally oblique, but lying in a contrary direction. The circumstance of their being oblique is not necessary to produce sound, but it gives motion to the plate by the pass ing air. The connexion between the box and the bellows that supplies with air, is effected by means of a tube.
In the experiments made for the purpose of ascer taining the vibrations for each sound, the revolution of the plate was accomplished by wheel work, set in motion by a weight; the bellows were then put in ac tion only to judge whether the sounds of the instru ment agreed with the notes 'of the harmonica, which consists of an arrangement of iron or steel bars, made to vibrate by a bow.
Thus constructed, the instrument was made to pro duce the diatonic notes of the gamut, and even some beyond them; the revolutions of the plate were esti mated by the revolutions of a wheel, which turned with a velocity of thirteen times and a hall' less than that of the plate.
The following table is the result of these experi ments; hut the inventor or the instrument intends to refine and improve his machinery, and then repeat and extend them.
The first la corresponds to the second of the harmo nica, and is the unison of the common diapason.
if water is passed into the Sirene in place of air, sound is produced, even though the instrument be entirely immersed; and the same number of concus sions produces the same sound as in the air. It was owing to this circumstance of the instrument being sonorous in water, that it has acquired the name of Sirene.
The instrument now described is nearly the same as one invented by the late Dr. Robison and de scribed in his System of Mechanical Philosophy, vol.
iv. p. 40S. The following is the passage which con tains it.
It seems to be the general property of sounds that a certain frequency of the sonorus undulations gives a determined and unalterable musical note. The writer of this article has verified this by many exper iments. He finds that any noise whatever, if repeated 240 times in a second, at equal intervals, produces the note C sol fez ut of the guidonian gamut. If it be repeated 360 times, it produces the G so/ re ut, It was imagined that only certain regular agitations of the air, such as are produced by the tremor or vi bration of elastic bodies, are fitted for exciting in us the sensation of a musical note. But he found, by the most distinct experiments, that any noise what ever, created the same effect, if repeated with due frequency, not less than 30 or 40 times in a second. Nothing surely can have less pretension to the name of musical sound than the solitary snap which a quill makes when drawn from one tooth of a comb to another: but when the quill is held to the teeth of a wheel whirling at such a rate that 720 teeth pass un der it in a second, the sound of G in tilt is heard most distinctly; and if the rate of the wheel's motion he varied in any proportion, the noise made by the quill is mixed, in the most distinct manner, with the mu sical note corresponding to the frequency of the snaps. The kind of the original noise determines the kind of the continuous sound produced by it, making it harsh and fretful, or smooth and mellow, according as the original noise is abrupt or gradual; but even the most abrupt noise produces a tolerably smooth sound when sufficiently frequent. Nothing can be more abrupt than the snap now mentioned, yet the g produced by it has the smoothness of a bird's chirrip. An experiment was made of a sound which was less promising than any that can be thought of. A stop cock was so constructed that it opened and shut the passage through a pipe 720 times in a second. This apparatus was fitted to the pipe of a conduit leading front the bellows to the wind chest of an organ. The air was allowed to pass gently along this pipe by the opening of the cock. When this was repeated 720 times in a second, the sound g in all was most smooth ly uttered, equal in sweetness to a clear female voice. When the frequency was reduced to 360, the sound was that of a clear but rather harsh man's voice. The cock was now altered in such a manner that it never shut the hole entirely, but left about one-third of it open. When this was repeated 720 times in a second, the sound was uncommonly smooth and sweet. When reduced to 360, the sound was more mellow than any man's voice at the same pitch. Various changes were made in the form of the cock, with the intention of rendering. the primitive noise more analo gous to that produced by a vibrating string. Sounds were produced which were pleasant in the extreme. The intelligent reader will see here an opening made to great additions to practical music, and the means of producing musical sounds, of which we have at present scarcely any conception; and this manner of producing them is attended with the peculiar ad vantage, that an instrument so constructed can never go out of tune in the smallest degree. See the .111 nales de China. el de Phys. vol. xi i. p. 167, and Robison's ,517/siem of Mechanical Philosophy, vol. iv. p. 903-405.