On the Sireiie, a new Acoustic Imlrumenl. 2S3 



ter principle, precipitable by acetate of lead; a volatile oil; a 

 fixed oil; albumen; animalized matter; mucus; saccharine 

 mucus ; a yellow bitter principle, not precipitable by the acetate 

 of lead; and mineral salts. 



XLIII. On the Sirene, a new Acoustic Instrument designed to 

 measure the Vihrations of Air which constitute Sound. By 

 Baron Cagniard de la Tour*. 



Xf the sound produced by instruments is omng principally, as 

 philosophers believe, to the regular succession of multiplied shocks 

 which they give to the atmospheric air by their vibrations, it 

 seems natural to think, that by means of a mechanism so com- 

 bined as to strike the air with the same swiftness and the same 

 regularity, the production of sound may be effected. 



Such, in fact, is the result which I have obtained by means of 

 an ajjparatus constructed by me, of which the following is the 

 mode of operation : The wind of a pair of bellows is made to 

 issue through a sniall orifice, covered by a circular plate, move- 

 able on a centre placed at a little distance from the aperture. The 

 circular plate has a number of oblique equidistant holes made 

 through it, in a circle round the axis, which passes over the ori- 

 fice of the bellows : when this plate is made to revolve, (which, 

 by the obliquity of the holes, may be effected by the current of 

 the air, or otherwise by proper mechanism,) the aperture is alter- 

 nately open and shut to the passage of the air ; and thus a regu- 

 lar series of blows are given to the external air, and sounds ana- 

 logous to the human voice are produced, and more or less acute 

 according to the velocity with which the plate revolves. In place 

 of one aperture many are used, which are opened and shut simul- 

 taneously, by which means, without interfering with the height 

 of the sound, its strength is increased. 



The instrument is a circular copper box four inches in diame- 

 ter. Its upper surface is pierced by 100 oblique apertures, each 

 a quarter of a line in width and two lines long : on the centre 

 of this surface is an axle upon which the circular plate turns : 

 this plate has also 100 apertures corresponding to those below, 

 and with an equal obliquity, but in an opposite direction. The 

 obliquity is not necessary to the production of the sounds, but it 

 serves to give motion to the plate by the currents of air. The 

 box is, by a tube, connected with the bellows that supply the air. 



In the experiments to ascertain the vibrations for each sound, 

 the plate was made to revolve by wheel-work moved by a weight. 

 The bellows were then used only for the purpose of judging whc- 



• From Aiwtka de Chitmc, toin. xii. p. 1G7. 



thcr 



