Mechanical Science. 175 



ment is described as the invention of M. Schortmann, of Butt- 

 stead. The tones are produced by short rods of burnt wood, of 

 various lengths and breadths, put into vibration by a current of 

 air. Its pianissimo perfectly resembles the iEolian harp, and 

 it is described as imitating the harmonica, clarinet, horn, haut- 

 boy, and violin, with much exactness. 



7. New Acoustical Machine : The Siren, — This instrument, 

 intended to measure the number of vibrations of the air re- 

 quired for the production of a sound, is the invention of the 

 Baron Cagniard de la Tour. It was constructed on the idea, 

 that if, as is generally admitted, the sound of instruments is 

 occasioned 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 produce sound. 



The method consists in passing air from a bellows, by a 

 small orifice which is covered by a circular plate, moveable on 

 a centre, at a little distance on the side of the aperture. This 

 plate has a certain number of oblique holes made through it in 

 a circle round the axis, which passes over the orifice of the 

 bellows, and the holes are placed at exactly equal distances 

 from each other. When the plate is made to revolve, which 

 from the obliquity of the holes may be done by the current of 

 air itself, or otherwise by mechanism, the aperture is alternately 

 open and shut to the passage of the air, by which means a re- 

 gular series of blows are given to the external air, and produces 

 sound analogous to the human voice, and more or less acute, 

 according to the greater or lesser rapidity of the plate. 



In the instrument, in place of one aperture many are used, 

 which are opened and shut simultaneously, 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 diameter ; the upper surface of this box is pierced by a 

 hundred oblique apertures, each a quarter of a line in width, 

 and two lines long ; on the centre of this surface is an axis, 

 upon which the circular plate moves ; this plate has also a 

 hundred apertures, corresponding to those below, and with an 



