6Q ON THE PHYSIOLOGICAL CAUSES OF 



the human larynx, the metal tongues of the harmonium, 

 the reeds of the clarionet, oboe and bassoon, the trembling 

 lips of the trumpeter, or the air cut by a sharp edge in 

 organ pipes and flutes. 



A tone of the same number of vibrations has always 

 the same pitch, by whichever one of these instruments it 

 is produced. That which distinguishes the note A of a 

 piano for example, from the equally high A of the violin, 

 flute, clarionet, or trumpet, is called the quality of the 

 tone, and to this we shall have to recur presently. 



As an interesting example of these assertions, I beg to show 

 you a peculiar physical instrument for producing musical tones, 

 called the siren, Fig. 1, which is especially adapted to establish 

 the properties resulting from the ratios of the numbers of vibra- 

 tions. 



In order to produce tones upon this instrument, the portventg 

 go and gi are connected by means of flexible tubes with a 

 bellows. The air enters into round brass boxes, ao and aj, and 

 escapes by the perforated covers of these boxes at Cq and Cj. But 

 the holes for the escape of air are not perfectly free. Immediately 

 before the covers of both boxes there are two other perforated 

 discs, fastened to a perpendicular axis k, which turns with great 

 readiness. In the figure, only the perforated disc can be seen at 

 Cq, and immediately below it is the similarly perforated cover of 

 the box. In the upper box, c,, only the edge of the disc is 

 visible. If then the holes of the disc are precisely opposite to 

 those of the cover, the air can escape freely. But if the disc is 

 made to revolve, so that some of its unperforated portions stand 

 before the holes of the box, the air cannot escape at all. On 

 turning the disc rapidly, the vent-holes of the box are alternately 

 opened and closed. During the opening, air escapes; during 

 the closure, no air can pass. Hence the continuous stream of 

 air from the bellows is converted into a series of discontinuous 

 puffs, which, when they follow one another with suflicient 

 rapidity, gather themselves together into a tone. 



Each of the revolving discs of this instrument (which is more 

 complicated in its construction than any one of the kind hitherto 

 made, and hence admits of a much greater number of combina- 



