422 



Acoustics. 



No. 53215 



53 215. 1 : 6. 



53 216. 1 : 8. 



53 219. 1 : 6. 



53,215. Double Siren after Helmholtz, for working by means of compressed air, Figure, 

 with counting mechanism which closes an electric contact when set into action (Helm- 

 holtz, Tonempfindungen, Fig. 56, pp. 268, 291, 303, 652; M. P. I, Fig. 816 [841]; W. D. 

 pp. 260 and 330) 



The Double Siren is very suitable for a large number of important experiments in acoustics and 

 the theory of music, being particularly adapted for these purposes since tin- ratio of the frequencies 

 of the single tones always remains unaltered. The following intervals of tone can lie produced: unison, 

 octaves, fifths, fourths, major third, minor third, whole tone and semi-tone. Special mention may be 

 made of the experiments on the interference of sound, on vibration, on deep and deepest tones, on 

 vibrations of the overtones, and on combined tones. The perforations of the one disc correspond to 

 the tone ratios c : e : g : d,, the perforations of the other correspond to d : g : b : c t . The upper wind 

 chest can be turned by a handle for the purpose of obtaining in the upper siren any phase difference 

 as against the lower one. 



Cl. 1059, 1060, 

 1055. 



s. d. 



16. 0. 





