158 



Lord Rayleigh's Acoustical Observations. 



regular, it is sufficiently powerful to prevent more than one 

 note being sounded. 



In the experiments that I have tried, the pipes were blown 

 from a bellows provided with a special regulator, and the 

 pitches of the various notes were determined by counting the 

 beats for 20 seconds between them and a somewhat sharper 

 note on a harmonium. Sometimes the blown ends of the 

 pipes were near together, and sometimes (in the case of open 

 pipes) the unblown ends ; but during the course of an experi- 

 ment the positions of the pipes were not altered. In order 

 to prevent a pipe speaking, I placed some cotton wool over the 

 wind-way, and sometimes inserted a stopper; so that the pitch 

 of the pipe as a resonator was entirely altered. The following 

 are the details of some of the observations : — 



I. Sept. 23. Open metal pipes about 2 feet long, one of 

 them provided with an adjustable paper slider for modifying 

 the pitch. Blown ends near one another ; unblown ends distant. 



Beats per second with harmonium-note. 



One pipe alone. 

 4-5, 4-5 



Both pipes together. 

 3-2, 3-1 ; 



Other pipe alone. 

 5-0, 4-8 



So that the note given by both pipes together is decidedly 

 sharper than those of the separate pipes. 



II. Sept. 23. Same pipes as in I. Unblown ends 

 one another ; blown ends distant. 



Beats per second with harmonium-note. 



near 



One pipe alone. 



4-8 



Other pipe alone. 

 5-1 



Both pipes together. 

 3-8 



III. Sept. 25. Same pipes placed parallel to one another 

 at a distance of about 14 inches. 



Beats per second with harmonium-note. 



Both pipes together. 



5-00, 5-15 



One pipe alone. Other pipe alone. 



5-15, 5-20 5-30, 5-45 



The note of both pipes together is somewhat higher than 

 the notes of the single pipes. 



IY. Sept. 26. Same pipes. Unblown ends near ; blown 

 ends distant. 



Beats per second. 



Both pipes together. 

 5-35, 5-50, 5-45 



One pipe alone. Other pipe alone. 

 5-80,5-85 7-15,7-50,7-45 



Y. Sept. 26. Two bottles, tuned with water to about g, 

 were blown by wind issuing from flattened tubes connected 



