340 Lord Bayleigh's Acoustical Observations. 



of steam 



3-409 x T ^- r =-3796. 

 17-yb 



That is to say, the kinetic theory and the thermal determina- 

 tion give almost identically the same number. 



This is, I believe, the first experimental proof that the law 

 of "inversely as the molecular weights " applies to compound 

 gases. 



XLI. Acoustical Observations. — IV. By Lord Bayleigh, 

 P.P.S., Professor of Experimental Physics in the University 

 of Cambridge* . 



On the Pitch of Organ-pipes. — Slow versus quick Beats for comparison 

 of Frequencies of Vibration.— Estimation of the Direction of Sounds with 

 one ear. — A Telephone-experiment. — Very high Notes. — Rapid Fatigue 

 of the Ear. — Sensitive Flames. 



On the Pitch of Organ-pipes. 



IN the Philosophical Magazine for June 1877 I described 

 some observations which proved that the note of an open 

 organ-pipe, when blown in the normal manner j was higher in 

 pitch than the natural note of the pipe considered as a reso- 

 nator. The note of maximum resonance was determined by 

 putting the ear into communication with the interior of the 

 pipe, and estimating the intensity of sounds of varying pitch 

 produced externally. 



A more accurate result may be obtained with the method 

 used by Blaikleyf, in which the external sound remains con- 

 stant and the adjustment is effected by tuning the resonator 

 to it. About two inches were cut off the upper end of a two- 

 foot metal organ-pipe, and replaced by an adjustable paper 

 slider. At a moderate distance from the lower end of the 

 pipe a tuning-fork was mounted, and was maintained in 

 regular vibration by the attraction of an electromagnet 

 situated on the further side, into which intermittent cur- 

 rents from an interrupter were passed. Neither the fork 

 nor the magnet were near enough to the end of the pipe 

 to produce any sensible obstruction. By comparison with a 

 standard, the pitch of the fork thus vibrating was found to be 

 255 of Konig's scale. The resonance of the pipe was observed 

 from a position not far from the upper end, where but little of 

 the sound of the fork could be heard independently; and the 



* Communicated hv the Author, 

 t Phil. Mag. May 1879. 



