[ 216 ] 



XXVII. Notes on theTheory of Sound. By R. H. M. BosAN- 



QUETj Fellow of St. Johns College, Oxford. 

 [Continued from p. 136.] 



FROM the above principles the proportion of the issuing 

 energy which reenters the tube can be immediately de- 

 duced. In the case of outward flow, one fourth of the issuing 

 energy reenters the tube ; in the case of inward flow, the 

 whole. (The reentering quantity is measured in the first case 

 bv 



in the second case by 



Q2-y 



f 



If the air is flowing outward half the time and inward half the 

 time, the energy lost in a complete period Avill be half the 

 whole ; if the period be not divided symmetrically between 

 the inward and outward flow, the case will be different. It is 

 difficult to submit this to the test of experiment ; but it may 

 be done in simple cases by testing the resonance to tuning- 

 forks diflering in pitch from the proper note of the resonator 

 or pipe considered. 



The following approximate result of experiment is now 

 enunciated, so far as I am aware, for the first time. 



The character of the sympathetic vibration of all resonators 

 which communicate with the outer air by simple openings is 

 approximately the same when referred to Helmholtz's scale 

 (Ellis's ' Helmholtz,' p. 213); i. e. the difference of pitch in 

 the exciting tone which reduces the intensity to ^ is the 

 same ; and the number of vibrations after which the energy 

 of the vibration reduces to ^ is the same. I had been under 

 tlie impression, the origin of which I cannot now trace, that 

 resonators which had apertures small compared with their length 

 stood higher in the scale of retention than such as have large 

 apertures. It is on experimental grounds that I have come 

 to recognize the fallacy of this. The following is the simplest 

 crucial experiment. 



A bottle resonator with small aperture resounds to e\)''. A 

 brass tube about an inch in diameter, open at both ends, re- 

 sounds to the same note. A c^' fork, a minor third below, is 

 struck, and rapidly passed over the apertures of bottle and 

 tube alternately. If the experiment is properly arranged, 

 the sympathetic response is about equal in the two cases. 



