842 Lord Rayleigh's Acoustical Observations. 



Pressxire, in 



Difference of i 



Remarks . 



inches. 



frequencies. 





4-2 



4-11-0 





272 



93 





226 



8-4 





1-86 



71 





1-53 



5-6 





1-32 



4-2 





106 



2-1 





•88 



1-5 





•82 



+ "I 





■75 



— o 





•68 



1-2 





•64 



2-3 





•57 



3-9* 



About this point a discordant high note comes 

 in alongside of the normal note. 



•53 



3-7 





•48 



3-1* 



Here the discordant note ceases. 



•46 







•40 







•391 

 ■38/ 



- 4-ii 





■35 



* 



* About this point the octave of the normal 

 note is heard, after which the normal note 

 itself disappears. 



■30 







The normal note l'eappears. the octave con- 

 tinuing. 

 The octave goes, and then the normal note, 



•26 











after which there is silence. 



•20 



+ 



Octave comes in again, and then the normal 

 . note, at a pitch which falls from consider- 



•11 





ably above to a little below the natural 

 I pitch. At the lowest pressures the normal 

 note is unaccompanied by tbe octave. 



Slow versus quick Beats for comparison of Frequencies of 

 Vibration. 



Most of those who have had experience in counting beats 

 have expressed a preference for somewhat quick beats. Per- 

 haps the favourite rapidity has been four beats per second. 

 There is no doubt that in the case of insufficiently sustained 

 sounds slow beats are embarrassing. The observer gets con- 

 fused between the fall of sound which is periodic and that 

 which is due to the dying away of the component vibrations. 

 and loses his place, as it were, in the cycle. But it is also 

 possible, I think, to trace an impression that, independently of 

 the risk of confusion, quick beats can be counted with greater 

 accuracy than slow ones. It is indeed true that the number 

 of beats" in a given time, such as a minute, can be determined 

 with greater relative accuracy when there are many than 

 when there are few ; but it is also true, as a little considera- 

 tion will show, that in the comparison of frequencies we are 



