Sensitiveness of the Ear to Pitch. 



597 



fork. The amplitude of vibration of the prongs of the fork 

 was under continuous observation with the aid of a micro- 

 scope. From this could be inferred the energy in the fork 

 at any time and the rate at which it was lost. The loss was 

 greatest when the resonator was in action, and the excess 

 was taken to represent the energy converted into sound. 

 From this again the condensation in the progressive waves 

 at a given distance could be calculated. It was remarked 

 that the numbers thus obtained were " somewhat of the 

 nature of upper limits, for they depend upon the assumption 

 that all the dissipation due to the resonator represents pro- 

 duction of sound. This may not be strictly the case even 

 with the moderate amplitudes here in question, but the 

 uncertainty is far less than in the case of resonators or 

 organ-pipes caused to speak by wind." 



In a careful re-examination of this question, M. Wien * t 

 working with the telephone, finds not only a still higher 

 degree of sensitiveness but a much more rapid variation 

 with pitch. In the following extract from his table xiv., 

 N represents the frequency and A the proportional excess 

 of pressure, equal to ys, where 7 is the ratio of specific heats 

 of air (1'41). The higher degree of sensitiveness may be 



K 



1 



A. 



X. 



A. 



50 



1-OxlO- 7 



1600 



1-4 xlO" 11 



100 



rixio~ s 



3200 



1-lxlO- 11 



200 



1-0 xio--' 



6400 



2-3 XlO" 11 



400 



1-2X10- 1 " 



12800 



SOxlO- 11 



800 



2-3xl0" n 







partly explained by the greater precautions taken to ensure 

 silence and by the sounds under observation being rendered 

 intermittent : or, on the other hand, my estimates of sen- 

 sitiveness ma}' have been too low in consequence of the 

 already named assumption that all the excess of damping 

 due to the resonator represented production of sound. With 

 respect to the dependence on pitch, Wien remarks that my 

 own observations f on the minimum current in the telephone 



* Pfliiger's Arch, xcvii. p. 1, 1903. 



f Phil: Mag. xxxviii. p. 285. 1894: Scientific Papers, iv. p. 109. 



