352 Mr. H. E. Roaf on the Analysis of 



of the organ of Corti, will aid the analysis o£ the pressure 

 variations. 



The factor that is analysed is acceleration, which is pro- 

 portional to the second differential coefficient of pressure in 

 relation to time. The pressure-time relation is a sine curve, 



therefore -j-^ — —sin X. 



It must be remembered that a tone depends not on a single 

 rise of pressure but on a succession of pressures, so that 

 continuous movement occurs only at the part of the basilar 

 membrane where the inertia and friction produce sufficient 

 pressure to deform the basilar membrane. 



The hypothesis of M. Meyer * does not treat the subject 

 from the same physical standpoint as that described herein, 

 because his hypothesis is based on the amplitude of the wave 

 and not its frequency, nor do other hypotheses such as those 

 o£ E. ter Kuile t and of Hurst J explain analysis on the 

 same basis. 



It is assumed that the number of nerve-fibres and end 

 organs are sufficient to account for the various frequencies 

 distinguishable by the ear. 



The mechanical conditions described above do not depend 

 upon the presence of an organ of Corti, but the problem of 

 tone analysis in birds requires further investigation. The 

 exact anatomical arrangement of the cochlea and the range 

 of tone analysis must be compared. 



In order to show that a mechanism such as that described 

 can analyse complex pressure waves, several models have 

 been made of which the simplest for purposes of demonstra- 

 tion is that shown in fig. 3. 



A glass U tube was made with a narrowed portion in the 

 connecting limb to damp the oscillations, and several smaller 

 tubes were blown on one limb of the U. The open ends of 

 the side tubes are closed by glass bulbs of different sizes to 

 represent the different elasticities of the parts of the basilar 

 membrane. The apparatus is filled with water and a rubber 

 bulb is fastened to the U tube at A : pressure variations are 

 made by squeezing A. 



With such a large scale apparatus it is not to be expected 

 that it will respond to such rapid pressure variations as most 

 sound waves, but it will respond to slower variations. For 



* M. Mever, Arch. f. d. yes. Physiol, vol. lxxviii. p. 346 (1899) and 

 vol. lxxxi. p"! 61 (1900). 



t E. ter Kuile, Arch. f. d. yes. Physiol, vol. lxxix. p. 1-16 (1900). 

 t C. H. Hurst, Trans. L'pool. Biol. Soc. vol. ix. p. 321 (1895). 



