ESSAY-REVIEWS 667 



ear respond at once, and that all the nerve fibres have to convey to the brain the 

 same messages, which consist of four impulses for each wave. Thus, on this view, 

 the ear accomplishes no analysis, in the sense in which the term is understood 

 for the resonance theory. The only so-called analysis which they suppose the 

 ear to accomplish is that of noting the amplitudes and times appropriate to the 

 four points in each wave. Thus the duty of conveying four impulses per wave is 

 put upon the nerves and that of receiving and noting them is put upon the brain. 



As to the probability or possibility of these heavy demands upon the nervous 

 organisms being met, the physicist as such has perhaps no right to speak. But 

 there are other aspects of the matter which solicit his attention. 



The present authors find difficulty in accepting the resonance theory because 

 liquids intervene between the foot of the stapes and the basilar membrane, Corti 

 arches, and hairlets. They conclude that because liquids are incompressible the 

 liquids present in the internal ear must move in a piece and affect all the 

 graduated mechanisms equally and simultaneously. But, although a liquid is 

 nearly incompressible, it is freely deformable. Hence, if the various parts of this 

 mechanism were tuned to different frequencies, what is there to prevent those and 

 those only responding which are in tune with the pressure wave arriving ? 

 Similarly, when their other objections to the resonance theory are subjected to the 

 scrutiny natural to a physicist it would appear that few if any survive. 



The supposition of the authors that four nerve impulses are produced by each 

 pressure wave received seems improbable, but, if supported by any adequate 

 reason or experimental evidence, might have to be accepted. At present, how- 

 ever, it appears to lack all such confirmation. 



As to the mechanisms which are specially concerned in stimulating the nerve 

 fibres, Helmholtz at first regarded the Corti arches as playing the role of 

 resonators, later the basilar membrane was substituted. The present authors 

 regard the basilar membrane as raising one corner of the triangular Corti arches 

 which rock about their second corners, and by their third corners actuate the 

 roots of the hairlets whose tips are in the tectorial membrane, the nerve fibres 

 ending at the roots of the hairlets being accordingly stimulated. This may be 

 quite correct, but forms no disproof of the resonance theory. 



On the contrary, the modification in question could be regarded as another 

 variation of detail, leaving all the essential principles of resonance undisturbed. 

 Indeed, there are distinct difficulties in supposing that any sufficient motions 

 could be produced by these rapid alternations of liquid pressure save only in parts 

 of the mechanism tuned to about the same frequency. 



Though Sir Thomas Wrightson's view of audition in its present form seems 

 unlikely to appeal to the physicist (apart from experimental support), it is con- 

 ceivable that some modification of it might prove more successful. 



The whole subject is highly controversial, but, even to those who hold no brief 

 for any special theory and are anxious to welcome truth from every quarter, it 

 appears that there is nothing here to overthrow (or sensibly weaken) the strong 

 position at present held by the so-called resonance theory of Helmholtz. 



