December 5. 1918] 



NATURE 



26- 



favourable impression. Sugar analysis, for ex- 

 ample, which is often treated much too scantily 

 in general treatises, receives adequate attention 

 in the work under review. This chapter, in fact, 

 is excellent, and one oi the besl in the bonk. The 

 on on milk is quite good generally, but for 

 use in this country it would have been improved 

 by including the standard requirements and adapt- 

 ing it to English practice, much in the same way 



he chapter on beer has been treated. Of the 



other sections, those on spirituous liquors, colour- 

 ing matters, and textile articles may be singled 



out for commendation. The Allen-Marquardt 

 method of determining higher alcohols, however, 

 is not included in the first-mentioned group; pre- 

 sumably it is not in favour with Italian chemists. 



onal references are given, but more might 

 well be included, for the benefit of readers who 

 maj wish to consult the original descriptions. For 

 example, both the Denizes colorimetric and 

 Thorpe and Holmes's gravimetric method of esti- 

 mating methyl alcohol are described, but without 

 reference either to the authors or to the original 

 papers. 



These omissions, however, are minor matters. 

 The work, as a whole, will be found useful and 

 practical ; it well deserves a place in the analyst's 

 library. A meed of praise is certainly due to the 

 translator, who has done his work very well 

 indeed. C. SlMMOXDS. 



OUR BOOKSHELF. 

 Contouring <niil Map-reading. By B. C. Wallis. 



Pp. 48. Price 2s. 

 Macmillan's Geographical Exercise Books: VII. — 



Physical Geography. With Questions. By 



B. C. Wallis. Pp. 48. (London: Macmillan 



and Co., Ltd., n.d.) Price is. 6d. 

 These books, which form parts of a series by the 

 same author, have the advantage of being com- 

 piled by a teacher of wide experience who has 

 given much thought to the presentment and map- 

 ping of geographical data. Mr. Wallis has shown 

 considerable ingenuity in devising some of his 

 exercises, and to a gnat degree has managed to 

 avoid the trivial and merely mechanical tasks 

 which often make such work- irksome and of little 

 value. In the volume on contouring and map- 

 reading, which is specially to be recommended, 

 advantage has been taken of the interest the war 

 has given to geographical study in making tise of 

 many excellent war-maps in setting questions. 

 Attention should also be directed to the exercises 

 in making sketches from contour maps, though 

 perhaps the method requires rather more explana- 

 tion than is offered. In the glossary in the volume 

 on physical geography the definition of barometric 

 gradient requires revision. But the feature that 

 gives the books great value is thai every exercise 

 has to be done on an accompanying map or dia- 

 gram. The maps are clear and well printed, 

 even to the smallest details. These books should 

 give pupils an excellent grounding in the use and 

 < i >ns! ruction of maps. 



NO. 2562, VOL. I02] 



LETTERS TO THE EDITOR. 

 '.The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of. rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



The Perception of Sound. 



I would first thank tlu.se correspondents who have 

 replied 10 my difficulties with respect to certain theories 

 ol the function of the cochlea. Unfortunately, the 

 fundamental physical difficulty has not received the 

 consideration that I hoped for, probably because it 

 was not made sufficiently clear. Sir Thomas Wright- 

 son (Nature, November 7) gives a quotation from 

 I lelmholtz which does not, seem to me to meet the 

 case, but perhaps it was written in connection with 

 a different aspect of the problem. It is not obvious 

 how the dimensions of the space filled with liquid in 

 relation to the wave-length of the vibrations affect 

 the nature of the process. If it were the case, the 

 conduction of sound in liquids should be of a different 

 nature according to the dimensions of the vessel and 

 the pitch of the note. May I, therefore, put the 

 question in another way? 



When sound-waves impinge on water and are con- 

 ducted through it, there could not be the necessarv 

 condensations and rarefactions unless the mass of 

 water in front of the advancing wave offered sufficient 

 resistance by its inertia to enable the local compres- 

 sion to take place. If the column of water moved as 

 a whole in the way assumed by Sir Thomas Wright- 

 son's theory, it could not conduct sound-waves as 

 such, since there would be no possibility for the forma- 

 tion of any local differences of density. Now the 

 impulses impressed by the stapes on the liquid of the 

 cochlea are identical in time-course with sound-waves, 

 and the nature of the disturbances in this liquid must 

 be the same as if it were conducting sound. Of course, 

 the column of liquid moves as a whole to relatively 

 slow rates of incidence of energy. If a short, sharp 

 tap be made on a membrane at one end of a column 

 of water, the ear at the other end does not perceive 

 the sound at the moment at which the blow is given; 

 the transmission is bv a wave. If it were necessary 

 that the whole column of water should be moved, a 

 large expenditure of energy would be required. It 

 seems to be assumed that the force available is too 

 small to do anything but move the liquid column in 

 the cochlea as a whole, unequal to effect anything in 

 the nature of a compression. But is this so? The 

 force is concentrated into a very minute space. On 

 the whole, I can see no alternative but the conclusion 

 that the waves to which the organ of Corti responds 

 are the same as sound-waves. I regret that Lord 

 Rayleigh in his letter (Nature, November 21) has 

 overlooked this point, about which his statement would 

 have carried so much weight. It is important, how- 

 ever, that he does not see so many difficulties in the 

 resonance theory as others do. 



I cannot quite follow Sir Thomas Wrightson's 

 explanation bow there is produced a difference of 

 pressure between the two sides of the basilar mem- 

 brane. It seems to assume that there is a wave of 

 pressure^ that is, a sound-wave. Although the helico- 

 trema is small, the volume of liquid moved through 

 it is verv minute (0075 cub. mm. as a maximum, 

 p. .,11 of Sir Thomas ' Wrightson's hook), and the 

 existence of a difference of mechanical pressure is 

 difficult to believe. The hairlets would not be bent 

 unit 5S there were such a difference. 



