Nqvember 2i, 1918] 



NATURE 



225 



funds, al thi leading members of the 



University. At the time of its erection the ob- 

 servatory was one of the largest and best-equipped 

 in the' world, and its equipment has been well 

 maintained by t!ic recent addition of a splendid 

 telescope of j-i-in. aperture for photographic work, 

 and one of iS-in. aperture for visual work, on the 

 same mounting. Just previous to the foundation 

 of the observatory the trustees sanctioned the 

 building i>! the Radcliffe Infirmary, which has 

 ever since remained the chief county hospital. 



In addition to a description of the Radcliffe 

 foundations, Dr. N'ias (himself an ex-travelling 

 fellow) gives a brief but interesting biography of 



• I !n- book contains numerous portraits 

 and illustrations, and is beautifully printed and 



il. but it is to be feared that its circulation 

 will be limited by its somewhat excessive price. 



H. M. V. 



OIR BOOKSHELF. 



Elements of the Electromagnetic Theory of Light. 

 Bj Dr. Ludwik Silberstein. Pp. vii + 48. (Lon- 

 don : Longmans, Green, and Co., 1918.) Price 

 35. '></. net. 



This little volume is re-written from the author's 

 Polish treatise on electricity and magnetism 

 (3 vols., Warsaw, 1908-13). It is a compact 

 resume of the main results of the electromagnetic 

 theory of light in so far as it can be carried with- 

 out reference to the electron theory. The main 

 purpose seems to be to present the subject to the 

 i-h reader in vectorial notation, following the 

 symbolism of the author's "Vectorial Mechanics" 

 millan, 1913). It would have added to the 

 •lsefulness of a book designed for beginners in the 

 subject if a short exposition of the meaning of 

 notation had been prefixed, an addition which 

 would have helped to familiarise the rising 

 generation with a very important calculus. 



A useful historical survey of earlier aether- 

 theories is given in the second chapter. 



The Exploitation of Plants. By Various Writers. 



Edited by Prof. Oliver. (Trie Imperial Studies 

 S.) Pp. vii+170. (London: J. M. Dent 



and Sons, Ltd., 1917.) Price 2S. fad. net. 



< >i iver has done a useful piece of work in 

 bringing together, within the compass of a small 

 volume, .1 series of lectures on "The Exploitation 

 of Plants in the Service of Man," which was de- 

 livered at University College, London, in 1917. In 

 such a collection it is inevitable that there should 

 be differences in relative values, but the standard 

 of the best is very high. Amongst those which 

 strike us as particularly good are the contributions 

 of Prof. Oliver himself, and that of Dr. Willis, 

 formerly director of the celebrated gardens at 

 Peradeniya. As might perhaps have been antici- 

 pated, these are concerned with the reclamation of 

 waste lands and with the rubber industry respec- 

 tively. Both are characterised by lust -hand know- 

 and that indefinable but verv real quality 

 that attaches to pioneer work. Dr. Balls con- 



no. 2560, vol. 102] 



ti niles a suggestive article nn cotton and its 

 problems, but here and there he is inclined, per- 

 haps, to assume a more extensive technical 

 acquaintance with the subject on the part of the 

 than the latter could actu illv justify. 



I )ne essay is markedly and the in- 



structed reader will find some entertain; 

 formation " in the lecture dealing with the plant 

 as healer. Amongsl other curious statements, the 

 account therein given of the cinchona enterprise 

 in Ceylon manages in a Few lines to convey a 

 thoroughly misleading impression of the causes 

 winch led to the collapse Of tiiat particular 

 industry in the island. 



Hut a book of this kind should, after all, be 

 judged on its merits as a whole, and while it 

 must be admitted to contain some dross, the 

 greater part of it is good, and the best is really- 

 first-rate. 



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 conuuvnications.] 



The Perception of Sound. 



I do not think that Helmholtz's theory of audition, 

 whatever difficulties there may be in it, breaks down 

 so completely as Dr. Perrett represents (Nature, 

 November 71. According to him, one consequence of 

 the theor\ would be that "when a tuning-fork is 

 made to vibrate, no note can be heard, but only an 

 unimaginable din." I cannot admit this inference. 

 It is true that Helmholtz's theory contemplates the 

 response in greater or less degree of a rather large 

 number of " resonators " with their associated nerves, 

 tin natural pitch of the resonators ranging over a 

 certain interval. But there would be no dissonance, 

 for in Helmholtz's view dissonance depends upon inter- 

 mittent excitation of nerves, and this would not occur. 

 So long as the vibration is maintained, every nerve 

 would be uniformly excited. Neither is there any 

 difficulty in attributing a simple perception to a rather 

 complicated nervous excitation. Something of this' 

 kind is involved in the simple perception of yellow, 

 resulting from a combination of excitations which 

 would severally cause perceptions of red and green. 



The fundamental question would appear to be the 

 truth or otherwise of the theorv associated with the 

 name of J. Midler. Whatever may be the difficulty 

 of deciding it, the issue itself is simple enough. Can 

 more than one kind of message he conveyed by a 

 single nerve? Does the nature of the message depend 

 upon how the nerve is excited? In the case of sound 

 — say from a fork of frequency 256— is there anything 

 periodic of this frequency going on in the nerve, or 

 nerves, which carrv the message? It is rather difti* 

 cult to believe it, especially when we remember that 

 frequencies up to 10,000 per second have to he reckoned 

 with. Even if we could accept this, what are we to 

 think when we come to nerves conveying the sensa- 

 tion of light? Can we believe that there are processes 

 in action along the nerve repeated in 15 times per 

 second ? 



I do not touch upon the anatomical matters treated 

 by Sir T. YVrightson and Prof. Keith, or upon the 

 phonetic evidence brought forward with authority by 

 Dr. Perrett. RAYLEIGH. 



