486 



NATURE 



[March 26, 1903 



We have read some of the chapters with considerable 

 interest and pleasure, notably those which deal with 

 the phenols and with the carbohydrates, the subjects 

 of which are carefully and fully dealt with. In some 

 parts of the book, however, the explanations are not 

 so clear as we could have wished, the reactions being 

 given with little or no attempt at an explanation. Now 

 the average student requires a considerable amount of 

 explanation in order that he may understand the sub- 

 ject. As an example of want of clearness we think 

 it would have been wise to give some explanation of 

 the probable mechanism of the process involved in the 

 preparation of benzaldehyde by the action of metallic 

 nitrate* on benzyl chloride, and some explanation of 

 Reimer's reaction would not have been out of place. _ 

 The book is well printed, and the proofs have evi- 

 dently been very carefullv corrected. Taken as a 

 whole, we consider Dr. Cohen's book a very useful 

 compilation ; from the preface we had expected to find 

 a book written on new and original lines; in this, , 

 however, we were disappointed. F. M. P. 



Nature Studies (Plant Life). By G. F. Scott Elliot. 1 

 Pp. viii + 352. (London : Blackie and Son, Ltd., 

 1903.) Price 35. 6d. 

 It is not evident whether the author intends this book 

 as a contribution to the subject of "nature-study," 

 which is now attracting so much attention. Certainly 

 the first and most essential feature of nature-study, 

 namely, personal observation, is not emphasised, nor is 

 the discursive style which the author adopts calculated 

 to induce careful and accurate investigation. A large 

 mass of information has been brought together, com- 

 piled from books on bionomics and original papers. 

 The book begins with the flower and fruit, and the 

 vegetative portions follow, an arrangement which has 

 its advantages since morphology is sacrificed to bio- 

 nomics. The relations between animals and plants are 

 well brought out, but less prominently so the relations 

 between plants inter se. The study" of plant associa- 

 tions begins with the Cryptogams, and here, as indeed 

 in most of the chapters, the matter is too fragmentary ; 

 only occasionally, as, for instance, in the chapters on 

 seaweeds, or when describing the lichens, does Mr. 

 Scott Elliot take the necessary space to do justice to 

 himself and his subject. The concluding chapters deal- 

 ing with the origin and development of the English 

 flora introduce a subject which is well worth studying. 



Das Objectiv im Dicnste der Photographic. By Dr. 



E. Holm. Pp. xvi + 142. (Berlin : Gustav Schmidt, 



1902.) Price 2 marks. 

 Those photographers, whether professional or amateur, 

 who are able to read German will find this book full 

 of useful information and valuable hints regarding 

 the properties and use of the photographic objective. 

 So numerous, so varied in construction, and so different 

 in price are lenses of to-day that it is important that 

 the photographer should know something of their 

 nature and capabilities before investing in one or more 

 of them. The present book is intended to give the 

 reader a good all-round idea of not only the properties 

 of lenses, their errors, corrections, the different kinds 

 available, and hints on choosing them, but also how to 

 use them when obtained. Although the text quite 

 fulfils this object, the very excellent set of reproductions 

 illustrating all the kinds of results which accrue from 

 good or bad focusing, setting, choice of position, &c, 

 adds greatly to its value, and demonstrates better than 

 any words could do the points to be observed. The 

 telephotographic lens is also included in these pages, 

 and the book concludes with quite a full index. 



NO. 1743, VOL. 67] 



LETTERS TO THE EDITOR. 



[Tlie Editor does not hold himself responsible for opinions ex- 

 pressed 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.] 



Permanent Electric Vibrations. 



In his "Electric Waves" (see p. 361) Mr. Macdonald 

 considers that electric waves may be propagated 

 round a ring without being subject to any loss by 

 radiation. The question whether this is possible is 

 of great interest, as such waves might play an im- 

 portant part in atomic phenomena. It seems, how- 

 ever, that such waves cannot exist, except possibly in 

 exceptional cases. For consider a spherical surface to be 

 drawn enclosing the whole of the vibrating system. The 

 electric force cannot vanish at all points of this surface, for 

 the sphere may be as close to the conductors as we please. 

 From the value of the force, and the condition that at 

 infinity any motion that there may be must consist of 

 outwardly progressing waves, we can find by spherical 

 harmonic analysis the field at any point outside the sphere. 

 The result is that in any case the field cannot at all distant 

 points be of an order lower than that of i/r; there must 

 be loss of energy by radiation. For a thin circular wire 

 a fundamental mode of vibration is determined, to a first 

 approximation at least, in Proc. Camb. Phil. Soc, vol. ix. 

 p. 326 ; and the case of a wave progressing round the wire 

 can be deduced by compounding two such vibrations differ- 

 ing in phase. The determination of the resultant disturb- 

 ance at a great distance involves Bessel's functions in 

 general, but it can be proved without difficulty that for 

 points on or near to the axis of the ring it consists of 

 divergent waves. The consequent rate of loss of energy 

 is of the order of unity, while the energy held is of the order 

 of log (a/e), where e. is the radius of the wire and a that of 

 the circle. The decrement is hence of the order of 

 i/log(a/6), as found in the paper referred to. 



On the other hand, it is hard to find a flaw in Mr. Mai ■ 

 donald's general reason for the absence of radiation in this 

 case, and the possibility of non-radiating systems is sug- 

 gested by the case of a uniformly and superficially charged 

 dielectric sphere of unit specific inductive capacity. I( it 

 performs small simply periodic oscillations, each point of 

 its surface may be treated as a Hertzian oscillator. On 

 evaluating the external field, we find that the variable part 

 of it is the same as if the charge were collected at the centre 

 and multiplied by (sin \a)/\a, where a is the radius of the 

 sphere, and 2ir/\ is the wave-length in free ether correspond- 

 ing to the frequency of the oscillation. Hence, if this 

 wave-length is a submultiple of the diameter of the sphere, 

 there is no external oscillating field. 



H. C. POCKLINGTON. 



The Bearing of Recent Discoveries on the Physics 

 of Taste and Smell. 



One of the first experimental papers on the nature of the 

 stimulus given to the organs of taste or smell by sapid or 

 odorous substances is, I think, that by the Hon. R. Boyle 

 (" Experiments and Observations about the Mechanical 

 Production of Tasts (sic)," London, 1675), in which he puts 

 forward a theory of irritation by particles which penetrate 

 and irritate more or less according to their size and shape. 

 After this a chemical theory of taste seemed to gain ground, 

 and Graham laid down the principle that only soluble sub- 

 stances are sapid, and that further only crystalloid solutes 

 are sapid (see Rain, "Senses and Intellect," 1864). Then 

 in 1882 Sir W. Ramsay very tentatively put forward 

 a dynamical theory from analogy with optics and sound 

 (Nature, xxvi. 1S7). He proposed that very light molecules 

 vibrating at a high rate are inodorous, taking as the limit 

 a molecular weight of about 30. On the other hand very 

 heavy molecules would be odourless, because vibrating too 

 slowly, whereas those vibrating at a rate between these 

 limits would find the nerve-cells capable of response. Thus 

 he accounted for the want of odour on the part of 

 H, CH„ O, N, H,0, &c. Similar views were later ex- 



