July i6, 1903^ 



NA TURE 



245 



species may arise in a pathological structure, though in 



our opinion he establishes his contention. 



The book is undoubtedly a stirring contribution to 

 botanical science, and ought to stimulate research in 

 many directions, and although it escapes the responsi- 

 bilities of being a great work, it is certainly one that 

 must be on the shelves of every investigator of first 

 rank who has anything to do with the anatomy or 

 pathology of plants. We cordially welcome this in- 

 tiresting book as a pioneer work of what will grow- 

 to be an immense subject. 



COMETS AND THEIR TAILS. 

 Comets and their Tails, and the Gegenschein Light. 

 By Frederick G. Shaw. Pp. 70. (London : Bailli^re, 

 Tindall, and Cox, 1903.) 



THE theory of comet's tails has not yet arrived at its 

 ultimate destiny, which we suppose is that of be- 

 coming an orthodox branch of applied mathematics ; 

 anu consequently it still possesses a fascination for the 

 world at large. True, the phenomena have been dis- 

 cussed by Prof. Bredichin, in a succession of papers 

 that now go back nearly thirty years ; but the origin of 

 the forces required for Bredichin 's theory is very ob- 

 scure, and the net result is to excite rather than to re- 

 move conjecture. During the last few years the 

 general mental ferment over the new views of the con- 

 stitution of matter has given a fresh stimulus to specu- 

 lators in this part of astronomy, and a considerable 

 literature has already gathered round the suggestions 

 of J. J. Thomson, Arrhenius and Deslandres. 



Mr. Shaw, whose book now lies before us, is not a 

 follower of any of these schools ; he holds that the 

 comet's tail is caused by the rays of the sun being 

 altered (by concentration and refraction) by their pas- 

 sage through the cometic atmosphere, and thus ren- 

 dered more capable of being reflected from the meteoric 

 matter in the neighbourhood. In other words, the tail 

 does not really exist; it is merely a local illumination 1 

 of the general circumambient dust of space. The idea 

 bears some resemblance to the now frequently accepted ; 

 explanation of the lighting-up of the Nova Persei | 

 nebula. ! 



After stating this theory, and offering a general justi- 

 fication, the author proceeds to examine the records of 

 the great comet of 1858 in the light of it. For this 

 purpose he uses G. P. Bond's monograph to a con- 

 siderable extent, a mistake which occurs in the first 

 plate of the Harvard astronomer's account being un- 

 fortunately twice reproduced ; the point chiefly dwelt 

 on is the sympathy between the phenomena of the 

 nucleus and those of the tail. 



The work as a whole is brief, its tone is very 

 modest, and it is not claimed that the theory has been 

 worked out in detail. It is therefore scarcely fair to 

 blame the author for the difficulty which one finds in 

 attempting to explain by causes of this kind the singu- 

 larly complex character of cometary appendages. But 

 any theory of the kind must offer some explanation of 

 their most constant and remarkable features, such as 

 the multiplicity of tails, their curvature, and the 

 "broken" appearances often seen; and it may be 

 NO. 1759. VOL fS8l 



doubted whether the author's theory in its present state 

 is capable of meeting these demands. " So-called 

 secondary tails, &c.," he accounts for "by irregular 

 ebullitions of gas from the comet," presumably giving 

 rise to special fields of refracted rays. 



But at the root of the whole matter lies the question 

 of whether refraction in the cometic envelope is likely 

 to take place at all on a scale comparable with that 

 required by Mr. Shaw's hypothesis, and at present ob- 

 servation seems to negative this possibility. 



The latter part of the book is devoted to the Gegen- 

 schein, for which a similar explanation is given — the 

 refraction being in this case produced by the earth's 

 atmosphere, and the phenomenon being due to the re- 

 flection of this refracted light from meteoric dust. An 

 interesting criticism of Barnard's views is given. 



OUR BOOK SHELF. 

 Physical Chemistry for Physicians and Biologists. 

 By Ernst Cohen. Authorised Translation from the 

 German by M. H. Fischer. Pp. ix + 343. (New 

 York : Henry Holt and Co., 1903.) 

 Physiologists and pharmacologists have from the 

 first been ready to adopt and apply the recent theories 

 of physical chemistry. Indeed, the eagerness with 

 which these theories have been received by biologists 

 has frequently led to their misapplication, inasmuch 

 as the conditions existing in the animal organism are 

 so widely different from those for which the theories 

 were developed, that direct adoption of purely physico- 

 chemical results is in nine cases out of ten inadmis- 

 sible. In the book before us we have a series of seven- 

 teen lectures delivered by an energetic worker in pure 

 physical chemistry to an audience of physicians. The 

 physicochemical principles bearing on biological prob- 

 lems are expounded, the chief methods of experiment 

 adequately described, and, what is of most import- 

 ance, a critical account is given of many of -their 

 applications. These applications include, for ex- 

 ample, disinfection in the light of the theory of electro- 

 lytic dissociation, the pharmacology of complex 

 mercury salts and of uric acid solvents from the same 

 point of view, the taste of dilute solutions, osmotic 

 analysis, and the toxicity of electrolytic solutions. The 

 book is admirably adapted to its purpose, and may be 

 heartily recommended. 



Trapper "Jim." By Edwyn Sandys. Pp. ix + 441; 



illustrated. (New York and London : Macmillan 



and Co., Ltd., 1903.) Price 65. net. 

 Although, as indicated by its title, this admirable 

 little volume is devoted rather to sport and trapping 

 than to natural history, yet it contains scattered 

 through its pages such excellent descriptions of the 

 wild life of the United States that the naturalist can- 

 not fail to find much valuable information with regard 

 to the habits of many of the mammals and birds 

 mentioned. Specially interesting are the notes on the 

 various species of American hares, and it; will come as 

 a revelation to many that the so-called " jack-rabbit " 

 {Lepus callotis) is probably the fleetest member of all 

 its tribe. Many references are made to the need for 

 the cultivation of a true sporting instinct among 

 hunters, that is to say, to the enjoyment of the sport 

 itself, as distinct from making a "big bag." The 

 name of Mr. Sandys is too well known as a writer on 

 the sport and popular natural history of North America 

 to stand in need of any commendation on our part, but 

 we may safely say that his popularity will certainly 

 be enhanced by his latest effort. ' R. L. 



