i86 



NA TURE 



[December i6, 1909 



subject, and the biological side of the question as 

 regards colour mimicry in animals. It is illustrated 

 with three plates in colours. 



The author first discusses the nature of white light, 

 its decomposition and recomposition, the nature of 

 the colours shown by coloured objects, pigments, 

 dyes, &'C., and their effects on the reflection, absorp- 

 tion, and transmission of white light, with special 

 reference to the coloured glasses to be used as filters 

 in three-colour photography. Then the various pro- 

 cesses by Ducos du Hauron, Ives, Sanger Shepherd, 

 Joly, Miethe, Lumiere, and others for producing 

 coloured photographs by the additive and subtractive 

 methods of colour mixtures, dependent on the theorv 

 of triple-colour sensations enounced by Young, Helm- 

 holtz, and Clerk Maxwell. 



The discussion of the Becquerel and Lippmann 

 direct methods of colour photography, founded on 

 Zenker's theory (1868) of interference and stationary 

 waves producing an alteration of the structure of the 

 sensitive film by reflection, corresponding to the wave- 

 length of the light acting on it, is interesting, be- 

 cause of the author's confirmation of the theory in 

 iSgo, and its practical adaptation by Lippmann in 

 i8gi. The other direct methods, dependent on 

 changes- of colour in sensitive films of silver chloride 

 and subchloride, discovered by .Seebeck and worked 

 out by Becquerel, Poitevin, and Niepce de St. Victor, 

 also the " bleach-out " methods of VVorel, Neuhauss, 

 Smith, and others are explained. After a short notice 

 of the theories of colour perception, the discourse con- 

 cludes with some very interesting remarks regarding 

 the protective colour adaptation of animals, and the 

 researches of Poulton, Standfiiss, Weismann, Her- 

 bert Spencer, and others, illustrated by a coloured 

 plate showing protective mimicry in insects. 



Though the subject is dealt with briefly and 

 theoretically, the book will be useful as a summary 

 of results already achieved, and particularly for the 

 literary and other information given in the notes. 

 We note one omission in the list of books at p. 49 — 

 Dr. H. W. Vogel's "Die Photographic farbige 

 Gegenstande," 18S5. Those interested will find 

 further information in Prof. Wiener's papers in 

 Wiedemanyi's Annalen, xxxi., 1887, p. 619; xl., 1890, 

 p. 203; Iv., 1895, p. 225; and Eder's "Jahrbuch fiir 

 Photographic," 1896, p. 55. J. W. 



OUR BOOK SHELF. 

 Outlines of Chemistry, with Practical Worh. By 

 Dr. H. J. H. Fenton, F.R.S. First part. Pp. xvi + 

 365. (Cambridge : The University Press, 1909.) 

 Price 9^. net. 

 This book embodies the substance of a course, or 

 part of a course, of lectures which the author gives to 

 candidates for the Natural Science Tripos at Cam- 

 bridge. Supplemented in practice by experiments 

 appropriate to the topics of each lecture,' it is intended 

 to give the student a lead to the study of standard 

 chemical literature. Mr. Fenton explains the difficulty 

 of the circumstances under which the teaching has to 

 be done, and he appears rather as one who has to 

 comply with an established system than the exponent 

 ■of a system that he thinks the best, or even very good. 

 ■'ilo one, of any modesty, who is engaged in teaching 

 NO. 2094, VOL. 82] 



chemistry to university students at the present day 

 will be very dogmatic about the details of the course 

 that should be followed. The subject has become so 

 vast and so varied that personal predilections and 

 capacities may lead to courses very different from one 

 another and yet of no very different merit. Two ex- 

 tremes may be found in the tendency of one kind of 

 teacher to produce a chemist well informed about 

 substances and another kind to produce a chemist well 

 informed about principles; the first would ordinarily 

 be the better craftsman, the second the clearer thinker. 



The tendency of the Cambridge Tripos system is not 

 unnaturally towards making chemistry as much like 

 physics as possible, and accordingly the Tripos can- 

 didates are led to concern themselves with theoretical 

 and physical chemistry to an extent which seriouslv 

 limits their chances of acquiring that personal 

 familiarity and facility with individual chemical 

 substances which in earlier days was one good out- 

 come of the ri)iime of analysis. It leads also to a 

 subordination of chemistry in relation to industrial 

 and practical problems. It is possible that some 

 readjustment might be worth considering, having 

 regard to the increasing importance of the Cambridge 

 school and especially to the influence which Cam- 

 bridge graduates exercise in the secondary schools. 



However this may be, Mr. Fenton, on the lines he 

 had adopted, has written a book that must be rated 

 very highly. It is marked throughout by the lucidity 

 and scientific restraint to which we have been accus- 

 tomed in all his writings; it is very thorough and 

 comprehensive, and it shows a real grasp of the in- 

 wardness of a good many things about which there 

 has been a good deal of loose writing and, presumably, 

 loose thinking. It is a book that may be read with 

 profit by every student of chemistry at some stage of 

 his career — perhaps for most at some late stage, when 

 reviews are so valuable, especially if they are free 

 from special pleading. As an example of the 

 excellent substance and form of the book, the chapters 

 on acids, bases and salts may be specially cited, but 

 there is, in fact, little departure from a high level 

 of exposition throughout the work. It seems very 

 likely that the second volume, which is promised, 

 should the first prove acceptable, will be clearly called 

 for. A. Smithells. 



The Kea: a New Zealand Problem. By G. R. Mar- 

 riner. Pp. 151. (London : Williams and Norgate, 

 1909.) Price ys. 6d. net. 

 Few birds have attained to greater notoriety than the 

 New Zealand kea, and every naturalist has long been 

 familiar with the strange story of its sheep-killing pro- 

 pensities. The change of habit which it is supposed 

 to have undergone since the introduction of sheep 

 into New Zealand has formed the subject of much 

 discussion by writers on evolution, but it appears that 

 a great deal of theorising has been based upon a singu- 

 larly small amount of trustworthy evidence. Serious 

 doubt having been cast upon the generally accepted 

 stories, Mr. G. R. Marriner, the curator of the public 

 museum at Wanganui, set himself the task of col- 

 lecting all the evidence available and personally 

 investigating the habits of this remarkable bird, and 

 the results of his inquiry have been published in a 

 very valuable and readable book. The case has been 

 fairly tried, and the kea stands condemned on abun- 

 dant evidence. The executioners have long been at 

 work. They did not think it necessary to wait for 

 the result of the trial, and the large sums of blood- 

 money paid for kea heads must have done a good 

 deal to keep the birds in check, though their haunts 

 in the remote mountain regions of the South Island 

 are often so inaccessible that it may well be doubted 

 whether thev will ever be exterminated. Those who 



