August, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



519 



results; " that in intensification, " during re-blackening the 

 silver niercurous compound formed in the bleaching is re- 

 duced to metal," while the very first blackening formula 

 given has not this effect; that " the smaller the stop, the 

 finer will be the detail, the more vigorous the negative, and 

 the greater the latitude in exposure;" and so on. Not- 

 withstanding such statements, the manual will be found 

 useful by beginners, and the three illustrations showing the 

 same subject as taken on a slow, a medium, and a rapid 

 plate will be a welcome guide to many in their choice of 

 plates. 



Photographic Enamels. I'roni the French of Rene 

 I)'l leliecourt (London: Iliffe and .Sons, Limited, 1905; 

 price 2s. 6d. net). — The production of enamels is a branch, or 

 rather |)crhaps an application, of photography that is 

 hardly referred to in general text-books, for the sufficient 

 reason that it is only an exceedinglv small proportion of 

 those who are interested in photography that care to trouble 

 themselves about it. But the making of photo-enamels 

 has had a measure of commercial importance for a genera- 

 tion or more, and is an art that deserves more patronage 

 than it receives. It is, moreover, a very interesting subject 

 for an amateur to work at, especially if he has had any 

 ex]iorience in chemical operations, and the manipulation of 

 furnaces. We therefore welcome this translation of that 

 part of M. Rene D'Heliecourt's " La Photographic 

 \ntrifiee " that refers definitely to this subject. The in- 

 structions given are clear and concise, and are not confined 

 to one method, but satisfactorily cover the subject. It is 

 essentially a practical guide, and will be much appreciated 

 by those who wi'^li tn experiment in this direction. 



PHYSICS. 



Physical Optics, by R. W. Wood (Macmillan.and Co.; 

 15s. net). This is in many respects a notable book, in so 

 much as it may be considered supplementary to previously 

 existing text-books. In Preston's " Theory of Light " the 

 most modern developments are practically ignored, and 

 although the gap is in part fdled by more recent text-books, 

 there was great need of one which should deal adequately 

 with the experimental as well as the theoretic side of the 

 subject. Special stress has been laid on this in the present 

 volume, and all who have followed the numerous publica- 

 tions of Professor Wood during the last ten years will 

 cordially recognise that no one could have been found W'ith 

 a better equipment for the work. Some may regret that the 

 theoretic side is sometimes rather cramped ; we advisedly 

 used the word " supplementary " above. The reader may 

 often require to turn to other sources for further inform.a- 

 tion. The aim of the author has been chielly to supply 

 what cannot be found elsewhere in collected form. The 

 treatment of the subject is eminently original. For a book 

 of its standard, it is unusually full of numerical illustrations 

 of theory. This will be found of great help to a private 

 student. The e.xperimcnts, specially devised bv Professor 

 Wood, are often of a very simple character, which an 

 amateur may carry out. Special stress is laid on dispersion, 

 absorption, the optical properties of metals, lluorescence 

 and phosphorescence, the nature of white light, Ihe relative 

 motion of the ether and matter. The explanations are 

 based mainly upon the electromagnetic theory. There .arc 

 a large number of figures in the text ; and very many of 

 these have a very fresh appearance. We notice a few mis- 

 takes ; the author repeats a common error in asserting that 

 all the secondary maxima of a diffraction grating are given 

 by_ the equation, n tan z- tan nz ; it has fairly recently been 

 pointed out that when n is odd, one such maximum fails 

 to be included in (his set. The proper expression, which in- 

 cludes all, is n cot nz -cotz. The figure (Fig. 144) which 

 shows Ihe graphical solution of the insufTicient equation is 

 wrong in showing a solution at x/.j ; such a solution does not 

 exist. There arc other misleading statements in the same 

 section. The book, however, is wonderfully free from 

 errors of all kinds, and it will doubtless at once take a 

 leading place as a text-book for senior students. 



MISCELLANEOUS. 



" Science Progress. " — Science Progress in the 

 Twentieth Century. A quarterlv journal of scientific 

 thought. No. I, July, 1006. (John Murray, 5s. net).- - 

 .After some years of discontinu;mce the courageous 



attempt to present periodically a competent review 

 of current scientific work for scientific readers has been 

 revived under its old title of Science Proqress. The at- 

 tempt was courageous formerly, and it failed from a want 

 of support among scientific people who are, perhaps, too 

 prone to become immersed in their own special subjects and 

 to neglect and lose touch with progress in other branches of 

 science. But the attempt is no less courageous now, be- 

 cause while science tends more and more to specialisation, 

 the public or popular interest in science — perhaps owing to 

 the fact of specialisation in science — grows less and less. 

 In the so-called dead sciences specialisation and mathema- 

 tics are lifting their details far above the heads of the 

 public, and in the " natural " sciences cycling and the 

 camera have diverted po[)ular attention from more sedate 

 pursuits and from the quiet observation of Nature. None 

 the less, we hope and believe that Science I'rnrjre.is in its 

 new garb and condition will find a public of its own, as it 

 well cicserves to do. Great Britain, despite the scientific 

 ignorance of the great mass of its people, and di'spite the 

 natural unwillingness to spend money on scientific litera- 

 ture, is very well served by its scientific periodicals, two of 

 which will compare with the publications of anv other 

 country. But it needed a more solid review, a kind of 

 Ninefcenfh Century and After of science; and we sincerely 

 hope that Science Progress will prove the real scientific 

 quarterly. It makes an excellent start in its first number 

 with articles, among others, by Dr. B. J. Collingwood on 

 "Chloroform a Poison"; by Mr. .'\. D. Hall on "The 

 Solvent .'\ction of Roots on the Soil Particles"; by Mr. 

 F. V. Theobald on " Injurious Insects"; and articles on 

 "Chemical and .Structural Crystallograph)'," by Mr. 

 .\. E. H. Tutton ; on "The Geological Plans of Some 

 .\ustralian Mining-Fields," by Mr. J. W. Gregory, F.R..S. ; 

 on " The Corn .Smuts and Their Propagation," by Dr. T. 

 Johnson ; and on " Nehemiah Grew and the Study of Plant 

 Anatomv," by Dr. Agnes Robertson. 



Vivisection ; Doubtfully Useful and Certainly Wrong, by 

 J. P. Hopps. (Lontlon : Henderson, 1906, 42 [ip. ; price 

 6s. 6d.). — The author of this pamphlet mav be congr.-itulated 

 on the thoroughly temperate and fair manner in which he 

 has argued the case against vivisection. In manv respects, 

 especially as regards prohibition of vivisection without 

 anaesthetics, we are disposed to agree with his views ; 

 although we may be permitted to doubt whether he has 

 demonstrated that vivisection is useless. One point he 

 seems to have missed, namely, that vivisection might per- 

 fectly well be prohibited altogether for a period, till some 

 special new subject requires investigation. That the 

 practice ought to bo abolished when employed merely for 

 purposes of demonstration we are convinc(-d. 



Ethics, by C. W. Salceby, M.D. (Jack's Scientific Series ; 

 price IS.) — This forms an excellent little treatise on that 

 abstruse subject, Kthics, and the connections between 

 morality and religion. .Some of the most interesting chap- 

 ters are those on " The Object of Life," " Egoism and 

 .Mtruism," and the " Worship of Truth." There is much 

 to ponder over on reading this book, and as it only fills 

 115 small pages, it is not too tediously long, as is the case 

 with many other works of the kind. 



"Spiritualism," by Edward T. Bennett, is one of J.ack's 

 Scientific Series (is. net).- Both believers and non-be- 

 lievers cannot fail to be highly impressed with the many 

 uncanny stories here told. ^Ir. Bennett was assistant secre- 

 tarv to the .Society for Psychical Research, and, therefore, 

 is in a good position to obtain all the best and most reliable 

 accounts of the strange things that liave happened in in- 

 vestigating this subject. .Vnd he, very rightly, takes care 

 to repeat onlv statements of facts which are thoroughly well 

 authenticated. .Accounts of movements of objects, produc- 

 tion of sounds, and appearance of light without any ap- 

 p.arent phvsical cause, form the chief part of the contents of 

 the book, while chapters are also included on The Divining 

 Rod, Thought-Transference Drawings, Materialisations, 

 and other matters. 



The Engineer's Pocket Dictionar>-. French-English, by 



M. Lvoff (Percival Marshall, is. 6d. netl, is ;i most handy 

 and neatly got-up list of technical words in I'rench, with the 

 English equivalent. 



