FiEBRUARY 9, 191 1] 



NATURE 



467 



The new matter is presented in a very lucid form, 

 and from the instructions and detailed explanations, 

 which are intended to lighten the work of the teacher, 

 the average student should find little difficulty in 

 working intelligently in the laboratory- without much 

 supervision. 



In connection with the formulation of chemical 

 changes, a brief reference is made to the theory of 

 electrolvtic dissociation, and the reader is informed 

 that the reactions involved in analysis are, as a rule, 

 ion reactions. If this is really the case, it is difficult 

 to justify the author's use of ordinary chemical equa- 

 tions in oreference to ionic equations, even if it be 

 admitted, that, in some cases, the representation of 

 oxidation and reduction changes is not quite so simple 

 when the ions are taken into consideration. 



In view of the undoubted merits which the bo<^ 

 possesses, it is distinctly unfortunate that nearly two- 

 thirds of the contents should be a mere copy of a pre- 

 vious and ver\- recent publication. There is nothing 

 in the titles of the two books to suggest such a large 

 measure of identity in respect of text and diagrams 

 to prospective purchasers, and it is to be regretted that 

 the publishers should have seen fit to proceed to pub- 

 lication in this particular way. H. M. D. 



MATHEMAllCS .4XD OPHTHALMOLOGY. 

 The Prescribing of Spectacles. By A. S. Percival. 

 Pp. vi+159. (Bristol: John Wright and Sons, 

 Ltd. ; London : Simpkin, Marshall, Hamilton, 

 Kent and Co., Ltd., 1910.) Price 55. 6d. net. 

 "TAR. A. S. PERCIVAL is one of the most eminent 

 ■L' of the comparatively few English ophthalmo- 

 logists who have shown the requisite knowledge to 

 treat mathematically in an exhaustive manner optical 

 problems connected with the eye. The ordinary 

 student of ophthalmology is content to accept on 

 authority- the results obtained by others, or at most 

 to study such geometrical expositions as may be 

 readily understood. Indeed, he is generally wholly 

 incapable of comprehending an analytical proof, and 

 nothing is so abhorrent to his mind as an algebraical 

 formula. It is greatly to be deplored that more 

 emphasis is not laid upon the acquirement of a good 

 knowledge of physiological optics, a subject which 

 necessarily forms the very foundation of ophthal- 

 mology. Moreover, by far the greater part of everv 

 ophthalmic surgeon's work consists in the correction 

 of errors of refraction, of defects in muscle balance, 

 and other problems of an essentially optical nature. 

 Only those who have given assiduous attention to the 

 mathematical conditions presented by these problems 

 can appreciate the help which this arduously acquired 

 knowledge gives them. It is a humiliating fact that 

 many practising opticians are far better equipped in 

 this respect than most c^hthalmic surgeons, and if the 

 latter seriously expect to hold their own against the 

 encroachments of the former they must outrival them 

 on their own ground. 



Dr. Percival's little book will prove of valuable 



service in the task. All the common problems which 



daily confront the surgeon in ordering spectacles for 



errors of refraction and defects of muscle balance are 



NO. 2154, VOL. 85] 



discussed, and the underhnng principles lucidly ex- 

 plained. In most cases mathematical proofs, culled 

 from the author's work on optics and other original 

 papers, are set forth. Dr. Percival's name is specially 

 associated with the formulae for periscopic glasses, 

 and the inquiring student will here be enabled to find 

 out how the formulae were arrived at, and why such 

 lenses are to be preferred. A few paragraphs, such 

 as the pinhole test of ametropia, might have been 

 omitted as of little practical value, and the student 

 would do well to read Maddox's book on the " Ocular 

 Muscles " in conjunction with the chapter devoted to 

 the subject in this work. The author's advice is 

 always founded on a secure scientific basis, and such 

 paragraphs as the following show that he is not car- 

 ried away by purely theoretical conceptions. In speak- 

 mg of the association between accommodation and 

 convergence he says : — 



"Clearly, if the relation between the two functions is 

 unfitted for present requirements, and if there is no 

 sufficient faculty of adaptation that can be brought 

 into play by training, we should make the glasses 

 suit the patient, instead of vainly attempting to make 

 the patient suit the glasses." 



And again : — 



'• In conclusion, I would say that although few 

 patients will require such a complete examination as 

 is here suggested, yet it is well to investigate the 

 relationship of these functions of convergence and 

 accommodation whenever symptoms still persist after 

 the correction of any refractive errors and hyperphoria 

 that may exist." 



We can cordially recommend the book, and we hope 

 that it may stimulate many ophthalmic surgeons to 

 acquire a more profound knowledge of this branch of 

 their subject. 



THE BEETLES OF INDIA. 

 The Fauna of British India, including Ceylon and 

 Burma : Coleoptera Lamellicornia {Cetoniinae and 

 Dynastinae). By G. J. Arrow. Pp. xiv + 322 + ii 

 coloured plates, and 76 illustrations in the text. 

 (London : Taylor and Francis, 1910.) 



I'^HE beetles of India are an enormous subject, and 

 the volume before us only deals with two sub- 

 families of the great group Lamellicornia, the first 

 of which, though comprising the well-known and 

 extremely interesting rose-chafers, is only represented 

 by a few species in Britain, while the Dynastinae, 

 though a few species are found in southern Europe, 

 is not represented in the British fauna at all. Two 

 hundred and eighty-seven species of these two sub- 

 families are here described as belonging to the Indian 

 fauna, but the editor's estimate of these being "'per- 

 haps less than one-sixth of the great ' series ' of 

 Lamellicornia," is perhaps somewhat too high, when 

 we consider that the Lamellicornia include the whole 

 of the chafers, the saa'ed beetles, and the stag- 

 beetles. 



Mr. Arrow has been fortunate in receiving the 

 cooperation of the curators of most of the principal 

 entomological collections in Europe and India, and 

 of many enthusiastic and experienced collectors in 

 India and Ceylon, and his work may therefore be 

 taken as a trustworthy epitome of what is at present 



