36 



KNOWLEDGE. 



January. 1911. 



for most of these are still very defective. Tlie composition 

 of the matter thus carried to the ocean is discussed, and a 

 special study is made of the factors used in Professor Joly's 

 method of estimating the age of the ocean by means of the 

 sodium content. Using Dr. Clarke's new figures. G. F. BecUer 

 attaclis the problem of the age of the earth by Joly's well- 

 known method. The chief new point introduced by Becker 

 is that the increment of sodium to the sea during geological 

 time has not been uniform but asymtotic. He conceives that 

 the Archaean and massive igneous rocks which supply the 

 great mass of the sodium originally occupied a far larger area, 

 and were thus more exposed to denudation than they are now. 

 Consecjuenth- the supply of sodium to the sea tends to suffer 

 an asymtotic diminution with the lapse of time. With the 

 new considerations and the revised data, the age of the ocean 

 is now estimated at between 46'0 and 74'4 millions of years. 

 The data for Lord Kelvin's method are similarly revised, and 

 a final estimate of fifty-five to seventy millions of years for 

 the age of the earth (starting from the consistciitior stntus\ 

 is arrived at. limits not differing greatly from those found by 

 Joly's method. 



PHYSICS. 



The Principles and Mctlioiis tif Gcunictriccd Optics. — 



By James P. C. Soi'thall. 626 pages. 170 illustrations. 



9i-in. X6-in. 



iMacniillan & Co. Price 25 - net. I 



The Germans have taken possession of the great province 

 of .Applied Optics. The remarkable theoretical work of 

 Petzval, Seidel. and Abbe, together with the svstematic 

 investigation, undertaken and carried through by Abbe and 

 Schott, of the " optical properties of all know n substances 

 which undergo vitreous fusion and solidify in non-crystalline 

 transparent masses," has led to the establishment of the Jena 

 " Glastechnisches Laboratorium." Not only so, but until 

 quite recently there has been no English treatise on Optics in 

 which any reference to the later German theoretical work 

 could be found. This book is a very successful attempt to 

 supply the deficiency, and it is likely to be found indispensable 

 as a book of reference. After a chapter on the fundamental 

 laws of Optics, the characteristic properties of rays of light 

 are considered, such as the principle of the shortest route, 

 with an account of Sturm's theory of astigmatism. Then 

 follow Reflexion and Refraction at plane surfaces, with a 

 thorough discussion of prisms and prism-systems. .After 

 chapters on the reflexion and refraction of paraxial rays at 

 spherical surfaces, comes a full account of Abbe's theory of 

 Optical Imagery, by means of which it is possible to separate 

 theoretical from mechanical impossibilities. The theory of 

 Spherical .Aberrations and Colour-phenomena also receive full 

 treatment. A pleasing feature of the book is the fulness with 

 which the history of Optics is treated. The author's affection 

 for his subject is evident, and amid large arrays of determinants 

 and pages of symbols the human element is never lost sight of. 

 I'ull references to original sources are given, and in particular 

 the author acknowledges his indebtedness to Czapski's great 

 work. The book forms an excellent general introduction to 

 the speci.al theory of optical instruments, and another book 

 dealing fully with the different types of instruments may 

 possibly follow in time. 



Tlic Yoiin^ Electrician. — H\- Hammo.nd Hall. 306 pages. 

 93 illustrations. S-in. X4-in. 



(Methuen & Co. Price 5 -.) 



A thoroughly practical book and one from which, if a boy 

 conscientioush- worked (with a little sympathetic assistance) 

 the series of experiments so subtly set forth in the succeeding 

 pages, he would gain an excellent knowledge of the fascinating 

 subject of electricity. Quite unlike the majority of " young '" 

 books it is practically written and yet is understandable by 

 the uninitiated ; and the final chapter, which deals with Wire- 

 less Telegraphy, leaves one like Oliver Twist. 



One would suggest, just for boys' books, that the necessaries 

 for the experiments and the construction of the models be 

 tabulated, and the illustrations and diagrams should also be on 

 the opposite page. 



PHYSIOLOGY. 



The Physioloiiy and Hygiene of Sleep. — By Davih Fraslr 

 Harris. M.D., CM.. F.R.S.E. 19 pages. 7-in. X 5-in. 



(Cornish Bros. Price 3d.) 



The .Annual Public Lectures on " The Laws of Health " of 

 the .Midland Institute, Birmingham, are always interesting and 

 instructive, and this year's lecture, delivered in September. 

 1910. and here reproduced in the form of a small booklet is 

 certainly one of the best. Dr. Eraser Harris divides the causes 

 that normally lead to and produce sleep into four classes : — 

 The action of fatigue toxins from muscular and mental work ; 

 the diminution of the cerebral blood flow ; the regular recurrence 

 or, better, absence of sensations from the external world ; and 

 lastly the purely psychic causes, the absence of ideas, worries, 

 emotions and the like. He gives us numerous examples of 

 each of these types of sleep and shows how the opposite 

 conditions may give rise to insomnia. Particularly would we 

 agree with him, when he points out the general inconvenience 

 that results from the action of those w-ho go about our streets 

 late at night, singing and shouting, and asks for legislation to 

 stop this practice. Lastly, working along these same lines, 

 some simple but excellent advice is given for the recall of 

 " Sleep. O gentle Sleep. Nature's soft nurse I " by those who 

 have lost her companionship. The booklet contains one of 

 the best descriptions in popular language of the Physiology of 

 Sleep that we have yet seen. 



ZOOLOGY. 



Tlie Buul; of the .Animal Kingdom. — By W. Percival 

 \Vestell. 379 pages. 274 illustrations. 7-in. X9-in. 



(J. M. Dent cS: Co. Price 10/6 net.) 



Mammals are not classified in this book on any systematic 

 plan, for it is not intended to be a scientific treatise, but, as 

 the writer hopes, will appeal not only to young folks in the 

 homeland and in other places where English is spoken, but 

 also to adults who have a general interest in the subject. The 

 creatures, therefore, are grouped together according to their 

 exceptional size, their means of protection, and their ways of 

 obtaining their prey. The large number of photographic 

 illustrations, by Mr. W. S. Berridge, adds greatly to the 

 attractiveness of the book, and Mr. Westell has gone to some 

 of the best authorities for information that is not within his 

 own experience. V\'e learn that if this book has the reception 

 that it deserves it will be followed by another dealing 

 with birds. 



XOTirE.S. 



THE SCIENTIST'S REFERENCE BOOK AND 

 D I .A RV. — The present form of this useful annual consists of 

 two books joined together but opening different ways. The first 

 of these contains a diary with useful hints with regard to First 

 Aid. and a Daily Wants dictionary, which gives much valuable 

 information that is often required at a moment's notice. The 

 other book consists of tables and various facts, under the 

 headings of the different sciences, which are likely to be wanted 



by scientific people. A certain number of leaves are also left 

 blank for memoranda. 



Messrs. James Woolley, Sons and Company are to be 

 congratulated on the publication. Some of the information 

 with regard to the Scientific Societies is not quite up to date : 

 for the Royal -Anthropological Institute, the Zoological Society, 

 and the Selborne Society, among others, ha\ c changed their 

 addresses recently. 



