May. 1911. 



KNOWLEDGE. 



201 



engines of 100 H.F. : and aviators and engineers who are 

 catering for a\iators' wants are scheming to produce engines 

 of larger and larger horse-power. Aviators are impressed 

 with the well-known law, that the pressure supporting an\' 

 given surface varies directh' as the square of the velocity of 

 the machine through the air, or what amounts to the same 

 thing, of the air past the machine. Unfortunately, there is 

 another law. viz.. that the power required varies as the cube 

 of the velocity. Lilienthal believed in reducing the power, 

 and we believe that a careful study of the experiments he 

 made, and of the laws which he worked out, will lead to a 

 reduction of power, and to a real advance in aeroplanes, on 

 the lines upon which he worked. 



Inventors of aeroplanes appear to have availed themselves 

 to a considerable extent of the facts which his experiments 

 brought out, but to have parted company with him at a certain 

 point. Possibly in a little while the course may be reversed. 



We heartily recommend the book to anyone who wishes to 

 get a sound knowledge of the principles of bird flight, and of 

 the classical experiments that Lilienthal made. ^ .- ... 



.A.STKONOMV. 



Ainiiiiiii\s Astrdiioiiiiijucs pour I'll! ct 1912 de I'Observa- 



toire Royal de Belgiquc public par les soins de G. Lecoin'TI:. 



liirecteur Scientifique du Service .A.stronomique. lyil — 299 



pages: 1912 — 167 pages l7-in. x 5-iu.i 



These well-known .Annuaires, which ha\e been published 

 each year since 1S34 without interruption, give in an accessible 

 form practically all the astronomical data required by amateur 

 astronomers together with considerable meteorological and 

 magnetic data often required by practical astronomers. 



There is no work in English which corresponds to these 

 .\nnuaires, but most astronomers have felt the need of such 

 handbooks which give in a concise form, without the 

 academical detail of the Nautical .Almanac, the chief 

 observable phenomena. 



Each edition contains a useful map of the world illustrating 

 the time zones and showing which coimtries have adopted the 

 standard time system. 



The Annuaire for 1912 is specially interesting as it 

 summarizes the observations made upon Halley's comet from 

 the date of its re-discovery in 1910 and four plates illustrate the 

 comet's changes during the period it was under obser\ ation. .'\ 

 further plate shows a star chart with the path of the comet at the 

 time of inferior conjunction and now that the elements of the 

 comet are so well known it may be possible to at least trace 

 the comet photographically through a much longer period than 

 has ever been done before. 



The Annuaires are fairly comprehensive and e.xplanatory 

 and can be recommended as a useful " companion " to 

 practical observers. ... j. 



BOTAXY. 



1 1 I Tlic Livcricurts, British and Forci<^:t. — By Si R Ed\v.\rd 

 Fkv. 74 pages. 47 illustrations. 7|--in X 5-in. 



D.win W'lLso.N. 



Willidiii Tlioinsoii — Lord I\ch-iii. — By 

 56 pages. S'-in. X j.j-in. 



(Glasgow : John Smith & Son. Price 2 - net. cloth ; 

 1 - net, paper.) 



Reviewing books would be a very pleasant pastime, if they 

 were all so fascinating as this one. It is thoroughly enjoyable 

 — delightfully original. Much sound philosophy and a true 

 glimpse of a great man of true scientific spirit is included in 

 fifty-six pages of real literature abounding with amusement. 

 Read how Lord Kelvin was the " righteous soul in harmony with 

 things in general." There is a chapter which ends " failing to 

 realise the deep and irresistible power of capillary (and other l 

 attractions " ! 'I'here is no doubt as to the deep attractiveness 

 of the book. . ^ ^ 



A. C. E. 



(Witherby & Company. Price 



r.et. 



211 pages. 



(21 Mosses and Liverworts. — By T. H. Russi;i.i 

 10 plates. Si-in. X 5.*-in. 



(Sampson Low & Company. Price 45 net.) 



These two books are alike in many respects. Both attempt 

 to deal in a more or less " popular " style with a remarkable 

 group of plants, which has, by many botanists, been regarded 

 as occupying a central position in the vegetable kingdom, and 

 forming a transition from the green algae on one hand and the 

 great fern and flowering plant alliance of the vascular plants 

 on the other. This group, the bryophyta, has, until recentlv, 

 been divided by general consent into two classes — the Liver- 

 worts and the Mosses — though there are signs that this twofold 

 division is breaking up and will be replaced by a more scientific 

 system of classification based upon the results of recent work 

 on the morphology and development of these interesting plants. 



(1) Sir Edward Fry's little book is chiefly a mixture of 

 borrowings from ancient and modern authors, and cannot be 

 said to present anything like an accurate view of the structure, 

 biology, classification and relationships of the Liverworts. 

 The extremely small portions of the book that appear to be 

 based upon the author's own studies are chiefly remarkable 

 for eccentric spellings, such as " antherizoids " and " amphi- 

 gastra." strange interpretations of the functions of wrongly 

 described structures, and some of the worst drawings in 

 a badly-illustrated book. 



However, it is just possible that some amateur naturalists 

 into whose hands this book may fall will find in it something 

 to stimulate curiosity concerning the much-neglected Liver- 

 worts, and to impel them to obtain a more reliable guide to 

 the study of these plants. For the structure and development 

 of these plants, it is quite evident that we have as yet no 

 " popular '■ work that can be recommended to the general 

 reader, though the botanical student will find practically all 

 he requires in the works of Campbell and Goebel. It is only 

 fair to mention that Sir E. Fry gives the names of these works 

 in the last few pages of his little book. .\s little books of this 

 kind appear to find a sale, we must admit that with all their 

 faults they may serve a useful purpose. 



(21 Mr. Russell's more comprehensive and ambitious work 

 has quickly passed into a second edition — a fact which testi- 

 fies rather to the growth of interest in the Mosses and Liver- 

 worts than to the merits of this particular book. Certainly 

 this book will aid the beginner to recognise some of the 

 commoner British species belonging to these groups, though 

 the author is obviously uuich less familiar with the Liverworts 

 than with the Mosses. The book is written in a bright and 

 interesting style, and the author has wisely refrained from 

 nmch generalisation and discussion on the morphology, 

 biology, and classification of these plants. Some of the 

 illustrations are fairly good, but perhaps the best feature of 

 the book is the chapter of nearly forty pages on the 

 collection and preservation (including microscopic mounting) 

 of specimens. 



It may appear somewhat harsh to criticise adversely such 

 books as Sir E. Fry's and Mr. Russell's, since the avowed 

 object of the author in each case is merely that of arousing 

 interest in the plants dealt with and pointing the way to more 

 advanced and systematic study with the aid of larger works. 

 If the writers of such books would simpK' confine themsehes 

 to what they are more or less familiar with — rthe general 

 characters of the commoner species and their habitats, and 

 methods of collection and preservation — they would entirely 

 disarm the criticism which, as it is, they provoke by their ill- 

 informed and totally unnecessary treatment of the scientific 

 aspects of the subject. If it is considered necessary to touch 

 upon these topics, it would be much better to give a series of 



