462 



NATURE 



[December 8, 1921 



is based. The principles are clearly and concisely 

 stated, the author's aim beingf to develop the 

 reasoning power of the student, and not merely to 

 give him disconnected facts. 



The junior student who has no teacher will 

 probably find many difficulties in the book. The 

 two-wattmeter method of measuring power in 

 three-phase circuits is given so concisely that we 

 doubt whether any reader who comes across it 

 for the first time will be able to follow the reason- 

 ing. We think also that it is a pity Kelvin's law for 

 the maximum efficiency of power transmission 

 lines is merely stated ; a proof could have been 

 given in two or three lines. 



The author has adopted the recommendation of 

 the International Electrical Commission, and calls 

 the unit tube of induction the Maxwell. He, 

 however, calls the unit of magnetic flux density 

 — ri.e. a Maxwell per square centimetre — the 

 Gauss. The recommendation of the I. E.G. is 

 that the unit of magnetic force be called the 

 Gauss. Magnetic force is not mentioned at all, 

 and up to a certain point the author seems to get 

 on very well without it. His definition, however, of 

 permeability as the ratio of the magnetic flux at 

 a point in the medium to the magnetic flux at 

 the same point if an infinitesimal portion of the 

 medium at the point were removed and air sub- 

 stituted is open to criticism. 



Teachers find it difficult to give a satisfactory 

 definition of the capacity — or, as the Americans 

 call it, the capacitance — of a condenser. In this 

 book it is defined by means of the charging 

 current for a given sine-shaped wave of potential 

 difference applied to its electrodes, and this gets 

 over many difficulties. Mercury arc rectifiers, 

 which can often advantageously replace rotary — 

 or, as the Americans call them, synchronous — 

 converters receive a chapter to themselves. The 

 book concludes with a large number of photo- 

 graphic reproductions of the latest types of elec- 

 trical machinery and apparatus. Some of these, 

 however — e.g. the electrolytic lightning arrester — 

 are not described in the text. A. R. 



British Scientific and Technical Books. 



A Catalogtte of British Scientific and Technical 

 Books Covering every Branch of Science and 

 Technology , carefully Classified and Indexed. 

 Prepared by a Committee of the British Science 

 Guild. Pp. xviii 4- 376. (London : British 

 Science Guild, 6 John .Street, Adelphi, W.C.2, 

 1921.) I05. net. 



IT would be difficult to discover many readers of 

 Nature who would not be interested in the 

 present volume, and would not find it a useful 

 NO. 2719, VOL. 108] 



addition to their libraries. Hitherto the informa- 

 tion within its covers has been obtained only by 

 the wearisome perusal of some 120 publishers' 

 lists, with their varying methods of classification. 



The volume is a result of a desire of the British 

 Science Guild to make a complete record of scien- 

 tific and technical books, other than those intended 

 for primary schools and elementary volumes of 

 like nature, in the current lists of publishers in 

 the United Kingdom. No attempt at selection 

 has been made by the Committee, and the present 

 writer is of the opinion that this course is a wise 

 one. There are many works which are condemned 

 by one authority and yet are recommended by 

 another. The whole difference lies in the point of 

 vision and the purpose for which the work is 

 wanted. This being so, it is far better to place 

 before the inquirer a list of books on a given 

 subject and let him make his choice, knowing as 

 he probably does his own requirement. If skilled 

 advice be needed, with such a list at hand it is 

 probable that any expert would be willing to give 

 advice. 



The entries are arranged in subject order in a 

 classification devised to be such that, so far as 

 practicable, related subjects are placed near to 

 one another, the titles under each head or sub- 

 head being arranged alphabetically according to 

 authors' names. 



If there is any doubt as to the particular group 

 or groups in which a subject would appear, a 

 reference to the alphabetical subject index at the 

 end of the volume at once indicates where it will 

 be found. This alphabetical subject index adds 

 considerably to the value of the work, as it is a 

 guide to the contents, rather than a mere indica- 

 tion of the titles, and it is evident that much care 

 has been taken in its compilation. A very com- 

 plete alphabetical list of authors, collaborators, 

 and translators is also included. 



The insertion of the date of publication of 

 nearly every item is an extremely useful feature. 

 This information very seldom appears in a pub- 

 lisher's catalogue, and one is left in ignorance 

 as to whether a book is twenty years old, or the 

 latest publication on the subject. 



Apart from the purpose for which the work has 

 been produced, it constitutes a valuable post-war 

 survey of the British resources in this field of 

 literature. With its aid some lacunae may be dis- 

 closed which, it is hoped, British authors and 

 publishers will be quick to fill. 



The trustworthiness of the volume has been 

 very thoroughly tested, and although some hun- 

 dreds of items have been checked, the reviewer 

 found no serious reason for criticism. A few 

 prices are not correct, but this is only to be 



