NATURE 



[November 2, 191 1 



question. The author's reasons for following this 

 method are not apparent, but we are tempted to believe 

 that it is in order to conform with the regulations of 

 the University of London, which still insist that the 

 pass degree in physics should be obtainable without 

 a knowledge of the calculus. 



The earlier chapters of the book are devoted to the 

 principles of mechanics, special attention being paid to 

 oscillatory and gyrostatic motion. The simpler parts 

 of the subject seem somewhat curtailed, but that is, 

 perhaps, excusable in view of the very comprehensive 

 nature of the book. Following chapters on gravitation 

 and elasticity, we find surface tension very fully 

 treated, and it is noticeable that the author very 

 properly points out the inaccuracy of the statement 

 often made, that the surface tension is equal to the 

 surface energy per unit area. Chapters xi. to xiv. 

 introduce subjects the inclusion of which renders this 

 book unique. The author deals in a simple yet de- 

 tailed and exact manner with the motion of fluids, 

 including applications to the properties of vortex fila- 

 ments and the waves on the surfaces of liquids. In 

 the concluding chapter there is also to be found much 

 that is new from the student's point of view. The 

 consideration of the kinetic theory of gases is more 

 complete in many respects than that which has usually 

 been given, particularly with respect to the influence 

 of the finite size of the molecules and the various 

 methods of estimating their size and number. 



As in Mr. Edser's other books in this series, the 

 printing is excellent, and the heavy type used in the 

 more important statements is very desirable. Good 

 figures and diagrams form another pleasing feature. 

 A wealth of examples (to which answers are given) 

 should enable the student to become thoroughly 

 acquainted with the principles described, and there is 

 little doubt that the book, both from its general excel- 

 lence and unique features, and notwithstanding the 

 calculus methods referred to, will become almost in- 

 dispensable to the students of physics. 



MARINE ENGINES. 

 Marine Engine Design, including the Design of Turn- 

 ing and Reversing Engines. By Prof. Edward M. 

 Bragg. Pp. 172. (London : Constable and Co., 

 Ltd., 191 1.) Price 8^. net. 

 T N this small book the author has endeavoured to 

 -L describe methods by which the 

 "detailed design of the principal parts of marine 

 engines can be determined, and has concen- 

 trated the results of several years of experi- 

 ence in teaching the subject of marine engine design 

 to students of the University of Michigan." 



Within these modest limits the volume should prove 

 useful as a class-book for students, although it cannot 

 be admitted that Mr. Bragg is accurate in the opinion, 

 expressed in his preface, that 



"most of the text-books on the subject of marine 

 engines deal only in a general way with the subject 

 of design, and particularly ... as referring to the 

 numerous coordinating parts of the modern marine 

 engine." 



On the contrary, many excellent text-books exist- 

 in English, French, and German— which contain full 

 NO. 2192, VOL. 88] 



discussions of design of details for marine engines anH 

 numerous examples drawn from actual practice. Tl 

 distinctive feature of the book under review is reall\ 

 found in its exclusive devotion to details of design, 

 whereas preceding text-books have been more com- 

 prehensive in scope, and as a consequence are larger 

 and more expensive. 



Prof. Bragg confines attention to marine engin< 

 of reciprocating types; he leaves untouched problcMi 

 connected with steam turbines as applied to ship- 

 propulsion, although these are undoubtedly of primary 

 importance in present circumstances. Rules ar ' 

 specimen calculations are given for determining t! 

 dimensions of cylinders, the "cut-off" in the admi 

 sion of steam, the length of stroke, and other pa 

 ticulars for engines of specified powers and given 

 rates of revolution. Steam speeds, valve diagram- 

 valves, and valve-gear are treated at consideral 

 length. Attention is directed also to methods i' 

 calculating the strengths of many of the principal fix' 

 and moving parts of reciprocating marine engine^ 

 in some cases the rules for details of marine engir 

 issued by the principal societies established for v.. 

 survey and classification of merchant shipping ar 

 reproduced. 



The last two sections of the book contain a full 

 discussion of the details of design for auxiliary 

 engines fitted for the purpose of turning the cranl: 

 shafts over — when valves are being set or when t' 

 main engines are being overhauled — and of desig: 

 for small engines used for reversing the main engin 

 in steamships. About one-sixth of the total spa. 

 in the volume is devoted to these subjects, althou;^ 

 they are unquestionably of less relative important 

 than must be assigned to other matters, to vvhi( 

 less attention has been devoted by the author. H 

 hope and expectation, as expressed in the preface, a.; 

 that by keeping the book " free from the descripti\ 

 part of the subject it will fill a decided void " and ' 

 "much more readily available " than other text-booj^ 

 " for the particular use for which it is intended." The 

 majority of students will, in all probability, favour 

 the use of text-books which are less restricted in air 

 and are richer in descriptions and illustrations ui 

 various types of engines. This opinion, however, in 

 no sense reflects on the manner in which the author 

 has done his work; and, of course, he is entitled to 

 form and act upon his own estimate of the kind 

 of text-book likely to prove of most service to students 

 of marine engineering. W. H. W. 



OUR BOOK SHELF. 



Puppets: a Work-a-Day Philosophy. By George 

 Forbes, F.R.S. Pp. ix-i-183. (London: Macmillan 

 and Co., Ltd., 191 1.) Price 35. 6d. net. 

 This is a philosophical sketch, or skeleton, clothed 

 upon with the human interest of a story. A party of 

 happy and well-to-do people are staying at a Scottish 

 castle, and James Gordon expounds to them his philo- 

 sophical views. These are of the idealistic kind, which 

 may roughly be called Berkeleyan, and Gordon 

 develops them very ingeniously, making some use of 

 the modern psychological doctrine of the subconscious. 

 All our knowledge of the world is a mental know- 

 ledge ; all "things" are thoughts or, at least, cannot 



