392 Notices respecting JS 7 eiv Books. 



stands to gain and not to lose by insisting that every scientific 

 fact is what it is, always for some observer in some system of 

 reference, and that every description of scientific fact must take 

 the observer and his system into account as factors. If this be 

 metaphysics, science has nothing to fear from it, but everything 

 to fear from disregarding it. There is, however, a metaphysics 

 which brings sterility alike to philosophy and to science. This is 

 the affirmation of an existence which is not what it is to any 

 observer. It is named in philosophy the thing-in-itself and 

 physical science has no need of it. 



I have only to add that the central portion of the book is 

 certainly difficult but the whole is in the author's inimitable style 

 and bright throughout with his wonderful humour. 



H. Wildon Care. 



A Treatise on Gyrostatics and Rotational Motion. 

 By Akdrew Gray, F.R.S. (Macmillan & Co. £2 2s. net.) 



Prof. Gray has produced in this volume a very complete account 

 of gyrostatics, which will be welcomed by students of applied 

 mathematics and technical students generally. All who are 

 engaged in the study of this subject will be grateful to the author 

 for bringing together in such an attractive form the many inter- 

 esting matters set forth in the pages of this book. 



Following the discussion of elementary principles in the earlier 

 chapters, a number of illustrations of the practical applications of 

 gyrostatic action are given. The reader is also provided with a 

 concise treatment of elliptic integrals, with the numerical solution 

 of problems relating to rotating bodies. The numerical examples 

 occurring in various parts of the book will be especially valuable, 

 and should do much to encourage further investigation. In suc- 

 ceeding chapters the author gives an exhaustive treatment of the 

 general dynamics of rotating systems, and a comprehensive dis- 

 cussion of more advanced gyrostatic problems, including the 

 whirling of shafts and chains. 



We are glad to commend this excellent and authoritative treatise, 

 the work of one who has done much towards the development of 

 this branch of science. It is to be hoped that Prof. Gray will find 

 it possible to issue in the near future the supplementary volume 

 dealing with gyrostatic devices of use in engineering and naval 

 and military affairs. • 



The excellence of the printing and diagrams should not be 

 overlooked. The book is well produced, has a useful index, and 

 as a work of reference will be found indispensable to all interested 

 in this fascinating subject. 



