314 SCIENCE PROGRESS 



It may be mentioned that the author does not consider it necessary to 

 abandon the conception of the existence of an aether, although it is diffi- 

 cult to ascertain what role is now left for the aether to perform. This 

 attitude may afford some comfort to those to whom the necessity of 

 abandoning the aether is a bar to acceptance of Einstein's theory. 



The book is excellently written, and although primarily intended for 

 readers without technical knowledge, it will also be of value to those who 

 are able to go into the mathematics of the subject. To them, Prof. Edding- 

 ton's commentary on the argument cannot fail to prove illuminating. The 

 style is admirable throughout, except for the final paragraph in the book. 

 (" We have found a strange footprint on the shores of the unknown. We 

 have devised profound theories, one after another, to account for its origin. 

 At last, we have succeeded in reconstructing the creature that made the 

 footprint. And lo ! it is our own.") We hope that this last sentence will 

 be altered in a future edition. 



H. S. J. 



PHYSICS 



A Handbook of Physics Measurements. By Ervin S. Ferry, in collabora- 

 tion with O. W. SiLVEY, G. W. Sherman jr., and D. C. Duncan. 

 [Vol. i, pp. xi + 251, with 146 figures. Vol. ii, pp. x + 233, with 

 128 figures.] (New York : John Wiley & Sons ; London : Chapman 

 & Hall, 1 91 8. Price 9s. 6d. net each volume.) 



Of these two volumes, the first deals with fundamental measurements, 

 properties of matter, and optics ; and the second with vibratory motion, 

 sound, heat, electricity, and magnetism ; and in the two volumes 108 experi- 

 ments in all are described. 



There are several features of value. The work is self-contained ; each 

 section commences with a general account of the instruments and methods 

 utilised in the subsequent experiments, and each individual experiment 

 consists of an explanation of its theory followed by an account of the method 

 of performing the experiment. This insures the student thoroughly under- 

 standing from the beginning what the experiment is designed to prove, and 

 how it does so. The most important sources of error are pointed out, and 

 means are indicated by which the errors can be eliminated, reduced to a 

 minimum, or allowed for. It is very necessary that students should realise 

 why, e.g., Joule's determination of the mechanical equivalence of heat must 

 possess a much greater weight than their own. 



The experiments have been well selected on the whole : both in the 

 selection and the method of treatment, the authors' extensive teaching ex- 

 perience is evidenced. Apparatus of standard type has, in general, been 

 described, and where improvised apparatus is used, it will be good for the 

 student to construct it himself. More can be learnt from self-constructed 

 rough apparatus, which can necessarily only give a relatively inaccurate 

 result, than from expensive and delicate apparatus the facility of using 

 which to its full advantage the student has not acquired. 



The two volumes should prove very valuable to those responsible for 

 preparing courses in practical physics. 



H. S. J. 



Relativity : The Special and the General Theory. A Popular Exposition. 

 By Albert Einstein, Ph.D., Professor of Physics in the University of 

 Berlin. Authorised translation by R. W. Lawson, D.Sc. [Pp. xiii 

 -f 138, with 5 diagrams and a portrait of the author.] (London : 

 Methuen & Co., 1920. Price 5s. net.) 



This account of the special and general theories of relativity by Prof. Einstein 

 himself can be recommended, particularly to those who, whilst not having had 



