774 SCIENCE PROGRESS 



Einstein treatment of the optical and electrical phenomena in moving systems ; 

 the second the work of Einstein, Minkowski, and their disciples on the theory of 

 relativity. Thus the author devotes considerably more than half of his work to 

 setting out the classical work of Maxwell, Hertz, and Heaviside. His object, as 

 stated by himself, is somewhat in the nature of a protest against the haste of 

 some of the ultra-moderns to throw the powerful theories of the great physicists 

 of the last generation overboard ; he warns them lest, having driven out the old 

 gods, they be compelled to bring them back, should those who have replaced 

 them not fulfil expectation. We think that most physicists will be able to 

 sympathise with this point of view, but at the same time we do not consider that 

 the presentation of the older work is sufficiently original or convenient to justify 

 the amount of space devoted to it. A competent knowledge of the work of the 

 Maxwell-Hertz school, and a clear realisation of the points in which it comes into 

 conflict with experience, is, of course, a necessary preliminary to an understanding 

 of the principle of relativity, and what it seeks to do ; but in view of the large 

 number of excellent books on the older electrodynamics we find the present book 

 unnecessarily diffuse. 



The second part of the book deals with the modern theory of relativity, and 

 seeks in particular to reduce the brilliant work of Minkowski to a form more 

 easily understandable than that of the original papers. Einstein's concept of 

 simultaneity and the fundaments of his theory are clearly exposed. The author 

 finds an objection to the theory in the assumption which makes co-ordination of 

 times dependent on so arbitrary a thing as the velocity of light — a difficulty which 

 must have struck every one on their first approach to the principle. It is hard to 

 answer the objection ; probably the best justification of the whole theory is the 

 way in which it gives the dragging coefficient required by Fresnel's formula and 

 the Fiseau experiment, the negative results of the Michelson-Morley and all 

 allied experiments, and the appeal of a transformation which makes the equations 

 invariant. Minkowski's mechanics and electrodynamics are developed in two 

 sections, but, while adequately exposed, are not made much clearer than in the 

 original papers. 



The book has all the thoroughness of a German work of the old school, and is 



a formidable addition to the works on relativity. 



E. N. da C. Andrade. 



Rays of Positive Electricity, and their Application to Chemical Analysis. 

 By Sir J. J. Thomson. [Pp. vi + 132.] (London : Longmans, Green & Co., 

 191 3. Price $s. net.) 



To the various series of scientific monographs now appearing Messrs. Longmans, 

 Green & Co. now add their " Monographs on Physics," under the joint editorship 

 of Sir J. J. Thomson and Dr. F. Horton. The first volumes include one on 

 positive rays by Sir J. J. Thomson, and one on the photoelectric effect by 

 Dr. Allen, reviewed elsewhere. 



The book on positive rays is not a general account of all the work which has 

 been done on the subject, but rather an account of the recent experiments of the 

 distinguished author, which has thrown so much light on the nature and charge 

 of the material carriers of electricity at low pressure, together with a few selected 

 researches of other authors whose results are of interest in this connection. It 

 is to be welcomed as giving an authoritative summary of the methods and results 

 of his investigation of the last seven years in this field. The general method 

 consists in subjecting a beam of positive rays, passing through a single fine hole 



