﻿336 Notices respecting New Boohs. 



important feature of the book is the attempt to make the subject 

 as real as possible by an examination of the experimental data 

 which are the main foundation of it. In most of the expositions 

 of the theory of relativity this experimental foundation is almost 

 lost sight of in the array of mathematical equations which, in 

 some quarters at any rate, seem to be the only vital thing. "We 

 still meet with people who imagine that the whole of mechanics 

 is a series of deductions from Newton's Law of Motion ; and that 

 in the exposition of mechanics no appeal is necessary to experiment. 

 The same might have been said of the p re-Newtonian principles 

 which experiment has shown to be erroneous. The same fascina- 

 tion for general principles led Einstein himself to forsake earlier 

 methods and to enunciate two general principles from which all 

 deductions were to be made. Dr. Silberstein is careful to sketch 

 the historical development of the subject from Maxwell, through 

 Hertz, Heaviside and Lorentz, to the final enunciation of his 

 fundamental principles by Einstein. In this sketch he is equally 

 careful to explain the part which the appeal to experiment has 

 taken. The result is that this presentation of the theory has 

 a real look about it, in contradistinction to those expositions which 

 are carried away by the fascination of the universalisation of the 

 application to moving bodies of a set of equations which were 

 primarily put forward to apply only to bodies at rest. The fact 

 is that without the result of Michelson and Morley's experiment 

 there would be no justification for the theory at all. It is because it 

 gives the most direct explanation of their null result and is at the 

 same time not at variance with any other experimental fact, that 

 the theory may claim serious consideration. So much does the 

 reviewer feel this to be true that he would go further, and declare 

 that it will only be when further experimental data of a crucial 

 kind are obtained that the theory will run much chance of becoming 

 definitely accepted as scientific knowledge. 



Meanwhile it is necessary that the consequences of the theory 

 should be examined in detail ; for by doing this, information may 

 be gained of the kind of way in which further appeal to experiment 

 may be made. It is with this object in view that we would 

 recommend the present volume to be studied. 



"With regard to the mathematical methods adopted, we may 

 point out that most use is made of quaternionic formulae ; but 

 these are fully explained : so that no one need be deterred on this 

 account. Some use is also made of the matrix method of repre- 

 sentation employed by Minkowski. 



It must not be thought that Dr. Silberstein is merely an 

 expositor of other people's work. The whole book savours of 

 originality, and no one who wishes to be abreast of this revolu- 

 tionary subject can afford to leave the book on one side. 



It is beautifully printed and appears to be very free from typo- 

 graphical errors. 



