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XXIX. Notices respecting JSew Books. 



The Theory of the Relativity of Motion. By Professor B,. C. 

 Tolman. University of California Press. Pp. ix + 225. 



r FHE writer of a book on relativity lias a double task, firstly to 

 -*- explain clearly the nature of the assumptions on which the 

 theory rests and their experimental justification, and secondly to 

 develop mathematically the characteristic transformations and their 

 consequences. Of these the first is the harder, since, while the 

 mathematics of the simple theory are straightforward, and 

 present no difficulty to the student furnished with the necessary 

 technical equipment, the fundamental concepts are rather in 

 seeming contradiction to, than a natural development of, what 

 he has already learnt in mechanics. That the mass of a moving 

 body depends on its velocity and the length of it on its orientation, 

 that the result of compounding any two velocities (even collinear) 

 less than that of light gives a velocity still less than that of light — 

 to make these things even reasonable demands a very careful and> 

 logical exposition of the bases of the theory. We do not think 

 that Professor Tolman has devoted enough care to the preliminary 

 explanations. The ideas of Presnel and his successors receive a 

 bare mention, yet it is by explaining these, and describing the 

 difficulties solved and the fresh ones encountered that the mind 

 can be gradually led to the staudpoint of the relativists. Con- 

 sidering that the book is intended as an introduction to the 

 subject, the diuiculties presented to the mind trained in the older 

 electrodynamics have been handled somewhat perfunctorily. 



The order in which the subject is presented is the reverse of 

 the historical. The electrodynamic equations, in which the theory 

 originated, are not presented until Chapter XII. , the previous 

 chapters being devoted to the relativistic dynamics of particles and 

 elastic bodies. The historical order is the more natural one, and the 

 more convincing for the physicist, since, after all, the only expe- 

 rimental confirmations of the theory are to be found in the realm 

 of electromagnetic phenomena (including, of course, light). The 

 scope and nature of the experimental results in question might 

 have been made clearer. 



The chapter on chaotic motion of particles contains no reference 

 to the work of Jiittner, and that on the dynamics of elastic bodies 

 no reference to Herglotz, Born or Lamia. The book, being in- 

 tended as an introductory treatise, does not handle the generalized 

 theory of relativity. The last chapter contains an interesting 

 exposition of four-dimensional analysis, based upon the work of 

 Wilson and Lewis, and elsewhere the work of the American 

 relativists is well represented. 



