REVIEWS 485 



in book form. There have been considerable additions made to the first 

 edition, and parts have been rewritten to bring the subject-matter up to date. 

 For example, a description of the Knudsen radiometer gauge, which is 

 displacing the McLeod for some purposes, is given in Chapter I. Some new 

 theoretical investigations bearing on the equilibrium of electron atmospheres, 

 due to von Laue, appear in Chapter II. Quite a body of new information 

 is given concerning the temperature variation of electronic emission. 



The book still remains an indispensable companion for those whose 

 interest in thermionics extends beyond the sketchy acquaintance of the 

 textbook reader. 



J. R. 



La Physique Theorique Nouvelle. Par Julien Pacotte. [Pp. vii+182.] 

 (Paris : Gauthier-Villars. Price 12 frs.) 



This is a very ambitious book. It attempts, according to Borel (the writer 

 of the preface) " to resume, in a book of modest dimensions, without mathe- 

 matical equipment the totality of theories which constitute the new theoretical 

 physics." We fail to see where the book lacks mathematical equipment. 

 For the most part, in treating mathematical physics, the book uses the 

 mathematical equations " written in words " [vide p. 65). To those 

 interested the equations written in symbols would make the reading easier. 

 (Compare, for instance, the plan adopted by Whittaker in his History of 

 Ether and Electricity.) The general theory of relativity seems to be too 

 recent to be included in the " ensemble." 



To those interested in experimental physics Chapter IV would appeal most. 



On the whole the book is very sound. 



J. R. 



Philosophy and the New Physics. By L. Rougier. Translated from the 

 French by M. Masius. [Pp. xi + 159.] (Philadelphia : Blakiston's 

 Son & Co.) 



The book deals with a metaphysical problem which existed half a century 

 ago, when natural phenomena were interpreted in terms of two groups of 

 substances — matter which possessed weight, and certain fluids or so-called 

 fluids (caloric, electrical and magnetic, etc.) which were devoid of weight. 



The problem was this — how was it possible for the imponderable to affect 

 ponderable matter ? There seemed to be some link missing in this method of 

 interpretation. 



The development of physics and physical theories since that time has 

 been effective in removing the problems, as now everything is interpreted 

 in terms of one agent, energy — with the possibility of existing in one of two 

 forms — that which we ordinarily call matter, and that which we call radia- 

 tion, but both similar in nature and possessing inertia. 



This development is very carefully traced, the experimental data upon 

 which progress depended being indicated clearly, step by step. 



Initially we get the attempts to explain all actions in terms of matter, 

 even action at a distance. Then the idea of the space surrounding matter 

 playing a part, originated by Faraday, brought out the localisation of energy 

 in the dielectric medium rather than in the matter itself. Later the study of 

 cathode rays, bringing out the fact that their inertia is wholly electromagnetic, 

 and the researches revealing the ubiquity of the electron naturally seemed to 

 lead to the conclusion that all matter is really energy. The pressure of 

 radiation also emphasises the fact that radiant energy possesses inertia. 



The author gives an extremely good general survey of this field, and passes 

 on to show the effect of Einstein's relativity principle and Planck's quantum 

 hypothesis on the interpretation of phenomena. 



The book is an extremely good introduction to an understanding of these 



