286 Notices respecting New Books. 



obtain a pure number, say 



Cl = Em-W- 2 , c 2 = \EKe~ 2 ; 

 and, in order that (f> may be of the dimensions of energy per 

 unit volume per unit wave-length, we find that <f> must be of 

 the form 



= \- 4 E/(^c 2 ); 

 whence, on passing to the limit as before, we obtain 

 (/> =\- 4 E/(\E). 

 Stefan's formula follows on integration with respect to A. 

 in the form SE 4 , the value S being of course identical with 

 the former 16 B~ 4 cr. 



Hence it appears that the argument can be moJified 

 without trouble, so that the conception of temperature dis- 

 appears altogether, being replaced by the conception of 

 energy. The objection brought against my original argu- 

 ment, namely, that " temperature is and can be defined 

 only in terms of the properties of matter, and in fact in 

 terms of properties which are common to all matter/' must, I 

 think, be withdrawn when " energy " is substituted for 

 " temperature." J. H. Jeans. 



Princeton, N.J. 



XX. Notices respecting New Books. 

 The Electron Theory. A Popular Introduction to the new Theory 

 of Electricity and Magnetism. By E. E. Eoubnieb d'Albe, 

 B.Sc, A.K.C.Sc. With a Preface by G. Johnstone Stoney, 

 M.A., Sc.D., E.RS. London : Longmans, Green, & Co. 

 1906. Pp. xxiv + 312. 



r PHE great interest which is being evinced by all educated people 

 -*- in the new views regarding the nature of matter that have 

 been forced upon the scientific world by the brilliaut researches of 

 the last decade should secure a wide circulation for this book. In 

 simple and easy language, free from unnecessary technicalities, 

 the author presents to his readers an account of the electron 

 theory, and shows how the theory may be made to interpret in a 

 satisfactory manner all the old familiar facts, as well as discoveries 

 of more recent origin. A brief sketch of the development of the 

 electron theory is first given, and is followed by an account of the 

 elementary facts of electricity and magnetism, couched in terms 

 suitable to the new conceptions introduced by the electron theory. 

 This part of the book is, in a sense, an elementary text-book 

 written on entirely up-to-date lines. A commendable feature is 

 the frequent use of arithmetical calculation for the purpose of 

 arriving at results which give the reader a correct notion of the 

 magnitude of the various effects discussed. The later chapters 

 are mainly devoted to recent advances, and include an account of 

 the electromagnetic theory of light, of magneto-optic phenomena, 

 of radio-activity, and a discussion of the constitution of the 



