Notices respecting New Books. 243 



the recent determination, by the author and Mr. Morby, of the 

 Dynamical Equivalent of Heat. 



To the student of physics as well as the advanced student of 

 engineering, the volume is full of interest and suggestion. But — 

 if we except a few of the shorter papers — the reading of it is a 

 task demanding great mental concentration, and advanced 

 mathematical knowledge ; it is not a task to be undertaken light- 

 heartedly. 



A word of praise is due to the publishers for the beautiful 

 " get-up " of the book. 



Electricite et Optique. La Lumiere et les Theories Electrodyna- 

 miques. Lemons professees a la Sorbonne en 1888, 1890 et 1899 

 par H. Poincare, Membre de VInstitut. Deuxieme edition, revue et 

 completee par Jui.es Blondin et Eugene Xeculcea. Paris : 

 Georges Carre et C. Naud, 1901. Pp, x + 641. 



For elegance and clearness of treatment, French writers of text- 

 books are probably unsurpassed, and of these admirable qualities 

 the book now under review is not an unfavourable example. Its 

 distinguished author has already, by his numerous publications on 

 various branches of mathematical physics, done splendid service in 

 removing the difficulties and clearing up the perplexities which 

 beset the student of the various rival theories whose aim is to 

 provide a purely dynamical explanation of all physical phenomena. 

 A large portion of the book before us has already been previously 

 published, but it now appears in a revised form, and with im- 

 portant additions necessitated by recent advances in the subject. 



The book is divided into tour parts. Part I. commences with a 

 sketch of the earlier electrical theories, the more important 

 theorems and formulas of electrostatics being established ; this is 

 followed by Maxwell's theory of electric displacement, the short- 

 comings and difficulties of which are subjected to a clear and 

 searching analysis. Xext comes an account of Poisson's theory 

 of dielectrics, and of Maxwell's theory of the forces exerted 

 between charged conductors. The four chapters which follow 

 deal with the theory of electric currents in linear and solid con- 

 ductors, magnelism, electromagnetism, and electrodynamics. Next 

 come two chapters in which the theory of electromagnetic induc- 

 tion is developed, and the equations of the electromagnetic field 

 are established. The way having been thus paved for it, the 

 electromagnetic theory of light is fully considered in the next 

 chapter, and this is succeeded by the concluding chapter of Part I., 

 which deals with the magnetic rotation of the plane of polari- 

 zation. 



In Part II. the author considers the older electrodvuamical 



