[ 361 ] 

 XXXIX. Notices respecting JSew Books, 



Elements of the Electromagnetic Theory of Light. By Ltjdwik 

 Silbbrstbzn", Ph.D. Pp. vii + 48. Longmans, Green & Co. 

 Price 3s. 6d. net. 



TN this elegant little volume of 48 pages are condensed the chief 

 -*■ consequences which follow mathematically from the Hertz- 

 Heaviside form of Maxwell's equations. The vectorial treatment 

 effects a great economy of space as compared with the old Cartesian 

 splitting of every vector into its three components, and, since the 

 time has now been reached when, it is hoped, the elementary 

 vectorial operations are familiar to every student, the method is 

 the natural one to adopt in expounding the subject. Plane waves 

 only are considered, and their reflexion and refraction, polarization, 

 and double refraction in crystals handled briefly yet convincingly. 

 This development of the simple theory is clear and satisfactory, 

 and likely to be extremely useful to one whose acquaintance with 

 the subject is not very deep : to the maturer student the chief 

 interest of the book is the excellent historical account of the work 

 preceding the electromagnetic theory, which occupies the first 

 fifteen pages or so. In this the successive difficulties met by the 

 elastic solid theory are succinctly exposed, and the many inge- 

 nious hypotheses put forward to solve the vexed question of 

 the longitudinal waves are detailed. The striking advantages 

 of the electromagnetic theory are thus thrown into relief. There 

 are, we think, few who will not find something new to them in 

 this well-planned critical sketch of one of the most interesting 

 chapters of physics. 



Stoichiometry . By Sydney Young, D.Sc, F.R.S. Longmans, 

 Green & Co. Second Edition. Pp. xii + 363. Price l'2s. 6d. net. 



It is eleven years since the first edition of Professor Young's book 

 appeared, and during that time the discovery of isotopes, the 

 other developments of the study of radioactivity, and the mea- 

 surement of X-ray spectra have led to considerable modifications 

 of and additions to previous ideas on the subject of atomic weight. 

 In this second edition Professor Young has introduced a short 

 discussion of the modern views of the nature of an element and 

 the existence of isotopes, and gives an account of Soddy's theories, 

 but it is remarkable that he contents himself with a passing 

 reference, which is not even indexed, to X-ray spectra, and has 

 no word of Moseley's atomic members, which confirm the im- 

 pression given by the chemical properties of the elements con- 

 cerned that there is something wrong in the position of Argon and 

 Potassium, Tellurium and Iodine, Cobalt and Nickel in the periodic 

 table, when the elements are arranged in order of the atomic 

 weight. The physicist will also miss the lack of any reference in 

 the sketch of the kinetic theory to recent experimental con- 

 firmation, or to Ramsay's determination of the atomic weight of 



Phil Mag. S. fi. Vol. 36 No. 214. Oct. 1918. 2 B 



