328 Scientific Intelligence. 



originality for the convention of signs is claimed. This conven- 

 tion is not new, for it is used by such authorities as Czapski 

 (1893), Kayser (1900), Southall (1910), etc. Again, on page 41, 

 we find the following remarkable definition of a principal section 

 of a prism, namely : " The median vertical plane that bisects the 

 apical angle is called the principal plane, ..." h. s. u. 



15. An Introduction to Mathematical Physics; by R. A. 

 Houston. Pp. ix, 199, London, 1912 (Longmans, Green and Co.) 

 — To the study of this book the student is supposed to bring a 

 thorough knowledge of the calculus and a rather extensive 

 acquaintance with the phenomena of physics. A considerable 

 familiarity with dynamics is also presupposed. The first chapter 

 is devoted to the subject of attraction, (gravitational and electro- 

 static), and covers the discussion of the fields due to lines, planes, 

 spheres, cylinders, and ellipsoids, by the usual methods. The 

 second chapter covers a considerable portion of classical hydro- 

 dynamics ; and the third, of Fourier series and heat conduc- 

 tion. In the fourth chapter on wave motion the various types 

 of waves in strings and rods are considered in some detail and 

 much attention is given to water waves. The fifth chapter is on 

 electromagnetic theory and the major portion of it is devoted to 

 electric waves and light. The last chapter is on thermodynamics, 

 and covers the usual classical theory with applications to ideal 

 gases. 



It is obvious from the above summary that there is an immense 

 amount of ground covered in the short space of two hundred pages. 

 In order to accomplish this the author has had in almost every 

 instance to sacrifice the physical to the mathematical discussion 

 of the various topics. The book is however clearly and logically 

 written and should form a valuable work of reference for advanced 

 students. l. p. w. 



16. Practical Measurements in Radio- Activity ; by W. 

 Makower and H. Geiger. Pp. 151, London, 1912 (Longmans, 

 Green and Co.). — In an experimental science it is always advan- 

 tageous when a precise and detailed description of the customary 

 technical procedure and methods is available for the instruction 

 of those without previous experience who desire to carry out 

 practical work in the subject. The book at hand fulfils these 

 requirements in a thoroughly satisfactory manner and supplies, 

 in a very systematic manner, much valuable information not to 

 be obtained from other sources. The construction, principles 

 and adjustments of electrometers and electroscopes are first 

 discussed in a comprehensive manner, the various types of radia- 

 tion emitted by radio-active bodies and the methods by which 

 they are identified and measured are next considered, while suc- 

 ceeding chapters on the active deposits and radio-active recoil, 

 radio-active transformations, standard measurements, and the 

 separation of radio-active substances supply a large amount of 

 important data in connection with these branches of the subject. 

 The book marks a very distinct advance over anything of a simi- 



