REVIEWS 66i 



PHYSICS 



Ions, Electrons, and Ionising Radiations. By J. A. Crowther, Sc.D. [Pp. 

 xii + 276, with 95 diagrams.] (London : Edward Arnold, 1919. 

 Price 125. 6d. net.) 

 As it is stated in the preface, the book " is not a popular exposition of the 

 ' new physics,' nor is it a compendious synopsis of the whole subject," but 

 a textbook for the student grounded in the more elementary portions of 

 physics. 



The subject-matter begins with the passage of a current through an 

 ionised gas. Methods of measuring the current are clearly described, a 

 discussion on the relative sensitiveness of the electrometer and the electro- 

 scope being particularly useful and practical. The classical researches of 

 Sir J.J. Thomson, C. T. R. Wilson, Millikan, and Perrin, on the charge carried 

 by an ion, are fully considered. The spark discharge is dealt with somewhat 

 mathematically, but the subsequent chapter on the phenomena of the discharge 

 tube is fascinating reading. Cathode and positive rays receive full delibera- 

 tion, as also the emission of electricity by hot bodies and photo-electricity. 



In a chapter on X-rays one finds that their penetrating power " depends 

 principally upon density," which is rather a loose statement. Further, the 

 modern demand for the " radiator " Coolidge tube rather contradicts the 

 statement that " no cooling device is necessary " with this type of tube. 

 To maintain the historical sequence one would have thought that the work 

 of Barkla on the absorption of X-rays and the production of the characteristic 

 radiations would have preceded the work of Lane and Sir W. H. Bragg and 

 his son. A fuller description of Moseley's experiments would have been 

 appreciated. 



Nearly a quarter of the book deals with radio-activity. The classical 

 experiments illustrating the nature of the L-rays are clearly described, though 

 Becquerel's experiment disclosing the nature of the B particles has not 

 received the same lucid treatment. Gamma-rays, and the secondary B-rays 

 produced by their impact with matter, are reviewed somewhat rapidly, but 

 the theory of radio-active change is given at length, and a chapter dealing 

 with some problems in radio-activity is interesting. 



The last section of the book, dealing with the electron theory of matter, 

 begins with a resume of the results of the experiments throwing light on the 

 nature of matter. The Zeeman effect, metallic conduction, and the laws of 

 Wiedemann and Franz, are discussed and explained by the theory. 



Throughout the book the diagrams are numerous, simple, and clearly 

 drawn. The two plates showing C. T. R. Wilson's " cloud " photographs 

 and positive ray parabolas are a valuable addition to the text. Graphs 

 illustrating experimental and theoretical results are abundant, though one 

 regrets that the curves, for the K and for the L series, showing the propor- 

 tionality of the atomic number to the square root of the frequency, are missing. 

 In the main, the book justifies the claim of the author in that it is a " reason- 

 ably complete account of the present state of the subject," and is a valuable 

 addition to physical literature. 



L. H. C. 



CHEMISTRY 



A Treatise on Chemistry, Vol. I, The Non-metallic Elements. By the Rt. 

 Hon. Sir H. E. Roscoe, F.R.S., and C. Schorlemmer, F.R.S. Fifth 

 Edition, revised by Dr. J. C. Cain. [Pp. xv 4- 968, with 226 illus- 

 trations and a portrait of John Dalton.] (London : MacmiUan & Co., 

 1920. Price, 305. net.) 



Since the appearance of the fourth edition of Roscoe and Schorlemmer's 

 Treatise, chemistry has suffered a severe loss by the death of Sir Henry 

 Roscoe, and by a sad chance the issue of the present (fifth) edition of vol. i 



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