302 Scientific Intelligence, 



which by chemical methods shows an atomic weight of 20.200 

 has been proved to contain two isotopes having respectively 

 atomic weights of 20.00 and 22.00 in proportion of 90 per cent 

 and 10 per cent with a faint possibility of a third of mass 21. 

 Likewise chlorine which by the method of combining volumes 

 is found to have an atomic weight of 35.46 shows no indication 

 of a line corresponding to this mass but does give definite lines 

 indicating masses 35 and 37. The unquestionable accuracy of 

 its combining weight and the striking whole number masses given 

 on its mass spectrum by its individual particles leaves little 

 doubt that its chemical atomic weight is a statistical average. 

 The investigation which has been extended to more than fifty 

 atomic and molecular weights indicates the very interesting and 

 important result that all these masses as determined by Mr. 

 Aston are integers except in the case of hydrogen. 



Isotopes have been of use to chemists in various ways as, e. g., 

 the determination of sparingly soluble lead salts has been made 

 with ease. Their use has a:^orded a test of the Nernst theory of 

 E.M.F. at concentrations completely beyond the range of ordinary 

 methods and has recently given a direct demonstration of the 

 separated existence of ions in an electrolyte. — Froc. Boy. Soc.^ 

 99, 87, 1921. F. E. B. 



6. Wireless Telegraphy and Telephony ; by L. B. Turner, 

 pp. xii, 195. Cambridge, 1921 (Cambridge University Press). — 

 The author is a fellow of King's College and has been connected 

 with the Signals Experimental Establishment of the Royal Engi- 

 neers at Woolwich. This book occupies a position intermediate 

 between the requirement of the student for a treatise on radio- 

 engineering and that of the wireless operator. The need for 

 instance of the electrical engineer who had never studied this 

 particular branch of the subject was in mind in the preparation 

 of what is described as an outline of the frame work of a great 

 and growing subject. It will be understood consequently that 

 the treatment is distinctly topical, rather than compendious, with 

 the discussion full in some cases and scant in others. 



After a brief introductory chapter, electromagnetic radiation 

 is taken up but not very satisfactorily presented. The mathe- 

 matics of this and the following chapter is hardly more than the 

 formulation of the physical conditions and a quotation of the 

 results of their mathematical analysis. The reader is either pre- 

 sumed to be familiar with alternating current theory or must 

 consult a treatise on the subject. 



Chapter IV gives an interesting account of the production of 

 high frequency currents by spark, alternator, arc, and vacuum 

 tube methods and is followed by a chapter on the detection of 

 these currents. The remainder of the book is occupied with the 

 theory and applications of the thermionic vacuum tube, the new 



