REVIEWS 545 



follow chapters on all the main problems connected with solids — the velocity of 

 emission of the liberated electrons, the effect of varying the frequency and state 

 of polarisation of the light, the effect in thin films, in non-metals, and in fluorescent 

 and phosphorescent substances. The final chapter deals with the sources of 

 light used, and resumes much information extremely valuable to the practical 

 worker. In the course of the book one meets with interesting points which have 

 escaped the notice of English physicists, such as Pohl and Pringsheim's sugges- 

 tion to account for the increased sensitiveness of the colloidal modification of 

 metals, and the isolated experiments of Dernber on the production of positive rays 

 by light. The style throughout is clear and concise. 



Unfortunately the work of Freydenhagen and Kiistner, which has pointed to 

 a very great reduction of the effect by the special treatment of the metals in high 

 vacua, appeared too late to be mentioned in the book. Whatever may prove to 

 be the correctness of the interpretation placed upon these experiments, there is no 

 doubt that the nature of the phenomena involved in the photo-electric effect is 

 very obscure. Dr. Hughes gives an excellent account of all the work done up to 

 the end of 1913 : extensive and painstaking as it has been, the subject still seems 

 to await decisive experiments which enable us to put a satisfactory interpretation 

 on the facts already known. 



E. N. DA C. A. 



TELEGRAPHY 



Text-book of Wireless Telegraphy. By Rupert Stanley, B.A., M.I.E.E. 

 [Pp. xi + 344, with illustrations.] (London : Longmans, Green & Co., 1914. 

 Price 7s. 6d. net.) 



A BOOK on wireless telegraphy that begins with the sentence, " In its first state 

 the earth was a mass of gaseous matter or nebulas at a very high temperature, 

 revolving round the sun," is a book of a new type. The author recognises that, 

 in its latest development, the study of radio-telegraphy involves a knowledge, 

 not merely of electrotechnics, but of the constitution of the earth's crust and of 

 the atmosphere that surrounds it ; that the study of the problems of wireless 

 telegraphy has for its laboratory the entire globe ; and that wireless signalling 

 is a subject which, while of fascinating interest to the electrical engineer, opens 

 up possibilities of the examination of the nature of the upper atmosphere which, 

 hitherto, have hardly been realised. The early chapters, after the opening one, are 

 such as might be found in any text-book on electricity and magnetism ; unfortunately 

 for the student they are seldom found there. The chief electrical and mag- 

 netic phenomena are dealt with from the standpoint of the electron theory, 

 now accepted as the most likely explanation of all electrical action, and the result 

 is a clear statement which should make them intelligible even to those who 

 may not have had much scientific training. The section dealing with " How 

 ether waves are propagated and received " is an admirable statement of the 

 theories now recognised as the best explanation of the observed effects. In 

 this chapter it is stated that " The whole question of ether wave propagation 

 is one of the outstanding problems of radio-telegraphy," a statement with which 

 every worker in wireless telegraphy will agree. The author is to be congratu- 

 lated on his lucid account of the causes of the phenomena that have been 

 observed, as far as it is possible to treat them at present. The chapters 

 dealing with the coupling of circuits and of the systems of transmission now in 



36 



