348 Scientific Intelligence. 



trostatic Deflection of the Particle. Effect at Very Low Pres- 

 sures. Discussion of the Photographs. Negatively Charged 

 Particles. Atoms Carrying Two or More Positive Charges. 

 Methods for Measuring the Number of the Positively Electrified 

 Particles. Retrograde and Anode Rays. Anode Rays. Dop- 

 pler Effect Shown by the Positive Rays. Spectra Produced by 

 Bombardment with Positive Rays. Disintegration of Metals 

 under the Action of Positive Rays. On the Ilse of the Positive 

 Rays for Chemical Anatysis. On the Nature of X 3 the Substance 

 giving the '3' Line. Evolution of Helium and Neon." In his 

 preface the author says; — "I have described at some length the 

 application of Positive Rays to chemical analysis; one of the main 

 reasons for writing this book was the hope that it might induce 

 others, and especially chemists, to try this method of analysis." 

 It will be very surprising if this hope is not vain, at least in so far 

 as it relates to chemists, because practically no data are recorded 

 which would enable a beginner in the subject either to order the 

 necessary apparatus or to apply the general principles laid down, 

 without spending a very large amount of time in letter writing 

 or in performing preliminary experiments. The proof seems to 

 have been read hurriedly since a number of typographical errors 

 have been overlooked and since several of the figures lack the 

 reference letters used in the text. The book will be chiefly use- 

 ful to those who are already familiar with the original articles 

 published in the Philosophical Magazine and elsewhere, and 

 who desire to review the whole subject without undue labor. 



h. s. u. 

 7. Photo- Electricity ; by H. Stanley Allen - . Pp. x, 221; 35 

 figures. London, 1913 (Longmans, Green and Co.). — "The present 

 book is based on a course of advanced lectures delivered by the 

 author at King's College, London, during the Lent Term of 1910; 

 but the greater part has been entirely rewritten so as to incorpo- 

 rate the results of the large amount of research carried out in the 

 three years since these lectures were given." The introductory 

 chapter, which gives an outline of the whole field, is followed by 

 chapters on the emission of electrons in a vacuum, on the veloc- 

 ity of the electrons, and on the photo-electric current in gases at 

 various pressures respectively. After discussing photo-electric 

 substances in the various physical states the author turns his atten- 

 tion to the influence on the photo-electric discharge produced by 

 temperature, and by the character, intensity and plane of polariza- 

 tion of the exciting light. The remaining chapters deal with the 

 theories of photo-electric action, photo-electric fatigue, fluores- 

 cence and phosphorescence, and photo-chemical actions and pho- 

 tography. The volume ends with both author and subject indices. 

 The text is a valuable contribution to this branch of physics 

 because in it are brought together, in English, for the first time, 

 the experimental results and hypotheses which are widely scat- 

 tered in the various scientific journals. Furthermore, the appear- 

 ance of this book is especially timely since the most recent work 



