146 Scientific Intelligence. 



and Hahn she showed by the magnetic spectrum method, in the 

 year 191 1, that the velocities of these rays vary from - 33 to 0-39 

 of the velocity of light. Thus it appears that these are the 

 slowest /3-rays that have as yet been successfully studied electro- 

 scopically. The absorption coefficients in aluminium were found 

 to be about 5500 cm -1 . Therefore the value 130 cm -1 given by 

 Kovarik and generally incorporated in the recent literature of the 

 subject is now to be considered incorrect. 



The author adduces evidence to show that the absorption 

 (Steckenbleiben) of /3-rays by matter cannot consist in the gradual 

 nullification of the speed by numerous successive collisions with 

 the molecules. The /3-particles presumably penetrate into the 

 interior of the absorbing atoms and are held fast there under cer- 

 tain conditions, that is, they lose their energy in one single colli- 

 sion. — Phys. Zeitschr., August 1, 1915, p. 272. h. s. u. 



8. Introduction to Magnetism and Electricity ; by E. W. E. 

 Kempson. Pp. viii, 240, with 158 figures. New York, 1915 

 (Longmans, Green and Co.). — The following sentences quoted 

 Irom the author's preface give a concise idea of the origin and 

 object of the text. " This book is made up from lecture notes 

 for a year's course of Electricity and Magnetism as given to Sci- 

 ence Forms in the Upper School at Rugby." " It should be 

 understood that students using this book are expected to have at 

 least one period of say one and a half or two hours per week of 

 practical work in the laboratory, as well as a course of lectures 

 and discussions on the subject." 



In arranging and presenting the material a special effort has 

 been made to emphasize the identity of electricity generated in 

 different ways and, in particular, to use the study of static phe- 

 nomena as a real help to the correct understanding of electricity 

 in motion. The first three chapters (46 pages) are devoted to 

 magnetism and the remaining sixteen to electricity. A proper 

 appreciation of the experiments suggested is facilitated by clear 

 diagrams of the apparatus to be employed and by graphical and 

 numerical illustrations of the results obtained in practice. A 

 summary of the most important facts presented is given at the 

 end of each chapter. Also, with the exception of Chapters I and 

 XV, a set of problems (147 in all) for solution by the student 

 follows each summary. Numerical answers are given immediately 

 before the index. So far as we can judge, without testing the 

 text with classes of beginners, the book seems to be admirably 

 designed to meet the requirements of its readers. h. s. u. 



9. An Introduction to the Mechanics of Fluids,' by Edwin 

 H. Barton. Pp. xiv, 249, with 130 figures. London, 1915 (Long- 

 mans, Green and Co.). — In writing this book the author has 

 endeavored to make it suitable for candidates for entrance scholar- 

 ship and other university examinations, for naval and military 

 preparation, and for those technical students taking the Board of 

 Education's lower examination in Theoretical Mechanics (Fluids), 

 or any of a similar character held by the various provincial edu- 



