SCIENCE 



29 



In carrying out his purposes, the author 

 has very properly included a brief treatment 

 of exact and inexact differentials, Fourier's 

 series, and the application of imaginary num- 

 bers to the solution of some differential equa- 

 tions that are important in mathematical 

 physics. 



The final chapter of the book is devoted to 

 directions for the representation of experi- 

 mental data by mathematical functions, but 

 the presentation is so brief that it is doubtful 

 if the biologist or chemist could carry the 

 directions into numerical effect without more 

 mathematics than is given in this book. 



On the whole, the author has shown good 

 judgment in the selection of material for his 

 purposes, and the biologist and chemist not 

 familiar with the calculus will find the book 

 of value. 



H. L. RiETZ 



Radioactive Substances and Their Radiations. 



By E. Rutherford. Cambridge, University 



Press. 1913. Pp. vii + YOO. Price, $4.50. 



The subject of radioactivity is now just six- 

 teen years old, yet the volume of its literature 

 already compares favorably with that of any 

 of the other grand divisions of physics and two 

 compendious text-books, Rutherford's and 

 Madame Curie's — not to mention a host of less 

 pretentious treatments — are available to initi- 

 ate the student into its mysteries. 



It is now eight years since the second edition 

 of Rutherford's " Radioactivity " appeared, and 

 in view of the fact that this period covers one 

 half of the life of the science, it is scarcely to 

 be expected that its present status could be 

 adequately presented by a mere revision of 

 that book. And it is to the author's credit that 

 he has not attempted to patch the new mate- 

 rial into the old frame, but has instead built 

 an entirely new framework and merely utilized 

 the old lumber wherever it still proved service- 

 able. 



Out of a total of 700 pages, only about 150 

 are taken from the former work. Despite this 

 fact, the present book makes very much the 

 same impression as did its predecessor, whether 

 it is given merely a cursory glance or whether 

 it is made the subject of careful study. This 

 is because the big problems of radioactivity 

 were correctly solved at the start, and that 

 largely by Rutherford himseK. It is one of 

 the most notable facts connected with this 

 notable subject that within eight years of the 

 discovery of the first radioactive rays, the phe- 

 nomena of radioactivity should have been so 

 thoroughly worked out and so unerringly in- 

 terpreted that scarcely a viewpoint then taken 

 in a book of 560 pages needs, after eight more 

 years of exceedingly active experimenting, to 

 be discarded. 



The differences between the old book and the 

 new are to be found not so much in method of 

 treatment or in order of presentation, as in 

 the incorporation of the new material which 

 has accumulated within the past eight years. 

 Much of this material has grown out of re- 

 searches conducted in Rutherford's own lab- 

 oratory. The additions have come chiefly 

 from the careful study of the following sub- 

 jects, none of which are found in the old text. 



1. The range of the alpha particle, the law 

 of its scattering in passing through matter, 

 and the stopping power of substances for it. 

 Through studies in these fields has come a 

 great addition to our knowledge of the nature 

 of the atom and the character of radioactive 

 changes. 



2. The phenomena of recoil, undiscovered 

 when the old book was written, but recently 

 diligently studied and shown to be invaluable 

 as a means of separating radioactive products. 



3. The methods of directly counting the 

 alpha particles, one of which, namely, the scin- 

 tillation method, has recently been of great 

 help in the study of the short-lived products. 



4. The scattering and change in velocity of 

 the Beta rays in passing through matter and 

 the remarkable resolution into a large number 

 of homogeneous components of the Beta rays 

 emitted by Radium C — studies which have 

 thrown new light on the nature of the atom. 



