Chemistry and Physics. 579 



corpuscle as determined experimentally and as deduced from 

 electrical theory. The fourth chapter is concerned with that 

 theory of metallic conduction which is based upon the assumption 

 that the current is carried by free electrons. Although this 

 theory is very successful in explaining most of the facts of metal- 

 lic conduction, there are difficulties in connection with it which 

 have led Professor Thomson to bring forward another theory, 

 not quite so simple and perspicuous as the first, but free from 

 some of its troubles ; this theory is the subject of the fifth 

 chapter. The sixth chapter gives an account of the author's 

 remarkable speculations with regard to the structure of the atom, 

 in which it is shown that a purely electrical model can account 

 for many of the chemical properties of atoms and in particular 

 for the valence relations of the periodic system. The seventh 

 and final chapter deals with the considerations which have 

 recently led the author to reduce his estimate of the number of 

 corpuscles in the atom from many thousands to a number 

 approximately equal to the atomic weight ; and the chapter closes 

 with an ingenious attempt to account for the mass of the atom 

 in terms of the ether, but on quite different lines from the electro- 

 dynamic explanation of the mass of the electron. h. a. b. 



13. Magneto- und Electro- Optik ; von Dr. Waldemae Voigt. 

 Pp. xix + 396. Leipzig, 1908 (B. G. Teubner).— The effects pro- 

 duced by magnetic and electric fields upon the optical properties 

 of bodies have been recognized as of great importance to the 

 theory of the ether, ever since the original discovery of the 

 Faraday Effect. They have, however, proved very difficult to 

 deal with either experimentally or mathematically, and not very 

 much real progress was made until the discovery of the Zeeman 

 Effect in 1896. This led to a great number of very interesting 

 and significant experimental investigations ; and the application 

 of the electrical theory of light to these observations has resulted 

 in a very important body of theoretical knowledge which is 

 not yet as familiarly known by most physicists as it should be. 

 The present book by Professor Voigt, to whom we owe many 

 important contributions to the mathematical side of this subject, 

 will enable us to acquire this knowledge far more easily and 

 satisfactorily than has been possible hitherto. Successive chap- 

 ters deal with the Faraday Effect, the Zeeman Effect, the 

 connection between the two, the effects observed in absorbing 

 crystals by Jean Becquerel, and the two Kerr Effects. Experi- 

 mental methods and results are described and illustrated by 

 excellent reproductions of photographic spectra ; and the theory 

 of these phenomena is developed to a greater extent, probably, 

 than it has reached in the hands of any other writer. Some parts 

 of the book are unquestionably difficult, but the subject of which 

 it treats is not an easy one. h. a. b. 



14. The Evolution of Forces ; by Dr. Gustave Le Box. Pp. 

 xv + 388. New York, i 908 (D. Appleton & Co. The International 

 Scientific Series). — The author of the present work is well known 



