Notices respecting New Boohs. 865 



of equilibrium. The treatment throughout is exceedingly simple 

 and yet thorough ; indeed we are not acquainted with any book 

 in which the theoretic side is more lucidly and satisfactorily treated. 

 If we may express any regret, it is that experimental data are not 

 co-mingled with the theoretic. No doubt there are certain ad- 

 vantages in the method adopted. The thread of theory may easily 

 be broken if loaded with too great a weight of fact. Moreover, 

 we have not the slightest doubt that Dr. van der Waals would be 

 the last man in the world to recommend that a student's attention 

 should be confined exclusively to the work before us. Be this as 

 it inay,this treatise (of which the first part only is yet published) pro- 

 mises to be one of the most important elementary accounts of the 

 subject. We may draw attention in particular to the concluding- 

 section on Laplace's Theory of Capillarity and on the capillary 

 layer. 



Magneto- unci Electrooptik. By Dr. Woldemae Voigt. With 

 figures in text. Leipzig : B. G-. Teubner, 1908. Price 14 

 marks. 



Workees in electro-optics and others will welcome this volume, 

 which represents the lectures given by the author for some years 

 past. There is probably no subject which at the present time is more 

 revelatory of the structure of the atom than the one with which 

 it deals, and there is no one more qualified than Dr. Yoigt to deal 

 with it. A general idea of the scope of the book can be conveyed 

 by the titles of the chapters. These are : — 1. The Faraday effect. 

 2. The Zeeman effect. 3. The Theory of magneto-optic effect for 

 normal isotropic bodies. 4. Investigation of the theory of more- 

 complicated types of Zeeman effect. 5. Magneto-optic effect in 

 absorbing crystals. 6. The magneto-optic Kerr effect. 7. The 

 electron theory of the magnetic Kerr effect. 8. Electro-optic action 

 in isotropic and anisotropic bodies. 9. Oscillations of " bound ' 

 electrons uuder the influence of electric fields. 10. The electron 

 theory of electro-optic effects. It is surprising how successful the 

 few assumptions underlying the electron hypothesis are in ac- 

 counting for the complicated phenomeua concerned. It is true 

 that there are at present relations which are inexplicable at present 

 on this hypothesis. Considering, however, that we are obliged to 

 assume a particular character of the electronic system — and the 

 chances against assuming the right one must be amazingly 

 great — it is remarkable that any success at all is achieved. In 

 agreement with this statement is the fact that the phenomena 

 which are most fully explained are those which are independent 

 of the precise structure of the atom. Those who desire the most 

 complete presentation of this subject both from the theoretic and 

 the experimental side will find here what thev wish. 



