Febkuakt 11, 1910] 



SCIENCE 



221 



without undue regard to " requirements " of 

 any kind. 



All teachers of physics, whether in the sec- 

 ondary school or the college are under great 

 obligations to Mr. Kent for his clear, excellent 

 and simple explanation of this debated subject. 

 Franklin T. Jones 

 University School, 

 Cleveland, Ohio 



note on free public museums 



While reading Mr. Henry L. Ward's very 

 excellent paper on " Modern Exhibitional 

 Tendencies of Museums of Natural History 

 and Ethnology designed for Public Use," re- 

 cently published,' the following interesting 

 statement was noted: 



In fact, to the best of my knowledge, the Public 

 Museum of the City of Milwaukee was the first 

 institution of this nature to throw open its doors 

 for the free admission of the public on every day 

 of the year, a regulation to that eifect having 

 been adopted and put into force in December, 

 1905. 



It is exceedingly gratifying to note that this 

 progressive institution has been among the 

 first to recognize that public museums are for 

 the people and that all should be admitted 

 freely with as little hindrance as possible. In 

 this commendable movement, however, the 

 Chicago Academy of Sciences has about ten 

 years' priority over the Milwaukee Museum, 

 its doors having been continuously open to the 

 public since October 1, 1894. The hours are 

 9 A.M. to 5 P.M. week days and 1 to 5 p.m. 

 Sundays. It is interesting to note that the 

 Willner bequest of $100,000 recently received 

 by the academy was won because the children 

 were allowed free access to the building, espe- 

 cially on Sunday afternoons, and were given 

 more or less attention. Mr. Willner once said 

 to a friend, as he observed the interest of the 

 children in the museum exhibits, " I think 

 this institution is deserving of support." The 

 fact that the academy received one third of his 

 fortune is ample evidence that he believed in 

 the educative value of institutions of this 

 character. 



Frank 0. Baker 



* Trans. Wis. Acad. Sciences, Arts and Letters, 

 XVI., pp. 325-342, 1908. 



SCIENTIFIC BOOKS 

 The Theory of Electrons and Its Applications- 



to the Phenomena of Light and Radiant 



Heat. By H. A. Lorentz. 



This book is based upon the course of lec- 

 tures delivered by Professor Lorentz at Co- 

 lumbia University in March and April, 1906. 

 But the author has introduced into the book 

 considerable material not given in the lectures 

 and has also given in the form of notes many- 

 mathematical proofs which were omitted in 

 the lectures. 



It was naturally expected that this book by 

 an author, who is himself responsible for a 

 large part in the remarkable development of 

 the modern theory of electrons, would prove- 

 of absorbing interest to physicists and to 

 those in general who have any knowledge of 

 the importance and fascination of the sub- 

 ject. As was expected, this is the case. 



The author states in his preface that he is 

 perforce obliged to restrict himseK greatly in 

 discussing the applications of the theory as 

 to the number of topics considered, and re- 

 marks that the work of Voigt on magneto- 

 optical phenomena, of Planck on radiation, 

 and of Einstein on the principle of relativity, 

 has not received the attention which its impor- 

 tance would justify. The scope of the book 

 will to some extent be revealed in the present 

 brief review. 



In the first chapter the fundamental 

 formulse of the electron theory are derived 

 from Maxwell's well-known theory, with the 

 aid of auxiliary hypotheses which the nature 

 of the subject demands. Referring to Max- 

 well's equations, the author calls attention to- 

 the fact that, while they are useful and ade- 

 quate in the treatment of many problems,, 

 there are yet many problems for which they- 

 are not. He goes on to say: 



Moreover, even if they were so, this general 

 theory, in which we express the peculiar proper- 

 ties of different ponderable bodies by simply as- 

 cribing to each of them particular values of the 

 dielectric constant, the conductivity and the mag- 

 netic permeability, can no longer be considered 

 satisfactory when we wish to obtain a deeper- 

 insight into the nature of the phenomena. If we- 

 wish to understand the way in which electric and 

 magnetic properties depend on the temperature,. 



