i62 SCIENCE PROGRESS 



The book should be read by all those who desire to become acquainted not 

 only with the fundamental changes which the Relativity Principle introduces into 

 our conceptions, but also with the problems which still await solution and the 

 attempts which have been made in that direction. 



J. R. 



Molecular Physics. By James Arnold Crowther, M.A. Reprinted from the 

 Chemical World. [Pp. viii+167, with diagrams and illustrations.] (Lon- 

 don : J. & A. Churchill, 1914. Price $s. 6d. net.) 



This little volume is reprinted from a series of articles which appeared in the 

 Chemical World, and forms one of the publishers' Text-books of Chemical 

 Research and Engineering. Although named molecular physics it of necessity 

 deals extensively with what we may call atomic physics. The book serves quite 

 a useful purpose, more especially for chemical investigators and engineers, in that 

 it gives a very succinct account of the latest work and conceptions regarding the 

 structure of atoms and molecules, without venturing too deeply into a mass of 

 mathematical detail. Chap. I. is historical and introductory and leads up to 

 Chap. II., where the physics of the electron are treated. The cathode rays are 

 described and the various methods of evaluating the ratio m\e. Then follows a 

 description of Wilson's expansion experiments, and the measurement of e and 

 finally of m. Two very fine photographs due to Wilson are included in the 

 chapter showing the tracts of a particles and of the ions produced by the passage 

 of Rontgen rays through the expansion chamber. 



In Chap. III. the positive particle is introduced, and in Chap. IV. a very 

 concise account is given of Thomson's new method of chemical analysis by the 

 photography of these rays from different substances. The apparatus used is 

 clearly described, and by the courtesy of Prof. Sir J. J. Thomson the author has 

 been able to illustrate the text with photographs made from some of the original 

 experimental negatives. Apart from Prof. Thomson's own book on the subject, 

 this is the best presentation of this new and extremely fine method of analysis 

 which we have seen. One interesting feature found here, as indeed throughout 

 the whole book, is the way in which the author looks ahead and delights the 

 imagination with a peep into the region of future investigation and possibilities. 

 The next chapter deals more fully with the electron — the tubes of force surround- 

 ing it at rest and in motion— the variability of its mass at high speeds, and the 

 purely " electrical " conception of mass. 



The Chemistry of the Model Atom (Chap. VI.) is based on the original Thomson 

 idea of concentric spheres of increasing numbers of electrons. 



A description of these views is interesting in itself, but it must be remembered 

 that here the author departs from the solid ground of experimental fact into the 

 domain of speculative although somewhat plausible theory. 



Under the Vibration of the Atom (Chap. VII.), the probable electro-magnetic 

 nature of light, the Zeeman effect and line spectra are shortly reviewed. 



Chap. VIII. considers various phenomena of matter such as viscosity, vapori- 

 sation, conduction of heat and electricity in the light of what has been previously 

 learnt regarding electrons, atoms, and molecules, while the final chapter is taken 

 up with a brief account of radioactivity. 



For the benefit of those readers who wish to revise the derivation of some of 

 the more important formula?, there are short appendices on electrostatic and 

 magnetic deflection, the electro-magnetic mass of an electron and the Zeeman 



