REVIEWS 5i7 



PHYSICS 



The Electron. Its Isolation and Measurement and the Determination of some of 

 its Properties. By R. A Millikan, Professor of Physics at the University 

 of Chicago. [Pp. xii + 268, with 33 diagrams and photographs, including 

 5 plates.] (Chicago : University of Chicago Press, 1917. Price $1.50 net.) 



IT is probable that this little book by Prof. Millikan will become a classic on its 

 subject, for, being admirably written in semi-popular style, it must appeal strongly 

 to all those who are in any way interested in the progress of our knowledge of 

 ultimate things. At the same time the very complete experimental details, the 

 discussions based on the latest researches, and the mathematical appendices make 

 it also a book for the specialist. The contents may be divided roughly into three 

 parts. First comes a most lucid account of the history of electrical theories from 

 Franklin to Johnstone Stoney and J. J. Thomson : next a full description of the 

 author's oil-drop method of determining the magnitude of the electron (e) with its 

 corollary, the proof of the atomic nature of electricity: finally a discussion of the 

 probable structure of the material atom and of that outstanding problem of physics 

 the nature of radiant energy. There are, in addition, chapters on the Mechanism 

 of Ionisation (with the final conclusion that in every case one electron and one 

 only is removed from the atom) ; on the Sub-electron, of the existence of which 

 there is at present, in the author's opinion, no evidence ; and on Brownian 

 Movements in Gases. In this last chapter Prof. Millikan is able to quote inde- 

 pendent measurements of Brownian movements lately obtained by Nordlund 

 (1914) and Westgren (191 5), in addition to those obtained by his colleague Dr. 

 Harvey Fletcher, which give a value for Avogadro's number in close agreement 

 with that deduced from his own value of e (namely 6'o6 x io 33 ) and much lower than 

 the value (685 x io 23 ) previously taken by Perrin as most likely to be correct. 

 This agreement is, of course, of fundamental importance as substantiating the 

 accuracy claimed for the oil-drop method. It is remarkable that the latest oil- 

 drop experiments, completed in August 1916 and pushed to the utmost limit of 

 precision, give exactly the same value of e (4774 x icr 10 ) as those previously 

 published in 1913, a new value for the viscosity of air obtained by Dr. Harrington 

 in Prof. Millikan's laboratory exactly compensating for the small difference (0*07 



per cent.) that would otherwise have been obtained ! 



D. O. W. 



Continuity ; or, From Electrons to Infinity. By P. S. G. Dubash, D.Sc, 

 Phil.B., Phy.M., F.S.P., F.B.E.A., F.P.C. [Pp. 60, with 2 diagrams.] 

 (Blackburn: George Toulmin & Sons, 1917. Price is. bd. net.) 

 THIS curious little book has been written with the idea of popularising science 

 among the philosophically minded people of the East, the more especially by way 

 of showing that the doctrine of the re-incarnation of the soul is not forbidden by 

 the tenets of science, but follows almost as a natural sequence from the continuity 

 which the author tries to trace in the evolution of man from the electron ! The 

 larger part of the thesis, which is concerned with the development of human life, 

 contains nothing very novel, it being the author's purpose to show not that the 

 chain of evolution is always unbroken but that the successive stages, as for example 

 from the vegetable to the animal kingdoms, are so intermingled at their borders 

 that no definite line of demarcation can be drawn. Passing beyond this stage into 

 the ultra-physical region, it is suggested that death is simply the passage of "an 

 entity from its three-dimensional shape into the fourth-dimensional form," which 

 requires the "sixth sense" for its realisation. Finally, the author propounds a 



