152 SCIENCE PROGRESS 



lines, but it is characterised by great care in the development of the ideas, as, for 

 instance, in the passage from point charge to continuous distribution, and thence 

 to surface distribution and double sheets. All the well-known geometrical dis- 

 tributions of charge and their fields are treated with a free use of the Legendre 

 and Bessel functions, without overburdening the pages with purely analytical 

 mathematics, and there is a very good account of the application of conformal 

 representation and inversion to electrostatic problems. After developing the 

 Faraday-Maxwell theory of electrostatic action the author gives a very full chapter 

 on the theory of polarised media, using Larmor's mode of presentation, with a 

 section on Lorentz's theory as to the mechanism of dielectric polarisation. A 

 chapter on Magneto-statics includes not only much classical material, but intro- 

 duces sections dealing with Langevin's and Weiss's treatment of paramagnetism 

 and ferromagnetism. Under "Kinetics" the author treats the phenomena of 

 metallic conduction and electrolysis, gives Lorentz's electron theory of the 

 mechanism of metallic conduction and some account of electric currents in gases, 

 with the methods of determining the charge and mass of an electron. 



The second part, dealing with " Dynamics," begins with a general account of 

 the equations of the electromagnetic field, introduces the " retarded " potentials, 

 and discusses very thoroughly the complete constituents of an electric current in the 

 most general sense. Two chapters treat some special electromagnetic fields and 

 the electrodynamics of linear currents ; and two more deal with electromagnetic 

 oscillations and waves. In these, in addition to the usual theory of the Hertzian 

 oscillator, an account is given of Love's extension to the more practical case 

 when damping is taking into account. These matters naturally lead to some 

 discussion of radiation in general. Two concluding chapters deal with general 

 electrodynamic theory both for stationary and moving media on the basis of the 

 principle of least action, and constitute, in the writer's view, the most valuable part of 

 the book, inasmuch as they present in a compact form material hitherto scattered 

 over many books and papers. The book as a whole is a very valuable addition 

 to the literature of the subject, not only on account of the wide field covered, 

 but also because of the care exhibited in the selection and treatment of the 

 material. The form of the theory adopted is so general that it can include 

 the most recent speculations on such matters as the nature of radiation and the 

 relativity view of time and space without being dependent for consistency on 

 the truth of such views. In its 700 pages is summarised a body of knowledge 

 which will put the reader, as it were, right on the threshold of present-day 

 research in theoretical electricity and magnetism. There is a collection of over 

 three hundred examples on which the mathematically-minded student can try 

 his prowess. 



J. R. 



Lecture Notes on Light. By J. R. Eccles, M.A., Assistant Master at Gresham's 

 School, Holt. [Pp. viii + 217.] (Cambridge: University Press, 1917. 

 Price 12s. bd. net, with Diagrams ; ^s. net, without.) 



THERE is still a difference of opinion as to the manner in which students should 

 record the information given to them in their lectures. A few teachers prefer the 

 class to give them an undivided attention during the lecture and to rely on the 

 text-book for a permanent reference. In the vast majority of cases notes are 

 taken, and the rate at which the ground is covered must be regulated to enable 

 this to be done. Even then the weaker brethren produce but a sorry record, and 



