156 SCIENCE PROGRESS 



Essai philosophique sur les ProbabUit6s. Par Pierre-Simon Laplace. 

 Les maitres de la pensee scientifique. Collection de m6moires et 

 ouvrages. Publiee par les soins de Maurice Solovine. [Two volumes. 

 Pp. xi + loi, io8.] (Paris : Gauthier-Villars&Cie.igai. Price 7 fr.) 



The excellent series of texts of the classics of science, of which these two 

 volumes form part, has already been welcomed in Science Progress (January 

 1922, p. 474). The editorial apparatus consists solely in a brief but useful 

 biographical sketch. 



Laplace's Essai, which was published separately in 1814, but which is also 

 to be found as the Introduction to his Theorie analytique des probahiliUs, is 

 too well known, at least by repute, to require much comment. Laplace has 

 been blamed for his too sparing use of symbols in this work ; it is probably 

 true that his section on the generating function " would not be intelligible 

 to a reader unless he were able to master the mathematical theory delivered 

 in its appropriate symbolic language," and it is perhaps a little difficult to 

 recognise in " une expression tres simple, que Ton obtient en integrant le 

 produit de la differentiale de la quantite dont le r^sultat deduit d'un grand 

 nombre d 'observations s'ecarte de la verite, par une constante moindre que 

 runit6, dependante de la nature du probleme, et elevee &. une puissance dont 

 I'exposant est le rapport du carre de cet ecart au nombre des observations " 

 the ordinary error-function. But the Essai is very well worth reading, and 

 it is to be hoped that the appearance of this convenient edition will make it 

 more widely read. 



F. P. W. 

 PHYSICS 



Moderne Magnetik. Von Felix Auerbach. [Pp. viii + 304, with 167 text 

 figures.] (Leipzig: Johann Ambrosius Earth, 1921. Price 48 

 marks.) 



This book contains a good account of the experimental facts of magnetism, 

 and a fairly adequate account of the theories, as far as that can be done with 

 a minimum of mathematics. A similar book in EngUsh would indeed be wel- 

 come. Facts and theories are brought home by means of excellent figures 

 and appropriate tables. There is a good account of Magneto-Optics, a subject 

 usually treated from the standpoint of Physical Optics, and a good summary 

 of the main results concerning the Zeeman effect. 



Of the omissions which occur to the writer, the two most important are 

 the absence of any reference to Oxley's work on change of magnetic properties 

 with change of state and, in the chapter on Magnetic Measurements, absence 

 of a description of the Grassot fiuxmeter. 



The usefulness of the book would be increased by suitable references to 

 the literature of the subject. 



J. R. 



Modern Electrical Theory. Supplementary Chapters. Chapter XV, Series 

 Spectra. By N. R. Campbell, Sc.D. [Pp. vii 4- 109.] (Cambridge : 

 at the University Press, 192 1. Price 105. 6d. net.) 



This is really a monograph on optical and X-ray series spectra. As stated 

 in the preface, the author proposes to supplement and ultimately to replace 

 his well-known book of this title, by issuing from time to time similar mono- 

 graphs dealing with new developments and bringing his original work up to 

 date. 



This chapter is marked by the lucidity and thoroughness of the former 

 work. It is not intended for the expert, but for students who, fresh from 

 graduation, wish to get quickly into touch with research. It is explanatory 

 of the main facts of series spectra, and in theory is based on Bohr's conception 



