Chemistry and Physics. 283 



the Faraday and the Oersted effects. This method seems to have 

 the purpose not of making the fundamental principles clear so 

 much as to lead by the shortest step from experimental facts to 

 the mathematical statement of relations between certain quanti- 

 ties as measured in the electromagnetic system of units. Thus 

 for example, assuming Joule's law, namely that the rate of gen- 

 eration of heat in a wire is proportional to the square of the 

 current, the resistance R is introduced as a constant of propor- 

 tionality. As a sequence electromotive force is defined as the 

 rate at which a generator does work per ampere of current. Such 

 a statement reminds one of the definition of force as the space 

 rate of variation of the energy in a field, and though all of these 

 definitions are mathematically correct, few physics teachers 

 would regard them as very helpful to a beginner. 



After the first four chapters which treat of electric currents, 

 two are devoted to electrostatics and one to electron theory. Four 

 appendices discuss the Magnetism of Iron, Alternating Currents, 

 Electrical Measurements, and Corresponding Equations. 



p. E. B. 



11. Die Stellung der Belativitdtstheorie in der geistigen 

 Entwicklung der Menschheit ; by Joseph Petzoldt. Dresden, 

 Sibyllen-Verlag, 1921, 125 pp. — This account of the relativity 

 principle is written in popular form and without the use of 

 mathematical symbols. The author is particularly interested in 

 the philosophic aspects of the theory, and devotes half the book to 

 the historical development of the ideas underlying Einstein's 

 theories. The account of the Michelson-Morley experiment is 

 followed by a discussion of the special theory of relativity. The 

 treatment of Einstein 's theory of gravitation, however, seems too 

 brief to give the reader an adequate idea of the significance of 

 this important advance in mathematical physics. l. p. 



II. Geology. 



1. The Earth's Axes and Triangulation; by J. de Graaff 

 Hunter. Professional Paper No. 16, Survey of India. Pp. 217 ; 

 and with six charts and appendix. Dehra Dun, 1918. — This 

 book contains results of a research by J. de Graaff Hunter, 

 Mathematical Adviser to the Survey of India, which he conducted 

 with a view to developing methods by which the triangulation of 

 India, which was originally computed on the obsolete Everest 

 spheroid, might be referred to what Hunter calls the Helmert 

 spheroid. 



The Everest spheroid was adopted for the triangulation of 

 India many years ago and, as in nearly all countries, the officials 

 responsible for the triangulation have hesitated to make a change 

 to a spheroid that is much nearer the truth, but in most cases 

 such a change has been made. In the United States, Bessel's 



