366 SCIENCE PROGRESS 



and a number of fixed mirrors, monochromatic light correspond- 

 ing to the green mercury line was directed, after a series of 

 reflections, on to a Michelson interferometer. The wheel was 

 now rotated about eighty times per second, and according to 

 the second postulate applied to the Doppler effect so produced, 

 there should have been a displacement of about o'y of a fringe 

 for the dimensions of the apparatus used. Majorana asserts 

 that he obtained a displacement between 0"j and o*8 of a fringe, 

 and considers this result to be in direct support of the postulate. 

 He promises further work and results in a later publication. 

 In view of the fact that his experiment is a " positive " test 

 and not " negative " like the now classical researches of 

 Michelson, Morley, Trouton, Noble, etc., his further results 

 and criticisms should engage some attention. 



The London Physical Society has just published a report 

 on The Relativity Theory of Gravitation from the pen of Professor 

 Eddington. In view of the difficulty of obtaining the papers 

 in which, during the years 191 5 and 191 6, Einstein developed 

 his hypothesis to its present form, this volume of ninety pages 

 is extremely welcome to physicists. Its first chapter is devoted 

 to a brief account of the early or restricted principle of rela- 

 tivity. In Chapter II. the relations of Space, Time, and Force 

 are dealt with, and Einstein's new principle of Equivalence 

 explained. Chapter III. gives sufficient of the absolute differ- 

 ential calculus of Ricci and Levi Civita (a comparatively new 

 mathematical weapon admirably adapted for the development 

 of ideas involved in Einstein's work) to enable the reader to 

 follow the analysis. Chapters IV., V., VI., deal with Einstein's 

 law of gravitation, the resulting equations of motion and the 

 crucial phenomena, such as the motion of the perihelion of a 

 planet and the deflection of a ray of light by the gravitational 

 field of a sun or planet. The seventh chapter deals with the 

 reduction of the mathematical equations to the form required 

 by the principle of Least Action, and the eighth and final 

 chapter treats of the possibility of absorbing " absolute rota- 

 tion " within the framework of generalised relativity. 



PHYSICAL CHEMISTRY. By Prof. W. C. McC. Lewis, M.A., D.Sc, 

 University, Liverpool. 



Chemical Reaction and Ionisation. — Since it was first recognised 

 that the electron plays a fundamental part in the structure 



