On Relativity and Electrodynamics. 205 



inclination of the equator to the ecliptic and in the planetary 

 precession, but these would be within the probable errors. 



We can conclude therefore that Dr. Silberstein's theory, 

 combined with gravitating matter near the sun, can give 

 an excellent representation of the secular inequalities of 

 the inner planets. 



June 22, 1918. 



X VII. On Relativity and Electrodynamics. 

 To the Editors of the Philosophical Magazine. 

 Gentlemen, — 



IN your number for April 1918 Mr. G. W. Walker discusses 

 the transverse inertia of an electron. After quoting 

 " experiments by Kaufmann, Bestelmeyer, and others" which 

 " have been offered as experimental proof that the formula, 

 for transverse inertia of a contracted electron on relativity 

 doctrine is correct,''' he expresses himself as follows : — 



" I doubt if many people in this country realize the very 

 meagre character of the experimental results, and I therefore 

 give a full-sized reproduction of the photographic plate from 

 which Kaufmann made his measurements. " 



One is led to suppose that some important researches,, 

 achieved since the time Mr. Walker was working side by 

 side with Mr. Kaufmann in the laboratory in Gottingen, 

 must have escaped his notice. Moreover, the statements 

 quoted above tend to raise a feeling of surprise, if one 

 remembers that Bestelmeyer's experiments failed to decide 

 either against or in favour of the Lorentz-Einstein formula, 

 and that Kaufmann finally considered his (" meagre ") results 

 to plead against this formula. 



It seems therefore to be worth while to draw attention to 

 the experiments of G. Neumann*, who improved a method 

 devised by Bucherer in order to meet the criticisms raised 

 by Bestelmeyer against Bucherer. He obtained results 

 which fully confirmed Bucherer's view and which appear to 

 establish beyond doubt the correctness of the Lorentz-Einstein 

 formula for electrons moving with speeds from U - 4 up to 0*7 

 of the velocity of light. 



More recently Prof. Ch. E. Guye and Mr. Oh. Lavanchy jy 



* G. Neumann, "Die trage Masse schnell bewegter Elektronen," Ann. 

 d. Phys. xlv. p. 529 (1914). See also CI. Schaefor, Verh. d. D. Phys. 

 Ges. xv. p. 935 (1915) and Phys. Zschr. xiv. p. 1117 (1913). 



t Ch. E. Guye et Ch. Lavanchy, " Verification experinientale de la 

 formule de Lorentz-Einstein par les rayons cathodiques de grande vitesse,"' 

 Arch. d. Sc. phys. et nat. xlii. (1916). 



