198 Scientific Intelligence. 



one series and four in the other. The third series calculated by 

 Rossi consists of single lines all of which fall Avithin the ultra- 

 violet region. Finall\7, by using a quartz " end-on " spectrum- 

 tube with neon at a pressure of about 4 mms., five new lines were 

 discovered having respectively the following wave-lengths and 

 intensities : 2352-0 (0), 2396-5 (2), 2464-0 (1), 2639-9 (1), and 

 2660-0 (0). — Phil. Mag., vol. xxvi, Dec, 1913, p. 981. h. s. tj. 



9. The Mass of Rapidly Moving Electrons. — It is a matter of 

 great theoretical importance to obtain experimental data which 

 will enable a final decision to be reached concerning the relative 

 merits of the theories of Abraham and Lorentz-Einstein. As is 

 well-known, the experimental data of Bucherer and Wolz favored 

 the longitudinal contraction of swift electrons as assumed in the 

 theory of Lorentz, but Bestelmeyer has raised objections which 

 cannot be disregarded. One of Bestelmeyer's adverse criticisms of 

 the work of Bucherer and Wolz is that the number of experimen- 

 tal data obtained by these investigators is too small to justify the 

 conclusion that Abraham's theory of a rigid, spherical electron 

 is untenable. This objection has been removed by the recent 

 work of Gunther Neumann which was carried out at Breslau 

 under the direction of Clemens Schaefer. 



The method of crossed fields was employed. The apparatus 

 formerly used by Bucherer was borrowed and partly remodeled. 

 Twenty-six negatives were selected for the final calculations. 

 The speeds of the electrons emitted by the radium salts varied 

 from - 4 to 0-8 of the speed of light. For each speed observed, 



the values of — (for small speeds) were calculated by aid of the 



m 



formulae deduced on the theories of Abraham and Lorentz-Ein- 

 stein. The resulting values of — are plotted as ordinates on a 



diagram having as abscissae the ratio of the corresponding elec- 

 tronic speed to the speed of light. The points derived from the 

 formula of Lorentz fall close to a straight line parallel to the axis 

 of abscissas, whereas the points pertaining to the hypothesis of 

 Abraham show a systematic deviation from a constant value of 



— as the speed increases. Also Bucherer's data give points which 



lie almost exactly on the mean straight line representing Neu- 

 mann's experimental results. Between 0*4 and 0*7 of the speed 

 of light the theory of Lorentz-Einstein is verified to about 1*5 

 parts in a thousand. Because of the ever increasing experimental 

 difficulties as the speed of light is approached, the verification is 

 not quite so good in the interval 0-7 to 0*8. On the other hand, 

 the curve representing the hypothesis of Abraham consistently ap- 

 proaches the axis of abscissas until, at the speed-ratio 0*8, a devi- 



ation of about 8 per cent from the value of — at low speeds is 



r m 



attained. It is therefore clear that the work of Neumann has 



