Page:Über die Konstitution des Elektrons (1906).djvu/2

total inertial mass of a moving charge, had consequently to be a function of its velocity.

The observations at cathode ray gave at the beginning no such variability of inertial mass, which of course wasn't easily observable, since the easily attainable velocities were still too small to cause a noticeable mass-increase. The experimental verification of mass-variability with respect to these rays, was first achieved by H. Starke^[1] some time after the author^[2] has verified the actual mass-variability by observation of $\beta$-rays or radium.

The $\beta$-rays or radium show, as it is known, qualitatively the same properties as cathode rays; they are magnetically^[3] and electrically^[4] deflectable, and they carry an electric charge with them.

In quantitative respects, they are different from the cathode rays even under crude observation, in so far as they have a much higher penetration capability as the other ones. Now, since it is known that the penetrating power increases with velocity, the assumption was near at hand, that $\beta$-rays would have a considerable higher velocity than cathode rays. However, consequently it was also to be hoped, that the dependence of mass from velocity for $\beta$-rays can clearly be shown. This assumption was confirmed by my (still quite crude) measurements in the year 1900^[5]. The quite large mass-variability also demonstrated, that the portion of pure electromagnetic mass is very great if not overwhelming in comparison to a possible mechanic or material mass. The attempt to calculate both

1. H. Starke, Verh. d. D. Physik. Ges. 5. p. 241. 1903.
2. W. Kaufmann, Gött. Nachr. 1901. Heft 1; 1902. Heft 5; 1903. Heft 3. Phys. Zeitschr. 4. p. 55. 1902
3. F. Giesel, Wied. Ann. 69. p. 834. 1899; St. Meyer u. E. v. Schweidler, Phys. Zeitschr. 1. p. 90. 1899; H. Becquerel, Compt. rend. 129. p. 996. 1899.
4. H. Becquerel, Compt. rend. 130. p. 819. 1900; E. Dorn, Abh. Nat. Ges. Halle 22. p. 44. 1900.
5. W. Kaufmann, l. c.