Paul Ehrenfest

“ Yet it is only necessary to sacrifice the latter theorem too, as we already sacrificed the energy theorem – then we are able to define any desired apparent mass of the Lorentz electron, thus one can bring any measuring result in agreement with the relativity principle. (However, the value of zero for the apparent mass offers itself as the most simple one; like a macroscopic condenser shall obtain no increase of mass by a charge according to relativity theory.) ”

“ When one calculates the longitudinal mass of the deformable electron in the usual manner, then one has to ascribe to the electron a non-electromagnetic energy of interior deformation forces, to maintain the energy theorem. ”

“ In the case of motion, the forces exerted upon each other by the volume elements of the electron, are not directed any more in the direction of the connecting line. Thus every element-couple provides a torque. ”