Max Abraham

“ The negative result of experiments, whose sensitivity is sufficient to discover an influence of second order, provides considerable difficulties for the electron theory. In two papers [4] , Lorentz sought to overcome these difficulties. In the second of the cited papers, he states a system of hypotheses, which are sufficient to give account for all negative experimental results:
H. Due to Earth's motion, the bodies experience a certain contraction parallel to the direction of motion. ”

“ H. A. Lorentz announces it with all restraint; he doesn't go so far as to state it as probable. Indeed, most serious objections can be raised against this hypothesis.
If such an electron is accelerated, its oblateness becomes increased; thus work must be performed against the electric forces. While (for the undeformable electron) the increase of energy is equal to the work performed by the external electric forces, this is not taken place here any more; the energy increase when the velocity increases, is greater as the work of the external forces. ”

“ The necessity to introduce non-electromagnetic forces shows, that the hypothesis of the deformable Heaviside ellipsoid, although it is mathematically simpler in a certain sense, is physically far more complicated though, as the hypothesis of the rigid spherical electron. ”

“ A statement is supplemented to them concerning the force (at a given field) acting upon a volume element filled by electricity:
D. The electromagnetic force is additively composed of forces, acting in the electric field upon resting electrons, and in the magnetic field upon moving electrons. ”