"The modern theory of electrical and allied optical phenomena... [i.e.,] the "electron theory," means practically a return to views as laid down in the sixties and seventies by Wilhelm Weber and Zöllner, but modified by the results of Maxwell's and Hertz's researches. W. Weber imagined electric phenomena as the actions of elementary electrical particles—so called "electric atoms"—whose mutual influence depended not only upon their positions but also upon their relative velocities and accelerations. Although Weber succeeded by means of his hypothesis in completely describing the electrodynamical phenomena known at his time, and even in giving a quantitatively useful explanation of the correspondence between electric and thermal conduction in metals, as well as Ampère's molecular currents in magnets, still his theory was far from becoming the common property of physicists of his day. The reason for this negative success may be sought for in the fact that most of the laws of electrodynamics when expressed from the standpoint of pure phenomenology in the shape of differential equations, are much more simple and convenient than Weber's formulæ. In addition, Weber makes no attempt to calculate the size of his electrical atoms and to test the result... And, finally, the work of Faraday and Maxwell brought about a general feeling that in electric and magnetic phenomena a finite rate of propagation would have to take the place of action at a distance. This demand was already put forward by Gauss in letter to Weber in 1845..."