done, deducing from it the relation between the velocity and the ratio of the charge to the total apparent mass, a ratio we shall call ε.
One might suppose there are several species of rays, each characterized by a fixed velocity, by a fixed charge and by a fixed mass. But this hypothesis is improbable; why, in fact, would all the corpuscles of the same mass take always the same velocity? It is more natural to suppose that the charge as well as the real mass are the same for all the projectiles, and that these differ only by their velocity. If the ratio ε is a function of the velocity, this is not because the real mass varies with this velocity; but, since the fictitious electromagnetic mass depends upon this velocity, the total apparent mass, alone observable, must depend upon it, though the real mass does not depend upon it and may be constant.
The calculations of Abraham let us know the law according to which the fictitious mass varies as a function of the velocity; Kaufmann's experiment lets us know the law of variation of the total mass.
The comparison of these two laws will enable us therefore to determine the ratio of the real mass to the total mass.
Such is the method Kaufmann used to determine this ratio. The result is highly surprising: the real mass is naught.
This has led to conceptions wholly unexpected. What had only been proved for cathode corpuscles was extended to all bodies. What we call mass would be only semblance; all inertia would be of electromagnetic origin. But then mass would no longer be constant, it would augment with the velocity; sensibly constant for velocities up to 1,000 kilometers a second, it then would increase and would become infinite