Classical physicists held to the view that optical and electromagnetic experiments would surely reveal absolute Galilean motion, and they were not perturbed by the fact that as a result Newtonian mechanics might have to be abandoned. Indeed, doubts as to the validity of Newtonian mechanics already presented themselves when Kaufmann and Bucherer showed that electrons in very rapid motion appeared to increase in mass—a phenomenon which was of course incompatible with the Newtonian belief in the invariance of mass, unless some hypothesis ad hoc was to be invoked. It is true that Michelson’s very refined test attempted in 1887 failed to detect any influence of absolute Galilean motion in a certain optical experiment; but it was always assumed that an explanation for this failure would be forthcoming sooner or later, and that other experiments would be successful where Michelson’s had failed. When, therefore, Einstein suggested as a principle of nature that, regardless of whether or not the ether was a necessary hypothesis, Galilean motion through the ether or through space would [Pg 118] never be detected by any type of experiment, whether optical or electromagnetic or mechanical, the majority of physicists paid little heed to the new doctrine. It must not be thought that this hostility of classical physicists to the Einstein theory in its initial stages was due solely to their belief in the absolute and objective nature which it appeared inevitable to credit to the ether. It was due also to other reasons which we shall now proceed to investigate.