The Theory of Relativity is initially quite controversial. In 1906, Walter Kaufmann conducts an experiment, which he claims provides evidence disproving Einstein’s prediction on how the mass of electrons is dependent on their speed. The prediction is not confirmed until two years later, by the work of Alfred Bucherer.

Einstein has more luck with his theory on the Brownian Motion of microscopic particles: its quantitative confirmation is supplied by Jean Perrin since 1908, resulting in the general acceptance of the atomic structure of matter.

Only for Einstein’s light quantum hypothesis does decisive experimental evidence remain elusive for several years.