The spin of the photon was the object of lively debate. The question was whether the phenomenon of polarisation of light could be explained by the assumption of a spin of the photon. Otto Robert Frisch [1] (1904–1979, Fig. 5.1), the Austrian physicist who, with his aunt Lise Meitner (1878–1968), gave the first theoretical explanation of nuclear fission—coining the term—and detected experimentally the fission fragments, and the Nobel (1966) laureate Alfred Kastler [2] (1902–1984, see Fig. 5.1), who discovered and developed optical methods for studying Hertzian resonances in atoms, surmised there is none.