The Viennese scientist Erwin Schrödinger became world famous at a relatively late age, that is, for a theoretical physicist active during the 1920's. In 1926, when he was already a doddering thrty-eight, he was still capable of developing a new quantum theory of atomic structure. His new theory was presented as an alternative to the theory of matrix mechanics, which had been formulated by Werner Heisenberg along with Max Born and Pascual Jordan some months previously. Matrix mechanics was a rather abstract and predominantly mathematical theory, which had deliberately refrained from putting forward claims about the unobservable world of atoms. The great advantage of wave mechanics, Erwin Schrödinger repeatedly emphasized, was that it appeared to promise a visualizable, realistically interpretable description of atomic structure. Thus, in his first paper on wave mechanics, Schrödinger spoke of his theory as representing: "some vibrational process in the atom, which would more nearly approach reality than the electronic orbits, the real existence of which is very much questioned today".¹