The history and scientific results of the Stern-Gerlach-Experiment SGE performed in 1922 in Frankfurt are revisited. This experiment gave first direct evidence for angular momentum quantization in the quantum world and for the existence of "Richtungsquantelung" RQ (directional quantization) of all angular momenta in the process of measurement. Furthermore it measured for the first time a ground state property of an atom and it discovered almost also the electron spin.
Historic facts of the original SGE are described. Einsteins "Paradoxon" and his "Gedanken-experiment" of a three-stage SGE are presented together with the realization of this experiment by Stern, Phipps, Frisch and Segrè. Einsteins proposed experimental set-up can be considered as a pre-Rabi apparatus with time-varying fields. The consequences of a finite and "unlimited sharp" for directional quantization RQ are discussed. In full agreement with the Schrödinger equation RQ appears as a general feature of quantum measurements. Last not least the early history of the "almost" electron spin discovery in the SGE is revisited.
Professor Dr. Horst Schmidt-Böcking received his Ph.D. in 1969. He was then conducting researches on nuclear and atomic physics at Heidelberg University and University of Frankfurt. In August 1982, he became Professor at the University of Frankfurt (heavy ion physics). His honor included: 2008 Davisson-Germer award of the American Physical society, 2009 Order of Merit of the Federal Republic of Germany, 1st Class, and 2010 Stern-Gerlach Medal of the German Physics Society.