Braunschweig: Vieweg & Berlin, 1922.
First edition, the very rare offprints, of the famous Stern-Gerlach experiment, which demonstrated the spatial quantization predicted by the Bohr-Sommerfeld quantum theory of the atom and (although this was not realised until later) the existence of electron spin. “This direct demonstration of spatial quantization was immediately accepted as among the most compelling evidence for quantum theory” (Friedrich & Herschbach, p. 57). “The Stern-Gerlach experiment is undoubtedly one of the great achievements of experimental physics” (Longair, p. 154). In a letter of March 1922 to Max Born, Einstein wrote: “The most interesting achievement at this point is the experiment of Stern and Gerlach.” “Perhaps no other experiment is so often cited for elegant conceptual simplicity. From it emerged both new intellectual vistas and a host of useful applications of quantum science” (Friedrich & Herschbach, p. 53). Stern continued his work on atomic and molecular beams, and was awarded the Nobel Prize in Physics 1943 “for his contribution to the development of the molecular ray method and his discovery of the magnetic moment of the proton.” No copies of these offprints located on OCLC, and no copies in auction records.
“In 1921, the most advanced quantum theory was still the Bohr model, as generalized for a hydrogenic atom in 1916 by Arnold Sommerfeld and, independently, by Peter Debye. Their proposed quantization conditions implied that Bohr’s quasiplanetary electron orbits should assume only certain discrete spatial orientations with respect to an external field … [Stern] recognized that, according to the Bohr model, the space quantization should be only twofold, as the projection of the orbital angular momentum was limited to ±h/2 . The twofold character made feasible a decisive test of spatial quantization using magnetic deflection of an atomic beam. Despite the smearing effect of the velocity distribution, in a strong enough field gradient the two oppositely oriented components should be deflected outside the width of the original beam. Classical mechanics, in contrast, predicted that the atomic magnets would precess in the field but remain randomly oriented, so the deflections would only broaden (but not split) the beam. Thus, Stern thought he had in prospect an experiment that, “if successful, [will] decide unequivocally between the quantum theoretical and classical views”” (Friedrich & Herschbach, p. 54-55).
“Although simple in principle, the experiment was ambitious in practice. Stern asked Gerlach from the Institute of Experimental Physics to join forces with him … The main experimental problems were mechanical precision (the deflection in the field was only about 0.1 mm) and reliable vacuum (the mercury pumps, made of glass, tended to break). To get a deposit of silver that could be made visible by chemical treatment, stable conditions had to be maintained for hours. The inhomogeneous magnetic field was produced by an electromagnet with pole shoes of rather different shapes. One had the form of a knife-edge, the one opposite carried a groove. The direction of the field was from the edge to the groove, the field strength being higher near the edge.
“In November 1921 Stern and Gerlach observed a broadening of the beam [this was reported in ‘Der experimentelle Nachweis des magnetischen Moments des Silberatoms,’ Zeitschrift für Physik, Band 8, 1922, pp. 110-111]. Its size increased from 0.1 mm to about 0.3 mm if the field was turned on. This result proved that silver atoms possess a magnetic moment. With a still better collimated beam in February 1922 the splitting of the beam into two was observed [reported in the first offered paper]. Spatial quantization was established” (Brandt, pp. 124-126).
“After further experimental refinements and careful analysis, Gerlach and Stern were even able to determine, within an accuracy of about 10%, that the magnetic moment of the silver atom was indeed one Bohr magneton [this is reported in the second offered paper]. This direct demonstration of spatial quantization was immediately accepted as among the most compelling evidence for quantum theory. Yet the discovery was double-edged. Einstein and Paul Ehrenfest, among others, struggled to understand how the atomic magnets could take up definite, preordained orientations in the field. Because the interaction energy of atoms with the field differs with their orientation, it remained a mystery how splitting could occur when atoms entered the field with random orientations and their density in the beam was so low that collisions did not occur to exchange energy” (Friedrich & Herschbach, p. 57).
“Only after the advent of quantum mechanics it became clear that the atoms themselves are not turned but that their quantum-mechanical wave function assumes one of its possible values in the apparatus. In quantum mechanics the concept of electrons orbiting the nucleus loses its meaning. There is still an orbital angular momentum but for the ground state of an electron in the outermost shell of an atom this angular momentum and its associated magnetic moment is zero. However, the electron possesses an intrinsic angular momentum or spin, the z-component of which can have exactly two spatial orientations. Also the electron spin is associated with a magnetic moment and it is that magnetic moment which was observed in the Stern-Gerlach experiment” (Brandt, p. 126). “The gratifying agreement of the Stern–Gerlach splitting with the old theory proved to be a lucky coincidence. The orbital angular momentum of the silver atom is actually zero, not h/2 as presumed in the Bohr model. The magnetic moment is due solely to a half unit of spin angular momentum, which accounts for the twofold splitting. The magnetic moment is nonetheless very nearly one Bohr magneton, by virtue of the Thomas factor of two, not recognized until 1926. Nature thus was duplicitous in an uncanny way” (Friedrich & Herschbach, p. 57).
“Descendants of the Stern–Gerlach experiment and its key concept of sorting quantum states via space quantization are legion. Among them are the prototypes for nuclear magnetic resonance, optical pumping, the laser, and atomic clocks, as well as incisive discoveries such as the Lamb shift and the anomalous increment in the magnetic moment of the electron, which launched quantum electrodynamics. The means to probe nuclei, proteins, and galaxies; image bodies and brains; perform eye surgery; read music or data from compact disks; and scan bar codes on grocery packages or DNA base pairs in the human genome all stem from exploiting transitions between space-quantized quantum states” (Friedrich & Herschbach, p. 53).
“Otto Stern (1888-1969), who planned the experiment on space quantization, was … a follower of Einstein in Prague and Zurich, where he had vowed to abandon physics if Bohr’s ideas were true. I consider him one of the major physicists of the century. Starting in 1920, he devoted himself to the development of the molecular beam method” (Segré, p. 138).
Brandt, The Harvest of a Century, 2009 (Chapter 30, ‘Stern and Gerlach observe spatial quantization (1922)’); Friedrich & Herschbach, ‘Stern and Gerlach: How a bad cigar helped reorient atomic physics,’ Physics Today 56 (2003), pp. 53-59; Longair, Quantum Concepts in Physics, 2013; Segré, From X-rays to Quarks, 1980.
Together two offprints from Zeitschrift für Physik, Band 9, Heft 6. 8vo, pp. pp. 349-352; 353-355 [1, blank], with five diagrams in text of first item. Original printed wrappers, stapled as issued.