DISCOVERY OF SPATIAL QUANTIZATION - THE STERN-GERLACH EXPERIMENT

STERN, O. [OTTO] (+) WALTHER GERLACH.

Ein Weg zur experimentellen Prüfung der Richtungsquantelung im Magnetfeld [in: Zeitschr. für Physik vol. 7, 1921:] (+) Der experimentelle Nachweis des magnetischen Moments des Silberatoms [in Zeitschr. für Physik vol. 8, 1922] (+) Der experimentelle Nachweis der Richtungsquantelung im Magnetfeld. [in Zeitschr. für Physik vol. 9, 1922:].

Berlin, Julius Springer, 1921 & 1922. 8vo. Entire volumes 7-9, 1921 and 1922, of "Zeitschrift für Physik" bound in three contemporary half cloth bindings over marbled boards, volumes 7 and 8 in uniform bindings, volume 9 slightly differing, with more gilding to spine. Tiny marginal dampstain to the first leaves of vol. 9, and large library-stamp to front free end-papers of volumes 7-8, otherwise, all three volumes fine, clean, and tight. All three title-pages with library-stamp. Pp. 249-53; 110-11; 349-55. [Entire volumes: VI, 414 pp; IV, 419 pp.; IV, 412 pp.].

First printing of Stern and Gerlach's seminal papers in which the first spatial quantization, atomic magnetic moments, was first presented. With these papers, the first clear proof for the spin of the electron appeared, profoundly influencing the world of physics. The discovery of the deflection of particles is often used to illustrate basic principles of quantum mechanics and demonstrates that electrons and atoms have inherent quantum properties.

Spatial quantization had been introduced merely as a theoretical concept by Sommerfeld in 1916, but no one before Stern had ever empirically demonstrated its existence, and some physicists even considered it to be nothing more than a mathematical tool. In his 1921-paper Stern proposed an empirical test:
"The idea for the experiment proposed by Stern was simple enough. A beam of silver atoms is produced by letting silver evaporate in an oven with a small opening. The beam is collimated and travels in X direction until it falls on a glass plate. Between collimators and plate an inhomogeneous magnetic field is produced. It points in y direction and also changes its strength as a function of y. If the atoms possess a magnetic moment, the field pulls them away from the X axis. If the moments are oriented at random, there will be a broadening of the beam. But if spatial quantization exists with just two possible orientations, then the beam will be split in two. Half the atoms are pulled in the positive and half in the negative y direction. It should be treated as a spinning top with a magnetic needle in its axis." ( Brandt. The Harvest of a Century, p. 124).

In November 1921, Stern and Gerlach observed a broadening of the beam, its size increased from 0.1 mm till 0.3 mm when the field was turned on. "This result proved that silver atoms possess a magnetic moment. With a still better collimated beam in February 1922 where the splitting of the beam into two was observed. Spatial quantization was established." ( Brandt. The Harvest of a Century, p. 124).

Only after the birth 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.
The discovery penetrated all aspects of physics; it was documented that electrons are responsible for the hyperfine structure of the spectroscopic lines and more generally that the direct observation of the spin of the electron is the most clear evidence of quantization in quantum mechanics.

The three volumes also contains the following papers of interest:
1. Born, Max. Über elektrostatische Gitterpotentiale. Bd. 7. pp. 124-140.
2. Born, Max. Zur Thermodynamik der Kristallgitter. Bd. 7. pp. 217-248.
3. Geiger, H. Reichweitemessungen an alfa-Strahlen. Bd. 8. pp. 45-58.
4. Brody, E. & Max Born. Bemerkungen zy unseren Abhandlungen "Über die Schwingungen eines mechanischen Systems mit endlicher Amplitude und ihre Quantelung" [...] . Bd. 8. Pp. 205-208.
5. Heisenberg, Werner. Zur Quantentheorie der Linienstruktur und der anomalen Zeemaneffekte. Bd. 8. pp. 273-297.
6. Bohr, Niels. Der Bau der Atome und die physikalischen und chemischen Eigenschaften der Elemente. Bd. 9. pp. 1-67.

And many others.

Order-nr.: 43611