7 2 D O C U M E N T 2 3 J U L Y 1 9 2 5 Landé[27] in Tübingen einen Vortrag halten, dann fahre ich ins Engadin zu den Mei- nen. Im Oktober soll ich nach Cambridge, Kapitza hat mich eingeladen und im Winter sollen wir alle zum russischen Physikertag nach Moskau, Joffé will uns die Reise bezahlen. Du siehst, wir kommen auch in der Welt herum, wenn auch nicht nach Japan und Argentinien.— Noch eins: Heute im astronomischen Kolloquium hat Kienle[28] von einer neuen, schönen Arbeit berichtet (vom Mt. Wilson, glaube ich): Der Begleiter des Sirius ist einer jener rätselhaften winzigen Zwerge mit rie- siger Masse, Dichte 28000, also nach Eddington eine Anhäufung nackter Kerne und Elektronen. Jetzt ist die Rotverschiebung (von circa 20 km/sec) nachgewiesen genau entsprechend der riesigen Dichte (kleiner Radius!).[29] Nun aber Schluß. Grüß Deine Frau und Töchter herzlich.[30] Dein Born. ALS [8 177]. Einstein and Born 1969, pp. 119–121. [1]Hedwig Born-Ehrenberg (1882–1972), Irene (1914–2003), and Gritli Born (1915–2000). [2]Niels Bohr (1885–1962) was Professor of Theoretical Physics at the University of Copenhagen. [3]Einstein 1924o and 1925f (Vol. 14, Docs. 283 and 385). [4]Bose 1924a, 1924b Einstein 1924l (Vol. 14, Doc. 305). [5]Paul Ehrenfest. [6]Broglie 1924 or Broglie 1925. [7]Walter Elsasser (1904–1991) was a doctoral candidate in Göttingen. On 18 July he submitted a short paper (Elsasser 1925) in which he pointed out that the anomalous results of experiments involv- ing electrons by Carl Ramsauer, and by Clinton Davisson and Charles Kunsman, could at least qual- itatively be explained by assuming that electrons behave as waves with a De Broglie wavelength. Ramsauer had found that the mean free path of electrons in noble gases becomes infinite at small velocities (Ramsauer 1923 see also Born to Einstein, 29 November 1921 [Vol. 12, Doc. 308] for an earlier discussion of this result) Davisson and Kunsman had studied the scattering of low-speed elec- trons by various metals and had found an intensity pattern for the scattered electrons that could not be explained classically (Davisson and Kunsman 1923). [8]See Compton 1923a, Duane 1923, and Epstein and Ehrenfest 1924. They treated X-ray scatter- ing by crystals on the assumption that the transfer of momentum between the X-rays and the crystal lattice is quantized. Paul Epstein. [9]In 1924–1925, Born and several other authors developed a correspondence-principle technique to construct quantum formulas from classical ones in such a way that the former reduce to the latter in the limit of high quantum numbers (see Kramers 1924a, 1924b Vleck 1924a, 1924b Born 1924). Part of this technique was to replace derivatives with respect to action variables with difference quotients. [10]Pascual Jordan (1902–1980) was Assistent at the University of Göttingen. [11]See Born and Jordan 1925a. [12]James Franck (1882–1964) was Professor of Experimental Physics at the University of Göttin- gen. The result of the investigation of atomic collisions was published the following year (Franck and Jordan 1926). [13]See Einstein 1925o (Vol. 14, Doc. 425) for his comments on Jordan 1924, in which Einstein’s proposal to ascribe momentum to light quanta (see Einstein 1917c) is criticized. [14]Werner Heisenberg (1901–1976) and Friedrich Hund (1896–1997) were Privatdozenten in physics at the University of Göttingen. [15]“Term-Zoologie” (“term zoology”) refers to semi-empirical rules for multiplets involving arbitrarily introduced quantum numbers. On 28 July 1925, Heisenberg gave a talk in Cambridge with the title “Termzoologie und Zeemanbotanik” (“Term zoology and Zeeman botany” see Mehra and Rechenberg 1982, pp. 320–321).
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