1 8 8 D O C . 1 1 6 L E C T U R E S B O N N Published in Physikalische Zeitschrift 24 (1923): 472–473, 484. Published 15 November 1923. [1]The discussion followed Joos 1923, which reports on an experimental attempt to observe the directedness of atomic emission processes, as predicted by Einstein’s quantum theory of radiation (Einstein 1916n [Vol. 6, Doc. 38] see also its republication, Einstein 1917c). The preliminary results seemed to indicate the presence of such a directedness. A few weeks later, Arnold Sommerfeld wrote to Arthur H. Compton: “Your discovery of the change in wavelength of Röntgen rays keeps the sci- entific world in Germany extremely busy. I was together with Einstein and Kossel in August, and our chief topic of discussion was your effect. Also, at the meeting of physicists in Bonn it was discussed in connection with an -ray scintillation experiment for visually proving the asymmetry of emission. Joos’ report on it appears in the Physikalische Zeitschrift. The result, however, is certainly not yet con- clusive” (“Ihre Entdeckung der Wellenlängen-Änderung der Röntgenstrahlen beschäftigt auch in Deutschland die wissenschaftliche Welt auf’s lebhafteste. Ich war im August mit Einstein und Kossel zusammen und wir diskutierten hauptsächlich über Ihren Effekt. Ebenso wurde auf dem Physikertag in Bonn darüber verhandelt im Anschluss an einen Versuch mit Lichtblitzen von -Strahlen, die Ein- seitigkeit der Emission visuell nachzuweisen. Der Bericht darüber von Joos erscheint in der Physikal. Zeitschr. Das Ergebnis ist aber sicher noch nicht beweisend” Arnold Sommerfeld to Arthur H. Compton, 9 October 1923, Sommerfeld 2004, p. 153). For further historical discussion, see also Stuewer 1975, pp. 246–249. [2][5 184] is a manuscript of this comment. [3]See Compton 1923 for his experiment for Einstein’s interest in the Compton effect, see note 1 above, and also Doc. 99, note 3, and Einstein 1924e (Doc. 236). [5 186] is a manuscript of this comment. [4]The discussion followed Hopmann 1923, which presents an analysis of the observations of the September 1922 eclipse expedition to Wallal, Western Australia. The first results of the expedition, which confirmed gravitational light deflection, had been communicated to Einstein in Doc. 14. [5]The Berlin astronomer Leopold Courvoisier (1873–1955) had published observations that indi- cated that stars undergo periodic systematic displacements of their positions. He had found that stars were displaced away from the Sun in all directions and that this displacement diminished from 0″.5 near the Sun to zero at 180º (see Courvoisier 1913 these observations were never duplicated by any- one else). Courvoisier attributed this phenomenon, which he called “annual refraction” (“jährliche Refraktion”) and which became known also as the “Courvoisier effect,” to the motion of the Earth through the ether. In Hopmann 1923 it was concluded that both the Courvoisier effect and gravita- tional light deflection could account for the stellar displacement observations. An analysis published the next year (Trumpler 1924), however, criticized Hopmann 1923 and concluded that the Courvoisier effect did not provide a satisfactory explanation of the observed displacements. See also De Andrade Martins 2011 for more on Courvoisier and his work. α α