1 5 4 D O C U M E N T 8 8 J U L Y 1 9 2 3 the source of geomagnetism can be found in terrestrial electric currents fed by heat currents (see Einstein to Hermann Anschütz-Kaempfe, 17 September 1921 [Vol. 12, Doc. 237] and 18 June 1922 [Vol. 13, Doc. 239], as well as to Max Schuler, 1 December 1921 [Vol. 12, Doc. 309]). [5]A week earlier, he had mentioned planned experiments to Hendrik A. Lorentz (see Doc. 78). An experimental investigation into an empirical consequence of his affine field theory was carried out in collaboration with Hermann Mark (see Doc. 152). [6]Paul Langevin. [7]The planned rally under the slogan “Nie Wieder Krieg,” to be held in Berlin on 30 July (see Doc. 88, note 2). [8]James Franck. [9]For a discussion of Einstein’s attempts at testing an empirical consequence of the affine field the- ory, see the Introduction, pp. xli–xliii. 88. To Paul Langevin [Berlin,] 22. VII. 23. Liebster Langevin! Ich bin ganz glücklich, dass Ihr kommt. Sie müssen bei mir wohnen, da die bei- den Töchter fort sind,[1] in deren Zimmer Ihr ganz behaglich untergebracht seid. Es ist wunderbar von Ihnen, dass Sie zu der Veranstaltung herkommen.[2] Ich war auf- gefordert, dort zu sprechen, habe aber nur eine kurze schriftliche Konfession gege- ben, da mir das persönliche Auftreten unmöglich ist.[3] Schreiben Sie mir bitte Zug und Bahnhof Ihrer Ankunft. Mit herzlichen Grüssen an Sie und Ihren Herrn Sohn[4] Ihr A. Einstein. Es ist eine grosse That von Ihnen, dass Sie zu dieser Veranstaltung kommen. AKSX (Luce Langevin). [15 364]. The card is addressed “Prof. P. Langevin Collège de France Paris.” An unknown hand has crossed out “Collège de France” and inserted “10 bis Bd du Port Royal 10 bis” before “Paris” and “Veme” after “Paris.” The card is postmarked “Berlin 23. 7. 23 2–3 N[achmittags].” [1]Ilse and Margot Einstein. [2]According to Einstein, Langevin planned to attend a pacifist demonstration in Berlin (see Doc. 87). On 30 July, Einstein and Langevin attended a public rally held under the slogan “Nie wieder Krieg” at the Kliems Festsäle in Berlin. At the rally, Langevin was forbidden from addressing the crowd by the Berlin Police president, Wilhelm Richter, who claimed he could not guarantee his safety due to anti-French sentiment. His address, which advocated a policy of reconciliation between Ger- many and France and supported Germany entering the League of Nations, was read to the crowd in German translation. In a second meeting held in the evening at the Ebenholzsaal of the “Rheingold” restaurant, Lan- gevin addressed the audience in French and advocated for international understanding, “honest repa- rations” (“ehrliche Wiedergutmachung”), and the normalization of relations between France and Germany (see Berliner Tageblatt, 30 July 1923, EE, and 31 July 1923, EE Die Welt am Montag, 30 July 1923 and Vossische Zeitung, 31 July 1923, ME). In his address to the meeting, Einstein sup- ported Germany’s membership in the League of Nations (see Appendix B). [3]The brief statement was most likely Doc. 85, as it includes a reference to a pacifist delegation visiting from France. [4]Jean Langevin (1898–1991).