D O C U M E N T 2 4 5 A P R I L 1 9 2 6 4 1 3 TLS. [20 086]. [1]Doc. 239. [2]Karl-Oskar Bertling. [3]Arthur Liebert (Arthur Levy 1878–1946) was president of the Kant-Gesellschaft (Wirth 2004). For Reichenbach’s disparaging opinion of the Kant-Gesellschaft, see, e.g., Reichenbach 1920, p. 104, note 2. [4]The note was attached to Doc. 235. Einstein had criticized it in Doc. 239. [5]The expression “graphische Darstellung” is borrowed from Eddington 1925a, where it appears as a translation of “graphical representation” (Eddington 1923). For Eddington, graphical representa- tions are geometrical visualizations of physical quantities, e.g., pressure-volume diagrams of an ideal gas, which, however, do not make any hypothesis as to the ultimate nature of the quantities repre- sented. In Eddington’s view, Weyl’s non-Riemannian geometry is not the real geometry of spacetime, as Weyl claimed, but merely a “graphical representation.” The “natural geometry” is the geometry of rods and clocks, which is exactly Riemannian. [6]Reichenbach insists that in his theory, material points of unit mass and arbitrary charge move on the straightest lines defined by his asymmetric connection . In the note, he writes that “a charged test particle creates its own displacement geometry depending on the strength of its charge” (“Ein geladener Massenpunkt schafft sich also selbst seine eigene Verpflanzungsgeometrie je nach der Stärke seiner Ladung,” p. 7). Indeed, Reichenbach’s definition of the connection (see Doc. 239, note 4) hides the fact that its antisymmetric part will depend on a particle’s charge, which it must, given that his geodesic equation is designed to be equivalent to the Lorentz force law. Effectively, this amounts to introducing a different affine connection for each of a particle’s possible charges (or charge/mass ratios). See Giovanelli 2016 for further analysis. [7]He was working on Reichenbach 1928 (see Reichenbach to Moritz Schlick, 6 December 1926, NL-HN, Vienna Circle Archive). Sec. 49 of the book is based on the note attached to Doc. 235. [8]Reichenbach’s theory takes rods and clocks as the “physical indicators” of the metric tensor and charged unit masses as physical indicators of his asymmetric connection . He argues that Weyl’s, Eddington’s, and Einstein’s theories suffer from the fact that they don’t associate physical indicators with their respective connections. [9]Possibly sec. 50 of Reichenbach 1928. 245. From George Y. Rainich Johns Hopkins University, Baltimore Md. U.S.A., 5 April 1926 Sehr geehrter Herr Einstein! Ich habe Ihren freundlichen Brief vom 8. III. 26[1] erhalten und ich ersehe aus ihm dass ich mich in der für die Physica bestimmten Notiz nicht klar genug gefasst habe.[2] Ich danke Ihnen für das Eingehen auf diese Frage in Ihrem Briefe, ich glau- be dass ich jetzt Ihren Gesichtspunkt vollständig verstanden habe und ich erlaube mir meinerseits Ihnen meinen Standpunkt klarmachen zu versuchen. 1. Es scheint mir dass die von Ihnen angedeutete Schwierigkeit darauf zurück- geführt werden kann, dass Sie die Eigenschaften der Teilchen durch das „Feld in- nerhalb der Materie“ charakterisieren wollen. Selbstverständlich berauben Sie sich dadurch der Möglichkeit die Beziehungen zwischen zwei Teilchen direkt zu Γμν τ gμν Γμν τ