1 8 8 D O C U M E N T 9 7 D E C E M B E R 1 9 2 7 Published in Deutsche Literaturzeitung, Issue 1, 1928. [1] Reichenbach 1928. On 23 October 1927, Einstein had reported to Elsa Einstein (Doc. 74) that he was finished reading Reichenbach’s book on 1 December 1927, Reichenbach sent Einstein the proofs because he had been told that Einstein was willing to write a review of the book (Abs. 295). [2] Reichenbach 1928, sec. 1, §14, where he attributes the term “implicit definition” to Schlick 1918, pp. 30–37 (as he had before in Reichenbach 1920, p. 33.) Einstein himself did likewise in Einstein 1921c (Vol. 7, Doc. 52). [3] Reichenbach 1928, sec. 1, §4. See also Schlick 1918. [4] Reichenbach 1928, sec. 1, §13. See also Reichenbach 1920 and Einstein 1924n (Vol. 14, Doc. 321). [5] See especially Reichenbach 1928, sec. 3, §27. As Reichenbach himself notes, the discussion there is only a summary of Reichenbach 1924. [6] Reichenbach 1928, sec. 2, §19 and §20. [7] Reichenbach 1928, sec. 1, §5. For Einstein’s own wrestling with the concept of a rigid body, see Giovanelli 2014. [8] In sec. 4, part C, §44, Reichenbach argues that the three-dimensionality of space is an objective feature of the world. His justification of the claim relies on his conviction that there can only be properly causal laws of nature if there are three spatial dimensions and one temporal dimension. Reichenbach addressed the latter in §43. Kaluza-Klein theory, having been recently revisited by Einstein in Einstein 1927i and 1927j (Vol. 15, Docs. 459 and 480), assumes that space-time is five- dimensional: four spatial and one temporal dimension. However, this is not in contradiction with Reichenbach’s arguments for the logically separate claim that the dimensionality of space or space- time, whatever it may be, cannot be a dynamical quantity. [9] The draft of what would become this appendix was discussed in detail in correspondence between Einstein and Reichenbach in 1926 see Vol. 15, Introduction, sec. III. [10] In Einstein’s and Reichenbach’s discussion on the draft of the appendix (see the preceding note), Einstein and Reichenbach had already agreed that it would be inappropriate to interpret general relativity as showing that physics, and gravity in particular, is reduced to space-time geometry. See especially Reichenbach to Einstein, 4 April 1926 (Vol. 15, Doc. 244) and Einstein to Reichenbach, 8 April 1926 (Vol. 15, Doc. 249). For further elaboration by Einstein, see Doc. 6 for analysis, see Lehmkuhl 2014 and Giovanelli 2016. 97. From Paul Ehrenfest Leiden, 2 Dezember 1927. Lieber Einstein! Aus dem beiliegenden Brief von mir an Frau Curie[1] wirst du unmittelbar erse- hen, worum es sich in dem noch weiter beigefuegten Bericht des Hilfs Commitees russischer Gelehrter und Schriftsteller in Deutschland handelt.[2] Verzeih, dass die Copie etwas schwer lesbar ist. Das viel besser lesbare Original habe ich an Frau Curie gesendet und eine Copie auch an Lorentz[3] gegeben. Ich hoffe sehr dass man DURCH ZERLEGUNG IN STUECKE manches von seiten Eurer Commission thun koennte. Mein Correspondent der Philosoph S. Frank[4] (Berlin-Halensee, Joachim Fried- richstr 48) ist ein Mann den ich schon seit etwa zwanzig Jahren gut kenne und SEHR schaetze, vor allem auch wegen seiner stets ganz besonders unabhaengigen