458 DOCUMENT 390 MAY 1912 Walther Nernst for Friday, 19 April, at 3 p.m. and in the evening respectively, are deleted. An undeleted notation to meet Warburg on Friday at 3 p.m. appears on [p. 58]. The notation "Marschallbrücke" in the "Scratch Notebook," [p. 59], probably indicates Ein- stein's intention of visiting the institutes of chemistry (Nernst) and physics (Heinrich Rubens) of the University of Berlin, which were located nearby. Another note indicating that he planned a rendezvous at the Town Hall of Steglitz with Haber appears on the same page. [5]Wannsee is a heavily forested lake district in southwest Berlin. [6]Paula Einstein, LÖWENTHAL's sister. [7]Pauline Einstein kept the household of Emil Oppenheimer in Heilbronn (see Doc. 285, note 5). [8]The fatal situation is presumably a reference to the fact that Pauline Einstein was thinking of taking on household duties in the home of her brother Jacob and sister-in-law Julie Koch (1857-1914). This in turn may have been discussed when Einstein visited the Kochs in Ber- lin/Charlottenburg the previous Wednesday evening, 17 April (see Einstein's "Scratch Note- book" [Vol. 3, Appendix A], [p. 36]). On Julie Koch's death two years later, Pauline Einstein assumed responsibility for the household of her widowed brother (see Doc. 511). [9]In the event of Oppenheimer's death and the loss of her housekeeping position, Pauline Einstein would need assistance not only to support herself but also to repay old debts (see Doc. 13, note 6), owed primarily to her brother-in-law, Rudolf Einstein (see Einstein to Mileva Marie, 23 March 1901 [Vol. 1, Doc. 93], note 15). [10]Einstein's sister Maja Winteler-Einstein. [11]Einstein's Institute of Theoretical Physics of the German University was housed in the Faculty of Natural Sciences. [12]Löwenthal later attached a cover note to a set of letters from Einstein, of which this is the first, in which she characterized them as "especially beautiful letters from the best years!" ("[b]esonders schöne Briefe aus bester Zeit!"). 390. To Paul Ehrenfest [Prague, 2 May 1912] Lieber Herr E! Ich glaube, Sie haben da Unrecht. Wenn eine Lichtquelle Licht von Fre- quenz v und Wellenlänge X erzeugt, so verwandelt sich dies Licht für beweg- ten Beobachter nach Ritz in Licht von anderem v (v') und genau demselben X.[1] Für dies Licht gelten dann für den neuen Beobachter nach Voraussetzung genau die gewöhnlichen Gesetze, nur ist c ein anderes als für ruhendes Licht. Beugungserscheinungen haben aber mit c nichts zu thun, sondern sie lassen sich durch X allein ausdrücken, das für den neuen Beobachter dasselbe ist wie für den ursprünglichen. Sie haben sich da wohl geirrt. Mit den besten Grüssen Ihr Einstein. AKS (NeLR, Arch. 475). [9 328]. The postcard is addressed "Herrn Dr. P. Ehrenfest Lopu- chinskaja 7 Petersburg.," and postmarked "Praha 1 Prag 1 2.V.12-3." The name and address are transliterated into Cyrillic script in another hand. [1]Ehrenfest had apparently objected to Einstein's discussion of Walter Ritz's emission the- ory of light in Doc. 384 (see in particular "Fall 1)" in that letter).