x l v i I N T R O D U C T I O N T O V O L U M E 1 4 States and accept an offer from Columbia University (Doc. 140). By noon on 8 November, Einstein had arrived in Leyden, taking refuge with the Ehrenfests (Doc. 141). In a dark mood, he penned an aphorism: “The nations don’t care about their history” and “bad experiences have to be gone through over and over again” (Doc. 144). A few days later he received reports that the situation in Berlin had stabilized (Doc. 145), and soon thereafter no longer envisaged leaving Germa- ny for good. Nevertheless, he decided to remain in Leyden until the threat of a right-wing putsch had passed (Doc. 150). Max Planck, shocked and outraged upon hearing of Einstein’s flight, promised to act, and implored Einstein not to make any irreversible decisions (Doc. 143). But upon further investigating the matter, Planck concluded that there had been no con- spiracy against Einstein (Doc. 157). Einstein stayed on in the Netherlands to attend a special ceremony at which he was awarded the gold medal of the Dutch Society for the Advancement of Science, Medicine, and Surgery (Doc. 160). He was enjoying “this quite cheerful banish- ment” (Doc. 171), and further postponed his return so that he could deliver a lecture to the engineers of the Philips Lamp Factory, with whom he intended to affiliate himself commercially, as he had done in the past with the Schweizerische Auerge- sellschaft and with Hermann Anschütz-Kaempfe’s gyrocompass factory in Kiel (Doc. 176). He received two more offers for positions at foreign universities: Albert A. Michelson proposed a professorship at the University of Chicago, and Marcel Grossmann held out the prospect of an appointment back in Zurich (Docs. 169, 186). Einstein eventually returned to Berlin on 23 December (Doc. 179). The un- planned and extended stay in Leyden was a scientifically productive time. During November and December 1923 he worked on a number of topics that had preoccu- pied him during the past six months. IV As noted earlier, by late May 1923 Einstein’s engagement with the affine theory had led to a negative assessment of the theory’s potential. The revival of the approach, in which he investigated an empirical implication, had not yielded any positive result by the time he went to Lautrach in August. But his interest in the quantum theory of radiation must have been rekindled through conversations with Sommerfeld and Kossel in Lautrach, the subsequent experimental efforts in Berlin by Mark, Pringsheim, and Szilard, and by his discussions with Ehrenfest on Pauli’s paper during his stay in Leyden in October 1923.