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 6 What is notably lacking in Einstein’s interventions in the proceedings is evi- dence of the reportedly fierce debate with Bohr, a debate that has often been pre- sented as among the most significant aspects of the 1927 Solvay conference.[14] Paul Ehrenfest, who also participated in these discussions, described them a few days later with great excitement: “Bohr from out of the philosophical smoke clouds constantly searching for the tools to crush one example after another. Einstein like a jack-in-the-box: jumping out fresh every morning. Oh, that was priceless.” (Ehrenfest to Goudsmit, Uhlenbeck, and Diecke, 3 November 1927 quoted in Mehra and Rechenberg 2000, pp. 251–253). However, because these conversa- tions mainly took place at mealtimes or while walking between the hotel and the conference venue, the textual evidence concerning their content is not substantial.[15] We do, however, have one further document in Einstein’s hand—a short note that appears to have been passed back and forth between Einstein and Ehrenfest during Compton’s report on Tuesday morning (see Doc. 75). Ehrenfest writes to Einstein: “Don’t laugh!! There is a special department in purgatory for ‘professors of quantum theory,’ and there you will receive lectures on classical physics for ten hours a day.” Einstein responds to his friend: “I’m only laughing at the naïveté. Who knows who’ll be laughing in a few years?” II. German and European Politics During the period of this volume, the fourth, center-right coalition cabinet of the Catholic German Center Party’s leader Wilhelm Marx faced ongoing cri- ses, including a conflict over the drafting of a “Christian” school law, and was eventually brought down. The social democrat Hermann Müller emerged as chancellor from the ensuing elections of May 1928 and formed a new cabinet composed of elements from the German left, center, and right. However, his government was in permanent crisis owing to the weak commitment of the major member parties to the coalition.[16] German foreign affairs remained inexorably entangled with its domestic politi- cal developments but nevertheless achieved some successes. In addition to contin- ued engagement with the League of Nations, the minister of foreign affairs, Gustav Stresemann, signed the international Kellogg-Briand Pact in August 1928, aimed at renouncing war as an instrument of national policy. The Reichstag ratified the Geneva Convention banning the use of poison gas in April 1929.[17] Its diplomatic accomplishments spurred the German government to reopen rep- arations negotiations to decrease their punitive financial burden and ultimately achieve economic self-responsibility. The deliberations led to the Young Plan of June 1929, which aimed to drastically reduce wartime debt and end the foreign control of the German economy.[18] However, contentious internal deliberations