l x x x i i I N T R O D U C T I O N T O V O L U M E 1 4 travel diary: “Finally free but more dead than alive” (Doc. 455). On 11 May he sailed from Rio on board the SS Cap Norte, disembarked in Hamburg on 31 May, and arrived in Berlin the next day. [1]In Kantara, Egypt, where he arrived on 1 February 1923, Einstein gave an interview in which he apparently talked about the ideas contained in this new paper. A brief report of that interview was pub- lished in the New York Times three weeks later, on 23 March 1923, based on a note distributed by the Associated Press, dated 22 March, when Einstein stopped over in Zurich on his way back to Berlin. [2]See Frenkel 1988. [3]Stuewer 1975, p. 223. [4]Compton 1923a. [5]See Eckert 2013, p. 349. [6]See Sommerfeld 2004, p. 144. [7]Sommerfeld began to include discussions of the Compton effect in his subsequent lectures at Berkeley, at the National Bureau of Standards in Washington, and elsewhere during his travels through the U.S. in early 1923, before returning to Munich by April. On 8 May he wrote to Paul Epstein at Caltech in Pasadena: “Whether Compton is correct? Duane and Richtmeyer have strong doubts. I myself am uncertain of it. What is with the question of the limb-effect? And what did Ross find with certainty at Lelan[d] Stanford when he repeated the experiment?” (Arnold Sommerfeld to Paul Epstein, 8 May 1923, CaPsCA, Epstein Papers.) Among the auditors of Sommerfeld’s lec- tures had been P. A. Ross from Stanford, who had immediately attempted to reproduce Compton’s effect. His negative result was published in the 25 May 1923 issue of Science (Ross 1923). [8]See Stuewer 1975, pp. 249–272. [9]Despite what appear to have been lively exchanges, Einstein found Sommerfeld and Kossel “too intellectual, too far from simplicity” (Doc. 100). [10]A similar idea had been formulated and tested in a paper by Sommerfeld’s colleague Helmuth Kulenkampff at the Technische Hochschule in Munich, received by the Zeitschrift für Physik on 20 August 1923 (Kulenkampff 1923). But Kulenkampff was interested in testing the Compton effect for reflected beams, and did not discuss the materials that Einstein and Mark were using. [11]Sixty years later, in a letter to Gerald Holton, Hermann Mark provided insight into the back- ground of their experiment. He wrote: “It all had to do with the controversy about the Compton Effect which raged in 1923 between H. A. Compton (St. Louis University) and G. L. Clark and William Duane (Harvard University) Einstein was, of course, deeply interested in its outcome […]. In the Summer of 1923 Einstein, who had just returned from Japan via Palestine came to our Institute and showed me a paper by H. A. Compton (May issue of Physical Review 21, 483, 1923) which described the famous scattering experiment of X-rays by individual electrons. It was the first direct and incon- trovertible proof for the light quantum theory. However, Einstein told us that other prominent physi- cists in England—C.T.R. Wilson, C. G. Darwin, J. H. Jeans and C. G. Barkla—and most of all, William Duane in Harvard, had not been able to confirm Compton's results and ascribed the ‘dis- placed’ radiation to the pressure of some erratic scattering. He asked me whether we could duplicate Compton’s experimental set-up and explore whether we could discover a sharp ‘displaced’ line. I said that I would be glad to try and my two letters to Einstein referred to the tests I carried out during the Fall of 1923. Einstein, who was in Berlin most of this time, wrote only two postcards but came often to the Institute to discuss the experiments and to talk physics in general terms with our group which at that time included M. Polanyi, L. Szilard, E. Wigner and S. N. Bose. Early in 1924, after a few meetings between Compton and Duane, there could be no doubt anymore about the reality of the Compton Effect and Dr. Kallmann who worked with me and I decided that it would make no sense any more to research Compton’s experiments but we should rather try to get good photographic pic- tures of the ‘classical’ and ‘displaced’ lines and study other aspects of the Compton scattering (Comp. H. Kallmann and H. Mark Naturw. 13, 297, 1022, 1925 Z.F. Phys. 36, 120 1926). The postcards of Einstein I kept in my files but in 1938 when I was Professor at the University of Vienna, the Nazis