x x x v i I N T R O D U C T I O N T O V O L U M E 1 3 make the continuation of his research temporarily impossible!” (see note 261 to Doc. 379). Among the more outlandish offers was a lucrative proposal that Einstein deliver one hundred lectures in the United States for $50,000 (Doc. 437). The half-year tour to Japan, Palestine, and Spain provided a welcome hiatus from all these quandaries. During the quiet leisure time on board the steamer on his return from Japan, Einstein delved into the technical intricacies of Eddington’s re- cent approach toward a unified field theory and wrote Einstein 1923e (Doc. 425). I During the month of January 1922, Einstein had to revise his own understanding of an experiment he had conceived in 1921 to determine the nature of light (see Vol. 12, Introduction, sec. VI, pp. l–lvii). The experiment was to examine light radiation emitted by canal rays, that is, by a beam of atoms moving at high speed. Einstein’s idea was to observe this radiated light after it had passed through a dispersive medium. According to the Maxwellian wave picture, he believed, one should observe a deflection of the light, whereas no deflection should occur if light is emitted as quanta (see Einstein 1922a [Vol. 7, Doc. 68]). Einstein’s proposed experiment met with criticism, which only intensified with time. Hendrik A. Lorentz was the first to criticize the canal ray experiment in a de- tailed letter of 13 November 1921 (Vol. 12, Doc. 298). He attempted to convince Einstein that, according to Einstein’s own ideas, an (extremely weak) wave of some kind accompanied the light particle asking whether light consists of waves or of particles was the wrong question. By the end of 1921, Einstein had reported to his friends and colleagues that the result of the canal ray experiment, carried out in Berlin by Hans Geiger and Walther Bothe, was clearly negative (i.e., no deflection was observed). He considered the result highly significant and thought it unambiguously spoke against the wave pic- ture of light. To Hermann Weyl he wrote on 22 December 1921: “The canal ray ex- periment has a negative result, which ultimately means a refutation of the field theory of electricity. Now what?” (Vol. 12, Doc. 336). And just before the end of the year, in a letter to Hedwig and Max Born of 30 December 1921, he called the outcome of the experiment “my strongest scientific experience in years” (Vol. 12, Doc. 345). With the interpretation of the canal ray experiment still undecided at the conclu- sion of Volume 12, the present volume begins with Einstein’s attempt to come to