I N T R O D U C T I O N T O V O L U M E 1 5 l x x i i i anarchists Sacco and Vanzetti. In April 1927, only one day after they were sen- tenced to death, he cosigned a cable to President Calvin Coolidge with Romain Rolland and Henri Barbusse, demanding that they be released from imprisonment (Doc. 511). In February 1927, he contributed a short piece to a commemorative issue to cel- ebrate ten years of the Prague Urania, an institution dedicated to the popularization of science, which was directed against the elitism of intellectuals.[42] In his state- ment, Einstein attacked the “certain arrogance of intellectually productive people” and criticized their lack of awareness that their opportunity to be creative intellec- tually was due to “the freedom enabled by the labor of others” (Doc. 491). VII. Of Waves and Particles: The Emil Rupp Affair Sometime around March 1926, the astronomer Walter Grotrian drew Einstein’s attention to a recent paper by Emil Rupp (Rupp 1926a) on the interference of light emitted by canal rays. Leo Szilard obtained a copy of the paper for Einstein (Doc. 221), and two days later Einstein submitted a “Proposal” to the Prussian Academy for a similar experiment, one that would decide whether excited atoms emit light instantaneously (in quanta), or in a finite time (in waves). Einstein expected quantum emission to be confirmed by experiment (Doc. 223). This was not the first time that Einstein had turned to canal rays for settling this issue. In 1922 he had suggested that, if the rays were allowed to pass through a dis- persive medium, an observed deflection would corroborate their wave character, while a lack of deflection would demonstrate that they consist of quanta (Einstein 1922f [Vol. 7, Doc. 68]). Because no deflection was observed at the time, Einstein interpreted the result as “a refutation of the field theory of electricity.” Soon there- after, however, he had to admit that wave theory would have given the same result (Einstein to Paul Ehrenfest, 26 January 1922 [Vol. 13, Doc. 37]). The following year, Compton’s experiment sparked anew his hope for an experimentum crucis be- tween wave and corpuscular theory (Einstein et al. 1923 [Vol. 14, Doc. 11]). Rupp’s results now seemed to open a new opportunity. In a paper based on his doctoral dissertation, he reported that he had investigated the light produced by ca- nal rays with a Michelson interferometer and determined the maximum coherence length of the light. For the case of Hβ canal rays this turned out to be 15.2 cm. Eduard Rüchardt doubted that Rupp’s experimental setup could have yielded the purported results (Rüchardt 1926). Robert d’Escourt Atkinson complained about the absence of details on the manner in which Rupp had compensated for the Dop- pler shift caused by both the motion of light-emitting particles in the beam and their