1 8 2 D O C U M E N T 9 4 N O V E M B E R 1 9 2 7 ALS. [20 411]. [1] Rupp (1898–1979) was Assistent at the University of Göttingen. [2] The experiment was first described in Emil Rupp to Einstein, 23 March 1926 (Vol. 15, Doc. 233) in his letter to Einstein of 8 November 1926 (Vol. 15, Doc. 410), Rupp announced his intention to carry it out. For Rupp’s experiments on canal rays, see Dongen 2007a and 2007b. [3] See Rupp 1928a for a more detailed report. [4] See Vol. 15, Introduction, sec. VII, for a discussion of the “wire grid experiment” (“Gitterver- such”), performed by Rupp at Einstein’s instigation. [5] Caption: A[uf]hellung d bei verschiedenen frequenze[n] n an der Kerrzelle [6] Captions: I = Intensität der Resonanzlampe R d = durchgelassene Intensität durch A s = Schwärzungsmarken [5] [6]