1 3 0 D O C . 4 3 L I G H T I N D I S P E R S I V E M E D I A Published in Preußische Akademie der Wissenschaften (Berlin). Physikalisch-mathematische Klasse. Sitzungsberichte (1922): 18–22. Submitted 2 February 1922, published 27 February 1922. A manu- script is also available [1 024]. Significant variations between the printed text and the manuscript are noted. [1]Einstein 1922a (Vol. 7, Doc. 68) for its early critiques, see Raman 1922 and Breit 1922. [2]For Max von Laue’s criticism, see Doc. 25. [3]In his letters, written after the completion of Doc. 29, Ehrenfest entered into a controversy with Einstein, pointing out that one had to take into account the distinction between phase velocity and group velocity for the wave-theoretical analysis of the canal ray experiment. Einstein admitted that Ehrenfest was correct in Doc. 37. [4]The following discussion arose from a calculation that was first given on pp. 6–10 of Doc. 29. [5]In the manuscript, “Wellenzug” was corrected from “Wellengruppe.” [6]Einstein is neglecting terms of order see Doc. 29, eq. (7). [7]In the manuscript, “Wellenzug” was corrected from “Wellengruppe.” [8]In the manuscript, “Wellenzug” was corrected from “Wellengruppe.” [9]The equation should read . [10]In the manuscript, “aus einer Wellengruppe” was corrected from “aus der Strahlungsgruppe.” [11]In Doc. 29, Einstein had argued that the relevant velocity here was the phase velocity rather than the group velocity, and hence had deduced that x would not vanish but rather give the expression for a circular path of the light ray. In Doc. 37, he had indicated that he had found a mistake in his earlier calculation after the correction of which the previous argument no longer holds. [12]Emil Warburg, Hans Geiger, Walther Bothe. For a historical discussion of Einstein’s canal ray experiment, see Klein, M. 1970b and Vol. 12, the Introduction, pp. lv–lvii. ξ2 H ω0 γξ) + ( 1 1 c -- - r0 x r0 ----ξ – n0 dn dω ------ -γξ + – α + = V0