D O C U M E N T 2 9 O P T I C A L E X P E R I M E N T 1 0 5 [11]This extra factor of n was disputed by Walther Bothe (see his letter to Einstein of 7 December 1921 [Vol. 12, Doc. 316]). [12]The l in the last factor should be a 1. For the calculation, Einstein invokes eq. (1): . [13]The lens used in the actual experiment had a focal length of 15 mm (see the typescript for the experimental part of this paper by Geiger and Bothe [2 088]). [14]See eq. (3) of Einstein 1922a (Vol. 7, Doc. 68). [15]The extant, remaining pages of the manuscript appear to contain fragments of the appendix that Einstein added in response to Laue’s criticism. The missing pages may have contained an earlier ver- sion of parts of Einstein 1922f (Doc. 43), in which he would have considered wave propagation according to conditions I, II, and III on pp. 20 and 21 of Doc. 43. [16]For , this equation is equivalent to eq. (6) of Doc. 43. [17]In Doc. 43, Einstein will take the group velocity rather than the phase velocity as the relevant quantity for this condition, in which case the argument for a non-vanishing value of x breaks down (see Doc. 43, note 11). ν ν0 1 q c -- - cosϑ + ν0 1 q c -- - sinϑ' + = = V0 c n0 ⁄ = Vg V0