D O C U M E N T 3 0 7 J U N E 1 9 2 6 3 2 3 less distinct toward 15°, then distinct again between 25° & 40°, but not as (¢bright²) sharply distinct as in b strong drop at 45°. a′. Light of Hg-glow discharge. Result as in a. This series of experiments was repeated during 3 nights, 4–5 times, with the same result. Furthermore: Tube reassembled, rotated 180°. Canal ray direction ↓. Experi- ment a & b performed. Mirror turning now reversed ↑. Comparison with the theory: , . If the lead of the screw is 0.3 mm, the change in angle during one revolution amounts to . The interferences with canal ray light must hence be the sharpest at about of a turn of the screw. This setting of the interferometer to interferences of equal inclination caused much trouble. In particular, it was a pure test of patience to get the axis of mirror S2 exactly vertical. I employed charge-change glow for the adjustment. I did not perform the experiment with 2 lenses, which would intensify the effect somewhat. Please let me know if it is required. Would you please give me your opinion on whether & in what direction this ex- periment & the grating experiment ought to be supplemented so that I can still com- plete all the needed experiments as soon as possible here, before I leave for Göttingen?[8] Respectfully yours, E. Rupp 307. To Paul Ehrenfest [Berlin,] 18 June 1926 Dear Ehrenfest, Alas, it is impossible for me to get away now,[1] especially since I have to travel to Zurich around July 10th to see my boy and spend the vacation with him.[2] And that, notwithstanding the enticing subject and Galinka’s pretty sketch.[3] The exper- iments with the canal rays are finished and speak very clearly: all the consequences of the Maxwell equations apply to the emission of the interference field. The light emitted by a moving canal ray particle, which interferes with a difference in path, is emitted at different places. You suspected it would be so.[4] Schrödinger’s papers β v c -- 2( a1 a2) – f ------------------------ - 1.9 107 ⋅ 3 1010 ⋅ ------------------- ------ 20 14 - 9 10 4– ⋅ = = = β 2 -- - 4.5 10 4– ⋅ = 0.03 7 ---------- - 4 10 3– ⋅ = 1 2 -- -