3 0 8 D O C U M E N T 2 9 1 M A Y 1 9 2 6 2) Velocity distribution of the beam, with Hg quite strong. Acts like ray scatter- ing. 3) Stationary intensity cannot be eliminated using Hg, despite good cooling.[5] (The stationary intensity is very strong in decaying glow even for alkalis, as the ex- posures by H. Kerschbaum, Ann. d. Phys. 79. plate 7 show.)[6] One will therefore always only be able to obtain a superposition of continuous interference fringes & the expected effect. The minima will become more blurred the lower the total ray intensity is hence they will become less clear with a finer grating. 4) Errors in the optical part of the interferometer, which can partly generate “white” fringes, partly continuous fringes cannot be controlled in detail. What happens if the grating becomes increasingly finer? The intensity becomes weaker, & the minima, which on their own are wide, become flatter, & continuous interferences will probably be obtained. In looking forward to your valued response, I remain very sincerely yours, E. Rupp 291. To Emil Rupp [Berlin,] 21 May 1926 Dear Mr. Rupp, The results[1] still cannot be viewed as a confirmation of the theory ¢leaving out of consideration that it has not been shown yet that omitting the two lenses would not change anything in the effect.² however, it is very nice to know that the omis- sion of the two lenses did not destroy the effect, after all. Now I am only concerned about the following: 1) The distance between positions of optimal interference should be five times smaller for the grid 0.02 mm than for the grid 0.1 mm. (In your experiments it is only twice as small.) 2) The absolute value of the distance of positions of optimal interference is also wrong. If b is the distance between neighboring grating lines, v the velocity of the canal rays, then this distance should be ,[2] and hence cm in your first experiment. But according to your exper- iment, it is 30 cm. Or is this distance in your grid cm, because the widths b c v -- 0.01 3 1010 ⋅ 1.9 107 ⋅ ------------------- - ⋅ 16 = 2 0.01 ⋅