D O C U M E N T 2 9 6 M A Y 1 9 2 6 3 1 3 respond to some extent. Unfortunately, it often falls short of this effect. So, it makes little sense. Well, where was I then? I think I was just talking about Max Reger, my usual topic of conversation with you. No, rather, about something else. About the tech- nique of letter writing. I meant to say: It is always nice to have at hand the most recent letter of the individual to whom one is writing, more or less as a starting point for one’s own letter. Unfortunately (I said to myself), I don’t have his letter here. A pity, no doubt, the answer to my question as to when the meeting in Geneva is happening would be in it.[5] So that it does not suddenly crash in and spoil the most wonderful holiday plans. Perhaps some other starting point. So I have to make do without one. (That’s what I thought without the slightest ulterior objective.) Best wishes from your Teddy 296. From Emil Rupp [Heidelberg,] 31 May 1926 Dear Professor, Thank you very much for your esteemed letter of May 21.[1] Unfortunately, I must first correct the figures on the gratings used. The one grid grating has 100 light & dark divisions to 1 cm, i.e., the center distance light–light is 2 · 0.01 cm. The other grid grating has 200 divisions/cm, therefore the distance between two corresponding grating lines: 2 · 0.05 cm (not 0.02 cm, as I had carelessly miswrit- ten in the last letter).[2] I did not use a pure decaying glow in the previous experiments, in order to obtain as great a luminous intensity as possible (vacuum in the observation space 0.08– 0.001 mm Hg).[3] Over the past few days, I have been conducting experiments with the best possible decaying glow light (vacuum 0.001 mm). In order to get sufficient luminous intensity, the current strength in the discharge space was raised from 4.5 to 8–10 milliamps, which strains the discharge tube greatly & only permits exper- iments of short duration. The setup was: interferometer without lenses. Beam vel. = Hg 546 mμ. a) grating with corresponding line distances 0.02 cm diaphragm before the canal ray (gaps + lines) 2 mm the same " " " 4 " effect 1.9 107 ⋅ }