3 0 2 D O C U M E N T 2 8 4 M A Y 1 9 2 6 284. From Emil Rupp [Heidelberg,] 14 May 1926 Dear Professor, With grateful thanks I confirm receipt of your letter of 5 May & your manuscript of 9 May [19]26.[1] I leave to you the decision about whether to publish both papers[2] in immediate succession or together in one article. You may also determine where it will be published. May I keep your manuscript until my exper- imental research is completed? I have concluded the grating experiment to some degree: Setup I. as already described[3] I reduced the distance KQ to 1.8 cm. PQ & L1 lie directly next to each other. Hg-line 546 mȝ. Velocity . Results: (a) With grating 0.1 mm distance. Intensity was estimated by turning the grating 90° (// to the beam), whereby the interferences were visible in full defi- nition. (b) as above grating 0.2 mm 1.9 107cm/sec ⋅