D O C S . 3 9 8 , 3 9 9 A P R I L 1 9 2 0 3 3 3 398. From Felix Klein Göttingen, 28 April 1920 Dear Colleague, Mr. Einstein, As Hilbert is only returning from his Easter trip a few days from now, I am send- ing to you directly the enclosed Annalen circular with the request that you return the same to me very soon with your signature and any comments. These “circulars” are traditionally the means of maintaining a certain internal cohesion among the various members of the Annalen’s editorial board.[1] I would especially like to draw your attention to the part in Blumenthal’s letter underlined by me in blue. We all enthusiastically applauded the resumption of clos- er ties with the Annalen der Physik but we must not fail to recognize the new seri- ous intrinsic difficulty. Modern physical production, as it is represented for ex. in the Physikalische Zeitschrift, suffers from a restlessness that does not mix easily with the introspection necessary for mathematical papers. Therefore, I would be particularly grateful if you would help assure the appearance of suitable papers for the Annalen. Unfortunately, I myself was much distracted last year from my rel[ated] efforts. At the urging of my friends, I had to start concerning myself with the preparations for reprinting my old abstract mathematical papers.[2] In the past quarter I have not been able to accomplish much at all, however, because a long-lasting bout of flu overshadowed my other sundry complaints.– Luckily, at the moment work on the mathematical encyclopedia is making better progress again. In particular, we are approaching relativity theory from astronomical and physical angles (Kottler under the supervision of Oppenheim, Pauli under the supervision of Sommerfeld).[3] If only we managed to resurrect our Göttingen physics![4] With best regards, yours sincerely, Klein. 399. To Paul Oppenheim 29 April 1920 [Not selected for translation.]