8 6 D O C . 1 0 3 S E P T E M B E R 1 9 1 9 from other sections, many of whom are worth keeping up with in Zurich. This is naturally a powerful way for a foreigner who has not yet acclimatized himself to feel at home in Switzerland and thus I come to the conclusion that the trip to Luga- no was actually quite worthwhile. I received a long letter yesterday from Ehrenfest: he received a call from the new Ukrainian Academy of Sciences in Kiev and is, in principle, not disinclined to ac- cept the same. However, he thinks that he would be more useful as an external member residing in Leyden with the task of advising young Russians who are studying abroad and, in general, acting as a link between Russian and Western Eu- ropean science. Besides, there is no question of his settling in Russia before the conditions there have consolidated completely. In begging your pardon for the inconvenience caused by my letter, I remain in sincere admiration, yours very truly, Paul Epstein. 103. To Paul Ehrenfest [Berlin,] 12 September 1919 Dear Ehrenfest, Your proposal is so fabulous and your words are so warm and friendly that you will hardly grasp how your letter has set my mind awhirl.[1] You certainly know how charmed I am with Leyden! And you know how fond I am of you all. But things are not so simple for me that I can just follow my heart’s impulse to do what is right. I am sending you a letter that Planck sent to me in Zurich.[2] I consequently promised him I won’t turn my back on Berlin unless conditions arise that would make such a step seem natural and proper.[3] You can scarcely imagine what sacri- fices are being made here in the difficult financial situation overall to make it pos- sible for me to stay, and to maintain my family in Zurich![4] It would be doubly re- pulsive of me if, just at the moment when my political hopes are being realized, I turned my back, without good reason, perhaps in part for the sake of material ad- vantage, on people who have shown me affection and friendship and to whom my leaving at this so-called dishonorable time would be doubly painful. You cannot imagine how much warmheartedness surrounds me here and this not only from those who lap up the droplets I sweat from my brainy brow.[5] So you see where I stand. I can go away from here only if there is a turn of events that make it impossible for me to continue to stay. Such a change could occur. If it