1 3 6 D O C U M E N T S 1 1 4 , 1 1 5 N O V E M B E R 1 9 2 5 114. To Paul Ehrenfest [Berlin, 20 November 1925] Dear Ehrenfest, I cannot write to Bohr.[1] If he wants to come, then he will certainly come, if he does not dread the fatigue and hustle. One should not press him. I am already very much looking forward to Leyden. If Bohr comes, it would perhaps be better for me to stay somewhere else this time. Think about your poor women folk[2] and your- self. Ask young Onnes,[3] whom I like so much. Ask him, however, only after Bohr has committed. Planck cannot come, but was very pleased with the invitation.[4] I am also very pleased about Langevin.[5] Closer relations between professorial factotums[6] are no longer needed after Locarno.[7] They would have been good as avant-garde as reserve forces they are irrelevant.[8] Heisenberg has laid a big quan- tum egg.[9] In Göttingen they believe it (I don’t). Eddington has done a very nice investigation of Planck’s law and improved my derivation of 1917.[10] My work from last summer is useless.[11] I now have an interesting idea about the theory of electricity, but I don’t know whether it will lead to useful solutions. Warm regards to all of you, your Einstein 115. From Max Planck Berlin NW 7, Unter den Linden 38, 20 November 1925 Dear Colleague, Yesterday, we deliberated in the secretary’s office about the Academy’s congrat- ulatory remarks for the Lorentz anniversary celebration, and it was decided that, since this is a 50-year doctoral anniversary, a written address is the most dignified form.[1] You will therefore soon be asked by the presiding secretary, Mr. Roethe, to write and submit such an address (possibly to be read).[2] Perhaps that would also be more comfortable for you than an oral speech. With regard to the form and the scope of the address, you might possibly refer to the one that our colleague Rubens wrote for the 50-year doctoral anniversary of Warburg: it is in our meeting reports for the year 1917, page 269.[3] If you like, you can certainly show me the draft at the next colloquium.[4] In any case, I think that it will make a good impression if, at the big anniversary celebra- tion, the Berlin Academy will also present its congratulations in a dignified form. With kind regards, your Planck