D O C U M E N T 1 2 4 D E C E M B E R 1 9 2 5 1 4 5 fact that a quantum’s momentum is proportional to its energy, a molecule’s momen- tum is the square root of its energy.)— I am terribly sorry that the article I am sending you now is chock-full of boring calculations. But I do think that all the error assessments really are indispensable.[8] This stuff looks so long-winded only in writing, you know in reality it is all ex- tremely simple. I thank you, dear professor, again very much for you generous interest, cordially and sincerely yours,[9] E. Schrödinger 124. To Elsa Einstein [Leyden,] Monday [7 December 1925][1] Dear Else, My letter was not furious at all. By contrast, your letter cost 20 cents postage due and, besides that, the goose cracklings arrived in totally torn-up packaging. Despite that and despite Ehrenfest’s[2] medical warning, I gobbled it down, right away, in fact. I immediately sent the receipt and power of attorney to the respective places and, also, I have already finished writing the obituary for Prof. Julius.[3] I won’t ar- rive until a week from Wednesday in the morning, since I still have to be at a meet- ing Tuesday afternoon in Haarlem.[4] Friday is the famous jubilee celebration.[5] I received a letter from Planck indicating that Röthe protested against my speech be- cause of the warm tone.[6] I’m glad I sent Planck the thing first, so he, poor fellow, had to fight the thing out in the buffalo herd. Now, they’re going to send me another speech for Lorentz—I couldn’t care less. Have Ilse get the injections—perhaps it will help.[7] Yesterday, I was at the De Haas’s,[8] who were very pleased with the little book. I’m working quite a bit, but not terribly much, so the stay is doing me a lot of good. It is dreadfully cold.[9] Ta- nia is more cheerful than before Gallia, somewhat ill.[10] I feel sorry for Auntie I dare say that the patient is difficult.[11] The beginning and the end of life are damned difficult, and in between things don’t always run smoothly but everything passes and is quickly forgotten. Best regards to you and the old and young from your Albert