2 7 2 D O C U M E N T 2 5 7 A P R I L 1 9 2 6 It also seems to me that the equation should have a structure in which the inte- gration constant of the energy does not occur. This indeed is the case in the equation set up by me (without my therefore wanting to grant it any physical meaning, since I haven’t sufficiently reflected upon it). Kind regards, your A. Einstein The idea behind your paper is evidence of true ingenuity![2] 257. To Eduard Einstein [Berlin,] 17 April 1926 Dear Tete, I very much enjoyed your witty little letter.[1] Reading it, I really felt like a hen that has hatched a duck egg. I particularly liked your self-analysis because it is so honest in its vacillations and comical at the same time. Although one must strive to become a proper fellow, one must not take oneself too seriously. For one is a critter that barely became two-legged via the ape, a short-lived snippet of consciousness heavily burdened with atavistic instincts, which preserve life. Consequently, we must all be quite modest, if we do not wish to deceive ourselves and our fellow creatures, which does not happen with the better ones. I’m very much looking forward to the summer.[2] Inquire about a spot high up, where it is not too overrun with snooty foreigners (Engstlenalp?). We will not be able to go up there until the end of July because the meetings in Geneva are before that.[3] But you can come there with me so we can be together as much as possible. I’m not saying anything about Albert because he really must study like crazy.[4] Then, he intends to try his wings. He just needs to learn Spanish if he wants to go to South America [5] that is an absolute necessity. I have some connections there and hope to be able to arrange something for him there after he has learned Spanish. I am working very hard and accomplish little. I am actually glad that neither of you is going into science because it is difficult, full of futile hard work. And yet, I am, so to speak, among those favored by destiny! Tell Mama that she should not be down in the mouth.[6] I was also pleased that the business with the mortgage still has a long time to go.[7] I forwarded your letter to Kerr, because he will certainly be amused about the effect of his books [8] I know him very well. He mostly writes theater criticism for the Tageblatt, writes some- what bizarrely, but understands a great deal about it. Warm regards from your Papa