2 5 0 D O C U M E N T 2 4 1 A P R I L 1 9 2 6 and s2 toward each other, this disturbing influence caused by the velocity v of the canal rays will be removed (by the differing path differences). The tilt angle ß of both mirrors needed for this is determined by the equation . This tilt angle would probably be determinable because it would result as the dif- ference, if one adjusts to the clearest interference, first with a light source at rest, then with canal rays.[16] In applying the wave theory to this experiment, it is essential that light that is capable of interference be emitted by a particle at different times in different loca- tions this notion is particularly challenging for quantum theory. According to your findings, the performance of this experiment should come easily to you. However, no optically vaguely defined body may be present between the canal ray and the interference apparatus, of course. Kind regards, your A. Einstein P.S. I am, naturally, glad to provide you with further information. I would be very pleased if clear results emerged from this. 241. From Eduard Einstein Zurich, 1 April [1926][1] Dear Papa, It’s been quite a long while since the last time I wrote you. But that’s not my fault, because I have an excuse: Mama forgot to give me your letter.[2] (Yes, you don’t need to laugh so incredulously, even though it is April 1st!) I’m glad that you liked my verses.[3] That is, to be precise, I don’t, of course, know whether you liked them, since as a kindly father you obviously could only compliment me about them. But I want to assume that you enjoyed them and send you herewith two short poems that I have written since.[4] Another thing I wrote is a street-ballad[5] which is composed of 145 double-line verses. (Match that!)[6] It was received with rapturous applause during an evening out with the class, when I read it out. By the way, you needn’t think (I can imagine you thinking this) that I sit around all day churning out verses. It’s simply so phenomenally easy for me that I can dash down the longest “poetic works” within a matter of minutes. You proposed in your letter in a side remark that I write about myself, about what gives me pleasure and what bothers me.[7] I’ll separate this difficult task into 3 subdivisions: (1) I myself, (2) What gives me pleasure, and (3) What bothers me. β v c -- bΔ aF -- - --- ⋅ =