D O C U M E N T 2 4 8 A P R I L 1 9 2 6 2 6 3 Piggishly (!!!!) formulated, I believe that one can describe SOME THINGS about the polarization of light from the hypothesis that “every corpuscle of light in the world carries an angular momentum h/2π, where the axis of the momentum can still tilt variously against the direction of propagation—from linear up to circular polarized light.”— Is it possible to assign a relativistically stable meaning to this statement— REGARDLESS of whether one must reject it directly for other reasons?[6] III. For a homogeneous system of waves that is emitted by a moving atom, one can speak unambiguously of a “color at rest,” by referring to a system in which the emitting atom is resting and hence where the waves are concentric spheres.— For corpuscles of light, on the contrary, nothing of the like succeeds.— And for two corpuscles of light whose world lines are not exactly parallel, it cannot be as- serted anymore which of the two is an X-ray corpuscle and which is infrared. Nor how direly they are that. I find this to be a strange difference.— My question: Did I make any mistake? Does this strange difference between the wave and corpuscle theories of light really exist with respect to relativity theory?[7] — Oh yes, isn’t there in principle a crucial experiment that can decide on this point between the wave and corpuscle theories?— naturally, only in the domain of spherical waves, not in that of plane waves. IV. A man by the name of Lanzcos has lately been publishing a lot in the Zeitschrift für Physik.[8] Do you understand what he is after? And well, yes, can you tell me very briefly whether it’s CHILDISH or whether it has substance?— Reply succinctly to this question. V. Perhaps I shall have to be in Russia on the Volga in June, or maybe not.— I have left the final decision in Joffe’s hands.[9] — If not, then I would like to go to Göttingen in June for about two weeks and, if possible, see you for a little bit as well somewhere in Germany.— You know that in June, lectures in Leyden will have ceased, but not the laboratory sessions and the colloquium.— The question is: Would you be prepared to come to Leyden sometime before the end of May or after July 1, or would you, for God’s sake, like to be left in peace this spring?[10] — You do know how happy all of us here are to have you here with us for two weeks.— On the other hand, though, you also know how well we understand how much you would like to be left in peace for just a little while.— What is absolutely of the utmost importance to us is that you think of Leyden sympathetically and that it doesn’t torment you. NNNNNNNNNNNNNN My wife[11] is very happy in Moscow I am just afraid that she will become com- pletely exhausted. She has to live with (extraordinarily dear and interesting)