2 6 8 D O C U M E N T 2 5 3 A P R I L 1 9 2 6 .[5] [Bad comparison in the end. It appears that 3 components of I can be freely cho- sen.] If the thing has the velocity of light, the angular momenta at rest will have to be infinitely small so that the result is finite. Then vanishes as well, so the gist of it doesn’t help explain the displacement of the angular momentum along the magnetic lines of force. I don’t particularly like this contorted thing. I am rather inclined to doubt whether the theorem of angular momentum can be upheld in quantum theory. In any event, its significance is much less profound than the momentum theorem. III. You didn’t make a mistake. One can’t say which of two light quanta is red- der. But with reference to a particular system, every emission has a color of its own, . For the wave field, though, emission has a definite ν only with reference to a suitable system. This is repugnant but I don’t see how possibly to get rid of this meow field, in view of the interference Rupp is supposedly doing an experiment on this. He has probably already done it, but… he doesn’t know.[6] In order to get a clear interference in his experiment, he has to set the mirrors a bit differently (ac- cording to the wave theory) than for a light source at rest.[7] This has its reasons, because interfering wave planes are emitted at different times, hence at different lo- cations, which can be compensated for by adjusting the mirrors. IV. Lanczos is capable,[8] but I haven’t seen anything from him yet that gives me the impression of a true discovery. He certainly is talented technically. V. I don’t know yet whether I am coming to Leyden in spring. Do, at any rate, come and see me if you’re going to Göttingen anyway it’s better than meeting any- where else. The Born-Heisenberg thing is probably not correct, after all.[9] It ap- pears to be impossible to make an unequivocal correspondence between a matrix function and a normal one. After all, a matrix problem should unambiguously cor- respond to a mechanical problem. Schrödinger, by contrast, created a very different kind of highly ingenious theory of quantum states, in which he allows De Broglie waves to play in phase space. These matters are appearing in the Annalen.[10] Not such an infernal machine, but rather a clear idea and—“compelling” in its imple- mentation. Am I coming in July? I hardly think so, because I have to visit my boy in Swit- zerland, where there’s another deadly boring meeting of the L[eague of] N[ations] Committee.[11] Ornstein is in Palestine to supervise the construction of the univ[er- sity]’s physics institute.[12] I’ll have trouble shielding it from the perils of his im- periousness. The installations must be purchased by the man who will be working I12 I12)0 ( 1 v2 – ----------------- -= I34 v I31)0 ( 1 v2 – ----------------- -–= I23 ν E h --- =