2 7 2 D O C U M E N T 2 7 6 O C T O B E R 1 9 2 8 Granting me leave as assistant will also not pose any problems, given the generally positive attitude of the entire faculty toward me, and the corresponding means for arranging it will certainly be found. The only point that has not yet been settled is the date of my departure here— but I can safely assume that this question is only a detail. As assistant for the teach- ing laboratory, I cannot leave my position here on short notice since I have to in- troduce my successor or substitute to the duties there. Now Madelung himself will have to look around for a substitute, and that will no doubt require a certain amount of time. And I will have to wait for the next faculty meeting, at least. So I don’t believe that I can depart before November 1—perhaps even another week will be necessary. However, I hope that we can readily come to an agreement on this ques- tion by correspondence. Since there would seem to be no factual obstacles in any direction, I look for- ward to my immediate future with pleasure, and can only hope that you have not overestimated my talents. With best regards, yours sincerely, Lanczos 276. From Max von Laue Zehlendorf, 1 October 1928 Dear Einstein, Hearty thanks for your kind letter of 29 September.[1] Insofar as Lanczos[2] agrees to your plan and can get himself released from Frankfurt, I see no difficulties that would present a serious obstacle. We can certainly arrange the necessary salary here. Now to your paradox. As you have drawn the setup, every change in the charge would require radial currents in the disk, and these, together with the magnetic field perpendicular to the disk, produce a torque. Then the reciprocal process seems to me to be that a rotation of the disk produces radial induction currents within its plane. Your induction of ring currents in the disk at rest owing to a variation in the magnetic field strength is, in my opinion, not in any such reciprocal relationship to the process of charging. Finally another question, which you should not take amiss. It is hardly possible to keep all the reprints that one receives. Now I still have here a few reprints of my three articles in Wien’s handbook[3] (“The Optics of Moving Bodies,” “Reflection and Refraction,” “Interference and Diffraction”).[4] Would you like me to send you one? With warm regards and best wishes for your health, your M. Laue
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