D O C S . 2 7 4 , 2 7 5 S E P T E M B E R – O C T O B E R 1 9 2 8 2 7 1 P.S. There is a strange electromagnetic paradox A charged metal disk, free to rotate, suspended in a variable magnetic field. If the field is varied while the charge on the disk re- mains constant, then a torque appears owing to the in- duced electric field (circular). If, however, the charge is varied while the field remains constant, then no torque is produced. If one allows the field and the charge to change in the same sense, so that and the charge retain the same phase, then there are angular momenta of the same sign. Can that indeed be true? My instinct bridles at the thought. It could be tested with a solenoid. 274. To Erwin Madelung[1] [Scharbeutz, 29 September 1928][2] … As I was recently discussing some problems of relativity theory with Mr. Lanczos,[3] I got the impression that our working together in the coming years could be very productive. Thus, I am now directing the request to you that you give Mr. Lanczos the opportunity to have a year’s leave from Frankfurt so that he can spend that time here in Berlin… I heard with great interest from Mr. L. about your electrostatic potential sniffer,[4] a very ingenious idea, which I will naturally keep confidential… 275. From Cornel Lanczos Frankfurt am Main, 1 October 1928 Dear Professor, I will of course accept your kind offer with great pleasure.[1] As to my leave of absence here, I have already spoken to Madelung, and then the two of us discussed it with the dean of the faculty (Hellinger).[2] Madelung has treated the matter from a very generous standpoint. He emphasized over and over that the decision should be based solely on my personal interests (which in this case are not at all problem- atic), and all the other interests, of the university, the institute, etc. should be quite indifferent.[3] Granting me a leave of absence as lecturer is a purely formal matter. dh dt