D O C U M E N T 4 3 7 D E C E M B E R 1 9 2 6 4 1 5 437. To George E. Hale [Berlin,] 25 December 1926 Dear Mr. Hale, If only it were true that I had a theory of the terrestrial magnetic field![1] Al- though a couple of years ago I did brood over such an egg, nothing living hatched out of it. The original thought was this:[2] There is a dimensional equation, in symbols, This dimensional relation suggested to me that the ponderable mass had electro- magnetic functions of some kind, and that the ponderable mass m somehow be- haved like the electrostatic one . If, for example, one considers that this action were such that a rotating ponderable body produced a magnetic ¢electric² effect like a corresponding rotating charge density (of negative sign), then one gets the mag- netic terrestrial field in the right order of magnitude.[3] This way there also results, in order of magnitude, the ratio of the solar field to the terrestrial field. Finally, this additionally “explains,” in an argumentation made up in a kind of delirium, that the solar-spot vortices produce the strong magnetic field established by you. I tried very hard, of course, to set up a theory that puts these fantasies into a log- ical form. But that has not worked for me in any way whatsoever. Experiments that I had thought up in loose connection with this approach also came out negative.[4] So, I did not reach the goal, but I still don’t know whether a very fundamental un- known effect was participating in the field of rotating celestial bodies, after all. In any event, all the attempts at an explanation up to now appear to me to be unten- able, and I am also convinced that the hitherto known laws are incapable of ex- plaining this confounded phenomenon. I am very sorry to have to disappoint you in this way, but “no wretch can give more than he has.” It is very laudable that Mr. Kennedy and also Mr. Millikan are repeating Miller’s experiments with more critical rigor.[5] I was actually quite firmly convinced that, with Miller, temperature influences were involved. Here also (in Europe), very pre- cise experiments have been performed at high altitude of the kind of the Trouton- Nobel experiment, with a negative result.[6] quantity of electrostat. electricity constant of gravitation ponderable mass × = ε m κ = m κ