1 6 2 D O C . 1 8 9 D E C E M B E R 1 9 1 9 Thereupon, a long period of debate: How far does this generalization go? Only at the end of 1915: requirement of general covariance leads to Newton, agrees with the energy-momentum law, and furnishes the perihelion motion of Mercury (is any- way the simplest, considering the impossibility of maintaining the Euclidean metric). 1917: emergence of the possibility that the metric field is entirely deter- mined by matter (cosmological problem). Obviously, one does not need to retrace the step of 1917. But then the mean den- sity of matter must be assumed as vanishingly small, which seems horrible to me. – I am very happy about the prospect you are opening for me regarding my cometary existence at Leyden. If something should come of it, I certainly shall accept. If not, though, i.e., if it cannot be done on your side, I shall be mindful that we meet more often than previously. Writing about Julius’s theory does not come easily to me because I do not have a secure grip on this vast subject. It’s an audacity on my part to meddle into it. Lorentz’s lectures are magnificent. Have they appeared in German as well? I ought to know that too. In the Zionist affair you surely can be useful without having to go on trips, for ex., by discussing things with Ornstein. I think that polytechnic and university should not be separated. Carathéodory, who is also occupied with the problem of an exotic university (Saloniki), put this idea into my head. We shall procure the musical instruments as soon as we can, when we find something at a truly worthwhile price for you. Should the violin for Galinka also be a 4/4 (full-size) violin? I would not advise that you get a smaller one. You can just owe me the money in marks which you can keep there for now. In a paper by Pauli (Phys. Zeitschr.) on Weyl’s theory the consequence of the primary deficiency of this theory is already revealed (in general, nonexistence of static solutions with nonvanishing electric potentials). It is incomprehensible to me how Weyl himself and all the others do not immediately feel the counterempirical quality of the theory’s underlying idea. I feel terribly sorry for Planck. The message about the Nobel Prize just happened to arrive with the message about the fatal illness of his second daughter. Now, of the four children from his first marriage, only one is left. The two daughters were splendid persons and all of them completely healthy. Anti-Semitism is strong here and political reaction is violent, at least among the “intelligentsia.” I noticed it particularly in Rostock. Where is all of this supposed to lead? They have not grasped the situation (do or die) and aren’t going to grasp it. My mother isn’t here yet, but is coming very soon the accommodation problems haven’t quite been overcome yet. It’s going to be a terribly exhausting affair for my wife. Debye is going to Zurich—so I gather, at least, from a friend over there. Scientifically, no news. I am so busy with all sorts of minutiae that I never get around to reflection.