D O C . 7 5 J U L Y 1 9 1 9 6 3 World]) that you are also of this view (p. 26, bottom).[9] In any event, I would have liked to clarify this opinion in a discussion with you. This way of considering the relativity of inertia will perhaps seem very primitive to you, which it undoubtedly is. But it was only thus that I could attach my sense of Mach’s considerations, in which he showed inertia as possibly determined by the presence of the other bodies.[10] I would like to ask you please to send me a reprint of your papers on this subject![11] Another problem I would like to have elucidated regards the closure of the world, in which the λ-term serves in the field equations.[12] It is true, isn’t it, that your reason for it is that in this way you do not need any boundary conditions, which would otherwise come out noninvariant! In his book Weyl rejects this but, as I believe, not justifiably, for in his consideration he also needs a boundary condi- tion, albeit not infinitely far away: he is thinking of an initial condition.[13] Howev- er, I do not understand the other reason that Weyl provides for the closure of the world: that otherwise the entirety of the fixed stars would have long since scattered apart.[14] Why should one believe that? Are the velocities so large that the stars could fly outside of the region of attraction? And Weyl’s postulation that a uniform distribution of stars at rest within a static gravitational field, as an ideal state of equilibrium, should be compatible with the laws of gravitation (p. 223) I absolutely do not understand. I do not find these reasons convincing enough.—And the λ-term really is not aesthetically pleasing! No less the mode by which it should emerge from Hamilton’s principle. One really should not use it without compelling need! Weyl’s book afforded me much pleasure, also by his subjective statements. His way of indicating geodetic differentiation with curly brackets is not as simple as it can be. I was enormously pleased that last year I saw how simple the situation is there. I sent you the paper on the compass bodies.[15] It was interesting, though, that Weyl was at the same time publishing his paper at the Berlin Academy on gravita- tion and electricity, where he “transplants” “vector spaces” in such a way as to in- clude the compass body’s geodetic displacement (= vector space) as a special case.[16] I found Weyl’s idea in this paper magnificent. You objected that the constancy of spectra would be improbable if the atoms’ diverse experiences were to alter their measurements, even the temporal measurement of their periods of vibration.[17] When I read that, the following occurred to me. The charges do not change conse- quently, Bohr’s restricted electron orbits also do not change, at least if the electrons are fresh ones not spoiled by migration.—But do you really believe that the nega- tive result of St. John’s measurements of solar spectrum lines could not be ex- plained by compensating the gravitational shift with Weyl’s electric one, arising
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