D O C . 5 9 J U N E 1 9 1 9 4 9 Weyl wants to come here during the last week of July—at the invitation of the Wolfskehl Foundation. Perhaps your path will lead you just then through Göttin- gen. Weyl wishes to talk about his ideas regarding gravitation and electricity.[5] With cordial regards, yours, Hilbert. 59. To David Hilbert Berlin, 11 June 1919 Dear Colleague, I myself do not know whether I have hit upon the right thing with this notice.[1] It refers to the hypothesis of a cosmic pressure (already taken similarly into consid- eration by Poincaré, in order to make the electron comprehensible), which is elim- inated only with my approach.[2] The equation (4a) is correctly formed. If one writes (1a) in the form then upon calculating the divergence (in the sense of gen. cov[ariant] theory), the left-hand side disappears identically the first term on the right-hand side yields the second, apart from the factor :[3] or or . From this (4a) follows immediately. I have to lecture all of July in Zurich (second half of a course on 〈general〉 rela- tivity), thus unfortunately will not be able to be in G[öttingen].[4] As a series of ideas, I admire Weyl’s theory very much.[5] But I do not think that it draws reality closer. It seems to me unfounded to abandon the natural meaning of ds, considering that one is forced to put the field equations as equations of the fourth order.[6] In doing so, the summation from independent summands remains in the Hamiltonian function. With cordial regards, yours, A. Einstein. Rik 1 2 --gikR - – 1 - ,–=Rikg--4ikTκ –κ ϕσαJα g, ⋅ 4 -- -–1 ∂ ∂xα --------( δi α R –g) ⋅ 1∂gik 2 -----------( - ∂xα - gikR –g), – ∂R –g ∂xα ----------------- R------------- ∂ –g ∂xα – –g ∂R ∂xα --------