6 0 D O C U M E N T 4 5 S E P T E M B E R 1 9 2 7 shadows, and only a kind of union of the two should maintain its independence” (Minkowski).[7] The world of physical events is a “four-dimensional continuum” in the theory of general relativity. It has a “non-Euclidean structure,” i.e., Euclidean geometry, built on principles or “axioms” known from school, is not valid. For its description we use the so-called Gaussian coordinate systems, which one can con- sider to be derived from the Cartesian system described above in such a way that the flat, mutually perpendicular coordinate planes have become arbitrarily curved surfaces. The principle of general relativity can now finally be stated as follows: All Gaussian coordinate systems are in principle equivalent for the formulation of the laws of nature.[8] Summarized concisely, the progress that was made possible by the theory of general relativity lies in the fact that it yields a general theory of gravitation, and that it has demonstrated that, and the extent to which, geometry, i.e., the metric be- havior of solid bodies and clocks, is dependent on physical causes. Therefore it has unified geometry and physics. Prof. Dr. Albert Einstein[9] 45. To Nathan Straus[1] [Berlin,] 7 September 1927 Dear Mr. Nathan Straus,[2] I am very pleased that you have also come to the conviction that a change in the leadership of the University of Jerusalem is urgently necessary.[3] In the interim I have received further worrisome communications that have convinced me even more of the intolerability of the current situation.[4] A session of the academic council will be held here in October, at which I will present this view with great determination.[5] You would be doing the cause a great service if you would con- tribute your view that also in America a clear insight into the existing situation would be gained. In particular, it would be important to enlighten Mr. F. Warburg and the leading people in the medical association.[6] The latter is all the more nec- essary because the leadership of Hadassah, which is completely under American influence, gives rise to serious complaints.[7] They even caused the only truly capable researcher there, a certain Dr. Felix, who could have been invaluable for the university, to leave Palestine.[8] If it is not still possible to make a radical change in the leadership of the university this year, I will consider myself forced to with- draw from the board of trustees and the academic council. I will also not hesitate to [---] these steps in the Jew[ish] [---] Kind regards,[9]