D O C U M E N T 9 7 D E C E M B E R 1 9 2 7 1 1 3 verifiable through a pure “inner vision,” and is therefore necessary for us as the ba- sis of all physics, is convincingly rebutted in this manner. For the initiated, such a demonstration may no longer be necessary, but it is certainly useful for those who are still learning. The next two sections, dedicated to the concept of time (pp. 130–242), treat in depth but in readily readable form the author’s axiomatics of the special theory of relativity. Here, particular emphasis is placed upon clearly sorting out what is a log- ically arbitrary determination in the relativistic definition of simultaneity, and what is hypothetical, that is, suppositions about the character of nature. Furthermore, in the analysis of the concept of time, the author pays particular attention to the ques- tion of how far one can go without introducing the concept of the rigid body.[7] This is followed by a section on “space-time manifolds permeated by gravita- tion,” a clear analysis of the premises of the general theory of relativity. In this sec- tion, there is also an investigation of the question as to what extent the dimensionality is something objective, that is founded in nature. The answer given does not, however, earn my undivided applause. But it is certainly meritorious to have seriously taken up this important question at all.[8] In an appendix, the fundamentals of the Weyl-Eddington theory are then de- scribed in clear terms, and especially the sensitive question of the correspondence of these theories to reality is dealt with.[9] In this chapter, as well as in the preceding ones, the groundlessness of the thesis is asserted—in my opinion quite rightly— according to which the theory of relativity is an attempt to reduce physics to geometry.[10] Berlin Albert Einstein 97. From Paul Ehrenfest Leiden, 2 December 1927 Dear Einstein, From the enclosed letter that I wrote to Mrs. Curie[1] you will immediately see what is at issue in the report, also enclosed, of the Aid Committee for Russian scholars and writers in Germany.[2] Please pardon the fact that the copy is a little hard to read. I sent the much more legible original to Mrs. Curie and also gave a copy to Lorentz.[3] I hope very much that BY DIVIDING INTO PARTS your com- mittee will be able to do many things. My correspondent, the philosopher S. Frank[4] (Berlin-Halensee, Joachim Frie- drichstr. 48) is a man whom I have known very well for about twenty years and es- teem VERY highly, particularly because of his unusually independent behavior in