6 6 D O C S . 7 8 , 7 9 J U L Y 1 9 1 9 diameter. If K quite correctly sees the measuring unit of as shortened, then why not also the “moving” edge? It would be quite a different situation, of course, if measured the edge of the disk at rest in K. Then, seen from K, it would obtain a value larger than π. A measurement within system , however, can only result in π, since edge and measuring rod, judged from K, do shorten equally, but for there is absolutely no change. The wording at this place in your paper does not nec- essarily contradict the interpretation presented here, as I just saw from a rereading, but as Weyl (p. 175), Bloch (p. 96), and Schlick (p. 45) show, misinterpretation is easily possible.[4] For the clocks, obviously, the same applies: the observer in the primed system does not notice any lag and “obvious” in your popular account (p. 54, last line) re- fers to the observer in the unprimed system.[5] I would be very grateful if you would inform me of your view and possibly show me where my error lies. Your theory of gravitation is wonderful. Although lacking the mathematical knowledge to delve into its details, I do think that it is completely clear to me in principle. Epistemologically, I did not come across the slightest obstacle. Naturally, I am waiting with bated breath for the result of the English expeditions.[6] Allow me to take this opportunity to express my most cordial thanks for your kind, warm intercession on my behalf in Dresden, about which Prof. Helm wrote me.[7] With most obliging regards, very truly yours, J. Petzoldt. 78. To Adriaan D. Fokker 30 July [1919] [Not selected for translation.] 79. To Auguste Hochberger Lucerne, Rosenau Sanatorium, 30 July [1919][1] Dear Guste,[2] To my great joy I hear that you want to visit Mama here.[3] How very happy Mama is about it cannot be put into words, but you yourself will know exactly how K′ K′ K′ K′
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