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
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
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
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
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
To my great joy I hear that you want to visit Mama
How very happy
Mama is about it cannot be put into words, but you yourself will know exactly how
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