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188. To Elsa Einstein
[Leyden,] Sunday. [31 October 1920]
Dear Else,
Yesterday I was at the Academy together with Langevin &
evening I was invited by Zeeman while the other two were visiting
Frenchmen are soon leaving and I would do so, too, if I hadn’t rescheduled my talk
in Hannover to the
Now it’ll take a whole week more until I’m finally back
with all of you. In the interim, work is being accomplished and otherwise the living
is nice. I have become frightfully fat. Ehrenfest is suffering somewhat from a stom-
ach problem, a little similar to how it had been with
He couldn’t come along
yesterday to Amsterdam.
Kisses to all of you, yours,
189. From Adriaan D. Fokker
Delft, 2, Rotterdamsche Way, 2 November 1920
Dear Professor,
One always wants to ask you more questions. Now the following problem has
entered my head.
In a Euclidean-Minkowskian space-time ( 1, 1, 1,
a gyroscope is made
to describe a plane circle at a certain velocity. If the rotational axis is not set verti-
cally to the circle’s plane, will the gyroscope exhibit no precession?
According to the Lorentz contraction, the “center of inertia” of the gyroscope
masses do not lie along the axis. This could be a reason for precessions.
This problem occurs to me because it might be able to explain the discrepancy
between Schouten’s calculation and
One would expect, though, that such
a precession would be dependent upon the magnitude of the velocity of rotation
(because at a faster rotation the center of inertia shifts farther away from the axis of
rotation) and this would make the explanation for the discrepancy illusory.
Did you ever worry about this idea? What should one believe?– Tomorrow we
are going to be at Ehrenfest’s around 11 until half past 11 to say
If you
would like to telephone Ehrenfest, he could give me your response.
So you are traveling on Thursday?
Most cordial greetings from both of
and so long! Yours most sincerely,
A. D. Fokker.
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