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208. From Heike Kamerlingh Onnes
Leyden, Huize ter Wetering Haagweg, 23 November 1920
Dear Colleague and Friend,
Most cordial thanks, also in my wife’s name, for your kind letter, as well as to
your esteemed wife for the kind letter to my wife. I must now restrict myself to a
single word of friendship, because I just received from our coll. Trowbridge the fol-
lowing invitation for you, which I believe is best dispatched via registered express
mail.[1]
I am very willing, of course, to telegraph the reply to our coll. Trowbridge, as
telegraphing from Germany is perhaps not so secure either, and Trowbridge turned
to me for this reason as well. But perhaps just because he suspected that you were
here and your address is in any case known to be over here with me. At any rate,
by choosing me as spokesman, he has done me a great favor.
Very warm greetings. I want to get this letter out into the post as quickly as pos-
sible. Cordially and sincerely yours,
H. Kamerlingh Onnes
209. To Paul Ehrenfest
[Berlin,] 26 November 1920
Dear Ehrenfest,
You are a man of sterling worth and you are right. I asked for 15,000 dollars each
from the Universities of Princeton and
Wisconsin.[1]
That will probably scare them
off, so I will be able to stay contentedly at home. If they do bite into the big sour
apple, I actually will buy myself economic freedom, which is nothing to scoff at.
I really do believe that the Hall effect works like that and am happy that you
agree.
Either the field is gradually compensated by eddy currents in such a way that the
electromotive force in the whole superconductor can be derived from a potential,
or the Hall force generates currents that grow until the respective local supercon-
ductivity is destroyed. Experiments speak for the first
possibility.[2]
Experiment:
Gradual shielding off a magnetic field permeating a current-carrying plate. Process
could be done as slowly as you like, in accordance with the chosen current intensi-
ty. I hope Kamerlingh Onnes does these experiments.
I am going to decline the invitation sent by Kamerlingh
Onnes,[3]
for the time
being, in consideration of the pending negotiations with the two universities.
What’s the news on your America plans? It really would be nice if all three of us
could set off together. I don’t know yet whether I would take my wife along. Prob-
ably nothing will come of the matter at all.