D O C U M E N T 9 9 A U G U S T 1 9 2 0 2 2 9
You ask for information about the damage to the
—well, the repairs are
not at all major but are not yet completed at the moment because the man wanted
to deal with the drying of the varnish first.—The repair costs won’t be high enough
to warrant demanding compensation.—Ugh—how boring this is!
and I are arranging everything so that (1) you get a visa valid
for the whole
(2) that your talk can take place on October 6th or
(you’ll get a report from me about that in a few days).
Your chair received 3 em-
inently capable men as Trustees, (1) Coebergh—a reputable Leyden notary; (2)
Pateijn—a very big fish from the Foreign Ministry; (3) Zeeman, the

In other words, Mr. Einstein can be counted on to be a man upon whom even
people can depend not to mess around. I hope you won’t prove
yourself unworthy of “this bourgeois trust placed in you”! (Otherwise many a per-
son dear to you will be directly hit!)—It’s like marrying a countess.—We, however,
are the mothers-in-law.
Langevin is surely certain to come. Weiss, hopefully,
Your theoretical
optimism regarding the treatment of paramagnetism surprises
netism of gases, yes, fine. But paramagnetism of solids?!—Treating them as gases
is surely nonsense.—It really is hard to believe that the “molecular magnets” [Ele-
mentarmagneten] can rotate force-free within a crystal (like molecules in a gas). So
one would first have to explain
why molecular magnets whose orientations are held by strong forces within a crys-
tal lattice can nevertheless obey CurieÊs law: [12] [gadolinium
sulfate follows this law very exactly up to
So the mystery is: If molecular magnets are fixed in orientation by very firm crys-
tal forces, then where does the great
of a crystal powder at T 0
(for freely rotating magnets, simply conceived) come from?
Weiss published (C. R. 1913) something incorrect on
I see only the two following possibilities toward solving the puzzle:
Assumption A. Each molecular magnet can assume two opposite orientations
within the crystal with equal ease (pot. energy of = potent. energy of ) all
divergent ones , ), with much difficulty (large potential energy).
If one calculates (for crystal powder or a crystalline aggregate) the susceptibility in
a magnetic field one thus obtains exactly LangevinÊs
(Very similar to
the derivation of the formula for osmot.
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