D O C U M E N T S 4 3 , 4 4 F E B R U A R Y 1 9 2 1 3 7
less well known and in part still fragmentary nonrelativistic research (or consider-
ations). But you are totally free. People will be coming then from Utrecht and
Amsterdam as well as from Delft.
Warm greetings to all of you and don’t forget us completely.—Yours,
P. Ehrenfest.
How’s your
health?[8]
I’m racking my brains about a halfway rational dispersion theory of the Bohr
atom—but it’s not working out.
Do we have to take care of your Dutch visa again or is it automatic now?
43. From Max M. Warburg[1]
Hamburg, 8 February 1921
Dear Professor,
I do not want to neglect to inform you that I received a telegram today from my
brother
Paul[2]
in which he briefly informs me that an arrangement in the amount
you
wish[3]
is not possible at the moment. He will write me more, no doubt. But I
just wanted to let you know right away about the telegram.
With friendly greetings,
also[4]
for your esteemed wife, entirely yours,
Max M. Warburg.
44. From Friedrich Carl von Siemens[1]
Berlin NW6, 15 Schiffbauerdamm, 10 February 1921
Highly esteemed Professor,
I ask Your Honor please to allow me to take a stand on the criticism of my paper,
“In the Era of
Coal”[2]
[Im Zeitalter der Kohle], recently expressed in Alexander
Moszkowski’s interesting book, Einstein, Insights into His World of Ideas
[Einstein, Einblicke in seine Gedankenwelt]. If it were merely a matter of justifying
my personal view, I would not write these lines, despite the understandable wish
not to be unfairly judged by you in particular, but would respect the shield that Mr.
Moszkowski holds over your head in the introduction to his
book.[3]
There is, how-
ever, a more serious reason for making an attempt at eliminating any misunder-
standings regarding my guiding principles about coal; specifically, it is that a
correct and possibly far-reaching assessment of coal for present and future German
economic activities is of such great necessity that any weakening of its significance
can only be detrimental to our fatherland.