D O C U M E N T 2 3 1 D E C E M B E R 1 9 2 0 3 3 1
First, as far as the publication of papers by me on the relativity problem is con-
cerned, a collection of the more important ones already exists that appeared with
Teubner in German, which I am having forwarded to you at the same
time.[2]
Of
course I have no objection to a translation by you and Dr.
Perett.[3]
Might it not
seem appropriate to you to translate the papers by Lorentz and Minkowski as well?
As regards the finances, I would be satisfied if I received one shilling per copy.
Your offer to lend journals to me and send them to me regularly demonstrates a
sense of good will rarely encountered in this
world.[4]
I warmly shake your hand
for it. However, I am not in a position to make use of your great kindness because
I am anyway not in a position to study so many papers myself; I learn about most
of them from oral reports at our
colloquium,[5]
during which the papers by English
physicists are frequently and thoroughly discussed. Recently, the papers by Aston,
especially, found enthusiastic reception among
us.[6]
In thanking you heartily again for your kind letter, I am with amicable regards,
yours,
231. From Erwin Freundlich
[Potsdam,] 14 December 1920
Dear Einstein,
Below are the requested densities: the formula for the spatial density in star
clusters is set in the following
manner:[1]
the corresponding apparent density projected
onto a plane is:
& a are constants; = number of stars per unit area in the center of the cluster.
The total number of stars
; a thus means the radius of the corresponding homogeneous
cluster with the same total number of stars and a mean density equal to the central
density in the real star cluster.
According to this formula the drop in density in the Messier 3 cluster (N[ew]
G[eneral] C[atalogue] 5272) for a count of all the stars up to a limiting size class,
without taking types into
consideration:[2]
r
3
4
-- -
N
a
--- -
1
r2
a2
-----
+
2 –5
= =
f r N 1
r2
a2
---- -+
2–
=
N N
a2
=