426
DOCUMENT 320
APRIL 1917
ALS
(GyGöU,
Cod. Ms.
F.
Klein
22B
:
Einstein,
1).
[14 421].
At
the
head of
the
document the
reci-
pient
has written: “Einstein
an
Klein. Herrn Baade und Fredericks
zu
fr.
Kenntnisnahme und Rück-
gabe am
Sonnabend. K.”
Wilhelm
Heinrich
Walter
Baade (1893-1960)
was a
student at the Univer-
sity
of
Göttingen
and
an
Assistent
of
Klein.
Vsevolod
Konstantinovich
Fréedericksz
(1885-1945),
a
Russian
physicist,
worked
as
Hilbert’s
private
assistant.
[1]After
reading
Einstein
1917b
(Vol.
6,
Doc.
43),
Klein had drawn Einstein’s attention to his
own
investigations
from 1871
on
non-Euclidean
geometry (Klein,
F.
1871) and,
in
particular,
to the fact
that besides
spherical geometry
there is another
geometry
with constant
positive
curvature,
namely
elliptic geometry
(see Klein, F. 1918b,
p.
405).
The
latter is obtained
from the
former
through
the
identification
of
antipodal
points
(for
a
brief
discussion,
with references to Klein’s
work,
see
Pauli
1921,
sec. 18).
It
turns
out, however,
that Klein made this
suggestion
not
for
the
space
of
constant
curvature
in Einstein’s
cosmological
model but for the
space-time
of
constant curvature in De Sitter’s
alternative model
(see
Doc.
552,
note
3,
for
more on
this
conflation).
The
papers
that Klein
sent,
most
likely,
included Klein,
F.
1871 and Klein,
F.
1890
(which
is referred to
in
Klein, F. 1918b,
p. 406).
[2]The paper
is Einstein
1917b
(Vol.
6,
Doc.
43),
in
which Einstein
considers
a
spatially
closed
spherical
universe.
[3]To
which Einstein responded in Doc. 300.
Erwin
Freundlich had
been
Klein’s doctoral student
in
Göttingen,
completing
a
dissertation in 1910
on
functional
analysis.
[4]An
allusion to
Willem
de Sitter’s
position (see,
for
instance,
Doc.
313;
for
further
discussion,
see
the editorial note “The
Einstein-De
Sitter-Weyl-Klein Debate,”
pp.
351-357).
[5]See Hilbert
1917.
[6]See
Droste 1916b. Johannes Droste’s
(independent)
derivation
of
the Schwarzschild solution
was
earlier
published
in
Droste
1916a.
[7]See
Lorentz 1915c, 1916b, 1916c, 1916d, 1917a,
and Doc.
315,
which refers
to
results that
were
published
in
Lorentz
and
Droste
1917a,
1917b
(see
Kox 1992
for
a
review
of
Dutch work in
general
relativity
in the
years
1915-1920). The next
year,
Klein
critically
reviewed
the
pertinent
literature
(including
the
papers by
the
Leyden group)
in
Klein, F.
1918a and 1918b.
320.
To
Moritz
Schlick
[Berlin,] Sonntag.
[1
April 1917]
Lieber Herr
Kollege!
Ich danke Ihnen bestens für die freundliche
Zusendung
der
Separate.[1]
Ihre
vor-
treffliche Arbeit
hat
schon manchem das Verständnis der Theorie
vermittelt,
wie
ich mich
überzeugt
habe. Mit der
von
Ihnen
geplanten
kleinen
Aenderung
bin ich
einverstanden.[2] Es wird mich sehr
freuen,
wenn
Sie mich
wieder
einmal aufsu-
chen. Dann
können
wir
uns
auch
über
die
Frage
der Konstitution des Raumes
un-
terhalten.
Ich
empfehle
Ihnen
meinen
alten
Bekannten
Hopf,
einen
tüchtigen Phy-
siker,
der auch in
Adlershof
physikalisch beschäftigt ist.[3]
Es
grusst
Sie bestens
Ihr
A. Einstein.
AKSX
(NeHR,
Vienna Circle
Archive). [73 775].
The
verso
is addressed “Herrn Dr. M. Schlick
Phys.
Abt. d.
Kgl.
Flugzeugmeisterei
Moltkestr
18 Adlershof,”
and
postmarked
“Berlin-Wilmersdorf
1
1.4.17.
6-7N[achmittags].”
[1]Reprints of
Schlick 1917a.