DOCS.
243,
244
JULY
1916 239
the
previous occasion,
and
the
same
considerations
are
perhaps
still valid
now as
well. He
may
be
the
most
highly
skilled
operator of
the
instruments,
but
he
surely
remains far behind
Küstner
in
an
overall command
of
these sciences.
Among
the
named, Hertzsprung
is
the
most
original;
he has done
many very
fine
things, yet
always
within
a
limited
area.
I
am
inclined to
doubt
whether he has
a
sufficient
command
of
the
major
problems
of today
to direct
a large
observatory
(which
is
quite
another
matter
than
doing
research
on
one’s
own).
The
same
applies
to
Ludendorff,
whose researches
on
spectroscopic binary
stars[4] I
value
very highly,
incidentally.
Küstner
has
perhaps not
achieved
as
much
as
the
others in
the
area
of
astrophysics:
The Bonn
Observatory’s
limited
equipment
also
forced
him to
specialize,
but
his
determinations
of motion
along
the
line
of
vision[5]
and his
papers
in
photometry,[6]
in addition
to
his
catalog
of
10,000 stars,[7]
are
certainly
research
of
the
highest
order.
That
with such limited
means
he
turned
to
new
methods
at
all,
besides his
extensive,
purely
astronomical
work,
shows
that
he
is
a
man-I
would
say
he
is
the
only
man
in
Germany
now-who
thoroughly grasps
the
major
modern-day problems
and who
can
still
contribute
much,
particularly
in
the
field
of
precision astrophysics, as
well
as
toward
the
fusion
of
astrophysical
and
astronomical
methods-where,
in
my
view,
the future
lies.
As
theoreticians,
none
of the named
are
comparable
to
Schwarzschild,
of
course-as general astronomers, only
Küstner
is
on
the
same
level-as
observers,
Küstner
is undoubtedly
superior
to Schwarzschild
as
well
as
the
others, probably.
Among
the
named,
I just
know
Hertzsprung personally
and
thus
cannot make
a
comparison
of
their
personal qualities.
I
am now
occupied
with
writing
a
small
paper
for
the
Monthly
Notices
of
the
Royal
Astron.
Soc.
(London)
on
the
new
theory of
gravitation
and its
astronom-
ical
consequences.[8]
Your
theory
still
seems
to be almost
entirely
unknown in
England.[9]
If
you
have made
new
discoveries
recently,
I
would be
very pleased
if
you
could
report
them
to
me
as
soon as possible;
and
your
advice
on
my
work
is
anyway very
welcome.
Yours
very truly,
W. de
Sitter.
244. From Willem de Sitter
Loenen, 27
July
1916
Dear
Colleague,
Your
postcard
arrived
a
few
hours after
my previous
letter[1]
had been
put
in
the
mail. Mr.
Müller[2]
certainly
has done
very good astrophysical work; specif-
ically,
photometry
at
Potsdam,
which
was
probably
carried out
principally by