DOCS.
326,
327 APRIL
1917
317
the abundance
of
primary
material,
I
would first
like
to
get one or
two important
pointers. Mach,
with
whom
I
have
exchanged
a
couple
of
brief
letters
on
this,
could not refer to
anything either, unfortunately.[3]
I
do not want to
trouble
you
in
any way
with this
inquiry.
But
it
really
is
possible
that
by
chance
you might
be able
to
give me some
information
on
this
point.
I
might
be
holding
a
lecture in Berlin in
a
while
and,
if this would not
disturb
you,
would
like to
come
to
see you.
In
expressing my special admiration,
I
am
yours very truly,
Dr.
Otto Neurath.
327.
From Willem de Sitter
Doorn,
18
April
1917
Dear
Einstein,
The
main
point
in
our
“difference
in
creed”[1] is
that
you
have
a
specific
belief
and
I
am a
skeptic.
Observations
will
never
be
able to
prove
that
A
vanishes,
only
that
A
is
smaller
than
a
given
value.
Today
I
would
say
that
A
is
certainly
smaller
than
1045cm2
and
is probably
smaller
than
1050.
Maybe
one
day
observations
will
also
provide
a
specific
value for
A,
but
up
to
now
I have
no knowledge
of
anything
pointing
to
this.[2]
The
problem
of
the
discontinuity
in
ds2
=
dx2dy2dz2+dt2/(1+x2+y2+z2r2/4R2)
is actually
not
interesting,[3]
because
the
hyperboloid
4R2
+
x2
+
y2
+
z2

t2
=
0
intersects
the
taxis
at t
=
±2R, and the
natural
distance of these
points
to
the
origin
is /2R
dt/1t24R2
=
00
and not finite
as
you initially thought.[4]
The
length
of
the
xaxis,
on
the
other
hand,
is /
dx1+x2/4R2
=
nR, hence finite.[5]
“My”[6]
fourdimensional world also
has the
A
term,
but
no
“world matter.”[7]
With
cordial
regards,
W. de Sitter.