570
DOCS.
550,
551 MAY
1918
result
is
that
a glowing body
has
an
outer
layer
of
electrons,
which has
a
“surface
pressure” (negative
surface
tension)
still
dependent
on
temperature.
On curved
surfaces,
a
“capillary pressure”
is
produced
entirely as
in
capillarity,
just of
the
opposite sign.
The
thermodynamics
of
this outer
layer
can
also be
developed
easily.[3]
With
cordial
regards, yours,
M.
von
Laue.
551.
To Hermann
Weyl
[Berlin,]
31
June
[May]
1918[1]
Dear
Colleague,
I
am glad
that
you
have
put
the
zone
affair in
order,
now.[2] The
result
of
your
calculation
now
corresponds completely
with
what had
to
be
expected.[3]
You
probably
already
sent
the
relevant correction to
Springer;
I
asked him to
wait
with the
printing
until
your
decision
arrived.[4]
Let’s
hope
the abominable
paper
shortage
does not
delay
the
appearance
of
your
book![5]
Now
to
the
question: spherical
or
elliptic.[6] I
do not
think that there
is
a
possi-
bility
of
really deciding
this
question
through
speculative
means.
A
vague feeling
leads
me
to
prefer
the
spherical one, though.
For
I
sense
that
those manifolds
are
the
simplest
in which
any
closed
curve can
be
contracted
continuously
to
one
point.
Other
people
must have
this
feeling
as well;
since otherwise
the
case
where
our
space
could be Euclidean and finite would
surely
also have been
taken
into
consideration
in
astronomy.
The two-dimensional Euclidean
space
would then
have
the
connectivity
properties
of
an
annulus.
It
is
a
Euclidean
plane,
on
which
every phenomenon
is
doubly periodic,
where
points
lying on
the
same
period
grid
are
identical. In
a
finite Euclidean
space
there
would be
three
kinds of closed
curves
not
continuously
reducible to
one
point. Analogously,
an
elliptic space,
in
contrast
to
the
spherical one, possesses
one
sort
that
cannot
be
contracted
continuously
to
one
point;
that
is
why
it
appeals
to
me
less
than the
spherical
one.
Can it be
proved
that the
elliptic space
is
the
only variety
of
the
spherical
space
that
can
be
obtained
through
the
addition
of
periodicity properties?
It
seems
to be
so.
Now
once again
to
your
Academy
paper.[7]
Could
one
really charge
the
Lord
with
inconsequence
for
not
seizing
the
opportunity
you
have found
to
harmonize
the
physical
world?[8] I
think
not. In
the
case
where
He
had
made
the
world
according
to
you, Weyl
II would have
come
along,
you
see,
to address Him
re-
proachfully thus:[9]