192
DOCS.
188,
189
FEBRUARY
1916
spherical space
but
only
a
sphere
of
radius
a0
within
this
space.
It
is just
from
the
increase in
the
velocity
of
light
that
it becomes noticeable whether
you
are
nearer
to
the
center
or nearer
to the surface.
Here it
is
even more
obvious
than
in
the
case
of
the
outer
field,
that
r
has
absolutely
no
physical meaning,
but
is just
a
variable
making
the
|guv|’s
equal
to
1.
This
looks
as
if it
must
be
possible
to find
a
condition
other than |guv|
=
1,
making
the
field
equations even simpler.
Interlineations
at end of second
paragraph:
“that
observations
within the
Milky Way
are
significant
for
the
entire
system.”
189. To
Arnold Sommerfeld
[Berlin, 8
February
1916]
Dear
Sommerfeld,
Your
letter
pleased
me
very
much,
your
report
on
the
theory
of
spectral
lines
enchanted
me.
A
revelation!
Just
one
thing
I still did not
grasp.
If in
v=N(1/n2-1/m2)
n=2
n
=
2
causes a
division into
two,[1]
then
surely
m
=
m
should also
cause a
division
into
m
parts,
so
that in
general a
division of
n
.
m
would have
to
be
expected.
This
is not
supposed
to
be
an
objection, though.
I
am
much
rather
convinced
that
you
are
right.- I
have found
a
lecture
experiment
to
demonstrate
conveniently
Ampere’s
currents
(already
tried
out).[2]
You
will
be convinced of
the
general
theory of rel.
when
you
have
studied it.
That
is
why
I
am
not
mentioning
a
word in its defense.
Hearty congratulations
on
your
fine
discovery
and
best
regards,
yours,
Einstein.