246
DOCS.
336,
337
JANUARY
1912
336. To
Erwin Freundlich
Prague,
8 January
1912
Esteemed
Colleague:
I
am
extremely
pleased
that
you
have
taken
up
the
question
of the
bending
of
light
with
so
much
zeal,
and
am
very
curious
to
know what
the examination of the
existing
plates
will
show.[1]
The
question
involved
is
of
quite
fundamental
significance.
From the
theoretical
standpoint
there
is
a
rather
great
probability
that
the effect
really
exists.
If
your
daylight
observations of
fixed stars in
the sun's
vicinity
will
really
succeed,
then
we
will
soon
know
for
sure.
Did
you already
calculate how low
the
density
of
the sun's
atmosphere
must
be in
order
for
the
fixed stars to be observable
through
it?
Owing
to
opalescence dispersion
(cause
of the luminescence of the
blue
sky, Rayleigh),[2]
at
the
enormously
large
wavelengths
no
light
should
pass through
undeflected
even
at
quite
low densities.
In that
way
one
obtains
an
upper
bound
on
the
density
of the
upper
layers
of the sun's
atmosphere,
and thus
also
an
upper
bound
for
deflection
through
refraction.
From
my
paper[3]
you
can
also
see
that
a
small
red
shift
of
the
sun's
spectral
lines
(by
ca.
0.01
angstrom)[4]
is
to be
expected, according
to
the
theory.
Unfortunately, however,
the
broadening
of the
spectral
lines
toward
both
sides
depends
on
a
variety
of
causes
(pressure-dispersion
of
light
(Julius)-motion
(Doppler)),
so
that
a compelling
interpretation
can hardly
be
achieved.[5]
Are there
no
extremely
sharp
lines
(i.e.,
not
wider
than
0.02
angstrom)
to be
found
among
the lines
of
the sun?
I
am writing
to
you
about
this
only
because
I
do
not believe
that
unambiguous
results
can
be
obtained
in this
way.
Please
keep
me
up to
date about
your investigations,
with which
I
wish
you
much
luck.
With best
regards,
yours
truly,
A.
Einstein
337.
From
George
Pegram[1]
[New York]
9 January
1912
Prof. Dr. A.
Einstein,
The
University
Zurich, Switzerland.
Dear
Sir:
I
write
to inquire
whether
or
not
you
would
care
to
consider
a
proposition
for
you
to
come
to
Columbia
University
in
the
City
of
New York
as a
special
lecturer
in
physics
sometime between
October
1,
1912 and
May
1,
1913.
While I
am
not
authorized
to