DOC.
483
NOVEMBER
1913 361
483.
From
George
Hale
November
8th,
1913
Professor Dr.
A. Einstein,
Technische
Hochschule,
Zürich, Switzerland.
Dear Professor Einstein:
I
have
delayed replying
to
your
kind
letter of October
14th[1]
until I could
consult
Director
Campbell
of
the Lick
Observatory,[2]
who I knew to
be
interested
in
the
problem
you
describe.
He
writes
me
that
he has
undertaken
to
secure
eclipse
photographs
of
stars
near
the
sun
for Doctor
Freundlich[3]
of
the Berlin
Observatory,
who will
measure
them
in the
hope
of
detecting
differential
deflections.
Doubtless
he will
send
you
further
particulars,
as
I
requested
him
to
communicate
directly
with
you.[4]
I
fear there
is
no possibility
of
detecting
the
effect in full
sunlight,
for the
following
reasons:
1.
The
sky
increases
greatly
in
brightness
near
the
sun,
even
under
good observing
conditions.
I cannot
now say
at
what distance
bright
stars
would be
visible,
but
will have
observations made
to
determine
this.
2.
On
Mount
Wilson[5]
the best definition of
the
solar
image
is
obtained
only
for
about
an
hour
in
the
early
morning.
Hence
the
atmospheric
refraction,
changing
rapidly
with
the hour
angle,
would be
a
troublesome
obstacle.
3.
It
would be
necessary
to
measure
the differential
change
in
distance of the
star
from
the sun's
limb,
which would be difficult
because of
the low
precision
of micrometer
settings
on
the
limb,
and the
large
distance
(probably
much
beyond
the
range
of
an
ordinary micrometer).
The
eclipse
method,
on
the
contrary,
appears
to be
very promising,
as
it
eliminates
all
of these
difficulties,
and
the
use
of
photography
would allow
a
large
number
of
stars
to be
measured.
I
therefore
strongly
recommend that
plan.
In
a
short
time,
as soon as some
additional data
are
available,
I wish to ask
your
opinion regarding
the
theory
of the
general
solar
magnetic
field which I have
recently
detected
by
observation
of
the Zeeman
effect.[6]
Believe
me,
with kind
regards
to
Professor
Maurer,[7]
Yours
very sincerely,