DOC.
310
NOVEMBER
1911 225
Unfortunately,
I have been
so
busy
with
other
things lately
that
I
cannot
yet
submit
to
you
a
letter
to
Adams.[5]
But I will
certainly
think about
it. I
recently
received
a
beautiful
paper
from
Adams
on
the
spectrographic
determination of the solar rotation
time.[6]
It
contains
magnificent reproductions
of
photographs
with such
a
high
dispersion
that
1
Ä
=
8
mm.
All
of
the lines
are
blurred,
washed
out, exactly as
they
would have
to look if
they
were
brought
about
solely by
anomalous
dispersion.
Their
widths
vary
greatly,
and thus
are
not due
merely
to
technical
errors or imprecise focusing.
But
a
fine
dark
core
(the true absorption
line)
cannot be
recognized
at all in
any
of the
narrower
lines
(at
least
not in this
reproduction).
Could this
mean
that
in
the
case
of the weaker
lines
the real
absorption
is much
too
monochromatic? I
do not
dare
to believe
it,
because it would be too
beautiful
a
confirmation of
my
theory
of the Fraunhofer
lines.[7]
You
are right
that
all
of
the
core
lines,
if
they
were
visible, would, according
to
your
theory,
have to
experience
a
red
shift,[8]
but
according
to
my
explanation they
would
not.[9]
(With
the
exception,
of
course,
that
in
the
case
of the
very
strong
lines such
as
H
and
K,
where
even
the
region
between the
maximum and the minimum
of
the
dispersion
curve might
be
observable,
the
core
line, too,
can
display asymmetry
and
thus
a
displacement,[10]
which
indeed
is
the
case according
to
the
investigations
of
St.
John
and
Deslandres.)[11]
But
what about the
moderately strong
lines
of the solar
spectrum,
which show wide
washed-out
edges,
and in which
the dark
core can
be
distinguished very clearly?
Here
belong
the
hydrogen lines,
calcium
X
4227,
the D-lines
of
sodium,
the
b-lines
of
magnesium.
Of
course,
in
order
to
study possible
displacements
of
such
lines, people
have
directed
their attention
especially
to
the dark
core;
and it
really
turned
out
that
exactly
these
lines failed
to
show
a
red
shift!
(Adams,
"An
Investigation
of
the
Displacements
of
the
Spectrum
Lines
at
the
Sun's
Limb,"
Contrib.
from
the Mount
Wilson
Solar
Observatory,
No.
43, p. 7,
and
Astrophysical
Journal
31, p.
36
(1910)).[12]
Adams
himself considers
this
result
incompatible
with
my
conception
(ibid, p.
28);[13]
but
he
obviously
did not
quite
understand the
connection.
It
is
precisely
these observations that
seem
to
me
to be
easily explainable
from
the
dispersion
theory.[14]
It
would be
of
enormous
interest
if,
at
Mount
Wilson,
the
rich
observational material
were,
for
once,
also
investigated
with
respect
to the
possible
consequences
of
gravitation
and anomalous
dispersion
instead of
being investigated only
from
the
points
of
view
of
the
pressure,
and
the
Doppler
and
Zeeman
effects.
Cordial
greetings,
also
on
behalf
of
my
wife and children. We
often
fondly
recall
your
pleasant
visit.