80
DOCS. 109-111
JULY 1908
we
do not know
anything
about the
nature
of
the
process
of
light
absorption,
one can
very
well be in
doubt,
a
priori,
about
how
things really
work.
I would be
very
grateful
if
you
could
briefly
advise
me
about
this matter,
in
case you
know
of
pertinent
facts.
Respectfully,
A.
Einstein
Aegertenstr. 53
Bern
110.
From
August Hagenbach
Basel,
9
July
1908
To Dr.
Einstein,
Bern
Highly
esteemed
Sir:
If
I
understand
your inquiry
correctly,[1]
all
you
are
asking
is
whether
two
ray
bundles
that
are
capable
of
interfering preserve
this
property
if
they
pass
through absorbing
media.
I
do
not
know
of
any
facts
that
would
speak
against
that.
Thus,
Fresnel's mirror
experiment
can
be
done
with
interposed
pieces
of
colored
glass.
Also,
there
is
no change
in the direction of
oscillation,
in
my opinion,
in dichroitic
etc.
crystals,
that
is,
the
capacity
for
interference
is preserved. I
think that
the view
that
only
the
amplitude
changes
in
absorption is
correct;
at
least
I
am
not
aware
of
anything
contradictory
having
been
found.
But
I have
never
done
any special
work in this
area,
and
for that
reason am
not
able
to
give you
more
detailed information.
Respectfully,
Aug.
Hagenbach
111.
To
August Hagenbach
Bern, 14
July
1908
Highly
esteemed
Prof.
Hagenbach:
Thank
you
so
much for
your
kind letter, in which
you
respond
so
quickly
to
my
inquiry.[1]
Even
if the
arguments presented
have
not
convinced
me completely,
I
am
indebted
to
you
to
for
the
information that there
are no
observations known
to the
experts
that
would make the
theory
of
absorption
seem
inadequate.
What
you
have said
about Fresnel's mirror
experiment
has not convinced
me completely
because
it does
not
involve
two
separated ray bundles,
with
each,
by
itself,
undergoing partial absorption.
Respectfully,
and
thanking
you again,
I
remain
yours truly,
A.
Einstein