DOC.
18
DISCUSSION OF DOC.
16
227
to
hear
a
few words about that.
Einstein:
According
to
the
theory, a
mutual effect of the electric field and the
gravitational
field does of
course
occur,
but it
is
so
small that it
seems
futile
to
try
to
prove
it
experimentally. Only
the
bending
of
light rays by
the
gravitational
field
of the Sun
seems
to
be within the
range
of
observable effects.
Hasenöhrl:
I
would like
to
ask
Mr.
Einstein,
if
I may,
how
firmly
he is convinced
[12]
that the deflection of
a
light ray by
the solar
gravitational
field
by one
second,
if
it
indeed takes
place,
will
actually
be observable and
can
actually
be measured.
Einstein:
According
to
the
opinion
of
the
astronomers
whom I have
consulted,
the confirmation of such
a
deflection
is
absolutely
within the realm
of
possibility.
[13]
Jäger:
But will the
astronomers
then
not
find
many
other
explanations
for such
[14]
a
deflection?
Einstein:
I
do
not
think
so; 1/R comes
into
it.
Any atmospheric
influence would
decrease much faster with the distance. So
I
do
not
think that such
a
deflection will
be
explained
in
any
other
way. [15]
Zemplen (in
answer
to
a question by
Schütz):
Eötvös's method
is
based
on
the
[16]
fact that the
gravitation
on
the surface of
the Earth is
a
resultant of the
centrifugal
force and
the
mass
attraction.
If
the
specific
mass
attraction
were
different for
different
substances,
then the
gravity
of the
two different substances would
come
out
different
not
only
with
respect
to
magnitude
but also with
respect
to
direction.
Thus,
if
weights
of different
substances
are
suspended
from the
two
ends
of
a
torsion
balance
bar,
then the difference in the direction
of
the
attacking gravitational
forces
would
cause a
torsion
of
the wire. Since this has
not
been
observed,
in
spite
of the
fact that the
most meticulous
experiments
have been
attempted,
Eötvös deduced
as
far back
as more
than 20
years ago,
and with
an accuracy
of
1/20,000,000,
that the
specific mass
attraction
is
independent
of the nature of the substance. In
more
recent
experiments,
done
jointly
with Pekar and
Fekete,
it
was
possible
to
increase this
accuracy
to
1/100,000,000. (See Eötvös,
Mathem.
u.
naturw.
Berichte
aus
Ungarn
VIII,
1890;
Beiblätter
zu
den
Ann. d.
Phys. 15 (1891):
688;
"Über
geodätische
Arbeiten in
Ungarn,
besonders über
Beobachtungen
mit der
Drehwage, Kap.VI"
in
the
Abhandlungen
der
XVI. allgemeinen Konferenz
der
internationalen
Erdmessung.
1909.)
[17]
Mie:
From what
Mr.
Einstein
has said about the
importance
of Eötvös's
experiments,
one
might perhaps
conclude that
I
did
not
check
my theory sufficiently
as regards
its
agreement
with the results
of
those
experiments.
This is
not
the
case.
I
do
assume,
of
course,
that the inertial
mass
and the
gravitational
mass are
not
absolutely
identical. But the ratio of the
two
masses
deviates
(because
of the thermal
motion
of
the
molecules)
so
little from
a
constant value
that the
deviations
can
by
no
means
be
proved experimentally.
In the most favorable
case
the deviations amount