292 DOC. 27 ON THE
THEORY
OF GRAVITATION
The Einstein-Grossmann
theory
is
more complicated
than that of Nordström in
that
it
violates the
just-mentioned principle
of the
constancy
of the
velocity
of
light
and
thereby
necessitates
a
generalization
of the
theory
of
relativity.
But in
return,
it
eliminates
an epistemological
weakness that hitherto attached to mechanics and that
[4]
has
long
been felt
by perspicacious epistemologists, especially by
Ernst Mach.
The law
of
motion
of
the material
point,
and therewith the whole
of
mechanics,
indeed the whole
of
theoretical
physics,
were
based
by
Galileo and Newton
on
the
concept
of
acceleration.
But
a simple analysis
shows that acceleration
is
accessible
to
observation
only
as
relative acceleration with
respect
to
other
bodies,
that
we are
only
able
to
define
a
relative acceleration. It
is
therefore doubtful that the Galilean-
Newtonian law
of
motion,
which
says
that bodies
exert
a
resistance
to
acceleration,
says
something
about
an
acceleration in itself
(absolute acceleration, not
relative
acceleration).
The
new
theory
of
gravitation
avoids this
inconsistency; according
to
[5]
this
theory,
inertia shows
up
as a
resistance
against
the relative acceleration
of
bodies.
A decision between the
two theories
by way
of
experiment
is
possible
insofar
as
according
to
the Einstein-Grossmann
theory,
but
not
according
to
the Nordström
theory,
the
gravitational
field
must
cause a
bending
of
light rays.
Since the
only
gravitational
field able
to
produce
an
observable
bending
of the
rays
is that
of
the
sun,
careful
preparations
have been made for the solar
eclipse
that will take
place
in
August
1914:
photographing
of
the fixed stars
near
the
sun
should establish whether
[6]
this
bending
of
rays is
actually present or
not.
(Author's
report)