176
DOC.
181
JANUARY
1916
sufficient
to
produce
secular effects accessible
to
observation. If
M
is
taken
for
planetary
masses,
then this
relative
quantity is
diminished
significantly. However,
secular variations
that
are
produced
by
the
interaction
of
the
planets
only
amount
to at most
1,000"
in
100
years.
According
to
the
theory,
they
would be modified
by
the
tiny
fraction
indicated. Thus
a more
exact
development
of the
perturbation
calculation to
modify
orbital
motion
theory
cannot
provide
anything
within
the
reach of observation.
2)
The
statement
that
“the fixed-star
system”
is
rotation-free
undoubtedly is
meant in
a
relative
sense,
which
is
described
by
a
comparison.
The Earth’s
surface
is
irregular
as
long
as
I
envisage very
small sections of it.
But it
approaches
the
flat basic form when
I
envisage larger
sections of
it,
whose
dimensions
are
still small
against
the
length
of the
meridian.
This
basic form
becomes
a
curved surface when
I
envisage
even larger
sections.
Likewise for
the
gravitational field.
On
a
small scale
the
individual
masses
produce
gravitational fields
that
even
with
the
most
simplifying
choice of ref-
erence
system
reflect
the character
of
a quite irregular
small-scale
distribution
of
matter.
If I
regard
larger regions, as
those available
to
us
in
astronomy,
the
Galilean reference
system provides
me
with
the
analogue
to
the
flat basic form
of
the Earth’s
surface in
the
previous comparison.
But
if I
consider
even
larger
regions,
a
continuation
of
the
Galilean
system providing
the
description
of
the
universe in
the
same
dimensions
as
on
a
smaller scale probably does not
exist,
that
is,
where
throughout,
a
mass-point sufficiently
removed from
other
masses
moves
uniformly
in
a
straight line.
Ultimately, according
to
my
theory,
inertia
is simply
an
interaction between
masses,
not
an
effect
in which
“space”
of itself
were
involved,
separate
from
the
observed
mass.
The
essence
of
my
theory is
precisely
that
no
independent
properties
are
attributed
to
space
on
its
own.
It
can
be
put
jokingly
this
way.
If
I
allow all
things
to
vanish from
the
world,
then
following
Newton,
the
Galilean
inertial
space remains;
following my
interpretation,
however, nothing
remains.
3)
As
concerns
Jupiter, I
understand
that
it
is
a
difficult
proposition
for
astron-
omers.[3]
However,
in
my
view
the
importance
of
the
matter
supports
only
one
standpoint,
and
that
is:
It
has to work!
Jupiter’s
moons
could
serve
in
studying
closely
the
systematic errors
of which
you speak;
for
the
apparent
displacement
of
Jupiter’s
moons
through
light
deflection
is
entirely negligible owing
to
the
smallness of
the
moon-Jupiter
distance. The
angle
to be confirmed amounts to
2
.
0.02" and
is
thus
within
the
order
of currently
attainable
precision.
4)
It
never
occurred
to
me
to
think of
a
clique against
Freundlich.
It
is
generally
far from
my
mind
to
think
of such
things.
Struve’s
attitude
is
understandable.[4]