DOC. 47
JANUARY
1915 61
Earth’s
surface
is
also due
to
this. Thus the
following things can
be
compared:
Geometrical
equivalency
of
directions
Kinematic
equivalency
of
the
variously moving
refer-
ence
systems
Preference for
one
direction
without
physical
cause
Preference for
a
state
of
motion
without
allowing
a
physical
cause
In
reality, falling &
pref-
erence
for
the
vertical
are
determined
by
the
Earth’s
mass
In
reality,
the inertial
be-
havior
of
bodies
as
well
as
the
Galilean reference
sys-
tem
are
determined
by
the
other
perceptible things
of
the
world
(their
position
and
condition)
I believe
that
this
comparison gets
to
the
core
of
the
matter.
I
also believe
that
a
time
will
come
when
physicists
will
be
very
astonished
that their
predecessors
did not balk at
the
a
priori
preferred
(without
physical
cause)
reference
systems
(Galilean).
I firmly
contest
the
argument including
coriolis and
centrifugal
force.
The
complete
gravitational field
always
contains
components
that
act
upon
the
bod-
ies like
coriolis and
centrifugal
forces. I
imagine
that
those
components
in
con-
strained
space-time
regions
could be
made
to vanish in
certain
cases
if,
for
ex.,
the
gravitational field
originates
from
a
single
mass
situated
within
the
“finite
realm”; but
I
do
not
believe
that
the
equations
of
motion valid in
this
case are
general
natural
laws. I
think that
motion
equations
of
the
kind
m"
d2x"
IF
xp
-
xv
/LLIS
'
flV
cannot
suffice
generally (quite
apart
from
the
modification
produced
as a conse-
quence
of
the
original
theory of
relativity).
I
imagine
it would be
impossible
to
cause
other
components
(e.g.,
the
“coriolis
forces”)
to
vanish
everywhere through
an
appropriate
selection of
the
coordinate
system.
Although
I
also
prefer
certain reference
systems,
the
fundamental difference to
the
Galilean
preference
is, however,
that
my
coordinate selection makes
no
phys-
ical
assumptions
about
the
world;
let
this
be
illustrated
by
a
geometric compari-
son.
I have
a
plane
of
unknown
description
which
I want
to
subject
to
geometric