DOC.
47
255
itself is
whether the principle of
relativity is limited
to
nonaccelerated
moving
systems.
In
order
not
to
leave this
question
totally
undiscussed, I
added to
the
present
paper
a
fifth
part
that contains
a
novel
consideration,
based
on
the
principle of
relativity,
on
acceleration
and
gravitation.
I.
KINEMATIC
PART
§1.
Principle
of constancy of the
velocity
of
light.
Definition
of
time. Principle
of
relativity.
To
be
able
to
describe
a
physical
process,
we
must be
able
to
evaluate
the
changes
taking
place at
the individual points of the
space
as
functions
of
position and
time.
To
determine the
position
of
a process
of infinitesimally
short duration
that
occurs
in
a
space
element (point event)
we
need
a
Cartesian
system
of
coordinates, i.e.,
three
mutually
perpendicular rigid rods rigidly connected
with
each
other,
and
a
rigid unit
measuring
rod.1
Geometry
permits
us
to
determine the
position of
a
point,
i.e., the location of
a
point
event,
by
means
of three
numbers
(coordinates
x,
y,
z).2
To
evaluate the time of
a
point
event,
we
use a
clock that is
at rest
relative
to
the
coordinate
system
and
in
whose
immediate
vicinity the
point
event
takes place.
The
time of the
point event
is defined
by
the
simultaneous clock
reading.
Imagine
that clocks
at
rest
with respect
to
the coordinate
system
are
arranged at
many
points. Let
all
these clocks
be
equivalent, i.e., the
difference
between
the
readings
of
two
such
clocks shall
remain
unchanged
if
they
are
arranged
next to each
other. If these clocks
are
imagined
to be
set
in
some
manner,
then the
totality
of the clocks,
provided
they
are
arranged
sufficiently
closely, will
permit
the
temporal
evaluation of
any
point
event,
say
by
using
the
nearest
clock.
1Instead of
speaking
of
"rigid" bodies,
we
could
equally
well
speak,
here,
as
well
as
further
on,
of
solid
bodies not
subjected to
deforming
forces.
2For
this
one
also
needs
auxiliary rods
(rulers,
compasses).
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