252
THE
RELATIVITY PRINCIPLE
Doc. 47
ON
THE
RELATIVITY PRINCIPLE
AND
THE CONCLUSIONS
DRAWN
FROM
IT
by
A.
Einstein
[Jahrbuch
der Radioaktivität
und
Elektronik
4 (1907):
411462]
Newton's equations
of
motion
retain their
form
when
one
transforms
to
a
new
system
of coordinates that is in
uniform
translational
motion
relative
to
the
system
used
originally
according
to
the
equations
x'
=
x

vt
x'
=
y
z]
=
z
.
As
long
as one
believed
that all of physics
can
be
founded
on
Newton's
equations
of motion,
one
therefore could
not doubt
that the
laws
of
nature
are
the
same
without
regard to
which of
the coordinate
systems
moving
uniformly
(without
acceleration) relative
to
each
other
they
are
referred.
However,
this
independence
from the state
of
motion of
the
system
of
coordinates used,
which
we
will call "the
principle of
relativity,"
seemed
to have been
suddenly
called
into
question
by
the brilliant confirmations
of
H. A.
Lorentz's
electrodynamics
of
moving
bodies.1
That
theory
is built
on
the
presupposition
of
a
resting,
immovable,
luminiferous
ether;
its basic
equations
are
not
such
that
they
transform
to
equations of
the
same
form
when
the
above
transformation
equations
are
applied.
After the
acceptance
of
that
theory,
one
had to expect
that
one
would
succeed in
demonstrating
an
effect
of
the terrestrial
motion
relative
to
the
luminiferous ether
on
optical
phenomena.
It is
true
that
in
the
study
cited
[2]
Lorentz
proved
that in optical
experiments,
as a
consequence
of
his basic
assumptions,
an
effect
of
that relative motion
on
the
ray
path
is
not to be
expected
as
long
as
the calculation
is limited
to terms
in which
the ratio
[1]
1H.
A.
Lorentz, Versuch einer Theorie
der elektrischen
und optischen
Erscheinungen
in
bewegten Körpern. [Attempt
at
a
theory
of
electric
and
optical
phenomena
in
moving
bodies]
Leiden, 1895. Reprinted
Leipzig,
1906.