DOC.
2
RELATIVITY AND
ITS CONSEQUENCES
117
Doc.
2
The
Principle
of
Relativity
and Its
Consequences
in Modern
Physics
by
A. Einstein
[Archives
des sciences
physiques
et
naturelles
29
(1910):
5-28;
125-144]
§1.
The
Ether
When
it
was
realized that
a profound
analogy
exists
between the
elastic
vibrations of
ponderable
matter and
the
phenomena
of interference
and diffraction
of
light,
it could
not be
doubted that
light
must
be considered
as a
vibratory
state
of
a
special
kind of
matter.
Since,
moreover,
light can
propagate
in
places
devoid
of
ponderable
matter,
one
was
forced to
assume
for
the
propagation
of
light a special
kind
of
matter
that
is
different
from
ponderable
matter,
and that
was
given
the
name
"ether."
Since
the
velocity
of
light
propagation
in
bodies of
low
density,
such
as
gases,
is
more or
less
the
same as
in
a
vacuum,
it
had
to
be assumed that the ether
is
the
principal
carrier of
light
phenomena
in
these bodies
as
well.
Finally,
the
hypothesis
of the
presence
of ether
in
the interior
of
liquids
and
solids
was
also
necessary
in
order
to make it
possible
to
understand the
propagation
of
light
in
these
bodies,
since it
was
impossible
to
explain
the
great
velocity
of
propagation
by
the
elastic
properties
of
ponderable
matter alone.
For
all
these
reasons,
the
existence
of
a special
medium
permeating
all matter
seemed
beyond
dispute,
and the ether
hypothesis
formed
an
essential
part
of the
picture
of
the universe
which
presented
itself
to
the
physicists
of the
last
century.
The introduction of the
electromagnetic theory
of
light
brought
about
a
certain
modification
of the ether
hypothesis.
At
first
the
physicists
did not
doubt that the
electromagnetic
phenomena
must
be reduced
to
the modes of
motion
of
this medium.
But
as they
gradually
became convinced
that
none
of the
mechanical
theories of ether
provided a particularly
impressive
picture
of
electromagnetic phenomena, they
got
accustomed
to
considering
the electric
and
magnetic
fields
as
entities
whose mechanical
interpretation
is
superfluous.
Thus, they
have
come
to view
these
fields in
the
vacuum
as
special
states
of
the ether that do
not
require
an analysis
in
greater depth.
What the
mechanical
interpretation
of
optical
and
electromagnetic phenomena
has
in
common
with
the
purely electromagnetic interpretation
is
the
fact
that both
view
the
electromagnetic
field
as a special
state
of
a
hypothetical
medium
filling
the
whole
of
space.
This is
where these
two
interpretations
differ
fundamentally
from
the
emission
theory proposed
by
Newton,
according
to which
light
consists
of
particles
in
motion.
According
to
the latter
theory,
a
space
containing
neither
ponderable
matter
nor
light