DOC. 38 ETHER AND RELATIVITY 161
ETHER
AND
THE THEORY
OF
RELATIVITY
HOW
does
it
come
about that
alongside
of
the
idea
of
ponderable
matter,
which is derived
by
abstrac-
tion from
everyday life,
the
physicists
set
the
idea
of
the
existence
of
another
kind
of
matter,
the ether?
The
explana-
tion
is
probably
to be
sought
in those
phenomena
which
have
given
rise to
the
theory
of action at
a
distance,
and
in
the
properties
of
light
which have led to
the
undulatory
theory.
Let
us
devote
a
little
while to
the
consideration
of
these two
subjects.
Outside of
physics we
know
nothing
of
action at
a
distance. When
we
try
to connect
cause
and
effect in
the
experi-
ences
which
natural
objects
afford
us,
it
seems
at first
as
if
there
were
no
other
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