DOC.
38 ETHER AND RELATIVITY 171
ETHER
AND
RELATIVITY
13
conception suggests
itself
the
more readily
as, according
to Lorentz’s
theory,
electro-
magnetic
radiation, like
ponderable
matter,
[14]
brings impulse
and
energy
with
it,
and
as, according
to
the
special
theory
of
relativity,
both
matter
and radiation
are
but
special
forms of
distributed
energy,
ponderable
mass
losing
its
isolation
and
appearing as a special
form of
energy.
More
careful reflection teaches
us,
how-
ever,
that the
special
theory
of
relativity
does not
compel us
to
deny
ether. We
may
assume
the
existence
of
an
ether;
only we
must
give up
ascribing
a
definite
state
of
motion
to
it,
i.e.
we
must
by
[15]
abstraction take
from
it the last
mechan-
ical
characteristic
which Lorentz
had
still
left
it.
We shall
see
later that this
point
of
view,
the
conceivability
of
which I
shall
at
once
endeavour
to
make
more
intelligible
by
a
somewhat
halting
com-
parison,
is
justified
by
the
results of
the
general
theory
of
relativity.
Think
of
waves on
the
surface
of
water.
Here
we can
describe two
entirely
differ-
ent
things.
Either
we
may
observe
how