220
DOC.
225
JUNE
1916
to all these
phenomena)
to
think
of
an
ether
in which the
standing
waves are
located.
Mach,
whose
interpretation
you
have
espoused,[6]
in
discussing
similar
exper-
iments also felt
the
need for
assuming something
situated
externally
to
the Earth
that determined the
phenomena.
Following
his chain of
reasoning
a
defining
mo-
ment
would be
sought
in
the
influence
of
“distant
bodies in
the
universe,”
let’s
say,
of
fixed stars. Thus
one
would
say,
it
is
the
fixed stars which
determine the
cycli-
cal
course (or
the
static
state)
of
the
nodes
in
the
circular cable.
Now,
although
this
interpretation
seems
to
me
very
much
less
manifest
than the
hypothesis
of
an
ether, I
could
accept
it
nonetheless,
if in
comparison
to
this
hypothesis
it
offered
some
advantage.
But
such
an
advantage
I
am
unable to
see.
For if
we
must
assume
that the Earth’s
rotation,
with
reference to
the
fixed
stars,
has
an
observable
influence
on electromagnetic phenomena,
then
we may
not
deny
from
the
start
the
possibility
of
a
similar influence
of
a
translation
by
the Earth
or
the
solar
system
relative
to
the
fixed
stars.
Then
we are
exactly
as
far
as
with the
ether
hypothesis
and
we
must
examine
through
experiment
whether
perhaps
any
effect
of
a
translation
exists. Even
now a
relativity
postulate
would be
out
of
the
question.
By
the
way,
both
interpretations,
influence of
fixed
stars
and ether
hypothesis,
are
basically
not
even
very
different from each
other,
it
seems
to
me.
Supposing
I
assumed
the
nodes’ motion
or
rest in
our
annular
cable
were
determined
by
the
fixed stars’ influence.
Then,
in order to establish to
some
extent
the
nature of
this
influence,
I
can
simultaneously
assume a system
of
points rigidly
connected
to
one
another within
the
cable
as a
connecting
link between
the
fixed
stars and
electromagnetic
waves.
I
shall
say,
the said influence manifests itself in
that with
reference to
this
point
system,
which
is
itself connected
to
the
fixed stars,
the
nodes have fixed
positions.
The
step
from
this
point
system
to
an
ether
is not
far.
Obviously,
other
experiments also, e.g.,
the
ones
discussed
by you
and
Mach,[7]
give
occasion for
very
similar
observations,
and
the
above considerations will
by
no
means
be
new
to
you.
The main
point
in
them
is actually
that
departures
from
relativity
theory
to
the
“fixed-star
hypothesis”
would also be
very
well
con-
ceivable. I
do not need to mention that, also in
my opinion,
not
only
the
theory
of
relativity
but
also
your
gravitation theory
can
remain valid in
their
entirety.
They will just
not
impose
themselves
on us so
much
as
the
only possible
ones.
I
hope very
much
that
you
will stay well. As
regards us, unfortunately,
since
many years now
already, my
wife
often suffers
under
changes
in
the
weather,
which
is
connected
with
a
deficiency
in
the
thyroid
gland;
but otherwise
we are
nice
and