174 DOC. 38 ETHER AND RELATIVITY
16
SIDELIGHTS
ON
RELATIVITY
electromagnetic
field
there
occur,
in
addition
to
the
densities of
the
electric
charge,
only
the intensities
of
the
field.
The
career
of
electromagnetic processes
in
vacuo
appears
to be
completely
determined
by
these
equations,
uninfluenced
by
other
phy-
sical
quantities.
The
electromagnetic
fields
appear
as
ultimate,
irreducible
realities,
and
at first
it
seems superfluous
to
postu-
late
a homogeneous, isotropic
ether-
medium,
and
to
envisage electromagnetic
fields
as
states of
this
medium.
[17]
But
on
the other hand there
is
a weighty
argument
to be adduced
in
favour of
the
ether
hypothesis.
To
deny
the ether
is
ultimately
to
assume
that
empty
space
has
no physical qualities
whatever. The
fundamental
facts of mechanics do
not
harmonize
with this
view.
For the
me-
chanical
behaviour
of
a corporeal system
hovering freely
in
empty
space depends
not
only
on
relative
positions (distances)
and relative
velocities,
but
also
on
its
state of rotation, which
physically
may
be
taken
as a
characteristic not
apper-
taining
to
the
system
in itself.
In
order
[16]