The Sleepwalkers (90 page)

The
principal
advantage
of
the
Copernican
system
over
the
Ptolemaic
is
greater
geometrical
simplicity
in
one
essential
respect.
By
transferring
the
hub
of
the
universe
from
the
earth
to
somewhere
in
the
vicinity
of
the
sun,
the
retrograde
motions
of
the
planets,
which
had
so
much
worried
the
ancients,
disappeared.
It
will
be
remembered
that
during
their
annual
procession
along
the
Zodiacal
lane,
the
planets
occasionally
come
to
a
standstill,
reversing
their
direction
for
a
while,
and
then
resume
their
progress
again.
So
long
as
the
earth
was
the
hub
of
the
universe,
this
phenomenon
could
be
"saved"
by
adding
more
epicycles
to
the
clockwork,
but
there
was
no
natural
reason
why
the
planets
should
behave
as
they
did.
But
if
the
hub
was
near
the
sun,
and
the
earth
turned
round
it
together
with
the
other
planets,
it
was
obvious
that
each
time
the
earth
"overtakes"
one
of
the
outer
planets
(which
circle
at
a
slower
rate)
that
planet
will
appear
to
recede
for
a
while;
and
each
time
the
earth
itself
is
overtaken
by
the
faster
moving
inner
planets,
an
apparent
reversal
of
direction
will
again
result.

This
was
an
enormous
gain
in
simplicity
and
elegance.
On
the
other
hand,
the
shifting
of
the
centre
of
the
universe
to
a
place
in
the
vicinity
of
the
sun
entailed
an
almost
equal
loss
in
plausibility.
Previously,
the
universe
had
possessed
a
solid
hub,
the
earth,
a
very
solid
and
tangible
hub
indeed;
now
the
whole
world
was
hinged
on
a
point
in
empty
space.
Moreover,
that
imaginary
point
was
still
defined
by
the
orbit
of
the
earth,
and
the
motions
of
the
whole
system
still
depended
on
the
motions
of
the
earth.
Not
even
the
planes
of
the
planetary
orbits
met
in
the
sun;
they
oscillated
in
space,
again
according
to
the
position
of
the
earth.
The
Copernican
system
was
not
a
truly
heliocentric
one;
it
was
a
vacuo-centric
system,
so
to
speak.

If
it
was
to
be
considered
merely
as
sky-geometry,
without
reference
to
physical
reality
–
as
Osiander's
preface
affirmed
–
this
did
not
matter
too
much.
But
in
his
text
Copernicus
repeatedly
affirmed
that
the
earth
really
moved,
and
thereby
exposed
his
whole
system
to
judgement
based
on
real,
physical
considerations.
And
from
that
point
of
view
the
system
was
untenable.
Ptolemy's
forty
crystal-wheels
on
wheels
had
been
bad
enough,
but
at
least
the
whole
machinery
was
supported
by
the
earth.
Copernicus'
machine
had
even
more
wheels,
but
it
was
supported
neither
by
the
earth,
nor
by
the
sun;
it
had
no
physical
centre.
Moreover,
the
centre
of
Saturn's
orbit
lay
outside
the
sphere
of
Venus,
and
the
centre
of
Jupiter's
orbit
near
the
sphere
of
Mercury.
How
could
these
spheres
function
without
colliding
and
interfering
with
each
other?
Then
again,
Mercury,
that
most
recalcitrant
of
all
planets,
had
to
be
accorded
an
oscillatory
motion
along
a
straight
line.
But
straight
motion
was
considered
by
Aristotle,
and
Copernicus,
as
impossible
for
a
heavenly
body;
hence
it
had
to
be
resolved
into
the
combined
motion
of
two
more
spheres,
one
revolving
inside
the
second;
and
the
same
artifice
had
to
be
employed
to
"save"
the
wobbling
motion
of
the
earth's
axis
and
all
motions
in
latitude.
By
now
the
earth
had
no
less
than
nine
independent
circular
motions.
But,
the
bewildered
reader
of
Copernicus
asked,
if
the
earth's
motion
is
real
,
then
the
nine
wheels
on
which
it
turns
must
also
be
real
–
where
are
they?

Instead
of
the
harmonious
simplicity
which
the
opening
chapter
of
the
Revolutions
promised,
the
system
had
turned
into
a
confused
nightmare.
To
quote
a
modern
historian,
who
trespassed
into
science
with
an
unprejudiced
eye:

"When
you
go
down,
so
to
speak,
for
the
third
time,
long
after
you
have
forgotten
everything
else
in
this
lecture,
there
will
still
float
before
your
eyes
that
hazy
vision,
that
fantasia
of
circles
and
spheres
which
is
the
trademark
of
Copernicus."
¹⁴