The Sleepwalkers (18 page)

But
it
was
also
a
landmark
in
another
direction.
It
separated
neatly
two
phenomena
which
had
previously
been
mixed
up:
the
succession
of
day
and
night,
that
is,
the
diurnal
rotation
of
the
sky
as
a
whole;
and
the
annual
motions
of
the
seven
wandering
planets.

The
next
improvement
of
the
model
concerned
the
daily
motions.
The
central
fire
dropped
out;
the
earth,
instead
of
going
round
it,
was
now
made
to
spin
on
her
own
axis,
like
a
top.
The
reason
was,
presumably,
⁴
that
the
Greek
seafarers'
growing
contacts
with
distant
regions
–
from
the
Ganges
to
the
Tagus,
from
the
island
of
Thule
to
Taprobrana
–
had
failed
to
produce
any
sign,
or
even
rumour,
of
the
central
fire
or
the
antichton
,
both
of
which
should
have
been
visible
from
the
other
side
of
the
earth.
I
have
said
before
that
the
Pythagoreans'
world-view
was
elastic
and
adaptable.
They
did
not
drop
the
idea
of
the
central
fire
as
a
source
of
heat
and
energy;
but
they
transferred
it
from
outer
space
into
the
core
of
the
earth;
and
the
counter-earth
they
simply
identified
with
the
moon.
⁵

The
next
great
pioneer
in
the
Pythagorean
tradition
is
Herakleides
of
Pontus.
He
lived
in
the
fourth
century
B.C.,
studied
under
Plato,
and
presumably
also
under
Aristotle;
hence,
by
chronological
order,
he
ought
to
be
discussed
after
these.
But
I
shall
first
follow
the
development
of
the
Pythagorean
cosmology,
the
boldest
and
most
hopeful
in
antiquity,
to
its
end
–
which
came
in
the
generation
after
Herakleides.

Herakleides
took
the
earth's
rotation
round
its
own
axis
for
granted.
This
explained
the
daily
round
of
the
skies,
but
left
the
problem
of
the
annual
motion
of
the
planets
untouched.
By
now,
these
annual
motions
had
become
the
central
problem
of
astronomy
and
cosmology.
The
multitude
of
fixed
stars
presented
no
problem.
They
never
altered
their
positions
relative
to
each
other
or
to
the
earth.
⁶
They
were
a
permanent
guarantee
of
law
and
order
and
regularity
in
the
universe,
and
could
be
imagined,
without
much
difficulty,
as
a
pattern
of
pin-heads
(or
pin-holes)
in
the
celestial
pin-cushion
which
either
turned,
as
a
unit,
around
the
earth,
or
appeared
to
do
so
owing
to
the
earth's
rotation.
But
the
planets,
the
tramp
stars,
moved
with
a
shocking
irregularity.
Their
only
reassuring
feature
was
that
they
all
moved
along
the
same
narrow
belt
or
lane
looped
around
the
sky
(the
Zodiac):
which
meant
that
their
orbits
all
lay
very
nearly
in
the
same
plane.

To
get
an
idea
of
how
the
Greeks
perceived
the
universe,
imagine
all
transatlantic
traffic
–
submarines,
ships,
aircraft
–
to
be
confined
to
the
same
trade-route.
The
"orbits"
of
all
craft
will
then
be
along
concentric
circles
round
the
earth's
centre,
all
in
the
same
plane.
Let
an
observer
lie
on
his
back
in
a
cavity
in
the
centre
of
the
transparent
earth,
and
watch
the
traffic.
It
will
appear
to
him
as
points
moving
at
different
speeds
along
a
single
line:
his
zodiacal
lane.
If
the
transparent
sphere
is
set
rotating
round
the
observer
(who,
himself,
remains
at
rest)
the
traffic-lane
will
rotate
with
the
sphere,
but
the
traffic
will
still
remain
confined
to
this
lane.
The
traffic
consists
of:
two
submarines
ploughing
the
waters
at
different
depths
under
the
lane:
they
are
the
"lower"
planets,
Mercury
and
Venus;
then
a
single
ship
with
blazing
lights:
the
sun;
then
three
aeroplanes
at
different
heights:
the
"upper"
planets,
Mars,
Jupiter
and
Saturn,
in
that
order.
Saturn
would
be
very
high
up
in
the
stratosphere;
above
it
there
is
only
the
sphere
of
the
fixed
stars.
As
for
the
moon,
she
is
so
close
to
the
observer
in
the
centre,
that
she
must
be
considered
a
ball
rolling
on
the
concave
wall
inside
his
cavity;
but
still
in
the
same
plane
with
all
the
other
craft.
This,
then,
in
broad
outlines,
is
the
antique
model
of
the
world
(
Fig.
A
).