The Sleepwalkers (248 page)

In
1686,
goaded
on
by
Halley,
Newton
arrived
at
his
ultimate
synthesis.
He
computed
the
force
of
the
earth's
attraction
on
the
moon,
and
showed
that
this,
combined
with
the
moon's
own
centrifugal
force,
satisfied
the
moon's
observed
motions.
Next
he
computed
the
sun's
attraction
on
the
planets,
and
demonstrated
that
the
orbit
produced
by
a
force
of
attraction
which
diminished
with
the
square
of
distance
was
a
Keplerian
ellipse
with
the
sun
in
one
focus;
and
conversely,
that
an
elliptic
orbit
required
a
gravitational
force
obeying
the
inverse
square
ratio.
Kepler's
Third
Law
relating
the
duration
of
the
planets'
periods
to
their
mean
distances
from
the
sun
became
a
cornerstone
of
the
system;
and
the
Second
Law
–
equal
areas
being
swept
out
in
equal
times
–
was
now
shown
to
hold
for
any
central
orbit.
Comets
were
shown
to
move
either
in
very
elongated
ellipses
or
in
parabolas,
receding
into
the
infinity
of
space.
Newton
further
proved
that
any
object
above
the
earth's
surface
behaved
as
if
the
whole
mass
of
the
earth
were
concentrated
in
its
centre;
which
made
it
possible
to
treat
all
heavenly
bodies
as
if
they
were
mathematical
points.
Lastly,
all
observable
motion
in
the
universe
was
reduced
to
four
basic
laws:
the
Law
of
Inertia;
the
Law
of
Acceleration
under
an
impressed
force;
the
Law
of
Reciprocal
Action
and
Reaction;
and
the
Law
of
Gravity.

The
miracle
was
completed;
the
fragments
had
all
flown
together
in
this
reversed
explosion
and
were
fused
into
a
smooth,
compact,
innocent-looking
body;
and
had
Donne
still
been
alive,
he
could
have
reversed
his
lament
into
a
triumphant:
"'Tis
all
in
one
piece,
all
coherence
now."

The
motions
of
sun,
moon
and
the
five
vagabond
stars
had
been
the
main
problem
of
cosmology
since
the
days
of
the
Babylonians.
Now
that
they
were
all
shown
to
follow
the
same
simple
laws,
the
solar
system
was
recognized
as
an
integrated
unit.
The
rapid
progress
of
astronomy
and
astrophysics
soon
led
to
the
further
realization
that
this
unit
was
merely
a
subdivision
of
a
larger
one:
our
galaxy
of
millions
of
stars
of
roughly
the
same
nature
as
our
sun,
some
of
them,
no
doubt,
also
surrounded
by
planets;
and
that
our
galaxy
again
was
merely
one
among
other
galaxies
and
nebulae
in
various
stages
of
their
evolution,
yet
all
governed
by
the
same
universal
set
of
laws.

But
these
developments
no
longer
concern
us.
With
the
publication
of
Newton's
Principia
in
1687
A.D.,
cosmology
became
a
disciplined
science;
and
at
this
point
our
narrative
of
man's
changing
vision
of
the
universe
must
end.
The
wild
dance
of
shadows
thrown
by
the
stars
on
the
wall
of
Plato's
cave
was
settling
into
a
decorous
and
sedate
Victorian
waltz.
All
mysteries
seemed
to
have
been
banished
from
the
universe,
and
divinity
reduced
to
the
part
of
a
constitutional
monarch,
who
is
kept
in
existence
for
reasons
of
decorum,
but
without
real
necessity
and
without
influence
on
the
course
of
affairs.

It
remains to discuss some implications of the story.

CHRONOLOGICAL
TABLE TO PARTS FOUR AND FIVE