The Sleepwalkers (91 page)

2.
The
Arguments
for
the
Earth's
Motion

In
fact,
Copernicus
carried
orthodoxy
regarding
circles
and
spheres
even
further
than
Aristotle
and
Ptolemy.
This
becomes
evident
where
he
tries
to
prove
the
earth's
motion
by
physical
arguments.
It
may
be
objected,
he
says,
that
all
heavy
things
gravitate
towards
the
centre
of
the
universe;
but
if
the
earth
moves,
it
is
no
longer
in
the
centre.
This
objection
he
answers
as
follows:
¹⁵

"Now
it
seems
to
me
gravity
is
but
a
natural
inclination,
bestowed
on
the
parts
of
bodies
by
the
Creator
so
as
to
combine
the
parts
in
the
form
of
a
sphere
and
thus
contribute
to
their
unity
and
wholeness.
And
we
may
believe
this
property
present
even
in
the
Sun,
Moon
and
Planets,
so
that
thereby
they
retain
their
spherical
form
notwithstanding
their
various
paths."

Thus
the parts of a whole stick together because of their desire to make a
perfect shape; gravity, to Copernicus, is the nostalgia of things to
become spheres.

The
other
classic
objections
were,
mainly,
that
a
falling
body
would
be
"left
behind"
by
the
moving
earth;
that
the
atmosphere,
too,
would
be
left
behind;
and
that
the
earth
itself
would
fly
apart
owing
to
the
disruptive
force
of
its
rotation.
Copernicus
counters
these
Aristotelian
objections
with
an
even
more
orthodox
interpretation
of
Aristotle.
Aristotle
distinguished
between
"natural"
and
"violent"
motion.
Natural
motion,
says
Copernicus,
cannot
lead
to
violent
results.
The
natural
motion
of
the
earth
is
to
turn;
being
spherical
in
form
it
simply
cannot
help
turning.
Its
rotation
is
a
natural
consequence
of
its
sphericity,
just
as
gravity
is
the
natural
longing
for
sphericity.

"But
if
one
holds
that
the
earth
moves
,
he
will
also
say
that
this
motion
is
natural,
not
violent.
Things
which
happen
according
to
nature
produce
the
opposite
effects
to
those
due
to
force.
Things
subjected
to
violence
or
force
will
disintegrate
and
cannot
subsist
for
long.
But
whatever
happens
by
nature
is
done
appropriately
and
preserves
things
in
their
best
conditions.
Idle,
therefore,
is
Ptolemy's
fear
that
the
earth
and
everything
on
it
would
be
disintegrated
by
rotation
which
is
an
act
of
nature,
entirely
different
from
an
artificial
act
or
anything
contrived
by
human
ingenuity..."
¹⁶

In
a
word,
the
rotation
of
the
earth
engenders
no
centrifugal
forces.

After
this
scholastic
sleight-of-hand,
Copernicus
reverses
the
argument:
if
the
universe
were
turning
round
the
earth,
with
incomparably
greater
speed,
would
it
not
be
in
even
greater
danger
of
flying
apart?
But
evidently
on
Copernicus'
own
argument
that
natural
rotation
is
not
disruptive,
the
universe
in
this
case
would
be
equally
safe,
and
the
question
remains
undecided.

He
turns
next
to
the
objection
that
falling
bodies
and
the
air
would
be
left
behind
by
the
earth's
motion.
His
answer
again
is
strictly
Aristotelian:
since
the
nearer
atmosphere
contains
an
admixture
of
earthy
and
watery
matter,
it
follows
the
same
natural
law
as
the
earth:
"bodies
which
fall
because
of
their
weight,
must,
because
of
their
maximum
of
earthiness,
doubtless
participate
in
the
nature
of
the
whole
to
which
they
belong".
In
other
words,
clouds
and
falling
stones
keep
pace
with
the
earth
not
because
they
share
its
physical
momentum
–
a
concept
totally
alien
to
Copernicus
–
but
because
they
share
in
the
metaphysical
attribute
of
"earthiness",
and
therefore
circular
motion
is
"natural"
to
them.
They
follow
the
earth
by
affinity
or
sympathy.

Lastly,

"we
conceive
immobility
to
be
nobler
and
more
divine
than
mutability
and
instability,
which
latter
is
therefore
more
appropriate
to
the
earth
than
to
the
universe.
I
add
to
this
that
it
would
seem
quite
absurd
to
attribute
motion
to
that
which
contains
and
locates,
rather
than
to
that
which
is
contained
and
located
–
namely,
the
earth."

Apart
from
the
greater
geometrical
simplicity
of
his
system
as
a
means
of
saving
the
phenomena,
this
is
all
that
Copernicus
has
to
say,
by
way
of
physical
arguments,
in
support
of
the
motion
of
the
earth.