The Sleepwalkers (231 page)

"...
straight
motion
being
by
nature
infinite
(because
a
straight
line
is
infinite
and
indeterminate),
it
is
impossible
that
anything
should
have
by
nature
the
principle
of
moving
in
a
straight
line;
or,
in
other
words,
towards
a
place
where
it
is
impossible
to
arrive,
there
being
no
finite
end.
For
nature,
as
Aristotle
well
says
himself,
never
undertakes
to
do
that
which
cannot
be
done,
nor
endeavours
to
move
whither
it
is
impossible
to
arrive."
¹²

This
belief
contradicts
Galileo's
intimate
knowledge
of
centrifugal
forces,
the
tendency
of
an
object
moving
in
a
circle
to
fly
off
at
a
tangent
in
a
straight
line.
On
the
second
day
another
classic
objection
against
the
earth's
rotation,
that
bodies
not
attached
to
the
earth
would
fly
off
into
space,
is
admitted
by
Galileo
as
valid
in
theory,
but
negligible
in
practice,
because
the
centrifugal
force
is
so
much
smaller
than
the
earth's
attraction.
¹³
He
thus
asserts
in
one
passage
that
a
stone
lying
in
a
field
has
a
natural
tendency
to
persist
in
its
circular
motion,
and
in
another
that
it
has
a
natural
tendency
to
fly
off
in
a
straight
line.
Similarly,
he
believed
that
freely
falling
bodies
describe
a
circular
path.
¹⁴
Thus
even
this
most
determined
opponent
of
Aristotelianism
could
not
rid
himself
of
the
old
circular
obsession
–
which
partly
explains
Galileo's
rejection
of
Kepler's
Laws.

The
second
day
ends,
on
Galileo's
own
admission,
in
a
stalemate.
He
has
refuted
the
objection
that
on
a
rotating
earth
detached
bodies
would
be
left
behind,
etc.;
but
he
has
not
proved
that
the
earth
does
rotate.
On
either
hypothesis,
whether
she
moves
or
stands
still,
stones
would
fall
and
birds
would
fly
as
they
do.

The
third
day
is
concerned
with
the
astronomical
arguments
for
and
against
Copernicus,
and
here
Galileo
is
downright
dishonest.
He
first
shows
that
the
Copernican
system
is
superior
to
the
Ptolemaic
by
the
familiar
arguments
from
the
Jupiter
moons
and
the
phases
of
Venus.
He
then
explains
that
to
"save"
the
planets'
apparent
stations
and
retrogressions,
Ptolemy
had
to
introduce
"very
great
epicycles"
which
Copernicus
was
able
to
dispense
"with
one
single
motion
of
the
earth".
But
he
breathes
not
a
word
about
the
fact
that
Copernicus,
too,
needs
a
whole
workshop
full
of
epicycles;
he
keeps
silent
about
the
eccentricity
of
the
orbits,
the
various
oscillations
and
librations,
the
fact
that
the
sun
is
neither
in
the
centre
of
the
motions,
nor
lies
in
their
plane;
in
a
word,
he
deliberately
evades
the
real
problems
of
astronomy
which
had
started
Tycho
and
Kepler
on
their
quest.
The
planets
all
move
in
perfect
circles
at
uniform
linear
velocities
around
the
sun
(which,
for
instance,
would
make
Saturn's
period
twenty-four
years
instead
of
thirty).
¹⁵
All
problems
appear
solved
"with
admirable
facility";
for
"in
the
Ptolemaic
hypothesis
there
are
the
diseases,
and
in
the
Copernican
their
cure."
¹⁶

It
is
true
that
Galileo
was
writing
for
a
lay
audience,
and
in
Italian;
his
account
however,
was
not
a
simplification
but
a
distortion
of
the
facts,
not
popular
science,
but
misleading
propaganda.
Even
his
latest,
admiring
biographer
is
prompted
to
the
remark:

"A
drastic
simplification
of
Copernicus
may
have
seemed
to
him
an
easier
didactic
device.
This
is,
at
least,
the
charitable
hypothesis.
But
the
problem
remains
of
how
Galileo
could
commit
the
capital
error,
against
which
he
had
warned
others
so
many
times,
of
constructing
theories
in
defiance
of
the
best
results
of
observation."
¹⁷

Even
so,
the
arguments
are
again
inconclusive,
for
all
that
Salviati
succeeds
in
proving
against
Simplicio
is
that
the
heliocentric
system
saves
the
phenomena
more
elegantly
than
the
geocentric,
but
not
that
it
is
true.
Moreover,
he
keeps
silent
about
the
fact
that
the
Tychonic
system
fits
the
phenomena
equally
well.

To
break
the
stalemate,
the
famous
theory
of
the
tides
is
brought
out
on
the
fourth
day.
But
before
that,
at
the
end
of
the
third,
a
new
and
unexpected
argument
makes
its
appearance.
It
is
derived
from
the
sunspots,
and
is
introduced
with
a
flourish: