The Sleepwalkers (243 page)

The
confusion
was
made
even
worse
by
the
last
of
the
preNewtonian
giants,
Descartes.
According
to
him,
inertia
made
bodies
persist
not
in
circular
but
in
straight
motion.
This
was
the
most
bewildering
view
of
all,
for
heavenly
bodies
might
move
in
circles
or
ellipses,
but
they
certainly
did
not
move
along
straight
lines.
Descartes
therefore
assumed
that
the
planets
were
whirled
round
by
vortices
in
an
all-pervading
ether
–
an
elaboration
of
Kepler's
rotating,
sweeping
brooms.
¹

There
was,
then,
complete
disagreement
(a)
on
the
nature
of
the
force
which
drives
the
planets
round
and
keeps
them
in
their
orbits,
and
(b)
on
the
question
what
a
body
in
the
vastness
of
space
would
do
with
itself
if
it
were
left
alone,
that
is,
without
external
agents
acting
on
it.
These
questions
were
inextricably
mixed
up
with
the
problem
of
what
"weight"
really
meant,
with
the
mysterious
phenomenon
of
magnetism,
and
with
the
perplexities
of
the
emergent
concepts
of
physical
"forces"
and
"energies".

2.
What is "Weight"?

The
telescope
had
shown
that
the
moon
had
a
rugged
surface
much
like
the
earth,
and
that
the
sun
was
apt
to
break
out
in
spots;
this
led
to
a
growing
conviction
that
heavenly
bodies
were
of
earthly
nature
and
would
tend
to
behave
in
the
same
manner
as
things
behave
on
earth.
Now
the
most
conspicuous
quality
in
which
all
bodies
on
earth
shared
was
weight
–
the
tendency
to
press
or
fall
downward
(unless
forced
upward
by
the
pressure
of
heavier
substances).
In
the
old
philosophy,
this
was
satisfactorily
explained
by
the
fact
that
every
earthly
object
tended
to
move
towards
the
centre
of
the
world
or
away
from
it
–
whereas
objects
in
the
sky
obeyed
different
laws.
In
the
new
philosophy,
this
dualism
was
denied,
and
the
position
of
the
earth
in
the
centre
of
the
world
was
equally
denied.
But
while
it
played
havoc
with
the
old
commonsense
beliefs,
the
new
philosophy
provided
no
answers
to
the
problems
which
it
raised.
If
the
moon,
the
planets
and
comets
were
of
the
same
nature
as
bodies
on
earth,
then
they
too
must
have
"weight";
but
what
exactly
does
"the
weight"
of
a
planet
mean,
what
does
it
press
against
or
where
does
it
tend
to
fall?
And
if
the
reason
why
a
stone
falls
to
earth
is
not
the
earth's
position
in
the
centre
of
the
universe,
then
just
why
does
the
stone
fall?

One
may
note
in
passing
that
some
of
our
logical
positivists
transferred
into
the
seventeenth
century
would
have
dismissed
the
question
what
a
planet
"weighs"
as
meaningless
with
an
airy
wave
of
the
hand;
and
if
their
attitude
had
prevailed,
the
scientific
revolution
would
not
have
taken
place.
As
it
happened,
the
leaders
of
the
movement
tried
to
wriggle
out
from
between
the
horns
of
the
dilemma,
each
after
his
own
fashion,
without
much
regard
for
semantic
purity.
Copernicus
tentatively
suggested
that
objects
on
the
sun
and
moon
had
weight
as
bodies
on
earth,
and
that
"weight"
meant
the
tendency
of
all
matter
to
arrange
itself
in
spherical
shape
around
a
centre.
Galileo
believed
that
"weight"
was
an
absolute
quality
of
all
terrestrial
matter,
which
did
not
require
a
cause
and
was
in
fact
indistinguishable
from
its
inertia;
whereas
in
heavenly
bodies
"weight"
became
somehow
identical
with
their
persistence
in
moving
along
a
circular
path.
Kepler
was
the
first
to
explain
"weight"
as
the
mutual
attraction
between
two
bodies;
he
had
even
postulated
that
two
bodies
in
space,
exposed
to
no
other
influence,
would
approach
each
other
and
would
meet
at
an
intermediary
point,
so
that
the
distances
covered
by
each
would
be
in
inverse
ratio
to
their
masses,
and
he
correctly
attributed
the
tides
to
the
attraction
of
the
sun
and
moon;
yet,
as
we
saw,
at
the
decisive
moment
he
shrank
back
from
the
fantastic
notion
of
a
gravitational
anima
mundi
.

3.
The Magnetic Confusion

The
confusion
was
further
increased
by
William
Gilbert's
sensational
theory
that
the
earth
was
a
giant
loadstone,
which
induced
Kepler
to
identify
the
sun's
action
on
the
planets
as
a
"magnetic"
force.
It
was
quite
natural,
and
indeed
logical,
that
this
confusion
between
magnetism
and
gravity
should
arise,
for
the
loadstone
was
the
only
concrete
and
tangible
demonstration
of
the
mysterious
tendency
of
matter
to
join
matter
under
the
influence
of
a
"force"
which
acted
at
a
distance
without
contact
or
intermediaries.
Hence
the
magnet
became
the
archetype
of
action-at-a-distance
and
paved
the
way
for
universal
gravity.
Without
Dr.
Gilbert,
man
would
have
been
much
less
prepared
to
exchange
the
homely
and
traditional
view
that
"weight"
meant
the
natural
tendency
of
bodies
to
fall
towards
the
centre
for
the
adventurous
notion
that
it
meant
the
grappling
of
bodies
at
each
other
across
empty
space.
Magnetism
demonstrated
that
this
grappling
by
ghostly
fingers
was
a
fact,
that
iron
filings
rushed
to
a
magnet
as
by
secret
command,
as
stones
rushed
to
the
earth;
and
for
about
half
a
century
the
two
phenomena
were
either
identified,
or
regarded
as
Siamese
twins.
Moreover,
the
word
"magnetism"
was
used
in
a
broader,
metaphorical
sense;
it
had
a
profoundly
appealing
ambiguity
as
another
Janus-faced
agency
which
pertained
both
to
the
world
of
the
spirit
and
of
matter.
On
the
one
hand,
the
magnet
sent
out
its
energy,
as
exact
science
demanded,
"without
error
...
quick,
definite,
constant,
directive,
motive,
imperant,
harmonious"';
on
the
other
hand,
it
was
something
animate
and
living,
it
"imitates
a
soul",
nay,
it
was
the
very
"soul
of
the
earth",
its
"instinct
of
selfpreservation".
"The
magnetic
effluvium
of
the
earth
reaches
out
like
in
arm
clasping
round
the
attracted
body
and
drawing
it
to
itself."
This
arm
"must
needs
be
light
and
spiritual
so
as
to
enter
the
iron",
but
at
the
same
time
it
must
also
be
material
–
a
thin
and
rare
ether.
²