The Sleepwalkers (201 page)

Thus
ends
the
prelude.
The
journey
itself,
the
demon
explains,
is
only
possible
during
an
eclipse
of
the
moon,
and
must
therefore
be
completed
in
four
hours.
The
traveller
is
propelled
by
the
spirits,
but
he
is
subject
to
the
laws
of
physics;
it
is
at
this
point
that
science
takes
over
from
fantasy:

"The
initial
shock
[of
acceleration]
is
the
worst
part
of
it,
for
he
is
thrown
upward
as
if
by
an
explosion
of
gunpowder...
Therefore
he
must
be
dazed
by
opiates
^‡
beforehand;
his
limbs
must
be
carefully
protected
so
that
they
are
not
torn
from
him
and
the
recoil
is
spread
over
all
parts
of
his
body.
Then
he
will
meet
new
difficulties:
immense
cold
and
inhibited
respiration...
When
the
first
part
of
the
journey
is
completed,
it
becomes
easier
because
on
such
a
long
journey
the
body
no
doubt
escapes
the
magnetic
force
of
the
earth
and
enters
that
of
the
moon,
so
that
the
latter
gets
the
upper
hand.
At
this
point
we
set
the
travellers
free
and
leave
them
to
their
own
devices:
like
spiders
they
will
stretch
out
and
contract,
and
propel
themselves
forward
by
their
own
force
–
for,
as
the
magnetic
forces
of
the
earth
and
moon
both
attract
the
body
and
hold
it
suspended,
the
effect
is
as
if
neither
of
them
were
attracting
it
–
so
that
in
the
end
its
mass
will
by
itself
turn
toward
the
moon."

____________________

In
the
Astronomia
Nova
Kepler
had
come
so
close
to
the
concept
of
universal
gravity,
that
one
had
to
assume
the
existence
of
a
psychological
blockage
which
made
him
reject
it.
In
the
passage
just
quoted
he
not
only
takes
it
for
granted,
but,
with
truly
astonishing
insight,
postulates
the
existence
of
"zones
of
zero
gravity"
–
that
nightmare
of
science
fiction.
Later
on
in
the
Somnium
he
took
a
further
step
in
the
same
direction
by
assuming
that
there
are
spring
tides
on
the
moon,
due
to
the
joint
attraction
of
sun
and
earth.

The
journey
completed,
Kepler
proceeds
to
describe
conditions
on
the
moon.
A
lunar
day,
from
sunrise
to
sunset,
lasts
approximately
a
fortnight,
and
so
does
a
moon-night
–
for
the
moon
takes
a
month
to
turn
once
round
its
axis,
the
same
time
it
takes
to
complete
a
revolution
round
the
earth.
As
a
result,
it
turns
always
the
same
face
to
the
earth,
which
the
moon-creatures
call
their
"volva"
(from
revolvere
,
to
turn).
This
face
of
the
moon
they
call
the
Subvolvan
half,
the
other
is
the
Prevolvan
half.
Common
to
both
halves
is
that
their
year
consists
of
twelve
days-and-nights,
and
the
resulting
dreadful
contrasts
of
temperature
–
scorching
days,
frozen
nights.
Common
to
both
are
also
the
queer
motions
of
the
starry
sky
–
the
sun
and
planets
scuttle
incessantly
back
and
forth,
a
result
of
the
moon's
gyrations
round
the
volva.
This
"lunatic"
astronomy
–
in
the
legitimate
double
meaning
of
the
word
–
which
Kepler
develops
with
his
usual
precision,
is
sheer
delight;
nobody
before
(nor
since,
as
far
as
I
know)
had
attempted
such
a
thing.
But
when
it
comes
to
conditions
on
the
moon
itself,
the
picture
becomes
grim.

The
Prevolvans
are
the
worst
off.
Their
long
nights
are
not
made
tolerable
by
the
presence
of
the
huge
volva,
as
on
the
other
hemisphere,
for
the
Prevolvans
of
course
never
see
the
earth.

Their
nights
are
"bristling
with
ice
and
snow
under
the
raging,
icy
winds."
The
day
that
follows
is
no
better:
for
a
fortnight
the
sun
never
leaves
the
sky,
heating
the
air
to
a
temperature
"fifteen
times
hotter
than
our
Africa".