The Sleepwalkers (226 page)

2.
The Comets

The
next
two
years
he
was
mostly
ill,
but
did
some
minor
work,
such
as
the
construction
of
a
naval
telescope,
and
also
made
an
attempt,
which
failed,
to
use
the
periods
of
the
Jupiter
moons
as
an
aid
to
determine
geographical
longitude.
It
was
apparently
the
last
time
he
took
a
positive
interest
in
astronomical
research.

After
two
years,
in
1618,
he
could
hold
back
no
longer,
and
sent
his
treatise
on
the
tides
to
Archbishop
Leopold
of
Austria,
describing
it
in
his
covering
letter
as
a
"poetical
conceit
or
dream"
written
at
the
time
when
he
believed
the
Copernican
system
to
be
true,
and
before
being
taught
better
by
the
decision
of
the
authorities
who
were
"guided
by
a
higher
insight
than
any
to
which
my
humble
mind
can
of
itself
attain."
He
hoped,
no
doubt,
that
the
treatise
would
be
printed
in
Austria
without
formal
authorization
on
his
part,
but
it
came
to
nothing.

In
the
same
year
three
comets
appeared
in
the
sky.
They
announced
the
beginning
both
of
the
Thirty
Years
War,
and
of
the
most
disastrous
of
the
many
controversies
in
which
Galileo
became
involved.

It
was
caused
by
a
lecture,
subsequently
published,
by
the
Jesuit
Father
Horatio
Grassi
of
the
Collegium
Romanum
.
It
expressed
the
correct
view
that
comets
move
in
regular
orbits
like
planets,
at
a
distance
far
greater
than
the
moon's.
In
support
of
this
view,
Grassi
quoted
with
approval
Tycho's
conclusions
regarding
the
famous
comet
of
1577.
The
treatise
was
a
further
step
in
the
Jesuits'
retreat
from
Aristotle,
who
had
maintained
that
comets
were
earthly
exhalations
in
the
sublunary
sphere,
and
a
further
sign
of
the
Order's
implicit
endorsement
of
the
Tychonic
system.

When
Galileo
read
the
treatise,
he
had
an
outburst
of
fury.
He
covered
its
margins
with
exclamations
like
"piece
of
asininity",
"elephantine",
"buffoon",
"evil
poltroon",
and
"ungrateful
villain".
The
ingratitude
consisted
in
the
fact
that
the
treatise
did
not
mention
Galileo's
name
–
whose
only
contribution
to
the
theory
of
comets
had
been
a
casual
endorsement
of
Tycho's
views
in
the
Letters
on
Sunspots
.
⁴

But
now
the
situation
had
changed.
The
Tychonic
compromise
must
be
rejected,
so
that
the
choice
should
remain
confined
to
the
discredited
Ptolemy
and
to
Copernicus.
Galileo
abruptly
reversed
his
own
arguments:
he
decided
that
comets
are
not
real
objects
at
all,
but
optical
illusions
like
the
aurora-borealis
or
the
mock-suns,
caused
by
the
reflection
of
earthly
vapours,
which
reach
up
into
the
sky
past
the
moon.
If
they
were
real,
they
ought
to
appear
larger
as
they
approach
the
earth
and
smaller
as
they
recede,
whereas,
according
to
Galileo,
comets
appear
at
their
full
size
and
then
vanish
altogether.

Apart
from
wishing
to
prove
that
Tycho
and
Grassi
understood
nothing
of
astronomy,
Galileo
had
another
motive
for
denying
that
comets
exist:
their
paths
were
so
markedly
elliptic,
that
they
could
not
be
reconciled
with
the
circular
orbits
in
which
all
real
heavenly
objects
must
move
around
the
sun.

Galileo
did
not
attack
Grassi
directly,
under
his
own
name,
but
let
his
former
pupil
Mario
Guiducci,
sign
a
Discourse
on
Comets
–
the
manuscript
of
most
of
which
survived,
and
is
in
Galileo's
handwriting.
At
the
end
of
the
treatise,
Grassi
is
reproached
for
failing
to
mention
Galileo's
discoveries,
and
Father
Scheiner
for
"misappropriating
the
discoveries
of
others".

Since
Galileo
had
not
signed
with
his
own
name,
Grassi
now
replied
under
a
transparent
anagram
as
"Lothario
Sarsi
Sigensano"
(for
Horatio
Grassi
Salonensi).
He
ignored
Guiducci,
and
attacked
Galileo
with
vehemence.
He
showed
that
Galileo
claimed
priority
for
discoveries
which
were
not
his
own,
and
took
up
the
challenge
about
the
Tychonic
system:
since
Ptolemy
was
refuted
and
Tycho
rejected
by
Galileo,
does
he
mean
that
Grassi
should
have
endorsed
Copernicus,
condemned
and
abhorred
by
every
good
Catholic?

Grassi's
pamphlet
was
published
in
1619
under
the
title
The
Astronomical
and
Philosophical
Balance
.
Galileo's
answer
was
the
famous
Il
Saggiatore
–
The
Assayer
,
who
measures
things
on
the
finer
balance
designed
for
precious
metals.
It
took
him
two
years
to
write
it,
and
it
was
published
in
1623
only,
four
years
after
Grassi's
counter-attack.