After his rebuff in Rome, Galileo returned to Florence,
where he settled in the well-appointed villa of Bellosguardo, on
a hill west of the city. His choice of residence was based, in
part, on its proximity to a Franciscan convent, where two of his
daughters had recently entered as nuns. (Their illegitimate birth
deprived them of favorable marriage prospects, and so their acceptance
by the convent provided a security they could not otherwise have
hoped for.) Galileo was very close to his two daughters, particularly
the eldest, Virginia, now known as Sister Mary Celeste, who would
become a great support to him in his old age. Meanwhile, the Church's
prohibitions had not diminished his intellectual fire, although
for a time he channeled it into more minor pursuits, focusing on
safer topics like magnets and motion, the construction of a microscope, and
even plans for flood control in northern Italy. But his inability to
explore his true interests wore on him, and for a time Galileo seems
to have sunk into a deep depression, worsened by bouts of illness
and hypochondria. Moreover, from 1617 to 1619, a series of terrible
winters ruined the economy of Florence, making his gloomy predicament
all the worse.
Eventually, however, his spirits revived; Galileo was
soon fired up again in astronomical debate, as the August 1618
appearance of a magnificent comet sparked disagreement between
his disciples and the Jesuit astronomers. While the Church scientists
maintained that comets originated beyond the moon, Galileo's theory
held (mistakenly) that they emanated from the earth's atmosphere.
Now jumping personally into the fray, Galileo assisted one of his
followers, Mario Guiducci, in writing a pamphlet objecting to the Jesuit
view. The pamphlet employed such harsh language–referring to "absurdities"
and "monstrosities" of their theory–that the Jesuits recoiled in
bitter enmity. They responded to the Guiducci-Galileo treatise
in harsh and cutting terms, thus inviting a counter-thrust from
the proud Galileo. However, he waited two years before delivering
it, composing in the meantime the 1622 treatise "The Assayer,"
which issued a rallying cry for what he believed to be the true
path of scientific thought: "Philosophy is written in this grand book,
the universe, which stands continually open to our gaze," he wrote.
"But the book cannot be understood unless one first learns to
comprehend the language and read the letters in which it is composed,"
he went on: "It is written in the language of mathematics, and
its characters are triangles, circles, and other geometric figures...
Without these, one wanders about in a dark and obscure labyrinth."
In his heart, he was still the eager student at the University of
Pisa, entranced by the glorious vistas of mathematics.
Meanwhile, political developments gave Galileo reason
for a new optimism. September 1621 saw the death of Galileo's
old nemesis, Cardinal Bellarmine. In January of that year, Pope
Paul V had died as well, being replaced by the elderly Gregory
XV, who passed away in turn in June of 1623. His successor was
Urban VIII, a liberal churchman with a bent for science and a special
fondness for Galileo.
At home in Bellosguardo, Galileo rejoiced at the election,
and quickly dedicated "The Assayer" to the new Pope, who allowed
it to be published and reportedly roared with laughter at Galileo's verbal
tweaking of the Jesuits. Heartened, Galileo journeyed to Rome
in April of 1624, and received warm welcome from Urban, who loaded
him with gifts and praise–but refused to lift the Inquisition's
ban on the Copernican theory. He and Galileo sparred over the
issue, and his arguments seem to have stuck in Galileo's head, for
he would put them in the mouth of a foolish character in his forthcoming
work, the Dialogue Concerning the Two Chief World Systems.
This would be a colossal blunder. For now though, Urban seemed
to point the way to reconciliation when he declared that the Church
had never "condemned nor ever would condemn the doctrine [of heliocentricity]
as heretical, but only as rash." Galileo returned home in June,
and, encouraged by the new leniency of Rome's position, set to
work on what would become his masterpiece.
Galileo worked on the Dialogue Concerning the
Two Chief World Systems intermittently over a period of
five years, from 1624 to 1629. His labor encountered frequent
interruptions, first in the form of persistent ill health and then
by his temporary appointment to the ruling council of Tuscany under
Cosimo II's son Ferdinand, but he persevered, and completed his
labors. As its title suggests, the work took the form of a dialogue
between three speakers: Salviati, a Copernican who speaks for Galileo
himself; Sagredo, an open-minded gentleman who gradually comes
to accept Salviati's arguments; and Simplicio, a defender of the
Ptolemaic world-view, whose simplistic dogmatism falls to Salviati's
keen insights. The dialogue form allowed him to claim impartiality–
he was "equally" presenting both views–although
in fact, of course, he clearly weighted the dialogue toward the
Copernican point of view. Nevertheless, it seemed that the text
would pass muster with the Catholic authorities: Galileo visited
Rome in the spring of 1630, and obtained tentative permission for
the publication of the Dialogue, on condition that
certain changes be made, and that rigorous care be taken that the
heliocentric theory be treated explicitly as a hypothesis. But
now a plague swept Florence, and Galileo was called home; as disease
descended upon northern Italy and communications broke down, Church
authorities agreed that Galileo need not come to Rome for more
revisions: the work could be published, as long as Galileo included
an orthodox preface and conclusion, penned by the censors in Rome.
The Dialogue was published according to orders
in Florence in February 1632. It marked a great triumph for Galileo:
his arguments for Copernicus's system stood in print at last, and
with the blessing of the Church. But this triumph would be short-lived.
