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GALILEI, GALILEO (b. Pisa, Italy, 15 February
1564; d. Arcetri, Italy, 8 January 1642), physics,
Controversies at Florence.
for the Jesuit Christoph Scheiner, asking Galileo's
opinion of it. Galileo replied in three long letters
during 1612, demolishing Scheiner's conjecture that
the spots were tiny planets. He asserted also that he
had observed sunspots much earlier and had shown
them to others at Rome early in 1611. This set the
stage for a deep enmity of Scheiner toward Galileo,
which, however, did not take active form at once.
Galileo's Letters on Sunspots was published at
Rome in 1613 under the auspices of the Lincean
Academy. In this book Galileo spoke out decisively
for the Copernican system for the first time in print.
In the same book he found a place for his first published
mention of the concept of conservation of
angular momentum and an associated inertial concept.
During its composition he had taken pains to
determine the theological status of the idea of incorruptibility
of the heavens, finding that this was regarded
by churchmen as an Aristotelian rather than
a Catholic dogma. But attacks against Galileo and
his followers soon appeared in ecclesiastical quarters.
These came to a head with a denunciation from the
pulpit in Florence late in 1614.
In December 1613 it had happened that theological
objections to Copernicanism were raised, in Galileo's
absence, at a court dinner, where Galileo's part was
upheld by Benedetto Castelli. Learning of this,
Galileo wrote a long letter to Castelli concerning the
inadmissibility of theological interference in purely
scientific questions. After the public denunciation in
1614, Castelli showed this letter to an influential
Dominican priest, who made a copy of it and sent
it to the Roman Inquisition for investigation. Galileo
then promptly sent an authoritative text of the letter
to Rome and began its expansion into the Letter to
Christina, composed in 1615 and eventually published
in 1636. Galileo argued that neither the Bible nor
nature could speak falsely and that the investigation
of nature was the province of the scientist, while the
reconciliation of scientific facts with the language of
the Bible was that of the theologian.
The book on bodies in water drew attacks from
four Aristotelian professors at Florence and Pisa,
while a book strongly supporting Galileo's position
appeared at Rome. Galileo prepared answers to his
critics, which he turned over to Castelli for publication
in order to avoid personal involvement. Detailed
replies to two of them (Colombe and Grazia), written
principally by Galileo himself, appeared anonymously
in 1615, with a prefatory note by Castelli
implying that he was the author and that Galileo
would have been more severe.
Late in 1615 Galileo went to Rome (against the
advice of his friends and the Tuscan ambassador) to
clear his own name and to prevent, if possible, the
official suppression of the teaching of Copernicanism.
In the first, he succeeded; no disciplinary action
against him was taken on the basis of his letter to
Castelli or his Copernican declaration in the book on
sunspots. In the second objective, however, he failed.
Pope Paul V, irritated by the agitation of questions
of biblical interpretation—then a bone of contention
with the Protestants—appointed a commission to
determine the theological status of the earth's motion.
The determination was adverse, and Galileo was
instructed on 26 February 1616 to abandon the holding
or defending of that view. No action was taken
against him, nor were any of his books suspended.
A book by the theologian Paolo Antonio Foscarini
reconciling the earth's motion with the Bible was
condemned, and the work of Copernicus and a commentary
on Job by Diego de Zuñiga were suspended
pending the correction of a few passages. One contemporary
document, bound into the proceedings but
of uncertain reliability, states that Galileo was also
ordered never to discuss the forbidden doctrine again.
If such an order was given, it was in contravention
of certain specific instructions of the pope and had
no legal force.
Returning to Florence, Galileo took up a practical
and noncontroversial problem, the determination of
longitudes at sea. He believed that this could be solved
by the preparation of accurate tables of the eclipses
of the satellites of Jupiter, which were of frequent
occurrence and could be observed telescopically from
any point on the earth. As a practical matter, the
eclipses could neither be predicted with sufficient
accuracy nor observed at sea with sufficient convenience
to make the method useful.
It is probable that Galileo also returned during this
period to his mechanical investigations, interrupted
in 1609 by the advent of the telescope. A Latin treatise
by Galileo, De motu accelerato, which correctly
defines uniform acceleration and much resembles the
definitive text reproduced in his final book, seems to
date from this intermediate period, and copies of
many of his propositions in kinematics exist in the
handwriting of Mario Guiducci, who studied under
Galileo at this time.
In 1618 three comets attracted the attention of
Europe and became the subject of many pamphlets
and books. One such book was printed anonymously
by Orazio Grassi, the mathematician of the Jesuit
Roman College. Galileo was bedridden at the time,
but he discussed his views on comets with Guiducci,
who then delivered lectures on them to the Florentine
Academy and published them over his own
name. In these lectures, which were largely dictated