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Galileo
Picture of Galileo
Galileo (1564-1642), Italian physicist
and astronomer, who, with the German astronomer Johannes Kepler,
initiated the scientific revolution that flowered in the work of
the English physicist Sir Isaac Newton. Born Galileo Galilei, his
main contributions were, in astronomy, the use of the telescope
in observation and the discovery of sunspots, lunar mountains and
valleys, the four largest satellites of Jupiter, and the phases
of Venus. In physics, he discovered the laws of falling bodies
and the motions of projectiles. In the history of culture,
Galileo stands as a symbol of the battle against authority for
freedom of inquiry.
Galileo was born near Pisa, on February
15, 1564. His father, Vincenzo Galilei, played an important role
in the musical revolution from medieval polyphony to harmonic
modulation. Just as Vincenzo saw that rigid theory stifled new
forms in music, so his eldest son came to see Aristotelian
physical theology as limiting scientific inquiry. Galileo was
taught by monks at Vallombroso and then entered the University of
Pisa in 1581 to study medicine. He soon turned to philosophy and
mathematics, leaving the university without a degree in 1585. For
a time he tutored privately and wrote on hydrostatics and natural
motions, but he did not publish. In 1589 he became professor of
mathematics at Pisa, where he is reported to have shown his
students the error of Aristotle's belief that speed of fall is
proportional to weight, by dropping two objects of different
weight simultaneously from the Leaning Tower. His contract was
not renewed in 1592, probably because he contradicted
Aristotelian professors. The same year, he was appointed to the
chair of mathematics at the University of Padua, where he
remained until 1610.
At Padua, Galileo invented a calculating
“compass” for the practical solution of mathematical
problems. He turned from speculative physics to careful
measurements, discovered the law of falling bodies and of the
parabolic path of projectiles, studied the motions of pendulums,
and investigated mechanics and the strength of materials. He
showed little interest in astronomy, although beginning in 1595
he preferred the Copernican theory —that the earth revolves
around the sun—to the Aristotelian and Ptolemaic assumption
that planets circle a fixed earth. Only the Copernican model
supported Galileo's tide theory, which was based on motions of
the earth. In 1609 he heard that a spyglass had been invented in
Holland. In August of that year he presented a telescope, about
as powerful as a modern field glass, to the doge of Venice. Its
value for naval and maritime operations resulted in the doubling
of his salary and his assurance of lifelong tenure as a
professor.
By December 1609, Galileo had built a telescope of 20 times
magnification, with which he discovered mountains and craters on
the moon. He also saw that the Milky Way was composed of stars,
and he discovered the four largest satellites of Jupiter. He
published these findings in March 1610 in The Starry Messenger
(trans. 1880). His new fame gained him appointment as court
mathematician at Florence; he was thereby freed from teaching
duties and had time for research and writing. By December 1610 he
had observed the phases of Venus, which contradicted Ptolemaic
astronomy and confirmed his preference for the Copernican system.
Professors of philosophy scorned
Galileo's discoveries because Aristotle had held that only
perfectly spherical bodies could exist in the heavens and that
nothing new could ever appear there. Galileo also disputed with
professors at Florence and Pisa over hydrostatics, and he
published a book on floating bodies in 1612. Four printed attacks
on this book followed, rejecting Galileo's physics. In 1613 he
published a work on sunspots and predicted victory for the
Copernican theory. A Pisan professor, in Galileo's absence, told
the Medici (the ruling family of Florence as well as Galileo's
employers) that belief in a moving earth was heretical. In 1614 a
Florentine priest denounced Galileists from the pulpit. Galileo
wrote a long, open letter on the irrelevance of biblical passages
in scientific arguments, holding that interpretation of the Bible
should be adapted to increasing knowledge and that no scientific
position should ever be made an article of Roman Catholic faith.
Early in 1616, Copernican books were subjected to censorship by
edict, and the Jesuit cardinal Robert Bellarmine instructed
Galileo that he must no longer hold or defend the concept that
the earth moves. Cardinal Bellarmine had previously advised him
to treat this subject only hypothetically and for scientific
purposes, without taking Copernican concepts as literally true or
attempting to reconcile them with the Bible. Galileo remained
silent on the subject for years, working on a method of
determining longitudes at sea by using his predictions of the
positions of Jupiter's satellites, resuming his earlier studies
of falling bodies, and setting forth his views on scientific
reasoning in a book on comets, The Assayer (1623; trans. 1957).
In 1624 Galileo began a book he wished to call “Dialogue on
the Tides,” in which he discussed the Ptolemaic and
Copernican hypotheses in relation to the physics of tides. In
1630 the book was licensed for printing by Roman Catholic censors
at Rome, but they altered the title to Dialogue on the Two Chief
World Systems (trans. 1661). It was published at Florence in
1632. Despite two official licenses, Galileo was summoned to Rome
by the Inquisition to stand trial for “grave suspicion of
heresy.” This charge was grounded on a report that Galileo
had been personally ordered in 1616 not to discuss Copernicanism
either orally or in writing. Cardinal Bellarmine had died, but
Galileo produced a certificate signed by the cardinal, stating
that Galileo had been subjected to no further restriction than
applied to any Roman Catholic under the 1616 edict. No signed
document contradicting this was ever found, but Galileo was
nevertheless compelled in 1633 to abjure and was sentenced to
life imprisonment (swiftly commuted to permanent house arrest).
The Dialogue was ordered to be burned, and the sentence against
him was to be read publicly in every university.
Galileo's final book, Discourses
Concerning Two New Sciences (trans. 1662-65), which was published
at Leiden in 1638, reviews and refines his earlier studies of
motion and, in general, the principles of mechanics. The book
opened a road that was to lead Newton to the law of universal
gravitation that linked Kepler's planetary laws with Galileo's
mathematical physics. Galileo became blind before it was
published, and he died at Arcetri, near Florence, on January 8,
1642.
Galileo's most valuable scientific contribution was his founding
of physics on precise measurements rather than on metaphysical
principles and formal logic. More widely influential, however,
were The Starry Messenger and the Dialogue, which opened new
vistas in astronomy. Galileo's lifelong struggle to free
scientific inquiry from restriction by philosophical and
theological interference stands beyond science. Since the full
publication of Galileo's trial documents in the 1870s, entire
responsibility for Galileo's condemnation has customarily been
placed on the Roman Catholic church. This conceals the role of
the philosophy professors who first persuaded theologians to link
Galileo's science with heresy. An investigation into the
astronomer's condemnation, calling for its reversal, was opened
in 1979 by Pope John Paul II. In October 1992 a papal commission
acknowledged the Vatican's error.
( Ptolemy - Copernicus - Kepler - Galileo - Newton )
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Copyright JoaoVicente.
Last update: 11/02/98.
