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Galileo Galilei, talian 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.
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.
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.
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