Galileo Galilei
Galileo Galilei, a pioneer of modern physics and telescopic
astronomy, was born near Pisa, Italy, on Feb. 15, 1564. In 1581 he
entered the University of Pisa as a medical student, but he soon
became interested in mathematics and left without a degree in 1585.
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After teaching privately at Florence, Galileo was made
professor of mathematics at Pisa in 1589. There he is said
to have demonstrated from the Leaning Tower that
Aristotelian physics was wrong in assuming that speed of
fall was proportional to weight; he also wrote a treatise on
motion, emphasizing mathematical arguments. In 1592, Galileo
became professor of mathematics at the University of Padua,
where he remained until 1610. He devised a mechanical
calculating device now called the sector, worked out a
mechanical explanation of the tides based on the Copernican
motions of the Earth, and wrote a treatise on mechanics
showing that machines do not create power but merely
transform it.
In 1602, Galileo resumed his investigations of motion
along inclined planes and began to study the motion of
pendulums. By 1604 he had formulated the basic law of
falling bodies, which he verified by careful measurements.
Late in 1604 a supernova appeared, and Galileo became
involved in a dispute with philosophers who held (with
Aristotle) that change could not occur in the heavens.
Applying the mathematics of parallax, Galileo found the star
to be very distant, in the supposedly unchangeable regions
of the cosmos, and he attacked Aristotelian qualitative
principles in science. Returning to his studies of motion,
he established quantitatively a restricted inertial
principle and determined that projectiles moved in parabolic
paths. In 1609 he was writing a mathematical treatise on
motion when news arrived of the newly invented Dutch
telescope. He was so excited by its possible scientific
applications that he put other work aside and began to
construct his own telescopes.
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By the end of 1609, Galileo had a 20-power telescope that enabled
him to see the lunar mountains, the starry nature of the Milky Way,
and previously unnoted "planets" revolving around Jupiter. He
published these discoveries in The Starry Messenger (1610), which
aroused great controversy until other scientists made telescopes
capable of confirming his observations. The Grand Duke of Tuscany
made him court mathematician at Florence, freeing him from teaching
to pursue research. By the end of 1610, he had observed the phases of
Venus and had become a firm believer in the Copernican heliocentric
world system. He was vigorously opposed in this belief, because the
Bible was seen as supporting the opposite view of a stationary Earth.
Galileo argued for freedom of inquiry in his Letter to the Grand
Duchess Christina (1615), but despite his argument that sensory
evidence and mathematical proofs should not be subjected to doubtful
scriptural interpretations, the Holy Office at Rome issued an edict
against Copernicanism in 1616.
In 1623, Maffeo Barberini, long friendly to Galileo, became pope
as Urban VIII, and Galileo obtained his permission to write a book
impartially discussing the Ptolemaic and Copernican systems. This
became Galileo's famous Dialogue Concerning the Two Chief World
Systems (1632), for which he was called to Rome for trial by the
Inquisition on the grounds that in 1616 he had been personally
ordered never to defend or to teach Copernicanism. In June 1633,
Galileo was condemned to life imprisonment for "vehement suspicion of
heresy." His Dialogue was banned, and printers were forbidden to
publish anything further by him or even to reprint his previous
works. Outside Italy, however, his Dialogue was translated into Latin
and was read by scholars throughout Europe.
Galileo's sentence was swiftly commuted to house arrest, at first
under custody of the friendly archbishop of Siena and then at his own
villa in Arcetri, near Florence. There Galileo resumed and completed
his Paduan studies on motion and on the strength of materials,
published at Leiden as Discourses and Mathematical Demonstrations
Concerning Two New Sciences (1638). He rightly regarded this as
containing the elements of a new physics that would be carried
further by his successors. Galileo died at Arcetri on Jan. 8, 1642.
Among Galileo's students was Benedetto Castelli, founder of the
science of hydraulics and teacher of Bonaventura Cavalieri and
Evangelista Torricelli. Cavalieri formulated principles that were
important to the development of the calculus, and Torricelli devised
the barometer and explained phenomena of atmospheric pressure.
Outside Italy, Galileo's influence was not great, except in making
scientists conscious of the need for freedom of inquiry. As he had
seen, not only religious but philosophical tradition had to yield to
observation and measurement if science were to prosper. In 1992, Pope
John Paul II acknowledged the church's error in condemning Galileo's
work.
Stillman Drake
Bibliography: Biagioli, Mario, Galileo, Courtier (1993); Butts, R.
E., and Pitt, J. C., eds., New Perspectives on Galileo (1978); Drake,
Stillman, Discoveries and Opinions of Galileo (1957), Galileo Studies
(1970), and Galileo at Work--His Scientific Biography (1978);
Gingerich, Owen, "How Galileo Changed the Rules of Science," Sky and
Telescope, March 1993; Redondi, Pietro, Galileo: Heretic (1987);
Reston, James, Jr., Galileo: A Life (1994); Santillana, Giorgio de,
The Crime of Galileo (1955); Wallace, W. A., Galileo and His Sources
(1984) and Galileo's Logical Treatises (1992).
Last modified on: Thursday, October 30, 1997.