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GALILEI, GALILEO (b. Pisa, Italy, 15 February
1564; d. Arcetri, Italy, 8 January 1642), physics,
astronomy.
are the life and works of Galileo, whose personal
conflict with religious authority dramatized the extent
and profundity of the changing approach to nature.
Early Years.
Galileo's father was Vincenzio Galilei,
a musician and musical theorist and a descendant of
a Florentine patrician family distinguished in medicine
and public affairs. He was a member of the
Florentine Camerata, a cultural group which included
musicians whose devotion to the revival of Greek
music and monody gave birth to opera. It was headed
by Giovanni Bardi, who sponsored Vincenzio's musical
studies under Gioseffo Zarlino at Venice around
1561. In 1562 he married Giulia Ammannati of
Pescia, with whom he settled at Pisa. Galileo was the
eldest of seven children. His brother Michelangelo
became a professional musician and spent most of
his life abroad. Two of his sisters, Virginia and Livia,
married and settled in Florence. Of the other children
no record survives beyond that of their births.
Galileo was first tutored at Pisa by one Jacopo
Borghini. Early in the 1570's, Vincenzio returned to
Florence, where he resettled the family about 1575.
Galileo was then sent to school at the celebrated
monastery of Santa Maria at Vallombrosa. In 1578
he entered the order as a novice, against the wishes
of his father, who removed him again to Florence
and applied unsuccessfully for a scholarship on his
behalf at the University of Pisa. Galileo resumed his
studies with the Vallombrosan monks in Florence
until 1581, when he was enrolled at the University of
Pisa as a medical student.
The chair of mathematics appears to have been
vacant during most of Galileo's years as a student
at Pisa. His formal education in astronomy was thus
probably confined to lectures on the Aristotelian De
caelo by the philosopher Francesco Buonamici. Physics
was likewise taught by Aristotelian lectures, given
by Buonamici and Girolamo Borro. As a medical
student, Galileo may have received instruction from
Andrea Cesalpino. His interest in medicine was not
great; he was instead attracted to mathematics in
1583, receiving instruction from Ostilio Ricci outside
the university. Ricci, a friend of Galileo's father and
later a member of the Academy of Design at
Florence, is said to have been a pupil of Niccolò
Tartaglia. Galileo's studies of mathematics, opposed
at first by his father, progressed rapidly; in 1585 he
left the university without a degree and returned to
Florence, where he pursued the study of Euclid and
Archimedes privately.
From 1585 to 1589 Galileo gave private lessons in
mathematics at Florence and private and public instruction
at Siena. In 1586 he composed a short work,
La bilancetta, in which he reconstructed the reasoning
of Archimedes in the detection of the goldsmith's
fraud in the matter of the crown of Hieron and described
an improved hydrostatic balance. During the
same period he became interested in problems of
centers of gravity in solid bodies. During a visit to
Rome in 1587, he made the acquaintance of the Jesuit
mathematician Christoph Klau (Clavius). In 1588 he
was invited by the Florentine Academy to lecture on
the geography of Dante's Inferno treated mathematically.
In the same year he applied for the chair
of mathematics at the University of Bologna, seeking
and obtaining from Guidobaldo del Monte an endorsement
based on his theorems on the centers of
gravity of paraboloids of revolution. The chair was
awarded, however, to Giovanni Antonio Magini,
probably on the basis of his superiority in astronomy,
a subject in which Galileo appears to have shown
little interest up to this time.
While Galileo was residing in Florence, his father
was engaged in a controversy with Zarlino over
musical theory. To destroy the old numerical theory
of harmony, Vincenzio performed a series of experimental
investigations of consonance and its relation
to the lengths and tensions of musical strings. These
he embodied in a published polemic of 1589, the
Discorso intorno all'opere di messer Gioseffo Zarlino
da Chioggia, and two unpublished treatises that survive
among Galileo's papers. It is probable that
Galileo's interest in the testing of mathematical rules
by physical observations began with the musical experiments
devised by his father during these years.
Professorship at Pisa.
In 1589, on the recommendation
of Guidobaldo, Galileo gained the chair
of mathematics at the University of Pisa. The philosopher
Jacopo Mazzoni, who came to Pisa at the same
time, and Girolamo Mercuriale, professor of medicine,
were close friends of the young mathematician.
Luca Valerio, a Roman mathematician noted particularly
for his later treatise on centers of gravity, met
Galileo on a visit to Pisa and later corresponded with
him. With other professors at Pisa, however, Galileo's
relations were not so cordial, chiefly because of his
campaign to discredit the prevailing Aristotelian
physics to the advantage of his mathematical chair.
His alleged demonstration at the Leaning Tower of
Pisa that bodies of the same material but different
weight fall with equal speed—if actually performed—was
clearly not an experiment but a public challenge
to the philosophers.
During Galileo's professorship at Pisa, he composed
an untitled treatise on motion against the Aristotelian
physics, now usually referred to as De motu.
Its opening sections developed a theory of falling
bodies derived from the buoyancy principle of Archimedes,