| GALILEO (1564-1642), Italian physicist
and astronomer commonly known as Galileo, was born in Pisa February 15,
1564, of a noble and ancient Florentine family. His father was a man of
talent and learning who had a good knowledge of mathematics but was poor.
As a child, Galileo constructed ingenious toys and models of machinery.
In 1581 he entered the University of Pisa, where his him to study medicine.
At Pisa, from observing the swinging of a lamp in the cathedral, he was
led to discovering the isochronism of the pendulum. He played the lute
and the organ, and was a skilled draughtsman and painter. He wished
to study mathematics, but his father objected on the grounds that his medical
studies would suffer. However, Galileo received secret instruction
from Osilio Ricci, one of the professors at the university, and he soon
became primarily interested in mathematics and physics. In 1588, when
he was twenty-four, he invented a hydrostatic balance by means of which
the specific gravity of solids could be ascertained, and in the same
year he wrote a treatise on the center of gravity in solids which aroused
much attention, though it was not published until 1638. In 1589 he was
appointed to a lectureship of mathematics at the University of Pisa, and
at Pisa he demonstrated publicly, at the Leaning Tower, that the velocity
of falling bodies is independent of their weight. This demonstration aroused
the antagonism of his colleagues at the university, who quoted passages
from Aristotle stating, "If two different weights of the same material
were let fall from the same height, the heavier one would reach the ground
sooner than the other, in the proportion of their weights." He discovered
also at this time that a projectile follows a parabola in flight. These
and other unorthodox views aroused so much antagonism that Galileo resigned
and returned to Florence. The influence of friends in the Venetian senate
caused him to be nominated in 1592 to the chair of mathematics in the University
of Padua, where he remained eighteen years. He reinvented the thermometer,
originally conceived in the third century by Hero, the Greek scientist,
and it was at Padua that Galileo appears to have first accepted the doctrines
of Copernicus. His reputation grew, his appointment was renewed three times,
and his salary was increased.
In 1609, on hearing of a telescope
or spyglass devised by Hans Lippershey, a Dutch maker of eyeglasses, Galileo
began to construct telescopes himself. By means of them he became the first
investigator to observe the lunar "seas" and craters, the inner planets
as discs undergoing the moon's phases, and the myriad of stars beyond the
range of the unaided eye. He found that the Milky Way consisted of innumerable
stars arranged in groups and clusters. and discovered Jupiter’s four bright
satellites, but found Saturn mystifying because of the insufficient telescopic
power of his instruments. Galileo stressed that evidence of the truth of
the Copernican system was offered by his telescopic discoveries, but such
comments served only to antagonize theologians, who found his theories
heretical. Cosimo II, Grand Duke of Tuscany, offered him the chair of mathematics
at the University of Pisa, where he was not required to reside nor to give
lectures except on extraordinary occasions to sovereign princes and other
strangers of distinction. Galileo moved from Pisa to Florence, where he
continued his planetary observations. In 1611 he observed sunspots. His
announcement of discoveries supporting the Copernican system intensely
annoyed the followers of Aristotle, who quoted passages from Aristotle's
works and from the Scriptures describing the earth as the center of the
universe. In February 1616 theologians of the Holy Office characterized
as heretical the proposition "that the sun is immovable in the center of
the world and that the earth has a diurnal motion of rotation," and Pope
Paul V warned Galileo not to advocate the condemned doctrine. In 1632,
however, Galileo published A Dialogue on the Two Principal Systems of the
World containing an exposition of the Copernican system. It aroused so
much attention throughout Europe that its sale was prohibited, and in the
following year Galileo was summoned to Rome, where he was examined by the
Inquisition, and forced to kneel before a vast assembly and renounce his
findings His indefinite term of imprisonment was commuted, how ever, and
he was soon allowed to return to Florence. He continued to make further
researches on dynamics, discovered the moon's librations in 1637, and published
results of all his findings. His last eight years were spent in his villa
at Arcetri where he died on January 8, 1642.
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