Galileo Galilei


Galileo Galilei was a pioneer of modern physics and
telescopic astronomy who was born on February 15, 1564 near
Pisa, Italy. As an Italian physicist and astronomer, he was
the first to use the telescope to discover many
undiscovered realms of space. His discoveries of sunspots,
lunar mountains and valleys, and the satellites of Jupiter
formed the basis of modern astronomy. His discoveries
opened a gateway into the unexplored areas of the universe.
Galileo's education began in Vallambrosa where he was
taught by monks, but the takeoff point of his career was
when he registered at the University of Pisa at the age of
seventeen. Here the power of mathematical reasoning
interested him so much that he became interested in
applying it to the events that occur in nature. He learned
of the studies of Aristotle and studied his writings on
logic, motion, and the structure of the universe. Over the
years Galileo criticized and refuted many of Aristotle's
views. He became one of the most relentless demolishers of
Aristotle's doctrines. 

Galileo's studies began in the Cathedral of Pisa one day as
Galileo was watching a lamp which was swinging from the
ceiling. He observed a rhythm in the swings of the lamp and
noticed that the lamp always took the same time to go from
one end of its swing to the other. His goal was to find out
whether or not all of the swings took the same amount of
time. He and a friend both made pendulums and decided to
count the number of oscillations that the pendulums made in
a given amount of time. They found that both pendulums made
the same number of oscillations at the same time. Thus he
discovered the law of isochronism, or equality of time, of
oscillations. By 1586, Galileo left the University of Pisa
and went back to his family in Florence. 

In Florence, Galileo applied himself to geometry and from
the study of Euclid he soon passed to that of other ancient
mathematicians, especially Archimedes. Galileo found in
Archimedes a teacher for whom he learned the power and the
wide intellectual range of mathematical reasoning. Galileo
studies produced two books that he wrote during this
period. One, in Latin contains the theorems to determine
the center of gravity of solid bodies, made him known among
mathematicians of his time. The other book, called the
Little Balance, was written in Italian. In this book he
told how he read the story of Archimedes and the studies of
bodies immersed in water. 

In the fall of that year Galileo moved to Pisa where he
studied while he continued to teach at the university,In
this period he resumed his study of motion and wrote a
short book in Latin know as De Motu (On Motion). In De Motu
, Galileo tried to disprove some of Aristotle's main views
about motion. One of his objections was the assertion that
motion, in the absence of the direct action of a force, is
maintained by the medium in which it takes place. De Motu
represents Galileo's first step in his systematic study of
motion and is a key point of reference in Galileo's
intellectual development. It shows that Galileo had already
started the deep process of original thinking and critical
revision of Aristotle's principles which lasted throughout
his life.
At about this time Galileo tried to disprove one particular
statement of Aristotle's. Aristotle said that when bodies
of the same material but of different weights fall freely,
they fall with speeds proportional to their weights. To
prove that lighter and heavier objects fall at the same
speed, Galileo climbed to the top of the Leaning Tower of
Pisa while the entire body of students gathered in the
square below to watch the demonstration. From the top of
the tower, Galileo let go two objects of the same substance
but of different weights at exactly the same time. They
reached the ground at exactly the same time. This story may
or may not be true, but was also proved by the Dutch
mathematician Simon Stevinus.
At the age of 28, Galileo moved to Padua. These years were
said to be the best eighteen years of his life. Galileo
made friends among the nobles and the rich Venetians. One
of his most important friends, Giovanni Francesco Sagredo,
used his position to improve Galileo's status as a
scientist at the University. Following Sagredo's death,
Galileo's friend lived on as a character in two of his best
books, Dialogue of the Two Greatest Systems of the World
and Two New Sciences. Galileo became a professor at the
University of Padua and began to teach large numbers of
students. During these years Galileo wrote many of his
greatest books, including Fortifications, Military
Constructions, and Mechanics. The last and most important
was a true engineering textbook which described the action
of simple machines such as the lever, pulley, screw, and
inclined plane. He also dealt with problems of falling
bodies which he took up again in later years.
In 1597, Galileo built an instrument which illustrates both
his competence in mathematical calculation and his great
craftsmanship. This device was known as the geometric and
military compass. It was a combination of a divider and
slide rule. It helped to solve a large number of
mathematical and geometric problems, including the
extraction of square and cubic roots. Because the end of
the sixteenth century was a period of conflict, Galileo
stressed military uses of this instrument. For instance,
the compass was used to determine relations of weight and
size of cannon balls, to regulate the front and side
formations of armies, and to measure the inclination of a
wall. Galileo sold so many that he could not produce enough
to fit the demand. The compass later became one of the most
useful and widely used inventions.
Galileo's most important scientific achievements in the
period at Padua were in two fields: the study of motion and
astronomy. In the field of motion he resumed the study
started in Pisa with observations on pendulums and falling
bodies. Galileo published these observations in 1638, in
the book Two New Sciences. 

Later, Galileo began to admire the work of a man named
William Gilbert, who had published a book called De Magnete
(Concerning the Magnet). Magnetism had been a well known
property of lodestone and iron at that time and was used by
navigators to make magnetic needles. Galileo, who did not
accept the authority of written word, performed Gilbert's
experiments himself. He wrote a new book called The
Dialogue, in which he told of how he became convinced that
the power of the stone is not increased by the weight of
the object.
Galileo's research on magnetism was yet a minor episode in
his scientific activity.
On October 9, 1604, a new star appeared in the sky. This
new star emerging aroused Galileo's scientific curiosity
and initiated his career as a stargazer. Shortly after the
star appeared, Galileo began to make systematic
observations He began to measure its height in the sky and
began to check whether its position in respect to other
stars varied from night to night. After having observed it
for several weeks, he gave three public lectures to
describe his findings and drew large crowds. A very
important invention emerged in 1609. In the early summer he
was in Venice when he heard that a certain Fleming had
constructed an eye-glass by which distant objects were seen
nearby. Galileo went back to Padua at once to think of how
he could build a similar instrument. He concluded that the
effect could be achieved by the combination of a convex and
concave glass. Galileo mounted the two lenses at the ends
of a lead tube, and his first telescope came into being.
At once he realized the great importance of his instrument,
both in science and in practical life. He realized it might
modify the art of war because it would permit sighting of
the enemy at much greater distance that usual. Galileo must
have shown the instrument to his friends or talked about
it, for soon the rumor spread that he had invented it. In a
letter to his brother in law Galileo stated: "And news
having reached Venice...I was called by the Most Serene
Signory six days ago, to whom it was my duty to show it as
well as to the whole Senate, to the intense astonishment of
all." Galileo indeed showed his telescope and it indeed
astonished all.
Senators and noblemen gathered around in the Palazzo
Ducale. The professor from Padua stood with his telescope
on the marble floor. His telescope was a sheet of metal,
covered by crimson sateen, of about the length of 24 inches
and the diameter of about one and three quarter inches in
diameter, with two glasses, one at each end. Galileo,
needing more room climbed the steep stairs of the bell
tower of San Marco across the Piazzetta and demonstrated
its ability to represent an object fifty miles off as
appearing five miles away. Galileo's telescope opened a new
door to the universe.
Once more Galileo showed his craftsmanship. The first
telescope he built had a magnification of three diameters,
the second eight diameters and finally he built one
magnifying 33 diameters. He increased the size of his
lenses, stopping at the point where a further increase
would result in the distortion of images. No instrument but
the telescope could give Galileo the feeling of how much
the power of the senses could be enlarged. For the first
time he could see distant things as well as if they were
close by and discover the existence of objects that up till
then had been too far away to be visible. Many new things
in space appeared to him.
The moon appeared very different to him, and among its new
strange features were prominences and cavities in its
surface. Many of these were comparable to mountains and
crevices in the Earth's surface. Galileo calculated the
height of lunar mountains and concluded correctly that some
are as high as four miles. he calculated that these
mountains were higher than any mountain on the Earth.Mount
Everest is actually five and a half miles high.
The telescope still had more marvels marvels in store.
Galileo soon discovered four small planets revolving around
the planet Jupiter, as the moon revolves around the Earth.
He named Jupiter's satellites the Medicean Satellites and
this remained his favorite astronomical discovery. He
observed the satellites of Jupiter and studied their
motion. He used this to predict the satellite's positions
so accurately that navigators would be able to rely on them
to guide their ships. He spent year after year observing
the Medicean planets with his telescope. 

Less than a month later Galileo announced another detail
noticed by him. He described the phases of Venus. He said
that he began to observe Venus with his instrument and saw
it was growing in size daily, keeping its roundness until
it eventually arrived a great distance from the sun and
started to lose its roundness on its eastern side. A few
days later, it diminished to a half circle. Then it
transformed into a horned shape and it became thinner until
it vanished. Copernicus had been disappointed not to see
the phases of Venus. The fact is that the phases of Venus
are undetectable with the naked eye.
Soon afterward he made another important observation, that
of sunspots. He described them as being dark spots seen in
the solar disk. Some were always produced and others are
being dissolved. They varied in duration from one or two
days to thirty or forty. Their shapes continually changed,
some quickly and violently, and some more slowly and
moderately. In addition to changing shape, some of them
divided into three or four, and some of them united into
one. Besides all of these disordered movements they have in
common a general uniform motion across the face of the sun
in parallel lines. From this motion was learned that the
sun was absolutely spherical, that it rotates west to east
around its center, and completes its entire revolution in
about a lunar month. Thus the sun had blemishes on its
surface, and it rotates around its axis as the Earth and
moon do.
During all of these years, the Inquisition had been
observing Galileo. The Inquisition was the high tribunal of
the Roman Church. During the Counter Reformation, the
Inquisition played a very important role. Working in
secrecy, it spotted, investigated, and prosecuted those
suspected of heresy, trying to suppress it before it could
spread. It exerted censorship to avoid the distortion of
the Catholic doctrine, and issued the Index of Prohibited
Books. To be tried by the Inquisition was something noone
could take lightly. 

Galileo kept talking in favor of the Copernican doctrine,
and while he busied himself with this, the Inquisition went
on examining his case. On February 23 a group of eleven
theologians was convened to examine his beliefs in science,
or at least what the Inquisition said were his beliefs. Two
propositions were submitted by the theologians: 1) The Sun
is the center of the world and hence immovable of local
motion. 2) The Earth is not the center of the world, or
immovable, but moves according to the whole itself and also
with diurnal motion. Neither of these were quoted from his
writings. on the Pope's instruction, Cardinal Bellarmine
called Galileo to his palace and told Galileo that he was
not to hold, teach, or defend the condemned opinion of
Copernicus. A few days later De Revolutionibus, which the
Pope had accepted, was condemned and prohibited until it be
Later, with the publish of The Dialogue, there was a clash
of personalities between Pope Urban VIII and Galileo.
Behind this clash were the long standing traditions and
authority of the Church and the need for freedom of thought
in science. The Chuch would not easily accept views that
went against tradition. As it happened, the conflict
between science and theology gathered so early that the
Church took strong action against the founder of modern
science. Galileo was summoned to Rome. He pleaded for time
and clemency, but the Pope was inflexible. The trial of
Galileo as a heretic had begun.
Galileo arrived in Rome in February 1633 and stayed there
five months. These months were filled wit questionings by
the Inquisitors. The purpose was to see whether Galileo was
still holding the prohibited doctrine and whether in
writing The Dialogue he had disobeyed orders. The trial
turned into gradual spiritual pressure in which they tried
to make Galileo believe a sin that he had not committed. On
June 22, 1633, Galileo was taken to the large hall of a
monastery in the center of Rome. He knelt as the sentence
was read to him: "We say, pronounce, sentence and declare
that you, Galileo, for the things found in the trial and
confessed by you have made yourself suspected of heresy. We
order that the book The Dialogue by Galileo Galilei be
prohibited by public edict. We condemn you to formal
prison...and we impose on you that for the next three years
you say the seven penitential psalms once a week." 

In the final years Galileo completed his book Two New
Sciences. Galileo's eyes had bothered him for many years.
He had been complaining of eye pain because of long hours
of studying. He lost sight in his right eye first, then the
left. During the last four years of his life he was
completely blind. In November 1641 a slow fever seized
Galileo and his arthritic pains had become more. This was
his last illness. He died on January 8, 1642 at almost 78
years of age. 


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