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Galileo Galilei's parents were Vincenzo Galilei and
Guilia Ammannati. Vincenzo, who was born in Florence in 1520, was a teacher of
music and a fine lute player. After studying music in Venice he carried out
experiments on strings to support his musical theories. Guilia, who was born in
Pescia, married Vincenzo in 1563 and they made their home in the countryside
near Pisa. Galileo was their first child and spent his early years with his
family in Pisa.
..
In 1572, when Galileo was eight years old, his family returned
to Florence, his father's home town. However, Galileo remained in Pisa and lived
for two years with Muzio Tedaldi who was related to Galileo's mother by
marriage. When he reached the age of ten, Galileo left Pisa to join his family
in Florence and there he was tutored by Jacopo Borghini. Once he was old enough
to be educated in a monastery, his parents sent him to the Camaldolese Monastery
at Vallombrosa which is situated on a magnificent forested hillside 33 km
southeast of Florence. The Camaldolese Order was independent of the Benedictine
Order, splitting from it in about 1012. The Order combined the solitary life of
the hermit with the strict life of the monk and soon the young Galileo found
this life an attractive one. He became a novice, intending to join the Order,
but this did not please his father who had already decided that his eldest son
should become a medical doctor.
..
Vincenzo had Galileo return from Vallombrosa to Florence and
give up the idea of joining the Camaldolese order. He did continue his schooling
in Florence, however, in a school run by the Camaldolese monks. In 1581 Vincenzo
sent Galileo back to Pisa to live again with Muzio Tedaldi and now to enrol for
a medical degree at the University of Pisa. Although the idea of a medical
career never seems to have appealed to Galileo, his father's wish was a fairly
natural one since there had been a distinguished physician in his family in the
previous century. Galileo never seems to have taken medical studies seriously,
attending courses on his real interests which were in mathematics and natural
philosophy. His mathematics teacher at Pisa was Filippo Fantoni, who held the
chair of mathematics. Galileo returned to Florence for the summer vacations and
there continued to study mathematics.
..
In the year 1582-83 Ostilio Ricci, who was the mathematician of
the Tuscan Court and a former pupil of Tartaglia,
taught a course on Euclid's
Elements at the University of Pisa which Galileo attended. During the
summer of 1583 Galileo was back in Florence with his family and Vincenzo
encouraged him to read Galen to further his medical studies. However Galileo,
still reluctant to study medicine, invited Ricci (also in Florence where the
Tuscan court spent the summer and autumn) to his home to meet his father. Ricci
tried to persuade Vincenzo to allow his son to study mathematics since this was
where his interests lay. Certainly Vincenzo did not like the idea and resisted
strongly but eventually he gave way a little and Galileo was able to study the
works of Euclid
and Archimedes
from the Italian translations which Tartaglia
had made. Of course he was still officially enrolled as a medical student at
Pisa but eventually, by 1585, he gave up this course and left without completing
his degree.
..
Galileo began teaching mathematics, first privately in Florence
and then during 1585-86 at Siena where he held a public appointment. During the
summer of 1586 he taught at Vallombrosa, and in this year he wrote his first
scientific book The little balance [La Balancitta] which described Archimedes'
method of finding the specific gravities (that is the relative densities) of
substances using a balance. In the following year he travelled to Rome to visit
Clavius
who was professor of mathematics at the Jesuit Collegio Romano there. A topic
which was very popular with the Jesuit mathematicians at this time was centres
of gravity and Galileo brought with him some results which he had discovered on
this topic. Despite making a very favourable impression on Clavius,
Galileo failed to gain an appointment to teach mathematics at the University of
Bologna.
..
After leaving Rome Galileo remained in contact with Clavius
by correspondence and Guidobaldo
del Monte was also a regular correspondent. Certainly the theorems which
Galileo had proved on the centres of gravity of solids, and left in Rome, were
discussed in this correspondence. It is also likely that Galileo received
lecture notes from courses which had been given at the Collegio Romano, for he
made copies of such material which still survive today. The correspondence began
around 1588 and continued for many years. Also in 1588 Galileo received a
prestigious invitation to lecture on the dimensions and location of hell in
Dante's Inferno at the Academy in Florence.
..
Fantoni left the chair of mathematics at the University of Pisa
in 1589 and Galileo was appointed to fill the post (although this was only a
nominal position to provide financial support for Galileo). Not only did he
receive strong recommendations from Clavius,
but he also had acquired an excellent reputation through his lectures at the
Florence Academy in the previous year. The young mathematician had rapidly
acquired the reputation that was necessary to gain such a position, but there
were still higher positions at which he might aim. Galileo spent three years
holding this post at the university of Pisa and during this time he wrote De
Motu a series of essays on the theory of motion which he never published. It
is likely that he never published this material because he was less than
satisfied with it, and this is fair for despite containing some important steps
forward, it also contained some incorrect ideas. Perhaps the most important new
ideas which De Motu contains is that one can test theories by conducting
experiments. In particular the work contains his important idea that one could
test theories about falling bodies using an inclined plane to slow down the rate
of descent.
..
In 1591 Vincenzo Galilei, Galileo's father, died and since
Galileo was the eldest son he had to provide financial support for the rest of
the family and in particular have the necessary financial means to provide
dowries for his two younger sisters. Being professor of mathematics at Pisa was
not well paid, so Galileo looked for a more lucrative post. With strong
recommendations from Guidobaldo
del Monte, Galileo was appointed professor of mathematics at the University
of Padua (the university of the Republic of Venice) in 1592 at a salary of three
times what he had received at Pisa. On 7 December 1592 he gave his inaugural
lecture and began a period of eighteen years at the university, years which he
later described as the happiest of his life. At Padua his duties were mainly to
teach Euclid's
geometry and standard (geocentric) astronomy to medical students, who would need
to know some astronomy in order to make use of astrology in their medical
practice. However, Galileo argued against Aristotle's
view of astronomy and natural philosophy in three public lectures he gave in
connection with the appearance of a New Star (now known as 'Kepler's
supernova') in 1604. The belief at this time was that of Aristotle,
namely that all changes in the heavens had to occur in the lunar region close to
the Earth, the realm of the fixed stars being permanent. Galileo used parallax
arguments to prove that the New Star could not be close to the Earth. In a
personal letter written to Kepler
in 1598, Galileo had stated that he was a Copernican (believer in the theories
of Copernicus).
However, no public sign of this belief was to appear until many years later.
..
At Padua, Galileo began a long term relationship with Maria
Gamba, who was from Venice, but they did not marry perhaps because Galileo felt
his financial situation was not good enough. In 1600 their first child Virginia
was born, followed by a second daughter Livia in the following year. In 1606
their son Vincenzo was born.
We mentioned above an error in Galileo's theory of motion as he
set it out in De Motu around 1590. He was quite mistaken in his belief
that the force acting on a body was the relative difference between its specific
gravity and that of the substance through which it moved. Galileo wrote to his
friend Paolo Sarpi, a fine mathematician who was consultor to the Venetian
government, in 1604 and it is clear from his letter that by this time he had
realised his mistake. In fact he had returned to work on the theory of motion in
1602 and over the following two years, through his study of inclined planes and
the pendulum, he had formulated the correct law of falling bodies and had worked
out that a projectile follows a parabolic path. However, these famous results
would not be published for another 35 years.
..
In May 1609, Galileo received a letter from Paolo Sarpi telling
him about a spyglass that a Dutchman had shown in Venice. Galileo wrote in the
Starry Messenger (Sidereus Nuncius) in April 1610:-
About ten months ago a report reached my ears that a certain Fleming had constructed a spyglass by means of which visible objects, though very distant from the eye of the observer, were distinctly seen as if nearby. Of this truly remarkable effect several experiences were related, to which some persons believed while other denied them. A few days later the report was confirmed by a letter I received from a Frenchman in Paris, Jacques Badovere, which caused me to apply myself wholeheartedly to investigate means by which I might arrive at the invention of a similar instrument. This I did soon afterwards, my basis being the doctrine of refraction.
In about two months, December and January, he made more discoveries that changed the world than anyone has ever made before or since.
I hold that the Sun is located at the centre of the revolutions of the heavenly orbs and does not change place, and that the Earth rotates on itself and moves around it. Moreover ... I confirm this view not only by refuting Ptolemy's and Aristotle's arguments, but also by producing many for the other side, especially some pertaining to physical effects whose causes perhaps cannot be determined in any other way, and other astronomical discoveries; these discoveries clearly confute the Ptolemaic system, and they agree admirably with this other position and confirm it.
Philosophy is written in this grand book, the universe, which stands continually open to our gaze. But the book cannot be understood unless one first learns to comprehend the language and read the characters in which it is written. It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures without which it is humanly impossible to understand a single word of it; without these one is wandering in a dark labyrinth.
I assume that the speed acquired by the same movable object over different inclinations of the plane are equal whenever the heights of those planes are equal.
The time in which a certain distance is traversed by an object moving under uniform acceleration from rest is equal to the time in which the same distance would be traversed by the same movable object moving at a uniform speed of one half the maximum and final speed of the previous uniformly accelerated motion.
One would expect that Galileo's understanding of the pendulum,
which he had since he was a young man, would have led him to design a pendulum
clock. In fact he only seems to have thought of this possibility near the end of
his life and around 1640 he did design the first pendulum clock. Galileo died in
early 1642 but the significance of his clock design was certainly realised by
his son Vincenzo who tried to make a clock to Galileo's plan, but failed.
..
It was a sad end for so great a man to die condemned of heresy.
His will indicated that he wished to be buried beside his father in the family
tomb in the Basilica of Santa Croce but his relatives feared, quite rightly,
that this would provoke opposition from the Church. His body was concealed and
only placed in a fine tomb in the church in 1737 by the civil authorities
against the wishes of many in the Church. On 31 October 1992, 350 years after
Galileo's death, Pope John Paul II gave an address on behalf of the Catholic
Church in which he admitted that errors had been made by the theological
advisors in the case of Galileo. He declared the Galileo case closed, but he did
not admit that the Church was wrong to convict Galileo on a charge of heresy
because of his belief that the Earth rotates round the sun.
..
Article by: J J O'Connor and E F
Robertson
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