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Person: Galilei, Galileo

Galileo Galilei was an Italian scientist who formulated the basic law of falling bodies, which he verified by careful measurements. He constructed a telescope with which he studied lunar craters, and discovered four moons revolving around Jupiter and espoused the Copernican cause.

Mathematical Profile (Excerpt):

• 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.
• Vincenzo had Galileo return from Vallombrosa to Florence and give up the idea of joining the Camaldolese order.
• 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.
• Galileo never seems to have taken medical studies seriously, attending courses on his real interests which were in mathematics and natural philosophy.
• 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.
• 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.
• Galileo began teaching mathematics, first privately in Florence and then during 1585-86 at Siena where he held a public appointment.
• 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.
• 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).
• 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.
• 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.
• 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.
• 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).
• 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.
• We mentioned above an error in Galileo's theory of motion as he set it out in De Motu around 1590.
• 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 May 1609, Galileo received a letter from Paolo Sarpi telling him about a spyglass that a Dutchman had shown in Venice.
• From these reports, and using his own technical skills as a mathematician and as a craftsman, Galileo began to make a series of telescopes whose optical performance was much better than that of the Dutch instrument.
• To improve on this Galileo learned how to grind and polish his own lenses and by August 1609 he had an instrument with a magnification of around eight or nine.
• Galileo immediately saw the commercial and military applications of his telescope (which he called a perspicillum) for ships at sea.
• They were very impressed and, in return for a large increase in his salary, Galileo gave the sole rights for the manufacture of telescopes to the Venetian Senate.
• Galileo claimed to have seen mountains on the Moon, to have proved the Milky Way was made up of tiny stars, and to have seen four small bodies orbiting Jupiter.
• The Venetian Senate, perhaps realising that the rights to manufacture telescopes that Galileo had given them were worthless, froze his salary.
• However he had succeeded in impressing Cosimo and, in June 1610, only a month after his famous little book was published, Galileo resigned his post at Padua and became Chief Mathematician at the University of Pisa (without any teaching duties) and 'Mathematician and Philosopher' to the Grand Duke of Tuscany.
• In 1611 he visited Rome where he was treated as a leading celebrity; the Collegio Romano put on a grand dinner with speeches to honour Galileo's remarkable discoveries.
• He was also made a member of the Accademia dei Lincei (in fact the sixth member) and this was an honour which was especially important to Galileo who signed himself 'Galileo Galilei Linceo' from this time on.
• While in Rome, and after his return to Florence, Galileo continued to make observations with his telescope.
• Galileo first turned his telescope on Saturn on 25 July 1610 and it appeared as three bodies (his telescope was not good enough to show the rings but made them appear as lobes on either side of the planet).
• Continued observations were puzzling indeed to Galileo as the bodies on either side of Saturn vanished when the ring system was edge on.
• However, Galileo knew that all his discoveries were evidence for Copernicanism, although not a proof.
• However Galileo already knew that a body would fall in the observed manner on a rotating Earth.
• Other observations made by Galileo included the observation of sunspots.
• Since they had been born outside of marriage, Galileo believed that they themselves should never marry.
• Although Galileo put forward many revolutionary correct theories, he was not correct in all cases.
• A serious consequence of this unfortunate argument was that the Jesuits began to see Galileo as a dangerous opponent.
• Despite his private support for Copernicanism, Galileo tried to avoid controversy by not making public statements on the issue.
• Castelli had been a student of Galileo's and he was also a supporter of Copernicus.
• Castelli defended the Copernican position vigorously and wrote to Galileo afterwards telling him how successful he had been in putting the arguments.
• Galileo, less convinced that Castelli had won the argument, wrote Letter to Castelli to him arguing that the Bible had to be interpreted in the light of what science had shown to be true.
• Galileo had several opponents in Florence and they made sure that a copy of the Letter to Castelli was sent to the Inquisition in Rome.
• In 1616 Galileo wrote the Letter to the Grand Duchess which vigorously attacked the followers of Aristotle.
• They condemned the teachings of Copernicus, and Bellarmine conveyed their decision to Galileo who had not been personally involved in the trial.
• Galileo was forbidden to hold Copernican views but later events made him less concerned about this decision of the Inquisition.
• Most importantly Maffeo Barberini, who was an admirer of Galileo, was elected as Pope Urban VIII.
• This happened just as Galileo's book Il saggiatore (The Assayer) was about to be published by the Accademia dei Lincei in 1623 and Galileo was quick to dedicate this work to the new Pope.
• Galileo, therefore, decided to publish his views believing that he could do so without serious consequences from the Church.
• However by this stage in his life Galileo's health was poor with frequent bouts of severe illness and so even though he began to write his famous Dialogue in 1624 it took him six years to complete the work.
• Galileo attempted to obtain permission from Rome to publish the Dialogue in 1630 but this did not prove easy.
• In February 1632 Galileo published Dialogue Concerning the Two Chief Systems of the World - Ptolemaic and Copernican.
• The climax of the book is an argument by Salviati that the Earth moves which was based on Galileo's theory of the tides.
• Galileo's theory of the tides was entirely false despite being postulated after Kepler had already put forward the correct explanation.
• It was unfortunate, given the remarkable truths the Dialogue supported, that the argument which Galileo thought to give the strongest proof of Copernicus's theory should be incorrect.
• Shortly after publication of Dialogue Concerning the Two Chief Systems of the World - Ptolemaic and Copernican the Inquisition banned its sale and ordered Galileo to appear in Rome before them.
• Galileo's accusation at the trial which followed was that he had breached the conditions laid down by the Inquisition in 1616.
• However a different version of this decision was produced at the trial rather than the one Galileo had been given at the time.
• Found guilty, Galileo was condemned to lifelong imprisonment, but the sentence was carried out somewhat sympathetically and it amounted to house arrest rather than a prison sentence.
• After Galileo had completed work on the Discourses it was smuggled out of Italy, and taken to Leyden in Holland where it was published.
• 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.
• 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.

Born 15 February 1564, Pisa (now Italy). Died 8 January 1642, Arcetri near Florence (now Italy).

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Tags relevant for this person:

Analysis, Astronomy, Geography, Geometry, Origin Italy, Physics, Special Numbers And Numerals

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References

Adapted from other CC BY-SA 4.0 Sources:

1. O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive