Galilei, Galileo (1564-1642)
Born into a slightly decayed Florentine patrician family, Galileo entered the university of Pisa in 1581 to study medicine. However, he became so attracted to mathematics (traditionally against his father's wishes) that in 1585 he returned to Florence to study mathematics, and taught it there and at Siena. He was much influenced in this by Guidobaldo del Monte and, through him, by Archimedes. Thanks to Guidobaldo's patronage he obtained the chairs of mathematics at Pisa in 1589 and at Padua in 1592. While at Pisa he wrote De motu (on motion), an anti-Aristotelian, Archimedean work of physics which does not yet show a complete understanding of the law of falling bodies which he was to discover only in 1604. If he had ever dropped weights from the Leaning Tower of Pisa (probably he did not), it would have been as a test of the theory he then held, that only bodies of the same material fall at the same speed, whatever their weight. At Padua he lectured on mathematics, astronomy and mechanics and gave private instruction in military engineering. He was not then much interested in astronomy, although he privately claimed to be a Copernican in 1597.
In the summer of 1609 his life and work were drastically altered by reports from Holland about a new optical instrument. From the description of its properties he was quickly able to put together an effective combination of lenses (a plano-convex objective with plano-concave eyepiece); with improvements it became the best telescope in existence. With it he saw those celestial phenomena which he described in Sidereus nuncius (Starry messenger; 1610): myriads of stars invisible to the naked eye; the planets differing from the stars in having disks; the configuration of the Moon (clearly like the Earth); the four satellites or moons of Jupiter. Arguing from analogy he emerged as a Copernican, a conviction soon strengthened when he detected the phases of Venus and the shape of Saturn (actually its rings). All this secured for him fame and the post of mathematician and philosopher to the Grand Duke of Tuscany in Florence. In 1611 he visited Rome, was elected to the Lincean Academy and convinced many Jesuit astronomers of the reality of his discoveries. After returning to Florence he involved himself in many controversies: on floating bodies, on sunspots, on the relation of scientific and theological proof, and (later) on comets. By 1615 many theologians publicly opposed Copernicanism which was, for the first time, officially condemned. When Galileo went again to Rome (with his newly invented microscope) he failed to convince the Pope and cardinals that Copernicanism was really consonant with Biblical authority, and in 1616 he was told to cease holding or teaching Copernican cosmology.
Only temporarily discouraged, Galileo returned to Rome in 1624, seeking permission from the new pope, Urban VIII, to discuss Copernicanism in print. The Pope agreed, provided that Galileo fairly set out the Ptolemaic point of view, reminding him that God was not constrained by human logic, so that human arguments from physical evidence (which Galileo thought he had) were fallible. In 1632 there appeared Dialogo sopra i due massimi sistemi del mondo (Dialogue concerning the two chief world systems), a convincing exposition of the Copernican system, with an account of Galileo's discoveries about falling bodies. It is written in Italian (Latin tr. 1635) as a Platonic dialogue between Salviati (a Copernican), Sagredo (an educated amateur) and Simplicio (a diehard but intelligent Aristotelian). Galileo was a witty and effective writer and the Dialogo presents a realistic defeat for Simplicio by the new Galilean science, the arguments used being mathematical, logical and empirical in turn. Salviati abolishes the traditional world-view step by step until, when Copernicanism is clearly triumphant, Simplicio takes refuge in the Pope's argument, to which the others calmly assent. The book aroused an immediate storm in clerical circles: it clearly went against the spirit if not the letter of the Pope's concessions towards Copernicanism, and there was the interdiction of 1616. The result was a dramatic trial, after which the Dialogo was put on the Index. Galileo was made to abjure Copernicanism and was sentenced to life imprisonment - commuted to house arrest first in Siena, later (1634) in his villa at Arcetri, outside Florence. Here he completed his other great work, Discorsi e dimostrazioni matematiche intorno a due nuove scienze (known in English as The two new sciences; London 1638), the two new sciences being the strength of materials and the study of moving bodies, already partly discussed in the Dialogo.
Galileo's youth was passed in the atmosphere of late Renaissance Tuscany and Venice, but by his new discoveries in astronomy and physics (all made after the age of 40) he became one of the creators of 'the new philosophy' which is recognizably a part of modern science. Both his discoveries and his scientific method greatly influenced the development of the scientific revolution. Many of the problems then solved had first been posed by Galileo. His trial made him a hero of science in the struggle against authority.
