GALILEO GALILEI (1564-1642),

      Italian mathematician, astronomer and physicist, who made three significant contributions to the founding of modern scientific thought:

(1) As the first man to use the telescope to study the skies, Galileo amassed evidence that proved the earth revolves around the sun and is not the center of the universe as had been believed. His system was such a radical departure from accepted thought that the Inquisition tried Galileo in Rome, ordered to recant and forced to spend the last eight year of his life under house arrest.

(2) Galileo informally stated the principle later embodied in Newton’s first two laws. Because of his pioneer work in gravitation and motion and in the combining of mathematics analysis with experimentation, Galileo often is referred to as the father of modern mechanics and experimental physics.

(3) Perhaps the most far-reaching of Galileo’s achievements was his re-establishment of mathematical rationalism against Aristotle’s logico-verbal approach, and his insistence that that “book of Nature is written in mathematical characters.” Through this he was able to found the modern experimental method. (SEE RATIONALISM: EPISTEMOLOGICAL RATIONALISM.)

Legend of the Lamp.¾ Galileo was born Pisa on Feb. 15, 1564, the son of Vincenzo Galileo, a musician. He received his early education at the monastery of Vallombrosa near Florence, where his family had moved in 1574, and in 1581 entered the University of Pisa to study medicine. While the Pisa cathedral during his first year at the University, Galileo supposedly observed a lamp always required the same amount of time to complete an oscillation, no mater how large the range of the swing. Later in life Galileo verified this observation experimentally and suggested that the principle of the pendulum might be applied to the regulation of clock.

      Until he supposedly observed the swinging lamp in the cathedral, Galileo had received no instruction in mathematics. 

      Than a geometry lesson he overheard by chance awakened his interest, and he began to study mathematics and science with Ostilio Ricci. But in 1585, before he had received a degree, he was withdrawn from the university because of lack of funds. He returned to Florence, lectured at the Florentine academy and in 1586 published an essay describing the hydrostatic balance, the invention of which made his name known through  Italy. In 1588 a treatise on the center of gravity in solids won for Galileo the honorable but not lucrative post of mathematics lecturer at the university of Pisa.

      Galileo then began his research into the theory of motion, first disproving the Aristotelian contention that bodies of different weights fall at different speeds. Because of financial difficulties, Galileo in 1592, applied and was awarded the chair of mathematics at Padua, where he was to remain for 18 years and performed the bulk of his most outstanding work. At Padua  he continued his research on motion. He also gave the law of parabolic fall with its inertial component. The legend of his dropping weights from the leaning tower of Pisa apparently has no basis in fact.

Research with the telescope. – Galileo became convinced early in life of the truth of the Copernican theory but was deterred from avowing his opinions- as shown in his letters of April 4, 1597, to Kepler – Because of

 fear of ridicule. While in Venice in the spring of 1609, Galileo learned of the recent invention of telescope. After returning to Padua he built a telescope of threefold magnifying power and quickly improved it to a  power of 32. because of the method Galileo devised for checking the curvature of the lenses, his telescopes were the first that could be used for astronomical observations, and they soon were in demand in all parts of Europe.

      As the first person to apply the telescope to a study of the skies, Galileo in late 1609 and early 1610 announced a series of astronomical discoveries. He found the surface of the moon was irregular and not smooth as had been supposed: he observed that the Milky Way was composed of collection of distant stars: he discovered the satellites of Jupiter and named them Sidera Medicea in honor of his former pupil and future employer, CasimoII, grand duke of Tuscany. Galileo also observed spots on the sun, the phases of Venus and what appeared to him as te three forms of Saturn. His first decisive astronomical observations were published in 1610 in Sidereus Nunicus.

      Although the Venetian senate had granted Galileo in lifetime appointment as professor at Padua because of his findings with the telescope, he left in summer of 1610 to become “first philosopher and mathematician” to the grand duke of Tuscany, an appointment that enabled him to devote more time to research.

Conflict with Rome. In 1611 Galileo visited Rome and demonstrated his telescope to the most eminent personages at the pontifical court. Encouraged by the flattering reception accorded to him, he ventured in his letters on the Sunspots, printed at Rome in 1613, to take up a more definite position on the Copernican theory.  Movement of the spots across the face of the sun, Galileo maintained, proved Copernicus was right and Ptolemy wrong.

      The great expository gifts of Galileo and his choice of Italian, in which he was acknowledged master of style, made his  thoughts popular beyond the confines of  the universities and created a powerful movement of opinion. The Aristotelian professors, seeing their vested interests threatened, united  against him. They strove to cast suspicion upon him in the eyes of ecclesiastical authorities because of contradiction between the Copernican theory and the Scriptures. They obtained the corporation of the Dominican preachers, who fulminated from the pulpit against the  new impiety of “mathematicians” and secretly denounced Galileo to the Inquisition for blasphemous utterances which had been freely invented.  Galileo, gravely alarmed, agreed with one of his pupils, B. Castelli, a Benedictine monk, that something should be done to forestall a crisis. He accordingly wrote letters meant for the grand duke and for the Roman authorities in which he pointed out the danger, reminding the church of its standing practice of interpreting scripture allegorically whenever it came into conflict with scientific truth, quoting patristic authorities and warning that it would be “ a terrible determent for the souls if people found themselves convinced by proof of something that it was made then a sin to believe”.   He even went to Rome in person to beg the Authorities to leave the way open for a change. A number of ecclesiastical experts were on his side. Unfortunately, Cardinal Bellarmine, the chief theologian of the church, was unable to appreciate the importance of the new theories. He clung to the time-honored belief that “mathematical hypotheses” have nothing to do with physical reality. He only saw the  danger of a “scandal” which might undermine Catholicity in its fight with Protestantism. He accordingly decided that the best thing would be to check the whole issue by having Copernicanism  declared “false and erroneous” and the book of Copernicus suspended by the congregation of the Index. The decree came out on March 5, 1616. on the  previous February 26, however, as an act of personal consideration, Cardinal Bellarmine had granted an audience to Galileo and informed him of the forthcoming  decree, warning him that he must henceforth neither “hold nor defend” the doctrine, although it could still be discussed as mere “mathematical supposition.”

      For the next seven years Galileo led a life of studious retirement in his house in Bellosguardo near Florence. At the end of that time 1623, he replied to a pamphlet by Orazio Grassi, about the nature of comets: the pamphlet clearly had been aimed  at Galileo. The reply, titled Saggiatore… was a brilliant polemic on physical reality and an exposition of the new scientific method. Galileo distinguished in it between the primary mathematical properties of matter  and the others, and wrote the famous pronouncement that the “Book of Nature is written in mathematical characters.” The book was dedicated to the new pope, Urban VIII, who as Maffeo Barberini had been a longtime friend protector of Galileo. Pope Urban received the dedication enthusiastically.

      In 1624, Galileo again went to Rome, hoping to obtain a revocation of the degree of 1616. this he did not to get, but he obtained permission from the pope to write about the “system of the world” both Ptolemaic and Copernican, so long as discussed them noncommittally and came to the conclusion dictated to him in advance by the pontiff, that we cannot presume to know how the world is really made because God could have brought about the same effects in ways unimagined by us, and we must  not restrict HIS omnipotence. These instructions were confirmed in writing by the head censor, Monsignor Riccardi

      Galileo returned to Florence and spent the next several years working on his great Dialogo dei Massimi Sistemi “Dialogue of the two Chief World Systems”. As soon as it came out in 1632, with the full imprimatur of censors, it was greeted with a tumult of applause from every part of Europe as a literary and philosophical masterpiece.

      On the crisis which followed we have only inferences. It was pointed out to the pope that despite its noncommittal title, the work was a compelling and unabashed plea for the  Copernican system. The strength of argument made the prescribed conclusion at the end look anticlimactic and pointless. The Jesuits insisted that it could have worse consequences on  the established system of teaching “than Luther and Calvin put together.” The pope in anger ordered a persecution. The author being covered by license, the only legal  measures would be to disavow the licensers, the only legal measures would be to disavow the licensers and prohibit the book. But at that point a document was “discovered” in the file, to the effect that during his audience with Bellarmine on February 26, 1616, Galileo had been specifically enjoined from “ teaching or discussing Copernicanism in any way.” Under the penalties of the Holy Office. His license, it was concluded, had therefore been “extorted” under false pretences.(the consensus of historians, based on evidence made available when the file was published in 1877, has been that the document was a planet and that Galileo was never so enjoined.) the church authorities, on strength of the “new” document, were able to persecute him for “vehement suspicion of heresy.” Notwithstanding his pleas of illness and old age, Galileo was compelled to journey to Rome in Feb. 1633 and stand trial. He was treated  with special indulgence and not jailed. In a rigorous interrogation on April 12, he steadfastly denied  any memory of the 1616 injunction. The commissary general of Inquisition, obviously sympathizing whit him,  discreetly outlined for the authorities a way in witch he might be let off with a reprimand, but on June 16 the congregation decreed that he must be sentenced. The sentence was read to rim on June   21: he was guilty of having “held and thought” the Copernican doctrine and was ordered to recent. Galileo recited a formula in which he  “ abjured, cursed and detested” his past errors. The sentence carried imprisonment but this portion of the penalty was immediately commuted by the pope into house arrest and seclusion on his little estate at Arcetri near Florence, where he returned in Dec. 1633. the house arrest remained in effect through  the last eight years of his life.

      Although confined to his estate, Galileo’s prodigious mental activity continued undiminished to the last. In 1634 he completed his  “Dialogue on two Sciences…”, in which he recapitulated the results of his early experiments and his mature meditations on most valuable work, was printed by the Elzevirs at Leiden in 1638. His  last telescopic discovery- that of the moon’s diurnal and monthly librations- was made in 1637, only a few months before he became blind. But the fire on his genius was not even yet extinct. He continued his scientific correspondence with unbroken interest and undiminished acumen: he thought out the application of the pendulum to the regulation of clockwork, which Christiaan Huygens put into practice in 1656: he was engaged in dictating to his disciples, Viviani and Torricelli, his latest ideas on the theory of impact when he was seized with the slow fever which resulted in his  death at Arcetri on January 8, 1642.   

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