GALILEO, girle-10), GALILEO GALILEI, git'le-lit/6 (1564-1642). An Italian physicist and astronomer, one of the founders of modern experi mental science. He was born in Pisa, in February, 1564, of a Florentine family more ancient than opulent. By desire of his father, a mathematician of considerable ability, he directed his early stud ies to medicine and the prevailing Aristotelian philosophy, the dogmas of which he soon came to disbelieve. Later, however, while still at the Uni versity of Pisa, he devoted himself to the study of mathematics and physical science. At the age of eighteen he made one of his most important discoveries. Happening on one occasion to ob serve, in the Cathedral of Pisa, the oscillation of a lamp casually set in motion, he was struck with the apparent measured regularity of its vibra tions; and having tested the correctness of this. observation by comparing the beat of his own. pulse with the action of the pendulum, he con cluded that by means of this equality of oscilla tion a simple pendulum might become an agent in the exact measurement of time. This discovery he subsequently utilized by the successful appli cation of the pendulum in constructing a clock for astronomical purposes. His bias toward me chanical construction and experimental science received a new impulse from his intercourse with a friend of his father's, Ostilio Riccio, who con sented to give him systematic instruction in pure mathematics. Such was Galileo's absorption and delight in his new studies that his father at length sanctioned his abandonment of the art of medicine, in order that he might concentrate his powers on his chosen sciences. The first fruit of his geometrical investigations was the inven tion of a hydrostatic balance, by which the spe cific gravity of solid bodies might be ascertained with great accuracy. In 1589, the fame of Gali leo's extraordinary learning having reached the Grand Duke of Tuscany, he was appointed pro fessor of mathematics in the University of Pisa. About this period he turned his attention to the then very imperfectly comprehended laws of bodies in motion; and in opposition to accepted notions, he propounded the theorem that all fall ing bodies, great or small, descend with equal velocity. This soon led him to the discovery of the law regulating the motion of falling bodies, which was proved correct by experiments made from the summit of the leaning tower of Pisa, greatly to the chagrin of the Aristotelians, whose enmity to Galileo had now grown more decided_ In consequence, he relinquished his chair at Pisa, and retired to Padua, where, in 1592, he accepted the invitation of the Venetian Senate to lecture on mathematics in the university for the space of six years. It is also said, however, that Galileo lost his chair at Pisa, from having ridiculed the mechanical pretensions of Giovanni de' Medici, son of Cosimo I. Galileo's engagement at Padua was eventually prolonged to the term of eighteen years; but so urgent was his desire to return to his birthplace, that he sought a restoration to his former post at Pisa, and was gratified by an assent being accorded by Cosimo II., with ex emption from any but a voluntary exercise of the duties of professorship. During his sojourn at Padua, his course of lectures enjoyed extraor dinary popularity; crowds of pupils flocked to hear him from all parts of Europe; and he was the first to adapt the Italian idiom to philosophical instruction. Among his various discoveries may be noticed a. species of thermometer, a propor tional compass or sector, and, more important than all, the construction of the refracting tele scope for astronomical investigation. In 1609 he offered his first complete telescope to the Doge of Venice, Leonardi Deodati, by whom it was tested from the tower of Saint Mark. In the same year he constructed a microscope; and then com menced his astronomical researches by means of his own telescope. He speedily concluded that the
moon, instead of being a self-luminous and per fectly smooth sphere, owed her illumination to reflection, and presented an unequal surface deeply furrowed by valleys and mountains of great extent. The Milky Way he pronounced a tract of countless separate stars; and these dis coveries were crowned by a still more important series of observations, which led to the discovery of the four satellites of Jupiter on the night of January 7, 1610 (though it was not till the 13th of the same month that he.came to the conclusion that they were satellites, and not fixed stars), which he named the Medicean stars. He also was the first to note movable spots on the disk of the sun, from which he inferred the rotation of that orb. He returned to Tuscany in 1610, where renewed quarrels with the Aristotelians dis quieted and imbittered his existence. In 1611 he visited Rome and was received with great dis tinction, being enrolled a member of the Lincei Academy; but four years later, on a second visit, his reception was widely different, as by that time, in his work on the solar spots, he had openly advocated the Copernican system, and was in consequence denounced as a propounder of heretical views. He repaired again to Rome, to demand an experimental inquiry into the soundness of his views; but the Grand Duke, ap prehending Inquisitorial dangers for his favorite, summoned him back to Tuscany; at the same time the Pope, through the famous Cardinal i3ellarmin (a sincere friend of Galileo's), com manded him to abstain from all future advocacy of heretical doctrines. Some time after, Galileo wrote his most famous work in the form of a dialogue between three fictitious interlocutors, the one in favor of the Copernican system, the second an advocate of the Ptolemaic, and the third a satirical personage who begins by agree ing with the Ptolemaic arguer, but usually ends by being convinced by the Copernican, and then assists in belaboring poor Simplicio, the sup porter of Ptolemaic motion. In 1630 Galileo con trived to obtain the Papal imprimatur, which was subsequently revoked; but having got a similar authorization at Florence, he published, in 1632, this exposition of his opinions under the title of Un dialog° intorno i due massinii sistemi del mondo. Hardly had the work been issued, when it was given over to the jurisdiction of the In quisition. Pope Urban VIII., previously Cardinal liarberini, and until now a friend and eulogist of Galileo, was led to believe that Galileo had satirized him in this work under the name of Situplicio, as one who is careless about scientific truth, and who timidly adheres to the saws of antiquity. In spite of his advanced years and heavy infirmity, Galileo was summoned before the Inquisition to answer for his heresies. After a wearisome trial and incarceration, his judges condemned him to abjure by oath on his knees his scientific creed. This he did. The question as to whether Galileo was actually put to the tor ture is still open to dispute, though it is certain that he was threatened with it. Ilis famous whisper. Ii par si nitiove ("But nevertheless it does move"), is a fiction. Galileo was sen tenced to an indefinite term of imprisonment by the Inquisition, which was soon commuted by Pope Urban, at the request of Ferdinand, the Grand Duke of Tuscany, into permission to reside at Siena, and finally at Florence, should the prisoner's health require the change. In his re treat at Arcetri he continued his researches, even when hearing grew enfeebled and sight was extinguished. He died on January 8. 1642. at the age of seventy eight, and was interred by ducal orders in the Cathedral of Santa Croce, where a majestic monument symbolizes his great achieve ments.