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Galileo Biography

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GALILEO, or GALILEO GALILEI, (1564-1642). An Italian physicist and astronomer, one of the founders of modern experimental 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 studies to medicine and the prevailing Aristotelian philosophy, the dogmas of which he soon came to disbelieve. Later, however, while still at the University of Pisa, he devoted himself to the study of mathematics and physical science. At the age of 18 he made one of his most important discoveries. Happening on one occasion to observe, in the cathedral of Pisa, the oscillation of a lamp casually set in motion, he was struck with the apparent measured regularity of its vibrations; and having tested the correctness of this observation by comparing the beat of his own pulse with the action of the pendulum, he concluded that by means of this equality of oscillation a simple pendulum might become an agent in the exact measurement of time. This discovery he subsequently utilized by the successful application of the pendulum in constructing a clock for astronomical purposes. His bias towards mechanical construction and experimental science received a new impulse from his intercourse with a friend of his father’s, Ostilio Riccio, who consented 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 invention of a hydrostatic balance, by which the specific gravity of solid bodies might be ascertained with great accuracy. In 1589, the fame of Galileo’s extraordinary learning having reached the Grand Duke of Tuscany, he was appointed professor of mathematics in the University of Pisa. About this period he turned his attention to the then very imperfectly comprehended laws of bodies in motión; and, in opposition to accepted notions, he propounded the theorem that all falling 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 18 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 exemption from any but a voluntary exercise of the duties of professorship. During his sojourn at Padua his course of lectures enjoyed extraordinary 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 proportional compass or sector, and, more important than all, the construction of the refracting telescope 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 St. Mark. In the same year he constructed a microscope; and then commenced his astronomical researches by means of his own telescope. He speedily concluded that the moon, instead of being a self-luminous and perfectly 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 discoveries 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 Jan. 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 disquieted and embittered his existence. In 1611 he visited Rome and was received with great distinction, 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, apprehending inquisitorial dangers for his favorite, summoned him back to Tuscany; at the same time the Pope, through the famous Cardinal Bellarmin (a sincere friend of Galileo’s), commanded 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 agreeing with the Ptolemaic arguer, but usually ends by being convinced by the Copernican, and then assists in belaboring poor Simplicio, the supporter of Ptolemaic motion. In 1630 Galileo contrived 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 dialogo dei due massimi sistemi del mondo. Hardly had the work been issued, when it was given over to the jurisdiction of the Inquisition. Pope Urban VIII, previously Cardinal Barberini, 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 Simplicio, as one who is careless about scientific truth, and who timidly adheres to the saws of antiquity. On Sept. 23, 1632, Galileo was cited to appear for the second time before the Inquisition. During his protracted trial he was allowed to reside as a prisoner in the house of the Tuscan Ambassador. His judges condemned him to abjure his scientific theory. This he did. That he was actually put to the torture is now no longer a question open to dispute, though it is true he was threatened with it. His famous whisper, E pur si muove (But nevertheless it does move), is a fiction. Galileo was sentenced to an indefinite term of imprisonment by the Inquisition. This was soon commuted by Pope Urban, at the request of Ferdinand of Tuscany, into permission to reside at Siena and finally at Florence. He died on Jan. 8, 1642, at the age of 78, and was interred by ducal orders in the cathedral of Santa Croce, where a majestic monument symbolizes his great achievements.

Galileo’s disposition was truly genial; he enjoyed with keenness the social wit and banter of his friends and the pleasures of the banquet; and the readiness with which he offered or accepted atonement modified a somewhat irascible disposition. The great deficiencies in his character were a want of tact to keep out of difficulties and a want of moral courage to defend himself when involved in them. His biting, satirical turn, more than his scientific tenets, was the cause of his misfortunes. Galileo was of small stature, but of a robust and healthy frame; his countenance was attractive, and his conversation cheerful. He loved art and cultivated especially music and poetry. His style is nervous, flowing, and elegant.

We may briefly recapitulate Galileo’s most important contributions to physical science under the following heads: (1) the relation between space and time in the case of falling bodies; (2) the path of projectiles is a parabola; (3) the isochronism of the pendulum; (4) the partial discovery that suction is owing to the pressure of the atmosphere; (5) the reinvention of Aristotle’s theory respecting sound; (6) the invention of the telescope; (7) the discovery of the satellites of Jupiter, phases of Venus, and spots on the sun. For the nature of these discoveries, see Pendulum; Falling Bodies; Projectiles; etc.

The New International Encyclopaedia, Vol. IX (New York: Dodd, Mead & Co., 1920) 410-411.