GALILEI, GALILEO, the creator of experimental science, was born at Pisa on Feb. 15 1564. He belonged to a Florentine family more ancient than opulent. G., by desire of his father, exclusively directed his early studies to medicine, and the prevailing Aristo telian philosophy, the dogmas of which he soon ventured to disbelieve and despise. 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, G. wax 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 (q.v.) might become an invaluable 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. G.'s irre pressible bias towards mechanical constructions and experimental science received a new impulse from his intercourse with a friend of his father's, °still° Riccio, professor of matheinatics, who, in compliance with the youth's entreaties, initiated him into the principles of mathematics. Such was G.'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 it hydrostatic balance, by which the specific gravity of solid bodies might be ascertained with the nicest accuracy. In 1589, the fame of G.'s extraordinary learning having reached the grand duke of Tuscany, this enlightened prince appointed him professor of mathematics iu the university of Pisa, where he covertly inculcated many of those great innovations iu physical science which have since added such luster to his memory. About this period he turned his attention to the then very imperfectly comprehended laws of bodies in motion; and in opposition to all received systems, he propounded the novel theorem, that all falling bodies, great or small, descend with equal velocity. This soon led him to the discovery of "the three laws of motion," and the law regulating the motion of falling bodies, which is expressed by the formula S = This theory of falling bodies was proved correct by several experiments which were made from the summit of the leaning tower of Pisa, greatly to the chagrin of the Aristotelians, whose enmity to G. now grew more decided. In consequence, he deemed it prudent to relinquish his chair at Pisa, and retired to Padua, where he accepted the offer of the Venetian senate to lecture on mathematics in the university for the space of six years. It is also said, however, that G. lost his chair at Pisa, from having ridiculed the mechanical pretensions of John de' Medici, son of Cosmo I. G.'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 eagerly accorded by Cosmo de' Medici, with exemption from any but a voluntary exercise of the duties of the 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 the various and noble discoveries with he enriched science, 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 he offered his first complete telescope to the doge of Venice, Leonardi Deodati, by whom it was tested from the tower of St. Mark with equal surprise and delight. In the same year he constructed a microscope; and then this indefatigable interpreter of the mysteries of nature 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 tie pronounced a track of countless separate stars; and these discoveries were crowned by a still more important series of observations, Mlle!' led to the discovery of the four satellites of Jupiter on the night of Jan. 7. 1010 (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, in honor of his constant protectors in that family. He also was the first to note movable spots on the disk of the sun, from which he inferred the rotation of that orb. Encircled by the luster of these sublime discoveries, he departed from Padua, and 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 repeating the visit, his reception was widely differ ent, as by that time in his work on the solar spots lie had openly advocated the Coper nican 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, sum moned him back to Tuscany; at the same time the pope, through the famous cardinal Bellarmine (a sincere friend of G.'s), commanded him to abstain from all future advo cacy of his heretical doctrines. Some time after, he 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 rabid sup porter of the Aristotelian school. Of course, the whole weight of the proof falls into the Copernican scale; and nothing can exceed the classic beauty of this composition, or the compactness Of the chain of its argument. In 1630, G. contrived to obtain the papal imprimatur, which was subsequently revoked; but having got a similar authorization at Florence, he published, in 1632, this exponent of his opinions under the title of Utz Dialogo intorno i due illassimi Sistemi del cifondo. Hardly had the work been issued, when it was given over to the jurisdiction of the inquisition. Pope Urban, previously cardinal Barberini, and, until now, a friend and eulogist of G., was led to believe that G. had satirized him in this work under the title of Simplicio, as one who is care less about scientific truth, and who timidly adheres to the saws of antiquity. He resolved to punish the audacious philosopher. In spite of his 70 years and heavy infirmities, G. was summoned before the inquisition to answer for his heresies. After a wearisome trial and incarceration, his judges condemned G. to abjure by oath on his knees the sublime truths of his scientific creed. This he was weak enough to do. His latest biographer, 31. Philarete Chasles, however, denies that G. was put to the torture, and pronounces the letter of G. to iteinecci, from which Tiraboschi quotes to prove it, a forgery. His famous whisper, .E pur si stucco ("But nevertheless it does move"), is, also in danger of being regarded as a fiction. G. was sentenced to an indefinite term of imprisonment in 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 retreat at Arcetri, he continued with unflagging ardor his learned researches, even when hear ing grew enfeebled and sight was extinguished. 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. His disposition was truly genial; he enjoyed with keenness the social wit and banter of his chosen friends, and the generous pleasures of the banquet; and the readiness with which he offered or accepted atone ment, 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 physical dis coveries, was the cause of his misfortunes. The dignitaries or the church who perse cuted G., warned him beforehand in the friendliest way to be " more prudent." Their conduct in persecuting opinion, or rather, in G.'s case, demonstrated fact, is of course utterly inexcusable; but there is no reason why we should run to the other extreme, and declare G. to be a martyr. No great man had ever less claim to the title. It is also right to add, that the congregation of the inquisition by which G. was condemned, is not believed by Roman Catholics to speak with the plenary authority of the Catholic church, nor are its decisions regarded as infallible even by the most extreme ultramon tanes. G. 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. Ariosto he knew almost by heart, and appreciated keenly the beauties of this great classic. Tasso, on the other hand, lie unduly depreciated, and inflicted much pain on the sensitive spirit of the poet by his severe criticism entitled Considerazioni al lasso. His own style is nervous, flowing, and elegant. The best edition of G:'s col lected works is that by Alfieri (6 vols., Flor. 1842-56). See Viviani's Life of G. ; Brew ster's sketch; 31. Chasles's Galileo Galilei (1862); Pieralisi's Urban° VIII. e G. (1875); Gebler's G. and die Rcimische Curie (1876); Berti's Copernico eil ricende del Sistema Coper nican° and 11 PrOCCSRO Originate di G. (Rome. 1876); the Quarterly Review for April, 1878; and Riccardi's Bibliographia Galileiana (1873). We may briefly recapitulate G.'s most important contributions to physical science under the following heads: 1. The relation between space and time in the case of falling bodies, also the "three laws of motion:" 2. The path of projectiles is a parabola; 3. The isochronism of the pendulum; 4. That air has weight, also partial discovery that suction is owing to the pressure of the atmos phere; 5. The re-invention 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, FALLLNG BODIES, PROJECTILES, etc. .