Galilei, GALILEO, one of the fathers of experimental science, was born at Pisa on the 18th of February 1564. By the desire of his father, the descendant of an ancient Florentine family, Galileo directed his early studies to medicine, and of course the prevailing Aristotelian philosophy; but the dogmas of this last he soon ventured to disbelieve and despise. Entering the university of Pisa in 1581, he made there two years later one of his most important discoveries. Happening to observe the oscillations of a bronze lamp in the cathedral of Pisa, he was struck with the fact that the oscillations, no matter what their range, seemed to be accomplished in equal times. The correctness of this observation he at once proceeded to test, and then, comparing the beat of his own pulse with the action of the pendulum, he concluded that by means of this equality of oscillation the simple pendulum might be made an invaluable agent in the exact measurement of time, a discovery which he utilised some fifty years later in the construction of an astronomical clock. About this time his irrepressible bias towards mechanical constructions and experimental science received a new impulse from his introduction to the principles of mathematics. The first fruit of his ardent pursuits of the new studies was the invention of a hydrostatic balance and the composition of a treatise on the specific gravity of solid bodies. These achievements secured him the appointment of professor of Mathematics in the university of Pisa, where he propounded the novel theorem, that all falling bodies, great or small, descend with equal velocity, and proved its correctness by several experiments made from the summit of the leaning tower of Pisa. This provoked the enmity of the Aristotelians, whose bitterness was exacerbated by the cutting sarcasms of the successful demonstrator. Nevertheless Galileo in 1591 deemed it prudent to resign his chair at Pisa, and retire to Florence, though another cause has been assigned for his resignation—viz. that he ridiculed the mechanical pretensions of Giovanni de’ Medici, son of Cosmo I.
In the following year he was nominated to the chair of Mathematics in the university of Padua, where his lectures attracted crowds of pupils from all parts of Europe. Here he taught and worked for eighteen years, from 1592 to 1610. It may be remarked parenthetically that he was the first to adapt the Italian idiom to philosophical instruction. Among the various discoveries with which he enriched science may be noticed a species of thermometer, a proportional compass or sector, and, more important than all, the refracting telescope for astronomical investigation. This last, however, he seems not to have invented entirely independently: an account of an instrument for enlarging distant objects, invented by a Dutchman, seems to have reached him whilst on a visit to Venice in May 1609; thereupon setting his inventive wits to work, he constructed an apparatus involving the principles of the telescope. Rapidly improving the construction of his original instrument, Galileo now began a series of astronomical investigations, all of which tended to convince him still more of the correctness of the Copernican heliocentric theory of the heavens, of the truth of which he seems indeed to have been early persuaded. He concluded that the moon, instead of being a self-luminous and perfectly smooth sphere, owed her illumination to reflection, and that she presented an unequal surface, diversified by valleys and mountains. The Milky-way he pronounced a track of countless separate stars. Still more important, however, was the series of observations which led to the discovery of the four satellites of Jupiter on the night of the 7th of January 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, in honour of his protectors, the Medici family. He also first noticed movable spots on the disc of the sun, from which he inferred the rotation of that orb. In this year he was recalled to Florence by the Grand-duke of Tuscany, who nominated him his philosopher and mathematician extraordinary, gave him a good salary, and exacted from him no duties save those of prosecuting his scientific investigations untramelled. At Florence, continuing his astronomical observations, he discovered the triple form of Saturn and the phases of Venus and of Mars.
In 1611 Galileo visited Rome and was received with great distinction, being enrolled a member of the Lincei Academy. Yet the publication, two years later, of his Dissertation on the Solar Spots, in which he openly and boldly professed his adhesion to the Copernican view, provoked against him the censure and warning of the ecclesiastical authorities. But this he partly brought upon himself by his aggressive attitude towards the champions of orthodoxy and even towards the Scriptures, whose astronomical system he hesitated not to challenge. Galileo, however, promised (26th February 1616) to obey Pope Paul V.’s injunction, thenceforward not to ‘hold, teach, or defend’ the condemned doctrines. After that he seems to have been again taken into favour by the pope and other high dignitaries of the church; indeed personally he seems never to have lost their esteem. But in 1632, ignoring his pledge, he published the Dialogo sopra i due massimi Sistemi del Mondo, a work written in the form of a dialogue between three fictitious interlocutors, the one in favour of the Copernican system, the second an advocate of the Ptolemaic, and the third a well-meaning but stupid supporter of the Aristotelian school. Hardly had the work been issued when it was given over to the jurisdiction of the Inquisition. Pope Urban VIII., previously Cardinal Barberini, a friend and admirer of Galileo, was led to believe that Galileo had satirised him in this work in the person of the third inter- locutor, as one who was careless about scientific truth, and who timidly adhered to the rigid traditions of antiquity. In spite of his seventy years and heavy infirmities Galileo was summoned before the Inquisition, and, after a wearisome trial and incarceration, was condemned to abjure by oath on his knees the truths of his scientific creed. Since the year 1761 a legend has been current to the effect that on concluding his recantation he exclaimed, sotto voce, 'E pur si muove' (Nevertheless it does move). The question whether he was put to the torture or no has given rise to a keen controversy, in which neither side can justly claim to have offered evidence that is finally conclusive. He was certainly subjected to the examen rigorosum, the last stage of which is actual torture. But the official accounts of the trial make no mention of this last stage having been reached. On the other hand, it has been asserted that the records of his trial have been tampered with. Galileo was further sentenced to an indefinite term of imprisonment in the dungeons of the Inquisition; but this was commuted by Pope Urban, at the request of Ferdinand, Duke of Tuscany, into permission to reside at Siena, and finally at Florence. In his retreat at Arcetri, near Florence, he continued with unflagging ardour his learned researches, even when hearing grew enfeebled and sight was extinguished. Just before he became totally blind, in 1637, he made yet another astronomical discovery, that of the moon's monthly and annual librations. He died on the 8th of January 1642, and was interred in the church of Santa Croce, the pantheon of Florence. His disposition was genial; he enjoyed the social wit and banter of his chosen friends; 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 tongue, more than his physical discoveries, was the cause of his misfortunes. He loved art, and cultivated especially music and poetry. Ariosto he knew almost by heart, and appreciated keenly the beauties of this classic. Tasso, on the other hand, he unduly depreciated, and severely criticised him in Considerazioni al Tasso. His own style is nervous, flowing, and elegant. In addition to the discoveries and inventions already recorded we owe to the genius of Galileo the formulation of the law of uniformly accelerated motion in the case of bodies falling freely towards the earth, the determination of the parabolic path of projectiles, the theory of virtual velocities, and the law that all bodies, even invisible ones like air, have weight. The best edition of Galileo's collected works is that by Alberi (16 vols. Flor. 1842-56).
See Viviani's Life of Galileo (1654); Henri Martin's Galilée (1868); H. de l'Épinois in Revue des Questions Historiques (1867), and Les Pièces du Procès de Galilée (1877); Gebler, Galileo und die Römische Curie (1876); Berti, Copernico e Sistema Copernicano, and Il Processo Originale di Galileo (1876); Wohlwill, Ist Galilei gefoltert worden? (1877); Favaro, Galileo Galilei (2 vols. Flor. 1882); Wegg-Prosser, Galileo and his Judges (1889).