GALILEI (GALILEO), the celebrated astronomer and mathematician, was the son of Vincenzo Galilei, a nobleman of Florence, not less distinguished by his quality and fortune, than conspicuous for his skill and knowledge in music; about some points in which science he maintained a dispute with the famous Zarlinas. His wife brought him this son, Feb. 19, 1564, either at Pisa, or, which is more probable, at Florence. Galileo received an education suitable to his birth, his taste, and his abilities. He went through his studies early, and his father then wished that he should apply himself to medicine; but having obtained at college some knowledge of mathematics, his genius declared itself decisively for that study. He needed no directions where to begin. Euclid's Elements were well known to be the best foundation in this science. He therefore set out with studying that work, of which he made himself master without assistance, and proceeded thence to such authors as were in most esteem, ancient and modern. His progress in these sciences was so extraordinary, that in 1589, he was appointed professor of mathematics in the university of Pisa, but being there continually harrassed by the scholastic professors, for opposing some maxims of their favourite Aristotle, he quitted that place at the latter end of 1592, for Padua, whither he was invited very handsomely to accept a similar profesşorship; soon after which, by the esteem arising from his genius and erudition, he was recommended to the friend-' ship of Tycho Brache. He had already, even long before 1586, written his "Mechanics," or a treatise of the benefits derived from that science and from its instruments, together with a fragment concerning percussion, the first published by Mersennus, at Paris, in 1634, in "Mersenni Opera," vol. I. and both by Menoless, vol. I.; as also his "Balance," in which, after Archimedes's problem of the crown, he shewed how to find the proportion of alloy, or mixt metals, and how to make the said instrument. These he had read to his pupils soon after his arrival at Padua, in

1593*.

While he was professor at Padua, in 1609, visiting Venice, then famous for the art of making glass, he heard of the invention of the telescope by James Metius, in Hol

While he was lecturer at Padua, Gustavus Adolphus king of Sweden was one of his hearers. The lectures then given by him still remain at Milan.

land. This notice was sufficient for Galileo; his curiosity was raised; and the result of his inquiry was a telescope of his own, produced from this hint, without having seen. the Dutch glass. All the discoveries he made in astronomy were the easy and natural consequences of this invention, which opening a way, till then unknown, into the heavens, gave that science an entirely new.face. Galileo, in one of his works, ridicules the unwillingness of the Aristotelians to allow of any discoveries not known to their master, by introducing a speaker who attributes the telescope to him, on account of what he says of seeing the stars from the bottom of a deep well. "The well," says he, "is the tube of the telescope, the intervening vapours answer to the glasses." He began by observing the moon, and calculating the height of her mountains. He then discovered four of Jupiter's satellites, which he called the Medicean stars or planets, in honour of Cosmo II. grand duke of Tuscany, who was of that noble family. Cosmo now recalled him from Padua, re-established him at Pisa, with a very handsome stipend, in 1610; and the same year, having lately invited him to Florence, gave him the post and title of his principal philosopher and mathematician.

It was not long before Galileo discovered the phases of Venus, and other celestial phænomena. He had been, however, but a few years at Florence, before he was convinced by sad experience, that Aristotle's doctrine, however ill-grounded, was held too sacred to be called in question. Having observed some solar spots in 1612, he printed that discovery the following year at Rome; in which, and in some other publications, he ventured to assert the truth of the Copernican system, and brought several new arguments to confirm it. This startled the jealousy of the Jesuits, who procured a citation for him to appear before the holy office at Rome, in 1615, where he was charged with heresy, for maintaining these two propositions; 1. That the sun is in the centre of the world, and immoveable by a local motion; and, 2. That the earth is not the centre of the world, nor immoveable, but actually moves by a diurnal motion. The first of these positions was declared to be absurd, false in philosophy,

He demonstrated a very sensible change in the magnitude of the apparent diameters of Mars and Venus;

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a phenomenon of great consequence to prove the Copernican theory.

and formally heretical, being contrary to the express word of God; the second was also alleged to be philosophically false, and, in a theological view, at least erroneous in point of faith. He was detained in the inquisition till Feb. 1616, on the 25th of which month sentence was passed against him; by which he was enjoined to renounce his beretical opinions, and not to defend them either by word or writing, nor even to insinuate them into the mind of any person whatsoever; and he obtained his discharge only by a promise to conform himself to this order. It is hard to say whether his sentence betrayed greater weakness of understanding, or perversity of will. Galileo clearly saw the poison of both in it; and therefore following the known maxim, that forced oaths and promises are not binding to the conscience, he went on, making further new discoveries in the planetary system, and occasionally publishing them with such inferences and remarks as necessarily followed from them, notwithstanding they tended plainly to establish the truth of the above-mentioned condemned propositions.

He continued many years confidently in this course, no juridical notice being taken of it; till he had the presumption to publish at Florence his " Dialogi della due massime Systeme del Mondo, Tolemaico et Copernicano;" dialogues of the two greatest systems of the world, the Ptolemaic and Copernican, in 1632. Here, in examining the grounds upon which the two systems were built, he produces the most specious as well as strongest arguments for each of those opinions; and leaves, it is true, the question undecided, as not to be demonstrated either way, while many phænomena remained insolvable; but all this is done in such a manner, that his inclination to the Copernican system might be easily perceived. Nor had he forborne to enliven his production by several smart strokes of raillery against those who adhered so obstinately, and were such devotees to Aristotle's opinions, as to think it a crime to depart from them in the smallest degree. This excited the indignation of his former enemies, and he was again cited before the inquisition at Rome; the congregation was convened, and, in his presence, pronounced sentence against him and his books. They obliged him to abjure his errors in the most solemn manner, committed him to the prison of their office during pleasure, and enjoined him, as a saving penance, for three years, to repeat

once a week the seven penitential psalms; reserving, however, to themselves the power of moderating, changing, or taking away altogether, or in part, the abovementioned punishment and penance. Upon this sentence he was detained a prisoner till 1634, and his "Dialogues of the System of the World" were burnt at Rome. We rarely meet with a more glaring instance of blindness and bigotry than this; and it was treated with as much contempt by our author as consisted with his safety.

He lived ten years after it, seven of which were employed in making still further discoveries with his telescope; but, by continual application to that instrument, added to the damage he received in his sight from the nocturnal air, his eyes grew gradually weaker, till, in 1639, he became totally blind. He bore this great calamity with patience and resignation, worthy of a philosopher. The loss neither broke his spirit, nor hindered the course of his studies. He supplied the defect by constant meditations, by which he prepared a large collection of materials; and began to dictate his own conceptions, when, by a distemper of three months continuance, wasting away by degrees, he expired at Arcetri near Florence†, Jan. 8, 1642, in the same year that Newton was born. In stature he was small, but in aspect venerable, and his constitution vigorous; in company he was affable, free, and full of pleasantry. He took great delight in architecture and painting, and designed extremely well. He played exquisitely on the lute; and whenever he spent any time in the country, he took great pleasure in husbandry. His learning was very extensive; and he possessed in a high degree a clearness and acuteness of wit. From the time of Archimedes, nothing had been done in mechanical geometry till Galileo, who, being possessed of an excellent judgment, and great skill in the most abstruse points of geometry, first extended the boundaries of that science, and began to reduce the resistance of solid bodies to its laws. Besides applying geometry to the doctrine of motion, by which philosophy became established on a sure foundation, he made surprising discoveries in the heavens by means of

It will appear more extraordinary, when it is considered that the prosecution was begun and carried on by the Jesuits, an order instituted to be a seminary of learning, in the view of producing champions of the papal chair.

In the last eight years of his life he lived out of Florence, sometimes in the neighbouring towns, and sometimes at Sienna. Vittorio Siri's "IL Mercurio," &c.

his telescope. He made the evidence of the Copernican system more sensible, when he shewed from the phases of Venus, like to those of the moon, that Venus actually revolves about the sun. He proved the rotation of the sun on his axis from his spots; and thence the diurnal rotation of the earth becaine more credible. The satellites that attend Jupiter in his revolution about the sun, represented, in Jupiter's smaller system, a just image of the great solar system; and rendered it more easy to conceive how the moon might attend the earth, as a satellite, in her annual revolution. By discovering hills and cavities in the moon, and spots in the sun constantly varying, he shewed that there was not so great a difference between the celestial bodies and the earth as had been vainly imagined.

He rendered no less service to science by treating, in a clear and geometrical manner, the doctrine of motion, which has justly been called the key of nature. The rational part of mechanics had been so much neglected, that hardly any improvement was made in it for almost 2000 years. But Galileo has given us fully the theory of equable motions, and of such as are uniformly accelerated or retarded, and of these two compounded together. He was the first who demonstrated that the spaces described by heavy bodies, from the beginning of their descent, are as the squares of the times; and that a body, projected in any direction not perpendicular to the horizon, describes a parabola. These were the beginnings of the doctrine of the motion of heavy bodies, which has been since carried to so great a height by Newton. In geometry, he invented the cycloid, or trochoid; though the properties of it were afterwards chiefly demoustrated by his pupil Torricelli. He invented the simple pendulum, and made use of it in his astronomical experiments: he had also thoughts of applying it to clocks; but did not execute that design : the glory of that invention was reserved for his son Vicen zio, who made the experiment at Venice in 1649; and Huygens afterward carried this invention to perfection. Of Galileo's invention also, was the machine, with which the Venetians render their Laguna fluid and navigable. He also discovered the gravity of the air, and endeavoured to compare it with that of water, besides opening up several other inquiries in natural philosophy. In short, he was not esteemed and followed by philosophers only, but was honoured by persons of the greatest distinction of all nations.