In 1618 the appearance of three comets gave him an opportunity to communicate to his friends some general observations, on these bodies. His scholar, Mario Guiducci, wrote a work immediately after, in which he severely condemned the Jesuit Grassi. Supposing Galileo to be the author, Grassi attacked him. Galileo replied in his a master piece of eloquence, pronounced by Algarotti to be the finest controversial work Italy has ever produced, and, notwithstanding the errors con tained in it, a work always worthy to be read.
About this time he completed his famous work, in which, without giving his own opinion, he introduces three persons in a dialogue (Dialogue on the Two Chief Systems of the World'), of whom the first defends the Copernican system, the second the Ptolemaic, while the third appears as a blind and unrea soning supporter of the views of Aristotle. With this work, in which the greatest elegance and accuracy of style is united with the clear est and most concise statements, Galileo went to Rome in 1630, and succeeded in obtaining the privilege to print it. Having obtained the same permission in Florence, he published it there in 1632 —(Dialogo di Galileo Galilei, dove ne' Congressi di quattro Giornate si dis corre de' due massimi Sistemi del Mondo, Tole maico et Copernicano.' Scarcely had it ap peared when it was attacked by the disciples of Aristotle, and most violently of all by Scipione Chiaramonti, teacher of philosophy at Pisa. A congregation of cardinals, monks and mathematicians examined his work, con demned it as highly dangerous, and summoned him before the tribunal of the Inquisition. The veteran philosopher was compelled to go to Rome, and in June 1633 was condemned to re nounce, in presence of a great assembly, kneel ing before them, with his hand upon the gos pel, the great truths he had maintained. Corde sincero et fide non ficta, abjuro maledico et detestor supradictos errores et hereses,' was the formula which he was compelled to pro nounce. His famous whisper, 'But neverthe less it [the earth] does move," is a fiction. He was sentenced to the dungeons of the Inquisi tion for an indefinite time, and every week, for three years, was to repeat the seven peni tential psalms of David. His 'Dialog& was
prohibited and. his system condemned as con trary to the Bible. His judges were merciful enough to commute his sentence of imprison ment to banishment to the villa of the grand duke of Tuscany at Rome, then to the archie piscopal palace at Sienna, and soon after he was allowed to return to Arcetri, not far from Florence.
He employed his last years here principally in the study of mechanics and projectiles. The results are found in two important works on the laws of motion, the foundation of the pres ent system of physics and astronomy. At the same time he tried to make use of Jupiter's satellites for the calculation of longitudes; and though he brought nothing to perfection in this branch, he was the first who reflected systemat ically on such a method of fixing geographical longitude. He was at this time afflicted with a disease in his eyes, one of which was wholly blind, and the other almost useless, when, in 1637, he discovered the libration of the moon. Blindness, deafness, want of sleep and pain in his limbs united to embitter the last years of Galileo's life. He died in the year Newton was born, and his relics were ultimately deposited in the church of Santa Croce, at Florence, where a splendid monument was erected to him near that of Michelangelo.
Galileo was of diminutive size, but strong and healthy. His countenance was agreeable; his conversation lively. He loved music, draw ing and poetry. He knew Ariosto by heart; and in one of his works, first printed in 1793, 'Considerazioni al Tasso,' the product of his leisure hours, he points out the superiority of Ariosto to Tasso, whom he criticizes very severely. His style is lively, natural and fluent. His collected works have been edited by Alberi (16 vols., Florence 1842-56). Consult Brewster, 'Martyrs of Science' (London 1841) • Chasles,
Galilei' (Paris 1862) ; Epinois, H. de 1',