It was not long before Galileo had new and equally important matter to announce. He observed a remarkable appearance in Saturn, as if it were composed of three stars touching each other; his telescope was not sufficiently powerful to resolve them into Saturn and his ring. Within a month he ascertained that Venus exhibits phases like those of the moon--a discovery of great importance in confirming the Copernican system. The same phenomenon he afterward detected in Mars. We close the list with the discovery of the revolution of the sun round his axis, in the space of about a lunar month, derived from careful observation of the spots on his surface.
About this time (1610-1611) Galileo took up his abode in Tuscany, upon the invitation of the grand duke, who offered to him his original situation at Pisa, with a liberal salary, exemption from the necessity of residence, and complete leisure to pursue his studies. In 1612 he published a discourse on "Floating Bodies," in which he investigates the theory of buoyancy, and refutes, by a series of beautiful and conclusive experiments, the opinion that the floating or sinking of bodies depends on their shape.
Neither Copernicus nor his immediate followers suffered inconvenience or restraint on account of their astronomical doctrines; nor had Galileo, until this period of his life, incurred ecclesiastical censure for anything which he had said or written. But the Inquisition now took up the matter as heretical and contrary to the express words of Scripture; and in 1616, Copernicus's work, "De Revolutionibus," Kepler's "Epitome," and some of Galileo's own letters, were placed on the list of prohibited books; and he himself, being then in Rome, received formal notice not to teach that the earth revolves round the sun. He returned to Florence full of indignation; and considering his hasty temper, love of truth, and full belief of the condemned theory, it is rather wonderful that he kept silence so long, than that he incurred at last the censures of the hierarchy. He did, however, restrain himself from any open advocacy of the heretical doctrines, even in composing his great work, the "Dialogue on the Ptolemaic and Copernican Systems." This was completed in 1630, but not printed till 1632, under license from officers of the church, both at Rome and Florence. It is a dialogue between Simplicio, an Aristotelian, Salviati, who represents the author, and Sagredo, a half convert to Salviati's opinions. It professes "indeterminately to propose the philosophical arguments, as well on one side as on the other;" but the neutrality is but ill kept up, and was probably assumed, not with any hope that the court of Rome would be blinded as to the real tendency of the book, but merely that it would accept this nominal submission as a sufficient homage to its authority. If this were so, the author was disappointed; the Inquisition took cognizance of the matter, and summoned him to Rome to undergo a personal examination. Age and infirmity were in vain pleaded as excuses; still, through the urgent and indignant remonstrances of the Grand Duke of Tuscany, he was treated with a consideration rarely shown by that stern tribunal. He was allowed to remain at the Florentine ambassador's palace, with the exception of a short period, from his arrival in February, until the passing of sentence, June 21, 1633. He was then condemned, in the presence of the Inquisitors, to curse and abjure the "false doctrines," which his life had been spent in proving, to be confined in the prison of the Holy Office during pleasure, and to recite the seven penitential psalms once a week during three years. The sentence and the abjuration are given at full length in the "Life of Galileo," in the "Library of Useful Knowledge." "It is said," continues the biographer, "that Galileo, as he rose from his knees, stamped on the ground, and whispered to one of his friends, '_e pur si muove_,' it does move though."