GALILEI, GALILEO (b. Pisa, Italy, 15 February 1564; d. Arcetri, Italy, 8 January 1642), physics, astronomy.

    for the Jesuit Christoph Scheiner, asking Galileo's opinion of it. Galileo replied in three long letters during 1612, demolishing Scheiner's conjecture that the spots were tiny planets. He asserted also that he had observed sunspots much earlier and had shown them to others at Rome early in 1611. This set the stage for a deep enmity of Scheiner toward Galileo, which, however, did not take active form at once.

Galileo's Letters on Sunspots was published at Rome in 1613 under the auspices of the Lincean Academy. In this book Galileo spoke out decisively for the Copernican system for the first time in print. In the same book he found a place for his first published mention of the concept of conservation of angular momentum and an associated inertial concept. During its composition he had taken pains to determine the theological status of the idea of incorruptibility of the heavens, finding that this was regarded by churchmen as an Aristotelian rather than a Catholic dogma. But attacks against Galileo and his followers soon appeared in ecclesiastical quarters. These came to a head with a denunciation from the pulpit in Florence late in 1614.

In December 1613 it had happened that theological objections to Copernicanism were raised, in Galileo's absence, at a court dinner, where Galileo's part was upheld by Benedetto Castelli. Learning of this, Galileo wrote a long letter to Castelli concerning the inadmissibility of theological interference in purely scientific questions. After the public denunciation in 1614, Castelli showed this letter to an influential Dominican priest, who made a copy of it and sent it to the Roman Inquisition for investigation. Galileo then promptly sent an authoritative text of the letter to Rome and began its expansion into the Letter to Christina, composed in 1615 and eventually published in 1636. Galileo argued that neither the Bible nor nature could speak falsely and that the investigation of nature was the province of the scientist, while the reconciliation of scientific facts with the language of the Bible was that of the theologian.

The book on bodies in water drew attacks from four Aristotelian professors at Florence and Pisa, while a book strongly supporting Galileo's position appeared at Rome. Galileo prepared answers to his critics, which he turned over to Castelli for publication in order to avoid personal involvement. Detailed replies to two of them (Colombe and Grazia), written principally by Galileo himself, appeared anonymously in 1615, with a prefatory note by Castelli implying that he was the author and that Galileo would have been more severe.

Late in 1615 Galileo went to Rome (against the advice of his friends and the Tuscan ambassador) to clear his own name and to prevent, if possible, the official suppression of the teaching of Copernicanism. In the first, he succeeded; no disciplinary action against him was taken on the basis of his letter to Castelli or his Copernican declaration in the book on sunspots. In the second objective, however, he failed. Pope Paul V, irritated by the agitation of questions of biblical interpretation—then a bone of contention with the Protestants—appointed a commission to determine the theological status of the earth's motion. The determination was adverse, and Galileo was instructed on 26 February 1616 to abandon the holding or defending of that view. No action was taken against him, nor were any of his books suspended. A book by the theologian Paolo Antonio Foscarini reconciling the earth's motion with the Bible was condemned, and the work of Copernicus and a commentary on Job by Diego de Zuñiga were suspended pending the correction of a few passages. One contemporary document, bound into the proceedings but of uncertain reliability, states that Galileo was also ordered never to discuss the forbidden doctrine again. If such an order was given, it was in contravention of certain specific instructions of the pope and had no legal force.

Returning to Florence, Galileo took up a practical and noncontroversial problem, the determination of longitudes at sea. He believed that this could be solved by the preparation of accurate tables of the eclipses of the satellites of Jupiter, which were of frequent occurrence and could be observed telescopically from any point on the earth. As a practical matter, the eclipses could neither be predicted with sufficient accuracy nor observed at sea with sufficient convenience to make the method useful.

It is probable that Galileo also returned during this period to his mechanical investigations, interrupted in 1609 by the advent of the telescope. A Latin treatise by Galileo, De motu accelerato, which correctly defines uniform acceleration and much resembles the definitive text reproduced in his final book, seems to date from this intermediate period, and copies of many of his propositions in kinematics exist in the handwriting of Mario Guiducci, who studied under Galileo at this time.

In 1618 three comets attracted the attention of Europe and became the subject of many pamphlets and books. One such book was printed anonymously by Orazio Grassi, the mathematician of the Jesuit Roman College. Galileo was bedridden at the time, but he discussed his views on comets with Guiducci, who then delivered lectures on them to the Florentine Academy and published them over his own name. In these lectures, which were largely dictated