GALILEO GALILEI, (1564-1642), Italian mathematician and scientist, usually known simply as ‘Galileo’. An early attempt to enter the monastic life was foiled by his father, the musical theorist Vincenzio Galilei, who envisaged a medical career for his son. Nevertheless Galileo did not complete his medical course at the University of Pisa, but turned to mathematics and in 1589 became professor of mathematics at Pisa; in 1592 he was appointed to the more lucrative chair at Padua.

At this time he developed ideas on a new science of motion that eventually found mature expression in his Discorsi e Dimostrazioni Matematiche intorno à Due Nuove Scienze (1638). By asking, not about the causes of motion, but rather how they would occur in certain ideal situations, he concluded that an unimpeded horizontal motion would continue indefinitely at uniform speed, and an unimpeded vertical motion would be uniformly accelerated—ideas that can be seen as leading towards Newtonian physics.

In 1609 Galileo heard of a new optical instrument, later known as the telescope; he soon had exemplars made for himself and embarked on a systematic observation of the heavens. His results, which he used for supporting a heliocentric Copernican cosmology, were published in Sidereus Nuncius (1610) and Istoria e Dimostrazioni intorno alle Macchie Solari (1613). In 1610 he moved to Florence as Chief Mathematician and Philosopher to the Grand Duke of Tuscany, and soon the theological implications of Copernicanism became a matter of great concern (which they had not been hitherto). Galileo in 1615 composed a long letter (pub. in 1636, Lettera a Madama Cristina di Lorena, Granduchessa di Toscana) on the relation of astronomy to Scripture, in which he advocated a liberal use of the principle of accommodation in interpreting biblical passages seemingly inconsistent with the motion of the earth. Matters came to a head in 1615 and early 1616 when the theologians of the Holy Office asserted that to maintain the immobility and centrality of the sun as opposed to that of the earth was heretical, and soon Copernicus’ De revolutionibus orbium caelestium (pub. in 1543) was placed on the Index, pending correction. Galileo was informed of the decision and was reported to have acquiesced in it. For some years he was publicly silent about Copernicanism, but when his friend Maffeo Barberini became Pope Urban VIII in 1623, he gained the impression that he could discuss the new system, provided that he treated it as hypothetical and did not introduce biblical arguments. The result was his Dialogo sopra i Due Massimi Sistemi del Mondo (1632), which was more faithful to the letter than the spirit of this understanding, and contained an apparent insult to the Pope. Galileo was summoned before the Inquisition, made to recant, and spent the rest of his life under house arrest. His famous words Eppur si muove (None the less it does move) seem to be legendary. The ‘Galileo Affair’ has been a continuing leitmotif in accounts of the meeting of science and religion, and Pope John Paul II in 1981 appointed a commission to study the case and in 1992 endorsed its report admitting the ‘subjective error’ of Galileo’s judges.

The standard edn. of his works is the ‘Edizione nationale’ by A. Favoro (20 vols., Florence, 1890–1909; repr. 1968). Eng. trs. include Discoveries and Opinions of Galileo, tr. S. Drake (Garden City, NY, 1957; tr. of Siderius Nuncius and Lettera a Madama Cristina di Lorena, with extracts from other works); Siderius Nuncius, tr. A. van Helden (Chicago, 1989); Dialogo sopra i Due Massimi Sistemi del Mondo, tr. S. Drake (Berkeley, Calif., etc., 1953); and Discorsi e Dimostrazioni, tr. id. (Madison, Wis., 1974). The secondary bibl. is vast; E. McMullin (ed.), Galileo: Man of Science (New York and London [1967]) incl. convenient updating of bibls. of Carli, Favaro and Boffito (see below). Useful biogs. by L. Geymonat (Turin, 1957; Eng. tr., New York and London, 1965), S. Drake, Galileo at Work: His Scientific Biography (Chicago and London, 1978), and, on an introductory level, id., Galileo (Past Masters, Oxford, 1980). S. M. Pagano (ed.), I Documenti del Processo di Galileo Galilei (Collectanea Archivi Vaticani, 21; 1984). Eng. tr. of various primary docs., with introd., by M. A. Finocchiaro, The Galileo Affair: A Documentary History (Berkeley, Calif., etc. [1989]). Secondary works dealing with Galileo’s relations with the Church include G. de Santillana, The Crime of Galileo (1958); J. J. Langford, Galileo, Science and the Church (New York, 1966; 3rd edn., Ann Arbor, [1992]); P. Poupard (ed.), Galileo Galilei: 350 ans d’histoire 1633–1983 (Tournai [1983]); O. Pedersen, ‘Galileo and the Council of Trent: The Galileo Affair Revisited’, Journal for the History of Astronomy, 14 (1983), pp. 1–29; G. V. Covne, SJ, and others (eds.), The Galileo Affair: A Meeting of Faith and Science. Proceedings of the Cracow Conference, 24 to 27 May 1984 (Vatican City, 1985); R. S. Westfall, ‘The Trial of Galileo: Bellarmino, Galileo, and the Clash of Two Worlds’, Journal for the History of Astronomy, 20 (1989), pp. 1–23, repr., with other material, Essays on the Trial of Galileo (Vatican City, 1989); A. Fantoli, Galileo: Per la Copernicanesimo e per lit Chiesa (Studi Galileani, 2; ibid., 1993; Eng. tr., ibid. 3 [1994]; 2nd edn., 1996). P. Redondi, Galileo eretico (1983; Eng. tr., Princeton, NJ, 1987; London, 1988), argues provocatively that the underlying cause of Galileo’s condemnation was his espousal of an atomism that was seen as inconsistent with the doctrine of transubstantiation. Bibl. covering the period 1568–1895 by A. Carli and A. Favaro (Rome, 1896); 1896–1940 by G. Boffito (ibid., 1943); and 1942–1964 by E. Gentili (Milan, 1966). S. Drake in Dictionary of Scientific Biography, 5 (1981 edn.), pp. 237–49, s.v.; U. Baldini in Dizionario Biografico degli Italiani, 51 (1998), pp. 473–86, s.v.

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