BOOKS ERNAN MCMULLIN


THE MAN WHO SAW TOO MUCH


Galileo J. L. Heilbron OXFORD UNIVERSITY PRESS, 508PP, £20 ■Tablet Bookshop price £18


G 01420 592974


alileo has attracted the attention of biographers more, perhaps, than any other figure in the intensively studied history of the sciences. His


Starry Messenger marked a turning point in that history: no longer would those sciences be dependent on the limited reach of the unaided human senses. His Two New Sciences combined mathematics with experiment and idealisation, pointing to a new and powerful way to investigate the natural world. His Dialogue Concerning the Two Chief World Systems aimed to reorder the planetary uni- verse, setting the Earth in motion and the Sun at rest. More than enough drama in all this to keep biographers busy. John Heilbron’s ambitious new biography casts his net more widely. What sort of person was Galileo? Apart from mathematics and natural philosophy, what were his interests? How did he relate to his family? To his patrons? To his colleagues? To those he regarded as rivals? Heilbron has a knack of unearthing illuminating detail, of pointing up overlooked connections. His familiarity with the stream of correspondence from, to and about Galileo allows him to put his finger unerringly on just the right letter at the right moment. The young Galileo had an impressively wide


range of humanistic interests. An accom- plished lutenist like his father, he composed sonnets of modest quality, and was passionate in his literary preferences, honouring Dante and Petrarch and most especially Ludovico Ariosto, author of Orlando Furioso, an immense poem of unrequited love and fan- tastic travels. The “ironic humour and scholarly arrogance” that would characterise his later writing were already in evidence. While teaching at the University of Padua (1592-1609), he frequented nearby Venice, with its active nightlife and its renowned circle of intellectuals, one of whom, the con- troversial Paolo Sarpi, became his close colleague. It was in Padua that he turned an improved version of the already widely known telescope to the skies, with startling results. His discovery of the Sun-aligned phases of


Venus undermined the traditional geocentric systems of both Aristotle and Ptolemy, leaving only two other alternatives in contention, the Copernican heliocentric and the Tychonic geocentric (Sun, accompanied by the planets, circling the Earth). Regarding the latter as altogether far-fetched, Galileo declared for the Copernican system in a work on the newly discussed sunspots. Unfortunately, post- Reformation sensitivities made this a time when departure from the literal in the inter- pretation of Scripture tended to be suspect … and the Sun’s motion and the Earth’s immo- bility are mentioned several times in Scripture. Indeed, because of this, the Copernican alter- native had already been denounced by Catholic theologians. Sensing the danger, Galileo laid out a series of reasons in a letter to a friend why the Scripture passages in ques- tion ought not be taken literally. The letter led to his being denounced to the Holy Office, as were the similar views of Paolo Foscarini, a respected theologian. Prodded into action by Pope Paul V, the Congregation of the Index banned Copernicus’ De Revolutionibus in 1616, declaring that holding the Sun to be at rest and the Earth in motion is “absurd in philosophy (science), as well as contrary to Scripture”. Galileo was privately enjoined by Cardinal Bellarmine to abandon the con- demned view. To Roman eyes, this revisionist reading of Scripture “looked like the budding of a new head of the Protestant hydra”. Back in Florence, Galileo was “sick, muzzled,


frustrated, melancholic, irrational” and eager to assert his own priority in regard to the celestial discoveries. He had already belittled the role that the Jesuit Christoph Scheiner had played in the discovery of the sunspots. Now it was the turn of another Jesuit, Orazio Grassi, to suffer. Their disagreement was about the nature of the great comet of 1618. Following Tycho and the Jesuit astronomers of the Collegio Romano, Grassi took it to be a body in orbit somewhere beyond the Moon. Galileo, on the contrary, placed it as an exhal- ation from the Earth moving in a straight line upwards, shining by reflected sunlight. What was extraordinary about the ensuing debate (apart from the fact that, in terms of the avail- able evidence, Grassi was more or less right about the comet and Galileo definitely wrong) was the highly personal character of Galileo’s attack on the “blind chicken poking in the dust”. Heilbron speculates that the extrava- gance of Galileo’s accusations against Grassi may have been, in part, “to repay the Jesuit mathematicians for deserting [him] in 1616”. The ascension in 1623 to the papacy of


Galileo’s friend, Maffeo Barberini, as Urban VIII, encouraged Galileo to seek to have the Copernican issue reopened. Urban assented but on the express condition that Copernican- ism be treated as an “hypothesis” only. Harking back to the critique of Aristotle’s natural phi-


Galileo Galilei as


portrayed by the artist Sustermans in 1635. Palazzo Pitti,


Florence


losophy by the nominalist theologians of the fourteenth century, he insisted that one could not claim to demonstrate the (unseen) double motion of the Earth as cause of the observed phenomena. To do so would imply that God could not bring those phenomena about in a different way, thus, in effect, calling God’s omnipotence into question. What Galileo was forbidden to do was to claim to demonstrate the Earth’s motion and the Sun’s rest, instead of posing it as an hypothesis. When Dialogue Concerning the Two Chief


World Systems appeared in 1632 after pro- longed negotiations with the censors in Rome and Florence, Urban’s reaction was violent: the book “involves great harm to religion (indeed, the worst ever conceived)”; it is “per- verse”, “dangerous”, “pernicious”. So strong a reaction can best be explained by Urban’s belief that Galileo had violated the condition laid on him: he had, in effect, challenged God’s omnipotence, and to make matters worse, had placed the required assent to Urban’s the- ological reasoning in the mouth of Simplicio, the invariably refuted Aristotelian spokesman. In the interrogations that followed, Galileo insisted over and over again that he had not claimed demonstration, but his judges did not agree. He gambled – and lost. He was convicted on “suspicion of heresy”, the grounds for which were that he had “held and believed [the Copernican] doctrine which is false and contrary to Scripture … and that one may hold and defend as probable an opin- ion after it has been declared and defined to be contrary to Scripture”, leaving behind a host of questions about the procedures fol- lowed in 1616 as well as in the trial of 1633, and about how, when, and even if, in fact, Copernicanism had become a heresy. Heilbron deals briskly and fairly here with the luxuri- ating trial literature which long ago acquired a life of its own. His absorbing chronicle comes gently to a close as the light fades for someone who once saw further than anyone before him had done, now in his own words, “restricted to the space my body occupies”. This gracefully written work is science biog- raphy at its best.


19 February 2011 | THE TABLET | 21


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