Galileo: Watcher of the Skies
David Wootton

The young Galileo acquired the standard humanist education of the day – Latin, Greek, Aristotelian logic – from schoolteachers, first in Pisa, and then in Florence, where he moved around the time of his tenth birthday with his mother and his sister Virginia (born a year before, in 1574) to join his father, who was slowly making his way at the Medici court.
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When Galileo was sixteen his father resolved to find the money to put him through university in Pisa. His plan was for him to become a doctor: indeed he had named him Galileo after a famous ancestor who had been a doctor; this was the original Galileo from whom the Galilei family claimed descent.
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Galileo's father must have been an important influence upon the young Galileo. Vincenzo was the author of a significant work of musical theory, the Dialogue on Ancient and Modern Music (1581):12 Galileo was following in his father's footsteps when he wrote dialogues in Italian.
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Vincenzo conducted experiments, and Galileo certainly knew of these and may have helped set them up. Vincenzo showed that it was not just the length of a string that determined the note it played, but its material, diameter and tension;
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Vincenzo saw himself as a great man who, for all his modest success at court, had never been given his due.
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Galileo was born in Pisa, spent much of his childhood there, went to university there, and got his first proper job there. But Viviani thought it important to stress that his father was a Florentine gentleman
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Throughout his life Galileo referred to himself as a Florentine gentleman,
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Florence was the capital of Tuscany, with a population of eighty thousand. There power was concentrated and fashions were
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An enemy, denouncing him to the Inquisition, said that he represented himself as a Florentine, but that he was in fact a Pisan.
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Throughout Galileo's life, the balance of wealth and power in Europe was slowly shifting from south to north, from Catholic to Protestant,
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Although at the end of his life Galileo was desperate to have his books published in Latin, the language of international intellectual life, and although this was the language in which he lectured throughout his career as a university teacher, he wrote only one short book in Latin: The Starry Messenger. He preferred, like his father, to write in Tuscan, the language of a Florentine, of Dante, of Tasso, of Ariosto.
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in the circle around Florence within which Galileo travelled there were in 1600 some sixteen cities with a population of more than ten thousand, as against seven in the whole of France and four in England.
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By publishing in Italian Galileo was appealing against the universities to an educated laity, just as Luther, by publishing in German, was appealing against the theologians to an educated laity.
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Galileo was sent to university in 1581 to study medicine. Medicine was not only the path to a well-paid career; it was also the most empirical and practical of all the sciences, the one least tainted by abstract theorising, and so a suitable choice for the anti-Pythagorean Vincenzo's eldest son.
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Astrology was a recognised part of respectable medicine, and astronomy and astrology were not separate disciplines, but two aspects of one enterprise.
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Stillman Drake, the greatest of English-language Galileo scholars, who wanted to claim that Galileo had learnt the experimental method from his father, pointed out that he may well have been introduced to the pendulum by his father's experiments with weights on strings, and was willing to concede that he may have started experimenting with pendulums as a young man.
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Archimedes was a revelation. Throughout the rest of his life, Galileo's admiration for Archimedes, the Greek mathematician, engineer and scientist of the third century BC, knew no bounds. ‘It is all too obvious that no one else has ever been nearly as clever as he was.’1
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The threads, if they have been wound properly around the arm, are too fine and too close together to be counted by eye. You count them by running a very sharp knife gently and slowly (‘adagio, adagio’) across them. You can then both hear and feel the number of threads that pass under the knife's blade. Galileo has thus achieved a new precision in measuring the difference between two weights.
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Shortly after writing The Little Balance, in the last months of 1587, Galileo sent to the leading mathematicians of northern Italy his solutions to a problem that derived from Archimedes' work.1 He had been working on this problem for a couple of years. It had apparently been presented to him by the Marchese Guidobaldo del Monte, who was to become Galileo's first patron,
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Ours is a visual culture, and Galileo is one of the people who constructed that culture.
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The fundamental realisation that our own capacity to see depends on a lens within the eye came only with Kepler's Optics of 1604, just before the invention of the telescope. And so sight, particularly when dependent on a lens, was to be trusted only when it could be confirmed by touch or sound or smell.
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epicycles on circles, effectively spirals. According to the philosophers these were merely hypotheses to ‘save the appearances’, workarounds to produce results that matched the data. In reality, they insisted, the planets were attached to crystalline orbs that performed perfect circles in the heavens. The result was mutual incomprehension, beautifully illustrated in 1616 when Cardinal Bellarmine argued that Copernicanism was a hypothesis just like epicycles – no one thought they were real, so why should anyone imagine that Copernicanism was
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There is a telling indication from Galileo's own world that his reliance on visual information was in step with the times. In 1611 he was invited to join the Accademia dei Lincei, the Academy of the Lynx-Eyed,
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he adopts the lynx's eye as one of his three personal symbols (the others being the parabola of the projectile and the Medicean stars).14 We should not be surprised to find an opponent complaining of the Linceans that they placed too much reliance on the acuteness of their eyesight.
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For an Aristotelian philosopher seeing was not the same as believing.
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in The Assayer Galileo tells us that sight is the supreme sense, the one we rely on for knowledge.
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It is worth stressing this, because Galileo was not a particularly good father, and in later life he rarely showed any interest in the welfare of others. His work was soon to become more important to him than his loved ones.
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For Galileo's enterprise – the enterprise he shared with his fellow Linceans – was well described by his friend Federico Cesi: ‘What we are engaged in is the destruction of the principal doctrines of the philosophy which is currently dominant, the doctrine of “il maestro di color che sanno”’ – quoting Dante's description of Aristotle as the master of those who know. 3
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his annual salary was sixty florins, significantly less than the income of a good stonemason.
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it is known that by 1612 Giorgio Coresio had tried dropping objects of different weights but the same material from the top of the Leaning Tower of Pisa. The result, he claimed, vindicated Aristotle, for speed of fall proved proportional to weight.
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But in this case there is a manuscript on natural motion, apparently written in the period 1589–92, in which Galileo confidently claims that he knows what will happen in such a test: at first, he tells us, the lighter object moves faster, but then it is overtaken by the heavier object, which reaches the bottom ahead of it. He has, he tells us, repeated this experiment many times.
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scepticism appears well grounded, for if you drop two objects of the same material but very different weights from a high tower you do not get the results Viviani and Galileo describe: the heavier object will hit the ground well before the lighter object, and this is because the resistance of the air has more effect on the lighter object than on the heavier.
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In 1638 Galileo published Two New Sciences. There he described a high tower experiment (he never refers explicitly to the Leaning Tower of Pisa) in which a heavy object and a light object of the same material are dropped, one object being a hundred times the weight of the other. The heavy object reaches the ground only two inches
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March of 1641 Vincenzo Renieri set out to replicate Galileo's experiment by dropping a cannonball and a musket ball from the Leaning Tower of Pisa.13 The cannonball reached the bottom, he told Galileo, a good palm's width ahead of the musket ball: let us say six inches, instead of Galileo's two inches.
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to have been 174 centimetres, or 5 feet 8½ inches.
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there can be only one answer to our problem: both Galileo and Renieri failed to drop the two unequally sized objects simultaneously.
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Galileo describes three experiments in his early manuscripts on moving bodies, On Motion
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It was reason, not experience, that generated science, because science is the study of necessary or causal relationships.
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he maintains that it is necessary ‘to employ reasoning at all times rather than examples (for what we seek are the causes of effects, and these causes are not given to us by experience)’.
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Impressed force naturally dissipates; impetus continues until it encounters some form of obstruction or resistance.
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So far I have written about On Motion as if it were a finished text. But it is not. It is a series of drafts and notes, which were evidently abandoned unfinished.
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now he discovered that Benedetti had already published a similar argument. He would have to look for another way to make his reputation.
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Galileo does not seem to have been a success in his first job. Not only was his salary low, but it was reduced by fines for missing lectures and for failing to wear the required academic dress, the toga, a sort of cassock or academic gown (which can be clearly seen in every portrait of Galileo).
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In February 1592 Guidobaldo del Monte invited Galileo to come to Venice that summer: he would try to fix him up with something there.2 That
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Yet the record that survives from this period is thin, even meagre: one great book, or rather pamphlet, The Starry Messenger, published in 1610; a privately printed instruction manual and a printed protest against a plagiarist;
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What is now called physics was then a branch of philosophy, and philosophy, as a deductive science which described how things must be, was accepted as superior to astronomy, a descriptive science which described how things seem to be.
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A crucial reason for the lack of support for Copernicanism lies in the existence of a new alternative to the geocentric system of Ptolemy and the heliocentric system of Copernicus.
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Matters were to change in 1609 – new evidence from telescopic
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observations, above all the observations of Galileo, became available; and in the same year Johannes Kepler published his New Astronomy, in which he argued that no theory which insisted on circular movement could account for the orbit of Mars, which was, he claimed, an ellipse. Galileo, who was at the forefront of the telescopic revolution, simply avoided discussing Kepler's revolutionary proposals
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Bruno had invented a new dialogue form, in which the disciples and opponents of an unnamed philosopher (referred to as ‘il nolano’, for Bruno was from Nola) discuss his views in his absence.
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Galileo's first documented contact with a committed Copernican came in August 1597.8 He wrote a letter to Kepler,
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Kepler must have been astonished to receive a letter out of the blue in which Galileo, who was quite unknown to him, declared that he had been a Copernican for a number of years.
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Galileo was not a Copernican when he left Pisa in the summer of 1592, but he must have become one very soon thereafter.
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1592, del Monte's notes on an experiment that he and Galileo probably conducted together, the idea for which may indeed have been Galileo's.16 The experiment was very simple. Take a hard ball and coat it with a substance that would leave a mark;
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Nothing would have prepared Galileo and Guidobaldo for a symmetrical path. The path, they would have felt sure, ought not to be symmetrical because the upward path was determined by impressed force and the downward path by weight.
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In Aristotelian terms it should be exactly the other way round: forced movements should be constantly changing, while natural movements should be stable and continuing.
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He had seen that the traditional assumption that one movement must predominate over another was false: an object could be moving in two quite different ways simultaneously.
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What Galileo had now seen was precisely the sort of curved trajectory which would be needed for Copernicus's theory to be correct, and he had also seen evidence in support of precisely the sort of circular inertia that would cause a falling object to remain constantly above the same spot on the earth's surface.
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his conversion implies an eagerness to embrace Copernicanism, for he had found no new evidence in favour of
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What Sarpi's notes show is that by the time Galileo arrived in Venice in 1592 he had formulated sophisticated responses to the standard arguments against a moving earth
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But by 1594, and probably in 1592, he had formulated a different principle of the relativity of movement: that movement at a constant speed is indistinguishable, unless there is an external reference point, from standing still.
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has used his new principle of the absolute relativity of movement, a principle which must be true if Copernicanism is to work, to explain a wide range of phenomena.
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Thomas Harriot had taken this argument for granted in naming the phenomenon, for the first time, ‘earthshine’.40 More to the point, it had been formulated by Sarpi in his notebooks long before he even met
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the subject was relevant because the Pythagoreans had held that the earth went round the sun, and Pythagoras was the major alternative to Plato for those concerned to read the universe in mathematical terms.
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Between 1591, when his father died, and 1610 Galileo was engaged in a constant struggle to make ends meet. It seems likely that his sister Virginia married
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In 1601 the marriage contract for his sister Livia provided for a dowry of 1,800 ducats,
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Nevertheless, in March 1605 he was being sued for money owing on Livia's dowry, in May he was facing legal action for money owing on Virginia's dowry,
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He came to hate teaching so much that he began to think of it as equivalent to prostitution.
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it.)8 It was Galileo's sector that brought him to the attention of Christina of Lorraine, the wife of the grand duke of Tuscany, Ferdinando I – she employed Galileo to teach its use to her son Cosimo
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But it is a fundamental fact that his approach to them was theoretical rather than practical. It was through his clarifying and simplifying the exposition of theoretical principles that Galileo thought that he would make it possible for his students to acquire practical competence.
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His fundamental theoretical claim (which he seems to have been the first to formulate) is that you never get out more work than you put in,
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Galileo thinks that all the simple machines work on the same principle: each represents a method for dividing a weight by multiplying a distance. If one of them is understood,
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‘We must assume that the plane is, so to speak, incorporeal.’13
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he was engaged in exactly the same sort of abstraction, the difference being that he was treating the real world as if this too were simply an imperfect realisation of a theoretical model.
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Galileo was an experimental scientist; it is much more straightforward to ask if he argued by deduction, or by induction from evidence – although
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It is absolutely clear that Galileo failed to grasp one of his central arguments, namely that vision depends solely on rays of light entering the eye, not (as had traditionally been assumed, and as Galileo went on assuming) on something going out from the eye to the perceived object – a failure that must have been a basic obstacle to Galileo's understanding of the workings of the telescope. He did not grasp the importance of Alhacen's work, or of Kepler's Optics (1604), which
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A second and more persuasive contention is that it was the result of reading a book whose importance has been consistently underestimated: William Gilbert's On the Magnet, published in 1600. Gilbert's
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the study of magnetism may provide no evidence in favour of the earth's rotation around the sun, but it does provide a new way of thinking about the daily rotation of the earth on its axis because it shows that this axis is something real, not something imaginary.
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Galileo had read Gilbert by 1602.
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He had also, in his textbook on mechanics, compared the force required to pull an object up an inclined slope (a perfectly smooth object up a perfectly smooth slope) with the force required to lift it vertically. It was easy to see that an inclined slope was simply a way of slowing down the acceleration of a falling object:
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every chord drawn to the lowest point of the circle represents an identical time of fall, what about every arc? Surely all pendulums of the same length should take the same time to swing through different arcs, whether wide or narrow?
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Gilbert had shown that you could prove theories through experiments. Could Galileo show through an experiment that all pendulums of the same length will swing through differing arcs in the same time?
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In a letter to Sarpi in 1604 he tried to formulate such a law in terms of the speed attained after falling a certain distance, but he soon realised the results were impossible. He then reformulated it in terms of speeds and times, and the results seemed coherent.15
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After 1602, after he read Gilbert, Galileo believed that scientific knowledge could advance both through deduction (as in the case of the law of chords) and through experimentation (as in the cases of the isochronicity of the pendulum and the law of acceleration).
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Later, he would say that his own method was very similar to Gilbert's – which was to indicate Gilbert's priority
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Gilbert had shown that experiments could add new knowledge: before Gilbert there was no proper theory of magnetism. But Galileo had shown something much more remarkable. He had shown that experiments could transform existing knowledge.
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Aristotle thought the job of science was to explain what he called ‘the phenomena’, but the word ‘phenomena’ included not only one's own direct experience, but also what was generally understood to be the case.
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Galilean science dealt, not with ‘the phenomena’, but with what would now be called – and what Galileo already called – the facts. And the facts had to be carefully established before they could be taken for granted.
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If Galileo had become an experimental scientist, it was not as an experimental scientist that he wanted to present himself to the world,
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In later years Galileo's friends were to urge him repeatedly to publish, yet he did not do so until 1638. This thirty-year delay cries out for an explanation. After all, Galileo
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If Copernicus was right, the distinction between a sublunary and superlunary world was misconceived: the earth was in the heavens, inseparable from them. If there was change on earth, then equally there could be change in the heavens.
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He gave a series of public lectures on the new star:
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It was written throughout in the local dialect, and belonged to a distinct local genre of sophisticated literary works that used Paduan dialogue for comic effect. Such works were aimed at the educated elite, not at the peasants who appeared in them. The implication of this little dialogue, which was published early in 1605, and naturally in Padua, was obvious: any dunderhead could follow Galileo's arguments better than a sophisticated Aristotelian philosopher.
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The claim has been made that Mauri was Galileo himself,5 and I tend to think (although there seems no prospect of certainty) that this claim is correct. The pamphlet is dedicated to Monsignor Luigi Capponi, the pope's treasurer general, who was later to prove a friend of Galileo's.
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Early in 1608, however, a Dutch spectacle maker discovered that if a convex lens was held behind a concave lens you saw an enlarged image. He mounted the lenses in a tube with a sliding mechanism, thereby making the first telescope (although the name, which is constructed out of the words for sight and distance in ancient Greek, was to come later, invented by Galileo's admirers).
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On his return to Padua, within the space of a few days at most, Galileo ‘reinvented’ the telescope: that is to say, he made a telescope without ever having seen
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Galileo's first telescope, using lenses made for spectacles, magnified only three times; the best Dutch telescopes of the day magnified about six times. The lens quality will have been poor
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Galileo soon had a telescope that magnified eight times. He took his improved telescope to Venice, where he displayed it to the city's rulers.
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agreed that he should receive an appointment at the university for life, and a salary of a thousand ducats a year. In return, he agreed to spend the rest of his life in the service of the Venetian state.
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But by the time the Senate came to vote on his reward it seems clear that they felt they had been misled. Galileo's new appointment – and his new salary – was now to begin only when his existing appointment came to an end. And the Senate decreed that his new salary was never to be increased; they might as well have said that
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But it is also the case that Galileo had and kept a lead in the production of high-powered telescopes. By the autumn of 1609 he had a telescope that magnified twenty times; by the beginning of 1613 one that magnified thirty times – and he was still ahead of the competition. He managed to stay ahead for twenty years.
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Galileo's mother was not alone in thinking she had a right to make money out of Galileo's discovery. Galileo sent a few telescopes to his brother so that his brother could give them to influential people and spread the word of Galileo's discoveries.
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Galileo's mother had told him that her son had been in trouble with the Inquisition in Florence, that she had given evidence against him, and that he in response had sworn at her, calling her a whore and an ugly old cow.
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effect did it have on Galileo to have a mother who was bullying and devious, who regarded everything that was his as rightfully hers, and who believed she had the right to police his words and his thoughts? We
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In the autumn of 1609, as the days shortened, Galileo turned his improved telescope on the heavens.
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He discovered that the Milky Way was not a mysterious white band in the sky, but a vast number of small stars, individually invisible to the naked eye.
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Invisible stars were a profoundly anomalous concept: what purpose could a star serve
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Moreover, near the margin between the illuminated and the unilluminated half he could see two anomalies.
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Galileo's interest in painting, and his experience of looking at paintings where tricks of light were used to convey textures and shapes, may have helped him understand what he was seeing.
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This provided an elegant confirmation of the Copernican view that there was no fundamental difference between the heavens and the earth: on 7 January Galileo sat down and wrote a letter
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That evening he turned his telescope to Jupiter and noticed three little stars arranged in a line with the planet, two to the east and one to the west: he assumed these were yet more new fixed stars.
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press on 12 March – was ‘Sidereus nuncius’, the Starry Message or Messenger
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And Galileo's message – made explicit only in his final revisions to the text – was that the earth is itself a spaceship.
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Fortunately Kepler produced a satisfactory account in the Dioptrics of 1611 – a work that Galileo was slow to read, and perhaps even slower to understand.
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Quickly the answer came back: it was written on 20 February and will have reached Galileo a few days later (Florence is 240 km from Padua, or at least two days on horseback). ‘Cosmic’ was too ambiguous; it would not automatically make people think of Cosimo. ‘Medicean’ was fine.28 Galileo had made his arrangements for publication at the end of January.
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There are three passages in the book in which Galileo declares his support for Copernicanism.
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Galileo began by writing a book that was open to a Tychonic interpretation, but he ended by writing one which was clearly directed as much against Tycho as against Ptolemy.
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He was on the threshold of publishing a book that would ‘stupefy’ the scholarly world. Success was assured. And so he decided to raise the stakes and make his success uncertain.
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Galileo's interests and those of the Medici were even more firmly tied together when, in May of 1610, Galileo agreed to move to Florence, to take up the world's first research professorship there.
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Both believed that by going to Florence he was placing himself in danger – danger of falling foul of the authorities in Rome. Cremonini had frequently been pursued by the Inquisition for denying the immortality of the soul (or rather, for teaching that Aristotle denied the immortality of the soul), but the Venetian government had always protected him.
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Venice had almost come to the point of war with Rome and Spain during the Interdict crisis of April 1606 to April 1607, and would have found herself under attack had she not had the support of the French.
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Now Galileo was joining the opposing side, for Florence was firmly allied to the Habsburg rulers of Spain and the Holy Roman Empire. In what have been called the ‘culture wars of late Renaissance Italy’ Galileo was changing sides.8
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Thus, well before Galileo discovered the telescope, well before he dedicated The Starry Messenger to Cosimo, he had set his heart on transferring from Padua to Florence.
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There was something more important to Galileo than a gold chain: he insisted that he must be appointed, not just as the grand duke's mathematician, but as his philosopher.
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Delle Colombe was supposed to meet with Galileo to debate his experiment, but he never turned up. Instead he went around the city, demonstrating his ability to float ebony on water in the public squares, and crying out that he had defeated Galileo.
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Maffeo Barberini – a Florentine whose relationship to Galileo was to prove of the foremost importance – took Galileo's side, while Ferdinando Gonzaga took Aristotle's.
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The retreat from public and court life that is already apparent in the Discourse on Floating Bodies was soon to be carried a stage further. By January of 1612 Galileo was effectively living in a villa in the countryside outside Florence: he had abandoned the house he had rented in the centre of Florence and had moved in with his friend Filippo Salviati.
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Galileo's treatise on floating bodies represents an important step in the process whereby a physics of qualities (‘light’ objects that move upwards in air, ‘flat’ objects that float in water) was replaced by a physics of quantities (in this case, specific gravities).
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For Aristotle all real knowledge was knowledge of necessary relationships, of logical deductions and causal interactions. For Galileo much knowledge consisted simply of the identification of what Hume would later call constant conjunctures, of laws rather than causes.
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In the whole of his lifetime not a single professor of philosophy in a European university supported him on any topic.
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The key advantage of moving to Florence was that it would enable him to travel to Rome as an intellectual in good standing, one in the service of a respectable Catholic ruler, and to renew contact with the Jesuits. Why leave Venice?
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But Galileo was certainly right to focus on the Jesuits, who were rapidly establishing themselves as the educators of the elite throughout Catholic Europe: there were 245 Jesuit colleges by the end of the sixteenth century. In Rome they ran what amounted to a research university, but one which trained educators who were sent out across the world.
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Galileo's strategy of alliance with the Jesuits was probably doomed from its inception,
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Galileo also had ten other telescopes capable of showing the moons of Jupiter, and these he intended to send off with copies of the book to relatives and allies of Cosimo – to the duke of Bavaria, to the elector of Cologne, to Cardinal del Monte (his old patron's powerful brother), to Spain, Poland, Austria, Urbino and even France.
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What he was offering were new facts, but the knowledge of nature came from philosophy, and philosophy had little to do with facts.
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One great philosopher, Galileo's good friend Cesare Cremonini, was so sure of this that he refused to look through the telescope, even when Galileo offered to bring it round to his house, saying that it would give him a headache (although he was happy to use one of the first microscopes – Aristotle had said nothing about the microscopic world, so the microscope was irrelevant to Cremonini's professional concerns as a philosopher).16
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late April Galileo had gone to Bologna and had tried to show his discoveries to twenty mathematicians there. Martin Horky quickly sent out letters claiming that no one had been able to see the moons of Jupiter (although Galileo had claimed that he could see them
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Further confirmation came from Kepler, who now had the use of the telescope sent by Galileo to the elector of Cologne (which certainly had not been intended for Kepler): he had observed the satellites on 5 September, in the company of Thomas Seget, who had evidently made his way from Venice to Prague.
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While he was there Cardinal Robert Bellarmine, himself a Jesuit, and acknowledged as the greatest authority of the day on all matters of
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doctrine, looked through Galileo's telescope and saw strange sights. He wrote to the mathematicians of the Roman College asking if they could confirm the telescopic discoveries reported in The Starry Messenger –
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anagram to Kepler (via the Medici ambassador in Prague) in July 1610, so that he could authenticate his claim to priority should anyone
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This second discovery, of the phases of Venus, was of fundamental importance.
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This was the first observation that was directly incompatible with the Ptolemaic cosmology, but it was perfectly compatible with Tycho Brahe's geo-heliocentric system.
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He was releasing his discoveries to the world in dribs and drabs, using Kepler to publish his findings as if he were running a scientific journal. In doing so Galileo was stepping away from an alternative model of scientific activity.
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Galileo was probably the first to see sunspots with a telescope. In July 1610, after the publication of The Starry Messenger but before he left for Florence, he showed them to a number of people in Venice.
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Castelli, however, had discovered that one could project the image of the sun onto a piece of paper held behind the telescope's lens. The
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He first announced this breakthrough to Cardinal Maffeo Barberini in Rome – who had supported him in his debate at the Medici court over things that float in water – and to Kepler.
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These were all the effects of foreshortening, as the spots were being seen edge-on rather than from directly overhead.
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In March 1613, as his letters on sunspots went through the press, Galileo supplied tables predicting the positions of the moons of Jupiter over the course of the next few months.
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Galileo is famous for arguing that religion and science must be kept separate, but in 1611–12 his goal was to bring religion and science into a new alliance.
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And the letters on sunspots contained an important passage where Galileo insisted that the sunspots demonstrated, against Aristotle, that the heavens were mutable, and
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that this corresponded precisely to the teaching of Holy Scripture.
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The censors adamantly refused to allow any theological discussion in the book on sunspots, and insisted that the question whether the Bible was compatible with Aristotelian teaching on the immutability of the heavens was far from straightforward, and was in any case a matter for theologians rather than mathematicians.
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By December of 1612 Galileo had virtually completed his career as a practising scientist.
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The first indication that Galileo's position might be deteriorating rather than improving came on the morning of 12 December 1613.1 Benedetto Castelli had breakfast with the grand duke, the duchess, and the grand duke's mother, Christina of Lorraine, who were on one of their periodic visits to Pisa. Also present, amongst others, was a Pisan Aristotelian philosopher, Cosmo Boscaglia.
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Castelli in reply defended Copernicanism, and had the support of everyone present, apart from Christina and Boscaglia. Galileo, having received a detailed account of the discussion from two sources, wrote a substantial letter back to Castelli on the twenty-first, and copies of this letter were soon in circulation.
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But a year after Galileo had written to Castelli, on 21 December 1614, a Dominican preacher in Florence, Tommaso Caccini, whose text for the day was the passage in the Old Testament about
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Punning on Galileo's name, he quoted Acts 1.11: ‘Men of Galilee, why do you stand looking up into the sky?’2 A number of weeks later, on 7 February 1615, another Dominican, Niccolò Lorini, sent a copy of Galileo's letter to Castelli to the Inquisition in Rome, which promptly opened a formal enquiry against Galileo.
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Galileo evidently got word of Lorini's intentions: on 16 February he sent a letter in his own defence to Piero Dini, a sympathetic Roman clergyman, suggesting he might pass it on to the leading Jesuit mathematician, Christopher Grienberger, and to the leading theologian on the Inquisition (and a Jesuit), Cardinal Bellarmine, which Dini promptly did – Galileo was clearly hoping that the Jesuits would take his side against his Dominican opponents.
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the Inquisition found that, even in the version supplied by Lorini, though the wording was sometimes unfortunate, the arguments were unexceptionable.
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Galileo's fundamental premise in the letter to Castelli was straightforward. The Bible is the word of God, but it is adapted to human capacities. So there are plenty of statements in the Bible that are not literally true
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Nature is, like the Bible, a book in which we can trace God's doings. But nature is not adapted or modified in order to be understood by us. So, when it comes to scientific questions, our direct knowledge of nature must always take priority over whatever the Bible may have to say on the subject because there are always grounds for uncertainty
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those passages in Galileo's text which he thought most shocking). Galileo's central claim is that the Scriptures are adapted to our understanding, while nature is not. Nature, he says, is ‘inexorable and immutable’.11 But of course it is a fundamental teaching of Christianity that nature is occasionally adapted in order to communicate with us – this is what a miracle
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In a move which was to characterise his arguments over the course of the subsequent year (and again in 1633), he insisted that he himself was motivated by zeal for the true religion, while his opponents were relying on a simulated piety.
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But the Inquisition was now interested in two questions. First, what else could be discovered about Galileo, for Lorini had claimed that Galileo and his followers (whom he called ‘galileisti’) ‘speak disrespectfully of the ancient Holy Fathers and St Thomas … and spread a thousand impertinences around’?15 And second, was Copernicanism now to be regarded as heretical?
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there are absolutely no spontaneous expressions of piety – such expressions occur only when he has himself been charged with impiety. And there are no attempts to invoke the ordinary, almost routine, miracles that formed a part of Counter Reformation spirituality. It would
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Galileo was profoundly reluctant to acknowledge the possibility of miracles.
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He was prepared to think of a divine architect who had constructed the universe and set it going according to inexorable laws, but he was profoundly unwilling to think of a God who intervened in his own creation. There is a telling marginal comment that Galileo wrote in 1619
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According to Caccini, Galileo had avowed his Copernicanism in his Letters on Sunspots, so the Inquisition ordered that a copy of the text be supplied to a panel of theologians. On 24 February 1616, these theologians proceeded to condemn two propositions: that the sun does not move, which they held to be ‘foolish and absurd in philosophy, and formally heretical
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In January of 1615, Bellarmine had told Prince Cesi that he thought Copernicanism was heretical,
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Bellarmine was, however, unconvinced: what Foscarini was asking, he said, was that the Church should ‘tolerate giving Scripture a meaning contrary to the Holy Fathers and to all the Greek and Latin commentators’, whereas the Council of Trent had specifically forbidden ‘interpreting Scripture against the common consensus of the Holy Fathers’.
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Yet Bellarmine was not advocating a ban on the discussion of Copernicanism.
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All the information that Galileo was receiving from Rome conveyed the same message – that there was no longer any real danger.
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He wanted to rise to Bellarmine's challenge, and prove beyond doubt that Copernicanism was true. And he felt that he would do far better if he could argue the question in person rather than in letters
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Everywhere he went he announced that Copernicus had provided an account of the physical structure of the universe, and not a mere mathematical model
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Because he put all his arguments in writing we can reconstruct what Galileo took to be the main contentions to be refuted in his campaign in support of Copernicanism.60 Of these there were five:
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His greatest success was with Cardinal Orsini, who, armed with Galileo's argument about the tides, approached the pope on his behalf on 24 February, the very day on which the panel of theologians ruled that Copernicanism was heretical.74
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Even more surprising is that the word ‘heresy’, which had been central to the judgement of the panel of theologians, appears nowhere in the Congregation's decree, Cardinal Barberini later claiming credit for its omission.
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On 3 March Bellarmine reported to a Congregation of the Inquisition that he had warned Galileo and that he had acquiesced.
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In 1633, however, when the Inquisition reopened its files on Galileo, a fourth document was discovered: the text of a formal warning read ‘successive ac incontenti’ (thereafter, indeed immediately) to Galileo
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When, in the 1860s, the record of the Inquisition's dealings with Galileo was made public, this document became the object of heated debate.
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modern scholars, however, are nearly all agreed that the document is genuine, and consequently that this warning was read to Galileo at his meeting with Bellarmine.
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As the years went by he either forgot or pretended to forget that Seghizzi had played any role in the proceedings.
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My guess, for what it is worth, is that Galileo did indeed demur when told to abandon Copernicanism.
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Hindsight is a wonderful thing, but with hindsight we can say that Galileo did himself more harm than good in visiting Rome in 1615–16.
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Piero Guicciardini.87 Guicciardini's assessment of Galileo as a courtier was harsh:
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This had to be shown in ways that experienced observers would have no difficulty in interpreting: in the provision, for example, of a ducal litter to carry Galileo home when he eventually returned to Florence.
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Galileo had naturally told all and sundry that he was regarded as indispensable, and he insisted that he could not now leave before the cardinal arrived without a serious loss of face.92
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On 11 March he managed to obtain a lengthy interview with the pope, in which he complained about the attacks of his enemies. The pope reassured him,
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Guicciardini, in any case, was now ready to kick him out. He had prepared the ground by calling in the accounts of Annibale Primi, the administrator at the Villa Medici.
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As for the ducal litter, Galileo had been told politely but firmly that none was available.
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In 1617 he rented a villa outside Florence, and spent almost all his time there. He passed over to Castelli the task of teaching the prince,
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At one point Cavalieri wrote to Galileo to ask if he could put in a word on his behalf with Cardinal Borghese, the pope's nephew and so the fount of all patronage in the Papal States.
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Then between August and November 1618, three comets appeared in the sky. All three were visible to the naked eye, the last to appear being ‘of such brightness that all eyes and minds were immediately turned toward it,
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there was one (perhaps only one) mathematician in Italy who never turned his eyes to the sky, and that, amazingly enough, was Galileo.
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But now Copernicus was forbidden, and so, by elimination, Tycho must be right.
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Galileo knows Tycho had hoped, and that the Jesuits continued to hope, that comets would provide evidence to refute Copernicanism.
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Rather foolishly (as Ciampoli pointed out at the time), he made clear that his enmity was not merely towards Grassi, but towards the whole of the Roman College – a fact which was immediately noted by the Jesuits.
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Galileo, however, egged on by his fellow Linceans, replied to Sarsi in a substantial book entitled The Assayer (1623),
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We have plenty of evidence of Grassi's attempts to restore good relations with Galileo.
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Grassi had made approach after approach after approach – and Galileo never
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sent back a single word of encouragement, continuing to lambast him as violently as ever in print.
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Galileo was not interested in collaborating with the Jesuits on their terms, and since he could no longer openly defend Copernicanism, he was no longer interested in seeking their approval.
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His strategy in 1611 had been an intelligent one; his proud rejection of Grassi's overtures in the years after 1618 was foolish and self-destructive, for he had nothing to gain by it, and he placed his own security at risk.
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Popular philosophy, he argues, is bound (like scholasticism) to claim that it knows all the answers; real philosophy begins with a recognition of the limits of our knowledge.
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Rather the view of himself as an eagle mobbed by starlings tells us exactly how he felt about the condemnation of Copernicanism.
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First, The Assayer contains the clearest exposition of Galileo's understanding of the role of facts in scientific argument
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Testimony, he insisted, was appropriate only for events which were not suitable for replication.
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For centuries a good collection of authorities – and Grassi had a very good collection of authorities – was seen as sufficient to establish a truth.
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Philosophy is written in this very great book which always lies open before our eyes (I mean the universe), but one cannot understand it unless one first learns to understand the language and recognize the characters in which it is written. It is written in mathematical language and the characters are triangles, circles and other geometrical figures; without these means it is humanly impossible to understand a word of it; without these there is only clueless scrabbling around in a dark labyrinth.
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In the final pages of The Assayer, Galileo also took the opportunity to provide what we might call a disenchanted account of matter: matter, he argued, is made up of tiny, indivisible particles whose only certain characteristic is that they have shape.
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Our other senses do not tell us how the world really is, but how it is for us.
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Galileo is arguing that quantitative knowledge is objective, while qualitative knowledge is subjective.
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This argument is now known as the distinction between primary and secondary qualities, and
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The atomism of The Assayer provoked a suspicion of heresy. One of the key points of disagreement between Protestants and Catholics was and is the belief of Catholics that, during Mass, the bread and wine are turned into the body and blood of Christ in their essence, even though in their accidents (their outward appearance) they remain bread and wine. By abolishing essences Galileo seemed to have declared the impossibility of transubstantiation. The book was consequently denounced to the Inquisition, and in his reply Grassi
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Galileo's On Motion had included a refutation of one of Aristotle's arguments against the possibility of a vacuum. He now knew that it is not difficult to create a vacuum.
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For the next generation it was also to become the crucial battleground between those who believed in a deductive science (Hobbes, Descartes) and those who believed in an experimental science (Pascal, Boyle). And whatever one might think of atomism, no one had ever said that belief in a vacuum was heretical – which was precisely why Galileo's pupils, such as Torricelli, were later to turn from astronomy to vacuum experiments, and why vacuum experiments were being conducted outdoors in the streets of Rome a few years after Galileo's death. Just as Galileo could have published his account of falling bodies at any time after 1608, so he could have turned at any time to work on vacuums.
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Diodati had written to Galileo in 1620 asking if he had plans for publication, and offering to help him get round any ‘local obstacles’ – news of the condemnation of Copernicanism was only now beginning to circulate amongst French intellectuals.55 Galileo replied making clear that he was prevented from publishing.
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Deprived of power in the state, excluded by his family even from playing a significant role in their vast commercial enterprises, Sagredo sought to make a little world of his own which he would rule over as an absolute, and sometimes cruel, despot.
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(People kept telling Galileo to read Kepler, but Galileo protested that he found him virtually unreadable.)
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Just when Galileo was feeling lonely and isolated, Maffeo Barberini, a Florentine, was elected pope on 6 August 1623, taking the name Urban VIII. He and Galileo had been on friendly terms since 1611, when Barberini had supported Galileo in a debate, conducted over the grand duke's dinner table, about why bodies float or sink.
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He praised Galileo in a poem he wrote in 1620, a copy of which he sent to Galileo accompanied by a letter signed ‘your brother’. As soon as he was elected he promoted two friends of Galileo's, fellow Linceans and fellow Florentines, Virginio Cesarini (who was sickly, and had not long to live) and Giovanni Ciampoli, to key positions in his administration, and he soon brought Galileo's closest collaborator, Castelli, to Rome to teach at the papal university.1 In return the Linceans promptly elected the pope's favourite nephew, Francesco, soon to be a cardinal, to their society.
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Galileo took it and threw it hard, straight up in the air. Stelluti immediately thought the key was lost: it would fall behind the boat in the water and would never be recovered.
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In all Galileo met with the pope six times, but if they ever discussed Copernicanism we have no direct knowledge of what was said.
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Judging by what happened later, however, it must have been during these conversations that Urban laid down two conditions for any publication on Copernicanism.
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In proposing this alliance, Urban must have thought that he was making an entirely reasonable request. Galileo had frequently claimed that what distinguished him from his opponents was
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he is saying that every competent person is a follower of either Tycho or Copernicus – there is no longer any scope for a defence of the traditional Ptolemaic view
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His exchanges with Grassi suggest that he was furious that it was Tycho who seemed to be ending up as the beneficiary of his astronomical discoveries.
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The Assayer had been denounced to the Inquisition: they assumed that Galileo had been charged with Copernicanism, although we now know that he had been accused of drawing a distinction between primary and secondary qualities that was incompatible with belief in transubstantiation.
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What, everyone asked, was Anna di Cosimo Dieciaiuti to Galileo, that he should arrange a respectable marriage for her and pay out as if she were his own daughter?
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Only one explanation fits all the evidence: Anna was Galileo's daughter, and
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Alberto, for his part, continued to write faithfully for some time, despite the fact that his letters received no reply. In November of 1639, entirely unaware that he had been disinherited, he even wrote formally asking for Galileo's approval for his forthcoming marriage – for, as he eloquently put it, Galileo was the only safe haven he had in all the world.30 Galileo certainly received the letter, but was only shamed into replying much later, when he learnt that his old friend Fulgenzio Micanzio had discovered that he had abandoned Alberto to his fate.
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Vincenzo was indeed removed from Rome as fast as possible, but Galileo did not denounce him, nor have him imprisoned for insubordination as later recommended by Castelli, who seems to have had no doubt that at a word from Galileo space would be found in the prisons of Florence for a disobedient young man. Instead he was shipped off to Poland, where his father had connections, and where he was safely out of reach of the Inquisition.
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He was spurred on by the news that the Dominican Niccolò Riccardi had been elected Master of the Sacred Palace.
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He had arrived carrying the completed manuscript of the Dialogue. He left having had an audience with the pope, and with a promise from Father Monster that he would need to make only a few small changes in order to get permission to publish.
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The year before, his brother Taddeo had commissioned a vast fresco covering an entire ceiling in the Palazzo Barberini.
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does not even shine like the moon, as he said it would if seen from the moon. This suggests the Barberini preferred Tycho Brahe to Copernicus – and this may have been a crucial factor in Galileo's decision to write his Dialogue as an attack on Ptolemy rather than on Tycho.
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frontispiece, which Galileo had engraved by Stefano della Bella. There Aristotle, shown as a feeble old man, Ptolemy, wearing a turban because he comes from Egypt, and Copernicus, wearing the clothes of a Polish priest, stand on the shore of the Florentine port of Livorno debating questions of physics and astronomy. But Copernicus looks nothing like the image of Copernicus that appears in other sources, where he is always portayed as young and clean-shaven.
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This fourth voice, the anonymous commentator, is indisputably a Copernican and can only be Galileo.
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The whole point of his argument that the tides were caused by the movement of the earth (an argument of which there had been no mention in the letter to Ingoli) was to prove Copernicanism to be the only possible account of the structure of the heavens.
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As for the pope, he had promised Galileo a pension.36 Galileo had got away with it so far, and surely his luck would hold. Galileo's luck did not hold.
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Urban was thus instinctively, consistently pro-French. But the Thirty Years War had begun in 1618, and in June of 1630 Sweden, encouraged by France, entered the war against the Habsburgs. If the pope was an ally of France, then he was also an ally of the Protestants and an enemy of Catholicism.
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In 1624 Urban had been proud of his Florentine origins and had surrounded himself with fellow Florentines. Now he began to worry that their loyalties were divided, rumours circulating in 1630 that the he had fallen out with Ciampoli, the secretary who handled all his diplomatic correspondence.
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Urban, who took astrology seriously, was profoundly alarmed. He could not sleep at night. He had all the birds in the papal gardens killed because the dawn chorus woke him from his fitful slumbers.
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The torture of a key witness on 26 August produced decisive evidence. And then on 7 November Morandi was found dead in his prison cell – some said he had been poisoned.
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On 11 September, without any fuss, he was granted an imprimatur by the Florentine ecclesiastical authorities – there was surely an understanding that the book would have to be cleared by Riccardi before it could be printed. Galileo must have been acutely aware that if he did not publish fast he might never publish at all: not only had his relationship with Rome deteriorated, but in October the plague took the life of his gardener, and in the months that followed the death toll in Florence rose inexorably. Galileo was now in a hurry – he was already at work on his next book.
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But the last letter Galileo dictated, when death was approaching, was a note to his beloved (the word is not, I think, too strong), thanking her for offering to sell him some cloth, and for keeping his interests in mind. By this time they both knew they would never meet again.
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The censor Galileo chose was a Dominican, Giacinto Stefani, and he chose well: according to Galileo, Stefani wept as he read the manuscript, so touched was he by Galileo's obedient submission to the requirements of the Church.2 Riccardi, on the other hand, began to get cold feet. He was coming to think that Stefani was the wrong man for the job,
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And so the grand duke instructed the ambassador himself to come to Galileo's aid, and Riccardi agreed to write a memo to the Florentine inquisitor explaining what the pope required.
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In annexing Urbino, Urban was thus demonstrating complete disregard for the wishes of the Florentine government.
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Galileo, for his part, assured the Florentine government (in a letter which is a breathtaking misrepresentation of the facts) that his book was far from being a defence of Copernicanism,
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Worse, Galileo claims that he had discovered the crucial new material that he lifts from Scheiner many years earlier and that he is arguing from his own observations; he thus not only plagiarises Scheiner but claims priority in making Scheiner's discovery.
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The phases of Venus had provided decisive telescopic evidence against the Ptolemaic system, but not against the Tychonic. Galileo now believed that the path followed by sunspots on the disc of the sun was the first observation that was incompatible with the Tychonic system
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Galileo has two motives here. In the first place he wants to suggest to his readers that his philosophy, like Plato's, is easier to reconcile with Christianity than is Aristotle's. Platonism is a sound choice for anyone claiming that their philosophy is compatible with the true faith.8 But something else is going on. Every important manuscript of Plato known to the Renaissance was the property of the grand duke of Tuscany. In invoking Plato, Galileo was thus complimenting his patron and engaging in an elementary form of cultural patriotism.
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Unhappy the land where heroes are needed. Bertolt Brecht, Life of Galileo (1938)
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the linen collars Galileo wears in his portraits will have been made, mended and starched by her.
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Publication of Galileo's book was completed on 21 February 1632, but the measures taken to prevent the spread of the plague meant that by the end of May only two copies had arrived in Rome,
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It was not until July that six more copies arrived, three of which were given to Galileo's close friends and supporters. Within days the authorities were trying to seize every copy in Rome
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The pope's complaint was that Galileo had failed to include at the end of his book the argument that he had insisted upon: that one cannot prove the truth of Copernicanism because God's power is such that he can achieve any natural effect by numerous different means, many of them beyond our comprehension. Galileo had made only a cursory reference to this argument, mocking the pope by giving it to Simplicio
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But it was clear from the beginning that the pope was not going to be satisfied with having the book prohibited. He wanted to see Galileo tried for heresy,
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But matters took a turn for the worse when the records of the Inquisition relating to the condemnation of Copernicanism in 1616 were reviewed, and it was found that Galileo had been forbidden to enter into any discussion of Copernicanism
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Galileo left Florence on 20 January 1633 and arrived in Rome twenty-five days later, having spent longer than he had expected in quarantine.21 He travelled in a ducal litter, but there was uncertainty as to whether he had
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Indeed he was a less than ideal house guest, keeping everyone awake for two nights in a row with his cries and screams.
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Galileo reported to the Inquisition on 12 April and was held there until his release on 30 April. He was now completely isolated and alone, and at night he cried out in pain.
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In the papers of the Congregation of the Index there exists an anonymous, undated report surveying the evidence that Galileo was guilty in The Assayer of denying transubstantiation – a report first published in 2001.
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So Galileo and Maculano reached a deal: Galileo would cooperate, and Inchofer's denunciation of The Assayer would be left to moulder in the files of the Congregation of the Index.
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He agreed only that anyone reading his Dialogue could easily form the impression that it had been written in defence of Copernicanism – he did not concede that this was his actual intention. In effect he agreed to plead guilty not to defending Copernicanism but to a lesser charge of appearing to do
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Maculano had achieved what he was aiming at: he had made no binding commitment as to the punishment Galileo was to receive, but had set things up so that Galileo could be released without undermining the authority of the tribunal, which was the outcome desired by his superior, Francesco Barberini, the cardinal-nephew.
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He had, he was forced to conclude, been led astray by pride – in other words, by intellectual ambition. As a result he had come to make the weaker argument seem the stronger.41
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Finally on Tuesday 21 June Galileo was required to report to the Inquisition. There he was once more interrogated.48 He denied ever having been committed to Copernicanism, although he said that before 1616 he had thought that either Copernicus or Ptolemy might be right. He insisted that his book should not be read as a defence of Copernicanism. He was threatened with torture and then held overnight. The next day he appeared, dressed in the white robes of a penitent, before the Congregation of the Inquisition at the monastery of Santa Maria sopra Minerva.
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Galileo had confessed not to being a Copernican but to having presented arguments in favour of Copernicanism with insufficient care. His sentence was read to him and he was required to abjure Copernicanism.
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Second, and perhaps more surprising, the pope had decreed on 16 June that Galileo was to abjure de vehementi, and in doing so had, apparently casually, classified Copernicanism as a heresy, which it had not previously been.
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Inquisitors in university towns across Italy were soon ordered to summon together the local professors of philosophy and mathematics and to read to them Galileo's condemnation, so that there could be no doubt that Copernicanism was now a heresy and Galileo's book a forbidden book;
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Eventually on 1 December the pope gave him permission to return to his villa at Arcetri outside Florence, where his movements were still to be restricted, and he was to avoid having more than one or two people at a time to visit him.63 He arrived home on 17 December 1633. Almost immediately he was visited by the grand duke in what amounted to an official display of solidarity. He was to live for a further eight years, but he was scarcely ever to leave home again.
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In 1638 he was formally told that if he discussed Copernicanism with anyone he would spend the rest of his life behind bars.
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Within a few weeks of Galileo's arrival in Siena work began on a Latin translation of the Dialogue, which was eventually published in Strasbourg in 1635.
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Only when all else failed did he turn to the Dutch firm of Elsevier, who had recently printed the Latin translation of the Dialogue and the first, bilingual (Italian and Latin) edition of the Letter to the Grand Duchess Christina in Strasbourg (the latter made possible because Galileo had arranged for the text of the letter to be smuggled out of Florence to Diodati; he was then sent the text of Diodati's preface, which he approved).3 Micanzio acted
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But Galileo must have taken an exquisite pleasure in using his meeting with Noailles as a cover story to explain how his manuscript had ended up in the hands of a Protestant publisher, for Noailles had obtained authorisation for the meeting from the pope himself.6 Galileo was, there can be no doubt, thumbing his nose at Urban.
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Since 1590 or so he had been working on his new science of movement, which he finally published in 1638. This new science was concerned with the acceleration of falling bodies, the isochronicity of the pendulum, the parabolic path of projectiles. All these discoveries, which constitute the foundation of modern physics, contain both an experimental and a theoretical or deductive component; in the published work theory is made, as far as possible, to predominate over experiment.
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When Galileo says that the book of nature is written in the language of mathematics, he means that real nature embodies principles derived from this idealised nature.
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The heavens had always been understood as a world of mathematical purity, but Galileo finds this purity precisely where all previous scientists had insisted it could not be found – on earth.
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By a remarkable reversal, Galileo then turns round (and there is evidence that he had started to do this even before the discovery of the telescope) and finds variation, imperfection, roughness rather than smoothness in the heavens:
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We can summarise very simply, if anachronistically, the complex and subtle arguments of the first of the two new sciences: Gulliver's worlds are impossible. There can be no Lilliputians or Brobdingnagians.
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Galileo invented two new physical sciences and a new cosmology. These three transformative discoveries had little in common with each other.
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I found him totally without sight and completely blind … he has a very severe hernia, constant pains in his guts, and a wakefulness such that, according to his own word and the reports of those who live with him, in twenty-four hours he never sleeps for a whole hour; and in other respects he is so reduced that he looks more like a corpse than a living person
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resolved if we recognise that his cosmogony derived from Plato's Timaeus. This gave him an immaterial Divine Love, capable of inspiring human minds; both an immaterial creator, the Platonic demiurge, and lesser material gods, the creators of mankind; and an anima mundi ordering and vivifying the whole.
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But Galileo went further in the direction of religious faith than Epicurus or Lucretius: the book of nature must, after all, have an author. To see the world as mathematical is (in Galileo's terms) to see it as rational, and to see it as rational is to see it as the product of an intelligent
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Galileo was the first modern scientist, arguably the first true scientist. He constructed a new generation of instruments to be used for scientific purposes: he invented the thermometer, the micrometer and the first accurate timepiece, the pendulum clock, and he transformed the telescope and the microscope from toys into tools for the discovery of invisible worlds.1 Galileo's ambition was to be a new Archimedes, but almost by accident he came across a new way of learning about nature, the experimental method, and as a result invented what we now call science. Before he could invent science he had to devise and defend an idea that seems to us so elementary that we take it entirely for granted: the idea of the fact.
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The competition between the new Galilean universe and the old Aristotelian one gave birth to a new word: cosmology. ‘Cosmos’ and ‘cosmology’ are words that appear in English in the 1650s, in response to the publication in 1635 of the Latin translation of Galileo's Dialogue under the novel title Systema cosmicum. The title itself was an afterthought, for when the frontispiece was commissioned the intention was to call the book the ‘Systema mundi’, or System of the World, in line with Galileo's own title ‘Sistemi del mondo’.
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But Galileo was a far less simple or straightforward character than most people, and often the key to understanding him is to recognise that he was determined to stand for contradictory principles. One fundamental conflict was over the nature of knowledge. The primary thrust of Galileo's new science was to argue that knowledge must be grounded in sensory experience – that seeing is believing. But almost equally powerful was the conviction that knowledge is about abstractions, and that it can go beyond and even against the evidence of our senses.
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For Galileo's life, like all our lives, was built around a series of choices. Some of those were intellectual choices. He chose not to become a careful experimental scientist,
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And he chose to abandon Venice, to fall out with the Jesuits and to earn the displeasure of Urban VIII, on each occasion because he felt belittled by the treatment he had received.
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He had close friends who admired him: Sagredo, Salviati, Castelli. He had six portraits of friends on the wall of his sitting room when he died,
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But what struck most people was his extraordinary willingness to stand alone.
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Outwardly, Galileo's path is easy to trace. For the first half of his life he was an obscure mathematician who published little, and nothing of importance. Yet during this time he made most of his great discoveries in physics, discoveries that he was to publish only at the end of his life. The second, and shortest, period in Galileo's life began in 1609, when he turned a telescope towards the sky.
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His Dialogue Concerning the Two Chief World Systems, the first great work of modern science, was published under licence in 1632 but condemned by the Inquisition in 1633: Galileo spent the rest of his life under house arrest, and there was a general ban on the publication of any of his works in any Catholic country. In 1636 he secretly arranged for the publication in Lutheran Strasbourg of the Letter to the Grand Duchess Christina, an argument for intellectual freedom, and in 1638 he arranged for the publication in Calvinist Holland of his Two New Sciences, the two sciences being the science of projectiles and the science of the strength of materials.
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One complaint was that by making the earth a heavenly body he had placed hell in the heavens; another was that in claiming there were other, uninhabited worlds he had made nonsense of the notion that this world existed because it was made for living creatures.22 Galileo was trampling down the barriers that kept apart God and the devil, the sacred and the secular, the mortal and the immortal.
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One day and night; in all their vast survey Useless besides, reasoning I oft admire How Nature wise and frugal could commit Such disproportions
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Galileo died quietly on 8 January 1642. He was seventy-seven. As soon as the news reached Rome instructions were sent that there was to be no tombstone, or any memorial within a church. (Viviani ended up turning the front of his house into a private memorial to Galileo, and left money in his will for a fine tomb.) A modest plaque was permitted in 1673, and a proper tomb finally allowed in 1737.
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unknown woman was found buried – perhaps reburied in 1674 – with him.
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the first legal reprinting of Galileo's Dialogue in the original Italian was in 1744, albeit accompanied by the condemnation of 1633 and Galileo's recantation. The Catholic Church did not formally permit the teaching of Copernicanism until 1820, although over the previous century restrictions on the discussion of his work had slowly broken down.2 And it was only in 1834, the year before Copernicus and Galileo were finally removed from the Index of forbidden books, that the English word ‘scientist’ first appeared in print.
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The first reiterates the view expressed by the Catholic Church itself in 1616 and in 1633: modern science, Galilean science, is fundamentally at odds with Christianity.
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One approach stresses that Galileo was never intended to be prevented from using Copernican theories as a mathematical hypothesis; he was simply forbidden to say that Copernicanism was true.
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The classic exponent of this view is the great historian of science (and practising Catholic) Pierre Duhem: his To Save the Appearances was published in 1906. A similar approach was taken by Arthur Koestler, in The Sleepwalkers (1959). Koestler argued that the truly important discoveries in astronomy were made by Johannes Kepler; Galileo overstated his own achievements in the Dialogue and thus provoked the Church into condemning him.
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This view, which presents Galileo as an overreacher, seems to me essentially correct.
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The alternative view is that the Church made a fundamental error of judgement. In his Letter to the Grand Duchess Christina (written in 1615) Galileo clearly demarcated different spheres for religion and science. There was, he insisted, no need for religious authorities to interfere with the enquiries of scientists. Many Catholic historians and philosophers would now argue that Galileo was right, and that the Church has finally come to adopt his position. This is the view expressed, for example, in Annibale Fantoli's study, and in a recent collection of essays edited by Ernan McMullin, The Church and Galileo (2005).
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Impossible or not, Galileo was right to ask for intellectual freedom, and Bellarmine wrong to deny it. But if the liberal Catholic position is helpful for understanding the events of 1616 it is much less helpful for understanding those of 1633. Urban VIII, unlike Bellarmine, was certainly willing to envisage the triumph of an anti-Aristotelian science – one of his first actions on being elected pope had been to bring Benedetto Castelli to teach at the pontifical university.
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One of my contentions in this book is that we need an explanation for Galileo's premature Copernicanism, and that such as explanation cannot be purely scientific: it must also be psychological.
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We can debate endlessly at what point it became ‘rational’ to adopt Copernicanism: the earliest date would be 1540, when the first summary of Copernicus's views, the First Report, was published; the latest would be 1838, when the movement of the earth was first reliably demonstrated by the measurement of stellar parallax
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In addition, an eastward deviation of bodies falling from a high tower, the opposite of the westward deviation predicted by the Aristotelians (the result of the fact that a body at the top of a tower is moving faster as it rotates around the centre of the earth than the foot of the tower is moving), had been measured in 1792.
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He would surely have claimed that the publication of his own Dialogue in 1632 marked the crucial moment at which any sensible person should have accepted the truth of Copernicanism. But in making such a claim he would have been profoundly wrong.
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Galileo had no decisive astronomical evidence that showed that the Copernican system was superior to the system of Tycho Brahe: the one argument he had, from the line of movement of sunspots across the face of the sun, was and still is highly contentious. He thought he could sidestep this fundamental difficulty. If the evidence provided by
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Galileo's theory of the tides was disastrous, both for him and for Catholic Europe, because, armed with it, he saw no need to respect the limits on debate imposed by the Church.
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In 1624 he was given permission by his friend the newly elected Pope Urban VIII to reopen the debate on Copernicanism, provided he respected certain conditions. By respecting the letter but not the spirit of these conditions, Galileo brought catastrophe on himself,
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The consequence of this is an interesting paradox: Galileo was the founder of modern science, but he was always a reluctant experimentalist, and consequently he never produced an unambiguous defence of the experimental method.
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Then in 1624, entirely unexpectedly, Galileo was offered the official encouragement he had always sought. But because the terms were not of his own choosing, because the support was conditional, he betrayed the pope, who was both his ally and his friend.
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who accused him of ‘stubbornly and perfidiously assassinating himself’.
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In 1983 Pietro Redondi published the original Italian edition of Galileo Heretic, the first major study to free itself of the intellectual framework inherited from Viviani and Favaro. Redondi maintained that the unspoken charge against Galileo was not Copernicanism but atomism.11 Atomism, as expressed by Galileo and by later seventeenth-century scientists and
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Shape, movement and resistance are the three crucial characteristics of the components of a machine, and these are the fundamental features or primary qualities of matter;
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Other characteristics, which Aristotelians had taken to be equally ‘real’ (colour, taste and sound), are purely subjective:
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But there was a particular and fundamental tension between atomism and Catholicism. Catholics believe that in the Mass, the liturgical re-enactment of the Last Supper,
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Urban VIII regarded the argument of the Dialogue as not only disloyal but impious. Here, as elsewhere, his judgement was sound. Galileo always acknowledged the authority of the Church and always claimed to be a pious Catholic.
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My account of Galileo in this book has been novel in three significant respects: I have emphasised his early Copernicanism, his reluctant empiricism and his private irreligion. I have also stressed his extraordinary intellectual ambition, his enormous vanity and his capacity for self-destruction: Galileo was no secular saint, although he was capable of pretending that he was. These new insights bring us, I believe, much closer to seeing Galileo as he saw himself, but they also make it clear that Koestler (who was wrong about many things) was right to portray him as the architect of his own downfall.
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Galileo was indeed a heretic; but worse (for heresy was much more common than historians have realised), he was disloyal and ungrateful. In the world of Counter Reformation Italy heresy often went unpunished; disloyalty and ingratitude, on the other hand, were never tolerated.
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[volume no.] [page no.], e.g. OG x 57. The first edition (1890–1909) is available online at www.gallica.fr (and large
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Koyré, Galileo Studies, 37–8; Ernan McMullin, ‘Galilean Idealization’, SHPS 16 (1985), 247–73; Peter K. Machamer, ‘Galileo's Machines, His Mathematics, and His Experiments’, in Machamer, ed., Cambridge Companion, 53–79.
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NOTE: koyre