Justified True Belief

(●) A cathedral canon in a corner of Poland who spent thirty years quietly working out that the ground under his feet was moving. + If you have ever sat in a train at a station and felt certain that the carriage on the next platform was sliding away, only to realise a moment later that yours was the one that had started, then you have had the thought that made Copernicus famous. He used the same illustration himself, borrowed from Virgil: we leave the harbour, and it is the land and the cities that seem to draw back from us. Everything we see in the sky, he argued, looks exactly the way it would look if the earth were the thing in motion. So perhaps it is. He was not a professional astronomer, because in 1500 there was barely such a job. He was a canon of the cathedral chapter at Frombork on the Baltic coast, which meant he was one of the sixteen churchmen who ran a cathedral, managed its farms, collected its rents, and voted on its business. He held a doctorate in canon law, which is the church’s own body of law, and alongside that he practised medicine, ran a district of estates for five years, commanded a castle through a siege, and wrote the standard Prussian memorandum on currency reform. The astronomy was done in the hours left over, in a tower on the cathedral wall, with wooden instruments he made himself. For a Christian reader he is worth knowing chiefly because the story everyone half remembers about him is not the story the documents tell. The man who moved the earth was a churchman. A cardinal in Rome wrote begging him to publish, a bishop badgered him for years to do it, and the book when it finally appeared was dedicated to Pope Paul III. One signature fact is worth carrying away: he had waited so long, and the printing took so long, that he saw the finished copy only on the day he died.

(●) 19 February 1473 AD: Born in Toruń, the youngest child of a merchant family on the Vistula. + Toruń was a prosperous Hanseatic town on the great Polish river, one of the trading towns bound together in the league that ran the commerce of the Baltic and the North Sea, a place of brick gables and grain barges, belonging to the kingdom of Poland since the Teutonic Knights had been forced to give it up a few years before his birth. His father, also called Niklas Koppernigk, had come up the river from Kraków and dealt in copper; his mother, Barbara Watzenrode, belonged to one of the town’s leading families. The surname is usually traced back to a Silesian village called Koperniki rather than to the metal, though the coincidence is the kind of thing people remember. He was the fourth and last child. His brother Andreas would follow him through university and into the same cathedral chapter; one sister, Barbara, became a nun, and the other, Katharina, married a Kraków merchant. It was an ordinary prosperous childhood in a trading town, and it ended early.

(●) c. 1483 AD: His father died, and an uncle who would become a prince-bishop took charge of his future. + Nicolaus was about ten when his father died. His mother’s brother, Lucas Watzenrode, stepped in, and it is hard to overstate what that meant. Watzenrode was a hard, clever, politically formidable churchman who in 1489 became Prince-Bishop of Warmia, and he ran his little territory like a man who intended to be obeyed. Warmia needs a word of explanation. It was a small prince-bishopric, a district governed in temporal as well as spiritual matters by its bishop, wedged into Royal Prussia under the Polish crown, with the lands of the Teutonic Knights pressing on it from two sides. Being its bishop meant being a ruler with a chancery, revenues, castles and an army to raise, as well as a diocese. Watzenrode’s plan for his nephews was the ordinary sensible plan of the age: a university education, then a canonry, which would give them a secure income for life and the leisure to be useful. The plan worked, and the leisure was put to a use nobody foresaw.

(●) 1491 – 1503 AD: Twelve years as a student in Kraków, Bologna, Rome, Padua and Ferrara. + He enrolled at the University of Kraków in the winter of 1491, where the arts faculty had a genuine reputation in astronomy, and where he began buying and annotating the books he would keep all his life. Several of them survive in Uppsala, margins crowded with his handwriting. In 1496 his uncle sent him to Bologna to read canon law, the church’s own legal system, which was the practical qualification for a career in administration. He lodged with an astronomer named Domenico Maria Novara and worked with him, and on 9 March 1497 the two of them watched the moon pass in front of the bright star Aldebaran. That observation is the earliest of his we have, and the point of it was not sentimental: the moon’s apparent size in Ptolemy’s theory should have varied far more than it visibly did, and here was a way to check. A canonry at Frombork had been granted him two years earlier through his uncle, and on 20 October 1497 he formally succeeded to it by proxy, still in Italy, which is to say he was given the income before he had done a day’s work for it. A canon was a member of the cathedral chapter, the corporation of clergy who own and administer a cathedral, and it did not require priesthood. The evidence suggests he took only minor orders, the lower grades of church service that stop short of ordination, since nobody in his lifetime, friend or enemy, ever calls him a priest, and most scholars now think he never was one. The rest of the twelve years reads like a tour, though it was nothing so leisurely. He spent the jubilee year of 1500 in Rome, one of the holy years in which the city fills with pilgrims come for the pardon the pope proclaims, and in November of it he stood somewhere in that crowded city watching a lunar eclipse. Then medicine at Padua. Then, on 31 May 1503, the doctorate in canon law, taken at Ferrara rather than at Bologna, where he had actually read the subject, for the plain reason that the graduation fees at Ferrara were cheaper. He never took a degree in astronomy. There was none to take.

(●) 1503 – 1512 AD: He came home to serve his uncle, and published a volume of Greek letters in his own Latin translation. + For most of a decade he lived at Lidzbark castle as his uncle’s physician and secretary, travelling with him to negotiations and to diets (the assemblies where the towns, the nobles and the bishops of Prussia settled their business with the crown), learning the trade of governing a small state at close range. The one book he published in these years, and the only book he published at all until the year of his death, is not the one anyone expects. In 1509 a Kraków press printed his Latin translation of eighty-five short Greek letters by Theophylact Simocatta, a seventh-century Byzantine writer, sorted into moral, rural and amorous. It was a young humanist’s calling card, proof that he could handle Greek, and he dedicated it to his uncle. Watzenrode died in 1512, and Copernicus settled at Frombork for good. The chapter’s canons lived in houses along the cathedral wall, and he took over a tower at the northwest corner, where he laid a paved platform for his instruments. Those instruments are worth picturing, because they explain a great deal. He used a triquetrum (three hinged wooden rods, used to measure the angle of a star above the horizon), a quadrant, which is a graduated quarter circle for reading off that same angle, and a gnomon, a vertical rod whose shadow tells the sun’s height. All were wooden, all were homemade, and none of them could see anything Ptolemy had not been able to see thirteen centuries earlier. What was new was not the eye. It was the arrangement.

(●) c. 1510 – 1514 AD: He wrote a short sketch putting the sun at the centre, and passed it round in manuscript rather than printing it. + The sketch is known as the Commentariolus, the "little commentary." It runs to a few handwritten leaves and opens with seven assumptions, among them that the earth is not the centre of the universe but only of the moon’s orbit, that all the spheres circle the sun, that the distance from the earth to the sun is nothing at all compared with the distance to the stars, and that the wandering back-and-forth of the planets in our sky comes from the motion of the earth and not from any motion of theirs. He never printed it. He handed it to people he trusted. We can date it because of a library list. In May 1514 a Kraków professor and physician named Matthew of Miechów catalogued his books, and among them noted a manuscript of six leaves setting out a theory that the earth moves. That is our evidence that the idea was in circulation by then. The little treatise itself was then lost for three centuries, until a copy turned up in Vienna and was printed in 1878, and another was found in Stockholm in 1881. Around the same time the church came asking for his help. The Fifth Lateran Council had taken up the reform of the calendar, and the request went out through Paul of Middelburg, Bishop of Fossombrone, who was leading the work. The problem was arithmetic, and it had been compounding quietly for twelve hundred years. The Julian year, the year of the calendar Julius Caesar had given the west, was about eleven minutes too long, which sounds like nothing at all until you let it run: eleven minutes a year since the Council of Nicaea in 325 AD, the gathering of bishops that fixed the rule for dating Easter, had pushed the spring equinox some nine days out of place. Easter, in other words, was being kept at the wrong time, and the church wanted a man who could count. Copernicus replied, in effect, that nobody yet knew the length of the year well enough to fix it, and went on measuring. He mentions the episode nearly thirty years later in the dedication of his book, and he is clearly still a little proud of having been asked.

(●) 1516 – 1526 AD: He ran a district of farms, held a castle through a war, and told the Prussian estates how to mend their coinage. + From 1516 the chapter posted him to Olsztyn as administrator of its estates, and his own ledger of the work survives. It is called the Locationes mansorum desertorum, the settlement of deserted holdings, and it is a list of abandoned farms being filled again, family by family, with the tenant’s name, the size of the holding and the plough-teams he brought. The man who rearranged the solar system spent those years arranging peasants and oxen. Then the war came, and it came close. The Teutonic Knights invaded in 1519, and in 1520 they burned the town of Frombork, which was not a distant piece of politics to him but a fire in the place where he had settled for good. When the winter of 1520 to 1521 closed in, the canon with the ledger of ploughs and tenants was the man left in charge of Olsztyn castle, organising its defence and writing to the king for troops. The castle held. The other trouble was money, and it was slower and worse. Prussia had several mints turning out coin of steadily falling silver content, so that a mark bought less each year while the old good coin vanished from circulation into people’s chests. Copernicus wrote a memorandum on it in 1517, addressed the Prussian diet at Grudziądz in 1522, and produced his finished treatise, Monetae cudendae ratio, in 1526. Its argument is that debasement, the quiet practice of putting less silver in a coin while calling it by the same name, is a tax nobody voted for, that it wrecks trade, and that bad coin drives out good, a rule the English would later attach to the name of Thomas Gresham. He also told the estates what nobody wanted to hear: there must be one mint and one standard, and the profits of striking money must stop being treated as revenue.

(●) 1538 – 1539 AD: A new bishop ordered him to dismiss his housekeeper, and after some resistance he complied. + Johannes Dantiscus, a poet and diplomat of considerable charm and no great patience, became Bishop of Warmia in 1537, and he set about tightening the discipline of his clergy at precisely the moment when the Reformation had made clerical households a matter of public argument. Several of the Frombork canons were told to put their women out of their houses. Copernicus, by then in his sixties, kept house with Anna Schilling, a woman from Gdańsk who was a relative of his. The correspondence survives, and it is uncomfortable reading. Dantiscus wrote repeatedly; Copernicus answered on 2 December 1538 that he would do as he was told, but that an honest housekeeper who was also a kinswoman was not easy to find in a hurry. The bishop was not satisfied, and spoke to him about it twice more in person. On 11 January 1539 Copernicus reported that he had dismissed her, and in March she went back to Gdańsk. What lay behind it we simply do not know. The documents record a bishop’s suspicion and an old man’s reluctance, and they do not record anything else.

(●) 1539 – 24 May 1543 AD: A young Lutheran talked him into printing De revolutionibus, and the finished book reached him on the day he died. + In May 1539 a twenty-five-year-old professor of mathematics from Wittenberg arrived at Frombork and asked to be taken on as a pupil. His name was Georg Joachim Rheticus, he was a Lutheran, and Warmia was a Catholic bishopric whose bishop was busy forbidding Lutheran books. Copernicus took him in, and Rheticus stayed about two years. It is one of the more cheerful facts of the sixteenth century. Rheticus read the manuscript, understood it, and did what his teacher would not: he published. His Narratio Prima, the "first account," came off a Gdańsk press in 1540 and told Europe what was in the unpublished book. Nothing terrible happened, which was the argument Copernicus needed. The trigonometry section was printed separately at Wittenberg in 1542, and the whole work went to the press of Johannes Petreius in Nuremberg, with Rheticus supervising. Then Rheticus left for a chair at Leipzig and handed the proofs to Andreas Osiander, a Lutheran preacher in the city, who added an unsigned note to the reader saying that the book’s hypotheses need not be true, nor even probable, but were offered only to make calculation possible. Copernicus had suffered a stroke by the end of 1542. Tiedemann Giese, Bishop of Chełmno and his closest friend, wrote to Rheticus on 26 July 1543 that Copernicus had lost his memory and his mental vigour many days before, and saw the completed book only at his last breath, on the day he died. That day was 24 May 1543. He was buried under the floor of his own cathedral, in a spot nobody troubled to mark, and for four and a half centuries nobody could say which spot it was. Then archaeologists digging there in 2005 turned up the skeleton of a man of about the right age, and in 2008 it was matched to hairs caught in one of his own books, the same DNA in the grave and in the pages he had read. In May 2010 he was buried at Frombork a second time, with a marked grave.

What He Taught

(T1) The earth is not the still point of the world; it turns once a day and travels round the sun once a year. + Everyone before him had a very good reason for thinking otherwise, and it is worth feeling the force of it. Drop a stone from a tower and it lands at the foot of the tower. Shoot an arrow straight up and it comes down beside you. If the earth were spinning, the ancients argued, the ground would have slid out from under both of them, and a bird that left its branch would never find its way home. Aristotle had explained falling as heavy things seeking the centre of the universe, so if the earth is not at that centre, why does anything fall at all? Copernicus answered that the air belongs to the earth and turns with it, so that the arrow, the bird and the stone are carried along with everything else and notice nothing, exactly as a passenger below decks notices nothing of the ship’s speed. And he cut the Aristotelian knot by redefining heaviness: heavy things are not seeking the centre of the universe, they are seeking their own whole, which is why the bits of a round earth gather themselves into a ball, and why he was willing to suppose the same of the moon and the other planets. That guess was better than his argument for it, and Newton would eventually supply the reason. There is also a simple question of economy. If the whole heaven turns round us every twenty-four hours, then the outermost sphere, unimaginably far away, must be sweeping through an unimaginable distance every day, and nobody can say what drives it. If instead the earth turns, one small body does one small turn, and the whole of that daily motion is accounted for. Copernicus thought it absurd to move the container in order to avoid moving the contents.

(Q) "Thus when I considered with myself what an absurd fairytale people brought up in the opinion, sanctioned by many ages, that the earth is motionless in the midst of the heaven, as if it were the center of it, would think it if I were to assert on the contrary that the earth is moved; I hesitated long whether I would give to the light my commentaries composed in proof of this motion." + Source: De revolutionibus, Preface to Pope Paul III (Stimson translation, 1917). He is telling the pope why the book took so long. What he feared was not a tribunal but a laugh, and he says as much a few lines later: it was "the scorn which was to be feared on account of the novelty and the absurdity of the opinion" that made him set the finished manuscript aside.

(T2) Put the sun in the middle, and the planets fall into an order that cannot be rearranged. + Start with the thing that had embarrassed astronomers for fourteen centuries. Watch Mars night after night against the stars and it moves steadily eastward, then slows, then stops, then goes backwards for a few weeks, then stops again and resumes. This is called retrograde motion, and it is exactly what you see when you overtake a slower car on a motorway: for a moment the other car seems to slide backwards against the hedges behind it, though it is doing nothing of the kind. Copernicus said that is precisely what is happening. The earth, on a faster inner track, laps Mars and leaves it apparently drifting back. Every planet’s backward loop falls at the moment when it and the earth pass one another, the earth overtaking Mars, Jupiter and Saturn from the inside and being overtaken in its turn by Mercury and Venus, which on the old view was an unexplained coincidence repeated five times over. Then comes the part that convinced mathematicians. In Ptolemy’s system, the order of the planets outward from the earth was partly a matter of taste, and astronomers really did argue about whether Mercury and Venus sat above the sun or below it, because nothing in the system decided it. Once the sun is at the centre, nothing is left to taste. Each planet’s distance and its year are locked together: Mercury takes eighty-eight days, Venus about seven and a half months, the earth one year, Mars not quite two, Jupiter twelve, Saturn thirty. The system had a floor plan for the first time, and you could not move a room without wrecking the house. One consequence he had to swallow whole. If the earth swings from one side of its orbit to the other over six months, the nearer stars should appear to shift slightly against the farther ones, the way your thumb held at arm’s length jumps against the far wall when you look with one eye and then the other. That shift is called parallax, and nobody could detect any. Copernicus concluded that the stars must be so enormously far off that the whole width of the earth’s orbit counts for nothing beside the distance, which is true, and which was so hard to believe that Tycho Brahe later rejected the whole system rather than accept the emptiness it required. The first measurement of a stellar parallax came in 1838, nearly three centuries after his death.

(Q) "I found at length by much and long observation, that if the motions of the other planets were added to the rotation of the earth and calculated as for the revolution of that planet, not only the phenomena of the others followed from this, but also it so bound together both the order and magnitude of all the planets and the spheres and the heaven itself, that in no single part could one thing be altered without confusion among the other parts and in all the universe." + Source: De revolutionibus, Preface to Pope Paul III (Stimson translation, 1917). This is his own account of what persuaded him, and it is an argument from fit rather than from any new measurement. He had no telescope and no observation Ptolemy lacked. What he had was a system whose parts could not be shuffled.

(T3) An astronomy assembled out of unrelated parts is a monster rather than a man. + What set him off was not a failure of prediction. The old astronomy predicted tolerably well. What set him off was a rule everyone claimed to keep and nobody kept. The rule was that heavenly motion must be uniform and circular: steady, unvarying, going round. Ptolemy could not make the planets behave under that rule, so he introduced a device called the equant. Picture a carousel. The horses go round the centre, but the operator has planted his pole off to one side, and the motion is called even because it looks even from his pole, not from the middle of the ride. Measured from the centre of its own circle, a planet on an equant speeds up and slows down. Copernicus thought this was simply cheating, a rule honoured in the words and abandoned in the working, and he says the ancients had admitted principles "which appear to contravene the first principles of equality of motion." Behind that complaint lies a bigger one. Ptolemaic astronomy handled each planet as a separate problem, with its own circles fitted to its own observations, and there was no way to get from the pieces to the whole. Nothing told you how big the system was or in what order it stood. That is the point of his best image: parts that are each well made and belong to no single body. He wanted an astronomy whose pieces implied each other, and the word he uses for what he was after is symmetria, the fitting together of parts into one measured whole.

(Q) "It is with them as if a man should take from different places, hands, feet, a head and other members, in the best way possible indeed, but in no way comparable to a single body, and in no respect corresponding to each other, so that a monster rather than a man would be constructed from them." + Source: De revolutionibus, Preface to Pope Paul III (Stimson translation, 1917). He is describing the astronomers who worked with eccentrics and epicycles, which are circles whose centre sits off to one side of the earth and small circles that ride round on the rim of larger ones, and the complaint is not that their answers were wrong but that their universe had no single shape. The sentence has outlived its occasion; it is as good a description of a badly built theory as anyone has written.

(T4) The world is a machine built for us by the best and most systematic builder of all, so astronomy is meant to find out how it actually is. + There were two ways to be an astronomer in 1540, and the difference decides everything that came afterwards. The first way is to treat your circles as a calculating device. Nobody supposes the sky is made of the things in your diagram; the diagram is a machine for producing the right numbers, and if a different machine produced them you would be equally content. Philosophers call this instrumentalism, the view that a theory is a tool rather than a description. The second way is to believe that the diagram is telling you how the world is actually put together. That is realism, and Copernicus was a realist of the plainest kind. He did not think he had found a handier way to compute where Mars would be. He thought he had found out where Mars goes. His reason for expecting to be able to find out is theological, and he states it without fuss. The world is a machine made on a plan by the best and most orderly of makers, and a made thing has a real design that can be traced, which is why it galled him that the philosophers could give no settled account of it. Christians had been saying something like this for a long time. "The heavens declare the glory of God, and the sky above proclaims his handiwork." (Psalm 19:1). Paul takes it further and says God’s invisible attributes have been clearly perceived in the things that have been made (Romans 1:20). If the sky is workmanship, it has a real structure, and looking hard at it is not impiety but attention. The whole quarrel over Osiander’s anonymous preface, which offered the book to the reader as a mere hypothesis, turns on this one point, and Copernicus had died before he could answer it.

(Q) "It began to weary me that no more definite explanation of the movement of the world machine established in our behalf by the best and most systematic builder of all, existed among the philosophers who had studied so exactly in other respects the minutest details in regard to the sphere." + Source: De revolutionibus, Preface to Pope Paul III (Stimson translation, 1917). The builder is God, and the weariness is the point: a world made on a plan ought to be explicable, and it offended him that the experts could describe every detail of the sphere and still not say how the thing was arranged.

(Q) "If perchance there should be foolish speakers who, together with those ignorant of all mathematics, will take it upon themselves to decide concerning these things, and because of some place in the Scriptures wickedly distorted to their purpose, should dare to assail this my work, they are of no importance to me, to such an extent do I despise their judgment as rash." + Source: De revolutionibus, Preface to Pope Paul III (Stimson translation, 1917). He saw the objection coming, and this is the whole of his answer to it. He goes on to note that Lactantius, an early Christian writer of real eloquence and no mathematics, had made himself ridiculous by mocking the idea that the earth is a ball, and adds the line that has been quoted after him ever since: "Mathematics is written for mathematicians." Then he turns straight to the calendar and the good his work might do the church. Seventy-seven years later these were the sentences the Congregation of the Index ordered cut from the book.

What the Church Made of Him

(†) Rome asked him for help with the calendar, and the printed book opens with a cardinal begging him to publish. + Open a first edition of 1543 and the first thing after the title page is not Copernicus. It is a letter from Nikolaus von Schönberg, Cardinal of Capua, written from Rome on 1 November 1536, asking him to communicate his discovery to scholars and to send a copy of his work at the earliest possible moment. The cardinal even offers to pay a copyist. That letter was printed at the front of the book on purpose, as a testimonial, and behind it lay three decades of interest from exactly the quarter the modern story would not predict. The church had wanted this man’s help before he wanted the church’s. The calendar commission of the Fifth Lateran Council had written to him through Paul of Middelburg in the mid 1510s, back when the sun-centred theory existed only as a few handwritten leaves passed between friends. In 1533, with the book still unprinted and its author saying nothing, the papal secretary Johann Albrecht Widmannstetter stood in the Vatican gardens explaining the new theory to Pope Clement VII and several cardinals, and went away with a present for his trouble. Nearer home, Tiedemann Giese, Bishop of Chełmno, spent years pressing his friend to print, sometimes gently and sometimes with reproaches, and Copernicus says so himself in the dedication. That dedication is itself the point. He addressed the book to Pope Paul III, the pope of the Council of Trent, and told him frankly that he preferred to dedicate it to him rather than to anyone else so that nobody could say he was evading judgment.

(†) Lutheran Wittenberg took his mathematics and kept its distance from his cosmology. + The oddity of the whole affair is that the book was rescued by Protestants. Rheticus was a Wittenberg professor, the Narratio Prima was printed in Gdańsk, and De revolutionibus was printed in Lutheran Nuremberg. Melanchthon, who ran Lutheran education, let Rheticus go and kept his chair open for him. The reception there was split in a way that mattered. Andreas Osiander’s unsigned preface told readers the hypotheses need not be true; Rheticus and Giese were furious when they saw it, Giese asked the Nuremberg council to have the book reprinted without it, and the note went on misleading readers until Kepler named its author in print in 1609. Melanchthon himself, in his Initia doctrinae physicae of 1549, thought the earth’s motion contrary to both physics and Scripture and said so. Luther is reported to have brushed the idea aside at dinner on 4 June 1539, in the diary of the table talk kept by Anton Lauterbach, where he speaks of a fellow who wants to turn the whole of astronomy upside down; the remark was table talk written down by a listener, never a published judgment, and the more famous version calling Copernicus a fool comes from a later and less reliable editor. And yet the same Wittenberg made the book work. Erasmus Reinhold, Melanchthon’s own professor of mathematics, sat down with it and produced the Prutenic Tables in 1551, a complete set of ready-reckoned planetary tables computed by Copernican methods, and for the next half century much of Europe calculated with them whether or not it believed the earth moved. Christoph Clavius, the Jesuit mathematician who defended the Gregorian calendar of 1582, appealed to Copernicus’s measurement of the length of the year in its defence. Kepler and Galileo both learned their trade from a Copernican system that Protestant printers and Protestant professors had kept alive.

(†) The objection was always the verses that speak of a fixed earth, and it took seventy-three years to harden into an order. + The texts were never obscure ones. "He set the earth on its foundations, so that it should never be moved." (Psalm 104:5). The psalmist says the same of the world in Psalm 93:1, Ecclesiastes has the sun rising and going down and hurrying back to its place (Ecclesiastes 1:5), and Joshua commands the sun to stand still over Gibeon (Joshua 10:12-13). Read as astronomy, these settle the matter. Read as the Scriptures ordinarily speak, they describe the world as it is seen and lived in, which is how we all still speak when we say the sun came up at seven. That distinction had to be made, and Copernicus did not make it. Rheticus did, in a short treatise arguing that the earth’s motion is not contrary to Holy Scripture, which Giese in his letter of 26 July 1543 wanted bound into copies of the book. It was never printed in their lifetimes; it appeared anonymously in 1651 and was only identified as Rheticus’s work in the twentieth century. The argument had to be made again by Kepler, and then at far greater cost by Galileo. For seventy-three years nothing official happened at all. Then on 5 March 1616, in the first proceedings against Galileo, the Congregation of the Index suspended De revolutionibus donec corrigatur, until it should be corrected. The Congregation was the Roman body that ruled on what Catholics might read and kept the list of forbidden books that gave it its name, and suspending a book until correction was the mildest thing it could do short of leaving it alone. The corrections appeared in 1620: ten emendations, mostly removing sentences that spoke of the earth’s motion as fact rather than hypothesis, and among them the whole passage in the dedication that runs from the foolish speakers through the mockery of Lactantius. Owners were expected to strike the passages out by hand, and many copies survive with the lines obediently crossed through, and a good many more with the lines untouched. The general prohibition on books teaching the earth’s motion was dropped in 1758, and the title itself disappeared from the Index in 1835. One footnote is worth adding because the quotation is so often repeated: the line asking who will venture to place Copernicus above the Holy Spirit, attributed to Calvin for over a century, has never been found anywhere in Calvin’s works.

(†) Where his own work fell short: he would not give up the circle, and he would not answer the question he saw coming. + Two things in his own record deserve saying plainly. - The circle. He threw out Ptolemy’s equant because it broke the rule of uniform circular motion, and then he treated that rule as beyond question. Planets do not move on circles, and because his did, he had to keep adding small circles riding on larger ones to force the predictions into shape, so that his finished system was not appreciably simpler than the one it replaced and not appreciably more accurate. Kepler, who worked from Tycho Brahe’s far better observations, finally broke the circle in 1609 and found the ellipse, and only then did the sun-centred system start to earn its keep by prediction as well as by elegance. Copernicus had been right for reasons he could not fully make good. - The question he ducked. He knew perfectly well that people would come at him with Scripture, and his answer was a sentence of contempt and a jibe at Lactantius. Contempt is not an argument, and the work of showing how the psalms and Joshua are to be read fell to others: to Rheticus, whose treatise stayed in a drawer for a century, and eventually to Galileo, who had to make the case in a hostile room. A little patience in 1543 might have saved a great deal of grief in 1616. Neither fault touches his character as a churchman, and on that side the record is quiet. He said his offices, ran his estates honestly, doctored the poor of Warmia without fee by the accounts that survive, and left his books to the cathedral chapter. What he got wrong, he got wrong as a mathematician.