Mathematical advances that now seem trivial sharpened the tools of calculation in this age. Michael Stifel’s Arithmetica integra (1544) introduced our plus and minus signs, and Robert Recorde’s Whetstone of Wit (1557) first used our equals sign in print. The once famous arithmetics of Adam Riese persuaded Germany to pass from reckoning with counters to written computation. Johannes Werner published (1522) the first modern treatise on conic sections; and Georg Rheticus, besides serving as midwife to Copernicus, carried on the work of Regiomontanus in trigonometry.
Astronomy had at its disposal better calculations than instruments. On the basis of these calculations some astrologers predicted a second Deluge for February 11,1524, when Jupiter and Saturn would join in Pisces; thereupon Toulouse built an ark of refuge, and cautious families stored food on mountaintops.28 Most of the astronomical instruments were of medieval origin: celestial and terrestrial spheres, Jacob’s staff, an astrolabe, an armillary sphere, quadrants, cylinders, clocks, compasses, and several other devices, but no telescope and no photography. With this equipment Copernicus moved the earth.
Mikolai Kopernik, as Poland calls him, Niklas Koppernigk, as Germany calls him, Nicolaus Copernicus, as scholars call him, was born in 1473 at Thorn (Torun) on the Vistula in West Prussia, which, seven years before, had been ceded to Poland by the Teutonic Knights; he was a Prussian in space, a Pole in time. His mother came of a prosperous Prussian family; his father hailed from Cracow, settled in Thorn, and dealt in copper. When the father died (1483), the mother’s brother, Lucas Watzelrode, Prince Bishop of Ermland, took charge of the children. Nicolaus was sent at eighteen to the University of Cracow to prepare for the priesthood. Not liking the Scholasticism that had there suppressed humanism, he persuaded his uncle to let him study in Italy. The uncle had him appointed a canon of the cathedral at Frauenburg in Polish East Prussia, and gave him leave of absence for three years.*
At the University of Bologna (1497-1500) Copernicus studied mathematics, physics, and astronomy. One of his teachers, Domenico de Novara, once a pupil of Regiomontanus, criticized the Ptolemaic system as absurdly complex, and introduced his students to ancient Greek astronomers who had questioned the immobility and central position of the earth. Philolaus the Pythagorean, in the fifth century before Christ, had held that the earth and the other planets moved around Hestia, a central fire invisible to us because all known parts of the earth are turned away from it. Cicero quoted Hicetas of Syracuse, also of the fifth century before Christ, as believing that the sun, the moon, and the stars stood still, and that their apparent motion was due to the axial rotation of the earth. Archimedes and Plutarch reported that Aristarchus of Samos (310-230 B.C.) had suggested the revolution of the earth around the sun, had been accused of impiety, and had withdrawn the suggestion. According to Plutarch, Seleucus of Babylonia had revived the idea in the second century before Christ. This heliocentric view might have triumphed in antiquity had not Claudius Ptolemy of Alexandria, in the second century of our era, restated the geocentric theory with such force and learning that hardly anyone thereafter dared to challenge it. Ptolemy himself had ruled that in seeking to explain phenomena, science should adopt the simplest possible hypothesis consistent with accepted observations. Yet Ptolemy, like Hipparchus before him, to explain the apparent motion of the planets, had been compelled by the geocentric theory to assume a bewildering complexity of epicycles and eccentrics, † Could any simpler hypothesis be found? Nicole Oresme (1330-82) and Nicholas of Cusa (1401-64) had renewed the proposal of terrestrial motion; Leonardo da Vinci (1452-1519) had recently written: “The sun does not move.... . The earth is not in the center of the circle of the sun, nor in the center of the universe.30
Copernicus felt that the heliocentric theory could “save the appearances”—explain the observed phenomena—more compactly than the Ptolemaic view. In 1500, now twenty-seven, he went to Rome, presumably for the Jubilee, and gave lectures there in which, a tradition reports, he tentatively propounded the motion of the earth. Meanwhile his leave of absence expired, and he returned to his duties as canon in Frauenburg. But geocentric mathematics confused his prayers. He begged permission to resume his studies in Italy, proposing now to take up medicine and canon law—which to his superiors seemed more to the point than astronomy. Before the fifteenth century ended he was back in Italy. He received the degree of law at Ferrara (1503), apparently took no degree in medicine, and again reconciled himself to Frauenburg. Soon his uncle, probably to give him time for further study, appropriated him as secretary and physician (1506); and for six years Copernicus lived in the episcopal castle at Heilsberg. There he worked out the basic mathematics of his theory, and formulated it in manuscript.
When the kindly bishop died, Copernicus resumed his place in Frauenburg. He continued to practice medicine, treating the poor without charge.31 He represented the cathedral chapter on diplomatic missions, and prepared for King Sigismund I of Poland a plan for reforming the Prussian currency. In one of many learned essays on finance he stated what was later to be known as Gresham’s law: “Bad money .... drives the old, better money away”32—i.e., when a government issues a debased coinage, the good coins are hoarded or exported and disappear from circulation, the bad coins are offered as taxes, and the king is “paid in his own coin.” But amid these diverse concerns Copernicus continued his astronomic researches. His geographical location was unpropitious: Frauenburg was near the Baltic, and was half the time shrouded in mists or clouds. He envied Claudius Ptolemy, for whom “the skies were more cheerful, where the Nile does not breathe fogs as does our Vistula. Nature has denied us that comfort, that calm air”;33 no wonder Copernicus almost worshiped the sun. His astronomical observations were neither numerous nor precise, but they were not vital to his purpose. He used for the most part the astronomic data transmitted by Ptolemy, and proposed to prove that all received observations accorded best with a heliocentric view.
About 1514 he summarized his conclusions in a Little Commentary (Nicolai Copernici de hypothesibus motuum coelestium a se constitutis commentariolus). It was not printed during his lifetime, but he sent out some manuscript copies as “trial balloons.” He stated his conclusions with a matter-of-fact simplicity as if they were not the greatest revolution in Christian history:
1. There is no one center of all the celestial circles or spheres.
2. The center of the earth is not the center of the universe, but only of gravity and of the lunar sphere.
3. All the spheres [planets] revolve about the sun as their midpoint, and therefore the sun is the center of the universe.
4. The ratio of the earth’s distance from the sun to the height of the firmament is so much smaller than the ratio of the earth’s radius to its distance from the sun that the distance from the earth to the sun is imperceptible in comparison with the height of the firmament.
5. Whatever motion appears in the firmament arises not from any motion of the firmament, but from the earth’s motion. The earth together with its circumjacent elements performs a complete rotation on its fixed poles in a daily motion, while the firmament and highest heaven abide unchanged.
6. What appear to us as motions of the sun arise not from its motion but from the motion of the earth and our sphere, with which [motion] we revolve around the sun like any other planet....
7. The apparent retrograde and direct motion of the planets arises not from their motion but from the earth’s. The motion of the earth alone, therefore, suffices to explain so many apparent inequalities in the heavens.34
The few astronomers who saw the Commentariolus paid no great attention to it. Pope Leo X, informed of the theory, expressed an open-minded interest, and asked a cardinal to write to Copernicus for a demonstration of his thesis; for a time the hypothesis won considerable favor at the enlightened papal court.35 Luther, toward 1530, rejected the theory: “People give ear to an upstart astrologer who strove to show that the earth revolves, not the heavens or the firmament, the sun and the moon.... . This fool wishes to reverse the entire scheme of astronomy; but sacred Scripture tells us that Joshua commanded the sun to stand still, not the earth.” 36 Calvin answered Copernicus with a line from Psalm XCIII, I: “The world also is stabilized, that it cannot be moved”—and asked, “Who will venture to place the authority of Copernicus above that of the Holy Spirit?“37 Copernicus was so discouraged by the response to the Commentariolus that when, about 1530, he completed his major work, he decided to withhold it from publication. He calmly proceeded with his duties, delved a bit into politics, and, in his sixties, was accused of having a mistress.38
Into this resigned old age burst, in 1539, an enthusiastic young mathematician, Georg Rheticus. He was twenty-five, a Protestant, a protégé of Melanchthon, and a professor at Wittenberg. He had read the Commentariolus, he was convinced of its truth, he longed to help the old astronomer who, far off in an obscure Baltic outpost of civilization, was waiting so patiently for others to see, with him, the invisible rotation and revolution of the earth. The youth fell in love with Copernicus, called him “the best and greatest of men,” and was deeply impressed by his devotion to science. For ten weeks Rheticus studied the big manuscript. He urged its publication. Copernicus refused, but agreed to have Rheticus publish a simplified analysis of its first four books. So in 1540 at Danzig the young scholar issued his Narratio prima de libris revolutionum—First Account of the Books of the Revolutions of the celestial bodies. He sent a copy hopefully to Melanchthon. The kindly theologian was not convinced. When Rheticus returned to Wittenberg (early in 1540), and commended the Copernican hypothesis in his class, he was “ordered,” he says, to lecture instead on the Sphaera of Johannes de Sacrobosco.39 On October 16, 1541, Melanchthon wrote to a friend: “Some think it a distinguished achievement to construct such a crazy thing as that Prussian astronomer who moves the earth and fixes the sun. Verily, wise rulers should tame the unrestraint of men’s minds.”40
In the summer of 1540 Rheticus went back to Frauenburg, and stayed till September 1541. Repeatedly he begged his master to give his own text to the world. When two prominent clergymen joined in the appeal, Copernicus, perhaps feeling that he had now one foot safely in the grave, yielded. He made some final additions to the manuscript, and allowed Rheticus to send it to a printer in Nuremberg, who assumed all financial costs and risks (1542). As Rheticus had now left Wittenberg to teach in Leipzig, he delegated to his friend Andreas Osiander, a Lutheran minister at Nuremberg, the task of seeing the book through the press.
Osiander had already written to Copernicus (October 20, 1541) suggesting that the new view should be presented as an hypothesis rather than as proved truth, and in a letter of the same day to Rheticus he had pointed out that by this procedure “the Aristotelians and the theologians will easily let themselves be appeased.”41 Copernicus himself had repeatedly termed his theories hypotheses, not only in the Commentariolus but in his major text;42 at the same time his Dedication claimed that he had supported his views with “the most transparent proofs.” We do not know how he answered Osiander. In any case Osiander, without appending his own name, prefaced the book as follows:
To the reader, concerning the hypotheses of this work.
Many scientists, in view of the already widespread reputation of these new hypotheses, will doubtless be greatly shocked by the theories of this book.... . However .... the master’s .... hypotheses are not necessarily true; they need not even be probable. It is completely sufficient if they lead to a computation that is in accordance with the astronomical observations.... . The astronomer will most readily follow those hypotheses which are most easily understood. The philosopher will perhaps demand greater probability; but neither of the two will be able to discover anything certain .. . unless it has been made known to him by divine revelations. Therefore let us grant that the following new hypotheses take their place beside the old ones which are not any more probable. Moreover, these are really admirable and easy to grasp, and in addition we shall find here a great treasure of the most learned observations. For the rest let no one expect certainty from astronomy as regards hypotheses. It cannot give this certainty. He who takes everything that is worked out for other purposes, as truth, would leave this science probably more ignorant than when he came to it....43
This preface has often been condemned as an insolent interpolation.44 Copernicus may have resented it, for the old man, having lived with his theory for thirty years, had come to feel it as part of his life and blood, and as a description of the actual facts of the universe. But Osiander’s preface was judicious and just; it reduced the natural resistance of many minds to a disturbing and revolutionary idea, and it is still a good reminder that our descriptions of the universe are the fallible pronouncements of drops of water about the sea, and are likely to be rejected or corrected in their turn.
The book appeared at last, in the spring of 1543, with the title, Nicolai Copernici revolutionum liber primus (First Book of Revolutions); later the book came to be known as De revolutionibus orbium coelestium (On the Revolutions of the Celestial Orbs). One of the first copies reached Copernicus May 24, 1543. He was on his deathbed. He read the title page, smiled, and in the same hour died.
The Dedication to Pope Paul III was itself an effort to disarm resistance to a theory which, as Copernicus well knew, flagrantly contradicted the letter of Scripture. He began with pious assurances: “I still believe that we must avoid theories altogether foreign to orthodoxy.” He had long hesitated to publish, wondering “were it not better to follow the example of the Pythagoreans .... who were accustomed to transmit the secrets of philosophy not in writing but orally, and only to their relatives and friends.” But learned churchmen—Nicholas Schonberg, Cardinal of Capua, and Tiedeman Giese, Bishop of Kulm—had urgently recommended that he should publish his findings. (Copernicus felt it wise not to mention the Lutheran Rheticus.) He acknowledged his debt to Greek astronomers, but, by a slip of the pen, he omitted Aristarchus. He believed that astronomers were in need of a better theory than the Ptolemaic, for they now found many difficulties in the geocentric view, and were unable to calculate accurately, on that basis, the length of the year. And he appealed to the Pope, as a man “eminent... in the love of all learning, and even of mathematics,” to protect him against the “bites of slanderers” who, without adequate mathematical knowledge, would “assume the right to pass judgment on these things,” or would “attack this theory of mine because of some passage of Scripture....“45
The exposition begins with postulates: first, that the universe is spherical; second, that the earth is spherical—for matter, left to itself, gravitates toward a center, and therefore arranges itself into a spherical form; and third, that the motions of the celestial bodies are uniform circular motions, or are composed of such motions—for the circle is the “most perfect form,” and “the intellect shrinks with horror” from the supposition that the celestial motions are not uniform. (Reason in thought would be impossible unless there were reason in the behavior of the objects of thought.)
Copernicus notes the relativity of motion: “All change in position which is seen is due to motion either of the observer or of the thing looked at, or to changes in the position of both, provided that these are different. For when things are moved equally relatively to the same things, no motion is perceived as between the object seen and the observer.” 46 So the apparent daily rotation of the planets about the earth could be explained as due to a daily rotation of the earth on its axis; and the apparent annual movement of the sun around the earth can be explained by supposing the earth to move annually around the sun.
Copernicus anticipates objections. Ptolemy had argued that the clouds and surface objects of a rotating earth would fly off and be left behind. Copernicus answers that this objection would hold still more against the revolution of the major planets around the earth, since their great distances would imply vast orbits and extreme speeds. Ptolemy had further held that an object propelled directly upward from a rotating earth would not fall back to its point of origin. Copernicus replies that such objects, like the clouds, are “parts of the earth,” and are carried along with it. And to the objection that the annual revolution of the earth around the sun should manifest itself in a movement of the “fixed” stars (stars beyond our planetary system) as observed at opposite ends of the earth’s orbit, Copernicus answers that there is such a movement, but the great distance of the stars (“firmament”) makes it imperceptible to us. (A moderate degree of such movement is now observable.)
He sums up his system in a compact paragraph:
First and above all lies the sphere of the fixed stars, containing itself and all things, for that very reason immovable.... Of the moving bodies [planets] first comes Saturn, who completes his circuit in thirty years. After him Jupiter, moving in a twelve-year revolution. Then Mars, who revolves biennially. Fourth in order, an annual cycle takes place, in which... is contained the earth, with the lunar orbit as an epicycle. In the fifth place Venus is carried round in nine months. Then Mercury holds the sixth place, circulating in the space of eighty days. In the middle of all dwells the sun... Not ineptly some call it the lamp of the universe, others its mind, and others again its ruler... rightly, inasmuch as the sun, sitting on a royal throne, governs the circumambient family of the stars.... We find, therefore, under this orderly arrangement, a wonderful symmetry in the universe, and a definite relation of harmony in the motion and magnitude of the orbs, of a kind it is not possible to obtain in any other way.* 47
Generally an advance in human theory carries with it many remnants of the theory displaced. Copernicus based his conceptions on observations handed down by Ptolemy, and he retained much of the Ptolemaic celestial machinery of spheres, epicycles, and eccentrics; the rejection of these would wait for Kepler. Most eccentric of all was Copernicus’s calculation that the sun was not quite at the center of the earth’s orbit. The center of the universe, he reckoned, would be “three sun-diameters away from the sun”; and the centers of the planetary orbits were likewise outside the sun, and not at all identical. Copernicus transferred from the earth to the sun two ideas now rejected: that the sun is the approximate center of the universe, and that it is at rest. He thought of the earth as having not only an axial rotation and an orbital revolution, but a third motion, which he supposed necessary to explain the inclination of the earth’s axis and the precession of the equinoxes.
Consequently we must not smile in hindsight at those who took so long to adopt the Copernican system. They were required not only to set the earth turning and hurtling in space at an alarming speed, contrary to the direct evidence of the senses, but to accept a mathematical maze only slightly less bewildering than Ptolemy’s. Not until Kepler, Galileo, and Newton should work out the mechanism of the new theory to greater simplicity and accuracy would it appear clearly superior to the old; and even then we should have to say of the sun what Galileo may have said of the earth—eppur si muove. Meanwhile Tycho Brahe rejected the heliocentric hypothesis on the ground that Copernicus had not convincingly answered Ptolemy’s objections. More surprising than such a rejection is the relative celerity with which the new system was accepted by astronomers like Rheticus, Osiander, John Field, Thomas Digges, and Erasmus Reinhold—whose “Prutenic Tables” (1551) of celestial motions was in large part based on Copernicus. The Catholic Church raised no objection to the new theory so long as it represented itself as an hypothesis; but the Inquisition struck back mercilessly when Giordano Bruno assumed the hypothesis to be a certainty, and made explicit its consequences for religion. In 1616 the Congregation of the Index forbade the reading of De Revolutionibus “until corrected”; in 1620 it allowed Catholics to read editions from which nine sentences had been removed that represented the theory to be a fact. The book disappeared from the revised Index of 1758, but the prohibition was not explicitly rescinded till 1828.
The geocentric theory had fitted reasonably well a theology which supposed that all things had been created for the use of man. But now men felt tossed about on a minor planet whose history was reduced to a “mere local item in the news of the universe.”48What could “heaven” mean when “up” and “down” had lost all sense, when each would become the other in half a day? “No attack on Christianity,” wrote Jerome Wolf to-Tycho Brahe in 1575, “is more dangerous than the infinite size and depth of the heavens”—though Copernicus had not taught the infinity of the universe. When men stopped to ponder the implications of the new system they must have wondered at the assumption that the Creator of this immense and orderly cosmos had sent His Son to die on this middling planet. All the lovely poetry of Christianity seemed to “go up in smoke” (as Goethe was to put it) at the touch of the Polish clergyman. The heliocentric astronomy compelled men to re-conceive God in less provincial, less anthropomorphic terms; it gave theology the strongest challenge in the history of religion. Hence the Copernican revolution was far profounder than the Reformation; it made the differences between Catholic and Protestant dogmas seem trivial; it pointed beyond the Reformation to the Enlightenment, from Erasmus and Luther to Voltaire, and even beyond Voltaire to the pessimistic agnosticism of a nineteenth century that would add the Darwinian to the Copernican catastrophe. There was but one protection against such men, and that was that only a small minority in any generation would recognize the implications of their thought. The sun will “rise” and “set” when Copernicus has been forgotten.
In 1581 Bishop Kromer raised a monument to Copernicus against the inner wall of Frauenburg Cathedral, next to the canon’s grave. In 1746 the monument was removed to make place for a statue of Bishop Szembek. Who was he? Who knows?