SOURCE: "Copernicus: Science versus Theology" in The Tradition of Polish Ideals: Essays in History and Literature, Orbis Books (London) Ltd., 1981, pp. 132-49.

This paper is about a Polish citizen and about a revolution which he made. Unlike most Poles, he didn't know he was going to make a revolution, and he probably didn't intend it. He wrote a great and abstruse work, De Revolutionibus orbium coelestium, which hardly any of his contemporaries could read, let alone understand. It was intended to correct astronomical measurements; instead it revolutionized man's ideas about the universe and his place in it. We have never been quite comfortable in it since.

This paper is like Johann Kepler's ellipse—that is, it has two foci: the accomplishments of Copernicus and the question of the apparent conflict of science and theology. It is this way because, although the first depends very much on the second, they are not coterminous. The apparent conflict between science and theology appeared only in the ninety years following Copernicus' death.

In order to make clear the significance of Copernicus' work, it is necessary first to look briefly at the universe as it appeared to astronomers after the Copernican Revolution, then at the universe of the ancients, and then at the Copernical Revolution itself—in which was embodied the apparent clash of science and theology.

The universe, by the beginning of the eighteenth century, was accepted as being infinite, with the mathematical probability of the duplication of our world and system somewhere else in the heavens. The universe had no centre and no limits. And it had no cosy, special man-centred purpose about it. Our particular small part of this universe was regarded as centring on the sun. Planets, among them the Earth, revolved around the sun in rounded elliptical orbits with the sun in one focus of the ellipse. These planets moved, according to the principle of inertia, having been set in their curved pattern in much the same way as a projectile; and they remained in that curved pattern for the same reason that a projectile remains in its trajectory—a balance of the centrifugal force flinging the planet into orbit, and the centripetal force of the sun's gravity holding it in orbit. The orbits of the planets are not entirely harmonious or regular, nor is their speed, since they are acted on by the gravity of other planets when they come close to one another. This fact enabled astronomers to predict the existence of the two most distant planets—Neptune and Pluto—years before they actually discovered them. But generally the speed of the orbits around the sun is regulated according to the distance of the planet in its orbit from the sun. A line drawn from the sun to the planet moving in its orbit will describe equal areas in equal times. Hence the planets move fastest when close to the sun, and slowest when farthest away from it. The Earth, which is closest to the sun in January, moves fastest then, and slowest in summer. The relative speeds of the planets are harmonized according to the formula that the ratio of the squares of the periods of the orbits of any two planets is equal to the ratio of the cubes of their mean distances from the sun.

The Earth revolves clockwise in its orbit about the sun in 365 days, 5 hours, 48 minutes and 46 seconds, and rotates once in a little less than 24 hours, a rotation that is gradually getting slower due to tidal friction and other physical pressures. The axis of the Earth, which is inclined at an angle of 23 and one-half degrees to the perpendicular of the plane of the Earth's orbit, has a slight wobble in it which describes a circle of 23 and one-half degrees from its centre, a wobble which completes this circle every 26,000 years, or thereabouts, resulting in an apparent movement of the position of the north celestial pole—providing the Earth with five successive pole stars in the process. This movement is due to the pull of the gravity of the moon. In antiquity, it was called the precession of the equinoxes.

The moon revolves around the Earth once every 27 and one-third days on average, but because its rotation in the face of the sun is slightly slower, it completes a cycle of its phases only in 29 and one-half days (on average). It also wanders north and south of the plane of the Earth's orbit, a fact which ensures that eclipses do not happen regularly but only a few times a year.

As can be seen, the post-Copernican universe is rather a colourless place. It could be thoroughly measured and conceptualized, long before it was proven experimentally in 1957 when the first sputnik demonstrated physically that Copernicus, Kepler and Newton had been right. The idea of a limitless universe has a profound and negative effect on the way we view our place in things. In effect it has no active part in our lives. With the possible exception of some devoted professional astronomers, we do not feel ourselves to be at one with the spiral nebulae moving and multiplying in the heavens at incredible speeds; we do not depend on this universe as our ancestors did on theirs to help determine our ideas about physics and chemistry, mechanics and medicine, economics and sociology, theology, prophecy and eschatology. Even the word 'heavens' is now inapplicable, for in antiquity and medieval times it was defined as the celestial abode of immortal beings, the habitation of God and His angels, and of beatified spirits. Copernicus did not intend to create this sort of universe, though he was responsible for its conception.

Keep now this universe in mind, while we go back more than two thousand years to the world of our ancestors and predecessors; and we will, as they did, look up to the heavens on a clear summer evening and endeavour to relate the panorama of the heavens to our life here below. It is not difficult. The great canopy appears to rotate across the sky from the eastern to the western horizon, circling on the pole star, visible in our latitude about 50 degrees above the northern horizon. It is not hard to imagine, as the ancients imagined, that this amazing sight has a personal importance for us. We can see that the stars have a fixed position with relation to Earth, set in a canopy that rotates regularly above us. In the daytime, we can notice that the sun moves daily westward across the skies, north and south from vernal equinox to vernal equinox, and, if we observe very closely and take careful notes, slowly eastward, circling the heavens once a year.

Very early, men began to conceptualize all this—to make a picture out of their observations and calculations to help their memories and demonstrate a logical relationship between the observations. Like all good conceptual schemes, that created by the Greeks two thousand years ago in the two-sphere universe was logical in explaining the known facts, and it was psychologically satisfying in that it gave a convenient and easily acceptable picture which could be fitted into people's impressions of things as they are—into their cosmologies, which are ideas of the universe as an ordered whole. This scheme lasted for two thousand years, and Copernicus had to work from it and was able to change it very little. This is because it was satisfactory for most purposes, and because men work from what they know to what they do not know, not from total ignorance to total knowledge. Copernicus changed a vital part of this scheme, but only a part; and he learned enormously from the past and from this particular scheme. That is what Newton meant when he said that he had seen farther than most men because he stood on the shoulders of giants. Copernicus, too, stood on the shoulders of giants—the men who had conceptualized the heavens.

The two-sphere universe was made up of a fixed sphere, the Earth, centrally located in a huge rotating sphere marked with the stars, outside of which there was nothing. The planets—Moon, Mercury, Venus, Sun, Mars, Jupiter and Saturn moved in between the two spheres on orbits centred on the Earth. These planets, unlike the stars, wandered. The phases of the moon did not correspond with its revolutions around the Earth; the planets appeared to retrogress or backtrack in their paths, at which time they appeared brightest; and the two inner planets—Mercury and Venus—appeared to be tied very closely to the sun. This description does not explain the real problem of the planets which is one not of describing how they move, but of measuring their movement exactly so as to be able to predict and track them. It was this problem, of measurement not description, which Copernicus set himself to solve. In the course of it he profoundly changed the description.

This distinction may be best illustrated by the two great schools of astronomy in antiquity: the homocentric school associated with the Hellenic philosophers Eudoxus and Aristotle in the fourth century B.C., and the mathematical school associated with the Hellenistic astronomer Ptolemy in the second century A.D. The homocentric system, especially as developed by Aristotle, went far beyond astronomy. It depended on a conceptual system of interlocking spheres, the outer driving the inner, but rotating in different planes. These spheres, which were supposed to be made up of a crystalline ethereal substance, apparently incorruptible, carried the various planets around with them, and their effect was to make the planets follow a figure-eight path, which was supposed to account for the retrograde motion. It took no account of the variations in distances of the heavenly bodies from the Earth, nor of eclipses. It was enormously influential because it was supported by Aristotle, the most influential of the ancients. But it was accepted also because Aristotle went much further than his predecessors had done in explaining the universe. The elements of the Earth—earth, water, air and fire—he also arranged in concentric circles which, however, were disturbed by the movement of the moon which mixed them up. Indeed, change, degeneration and corruption were natural to the Earth, as immutability and perfection were peculiar to the heavens. The Earth stood still and changed; the heavens moved, yet were unchangeable. Motion in the heavens, which was natural, was always circular; motion on Earth was in a straight line, and always required a mover, except in the case of natural motion, which was to the centre of the Earth. It followed that there could be no movement of the Earth, since all objects moved naturally towards its centre. This separation of terrestial and celestial physics proved to be one of the greatest stumbling blocks in the way of adopting the Copernican system. Space, according to Aristotle, was filled because nature abhorred a vacuum; hence it was possible to have movers in space—one homocentric circle moving another. The universe must be a closed one, because otherwise it would have no centre at which the Earth could concentrate. In any case, in an infinite universe, the known uniqueness of the Earth would vanish.

The scheme was coherent with observation, but not logical so far as measurement went. It was to be integrated in detail into Christian theology in the Middle Ages, creating a universe with religious as well as physical purpose. Hell was at the centre of the corruptible Earth, and all corruptible matter gravitated there; God's throne was beyond the stellar sphere; each planetary sphere was pushed by an angel. Distance and unchangeableness made heaven a logical place for the mysterious gods. Astrologers, too, found this mysterious distance convenient for giving the essential air of mystery to their trade. Astrology was a pseudo-science and disapproved of by the Church; but the Church's demand for accurate astronomical tables provided the largest impetus for astrological exploration in the fifteen hundred years between Ptolemy and Copernicus. However, the Aristotelian system had almost nothing to do with mathematics.

Mathematical explanations were developed in the system of Ptolemy, in his great work the Almagest (Mathematike Syntaxis) about 150 A.D. Ptolemy was not interested in a qualitative description of the universe, but rather in a mathematical measurement and explanation of the motions. He developed geometric explanations of the irregularities of the planets. First, the epicycle—this was a circle in which a planet revolved about a point that was attached to a main orbit called a deferent. Depending on the size and speed of the epicycle and the deferent, the retrogression of planets could be accounted for by this means. Second, minor epicycles were used to account for small quantitative differences between theory and observations. Ptolemy had five major epicycles—Copernicus got rid of them, but had to keep the minor ones. The epicycle caused the planet to go through its orbit in large loops. Third, eccentrics: these were centres of orbits which themselves revolved about another centre, giving somewhat the same effect as the crankshaft of a car. Fourth, equants: these were used to explain the fact that the summer season—between 21 March and 23 September—is six days longer than the winter season—from 23 September to 21 March.

Ptolemy said that the rate of revolution of the sun in its ecliptic, or path through the heavens, was uniform, not with respect to its own centre, but with respect to an equant point displaced from that centre. Copernicus disapproved of this because it was messy and unsymmetrical. He got rid of the equant from his system. All sorts of combinations of these devices could be used to explain the geometry of the universe. Ptolemy's successors over nearly 1500 years kept adding to the scheme to account for inaccuracies, until there were about eighty epicycles. It was partly to clean up Ptolemy and make him mathematically more accurate that Copernicus undertook his great work. Meanwhile Ptolemy gave no clear conceptual picture of the universe, and Aristotle gave no mathematical scheme to support the idea of homocentric spheres.

Astronomers took their mathematics from Ptolemy, cosmologists their scheme from Aristotle, and the disharmony was ignored. Only after the thirteenth century was the disharmony much discussed, and in the process the defects of each became clear. The Ptolemaic scheme was logical, the Aristotelian scheme was satisfying, and though alternative schemes were put forward by the ancients—including a moving Earth suggested by Aristarchus—and though the scholastic philosophers from the thirteenth century on increasingly criticized Aristotle, the systems were still more coherent than the unsupported bright ideas brought forward as alternatives.

Indeed, the Church provided, during the later Middle Ages, the intellectual matrix within which modern science was born. The central interest of the Middle Ages was theological rather than scientific, and science was supposed to explain the 'mysterious ways' in which God moved in the natural universe 'His wonders to perform'. The Aristotelian scheme provided the framework after the thirteenth century for this explanation.

The centuries of scholasticism were the centuries in which the tradition of ancient science and philosophy was reconstituted, assimilated and vigorously tested for adequacy. The new scientific theories of the sixteenth and seventeenth centuries emerged largely from the debate and examination to which all phenomena were subjected by the medieval philosophers. They had an unbounded faith in the capacity of human reason to solve the problems of science, and modern science has inherited this. More important, they had a disciplined way of going about their enquiries and recording the results. If you wish to judge the superiority of the scholastics in this regard, just compare the scientific results of working from a subtle and many-sided philosophy such as the Christian in the fifteenth and sixteenth centuries, with those of working from the simplistic and superficial philosopies of China and India in the same period. The one produced modern science; the other retarded scientific development until the twentieth century.

Copernicus stood on the shoulders of giants, but most of those shoulders were clothed in the uniform of the medieval Church. This is worth remembering, because in Copernicus' own lifetime most of the great work of the medieval Church, including the beginnings of modern science, was called in question by the Renaissance thinkers, and the degree to which Copernicus is supposed to have shared these criticisms depends on the identification of his principal inspiration. If his opposition to existing astronomy may be seen to arise out of a strong theoretical antipathy to scholasticism, his inspiration concerning the movement of the Earth can be traced to purely geometric origins. Renaissance humanism, as well as being childishly anti-scholastic and anti-scientific, inspired, too, in its neo-Platonic aspects, a non-theological, other-wordly idea of the universe, depending on the mystic magic of geometry and the worship of the sun as the source of all vital principles.

Copernicus, following his teacher at Bologna, Domenico Maria de Novara, complained in his preface to De Revolutionibus that the homocentric astronomers had been unable to establish a system that agreed with the phenomena; while the Ptolemaic astronomers had been unable to deduce 'the shape of the Universe and the unchangeable symmetry of its parts'. But undoubtedly the most famous piece of evidence for regarding Copernicus as inspired by a dogmatic neo-Platonic sunworship is his justification for placing the sun at the centre of the Universe, written in Chapter 10, Book I of De Revolutionibus.

In the middle of all sits the Sun enthroned. In this most beautiful temple could we place this Luminary in any better position from which he can illuminate the whole at once? He is rightly called the Lamp, the Mind, the Ruler, of the Universe; Hermes Trismegistus names him the Visible God; Sophocles' Electra calls him the All-Seeing. So the Sun sits as upon a royal throne ruling his children the planets which circle around him.

Thomas Kuhn also suggests that since no fundamental new astronomical discovery occurred during Copernicus' lifetime to persuade him of the necessity of change, the inspiration for the revolution must be sought in 'the larger intellectual milieu inhabited by astronomy's practitioners'.¹ It was on this ground that historians have suggested that Copernicus was a neo-Platonic crackpot, a sun-worshipper, suffering from spheromania.

On the other hand, if we examine the text of Copernicus' preface to De Revolutionibus, which may have been begun while he was still a student at Cracow, and if, in particular, we look at the practical problems facing Copernicus and all other astronomers of his time, then the inspiration for his great idea appears to be a purely practical one—the need to make Ptolemaic astronomy more accurate for calendar, astrological and other computational purposes.

The improvement in classical learning had now made it clear that the inadequacies of Ptolemy were not simply due to bad translation; and geographic exploration, having discredited Ptolemy's geography, by analogy cast doubt on his astronomy as well. Most eloquent of all, the Julian Calendar was ten days out of harmony with sidereal time and, as Copernicus had pointed out when asked to reform it in 1514 by Pope Leo X, this required first that the precise movements of the sun and moon be ascertained. As soon as one addressed oneself to this problem, it was necessary to consider the problem of the 'precession of the equinoxes' (due, we now know, to the wobble in the Earth's axis, operating over 26,000 years) and the shift in the stellar longitudes that results from it. Recently it has been suggested, on good evidence, that Copernicus came to his idea of a moving Earth by the successive stages of endeavouring to correct the Calendar, and explain the precession of the equinoxes; and that he came on it not latter than 1497, while he was still a young student at the Jagiellonian University.² Certainly it is the problem of the precession of the equinoxes which underlay his opening complaint to Pope Paul that 'the mathematicians are so unsure of the movements of the Sun and Moon that they cannot even explain or observe the constant length of the seasonal year'.

In fact, these two interpretations of Copernicus—as neo-Platonic mathematical fanatic, and as practical astronomer endeavouring to reform the Calendar—can be reconciled. He was both. In his early years at Cracow, interested in the reform of the Calendar and the key problem of the equinoxes, and not being in touch with the latest intellectual currents—not even possessing a copy of Ptolemy's Almagest before 1497—he was necessarily the practical astronomer. It was in Cracow, almost certainly, that he decided to try to solve the problem of the precession of the equinoxes by moving the Earth in the scheme. He was certainly not at this time a fanatical neo-Platonic opponent of scholastic learning—indeed he never became one, endeavouring to preserve as much as possible of the old Aristotelian universe. We should emphasize this. Copernicus was never at any time in conscious conflict with Aristotelianism or the Church. Later, when he went to Italy, he was caught up in the neo-Platonic intellectual tide, and developed the argument of mathematical disharmony against the Ptolemaic and Aristotelian astronomers. He also developed here the astronomical and mathematical skill without which his central idea would have remained just a guess. It is important to remember that what made the revolution was that Copernicus was a very competent astronomer, who rejected for professional reasons a long-accepted scientific tradition. His neo-Platonic bias, especially in favour of pure geometric circles, coupled with his technical proficiency, would lead him all the more quickly to challenging Ptolemy, as he makes clear in the preface to Paul III. This I believe to be the true sequence of inspiration for the ideas of the moving Earth and the heliocentric universe.

What did Copernicus actually say in his great book? We can only give a brief and non-mathematical summary here. He began by explaining that well-known phenomena such as the daily turning of the heavens, the seasonal travel of the sun through the ecliptic, and the precession of the equinoxes can be accounted for by reference to corresponding motions which he attributed to the Earth—specifically the daily rotation of the Earth on its axis, its yearly revolution around the sun, and its wobble on its own axis every 26 000 years. Secondly, by means of a skilfully-chosen combination of epicycles, the relative sizes of which were determined from selected observations, he was able to give a representation of the moon's motion from night to night without assuming, as Ptolemy had done, variations in the moon's distance from the Earth and its apparent size out of all proportion to what observation reveals. But Copernicus made no improvement on Ptolemy's calculations. The most important part of De Revolutionibus is contained in Book V, which discusses the planets. Copernicus shows that according to his hypothesis, the characteristic apparent motions of the planets including retrogression and the closeness of Mercury and Venus to the sun can be accounted for as optical effects resulting from the revolution of the observer moving on the Earth around the sun. This eliminated Ptolemy's five major epicycles. The minor epicycles were still retained to account for minor fluctuations in the rates of planetary motion. Copernicus also found that it was possible, by observing a planet from two points on the Earth's orbit, to determine the relative distances of the planet and Earth from the sun.

The significance of his work can now be judged. Copernicus, we can see, retained most of the Aristotelian universe (including especially the perfect circular orbits for the planets and the innate naturalness of the Earth's circular motion). He even had to introduce a superfluous third motion (which he also used to explain the precession of the equinoxes), a motion of the Earth's axis around 23 and one-half degrees to account for the Earth being simultaneously fixed in a sphere and keeping the slant of its axis always parallel to a line drawn through the centre of the sun. His planetary mathematical system, which he intended to be an improvement on Ptolemy, does not work and is, if anything, worse than Ptolemy's inaccuracy. But qualitatively he did what he did not intend: he challenged the Aristotelian system. He gave a better conceptual description, accounting better for retrograde motion and the closeness of Mercury and Venus to the sun than Aristotle had done. And his scheme did unite the system of the planets harmoniously. According to Copernicus:

… the orders and magnitudes of all the stars and spheres … became so bound together that nothing in any part thereof could be moved from its place without producing confusion of all parts and the universe as a whole.

But the real significance of Copernicus' work lies in the future, in the reactions that other people were forced to make to it. He had recognized the need for technical change; he had directed attention to the motion of the Earth; and he had given sufficient mathematical evidence to back up this idea so that never again could astronomers ignore its implications. They had to argue for or against it, test it, investigate it. And the more they did, the more they discovered of the supporting evidence that Copernicus had not discovered, the more they contributed to the Copernican Revolution. Only gradually, however, did the full implications become apparent: that Earth's motion implied a fixed heaven of stars, and required that this should be an enormous distance away in order that the motions of the Earth should not give the impression of movement or irregularity in the stars; that the concentric Aristotelian spheres were lost; that the distinction between terrestial corruption and celestial purity was gone beyond hope of recall. The growing bitterness of opposition to Copernicus' ideas by the beginning of the seventeenth century is largely due to the fact that the system was succeeding.

It was at this point, in the ninety years following Copernicus' death in 1543, that the apparent clash between science and theology emerged. The first theological attack against Copernicanism, like the first lay attacks, concentrated on the absurdity of the idea of the Earth moving. Martin Luther called Copernicus a fool for forgetting that Joshua had commanded the sun and the moon (not the Earth) to stand still. Melanchthon and Calvin similarly regarded him as being ridiculous to place his ideas in competition with the truth of Holy Scripture. But by 1600 Protestants were labelling Copernicus as an atheist and an infidel, and increasingly the Catholics were inclined to view his influence as heretical.

Copernicus' proposal raised important questions for Christian cosmology, morality and theology. If the Earth was merely one of the six planets, how were the stories of the Fall and Salvation to be preserved? More especially, if there were other bodies essentially like the Earth, God's goodness would command that they be peopled too; but how could these people be descendants of Adam and Eve, and how could they have inherited Original Sin, the element which explains man's otherwise inexplicable trial on this imperfect Earth? How could beings on other worlds know of the Saviour who gave them the possibility of Salvation? If the Earth is a part of the infinite heavens, what becomes of the division between terrestial corruption and celestial perfection, of God's abode in a perfect heaven, and of man's intermediate position between the devils and the angels? As knowledge supporting Copernicanism grew, the time approached when Christians would have to change their cosmology.

For the Protestants, the reasons for resistance were obvious. They had just undertaken a religious revolution, partly on behalf of re-emphasizing the supermacy of Scriptural truth above all other doctrines and practices of the Church. To them this work of a canon of the Church of Rome could be regarded as yet another attempt by that Church to undercut Scripture. Reinhold, Osiander and Rheticus, all from Protestant districts, and all associates of Copernicus, found it necessary to modify their support for Copernicanism by saying that the astronomical calculations were simply mathematical abstractions and not representations of reality.

But the increasing opposition of the Catholic Church is harder to account for. Before 1600, as during the Middle Ages, there had been wide latitude for scientific speculation. Oresme and Nicholas Cusanus—the latter a cardinal—had propounded new cosmologies and had not worried about conflicts with Scripture; the reformed calendar, decreed by Pope Gregory XIII in 1582, had been based on Copernicus' calculations. But in the conditions of the conflict with the Protestants in the sixteenth century, Catholic doctrine was tightened up, scriptural references were more exactly observed, and heresies more harshly dealt with. In the circumstances, the authorities probably exaggerated the dangers of the crisis, and showed an unfortunate tendency to nail their colours to the mast in circumstances where it was clear that they would have to climb up and unnail them shortly. The case of Giordano Bruno illustrates this alarm. He was an alchemist and astrologer, often called the last magician and the first scientist. He found Copernicus' ideas useful in his neo-Platonic vision of the universe. He was executed in 1600 for heresies concerning the Trinity. But the Church almost certainly associated Copernicanism with Bruno. Good Catholics, including Cardinal Bellarmine who was to lead the condemnation of Galileo's Copernicanism in 1616, could see the clash coming and hoped to avoid it, especially as new evidence was being discovered yearly in support of the Copernican system.

In any case Copernicanism and the Church were on a collision course before 1616. In his contention with Bellarmine in 1615 and 1616, Galileo endeavoured to convert the Church to Copernicanism, and Bellarmine endeavoured to save it from the consequences of Galileo's outspoken discrediting of the Church's cosmology, and Galileo from the consequences of his outspokenness. Since 1609 Galileo had been using a telescope to contribute new qualitative data—new descriptive data—to support Copernicanism, and to persuade the Church to admit that Copernicanism represented reality rather than merely a convenient mathematical hypothesis. In the telescope the shape of the stars was different (refined from blobs to points of light), stars appeared and disappeared, the Milky Way was seen to be a vast collection of millions of stars. Suddenly, the infinity of worlds declared by Nicholas Cusanus and Giordano Bruno appeared to be a probability. The surface of the moon seemed to be not much different from that of the Earth. Spots appeared on the face of the sun; Jupiter had moons revolving around it. There was now less and less reason for the distinction between a corruptible changing Earth and a pure immutable heaven.

But in 1616 Galileo found that this sort of evidence did not do him any good, because it could not provide direct proof of the Copernican theses. The Ptolemaic universe contained enough space in which to include the distant stars, now that these were reduced in size by the telescope; the moons of Jupiter didn't prove that the Earth acted in the same way; and the imperfections in the movements of the planets could be explained by epicycles. Indeed, the Danish astronomer Tycho Brahe had already developed a modified Earthcentered pattern of the universe using Copernicus' mathematics and improving on them, and producing in the process a more accurate system. Hence it was that Galileo was defeated in disputation by Bellarmine. He was right, but he could not prove it, and that is almost as bad as being wrong. He was not required to recant his beliefs, but merely made a private undertaking not to publish them. But because the undertaking was private and equivocal he, later, under a new pope, thought he was free to publish his Dialogues Concerning the Two Chief Systems of the World. In 1633 he was once more condemned by the Church. This time he was placed under house arrest and the Copernican theses were unequivocally condemned as descriptions of reality. Not until 1752 was this sentence reversed; not until 1822 were Copernican books permitted by the Church to be published.

The Church, as Galileo warned, had put itself in an impossible position, just at a time when the last proofs of the Copernican system were about to be established. Tycho Brahe by 1604, for all his conservatism, had already made enough new observations to discredit the idea of the immutability of the heavens; Kepler by 1630 has established the elliptical orbits of the planets, the equal areas in equal times law, and the equality of ratios between the squares of the periods of orbits and the cubes of the mean distances of planets from the sun. The final integration of the mechanical universe came in the fifty years after Galileo's second condemnation, in which astronomy and celestial mechanics went far beyond anything envisaged by Copernicus. The idea of the infinite universe was revived from the ancients and applied to the new framework; Descartes revived the Aristotelian idea of the full universe in the corpuscular theory to account for the motions of planets, and in the doctrine of inertia went part-way to explaining the force of orbits; magnetism was used to explain gravity and the pull of the sun; the theory of the pendulum was employed to explain the ellipse; and finally Sir Isaac Newton in 1687 set out a full, integrated, mathematically proven system of celestial mechanics accounting for the motions and the balance of forces that explain the motions of the planets.

Copernicus' work now stood justified and integrated in a complete world system which had totally replaced the Aristotelian and Ptolemaic ones. He had not set out to do this. Nor had he dreamed that his discoveries would alienate the Church. He had merely endeavoured to correct the Ptolemaic mathematics. But the conceptual device that he adopted to do this, exchanging the roles of the Earth and the sun, made a vital change in the conceptual framework of the universe, and in the cosmologies tied to it. More important, perhaps, it forced an adjustment in all aspects of the two systems. We can now appreciate that Copernicus created a framework in which each set of answers in science brought forth a new set of questions. Copernicanism, as Newton left it, has now itself been successfully challenged, but we have become used to this repeated challenging and steady acceleration in the growth of scientific knowledge. This was not the case in the Age of Copernicus, but he helped to make it so. As Lord Acton wrote: 'Copernicus erected an invincible power that set forever the mark of progress upon the time that was to come'.

Notes

¹ Thomas Kuhn, The Copernican Revolution (New York, 1959), p. 132.

² Jerome R. Ravetz, 'The Origins of the Copernican Revolution', Scientific American, 215, No. 4 (October 1966), pp. 88-98.