Mathematics and Instruments
Advances in mathematics, which seem commonplace today, made the tools of calculation more exact and efficient in that age. Michael Stifel's Arithmetica Integra (1544) introduced the signs for addition and subtraction, and Robert Recorde's The Whetstone of Witte first printed the modern sign of equality. The reckoning books of Adam Riese, long famous, led the Germans from counting with counters to calculating in writing. Johannes Werner published the first treatise in modern style on conic sections (1522), and Georg Rheticus, besides being Copernicus's pupil, continued Regiomontanus's work in trigonometry. Astronomy relied more on trustworthy calculation than on instruments. On the strength of such calculations some astrologers predicted that the conjunction of Jupiter and Saturn in Pisces on 11 February 1524 would bring a second Noah's flood; the city of Toulouse is said to have built a great ark, and prudent families stored provisions on mountaintops. Most astronomical instruments were medieval in origin: celestial and terrestrial globes, graduated staffs for measuring altitude, astrolabes, armillary spheres, clocks and compasses. There was no telescope (the source also mentions a photographic camera, which is plainly an anachronism). With this equipment Copernicus moved the earth.
The Early Life of Copernicus
Mikolaj Kopernik, as Poland calls him, Nikolaus Kopernikus as Germany does, and Nicolaus Copernicus as the learned world knows him, was born in 1473 at Torun (Thorn) on the Vistula in West Prussia, a city that the Teutonic Knights had ceded to Poland seven years before. In place he was thus a Prussian, in time a Pole. His mother came from a wealthy Prussian family; his father, who had come from Krakow, settled at Torun and traded in copper. When the father died (1483), the mother's brother, Lucas Watzenrode, bishop of Ermland, took charge of the children.
At eighteen Nicolaus was sent to the University of Krakow to study theology. There he found the stifling rule of scholasticism over humanism at odds with his own thinking, and persuaded his uncle to send him to Italy. The bishop appointed him a canon of the cathedral of Frauenburg in the Polish part of East Prussia (the source's phrasing) and gave him a three-year leave.
At the University of Bologna (1497-1500) Copernicus studied mathematics, natural science and astronomy. One of his teachers, Domenico Maria Novara, himself once a pupil of Regiomontanus, found the Ptolemaic system confused and cumbersome, and introduced his students to the ideas of ancient Greek astronomers who had doubted the earth's rest and centrality.
Forerunners of the Sun-Centered Idea
Philolaus, a Pythagorean of the fifth century BC, held that the earth and the other planets revolve around a central fire called Hestia, hidden from men because all the inhabited parts of the earth face away from it. Cicero mentions Hicetas of Syracuse, also of the fifth century BC (as the book has it), who held that sun, moon and stars are all fixed and their apparent motion results from the earth's rotation on its axis. Archimedes and Plutarch report that Aristarchus of Samos (310-230 BC) pointed to the earth's motion around the sun, was charged with impiety, and retracted. According to Plutarch, Seleucus of Babylon revived the theory in the second century BC. The sun-centered theory might have advanced and triumphed in antiquity, but Claudius Ptolemy of Alexandria in the second century AD restated and established the earth-centered theory with such power and mastery that no one dared go against it.
It was Ptolemy who first ruled that science, in explaining phenomena, should adopt the simplest possible hypothesis that agrees with general observation; yet Ptolemy himself, like his predecessor Hipparchus, had to assume a confusing tangle of epicycles and eccentrics to explain the apparent motions of the planets on an earth-centered basis. Could a simpler hypothesis be found? Nicole Oresme (1330-1382) and Nicholas of Cusa (1410-1464) had revived the idea of the earth's motion, and Leonardo da Vinci (1452-1519) had just written: "The sun does not move ... the earth is neither at the center of the sun's orbit nor at the center of the universe." Copernicus felt the sun-centered hypothesis could "save the appearances," that is, explain astronomical phenomena, far more simply than Ptolemy's.
Rome, Ferrara and Frauenburg
In 1500, aged twenty-seven, Copernicus went to Rome, where, as the story goes, he tentatively proposed the earth's motion in lectures. His leave then ended and he returned to his duties at Frauenburg. But the mathematics of the earth-centered theory disturbed his prayers; he asked permission to continue his studies in Italy, promising this time to study medicine and canon law, which seemed to his superiors more suitable than astronomy. (The source says this happened "before the fifteenth century ended," though 1500 is the first year of the sixteenth.) He took his degree in law at Ferrara (1503), apparently took no degree in medicine, and again settled to his service at Frauenburg. Soon his uncle, perhaps to give him a new chance to study, chose him as secretary and physician (1506), and Copernicus lived six years in the episcopal castle at Heilsberg. There he founded his theory on mathematical calculation and set it down in an orderly manuscript.
When the kindly bishop died, Copernicus took up his duties at Frauenburg cathedral. He went on practicing medicine, treating poor patients free of charge. The cathedral chapter assigned him to political missions, and for Sigismund I of Poland he drew up a plan to reform the currency of Prussia. In one of his several learned essays he set down what was later named "Gresham's law": bad money drives out good. When a state puts cheap coin into circulation, good coin is naturally hoarded or exported and so drops out of circulation, while on the other side every cheap coin is paid to the treasury as tax, so the king "gets back his own bad coin." All the while, Copernicus never gave up his astronomical studies. His home was geographically unfavorable: Frauenburg lies near the Baltic and was half the time under mist and cloud. He envied Ptolemy, for whom "the sky was more cheerful and the Nile did not breathe out mist as our Vistula does; nature has denied us that ease and calm air." No wonder Copernicus almost worshiped the sun.
The Little Commentary
His observations were neither accurate nor numerous, and for his purpose such researches were not vital. For the most part he used Ptolemy's assumptions and data, and his aim was to show that all the gathered observations fit best with the sun-centered theory. Around 1514 Copernicus summarized the results of his research in a brief work, the Commentariolus (Short Commentary on the Revolutions of the Heavenly Spheres). It was not printed in his lifetime, but he sent a few manuscript copies around as "trial balloons." Copernicus stated the substance of his thought with simplicity and humility, as if it were not the greatest revolution in the history of Christianity:
- There is no single center for all the celestial orbs or spheres.
- The center of the earth is not the center of the universe, but only of gravity and of the lunar sphere.
- All the spheres [planets] revolve around the sun as their midpoint, and therefore the sun is the center of the universe.
- The distance from earth to sun, compared with the distance to the sphere of the fixed stars, is so much smaller than the ratio of the earth's radius to its distance from the sun that the earth-sun distance is imperceptible beside the distance to the stars.
- Every motion seen in the heavens comes not from the motion of the heavens themselves but from the earth's: the earth, with its surrounding elements, turns once daily on its fixed poles, while the sphere of the stars remains unchanged.
- What appears to us as the motions of the sun is not its own motion but that of the earth and its orbit, with which we revolve around the sun like any other planet.
- The apparent forward and retrograde motions of the planets come not from their own motion but from the earth's.
The motion of the earth alone, therefore, suffices to explain all the apparent irregularities of the heavens. The few astronomers who looked at the work paid it no attention.
Popes, Reformers and the Silent Years
When Pope Leo X learned of Copernicus's theory he showed scholarly interest in it and had a cardinal write to Copernicus asking for practical proof; for a time the new hypothesis was a special subject of attention at the enlightened papal court. Shortly before 1530 Luther rejected it: "People give ear to a new-fangled astrologer who wants to prove that the earth turns, not the heavens or the firmament, nor the sun and moon ... This fool wishes to turn the whole art of astronomy upside down; but Scripture tells us that Joshua commanded the sun to stand still, not the earth." Calvin answered Copernicus by quoting Psalm 93:1, "the world also is stablished, that it cannot be moved," and asked, "Who will venture to place the authority of Copernicus above that of the Holy Spirit?"
Copernicus was so discouraged by the reaction that when he finished his major work around 1530, he decided against publishing. He returned to his church duties in perfect calm, dabbled a little in politics, and in his sixties was accused of keeping a woman in his household (the source's allusion; he is reported to have complied with the order to send her away). In old age he was resigned to fate, until in 1539 a young mathematician of passionate zeal, Georg Rheticus, came on the scene. Rheticus, twenty-five, a Protestant, a protege of Melanchthon and a professor at Wittenberg, had read the Commentariolus and accepted its truth. He longed to help the old astronomer, waiting patiently at one of the remotest outposts of civilization on the Baltic until others, too, would grasp the invisible turning of the earth. The young man fell in love with Copernicus, called him "the best and greatest of men," and was astonished to find him so devoted to and captivated by science. Rheticus studied the bulky manuscript for ten weeks, then insisted that it be published.