But if one were to contradict Aristotle on two important points, on what other points might one feel free to contradict him—or his great follower, Thomas Aquinas? The early sixteenth century was not a time when most people enjoyed or looked forward to change in their beliefs and ideas about the world. They preferred to have things stay pretty much the same. Copernicus knew that the publication of his book would create a great controversy, at the best—and at the worst might result in severe attacks upon him. He therefore held off publishing it until the end of his life—and died before he could see the changes its publication would produce.
Copernicus’s book need not be read through from beginning to end. There are, for example, many complex geometrical theorems whose demonstrations are hard to follow. The main argument, though, is clear and set forth in lucid prose.
WILLIAM GILBERT
1540?–1603
On the Lodestone
William Gilbert was a famous physician who carved out a prosperous London practice for himself during the last half of the sixteenth century. Born at Colchester in about 1540, he was named in 1601 physician to Queen Elizabeth and thereupon moved to court. The Queen died shortly thereafter but her successor, James I, reappointed Gilbert royal physician immediately. Gilbert took considerable satisfaction in the fact that the only personal legacy in the Queen’s will provided a fund for the prosecution of his experiments. But all these high hopes came to an end with Gilbert’s death, probably of the plague, in 1603.
Gilbert’s reputation as a physician was local, but he was famous throughout England and Europe for a book, De Magnete (On the Lodestone), which he had published in the year 1600. This book, which remains highly readable today, is full of things that were wonderful to Gilbert’s contemporaries and that are still of interest.
Gilbert was not the first to recognize the existence of lodestone (that is, magnetic iron oxide). The Greeks and the Chinese, among other peoples, had known of the magnetic properties of this iron ore compound since at least 500 BCE. But he was the first to conduct careful and duplicable experiments with lodestone. Most important, he was the first to recognize that the Earth itself is a great lodestone and that there is no difference except in size between a simple spherical magnet held in the hand and the great globe on which we stand.
As a young man, Gilbert had traveled on the Continent and had there met many persons who later became notable in science. He corresponded with them throughout the rest of his life. In his London house he possessed a large collection of minerals, instruments, and books, and he held regular meetings of other Londoners interested in scientific subjects, where his experiments were presented and discussed and where he reported on discoveries made abroad. These meetings, which are thought to have anticipated the later organization of the Royal Society, helped to create a wide respect for Gilbert and his ideas not only about lodestone but also about the Earth and its place in the universe. Thus, when Gilbert accepted without a murmur the revolutionary assumptions of Copernicus about the structure of the cosmos, it was easy for learned Englishmen to do likewise. This is one reason why English science during the seventeenth century—the century following Gilbert’s death—was the best in the world.
Gilbert’s most vigorous arguments in On the Lodestone are reserved for his demolition of the Ptolemaic hypothesis of the so-called primum mobile, or first mover. According to Ptolemy, the second-century astronomer, the Earth stood still at the center of a nest of concentric spheres, each bearing a planet (or the Moon and the Sun), all of which revolved once every day around the Earth. But why did the spheres move? What provided their motive force?
For Ptolemy there were nine material (though quintessential) spheres that turned around the Earth: the spheres of the Moon, of Mercury, of Venus, of the Sun, of Mars, of Jupiter, of Saturn, of the Ecliptic, and of the Fixed Stars. Each of these spheres had its specific motion or motions—some of them very complicated. But they all shared a common diurnal motion as they were swept around from east to west by the primum mobile. This was a tenth sphere, material but invisible, that surrounded all the other heavens and whirled them around with inconceivable force and, as Copernicus noted, inconceivable speed.
For Gilbert, this primum mobile was sheer nonsense. It “presents no visible body, is in no wise recognizable; it is a fiction believed in by some philosophers (i.e., scientists), and accepted by weaklings.”
Surely that [notion of the primum mobile] is superstition, a philosophic fable, now believed only by simpletons and the unlearned; it is beneath derision; and yet in times past it was supported by calculation and comparison of movements, and was generally accepted by mathematicians while the importunate rabble of philophasters egged them on.
What chance had the Ptolemaic geocentric theory against such fierce eloquence—and such good sense?
Gilbert’s hard-headed insistence that scientists look not at books but at things helped to shape the future of English science. It also helped to shape the future of all science. The year 1600, which saw the publication of De Magnete, was crucial in human history. Before that, the world was primarily medieval. After it, the world was becoming modern.
JOHANNES KEPLER
1571–1630
The Epitome of Copernican
Astronomy
Johannes Kepler was a German who, unlike his predecessor Copernicus, had to struggle to obtain an education. He was born in Wurtemburg in 1571. His father was a soldier of fortune and a tavern keeper, but he himself was a sufficiently brilliant student on the rare occasions when he was allowed to go to school that influential persons noticed him. The Church, that discoverer of talent wherever it might exist, determined that, if properly trained, Kepler might become a faithful servant. He was sent to seminary and college and finally (in 1589) to the University at Tubingen, where for the first time he was introduced to the astronomical theories of Copernicus. He very soon decided that he could do better, although it was many years before he was willing to publish his theories.
His most important book was both a paean of praise of and an apology to the memory of Copernicus. Entitled The Epitome of Copernican Astronomy (1618–21), it hewed to the Copernican line wherever its author felt he could. But it made substantial and significant departures from Copernicus at crucial points.
Kepler agreed with Copernicus (and disagreed with Ptolemy) in holding that the planets, including the Earth, revolve around the Sun, which is the center of the universe, and that the Earth rotates on its axis from west to east thus producing the apparent motion of the heavens around the Earth from east to west. He agreed with Copernicus on many minor points as well. But he disagreed on three main points.