The greatest achievements in the Scientific Revolution of the sixteenth and seventeenth centuries came in the fields most dominated by the ideas of the Greeks - astronomy, mechanics, and medicine. The cosmological views of the Later Middle Ages had been built on a synthesis of the ideas of Aristotle, Ptolemy (the greatest astronomer of antiquity, who lived in the second century C.E.), and Christian theology. In the resulting Ptolemaic (tahl-uh-MAY-ik) or geocentric conception, the universe was seen as a series of concentric spheres with a fixed or motionless earth at its center. Composed of the material substances of earth, air, fire, and water, the earth was imperfect and constantly changing. The spheres that surrounded the earth were made of a crystalline, transparent substance and moved in circular orbits around the earth. Circular movement, according to Aristotle, was the most “perfect” kind of motion and hence appropriate for the “perfect” heavenly bodies thought to consist of a nonmaterial, incorruptible “quintessence.” These heavenly bodies, pure orbs of light, were embedded in the moving, concentric spheres, which in 1500 were believed to number ten. Working outward from the earth, eight spheres contained the moon, Mercury, Venus, the sun, Mars, Jupiter, Saturn, and the fixed stars. The ninth sphere imparted to the eighth sphere of the fixed stars its motion, and the tenth sphere was frequently described as the prime mover that moved itself and imparted motion to the other spheres. Beyond the tenth sphere was the Empyrean Heaven - the location of God and all the saved souls. This Christianized Ptolemaic universe, then, was finite. It had a fixed outer boundary in harmony with Christian thought and expectations. God and the saved souls were at one end of the universe, and humans were at the center. They had been given power over the earth, but their real purpose was to achieve salvation.
This conception of the universe, however, did not satisfy professional astronomers, who wished to ascertain the precise paths of the heavenly bodies across the sky. Finding that their observations did not always correspond to the accepted scheme, astronomers tried to “save appearances” by developing an elaborate system of devices. They proposed, for example, that the planetary bodies traveled on epicycles, concentric spheres within spheres, that would enable the paths of the planets to correspond more precisely to observations while adhering to Aristotle’s ideas of circular planetary movement.
Nicolaus Copernicus (nee-koh-LAU-uss kuh-PURR-nuh-kuss) (1473-1543) had studied both mathematics and astronomy first at Krakow in his native Poland and later at the Italian universities of Bologna and Padua. Before he left Italy in 1506, he had become aware of ancient views that contradicted the Ptolemaic, earth-centered conception of the universe. Between 1506 and 1530, he completed the manuscript of his famous book, On the Revolutions of the Heavenly Spheres, but his own timidity and fear of ridicule from fellow astronomers kept him from publishing it until May 1543 , shortly before his death.
Copernicus was not an accomplished observational astronomer and relied for his data on the records of his predecessors. But he was a mathematician who felt that Ptolemy’s geocentric system was too complicated and failed to accord with the observed motions of the heavenly bodies (see the box above). Copernicus hoped that his heliocentric or sun-centered conception would offer a simpler and more accurate explanation.
Copernicus argued that the universe consisted of eight spheres with the sun motionless at the center and the sphere of the fixed stars at rest in the eighth sphere. The planets revolved around the sun in the order of Mercury, Venus, the earth, Mars, Jupiter, and Saturn. The moon, however, revolved around the earth. Moreover, according to Copernicus, what appeared to be the movement of the sun and the fixed stars around the earth was really explained by the daily rotation of the earth on its axis and the journey of the earth around the sun each year.
Copernicus, however, was basically conservative. He did not reject Aristotle’s principle of the existence of heavenly spheres moving in circular orbits. As a result, when he put forth the calculations to prove his new theory, he retained about half of Ptolemy’s epicycles and wound up with a system somewhat simpler than that of the Alexandrian astronomer but still extremely complicated.
Nevertheless, the shift from an earth-centered to a sun-centered system was significant and raised serious questions about Aristotle’s astronomy and physics despite Copernicus’s own adherence to Aristotle. It also seemed to create uncertainty about the human role in the universe as well as God’s location. Protestant reformers, adhering to a literal interpretation of Scripture, were the first to attack the new ideas.
Martin Luther thundered against “the new astrologer who wants to prove that the earth moves and goes round.... The fool wants to turn the whole art of astronomy upside down. As Holy Scripture tells us, so did Joshua bid the sun stand still and not the earth.” Luther’s cohort at Wittenberg, Philip Melanchthon, condemned Copernicus as well:
The eyes are witness that the heavens revolve in the space of twenty-four hours. But certain men, either from the love of novelty, or to make a display of ingenuity, have concluded that the earth moves, and they maintain that neither the eighth sphere [of the fixed stars] nor the sun revolves.... Now it is a want of honesty and decency to assert such notions publicly, and the example is pernicious. It is the part of a good mind to accept the truth as revealed by God and to acquiesce in it.
The Catholic Church remained silent for the time being; it did not denounce Copernicus until the work of Galileo appeared. The denunciation came at a time when an increasing number of astronomers were being attracted to Copernicus’s ideas.
Copernicus did not have a great impact immediately, but doubts about the Ptolemaic system were growing. The next step in destroying the geocentric conception and supporting the Copernican system was taken by Johannes Kepler. It has been argued, however, that Kepler’s work would not have occurred without the material provided by Tycho Brahe (TY-koh BRAH).
A Danish nobleman, Tycho Brahe (1546-1601) was granted possession of an island near Copenhagen by King Frederick II. On it, Brahe built the elaborate Uraniborg Castle, which he outfitted with a library, observatories, and instruments he had designed for more precise astronomical observations. For twenty years, Brahe patiently concentrated on compiling a detailed record of his observations of the positions and movements of the stars and planets, a series of observations described as the most accurate up to that time. This body of data led him to reject the Aristotelian-Ptolemaic system, but at the same time he was unable to accept Copernicus’s suggestion that the earth actually moved. Brahe’s last years were spent in Prague as imperial mathematician to Emperor Rudolf II, who took a keen interest in astronomy, astrology, and the Hermetic tradition. While he was in Prague, Brahe took on an assistant by the name of Johannes Kepler.
Johannes Kepler (yoh-HAHN-us KEP-lur) (1571-1630) had been destined by his parents for a career as a Lutheran minister. While studying theology at the university at Tubingen (TOO-bing-un), however, he fell under the influence of Michael Mastlin (MEST-lin), Germany’s best-known astronomer, and spent much time pursuing his real interests, mathematics and astronomy. He abandoned theology and became a teacher of mathematics and astronomy at Graz in Austria. Kepler’s work illustrates well the narrow line that often separated magic and science in the early Scientific Revolution. An avid astrologer, Kepler had a keen interest in Hermetic mathematical magic. In a book written in 1596, he elaborated on his theory that the universe was constructed on the basis of geometric figures, such as the pyramid and the cube.
Believing that the harmony of the human soul (a divine attribute) was mirrored in the numerical relationships existing between the planets, he focused much of his attention on discovering the “music of the spheres.” Kepler was also a brilliant mathematician and astronomer and, after Brahe’s death, succeeded him as imperial mathematician to Rudolf II. There he gained possession of Brahe’s detailed astronomical data and, using them, arrived at his three laws of planetary motion. These laws may have confirmed Kepler’s interest in the “music of the spheres,” but more important, they confirmed Copernicus’s heliocentric theory while modifying it in some ways. Above all, they drove another nail into the coffin of the Aristotelian-Ptolemaic system.
Kepler published his first two laws of planetary motion in 1609. Although at Tubingen he had accepted Copernicus’s heliocentric ideas, in his first law he rejected Copernicus by showing that the orbits of the planets around the sun were not circular but elliptical, with the sun at one focus of the ellipse rather than at the center. In his second law, he demonstrated that the speed of a planet is greater when it is closer to the sun and decreases as its distance from the sun increases. This proposition destroyed a fundamental Aristotelian tenet that Copernicus had shared - that the motion of the planets was steady and unchanging. Published ten years later, Kepler’s third law established that the square of a planet’s period of revolution is proportional to the cube of its average distance from the sun. In other words, planets with larger orbits revolve at a slower average velocity than those with smaller orbits.
Kepler’s three laws effectively eliminated the idea of uniform circular motion as well as the idea of crystalline spheres revolving in circular orbits. The basic structure of the traditional Ptolemaic system had been disproved, and people had been freed to think in new ways about the actual paths of planets revolving around the sun in elliptical orbits. By the end of Kepler’s life, the Ptolemaic system was rapidly losing ground to the new ideas (see the box above). Important questions remained unanswered, however: What were the planets made of ? And how could motion in the universe be explained? It was an Italian scientist who achieved the next important breakthrough to a new cosmology by answering the first question and making important strides toward answering the second.
Galileo Galilei (1564-1642) taught mathematics, first at Pisa and later at Padua, one of the most prestigious universities in Europe. Galileo was the first European to make systematic observations of the heavens by means of a telescope, thereby inaugurating a new age in astronomy. He had heard of a Flemish lens grinder who had created a “spyglass” that magnified objects seen at a distance and soon constructed his own after reading about it. Instead of peering at terrestrial objects, Galileo turned his telescope to the skies and made a remarkable series of discoveries: mountains and craters on the moon, four moons revolving around Jupiter, the phases of Venus, and sunspots. Galileo’s observations demolished yet another aspect of the traditional cosmology in that the universe seemed to be composed of material substance similar to that of the earth rather than ethereal or perfect and unchanging substance.
Galileo’s revelations, published in The Starry Messenger in 1610 (see the box on p. 484), stunned his contemporaries and probably did more to make Europeans aware of the new picture of the universe than the mathematical theories of Copernicus and Kepler did.
The English ambassador in Venice wrote to the chief minister of King James I in 1610:
I send herewith unto His Majesty the strangest piece of news ... that he has ever yet received from any part of the world; which is the annexed book of the Mathematical Professor at Padua [Galileo], who by the help of an optical instrument ... has discovered four new planets rolling about the sphere of Jupiter. ... So upon the whole subject he has first overthrown all former astronomy . . .. By the next ship your Lordship shall receive from me one of the above instruments [a telescope], as it is bettered by this man?
During a trip to Rome, Galileo was received by scholars as a conquering hero. Grand Duke Cosimo II of Florence offered him a new position as his court mathematician, which Galileo readily accepted. But even in the midst of his newfound acclaim, Galileo found himself increasingly suspect by the authorities of the Catholic Church.
GALILEO AND THE INQUISITION In The Starry Messenger, Galileo had revealed himself as a firm proponent of Copernicus’s heliocentric system. The Roman Inquisition (or Holy Office) of the Catholic Church condemned Copernicanism and ordered Galileo to reject the Copernican thesis. As one cardinal commented, “The intention of the Holy Spirit is to teach us not how the heavens go, but how to go to heaven.” The report of the Inquisition ran:
That the doctrine that the sun was the center of the world and immovable was false and absurd, formally heretical and contrary to Scripture, whereas the doctrine that the earth was not the center of the world but moved, and has further a daily motion, was philosophically false and absurd and theologically at least erroneous.
Galileo was told, however, that he could continue to discuss Copernicanism as long as he maintained that it was not a fact but a mathematical supposition. It is apparent from the Inquisition’s response that the church attacked the Copernican system because it threatened not only Scripture but also an entire conception of the universe (see the box on p. 485). The heavens were no longer a spiritual world but a world of matter. Humans were no longer at the center, and God was no longer in a specific place. The new system raised such uncertainties that it seemed prudent simply to condemn it.
Galileo, however, never really accepted his condemnation. In 1632, he published his most famous work, Dialogue on the Two Chief World Systems: Ptolemaic and Copernican. Unlike most scholarly treatises, it was written in Italian rather than Latin, making it more widely available to the public, which no doubt alarmed the church authorities. The work took the form of a dialogue among Simplicio, a congenial but somewhat stupid supporter of Aristotle and Ptolemy; Sagredo, an open-minded layman; and Salviati, a proponent of Copernicus’s ideas. There is no question who wins the argument, and the Dialogue was quickly perceived as a defense of the Copernican system. Galileo was dragged once more before the Inquisition in 1633, found guilty of teaching the condemned Copernican system, and forced to recant his errors. Placed under house arrest on his estate near Florence, he spent the remaining eight years of his life studying mechanics, a field in which he made significant contributions.
GALILEO AND THE PROBLEM OF MOTION One of the problems that fell under the heading of mechanics was the principle of motion. The Aristotelian conception, which dominated the late medieval world, held that an object remained at rest unless a force was applied against it. If a force was constantly exerted, then the object moved at a constant rate, but if it was removed, then the object stopped. This conception encountered some difficulties, especially with a projectile thrown out of a cannon. Late medieval theorists had solved this problem by arguing that the rush of air behind the projectile kept it in motion. The Aristotelian principle of motion also raised problems in the new Copernican system. In the Ptolemaic system, the concentric spheres surrounding the earth were weightless, but in the Copernican system, if a constant force had to be applied to objects to cause movement, then what power or force kept the heavy earth and other planets in motion? Galileo made two contributions to the problem of motion. First, he demonstrated by experiments that if a uniform force was applied to an object, it would move at an accelerated speed rather than a constant speed. Moreover, Galileo discovered the principle of inertia when he argued that a body in motion continues in motion forever unless deflected by an external force. Thus, a state of uniform motion is just as natural as a state of rest. Before Galileo, natural philosophers had tried to explain motion; now their task was to explain changes in motion.
The condemnation of Galileo by the Inquisition, coming at a time of economic decline, seriously undermined further scientific work in Italy, which had been at the forefront of scientific innovation. Leadership in science now passed to the northern countries, especially England, France, and the Dutch Netherlands. By the 1630s and 1640s, no reasonable astronomer could overlook that Galileo’s discoveries, combined with Kepler’s mathematical laws, had made nonsense of the Aristotelian-Ptolemaic world system and clearly established the reasonableness of the Copernican model. Nevertheless, the problem of explaining motion in the universe and tying together the ideas of Copernicus, Galileo, and Kepler had not yet been solved. This would be the work of an Englishman who has long been considered the greatest genius of the Scientific Revolution.
Born in the English village of Woolsthorpe in 1642, Isaac Newton was an unremarkable young man until he attended Cambridge University. His first great burst of creative energy came in 1666, when fear of the plague closed Cambridge and forced him to return to Woolsthorpe for eighteen months. There Newton discovered his creative talents: “In those days I was in the prime of my life for invention and minded mathematics and philosophy more than at any time since.” During this period, he invented the calculus, a mathematical means of calculating rates of change; began his investigations into the composition of light; and inaugurated his work on the law of universal gravitation. Two years after his return to Cambridge, in 1669, he accepted a chair in mathematics at the university. During a second intense period of creativity from 1684 to 1686, he wrote his famous Principia (prin-SIP-ee-uh) (see the box on p. 487). After a nervous breakdown in 1693, he sought and received an administrative post as warden of the royal mint and was advanced to master of the mint by 1699, a post he held until his death in 1727. Made president of the Royal Society (see “The Scientific Societies” later in this chapter) in 1703 and knighted in 1705 for his great achievements, Sir Isaac Newton is to this day the only English scientist to be buried in Westminster Abbey.
NEWTON AND THE OCCULT Although Newton occupies a very special place in the history of modern science, we need to remember that he, too, remained extremely interested in aspects of the occult world. He left behind hundreds of manuscript pages of his studies of alchemy, and in fact, his alchemical experiments were a major feature of his life until he moved to London in 1696 to become warden of the royal mint. The British economist John Maynard Keynes said of Newton after examining his manuscripts in 1936:
Newton was not the first of the age of reason. He was the last of the magicians .... He looked on the whole universe and all that is in it as a riddle, as a secret which could be read by applying pure thought to certain evidence, certain mystic clues which God had laid about the world to allow a sort of philosopher’s treasure hunt to the esoteric brotherhood. He believed that these clues were to be found partly in the evidence of the heavens and in the constitution of elements, ... but also partly in certain papers and traditions handed down by the brethren in an unknown chain back to the original cryptic revelation in Babylonia.
Although Newton may have considered himself a representative of the Hermetic tradition, he chose, it has been recently argued, for both political and psychological reasons to repress that part of his being, and it is as the “symbol of Western science” that he came to be viewed.
UNIVERSAL LAW OF GRAVITATION Newton’s major work, the “hinge point of modern scientific thought,” was his Mathematical Principles of Natural Philosophy, known simply as the Principia, the first word of its Latin title. In this work, the last highly influential book in Europe to be written in Latin, Newton spelled out the mathematical proofs demonstrating his universal law of gravitation. Newton’s work was the culmination of the theories of Copernicus, Kepler, and Galileo. Though each had undermined some part of the Aristotelian-Ptolemaic cosmology, until Newton no one had pieced together a coherent synthesis for a new cosmology.
In the first book of the Principia, Newton defined the basic concepts of mechanics by elaborating the three laws of motion: every object continues in a state of rest or uniform motion in a straight line unless deflected by a force, the rate of change of motion of an object is proportional to the force acting on it, and to every action there is always an equal and opposite reaction. In book 3, Newton applied his theories of mechanics to the problems of astronomy by demonstrating that these three laws of motion govern the planetary bodies as well as terrestrial objects. Integral to his whole argument was the universal law of gravitation, which explained why the planetary bodies did not go off in straight lines but continued in elliptical orbits about the sun. In mathematical terms, Newton explained that every object in the universe was attracted to every other object with a force (gravity) that is directly proportional to the product of their masses and inversely proportional to the square of the distances between them.
The implications of Newton’s universal law of gravitation were enormous, even though another century would pass before they were widely recognized. Newton had demonstrated that one universal law, mathematically proved, could explain all motion in the universe, from the movements of the planets in the celestial world to an apple falling from a tree in the terrestrial world. The secrets of the natural world could be known by human investigations. At the same time, the Newtonian synthesis created a new cosmology in which the world was seen largely in mechanistic terms. The universe was one huge, regulated, and uniform machine that operated according to natural laws in absolute time, space, and motion. Although Newton believed that God was “everywhere present” and acted as the force that moved all bodies on the basis of the laws he had discovered, later generations dropped his spiritual assumptions. Newton’s world-machine, conceived as operating absolutely in time, space, and motion, dominated the Western worldview until the twentieth century, when the Einsteinian revolution, based on the concept of relativity, superseded the Newtonian mechanistic concept.
Newton’s ideas were soon accepted in England, possibly out of national pride and conviction and, as has been argued recently, for political reasons (see “Science and Society” later in this chapter). Natural philosophers on the Continent resisted Newton’s ideas, and it took much of the eighteenth century before they were generally accepted everywhere in Europe. They were also reinforced by developments in other fields, especially medicine.