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COSMOLOGY

COSMOLOGY. During the fifteenth century, the cosmological systems of the Epicurean atomists, Plato, and the Stoics were known from antiquity, but the cosmology that was taught in universities throughout Europe was that of Aristotle, as augmented by Ptolemy. By the beginning of the eighteenth century a new cosmology, associated with the names of Copernicus, Kepler, Galileo, Descartes, and Newton, had almost completely replaced the earlier consensus. The present article considers the cosmologies of these main figures and reviews changes in historians' understanding of the causes of the scientific revolution.

ARISTOTLE'S COSMOS

Aristotle's cosmos was finite, spherical, and full. Its outer boundary was a sphere carrying the fixed stars. Its center was the Earth, and the sphere carrying the Moon divided the cosmos into a terrestrial portion and a celestial portion. The region beneath the Moon consisted of four elements, each endowed with the tendency to return to its natural place by a motion along a radius of the cosmos. The element Earth tended to seek the center; water moved naturally to a sphere surrounding the central globe of Earth; air sought a sphere concentric to water, and fire, which in its pure form was quite transparent, would naturally move to the region above the air and beneath the Moon. The general structure of the world reflected its elementary constitution, with most earth covered by water and both inner elements covered by air. Only the sphere of fire was not directly observable, although it was a theoretical necessity. Mixing and transmutation created complex combinations of elements, such as people, plants, and animals. Changes in the proportions of the four elements explained terrestrial change, especially growth and decay.

By contrast, the heavens consisted of a single element, ether, which was already in its natural place, and moved naturally in a circle, at constant speed, around the central earth. Deprived of the opportunity for transmutation or mixing of elements, the heavens were incapable of physical change. The order of the heavenly bodies was determined partly by observation and partly by convention. Eclipses and occultations made it clear that the Moon was the closest heavenly body and the fixed stars were the most distant. Mars, Jupiter, and Saturn could be ordered according to their periods of return, with the longest being the farthest away. However, the periods of return for the remaining planets and the Sun were not distinguishable. The locations of the five known planets were divided by the zone occupied by the Sun, and, beyond the Moon, an ordering of Mercury, followed by Venus, followed by the sun became conventional.

The heavens consisted of nested concentric shells. A single heavenly body was confined within and carried by each shell. Physically, the heavenly bodies were believed to be denser regions in the ether. During the fifteenth and sixteenth centuries, followers of Averroes (Ibn Rushd) and Ptolemy violently disagreed over the inner structure of these shells.

In the Almagest Ptolemy had introduced a system of moving circles carrying other circles to explain the details of planetary motion. In the Planetary Hypotheses he introduced a corresponding set of physical models, which Arabic commentators presented as sets of hollow orbs carrying smaller spheres within them. These, in turn, carried individual planets. Ptolemaic astronomers assumed that the orb clusters for different planets fitted perfectly inside one another, and were thereby able to calculate the distances of planets, including the Sun, and their relative sizes. But most importantly, Ptolemy's mathematical apparatus allowed the calculation of planetary positions with an accuracy sufficient, for example, to predict eclipses of the Sun and Moon, and approximate conjunctions and other planetary alignments important in astrology. These models were presented in Georg Peurbach's Theoricae novae planetarum (c. 1474), which rapidly became a standard text. Averroists objected to the eccentric circles and epicycles used by their rivals on the grounds that they were not strictly centered on the Earth. They proposed that planets were carried by a series of nested orbs, exactly concentric to the Earth, but, as late as the 1530s, attempts to construct predictive models failed. Copernicus was exposed to both viewpoints during his education.

THE NEW COSMOLOGIES

Motivated by a desire to establish an absolute order for the planets, Copernicus moved the center of the cosmos to the Sun (On the Revolutions of the Heavenly Spheres, 1543). In other respects, his cosmology was conservative. He continued to assume that the planets were carried by orbs and that the sphere of fixed stars was the boundary of a finite universe, although his shift of center created large and inexplicable gaps between orbs, and especially between the outermost planet, Saturn, and the fixed stars. These gaps were later explained by Kepler using the geometrical construction introduced in the Mysterium Cosmographicum (1596). The immediate reaction, led by astronomers at the Lutheran University of Wittenberg, was to adapt Copernicus's new models to an Earth-centered system and to reject his cosmology on physical and scriptural grounds.

To remove Aristotle's cosmology, it was necessary to undermine his account of the construction of the heavens. Two major factors began this process: the revival of Stoic physics and precise observations of comets. Aristotle had taught that comets, which appeared and vanished at irregular intervals, must be long-lasting fires in the region below the Moon, because there could be no change in the heavens. In 1572 a nova suggested that change did occur in the heavens. Attempts to measure comets' distances placed them in the heavens. At the same time, the revival of Stoic physics suggested that the heavens might be filled by a continuous fluid rather than Aristotle's solid spheres. Tycho Brahe in Denmark and Michael Maestlin in Germany both measured precise distances for a comet that appeared in 1577. Both concluded that the comet had moved through a series of Aristotle's Earth-centered spheres and that any spheres must be centered on the Sun. Maestlin became a Copernican, later teaching his ideas to Johannes Kepler. But Brahe was unable to accept the motion of the Earth and developed a new cosmology in which the Earth remained the center, the Moon and Sun circled the Earth, and the remaining planets circled the Sun. To avoid the overlap his system created between the orbs of Mars and the Sun, Brahe adopted fluid heavens in which celestial spheres were no more than geometrical boundaries.

Today, Johannes Kepler is credited with discovering the three laws of planetary motion that bear his name, but his innovations were not generally accepted until Isaac Newton showed that they followed from his own theory. Kepler introduced the modern concept of an orbit, located the cause of planetary motion in the Sun, and replaced the circles of traditional astronomy with ellipses, but he continued to regard the fixed stars as the boundary of a finite universe. Like Tycho, he adopted a theory that made the substance of the heavens a fluid. The unprecedented accuracy of his astronomical tables advertised the importance of his insights after his death in 1630.

Galileo Galilei, by contrast, preserved many features of traditional cosmology. He never adopted Kepler's ellipses and denied that comets were celestial objects. However, his telescopic discoveries offered a host of new observational evidence supporting Copernicus. Jupiter's moons showed that the Averroists were wrong in demanding a single center of rotation for the cosmos. Sunspots and the observation of terrestrial features on the Moon showed that the heavens were not changeless and suggested that a single physics should embrace both heavens and Earth. The cycle of phases displayed by Venus showed that it, at least, circled the Sun. It was possible to accommodate all of these innovations in a modified Aristotelian scheme (as postulated by Du Chevreul in 1623), but the motions of comets and their implications for the substance of the heavens were unaccounted for. In the climate created by the Catholic Church's condemnation of Copernicanism in 1616 and 1633, Tycho Brahe's system became the most attractive option to anyone wishing to reconcile religious orthodoxy, traditional physics, and new astronomical discoveries. Jesuits exported it to China, and it was taught in Northern European universities into the eighteenth century.

Galileo's later work helped revive the ancient theory that matter was composed of atoms, a viewpoint that was being developed by Beeckman, Gassendi, and Descartes. The latter delayed publishing an atomistic cosmology because of Galileo's condemnation. In Le Monde, finished in 1633, but not published until 1664, Descartes described a cosmos filled by vortices of atoms. Stars naturally formed at the center of each vortex, while matter falling onto their surface caused sunspots. A large enough quantity of infalling material formed a crust over the entire star, which then became free of its vortex and wandered through the heavens, appearing as a comet. When finally captured by another vortex, the comet became a planet. Descartes therefore explained many new discoveries in a single scheme that was inherently heliocentric, although the sun was now just one among many vortex centers scattered throughout space.

Newton's synthesis (1689) provided a detailed mathematical physics that unified the heavens and the Earth. The planets were now held in place not by vortices, but by universal gravitation. Comets were divided into returning and nonreturning, and the reappearance of Halley's comet in 1758 was a highly visible success. With the general acceptance of Newton's system, cosmology assumed a form that persisted until the early twentieth century. As with Descartes, the Sun was identified as a star. The planets with their attendant satellites were bound to the Sun, but were not unique; other stars were assumed to be the centers of other planetary systems. Comets were definitely celestial, although only the determination of the numerical value of Newton's Universal Gravitational Constant allowed the recognition of their diminutive mass in comparison to planets or stars. Newton's First Law required that inertial motion continue indefinitely and implied a universe that was infinite in space.

THE NATURE OF THE SCIENTIFIC REVOLUTION

The changes in cosmology just described have often been taken as the centerpiece of an event known as the scientific revolution, usually described as the replacement of Aristotle's scientific system with modern mathematical physics, based on experimental evidence. But recent historiography has tended to emphasize continuity with earlier achievements. It is now clear that the modern conception of experiment developed over a long period, with important changes beginning in the sixteenth century with the work of astronomers and early mathematical physicists. Kepler's unification of physics and mathematical astronomy became an important precedent, although it was more important with hindsight, after the development of new mathematical techniques for doing physics by Descartes, Newton, and their contemporaries. The work of Boyle and other members of the early Royal Society, as well as members of similar institutions in France and Italy, also contributed, although the modern conception of experiment did not emerge until the power of the new mathematical methods had been reconciled with the empiricism advocated by Bacon, a process that continued from Newton's career through the development of mathematical physics in France during the Enlightenment. Galileo's use of experiment resembles the earlier, rather than the later, concept. He was clearly not the originator of the experimental method, and modern research also demonstrates that his ideas on physics and scientific method in general were transformations of existing ideas rather than complete novelties.

Recent historians also give a more equal role to noncanonical sciences such as alchemy and astrology in the development of modern science. Alchemy clearly contributed to the replacement of Aristotle's theory of the terrestrial elements. Astrology remained important as the main motive for the study of astronomy and cosmology because of applications including medical diagnosis and treatment, weather prediction, and political planning. Although most practitioners followed the great Lutheran reformer and educator Philipp Melanchthon in believing that the heavens predisposed rather than compelled terrestrial events, casting horoscopes was a professional skill prized by the patrons of Tycho Brahe, Kepler, and Galileo. Alchemy was gradually transformed, first into the phlogiston theories of Stahl and his contemporaries, and then into the modern discipline of chemistry at the hands of Lavoisier. The disappearance of astrology lacks a generally agreed explanation. In England, at least, its public suppression may have had less to do with the development of the new science and new scientific societies after the Civil War than with the fact that its supporters were on the losing side after the Restoration of Charles II.

The supposed warfare between science and religion is now recognized to be largely a fiction of late-nineteenth-century historiography. Both Catholic and Protestant churches were active in supporting and sometimes opposing the new science. During the sixteenth century, for example, followers of Melanchthon arranged for the publication of Copernicus's work and actively spread his ideas, although, initially, they accepted his mathematical astronomy and rejected his cosmology. The trial of Galileo in 1633 cannot be attributed solely to his defense of Sun-centered cosmology. Other factors may include the dynamics of patronage (Galileo's patron Ciampoli offended the pope; other supporters had died) and internal church politics (the potential rebellion of a Spanish faction over the pope's handling of the Counter-Reformation). The condemnation of Copernicanism, and especially the outbreak of the Thirty Years' War in 1618, created new difficulties, but the Jesuit order of the Catholic Church remained at the forefront of scientific research. Kepler and Newton both saw their religious beliefs as integral to, rather than separable from, their scientific work.

The importance of new career paths and new scientific institutions has qualified earlier accounts of the scientific revolution. Copernicus was a lowly member of the Catholic hierarchy, who, until almost the end of his life, pursued his research essentially in private. His earliest supporters were university teachers, like Melanchthon's followers at Wittenberg and Maestlin at Tübingen. But his most important successors were courtiers whose research was supported by patronage. Tycho Brahe was financed by the king of Denmark, and later the Holy Roman emperor, who also supported his successor Kepler. Galileo moved from a university post to the court of the Medici in Florence, where he did his most important work. The first scientific societies appeared during the seventeenth century and provided new avenues of scientific communication, including published proceedings and journals, and new forms of support for scientists. In later life, Newton dominated the Royal Society of London. But the acceptance of Newton's system in Germany, and especially in France, followed the adoption of the new science as an intellectual fashion by the upper classes throughout Europe. This process depended upon the ascendancy of another social forum, the salon, where, for the first time since antiquity, women made major contributions to science.

The scientific revolution was not the work of a few great men, nor the result of changes that occurred only in the mathematical sciences, or in sciences that still exist today. It was not the result of the sudden appearance of the modern conception of experiment, nor did it come about because of any early separation between science and religion. There are profound differences between the content, method, and structure of the sciences from the origin to the close of the early modern period, but these changes are now regarded as the result of a complex combination of intellectual, theological, social, and institutional causes.

See also Alchemy; Aristotelianism; Astrology; Bacon, Francis; Boyle, Robert; Brahe, Tycho; Charles II (England); Copernicus, Nicolaus; Descartes, René; Enlightenment; Galileo Galilei; Gassendi, Pierre; Kepler, Johannes; Lavoisier, Antoine; Medici Family; Melanchthon, Philipp; Newton, Isaac; Scientific Revolution; Stoicism; Thirty Years' War (1618–1648)

BIBLIOGRAPHY

Primary Sources

Aiton, E. J. "Peurbach's Theoricae Novae Planetarum:A Translation with Commentary." Osiris, 2nd series, 3 (1987): 5–44.

Brahe, Tycho. De Mundi Eetherei Recentioribus Phaenomenis. Uraniborg, 1588. Tycho's book on comets and his new cosmic scheme.

Chevreul, Jacques du. Sphaera. Paris, 1623. Contains an Aristotelian cosmic scheme that accommodates all Galileo's telescopic discoveries. (See also Ariew, below.)

Copernicus, Nicolaus. On the Revolutions of the Heavenly Spheres. Translated by A. M. Duncan. New York, 1976. Translation of De Revolutionibus Orbium Coelestium (1543).

Galilei, Galileo. Dialogue Concerning the Two Chief World Systems, Ptolemaic & Copernican. Translated by Stillman Drake. Berkeley, 1967. English translation of Dialogo sopra i due massimi sistemi del mondo, Tolemaico e Copernicano (1632), the work for which Galileo was condemned.

Goldstein, Bernard R. "The Arabic Version of Ptolemy's Planetary Hypotheses." Transactions of the American Philosophical Society 57 (1967), Part 4. Presents Ptolemy's physical models.

Descartes, René. The World and Other Writings. Translated by Stephen Gaukroger. Cambridge, U.K., 1998. English versions of Le monde de Mr Descartes; ou, Le traite de la lumiere. Paris, 1664.

Ptolemy's Almagest. Translated by G. J. Toomer. New York, 1984. Ptolemy's main work on mathematical astronomy. (See also Goldstein, above.)

Secondary Sources

Aiton, E. J. The Vortex Theory of Planetary Motions. London, 1972. Cartesian cosmology.

Ariew, Roger. Descartes and the Last Scholastics. Ithaca, N.Y, 1999. Presents Descartes in the context of Aristotelian responses to the new philosophy and science, including the work of Du Chevreul.

Barker, Peter, and Roger Ariew, eds. Revolution and Continuity: Essays in the History and Philosophy of Early Modern Science. Washington, D.C., 1991. Appraises the alleged discontinuity between medieval and modern science.

Biagioli, Mario. Galileo Courtier: The Practice of Science in the Culture of Absolutism. Chicago, 1993.

Dear, Peter. Revolutionizing the Sciences: European Knowledge and its Ambitions, 1500–1700. Princeton, 2001. Sound introduction that balances the contributions of canonical and noncanonical sciences.

Densmore, Dana. Newton's Principia: The Central Argument. Santa Fe, N.M., 1995. Translation, with notes, and expanded proofs of key mathematical arguments in Principia Mathematica (1687).

Osler, Margaret J., ed. Rethinking the Scientific Revolution. Cambridge, U.K., 2000. New historiography for early modern science.

Sutton, Geoffrey V. Science for a Polite Society: Gender, Culture, and the Demonstration of Enlightenment. Boulder, Colo., 1995. The social framework of Cartesian and Enlightenment science.

Westman, Robert S. "The Astronomer's Role in the Sixteenth Century: A Preliminary Survey." History of Science 18 (1980): 105–147. Classic study of the transition from university support to patronage support in early modern science.

PETER BARKER