In the 19th century the term science, which hitherto was applied to any body of systematic knowledge, came to denote an organized inquiry into the natural and physical universe. This article will be confined to this more recent and restrictive definition. SCIENCE IN THE ANCIENT WORLD Out of small beginnings that human enterprise called science emerged some five millennia ago among the evolving civilizations of the Near East--in Mesopotamia and along the Nile River. Undoubtedly, the original impulse for scientific activity was the need for technologies to satisfy material necessities. Thus, elementary forms of arithmetic, geometry, and astronomy developed in order to supply the growing needs of engineering, time reckoning, accounting, land measurement, and agriculture. The relatively sophisticated techniques of surgery and the extensive use of medicaments filled the needs of early medicine. Astronomical observations and numerical calculations became intricately involved with the emerging mystical and religious systems, thus resulting in the growth of astrology and numerology, particularly among the Babylonians and Assyrians. It would be simplistic, however, to claim that the need for technologies--both secular and religious--was the sole incentive for scientific activity, at least with regard to the later phases in the development of Near Eastern civilizations. By the middle of the 2d millennium BC, the accumulation of wealth and leisure brought about the introduction of curiosity as an important contributing factor in the domain of technology. Thus, attempts were made to solve a variety of numerical and algebraic equations that could have had no immediate practical uses and to discern the underlying patterns of empirical calculations. The Greeks It was the Greeks, however, who introduced high-powered geometry and rigorous reasoning, as well as speculations about the nature of the universe. The impetus for this scientific leap is usually attributed to \TThales of Miletus\t, a merchant who, by the beginning of the 6th century BC, had abandoned his vocation in favor of science. Thales' travels, no doubt, had acquainted him with the wide-ranging mathematical and astronomical achievements of the Egyptians and Babylonians, which he helped introduce into the Greek world. In addition, he initiated the practice of speculating freely on cosmology, positing water as the fundamental element out of which the universe was fashioned. For the next two centuries the \Tpre-Socratic\t philosophers continued to speculate about the nature of the physical world. Perhaps the most famous of their ideas involved the dichotomy between "Being" and "Becoming" associated with \THeraclitus\t and \TParmenides\t: the world as eternally changeless and the world as a place of perpetual motion. An alternative cosmology was offered by \TDemocritus\t, whose atomistic theory viewed the universe as a motionless void, interrupted only by islands of matter. Such matter was the product of the chance configuration of atoms--solid, indivisible, and eternal--which, owing to their different shapes and properties, produced the variety of existing substances as well as all sensations. The most important speculation for the future development of science was the number theory of the \TPythagoreans\t, which viewed numbers as the principle of all things. The Pythagorean number theory not only had enormous implications for the development of mathematics, but its assumption of an orderly, symmetric universe would inform future cosmology as scientists struggled to discover the shape of the Earth and the laws governing the motion of the heavenly bodies. The pre-Socratic predilection for speculative physical hypotheses eventually resulted in a reaction against science in the 4th century BC. \TSocrates\t blamed sterile speculation for the neglect of man as the important focus of nature; instead of the universe, the proper goal of human inquiry should be truth, justice, and virtue in human conduct. In his search for a program to facilitate this inquiry, Socrates developed a powerful dialectical reasoning as a method of attaining truth. Despite the antiscientific impetus behind Socrates' humanism, his dialectical method could be employed as a tool in the realm of nature as well. Such an application was demonstrated by Socrates' most distinguished pupil, \TPlato\t, who also had been greatly influenced by Pythagorean number theory--an influence that can be detected in his cosmology in the Timaeus. The fusion of these two traditions resulted the creation of Plato's doctrine of Forms, which postulated a realm of pure ideas, or essences, that existed above and beyond the illusory sensory world. Although Plato considered observations and experiments worthless, even harmful, to this domain of abstract ideas, he nevertheless believed that mathematics, which promised certitude and embodied pure ideas, was the proper pedagogical device for training the mind in the abstract reasoning necessary to comprehend the realm of Forms. This elevation of mathematics to the pinnacle of scientific activity extended Pythagorean influence over Greek mathematics, and eventually contributed to the role played by mathematics in modern science. One of the many talented mathematicians and astronomers to pass through Plato's Athenian Academy was \TEudoxus of Cnidus\t, whose theory of homocentric spheres contributed to the concept of planetary motion, and whose theories of magnitude and exhaustion helped to advance geometry. The most distinguished student to emerge from the Academy, however, was \TAristotle\t, who also turned out to be the most severe critic of Plato's doctrine of Forms as well as of his ideas about mathematics. Like Socrates and Plato before him, Aristotle stressed the importance of correct reasoning in the attainment of true knowledge. However, unlike his two predecessors, he replaced dialectic with syllogistic logic--the drawing of conclusions from assumed postulates--which became the core of the Aristotelian deductive method. The science that emerged from this was qualitative, strongly grounded in common sense, and its physics was purged of mathematics. Equally important, it distinguished sharply between the celestial and the terrestrial domains. The former was placed beyond the grasp of human experience, while the latter was organized into a comprehensive system that encompassed the entire gamut of human knowledge, from biology, zoology, and cosmology to ethics, politics, and metaphysics. Aristotelian cosmology was based on the notion of an enclosed cosmos comprising a series of concentric, crystalline spheres revolving around a stationary Earth. Motion was supposedly provided by the prime mover and, once initiated, would remain circular, uniform and eternal. Aristotle's biological ideas were perhaps the most original facet of his corpus, for they were based on his own profound firsthand observations and experiments. Hellenistic and Roman Science With the spread of Greek culture into the Near East in the 4th century BC, Alexandria in Egypt replaced Athens as the center of science. This shift was facilitated by the liberal patronage of learning and the erection of a magnificent library by the Ptolemaic rulers of Egypt. In Alexandria the golden age of Greek geometry reached its zenith. Both \TEuclid\t'S Elements of Geometry and the work on conic sections by his younger contemporary, \TApollonius of Perga\t, were carried out there. Even science outside Alexandria--such as Archimedean geometry and mechanics in Syracuse--was the product of men who studied in, or were influenced by, Alexandrian science. Greek astronomy underwent a similarly fruitful period in Alexandria, commencing with the work of \TAristarchus of Samos\t, whose \Theliocentric world system\t later became the basis for a similar one by \TCopernicus\t, and culminating in the 2d century AD with a magnificent astronomical synthesis, the Almagest, of \TPtolemy\t. Although the Romans incorporated much of Greek culture, they remained oblivious--if not outright disdainful--of Greek science. Essentially utilitarian in outlook, Roman civilization cared little for cosmological speculations, still less for Greek mathematical sciences, save for its application to engineering. What the Romans lacked in scientific curiosity and originality, however, they somewhat compensated for by a fascination with encyclopedic knowledge and technology. The two best examples are the massive compendium of knowledge of \TVarro\t, which would lay the foundation for the medieval classification of knowledge and system of education, and the colossal, and sometimes highly entertaining, compilation of natural phenomena called Natural History, by \TPliny the Elder\t. Although synthetic and for the most part derivative, these works conveniently amalgamated existing scientific knowledge. Another scientific writer of the Roman period was the Greek \TGalen\t of Pergamum (AD 130-200), whose survey of ancient anatomy, physiology, and medicine dominated European science until the 17th century. SRABO of Pontus (c. 63 BC-AD c. 21) and the Spaniard Pomponius Mela (1st century AD), both of whom worked in Rome, helped expand the field of geography. THE MIDDLE AGES AND THE RENAISSANCE The Christian church in the early Middle Ages was essentially ambivalent to Greek and pagan science and philosophy. The dilemma facing the early church fathers was both how to amalgamate the knowledge of "heathens" and how to define the boundaries between reason and faith. On the one hand, if Christianity was to compete for the minds, as well as the hearts, of Hellenists, Jews, and Romans, it could hardy afford to be too narrowly based on scripture. (Significantly, many of the early fathers were themselves educated in classical philosophy.) On the other hand, the fathers were also aware of the "corrupting" influence that the myriad of rational philosophies and mystical systems could exert upon the new region. A partial resolution to this problem was accomplished by St. \TAugustine\t in the 5th century AD. However, the chaos that resulted in Europe from the Germanic invasions and the collapse of the Western Roman Empire in the 5th century postponed the real debate about the role of pagan rationalistic science in a Christian society for at least another seven centuries. China and India In many areas of science during the Middle Ages the Chinese achieved advances well ahead of their European counterparts. Nevertheless, the Chinese were predominantly a technological, rather than a scientific, society. The reason may be found in Chinese philosophy. Taoism, and especially Confucianism, did not differentiate between the domains of human beings and nature. Instead, the world was conceived of as a vast organism in which the five "phases"--water, fire, metal, wood, and earth--and the two principal forces, yin and yang, were in constant interaction as they sought their affinities. The result was a predilection for mystical thinking, especially among Taoists. Conversely, the Confucians, who tended to dominate the scientific domain, embraced a utilitarian view of life, thus informing Chinese science with its predominantly technological character. Thus the Chinese had virtually no geometry (the forte of the Greeks), yet possessed a well-developed arithmetic and algebra, which apparently included even an acquaintance with the BINOMINAL THEOREM. In a similar manner, the Chinese demonstrated a flair for inventing calculating devices, such as the counting rod and the abacus, but showed no interest in developing a general theory of equations. This utilitarian bias is evident in other scientific domains as well. In astronomy the Chinese were diligent in their observations of the heavens, in reckoning time, and in developing instruments. Nevertheless, there occurred little sustained and independent discussion of cosmologies. Although the fields of chemistry and physics attracted much attention, virtually every discovery had a practical application. Finally, the development of a sophisticated corpus of medicine, much in advance of medieval European medicine, is yet another indication of their practical bent. Hindu science followed a somewhat different development. Before the 5th century BC, when Mesopotamian and Greek ideas began to infiltrate into India, Hindu astronomy was little more than primitive calendrical computation. Following a short period of flirtation with cosmologies, however, Hindu astronomy rapidly deteriorated again into practical astrology. In mathematics the Hindus, even more than the Chinese, developed a powerful arithmetic and algebra; they also showed a more than passing interest in geometry. Some significant work by Hindu mathematicians, including the so-called "Arabic" numerals, was later incorporated into Islamic science and eventually transmitted to Europe. The Islamic World In contrast to Chinese and Hindu science, Islamic science came to exert an immense influence on the West, partly because of the geographical proximity of the two cultures and partly because both cultures shared a common Greek heritage. Following a period of rapid conquest in the 7th and 8th centuries, an Arab Muslim empire was established in western Asia, north Africa, and Spain. By the second half of the 8th century, its rulers, the Abbasid caliphs in Baghdad, became munificent patrons of learning. In this role they both encouraged the collection and translation into Arabic of the huge corpus of Greek knowledge and generously supported scientific activity. One of the most notable scientists to benefit from their patronage was al-\TKindi\t, the driving force behind the creation of a new Islamic philosophy and the author of an important work in optics. A younger contemporary, al-\TBattani\t, was an astronomer who carried out his work in Baghdad, where an observatory had been constructed as early as AD 829. The Persian al-Kwarizmi introduced into Islamic science both Hindu numerals and algebra, as well as the Hindu model of astronomical tables. Other eminent scientists included the mathematicians Thabit ibn Qurra (c. 836-901) and Abu'l Wafa and a most original man of optics, Ibn al-Haytham (Alhazen; c. 965-1039). In medicine the practical work and encyclopedic compilations of al-Razi (Rhazes c. 1149-1209) and Ibn Sina (\TAvicenna\t) became enormously influential in Europe during the late Middle Ages and Renaissance. Also important was the alchemical corpus of Jabir ibn Hayyan (\TGeber\t), which introduced the discipline into Europe. Islamic science and philosophy emerged, in large part, in response to the Islamic theological assumption that nature contains "signs," and the unearthing of such signs would bring the believer closer to God. Thus, Islam witnessed a philosophical attempt to reconcile faith and reason that is reminiscent of the attempts of Christianity. However, a strong rationalistic trend, such as can be detected in al-Razi in the 10th century, or Ibn Rushd (\TAverroes\t) in the 12th, heralded a religious reaction against philosophy and science. This reaction, accompanied by the decay of western Islam from the 12th century, resulted in stagnation and the eventual decline of Islamic science and philosophy. In eastern Islam, however, the vitality continued into the 15th century. The Medieval West At the very time when a decline began in Islamic science, the Latin West was exhibiting a renewed interest in philosophical and scientific matters. Undoubtedly, the Christian reconquest of Spain and Sicily in the 11th century contributed to this revival, for the Christians were now able and willing to absorb the vast repository of Greek knowledge preserved in Arabic as well as to incorporate the original work of Muslim scientists during the previous three centuries. The result was a major movement involving the collection of manuscripts, their translation into Latin, and the addition of commentaries. The West thus regained not only the entire Aristotelian corpus, but also the works of Euclid and Ptolemy. For the next three centuries Europe's established universities would serve as centers for scientific studies, thereby helping to establish the undisputed authority of Aristotle. By the middle of the 13th century, Thomas \TAquinas\t produced a synthesis between Aristotelian philosophy and Christian doctrine. He stressed the harmony between reason and faith, thus establishing the foundation of natural theology. But the Thomist synthesis did not go unchallenged. In 1277, shortly after Aquinas's death, the archbishop of Paris condemned some 219 propositions (mainly of Aristotle) contained in his writings. As a result of this condemnation, the nominalist alternative associated with \TWilliam of Occam\t was developed; nominalism, which tended to separate science from theology, would become a cornerstone in the redefinition of the spheres of science and religion in the 17th century. During the 13th and 14th centuries, European scholars seriously undermined certain fundamental aspects of Aristotle's methodology and physics. The English Franciscans Robert \TGrosseteste\t and Roger \Tbacon\t introduced mathematics and the experimental method into the domain of science and also contributed to the discussion of vision and the nature of light and color. Their successors at Merton College, Oxford, introduced quantitative reasoning and physics via their novel treatment of accelerated motion. Across the Channel, in Paris, Jean \TBuridan\t and others elaborated on the concept of impetus, while Nicolas Oresme (1130-1382) introduced some bold views into astronomy that would open the door for the more speculative ideas of \TNicholas of Cusa\t concerning the motion of the Earth and the concept of an infinite universe. However, another two centuries would pass before this still largely scholastic discussion would be resumed. In the meantime, the Renaissance opened up new opportunities. Large numbers of Greek manuscripts were brought to the West by Byzantine refugees fleeing the Turks in the 15th century. The invention of printing made these books available in a new wave of editions and translations that revolutionized science. Architecture began to utilize, in new ways, the growing knowledge of perspective and anatomy, thus heralding a new breed of "scientists" who appreciated both the theoretical knowledge of the schools and the technologies to be learned from craftspersons and artisans. Indeed, it was the interaction between the scholarly tradition and the scientists' interest in practical technologies that set the stage for the scientific revolution. THE RISE OF MODERN SCIENCE The publication of Nicolaus \TCopernicus\t's \TDe\t REVOLUTIONIBUS ORBIUM COELESTIUM (On the Revolutions of the Heavenly Spheres) in 1543 is traditionally considered the inauguration of the scientific revolution. Ironically, Copernicus had no intention of introducing radical ideas into cosmology. His aim was only to restore the purity of ancient Greek astronomy by eliminating novelties introduced by Ptolemy. And with such an aim in mind he modeled his own book, which would turn astronomy upside down, on Ptolemy's Almagest. At the core of the Copernican system is the concept of the stationary Sun at the center of the universe, and the revolution of the planets, Earth included, around the Sun. The Earth was ascribed, in addition to an annual revolution around the Sun, a daily rotation around its axis. Copernicus's greatest achievement is his legacy. By introducing mathematical reasoning into cosmology, he dealt a severe blow to Aristotelian common-sense physics. His concept of an Earth in motion launched the notion of the Earth as a planet. And his explanation that he had been unable to detect stellar parallax because of the enormous distance of the sphere of the fixed stars opened the way for future speculation about an infinite universe. Nevertheless, Copernicus still clung to many traditional features of Aristotelian cosmology. He continued to advocate the entrenched view of the universe as a closed world and to see the motion of the planets as uniform and circular. Thus, in evaluating Copernicus's legacy, it should be noted that he set the stage for far more daring speculations than he himself could make. Brahe and Kepler Most of Copernicus's contemporaries regarded his heliocentric cosmology as bold and unwarranted speculation; it gained converts in the scientific community before the early 17th century. A major impediment to its reception was the existence of yet another planetary theory that took a stance halfway between the Ptolemaic and Copernican systems. This rival theory was devised by the Danish nobleman Tycho \TBrahe\t, who was the greatest observational astronomer since Ptolemy. Brahe's detailed observations of the appearance of an "new star" (nova) in 1572, and a comet five years later, called into question the notion of immutability of the heavens. His observations convincingly demonstrated not only that both events occurred well above the allegedly perfect and uncorruptible lunar region, but that crystalline spheres could not exist since the path of the comet would have to cut through them. Despite this rejection of certain elements of traditional astronomy and physics, Brahe nevertheless refused to accept the reality of heliocentrism. Instead, he devised an alternative system according to which the five planets indeed revolved around the Sun, but, in turn, the entire system revolved around the stationary Earth and Moon. The fame of Brahe, combined with his construction of a system capable of accommodating all observable phenomena, caused many who were wary of Copernicanism, yet equally dissatisfied with the Ptolemaic system, to adopt Brahe's alternative theory. Johannes \TKepler\t, who succeeded Brahe as mathematician to the Holy Roman emperor Rudolf II, used the data amassed by his predecessor to vindicate Copernicanism and transform modern astronomy. A deeply pious man who believed that the glory of God was manifest in his creation, Kepler found in astronomy a religious vocation. His piety was matched by his commitment to Copernicanism and Renaissance Neoplatonism, both of which spurred his indefatigable search for harmonious patterns he knew must exist in the heavens. The immediate result of his quest was the discovery of his three planetary laws. The first two--formulated in his Astronomia nova (The New Astronomy) of 1609--destroyed the theory of circular and uniform motion. The first law stated that all planets move in elliptical orbits when the Sun is at one focus of the ellipse. The second stated that the velocity of a planet drops as its distance from the Sun increases, so that if a line were to be drawn from the planet to the Sun, equal areas in space would be swept in equal times. Ten years later Kepler published his third law in the Harmonice mundi (The Harmony of the World), announcing the symmetry he so longed for: the squares of the times it takes any two planets to complete their revolution around the Sun are proportional to the cubes of their average distance from the Sun. Galileo The heavy metaphysical underpinning of Kepler's laws, combined with an obscure style and a demanding mathematics, caused most contemporaries to ignore his discoveries. Even his Italian contemporary \TGalileo\t, who corresponded with Kepler and possessed his books, never referred to the three laws. Instead, Galileo provided the two important elements missing from Kepler's work: a new science of dynamics that could be employed in an explanation of planetary motion, and a staggering new body of astronomical observations. The observations were made possible by the invention of the telescope in Holland c. 1698 and by Galileo's ability to improve on this instrument without ever having seen the original. Thus equipped, he turned his telescope skyward, and saw some spectacular sights. The results of his discoveries were immediately published in the Sidereus nuncius (The Starry Messenger) of 1610. Galileo observed that the Moon was very similar to the Earth, with mountains, valleys, and oceans, and not at all that perfect, smooth spherical body it was claimed to be. He also discovered four moons orbiting Jupiter. As for the Milky Way, instead of being a stream of light, it was, rather, a large aggregate of stars. Later observations resulted in the discovery of sunspots, the phases of Venus, and that strange phenomenon which would later be designated as the rings of Saturn. Having announced these sensational astronomical discoveries-- which reinforced his conviction of the reality of the heliocentric theory--Galileo resumed his earlier studies of motion. He now attempted to construct a comprehensive new science of mechanics necessary in a Copernican world, and the results of his labors were published in Italian in two epochmaking books: Dialogue Concerning the Two Chief World Systems (1632) and Discourses and Mathematical Demonstrations Concerning Two New Sciences (1638). His studies of projectiles and free-falling bodies brought him very close to the full formulation of the laws of inertia and acceleration (the first two laws of Isaac \TNewton\t). Galileo's legacy includes both the modern notion of "laws of nature" and the idea of mathematics as nature's true language. He contributed to the mathematization of nature and the geometrization of space, as well as to the mechanical philosophy that would dominate the 17th and 18th centuries. Perhaps most important, it is largely due to Galileo that experiments and observations serve as the cornerstone of scientific reasoning. Today, Galileo is remembered equally well because of his conflict with the Roman Catholic church. His uncompromising advocacy of Copernicanism after 1610 was responsible, in part, for the placement of Copernicus' De revolutionibus on the Index of Forbidden Books in 1616. At the same time, Galileo was warned not to teach or defend Copernicanism in public. The election of Galileo's friend Maffeo Barberini as Pope Urban VIII in 1624 filled Galileo with the hope that such a verdict could be revoked. With perhaps some unwarranted optimism, Galileo set to work to complete his Dialogue (1632). However, Galileo underestimated the power of the enemies he had made during the previous two decades, particularly some Jesuits who had been the target of his acerbic tongue. The outcome was that Galileo was summoned to Rome and there forced to abjure, on his knees, the views he had expressed in his book. Ever since, Galileo has been portrayed as a victim of a repressive church and a martyr in the cause of freedom of thought; as such he has become a powerful symbol. Newton Despite his passionate advocacy of Copernicanism and his fundamental work in mechanics, Galileo continued to accept the age-old views that planetary orbits were circular and the cosmos an enclosed world. These beliefs, as well as a reluctance rigorously to apply mathematics to astronomy as he had previously applied it to terrestrial mechanics, prevented him from arriving at the correct law of inertia. Thus, it remained for Isaac \TNewton\t to unite heaven and earth in his immense intellectual achievement, the Philosophiae naturalis principia mathematica (Mathematical Principles of Natural Philosophy), which was published in 1687. The first book of the Principia contained Newton's three laws of motion. The first expounds the law of inertia: every body persists in a state of rest or uniform motion in a straight line unless compelled to change such a state by an impressing force. The second is the law of acceleration, according to which the change of motion of a body is proportional to the force acting upon it and takes place in the direction of the straight line along which that force is impressed. The third, and most original, law ascribes to every action an opposite and equal reaction. These laws governing terrestrial motion were extended to include celestial motion in book 3 of the Principia, where Newton formulated his most famous law, the law of gravitation: every body in the universe attracts any other body with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The Principia is deservedly considered one of the greatest scientific masterpieces of all time. But in 1704, Newton published this second great work, the Opticks, in which he formulated his corpuscular theory of light and his theory of colors. In later editions Newton appended a series of "queries" concerning various related topics in natural philosophy. These speculative, and sometimes metaphysical, statements on such issues as light, heat, ether, and matter became most productive during the 18th century, when the book and the experimental method it propagated became immensely popular. The Life Sciences Although not as spectacular as the developments in the mathematical and physical sciences, the biological and life sciences also produced some important developments in this period. In 1543, the very year in which Copernicus's masterpiece appeared, Andreas \TVesalius\t published his De humani corpuris fabrica (On the Fabric of the Human Body). The book was seminal to the development of anatomy, for it both provided a far more accurate and detailed account of the organs and structure of the human body (based upon Vesalius's own dissections) and included superb illustrations that were a vast improvement on any other available text. It remained for the Englishman William \THarvey\t, however, to use this anatomical knowledge and respect for detail to bring about a major discovery concerning the human body. In 1628, Harvey, in his De Motu cordis et sanguinis (On Motion of the Heart and Blood), set out his discovery of the circulation of the blood. Basing his theory on the fact that the heart pumps more blood in one hour than is contained in the entire human body, Harvey also introduced quantitative reasoning into biology. Additional discoveries had to await the invention of the microscope in mid-century, for even Harvey could not prove the existence of the passages between the arteries and veins he had predicted. The capillaries were first seen in 1661 by the Italian Marcello \TMalpighi\t. The following decades witnessed a series of microscopical observations by English and Dutch scientists, notably Robert \THooke\t, Nehemiah \TGrew\t, Antoni van \TLeeuwenhoek\t and Jan \TSwammerdam\t. Such observations brought about important discoveries in the study of blood, insects, embryology, and plant physiology. Despite these advances, however, there was still little attempt to transcend the level of empirical observations and provide a theoretical framework. Modern biology was to be born only in the middle of the 19th century. The Effects of the Scientific Revolution It must be stressed that the scientific revolution was more than a series of spectacular accomplishments by individual scientists. The invention of printing in the second half of the 15th century transformed science, as it did every other scholarly discipline. It enabled the rapid diffusion and dissemination of new scientific ideas to a rapidly growing literate public. In a similar way, the mathematization of nature and the emergence of experimental science would have been inconceivable without the invention of a variety of instruments--including the telescope, the microscope, time-keeping devices, thermometers, and the air pump--which allowed large numbers of people to carry out the observations, measurements, and experiments upon which scientific theories were constructed. Finally, the 17th century marked the beginning of the institutionalization and professionalization of science, which continued until the 19th century. The foundation of national scientific societies (London, 1660; Paris 1666; Berlin, 1700; St. Petersbury, 1724) was crucial for the formation of group identity and solidarity. Most important, these societies served as clearing houses for ideas and experiments, perfected rules and regulations for their evaluation, and generated interaction and collaboration between like-minded researchers. To such societies is also owed the development of scientific periodicals, the wide distribution of which was an important factor in the diffusion and propagation of scientific knowledge. The impact of the Newtonian accomplishment was enormous. Newton's two great books resulted in the establishment of two traditions that, though often mutually exclusive, nevertheless permeated into every area of science. The first was the mathematical and reductionist tradition of the Principia, which like Rene \TDescartes\t' mechanical philosophy, propagated a rational, well-regulated image of the universe. The second was the experimental tradition of the Opticks, somewhat less demanding than the mathematical tradition, owing to the speculative and suggestive queries appended to the Opticks, highly applicable to chemistry, biology, and the other new scientific disciplines that began to flourish in the 18th century. This is not to imply that everyone in the scientific establishment was, or would be, a Newtonian. Newtonianism had its share of detractors. Rather, the Newtonian achievement was so great, and its applicability to other disciplines so strong, that although Newtonian science could be argued against, it could not be ignored. In fact, in the physical sciences an initial reaction against universal gravitation occurred. For many, the concept of action at a distance seemed to hark back to those occult qualities which the mechanical philosophy of the 17th century had done away with. By the second half of the 18th century, however, universal gravitation would be proved correct, thanks to the work of Leonhard \TEuler\t, A.C. \TClairaut\t and Pierre Simon de \TLaplace\t, the last of whom announced the stability of the solar system in his masterpiece Celestial Mechanics (1799-1825). Newton's influence was not confined to the domain of the natural sciences. The \Tphilosophes\t of the 18th-century \TEnlightenment\t sought to apply scientific methods to the study of human society. To them, the empiricist philosopher John Locke was the first person to attempt this. They believed that in his Essay on Human Understanding (1690) Locke did for the human mind what Newton had done for the physical world. Although Locke's psychology and epistemology was to come under increasing attack as the 18th century advanced, other thinkers such as Adam Smith, David Hume, and Abbe de Condillac would aspire to become the Newtons of the mind or the moral realm. These confident, optimistic men of the Enlightenment argued that there must exist universal human laws that transcend differences of human behavior and the variety of social and cultural institutions. Laboring under such an assumption, they sought to uncover these laws and apply them to the new society they hoped to bring about. As the 18th century progressed, the optimism of the philosophes waned and a reaction began to set in. Its first manifestation occurred in the religious realm. The mechanistic interpretation of the world--shared by Newton and Decartes-- had, in the hands of the philosophes, led to materialism and atheism. Thus, by mid-century the stage was set for a revivalist movement, which took the form of Methodism in England and Pietism in Germany. By the end of the century the romantic reaction had begun. Fueled in part by religious revivalism, the romantics attacked the extreme rationalism of the Enlightenment, the impersonalization of the mechanistic universe, and the contemptuous attitude of "mathematicians" toward imagination, emotions, and religion. The romantic reaction, however, was not antiscientific; its adherents rejected a specific type of the mathematical sciences, not the entire enterprise. In fact, the romantic reaction, particularly in Germany, would give rise to a creative movement--the Naturphilosophie--that in turn would be crucial for the development of the biological and life sciences in the 19th century, and would nourish the metaphysical foundation necessary for the emergence of the concepts of energy, forces, and conservation. THE NINETEENTH AND TWENTIETH CENTURIES The theory of \Tevolution\t owes its emergence to developments in a variety of fields, including the previously mentioned Naturphilosophie. Owing in large part to the cosmological theories of Immanuel Kant, Thomas Wright (1711-1786), and Laplace in the second half of the 18th century, people now began to realize that the universe had to be far older than the 6,000 years computed by chronologers on the basis of the Book of Genesis. Some wished to resolve this problem by separating the history of the Earth from the history of the universe, and thus exempt the story of creation from scientific scrutiny. Another conservative view was promoted by Abraham \TWerner\t, a renowned German geologist and minerologist, who argued that the Earth once had covered by a primordial ocean, and that all rocks were formed, either as sediments or by precipitation, following its regression. This "Neptunist" theory fit in with the biblical story of the deluge--although Werner did concede that the earth might be a million years old--but it failed to account for the disappearance of this ocean. A more radical stance was taken by the Scot James \THutton\t in his Theory of the Earth (1795). In his "Vulcanist" theory, Hutton insisted that only forces operative in nature today could account for the shape of the Earth and the formation of rocks, and therefore volcanic activity in the crust of the earth must have been the shaping mechanism at work. This "uniformitarianism" theory demanded an even longer period for the Earth's creation and omitted altogether any catastrophic flood. (See also \Tcatastrophism\t; \Tuniformitarianism\t.) Theorizing of this sort gave way to more sophisticated concepts of Earth time as the science of geology advanced. The development of stratigraphy made possible the identification of the types of rock strata according to fossil deposits, thereby allowing for a closer estimation of the age of the rocks. Further strides in geology and paleontology would allow closer investigation of these deposited fossils, their ages, and their evolution. The Darwinian Theory In many way Newton's relationship to the scientific revolution paralleled the relationship of Charles \TDarwin\t to 19th century science. Like Newton, Darwin amalgamated ideas and concepts from a variety of disciplines, synthesizing them into a coherent and powerful theory. In Darwin's case, this was the theory of evolution. Evolutionary ideas had been in the air for some time. Charles' own grandfather, Erasmus \TDarwin\t, had already argued in the late 18th century that competition for resources could explain evolution, while the Frenchman Jean Baptiste \TLamarck\t had developed the alternative view that inheritance of acquired characteristics was the determining factor in the evolution of species. Equally important for Darwin's formative ideas was the powerful model of evolution provided by geology. Hence, when Darwin embarked upon his epoch-making voyage aboard the Beagle, his mind was primed to appreciate the botanical, zoological, and geological structures he was to encounter in South America. In 1838, two years after he returned from his voyage, Darwin read Thomas Malthus' An Essay on the Principle of Population (1798), which provided him with the mechanism necessary to explain evolution--natural selection. Twenty years later, Darwin published his theory in On the Origin of Species (1859). He emphasized the geographical distribution of species in time and space, pointing out the enormous rate of extinction of species unable to adapt themselves to environmental changes. Survival in nature, he claimed, was determined by natural selection, which caused selective adaptation over long periods of time, thereby ensuring that favorable modifications were transmitted to future generations. (Herbert \TSpencer\t later called this idea "the survival of the fittest.") Those species which survived evolved into higher forms of life. Eventually humans took their place in this evolutionary framework: in his Descent of Man (1871) Darwin argued that they too had evolved from a lower form. He was unable, however, to account for the mechanism that permitted the transmission of the favorable characteristics. Ironically, in 1865, Gregor \TMendel\t announced his discovery of just such a mechanism--heredity--but his idea was allowed to sink into obscurity until 1900. Nineteenth Century Physics Despite the overriding significance of Darwinian theory, other important developments also took place during the 19th century. Fundamental work was carried out in physics, thus bringing classical physics to a pinnacle--only to be toppled by the turn of the century. Early in the century the study of light had undergone a major transformation when the research of Thomas \TYoung\t and Augustine \TFresnel\t replaced Newton's corpuscular theory with a wave theory of light. The study of heat also generated much interest during the first half of the century, culminating in the formulation of the principle of the conservation of energy by Hermann \THelmholtz\t in 1847, and the first two laws of thermodynamics by Rudolf \TClausius\t in 1859. Equally revolutionary was the work of Michael \TFaraday\t and James Clerk \TMaxwell\t in generating the theory of \Telectromagnetism\t; the discovery of X rays by Wilhelm \TRoentgen\t in 1895; and the discovery of the electron by Joseph John \TThomson\t some two years later. All of these developments contributed to the revolution in physics that took place in the following decade. Biology and Chemistry Rapid advances were taking place in other fields as well. The combined effect of the metaphysical foundations that had been laid by the romantic movement, and the perfection of microscopy, resulted in the birth of modern biology. Most important was the realization that the cell constitutes the fundamental unit in organic bodies. It was Theodor \TSchwann\t who announced the new cell theory in 1839. Then in rapid succession came the discovery of protoplasm as the constituent material of the cell, of the production of new cells as the result of division of existing cells and of the structure and composition of the cell nucleus; in addition, chromosomes were identified within this nucleus. The research of Karl Ernst von \TBaer\t revived epigenesis--the evolutionary growth of the embryo from the female egg fertilized by the male sperm--a theory that was originated by William Harvey in 1651 but, during the 18th century, lost ground to the rival preformationist theory, which viewed embryonic development as the unfolding of already existing forms. In chemistry, following the overthrow by Antoine \TLavoisier\t of the phlogiston theory, John \TDalton\t developed his atomic theory in the early years of the 19th century, thus enabling chemists to calculate the relative weight of atoms. It was also during these early years of the century that Amedeo \TAvogadro\t formulated his hypothesis concerning the binding together of atoms into molecules--a theory not accepted, however, until the 1860s. By 1858, F. A. \TKekule von Stradonitz\t had discovered the structure of the organic compound; Dimitry \TMendeleyev\t's discovery of the periodic law followed in the next decade. The Professionalization of Science The major scientific developments that took place during the 19th and 20th centuries would have been inconceivable without the total transformation of the way science was conducted. One of the most dramatic changes involved the shift of scientific activity away from the domain of the secluded--sometimes amateur--mathematician or natural philosopher to the sphere of professional science as it is known today. As mentioned earlier, this process began in the 17th century when science was just gaining its autonomy and the scientific community began to band together into institutions that would cultivate and promote science, develop codes and procedures regulating research, and generally oversee conduct and publications. However, what began as an association of like-minded private individuals had become a large-scale industry by the beginning of the 19th century; science would no longer be the disinterested study it had hitherto been, but a matter of national importance, glory, and profit. Hand-in-hand with increasing institutionalization and professionalization of science came the inevitable formation of disciplinary boundaries. The "natural philosophers" that dominated the early modern period gave way to scientific specialists in the 19th century. Thus, by the end of the 18th century chemistry and geology had been added to the ancient disciplines of mathematics and astronomy; physics and biology followed in the 19th century. This emergence of disciplines certainly reflected the specialization of scientific knowledge that took place during these centuries; it also reflected the specialization of scientific knowledge that took place during these centuries; but it also reflected, however, the changes that were occurring within the universities--where scientific inquiry was to be increasingly concentrated--such as the establishment of departments and professorships and the increasing competition for resources. This fragmentation of the scientific establishment accelerated rapidly during the 20th century, fueled by the attempts of various practitioners who shared a special body of knowledge, methodology, or technique to differentiate themselves from other practitioners. And while this search for a distinct scientific identity was in part justified by differing attitudes toward scientific issues, the intensified scramble for funds, positions, and students cannot be ignored as an important motive. The French Revolution (1789-99) in large part triggered the dramatic transformation that occurred in scientific and technological education. In an attempt to harness the fruits of revolution to the service of the state, the French republican government initiated the establishment of technical and engineering colleges--in which both professors and students would be salaried by the state--that were intended for the instruction of pure as well as applied science. The lead in this development, however, shifted rapidly to Germany where, following the humiliating German defeats by Napoleon, a major reorganization took place. Owing largely to the work of Wilhelm von Humboldt, a new type of university emerged-- controlled and financed by the state but allowing its professors complete freedom. The result was to transform the German universities into pure research centers and eventually into the site of major research laboratories. This phenomenon was accompanied by the foundation of dozens of technical schools for such subjects as mining, textiles, and engineering. By 1900, German universities and scientific laboratories had become the best in the world, drawing students from all over Europe as well as from the United States. Germany's example prompted other governments to emulate its scientific educational establishment, especially as it became increasingly clear that such academic and technical excellence was giving Germany an important industrial and military advantage. Thus, by the end of the 19th century, science had once again become a university-based activity. Science and Technology These organizational developments were closely tied to the growing role of science in developing technologies. While science per se had relatively little to do with bringing about the Industrial Revolution, by the 19th century science rather than empiricism was at the core of technological advance. In particular, the emergence of chemistry created new opportunities for industry via the discovery of a variety of synthetic dyestuffs, which resulted in the mass production of textiles. Electromagnetism was the next field to generate major industrial opportunities: the dynamo, the telegraph, and the electric light are only a few early examples in a field that with increasing rapidity would provide new and better sources of power. The relationship between science and technology was not one-sided. Science not only assisted technology; it became a major beneficiary of technology, which made available a variety of instruments and apparatuses without which many of the discoveries of the late 19th and 20th centuries would have been impossible. Optical instruments were crucial for both the biological sciences and astronomy, as was photographic equipment. By the 20th century there had evolved an intricate, mutually dependent, relationship between the domains of science and technology. In addition, the very fact that science was now operating on such a large scale meant that no individual could afford to engage in science without major financial support from state or industry. Thus, the development of science as the product of laboratories and its reliance on expensive equipment necessitated the placement of scientific activity on a new, more secure footing than had ever previously existed. Science in the 20th Century It is within the context of this major transformation of the scientific enterprise into a rich, confident industry involving researchers and students that 20th-century science should be viewed. Some commentators have even tended to regard the last century or so as the real period of the scientific revolution. Not only is the output of science being doubled every 15 years or so, but 90 percent of all scientists who have ever lived are still alive today. It is certainly undeniable that 20th-century science is vastly different from the science of previous centuries. The 20th century opened with a new revolution in physics; it continued with a radical alteration of the knowledge of the origins and shape of the universe and a new image of the planet Earth. And perhaps its culmination will be the complete understanding of the innermost constituents and workings of the human mind and body. In 1900, Max \TPlanck\t promulgated his revolutionary idea that energy is not emitted continuously, but in discrete quanta, or packets, proportional to the frequency of radiation. Coming only three years after J. J. Thompson's discovery of the electron, Planck's idea would become crucial in the future study of the atom. But first an even greater revolution had to unfold: \TEinstein\t's demonstration of the special theory of relativity in 1905. The theory stated that all physical laws are the same for all inertial observers, and that the speed of light is the same for all observers, irrespective of the light source or the observers' motion. Thus, the notion of absolute space and time was abolished and the intercovertibility of mass and energy demonstrated, as expressed in the famous equation E=mc2. Ten years later Einstein proceeded with the general theory of \Trelativity\t, and Werner \THeisenberg\t introduced his uncertainty principle in 1927. In astronomy the work of the American Edwin Powell \THubble\t in the 1920s also dramatically shifted concepts of the universe. He demonstrated that the universe is not only composed of innumerable galaxies, but that it is expanding, and that velocity of the receding galaxies is proportional to their distances. Such a theory naturally sparked renewed interest in the issue of how the universe began. By reversing the calculation of the receding galaxies, it was possible to ascribe to the universe an age of some 20 billion years; at the beginning of that time it existed in a state of extreme density and immense temperature. Then, following a gigantic explosion--the so-called big \Tbig bang\t--a process of cooling ensued, atoms were created and distributed in space, and the universe began its expansion. During the 1910s, Alfred Lothar \TWegener\t focused on the question of Earth history in his \Tcontinental drift\t theory. According to Wegener, up until 200 million years ago the land on Earth was in the shape of a supercontinent that he called Pangaea (Greek, "all land"); the supercontinent broke into several pieces which then drifted apart to form the present continents. Wegener, however, was unable to provide any satisfactory mechanism to explain this phenomenon, and it was not until after his death in 1930 that the results of experimental work introduced the new science of \Tplate tectonics\t, which was capable of explaining such changes in the Earth's structure. Finally, the study of life took a leap forward in the first decade of the 20th century when the results of research into the cell nucleus and the rediscovery of Mendel's heredity theory brought about thew development of \Tgenetics\t. Once the chromosomes had been established as housing the hereditary material, intensive research was directed at identifying the chemical material of the genes. The subsequent discovery that the chromosomes contained protein and nucleic acid set in motion a new race to discover the exact genetic structure; the first to penetrate this mystery were Francis \TCrick\t and James \TWatson\t, who worked out the "double helix" structure of \TDNA\t. Efforts to further break down the genetic code have continued to the present, helping not only to refine the knowledge of heredity and evolution, but to create yet another point of contact between science and technology--\Tgenetic engineering\t. Mordechai Feingold Bibliography: Ben David, Joseph, The Scientist's Role in Society, 2d ed. (1984); Chalmers, Alan, What is This Thing Called Science? (1985); Cohen, Morris R., Reason and Nature: An Essay on the Meaning of Scientific Method (1931; repr. 1985); Giere, R. N., Understanding Scientific Reasoning, 2d ed. (1984); Gillespie, Charles, The Edge of Objectivity (1960); Goodlad, J. S., Science for Non-Scientists (1983); Harre, R., The Philosophies of Science (1972); Jeffreys, Harold, Scientific Inference, 3d ed. (1973); Kline, Morris, Mathematics in Western Culture (1964); Kuhn, Thomas S., The Structure of Scientific Revolutions, 2d ed. (1970); Latakos, Imre, and Musgrave, A., Criticism and the Growth of Knowledge (1970); Lindberg, David, ed., Science in the Middle Ages (1978); Lindberg, David, and Numbers, Ron, eds., God and Nature (1986); Lloyd, G. E. R., Early Greek Science (1970); Mason, Stephen F., A History of the Sciences (1962); Morris, Richard, Dismantling the Universe (1983); Nasr, Seyyed H., Science and Civilization in Islam (1968); Needham, Joseph, Science and Civilization in Islam, 6 vols. to date (1954-86); Neugebauer, Otto, The Exact Sciences in Antiquity (1957); Richards, Stewart, Philosophy and Sociology of Science (1984); Whitley, Richard, The Intellectual and Social Organization of the Sciences (1984). See also: \Tastronomy, history of\t; \Tbiology\t; \Tbotany\t; \Tchemistry, history of\t; \Tmathematics, history of\t; \Tphysics, history of\t.