Some famous Scientists Biography

Albert Einstein

INTRODUCTION

Einstein, Albert (1879-1955), German-born American physicist and Nobel laureate, best known as the creator of the special and general theories of relativity and for his bold hypothesis concerning the particle nature of light. He is perhaps the most well-known scientist of the 20th century.

HIS LIFE

Einstein was born in Ulm on March 14, 1879, and spent his youth in Munich, where his family owned a small shop that manufactured electric machinery. He did not talk until the age of three, but even as a youth he showed a brilliant curiosity about nature and an ability to understand difficult mathematical concepts. At the age of 12 he taught himself Euclidean geometry.

Einstein hated the dull regimentation and unimaginative spirit of school in Munich. When repeated business failure led the family to leave Germany for Milan, Italy, Einstein, who was then 15 years old, used the opportunity to withdraw from the school. He spent a year with his parents in Milan, and when it became clear that he would have to make his own way in the world, he finished secondary school in Arrau, Switzerland, and entered the Swiss National Polytechnic in Zürich. Einstein did not enjoy the methods of instruction there. He often cut classes and used the time to study physics on his own or to play his beloved violin. He passed his examinations and graduated in 1900 by studying the notes of a classmate. His professors did not think highly of him and would not recommend him for a university position.

For two years Einstein worked as a tutor and substitute teacher. In 1902 he secured a position as an examiner in the Swiss patent office in Bern. In 1903 he married Mileva Maric, who had been his classmate at the polytechnic. They had two sons but eventually divorced. Einstein later remarried.

EARLY SCIENTIFIC PUBLICATIONS

In 1905 Einstein received his doctorate from the University of Zürich for a theoretical dissertation on the dimensions of molecules, and he also published three theoretical papers of central importance to the development of 20th-century physics. In the first of these papers, on Brownian motion, he made significant predictions about the motion of particles that are randomly distributed in a fluid. These predictions were later confirmed by experiment.

The second paper, on the photoelectric effect, contained a revolutionary hypothesis concerning the nature of light. Einstein not only proposed that under certain circumstances light can be considered as consisting of particles, but he also hypothesized that the energy carried by any light particle, called a photon, is proportional to the frequency of the radiation. The formula for this is E = hv, where E is the energy of the radiation, h is a universal constant known as Planck's constant, and v is the frequency of the radiation. This proposal—that the energy contained within a light beam is transferred in individual units, or quanta—contradicted a hundred-year-old tradition of considering light energy a manifestation of continuous processes. Virtually no one accepted Einstein's proposal. In fact, when the American physicist Robert Andrews Millikan experimentally confirmed the theory almost a decade later, he was surprised and somewhat disquieted by the outcome.

Einstein, whose prime concern was to understand the nature of electromagnetic radiation, subsequently urged the development of a theory that would be a fusion of the wave and particle models for light. Again, very few physicists understood or were sympathetic to these ideas.

EINSTEIN'S SPECIAL THEORY OF RELATIVITY

Einstein's third major paper in 1905, "On the Electrodynamics of Moving Bodies," contained what became known as the special theory of relativity. Since the time of the English mathematician and physicist Sir Isaac Newton, natural philosophers (as physicists and chemists were known) had been trying to understand the nature of matter and radiation, and how they interacted in some unified world picture. The position that mechanical laws are fundamental has become known as the mechanical world view, and the position that electrical laws are fundamental has become known as the electromagnetic world view. Neither approach, however, is capable of providing a consistent explanation for the way radiation (light, for example) and matter interact when viewed from different inertial frames of reference, that is, an interaction viewed simultaneously by an observer at rest and an observer moving at uniform speed.

In the spring of 1905, after considering these problems for ten years, Einstein realized that the crux of the problem lay not in a theory of matter but in a theory of measurement. At the heart of his special theory of relativity was the realization that all measurements of time and space depend on judgments as to whether two distant events occur simultaneously. This led him to develop a theory based on two postulates: the principle of relativity, that physical laws are the same in all inertial reference systems, and the principle of the invariance of the speed of light, that the speed of light in a vacuum is a universal constant. He was thus able to provide a consistent and correct description of physical events in different inertial frames of reference without making special assumptions about the nature of matter or radiation, or how they interact. Virtually no one understood Einstein.

EARLY REACTIONS TO EINSTEIN

The difficulty that others had with Einstein's work was not because it was too mathematically complex or technically obscure; the problem resulted, rather, from Einstein's beliefs about the nature of good theories and the relationship between experiment and theory. Although he maintained that the only source of knowledge is experience, he also believed that scientific theories are the free creations of a finely tuned physical intuition and that the premises on which theories are based cannot be connected logically to experiment. A good theory, therefore, is one in which a minimum number of postulates is required to account for the physical evidence. This sparseness of postulates, a feature of all Einstein's work, was what made his work so difficult for colleagues to comprehend, let alone support.

Einstein did have important supporters, however. His chief early patron was the German physicist Max Planck. Einstein remained at the patent office for four years after his star began to rise within the physics community. He then moved rapidly upward in the German-speaking academic world; his first academic appointment was in 1909 at the University of Zürich. In 1911 he moved to the German-speaking University at Prague, and in 1912 he returned to the Swiss National Polytechnic in Zürich. Finally, in 1914, he was appointed director of the Kaiser Wilhelm Institute for Physics in Berlin.

THE GENERAL THEORY OF RELATIVITY

Even before he left the patent office in 1907, Einstein began work on extending and generalizing the theory of relativity to all coordinate systems. He began by enunciating the principle of equivalence, a postulate that gravitational fields are equivalent to accelerations of the frame of reference. For example, people in a moving elevator cannot, in principle, decide whether the force that acts on them is caused by gravitation or by a constant acceleration of the elevator. The full general theory of relativity was not published until 1916. In this theory the interactions of bodies, which heretofore had been ascribed to gravitational forces, are explained as the influence of bodies on the geometry of space-time (four-dimensional space, a mathematical abstraction, having the three dimensions from Euclidean space and time as the fourth dimension).

On the basis of the general theory of relativity, Einstein accounted for the previously unexplained variations in the orbital motion of the planets and predicted the bending of starlight in the vicinity of a massive body such as the sun. The confirmation of this latter phenomenon during an eclipse of the sun in 1919 became a media event, and Einstein's fame spread worldwide.

For the rest of his life Einstein devoted considerable time to generalizing his theory even more. His last effort, the unified field theory, which was not entirely successful, was an attempt to understand all physical interactions—including electromagnetic interactions and weak and strong interactions—in terms of the modification of the geometry of space-time between interacting entities.

Most of Einstein's colleagues felt that these efforts were misguided. Between 1915 and 1930 the mainstream of physics was in developing a new conception of the fundamental character of matter, known as quantum theory. This theory contained the feature of wave-particle duality (light exhibits the properties of a particle, as well as of a wave) that Einstein had earlier urged as necessary, as well as the uncertainty principle, which states that precision in measuring processes is limited. Additionally, it contained a novel rejection, at a fundamental level, of the notion of strict causality. Einstein, however, would not accept such notions and remained a critic of these developments until the end of his life. "God," Einstein once said, "does not play dice with the world."

WORLD CITIZEN

After 1919, Einstein became internationally renowned. He accrued honors and awards, including the Nobel Prize in physics in 1921, from various world scientific societies. His visit to any part of the world became a national event; photographers and reporters followed him everywhere. While regretting his loss of privacy, Einstein capitalized on his fame to further his own political and social views.

The two social movements that received his full support were pacifism and Zionism. During World War I he was one of a handful of German academics willing to publicly decry Germany's involvement in the war. After the war his continued public support of pacifist and Zionist goals made him the target of vicious attacks by anti-Semitic and right-wing elements in Germany. Even his scientific theories were publicly ridiculed, especially the theory of relativity.

When Hitler came to power, Einstein immediately decided to leave Germany for the United States. He took a position at the Institute for Advanced Study at Princeton, New Jersey. While continuing his efforts on behalf of world Zionism, Einstein renounced his former pacifist stand in the face of the awesome threat to humankind posed by the Nazi regime in Germany.

In 1939 Einstein collaborated with several other physicists in writing a letter to President Franklin D. Roosevelt, pointing out the possibility of making an atomic bomb and the likelihood that the German government was embarking on such a course. The letter, which bore only Einstein's signature, helped lend urgency to efforts in the U.S. to build the atomic bomb, but Einstein himself played no role in the work and knew nothing about it at the time.

After the war, Einstein was active in the cause of international disarmament and world government. He continued his active support of Zionism but declined the offer made by leaders of the state of Israel to become president of that country. In the U.S. during the late 1940s and early '50s he spoke out on the need for the nation's intellectuals to make any sacrifice necessary to preserve political freedom. Einstein died in Princeton on April 18, 1955.

Einstein's efforts in behalf of social causes have sometimes been viewed as unrealistic. In fact, his proposals were always carefully thought out. Like his scientific theories, they were motivated by sound intuition based on a shrewd and careful assessment of evidence and observation. Although Einstein gave much of himself to .political and social causes, science always came first, because, he often said, only the discovery of the nature of the universe would have lasting meaning. His writings include Relativity: The Special and General Theory (1916); About Zionism (1931); Builders of the Universe (1932); Why War? (1933), with Sigmund Freud; The World as I See It (1934); The Evolution of Physics (1938), with the Polish physicist Leopold Infield; and Out of My Later Years (1950). Einstein's collected papers are being published in a multivolume work, beginning in 1987

Blaise Pascal

INTRODUCTION

Pascal, Blaise (1623-1662), French philosopher, mathematician, and physicist, considered one of the great minds in Western intellectual history.

Pascal was born in Clermont-Ferrand on June 19, 1623, and his family settled in Paris in 1629. Under the tutelage of his father, Pascal soon proved himself a mathematical prodigy, and at the age of 16 he formulated one of the basic theorems of projective geometry, known as Pascal's theorem and described in his Essay pour les coniques (Essay on Conics, 1639). In 1642 he invented the first mechanical adding machine. Pascal proved by experimentation in 1648 that the level of the mercury column in a barometer is determined by an increase or decrease in the surrounding atmospheric pressure rather than by a vacuum, as previously believed. This discovery verified the hypothesis of the Italian physicist Evangelista Torricelli concerning the effect of atmospheric pressure on the equilibrium of liquids. Six years later, in conjunction with the French mathematician Pierre de Fermat, Pascal formulated the mathematical theory of probability, which has become important in such fields as actuarial, mathematical, and social statistics and as a fundamental element in the calculations of modern theoretical physics. Pascal's other important scientific contributions include the derivation of Pascal's law or principle, which states that fluids transmit pressures equally in all directions, and his investigations in the geometry of infinitesimals. His methodology reflected his emphasis on empirical experimentation as opposed to analytical, a priori methods, and he believed that human progress is perpetuated by the accumulation of scientific discoveries resulting from such experimentation.

LATER LIFE AND WORKS

Pascal espoused Jansenism and in 1654 entered the Jansenist community at Port Royal, where he led a rigorously ascetic life until his death eight years later. In 1656 and 1657 he wrote the famous 18 Letters provincials (Provincial Letters), in which he attacked the Jesuits for their attempts to reconcile 16th-century naturalism with orthodox Roman Catholicism. His most positive religious statement appeared posthumously (he died August 19, 1662); it was published in fragmentary form in 1670 as Apologia de la religion Chretien (Apology of the Christian Religion). In these fragments, which later were incorporated into his major work, he posed the alternatives of potential salvation and eternal damnation; with the implication that only by conversion to Jansenism could salvation be achieved. Pascal asserted that whether or not salvation was achieved, humanity's ultimate destiny is an afterlife belonging to a supernatural realm that can only be known intuitively. Pascal's final important work was Pensées sur la religion ET sur quelques autres sujets (Thoughts on Religion and on Other Subjects), also published in 1670. In the Pensées Pascal attempted to explain and justify the difficulties of human life by the doctrine of original sin, and he contended that revelation can be comprehended only by faith, which in turn is justified by revelation. Pascal's writings urging acceptance of the Christian life contain frequent applications of the calculations of probability; he reasoned that the value of eternal happiness is infinite and that although the probability of gaining such happiness by religion may be small it is infinitely greater than by any other course of human conduct or belief. A reclassification of thePensées, a careful work begun in 1935 and continued by several scholars, does not reconstruct the Apologia, but allows the reader to follow the plan that Pascal himself would have followed.

EVALUATION

Pascal was one of the most eminent mathematicians and physicists of his day and one of the greatest mystical writers in Christian literature. His religious works are personal in their speculation on matters beyond human understanding. He is generally ranked among the finest French polemicists, especially in the Letters provincials, a classic in the literature of irony. Pascal's prose style is noted for its originality and, in particular, for its total lack of artifice. He affects his readers by his use of logic and the passionate force of his dialectic.

Earnest Rutherford

INTRODUCTION

Rutherford, Ernest, 1st Baron Rutherford of Nelson and Cambridge (1871-1937), British physicist, who became a Nobel laureate for his pioneering work in nuclear physics and for his theory of the structure of the atom.

RUTHERFORD'S EARLY LIFE

Rutherford was born in Nelson, New Zealand, and educated at the University of New Zealand and the University of Cambridge. He was professor of physics at McGill University in Montréal, Québec, Canada, from 1898 to 1907 and at the University of Manchester in England during the following 12 years. After 1919 he was professor of experimental physics and director of the Cavendish Laboratory at the University of Cambridge and also held a professorship, after 1920, at the Royal Institution of Great Britain in London.

RUTHERFORD'S WORK

Rutherford was one of the first and most important researchers in nuclear physics. Soon after the discovery of radioactivity in 1896 by the French physicist Antoine Henri Becquerel, Rutherford identified the three main components of radiation and named them alpha, beta, and gamma rays. He also showed that alpha particles are helium nuclei. His study of radiation led to his formulation of a theory of atomic structure, which was the first to describe the atom as a dense nucleus about which electrons circulate in orbits.

In 1919 Rutherford conducted an important experiment in nuclear physics when he bombarded nitrogen gas with alpha particles and obtained atoms of an oxygen isotope and protons. This transmutation of nitrogen into oxygen was the first artificially induced nuclear reaction. It inspired the intensive research of later scientists on other nuclear transformations and on the nature and properties of radiation. Rutherford and the British physicist Frederick Soddy developed the explanation of radioactivity that scientists accept today. The rutherford, a unit of radioactivity, was named in his honor.

RUTHERFORD'S LATER LIFE

Rutherford was elected a fellow of the Royal Society in 1903 and served as president of that institution from 1925 to 1930. He was awarded the 1908 Nobel Prize in chemistry, was knighted in 1914, and was made a baron in 1931. He died in London on October 19, 1937, and was buried in Westminster Abbey. His writings include Radioactivity(1904); Radiations from Radioactive Substances (1930), which he wrote with British physicists Sir James Chadwick and Charles Drummond Ellis, and which has become a standard text; and The Newer Alchemy (1937). In 1997 the International Union of Pure and Applied Chemistry announced that the chemical element with the atomic number 104 would officially be given the name rutherfordium (Rf) in Rutherford's honor

Galileo Galielo

INTRODUCTION

Galileo (1564-1642), Italian physicist and astronomer, who, with the German astronomer Johannes Kepler, initiated the scientific revolution that flowered in the work of the English physicist Sir Isaac Newton. Born Galileo Galilei, his main contributions were, in astronomy, the use of the telescope in observation and the discovery of sunspots, lunar mountains and valleys, the four largest satellites of Jupiter, and the phases of Venus. In physics, he discovered the laws of falling bodies and the motions of projectiles. In the history of culture, Galileo stands as a symbol of the battle against authority for freedom of inquiry.

GALILEO'S EARLY LIFE

Galileo was born near Pisa, on February 15, 1564. His father, Vincenzo Galilei, played an important role in the musical revolution from medieval polyphony to harmonic modulation. Just as Vincenzo saw that rigid theory stifled new forms in music, so his eldest son came to see Aristotelian physical theology as limiting scientific inquiry. Galileo was taught by monks at Vallombrosa and then entered the University of Pisa in 1581 to study medicine. He soon turned to philosophy and mathematics, leaving the university without a degree in 1585. For a time he tutored privately and wrote on hydrostatics and natural motions, but he did not publish. In 1589 he became professor of mathematics at Pisa, where he is reported to have shown his students the error of Aristotle's belief that speed of fall is proportional to weight, by dropping two objects of different weight simultaneously from the Leaning Tower. His contract was not renewed in 1592, probably because he contradicted Aristotelian professors. The same year, he was appointed to the chair of mathematics at the University of Padua, where he remained until 1610.

GALILEO'S WORK

At Padua, Galileo invented a calculating "compass" for the practical solution of mathematical problems. He turned from speculative physics to careful measurements, discovered the law of falling bodies and of the parabolic path of projectiles, studied the motions of pendulums, and investigated mechanics and the strength of materials. He showed little interest in astronomy, although beginning in 1595 he preferred the Copernican theory—that the earth revolves around the sun—to the Aristotelian and Ptolemaic assumption that planets circle a fixed earth. Only the Copernican model supported Galileo's tide theory, which was based on motions of the earth. In 1609 he heard that a spyglass had been invented in Holland. In August of that year he presented a telescope, about as powerful as a modern field glass, to the doge of Venice. Its value for naval and maritime operations resulted in the doubling of his salary and his assurance of lifelong tenure as a professor.

By December 1609, Galileo had built a telescope of 20 times magnification, with which he discovered mountains and craters on the moon. He also saw that the Milky Way was composed of stars, and he discovered the four largest satellites of Jupiter. He published these findings in March 1610 in The Starry Messenger (translated in  1880). His new fame gained him appointment as court mathematician at Florence; he was thereby freed from teaching duties and had time for research and writing. By December 1610 he had observed the phases of Venus, which contradicted Ptolemaic astronomy and confirmed his preference for the Copernican system.

SCIENTIFIC PUBLICATIONS

Professors of philosophy scorned Galileo's discoveries because Aristotle had held that only perfectly spherical bodies could exist in the heavens and that nothing new could ever appear there. Galileo also disputed with professors at Florence and Pisa over hydrostatics, and he published a book on floating bodies in 1612. Four printed attacks on this book followed, rejecting Galileo's physics. In 1613 he published a work on sunspots and predicted victory for the Copernican theory. A Pisan professor, in Galileo's absence, told the Medici (the ruling family of Florence as well as Galileo's employers) that belief in a moving earth was heretical. In 1614 a Florentine priest denounced Galileists from the pulpit. Galileo wrote a long, open letter on the irrelevance of biblical passages in scientific arguments, holding that interpretation of the Bible should be adapted to increasing knowledge and that no scientific position should ever be made an article of Roman Catholic faith.

Early in 1616, Copernican books were subjected to censorship by edict, and the Jesuit cardinal Robert Bellarmine instructed Galileo that he must no longer hold or defend the concept that the earth moves. Cardinal Bellarmine had previously advised him to treat this subject only hypothetically and for scientific purposes, without taking Copernican concepts as literally true or attempting to reconcile them with the Bible. Galileo remained silent on the subject for years, working on a method of determining longitudes at sea by using his predictions of the positions of Jupiter's satellites, resuming his earlier studies of falling bodies, and setting forth his views on scientific reasoning in a book on comets,The Assayer (1623; translated in 1957).

In 1624 Galileo began a book he wished to call "Dialogue on the Tides," in which he discussed the Ptolemaic and Copernican hypotheses in relation to the physics of tides. In 1630 the book was licensed for printing by Roman Catholic censors at Rome, but they altered the title to Dialogue on the Two Chief World Systems (translated in 1661). It was published at Florence in 1632. Despite two official licenses, Galileo was summoned to Rome by the Inquisition to stand trial for "grave suspicion of heresy." This charge was grounded on a report that Galileo had been personally ordered in 1616 not to discuss Copernicanism either orally or in writing. Cardinal Bellarmine had died, but Galileo produced a certificate signed by the cardinal, stating that Galileo had been subjected to no further restriction than applied to any Roman Catholic under the 1616 edict. No signed document contradicting this was ever found, but Galileo was nevertheless compelled in 1633 to abjure and was sentenced to life imprisonment (swiftly commuted to permanent house arrest). The Dialogue was ordered to be burned, and the sentence against him was to be read publicly in every university.

Galileo's final book, Discourses Concerning Two New Sciences (translated in 1662-65), which was published at Leiden in 1638, reviews and refines his earlier studies of motion and, in general, the principles of mechanics. The book opened a road that was to lead Newton to the law of universal gravitation that linked Kepler's planetary laws with Galileo's mathematical physics. Galileo became blind before it was published, and he died at Arcetri, near Florence, on January 8, 1642.

GALILEO'S SCIENTIFIC CONTRIBUTION

Galileo's most valuable scientific contribution was his founding of physics on precise measurements rather than on metaphysical principles and formal logic. More widely influential, however, were The Starry Messenger and the Dialogue, which opened new vistas in astronomy. Galileo's lifelong struggle to free scientific inquiry from restriction by philosophical and theological interference stands beyond science. Since the full publication of Galileo's trial documents in the 1870s, entire responsibility for Galileo's condemnation has customarily been placed on the Roman Catholic church. This conceals the role of the philosophy professors who first persuaded theologians to link Galileo's science with heresy. An investigation into the astronomer's condemnation, calling for its reversal, was opened in 1979 by Pope John Paul II. In October 1992 a papal commission acknowledged the Vatican's error.

Nicolaus Copernicus

INTRODUCTION

Copernicus, Nicolaus (1473-1543), Polish astronomer, best known for his astronomical theory that the sun is at rest near the center of the universe, and that the earth, spinning on its axis once daily, revolves annually around the sun. This is called the heliocentric, or sun-centered, system.

EARLY LIFE AND EDUCATION

Copernicus was born on February 19, 1473, in Thorn (now Torun), Poland, to a family of merchants and municipal officials. Copernicus's maternal uncle, Bishop Lukasz Watzenrode, saw to it that his nephew obtained a solid education at the best universities. Copernicus entered Jagiellonian University in 1491, studied the liberal arts for four years without receiving a degree, and then, like many Poles of his social class, went to Italy to study medicine and law. Before he left, his uncle had him appointed a church administrator in Frauenberg (now Frombork); this was a post with financial responsibilities but no priestly duties. In January 1497 Copernicus began to study canon law at the University of Bologna while living in the home of a mathematics professor, Domenico Maria de Novara. Copernicus's geographical and astronomical interests were greatly stimulated by Domenico Maria, an early critic of the accuracy of the Geography of the 2nd-century astronomer Ptolemy. Together, the two men observed the occultation (the eclipse by the moon) of the star Aldebaran on March 9, 1497.

In 1500 Copernicus lectured on astronomy in Rome. The following year he gained permission to study medicine at Padua, the university where Galileo taught nearly a century later. It was not unusual at the time to study a subject at one university and then to receive a degree from another—often less expensive—institution. And so Copernicus, without completing his medical studies, received a doctorate in canon law from Ferrara in 1503 and then returned to Poland to take up his administrative duties.

RETURN TO POLAND

From 1503 to 1510, Copernicus lived in his uncle's bishopric palace in Lidzbark Warminski, assisting in the administration of the diocese and in the conflict against the Teutonic Knights. There he published his first book, a Latin translation of letters on morals by a 7th-century Byzantine writer, Theophylactus of Simocatta. Sometime between 1507 and 1515, he completed a short astronomical treatise, De Hypothesibus Motuum Coelestium a se Constitutis Commentariolus (known as the Commentariolus), which was not published until the 19th century. In this work he laid down the principles of his new heliocentric astronomy.

After moving to Frauenberg in 1512, Copernicus took part in the Fifth Lateran Council's commission on calendar reform in 1515; wrote a treatise on money in 1517; and began his major work, De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres), which was finished by 1530 but was first published by a Lutheran printer in Nürnberg, Germany, just before Copernicus's death in 1543.

EARLY 16TH-CENTURY COSMOLOGY

The cosmology that was eventually replaced by Copernican theory postulated a geocentric universe in which the earth was stationary and motionless at the center of several concentric, rotating spheres. These spheres bore (in order from the earth outward) the following celestial bodies: the moon, Mercury, Venus, the sun, Mars, Jupiter, and Saturn. The finite outermost sphere bore the so-called fixed stars. (This last sphere was said to wobble slowly, thereby producing the precession of the equinoxes.)

One phenomenon had posed a particular problem for cosmologists and natural philosophers since ancient times: the apparent retrograde (backward) motion of Mars, Jupiter, and Saturn. From time to time the daily motion of these planets through the sky appears to halt and then to proceed in the opposite direction. In an attempt to account for this retrograde motion, medieval cosmology stated that each planet revolved on the edge of a circle called the epicycle, and the center of each epicycle revolved around the earth on a path called the deferent.

THE COPERNICAN SYSTEM AND ITS INFLUENCE

The major premises of Copernicus's theory are that the earth rotates daily on its axis and revolves yearly around the sun. He argued, furthermore, that the planets also circle the sun, and that the earth precesses on its axis (wobbles like a top) as it rotates. The Copernican theory retained many features of the cosmology it replaced, including the solid, planet-bearing spheres, and the finite outermost sphere bearing the fixed stars. On the other hand, Copernicus's heliocentric theories of planetary motion had the advantage of accounting for the apparent daily and yearly motion of the sun and stars, and it neatly explained the apparent retrograde motion of Mars, Jupiter, and Saturn and the fact that Mercury and Venus never move more than a certain distance from the sun. Copernicus's theory also stated that the sphere of the fixed stars was stationary.

Another important feature of Copernican theory is that it allowed a new ordering of the planets according to their periods of revolution. In Copernicus's universe, unlike Ptolemy's, the greater the radius of a planet's orbit, the greater the time the planet takes to make one circuit around the sun. But the price of accepting the concept of a moving earth was too high for most 16th-century readers who understood Copernicus's claims. In addition, Copernicus's calculations of astronomical positions were neither decisively simpler nor more accurate than those of his predecessors, even though his heliocentric theory made good physical sense, for the first time, of planetary movements. As a result, parts of his theory were adopted, while the radical core was ignored or rejected.

There were but ten Copernicans between 1543 and 1600. Most worked outside the universities in princely, royal, or imperial courts; the most famous were Galileo and the German astronomer Johannes Kepler. These men often differed in their reasons for supporting the Copernican system. In 1588 an important middle position was developed by the Danish astronomer Tycho Brahe in which the earth remained at rest and all the planets revolved around the sun as it revolved around the earth.

After the suppression of Copernican theory occasioned by the ecclesiastical trial of Galileo in 1633, some Jesuit philosophers remained secret followers of Copernicus. Many others adopted the geocentric-heliocentric system of Brahe. By the late 17th century and the rise of the system of celestial mechanics propounded by the English natural philosopher Sir Isaac Newton, most major thinkers in England, France, the Netherlands, and Denmark were Copernicans. Natural philosophers in the other European countries, however, held strong anti-Copernican views for at least another century.

Marie Curie

INTRODUCTION

Curie, Marie (1867-1934), Polish-born French chemist who, with her husband Pierre Curie, was an early investigator of radioactivity. Radioactivity is the spontaneous decay of certain elements into other elements and energy. The Curies shared the 1903 Nobel Prize in physics with French physicist Antoine Henri Becquerel for fundamental research on radioactivity. Marie Curie went on to study the chemistry and medical applications of radium. She was awarded the 1911 Nobel Prize in chemistry in recognition of her work in discovering radium and polonium and in isolating radium.

MARIE'S EARLY LIFE

Marie Curie's maiden name was Maria Sklodowska, and her nickname while growing up was Manya. She was born in Warsaw at a time when Poland was under Russian domination after the unsuccessful revolt of 1863. Her parents were teachers, but soon after Manya (their fifth child) was born, they lost their teaching posts and had to take in boarders. Their young daughter worked long hours helping with the meals, but she nevertheless won a medal for excellence at the local high school, where the examinations and some classes were held in Russian. No higher education was available to women in Poland at that time, so Manya took a job as a governess. She sent part of her earnings to Paris to help pay for her older sister's medical studies. Her sister qualified as a doctor and married a fellow doctor in 1891. Manya went to join them in Paris, changing her name to Marie. She entered the Sorbonne (now the Universities of Paris) and studied physics and mathematics, graduating at the top of her class. In 1894 she met the French chemist Pierre Curie, and they were married the following year.

MARIE'S WORK

From 1896 the Curies worked together on radioactivity, building on the results of German physicist Wilhelm Roentgen (who had discovered x rays) and Henri Becquerel (who had discovered that uranium salts emit similar radiation). Marie Curie discovered that the metallic element thorium also emits radiation and found that the mineral pitchblende emitted even more radiation than its uranium and thorium content could cause. The Curies then carried out an exhaustive search for the substance that could be producing the radioactivity. They processed an enormous amount of pitchblende, separating it into its chemical components. In July 1898 the Curies announced the discovery of the element polonium, followed in December of that year with the discovery of the element radium. They eventually prepared 1 g (0.04 oz.) of pure radium chloride from 8 metric tons of waste pitchblende from Austria. They also established that beta rays (now known to consist of electrons) are negatively charged particles.

In 1906 Marie took over Pierre Curie's post at the Sorbonne when he was run down and killed by a horse-drawn carriage. She became the first woman to teach there, and she concentrated all her energies into research and caring for her daughters. The Curies' older daughter, Irene, later married Frederic Joliot and became a famous scientist and Nobel laureate herself. In 1910 Marie worked with French chemist André Debierne to isolate pure radium metal. In 1914 the University of Paris built the Institute du Radium (now the Institute Curie) to provide laboratory space for research on radioactive materials.

MARIE'S DEATH

At the outbreak of World War I in 1914, Marie Curie helped to equip ambulances with X-ray equipment, which she drove to the front lines. The International Red Cross made her head of its Radiological Service. She and her colleagues at the Institute du Radium held courses for medical orderlies and doctors, teaching them how to use the new technique. By the late 1920s her health began to deteriorate: Continued exposure to high-energy radiation had given her leukemia. She entered a sanatorium at Haute Savior and died there on July 4, 1934, a few months after her daughter and son-in-law, the Joliot-Curies, announced the discovery of artificial radioactivity.

Throughout much of her life Marie Curie was poor, and she and her fellow scientists carried out much of their work extracting radium under primitive conditions. The Curies refused to patent any of their discoveries, wanting them to benefit everyone freely. The Nobel Prize money and other financial rewards were used to finance further research. One of the outstanding applications of their work has been the use of radiation to treat cancer, one form of which cost Marie Curie her life.

Pierre Gassendi

INTRODUCTION

Gassendi, Pierre (1592-1655), French philosopher and savant, born in Champtercier, near Digne, and educated at Digne and at the universities of Aix-en-Provence and Avignon.

GASSENDI'S LIFE

In 1617 he was appointed professor of philosophy at the University of Aix-en-Provence. During the next years he taught, traveled to Flanders and Holland, and worked on studies in science and philosophy. In 1634 he was appointed provost of the cathedral at Digne, and in 1645 he became professor of mathematics at the College Royal in Paris. He retired in 1648. As a philosopher he first became known through his attacks on the theories of Aristotle; he also participated in a controversy with the French philosopher René Descartes over the nature of matter.

GASSENDI'S WORK

In 1647 his De vita ET Moribus Epicure (On the Life and Character of Epicurus) was published, followed two years later by two more works on the ancient Greek philosopher Epicurus. Gassendi theories are considered to have prepared the way for modern empirical methods, anticipating those of the English philosopher John Locke and the French philosopher Étienne Bonnot de Condillac; he was chiefly responsible for reviving interest in the philosophy of Epicureanism in modern times. His scientific work was mainly in the fields of astronomy and cartography.

Robert Boyle

INTRODUCTION

Boyle, Robert (1627-1691), English natural philosopher and one of the founders of modern chemistry. Boyle is best remembered for Boyle's law, a physical law that explains how the pressure and volume of a gas are related. He was instrumental in the founding of the Royal Society, a British organization dedicated to the advancement of the sciences. Boyle was also a pioneer in the use of experiments and the scientific method to test his theories.

BOYLE'S LIFE

Boyle was born in Lismore Castle in Lismore, Ireland. His father was Richard Boyle, who was the first earl of Cork. Robert learned to speak French and Latin as a child and went to Eton College in England at the early age of eight.

In 1641 Boyle began a tour of Europe, returning to England in 1644. He settled there, because Ireland was in turmoil over colonization efforts by English Protestants. Boyle had inherited parts of several estates upon his father's death in 1643, and income from these allowed him to live independently. He joined a group known as the Invisible College, whose aim was to cultivate ideas called the "new philosophy." The new philosophy included new methods of experimental science, in which scientists sought to prove or disprove hypotheses through careful experiments. Boyle moved to Oxford, which was one of the meeting places of the Invisible College, in 1654. King Charles II granted a charter in 1663 that allowed the Invisible College to become the Royal Society of London for Improving Natural Knowledge, and Boyle was a member of its first council. (He was elected president of the Royal Society in 1680, but declined the office.) He moved to London in 1668 and lived with his sister until his death in 1691.

BOYLE'S WORK

Boyle carried out his most active research while he lived in Oxford. Much of his research dealt with the behavior of gases, including the earth's atmosphere. By careful experiments, he established Boyle's law. Boyle's law states that the volume of a given amount of gas varies inversely with its pressure, if temperature is constant. This means that at a constant temperature, the pressure of a gas will increase as the volume of the gas is decreased, and vice versa. Boyle determined the density of air in the earth's atmosphere and pointed out that the weight of objects varies with changes in atmospheric pressure. He compared the lower layers of the earth's atmosphere to a number of sponges or small springs that the weight of the layers above compresses. In 1660 Boyle published these findings in a book entitled The Spring of Air.

A year later Boyle published The Skeptical Chemist, in which he criticized previous researchers for believing that salt, sulfur, and mercury were the "true principles of things." He advanced the view that the basic elements of matter are "corpuscles," or particles, of various sorts and sizes. Boyle believed that these corpuscles were capable of arranging themselves into groups, and that each group constituted a chemical substance. He successfully distinguished between mixtures (substances mixed together) and compounds (chemically bonded substances) and showed that a compound can have very different qualities from those of its constituents.

Boyle studied the chemistry of combustion around 1660 with the assistance of his pupil Robert Hooke. They pumped the air out of a jar and showed that neither charcoal nor sulfur burns in a vacuum, although both substances burn in the presence of air. Boyle then found that a mixture of either substance with saltpeter (potassium nitrate) catches fire even when in a vacuum and concluded that combustion must depend on something common to both air and saltpeter. The component of air and saltpeter that allows combustion was not isolated until British chemist Joseph Priestly did so in 1774. This substance was not given its present name until French chemist Antoine Lavoisier named it oxygen three years later.

Boyle also coined the term analysis and used many of the reactions that modern qualitative chemists use today. He introduced certain plant extracts, notably litmus, which indicates whether a substance is an acid or a base. In 1667 he was the first to study the phenomenon of bioluminescence, the emission of light from living organisms. He showed that fungi and bacteria require air (oxygen) for luminescence, becoming dark in a vacuum and glowing again when air is readmitted. Boyle drew a comparison between a glowing coal and phosphorescent wood, although oxygen was still not known and combustion was not properly understood. Boyle also seems to have been the first to construct a small, portable, box-type camera obscure in about 1665. A camera obscure is a system used to project an image onto a surface. Boyle's camera obscure could be extended or shortened like a telescope to focus an image on a piece of paper stretched across the back of the box opposite the lens.

In 1665 Boyle published the first account in England of the use of a hydrometer for measuring the density of liquids. The instrument he described is essentially the same as those in use today. Hydrometers consist of a sealed capsule of lead or mercury inside a glass tube into which the liquid being measured is placed. The height at which the capsule floats represents the density of the liquid. Boyle is also credited with the invention of the match. In 1680 he found that he could produce fire by drawing a sulfur-tipped splint through a fold in a piece of paper that was coated with phosphorous. Boyle experimented in animal physiology, although he disliked performing actual dissections. He also carried out experiments in the hope of changing one metal into another.

Boyle was interested in theology as well as science. He spent large sums on biblical translations and learned Hebrew, Greek, and Syria in order to further his studies of the Scriptures. He founded the Boyle Lectures for defending Christianity against other religions.

Boyle accomplished much important work in physics. He studied the behavior of gases, the role of air in allowing sound to travel, and the outward force of water in the process of freezing. He was also interested in the ability of crystals to bend light, the density of liquids, electricity, color, and the behavior of liquids at rest, among other physical topics. Boyle's greatest fondness was researching in chemistry. He was the main agent in changing the unscientific field of alchemy, which was mostly concerned with turning common metals into precious metals, into modern scientific chemistry. He was the first person to work toward removing the mystique around chemistry and to change it into a pure science. He questioned the basis of the chemical theory of his day and taught that chemistry's purpose was to determine the compositions of substances.

Sir Issac Newton

INTRODUCTION

Newton, Sir Isaac (1642-1727), English physicist, mathematician, and natural philosopher, considered one of the most important scientists of all time. Newton formulated laws of universal gravitation and motion—laws that explain how objects move on Earth as well as through the heavens. He established the modern study of optics—or the behavior of light—and built the first reflecting telescope. His mathematical insights led him to invent the area of mathematics called calculus (which German mathematician Gottfried Wilhelm Leibniz also developed independently). Newton stated his ideas in several published works, two of which, Philosophize Naturalism Principia Mathematical (Mathematical Principles of Natural Philosophy, 1687) and Optics (1704), are considered among the greatest scientific works ever produced. Newton's revolutionary contributions explained the workings of a large part of the physical world in mathematical terms, and they suggested that science may provide explanations for other phenomena as well.

Newton took known facts and formed mathematical theories to explain them. He used his mathematical theories to predict the behavior of objects in different circumstances and then compared his predictions with what he observed in experiments. Finally, Newton used his results to check—and if need be, modify—his theories. He was able to unite the explanation of physical properties with the means of prediction. Newton began with the laws of motion and gravitation he observed in nature, and then used these laws to convert physics from a mere science of explanation into a general mathematical system with rules and laws. His experiments explained the phenomena of light and color and anticipated modern developments in light theory. In addition, his invention of calculus gave science one of its most versatile and powerful tools.

EARLY LIFE AND EDUCATION

Newton was born in Wools Thorpe, Lincolnshire, in England. Newton's father died before his birth. When he was three years old, his mother remarried, and his maternal grandmother then took over his upbringing. He began his schooling in neighboring towns, and at age ten was sent to the grammar school at nearby Grantham. While at school he lived at the house of a pharmacist named Clark, from whom he may have acquired his lifelong interest in chemical operations. The young Newton seems to have been a quiet boy who was skilled with his hands. He made sundials, model windmills, a water clock, a mechanical carriage, and flew kites with lanterns attached to their tails. However, he was (as he recounted late in his life) very inattentive at school.

In 1656 Newton's mother, on the death of her second husband, returned to Wools Thorpe and took her son out of school in the hope of making him a farmer. Newton showed no talent for farming, however, and according to legend he once was found under a hedge deep in study when he should have been in the market at Grantham. Fortunately, Newton's former teacher at Grantham recognized the boy's intellectual gifts and eventually persuaded Newton's mother to allow him to prepare for entrance to University of Cambridge. In June 1661 Trinity College at Cambridge admitted Newton as a subsizar (a student required to perform various domestic services). His studies included arithmetic, geometry, trigonometry, and, later, astronomy and optics. He probably received much inspiration at Trinity from distinguished mathematician and theologian Isaac Barrow, who was a professor of mathematics at the college. Barrow recognized Newton's genius and did all he could to cultivate it. Newton earned his bachelor's degree in January 1665.

EARLY SCIENTIFIC IDEAS

When an outbreak of bubonic plague in 1665 temporarily shut down University of Cambridge, Newton returned to Wools Thorpe, where he remained for nearly two years. This period was an intellectually rich one for Newton. During this time, he did much scientific work in the subjects he would spend his life exploring: motion, optics, and mathematics.

At this point, according to his own account, Newton had made great progress in what he called his mathematical "method of fluxions" (which today we call calculus). He also recorded his first thoughts on gravitation, inspired (according to legend) by observing the fall of an apple in an orchard. According to a report of a conversation with Newton in his old age, he said he was trying to determine what type of force could hold the Moon in its path around Earth. The fall of an apple led him to think that the attractive gravitational force acting on the apple might be the same force acting on the Moon. Newton believed that this force, although weakened by distance, held the Moon in its orbit.

Newton devised a numerical equation to verify his ideas about gravity. The equation is called the inverse square law of attraction, and it states that the force of gravity (an object's pull on another object) is related to the inverse square of the distance between the two objects (that is, the number 1 divided by the distance between the two objects times itself). Newton believed this law should apply to the Sun and the planets as well. He did not pursue the problem of the falling apple at the time, because calculating the combined attraction of the whole Earth on a small body near its surface seemed too difficult. He reintroduced these early thoughts years later in his more thorough work, the Principia.

Newton also began to investigate the nature of light. White light, according to the view of his time, was uniform, or homogeneous, in content. Newton's first experiments with a prism called this view of white light into question. Passing a beam of sunlight through a prism, he observed that the beam spread out into a colored band of light, called a spectrum. While others had undoubtedly performed similar experiments, Newton showed that the differences in color were caused by differing degrees of a property he called refrangibility. Irrefrangibility is the ability of light rays to be refracted, or bent by a substance. For example, when a ray of violet light passes through a refracting medium such as glass, it bends more than does a ray of red light. Newton concluded through experimentation that sunlight is a combination of all the colors of the spectrum and that the sunlight separates when passed through the prism because its component colors are of differing irrefrangibility. This property that Newton discovered actually depends directly on the wavelengths of the different components of sunlight. A refracting substance, such as a prism, will bend each wavelength of light by a different amount.

The Reflecting Telescope

In October 1667, soon after his return to Cambridge, Newton was elected to a minor fellowship at Trinity College. Six months later he received a major fellowship and shortly thereafter was named Master of Arts. During this period he devoted much of his time to practical work in optics. His earlier experiments with the prism convinced him that a telescope's resolution is limited not so much by the difficulty of building flawless lenses as by the general refraction differences of differently colored rays. Newton observed that lenses refract, or bend, different colors of light by a slightly different amount. He believed that these differences would make it impossible to bring a beam of white light (which includes all the different colors of light) to a single focus. Thus he turned his attention to building a reflecting telescope, or a telescope that uses mirrors instead of lenses, as a practical solution. Mirrors reflect all colors of light by the same amount.

Scottish mathematician James Gregory had proposed a design for a reflecting telescope in 1663, but Newton was the first scientist to build one. He built a reflecting telescope with a 1.3-in (3.3-cm) mirror in 1668. This telescope magnified objects about 40 times and differed slightly from Gregory's in design. Three years later, the Royal Society, England's official association of prominent scientists and mathematicians, invited Newton to submit his telescope for inspection. He sent one similar to his original model, and the Society established Newton's dominance in the field by publishing a description of the instrument.

Calculus (Newton's "Fluxional Method")

In 1669 Newton gave his Trinity mathematics professor Isaac Barrow an important manuscript, which is generally known by its shortened Latin title, De Analysis. This work contained many of Newton's conclusions about calculus (what Newton called his "fluxional method"). Although the paper was not immediately published, Barrow made its results known to several of the leading mathematicians of Britain and Europe. This paper established Newton as one of the top mathematicians of his day and as the founder of modern calculus (along with Leibniz). Calculus addresses such concepts as the rate of change of a certain quantity, the slope of a curve at a given point, the computation of maximum and minimum values of functions, and the calculation of areas bounded by curves. When Barrow retired in 1669, he suggested to the college that Newton succeed him. Newton became the new professor of mathematics and chose optics as the subject of his first course of lectures.

Newton's First Published Works

In early 1672 Newton was elected a Fellow of the Royal Society. Shortly afterward Newton offered to submit a paper detailing his discovery of the composite nature of white light. Much impressed by his account, the Society published it. This publication triggered a long series of objections to Newton's scientific views in general, mostly by European scientists from outside England. Many of the criticisms later proved unsound. The strongest criticism of Newton's work, however, concerned his work on the theory of gravity and came from English inventor, mathematician, and curator of the Royal Society Robert Hooke. Hooke insisted that he had suggested fundamental principles of the law of gravitation to Newton. Newton answered these objections carefully and at first patiently but later with growing irritation. These public arguments aggravated Newton's sensitivity to criticism, and for several years he stopped publishing his findings.

THE PRINCIPIA MATHEMATICA AND LAWS OF MOTION

By 1679 Newton had returned to the problem of planetary orbits. The idea of a planetary attraction based on the inverse square of the distance between the Sun and the planets (which he had assumed in his early calculations at Wools Thorpe) ignited wide debate in the scientific community. This law of attraction follows, in the simple case of a circular orbit, from German astronomer Johannes Kepler's Third Law, which relates the time of a planet's revolution around the Sun to the size of the planet's orbit. The law of attraction also takes into account the centripetal acceleration of a body moving in a circle, given by Dutch astronomer Christian Huygens in 1673. The problem of determining the orbit from the law of force had baffled everyone before Newton, who solved it in about 1680.

In August 1684 English astronomer Edmond Halley visited Cambridge to consult with Newton on the problem of orbits. During a discussion with Halley about the shape of an orbit under the inverse square law of attraction, Newton suggested that it would be an ellipse. Unable to find the calculation from which he had derived the answer, Newton promised to send it to Halley, which he did a few months later. On a second visit Halley received what he called "a curious treatise de motu" (de motu means "on motion"), which at Halley's request was registered with the Royal Society in February 1685.

This tract on the laws of motion formed the basis of the first book of Philosophize Naturalism Principia Mathematical. Scientists and scholars consider this work a milestone of scientific inquiry, and its composition in the span of about 18 months was an intellectual feat unsurpassed at that time. Halley played a substantial role in the development of the Principia. He tactfully smoothed over differences between Newton and Hooke, who insisted that Newton had stolen some of his ideas. Newton angrily decided to suppress the third section of this work, but Halley persuaded Newton to publish it. Halley managed Newton's work through publication and underwrote the cost of printing.

The Principia finally appeared in the summer of 1687. The scientific community hailed it as a masterpiece, although Newton had intentionally made the book difficult "to avoid being baited by little smatters in mathematics." The book's grand unifying idea of gravitation, with effects extending throughout the solar system, captured the imagination of the scientific community. The work used one principle to explain diverse phenomena such as the tides, the irregularities of the Moon's motion, and the slight yearly variations in the onset of spring and autumn.

NEWTON'S LATER WORK

A few months before publication of the Principia, Newton emerged as a defender of academic freedom. King James II, who hoped to reestablish Roman Catholicism in England, issued a mandate to Cambridge in February 1687. This mandate called on the university to admit a certain Benedictine monk, Alban Francis, to the degree of Master of Arts without requiring him to take the usual oaths of allegiance to the Crown. The university saw this mandate as a request to grant preferential treatment to a Catholic and as a threat both to tradition and standards, so it steadfastly refused. Newton took a prominent part in defending the university's position. The university senate appointed a group (including Newton) to appear before a government commission at Westminster, and they successfully defended the university's rights. After the downfall of James II in the Glorious Revolution of 1688, Newton was elected a representative of the university in the Convention Parliament, in which he sat from January 1689 until its dissolution a year later. While he does not appear to have taken part in debate, Newton continued to be zealous in upholding the privileges of the university.

Newton's public duties brought a change to his retiring mode of life and required frequent journeys to London, where he met several prominent writers and intellectuals, most notably philosopher John Locke and diarist and civil servant Samuel Pepys. In the early 1690s, possibly in response to the intellectual exertion of writing the Principia, Newton suffered a period of depression. Opinions differ among Newton's biographers as to the permanence of the effects of the attack.

In the years after his illness, Newton summoned the energy to attack the complex problem of the Moon's motion. This work involved a correspondence with John Flams teed, England's first Astronomer Royal, whose lunar observations Newton needed. However, misunderstandings and quarrels marred their relationship, which ended sourly. In 1698 Newton tried to carry his lunar work further and resumed collaboration with Flams teed, but difficulties arose again and Newton accused Flams teed of withholding his observations. The two scientists had not resolved the dispute when Flams teed died in 1719.

In 1696 Newton's friends in the government secured a paying political post for him by appointing him warden of the mint. This position required that he live in London, where he resided until his death. Newton's work at the mint included a complete reform of the coinage. In order to combat counterfeiting, he introduced the minting of coins of standard weight and composition. He also instituted the policy of minting coins with milled edges. Newton successfully carried out these tasks, which demanded great technical and administrative skill, in the three years leading up to November 1699. At that time his peers promoted him to the mastership of the mint. This position was a well-paid post that Newton held for the rest of his life.

In 1701 Newton resigned his chair and fellowship at Cambridge and in 1703 was elected president of the Royal Society, an office to which he was reelected annually thereafter. In 1704, a year after the death of his rival Hooke, he brought out his second great treatise, Optics, which included his theories of light and color as well as his mathematical discoveries. Unlike the Principia, which was in Latin, Optics was written in English, but Newton later published a Latin translation. Most of Newton's work nutpicks was done long before he relocated to London. One of its most interesting features is a series of general speculations added to the second edition (1717) in the form of "Queries," or questions, which bear witness to his profound insight into physics. Many of his questions foreshadowed modern developments in physics, engineering, and the natural sciences.

In 1705 Queen Anne knighted Newton. By this time Newton was the dominant figure in British and European science. In the last two decades of his life, he prepared the second and third editions of the Principia (1713, 1726) and published second and third editions of Optics (1717, 1721) as well.

During these last two decades Newton was entangled in a lengthy and bitter controversy with Leibniz over which of the two scientists had invented calculus. This controversy embittered Newton's last years and harmed relations between the scientific communities in Britain and on the European continent. It also slowed the progress of mathematical science in Britain. Most scholars agree that Newton was the first to invent calculus, although Leibniz was the first to publish his findings. Mathematicians later adopted Leibniz's mathematical symbols, which have survived to the present day with few changes.

NEWTON'S IMPACT ON SCIENCE

Newton's place in scientific history rests on his application of mathematics to the study of nature and his explanation of a wide range of natural phenomena with one general principle—the law of gravitation. He used the foundations of dynamics, or the laws of nature governing motion and its effects on bodies, as the basis of a mechanical picture of the universe. His achievements in the use of calculus went so far beyond previous discoveries that scientists and scholars regard him as the chief pioneer in this field of mathematics.

Newton's work greatly influenced the development of physical sciences. During the two centuries following publication of the Principia, scientists and philosophers found many new areas in which they applied Newton's methods of inquiry and analysis. Much of this expansion arose as a consequence of the Principia. Scientists did not see the need for revision of some of Newton's conclusions until the early 20th century. This reassessment of Newton's ideas about the universe led to the modern theory of relativity and to quantum theory, which deal with the special cases of physics involving high speeds and physics of very small dimensions, respectively. For systems of ordinary dimensions, involving velocities that do not approach the speed of light, the principles that Newton formulated nearly three centuries ago are still valid.

Besides his scientific work, Newton left substantial writings on theology, chronology, alchemy, and chemistry. In 1725 Newton moved from London to Kensington (then a village outside London) for health reasons. He died there on March 20, 1727. He was buried in Westminster Abbey, the first scientist to be so honored.

Sir Wiliam Herschel

INTRODUCTION

Herschel, Sir William (1738-1822), German-born British astronomer, who made many important contributions to astronomy.

HERSCHEL'S EARLY LIFE

Originally named Friedrich Wilhelm Herschel, he was born in Hannover, Germany. At the age of 19 he went to England, working as a music teacher and organist but devoting all his spare time to astronomy and mathematics.

HERSCHEL'S WORK

Unable to procure adequate instruments, he constructed and constantly improved his own telescopes. In 1774, with the aid of his sister Caroline (also an astronomer), he began a comprehensive and systematic survey of the heavens. In 1781 he discovered a new planet, which he named Georgium Sidus in honor of George III, king of the United Kingdom of Great Britain and Ireland, but which is now universally called Uranus. A year later he was appointed private astronomer to the king, a position that enabled him to devote all his time to his astronomic pursuits. He erected a telescope at Slough with a 48-in (1.22-m) mirror and a focal length of 40 ft. (12.2 m). Using this, he discovered two satellites of Uranus and the sixth and seventh satellites of Saturn. He studied the rotation period of many planets and the motion of double stars, and also cataloged more than 800 double stars. He studied nebulas, contributing new information on their constitution and increasing the number of observed nebulas from about 100 to 2500. Herschel was the first to propose that these nebulas were composed of stars.

HERSCHEL'S LATER LIFE

He was elected to the Royal Society in 1781 and knighted in 1816. He is considered the founder of sidereal astronomy.