Newton,
Sir Isaac

I 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 (*see *Mechanics). 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, *Philosophiae** Naturalis Principia Mathematica*
(Mathematical Principles of Natural Philosophy, 1687) and *Opticks**
*(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 (*see *Deduction).
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, 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.

II EARLY LIFE AND EDUCATION

Newton was born in Woolsthorpe,
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 Woolsthorpe 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.

III EARLY SCIENTIFIC IDEAS

When an outbreak of bubonic plague in 1665
temporarily shut down University of Cambridge, Newton returned to Woolsthorpe, 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.
Refrangibility 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 refrangibility.
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.

A 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.

B 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 Analysi*. 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.

C 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.

IV 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 Woolsthorpe) 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 (*see *Kepler’s Laws). The law of attraction also takes into
account the centripetal acceleration of a body moving in a circle, given by
Dutch astronomer Christiaan 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. *See also *Mechanics: *Newton’s
Three Laws of Motion*.

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 *Philosophiae** Naturalis Principia Mathematica*.
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 smatterers 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.

V 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 Flamsteed,
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 Flamsteed, but difficulties arose
again and Newton accused Flamsteed of withholding his
observations. The two scientists had not resolved the dispute when Flamsteed 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, *Opticks**,*
which included his theories of light and color as
well as his mathematical discoveries. Unlike the *Principia*, which was in
Latin, *Opticks* was written in English, but
Newton later published a Latin translation. Most of Newton’s work on *Opticks* 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 *Opticks*
(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.

VI 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.

Contributed By: Richard S. Westfall

**Microsoft ® Encarta ® Reference Library 2003.** ©
1993-2002 Microsoft Corporation. All rights reserved.

**Newton,
Sir Isaac**

**b****. Dec. 25, 1642
[Jan. 4, 1643, New Style], Woolsthorpe, Lincolnshire,
Eng.**

d. March 20 [March 31], 1727, London

English physicist and mathematician, who was the culminating figure of the scientific revolution of the 17th
century. In optics, his discovery of the composition of white light integrated
the phenomena of colours into the science of light and laid the foundation for
modern physical optics. In mechanics, his three laws of motion, the basic
principles of modern physics, resulted in the formulation of the law of
universal gravitation. In mathematics, he was the original discoverer of the
infinitesimal calculus. Newton's Philosophiae Naturalis Principia Mathematica (*Mathematical
Principles of Natural Philosophy*), 1687, was one of the most important
single works in the history of modern science.

Born in the hamlet of Woolsthorpe, Newton was the only son of a local yeoman,
also Isaac Newton, who had died three months before, and of Hannah Ayscough. That same year, at Arcetri
near Florence, Galileo Galilei had died; Newton would
eventually pick up his idea of a mathematical science of motion and bring his
work to full fruition. A tiny and weak baby, Newton was not expected to survive
his first day of life, much less 84 years. Deprived of a father before birth,
he soon lost his mother as well, for within two years she married a second
time; her husband, the well-to-do minister Barnabas Smith, left young Isaac
with his grandmother and moved to a neighbouring village to raise a son and two
daughters. For nine years, until the death of Barnabas Smith in 1653, Isaac was
effectively separated from his mother, and his pronounced psychotic tendencies
have been ascribed to this traumatic event. That he hated his stepfather we may
be sure. When he examined the state of his soul in 1662 and compiled a catalog of sins in shorthand, he remembered "Threatning my father and mother Smith to burne them and the house over them." The acute sense of insecurity that rendered him obsessively anxious
when his work was published and irrationally violent when he defended it accompanied
Newton throughout his life and can plausibly be traced to his early years.

After his mother was widowed
a second time, she determined that her first-born son should manage her now
considerable property. It quickly became apparent, however, that this would be
a disaster, both for the estate and for Newton. He could not bring himself to
concentrate on rural affairs--set to watch the cattle,
he would curl up under a tree with a book. Fortunately, the mistake was
recognized, and Newton was sent back to the grammar school in Grantham, where
he had already studied, to prepare for the university. As with many of the
leading scientists of the age, he left behind in Grantham anecdotes about his
mechanical ability and his skill in building models of machines, such as clocks
and windmills. At the school he apparently gained a firm command of Latin but
probably received no more than a smattering of arithmetic. By June 1661, he was
ready to matriculate at Trinity College, Cambridge, somewhat older than the
other undergraduates because of his interrupted education.

When Newton arrived in
Cambridge in 1661, the movement now known as the scientific revolution was well
advanced, and many of the works basic to modern science had appeared.
Astronomers from Copernicus to Kepler had elaborated
the heliocentric system of the universe. Galileo had proposed the foundations
of a new mechanics built on the principle of inertia. Led by Descartes,
philosophers had begun to formulate a new conception of nature as an intricate,
impersonal, and inert machine. Yet as far as the universities of Europe,
including Cambridge, were concerned, all this might well have never happened.
They continued to be the strongholds of outmoded Aristotelianism,
which rested on a geocentric view of the universe and dealt with nature in
qualitative rather than quantitative terms.

Like thousands of other
undergraduates, Newton began his higher education by immersing himself in Aristotle's
work. Even though the new philosophy was not in the curriculum, it was in the
air. Some time during his undergraduate career, Newton discovered the works of
the French natural philosopher René Descartes and the other mechanical
philosophers, who, in contrast to Aristotle, viewed physical reality as
composed entirely of particles of matter in motion and who held that all the
phenomena of nature result from their mechanical interaction. A new set of
notes, which he entitled "Quaestiones Quaedam Philosophicae"
("Certain Philosophical Questions"), begun sometime in 1664, usurped
the unused pages of a notebook intended for traditional scholastic exercises;
under the title he entered the slogan "Amicus Plato amicus Aristoteles magis amica veritas" ("Plato
is my friend, Aristotle is my friend, but my best friend is truth").
Newton's scientific career had begun.

The "Quaestiones"
reveal that Newton had discovered the new conception of nature that provided
the framework of the scientific revolution. He had thoroughly mastered the
works of Descartes and had also discovered that the French philosopher Pierre Gassendi had revived atomism, an alternative mechanical
system to explain nature. The "Quaestiones"
also reveal that Newton already was inclined to find the latter a more
attractive philosophy than Cartesian natural philosophy, which rejected the
existence of ultimate indivisible particles. The works of the 17th-century
chemist Robert Boyle provided the foundation for Newton's considerable work in
chemistry. Significantly, he had read Henry More, the Cambridge Platonist, and
was thereby introduced to another intellectual world, the magical Hermetic
tradition, which sought to explain natural phenomena in terms of alchemical and
magical concepts. The two traditions of natural philosophy, the mechanical and
the Hermetic, antithetical though they appear, continued to influence his
thought and in their tension supplied the fundamental theme of his scientific
career.

Although he did not record it
in the "Quaestiones," Newton had also begun
his mathematical studies. He again started with Descartes, from whose *La Géometrie* he branched out into the other literature of
modern analysis with its application of algebraic techniques to problems of
geometry. He then reached back for the support of classical geometry. Within
little more than a year, he had mastered the literature; and, pursuing his own
line of analysis, he began to move into new territory. He discovered the
binomial theorem, and he developed the calculus, a more powerful form of
analysis that employs infinitesimal considerations in finding the slopes of
curves and areas under curves.

By 1669 Newton was ready to
write a tract summarizing his progress, *De Analysi
per Aequationes Numeri Terminorum Infinitas*
("On Analysis by Infinite Series"), which circulated in manuscript
through a limited circle and made his name known. During the next two years he
revised it as *De methodis serierum
et fluxionum* ("On
the Methods of Series and Fluxions"). The word fluxions,
Newton's private rubric, indicates that the calculus had been born.
Despite the fact that only a handful of savants were even aware of Newton's
existence, he had arrived at the point where he had become the leading
mathematician in Europe.

When Newton received the
bachelor's degree in April 1665, the most remarkable undergraduate career in
the history of university education had passed unrecognized. On his own,
without formal guidance, he had sought out the new philosophy and the new
mathematics and made them his own, but he had confined the progress of his
studies to his notebooks. Then, in 1665, the plague closed the university, and
for most of the following two years he was forced to stay at his home,
contemplating at leisure what he had learned. During the plague years Newton
laid the foundations of the calculus and extended an earlier insight into an
essay, "Of Colours," which contains most of the ideas elaborated in
his *Opticks*. It was during this time that he
examined the elements of circular motion and, applying his analysis to the Moon
and the planets, derived the inverse square relation that the radially directed force acting on a planet decreases with
the square of its distance from the Sun--which was later crucial to the law of
universal gravitation. The world heard nothing of these discoveries.

Newton was elected to a
fellowship in Trinity College in 1667, after the university reopened. Two years
later, Isaac Barrow, Lucasian professor of
mathematics, who had transmitted Newton's *De Analysi*
to John Collins in London, resigned the chair to devote himself
to divinity and recommended Newton to succeed him. The professorship exempted
Newton from the necessity of tutoring but imposed the duty of delivering an
annual course of lectures. He chose the work he had done in optics as the
initial topic; during the following three years (1670-72), his lectures
developed the essay "Of Colours" into a form which was later revised to
become Book One of his *Opticks*.

Beginning with Kepler's *Paralipomena* in
1604, the study of optics had been a central activity of the scientific
revolution. Descartes's statement of the sine law of
refraction, relating the angles of incidence and emergence at interfaces of the
media through which light passes, had added a new mathematical regularity to
the science of light, supporting the conviction that the universe is
constructed according to mathematical regularities. Descartes had also made
light central to the mechanical philosophy of nature; the reality of light, he
argued, consists of motion transmitted through a material medium. Newton fully
accepted the mechanical nature of light, although he chose the atomistic
alternative and held that light consists of material corpuscles in motion. The
corpuscular conception of light was always a speculative theory on the
periphery of his optics, however. The core of Newton's contribution had to do
with colours. An ancient theory extending back at least to Aristotle held that
a certain class of colour phenomena, such as the rainbow, arises from the
modification of light, which appears white in its pristine form. Descartes had
generalized this theory for all colours and translated it into mechanical
imagery. Through a series of experiments performed in 1665 and 1666, in which
the spectrum of a narrow beam was projected onto the wall of a darkened
chamber, Newton denied the concept of modification and replaced it with that of
analysis. Basically, he denied that light is simple and homogeneous--stating
instead that it is complex and heterogeneous and that the phenomena of colours
arise from the analysis of the heterogeneous mixture into its simple
components. The ultimate source of Newton's conviction that light is
corpuscular was his recognition that individual rays of light have immutable
properties; in his view, such properties imply immutable particles of matter.
He held that individual rays (that is, particles of given size) excite
sensations of individual colours when they strike the retina of the eye. He
also concluded that rays refract at distinct angles--hence, the prismatic
spectrum, a beam of heterogeneous rays, *i.e.,* alike incident on one face
of a prism, separated or analyzed by the refraction into its component parts--and
that phenomena such as the rainbow are produced by refractive analysis. Because
he believed that chromatic aberration could never be eliminated from lenses,
Newton turned to reflecting telescopes; he constructed the first ever built.
The heterogeneity of light has been the foundation of physical optics since his
time.

There is no evidence that the
theory of colours, fully described by Newton in his inaugural lectures at
Cambridge, made any impression, just as there is no evidence that aspects of
his mathematics and the content of the *Principia*, also pronounced from
the podium, made any impression. Rather, the theory of colours, like his later
work, was transmitted to the world through the Royal Society of London, which
had been organized in 1660. When Newton was appointed Lucasian
professor, his name was probably unknown in the Royal Society; in 1671,
however, they heard of his reflecting telescope and asked to see it. Pleased by
their enthusiastic reception of the telescope and by his election to the society,
Newton volunteered a paper on light and colours early in 1672. On the whole,
the paper was also well received, although a few questions and some dissent
were heard.

Among the most important
dissenters to Newton's paper was Robert Hooke, one of
the leaders of the Royal Society who considered himself the master in optics
and hence he wrote a condescending critique of the unknown parvenu. One can
understand how the critique would have annoyed a normal man. The flaming rage it provoked, with the desire publicly to humiliate Hooke, however, bespoke the abnormal. Newton was unable
rationally to confront criticism. Less than a year after submitting the paper,
he was so unsettled by the give and take of honest discussion that he began to
cut his ties, and he withdrew into virtual isolation.

In 1675, during a visit to
London, Newton thought he heard Hooke accept his
theory of colours. He was emboldened to bring forth a second paper, an
examination of the colour phenomena in thin films, which was identical to most
of Book Two as it later appeared in the *Opticks*.
The purpose of the paper was to explain the colours of solid bodies by showing
how light can be analyzed into its components by reflection as well as
refraction. His explanation of the colours of bodies has not survived, but the
paper was significant in demonstrating for the first time the existence of
periodic optical phenomena. He discovered the concentric coloured rings in the
thin film of air between a lens and a flat sheet of glass; the distance between
these concentric rings (Newton's rings) depends on the increasing thickness of
the film of air. In 1704 Newton combined a revision of his optical lectures
with the paper of 1675 and a small amount of additional material in his *Opticks*.

A second
piece which Newton had sent with the paper of 1675 provoked new controversy. Entitled
"An Hypothesis Explaining the Properties of Light," it was in fact a
general system of nature. Hooke apparently claimed
that Newton had stolen its content from him, and Newton boiled over again. The
issue was quickly controlled, however, by an exchange of formal, excessively
polite letters that fail to conceal the complete lack of warmth between the
men.

Newton was also engaged in
another exchange on his theory of colours with a circle of English Jesuits in Liège, perhaps the most revealing exchange of all. Although
their objections were shallow, their contention that his experiments were
mistaken lashed him into a fury. The correspondence dragged on until 1678, when
a final shriek of rage from Newton, apparently accompanied by a complete
nervous breakdown, was followed by silence. The death of his mother the
following year completed his isolation. For six years he withdrew from
intellectual commerce except when others initiated a correspondence, which he
always broke off as quickly as possible.

During his time of isolation,
Newton was greatly influenced by the Hermetic tradition with which he had been
familiar since his undergraduate days. Newton, always somewhat interested in
alchemy, now immersed himself in it, copying by hand treatise after treatise
and collating them to interpret their arcane imagery. Under the influence of
the Hermetic tradition, his conception of nature underwent a decisive change.
Until that time, Newton had been a mechanical philosopher in the standard
17th-century style, explaining natural phenomena by the motions of particles of
matter. Thus, he held that the physical reality of light is a stream of tiny corpuscles
diverted from its course by the presence of denser or rarer media. He felt that
the apparent attraction of tiny bits of paper to a piece of glass that has been
rubbed with cloth results from an ethereal effluvium that streams out of the
glass and carries the bits of paper back with it. This mechanical philosophy
denied the possibility of action at a distance; as with static electricity, it
explained apparent attractions away by means of invisible ethereal mechanisms.
Newton's "Hypothesis of Light" of 1675, with its universal ether, was
a standard mechanical system of nature. Some phenomena, such as the capacity of
chemicals to react only with certain others, puzzled him, however, and he spoke
of a "secret principle" by which substances are "sociable"
or "unsociable" with others. About 1679, Newton abandoned the ether
and its invisible mechanisms and began to ascribe the puzzling
phenomena--chemical affinities, the generation of heat in chemical reactions,
surface tension in fluids, capillary action, the cohesion of bodies, and the
like--to attractions and repulsions between particles of matter. More than 35
years later, in the second English edition of the *Opticks*,
Newton accepted an ether again, although it was an
ether that embodied the concept of action at a distance by positing a repulsion
between its particles. The attractions and repulsions of Newton's speculations
were direct transpositions of the occult sympathies and antipathies of Hermetic
philosophy--as mechanical philosophers never ceased to protest. Newton,
however, regarded them as a modification of the mechanical philosophy that
rendered it subject to exact mathematical treatment. As he conceived of them,
attractions were quantitatively defined, and they offered a bridge to unite the
two basic themes of 17th-century science--the mechanical tradition, which had
dealt primarily with verbal mechanical imagery, and the Pythagorean tradition,
which insisted on the mathematical nature of reality. Newton's reconciliation
through the concept of force was his ultimate contribution to science.

The title page from Newton's *De Philosophiae
Naturalis Principia Mathematica,*
London, 1687.

Newton originally applied the idea of attractions and repulsions
solely to the range of terrestrial phenomena mentioned in the preceding
paragraph. But late in 1679, not long after he had embraced the concept,
another application was suggested in a letter from Hooke,
who was seeking to renew correspondence. Hooke mentioned
his analysis of planetary motion--in effect, the continuous diversion of a
rectilinear motion by a central attraction. Newton bluntly refused to
correspond but, nevertheless, went on to mention an experiment to demonstrate
the rotation of the Earth: let a body be dropped from a tower; because the
tangential velocity at the top of the tower is greater than that at the foot,
the body should fall slightly to the east. He sketched the path of fall as part
of a spiral ending at the centre of the Earth. This was a mistake, as Hooke pointed out; according to Hooke's
theory of planetary motion, the path should be elliptical, so that if the Earth
were split and separated to allow the body to fall, it would rise again to its
original location. Newton did not like being corrected, least of all by Hooke, but he had to accept the basic point; he corrected Hooke's figure, however, using the assumption that gravity
is constant. Hooke then countered by replying that,
although Newton's figure was correct for constant gravity, his own assumption
was that gravity decreases as the square of the distance. Several years later,
this letter became the basis for Hooke's charge of
plagiarism. He was mistaken in the charge. His knowledge of the inverse square
relation rested only on intuitive grounds; he did not derive it properly from
the quantitative statement of centripetal force and Kepler's
third law, which relates the periods of planets to the radii of their orbits.
Moreover, unknown to him, Newton had so derived the relation more than ten
years earlier. Nevertheless, Newton later confessed that the correspondence
with Hooke led him to demonstrate that an elliptical
orbit entails an inverse square attraction to one focus--one of the two crucial
propositions on which the law of universal gravitation would ultimately rest.
What is more, Hooke's definition of orbital
motion--in which the constant action of an attracting body continuously pulls a
planet away from its inertial path--suggested a cosmic application for Newton's
concept of force and an explanation of planetary paths employing it. In 1679
and 1680, Newton dealt only with orbital dynamics; he had not yet arrived at
the concept of universal gravitation.

Nearly five years later, in
August 1684, Newton was visited by the British astronomer Edmond Halley, who
was also troubled by the problem of orbital dynamics. Upon learning that Newton
had solved the problem, he extracted Newton's promise to send the
demonstration. Three months later he received a short tract entitled *De Motu* ("On Motion"). Already Newton was at
work improving and expanding it. In two and a half years, the tract *De Motu* grew into Philosophiae Naturalis Principia Mathematica,
which is not only Newton's masterpiece but also the fundamental work for the
whole of modern science.

Significantly, *De Motu* did not state the law of universal gravitation.
For that matter, even though it was a treatise on planetary dynamics, it did
not contain any of the three Newtonian laws of motion. Only when revising *De
Motu* did Newton embrace the principle of inertia
(the first law) and arrive at the second law of motion. The second law, the
force law, proved to be a precise quantitative statement of the action of the
forces between bodies that had become the central members of his system of
nature. By quantifying the concept of force, the second law completed the exact
quantitative mechanics that has been the paradigm of natural science ever
since.

The quantitative mechanics of
the *Principia* is not to be confused with the mechanical philosophy. The
latter was a philosophy of nature that attempted to explain natural phenomena
by means of imagined mechanisms among invisible particles of matter. The
mechanics of the *Principia* was an exact quantitative description of the
motions of visible bodies. It rested on Newton's three laws of motion: (1) that
a body remains in its state of rest unless it is compelled to change that state
by a force impressed on it; (2) that the change of motion (the change of
velocity times the mass of the body) is proportional to the force impressed;
(3) that to every action there is an equal and opposite reaction. The analysis
of circular motion in terms of these laws yielded a formula of the quantitative
measure, in terms of a body's velocity and mass, of the centripetal force
necessary to divert a body from its rectilinear path into a given circle. When
Newton substituted this formula into Kepler's third
law, he found that the centripetal force holding the planets in their given
orbits about the Sun must decrease with the square of the planets' distances
from the Sun. Because the satellites of Jupiter also obey Kepler's
third law, an inverse square centripetal force must also attract them to the
centre of their orbits. Newton was able to show that a similar relation holds
between the Earth and its Moon. The distance of the Moon is approximately 60
times the radius of the Earth. Newton compared the distance by which the Moon,
in its orbit of known size, is diverted from a tangential path in one second
with the distance that a body at the surface of the Earth falls from rest in
one second. When the latter distance proved to be 3,600 (60 60) times as great
as the former, he concluded that one and the same force, governed by a single
quantitative law, is operative in all three cases, and from the correlation of
the Moon's orbit with the measured acceleration of gravity on the surface of
the Earth, he applied the ancient Latin word *gravitas* (literally,
"heaviness" or "weight") to it. The law of universal
gravitation, which he also confirmed from such further phenomena as the tides
and the orbits of comets, states that every particle of matter in the universe
attracts every other particle with a force that is proportional to the product
of their masses and inversely proportional to the square of the distance
between their centres.

When the Royal Society
received the completed manuscript of Book I in 1686, Hooke
raised the cry of plagiarism, a charge that cannot be sustained in any
meaningful sense. On the other hand, Newton's response to it reveals much about
him. Hooke would have been satisfied with a generous
acknowledgment; it would have been a graceful gesture to a sick man already
well into his decline, and it would have cost Newton nothing. Newton, instead,
went through his manuscript and eliminated nearly every reference to Hooke. Such was his fury that he refused either to publish
his *Opticks* or to accept the presidency of the
Royal Society until Hooke was dead.

The *Principia*
immediately raised Newton to international prominence. In their continuing
loyalty to the mechanical ideal, Continental scientists rejected the idea of action
at a distance for a generation, but even in their rejection they could not
withhold their admiration for the technical expertise revealed by the work.
Young British scientists spontaneously recognized him as their model. Within a
generation the limited number of salaried positions for scientists in England,
such as the chairs at Oxford, Cambridge, and Gresham College, were monopolized by the young Newtonians of the next
generation. Newton, whose only close contacts with women were his unfulfilled
relationship with his mother, who had seemed to abandon him, and his later
guardianship of a niece, found satisfaction in the role of patron to the circle
of young scientists. His friendship with Fatio de Duillier, a Swiss-born mathematician resident in London who
shared Newton's interests, was the most profound experience of his adult life.

Almost immediately following
the *Principia'*s publication, Newton, a fervent
if unorthodox Protestant, helped to lead the resistance of Cambridge to James II's attempt to Catholicize it. As a consequence, he was
elected to represent the university in the convention that arranged the
revolutionary settlement. In this capacity, he made the acquaintance of a
broader group, including the philosopher John Locke. Newton tasted the
excitement of London life in the aftermath of the *Principia*. The great
bulk of his creative work had been completed. He was never again satisfied with
the academic cloister, and his desire to change was whetted by Fatio's suggestion that he find a position in London. Seek
a place he did, especially through the agency of his friend, the rising
politician Charles Montague, later Lord Halifax. Finally, in 1696, he was
appointed warden of the mint. Although he did not resign his Cambridge appointments
until 1701, he moved to London and henceforth centred his life there.

In the meantime, Newton's
relations with Fatio had undergone a crisis. Fatio was taken seriously ill; then family and financial
problems threatened to call him home to Switzerland. Newton's distress knew no
limits. In 1693 he suggested that Fatio move to
Cambridge, where Newton would support him, but nothing came of the proposal.
Through early 1693 the intensity of Newton's letters built almost palpably, and
then, without surviving explanation, both the close relationship and the
correspondence broke off. Four months later, without prior notice, Samuel Pepys and John Locke, both personal friends of Newton,
received wild, accusatory letters. Pepys was informed
that Newton would see him no more; Locke was charged with trying to entangle
him with women. Both men were alarmed for Newton's sanity; and, in fact, Newton
had suffered at least his second nervous breakdown. The crisis passed, and
Newton recovered his stability. Only briefly did he ever return to sustained
scientific work, however, and the move to London was the effective conclusion
of his creative activity.

As warden and then master of
the mint, Newton drew a large income, as much as 2,000 per annum. Added to his
personal estate, the income left him a rich man at his death. The position,
regarded as a sinecure, was treated otherwise by Newton. During the great recoinage, there was need for him to be actively in
command; even afterward, however, he chose to exercise himself in the office.
Above all, he was interested in counterfeiting. He became the terror of London
counterfeiters, sending a goodly number to the gallows and finding in them a
socially acceptable target on which to vent the rage that continued to well up
within him.

Newton found time now to
explore other interests, such as religion and theology. In the early 1690s he
had sent Locke a copy of a manuscript attempting to prove that Trinitarian
passages in the Bible were latter-day corruptions of the original text. When
Locke made moves to publish it, Newton withdrew in fear that his
anti-Trinitarian views would become known. In his later years, he devoted much
time to the interpretation of the prophecies of Daniel and St. John, and to a
closely related study of ancient chronology. Both works were published after
his death.

In London, Newton assumed the
role of patriarch of English science. In 1703 he was elected President of the
Royal Society. Four years earlier, the French Académie
des Sciences (Academy of Sciences) had named him one of eight foreign
associates. In 1705 Queen Anne knighted him, the first occasion on which a
scientist was so honoured. Newton ruled the Royal Society magisterially. John Flamsteed, the Astronomer Royal, had occasion to feel that
he ruled it tyrannically. In his years at the Royal Observatory at Greenwich, Flamsteed, who was a difficult man in his own right, had
collected an unrivalled body of data. Newton had received needed information
from him for the *Principia*, and in the 1690s, as he worked on the lunar theory, he again required Flamsteed's
data. Annoyed when he could not get all the information he wanted as quickly as
he wanted it, Newton assumed a domineering and condescending attitude toward Flamsteed. As president of the Royal Society, he used his
influence with the government to be named as chairman of a body of
"visitors" responsible for the Royal Observatory; then he tried to
force the immediate publication of Flamsteed's catalog of stars. The disgraceful episode continued for
nearly 10 years. Newton would brook no objections. He broke agreements that he
had made with Flamsteed. Flamsteed's
observations, the fruit of a lifetime of work, were, in effect, seized despite
his protests and prepared for the press by his mortal enemy, Edmond Halley. Flamsteed finally won his point and by court order had the
printed catalog returned to him before it was
generally distributed. He burned the printed sheets, and his assistants brought
out an authorized version after his death. In this respect, and at considerable
cost to himself, Flamsteed was one of the few men to
best Newton. Newton sought his revenge by systematically eliminating references
to Flamsteed's help in later editions of the *Principia*.

In Gottfried Wilhelm Leibniz,
the German philosopher and mathematician, Newton met a contestant more of his
own calibre. It is now well established that Newton developed the calculus before
Leibniz seriously pursued mathematics. It is almost universally agreed that
Leibniz later arrived at the calculus independently. There has never been any
question that Newton did not publish his method of fluxions; thus, it was
Leibniz's paper in 1684 that first made the calculus a matter of public
knowledge. In the *Principia* Newton hinted at his method, but he did not
really publish it until he appended two papers to the *Opticks*
in 1704. By then the priority controversy was already smouldering. If, indeed,
it mattered, it would be impossible finally to assess responsibility for the
ensuing fracas. What began as mild innuendoes rapidly escalated into blunt
charges of plagiarism on both sides. Egged on by followers anxious to win a
reputation under his auspices, Newton allowed himself to be drawn into the
centre of the fray; and, once his temper was aroused by accusations of
dishonesty, his anger was beyond constraint. Leibniz's conduct of the
controversy was not pleasant, and yet it paled beside that of Newton. Although
he never appeared in public, Newton wrote most of the pieces that appeared in
his defense, publishing them under the names of his
young men, who never demurred. As president of the Royal Society, he appointed
an "impartial" committee to investigate the issue, secretly wrote the
report officially published by the society, and reviewed it anonymously in the *Philosophical
Transactions*. Even Leibniz's death could not allay Newton's wrath, and he
continued to pursue the enemy beyond the grave. The battle with Leibniz, the
irrepressible need to efface the charge of dishonesty, dominated the final 25
years of Newton's life. It obtruded itself continually upon his consciousness.
Almost any paper on any subject from those years is apt to be interrupted by a
furious paragraph against the German philosopher, as he honed the instruments
of his fury ever more keenly. In the end, only Newton's death ended his wrath.

During his final years Newton
brought out further editions of his central works. After the first edition of
the *Opticks* in 1704, which merely published
work done 30 years before, he published a Latin edition in 1706 and a second
English edition in 1717-18. In both, the central text was scarcely touched, but
he did expand the "Queries" at the end into the final statement of
his speculations on the nature of the universe. The second edition of the *Principia*,
edited by Roger Cotes in 1713, introduced extensive alterations. A third
edition, edited by Henry Pemberton in 1726, added little more. Until nearly the
end, Newton presided at the Royal Society (frequently dozing through the
meetings) and supervised the mint. During his last years, his niece, Catherine
Barton Conduitt, and her husband lived with him.

Philosophiae Naturalis Principia Mathematica
(1687; *Mathematical Principles of Natural Philosophy*, 1729); *Opticks* (1704); *Arithmetica**
Universalis* (1707; *Universal Arithmetick*, 1720); *The**
Chronology of Ancient Kingdoms Amended* (1728); *Observations Upon the
Prophecies of Daniel and the Apocalypse of St. John* (1733).

I. Bernard Cohen, *Introduction
to Newton's "Principia"* (1971), a history of the development and
modification of Newton's major work, is the first volume of Cohen's edition of
the *Principia* and includes variant readings. Additional collections of
Newtonian materials, all with valuable introductory essays, include D.T.
Whiteside (ed.), *The Mathematical Papers of Isaac Newton*, 8 vol.
(1967-81); A. Rupert Hall and Marie Boas Hall (eds. and trans.), *Unpublished
Scientific Papers of Isaac Newton* (1962, reissued 1978); I. Bernard Cohen
and Robert E. Schofield (eds.), *Isaac Newton's Papers & Letters on
Natural Philosophy and Related Documents*, 2nd ed. (1978); and H.W. Turnbull
*et al.* (eds.), *Correspondence*, 7 vol. (1959-77), a collection of
Newton's letters, 1661-1727. Peter Wallis and Ruth Wallis, *Newton and Newtoniana, 1672-1975* (1977), is
a bibliography.

A standard biography of
Newton is David Brewster, *Memoirs of the Life, Writings, and Discoveries of
Sir Isaac Newton*, 2 vol. (1855, reprinted 1965). A more modern work by
Richard S. Westfall, *Never at Rest: A Biography of Isaac Newton* (1980,
reissued 1990), also available in a shorter version, *The Life of Isaac
Newton* (1993), is a comprehensive study of Newton in light of new
scholarship. Gale E. Christianson, *In the Presence of the Creator: Isaac
Newton and His Times* (1984), includes much contextual information. Frank E.
Manuel, *A Portrait of Isaac Newton* (1968, reprinted 1990), offers a
fascinating Freudian analysis, and his *The Religion of Isaac Newton*
(1974) is a thorough discussion of his religious thought. Derek Gjertsen, *The Newton Handbook* (1986), comprises
hundreds of brief entries on topics related to Newton and his era.

General treatments of the major
problems in Newtonian science are found in Cohen's *Franklin and Newton*
(1956, reissued 1966); John Fauvel (ed.), *Let
Newton Be!* (1988), a collection of essays on Newton and his work, with
illustrations; and A. Rupert Hall, *Isaac Newton, Adventurer in Thought*
(1992), a summary of recent research. John Herivel, *The** Background to Newton's Principia: A Study of
Newton's Dynamical Researches in the Years 1664-84* (1965); and Richard S.
Westfall, *Force in Newton's Physics* (1971), explore the development of Newton's
mechanics. Newton's *Optiks* is treated in
Hall's *All Was Light* (1993). Betty Jo Teeter Dobbs, *The Foundations
of Newton's Alchemy* (1975, reissued 1983), and *The Janus
Faces of Genius* (1991), examine Newton's alchemical studies. Cohen's *The
Newtonian Revolution* (1980), evaluates the
historical importance of Newton's style of scientific thought. Alexandre Koyré, *Newtonian
Studies* (1965), contains a collection of essays by one of the master
historians of science. Phillip Bricker and R.I.G. Hughes (eds.), *Philosophical
Perspectives on Newtonian Science* (1990), is an advanced treatment,
requiring familiarity with Newton's texts.