Isaac Newton

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 ddeveloped 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 ttheories 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 tthe 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 aat 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 iin 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 oone 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 ddivided 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 Reflecting telescope

In October 1667, soon after his return to Cambridge, Newton was elected to a mminor 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 bby 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 aa 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 iinstrument.

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 tthe 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 ...