Sir Isaac Newton
English scientist, astronomer, and mathematician

1642 - 1727

Calculus is the branch of mathematics that deals with changing quantities. Students usually learn it in college after they have mastered algebra, geometry, and trigonometry.

Calculus is the language in which engineers, physicists, and other scientists develop theories and solve practical problems. For example, the laws of aerodynamics are expressed in terms of calculus. An airplane designer can use these laws to calculate the changing forces that affect an airplane during flight. Calculus has also stimulated many new directions in mathematics since its development in the 1600's.

Sir Isaac Newton, an English scientist, astronomer, and mathematician, invented a new kind of mathematics, discovered the secrets of light and color, and showed how the universe is held together. He is sometimes described as "one of the greatest names in the history of human thought " because of his great contributions to mathematics, physics, and astronomy.

Newton discovered how the universe is held together through his theory of gravitation. He discovered the secrets of light and color. He invented a branch of mathematics, calculus, also invented independently by Gottfried Leibniz, a German mathematician. Newton made these three discoveries within 18 months from 1665 to 1667.

The theories of motion and gravitation. Newton said the concept of a universal force came to him while he was alone in the country. He had been forced to flee there because of the outbreak of plague in the city of Cambridge. During this time, Newton suddenly realized that one and the same force pulls an object to earth and keeps the moon in its orbit. He found that the force of universal gravitation makes every pair of bodies in the universe attract each other. The force depends on (1) the amount of matter in the bodies being attracted and (2) the distance between the bodies. The force by which the earth attracts or pulls a large rock is greater than the pull on a small pebble because the rock contains more matter. The earth's pull is called the weight of the body. With this theory, Newton explained why a rock weighs more than a pebble.

He also proved that many types of motion are due to one kind of force. He showed that the gravitational force of the sun keeps the planets in their orbits, just as the gravitational force of the earth attracts the moon. The falling of objects on earth seems different from the motion of the moon because the objects fall straight down to the earth, while the moon moves approximately in a circle around the earth. Newton showed that the moon falls just like an object on earth. If the moon did not fall constantly toward the earth, it would move in a straight line and fly off at a tangent to its orbit. Newton calculated how much the moon falls in each second and found the distance is 1/3600 of the distance an object on earth falls in a second. The moon is 60 times as far from the earth's center as such an object. Consequently, the force of the earth on an object 60 times as far away as another object is 1/3600.

The Principia. Newton concluded his first investigations on gravity and motion in 1665 and 1666. Nothing was heard of them for nearly 20 years. His original theory had been based on an inaccurate measurement of the earth's radius, and Newton realized differences between the theory and the facts. Although he later learned the true value of the earth's size, he was not led to complete his investigation or to produce a book for publication.

One day in 1684, Edmond Halley, an English astronomer, Robert Hooke, an English scientist, and Christopher Wren, the architect, were discussing what law of force produced the visible motion of the planets around the sun. They could not solve this problem. Halley went to Cambridge to ask Newton about it. He found Newton in possession of complete proof of the law of gravity. Halley persuaded Newton to publish his findings. Halley paid all the expenses, corrected the proofs, and laid aside his own work to publish Newton's discoveries. Newton's discoveries on the laws of motion and theories of gravitation were published in 1687 in Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). This work, usually called Principia or Principia Mathematica, is considered one of the greatest single contributions in the history of science. It includes Newton's laws of motion and theory of gravitation. It was the first book to contain a unified system of scientific principles explaining what happens on earth and in the heavens.

Light and color. Newton's discoveries in optics were equally spectacular. He published the results of his experiments and studies in Opticks (1704).

Newton's discoveries explained why bodies appear to be colored. The discoveries also laid the foundation for the science of spectrum analysis. This science allows us to determine the chemical composition, temperature, and even the speed of such hot, glowing bodies as a distant star or an object heated in a laboratory.

Newton discovered that sunlight is a mixture of light of all colors. He passed a beam of sunlight through a glass prism and studied the colors that were produced. A green sweater illuminated by sunlight looks green because it largely reflects the green light in the sun and absorbs most of the other colors. If the green sweater were lighted by a red light or any color light not containing green, it would not appear green.

The study of light led Newton to consider constructing a new type of telescope in which a reflecting mirror was used instead of a combination of lenses. Newton's first reflecting telescope was 6 inches long, and, through it, Newton saw the satellites of Jupiter.

Newton was born at Woolsthorpe, Lincolnshire, on Dec. 25, 1642. He attended Grantham grammar school. As a boy, he was more interested in making mechanical devices than in studying. His youthful inventions included a small windmill that could grind wheat and corn, a water clock run by the force of dropping water, and a sundial. He left school when he was 14 to help his widowed mother manage her farm. But he spent so much time reading, he was sent back to school.

He entered Trinity College, Cambridge University, in 1661. He showed no exceptional ability during his college career and graduated in 1665 without any particular distinction. He returned to Cambridge as a fellow of Trinity College in 1667.

Newton became professor of mathematics at Cambridge in 1669. He lectured once a week on arithmetic, astronomy, geometry, optics, or other mathematical subjects. He was elected to the Royal Society in 1672.

Newton became active in public life after the publication of Principia. He became the Cambridge University member of Parliament in 1689 and held his seat until Parliament dissolved the following year. He became warden of the mint in 1696. He was appointed master of the mint in 1699, a position he held until his death.

In 1699, he also became a member of the Royal Society council and an associate of the French Academy. He was elected to Parliament again from the university in 1701. He left Cambridge and settled permanently in London in 1701. He became president of the Royal Society in 1703 and was reelected annually until his death. Queen Anne knighted Newton in 1705. He died in 1727 and was buried in Westminster Abbey.

Personal characteristics. Newton did not enjoy the scientific arguments that arose from his discoveries. Many new scientific theories are opposed violently when they are first announced, and Newton's did not escape criticism. He was so sensitive to such criticism that his friends had to plead with him to publish his most valuable discoveries.

Newton was a bachelor who spent only part of his time studying mathematics, physics, and astronomy. He was also a student of alchemy and made many alchemical experiments. He also spent a great deal of his time on questions of theology and Biblical chronology.

As a professor, he was very absent-minded. He showed great generosity to his nephews and nieces and to publishers and scientists who helped him in his work.

He was modest in his character. He said of himself shortly before his death, "I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."

Albert Einstein, the German-born American physicist, rejected Newton's explanation of universal gravitation but not the fact of its operation. He said that his own work would have been impossible without Newton's discoveries. He also said that the concepts Newton developed "are even today still guiding our thinking in physics."

Contributor: Margaret C. Jacob, Ph.D., Prof. of History, New School for Social Research.

Additional resources

Parker, Steve. Isaac Newton and Gravity. Chelsea Hse., 1995. Younger readers.

Westfall, Richard S. The Life of Isaac Newton. Cambridge, 1993. A condensed version of Never at Rest, published in 1981.


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