Isaac Newton showed that a prism of glass can separate
white light into a spectrum of colors.

SHIRLEY GRIFFITH: This is Shirley Griffith.

STEVE EMBER: And this is
Steve Ember with the VOA Special English program EXPLORATIONS. Today we tell
about one of the world's greatest scientists, Isaac Newton.

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SHIRLEY GRIFFITH: Much of today's science of physics is based
on Newton's discovery of the three laws of motion and his theory of gravity.
Newton also developed one of the most powerful tools of mathematics. It is the
method we call calculus.

Late in his life, Newton said of his work: "If
I saw further than other men, it was because I stood on the shoulders of giants.
"

STEVE EMBER: One of those giants was the great Italian scientist,
Galileo. Galileo died the same year Newton was born. Another of the giants was
the Polish scientist Nicholas Copernicus. He lived a hundred years before
Newton.

Copernicus had begun a scientific revolution. It led to a
completely new understanding of how the universe worked. Galileo continued and
expanded the work of Copernicus.

Isaac Newton built on the ideas of
these two scientists and others. He found and proved the answers for which they
searched.

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SHIRLEY GRIFFITH: Isaac Newton was born in
Woolsthorpe, England, on December twenty-fifth, sixteen forty-two.

He
was born early. He was a small baby and very weak. No one expected him to
survive. But he surprised everyone. He had one of the most powerful minds in
history. And he lived until he was eighty-four.

Newton's father died
before he was born. His mother married again a few years later. She left Isaac
with his grandmother.

The boy was not a good student. Yet he liked to
make things, such as kites and clocks and simple machines.

STEVE EMBER:
Newton also enjoyed finding new ways to answer questions or solve problems. As a
boy, for example, he decided to find a way to measure the speed of the
wind.

On a windy day, he measured how far he could jump with the wind at
his back. Then he measured how far he could jump with the wind in his face. From
the difference between the two jumps, he made his own measure of the strength of
the wind.

Strangely, Newton became a much better student after a boy
kicked him in the stomach.

The boy was one of the best students in the
school. Newton decided to get even by getting higher marks than the boy who
kicked him. In a short time, Newton became the top student at the
school.

SHIRLEY GRIFFITH: Newton left school to help on the family
farm.

It soon became clear, however, that the boy was not a good farmer.
He spent his time solving mathematical problems, instead of taking care of the
crops. He spent hours visiting a bookstore in town, instead of selling his
vegetables in the market.

An uncle decided that Newton would do better
as a student than as a farmer. So he helped the young man enter Cambridge
University to study mathematics.

Newton completed his university studies
five years later, in sixteen sixty-five. He was twenty-two years old.

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STEVE EMBER: At that time, a deadly plague was spreading across
England. To escape the disease, Newton returned to the family farm. He did more
thinking than farming. In doing so, he found the answers to some of the greatest
mysteries of science.

Newton used his great skill in mathematics to form
a better understanding of the world and the universe. He used methods he had
learned as a boy in making things. He experimented. Then he studied the results
and used what he had learned to design new experiments.

Newton's work
led him to create a new method in mathematics for measuring areas curved in
shape. He also used it to find how much material was contained in solid objects.
The method he created became known as integral calculus.

SHIRLEY
GRIFFITH: One day, sitting in the garden, Newton watched an apple fall from a
tree. He began to wonder if the same force that pulled the apple down also kept
the moon circling the Earth. Newton believed it was. And he believed it could be
measured.

He called the force "gravity." He began to examine it
carefully.

He decided that the strength of the force keeping a planet in
orbit around the sun depended on two things. One was the amount of mass in the
planet and the sun. The other was how far apart they were.

STEVE EMBER:
Newton was able to find the exact relationship between distance and gravity. He
multiplied the mass of one space object by the mass of the other. Then he
divided that number by the square of their distance apart. The result was the
strength of the gravity force that tied them to each other.

Newton
proved his idea by measuring how much gravity force would be needed to keep the
moon orbiting the Earth. Then he measured the mass of the Earth and the moon,
and the distance between them. He found that his measurement of the gravity
force produced was not the same as the force needed. But the numbers were
close.

Newton did not tell anyone about his discovery. He put it aside
to work on other ideas. Later, with correct measurements of the size of the
Earth, he found that the numbers were exactly the same.

SHIRLEY
GRIFFITH: Newton spent time studying light and colors. He used a three-sided
piece of glass called a prism.

He sent a beam of sunlight through the
prism. It fell on a white surface. The prism separated the beam of sunlight into
the colors of a rainbow. Newton believed that all these colors -- mixed together
in light -- produced the color white. He proved this by letting the beam of
rainbow-colored light pass through another prism. This changed the colored light
back to white light.

STEVE EMBER: Newton's study of light led him to
learn why faraway objects seen through a telescope do not seem sharp and clear.
The curved glass lenses at each end of the telescope acted like prisms. They
produced a circle of colored light around an object. This created an unclear
picture.

A few years later, Newton built a different kind of telescope.
It used a curved mirror to make faraway objects seem larger.

Light
reflected from the surface of the mirror, instead of passing through a curved
glass lens. Newton's reflecting telescope produced much clearer pictures than
the old kind of telescope.

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SHIRLEY GRIFFITH: Years
later, the British astronomer Edmund Halley visited Newton. He said he wanted
Newton's help in finding an answer to a problem no one had been able to solve.
The question was this: What is the path of a planet going around the
sun?

Newton immediately gave Halley the answer: an egg-shaped path
called an ellipse.

Halley was surprised. He asked for Newton's proof.
Newton no longer had the papers from his earlier work. He was able to recreate
them, however. He showed them to Halley. He also showed Halley all his other
scientific work.

STEVE EMBER: Halley said Newton's scientific
discoveries were the greatest ever made. He urged Newton to share them with the
world.

Newton began to write a book that explained what he had done. It
was published in sixteen eighty-seven. Newton called his book “The Mathematical
Principles of Natural Philosophy.” The book is considered the greatest
scientific work ever written.

SHIRLEY GRIFFITH: In his book, Newton
explains the three natural laws of motion. The first law is that an object not
moving remains still. And one that is moving continues to move at an unchanging
speed, so long as no outside force influences it.

Objects in space
continue to move, because nothing exists in space to stop them.

Newton's
second law of motion describes force. It says force equals the mass of an
object, multiplied by the change in speed it produces in an object.

His
third law says that for every action, there is an equal and opposite
reaction.

STEVE EMBER: From these three laws, Newton was able to show
how the universe worked. He proved it with easily understood mathematics.
Scientists everywhere accepted Newton's ideas.

The leading English poet
of Newton's time, Alexander Pope, honored the scientist with these words:
"Nature and nature's laws lay hid in night. God said, --'Let Newton be!' - and
all was light. "

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SHIRLEY GRIFFITH: This Special English
program was written by Marilyn Christiano and Frank Beardsley. This is Shirley
Griffith.

STEVE EMBER: And this is Steve Ember. Listen again next week
for another Explorations program on the Voice of America.