17th Century Scientists

By Tim Lambert

Science flourished in the 17th century. The ancient Greeks could be said to be scientists. They thought by using their reason they could work out why the natural world behaves as it does. However, the Greeks never tested their theories by carrying out practical experiments. As a result, many of their ideas about the natural world were wrong.

Unfortunately, the ancient Greek philosophers were held in very high esteem and for centuries hardly anyone questioned their theories. This began to change in the late 16th century and the early 17th century. People began to conduct experiments to see if theories about the world were true.

In England, a man named Francis Bacon (1561-1626) declared that people should not accept that a theory was true just because a Greek philosopher said it was. He argued that careful observation and experiment were the keys to finding out how the natural world works. Gradually this new method of understanding the world took over. By the late 17th century the new scientific approach had triumphed everywhere in Europe. By then scientists were carrying out careful observations and experiments to find out how the world works.

There was a change in attitude during the 17th century. Previously people saw nature almost like a living thing. Now they began to see it as a machine (Isaac Newton called God the ‘Divine Watchmaker’). Furthermore, Francis Bacon believed that science (or natural philosophy as it was called) could greatly improve people’s lives. By the late 17th century there was a new mood of optimism and science was making great progress.

Things began to change in the 16th century. In the 2nd century AD, an astronomer called Ptolemy stated that the Earth is the center of the universe. The sun and the other planets orbit the Earth. In the 16th century, a Polish clergyman called Nicolaus Copernicus (1473-1543) realized this is untrue. The Earth and the other planets orbit the Sun. However, his theory was not published until just before his death.

Another great astronomer of the 16th century was Tycho Brahe (1546-1601). He made accurate observations of the positions of stars. However, Brahe did not accept the Copernican theory. Instead, he believed that the Sun revolved around the Earth and the other planets revolved around the Sun. In 1572 Brahe saw a new star (a nova). The Greek philosopher Aristotle said the heavens were unchanging. Change and decay, he said, only happened on Earth. Obviously, Aristotle was wrong.

He was followed by Johannes Kepler (1571-1630). In the 16th century, people believed that the planets move in circles. Kepler showed they orbit the Sun in ellipses and they move faster as they approach the Sun. Kepler published two laws of planetary motion in 1609. He published a third in 1619. Furthermore, in 1604, Kepler published a book on Optics.


One of the most famous scientists of all time was Galileo. In 1589 Galileo became a lecturer in mathematics at Pisa University. At that time the ancient Greek philosopher Aristotle was held in very high esteem and many people accepted his ideas without question. However, Galileo did not. Aristotle said that if two objects, a heavy one and a light one both fall from a height the large one will reach the ground first.

According to legend, Galileo tested the theory by dropping two different weights from the Leaning Tower of Pisa. Both hit the ground at the same time. However many people now believe this famous experiment is a myth. it never actually took place. In any case, other scholars had already concluded that Aristotle was wrong.

Then in 1509, Galileo heard of a new invention from Holland. A man named Hans Lippershey had invented the telescope. Galileo made his own telescope and soon improved it. Using a telescope Galileo was able to see several things invisible to the naked eye. Firstly he could see many stars not visible without a telescope. Secondly, the ancient Greeks believed that the Moon was smooth. Looking through a telescope Galileo could see the Moon’s surface is rough, with mountains and craters.

He also discovered 4 small ‘moons’ orbiting the planet Jupiter. At the time these were astonishing discoveries. Until then nobody knew that any of the other planets, apart from Earth, had ‘moons’. In 1610 Galileo wrote a book called Sidereus Nuncius or The Sidereal Messenger.

At that time astronomers were debating sunspots. A German named Christoph Scheiner claimed that they were satellites of the sun. In 1613 Galileo argued that sunspots are actually on the surface of the sun. Copernicus also argued that the Earth and the other planets orbit the Sun. At first, the church did not have a problem with his theory. However, opinion gradually hardened and in 1616 the Copernican theory was declared heretical.

There is a passage in the Old Testament where a prophet named Joshua commanded the Sun to stand still in the sky (Joshua 10:12-13). Some scholars said this meant the Sun must move. Of course, Joshua knew nothing about Astronomy. To him, the Sun appeared to move across the sky. Naturally, he would command the Sun to stand still and to him, it would have appeared to stand still. The church’s objection to the Copernican theory was based on a misinterpretation of the Bible.

However, Galileo was a resolute supporter of the Copernican theory. In 1632 he published a book called Dialogue Concerning the Two Chief World Systems. As a result, he was summoned to Rome to be examined by the Inquisition. He arrived in January 1633. Galileo was threatened with torture unless he renounced the Copernican theory. Not surprisingly he agreed to do so. Nevertheless, he was put under house arrest for the rest of his life.

In 1634 Galileo published a book about mechanics called Dialogue Concerning Two New Sciences. Then in 1637, he noticed that the moon moved slightly from side to side. Galileo died on 8 January 1642 aged 77.

The Advance of Medicine

At this time doctors made great progress in understanding how the human body works. In 1628 William Harvey published his discovery of how blood circulates the body. The Roman writer Galen said that blood passes from one side of the heart to the other through the septum. However, by 1555 the great surgeon Vesalius had concluded that no such holes exist and that blood can not pass from one side of the heart to the other in that way.

In 1559 a man named Realdo Colombo demonstrated that blood travels from one side of the heart to the other through the lungs. Eventually, William Harvey realized that the heart is a pump. Each time it contracts it pumps out blood. Harvey then estimated how much blood was being pumped each time. The Roman writer Galen believed that the body constantly makes new blood and uses up the old (rather like an engine using up petrol). However, Harvey realized this is not true. Instead, the blood circulates the body.

In the 17th century, medicine was still handicapped by wrong ideas about the human body. Most doctors still thought that there were four fluids or ‘humors’ in the body, blood, phlegm, yellow bile, and black bile. Illness resulted when you had too much of one humor. Nevertheless, during the 17th century, a more scientific approach to medicine emerged and some doctors began to question traditional ideas. In the 17th century, medicine was helped by the microscope (invented at the end of the 16th century). In 1658 Jan Swammerdam first observed red blood corpuscles. In 1661 Marcello Malpighi discovered capillaries. Then in 1665 Robert Hooke was the first person to describe cells in his book Micrographia.

Isaac Newton

Isaac Newton is Britain’s greatest scientist. Britain’s oldest scientific society began in 1645 when a group of philosophers and mathematicians began holding meetings to discuss science or natural philosophy as it was called. Charles II was interested in science and in 1662 he granted them a charter and they became the Royal Society.

In 1667 Isaac Newton was elected a fellow of Trinity College. The same year he was elected a member of the Royal Society. In February 1672 a paper he wrote about light and colors was read to the society. In 1669 Newton became Lucasian professor of mathematics. In the meantime, in 1668, he invented a reflecting telescope.

Newton published his masterpiece Philosophiae Naturalis Principia Mathematica in 1687. It set out his theory of gravity and his laws of motion. Newton realized that there is a universal force (gravity) that attracts all objects in the universe to each other. His theory of gravity explained the movements of the planets. In 1704 Newton also published a book on light called Optics. Newton showed that white light is made up of several colors. Meanwhile, in 1704 he published another great work about light. Isaac Newton died on 20 March 1727.

Many other scientists worked in the late 17th century. Christiaan Huygens (1629-1695) discovered Titan, the moon of Saturn. In 1656 he made the first pendulum clock, which made an accurate measurement of time possible. Antonie van Leeuwenhoek (1632-1723) made his own microscopes and through them, he made many observations. Meanwhile, in 1661 Robert Boyle (1627-1691) published The Skeptical Chemist, which laid the foundations of modern chemistry. Boyle rejected the Greek thinker Aristotle’s idea that the world is made up of four elements, water, earth, fire, and air. Boyle is also famous for Boyle’s law (The volume of a gas kept at a constant temperature is inversely proportional to its pressure).

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