Overview: Physical Sciences 1700-1799

Overview

During the 1500s, Polish astronomer Nicolas Copernicus (1473-1543) proposed that Earth orbits around the sun rather than vice versa. Copernicus's view was seen as a challenge to widely held beliefs about the universe. These beliefs, however, were based on traditional interpretations of the Bible rather than on scientific observations. The Italian astronomer Galileo Galilei (1564-1642) defended Copernicus's ideas in 1632. In the process, he helped to promote the idea that science should be based on experiment and observation as opposed to faith or reasoning alone. This way of approaching science came to be known as the scientific method and had a great impact on the physical scientists of the 1700s.

The eighteenth century is often referred to as the Enlightenment or the Age of Reason. Scientists stopped relying on untested ideas in ancient texts and began conducting their own experiments and making their own observations. In 1671 Isaac Newton (1642-1727) published his three laws of motion and his law of gravitation. His work showed that the forces of nature are not random, but operated by certain rules. Afterward, scientists came to believe that similar rules would be discovered to explain every phenomenon in the universe.

Physics

During the 1700s, scientists made discoveries about the basic nature of phenomena such as gravity, electricity, and heat. For instance, Benjamin Franklin (1706-1790) suggested the idea of positive and negative electrical charges, and he performed his famous kite experiment in which he showed that lightning is electricity. He also (incorrectly) proposed that electricity involved the exchange of an invisible electrical fluid. (It is now known that electricity involves the exchange or movement of electrons.)

Charles Coulomb (1736-1806) showed that the electrical force between two oppositely charged objects depends on both the size of the charges and on the distance between the objects. These observations mirrored Newton's law of gravitation, which states that the force of gravity between two objects depends on their mass and the distance between them. Coulomb went on to show that a similar law applied to magnetic force.

Another phenomenon physicists investigated during the 1700s was heat. The first step toward determining the nature of heat was the creation of instruments to measure temperature. In 1714 Gabriel Fahrenheit (1686-1736) created a mercury-filled thermometer that was based on the boiling and freezing points of water. In 1742 Anders Celsius (1701-1744) created a similar thermometer, but unlike Fahrenheit, he separated the interval between the boiling and freezing points of water into 100 equal divisions.

Once temperature could be accurately measured, scientists could then perform more useful experiments with heat. Pierre Prévost (1751-1839), for example, determined that cold is the absence of heat and that all objects radiate heat regardless of temperature. (He also believed that heat is an invisible fluid, an idea that persisted into the 1800s.) Joseph Black (1728-1799) found that it takes about five times as much heat to turn boiling water into steam as it does to bring water to the boiling point. Using Black's work, James Watt (1736-1819) developed a practical steam engine. The steam engine eventually became a cheap source of power for both transportation and industry.

New fields of physics developed during the 1700s as well. Daniel Bernoulli (1700-1782) established hydrodynamics—the study of the motion of fluids—and Ernst Chladni (1756-1827) became known as the father of acoustics—the study of sound waves.

Chemistry

In the 1600s Georg Stahl (1660-1734) proposed that objects release an invisible fluid called phlogiston when they burn. This belief held throughout much of the 1700s. Then, in 1791, Antoine Lavoisier (1743-1794) published the results of experiments that disproved the existence of phlogiston. Lavoisier showed that burning results in the gain of oxygen from the air rather than a loss of invisible fluid. (The fluids used to describe electricity, heat, and burning were called imponderable fluids; none of these fluids actually exists.) Lavoisier's experiments also provided evidence for the law of conservation of mass—the idea that the mass of the products of a chemical reaction is equal to the mass of the reactants.

As chemists began to adopt the scientific method during the eighteenth century, they discovered many new compounds. For instance, Joseph Priestly (1733-1804) was the first to discover numerous gases, including ammonia, carbon monoxide, and hydrogen sulfide (the gas responsible for the smell of rotten eggs). Most importantly, however, he is generally credited with the discovery of oxygen.

In addition to gases, many new elements were also isolated during this time period, many of them by Swedish scientists. Georg Brandt (1694-1768) discovered cobalt, Johann Gahn (1745-1818) discovered manganese, Peter Hjelm (1746-1813) discovered molybdenum, and Baron Axel Cronstedt (1722-1765) discovered nickel. Another Swedish scientist who worked with many of these men and encouraged them in their work was Karl Scheele (1742-1786). Although he is not generally credited with the discovery of any element, he made contributions to the discovery of several. He was also the first to isolate many types of acids.

Astronomy

Newton's laws of motion and gravitation could be used to describe the motion of planets and moons. For instance, in 1789 Benjamin Banneker (1731-1806) accurately predicted a solar eclipse. Edmond Halley (1656-1742) showed that Newton's laws applied to comets as well. He analyzed records of past comet appearances and found what seemed to be a pattern. Based on his observations, he correctly predicted that one of these comets (now known as Halley's comet) would appear again in 1758.

Some astronomers in the eighteenth century rather naively assumed that Newton's laws left little for them to discover. In 1781 William Herschel (1738-1822) proved them wrong. Using a large telescope of his own design, he discovered the planet Uranus, a finding that greatly renewed interest in the field of astronomy.

Some astronomers began to consider the origin of the solar system from a purely scientific point of view rather than from a religious or spiritual perspective. In 1796 Pierre Laplace (1749-1827) suggested that the Sun had formed from a spinning cloud of gas that had condensed as it increased in speed. A modified version of Laplace's idea came to be accepted in the twentieth century.

Earth Sciences

In the 1700s geologists began to consider the age of Earth itself. In 1654 James Ussher (1581-1656) concluded that Earth was created in 4004 b.c., based on the timeline of the Bible. One of the first scientists to challenge Ussher's work was Georges Buffon (1707-1788). In 1749 Buffon proposed that Earth was between 75,000 and 100,000 years old. He believed that Earth originated as the result of a comet collision with the Sun, and he based his estimate of Earth's age on the time it would take the planet to cool after its formation from such a collision. (Earth is now estimated to be about 4.6 billion years old.)

Geologists also began to investigate the origin of Earth's rocks and landforms. Abraham Werner (1750-1817) proposed that the main force that shaped Earth was erosion, which wore away the land and carried sediments to the ocean. These sediments then settled out of the water, and pressure changed them to sedimentary rock. Werner recognized that sedimentary rock formed in layers and that the deepest layers were the oldest.

Like Werner, James Hutton (1726-1797) believed that erosion was a major force in the formation of Earth's surface. However, he also believed that volcanoes played an equally important role. He stated that these two forces (erosion and volcanic activity) were at work in the past just as they are in the present. Over long periods, he proposed, these forces could account for the appearance of Earth today. Like Buffon, Hutton came to the conclusion that Earth must be much older than scientists had previously believed. Both men faced opposition from those who saw their work as a challenge to the story of Earth's creation in the Bible. Nevertheless, many of Hutton's ideas came to form the basis of the new science of geology.

Conclusion

By the end of the 1700s physical scientists had used the scientific method to make significant strides toward understanding some of the large questions of science. Astronomers had shown that the solar system was larger and more complex than previously thought. Geologists had started to form theories about Earth's origin and age, despite the religious opposition that they sometimes faced. Physicists had begun to resolve some of the mysteries surrounding heat, electricity, and magnetism, and chemists had carefully catalogued many different types of compounds and elements.

Science began to expand in many directions during the Age of Reason, and the body of knowledge increased dramatically. As a result, scientists would become more specialized in the following century. During the 1800s, further discoveries would be made regarding the nature of heat, magnetism, and especially electricity. Chemists would begin to investigate the nature of the atom, and geologists would develop a timeline of Earth's history. And with the invention of better instruments, astronomers would make discoveries about the composition of and distances between stars. All areas of physical science, however, would continue to rely upon the scientific method.

STACEY R. MURRAY