Eighteenth Century Science

The seventeenth century had been made memorable in the sciences by the discoveries of Galileo and Kepler in astronomy, of Harvey, Leeuwenhoeck, Malpighi and Grew in biology, of Boyle in chemistry, and of Guericke, Newton, Huyghens and Roemer in physics. Thus astronomy was put upon a firm foundation and much was done for physics. The eighteenth century was to see in physics the opening up of the field of electricity, and the first beginning of the conception of heat in terms of motion; the foundation of modern chemistry and geology, and the development in astronomy of the nebular hypothesis of the growth of the universe.

The century opened (1701) with the first attempts in organic chemistry made by Boerhaave. He decomposed organic substances such as plants by sublimation and showed that the substances in the plants are taken up from the earth in which they grow after first being dissolved in the water that soaks down from the rains. He followed up these facts by showing that animals are made up of reorganized vegetable matter. His analyses were, of course, imperfect, because chemistry knew nothing as yet of even such elements as oxygen, hydrogen, nitrogen or carbon, the chief components of organisms. In fact, during the first half of the century, chemistry was retarded by the acceptance of Stahl’s phlogiston theory, which was that burning is the release of an imaginary substance called phlogiston, supposed to exist in all things capable of combustion.

In botany the work of the century was mostly descriptive and systematizing by Linnaeeus.

Hailer and Hunter made a beginning in comparative anatomy by trying to compare similar organs in different animals, and Button attempted to describe all the known animals of the globe.

In physics the latter half of the century opened with the demonstration of the identity of electricity with lightning by Franklin (1752). Hitherto electricity had been a plaything. Franklin showed that it is in reality a giant. In 1760 Black discovered latent heat and in 1765 Watt applied the principle to the construction of the first practical steam-engine. Galvani (in 1789) found electricity to be present in animals and noted its effects in contracting the muscles. Volta in 1792 discovered chemical electricity and invented his battery, or "voltaic pile," to produce it. Rumford by studying the effect of motion in producing heat gave the old caloric theory that heat is a substance a severe shock, and opened the way for the nineteenth century conception of the conservation of energy.

In the latter half of the century Hutton and Smith laid the first foundation in geology by studying the formation of the earth.

In astronomy the century ended with a theory of the development of the universe. Lagrange (1736–1813) and Laplace (1749–1827) worked out mathematically the oscillations in the solar system caused by the interaction of its parts and showed its stability. Herschel (1738–1822) discovered the planet Uranus in 1781; found pairs of stars revolving round each other, thus demonstrating that the law of gravitation holds not only in our solar system but in the universe; showed that our solar system seems to be moving in a mass toward the far-off constellation of Hercules, and pointed out that some star clusters seem to consist of dispersed "star-matter" or gases. On these foundations Laplace built his hypothesis of the development of the universe from original gases.

Meantime, toward the close of the century, chemistry had supplied the conception of such gases. In 1756 Black by pouring acidulated water on limestone discovered carbonic acid gas; in 1766 Cavendish obtained hydrogen by pouring sulphuric acid and water on zinc. In 1774 Priestley procured oxygen by heating mercuric oxide, and later (1784) Cavendish combined this new gas with hydrogen by means of an electric spark passed through the mixture and found that they made water. Lavoisier revolutionized chemistry (1778) by showing that all combustion is the effect of combination with oxygen, thus overthrowing the old phlogiston theory. Chemistry had begun to grasp the elements of matter, and was on the high road toward being an exact science.