His greatest achievement was in astronomy. Galileo, Copernicus, and other investigators had already concluded that the earth is but one of many similar bodies moving around the sun, which in turn is only one of countless suns—for every star is a sun. Now Newton wondered what held these mighty spheres in their places in space, for they appeared to move in definite and well-regulated orbits without any visible support or prop. It is alleged that the answer to the problem was suggested by the great philosopher's observation of a falling apple. The same invisible force that made the apple fall to the ground must, he is said to have reasoned, control the moon, sun, and stars. The earth is pulled toward the sun, as the apple to the earth, but it is also pulled toward the stars, each of which is a sun so far away that it looks to us very small. The result is that the earth neither falls to the sun nor to any one star, but moves around the sun in a regular path.
This suggestive principle by which every body in the universe is pulled towards every other body, Newton called the law of universal gravitation. Newton's law [Footnote: It was really only a shrewd guess, but it appears to work so well that we often call it a "law.">[ was expressed in a simple mathematical formula [Footnote: "The force increases directly in proportion to the product of the masses, and inversely in proportion to the square of the distance.">[ by means of which physics and astronomy were developed as mathematical sciences. When a modern astronomer foretells an eclipse of the sun or discusses the course of a comet, or when a physicist informs us that he has weighed the earth, he is depending directly or indirectly upon Newton's discovery.
[Sidenote: Experimental and Applied Science]
The brilliance of Sir Isaac Newton's individual achievement should not obscure the fame of a host of other justly celebrated scientists and inventors. One of Newton's contemporaries, the German philosopher Gottfried Wilhelm von Leibnitz (1646-1716), elaborated a new and valuable branch of mathematics, the differential calculus, [Footnote: The credit for this achievement was also claimed by Newton.] which has proved to be of immense service in modern engineering. At the same time, the first experiments were being made with the mysterious potencies of electricity: the electrical researches of Benjamin Franklin (1706-1790), his discovery that flashes of lightning are merely electrical phenomena and his invention of the lightning rod are too familiar to need repeating; the work of Luigi Galvani (1737-1798) and of Count Alessandro Volta (1745-1827), two famous Italian physicists, is less well known, but their labors contributed much to the development of physical science, and their memory is perpetuated whenever the modern electrician refers to a "voltaic cell" or when the tinsmith speaks of "galvanized" iron. In this same period, the first important advances were made in the construction of balloons, and the conquest of the air was begun. In the eighteenth century, moreover, the foundations of modern chemistry were laid by Joseph Priestley (1733- 1804), Antoine Laurent Lavoisier (1743-1794), and Henry Cavendish (1731-1810); oxygen was discovered, water was decomposed into its elements, and the nomenclature of modern chemistry had its inception. In medicine and surgery, too, pioneer work was done by John Hunter (1728-1793), a noted Scotch surgeon and anatomist, and by the Swiss professor Albrecht von Haller (1708-1777), the "father of modern physiology"; the facts which eighteenth-century physicians discovered regarding the circulation of the blood made possible more intelligent and more effective methods of treating disease; and just at the close of the eighteenth century, Edward Jenner (1749-1823), an English physician, demonstrated that the dread disease of smallpox could be prevented by vaccination. Geographical knowledge was vastly extended by the voyages of scientific explorers, like the English navigator Captain James Cook [Footnote: The Captain Cook who discovered, or rediscovered, Australia. See above, P. 340.] (1728-1779) and the French sailor Louis de Bougainville (1739-1811), in the hitherto uncharted expanses of the southern Pacific. Furthermore, since these explorers frequently brought home specimens of unfamiliar tropical animals and plants, rich material was provided for zoology and botany, which, thanks to the efforts of the Frenchman Georges de Buffon (1707-1788) and of the Swede Carolus Linnaeus (1707-1778), were just becoming important sciences.
[Sidenote: Popularity of the New Science]
One reason for the rapid development of natural science in the eighteenth century was the unprecedented popularity and favor enjoyed by scientists. Kings granted large pensions to scientists; British ministers bestowed remunerative offices, and petty princes showered valuable gifts upon them. Pretentious observatories with ponderous telescopes were built, often at public expense, in almost every country of Europe. Groups of learned men were everywhere banded together in "academies" or "societies." The "Royal Society" of London, founded in 1662, listened to reports of the latest achievements in mathematics, astronomy, and physics. The members of the _Académie française (French Academy) were granted pensions by Louis XIV and even reckoned Newton among their honorary members.
Never before had there been such interest in science, and never before had there been such opportunity to learn. Printing was now well developed; the learned societies and observatories published reports of the latest development in all branches of knowledge. Encyclopedias were gotten out professing to embody in one set of volumes the latest information relative to all the new sciences. Books were too expensive for the common person, but not so for the bourgeoisie, nor for numerous nobles. Indeed, it became quite the fashion in society to be a "savant," a scientist, a philosopher, to dabble in chemistry, perhaps even to have a little laboratory or a telescope, and to dazzle one's friends with one's knowledge.
[Sidenote: The Spirit of Progress and Reform]
It seemed as if the golden age was dawning: the human mind seemed to be awakening from the slumber of centuries to con the world, to unravel the mysteries of life, and to discover the secrets of the universe. Confident that only a little thought would be necessary to free the world from vice, ignorance, and superstition, thinkers now turned boldly to attack the vexing problems of religion and morality, to criticize state, society, and church, and to point the way to a new and earthly paradise.
This tendency—this enthusiasm—has usually been styled "rationalism" because its champions sought to make everything rational or reasonable. Its foremost representatives were to be found in Great Britain between 1675 and 1725. They wrote many books discussing abstruse problems of philosophy, which can have slight interest for us; but certain ideas they had of very practical importance, ideas which probably found their most notable expression in the writings of John Locke (1632-1704). Locke argued (1) that all government exists, or should exist, by consent of the governed—by a "social" contract, as it were; (2) that education should be more widespread; (3) that superstition and religious formalism should not be allowed to obscure "natural laws" and "natural religion"; and (4) that religious toleration should be granted to all but atheists.