The history of science during the 18th and 19th cent. is largely the history of the individual branches as they developed into the traditional forms by which they are still recognized today.The Evolution of Mathematics and Physics
In mathematics the calculus invented by Newton and G. W. Leibniz was developed by the Bernoullis, Leonhard Euler, and J. L. Lagrange into a powerful tool that was to be used not only in mathematics but also in physics and astronomy. Newtonian physics spread to the Continent slowly, its acceptance being hindered by adherents of the older Cartesian philosophy and by disputes over priority in the invention of the calculus. However, by the late 18th cent. it was firmly established. Other branches of physics came into their own during this period. The study of electricity expanded to include electric currents and magnetism, and it was finally synthesized in the theory of electromagnetic radiation of J. C. Maxwell in the second half of the 19th cent. These discoveries provided the foundation for the technological advances in communications and in other fields using electrical energy. The wave theory of light was revived at the beginning of the 19th cent. by Thomas Young and developed by others; Maxwell's theory showed that light was one form of electromagnetic energy. In the 18th cent. scientists thought that heat was a kind of fluid called caloric. However, by the early 19th cent. it became apparent that heat is a form of motion—the motion of the particles of which substances are composed. The classical theory of heat and thermodynamics was developed by J. P. Joule, Lord Kelvin, R. J. E. Clausius, and others, who showed the relation between heat and other forms of energy and formulated the law of conservation of energy. Maxwell, Ludwig Boltzmann and others developed statistical mechanics, which treats matter as a large aggregate of many particles and applies statistical methods to the prediction of its behavior.
Chemistry became increasingly quantitative and experimental during the 18th cent. Joseph Priestley and other English scientists made a number of discoveries which served as the basis for A. L. Lavoisier's explanation of the role of oxygen in combustion and respiration. John Dalton proposed the modern version of the atomic theory in the early 19th cent. and Dmitri Mendeleev, in his periodic table, showed how the chemical elements described by the atomic theory could be arranged in a systematic way. In the mid-19th cent. R. W. Bunsen and G. R. Kirchhoff developed spectroscopy as a tool for chemical analysis. Also in the 19th cent., the synthesis of urea by Friedrich Wöhler (1828) established that organic substances are composed of the same kinds of atoms as inorganic substances, thus opening a new era in the study of organic chemistry.
Astronomy progressed on the theoretical level through the contributions to celestial mechanics of P. S. Laplace and others, and on the observational level through the work of many scientists. They included William Herschel, who built telescopes and discovered Uranus (1781), the first planet found in modern times, and his son John Herschel, who extended his father's observations to the Southern Hemisphere skies and pioneered in astrophotography, which in modern astronomy is the chief method of observation. Another tool that found important application in astronomy was the spectroscope. Increasingly astronomers made use of the instruments, techniques, and theories of other fields, particularly physics.
Modern geology may be said to date from the work of James Hutton, who postulated (1785) that the geologic processes and forces that had shaped the earth were still in operation and could be observed directly. Georges Cuvier, the French naturalist, founded the field of comparative anatomy and applied its principles to geology in the study of the fossil remains of animals of the distant past, thus also founding the field of paleontology.
In biology Carolus Linnaeus instituted a system of classification of animals and plants, and improvements in this system helped scientists to arrange different forms of life according to complexity, suggesting to some that organisms may evolve from simple to complex forms. In the 19th cent. K. E. von Baer founded the field of embryology, the study of the earliest stages of different forms of life, and Matthias Schleiden and Theodor Schwann identified the cell as the basic unit of living matter. In medicine the treatment of disease was furthered by the introduction of smallpox vaccination by Edward Jenner and the recognition of the role of germs and viruses in causing diseases. A number of ways of reducing the growth of such organisms were introduced, including pasteurization of foods and antiseptic surgery. Anesthetics were introduced in the 19th cent. by several scientists, and, through chemistry, new medications were developed that aimed at treatment of specific ailments.
Some of the greatest changes were in the area of technology, in the development of new sources of energy and their application in transportation, communications, and industry. Among the important aspects of the Industrial Revolution were the invention of the steam engine by James Watt and its use in factories, mines, ships, and railroad engines; the development of the internal-combustion engine and the companion growth of petroleum technology to provide fuel for it; the invention of many different kinds of agricultural machinery and the resulting enormous increase in productivity; the improvement of many metallurgical processes, particularly those involving iron and steel; and the invention of the electric generator, electric motor, and numerous electric devices that are now commonplace.