Overview: Physical Sciences 1800-1899

The end of the eighteenth century found two basic Newtonian ideas triumphant. Scientists carefully experimented with natural phenomena and measured important features of these happenings, trying all the while to establish quantitative relations among the changing elements, The paradigm for this is found in Isaac Newton's (1642-1727) landmark 1704 work, Opticks. Another Newtonian paradigm was his theory of gravitation. Here one takes a mechanical model of small particles with forces of attraction or repulsion between any two of them, and then proceeds to deduce their behavior following from some basic force laws. Both the Newtonian experimental method and the Newtonian mechanical model of the universe were widely accepted by those investigating the physical world.

Physics

An amazing discovery occurred at the very beginning of the nineteenth century: electricity could be generated and made to flow in a current. Sir Humphry Davy (1778-1829) immediately used this current of electricity to analyze the chemical composition of a number of substances. A little later, Hans Christian Oersted (1777-1851), a Danish scientist, noticed that flowing electricity created magnetic effects, which was followed by the discovery by British scientist Michael Faraday (1791-1867)that moving magnets could conversely create electric currents. All of this experimental work called for a theoretical explanation, which scientists required to be mathematically rigorous and precise. The grand theory of James Clerk Maxwell (1831-1879) did just that in 1862.

Scientists had known many of the properties of light for a long time. Yet early in the nineteenth century several novel properties were discovered. The most important of these were that: 1) beams of light can "interfere" with each other; and 2) reflected light is polarized (which is why some sunglasses can reduce the glare of reflected sunlight). These observations were instrumental in leading to a new wave theory of light, which ultimately replaced the earlier Newtonian particle theory. Both Thomas Young (1773-1829) and Augustin Fresnel (1788-1827) are credited with the development of this wave theory. It was Maxwell later in the century who declared that light waves in a medium called the ether could be represented as electromagnetic vibrations in this ether.

Maxwell's theory also implied that oscillating electric charges would produce invisible electromagnetic waves traveling through the surrounding space. Heinrich Hertz (1857-1894) devised experiments to produce and detect these waves, which are the basis for radio and television today.

No new properties of heat were discovered at the beginning of the century. Instead, scientists investigated the way that heat engines were capable of doing work, either pumping water from flooded mines or turning a huge flywheel, which in turn could power smaller machines. French scientist Sadi Carnot (1796-1832) published his theories about ideal, perfectly efficient engines early in the century. The focus on the conversion of heat to mechanical work led English scientist James Joule (1818-1889) to investigate the reverse process—namely, the conversion of mechanical work to heat. These researches (and many others) led to the concept of "energy," which can take many forms, heat being one of them. The notion of energy was introduced with the Law of Conservation of Energy, which states that energy is neither created nor destroyed; it only changes from one form to another.

It is common knowledge that heat flows from hotter to cooler bodies. In the course of investigating, for instance, how the temperature changes in time along a metal rod with one end in a furnace, Joseph Fourier (1768-1830) used a mathematical approach that had far-reaching consequences for the use of mathematical techniques in the physical sciences. This natural tendency of heat to flow from hotter to cooler bodies was described by another important law propounded by Rudolf Clausius (1822-1888) towards the end of the century. The assertion that in a closed system the total amount of heat available to do work gradually gets smaller is known as The Second Law of Thermodynamics.

At the beginning of the century most scientists considered heat to be a weightless fluid. Electricity too was thought to be a fluid. Yet as time went on, more and more scientists attempted to give a theoretical explanation of all observable effects in terms of small unobservable particles of matter and their interactions according to mechanical laws. Thus, the pressure of an enclosed gas was attributed to the impact of minute particles on the wall of the container. Temperature likewise was the observable effect of the energy of the constituent particles making up the gas. But in order to give a complete mathematical treatment of the behavior of these collections of particles, scientists had to appeal to statistical averages and probabilities. This was a novel approach to explaining the observable world, because the earlier Newtonian model relied on strictly deterministic connections between causes and effects. American scientist Josiah Willard Gibbs (1839-1903) played a major role in this development, as did German scientist Ludwig Boltzmann (1844-1906).

Chemistry

The Newtonian model, which saw the world as composed of small particles of matter attracting and repelling one another according to strict mathematical laws, was extremely fruitful. At the beginning of the century John Dalton (1766-1844) was inspired to develop the atomic theory of chemical substances. In this theory chemical elements were each composed of qualitatively similar atoms, and atoms combined in a fixed ratio to make chemical compounds. The atoms of different elements differed by weight, so the atoms of any one element all had the same weight and the molecules of any distinct chemical compound also had the same weight, because the proportions of the atoms in the compound were fixed. Yet no one was able to arrive at consistent results using this atomic theory until Amedeo Avogadro (1776-1856). He proposed that equal volumes of gases at the same temperature and pressure have the same number of molecules. Once that principle was understood late in the century, the relative weights of molecules and thus atoms could be fixed. This led quickly to Dmitri Mendeleyev's (1834-1907) table arranging the chemical elements by weight in a pattern of recurring properties.

Even before these results, it was discovered that substances with the same chemical composition sometimes had different properties. This was especially evident in the so-called organic chemicals—those that contain carbon. This led to the recognition that the structure of molecules—how the atoms are arranged—is as important as the chemical composition. All these developments led to the astonishing development of chemical science, with its delicate instrumentation and fine measuring devices, and chemical engineering, with its abundance of synthetic substances.

Earth Sciences

An overview of the nineteenth century would not be complete without a reference to the important developments in geology that turned this discipline from an apology for the Biblical account of creation into a science of discovery. The evidence for glaciation was recognized. The layers of different sorts of rocks were traced and plotted from country to neighboring country. The identification of these strata was made possible by the correlation of the fossils found within them. And the fossil record helped to establish a time order for geologic processes. The length of time for geological changes to occur was a discovery that surprised many people: the earth was much older than anyone had thought.

Astronomy

Astronomy, which began the century carefully mapping the positions of heavenly bodies by means of larger and better calibrated telescopes, discovered in the middle of the century that starlight could be analyzed by a spectroscope, and thus the chemical composition of the stars could be determined. Techniques for measuring the distance to stars were also developed. The newly developed technology of photography helped enormously in these tasks. As geology expanded the time scale of our world, so did astronomy expand the spatial dimensions of our universe.

Conclusion

As the century drew to a close, many physical scientists felt that nearly everything had been discovered about the physical world. The only thing left to do was to apply what we had already learned about the world. Except, as the scientist William Thomson (better known as Lord Kelvin; 1824-1907) pointed out, there were two tiny clouds darkening the prospects for all the wonderful mechanical explanations of the world: the difficulty of accounting for the motion of Earth through the ether, and the inability to account for the energy distribution of certain sorts of radiation. We shall see that these two "clouds" were in reality the two doors to the new physical sciences of the twentieth century.

MORTON L. SCHAGRIN