Unification: Nineteenth-Century Advances in Electromagnetism

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Unification: Nineteenth-Century Advances in Electromagnetism

Overview

Advances in nineteenth-century concepts of electromagnetism moved rapidly from experimental novelties to prominent and practical applications. At the start of the century gas and oil lamps burned in homes, but by the end of the century electric light bulbs illuminated an increasing number of electrified homes. By mid-century (1865) a telegraph cable connected the United States and England. Yet, within a few decades, even this magnificent technological achievement was eclipsed by advancements in electromagnetic theory that spurred the discovery and development of the radio waves that sparked a twentieth-century communications revolution. So rapid were the advances in electromagnetism that by the end of the nineteenth century high energy electromagnetic radiation in the form of x rays was used to diagnose injury. The mathematical unification of nineteenth century experimental work in electromagnetism profoundly shaped the relativity and quantum theories of twentieth-century physics.

Background

In the late-eighteenth and nineteenth centuries philosophical and religious ideas led many scientists to accept the argument that seemingly separate forces of nature (e.g., electricity, magnetism, light, etc.) shared a common and fundamental source. In addition, profound philosophical and scientific questions posed by Isaac Newton's Opticks (published in 1704) regarding the nature of light still dominated the nineteenth century intellectual landscape. Accordingly, in addition to a search for a common source of all natural phenomena, an elusive "ether" through which light could pass was thought necessary to explain the wave-like behavior of light.

The discovery of the relationship between electricity and magnetism at the end of the eighteenth century and the beginning of the nineteenth century was hampered by a rift in the descriptions and models of nature used by mathematicians and experimentalists. To a significant extent, advances in electromagnetic theory during the nineteenth century mirrored unification of these approaches. The culmination of this merger was Scottish physicist James Clerk Maxwell's (1831-1879) development of a set of equations that accurately described electromagnetic phenomena better than any previous nonmathematical model.

The development of Maxwell's equations embodied the mathematical genius of the German mathematician Carl Friedrich Gauss (1777-1855), the reasonings and laboratory work of French scientist André Marie Ampère (1775-1836), the observations of Danish scientist Hans Christian Oersted (1777-1851), and a wealth of experimental evidence provided by English physicist and chemist Michael Faraday (1791-1867).

Although improved mathematical reasoning allowed for deeper understandings of electrical and magnetic experimentation, the emergence of technological society drove the translation and articulation of electromagnetism into the practical world of technological innovation. Simple observations made by scientists—including Benjamin Franklin—during the mid-eighteenth century continued to intrigue scientists and inventors who sought to carry on Franklin's practical descriptions of electrical phenomena. In addition, as the nineteenth century progressed electricity itself came to play an important role as increasingly technological societies attempted to develop the machines and tools needed to meet the needs of rapidly expanding populations and burgeoning urban societies.

Impact

In 1820 Oersted demonstrated the relationship of magnetism to electricity by placing a wire near a magnetic compass. When an electric current was applied to the wire the compass needle showed a deflection characteristic of a changing magnetic field. Inspired by Oersted's demonstrations, a year later Faraday—the devout son of a blacksmith—proved his genius in the practical world of laboratory experimentation by developing a "rotator" now credited as the first electric motor. Faraday's initial apparatus consisted of an electrical current carrying wire rotating about a magnet. Subsequently, Faraday also clearly demonstrated the converse induction of current by rotating magnets about the wire. Although it was another half century before their widespread production, the first practical electric motors were all designed according to principals documented by Faraday. Faraday's method to produce electric current with magnets—known as electromagnetic induction—is a method still used by modern power generators.

Faraday's subsequent publication of his work with electromagnetic induction in 1831 formed the basis of a collection of papers eventually published as Experimental Researches in Electricity. Faradays' work became the standard authoritative reference for nineteenth century scientists and is credited as inspiring and guiding inventors such as Thomas Edison (1847-1931).

During the last decades of the nineteenth century, electric motors drove an increasing number of time- and labor-saving machines that ranged from powerful industrial hoists to personal sewing machines. Electric motors proved safer to manage and more productive than steam or fuel burning engines. In turn, the need for the production of electrical power spawned the construction of dynamos, central power stations, and elaborate electrical distribution systems.

Ampère, a professor of mechanics at the Ecole Polytechnique in Paris, was another influential nineteenth-century scientist influenced by Oersted's observations. Ampère's subsequent influence on the theoretical development of electromagnetic theory is thought by many historians of science to be similar to the influence of Newton's contributions to a functional understanding of gravity. Ampère deepened and tightened the relationship between electrical and magnetic phenomena through a series of brilliantly devised experiments that demonstrated the fundamental principles of electrodynamics (the effects generated by electrical current). Although Ampère made a number of experimental revelations of his own, it was his mathematical brilliance that laid the foundation for subsequent development of electromagnetic theory by quantifying and translating physical electromagnetic phenomena observed by Faraday and other experimentalists into the language of mathematical formulations.

The culminating fusion of nineteenth-century experimentation and mathematical abstraction of electromagnetism came with the development of Maxwell's equations of the electromagnetic field. These four famous equations united concepts regarding electricity, magnetism, and light. Maxwell's equations were, however, more than mere mathematical interpretations of experimental results. By developing precise formulas with enormous predictive power, Maxwell set the stage for the formation of quantum and relativity theory. Twentieth-century giants such as Max Planck (1858-1947), Albert Einstein (1879-1955), and Niels Bohr (1885-1962) all credited Maxwell with laying the foundations for modern physics.

Maxwell collected and first published his electromagnetic field equations in 1864. By 1873 Maxwell's publication, Electricity and Magnetism, fully articulated the known laws of electromagnetism. Perhaps most importantly, Maxwell propositions regarding the propagation of electricity and magnetism resulted in the theory of the electromagnetic wave, and thereby allowed the unification of known electrical and magnetic phenomena into the electromagnetic spectrum.

Although empirical proof of the existence of the electrons did not come until the end of the nineteenth century, Maxwell's equations established that the electric charge is a source of an electric field and that electric lines of force begin and end on electric charges (though this is not necessarily true in a changing magnetic field). In addition, prior to Maxwell's equations it was thought that all waves required a medium of propagation. Maxwell's equations established for scientists that, no matter how counter-intuitive, electromagnetic waves do not require such a medium. That an "ether" or transmission medium was unnecessary for the propagation of electromagnetic radiation (e.g., light) was subsequently demonstrated by the ingenious experiments of Albert Michelson (1852-1931)and Edward Morley (1838-1923).

With his electromagnetic field equations, Maxwell was able to calculate the speed of electromagnetic propagation. When Maxwell's calculated speed of electromagnetic propagation fit well with experimental determinations of the speed of light, Maxwell and other scientists realized that visible light was simply a part of an electromagnetic spectrum. Subsequently, not only did the emerging concept of an electromagnetic spectrum explain much of the phenomena associated with visible light, it also predicted that visible light was only a small part of the spectrum. Based on this insight German physicist Heinrich Rudolf Hertz (1857-1894) in 1888 demonstrated the existence of radio waves.

Hertz regarded Maxwell's equations as a path to a "kingdom" or "great domain" of electricity in which all electromagnetic radiation is understood to be but a slightly differing manifestation of the same electromagnetic phenomena—differing only in terms of wavelength and frequency. Exploration of the electromagnetic spectrum resulted in both theoretical and practical advances. Near the end of the nineteenth century Wilhelm Roentgen's discovery of high energy electromagnetic radiation in the form of x rays, for example, found its first practical medical use.

Maxwell's mathematical unification of experimental work in electromagnetism laid the foundation for the development of relativity and quantum theory. The equations remain a powerful tool to understand electromagnetic fields and waves. Indeed, the equations still have many practical applications, including the design of electrical transmission lines and electromagnetic (e.g., radio, television, microwave, etc.) antenna.

Although the development of radio was largely accomplished in the early years of the twentieth century, its genesis was in the advancement of the nineteenth-century understanding of electromagnetism. Not until the development of the Internet nearly a century later would another technology besides radio so completely tear down the walls of geographic distance in human society. For the first time humans could communicate in their language over long distances with immediacy and spontaneity. Divergent and diverse societies became, for the first time, united in an increasingly global civilization.

The study of the interaction of the fundamental forces of nature—including electromagnetism—dominates many modern research programs.

K. LEE LERNER