Hans Christian Oersted

1777-1851

Danish Physicist

In 1820 Hans Oersted described the action of an electric current on a magnetized needle, demonstrating a connection between electric and magnetic forces unexpected by the majority of researchers in electricity and magnetism. His observation stimulated further work on electromagnetic phenomena by numerous investigators, including André Ampère (1775-1836) and Michael Faraday (1791-1867), leading to a grand synthesis in 1873 by English physicist James Clerk Maxwell (1831-1879). Maxwell's equations explained the behavior of light as an electromagnetic wave, led to the discovery of radio waves, and posed questions concerning the velocity of light which would lead to Einstein's theory of relativity.

Oersted received a broad education in scientific subjects at the University of Copenhagen, receiving a degree in pharmacy in 1797. Two years later he received his doctorate for a thesis that argued for the importance of the philosophy of Immanuel Kant (1724-1804) for the study of nature. In 1801 Oersted built his own version of the Voltaic pile, invented the year before by Alessandro Volta (1745-1827), and used it to gain entrance to laboratories throughout the German-speaking world. At the same time, he was able to attend lectures on the "Naturphilosophie" being developed by a number of German scholars. Always interested in philosophical simplicity, Oersted was suspicious of the new chemistry introduced by Antoine Lavoisier (1743-1794) with its numerous chemical elements, preferring the "chemistry of opposites" proposed by Hungarian chemist J. J. Winterl. Drawing from Kant the notion that there are only two basic forces, attraction and repulsion, Oersted came to believe that the various forces apparent in nature were all versions of the same basic two.

By 1820 the majority of physicists believed that electricity and magnetism were unrelated, although they had some superficial similarities. Oersted, in contrast, believed that the same electric current that could produce light or heat or chemical effects depending on the size and surroundings of the wire that carried it must also be the source of magnetic effects, though not in the direction in the current. By sending a current down a wire passing by a magnetic compass, he was able to produce a slight deflection of the compass needle. Refining the experiment over the next few months, he was able to demonstrate that the lines of the magnetic field run in circles about a current carrying wire.

Building on Oersted's result, the French physicist Ampère , and later Biot and Savart, was able to determine the detailed magnetic interaction between electrical circuits. Ampère also provided an explanation for the existence of permanent magnets as materials with built-in electrical currents. Seeing that an electrical current could produce magnetic effects, the logical question arose as to whether a magnetic field could produce an electrical effect. English physicist and chemist Michael Faraday provided the correct connection about 10 years later by the discovery of electromagnetic induction, that is, the creation of a voltage by changing the magnetic fluxthrough a surface. The results of Ampère and Faraday attracted the attention of the James Clerk Maxwell, who had the mathematical skills needed to express the experimental conclusions in the form of differential equations. Maxwell then noted that his equations could take the form describing transverse waves in empty space, waves that traveled with a speed related to the force constants appearing in the Coulomb electrostatic force law and the Ampère law for the magnetic force. Numerically, the speed of Maxwell's waves turned out to be three hundred million meters per second, the known speed of light in vacuum, thus suggesting that light was an electromagnetic wave. The creation of lower frequency radio waves, and Einstein's theory of relativity, needed to explain how the speed of Maxwell's waves could be the same as measured by all observers soon followed Maxwell's discovery.

Oersted remained fascinated with philosophy and at the time of his death was writing articles for a book entitled The Soul in Nature. While Oersted's bias against atomic theory and the growing list of chemical elements was certainly incorrect in hindsight, the search for a unified description of the forces of nature remains an important theme in modern physics.

DONALD R. FRANCESCHETTI