[b. Angoulême, France, June 14, 1736, d. Paris, August 23, 1806]

Although Coulomb is best remembered for his work with electric charges, he was also the first to show that the force of friction is always proportional to the pressure exerted at 90° to the surface. His experiments with electricity, using a sensitive apparatus called the torsion balance, showed that the force between two charges displays inverse variation with respect to the square of the distance between the charges and direct variation with respect to the product of their size (mathematically the same as the law of gravity).

The French physicist Charles Augustin de Coulomb (1736-1806) was famous for establishing the relation for computing the force between electrical charges. He also did pioneering work on sliding and fluid friction.

Charles Augustin de Coulomb was born into a distinguished family of Angoulême on June 14, 1736. After being educated in Paris, he spent 9 years in Martinique as an army engineer. Ill health forced him to return to France in 1776, where during the next 13 years his scientific work brought him fame, military advancement, and membership in the Royal Academy of Sciences. He was appointed intendant of France's waters and fountains in 1784. The next 5 years were spent in writing his memoirs on electricity and magnetism. Coulomb had become a noted and influential figure in the academic world but resigned all his positions at the outbreak of the Revolution. He returned to Paris in 1802 for an appointment as one of the inspector generals of public instruction.

Coulomb's 1779 memoir, The Theory of Simple Machines, is a compilation of his early experiments on statics and mechanics in which he makes the first formal statement of the laws governing friction. In 1784 he studied torsional elasticity, finding the relationship between the various factors involved in the small oscillations of a body subjected to torsion.

His most notable papers are the seven which Coulomb presented before the academy in 1785 and 1786. In the first he announced the measurement of the electrical forces of repulsion between electrical charges. He extended this work to the forces of attraction in his second memoir. This led to further quantitative work and his famous law of force for electrostatic charges (Coulomb's law). The subsequent papers dealt with the loss of electricity of bodies and the distribution of electricity on conductors. He introduced the "proof plane" and by using it was able to demonstrate the relationship between charge density and the curvature of a conducting surface.

Magnetism was the subject of Coulomb's early studies and the one to which he returned in later years. He noted that magnetism obeyed a relation of attraction and repulsion similar to that for electrical forces. He also established the equation of motion of a magnet in a magnetic field, showing the derivation of the magnetic moment from the period of small oscillations.

In 1801 Coulomb published another important paper, in which he presented the results he obtained by allowing a cylinder to oscillate in a liquid, thus providing a way to find relative liquid viscosities.

Of Coulomb, Thomas Young wrote, "his moral character is said to have been as correct as his mathematical investigations." He remained in Paris until his death on Aug. 23, 1806.

Further Reading

Most of the information on Coulomb is in French. In English, descriptions of his experiments are in William Francis Magie, A Source Book in Physics (1935); Duane Roller and Duane H. D. Roller, The Development of the Concept of Electric Charge: Electricity from the Greeks to Coulomb (1954); and Morris H. Shamos, ed., Great Experiments in Physics (1960). For general background on the scientific environment of the time see Abraham Wolf, A History of Science, Technology and Philosophy in the Eighteenth Century (1939). Brief references also appear in A History of the Theories of Aether and Electricity: From the Age of Descartes to the Close of the Nineteenth Century (1910), and Hugh Hildreth Skilling, Exploring Electricity: Man's Unfinished Quest (1948).

For more information on Charles-Augustin de Coulomb, visit Britannica.com.

(kū'lŏm, kūlŏm', Fr. shärl ōgüstăN' də kūlôN') , 1736–1806, French physicist. In 1789 he retired from his posts as military engineer and as superintendent of waters and fountains and devoted himself to continuing his scientific research. He was known for his work on electricity, magnetism, and friction, and he invented a magnetoscope, a magnetometer, and a torsion balance that he employed in determining torsional elasticity and in establishing Coulomb's law. The unit of quantity of electric charge, the coulomb, is named in his honor.

Bibliography

See study by C. S. Gilmor (1971).

Coulomb, Charles-Augustin De (1736–1806), one of France's greatest engineers, who also made major contributions to the field of physics. Not only did he establish "Coulomb's laws"—by showing experimentally that the force between two electric charges, and similarly between two magnetic poles, is inversely proportional to the square of the distance between them—he played a key role more generally in the transformation of physics in the years around 1800 from a qualitative science into a quantitative, mathematical one. Coulomb was born at Angoulême on 14 June 1736, the son of a petty government official. After studying for a time in Paris and in Montpellier, he was briefly an adjunct member of the mathematical section of the Montpellier Academy of Sciences before entering the best engineering school in Europe, the École du génie at Mézières, in 1760. Upon graduation in November 1761, he became an officer in the French army's engineering corps.

Coulomb spent the years from 1764 to 1772 in the French West Indian colony of Martinique, successfully supervising the construction of major new fortifications to replace those destroyed by the British during the Seven Years' War. A series of postings followed in France itself, during which Coulomb had sufficient free time to write up his analyses of various traditional problems in structural mechanics, building on his experiences in Martinique. His paper created a very favorable impression when he presented it to the Académie Royale des Sciences in Paris in 1773, and in the following year he was appointed a correspondant (corresponding member) of the academy.

In his paper, Coulomb studied the role of friction and cohesion in several traditional problems of structural engineering. His analyses, in which he pioneered the use of variational calculus in engineering theory, were a significant advance over anything that had been previously achieved. He arrived at general solutions that, as more engineers became familiar with mathematics, became part of the standard approach to the subject. His analysis of the pressure on retaining walls led him to "Coulomb's equation," which remains the starting point of scientific soil mechanics.

During the next few years, Coulomb contributed a number of other papers on engineering topics to the Académie Royale des Sciences. In addition, beginning with work reported in a prizewinning essay on magnetic compasses submitted to the academy in 1777, he extended his research into the realm of physics. Success in 1781 in another of the academy's prize competitions, this time on friction between sliding and rolling surfaces, consolidated his reputation, and on 12 December of that year he was elected a member of the academy's section for mechanics.

In his investigation of friction, Coulomb combined quantitative experimental research with mathematical analysis in a way that was highly unusual at the time but that was characteristic of all his work. His paper was of immediate relevance to engineering practice, and his analysis became, for over a century, the starting point for all serious studies of friction.

Central to Coulomb's 1777 essay on magnetic compasses was his decision to suspend the compass needle from a thread, rather than mounting it on a pivot, as had traditionally been done. This led him to undertake a general investigation of torsion in threads and wires, which in turn provided him with the basis for his most famous invention, the torsion balance, which measures very small forces by the amount of twist they produce in a suspended thread or wire. The new balance was the tool with which Coulomb established the laws of electric and magnetic action in experiments that he reported to the academy between 1785 and 1791.

As a member of the Académie Royale des Sciences and also, from 1784, as superintendent of water supplies to the royal estates in and around Paris, Coulomb was one of the leading technocrats of late-eighteenth-century France. When the academy was abolished in the revolutionary fervor of 1793, Coulomb retired for safety to his house in the country. He became a member of the new Institut de France at its foundation in 1795, and for the next few years, despite declining health, continued to present papers regularly.

Throughout his career, Coulomb espoused a characteristically eighteenth-century view of nature according to which material corpuscles were bound together by short-range forces such as cohesion and elasticity. Much of his groundbreaking research into friction, torsion, and the strength of materials was concerned with the limits of action of these forces. He was one of the chief architects of the "two-fluid" theories of electricity and magnetism that dominated these fields throughout the nineteenth century.

Bibliography

Primary Source

Mémoires de Coulomb. Edited by A. Potier. Paris, 1884.

Secondary Sources

Gillmor, C. Stewart. Coulomb and the Evolution of Physics and Engineering in Eighteenth-Century France. Princeton, 1971.

Heilbron, J. L. Electricity in the 17th and 18th Centuries: A Study of Early Modern Physics. Berkeley, 1979.

Heyman, Jacques. Coulomb's Memoirs on Statics: An Essay in the History of Civil Engineering. Cambridge, U.K., 1972.

—R. W. HOME