Coulomb, Charles-Augustin De (1736–1806)

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COULOMB, CHARLES-AUGUSTIN DE (1736–1806)

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.

See also Engineering ; Physics .