Charles-Augustin de Coulomb

French engineer

• Born: June 14, 1736; Angoulême, France
• Died: August 23, 1806; Paris, France

Eighteenth-century French engineer and physicist Charles-Augustin de Coulomb investigated aspects of structure and applied mechanics while building military forts. He later conducted research into multiple areas of physics, including friction, torsion, electricity, magnetism, and hydraulics.

Primary field: Physics

Specialties: Mechanics; electromagnetism; hydrology

Early Life

Charles-Augustin de Coulomb was born on June 14, 1736, in the town of Angoulême in southwestern France. His father, Henri Coulomb, was a former military officer–turned lawyer and influential local administrator. His mother, Catherine Bajet, was related to the wealthy de Sénac lineage.

Raised into his adolescence in his hometown, Coulomb accompanied his parents when they relocated to Paris. There, he enrolled at Collège Mazarin (also known as “the College of Four Nations”), an institution associated with the University of Paris. At the university, Coulomb received a classical education, taking courses in language, literature, and philosophy. He concentrated heavily on science as well, studying mathematics, chemistry, botany, and astronomy. He also attended lectures at the prestigious Collège de France, where research was emphasized.

After Coulomb graduated from Collège Mazarin in the mid-1750s, there was a rift in the Coulomb family. Henri Coulomb had made a series of unwise financial investments that severely depleted the Coulomb fortune, and the resulting tension caused Coulomb’s parents to split apart. Henri Coulomb moved to Montpellier, near the Mediterranean coast, while Catherine Bajet remained in Paris. Coulomb subsequently had a falling-out with his mother over his future career: she wanted him to become a doctor, while he wanted to become a mathematician or an astronomer. The argument escalated until Bajet finally disowned her son. As a consequence, Coulomb left Paris to live with his father.

In Montpellier, Coulomb in 1757 joined the local scientific society and presented papers on several topics. Two years later, he headed north to Mézières, near the Belgian border, to take the entrance examination at the École Royale du Génie (Royal Engineering School), a military institution founded in 1748. Admitted in early 1760, he graduated with a degree in engineering in late 1761, at the rank of lieutenant with the Corps du Génie (Engineering Corps).

Life’s Work

After graduation from the Royal Engineering School, Coulomb was posted to the fortified military port of Brest, a French naval base in northwest France. In 1764, he was transferred to the French-controlled eastern Caribbean island of Martinique, where he oversaw construction of Fort Bourbon (later called Fort Desaix). The job lasted for eight years, during which time Coulomb—plagued with a succession of tropical diseases that adversely affected his health for the rest of his life—conducted numerous studies on soil mechanics, vaulted arches, masonry piers, and other engineering concerns.

Coulomb returned to France at the rank of captain in 1772. Stationed at a quiet outpost, the fortress of Bouchain in the northeastern corner of the country, he had time to set down some of his thoughts on applied mechanics. In 1773, he submitted the first of numerous papers to the Académie Royale des Sciences in Paris. Four years later, his treatise on the magnetic compass—in which he described his invention, the torsion balance—won him a share of the Academy’s grand prize.

In 1779, Coulomb was transferred again, this time to the military harbor at Rochefort in southwestern France. At the port, he worked with renowned military engineer and fellow Angoulême native Marc René, the Marquis de Montalembert. Together, they built a wooden fort to control the mouth of the Charente River estuary on Île d’Aix, a strategic island that had figured prominently in the Seven Years’ War (1756–63). Coulomb meanwhile continued his research into applied mechanics, conducting experiments on the friction of machinery and the elasticity of various materials in the shipyards of the port. His 1781 treatise, Theory of Simple Machines, won the Paris Academy’s grand prize and earned him election into the academy.

Coulomb’s fame gained him entry into the bureaucracy of Paris. As an engineering consultant, he served the French government in a variety of capacities, participated in numerous tasks for the Paris Academy, and conducted research in a number of diverse areas. In the early 1780s, Coulomb was tasked with recommending improvements to harbors and canals in the region of Brittany. In 1784, he was named keeper of the royal fountains and put in charge of the main water supply in Paris. He became a member of a committee formed to standardize weights and measures. He also traveled to London to investigate hospitals as part of a program to reform education and medical facilities throughout France.

Late in the 1780s, Coulomb became romantically involved with a much younger woman, Louise Françoise LeProust Desormeaux. She gave birth to two illegitimate sons in 1790 and 1797, before the couple eventually married in 1802.

Due to the outbreak of the French Revolution (1789–99), Coulomb officially resigned his commission with the Engineering Corps in 1791. In 1793, after the Paris Academy was abolished, he was relieved of his duties as water master of Paris, and the weights and measures commission was disbanded. Coulomb subsequently retired to his country home in Blois, south of Paris, to concentrate on scientific research. A frequent guest was scientist and fellow military engineer Jean-Charles de Borda, who participated in various experiments with his friend.

In 1795, the revolutionary government recalled Coulomb to Paris, where he was appointed to a new weights and measures committee. The committee established what later would become the metric system. The Institut de France, the successor of the Paris Academy, was founded that same year and elected Coulomb as a member. Though Coulomb was enfeebled by the effects of the tropical diseases he had survived in Martinique, in 1802 he began serving as Inspector-General of Public Instruction. After four years of service, a weakened Coulomb died on August 23, 1806, two months after his seventieth birthday.

Impact

Over his twenty-year career as a military engineer, Coulomb did not create original designs for the fortifications on which he worked. This was not due to a lack of ability, but rather a lack of opportunity. Throughout the eighteenth century, the French army was committed to the principles and construction methods of master builder Sébastien le Prestre, Marquis de Vauban (1633–1707), whose defensive and offensive tactics had been tested and proven numerous times since the middle of the previous century. Though more successful at initiating than withstanding sieges, Vauban built or renovated dozens of French forts.

As a military engineer under orders, Coulomb was required to follow his predecessor’s system of fortifications. Called the Vauban style, the designs took advantage of the natural features of the terrain, bristling with towers and providing overlapping fields of fire against attackers.

Despite the constriction of building to a formula, Coulomb nonetheless helped advance the art of military engineering by observing, measuring, and calculating a variety of structural forces related to his work. He was the first to focus on the study of static and sliding friction, which later became part of tribology, the study of interacting surfaces in relative motion. He also formulated a theory of soil mechanics still used in modern engineering, investigated stress and force, and experimented with the breaking points of columns and arches.

In the latter half of his life, Coulomb concentrated on investigations into a wide range of diverse subjects, including electricity, hydraulics, and magnetism. His invention of the torsion balance allowed him to devise what became known as Coulomb’s Law, regarding the behavior of electrical charges. His studies of friction and cohesion were expanded upon by German civil engineer Christian Otto Mohr (1835–1918). This led to the Mohr-Coulomb theory, a set of mathematical formulas for mechanics and engineering. In his honor, the International System of Units (SI)—which was officially adopted by the eleventh General Conference on Weights and Measures in 1960—created the coulomb, a measurement defined as the electrical charge delivered in one second with a constant current of one ampere.

Bibliography

Langins, Janis. Conserving the Enlightenment: French Military Engineering from Vauban to the Revolution. Cambridge: MIT P, 2003. Print. A study of eighteenth-century French military construction techniques as exemplified in projects of the type worked on by Coulomb. Includes renderings and blueprints of actual installations. Illustrations, bibliography, index.

Pickover, Clifford A. Archimedes to Hawking: Laws of Science and the Great Minds behind Them. New York: Oxford UP, 2008. Print. An illustrated examination, supplemented with biographical details and explanations, of some of the most important scientific discoveries that resulted in eponymous laws, such as Coulomb’s Law. Illustrations, bibliography, index.

Popov, Valentin L. Contact Mechanics and Friction: Physical Principles and Applications. Berlin: Springer, 2010. Print. Discusses the technological aspects of friction and lubricants—an area in which Coulomb conducted pioneering research. Illustrations, bibliography, index.