Charles-Augustin de Coulomb

Charles-Augustin de Coulomb invented a device, dubbed the torsion balance, that allowed him to measure very small charges and experimentally estimate the force of attraction or repulsion between two charged bodies.

coulomb01The data he obtained through his extensive use of the torsion balance enabled Coulomb to formulate one of the fundamental laws of electromagnetism, which bears his name (Coulomb's law).

Coulomb was a Frenchman born on June 14, 1736. Both sides of his family were well respected and wealthy, which allowed Coulomb to be raised as a child of privilege and garnered him an excellent education. He attended Mazarin College in Paris before his father’s poor business decisions strained the family’s finances, resulting in the elder Coulomb’s relocation to Montpelier. Although his mother remained in Paris, the younger Coulomb soon chose to join his father. While living in Montpelier, Coulomb joined the Academy of Sciences there and presented several papers to the organization, chiefly focusing on topics in astronomy and mathematics.

When his interests turned to engineering, Coulomb decided to return to Paris for a short time, where he would have access to the better tutoring he believed he needed to pass exams required to gain entry into the Royal School of Engineering. In 1760 he began his formal studies at the institution, completing them less than two years later. After graduation, he embarked on a long career within the Military Engineering Corps. His duties forced him to make several moves over the subsequent decades. A particularly long stint in the West Indies left his health in a deteriorated state. He never fully recovered, even following his return to France in the early 1770s.

His work involving engineering and mechanics provided Coulomb with a firm foundation on which his later theoretical efforts were built. He submitted his first treatise to the Academy of Sciences in Paris in 1773, and many more would follow on topics ranging from mathematical solutions of engineering problems to studies of friction, elasticity, electricity and magnetism. In 1777 Coulomb was awarded part of the Academy’s grand prize for a paper discussing the magnetic compass, which included an early description of his torsion balance. In 1781 he was sole recipient of the prize for a groundbreaking examination of friction. The strength of the latter treatise was largely responsible for Coulomb’s subsequent election into the Academy and his being awarded a permanent post in Paris, where he sometimes served as an engineering consultant but spent most of his time carrying out scientific research.

Coulomb published a series of important papers on electricity and magnetism in the late 1780s. One was a thorough discussion of Coulomb’s experiments with electrostatic forces and a description of the inverse square law that they led Coulomb to posit. Similar to Isaac Newton’s inverse square law of gravitational force, Coulomb’s law states that the electric force between charged objects inversely depends upon the distance between the objects. That is, like gravity, the electric force acts in a line between two objects and decreases with the square of the distance between them. The primary difference between the law for gravity and that for electric force is that gravitation is influenced by the mass of the objects, whereas Coulomb’s law depends upon the charge of the objects involved. When the objects in question are both positively or both negatively charged, the forces between them are repulsive, but attractive forces arise between objects carrying opposing charges.

The start of the French Revolution considerably impacted Coulomb, as it did most inhabitants of France. The changes spurred Coulomb to retire from the bustle of Paris to a quiet estate in the town of Blous, where he could carry out his scientific studies in relative peace. Due to his retirement from the Engineering Corps and the disbandment of many of the committees and organizations to which he belonged, Coulomb had ample time to research a wide assortment of topics, but his most long-lasting achievements continued to be in the realm of electricity and magnetism. His study of electrostatic forces was fundamental to the field and his study of attractive and repulsive forces between magnetic poles laid the groundwork for Siméon-Denis Poisson’s mathematical theory of magnetic forces.

In his later years, Coulomb returned to Paris, became one of the first members of the newly formed French National Institute, and accepted an appointment as Inspector of Public Instruction. His health grew progressively worse, leading to his death on August 23, 1806. Posthumously he was honored by the adoption of an SI unit of electric charge bearing his name. The coulomb (C) is equivalent to the charge transferred by a current of 1 ampere in 1 second.