Charles Augustin de Coulomb .

Charles Augustin de Coulomb was born on June 14, 1736 in Angoulême, France.

His father was Henry Coulomb, whos family were important in the legal profession and in the administration of the Languedoc region of France, his mother was Catherine Bajet who came from a wealthy family.

After being brought up in Angoulême, the capital of Angoumois in southwestern France, Coulomb's family moved to Paris. In Paris he entered the Collège Mazarin, where he received a good classical grounding in language, literature, and philosophy, and he received the best available teaching in mathematics, astronomy, chemistry and botany. At this stage in his education there was a crisis for Coulomb. Despite his father's good standing, he had made unsuccessful financial speculations, had lost all his money and moved from Paris to Montpellier. Coulomb's mother remained in Paris but Coulomb had a disagreement with her over the direction his career should take so he left Paris and went to Montpellier to live with his father. At this time Coulomb's interests were mainly in mathematics and astronomy and he joined the Society of Sciences in Montpellier in March 1757 and read several papers on these topics to the Society.

Coulomb wanted to enter the Ecole du Génie at Mézières but realised that to succeed in passing the entrance examinations he needed to be tutored. In October 1758 he went to Paris to receive the tutoring necessary to take the examinations. Camus had been appointed as examiner for artillery schools in 1755 and it was his Cours de mathématique that Coulomb studied for several months. In 1758 Coulomb took the examinations set by Camus which he passed and he entered the Ecole du Génie at Mézières in February 1760. He formed a number of important friendships around this time which were important in his later scientific work, one with Bossut who was his teacher at Mézières and the other with Borda. Coulomb graduated in November 1761 from Ecole du Génie at Mézières, a trained engineer with the rank of lieutenant in the Corps du Génie. Over the next twenty years he was posted to a variety of different places where he was involved in engineering, in structural design, fortifications, soil mechanics, and many other areas.

In 1764 Coulomb was put in charge of the building of the new Fort Bourbon under the orders of the lieutenant-colonel of Rochemore, as the French colony was insulated in the middle of the English and Spanish possessions following the Seven Years' War. This task was to occupy him until June 1772. It was a period during which he showed the practical side of his engineering skills which were needed to organise the construction, but his experiences would play a major role in the later theoretical papers he wrote on mechanics. Coulomb's health was not good and the illnesses which he suffered while on Martinique left him in poor health for the rest of his life.

On his return to France, with the rank of Captain, Coulomb began to write important works on applied mechanics and he presented his first work, "Sur une application des règles, de maximis et minimis à quelque problèmes de statique, relatifs à l'architecture", to the Académie des Sciences in Paris in 1773. Perhaps the most significant thing from a mathematical point of view is Coulomb's use of the calculus of variations to solve engineering problems. Coulomb wrote on structural analysis, the fracture of beams, the fracture of columns, the thrust of arches and the thrust of the soil. The paper was certainly highly valued by the Académie des Sciences for it led to him being named as Bossut's correspondent on 6 July 1774.

In 1777 he wrote a famous paper on the magnetic compass which he submitted to the Grand Prix of the Académie des Sciences. This paper won Coulomb a share of the prize and it contained his first work on the torsion balance.

Coulomb had invented a torsion balance (illistrated left) which could measure electrostatic force. Inside the balance are two balls of pith. One is mounted and unmovable, the other, suspended on a thread, can spin around. When the two pith balls are enegized by an electrostatic charge the moveable one will be rotate away from the stationary one, if they both receive the same type of charge (positive or negative). The moveable ball will be attracted to and will rotate towards the stationary pith ball if each receives a different charge. The distance the ball rotates is used to measure the electrostatic force. Coulomb was able to measure the torsion on the fiber with the scale near the top of the device and the distance between the balls on the scale that circumscribed the jar. He was able to derive a mathematical equation that described the relationship between these two variables. The force between two small, charged spheres is shown to be proportional to the magnitude of either charge and inversely proportional to the square of the distance between centers. There was one drawback with this torsional balance device; it requires low humidity!

In 1779 Coulomb was sent to Rochefort to collaborate with the Marquis de Montalembert in constructing a fort made entirely from wood near Ile d'Aix. Like Coulomb, the Marquis de Montalembert had a reputation as a military engineer designing fortifications, but his innovative work had been criticised by many French engineers because he viewed fortresses as 'nothing more than immense permanent batteries designed to pour overwhelming fire on attacking armies'.

During his time at Rochefort, Coulomb carried on his research into mechanics, using the shipyards in Rochefort as laboratories for his experiments. He did research on friction of machinery, on windmills, and on the elasticity of metal and silk fibres. His studies into friction in Rochefort led to Coulomb's major work on friction Théorie des machines simples which won him the Grand Prix from the Académie des Sciences in 1781.

This 1781 paper changed Coulomb's life. He was elected to the mechanics section of the Académie des Sciences as a result of this work, and he moved to Paris where he now held a permanent post. He never again took on any engineering projects, although he did remain as a consultant on engineering matters, and he devoted his life from this point on to physics rather than engineering. Coulomb developed his law as an outgrowth of his attempt to investigate the law of electrical repulsions as stated by Joseph Priestley of England. With this in mind he invented more sensitive apparatus to measure the electrical forces involved in Priestley's law. He also established the inverse square law of attraction and repulsion of unlike and like magnetic poles, which became the basis for the mathematical theory of magnetic forces developed by Siméon-Denis Poisson.

He wrote and submitted 7 important treatises on electricity and magnetism to the Académie des Sciences between 1785 and 1791. In these papers he developed a theory of attraction and repulsion between bodies of the same and opposite electrical charge. He demonstrated the inverse square law for such forces and went on to examine perfect conductors and dielectrics. He suggested that there was no perfect dielectric, proposing that every substance has a limit above which it will conduct electricity. These fundamental papers put forward the case for action at a distance between electrical charges in a similar way as Newton's theory of gravitation was based on action at a distance between masses.

Although these papers on electricity and magnetism were the most important of Coulomb's work over this period, they were only a small part of the work he undertook. In all he presented 25 papers to the Académie des Sciences between 1781 and 1806. Coulomb worked closely with Bossut, Borda, de Prony, and Laplace over this period. Remarkably he participated in the work of over 300 committees of the Academy. His engineering consultancy, the most dramatic of which was his report on canal and harbour improvements in Brittany in 1783-84 (he had been pressed into this task against his better judgement and he ended up taking the blame when criticisms were made and he spent a week in prison in November 1783), was also taking some of his time and it is a wonder how he managed to do it all! Don't forget that there were no telephones, computers, internet or air travel at that time!

He undertook services for the French government in such varied fields as education and reform of hospitals. In July 1784 he was appointed to look after the royal fountains and took charge of a large part of the water supply of Paris. In 1787 he made a trip to England to report on the conditions in the hospitals of London. When the French Revolution began in 1789 many institutions were reorganised, not all to Coulomb's liking. On 26 February 1790 Coulomb's first son was born. He was not married to Louise Françoise LeProust Desormeaux who was the mother of his son. He retired from the Corps du Génie in 1791. At about the same time that the Académie des Sciences was abolished on 8 August 1793, he was removed from his role in charge of the water supply and, in December the same year, the weights and measures committee on which he was serving was also disbanded. Coulomb and Borda retired to the country to do scientific research in a house he owned near Blois. He was recalled to Paris for a time in order to take part in the new determination of weights and measures, todays Metric System, which had been decreed by the Revolutionary government. The Académie des Sciences was replaced by the Institut de France and Coulomb was elected to the Institute in December 1795.

July 30, 1797 saw the birth of his second son and, in 1802, he married Louise Françoise LeProust Desormeaux, the mother of his two sons.

between 1802 and his death in 1806 Coulomb was involved with services to education, he was inspector general of public instruction and, in that role, he was mainly responsible for setting up the lycées across France.

Coulomb died at home in Paris, France, on August 23, 1806.

The coulomb, a unit of electric charge, was named in his honour. The coulomb is defined as the quantity of electricity transported in one second by a current of one ampere:

1C=1A·1S
It is approximately equivalent to 6.24x10¹⁸ electrons.

It can also be defined in terms of capacitance and voltage, where one coulomb is defined as one farad of capacitance times one volt of electric potential difference:

1C=1F·1V

The ampere was historically a derived unit - being defined as 1 coulomb per second. Therefore the coulomb, rather than the ampere, was the SI base electrical unit. However in 1960 the SI system made the ampere the base unit.