Charles Augustin de Coulomb
Born: 14 June 1736 in Angoulême, France
Died: 23 Aug 1806 in Paris, France
Charles Augustin Coulomb's father was Henry Coulomb
and his mother was Catherine Bajet. Both his parents came from families which
were well known in their fields. His father's family were important in the
legal profession and in the administration of the Languedoc region of France,
and his mother's family were also quite wealthy. 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 stage Coulomb's interests were mainly in
mathematics and astronomy and while in Montpellier he joined the Society of
Sciences there in March 1757 and read several papers on these topics to the
Society.
Coulomb wanted to enter the École 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 École du Génie at Mézières in February 1760. He
formed a number of important friendships around this time which were imporatnt
in his later scientific work, one with
Bossut who was his teacher at Mézières and the other
with Borda.
Coulomb graduated in November 1761. He was now 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. His first posting was to Brest but in February
1764 he was set to Martinique in the West Indies. Martinique fell under the
sovereignty of France under Louis XIV in 1658. However Martinique was attacked
by a number of foreign fleets over the following years. The Dutch attacked it
in 1674 but were driven off, as were the English in 1693 and the English again
in 1759. Martinique was finally captured by the English in 1762 but were
returned to France under the terms of the Treaty of Paris in 1763. The French
then made attempts to make the island more secure by building a new fort.
Coulomb was put in charge of the building of the new
Fort Bourbon and this task occupied 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 memoirs he wrote on mechanics. As far as Coulomb's health
was concerned these were difficult years 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, Coulomb was sent to Bouchain.
However, he now began to write important works on applied mechanics and he
presented his first work to the Académie des Sciences in Paris in 1773.
This work, Sur une application des règles, de maximis et minimis
à quelque problèmes de statique, relatifs à l'architecture
was written (in Coulomb's words, see for example):-
... to determine, as far as a combination of
mathematics and physics will permit, the influence of friction and cohesion in
some problems of statics.
Perhaps the most significant fact about this memoir
from a mathematical point of view is Coulomb's use of the calculus of
variations to solve engineering problems. As Gillmor writes in:-
In this one memoir of 1773 there is almost an
embarrassment of riches, for Coulomb proceeded to discuss the theory of
comprehensive rupture of masonry piers, the design of vaulted arches, and the
theory of earth pressure. In the latter he developed a generalised sliding
wedge theory of soil mechanics that remains in use today in basic engineering
practice. A reason, perhaps, for the relative neglect of this portion of
Coulomb's work was that he sought to demonstrate the use of variational
calculus in formulating methods of approach to fundamental problems in
structural mechanics rather than to give numerical solutions to specific
problems.
It is often the case that a sophisticated use of
mathematics in an application to an area where most have less mathematical
sophistication, gives the work a long term values which is not often seen at
the time. The memoir was certainly highly valued by the Académie des
Sciences for it led to him being named as
Bossut's correspondent on 6 July 1774. From Bouchain, Coulomb was next
posted to Cherbourg. While he was there he wrote a famous memoir on the
magnetic compass which he submitted for the Grand Prix of the Académie
des Sciences in 1777.
This 1777 paper won Coulomb a share of the prize and
it contained his first work on the torsion balance:-
... his simple, elegant solution to the problem of
torsion in cylinders and his use of the torsion balance in physical
applications were important to numerous physicists in succeeding years. ...
Coulomb developed a theory of torsion in thin silk and hair threads. Here he was
the first to show how the torsion suspension could provide physicists with a
method of accurately measuring extremely small forces.
Another interesting episode occurred during the time
which Coulomb spent at Cherbourg. Robert-Jacques Turgot was appointed
comptroller general by Louis XVI on 24 August 1774. He began to feel threatened
by his political opponents in 1775 and began a series of reforms. Among these
was the reform of the Corps du Génie and Turgot called for memoirs on
its possible reorganisation. Coulomb submitted a memoir giving his ideas and it
is a fascinating opportunity to understand his political views. Coulomb wanted
the state and the individual to play equal roles. He proposed that the Corps du
Génie in particular, and all public service in general, should recognise
the talents of its individual members in promotion within the organisation.
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:-
Viewing fortresses as nothing more than immense
permanent batteries designed to pour overwhelming fire on attacking armies,
Montalembert simplified the intricate geometric designs of Vauban and relied on
simple polygonal structures, often with detached peripheral forts instead of
projecting bastions.
During his time at Rochefort, Coulomb carried on his
research into mechanics, in particular using the shipyards in Rochefort as
laboratories for his experiments. 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. In this
memoir Coulomb:-
... investigated both static and dynamic friction of
sliding surfaces and friction in bending of cords and in rolling. From
examination of many physical parameters, he developed a series of two-term
equations, the first term a constant and the second term varying with time,
normal force, velocity, or other parameters.
Because of this prize winning work, the authors of
write:-
Coulomb's contributions to the science of friction
were exceptionally great. Without exaggeration, one can say that he created
this science.
In fact this 1781 memoir 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. He wrote seven important treatises on
electricity and magnetism which he submitted to the Académie des
Sciences between 1785 and 1791. These seven papers are discussed in [6] where
the author shows that Coulomb:-
... had obtained some remarkable results by using the
torsion balance method: law of attraction and repulsion, the electric point
charges, magnetic poles, distribution of electricity on the surface of charged
bodies and others. The importance of Coulomb's law for the development of
electromagnetism is examined and discussed.
In these he developed a theory of attraction and
repulsion between bodies of the same and opposite electrical charge. He
demonstrated an 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.
These papers on electricity and magnetism, although
the most important of Coulomb's work over this period, were only a small part
of the work he undertook. He presented twenty-five memoirs 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 310 committees of the Academy. He still was
involved with engineering projects as a consultant, 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.
He also undertook services for the respective French
governments in such varied fields as education and reform of hospitals. In 1787
he made a trip to England to report on the conditions in the hospitals of
London. 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. On 26 February 1790
Coulomb's first son was born, although he was not married to Louise
Françoise LeProust Desormeaux who was the mother of his son.
When the French Revolution began in 1789 Coulomb had
been deeply involved with his scientific work. Many institutions were
reorganised, not all to Coulomb's liking, and he retired from the Corps du
Génie in 1791. At about the same time that the Académie des
Sciences was abolished in August 1783, he was removed from his role in charge
of the water supply and, in December 1793, 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.
The Académie des Sciences was replaced by the
Institut de France and Coulomb returned to Paris when he was elected to the
Institute in December 1795. On 30 July 1797 his second son was born and, in
1802, he married Louise Françoise LeProust Desormeaux, the mother of his
two sons. We mentioned above that Coulomb was involved with services to
education. These were largely between 1802 and 1806 when he was inspector
general of public instruction and, in that role, he was mainly responsible for
setting up the lycées across France.
Let us end with quoting the tribute paid to him
by Biot who wrote:-
It is to Borda
and to Coulomb that one owes the renaissance of true physics in France, not a
verbose and hypothetical physics, but that ingenious and exact physics which observes
and compares all with rigour.
J J O'Connor and E F Robertson
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