Charles-Augustin de Coulomb - Research

Research

In 1784, his memoir Recherches théoriques et expérimentales sur la force de torsion et sur l'élasticité des fils de metal (Theoretical research and experimentation on torsion and the elasticity of metal wire) appeared. This memoir contained the results of Coulomb's experiments on the torsional force for metal wires. His general result is,

"... the moment of the torque is, for wires of the same metal, proportional to the torsional angle, the fourth power of the diameter and the inverse of the length of the wire..."

In 1785, Coulomb presented his first three reports on Electricity and Magnetism:

- Premier Mémoire sur l’Électricité et le Magnétisme. In this publication, Coulomb describes "How to construct and use an electric balance (torsion balance) based on the property of the metal wires of having a reaction torsion force proportional to the torsion angle." Coulomb also experimentally determined the law that explains how "two bodies electrified of the same kind of Electricity exert on each other." On page 574 he states:

Il résulte donc de ces trois essais, que l'action répulsive que les deux balles électrifées de la même nature d'électricité exercent l'une sur l'autre, suit la raison inverse du carré des distances.

Translation: It follows therefore from these three tests, that the repulsive force that the two balls -- electrified with the same kind of electricity -- exert on each other, follows the inverse proportion of the square of the distance.

- Second Mémoire sur l’Électricité et le Magnétisme. In this publication, Coulomb carries out the "determination according to which laws both the Magnetic and the Electric fluids act, either by repulsion or by attraction." On page 579, he states that the attractive force between two oppositely charged spheres is proportional to the product of the quantities of charge on the spheres and is inversely proportional to the square of the distance between the spheres.

- Troisième Mémoire sur l’Électricité et le Magnétisme. "On the quantity of Electricity that an isolated body loses in a certain time period, either by contact with less humid air or in the supports more or less idio-electric."

Four subsequent reports were published in the following years:

- Quatrième Mémoire "Where two principal properties of the electric fluid are demonstrated: first, that this fluid does not expand into any object according to a chemical affinity or by an elective attraction, but that it divides itself between different objects brought into contact; second, that in conducting objects, the fluid, having achieved a state of stability, expands on the surface of the body and does not penetrate into the interior." (1786)

- Cinquième Mémoire "On the manner in which the electric fluid divides itself between conducting objects brought into contact and the distribution of this fluid on the different parts of the surface of this object." (1787)

- Sixième Mémoire "Continuation of research into the distribution of the electric fluid between several conductors. Determination of electric density at different points on the surface of these bodies." (1788)

- Septième Mémoire "On magnetism" (1789)

Coulomb explained the laws of attraction and repulsion between electric charges and magnetic poles, although he did not find any relationship between the two phenomena. He thought that the attraction and repulsion were due to different kinds of fluids.