Milestones:Ampere discovers Electrodynamics, 1820

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The Birth of Electrodynamics, 1820-1827


Stimulated by experimental reports that an electric current could deflect a compass needle, André-Marie Ampère discovered the fundamental law of electrodynamics, the science of interactions between electric currents. He then developed the theory that electric currents are responsible for magnetism. These achievements formed the basis for electrical technologies, including electric motors and generators. In 1881, the International Electrical Congress named the unit of electric current the ‘ampere’ (A).

Street address(es) and GPS coordinates of the Milestone Plaque Sites

3 rue d'Ulm 75005 Paris, 48.84534°N, 2.34546°E, 3 rue d'Ulm 75005 Paris, 48.84534°N, 2.34546°E

Details of the physical location of the plaque

Proposed Milestone Plate to be fixed on the wall in “College de France” in Paris, where Ampere was the head of the Chair of Experimental Physics.

How the intended plaque site is protected/secured

The “College de France” in Paris, is one of the most prestigeous public academic scientific establishments . Of course the place in which the plaque will be fixed will be well protected/secured

Historical significance of the work

André-Marie Ampère (1775-1836), bathed in the encyclopedic spirit of the French Enlightenment of the XVIIIth century, was engaged in nearly all disciplines of human thought. Mathematician, chemist, biologist, poet, linguist, philosopher, metaphysician. However, his genius literally exploded in 1820 as a physicist when, fascinated by the Danish Oersted’s experience, he developed in a few months the whole theory of electrodynamics. From his first contribution at French Science Academy on 18th of September 1820 to the first trimester of 1821, he built the main concepts which will become the cornerstone of Maxwell’s electromagnetism laws.

With Ampère, the phenomena of magnets are brought back to those of galvanism. These are due to electrical currents in planes perpendicular to magnets’ axis, including for earth’s magnetism.

Ampère is the first scientist who made clear distinction between current and voltage and the inventor of electrical current. This main contribution will be recognized during the first international congress of electricity in 1881 by naming “ampere” (A) the international unit of electrical current.

He highlights and characterizes the attractions and repulsions between currents. In particular, he defined a simple rule to determinate the direction and sense of the interaction between a conductor and a needle of magnet, the famous “Bonhomme d’Ampère” rule. He defined at the end of 1820 the formula for interactions between elementary conductors.

Ampère invented various astatic devices to overcome the earth’s magnetic field during experimentations. Ampère also invented solenoids, discovered the temporary magnetization of iron and invents electromagnets. He is the first to have the idea of the electromagnetic telegraph.

In 1826, Ampère publishes “Mathematical theory of electrodynamic phenomena uniquely derived from experiments” which concluded his intensive work on electrodynamics

Features that set this work apart from similar achievements

A short and intense moment in Ampère's life, between 1820 and 1826, led him go down in history as the discoverer of electrodynamics. It brought to light a brilliant man animated by an incredible intuition associated with a remarkable intellectual audacity, and an ingenious experimenter despite an almost total absence of experimental measurements. But behind this facade also hides a tormented intellectual, torn between his own contradictions: his exchanges with Augustin Fresnel (1788-1827) lead him to be intimately convinced by a propagation from near to near in the “ether” to explain the existence of electromagnetic phenomena in matter which is consistent with his early vision, but in contradiction with the Newtonian formulation of his fundamental law assuming actions at a distance. Because of its audacity, Ampère's approach had the effect of a bomb in the scientific community: at first completely rejected, it then brought about a consensus thanks to Ampère's determination. The devices that he designed did not all exist, but they were objects of thought which allowed him to intertwine qualitative experiments and theoretical formulations, always in search of a logical homogeneity between the "universal judgment" of the theory and the "particular judgment" of the experiment, according to the expressions of G. Canguilhem. This exceptional scientific approach allowed Ampère to establish a universal law unifying electricity and magnetism, which made Œrsted's discovery a scientific revolution giving birth to electromagnetism.

Significant references

Media:Ampère_200 ans_HF_anglais.ppt<br><br> Media:Texte_Ampère_Milestone_HF.pdf<br><br> Media:Maxwell citation.pdf <br><br> Media:Mailloux and Crocker.pdf<br><br> Media:Blondel.pdf

Supporting materials

See above