1820, André-Marie Ampère discovers electrodynamics

It's 1820 and Ampère discovers the electromagnetics. André-Marie Ampère is the great scientist, born in Lyon, who discovered the electric current in 1820. The Newton of electricity, as the great physicist Maxwell had described it. At that time, electricity is still very little known and has no practical application. We know about electrical charges. Those obtained by rubbing an amber or glass stick that attracts straw foetuses. The cloud that produces lightning. Those created by combining two metals in a conductive liquid. It is the battery the Italian Volta invented shortly before. We also know magnets like this magnesia stone, natural iron oxide, which orients at the surface of the earth in the needle of the compass. But we make no connection between electric charge and magnet. In 1819, the Danish physicist Ørsted brings a wire connected to a Volta battery close to a magnetic mobile needle. Immediately, the needle deflects and leaves the direction of the pole. On September the 11th, 1820, the experiment is reproduced at the Paris Academy of Sciences. For Ampère, who attends, it is a shock. The stroke of genius that will give birth to electrodynamics. The science of interactions between electric currents. A week later, he sets out his fundamental hypothesis on the existence of electric currents in magnets, including for earth magnetism. Ampère announces that in the absence of earth magnetism, the needle would orient perpendicularly to the wire. And it demonstrates this by inventing a magnetic needle called a static. He highlights and characterizes the electrodynamic forces between conductors. Ampère shows that the magnetic needle deviates similarly all along the wire, even very far from the battery. This characteristic property of the circuit as a whole is a quantity, the electric current. He is the first to clearly distinguish the basic concepts of voltage and current. André-Marie imagines using this property to build an electric telegraph that will become reality with the invention of the Morse code. In 1881, the Congress of Electricians paid homage to him by naming Ampères the International Current Unit. Ampère shows that the two wires wound in turns, spirals or helices, behave exactly as two magnetic poles would. By placing with the physicist Arago a soft iron cylinder in the center of the helical wire, which he calls a solenoid, he discovers the temporary magnetization, which is at the base of the electromagnet. Ampère also makes the rotation of a magnet around its axis, which already prefigures the electric motor. Finally, he defines the mathematical laws of interaction between two elementary conductors and deduces the formula for macroscopic conductors. This is the culmination, in 1826, of his work on electrodynamics. Today, electrodynamics is present everywhere in the production and the use of electricity that enlightens us, nourishes, transports, cares for and connects us.