Andre-Marie Ampere is best known for his investigations of the relationship between electric current and magnetism and the equations he made for calculating the amount and type of magnetic force produced by different currents. An important unit for the magnitude of electric current, the ampere, is named for him.
Andre-Marie Ampere's most famous discoveries derive from an observation by a Danish physicist, Hans Christian Orsted, in 1820. This observation indicated that a compass needle is affected when going past a current carrying wire. Up until that point, it was thought that magnetism and electricity were unconnected. Once news of the discovery reached him, Ampere immediately began investigating. His first device used a single wire and a compass needle. He observed that the compass needle moved through a series of loops along a plane perpendicular to the direction of current when it was moved close to it.
His next experiments involved two wires and the forces that arise between them when current is passed through them. He discovered that, when the current in two wires is flowing in the same direction, they are attracted to one another, and that they repel each other when the current in one wire is reversed.