Mémoires sur l'action mutuelle de deux courans électriques, sur celle qui existe entre un courant électrique et un aimant ou le globe terrestre, et celle de deux aimans l'un sur l'autre.
André Marie Amperè(1775-1836)
 Using Volta’s battery with which he was able to supply a strong, constant current, Oersted, a professor of physics at Copenhagen, discovered that the compass needle rotated as the wire carrying current was brought closer to it. As the current was altered in the opposite direction, the needle rotated in a contrary direction. Through this experiment Oersted had demonstrated that magnetism was related closely to electricity. When this discovery was reported in 1820 at the French Académie Royal des Sciences, Ampere, a professor of mathematics at the Ecole Polytechnique, immediately experimented with this phenomenon in order to determine the precise relationship between magnetism and current-flow. He succeeded with this and reported the results in the above paper to the Academie des Sciences in two weeks.
 In this paper, Ampere studied how magnetic forces affect each other between two current-carrying conductors. If the magnetic forces attracted each other, the conductor currents flowed in the same direction. If the magnetic forces repelled each other, the currents flowed in the opposite direction. He also studied the magnetic properties of the current-carrying coil, which he called the solenoid, analyzed those experiments mathematically, and reduced them to a formula which is presently known as Ampere’s law.
 Thus, Ampere established the quantitative method in electricity, and initiated the areas of electro-magnetism and electro-dynamics. Furthermore he introduced the idea in which the quantity (the scalar) has a direction, that is, he prepared the way for vector analysis. For these achievements, the unit that measures the strength of electric current subsequently came to be called the “ampere”.