Substances placed near a magnetizing force are affected by it, and the substances take on magnetic properties. The amount of magnetism induced into a body by a magnetizing force (H) is called flux density (B). The intensity of the flux density (B) is affected by the intensity of the magnetizing force (H), the qualities of the substance, and by the intervening media between the systems.

In the same year, Jean-Baptiste Biot ( 1774-1862) and Félix Savart discovered that the intensity of the magnetic field set up by a current flowing through a wire is inversely proportional to the distance from the wire. This relationship is now known as the Biot-Savart law.

Michael Faraday (1791-1851) also conducted many experiments and his experiments lead to his visual models of electro-magnetism, which were formalized into mathematical models by James Maxwell (1831-1879).