<P> Almost three centuries later, William Gilbert of Colchester replicated Petrus Peregrinus' work and was the first to state explicitly that Earth is a magnet . Published in 1600, Gilbert's work, De Magnete, helped to establish magnetism as a science . </P> <P> In 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law . Charles - Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated . Building on this force between poles, Siméon Denis Poisson (1781--1840) created the first successful model of the magnetic field, which he presented in 1824 . In this model, a magnetic H - field is produced by' magnetic poles' and magnetism is due to small pairs of north / south magnetic poles . </P> <P> Three discoveries challenged this foundation of magnetism, though . First, in 1819, Hans Christian Ørsted discovered that an electric current generates a magnetic field encircling it . Then in 1820, André - Marie Ampère showed that parallel wires with currents attract one another if the currents are in the same direction and repel if they are in opposite directions . Finally, Jean - Baptiste Biot and Félix Savart discovered the Biot--Savart law in 1820, which correctly predicts the magnetic field around any current - carrying wire . </P> <P> Extending these experiments, Ampère published his own successful model of magnetism in 1825 . In it, he showed the equivalence of electrical currents to magnets and proposed that magnetism is due to perpetually flowing loops of current instead of the dipoles of magnetic charge in Poisson's model . This has the additional benefit of explaining why magnetic charge cannot be isolated . Further, Ampère derived both Ampère's force law describing the force between two currents and Ampère's law, which, like the Biot--Savart law, correctly described the magnetic field generated by a steady current . Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism . </P>

Who discovered the direction of magnetic field lines