The electric field produced by an electric current in a conductor in a magnetic field. The electric field, which is perpendicular to both the current and the magnetic field, is the reaction field (in a bounded conductor) that balances the magnetic force on moving charges. It is named after Edwin H. Hall, who in 1879 first discovered this effect in laboratory investigations of gold. The Hall effect is a determinant in the behavior of the electrical currents generated by winds in the lower ionosphere, since these winds advect the ionized layers across the earth's magnetic field and produce a complex electrical current system in the ionosphere. The current system in turn produces small changes in the earth's magnetic field as measured at the surface. See also magnetic induction.