Demonstration of the Oersted effect. This is the deflection of a compass needle by a current in a nearby wire, first noticed by the Danish physicist Hans Christian Oersted in 1820. This was the first time the electric and magnetic forces had been connected, and led to the development of the laws of electromagnetism. A current flowing through a wire creates a circular magnetic field around it, whose strength is proportional to the current and inversely proportional to the distance from the wire. This deflects the needle so that it is perpendicular to the wire.