Maxwell developed the electromagnetic theory. Ampere assumed that magnetic effects are due to very tiny circular currents which flow continuously. Whilst investigating the effect of currents on circuits in which there was no current Faraday made the following discovery in 1831. He observed that whenever the current was started or broken in the first (primary) circuit, the needle of a galvanometer in the second (secondary) circuit was deflected. The laws of induction, as Faraday termed, are of the greatest import in electrical engineering. The effect which self-induction has on electricity in motion is very similar to the part played by inertia when ordinary masses are set in motion. When the potential difference has ceased to exist the self-induction causes the motion not to be interrupted, but, shooting beyond the equilibrium position, a new charge and potential are produced, first on one side and then on the other.