This is an early example of the work of Alexander Bain (1810- 1877), a Scottish clockmaker and one of the pioneers of electric clocks. The pendulum bob is magnetised and swings into the two coils fixed to the case. Currents running through the coils produce magnetic forces to make up the energy lost by friction, and keep the pendulum swinging. A sliding contact moved by the pendulum switches the currents through the coils as required.
© Science Museum / Science & Society Picture Library