A battery at the University of Oxford has been incessantly ringing two bells for 186 years, but no one knows exactly why it’s lasted so long. Built by Watkins and Hill, a London instrument manufacturing firm, the battery is made up of dry piles, which means it contains no liquid like the batteries today. A small hanging metal ball (the clapper) bounces back and forth between two brass bells using electrostatic forces, ringing roughly twice per second. The battery produces high voltage but extremely low current, meaning it drains very slowly. Scientists refuse to open or dismantle the battery because doing so would let moisture in and end the historic experiment. Today, the battery is safely housed behind glass at Oxford's Clarendon Laboratory, ringing so quietly now that you can barely hear it. In order to solve the mystery of the Oxford Electric Bell once and for all, researchers will likely have to wait until either the battery finally loses its charge or else the ringing mechanism breaks on its own from old age. For now, though, the contraption stands as the “longest running science experiment.”
