The London firm that made the pair of brass bells set up by an Oxford clergyman in 1840 wrote that the batteries behind them would normally last only three or four years. The clapper, 4 millimeters across, is still crossing between the two bells twice a second, and nobody has opened the batteries to see exactly what is inside.

A 184-year-old experiment in a Oxford lab keeps ringing against all odds—and scientists refuse to peek inside to solve its greatest mystery. The post The London firm that made the pair of brass bells set up by an Oxford clergyman in 1840 wrote that the batter…