Like scientific mysteries? Then check out the Oxford Electric Bell, a battery-powered device that's still ringing 175 years after it was made, the Smithsonian reports. Sitting in the Clarendon Laboratory at Oxford University, it makes a little metal ball move swiftly back and forth between two bells.
How its early electric battery (or "dry pile") works remains unknown—and nobody's sure what it's made of. "But it is clear that the outer coating is of sulphur, and this seals in the cells and the electrolyte," writes a former researcher in the European Journal of Physics.