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. It also resembles piles by the 19th-century physicist and priest Giuseppe Zamboni, who made batteries by gluing together alternate layers of tin foil and paper covered with zinc sulphate and manganese dioxide. However it's made, the Guinness Book of World Records calls it the "world's most durable battery."
We know it was built by a London instrument-manufacturing firm and acquired by an Oxford physics professor in the 1800s. His attached note, "Set up in 1840," dates the device, but the Oxford Physics Department says a second note may date it to 1825. We also know it inspired a physicist to create a similar battery for British infrared telescopes during World War II. But the device now pulls a mere 1 nanoAmp for each oscillation of the ball, which is barely a current at all—so "at this point, we’re probably not going to build a better battery thanks to this experiment," says Motherboard. One bright spot: The Bell, which has rung about 10 billion times, creates such a tiny sound that the human ear can't even hear it, meaning it won't drive anyone crazy. (Read about "more secrets" given up by the famous Antikythera Mechanism.)