A battery has been ringing the same bell since 1840 and nobody knows why it still works
It's rung roughly ten billion times behind two panes of glass at Oxford, and the scientists who study it still can't tell you what's inside it.
In a corridor at Oxford's Clarendon Laboratory sits a small apparatus called the Oxford Electric Bell, wired up in 1840 and still going. Two brass bells, a metal clapper suspended between them, and two "dry pile" batteries doing the work — the clapper gets charged by one bell, flung toward the other by electrostatic repulsion, discharged, and flung back, over and over, at a steady two beats per second.
It has rung an estimated ten billion times. Guinness recognizes it as the world's most durable battery. And here's the part that should bother anyone who trusts modern instrumentation: nobody knows exactly what the dry piles are made of. They're coated in sulfur for insulation, likely built as a Zamboni pile — a type of battery from the early 1800s — but the university has never dared crack one open to check, because doing so would end the experiment permanently, and 185 years of continuous data outweighs the curiosity.
You can't hear it anyway. The bell is sealed behind two layers of glass, both to protect the mechanism and because a chime every half-second for nearly two centuries would have driven every physicist in the building to violence. It rings in total, permanent silence, for no audience, and will keep doing so until the piles finally discharge evenly or the clapper wears through — nobody knows which will happen first, or when.
The most reliable machine in that building isn't the one anyone fully understands. It's the one nobody's willing to risk understanding better.