Long before Edison, a working light source turned up by accident. In 1675, the French astronomer Jean Picard noticed that the mercury in his barometer glowed as he carried it across a dark room. The faint light, later called "barometric light," drew the interest of some of the era's biggest scientific names before the trick faded into obscurity.
In a recent video, the YouTuber styropyro (Drake Anthony) rebuilt it. He sealed a little mercury inside an evacuated glass flask, and shaking it made the metal give off a ghostly glow. The effect is triboelectric: as the mercury slides over the glass, it builds a static charge, and once that charge climbs high enough, it ionizes the last traces of gas inside and makes light. Bends in the tube, which splatter the mercury around, make it brighter.
When he backfilled a pumped-down flask with a little neon, it lit up so easily and so brightly he could read by it. "This is one of the coolest things I've ever made," he says.
Previously:
• Watch a crushed Life Saver emit light at 28,000 frames per second
• X-rays made from Scotch tape
• No one knows why dark side of Venus has a faint glow
