Mechanical light bulb from 1675 [video]

**TL;DR:** Derek Anthony recreated the 1675 effect of mercury glowing in a vacuum glass tube when shaken, and then improved it by adding neon gas to create a surprisingly bright "mechanical light bulb." ## Background: A 1675 Accidental Discovery As early as 1675, astronomer Jean Picard noticed that the mercury in his barometer glowed when moved at night. This chance observation prompted many famous scientists of the time to study the effect: shaking mercury in an evacuated glass container produces a faint glow. Derek Anthony had been interested in this effect for a long time, but only recently got the vacuum pump and noble gases needed to reproduce it. ## Building the First Mechanical Light Bulb: Pure Mercury Vacuum System ### Glassblowing Challenges Derek attached a neck to the top of a flask so it could be connected to a vacuum pump. He used a propane torch and two parallel medical oxygen concentrators as the heat source. Because congenital strabismus gives him no depth perception, he had difficulty aligning the glass pieces accurately in the flame. On the first attempt, the joint was severely misaligned and leaked badly. He admits: "This is really hard for me because I can't judge distances. I can't catch a ball, and judging distances between objects is very difficult for me because I have no depth perception." After a second try, he ended up with a "pretty crappy joint," but it was barely usable. ### Filling with Mercury and Evacuating Derek injected about 2 pounds (approx. 900 grams) of mercury into the flask using a syringe. He emphasizes: "Mercury toxicity—the pure metal form is fairly inert, but if you spill it indoors, the mercury vapor is very easily absorbed by the body and can cause problems quickly." He stuffed a small piece of glass wool into the neck of the flask to prevent bubbles from bursting and splashing mercury under vacuum. He then connected the flask to the vacuum pump and slowly pumped it down to about 3–5 millitorr (roughly 6–7 parts per million atmospheric pressure). Because mercury itself evaporates, the residual gas included some mercury vapor and contaminants released from the glass. ### Sealing and Testing Derek sealed the neck by melting it with the torch. The sealing process was also difficult—he lacked a glassworking burner tip that could heat a ring at once, so he had to manage as best he could. When he shook the flask, only in complete darkness could he see a very faint, ghostly glow. When he excited the flask externally with a Tesla coil, it emitted a diffuse white-violet plasma glow. He concluded: "The effect isn't particularly sensitive to vacuum level, but it is sensitive to the purity of the mercury and the cleanliness of the glass. My mercury was dirty, so the effect wasn't very bright. With cleaner mercury, it might be better." ## Improvement: Adding Neon to Enhance the Effect ### Repairing the Old Flask Derek repaired the failed "crappy flask" from earlier and tried glassblowing again. He scored the glass tube with a quartz crystal and accelerated the crack with water. After painstaking work, he attached a new neck—still not perfect, but usable. ### Evacuating and Adding Neon After evacuating the second flask, instead of sealing it directly, he backfilled it with about 100 millitorr of neon gas. He notes: "Neon works best." He then ignited it with a Tesla coil, producing a brilliant glow with astonishing brightness. He marveled: "I've never seen anything like this. This is one of the coolest things I've ever made. It's so striking. You could even read by this light. It's so easy to light up." ### Sealing and Final Demonstration After sealing the neon-filled flask, it emitted strong light even without a Tesla coil—just a light shake made it glow intensely. In Derek's demonstration, the effect was clearly visible even in bright room light, with the glow illuminating his hand and the surroundings. ## Conclusion Derek successfully recreated the 1675 mechanical light bulb effect and boosted its brightness to a practical level by adding neon gas. He points out that this system is essentially a light bulb that uses mechanical motion to excite plasma, requiring no external electric field. Although the fabrication process was challenging (especially glassblowing), the final result left him very satisfied. **Source:** [YouTube: Mechanical light bulb from 1675 [video]](https://www.youtube.com/watch?v=0Y-9GbsS9Fg)