“Who invented the light bulb?” The question is an easy way to start an argument between historians of science.

A lot of people instinctively say “Thomas Edison,” despite plenty of others having invented various kinds of “light bulbs” in the decades before him. But the potential timeline of light bulbs starts way earlier than most people think.

Because depending on your definition, this wasn’t the first lightbulb, nor this and maybe not even this. Arguably, the first light-bulbs were barometric lights like this one that emitted a mysterious glow from glass containers of mercury. And they stayed mysterious for a long time, because their discovery came centuries before we understood what electricity actually was. [Intro music] Thanks to Brilliant for supporting this SciShow video!

As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. One evening in the late 1670s, astronomer Jean-Félix Picard noticed something weird in a piece of lab equipment. That’s -Félix Picard, not the other Jean Picard with his head in the stars.

Anyway, not-a-starship-captain Picard was in a dimly lit room with his barometer, an instrument for measuring air pressure. Early barometers were basically partially filled tubes of mercury closed off at one end and flipped upside down. The greater the air pressure, the more mercury would be pushed up the tube.

And as the mercury inside Picard’s barometer sloshed around, it glowed., He reported this strange observation to the French Academy of Sciences, where it initially got a lot of attention. It spurred the famous mathematician Johann Bernoulli to launch his own investigation, spinning vials of mercury around and around to produce an eerie glow from inside. The general consensus among scientists was there was probably some kind of mysterious substance that shook out of the mercury and emitted light.

With hindsight, this was wrong but—spoiler alert— not that wrong. Despite the mystery, the scientific establishment quickly lost interest in what came to be known as barometric light. It sounds surprising, but there was a whole lot of science going on at the time.

This was the era when people like Isaac Newton were at the height of their glory, basically inventing modern physics. But Newton isn’t the hero of this particular story. It was his assistant, Francis Hauksbee, who picked up the barometric light problem in 1705.

Hauksbee wanted to work out what was really going on. Rather than throwing out his shoulder continuously spinning glass vials around, he came up with something a little different. Hauksbee set up a nine-inch glass sphere hooked up to a hand crank.

By pumping the air out of the sphere and putting some mercury in it, he could get the whole thing to glow by turning the crank and spinning the sphere. Lo and behold… a hand powered lightbulb! Not enough to light up the room or anything… but still.

And it didn’t stop there. Hauksbee worked out that if he put his hand on the sphere while it was spinning around, it glowed even brighter than before! Weirder still, touching the sphere while it spun around made tiny bits of material like thread and brass start sticking to it.

He recognized this as a force of “electrical” attraction, and supported the idea that some special substance was jiggled out of the mercury which caused the glow. But Hauksbee wasn’t the only one tinkering around with barometric light. Across the Channel in France, the physicist Pierre Polinière was also tackling the same problem, a little differently.

Polinière used simple glass tubes with some mercury inside that he shook around in a range of setups. For instance, he discovered he could get the mercury vial to glow just by slapping it instead of spinning it. He also noticed if he put some sand into it, it would stop glowing in the parts where the sand had settled on the inside.

All And this led him to the conclusion that the motion of the shaking itself was somehow causing light to be emitted, not just some mysterious substance being shaken out of the mercury. In the annals of history, Hauksbee gets most of the attention, but both he and Polinière had pieces of this particular puzzle. Today, we know what was responsible for the glowing of barometric light: frictional electricity.

Ever rub a balloon against your hair and stick it to a wall? That’s frictional electricity in action. Maybe you know it as static electricity.

When certain materials rub against each other, they transfer electrons, the negatively charged particles that normally lurk in atoms along with positive protons so everything is neutral. But during the rubbing, those electrons can escape from the atoms they’re usually found in, causing an electrical imbalance. In other words kinetic energy gets turned into electric potential energy.

A similar thing happens with the mercury in the glass. When mercury sloshes around, it rubs against the glass and loses some electrons to it. That makes the glass negatively charged and the mercury positively charged, setting up an electric potential.

And, since opposite charges attract, the mercury kind of sticks to the glass. But when the container gets moved around, some of the positively charged mercury separates from the glass. Because the negative electrons in the glass want to connect with positive charges, a whole bunch of them leap from the glass to the mercury to recombine.

And when they reconnect, the charges release their electric potential energy as light. The very same barometric light Picard and others had observed. In fact, this is basically what lightning is!

Only the charges reconnect in the air on a path between the clouds and the ground, releasing a lot of light and energy. The fact that frictional electricity was at play also explains why Hauksbee rubbing his hand on the sphere had the effect it did. His hand was providing even more friction, which was transferring even more electrons to generate more potential energy that would eventually convert to light.

It also made the glass electrically charged so that small objects like papers and thread would be attracted to it. So motion, as Polinière had suspected, is what generated the electrical attraction Hauksbee was interested in, which is ultimately what produced light. Hauksbee’s experiments are considered a pivotal moment in the history of electricity.

Although “electrons” as such wouldn’t be discovered until nearly two centuries later, Hauksbee’s investigations gave scientists insights into the nature of how objects become electrically charged, going on to inspire some of the earliest electrical components. And it’s pretty remarkable that Hauksbee’s light bulbs, arguably the first ever… were literally lightning in a bottle. Which, somehow, is even cooler than one of these.

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