Physics Rediscovered #16: The shocking origins of electricity and magnetism
There is a chance that you’ve felt something when you saw that a new episode of Physics Rediscovered just dropped. I’m hoping that it was a jolt of excitement.
However, it could’ve been that of an electrostatic discharge. You’ve probably built up a lot of energy when you shuffled to the screen, on which you are reading this. The moment you touched it, all that energy went away, possibly in an arc of lightning.
Or maybe, just before touching the screen, you’ve decided to pet your cat and gave it a shock in the process. It probably wasn’t the first time so now it doesn’t like you very much, but sticks around for the free food.
So, you could’ve used all that power to solve the world’s energy problems, but instead you’ve decided throw around lightings like you’re Thor or something. I won’t even comment on the animal abuse.
Humans throughout history have all had the same experiences, maybe minus the screen part. However, the most common and reproducible aspect of this bizarre phenomenon spanning across millennia and cultures was evident in amber or elektron, as the Greeks called it.
These pieces of fossilized tree resin, which you can find at seashores, where they lay for millions of years, forming under the crushing pressure of layers upon layers of sediment, are not only a source of ancient mosquitos, but also seem to attract feathers and other light objects when rubbed vigorously.
That was cool and mysterious, and something you could impress someone with on a first date. However, if you wanted a guaranteed second and even a third date, you would bring a lodestone.
This lump of iron was much more rare than amber and didn’t need to be rubbed or anything. It pulled in pieces of metal completely on its own and, if properly shaped, seemed to point towards a mysterious direction. Very soon, people (like the Chinese and maybe Olmecs) realized that lodestones could be used for navigation, which made them the granddaddies of modern compasses.
As to why these things behaved the way they did, no one wanted to say magic, but basically magic.
Looking for a genie
Fast forward to the 1600s and… not much has changed. Neither the effects of amber or lodestone really got the same geometrical attention as optics or mechanics. As a result, these effects never got the same rigorous description as the domains of Newton.
It’s the 17th century, so an idea of a strict physical experiment doesn’t really exist yet, as Galileo is just starting to make waves. That being said, it is a time where people try stuff to see what happens. As a result, we’ve discovered that there are many more materials, beside amber and lodestones, that exhibit similar funky behavior.
Language was also trying to keep up and Sir Thomas Browne (who also introduced computer) uses the word electricity for the first time in 1646. He mentions it in his Pseudodoxia Epidemica, which is like a popular science book of the time. It deals with debunking various superstitions, like the existence of basilisks, gryphons and unicorns, for example. At the same time Browne was a firm believer in witchcraft and may have had a hand in sentencing a woman or two for that totally real crime. Some people can compartmentalize like it’s a superpower…
Anyway, monkeys like us really like to touch everything we see and put it in our mouths. With an ever increasing array of stuff that was electric and magnetic I’m confident, that someone tried to swallow enough lodestones to become a human compass. For sure such heroes existed, though now lost to history.
Fortunately, we do know of others who weren’t far off. One of those was Charles François Dufay. I guess someone, at some point, told him that there’s a genie hidden out the somewhere and it was his job to find it. On mission, he went about rubbing everything is sight, like a maniac.
It’s unlikely that Dufay found any genies, but by 1733 he managed to classify a bunch stuff as electric - stuff that can be electrified by rubbing it and non-electric - stuff that cannot. Moreover, his also noticed that bringing something in contact with an electric also makes it electric, which seemed most pronounced with metals.
We, humans, love ourselves some categorization and Dufay’s work quickly became super popular. Further extended by his disciple, Jean-Antoine Nollet (more about him in a bit), it became the standard of thinking for everyone dabbling with electric stuff.
You don’t break the jar, the jar breaks you
Despite their popularity, Dufay’s and Nollet’s schemes had embarrassing problem. These couldn’t really explain all that much. Yeah, you could do something crazy in the lab, assign it a recognized category, but that’s about it. Categories alone are insufficient to predict new outcomes.
This became painfully obvious (and obviously painful) with the “Leiden jar” invented independently by Ewald Georg von Kleist and Pieter van Musschenbroek (from Leiden university).
You can check out different designs here, but in its essence, it was a glass jar filled with water, with a wire sticking out of the water. Here’s how it works. First, you hold the jar in one hand and electrify the wire, and the water with a generator (rubbing something vigorously). Second, you touch the wire with your other hand and give yourself a solid shock to remind yourself that you can still feel something.
From today’s perspective this may not seem like a jaw-dropping invention. However, this is what Musschenbroek wrote to his friend:
"I am going to tell you about a new but terrible experiment which I advise you not to try yourself, nor would I, who have experienced it and survived by the grace of God, do it again for all the kingdom of France…”
He then explains the details of the setup and ends with:
“…I have found out so much about electricity that I have reached the point where I understand nothing and can explain nothing.”
He wasn’t alone there as the Dufay-Nollet system was hopeless at explaining the jar, as well. It could shock you like no other friction-based device. How was it able to accumulate so much electricity by just holding glass in your hand? No one had any idea.
The Leiden jar quickly became popular across the world and soon, people were shocking themselves and others as an idea of prime entertainment. Nollet saw that the jar is the future and wasn’t about to capitulate. He also wanted to shock people, but not just one or two, once in a while. Nothing less then 200, at once, would satisfy him and that’s exactly what he got.
Nollet, somehow, convinced 200 monks to form a human circle with a circumference of 1.6 km (or a mile for you Americans). He used multiple Leiden jars is order to shock them and record their screams, in order to figure out how fast electricity spreads. Very fast as it turned out.
I wonder if he had to repeat the experiment for consistent results. I mean, can you imagine how that conversation went?
“Messieur Nollet, are you sure this is safe?“ asked the friar, visibly concerned by the battery of Leiden jars being connected by suspiciously eager Nollet’s staff.
“Absolutely!“ said Nollet. “I’ve shocked myself thousands of times and I’m perfectly fine,“ he assured, punctuating every other word with an involuntary twitch.
That’s what I call vision. I’m tempted to say that we are looking at the first ever circular particle accelerator. That wouldn’t be technically correct, I guess, but you know… and it’s made of humans… Nevertheless, the exact workings of the Leiden jar remained a mystery, despite Nollet going full mad scientist.
Do you have the constitution to do science?
Electricity at the time was described as a type of enigmatic matter (existing alongside common matter) that permeated all of reality. It was emerging from electrics sending out its tendrils to enter other matter and grab it, while repelling tendrils from other electrics. At the same time matter would send out tendrils to seek out electrics in the vicinity. At least that’s how Nollet saw it.
Perhaps somewhat bizarre, but not totally unjustified. After all, that’s kind of how it looks when you hold an electrified object next to someone’s hair and witness the hair get “grabbed“, and adjust itself to the shape of the mysterious tendrils.
However, this was not good enough for a certain American (for that became a word) going by Benjamin Franklin. The name might sound familiar. It’s the dude looking at you from a 100 dollar bill with, what to me looks like a mixture disappointment, disgust and resignation.
He wondered, why would you do something with two electricities, when you can do it with one. Also, what if that one electricity is conserved?
Franklin imagined electricity as a special fluid present in all matter. When you’d electrify something, you’d simply accumulate more of that fluid, borrowing from somewhere else. Hence, Franklin would label the excess of electricity as “+“ and the deficit as “-“. In such a system releasing electricity would mean restoring the balance, so charge flowing from + to -.
That might’ve made sense at the time, but today we know that it is exactly the other way around. Knowing that, we’ve decided to fix this misconception and proceed with the proper labelling of the direction of the flow. We did this in order not to cause any further confusion and operate within a logical and consistent scheme… nah, just kidding. We stuck to Franklin’s original, misguided convention, which annoys the hell out of people to this day. Apparently, it’s too late to do anything about this now. We did this to ourselves…
Anyway here are some of Franklin’s thoughts on the nature of electricity from his Experiments and Observations on Electricity (1751):
”The electrical matter consists of particles extremely subtle, since it can permeate common matter, even the densest metals, with such ease and freedom as not to receive any perceptible resistance…”
or
”Electrical matter differs from common matter in this, that the parts of the latter mutually attract, those of the former mutually repel each other...”
and
”Thus common matter is a kind of sponge to the electrical fluid. And as a sponge would receive no water if the parts of water were not smaller than the pores of the sponge…”
It’s impossible to talk about Benjamin Franklin without mentioning his most famous experiment. It’s the one where he was trying to catch lightning with a kite, probably being as high as one, given how ridiculous the whole thing was. Who was flying the kite? His son, obviously - Franklin went full biblical Abraham on this one.
Ok, in all fairness he wasn’t really trying to catch a real lightning. That would mean frying his son and likely exploding the whole experimental setup. This is something that Georg Wilhelm Richmann would confirm if he could… Franklin’s real goal was to charge a Leiden jar using electricity from the air. That he managed to do, thus confirming a long standing suspicion, that the electricity in the sky is the same as the one created by rubbing stuff in the lab.
While catching lighting might’ve been too much, redirecting it was a whole different story. Franklin introduced the lightning rod to do just that, saving, among other things, a bunch of churches from the wrath of god.
Despite being full of fun ideas, Franklin’s thinking didn’t rub everyone the right way. Nollet was especially vocal in his opposition and was super annoyed that the lightning rod actually worked. A nerd fight broke out, but Nollet just didn’t have that Founding Father swag about him and soon became somewhat forgotten.
Disgusting, repulsive matter
If by any chance, gentle reader, you’re an American patriot and getting all choked up about Benjamin Franklin, then let me stop you right there.
Perhaps you’ve picked up on this, but Franklin’s approach had a serious problem. A deficiency of electrical fluid was labeled as “-“ and two minuses seemed to repel one another. So, how exactly the absence of electrical fluid causes repulsion?
That made little to no sense and Franklin himself pretended the problem doesn’t exist. “Lalalala, can’t hear you!” and other counter-arguments like that.
Even if we join in this electrical denial, whether you’re team Nollet or team Franklin, all of the argumentation so far was just a bunch of energetic hand-waving. This is a technique physicists developed and perfected over the centuries in order to compensate for insufficient arguments.
Could anyone be bothered with at least a little bit of mathematics in all of this, maybe? The answer was yes - Franz Aepinus could be bothered. Being a psychofan of Franklin and Newton, he decided to merge their thinking.
First, he needed to make up for the shortcomings of Franklin and his problems with repulsion. With that in mind, he made the brave assumption that ordinary matter repulses other ordinary matter by default. That’s why “-“ and “-“ (lack of electricity) seem to get away from each other. Only the presence of electrical fluid negates that natural repulsion and things make sense again.
Having the basics of interactions grounded, Aepinus proceeded to geek out on the subject and eventually arrived at a Newtonian, differential description of the forces between electric and ordinary matter.
This was a biggie. Not only did he reduce the rate of injury from the excessive hand-waving by introducing solid math to the problem, he kinda made sense of induction. Experiments showed that in order to achieve electric effects, one didn’t need to make electric objects touch - they just needed to be close enough. With the Newtonian force approach, electricity could be seen as working at a distance, just like gravity. No one knew why exactly, but at least the math was familiar, so there...
Not so brute force
All this fighting, masochistic experiments and fancy math games, yet a very basic question persisted. How much electricity is there?
Maybe there was 7 of electricity of even 12? Several strategies were applied to tackle this question. You could, for example measure the longest length of a spark that jumps from a charged object. Alternatively, you might be tempted to take a piece “standard“ wire and see how much of it fuses, when you discharge a Leiden jar into it.
These were valiant attempts, for sure, but hardly controlled experiments. The need for more sophisticated measurements was getting ever more pressing.
The thing that came to everyone’s mind apparently was: look, there’s so much repulsion between electrified stuff! Well, how much repulsion is there? It’s like many degrees of repulsion, bro.
That totally historically accurate conversation makes sense only if you take a look at early, was we started calling, electroscopes.
Basically it came down to measuring the angular separation of some charged objects. It could be a pair of gold leaves (on the left) or a pendulum on a circular pivot (right). Yeah, yeah, super impressive, I know. We needed to do better… and we did.
Let me just say this: torsion balances.
Some of the members of our race are actually pretty smart and so they’ve figured out that one could measure a lot of stuff, and pretty precisely, with those contraptions. It all came down to twisting something and knowing how much you need push that something to prevent it from untwisting (torsion) and making it stable and balanced (balance, duh).
One of the most famous of these was used by Henry Cavendish to confirm Newton law of gravity. The other famous one was by Charles-Augustin de Coulomb. He woke up and chose force. Specifically, how much of it electricity exerts on its surroundings. It went something like this:
The torsion wire was well calibrated (though some were skeptical) so he knew how much force was needed to twist it by some angle. Therefore, once the rod stopped moving and settled, Coulomb knew how much force the red ball and brass disc were experiencing.
Whatever the model of the electric force would look like, Coulomb figured it must have had something to do with distance and the amount of electric fluid (or charge).
Distance came first.
As the rod stabilized, the distance between the brass disc and red ball could be measured resulting in a force-distance point pair. By manually adjusting the default twist of the torsion wire, Coulomb could demand more force to prevent untwisting. This brought the disc and ball closer together and created another pair point. Rinse and repeat. With all that done he got a force (F) - distance (r) relationship that went like one over distance squared (often called the inverse square law):
Now for the charge.
This one was more challenging. Everyone observed that a charged body doesn’t seem to exert force on a non-charged body except for induction effects, but these were smaller in magnitude than the ones Coulomb was interested. This suggested that the force being something like “charge + charge” didn’t make sense because if one charge was 0 we would still get a non-zero force.
Next was multiplication, which also seemed somewhat inspired by Newton’s law of gravity, where we have “mass x mass“. This seemed like a candidate, but there was another problem there. Coulomb didn’t really know how much charge something has, only that it has some. What to do now? Well, there’s a trick to it.
First, he would measure the force with the charges on the ball and disc, whatever these might have been. Next, he would take out the red ball from the container and touch it with an identical uncharged ball. He figured, that whatever the original charge on the red ball was, half of it would now be transferred to the uncharged ball. He would then put the original, red ball (now with half the original charge) back into the container and measure the new value of force. Do the same thing again and you will have a quarter of the original charge and so on.
Multiplication seemed to make sense and the force seemed to be like:
where the qs are the respective charges and can be either positive or negative. Putting the two together he got:
where k is the proportionality constant, which we today call by Coulomb’s name.
Look at that. All it took was a piece of twisty wire and a few experiments on humans in order to discover the fundamental law of electrostatic force.
With this monumental milestone we’ll take a break now, before we explore how people wanted to use electricity to bring dead things back to life (insert evil laugh here).
See you on the next episode of Physics Rediscovered!