Time to Talk About Clocks

a conference. After my talk, a couple of really friendly locals offered to give me a walking tour of Berlin, and so we kind of set out to explore the city and at one point we ducked into a luxury clock shop and I got a nice explanation, half of it in German, of the inner workings of some of the more intricate clocks there. And it was really interesting and incredible to see the workmanship that went into creating

these clocks. And I thought, well, it's about time to talk about time, or rather to talk about how we mark the passage of time. So today we're gonna talk about clocks. Now, most of this episode I'm going to focus on mechanical clocks, but you know me, I like to talk about precursors. And history leading up to the development of technology. And so we'll first take a quick look back at some of the earliest timekeeping technologies before the invention of the mechanical clock. So to count as

a clock, you really need two elements. The first is some sort of consistent, regular action or process that gives you the ability to mark off equal increments of time. In theory, this could be something like the rate that water drips out of a container, which is the basis of many water clocks, or sands through an hourglass, so are the days of our lives. But we'll talk more about water clocks later. With mechanical clocks, it's the rate

at which parts move within the clock itself. In order to keep time, you have to find a way to regulate that so that it is consistent. So that's element number one. The second element you need for a clock is some sort of way to keep track of the increments of time so that you know what time it is. You need a way to be able to read the time. So early clocks, some of the early mechanical clocks that came out of Europe didn't have a dial or a

face or hands or anything like that. They were really automated systems to chime bells, so it was the chime of the bell that would indicate what the time was. That was the best you could do. But later on it would be a mechanical clock with a dial and a face with hands on it, and that would be the part that tells you what the time is. So it's not enough that the clock keeps time. It also has to communicate that or display it in some way. So those are the two elements you need for it

to be a clock. Now, since ancient times, people have found ways to mark the passing of time, everything from various versions of calendars to massive structures that could tell you all about when certain things are going to happen, like equal n ox Is. I mean, you've heard about structures like Stonehenge, But if you're talking about time, as in dividing up the increments of a day, you kind of have to look at the people's of Summer and

ancient Egypt and their use of sun dials. The most primitive type of sun dial would be a stick stuck in the ground, and you can mark the passing of time by observing where the stick's shadow falls as the sun's position overhead changes throughout the day. Sun dials tend to be a bit more robust than a stick stuck in the ground. The sun dials of ancient summer were pretty much gone by the time historians got around to documenting these kinds of things, but there were still some

that existed in Egypt. Now we know that the ones in Egypt were predated by the ones that were in sumer but we just don't have any examples of those so UH. In Egypt you could find things like obelisks. The obelisks dates to at least thirty d b c e before Common era. The shadows cast by those structures could help people mark the passing of time, and in fact, you might end up seeing one that has markings on

the ground that indicates such. Now, both the Sumerians and the Egyptians created divisions for daytime, similar to the way we have ours. The Egyptians created ten segments of daytime between UH and between two and four for night time, but of course you couldn't track nighttime with a sun dial because for a sundal to work, you kind of need a sun and at nighttime that's in short supply. The same was true on any days with whether that

would obscure the sun. Obviously, tracking time on those days would become difficult, but on clear days you could track the passing of time fairly well. The Egyptians would create markings on the ground that would indicate the time of day, so you'd see where the shadow falls. If it falls in atcular section, then you know it's time for lunch

or I don't know. To listen to the New Bengals single if the Earth's axis didn't have a tilt to it relative to the position of the Sun, this would be a consistent way to track the time of day. But because of that tilt, during different parts of the year, the sun will occupy a slightly different part of the sky. This also depends upon where north or south of the

equator you are. If you're right, if you're very close to the equator, the variation is slight, but the further way you are from the equator, the greater the variation is. And because of that tilt, during different parts of the year, the sun will occupy those different areas of the sky, meaning the shadow that it casts on the ground from any object is going to be different at one time

of year than at a different time of year. The Egyptians had all this sussed out, and they would include indicators for the time of year so that timekeeping could remain fairly accurate. And it was easy to see which days were the longest and the shortest, because on the longest day, the obelisk would cast a longer shadow because the sun would appear lowest in the sky as it crossed overhead. On the shortest day, the shadow would be short as the Sun would pass closer to directly overhead.

So little indicators there that can tell you more about the time of year. Now, the fact that the Earth is round, sorry flat earther's it also meant that you couldn't just design a universal sun dial that's going to be accurate wherever you go all year round. As you travel north or south, the angle of the Sun's light hitting your sun dial changes, and so you have to take that into account. A sun dial must be designed for the specific location if you want the time markings

to be accurate throughout the year. The sun dial made its way to Greece and from there pretty much everywhere else. The Greeks created some pretty cool sun dials, including hemispherical sun dials. Now, as this name suggests. These sun dials used a hemispherical surface upon which shadows would fall. Typically the surface kind of like a bowl that have been

cut in half or even quartered. So you had this this little bowl shaped area, but not a not a full bowl with lines on the inside to mark time segments. And the object that was to cast a shadow would be an appropriate distance from the sides of that bowl, and it's orientation would be such that no matter which way it's facing, it's facing away where the sun is

always going to cast a shadow against the bowl. So you want to make sure that it's facing the right direction, otherwise you get a part of the day where the shadow would be outside the bowl and you would say it is the end of times and cause a panic. Now. I learned more about Sundale construction by visiting a website called sun dials dot org. It's a site dedicated to the art and science of sun dials, which is pretty fascinating stuff, even to a liberal arts major such as myself.

For one thing, I learned that the two parts of your basic sun dial, like the kind you might see in a park or a garden, are the dial plate and the nomon g n O m o n The gnomon is the thing that casts a shadow onto the dial plate. And you've probably seen sun dials that have a common nomon that has set an angle respective to the dial plate, so it comes up almost like a triangle sticking up out of this circular dial. I learned from sundals dot org that that angle should equal the

location's latitude. The markings on the dial plate also depend upon the latitude of the location. Only by pairing these two will you get a reliable way to mark the passage of time throughout the year at that location, and of course only on sunny days. Sun dials would continue to be an important method of timekeeping for thousands of years. It was only with the development and refinement of mechanical clocks that sun dials even fell out of use in

naval ships in the seventeen hundreds. But sun dials were just one method of keeping time in those early days. Another method was to use a water clock. Now, a basic water clock is sort of like an hour glass, which of course is another form of ancient timekeeping, but we'll set that aside. So you have two containers, typically in a very simple water clock, connected by a tube

or a channel of some sort. One container is set higher than the other, and it has water in it, and gravity pulls that water, so it flows down into the lower container through the tube or the channel in a more or less controlled way. The lower container has markings on the inside of it indicating how much time has passed based upon the amount of water in the second container. Occasionally you have to dump out the water in the lower container and refill the water in the

upper container. Otherwise the clock just runs out of water. You can't tell the time anymore. It's kind of like if a a watch that has a spring in it, once it unwinds all the way, it won't keep time anymore. Same sort of thing here. Now. The method had one major advantage over sun dials, because it would work what there the sun was out or not. But it wasn't necessarily always consistent. Even a well designed water clock couldn't regulate the flow of water precisely enough to keep excellent time.

But it worked well enough for most folks. It wasn't like you had a whole bunch of people saying, uh, you know, over here in the fiefdom, I've gotta go meet my lord for talking about how much corn. I've harvested um, and I've got a three fifteen meeting, so i really need this water clock to be precise. Now, that just didn't happen in those days. Now, water clocks date as far back as fifteen hundred b c. E.

The Greeks would call their water clocks clipsid draws. Now that actually means water thieves, as the word comes from clip time, meaning to steal. You might have heard the term kleptomaniac that's someone who has a compulsion to steal things, and high door, which means water. They started using water clocks around three b C. And then since than everyone uses clepsydras to be the term for water clocks. And

there are several variations. I described the simple one just a second ago, but others might involve one vessel dipping water out of a small hole into a second vessel which has markings on this inside identicate the passing of time. Or you could have a single vessel with markings on the inside that are revealed as the water level decreases when water drips out of it. So, in other words, you create a small hole in a vessel, you fill the vessel with water, and it's sort of a reverse

of what I was talking about. Before the more water leaks out of the container, you see more markers telling you what hour it is. In North Africa, people would mark time by placing a metal bowl with a hole in it inside a larger container of water, and they marked the passing of time by the sinking of that metal bowl. It would sink within a certain amount of time, and that method was used in some parts of Africa as late as the twentieth cent well. Many water clocks

were simple, some were devilishly complicated. For example, the water clock tower built by Sue Song in the eleventh century CE. Historians descriptions of Sue Song put him in that rare category of humans that includes other amazing polly maths like Leonardo da Vinci. He was a cartographer, he was a mathematician, he was a physician, and he was a horologist. Now

that last one essentially means he was a clockmaker. Sue Song and a team of mathematicians came up with the idea for the mechanics that would make the clock tower possible. The tower was pretty tall, uh. It had inside of it several levels, like it was three stories tall. The top level had a model of the universe on it. The middle one had kind of a a globe to show you what constellations would be where at what point point of the year, so sort of an astronomical slash

astrological clock. And then the base level had the actual time piece itself. Uh. There was a vertically aligned water wheel which was eleven feet in diameter, So think of a wheel on its side. It's it's you know, vertically aligned,

it's got scoops on the outer edge of it. Water would flow from a giant container through a narrow slit at the container's base, and that water would then fill whichever of the thirty six scoops mounted on the outside of the wheel was level with that that drainage spot. So water flows out of the container and it starts to fill up that that scoop. Once the scoop got heavy enough, the wheel would rotate, which in turn would power all the other gears in the tower and help

keep time. Now, a series of horizontally aligned gears on this tower had small figurines mounted to the outer edges. So these gears are are all horizontal, not vertical, so they're at a nine degree angle relative to the water wheel.

The figurines were positioned in such a way to be easily seen through windows of the tower, So if you looked at the tower from the outside, you'd see these little figures in various windows along that side, like three levels of them, with one window showing certain figures that indicate a certain increment of time. The figures all carried signs that represent numbers. That means they were effectively digit counters, so you look at the figures and you could suss

out what time it is. But Sue Song had to come up with a way to make this a steady, regular series of events. If you left this on its own, if you just had a big water wheel and you were having water flow into these scoops, the water wheel would eventually just start turning continuously as long as there was water to push it, which means all the figures would constantly be in motion, and that could be tricky

to read the time, especially between minutes. So you know, you could have a figure that's half in view and half out of you you're not really sure what time it is. So Song need a way to keep a gear in position for a certain interval a given amount of time, such as a minute, and so he and his team had to come up with a way of stopping gears, but only temporarily, so that the passage of time could be more regularly communicated. So he and his team created a clever gadget that would end up being

an important part of clocks for centuries. It's called an escapement. So what is an escapement. We'll go into that in just a bit, but first let's take a quick break to thank our sponsor. Okay, So, an escapement, what isn't well in clocks is an element within a device that regulates the turning of other gears. You can think of it as a lock that unlocks itself at consistent intervals to allow gears to turn before locking back in place. And if you've ever seen a pendulum clock, that the

purpose for that pendulum. But we'll get into that a little bit later. Sue Song created an escapement to lock the gears in place in his water tower until there was a need for them to shift to the next increment of time. Sue Song's approach was using a balance called a steel yard. It's all one word. Steel yards are pretty cool applications of one of the simplest machines

the lever. If you have a lever with a pivot point in the exact center of its length, assuming the mass is equal on both sides, the lever will balance out if you put two equal weights, two equal masses really on either end, and it remains balanced. Well. It does so because of this very nature of levers. So are you with me so far? Now imagine that we move that pivot point more toward the right side of the lever. That would mean that more of the lever's

mass is on the left side. The right side is shorter than the left side because we've moved the pivot point closer to the right end. So if you just step back the left side, the lever will be on the ground. It's gonna tilt downward it until it's either on the ground, or if you haven't suspended in the air, it's gonna be dangling vertically with the short end at the top, you know, the bit that's closer to the pivot. So to balance it out, you would have to put

more weight on the right side. You would have to have more mass to equal out the mass that's on the left and balance it all out. This is how a steel yard works, and you may have used one of these with weight scales. If you've ever stepped on a scale that requires you to move a counterweight along an arm, you've used a steel yard. The trick is to get the counterweight adjust the right spot on the lever to make the arm balance out. If the counterweight is too close to the pivot point, the arm will

be up in the air. It will say no, you weigh more than that. You need to push that counterweight further towards the end of the arm. If it's too close to the end of the arm, it's gonna go down as far as it can go. Like in a scale, there's typically a little stop point and it'll just sink to the bottom. So getting the counterweight in the right position makes the arm ba elens in the middle, and the position of the counterweight will tell you how much

you way. There will be some marking. They're saying, congratulations, away a hundred fifty pounds. Sue Song's tower used a steel lyard kind of like this. Now, I want you to imagine a vertical wheel made of spoons. All right, All the spoons are facing in the same direction, and all the scoop parts of the spoon are faced in such a way where they're you know, they're just if you were to stack them in a stack, they would all be stacked together perfectly, but you've fanned them out

into this circle. It's a vertical circle. Uh. And imagine we're looking at this wheel from the side, so we're looking at the profile of the wheel, not dead on position. Halfway up the wheel to one side is a chamber of water that can flow out into the empty spoon that is next to it. The one that's closest to it. Will say that this this spoon is parallel to the ground, So this is the one that is at the three o'clock position for those of you who still know how

to read analog clocks. On the other side of the wheel, over at the nine o'clock position is a weighted arm, and it rests on the back of the spoon opposite to the one getting filled. And the weighted arm, it can't reverse the direction of the wheel. It just holds it in place. The weight of that arm just keeps it locked there. But the weighted arm is on a pivot, so it can be lifted if enough force is applied. Now, as soon as the spoon fills with water, it gets heavier.

When it gets heavy enough to counteract the weighted arm on the other side, the weighted arm pivots up. This allows the wheel of spoons to turn in one increment. It turns so that the next spoon is moved into place. The weighted arms slips off the back of the spoon it had been on and comes down to prevent the next one from moving upward, locks it into place. That whole process repeats, and that's basically how siouxs Song's escapement worked.

As long as there was water steadily flowing into the tower, the clock would keep accurate time. Now I wish I could tell you that you could go and visit this amazing clock tower in Kaifeng, but sadly you can't. The tower was finished in ten ninety four. Sue Song himself died in eleven oh one, which means he didn't live to see his amazing creation disassembled by soldiers. After the Manchurian Army invaded Kaifeng, they took the clocks pieces back

to their capital, which is today's modern Beijing. They attempted to reassemble it, but the complex nature of the clock confounded them and it never worked again. There is, however, a working replica of the tower in the Gishido Suwako Watch and Clock Museum in the Nagano Prefecture in Japan. I've seen photos of it and it is gorgeous. I hope one day to see it in person. This particular replica was built based upon the best understanding of sus

Song's designs. Many of those designs survived all of that invade Jian issue, but there were little details left out, so people the modern replica makers had to kind of fudge things here and there to make it work properly. So it may not be one to one a replica, but it's really close and it looks amazing in the pictures I've seen. This escapement would prove to be a very important component of clocks and watches as the art

and science of clockmaking evolved. As for purely mechanical clocks that did not depend upon water, their origin is somewhat lost to time, which is not an irony but seems fitting. Monasteries were building clock towers called turret clocks as early as the fourteenth century, at least maybe earlier. These were massive towers that passed marked the passing of time by tolling a bell, so there were no dials or hands or other indications of what time it is. The machinery

was large and relied upon weights and gears. Now, the weight is a very important part of these early make chanical clocks. And here's how a weighted clock works. Now, imagine you have an axle wound around That axle is a cable or rope. If you were to pull on that cable or rope, it would provide enough rotational force to make the axle rotate. At the end of this rope is a heavy weight, and if you lock the

axle into place, the weight represents potential energy. Right it's hanging it suspended above the ground, but the wheel is locked so it cannot turn. That's potential energy. The weight has the potential to move the clock or move this wheel this axle. Gravity is pulling the weight down towards the center of the earth, and once you unlock the wheel, it allows that potential energy to convert into kinetic energy.

The weight will start to drop toward the ground and it applies for uce to the rope, which thus applies force to the axle, causing it to rotate. And then it can end up making other elements of the clock move as well. You have gears and pinions and stuff, and they're all interlocked, and that allows for or the operation of a clock, which ultimately makes a bell go ding dong ding. But here's a problem. Gravity causes acceleration.

Things do not fall at a steady velocity. The velocity is always increasing as long as the fall is continuing, at least until you hit terminal velocity. So everything accelerates according to the gravitational pull of the Earth. At least stuff dropped here on Earth does that. If you were to drop something on Mars, it would accelerate according to Mars's gravity, not Earth's gravity, even if it originally came

from Earth, because Mars just don't care. But here on Earth we know gravitational acceleration is equal to nine point eight meters per second per second. So if you drop a weight high enough for it to fall for several seconds, each second that passes will see the velocity of the falling object increase by nine point eight meters. So after one second, the weight is falling at nine point eight

ms per second downwards. During second number two, the weight is falling at nineteen point six meters per second downwards, and so on. It increases each second the weights falling speed increases until the weight achieves terminal velocity. I mentioned that earlier. This is the speed and object reaches when the resistance of the medium it is falling through. In our examples, we're just talking about Earth, so we're talking

about Earth's atmosphere. When the resistance of Earth's atmosphere is enough to prevent it from accelerating further, then the object has reached terminal velocity. So eventually, falling speed does top out, and it remains consistent at that point until you know, you collide with the ground, in which case the falling speed stops and the splatting speed begins. Okay, but what

does that have to do with clocks. Well, remember at the top of the show I said that a clock needs some sort of consistent, regular action or process that gives you the ability to mark off equal increments of time. If you have an accelerating falling weight, it's tricky to use it as a means for the rest of your structure, right because it would have to account for that acceleration.

You would have to have some really complex machinery that would operate in such a way to counteract that acceleration. You'd much rather have a regular force that remains consistent in speed and power, something that's not going to increase an amplitude over time. And that's where the design of an escapement is so important. The escapement design allows clockmakers to regulate this action and make sure it happens at these regular intervals. Now, the oldest surviving mechanical clock in

England is Salisbury Cathedral's clock. The clock dates to probably around thirteen eighty six. According to historians, this is not necessarily the oldest surviving mechanical clock in the world. There's actually some controversy about that, but this is certainly the oldest surviving one in England. And I saw that clock in person back in nine. I even had a photo taken of me appearing to set my watch according to the clock, which at the time I consider it to

be high comedy. And let's be honest, I'd probably do the exact same thing today if I were to visit. The Salisbury Cathedral clock originally had was called a verge and folio escapement. Now, this is a tricky thing to describe in an audio podcast, but I'm gonna try and

do my best. Imagine that you have a vertically aligned wheel, kind of similar to the water wheel I was talking about, but instead of the wheel's edge ending in scoops, the wheel has pegs sticking out along the rim on one side of it alright, So one side of the wheel is is just flat, it's featureless. The other side of the wheel has pegs sticking out right along the edge at regular intervals. This is called the escape wheel. The wheel is on an axle, and that axle at some

point has a weight attached to it. So left on its own, the wheel would rotate as the weight falls, with the rotation accelerating as the weight accelerated during its fall. So we would have to have something to regulate the wheel's rotation. The force applied to the axle should remain steady, so we can't mess with the weight. We can't change that. We need to have some other way to alter this, and that would be the verge and folio. Position. Next to this vertical wheel, the one that has the pegs

the escape wheel, you have a vertical rod. This rod is called the verge. The verge can rotate on its axis in either direction of rotation along its respective orientation. The rod has two stoppers or protrusions that are called palettes. They're like flaps like you know, they could just be a little square flaps that stick out from the rod

to the side. One of those positioned near the top of the vertical wheel, and one of them is positioned towards the bottom of the vertical wheel, and their their alignem is slightly offset in respect to the axis of the verge. That means that they can catch the pegs of the rotating vertical wheel at different points. So you have these pegs that can come into contact with these palettes, and when they do, obviously there's there's an impact there.

There's a collision, and it causes the verge to rotate and it puts the other palette, the one on the opposite side of the verge, into the right position to catch the pegs on the opposite end of the wheel. So one palette is always going to be pushed in one direction of rotation for the verge, the other palette is always going to be pushed in the other direction of rotation for the verge. Because you have this ninety degree difference of orientation with respect to the the escape wheel.

So the the the attached to the very top of the verge is a horizontally balanced lever. It's actually kind of kind of like another horizontal rod that's on the very top of the verge. There's weights attached to either end. This is called the folio, and it swings back and forth, it oscillates. So how does it work? Well, As I said, one palette is position so it catches pegs at the top of the vertically aligned wheel, the escape wheel. The

other palettes at the bottom. They're offset, so one pallet makes contact with the pegs, the other one is free and clear. It doesn't interfere because otherwise, if you had both palettes positioned so that they locked in with the pegs, no movement could happen. You would effectively have a break

on that escape wheel and it would just not rotate. So, as the vertical wheel turns, a peg at the top of the wheel catches the top pallett and provides enough force to push it and rotate the verge on its axis. The folio at the top would rotate accordingly. Now, that puts the palette at the lower end of the the lever in position to catch a peg at the bottom

of the vertical wheel the escape wheel. Because of the alignment of the virgin wheel, this creates a force opposing the direction of the folio's previous rotation, making it rotate the other way or oscillate. Uh. This is similar to the oscillations of a pendulum, and we'll cover that when we get to pendulum clocks. The pegs will catch the

pallets and create this TikTok sound you here with a clock. Uh. It's the pegs making contact with those pallets and making the folio swing one way or swing the other way. The weights on the folio give it enough inertia to keep it from rotating too far and provide just enough force to regulate the turning of the vertical wheel. The escape wheel is just one part of the clock. The elements that actually track the time, as in the ones that govern the movements of the hands on a dial

face or govern when a bell gets struck. That's called the train or wheel work of a clock. These are all the gears that transmit motion to the parts of the clock that illustrate the time or market in some way. In the earlier clocks, this was pretty primitive, as originally again, there were no dials or hands to turn. There just need to be a way to designate an hour had passed. Later, clocks would add an hour hand, but no minute hand, so you would be able to see what hour it was.

But that was it. As clocks became more complicated than necessity for precision increased, wheels and pinions have to be crafted precisely to transmit motion as steadily as possible in order for this to work. Now you might wonder what happens when the weight that's providing the force to turn all this machinery reaches the ground. What happens is the whole thing stops. You have to wind the mechanism so that the weight is lifted back to the top, creating

that potential energy necessary for the clocks operation. This it is true of other mechanical clocks as well, whether the force comes from a suspended weight or a spring. With a spring, you have to wind it to increase its potential energy before you let go and it starts to convert it into kinetic energy. In fact, spring powered clocks would emerge before pendulum clocks did. Peter Henline of Nuremberg

gets the credit for inventing spring clocks. Early in the sixteenth century, sometime between fifteen hundred and fifteen ten, hen Line would use a coiler metal while entightly to provide the potential energy necessary to drive clockwork. The spring would have a natural tendency to unwind and assume its normal shape, so winding it would build up that potential energy, and using an escapement kept the unwinding to a somewhat regular

series emotions. And as the coil unwinds, the amount of force it exerts decreases, which actually meant that a clock would start to run more slowly and begin to lose time. To get it going again, you have to wind it up again. Now, these early clocks weren't exactly the most accurate. According to the Anderson Institute, the big ones could be off by as much as an hour per day, and they only marked the passing of an hour at a time,

with no indication for smaller increments. Still, it was a way to keep track of time that didn't require members of the church to track it themselves and then hike up to the top of a bell tower and give it the old toll. And if you're wondering how they told time at night before they had mechanical clocks. It usually involved burning something that had a pretty steady combustion rate. This included candles that would burn at a pretty steady

and predictable rate. You'd have to figure out how big your candle needed to be and make the wax as consistent as you could, and try and keep track that way. You would just mark it on the candle, and when the candle burned down to a certain amount, you knew an hour had passed. It wasn't down to the minute, but it served well enough for the chiming of bells. Now, in our next part, we're gonna talk about pendulum clocks.

But before I get into that, one thing I want to mention is if the version folio description has completely baffled, you do a search for the terms on YouTube, because there are lots of illustrations on there that will show you exactly what I'm talking about folio. By the way, it's spelled fo L I O T, and you can see exactly the mechanisms I'm mentioning and see how they were able to regulate the turning of gears. And before I get into pendulum clocks, I need to take another

quick break and thank my sponsor the virgin folio. Escapement was the dominant method of regulating the motion of mechanical clocks for a couple of centuries. But then an Italian smarty pants by the name of Galileo Galilei made an interesting observation. He discovered that a pendulum takes the same amount of time to complete one full swing out and back, over and over and over again. The time for one complete cycle is what we call a period. So the period of a swing remains the same even as the

pendulum's swing decreases in amplitude. So what do I mean by that? Well, if we were working with a pendulum mounted on a massless rod or a line uh and had a frictionless pivot, then the pendulum is always going to return to the same height as its initial release.

But that's not how the real world works. So let's say you tie a rope to the limb of a tree, and on the other end of the rope you tie a bowling ball, and you get on a step ladder, and you're are far enough back so that the line is taught between the limb and the bowling ball, and you're standing at a certain level. You're holding the bowling ball right up to your chin. With the that line there, you let go of the bowling ball. And by the way I say let go, you don't push the bowling ball,

but you just let go. Now if you do that, is it going to swing back and knock your teeth out? No, it won't, And the reason for that is because elements like friction and drag are sapping some of the energy from the overall system. The returning bowling ball doesn't have the same amount of energy that the departing bowling ball had, so it doesn't rise up as high as when you dropped it, which means you get to keep your choppers. Congratulations,

go brush your teeth. But even though the bowling ball isn't rising up to the starting height of its release, the journey of its swing, its period will remain the same. That time remains the same, at least for small amplitudes. This story is different if you're swinging that sucker really hard, But for simple pendulums at small amplitudes, this is true.

The ball isn't traveling as far on each swing because it's losing that energy to friction and drag, but it's also not swinging quite as quickly per swing, so it's not going as far, but it's also moving a little more slowly, and the overall amount of time it takes to complete one period remains constant. Now that means if you make a pendulum of a precise length, you can

create a swing of one second. The period of a pendulum swing can be expressed as an equation, and the period is equal to two times pie times the square

root of the length of the pendulum divided by gravity's acceleration. Now, ignoring for a moment that gravity's acceleration is not uniform everywhere on Earth due to several factors that really are too complicated for us to get into here, we can simplify this to say that a pendulum of nine nine millimeters or about thirty nine inches is the right length to have a swing period of a second. Now, Galileo recognized the potential for pendulums in timekeeping, but he never

built a clock using one. That honor goes to a Dutch scientist named Christian Hygens, who in the mid seventeenth century figured it out. He used the oscillation of a pendulum to regulate the motions of clockwork in many ways. It was similar to the virgin folio design, except instead of relying upon a weighted lever and inertia, Hygen's design relied on the natural oscillation of a pendulum of an

appropriate length. So how does a pendulum escapement work. The escapement still engages a gear, preventing it from rotating freely, and as the pendulum swings, it rocks the escapement so that it disengages with the gear, and the gear begins to rotate. At the end of the pendulums period, when it returns to its starting point, the escapement is locked back into position and the whole process start again. But I'm sure you're all wondering how the pendulum keeps moving.

I mean, if it's losing energy with each swing, how does it continue more for more than just a few seconds without adding more energy to the pendulum. It's eventually just going to slow down and stop swinging completely. I mean I talked about this with friction and drag. Well, Hygen's got around this by designing a gear that would give the pendulum a little nudge each time the escapement disengaged, so it provides just enough force to counteract dragon fiction friction.

So it worked. Hygen's initial design was accurate enough to keep time within about a minute per day, meaning you'd only lose sixty seconds during a day long operation of one of his clocks, which was incredible for the time, and he improved upon his design within his own lifetime. He cut it down to losing only ten seconds per day, which is not bad for an entirely new method of

regulating gear rotation. Pendulums do come with a couple of complications, however, so it doesn't matter what the mass of the pendulum is. By the way, you don't whatever the bob is at the end of your pendulum. That mass can be anything. It's that it's immaterial. It's the length of the pendulum that's that's important, not the bob, the mass of the bob, except that you don't want something so massive that's going to cause damage to the clock itself. But that pendulum's

length is incredibly important. And this is where we get into some trouble because of temperatures. Most pendulums are made of metal, and metal has a tendency to expand in the presence of heat or contract when it gets colder. And since the pendulum's period is dependent in part upon its length, this poses a problem. A precisely designed pendulum might swing it exactly one second per period, but or have a period of one second is the more appropriate

way of saying that. But if the length of that pendulum were to change, it would no longer be true. The period would be slightly off from a second, and that would be enough to cause errors in timekeeping. Clockmakers recognize that issue and they try to fix it in different ways. The most common way was do you use alloys of metals for pendulums. So an alloy is a combination of two or more metals, and one of the interesting features of alloys is that you can mix together

metals that have different coefficients of expansion. So if you do this carefully enough, you can cancel out the effects of temperature to a great deal. So, for example, you can use zinc and iron or brass and steel and pair them together in this way, and that ends up reducing that effects so that the clock can be more accurate no matter what the temperature happens to be. For a pendulum clock to be really accurate, you have to reduce the impact the impulse of the impulse of the

turning crown wheel. The crown wheel is the element that the escapement locks into, so you have to reduce the impact of its motion on the pinchul lium itself and needs to give just the right impulse to keep the pendulum from swinging and no or or less than that. Ideally it would be uniform every single time, meaning you have very precise distances between pegs on the crown so that it's impact on the escapement would remain consistent no

matter where it is in the crown wheels rotation. There was a guy named Edward Beckett who later on would be lorded and would be known as Lord Grimthorpe, which is possibly the coolest title I've ever seen. He invented what was called the double three legged gravity escapement, which honestly sounds like a routine you'd see at Sercla, but in fact it was a particular arrangement that allowed for extremely consistent operation. He used it to build an enormous

clock over at Westminster. The clock is world famous, and actually people generally call it by the name of the huge bell that is also in that clock tower, and people just called the whole thing by the bell's name. That bell's name, by the way, is Big Ben I would describe to you how his escapement works, but I'm pretty sure my brain would melt as I tried to

do this without the use of visual aids. Fortunately, there are videos about the double three legged gravity escapement on YouTube that show exactly how this works, and it is fascinating. I I it really drives home the fact that engineers are remarkable people who are way smarter than I am, and I highly recommend you go and check these videos out to get an appreciation for the actual clockwork that makes the regulation possible. And that pretty much wraps up

this episode of tech stuff. But there's a lot more to talk about with watches and clocks. I'm sure in a future episode I'll tackle things like quartz watches, which rely upon the peculiar piezo electric qualities of quartz, and I'll talk about other types of time keeping, things like atomic clocks and how those work. But for now, I'm going to say it's time to conclude this episode and remind you the next time you look at a clock, think about all the amazing work it took to make

it all work out properly. From physics to mathematics to engineering to craftsmanship. A clock represents lifetimes of genius, so take some time to appreciate it. If you guys have suggestions for something I should cover in a future episode of tech Stuff, or maybe there's a guest you would like me to try and book on the show for an interview, or a guest host to talk about specific topic,

let me know. Send me a message. The email for the show is text Stuff at how stuff works dot com, or you can always drop me a line on Twitter or Facebook. The handle for both of those is tech Stuff hs W. Remember we've got an Instagram account. You can see all sorts of cool and interesting tech related images that Crystal has been posting to that, so check that out. And of course I record this show on Wednesdays and Fridays, and typically I live stream it. If I am doing it on my own, it's to is

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