Speaker 1: Again in text with technology with tech Stuff from stuff
Speaker 1: works dot com. Hey there, and welcome to tech Stuff.
Speaker 1: I am your host, Jonathan Strickland. I'm an executive producer
Speaker 1: here at how Stuff Works, and I love all things tech,
Speaker 1: and today I wanted to talk about something that I've
Speaker 1: always found interesting but also intimidating. A couple of years ago,
Speaker 1: I traveled to Berlin, Germany to give a talk at
Speaker 1: a conference. After my talk, a couple of really friendly
Speaker 1: locals offered to give me a walking tour of Berlin,
Speaker 1: and so we kind of set out to explore the
Speaker 1: city and at one point we ducked into a luxury
Speaker 1: clock shop and I got a nice explanation, half of
Speaker 1: it in German, of the inner workings of some of
Speaker 1: the more intricate clocks there. And it was really interesting
Speaker 1: and incredible to see the workmanship that went into creating
Speaker 1: these clocks. And I thought, well, it's about time to
Speaker 1: talk about time, or rather to talk about how we
Speaker 1: mark the passage of time. So today we're gonna talk
Speaker 1: about clocks. Now, most of this episode I'm going to
Speaker 1: focus on mechanical clocks, but you know me, I like
Speaker 1: to talk about precursors. And history leading up to the
Speaker 1: development of technology. And so we'll first take a quick
Speaker 1: look back at some of the earliest timekeeping technologies before
Speaker 1: the invention of the mechanical clock. So to count as
Speaker 1: a clock, you really need two elements. The first is
Speaker 1: some sort of consistent, regular action or process that gives
Speaker 1: you the ability to mark off equal increments of time.
Speaker 1: In theory, this could be something like the rate that
Speaker 1: water drips out of a container, which is the basis
Speaker 1: of many water clocks, or sands through an hourglass, so
Speaker 1: are the days of our lives. But we'll talk more
Speaker 1: about water clocks later. With mechanical clocks, it's the rate
Speaker 1: at which parts move within the clock itself. In order
Speaker 1: to keep time, you have to find a way to
Speaker 1: regulate that so that it is consistent. So that's element
Speaker 1: number one. The second element you need for a clock
Speaker 1: is some sort of way to keep track of the
Speaker 1: increments of time so that you know what time it is.
Speaker 1: You need a way to be able to read the time.
Speaker 1: So early clocks, some of the early mechanical clocks that
Speaker 1: came out of Europe didn't have a dial or a
Speaker 1: face or hands or anything like that. They were really
Speaker 1: automated systems to chime bells, so it was the chime
Speaker 1: of the bell that would indicate what the time was.
Speaker 1: That was the best you could do. But later on
Speaker 1: it would be a mechanical clock with a dial and
Speaker 1: a face with hands on it, and that would be
Speaker 1: the part that tells you what the time is. So
Speaker 1: it's not enough that the clock keeps time. It also
Speaker 1: has to communicate that or display it in some way.
Speaker 1: So those are the two elements you need for it
Speaker 1: to be a clock. Now, since ancient times, people have
Speaker 1: found ways to mark the passing of time, everything from
Speaker 1: various versions of calendars to massive structures that could tell
Speaker 1: you all about when certain things are going to happen,
Speaker 1: like equal n ox Is. I mean, you've heard about
Speaker 1: structures like Stonehenge, But if you're talking about time, as
Speaker 1: in dividing up the increments of a day, you kind
Speaker 1: of have to look at the people's of Summer and
Speaker 1: ancient Egypt and their use of sun dials. The most
Speaker 1: primitive type of sun dial would be a stick stuck
Speaker 1: in the ground, and you can mark the passing of
Speaker 1: time by observing where the stick's shadow falls as the
Speaker 1: sun's position overhead changes throughout the day. Sun dials tend
Speaker 1: to be a bit more robust than a stick stuck
Speaker 1: in the ground. The sun dials of ancient summer were
Speaker 1: pretty much gone by the time historians got around to
Speaker 1: documenting these kinds of things, but there were still some
Speaker 1: that existed in Egypt. Now we know that the ones
Speaker 1: in Egypt were predated by the ones that were in
Speaker 1: sumer but we just don't have any examples of those
Speaker 1: so UH. In Egypt you could find things like obelisks.
Speaker 1: The obelisks dates to at least thirty d b c
Speaker 1: e before Common era. The shadows cast by those structures
Speaker 1: could help people mark the passing of time, and in fact,
Speaker 1: you might end up seeing one that has markings on
Speaker 1: the ground that indicates such. Now, both the Sumerians and
Speaker 1: the Egyptians created divisions for daytime, similar to the way
Speaker 1: we have ours. The Egyptians created ten segments of daytime
Speaker 1: between UH and between two and four for night time,
Speaker 1: but of course you couldn't track nighttime with a sun
Speaker 1: dial because for a sundal to work, you kind of
Speaker 1: need a sun and at nighttime that's in short supply.
Speaker 1: The same was true on any days with whether that
Speaker 1: would obscure the sun. Obviously, tracking time on those days
Speaker 1: would become difficult, but on clear days you could track
Speaker 1: the passing of time fairly well. The Egyptians would create
Speaker 1: markings on the ground that would indicate the time of day,
Speaker 1: so you'd see where the shadow falls. If it falls
Speaker 1: in atcular section, then you know it's time for lunch
Speaker 1: or I don't know. To listen to the New Bengals
Speaker 1: single if the Earth's axis didn't have a tilt to
Speaker 1: it relative to the position of the Sun, this would
Speaker 1: be a consistent way to track the time of day.
Speaker 1: But because of that tilt, during different parts of the year,
Speaker 1: the sun will occupy a slightly different part of the sky.
Speaker 1: This also depends upon where north or south of the
Speaker 1: equator you are. If you're right, if you're very close
Speaker 1: to the equator, the variation is slight, but the further
Speaker 1: way you are from the equator, the greater the variation is.
Speaker 1: And because of that tilt, during different parts of the year,
Speaker 1: the sun will occupy those different areas of the sky,
Speaker 1: meaning the shadow that it casts on the ground from
Speaker 1: any object is going to be different at one time
Speaker 1: of year than at a different time of year. The
Speaker 1: Egyptians had all this sussed out, and they would include
Speaker 1: indicators for the time of year so that timekeeping could
Speaker 1: remain fairly accurate. And it was easy to see which
Speaker 1: days were the longest and the shortest, because on the
Speaker 1: longest day, the obelisk would cast a longer shadow because
Speaker 1: the sun would appear lowest in the sky as it
Speaker 1: crossed overhead. On the shortest day, the shadow would be
Speaker 1: short as the Sun would pass closer to directly overhead.
Speaker 1: So little indicators there that can tell you more about
Speaker 1: the time of year. Now, the fact that the Earth
Speaker 1: is round, sorry flat earther's it also meant that you
Speaker 1: couldn't just design a universal sun dial that's going to
Speaker 1: be accurate wherever you go all year round. As you
Speaker 1: travel north or south, the angle of the Sun's light
Speaker 1: hitting your sun dial changes, and so you have to
Speaker 1: take that into account. A sun dial must be designed
Speaker 1: for the specific location if you want the time markings
Speaker 1: to be accurate throughout the year. The sun dial made
Speaker 1: its way to Greece and from there pretty much everywhere else.
Speaker 1: The Greeks created some pretty cool sun dials, including hemispherical
Speaker 1: sun dials. Now, as this name suggests. These sun dials
Speaker 1: used a hemispherical surface upon which shadows would fall. Typically
Speaker 1: the surface kind of like a bowl that have been
Speaker 1: cut in half or even quartered. So you had this
Speaker 1: this little bowl shaped area, but not a not a
Speaker 1: full bowl with lines on the inside to mark time segments.
Speaker 1: And the object that was to cast a shadow would
Speaker 1: be an appropriate distance from the sides of that bowl,
Speaker 1: and it's orientation would be such that no matter which
Speaker 1: way it's facing, it's facing away where the sun is
Speaker 1: always going to cast a shadow against the bowl. So
Speaker 1: you want to make sure that it's facing the right direction,
Speaker 1: otherwise you get a part of the day where the
Speaker 1: shadow would be outside the bowl and you would say
Speaker 1: it is the end of times and cause a panic. Now.
Speaker 1: I learned more about Sundale construction by visiting a website
Speaker 1: called sun dials dot org. It's a site dedicated to
Speaker 1: the art and science of sun dials, which is pretty
Speaker 1: fascinating stuff, even to a liberal arts major such as myself.
Speaker 1: For one thing, I learned that the two parts of
Speaker 1: your basic sun dial, like the kind you might see
Speaker 1: in a park or a garden, are the dial plate
Speaker 1: and the nomon g n O m o n The
Speaker 1: gnomon is the thing that casts a shadow onto the
Speaker 1: dial plate. And you've probably seen sun dials that have
Speaker 1: a common nomon that has set an angle respective to
Speaker 1: the dial plate, so it comes up almost like a
Speaker 1: triangle sticking up out of this circular dial. I learned
Speaker 1: from sundals dot org that that angle should equal the
Speaker 1: location's latitude. The markings on the dial plate also depend
Speaker 1: upon the latitude of the location. Only by pairing these
Speaker 1: two will you get a reliable way to mark the
Speaker 1: passage of time throughout the year at that location, and
Speaker 1: of course only on sunny days. Sun dials would continue
Speaker 1: to be an important method of timekeeping for thousands of years.
Speaker 1: It was only with the development and refinement of mechanical
Speaker 1: clocks that sun dials even fell out of use in
Speaker 1: naval ships in the seventeen hundreds. But sun dials were
Speaker 1: just one method of keeping time in those early days.
Speaker 1: Another method was to use a water clock. Now, a
Speaker 1: basic water clock is sort of like an hour glass,
Speaker 1: which of course is another form of ancient timekeeping, but
Speaker 1: we'll set that aside. So you have two containers, typically
Speaker 1: in a very simple water clock, connected by a tube
Speaker 1: or a channel of some sort. One container is set
Speaker 1: higher than the other, and it has water in it,
Speaker 1: and gravity pulls that water, so it flows down into
Speaker 1: the lower container through the tube or the channel in
Speaker 1: a more or less controlled way. The lower container has
Speaker 1: markings on the inside of it indicating how much time
Speaker 1: has passed based upon the amount of water in the
Speaker 1: second container. Occasionally you have to dump out the water
Speaker 1: in the lower container and refill the water in the
Speaker 1: upper container. Otherwise the clock just runs out of water.
Speaker 1: You can't tell the time anymore. It's kind of like
Speaker 1: if a a watch that has a spring in it,
Speaker 1: once it unwinds all the way, it won't keep time anymore.
Speaker 1: Same sort of thing here. Now. The method had one
Speaker 1: major advantage over sun dials, because it would work what
Speaker 1: there the sun was out or not. But it wasn't
Speaker 1: necessarily always consistent. Even a well designed water clock couldn't
Speaker 1: regulate the flow of water precisely enough to keep excellent time.
Speaker 1: But it worked well enough for most folks. It wasn't
Speaker 1: like you had a whole bunch of people saying, uh,
Speaker 1: you know, over here in the fiefdom, I've gotta go
Speaker 1: meet my lord for talking about how much corn. I've
Speaker 1: harvested um, and I've got a three fifteen meeting, so
Speaker 1: i really need this water clock to be precise. Now,
Speaker 1: that just didn't happen in those days. Now, water clocks
Speaker 1: date as far back as fifteen hundred b c. E.
Speaker 1: The Greeks would call their water clocks clipsid draws. Now
Speaker 1: that actually means water thieves, as the word comes from
Speaker 1: clip time, meaning to steal. You might have heard the
Speaker 1: term kleptomaniac that's someone who has a compulsion to steal things,
Speaker 1: and high door, which means water. They started using water
Speaker 1: clocks around three b C. And then since than everyone
Speaker 1: uses clepsydras to be the term for water clocks. And
Speaker 1: there are several variations. I described the simple one just
Speaker 1: a second ago, but others might involve one vessel dipping
Speaker 1: water out of a small hole into a second vessel
Speaker 1: which has markings on this inside identicate the passing of time.
Speaker 1: Or you could have a single vessel with markings on
Speaker 1: the inside that are revealed as the water level decreases
Speaker 1: when water drips out of it. So, in other words,
Speaker 1: you create a small hole in a vessel, you fill
Speaker 1: the vessel with water, and it's sort of a reverse
Speaker 1: of what I was talking about. Before the more water
Speaker 1: leaks out of the container, you see more markers telling
Speaker 1: you what hour it is. In North Africa, people would
Speaker 1: mark time by placing a metal bowl with a hole
Speaker 1: in it inside a larger container of water, and they
Speaker 1: marked the passing of time by the sinking of that
Speaker 1: metal bowl. It would sink within a certain amount of time,
Speaker 1: and that method was used in some parts of Africa
Speaker 1: as late as the twentieth cent well. Many water clocks
Speaker 1: were simple, some were devilishly complicated. For example, the water
Speaker 1: clock tower built by Sue Song in the eleventh century CE.
Speaker 1: Historians descriptions of Sue Song put him in that rare
Speaker 1: category of humans that includes other amazing polly maths like
Speaker 1: Leonardo da Vinci. He was a cartographer, he was a mathematician,
Speaker 1: he was a physician, and he was a horologist. Now
Speaker 1: that last one essentially means he was a clockmaker. Sue
Speaker 1: Song and a team of mathematicians came up with the
Speaker 1: idea for the mechanics that would make the clock tower possible.
Speaker 1: The tower was pretty tall, uh. It had inside of
Speaker 1: it several levels, like it was three stories tall. The
Speaker 1: top level had a model of the universe on it.
Speaker 1: The middle one had kind of a a globe to
Speaker 1: show you what constellations would be where at what point
Speaker 1: point of the year, so sort of an astronomical slash
Speaker 1: astrological clock. And then the base level had the actual
Speaker 1: time piece itself. Uh. There was a vertically aligned water
Speaker 1: wheel which was eleven feet in diameter, So think of
Speaker 1: a wheel on its side. It's it's you know, vertically aligned,
Speaker 1: it's got scoops on the outer edge of it. Water
Speaker 1: would flow from a giant container through a narrow slit
Speaker 1: at the container's base, and that water would then fill
Speaker 1: whichever of the thirty six scoops mounted on the outside
Speaker 1: of the wheel was level with that that drainage spot.
Speaker 1: So water flows out of the container and it starts
Speaker 1: to fill up that that scoop. Once the scoop got
Speaker 1: heavy enough, the wheel would rotate, which in turn would
Speaker 1: power all the other gears in the tower and help
Speaker 1: keep time. Now, a series of horizontally aligned gears on
Speaker 1: this tower had small figurines mounted to the outer edges.
Speaker 1: So these gears are are all horizontal, not vertical, so
Speaker 1: they're at a nine degree angle relative to the water wheel.
Speaker 1: The figurines were positioned in such a way to be
Speaker 1: easily seen through windows of the tower, So if you
Speaker 1: looked at the tower from the outside, you'd see these
Speaker 1: little figures in various windows along that side, like three
Speaker 1: levels of them, with one window showing certain figures that
Speaker 1: indicate a certain increment of time. The figures all carried
Speaker 1: signs that represent numbers. That means they were effectively digit counters,
Speaker 1: so you look at the figures and you could suss
Speaker 1: out what time it is. But Sue Song had to
Speaker 1: come up with a way to make this a steady,
Speaker 1: regular series of events. If you left this on its own,
Speaker 1: if you just had a big water wheel and you
Speaker 1: were having water flow into these scoops, the water wheel
Speaker 1: would eventually just start turning continuously as long as there
Speaker 1: was water to push it, which means all the figures
Speaker 1: would constantly be in motion, and that could be tricky
Speaker 1: to read the time, especially between minutes. So you know,
Speaker 1: you could have a figure that's half in view and
Speaker 1: half out of you you're not really sure what time
Speaker 1: it is. So Song need a way to keep a
Speaker 1: gear in position for a certain interval a given amount
Speaker 1: of time, such as a minute, and so he and
Speaker 1: his team had to come up with a way of
Speaker 1: stopping gears, but only temporarily, so that the passage of
Speaker 1: time could be more regularly communicated. So he and his
Speaker 1: team created a clever gadget that would end up being
Speaker 1: an important part of clocks for centuries. It's called an escapement.
Speaker 1: So what is an escapement. We'll go into that in
Speaker 1: just a bit, but first let's take a quick break
Speaker 1: to thank our sponsor. Okay, So, an escapement, what isn't
Speaker 1: well in clocks is an element within a device that
Speaker 1: regulates the turning of other gears. You can think of
Speaker 1: it as a lock that unlocks itself at consistent intervals
Speaker 1: to allow gears to turn before locking back in place.
Speaker 1: And if you've ever seen a pendulum clock, that the
Speaker 1: purpose for that pendulum. But we'll get into that a
Speaker 1: little bit later. Sue Song created an escapement to lock
Speaker 1: the gears in place in his water tower until there
Speaker 1: was a need for them to shift to the next
Speaker 1: increment of time. Sue Song's approach was using a balance
Speaker 1: called a steel yard. It's all one word. Steel yards
Speaker 1: are pretty cool applications of one of the simplest machines
Speaker 1: the lever. If you have a lever with a pivot
Speaker 1: point in the exact center of its length, assuming the
Speaker 1: mass is equal on both sides, the lever will balance
Speaker 1: out if you put two equal weights, two equal masses
Speaker 1: really on either end, and it remains balanced. Well. It
Speaker 1: does so because of this very nature of levers. So
Speaker 1: are you with me so far? Now imagine that we
Speaker 1: move that pivot point more toward the right side of
Speaker 1: the lever. That would mean that more of the lever's
Speaker 1: mass is on the left side. The right side is
Speaker 1: shorter than the left side because we've moved the pivot
Speaker 1: point closer to the right end. So if you just
Speaker 1: step back the left side, the lever will be on
Speaker 1: the ground. It's gonna tilt downward it until it's either
Speaker 1: on the ground, or if you haven't suspended in the air,
Speaker 1: it's gonna be dangling vertically with the short end at
Speaker 1: the top, you know, the bit that's closer to the pivot.
Speaker 1: So to balance it out, you would have to put
Speaker 1: more weight on the right side. You would have to
Speaker 1: have more mass to equal out the mass that's on
Speaker 1: the left and balance it all out. This is how
Speaker 1: a steel yard works, and you may have used one
Speaker 1: of these with weight scales. If you've ever stepped on
Speaker 1: a scale that requires you to move a counterweight along
Speaker 1: an arm, you've used a steel yard. The trick is
Speaker 1: to get the counterweight adjust the right spot on the
Speaker 1: lever to make the arm balance out. If the counterweight
Speaker 1: is too close to the pivot point, the arm will
Speaker 1: be up in the air. It will say no, you
Speaker 1: weigh more than that. You need to push that counterweight
Speaker 1: further towards the end of the arm. If it's too
Speaker 1: close to the end of the arm, it's gonna go
Speaker 1: down as far as it can go. Like in a scale,
Speaker 1: there's typically a little stop point and it'll just sink
Speaker 1: to the bottom. So getting the counterweight in the right
Speaker 1: position makes the arm ba elens in the middle, and
Speaker 1: the position of the counterweight will tell you how much
Speaker 1: you way. There will be some marking. They're saying, congratulations,
Speaker 1: away a hundred fifty pounds. Sue Song's tower used a
Speaker 1: steel lyard kind of like this. Now, I want you
Speaker 1: to imagine a vertical wheel made of spoons. All right,
Speaker 1: All the spoons are facing in the same direction, and
Speaker 1: all the scoop parts of the spoon are faced in
Speaker 1: such a way where they're you know, they're just if
Speaker 1: you were to stack them in a stack, they would
Speaker 1: all be stacked together perfectly, but you've fanned them out
Speaker 1: into this circle. It's a vertical circle. Uh. And imagine
Speaker 1: we're looking at this wheel from the side, so we're
Speaker 1: looking at the profile of the wheel, not dead on position.
Speaker 1: Halfway up the wheel to one side is a chamber
Speaker 1: of water that can flow out into the empty spoon
Speaker 1: that is next to it. The one that's closest to it.
Speaker 1: Will say that this this spoon is parallel to the ground,
Speaker 1: So this is the one that is at the three
Speaker 1: o'clock position for those of you who still know how
Speaker 1: to read analog clocks. On the other side of the wheel,
Speaker 1: over at the nine o'clock position is a weighted arm,
Speaker 1: and it rests on the back of the spoon opposite
Speaker 1: to the one getting filled. And the weighted arm, it
Speaker 1: can't reverse the direction of the wheel. It just holds
Speaker 1: it in place. The weight of that arm just keeps
Speaker 1: it locked there. But the weighted arm is on a pivot,
Speaker 1: so it can be lifted if enough force is applied. Now,
Speaker 1: as soon as the spoon fills with water, it gets heavier.
Speaker 1: When it gets heavy enough to counteract the weighted arm
Speaker 1: on the other side, the weighted arm pivots up. This
Speaker 1: allows the wheel of spoons to turn in one increment.
Speaker 1: It turns so that the next spoon is moved into place.
Speaker 1: The weighted arms slips off the back of the spoon
Speaker 1: it had been on and comes down to prevent the
Speaker 1: next one from moving upward, locks it into place. That
Speaker 1: whole process repeats, and that's basically how siouxs Song's escapement worked.
Speaker 1: As long as there was water steadily flowing into the tower,
Speaker 1: the clock would keep accurate time. Now I wish I
Speaker 1: could tell you that you could go and visit this
Speaker 1: amazing clock tower in Kaifeng, but sadly you can't. The
Speaker 1: tower was finished in ten ninety four. Sue Song himself
Speaker 1: died in eleven oh one, which means he didn't live
Speaker 1: to see his amazing creation disassembled by soldiers. After the
Speaker 1: Manchurian Army invaded Kaifeng, they took the clocks pieces back
Speaker 1: to their capital, which is today's modern Beijing. They attempted
Speaker 1: to reassemble it, but the complex nature of the clock
Speaker 1: confounded them and it never worked again. There is, however,
Speaker 1: a working replica of the tower in the Gishido Suwako
Speaker 1: Watch and Clock Museum in the Nagano Prefecture in Japan.
Speaker 1: I've seen photos of it and it is gorgeous. I
Speaker 1: hope one day to see it in person. This particular
Speaker 1: replica was built based upon the best understanding of sus
Speaker 1: Song's designs. Many of those designs survived all of that
Speaker 1: invade Jian issue, but there were little details left out,
Speaker 1: so people the modern replica makers had to kind of
Speaker 1: fudge things here and there to make it work properly.
Speaker 1: So it may not be one to one a replica,
Speaker 1: but it's really close and it looks amazing in the
Speaker 1: pictures I've seen. This escapement would prove to be a
Speaker 1: very important component of clocks and watches as the art
Speaker 1: and science of clockmaking evolved. As for purely mechanical clocks
Speaker 1: that did not depend upon water, their origin is somewhat
Speaker 1: lost to time, which is not an irony but seems fitting.
Speaker 1: Monasteries were building clock towers called turret clocks as early
Speaker 1: as the fourteenth century, at least maybe earlier. These were
Speaker 1: massive towers that passed marked the passing of time by
Speaker 1: tolling a bell, so there were no dials or hands
Speaker 1: or other indications of what time it is. The machinery
Speaker 1: was large and relied upon weights and gears. Now, the
Speaker 1: weight is a very important part of these early make
Speaker 1: chanical clocks. And here's how a weighted clock works. Now,
Speaker 1: imagine you have an axle wound around That axle is
Speaker 1: a cable or rope. If you were to pull on
Speaker 1: that cable or rope, it would provide enough rotational force
Speaker 1: to make the axle rotate. At the end of this
Speaker 1: rope is a heavy weight, and if you lock the
Speaker 1: axle into place, the weight represents potential energy. Right it's
Speaker 1: hanging it suspended above the ground, but the wheel is
Speaker 1: locked so it cannot turn. That's potential energy. The weight
Speaker 1: has the potential to move the clock or move this
Speaker 1: wheel this axle. Gravity is pulling the weight down towards
Speaker 1: the center of the earth, and once you unlock the wheel,
Speaker 1: it allows that potential energy to convert into kinetic energy.
Speaker 1: The weight will start to drop toward the ground and
Speaker 1: it applies for uce to the rope, which thus applies
Speaker 1: force to the axle, causing it to rotate. And then
Speaker 1: it can end up making other elements of the clock
Speaker 1: move as well. You have gears and pinions and stuff,
Speaker 1: and they're all interlocked, and that allows for or the
Speaker 1: operation of a clock, which ultimately makes a bell go
Speaker 1: ding dong ding. But here's a problem. Gravity causes acceleration.
Speaker 1: Things do not fall at a steady velocity. The velocity
Speaker 1: is always increasing as long as the fall is continuing,
Speaker 1: at least until you hit terminal velocity. So everything accelerates
Speaker 1: according to the gravitational pull of the Earth. At least
Speaker 1: stuff dropped here on Earth does that. If you were
Speaker 1: to drop something on Mars, it would accelerate according to
Speaker 1: Mars's gravity, not Earth's gravity, even if it originally came
Speaker 1: from Earth, because Mars just don't care. But here on
Speaker 1: Earth we know gravitational acceleration is equal to nine point
Speaker 1: eight meters per second per second. So if you drop
Speaker 1: a weight high enough for it to fall for several seconds,
Speaker 1: each second that passes will see the velocity of the
Speaker 1: falling object increase by nine point eight meters. So after
Speaker 1: one second, the weight is falling at nine point eight
Speaker 1: ms per second downwards. During second number two, the weight
Speaker 1: is falling at nineteen point six meters per second downwards,
Speaker 1: and so on. It increases each second the weights falling
Speaker 1: speed increases until the weight achieves terminal velocity. I mentioned
Speaker 1: that earlier. This is the speed and object reaches when
Speaker 1: the resistance of the medium it is falling through. In
Speaker 1: our examples, we're just talking about Earth, so we're talking
Speaker 1: about Earth's atmosphere. When the resistance of Earth's atmosphere is
Speaker 1: enough to prevent it from accelerating further, then the object
Speaker 1: has reached terminal velocity. So eventually, falling speed does top out,
Speaker 1: and it remains consistent at that point until you know,
Speaker 1: you collide with the ground, in which case the falling
Speaker 1: speed stops and the splatting speed begins. Okay, but what
Speaker 1: does that have to do with clocks. Well, remember at
Speaker 1: the top of the show I said that a clock
Speaker 1: needs some sort of consistent, regular action or process that
Speaker 1: gives you the ability to mark off equal increments of time.
Speaker 1: If you have an accelerating falling weight, it's tricky to
Speaker 1: use it as a means for the rest of your structure,
Speaker 1: right because it would have to account for that acceleration.
Speaker 1: You would have to have some really complex machinery that
Speaker 1: would operate in such a way to counteract that acceleration.
Speaker 1: You'd much rather have a regular force that remains consistent
Speaker 1: in speed and power, something that's not going to increase
Speaker 1: an amplitude over time. And that's where the design of
Speaker 1: an escapement is so important. The escapement design allows clockmakers
Speaker 1: to regulate this action and make sure it happens at
Speaker 1: these regular intervals. Now, the oldest surviving mechanical clock in
Speaker 1: England is Salisbury Cathedral's clock. The clock dates to probably
Speaker 1: around thirteen eighty six. According to historians, this is not
Speaker 1: necessarily the oldest surviving mechanical clock in the world. There's
Speaker 1: actually some controversy about that, but this is certainly the
Speaker 1: oldest surviving one in England. And I saw that clock
Speaker 1: in person back in nine. I even had a photo
Speaker 1: taken of me appearing to set my watch according to
Speaker 1: the clock, which at the time I consider it to
Speaker 1: be high comedy. And let's be honest, I'd probably do
Speaker 1: the exact same thing today if I were to visit.
Speaker 1: The Salisbury Cathedral clock originally had was called a verge
Speaker 1: and folio escapement. Now, this is a tricky thing to
Speaker 1: describe in an audio podcast, but I'm gonna try and
Speaker 1: do my best. Imagine that you have a vertically aligned wheel,
Speaker 1: kind of similar to the water wheel I was talking about,
Speaker 1: but instead of the wheel's edge ending in scoops, the
Speaker 1: wheel has pegs sticking out along the rim on one
Speaker 1: side of it alright, So one side of the wheel
Speaker 1: is is just flat, it's featureless. The other side of
Speaker 1: the wheel has pegs sticking out right along the edge
Speaker 1: at regular intervals. This is called the escape wheel. The
Speaker 1: wheel is on an axle, and that axle at some
Speaker 1: point has a weight attached to it. So left on
Speaker 1: its own, the wheel would rotate as the weight falls,
Speaker 1: with the rotation accelerating as the weight accelerated during its fall.
Speaker 1: So we would have to have something to regulate the
Speaker 1: wheel's rotation. The force applied to the axle should remain steady,
Speaker 1: so we can't mess with the weight. We can't change that.
Speaker 1: We need to have some other way to alter this,
Speaker 1: and that would be the verge and folio. Position. Next
Speaker 1: to this vertical wheel, the one that has the pegs
Speaker 1: the escape wheel, you have a vertical rod. This rod
Speaker 1: is called the verge. The verge can rotate on its
Speaker 1: axis in either direction of rotation along its respective orientation.
Speaker 1: The rod has two stoppers or protrusions that are called palettes.
Speaker 1: They're like flaps like you know, they could just be
Speaker 1: a little square flaps that stick out from the rod
Speaker 1: to the side. One of those positioned near the top
Speaker 1: of the vertical wheel, and one of them is positioned
Speaker 1: towards the bottom of the vertical wheel, and their their
Speaker 1: alignem is slightly offset in respect to the axis of
Speaker 1: the verge. That means that they can catch the pegs
Speaker 1: of the rotating vertical wheel at different points. So you
Speaker 1: have these pegs that can come into contact with these palettes,
Speaker 1: and when they do, obviously there's there's an impact there.
Speaker 1: There's a collision, and it causes the verge to rotate
Speaker 1: and it puts the other palette, the one on the
Speaker 1: opposite side of the verge, into the right position to
Speaker 1: catch the pegs on the opposite end of the wheel.
Speaker 1: So one palette is always going to be pushed in
Speaker 1: one direction of rotation for the verge, the other palette
Speaker 1: is always going to be pushed in the other direction
Speaker 1: of rotation for the verge. Because you have this ninety
Speaker 1: degree difference of orientation with respect to the the escape wheel.
Speaker 1: So the the the attached to the very top of
Speaker 1: the verge is a horizontally balanced lever. It's actually kind
Speaker 1: of kind of like another horizontal rod that's on the
Speaker 1: very top of the verge. There's weights attached to either end.
Speaker 1: This is called the folio, and it swings back and forth,
Speaker 1: it oscillates. So how does it work? Well, As I said,
Speaker 1: one palette is position so it catches pegs at the
Speaker 1: top of the vertically aligned wheel, the escape wheel. The
Speaker 1: other palettes at the bottom. They're offset, so one pallet
Speaker 1: makes contact with the pegs, the other one is free
Speaker 1: and clear. It doesn't interfere because otherwise, if you had
Speaker 1: both palettes positioned so that they locked in with the pegs,
Speaker 1: no movement could happen. You would effectively have a break
Speaker 1: on that escape wheel and it would just not rotate. So,
Speaker 1: as the vertical wheel turns, a peg at the top
Speaker 1: of the wheel catches the top pallett and provides enough
Speaker 1: force to push it and rotate the verge on its axis.
Speaker 1: The folio at the top would rotate accordingly. Now, that
Speaker 1: puts the palette at the lower end of the the
Speaker 1: lever in position to catch a peg at the bottom
Speaker 1: of the vertical wheel the escape wheel. Because of the
Speaker 1: alignment of the virgin wheel, this creates a force opposing
Speaker 1: the direction of the folio's previous rotation, making it rotate
Speaker 1: the other way or oscillate. Uh. This is similar to
Speaker 1: the oscillations of a pendulum, and we'll cover that when
Speaker 1: we get to pendulum clocks. The pegs will catch the
Speaker 1: pallets and create this TikTok sound you here with a clock. Uh.
Speaker 1: It's the pegs making contact with those pallets and making
Speaker 1: the folio swing one way or swing the other way.
Speaker 1: The weights on the folio give it enough inertia to
Speaker 1: keep it from rotating too far and provide just enough
Speaker 1: force to regulate the turning of the vertical wheel. The
Speaker 1: escape wheel is just one part of the clock. The
Speaker 1: elements that actually track the time, as in the ones
Speaker 1: that govern the movements of the hands on a dial
Speaker 1: face or govern when a bell gets struck. That's called
Speaker 1: the train or wheel work of a clock. These are
Speaker 1: all the gears that transmit motion to the parts of
Speaker 1: the clock that illustrate the time or market in some way.
Speaker 1: In the earlier clocks, this was pretty primitive, as originally again,
Speaker 1: there were no dials or hands to turn. There just
Speaker 1: need to be a way to designate an hour had passed. Later,
Speaker 1: clocks would add an hour hand, but no minute hand,
Speaker 1: so you would be able to see what hour it was.
Speaker 1: But that was it. As clocks became more complicated than
Speaker 1: necessity for precision increased, wheels and pinions have to be
Speaker 1: crafted precisely to transmit motion as steadily as possible in
Speaker 1: order for this to work. Now you might wonder what
Speaker 1: happens when the weight that's providing the force to turn
Speaker 1: all this machinery reaches the ground. What happens is the
Speaker 1: whole thing stops. You have to wind the mechanism so
Speaker 1: that the weight is lifted back to the top, creating
Speaker 1: that potential energy necessary for the clocks operation. This it
Speaker 1: is true of other mechanical clocks as well, whether the
Speaker 1: force comes from a suspended weight or a spring. With
Speaker 1: a spring, you have to wind it to increase its
Speaker 1: potential energy before you let go and it starts to
Speaker 1: convert it into kinetic energy. In fact, spring powered clocks
Speaker 1: would emerge before pendulum clocks did. Peter Henline of Nuremberg
Speaker 1: gets the credit for inventing spring clocks. Early in the
Speaker 1: sixteenth century, sometime between fifteen hundred and fifteen ten, hen
Speaker 1: Line would use a coiler metal while entightly to provide
Speaker 1: the potential energy necessary to drive clockwork. The spring would
Speaker 1: have a natural tendency to unwind and assume its normal shape,
Speaker 1: so winding it would build up that potential energy, and
Speaker 1: using an escapement kept the unwinding to a somewhat regular
Speaker 1: series emotions. And as the coil unwinds, the amount of
Speaker 1: force it exerts decreases, which actually meant that a clock
Speaker 1: would start to run more slowly and begin to lose time.
Speaker 1: To get it going again, you have to wind it
Speaker 1: up again. Now, these early clocks weren't exactly the most accurate.
Speaker 1: According to the Anderson Institute, the big ones could be
Speaker 1: off by as much as an hour per day, and
Speaker 1: they only marked the passing of an hour at a time,
Speaker 1: with no indication for smaller increments. Still, it was a
Speaker 1: way to keep track of time that didn't require members
Speaker 1: of the church to track it themselves and then hike
Speaker 1: up to the top of a bell tower and give
Speaker 1: it the old toll. And if you're wondering how they
Speaker 1: told time at night before they had mechanical clocks. It
Speaker 1: usually involved burning something that had a pretty steady combustion rate.
Speaker 1: This included candles that would burn at a pretty steady
Speaker 1: and predictable rate. You'd have to figure out how big
Speaker 1: your candle needed to be and make the wax as
Speaker 1: consistent as you could, and try and keep track that way.
Speaker 1: You would just mark it on the candle, and when
Speaker 1: the candle burned down to a certain amount, you knew
Speaker 1: an hour had passed. It wasn't down to the minute,
Speaker 1: but it served well enough for the chiming of bells. Now,
Speaker 1: in our next part, we're gonna talk about pendulum clocks.
Speaker 1: But before I get into that, one thing I want
Speaker 1: to mention is if the version folio description has completely baffled,
Speaker 1: you do a search for the terms on YouTube, because
Speaker 1: there are lots of illustrations on there that will show
Speaker 1: you exactly what I'm talking about folio. By the way,
Speaker 1: it's spelled fo L I O T, and you can
Speaker 1: see exactly the mechanisms I'm mentioning and see how they
Speaker 1: were able to regulate the turning of gears. And before
Speaker 1: I get into pendulum clocks, I need to take another
Speaker 1: quick break and thank my sponsor the virgin folio. Escapement
Speaker 1: was the dominant method of regulating the motion of mechanical
Speaker 1: clocks for a couple of centuries. But then an Italian
Speaker 1: smarty pants by the name of Galileo Galilei made an
Speaker 1: interesting observation. He discovered that a pendulum takes the same
Speaker 1: amount of time to complete one full swing out and back,
Speaker 1: over and over and over again. The time for one
Speaker 1: complete cycle is what we call a period. So the
Speaker 1: period of a swing remains the same even as the
Speaker 1: pendulum's swing decreases in amplitude. So what do I mean
Speaker 1: by that? Well, if we were working with a pendulum
Speaker 1: mounted on a massless rod or a line uh and
Speaker 1: had a frictionless pivot, then the pendulum is always going
Speaker 1: to return to the same height as its initial release.
Speaker 1: But that's not how the real world works. So let's
Speaker 1: say you tie a rope to the limb of a tree,
Speaker 1: and on the other end of the rope you tie
Speaker 1: a bowling ball, and you get on a step ladder,
Speaker 1: and you're are far enough back so that the line
Speaker 1: is taught between the limb and the bowling ball, and
Speaker 1: you're standing at a certain level. You're holding the bowling
Speaker 1: ball right up to your chin. With the that line there,
Speaker 1: you let go of the bowling ball. And by the
Speaker 1: way I say let go, you don't push the bowling ball,
Speaker 1: but you just let go. Now if you do that,
Speaker 1: is it going to swing back and knock your teeth out? No,
Speaker 1: it won't, And the reason for that is because elements
Speaker 1: like friction and drag are sapping some of the energy
Speaker 1: from the overall system. The returning bowling ball doesn't have
Speaker 1: the same amount of energy that the departing bowling ball had,
Speaker 1: so it doesn't rise up as high as when you
Speaker 1: dropped it, which means you get to keep your choppers. Congratulations,
Speaker 1: go brush your teeth. But even though the bowling ball
Speaker 1: isn't rising up to the starting height of its release,
Speaker 1: the journey of its swing, its period will remain the same.
Speaker 1: That time remains the same, at least for small amplitudes.
Speaker 1: This story is different if you're swinging that sucker really hard,
Speaker 1: But for simple pendulums at small amplitudes, this is true.
Speaker 1: The ball isn't traveling as far on each swing because
Speaker 1: it's losing that energy to friction and drag, but it's
Speaker 1: also not swinging quite as quickly per swing, so it's
Speaker 1: not going as far, but it's also moving a little
Speaker 1: more slowly, and the overall amount of time it takes
Speaker 1: to complete one period remains constant. Now that means if
Speaker 1: you make a pendulum of a precise length, you can
Speaker 1: create a swing of one second. The period of a
Speaker 1: pendulum swing can be expressed as an equation, and the
Speaker 1: period is equal to two times pie times the square
Speaker 1: root of the length of the pendulum divided by gravity's acceleration. Now,
Speaker 1: ignoring for a moment that gravity's acceleration is not uniform
Speaker 1: everywhere on Earth due to several factors that really are
Speaker 1: too complicated for us to get into here, we can
Speaker 1: simplify this to say that a pendulum of nine nine
Speaker 1: millimeters or about thirty nine inches is the right length
Speaker 1: to have a swing period of a second. Now, Galileo
Speaker 1: recognized the potential for pendulums in timekeeping, but he never
Speaker 1: built a clock using one. That honor goes to a
Speaker 1: Dutch scientist named Christian Hygens, who in the mid seventeenth
Speaker 1: century figured it out. He used the oscillation of a
Speaker 1: pendulum to regulate the motions of clockwork in many ways.
Speaker 1: It was similar to the virgin folio design, except instead
Speaker 1: of relying upon a weighted lever and inertia, Hygen's design
Speaker 1: relied on the natural oscillation of a pendulum of an
Speaker 1: appropriate length. So how does a pendulum escapement work. The
Speaker 1: escapement still engages a gear, preventing it from rotating freely,
Speaker 1: and as the pendulum swings, it rocks the escapement so
Speaker 1: that it disengages with the gear, and the gear begins
Speaker 1: to rotate. At the end of the pendulums period, when
Speaker 1: it returns to its starting point, the escapement is locked
Speaker 1: back into position and the whole process start again. But
Speaker 1: I'm sure you're all wondering how the pendulum keeps moving.
Speaker 1: I mean, if it's losing energy with each swing, how
Speaker 1: does it continue more for more than just a few
Speaker 1: seconds without adding more energy to the pendulum. It's eventually
Speaker 1: just going to slow down and stop swinging completely. I
Speaker 1: mean I talked about this with friction and drag. Well,
Speaker 1: Hygen's got around this by designing a gear that would
Speaker 1: give the pendulum a little nudge each time the escapement disengaged,
Speaker 1: so it provides just enough force to counteract dragon fiction friction.
Speaker 1: So it worked. Hygen's initial design was accurate enough to
Speaker 1: keep time within about a minute per day, meaning you'd
Speaker 1: only lose sixty seconds during a day long operation of
Speaker 1: one of his clocks, which was incredible for the time,
Speaker 1: and he improved upon his design within his own lifetime.
Speaker 1: He cut it down to losing only ten seconds per day,
Speaker 1: which is not bad for an entirely new method of
Speaker 1: regulating gear rotation. Pendulums do come with a couple of complications, however,
Speaker 1: so it doesn't matter what the mass of the pendulum is.
Speaker 1: By the way, you don't whatever the bob is at
Speaker 1: the end of your pendulum. That mass can be anything.
Speaker 1: It's that it's immaterial. It's the length of the pendulum
Speaker 1: that's that's important, not the bob, the mass of the bob,
Speaker 1: except that you don't want something so massive that's going
Speaker 1: to cause damage to the clock itself. But that pendulum's
Speaker 1: length is incredibly important. And this is where we get
Speaker 1: into some trouble because of temperatures. Most pendulums are made
Speaker 1: of metal, and metal has a tendency to expand in
Speaker 1: the presence of heat or contract when it gets colder.
Speaker 1: And since the pendulum's period is dependent in part upon
Speaker 1: its length, this poses a problem. A precisely designed pendulum
Speaker 1: might swing it exactly one second per period, but or
Speaker 1: have a period of one second is the more appropriate
Speaker 1: way of saying that. But if the length of that
Speaker 1: pendulum were to change, it would no longer be true.
Speaker 1: The period would be slightly off from a second, and
Speaker 1: that would be enough to cause errors in timekeeping. Clockmakers
Speaker 1: recognize that issue and they try to fix it in
Speaker 1: different ways. The most common way was do you use
Speaker 1: alloys of metals for pendulums. So an alloy is a
Speaker 1: combination of two or more metals, and one of the
Speaker 1: interesting features of alloys is that you can mix together
Speaker 1: metals that have different coefficients of expansion. So if you
Speaker 1: do this carefully enough, you can cancel out the effects
Speaker 1: of temperature to a great deal. So, for example, you
Speaker 1: can use zinc and iron or brass and steel and
Speaker 1: pair them together in this way, and that ends up
Speaker 1: reducing that effects so that the clock can be more
Speaker 1: accurate no matter what the temperature happens to be. For
Speaker 1: a pendulum clock to be really accurate, you have to
Speaker 1: reduce the impact the impulse of the impulse of the
Speaker 1: turning crown wheel. The crown wheel is the element that
Speaker 1: the escapement locks into, so you have to reduce the
Speaker 1: impact of its motion on the pinchul lium itself and
Speaker 1: needs to give just the right impulse to keep the
Speaker 1: pendulum from swinging and no or or less than that.
Speaker 1: Ideally it would be uniform every single time, meaning you
Speaker 1: have very precise distances between pegs on the crown so
Speaker 1: that it's impact on the escapement would remain consistent no
Speaker 1: matter where it is in the crown wheels rotation. There
Speaker 1: was a guy named Edward Beckett who later on would
Speaker 1: be lorded and would be known as Lord Grimthorpe, which
Speaker 1: is possibly the coolest title I've ever seen. He invented
Speaker 1: what was called the double three legged gravity escapement, which
Speaker 1: honestly sounds like a routine you'd see at Sercla, but
Speaker 1: in fact it was a particular arrangement that allowed for
Speaker 1: extremely consistent operation. He used it to build an enormous
Speaker 1: clock over at Westminster. The clock is world famous, and
Speaker 1: actually people generally call it by the name of the
Speaker 1: huge bell that is also in that clock tower, and
Speaker 1: people just called the whole thing by the bell's name.
Speaker 1: That bell's name, by the way, is Big Ben I
Speaker 1: would describe to you how his escapement works, but I'm
Speaker 1: pretty sure my brain would melt as I tried to
Speaker 1: do this without the use of visual aids. Fortunately, there
Speaker 1: are videos about the double three legged gravity escapement on
Speaker 1: YouTube that show exactly how this works, and it is fascinating.
Speaker 1: I I it really drives home the fact that engineers
Speaker 1: are remarkable people who are way smarter than I am,
Speaker 1: and I highly recommend you go and check these videos
Speaker 1: out to get an appreciation for the actual clockwork that
Speaker 1: makes the regulation possible. And that pretty much wraps up
Speaker 1: this episode of tech stuff. But there's a lot more
Speaker 1: to talk about with watches and clocks. I'm sure in
Speaker 1: a future episode I'll tackle things like quartz watches, which
Speaker 1: rely upon the peculiar piezo electric qualities of quartz, and
Speaker 1: I'll talk about other types of time keeping, things like
Speaker 1: atomic clocks and how those work. But for now, I'm
Speaker 1: going to say it's time to conclude this episode and
Speaker 1: remind you the next time you look at a clock,
Speaker 1: think about all the amazing work it took to make
Speaker 1: it all work out properly. From physics to mathematics to
Speaker 1: engineering to craftsmanship. A clock represents lifetimes of genius, so
Speaker 1: take some time to appreciate it. If you guys have
Speaker 1: suggestions for something I should cover in a future episode
Speaker 1: of tech Stuff, or maybe there's a guest you would
Speaker 1: like me to try and book on the show for
Speaker 1: an interview, or a guest host to talk about specific topic,
Speaker 1: let me know. Send me a message. The email for
Speaker 1: the show is text Stuff at how stuff works dot com,
Speaker 1: or you can always drop me a line on Twitter
Speaker 1: or Facebook. The handle for both of those is tech
Speaker 1: Stuff hs W. Remember we've got an Instagram account. You
Speaker 1: can see all sorts of cool and interesting tech related
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Speaker 1: that out. And of course I record this show on
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Speaker 1: I am doing it on my own, it's to is
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Speaker 1: I need to address, like maybe I gave an explanation
Speaker 1: that was a little too vague and I should go
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