In Our Time - Archive: The Measurement of Time

Episode Date: October 12, 2026

Misha Glenny chooses the first of his archive picks - bringing back classic conversations from the In Our Time archive, every Monday. Humans have tried to calculate, regulate, and measure time for thousands of years: from systems based on tracking sunrise and sunset, to the invention of increasingly precise mechanical alarm clocks and astrolabes. In this archive episode, first released in March 2012, Melvyn Bragg and guests discuss the methods used to measure time throughout human history. Early civilisations used the movements of heavenly bodies to tell the time, but in the ancient world there were also sophisticated timekeeping devices such as water clocks. The development of mechanical clocks in Europe emerged in the medieval period, when monks used such devices to sound an alarm to signal it was the hour to pray, although these clocks did not tell them the time. For hundreds of years clocks were inaccurate and it proved hard to remedy the problems, let alone settle on a standard time that a whole country should follow. It was the advent of the railways that meant time finally became standardised in Britain during the mid-19th century, and in 1884 Greenwich became the prime meridian of the world. Atomic clocks now mark the passing of the days, hours, and minutes and they are capable of keeping time to a second in 15 million years. With Kristen Lippincott Former Director of the Royal Observatory, Greenwich Jim Bennett Director of the Museum of the History of Science at the University of Oxford Jonathan Betts Senior Curator of Horology at the Royal Observatory, Greenwich Producer: Natalia Fernandez In Our Time is a BBC Studios production A world-class seminar every week. Spanning history, religion, culture, science and philosophy, In Our Time celebrates the pursuit of knowledge and the enduring power of ideas. In each episode, host Misha Glenny and expert guests explore the characters, events and discoveries that have shaped our world. On Thursdays, hear brand-new episodes hosted by Misha Glenny and leading academics. On Mondays, discover Misha's Archive Picks: classic conversations from the In Our Time archive, originally presented by Melvyn Bragg.

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Hello, I'm Tom Gatti, literary editor and host of the Observer Book Club podcast. Join me for in-depth conversations with some of the world's best writers, such as Elif Sheffat, Douglas Stewart and Robert McFarlane. At The Observer, we have a passion for storytelling, whether rooted in fact or fiction. The Observer Book Club is a place where great stories and big ideas come together. You can find it wherever you get your podcasts. Hello, Misha Gleney here.

Welcome to the first of my archive picks. Every Monday I'll be exploring the riches from the In Our Time Archive and bringing back an episode hosted by Melvin Bragg that I think deserves another listen. And you'll still find brand new episodes of In Our Time every Thursday. For the first in this series of archive editions, we're starting with an episode on the measurement of time. Measuring time starts with the sun, the moon and the stars,

in that order, unless you're indigenous. to the Arctic, in which case the last two often muscle out the first. But did you know why we then started measuring hours in multiples of 60? Or that water dripping into a bowl determined how long you were allowed to speak in court? We've only been measuring time with any accuracy for about 500 years. But as Melvin and his guests in this week's archive episode of In Our Time Observe, we've been obsessed by the need to calibrate and catch this intangible concept for much, much longer.

I hope you enjoy listening. Hello, we'll be talking about time. You can't stop it, you can't touch it, but it threatens to take over our lives, and it's hard to imagine a time when the days and nights weren't divided up into the hours and minutes that we know today. It was only in the late 19th century

that time was standardized globally, and that Greenwich was chosen as the location of the prime meridian. The history of the measurement of time is a long one, from earlier man tracing his days, from sunrise to sunset to the advent of atomic clocks in the 1950s. We've constantly striven to calculate and control the time. But how did mechanisms for measuring time develop into such precise machines, and how did the changes in society drive the need for such precise timekeeping?

With me to discuss the history of the measurement of time are Kristen Lippincott, former director of the Royal Observatory Greenwich, Jim Bennett, director of the Museum of the History of Science at the University of Oxford, And Jonathan Betts, Senior Curator of Horology at the Royal Observatory, Renich. Kristen Lippincott, how did earliest civilizations measure using the natural phenomenon, measure time? Well, I think the thing one has to do, because it's so hard to think about time without thinking about watches. But imagine that you're primitive man and what you're noticing going around you. And essentially, the first thing you're going to notice is the sun, because that separates the light into the dark.

then you start to notice the phases of the moon and then finally you start to notice the regular cycle of the stars so you can see in all of these ancient people's minds they had three different components that were naturally dividing up their day and how did they set about calculant do we a record of the earliest calculations

we don't have any calculations well until quite late which say 2,500 BC but we know that people were watching things like the phases of the moon because we have ancient bones like shoulder bones or narwhal bones where they have actually carved the different phases of the moon in a regular way. So it's something that they were tracking, but measuring comes quite late. Were they tracking the stars as well? Earlier than 2,500 BC, which is long enough ago.

Very, very early, they were primarily interested in what we'd call horizon phenomenon, i.e. what's rising on the horizon or setting on the horizon with the sun? Because the sun was always the primary deity in all of the religions that basically were below the Arctic Circle. Of course, above the Arctic Circle, like with the Inuit, you get a moon goddess instead because they didn't see the sun for half the year. Did they have any technology to help them to look, or were they just using what we call the naked eye? Very early on they were probably using, well first of all they were using land masses. So they would have, and this is why you'd have a sacred mountain or a sacred stream that would be maybe pointing to the west or maybe pointing to the east.

And they would use the land masses to define how they would measure the passage of the sun or the passage of the stars. So when the sun is above that mountain there? We know that it's the spring equinox or something like that or the winter solstice. And then, of course, much later, you get them setting up big stones. They make their own artificial mountains. And how far did that take them? I mean, with that, as it were, with those observations, what were they able to do with it? Well, this is very problematic because historians tend to be sort of positive in hindsight.

And there are so many people who say something, you know, Stonehenge shows you every single celestial phenomenon. including fleas, jumping off dogs. We really don't know how they use these other in a very broad way for things like winter solstice, summer solstice, and the two equinoxes. So the darkest time of the year, the lightest time of the year, and then points where the year changed. We know that. We know that.

But nothing much more than that. Well, it depends on whom you speak. I read that the Babylonians began to use mathematics with relation to the sun, the moon and the stars. Could you give us some notion of what? what they arrived at. Well, the Babylonians were the great mathematicians of antiquity. The Egyptians had worked up to a similar way of dividing time,

but from a completely different way. But the Babylonians were fascinated by numbers, and they had what's known as a sexagesimal system, 60-based. And the reason that they love the number 60 was it could be divided by the widest number of other numbers without having any remainders, because the maths hadn't gone to the same. to the stage where they knew how to deal with fractions.

So you get 60 and it can be divided by 24, 20, 15, 6, 5, 3. And so they could do all these mathematical calculations. And they were the ones who decided that there would be 360 degrees in a circle. And then from that there would be 360 degrees, you know, or 60 degrees in an hour. So just a second. They just decided that. They arrived at 60 because it was mathematically convenient. It was mathematically perfect for them.

It imposed 60 on the whole system they then erected, which we still use today? Exactly. So was it very, sorry, I'm intrigued by this. Did they arrive at 60 because it was simply, as I've said, mathematically convenient, or was there something in it more than that, that from their lunar observations, no, no? No, nothing.

I mean, if you think about a circle, why would you divide it into 360? What you want to do is divide it into something that works really well for you, and that's how they decided to do it. Jim Bennett, the earliest measuring things, among the earliest, we're going to be tentative here, were water clocks. They were favoured, particularly by the ancient Egyptians. They were quite early, weren't there?

They were the earliest. If they were, how do they work? Well, it's interesting. Kristen has begun by drawing our attention to the heavens. I want to take a different tack and ask you to think about dripping tap, I'm afraid, something much more mundane. If you have a tap dripping slowly into a bowl, say, in the sink, that marks the passage of time.

You can see the surface of the water rising. You might put a stick vertically into it. you might graduate the stick, you'll be able to start not marking something like the hours. So that's essentially a water clock in its simplest form. You can do it differently. You might fill the bowl up and have a hole in it, and it would drip out, so that the level would descend past your stick. You'd put the stick in upside down.

You might even have a bowl which has a hole in it, and you put it in a bigger bowl, and it gradually sinks, so that the levels are visible within your stick. your bull. So there are lots of variance in this. Those kinds of devices become quite popular and become quite common. When's it possible?

Well, the trouble is that they're ubiquitous across all sorts of cultures. So about 1,400 BC? That's all. Oh, certainly, yes. I mean, the Babylonians used them. The Egyptians, as you said, use them. The Greeks and Romans used them. They're very, become quite sophisticated in ancient perjure. So I just want to get it absolutely clear. What are they telling you? So you've got a stone jar with a hole in it, you fill it with water, the water drips out. How do you measure

that it's coming out in relation to what you want to know about time? What specifically do you do? That's perfectly the right question, because these things are okay for measuring duration. If, for instance, someone in a court proceeding has a certain amount of time to present his case, then it'll be limited by a device like that. So in a court proceeding, I'm sorry to miss up a doubt, but in a court proceeding, you have a water o'clock and you say you have 2,200 drips to make your speech. Yes. Right.

Yes. Or marks of this graduated rule that I'm postulating is inside the vessel. And for instance, in Caesar says that such devices, portable devices, were used to time the watches in military camps. But that's all very well for duration. But the point of your question, I think, is how does that relate into the bigger questions about timekeeping? which Kristen was talking about. I'd say you have to somehow key all this in to sunrise and sunset. It has in the end to mark out the divisions of the day.

And that's tricky. You might start your water clock at sunrise, set it off then, but early civilizations tended to take sunrise as the beginning of the day and sunset as the end of the day. So Deser of different lengths. in the summer you had longer days and therefore longer hours because they're almost 12 hours in the day and you had short nights in the

summer and short hours in summer night times and the reverse in the winter so the length of an hour was changing all the way through the year and what this meant was that you needed a lot of different sticks which were differently calibrated which you would use at different times of the year so that becomes increasingly sophisticated. I don't want to only to talk about sticks

and bowls and so on in relation to Klepsidro or water clocks, because they become very sophisticated in medieval Islam, for instance, and in China, around the same sort of period, around a thousand, let's say, roughly

AD, you get machines that have mechanical components. There's a kind of bolt-on sets of mechanisms which are controlled, their operation is regulated by a controlling. And they're taking on the Babylonian 60 notion and trying to get to the hour as equally as they can.

Well, minutes don't really come in to this kind of technology. So what are they measuring? They're measuring hours. They're measuring ours and portions of an R. It's true. With the Book of Rove. It becomes very sophisticated. Yes, indeed.

What about sundials, Jim? Well, we've already mentioned sunrise and sunset, so you've already got that idea of the day being demarcated by the observance of the action of the sun or the motion of the sun. Then within that, it's very easy to begin to notice that shadows change as the day progresses. They shorten as you get towards a noon and then they lengthen again as you get towards sunset.

That's one thing that you observe very readily. You also observe that shadows move around as the sun passes over. So you begin to notice that there are ways of marking the passage of the day by observing these shadows. It's not simple, though, because you very quickly realize that unless you have some very clever geometry, a relatively clever geometry, the pattern of the markings that you might lay out to observe the passage of the shadow need to be different, at different times of the year. The way to get around that, I know it's getting a little complicated,

but there are lots of ways of marking the time by the passage of the sun, the altitude of the sun, for instance. It's height above the horizon, goes up and then down. The angle that the sun makes as it passes through what horologists call the R angle

or what astronomers call the right ascension. So the angle parallel to the equator changes regularly as the day progresses. And you can develop a a sun dial technology which copes with all of this and has a whole different range of sun dials which use the motion of the sun

in different ways and before I have to stop I just want to say that in the Renaissance and in the 16th century the most able astronomers were involved with this mathematical discipline it wasn't we shouldn't think of it in terms of the very simple common garden dials you might buy in a garden centre today it's not like that at all as a much more sophisticated

astronomical and geometrical discipline. Exactly what you three were doing down in Greenwich. It's measurement, measurement, measurement, measurement. And that's why we're all friends. Jonathan Betz. Can you take us from measuring time that Jim Bennett's the way that he's talked about it, to the movements of the sun and the moon marked by mechanical clocks? Well, Jim's referred to semi-mechanical devices in China and Islam,

but the earliest evidence for mechanical clocks as we know them, in our world, seems to come from the records of the monasteries of central and northern Europe in the late 13th century. One of the earliest references is actually from England, the records of Dunstable Priory in the late 1290s. The reason why we're uncertain about this is because these records were mostly in Latin, and the references to sundials and to what we believe to be mechanical clocks used the same term, Oralogium or Loge. And it's only when you start to see references to paying sums of money for, say, putting a little oil to Ye Orloge, or a new rope for Yeoogium, that you begin to realize that we're not talking about a sundial here.

This is something mechanical. Sort of characterising these things, I suppose by modern standards, we would think of them as very crude. They were made almost entirely of iron. they were, by our standards, hopelessly inaccurate. These machines weren't capable of measuring time better than quarter an hour, 20 minutes a day. One thing that has to be said is that the community within the monastery and the associated areas around would only have had this one clock. So it didn't actually matter whether it was fast or slow by 20 minutes a day or so

because everybody agreed what time it was and it didn't actually matter that much. So this was religious driven. They wanted a clock to wake up. the first monk in the middle of what we would call the night or they would call the beginning of the morning and he worked up the others in order to get on with the seven different prayers. Absolutely. You could see this as a kind of these early mechanical clocks were sort of modern conveniences in a sense.

They were automatic striking machines to save the sacrists and the duty of getting up and striking the hours throughout the night for prayer but also used during the day but principally at night and of course in cloudy weather. Is it in Salis really? Yes. Well the early early surviving, we believe to be at Salisbury. It's debated by horologists, what isn't, by

we argumentative bunch, but most people I think accept that the Salisbury Cathedral clock is the oldest surviving from 1386. So this is a real development here. So the whole idea of having a clock moves on, or is it just taking up what the Chinese and they did in Islam? Well, that too is very much debated. I think for my money, it was a case of reinvention. Um, what occurred before, what Jim has described, were actually quite complex devices, which were kind of machines which provided you with a uniform drive. They weren't, I think, conceived in quite the same way

as these early mechanical clocks, which were timekeeping devices. These earlier semi-mechanical machines from China and from the Arabia were sort of constant drive mechanisms for calendrical and astronomical indications. Can you tell us again briskly about weight-driven clocks in the medieval period? Well, they all were, basically.

Mechanical clocks need some form of driving force to keep them moving forward. And what is an essential element which kind of defines what we think of today as the modern mechanical clock is that it has to have this slightly scientific-sounding thing called an escapement and oscillator. No need to panic about that. It's very straightforward. It's just the sort of... You're going to tell us all about it. had a slightly horrified look at the escapement and oscillator.

I like to say it's the sort of beating heart, if you like. Imagine that. It's the beating heart of the clock. It's the thing which actually measures out the time. And over the years, it was developments in the escapement and oscillator, which basically gave us the modern mechanical clocks we have, which keep fantastic time. In those early days, the escapement and oscillator was a relatively crude thing. It was just a swinging bar or something.

times a wheel, and it was driven entirely by the clockwork. Now, if the clockwork drove it a bit harder, it would go faster, and if it drove it a bit lighter, it would go slower. Of course, it was weight driven, so you might say, well, as it's weight driven and its gravity, which is uniform, why didn't it keep good time? The answer to that is that the mechanism itself was fairly crudely constructed, hence we get sort of plus or minus 20 minutes a day. We get that way like that. Well, quite. So just let's whiz around a little bit before we start to concentrate on what's happening in Europe,

Christian Lipingot. There are different cultures that are different ways of telling what we call telling time. Can you just indicate a few of them? Yes. I mean, one of the things that we've already mentioned, which I think is pivotal to this whole discussion, is when we're talking about time measurement, we're talking about two different kinds of things. So one is interval measurement, which you're trying to get more and more precise as to how long an interval is. and the other is trying to figure out some way to make a machine

to track the movement of the sun, the moon, and the stars. So that's where it really sort of divides. It comes together several times during the next several millennium. But for example, one of the things you might do in China, for example, they say very, very early on in the records, that time was defined as how long it takes to burn an incense stick. So it's a bit like what Jim's talking about by the length of a stick. that you might measure water,

but instead it's an incense stick. And the earliest ones of these incense clocks, that ones in Japan were called Jikoban, and they would be little blocks of instance that you knew would burn, say, for whatever an hour was. And then you'd go say your prayers, and then you'd like another one.

So it's just measuring intervals of time. Another one, which my particular favorite, is called a Jokoban, which means the constant incense board. and what that was was a long trail, sometimes made in a pattern of flowers or sometimes just straight, that had different smells of incense at regular intervals.

So say if you were trying to have a long Buddhist meditation during the middle of the night, or you're writing your novel, and you wanted to know the change of the time, but you didn't want to be interrupted. You would sort of, for the first couple of hours, you would smell peach, and then as you were thinking about something else,

you'd smell pine, and then later you would measure It's a bit like those air fresheners that change smell. But this would be during the night so that you would be aware of the passage of time, but not oppressed by it. Growing businesses deal with the same problem. Too many tools, too much back and forth and not enough time. Odu helps bring it all together. It's an all-in-one business management platform fully integrated from sales and accounting to inventory and marketing.

So your team can spend less time chasing information and focus on growth. Whether you're in retail, manufacturing or service, Odu gives you one place to manage your business. Visit Odu.com to book a demo. It's O'DOO.com. Hello, I'm Tom Gatti, literary editor and host of the Observer Book Club podcast. Join me for in-depth conversations with some of the world's best writers, such as Elif Shafak, Douglas Stewart and Robert McFarlane.

At The Observer, we have a passion for storytelling, whether rooted in fact or fiction. The Observer Book Club is a place where great stories and big ideas come together. You can find it wherever you get your podcasts. Jim Bennett, the weight driven clocks were replaced by spring-diven clocks. Is there a feeling that among a certain group of people that this is something they have to crack, they have to explore, is there a drive to make it more and more precise? So are these things just turning up as convenient as in the medieval monasteries?

What drives the operative word, of course, because we're talking about an alternative drive here. I think alternative is the other word because it isn't that the spring-driven clocks replace the weight-driven, but they certainly become a new part of the technological repertoire for clockmakers in the 15th century. Springs are already being used to drive other machines, and it would be convenient to use them for clocks in some ways, because the clock could then become a bit more portable, for example. There is a big problem which is relevant to something Jonathan said about the constant force that you take for granted with gravity, certainly within the limits of accuracy of these kinds of clocks.

Gravity is constant, wherever the way it is. With a spring, it's not like that at all, as you'll immediately realize. Once you've tightened up a spring, when it's really taught, it's exercising a maximum force, and that force changes a lot when it's run down. So that's going to affect the going of the clock. And it's very interesting that quite a sophisticated solution to that comes immediately with a thing called the fusie,

where the maximum force is delivered closest to the axis, which is driving the set of gears that run through the clock. And then as the spring runs down, the mechanical advantage, as mechanists would say, increases by delivering that force. further away. So the law of the lever takes care of this and evens this out. That's, I think, very clever. And the fact that that's so early indicates that we're talking here about really high-tech design, things that were important, that were worth giving a lot of thought

to. So that helps to place it. I mean, these technological developments may sound a bit dry. if we just talk about them barely, you know, as technology. But if we think about why people are investing time and effort into these developments, then it places the whole idea and the importance of horology in a different context. Why do you think they are devoting time and energy to this, Jonathan Betts, the social implications of the spring-driven clock, the 15th century that, isn't it, Jim? Well, the spring-driven clock is a different thing from the spring-driven... Oh, so it's being driven clock, yes, is 15th century indeed.

Sorry, sorry. Yes, I think it's, Jim was touching on an important point here, something I might have said earlier, which is although we refer to these as relatively crude devices, we shouldn't see them that way at all. These were the height of sophistication at the time. They were, after all, the very beginnings, along with millwork of all of the gear technologies which followed,

and we have to see them as extremely sophisticated devices. The introduction of the spring, as Jim has said, made the clocks portable. It also enabled them to be made smaller. And so that by this stage, of course, we've moved from the monasteries into private ownership. And these things took on a whole new function. They weren't principally for telling the time of day, right up until, you could say the 19th century, the sundial was for most ordinary people, by far the most accurate way of telling the time.

Even in this country? Yeah, well, yes. When it was out, of course. But if it wasn't, then, of course, you had to rely on whatever mechanical clocks there were. Incidentally, there was something else which is important to say, which is the very early mechanical clocks, did not tell you the time. They sounded the hours. They didn't show you the time.

These early clocks in the monocles usually did not have dials, and they simply sounded the hour. And the dials appeared about a century later in the 14th century and were usually had to be. were divided into 24, not the 12 hours we are familiar with today, which came along a century after that. The 24 hours on these early dials was, for a good reason, it was because these dials were actually representing, the idea of them was, that they were mimicking what the sun dial did. These early clocks with dials were seen as a kind of repeating a sundial,

and so the hour hand was rather like the sun, in a sense. And it's sort of food for thought in a way that if you think about what clockwise is, we all take it to granted, don't we? But in fact, clockwise is only clockwise because of these early clocks having been made in the Northern Hemisphere. So here's a thought for you that if the early civilisations had developed clockwork

in Australia or South America, clockwise would be the other way. It's only clockwise because of that's the way the shadow on the sun dial goes. Kristen Livingcott, we come to the invention of the pendulum, which is a very significant development. Can you tell us how that came about and what its significance was?

Well, because it's a significant development, everybody has claimed ownership of it. And there's a number of people who even think that Leonardo, along with the bicycle and the armored car, invented pendulum. The other person for whom there's a great claim is Galileo. But unfortunately, a lot of the information that we get about these early years is from his biography. was a student of his who was writing much, much later. But his biographer claimed that in 1583, Galileo

was allegedly going to mass in Pisa Cathedral and noticed that one of the lamps, it may have been an incense burner, but I have a feeling it was one of the lamps in the nave, was going back and forth, oscillating, and he noticed it was regular, and he said, well, since this is so regular,

might it be a good idea for something to do with clocks to regulate clocks. However, the notes, his first notes, don't appear until 1588, and it's really not until 1602 quite later, but he says, ah, I see what it is, is regardless of how wide the arc is, the length of the pendulum will determine its beat or its period. And he was the first one really to say that. But he never, as far as we know, invented a pendulum clock that. actually was functional and that was left to Haugens.

Let's go to Haarhanz then, Jim Bennett, a Dutch astronomer and say what he did with... Did he take it, do we do have evidence that he took this from Galileo? The idea was independent, does these things often are now? Yes, I'm not sure about that. Certainly, Huygens' pendulum

and the Huygens' clock looks nothing like the Galileo drawing that we have. So it may have been known. Other people were interested in using pendulums for timing things. Huygens had a particular angle on this, I suppose.

I mean, it's important that you introduced him as an astronomer. It's very important to realize that this is being driven by the scientists at this stage. There's no particular reason Jonathan was saying, what's a clock for? It's not for telling the time. There's no particular reason for

the domestic clocks that we're talking about to have an imperative of having this greater accuracy. But the scientists need that. A clock has always been, or for a long time, certainly since the time of Ticobrahe, has been a measuring device within the practice of astronomy. You can measure one of the coordinates

because the Earth is turning around at a constant rate. You can measure one of the coordinates for astronomical position using a clock. A clock, the passage of time, is equivalent to the measurement of that angle. So that has to be as accurate as possible. And there's another funny reason, in a less well-known reason,

scientists that this is we're looking at for a standard length which would be available all over the world that everyone could use. Remember that there are standards of all sorts of standards of lengths in different cities and different states and for measuring different things and so on. The whole thing is completely chaotic in relation to standards of length. And it occurred to a number of people, the early fellows of their Royal Society, for example, that a seconds pendulum beating seconds is going to be the same length everywhere. Roughly speaking, there was an issue about that, but nonetheless,

that was a good start for a standard length that we'd have. And Huygens was very interested in that. And if you're going to test that and swing your pendulum, you need a device for counting those springs. So you're getting towards a second scientific interest in using the pendulum. If we go back to Jonathan's idea of the escapement and the oscillator, here we now have an independent oscillator, one that has a natural period of its own,

and which can control at last. or begin to start hoping to control the movement of a clock as opposed to, as John Thomas was saying earlier, the clock controlling the oscillator. And quite soon after, Jonathan Betz, in the 17th century, clockmaking took off particularly in London and it became a great centre of clockmaking. Why was that?

It's true, and it's rather extraordinary, actually, that this was a Dutch invention, and it wasn't the Dutch nor the French that really took it and ran with it. I mean, they did, of course, they made early pendulum clocks, but it seems to be the period in which there was a great flowering

of the clockmaking industry in London. And it was a tremendously exciting time. Why do you think it was then? I think the time was right, basically. The right people were in place, and our industry was growing just as the great golden age of Renaissance German clockmaking was diminishing.

London was finding its feet. Jonathan, it could have also been because there were the religious wars in the Netherlands and so a lot of people were fleeing to England. Well, it's certainly true that we call it the English Golden Age, but of course it was very much based on partly on the great talents of Huguenot Craftsmen. We mustn't say it's entirely English. Everything came together culturally and technically. What was important about the pendulum was that it was probably the greatest single improvement in timekeeping

from quarter an hour, 20 minutes a day, you had seconds a day out of pendulums, especially if the longer pendulums were used, you could really get a few seconds a day out of them. It was monumentally important. And it was the likes of the great clot-making families, the Froman Teals, fathered by the wonderfully named Ahazuerus Froman Teal, and of course the father of English watchmaking Thomas Tompian and others who founded this Golden Age, which is nominally a period of 100 years from 16,

1550 to 1750, but the first 50 years saw pretty much the development of the modern mechanical clock. All the features of the modern clock of the 20th century were in place by 1700. Kristen Lippen got the sun provided an obvious way of telling the time, but wasn't entirely straightforward. Can you tell us, can you explain this phrase the equation of time? Yes, well, it goes back to this problem of measuring interval versus measuring how the sun passes. one of the things when John Flamsteed was first set to measure the holes of the skies, he had to determine whether or not that the Earth was rotating at a constant speed.

Ptolemy had said it was, but nobody had actually had a clock that was accurate enough in order to test it against. So John Flamsteed started to do this and realized... Down in Greenwich. Sorry, yes, down in the 1670s, down in Greenwich. And he was the first to realize that the... that the sun, vis-a-vis an interval measuring device such as a clock, goes faster or slower during the year. So, for example, on November 4th, a sundial, which is measuring the sun is 16 minutes faster than the clock would be.

And in, say, February, it would be 15 minutes slower. So what happened was you have this distance between what the sun is telling you and what a clock is telling you. and he created something called the equation of time, which would tell you exactly how fast or how slow your clock was running vis-a-vis the sun. Jim Bennett, one way this got into public consciousness at that time was the fight for the clock that helped with the longitude problem and the Harrison clock.

How important was that in the general development of timekeeping? Well, again, the drive for accuracy isn't coming out of domestic timekeeping here. it's coming out of navigational necessity. I think it's now so well known, the story of longitude is so well known, that I needn't rehearse that need. But basically, it's impossible to find a longitude astronomically at sea. You can do it on land.

There are various clever ways of doing it, which require sophisticated instruments that aren't transportable, don't work on ship. Nonetheless, it didn't stop people trying to do that in the 18th century. and also trying to develop clocks that could go to sea. We mentioned Huygens and Huygens' pension. Huygens immediately, even though I stressed his interest as a scientist, he does go into a commercial interest.

He has a clockmaker who makes clocks. He's hoping to make money out of that. And he also makes a longitude clock, which he takes to see, and hopes he can make money out of that. So Huygens wasn't entirely above all of this worldly interest, as well as the astronomical interest. Everyone's perfectly well aware. That's why the Grinch Observatory has found it,

that we have a big problem, navigationalally speaking, with longitude, and there will be a number of other, there are possible solutions. Grinch, of course, is predicated on an astronomical solution, but the rival solution is to take a clock to sea, to use the fact that the Earth is turning constantly, at a constant speed,

that the angle of the turn, can be measured, as I said earlier, by a clock, and that angle, that time difference, will be equivalent to the angular distance that the earth has moved. So in a way we go back to Kristen's point here about duration, the longitude clock that you take to see isn't for telling the time.

It's in a sense for measuring duration. It's for measuring, it's for providing a constant, measure of duration which represents then the local time at a distant place probably your point of departure or a standard meridian. You compare that with the real time,

the local time that you can readily find and you have a measure of your longitude. But it's interesting that like the alphabet like numbers, like a lot of the great basic things that have happened, it's trade and that is driving this as well. It's trade that's driving this more accurate clockmaking.

Trade and empire. Trade and empire. Yes, trade because of empire. I would have anyway, but it is trade. Kristen Libbing got, we, moving from the sea to the land, the development of the railways, references being made several times in this program to different places. Bristol had a different time from London and so on. This didn't work, so they were looking for a national time and then a global time.

Can you take us through that? Yes. Well, in England, for example, in the 1840s, everyone kept local time. So that, as you were saying, Bristol might be, say, 20 minutes behind London, because that was the time that the sun passed the local meridian at noon. But with travel, with commerce, you suddenly had people, if you like, being able to move faster than the sun. So if you left London and took a train to Bristol, you would arrive 20 minutes early by the Bristol time. So it was really in the 18, about 1847, that there was an internet, our ennance, our national, national railway time system that was based on Greenwich Mean Time.

Was there much resistance to it? There was a lot of resistance. We want our own time in Bristol. There was two, the number of things. First it was we want our own time in Bristol. Secondly, it was called railway aggression. The idea of the way that we might fear global companies, they were fearing this idea of an anonymous government.

The third thing was religious. people said, well, God put the sun there for a reason. It's not for us as men to think up a different time system. And the final people who actually resisted it were the astronomers because they were saying, no, no, let's go back to measuring the stars and you can't just arbitrarily say this is an hour, this isn't an hour. We really should have local time. Does this actually mark the point where men and women are starting to say,

look, we control it, not the sun and the stars in the moon? Well, this, basically what is happening is it's really back to what one might call commerce and communication. It really was the problem is if you could talk to somebody who was in a different local time system, how would you know what time it was? And we saw even this recently in the first Iraq war when George Bush Sr. said something like, we will strike at five. And immediately the phones were hot. And everyone was saying, five o'clock, when? was it Greenwich Mean Time? So they had to like do a double take

and say, well we meant European time and people forget that there are different times because we are on a rotating rock. But still there's a great standardisation Railways 1840s this country. Then we moved on Jonathan. That's the even greater leap forward which resulted in Greenwich Mean Town.

How did we get there? And why was Greenwich chosen? Well, it was a global version of what Kristen has just described nationally, basically. And what we experienced today with our international time zone system really came out of longitude and cartography, really. It was a need to have a single meridian across the world that inspired the International Meridian Conference in 1884 in Washington, in which the principal concern was having an agreed meridian for cartography, so that all the charts in the world would relate to one meridian. And at that point, 72% of the world's shipping, were using charts, global charts, with Greenwich as the prime meridian. And so, although of course, it was going to be a political decision, it could be argued that it was very much a common sense decision

that Greenwich was chosen at that point. And out of that, naturally came the decision that the prime reference meridian would also be for calendar and time as well as for cartography. So that's how we ended up having the reference meridian for the time zone system, then followed from it. I hesitate to mention this, but France went off in a huff and refused to join for 30 years. Well, they abstained. They didn't actually vote against. Instead of 30 years, it's quite an abstention.

It is. And when they did accept it, it has to be said, they did so in a mealy-mouthed kind of way. It was finally enough enough. Enough about that. Fine people. Right. Jim and Jim Bennett, now we move on to this perpetual drive for accuracy, more and more accuracy. So we come to quartz. Again, coming out of a scientific agenda. Because now this is radio engineers who need a standard frequency. It's a bit like the standard of length that Huygens was after. This is a 20th century standard that's needed by radio engineers. And it was known that certain, the mechanical systems that oscillate at very precise and regular frequencies.

And one of those depends on a quartz crystal. Quartz crystal is particularly useful in this respect because it has a pizzoelectric effect. That's to say if you bend it, it creates a redistribution of electric charge across the crystal. So you can, if you cut it in particularly advantageous ways and then set it up so that you can manipulate this, you can start the resonant frequency of a mechanical frequency, it's a mechanical resonance now of the crystal using an electric stimulus. And once it's off and you maintain it, it's the old sort of oscillator idea again that Jonathan brought in, now a new sort of oscillator,

you can have a new order of magnitude of accuracy from this oscillator. And then in the 1950s, we come to the atomic measurement. That's right. This was a sort of refinement of courts, really. Atomic clocks actually have as their time standard, a quartz clock. In simple terms, what an atomic clock does is to kind of fine-tune the courts and watch how that courts is behaving. and it uses atomic technology to kind of check how the courts is,

how the frequency of the courts is running. In simple terms, you have a sort of microwave oven, if you like, which is being controlled by the courts. And in the case of the modern atomic clocks, where they use cesium atoms pass through the microwave oven, and they will change their state only at a very, very precise frequency. So you can trim your courts by watching these atoms, and that enables this course to be fantastically accurate.

Finally, Kristen Lippen-God, is there a sense in which this worries you? It worries me tremendously, and we're now coming to the hairy topic of the leap second. You've got about that time. Essentially, we have a choice. Do we actually think that the sun, the stars and the moon are important to our lives, or do that we think that our lives should be controlled by intervals? Well, you've been very good. I was expecting it another 40 seconds.

Oh, I can say, I vote for the sun and the moon and the stars. You're a sun and the moon person. Thank you very much, Kristen Lippenigod, Jim Bennett and Jonathan Betts. Next week we'll be talking about the Society of Friends, the Quakers, 17th century radicals. Thank you very much for listening. Thank you for listening to this archive episode of In Our Time. Every Monday, I revisit one of more than a thousand episodes in our archive, and on Thursdays you'll still find brand new episodes of It in Our Time.

Listen first on BBC Sounds or wherever you get your BBC podcasts. Hello, I'm Tom Gatti, literary editor and host of the Observer Book Club podcast. Join me for in-depth conversations with some of the world's best writers, such as Elief Sheffat, Douglas Stewart and Robert MacFarlane. At The Observer, we have a passion for storytelling, whether rooted in fact or fiction. The Observer Book Club is a place where great stories and big ideas come together. You can find it wherever you get your podcasts.