Timekeeping leading up to the marine chronometer is also very interesting. Note that none of the timekeeping devices mentioned in the article would work very well at sea, making it impossible to accurately determine your longitude. Solving that proved to be extremely difficult.
> John Harrison was a carpenter by trade who was self-taught in clock making. During the mid-1720s he designed a series of remarkable precision longcase clocks. These clocks achieved an accuracy of one second in a month, far better than any clocks of the time.
Wow. I own Tissot and Casio hand clocks and both are significantly worse precision. Are there any available clocks with that precision? Of course with GPS, WiFi and other wireless ways to access atomic clocks that's not so important, but still interesting.
A cheap watch or clock will use an off-the-shelf crystal oscillator, where you'll be lucky if it's accurate to 20 seconds in a month.
A temperature compensated crystal oscillator (TCXO) can do better than one second per month, but probably not better than a second every 2 months.
An oven controlled crystal oscillator (OCXO) or a double ovenized crystal oscillator can get an order of magnitude better than that, But they start costing between $50 and $1,000. Beyond that you get into funky stuff like rubidium or cesium atomic clocks. There are, notably, miniaturized atomic clocks these days - about 2" x 2" - So you could technically put one into a wall clock, although they cost about $2,000.
These days it's usually cheaper to use GPS to control a temperature compensated oscillator, which we call a GPSDO (gps disciplined oscillator).
The mems temperature controlled oscillators are also very good, 0.05ppm range (about a second every 8 months). They are tiny and low power, but still >$79.
If you have AM-based clocks, you might find that these work better. However, nobody advertises which module they're using, so it's kind of a crapshoot. I specifically bought a phase modulation WWVB receiver and it reliably receives the signal every night. I also have a random $7 clock from Amazon that pretty much synchronizes every night. Living in NYC, this is truly amazing to me; I never ever got the AM signal here.
Thanks for that! Didn't know there were two kinds of radios.
I have one clock that always works perfectly, syncs after DST 100% of the time. Another that always requires manual reset twice a year, defeating it's purpose.
It's an incredible feat to me that a single station can broadcast to the almost the entire US, Mexico, and even parts of South America at the right time of day [0]. (I believe this is why many clocks check for the signal overnight.) It's achieved by using an extremely low frequency, at 60 kHz. The antenna is enormous and suspended between 4 towers.
Communication with subs uses ELF/SLF (3-300 Hz) when they're underwater--in the US case from some big communications stations. The coastal VLF stations, like in Cutler Maine are more in the 24 kHz range. As I recall, at one point, there were ecological concerns with the ELF stations but apparently the projects ended up going ahead.
The rubidium standards show up on eBay a lot for much less, but I don't know if they're still accurate and reliable after being used for years, I would imagine they're replaced for a reason
It should be noted that Harrison's watches were low-volume productions, so could be tuned very accurately—and their accuracy was a matter of life and death for ships and their crew. Most mechanical watches 'normal' people can get nowadays are produced at much higher volumes, and so aren't adjusted as much—especially since few people demand it and are willing to pay for it:
The Harrison watches/clocks were built for the British government/Navy, so were fairly price insensitive (military procurement and such).
Being 1 minute off in time throws off distance by 15 nautical miles (~28 km), so being off by a second can cause about 500m worth of position inaccuracy.
Also: it may not be a big deal if your clock/watch drifts as long as it does so at a known, consistent rate which you can adjust for.
> Modern sextants can read the angle to a 0.1 minute level of accuracy, i.e. one-600th of a degree or one-tenth of a mile. In practice, actual accuracy to one-half mile is acceptable and quite good. The usual standard is accuracy to within five miles. The sextant (or octant) is meant to get the ship across the ocean. Once near the coast (20-100 miles) the more accurate techniques of piloting are relied upon for a safe landfall. The sextant is still the standard instrument for taking the observations required for celestial navigation.
One thing that helps with a pitching deck is that the horizon and object remain the same angle. Like a camera following race car, the objects move together.
> The Scilly naval disaster of 1707 was the loss of four warships of a Royal Navy fleet off the Isles of Scilly in severe weather on 22 October 1707.[a] Between 1,400 and 2,000 sailors lost their lives aboard the wrecked vessels, making the incident one of the worst maritime disasters in British naval history.[2] The disaster has been attributed to a combination of factors, including the navigators' inability to accurately calculate their positions, errors in the available charts and pilot books, and inadequate compasses.[3]
Yeah I get that it's important, I just didn't realize that angles could be meaured so accurately by eye at that time (especially on a ship that's moving around on even a moderate sea).
> I just didn't realize that angles could be meaured so accurately by eye at that time
Sextants have a bit of magnification (usually 4x, but sometimes 7x or higher). Higher mag allows for better accuracy at the cost of more shaking of the view.
As I understood the exhibits in Greenwich, the Harrison clocks were largely eclipsed by cheaper versions by the time payment issues were resolved and they made it into widespread production.
technically it's "electromechanical" but does not use GPS, WiFi, quartz, or atomic methods. To make thigns this accurate you need extremely good temperature compensation, close-to-frictionless bearings, run in a vacuum, use a pair of pendulums, etc.
When you reach that level of accuracy, you end up basically building a sensitive measurement device that is influenced by second and third order terms like subtle changes in the shape of the earth.
> Are there any available clocks with that precision?
Yes! The term you need to type into Google is "High Accuracy Quartz". The most easily available wristwatches with this level of accuracy are the Bulova Precisionist line.
If you ever find yourself stranded back in time at that spot, skip over the fancy clocks and invent a radio transmitter that can send out a powerful pulse for "it's noon in $city" once a day.
Then sailing ships can manage with simple receiver plus clock just good enough to measure 12 hours. The time delta between receiving the land-broadcast and their own observed noon will tell them their relative longitude.
Since you aren't trying to encode any other information in this pulse, that makes the job a lot easier than if you were trying to make a wireless telegraph.
If you want to restrict who can benefit (e.g. to support a particular military that happened to recognize your time-traveler genius) plan random offsets for when you will be triggering it, and give authorized users a copy of the offsets.
IANAMariner, but I'm assuming the sextant would already be invented, since it would also be important for determining latitudes.
The goal is to figure out when the sun is as-close-as-possible to the reference vector "straight up". On land, we might determine that vector using gravity and a plumb-bob, which is indeed going to be a lot harder on a rolling ship.
However way out at sea, a new option exists: The horizon is no longer an arbitrary mishmash of mountains and hills, but instead self-leveling water in every direction [0], meaning you can safely assume "straight up" is 90 degrees [1] from all points on the horizon.
So you'd measure the angle between the sun and the nearest horizon, and then noon would be when that angle hits its minimum.
[0] Tides exist, but I assume they aren't likely to cause one direction to be significantly higher than the other.
[1] Unless you're measuring from very high up above sea-level, but if the civilization can make ships that big then you probably don't need much navigational help.
I'd just like to throw out a recommendation here for the book Longitude by Dava Sobel. It's about the invention of the marine chronometer by a self-taught carpenter. Fascinating read, and a real page turner too.
I’m reading and so far enjoying “A Brief History of Timekeeping” by Chad Orzel.
Not to discount Harrison’s achievements, but there are other interesting navigational approaches - using Tobias Mayer’s Lunar tables:
> Mayer is far less celebrated than Harrison, but his method was in many ways the more immediately successful of the two
Or, if society were to collapse and rebuild, Lewis Dartnell proposes a radio in “The Knowledge”, since a radio transmitter is probably simpler to build than an accurate chronometer.
Great article that covers some fantastic examples of sun-based time. If you want to read about two more, Seiko has a great article [1] about a traditional Japanese clock (Wadokei) which had moving indices based on the seasons.
The local time we keep today is supremely useful for global synchronization, but is disconnected from the natural world. I came across this example (Wadokei) after making an app for myself to track the moon above and below the horizon and doing some research after creating a similar style clock which uses the sun as the anchor of the clock (high noon is the top of the clock, instead of 12 noon). This one is a full-day clock that shows the hours of the “local time” day as well as the positioning of the sun and moon. The hours shift dramatically during the peak of summer and depths of winter, especially at extreme latitudes [2]. You can really get a sense of the length of the daylight and how it changes by using any of these sun-based clocks.
Early hours were not uniform in length (they couldn’t be, really, with a sundial). The Babylonians (and the Egyptians after them) divided day (daylight) into twelve equal regions and night (between sunset and dawn) into twelve equal periods, but day and night hours were not the same length, nor were those of successive days or nights.
Parasite was a kind of job: if you were rich you had a parasite or two who would accompany you when you were out and about. You paid for their food and upkeep and in exchange everyone could see how rich and generous you were.
Another interesting thing is how Western clock technology was adapted to fit traditional Japanese notions of time, in the pre-Meiji era (after which, Japan adopted Western time.)
A Japanese clock (和時計, wadokei) is a mechanical clock that has been made to tell traditional Japanese time, a system in which daytime and nighttime are always divided into six periods whose lengths consequently change with the season. Mechanical clocks were introduced into Japan by Jesuit missionaries (in the 16th century) or Dutch merchants (in the 17th century).
And on a related note, Lewis Mumford, a philosopher and writer, wrote quite a bit about how clocks were (in his view) the necessary invention for capitalism to flourish:
The first phase of technically civilized life (AD 1000 to 1800) begins with the clock, to Mumford the most important basis for the development of capitalism because time thereby becomes fungible (thus transferable). The clock is the most important prototype for all other machines.
> And on a related note, Lewis Mumford, a philosopher and writer, wrote quite a bit about how clocks were (in his view) the necessary invention for capitalism to flourish.
Szabo also takes this up in his excellent essay "A Measure of Sacrifice":
Fair broadcast and verification of time was thus of fundamental importance to the most common contractual relationship in the new European cities. In agricultural societies, including medieval Europe, serfdom and slavery had provided most of the labor. Most workers in a modern economy earn wages based on a time rate. Along with or following the rise of the time-rate institution – including the contracts themselves, the laws and regulations governing the contracts, and the technology to fairly measure the principal quantity – came the growth of related economic institutions, such as the joint stock company. These institutions enabled a boom in productivity and the spectacular rise of Europe from its darkest ages to the modern era. We will now chart the rise of the clocks and the institutions they supported.
One of the medieval time measurements were standard prayers - a Pater Noster is about the same amount of time each time, and a decade of a rosary for a given person will be pretty consistent.
Two more modern anecdotes of using songs for rhythm or timing:
The ideal pace for CPR chest compressions is pretty much exactly Stayin' Alive by Bee Gees. Or if you like darker humor, Another One Bites the Dust by Queen.
At the peak of COVID-19, the recommended duration for hand washing was Happy Birthday twice.
Reminds me of how the Pueblo leader Popé distributed ropes with knots tied in them to various groups across the region to coordinate his attack. Every day each group would untie one knot in their rope, and when all the knots were untied they were to attack the Spanish.
traditionally, every culture used seasonal/unequal hours! just, in Europe, the advantage of mechanical clocks was so great that the culture changed to fit the technology
There is a really nice surviving water clock from the early Imperial era in China that was discovered in the 1970s [1]. The Imperial bureaucracy was sophisticated enough at this point that official timekeeping equipment like this was carefully tracked. The water clock has an inscription that details where it was made (Qianzhang), when it was made (27 BC), and how heavy it is 32 "Jin").
There is a text written a few decades after this water clock was made that provides enough detail to approximately reconstruct how astronomers used it for their measurements. In essence they would calibrate the water clock against the motion of the Sun so that they could correspond some volume of water to a 24 hour period. Then they would measure the amount of water that flowed from the transit of one star to another to figure out the separation of those stars in right ascension. The measurements were sophisticated enough that they apparently took into account factors like humidity and temperature when using the water clock.
Often we wonder what distinguishes humans from other animals. Measurement and optimization. Do other species measure, and optimize? Others use tools, but do they optimize?
> When an insect or spider crawling along the leaves contacts a hair, the trap prepares to close, snapping shut only if a second contact occurs within approximately twenty seconds of the first strike.
> ...
> The mechanism is so highly specialized that it can distinguish between living prey and non-prey stimuli, such as falling raindrops; two trigger hairs must be touched in succession within 20 seconds of each other or one hair touched twice in rapid succession, whereupon the lobes of the trap will snap shut, typically in about one-tenth of a second.
> ...
> Most plants accumulate starch by day, then metabolize it at a fixed rate during night time. However, if the onset of darkness is unusually early, Arabidopsis thaliana reduces its use of starch by an amount that effectively requires division. wever, there are alternative explanations, such as feedback control by sensing the amount of soluble sugars left. As of 2015, open questions remain.
Ants, of course, famously optimize. I think most creatures optimize somehow, I mean doing things wastefully is way to end up with an energy deficit, aka starve.
Humans have an interesting tendency to bump themselves out of local optima, via instincts called “boredom” and “curiosity.” These are not strictly human traits I think, but humans tend to get bored more often than other creatures, tend to accumulate large amount of resources which allow them to follow their curiosity a bit further, and are very good at communicating the results of this boredom.
>> Do other species measure, and optimize? Others use tools, but do they optimize?
They all do. Think of locomotion. Most every animal that can move has a few different ways of doing it. We can walk, or run. An eagle can fly direct or take a circuitous route between updrafts. A whale has sprint mode or easy cruise mode. We are all constantly optimizing how we move in order to minimize expended energy to accomplish a given task.
How would you define optimization? As in time management? Making some process take less effort perhaps? I’d say my cat fits the bill. She seems to have a better sense of time and keeping to her schedule than I do. She has also figured out many optimizations for her life that make sense to her. For example her path routing ability while running full speed is pretty amazing, she manages to figure out routes that keep her on a vector enabling full tilt acceleration vs turning and walking around furniture like us humans do with our poorly optimize walking.
I sometimes watch those TV shows about ancient civilizations. They often talk about "astonishing" astronomy they used.
In reality, all they did was track the sun. This can be done simply by putting a vertical stick in the ground, and marking the path the tip of the stick traces in the ground. This way, the calendar and solstices can be accurately determined.
The shows will also talk about the "amazing" technology that enabled, say, a hole in a wall to shine on a statue for one special day a year. Again, rather simple to do using the same idea as the stick in the ground.
The third thing that annoyed me was their "incredible" astronomical knowledge in predicting eclipses. All that is is collecting observations over decades and then recognizing the pattern. There is no astronomical knowledge involved. They still had no idea what the sun, moon, and planets were, nor even the layout of the solar system.
> They still had no idea what the sun, moon, and planets were,
The composition of celestial bodies is useless trivia until you have some very modern material and energy sciences that might start turning to them for inspiration. There will almost certainly be a collapse of the modern world, and losing that information will be the very very least of our problems.
> nor even the layout of the solar system.
Depending on which civilizations you're talking about and how ancient you mean, the paths of visible roving bodies (planets) were actually pretty well known in many places for thousands of years. The models used to anticipate positions were often more convoluted than ours, but projected space and heliocentrism are ultimately just an optimization that wasn't obvious, necessary, or meaningful given what little practical use there was to the paths of those planets until very recently.
What those pop history shows mostly achieve is just reminding people that astronomical and scientific knowledge didn't start in the European Enlightenment, which is the takeaway that many people (in the US, especially) carry after high school. They're not really meant for someone like yourself. There's much more you might actually be impressed by in academic history/archaeology/anthropology and even in certain written pop history sources.
Also worth noting that pretty much every ancient civilization ended up figuring out the order of the planets, at least relative to earth. (It turns out not to be so difficult since this is directly related to their sidereal periods.)
If you stand at the center of a circle, and have a man walk a circle at radius r from you, and another man walk a circle at radius 2r, it will take the second man twice as long to complete the circle.
It's not a great leap to apply that to the planets.
But it's not proof that the planets were ordered that way.
Science happens when one invents an explanation for observed phenomena, and then the explanation (theory) makes a prediction, then an experiment is devised, and the theory is validated if the prediction matches the theory, or tossed aside if it doesn't. In other words, the scientific method. That appeared fairly recently, and the consequences were an explosion of knowledge.
> There will almost certainly be a collapse of the modern world
I hope your certainty is misplaced; this is just about the most horrifying prediction I can imagine.
As far as I can tell, we're at a particularly precarious transition point with regard to how much energy we consume. If society "collapses" before hitting some technological checkpoint we don't get to try again - at least, not for a looong time - because we've nearly used up all of the low-hanging fruit in the planet's energy resources (fossil fuels).
Sure they watched the paths. That doesn't tell them what they were, how far away they were, helicentric vs geocentric, etc. Anybody can watch paths and notice they repeat.
> heliocentrism are ultimately just an optimization that wasn't obvious, necessary, or meaningful given what little practical use there was to the paths of those planets until very recently
True, but that wasn't my observation. My observation is it was not advanced, sophisticated, etc.
It was actually extremely complex and sophisticated. Getting accurate measurements was seriously tricky and making sense of them involved doing complex calculations (particularly spherical trigonometry) by hand. Some phenomena, like the precession of the equinoxes, required aggregating observations which had been taken over several centuries.
A good book to get a sense of this complexity is “The Light Ages” by Seb Falk.
I think you're underselling the accomplishment of determining some of these things, particularly predicting eclipses. And I think there's quite a bit to be said about novel applications that emerge out of tracking the sun, like announcing seasons for citizens to help know when to plant, reap, store, etc. to manage agriculture across empire. Often they amazing thing was taking a small thing and spinning into a massive, society-impacting solution.
One of the most impressive aspects of Babylonian and Chinese eclipse predictions was simply the social organization that was required to collect the necessary data. These records were collected almost continuously over centuries. The Babylonian astronomical records which span around seven centuries and are arguably the longest continuous scientific program any civilization has produced.
It then helped establish the study of the precession. Hipparchus used the Babylonian astronomical information to look into changes over hundreds of years.
> In 1900, Franz Xaver Kugler demonstrated that Ptolemy had stated in his Almagest IV.2 that Hipparchus improved the values for the Moon's periods known to him from "even more ancient astronomers" by comparing eclipse observations made earlier by "the Chaldeans", and by himself. However Kugler found that the periods that Ptolemy attributes to Hipparchus had already been used in Babylonian ephemerides, specifically the collection of texts nowadays called "System B" ....
> Earlier Greek astronomers and mathematicians were influenced by Babylonian astronomy to some extent, for instance the period relations of the Metonic cycle and Saros cycle may have come from Babylonian sources (see "Babylonian astronomical diaries"). Hipparchus seems to have been the first to exploit Babylonian astronomical knowledge and techniques systematically.
> ...
> Hipparchus probably compiled a list of Babylonian astronomical observations; Gerald J. Toomer, a historian of astronomy, has suggested that Ptolemy's knowledge of eclipse records and other Babylonian observations in the Almagest came from a list made by Hipparchus. Hipparchus's use of Babylonian sources has always been known in a general way, because of Ptolemy's statements, but the only text by Hipparchus that survives does not provide sufficient information to decide whether Hipparchus's knowledge (such as his usage of the units cubit and finger, degrees and minutes, or the concept of hour stars) was based on Babylonian practice
> you're underselling the accomplishment of determining some of these things, particularly predicting eclipses
If you keep records over the decades, you can predict it. It's just a pattern, not an understanding. It wasn't until the last century, however, that the application of math to the precise orbits was able to predict the track of an eclipse very accurately.
> If you keep records over the decades, you can predict it.
Of course we know that now, but that level of understanding is hardly trivial to societies at those levels of development. To use our current understanding to be so underwhelmed - and to not be at all impressed by the scale at which they applied it for transforming and modernizing aspects of their growing societies - I don't know man, it honestly kind of shocks me and bums me out in equal measure.
When I was a boy, I had a newspaper route. It required me to deliver the newspapers at around 5AM, when it was still dark. While biking around the neighborhood throwing newspapers at houses, I would also watch the night sky.
It wasn't long before I started noticing patterns.
Ancient people also lived largely outside. They'd see the patterns, too. This isn't amazing or sophisticated or incredible.
Those kinds of shows can be sensationalized and shallow, but if you're interested in learning more in depth about ancient astronomy (shameless plug) I have been doing a podcast on the subject. So far I've covered the astronomy of the Babylon, Greece, Rome, India, prehistoric Europe, Subsaharan Africa, and am currently five episodes into the astronomy of premodern China.
Something one might like as a continuation of the article is digital sundials. Apart from types listed on wikipedia, there are 3D-printed versions etc.
No. The English terms "earlier" and "later" refer to the progression of time from the past (earlier) towards the present and future (later); they do not refer to the number itself being larger except incidentally. (The etymologies here are that "earlier" comes from "ere" meaning "before" or "soon", "later" comes from various "lat-" roots meaning "sluggish" or "lazy" hence starting after their appointed time.)
So for example the Wikipedia article on Hellenistic Palestine contains the opening line,
> The region came first under Ptolemaic rule beginning in the late 4th century BCE with Ptolemy I Soter, followed by Seleucid rule beginning in the early 2nd century BCE with Antiochus III the Great.
It then clarifies that the events of the late 4th century BCE include events in ~320 BCE, and that the early 2nd century stuff happened in ~198 BCE. This is a standard usage of those terms "early" and "late" as applied to those centuries, the 4th (400 BCE - 301 BCE) and 2nd (200 BCE - 101 BCE).
I think the issue primarily is that there are two frames of reference used: "earlier" / "later" terms use the absolute frame of reference (time progressing forward), the numerical terms ("100s" / "4th century") are relative to the common era (higher BCE numbers mean further back in time).
To me it is confusing that they've mixed the two, even though it is convention to do so.
Fascinating article. This has inspired me to make a sundial that works inside my NYC apartment. Ideally, there's some reflective device pointed outside and some warping that happens to allow the sundial to work inside.
I was thinking about this while watching an amazing Chinese historical drama, "Longest Day in Chang'an," which has a "24"-like real-time structure. But instead of the beep... beep... beep... you have this one guy in an official building intently watching a water clock and pretty much every episode he bangs a drum on the hour and yells out the exact time and a kind of proverb, like "1 o clock!! The shadows reappear!"
Great show and there are lots of interesting historical details like this. Good post too.
Toward the end of the article there are descriptions of Al-Jazari water clocks but did not mention about the infamous Alhambra Palace lions water clock, and most likely it was based on Al-Jazari inventions. Since Alhambra Palace construction was started in the same century of Al-Jazari death (13th century AD) it's very plausible that it's based on his work.
Al-Jazari invented hundreds of inventions including mechanical robots that were said to be copied by later scientist and engineers including Leonardo da Vinci, and we know that good artists copy but great artists steal [1].
During a visit to Alhambra Spain it was claimed the water will gush out from each of the lion figure's mouth fountain for every hour, in sequence of turns not unlike our clock now but it all based on water. Perhaps this is possible due to the Al-Jazari water clock invention but no one know how it was originally working [2].
It's a shame that indispensable knowledge like this has been lost forever and this also happened to the earliest earthquake sensor instrument invented by Zhang Heng back in 132 A.D. He called his seismoscope Houfeng Didong Yi, meaning an "instrument for measuring the seasonal winds and the movements of the Earth." Now the working replica has been recreated but only until very recently they had managed to recreate the functioning replica but knowledge regarding the actual original working mechanism has been lost forever [3]. Ironically after more than 2000 years later and USD1 Billion spent for the earthquake sensors system installations, the latest system with 15K sensor stations throughout China, it still cannot predict the earthquakes but only provide alerts to the authority after the main earthquake has happened somewhere in China [4],[5].
[1] The Relation between Al-Jazari of the East and Leonardo da Vinci of the West:
Court of the Lions (14th c.) in the Alhambra palace is my favorite water clock.
A large pool of water is surrounded by 12 lions that would spout water from their mouths and depending on the hour of the day (1 o'clock, 2 o'clock, etc), the water comes from Lion 1, Lion 2, Lion 3, etc. https://en.wikipedia.org/wiki/Court_of_the_Lions
what, no astrolabe? astrolabes are the direct precursor to mechanical clocks, you can think of them as a slide rules with a inclinometer and a star map, and their primary application was to convert the altitude of visible stars or the sun into the current time
https://www.rmg.co.uk/stories/topics/harrisons-clocks-longit...