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Centuries-Old Longitude Clock Runs Again
douglips writes "BBC News has published a story about John Harrison's H4 chronometer and how it has been wound up for the UK's National Science Week.
After 40 years of work [Harrison] proved in 1764 that a clock could be used to locate a ship's position at sea with extraordinary accuracy." Ah, the GPS system of its day. T. adds: This is the timekeeping device which Dava Sobel wrote about in Longitude .
This site tells much about Harrison's H.4 Timepiece (picture). Don't forget to visit the official site.
I seem to recall some TV show...within the last 2 years, at least, about this clock and the efforts that led to it. Was it based on the book? I think it was on PBS.
Anyone remember this?
Pretty interesting concept for its time. Pretty easy to think of if you could see the big picture. But back then, they couldn't. Gotta hand it to Harrison. Good idea.
Job? I don't have time to get a job! Who will sit around and bitch about being broke and unemployed then?
I saw the special about Harrison and his clock just a few days after I read 'The Theif of Time', arguably one of Pratchett's better books of the aging Discworld series. Not surprisingly, the non-plot themes are somewhat similar... the quest for the perfect material with which to build clock springs.
Reading about this makes me want to read it again.
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The interesting thing about the Harrison clocks, is not only were they the GPS of their day, they were also the atomic clocks of their day.
The Harrison clocks, created in the 1700's, are still more accurate than your average digital watch today.
That is what screwed everyone up at the time, because the majority of folks were into heavy metal and wood and so on. Pendulums are messy on ships.
The spinning mechanisms of mechanical watches are much more stable, and this, with the miniaturization, proved to be the key.
The professionals could not deal with a simple "watch" that was the first chronometer.
"It is a greater offense to steal men's labor, than their clothes"
James Burke mentions this in the Connections tv series. A lot of people tried and failed to make a clock accurate at sea.
I wish I could get that series on DVD.
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I was in London last November, and visited the Royal Observatory in Greenwich. I was familiar with the Harrison clocks and story, but I hadn't known they were kept there. So it was a pleasant surprise to find them there. If you're a geek and you happen to be in London, it's well worth your time to go take a look.
The first three clocks are these large (roughtly 1.5 ft in each dimension) contraptions with lots of visible moving parts, wooden gears, etc. Then you get to H4, and it's this elegant little package. The leap between the first three clocks and the fourth is enormous.
There's a fair amount of other neat stuff at Greenwich, too. They have a number of displays about the development of "time infrastructure". I remember reading one bit that talked about how, in 1852 (I believe), Greenwich began transmitting the time to the rest of England via telegraph. I couldn't help but be reminded of how clock signals are distributed around a CPU and other synchronous logic devices, and think that maybe humanity is somewhat more borg-like than we usually acknowledge.
I definitely agree that the book is an interesting read. Until i came across it, I'd always had the misconception that seafarers could actually determine their relative position to a fixed departure point via the stars. when in fact only the latitude was figurable.
(there is also a description in the book about the rival scheme involving telescopes and star charts fiercely backed by the Royal Astronomer)(can't recall his name -- Maskelyne?)
if you think about it, the pre-Harrison sea captains were a pretty courageous lot -- imagine setting out on a journey and not *really* knowing for sure how far you'd actually travelled! (in terms of degrees of longitude)
Harrison's sea clocks are a great example of a disruptive technology. His clocks were competing against stellar navigation, and the judging for the award he earned after decades of stonewalling, was done by the royal astronomers. Also - I'm finally posting (my first post!) because for some reason it drove me crazy to read on the main page that it was a clock (singular) that provided a longitudinal position. It takes 2. One set to GMT, the other set to local time, determined by solar noon. The difference provided the longitude. (1 hour = 15 degrees) And it was the ability of H's clocks to keep gmt accurately - (to Jamaica and back!) that made it effective. JGG
There's a surrealistic novel by Umberto Eco about attempts to solve the longitude problem through alchemy and strange "scientific" experiments 120 years before Harrison. It deals with the blury line between science and supersition at that time (not that it's all that clear now), and with the importance of knowing longitude for military advantage and empire building. A very strange story told through the eyes of a clueless young nobelman trapped into an insane voyage of discovery.
Um, it took me to the NOVA web page.
Mod this reply down please.
--- Journals are boring; Go to my web page instead
True enough, but then at the time the only comparison _were_ watches, even though it is a bit larger. The technology was of the same class, which is why the judges had so much problem with it. They had no way comprehending the technology of a "watch" on steroids
"It is a greater offense to steal men's labor, than their clothes"
There are now a number of radio controlled watches on the market. They may not be accurate to eight seconds in six months but every night they tune into WWVB (in the USA, there are european models as well) and set themselves to UTC. If your reception is good they stay within one second of UTC.
burris
(chime head)
do bot discount the utility of knowing where you are at. the modern stock market came up because bizzes were able to trade and do shit like predict the weather and their upcoming returns.
:when my ship comes in."
Investment in the future used to be a non-rational thing. Due to the cultural and religious shit that was impressed upon your kids, you could count on their supporting you in their old age.
When the advanced navigational techniques of the 16th and 17th centuries were developed, people could predict their futures. They would say,
When my ship comes in sounds antique and slow, because a ship could take 2-3 years between leaving, laden with cargo, and returning, bursting with trade.
But, compared to the generation-long gambles on farms and marriages (the prominent speculations of their time), a ship coming in was as rapid a return on investment as a new technology can be today.
It's great to know where we are - exactly where we are, in physical time in space. I am in awe of it, myself. Place yourself in the proper context of history, and you will know the context of your own experience.
Goat sex free since 2001
Clocks in heavier gravitational fields tick at a slower rate.
Clocks in faster relative motion tick slower.
So:
A clock at the equator ticks slower than a clock at the north pole, because the relative velocity of objects at the equator is higher than those at the poles (the axis of spin) due to earth's rotation, but,
The equator clock will tick faster because it's located farther from the earth's center of mass (due to earth's spin, it bulges a bit in the middle) resulting in slightly lower gravity- and the effects don't always cancel each other out.
So then,
Relativity predicts that atomic clocks onboard GPS satellites will tick faster by about 50 microseconds per day (compared to ground-based clocks), due to the weaker gravitational field in orbit, but,
They also will tick slower by about 7.2 microseconds per day, due to the satellites' orbital velocity.
GPS's designers compensate for this by changing base time rate for the clocks onboard satellite.
Fun facts:
The cesium atomic clocks onboard GPS satellites are accurate to about one nanosecond, and light travels about one foot in one nanosecond. Hence, the best accuracy of GPS is about one foot.
GPS satellites have been used to experimentally verify that light moves at constant speed at all times/locations visited by earth.
And there are other confirmed predictions as well. One other I've heard is that GPS's radio signals experience frequency shift due to earth's gravitational field (photons want top accelerate but can't surpass C, so the acceleration energy increases their frequency) and this had to be compensated for as well.
Time be time.
Big Daddy, Johnny, Burp, Aunt Zelda, Scott, Slurp, Big Momma
I've tuned my digital to accuracy within 10 seconds a year, but this is at room-temperature. The quartz crystals used in modern watches (be it digital or analogue) are quite sensitive to heat and a few degrees can alter accuracy plus or minus several seconds a month. (I'm a watchmaker by trade, so we have the equipment to do this, and I'm using a digital because I require the convenience of some of its additional functions over my Omega automatic)
Many (most in fact) modern quartz watches by default are not overly accurate, even expensive ones often can be out by as much as 2 minutes a month. If you're lucky they have a trimpot on the circuit - most don't.
I confess I haven't seen the movie. I hope the movie didn't say the first 3 clocks didn't work at sea.
The H1 worked quite well during its sea trial. Harrison could have won the Longitude prize based on the trial of the H1 if he hadn't been such a perfectionist, and declared he could do even better, thus putting off an immediate financial gain. By the time the H2 was ready, there was a change in leadership at the Royal Observatory, now hostile to Harrison's efforts.
(I'm writing this from memory, so I don't remember the details. I believe at least 3 of the clocks were tested at sea, some under conditions intended to make them look bad, such as not being wound consistently.)
It took over 45 years to develop a watch that kept time accurately at see. And loosing over a second a day of accuracy was considered accurate!
It is amazing to think about the rate at which technology is improving. The changes we see in our life time are clear evidence of an acceleration in the rate at which technology is advancing. It was only since about the time of Jules Verne that technology has begun to change rapidly enough that humans recognize its effect on society. It was this recognition that was necessary to give birth to speculation about the effect of technology on the future, otherwise know as science fiction.
[news for me, stuff that doesn't matter]
They are at the greenwich museum. The early clocks were made mostly of brass so they are big shiny metal things. With enough Lego's you could make your own working copy.
The Museum is in Greenwich England. Its at 51 degrees, 28 minutes 38 seconds north of the Equator but I don't remember what its longitiude is but its close to London.
Mechanical clocks and watches are still hand manufactured by a company in sweeden after 200 years. They are accurate up to 1/10 of a second per week and the spring mechanisms have gotten so advanced that they go for a month without rewinding them. This may not sound so impressive in a large clock, but consider that this is all done in a watch! The only downside is due to the lack of trained watchmakers and the fact that these are all handmade, each watch can run you several thousand dollars! But think of all the money you'd save on batteries.
Pretty interesting, nonetheless.
pr0n - keeping monitor glass spotless since 1981.
The DVD *was* available, and may be again as the video is being (re-?)released and available from Amazon (DVD/VHS) and also Blackstar.
insignificant sig
I haven't been able to find a picture of H5 anywhere. Is it still in one piece?
IIRC from reading Longitude, some of Harrison's earlier models (perhaps as early as H1 or H2) actually performed more than adequately during sea trials. As for certifying the results of the sea trials of Harrison's clocks (and giving Harrison a rather hefty prize), the Board of Longitude never actually did this due to alot of political Chicanery (there were astronomers on the board who favored a Rube Goldberg method of measuring the moons of Jupiter (Saturn?))
A bit of trivia, I was watching My Fair Lady recently and if you remember the foreign accented professional rival of Higgins at the Diplomatic Ball is revealed to be the affected son of a provincial watchmaker who becomes rich. I assumed this was an allusion to the Harrison episode (he eventually did get a huge prize awarded by the King).
It is by coff... er, will, alone I set my mind in motion...
Mechanical watches are made by dozens of companies today, including Swiss Rolex, Omega, IWC and dozens of others, even Swatch. Even Seiko makes mechanicals (although mostly for the Asian market). The Chinese make a bunch of cheap movements and the Russian company Poljot makes an interesting line of affordable watches. Accuracy ranges from +/- 1 second per day on high-end Swiss watches to +/- 20 seconds per day on the Russians. In general anything under +/- 6 seconds per day is considered good. However, there can be a great deal of variation from watch to watch. Rolex, Omega and other mass market companies do little or no hand work in their mass market lines. When you get to a company link JLC, and others, every watch gets some hand fit and finish. However, none of them can be wound only once per month. Most have about a 40 hour power reserve. A few have an 8 day reserve (notably an IWC, and an Eberhard. Of course just about every company offers an automatic watch that is wound by the movement of the wrist through out the day. Those watches should "never" need winding if worn every day or two. Everything you ever wanted to know about mechanical watches can be found at Timezone. Be forewarned, most of these guys think of watches under about $5,000 as "mid priced".
Even if the quartz watch is not accurate if its drift is known and charted then over a year the watch will win with the corrections reliably applied
That is the crux of using time for navigation - time piece accuracy is not important, consistancy is. You need a timepeice that has a known correction factor, so you can determine the correct local time. That is why we had the same quartermaster wind the chronometer the same number of times at teh same time every day - to avoid changing the mechanical response of the device - keeping the correction factor the same. We never told time with it, but it was vital when shooting the stars.
I'm a consultant - I convert gibberish into cash-flow.
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Harrison's "gridiron pendulum" DID compensate for temperature variations very well. He used concepts from this in developing the H4. It's really quite remarkable for its day, when you consider that modern clockmakers don't bother to include this near-250-year-old technology.
There's a reason for that: it makes such a clock terribly expensive. Few people have need for such an accurate chronograph: need does not justify the cost. Really, the only people who have such a need are those who depend on a consistent time source over a long period, typically mariners. Most mariners now receive a time signal from a radio tuned to an atomic clock (which is really all GPS is), so they don't need a consistent chronograph.
H4 is surprisingly accurate, but not nearly as accurate as Harrison's longcase clocks, which varied by less than a second per month, at a time when a "good" chronograph varied by minutes per day.
Also interesting is the carriage house clock which has been running continuously for something like 240 years, having been stopped for cleaning only once and never for repair, and never lubricated.
Harrison's cabinetmaking skills are what led to his ability to make such fantastic clocks: it sounds strange to use wooden gears, but the woods chosen for the gears are extremely durable and self-lubricating.
Ignoring the technological merits of the invention, "The remarkable, unique Harrison clock LIVES".
I read the book, the illustrated version. You should, too. The person who said "The...clock LIES" obviously has never read the book.
Give me my freedom, and I'll take care of my own security, thank you.
Hmm. My understanding was that the award was for developing a solution to accurately determining longitude by whatever means.
It was theorized that an accurate and consistent clock could be used to determine longitude, however none had been made at that time so it could not be proven. Other solutions proposed involved various methods of celestial and solar navigation, but each of those solutions proved to have critical shortcomings.
With H4, Harrison was able to prove in sea trials that an accurate chronograph could be used to determine longitudinal position with acceptable accuracy.
Give me my freedom, and I'll take care of my own security, thank you.
Clocks below you tick more slowly, and clocks above you tick more quickly. This would be true even in a uniform gravitational field. Of course, the gravitational field around the Earth isn't uniform, so clocks below you tick more and more slowly the more down they are. So, there's a linear change and a nonlinear change. Fortunately, the linear part can be compensated with a constant factor, so it doesn't require much math. Also, the nonlinear part isn't so great as long as you are on the surface, and you can't get the signals in deep mine shafts anyway.
Each GPS satellite has two cesium and two rubidium atomic clocks on board. Belt, meet Suspenders. Suspenders, meet Belt.
burris
the death toll in London and its environs from V1 and V2's was horrendous
Nah, not really. I mean, one nearly got my mother's family so I shouldn't make light of it, but on average I think each V2 killed one person. Not sure about V1s, but you could hear those coming, or rather, when you stopped hearing them buzz, they were coming.
Normal bombs were much worse - total civilian dead in UK was about 146000. Of course, this is in turn nothing like as bad as Germany - 2.3 million civilian deaths from bombing - 80000 in one night, for example.