Interesting features of John Harrison's sea clocks | Hacker News Reader

Interesting features of John Harrison's sea clocks

incoherency.co.uk

100 pointssurprisetalk38 comments

Happy to see this post on HN. As a college prof, I've spend many years studying the history of 1700s navigation and taking student groups to Greenwich to see and study H1 (H2, H3 and H4). I love these clocks and all of the stories behind them. The serious enthusiast will find a lot of technical details on the Harrison's clocks in this book https://www.amazon.com/Marine-Chronometers-Greenwich-Catalog... and this one https://www.amazon.com/Marine-Chronometer-Its-History-Develo.... I've also collected all of my pedagogy on 1700s navigation into a this book: https://www.amazon.com/Longitude-Time-Navigation-Tom-Bensky-... where I dive somewhat into the innards of H1. To answer another post: H1 has been fully disassembled and reassembled with XRF done throughout.

"...fully disassembled and reassembled with XRF done throughout.

Well, hopefully, that answers my point about the clocks' materials and an XRF analysis. Did that reveal anything of significance?

From points/questions raised by James Stanley and my ignorance of this recent work it seems these facts ought to be more widely known. (Ouch, the price of Marine Chronometers at Greenwich unfortunately has to mean that information is confined to Diehards.)

Is there a way to buy your "Longitude, Time and Navigation" book as a physical book?

Hello and thanks for our interested. There's a paperback version here: https://www.amazon.com/Longitude-Time-Navigation-Tom-Bensky/... (same ed. as the Kindle version).

Neat, thanks! I've ordered a copy.

XRF?

XRF=x-ray fluorescence. You shoot X-rays into a metal, typically the gamma rays from an Am-241 source. This causes atoms in the metal to fluoresce their own gamma rays that are a (somewhat) unique signature of the atom itself. So in sum, XRF allow one to non-destructively determine the atomic constituents of a bulk material (but 'heavy' materials..heavier than Silicon for example).

Fascinated by "lignum vitae" mentioned several times. A little googling and I'm even more intrigued by this special wood.

Example, one of the first results to come up:

https://www.core77.com/posts/25224/lignum-vitae-wood-so-bad-...

Sadly it is an endangered species so it is illegal to trade now, I understand the best way to get it is to buy antique crown-green bowls and cut them up.

Also, lignum vitae used to make good bearings, not only is it hard-wearing, 'waterproof' and rot proof when compared to most other woods but also it's self-lubricating.

It's a wonderful and useful timber, it's a damn shame it's been necessary to add it to the CITES Treaty (as it's such a slow grower).

Didn't know Crown Green Bowls was a game — and I assume it's the balls that are made from Lignum Vitae.

https://en.wikipedia.org/wiki/Crown_green_bowls

Yes, the balls are (historically) lignum vitae. I don't know why they're called bowls instead of balls.

Like many quirks in English, we can blame the French:

https://www.etymonline.com/word/bowls#etymonline_v_32538

Boule is the modern French name for a likely similar game (I don't play either). And of course the Italians have bocce.

I had no idea that Harrison's clocks were so complex. His obsession with friction and changing conditions was clearly necessary, in retrospect, but WOW. The extensive use of "anti-friction" wheels, and even portions of a wheel, is very cleaver, but at some point the things look like he's trying to win the clockmakers version of an Obfuscated C contest[1].

No wonder the Longitude Board gave him such grief. It must have seemed like he was deliberately trying to hide secrets from them. Unless you understood how important friction and temperature were in causing the drift of clocks at that time, it would have all seemed like unnecessary complexity.

[1] https://ioccc.org/

Perhaps winning an Obfuscated Clock contest would keep copycats at bay and allow you a contract to service the devices for the remainder of your life.

> like he was deliberately trying to hide secrets from them

It can't have helped that by all accounts he was extremely verbose in spoken communication, and almost impenetrable in written communication.

Thought this was very interesting - https://www.theguardian.com/science/2015/apr/19/clockmaker-j...

It mentions - "scientists revealed that a clock that had been built to the clockmaker’s exact specifications had run for 100 days during official tests and had lost only five-eighths of a second in that period."

While "a typical quartz clock or wristwatch will gain or lose 15 seconds per 30 days" (https://en.wikipedia.org/wiki/Quartz_clock#Accuracy). You can get temperature compensated quartz watches etc. though, which perform better apparently, but found it pretty interesting that a mechanical clock can best standard quartz technology.

That's certainly hasn't been my experience, all my watches have kept an accuracy if a few seconds over a year.

That greatly undersells the accuracy of quartz watches. An individual unit may gain or lose 15 seconds per month (though that level of inaccuracy would be unusual), but that given unit will consistently gain or lose almost the exact same amount of time every month.

After you have measured the relative speed of a given quartz movement, it becomes trivial to obtain the correct time (for, e.g., navigation purposes).

For what it’s worth, the NBS and US Naval Observatory switched from mechanical (pendulum) clocks to quartz during the Great Depression.

If it's known to lose a reliable amount of time per month, can't you recalibrate it to make it that much slower?

It's a pain in the butt. Recalibration means physically trimming the crystal. Which side you trim depends on whether it's too fast or too slow. It's really fiddly though (especially too slow, which requires grinding the ends down instead of the face). Even in the 20s they would have been producing these dozens at a time with a big lapping wheel, so they could just pick a better crystal from the same batch.

It would be possible to make the IC adjustable (e.g. a tiny microcontroller) so that it could compensate for the difference without having to modify the crystal.

If you're interested in the subject, the book "Longitude" by Dava Sobel (mentioned in Resources) is a very good read with lots of historical perspective on how these clocks were built.

Seconded! It is a wonderful book. Also an easy read and not very long.

I can't agree more, I've not seen a better book on the subject and Sobel's writing makes it an enjoyable read (I still have my copy of it).

Made into a four-part mini-series with Jeremy Irons and Michael Gambon:

* https://en.wikipedia.org/wiki/Longitude_(TV_series)

* https://en.wikipedia.org/wiki/Longitude_(book)

Very enjoyable (albeit long) and available on YouTube: https://www.youtube.com/watch?v=LHvt48S9l4w

I was lucky enough to come across this book in elementary or middle school and found it absolutely mind blowing. In retrospect it exposed me to what are still among the most important ideas sloshing around my brain:

1. The realization of how much of the world has to be “invented.” Latitude and longitude didn’t strike me as an invention, but they are, and more interestingly longitude specifically is a conceptual invention that more or less had to sit downstream of a rather immense physical invention (Harrison’s clocks).

2. “The world has a surprising amount of detail”: as evidenced by looking at H1, H2, etc… there’s a lot you have to account for to achieve the apparently simple task of measuring time aboard a ship.

3. The social components to invention/discovery/progress: The competitions, funding/lack thereof, the need for “evangelism” around the different approaches, the need to find patrons (VC’s basically) to create a breakthrough, etc.

This book would make a great gift to an intellectually-inclined young person in your family!

I saw Harrison's clocks years ago during a visit to Greenwich but there was no way I could have fathomed out how they worked from such a short visit (even if I were able).

This story surprised me because I'd have thought by now that Harrison's clocks would have been analyzed to the nth degree and copies of them made given their historical significance.

In recent years we've seen considerable efforts made in trying to reverse engineer the Antikythera mechanism so it's surprising a similar effort hasn't gone into a full understanding of these wonderful clocks, especially given that we have them both intact and in good combination.

It seems to me we should not only have a full mechanical understanding of these clocks together with a good rationale for why Harrison tackled the problem as he did but also that an x-ray fluorescence (XRF) analysis should be done on the metals used in their construction.

Assuming Harrison used the best materials available in the Eighteenth Century then an XRF analysis would give us a better understanding of the composition of those materials and of their production but also of the metrology methods in use in Harrison's time.

These old ship clock were the peak of engineering at the time. Accuracy was very much a necessity, being one second off London time means a 4 mile error when determining position IIRC.

I wonder if this is the first example of government IT project specification failure?

What the navy wanted was a simple way to calculate a ship's position - which is exactly what they ended up with. What they didn't anticipate is that each device would cost twice as much as the ship it was going on.

That just increases the cost of the ship. It has become part of the ship’s navigation system. Not really a failure, just a justifiably expensive enhancement.

There is a great Map Men Episode about the Longitude Problem[1]

[1] https://www.youtube.com/watch?v=3mHC-Pf8-dU

After reading Dava Sobel's book 20 years ago I made sure to go to Greenwich to see the clocks when I was in London in 2005. They are both amazing engineering and works of art.

If he made the most accurate clock in the world, how would he know?

The prize here was for most accurate at sea, so compare with more accurate land clocks. But in general?

If salt should lose its savour, with what shall it be salted?

... tried feeling bits of himself to see where he might be hurt. Wherever he touched himself, he encountered a pain. After a short while he worked out that this was because it was his hand that was hurting.a

I think he watched for a particular star to disappear behind his neighbour's chimney, from a fixed vantage, on the understanding that this should always take exactly 1 day, and by measuring how many seconds have elapsed on your clock you know how well your clock has kept time over the previous day.

You build two or three of them and compare them to each other. That's how a lot of pushing the boundaries of stability or precision is evaluated.

Also worth checking out the authors other posts and projects

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