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Interesting features of John Harrison's sea clocks

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Re: Interesting features of John Harrison's sea clocks

#31

Post by mauvehaus »

jstanley wrote: post #27
JKCalhoun wrote: post #26

Earlier quoted context omitted.

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.

Re: Interesting features of John Harrison's sea clocks

#32

Post by canjobear »

labcomputer wrote: post #8
anfractuosity wrote: post #3

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…

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…

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

Re: Interesting features of John Harrison's sea clocks

#33

Post by tbensky »

jstanley wrote: post #25
tbensky wrote: post #21

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 h…

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).

Re: Interesting features of John Harrison's sea clocks

#34

Post by AlotOfReading »

canjobear wrote: post #32
labcomputer wrote: post #8

Earlier quoted context omitted.

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…

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.

Re: Interesting features of John Harrison's sea clocks

#35

Post by jstanley »

tbensky wrote: post #33
jstanley wrote: post #25

Earlier quoted context omitted.

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.

Re: Interesting features of John Harrison's sea clocks

#36

Post by jstanley »

AlotOfReading wrote: post #34
canjobear wrote: post #32

Earlier quoted context omitted.

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.

Re: Interesting features of John Harrison's sea clocks

#37

Post by kwhitefoot »

tbensky wrote: post #21

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 h…

XRF?

Re: Interesting features of John Harrison's sea clocks

#38

Post by rcxdude »

hyperthesis wrote: post #28

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 h…

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.

Re: Interesting features of John Harrison's sea clocks

#39

Post by tbensky »

kwhitefoot wrote: post #37
tbensky wrote: post #21

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 h…

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).
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