So long, and thanks for all the longitude

After 19 years of tinkering John Harrison finally worked all the bugs out of his time-piece, the marine chronometer. To prove its reliability, he took it on a voyage from England to Jamaica.

“Harrison conducted a round-trip test at sea from Britain to Jamaica through the Caribbean via the Atlantic from 1761 to 1762. The watch lost only 5.1 seconds in 81 days, reaching the level of accuracy required to receive a £20,000 reward.

But just then a rival named Nevil Maskelyne, the head of the Greenwich Observatory and a member of the Commissioners for the Discovery of the Longitude, was vying to receive the same award for his astronomical theory. Maskelyne refused to recognize Harrison’s success. To Harrison’s chagrin, he was granted only a few thousand pounds.”
https://museum.seiko.co.jp/en/knowledge/inventors_02/

Well, how do you like that? This is why Maskelyne is always cast as the villain in this story. Seems like a conflict of interest to be on the Longitude Board if you’re also a competitor for the prize. It would be quite a while before Harrison finally got his reward—and that was only because King George III* stepped in to make the Board pay up.

My pal Kathryn Lasky wrote an award-winning book about John Harrison’s story, The Man Who Made Time Travel:
https://www.kathrynlasky.com/books/book/the-man-who-made-time-travel

Kathryn and I worked on Two Bad Pilgrims together. https://www.kathrynlasky.com/books/book/two-bad-pilgrims

* George III ruled Great Britain during the American Revolution. He was an enthusiastic friend to the Royal Navy. It was George who decreed that his sailors could toast the king’s health sitting down, because the deck-beams in the wardroom (officers’ dining room) were so low you’d likely crack your head if you stood.

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It’s 2 metals in 1!

This next part is crazy. I don’t know how Harrison dreamed up this idea. I don’t know how it’s even possible. Maybe a reader with experience in welding can help me out.*

Because metal springs are susceptible to temperature changes, which make them less reliable and accurate, Harrison invented the bimetallic strip. It is 2 metals, like steel and brass, welded together.

Did you get that? It’s possible to weld, or fuse, or something, steel and brass now. The watch’s mainspring needs always to be springy. When it’s cold, the spring becomes too stiff. When it’s hot, the spring becomes too loose. Harrison fused two metals together—steel and brass—in a spring. If the steel were too tight, the brass would keep it loose. If the brass were too loose, the steel would tighten it up. This way the spring would keep the same springiness no matter the temperature.

* This weekend I had the pleasure of consulting 2 engineers, my sister’s boyfriend Dave and my nephew Andrew. They tell me with enough heat, two different metals can be fused together. The two metals would be hammered together many times under heat until they were one. Andrew added that it’s only air molecules that keep metals from fusing together in the first place.

https://pineknollclockshop.blogspot.com/2012/07/making-clock-spring.html

http://www.edubilla.com/invention/bimetallic-strip/
https://books.google.com/books?id=6nBaPUlmSaEC&pg=PA546&lpg=PA546&dq=harrison+bimetallic+strip+spring&source=bl&ots=HjZiOZ5FI-&sig=ACfU3U1JQe0j77cZ9JM0nte1fIEWqFmR6g&hl=en&sa=X&ved=2ahUKEwjk2dOl083pAhUKAZ0JHafLCbcQ6AEwDXoECAwQAQ#v=onepage&q=harrison%20bimetallic%20strip%20spring&f=false

Thermobimetals

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

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Hot- and cold-running time

After breaking his heart trying to perfect a clock to keep accurate time on the high seas, Harrison refused to give up. He turned instead to perfecting a watch.

No more worrying about pendulums!* Harrison got straight to work on a ship’s timepiece that uses a metal spring and balance wheel. That good ol’ metal spring and balance wheel would do the trick. No problems with a metal spring and balance wheel, no sir.

Well, maybe one small problem. When metal is warm, it expands slightly. When it cools, it contracts. This spring-powered timepiece was expected to be used in both tropical and arctic conditions. The temperature would change the character of the metal, which would make it less reliable, which would make the timepiece less accurate.

Now what?

* Okay, okay, pendula for you Latin nerds.

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Watch works

You remember an escapement is a way of slowly releasing energy that powers a clock. A watch didn’t use a pendulum for its escapement—it used a coiled metal mainspring and balance wheel. You wind the spring tightly and the spring wants to unwind. As it unwinds, its energy is released to oscillate the balance wheel back and forth. As the balance wheel oscillates, it swings a little fork side-to-side which stops and releases a gear. This is the watch’s escapement. No matter how the watch is bounced around, the spring keeps on releasing energy at a steady, reliable pace.

The wound-up spring wants to uncoil, to expand. As it expands, it pushes and turns the balance wheel. But the balance wheel is weighted so it only turns so far and then it swings back. When the balance wheel swings back it tightens the spring again. The wound-up spring wants to uncoil, to expand. As it expands, it pushes and turns the balance wheel. But the balance wheel is weighted so it only turns so far and then it swings back. When the balance wheel swings back it tightens the spring again. (Repeat over and over and over and…)

https://sciencing.com/analog-clocks-work-4912745.html
https://www.jcwa.or.jp/en/time/qa/qa07.html
https://www.wixonjewelers.com/education-type/watch-movements/
https://malalan.eu/how-it-works-escapement/
This beautiful video has French narration but the visuals are self-explanatory: The escapement animation starts at 3:30.

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Keep on trying

With John Harrison’s innovations, his clocks were more precise than any clock had ever been. The bad news was: his clocks still weren’t precise enough to win the Longitude Prize. “The amount awarded under the Act was commensurate with the accuracy of the invention in determining longitude: 10,000 pounds for 1 degree, £15,000 for 2/3 of a degree, and £20,000 for 1/2 of a degree.”

Rather than give up, Harrison tried something different. Instead of designing a precision clock, he turned to designing a precision watch. A watch is an analogue or mechanical (not digital) timekeeping device small enough to carry around with you. You can hold one in your hand. People attached an end of a chain to their watch, attached the other end to a belt loop or button-hole and kept the watch in a pocket.

Random side-note: A pocket-watch and chain play a part in the O. Henry short story, The Gift Of The Magi. https://www.enotes.com/topics/gift-magi Spoiler alert! DON’T unlock the summary until you’ve had the pleasure of reading the story itself.

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The Grasshopper

Since John Harrison was a cabinet-maker, he knew all about constructing things from wood. In fact, the first clocks he built as a young man had all-wood mechanisms. When designing a ship’s clock, he replaced many metal parts with wooden ones. Harrison used an oily wood named Lignum Vitae which didn’t need to be lubricated. Then, he designed a brand-new kind of escapement: the Grasshopper. The Grasshopper escapement worked with way less contact with the clock’s gears, which meant less lubrication was needed.

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A dumbbell idea

The problem with clocks in the 1700s: the ship’s rocking messed up a clock’s pendulum movement; the salty sea air corroded the metal gears; changes in temperature and humidity made metal clock parts expand & contract. All these things made a clock inaccurate—it was too slow or too fast.

Harrison came up with some innovative ideas to counter-act these problems. The first one was a dumbbell-style of pendulum. Instead of a rod with a weight at the bottom swinging from an axis, Harrison put the axis in the middle of 2 rods with weights at top and bottom—then he connected them with springs so they would keep moving back and forth no matter how the ship bounced around.

Standard-issue pendulum at the left; Harrison’s dumbbell movement at the right.

Start at 1:00—

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The clockmaker

In our last post you saw how to find your location by observing the moon and stars to calculate lunar distance. The object is to know both your local time and prime meridian time, or Greenwich Mean Time. A navigator needs to be an astronomer and a math whiz to use this method.

You may have asked yourself, “Wouldn’t it be easier to keep 2 clocks aboard the ship—one showing Greenwich Mean Time and the other kept to local time?” That’s an excellent question and I’m glad you asked it. In fact, that’s the question John Harrison asked.

John Harrison, English inventor and horologist, 1767.

John Harrison was a cabinet-maker with a side business building and repairing clocks. To win the Longitude Prize, he went for a straightforward solution: build an accurate clock that always, ALWAYS showed precisely the correct time in Greenwich.

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Lunar distancing

Okay, let’s say you’re in a rowboat at night with some friends—and you haven’t seen land for a while. You’re LOST. Nobody’s getting a signal on their cellphones, so you don’t know where you are. The strange old lady at the boat rental place left nothing but a weird navigational device; a map; and a book of star charts in the boat’s locker. Your friends are getting panicky and start blubbering. What do you do?

Because you’re a devoted reader of The Western Civ User’s Guide to Time and Space, you know exactly what to do. You tell your pals to stop their noise so you can concentrate. It’s a clear moonlit night, so you can see the moon, stars, and the horizon. You pick up the lovely brass sextant and set its sights on the moon—and a star, how about Regulus, just there to the left? You measure the altitude (how high above the horizon) of the moon; the altitude of Regulus; and the distance between them. You figure the angle of the 2 lines from you to the moon and you to Regulus. You do this measuring not in feet or miles but in degrees.

From the moon’s altitude you know what time it is (http://www.astrotulsa.com/page.aspx?pageid=27, scroll down)—and your latitude, too (http://www.lewis-clark.org/article/1268). Knowing the distance from the moon to Regulus, you pick up the book of star charts and find that lunar distance for your local time. Run your finger down the chart to find what time it is in Greenwich, England where it’s zero degrees longitude. The difference in time will tell you your longitude (15° for every hour, 1° for every 4 minutes). Find your latitude and longitude on the map and start rowing home. You don’t even need a compass—you keep Polaris, the North Star, above your right knee as you row.

You get safely back to land! Your friends can’t believe you saved the day with that stupid book. The lady at the boat rental gives you a wink and you all go home to bed.

This is how Nevil Maskelyne proposed finding your position while at sea.

https://theskylive.com/moon-info
https://www.rmg.co.uk/discover/behind-the-scenes/blog/time-solve-longitude-lunar-distance-method
I haven’t read these, but here’s a short list of books about ocean-going girls: https://books.google.com/books/about/From_Cabin_Boys_to_Captains.html?id=wBDWSAAACAAJ

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The astronomer

Gerard van der Puyl’s portrait of Nevil Maskelyne—just gorgeous. What a painter.

Nevil Maskelyne was the fifth Astronomer Royal at Greenwich Observatory. He proposed using the positions of the stars, planets and their moons as a method of calculating your position on Earth, just as Galileo had proposed using the moons of Jupiter as a universal clock. Maskelyne was a hard worker and determined to win that Longitude Prize. He believed that with accurate charts of stars’ positions, you could find longitude anywhere on Earth. At the Observatory, Maskelyne and a team of astronomers ‘worked feverishly through the year 1766, preparing tables for the new Nautical Almanac and Astronomical Ephemeris. Published first with data for the year 1767, it included daily tables of the positions of the Sun, Moon, and planets and other astronomical data, as well as tables of lunar distances giving the distance of the Moon from the Sun and nine stars suitable for lunar observations.’

Here’s Maskelyne in a nutshell:

Oops! Okay here’s Maskelyne in brief:

Sorry! Sorry! Here it is: Maskelyne’s idea was that you have a point zero of longitude—the Prime Meridian—as a reference point for time. Longitude is time measured in degrees. Each hour is 15° of longitude. When you’re at sea you take 2 measurements: the Sun’s position and the moon’s position. The Sun’s position tells you what your local time is; you find the moon’s position (the distance from the moon to one of the 9 suitable stars) in your almanac to tell what time it is at the Prime Meridian. The difference between your time and Prime Meridian time can be converted into degrees, which gives you your longitude.

You’re probably thinking: ‘Okay, Manders, how exactly do you measure the Sun and the moon? Usually when the moon’s out it’s nighttime.’ That’s an excellent point! You measure the Sun during the day and adjust the ship’s clock to the local time, maybe?

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

https://academic.oup.com/astrogeo/article/56/6/6.33/241325

https://www.rmg.co.uk/discover/behind-the-scenes/blog/time-solve-longitude-lunar-distance-method

https://www.newscientist.com/article/mg21028141-500-into-the-breeches-a-makeover-for-longitudes-villain/

https://prabook.com/web/nevil.maskelyne/3771685#

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