Monthly Archives: February 2020

The amazing fantastic clock of Piazza San Marco

In 1493, the Venetian Republic commissioned the clockmaker Giovan Paolo Rainieri, from the town of Reggio Emilia, to design and build a clock. This clock would be big and beautiful and expensive—a tower would be designed and built on Saint Mark’s Plaza to house it. It would face the lagoon and the sea beyond, so the whole world could see how prosperous was Venice.

If you visit Venice you can see the Rainieri clock. Its face is decorated in gold and lapis lazuli (a mineral you make blue out of—blue paint ain’t cheap); the hand tells what hour it is and the current zodiac sign; above the clock is a statue of the Virgin Mary and Baby Jesus (made of gilded copper); twice a year a mechanical angel and three wise men parade in front of Mary and tip their crowns to her; above Mary is the lion of Saint Mark with his paw on the Gospel (the statue of the praying doge isn’t there anymore); and at the top, every hour two bronze giants ring an enormous bell with their hammers.

The entire contraption from top to bottom used a verge and foliot escapement to regulate the gears.

https://www.atlasobscura.com/places/torre-dell-orologio-venice-clock-tower
https://en.wikipedia.org/wiki/St_Mark%27s_Clock

https://en.wikipedia.org/wiki/St_Mark%27s_Clocktower

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Happy Fat Tuesday!

I used to make up these puzzles for my Sunday school class. Apologies to the JUMBLE® guys: Henri Arnold, David L. Hoyt and Jeff Knurek!

Speaking of libraries, I’ll be at the Grove City Community Library this Friday (2/28/20) evening 6:00-7:00 to talk about illustrating kids’ books. If you’re in the neighborhood, please stop by!

How to slow down a clock

How did they do it?

Those medieval clock-designers came up with a system to slow down the unwinding. First, they attached a gear around the drive-shaft that meshed with a couple of other gears. As you saw with Archimedes’ odometer, the ratio of gear sizes and number of teeth-per-gear can control how fast one gear turns another gear.

That still wasn’t slow enough, though. You want a clock to operate for at least 24 hours before you have to wind it again. How can you make that unwinding even slower?

The answer: an invention called an escapement. An escapement is a mechanical device that interferes with the gear. It actually stops the gear’s movement for a fraction of a second, then lets go for a fraction of a second, stops it, lets go, stops it, lets go, stops it, lets go. The first escapement was called the verge and foliot. The verge is a second shaft (not the drive-shaft) with two paddles, or pallets, set at 90 degrees to each other. These pallets interact with a saw-toothed gear which is powered by the drive shaft. As the drive-shaft turns the saw-toothed gear, one pallet stops the gear for a moment until the other pallet is pushed aside.

This stop-and-let-go motion is controlled even further by a bar at the top of the verge shaft, called the foliot. The foliot has a weight hung on each end so that inertia (the weights’ unwillingness to move) slows down oscillation of the verge-shaft. You can control how fast the foliot swings back and forth by moving the weights closer or farther from the center.

https://aapt.scitation.org/doi/10.1119/1.3479712




https://www.mpoweruk.com/timekeepers.htm
https://www.uh.edu/engines/epi1506.htm

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Mechanical clocks

Sometime in the 1200s mechanical clocks began being designed and built. When I say mechanical, I mean there are several moving parts in the design. We’ve already seen sundials and water clocks and hourglasses. Water clocks and hourglasses use the release of energy to tell time, as water or sand run out of one container into another. The mechanical clock is different—it uses the release of energy to make it run but has a system of gears and stops to control that energy.

Like those older clocks, medieval mechanical clocks use gravity to supply their energy. A weight is tied to a long rope that is wound around a drive-shaft. When you let go of the weight, the rope unwinds and turns the shaft. The drive-shaft has an arrow attached at its end to point to the hour on a circular clock face. So far, so good—but the drive-shaft will turn really fast for a few seconds, the arrow will whiz around the clock face and then you’d have to wind the rope around again. You still wouldn’t know what time it is. What you need for a clock is a slo-o-o-ow release of energy. How can you slow down the unwinding of that rope?

Sailing the ocean blue

As you know if you’ve been loyally reading this blog, silk and spices from Asia had become big business in Europe. European merchants who wanted to trade in the far East were finding overland routes through the MidEast and Asia too dangerous, or taxed to unprofitability, or closed off completely by the Ottoman Empire. In fact, the Ottomans were doing their best to expand their empire to include Europe.

The Venetians had a monopoly on the sea-routes that they protected with their navy. Other European cities who wanted to do business with the far East were shut out. They had compasses and maps and ships but had no way to get to the East.

Or did they?

Christopher Columbus was a sailor, chartmaker and trader from Genoa, Italy. He’d done some trading along the west coast of Africa. Columbus had studied Eratosthenes and reasoned that if Earth were round, he could travel west to reach the far East. To do that, he needed ships, money and royal patronage—the blessing of a king or queen.

King Ferdinand II and Queen Isabella I ruled the cities of Aragon, Castile, and Leon in Spain. Spain had been part of the sultanate, the Ottoman Empire, for nearly eight centuries. Ferdinand and Isabella wanted to reassert Christian control over their country—they had succeeded with military force early in 1492 at the Battle of Granada. Another way to take control might be to open up trade with the far East by working around the Ottomans. After a few interviews, Columbus persuaded Ferdinand and Isabella that he could take the back way around the globe to reach the East.

They finally gave him the green light and in ad 1492 Christopher Columbus began his voyage to the East Indies with the ships Nina, Pinta & Santa Maria.

The lovely little caravel—a Portuguese-designed ship like the ones Columbus used on his voyage

https://www.britannica.com/biography/Christopher-Columbus
https://www.britannica.com/place/Spain/The-conquest-of-Granada
https://www.newworldencyclopedia.org/entry/Fall_of_Granada
https://en.wikipedia.org/wiki/Caravel

If you like your history served with gorgeous illustrations, get your hands on Bjorn Langstrom’s book about Columbus. Mr Langstrom has written and illustrated 3 books about ships that I know of. See if your library has this one.

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Maps, we need maps!

As we’ve seen, Venice was hopping with trade on the Mediterranean Sea and beyond. With their compasses and astrolabes and lightly-built galleons, Venetian traders traveled all over the known world. Likewise, traders from all over the world stopped in Venice. Compasses work best with a map, so Venice’s map-making (cartography) business was booming.

In ad 1450, in a monastery in Venice, there lived a monk named Fra Mauro (Brother Mauro). Fra Mauro was an extraordinary cartographer and his map is the one you see pictured here. It’s about 6 feet across.

It’s not easy to recognize all the continents right away, because he drew it with North at the bottom. We’re used to seeing North at the top of maps. I’m not sure when it became standard practice to put North at the top. Over at the extreme right, you can see a little compass-rose with North pointing down. As you work your way left from there, you’ll see Spain and Portugal, the Straits of Gibraltar where Europe almost touches Africa, and the Mediterranean Sea where the boot of Italy is kicking up rather than down. The shapes of Africa and Asia are difficult to recognize, too. It would be a while before cartographers could accurately survey land masses. Africa is in the upper-right. Asia takes up almost all the the left half of the map.

The New World—the Americas and Australia—hadn’t been discovered yet.

Here’s an article about Fra Mauro, with some close-ups of his map.

How to not get lost

Here’s a simple compass

The compass was developed into a compact design. Instead of balancing an iron spoon or floating a piece of magnetized iron in a bowl of water, compass designers suspended a magnetized iron arrow on a thin metal pin over a round card with directions displayed on it. The arrow and card were put in a round brass housing to protect them. Brass can’t be magnetized, so the housing didn’t interfere with the arrow’s attraction to the north pole.

This compass is designed to be used on a boat. Instead of a needle, the entire card spins on an axis to point north. The compass is mounted on gimbals—the outside ring is mounted to the wooden box on the right and left sides. The compass is mounted to the ring top and bottom. This allows it to stay level while the boat bounces around on the waves.

Compass-makers put North, South, East and West (the cardinal directions) on their compass cards, then NorthNorthEast, NorthEast, EastNorthEast, EastSouthEast, SouthEast, SouthSouthEast, SouthSouthWest, SouthWest, WestSouthWest, WestNorthWest, NorthWest, NorthNorthWest and eventually all 32 points of direction.

Compass rose

Mapmakers began to indicate North on their maps so that you could line your map up with the compass’ arrow. This became the lovely compass rose you see on those gorgeous old maps.

This is the kind of compass my pals and I used in the Boy Scouts. The ring is aluminum, I think, and has 360 degrees marked along the bottom edge. The rectangular base is clear plastic so you can see a map through it. It also has a ruler along the side. They make ’em with a magnifying glass in the plastic now.

You’re never lost if you have a map and a compass. Sea-farers were the first to use this technology but it works on land, too! There’s a scene in the movie The Big Country (it’s about a sea captain who decides to settle in the old American West) where sea-captain Gregory Peck goes exploring the countryside for a few days and all the ranchers are worried sick that he got lost in the desert. Everyone is relieved when he rides back to the ranch without a scratch. “How did you not get lost?” they want to know. Greg can’t understand what the fuss is about. “I had a compass,” he says. An epic Western—great soundtrack, too.

https://www.nationalgeographic.org/encyclopedia/compass/

http://www.historyofcompass.com/compass-history/history-of-the-magnetic-compass/

https://www.smith.edu/hsc/museum/ancient_inventions/compass2.html

https://spectrum.ieee.org/the-institute/ieee-history/history-lesson-the-magnetic-compass

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More miles per galleon!

The magnetic compass appeared in Europe sometime in the late ad 1100s. No doubt compasses were traded along the Silk Road.

The compass was being used in the West at the same time Venice’s sea-trade flourished. Before the compass, sea-travel was limited to the few uniformly sunny months—June through September. The rest of the year sailors stayed home because they had no way to navigate. Let’s stop for a second to appreciate what was happening. China had the compass for centuries and used it to achieve spiritual harmony—chi—when they built houses or arranged furniture and gardens. The compass slowly moved west along the Silk Road—possibly it was thought of as a novelty item.

Meanwhile back in Venice and Genoa and other Mediterranean sea-faring towns, the merchants can only make money when the sun’s shining. They’re pacing back and forth and tearing their hair out because they have these new, flexible, easily-steerable ships; they have the merchandise; they have the sailors—but their ships can’t leave port for eight months out of the year because it’s cloudy!

Then, suddenly, miraculously, the compass drops into their laps. What do they do? They seize on it! They exploit it! Now mariners can go to sea, trade and make money all year round.

You’re probably thinking, “Hold on, Manders. What about that astrolabe-thinghy you were going on about a few posts earlier—how come sea-farers didn’t use that to navigate?” I have to admit, that’s a good question. Here’s the answer: If you can’t see the Sun or the stars, you can’t navigate with an astrolabe. The compass points North even when it’s cloudy. With it, the Venetians could find their way no matter the weather.

This is what happens when you have a free market. People want to trade, make money. When a new piece of technology comes along they figure out how to exploit that technology. A similar thing happened in the last few decades with the internet. The US military invented the internet for its own communications, but the business world seized it and transformed it into the world wide web.

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The Chinese invent the compass

A thin piece of magnetized iron in the shape of a fish (or a shallow boat) floats in water and points north.

The magnetic compass was invented in China sometime between the 2nd century bc and ad 1st century. They used it to make sure streets and houses aligned with the Earth in a harmonious way—what is called feng shui. The Chinese later figured out they could use a compass for finding their way on the ocean (ad 1040-44).

This carefully-balanced magnetized iron spoon points north with its handle.

How you can harness the awesome and terrible forces of the Earth’s core

We learned last post that the Earth’s core is surrounded by molten metal, which exerts a magnetic field around the planet. Some metals can be magnetized. They can be made into a magnet, so they exert a force on other metals without touching them. Iron and steel can be magnetized.

The thing about Earth’s giant magnetic field is that magnetized metals—if they can—try to line up with it. If you were to take a small piece of iron or steel (like a needle) and rub it a few times with a magnet, it will try to align itself with Earth’s North and South. You could make it easier for the needle if you float it on a piece of styrofoam or cork in a bowl of water. After the needle settles down it will point North-South. Congratulations! You built a compass.

Here’s what you’ll need: a bowl, water, a needle, a piece of cork or styrofoam, and a magnet. I got my magnet off of the refrigerator door. If you cut a slice off the cork, get someone to do it with a craft knife. Use a cutting board! Don’t cut it on your mom’s good dining room table. I don’t want angry messages in the comments section.

Rub the needle with the magnet a bunch of times.

Stick the needle halfway through the cork. It may be a good idea to put the butt-end of the needle on a cutting board and press the cork down onto it.

Fill the bowl with water and float the needle and cork in the water. After a little while the needle will point north-south.

https://www.wikihow.com/Make-a-Compass

https://www.siyavula.com/read/science/grade-10/classification-of-matter/02-classification-of-matter-08

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