Tag Archives: clock

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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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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Hey, what time is it?

We’ve talked about telling time with sundials and water clocks and hourglasses. Those things are a headache to carry around. Mechanical clocks, like a pendulum clock, wouldn’t be invented until 1637. What if you’re traveling around in ad 800—how do you know what time it is?

One way to tell time was this fantastic little device called an astrolabe.

This sketch is based on a beautiful antique brass astrolabe.

Wherever you happen to be, if you can see the Sun or the stars, you can tell the time if you’re carrying an astrolabe with you. The main feature of an astrolabe is a flat map of the sky—with the stars and planets on a grid. The grid—called a climate—shows the sky as it appears in your part of the world. It’s circular and fits into a circular frame, called the mater (Latin for ‘mother’). On top of the climate is the rete (Latin for ‘net’), an openwork circular plate with pointers that you can line up to point at the Sun or a specific star on the climate. On top of that is a sighter—a straight arrow kind of piece. All these spin on the same axis. You pick a star, adjust the rete to point at your star on the climate, and hold up the astrolabe and sight the actual star along the sighter. When the sighter lines up with the star, you can read the time with remarkable accuracy. Here’s a video showing how it’s done. This guy even made his own astrolabe. And here’s more.

Here’s a website that explains how to use an astrolabe and even gives you pdfs you can download and print to make your own.

Read this now! Time is running out!

Hourglasses are good timers that are easy to use, so they’ve been part of people’s lives for centuries. My mom used to have a little one that measured 3 minutes—just right for boiling an egg.

The hourglass became a symbol for time itself, and just how quickly it seems to pass. Go into an old cemetery and you might see one carved into a tombstone—eeek!

On some computers a little icon of an hourglass shows up to tell you that your program is still loading.

By golly, I would have committed murder to own that Wizard of Oz hourglass when I was an art student, How about the lucky prop artist who got to design it!

If you ever saw the old Wizard of Oz movie with Judy Garland, you’ll remember that terrifying big hourglass that belonged to the Wicked Witch of the West. Here’s a website that tells how hourglasses are made. This one’s good, too.

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Hourglasses

An hourglass is a device that measures time. It’s two glass bulbs joined together by a skinny neck. There’s sand inside, so when you set the hourglass with the sand-filled bulb on top, the sand trickles through the neck into the empty bulb below. The hourglass maker put in exactly an hour’s worth of sand, so when the top bulb is empty, one hour has passed. The whole contraption is contained in a frame so it can be stood on either end.

Hourglassses are sometimes called ‘sand clocks,’ but they’re timers. Remember the early Egyptian water clocks? They were timers, too, until Ctesibius figured how to make clocks out of them.

Legend says that a French monk called Liutprand (Lee-UT-prond) invented the hourglass in the 8th century ad. There doesn’t seem to be solid evidence to support or deny that. Charlemagne is supposed to have owned a 12-hour hourglass—Liutprand was French, Charlemagne was French, so maybe there’s a connection? And I guess I’d have to admit that at 12 hours, that hourglass was a clock.

https://www.guinnessworldrecords.com/world-records/first-hourglass

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Ancient Egyptian water wristwatches never caught on