Striking clock facts for kids
A striking clock is a special kind of clock that tells you the time by making sounds. It uses a bell, a gong, or another noisy device to announce the hours. Most striking clocks today use a 12-hour system. This means they strike once at 1:00 am, twice at 2:00 am, and so on, up to twelve times at 12:00 noon. Then, they start again, striking once at 1:00 pm, and continue this pattern until 12:00 midnight.
Long ago, the sound a clock made was more important than its clock face. The very first clocks struck the hours but didn't have dials to read the time. Mechanical clocks became popular in Europe in the 12th century. People needed them to ring bells for daily prayers. The first mechanical clocks were huge striking clocks. They were put in towers at monasteries or public squares. This way, their loud bells could be heard far away.
Some early clocks, especially in Italy, struck up to 24 times. This was because they used the 24-hour clock system. But as the modern 12-hour clock became common, especially in Great Britain, 12-hour striking became the standard. Many striking clocks also play short tunes on the quarter-hours. The most famous tune is the Westminster Quarters.
Today, we don't really need clocks to strike the time. We have watches and phones! But striking clocks are still loved for their history, tradition, and beauty. Famous clock towers around the world still strike the hours. Good examples are Big Ben in London and the Kremlin Clock in Moscow. Many homes also have striking clocks like mantel clocks, cuckoo clocks, and grandfather clocks.
A typical striking clock has two main parts that work with gears. One part is the timekeeping train. This part measures the passage of time. The other part is the striking train. This part makes the bell ring.
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How Clocks First Struck the Hour
The simplest type of striking clock just rings a bell once every hour. This is called a passing strike clock. It was easy to build. A special part called a cam was attached to a spinning rod. This rod turned once every hour. The cam would lift a hammer and then let it drop, hitting the bell.
The very first tower clocks in Medieval Europe used this passing strike method. They were often water clocks. They rang once for each prayer time.
Early Clocks Around the World
Before European clocks, China had amazing water-powered clocks. The scientist Zhang Heng (78–139 AD) developed this technology. Later, a Chinese monk and inventor named Yi Xing (683–727) made a spinning celestial globe. It was moved by a water clock. This clock had wooden figures that struck a drum and a bell. The bell rang every hour, and the drum every quarter-hour.
Another early striking clock was in Damascus, Syria. It was a clock tower near the Umayyad Mosque. This clock struck once every hour. A book from 1203, On the Construction of Clocks and their Use, describes it.
One of the oldest clock towers still standing is St Mark's Clocktower in Venice, Italy. The St Mark's Clock was put together in 1493. Two bronze statues, called the Due Mori (Two Moors), strike the great bell at the top of the tower.
Counting the Hours with Strikes
In the 14th century, during a time when many tower clocks were being built in Europe, clocks started striking the bell multiple times to count out the hours. The clock of the Beata Vergine in Milan, built around 1330, was one of the first. A writer named Galvano Fiamma wrote about it in 1335. He said it had a huge clapper that struck a bell 24 times for the 24 hours of the day and night. This helped people tell one hour from another.
The famous astronomer Richard of Wallingford also designed a clock in 1327 that struck 24 hours.
Some rare clocks use a special way of striking called "Roman Striking." This was invented by Joseph Knibb. A large bell makes a low sound for "five," and a small bell makes a high sound for "one." For example, four o'clock would be a high sound then a low sound. Eleven o'clock would be two low sounds then a high sound. This method saves the clock's power. For example, "VII" (seven) would only need three strikes instead of seven. Clocks with this system often show four o'clock as "IV" on their face, not "IIII."
How Clocks Count: The Countwheel
Clockmakers came up with two main ways for clocks to count the hours correctly. The first way, used in the 14th century, is called "countwheel striking." This system uses a wheel with unevenly spaced notches on its side. This countwheel controls how the striking train moves.
When the clock is ready to strike, a lever lifts out of a notch on the countwheel. The uneven notches let the striking train move just enough to ring the bell the correct number of times. Then, the lever falls back into the next notch, stopping the striking train.
The problem with the countwheel is that it works separately from the clock's timekeeping part. If the clock stops striking for some reason, the countwheel can get out of sync with the hands. Then, someone has to manually adjust it to match the correct time.
How Clocks Count: Rack Striking
In the late 1600s, rack striking was invented. This system is named after a "rack and snail" mechanism that controls it. The distance a special rack is allowed to fall is set by a snail-shaped part. This controls how many times the bell rings. We don't know who invented it, but it was a big improvement.
The snail-shaped part is connected to the clock's timekeeping gears. It turns once every twelve hours. The snail is largest at the one o'clock position. This lets the rack move only a short distance. It is smallest at the 12 o'clock position. This allows the rack to move the farthest. The striking stops when the rack can't move any further.
Because the snail moves with the hour hand, rack striking rarely gets out of sync. Rack striking also made it possible to create repeating clocks. These clocks can repeat the last hour struck when you push a button. Rack striking quickly became the standard way striking clocks work, even today.
Main Parts of a Striking Clock
All clocks that strike the hour have these important parts:
- Power Source – This is usually a second weight on a cord (P) in clocks that use weights. In clocks that use springs, it's another mainspring. Older clocks sometimes used one power source for both timekeeping and striking. But better clocks use separate power sources. This is because striking uses a lot of energy. Also, it protects the delicate timekeeping parts from the bigger movements of the striking parts.
- Striking Train – This is a set of gears (G, H). It takes the power from the source and sends it to the hammer that rings the bell. In old clocks, this gear set was often the same as the clock's timekeeping gears. It was placed next to them.
- Regulator – This part stops the striking train from running too fast. Without it, the striking train would spin out of control. Most clocks use a simple fly fan (K). This is a flat piece of metal on the fastest spinning gear. It beats the air, and the air friction slows the train down.
- Count Mechanism – This is the most important part for striking. It lets the striking train start at the right time and counts the correct number of strikes. Almost all modern clocks use the rack and snail system. The snail (N) is usually on the same shaft as the hour hand. A release lever (L) lets the rack fall when it's time to strike.
- Hammer and Gong – The hammer lever (F) is moved by pins or teeth (G) on one of the striking train wheels. As the wheel turns, the pin lifts the hammer lever. Then the lever slips off the pin, letting the hammer drop and hit the gong (E). Early house clocks used round bells. Later clocks used gongs made of long steel tubes or bars. These sound more like big church bells. Smaller clocks use coiled steel wires that make a spiral shape to save space.
Clocks that do more than just strike the hours are called "chiming clocks." They might chime on the quarter hours or play short tunes. These extra features usually have their own separate striking mechanism, called the "chiming train." These clocks have three weights or mainsprings: one for timekeeping, one for striking, and one for chiming.
How Rack Striking Works
Let's look at how the rack and snail striking mechanism works. The letters refer to the diagram above.
The release lever (L) holds the rack (M) up when the clock is not striking. On the shaft of the minute hand, there is a small part that sticks out. As the hour gets close, this part slowly lifts the release lever. This allows the rack to fall until its point rests on the snail (N). The position of the snail decides how far the rack can fall. This then sets the number of strikes.
Exactly on the hour, the striking train (G, H, K) is released and starts to turn. As it turns, the pins (G) repeatedly lift the hammer (F) and let it drop. This rings the gong (E). The gears are set up so that the wheel (H) turns once for each strike. A small pin (S) on this wheel catches the rack teeth. It lifts the rack up by one tooth each turn. When the rack reaches the end of its teeth, it stops the striking train from turning. So, the number of strikes matches the number of rack teeth that were used. This number depends on where the snail is positioned.
Different Kinds of Striking Clocks
Here are some special types of striking clocks:
- Chiming clock – These clocks strike on the hours and also chime on the quarter hours. They often play parts of a tune like Westminster Quarters.
- Repeater – This is a striking clock that can repeat the last hour struck. You just push a button, which is helpful for telling time in the dark.
- Musical clock – These clocks play tunes on a music box in addition to telling the time.
- Automaton clock – These clocks have moving figures that perform different actions, usually when the clock strikes the hours.
- Cuckoo clock – A specific type of automaton clock from Germany. It has a moving bird that pops out and makes birdcall sounds when the clock strikes.
- Ship's bell clock – These clocks strike the ship's bells instead of the hours, using a special pattern for ship's time.
Some quartz clocks today use electronics to make the sounds of a chiming or striking clock. Other quartz striking clocks use electricity to strike real bells or gongs.
See also
- Alarm clock
- Repeater watches (horology)
- St. Michael's chimes
- Thirteenth stroke of the clock
- Westminster Chimes
- Whittington chimes
- Water clock
