Striking clock - AbsoluteAstronomy.com

A striking clock is a clock

Clock

A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

that sounds the hour

Hour

The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...

s audibly on a bell

Bell (instrument)

A bell is a simple sound-making device. The bell is a percussion instrument and an idiophone. Its form is usually a hollow, cup-shaped object, which resonates upon being struck...

or gong

Gong

A gong is an East and South East Asian musical percussion instrument that takes the form of a flat metal disc which is hit with a mallet....

. In 12 hour striking, used most commonly in striking clocks today, the clock strikes once at 1 AM, twice at 2 AM, continuing in this way up to twelve times at 12 noon, then starts over, striking once at 1 PM, twice at 2 PM, up to twelve times at 12 midnight.

The striking feature of clocks was originally more important than their clock face

Clock face

A clock face is the part of an analog clock that displays the time through the use of a fixed numbered dial or dials and moving hands. In its most basic form, recognized universally throughout the world, the dial is numbered 1–12 indicating the hours in a 12-hour cycle, and a short hour hand...

s; the earliest clocks struck the hours, but had no dials to enable the time to be read. The development of mechanical clocks in Europe was motivated by the need to ring bells upon the canonical hours
Canonical hours
Canonical hours are divisions of time which serve as increments between the prescribed prayers of the daily round. A Book of Hours contains such a set of prayers....

to call the community to prayer. The earliest known mechanical clocks were large striking clocks installed in towers in monasteries or public squares, so that their bells could be heard far away. Though an early striking clock in Syria

Syria

Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....

was a 12-hour clock, many early clocks struck up to 24 strokes, particularly in Italy

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, where the 24 hour clock, keeping Italian hour

Hour

The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...

s, was widely used in the 14th and 15th centuries. As the modern 12 hour clock became more widespread, particularly in Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

and Northern Europe

Northern Europe

Northern Europe is the northern part or region of Europe. Northern Europe typically refers to the seven countries in the northern part of the European subcontinent which includes Denmark, Estonia, Latvia, Lithuania, Norway, Finland and Sweden...

, 12 hour striking became more widespread and eventually became the standard.

A typical striking clock will have two gear train

Gear train

A gear train is formed by mounting gears on a frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, this provides a smooth transmission of rotation from one gear to the next.The transmission of...

s, because a striking clock must add a striking train that operates the mechanism that rings the bell in addition to the timekeeping train that measures the passage of time

Time

Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

Passing strike

The most basic sort of striking clock simply sounds a bell once every hour. This sort of striking clock is called a passing strike clock. It is far simpler to create such a clock; all that must be done is to attach a cam to a shaft that rotates once an hour; the cam raises and then lets fall a hammer that strikes the bell. Originating before the mechanical clock itself, in water clock

Water clock

A water clock or clepsydra is any timepiece in which time is measured by the regulated flow of liquid into or out from a vessel where the amount is then measured.Water clocks, along with sundials, are likely to be the oldest time-measuring instruments, with the only exceptions...

s, such clocks were the earliest striking clocks; they rang once for each canonical hour, and were used as reminders to summon monk

Monk

A monk is a person who practices religious asceticism, living either alone or with any number of monks, while always maintaining some degree of physical separation from those not sharing the same purpose...

s or nun

Nun

A nun is a woman who has taken vows committing her to live a spiritual life. She may be an ascetic who voluntarily chooses to leave mainstream society and live her life in prayer and contemplation in a monastery or convent...

s to their prayers. This sort of striking is still found in some skeleton clock

Skeleton clock

A skeleton clock is any clock or wristwatch, though typically mechanical in nature, in which the parts that usually conceal the inner workings of the mechanism have been removed or significantly modified so as to display these inner parts....

s. It does not require a separate gear

Gear

A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....

train to arm and release the single stroke sounded.

The Tang Dynasty

Tang Dynasty

The Tang Dynasty was an imperial dynasty of China preceded by the Sui Dynasty and followed by the Five Dynasties and Ten Kingdoms Period. It was founded by the Li family, who seized power during the decline and collapse of the Sui Empire...

Chinese

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

Buddhist monk and inventor Yi Xing

Yi Xing

Yi Xing , born Zhang Sui , was a Chinese astronomer, mathematician, mechanical engineer,and Buddhist monk of the Tang Dynasty...

(683–727) created a rotating celestial globe that was given motive power by hydraulics

Hydraulics

Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...

of a turning waterwheel (acting as a large escapement

Escapement

In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...

), in the tradition of Zhang Heng

Zhang Heng

Zhang Heng was a Chinese astronomer, mathematician, inventor, geographer, cartographer, artist, poet, statesman, and literary scholar from Nanyang, Henan. He lived during the Eastern Han Dynasty of China. He was educated in the capital cities of Luoyang and Chang'an, and began his career as a...

(78–139). This featured two wooden gear jacks on its horizon surface

Celestial horizon

The celestial horizon, also called the rational horizon, is a great circle parallel to the horizon, in which a plane at right angles to Zenith and Nadir lines are passing through the centre of the earth and intersects the celestial sphere, the center of which is the center of the Earth....

with a drum and a bell, the bell being struck automatically every hour and the drum being struck automatically every quarter hour. It is recorded that Confucian

Confucianism

Confucianism is a Chinese ethical and philosophical system developed from the teachings of the Chinese philosopher Confucius . Confucianism originated as an "ethical-sociopolitical teaching" during the Spring and Autumn Period, but later developed metaphysical and cosmological elements in the Han...

students in the year 730 were required to write an essay on this device in order to pass the Imperial examinations. The use of clock jacks to sound the hours were used in later clock tower

Clock tower

A clock tower is a tower specifically built with one or more clock faces. Clock towers can be either freestanding or part of a church or municipal building such as a town hall. Some clock towers are not true clock towers having had their clock faces added to an already existing building...

s of Song Dynasty

Song Dynasty

The Song Dynasty was a ruling dynasty in China between 960 and 1279; it succeeded the Five Dynasties and Ten Kingdoms Period, and was followed by the Yuan Dynasty. It was the first government in world history to issue banknotes or paper money, and the first Chinese government to establish a...

China, such as those designed by Zhang Sixun

Zhang Sixun

Zhang Sixun was a Chinese astronomer and military engineer from Bazhong, Sichuan during the early Song Dynasty . He is credited with creating an armillary sphere for his astronomical clock tower that employed the use of liquid mercury...

and Su Song

Su Song

Su Song was a renowned Chinese polymath who specialized himself as a statesman, astronomer, cartographer, horologist, pharmacologist, mineralogist, zoologist, botanist, mechanical and architectural engineer, poet, antiquarian, and ambassador of the Song Dynasty .Su Song was the engineer of a...

in the 10th and 11th centuries, respectively.

A striking clock outside of China was the clock tower near the Umayyad Mosque

Umayyad Mosque

The Umayyad Mosque, also known as the Great Mosque of Damascus or formerly the Basilica of Saint John the Baptist , is located in the old city of Damascus, is one of the largest and oldest mosques in the world...

in Damascus

Damascus

Damascus , commonly known in Syria as Al Sham , and as the City of Jasmine , is the capital and the second largest city of Syria after Aleppo, both are part of the country's 14 governorates. In addition to being one of the oldest continuously inhabited cities in the world, Damascus is a major...

, Syria

Syria

, which struck once every hour. It was constructed by the Arab engineer al-Kaysarani in 1154. The Florentine

Florence

Florence is the capital city of the Italian region of Tuscany and of the province of Florence. It is the most populous city in Tuscany, with approximately 370,000 inhabitants, expanding to over 1.5 million in the metropolitan area....

writer Dante Alighieri

Dante Alighieri

Durante degli Alighieri, mononymously referred to as Dante , was an Italian poet, prose writer, literary theorist, moral philosopher, and political thinker. He is best known for the monumental epic poem La commedia, later named La divina commedia ...

made a reference to the gear works of striking clocks in 1319. The most famous original striking clock tower still standing is possibly the one in St Mark's Clocktower

St Mark's Clocktower

The Clock Tower in Venice is an early renaissance building on the north side of the Piazza San Marco at the entrance to the Merceria. It comprises a tower, which contains the clock, and lower buildings on each side. It adjoins the eastern end of the Procuratie Vecchie...

in St Mark's Square, Venice

Venice

Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...

. The St Mark's Clock

St Mark's Clock

For the building containing the clock see the article on the ClocktowerSt Mark's Clock is the clock housed in the Clocktower on the Piazza San Marco in Venice adjoining the Procuratie Vecchie...

was assembled in 1493, by the famous clockmaker Gian Carlo Rainieri from Reggio Emilia

Reggio Emilia

Reggio Emilia is an affluent city in northern Italy, in the Emilia-Romagna region. It has about 170,000 inhabitants and is the main comune of the Province of Reggio Emilia....

, where his father Gian Paolo Rainieri had already constructed another famous device in 1481. In 1497, Simone Campanato moulded the great bell (h. 1,56 m., diameter m. 1,27), which was put on the top of the tower where it's alternatively beaten by the Due Mori (Two Moors
Moors
The description Moors has referred to several historic and modern populations of the Maghreb region who are predominately of Berber and Arab descent. They came to conquer and rule the Iberian Peninsula for nearly 800 years. At that time they were Muslim, although earlier the people had followed...

), two bronze statues (h. 2,60) handling a hammer.

Counting the hours

During the great wave of tower clock building in 14th century Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, around the time of the invention of the mechanical clock itself, striking clocks were built that struck the bell multiple times, to count out the hours. The clock of the Beata Vergine (later San Gottardo) in Milan

Milan

Milan is the second-largest city in Italy and the capital city of the region of Lombardy and of the province of Milan. The city proper has a population of about 1.3 million, while its urban area, roughly coinciding with its administrative province and the bordering Province of Monza and Brianza ,...

, built around 1330, was one of the earliest recorded that struck the hours. In 1335, Galvano Fiamma

Galvano Fiamma

Galvano Fiamma was an Italian Domincan and chronicler of Milan.He was chaplain to the Milanese lord Galeazzo II Visconti.He wrote several chronicles dealing with the history of Milan and exalting the Visconti, who by his day had in effect become its ruling dynasty.His numerous historical writings...

wrote: The astronomical clock designed by Richard of Wallingford

Richard of Wallingford

Richard of Wallingford was an English mathematician who made major contributions to astronomy/astrology and horology while serving as abbot of St Albans Abbey in Hertfordshire.-Biography:...

in 1327 and built around 1354, also struck 24 hours.

Some rare clocks use a form of striking known as "Roman Striking" (invented by Joseph KNIBB

Joseph Knibb

Joseph Knibb was an English clockmaker.-Biography:He was born as the fifth son of Thomas Knibb, yeoman of Claydon, in 1640. He was cousin to Samuel Knibb, clockmaker, to whom he was apprenticed in 1655. After serving his seven years he moved to Oxford in 1662, the year Samuel moved to London.In...

), where a large bell or lower tone is sounded to represent "five", and a small bell or high tone is sounded to represent "one". For example, the hour of four o'clock would be sounded as a high tone followed by a low tone, whereas the hour of eleven o'clock would be sounded by two low tones followed by a high tone. Clocks using this type of striking usually represent four o'clock on the dial with an "IV" rather than the more common "IIII".

Countwheel

Two mechanisms have been devised by clockmaker

Clockmaker

A clockmaker is an artisan who makes and repairs clocks. Since almost all clocks are now factory-made, most modern clockmakers only repair clocks. Modern clockmakers may be employed by jewellers, antique shops, and places devoted strictly to repairing clocks and watches...

s to enable striking clocks to correctly count out the hours. The earlier, what appeared in the first striking clocks in the 14th century, is called countwheel striking. This uses a wheel that contains notches on its side, spaced by unequal, increasing arc

Circle

A circle is a simple shape of Euclidean geometry consisting of those points in a plane that are a given distance from a given point, the centre. The distance between any of the points and the centre is called the radius....

segments. This countwheel governs the rotation of the striking train. When the striking train is released by the timekeeping train, a lever is lifted from a notch on the countwheel; the uneven notches allow the striking train to move only far enough to sound the correct number of times, after which the lever falls back into the next notch and stops the striking train from turning further.

The countwheel has the disadvantage of being entirely independent of the timekeeping train; if the striking train winds down, or for some other reason the clock fails to strike, the countwheel will become out of synch with the time shown by the hands, and must be resynchronized by manually releasing the striking train until it moves around to the correct position.

Rack striking

In the late seventeenth century, rack striking was invented. Rack striking is so called because it is regulated by a rack and snail mechanism. The distance a rack

Lever

In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

is allowed to fall is determined by a snail-shaped cam

Cam

A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path...

, thereby regulating the number of times the bell is allowed to sound. The rack and snail was invented by British clergyman Edward Barlow in 1676.

The snail-shaped cam is a part of the timekeeping train that revolves every twelve hours; often, the snail is attached to the center wheel that drives the hour hand of the clock. Like the countwheel, the cam stops the striking train when the appropriate count has been reached. The diameter of the cam is largest at the one o'clock position, permitting the rack to move only a short distance, after which the striking train is stopped; it is smallest at the twelve o'clock position, which allows the rack to move the farthest.

Because it is linked to the timekeeping train, rack striking seldom becomes desynchronized from the hands. Rack striking also made possible the repeating clock, which can be made to repeat the last hour struck by pressing a button. Rack striking became the standard mechanism used in striking clocks down to the present.

Parts of mechanism

All hour striking mechanisms have these parts (the letters below refer to the diagram at left):

Power source - This is usually identical to the device that powers the clock's timekeeping mechanism: in weight driven clocks it is a second weight on a cord (P), in spring driven clocks it is another mainspring
Mainspring
A mainspring is a spiral torsion spring of metal ribbon that is the power source in mechanical watches and some clocks. Winding the timepiece, by turning a knob or key, stores energy in the mainspring by twisting the spiral tighter. The force of the mainspring then turns the clock's wheels as it...

. Although older one-day (30-hour) clocks often used a single weight or mainspring to drive both the timekeeping and striking trains, better clocks used a separate power source, because the striking mechanism consumes a lot of power and often has to be wound more frequently, and also to isolate the delicate timekeeping train from the large movements that occur in the striking train. Winding a striking clock requires winding both the timing and striking parts separately.
Striking train - This is a gear train
Gear train
A gear train is formed by mounting gears on a frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, this provides a smooth transmission of rotation from one gear to the next.The transmission of...

(G,H) that scales down the force of the power source and transmits it to the hammer mechanism which rings the gong. In antique clocks, to lower the manufacturing cost, it was often exactly the same as the timing train that ran the clock's timekeeping part, and installed parallel to it, on the left side as one faces the clock.
Regulator - A device to prevent the striking train from running too fast, and control the speed of striking. If it wasn't present, the striking train when released would run out of control under the force of the spring or weight. In most clocks it is a simple fan fly (K), a flat piece of sheet metal mounted on the fastest turning gear shaft. When the striking train turns, this beats the air, and the air friction limits the speed of the train. Striking watches and some modern clocks use a centrifugal governor
Centrifugal governor
A centrifugal governor is a specific type of governor that controls the speed of an engine by regulating the amount of fuel admitted, so as to maintain a near constant speed whatever the load or fuel supply conditions...

instead.
Count mechanism - This is the critical part mentioned above, that releases the striking train at the proper time and counts out the proper number of strikes. It is the only part of the striking mechanism that is attached to the clock's timekeeping works. Virtually all modern clocks use the rack and snail. The snail (N) is usually mounted on the clock's center wheel shaft, which turns once every 12 hours. There is also a release lever (L) which on the hour releases the rack and allows the timing train to turn.
Hammer and gong - The hammer lever (F) is actuated by pins or teeth (G) on one of the striking train wheels. As the wheel turns the pin lifts the hammer lever, until the lever slips off the pin, allowing the hammer to drop, hitting the gong
Gong
A gong is an East and South East Asian musical percussion instrument that takes the form of a flat metal disc which is hit with a mallet....

(E). Early house clocks used traditional hemispherical shaped bell
Bell (instrument)
A bell is a simple sound-making device. The bell is a percussion instrument and an idiophone. Its form is usually a hollow, cup-shaped object, which resonates upon being struck...

s. Later house clocks used gongs made of long steel tubes or bars, which have a sound more like large church bell
Church bell
A church bell is a bell which is rung in a church either to signify the hour or the time for worshippers to go to church, perhaps to attend a wedding, funeral, or other service...

s. Mantel and other small clocks use thick hardened steel wires, which are coiled into a spiral to save space.

Clocks that have more elaborate functions than just striking the hours, such as chiming the quarter hours, or playing tunes, are called 'chiming clocks' by clockmakers. The additional functions are usually run by a second complete striking mechanism separate from the (hour) striking train, called the chiming train. These clocks have three weights or mainsprings, to power the timing train, striking train, and chiming train.

How it works

This describes how the rack and snail striking mechanism works. The labels refer to the drawing above.

The release lever (L) holds the rack (M) up when the clock is not striking. On the shaft of the minute hand (not shown), which rotates once per hour, there is a projection. As the change of the hour approaches, this projection slowly lifts the release lever, allowing the rack to fall until its point rests on the snail (N). The amount the rack can fall, and thus the number of strikes, is determined by the position of the snail. Exactly on the hour the striking train (G, H, K) is released and begins to turn. As it turns, the pins (G) repeatedly lift the hammer (F) and allow it to drop, ringing the gong (E). The gear ratios are arranged so that the gear wheel (H) makes one revolution each strike. A small pin (S) on this wheel engages the rack teeth, lifting 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 is equal to the number of teeth of the rack which are used, which depends on the position of the snail.

Types of striking clocks

Specialized types of striking clocks:

Chiming clock - Strikes on the hours and chimes on the quarter hours, often playing fragments of a tune such as Westminster Quarters.
Repeater - a striking clock which can repeat the strikes at the push of a lever, for telling the time in the dark.
Musical clock
Musical clock
A Musical clock is a clock that marks the hours of the day with a musical tune played from a spiked cylinder either on bells, organ pipes, bellows, combs and even dulcimer strings....

- plays tunes on a music box in addition to counting the time
Automaton clock
Automaton clock
An automaton clock or automata clock is a type of striking clock featuring automatons. Clocks like these were built from the Middle Ages through to Victorian times in Europe. A Cuckoo clock is a simple form of this type of clock. The automatons usually perform on the hour, half-hour or...

- with mechanically animated figures that periodically perform various displays, usually as a part of the clock striking the hours.
- Cuckoo clock
  Cuckoo clock
  A cuckoo clock is a clock, typically pendulum-regulated, that strikes the hours with a sound like a common cuckoo's call and typically has a mechanical cuckoo that emerges with each note...
  
  - a specific type of automaton clock which originated in Germany
  Germany
  Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
  
  , which displays an animated bird and plays imitation birdcalls in addition to striking on a bell or gong.
Ship's bell clock - strikes the ship's bells
Ship's bells
A ship's bell is usually made of bronze, and often has the ship's name engraved or cast on it. The ship's cook traditionally has the job of shining the ship's bell.-Timing of duty periods:...

of a nautical watch instead of the hours.

Some quartz clock

Quartz clock

A quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than good mechanical clocks...

s also contain speakers and sound chips that electronically imitate the sounds of a chiming or striking clock. Other quartz striking clocks use electrical power to strike bells or gongs.