A
striking clock is a
clockA clock is an instrument used to indicate, measure, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell"...
that sounds the
hourThe hour is a unit of time. It is not an SI unit but is accepted for use with the SI.-Definition:In modern usage, an hour is a unit of measurement of time of the duration of 60 minutes, or 3600 seconds...
s audibly on a
bellA 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
gongA gong is an East and South East Asian musical instrument that takes the form of a flat metal disc which is hit with a mallet.Gongs are broadly of three types. Suspended gongs are more or less flat, circular discs of metal suspended vertically by means of a cord passed through holes near to the top...
.
The striking feature of clocks was originally more important than their
clock faceA 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 hoursCanonical hours are divisions of time, developed by the Christian Church, serving as increments between the prescribed prayers of the daily round...
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
SyriaSyria , 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
ItalyItaly , officially the Italian Republic , is a country located on the Italian Peninsula in Southern Europe and on the two largest islands in the Mediterranean Sea, Sicily and Sardinia. Italy shares its northern, Alpine boundary with France, Switzerland, Austria and Slovenia...
, where the 24 hour clock, keeping Italian
hourThe hour is a unit of time. It is not an SI unit but is accepted for use with the SI.-Definition:In modern usage, an hour is a unit of measurement of time of the duration of 60 minutes, or 3600 seconds...
s, was widely used in the 14th and 15th centuries. The 12 hour clock, and consequently 12 hour striking, became more widespread, particularly in
BritainGreat Britain is an island lying to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island. With a population of about 59.6 million people, it is the third most populated island on Earth. Great Britain is surrounded by over 1000 smaller...
and
Northern EuropeNorthern Europe is the northern part or region of Europe. The United Nations defines Northern Europe as including the following countries and dependent regions:** ** ** Ireland** Svalbard and Jan Mayen** ** Channel Islands: and...
, and eventually became the standard.
A typical striking clock will have two
gear trainA gear train is a set or system of gears arranged to transfer rotational torque from one part of a mechanical system to another.Gear trains consists*Driving gears - attached to the input shaft*Driven gears/Motor gears - attached to the output shaft...
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
timeTime is a component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify 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 clockA 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 being...
s, such clocks were the earliest striking clocks; they rang once for each canonical hour, and were used as reminders to summon
monkA monk is a person who practices religious asceticism, living either alone or with any number of monks, whilst always maintaining some degree of physical separation from those not sharing the same purpose...
s or
nunA Nun, or also known as a Sister in some cases, is a woman who has taken special vows committing her to a religious 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 clockA 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
gearA gear is a component within a transmission device that transmits rotational torque by applying a force to the teeth of another gear or device. A gear is different from a pulley in that a gear is a round wheel that has linkages that mesh with other gear teeth, allowing force to be fully...
train to arm and release the single stroke sounded.
The
Tang DynastyThe 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...
ChineseChina is a cultural region, an ancient civilization, and, depending on perspective, a national or multinational entity extending over a large area in East Asia....
Buddhist monk and inventor
Yi XingYi 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
hydraulicsHydraulics 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
escapementIn mechanical watches and clocks, an escapement is a device which converts continuous rotational motion into an oscillating or back and forth motion....
), in the tradition of
Zhang HengZhang Heng was an astronomer, mathematician, inventor, geographer, cartographer, artist, poet, statesman, and literary scholar from Nanyang, Henan, and 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 minor...
(78–139). This featured two wooden gear jacks on its
horizon surfaceThe 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
ConfucianConfucianism is a Chinese ethical and philosophical system developed from the teachings of the Chinese philosopher Confucius . It is a complex system of moral, social, political, philosophical, and quasi-religious thought that has had tremendous influence on the culture and history of East Asia...
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 towerA clock tower is a tower built with one or more clock faces. The clock tower is usually part of a church or municipal building such as a town hall, but many clock towers are free-standing....
s of
Song DynastyThe 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 SixunZhang 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 SongSu Song was a renowned Chinese 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 water-driven astronomical clock tower in...
in the 10th and 11th centuries, respectively.
A striking clock outside of China was the clock tower near the
Umayyad MosqueThe Ummayad Mosque, also known as the Grand Mosque of Damascus , is one of the largest and oldest mosques in the world...
in
DamascusDamascus is the capital and largest city of Syria. It is the oldest continuously inhabited city in the world and its current population is estimated at about 1,669,000...
,
SyriaSyria , 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....
, which struck once every hour. It was constructed by the Arab engineer al-Kaysarani in 1154. The
FlorentineFlorence is the capital city of the Italian region of Tuscany and of the province of Florence...
writer
Dante AlighieriDurante degli Alighieri , commonly known as Dante, was an Italian poet of the Middle Ages. His central work, the Divina Commedia , is often considered the greatest literary work composed in the Italian language and a masterpiece of world literature.In...
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 ClocktowerSt Mark's Clocktower is a clock tower situated on St Mark's Square in Venice, adjoining the Procuratie Vecchie. It houses the most important clock in the city, St Mark's Clock ....
in St Mark's Square,
VeniceVenice is a city in northern Italy, the capital of the region Veneto, a population of 271,367 . Together with Padua, the city is included in the Padua-Venice Metropolitan Area . The city historically was an independent nation...
. The
St Mark's ClockSt Mark's Clock is the clock housed in the St Mark's Clocktower, on St Mark's Square in Venice, adjoining the Procuratie Vecchie. The first clock housed in the tower was built and installed by Gian Paulo and Gian Carlo Rainieri, father and son, between 1496 and 1499, and was one of a number of...
was assembled in 1493, by the famous clockmaker Gian Carlo Rainieri from
Reggio EmiliaReggio Emilia is an affluent city in northern Italy, in the Emilia-Romagna region. It has about 167,013 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 MoorsThe description Moors has referred to several historic and modern populations of Muslim people of Berber, Black African and Arab descent from North Africa, some of whom came to conquer and occupy the Iberian Peninsula for nearly 800 years. The North Africans termed it Al Andalus, comprising most...
), two bronze statues (h. 2,60) handling a hammer.
Counting the hours
During the great wave of tower clock building in 14th century
EuropeEurope 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 water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains , and the Black Sea to the southeast...
, 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
MilanMilan in Italy, is the capital of the region of Lombardia and of the province of Milan. The city proper has a population of about 1.3 million, while the urban area is the fifth largest in the E.U. with an estimated population of 4.3 million...
, built around 1330, was one of the earliest recorded that struck the hours. In 1335,
Galvano FiammaGalvano Fiamma was an Italian Domincan and chronicler of Milan.He was chaplain to the Milanese lord Galeazzo II Visconti. His numerous historical writings include the Chronica Galvagnana, the Chronicon extravagans de antiquitatibus Mediolani, the Chronicon maius, and the Manipolus florum seu...
wrote: The astronomical clock designed by
Richard of WallingfordRichard 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....
in 1327 and built around 1354, also struck 24 hours.
Some rare clocks use a form of striking known as "Roman Striking", 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
clockmakerA clockmaker is an artisan who makes and repairs clocks. Since almost all clocks are now factory-made, most clockmakers today just repair clocks. However, originally they were master craftsmen who designed and built clocks by hand...
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
arcA circle is a simple shape of Euclidean geometry consisting of those points in a plane which are equidistant from a given point called the centre. The common distance of the points of a circle from its center is called its 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
rackIn physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to another object....
is allowed to fall is determined by a snail-shaped
camA 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
For the 2007 novel by Jay Lake, see Mainspring .A mainspring is a spiral 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...
. 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
A gear train is a set or system of gears arranged to transfer rotational torque from one part of a mechanical system to another.Gear trains consists*Driving gears - attached to the input shaft*Driven gears/Motor gears - attached to the output shaft...
(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
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
A gong is an East and South East Asian musical instrument that takes the form of a flat metal disc which is hit with a mallet.Gongs are broadly of three types. Suspended gongs are more or less flat, circular discs of metal suspended vertically by means of a cord passed through holes near to the top...
(E). Early house clocks used traditional hemispherical shaped bellA 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 bellA 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 striking the quarter hours, or playing tunes, are called by clockmakers 'chiming clocks'. 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
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 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 quarter hours as well as the hours, and often plays fragments of a tune, usually Westminster Quarters
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.
- Repeater - a striking clock which can repeat the strikes at the push of a lever, for telling the time in the dark.
- 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
An automaton clock is a type of striking clock featuring automatons. Clocks like these were often built during the Middle Ages in Europe. A Cuckoo clock is a simple form of this type of clock. Often, the automatons come out on the hour to strike the bells, with Death often being one of the figures,...
- with mechanically animated figures that periodically perform various displays, usually as a part of the clock striking the hours.
- Cuckoo clock
A cuckoo clock is a clock, typically pendulum-driven, that strikes the hours using small bellows and pipes that imitate the call of the Common Cuckoo in addition to striking a wire gong...
- a specific type of automaton clock which originated in GermanyGermany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium,...
, 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
A ship's bell is usually made of brass, and has the ship's name engraved on it.Strikes of a ship's bell are used to indicate the hour aboard a ship and thereby to regulate the sailors' duty watches....
of a nautical watch instead of the hours.
Some
quartz clockA 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 attempt to imitate the sounds of a chiming or striking clock. Other quartz striking clocks use electrical power to strike bells or gongs.