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Clock

clockstimepiecemechanical clock
The verge (or crown wheel) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks'.
A major advance occurred with the invention of the verge escapement, which made possible the first mechanical clocks around 1300 in Europe, which kept time with oscillating timekeepers like balance wheels.

Escapement

detent escapementCross-beat escapementduplex escapements
The verge (or crown wheel) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks'.
The invention of the first all-mechanical escapement, the verge escapement, in 13th-century Europe initiated a change in timekeeping methods from continuous processes, such as the flow of water in water clocks, to repetitive oscillatory processes, such as the swing of pendulums, which could yield more accuracy.

Pocket watch

pocketwatchfob watchwatch fob
Verge escapements were used from the 14th century until the mid 19th century in clocks and pocketwatches.
Up to the 1720s, almost all watch movements were based on the verge escapement, which had been developed for large public clocks in the 14th century.

Balance wheel

foliotcompensation balanceauxiliary temperature compensation
They kept time by using the verge escapement to drive the foliot, a primitive type of balance wheel, causing it to oscillate back and forth.
It is an improved version of the foliot, an early inertial timekeeper consisting of a straight bar pivoted in the center with weights on the ends, which oscillates back and forth.

Pendulum

pendulumssimple pendulumpendula
This caused a shift from measuring time by continuous processes, such as the flow of liquid in water clocks, to repetitive, oscillatory processes, such as the swing of pendulums, which had the potential to be more accurate.
The existing clock movement, the verge escapement, made pendulums swing in very wide arcs of about 100°.

Pendulum clock

regulator clockClock pendulumregulator
The verge was only used briefly in pendulum clocks before it was replaced by the anchor escapement, invented around 1660 and widely used beginning in 1680.
The introduction of the pendulum, the first harmonic oscillator used in timekeeping, increased the accuracy of clocks enormously, from about 15 minutes per day to 15 seconds per day leading to their rapid spread as existing 'verge and foliot' clocks were retrofitted with pendulums.

Balance spring

hairspringisochronousbalance spring or "hair spring
A similar increase in accuracy in verge watches followed the introduction of the balance spring in 1658.
Before that time, balance wheels or foliots without springs were used in clocks and watches, but they were very sensitive to fluctuations in the driving force, causing the timepiece to slow down as the mainspring unwound.

Fusee (horology)

fuseefuseeschain and fusee
Verge watches and clocks are sensitive to changes in the drive force; they slow down as the mainspring unwinds. This is called lack of isochronism. It was much worse in verge and foliot clocks due to the lack of a balance spring, but is a problem in all verge movements. In fact, the standard method of adjusting the rate of early verge watches was to alter the force of the mainspring. The cause of this problem is that the crown wheel teeth are always pushing on the pallets, driving the pendulum (or balance wheel) throughout its cycle; it is never allowed to swing freely. All verge watches and spring driven clocks required fusees to equalize the force of the mainspring to achieve even minimal accuracy.
The primitive verge and foliot timekeeping mechanism, used in all early clocks, was sensitive to changes in drive force.

Mainspring

springspring motorspring-wound
Verge watches and clocks are sensitive to changes in the drive force; they slow down as the mainspring unwinds. This is called lack of isochronism. It was much worse in verge and foliot clocks due to the lack of a balance spring, but is a problem in all verge movements. In fact, the standard method of adjusting the rate of early verge watches was to alter the force of the mainspring. The cause of this problem is that the crown wheel teeth are always pushing on the pallets, driving the pendulum (or balance wheel) throughout its cycle; it is never allowed to swing freely. All verge watches and spring driven clocks required fusees to equalize the force of the mainspring to achieve even minimal accuracy.
This was especially true of the primitive verge and foliot type used before the advent of the balance spring in 1657.

Salisbury cathedral clock

a clock thereclocklarge clock
Salisbury cathedral clock—oldest known operating clock, with verge and foliot escapement.
At that time it had a pendulum, which appeared to have been installed at a later date, replacing a verge and foliot.

Anchor escapement

deadbeat escapementdeadbeatpocket watch
The verge was only used briefly in pendulum clocks before it was replaced by the anchor escapement, invented around 1660 and widely used beginning in 1680.
The anchor was the second widely used escapement in Europe, replacing the 400-year-old verge escapement in pendulum clocks.

Dover Castle Clock

Dover Castle Clock old known operating clock with its original verge and foliot escapement.
The Dover is one of the few surviving clocks from this era that still has its original foliot, a primitive balance wheel which was the timekeeper used in the earliest clocks, consisting of a bar with weights hanging from the ends, which rotates back and forth.

Christiaan Huygens

HuygensHuygens, ChristiaanChristiaan
Christiaan Huygens in 1674 showed that a pendulum swinging in a wide arc is an inaccurate timekeeper, because its period of swing is sensitive to small changes in the drive force provided by the clock mechanism.
Watches in the time of Huygens and Hooke, however, employed the very undetached verge escapement.

Galileo Galilei

GalileoGalileanGalilei
Galileo's escapement - the first proposed pendulum clock escapement by Galileo Galilei.
The clock was never built and, because of the large swings required by its verge escapement, would have been a poor timekeeper.

Galileo's escapement

Galileo's escapement - the first proposed pendulum clock escapement by Galileo Galilei.
The existing clocks of the time which used the verge escapement with a crude balance wheel were very inaccurate.

History of technology

historian of technologytechnologytechnological growth
Its invention is important in the history of technology, because it made possible the development of all-mechanical clocks.

Continuous function

continuouscontinuitycontinuous map
This caused a shift from measuring time by continuous processes, such as the flow of liquid in water clocks, to repetitive, oscillatory processes, such as the swing of pendulums, which had the potential to be more accurate.

Oscillation

oscillatorvibrationoscillators
This caused a shift from measuring time by continuous processes, such as the flow of liquid in water clocks, to repetitive, oscillatory processes, such as the swing of pendulums, which had the potential to be more accurate.

Clock tower

clocktowertower clockcastle clock
Starting in the 13th century, large tower clocks were built in European town squares, cathedrals, and monasteries.

Villard de Honnecourt

Villard’s
There has been speculation that Villard de Honnecourt invented the verge escapement in 1237 with an illustration of a strange mechanism to turn an angel statue to follow the sun with its finger, but the consensus is that this was not an escapement.

Dunstable Priory

DunstablePrioryPriory at Dunstable
One candidate is the Dunstable Priory clock in Bedfordshire, England built in 1283, because accounts say it was installed above the rood screen, where it would be difficult to replenish the water needed for a water clock.

Bedfordshire

BedfordCounty of BedfordBDF
One candidate is the Dunstable Priory clock in Bedfordshire, England built in 1283, because accounts say it was installed above the rood screen, where it would be difficult to replenish the water needed for a water clock.

Rood screen

rood loftchancel screenchoir screen
One candidate is the Dunstable Priory clock in Bedfordshire, England built in 1283, because accounts say it was installed above the rood screen, where it would be difficult to replenish the water needed for a water clock.

Richard of Wallingford

The earliest description of an escapement, in Richard of Wallingford's 1327 manuscript Tractatus Horologii Astronomici on the clock he built at the Abbey of St. Albans, was not a verge, but a variation called a 'strob' escapement.

St Albans Cathedral

St Albans AbbeySt AlbansAbbey
The earliest description of an escapement, in Richard of Wallingford's 1327 manuscript Tractatus Horologii Astronomici on the clock he built at the Abbey of St. Albans, was not a verge, but a variation called a 'strob' escapement.