When was the escapement first used inn mechanical watches and clocks?
Lever escapement
The lever escapement, invented by British clockmaker Thomas Mudge in 1755, is a type of escapement that is used in almost all mechanical watches, as well as small mechanical non-pendulum clocks, alarm clocks, and kitchen timers.
Watch
The increased accuracy of the balance wheel focused attention on errors caused by other parts of the movement, igniting a two-century wave of watchmaking innovation. The first thing to be improved was the escapement. The verge escapement was replaced in quality watches by the cylinder escapement, invented by Thomas Tompion in 1695 and further developed by George Graham in the 1720s. Improvements in manufacturing such as the tooth-cutting machine devised by Robert Hooke allowed some increase in the volume of watch production, although finishing and assembling was still done by hand until well into the 19th century.
George Bennett Bowell
Bowell's last involvement in horology was in collaboration with Reginald Brabazon, 13th Earl of Meath, leading to a patent in 1937 for a clock escapement in which a constant force could be delivered, with unlocking independent of battery voltage.
Escapement
Purchasers no longer buy mechanical watches primarily for their accuracy, so manufacturers had little interest in investing in the tooling required, although finally Omega adopted it in 1990.
Louis Moinet
As a maker of precision instruments, Louis Moinet perfected various techniques in these fields and developed several important new improvements. To enhance his astronomical observations, he invented a sensational instrument: a counter in the shape of a watch displaying 60ths of a second. The obvious advantage was a degree of superior to any other time measurement. One of its particularly original features was a jewelled escapement that oscillated at 216,000 vibrations per hour without any trace of wear nor increased friction during prolonged use.
Escapement
It could be regarded as having its distant origins in the escapement invented by Robert Robin, C.1792, which gives a single impulse in one direction; with the locking achieved by passive lever pallets, the design of the coaxial escapement is more akin to that of another Robin variant, the Fasoldt escapement, which was invented and patented by the American Charles Fasoldt in 1859.
Both Robin and Fasoldt escapements give impulse in one direction only.
The latter escapement has a lever with unequal drops; this engages with two escape wheels of differing diameters. The smaller impulse wheel acts on the single pallet at the end of the lever, whilst the pointed lever pallets lock on the larger wheel.
The balance engages with and is impelled by the lever through a roller pin and lever fork. The lever 'anchor' pallet locks the larger wheel and, on this being unlocked, a pallet on the end of the lever is given an impulse by the smaller wheel through the lever fork. The return stroke is 'dead', with the 'anchor' pallets serving only to lock and unlock, impulse being given in one direction through the single lever pallet.
As with the duplex, the locking wheel is larger in order to reduce pressure and thus friction.
Electric watch
In horology the term electric watch is used for the first generation electrically-powered wristwatches which were first publicly displayed by both Elgin National Watch Company and LIP on the 19th of March 1952 with working laboratory examples in Chicago and Paris. Hamilton would be the first to produce and retail an electric watch beginning in 1957, before the commercial introduction of the quartz wristwatch in 1969 by Seiko with the Astron. Their timekeeping element was either a traditional balance wheel or a tuning fork, driven electromagnetically by a solenoid powered by a battery. The hands were driven mechanically through a wheel train. They were superseded by quartz watches, which had greater accuracy and durability due to their lower parts count. Recent automatic quartz watches, which combine mechanical technology with quartz timekeeping, are not included in this classification.
Pin-pallet escapement
A Roskopf, pin-lever, or pin-pallet escapement is an inexpensive, less accurate version of the lever escapement, used in mechanical alarm clocks, kitchen timers, mantel clocks and, until the 1970s, cheap watches now known as pin lever watches. It was patented by German watchmaker Georges Frederic Roskopf in 1867, suggested to Roskopf by Jules Grossmann.
Escapement
In the late 19th century, electromechanical escapements were developed for pendulum clocks. In these, a switch or phototube energised an electromagnet for a brief section of the pendulum's swing. On some clocks the pulse of electricity that drove the pendulum also drove a plunger to move the gear train.
Echappement naturel
The last of the four watches, 1484, does not now possess an échappement naturel but a double-wheel Robin escapement, a hybrid of the lever escapement and the chronometer escapement. Work started on the watch prior to September 1803. Sagedieu worked on an unspecified escapement between 10 February and 27 July 1804. Not much happened to the watch for six months except some jewel holes from Hooker, Breguet’s jewel specialist brought from London. Lapieur then worked on an échappement naturel between the end of January and early May 1806. From the position of the original pivot hole for the second escape wheel, the two escape wheels appear to have had a 2:1 ratio of their size. The most likely tooth counts appear to be 8:4, the same as Lapieur made earlier for watch 1085 above. The watch was cased by Tavernier in June and Herault completed the repassage in August. In November 1806, Bernaudat was paid 300 Francs for 'ouvrage et visitage'. This considerable sum could have been for the removal of the échappement naturel and the construction of its current coaxial double-wheel Robin escapement. Nothing much happened again until mid-October 1808 when Bernaudat was paid another 60 Fr for changes to the escapement. At some stage the stop-work was replaced in a new sink in the barrel cap with a standard Geneva variety rather than Breguet’s own design. No more work was done on the watch and another year and a half passed before it was sold to General Labadie on 28 Mar 1810 for the price of 1800 Francs.
Escapement
The 'Double Three-legged Gravity Escapement' shown here is a form of escapement first devised by a barrister named Bloxam and later improved by Lord Grimthorpe. It is the standard for all really accurate 'Tower' clocks. 
In the animation shown here the two "gravity arms" are coloured blue and red. The two three-legged escape wheels are also coloured blue and red. They work in two parallel planes so that the blue wheel only impacts the locking block on the blue arm and the red wheel only impacts the red arm. In a real escapement these impacts give rise to loud audible "ticks" and these are indicated by the appearance of a * beside the locking blocks. The three black lifting pins are key to the operation of the escapement. They cause the weighted gravity arms to be raised by an amount indicated by the pair of parallel lines on each side of the escapement. This gain in potential energy is the energy given to the pendulum on each cycle. For the Trinity College Cambridge Clock a mass of around 50 grams is lifted through 3 mm each 1.5 seconds - which works out to 1 mW of power. The driving power from the falling weight is about 12 mW, so there is a substantial excess of power used to drive the escapement. Much of this energy is dissipated in the acceleration and deceleration of the frictional "fly" attached to the escape wheels.
Pin-pallet escapement
Another escapement also called a "pin pallet escapement", unrelated to the Roskopf above, is the Brocot escapement, invented in 1823 by Louis-Gabriel Brocot and improved by his son Achille, and used in 19th century French pendulum clocks. It is a variation of the anchor escapement in which the pallets are semicircular pins. The escapement is often revealed in a cutout on the clock's face.
Clock
During the 15th and 16th centuries, clockmaking flourished, particularly in the metalworking towns of Nuremberg and Augsburg, and in Blois, France. Some of the more basic table clocks have only one time-keeping hand, with the dial between the hour markers being divided into four equal parts making the clocks readable to the nearest 15 minutes. Other clocks were exhibitions of craftsmanship and skill, incorporating astronomical indicators and musical movements. The cross-beat escapement was invented in 1584 by Jost Bürgi, who also developed the remontoire. Bürgi's clocks were a great improvement in accuracy as they were correct to within a minute a day. These clocks helped the 16th-century astronomer Tycho Brahe to observe astronomical events with much greater precision than before.
United States Penitentiary, Marion
The first escape from USP Marion occurred on October 10, 1975, when five inmates used a homemade electronic device to open the front gates of the prison. One of them had been an electrician and was assigned to work on the lock mechanisms of all of the doors in the main corridors. He also converted a radio into a remote control, with which he opened all of the doors. The five escapees were all eventually captured and returned to prison, the last one being apprehended in Canada on October 31, 1975.
Echappement naturel
A fifth watch could have been made during the development period for the échappement naturel. Watch number 2179 is a gold repeating watch of ‘normal’ size and is described on a Breguet certificate from 1971 as having an échappement naturel . However, it was catalogued for a sale in 2002 of items from the Time Museum by Anthony Randall as having a double lift Robin escapement. It is quite probable that work was started on this watch with a view to it having an échappement naturel but, like watch 1484, it was completed and taken into stock with a Robin escapement. Photocopies of the workbook entry accompanying the sale of the watch stated that its construction was started in 1806, after the delivery of both watch 1135 and watch 1711. It was sold on 29 December 1823 to the Duchess of Dalmatia for the price of 3200 Francs.
Echappement naturel
In contrast with the drawn out construction of 1135, this watch was produced quite quickly. The ébauche was made by Benoit and delivered in November 1804, Tavernier supplied the case in December 1804, Kehlhoff the escapement on 26 December 1804 and its repassage was completed by Bernaudat on 12 Feb 1805. There was now a delay of several months during which the final work was done on the dial and hands before being delivered to the buyer M. Galakoff on 5 September 1805 for the price of 3360 Francs. Mr. Galakoff had some problems with it, there were a couple of jobs done to it in the first few weeks, for example a new front crystal. Breguet bought the watch back from Mr. Galakoff in May 1806, had Tavernier engine-turn the back and re-numbered it as 2099 before selling it to M. Castaneda, an agent for the Spanish royal family, on 14 June 1806. 
The dates of the changes to the escapement of watch 1135 and the dates of construction of the escapement for watch 1711 overlap. It is therefore possible that lessons learned from the construction of watch 1135 were incorporated in 1711 and perhaps vice versa. In this watch the driven escape wheel was smaller, presumably because Breguet had come to the view that this was beneficial. George Daniels pointed out that this reduction of the size and inertia of the driven wheel resulted in improved escapement performance. It was obviously not thought at the time to be beneficial enough to delay 1135 and redesign its escapement and train although the final escapement work was done after that of 1711.
In this watch the driving escape wheel had 5 impulse teeth and the driven had 4. This was a relatively minor development from the design used in watch 1135.
Grasshopper escapement
A grasshopper escapement is an essential part of a sculptural clock by Martin Burgess, known as Burgess Clock B. One of a pair based on the technology of the late regulator clock by John Harrison, it was completed by Charles Frodsham & Company at the request of its owner, Donald Saff. After successful testing there it was transferred to the Royal Observatory, Greenwich for a detailed assessment of its long-term performance. This was overseen by the Worshipful Company of Clockmakers and the National Physical Laboratory, whose representatives attached tamper-proof seals to the case of the clock. Although the clock is electrically-wound, thus preventing any disturbance whatever of the clock during the assessment, it is otherwise entirely mechanical. At the end of a period of one-hundred days, the maximum error had not exceeded five-eighths of a second - no allowance for a steady drift of time (rate) having had to be applied. As a result, on the 18th of April 2015, the Guinness World Records organisation presented a World Record certificate to Martin Burgess for having made the most accurate purely mechanical clock working in free air. The clock remains at the ROG; in 2017 it was moved to the gallery containing the Harrison marine timekeepers where its performance continues to be monitored.
Alcatraz Federal Penitentiary
On June 11, 1962, Frank Morris, John Anglin, and Clarence Anglin carried out one of the most intricate escapes ever devised. Behind the prisoners' cells in Cell Block B (where the escapees were interned) was an unguarded wide utility corridor. The prisoners chiselled away the moisture-damaged concrete from around an air vent leading to this corridor, using tools such as a metal spoon soldered with silver from a dime and an electric drill improvised from a stolen vacuum cleaner motor. The noise was disguised by accordions played during music hour, and the progress was concealed by false walls which, in the dark recesses of the cells, fooled the guards.
Verge escapement
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 problem with the verge was that it required the pendulum to swing in a wide arc of 80° to 100°. 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.
Watch
A major cause of error in balance wheel timepieces, caused by changes in elasticity of the balance spring from temperature changes, was solved by the bimetallic temperature compensated balance wheel invented in 1765 by Pierre Le Roy and improved by Thomas Earnshaw. The lever escapement was the single most important technological breakthrough, and was invented by Thomas Mudge in 1759 and improved by Josiah Emery in 1785, although it only gradually came into use from about 1800 onwards, chiefly in Britain.
Anchor escapement
The deadbeat form of the anchor escapement is less tolerant of inaccuracy in its manufacture or wear during operation and was initially used only in precision clocks, but its use spread during the 19th century to most quality pendulum clocks. Almost all pendulum clocks made today use it.
George Graham (clockmaker)
The deadbeat escapement is often erroneously credited to George Graham who introduced it around 1715 in his precision regulator clocks. However it was actually invented around 1675 by astronomer Richard Towneley, and first used by Graham's mentor Thomas Tompion in a clock built for Sir Jonas Moore, and in the two precision regulators he made for the new Greenwich Observatory in 1676, mentioned in correspondence between Astronomer Royal John Flamsteed and Towneley
Escapement
However, none of these were true mechanical escapements, since they still depended on the flow of liquid through an orifice to measure time. For example, in Su Song's clock, water flowed into a container on a pivot. The escapement's role was to tip the container over each time it filled up, thus advancing the clock's wheels each time an equal quantity of water was measured out. The time between releases depended on the rate of flow, which decreased with water pressure as the level of water in the source container dropped. The development of mechanical clocks depended on the invention of an escapement which would allow a clock's movement to be controlled by an oscillating weight. Unlike the continuous flow of water in the Chinese device, the medieval escapement was characterized by a regular, repeating sequence of discrete actions and the capability of self-reversing action:
Pierre Beaumarchais
At the time, pocket watches were commonly unreliable for timekeeping and were worn more as fashion accessories. In response to this, Beaumarchais spent nearly a year researching improvements. In July 1753, at the age of twenty one, he invented an escapement for watches that allowed them to be made substantially more accurate and compact.
Thomas Earnshaw
Thomas Earnshaw (4 February 1749 in Ashton-under-Lyne – 1 March 1829 in London) was an English watchmaker who, following John Arnold's earlier work, further simplified the process of marine chronometer production, making them available to the general public. He is also known for his improvements to the transit clock at the Royal Greenwich Observatory in London and his invention of a chronometer escapement and a form of bimetallic compensation balance.
In 1780, he devised a modification to the detached chronometer escapement, the detent being mounted on a spring instead of on pivots. This spring detent escapement was patented by Thomas Wright (for whom he worked) in 1783. Whilst initially the design was crude and unsuccessful, with modifications it later became the standard form in marine chronometers, following the invention of the detent escapement by Pierre Le Roy in 1748. John Arnold also invented a similar escapement in 1782.
Verge escapement
For the first two hundred years or so of the mechanical clock's existence, the verge, with foliot or balance wheel, was the only escapement used in mechanical clocks. In the sixteenth century alternative escapements started to appear, but the verge remained the most used escapement for 350 years until mid-17th century advances in mechanics, resulted in the adoption of the pendulum, and later the anchor escapement.
Since clocks were valuable, after the invention of the pendulum many verge clocks were rebuilt to use this more accurate timekeeping technology, so very few of the early "verge and foliot" clocks have survived unaltered to the present day.
Fusee (horology)
In pocketwatches, the verge escapement, which required a fusee, was gradually replaced by escapements which were less sensitive to changes in mainspring force; the cylinder and later the lever escapement. In 1760, Jean-Antoine Lépine dispensed with the fusee, inventing a "going barrel" to power the watch gear train directly. This contained a very long mainspring, of which only a few turns were used to power the watch. Accordingly, only a part of the mainspring's 'torque curve' was used, where the torque was approximately constant. In the 1780s, pursuing thinner watches, French watchmakers adopted the going barrel with the cylinder escapement. By 1850, the Swiss and American watchmaking industries employed the going barrel exclusively, aided by new methods of adjusting the balance spring so that it was isochronous. England continued to make the bulkier full plate fusee watches until about 1900 They were inexpensive models sold to the lower classes and were derisively called "turnips". After this, the only remaining use for the fusee was in marine chronometers, where the highest precision was needed, and bulk was less of a disadvantage, until they became obsolete in the 1970s.
Pin-pallet escapement
An escapement is the mechanism in a mechanical timepiece that gives the balance wheel pushes to keep it moving back and forth, and releases the timepiece's gears to advance a fixed amount with each swing of the wheel, thus moving the hands forward at a steady rate. The pin pallet escapement is similar to the lever escapement, which is used in quality watches, except that the horizontal jewel pallets on the lever are replaced with vertical metal pins, and the shape of the escape wheel teeth is modified.
Escapement
Jost Bürgi invented the cross-beat escapement in 1584, a variation of the verge escapement which had two foliots which rotated in opposite directions. According to contemporary accounts, his clocks achieved remarkable accuracy of within a minute per day, two orders of magnitude better than other clocks of the time. However, this improvement was probably not due to the escapement itself, but rather to better workmanship and his invention of the remontoire, a device which isolated the escapement from changes in drive force. Without a balance spring, the crossbeat would have been no more isochronous than the verge.
Galileo's escapement
Galileo's escapement is a design for a clock escapement, invented around 1637 by Italian scientist Galileo Galilei (1564 - 1642). It was the earliest design of a pendulum clock. Since he was blind, Galileo described the device to his son, who drew a sketch of it. The son began construction of a prototype, but both he and Galileo died before it was completed.
History of watches
The History of Watches began in 16th century Europe, where watches evolved from portable spring-driven clocks, which first appeared in the 15th century.
The watch which developed from the 16th century to the mid 20th century was a mechanical device, powered by winding a mainspring which turned gears and then moved the hands, and kept time with a rotating balance wheel. The invention of the quartz watch in the 1960s, which ran on electricity and kept time with a vibrating quartz crystal, proved a radical departure for the industry. During the 1980s quartz watches took over the market from mechanical watches, an event referred to as the "quartz crisis". Although mechanical watches still sell at the high end of the market, the vast majority of watches now have quartz movements.
Omega SA
In 1999, after the successful development of Calibre 2500, Omega made history by introducing the first mass-produced watch incorporating the coaxial escapement — invented by English watchmaker George Daniels. Considered by many to be one of the more significant horological advances since the invention of the lever escapement, the coaxial escapement functions with virtually no lubrication, thereby eliminating one of the shortcomings of the traditional lever escapement. Through using radial friction instead of sliding friction at the impulse surfaces the coaxial escapement significantly reduces friction, theoretically resulting in longer service intervals and greater accuracy over time.
Riefler escapement
The Riefler escapement is a mechanical escapement for precision pendulum clocks invented and patented by German instrument maker Sigmund Riefler in 1889. It was used in the astronomical regulator clocks made by his German firm Clemens Riefler from 1890 to 1965, which were perhaps the most accurate all-mechanical pendulum clocks made.
George Graham (clockmaker)
Between 1730 and 1738, Graham had as an apprentice Thomas Mudge, who went on to be an eminent watchmaker in his own right, and invented the lever escapement, an important development for pocket watches.
Escapement
In China, the Tang dynasty Buddhist monk Yi Xing along with government official Liang Lingzan made the escapement in 723 (or 725) to the workings of a water-powered armillary sphere and clock drive. Song dynasty (960–1279) horologists Zhang Sixun (fl. late 10th century) and Su Song (1020–1101) duly applied escapement devices for their astronomical clock towers, before the technology stagnated and retrogressed. According to historian Derek J. de Solla Price, the Chinese escapement spread west and was the source for Western escapement technology. According to Ahmad Y. Hassan, a mercury escapement in a Spanish work for Alfonso X in 1277 can be traced back to earlier Arabic sources. Knowledge of these mercury escapements may have spread through Europe with translations of Arabic and Spanish texts.
Time travel
One of the first stories to feature time travel by means of a machine is "The Clock that Went Backward" by Edward Page Mitchell, which appeared in the "New York Sun" in 1881. However, the mechanism borders on fantasy. An unusual clock, when wound, runs backwards and transports people nearby back in time. The author does not explain the origin or properties of the clock. Enrique Gaspar y Rimbau's "El Anacronópete" (1887) may have been the first story to feature a vessel engineered to travel through time. Andrew Sawyer has commented that the story "does seem to be the first literary description of a time machine noted so far", adding that "Edward Page Mitchell's story 'The Clock That Went Backward' (1881) is usually described as the first time-machine story, but I'm not sure that a clock quite counts." H. G. Wells's "The Time Machine" (1895) popularized the concept of time travel by mechanical means.
Anchor escapement
The anchor escapement was probably invented by British scientist Robert Hooke around 1657, although some references credit clockmaker William Clement, who popularized the anchor in his invention of the longcase or grandfather clock around 1680. When Clement's clock appeared Hooke claimed the invention of the escapement, saying that he had shown a clock with the same escapement to the Royal Society soon after the great fire of 1666. The earliest known anchor clock is Wadham College Clock, a tower clock built at Wadham College, Oxford, in 1670, probably by clockmaker Joseph Knibb. The anchor became the standard escapement used in almost all pendulum clocks.
Escapement
A gravity escapement uses a small weight or a weak spring to give an impulse directly to the pendulum. The earliest form consisted of two arms which were pivoted very close to the suspension spring of the pendulum with one arm on each side of the pendulum. Each arm carried a small dead beat pallet with an angled plane leading to it. When the pendulum lifted one arm far enough its pallet would release the escape wheel. Almost immediately another tooth on the escape wheel would start to slide up the angle face on the other arm thereby lifting the arm. It would reach the pallet and stop. The other arm meanwhile was still in contact with pendulum and coming down again to a point lower than it had started from. This lowering of the arm provides the impulse to the pendulum. The design was developed steadily from the middle of the 18th century to the middle of the 19th century. It eventually became the escapement of choice for turret clocks, because their wheel trains are subjected to large variations in drive force caused by the large exterior hands, with their varying wind, snow, and ice loads. Since in a gravity escapement the drive force from the wheel train does not itself impel the pendulum but merely resets the weights that provide the impulse, the escapement is not affected by variations in drive force.
Finmere
The tower has also an historic turret clock that was installed in 1697. 22 donors between them raised the £8 10s 0d cost. The clock was altered with a new escapement and other alterations in 1858 and reinstalled in 1859. Dr James Clarke of Finmere House designed the escapement and paid the £10 cost of reinstallation, which was done by William Bayliss, the village carpenter.
Verge escapement
Most of the gross inaccuracy of the early verge and foliot clocks was not due to the escapement itself, but to the foliot oscillator. The first use of pendulums in clocks around 1656 suddenly increased the accuracy of the verge clock from hours a day to minutes a day. Most clocks were rebuilt with their foliots replaced by pendulums, to the extent that it is difficult to find original verge and foliot clocks intact today. A similar increase in accuracy in verge watches followed the introduction of the balance spring in 1658.
Escapement
Based on patents initially submitted by Rolex on behalf of inventor Nicolas Déhon, the constant escapement was developed by Girard-Perregaux as working prototypes in 2008 (Nicolas Déhon was then head of Girard-Perregaux R&D department) and in watches by 2013.
Anchor escapement
In horology, the anchor escapement is a type of escapement used in pendulum clocks. The escapement is a mechanism in a mechanical clock that maintains the swing of the pendulum by giving it a small push each swing, and allows the clock's wheels to advance a fixed amount with each swing, moving the clock's hands forward. The anchor escapement was so named because one of its principal parts is shaped vaguely like a ship's anchor.
List of Alcatraz escape attempts
Frank Morris, John Anglin and Clarence Anglin successfully carried out one of the most intricate escapes ever devised, on June 11, 1962. Behind the prisoners' cells in Cell Block B (where the escapees were interned) was an unguarded wide utility corridor. The prisoners chiseled away the moisture-damaged concrete from around an air vent leading to this corridor, using tools such as metal spoons and forks soldered with silver from a dime and an electric drill improvised from a stolen vacuum cleaner motor. The noise was disguised by accordions, played during music hour (about 1 hour and a half), and their progress was concealed by false walls, which, in the dark recesses of the cells, fooled the guards.
Escapement
The detent is a detached escapement; it allows the balance wheel to swing undisturbed during most of its cycle, except the brief impulse period, which is only given once per cycle (every other swing). Because the driving escape wheel tooth moves almost parallel to the pallet, the escapement has little friction and did not need oiling. For these reasons among others the detent was considered the most accurate escapement for balance wheel timepieces. John Arnold was the first to use the detent escapement with an overcoil balance spring (patented 1782) and with this improvement his watches were the first really accurate pocket timekeepers, keeping time to within 1 or 2 seconds per day. These were produced from 1783 onwards.
Verge escapement
How accurate the first verge and foliot clocks were is debatable, with estimates of one to two hours error per day being mentioned, although modern experiments with clocks of this construction show accuracies of minutes per day were achievable. Early verge clocks were probably no more accurate than the previous water clocks, but they did not freeze in winter and were a more promising technology for innovation. By the mid-17th century, when the pendulum replaced the foliot, the best verge and foliot clocks had achieved an accuracy of 15 minutes per day.
Escapement
Both techniques used escapements, but these have only the name in common. The Chinese one worked intermittently; the European, in discrete but continuous beats. Both systems used gravity as the prime mover, but the action was very different. In the mechanical clock, the falling weight exerted a continuous and even force on the train, which the escapement alternately held back and released at a rhythm constrained by the controller. Ingeniously, the very force that turned the scape wheel then slowed it and pushed it part of the way back... In other words, a unidirectional force produced a self-reversing action—about one step back for three steps forward. In the Chinese timekeeper, however, the force exerted varied, the weight in each successive bucket building until sufficient to tip the release and lift the stop that held the wheel in place. This allowed the wheel to turn some ten degrees and bring the next bucket under the stream of water while the stop fell back... In the Chinese clock, then unidirectional force produced unidirectional motion.
Escapement
However the verge was the standard escapement used in every other early clock and watch, and remained the only escapement for 400 years. Its friction and recoil limited its performance, but the accuracy of these verge and foliot clocks was more limited by their early foliot type balance wheels, which because they lacked a balance spring had no natural "beat", so there was not much incentive to improve the escapement.
History of watches
The introduction of the quartz watch in 1969 was a revolutionary improvement in watch technology. In place of a balance wheel which oscillated at 5 beats per second, it used a quartz crystal resonator which vibrated at 8,192 Hz, driven by a battery-powered oscillator circuit. In place of a wheel train to add up the beats into seconds, minutes, and hours, it used digital counters. The higher Q factor of the resonator, along with quartz's low temperature coefficient, resulted in better accuracy than the best mechanical watches, while the elimination of all moving parts made the watch more shock-resistant and eliminated the need for periodic cleaning. The first digital electronic watch with an LED display was developed in 1970 by Pulsar. In 1974 the Omega Marine Chronometer was introduced, the first wrist watch to hold Marine Chronometer certification, and accurate to 12 seconds per year.
Accuracy increased with the frequency of the crystal used, but so did power consumption. So the first generation watches had low frequencies of a few kilohertz, limiting their accuracy. The power saving use of CMOS logic and LCDs in the second generation increased battery life and allowed the crystal frequency to be increased to 32,768 Hz resulting in accuracy of 5–10 seconds per month. By the 1980s, quartz watches had taken over most of the watch market from the mechanical watch industry. This upheaval, which saw the majority of watch manufacturing move to the Far East, is referred to in the industry as the "quartz crisis".
Thomas Mudge (horologist)
Thomas Mudge (1715 – 14 November 1794, London) was an English horologist who invented the lever escapement, the greatest single improvement ever applied to pocket watches.
Grasshopper escapement
The grasshopper escapement is a low-friction escapement for pendulum clocks invented by British clockmaker John Harrison around 1722. An escapement, part of every mechanical clock, is the mechanism that gives the clock's pendulum periodic pushes to keep it swinging, and each swing releases the clock's gears to move forward by a fixed amount, thus moving the hands forward at a steady rate. The grasshopper escapement was used in a few regulator clocks built during Harrison's time, and a few others over the years, but has never seen wide use. The term "grasshopper" in this connection, apparently from the kicking action of the pallets, first appears in the "Horological Journal" in the late 19th century.
Rolex
On 10 March 1943, while still a prisoner of war, Corporal Clive James Nutting, one of the organizers of the Great Escape, ordered a stainless steel Rolex Oyster 3525 Chronograph (valued at a current equivalent of £1,200) by mail directly from Hans Wilsdorf in Geneva, intending to pay for it with money he saved working as a shoemaker at the camp. The watch (Rolex watch no. 185983) was delivered to Stalag Luft III on 10 July that year along with a note from Wilsdorf apologising for any delay in processing the order and explaining that an English gentleman such as Corporal Nutting "should not even think" about paying for the watch before the end of the war. Wilsdorf is reported to have been impressed with Nutting because, although not an officer, he had ordered the expensive Rolex 3525 Oyster chronograph while most other prisoners ordered the much cheaper Rolex Speed King model which was popular because of its small size. The watch is believed to have been ordered specifically to be used in the Great Escape when, as a chronograph, it could have been used to time patrols of prison guards or time the 76 ill-fated escapees through tunnel 'Harry' on 24 March 1944. Eventually, after the war, Nutting was sent an invoice of only £15 for the watch, because of currency export controls in England at the time. The watch and associated correspondence between Wilsdorf and Nutting were sold at auction for £66,000 in May 2007, while at an earlier auction in September 2006 the same watch fetched A$54,000. Nutting served as a consultant for both the 1950 film "The Wooden Horse" and the 1963 film "The Great Escape". Both films were based on actual escapes which took place at Stalag Luft III. It was also reported that in November 2013 the Rolex Speed King owned by Flight Lieutenant Gerald Imeson during the Great Escape was sold for £60,000.
Georges Frederic Roskopf
Roskopf was granted US patent No. 75,463 10 Mar. 1868, for a changeable escapement for watches (this patent said that the escapement could be adapted for use with a cylinder or lever as well as a pin pallet). Roskopf patented his watch in France with French patent No. 80611 of 25 Mar. 1868 for a watch with a type of platform escapement. He patented his designs in several countries (Belgium, No. 21988, 3 Aug. 1867) but never in Switzerland, because Switzerland did not yet have a patenting system, and because the idea had been used there before his use of it.
Rasmus Sørnes
In the 1937 he constructed his first astronomical clock, showing standard and greenwich time, all solar and lunar cycles and phases, julian calendar, high and low tides and sunset/sunrise. The firmament is visualized on a two-dimensional dial, holes are drilled for the larger stars and the dial is illuminated from behind to make the stars visible in the evening. A switch allows the clock to be run forward and backwards in time. The clock is controlled by Sørnes' own invention, an electromagnetic balance wheel escapement. It feeds the system with a constant revolution of one rotation per second and is in this clock powered by two 1.5 V batteries. He experimented with the escapement for many years but eventually resorted to more traditional solutions. The accuracy of the celestial orbits suffered as the calculations were based on regular calendars without full correction of the irregularities. Around at the same time he designed and constructed a large reflecting telescope.
Turret clock
The Heinrich von Wieck clock in Paris dating from 1362 is the first clock of which it is known with certainty that it had a foliot and a verge escapement. The fact that there is a sudden increase in the number of recorded turret clock installations points to the fact that these new clocks use verge & foliot. This happens in the years 1350 and onwards.
Escapement
Since 1658 when the introduction of the pendulum and balance spring made accurate timepieces possible, it has been estimated that more than three hundred different mechanical escapements have been devised, but only about 10 have seen widespread use. These are described below. In the 20th century, electric timekeeping methods replaced mechanical clocks and watches, so escapement design became a little-known curiosity.
List of Dutch inventions and innovations
The first mechanical clocks, employing the verge escapement mechanism with a foliot or balance wheel timekeeper, were invented in Europe at around the start of the 14th century, and became the standard timekeeping device until the pendulum clock was invented in 1656. The pendulum clock remained the most accurate timekeeper until the 1930s, when quartz oscillators were invented, followed by atomic clocks after World War 2.
Escapement
Although some sources claim that French architect Villard de Honnecourt invented the first escapement around 1237 due to a drawing in his notebooks of a rope linkage to turn a statue of an angel to follow the sun, the consensus is that this was not an escapement. The first mechanical escapement, the verge escapement, was used in a bell ringing apparatus called an "alarum" for several centuries before it was adapted to clocks. In 14th-century Europe it appeared as the timekeeper in the first mechanical clocks, which were large tower clocks. Its origin and first use is unknown because it is difficult to distinguish which of these early tower clocks were mechanical, and which were water clocks. However, indirect evidence, such as a sudden increase in cost and construction of clocks, points to the late 13th century as the most likely date for the development of the modern clock escapement. Astronomer Robertus Anglicus wrote in 1271 that clockmakers were trying to invent an escapement, but hadn't been successful yet. On the other hand, most sources agree that mechanical escapement clocks existed by 1300.
History of timekeeping devices
The Rev. Edward Barlow invented the rack and snail striking mechanism for striking clocks, which was a great improvement over the previous mechanism. The repeating clock, that chimes the number of hours (or even minutes) was invented by either Quare or Barlow in 1676. George Graham invented the deadbeat escapement for clocks in 1720.
History of watches
The timekeeping mechanism in these early pocketwatches was the same one used in clocks, invented in the 13th century; the verge escapement which drove a foliot, a dumbbell shaped bar with weights on the ends, to oscillate back and forth. However, the mainspring introduced a source of error not present in weight-powered clocks. The force provided by a spring is not constant, but decreases as the spring unwinds. The rate of all timekeeping mechanisms is affected by changes in their drive force, but the primitive verge and foliot mechanism was especially sensitive to these changes, so early watches slowed down during their running period as the mainspring ran down. This problem, called lack of isochronism, plagued mechanical watches throughout their history.
Escapement
It was used in quality English pocketwatches from about 1790 to 1860,
Escapement
In the deadbeat, the pallets have a second curved "locking" face on them, concentric about the pivot on which the anchor turns. During the extremities of the pendulum's swing, the escape wheel tooth rests against this locking face, providing no impulse to the pendulum, which prevents recoil. Near the bottom of the pendulum's swing the tooth slides off the locking face onto the angled "impulse" face, giving the pendulum a push, before the pallet releases the tooth. This was the first escapement to separate the locking and impulse actions of the escapement. The deadbeat was first used in precision regulator clocks, but due to greater accuracy superseded the anchor in the 19th century. It is used in almost all modern pendulum clocks except for tower clocks which often use gravity escapements.
Echappement naturel
Breguet used the escapement in a few clocks although the escapement's self-starting ability is less of an advantage. Two carriage clocks are known, number 2516 sold in 1811 and number 262 sold in 1826. He also used it in a compteur militaire (number 1638 sold in 1814), a specialised watch used to regulate marching. The ability to sustain rough handling would have been more of an advantage for this but the potential for highly accurate timekeeping would appear to make this refinement redundant. Finally, he made two marine chronometers with the escapement with the added refinement of four separate barrels.
Jost Bürgi
It is undocumented where he learned his clockmaking skills, but eventually he became the most innovative clock and scientific instrument maker of his time. Among his major horological inventions were the cross-beat escapement, and the remontoire, two mechanisms which improved the accuracy of mechanical clocks of the time by orders of magnitude. This allowed for the first time clocks to be used as scientific instruments, with enough accuracy to time the passing of stars (and other heavenly bodies) in the crosshairs of telescopes to start accurately charting stellar positions.
History of watches
The lever escapement, invented by Thomas Mudge in 1759 and improved by Josiah Emery in 1785, gradually came into use from about 1800 onwards, chiefly in Britain; it was also adopted by Abraham-Louis Breguet, but Swiss watchmakers (who by now were the chief suppliers of watches to most of Europe) mostly adhered to the cylinder until the 1860s. By about 1900, however, the lever was used in almost every watch made. In this escapement the escape wheel pushed on a T shaped 'lever', which was unlocked as the balance wheel swung through its centre position and gave the wheel a brief push before releasing it. The advantages of the lever was that it allowed the balance wheel to swing completely free during most of its cycle; due to 'locking' and 'draw' its action was very precise; and it was self-starting, so if the balance wheel was stopped by a jar it would start again.
History of timekeeping devices
The first geared clock was invented in the 11th century by the Arab engineer Ibn Khalaf al-Muradi in Islamic Iberia; it was a water clock that employed a complex gear train mechanism, including both segmental and epicyclic gearing, capable of transmitting high torque. The clock was unrivalled in its use of sophisticated complex gearing, until the mechanical clocks of the mid-14th century. Al-Muradi's clock also employed the use of mercury in its hydraulic linkages, which could function mechanical automata. Al-Muradi's work was known to scholars working under Alfonso X of Castile, hence the mechanism may have played a role in the development of the European mechanical clocks. Other monumental water clocks constructed by medieval Muslim engineers also employed complex gear trains and arrays of automata. Like the earlier Greeks and Chinese, Arab engineers at the time also developed a liquid-driven escapement mechanism which they employed in some of their water clocks. Heavy floats were used as weights and a constant-head system was used as an escapement mechanism, which was present in the hydraulic controls they used to make heavy floats descend at a slow and steady rate.
Elephant clock
In China clock escapement mechanism was invented by the polymath and buddhist monk Yi Xing as well as the hydraulic powered waterwheel and water clock in the mechanically-driven and rotated equatorial armillary sphere of the polymaths Zhang Heng and Ma Jun. The Elephant clock had some design differences compared to earlier Indian and Chinese clocks and the various elements of the clock are in the housing (howdah) on top of the elephant.
Escapement
Pendulum-based clocks can achieve outstanding accuracy. Even into the 20th century, pendulum-based clocks were reference time pieces in laboratories.
Watch
The first quartz watch to enter production was the Seiko 35 SQ Astron, which hit the shelves on 25 December 1969, swiftly followed by the Swiss Beta 21, and then a year later the prototype of one of the world's most accurate wristwatches to date: the Omega Marine Chronometer. Since the technology having been developed by contributions from Japanese, American and Swiss, nobody could patent the whole movement of the quartz wristwatch, thus allowing other manufacturers to participate in the rapid growth and development of the quartz watch market. This ended—in less than a decade—almost 100 years of dominance by the mechanical wristwatch legacy. Modern quartz movements are produced in very large quantities, and even the cheapest wristwatches typically have quartz movements. Whereas mechanical movements can typically be off by several seconds a day, an inexpensive quartz movement in a child's wristwatch may still be accurate to within half a second per day—ten times more accurate than a mechanical movement.
Verge escapement
The verge escapement dates from 13th-century Europe, where its invention led to the development of the first all-mechanical clocks. Starting in the 13th century, large tower clocks were built in European town squares, cathedrals, and monasteries. 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. The foliot was a horizontal bar with weights near the ends, and the rate of the clock could be adjusted by moving the weights in or out on the bar.
Verge escapement
Verge escapements were used in virtually all clocks and watches for 400 years. Then the increase in accuracy due to the introduction of the pendulum and balance spring in the mid 17th century focused attention on error caused by the escapement. By the 1820s, the verge was superseded by better escapements, though many examples of mid 19th century verge watches exist, as they were much cheaper by this time.
Escapement
The lever escapement, invented by Thomas Mudge in 1750, has been used in the vast majority of watches since the 19th century. Its advantages are (1) it is a "detached" escapement; unlike the cylinder or duplex escapements the balance wheel is only in contact with the lever during the short impulse period when it swings through its centre position and swings freely the rest of its cycle, increasing accuracy, and (2) it is a self-starting escapement, so if the watch is shaken so that the balance wheel stops, it will automatically start again. The original form was the rack lever escapement, in which the lever and the balance wheel were always in contact via a gear rack on the lever. Later, it was realized that all the teeth from the gears could be removed except one, and this created the detached lever escapement. British watchmakers used the English detached lever, in which the lever was at right angles to the balance wheel. Later Swiss and American manufacturers used the inline lever, in which the lever is inline between the balance wheel and the escape wheel; this is the form used in modern watches. In 1867 Georges Frederic Roskopf invented an inexpensive, less accurate form called the Roskopf or pin-pallet escapement, which was used in cheap "dollar watches" in the early 20th century and is still used in cheap alarm clocks and kitchen timers.
Echappement naturel
The first group contains four watches which were made as part of the development of the escapement. Each watch in this group is different and each watch is part of a linear development of the escapement from the first watch, started in 1802, to the last started in 1806. The four watches seem to be of two types. The first two watches share the features of both being small, having the rarer gold dials and apparently were planned to have new escapement at the outset. The second two watches were of the usual size for men’s watches, they had the more normal silver and enamel dials and it would appear that neither was initially planned to contain the new escapement but were taken from stock and upgraded. They also show some of the improvements in design that led to the final use of the escapement in a series of tourbillon garde-temps made after 1808. For example, the driven escape wheels are smaller than the drivers and a sprung setting for the detent is introduced.
Science and technology of the Tang dynasty
Technology during the Tang period was built also upon the precedents of the past. The mechanical gear systems of Zhang Heng (78-139) and Ma Jun (fl. 3rd century) gave the Tang engineer, astronomer, and monk Yi Xing (683-727) inspiration when he invented the world's first clockwork escapement mechanism in 725. This was used alongside a clepsydra clock and waterwheel to power a rotating armillary sphere in representation of astronomical observation. Yi Xing's device also had a mechanically timed bell that was struck automatically every year, and a drum that was struck automatically every quarter-hour; essentially, a striking clock. Yi Xing's astronomical clock and water-powered armillary sphere became well known throughout the country, since students attempting to pass the imperial examinations by 730 had to write an essay on the device as an exam requirement. However, the most common type of public and palace timekeeping device was the inflow clepsydra. Its design was improved "c". 610 by the Sui-dynasty engineers Geng Xun and Yuwen Kai. They provided a steelyard balance that allowed seasonal adjustment in the pressure head of the compensating tank and could then control the rate of flow for different lengths of day and night.
Escapement
However, the escapement had disadvantages which limited its use in watches: it was fragile and required skilled maintenance; it was not self-starting, so if the watch was jarred in use so the balance wheel stopped, it would not start up again; and it was harder to manufacture in volume. Therefore, the self-starting lever escapement became dominant in watches.
Escapement
Invented around 1974 and patented 1980 by British watchmaker George Daniels, the coaxial escapement is one of the few new watch escapements adopted commercially in modern times. It can be classed as a detached escapement.
Grasshopper escapement
A grasshopper-type escapement is used in an entirely new mechanism intended for wristwatches. This new type of mechanical regulator uses flexible structures both in the escapement and the oscillator. A silicon wheel oscillates about 86,400 times an hour, approximately three times faster than in conventional wristwatches. The initial development was done at the Swiss Center for Electronics and Microtechnology (CSEM) with Pierre Genequand, a Swiss physicist, as lead inventor. By eliminating friction as much as possible, such a watch can run for more than a month after rewinding, an exceptional power-reserve. The prototype of such a new calibre (movement) has been exhibited by Parmigiani Fleurier.
Pendulum clock
Although the escapement is necessary, its force disturbs the natural motion of the pendulum, and in precision pendulum clocks this was often the limiting factor on the accuracy of the clock. Different escapements have been used in pendulum clocks over the years to try to solve this problem. In the 18th and 19th century escapement design was at the forefront of timekeeping advances. The anchor escapement (see animation) was the standard escapement used until the 1800s when an improved version, the deadbeat escapement took over in precision clocks. It is used in almost all pendulum clocks today. The remontoire, a small spring mechanism rewound at intervals which serves to isolate the escapement from the varying force of the wheel train, was used in a few precision clocks. In tower clocks the wheel train must turn the large hands on the clock face on the outside of the building, and the weight of these hands, varying with snow and ice buildup, put a varying load on the wheel train. Gravity escapements were used in tower clocks.
Verge escapement
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'. Its origin is unknown. Verge escapements were used from the 14th century until the mid 19th century in clocks and pocketwatches. The name verge comes from the Latin "virga", meaning stick or rod.
History of timekeeping devices
In England, the manufacturing of pendulum clocks was soon taken up. The longcase clock (also known as the grandfather clock) was first created to house the pendulum and works by the English clockmaker William Clement in 1670 or 1671; this became feasible after Clement invented the anchor escapement mechanism in about 1670. Before then, pendulum clocks used the older verge escapement mechanism, which required very wide pendulum swings of about 100°. To avoid the need for a very large case, most clocks using the verge escapement had a short pendulum. The anchor mechanism, however, reduced the pendulum's necessary swing to between 4° to 6°, allowing clockmakers to use longer pendulums with consequently slower beats. These required less power to move, caused less friction and wear, and were more accurate than their shorter predecessors. Most longcase clocks use a pendulum about a metre (39 inches) long to the center of the bob, with each swing taking one second. This requirement for height, along with the need for a long drop space for the weights that power the clock, gave rise to the tall, narrow case.
History of timekeeping devices
The earliest known clock with a water-powered escapement mechanism, which transferred rotational energy into intermittent motions, dates back to 3rd century in ancient Greece; Chinese engineers later invented clocks incorporating mercury-powered escapement mechanisms in the 10th century, followed by Iranian engineers inventing water clocks driven by gears and weights in the 11th century.
Turret clock
The first all-mechanical clocks which emerged in the 14th century kept time with a verge escapement and foliot. In the second half of the 14th century, over 500 striking turret clocks were installed in public buildings all over Europe. This was the first time public clocks became easy to maintain, as water clocks needed more or less constant attention, so only wealthy institutions with enough manpower could maintain them. The verge and foliot mechanical clocks were relatively easy to maintain and so found their way into many churches, bell towers and town halls. This new technology spread quite fast (within a decade all over Europe).
History of watches
A great leap forward in accuracy occurred in 1657 with the addition of the balance spring to the balance wheel, an invention disputed both at the time and ever since between Robert Hooke and Christiaan Huygens. Prior to this, the only force limiting the back and forth motion of the balance wheel under the force of the escapement was the wheel's inertia. This caused the wheel's period to be very sensitive to the force of the mainspring. The balance spring made the balance wheel a harmonic oscillator, with a natural 'beat' resistant to disturbances. This increased watches' accuracy enormously, reducing error from perhaps several hours per day to perhaps 10 minutes per day, resulting in the addition of the minute hand to the face from around 1680 in Britain and 1700 in France. The increased accuracy of the balance wheel focused attention on errors caused by other parts of the movement, igniting a two century wave of watchmaking innovation.
Riefler escapement
Clemens Riefler precision regulator clocks achieved accuracies of 10 milliseconds per day, and were guaranteed to be within 30 milliseconds. With over 600 made, they were one of the most widely used astronomical regulators, and became the highest standard for timekeeping in the early 20th century. They were used worldwide in astronomical observatories, naval observatories, and as primary standards for electrical time dissemination services, which delivered time signals by telegraph wire. Riefler clocks had internal switch contacts for this purpose, which delivered a 1 Hz time signal to external equipment. The first time standard for the United States, provided by the Bureau of Standards (now NIST), was from 1904 to 1929 generated by Riefler clocks.
Tourbillon
In horology, a tourbillon (; "whirlwind") is an addition to the mechanics of a watch escapement. Developed around 1795 and patented by the French-Swiss watchmaker Abraham-Louis Breguet on June 26, 1801, a tourbillon aims to counter the effects of gravity by mounting the escapement and balance wheel in a rotating cage, to negate the effect of gravity when the timepiece (thus the escapement) is stuck in a certain position. By continuously rotating the entire balance wheel/escapement assembly at a slow rate (typically about one revolution per minute), the tourbillon averages out positional errors.
Watch
The pin-lever escapement (called the Roskopf movement after its inventor, Georges Frederic Roskopf), which is a cheaper version of the fully levered movement, was manufactured in huge quantities by many Swiss manufacturers as well as by Timex, until it was replaced by quartz movements.
History of watches
From about 1860, key winding was replaced by keyless winding, where the watch was wound by turning the crown. The pin pallet escapement, an inexpensive version of the lever escapement invented in 1876 by Georges Frederic Roskopf was used in cheap mass-produced watches, which allowed ordinary workers to own a watch for the first time; other cheap watches used a simplified version of the duplex escapement, developed by Daniel Buck in the 1870s.
History of timekeeping devices
Thomas Tompion was the first English clockmaker with an international reputation and many of his pupils went on to become great horologists in their own right, such as George Graham who invented the deadbeat escapement, orrery and mercury pendulum, and his pupil Thomas Mudge who created the first lever escapement. Famous clockmakers of this period included Joseph Windmills, Simon de Charmes who established the De Charmes clockmaker firm and Christopher Pinchbeck who invented the alloy pinchbeck.
L'Epée Clocks
Just seven years after launching this new line of business, L’Epée submitted its first patents to the authorities to establish and protect its expertise. The Manufacture won recognition throughout the clock making world for its high-quality platform escapements, several of which presented highly specific systems that were very useful at the time, placing the company at the forefront of the horological scene. Some of these patents, such as those protecting the "anti-knocking" system, the "auto-starting" mechanism, and the constant-force escapement, made a lasting impression on their era.
Congreve clock
Congreve appears to have been unaware that rolling ball clocks had been invented earlier by both Nicolas Grollier de Servière and Johann Sayller. Congreve's version differed from Grollier's rolling ball clock in that the ball travelled down a zig-zag rather than straight path. While Sayller's version had also used a zig-zag path, it had utilized a number of balls and a fixed table rather than the single ball and tilting table employed by Congreve. The "Extreme Detached Escapement" (as Congreve referred to his escapement design) was patented in 1808. Congreve, who was not a clock maker, hired Gravel and Tolkien to produce the first working version, which he then presented to the Prince of Wales in 1808. This version was weight-driven, but the second design, which appears to have been constructed by John Moxon, was spring-driven. The second model is in the collection of Buckingham Palace.
Mechanical engineering
The application of mechanical engineering can be seen in the archives of various ancient and medieval societies. In ancient Greece, the works of Archimedes (287–212 BC) influenced mechanics in the Western tradition and Heron of Alexandria (c. 10–70 AD) created the first steam engine (Aeolipile). In China, Zhang Heng (78–139 AD) improved a water clock and invented a seismometer, and Ma Jun (200–265 AD) invented a chariot with differential gears. The medieval Chinese horologist and engineer Su Song (1020–1101 AD) incorporated an escapement mechanism into his astronomical clock tower two centuries before escapement devices were found in medieval European clocks. He also invented the world's first known endless power-transmitting chain drive.
Escapement
Wristwatches and smaller clocks do not use pendulums as the timing device. Instead, they use a balance spring: a fine spring connected to a metal balance wheel that oscillates (rotates back and forth). Most modern mechanical watches have a working frequency of 3 to 4 Hz (3 - 4 cycles, or 6 - 8 beats per second, 21,600 - 28,800 beats per hour or bph). Faster or slower speeds are used in some watches (33,600 bph or 19,800 bph). The beats per minute depend on the balance spring's stiffness (spring constant); to keep time, the stiffness should not vary with temperature. Consequently, balance springs use sophisticated alloys; in this area, watchmaking is still advancing. As with the pendulum, the escapement must provide a small kick each cycle to keep the balance wheel oscillating. Also, the same lubrication problem occurs over time; the watch will lose accuracy (typically it will speed up) when the escapement lubrication starts failing.
Verge escapement
Its invention is important in the history of technology, because it made possible the development of all-mechanical clocks. 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. Oscillating timekeepers are used in all modern timepieces.
Anchor escapement
The anchor was the second widely used escapement in Europe, replacing the 400-year-old verge escapement in pendulum clocks. The pendulums in verge escapement clocks had very wide swings of 80° to 100°. In 1673, seventeen years after he invented the pendulum clock, Christiaan Huygens published his mathematical analysis of pendulums, "Horologium Oscillatorium". In it he showed that the wide pendulum swings of verge clocks caused them to be inaccurate, because the period of oscillation of the pendulum was not isochronous but varied to a small degree due to circular error with changes in the amplitude of the pendulum's swing, which occurred with unavoidable changes in drive force. The realization that only small pendulum swings were nearly isochronous motivated clockmakers to design small swing escapements.
The chief advantage of the anchor was that by locating the pallets farther from the pivot, the swing of the pendulum was reduced from around 100° in verge clocks to only 4°-6°. In addition to the improved accuracy due to isochronism, this allowed clocks to use longer pendulums, which had a slower 'beat'. Lower air drag meant they needed less power to keep swinging, and caused less wear on the clock's movement. The anchor also allowed the use of a heavier pendulum bob for a given drive force, making the pendulum more independent of the escapement (higher Q), and thus more accurate. These long pendulums required long narrow clock cases. Around 1680 British clockmaker William Clement began selling the first commercial clocks to use the anchor escapement, tall freestanding clocks with 1 meter (39 inch) seconds pendulums that came to be called longcase or 'grandfather' clocks. The anchor increased the accuracy of clocks so much that around 1680–1690 the use of the minute hand, formerly the exception in clocks, became the rule.
Escapement
In an effort to attract publicity, in recent decades some high end mechanical watch makers have introduced new escapements. None of these have been adopted by any watchmakers beyond their original creator.
Seconds pendulum
The 18th and 19th century wave of horological innovation that followed the invention of the pendulum brought many improvements to pendulum clocks. The deadbeat escapement invented in 1675 by Richard Towneley and popularised by George Graham around 1715 in his precision "regulator" clocks gradually replaced the anchor escapement and is now used in most modern pendulum clocks. Observation that pendulum clocks slowed down in summer brought the realisation that thermal expansion and contraction of the pendulum rod with changes in temperature was a source of error. This was solved by the invention of temperature-compensated pendulums; the mercury pendulum by George Graham in 1721 and the gridiron pendulum by John Harrison in 1726. With these improvements, by the mid-18th century precision pendulum clocks achieved accuracies of a few seconds per week.
Grasshopper escapement
John Harrison used the grasshopper escapement in his regulator clocks, and also for the first three of his marine timekeepers, H1 - H3. Determining longitudinal position was a major problem in marine navigation; Newton argued that astronomical positioning could be used, but an easier theoretical possibility was to use accurate knowledge of the time at a specific base location. The difference in time between local time, which was easy to measure, and the time at base gives the difference in longitude between the base and the ship, since 24 hours of time is equivalent to 360 degrees of longitude. A large prize was offered for a solution to the problem and Harrison devoted his life to devising and building highly accurate timekeepers. Precision and friction were the main problems. Two advantages of the grasshopper escapement are the repeatability of its operation and that it does not need lubrication. The repeatability of its operation is inherent in its design. One pallet is released only by the engagement of the other; the impulse given to the pendulum is thus completely regular in its timing. Lubricants available to Harrison were poor, messy and short-lived. This meant that conventional clocks had to be stopped frequently for cleaning and oiling. Using his clean and absolutely stable grasshopper escapement Harrison began a series of long-term investigations into the performance of clocks, leading to his invention of the gridiron pendulum which counteracted the effects of expansion and contraction with changing temperature. The performance of his improved clocks in turn gave him an accurate, convenient standard against which to test his marine timekeepers.
Josiah Emery
Josiah Emery (c. 1725-1797) was a watchmaker who improved Thomas Mudge's lever escapement in 1785. One of his watches was presented to Lord Nelson who was wearing it when he was killed by a sniper at the Battle of Trafalgar in 1805. Others were made for George III.
Josiah Emery was a Geneva watchmaker who set up in England at 33 Cockspur Street, Charing Cross, London. He was made an honorary member of the Guild of Clock Makers. He made good quality cylinder watches and used the pivoted detent escapement. Thomas Mudge invented the lever escapement, and Emery was the first watchmaker to use it and made some improvements.
Escapement
The great leap in accuracy resulting from the invention of the pendulum and balance spring around 1657, which made the timekeeping elements in both watches and clocks harmonic oscillators, focused attention on the errors of the escapement, and more accurate escapements soon superseded the verge. The next two centuries, the "golden age" of mechanical horology, saw the invention of perhaps 300 escapement designs, although only about 10 stood the test of time and were widely used in clocks and watches. These are described individually below.
Richard Towneley
Flamsteed wrote often to Towneley about the clocks, which were made to run for a year between windings. It proved difficult to keep both clocks running for a whole year and, in January 1678, Tompion replaced the original escapement with one of his own design. The clocks eventually went for four years without stopping and Flamsteed was able to prove to his own satisfaction that the Earth rotated at a constant speed. Although Towneley and Tompion could be considered the first people to attempt to make a deadbeat escapement, it was only in about 1715 that George Graham created one that was truly successful.
Escapement
The great clock at Westminster that rings London's Big Ben uses a double three-legged gravity escapement.
Verge escapement
It is believed that sometime in the late 13th century the verge escapement mechanism was applied to tower clocks, creating the first mechanical clock. In spite of the fact that these clocks were celebrated objects of civic pride which were written about at the time, it may never be known when the new escapement was first used. This is because it has proven difficult to distinguish from the meager written documentation which of these early tower clocks were mechanical, and which were water clocks; the same Latin word, "horologe", was used for both. None of the original mechanisms have survived unaltered. Sources differ on which was the first clock 'known' to be mechanical, depending on which manuscript evidence they regard as conclusive. 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. Another is the clock built at the Palace of the Visconti, Milan, Italy, in 1335. However, there is agreement that mechanical clocks existed by the late 13th century.