706:, a horizontal bar with weights at either end. The escapement consists of an escape wheel shaped somewhat like a crown, with pointed teeth sticking axially out of the side, oriented horizontally. In front of the crown wheel is a vertical shaft, attached to the foliot at the top, which carries two metal plates (pallets) sticking out like flags from a flag pole, oriented about ninety degrees apart, so only one engages the crown wheel teeth at a time. As the wheel turns, one tooth pushes against the upper pallet, rotating the shaft and the attached foliot. As the tooth pushes past the upper pallet, the lower pallet swings into the path of the teeth on the other side of the wheel. A tooth catches on the lower pallet, rotating the shaft back the other way, and the cycle repeats. A disadvantage of the escapement was that each time a tooth landed on a pallet, the momentum of the foliot pushed the crown wheel backward a short distance before the force of the wheel reversed the motion. This is called "
1417:
ratchet wheel via a pawl on the pendulum rod, and the ratchet wheel drove the rest of the clock train to indicate the time. The pendulum was not impelled on every swing or even at a set interval of time. It was only impelled when its arc of swing had decayed below a certain level. As well as the counting pawl, the pendulum carried a small vane, known as a Hipp's toggle, pivoted at the top, which was completely free to swing. It was placed so that it dragged across a triangular polished block with a vee-groove in the top of it. When the arc of swing of the pendulum was large enough, the vane crossed the groove and swung free on the other side. If the arc was too small the vane never left the far side of the groove, and when the pendulum swung back it pushed the block strongly downwards. The block carried a contact which completed the circuit to the electromagnet which impelled the pendulum. The pendulum was only impelled as required.
938:
1153:
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 1798, Louis Perron invented an inexpensive, less accurate form called the
1218:
pendulum swings back again, the other arm catches the wheel, pushes it back and releases the first arm, and so on. The grasshopper escapement has been used in very few clocks since
Harrison's time. Grasshopper escapements made by Harrison in the 18th century are still operating. Most escapements wear far more quickly, and waste far more energy. However, like other early escapements, the grasshopper impulses the pendulum throughout its cycle; it is never allowed to swing freely, causing error due to variations in drive force, and 19th-century clockmakers found it uncompetitive with more detached escapements like the deadbeat. Nevertheless, with enough care in construction it is capable of accuracy. A modern experimental grasshopper clock, the Burgess Clock B, had a measured error of only
1437:, the Synchronome switch and gravity escapement were the basis for the majority of their clocks in the 20th century. And also the basis of the slave pendulum in the Shortt-Synchronome free pendulum clock. A gathering arm attached to the pendulum moves a 15-tooth count wheel in one position, with a pawl preventing movement in the reverse direction. The wheel has a vane attached which, once per 30-second turn, releases the gravity arm. When the gravity arm falls it pushes against a pallet attached directly to the pendulum, giving it a push. Once the arm has fallen, it makes an electrical contact that energises an electromagnet to reset the gravity arm and acts as the half-minute impulse for the slave clocks.
721:. It was used in the first pendulum clocks for about 50 years after the pendulum clock was invented in 1656. In a pendulum clock, the crown wheel and staff were oriented so they were horizontal, and the pendulum was hung from the staff. However, the verge is the most inaccurate of the common escapements, and after the pendulum was introduced in the 1650s, the verge began to be replaced by other escapements, being abandoned only by the late 1800s. By this time, the fashion for thin watches had required that the escape wheel be made very small, amplifying the effects of wear, and when a watch of this period is wound up today, it will often be found to run very fast, gaining many hours per day.
1245:
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 the 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
1089:
cycle starts with a locking tooth resting against the ruby disk. As the balance wheel swings counterclockwise through its center position, the notch in the ruby disk releases the tooth. As the escape wheel turns, the pallet is in just the right position to receive a push from an impulse tooth. Then the next locking tooth drops onto the ruby roller and stays there while the balance wheel completes its cycle and swings back clockwise (CW), and the process repeats. During the CW swing, the impulse tooth falls momentarily into the ruby roller notch again but is not released.
678:
436:
artificial ruby), but even so, they normally require lubrication. Since lubricating oil degrades over time due to evaporation, dust, oxidation, etc., periodic re-lubrication is needed. If this is not done, the timepiece may work unreliably or stop altogether, and the escapement components may be subjected to rapid wear. The increased reliability of modern watches is due primarily to the higher-quality oils used for lubrication. Lubricant lifetimes can be greater than five years in a high-quality watch.
1461:
triggers an electromagnet slightly less than every thirty seconds. This electromagnet releases a gravity lever onto the escapement above the master pendulum. A fraction of a second later (but exactly every 30 seconds), the motion of the master pendulum releases the gravity lever to fall farther. In the process, the gravity lever gives a tiny impulse to the master pendulum, which keeps that pendulum swinging. The gravity lever falls onto a pair of contacts, completing a circuit that does several things:
315:
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, as do all liquid clocks. The rate of flow of a liquid through an orifice varies with temperature and viscosity changes and decreases with pressure as the level of liquid in the source container drops. 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.
143:, allowing the clock's gear train to advance or "escape" by a fixed amount. This regular periodic advancement moves the clock's hands forward at a steady rate. At the same time, the tooth gives the timekeeping element a push, before another tooth catches on the escapement's pallet, returning the escapement to its "locked" state. The sudden stopping of the escapement's tooth is what generates the characteristic "ticking" sound heard in operating mechanical clocks and watches.
1197:
1327:
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.
1001:
922:
790:
530:); 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.
1260:
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
1100:, there is little sliding friction during impulse since pallet and impulse tooth are moving almost parallel, so little lubrication is needed. However, it lost favor to the lever; its tight tolerances and sensitivity to shock made duplex watches unsuitable for active people. Like the chronometer, it is not self-starting and is vulnerable to "setting;" if a sudden jar stops the balance during its CW swing, it cannot get started again.
1347:
876:
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. The deadbeat was first used in precision regulator clocks, but because of its 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.
1045:
it leaves out the other side. The wheel usually had 15 teeth and impulsed the balance over an angle of 20° to 40° in each direction. It is a frictional rest escapement, with the teeth in contact with the cylinder over the whole balance wheel cycle, and so was not as accurate as "detached" escapements like the lever, and the high friction forces caused excessive wear and necessitated more frequent cleaning.
1291:
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1054:
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1264:, 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.
1249:, 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.
1132:
1303:
1120:
1358:, improved escapement designs are no longer motivated by practical timekeeping needs but as novelties in the high-end watch market. In an effort to attract publicity, in recent decades some high-end mechanical watchmakers have introduced new escapements. None of these have been adopted by any watchmakers beyond their original creator.
43:
1334:
The main advantage is that this enables both impulses to occur on or around the centre line, with disengaging friction in both directions. This mode of impulse is in theory superior to the lever escapement, which has engaging friction on the entry pallet. For long, this was recognized as a disturbing
1330:
The
Daniels escapement, however, achieves a double impulse with passive lever pallets serving only to lock and unlock the larger wheel. On one side, impulse is given by means of the smaller wheel acting on the lever pallet through the roller and impulse pin. On the return, the lever again unlocks the
1044:
Rather than pallets, the escapement uses a cutaway cylinder on the balance wheel shaft, which the escape teeth enter one by one. Each wedge-shaped tooth impulses the balance wheel by pressure on the cylinder edge as it enters, is held inside the cylinder as it turns, and impulses the wheel again as
966:
in 1780 and patented by Wright (for whom he worked) in 1783; however, as depicted in the patent it was unworkable. Arnold also designed a spring detent escapement but, with improved design, Earnshaw's version eventually prevailed as the basic idea underwent several minor modifications during the last
954:, although some precision watches during the 18th and 19th centuries also used it. It was considered the most accurate of the balance wheel escapements before the beginning of the 20th century, when lever escapement chronometers began to outperform them in competition. The early form was invented by
3143:
Hipp, Matth.(aeus): Sich selbst controlirende Uhr, welche augenbliklich anzeigt, wenn die durch
Reibung etc. verursachte Unregelmäßigkeit im Gang auch nur den tausendsten Theil einer Secunde ausmacht und welche ein mehr als hundertfach größeres Hinderniß überwindet, ehe sie stehen bleibt, als andere
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Since it is the slave pendulum that releases the gravity lever, this synchronization is vital to the functioning of the clock. The synchronizing mechanism used a small spring attached to the shaft of the slave pendulum and an electromagnetic armature that would catch the spring if the slave pendulum
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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,
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during the 13th century and was the crucial innovation that led to the development of the mechanical clock. The design of the escapement has a large effect on a timepiece's accuracy, and improvements in escapement design drove improvements in time measurement during the era of mechanical timekeeping
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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
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which had two foliots that 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,
435:
In many escapements, the unlocking of the escapement involves sliding motion; for example, in the animation shown above, the pallets of the anchor slide against the escapement wheel teeth as the pendulum swings. The pallets are often made of very hard materials such as polished stone (for example,
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The reliability of an escapement depends on the quality of workmanship and the level of maintenance given. A poorly constructed or poorly maintained escapement will cause problems. The escapement must accurately convert the oscillations of the pendulum or balance wheel into rotation of the clock or
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escapement. It consisted of a pair of escape wheels on the same axle, with alternating radial teeth. The verge rod was suspended between them, with a short crosspiece that rotated first in one direction and then the other as the staggered teeth pushed past. Although no other example is known, it is
1372:
The key component of this escapement is a silicon buckled-blade which stores elastic energy. This blade is flexed to a point close to its unstable state and is released with a snap each swing of the balance wheel to give the wheel an impulse, after which it is cocked again by the wheel train. The
1036:
in 1726, was one of the escapements which replaced the verge escapement in pocketwatches after 1700. A major attraction was that it was much thinner than the verge, allowing watches to be made fashionably slim. Clockmakers found it suffered from excessive wear, so it was not much used during the
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However, the escapement had disadvantages that 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,
820:
The anchor consists of an escape wheel with pointed, backward slanted teeth, and an "anchor"-shaped piece pivoted above it which rocks from side to side, linked to the pendulum. The anchor has slanted pallets on the arms which alternately catch on the teeth of the escape wheel, receiving impulses.
1416:
first mentioned a purely mechanical clock being driven by a switch called "echappement à palette". A varied version of that escapement has been used from the 1860s inside electrically driven pendulum clocks, the so-called "hipp-toggle". Since the 1870s, in an improved version the pendulum drove a
1326:
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
1322:
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
1259:
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
1244:
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 deadbeat pallet
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to which it has similarities, the balance wheel only receives an impulse during one of the two swings in its cycle. The escape wheel has two sets of teeth (hence the name 'duplex'); long locking teeth project from the side of the wheel, and short impulse teeth stick up axially from the top. The
970:
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
474:
depends slightly on the size of the swing. If the amplitude changes from 4° to 3°, the period of the pendulum will decrease by about 0.013 percent, which translates into a gain of about 12 seconds per day. This is caused by the restoring force on the pendulum being circular not linear; thus, the
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called "being in beat." This is because pushing a pendulum when it is moving towards mid-swing makes it gain, whereas pushing it while it is moving away from mid-swing makes it lose. If the impulse is evenly distributed then it gives energy to the pendulum without changing the time of its swing.
314:
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
466:
Escapements play a big part in accuracy as well. The precise point in the pendulum's travel at which impulse is supplied will affect how closely to time the pendulum will swing. Ideally, the impulse should be evenly distributed on either side of the lowest point of the pendulum's swing. This is
455:
The accuracy of a mechanical clock is dependent on the accuracy of the timing device. If this is a pendulum, then the period of swing of the pendulum determines the accuracy. If the pendulum rod is made of metal it will expand and contract with heat, lengthening or shortening the pendulum; this
336:
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.) Its origin and first use is unknown because it is difficult to distinguish which of these early tower
1460:
whose length changes very little with temperature, swings as free of external influence as possible sealed in a vacuum chamber and does no work. It is in mechanical contact with its escapement for only a fraction of a second every 30 seconds. A secondary "slave" pendulum turns a ratchet, which
1217:
invented in 1722. In this escapement, the pendulum is driven by two hinged arms (pallets). As the pendulum swings, the end of one arm catches on the escape wheel and drives it slightly backwards; this releases the other arm which moves out of the way to allow the escape wheel to pass. When the
243:
in the process. Once the spoon has emptied, it is pulled up again by the counterweight, closing the door on the pumice by the tightening string. Remarkably, Philo's comment that "its construction is similar to that of clocks" indicates that such escapement mechanisms were already integrated in
1152:
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
3153:
French patent for an electrical driven pendulum clock with hipp-toggle, May 27, 1863: "Pendule ou horloge électro-magnétique à appal direct d’électricité" - The evolution of the hipp-toggle is described by: Johannes Graf: Der lange Weg zur Hipp-Wippe. Ab wann werden Uhren von matthaeus Hipp
1016:
903:
Invented around 1741 by Louis Amant, this version of a deadbeat escapement can be made quite rugged. Instead of using teeth, the escape wheel has round pins that are stopped and released by a scissors-like anchor. This escapement, which is also called Amant escapement or (in
Germany)
821:
Operation is mechanically similar to the verge escapement, and it has two of the verge's disadvantages: (1) The pendulum is constantly being pushed by an escape wheel tooth throughout its cycle, and is never allowed to swing freely, which disturbs its isochronism, and (2) it is a
1424:
in large buildings to control numerous slave clocks. Most telephone exchanges used such a clock to control timed events such as were needed to control the setup and charging of telephone calls by issuing pulses of varying durations such as every second, six seconds and so on.
1185:
486:
As a rule, whatever the method of impulse the action of the escapement should have the smallest effect on the oscillator which can be achieved, whether a pendulum or the balance in a watch. This effect, which all escapements have to a larger or smaller degree is known as the
1455:
invented a free pendulum clock, patented in
September 1921 and manufactured by the Synchronome Company, with an accuracy of one-hundredth of a second a day. In this system the timekeeping "master" pendulum, whose rod is made from a special steel alloy with 36% nickel called
494:
Any escapement with sliding friction will need lubrication, but as this deteriorates the friction will increase, and, perhaps, insufficient power will be transferred to the timing device. If the timing device is a pendulum, the increased frictional forces will decrease the
456:
changes the time taken for a swing. Special alloys are used in expensive pendulum-based clocks to minimize this distortion. The degrees of arc in which a pendulum may swing varies; highly accurate pendulum-based clocks have very small arcs in order to minimize the
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who popularized it in 1715. In the anchor escapement the swing of the pendulum pushes the escape wheel backward during part of its cycle. This 'recoil' disturbs the motion of the pendulum, causing inaccuracy, and reverses the direction of the gear train, causing
503:. For gravity-driven clocks, the impulse force also increases as the driving weight falls and more chain suspends the weight from the gear train; in practice, however, this effect is only seen in large public clocks, and it can be avoided by a closed-loop chain.
1373:
advantage claimed is that since the blade imparts the same amount of energy to the wheel each release, the balance wheel is isolated from variations in impulse force due to the wheel train and mainspring which cause inaccuracies in conventional escapements.
533:
Pocket watches were the predecessor of modern wristwatches. Pocket watches, being in the pocket, were usually in a vertical orientation. Gravity causes some loss of accuracy as it magnifies over time any lack of symmetry in the weight of the balance. The
1476:
was running slightly late, thus shortening the period of the slave pendulum for one swing. The slave pendulum was adjusted to run slightly slow, such that on approximately every other synchronization pulse the spring would be caught by the armature.
1069:, and put in final form by Thomas Tyrer, who patented it in 1782. The early forms had two escape wheels. The duplex escapement was difficult to make but achieved much higher accuracy than the cylinder escapement, and could equal that of the (early)
1383:
with its Ulysse Anchor escapement have taken advantage of the properties of silicon flat springs. The independent watchmaker, De
Bethune, has developed a concept where a magnet makes a resonator vibrate at high frequency, replacing the traditional
1041:. The French solved this problem by making the cylinder and escape wheel of hardened steel, and the escapement was used in large numbers in inexpensive French and Swiss pocketwatches and small clocks from the mid-19th to the 20th century.
158:
Escapements are also used in other mechanisms besides timepieces. Manual typewriters used escapements to step the carriage as each letter (or space) was typed. Historically, a liquid-driven escapement was used for a washstand design in
813:, the first anchor clock to be sold commercially, which was invented around 1680 by William Clement, who disputed credit for the escapement with Hooke. The escapement increased the accuracy of pendulum clocks to such a degree that the
540:
was invented to minimize this: the balance and spring are put in a cage that rotates (typically but not necessarily, once a minute), smoothing gravitational distortions. This very clever and sophisticated clockwork is a prized
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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 (although some sources claim that French architect
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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
341:. 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
1479:
This form of clock became a standard for use in observatories (roughly 100 such clocks were manufactured), and was the first clock capable of detecting small variations in the speed of Earth's rotation.
937:
1057:
Duplex escapement, showing (A) escape wheel, (B) locking tooth, (C) impulse tooth, (D) pallet, (E) ruby disk. The pallet and disk are attached to the balance wheel arbor, but the wheel is not shown.
809:, and allowing the use of longer, slower-moving pendulums, which used less energy. The anchor is responsible for the long narrow shape of most pendulum clocks, and for the development of the
1338:
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.
979:(patented 1782), and with this improvement his watches were the first truly accurate pocket timekeepers, keeping time to within 1 or 2 seconds per day. These were produced from 1783 onwards.
408:, 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.
3340:: "A Complete Study in Theory and Practice of the Lever, Cylinder and Chronometer Escapements, Together with a Brief Account of the Origin and Evolution of the Escapement in Horology."
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in the 1990s. In Hall's paper, he reports an uncertainty of 3 parts in 10 measured over 100 days (an uncertainty of about 0.02 seconds over that period). Both of these clocks are
671:
Verge escapement showing (c) crown wheel, (v) verge rod, (p,q) pallets. Orientation is shown for use with a pendulum. When used with a foliot, the wheel and rod are vertical.
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in the 18th century, This may avoid the need for lubrication in the escapement (though it does not obviate the requirement for lubrication of other parts of the gear train).
499:, increasing the resonance band, and decreasing its precision. For spring-driven clocks, the impulse force applied by the spring changes as the spring is unwound, following
404:, 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
958:
in 1748, who created a pivoted detent type of escapement, though this was theoretically deficient. The first effective design of detent escapement was invented by
971:
little friction and does not need oiling. For these reasons among others, the detent was considered the most accurate escapement for balance wheel timepieces.
741:, a device that isolated the escapement from changes in drive force. Without a balance spring, the crossbeat would have been no more isochronous than the verge.
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were trying to invent an escapement, but had not yet been successful. On the other hand, most sources agree that mechanical escapement clocks existed by 1300.
93:
1323:
escapement, which was invented and patented by the
American Charles Fasoldt in 1859. Both Robin and Fasoldt escapements give impulse in one direction only.
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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.
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or a suspended weight, transmitted through the timepiece's gear train. Each swing of the pendulum or balance wheel releases a tooth of the escapement's
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decade of the 18th century. The final form appeared around 1800, and this design was used until mechanical chronometers became obsolete in the 1970s.
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463:
Pendulum-based clocks can achieve outstanding accuracy. Even into the 20th century, pendulum-based clocks were reference timepieces in laboratories.
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clocks: they use a pendulum as the timekeeping element, but electrical power rather than a mechanical gear train to supply energy to the pendulum.
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invented by W. H. Shortt in 1921, which had an uncertainty of about 1 second per year. The most accurate mechanical clock to date is probably the
1741:
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3131:
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The 'Double Three-legged
Gravity Escapement' shown here is a form of escapement first devised by a barrister named Bloxam and later improved by
3113:
1096:
escapement; the tooth resting against the roller adds some friction to the balance wheel during its swing but this is very minimal. As in the
805:
through to the 19th century. Its advantage was that it reduced the wide pendulum swing angles of the verge to 3–6°, making the pendulum nearly
518:(oscillations per second) or 6–8 beats per second (21,600–28,800 beats per hour; bph). Faster or slower speeds are used in some watches (33,600
135:) to replace the energy lost to friction during its cycle and keep the timekeeper oscillating. The escapement is driven by force from a coiled
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and introducing high loads into the system, leading to friction and wear. The main advantage of the deadbeat is that it eliminated recoil.
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Chamberlain 'It's About Time' Pages 428-429, also P.93 which shows a diagrammatic view of the escapement. Chamberlain 1978 Reprint
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of a second during 100 running days. After two years of operation, it had an error of only ±0.5 sec, after barometric correction.
591:
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The verge was the only escapement used in clocks and watches for 350 years. In spring-driven clocks and watches, it required a
127:
to move forward, advancing the clock's hands. The impulse action transfers energy to the clock's timekeeping element (usually a
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sources. Knowledge of these mercury escapements may have spread through Europe with translations of Arabic and Spanish texts.
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2006:
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1951:
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1369:
as working prototypes in 2008 (Nicolas Déhon was then head of Girard-Perregaux R&D department) and in watches by 2013.
775:, who drew a sketch of it. The son began construction of a prototype, but both he and Galileo died before it was completed.
203:, in 13th-century Europe initiated a change in timekeeping methods from continuous processes, such as the flow of water in
2609:
702:, also known as the crown-wheel escapement. It was used in the first mechanical clocks and was originally controlled by a
215:, which had the potential to be more accurate. Oscillating timekeepers are the controlling devices in all modern clocks.
1446:
3283:
3433:
3428:
3423:
1316:
61:
31:
3319:
2923:
A close look at clock A close look at clock 'B': and why pendulum clocks are even more interesting than atomic clocks
2830:
2702:
606:
239:. A counterweighted spoon, supplied by a water tank, tips over in a basin when full, releasing a spherical piece of
2147:
1791:
1489:
1033:
864:
1914:
1886:
1396:
In the late 19th century, electromechanical escapements were developed for pendulum clocks. In these, a switch or
602:
432:
watch gear train, and it must deliver enough energy to the pendulum or balance wheel to maintain its oscillation.
419:
in the 1920s, which became the most accurate clock by the 1930s, shifted technological research in timekeeping to
3438:
1149:
801:, the anchor (see animation to the right) quickly superseded the verge to become the standard escapement used in
545:
in wristwatches, even though the natural movement of the wearer tends to smooth gravitational influences anyway.
476:
3246:
1859:
972:
959:
552:
677:
514:
that oscillates (rotates back and forth). Most modern mechanical watches have a working frequency of 3–4
1888:
Exemplum: Model-book Drawings and the Practice of Artistic Transmission in the Middle Ages (ca. 900-ca. 1470)
1971:
Science and Civilisation in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering
1718:
1707:
Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering
1694:
Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering
1681:
Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering
1452:
750:
542:
288:
789:
92:
3091:
1471:
sends a pulse to a synchronizing mechanism that keeps the slave pendulum in step with the master pendulum.
1465:
energizes a second electromagnet to raise the gravity lever above the master pendulum to its top position,
1214:
1174:
869:
826:
759:
Original drawing from around 1637 of the pendulum clock designed by Galileo, incorporating the escapement.
440:
353:
2439:
p.126, this cites a letter of December 11, but he may have meant the September 22 letter mentioned above.
1261:
1154:
885:
333:
192:
2883:" escapement, called the 'grasshopper'... was of no practical value and need not be further described"
1738:
1319:, the coaxial escapement is one of the few new watch escapements adopted commercially in modern times.
1081:
from about 1790 to 1860, and in the Waterbury, a cheap American 'everyman's' watch, during 1880–1898.
291:, the Chinese escapement spread west and was the source of Western escapement technology. According to
2921:
3413:
2816:. Vol. 28 (11th ed.). Cambridge University Press. pp. 362–366, see end of page 363.
1376:
830:
763:
Galileo's escapement is a design for a clock escapement, invented around 1637 by Italian scientist
401:
361:
2686:
2586:
1544:
1196:
3295:
1280:
951:
560:
412:
284:
228:
112:
3058:
3371:
3337:
3024:
2864:
2639:
2615:
2552:
2529:
2523:
2502:
2496:
2472:
2428:
2395:
2389:
2352:
2331:
2321:
2260:
2254:
2233:
2206:
2178:
2153:
2126:
2120:
2102:
2080:
2029:
2002:
1975:
1947:
1920:
1892:
1865:
1838:
1832:
1767:
1660:
1652:
1628:
1576:
1557:
1000:
921:
842:
825:
escapement; the anchor pushes the escape wheel backward during part of its cycle. This causes
810:
784:
564:
556:
549:
342:
296:
164:
97:
3190:
2368:
2227:
1916:
The Portfolio of Villard de Honnecourt (Paris, Bibliothèque Nationale de France, MS Fr 19093)
829:, increased wear in the clock's gears, and inaccuracy. These problems were eliminated in the
3287:
1434:
1413:
1366:
1145:
1109:
1070:
984:
905:
860:
855:
The Graham or deadbeat escapement was an improvement of the anchor escapement first made by
714:
699:
655:
378:
374:
324:
300:
264:
200:
147:
116:
2498:
Time Restored:The Harrison timekeepers and R.T. Gould, the man who knew (almost) everything
1722:
1331:
larger wheel, which gives an impulse directly onto an impulse roller on the balance staff.
1015:
817:
was added to the clock face in the late 1600s (before this, clocks had only an hour hand).
665:
2375:
1745:
1659:. Technology and Change in History. Vol. 2. Leiden: Brill. pp. 343–369 (356f.).
963:
764:
527:
506:
Watches and smaller clocks do not use pendulums as the timing device. Instead, they use a
308:
292:
168:
151:
136:
3372:
Method for transmitting bursts of mechanical energy from a power source to an oscillating
423:
methods, and escapement design ceased to play a role in advancing timekeeping precision.
2680:
2580:
1739:
Transfer Of Islamic Technology To The West, Part II: Transmission Of Islamic Engineering
1538:
1346:
483:. To minimize the effect with amplitude, pendulum swings are kept as small as possible.
2770:
1385:
1184:
1029:
976:
856:
802:
772:
768:
755:
642:
507:
500:
397:
386:
224:
160:
101:
3407:
3378:
3214:
2807:
2802:
2549:
Britten's Watch & Clock Makers' Handbook Dictionary & Guide Fifteenth Edition
2406:
Letter 229 Flamsteed to Towneley (September 22, 1675), p.374, and Annotation 11 p.375
1523:
1518:
1401:
1380:
1210:
1066:
955:
928:
729:
703:
511:
444:
382:
260:
132:
3299:
1354:
Since accuracy is far greater than any mechanical watch is achievable with low-cost
1231:
690:
2985:
1421:
1355:
1246:
1158:
1131:
1062:
798:
416:
272:
252:
180:
176:
891:
389:
had no natural "beat", so there was not much incentive to improve the escapement.
17:
3232:
2289:
1503:
3343:
3144:
Uhren, in: Polytechnisches Journal 88, 1843, p. 258-264, 441-446, sheet IV and V
1651:
Lewis, Michael (2020). "Theoretical Hydraulics, Automata, and Water Clocks". In
1302:
1162:
1078:
1053:
896:
847:
806:
420:
338:
276:
268:
208:
204:
1290:
851:
Deadbeat escapement. showing: (a) escape wheel (b) pallets (c) pendulum crutch.
2710:
1365:
on behalf of inventor Nicolas Déhon, the constant escapement was developed by
814:
738:
718:
536:
346:
172:
124:
1532:. Vol. 28 (11th ed.). Cambridge University Press. pp. 362–366.
123:
that gives impulses to the timekeeping element and periodically releases the
3313:
3291:
2327:
1803:
1397:
400:
around 1657, which made the timekeeping elements in both watches and clocks
304:
236:
3346:, issued 23 March 1992, for a cycloidal pendulum similar to that of Huygens
3163:
287:, before the technology stagnated and retrogressed. According to historian
962:
around 1775, but with the detent pivoted. This escapement was modified by
3329:
638:
496:
475:
period of the pendulum is only approximately linear in the regime of the
471:
457:
405:
393:
212:
128:
1037:
18th century, except in a few high-end watches with cylinders made from
1268:
526:
bph). The working frequency depends on the balance spring's stiffness (
480:
280:
263:
made the escapement in 723 (or 725) to the workings of a water-powered
256:
1267:
The great clock in Elizabeth Tower at Westminster that rings London's
3154:
elektrisch angetrieben? In: Chronométrophilia No. 76, 2014, p. 67-77.
2902:
2732:
1723:
On the Origin of Clockwork, Perpetual Motion Devices, and the Compass
1074:
1006:
Cylinder escapement. The balance wheel is attached to the cylinder,
240:
199:
possible. The invention of the first all-mechanical escapement, the
2288:. National Association of Watch and Clock Collectors. Archived from
1119:
1021:
Animation of cylinder escapement showing how the cylinder part works
609:. Statements consisting only of original research should be removed.
2391:
The Correspondence of John Flamsteed, First Astronomer Royal, Vol.1
1943:
Heavenly Clockwork: The Great Astronomical Clocks of Medieval China
771:. Since he was by then blind, Galileo described the device to his
2122:
God's Clockmaker: Richard of Wallingford and the Invention of Time
1457:
1362:
1345:
1230:
1052:
890:
846:
788:
754:
689:
515:
248:
196:
120:
91:
1834:
Time in History: Views of Time from Prehistory to the Present Day
1802:(2). Inst. of Electrical and Electronic Engineers. Archived from
548:
The most accurate commercially produced mechanical clock was the
2960:
1940:
Needham, Joseph; Wang, Ling; de Solla Price, Derek John (1986).
1038:
732:
invented the cross-beat escapement in 1584, a variation of the
392:
The great leap in accuracy resulting from the invention of the
574:
439:
Some escapements avoid sliding friction; examples include the
195:
is that it was the key invention that made the all-mechanical
36:
1315:
Invented around 1974 and patented 1980 by British watchmaker
863:
in 1675 although it is often credited to Tompion's successor
3274:
Denny, Mark (June 2010). "The Tourbillon and How It Works".
3014:'English and American watches' George Daniels Published 1967
2801:
2582:
The Watch & Clock Makers' Handbook, Dictionary and Guide
1709:. Taipei: Caves Books Ltd, pp. 445 & 448, 469–471.
1517:
1137:
Animation of lever escapement showing movement of lever only
975:
was the first to use the detent escapement with an overcoil
283:(1020–1101) duly applied escapement devices for their
2831:"Wristwatch - 76.2.109 | National Watch & Clock Museum"
1350:
Illustration of the Constant Escapement by Girard-Perregaux
698:
The earliest mechanical escapement from about 1275 was the
223:
The earliest liquid-driven escapement was described by the
3359:
3114:"Exhaust mechanism having bistable and monostable springs"
943:
Earnshaw's detent escapement, used widely in chronometers.
737:
but rather to better workmanship and his invention of the
369:
possible that this was the first clock escapement design.
3132:"The evolution of the escapement and recent innovations"
833:, which slowly replaced the anchor in precision clocks.
352:
Actually, the earliest description of an escapement, in
3051:"Could you explain the mechanism of the coaxial watch?"
2863:. Springer Science and Business Media. pp. 17–19.
1256:. It is the standard for all accurate 'Tower' clocks.
1161:" in the early 20th century and is still used in cheap
598:
2585:(9 ed.). London: E. F. and N. Spon Ltd. pp.
2388:
Flamsteed, John; Forbes, Eric; Murdin, Lesley (1995).
2149:
History of the Hour: Clocks and Modern Temporal Orders
2025:
History of the Hour: Clocks and Modern Temporal Orders
1468:
sends a pulse to activate one or more clock dials, and
646:
so escapement design became a little-known curiosity.
1792:"Origin and Evolution of the Anchor Clock Escapement"
3365:
2800:
Beckett, Edmund; Cunynghame, Henry Hardinge (1911).
2323:
Biographical dictionary of the history of technology
1516:
Beckett, Edmund; Cunynghame, Henry Hardinge (1911).
1065:
around 1700, improved by Jean Baptiste Dutertre and
683:
Verge and foliot of De Vick clock, built 1379, Paris
271:, which was the world's first clockwork escapement.
1028:The horizontal or cylinder escapement, invented by
2256:Ever-changing Sky: A Guide to the Celestial Sphere
1646:
1644:
171:, while liquid-driven escapements were applied to
3247:"Synchronome - 中国天文学 - 两台摆的电子钟 Chinese Astronomy"
2633:
2631:
2028:. University of Chicago Press. pp. 105–106.
950:The detent or chronometer escapement was used in
908:escapement, is used quite often in tower clocks.
327:, was used in a bell-ringing apparatus called an
2205:. Upton, UK: The British Horological Institute.
2125:. UK: Hambledon & London. pp. 175–183.
1575:. Upton, UK: The British Horological Institute.
1209:A rare but interesting mechanical escapement is
1202:Animation of one form of grasshopper escapement.
1073:and when carefully made was almost as good as a
3215:"Electric clocks – a history through animation"
1271:uses a double three-legged gravity escapement.
767:(1564 - 1642). It was the earliest design of a
559:Littlemore Clock, built by noted archaeologist
56:for grammar, style, cohesion, tone, or spelling
3084:"The Omega Coaxial: An impressive achievement"
2986:"Where George Daniels shopped the Co-Axial..."
2860:The Mechanics of Mechanical Watches and Clocks
2674:
2672:
2670:
2611:The Mechanics of Mechanical Watches and Clocks
2229:Splitting the Second: The Story of Atomic Time
3320:Performance Of The Daniels Coaxial Escapement
3195:The University of Queensland - Physics Museum
3179:. N.A.G. Press Limited. pp. 92, 174–180.
1335:influence on the isochronism of the balance.
8:
3316:, with animated pictures of many escapements
2769:. The Waterbury Watch Museum. Archived from
2369:The Towneley Clocks at Greenwich Observatory
2354:Watch and Clockmaker's Handbook, 9th Edition
1451:In the 20th century, the English horologist
1061:The duplex watch escapement was invented by
843:Anchor escapement § Deadbeat escapement
364:, was not a verge, but a variation called a
155:from the 13th through the 19th century.
27:Mechanism for regulating the speed of clocks
2196:
2194:
1974:. Cambridge University Press. p. 443.
1891:. Amsterdam University Press. p. 185.
1785:
1783:
1505:The Watch and Clockmaker's Handbook, 4th Ed
1077:escapement. It was used in quality English
710:" and was a source of wear and inaccuracy.
479:. To be time-independent, the path must be
231:(3rd century BC) in his technical treatise
3360:American Watchmakers-Clockmakers Institute
2574:
2572:
2570:
2568:
2259:. UK: Cambridge Univ. Press. p. 183.
2152:. Univ. of Chicago Press. pp. 50–52.
1826:
1824:
1822:
1820:
1750:History of Science and Technology in Islam
3366:Federation of the Swiss Watch Industry FH
3077:
3075:
2929:. Harrison Decoded Conference. Greenwich.
2641:A Treatise on Watchwork, Past and Present
2418:Clocks and Watches: The leap to precision
2203:The Science of Clocks and Watches, 3rd Ed
1616:
1614:
1573:The Science of Clocks and Watches, 3rd Ed
625:Learn how and when to remove this message
80:Learn how and when to remove this message
2490:
2488:
2469:Technique and history of the Swiss watch
2467:Jaquet, Eugène; Chapuis, Alfred (1970).
2114:
2112:
1837:. Oxford Univ. Press. pp. 103–104.
1733:
1731:
1420:This type of clock was widely used as a
1361:Based on patents initially submitted by
637:Since 1658 when the introduction of the
377:clocks were more limited by their early
191:The importance of the escapement in the
3191:"Synchronome Master Clock (circa 1955)"
2888:Old Clocks and Watches and their Makers
2286:NAWCC Chapter 161 - Horological Science
1919:. Ashgate Publishing Ltd. p. 159.
1595:
337:clocks were mechanical, and which were
3005:Charles Gros 'Echappements' 1914 P.174
2891:. London: B. T. Batsford. p. 216.
2852:
2850:
2603:
2601:
2599:
2320:Lance Day and Ian McNeil, ed. (1996).
2314:
2312:
2310:
2308:
1235:Double three-legged gravity escapement
1097:
1085:
553:Shortt-Synchronome free pendulum clock
307:in 1277 can be traced back to earlier
3352:: Obituary of Professor Edward Hall,
2767:"A History of the Waterbury Watch Co"
2471:. London: Spring Books. p. 222.
2103:Medieval Technology and Social Change
2051:Medieval Technology and Social Change
1998:Medieval Technology and Social Change
1605:Medieval Technology and Social Change
733:
510:: a fine spring connected to a metal
323:The first mechanical escapement, the
146:The first mechanical escapement, the
7:
3164:ClockDoc. The Electric Clock Archive
3112:Déhon, Nicolas (December 16, 1999).
3057:. Europa star online. Archived from
3039:Gros Echappements 1914 P.184 Fig.213
2737:Glossary, Watch Collector's Paradise
2330:(Routledge Reference). p. 116.
2177:. New York: MacMillan. p. 180.
1657:Handbook of Ancient Water Technology
1627:. W.W. Norton & Co. p. 31.
1543:. London: Cassel & Co. pp.
2685:. London: Cassel & Co. p.
2001:. Oxford Univ. Press. p. 173.
3368:, watch industry trade association
2655:Reid's Treatise 2nd Edition p. 240
2146:Dohrn-van Rossum, Gerhard (1996).
2022:Dohrn-van Rossum, Gerhard (1996).
1861:A History of Mechanical Inventions
1696:. Taipei: Caves Books Ltd, p. 319.
1683:. Taipei: Caves Books Ltd, p. 165.
1379:with its Genequand escapement and
25:
2885:Britten, Frederick James (1899).
2638:Nelthropp, Harry Leonard (1873).
2579:Britten, Frederick James (1896).
2357:. E.F.& N. Spon. p. 108.
2053:. Oxford Press. pp. 119–127.
1125:Inline or Swiss lever escapement.
179:China and culminating during the
3398:Monochrome-watches, Xavier Markl
2201:Rawlings, Arthur Lionel (1993).
2076:Clocks and Culture, 1300 to 1700
1885:Scheller, Robert Walter (1995).
1762:Ajram, K. (1992). "Appendix B".
1624:Clocks and Culture, 1300 to 1700
1571:Rawlings, Arthur Lionel (1993).
1301:
1289:
1195:
1183:
1130:
1118:
1014:
999:
936:
920:
676:
664:
579:
211:processes, such as the swing of
41:
3245:Marilyn Shea (September 2007).
2857:Du, Ruxu; Xie, Longhan (2012).
2608:Du, Ruxu; Xie, Longhan (2012).
1308:Animation of coaxial escapement
1262:Trinity College Cambridge Clock
694:Animation of a verge escapement
358:Tractatus Horologii Astronomici
259:along with government official
3362:, non-profit trade association
3090:. TimeZone.com. Archived from
2942:"Building an Impossible Clock"
2351:Britten, Frederick J. (1896).
1864:. Courier Dover Publications.
1766:. Knowledge House Publishers.
1502:Britten, Frederick J. (1881).
1342:Other modern watch escapements
793:Animation of anchor escapement
385:, which because they lacked a
275:(960–1279) horologists
1:
3314:Mark Headrick's horology page
3276:IEEE Control Systems Magazine
2940:Love, Shayla (Jan 19, 2016).
1995:White, Lynn Townsend (1964).
1858:Usher, Abbott Payson (2013).
1392:Electromechanical escapements
717:to even out the force of the
360:on the clock he built at the
3284:IEEE Control Systems Society
3235:to display animated content)
2920:Van Baak, Tom (April 2015).
2903:"Harrison / Burgess Clock B"
2614:. Springer. pp. 26–29.
1946:. CUP Archive. p. 195.
1607:. Oxford Press. p. 187.
1190:Grasshopper escapement, 1820
1092:The duplex is technically a
987:became dominant in watches.
279:(fl. late 10th century) and
3394:Evolution of the escapement
3330:Watch and Clock Escapements
2835:nawcc.pastperfectonline.com
2731:Buser, Roland (June 2007).
2701:Mundy, Oliver (June 2007).
2501:. Oxford University Press.
1508:. London: W. Kent & Co.
1157:, which was used in cheap "
927:First detent escapement by
605:the claims made and adding
32:Escapement (disambiguation)
3470:
2765:Stephenson, C. L. (2003).
2378:Retrieved 16 November 2007
2173:Milham, Willis I. (1945).
2119:North, John David (2005).
2073:Cipolla, Carlo M. (2004).
1790:Headrick, Michael (2002).
1764:Miracle of Islamic Science
1621:Cipolla, Carlo M. (2004).
1552:Milham, Willis I. (1945).
1490:Escapement (radio control)
1444:
1278:
1172:
1107:
883:
840:
782:
748:
744:
653:
235:(chapter 31) as part of a
29:
2984:Thompson, Curtis (2001).
2818:The duplex escapement....
2522:Macey, Samuel L. (1994).
2232:. CRC Press. p. 30.
2063:White, 1966, pp. 126-127.
1084:In the duplex, as in the
1032:in 1695 and perfected by
477:small angle approximation
285:astronomical clock towers
219:Liquid-driven escapements
3449:Mechanical power control
3419:Ancient Greek technology
3356:(London), 16 August 2001
3344:US Patent number 5140565
2495:Betts, Jonathan (2006).
2427:. Taylor & Francis.
2253:Kaler, James B. (2002).
2079:. W.W. Norton & Co.
2049:White, Lynn Jr. (1966).
1968:Needham, Joseph (1965).
1913:Barnes, Carl F. (2009).
1796:Control Systems Magazine
1705:Needham, Joseph (1986).
1692:Needham, Joseph (1986).
1679:Needham, Joseph (1986).
1603:White, Lynn Jr. (1966).
1447:Shortt–Synchronome clock
895:Pin wheel escapement of
884:Not to be confused with
797:Invented around 1657 by
3444:Hellenistic engineering
3384:Alternative Escapements
3292:10.1109/MCS.2010.936291
2813:Encyclopædia Britannica
2679:Glasgow, David (1885).
2664:British patent no. 1811
1831:Whitrow, G. J. (1989).
1719:Derek J. de Solla Price
1556:. New York: MacMillan.
1537:Glasgow, David (1885).
1529:Encyclopædia Britannica
1453:William Hamilton Shortt
289:Derek J. de Solla Price
3454:Timekeeping components
3336:(magazine), 1904, via
3233:Adobe Shockwave Player
3049:Nicolet, J.C. (1999).
2961:"About George Daniels"
2682:Watch and Clock Making
2528:. Garland Publishing.
2423:Macey, Samuel (1994).
2282:"The Littlemore Clock"
1540:Watch and Clock Making
1351:
1236:
1215:grasshopper escapement
1175:Grasshopper escapement
1169:Grasshopper escapement
1086:chronometer escapement
1058:
900:
852:
794:
760:
695:
571:Mechanical escapements
441:grasshopper escapement
354:Richard of Wallingford
319:Mechanical escapements
244:ancient water clocks.
104:
2996:17 June 2001 Addendum
2773:on September 22, 2008
2644:. E. & F.N. Spon.
1349:
1234:
1155:pin-pallet escapement
1056:
894:
886:Pin-pallet escapement
850:
792:
758:
725:Cross-beat escapement
693:
411:The invention of the
334:Villard de Honnecourt
193:history of technology
95:
3130:Monochrome-watches,
3082:Odets, Walt (1999).
2591:cylinder escapement.
2525:Encyclopedia of Time
2425:Encyclopedia of Time
2280:Hall, E. T. (1996).
2226:Jones, Tony (2000).
2175:Time and Timekeepers
1554:Time and Timekeepers
1433:Designed in 1895 by
1165:and kitchen timers.
880:Pin wheel escapement
751:Galileo's escapement
745:Galileo's escapement
402:harmonic oscillators
30:For other uses, see
3324:Horological Journal
3175:Hope-Jones, Frank.
2733:"Duplex Escapement"
2703:"Watch Escapements"
2367:Smith, Alan (2000)
2302:Milham, 1945, p.180
1806:on October 25, 2009
1441:Free pendulum clock
1377:Parmigiani Fleurier
991:Cylinder escapement
952:marine chronometers
837:Deadbeat escapement
831:deadbeat escapement
362:Abbey of St. Albans
356:'s 1327 manuscript
345:wrote in 1271 that
3434:English inventions
3429:Chinese inventions
3424:Ancient inventions
3219:electric-clocks.nl
2790:Milham 1945, p.238
2755:Milham 1945, p.407
2562:Milham 1945, p.272
2457:Milham 1945, p.235
2448:Milham 1945, p.185
2374:2008-07-05 at the
1744:2008-02-18 at the
1429:Synchronome switch
1352:
1296:Coaxial escapement
1281:Coaxial escapement
1275:Coaxial escapement
1240:Gravity escapement
1237:
1059:
983:the self-starting
901:
853:
795:
761:
696:
590:possibly contains
413:crystal oscillator
229:Philo of Byzantium
150:, was invented in
117:mechanical watches
113:mechanical linkage
105:
60:You can assist by
18:Gravity escapement
3338:Project Gutenberg
3251:hua.umf.maine.edu
3055:Questions in Time
2959:Daniels, George.
2707:The Watch Cabinet
2508:978-0-19-856802-5
2478:978-0-600-03633-3
2415:Andrewes, W.J.H.
2401:978-0-7503-0147-3
1737:Ahmad Y. Hassan,
1666:978-90-04-11123-3
1049:Duplex escapement
912:Detent escapement
811:grandfather clock
785:Anchor escapement
779:Anchor escapement
635:
634:
627:
592:original research
565:electromechanical
557:electromechanical
550:electromechanical
472:pendulum's period
343:Robertus Anglicus
165:Hellenistic world
100:, widely used in
98:anchor escapement
90:
89:
82:
16:(Redirected from
3461:
3439:Greek inventions
3390:, September 2014
3350:findarticles.com
3303:
3262:
3261:
3259:
3257:
3242:
3236:
3230:
3228:
3226:
3211:
3205:
3204:
3202:
3201:
3187:
3181:
3180:
3172:
3166:
3161:
3155:
3151:
3145:
3141:
3135:
3128:
3122:
3121:
3109:
3103:
3102:
3100:
3099:
3079:
3070:
3069:
3067:
3066:
3046:
3040:
3037:
3031:
3021:
3015:
3012:
3006:
3003:
2997:
2995:
2993:
2992:
2981:
2975:
2974:
2972:
2971:
2956:
2950:
2949:
2937:
2931:
2930:
2928:
2917:
2911:
2910:
2899:
2893:
2892:
2881:
2875:
2874:
2854:
2845:
2844:
2842:
2841:
2827:
2821:
2820:
2805:
2797:
2791:
2788:
2782:
2781:
2779:
2778:
2762:
2756:
2753:
2747:
2746:
2744:
2743:
2728:
2722:
2721:
2719:
2718:
2709:. Archived from
2698:
2692:
2690:
2676:
2665:
2662:
2656:
2653:
2647:
2645:
2635:
2626:
2625:
2605:
2594:
2593:
2576:
2563:
2560:
2554:
2546:
2540:
2539:
2519:
2513:
2512:
2492:
2483:
2482:
2464:
2458:
2455:
2449:
2446:
2440:
2438:
2413:
2407:
2405:
2385:
2379:
2365:
2359:
2358:
2348:
2342:
2341:
2318:"Jost Burgi" in
2316:
2303:
2300:
2294:
2293:
2277:
2271:
2270:
2250:
2244:
2243:
2223:
2217:
2216:
2198:
2189:
2188:
2170:
2164:
2163:
2143:
2137:
2136:
2116:
2107:
2098:
2092:
2090:
2070:
2064:
2061:
2055:
2054:
2046:
2040:
2039:
2019:
2013:
2012:
1992:
1986:
1985:
1965:
1959:
1957:
1937:
1931:
1930:
1910:
1904:
1902:
1882:
1876:
1875:
1855:
1849:
1848:
1828:
1815:
1814:
1812:
1811:
1787:
1778:
1777:
1759:
1753:
1735:
1726:
1716:
1710:
1703:
1697:
1690:
1684:
1677:
1671:
1670:
1648:
1639:
1638:
1618:
1609:
1608:
1600:
1586:
1567:
1548:
1533:
1521:
1509:
1435:Frank Hope-Jones
1367:Girard-Perregaux
1305:
1293:
1227:
1226:
1222:
1199:
1187:
1146:lever escapement
1134:
1122:
1110:Lever escapement
1104:Lever escapement
1071:lever escapement
1018:
1003:
985:lever escapement
940:
924:
861:Richard Towneley
734:verge escapement
700:verge escapement
680:
668:
656:Verge escapement
650:Verge escapement
630:
623:
619:
616:
610:
607:inline citations
583:
582:
575:
525:
521:
489:escapement error
375:verge and foliot
325:verge escapement
299:escapement in a
265:armillary sphere
207:, to repetitive
201:verge escapement
148:verge escapement
85:
78:
74:
71:
65:
45:
44:
37:
21:
3469:
3468:
3464:
3463:
3462:
3460:
3459:
3458:
3404:
3403:
3400:, February 2016
3354:The Independent
3310:
3273:
3270:
3268:Further reading
3265:
3255:
3253:
3244:
3243:
3239:
3224:
3222:
3213:
3212:
3208:
3199:
3197:
3189:
3188:
3184:
3177:Electric Clocks
3174:
3173:
3169:
3162:
3158:
3152:
3148:
3142:
3138:
3134:, February 2016
3129:
3125:
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3106:
3097:
3095:
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3073:
3064:
3062:
3048:
3047:
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3034:
3022:
3018:
3013:
3009:
3004:
3000:
2990:
2988:
2983:
2982:
2978:
2969:
2967:
2958:
2957:
2953:
2939:
2938:
2934:
2926:
2919:
2918:
2914:
2901:
2900:
2896:
2884:
2882:
2878:
2871:
2856:
2855:
2848:
2839:
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2829:
2828:
2824:
2799:
2798:
2794:
2789:
2785:
2776:
2774:
2764:
2763:
2759:
2754:
2750:
2741:
2739:
2730:
2729:
2725:
2716:
2714:
2700:
2699:
2695:
2678:
2677:
2668:
2663:
2659:
2654:
2650:
2637:
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2629:
2622:
2607:
2606:
2597:
2578:
2577:
2566:
2561:
2557:
2547:
2543:
2536:
2521:
2520:
2516:
2509:
2494:
2493:
2486:
2479:
2466:
2465:
2461:
2456:
2452:
2447:
2443:
2435:
2422:
2414:
2410:
2402:
2387:
2386:
2382:
2376:Wayback Machine
2366:
2362:
2350:
2349:
2345:
2338:
2319:
2317:
2306:
2301:
2297:
2279:
2278:
2274:
2267:
2252:
2251:
2247:
2240:
2225:
2224:
2220:
2213:
2200:
2199:
2192:
2185:
2172:
2171:
2167:
2160:
2145:
2144:
2140:
2133:
2118:
2117:
2110:
2099:
2095:
2087:
2072:
2071:
2067:
2062:
2058:
2048:
2047:
2043:
2036:
2021:
2020:
2016:
2009:
1994:
1993:
1989:
1982:
1967:
1966:
1962:
1954:
1939:
1938:
1934:
1927:
1912:
1911:
1907:
1899:
1884:
1883:
1879:
1872:
1857:
1856:
1852:
1845:
1830:
1829:
1818:
1809:
1807:
1789:
1788:
1781:
1774:
1761:
1760:
1756:
1746:Wayback Machine
1736:
1729:
1717:
1713:
1704:
1700:
1691:
1687:
1678:
1674:
1667:
1653:Wikander, Örjan
1650:
1649:
1642:
1635:
1620:
1619:
1612:
1602:
1601:
1597:
1593:
1583:
1570:
1564:
1551:
1536:
1515:
1510:, p. 56-58
1501:
1498:
1486:
1449:
1443:
1431:
1410:
1394:
1344:
1313:
1312:
1311:
1310:
1309:
1306:
1298:
1297:
1294:
1283:
1277:
1254:Lord Grimthorpe
1242:
1224:
1220:
1219:
1207:
1206:
1205:
1204:
1203:
1200:
1192:
1191:
1188:
1177:
1171:
1142:
1141:
1140:
1139:
1138:
1135:
1127:
1126:
1123:
1112:
1106:
1094:frictional rest
1051:
1026:
1025:
1024:
1023:
1022:
1019:
1011:
1010:
1004:
993:
964:Thomas Earnshaw
948:
947:
946:
945:
944:
941:
933:
932:
925:
914:
889:
882:
859:to a design by
845:
839:
803:pendulum clocks
787:
781:
765:Galileo Galilei
753:
747:
727:
688:
687:
686:
685:
684:
681:
673:
672:
669:
658:
652:
631:
620:
614:
611:
596:
584:
580:
573:
528:spring constant
523:
519:
453:
429:
321:
293:Ahmad Y. Hassan
221:
189:
169:Ptolemaic Egypt
167:, particularly
152:medieval Europe
102:pendulum clocks
86:
75:
69:
66:
59:
46:
42:
35:
28:
23:
22:
15:
12:
11:
5:
3467:
3465:
3457:
3456:
3451:
3446:
3441:
3436:
3431:
3426:
3421:
3416:
3406:
3405:
3402:
3401:
3391:
3381:
3377:2013-06-29 at
3369:
3363:
3357:
3347:
3341:
3327:
3317:
3309:
3308:External links
3306:
3305:
3304:
3269:
3266:
3264:
3263:
3237:
3206:
3182:
3167:
3156:
3146:
3136:
3123:
3118:Google Patents
3104:
3088:The Horologium
3071:
3041:
3032:
3016:
3007:
2998:
2976:
2965:Daniels London
2951:
2932:
2912:
2907:leapsecond.com
2894:
2876:
2870:978-3642293085
2869:
2846:
2822:
2808:Chisholm, Hugh
2792:
2783:
2757:
2748:
2723:
2693:
2666:
2657:
2648:
2627:
2621:978-3642293085
2620:
2595:
2564:
2555:
2541:
2534:
2514:
2507:
2484:
2477:
2459:
2450:
2441:
2433:
2408:
2400:
2380:
2360:
2343:
2336:
2304:
2295:
2292:on 2007-12-24.
2272:
2265:
2245:
2238:
2218:
2211:
2190:
2183:
2165:
2158:
2138:
2131:
2108:
2093:
2085:
2065:
2056:
2041:
2034:
2014:
2007:
1987:
1980:
1960:
1952:
1932:
1926:978-0754651024
1925:
1905:
1897:
1877:
1871:978-0486143590
1870:
1850:
1843:
1816:
1779:
1772:
1754:
1727:
1711:
1698:
1685:
1672:
1665:
1640:
1633:
1610:
1594:
1592:
1589:
1588:
1587:
1581:
1568:
1562:
1549:
1534:
1524:Chisholm, Hugh
1512:
1511:
1497:
1494:
1493:
1492:
1485:
1482:
1473:
1472:
1469:
1466:
1445:Main article:
1442:
1439:
1430:
1427:
1409:
1406:
1393:
1390:
1386:balance spring
1356:quartz watches
1343:
1340:
1317:George Daniels
1307:
1300:
1299:
1295:
1288:
1287:
1286:
1285:
1284:
1279:Main article:
1276:
1273:
1241:
1238:
1201:
1194:
1193:
1189:
1182:
1181:
1180:
1179:
1178:
1173:Main article:
1170:
1167:
1159:dollar watches
1148:, invented by
1136:
1129:
1128:
1124:
1117:
1116:
1115:
1114:
1113:
1108:Main article:
1105:
1102:
1050:
1047:
1030:Thomas Tompion
1020:
1013:
1012:
1005:
998:
997:
996:
995:
994:
992:
989:
977:balance spring
942:
935:
934:
926:
919:
918:
917:
916:
915:
913:
910:
881:
878:
857:Thomas Tompion
841:Main article:
838:
835:
783:Main article:
780:
777:
769:pendulum clock
749:Main article:
746:
743:
726:
723:
682:
675:
674:
670:
663:
662:
661:
660:
659:
654:Main article:
651:
648:
643:balance spring
633:
632:
587:
585:
578:
572:
569:
522:bph, or 19,800
508:balance spring
458:circular error
452:
449:
428:
425:
398:balance spring
387:balance spring
383:balance wheels
320:
317:
255:Buddhist monk
220:
217:
188:
185:
161:ancient Greece
88:
87:
49:
47:
40:
26:
24:
14:
13:
10:
9:
6:
4:
3:
2:
3466:
3455:
3452:
3450:
3447:
3445:
3442:
3440:
3437:
3435:
3432:
3430:
3427:
3425:
3422:
3420:
3417:
3415:
3412:
3411:
3409:
3399:
3395:
3392:
3389:
3385:
3382:
3380:
3379:archive.today
3376:
3373:
3370:
3367:
3364:
3361:
3358:
3355:
3351:
3348:
3345:
3342:
3339:
3335:
3331:
3328:
3326:, August 2004
3325:
3321:
3318:
3315:
3312:
3311:
3307:
3301:
3297:
3293:
3289:
3285:
3281:
3277:
3272:
3271:
3267:
3252:
3248:
3241:
3238:
3234:
3220:
3216:
3210:
3207:
3196:
3192:
3186:
3183:
3178:
3171:
3168:
3165:
3160:
3157:
3150:
3147:
3140:
3137:
3133:
3127:
3124:
3119:
3115:
3108:
3105:
3094:on 2008-06-11
3093:
3089:
3085:
3078:
3076:
3072:
3061:on 2010-04-21
3060:
3056:
3052:
3045:
3042:
3036:
3033:
3030:
3026:
3020:
3017:
3011:
3008:
3002:
2999:
2987:
2980:
2977:
2966:
2962:
2955:
2952:
2947:
2943:
2936:
2933:
2925:
2924:
2916:
2913:
2908:
2904:
2898:
2895:
2890:
2889:
2880:
2877:
2872:
2866:
2862:
2861:
2853:
2851:
2847:
2836:
2832:
2826:
2823:
2819:
2815:
2814:
2809:
2804:
2803:"Watch"
2796:
2793:
2787:
2784:
2772:
2768:
2761:
2758:
2752:
2749:
2738:
2734:
2727:
2724:
2713:on 2007-10-13
2712:
2708:
2704:
2697:
2694:
2688:
2684:
2683:
2675:
2673:
2671:
2667:
2661:
2658:
2652:
2649:
2643:
2642:
2634:
2632:
2628:
2623:
2617:
2613:
2612:
2604:
2602:
2600:
2596:
2592:
2588:
2584:
2583:
2575:
2573:
2571:
2569:
2565:
2559:
2556:
2553:
2550:
2545:
2542:
2537:
2535:0-8153-0615-6
2531:
2527:
2526:
2518:
2515:
2510:
2504:
2500:
2499:
2491:
2489:
2485:
2480:
2474:
2470:
2463:
2460:
2454:
2451:
2445:
2442:
2436:
2434:0-8153-0615-6
2430:
2426:
2420:
2419:
2412:
2409:
2403:
2397:
2394:. CRC Press.
2393:
2392:
2384:
2381:
2377:
2373:
2370:
2364:
2361:
2356:
2355:
2347:
2344:
2339:
2333:
2329:
2325:
2324:
2315:
2313:
2311:
2309:
2305:
2299:
2296:
2291:
2287:
2283:
2276:
2273:
2268:
2266:0-521-49918-6
2262:
2258:
2257:
2249:
2246:
2241:
2239:0-7503-0640-8
2235:
2231:
2230:
2222:
2219:
2214:
2212:0-9509621-3-9
2208:
2204:
2197:
2195:
2191:
2186:
2184:0-7808-0008-7
2180:
2176:
2169:
2166:
2161:
2159:0-226-15511-0
2155:
2151:
2150:
2142:
2139:
2134:
2132:1-85285-451-0
2128:
2124:
2123:
2115:
2113:
2109:
2105:
2104:
2097:
2094:
2088:
2086:0-393-32443-5
2082:
2078:
2077:
2069:
2066:
2060:
2057:
2052:
2045:
2042:
2037:
2031:
2027:
2026:
2018:
2015:
2010:
2004:
2000:
1999:
1991:
1988:
1983:
1977:
1973:
1972:
1964:
1961:
1955:
1949:
1945:
1944:
1936:
1933:
1928:
1922:
1918:
1917:
1909:
1906:
1900:
1894:
1890:
1889:
1881:
1878:
1873:
1867:
1863:
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1854:
1851:
1846:
1840:
1836:
1835:
1827:
1825:
1823:
1821:
1817:
1805:
1801:
1797:
1793:
1786:
1784:
1780:
1775:
1773:0-911119-43-4
1769:
1765:
1758:
1755:
1751:
1747:
1743:
1740:
1734:
1732:
1728:
1724:
1720:
1715:
1712:
1708:
1702:
1699:
1695:
1689:
1686:
1682:
1676:
1673:
1668:
1662:
1658:
1654:
1647:
1645:
1641:
1636:
1634:0-393-32443-5
1630:
1626:
1625:
1617:
1615:
1611:
1606:
1599:
1596:
1590:
1584:
1582:0-9509621-3-9
1578:
1574:
1569:
1565:
1563:0-7808-0008-7
1559:
1555:
1550:
1546:
1542:
1541:
1535:
1531:
1530:
1525:
1520:
1519:"Watch"
1514:
1513:
1507:
1506:
1500:
1499:
1495:
1491:
1488:
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1426:
1423:
1418:
1415:
1414:Matthäus Hipp
1407:
1405:
1403:
1402:electromagnet
1400:energised an
1399:
1391:
1389:
1387:
1382:
1381:Ulysse Nardin
1378:
1374:
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1212:
1211:John Harrison
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1082:
1080:
1079:pocketwatches
1076:
1072:
1068:
1067:Pierre Le Roy
1064:
1055:
1048:
1046:
1042:
1040:
1035:
1034:George Graham
1031:
1017:
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978:
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956:Pierre Le Roy
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929:Pierre Le Roy
923:
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907:
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865:George Graham
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649:
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629:
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588:This section
586:
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558:
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539:
538:
531:
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286:
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278:
274:
270:
266:
262:
261:Liang Lingzan
258:
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226:
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175:beginning in
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133:balance wheel
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96:Animation of
94:
84:
81:
73:
70:February 2024
63:
57:
55:
50:This article
48:
39:
38:
33:
19:
3397:
3387:
3353:
3334:The Keystone
3333:
3323:
3279:
3275:
3256:November 10,
3254:. Retrieved
3250:
3240:
3225:November 10,
3223:. Retrieved
3218:
3209:
3198:. Retrieved
3194:
3185:
3176:
3170:
3159:
3149:
3139:
3126:
3117:
3107:
3096:. Retrieved
3092:the original
3087:
3063:. Retrieved
3059:the original
3054:
3044:
3035:
3029:0 900470 81X
3019:
3010:
3001:
2989:. Retrieved
2979:
2968:. Retrieved
2964:
2954:
2946:The Atlantic
2945:
2935:
2922:
2915:
2906:
2897:
2887:
2879:
2859:
2838:. Retrieved
2834:
2825:
2817:
2811:
2795:
2786:
2775:. Retrieved
2771:the original
2760:
2751:
2740:. Retrieved
2736:
2726:
2715:. Retrieved
2711:the original
2706:
2696:
2681:
2660:
2651:
2646:, p.159-164.
2640:
2610:
2590:
2581:
2558:
2548:
2544:
2524:
2517:
2497:
2468:
2462:
2453:
2444:
2424:
2417:
2411:
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2383:
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2322:
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2290:the original
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2275:
2255:
2248:
2228:
2221:
2202:
2174:
2168:
2148:
2141:
2121:
2101:
2096:
2075:
2068:
2059:
2050:
2044:
2024:
2017:
1997:
1990:
1970:
1963:
1958:, footnote 3
1942:
1935:
1915:
1908:
1903:, footnote 7
1887:
1880:
1860:
1853:
1833:
1808:. Retrieved
1804:the original
1799:
1795:
1763:
1757:
1749:
1714:
1706:
1701:
1693:
1688:
1680:
1675:
1656:
1623:
1604:
1598:
1572:
1553:
1539:
1527:
1504:
1478:
1474:
1450:
1432:
1422:master clock
1419:
1411:
1395:
1375:
1371:
1360:
1353:
1337:
1333:
1329:
1325:
1321:
1314:
1266:
1258:
1251:
1243:
1208:
1163:alarm clocks
1150:Thomas Mudge
1143:
1093:
1091:
1083:
1063:Robert Hooke
1060:
1043:
1027:
1007:
981:
969:
949:
902:
874:
854:
822:
819:
799:Robert Hooke
796:
762:
728:
712:
707:
697:
636:
621:
612:
589:
547:
543:complication
535:
532:
505:
493:
488:
485:
469:
465:
462:
454:
438:
434:
430:
417:quartz clock
410:
391:
371:
365:
357:
351:
339:water clocks
328:
322:
313:
273:Song dynasty
253:Tang dynasty
246:
232:
222:
205:water clocks
190:
181:Song dynasty
177:Tang dynasty
157:
145:
141:escape wheel
140:
108:
106:
76:
67:
54:copy editing
52:may require
51:
3414:Escapements
3388:Europa Star
2100:White 1966
1098:chronometer
973:John Arnold
960:John Arnold
899:tower clock
897:South Mymms
815:minute hand
807:isochronous
501:Hooke's law
427:Reliability
347:clockmakers
277:Zhang Sixun
269:clock drive
209:oscillatory
3408:Categories
3231:(requires
3200:2020-05-30
3098:2008-06-12
3065:2008-06-12
2991:2008-06-12
2970:2008-06-12
2840:2024-02-08
2777:2007-10-18
2742:2007-10-18
2717:2007-10-18
2691:, p137-154
2337:1134650205
2035:0226155102
2008:0195002660
1981:0521058031
1953:0521322766
1898:9053561307
1844:0192852116
1810:2007-06-06
1496:References
1408:Hipp clock
739:remontoire
730:Jost Bürgi
719:mainspring
599:improve it
561:E. T. Hall
537:tourbillon
421:electronic
233:Pneumatics
173:clockworks
125:gear train
109:escapement
62:editing it
3286:: 19–99.
2328:Routledge
1412:In 1843,
1398:phototube
906:Mannhardt
603:verifying
481:cycloidal
305:Alfonso X
303:work for
237:washstand
227:engineer
213:pendulums
3375:Archived
3300:24169789
2372:Archived
1742:Archived
1484:See also
870:backlash
827:backlash
639:pendulum
615:May 2019
497:Q factor
451:Accuracy
415:and the
406:horology
394:pendulum
163:and the
129:pendulum
2810:(ed.).
2106:, p.124
1655:(ed.).
1526:(ed.).
1269:Big Ben
1223:⁄
597:Please
301:Spanish
297:mercury
281:Su Song
257:Yi Xing
187:History
3298:
3221:. 2010
3027:
2867:
2618:
2589:–101.
2551:p.122
2532:
2505:
2475:
2431:
2398:
2334:
2263:
2236:
2209:
2181:
2156:
2129:
2091:, p.31
2083:
2032:
2005:
1978:
1950:
1923:
1895:
1868:
1841:
1770:
1725:, p.86
1663:
1631:
1579:
1560:
1075:detent
823:recoil
708:recoil
704:foliot
524:
520:
379:foliot
329:alarum
309:Arabic
251:, the
241:pumice
137:spring
121:clocks
3296:S2CID
3282:(3).
2927:(PDF)
2806:. In
1591:Notes
1547:–154.
1522:. In
1458:Invar
1363:Rolex
931:1748.
715:fusee
381:type
366:strob
249:China
225:Greek
197:clock
111:is a
3258:2011
3227:2011
3025:ISBN
2865:ISBN
2616:ISBN
2530:ISBN
2503:ISBN
2473:ISBN
2429:ISBN
2396:ISBN
2332:ISBN
2261:ISBN
2234:ISBN
2207:ISBN
2179:ISBN
2154:ISBN
2127:ISBN
2081:ISBN
2030:ISBN
2003:ISBN
1976:ISBN
1948:ISBN
1921:ISBN
1893:ISBN
1866:ISBN
1839:ISBN
1768:ISBN
1661:ISBN
1629:ISBN
1577:ISBN
1558:ISBN
1144:The
1039:ruby
641:and
470:The
396:and
295:, a
267:and
119:and
3288:doi
2687:137
2421:in
1545:137
1213:'s
773:son
601:by
443:of
247:In
131:or
115:in
107:An
3410::
3396:,
3386:,
3332:,
3322:,
3294:.
3280:30
3278:.
3249:.
3217:.
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3086:.
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3053:.
2963:.
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2735:.
2705:.
2669:^
2630:^
2598:^
2587:98
2567:^
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2326:.
2307:^
2284:.
2193:^
2111:^
1819:^
1800:22
1798:.
1794:.
1782:^
1748:,
1730:^
1721:,
1643:^
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1388:.
516:Hz
491:.
460:.
183:.
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3290::
3260:.
3229:.
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3120:.
3101:.
3068:.
2994:.
2973:.
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2873:.
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2780:.
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2720:.
2689:.
2624:.
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2404:.
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2242:.
2215:.
2187:.
2162:.
2135:.
2089:.
2038:.
2011:.
1984:.
1956:.
1929:.
1901:.
1874:.
1847:.
1813:.
1776:.
1752:.
1669:.
1637:.
1585:.
1566:.
1225:8
1221:5
1008:B
888:.
628:)
622:(
617:)
613:(
595:.
83:)
77:(
72:)
68:(
64:.
58:.
34:.
20:)
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