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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'. Verge escapements were used from the late 13th century until the mid 19th century in clocks and pocketwatches.
The first mechanical escapement, the verge escapement, was invented in medieval Europe 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 ...
The anchor was the second widely used escapement in Europe, replacing the primitive 400-year-old verge escapement in pendulum clocks. The pendulums in verge escapement clocks had very wide swings of 80° to 100°.
Salisbury Cathedral clock, restored. The Salisbury Cathedral clock is a large iron-framed tower clock without a dial, in Salisbury Cathedral, England.Thought to date from about 1386, it is a well-preserved example of the earliest type of mechanical clock, called verge and foliot clocks, and is said to be the oldest working clock in the world, [1] although similar claims are made for other clocks.
The pendulum clock with an anchor escapement, invented in 1670, was sufficiently independent of drive force so that only a few had fusees. [15] 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.
The first clock known to strike regularly on the hour, a clock with a verge and foliot mechanism, is recorded in Milan in 1336. [96] By 1341, clocks driven by weights were familiar enough to be able to be adapted for grain mills, [97] and by 1344 the clock in London's Old St Paul's Cathedral had been replaced by one with an escapement. [98]
Early balance wheels were pushed in one direction by the escapement until the verge flag that was in contact with a tooth on the escape wheel slipped past the tip of the tooth ("escaped") and the action of the escapement reversed, pushing the wheel back the other way. In such an "inertial" wheel, the acceleration is proportional to the drive force.
A string-suspended verge would reduce friction greatly and make the clock run more evenly; the foliot swings at an angle and not exactly horizontally; the escapement wheel and the pallets of the verge do not engage very exactly. This leads to the verge pallets "falling" onto the escapement teeth causing a lot of vibration in the verge and foliot.