Fusee (horology)
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A fusee is a cone-shaped pulley with a helical groove around it, wound with a cord or chain attached to the mainspring barrel of antique mechanical watches and clocks. It was used from the 15th centur
A fusee in a 1760 pocket watch by Johan Lindquist of Stockholm
A clock with the back plate off showing the fusee
Verge escapement
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The verge 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 tick
Fusee (horology)
…weight on a cord, which exerts a constant force to turn the clock's wheels, the force a spring exerts diminishes as the spring unwinds. The primitive verge and foliot timekeeping mechanism, used in all early clocks, was sensitive to changes in drive force. So early spring-driven clocks slowed down over their running…
One of the earliest existing drawings of a verge escapement, in Giovanni de Dondi's astronomical clock, the Astrarium, built 1364, Padua, Italy. This had a balance wheel (crown shape at top) instead of a foliot. The escapement is just below it. From his 1364 clock treatise, Il Tractatus Astrarii.
Modern reproduction of an early verge and foliot clock. The pointed-tooth verge wheel is visible, with the wooden foliot rod and suspended weight above it.
Salisbury Cathedral, medieval clock
Salisbury Cathedral 2012 12