French Brass Four-Glass Clock with Mercury Pendulum
A French brass four-glass clock, c.1890, retailed by Kohn Bros, Auckland, bell striking circular movement with mercury pendulum, white enamel dial, Roman numerals, visible Brocot escapement, Breguet hands. Slight faults, height 300
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- Movement - The technical name for the workings of a clock or watch, and does not include the dial or case.
- Brocot Escapement - The Brocot escapement was invented by the French clockmaker Achille Brocot in 1828. It is a type of escapement, which is a mechanism in a timepiece that controls the movement of the gears and regulates the timekeeping accuracy.
The Brocot escapement is a variation of the detent escapement and it is used in pendulum and spring-driven clocks. It uses a pair of pallets that engage and lock the escape wheel, allowing the clock's power to be transferred to the balance wheel. The escapement also allows the clock's gears to advance in small, precise increments, which helps to improve the clock's timekeeping accuracy. The Brocot escapement was widely used in 19th century for both domestic and public clocks, also it was widely used in marine chronometers.
The Brocot escapement is known for its high accuracy and stability - Pendulum - The pendulum was discovered around 1602 by Galileo Galilei, and was adopted for time keeping by the Dutch mathematician and natural philosopher, Christiaan Huygens, who excelled in astronomy, physics, and horology.
The pendulum comprises a metal rod usually of brass or steel with a metal disk, known as a bob, at the end. The movement of the pendulum is driven by weights or a spring, and as a pendulum swings in a regular arc, it was found accuracy could be controlled to within a few seconds a week.
Timekeeping can be adjusted by changing the height of the bob on the rod, making the pendulum either swing slower or faster.
The disadvantage of the pendulum was that changes in temperature also changed the length of the pendulum, interfering with the accuracy of the clock, and so in the 18th century two types of mercurial pendulums were invented which countered the movement in the steel rod.
The pendulum was the world's most accurate timekeeping technology until the invention of the quartz clock, regulated by a quartz crystal, in 1927.
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