A Jno Jackson silver windmill verge pair cased watch, the full plate movement with engraved and pierced balance cock, fusee and chain, turned pillars, worm and wheel barrel set between the plates, silver regulator disc. Movement signed 'Jno Jackson, Boston'. The polychrome dial depicting a fisherman in a windmill landscape with Arabic numerals. The plain silver inner case and outer case hallmarked London 1791. Provenance: Christie's 1980
- Movement - The technical name for the workings of a clock or watch, and does not include the dial or case.
- Pair Cased - A pair cased watch is one with a double case. The movement is encased, and for additional protection this is fitted into an outer case.
- Polychrome - Made or finished in many colours. For furniture, it is used to indicated a painted finish.
- Fusee - The fusee movement was used in clocks and pocket watches from the mid 17th century. The fusee is a cone shaped drum within the works that is linked to the barrel of the spring, usually by a length of chain.
As the mainspring loses its tension over time, the cone shaped barrel compensates for this by increasing the tension, by pulling the mainspring tighter, thus ensuring the time remains constant.
Use of the fusee in clocks was superseded by the "going barrel" in the mid 19th century and for pocket watches at the beginning of the 19th century.
The fusee continued to be used in marine chronometers until the 1970s.
- Barrel (in a Clock) - In a clock or watch, the barrel is a cylindrical component that stores the energy from the mainspring. As the mainspring is wound, it stores energy in the barrel. As the clock or watch runs, the energy is gradually released from the barrel, turning the clock's gears and keeping the time.
The barrel is typically located near the centre of the movement (the mechanism that powers the clock) and is connected to the center wheel, which drives the rest of the gears. The barrel typically has teeth on its outer surface that mesh with the gears in the movement, allowing it to transmit energy to the rest of the clock. Some barrels are designed to be wound by hand, while others are automatically wound by the motion of the wearer's arm.
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