A green onyx and glass mantle clock, late 19th to early 20th century, of elegant and restrained architectural styling, having an extended onyx cornice above a fully glazed cabinet enclosing a white metal dial with Roman numerals set within a decorative gilt cast bezel, with a mercury filled pendulum, and upon a stepped onyx base with low bracket feet; with key. Height 37 cm. Width 22 cm. Depth 15 cm
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- 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.
- Bezel - On a clock or watch, the bezel is the metal frame into which the watch or clock glass is fitted. In clocks, the bezel may include a hinge and a flange, in effect a door to the face of the clock. In jewellery the bezel is a band of metal with a projecting lip that holds the gemstone in its setting.
- Onyx - Onyx is a form of agate, used from antiquity and popular again in the 1920s and 30s. European onyx is generally green, but can be many other colours, and can contain bands of black and/or white.
This multicoloured stone is widely used for table tops, lamp bases and in jewellery. Some types of onyx are also used for cameos of which the upper white layer is cut away to reveal the colour beneath.
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