Widenham Marine Chronometer, London, Circa 1830
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A mahogany two day marine chronometer, no. 988, Widenham, London, circa 1830, 8 cm silvered dial with subsidiary seconds dial, fusee movement with maintaining power, Earnshaw's spring detent escapement with compensation balance and helical spring, brass bowl gimbal-mounted in a three tier mahogany case with carrying handles and ivory plaque, signed dial and movement, the case 15.5 cm high
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- Movement - The technical name for the workings of a clock or watch, and does not include the dial or case.
- Mahogany - Mahogany is a dense, close grained red-coloured timber from the West Indies and Central America. It was first imported into Europe in the the early 18th century and its use continued through the 19th century. It was popular for furniture making because of its strength, the wide boards available, the distinctive grain on some boards, termed flame mahogany and the rich warm colour of the timber when it was polished.. The "flame" was produced where a limb grew out from the trunk of the tree, and this timber was usually sliced into veneers for feature panels on doors, backs and cornices.
Some terms used to describe mahogany relate to the country from which it originally came, such as "Cuban" mahogany, "Honduras" mahogany etc. However unless the wood has been tested the names assigned are more a selling feature, rather than a true indication of the timber's origin. - Thomas Earnshaw Balance Springs - Thomas Earnshaw (1749 ? 1829 )was a British clock and watch maker who was a renowned inventor and craftsman. Earnshaw is credited with standardizing the design of the marine chronometer, making it a more reliable and accurate instrument for navigation. He also developed a process for hardening the balance springs used in chronometers, which made them more durable and resistant to temperature changes.
- 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Use of the fusee in clocks was superseded by the "going barrel" in the mid 19th century and for pocket watches at the beginning of the 19th century.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. - Tier - One or more under-shelves of a table or cabinet.
- Ivory - Ivory is a hard white material that comes from the tusks of elephants, mammoth, walrus and boar, or from the teeth of hippopotamus and whales. The ivory from the African elephant is the most prized source of ivory. Although the mammoth is extinct, tusks are still being unearthed in Russia and offered for sale.
Ivory has been used since the earliest times as a material for sculpture of small items, both in Europe and the east, principally China and Japan.
In Asia ivory has been carved for netsuke, seals, okimono, card cases, fan supports, animals and other figures and even as carved tusks.
In the last 200 years in Europe ivory has been used to carve figures, for elaborate tankards, snuff boxes, cane handles, embroidery and sewing accessories, in jewellery and as inlay on furniture. Its more practical uses include being used for billiard balls, buttons, and a veneers on the top of piano keys.
The use and trade of elephant ivory have become controversial because they have contributed to Due to the decline in elephant populations because of the trade in ivory, the Asian elephant was placed on Appendix One of the Convention on International Trade in Endangered Species (CITES), in 1975, and in January 1990, the African elephant was similarly listed. Under Appendix One, international trade in Asian or African elephant ivory between member countries is forbidden. Unlike trade in elephant tusks, trade in mammoth tusks is legal.
Since the invention of plastics, there have been many attempts to create an artificial ivory - Circa - A Latin term meaning 'about', often used in the antique trade to give an approximate date for the piece, usually considered to be five years on either side of the circa year. Thus, circa 1900 means the piece was made about 1900, probably between 1895 and 1905. The expression is sometimes abbreviated to c.1900.
- Maintaining Power - A horological term to describe a subsidiary driving force such as a spring or additional weight in a clock, which keeps the movement going while the mainspring is being rewound.
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