English silver open faced chronometer pocket watch Circa 1808

Silver chronometer by John Roger Arnold
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An English silver open faced pocket chronometer, circa 1808. Full plate movement, Arnold’s spring detent escapement, Z-balance with two weights and two screws, blued helical balance spring, very finely engraved balance cock. Later custom-made white enamel dial with Roman hours, outer minute divisions and sunk subsidiary seconds at 6 o’clock. Later custom-made plain case, case maker’s mark FT for Frederick Thoms and a London hallmark for 1891. Dial and movement signed and numbered, case numbered, case and movement with matching numbers.
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Diameter: 58 mm
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Weight: 187 g
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Signed: Jn R Arnold London Inv.t et Fecit
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Chronometers made by John Arnold and his son John Roger Arnold were valued very highly and usually in use for decades. The present timepiece is an excellent example. The movement was fitted into a new, custom-made case by Frederick Thoms, who was most likely the most famous case maker of his time. On the same occasion, the movement was updated with a new dial and a new set of hands.
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John Roger Arnold was born in 1769. He was the son of renowned British horologist John Arnold. He served an apprenticeship with both his father in 1783 and the eminent French watchmaker Abraham-Louis Breguet in Paris in 1792. In 1787, John Roger and his father founded the company, Arnold & Son. The younger Arnold became a member of the Clockmakers’ Company in 1796 and became a master in 1817. After his father’s death in 1799, he continued the business, taking up a partnership with E.J. Dent in 1830. The two craftsmen experimented heavily during their work together, in particular, they concentrated on the effects of magnetism on chronometers. Dent left Arnold in 1840, whereupon Arnold continued working on his own but died only three years later. Charles Frodsham bought the business after Arnold’s death in February 1843 and it flourished until 1858 under the name Arnold & Frodsham.