English chronometer with spring detent escapement Circa 1818

Silver open-faced chronometer 
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A heavy and rare pocket chronometer with spring detent escapement according to John Arnold, circa 1818.
Silver case, polished, tiered, with case maker punch mark TH ( Thomas Hardy). Numbered and signed enamel dial, with radial Roman hours, auxiliary seconds, and gold spade hands. Full plate movement, frosted, gilt, chain/fusee, round pillars, keywind, and signed; with spring detent escapement according to John Arnold, chronometer balance with four adjusting screw nuts and six screws, blued helical free-sprung balance spring with both sides passing, and chatoned diamond endstone on balance.
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Diameter: 59 mm
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Weight: 215 g
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Signed: John Roger Arnold, London
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John Roger Arnold (1769-1843)
John Roger Arnold was the son of renowned British horologist John Arnold. He began his apprenticeship with A.-L. Breguet in Paris in 1792. The younger Arnold became a member of the Clockmaker’s Company in 1796 and was a master in 1817. He took up a partnership with E.J. Dent in 1830 and 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 and Frodsham.