Important and early English silver pocket chronometer Circa 1778

Silver open faced chronometer by John Arnold
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An important and early English silver open faced pocket chronometer, circa 1778. Full plate movement, Arnold’s spring detent escapement, OZ balance, blued helical balance spring, very finely engraved pierced balance cock. White enamel dial with Roman hours, outer Arabic five minute numerals and subsidiary seconds at 6 o’clock. A later custom-made plain case.
Dial and movement signed and numbered.
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Diameter: 61 mm
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Weight: 171 g
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Signed: John Arnold London Invt. et Fecit
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Hans Stäger’s comments on this timepiece:
Unlike the 1/36, this chronometer does not have the slash yet and originally used Arnold’s pivoted detent escapement. Most likely Arnold set it into a new consular case in the early 1780s and at the same time fitted it with a spring escapement and an OZ balance.
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John Arnold was born in 1736 and died on August 11^th, 1799. He was an English watchmaker and inventor. Arnold was apprenticed to his father, who was also a clockmaker in Bodmin, Cornwell and probably also worked with his uncle, a gunsmith. Around 1755, at the age of 19, he left England and worked as a watchmaker in the Hague, Holland, returning to England around 1757. In 1762, he met William McGuire on whom he made a sufficient impression and McGuire gave him a loan, enabling him to set up a workshop at Devereux Court, Strand, London. By the time he was 28, Arnold’s watches, be they verge or cylinder, displayed interesting original components such as straight-line compensation curbs and minute repeating by increments of 10 minutes instead of the more common 15 minutes. In 1764, Arnold obtained permission to present an exceptionally small half-quarter repeating watch with a cylinder escapement mounted in a ring to King George III. He made another watch for the King around 1768, which was a gold and enamel pair-cased watch with a movement that had every refinement, including minute repetition and centre seconds. It was around 1770 that Arnold developed a portable precision timekeeper. His basic design was simple whilst consistently accurate and mechanically reliable. Importantly, the relatively simple and conventional design of his movement facilitated its production in quantity at a reasonable price whilst also enabling easier maintenance and adjustment. He successfully found a way to simplify Harrison’s timekeeper design. He established himself at 2 Adam Street, Adelphi Buildings, Strand, in 1771 and researched marine chronometers here over the next eleven years. Arnold was the first to design a watch that was both practical and accurate, and also brought the chronometer into use in its modern sense, as a precision timekeeper. His technical progress enabled the quantity production of marine chronometers for use on board ships from around 1782. Arnold was admitted to the Clockmakers’ Company in 1783. The important French watchmaker Abraham-Louis Breguet was a very good friend of Arnold. It appears Arnold gave Breguet permission to incorporate or develop any of Arnold’s inventions and techniques into his own watches. Arnold’s son John Roger Arnold was born in 1769 and served an apprenticeship with both his father and Abraham-Louis Breguet. In 1787, he and his father founded the company, Arnold & Son. John Arnold also appears to have been the first to think of the concept of the tourbillon. He seems to have experimented with his idea but died in 1799 before he could develop it further. It is known that Breguet made a successful and practical tourbillon mechanism around 1795 but, nevertheless, he acknowledged Arnold as the inventor by presenting his first tourbillon in 1808 to Arnold’s son John Roger. As a tribute to his friend Arnold Sr..