John Arnold, An unusual large silver openface pocket chronometer with double T balance, no. 02/43, 1777

gilt full plate movement, finely pierced and engraved balance cock, diamond endstone, Arnold's spring detent escapement converted by John Arnold from a pivoted detent, unusual 'double T' bi-metallic compensation balance, later blued steel helical spring, free sprung, white enamel dial, roman numerals, large subsidiary seconds, blued steel hands, minute hand with hallmark screw to hold it in place, polished silver consular case, dial and movement signed, case stamped with maker's mark TP, case hallmarked, London, 1777, accompanied by a copy of Randall, The Time Museum Catalogue of Marine Chronometers.

Christie's Geneva, November 7, 1977, lot 94.
Time Museum Inventory No. 1382

Randall, cat. no. 5

Born in Cornwall, John Arnold (1736-1799) represents one of the most famous English makers. He was apprenticed to his father and then travel led abroad where he learned to speak German. He came to London in 1762 and shortly thereafter presented a repeating watch mounted in a ring to King George III. This, and his ability to speak German, enabled him to establish himself at court. After about 1768, he began experiments to make an accurate timekeeper for use at sea. He realized that a detached escapement would be highly desirable and this led him to invent a detent escapement, circa 1781, which bears his name. To overcome isochronal variation he invented the helical balance spring.

John Harrison had led the way with his wonderful sea-clocks but it was Arnold who took the next steps in a relatively short time. Towards the end of the 18th century accurate marine chronometers became available in reasonable quantity at economical cost as a result of Arnold's work. Although Arnold's escapement was superseded by Thomas Earnshaw's, it was John Arnold who had paved the way forward.