Completed in 1781, the John Arnold pocketwatch numbered 23/78 is unique for a number of reasons. It features several inventions by John Arnold and other outstanding features including a pivoted detent escapement with a "double S" balance, a cylindrical balance spring, and a clever temperature compensation mechanism.

Furthermore, it is the only known example to have survived in its exact original condition without ever having undergone any restoration, with all parts including the silver case, enamel dial and movement perfectly intact and untouched.

This extraordinary result achieved at Sotheby's auction is an attestation to the pivotal role John Arnold played in advancing precision chronometry.

John Arnold rapidly established a reputation for outstanding mechanical expertise and was the first watchmaker to produce a jewelled ruby cylinder escapement. He showcased this in an exceptionally small half-quarter repeating watch mounted in a ring, which he offered to King George III. His growing fame attracted an affluent clientele. He could easily have lived comfortably, making exquisite repeating watches and calendar watches. But John Arnold was relentlessly driven by the greatest watchmaking challenge of his age: to build a timepiece that would enable ships to navigate safely, transform science and roll back the boundaries in astronomy. That challenge was precision, and Arnold made it his passion.

Between 1770 and 1790, he painstakingly refined the art of watchmaking, introducing decisive improvements that heralded the arrival of chronometry. It is to him we owe a series of trailblazing inventions that included a detent escapement, a helical balance spring, terminal curves that make the helical balance spring isochronous, the first-ever use of gold for balance springs, and a range of bimetallic balances that offset errors caused by temperature fluctuations.

Arnold's chronometers were used by some of the greatest explorers and navigators of his time on their epic voyages. His regulators and their continual refinement bear witness to the colossal progress of science and astronomy across Europe.

Arnold was also heir to a series of exceptional English watchmakers, each of whom advanced the art of watchmaking in his own way: George Graham, Thomas Tompion, Thomas Mudge and John Harrison. Arnold, however, was the first to usher watchmaking into the modern era by designing high-precision, reliable watches that were also relatively easy to manufacture. In its report on Arnold's pocket chronometer No. 2 in 1780, the Board of Longitude had this to say:

"So far as this watch has been tried, it must be acknowledged by all, that it is superior to every one that had been made before it. Nothing therefore seems to remain but for … Mr. Arnold … to make other watches … to entitle him to the second reward offered by Parliament for improvements in this branch of mechanics, and also to the universal approbation and applause of his fellow-citizens." (2)

 (2) The Monthly Review or Literary Journal, vol. 58 (London, 1780)

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