Thirty-Hour Boxed Marine Chronometer with Gold Helical Spring, No. 32/122

This chronometer employs several of John Arnold’s celebrated advancements. The spring detent escapement became an essential chronometer component, in use for over 150 years after its invention. This movement also has Arnold’s rare “YZ” balance, a three-armed bimetallic balance that gets its name from its resemblance to the letters.

Arnold sought to alleviate the effects of magnetism and oxidation on chronometers. He developed a gold/copper alloy that was hard but springy, non-magnetic, and rust-resistant, used in this example. The wooden boxes that Arnold used to house his chronometers made them vulnerable to the elements which caused corrosion - probably not because of Arnold’s “sweaty fingers,” as Arnold’s vitriolic rival Thomas Earnshaw suggested. His son, John Roger Arnold, moved to the more protective brass bowl mounted on gimbals in 1796.