One-Day Duration Marine Chronometer, No. 509

This fine marine timepiece by John Roger Arnold was crafted in the tradition of his father, John Arnold in several ways. The blued steel helical balance spring of the movement originated in a 1775 Arnold patent. Other features include the spring-detent escapement. The bimetallic “Z” balance appears to have been first used by the father-son duo in 1791. But there is at least one major difference between father and son: John Roger preferred to use gimbals and a brass bowl within a wooden box to house the movement. The brass enclosure better protects the movement from temperature and humidity changes. It also decreased the number of complaints from ship navigators about spiders getting into the wooden boxes.