H4 chronometer, outside and inside views After twenty-three years of tries since his first H1 marine clock meant to precisely metering time at sea, John Harrison's work has just come to its highlight with the completion of the H4 chronometer, as we all name it, or of the watch number one, as the old clockmaker names it. This is effectively the fourth chronometer attempted by John Harrison, 66 years old, to achieve the goal assigned by the Longitude Act forty-five years ago,

Aurore After having tackled the building of a marine watch in 1756, Pierre Le Roy, 50 years old, has reached a new step last year. It is said that the chronometer he presented to the Académie Royale des Sciences is as precise and reliable as famous Harrison's H4 made in 1759. ¤ Le Roy already invented the detent pivot escapement, or detached escapement, that he presented the Académie in 1748, the temperature-compensated balance by using bi-metallic components, and lately th

James Cook James Cook, the famous explorer, 44 years old by now, departs for his second voyage around the world with a copy of famous Watchmaker John Harrison’s H4, that is the watch K1, and three other time-keepers made last year. ¤ Harrison's H4 was the prototype which achieved to meet the accuracy requirement set by the Board of Longitude when crossing the Atlantic ocean. It completed it twice, in 1761 and 1763 - results met with some initial scepticism by the Board of L

Harrison's Chronometer H1 John Harrison, 43 years old, trials his first marine chronometer H1, built last year, on a round trip between London and Lisbon. A total failure on the way outward - it lost time -, the way back brings an encouraging success in the form of a precise landing against a 60-mile error in longitude for the traditional method of navigation by dead reckoning and by position shift through sun observation. This unexpected half-success rouses the Board of Lon