Finding longitude at sea means knowing the time at a reference port, and no clock could keep it through months of damp and pitching decks. John Harrison’s fourth attempt was not a cabinet but a watch, roughly the size of a large pocket watch, and it went to Jamaica in 1761 and came back having lost a handful of seconds. The Board of Longitude spent another decade arguing before it paid him.
Why this oneLongitude turned out to be a clockmaking problem, and everyone had been watching the sky.