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,

Isaac Newton The Longitude Act is passed by the Parliament ‘ for providing a Publick Reward for such Person or Persons as shall...

On the 22nd of October, three ships of the line, the 90-gun Association , the 70-gun Eagle , and the 50-gun Romney run aground on the Western reefs of Scilly islands. They founder with all hands but one. The fireship Firebrand also goes ashore and sinks with half her crew. The 90-gun St George and the fireship Phoenix strike on the reefs too but manage to get off. On her own, the 100-gun Royal Anne escapes the rocks within a hair. A thousand and three hundreds sail