Royal Observatory Greenwich, Harrison's H4 Timekeeper

United Kingdom · 2014 · 1st Class

This stamp features John Harrison's H4 marine chronometer, a revolutionary timekeeping device that solved the problem of accurately determining longitude at sea. The background shows a celestial map, linking the instrument to its astronomical and navigational purpose. The stamp is part of a set commemorating the 300th anniversary of the Longitude Act.

The Longitude Act of 1714 offered a massive prize for a practical method of determining longitude, a critical challenge for maritime navigation. Harrison's H4, completed in 1759, proved its accuracy on transatlantic voyages, ushering in a new era of safe and precise sea travel.