Used with permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
Navigation on charted or uncharted seas depended crucially on accurate, dependable time pieces in order to determine a ship's position based on the positions of celestial bodies. Many major disasters at sea were caused by faulty navigation due to inaccurate clocks that could not keep perfect time on pitching seas and in changing atmospheric conditions. The British Admiralty's Board of Longitudes offered a huge monetary prize for the successful development of a naval chronometer to determine longitude to within 60, 40, and 30 geographical miles at sea. John Harrison (1693-1776), a horologist, rose to the challenge and produced a series of five superb chronometers between 1736 and 1773, as the Board hedged on the reward, asking for more improvements. Harrison finally received his prize only after the intervention of King George III.