Devised by Admiral Sir Francis Beaufort in 1805 to help sailors describe wind at sea without instruments. Still used today — from marine forecasts to standard weather reports.
Beaufort's original 1805 scale had no wind-speed numbers — it was based purely on what Royal Navy sails could handle. Force 5 meant "topgallant sails set." Force 10 meant "close-reefed topsails and courses."
Wind speeds in miles per hour weren't added until 1906. Land criteria were added in 1926 by George Simpson. The scale caps at Force 12 (hurricane force); in 1946 five higher forces (13-17) were added for tropical cyclones, but almost nobody uses them.
Related: wind speed converter, EF scale, Saffir-Simpson.