Juan Fernandez (or Mas-a-Tierra), an island in the South Pacific, 400 miles from the coast of Chili, to which it belongs. Its area is eighteen miles by six miles. The interior is fertile, and fish in large quantities are taken upon the coast and cured by settlers for the Chilian market. Alexander Selkirk was alone on this island for four years (1705-9). It was used as a penal settlement from 1819 to 1835.