Scottish navigator who invented the sextant. Apprenticed to a shipmaster, Campbell joined the English navy. He advanced in rank to become the commander of several ships. In 1757 Campbell recommended that John Hadley's double-reflecting quadrant be altered to represent one-sixth of a circle, attaining a range of 120 degrees. Renamed the "sextant," Campbell's revised tool was useful in measuring horizontal angles and distances involving the Moon and planets. In 1782 Campbell was named the governor of Newfoundland.