GUNTER, EDMUND (1581-1626), English mathematician, of Welsh extraction, was born in Hertfordshire in 1581. He was educated at Westminster school, and in 1599 was elected a student of Christ Church, Oxford. He was professor of astronomy at Gresham college from 1619 until his death on Dec. Io, 1626. With Gunter's name are associated several useful inventions, descrip tions of which are given in his treatises on the Sector, Cross-staff, Bow, Quadrant and other Instruments. In 162o he published his Canon triangulorum. There is reason to believe that Gunter was the first to discover (in 1622 or 1625) that the magnetic declina tion at one place varies (see TERRESTRIAL MAGNETISM) . He introduced the words cosine and cotangent (see TRIGONOMETRY), and he suggested to Henry Briggs, his friend and colleague, the use of the arithmetical complement (see Briggs' Aritlimetica Logarithmica, cap. xv., and LOGARITHMS).
His practical inventions are Gunter's Chain, the chain in common use for surveying, 22 yd. long and divided into i oo links; Gunter's Line, a logarithmic line, the forerunner of the slide rule; Gunter's Quadrant, used to find the hour of the day, the sun's azimuth, etc., and also to take the altitude of an object in de grees; and Gunter's Scale (generally called by seamen the Gunter), a large plane scale, engraved with various lines of numbers and used to solve problems in navigation, trigonometry, etc., with the aid of a pair of compasses.