Gunter, EDMUND, mathematician, was born in Hertfordshire in 1581, and educated at Westminster and Christ Church, Oxford. Although he took orders and became a preacher in 1614, his mind was strongly bent towards mathematical studies, and in 1619 he obtained the professorship of Astronomy in Gresham College, London, a post which he held down to his death, 10th December 1626. His principal works are the Canon Trigonorum (Lond. 1620), a table of logarithmic sines and tangents to seven places of decimals, being the first table published in accordance with Briggs's system, and treatises on the Sector, Cross-staff, and other Instruments (1624). Gunter was the first to use the terms cosine, cotangent, and secant for the sine, tangent, and secant of the complement of an arc. To him are also due the invention of the surveying-chain (see CHAIN), a quadrant, and a scale, and the first observation of the variation of the compass.
The name of Gunter's Scale, or Gunter's Lines, is usually given to three lines to be seen on almost any sector, and marked N, S, T, meaning the lines of logarithmic numbers, of logarithmic sines, and of logarithmic tangents. To understand their construction and use requires a knowledge of logarithms; they are explained in every school-book of practical mathematics. The distances of the divisions marked 1, 2, 3, &c. on the line of log. numbers, represent the logarithms of those numbers—viz. 0, .301, .477, &c.—taken from a scale of equal parts. The other lines are constructed on an analogous plan. Calling to mind that multiplication of numbers is effected by the addition of the logarithms, division by their subtraction, involution by their multiplication, and evolution by their division, we are able to perceive with what ease many rough problems in areas, heights, cubic contents, and other matters may be performed through the agency of Gunter's Scale.