Edmund Gunter (158110 December 1626), was an English clergyman, mathematician, geometer and astronomer of Welsh descent. He is best remembered for his mathematical contributions, which include the invention of the Gunter's chain, the Gunter's quadrant, and the Gunter's scale. In 1620, he invented the first successful analogue device which he developed to calculate logarithmic tangents.
He was mentored in mathematics by Reverend Henry Briggs and eventually became a Gresham Professor of Astronomy, from 1619 until his death.
Biography
Gunter was born in Hertfordshire in 1581. He was educated at Westminster School, and in 1599 he matriculated at Christ Church, Oxford. He took orders, became a preacher in 1614, and in 1615 proceeded to the degree of bachelor in divinity. He became rector of St. George's Church in Southwark.
Mathematics, particularly the relationship between mathematics and the real world, was the one overriding interest throughout his life. In 1619, Sir Henry Savile put up money to fund Oxford University's first two science faculties, the chairs of astronomy and geometry. Gunter applied to become professor of geometry but Savile was famous for distrusting clever people, and Gunter's behaviour annoyed him intensely. As was his habit, Gunter arrived with his sector and quadrant, and began demonstrating how they could be used to calculate the position of stars or the distance of churches, until Savile could stand it no longer. "Doe you call this reading of Geometric?" he burst out. "This is mere showing of tricks, man!" and, according to a contemporary account, "dismissed him with scorne."
He was shortly thereafter championed by the far wealthier Earl of Bridgewater, who saw to it that on 6 March 1619 Gunter was appointed professor of astronomy in Gresham College, London. This post he held till his death. Therefore, a parcel of 10 square chains gives 1 acre. The area of any parcel measured in chains will thereby be easily calculated.
thumb|Table of Trigonometry, from the 1728 [[Cyclopaedia, or an Universal Dictionary of Arts and Sciences|Cyclopaedia, Volume 2 featuring a Gunter's scale]]
Gunter's quadrant
Gunter's quadrant is an instrument made of wood, brass or other substance, containing a kind of stereographic projection of the sphere on the plane of the equinoctial, the eye being supposed to be placed in one of the poles, so that the tropic, ecliptic, and horizon form the arcs of circles, but the hour circles are other curves, drawn by means of several altitudes of the sun for some particular latitude every year. This instrument is used to find the hour of the day, the sun's azimuth, etc., and to solve other common problems of the sphere or globe, and also to take the altitude of an object in degrees.
Gunter's scale
Gunter's scale or Gunter's rule, generally called the "Gunter" by seamen, is a large plane scale, usually long by about 1½ inches broad (40 mm), engraved with various scales, or lines. On one side are placed the natural lines (as the line of chords, the line of sines, tangents, rhumbs, etc.), and on the other side the corresponding artificial or logarithmic ones. By means of this instrument questions in navigation, trigonometry, etc., are solved with the aid of a pair of compasses.