Edmund Gunter (1581 - December 10, 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 took orders, became a preacher in 1614, and in 1615 proceeded to the degree of bachelor in divinity. Mathematics, however, which had been his favorite study in youth, continued to engross his attention, and on the 6th of March 1619 he was appointed professor of astronomy in Gresham College, London. This post he held till his death.

With Gunter's name are associated several useful inventions, descriptions of which are given in his treatises on the Sector, Cross-staff, Bow, Quadrant and other Instruments. He contrived his sector about the year 1606, and wrote a description of it in Latin, but it was more than sixteen years afterwards before he allowed the book to appear in English. In 1620 he published his Canon triangulorum.

There is reason to believe that Gunter was the first to discover (in 1622 or 1625) that the magnetic needle does not retain the same declination in the same place at all times. By desire of James I he published in 1624 The Description and Use of His Majesties Dials in Whitehall Garden, the only one of his works which has not been reprinted. He introduced the words cosine and cotangent, and he suggested to Henry Briggs, his friend and colleague, the use of the arithmetical complement (see Briggs Arithmetica Logarithmica, cap. xv.). His practical inventions are briefly noticed below:

Gunter's chain

Gunter's interest in trigonometry led him to develop a method of land surveying using triangulation. Linear measurements could be taken between topographical features such as corners of a field, and using triangulation the field or other area could be plotted on a plan, and its area calculated. A chain 22 yards long, with intermediate measurements indicated, was habitually used for the purpose, and is called Gunter's chain.

The length of the chain normally used led to the linear measurement of 22 yards being called a chain and this was still in use until about 1970.

Gunter's line

Table of Trigonometry, from the 1728 Cyclopaedia, Volume 2 featuring a Gunter's scale

A logarithmic line, usually laid down upon scales, sectors, etc. It is also called the line of lines and the line of numbers, being only the logarithms graduated upon a ruler, which therefore serves to solve problems instrumentally in the same manner as logarithms do arithmetically.

Gunter's quadrant

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 other common problems of the sphere or globe, and also to take the altitude of an object in degrees.

Gunter's scale

Generally called the "Gunter" by seamen, this is a large plane scale, usually 2 feet long by about 1 1/2 inches broad (600 mm by 40 mm), and engraved with various lines of numbers. 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.

See also

• Gresham Professor of Astronomy

External links

• O'Connor, John J; Edmund F. Robertson "Edmund Gunter". MacTutor History of Mathematics archive.  

This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.

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