EDMUND GUNTER - MATHEMATICIAN & INVENTOR

Gunter, Edmund (1581-1626), was of Welsh extraction, but was born in Hertfordshire in 1581.  He was educated on the royal foundation of Westminster school, and in 1599 was elected a student of Christ Church, Oxford.  After graduating bachelor and master of arts at the regular times, he took orders, became a preacher in 1614, and in November, 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 6th March, 1619, he was appointed to the professorship of astronomy in Gresham College, London.  This post he held till his death, which took place on 10th December, 1626.  With Gunter's name are associated several useful inventions, descriptions of which are given in his treatise on the Sector, Cross-staff, Bow, Quadrant, and other Instruments.  He had contrived his sector about the year 1606, and written a description of it in Latin.  Many copies were transcribed and dispersed, but it was more than sixteen years afterwards ere he allowed the book to appear in English.  In 1620 he published his Canon Triangulorum, a table of logarithmic sines and tangents (extended to 7 decimal places) for every degree and minute of the quadrant.  In later editions an account of the general use of the canon is prefixed, and Brigg's logarithms of the first 1000 numbers are appended.  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 places at all times.  By desire of James I, he published in 1624 The Description and Use of His Majestie's Dials in Whitehall Garden, the only one of his works which has not been reprinted.  He introduced the words co-sine and co-tangent for sine and tangent of the complement, and he suggested to Briggs, his friend and colleague, the use of the arithmetical complement (see Brigg's Arithmetica Logarithmica, cap. xv.).  His practical inventions are briefly noticed below.

Gunter's Chain, the chain in common use for measuring land, is 22 yards long and is divided into 100 links.  Its usefulness arises from its decimal or centesimal division, and the fact that 10 square chains make an acre.

Gunter's Line, 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 equinoxial, 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 by seamen the Gunter) is a large plane scale, usually 2 feet long by about 1-1/2 inches broad, 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.

Encyclopedia Britannica, 9th ed. (American Reprint), Vol. XI, Philadelphia, 1880