Dictionary of National Biography, 1885-1900/Gunter, Edmund
GUNTER, EDMUND (1581–1626), mathematician, born in Hertfordshire in 1581, was son of a Welshman, who formerly lived at Gunterstown, Brecknockshire. He was educated at Westminster School under Busby, and thence was elected in 1599 to Christ Church, Oxford, where he matriculated 25 Jan. 1599–1600. He became B.A. 12 Dec. 1603 and M.A. 2 July 1606, and, subsequently taking orders, proceeded B.D. 23 Nov. 1615 (Reg. Univ. Oxf., Oxf. Hist. Soc., ii. ii. 239, iii. 243). In 1615 he was presented to the living of St. George's, Southwark. While resident at Oxford he contributed to ‘Epithalamia; sive lucus Palatini in nuptias … Frederici comitis Palatini … et Elizabethæ,’ &c., 1613.
Gunter's ‘New Projection of the Sphere’ (in Latin) was circulated in manuscript in 1603, and gained for him the friendship of the Earl of Bridgewater, William Oughtred, Henry Briggs, and others. The English edition appeared in 1623. In 1618 he invented a small portable quadrant for more readily finding the hour and azimuth and for other useful astronomical and geometrical purposes, described in the appendix to his ‘Book of the Sector.’ On 6 March 1619 he was elected professor of astronomy in Gresham College. Henry Briggs [q. v.] was his colleague for a year; and their association doubtless led to Gunter's ‘Canon Triangulorum; or, Table of Artificial Sines and Tangents, to a radius of 100,000,000 parts to each minute of the Quadrant,’ 1620. This was the first table of its kind published, and did for sines and tangents what Briggs did for natural numbers. In these tables Gunter applied to navigation and other branches of mathematics his admirable rule ‘The Gunter,’ on which were inscribed the logarithmic lines for numbers, sines, and tangents of arches; and he showed how to take a back observation by the cross-staff, whereby the error arising from the eccentricity of the eye is avoided. Oughtred (Circles of Proportion) says: ‘The honour of the invention of Logarithms, next to the Lord of Marchiston, and our Mr. Briggs, belongeth to Master Gunter, who exposed their numbers upon a straight line. And what does this new instrument (of mine) called “Circle of Proportion” but only bow and reflect Master Gunter's line or rule?’
In 1622 Gunter discovered, by experiments made at the Limehouse, Deptford, the variation or changeable declination of the magnetic needle, his experiments showing that the declination had varied five degrees in forty-two years. Gunter gave a short account in his ‘Cross-Staff,’ bk. ii. ch. v., of this discovery, which seemed so strange that he suspected an error, and dropped his investigations. His professorial successor, Henry Gellibrand [q. v.], confirmed and established Gunter's results, and published them in 1635. Gunter made allowance for the variation when he drew the lines upon the dials in Whitehall Gardens. At the request of Prince Charles he wrote a description of their use, which was published in 1624. These dials were destroyed in 1697. Gunter's admirable rule of proportion, now called the line of numbers (‘Gunter's Line’ and ‘Gunter's Proportion’), and other lines laid down by it were fitted in the scale, which ever since has been called ‘Gunter's Scale.’ A description was given in his ‘Book of the Sector,’ and a more popular account of his ‘Line of Proportion’ was published by William Leybourn shortly afterwards. Gunter also introduced the well-known ‘Gunter's chain,’ now constantly used in land-surveying. He was the first who used the words cosine, cotangent, &c., and also introduced the use of arithmetical complements into the logarithmical arithmetic (Briggs, Arith. Log. cap. 15). De Morgan (Arith. Books, xxv.) favours Gunter's claim to the invention of the decimal separator.
He died at Gresham College, 10 Dec. 1626, and was buried in the church of St. Peter the Poor, Broad Street, where his two professorial successors, Gellibrand and Samuel Foster [q. v.], were very soon afterwards buried.
His works were collected in 1624, and the second edition was edited by Samuel Foster [q. v.], with additions, in 1636. The last edition (5th, 1673), edited by William Leybourn, contains additions by S. Foster, H. Bond, and Leybourn himself, who returns to the old system for the decimal separator.[Welch's Alumni Westmonasterienses, 1852; Hutton's Dictionary, 1815; B. Martin's Biog. Philos. 1764; English Cyclopædia; Wood's Athenæ Oxon. ed. Bliss, ii. 141, 405, iii. 423.]