Gunter, Edmund

Edmund Gunter, (born 1581, Hertfordshire, Eng.—died Dec. 10, 1626, London), English mathematician who invented many useful measuring devices, including a forerunner of the slide rule.

Gunter was professor of astronomy at Gresham College, London, from 1619 until his death. Descriptions of some of his inventions were given in his treatises on the sector, cross-staff, bow, quadrant, and other instruments. In Canon Triangulorum, or Table of Artificial Sines and Tangents (1620), the first published table of common logarithms of the sine and tangent functions, he introduced the terms cosine and cotangent. He also suggested to his friend Henry Briggs, the inventor of common logarithms, the use of the arithmetical complement.

Gunter’s practical inventions included Gunter’s chain. Commonly used for surveying, it was 22 yards (20.1 metres) long and was divided into 100 links. Gunter’s quadrant was used to find the hour of the day, the sun’s azimuth, and the altitude of an object in degrees. Gunter’s scale, or Gunter’s line, generally called the gunter by seamen, was a large plane scale with logarithmic divisions plotted on it. With the aid of a pair of compasses, it was used to multiply and divide. Gunter’s scale was an important step in the development of the slide rule.