GUNTER, EDMUND, was born in the county of Hertford, but descended originally from Gunter's Town, in Brecknockshire. lie was educated on the royal foundation at Westminster School, and elected thence to Chriatchnrch College, Oxford, in the year 1599, being then eighteen years of age, where he took the degrees in Arta. Mathematics were the prevailing studios of his youth, and about the year 1606 he invented the sector, and wrote the description and use of it in Lean, many copies of which were taken in writing, but none of them printed. After this be took orders, became a preacher, in 1614 was admitted to read the Sentencre, and proceeded to the degree of Bachelor in Divinity. But his genius still leading him chiefly to mathematical pursuits, when Mr. Williams resigned the professorship of astronomy in Gresham College, he was chosen to succeed him on the 6th of March 1619. He died on the 10th of December 1626, about the forty-fifth year of his age. (Ward, ' Lives of the Gresham Professors.') The works of Gunter are as follows:— 1. 'Canon Triangulorum,' 8vo, London, 1620, and 4to, 1023. A table of logarithmic since, &c., seven decimal places, the of the kind which were published on Briggs's system of logarithms.
2. ' Of the Sector, Croarstaff, and other Instruments' (first pub lished in 1624). The invention of the sector, which now forms a part of every case of drawing inntrtunents, is due to Gunter, and ita uses are described by him in three books. The cross-staff is not the sur veying instrument now known by that name, but an instrument for taking anglers, consisting of one straight line moving at right angles to with sights at their extremities.
3. ' The Description and Use of his Majesty's Dials in Whitehall Garden,' 4to, London, 1624. These dials (destroyed in 1697) were constructed by Gunter.
The first two of these works went through five editions, the fourth of which, purporting to be examined and enlarged by W. L. (William Leybonrn), contains improvements in the sector by Samuel Foster, Ac. The fifth, which is a reprint of the fourth, was published in 1673, and (with a new title-page only) in 1680.
Gunter's writings (the ' Canon Triangulorum ' excepted) consist almost entirely of a description of graphical methods of constructing problems in trigonometry, navigation, fie. He was the first who laid down a logarithmic scale upon wood, and used it for the purposes of the This Beale is still used, and goes by his name. The
common chain used by surveyors also goes by his name. The first observation of the variation of the compass is due to Gunter. Ward infers this from a letter of Dr. Wallis to Sir Hans Sloane, attributing the observation to a Gresham professor about 1625, which could be no other then Gunter. Other writers mention the same bat without stating their authority. The following is the account of Gunter himself ('On the book ii. ch. 5), in which the enunciation of the variation is an appendage to an example of the method of taking angles by the cross-staff, as follows :—" So that if the magnetical azimuth A Z M shall be 84* 7', and the sun's szimuth A Z N 72' 52', then must NZ M, the difference between the two give the variation to be 11' 15', as Mr. Borough heretofore found it by his observations at Litnehouse in the year 1580. But if the megnetical azimuth A Z M shall be 7V 7', and the sun's azimuth A Z N 72* 52', then shall the variation N Z M be only 6' 15', as I have sometimes found it of late. Hereupon I inquired after the place where Mr. Borough observed, and went to Limehouse with some of my friends, and took with us a quadrant of semidiameter, and two needles, the one above six inches and the other ten inches long, where I made the semidiameter of my hori zontal plane AZ 12 inches; and towards night, the 13th of June 1622, I made observation in various parts of the ground, and found as followeth." Eight observations are then given, the results of which are from 5' 40' to 6' 13', with a mean of 5° 58'.
Gunter is said to have been the first who introduced the words cosine, cotangent, &e., in place of sine of the complement, &c. In the preface of the ' Canon,' ha speaks of the "sine of the complement, which in one word may be called the cosine," as if ho were intro ducing a new word. There is also the testimony of Brigga ('Arith. Log.,' cap. 13) that Gunter suggested to him the use of the arithmetical complement. Whatever in short could be done by a well-informed and ready-witted person to make the new theory of logarithms more imme diately available in practice to those who were not skilful mathemati cians was done by Gunter.