Dec. 10, 1626: Measurement Man Meets the Measure of His Days
1626: Edmund Gunter dies. He invented tools for computation, navigation and surveying, and devised the trigonometry concepts of cosine and cotangent.
Gunter was born sometime in 1581 in Hertfordshire, England. He graduated from Christ Church, Oxford University, in 1603, received a divinity degree in 1615, and was rector of churches in Oxford and London.
Gunter used to hang out with geometry professor Henry Briggs at the newly founded Gresham College in London. Briggs was the main scientific proponent of Scottish mathematician John Napier‘s new invention: logarithms.
Gunter combined the logarithms with trigonometry in 1620 when he published Canon Triangulorum, or Table of Artificial Sines and Tangents, which included seven-figure tables of the logs of sines and tangents. Gunter was appointed professor of astronomy at Gresham that same year, thanks to the recommendation of his friend Briggs.
But Gunter was no ivory-tower theoretician. He wanted to build better tools for anyone who calculates, including mathematicians, astronomers, navigators and surveyors. He invented Gunter’s scale, a predecessor of the slide rule. It used a single set of logarithmic scales and a pair of dividers to simplify computation. Grateful sailors named the device the gunter. (William Oughtred soon placed two gunters side by side to create the beta version of the slide rule.)
In his 1624 book Description and Use of the Sector, the Crosse-staffe and Other Instruments, Gunter introduced the abbreviated notations sin for sine and tan for tangent. Depending on your personal relation with trigonometry, you also have Edmund Gunter to praise or curse for the words cosine and cotangent.
He also invented Gunter’s chain, a surveying instrument with 100 links. With a length of exactly 22 yards (or 4 rods or 1/10 furlong), it was 1/80 mile. One square chain is 66 feet by 66 feet, or 4,356 square feet, and an acre is conveniently 10 square chains, equal to 43,560 square feet or 1/640 of a square mile.
When Gunter measured the magnetic declination of a compass in 1622, he got different results from those obtained at the same location more than four decades earlier. He chalked it up to measurement error in the earlier observations.
Unbeknownst to him, Gunter was actually the first to observe and record the secular variation or drift of the Earth’s magnetic field. When Henry Gellibrand explained the phenomenon in 1634, he acknowledged Gunter’s contribution.
Gunter’s books were influential for decades after his death, with editions appearing all the way through 1680.
Source: MacTutor History of Mathematics (University of St. Andrews)
Photo: Gunter’s scale was a precursor of the slide rule: It needed a separate, geometric-divider instrument to measure logarithmic scales.
This article first appeared on Wired.com Dec. 10, 2008.
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