Gunter's Scale Signed Merrifield & Co.

In 1614 Scottish mathematician John Napier announced his discovery of logarithms. Within eight years, Edmund Gunter, an English clergyman who was interested in mathematics, had devised a scale on which logarithms could be multiplied and divided, by measuring the distance between two logarithmic numbers with a pair of dividers. Shortly thereafter, instrument makers were manufacturing wooden rules with standard (or "natural") scales typically used in navigation on one side and Gunter's logarithmic (or "artificial") scales on the other side.

This instrument, a precursor of the slide rule, became known as Gunter's scale. Since it was made of one piece of wood, the expansion and shrinking that happened at sea did not impede its operation. Thus, Gunter's scale remained popular with ship's navigators until the end of the 19th century, when new materials were available for the manufacture of slide rules. Surveyors, mechanics, craftsmen, and retailers also used Gunter's scales to make logarithmic and trigonometric calculations.

This 2' boxwood rule is identical to 319077 and 333945. The top of one side has a scale of inches, divided to tenths of an inch and numbered by ones from 23 to 1. On the left are 10" and 9" (divided to 1/2") plotting scales with diagonal scales at each end. In the middle are scales for rhumbs, chords, sines, tangents, and semitangents. On the right are scales for leagues, rhumbs, miles of longitude, and chords. Brass pins at the zero and 60° marks reduce wear from the points of dividers, which were used to transfer measurements between the scale and the user's drawing.

The other side has logarithmic scales: sines of rhumbs, tangents of rhumbs, line of numbers, sines of degrees, versines of degrees, and tangent of degrees. At the bottom edge are a meridional line and a scale of equal parts that divides 23" into 17 sections. The sections are numbered by tens from 60 to 10 and from 100 to 0.

On the side with the scale of inches, the rule is marked in the lower right corner: MERRIFIELD & C^O (/) NEW-YORK. Merrifield & Co. sold Gunter's scales in Boston and New York in the early 19th century.

References: Adler Planetarium, Webster Signature Database, http://historydb.adlerplanetarium.org/signatures/; Otto van Poelje, "Gunter Rules in Navigation," Journal of the Oughtred Society 13, no. 1 (2004): 11–22; George Curtis, A Treatise on Gunter's Scale, and the Sliding Rule (Whitehall, N.Y., 1824); Florian Cajori, "On the History of Gunter's Scale and the Slide Rule During the Seventeenth Century," University of California Publications in Mathematics 1, no. 9 (February 17, 1920): 187–209.

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