This scarce example of a ďGunterís RuleĒ is marked by the Merrifield Co., working in New York. Little seems to be known about Merrifield, except that they sold rules in Boston in the early 19th Century, and then moved to New York, marking rules there in the 1920s. Their principal produce appears to have been Gunterís Rules, made of boxwood (sometimes with brass tips and half bindings). I have heard of at least one example having ivory tips. This example is unbound, made of well darkened boxwood and having at least 15 small brass plugs with dimpled centers inserted into critical positions on the rule. These were for seating the point of a divider leg while measurements and calculations were being taken.
The Gunterís Rule was developed in the
early 17th century following the discovery of Logarithms by Napier
about 1616. In 1620 Alfred Gunter composed lines of logarithms and showed how
they could be used to carry out calculations using a set of dividers. By about
1630 the slide rule, had been developed to facilitate such calculations.
However, the moving scales on a slide rule were subject to error from the
expansion of wood under varying conditions of heat and humidity, and the original
Gunterís rule remained popular for use on ships at sea for solving navigation
On one side of this 2' boxwood rule is 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.
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 & CO (/) NEW-YORK. Merrifield & Co. Little appears to be known about Merrifield & Co. Apparently they operated in Boston by 1820, and during the 1820s moved to Boston. They were one of the earliest American rule makers, and examples are very scarce, with most being held in museum. This rule is dark, and there is a nick (saw kerf) in the bevel, about 2 inches from the left. It is a scarce rule, and presents a challenge for someone wanting to learn how to use it. Good+