English-Style Sector

This yellowed ivory instrument has two rectangular arms with flat edges and is held together by a circular brass hinge. The lower arm is broken. The scales run from top to bottom on each arm. On one side, each arm has a sine scale, running from 10 to 80 degrees; a tangent scale, running from 45 to 75 degrees; and a second tangent scale, running from 10 to 45 degrees. Spanning both arms on the outer edge are three scales: log tangent, running from 3 to 45 degrees; log sine, running from 1 to 70 degrees; and logarithmic numbers, running from 1 to 10 twice. A double line separates these scales from the inner, diagonal set of scales. The top face of the instrument has a scale of equal parts that divides one foot into 100 increments and runs from 90 to 10. There is no maker's mark.

The other side has a double scale along the fold line for regular polygons, labeled POL and running from 12 to 4 sides. Each arm has a scale of equal parts, running from 1 to 10 and labeled L; a secant scale, running from 20 to 75 and labeled s; and a scale of chords, running from 10 to 60 and labeled C. The scales for dialing typically found on 18th-century English-style sectors are not present. Spanning both arms on the outer edge is a scale of inches, running from 12 to 1 and divided to tenths of an inch. Compare to MA.321755, MA.333937, and 1985.0580.06.

This sector may have been used at the New York Meteorological Observatory in Central Park, established and directed by Daniel Draper from 1868 to 1911.

References: Christopher J. Sangwin, "Edmund Gunter and the Sector," January 21, 2003, http://web.mat.bham.ac.uk/C.J.Sangwin/Sliderules/sector.pdf; Robert S. Harding and Jeffrey L. Tate, "Draper Family Collection, ca. 1826–1936," Archives Center, National Museum of American History, http://amhistory.si.edu/archives/d8121.htm.

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