English-Style Sector by James Gilkerson

This ivory instrument has two rectangular arms with flat edges and a circular brass hinge. The scales run from top to bottom on each arm, unlike the paired double scales on Italian and French sectors. On one side, each arm has a sine scale, running from 10 to 90 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 sine, running from 2 to 70 degrees; log tangent, running from 1 to 45 degrees; and logarithmic, running from 1 to 10 twice and then from 10 to 20. The top face of the instrument has a scale of equal parts that runs from 100 to 10. The front is marked: *Gilkerson* (/) Tower-Hill-London.

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 upper arm has scales labeled Im and Ch that each run from 10 to 90. The lower arm has scales labeled La, running from 10 to 70; and H, running from I to VI. These four scales (inclinations of meridians, chords, latitudes, and hours) are associated with making sundials. Spanning both arms on the outer edge is a scale of inches, running from 11 to 1 and divided to tenths of an inch.

James Gilkerson was in business in Tower Hill, London, from 1809 to 1825. Donor Ada B. Richey reported that her husband's ancestor, Lt. Col. Alexander Matheson (b. 1788), was the original owner of this drawing instrument. He settled in Perth, Canada, after serving in the British army during the War of 1812.

References: Gloria Clifton, Directory of British Scientific Instrument Makers 1550–1851 (London: National Maritime Museum, 1995), 113; J. F. Heather, Mathematical Instruments: Their Construction, Adjustment, Testing, and Use, rev. ed. (London: Crosby Lockwood and Co., 1870), i:42–52; Samuel Sturmy, "The Art of Dialling," The Mariner's Magazine (London, 1669).

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