English-Style Sector Signed by Richard Glynne

This brass instrument has straight ends, and the hinge is decorated with a floral design. A rectangular brass piece fits between the arms when the sector is closed and swivels out to form a square corner when the sector is opened. The piece also fits into the groove on the other arm to hold the sector open at a fixed acute angle. One side has three double scales. Two are tangent scales, running from 45 to 75 degrees and from 10 to 45 degrees. The third is a sine scale, running from 10 to 90 degrees. The top of the upper arm has scales for hours, running from I to VI, and for chords, running from 10 to 90. The bottom of the lower arm has scales labeled "Latt" and "In : M." Both scales run from 10 to 90. These four scales were used for making sundials and are unique to sectors made in England. The sector is marked: R : Glynne : Fecit.

The other side has double scales labeled "Poll," running from 6 to 12; "sec," running from 20 to 75; "Lin," running from 2 to 10 on the upper arm and from 1 to 10 on the lower arm; and "Cho," running from 10 to 60. The "Poll" scale is not the usual scale for the side length of inscribed polygons, as the numbers start with 6 rather than with 3 and increase from the center to the ends of the legs instead of decreasing. The scale of chords is outside the scale of equally divided lines on the upper arm and inside the scale of equally divided lines on the lower arm. Three logarithmic scales are along the outer edge: "Tan," running from 1 to 45; "Sim" [sic], running from 1 to 80 (which is marked "60"); and "Num," running from 1 to 10 twice and then from 10 to 30. The outside face of the rule has a scale of inches that runs from 1 to 12 and is divided to tenths of an inch.

The London workshop operated by Richard Glynne (1681–1755) made globes, sundials, and drawing instruments. Glynne was in partnership with Anne Lea, his mother-in-law, from about 1712 to 1725, and he became so successful that he retired in 1729. For a sundial signed by Henry Wynne, under whom Glynne apprenticed from 1696 to 1705, see 1987.0851.01.

References: Adler Planetarium, Webster Signature Database, http://historydb.adlerplanetarium.org/signatures/; E. G. R. Taylor, The Mathematical Practitioners of Tudor & Stuart England (Cambridge: University Press, 1970), 293; Gloria Clifton, Directory of British Scientific Instrument Makers 1550–1851 (London: National Maritime Museum, 1995); Bruce Babcock, "A Guided Tour of an 18th-Century Carpenter's Rule," Journal of the Oughtred Society 3, no. 1 (1994): 26–34.

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