English-Style Sector Signed by Jesse Ramsden

The silver hinge is undecorated on this ivory instrument with rectangular arms. On one side and from the top down, 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 tangent, running from 2 to 30 degrees; log sine, running from 1 to 70 degrees; and logarithmic, labeled num and running from 1 to 10 twice and then from 10 to 20. The hinge is marked: Ramsden (/) London.

The other side has a double scale along the fold line for regular polygons, 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 Cho that each run from 10 to 90. The lower arm has scales labeled Lat, running from 10 to 70; and Hou, running from I to VI. These four scales 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.

After training under several notable makers of instruments, Ramsden operated his own shop from before 1765 to 1800. His equatorial telescopes and sextants were of especially high quality, and he invented a dividing engine for engraving angular divisions on circular instruments. The second model for his dividing engine is now owned by the Smithsonian, MA.215518.

The object was purchased in 1960.

References: Gloria Clifton, Directory of British Scientific Instrument Makers 1550–1851 (London: National Maritime Museum, 1995), 277; Anita McConnell, Jesse Ramsden (1735–1800): London's Leading Scientific Instrument Maker (Aldershot, England: Ashgate, 2007); Randall C. Brooks, "Dividing Engine," in Instruments of Science: An Historical Encyclopedia, ed. Robert Bud and Deborah Jean Warner (New York and London: Garland Publishing, 1998), 184–186.

Currently not on view