overall: .6 cm x 32.5 cm x 8 cm; 1/4 in x 12 25/32 in x 3 5/32 in
United Kingdom: England, London
This large brass instrument has two rectangular arms with flat ends and an undecorated hinge. 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. The top arm has a scale labeled "Rum." that runs from 1 to 8, and the lower arm has a scale labeled "Lon." that runs from 60 to 10. Spanning both arms on the outer edge are four scales: log tangents, running from 1 to 45 degrees; log sines, running from 1 to 90 degrees; log versed sines, running from 165 to 10 degrees; and logarithmic, labeled "Num." and running from 1 to 10 twice. The front is marked: Tho<sup>s</sup>. Harris & Son (/) British Museum London.
The other side has a double scale along the fold line for regular polygons, from 12 to 4 sides. Each arm has a "line of lines" scale, running from 1 to 10; a secant scale, running from 10 to 75; and a scale of chords, running from 10 to 60. The upper arm has a scale of equal parts, running from 90 to 10, and scales for the inclined meridian, chords, and sines, each running from 10 to 90. The lower arm has scales for tangents, running from 10 to 45; latitude, running from 10 to 90; hours, running from I to VI; and chords, running from 0 to 180. Spanning both arms along the outer edge is a scale of inches, running from 24 to 1 and divided to twentieths of an inch.
The London telescope maker Thomas Harris (about 1750–1827) took his son, William, as a partner in 1806. By 1817, the firm was located on Great Russell Street, across from the entrance to the British Museum, and presented itself as "opticians to the Royal Family." In 1846, the workshop moved to High Holburn Street; it remained in business until the 20th century.
References: Gloria Clifton, <i>Directory of British Scientific Instrument Makers 1550–1851</i> (London: National Maritime Museum, 1995), 125–126; Adler Planetarium, <i>Webster Signature Database</i>, http://historydb.adlerplanetarium.org/signatures/.