Accession No
1227
Brief Description
Gunter sector, by George Adams, English, 2nd half 18th Century
Origin
England; London; Fleet Street
Maker
Adams, George
Class
calculating; mathematics
Earliest Date
1750
Latest Date
1800
Inscription Date
Material
metal (brass); ivory
Dimensions
length 323mm; breadth 76mm; thickness 6mm
Special Collection
Robert Whipple collection
Provenance
Donated by Robert S. Whipple to the University of Cambridge in 11/1944 as part of the Whipple Museum of the History of Science’s founding collection. Purchased by Robert S. Whipple from T.H. Court in 1944.
Inscription
‘Adams,
Fleet Street.
London.’ (obverse)
Description Notes
12-inch ivory sector with brass hinge and shoulders.
Obverse has double scales of: ‘SIN’ divided [0] - 90˚, numbered by 10˚, 0 - 70˚ subdivided to 15´, 70˚ - 80˚ subdivided to 30´, 80˚ - 85˚ subdivided to 1˚; ‘TAN’ divided 45˚ - [75˚ 45´], numbered by 10˚ (and for 75˚), 45˚ - 50˚ subdivided to 30´, 50˚ - end subdivided to 15´; ‘TAN’ divided [0] - 45˚, numbered by 10˚, subdivided to 15´. On upper limb single scale of ‘Rum.’ divided [0] - 8, numbered by 1, subdivided to 0.25. On lower limb single scale of ‘M. Lon.’ [longitude] divided [0] - 60˚, numbered by 10˚, subdivided to 1˚. On the fully opened limbs scales of ‘NUMB’ (log numbers) divided 1 - 2[00] numbered ‘1’, ‘2’ ... ‘9’, ‘1’, ‘2’...’10’, ‘2’, 1 to 5 divided to 0.05, 5 - 1[0] subdivided to 0.2, 1[0] to 3[0] subdivided to 0.2, 3[0] to 6[0] subdivided to 0.5, 6[0] to 10[0] subdivided to 1, 10[0] to 2[00] subdivided to 2. A few brass reinforcing studs let in at significant points on the scales. Three brass pins to secure arms together
Condition good; complete
References
Events
Description
Sector
Sectors were used for calculation by navigators, surveyors, gunners and draftsmen (and, famously, by Galileo) from the about the mid 16th century to the mid 19th century. During the 16th century, they were used as general mathematical tools, but the introduction of logarithms drastically expanded their application. Usually made of brass, wood or ivory, they look like a jointed rule with scales engraved on either side.
Sectors use the principle of similar triangles (that the ratio of lengths of two sides of similar triangles will always be the same) with scales of proportion for calculating mathematical functions such as finding the line of equal parts, inscribing a rectangular polygon inside a circle of a given radius and protracting angles. This made them useful for similar calculations to a slide rule.
18/10/2002
Created by: Saffron Clackson on 18/10/2002
FM:39551
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