Accession No
1659
Brief Description
sector, English, circa 1650
Origin
England
Maker
Class
calculating; mathematics
Earliest Date
1650
Latest Date
1650
Inscription Date
Material
metal (brass)
Dimensions
length 160mm; breadth 32mm; thickness 4mm
Special Collection
Provenance
Purchased from Peter Delehar, 146 Portobello Road, London, W11, in 02/1975.
Inscription
Description Notes
Six inch brass sector with decorated hinge.
Obverse has double scales of: ‘L’ (lines or equal parts) divided [0] - 100, numbered by 10, subdivided to 0.5; ‘T’ (tangents) divided [0] - 45˚, numbered by 10˚, subdivided to 15´; continuation of tangents, divided 45˚ - 75˚, numbered by 10˚, subdivided to 1˚. On fully opened limbs, scales for twelfths and sixteenths of an inch, marked ‘12’ and ‘16’ respectively and divided [10] - [0] - 90 and [10] - [0] - 80 respectively with section before 0 divided to 0.5 and 1 respectively.
Reverse has double scales of: ‘S’ (sines) divided [0] - 90˚, numbered by 10˚, 0 - 40˚ subdivided to 15´, 40˚ - 70˚ subdivided to 30´, 70˚ - 80˚ subdivided to 1˚, 80˚ - 90˚ subdivided to 5˚; ‘C’ (chords) divided [0] - 90˚, numbered by 10˚, subdivided to 30´; ‘Pollygon’ divided 12 - 4, numbered by 1. On fully opened limbs single scales of elevenths and thirtieths of an inch, marked ‘11’ and ‘30’ respectively and divided [10] - [0] - 80 and [10] - [0] - [1]40 respectively with section before 0 divided to 0.5 and 1 respectively.
On fully opened edges of limbs, scale of inches divided [0] - 12, numbered by 1, subdivided to 0.1.
Two brass pins for securing limbs together.
Condition good (marked on reverse); 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:39545
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