Accession No

1014

Brief Description

boxwood Gunter sector, English, early 18th Century

Origin

England

Maker

Class

calculating; mathematics

Earliest Date

1700

Latest Date

1750

Inscription Date

Material

wood (boxwood); metal (brass)

Dimensions

length 238mm; breadth 45mm

Special Collection

Trinity College collection

Provenance

On loan from Trinity College, University of Cambridge from 1951.

Inscription

Description Notes

Boxwood sector consisting of two arms held together by flat circular brass hinge. Also brass pins to hold sector closed.

Obverse: three scale on both arms. These are a scale of sines, marked ‘S’, divided [0] - 90˚, numbered by 10˚; a scale of tangents, marked ‘T’, divided [0] - 45˚, numbered by 10˚; a second scale of tangents, marked ‘Tan’, divided 45˚ - [78˚], numbered by 5˚.
When the sector is opened out fully there are continuous scales along the outer edge. These are a scale of log tangents, marked ‘Tan’, divided 1˚ - 45˚ and back to 80˚, numbered 1, 2, 3…9, 10, 20,…80; a scale of log sines, marked ‘Sin’, divided 1˚ - 90˚, numbered 1, 2…9, 10, 20…90; a scale of chords, marked ‘Chords’, divided 0 - 90˚, numbered by 10˚; a scale of latitudes, marked ‘Latt’, divided 0 - 90˚, numbered by 10˚.

Reverse: three scales on both arms. These are a scale of chords, marked ‘C’, divided [0] - 60˚, numbered by 10˚; a scale of equal parts or lines, marked ‘L’, divided [0] - 10, numbered by 1; a scale of secants, marked ‘Sec’, divided 10˚ - 75˚, numbered by 10˚.
Along the outer edges forming continuous scales when the sector is fully open is a line of log numbers, marked ‘Num’, divided 1 - 10[0], numbered 1, 2, 3…9, 1, 12, 2[0], 3[0]…10[0]. Within this are a scale of hours, marked ‘Hours’, divided 0 - VI, numbered by I; and a scale of inclined meridians, marked ‘I M’, divided 0 - 90˚, numbered by 10˚.

Along the outer rim is a scale of inches, continuous when sector is fully open, divided [0] - 18, numbered by 1.

Various brass reinforcing studs.

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:40335