Accession No
0832
Brief Description
sector, by J. Gilbert, English, 1/2 18th Century
Origin
England; London
Maker
Gilbert, J.
Class
calculating; mathematics
Earliest Date
1700
Latest Date
1750
Inscription Date
Material
metal (brass)
Dimensions
length 162mm; breadth 36mm; thickness 3mm
Special Collection
Robert Whipple collection
Provenance
Purchased by Robert Stewart Whipple from T.H. Court, Harrow, England, on 07/04/1937.
Inscription
‘J Gilbert
London ‘ (on obverse)
Description Notes
Six inch sector with folding friction leaf. Double scales on obverse: ‘C’ divided [0] - 60 numbered by 10 subdivided to 30’; ‘Se’ divided 10 - 75 numbered by 10, 40 - 75 subdivided 1; ‘L’ (lines/ equal parts) divided [0] - 10 numbered by 1 subdivided to 0.05; ‘Pol’ divided 12 - 4 numbered by 1. On fully opened limbs, scale of inches divided [0] - [12] numbered by 1, subdivided to 0.1. On reverse, double scales: ‘S’ divided [0] - 90 numbered by 10, 0 - 70 subdivided to 30’, 70 - 85 subdivided to 1˚; ‘T’ divided [0] - 45 numbered by 10 subdivided to 15’; ‘Ta’ divided 45 - 75 numbered by 10 subdivided to 1˚. On the fully opened limbs scales of ‘T’ (log tangents) divided [1] - [40] numbered 2, 3 ... 10, 20, 30 1 - 10 subdivided to 10’, 10 - 20 subdivided to 15’, 20 - 30 subdivided to 20’, 30 - 40 subdivided to 30’; ‘S’ (log sines) divided 1 - 90 numbered 1,2,3...10,20...90, 1 - 10 subdivided to 10’, 10 - 20 subdivided to 15’, 20 - 30 subdivided to 30’, 30 - 70 subdivided to 1˚, 70 - 80 subdivided to 2˚; ‘N’ (log numbers) divided 1 - 10[0] numbered 1,2 ... 9, 1, 2... 10, 1 - 1[0] divided to 0.1, 1[0] - 3[0] divided to 0.5, 4[0] - 10[0] divided to 1.
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:39535
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