Accession No
0988
Brief Description
sector, by Dollond, English, 1800 (c)
Origin
England; London
Maker
Dollond
Class
calculating; mathematics
Earliest Date
1800
Latest Date
1800
Inscription Date
Material
metal (brass); ivory
Dimensions
length 161mm; breadth 35mm; thickness 3mm
Special Collection
Robert Whipple collection
Provenance
Inscription
‘Dollond,
London ‘ (on obverse)
Description Notes
Ivory sector with brass hinge and shoulders. Obverse carries double scales: ‘S’ divided 0 - 90 numbered by 10, 0 - 60 subdivided to 30’, 60 - 70 subdivided to 1˚, 70 - 85 subdivided to 2˚; ‘T’ divided [0] - 45 numbered by 10 subdivided to 15’; ‘T’ divided 45 - [76] numbered by 10, subdivided to 15’. On the fully opened limbs single scale of ‘TA’ (log tangents) divided 2 - 45 numbered 2,3 ... 10, 20, 30, 40, 45; ‘SI’ (log sines) divided [1] - [75] numbered 2,3 ... 10, 20 ... 70; ‘NU’ (log numbers) divided 1 - 2[00] numbered 1,2 ...9, 1[0], 2[0], 3[0] ... 10[0], 2[00]. Reverse carries double scales: ‘L’ (line of lines) divided [0] - 10 numbered by 1 subdivided to 0.05; ‘S’ (secants) numbered 20 - 75 numbered by 10 subdivided to 1, 60 - 70 subdivided to 30’, 70 - 75 subdivided to 15’; ‘C’ (chords) divided 0 - 60 numbered by 10 subdivided to 30’; ‘POL’ (polygons) divided 12 - 4 numbered by 1. Single scales on upper limb: ‘IM’ (inclined meridian) divided [0] - 90 numbered by 10 subdivided to 1; ‘Cho’ divided [0] - 90 numbered by 10 subdivided to 1. Single scales on lower limb ‘Lat’ divided 0 - 75 numbered by 10, 0 - 40 subdivided to 1, remainder divided to 2; ‘Hou’ divided 0 - VI numbered by I subdivided to 5’. On the fully opened limbs a scale of inches divided [0] - 12 numbered by 1 subdivided to 0.1. Brass studs let in at significant points on the scales.
Condition good (some staining to ivory); 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:39532
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