Accession No
1603
Brief Description
Galileo-type geometrical sector, Italian, 17th century
Origin
Italy
Maker
Class
calculating; mathematics
Earliest Date
1606
Latest Date
1700
Inscription Date
Material
metal (brass)
Dimensions
main sector length 274mm; breadth 45mm; thickness 6mm separate scales length 248mm; breadth 22mm; thickness 3mm
Special Collection
Provenance
Purchased from A. Davidson Ltd., Jermyn Street, London SW1, in 09/12/1971.
Inscription
Description Notes
Brass sector with decorated hinge and shoulders. Limbs terminating in scrolls.
Obverse carries double scales of: metals, marked ‘ORO’ (gold), ‘PI’ (lead), ‘AR’ (silver), ‘RA’ (copper), ‘FE’ (iron) ‘ST’ (tin), ‘MA’ (marble), ‘PIE’ (stone); unequal scale divided 1 - [152], numbered 1, 2...10, 15, 20, 25, 30, 40...100, [1]20, [1]40, 10 - 30 subdivided to 1, 30 - 100 subdivided to 2, 100 - end subdivided to 4; unequal scale divided 1 - [52], numbered 1, 2,...10, 15, 20...50, subdivided to 1; equal scale divided [16] - [262], numbered by 10, subdivided to 1.
Reverse carries double scales: two scales on same line divided 18 - [0], numbered by 1; scale divided 13 - 3, numbered by 1; scale divided 3 - 15, numbered by 1.
Two pairs of additional (and later?) calibrated limbs, with decorated shoulders (including a nymph blowing a horn). First pair has scales: one scale divided 1 - 64, numbered 1, 2, 3, 4, 5, 10, 15, 20...60, 64, subdivided to 1; next scale divided [0] - 90, numbered by 5, subdivided to 1; inner scale divided 2 - 20 numbered 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, subdivided to 1. Second pair has scales: outer scale 20 - 3, numbered 20, 15, 14...3, subdivided to 1; inner scale [0] - 100, numbered by 5, subdivided to 1. These limbs screw over the main limbs with the screws passing through holes in the latter.
Condition good; incomplete (two screws missing).
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:39549
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