Sector

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A sector is an instrument for solving computations which use the rules of proportion. This brass example was made in Portugal in the 18th century, and may have been used in artillery to calculate the trajectory of cannon shot.

The scales on this side of the instrument are entitled 'Linha das partes equais' ['line of Equal Parts'], 'Planos' ['planes'] and 'Poligonos' ['polygons']. There is also an edge scale entitled 'Bocas' for the calibre of guns.

The invention of the sector is attributed to Thomas Hood by the English, and to Galileo Galilei by the Italians. Both published quite independent accounts in 1598. The instrument had its origins in the earlier proportional compass and continued to develop with time.

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• Online ID: 000-100-104-288-C
• Image Rights Holder: National Museums Scotland
• Project: National Museums Scotland
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• Ref: National Museums Scotland  T.1984.173
• Date: 18th century
  
• Material: Brass
  
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• Where: Portugal
  
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• Description: Portuguese sector of brass, 18th century
  
• References:
  • Also see Hambly, Maya. Drawing Instruments 1580-1980. London: 1988, pp 135-6 
  • For the use of sector, see 'Sector' in Rees, A. (ed.), Cyclopedia vol 22, London: 1819 [unpaginated] 
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