Transit theodolite, presented to John Playfair, later used by Charles Piazzi Smyth

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This is a geodetic theodolite or portable altazimuth instrument by Edward Troughton, of London. Known as 'Playfair's Altazimuth', this fourteen-inch transit theodolite bears a silver inscription plate recording that it was presented to John Playfair (1748-1819), professor of natural philosophy at the University of Edinburgh, by the pupils of the higher mathematics class in 1806. It was subsequently used by Charles Piazzi Smyth (1819-1900) to survey the Great Pyramid in 1865. This instrument was made to Edward Troughton's 1792 design, and combines sturdiness with delicacy of adjustment and measurement.

The 18-inch double vertical circle measures altitudes, while the 15-inch horizontal circle, on which the rest of the instrument may revolve, measures to azimuth bearings. The finely-divided scales are marked out in silver let into the brass, and are read with micrometer microscopes.

The silver plate inset into the base reads: 'Joanni Playfair / Mathematicae nuper, nunc / Physicae in Academia Edinburgena / Professori Discipule Classis Mathescos / Sublimiosis, ut, quantum ejus / committati, diegentae, et ingeneo / deborent, testorentor, hunc Circulum / Astronomicum donerunt. / Edin. A.D. MDCCCVI.' The instrument is signed on the altazimuth circle 'Troughton London'.

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• Online ID: 000-180-001-001-C
• Image Rights Holder: National Museums Scotland
• Project: National Museums Scotland Part 2
  Project description   View all records in project
• Ref: National Museums Scotland  T.1955.22
• Date: 1806
  
• Material: Inscription: [In latin] Presented to John Playfair, Professor of Physics, Edinburgh, by the pupils of the higher mathematics class,
  Theodolite, transit
  
• Dimensions: 28.00" H; 14.75" D (transit circle)
  
• What: Theodolite, transit
  
• Subject: 5. CARTOGRAPHY, Surveying (Departmental Classification)
  
• Who: John Playfair, Professor of Physics (Owner)
  Troughton, London (Theodolite maker)
  
• Where: England, London
  
• Event:
• Description: Transit theodolite by Troughton bearing an inscription in latin indicating that it was presented to John Playfair, Professor of Physics, Edinburgh, by the pupils of the higher mathematics class, 1806
  
• References:
  • Described in the article 'Circle', chapter II, Edinburgh Encyclopaedia (1808-30), pp 492-4, and illustrated plate CXLVI. 
  • For Charles Piazzi Smyth, see Bruck, H.A. and M.T. The Peripatetic Astronomer: the Life of Charles Piazzi Smyth. Bristol, 1988, esp. p 105 
  • For Edward Troughton, see McConnell, Anita. Instrument Makers to the World: a History of Cooke, Troughton & Simms. York, 1992. 
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