made in London

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

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:	0504: 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,
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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