Altazimuth theodolite, 1775-1785.
© Science Museum / Science & Society Picture Library
The manufacture of this instrument is attributed to both Henry Hindley of York and John Smith. A theodolite is an altazimuth surveying instrument designed for taking angles in two coordinates. It is provided with both a vertical and a horizontal arc or circle and a telescopic sight, so that altitudes and azimuths can be taken from a single sighting.