© Science Museum / Science & Society Picture Library
This circumferentor was made by George Adams of London, one of the top instrument makers of the day. It was used between 1750-1763 on the survey of the Mason-Dixon line, in America. The instrument is inscribed in an engraved circle; 'Geo: Adams LONDON'. Circumferentors (with a full circle scale) and graphometers (with a half circle scale) were widely used for angle measurement in the 17th and 18th centuries. A joint on the support allowed for both vertical and horizontal use.