A small brass spirit level in its original mahogany carrying box. The instrument is enclosed in a brass tube and has crosshair sights on either end. It is inscribed 'Improved by Willm Stenson Junr' and was made in the second half of the 19th century.
The spirit level was used by a mine surveyor. It was used to ensure theodolites, or other measuring equipment, were flat and level before any measurements of horizontal and vertical angles were made. The Coal Mines Act of 1911, made it compulsory for mine owners to keep records of where their mines were sunk, and it was a mine surveyors job to make these detailed plans of colliery sites.
The science of surveying has always played an important role in the history of mining. The Ancient Egyptians were some of the first people to make use of surveying, employing it in the excavation of their gold mines from around 1400 BC.