Transit instrument with 30 in telescope by Elliott Bros, London (c.1896). Lacking iron stand and miniature lantern to illuminate the axis.
The instrument consists of a brass telescope with a reflector to illuminate the axis, a lantern, diagonal eyepiece, direct eyepieces of varying power and axis level. It can move up or down but not swivel and would have been mounted on a cast iron stand.
The instrument was used in the late 1890’s and 1900’s on the construction of the Talla water supply project which still supplies Edinburgh.
When first donated to the museum in 1987 little was known about the instrument however later research identified its very likely association with the Talla works (1897 – 1905). It is believed the setting out of the line and level of the Talla Aqueduct was done with great precision from observatories, the concrete pillars of which a number of which still survive, including one on a steep hillside near Tweedsmuir (NT 106 260).
Transit instruments were in use at the time for astronomical purposes to determine the positions of stars. Their use was also turned to land surveying and the setting out of civil engineering works. Rankine writes: “For setting out very long straight lines the theodolite is not sufficiently exact and it then becomes advisable to use a small transit instrument consisting simply of a telescope with a horizontal axis resting on a suitable stand so as to be capable of being turned over in a vertical plane.” (William John Macquorn Rankine. A Manual of Civil Engineering. London C. Griffin and Company, 1894.)
For a photograph and brief description of an observatory which housed this instrument click here.