6 in transit railway theodolite with longitudinal level over the telescope and constructed without an altitude circle. Reading to 10 seconds of arc. Trough compass and other accessories. Bronzed brass. 3-screw levelling head and tribrach.
Used for railway surveying; eg setting out masonry skew-arch bridges.
For a description of the setting out of a skew arch bridge see Figs 12 & 13 of Thomas Carfrae’s copy of W Davis Haskoll CE’s “Railway Construction for the Use of the Engineer Contractor &c” Atchley & Co London 1857. A book of instructions for the use of theodolites is in the collection (see 1998/001).