This sextant belonged to the famous Victorian engineer Isambard Kingdom Brunel. It has the optics open to view, in the manner of a marine sextant, but both its size and the absence of solar filters, indicate that this instrument is for surveying work, and so was appropriate for a railway engineer. He would have used this sextant for measuring distances and elevation when planning his constructions.
Brunel was undoubtedly a visionary engineer. He established the main lines of Britain’s Great Western Railway, designed steam trains and pioneering steam ships capable of traveling trans-Atlantic distances, including the SS Great Britain, and designed several bridges and other structures including the elegant Clifton Suspension Bridge in Bristol.