“Birkinshaw” railway chair in cast iron. One of three found near the Laigh Milton Viaduct (Kilmarnock and Troon Railway) during the viaduct conservation project (1995-96). The chair weighs 9.3 kg (20.4 lb).
For an article on the viaduct and its restoration see http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=1243.
For a detailed paper on the viaduct and its restoration see here.