Originally working in brickmaking in
Belfast, he invented machines used in that trade, before patenting the
screw-pile in 1833, for which he would later gain some fame. The screw-pile was used for the erection of
lighthouses and other structures on mudbanks and shifting sands, including bridges and piers. Mitchell's designs and methods were employed all over the world from
Portland breakwater to
Bombay bridges. Initially it was used for the construction of lighthouses on
Maplin Sands in the
Thames Estuary (the first light application, in 1838), the
Wyre Light at
Fleetwood in Lancashire (the first such beacon lit) completed, in 1839), and at
Belfast Lough where his lighthouse was finished in July 1844. In May 1851 he moved to
Cobh to lay the foundation for a
lighthouse on the Spit Bank; the success of these undertakings led to the use of his invention on the breakwater at
Portland, the viaduct and bridges on the
Bombay, Baroda and Central India Railway and a broad system of Indian telegraphs. While in Cork, Mitchell became friendly with
astronomer John Thomas Romney Robinson, and
mathematician George Boole. ==Awards and honours==