William Parsons, 3rd Earl of Rosse (1800–1867) of Birr Castle, Ireland; succeeded to the earldom on his father's death in February 1841; His largest and most expensive telescope project, the construction of a Newtonian reflector with a 6 ft aperture and a 4 ton mirror, known as ‘the monster telescope’ or ‘Leviathan of Parsonstown’, was completed in 1844 at a cost of £12,000. Also known as Lord Oxmantown