Lord Rosse's Great Telescope

From 1845 until 1917 the biggest telescope in the world was the 72-inch reflector built and operated by Lord Rosse at his Irish home. Patrick Moore visits Birr Castle in County Offaly, Eire, to discuss with the present Lord Rosse his great - grandfather's remarkable achievement in constructing the huge telescope, and his use of it to establish the spiral nature of galaxies.