The tube in which one was mounted is 58 feet long and 7 feet in diameter. It is slung on chains between two piers of masonry, and the telescope is moved and supported by a complex system of cast-iron platforms, triangles, and levers. It is the largest telescope in the world, and cost about £20,000 to construct. Observations were commenced in February, 1845. There are several smaller telescopes at the castle as well. The present Earl of Rosse is the third Earl, and, like his father, is an eminent scientist. AUTHORITIES CONSULTED. T. Cooke, “History of Birr,” &c. Cooke, “Picture of Parsonstown.” Brewer, “Beauties of Ireland.” Donovan, “Annals of the Four Masters.” S. Lee, “Dictionary of National Biography.” Parliamentary Gazetteer. Report of Historical MSS. Commission. _BLACK CASTLE, WICKLOW_ Wicklow is situated about twenty-five miles south-south-east of Dublin, and the ruins of the Black Castle occupy an isolated rocky promontory east of the town, and on the south side of the Leitrim river. The name Wicklow is likely to have been of Norwegian origin, but the meaning is uncertain. The Irish name Kilmantan signified S. Mantan’s Church. The castle followed the natural shape of the dark rock on which it was built, and from which, no doubt, the designation “Black” is taken. It was divided from the mainland by a chasm, which was probably bridged in former times. A few fragments of walls, with window openings, are all that remain. The fortress can never have been of large dimensions if it was confined to the rock on which the ruins now stand. In 1176, after Maurice FitzGerald had been recalled by Strongbow, he received a grant of the Castle of Wicklow, among other possessions, in lieu of his lands in Wexford, which King Henry wished to retain. From this it would appear to have been the site of an older fortification. Maurice FitzGerald began to erect a Norman stronghold on the promontory, but he died before it was completed. Soon after his death William FitzAdelm managed by falsehood to get possession of the Black Castle from his son Gerald, first Baron of Offaly, and surrendered him instead the unprotected Castle of Ferns. The Earl of Ormond being arraigned for treason in 1422, one of the charges against him was that he had retained William Edward, Constable of Arklow, in his service after he had assisted the O’Byrnes in seizing the King’s Castle of Wicklow. They killed John Liverpoole, the constable, and sent his head to the O’Byrne. They also imprisoned a priest, whom they found in the fortress, to hold for ransom. [Illustration: BLACK CASTLE, WICKLOW.]