William Parsons (1800–67), third earl of Rosse, was responsible for building the largest telescope of his time, nicknamed the 'Leviathan'. It enabled the earl to describe the spiral structure of galaxies. This volume reissues two contemporary accounts of the telescope. The first, published anonymously in 1844 and later revealed to be by Thomas Woods, provides a comprehensive description of the workings of both the 'Leviathan' and the smaller telescope which preceded it, with detailed accounts of the construction of both telescopes. The second, by another anonymous author, first appeared in the Dublin Review in March 1845, and outlines the history and problems of telescope manufacture from Galileo onwards. Together with a short account from 1842 of the Armagh observatory by its director, these works situate the telescopes, and the difficulties the earl faced during the eighteen years he took to build the 'Leviathan', in their wider context.