or roof over it. The enclosure has a diameter of 16-feet across. The telescope mounting was made by Grubb of Dublin. (Grubb would make telescopes for a century and half, later known as Grubb-Parsons) The telescope objective was doublet with 13.3 inches of aperture and 25 feet focal length. The Grubb mounting had a clockwork drive and weighed almost 2.4 metric tons (2.6 US tons), which rested on a limestone pillar. The lens was ground by Cauchoix of Paris using glass blanks by Guinand. The 13.3 inch lens was completed in 1831. Pierre-Louis Guinand (de fr) (20 April 1748, La Sagne — 13 February 1824, Les Brenets) was a Swiss who in the late 1700s came up with a breakthrough for making better quality and larger glass, and in time went on to teach a young Fraunhofer at Utzschinder's glassworks, and eventually started his own optical glass works. Guinand would supply glass for the Paris Observatory telescopes and also Cauchoix. Instruments Examples: 1831 Troughton transit with a 5-inch Tulley objective 1839 Ertel 3-foot meridian circle with 7 inches aperture 1842 Ertel 3 inch aperture comet seeker 3 foot Dollond refractor. (length not aperture in this case) 13-inch Cauchoix objective on Grubb mount. See also Markree Castle Craig telescope (refractor of the 1850s) Leviathan of Parsonstown (Big Irish metal-mirror (1.8 m) reflector after 1845) 40-foot telescope (Herschel's) List of astronomical observatories List of largest optical telescopes in the 19th century References Buildings and structures in County Sligo Astronomical observatories in the Republic of Ireland Defunct astronomical observatories Collooney