 His innovations for large telescopes included clock-driven polar mounts, whiffletree mirror mounting cells and Cassegrain reflector optics.Grubb helped build the famous telescope for William Parsons, 3rd Earl of Rosse, at Parsonstown (now known as Birr), County Offaly, Ireland.One of his earliest instruments - the telescope for Markree Observatory in County Sligo in the West of Ireland, supplied in 1834 - was, until 1839, the largest refracting telescope in the world.