The late Earl of Rosse, with a devotion to science which has few parallels, constructed this gigantic telescope, at his seat, Parsonstown, in the south of Ireland. To the frame of the vast instrument is fixed a large cubical wooden box, about eight feet wide; in this there is a door, through which two men go in to remove, or to replace, the cover of the mirror. To this box is fastened the tube, which is made of deal staves, and hooped like a huge cask. It is about 40 feet long, and 8 feet diameter in the middle. The Dean of Ely once walked through the tube with an umbrella up! The stupendous speculum weighs three tons; the casting and polishing of it were labours of wonderful skill. The telescope is not turned to any part of the sky, but limited to the range of half an hour on each side of the meridian, through which its motion is given by powerful clockwork, independent of the observer. For this purpose it stands between two pieces of masonry, of gothic design, which harmonize with Lord Rosse's castle; one of these piers sustaining the galleries for the observer, and the second the clockwork and other apparatus. There is an elegant arrangement of counterpoises to balance the enormous mass, so that a comparatively slight force only is required to elevate or depress it. A correspondent of the Mechanics' Magazine thus describes the capacity of this wonderful instrument:—

"Such is its power, that if a star of the first magnitude were removed to such a distance, that its light would be three millions of years in reaching us, this telescope would, nevertheless, show it to the human eye. Is it to be wondered at, then, that, with such an instrument, grand discoveries should be made? It has been pointed to the heavens; and, although in the beginning of its career, it has already accomplished mighty things. There are nebulous spots in the heavens which have baffled all the instruments hitherto constructed, but this telescope resolves their true character completely. Among the wonderful objects which have been subject to its scrutiny, is the nebula in the constellation of Orion. I have had an opportunity of examining it. It is one of the most curious objects in the whole heavens. It is not round, and it throws off furious lights. From the time of Herschel it has been subjected to the examination of the most powerful instruments—but it grew more and more mysterious and diverse in its character. When Lord Rosse's great telescope was directed to its examination, it for a long time resisted its power. He found it required patient examination—night after night, and month after month. At length, a pure atmosphere gave him the resolution of its constitution; and the stars of which it is composed burst upon the sight of man for the first time!"