This magnificent instrument stood on the lawn in the rear of Sir William Herschel’s house at Slough; and some of our readers, like ourselves, may remember its extraordinary aspect when seen from the Bath coach-road, and the road to Windsor. The difficulty of managing so large an instrument--requiring as it did two assistants in addition to the observer himself and the person employed to note the time--prevented its being much used. Sir John Herschel, in a letter to Mr. Weld, states the entire cost of its construction, 4000_l._, was defrayed by George III. In 1839, the woodwork of the telescope being decayed, Sir John Herschel had it cleared away; and piers were erected, on which the tube was placed, _that_ being of iron, and so well preserved that, although not more than one-twentieth of an inch thick, when in the horizontal position it contained within all Sir John’s family; and next the two reflectors, the polishing apparatus, and portions of the machinery, to the amount of a great many tons. Sir John attributes this great strength and resistance to the internal structure of the tube, very similar to that patented under the name of corrugated iron-roping. Sir John Herschel also thinks that system of triangular arrangement of the woodwork was upon the principle to which “diagonal bracing” owes its strength. THE EARL OF ROSSE’S GREAT REFLECTING TELESCOPE. Sir David Brewster has remarked, that “the long interval of half a century seems to be the period of hybernation during which the telescopic mind rests from its labours in order to acquire strength for some great achievement. Fifty years elapsed between the dwarf telescope of Newton and the large instruments of Hadley; other fifty years rolled on before Sir William Herschel constructed his magnificent telescope; and fifty years more passed away before the Earl of Rosse produced that colossal instrument which has already achieved such brilliant discoveries.”[25] In the improvement of the Reflecting Telescope, the first object has always been to increase the magnifying power and light by the construction of as large a mirror as possible; and to this point Lord Rosse’s attention was directed as early as 1828, the field of operation being at his lordship’s seat, Birr Castle at Parsonstown, about fifty miles west of Dublin. For this high branch of scientific inquiry Lord Rosse was well fitted by a rare combination of “talent to devise, patience to bear disappointment, perseverance, profound mathematical knowledge, mechanical skill, and uninterrupted leisure from other pursuits;”[26] all these, however, would not have been sufficient, had not a great command of money been added; the gigantic telescope we are about to describe having cost certainly not less than twelve thousand pounds.