was completed in 1774: but altogether he accomplished the construction of upward of five hundred specula of various sizes, selecting the best of them for his telescopes. After having established his fame by the discovery of a new planet, and fixed his residence at Slough, under the munificent patronage of George the Third, he completed the giant instrument that attracted travelers from all parts to the spot, and rendered it one of the most remarkable sites of the civilized world. The tube was forty feet long, the speculum four feet in diameter, three inches and a half thick in every part, and weighing nearly two tons. Its space-penetrating power was estimated at 192, that is, it could search into the depths of the firmament 192 times farther than the naked eye. We can form no adequate conception of this extent, but only feebly approximate to it. Sirius, a star of the first magnitude, is separated by an immeasurable distance from us. But stars of a far inferior order of magnitude are visible to the naked eye. These we may conclude to be bodies far more remote, and reasonably suppose the star which presents the faintest pencil of light to the eye to be at least twice or thrice the distance of Sirius. Yet onward, 192 times farther, the space-penetrating power of the telescope at Slough swept the heavens. It was completed in the year 1789, but the frame of the instrument becoming decayed, through exposure to the weather, it was taken down by Sir John Herschel in 1823. It will be convenient here to notice a reflecting telescope of far greater magnitude and power, recently constructed by the Earl of Rosse, and now in use at the seat of that nobleman, Birr Castle, in Ireland. The mechanical difficulties involved in this work, the patience, perseverance, and talent required to overcome them—and the great expenditure necessarily incurred—render the successful completion of this instrument one of the most extraordinary accomplishments of modern times; and entitle its owner and projector, from first to last, to the admiration of his countrymen. When the mechanical skill and profound mathematical knowledge essential to produce such a work are duly considered, together with the years devoted to previous experimenting, and an outlay of upward of twelve thousand pounds, this telescope must be regarded as one of the most remarkable and splendid offerings ever laid upon the altar of science. The speculum has a diameter of six feet, and therefore an area of reflecting surface nearly four times greater than that of the Herschelian, and its weight approaches to four tons. The casting—a work of no ordinary interest and difficulty—took place on the 13th of April, 1842, at nine in the evening; and as the crucibles poured forth their glowing contents—a burning mass of fluid matter, hissing, heaving and pitching—for the moment almost every one was anxious and fearful of accident or failure but Lord Rosse, who was