Page:Popular Science Monthly Volume 6.djvu/553

Rh Herschel died at Hanover, her native city, in 1849, at the age of ninety-eight. Sir John Herschel, the only son of the great astronomer, worthily continued these illustrious traditions. He resumed and completed the exploration of the heavens commenced by his father, at first at Slough, then at the Cape of Good Hope, where he transported a telescope of twenty feet. He died in 1871, after having contributed, by labors of the highest order, to the progress of science. One of his sons, Alexander Herschel, is equally devoted to astronomical pursuits.

The gigantic telescope of Lord Rosse, which was finished in 1845, the same year when the noble lord was elected representative peer of Ireland, is fifty-five feet in length, and has six feet of aperture. The mirror weighs over four tons, the tube seven tons, and the total weight exceeds eleven tons. The Leviathan, as this giant telescope is called, is suspended between two stone walls at Birr Castle, the hereditary residence of Lord Rosse, in King's County, Ireland. When, in 1826, the young Lord Oxmantown—the title that he then bore—turned his attention toward practical astronomy, there was no constructor capable of furnishing instruments such as he desired. William Herschel had kept the secret of the alloy he used for his mirrors, and the process by which he constructed them. James Short, the greatest constructor of the eighteenth century, so skillful in casting and polishing mirrors, had burned and destroyed before his death his whole stock of tools, in order to remain without a rival. Every thing was then to be discovered anew, and it took Lord Rosse twenty years before he attained the construction of a mirror by means of which he could sound the depths of space and resolve into a mass of stars the most of the nebulae toward which he directed his gigantic instrument. All the nebulæ, however, are not resolvable; some of them are decidedly agglomerations of cosmical matter not yet condensed. Lord Rosse was the first to demonstrate that the great nebula of Orion, one of the finest in the heavens that belongs to the last category, has within a few years changed its appearance in consequence of the concentration of the matter of which it is formed. This celebrated observer died in 1867; his son worthily continues the labors commenced by the father with such brilliant success.

Lord Rosse preferred mirrors to objectives, on account of the difficulty that attends the manufacture of objectives of large dimensions. But great improvements have since been made; Mr. Clark, an American, constructed in 1862 a powerful instrument, with an object-glass of eighteen and a half inches of aperture. Messrs. Cooke & Son, celebrated constructors of York, finished in 1868 an equatorial of twenty-five inches of aperture, and twenty-nine feet of focal length. The telescope of this gigantic apparatus is mounted on an iron column 350 feet high, and weighs nearly ten tons. This equatorial was constructed for Mr. Newall, proprietor of the submarine cable-works at Gateshead, near Newcastle; it is destined for the island of Madeira, where it will