Observations upon Uranus had shown the motions of that planet to present great irregularities, which could not be explained by the action of Jupiter and Saturn; and after carefully examining the analytical theory of Uranus, Leverrier, a young academi: cilia of France, in the summer of 1846, published the elements of an undiscovered planet, the cause of the perturbations. lie boldly predicted its existence, calculated its mass, and referred to its place iu the heavens; nod, scarcely a month afterwards, on the 23d of Sept., the hitherto concealed object (Neptune) was found by M. Galle of Berlin. But it has only been by accidental circumstances that France has the honor of this remark able achievement. Mr. Adams of Cambridge had arrived at results more perfect than those of Leverrier, and had communicated them to Mr. Challis, professor of A. at Cam bridge in Sept., 1845, a year before the discovery of the planet, and nearly a year before the publication of Levcrrier's final calculations. Mr. Challis, it appears, commenced a search for the planet on July 29th, and on Aug. 4th and 12th, he actually seized the planet, and recorded two positions of it, but did not recognize it, through not comparing his observations, which a pressure of occupation, and an impression that the discovery required a much more extensive search, prevented. But for this, and the non-publication
of the Cambridge mathematician's results at the time they were forwarded to Sir George Airy in Oct., 1845, the honorable position of 31. Leverrier would have been occupied by Mr. Adams, and that of 31. Galle by Mr. Challis.
The century, however, has been chiefly remarkable for its laborious efforts to correct, systematize, and extend the results of former discoveries. Admirable and extensive catalogues of stars and double stars, and of nebula?, have been made; and optical and other instruments have been brought to what appears almost a state of perfection, lord Rosse's reflecting telescope, with a speculum 6 ft. in diameter, being the triumph of modern mechanical and mathematical skill. In more recent years, research has been directed chiefly towards the physical nature of the sun and other heavenly bodies by means of spectrum-analysis. See SPECTRUM; SUN. •