URANUS, the next planet beyond Saturn, counting outwards from the sun. This important member of the planetary system was dis covered by Sir William Herschel in the year 1781. On the evening of the 13th of March of that year, while examining certain small stare in the constellation Gemini, the attention of the astronomer was drawn to a small star which appeared sensibly larger than those in its vicinity. With the view of testing the object he applied different magnifying powers to his telescope, whereupon he found that the apparent magni tude tude of the star in question varied in the direct ratio of the power, while the stars around it when similarly surveyed him exhibited only a slightly perceptible change of apparent diameter. Suspecting from this circumstance that the object was a comet, he proceeded to make careful observations of its position by measuring its distance from the stars near to it. A few nights only elapsed before he obtained undoubted evidence of the star being in a state of motion. It appeared to be travelling slowly in the order of the signs, in an orbit inclined at a small angle to the plane of the ecliptic. Having con tinued his observations down to the 19th of April, he then drew up an account of them, and communicated it to the Royal Society in a paper which was read before that body on the 26th of the same month. He appears to have been under the impression that the object discovered by him was no other than a comet.
Attempts were made by various astronomers on the Continent to determine the orbit of the supposed comet, on the hypothesis of its revolving in a parabola with a comparatively small perihelion distance ; but it was found impossible to represent the observed motion of the body in this manner, except for a very small arc of the orbit. At length Lexeil, in a paper which he communicated to the Academy of Sciences of St. Petersburg, announced certain facts, which seemed to indicate that the object discovered by Herschel was in reality a planet. In the first place, it differed from a comet in being well defined. On the other
hand, it did not exhibit the bright piercing light of the fixed stars. But while thus unlike a comet or a star, it exhibited several features which tended to support the idea of its being a planet. It was to be remarked that, like all the planets, it travelled in the celestial sphere in the order of the signs. Again, while it was actually situate near the ecliptic, its motion in latitude was exceedingly small, a circumstance which seemed to indicate that like the planets it revolved in an orbit, confined within the limits of the zodiac. But Lexell obtained still more convincing evidence in support of his suspicion that the object was a planet. Taking two extreme observations of its position, one of them by llerschel, dated March 17, 1781, and the other by Maskelyue, dated May 11, of the same year, he found that they might be well repre sented by supposing the body to revolve in a circular orbit, the radius of which amounted to 18'93, the radius of the earth's orbit being assumed equal to unity. Astronomers henceforward agreed in sup posing that the object discovered by Herschel was in reality a planet revolving around the sun in the region beyond Saturn. It was soon found, however, that a circular orbit was incapable of satisfying the observations, and that tho real orbit must be an ellipse of slight eccentricity. Laplace, in 1783, first determined the elliptic elements of the planet's orbit, which he communicated to the Academy of Sciences in the same year.
The right of naming the new planet belonged to the discoverer, who proposed to call it the Ceorgium Sidus, as a mark of gratitude to his munificent patron George III., under whose auspices he was enabled to prosecute his astronomical labours. This designation, however, was at variance with the nomenclature hitherto employed in the planetary system, and the name of Uranus, suggested by the German astronomer, Bode, is that by which it is usually designated.