Herschel found by micrometric) measures that the apparent diameter of the new planet, when viewed at its mean distance from the earth, amounted to 3'91. This gave 34,217 miles for the value of its absolute diameter. It was, therefore, after Jupiter and Saturn, by far the most considerable of the planetary bodies hitherto recognised as revolving around the sun.
It appeared from an examination of the recorded observations of Flamsteed and several succeeding astronomers, that Uranus had been observed on several occasions, previous to its actual discovery as a planet in 1781, under the impression of its being a fixed star. These early positions proved exceedingly valuable in enabling astronomers speedily to determine the elements of the orbit with a degree of pre cision which, from the slow motion of the planet, could otherwise have been expected to result only after the lapse of a considerable number of years. In 1790 Delambre obtained the prize of the Academy of Sciences of Paris for the construction of tables of the planet. These tables were founded on the observations made subsequently to the discovery of the planet in 1781, and on certain earlier determinations of its position. For several years they sufficed to represent the observed motion of the planet with tolerable precision, but eventually discordances becamo apparent, which continued to increase in magni tude from year to year. In 1821 Bouvard published new tables of the planet. They were based exclusively on the observations made after
the discovery of the planet by Herschel, their author having found it impossible to satisfy by means of the same orbit both the earlier and the more modern observations. These tables continued for a few years to represent the motion of the planet with all desirable precision ; but they, iu their turn, soon began to deviate from the results of observa tion, and the discordances continued steadily to increase in magnitude. The reader is aware that the study of these irregularities led to the discovery of a new planet beyond Uranus. In a preceding article [NEPTUNE) a detailed account has been given of the circumstances connected with this memorable triumph of science.
There exists some uncertainty with respect to the mass of the planet. The foregoing value was deduced by Bouvard from the observed perturbations of Saturn. Lamont, from the observed elon. gallons of the satellites, has determined the value of the mass to be tables of Uranus have been published subsequently to the 2 discovery of Neptune in 1846. A correct theory of the planet, with tables founded thereon, is still a desideratum in astronomy. It is to be presumed that M. be Ferrier, who is at present engaged in a syste matic investigation of the theory of the various bodies of the planetary system, will iu duo time aocomplish this important object.