DISCOVERY. The discovery of Neptune was an event unique in scientific history. It was the disturbance in the of Uranus, caused by the attractive force of Neptune, which led to its discovery. From 1690 to its discovery as a planet by Herschel, Uranus (q.v.) had been re peatedly- recorded as a fixed star. Earlier obser vations were found not to agree with later observations, and hence it became evident that either the earlier observations were erroneous or that Uranus was wandering from its ancient track. On October 21, 1845, John Couch Adams (q.v.) communicated to the loyal Astronomer estimates of the elements and position in the heavens of a planet. whose mass would account for the orbital irregularities of 'Uranus. This did not, however, lead to any search for the planet in the heavens, and the matter remained buried in obscurity. In the same year the attention of Jean Joseph Leverrier a teacher of astronomy in the Ecole Poly technique, was brought to the Cranian diffi culty. In two papers communicated to the French Academy, Leverrier proved that only an exterior body could produce the irregularities in the Uranian orbit. In a third paper. sub mitted August 31. 1846. he had computed the orbit of the supposed planet. the visibility of which he described as that of a star of the eighth magnitude. These results were communicated to Gallo of the Berlin Observatory. with a request to look for the planet in the place assigned to it. This Galle did in the evening of September 23d, and perceived a small body with a disk nearly 3" in diameter. The place where it was found was
within less than of the spot indicated. Be fore the news of the discovery reached England. it had already been duplicated. Under the di reet ion of Airy, director of the Grcenw•ieh Ob servatory, Challis of the Cambridge Observatory had commenced a se:n•ch for the planet July 29th. and recorded 3150 stars, three of whieh were different positions of the planet, recorded an August 4th, August 12th. and September 2901. Challis proceeded to map them. but as he had no good star map this required considerable time, and before this was aeeomplishod, news of discovery arrived from Berlin on October 1, 1846. Neptune lord already been seen by Lalande on the Sth and again on the 10th of May. 1795. but was taken to be a fixed star and repeatedly en tered in the catalogues as such till its discovery as a planet.
Neptune is attended by one satellite. which was discovered October 10. 1846, by Lassen. This satellite, like those of Uranus. differs from the satellites of other planets in the direction of its motion. which is front east to we::,t, in a plane inclined at an angle of 35 to that of the ecliptic. its period of revolution is 5 days 21 hours, and its distance trot the planet somewhat less than that of our 11104411 from the earth. For a c•ontplete avvolllit of the discovery of Neptune, consult Clerke. Ili-story .l.stronolny During the N nth century (London, 1890). :See