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 NERAC NEREUS have reached. But as the calculations of Ad- ams and Leverrier were based on the pertur- bations produced by Neptune while traversing but a small portion of his orbit, and as his ap- parent position in that portion is nearly the same as that of the hypothetical Neptune, it does not appear that the credit due to Adams and Leverrier can be appreciably diminished. Were it not, indeed, for the lucky chance that a planet's action could explain the observed discrepancies, whether that planet moved in the actual or hypothetical orbit, neither Adams nor Leverrier could have solved the problem without first abandoning their estimate of the mean distance. But it has not been shown that in this case they would not have modified their assumption to correspond with the facts before them. An investigation of the orbits of Neptune and Uranus, with general tables of the planet's motions, has been published by Prof. S. Newcomb in the " Smithsonian Contri- butions to Science " (May, 1865, and October, 1873). In these papers he discusses the ele- ments of the orbit of Neptune, the existence of an extra- Neptunian planet, the theoretical place of the planet between the years 1600 and 2000, and many other questions of great interest, with a profundity and elegance which has elicited the highest commendation. At least one satellite attends on Neptune, discov- ered by Mr. Lassell of Liverpool in 1847. It travels around the planet in a period of 5d. 21h. 8m., at a distance from his centre equal to 12 times his estimated radius, the maxi- mum observed elongation of the satellite from Nepjbune's centre amounting to 18". NERAC (anc. Neracurri), a town of France, in the department of Lot-et-Garonne, on the Baise, 16 m. S. W. of Agen; pop. in 1866, 7,717. The new town is handsome, and larger than the older part, with which it is connected by stone bridges. N6rac contains a large church and several other public buildings, and a statue of Henry IV., who spent a part of his youth here. It has manufactures of various articles, espe- cially corks for wine bottles. It was once the capital of the duchy of Albret, and has in- teresting relics of an old castle where Margaret of Navarre held her court, and where Calvin and other eminent reformers found an asylum. The former royal park now forms the prome- nade of La Garenne. NERBUDDA, a river of Hindostan, which rises about lat. 22 40' N., Ion. 81 50' E., nearly 3,500 ft. above the sea, and after a course of 800 m., generally W., through the Central Provinces, Indore, and Bombay, falls into the gulf of Cambay about lat. 21 40' N., Ion. 73 E. During the rains it rises in some places TO ft. and in others 20 above its level in the dry season. The Nerbudda has no tributaries worthy of notice. There are extensive forests on its banks. It flows rapidly, and in Malwa its channel is worn to a great depth through columnar basalt. The upper part of its course is obstructed by numerous rapids and falls. Near the foot of the Vindhya hills the Holkar State railway crosses the Nerbudda by means of an iron bridge 2,755 ft. long, resting on 13 brick piers. NEREIDS, in mythology. See NERETJB. NEREIDS, the name of the sea centipedes of the dorsibranchiate order of annelids, of which the genus nereis (Cuv.) is one of the best known forms. The class and ordinal characters are given under ANNELIDA. In the true nereids the tentacles are of even number; there is a single pair of maxillae in the proboscis; the branchiae are small plates in which a network of blood vessels is disposed ; each of the nu- merous feet has two tubercles, two bundles of bristles, and an under and an upper cirrus; the body is like that of a centipede, with many joints. They are active, crawling and swim- ming with facility; some live in crevices in rocks near the shore, in sponges, corals, desert- ed shells under stones, or wherever they can find a shelter ; others burrow in mud or sand, occasionally making tubes or sheaths, from which they protrude the anterior part of the body, and into which they retreat quickly when alarmed; some of the tropical species Common Sea Mouse (Aphrodita aculeata). are very large, and vividly phosphorescent at night. Their food consists of living and dead animal substances, such as marine worms and soft-bodied invertebrates. The species are nu-. merous, and are found on almost all coasts. The sea mice (aphrodita, Linn.) belong to the same order ; the body is broad and flat, with two longitudinal rows of wide membranous scales covering the back and concealing the branchiaa. The common sea mouse (A. acu- leata, Linn.) is 6 or 7 in. long and 2 broad, the back covered with a flax-like substance in which are mixed spines and softer bristles, the latter shining with all the tints of the rainbow, and rivalling in beauty the lustre of the hum- ming bird or the sparkling of the most bril- liant gems. NEREIS, a marine divinity in Greek and Ro- man mythology, son of Pontus amd Gaea (or, in the Roman myth, of Oceanus and Terra), and husband of Doris, who bore him 50 daugh- ters, the Nereids. Nereus was represented as a benevolent, wise, and gentle old man, one of the most unerring prophets among the minor divinities. He dwelt at the bottom of the sea (according to most authors, of the ^Egean sea,