NEPTUNE

September (1846); and so well had the determination been made, that the planet was actually discovered by Dr. Galle on the evening of the same day, and within 52 minutes of a degree of the place a igned by the mathematician. An announcement of the discovery was immediately published, and the astronomers of all countries concurred in regarding it as the most remark, able triumph of the theory of gravitation which had ever been achieved. ■ Soon after the existence of the planet had been verified by Dr. Galle, it began to be rumoured that Le Verrier was not the only claimant of the honour of the discovery, but that he had even been anticipated in some of his principal conclusions. Nothing, however, was generally known of the circumstances till the publication of the Monthly Notice of the Royal Astronomical Society of London for November, 1846, which contained a detailed statement of them drawn up by the Astronomer Royal, about the accuracy of which there could consequently not be a question. From this statement it appeared that so early as February, 1844, the Astronomer Royal was requested to furnish Mr. Adams, of St. John's College, Cambridge, with some observations of Uranus from the records of the observatory, as data for investigations in which he was engaged respecting the theory of Uranus; and that in the month of October in the following year (1845) Mr. Adams, having completed his calculations of the perturbations of that planet on the a umption of their being caused by the attraction of an exterior planet, left at the Royal Observatory a paper containing a complete set of elements of the orbit of the hypothetical planet, a value of its ma , and a table of differences of mean longitudes of Uranus as deduced from the theory, and as determined by actual observation. It further appears that the Astronomer Royal having only results before him, and being well aware of the difficulty of the investigation, requested from Mr. Adams some explanations to enable liim to form a better opinion as to the sufficiency of the hypothesis made to explain the observed discrepancies; that, from some unexplained reason, no answer was given to this request; that the matter rested in this state from the end of October, 1845, till the appearance of Le Verrier's second paper in June, 1846, which contained, as above stated, a determination of the longitude of the hypothetical planet; and that on comparing the two results they were found, when reduced to the same epoch, to differ only bv 3° 19'. The parties acquainted with Mr. Adams' results had now far stronger reasons than other astronomers for believing in the existence of the hypothetical planet as well as in the accuracy of its computed place. In so intricate an investigation, founded on data liable to more or le uncertainty, the risks of error were sufficiently numerous to justify hesitation even on the part of those best acquainted with the subject; but when the same result had been arrived at by two different computors independently of each other, the chances of error were almost annihilated. There could then hardly be a doubt as to the accuracy of the conclusion; and if Mr. Adams and his friends'had immediately published the fact, it is not improbable that other observers would have been led to look out for the planet. They did not, however, adopt this course, nor does it appear that they acquainted Le Verrier with the remarkable confirmation of his results, but they resolved to institute a search for the planet themselves with the great equatorial of the Cambridge Observatory. The plan adopted was one which, though it virtually ignored the accuracy of the calculations, could scarcely fail of being succe ful in time. It consisted, simply, in making a close examination of a part of the heavens 30° long, in the direction of the ecliptic, and 10° broad, having its centre at the place indicated by Le Verrier and Adams, and observing all the stars to the 11th magnitude inclusive, from time to time, so as to detect the planet by its change of place. Observations in pursuance of this plan were actually begun on the 29th of July, 1846, and continued during two months. On the 29th of September, Mr. Challis, the director of the observatory, read Le Verrier's paper of August 31, in which the po ibility of detecting the planet by its disc was suggested. Concurring in this idea Mr. Challis at once abandoned the plan he had been following, and on the evening of the same day began to observe within the limits indicated by Le Verrier. The planet, however, though observed as a star, was not recognised; on the next night observations could not be made, and on the following day information was received of Dr. Galle's discovery on the 23d of September. It is to be remarked that Dr. Galle had an advantage over Mr. Challis in the po e ion of a star-map, then recently published at Berlin, of the part of the heavens to which his search was directed. A star appeared in the field of the telescope which was not laid down in the map, and his attention was consequently directed to it till its true nature became evident by its proper motion. 1388 OLANIN. A circumstance deserving of notice Is, that notwithstanding the near coincidence of the predicted place with that at which the planet was actually found, the; elements of the hypothetical orbits determined both by LeVerrierand Adams were very wide of the truth. Thei mean distance they gave was rather more than 36 times i the mean distance of the earth from the sun (Le Verrier! 36-ir)39, Adams 37'2474), and the period of revolution i about 220 years. It is now known, however, that the periodic time is le than 165 years, and the mean distance only about 30 times that of the earth from the sun, the error in this respect being greater than the radius of Jupiter's orbit. It seemed difficult at first to conceive how elements so faulty should give so close an approximation to the true place of the planet, but the reason has been satisfactorily explained. NERVE. See Nervous System, in Dict. NEURAL ARCH. {Gt. nv^ov, a nerve.) In Anatomy, the arch of the vertebra or primary segment of the skeleton which protects a corresponding segment of the neural axis: it is posterior in Man, superior in other Vertebrates, and is formed by the "centrum," " neurapophyses," and " neural spine." l NEURAL AXIS. (Gr. veu^m, a nerve.) In Ana^ to my, the central trunk of the nervous system, con^ sisting of brain and myelon: it is sometimes called! "cerebro-spinal axis." NEURAPOPHY'SIS. (Gr. 'vcyjai/, and k^ixpvffi;, a proce .) In Anatomy, the autogenous vertebral element which forms the side or wall of the arch protecting the neural axis or central trunk of the nervous i system: it has been called the " vertebral lamina," and by So emmer ring the " radix arcus posterior is vertebrre." NINIVEH MARBLES. The name given to the collection of A yrian Antiquities, recently procured by the researches of Mr. Layanl at Niniveh, and deposited in the British Museum. NODAL POINTS. NODAL LINES. Under the term Vibration (Dict. of Scienck) it is stated that avi^ brating chord may spontaneously divide itself into any number of aliquot parts, each of which will vibrate separately as if it were fixed at its two extremities and formed a separate chord. The points of separation between two such contiguous parts, which participate neither in the vibration of the one nor the other, but remain at rest, are called Nodal Points. And in like manner, when elastic plates are put into a state of vibration, the molecules separate themselves into parcels which vibrate independently of each other, and the lines of separation thus formed, or lines of repose in which no vibration takes place, are called Nodal Lines. See Vibration. NO'NTRONITE. A nodular silicate of iron from Nontron, in France. NOPAL. The cactus upon which the cochineal insects breed. NORDHAU'SEN ACID. A peculiar sulphuric acid, intermediate between the anhydrous, and monohydrated acid, or oil of vitriol, so called from the place of its manufacture. NU'SSIERITE. In Mineralogy, a species of phosphate of lead from Nu itres, near Beaujeu. O. A contraction for Octarium, a pint. O'CTROIS. (A corruption of Lat. auctoritas.) The name given in France to the taxes levied on objects of consumption at the gates of many towns and cities, and applied partly to the general uses of the state, and partly to local purposes. There are nearly 1500 communes subjected to this tax, which amounts in some years to nearly 100,000,000of francs. The revenue of Paris from this source alone is upwards of 30,000,00(^ of francs. CENANTHIC ETHER. {Gr. vtvos, wine; ttyOo;, a flower.) A peculiar compound, upon which the fraJ grancy and persistent odour of certain wines depends. CENANTHY'LIC ACID. (See above.) An acid of a peculiar aromatic odour, obtained by the action o^ nitric acid on castor oil. OE'RSTEDITE. In Mineralogy (in honour of OerJ sted), a silico-titaniate of zirconia, from Arendal.inj Sweden. | (ESOPHAGI'TIS. (Gr.) Inflammation of the cesophagus. GE SOPH A GO' TO MY. (Gr. ei(ro(^yet, the gullet, and Tif^vo), I cut.) The operation of cutting into th€ oesophagus, or gullet, for the purpose of removing some foreign substance. O'KENITE. In Mineralogy (in honour of Oken), e hydratwl silicate of lime. O'LANIN. (Gr. eAf»y, OfV.) One of the ingredients Page 1406