PLANETARY SYSTEMS. 91 



iites or secondary planets, and myriads of comets, three of 

 which, known as the "planetary comets," do not pass beyond 

 the narrow limits of the orbits described by the principal 

 planets. We may, with no inconsiderable degree of proba- 

 bility, include within the domain of our Sun, in the immedi- 

 ate sphere of its central force, a rotating ring of vaporous mat- 

 ter, lying probably between the orbits of Venus and Mars, but 

 certainly beyond that of the Earth,=^ which appears to us in 



formal incompatibility between the observed motions of Uranus and 

 the hypothesis that he was acted on ojily by the Sun and known plan- 

 ets, according to the law of universal gravitation." Pursuing this idea, 

 Leverrier arrived at the conclusion that the disturbing cause must be a 

 planet, and, finally, after an amount of labor that seems perfectly over- 

 whelming, he, on the 31st of August, 1846, laid before the French In- 

 stitute a paper, in w^hich he indicated the exact spot in the heavens 

 where this new planetaiy body would be found, giving the following 

 data for its various elements : mean distance from the Sun, 36-154 times 

 that of the Earth; period of revolution, 217'387 years; mean long., 

 Jan. 1st, 1847, 318^ 47'; mass, ^ 3V0 ^h 5 heliocentric long., Jan. 1st, 

 1847, 326° 32'. Essential difficulties still intervened, however, and as 

 the remoteness of the planet rendered it improbable that its disk would 

 be discernible by any telescopic instrument, no other means remained 

 for detecting the suspected body but its planetary motion, which could 

 only be ascertained by mapping, after every observation, the quarter 

 of the heavens scanned, and by a comparison of the various maps. 

 Fortunately for the verification of Leverrier's predictions, Dr. Bremiker 

 had just completed a map of the precise region in which it was expect- 

 ed the new planet would appear, this being one of a series of maps 

 made for the Academy of Berlin, of the small stars along the entire zo- 

 diac. By means of this valuable assistance, Dr. Galle, of the Berlin 

 Observatory, was led, on the 25th of September, 184G, by the discov- 

 ery of a star of the eighth magnitude, not recorded in Dr. Bremiker's 

 map, to make the first observation of the planet predicted by Leverrier. 

 By a singular coincidence, Mr. Adams, of Cambridge, had predicted 

 the appearance of the planet simultaneously with M. Leverrier; but 

 by the concurrence of several circumstances much to be regretted, the 

 world at large were not made acquainted with Mr. Adams's valuable 

 discovery until subsequently to the period at which Leverrier published 

 his observations. As the data of Leverrier and Adams stand at present, 

 there is a discrepancy between the predicted and the true distance, and 

 in some other elements of the planet ; it remains, therefore, for these 

 or future astronomers to reconcile theory with fact, or perhaps, as in 

 the case of Uranus, to make the new planet the means of lea-ding to yet 

 greater discoveries. It would appear from the most recent observations, 

 that the mass of Neptune, instead of being, as at first stated, ^ jq o^h, is 

 only about _^__th that of the Sun, while its periodic time is now given 

 w^ith a greater probability at 166 years, and its mean distance from the 

 Sun nearly 30. The planet appears to have a ring, but as yet no ac- 

 curate observations have been inade regarding its system of satellites. 

 See Trans. Astron. Soc, and The Planai Neptune, 1848, by J . P. Nicholl. 1 

 — Tr. 



* " If there should be molecules in the zones diffused by the atmo» 



