Note. The elements of the orbits of Mercury, Venus, the Earth, Mars, Jupiter, Saturn, and Uranus, are those given by the late F. Baily, Esq., in his "Astronomical Tables and Formulæ," and are the same with those which form the basis of Delambre's tables, embodying the formulæ of Laplace. The elements of Uranus and Neptune can only be regarded as provisional; those of the former requiring considerable corrections, necessitated by the discovery of Neptune, but which, not being yet finally ascertained, by reason of the uncertainty still attending on the mass and elements of the latter planet, it was thought better to leave the old elements untouched than to give an imperfect rectification of them. The masses of the planets are those most recently adopted by Encke (Ast. Nachr. No. 443), on mature consideration of all the authorities, that of Neptune excepted, which is Prof. Pierce's determination from Bond's and Lassell's observation of the satellite discovered by the latter. The densities are Hansen's (A. N. 443.)

The elements of Vesta, Juno, Ceres, and Pallas, are the osculating elements for 1850, computed by Encke (A. N. 636.) [Those of Flora are from the computations of Brunnow (A. N. 645); of Victoria, Villarceaux (A. N. 741); of Iris, Schubers (A. N. 730); of Metis, Wolfers (A. N. 764); of Hebe, Luther (A. N. 721); of Parthenope, Galen (A. N. 757); of Astræa, D'Arrest (A. N. 626); of Egeria, D'Arrest (A. N. 749); of Irene, Vogel and Rümker (A. N. 765); and of Hygeia, Santini (A. N. 702.)

Of these last-mentioned small planets, Hygeia, Parthenope, and Egeria were discovered by Dr. Gasparis, at Naples, on April 12, 1849, May 11 and Nov. 2, 1850, respectively; Iris, Flora, Victoria, and Irene, by Mr. Hind, on Aug. 13 and Oct. 18, 1847, Sept. 13, 1850, and May 19, 1851, respectively. The elements of the recentlydiscovered small planets may undergo material corrections from further observation. Irene has a blue colour and a faint nebulous envelope. The orbits of Astræa and Hygeia approach at one point (their common node) within 0.006 of the radius of the earth's orbit. It will not be long before the planets themselves come within that proximity to each other (A. N. 752.) Victoria and Astræa are subject to variations of brightness, which indicate rotations on their axes, and dark spots (A. N. 760.) D'Arrest (A. N. 752) remarks that a relation subsists between the excentricities of the orbits of the small planets, and the inclinations of the planes in which they lie to the sun's equator, the more excentric orbits being the more inclined. While these sheets pass through the press, another, yet unnamed, is announced by M. de Gasparis.]

III.

SYNOPTIC TABLE OF THE ELEMENTS OF THE ORBITS OF THE SATELLITES, SO FAR AS THEY ARE KNOWN.

1 The distances are expressed in equatorial radii of the primaries. The epoch is Jan. 1, 1801, unless otherwise expressed. The periods, &c. are expressed in mean solar days.

The excentricities of the 1st and 2d Satellites are insensible, those of the 3d and 4th small, but variable, in consequence of their mutual
perturbation.

3. SATELLITES OF SATURN.

0

6

0

1

5

0 5

2

0 24

4

The longitudes are reckoned in the plane of the ring from its descending node with the ecliptic. The first seven satellites move in, or very nearly in, its plane; that of the 8th is inclined to it at an angle about half-way intermediate between the planes of the ring and of the planet's orbit.

The apsides of Titan have a direct motion of 30' 28" per annum in longitude (on the ecliptic).

The discovery of Hyperion is quite recent, having been made on the same night (Sept. 19, 1848), by Mr. Lassell, of Liverpool, and Prof. Bond, of Cambridge, U. S. Its distance and period are as yet hardly more than conjecture. Messrs. Kater, Encke, and Lassell agree in representing the ring of Saturn as subdivided by several narrow dark lines, besides the broad black divisions which ordinary telescopes show.

One only has been certainly observed,—its approximate period being 5a 20h 50m 45′′,—distance about 12 radii of the planet.

Tis the time of perihelion passage; w the longitude of the perihelion; and that of the ascending node for the epoch of the perihelion; , the inclination to the ecliptic; a, the semi-axis; &, the excentricity; P, the period in days.

INDEX.

N. B. The references are to the articles, not to the pages.

... attached to a reference number indicates that the reference extends to the article cited, and
several subsequent in succession.

Acceleration, secular, of moon's mean Argo, nebulæ in, 887. Irregular star ʼn