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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. SATELLLITES OF SATURN.
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%2811 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.
5. SATELLITES OF NEPTUNE. One only bas been certainly observed, -its approximate period being 54 205 50m 45', - distance about 12 radii of the planet
IV. ELEMENTS OF PERIODICAL COMETS AT THEIR LAST APPEARANCE.
T is the time of perihelion passage ; w the longitude of the perihelion; and that of the ascending node for the epoch of the perihelion ; i, the inclination to the ecliptic; a, the semi-axis ; €, the excentricity; P, the period in days.
N. B. The reader will find a complete list of elements of all known comets up to June, 1847, by all their several computors, in Prof. Encke's edition of Olbers's “ Abhandlung über die leichteste und bequemste Methode die Bahn eines Cometen zu berechnen.” The list is compiled by Dr. Galle. It contains orbits of 178 distinct comets. From an examination of these orbits we collect the following, as a more correct statement of cometary statistics than that in art. 601. viz. :— Retrograde comets under 10° inclination, 3 out of 15; under 20°, 9 out of 29. Retrograde comets, inoving in orbits sensibly elliptic, under 17° inclination, 0 out of 9. In such orbits, of all inclinations from 0 to 90°, 11 out of 37. Thus we see that the induction of that article is materially strengthened by the enlarged field of comparison.
N.B. The references are to the articles, not to the pages.
several subsequent in succession.
692. Of planetary orbits, 694. Li-
bration of, 694. Motion in orbits
Its uranographical effects, 333. Of tric orbits, 697...
stars, 820..., on sun's proper mo-
in constellation, 830.
Ascension, right, 108. (See Right ascen-
136. Of particular instruments. (See Asteroids, their existence suspected pre-
vious to their discovery, 505. Ap-
on surface of, 525. Elements, Appen-
sity, 37. Refractive power affected Astræa, discovery of, 505.
Astrometer, 783, 784.
figure of the earth, 220. Researches notions, 11.
Strata, 37. Causes refraction, 38.
Twilight, 44. Total mass of, 148.
Attraction of a sphere, 445–450. (See
Augustus, his reformation of mistakes
Australia, excessive summer tempera-
ture of, 369.
Axis of the earth, 82. Rotation per-
343. Of refraction, 343. Solar, 854. orbit, 373. Of sun's rotation, 392.
Axis of a planetary orbit. Momentary
variation of, caused by the tangential
periodical, 661... Invariability of,
675. Application to lunar, 676... | Azimuth, 103.- and altitude instru.
treme tenuity of, 558. General de.
scription of, 560. Motions of, and
described, 561... Parabolic, 564.
Elliptic, 567... Hyperbolic, 564. Di-
mensions of, 565. Of Halley, 567...
Of Cæsar, 573. Of Encke, 576. Of
Biela, 579. Of Faye, 584. Of
Lexell, 585. Of De Vico, 586. Of
Brorsen, 587. Of Peters, 588. Sy-
nopsis of elements (Appendix). In-
crease of visible dimensions in re-
ceding from the sun, 571.580. Great,
of 1843, 589... Its supposed identity
with many others, 594... Interest at-
tached to subject, 597. Cometary
statistics, and conclusions therefrom,
Commensurability (near) of mean mo-
tions; of Saturn's satellites, 550. Of
Of Jupiter and Saturn, 720. Earth
Compensation of disturbances, how ef-
Compression of terrestrial spheroid, 221.
Of gravity, 360. Revolution about, Conjunctions, superior and inferior, 473.
Perturbations chiefly produced at, 713.
produced by, 224. Illustrated, 225. exerted, 439.
Rising and setting of, 58.
Copernican explanation of diurnal mo-
tion, 76. Of apparent motions of
of, 291... Bremiker's, 506, and note. Correction of astronomical observations,
view of, 342...
cal, 100. Hour, 106. Divided, 163. and disturbed planets, 719. Meto-
Lunar, 922. Of indictions, 923.
Ratio of sidereal to solar, 305. 909.
ditto, invariable, 908. Civil and
astronomical, 147. Intercalary, 916.
Days elapsed between principal chro-
nological eras, 926. Rules for reckon-
ing between given dates, 927.
590.' Tails of, 556...566. 599. Ex- | Definitions, 82...