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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 reference! are to the articles, not to the pages.
... attached to a reference number indicates that the reference extends to the article cited, and
Abberatios of light explained, 329.
About We/a, 705.
Acceleration, secular, of moon's mean
Adams, 506. 767.
Adjustment, errors of, in instruments,
JEtna, portion of earth visible from, 32.
Air, rarefaction of, 33. Law of den-
Airy, G. B. Esq., his results respecting
Altitude and azimuth instrument, 187.
Andromeda, nebula in, 874.
Angle of position, 204. Of situation, 311.
Angles, measurement of, 163. 167.
Angular velocity, law of, variation of,
Anomalistic year, 384.
Anomaly of a planet, 499.
Annular nebulae, 875.
Apex of aberration, 343. Of parallax,
Apogee of moon, 406. Period of its
Apsides, 406. Motion of investigated,
692. Of planetary orbits, 694. Li-
Areas, Kepler's law of, 490.
Argelandcr, his researches on variable
Argo, nebulas in, 887. Irregular star Tj
Ascension, right, 108. (Sec Right ascen-
Asteroids, their existence suspected pre-
Astraa, discovery of, 505.
Astromeler, 783, 784.
Astronomy. Etymology, 11. General
Atmosphere, constitution of, 33... Pos-
Attraction of a sphere, 445—450. (See
Augmentation of moon's apparent dia-
Augustus, his reformation of mistakes
Australia, excessive summer tempera-
Axis of the earth, 82. Rotation per-
Axis of a planetary orbit. Momentary
Azimuth, 103.—and altitude instru-
Barometer, nature of its indication, 33.
Use in calculating refraction, 43. In
determining heights, 287.
of the earth, 220. Discovers parallax
of 61 Cygni,812.
distances, 505. Violated in the case
of Neptune, 507.
influence on Uranus, 760.
Casar, his reform of the Roman calen-
Calendar, Julian, 917. Gregorian'
Cause and effect, 439. and note.
Center of the earth, 80. Of the sun, 462.
Centrifugal force. Elliptic form of earth
Ceres, discovery of, 505.
Challis, Prof., 506, note.
Charts, celestial, 111. Construction
Chinese records of comets, 574. Of
Chronometers, how used for determining
Circle, arctic and antarctic, 94. Verti-
Clock, 151. Error and rate of, how
Clouds, greatest height of, 34. Magel-
Clusters of stars, 864... Globular, 867.
Collimation, line of, 155.
Coloured stars, 851...
Comets, 554. Seen in day-time, 555.
treme tenuity of, 558. General de-
Commenswability (near) of mean mo-
Compensation of disturbances, how ef-
Compression of terrestrial spheroid, 221.
Configurations, inequalities depending
Conjunctions, superior and inferior, 47J.
Consciousness of effect when force a
Constellations, 60. 301. How brought
Copernican explanation of diurnal mo-
Correction of astronomical observations,
Culminations, 125. Upper and lower,
Cycle, of conjunctions of disturbing
Day, solar, lunar, and sidereal, Itt
Days elapsed between principal chro-
Declination, 105. How obtained, 295.