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LIST OF PLATES.

Plate I. Frontispiece.

Fig. 1. Faculæ of the Sun.
Fig. 2. Spots on ditto.
Fig. 3. Appearance of ditto in a total Eclipse, showing the

red flames.
Fig. 4. 5. Spots as seen by Mr. Dawes.
Plate II. Fig. 1. Messier's 13th Nebula resolved into Stars.

Fig. 2. The Comet of 1819.

Fig. 3. The Nebula in Andromeda. Plate III. Fig. 1. Mars as seen August 16th, 1830.

Fig. 2. Jupiter as seen September 23rd, 1832.

Fig. 3. Saturn, showing the interior rings and belts. PLATE IV. Fig. 1. The great Nebula in Orion.

Fig. 2. The great Nebula in Argo. PLATE V. Fig. 1. Nebula (30 Doradûs) in the Nubecula Major. Fig. 2. Lunar Volcano, as shown by a 20 feet reflecting Te

lescope, aperture 18 inches. PLATE VI. Fig. 1. Various Appearances of Halley's Comet at its last

Apparition.
Fig. 2. Double Comet of Biela, as seen on its last return.
Fig. 3. Messier's 51st Nebula as shown by Lord Rosse's

great Reflector. PLATE A. Figures illustrative of the Perturbations of Uranus by Nep

tune.

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distance, and real diameter. First approximation to its orbit. An

ellipse about the Earth in the focus. Its excentricity and inclination.

Motion of its nodes and apsides. Of occultations and solar eclipses

generally. Limits within which they are possible. They prove the

Moon to be an opaque solid. Its light derived from the Sun. Its

phases. Synodic revolution or lunar month. Harvest Moon. Of
to their primaries, and consequent subordination of their motions.

Masses of the primaries concluded from the periods of their satellites.

Maintenance of Kepler's laws in the secondary systems. Of Jupiter's

satellites. Their eclipses, etc. Velocity of light discovered by their

means. Satellites of Saturn-of Uranus- of Neptune - 354

CHAPTER XI.

OF COMETS.

Great number of recorded comets. The number of those uprecorded

probably much greater. General description of a comet. Comets with-

out tails, or with more than one. Their extreme tenuity. Their

probable structure. Motions conformable to the law of gravity.

Actual dimensions of comets. Periodical return of several. Halley's

comet. Other ancient comets probably periodic. Encke's comet-

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