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Sevent circling moons cheer the slow wanderer on,
were what are now called the ansæ of his ring, the true shape of which was discovered by Huygens, about forty years after Galileo. From the discoveries made by him and other astronomers, it appears that this planet is surrounded by a broad thin ring, the edge of which reflects little or none of the sun's light to us; but the planes of the ring reflect the light in the same manner that the planet itself does; and, if we suppose the diameter of Saturn to be divided into three equal parts, the diameter of the ring is about seven of those parts. The ring is detached from the body of Saturn in such a manner that the distance between the innermost part of the ring and the body is equal to its breadth. Both the outward and inward ring of the rim is projected into an ellipse, more or less oblong, according to the different degrees of obliquity with which it is viewed. Sometimes the eye of the observer is in the plane of the ring, and then it becomes invisible, either because the outward edge is not fitted to reflect the sun's light, or because it is too thin to be seen at such a distance. As the plane of the ring keeps always parallel to itself, it disappears twice in every revolution of the planet: that is, once in about fifteen years, and he sometimes appears quite round for nine months together. At other times, the distance between the body of the planet and the ring is very perceptible, so much so, that a star has been seen through the opening. When Saturn appears round, if our eye be in the plane of the ring, it will seem as a dark line across the niiddle of the planet's disk, and if the eye be elevated about the plane of the ring, a shadowy belt will be visible, which is caused by the shadow of the ring, as well as by the interposition of part of it between the eye and the planet.
The shadow of the ring is broadest when the sun is most elevated, but its obscure parts appear broadest when the eye is most elevated above the plane of it. Wh it seems to be double, the ring next the body of the planet appears brightest; when the ring appears of an elliptical form, the parts about the ends of the largest axis are called ansæ, as has been mentioned. These, a little before and after the disappearing of the ring, are of unequal magnitude ; the largest ansa is longer visible before the planet's round phase, and it appears again sooner than the other. On the 1st of Oct. 1714, the largest ansa was on the east side, and on the 12th on the west side of the disk of the planet, which makes it probable that the ring has a rotation round an axis. Dr. Herschel has shewn that it revolves in its own plane in about 104 hours. The observations of this great philosopher have added greatly to our knowledge of Saturn's ring. According to him there is one single, dark, considerable broad belt or zone, which he has constantly found on the north side of the ring. As this dark belt is sub
Beyond moves Herschel I ; man decrepid grows
ject to no change whatever, it is probably owing to some permanent construction of the surface of the ring, this construction cannot be owing to the shadow of a chain of mountains, since it is visible all round on the ring, for there could be no shade at the ends of the ring. A similar argunient will apply against the opinion of very extended caverns. It is pretty evident that this dark zone is contained between two concentric circles, for all the phenomena correspond with the projection of such a zone. The nature of the ring Dr. Herschel thinks no less solid than that of Saturn itself, and it is observed to cast a strong shadow upon the planet. The light of the ring is also generally brighter than that of the planet; for the ring appears sufficiently bright when the telescope affords scarcely light enough for Saturn. The Doctor concludes, that the edge of the ring is not fat, but spherical, or spheroidical. The dimensions of the ring, or of the two rings, Dr. Herschel has given as follows:
Inner diameter of the smaller ring
146,345 184,393 190,248 204,883 20,000 7,200 2,839
Breadth of the inner ring
The conjectures relative to the nature of this ring have been various; some persons have imagined that the diameter of this planet was once equal to the present diameter of the outward ring, and that it was hollow; the present body being contained within the former surface, in some such a manner as a kernel is contained within its shell. They suppose, that in consequence of some concussion, or other cause, the outer shell fell down to the inner body, and left only the ring at the greater distance from the centre. This conjecture is in some measure corroborated by the consi. deration that both the planet and its ring performed their rotations about the same common axis, and in very nearly the same tine. Dr. Herschel, from the observations he made on the planet, concludes in the following words : “ It does not appear to me that there is sufficient ground for ad. mitting the ring of Saturn to be of a very changeable nature, and I guess that its phenomena will hereafter be so fully explained as to reconcile all observations. In the mean time, we must withhold a final judgment of its construction, till we can have more observations. Its division into Lwo very unequal parts can admit of no doubt."
Those other wonders in the immense profound,
The diameters of Saturn are not equal; they are probably in the proportion of about eleven to ten. This form compared with that of Jupiter, leads one to conclude that Saturn turns rapidly round his shorter axis, and that the ring moves in the plane of his equator. Huygens observed five belts upon this planet nearly parallel to the equator.
+ The orbits of all these satellites, except the fifth, are nearly in the same plane, which makes an angle with the plane of Saturn's vrbit of about 31°, and by reason of their being inclined at such large angles, they cannot pass across their primary, or bebind it, with respect to the earth, except when very near their node; so that eclipses of them happen much less frequently than of the satellites of Jupiter.
Till the time of Dr. Herschel, five satellites only were known, as connected with this planet ; this astronomer, in the years 1787 and 1788, discovered two others. These are nearer to Saturn ihan any of the other five; but to prevent confusion, they were nominated the sixth and seventh satellites. The fifth satellite has been observed to turn once round its axis, exactly in the time in which it revolves round Saturn; and in this respect it resembles our moon. Much more will be said of this planet in the MENTOR STELLARUM.
This planet entirely escaped the attention and notice of ancient astronomers. It was observed as a small star by Flamstead, Mayer, and Le Mounier ; but Dr. Herschel discovered its motion, and ascertained it to be a planet. Like Mars, Jupiter, and Saturn, it moves from west to east round the sun. The duration of its sidereal revolution is 30,689 days, or about 84 years. Its motion, which is nearly in the plane of the ecliptic, begins to be retrograde before and after opposition, when the planet is 1034° from the Sun; its retrograde motion continues lól days, and the arc of retrogradation amounts to rather more than 31°. If we judge of the distance of this planet by the slowness of its motions, it ought to be at the very confines of the planetary system.
The apparent magnitude of this planet is so small that it can seldom be seen with the naked eye. It is accompanied by six satellites. Its mean distance from the sun is about 1,800,000,000 miles. Its diameter is 48.times larger than that of the Earth, being more than 35,000 English miles. When seen from the Earth, its apparent diameter, or the angle which it subtends at the eye, is 3" 32". As the distance of this planet from the Sun is twice as great as that of Saturn, its disk will appear four times smaller, and is but little the object of notice, except with those who possess good instruments. When, however, the sky is very serene and clear, it may be found with the naked eye; and it appears a star of the
The amazing host of countless stars appears,
sixth magnitude, with a bluish white light, and a brilliancy between that of Venus and the Moon; but with a power of 200 or 300, the disk is visible, and very well defined.
The want of light, arising from the great distance of this planet from the Sun, is supplied by six satellites, all of which were discovered by Dr. Herschel. The first satellite revolves round its primary in 5d. 21h. 25m. ; the second, in 8d. 176.; the third, in 10d. 23h.; the fourth, in 13d. Ilb; the fifth in 38d. lh. 49ın.; and the sixth requires to complete its revolution nearly 108 days. The second and fourth of these satellites were discovered an the 11th of January, 1787. The other four were discovered in 1790, and 1794 ; but their distances and periodic times, though set down above, are not so accurately ascertained as the other two. It is a remarkable circumstance, however, that all the six satellites move in a retrograde direction, and in orbits lying in or nearly the same plane, and almost perpendicular to the ecliptic. La Place imagines that the first five satellites of the Georgian planet may be retained in their orbits by the action of the equator, and the sixth by the action of the interior satellites; and hence he concludes, that this planet revolves about an axis very little inclined to the ecliptic, and that the time of its diurnal rotation cannot be much less than that of Jupiter and Saturn.
The additions to our astronomical knowledge made by the discovery of this noble planet, and the other four smaller planetary bodies, hereafter described, as moving between Mars and Jupiter, do not merely present us with a few insulated facts similar to those with which we were formerly acquainted. They exhibit to us,” says Mr. Brewster, new and unexpected phenomena, which destroy that harmony in the solar system which appeared in the magnitudes and distances of the planets, and in the form and position of the orbits. The six planets which were formerly supposed to compose our system, were placed, excepting in the case of Mars and Jupiter, at somewhat regular distances from the Sun: they all moved from west to east, and at such intervals as to prevent any extraordinary derangements which might arise from their mutual action. Their magnitudes too, with the exception of Saturn, increased with their distance from the centre of the system; and the eccentricity, as well as the inclination of their orbits, was comparatively small. In the system, as it is now understood and delineated by the most accurate observers, we find four very small planets between the orbits of Mars and Jupiter, placed at nearly the same distance from the Sun, and moving in very concentric orbits, which intersect each other, and are greatly inclined to the plane of the ecliptic. The satellites of the Georgian planet, likewise, move almost at right angles to the plane.
Immortal Sage ! O for thy mighty soul Ptolomy! to whom science did unroll With richest knowledge stored her page sublime, Grac'd with the approving smiles of Truth and Time. Ah! vain the wish; yet not, perhaps, in vain The noble ardour that aspires to gain Knowledge, that bids the mental beam to shine With reason's radiance, and with truth divine : Knowledge, by which the soul, inspir'd and aw'd, Best comprehends an omnipresent God. Knowledge, which opes the eternal cause of thingsHeaven's beauteous plan, and Nature's hidden springs. Knowledge, the most admir'd, when understood Most glorious object of the wise and good :Knowledge, which shews, united in man's frame An earthly portion, an etherial flame ; This the frail body, that the immortal soul Subjected to the element's control. The watery this and the terrene compose, That with the fiery and the airy glows. Hence the four reigning humours, hence we scan The many-colour'd character of man, Trace his component elements, and see Why here they harmonize, there disagree; Why health here spreads her roseate smiles, and there Diseases' fierce relentless fiends appear; Why here we view him rude and unrefin'd, There deck'd with graces of the heart and mind; Why here of peace enamour'd, life's soft charms, There fond of glory 'midst the din of arms; Why here with sensibility endu’d, Humanely sad, in generous woes embru'd ;
of the orbit; and, what is still more surprising, the direction of their motion is opposite to that in which all the other planets and planetary bodies, whether primary or secondary, circulate round their respective centres."