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tude, owing to the unsteadiness of the observer's station on board a vessel; and more convenient and accurate modes have superseded it in navigation. To the inhabitants of Jupiter, the opportunity will occur of witnessing upwards of four thousand lunar eclipses, and as many solar, in the course of their year. To us, the planet with his moons, constituting what is technically called the Jovian system, exhibits a miniature picture of the great solar scheme. The laws which govern the planets in their revolution round the

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sun, govern the satellites in their revolution round their centre. They move in elliptical orbits, and, like the larger bodies, travel in a direction from west to east. Though insignificant in point of magnitude when compared with their primary, their united bulk is equal to thirteen of our moons. The first satellite will be a conspicuous object in the Jovian firmament, while, to it, the great planet will be exhibited on a scale of inconceivable magnificence, presenting every forty-two hours the varying forms of a crescent, a half and full moon, and a gibbous shape, appearing a thousand times larger than our moon appears to us in her corresponding phases.

SATURN. From the noblest of the planets in point of magnitude, we pass to the most extraordinary in architecture-an orb which would exhibit the most fascinating appearance to the eye but for its remoteness. An interval of space, nearly twice as great as the vast chasm between Jupiter and the sun, must be crossed to arrive at Saturn, whose mean distance from the solar body is about nine hundred millions of miles, and who never hails the terrestrials from any station nearer than eight hundred millions. He occupies a period of 10,759 solar days in accomplishing his circuit round the sun, having a mean daily motion among the stars of only about 2', the thirtieth part of a degree. If observed therefore entering a particular constellation of the zodiac, we may conclude that a period of two years and a half will elapse before he will bid it farewell. The year of the planet, extending to nearly thirty of ours, gives an age to his octogenarians, should there be any, parallel to that of a terrestrial born when the Jews were in Babylon, and surviving to be one of our contemporaries. His day is rather longer than that of Jupiter, but shorter by more than one half than our own, as he rotates upon his axis in 10h 29m. While appearing to the naked eye as a pale feeble point in the heavens, the Saturnian orb has an actual equatorial diameter of 79,160 miles, and a volume which is nine hundred times greater than that of the earth. Owing to his far removal from the central source of light and heat, his surface receives only the ninetieth part of these

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elements compared with that we enjoy ; but it is computed, that even the ninetieth part of the solar light exceeds the illuminating power of three thousand of our moons at the full, and would itself be amply sufficient for the purposes of life. If arrested in his orbital course, and abandoned to the force of the solar attraction, Saturn would drop to the sun in about five years and two months. His true form is a recent determination. Though not so swift upon his axis as Jupiter, the two diameters exhibit a greater difference, the polar being 6700 miles shorter than the equatorial, a degree of oblateness due to the greater lightness of his material in connection with his axical speed. It was formerly supposed that the diameter is not the greatest at the equator, but at some distance from it, and that the north polar region is much more flattened than the south. This was the conclusion of Sir W. Herschel; and it still passes current. But the real shape is that of an exact spheroid of considerable ellipticity.

Men had long been upon terms of acquaintance and familiarity with Saturn without suspecting the grandeur of his construction, or the remarkable apparatus with which he is furnished. The shepherd astronomers of Chaldea-the star-gazers of Egypt, Greece, and Rome the astrologers of the middle ages-Copernicus and Tycho Brahe-saw the planet only as a dull nebulous star slowly moving through the heavens. It was not until the earth had performed its annual circuit round the sun many thousand times, that the stately form and numerous attendants of the remote wanderer-hitherto deemed obscure and dreary-were revealed. At length, in the year 1610, Galileo sent to Keppler the enormous word,

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which veiled the Latin sentence to uninstructed eyes, introduced in a former page, and announced the most distant planet to be threefold. This was a glimpse caught of the annular appendage of Saturn, which Huygens, with a more perfect instrument, found to be a ring, at the same time discovering one of the satellites. The planet is now more fully known to us. It occupies an illustrious place in the system, having a train of eight moons, with two conspicuous rings encompassing its body-a peculiarity of structure without another example in the universe, so far as we are acquainted with it. The two

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rings are readily seen in good telescopes separated by a dark interval. But recently, using mightier instrumental power, the discovery has been made of a third, inside the other two, which seems to be composed of a substance altogether different. It is of a dusky aspect, and semi-transparent, as the ball of the planet can be seen through it. It has also been ascertained that there is a delicate sub-division of the outer ring, visible only near the extremities. The planet is not exactly central with reference to the annuli, but a

little to the west, a position which is found to contribute to the stability of the Saturnian system. The surface of the globe exhibits belts, bright and dark, which point to the same cause as similar phenomena in the case of Jupiter, whatever that cause may be. But, unlike his neighbour, the axis of Saturn is inclined 29° to the plane of his orbit. He has days and nights therefore of unequal length, a diversity of seasons, and alternately for years continued winter and darkness reign at his poles,

The satellites of Saturn have been named by Sir John Herschel, beginning with the innermost, Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, and Iapetus, after the Titanian divinities. Their respective distances from their primary vary from about half the distance of our own moon to upwards of two millions of miles. Their periodic revolutions also vary from twenty-two hours to seventy days. Little is known as to their precise magnitude, but the most distant is evidently the largest, and is supposed to be nearly equal to Mars in size. The first discovered, or the sixth as to distance, called in honour of the discoverer the Huygenian satellite, is the brightest. These two may be discerned with ordinary optical aid. The rest are more difficult objects, and it requires the mightiest telescopes to reach those, which just skirt the rings, discovered by Herschel. The dimensions of the two conspicuous rings, as given from the measurements of Struve, made at Dorpat in the year 1828, with Frauenhofer's large refractor, are as follows:

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The above measurements give to the exterior ring a width of 10,573 miles, and to the interior of 17,175 miles, making the entire width of the bright rings, including the interval, 29,539 miles. That these appendages are opaque substances is shown by the fact that they throw shadows on those parts of the planet that are on a line with them and the sun, and on the other hand they receive the shadow of the planet. Both these rings have a motion of rotation, accomplished in 10h 29m 17s, a condition plainly essential to their stability, the centrifugal force engendered by the rotatory motion balancing the attraction of the planet, and preventing their precipitation to its surface. But notwithstanding the centrifugal force, it may be demonstrated to be a condition necessary to the stable equilibrium of the rings, that they should not be of uniform thickness or density, otherwise the system would be in a state of unstable equilibrium, like that of a needle balanced on its point, and the slightest disturbance, such as must arise from the action of the satellites, would bring on a catastrophe. Accordingly, evidence appears that the rings are not alike in all their parts. The edge is not flat but spheroidal, and according to Messier the surface is diversified with inequalities, an irregularity of form which satisfies the demands of theory, and guarantees the preservation of this remarkable appendage. The system of Saturn, the most complicated with which we are acquainted, is an astonishing instance of artistic skill, of nicely adjusted mechanism-a ball launched in space, surrounded by ponderous zones, each independent of the other, all acted upon by the attraction of the sun and of the planets, and acted upon by one another and by the satellites of the planet- yet no confusion has arisen, but the original order is maintained, after the lapse of ages of constant antagonism!

The planet is here shown in different parts of its vast circuit round the sun, with the

earth in corresponding orbital positions. As the rings maintain the same inclination to the plane of the orbit, it is obvious at a glance that their aspect to a terrestrial spectator must greatly vary, in the course of revolution. Alternately one side is seen and then

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the other, and oval forms of different ellipticity are presented. It also happens that the earth being in the plane of the rings, or in a direct line between them and the sun, only the edge is turned to us, about a hundred miles thick. They are then invisible, except with the aid of the mightiest telescopic power, when a fine line appears drawn across the disk of the planet, projecting on each side. This occurs twice in each revolution, or once in every fifteen years. These are the phases of Saturn, exhibited in the side views, phenomena which astonished Galileo, and which Huygens was the first to explain. The appearance in the centre represents Saturn and his rings as he would be seen if placed perpendicularly above us.

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The annular apparatus of Saturn illustrates the resources of the Creator, and in connection with his moons is no doubt intended to give him compensation for a scanty supply of direct solar light. Three of the satellites are nearer to him than our moon to us, and the other four will be conspicuous objects in the heavens of the planet. The nearest satellite probably presents a disk equal in extent to nine or ten times that of our lunar

globe; and flying round its primary every twenty-two hours, a rapid succession of phases will be exhibited. But the rings are doubtless the chief glory of the Saturnian firmament at night, constituting a very noble spectacle, varying in their appearance according

to the position of the place of observation. From the polar regions they will scarcely be perceptible, but at thirty degrees from the poles a segment of them will be seen emerging above the horizon, increasing in altitude as equatorial latitudes are gained. Supposing them appendages of the earth, the sketch may

convey no inaccurate idea of their appearance, at about sixty degrees from the equator.

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URANUS. This remote and obscure body, removed to about twice the distance of Saturn from the sun, may be seen with the naked eye by a practised observer in fine weather when the moon is absent, and appears like a fixed star of the least visible magnitude, shining with a pale blue light. It was observed three times by Flamstead, once by Bradley, once by Mayer, eleven times by Lemonnier, who registered it among the stars; but Herschel discovered its planetary character at Bath in 1781, and thus effected an achievement, no parallel to which history before had chronicled. For some time previous, astronomers had been aware of the motions of Jupiter and Saturn being subject to certain perturbations which could not be explained; and it had been conjectured that some planet might revolve beyond the latter, which would account for them. The verification of this idea illustrates the accuracy of astronomical observations. The planet is situated at a mean distance from the sun of 1800 millions of miles, and has a path of more that 10,000 millions to traverse in revolution round him, accomplished in a period of eighty-four years. One circuit therefore has not been performed since it was discovered to be a member of the solar system. It moves over one degree of its orbit in eighty-five days, and is thus seven years in passing one constellation of the zodiac. Uranus, apparently insignificant in the heavens, is the third of the planets in magnitude, eighty times larger than the earth in volume, having a diameter of 35,000 miles. Six satellites, according to Herschel, attend his course. But this observation has not yet been fully verified. No other astronomer obtained a sight of any of these faint objects until the year 1848, when Sir John Herschel detected two, and so far confirmed his father's views. Two more have since been seen by Mr Lassell and M. Otto Struve. They revolve in orbits, the planes of which are nearly perpendicular to the ecliptic, and in a direction from east to west-singular anomalies-exceptions to the general laws of the system. All the other primary planets

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