other.* It revolves around its axis, and consequently, around Saturn, in 1040 hours, which is at the rate of a thousand miles in a minute, or 58 times swifter than the revolution of the Earth's equator.

When viewed from the middle zone of the planet, in the absence of the Sun, the rings will appear like vast luminous arches, extending along the canopy of heaven, from the eastern to the western horizon, exceeding in breadth a hundred times the apparent diameter of our Moon.

Besides the rings, Saturn is attended by seven satellites, which revolve about him at different periods and distances, and reciprocally reflect the Sun's rays on each other and on the planet. The rings and moons illuminate the nights of Saturn; the moons and Saturn enlighten the rings, and the planet and rings reflect the Sun's beams on the satel lites.

The fourth of these satellites (in the order of their distance) was first discovered by Huygens, on the 25th of March, 1655, and, in honour of the discoverer, was called the Huigenian Satellite. This satellite, being the largest of all, is seen without much difficulty. Cassini discovered the 1st, 2d, 3d, and 5th satellites, between October, 1671, and March, 1684. Dr. Herschel discovered the 6th and 7th in 1789. These are nearer to Saturn than any of the rest, though, to avoid confusion, they are named in the order of their discovery.

The sixth and seventh are the smallest of the whole; the first and second are the next smallest; the third is greater than the first and second; the fourth is the largest of them all; and the fifth surpasses the rest in brightness.

Their respective distances from their primary, vary from half the distance of our Moon, to two millions of miles. Their periodic revolutions vary from 1 day to 79 days. The orbits of the six inner satellites, that is, the 1st, 2d, 3d, 4th, 6th, and 7th, all lie in the plane of Saturn's rings, and revolve around their outer edge; while the 5th satellite deviates so far from the plane of the rings, as sometimes to be seen through the opening between them and the planet.

Laplace imagines that the accumulation of matter at Saturn's equator retains the orbits of the first six satellites in the plane of the equator, in the same manner as it retains the rings in that plane. It has been satisfactorily ascertained, that Saturn has a greater accumulation of matter about his

* This happens, as we have already shown, when Saturn is either in the 20th degree of Pisces, or the 20th degree of Virgo. When he is between these points, or in the 20th de gree either of Gemini or of Sagittarius, his ring appears most open to us, and more in the form of an oval, whose longest diameter is to the shortest as 9 to 4.

In what time does the ring complete its revolution on its axis, and, of course, around the planet? What is the rate per minute of its motion? How rapid is this, compared with the motion of the Earth's equator? What would be the appearance of the rings, if viewed from the middle zone of the planet, in the absence of the Sun? How many moons has Saturn? How are Saturn, his rings and satellites, severally, enlightened? What are the dates of their discovery, and the names of their discoverers? What are ther Comparative magnitudes, distances, and times of revolution? What is the position of their orbits with respect to the rings of Saturn? What docs Laplace imagine retains the orbits of Saturn's first six satellites in the plane of his equator?

equator, and consequently that he is more flattened at the poles, than Jupi ter, though the velocity of the equatorial parts of the former is much less than that of the latter. This is sufficiently accounted for by the fact, that the rings of Saturn lie in the plane of his equator, and act more powerfully upon those parts of his surface than upon any other; and thus, while they aid in diminishing the gravity of these parts, also aid the centrifugal force in flattening the poles of the planet. Indeed, had Saturn never revolved upon his axis, the action of the rings would, of itself, have been sufficient to give him the form of an oblate spheroid.

The theory of the satellites of Saturn is less perfect than that of the satellites of Jupiter. The difficulty of observing their eclipses, and of measuring their elongations from their primary, have prevented astronomers from determining, with their usual precision, their mean distances and revo lutions.

We may remark, with the Christian Philosopher, that there is no planet in the solar system, whose firmament presents such a variety of splendid and magnificent objects as that of Saturn.

The various aspects of the seven moons, one rising above the horizon, while another is setting, and a third approach ing to the meridian; one entering into an eclipse, and an other emerging from one; one appearing as a crescent, and another with a gibbous phase; and sometimes the whole of them shining in the same hemisphere, in one bright assemblage! The majestic motion of the rings,—at one time illuminating the sky with their splendour, and eclipsing the stars; at another, casting a deep shade over certain regions of the planet, and unveiling to view the wonders of the starry firmament, are scenes worthy of the majesty of the Divine Being to unfold, and of rational creatures to con template.

Such displays of Wisdom and Omnipotence, lead us to conclude that the numerous splendid objects connected with this planet, were not created merely to shed their lustre on naked rocks and barren sands; but that an immense popu lation of intelligent beings is placed in those regions, to enjoy the bounty, and adore the goodness, of their great Creator.

The following table exhibits the apparent and mean distances of the satellites from their primary, and the times of their periodical revolution. Their distances in miles were computed from their observed micrometer distances; the diameter of Saturn's equator being considered equal to 80,000 miles.

Why are astronomers less acquainted with the mean distances and revolutions of Saturn's satellites, than with those of Jupiter? Describe the firmament of Saturn, as illo minated by his rings and satellites.

Herschel is the most distant planet from the Sun that has yet been discovered. To the naked eye, it appears like a star of only the 6th or 7th magnitude, and of a pale, bluish white; but it can seldom be seen, except in a very fine, clear night, and in the absence of the Moon.

As it moves over but one degree of its orbit in 85 days, it will be seven years in passing over one sign or constellation. At present,* its mean right ascension is 3321°, and its declination 1519 S. It is therefore in the tail of Capricorn, making a small triangle with Deneb and Delta Algedi.

When first seen by Dr. Herschel, in 1781, it was in the foot of Gemini ; so that it has not yet completed two thirds of a revolution since it was first discovered to be a planet.

It is remarkable that this body was observed as far back as 1690. It was seen three times by Flamstead, once by Bradley, once by Mayer, and eleven times by Lemonnier, who registered it among the stars; but not one of them suspected it to be a planet.

The inequalities in the motions of Jupiter and Saturn, which could not be accounted for from the mutual attractions of these planets, led astronomers to suppose that there existed another planet beyond the orbit of Saturn, by whose action these irregularities were produced. This conjecture was confirmed March 13th, 1781; when Dr. Herschel dis covered the motions of this body, and thus proved it to be a planet.

Herschel is attended by six moons or satellites, which revolve about him in different periods, and at various dis

* Beginning of the year 1834.

What is the relative distance of the planet Herschel from the Sun? What is its appear ance to the naked eye? In what circumstances can it be seen? What is the rate of its motion in its orbit? What is its present position? What was its position when first dis covered to be a planet? How much, then, of its revolution has been completed, since it was first discovered? At how early a date was this body observed in the heavens? Who observed it, before it was discovered to be a planet? How many times was seen by them, respectively? What did they consider it to be? What led astronomen to suppose that there existed another planet beyond Saturn? When and by whom was Heschel discovered to be a planet? How many moons has it ?

tances. Four of them were discovered by Dr. Herschel, and two by his sister, Miss Caroline Herschel. It is possible that others remaín yet to be discovered.

Herschel's mean distance from the Sun is 1828 millions of miles; more than twice the mean distance of Saturn. His sidereal revolution is performed in 84 years and 1 month, and his motion in his orbit is 15,600 miles an hour. He is supposed to have a rotation on his axis, in common with the other planets; but astronomers have not yet been able to obtain any occular proof of such a motion.

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His diameter is estimated at 34,000 miles; which would make his volume more than 80 times larger than the Earth's To his inhabitants, the Sun appears only the part as large as he does to us; and of course they receive from him only that small proportion of light and heat. It may be shown, however, that the part of the Sun's light exceeds the illuminating power of 800 full Moons. This added to the light they must receive from their six satellites, will render their days and nights far from cheerless.

Such was the celestial system with which our Earth was associated at its creation, distinct from the rest of the starry hosts. Whatever may be the comparative antiquity of our globe, and the myriads of radiant bodies which nightly gem the immense vault above us, it is most reasonable to conclude, that the Sun, Earth, and planets, differ little in the date of their origin.

This fact, at least, seems to be philosophically certain, that all the bodies which compose our solar system must have been placed at one and the same time in that arrangement, and in those positions in which we now behold them; because all maintain their present stations, and motions, and distances, by their mutual action on each other. Neither could be where it is, nor move as it does, nor appear as we see it, unless they were all coexistent. The presence of each is essential to the system-the Sun to them, they to the Sun, and all to each other. This fact is a strong indication that their formation was simultaneous.

By whom were Herschel's satellites discovered? What is the distance of Herschel's orbit from the Sun? How much greater is this distance than that of Saturn? In what Aime is his sidereal revolution performed? What is the rate per hour of his motion in his orbit? Has he a rotation on his axis? What is his diameter estimated to be? How much larger would this make his volume than the Earth? How much less does the Sun appear to be to the inhabitants of Herschel, than he does to us? What degree of light and heat do they receive from him, compared with that received by the Earth? To the light of how many full moons is this degree of light equal? What reason have we to suppose that the different bodies of the solar system were created at the same time}

COMETS

Comets, whether viewed as ephemeral meteors, or as substantial bodies, forming a part of the Solar system, are objects of no ordinary interest.

When, with uninstructed gaze, we look upwards, to the clear sky of evening, and behold, among the multitudes of heavenly bodies, one, blazing with its long train of light, and rushing onward towards the centre of our system, we insensibly shrink back as if in the presence of a supernatural being.

But when, with the eye of astronomy, we follow it through its perihelion, and trace it far off, beyond the utmost verge of the solar system, till it is lost in the infinity of space, not to return for centuries, we are deeply impressed with a sence of that power which could create and set in motion such bodies.

Comets are distinguished from the other heavenly bodies, by their appearance and motion. The appearance of the planets is globular, and their motion around the Sun is nearly in the same plane, and from west to east; but the comets have a variety of forms, and their orbits are not confined to any particular part of the heavens; nor do they observe any one general direction.

The orbits of the planets approach nearly to circles, while those of the comets are very elongated ellipses. A wire hoop, for example, will represent the orbit of a planet. If two opposite sides of the same hoop, be extended, so that is shall be long and narrow, it will then represent the orbit of a comet. The Sun is always in one of the foci of the comet's orbit.

There is, however, a practical difficulty of a peculiar nature which embarrasses the solution of the question as to the form of the cometary orbits. It so happens that the only part of the course of a comet which can ever be visible, is a portion throughout which the ellipse, the parabola, and hyFerbola, so closely resemble each other, that no observations can be obtain ed with sufficient accuracy to enable us to distinguish them. In fact, the observed path of any comet, while visible, may belong either to an ellipse, parabola, or hyperbola.

That part which is usually brighter, or more opaque, than the other portions of the comet, is called the nucleus. This is surrounded by an envelope, which has a cloudy, or hairy appearance. These two parts constitute the body, and, in many instances, the whole of the comet.

What feelings does the contemplation of comets naturally excite? How are cometa distinguished from the other heavenly bodies? Describe their appearance and motion. Of what three parts may comets be considered to be composed? Describe these parts severally.