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plane of the ring passes between the Earth and Sun, it is also invisible, because its enlightened part is turned from us; and when it passes through the Sun it is also invisible, the edge only being illuminated: so that it may have, in the same year, two disappearances and reappearances. This takes place when Saturn is near the nodes of the ring.

The ring is a very beautiful object, seen in a good telescope, when in its most open state. It then appears elliptical, its breadth being about half its length. Through the space between the ring and the body, fixed stars have sometimes been seen. The surface of the ring appears more brilliant than that of Saturn.

Among the numerous discoveries of Dr. Herschel, those he has made with respect to Saturn and his ring are not the least. He has ascertained that the ring, which heretofore had generally been supposed single, consists of two, exactly in the same plane, and that they both revolve on their axis in the same time as Saturn, and in the plane of Saturn's equator. This is, however, doubted by Harding and Schroeter. See Dr. Brinkley's Astronomy.

Dr. Herschel also saw the ring when it has disappeared to other observers, either from the reflection of the edge, or from the dark side enlightened by the reflection of Saturn, as we see the whole Moon near new Moon. He observes that the ring is very thin, compared with its width, its thickness being about 1000 miles.

The outside diameter of the larger ring is 200,000 miles.

Its width

Distance between rings

Outside diameter of smaller ring

Its width

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At the mean distance of Saturn, the apparent diameter of the largest ring is about 47 seconds.

6. Saturn has also certain obscure zones, or belts, appearing at times across his disc, like those of Jupiter.

These zones, or belts, are supposed to be obscurations in his atmosphere, which Dr. Herschel has observed to be of considerable density.

7. Saturn has seven satellites revolving about bim in orbits nearly circular; of which the sixth

is seen without much difficulty, and was called the Huygenian satellite, from having been discovered by Huygens.

The 3d, 4th, 5th, and 7th were afterwards discovered. Dr. Herschel discovered the 1st and 2d.

It has long been supposed that the 7th (formerly the 5th) satellite revolved on its axis in the time of its revolution round Saturn. This has been confirmed by the observations of Dr. Herschel.

These satellites, except the 6th, require a very good telescope to render them visible. On which account they have been much less attended to than the satellites of Jupiter.

The periodical revolutions and distances of these satellites from the body of Saturn, expressed in semi-diameters of that planet, as well as in miles, are exhibited in the following table :

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In what time does Saturn revolve on its axis?

What is the shape of Saturn?

In what angle is Saturn's orbit inclined to the

plane of the ecliptic?

Is the apparent motion of Saturn subject to any irregularities?

What is the inclination of Saturn's ring to the

plane of the planet's orbit?

How many satellites has Saturn?

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Of Uranus H, and his Satellites.

1. Uranus, the most remote planet yet known in the solar system, performs its sidereal revolution in 30,688 days, 17 hours, 6 minutes, and 2 seconds, or nearly 84 years, which is the length of the planet's year: the inclination of its orbit to the plane of the ecliptic is about 46'; and the time of rotation on its axis, or the length of its day, has not been yet ascertained.

The planet Uranus had escaped the observation of ancient astronomers, its distance from the earth being so great, that it cannot be seen by the naked eye, except when the atmosphere is very clear, and then it appears like a star of the 6th magnitude. Its light is of a bluish white colour; it shows no disc but with a very gre great magnifying power.

Flamstead, at the end of the last century, and Mayer and Le Moniuer, in this, had observed Uranus as a small star. But it was not till 1781 that Dr. Herschel discovered its motion, and soon after, by following this star carefully, it has been ascertained to be a true planet. Like Mars, Jupiter, and Saturn, the apparent motion of Uranus is subject to irregularities. Its motion, which is nearly in the plane of the ecliptic, begins to be retrograde when, previous to the opposition, the planet is 1030 30 distant from the sun. ceases to be retrograde when, after the position, the planet in its approach to the sun is only 1030 30' distant from him. The duration of its retrogradation is about 151 days, and its arc of retrogradation about 30 36". The synodic revolution is completed in 369 days, 15 hours, 44 minutes, and 38 seconds.

It

2. The diameter of Uranus is 35,000 miles; its apparent diameter is very small, amounting not quite to 4 seconds; and its relative mean distance from the sun is 192, that of the earth being considered as 10.

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Uranus is much less than Jupiter, or Saturn: the relative is planet is 81.26, its mass 1.6904, and its density 0208; the size, mass, and density of the Earth being respectively considered as unity, or 1. And a body weighing 1 pound on the surface of the earth, would weigh.95 on the surface of Uranus.

TABLE,

Showing the mean distance of Uranus from the Sun, &c.

Mean distance in miles,

1,812,413,975

Eccentricity of its orbit,

85,052,560

Long. of ascending node Jan. 1st, 1801,
Long. of the perihelion at the same time,

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Heliocentric long. at the same time,
Geocentric long. at the same time,

9 16 10 0

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Greatest equation,

5 21 7

42

Mean daily motion in its orbit,

The sidereal motion of the apsides is about 3' 59" in a century; but the tropical motion is 1° 27' 29", according to the order of the signs.

The place of the nodes has a retrograde motion of 59 58" in a century; but, owing to the recession of the equinoctial points, their apparent motion is direct in the same time.

The inclination of the orbit is subject to a small increase of about 3" in one hundred years.

The greatest equation has a secular increase of about 11 seconds.

The intensity of light or heat on this distant planet is to that on the earth, with regard to the influence of the sun's rays, as 276 to 100,000, or as 1 to 362 nearly.

3. Dr. Herschel has discovered six satellites moving round Uranus, in orbits which are nearly in the same plane, and almost at right angles to the orbit of their primary.

Two of these satellites were discovered in 1787, and the other four in 1790 and 1794.

The periodic revolutions and the distances of these satellites, from the body of Uranus, expressed in semi-diameters of that planet, as well as in miles, are exhibited in the following table:

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Some astronomers imagine that the motion of these satellites is from east to west, or directly the reverse of all the planets, and other satellites; but this doubtless is an optical illusion, arising from the difficulty of ascertaining which part of the orbit inclines to the earth, and which declines from it. The incunauor of their orbits, and the place of their nodes, are not correctly ascertaine...

According to Dr. Brinkley, the relation of the periodic times, and distances of the satellites from their primary, hold in all the secondaries of each planet respectively.

It may also be observed, that the rotation of the sun and planets are all in the same direction.

QUESTIONS.

What is the length of the day on the surface of Uranus?

What is the diameter of Uranus in miles; and what its apparent diameter ?

What is the relative mean distance of Uranus from the sun, with respect to the earth?

How many satellites has Uranus, and by whom were they discovered?

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