In the former case, the solar rays reflected from the satellites have not so far to travel as in the latter. SATURN. Last, outmost Saturn walks his frontier round, The boundary of worlds, with his pale moons, Deep-dyed and dead, o'er this chill globe forlorn : In wintry hills of never-thawing ice. Such Saturn's earth; and even here the sight, This planet is distinguished from every other body in the heavens, so far as discoveries have yet gone, in the circumstance of being surrounded by a flat luminous ring, extending to a considerable distance from the body of the planet, in a manner analogous to the wooden horizon of an artificial globe. Till within sixty years ago, it was considered to be the furthest of all the planets; as we find the poet speak of it above. Saturn revolves round the Sun in an orbit, the mean distance of which from the Sun is about 900 millions of miles, about 9 times that of the Earth from the Sun: his diameter is about ten times, and his whole mag-... nitude about 1000 times, that of the Earth; and the Sun appears to him to have not aboveth part of the disk, or area, which he presents to the Earth; consequently, the light and heat received by Saturn from the Sun are less than that received by the Earth in the same ratio. Some persons have computed it to be about 500 times as much as that which is afforded by our full moon; whereas our sunlight is estimated at 300,000 times that of our moonlight. TELESCOPIC APPEARANCE OF SATURN. Saturn travels in his orbit about 21,000 miles an hour, and takes up nearly thirty years in passing once round the Sun. He revolves once on his axis in about 10 hours. The revolution on his axis produces the same effect as on other planets, namely, flattening him at the poles, and occasioning a protuberance at the equator: the two diameters have been stated as being about in the ratio of 2281 to 2061; it is, however, remarkable that the greatest diameter is not at the equator, but at a point nearly mid-way between the equator and the poles,-this gives to Saturn somewhat the appearance of a square with rounded corners, as may be observed in the figure above. This was one of the earliest subjects for discovery with the telescope. The density of this planet is about one half that of water. His orbit makes an angle of nearly 24° with the ecliptic; that is, this planet may have that latitude: and his axis is inclined to his orbit at an angle of about. 60°; which makes a great variety of seasons, though these be slow in coming round. His apparent diameter is, owing to his great distance, much the same at every part of his orbit, and subtends an angle of about 18". He may be seen in the heavens without the aid of a telescope, if we know at what place to look for him. His disk is crossed by obscure zones, or belts, like those of Jupiter, which vary in their figure according to the direction of the rings. When Galileo first presented his telescope towards Saturn, he perceived what appeared like two small bodies at the sides of the planet; and he thought at first that this planet was made up of three stars. It was soon found, however, that these lateral appendages changed their appearance, and assumed the form of a ring surrounding the planet. If we encircle a ball with a flat ring, and hold it in a particular position, the ring will appear as nothing more than a line across the ball; but, if we incline the latter a little, the ring will appear somewhat oval, or elliptical; and if we turn it round a quarter of a circle from its first position, the ring will appear as a perfect circle. Now the same thing occurs with regard to Saturn, except that we never see the ring as a perfect circle: it is sometimes a line, when the eye is in the plane of the ring; and at other times an ellipse, when the eye is inclined to that plane. The ring does not touch the planet; for a dark vacant space can be seen between them: indeed, the whole would appear dark, were it not that the Sun's light is reflected from it to the Earth: it does not shine by light reflected from the planet, but by that which is derived from the Sun; therefore there are some positions of the Sun, Earth, and Saturn, when the ring is invisible to us. The ring presents its edge towards the Earth every fifteen years, twice in the planet's revolution, but is seen as an elongated oval between those periods: in 1833 it presented its edge towards the Earth, and will do so again about 1848: at present the northern surface of the ring is visible to the Earth. Sir William Herschel made many careful observations on this ring, and found that it actually consists of two rings, one within another, with a dark space between them; the ring was found to reflect a stronger light than the body of the planet, and to cast a shadow on the planet, thereby proving its opacity. The latest measurements of this ring are as follow: Exterior diameter of exterior ring Miles. 176,418 79,160 19,090 1,791 100 Equatorial diameter of the body of the planet Thickness of the rings not exceeding Some observers have noticed, that not only does the entire ring appear divided into two, but the outer one is likewise subdivided into several concentric rings; this, however, has not been confirmed by Herschel and Struve, who have examined it with the finest telescopes ever constructed. The late Captain Kater, about the year 1825, examined this planet very carefully, and noticed the apparent division of the outer ring into several circles, as represented in the engraving. It seems that this circumstance had been noticed many years before by Mr. Short; and it had been considered as first settled by the elder Herschel, that there were altoge |