LETTER XXIII.
SATURN.—URANUS.—ASTEROIDS.
"Into the Heaven of Heavens I have presumed, An earthly guest, and drawn empyreal air."—Milton.
The consideration of the system of Jupiter and his satellites led us to review the interesting history of Galileo, who first, by means of the telescope, disclosed the knowledge of that system to the world. I will now proceed with the other superior planets.
Saturn, as well as Jupiter, has within itself a system on a scale of great magnificence. In size it is next to Jupiter the largest of the planets, being seventy-nine thousand miles in diameter, or about one thousand times as large as the earth. It has likewise belts on its surface, and is attended by seven satellites. But a still more wonderful appendage is its Ring, a broad wheel, encompassing the planet at a great distance from it. As Saturn is nine hundred millions of miles from us, we require a more powerful telescope to see his glories, in all their magnificence, than we do to enjoy a full view of the system of Jupiter. When we are privileged with a view of Saturn, in his most favorable positions, through a telescope of the larger class, the mechanism appears more wonderful than even that of Jupiter.
Saturn's ring, when viewed with telescopes of a high power, is found to consist of two concentred rings, separated from each other by a dark space. Although this division of the rings appears to us, on account of our immense distance, as only a fine line, yet it is, in reality, an interval of not less than eighteen hundred miles. The dimensions of the whole system are, in round numbers, as follows:
| Miles. | |
| Diameter of the planet, | 79,000 |
| From the surface of the planet to the inner ring, | 20,000 |
| Breadth of the inner ring, | 17,000 |
| Interval between the rings, | 1,800 |
| Breadth of the outer ring, | 10,500 |
| Extreme dimensions from outside to outside, | 176,000 |
Figure 60, facing page 247, represents Saturn, as it appears to a powerful telescope, surrounded by its rings, and having its body striped with dark belts, somewhat similar, but broader and less strongly marked than those of Jupiter. In telescopes of inferior power, but still sufficient to see the ring distinctly, we should scarcely discern the belts at all. We might, however, observe the shadow cast upon the ring by the planet, (as seen in the figure on the right, on the upper side;) and, in favorable situations of the planet, we might discern glimpses of the shadow of the ring on the body of the planet, on the lower side beneath the ring. To see the division of the ring and the satellites requires a better telescope than is in possession of most observers. With smaller telescopes, we may discover an oval figure of peculiar appearance, which it would be difficult to interpret. Galileo, who first saw it in the year 1610, recognised this peculiarity, but did not know what it meant. Seeing something in the centre with two projecting arms, one on each side, he concluded that the planet was triple-shaped. This was, at the time, all he could learn respecting it, as the telescopes he possessed were very humble, compared with those now used by astronomers. The first constructed by him magnified but three times; his second, eight times; and his best, only thirty times, which is no better than a common ship-glass.
It was the practice of the astronomers of those days to give the first intimation of a new discovery in a Latin verse, the letters of which were transposed. This would enable them to claim priority, in case any other person should contest the honor of the discovery, and at the same time would afford opportunity to complete their observations, before they published a full account of them. Accordingly, Galileo announced the discovery of the singular appearance of Saturn under this disguise, in a line which, when the transposed letters were restored to their proper places, signified that he had observed, "that the most distant planet is triple-formed."[13] He shortly afterwards, at the request of his patron, the Emperor Rodolph, gave the solution, and added, "I have, with great admiration, observed that Saturn is not a single star, but three together, which, as it were, touch each other; they have no relative motion, and are constituted of this form, oOo, the middle one being somewhat larger than the two lateral ones. If we examine them with an eyeglass which magnifies the surface less than one thousand times, the three stars do not appear very distinctly, but Saturn has an oblong appearance, like that of an olive, thus,