1 axis, is sharply divided into seasons, which however are here indicated by something else than a change of temperature; we refer to the effects produced by the presence of the strange ring appendage. To understand these effects, its appearance from the body of the planet must first be considered. As the plane of the ring lies in the plane of the planet's equator, an observer at the equator will only see its thickness, and the ring therefore will put on the appearance of a band of light passing through the east and west points and the zenith. As the observer, however, increases his latitude either north or south, the surface of the ring-system will begin to be seen, and it will gradually widen, as in fact the observer will be able to look down upon it; but as it increases in width it will also increase its distance from the zenith, until in lat. 63° it is lost below the horizon, and between this latitude and the poles it is altogether invisible. 275. Now the plane of the ring always remains parallel to itself, and twice in Saturn's year—that is, in two opposite points of the planet's orbit—it passes through the Sun. It follows, therefore, that during one half of the revolution of the planet one surface of the rings is lit up, and during the remaining period the other surface. At night, therefore, in one case, the ring-system will be seen as an illuminated arch, with the shadow of the planet passing over it, like the hour-hand over a dial; and in the other, if it be not lit up by the light reflected from the planet, its position will only be indicated by the entire absence of stars. 276. But if the rings eclipse the stars at night, they can also eclipse the Sun by day. In latitude 40° there occur in Saturn morning and evening eclipses for more than a year, gradually extending until the Sun is eclipsed during the whole day-that is, when its apparent path lies entirely in the region covered by the ring; and these total eclipses continue for nearly seven years: eclipses of one kind or another taking place for 8 years 292 days. This will give us an idea how largely the apparent phenomena of the heavens, and the actual conditions as to climates and seasons, are influenced by the presence of the ring. As the year of Saturn is as long as thirty of ours, it follows that each surface of the rings is in turn deprived of the light of the Sun for fifteen years. 277. We have now finished with the planets known to the ancients; the remaining ones, Uranus and Neptune, have been discovered in modern times-the former in 1781, by Sir Wm. Herschel, and the latter in 1846, independently, by Professor Adams and M. Leverrier. 278. Both these planets are situated at such enormous distances from the Sun, and therefore from us, that Uranus is scarcely, and Neptune not at all, visible to the naked eye. Owing to this remoteness, nothing is known of their physical peculiarities. We have already stated, however, that the motion of the satellites of Uranus, as well as of the solitary moon of Neptune, is in the opposite direction to that of all the other planetary members of the system. 279. The discovery of the planet Neptune is one of the most astonishing facts in the history of Astronomy. As we shall see in the sequel, every body in our system affects the motions of every other body; and after Uranus had been discovered some time, it was found, that, on taking all the known causes into account, there was still something affecting its motion; it was suggested that this something was another planet, more distant from the Sun than Uranus itself. And the question was, where was this planet, if it existed? When we come to consider the problem in all its grandeur, we need not be surprised that two minds, who felt themselves competent to solve it, should have independently undertaken it. As far back as July 1841, we find Mr. Adams determined to investigate the irregularities of Uranus: early in September 1846, the new planet had fairly been grappled. We find Sir John Herschel remarking, "We see it as Columbus saw America from the shores of Spain. Its movements have been felt trembling along the far-reaching line of our analysis with a certainty hardly inferior to ocular demonstration." On the 29th July, 1846, the large telescope of the Cambridge Observatory was first employed to search for the planet in the place assigned to it by Professor Adams's calculations. M. Leverrier, in September, wrote to the Berlin observers, stating the place where his calculation led him to believe it would be found: his theoretical place and Professor Adams's being not a degree apart. At Berlin, thanks to their star-maps, which had not yet been published, Dr. Galle found the planet the same evening, very near the position assigned to it by both Astronomers. LESSON XXII. - The Asteroids, or Minor Planets. Bode's Law. Size of the Minor Planets: their Orbits : how they are observed. and this series of numbers represents very nearly the distances of the ancient planets from the Sun, as follows: : Mercury, Venus, Earth, Mars, —, Jupiter, Saturn. This singular connexion was discovered by Titius, and is known by the name of Bode's Law. We see that the fifth term has apparently no representative among the planets. Although ignorant of the existence of any such relation between the distances of the planets, Kepler boldly attempted to bridge the gap between Mars and Jupiter by inventing an unknown body to revolve there. Up to the time of the discovery of Uranus the undetected planet did not reveal itself: when it was found, however, that the actual position of Uranus was very well represented by the next term of the series, 196, it was determined to make an organized search for it, and for this purpose a society of astronomers was formed; the zodiac was divided into 24 zones, each zone being confided to a member of the society. On the first day of the present century a planet was discovered and named Ceres, which, curiously enough, filled up the gap. But the discovery of a second, third, and fourth, named respectively Pallas, Juno, and Vesta, soon followed, and up to the present time (February 1889) no less than 284 of these little bodies have been detected. A list of them, with their symbols, will be found in the Appendix, Table I. 281. None of these planets, except occasionally Ceres and Vesta, can be seen by the naked eye; and this brings us at once to their chief characteristic—the largest minor planet is but 320 miles in diameter, and many of the smaller ones are less than 20. In fact, the whole of the 268 now known rolled into one would form a planet scarcely the size of our earth. 282. The orbits of those hitherto discovered, for the most part, lie nearer to Mars than Jupiter, and the orbits in some cases are so elliptical, that if we take the extreme distances into account, they occupy a zone 290,000,000 miles in width-the distance between Mars and Jupiter being 341,000,000. The planet nearest the Sun is 49 Medusa, whose journey round the Sun is performed in 3 years 43 days at a mean distance of 198,000,000 miles; the most distant one is 153 Hilda, whose year is nearly as long as 8 of ours, and whose mean distance is 367,400,000 miles. 283. Not only do some of the orbits approach those of comets in the degree of eccentricity, but they resemble K them in another matter-their great inclination to the ecliptic. The orbit of Pallas, for instance, is inclined FIG. 27.-Star Map, showing the path of a Minor Planet. 34° to the plane of the ecliptic; while Massilia is inclined but a few minutes of arc. 284. The minor planets lately discovered shine as stars |