"Saturn has eight moons outside his rings, the nearest, Mimas, being 115,000, and the farthest, Japetus, 220,400 miles from his ball. With the exception of Japetus, they revolve round him in the plane of his rings, and when these are seen edgewise, appear to run along it like beads on a string. "Uranus, the next planet visible, is a pale star of the sixth magnitude, 1,770 million miles from the sun, and completes his round in 84 years. His axis, differing from those of the foregoing planets, lies almost in the plane of his orbit, but we cannot speak as to his axial rotation. He is 31,000 miles in diameter, and somewhat heavier, bulk for bulk, than water. Four satellites revolve round him, the nearest, Ariel, being 103,500, and the farthest, Oberon, 347,500 miles distant. Unlike the orbits of the foregoing satellites, which are nearly in the same plane as the orbits of their primaries, those of the satellites of Uranus are almost perpendicular to his own. They are travelled in periods of two and a half to thirteen and a half days. "Neptune, invisible to the naked eye, but seen as a pale blue star in the telescope, is 2,780 million miles from the sun, and makes a revolution in 165 years. His diameter is about 35,000 miles, and his density rather less than that of water. "Neptune has one satellite, at a distance of 202,000 miles, which, like those of Uranus, revolves about its primary in an orbit at a considerable angle to his own in five days twenty-one hours. Both Neptune and Uranus are probably dying suns. "Comets of unknown number travel in long elliptical or parabolic orbits round the sun at great velocities. They seem to consist partly of glowing vapours, especially hydrogen, and partly of meteoric stones. 'Shooting stars,' that is to say, stones which fall to the earth, are known to swarm in their wake, and are believed to be as plentiful in space as fishes in the sea." "The trash or leavings of creation," said I reflectively. "And the raw material, for nothing is lost," rejoined Gazen. "Now, in spite of all its diversity, there is a remarkable symmetry in the solar system. The planets are all moving round the sun in one direction along circular paths. As a rule each is nearly as far again from the sun as the next within it. Thus, if we take Mercury as ¾ inch from the sun, Venus is about 1¼ inches, the Earth 2¼, Mars 2, the planetoids 5¼, Jupiter 9¾, Saturn 14, Uranus 36, and Neptune 60 inches. On the same scale, by the way, Enckes' comet at Aphelion, its farthest distance from the sun, would be about 12 feet; Donatis almost a mile; and Alpha Centauri, a near star in the Milky Way, some ten miles.