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.