rimaries, 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 3/4 inch from the sun,
Venus is about 11/4 inches, the Earth 21/4, Mars 2, the planetoids 51/4,
Jupiter 93/4, 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.

"The stately march of the planets in their orbits becomes slower the
farther they are from the sun. The velocity of Mercury in its orbit is
thirty, that of Jupiter is eight, and that of Neptune is only three
miles a second. On the other hand, the inner planets, as a rule, take
some twenty-four hours, and the outer only ten hours to spin round their
axis. The inner planets are small in comparison with the outer. If we
represent the sun by a gourd, 20 inches in diameter, Mercury will seem a
bilberry ({~FRACTION NUMERATOR ONE~}{~SUBSCRIPT ONE~}{~SUBSCRIPT SIX~} inch) Venus, a white currant, the Earth a black currant
(1/4 inch), Mars a red currant ({~VULGAR FRACTION ONE EIGHTH