asteroids, and its intra-Mercurial planets--one of which, Vulcan,
you have already discovered--is a beautiful sight. The planets
nearest the sun receive such burning rays that their surfaces are
red-hot, and at the equator at perihelion are molten. These are
not seen from the earth, because, rising or setting almost
simultaneously with the sun, they are lost in its rays. The
great planet beyond Neptune's orbit is perhaps the most
interesting. This we call Cassandra, because it would be a
prophet of evil to any visitor from the stars who should judge
the solar system by it. This planet is nearly as large as
Jupiter, being 80,000 miles in diameter, but has a specific
gravity lighter than Saturn. Bode's law, you know, says, Write
down 0, 3, 6, 12, 24, 48, 96. Add 4 to each, and get 4, 7, 10,
16, 28, 52, 100; and this series of numbers represents very
nearly the relative distances of the planets from the sun.
According to this law, you would expect the planet next beyond
Neptune to be about 5,000,000,000 miles from the sun. But it is
about 9,500,000,000, so that there is a gap between Neptune and
Cassandra, as between Mars and Jupiter, except that in
Cassandra's case there are no asteroids to show where any planet
was; we must, then, suppose it is an exception to Bode's law, or
that there was a planet that has completely disappeared. As
Cassandra would be within the law if there had been an
intermediary planet, we have good prima facie reason for
believing that it existed. Cassandra takes, in round numbers, a
thousand years to complete its orbit, and from it the sun, though
brighter, appears no larger than the earth's evening or morning
star. Cassandra has also three large moons; but these, when
full, shine with a pale-grey light, like the old moon in the new
moon's arms, in that terrestrial phenomenon when the earth, by
reflecting the crescent's light, and that of the sun, makes the
dark part visible. The temperature at Cassandra's surface is but
little above the cold of space, and no water exists in the liquid
state, it being as much a solid as aluminum or glass. There are
rivers and lakes, but these consist of liquefied hydrogen and
other gases, the heavier liquid collected in deep Places, and the
lighter, with less than half the specific gravity of ether,
floating upon it without mixing, as oil on water. When the
heavier penetrates to a sufficient depth, the interior being
still warm, it is converted into gas and driven back to the
surface, only to be recondensed on reaching the upper air. Thus
it may happen that two rains composed of separate liquids may
fall together. There being but little of any other atmosphere,
much of it consists of what you might call the vapour of
hydrogen, and many of the well-known gases and liquids on earth
exist only as liquids and solids; so that, were there mortal
inhabitants on Cassandra, they might build their houses of blocks
of oxygen or chlorine, as you do of limestone or marble, and use
ice that never melts, in place of glass, for transparence. They
would also use mercury for bullets in their rifles, just as
inhabitants of the intra-Vulcan planets at the other extreme
might, if their bodies consisted of asbestos, or were in any
other way non-combustibly constituted, bathe in tin, lead, or
even zinc, which ordinarily exist in the liquid state, as water
and mercury do on the earth.
"Though Cassandra's atmosphere, such as it is, is mostly clear,