tly, when astronomers learned by
the aid of their telescopes the countless number of the heavenly bodies,
it began to be doubted whether such an immense creation could be
destitute of intelligent creatures like man; and it was argued that most
likely the Almighty had supplied the heavenly bodies with inhabitants,
but had for some good reason thought best not to reveal the fact to us,
perhaps because our attention might be too much drawn away from the
truths that He wished us particularly to remember. At last, however, men
of science, continuing their researches, seem to be settling back in the
first opinion."

"Why is that?" asked Joe.

"Because they find reasons for thinking that our earth has had human
beings on it only a very little while in comparison with its own
existence. And if this world was millions of years without man, then, of
course, any or all the heavenly bodies may still be without any such
creature on them."

"Is there no better reason than that?" asked Joe.

"Yes, there is considerable evidence that the bodies nearest to us can
not be inhabited by any creatures at all like man. On the moon, for
instance, there is no air to breathe and no water to drink. And without
air and water there can be no grass, trees, or plants of any kind, and
no food for any animal. And besides starving, all creatures that we know
of would immediately freeze to death; for the moon is excessively cold.
The nights are about thirty times as long as ours, and allow each
portion of its surface to get so cold that nothing could live."

"How did the moon get so cold?" asked Joe. "What became of the heat?"

"It went off into the surrounding space, which is all very cold. Empty
space does not get warmed by the sun, whose heat seems chiefly to lodge
in solid bodies and dense fluids."

"But some of the planets are larger than the moon, are they not?" asked
Joe.

[Illustration]

"Yes, Jupiter, for instance, is very much larger than the moon and the
earth; and Professor Proctor tells us it will take Jupiter millions of
years to become as cool as the earth, while the moon was as cool as the
earth millions of years ago. Here is a picture of the planet; but its
surface is changing so constantly, that it seldom appears the same on
two nights in succession. Jupiter at present is wrapped in enormous
volumes of thin cloud that rises up from a melted and boiling mass in
the centre. Professor Newcomb supposes that there is only a
compa