heat kept on through space at the rate of one hundred and eighty
thousand miles a second, and will it continue to go on for ages to
come? If so, think of its distance now, and think of its still
going on, to be forever wasted! Rather say that the problem, What
becomes of it? is as yet unsolved.

Thus far I have described the greatest of problems; those which we
may suppose to concern the inhabitants of millions of worlds
revolving round the stars as much as they concern us. Let us now
come down from the starry heights to this little colony where we
live, the solar system. Here we have the great advantage of being
better able to see what is going on, owing to the comparative
nearness of the planets. When we learn that these bodies are like
our earth in form, size, and motions, the first question we ask
is, Could we fly from planet to planet and light on the surface of
each, what sort of scenery would meet our eyes? Mountain, forest,
and field, a dreary waste, or a seething caldron larger than our
earth? If solid land there is, would we find on it the homes of
intelligent beings, the lairs of wild beasts, or no living thing
at all? Could we breathe the air, would we choke for breath or be
poisoned by the fumes of some noxious gas?

To most of these questions science cannot as yet give a positive
answer, except in the case of the moon. Our satellite is so near
us that we can see it has no atmosphere and no water, and
therefore cannot be the abode of life like ours. The contrast of
its eternal deadness with the active life around us is great
indeed. Here we have weather of so many kinds that we never tire
of talking about it. But on the moon there is no weather at all.
On our globe so many things are constantly happening that our