knowledge enough, before you left the earth, to justify you in holding to
a strong probability of life beyond your own globe.

"Let us see what some of that knowledge is. You know, to begin with, that
one world is inhabited. Then if you should find other bodies as large as
the earth and bearing any resemblance to it, there would be no
improbability in the thought that they or some of them were filled with
life. The improbability is certainly taken away by the knowledge that one
such body, the earth, is inhabited.

"You start, then, without prejudice, on a voyage of discovery, aided by
your telescope and your reasoning faculties.

"First you find, within distances that you can easily measure, a small
group of dark bodies, which you have called planets, all apparently
governed by a common law, in obedience to which they are circling around a
large body of quite different character, which gives them light and heat.
Of these dark bodies, which shine in the sky only by reflected light, the
earth is one, and, you are surprised to find, not the most important one,
judging from all you can discover. Some of the others are much larger and
are attended by more satellites. In fact, the earth is indistinguishable
in this little group. While it is not the largest, neither is it the
smallest. It is not the farthest from the sun nor the nearest to it. It is
merely one among the number. And how much alike the members of this family
are. Your telescopes do not point out any material differences, although
each has its individual characteristics. Let us enumerate some of the many
points of resemblance. They all turn on themselves as well as revolve
around the sun. All see the night follow the day, and in most of them
there must occur the regular succession of seasons. To each one the sun is
the source of light and heat, many of them have moons, and all can see the