How Many Worlds?
"Professor," asked May, "are there more worlds with people on them like
this one of ours?"
"That is a hard question," said he. "For many ages it was believed that
there could be only one. More recently, 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
"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
"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
comparatively small core of liquid, the greater part of the planet being
made up of seething vapor. So you see it would be about as difficult to
live on Jupiter as in a steam-boiler, or a caldron of molten lead. Since
last summer a great red spot has been noticed on the surface of the
planet, which has attracted much attention. Some think it is an immense
opening, large enough for our earth to be dropped through."
"Are the other planets such dreadful places?" asked May.
"Saturn seems to be in about the same condition as Jupiter. Mars is
thought to be solid, and to have land, water, and air. It has also two
brilliant white spots on opposite sides, which are supposed to be vast
fields of ice and snow. But the water seems to be disappearing; and the
time when the planet could be inhabited is thought to be long gone by."
"Where does the water go?" asked Joe.
"Probably it sinks into the cracks or fissures which form in the crust
of the planet when it begins to shrivel up with the cold."
"Then it must be like a great frozen grave-yard," said May. "But is
there no other planet that is pleasanter to think about?"
"The one that seems on the whole to be most like our own is Venus, and
so Professor Proctor calls it our sister planet. It is so close to the
sun that it is hidden most of the time, being only seen for a while
before sunrise, and at other times a while after sunset. In the one case
it is called the morning, and in the other the evening star. Also there
is Mercury, still nearer the sun, and hidden almost all the time."
"Then," said May, "there seems to be no way of knowing anything about
there being people like us in other worlds; and the more we look into
it, the more uncertain we become."
"That is about the way the case stands," said the Professor. "But if
science continues to make as rapid progress as it has lately done, we
may hope that it will yet throw more light on the question."
"How many planets are there?" asked Joe.
"Until quite recent times there were supposed to be only the five we
have mentioned. Since the beginning of the present century about two
hundred little planets, called asteroids, have been discovered between
the orbits, or paths, of Mars and Jupiter. Then there are Uranus and
Neptune, very far off from the sun and from us, so much so that the
latter was mistaken for a fixed star."
"Professor," said May, "you mentioned the moon as being near to us. Can
you explain to us how its distance is measured, so that we can
"And then, Professor," said Jack, "I would like to know what parallax
"There," said Gus, "is another big word of Jack's—pallylacks,
knickknacks, gimcracks, slapjacks!"
"Hush, you goose."
"I think," said the Professor, "I can answer May's and Jack's questions
both at once, as they are very closely connected. Suppose that at night,
when you look down the street, you see two gas lamps, one much farther
off than the other. Then if you go across the street, the nearer lamp
will seem to move in the opposite way from what you did. Thus, in the
diagram, when you are at A, the nearer lamp is on the right of the
other, and when you go over to B and look at it, it is on the left. This
change in direction is called parallax. Now we can imagine the nearer
one of the lights to be the moon, and that an observatory, or tower with
a telescope in it, is located at A, from which the direction of the moon
is carefully noted at six o'clock in the morning. Then by six in the
evening the earth, spinning round on its axis, will have carried the
observatory about 8000 miles away from A, and placed it at, say, B. If
the moon's direction be again noted, it is very easy to calculate her
distance by a branch of mathematics called trigonometry, which Jack, I
have no doubt, has already studied."