revolution about our planet. So that, in the long run, to quote from my
astronomy, it keeps the same side always toward the earth; and today,
or, to be more correct, each night that the moon is visible, we see the
same face and aspect that Galileo did when he first looked at it
through his telescope, and, unless something happens, the same thing
will continue for thousands of years."

"Then we've never seen the other side of the moon?" asked Jack.

"Never; and that's why I wondered if the professor was going to attempt
to reach it. Perhaps there are people there, and air and water, for it
is practically certain that there is neither moisture nor atmosphere on
this side of Luna."

"Wow! Then maybe we'd better not go," said Jack, with a shiver. "What
will we do, if we get thirsty?"

"Oh, I guess we can manage, with all the apparatus we have, to distill
enough water," said Professor Henderson, with a smile. "Then, too, we
will take plenty with us, and, of course, tanks of oxygen to breathe.
But it will be interesting to see if there are people on the moon."

"If there are any, they must have a queer time," went on Mark.

"Why?" asked Jack, who wasn't very fond of study.

"Why? Because the moon is only about one forty-ninth the size of the
earth. Its diameter is 2,163 miles--only a quarter of the earth's--and,
comparing the force of gravity, ours is much greater. A body that
weighs six pounds on the earth, would weigh only one pound on the moon,