There was nothing to do but to leave, and it was with sad hearts that
Jack and his friends departed, their search having been unavailing.
They turned toward home, which they reached quite late, but found
nothing disturbed.

No one in Professor Henderson's house slept much that night, and in the
morning pale and wan faces looked at each other, all asking the same
question: "Where is Mark?"

But no one could answer.

They talked over the matter, and decided that Jack, with Andy and
Washington, should form a searching party to scour the surrounding
country. The two scientists were too old for such work, and, as the aid
of the police was not desired, it was felt that the three could do all
that was necessary.

Accordingly, while Professor Henderson and his German friend went to
work on the damaged motor, which did not need as much repairing as at
first was thought to put it in working shape again, Jack and the two
men started off to hunt for Mark.

They were gone all that day, returning very much discouraged at dusk,
saying that they could get no trace of him.

"I don't see where he can be!" exclaimed Jack desperately, for, though
the two lads were not related, they had been friends so long, and had
shared so many pleasures and dangers together, that they were like
brothers. "You won't start for the moon until you find him, will you,
Professor?" asked Jack.