despair of ever getting to the surface again, but the professor
had been prepared for this emergency, and he had built a strong
cylinder, into which all the travelers placed themselves. Then
it was projected into a powerful upward shooting column of water,
which Professor Henderson hoped would take them to the surface of
the earth. Nor was he mistaken. They had a terrible journey,
but came safely out of it.

They opened the cylinder, to find themselves floating on the sea,
and they were rescued by a passing vessel. Of course, they had
abandoned the Mermaid, leaving the craft in the center of the
earth, but they had brought back with them some valuable
diamonds, which formed their fortune.

This ended, for a time, the experiments of the professor, who
decided to settle down to a quiet life, and write out the
observations he had made on the three voyages. The boys wanted
to get an education, and, investing their share from the sale of
the diamonds, they took up a course at the Universal Electrical
and Chemical College. Each had an ambition to become as great an
inventor as was Professor Henderson, with whom they continued to
live in a small city on the Maine coast. Washington White and
Andy Sudds also dwelt with the professor, Andy going off on
occasional hunting trips, and Washington acting as a sort of body
servant to Mr. Henderson.

Jack and Mark had completed one term at the college, and were in
the midst of the second when this story opens.

They had not lost their love for making queer voyages, and one of