Later, in the submarine boat, the _Porpoise,_ the professor, with
his young assistants and others, voyaged under the sea to the South
Pole, the details of which voyage are related in the second volume of
the series, entitled "Under the Ocean to the South Pole."

In the third volume, "Five Thousand Miles Underground," is related the
building of that strange craft, the _Flying Mermaid_, and how the
voyagers journeyed to the center of the earth. The perils connected
with this experience satisfied all of them, as far as adventure went,
for some time. Jack and Mark prepared for, and entered, the Universal
Electrical and Chemical College.

Before the first year of their college course was completed, however,
Professor Henderson, in partnership with a brother scientist, Professor
Santell Roumann, projected and carried through a marvelous campaign
with the aid of Jack and Mark, which is narrated in our fourth volume,
entitled, "Through Space to Mars." In this book is told how the
projectile, _Annihilator_, was built and, the projectile being driven by
the Etherium motor, the party was transported to the planet Mars.

Later, because of some knowledge obtained from a Martian newspaper by
Jack, they all made a trip to the moon in search of a field of diamonds,
and their adventures as related in "Lost on the Moon" were of the most
thrilling kind. The projectile brought them safely home again and they
had now, for some months, been quietly pursuing their usual avocations.

The knowledge Jack Darrow and Mark Sampson had gained from textbooks,
and much from observation and the teachings of Professor Henderson,
had aided the lads in the building of the _Snowbird_. It was the first