For some time they undertook no further voyages, and the two boys, who
lived with Professor Henderson in a small town on the coast of Maine,
were sent to attend the Universal Electrical and Chemical College.
Washington remained at home to minister to the wants of the old
professor, and Andy Sudds went off on occasional hunting trips.

But the spirit of adventure was still strong in the hearts of the boys
and the professor. One day, in the midst of some risky experiments at
college, Jack and Mark, as related in "Through Space to Mars," received
a telegram from Professor Henderson, calling them home.

There they found their friend entertaining as a guest Professor Santell
Roumann, who was almost as celebrated as was Mr. Henderson, in the
matter of inventions.

Professor Roumann made a strange proposition. He said if the old
scientist and his young friends would build the proper kind of a
projectile, they could make a trip to the planet Mars, by means of a
wonderful motor, operated by a power called Etherium, of which Mr.
Roumann held the secret.

After some discussion, the projectile, called the _Annihilator_, from
the fact that it annihilated space, was begun. It was two hundred feet
long, ten feet in diameter in the middle, and shaped like a cigar. It
consisted of a double shell of strong metal, with a non-conducting gas
between the two sides.

Within it were various machines, besides the Etherium motor, which
would send the projectile along at the rate of one hundred miles a
second. This great speed was necessary in order to reach the planet