"A motor will be as good a name as any other. We'll call it the
Etherium motor."

"What will we call the other one?" asked Jack.

"What other one?"

"The motive power by which we are to go through the atmosphere of
the earth."

"Well, we can call that the atmospheric motor," replied Mr.
Roumann. "However, there is no hurry about that. I want to get
the work in the engine-room under way first."

He and the professor were soon deep in the discussion, while Jack
and Mark, with the aid of the machinists, were busy constructing
the main part of the projectile.

The first thing to be done was to build the shell of the
projectile. This consisted of plates of a new and peculiar
metal, invented by Professor Henderson. The plates were riveted
together, in the shape of a great cigar, two hundred feet long.
This work took some time, but, as the professor had in his shop
the proper machinery for it, a small force could accomplish a
great deal of work.

The rear of the projectile was to be occupied by the mysterious
apparatus that was to drive it through space. In this compartment
would be many strange machines, including the one which Mr. Roumann
had invented to use the terrific and secret force of which he was