a propeller to project from, and there is no provision for a
tube, such as we used to send compressed air from the Flying
Mermaid. Nor is there anything in front to pull the Annihilator
along."

"We need nothing like that," explained the German scientist.
"The powerful force which I discovered does not need a tube or a
propeller to enable it to be used. The simplest explanation of
it is that it consists of waves of energy, which pass from
certain square surfaces attached to the motor. The force flows
from the plates right through the stern of the ship, passing
through the metal without the necessity for any openings. The
wireless waves, as they may be called, act on the ether, and, by
pushing against it send the projectile forward, just as if it was
a stream of compressed air acting on the atmosphere, or a
propeller in the water. Of course, that is to be used when we
pass beyond the atmosphere. In the latter space I shall use a
different force, as I also shall when we approach Mars."

"Then you can't see this force?" asked Mark.

"No more than you can see the wireless impulses that flow from
the wires of an aerial station."

"Yet it's there, just the same," spoke Jack.

"Indeed, it is," answered the scientist. "But, now I must get
back to my motor."

"Yes," added Professor Henderson, "we must, all get busy. What