at the motionless Cardite motor over his head.

"There is but one way," he answered. "We must restore our centre of
gravity to where it was before. Then the projectile will right
herself."

"Can it be done?" asked Mark.

"It will be quite an undertaking, but we must attempt it. Bring some
tables and chairs, so I can stand up and reach the equilibrium
machine."

From where they had fallen to the ceiling, which was now the floor,
Jack and Mark brought tables and chairs, and made a sort of stepladder.
On this Professor Roumann mounted, and at once began the readjusting of
the centre of gravity.

It was hard work, for he had to labor with his arms stretched up in the
air, and any one who has even put up pictures knows what that means.
The muscles are unaccustomed to the strain. The German scientist,
though a strong man, had to rest at frequent intervals.

"We're falling rapidly," announced Jack, in a low voice, as he looked
at the height gauge.

"I am doing all I can," answered Mr. Roumann. "I think I will soon be
able to right the craft."

He labored desperately, but he was at a disadvantage, for the
_Annihilator_ was not now moving smoothly through space. With the