stopping of the motor she was falling like some wobbly balloon, swaying
hither and thither in the ether currents.

But Professor Roumann was not one to give up easily. He kept at his
task, aided occasionally by Professor Henderson and by the boys
whenever they could do anything.

Finally the German cried out:

"Ah, I have discovered the trouble. It is that scoundrel Axtell! See!"
And reaching into the interior of the machine he pulled out a small
magnet. To it was attached a card, on which was written:

"I told you I would have my revenge!" It was signed with Axtell's name.

"This was the dastardly plot he evolved," said Professor Roumann. "He
slipped this magnet into the equilibrium machine, knowing that in time
it would cause a deflection of the delicate needles, and so shift the
centre of gravity. He must have done this as a last resort, and to
provide for his revenge in case we discovered him on board after we
started. It was a cruel revenge, for had I not discovered it we would
soon all be killed."

"Is the machine all right now?" asked Jack.

"It will be in a few minutes. Here, take this magnet and put it as far
away from the engine room as possible."

It was the work of but a few minutes, now that the disturbing element
was removed, to readjust the gravity machine, and Mr. Roumann called: