"Tampering with the motor?"
"Yes. Some of the plates have been smashed. I believe there is some one concealed on board—some enemy of mine—who hopes to destroy us."
"What can we do?" asked Jack.
"Nothing, until the motor is repaired," replied the German scientist.
"But we are falling—"
"Yes, I know. But we can't fall with anything like the speed with which we were traveling, and though we may go downward, comparatively speaking, for a day or so, we can quickly regain our former place as soon as the motor is running again."
"But can you fix it?"
"Yes, I have some spare plates. But I wish you boys would make a search through the projectile."
"What for?" asked Mark.
"For the person who smashed the plates. I believe some one is concealed here who seeks to kill, us. We must find him."