"Yes, indeed," interjected Mr. Roumann. "Now I think we will slow down the motor somewhat. We must save some of the energy for our return trip, though I have a large surplus. Still, we cannot be too careful."

"Are we once more headed for Mars?" asked Mark.

"Yes, we are pointing directly toward it. Perhaps you boys will go and slow down the motor, while Professor Henderson and I make some scientific notes concerning the comet. It will be great information to the astronomers on earth. Many of their theories will be changed, I fancy."

Jack and Mark started for the engine-room.

They pa.s.sed through the living or dining-room, where Washington was setting the table for dinner.

"What I done tole yo'?" he demanded triumphantly. "I wasn't skeered ob no ole comet."

"That's right, Wash," admitted Mark. "You had one on us that time."

Andy Sudds was in one corner of the room, oiling his gun.

"Getting ready to go hunting?" asked Jack.

"Well, I heard Mr. Roumann say we'd be on Mars in a few days,"

replied the old man, "and if there's any game there I want to get a shot at it."

"That's right," said Jack. "I guess I'll take--"

He got no further. From the engine-room there sounded a tremendous racket, as if some one was pounding on the machinery with a big hammer.

"What's that?" cried Mark.

"Something's happened to the motor!" exclaimed Jack. "Maybe it's going too fast! Come on!"

They ran to the engine-room. The sight that met their eyes was a startling one.

Standing with his back to them was a strange man. Over his head he was swinging a sledge hammer, which he brought down with great force upon the Etherium motor.

"I'll smash it! I'll stop this machine! I'll send us all to the bottom of the universe!" the man was muttering.

"Quit that!" cried Jack, springing forward.

The man paused and turned.

"The crazy machinist!" shouted Jack. "h.e.l.l break the engine all to pieces!"

"That's what I will!" replied the infuriated man. "I'll end this voyage now!"

Once more he brought his hammer down on the machine, and the motor, with a hissing of gas and a shower of sparks, stopped working.

Jack and Mark were brave lads. They sprang upon the man, though he was large and strong, and his strength was added to by his insane fury.

In an instant they were in the midst of a fierce fight. The maniac tossed them aside as if they were mere infants, but they returned to the attack. They sought to hold his arms to prevent him from doing any further damage with the hammer. Fortunately for the lads, the man was forced to drop the weapon, to enable him to grapple with his two a.s.sailants.

"Can you hold him?" cried Mark.

"Not very well," panted Jack, as his grip of the man's arms was broken and he was flung across the room.

"Help! Help!" suddenly cried Mark. "The crazy machinist is here!"

Washington and Andy, in the living-room, heard the yells of the boys. They rushed to the scene, and, taking in the situation at a glance, flung themselves upon the unfortunate man, aiding the boys in holding him.

Even their strength was not sufficient, and it was not until Mr.

Roumann, leaving Professor Henderson in charge of the pilot house, had come up, that they were able to secure the maniac.

He was quickly bound with ropes, and placed in the storeroom as a prisoner, while the German turned his whole attention to the motor, a part of which had been broken. Once more the Annihilator had ceased to advance, and was falling through s.p.a.ce.

"Can you fix it?" anxiously asked Jack, who was panting from the terrible struggle.

"Yes," replied Mr. Roumann. "Fortunately he did not smash a vital part. I will soon have it running again."

In less than half an hour the motor was repaired, and was speeding the projectile on its way. It was not set at the greatest power, however, as Mr. Roumann did not want to put too much strain upon it.

"Now I have time to inquire how it happened," he said to the boys. "Tell me about it."

They related how they had come upon the crazy machinist.

"Then he has been hidden on board all the while," commented the German. "I was not mistaken in thinking some one opened that port after I closed it. He sneaked in here the night before we started, and has been waiting his chance to do us some damage.

It was he who smashed the plates."

"But where could he have concealed himself?" asked Jack.

"I don't know. We'll see if he will tell us."

They went to the storeroom, where the maniac was bound.

"Why did you try to damage my machinery?" asked Mr. Roumann.

"Because it is an infringement on my patent," was the surprising answer. "I invented a perpetual motion machine, for making dog biscuits, and you have used it to make your airship go.

Therefore I smashed it. I have the sole right to make dog biscuits for the king of the cannibal islands. I'm his private secretary."

"He is hopelessly insane," murmured Jack.

"I fear so," agreed Mr. Roumann. Then he asked: "Where have you been hiding?"

"Ah, I fooled you, all right," said the man with a cunning laugh.

"It was just like a game of hide and seek to watch you hunting for me, and me looking at you all the while. Ha, ha! Oh, I had a good place."

"Where was it?" asked Mr. Roumann soothingly.

"Right up there," answered the machinist, pointing to the roof of the storeroom. The German made an investigation, and discovered a small compartment where it had been intended to make a port, but the idea for which had not been carried out. This left a s.p.a.ce in the wall of the projectile, large enough for a man to conceal himself in. No one would suspect he was there.

"I sneaked on board one night," went on the man. "I managed to open a port into the storeroom. And I lived high, I can tell you."

"Golly! He's been at mah kitchen stuff!" exclaimed Washington.