"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."

"And I think I know who it is!" exclaimed Jack.

"Who?" asked Mr. Henderson.

"The crazy machinist. I believe he sneaked here through that open port leading into the storeroom."

"That's it!" cried Mr. Roumann. "He must have done this. See if you can't find him."

"Come on, Mark," said Jack. "We'll look for the rascal."

"And I'll help," added old Andy. "I'm pretty good on the trail.

Maybe I can locate him."

"Do so, then," advised the German. "The professor and I will repair the motor."

CHAPTER XVIII

A VAIN SEARCH

The boys, with the old hunter, immediately began a search.

Washington was needed to aid the two scientific men, who quickly prepared to subst.i.tute new plates for the smashed ones. The broken plates looked as if they had been struck with a sledge hammer.

Once the adventurers got used to the different motion of the projectile, which was now falling in some unknown direction of its own weight and not forced onward by the power of the motor, they did not notice anything strange.

"Let's begin at the pilot house and work back," proposed Andy.

"If that crazy machinist did the damage, it would be natural for him to want to get as far away as he could from the engine-room.

That place would be the pilot house."

So they searched there, but there was no sign of any one.

Indeed, it would have been a pretty small person who could have concealed himself in the prow of the projectile, occupied as it was with all sorts of mechanism.

"Well, he isn't here, that's certain," declared Andy, who had brought his gun along. "Now for the bunk-room."

There they had no better luck. They peered under the berths, above them, and even turned back the sheets and blankets to look for the intruder. He was not to be found.

Nor was he in the living-room, which was looked over from top to bottom, and every corner examined.

"If he's any place, it must be in the storeroom," declared Jack.

"Unless he's outside the projectile," suggested Mark.

"He couldn't live for a minute in a place without atmosphere,"

was Jack's opinion. "No, he's in here somewhere, and we must find him."

But it was more easily said than done. The storeroom contained many things, piled together, and it would have been easy for a person to conceal himself among them. The boys and the old hunter looked in every possible place, as they supposed, even taking down many boxes and barrels to peer behind them, but they did not find the man they sought.

"I don't believe he's here," said Jack as he paused in the hunt.

"Say, do you know, I have an idea," said Mark. "Maybe that motor broke itself."

"How could it do that?"

"Well, it might have got to going too fast, and the power may have broken the plates. Anyhow, we didn't hear any person in the engine-room, and there doesn't seem to be any one here."

"That's so."

"I'll make an affidavit that there ain't a person on this airship but ourselves," declared Andy.

"Let's ask Mr. Roumann if it's possible that the motor smashed itself," proposed Jack, and, having no further place to search, they went back to where the two scientists and Washington were busily engaged.

"Yes," replied Mr. Roumann, after Jack had stated his question.

"It's possible for that to have happened, but not very probable.

I think some person is hiding on board here, and that he did it."

"But we can't find any one."

"That may be. He is well concealed. Well you can't do anything more. Suppose you two boys turn in and help us?"

Jack and Mark were glad to get busy, and for several hours they labored in the engine-room, where the two scientists were toiling. As this rendered it unnecessary for Washington to be there, the colored man went to his kitchen, while Andy again made a vain search of the projectile, looking for the crazy man.

Though Mr. Roumann had provided duplicates of the power plates for the Etherium motor, it was quite a task to take out the broken pieces and insert the new ones.

"Can't you run the atmospheric motor while we're fixing this one?" asked Jack. "That would prevent us falling, I should think."

"No, for the reason that there is no atmosphere for it to work on," declared Mr. Roumann. "But don't worry. We shall soon be under way again. We will be somewhat delayed in reaching Mars, that is all."

They labored hard all the rest of that day and part of what corresponded to the night, though of course the daylight outside never ceased. Little of it could penetrate the projectile, however, for the big car was all sealed up, save for the observation window in the pilot house and one on the side.

"There," announced Mr. Roumann, after inserting the last new plate. "I think we are all right."

It had been nearly eighteen hours since the motor had so suddenly stopped.

"Will you start it now?" asked Jack.