usiness requirements.

Meanwhile Lieutenant Marbury remained as Tom's guest, and was helpful
in making suggestions that would enable the young inventor to meet the
government's requirements.

"I'd like, also, to get on the track of those spies who, I am sure,
wish to do you harm," said the lieutenant, "but clues seem to be scarce
around here."

"They are, indeed," agreed Tom. "I guess the way in which we handled
that fire in the red shed sort of discouraged them."

Lieutenant Marbury shook his head.

"They're not so easily discouraged as that," he remarked. "And, with
the situation in Europe growing more acute every day, I am afraid some
of those foreigners will take desperate measures to gain their ends."

"What particular ends do you mean?"

"Well, I think they will either try to so injure you that you will not
be able to finish this aerial warship, or they will damage the craft
itself, steal your plans, or damage some of your other inventions."

"But what object would they have in doing such a thing?" Tom wanted to
know. "How would that help France, Germany or Russia, to do me an
injury?"

"They are seeking to strike at the United States through you," was the
answer. "They don't want Uncle Sam to have such formidable weapons as
your great searchlight, the giant cannon, or this new warship of the
clouds."

"But why not, as long as the United States does not intend to go to war
with any of the foreign nations?" Tom inquired.

"No, it is true we do not intend to go to war with any of the
conflicting European nations," admitted Lieutenant Marbury, "but you
have no idea how jealous each of those foreign nations is of all the
others. Each one fears that the United States will cease to be neutral,
and will aid one or the other."

"Oh, so that's' it?" exclaimed Tom.

"Yes, each nation, which may, at a moments notice, be drawn into a war
with one or more rival nations, fears that we may throw in our lot with
its enemies."

"And, to prevent that, they want to destroy some of my inventions?"
asked Tom.

"That's the way I believe it will work out. So you must be careful,
especially since you have taken on so many new men."

"That's so," agreed the young inventor. "I have had to engage more
strangers than ever before, for I am anxious to get the Mars finished
and give it a good test. And, now that you have mentioned it, there are
some of those men of whom I am a bit suspicious."

"Have they done anything to