<SPAN name="chap09"></SPAN>
<h3> CHAPTER IX </h3>
<h3> THE RECOIL CHECK </h3>
<p>"Who is that?" asked Ned Newton, with a quick glance at his chum.</p>
<p>"I don't know," Tom answered. "I left orders we weren't to be disturbed
unless it was something important."</p>
<p>"May be something has happened," suggested the navy officer, "another
fire, perhaps, or a—"</p>
<p>"It isn't a fire," Tom answered. "The automatic alarm would be ringing
before this in that case."</p>
<p>The knock was repeated. Tom went softly to the door and opened it
quickly, to disclose, standing in the corridor, one of the messengers
employed about the shops.</p>
<p>"Well, what is it?" asked Tom a bit sharply.</p>
<p>"Oh, if you please, Mr. Swift," said the boy, "a man has applied for
work at the main office, and you know you left orders there that if any
machinists came along, we were to—"</p>
<p>"Oh, so I did," Tom exclaimed. "I had forgotten about that," he went on
to Lieutenant Marbury and Ned. "I am in need of helpers to rush through
the finishing touches on my aerial warship, and I left word, if any
applied, as they often do, coming here from other cities, that I wanted
to see them. How many are there?" Tom asked of the messenger.</p>
<p>"Two, this time. They both say they're good mechanics."</p>
<p>"That's what they all say," interposed Tom, with a smile. "But, though
they may be good mechanics in their own line, they need to have special
qualifications to work on airships. Tell them to wait, Rodney," Tom
went on to the lad, "and I'll see them presently."</p>
<p>As the boy went away, and Tom closed the door, he turned to Lieutenant
Marbury.</p>
<p>"You were about to give me another warning when that interruption came.
You might complete it now."</p>
<p>"Yes, it was another warning," spoke the officer, "and one I hope you
will heed. It concerns yourself, personally."</p>
<p>"Do you mean he is in danger?" asked Ned quickly.</p>
<p>"That's exactly what I do mean," was the prompt reply. "In danger of
personal injury, if not something worse."</p>
<p>Tom did not seem as alarmed as he might reasonably have been under the
circumstances.</p>
<p>"Danger, eh?" he repeated coolly. "On the part of whom?"</p>
<p>"That's just where I can't warn you," the officer replied. "I can only
give you that hint, and beg of you to be careful."</p>
<p>"Do you mean you are not allowed to tell?" asked Ned.</p>
<p>"No, indeed; it isn't that!" the lieutenant hastened to assure the
young man. "I would gladly tell, if I knew. But this plot, like the
other one, directed against the inventions themselves, is so shrouded
in mystery that I cannot get to the bottom of it.</p>
<p>"Our Secret Service men have been working on it for some time, not only
in order to protect you, because of what you have done for the
government, but because Uncle Sam wishes to protect his own property,
especially the searchlight and the big cannon. But, though our agents
have worked hard, they have not been able to get any clues that would
put them on the right trail.</p>
<p>"So we can only warn you to be careful, and this I do in all
earnestness. That was part of my errand in coming here, though, of
course, I am anxious to inspect the new aerial warship you have
constructed. So watch out for two things—your inventions, and, more
than all, your life!"</p>
<p>"Do you really think they would do me bodily harm?" Tom asked, a trifle
skeptical.</p>
<p>"I certainly do. These foreign spies are desperate. If they cannot
secure the use of these inventions to their own country, they are
determined not to let this country have the benefit of them."</p>
<p>"Well, I'll be careful," Tom promised. "I'm no more anxious than anyone
else to run my head into danger, and I certainly don't want any of my
shops or inventions destroyed. The fire in the red shed was as close as
I want anything to come."</p>
<p>"That's right!" agreed Ned. "And, if there's anything I can do, Tom,
don't hesitate to call on me."</p>
<p>"All right, old man. I won't forget. And now, perhaps, you would like
to see the Mars," he said to the lieutenant.</p>
<p>"I certainly would," was the ready answer. "But hadn't you better see
those men who are waiting to find out about positions here?"</p>
<p>"There's no hurry about them," Tom said. "We have applicants every day,
and it's earlier than the hour when I usually see them. They can wait.
Now I want your opinion on my new craft. But, you must remember that
it is not yet completed, and only recently did I begin to solve the
problem of mounting the guns. So be a little easy with your
criticisms."</p>
<p>Followed by Ned and Lieutenant Marbury, Tom led the way into the big
airship shed. There, swaying about at its moorings, was the immense
aerial warship. To Ned's eyes it looked complete enough, but, when Tom
pointed out the various parts, and explained to the government officer
how it was going to work, Ned understood that considerable yet remained
to be done on it.</p>
<p>Tom showed his official guest how a new system of elevation and
depressing rudders had been adopted, how a new type of propeller was to
be used and indicated several other improvements. The lower, or cabin,
part of the aircraft could be entered by mounting a short ladder from
the ground, and Tom took Ned and Lieutenant Marbury through the
engine-room and other compartments of the Mars.</p>
<p>"It certainly is most complete," the officer observed. "And when you
get the guns mounted I shall be glad to make an official test. You
understand," he went on, to Tom, "that we are vitally interested in the
guns, since we now have many aircraft that can be used purely for
scouting purposes. What we want is something for offense, a veritable
naval terror of the seas."</p>
<p>"I understand," Tom answered. "And I am going to begin work on mounting
the guns at once. I am going to use the Newton recoil check," he added.
"Ned, here, is responsible for that."</p>
<p>"Is that so?" asked the lieutenant, as Tom clapped his chum on the back.</p>
<p>"Yes, that's his invention."</p>
<p>"Oh, it isn't anything of the sort," Ned objected. "I just—"</p>
<p>"Yes, he just happened to solve the problem for me!" interrupted Tom,
as he told the story of the door-spring.</p>
<p>"A good idea!" commented Lieutenant Marbury.</p>
<p>Tom then briefly described the principle on which his aerial warship
would work, explaining how the lifting gas would raise it, with its
load of crew, guns and explosives, high into the air; how it could then
be sent ahead, backward, to either side, or around in a circle, by
means of the propellers and the rudders, and how it could be raised or
lowered, either by rudders or by forcing more gas into the lifting
bags, or by letting some of the vapor out.</p>
<p>And, while this was being done by the pilot or captain in charge, the
crew could be manning the guns with which hostile airships would be
attacked, and bombs dropped on the forts or battleships of the enemy.</p>
<p>"It seems very complete," observed the lieutenant. "I shall be glad
when I can give it an official test."</p>
<p>"Which ought to be in about a week," Tom said. "Meanwhile I shall be
glad if you will be my guest here."</p>
<p>And so that was arranged.</p>
<p>Leaving Ned and the lieutenant to entertain each other, Tom went to see
the mechanics who had applied for places. He found them satisfactory
and engaged them. One of them had worked for him before. The other was
a stranger, but he had been employed in a large aeroplane factory, and
brought good recommendations.</p>
<p>There followed busy days at the Swift plant, and work was pushed on the
aerial warship. The hardest task was the mounting of the guns, and
equipping them with the recoil check, without which it would be
impossible to fire them with the craft sailing through the air.</p>
<p>But finally one of the big guns, and two of the smaller ones were in
place, with the apparatus designed to reduce the recoil shock, and then
Tom decided to have a test of the Mars.</p>
<p>"Up in the air, do you mean?" asked Ned, who was spending all his spare
time with his chum.</p>
<p>"Well, a little way up in the air, at least," Tom answered. "I'll make
a sort of captive balloon of my craft, and see how she behaves. I don't
want to take too many chances with that new recoil check, though it
seems to work perfectly in theory."</p>
<p>The day came when, for the first time, the Mars was to come out of the
big shed where she had been constructed. The craft was not completed
for a flight as yet, but could be made so in a few days, with rush
work. The roof of the great shed slid back, and the big envelope
containing the buoyant gas rose slowly upward. There was a cry of
surprise from the many workmen in the yard, as they saw, most of them
for the first time, the wonderful new craft. It did not go up very
high, being held in place with anchor ropes.</p>
<p>The sun glistened on the bright brass and nickel parts, and glinted
from the gleaming barrels of the quick-firing guns.</p>
<p>"That's enough!" Tom called to the men below, who were paying out the
ropes from the windlasses. "Hold her there."</p>
<p>Tom, Ned, Lieutenant Marbury and Mr. Damon were aboard the captive Mars.</p>
<p>Looking about, to see that all was in readiness, Tom gave orders to
load the guns, blank charges being used, of course.</p>
<p>The recoil apparatus was in place, and it now remained to see if it
would do the work for which it was designed.</p>
<p>"All ready?" asked the young inventor.</p>
<p>"Bless my accident insurance policy!" exclaimed Mr. Damon. "I'm as
ready as ever I shall be, Tom. Let 'em go!"</p>
<p>"Hold fast!" cried Tom, as he prepared to press the electrical switch
which would set off the guns. Ned and Lieutenant Marbury stood near the
indicators to notice how much of the recoil would be neutralized by the
check apparatus.</p>
<p>"Here we go!" cried the young inventor, and, at the same moment, from
down below on the ground, came a warning cry:</p>
<p>"Don't shoot, Massa Tom. Don't shoot! Mah mule, Boomerang—"</p>
<p>But Eradicate had spoken too late. Tom pressed the switch; there was a
deafening crash, a spurt of flame, and then followed wild cries and
confused shouts, while the echoes of the reports rolled about the hills
surrounding Shopton.</p>
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